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ISBN print: 978-3-0364-2126-1
ISBN eBook: 978-3-0364-3126-0
DOI book: 10.4028/b-78IIak
© 2026 Trans Tech Publications Ltd, All Rights Reserved

Stacking Faults

Edited by
Sang Mo Koo
Hoon Kyu Shin

Stacking Faults

Special topic volume with invited peer-reviewed papers only

Edited by

Sang Mo Koo and Hoon Kyu Shin

Scientific.Net

Copyright © 2026 Trans Tech Publications Ltd, Switzerland

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Volume 1190 of
Materials Science Forum
ISSN print 0255-5476
ISSN web 1662-9752

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Materials Science Forum, ISSN: 1662-9752, Vol. 1190, pp -1-0

© 2026 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Accepted:
2026-05-13

Online:
2026-05-18

Preface

The original version of this paper is available on https://www.scientific.net/MSF.1190.-1.pdf

Silicon carbide ( SiC ) is a unique semiconductor with the ability to form polytypes, each characterised by a specific stacking sequence of Si−C bilayers. Among these, the 3C,4H, and 6 H polytypes are of particular technological importance due to their outstanding electrical, thermal, and mechanical properties, making silicon carbide a key material for high-performance electronic devices.

One of the most significant challenges in SiC crystal growth and epitaxy is the formation of planar defects, known as stacking faults, arising from local deviations from the ideal stacking order. These defects adversely affect carrier transport and device reliability of power devices.

The special edition focuses on the investigation of the various stacking faults found in SiC polytypes, analysing their crystallographic nature, formation mechanisms, characterisation methods, and their influence on device properties. By deepening understanding of the conditions that promote the development of these defects, researchers and engineers can improve the quality of SiC substrates and epitaxial layers, supporting the continued advancement and modernisation of related semiconductor technologies.

The presented edition will be helpful for a wide range of specialists in the semiconductor industry.

Table of Contents

Preface

Proton Implantation-Induced Reduction of SSF Width and Associated Adverse Effects in 4H-SiC Epitaxial Layers

Kazumi Takano, Yasuyuki Igarashi, Yohsuke Matsushita, Takuya Morita

Investigation on Bipolar Degradation Caused by In-Grown Stacking Fault in 3.3 kV SiC-MOSFET

Hiroki Niwa, Takanori Tanaka, Kazuya Tojima, Hiroyuki Amishiro, Yasuhiro Kagawa, Katsutoshi Sugawara, Tatsuro Watahiki

Process-Dependent Photoluminescence Behavior Evolution of Stacking Faults in 4H-SiC

Nadja Kölbel, Birgit Kallinger, Christian Kranert, Stephan G. Müller, Alesa Fuchs, Tobias Erlbacher, Firas Faisal, Jörg Schulze

Trial Implementation of Operando PL Spectrum Mapping Using a Mini-Spectrometer in EVC Screening of 4H-SiC Wafers

Kazumi Takano, Yasuyuki Igarashi, Yohsuke Matsushita, Takuya Morita

Quantitative Analysis of Excess Minority Carrier Density and Critical Duration in UV Irradiation-Based Screening for Bipolar Degradation in 4H-SiC

Yasuyuki Igarashi, Kazumi Takano, Yohsuke Matsushita, Takuya Morita

Challenges in 1SSF Detection in 4H-SiC Epilayer and Related Failure

Cristiano Calabretta, Cettina Bottari, Salvatore Adamo, Beatrice Carbone, Giovanni Maira, Fabiana Vento, Enzo Fontana, Nicolo Piluso, Mario S. Alessandrino, Alfio Russo, Patrick Fiorenza, Fabrizio Roccaforte, Andrea Severino

Exploring the Ion Implantation Mechanism for Suppressing Stacking Fault Expansion in 4H-SiC: A Fundamental Approach

Takashi Yoda, Masaki Sano, Jun Kojima, Shoichi Onda, Anton Myalitsin, Kuniyuki Kakushima, Takayuki Ohba, Atsushi Oshiyama, Kenji Shiraishi

Investigation of Spoke Pattern of Stacking Faults in 4H-SiC Wafers Grown by Physical Vapor Transport Method

Ze Yu Chen, Jian Pei Zhang, Shan Shan Hu, Kai Xuan Zhang, Yu Zhuo Li, Hao Chi Wang, Balaji Raghothamachar, Ya Fei Liu, Campbell Bouch, Ryan Philpott, Scott Turchetti, Pete Schunemann, Michael Dudley

Micropipes in SiC die Observed by Molten KOH Etching

Fabiana Vento, Nicolò Piluso, Cristiano Calabretta, Chiara Nania, Domenica Raciti, Ruggero Anzalone, Andrea Severino

Synchrotron X-Ray Topography Analysis of Low Angle Grain Boundaries Induced by Growth Step Flow in PVT-Grown 4H-SiC Crystals

Jian Pei Zhang, Ze Yu Chen, Yu Zhuo Li, Shan Shan Hu, Balaji Raghothamachar, Ya Fei Liu, Campbell Bouch, Ryan Philpott, Scott Turchetti, Pete Schunemann, Michael Dudley

Polytype Transitions in Silicon Carbide: A Macroscopic View

Jörg Pezoldt, Vladislav Kurtash, Frank Neubert

Depth-Dependent Suppression of Bipolar Degradation in 4H-SiC Diodes via Proton Implantation and Evaluation of Safe Operating Current Density Range

Atsushi Shimbori, Ryota Wada, Nobuhiro Tokoro, Takashi Kuroi, Hiu Yung Wong, Alex Q. Huang

Keywords Index

Authors Index

The original version of this eBook is available on https://www.scientific.net/book/stacking-faults/978-3-0364-3126-0

Materials Science Forum, ISSN: 1662-9752, Vol. 1190, pp 1-9

doi: 10.4028/p-besU1w

© 2026 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2025-09-11

Revised:
2025-12-29

Accepted:
2026-02-28

Online:
2026-05-18

Proton Implantation-Induced Reduction of SSF Width and Associated Adverse Effects in 4H-SiC Epitaxial Layers

The original version of this paper is available on https://www.scientific.net/MSF.1190.1.pdf

Kazumi Takano 1,a*, Yasuyuki Igarashi 1, b, Yohsuke Matsushita 1,c and Takuya Morita 1, d

1 ITES, 1-60 Kuribayashi, Otsu, Shiga 520-2151, Japan

a*kazumi_takano@ites.co.jp, byiga@ites.co.jp, cyohsuke_matsushita@ites.co.jp

dtakuya_morita@ites.co.jp 

Keywords: proton implantation, shockley-type stacking fault (SSF), photoluminescence (PL), UV irradiation.

Abstract

Proton implantation has been reported as an effective approach for suppressing bipolar degradation in 4H−SiC; however, implantation inevitably introduces lattice damage and point defects. In this work, we investigate: (i) suppression of Shockley-type stacking fault (SSF) expansion in both the proton-implanted layer and the region beyond the implanted layer, and (ii) adverse effects associated with proton implantation. Half of an n -type 4H−SiC epitaxial wafer was implanted with protons ( 350keV,1×1013 cm−2 ) and annealed at 1600∘C for 30 min for dopant activation with carbon capping. SSF expansion was induced by UV laser irradiation, and photoluminescence (PL) imaging was used to quantify SSF width and observe cross sections. The proton-implanted region exhibited clearly reduced SSF expansion, with the expanded SSF width typically about 30μ m smaller than that in the non-implanted region; cross-sectional PL further confirmed that SSFs did not propagate into the near-surface implanted layer. Additional experiments with varied implantation depth and dose revealed a linear relationship between SSF width and active drift-layer thickness (defined as the driftlayer thickness minus the proton implantation depth), consistent with geometric expectations from the wafer off-cut. However, PL observations also showed anomalous SSF morphologies and evidence of dislocations, indicating that proton implantation can generate new SSF nucleation sites. Furthermore, the band-to-band PL peak intensity decreased after implantation and did not recover after the activation anneal, suggesting persistent lattice damage, including in proton-traversed regions. These results highlight a trade-off between SSF-suppression benefits and implantationinduced degradation.

Introduction

The original version of this paper is available on https://www.scientific.net/MSF.1190.1.pdf

Ion implantation has long been recognized as a key technology for forming semiconductor junctions. Around 1950, R. S. Ohl and W. Shockley at Bell Telephone Laboratories patented the concept of creating junction layers using ion implantation [1,2]. In SiC (silicon carbide), in particular, p−n junction formation by thermal diffusion is extremely difficult; consequently, ion implantation is indispensable for device fabrication. Beyond junction formation, proton implantation has also been proposed as an effective means of suppressing bipolar degradation in 4H−SiC devices. Kato et al. demonstrated that bipolar degradation can be mitigated by proton implantation at doses exceeding 1×1012 cm−2, using simple PiN diodes subjected to pulsed current stress of approximately 200 A/cm2 [3,4]. They initially attributed the suppression mechanism mainly to the pinning of partial dislocations (PDs) by hydrogen and implantation-induced point defects, and therefore targeted proton implantation near the epitaxial/substrate interface, where basal-plane-related defects are prevalent.

Subsequent studies expanded the scope of proton implantation designs and revealed both beneficial and potentially adverse effects. Amishiro et al. fabricated SiC MOSFETs incorporating a sandwich-structured proton-implanted layer within the drift region and applied current stress of 420 A/cm2. They reported that the width of Shockley-type stacking faults (SSFs) became slightly narrower in the region beneath the proton-implanted layer [5]. In contrast, Uchida et al. reported that proton implantation into the top 0.5μ m of the drift layer significantly increased the concentration of Z1/2
point defects, and that the carrier lifetime did not recover even after activation annealing [6]. These reports indicate that while proton implantation can suppress degradation-related defect evolution, it also introduces lattice damage that may persist after high-temperature annealing. Bipolar degradation in 4H−SiC is closely linked to the expansion of SSFs originating from basal plane dislocations (BPDs). Such expansion is known to proceed via recombination-enhanced dislocation glide (REDG), where the recombination energy of injected electron-hole pairs acts as the driving force for dislocation motion and SSF growth. Conventionally, SSF expansion has often been evaluated using PiN diodes under current conduction (Fig. 1), where electrons and holes are injected into the drift region. However, when the primary objective is to isolate and evaluate the effect of proton implantation itself, the expansion-visualization-contraction (EVC) method (Fig. 2) [7] provides a simpler and effective alternative: electron-hole pairs can be generated by ultraviolet irradiation without fabricating PiN structures on epitaxial substrates. A critical point in proton implantation is that lattice damage is not confined to the intended implanted layer. In the drift region, proton implantation induces defects such as Z1/2 in the implanted layer. Moreover, when protons are implanted from the surface side, the layers traversed by protons prior to reaching the projected range are also expected to experience lattice damage. Therefore, suppression of bipolar degradation may occur not only in the implanted layer but also in these proton-traversed regions (Fig. 3). In our previous studies, degradation suppression was observed immediately after implantation and remained even after activation annealing, suggesting that persistent implantation-induced lattice damage may play a role beyond simply suppressing SSF expansion.
In this study, we investigate, using the EVC method, suppression of SSF expansion in the width direction in both the proton-implanted layer and the proton-traversed layer, and we further examine adverse effects associated with proton implantation. By correlating SSF behavior with implantation conditions and defect-related optical signatures, we aim to clarify the trade-off between SSFsuppression benefits and implantation-induced degradation.

[picture]

Fig. 1. Accelerated pulsed-current stress.

Fig. 1. Accelerated pulsed-current stress.

[picture]

Fig. 3. Proton Implantation.

Fig. 3. Proton Implantation.

[picture]

Fig. 2. EVC Screening.

Fig. 2. EVC Screening.

[picture]

Fig. 4. Calculation result by SRIM 2013.

Fig. 4. Calculation result by SRIM 2013.

Experiment 1: Experimental Procedure

The original version of this paper is available on https://www.scientific.net/MSF.1190.1.pdf

(1) Epitaxial wafers and proton implantation

The original version of this paper is available on https://www.scientific.net/MSF.1190.1.pdf

Two commercial n-type 4H-SiC epitaxial wafers (off-cut angle: 4∘ ) were used in this study. Epitaxial wafer A was a 100−mm-diameter 4H−SiC epi-wafer consisting of a heavily nitrogen-doped buffer layer (thickness: 1μ m; ND=1×1018 cm−3 ) and a lightly doped drift layer (thickness: 10μ m; ND=8×1015 cm−3 ). Protons were implanted into one half of the wafer surface (implantation energy: 350 keV ; dose: 1×1013 cm−2 ). After implantation, activation annealing was performed at 1600∘C for 30 min with carbon capping. The proton depth distribution in SiC was simulated using SRIM. The simulation indicates that the peak proton concentration is located at a depth of 2.5μ m from the incident surface, and the detailed depth profile is shown in Fig. 4.

Epitaxial wafer B was a 150−mm-diameter 4H−SiC epi-wafer with a heavily nitrogen-doped buffer layer (thickness: 3μ m; ND=1×1018 cm−3 ) and a lightly doped drift layer (thickness: 19μ m; ND=4.5×1015 cm−3 ). To clarify the relationship between SSF width and proton implantation conditions, four implantation conditions were prepared by combining two doses ( 1×1012 and 1×1015 cm−2 ) and two target depths (5μ m and 15μ m). (The target depth was adjusted by decelerating protons as they passed through aluminum foil, but details remain undisclosed).

(2) UV laser irradiation for inducing SSF expansion (EVC method)

The original version of this paper is available on https://www.scientific.net/MSF.1190.1.pdf

To induce SSF expansion, UV laser irradiation was performed based on the EVC method. The UV laser was the third harmonic of a YAG laser (wavelength: 355 nm ; repetition rate: 50 kHz ; pulse width: 20 ns ). To adjust the irradiance, the beam diameter was set to 1 mm(1240 W/cm2) and 3 mm (100 W/cm2). The irradiation area was scanned using the following two protocols:

Protocol 1(10×10 mm area): A linear scan at 3 mm/s with 15μ m line spacing over a 10×10 mm area for 4 h . The scanned area was centered on the boundary between the proton-implanted and unimplanted regions so that both regions were included in the same irradiation field.

Protocol 2 (four 5×5 mm areas): A linear scan at 1 mm/s with 15μ m line spacing over four nonadjacent, independent 5×5 mm areas for 3 h .

(3) Photoluminescence (PL) imaging and SSF-width measurement

The original version of this paper is available on https://www.scientific.net/MSF.1190.1.pdf

Expanded SSFs were evaluated by photoluminescence (PL) imaging. An ultra-high-pressure mercury lamp was used as the excitation source. The excitation light was passed through a cut-off filter to remove wavelengths below 350 nm . PL images were acquired at an observation wavelength of 420 nm using a 1 -megapixel cooled CMOS camera, providing a pixel resolution of approximately 1μ m. For the four regions irradiated under Protocol 2 (Section 2.2), the widths of ten SSFs in each region (i.e., 40 SSFs in total) were measured from the PL images to compare SSF expansion behavior among regions.

(4) Cross section sample preparation and cross-sectional PL observation

The original version of this paper is available on https://www.scientific.net/MSF.1190.1.pdf

Cross section specimens were prepared from the 10×10 mm irradiation area used in Protocol 1 (Section 2.2). To investigate the depth-wise positions of the expanded SSFs, cross-sectional PL imaging was performed for two representative SSFs.

[picture]

Fig. 5. Expansion by UV laser irradiation.

Fig. 5. Expansion by UV laser irradiation.

Result 1: Surface and Cross-Sectional PL Imaging

The original version of this paper is available on https://www.scientific.net/MSF.1190.1.pdf

Fig. 6 shows PL images of a 10×10 mm2 area with and without proton implantation. Fewer stripelike features were observed in the proton-implanted region, indicating suppressed expansion of barshaped Shockley-type stacking faults (SSFs) in the epitaxial layer. Consistently, the expanded SSF width in the proton-implanted region was approximately 30μ m smaller than that in the non-implanted region. Cross-sectional PL imaging (Fig. 7) further confirmed that SSFs did not propagate into the near-surface layer where protons were implanted.

For statistical evaluation, a two-sample t-test was performed using the widths of 10 SSFs measured within the same 5×5 mm2 area for each condition. As summarized in Table 1 and Fig. 8, a clear difference in SSF width was observed irrespective of the UV irradiance. The obtained p-values ( 1.03×10−17 and 2.56×10−16 ) indicate that the difference is statistically significant. These results demonstrate that proton implantation yields a consistent reduction in SSF expansion, regardless of the UV irradiation dose.

[picture]

Fig. 6. PL imaging after UV irradiation.

Fig. 6. PL imaging after UV irradiation.

[picture]

Fig. 7. Cross-section PL imaging.
Table 1. Test for the Difference of Means.

Fig. 7. Cross-section PL imaging. Table 1. Test for the Difference of Means.

[picture]

Fig. 8. PL image using BPF 420 nm .

Fig. 8. PL image using BPF 420 nm .

Experiments using epitaxial wafer B showed no measurable change in SSF width at an implantation dose of 1×1012 cm−2. At a higher dose of 1×1015 cm−2, the band-to-band PL emission was significantly weakened, which hindered observation of the buffer layer. Although previous results indicate that SSFs can also expand into the buffer layer, the present analysis focuses on SSF expansion within the drift layer.
Fig. 9 and Table 2 plot the relationship between the active drift-layer thickness (defined as the driftlayer thickness minus the proton implantation depth) and the SSF width for wafers A and B. A clear linear correlation is observed. The extracted slope was 13.7, which is close to the theoretical value of 14.2 calculated from the 4∘ off-cut angle using Eq. (1).
Width of SSF = Active drift-layer thickness / tan (Off-cut angle)

Table 2. Expansion Result.

| Drift layer | Proton Depth | Proton Density | Active layer | Width of SSF
wafer A | 10 | 0 | E12 | 10 | 149
2.5 | E12 | 7.5 | 107
wafer B | 19 | 5 | E15 | 14 | 200
15 | E15 | 4 | 44
| unit : μm |  | unit : cm⁻² |  |

[picture]

Fig. 9. Width of SSF.

Fig. 9. Width of SSF.

Experiment and Result 2: Adverse Effect

The original version of this paper is available on https://www.scientific.net/MSF.1190.1.pdf

As summarized in Table 1, the expanded SSFs in the non-implanted region showed a nearly constant width of approximately 150μ m, suggesting that SSF expansion occurred across the entire epitaxial layer. The apparent initiation points of SSF expansion were located either at the epitaxial/substrate interface or at the surface, and no initiation was observed in the middle of the epitaxial layer under the present observation conditions.

In the proton-implanted region, the SSF width was approximately 120μ m, which is comparable to the expansion length from the epitaxial/substrate interface to the lower boundary of the implanted layer. This is consistent with the notion that the implanted layer suppresses surface-initiated SSF expansion. Based on this suppression behavior, we expected that SSF expansion would predominantly originate from the epitaxial/substrate interface as shown in Fig. 10(a). However, SSFs with atypical morphologies, as exemplified in Fig. 10(b), were also observed (Fig. 11(a) yellow arrow). The SSFs observed in Fig. 8 were classified, and the results are summarized in Table 3.

[picture]

Fig. 10. Schematic Diagram of SSF.

Fig. 10. Schematic Diagram of SSF.

[picture]

Fig. 11. PL image.

Fig. 11. PL image.

Table 3. SSF Classification.

Expansion from | Fig.8 (a) | Fig.8 (b) | Fig.8 (c) | Fig.8 (d)
Surface side | 13 | 10 | 9 | 10
Substrate side | 15 | 13 | 14 | 15

To further examine possible initiation sites for SSF expansion, dislocation lines were imaged at wavelengths ≥700 nm. Carbon-core dislocations, which have been reported as potential initiation sites for SSF expansion, were observed not only near the epitaxial/substrate interface but also near the lower boundary of the proton-implanted layer (Fig. 11(b)). Because prior PL observations did not show BPDs at this position, the presence of carbon-core dislocations at this depth suggests that proton implantation may have introduced or activated defect structures relevant to SSF nucleation. Although the mechanism remains unclear, these results indicate a potential adverse effect whereby implantation-induced damage could facilitate additional SSF nucleation pathways.

Discussion

The original version of this paper is available on https://www.scientific.net/MSF.1190.1.pdf

The band-to-band emission peak at 390 nm in the PL spectrum is often used as a qualitative indicator of crystal quality; therefore, lattice damage introduced by ion implantation may manifest as a decrease in this peak intensity. Fig. 12 shows the PL spectra of wafer B measured before implantation, after proton implantation, and after activation annealing. After proton implantation, the band-to-band peak intensity decreased, and samples with higher doping concentrations exhibited lower peak heights (Fig. 12(a)). Fig. 12(b) presents the spectra after activation annealing; the band-to-band peak height was comparable to that measured immediately after implantation. Under the present annealing conditions, these observations suggest limited recovery of implantation-induced damage, which may be consistent with the persistence of the SSF-expansion suppression effect observed in our experiments.
In addition, as shown in Fig. 12(c), even at the same doping concentration, deeper implantation conditions were associated with lower band-to-band peak intensities. This trend suggests that residual lattice damage may extend beyond the nominal implanted layer into regions along the proton trajectory. Further investigation will be needed to determine the dominant defects responsible for the observed PL degradation.

[picture]

Fig. 12. PL spectrum.

Fig. 12. PL spectrum.

In contrast, the adverse effect (the appearance of additional nucleation sites) was not clearly observed in proton-traversed regions, but was observed primarily in regions where protons are expected to stop (i.e., near the peak of the implanted proton distribution). This suggests that, within the present doping range (approximately 1012−1015 cm−2 ), the nature of implantation-related damage may differ between the traversed and stopping regions. In the stopping region, hydrogen can accumulate locally; if the local concentration exceeds the solubility limit, hydrogen-related voiding and/or crack-like mechanical damage (microcrack-like damage) may occur in addition to point defects. However, we did not directly confirm the presence of actual cracks in this study. Such cracklike damage can generate stress fields distinct from those associated with point defects and may
influence defect formation and SSF nucleation. Therefore, the atypical SSF morphologies and the inferred increase in nucleation sites observed in this study may reflect a combination of electronic effects from point defects and crack-like mechanical damage associated with proton stopping.

Conclusion

The original version of this paper is available on https://www.scientific.net/MSF.1190.1.pdf

Using a UV-irradiation-based EVC method and PL imaging, we demonstrated that proton implantation suppresses SSF expansion in 4H-SiC epilayers. The SSF width in implanted regions was reduced (e.g., from approximately 150μ m to 120μ m in typical areas), and cross-sectional PL imaging confirmed that SSFs did not propagate into the near-surface region corresponding to the implanted layer. Moreover, the SSF width exhibited an approximately linear dependence on the effective driftlayer thickness, with a slope close to that expected from the 4∘ off-cut geometry. These results support the interpretation that the implanted layer acts as a barrier that limits SSF propagation.

At the same time, our observations suggest important adverse effects. The presence of atypical SSF morphologies and dislocation-related signatures indicates that proton implantation may introduce additional SSF nucleation sites, rather than solely pinning pre-existing partial dislocations. PL spectroscopy further showed that the band-to-band emission peak intensity decreased after proton implantation and remained low after activation annealing, suggesting limited recovery of implantation-induced lattice damage. The dependence on implantation depth also implies that residual damage may extend into regions traversed by protons.

Overall, proton implantation provides measurable suppression of SSF expansion, but it can also introduce persistent damage and potentially new defect-generation pathways. Therefore, optimization of implantation dose and depth, together with evaluation of both suppression efficacy and implantation-induced degradation, is essential for reliable application of this approach in 4H-SiC devices.

Acknowledgment

The original version of this paper is available on https://www.scientific.net/MSF.1190.1.pdf

METI R&D Support Program for Growth Oriented Technology SMEs Grant Number JPJ005698.

References

The original version of this paper is available on https://www.scientific.net/MSF.1190.1.pdf

W. Shockley, US Patent 2,666,814. (1949).

R.S. Ohl, US Patent 2,750,541. (1950).

Masashi Kato, Ohga Watanabe, Toshiki Mii, Hitoshi Sakane, Shunta Harada, Scientific Reports 12, 18790 (2022).

Shunta Harada, Toshiki Mii, Hitoshi Sakane, Masashi Kato, Scientific Reports 12, 13542 (2022).

Kazuya Ishibashi, Naoki Shikama, Hiroki Niwa, Takanori Tanaka, Hiroyuki Amishiro, Akifumi Imai, Katsutoshi Sugawara, Solid State Phenomena Vol. 376, pp. 33-40, (2025).

H. Uchida, M. Kobayashi, N. Hatta, S. Ishikawa, Y. Higashi, H. Sezaki, S. Harada and K. Kojima Solid State Phenomena Vol. 375, pp. 21-27, (2025).

Yasuyuki Igarashi, Kazumi Takano, Yohsuke Matsushita, Chiyomi Shibata, Defect and Diffusion Forum Vol. 425, pp. 75-82, (2023).

This ePub file was created using machine-generated methods and automated software to convert the source text into an ePub format and may contain formatting inconsistencies from the original version. Formatting may vary depending on the device used.

The original version of this eBook is available on https://www.scientific.net/book/stacking-faults/978-3-0364-3126-0

Materials Science Forum, ISSN: 1662-9752, Vol. 1190, pp 11-17

doi: 10.4028/p-yp6sOF

© 2026 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2025-09-12

Revised:
2025-12-19

Accepted:
2026-01-31

Online:
2026-05-18

Investigation on Bipolar Degradation Caused by In-Grown Stacking Fault in 3.3 kV SiC-MOSFET

The original version of this paper is available on https://www.scientific.net/MSF.1190.11.pdf

Hiroki Niwa 1,a*, Takanori Tanaka 2,b, Kazuya Tojima 2,c, Hiroyuki Amishiro 1,d, Yasuhiro Kagawa 2,e, Katsutoshi Sugawara 1,f and Tatsuro Watahiki 1, g

1 Advanced Technology R&D Center, Mitsubishi Electric Corp., Tsukaguchi-Honmachi 8-1-1, Amagasaki, Hyogo, 661-8661, JAPAN

2 Power Device Works, Mitsubishi Electric Corp., Imajuku-Higashi 1-1-1, Nishi-ku, Fukuoka, 8190192, JAPAN

a*Niwa.Hiroki@dp.MitsubishiElectric.co.jp, b Tanaka.Takanori@cb.MitsubishiElectric.co.jp, c  Ishibashi.Kazuya@ak.MitsubishiElectric.co.jp, d Amishiro.Hiroyuki@cb.MitsubishiElectric.co.jp, èKagawa.Yasuhiro@cj.MitsubishiElectric.co.jp,  fSugawara.Katsutoshi@ea.MitsubishiElectric.co.jp, g  Watahiki.Tatsuro@dx.MitsubishiElectric.co.jp

Keywords: body diode, bipolar degradation, leakage current degradation, in-grown stacking fault, BPD, failure analysis, PL imaging.

Abstract

This study investigates the role of in-grown stacking faults (SF) in the bipolar degradation of 3.3 kV SiC-MOSFETs, emphasizing their significant contribution to both on-resistance ( VDSon  ) and leakage current ( IDSX  ) degradation. A high current stress was applied to over 1,500 chips, resulting in 72 degraded devices, with 45 exhibiting notable IDSX  degradation. A detailed analysis revealed that most IDSX  degraded chips contained bar-shaped in-grown SFs, suggesting a correlation between these defects and leakage current degradation. These findings indicate that peculiar basal plane dislocations associated with in-grown SFs may be critical contributors to IDSX degradation, indicating the need for further research to elucidate the mechanisms behind this degradation in SiC-MOSFETs.

Introduction

The original version of this paper is available on https://www.scientific.net/MSF.1190.11.pdf

For many years, bipolar degradation has been one of the most important reliability issues in SiC MOSFETs [1-3]. In this phenomenon, Shockley-type stacking faults (SSFs) expand from basal plane dislocations (BPDs) during bipolar operation. For SiC-MOSFETs, this occurs during conduction through the body diode (BD), which leads to an increase in the on-resistance or forward voltage drop ( VDSon  of the MOSFET and VSDon  of the BD) and/or the leakage current during blocking mode ( IDSX  ) [4]. Most studies have focuses on VDSon  degradation, with very few addressing IDSX  degradation [47]. Idsx degradation does not always occur when SSFs expand, and its origin remains unclear.

Recently, expanded SSFs from BPDs gliding out from micropipes have been found to cause IDSX degradation after stressing more than 1,500 MOSFETs and analyzing degraded chips [8]. Indeed, all the IDSx degradations were attributed to SSFs originating from micropipes; they did not occur in SSFs from commonly observed BPDs within the substrate. A similar phenomenon has been observed in a few studies on IDSX degradation, which occurred in PiN diodes with half-loop arrays or BPDs owing to implantation damage [5, 6]. Therefore, IDSX degradation appears to occur in SSFs originating from some peculiar BPDs, such as interfacial dislocations or half-loop arrays, but not from SSFs expanding from BPDs inside the substrate.

Although peculiar BPDs may be the cause of IDSX degradation, the question remains as to whether other defects may cause it. In this study, we identify defects causing IDSX degradation in addition to known ones, such as micropipes. High-current stress was applied to the BD of 3.3 kV SiC-MOSFETs, and chips with bipolar degradation were identified. These degraded MOSFETs, especially the IDSx degraded MOSFETs, were analyzed in detail, and the crystal defects responsible for this degradation phenomenon were identified.

Experimental

The original version of this paper is available on https://www.scientific.net/MSF.1190.11.pdf

Figure 1 (a) shows the planar-type 3.3 kV SiC -MOSFET fabricated on an n+-type 4 H -SiC substrate prepared in this study. The size of the MOSFET was approximately 9×8 mm2. A different substrate vendor was used compared to the one in the previous study [8]. As the types and densities of crystal defects within the substrate differed by vendor, there is a higher possibility of obtaining new insights into the degradation phenomenon. During device fabrication, defect inspection using photoluminescence (PL) was performed after epitaxial growth and activation annealing. Figure 1 (b) illustrates the experimental flow of this study. After the device fabrication, an initial chip test was conducted to select "good" chips for the BD experiment. These "good" chips exhibited no abnormal I−V characteristics or signs of degradation. Subsequently, a high DC current stress of 300 A/cm2 at ~175∘C was applied to the BD of each chip. In the following chip test, chips with increased leakage current compared to the initial test were characterized as "IDSX degraded chips," while those showing only an increase in VDSon  (without IDSX  degradation) were characterized as " VDSon  degraded chips."

For the failure analysis of VDSon  degraded chips, PL imaging was performed after removing the electrodes and gate structures to analyze the expanded SSF. For IDSx degraded chips, the points of abnormal leakage were first identified using photoemission microscopy from the backside of the chip after removing the backside electrode. PL imaging was then performed after removing the frontside electrode and gate structures to analyze the expanded SSF. The results of photoemission microscopy and PL imaging were overlaid to identify the crystal defects causing abnormal leakage. For both types of degraded chips, the defect inspection results from the device fabrication process were reviewed, and the crystal defects responsible for the degradation were determined.

[picture]

Fig. 1. (a) Schematic cross-section of the planar-type 3.3 kV SiC-MOSFET investigated in this study. (b) Flow-chart of the experimental procedure. During failure analysis, photoemission microscopy and PL imaging were conducted to identify the crystal defects.

Fig. 1. (a) Schematic cross-section of the planar-type 3.3 kV SiC-MOSFET investigated in this study. (b) Flow-chart of the experimental procedure. During failure analysis, photoemission microscopy and PL imaging were conducted to identify the crystal defects.

Result of Body Diode Stress Test

The original version of this paper is available on https://www.scientific.net/MSF.1190.11.pdf

In this study, body diode stress was applied to more than 1,500 chips, and 72 were found to be degraded: 27 chips exhibited VDSon  degradation with no IDSX  degradation observed, and 45 chips exhibited IDSX degradation. Figure 2 shows the I−V characteristics of some of the IDSX degraded chips, where an abnormal leakage current can be observed. Failure analysis was conducted on these degraded chips to identify the origin of the degradation.

[picture]

Fig. 2. Leakage current characteristics of IDSX degraded chips. The compliance current in the measurement was set to 20μ A.

Fig. 2. Leakage current characteristics of IDSX degraded chips. The compliance current in the measurement was set to 20 μ A .

Analysis of Chips with Bipolar Degradation

The original version of this paper is available on https://www.scientific.net/MSF.1190.11.pdf

VDSonDegraded Chips.

The original version of this paper is available on https://www.scientific.net/MSF.1190.11.pdf

PL imaging was conducted on all VDSon  degraded chips, and the origin of the expanded SSFs was analyzed. Some of the PL images are presented in Fig. 3. Although most SSFs were caused by BPDs within the substrate (Fig. 3 (a)) or micropipes (Fig. 3 (b)), approximately 18% of the SSFs were attributed to in-grown stacking faults (SFs) (Fig. 3 (c)). In the PL image, the black SFs represent the in-grown SFs, while the white SFs represent the expanded SSFs. Such an expansion from an in-grown SF has been reported in recent years, where a BPD included in an in-grown SF became the nucleation source of SSFs [9]. The proportion of SSFs caused by in-grown SFs is significant and is a major contributor to VDSon  degradation.

[picture]

Fig. 3. PL images of VDSon  degraded chips with various origins of SSF. (a) SSF caused by BPDs within the substrate. (b) SSF caused by micropipe. (c) SSF caused by in-grown SF.

Fig. 3. PL images of V DSon degraded chips with various origins of SSF. (a) SSF caused by BPDs within the substrate. (b) SSF caused by micropipe. (c) SSF caused by in-grown SF.

I DSX Degraded Chips.

The original version of this paper is available on https://www.scientific.net/MSF.1190.11.pdf

Initially, the defect inspection results were reviewed to select chips for detailed analysis. Table 1 list the defect inspection results for each IDSX  degraded chip. Notably, most chips did not contain micropipes, as in a previous study [8], yet IDSX degradation still occurred. Upon closer examination, most chips were found to contain a bar-shaped in-grown SF, as shown in Fig. 4 (a). For those chips without bar-shaped in-grown SFs, triangular in-grown SFs were still present, as shown in Fig. 4 (b), suggesting in-grown SF has also caused the I DSX degradation. Therefore, some chips with bar-shaped in-grown SFs and all chips without bar-shaped in-grown SFs were selected for analysis to confirm it.

Table 1. Defect inspection results of IDSX  degraded chips.

With micropipe | 2 pcs
With bar-shaped in-grown SF | 38 pcs
Without micropipe | Without bar-shaped in-grown SF | 5 pcs

[picture]

Fig. 4. PL images of in-grown SF obtained by the defect inspection ( λ>660 nm ) during device fabrication. (a) Bar-shaped in-grown SF. (b) Triangular in-grown SF.

Fig. 4. PL images of in-grown SF obtained by the defect inspection ( λ > 660 n m ) during device fabrication. (a) Bar-shaped in-grown SF. (b) Triangular in-grown SF.

Figure 5 shows the failure analysis results of the IDSX  degraded chips. The IDSX  degraded chips were analyzed using photoemission microscopy and PL imaging to identify the source of abnormal leakage. In this chip, there was no micropipe, but a bar-shaped in-grown SF was present. After the BD stress, a white bar-shaped SF indicating the expanded SSFs was observed, having expanded from the bar-shaped in-grown SF. This indicates that bipolar degradation occurred because of the in-grown SF . Furthermore, the results of photoemission analysis revealed that abnormal leakage occurred along the black lines inside the bar-shaped SF, indicating that IDSX degradation also occurred because of the bar-shaped in-grown SF.

[picture]

Fig. 5. PL images and photoemission microscopy results of IDSX degraded chip with bar-shaped in-grown SF .

Fig. 5. PL images and photoemission microscopy results of I D S X degraded chip with bar-shaped in-grown SF .

Figure 6 shows the analysis results of the other IDsx degraded chips. As shown in Fig. 6 (a), there was a bar-shaped in-grown SF. However, after the BD stress, the long bar-shaped SSF expanding outside the in-grown SF was not observed, as shown in Fig. 5. Nevertheless, abnormal leakage occurred inside the in-grown SF. Although the bar-shaped SSF was not observed, SSFs other than the bar-shaped may have expanded inside the in-grown SF, causing the leakage current degradation for this chip. Because the expanded SSFs and in-grown SF may overlap, it was difficult to observe the SSFs. As shown in Fig. 6 (b), there was a triangular in-grown SF, but not a bar-shaped one. After the BD stress, a triangular SSF expanded outside the in-grown SF, and multiple emission points were observed inside the in-grown SF .

[picture]

Fig. 6. PL images and photoemission microscopy results of IDsx degraded chip. (a) Chip with bar-shaped in-grown SF, but without SSF expanding outside it. (b) Chip with triangular ingrown SF.

Fig. 6. PL images and photoemission microscopy results of I D s x degraded chip. (a) Chip with bar-shaped in-grown SF, but without SSF expanding outside it. (b) Chip with triangular ingrown SF.

A total of 10IDSX  degraded chips were analyzed. It was confirmed that all the abnormal leakage occurred from in-grown SFs in various ways, as shown in Figs. 5 and 6, regardless of the shape or expansion behaviors of the in-grown SFs and SSFs. All the chips without the bar-shaped in-grown SFs exhibited abnormal leakage from triangular in-grown SF. This indicates that most of the IDSX degradation observed in this study was also due to in-grown SFs, as most of the degraded chips contained a bar-shaped in-grown SFs inside the chip. Moreover, in this study, all chips containing bar-shaped in-grown SFs exhibited IDSx degradation after BD stress. By contrast, most triangular ingrown SFs did not induce IDSX  degradation. These results indicate that bar-shaped in-grown SFs are major contributors to IDSX  degradation.

Discussion

The original version of this paper is available on https://www.scientific.net/MSF.1190.11.pdf

From the analysis of IDSx degraded chips in the previous section, it was found that in-grown SFs can cause IDSX  degradation. This raises the question of whether there are similarities with previous reports. In the case of IDSX degradation caused by micropipes, abnormal leakage occurred at the SF originating from BPDs gliding out of the micropipe [8], which were referred to as peculiar BPDs. Therefore, the defect inspection results of in-grown SFs causing IDSX  degradation were re-examined to confirm whether such BPDs existed in this study. Figure 7 shows an enlarged view of the barshaped in-grown SFs depicted in Fig. 5. White lines moved after activation annealing, indicating the gliding of BPDs. This suggests that peculiar BPDs, likely interfacial dislocations, were also observed inside in-grown SFs. In fact, all bar-shaped in-grown SFs of the IDSX degraded chips were reexamined, and it was found that most of them contained gliding BPDs inside the in-grown SF. Therefore, SSFs originating from peculiar BPDs accompanied by the in-grown SFs may have caused
the abnormal leakage, similar to the case of micropipes. In the case of chips with bar-shaped in-grown SFs without gliding BPDs, this may be because the gliding BPDs and some portion of the in-grown SFs have overlapped, making it difficult to observe them during defect inspection. However, these results further suggest that certain peculiar BPDs are responsible for IDSX degradation. More studies will be needed to identify the specific structure of these BPDs or SSFs that induced abnormal leakage to clarify the origin of the leakage current degradation.

[picture]

Fig. 7. Enlarged view of the bar-shaped in-grown SF causing IDSX  degradation shown in Fig. 5.

Fig. 7. Enlarged view of the bar-shaped in-grown SF causing I DSX degradation shown in Fig. 5.

Summary

The original version of this paper is available on https://www.scientific.net/MSF.1190.11.pdf

This study investigated the impact of in-grown SFs on bipolar degradation in 3.3 kV SiC-MOSFETs, identifying these as significant contributors to IDSX degradation. A comprehensive analysis of over 1,500 chips subjected to high-current stress revealed that 72 devices exhibited degradation, with 45 specifically exhibiting IDSX  degradation. A detailed failure analysis indicated that most IDSX  degraded chips contained bar-shaped in-grown SFs, suggesting a link between these defects and abnormal leakage currents. This study highlighted the potential role of peculiar BPDs associated with in-grown SFs in the degradation process. These findings underscore the necessity of further research to elucidate the mechanisms underlying the bipolar degradation in SiC-MOSFETs.

References

The original version of this paper is available on https://www.scientific.net/MSF.1190.11.pdf

A. Galeckas, J. Linnros, and P. Pirouz, Appl. Phys. Lett., vol. 81 (2002), p. 883.

M. Skowronski and S. Ha, J. Appl. Phys., vol. 99 (2006), p. 011101.

K. Konishi, S. Yamamoto, S. Nakata, Y. Nakanishi, T. Tanaka, Y. Mitani, N. Tomita, Y. Toyoda, and S. Yamakawa, J. Appl. Phys., vol. 114 (2013), p. 014504.

A. Agarwal, H. Fatima, S. Haney, and S.-H. Ryu, IEEE Electron Device Lett., vol. 28 (2007), p. 587.

R. Stahlbush, Q. Zhang, A. Agarwal, and N. A. Mahadik, Mater. Sci. Forum, vol. 717-720 (2012), p. 387.

S. A. Mancini, S. Y. Jang, Z. Chen, D. Kim, J. Lynch, Y. Liu, B. Raghothamachar, M. Kang, A. Agarwal, N. Mahadik, R. Stahlbush, M. Dudley, and W. Sung, Proc. IRPS 2022, p. 62-1.

T. Ishigaki, T. Murata, K. Kinoshita, T. Morikawa, T. Oda, R. Fujita, K. Konishi, Y. Mori, and A. Shima, Proc. ISPSD 2019, p. 259.

H. Niwa, T. Tanaka, K. Ishibashi, H. Amishiro, A. Imai, Y. Kagawa, K. Sugawara, and T. Watahiki, Solid State Phenomena, vol. 375 (2025), p. 63.

E. Kodolitsch, A. Kabakow, V. Sodan, M. Krieger, H. Weber, and N. Tsavdaris, J. Phys. D: Appl. Phys., vol. 56 (2023) p. 315101.

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Materials Science Forum, ISSN: 1662-9752, Vol. 1190, pp 19-25

doi: 10.4028/p-2nuhGa

© 2026 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2025-09-11

Revised:
2025-12-24

Accepted:
2026-02-23

Online:
2026-05-18

Process-Dependent Photoluminescence Behavior Evolution of Stacking Faults in 4H-SiC

The original version of this paper is available on https://www.scientific.net/MSF.1190.19.pdf

N. Kölbel 1,a*, B. Kallinger 2,b, C. Kranert 2,c, St. G. Müller 2,d, A. Fuchs 2,e, T. Erlbacher 3,f, F. Faisal 3, g, J. Schulze 1,2, h

¹Friedrich-Alexander-Universität Erlangen-Nürnberg, Lehrstuhl für Elektronische Bauelemente, Cauerstraße 6, 91058 Erlangen, Germany

2 Fraunhofer IISB, Schottkystraße 10, 91058 Erlangen, Germany

3 Nexperia Deutschland GmbH, Stresemannallee 101, 22529 Hamburg, Germany

a*nadja.koelbel@fau.de,b birgit.kallinger@iisb.fraunhofer.de, c christian.kranert@iisb.fraunhofer.de, 

d stephan.mueller@iisb.fraunhofer.de, e alesa.fuchs@iisb.fraunhofer.de,

Keywords: stacking faults, device failure, defect, ion implant, photoluminescence, yield.

Abstract

The yield of power electronic devices is influenced by many factors including crystal defects like stacking faults (SFs). There are different types of stacking faults but their influence on the finished device and its performance and the behavior of SF during processing is not fully understood yet. With our contribution, we shed light on the issue, showing four different optically characterized subtypes of SFs with different electrical behavior that can already be found after implantation and wafer annealing in photoluminescence (UVPL) imaging. This enables a distinction between different SF classes without the need for a finally processed device and the corresponding electrical characterization. The goal of this paper is to illustrate an alternative for subdividing SF types that would otherwise be detected as triangular defects without any distinction and to show the different effects those subclasses have on finished devices with non-destructive methods that can be used in between device manufacturing steps. These results will be used as basis for further studies to confirm the found classes and to compare them with research about the different crystal structures by spectral PL measurements. For better understanding of the effect on the finished device, the PL imaging data is correlated with I-V characteristics of trenched diodes and the defect types are evaluated on their effect on the I-V characteristic, identifying 3 defect types with detrimental influence on the reverse bias and blocking voltage while the forward bias characteristic and I-V characteristic of one type is not effected by the defects.

Introduction

The original version of this paper is available on https://www.scientific.net/MSF.1190.19.pdf

Stacking faults (SFs) are well-known to be a limiting factor for the device yield of power electronic devices fabricated on SiC. They occur on 4H-SiC substrates and epitaxial layers as Shockley and Frank type stacking faults, as single or multiple stacking faults and form complexes such as the carrot defect [1,2]. Previous studies have reported [3,4] that some SF types can affect device performance and cause failure of devices, however which specific SF types cause electrical failure remains insufficiently understood. For instance, Baierhofer et al. [5] indicated that only approximately 66% of the defects identified by UVPL imaging as SFs without polytype inclusion will kill a SiC MOSFET device. Further, these defects result in different failure mechanisms. This finding indicates the necessity for a more detailed subclassification in addition to the known SF types of these defects and the investigation of process steps like implantation on the SF. This requires repeated in-line defect characterization and subsequent correlation with electrical data for better understanding of SF progression during device processing and final device performance.

Experimental

The original version of this paper is available on https://www.scientific.net/MSF.1190.19.pdf

We prepared eleven 150 mm SiC Wafers for pin diode fabrication with a standard 1200 V epitaxial layer with 13μ m thickness and a doping concentration of 9E+15 cm−3. After epitaxy and trench formation, they received implantation steps. A patterned nitrogen contact ( n+ ) as well as aluminum FFR ( p+ ) and aluminum contact ( p+ ) implantations with 0∘ was used. However, two wafer received this implantation under 17∘ tilt. Subsequently implant annealing was performed at 1700∘ for 30 min . The diodes were investigated repeatedly with various imaging methods utilizing the PL channel of the Lasertec SICA88 tool at different steps of processing. PL images were recorded on the substrates, after epitaxy and again after ion implantation and annealing. The samples were illuminated with a Hg−Xe lamp at an excitation wavelength of 313 nm . A 650 nm longpass filter was applied in front of the detector. The finished devices were then electrically characterized using I-V mapping on four different wafers. Over 30 devices of different designs and with and without defects were compared to get insight on the effect of the different defect types on device performance.

Results

The original version of this paper is available on https://www.scientific.net/MSF.1190.19.pdf

PL Imaging of epilayers.

The original version of this paper is available on https://www.scientific.net/MSF.1190.19.pdf

In the as grown epilayer, the SFs appear as dark triangles in the UVPL images of the PL channel of the SICA. After implantation and anneal, we observed a change in the luminescence signal. Thus, we identified four different subgroups of SF according to the UVPL signal. One example of each defect types (A-D) after epitaxy and after implant anneal are shown in figure 1.

PL Imaging after implant and anneal.

The original version of this paper is available on https://www.scientific.net/MSF.1190.19.pdf

After ion implantation and annealing, type A SF can be seen as a bright triangle. Type B appears as dark triangles with a darker surrounding area. Type C defects can be described as dark triangles with partially bright luminescent segments. Group D defects appear as bright triangles with a dark surrounding field, pointing towards a combination of type A and B defects. Additionally, we were able to locate the exact position of the defects within the device which allows exclusion of these SF for electrical characterization which are not located within the active-area.

[picture]

Fig. 1. PL images from the Lasertec SICA for each defect type after epitaxy as well as after implant and anneal. Each defect type shows a different luminescence signal after the anneal while after epitaxy each defect appears as a dark triangle.

Fig. 1. PL images from the Lasertec SICA for each defect type after epitaxy as well as after implant and anneal. Each defect type shows a different luminescence signal after the anneal while after epitaxy each defect appears as a dark triangle.

To compare the quantity of each defect type on the wafers, defects were counted in the PL images and assigned to the suitable SF type based on the visual criteria that were described above. A key challenge in process-accompanying SF analysis is choosing an imaging method that allows the same SF to be consistently located at each step, even across a large defect population. Therefore, defects in the PL images taken after epitaxy were correlated to the images after implant and anneal based on the coordinates on the wafer. This was possible due to the high accuracy of the automatic wafer alignment without the need of further adjustment of the scans and data. While the total number and local distribution of defects differs from wafer to wafer, counting from 10 defects per wafer to over 100, overall, a total number of 396 defects were evaluated. The occurrence of each defect type per wafer in percent is displayed in the bar plot in figure 2. The least common defect type on all wafers is the bright triangle type A , followed by the dark defect with surrounding dark area type B and type C . On wafer 4, 5, and 7 defect type A could not be detected at all. Overall, the most common defect type is D across all wafers except wafers 6 and 8 . This finding is coincidental with the implantation angle of 17∘ that was only used for these two wafers.

[picture]

Fig. 2. Ratios of defect type A, B, C and D on eleven wafers in percent. The data was generated by counting each defect type. The absolute number of defects varied for each wafer between 10 and 100 defects per wafer.

Fig. 2. Ratios of defect type A, B, C and D on eleven wafers in percent. The data was generated by counting each defect type. The absolute number of defects varied for each wafer between 10 and 100 defects per wafer.

Dark triangles with bright segments dominate as defects on wafers 6 and 8, whereas number of type D SF on these wafers was comparably low. This indicates that the implantation angle may have an impact on the formation of this defect subtype. However, given the limited number of defects and wafers, this observation lacks statistical significance. Nevertheless, in our present dataset the correlation appears too clear to be ignored. In existing studies, to the influence of the implantation an angle of 17∘ degree is connected to the implantation along the [ 11―23 ] direction of the silicon carbide lattice resulting in channeling and higher implantation depths.[6] We therefore plan additional studies to improve the statistical foundation, but also to investigate other parameters like different implantation angles, temperature, ion energy and dose.

Electrical Characterization

The original version of this paper is available on https://www.scientific.net/MSF.1190.19.pdf

To investigate effects associated to the different SF types on the device performance we characterized electrically the wafers by measuring I-V characteristics of each device. We analyzed I-V curves for almost 100 devices with defects and compared them to defect free devices. The remaining defects were removed from the statistics because they were not located in active device area. Future analysis of more defects and devices will provide more statistical support for these results. In figure 3 the reverse bias characteristic is shown for all four defect types and four reference devices without any SF . Curves of the reference devices typically are within the range of the plotted characteristics of the three examples. For forward bias, the characteristics from devices with or without defects were similar and did not show any differences or noteworthy effect. Devices that contained a visible SF of type A, B and D in the PL images showed a much lower breakdown voltage compared to devices without SFs (black curves). Defectfree devices upheld up to a voltage of about 700 V , while those with a SF exhibit a break down below 100 V reverse bias. The most detrimental effect on the breakdown voltage was observed for devices with type D SFs with an almost instant breakdown under reverse bias. Type C SFs did not appear to influence the breakdown voltage, as the I-V characteristics of devices with and without this defect type overlapped.

[picture]

Fig. 3. I-V reverse bias characteristics for type A (a), type B (b), type C (c) and type D (d), each with reference measurements of devices without defects (black lines).

Fig. 3. I-V reverse bias characteristics for type A (a), type B (b), type C (c) and type D (d), each with reference measurements of devices without defects (black lines).

Based on these diagrams the breakdown voltage under reverse bias was determined and is seen in figure 4 . The boxplot shows that the breakdown voltages for defect types A, B, and D cluster within a narrow range at low reverse-bias voltages. In contrast, type C spans a broader voltage range and has a higher median than the other defect types. Type D, despite having the largest sample size n, exhibits the tightest distribution and the lowest breakdown voltage.

[picture]

Fig. 4. The boxplot shows the distribution of breakdown voltage under reverse bias for the different defect types. The mean value is marked by a small cross, and n denotes the number of defects per type.

Fig. 4. The boxplot shows the distribution of breakdown voltage under reverse bias for the different defect types. The mean value is marked by a small cross, and n denotes the number of defects per type.

Outlook: PL Device Characterization

The original version of this paper is available on https://www.scientific.net/MSF.1190.19.pdf

For more detailed investigation of the structure of SFs in devices, Trench-MOSFETs were reprocessed to the pre-metal and pre-oxide state to be examined with UVPL. Initial testing of one of the reprocessed devices with a SF and different illumination sources and filters can be seen in figure 5. The sample was uniformly illuminated with 305 nm and examined with three different detector filters. A 430 nm bandpass filter, a 550 nm short pass and a 650 nm long pass filter were applied to examine the SFs in different luminescence ranges. The SF is visible in all of the shown images, but the details and fine structure varies for each filter and illumination source combination. Additional to the signal from the stacking faults, we observed dark vertical lines, especially at the bottom of images b ) and c ). In panel a ) and b ) the SF appears as a dark triangle while a thick black line appears on the right side of the SF when illuminated with 305 nm and with the BP and the shortpass filter. Panel c) shows the SF as a bright triangular shaped form with the black line again on the right side of the triangle. The combination of illumination sources and different filters allows a more detailed investigation of the SF and energy states in the crystal surrounding the defect. The configuration in panel c) is similar to the SICA, so the SF is probably a type A or D defect as it appears as a dark triangle in the image. The different filters could possibly help to investigate the SF PL types further and understand the origin of the different effects the types have on the finished devices.
For as grown epitaxy layers different PL wavelengths can be used for subclassification of stacking fault types. [7,8] Since the implantation changes the contrast and brightness of the SF as can be seen in figure 1, the SF cannot be classified after this process step by evaluating the PL emission images in dependence on the excitation wavelength.
The black vertical lines that are visible especially in the images b) and c) all seem to originate in the edge termination of the device. A possible reason for this could be degradation by the electrical testing that was conducted before the reprocessing of the devices, through propagation of defects caused by electrical stress as reported by Hatta et al. [9] The appearance of these lines as well as SF behavior in stressed devices need further investigation.

[picture]

Fig. 5. UVPL Images of a reprocessed MOSFET device with stacking faults. With 305 nm excitation source, a 430 nm bandpass, a 550 nm shortpass and a 650 nm longpass filter were applied to show the luminescence signal in different wavelength ranges.

Fig. 5. UVPL Images of a reprocessed MOSFET device with stacking faults. With 305 nm excitation source, a 430 nm bandpass, a 550 nm shortpass and a 650 nm longpass filter were applied to show the luminescence signal in different wavelength ranges.

Summary

The original version of this paper is available on https://www.scientific.net/MSF.1190.19.pdf

This study indicates that SFs change the appearance of the PL signal during device processing, particularly related to implantation steps. From the PL signal after implant and anneal different subtypes can be classified with indications that the subtype may correlate with implant parameters. This will be examined in further studies and will be cross referenced with PL spectroscopy to confirm the SF types and classification and if necessary, lead to process optimization. Importantly, the subtypes exhibit different impacts on device performance: while Types A, B, and D significantly degrade the reverse blocking capability of diodes, Type C shows no measurable effect on breakdown voltage. PL imaging can also be used for characterization of finished devices after electrical testing and to investigate the SF in more detail by the application of a range of filters. In addition, with spectral PL, this method will be used in further investigation of the origin of the subtypes and SF induced degradation.

References

The original version of this paper is available on https://www.scientific.net/MSF.1190.19.pdf

Tsuchida H, Kamata I, Nagano M (2008) Formation of basal plane Frank-type faults in 4H-SiC epitaxial growth. J Cryst Growth 310:757-765.

Zhao L (2020) Surface defects in 4H-SiC homoepitaxial layers. Nanotechnology and Precision Engineering 3:229-234.

Schoeck J, Schlichting H, Kallinger B, et al (2018) Influence of Triangular Defects on the Electrical Characteristics of 4H-SiC Devices. MSF 924:164-167. .

Das H, Justice J, Sunkari S, et al (2024) The Role of Defects on SiC Device Performance and Ways to Mitigate them. DDF 434:51-59.

Baierhofer D, Thomas B, Staiger F, et al (2023) Correlation of Extended Defects with Electrical Yield of SiC MOSFET Devices. DDF 426:11-16.

Belanche M, Yonezawa Y, Heller R, et al (2024) Aluminum channeling in 4H-SiC by highenergy implantation above 10 MeV . Material Science Semiconductor Processing 179:108461. .

Feng G, Suda J, Kimoto T (2008) Characterization of stacking faults in 4H-SiC epilayers by room-temperature microphotoluminescence mapping. Appl Phys Lett 92:221906. .

Odawara M, Kamei K, Miyasaka Y, et al (2014) Defects Grouping and Characterizations of PL-Imaging Methods for 4H-SiC Epitaxial Layers. MSF 778-780:382-385. .

Hatta N, Ishikawa S, Ozono K, et al (2023) Reduction of Forward Bias Degradation in 4H-SiC PiN Diodes Fabricated on 4H-SiC Bonded Substrates. Key Eng Mater 948:107-113. .

This ePub file was created using machine-generated methods and automated software to convert the source text into an ePub format and may contain formatting inconsistencies from the original version. Formatting may vary depending on the device used.

The original version of this eBook is available on https://www.scientific.net/book/stacking-faults/978-3-0364-3126-0

Materials Science Forum, ISSN: 1662-9752, Vol. 1190, pp 27-35

doi: 10.4028/p-5mleKn

© 2026 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2025-09-12

Revised:
2026-01-18

Accepted:
2026-03-21

Online:
2026-05-18

Trial Implementation of Operando PL Spectrum Mapping Using a Mini-Spectrometer in EVC Screening of 4H-SiC Wafers

The original version of this paper is available on https://www.scientific.net/MSF.1190.27.pdf

Kazumi Takano 1,a*, Yasuyuki Igarashi 1,b, Yohsuke Matsushita 1,c and Takuya Morita 1, d

1 ITES, 1-60 Kuribayashi, Otsu, Shiga 520-2151, Japan

a* kazumi_takano@ites.co.jp, b yiga@ites.co.jp, c yohsuke_matsushita@ites.co.jp,  dtakuya_morita@ites.co.jp

Keywords: PL mapping, proton implantation, Shockley-type stacking fault (SSF), photoluminescence (PL), UV irradiation, basal plane dislocation (BPD).

Abstract

We have been developing the expansion-visualization-contraction (EVC) method as an inspection technique for 4H−SiC wafers, in which Shockley-type stacking faults (SSFs) are intentionally expanded by UV irradiation and subsequently visualized to identify converted dislocations that are not directly detectable by conventional PL inspection. In this study, we demonstrate a low-cost "operando" PL spectrum mapping approach for the EVC tool by using the 355−nm expansion laser as the PL excitation source and adding only a miniature spectrometer via an optical fiber, avoiding the need for an expensive hyperspectral camera. Two experiments were performed. In Experiment 1, proton-implanted and non-implanted regions on n-type 4H−SiC epilayers were compared using EVC screening and PL imaging. The proton-implanted regions exhibited narrower SSF widths, and a two-sample t-test yielded extremely small p-values, indicating a statistically significant suppression effect that remained after activation annealing. In Experiment 2, a thick epilayer wafer containing polytype inclusions was screened. PL spectrum mapping identified not only 1SSF-related emission ( ~420 nm ) but also Frank-type components ( ~488 nm ) and polytype-inclusion-related emission ( ~540 nm ), revealing composite stacking faults expanded from inclusions. The results suggest that operando PL spectrum mapping can help distinguish stacking-fault types during EVC screening and potentially prevent unnecessary expansion of thermally uncontractable faults, thereby reducing yield loss.

Introduction

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We have been developing the EVC (Expansion-Visualization-Contraction) method as an inspection technique for 4H-SiC wafers [1]. In industry, photoluminescence (PL) inspection is widely used as one of the standard methods for evaluating 4H−SiC wafers and epitaxial layers [2]. PL inspection is effective for detecting basal plane dislocations (BPDs) in epitaxial layers; however, it cannot directly detect BPDs that convert into threading edge dislocations (TEDs) at the substrate/epilayer interface (i.e., BPD-origin TEDs). Both through-going BPDs and converted BPDorigin TEDs can trigger the expansion of stacking faults during current-induced degradation [3], and therefore both types of defects can critically affect the reliability and yield of final products.

To address this limitation, we propose to inspect BPD-origin TEDs-undetectable by conventional PL inspection-using the EVC screening method. The EVC screening method consists of three steps: (i) an Expansion step, in which SSFs are intentionally expanded in the epilayer by ultraviolet (UV) irradiation; (ii) a Visualization step, in which the converted dislocation is not directly observed but is instead identified as the source of Shockley stacking faults (SSFs); and (iii) a Contraction step, in which the expanded SSFs are contracted to recover wafer quality [1].

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Fig. 1. EVC Screening method.

Fig. 1. EVC Screening method.

Operando approaches have been reported for studying current-induced degradation in SiC devices. Because a biased device generally emits electroluminescence (EL), in-situ EL observation is possible in principle; however, observation is often hindered by metal electrodes. To overcome this, a method using comb-shaped electrodes has been proposed so that EL can be observed through open windows [4]. In addition, combined schemes have been reported in which the current stress is temporarily stopped and PL imaging is performed in between stress intervals [5]. Current-stress-based SSF expansion has the advantage of applying stress in a structure close to the final product. Nevertheless, it requires electrode fabrication and other processing steps starting from a bare wafer, which increases both time and cost. Moreover, when the SSF expansion is driven by wafer-origin BPDs, performing operando characterization directly at the wafer stage may reduce disturbances introduced by electrodes and electrical circuitry. For example, series resistance in electrodes can reduce the injected current, decrease the EL intensity, and potentially lead to misclassification. In-situ PL observation, on the other hand, typically requires a dedicated excitation source, microscope optics, and a 2D camera, resulting in a more complex and costly instrumentation.

In the EVC tool, operando PL observation is, in principle, achievable by alternating the Expansion and Visualization steps. However, implementing a mechanical system that repeatedly moves the wafer while maintaining high positional accuracy significantly increases cost. In this study, we exploit the fact that the third harmonic of a YAG laser (e.g., 355 nm ) used in the Expansion step can also serve as a PL excitation source. We investigate the feasibility of low-cost operando PL spectrum mapping [6] by adding only a miniature spectrometer, without employing an expensive hyperspectral camera. The ability to acquire PL spectrum mapping data at low cost is particularly attractive under limited development budgets.

Furthermore, if SF types can be identified from PL spectra, unnecessary expansion of SFs that are difficult to contract thermally (e.g., Frank-type faults) could be avoided, thereby preventing reduction of usable wafer area.
This paper reports a trial implementation of operando PL spectrum mapping as a pathway to enhance the functionality of the EVC tool. Specifically, we demonstrate the influence of activation annealing on proton-implanted wafers prior to electrode formation, and present an example of detecting Franktype SSFs that are difficult to contract.

Experimental Preparation: Installation of a Mini-Spectrometer

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A quartz optical fiber for collecting PL emission was mounted near the UV-laser irradiation spot used for SSF expansion. The fiber was connected to a compact multichannel Si-CCD spectrometer (FLAME-S, Ocean Optics; wavelength range: 220−850 nm ) for PL spectral measurements (Fig. 2).

Experiment 1: EVC Screening and PL Spectroscopy

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Samples and proton implantation

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Three commercial n-type 4H-SiC epitaxial wafers with a 4∘ off-cut were used in this study. The epitaxial structures are summarized in Table 1. Proton implantation was carried out from the epilayer surface under the conditions listed in Table 1. The projected implantation depths for wafers A and B
were calculated using SRIM2013 [7], and the results are shown in Fig. 4. For wafer C, protons were accelerated to 2 MeV and then decelerated by passing through an aluminum foil, adjusting the effective energies to the equivalent of 1.25 MeV and 600 keV . Fig. 3 shows the damage events calculated using SRIM2013.

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Fig. 2. Expansion process.

Fig. 2. Expansion process.

Table 1. Wafers.

| Active | Buffer layer | Drift Layer | Proton Implantation
| Annealing | Thickness (μm) | ND (cm⁻³) | Thickness (μm) | ND (cm⁻³) | (keV) | ND (cm⁻²)
Wafer A | YES | 1 | 1.00E+18 | 10 | 8.00E+15 | 350 | 1.00E+13
Wafer B | NO | 0.5 | 1.00E+18 | 8 | 1.00E+16 | 600 | 1.40E+14
Wafer C | YES | 3 | 1.00E+18 | 19 | 4.00E+15 | 600, 1250 | 1.00E+12

Expansion step (UV-irradiation)

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As an expansion step, wafers A and B were irradiated by a scanned UV laser over a 10×10 mm2 area spanning both the proton-implanted and non-implanted regions in order to induce and expand Shockley-type stacking faults (SSFs) (Fig. 3).

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Fig. 3. UV irradiation.

Fig. 3. UV irradiation.

Visualization step (PL imaging and SSF-width analysis)

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As a visualization step, the expanded SSFs were evaluated by PL imaging. The SSF widths in the proton-implanted and non-implanted regions were measured, and a two-sample t-test was performed to assess the difference in mean SSF width between the two regions. By comparing wafers A and B, we examined whether the SSF-expansion suppression effect of proton implantation is maintained after activation annealing (i.e., not deactivated by the annealing process).

Contraction step and reproducibility check

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As a contraction step, wafer B was annealed at 800∘C for 3 h to contract the expanded SSFs. The expansion and visualization steps were then repeated to evaluate the reproducibility of SSF initiation locations. This procedure was conducted to confirm that the EVC screening method does not adversely affect wafer quality.

PL spectroscopy for wafer-quality evaluation

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Using wafer C, PL spectra were measured before proton implantation, after proton implantation, and after activation annealing in order to evaluate changes in wafer quality associated with each processing step.

Result 1: EVC Screening and PL Spectroscopy

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Simulations by SRIM2013 [7]

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SRIM2013 simulations suggested that implanted protons accumulate at a depth of approximately 2.4μ m in wafer A and approximately 5μ m in wafer B (Fig. 4). Fig. 5 shows the vacancy concentration estimated from SRIM2013 calculations for proton implantation.

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Fig. 4. Proton Distribution.

Fig. 4. Proton Distribution.

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Fig. 5. Vacancy Distribution.

Fig. 5. Vacancy Distribution.

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Fig. 6. PL Images of Wafer A.

Fig. 6. PL Images of Wafer A.

UV-PL imaging of expanded SSFs

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Fig. 6 shows UV-PL images of SSFs expanded by the EVC procedure for wafer A. The SSFs in the proton-implanted region exhibited a narrower band width than those in the non-implanted region, indicating that proton implantation suppresses SSF expansion.

Repeatability of SSF expansion after contraction

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Fig. 7 shows UV-PL images acquired using a 420−nm band-pass filter (BPF420). The white regions correspond to SSFs. The lower half of the image is the proton-implanted area, where SSFs were observed as gray features against a darker background. Panel (a) corresponds to the first expansion step. After the contraction step, the white SSF contrast disappeared (b). Panel (c) shows the second expansion step, in which SSFs expanded again at the same locations. The white square feature in the lower right region was not an SSF and was attributed to contamination.

[picture]

Fig. 7. PL Images of Wafer B.

Fig. 7. PL Images of Wafer B.

Statistical comparison of SSF widths

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Ten stripe-like SSFs were selected from each area, and their widths were measured. For both proton-implanted wafer A and wafer B, the SSF widths in the epilayer differed between the protonimplanted and non-implanted regions. A two-sample t-test yielded extremely small p-values (Table 2), indicating a statistically significant difference. These results suggest that the SSF-expansion suppression effect appears immediately after proton implantation and remains effective even after activation annealing.

Table 2. T-TEST.

Wafer | Proton | Average of SSF widcth (μm) | Standard deviation | Difference in means | P value | 95% CI diff (equal var)
A | NO | 150.3 | 1.52 | 28.2 | 1.03E-17 | 26.4, 30.0
YES | 122.1 | 2.17
B | NO | 120.6 | 2.58 | 72.8 | 2.07E-24 | 70.9, 74.7
YES | 47.8 | 1.29

Reproducibility of SSF initiation locations

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[picture]

Fig. 8. PL Images of Wafer B.

Fig. 8. PL Images of Wafer B.

Fig. 8(a) shows the UV-PL image obtained after the first expansion step, while Fig. 8(b) shows the UV-PL image obtained after the second expansion step following a contraction process. For comparison, the extracted contours from (b) were colored in purple and overlaid onto (a), as shown in Fig. 8(c). Sixteen SSFs were observed after the first expansion, and fifteen SSFs were observed after the second expansion at nearly the same locations. This reproducibility suggests that the EVC procedure does not measurably degrade wafer quality under the present conditions.

PL spectra

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The PL spectra in Fig. 9 are consistent with the above EVC-based evaluation of proton implantation. The emergence of the SSF-expansion suppression effect after proton implantation agrees with the reduced intensity of the band-to-band emission peak at 390 nm following implantation. In addition, the persistence of the suppression effect after activation annealing is consistent with the observation that the 390−nm peak intensity decreased slightly after annealing but remained largely stable overall.

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Fig. 9. PL spectrum of Wafer C.

Fig. 9. PL spectrum of Wafer C.

Experiment and Result 2: EVC Screening of Polytype-Inclusion-Related Stacking Faults and in situ PL Spectral Mapping

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An epitaxial wafer containing multiple polytype inclusions was purchased (Fig. 10). The wafer was an n-type 150−mm-diameter 4H−SiC epitaxial wafer with a 4∘ off-cut, consisting of a heavily nitrogen-doped buffer layer ( 2μ m,1×1018 cm−3 ) and a lightly doped drift layer ( 60μ m,9×1014 cm−3 ).

Focusing on regions containing triangular stacking faults (SFs), we evaluated the wafer using the EVC screening. After 355−nm laser irradiation as the expansion step, UV-PL imaging with a 420−nm band-pass filter (BPF420) was performed as the visualization step, and numerous bar-shaped SFs were observed. At this stage, as a simulated operando observation, PL spectral mapping was carried out within the yellow dashed region in Fig. 12 The measurement was performed with a 0.25−mm step while the laser irradiance was attenuated to approximately 1/100. Subsequently, a contraction step was conducted by annealing at 800∘C for 3 h .

Fig. 11(a) shows a bar-shaped 1SSF originating from a basal plane dislocation (BPD), whereas Fig. 11(b) shows a bar-shaped SF expanded from an inclusion containing SFs; its morphology was slightly different from that of the 1SSF in Fig. 11(a). After the contraction process, the 1SSF in Fig. 11(a) disappeared completely, whereas part of the SF in Fig. 11(b) remained uncontracted. No further change was observed even after an additional 6 h of annealing. The remaining SF is therefore considered to be different from a BPD-originated 1SSF.

Fig. 12(a) shows a PL image obtained with BPF420, and Fig. 12(b) shows the corresponding spectral mapping at 420 nm . Both images capture approximately two sets of bar-shaped stacking faults. Fig. 12(c) shows representative spectra; because both SSFs exhibit a peak at 420 nm , their dominant component was attributed to 1 SSF .

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Fig. 10. Polytype inclusion with triangle SF.

Fig. 10. Polytype inclusion with triangle SF.

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Fig. 11. PL image using BPF 420 nm .

Fig. 11. PL image using BPF 420 nm .

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Fig. 12. (a) PL-imaging (b) PL-Spectrum ( 420 nm ) mapping.

Fig. 12. (a) PL-imaging (b) PL-Spectrum ( 420 nm ) mapping.

Fig. 13(a) shows a PL image obtained with BPF420, and Fig. 13(b) shows spectral mapping at 488 nm . The 488−nm mapping revealed enhanced intensity at SF positions connected to polytype inclusions. The spectra in Fig. 13(c) exhibit a 420−nm peak attributed to 1SSF, a 488−nm peak attributed to Frank-type stacking faults [8], and a 540−nm peak attributed to polytype inclusions. These results indicate that stacking faults expanding from polytype inclusions are of a composite type, including not only 1SSF but also Frank-type stacking faults. If the uncontracted SFs are Frank-type faults with high thermal stability, their persistence after 800∘C annealing can be reasonably explained. These findings suggest that PL spectral mapping performed as an operando observation during EVC screening could enable early identification of SFs that do not contract (e.g., Frank-type components) and may allow their expansion to be halted at an early stage.
Because uncontractable SFs can render the affected wafer area unusable, minimizing their lateral extent is desirable from a cost perspective, and operando PL spectral mapping is therefore beneficial.

[picture]

Fig. 13. (a) PL-imaging (b) PL-Spectrum ( 488 nm ) mapping.

Fig. 13. (a) PL-imaging (b) PL-Spectrum ( 488 nm ) mapping.

Conclusion

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A miniature-spectrometer-based operando PL spectrum mapping scheme was implemented for the EVC inspection method by reusing the 355−nm expansion laser as the PL excitation source and collecting emission through an optical fiber. In proton-implanted epilayers, EVC/PL imaging showed a statistically significant reduction in SSF width, and the suppression effect persisted after activation annealing.

For a thick epilayer wafer containing polytype inclusions, PL spectrum mapping distinguished composite stacking faults expanded from inclusions, comprising 1SSF-related emission ( ~420 nm ) together with Frank-type ( ~488 nm ) and inclusion-related ( ~540 nm ) components. These findings
indicate that low-cost operando PL spectrum mapping can enhance EVC screening by enabling early fault-type identification and by supporting strategies to avoid unnecessary growth of thermally persistent faults that can reduce usable wafer area.

Acknowledgment

The original version of this paper is available on https://www.scientific.net/MSF.1190.27.pdf

METI R&D Support Program for Growth-oriented Technology SMEs Grant Number JPJ005698

References

The original version of this paper is available on https://www.scientific.net/MSF.1190.27.pdf

Y. Igarashi, K. Takano, Y. Matsushita, C. Shibata, Defect and Diffusion Forum Vol. 425, pp. 75-82 (2023).

International Electrotechnical Commission Standard 63068-3 (2020).

A. Tanaka, H. Matsuhata, N. Kawabata, D. Mori, K. Inoue, M. Ryo, T.Fujimoto, T. Tawara, M. Miyazato, M. Miyajima, K. Fukuda, A. Ohtsuki, T. Kato, H. Tsuchida, Y. Yonezawa, T. Kimoto, J. Appl. Phys. Vol. 99, 011101 (2006).

C. Ota, J. Nishio, A. Okada, R. Iijima, 19th Conference on Defects, Vol.52, pp. 5109-5120 (2023).

K. Konishi, R. Fujita, A. Shima, J. Electron. Mater. Vol. 48, pp. 1704-1713 (2019).

G. Feng, J. Suda, T. Kimoto, Appl. Phys. Lett. Vol. 92, 221906 (2008).

Information on .

S. Hageali, H. Guthrey, S. Johnston, A.Norman, J. Soto, B. Odekirk, R. Stahlbush, N. Mahadik, B. Gorman, M. Al-Jassim, J. Appl. Phys. Vol. 134, 075704 (2023).

This ePub file was created using machine-generated methods and automated software to convert the source text into an ePub format and may contain formatting inconsistencies from the original version. Formatting may vary depending on the device used.

The original version of this eBook is available on https://www.scientific.net/book/stacking-faults/978-3-0364-3126-0

Materials Science Forum, ISSN: 1662-9752, Vol. 1190, pp 37-42

doi: 10.4028/p-0xM8R1

© 2026 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2025-09-13

Revised:
2026-01-18

Accepted:
2026-02-28

Online:
2026-05-18

Quantitative Analysis of Excess Minority Carrier Density and Critical Duration in UV Irradiation-Based Screening for Bipolar Degradation in 4H-SiC

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Yasuyuki Igarashi 1,a*, Kazumi Takano 1, b, Yohsuke Matsushita 1,c and Takuya Morita 1, d

1 ITES Co., Ltd., 1-60 Kuribayashi, Otsu, Shiga 520-2151, Japan

ª*yiga@ites.co.jp, bkazumi_takano@ites.co.jp, cyohsuke_matsushita@ites.co.jp,

dtakuya_morita@ites.co.jp

Abstract

Ultraviolet (UV) irradiation on 4H−SiC epitaxial wafers, conducted prior to metallized circuit formation, is widely used to reveal whether BPD (basal plane dislocation) induced nucleation and expansion of a single Shockley stacking fault (1SSF) occurs via recombination enhanced dislocation glide (REDG). However, the UV method has remained largely qualitative, and its quantitative relationship to forward bias current injection has not been established. Here, using the excess minority carrier density at the BPD-to-TED (threading edge dislocation) conversion point, we establish equivalence criteria between two stress modes (current density and UV irradiance) and introduce a previously overlooked requirement for pulsed UV laser sources: the minority carrier density must exceed a threshold and be sustained for a finite "critical duration," tcrit, defined as the minimum time required to initiate dislocation glide. Notably, tcrit shows only weak dependence on the bulk carrier lifetime ( τb ), offering a practical route to determine pulsed UV irradiation conditions that faithfully emulate forward bias stress, even when τb is unknown.

Keywords: 4H−SiC, bipolar degradation, basal plane dislocation, stacking fault, UV screening, recombination-enhanced dislocation glide, minority-carrier lifetime.

Introduction

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Bipolar degradation, caused by the nucleation and expansion of 1SSF (single Shockley stacking fault) from BPD (basal plane dislocation) remains a key reliability concern for 4H−SiC bipolar power devices like PiN diodes and the body diode in MOSFETs. The conventional method for evaluating the impact of process modifications on bipolar degradation typically requires the fabrication of metallized active devices, followed by current injection testing. While highly reliable, this approach is costly and time intensive. As a simplified alternative, ultraviolet (UV) irradiation has been widely employed at the pre-circuit formation stage to verify the presence of defect expansion. UV irradiation is known to induce the nucleation and expansion of 1SSF from BPD through recombination enhanced dislocation glide (REDG) mechanism, similar to current injection. However, this method has been limited to qualitative assessments of 1SSF behavior and has not enabled quantitative equivalence, such as estimating the UV irradiation intensity corresponding to a specific current rating.

We have proposed a UV irradiation-based screening method (called E-V-C method) to detect latent BPD-related defects at an early stage by leveraging the SF expansion governed by REDG mechanism [1]. For practical deployment of the screening, however, it is essential to establish a quantitative equivalence between UV irradiation and forward bias current injection stress. We define UV irradiation conditions as equivalent to current injections if they allow identification of defect expansion with the same accuracy as current stress. Prior work [2], referencing Tawara et al. [3], reported that bar shaped 1SSF expansion occurs above a threshold current density, though device doping profiles influence the threshold value. Importantly, if we focus not on the current density but on the excess minority carrier density at the conversion point from BPD to TED (threading edge dislocation), where the stacking fault begins to expand, this density remains invariant to the device profile and is therefore defined as the critical minority carrier density. Based on this insight, we sought
to link the two stress modes, current injection and UV irradiation, via the critical minority carrier density generated under each condition.

A fundamental distinction, however, exists between the two stress modes. Constant current injection yields a steady state carrier distribution, whereas pulsed UV irradiation produces a transient carrier distribution that rises sharply post-pulse and decays exponentially. Therefore, in this study, we first independently determine, by experiment, the threshold conditions for SF expansion in each stress mode, namely, the threshold current density and the threshold UV irradiance. We then estimated the excess hole distributions using numerical calculations. By assuming equivalence of the hole density at the TED conversion point, we derived a correlation model. The analysis reveals that pulsed UV laser irradiation requires that the excess carrier density must not only exceed the threshold value for each pulse, but it must also persist above the value for a finite duration, herein termed "the critical duration" tcrit, a parameter absent under constant current injection case. This paper details the derivation of this equivalence condition for PiN diodes, incorporating the critical duration.

Experiments and Results

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PiN diodes were fabricated on commercial n-type 100 mm,4H-SiC wafers ( 4∘ off-cut toward [1120] direction). The structure comprised a buffer layer ( 0.5μ m,1×1018 cm−3 ) and a drift layer ( 5.4μ m, 5×1015 cm−3 ), epitaxially grown on the substrate ( 350μ m,6×1018 cm−3 ). A 0.5μ mp+anode layer was formed by Al doping ( 4.1×1018 cm−3 ). Ni electrode was deposited on the backside, and Al combshaped electrodes ( 2 mm square chips) were patterned on half the wafer for accelerated current stress tests; the remaining half was reserved for UV stress experiments.

Accelerated current stress tests were conducted with pulsed currents of 250−400 A/cm2. 1SSF expansion was monitored using UV photoluminescence (UVPL, 420 nm band pass filter), tracking Si(g) dislocation glide velocities. In parallel, UV irradiation was applied using a 355 nm Nd:YAG pulsed laser ( 10 ns pulse, 20μ s period, duty 0.05%, max 211μ J/pulse,3 mm beam). Output was varied from 1−100% using an attenuator, and 1 SSF expansion was studied at 10%,25%,50%, and 100% power.

Under current stress, 329 bar shaped 1SSF sites from 43 chips were analyzed (Fig. 1(a)), while 11 sites were examined under UV stress (Fig. 1(b)). Measured glide velocities varied significantly at identical stress levels, presumably attributed to numerous factors in real devices that can impede the motion of the Si(g) dislocation (e.g., various crystallographic defects). Because the goal of this study is to evaluate the correlation between stress intensity and expansion, linear regression was applied to the maximum-velocity data points at each stress level (red markers in Fig. 1(a), and (b)), where the influence of impeding factors is presumed to be minimal. Threshold intensities, defined as the zerovelocity intercepts, were determined as 235 A/cm2 for current density and 36,650 W/cm2 for UV irradiance, indicating equivalence between the two [2].

[picture]

Fig. 1. Si(g) core glide velocity VS. stress intensity (current density (a) and irradiation power (b)).

Fig. 1. Si(g) core glide velocity VS. stress intensity (current density (a) and irradiation power (b)).

Numerical Analysis and Discussion

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The experimentally determined threshold current density of 235 A/cm2 and UV irradiance of 36,650 W/cm2 were used to estimate hole densities, assuming equivalence at the critical minority carrier density. The device structure was p+/n−/n+/n++(anode, drift, buffer, substrate), with particular emphasis on the buffer layer, where BPD-to-TED conversion predominates.

The excess hole density ΔpFB(x) under forward bias was calculated by solving the carrier transport equation, assuming quasi-Fermi potential continuity at interfaces (i.e., a continuous pn product). The computed values near the n+/n++interface aligned reasonably with literature ( 1.8−2.5×1016 cm−3 [3]), though slightly lower as shown in Fig. 2. Since the hole density depends on the bulk minority carrier lifetime τb in the n−layer, which is unknown, the calculation was carried out by varying τb from 50 ns to 2μ s. The minority carrier lifetimes in the buffer layer and the substrate are also unknown; therefore, with reference to previous studies [4-6], they were assumed to be τbuffer =30 ns and τsub =3 ns, respectively.

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Fig. 2. Depth profiles of hole density under forward bias stress for the current density of 235 A/cm2.

Fig. 2. Depth profiles of hole density under forward bias stress for the current density of 235 A / c m 2 .

In contrast, under UV irradiation stress the hole density generated by the laser pulses becomes a function of both time and space. The excess hole density ΔpUV(x,t) was obtained from diffusion equations with Robin-type boundary conditions for surface recombination, continuity of carrier density and flux at layer interfaces, and an initial distribution set by Lambert-Beer's law for optical absorption immediately after UV exposure. Although a Fourier-series analytical solution is possible, a large number of higher-order terms are required for convergence; therefore a one-dimensional backward Euler finite difference method was employed to reduce computational load. Simulations were run for τb=50 ns,200 ns, and 2μ s, as shown in Fig. 3(a), (b), (c), respectively. τbuffer  and τsub  were assumed to be the same as in forward bias case.

[picture]

Fig. 3. Depth profiles of hole density under UV irradiation stress for τb=50 ns,200 ns,2μ s for the UV irradiance of 36,650 W/cm2.

Fig. 3. Depth profiles of hole density under UV irradiation stress for τ b = 50 n s , 200 n s , 2 μ s for the UV irradiance of 36 , 650 W / c m 2 .

Since many BPD-to-TED conversion points are thought to distribute near the buffer/substrate and buffer/drift interfaces, the hole density at these locations was monitored over time. Figure 4 shows decay curves for τb=50 ns and 2μ s. Figure 5 overlays these curves with forward bias results (from Fig. 2). It is an enlarged view of Figure 4, highlighting the region that includes the point-within the range of τb=50 ns to 2μ s-at which the hole density under forward bias intersects with the decay curve of the hole density after UV pulse irradiation (i.e., the point where the two become identical). The vertical axis has been changed from a logarithmic scale to a linear scale.

Black triangles indicate the points where UV induced hole densities fall to the forward bias threshold level. This level can be interpreted as the minimum duration required for the initiation of 1SSF expansion. Specifically, it corresponds to the time needed for the leading edge of the Si(g) core dislocation to overcome the Peierls potential and initiate the local 4 H to 3 C transformation. This duration is defined as the critical time, tcrit. Notably, tcrit exhibits only a weak dependence on the bulk carrier lifetime in the drift layer, τ b. As shown in Figs. 2−4, the hole density in the buffer layer changes significantly with τb, but the direction of this change is the same under both forward bias and UV irradiation conditions. Consequently, terit itself is expected to vary little. By contrast, although not discussed in detail here, an increase in the minority carrier lifetime in the buffer layer or the substrate results in a longer tcrit -defined as the decay time required for the hole density after UV irradiation to converge to that under forward bias current injection-whereas a decrease leads to a shorter tcrit .

[picture]

Fig. 4. Decay curves of hole density.

Fig. 4. Decay curves of hole density.

[picture]

Fig. 5. The same hole density points
(Superimposed on Fig. 4 with Fig. 2).

Fig. 5. The same hole density points (Superimposed on Fig. 4 with Fig. 2).

As shown in Fig. 6, terit remained approximately constant ( ~50±5 ns ) across τb=50 ns to 2μ s, with negligible dependence on τ b. The same figure also shows (right y-axis) the τ b dependence of the hole density.

[picture]

Fig. 6. Critical duration ( tcrit  ) over the range of carrier lifetime from 50 ns to 2μ s.

Fig. 6. Critical duration ( t crit ) over the range of carrier lifetime from 50 ns to 2 μ s .

Therefore, a UV condition equivalent to a given forward bias condition can be defined by the following equation (1). At a conversion point x0 in the buffer

ΔpUV(x0,tcrit )=ΔpFB(x0).(1)

This provides a practical guideline for setting UV irradiation parameters for screening BPD-related defects. Moreover, the weak dependence of tcrit on carrier lifetime implies that even if τb is unknown, its impact on the equivalency is limited.

Summary

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We demonstrated that 1SSF nucleation/expansion under pulsed UV irradiation requires not only exceeding the threshold hole density but also sustaining it for the critical time tcrit. This duration represents the minimum time to overcome the Peierls barrier associated with the 4 H -to-3C transformation. Notably, torit is nearly independent of the bulk minority carrier lifetime τb in the n− layer. To replicate forward bias degradation via pulsed laser irradiation, conditions must yield hole densities matching those under forward bias, sustained for torit (Eq. (1)). The dependence of tcrit on the minority carrier lifetimes in the buffer layer and the substrate will be investigated in detail in future studies. While the equivalence estimation in this study relied on statistical analysis of multiple defects, future work will aim to directly validate Eq. (1) by examining the expansion behavior of identical defects. This will be pursued sequentially through UV stress, annealing-induced 1SSF contraction (300−600∘C), and subsequent current injection stress.

Acknowledgment

The original version of this paper is available on https://www.scientific.net/MSF.1190.37.pdf

This work was supported by the Ministry of Economy, Trade and Industry (METI) R&D Support Program for Growth-Oriented Technology SMEs (Grant No. JPJ005698). The authors gratefully acknowledge the technical guidance of Prof. Kato (Nagoya Institute of Technology) and Assoc. Prof. Harada (Nagoya University).

References

The original version of this paper is available on https://www.scientific.net/MSF.1190.37.pdf

Y. Igarashi, K. Takano, Y. Matsushita, C. Shibata, Defect and Diffusion Forum, vol. 425, p. 75, 2023.

Y. Igarashi, K. Takano, Y. Matsushita, C. Shibata, Defect and Diffusion Forum, vol. 434, p. 23, 2024.

T. Tawara, S. Matsunaga, T. Fujimoto, M. Ryo, M. Miyazato, T. Miyazawa, K. Takenaka, M. Miyajima, A. Otsuki, Y. Yonezawa, T. Kato, H. Okumura, T. Kimoto, and H. Tsuchida, J. Appl. Phys., vol. 123, 025707, 2018.

T. Tawara, T. Miyazawa, M. Ryo, M. Miyazato, T. Fujimoto, K. Takenaka, S. Matsunaga, M. Miyajima, A. Otsuki, Y. Yonezawa, T. Kato, H. Okumura, T. Kimoto, H. Tsuchida, J. Appl. Phys. 120, 115101 (2016).

A. Y. Polyakov, Q. Li, S. Wook Huh, M. Skowronski, O. Lopatiuk, L. Chernyak, and E. Sanchez, J. Appl. Phys. 97, 0537032005.

W. A. Doolittle, A. Rohatghi, R. Ahrienkel, D. Levi, G. Augustine, and R. H. Hopkins, Mater. Res. Soc. Symp. Proc. 483, 1971998.

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Materials Science Forum, ISSN: 1662-9752, Vol. 1190, pp 43-48

doi: 10.4028/p-1DCRuh

© 2026 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2025-09-13

Revised:
2025-12-21

Accepted:
2026-03-21

Online:
2026-05-18

Challenges in 1SSF Detection in 4H-SiC Epilayer and Related Failure

The original version of this paper is available on https://www.scientific.net/MSF.1190.43.pdf

C. Calabretta 1,a*, C. Bottari 1,b, S. Adamo 1,c, B. Carbone 1,d, G. Maira 1,e, F. Vento 1,f, E. Fontana 1, g, N. Piluso 1, h, M. S. Alessandrino 1,i, A. Russo 1,j, P. Fiorenza 2,k, F. Roccaforte 2,l, A. Severino 1,m

1 STMicroelectronics, Stradale Primosole 50, 95121 Catania, Italy

2 CNR-IMM, Strada VIII n. 5 - Zona Industriale, 95121, Catania, Italy

a * cristiano.calabretta01@st.com, b ketty.bottari@st.com, c salvatore.adamo1@st.com,

d  beatrice.carbone@st.com, e  giovanni.maira@st.com, f  fabiana.vento@st.com, enzo.fontana@st.com, h  nicolo.piluso@st.com, i  santi.alessandrino@st.com, 

jalfio-lip.russo@st.com, k  patrick.fiorenza@imm.cnr.it, 'fabrizio.roccaforte@imm.cnr.it, mandrea.severino@st.com 

Keywords: 1SSF, ELFR, micro photoluminescence, burger vector, BPD, IDSS.

Abstract

Basal plane dislocations (BPDs) represent one of the most detrimental defects in 4H−SiC epitaxial wafers, causing forward voltage degradation in bipolar and power FET devices through the formation and expansion of Shockley-type stacking faults (SSFs). This expansion is driven by the recombination-enhanced dislocation glide (REDG) mechanism during forward bias operation. Despite efforts to mitigate BPD effects by converting them into threading edge dislocations (TEDs) via buffer layer engineering, throughout the epitaxial growth SSFs can still nucleate and propagate, particularly under high current injection. This work presents a comprehensive analysis combining electrical characterization, fault localization technique, Scanning Electron Microscopy (SEM) and micro-photoluminescence ( μ-PL) to investigate SSF formation, crystallographic features, and their impact on device performance. The results underscore the critical role of advanced diagnostics and epitaxial process optimization in controlling SSF-related degradation and improving the reliability of SiC power devices.

Introduction

The original version of this paper is available on https://www.scientific.net/MSF.1190.43.pdf

All BPDs are considered one of the most harmful defects in SiC epitaxial wafers. They cause forward degradation, which manifests as an increased forward voltage drop, in SiC bipolar devices and body diodes junction within power MOSFET when they occur in the active region. During forward bias in a SiC pn junction, BPDs can lead to SSFs due to the injection of minority carriers. This expansion of stacking faults is driven by the electron-hole REDG process [1-2]. This phenomenon was initially observed as causing degradation in the forward characteristics of highvoltage SiC pin diodes, with its primary source identified as stacking faults expanding within the voltage-blocking region. SSF expansion from BPDs occurs during forward bias operation in 4H−SiC, leading to forward voltage drift in minority carrier SiC devices [3]. Additionally, SSF expansion has been linked to reverse bias breakdown voltage degradation [4]. To reduce the impact of these SSFs in the active drift layer, a highly doped buffer layer was developed to convert most BPDs into threading edge dislocations (TEDs) [5]. It is seldom observed that nominal current density degradation is generally not impacted. However, at exceptionally high current levels, the increased density of minority charge carriers can penetrate deeper into the buffer region, potentially triggering stacking fault growth at deeply embedded crystal defects within the buffer or even the n+substrate. In the case of unipolar devices during each turn-off event of a SiC MOSFET, the body diode is subjected to forward bias, which may induce the propagation of stacking faults within the n-type drift layer. The expanded stacking fault introduces a potential barrier that contributes to an increase in the on-resistance of the device. An increase in the drain leakage current after the current stress is expected [6].

Experimental

The original version of this paper is available on https://www.scientific.net/MSF.1190.43.pdf

In this experiment, 4H-SiC planar MOSFETs, fabricated on an epitaxial layer of almost 13μ m thickness with a doping concentration of about 1×1016 cm−3, were used.
Sample prepation from backside was performed with MultiPrep TM  Precision Polishing System (Allied High Tech Products) aimed to remove package frame and to reach SiC substrate. PHEMOS1000 Emission microscopy (Em.Mi.) was used to identify the coordinates of point of failure induced by electrical stress. Focused ion dual beam (FIB) -Helios 5UC - was employed to mark the position and identify the region to investigate. LabRam Odyssey Raman spectrometer equipped with a λ=320 nm (74x objective) wavelength and 600gr/mm grating was adopted to perform the 1SSF PL map.

Results and Discussion

The original version of this paper is available on https://www.scientific.net/MSF.1190.43.pdf

Sample analyzed in this work didn't exhibit any indicators of impending failure, offering no warning of electrical issues at the Electrical Wafer Sorting test (EWS). After assembly process, sample was subjected to Early Life Failure Rate (ELFR) test flow, not exhibiting any anomalous current trend. Following ELFR, some electrical parameters have been additionally tested in order to confirm the goodness of the piece. As shown in Fig. 1, electrical test for this device revealed a slight increase in drain leakage current at high bias ( 850 nA at 1200 V ) (Fig.1a) if compared to other parts subjected to the same test cycle in which IDSS value is lower than 200 nA (Fig 1b).

[picture]

Fig. 1. Drain leakage current (IDSS) trends for sample analyzed in this work (left) and a device subjected to same trials (EWS + ELFR + Final test) (right). NOTE: vertical scale in the two graphs is different, current values at 1200 V are reported for easy of reference.

Fig. 1. Drain leakage current (IDSS) trends for sample analyzed in this work (left) and a device subjected to same trials (EWS + ELFR + Final test) (right). NOTE: vertical scale in the two graphs is different, current values at 1200 V are reported for easy of reference.

After the above described preparation, the device was subjected to fault localization analysis, Sample was appropiately powered in IDSS configuration to identify the region in which current leakage is concentrated, Emitted photons where clearly detected and shown in Fig. 2 as pink spots. These emissions are in correspondence to a defect, well visible as dark line with IR camera.

[picture]

Fig. 2. Fault Localization by photon emission from backside.

Fig. 2. Fault Localization by photon emission from backside.

To better investigate the defect region was identified from backside to. Decapping of the package and total delayering steps allowed the observation of the failure region at the epitaxial level under the SEM. As shown in Fig. 3, some depressions on epitaxy surface are well visible in correspondence of hot spot region, crossed by the dark line visible in Fig. 2.

[picture]

Fig. 3. SEM image perfomed with FIB Helios 5UC showing depression on epitaxial layer and responsible to IDSS leakage.

Fig. 3. SEM image perfomed with FIB Helios 5UC showing depression on epitaxial layer and responsible to IDSS leakage.

Following the Emission Microscopy investigation and spatial localization of the failure with SEM, μ−PL analysis was performed to examine stacking faults extended within the 4H−SiC epilayers.

Fig. 4a presents the map obtained by centering the acquisition on the spectral region corresponding to stacking fault emission, revealing a characteristic triangular morphology. The spectral data reported in Fig. 4b highlights two distinct regions: region 1 corresponding to the μ-PL acquisition within the stacking fault area, showing SF layer emission at λ=424 nm, thereby identifying it as a single stacking fault ( 1 SSF) and region 2 , exhibiting only band-to-band emission with a peak at λ=389 nm [7].

Considering the 4∘ off-axis angle and the 1SSF length of approximately 150μ m, it can be inferred that the stacking fault originates from a BPD located just above the BPD-to-TED conversion zone, likely formed during the initial stages of epitaxial growth and subsequently propagated during electrical testing. Indeed, Lendenmann et al. reported a voltage drop occurring during forward operation [8], attributing it to BPDs acting as sources of SSFs. Specifically, a BPD dissociates into two partial dislocations with SSF forming between them. The expansion of the SSF is driven by the glide of these partial dislocations through the REDG mechanism. When a sufficiently large amount of excess carriers are injected, the Si-core partial dislocation starts to glide, which leads to 1SSF expansion. Both bipolar and unipolar SiC devices exhibit forward degradation when a BPD propagates along the active direction. Various types of stacking faults have been identified using UVbased PL mapping, revealing over 15 distinct SSF shapes in the active regions of degraded SiC devices following electrical stress testing. These SSF shapes have been categorized into multiple forms, including rectangular, triangular, and rhombic geometries [9-10-11-12-13-14]. The expansion of SSFs primarily takes place in the n -type region and is confined between the p+−n−and n−−n+ junctions. Notably, Si-core partial dislocations are mobile, whereas C-core partial dislocations remain immobile. Stahlbush et al [15] suggested that the observed expansion patterns are closely linked to
the Burgers vector and direction of the BPDs. Ijima [16] elucidates the relationship between the morphologies of expanded SSFs and the configurations of BPD segments in 4H-SiC epilayers. It was demonstrated that, considering three types of Burgers vectors, 2 varieties of PD loops, and 12 line directions, there exist 72 distinct crystallographic BPD structures. The specific shapes of the expanded SSFs were predicted by analyzing the glide behavior of the PDs. Through g·b analysis, the predicted SSF shapes were confirmed to correspond well with experimental results and a total of 38 different expanded SSF shapes were identified. This established correlation enables the determination of the Burgers vectors and line directions of the original BPD segments based on the observed shapes of the expanded SSFs.

[picture]

Fig. 4. a) 1 SSF imaging through m−PL intensity map centred at λ=424 nm; b) PL spectra within (1) and outside (2) the 1SSF; c) BPD evolution modeling, with initial direction and burger vector at at the beginning of the expansion of 1SSF d) Vesta 1SSF lattice simulation reporting the lattice stacking in correspondence of the fault.

Fig. 4. a) 1 SSF imaging through m − P L intensity map centred at λ = 424 n m ; b) PL spectra within (1) and outside (2) the 1SSF; c) BPD evolution modeling, with initial direction and burger vector at at the beginning of the expansion of 1SSF d) Vesta 1SSF lattice simulation reporting the lattice stacking in correspondence of the fault.

The characteristic morphology of the SSFs provides insight into the nature of the dislocations that bound them. From the μ-PL analysis, it can be inferred that the dislocation direction is [10-10] with a Burgers vector of (1/3)[11-20] [16] as schematized in Fig. 4c where SSF starting shape is reported. A BPD can possess any of six possible Burgers vectors; however, due to the symmetry of the crystal, only three Burgers vectors (1/3)[11−20],(1/3)[1−210], and (1/3)[−2110] need to be considered when analyzing 1SSF expansion. The dislocation line itself typically aligns with one of the six ⟨11−20⟩ crystallographic directions. In this study after repeated laser irradiations, the SSF does not exhibit any further lateral enlargement. This behavior strongly suggests that the SSF is confined by C-core dislocations both above and below, effectively limiting its expansion. Furthermore, the intensity variations observed from left to right correspond to the defect's emergence toward the surface along the crystallographic direction [11-20]. This directional extension is governed by the presence of Sicore dislocations at the leading edge, which defines the expansion front of the stacking fault according to the PD loop model[17]. Using Zhdanov's notation, the stacking sequence of the SSF is expressed as (1,3), and that of perfect SiC is (2,2). In the reported stacking representation of the bond configuration near the edge of a SSF in SiC (Fig. 4d), the left and right sides correspond to the perfect SiC crystal structure and the SSF region, respectively. Four slip planes, designated as α,β,γ, and δ, are identified. SSFs may form along these dislocation slip planes. For the specific 1SSF defect shape considered, according to the basal plane dislocation loop model [16], the C -core partial dislocations oriented along the [-1-120] and [11-20] crystallographic directions, are consistently located on the right side of the SSF, as reported in [18]. Consequently, the dislocation loop forms when the slip occurs on either the α or β slip planes. The Fig. 4d exemplifies the structural evolution from the perfect crystal stacking sequence, transitioning from an A′C′AB stacking to an A′BCA configuration through slip along the β plane.

Conclusion

The original version of this paper is available on https://www.scientific.net/MSF.1190.43.pdf

This study highlights the critical role of BPDs and the associated formation of 1 SSF in 4H−SiC epitaxial wafers, which can influence device performance through forward degradation mechanisms. Advanced diagnostic techniques, particularly μ-PL mapping, provide detailed spatial and spectral insights into the morphology and crystallographic nature of 1SSF within the epitaxial layers. The μ PL analysis effectively identifies and characterizes stacking fault expansions originating from BPDs, enabling precise localization and understanding of defect propagation. These insights are essential to guide epitaxial growth optimization and process control strategies, including thermal and oxidation treatments, to mitigate SSF-related degradation and enhance the reliability of SiC power devices. The integration of electrical testing with μ-PL and complementary microscopy techniques forms a comprehensive approach for monitoring stacking fault dynamics and improving wafer screening procedures.

Acknowledgment

The original version of this paper is available on https://www.scientific.net/MSF.1190.43.pdf

The authors would like to thank:

STMicroelectronics group involved in electrical stress in people of S. Bevilacqua, A. Terracina, L. Anoldo, G. Tosto;

GQR Laboratory of STMicrolectronics for their efforts in sample preparation and fault localization analysis, especially of G. Almirante, R. Lucifora, S. De Nizza, C. Realmuto.

References

The original version of this paper is available on https://www.scientific.net/MSF.1190.43.pdf

Feng, Gan, Jun Suda, and Tsunenobu Kimoto. Physica B: Condensed Matter 404, no. 23-24 :4745-4748, (2009).

Thierry-Jebali, N., C. Kawahara, T. Miyazawa, H. Tsuchida, and T. Kimoto. AIP Advances 5, no. 3 (2015).

Palanisamy, Shanmuganathan, et al. 2021 IEEE International Reliability Physics Symposium (IRPS). IEEE, (2021).

J Wang, Pin, et al. Materials Science in Semiconductor Processing .

Piluso, Nicolo, et al. "High Quality 4H-SiC Epitaxial Layer by Tuning CVD Process." Materials Science Forum. Vol. 963. Trans Tech Publications Ltd, 2019.

A. Agarwal, H. Fatima, S. Haney, and S. H. Ryu, IEEE Electron Device Lett. 28, 587 (2007).

Piluso, Nicolo, et al. " defects analysis by Micro Raman spectroscopy." Materials Science Forum. Vol. 821. Trans Tech Publications Ltd, 2015.

H. Lendenmann, F. Dahlquist, N. Johansson, R. Söderholm, P.Å. Nilsson, J.P. Bergman, and P. Skytt, Long term operation of 4.5 kV PiN and 2.5 kV JBS diodes, Mater. Sci. Forum 353356 (2001), pp. 727-730.

H. Jacobson, J. Birch, R. Yakimova, M. Syväjärvi, J.P. Bergman, A. Ellison, T. Tuomi, and E. Janzén, Dislocation evolution in 4H-SiC epitaxial layers, J. Appl. Phys. 91 (2002), pp. 63546360.

H. Jacobson, J.P. Bergman, C. Hallin, E. Janzén, T. Tuomi, and H. Lendenmann, Properties and origins of different stacking faults that cause degradation in SiC PiN diodes, J. Appl. Phys. 95 (2004), pp. 1485-1488.

S. Ha, M. Benamara, and M. Skowronski, Core structure and properties of partial dislocations in silicon carbide p-i-n diodes, Appl. Phys. Lett. 83 (2003), pp. 4957-4959.

S. Ha, M. Skowronski, and H. Lendenmann, Nucleation sites of recombination-enhanced stacking fault formation in silicon carbide p-i-n diodes, J. Appl. Phys. 96 (2004), pp. 393-398.

Calabretta, Cristiano, et al. "Impact of nitrogen on the selective closure of stacking faults in 3CSiC." Crystal Growth & Design 22.8 (2022): 4996-5003.

Calabretta, Cristiano, et al. "Exploring crystal recovery and dopant activation in coated laser annealing on ion implanted epitaxial layers." Materials Science in Semiconductor Processing 174 (2024): 108175.

Stahlbush, M.E. Twigg, J.J. Sumakeris, K.G. Irvine, and P.A. Losee, Mechanisms of stacking fault growth in SiC PiN diodes, Mater. Res. Soc. Symp. Proc. 815 (2004), p. 103.

Iijima, Akifumi, et al. Philosophical Magazine 97.30: (2017), 2736-2752.

Kimoto, Tsunenobu, and James A. Cooper. Fundamentals of silicon carbide technology: growth, characterization, devices and applications. John Wiley & Sons, 2014.

Matsuhata, Hirofumi, et al. "Contrast analysis of Shockley partial dislocations in 4H-SiC observed by synchrotron Berg-Barrett X-ray topography." Philosophical Magazine 94.15 (2014): 1674-1685.

This ePub file was created using machine-generated methods and automated software to convert the source text into an ePub format and may contain formatting inconsistencies from the original version. Formatting may vary depending on the device used.

The original version of this eBook is available on https://www.scientific.net/book/stacking-faults/978-3-0364-3126-0

Materials Science Forum, ISSN: 1662-9752, Vol. 1190, pp 49-54

doi: 10.4028/p-kNQ0l1

© 2026 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2025-09-26

Revised:
2026-01-06

Accepted:
2026-01-31

Online:
2026-05-18

Exploring the Ion Implantation Mechanism for Suppressing Stacking Fault Expansion in 4H-SiC: A Fundamental Approach

The original version of this paper is available on https://www.scientific.net/MSF.1190.49.pdf

Takashi Yoda 1,a*, Masaki Sano 3, b, Jun Kojima 4,c, Shoichi Onda 4, d, Anton Myalitsin 1,e, Kuniyuki Kakushima 1,2,f, Takayuki Ohba 1, g, Atsushi Oshiyama 4,5,h and Kenji Shiraishi 3,5,i

1 WOW Alliance, 2 School of Engineering, Institute of Science Tokyo, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan

3 Graduate School of Engineering, 4 Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya, Aichi 464-8603/8601, Japan

5 Center for Innovative Integrated Electronic Systems, Tohoku University,Sendai, 980-8572, Japan

a*yoda.t.efe9@m.isct.co.jp, b  sano.masaki.0328@outlook.jp, c  kojima.jun.t2@f.mail.nagoya-u.ac.jp, d  onda.shoichi.n9@f.mail.nagoya-u.ac.jp, e  anton@anvos-analytics.com,

f  kakushima.k.aa@m.titech.ac.jp, c  ohba.t.ac@m.titech.ac.jp, h  atsushi.oshiyama.b5@tohoku.ac.jp, ikenji.shiraishi.c2@tohoku.ac.jp

Abstract

Suppressing the expansion of Single Shockley-type stacking faults (1SSFs) is critical for the growing demand of high-performance power devices. However, the underlying suppression mechanism has not yet been fully elucidated. Through proton ion implantation studies, we have established a fundamental approach by modeling this phenomenon. Carbon vacancy ( Vc ) generated by high-energy proton implantation are found to play a significant role in suppressing the expansion of 1SSFs.

Keywords: silicon carbide (SiC), power devices, basal plane dislocations (BPDs), Single Shockleytype stacking faults (1SSFs), proton implantation, density functional theory (DFT), photoluminescence (PL), cathodoluminescence (CL), carbon vacancies ( Vc ).

Introduction

The original version of this paper is available on https://www.scientific.net/MSF.1190.49.pdf

Silicon carbide ( SiC ) power devices exhibit superior performance compared to conventional silicon-based counterparts, enabling operation at higher voltages and frequencies with enhanced power efficiency and reduced energy losses. However, during the epitaxial growth of SiC , basal plane dislocations (BPDs) propagate from the substrate into the epitaxial layer. Further complications arise from the fact that BPDs dissociate into pairs of partial dislocations (PDs) on the basal plane, accompanied by Single Shockley-type stacking faults (1SSFs), which expand when low-energy holes interact with the Si-core. The expansion of these 1SSFs leads to bipolar degradation [1]. Practical proposal to suppress the 1SSFs expansion have been actively developed and reported [2-11]. A standard solution is to design a recombination-enhancing buffer layer [12]. Proton implantation has also emerged as a promising technique for suppressing the formation of 1SSFs [13-16]. As alternative candidates, implantation techniques using helium and other ion species have been investigated [1719]. More recently hydrogen plasma treatment, which causes less damage to the device, has also been reported [20]. At the early stage of proton implantation development, various mechanisms for suppressing 1SSFs expansion, including hydrogen-related effects, were actively discussed. Nevertheless, as research on helium and other ion implantations has advanced, the role of vacancies has increasingly come into focus. In this study, we evaluate the impact of proton implantation on the suppression of the expansion of 1SSFs. Furthermore, we investigate the underlying suppression mechanisms by analyzing the atomic and electronic structures surrounding the 1SSFs.

Experimental and Modeling

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The epitaxial films used in this study consisted of a 10−μm-thick drift layer grown on an n-type 4H−SiC substrate. Two types of 4H−SiC epitaxial films were subjected to proton implantation at depths of 5μ m and 10μ m from the epitaxial surface, respectively. The proton implantation conditions were 0.6 MeV for the 5−μm depth and 0.95 MeV for the 10−μm depth, with an identical dose of 1×1015cm−2. Following proton implantation, the samples were irradiated with ultraviolet (UV) light to promote the expansion of 1SSFs. The UV irradiation was carried out using a 355 nm Nd:YAG laser with an output power of 10 W and a spot size of 3 mm in diameter. Photoluminescence (PL) imaging through a 420−nm bandpass filter was employed to monitor the evolution of 1SSFs. Specimens for scanning transmission electron microscopy (STEM) were prepared using a focused ion beam (FIB) system (Helios 660, FEI). Cross-sectional STEM observations of 1SSF edges were performed with a JEM-ARM300F2 (JEOL) operated at an acceleration voltage of 300 kV . Cross-sectional cathodoluminescence (CL) measurements were conducted using a Schottky-emission scanning electron microscope (SEM, S4300SE). The accelerating voltage was set to 10 kV with a beam current of ~2nA. CL spectra were collected at low temperature ( 28 K ) using a Si-CCD detector. For modeling basal plane dislocations (BPDs), 1SSFs, and vacancy structures, structural optimization and electronic state calculations were performed using the Vienna Ab initio Simulation Package (VASP), based on density functional theory (DFT) [21].

Results and Discussion

The original version of this paper is available on https://www.scientific.net/MSF.1190.49.pdf

We first evaluated photoluminescence (PL) imaging of the 10−μm-thick drift layer of 4H−SiC following proton implantation at a depth of 5μ m from the epitaxial surface (Fig. 1). Figure 2 shows a bright-field STEM cross-sectional image corresponding to the region indicated by the red arrow in Fig. 1. The image clearly demonstrates that proton implantation effectively suppresses the expansion of 1SSFs. The expansion of 1SSFs was terminated by a partial dislocation (PD) located at 5.8μ m below the surface of the epitaxial layer, which is nearly identical to the targeted implantation depth of 5μ m. Subsequently, cross-sectional CL measurement s were performed for both the 5−μm and 10−μm proton-implanted epitaxial layers, as shown in Fig. 3 and 4. Three main features were identified in the spectra: near-bandedge emission ( 375−400 nm ), broad emission ( 430−700 nm ), and silicon vacancy ( Vssi )-related emission ( 852 nm and around 950 nm ). Figure 5 shows the CL spectra near 380−nm peak wavelength, comparing the results for proton implantation

[picture]

Fig. 1. PL-Imaging after proton implantation. Red arrow indicates STEM area.

Fig. 1. PL-Imaging after proton implantation. Red arrow indicates STEM area.

depths of 5μ m and 10μ m from the epitaxial film surface.

[picture]

Fig. 2. BF-STEM cross sectional image of SSF expansion suppressed by proton irradiation.

Fig. 2. BF-STEM cross sectional image of SSF expansion suppressed by proton irradiation.

[picture]

Fig. 3. CL spectra of 5μ m depth proton irradiated sample.

Fig. 3. CL spectra of 5 μ m depth proton irradiated sample.

[picture]

Fig. 4. CL spectra of 10μ m depth proton irradiated sample.

Fig. 4. CL spectra of 10 μ m depth proton irradiated sample.

[picture]

Fig. 5. Cross sectional CL spectra after proton implantation up to 5μ m and 10μ m from the epitaxial film surface.

Fig. 5. Cross sectional CL spectra after proton implantation up to 5 μ m and 10 μ m from the epitaxial film surface.

[picture]

Fig. 6. CL area intensity depth profile between 5μ m and 10μ m depth proton implantation sample.

Fig. 6. CL area intensity depth profile between 5 μ m and 10 μ m depth proton implantation sample.

This peak is generally attributed to near-band-edge emission arising from transitions between the conduction band minimum (CBM) to the valence band maximum (VBM). The cumulative intensity distribution in the 375−400 nm range is presented in Fig. 6. The data reveal that, up to the proton implantation depth, only weak emission signals are detected, suggesting the presence of non-emissive centers in the implanted region, most likely associated with vacancies. Vsi-related emission was also observed in Figs. 3 and 4. However, since the majority of intrinsic defects in 4H-SiC are carbon vacancies ( VC ) due to their lower formation energy, the dominant defects are expected to be VC rather than VSi. It should be noted that CL measurements can sometimes enhance Vsi-related emission because of the deep and stable energy levels of VSi. In this study, the specific vacancy type could not be conclusively identified. Vacancies generated by proton implantation are likely to include Vc, Vsi, and their complexes. However, considering the formation energies and experimental support from previous defect studies using deep level transient spectroscopy (DLTS) after proton implantation [16], in which a peak assigned to the Z1/2 center (origination from VC ) was observed, VC is the most favorable to form and thus represents the most plausible candidate. A Fundamental analysis of the dynamic behavior of defects during ion implantation has been reported in [22]. Building on these insights, we investigated the mechanism responsible for the suppression of 1SSF expansion induced by proton implantation. To this end, we incorporated carbon vacancies ( Vc ) near the expanded 1SSFs in our model and performed first-principles calculations. The employed model is illustrated in Fig. 7. The green ball in Fig. 7 denotes the nearest-neighbor Si atom, the brown dotted circle represents a carbon vacancy ( Vc ). According to our calculations, once a Vc is created, the nearest Si atoms form a pair to achieve stabilization. Analysis of the atomic distance after geometry optimization shows bond lengths of 2.71\AA and 2.77\AA, respectively. Compared with the typical Si−Si bond length in the Si -core (~2.4\AA), the Si-Si pair distance is slightly larger.

[picture]

Fig. 7. Side view of the 4H−SiC model with SSF and VC. Enlarged view of the model vicinity of the VC are also depicted.

Fig. 7. Side view of the 4 H − S i C model with SSF and V C . Enlarged view of the model vicinity of the V C are also depicted.

To clarify the influence of Vc on 1SSFs expansion, we carried out a Local density of states (LDOS) analysis. The results indicate that both the Si−Si bond beneath the Vc and the Si−Si bond in Si -core introduce electronic states within the bandgap. Notably, the Si−Si bond in the vicinity of the Vc is associated with deeper states within the bandgap. Based on these findings, we propose the following mechanism: when a Vc is located near a 1SSF, electrons associated with the Si−Si bond at Vc site may transfer to the Si−Si bond in the Si -core, which is responsible for hole trapping. Consequently, the occupied Si-core can no longer capture holes, thereby suppressing the expansion of 1SSFs (Fig. 8).

[picture]

Fig. 8. The energy levels and wavefunctions of Si−Si bond in Vc (green energy level) and Si−Si bond in Si -core (red energy level), respectively.

Fig. 8. The energy levels and wavefunctions of S i − S i bond in Vc (green energy level) and S i − S i bond in Si -core (red energy level), respectively.

Summary

The original version of this paper is available on https://www.scientific.net/MSF.1190.49.pdf

In this study, we investigated the suppression mechanism of 1SSF expansion by evaluating the impact of proton implantation, with particular focus on vacancy-related effects, using cross-sectional CL spectra. In addition, we performed LDOS analysis to clarify the atomic and electronic structures around carbon vacancies. The results suggest that when carbon vacancies are formed in the vicinity of 1SSFs, suppressions of their expansion arises from the inhibition of hole capture at the Si -core by these vacancies. This study provides new insights into the mechanism of 1SSF suppression and may offer valuable guidance for future process improvement.

Acknowledgement

The original version of this paper is available on https://www.scientific.net/MSF.1190.49.pdf

A part of this work was supported by MEXT as "Program for promoting research on the supercomputer Fugaku" (Quantum theory-based multiscale simulations toward development of nextgeneration energy saving semiconductor devices, Project No. JPMXP1020200205). The authors wish to thank Toray Research Center for analysis and advice.

References

The original version of this paper is available on https://www.scientific.net/MSF.1190.49.pdf

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H. Tsuchida, K. Murata, T. Tawara et al., Suppression of Bipolar Degradation in 4H-SiC Power Devices by Carrier lifetime Control, IEDM (2019).

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T. Kimoto and H. Watanabe, Defect engineering in SiC technology for high-voltage power devices, Appl. Phys. Express, 13,120101 (2020).

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M. Kato, O. Watanabe, S. Harada and H. Sakane, Effects of proton implantation into 4H-SiC substrate: Stacking faults in epilayer on the substrate, Mater. Sci. Semicond. Process, 175, 108264 (2024).

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This ePub file was created using machine-generated methods and automated software to convert the source text into an ePub format and may contain formatting inconsistencies from the original version. Formatting may vary depending on the device used.

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Materials Science Forum, ISSN: 1662-9752, Vol. 1190, pp 55-62

doi: 10.4028/p-Jc6le5

© 2026 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2025-09-27

Revised:
2026-01-21

Accepted:
2026-01-31

Online:
2026-05-18

Investigation of Spoke Pattern of Stacking Faults in 4H-SiC Wafers Grown by Physical Vapor Transport Method

The original version of this paper is available on https://www.scientific.net/MSF.1190.55.pdf

Zeyu Chen 1,a, Jianpei Zhang 1, b, Shanshan Hu 1,c, Kaixuan Zhang 1, d, Yuzhuo Li1,e, Haochi Wang 1,f, Balaji Raghothamachar 1, g, Yafei Liu 2, h, Campbell Bouch 2,i, Ryan Philpott 2,j, Scott Turchetti 2,k, Pete Schunemann 2,l and Michael Dudley 1, m

1 Department of Materials Science & Chemical Engineering, Stony Brook University, Stony Brook, NY, 11794, USA

2 Onsemi, 55 Executive Drive, Hudson, NH, 03051, USA

a  zeyu.chen@stonybrook.edu, bjianpei.zhang@stonybrook.edu, c  shanshan.hu@stonybrook.edu, d  kaixuan.zhang@stonybrook.edu, e  yuzhuo.li@stonybrook.edu, f  haochi.wang@stonybrook.edu, g  balaji.raghothamachar@stonybrook.edu, h  yafei.liu@onsemi.com, iCampbell.Bouch@onsemi.com, jRyan.Philpott@onsemi.com, k  Scott.Turchetti@onsemi.com, 'Pete.Schunemann@onsemi.com,  mmichael.dudley@stonybrook.edu

Keywords: 4 H -SiC; Characterization; X-ray Topography; Defects

Abstract

Synchrotron monochromatic beam X-ray topography (SMBXT), synchrotron white beam X-ray topography (SWBXT) and high-resolution X-ray topography (HRXRT) were used to characterize a series of wafers sliced from two PVT-grown 4H−SiC boules under similar growth conditions. A unique spoke-shaped distribution of the threading screw/mixed dislocations (TSDs/TMDs) density map can be observed from wafers sliced from later stages of growth of both boules. Systematic sequential analysis of the SMBXT grazing incidence images and HRXRT reflection images of the wafers reveals the spoke patterns are formed due to continuous deflection process of TSDs/TMDs by thin layer of polytypes that propagate along step flow direction and expand vertically, leading to TSD density difference across the wafer. Regions with high TSD densities have higher growth rate, resulting in a ridge and valley structure. Generation of macrosteps in the valley regions due to regular step structure deflect more TSDs/TMDs that then form mixed type (Shockley+Frank) stacking faults.

Introduction

The original version of this paper is available on https://www.scientific.net/MSF.1190.55.pdf

Silicon carbide ( SiC ) is a semiconductor with a wide bandgap and exceptional electronic and physical properties, including high saturation velocity, high breakdown field, and excellent thermal conductivity [1]. These attributes make SiC a highly promising material for demanding applications involving high voltage, high power, and high temperature environments. The development of largescale, high-quality single crystal SiC substrate wafers is crucial for enhancing device performance and broadening its application scope. Among the available growth techniques, physical vapor transport (PVT) [2] is the most widely used method, as it allows the production of large SiC substrates with controllable growth rates. However, the presence of various crystallographic defects, such as threading screw/mixed dislocations (TSDs/TMDs) and micropipes (MPs) can significantly impact device performance, limiting the full potential of SiC-based technologies [3,4]. Therefore, the generation and impact of such defects during PVT growth should be thoroughly investigated to improve the growth process and furnace design.

Besides replication from the seed, TSDs/TMDs pairs are usually generated at the seed interface if large stress is present or at the interface of inclusions [5-7]. Deflections of TSDs/TMDs onto the basal plane have been observed previously [8], where TSDs/TMDs get deflected by macrosteps formed at the later stage of the growth when the curvature of the growth interface becomes higher. In this study, series of 4H−SiC wafers sliced from two boules grown under similar conditions were analyzed by synchrotron white beam X-ray topography (SWBXT) in 1-100 and 1-101 reflections to map the
distribution of stacking faults. Mappings of TSDs/TMDs densities were conducted by high resolution X-ray topography (HRXRT) in 0008 reflection, where relatively high density of TSDs/TMDs are nucleated at the beginning of the growth, that then continuously get deflected as the growth proceeds. Such deflected TSDs/TMDs can possibly dissociate into partials dislocations bounding Frank type/mixed (Frank+Shockley) type stacking faults [9,10], which will lead to increase of forward voltage and leakage currents [11-14]. The nature and mechanism of such deflection process need to be analyzed carefully in order to improve the design of the furnace and refine the growth processing.

Experiment

The original version of this paper is available on https://www.scientific.net/MSF.1190.55.pdf

Series of wafers sliced from two PVT-grown boules have been characterized and the position of the wafers with respect to the boules are shown in Fig. 1. Synchrotron Monochromatic Beam X-ray Topography (SMBXT) in grazing incidence geometry is an X-ray imaging technique capable of revealing the structural defects in the crystal up to a depth of 17μ m. Monochromatic beam (E=8.9KeV) is used in SMBXT and 11-28 grazing incident reflection is recorded on high resolution X-ray films. Synchrotron white beam X-ray topography (SWBXT) in transmission geometry are used to characterize stacking faults and 1-100 and 1-101 reflection via SWBXT were recorded. Experiments were carried out at Beamline 1-BM at the Advanced Photon Source (APS), Argonne National Laboratory. Ray-tracing simulation was conducted for inclusion contrast on topographs of 4H-SiC in 11-28 reflection through a Python algorithm based on orientation contrast model [15].

High-resolution x-ray topography (HRXRT) was performed using a Rigaku XRTMicron system. XRT image of TSDs/TMDs was acquired using g=[0008] in reflection geometry with CuKα radiation. TSD maps were generated by XRT Toolbox software, an automatic XRT data processing tool to generate defect analysis reports.

[picture]

Boule 1

Figure 1. Boule 1

[picture]

Boule 2

Figure 2. Boule 2

Fig. 1. Schematic diagram of PVT boules showing position of wafers sliced from the boules discussed in this study.

Results and Discussion

The original version of this paper is available on https://www.scientific.net/MSF.1190.55.pdf

Selected areas of HRXRT images in 0008 reflection of wafer1, 2, 4 and 5 of boule 1 are shown in Fig. 2(a), 2(b), 2(d), 2(e), 2(g) and 2(h), respectively with wafer1 closest to seed. Some of the line features observed on the topographs are highlighted by dashed red lines in images of wafer1 and wafer4, as shown in Fig. 2(a), 2(d) and 2(g). These features are observed to propagate and expand during growth as highlighted with orange dotted lines in images of wafer2 and wafer5, as shown in Fig. 2(b), 2(e) and 2(h). The stacked images, as shown in Fig. 2(c), 2(f) and 2(i), indicate that the line features propagate along the radial step flow direction and expand along [1-100] or [-1100] directions. To further investigate, SMBXTs in 11-28 reflection of wafer4 and wafer5 are shown in Fig. 3(a) and 3(b), where the line features are indicated by the red dotted line. Similar to the observation from HRXRT, the same line features can be detected from SMBXTs of wafer4 and wafer5, indicating that the line feature propagated in the boule on the basal plane during growth and deflected a bundle of TSDs/TMDs as indicated by the orange arrows. Ray tracing simulation was conducted to show contrast of a column of inclusion, where the result, as shown in Fig. 3(c), indicates white line contrast bounded by two dark lines, correlating with the line contrast observed from SMBXTs. Since the line
features have same contrast as a column of inclusions and they can propagate and expand on the basal plane, it strongly indicates that the line features are likely polytypes. Besides, since the width of the line feature in SMBXTs is around 40μ m comparable to the width of deflected TSDs/TMDs, the actual thickness of the polytype layers can be extremely small (tens of \AA ).

[picture]

Fig. 2. HRXRT images of (a) and (d) wafer 1 of boule 1; (b) and (e) wafer 2 of boule 1; (g) wafer 4 of boule 1 and (h) wafer 5 of boule 1. (c), (f) and (i) show stacked images of (a) and (b), (d) and (e), (g) and (h) respectively. Line features can be observed in individual images, and the stacked images indicate such line features propagate along step flow direction and expand along [1-100] or [-1100] direction.

Fig. 2. HRXRT images of (a) and (d) wafer 1 of boule 1; (b) and (e) wafer 2 of boule 1; (g) wafer 4 of boule 1 and (h) wafer 5 of boule 1. (c), (f) and (i) show stacked images of (a) and (b), (d) and (e), (g) and (h) respectively. Line features can be observed in individual images, and the stacked images indicate such line features propagate along step flow direction and expand along [1-100] or [-1100] direction.

[picture]

Fig. 3. 11-28 SMBXT of (a) wafer 4 and (b) wafer 5, showing that the line features deflect TSDs/TMDs. (c) shows ray tracing simulation of a column of inclusions.

Fig. 3. 11-28 SMBXT of (a) wafer 4 and (b) wafer 5, showing that the line features deflect TSDs/TMDs. (c) shows ray tracing simulation of a column of inclusions.

Deflection of TSDs/TMDs by polytype can be observed in Fig. 3(a) and 3(b). Fig. 4(a) depicts 3D schematic of nucleation of polytype, where 2D nucleation takes place on the flat terrace due to relatively fast growth, then the polytype will then expand with the step as shown in Fig. 4(b) and 4(c). The polytypes will deflect TSDs/TMDs, since the Burgers vectors of TSDs/TMDs in 4H are not
compatible with the polytype, and deflection onto the basal plane will be more energetically favorable. In addition, misfit stress between the polytype and the newly grown layer will also facilitate nucleation of new TSDs/TMDs as shown in Fig. 4(d).

[picture]

Fig. 4. Schematic of (a) nucleation of polytype, (b) and (c) deflection of TSDs/TMDs by polytype and (d) nucleation of TSDs/TMDs from polytype.

Fig. 4. Schematic of (a) nucleation of polytype, (b) and (c) deflection of TSDs/TMDs by polytype and (d) nucleation of TSDs/TMDs from polytype.

Fig. 5 shows the propagation and expansion of polytype at different parts of the wafer and with vertical step and curved step directions. At the beginning of the growth the step direction will be vertical near the central part of the wafer then slightly curved around the edge since the relatively flat growth front, as shown by T. Ailihumaer and coworkers [16]. Fig. 5(a) and 5(b) show propagation and expansion process of wafer 1 of boule 1 (stack image shown in Fig. 2(c) and 2(f)), and Fig. 5(c) and 5(d) show the process of wafer 4 of boule 1(stack image shown in Fig. 2(i)). As discussed above, the inner edge of the polytype will follow the step flow direction (perpendicular to step direction) and the other edge will expand along vertically, where faster growth takes place toward the edge of the wafer since C/Si ratio is higher at the position closer to the graphite crucible. Moreover, the polytypes expand quickly and occupy relatively large area of the wafer since the vertical step direction along [1-100] or [-1100] is the shortest distance to the edge of the wafer. Fig. 5(i) and 5(j) show comparison between polytype in wafer3 at early stage of growth and wafer7 at later stage of growth, where the size of the polytypes are slightly smaller in wafer7. When the growth proceeds to the later stage, the step direction will become curved as the curvature of the growth interface increases. Under such circumstances, the step direction will no longer be the shortest distance to the edge of the wafer, so the expansion will take place slightly slower, as indicated in Fig. 5(e) and 5(f). If the polytype is generated at the center of the wafer, both edges of the polytype will expand, since the gradient of C/Si ratio are similar for both sides.

Fig. 6(a) to 6(d) indicates TSDs/TMDs density map of wafer3, wafer6, wafer7 and wafer8, where red color means that TSDs/TMDs density is higher than manually set threshold value. Since deflections of TSDS/TMDs have been observed in HRXRT, the decrease of TSDs/TMDs density can be mainly attributed to deflections of TSDs/TMDs by the polytype layers. Even though deflection by polytype layers take place continuously starting from wafer1, such polytypes also nucleate new TSDs/TMDs as explained previously, so TSDs/TMDs density is relatively high at the early growth stage, as shown in Fig. 6(a). It should be noted that the remaining TSDs/TMDs formed a spoke-like pattern at the later stage of growth (Fig. 6(b) to 6(d). As the growth proceeds to wafer 6, the step direction becomes curved and the expansions of polytypes are slower. Fig. 6(e) depicts propagation and expansions of multiple polytypes, where one side of the polytypes at the inner region follow the step flow direction (dashed line) and the other side will expand (solid line), and polytype at the center will expand on both sides. It can be observed that the gaps between the polytypes, formed due to the difference between propagation and expansion direction, correlate with the spoke-like feature in Fig. 6(d), since fewer deflections will take place in the gap region.

Deflection process starts from the left side first (Fig. 6(b) and 6(c)) and the deflection on the right side of the wafer takes place at the later stage (Fig. 6(d)). As shown in Fig. 6(f), when the interface is slightly curved, the width of the terrace is longer on the left side, then as the curvature of the growth interface increase, the facet will migrate towards the center of the boule, shortening the terrace on the left side and terrace on the right side will become longer, where a longer width of the terrace will increase the probability of 2D nucleation of polytype.

[picture]

Fig. 5. Schematic of propagation and expansion of polytype with vertical step direction (a) and (b) near the edge; (c) and (d) near the center. Schematic of propagation and expansion of polytype with curved step direction (e) and (f) inner region of the wafer; (g) and (h) at the center of the curved step. HRXRD image of polytype of (i) wafer3 at early stage of the growth and (j) wafer7 at later stage of growth.

Fig. 5. Schematic of propagation and expansion of polytype with vertical step direction (a) and (b) near the edge; (c) and (d) near the center. Schematic of propagation and expansion of polytype with curved step direction (e) and (f) inner region of the wafer; (g) and (h) at the center of the curved step. HRXRD image of polytype of (i) wafer3 at early stage of the growth and (j) wafer7 at later stage of growth.

[picture]

Fig. 6. TSDs/TMDs density map from HRXRD of (a) wafer3, (b) wafer6, (c) wafer7 and (d) wafer8, where red color means that TSDs/TMDs density is higher than manually set threshold value. (e) shows propagation and expansion of polytypes on the left side of the wafer resulting in gaps between that correspond to the shape of the TSDs/TMDs density map in (d). (f) shows change of width of terrace as growth proceeds. where the terraces on the left side of the facet is narrower initially, then become longer as the growth proceeds.

Fig. 6. TSDs/TMDs density map from HRXRD of (a) wafer3, (b) wafer6, (c) wafer7 and (d) wafer8, where red color means that TSDs/TMDs density is higher than manually set threshold value. (e) shows propagation and expansion of polytypes on the left side of the wafer resulting in gaps between that correspond to the shape of the TSDs/TMDs density map in (d). (f) shows change of width of terrace as growth proceeds. where the terraces on the left side of the facet is narrower initially, then become longer as the growth proceeds.

[picture]

Fig. 7. SWBXT of wafer4 boule 2 in (a) 1−101 reflection and (b) 1−100 reflection, showing unique pattern of stacking faults where the spoke patterns are highlighted in dotted lines; (c) to (f): TSDs/TMDs density maps of wafers sliced from boule 2 at the position closer to the seed then further away from the seed.

Fig. 7. SWBXT of wafer4 boule 2 in (a) 1 − 101 reflection and (b) 1 − 100 reflection, showing unique pattern of stacking faults where the spoke patterns are highlighted in dotted lines; (c) to (f): TSDs/TMDs density maps of wafers sliced from boule 2 at the position closer to the seed then further away from the seed.

Wafer4 of boule 2 was analyzed by synchrotron white beam X-ray topography (SWBXT) in 1100 and 1-101 reflections. Mappings of TSDs/TMDs density for wafer1 to wafer4 sliced from boule 2 were conducted by HRXRD in 0008 reflection. As shown in Fig. 1, wafers sliced from boule 2 are from later stage of growth. Fig. 7(a) and 7(b) show the SWBXT in 1-100 and 1-101 reflections, where formation of stacking faults due to deflection of the TSDs/TMDs can be observed in the region between the spoke pattern which is highlighted by the dotted lines, where based on g.b analysis, majority of the stacking fault will be mixed type (Shockley+Frank), since 1-100 reflection shows stronger contrast of the faults [17]. Fig. 7(c) to 7(f) show density maps of TSDs/TMDs from the seed side (wafer1) to the dome side(wafer4), where higher density of TSDs/TMDs were observed near the facet region (Fig.7(c)) and the TSD/TMD density decreases as the wafer is closer to the dome side.

The pattern of wafer sliced from later stage of boule 2 show similarity to wafer8 of boule 1 (Fig. 6(d), indicating that deflections by polytypes exist in boule 2 as well. To further analyze the process, the TSDs/TMDs color maps are rescaled to see the difference on the spoke feature. Here, the spoke feature near the center of the wafer, highlighted by the red dotted box, will be specifically analyzed. Two areas with lower TSDs/TMDs density between the central spoke are highlighted by the white dashed line eclipse. Generally, TSDs/TMDs will have a faster growth rate than other parts of the crystal and form spiral steps during the growth [18], then when these steps merge, a growth island will be formed on the surface as shown in Fig. 8(a). When the growth proceeds, step bunching and polytypes will deflect TSDs/TMDs toward the step flow direction (Fig.8(b) and (c)). Since the density of TSDs/TMDs are lower on either side of the central spoke, as shown by the arrows of Fig.7(c), the growth rate along [000-1] will be slower in those regions, leading to ridge formation on the spoke positions, as shown in Fig.8(d). The ridge structure on the growth interface will be similar to star pattern observed from the facet [19]. Fig. 8(h) shows the top view of step structure of the ridge, where curved steps will form on the ridge (on the spoke position), while the valley will have normal steps conducive to forming a macrostep. Such step structure will suppress the formation of polytype on the ridge and the accumulated macrostep between the spoke can cause the deflection of TSDs/TMDs in
that region (Fig.8(e)), correlating with the decrease of TSDs/TMDs density between the spoke region in Fig. 7(d). Finally, as the growth interface becomes more convex, all the TSDs/TMDs will be deflected as shown in Fig. 8(f) and (g).

[picture]

Fig. 8. 3D schematic of (a) growth island formed due to faster growth rate at the region with higher TSDs/TMDs density, (b) and (c) deflection of TSDs/TMDs by step bunching and polytype, (d) ridge structure formation due to difference in TSDs/TMDs density, (e) deflection process between the spoke region, (f) and (g) defection of TSDs/TMDs by macrostep; (h) step structure on the ridge and valley.

Fig. 8. 3D schematic of (a) growth island formed due to faster growth rate at the region with higher TSDs/TMDs density, (b) and (c) deflection of TSDs/TMDs by step bunching and polytype, (d) ridge structure formation due to difference in TSDs/TMDs density, (e) deflection process between the spoke region, (f) and (g) defection of TSDs/TMDs by macrostep; (h) step structure on the ridge and valley.

Summary

The original version of this paper is available on https://www.scientific.net/MSF.1190.55.pdf

Synchrotron monochromatic beam X-ray topography, synchrotron white beam X-ray topography and high-resolution X-ray topography were used to characterize series of wafers sliced from two PVTgrown 4 H -SiC boules grown under similar conditions. Spoke pattern on TSDs/TMDs density map can be observed from wafer sliced from later stage of growth of both boules. Deflections of TSDs/TMDs by 2D nucleated thin polytype layers due to relatively fast growth rate have been observed, since Burgers vector of TSDs/TMDs in 4H structure is not compatible in polytype. The polytypes will propagate and expand, where one of the edges will follow the step flow direction and the other edge will expand along [1-100] and [-1100] directions. At the early stage of growth, the polytype will expand quickly due to vertical step structure, while it will slow down when the step structures become curved at the later stage of growth. The difference in direction between the propagation edge and the expansion edge facilitates the formation of the spoke pattern. Such pattern will give rise to faster growth rate along [000-1], leading to formation of ridge on the growth interface. The ridge structure will suppress the formation of polytype on the ridge and also accumulate macrosteps between the spokes that subsequently cause the deflection of TSDs/TMDs and formation of stacking faults. Processing parameters such as growth rate should be optimized to avoid formation of the polytypes and the deflections of TSDs/TMDs.

Acknowledgement

The original version of this paper is available on https://www.scientific.net/MSF.1190.55.pdf

Work supported by Onsemi. This research used resources of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704. This research used resources of the Advanced Photon Source (Beamline 1-BM), a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. The Joint Photon Sciences Institute at SBU provided partial support for travel and subsistence for access to Advanced Photon Source.

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Y. Yang, J. Guo, O. Goue, B. Raghothamachar, M. Dudley, G. Chung, E. Sanchez, J. Quast, I. Manning, D. Hansen, J. Electron. Mater. 45, 2066-2070 (2016)

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H. Peng, T. Ailihumaer, Y. Liu, B. Raghothamachar, X. Huang, L. Assoufid, M. Dudley. Journal of Applied Crystallography 54, 1225-1233 (2021)

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Materials Science Forum, ISSN: 1662-9752, Vol. 1190, pp 63-67

doi: 10.4028/p-3WKk3V

© 2026 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2025-09-11

Revised:
2025-12-19

Accepted:
2026-02-23

Online:
2026-05-18

Micropipes in SiC die Observed by Molten KOH Etching

The original version of this paper is available on https://www.scientific.net/MSF.1190.63.pdf

1 STMicroelectronics, Stradale Primosole, 50, Catania 95100, Italy

afabiana.vento@st.com, b  nicolo.piluso@st.com, c  cristiano.calabretta01@st.com, d  chiara.nania@st.com, e  domenica.raciti@st.com, f  ruggero.anzalone@st.com, g  andrea.severino@st.com

Keywords: KOH etching, micropipes, defects, SiC die, wide-bandgap materials.

Abstract

The growing demand for wide-bandgap (WBG) materials in the microelectronics industry has led to increased investment in medium- and high-voltage power products based on SiC technology. SiC offers an excellent balance between high voltage blocking capability, high temperature operation and high switching frequencies [1]. One key step in preparing highperformance devices is improving the growth process of SiC ingot material by Physical Vapor Transport (PVT). Epitaxial growth occurs through the chemical vapor deposition (CVD) method [2]. However, this method is reported to generate extended defects such as Complex Stacking Faults (formerly referred to as carrots) and Polytype Inclusions (formerly referred to as triangles or comets) and propagate defects pre-existing in the bulk material, such as micropipes (MPs) and threading screw dislocations (TSDs), which have a very high killer ratio in SiC devices [3, 4]. In this work, the KOH molten etching method was used to investigate the nature of the defects that caused device failures; Raman spectroscopy was also employed to identify the spectroscopic correspondence of the peaks of interest.

Introduction

The original version of this paper is available on https://www.scientific.net/MSF.1190.63.pdf

During the last decade the increasing demand for high-power devices has drawn attention to WideBandgap (WBG) semiconductors. WBG materials include silicon carbide (SiC), gallium nitride (GaN), aluminum nitride (AlN) [5]. Among these, SiC exhibits characteristics that make it suitable for high power and high efficiency applications. However, the excellent prospects for using this material depend on its crystallinity. Crystal growth occurs through chemical vapor deposition (CVD), which ensures high-quality and high-purity SiC layers. Since the stacking of crystallographic planes can assume three different positions, this gives rise to cubic, hexagonal, or rhombohedral lattice structures called polytypes. Each polytype has unique electrical properties; 4H−SiC is the polytype with attractive properties for power devices due to its very high electron mobility, high breakdown field, and high thermal conductivity [6, 7]. However, the high concentration of structural defects, both extended and point defects, formed during ingot growth may lead to deterioration in the performance and reliability of semiconductor devices [8].
The dislocations commonly found in 4H-SiC can be classified as Threading Screw Dislocations (TSDs), Threading Edge Dislocations (TEDs), Basal Plane Dislocations (BPDs), and Micropipes (MPs) [9]. Some of these defects, such as MPs or TSDs spreading in the epi layer, cause fatal damage. Their identification and classification are a priority for using SiC devices. To study these types of defects present in substrates or the epitaxial layer of SiC, selective chemical etching in KOH is extensively used [10]. In this work, considering defect-preferred corrosion using molten KOH , three different failed dies were selected and analyzed.
For clarity, other extended defects propagated from dislocations are classified as Complex Stacking Faults (formerly referred to as carrots) and Polytype Inclusions (formerly referred to as triangles and comets). The detection and study of these defects have been extensively addressed [11, 12], as they are the cause of early electrical failure (usually no electrical stress or reliability tests are needed).

Experiment

The original version of this paper is available on https://www.scientific.net/MSF.1190.63.pdf

Three different dies were selected from failed samples to analyze the defects that caused the burning. A nickel crucible filled with KOH pellets was used for etching the samples, and the temperature was set to 540∘C for 12 minutes. After etching, the dies were cooled to room temperature and then washed with deionized water and isopropyl alcohol. A confocal microscope and scanning electron microscope (SEM) were used to observe the morphology of the etch pits on the surface. Raman spectroscopy was employed to identify the spectroscopic correspondence of the peaks of interest.

Results and Discussion

The original version of this paper is available on https://www.scientific.net/MSF.1190.63.pdf

Three cases of failed dice were selected and treated with molten KOH .
In the first case (Fig.1a), the burn-in was revealed by optical inspection, showing that the failure seems to involve multiple defects. By zooming in on the region marked in red, it is possible to see one large defect (inside the green circle) accompanied by a small feature (inside the blue circle), connected to each other (orange circle). The FIB cuts (Fig.1b) performed in three different regions show the effect of the burn; however, they do not clarify the nature of the defect. Treating the sample with molten KOH (Fig.1c) reveals a micropipe (MP) on the surface, accompanied by another one highlighted by the green and orange traces. This phenomenon is due to the propagation of MPs generated in the substrate that evolve into the epitaxial layer, producing closed-core threading screw dislocations. Confirmation of the generation of closed-core threading screw dislocations is also provided by the presence of connections (orange circle) between the defects emerging on the surface. The two mechanisms involved during this propagation, which lead to the formation of closed-core screw dislocations, are reported in Fig. 2 [13].

[picture]

Fig. 1. In a) the electrical failure acquired with optical microscope with dissociation (orange circle) of the MP; in b) FIB cuts in three different regions (FIB 1, FIB 2, FIB 3) of the sample; in c) KOH etching of the die at temperature of 540∘C, and time of 12 min detected by x 20 and x 50 obj .

Fig. 1. In a) the electrical failure acquired with optical microscope with dissociation (orange circle) of the MP; in b) FIB cuts in three different regions (FIB 1, FIB 2, FIB 3) of the sample; in c) KOH etching of the die at temperature of 540 ∘ C , and time of 12 min detected by x 20 and x 50 obj .

[picture]

Fig. 2. Illustration of a micropipe evolution with no- dissociation and dissociation into several closed-core screw dislocations during epitaxial growth. In the case of VSpiral ≫VStepFlow (a) the MP does not experience dissociation. In case of VSpiral ≪VStepFlow (b) the MP undergoes dissociation [11].

Fig. 2. Illustration of a micropipe evolution with no- dissociation and dissociation into several closed-core screw dislocations during epitaxial growth. In the case of V Spiral ≫ V StepFlow ( a ) the MP does not experience dissociation. In case of V Spiral ≪ V StepFlow ( b ) the MP undergoes dissociation [11].

The second case reported in Fig. 3 shows a symmetrical burn whose crystallographic nature is not immediately visible with optical investigation (Fig. 3a). However, by treating the sample in molten KOH (Fig. 3b), the characteristic morphology around the hole attributable to a MP, where each fingerprint is at 60∘ to the next, is visible and confirmed by SEM analysis (Fig. 3c). In this case, the MP does not experience dissociation into closed-core threading screw dislocations because the device is characterized by only one burn on the surface.

[picture]

Fig. 3. In a) the electrical failure acquired with optical microscope; in b) KOH etching of the die at temperature of 540∘C, and time of 12 min ; in c) the comparison between the SEM acquisition and optical inspection of the MP.

Fig. 3. In a) the electrical failure acquired with optical microscope; in b) KOH etching of the die at temperature of 540 ∘ C , and time of 12 min ; in c) the comparison between the SEM acquisition and optical inspection of the MP.

In the third case shown in Fig. 4, the burn (Fig. 4a) detected through optical inspection does not show only a symmetric defect but also an additional feature (underlined in red). By subjecting the sample to KOH etching (Fig. 4b), a MP emerges from the inspected region, accompanied by additional features. To define the chemical nature of this feature, Raman analysis was conducted (Fig. 4c). The Raman spectrum of region 1, attributed to the micropipe, shows both the presence of 4H−SiC ( 777 cm−1 ) and the presence of polytype (it can be assumed be 15R−SiC ) due to the appearance of a pick between 780−790 cm−1. Focusing on Fig. 4c, region 2, the Raman analysis shows peaks that determine the only presence of 4H−SiC. This excludes the involving polytypes in the detected area. Usually, the polytype is detected at the edge of the features, resulting from the electrical burning.

[picture]

Fig. 4. In a) the electrical failure acquired with optical microscope; in b) KOH etching of the die at temperature of 540∘C, and time of 12 min ; in c) Raman inspection in regions 1 and 2 .

Fig. 4. In a) the electrical failure acquired with optical microscope; in b) KOH etching of the die at temperature of 540 ∘ C , and time of 12 min ; in c) Raman inspection in regions 1 and 2 .

Conclusion

The original version of this paper is available on https://www.scientific.net/MSF.1190.63.pdf

The growth conditions of 4H−SiC bulk material present significant challenges, particularly due to the presence of various crystal defects such as MPs, TSDs, and basal plane dislocations (BPDs). Among these, it is well known that MPs affect semiconductor quality and device performance because they cause electrical failures. Results from molten KOH etching, combined with SEM and Raman analysis, contribute to the investigation of the formation and propagation of defects. Understanding the evolution of electrical failures helps clarify the mechanisms involved, with the aim of controlling and managing MP density to improve the electrical efficiency of devices.

References

The original version of this paper is available on https://www.scientific.net/MSF.1190.63.pdf

Shenai, Krishna, Michael Dudley, and Robert F. Davis. "Current status and emerging trends in wide bandgap (WBG) semiconductor power switching devices." ECS Journal of Solid-State Science and Technology 2.8 (2013): N3055.

Gutkin, Mikhail Yu, et al. "Micropipe evolution in silicon carbide." Applied physics letters 83.11 (2003): 2157-2159.

N. Piluso, et al. "Influence of Starting Material on Final Device in SiC Power Technologies." 2025 IEEE International Reliability Physics Symposium (IRPS). IEEE, 2025.

T. Kimoto and J. A. Cooper, Fundamentals of Silicon Carbide Technology, Ieee, Wiley, (2014).

Wang, Yalin, Yi Ding, and Yi Yin. "Reliability of wide band gap power electronic semiconductor and packaging: A review." Energies 15.18 (2022): 6670.

Suthar, Anvi N., J. Venkataramanaiah, and Y. Suresh. "Conventional, wide-bandgap, and hybrid power converters: A comprehensive review." Renewable and Sustainable Energy Reviews 213 (2025): 115419.

Codreanu, C., et al. "Comparison of and mesfets performances." Materials Science in Semiconductor Processing 3.1-2 (2000): 137-142.

Ohtani, Noboru, et al., Journal of crystal growth 286.1 (2006): 55-60.

Wang, Rong, et al. "Impurities and defects in 4H silicon carbide." Applied Physics Letters 122.18 (2023).

Wang, Hejing, et al. "Micropipes in SiC single crystal observed by molten KOH etching." Materials 14.19 (2021): 5890.

P. Fiorenza, et. al., Materials Science in Semiconductor Processing 194, 109575 (2024).

Lei Xu, et. Al., Materials Science in Semiconductor Processing, Volume 195, (2025).

T. Kimoto and J. A. Cooper, Fundamentals of Silicon Carbide Technology, Ieee, Wiley, (2014).

This ePub file was created using machine-generated methods and automated software to convert the source text into an ePub format and may contain formatting inconsistencies from the original version. Formatting may vary depending on the device used.

The original version of this eBook is available on https://www.scientific.net/book/stacking-faults/978-3-0364-3126-0

Materials Science Forum, ISSN: 1662-9752, Vol. 1190, pp 69-77

doi: 10.4028/p-9ppZEB

© 2026 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2025-09-28

Revised:
2026-01-07

Accepted:
2026-01-31

Online:
2026-05-18

Synchrotron X-Ray Topography Analysis of Low Angle Grain Boundaries Induced by Growth Step Flow in PVT-Grown 4H-SiC Crystals

The original version of this paper is available on https://www.scientific.net/MSF.1190.69.pdf

Jianpei Zhang 1,a, Zeyu Chen 1, b, Yuzhuo LI 1,c, Shanshan Hu 1, d, Balaji Raghothamachar 1,e, Yafei Liu 2,f, Campbell Bouch 2, g, Ryan Philpott 2, h, Scott Turchetti 2,i, Pete Schunemann 2,j and Michael Dudley 1,k,*

1 Department of Materials Science & Chemical Engineering, Stony Brook University, Stony Brook, NY 11794 USA

2 Onsemi, 55 Executive Drive, Hudson, NH 03051 USA

a  Jianpei.zhang@stonybrook.edu, b  Zeyu.cheni@stonybrook.edu, c  Yuzhou.Li@stonybrook.edu, d  Shanshan.hu@stonybrook.edu, e  Balaji.ragnothamachar@stonybrook.edu, fYafei.Liu@onsemi.com, 9  Campbell.Bouch@onsemi.com, h  Ryan.Philpott@onsemi.com, iScott.Turchetti@onsemi.com, jPete.Schunemann@onsemi.com,  kMichael.Dudley@stonybrook.edu,

Keywords: 4 H -Silicon carbide, physical vapor growth, low-angle grain boundary, synchrotron x-ray characterization.

Abstract

Synchrotron X-ray topography (XRT) combined with ray-tracing simulation was employed to examine the distribution and formation mechanisms of LAGBs in off-axis 4H−SiC wafers grown by PVT. TED-LAGB networks were observed adjacent to the facet, along with three TED-LAGBs emanating from micropipes on the left edge of the wafer. Ray-tracing simulations enabled the identification of TED Burgers vectors by correlating simulated and observed contrast configurations. The results suggest that large TED-LAGB networks near facets originate from misorientations between growth fronts of horseshoe-shaped steps incorporating prismatic slip dislocations, induced by radial temperature gradients. Similarly, LAGBs associated with micropipes arise from localized step-flow perturbations. These findings provide a revised mechanism for TEDLAGBs formation, establishing a link between their spatial distribution and growth dynamics, and offering new insights into their role in determining the quality of 4H−SiC substrates.

Introduction

The original version of this paper is available on https://www.scientific.net/MSF.1190.69.pdf

Silicon carbide ( SiC ) is a wide-bandgap semiconductor with high breakdown field and strong electrical and thermal conductivity[1]. These properties make it an important material for modern power and electronic systems, such as inverters, on-board chargers, and converters for electric vehicles[2], [3]. However, the presence of defects in PVT-grown SiC crystals negatively affect the reliability and performance of SiC devices. Among various types of defects in SiC crystals, low-angle grain boundaries (LAGBs) are a commonly observed planar defect that limit yield and prevent the implementation of large SiC devices[4]. LAGBs form through the aggregation of different types of dislocations, usually threading edge dislocations (TEDs) or edge type basal plane dislocations (BPDs) to accommodate the misorientation of lattice planes[5]. TED-LAGBs lead to tilt along prismatic planes often associated with radial temperature gradients and the coalescence of growth steps, forming network-like structures across the wafer and producing noticeable lattice tilt. BPD-LAGBs, on the other hand, result from the aggregation of basal plane dislocations (BPDs), particularly those of opposite signs driven together under stress, giving rise to tilt of the basal plane[5]. These boundaries are usually found near wafer edges or stress-concentrated regions and can sometimes combine with TED arrays to form composite grain boundary structures. They are more likely to evolve into Shockley stacking faults during device operation, severely impacting the performance
and reliability of power devices[6, 7]. Classical formation mechanisms of <11―00> orientation LAGBs are generally associated with threading screw dislocations (TSDs), which act as growth centers by generating spiral steps[8]. TED-LAGBs formed as TEDs align along the <11―00> direction to accommodate the c -axis rotation between the TSDs and surrounding regions when growth centers converge. Step flow based mechanism was proposed by Cheng et al[9] indicating that radial temperature gradients drive horseshoe-shaped step flow from the facet, where merging fronts incorporate prismatic slip dislocations to form TED-LAGBs.

In this study, an unique distribution patterns of LAGBs observed in physical vapor transport (PVT) grown off-axis 4H−SiC wafers is investigated. Synchrotron X-ray topography (XRT) in both transmission and grazing geometry reveal the presence of LAGBs networks next to the facet regions as well as associated with micropipes on the left edge of the wafer. A systematic analysis has been carried out to identify the dynamics of step flow and the associated mechanisms of LAGB formation induced by its motion.

Experiment

The original version of this paper is available on https://www.scientific.net/MSF.1190.69.pdf

4H-SiC wafers grown by physical vapor transport (PVT) method with a 4∘ offcut were characterized by synchrotron x-ray topography (XRT)[10]. Both transmission and grazing-incidence geometries were employed, with topographs recorded under white-beam and monochromatic conditions, respectively. Synchrotron white beam x-ray topography (SWBXT) was recorded in a 112―0 reflection with the Si face as the beam exit surface. Synchrotron monochromatic beam x-ray topography (SMBXT) was recorded in 112―8 from the Si face of the wafer. Experiments were conducted at the Advanced Photon Source (APS) in the Argonne National Laboratory (ANL). Raytracing simulation was carried out based on the orientation contrast mechanism[11] for Burgers vector analysis of observed dislocations.

Results and Discussion

The original version of this paper is available on https://www.scientific.net/MSF.1190.69.pdf

TED-LAGB Network adjacent to the Facet. Schematic diagram shows the location of LAGB networks of the wafer indicated by the red lines (Fig. 1a). SMBXT recorded from the Si face of the wafer reveals this LAGB network consists of numerous black and white contrast TED-LAGB arrays each extending along the <11―00> directions which are marked with red lines. The optical image of the PVT-grown off-axis 4H−SiC wafer shows an unusual shape of the facet outlined with red line with three spikes along the <112―0> directions which are marked with green lines (Fig. 1c). In the facet regions, a star pattern that is also marked with green lines is observed with each line also following <112―0> directions, indicating that the spikes correspond to this star pattern (Fig. 1d). The SMBXT image recorded from the Si face of the wafer reveals a micropipe at the center of the star pattern marked with a red arrow in fig. 1e which is also crossing point of three spike. Similar pattern was reported by M. Sonoda et al[13], where the facet region showed hexagonal symmetry comprising six vicinal (0001―) C surfaces tilted toward <11―00> directions, indicating that these spikes originagte from the micropipe which act as the growth center during PVT growth.

To investigate the nature of dislocations comprising the LAGB network, ray-tracing-simulated TEDs with different Burgers vectors in the <112―8> reflection are compared with actual topographic observations. Simulation reveals distinct contrast configuration variation of TEDs with six different a-component Burgers vectors shown in Fig. 2 [12]. They appear as either dark contrast TEDs (Fig. 2a and b) or white contrast. TEDs with a distorted white center decorated by two dark arcs (Fig. 2cf). The Burgers vector of TEDs are perpendicular to the direction of each boundary.

[picture]

Fig. 1. (a) Schematic diagram shows the location of LAGB networks of the wafer indicated by red lines. (b) 112―8 SMBXT image recorded from the Si face showing the presence of a large TED-LAGB network noted with red lines. (c) Optical image of the wafer shows unusual shape of facet outlined with red line and three spikes coming from the facet indicated by green lines. (d) Optical image of the star pattern marked with green lines corresponding to these spikes.(e) Micropipe at the center of the star pattern noted with red arrow.

Fig. 1. (a) Schematic diagram shows the location of LAGB networks of the wafer indicated by red lines. (b) 11 2 ― 8 SMBXT image recorded from the Si face showing the presence of a large TED-LAGB network noted with red lines. (c) Optical image of the wafer shows unusual shape of facet outlined with red line and three spikes coming from the facet indicated by green lines. (d) Optical image of the star pattern marked with green lines corresponding to these spikes.(e) Micropipe at the center of the star pattern noted with red arrow.

[picture]

Fig. 2. Ray-tracing simulated 112―8 grazing-incidence x-ray topographs of TEDs with six different acomponent Burgers vectors [(a)-(f)] in 4H−SiC[12].

Fig. 2. Ray-tracing simulated 11 2 ― 8 grazing-incidence x-ray topographs of TEDs with six different acomponent Burgers vectors [(a)-(f)] in 4 H − S i C [ 12 ] .

[picture]

Fig. 3. Enlarged images of the TED-LAGB networks observed in 112―8SMBXT recorded from the Si face. Directions of TED arrays composing the LAGB network are highlighted by dotted lines. Contrasts of individual dislocations in each array marked with red boxes are enlarged showing that LAGBs along different <11―00> are composed of TEDs with different contrast and Burgers vectors in (a), (b), (c) and (d).

Fig. 3. Enlarged images of the TED-LAGB networks observed in 11 2 ― 8 S M B X T recorded from the Si face. Directions of TED arrays composing the LAGB network are highlighted by dotted lines. Contrasts of individual dislocations in each array marked with red boxes are enlarged showing that LAGBs along different < 1 1 ― 00 > are composed of TEDs with different contrast and Burgers vectors in (a), (b), (c) and (d).

Fig. 3 shows enlarged sections of these TED-LAGBs extending along all <11―00> directions. For the white TED boundary lying along [011―0], the enlarged image reveals that each TED with a white centered contrast has its top black contrast shifted more to the left and the bottom black contrast shifted more to the right. This configuration corresponds to the TED with Burgers vector b=1/3[211―0] (Fig. 3a). For the white TED boundary lying along [10-10], the enlarged image indicates that each white centered TED has its top black contrast shifted to the right and the bottom black contrast shifted to the left, which corresponds to a TED with Burgers vector b=1/3[12―10] (Fig. 3a). For the white TED boundary lying along [ 11―00 ], the enlarged image shows that each white centered TED has a larger top portion than bottom, top black contrast shifted to the left and the bottom black contrast shifted to the right, which corresponds to a TED with Burgers vector b=1/3[112―0] (Fig. 3b). For the black TED boundary lying along [10̄10], the enlarged image shows that each black centered TED has its top black arc shifted to the left side and bottom black arc shifts to the right side, which corresponds to a TED with Burgers vector b=1/3[1―21―0] (Fig. 3c). For the black TED boundary lying along [01 1―0], the enlarged image shows that each black centered TED has its top black arc shifted to the right side and bottom black arc shifted to the left side, which corresponds to a TED with Burgers vector b=1/3[2―110] (Fig. 3d).

Formation mechanism of TED LAGB Network adjacent to the Facet. A horseshoe-shaped growth step model to explain the TED LAGB network formation on PVT-grown 4H-SiC wafer was proposed by Cheng et al[9]: The crucible design of PVT growth has the heating induction coils encircling the growth cell, creating a radial temperature difference between the inner and outer region of the crystal, which temperature on the edge is higher than it on the center region. This causes diffusivity differences in adatoms deposited at various locations on the growth interface. Faster growth rate is expected at higher growth temperature[16]. Besides, higher growth temperatures
promote a smooth step morphology with smaller step heights, while lower temperatures increase step height and form large terraces, which introduce propagation speed variation during growth[17]. Observation of step morphology on initial grown 4H-SiC crystals reveals that steps originate from the growth facet position and propagate across the crystal radially[18]. Above all, step front near the crystal edge propagates faster than in the central region, a horseshoe-shaped growth step is formed.

The primary TED source of TED-LAGB networks is pre-existing prismatic slip dislocations in the adjacent regions [19]. Such dislocations are typically deformation-induced and arise from activation of the secondary slip system 1/3<112―0>{11―00}. The key factor enabling the activation of prismatic slip in 4H-SiC during PVT growth is thermal stress generated by the radial temperature gradients, which applies shear stress to all slip systems according to Schmid's law. Gliding of pre-existing TEDs on the secondary prismatic slip system will occur once the resolved shear stress exceeds the critical resolved shear stress (CRSS). This interpretation of having prismatic slip dislocations as the LAGB network dislocation source can be further verified by analyzing the prismatic slip dislocation distribution prediction model developed by Guo et al.[14]. in conjunction with ray-tracing simulation. Guo et al.'s study revealed screw-oriented prismatic slip dislocation segments as distinct straight linear contrast along one of the three [112―0] directions in synchrotron x-ray topographs near the periphery of 4H−SiC wafers[14]. Therefore, the horseshoe-shaped growth step incorporates prismatic slip dislocations to form LAGBs at its encountering location as the mobile TED segment glides behind the growth front and leaves a screw-oriented prismatic slip dislocation segment in its wake. Before the faces of the two growth fronts encounter each other, the original TED segment will escape the coalescing front, leaving a surface intersecting point of the screw-oriented prismatic slip dislocation segment. When the steps merge, in order to enable conservation of Burgers vector, the prismatic dislocations will be forced to redirect into TEDs exiting the top surface.

An analogous interpretation can be made for the LAGB network adjacent to the facet. Three spikes of facet emerging from the MP in the facet (Fig. 1(e)) extend along the [11̄20] directions (Fig. 4a). Due to the radial temperature gradient between the center and edge of the wafer, atoms deposited onto the terrace of the growth steps exhibit different diffusivities. Spikes closer to the edges of the boule propagate faster than the one between them, forming horseshoe shaped growth fronts on both sides. As growth continues, opposing spike fronts from each side converge first near the facet region, roughly along the horizontal direction (Fig. 4b-c). TED on the growth fronts will glide along [1 2―10 ] and [1―21―0] directions on the prismatic plane to form TED-LAGBs along [ 011―0 ] and [ 101―0 ] directions. The central spike will keep moving forward and it will encounter with other fronts on sides initially. As the central spike continues to advance, it will encounter the side fronts. To accommodate the misorientation introduced by the side front induced TED-LAGBs, the TED-LAGBs along the [1 1―00 ] direction will be formed(Fig. 4d). Each growth front undergoes this process, but due to changes in growth conditions process, the step flow pattern may slightly differ resulting in the formation of TED-LAGB networks in this region (Fig. 4e).

[picture]

Fig. 4. Schematic diagrams showing the formation mechanism of TED-LAGB networks coming from spikes based on the horse-shoe shape step flow mechanism.

Fig. 4. Schematic diagrams showing the formation mechanism of TED-LAGB networks coming from spikes based on the horse-shoe shape step flow mechanism.

TED-LAGB from Micropipes. Beyond the facet region, synchrotron XRT reveals LAGBs emanating from micropipes on the PVT-grown off-axis 4H−SiC wafer. Schematic diagram shows the location of LAGBs indicated by the blue lines(Fig. 5d). The SMBXT images (Fig.5a-c) reveals that these LAGBs noted with blue lines consisting very high density black or white contrast TED-LAGB arrays originates from contrasts associated with micropipes or micropipe arrays marked with green boxes. Optical images of MPs and MP arrays corresponding to those contrasts are observed indicated by green lines.

[picture]

Fig. 5. 112―8 Grazing-incidence synchrotron monochromatic beam x-ray topograph recorded from the Si face showing the presence of TED-LAGBs originating from micropipes marked with blue lines(a-c). The location of TED-LAGBs of the wafer indicated by the blue lines are shown on (d).

Fig. 5. 11 2 ― 8 Grazing-incidence synchrotron monochromatic beam x-ray topograph recorded from the Si face showing the presence of TED-LAGBs originating from micropipes marked with blue lines(a-c). The location of TED-LAGBs of the wafer indicated by the blue lines are shown on (d).

Formation mechanism of TED-LAGB from Micropipes. Based on these observations and horseshoe-shaped growth step model, we proposed a formation mechanism for LAGBs originating from MPs in the PVT-grown off-axis 4H-SiC boule in this study. Step flows merge together after the formation of TED-LAGBs near the facet and continue to propagate radially outward to other side of boule. When a MP is encountered, the step flow is pinned by the MP and the direction of the step flow changes to form a horseshoe-shaped growth step around the MP. When the two horse-shoe shaped growth fronts merge together, the pre-existing TEDs in this region will glide on the secondary
prismatic slip system to accommodate the misorientation between the fronts when the resolved shear stress exceeds the CRSS.When more growth steps accumulate during growth, each one undergoes this process repeatedly, but due to changes in growth conditions process, the step flow pattern may slightly differ from layer to layer resulting in the LAGB network adjacent to the MP cluster.

[picture]

Fig. 6. Schematic diagrams showing the formation mechanism of TED-LAGBs coming from micropipes based on the horse-shoe shape step flow mechanism.

Fig. 6. Schematic diagrams showing the formation mechanism of TED-LAGBs coming from micropipes based on the horse-shoe shape step flow mechanism.

Summary

The original version of this paper is available on https://www.scientific.net/MSF.1190.69.pdf

In this work, synchrotron X-ray topography and ray-tracing simulation are employed to investigate the distribution and formation mechanisms of LAGBs in PVT-grown 4H-SiC crystal. TED-LAGB networks next to the facet and three TED-LAGBs emanating from MPs are observed. Ray-tracing simulations enabled the identification of Burgers vectors of TEDs in these LAGBs from contrast configurations observed in synchrotron topographs. The results indicate that TED-LAGB networks next to the facet form to accommodate the misorientation between growth fronts of horseshoe-shaped steps, which incorporate prismatic slip dislocations originating from facet spikes under radial temperature gradients during growth. For TED-LAGBs emanating from micropipes, the MPs act as localized centers that also redirect step flows into horseshoe-shaped steps, thereby generating TEDLAGBs to accommodate the misorientation of those steps. Based on these observations, the role of step-flow dynamics and dislocation interactions in LAGB development is highlighted. These findings provide new insight into the origin of LAGBs in SiC crystals and their implications for substrate quality.

Acknowledgement

The original version of this paper is available on https://www.scientific.net/MSF.1190.69.pdf

Work was supported by Onsemi. Research used resources of the Advanced Photon Source (Beamline 1-BM), a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. This research used resources of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704. The Joint Photon Sciences Institute at SBU provided partial support for travel and subsistence at the Advanced Photon Source.

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The original version of this paper is available on https://www.scientific.net/MSF.1190.69.pdf

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Materials Science Forum, ISSN: 1662-9752, Vol. 1190, pp 79-87

doi: 10.4028/p-k0dpCG

© 2026 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2025-09-10

Revised:
2025-12-19

Accepted:
2026-02-23

Online:
2026-05-18

Polytype Transitions in Silicon Carbide: A Macroscopic View

The original version of this paper is available on https://www.scientific.net/MSF.1190.79.pdf

Jörg Pezoldt 1,a*, Vladislav Kurtash 1, b and Frank Neubert 2,c

1 FG Nanotechnologie, Institut für Mikro- und Nanoelektronik and Institut für Mikro- und Nanotechnologien MacroNano ® and Institut für Werkstofftechnik, Postfach 100565, 98684 Ilmenau, Germany

2 AMC - Analytik & Messtechnik GmbH Chemnitz, Heinrich-Lorentz-Str. 55, 09120 Chemnitz, Germany

ajoerg.pezoldt@tu-ilmenau.de, b  vladislav.kurtash@tu-ilmenau.de, c  FrankNeubert@gmx.net 

Keywords: polytype transition, polytype stability, defect formation, phase transition, thermodynamics, nonequilibriums state, device degradation, self-organization.

Abstract

Based on the analysis of the defect formation in silicon carbide polytypes in different semiconductor manufacturing processing steps, device operation and environmental-device interaction it is concluded that external material and energy fluxes are generally able to destabilize the polytype structure. The governing reason is the formation of stacking faults and instabilities of the partial dislocation associated with them. A new ansatz is proposed to describe the structural instabilities using none-equilibrium thermodynamics and entropy production. A criterial form for polyype transitions is proposed. The developed criterial form is applied to describe observed structural instabilities occurring under different external actions.

Introduction

The original version of this paper is available on https://www.scientific.net/MSF.1190.79.pdf

Polytypism is a special one dimensional form of polymorphism and a universal property of a wide range of metals, elemental and compound semiconductors, insulators and superconductors [1-5]. Prominent polytypic crystals belong to the AnB8−n(SiC,ZnS),MX2(CdI2) and ABX3 (Perovskites) crystal structure families. One of the structural preconditions for the occurrence of this phenomenon is a relative low stacking fault energy of stacking faults formed in a glide plane (basal plane) [6-10]. Another, the location in the John-Bloch diagram at the border between two structural ground states, for AnB8−n the wurtzite (2H) and sphalerite (3C) modifications [11]. Additionally, the possibility to form different modes of stacking of two dimensional structural compatible units along a defined crystallographic direction is required [12].

Polytypic and polymorphic structural variants behave thermodynamically different. The polymorphic modifications represent well defined thermodynamic phases, with well specified stability ranges of temperature, composition and pressure. The transition from one polymorph to another is a firstorder phase transformation. On the contrary, except for very few short period polytype modifications, no such physical factors have been found to govern the formation of polytypes. This is originated by small differences of formation and total energies between different polytypes structures [13-17]. The small energetic differences of the different polytype structures as well as the low stacking fault energies are less than the energetic disturbance in semiconductor technological processing steps and below the thermal energy at room temperature. As a consequence, different polytype appear under identical conditions of temperature and pressure and display syntactic coalescence and intergrowth of polytypes [18-21]. Additionally, this cause a specific type of defect formation, i.e. polytype lamella (syntactic inclusions) associated with stacking fault formation and local or global polytype transitions, during semiconductor device processing steps, i.e. thermal treatment [22, 23], thermo-mechanical stress [24], impurity diffusion [25], ion implantation and annealing [26-28], sputtering [29], etching [30], oxidation [31], metallization [32], crystal [33] and epitaxial [18, 34, 35] growth. Furthermore, polytype transitions occur during the operation of semiconductor devices [36-39].

According to published data polytype transformations are related to partial dislocation (PD) and stacking fault (SF) formation in the initial structure, i.e. structural "disorder". It can be hypotesized that at the very early stage the transformation process is related to point defect formation and their
selective coagulation leading to dislocation and stacking fault formation. The transformation processes occurring at nonequilibrium conditions can be considered as nonequilibrium phase transitions. The local structural changes induced by the SFs are polytype inclusions, i.e. able to act as information centers for the nucleation and growth of extended regions with a different polytype structures. Collective and selective interactions between these defects result in a stability loss of the original structure. Reaching the critical state, nonequilibrium polytype phase transition occur which lead to the formation of a new polytype structure better adapted to the exterior conditions. Schematically, the nonequilibrium phase transitions can be described as: Order → point defect/dislocation generation → stacking fault generation → defined disorder → "catastrophe" → new order. In Fig. 1 a generalizing scheme of polytype phase transition in terms of thermodynamic quantities and defect interactions is given. Energy dissipation in the crystal originating from incoming fluxes of mass, energy, impulse and entropy lead to an information excess in the initial polytype structure as a precondition for structural changes.

[picture]

Fig. 1. Polytype transition as nonequilibrium phase transitions.

Fig. 1. Polytype transition as nonequilibrium phase transitions.

Theoretically, the stability of different polytype structures without point and extended defects was studied in the framework of total energy calculations using different simulation approaches [13-16, 40]. In [3,40] the role of entropy for the stabilization of the polytype structure was discussed. In case of crystal growth the nucleation theory was used to assess the stability of the formation of different polytypes in dependence on supersaturation, Si to C ratio and doping [41, 42]. Alternatively, kinetic Monte Carlo [43-46] and molecular dynamic [47-48] approaches were applied. Another class of modelling polytype formation and transitions rely on dislocation and stacking fault reactions and their transformations [1, 49-51]. All this theoretical modelling approaches address singular initial material property conditions and specific material processing steps with a limited generalization ability to describe polytype transitions occurring at other semiconductor processing steps or during device operation.

In this contribution an ansatz is proposed which might pave the way for generalized macroscopic description of the defect related polytype transitions at arbitrary physical and chemical treatments.

Nonequilibrium Thermodynamic Model

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As shown above polytype transformations are interconnected with defect formations and can be considered as a specific type of defect formation. The percolation of the defect subsystem at a critical point transforms the initial crystal structure i into a new polytype modification j independent on the
physical nature of the action in the semiconductor fabrication processing step or during device operation [50,51]. The structural origin is the evolution of existing "disorder" (information excess) or the generation of "disorder" in the initial polytype structure i.

Within the framework of nonequilibrium thermo-

[picture]

Fig. 2. Scheme of the energetic states between two different structures i and j under equilibrium and nonequilibrium conditions.

Fig. 2. Scheme of the energetic states between two different structures i and j under equilibrium and nonequilibrium conditions.

The excess entropy formed in polytype S is associated with the energy dissipation in the polytypic single crystalline matrix material i due to the action of thermodynamic forces and linked fluxes of energy, mass and impulse of the physical interaction process. Introducing an ordering time of the initial polytype matrix j Pi→j[50] necessary to annihilate or incorporate the defects into the lattice and to rearrange the lattice stacking into the structure of the polytypic matrix under the conditions of the technological process under consideration. i can be determined using the entropy production Δμexc,i of the process and Δμexc , i  :

ΔSexc , i 

with i, and with Δμ as the ordering time of the ordering process i=TΔSexc , I . In the linear approximation of nonequilibrium thermodynamics the general form of total entropy production with fluxes i and conjugated driving forces j is [52]:

i

with j as the entropy production per unit volume and i→j as the volume. Taking into account that forces ΔSexc , crit  are affecting the fluxes Δμexc ,i by ΔSexc ,i Eq. 2 takes the form:

iΔSexc ,i

From Eq. 1 and 3 it follows that i is composed by the action of all fluxes and forces interacting with the polytypic crystalline matrix i. In table 1 a summary of thermodynamic forces and fluxes are given for which degradation of the polytype structure or polytype transitions were observed.

[picture]

Fig. 3. Scheme of the excess entropy formation in the polytype matrix τord i due to disordering and ordering by a technological process.

Fig. 3. Scheme of the excess entropy formation in the polytype matrix τ ord i due to disordering and ordering by a technological process.

The generalized interaction scheme explains the interrelation between ΔSexc ,i and dS/dt is shown in Fig. 3. It demonstrates that entropy production and the excess entropy formed in the polytypic matrix τord ,i affects the ordering time

ΔSexc,i=(dS/dt)τord,i(1)

by a positive feedback loop leading to an increase of τord ,i=∑m=1nτm through an increased defect density of the matrix crystal. Consequently, entropy production as a state function of nonequilibrium thermodynamics allows to formulate a stability criterial form of the polytype matrix τm in an interaction process with an arbitrary environment. The polytype matrix is stable if the following inequality if fulfilled:

m

here Jk is the critical excess entropy causing the instability of the polytype matrix and the onset of polytype transition in form of Xk.

Table 1 Collection of fluxes and forces in their thermodynamic description able to contribute to polytype defects formation or polytype transitions

Process | Thermodynamic force, X | Thermodynamic Flux, J
Heat flow | Temperature Gradient ∇(T⁻¹) | Heat Flux q
Current flow | Electric field ET-l | Electrical Current I
Plastic Deformation | Stress σT-l | Plastic Strain εp
Diffusion | Chemical Potential ∇(μCT⁻¹) | Diffusion Flux JD
Deposition Vapour/Gas Phase | Chemical Potential ∇(μPT⁻¹) | Diffusion Flux JP
Chemical Reaction | Reaction Affinity ART-l | Reaction Rate Rc
Particle irradiation | Particle Flux Density ART-l | Target Atom Velocity vp
Polishing/Wear | Friction Force FT-l | Relative Velocity Vr

dS/dt=∫σSdV=∫(∑kJkXk)dV(2)

and σs are the chemical potential due to a specific concentration and partial pressure, respectively. The forces and fluxes for deposition from vapour or gas phases are given for the diffusion limited case without convective or turbulent contributions.

[picture]

Fig. 4. Critical excess entropy of polytype transition V in the dependence on the shortest translation period Xl of the initial polytype structure.

Fig. 4. Critical excess entropy of polytype transition V in the dependence on the shortest translation period X l of the initial polytype structure.

The critical excess entropy related with the polytype transition from polytype Jk to polytype Jk=∑lBklXl was determined using physical vapour transport experiments in a sublimation growth cell applying a special SiC vapour distributor allowing for supersaturation distributions over the crystal surface at constant substrate temperatures [18,57]. For the investigations the following polytypes were used:

dS/dt=∫(∑k∑lBklXlXk)dV(3)

. The polytpes are ordered with respect to the shortest translation period which is the period containing fundamental stacking sequence characteristic for the given polytype, for example (22) or (32) for 4 H and 15 R , respectively. The expression for critical excess entropy ΔSexc, i crit, i, for polytype transition i was derived using Eq. 1 and 3 for the conditions of physical vapour transport growth and has the form;

dS/dt,τord ,i

with ΔSexc ,i as universal gas constant, iΔSexs ,i as the number of unit cells per mole of polytype τord i as critical growth rate for transition τord i and i as the vaporization rate of polytype

ΔSexc i=dS/dtτord i<ΔSexs crit i,(4)

. The obtained results are summarized in Fig. 4. The main findings are as follows. The critical excess entropy ΔSexc crit, i for polytype transition i→j is independent on the polytype structure of the initial polytype μC and depends only on the final polytype of the polytype transition μP. The value of i→j is decreasing if the shortest translation period λi of the transformation product is increasing. Consequently, the entropy barrier for transitions into a polytype structure with higher i is lower. This means that the transformation into polytypes with larger j requires a lower "disorder" (information excess), i.e. the formation and rearrangement of a lower defect concentration compared to the transition into a polytype with higher crystal symmetry, for example 3C-SiC. This is supported by the defect permutations needed to transform different hexagonal or rhombohedral polytypes into other hexagonal or rhombohedral polytypes compared to a transformation into the 3 C or 2 H structures [1,3,58]. As a consequence polytype transitions into polytypes with larger 4H,15R,6H,21R,8H,27R,33R,39R,19R occur at lower critical growth rates as reported in [56, 59-61].

Assuming now a defective polytype matrix. Defects can be dopants, dislocations, stacking faults or inclusions. Then, these defects increase the excess entropy ΔScrexc  and chemical potential of the matrix to i→j. It follows that the vaporization rate i→j changes into the vaporization rate of the defective matrix

ΔSexc crit ,i→jcr=(R/Ni)ln(1+(vcr,i→j/voi)), (5)

;

R

Combining Eq. 6 with 4 it follows:

Ni

Therefore, defective or strained substrates exhibiting an enhanced evaporation rate have a reduced entropy barrier for polytype transitions due to decreased disorder needed for the transition. As a consequence the critical growth rate for structural changes at a given substrate temperature decreases. This was observed in [57], where a reduction of the critical growth rate for the polytype transitions i,vcr and i→j on 6 H modified by boron diffusion in dependence on the near surface boron concentration was observed. The increase of the boron concentration decreased the critical growth rate. The same effect was detected for nitrogen implanted 6 H -SiC substrates in dependence on the implantation dose and for surfaces treated by polishing [57].

Thermo-plastic deformation of silicon carbide at different temperature and deformation conditions was studied in [24, 62-67]. In this studies it was revealed that beside dislocation related mechanisms, structural transitions in form of polytypic transformations are possible in the brittle [65,67] and ductile deformation region [49, 62, 66]. The observed structural transformation series are formally similar to polytype transformation series observed in growth experiments. Generally, the shortest translation period of the transformation product is smaller than the initial one. In [67] the transition sequence voi was observed in milling experiments with increasing milling time. In [24, 64] the possibility of polytype transitions i and polytype ΔScrexc crit,i→j was found. The polytype transformation of an arbitrary polytype into 3C is the most common one observed in mechanical treatments of SiC polytypes [24, 49, 62, 63, 65, 66]. In Fig. 5 the experimental critical initial stress as a function of the shortest translation period i→j of the initial polytype is given. The critical stress values for the polytype transitions are decreasing with increasing i. This behavior resembles the dependence of the critical growth rate of the onset of the polytype growth transitions in dependence on j published in [56].

For thermo-plastic deformation the entropy production can be written as [68]:

ΔScr exc  crit ,i→j

with λj as the sheer flow stress, λj as the shear strain rate ( λj density of mobile dislocation segments, λj as average velocity of the mobile dislocations), ΔScrexc  as average dislocation energy per unit length, Δμdef  as the dislocation density. Using Eq. 8 and the defect interaction model developed in [50, 51] the critical initial shear stress was estimated. The results of the analysis are given in Fig. 5. They show a reasonable agreement with experimental data

[picture]

Fig. 5. Polytype phase transitions in dependence on the shortest translation period voi and the initial elastic sheer stress.

Fig. 5. Polytype phase transitions in dependence on the shortest translation period v o i and the initial elastic sheer stress.

Summary

The original version of this paper is available on https://www.scientific.net/MSF.1190.79.pdf

External mass, entropy and energy fluxes are generally able to destabilize the polytype structure. The governing reason is the formation of stacking faults and instabilities of partial dislocations associated
with them. A new ansatz is proposed to describe the structural instabilities using nonequilibrium thermodynamics and the entropy production. A criterial form for polytype transitions is proposed. The criterial form is applied to describe observed structural instabilities occurring under different external actions.

Acknowledgement

The original version of this paper is available on https://www.scientific.net/MSF.1190.79.pdf

V. Kurtash gratefully acknowledges funding from the Thüringer Landesgraduiertenförderung AkZ 0051050-7150000163. A part of the results was obtained in the framework of PE624/1-1 supported by the German Research Foundation.

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The original version of this paper is available on https://www.scientific.net/MSF.1190.79.pdf

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The original version of this eBook is available on https://www.scientific.net/book/stacking-faults/978-3-0364-3126-0

Materials Science Forum, ISSN: 1662-9752, Vol. 1190, pp 89-94

doi: 10.4028/p-QUWd3K

© 2026 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Submitted:
2025-10-09

Revised:
2025-12-22

Accepted:
2026-02-23

Online:
2026-05-18

Depth-Dependent Suppression of Bipolar Degradation in 4H-SiC Diodes via Proton Implantation and Evaluation of Safe Operating Current Density Range

The original version of this paper is available on https://www.scientific.net/MSF.1190.89.pdf

Atsushi Shimbori 1,a*, Ryota Wada 2, b, Nobuhiro Tokoro 2,c, Takashi Kuroi 2, d, Hiu Yung Wong 3,e and Alex Q. Huang 1,f

1 J.J. Pickle Research Center, The University of Texas at Austin, 10100 Burnet Rd. Austin, TX 78758, USA

2 Nissin Ion Equipment Co, LTD, 75 Nishikujo Higashihieijo-cho, Minami-ku, Kyoto, Japan

3 San Jose State University, One Washington Square, San José, CA 95192, USA

a  ashimbo@utexas.edu, b  wada_ryota@nissin.co.jp, c  tokoro_nobuhiro@nissin-gr.com, d  kuroi_takashi@nissin.co.jp, ehiuyung.wong@sjsu.edu, f  aqhuang@utexas.edu

Keywords: SiC PiN Diode, Bipolar Degradation, Proton Implantation, Forward Voltage Drop, TCAD, Basal Plane Dislocation, Stacking Fault, Minority Carrier Lifetime, and Electroluminescence

Abstract

This work explores the role of implantation depth in suppressing bipolar degradation of 4H-SiC PiN diodes through proton implantation. Targeting depths aligned with active basal plane dislocations (BPDs) effectively reduces stacking-fault expansion, as confirmed by electroluminescence imaging [1,2]. From these observations, we quantified the effective range of suppression in both depth and safe operating current density. Room-temperature proton implantation ( 170keV,1×1016 cm−2 ) into the buffer reduced forward-voltage drift ΔF by 97% at 600 A/cm2. The implanted diode extended the safe operating current range to 1300 A/cm2,~200 A/cm2 higher than the reference, confirming effective suppression of bipolar degradation. Once the suppression barrier, defined as a critical excess hole density threshold, was exceeded, the proton-implanted diode exhibited explosive basal plane dislocation activity, leading to the formation of multiple bar-shaped stacking faults. These active BPDs are located deeper than the proton-implant tail, at a depth of around 11.4μ m; however, the threshold hole density required for their activation remains approximately the same (~4×1016 cm−3)[3].

Introduction

The original version of this paper is available on https://www.scientific.net/MSF.1190.89.pdf

[picture]

Fig. 1. Hole density distribution of the 4H−SiCPiN diode

Fig. 1. Hole density distribution of the 4 H − S i C P i N diode

One critical issue in the long-term reliability of 4H−SiC power MOSFETs is its body diode's VF (forward voltage drop) increase from the unique phenomenon of bipolar degradation. This is caused by the expansion of stacking faults (SFs) which originate from basal plane dislocations (BPDs) in the sublimation grown SiC substrate. Inserting a n+buffer layer with a short carrier lifetime is currently
the standard method in preventing electron-hole recombination from triggering SFs growth [4]. However, at higher current densities, the hole concentration can be substantial and reach the buffer/substrate interface where BPD-TED (threading edge dislocation) conversion points are present.

Fabrication

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An epitaxial layer, with a nitrogen doping concentration of 9×1015 cm−3 and a thickness of 10μ m, was grown by the CVD method with a high growth rate of 30μ m/hr. BPD density was further decreased by fast epitaxy and by adding a buffer layer with a thickness of 1μ m and a doping concentration of 2×1018 cm−3. Proton irradiation ( 1×1016 cm−2 at 170 keV , room temperature) was applied to the buffer layer prior to epitaxial growth to suppress stacking fault expansion with a non-implanted diode fabricated in parallel as a reference. To achieve high current density stress in the fabricated combshaped PiN diodes, surface doping at the anode was enhanced using a 30 nm Al capping layer. This approach shifted the first Al implantation peak closer to the surface, increasing the peak concentration near the metal-semiconductor interface to facilitate thin depletion tunneling (Fig. 2 (a)). As a result, a heavily doped p-type anode region with a peak concentration of 4×1020 cm−3 was formed through high-temperature Al implantation at 400∘C, followed by activation annealing at 1700∘C for 30 minutes. A low-temperature Ti-Pd based metallization stack ( Ti/Pd/Ti/Pt=2 nm/25 nm/40 nm/150 nm ), annealed at 700∘C for 1 min in Ar ambient, was employed for combshaped electrodes, achieving both precise pattern integrity and ultra-low specific contact resistance ( ρC=7.06×10−5Ω· cm2 ) required for EL emission analysis (Fig. 2(b)).

[picture]

Fig. 2. (a) Anode region SIMS profile and (b) Al vs Ti-Pd TLM contact evaluation comparison

Fig. 2. (a) Anode region SIMS profile and (b) Al vs Ti-Pd TLM contact evaluation comparison

Simulation and Numerical Analysis

The original version of this paper is available on https://www.scientific.net/MSF.1190.89.pdf

To accurately determine the threshold hole density at which bipolar degradation initiates in both reference and proton-implanted 4H−SiC PiN diodes, TCAD simulations were first calibrated against the I−V and C−V characteristics of simultaneously fabricated Ti-Pd-based circular diodes and subsequently extended to the comb-shaped electrode structure. During model validation, a slight deviation in the simulated I-V characteristics was observed, attributed to current-carrying limitations within the narrow electrode fingers of the comb-shaped layout rather than to contact resistance. EL analysis was then employed to identify the current density at which the initial onset of stacking fault (SF) expansion occurs, and to measure the maximum width W of a bar-shaped SSF. The high pulsed current required for this evaluation is limited primarily by the probe tip diameter rather than the anode contact resistance. To overcome this limitation, two probe tips were used on separate individual pads, each covering separate halves of the diode's conduction area.

[picture]

Fig. 3. TCAD simulation of hole density and H+profile at 1200−1400 A/cm2, showing delayed BPD activation beyond the implant tail edge

Fig. 3. TCAD simulation of hole density and H + profile at 1200 − 1400 A / c m 2 , showing delayed BPD activation beyond the implant tail edge

Fig. 3 shows the simulated hole density profiles superimposed against the hydrogen implant distribution under current stress levels of 1200 A/cm2 and 1400 A/cm2. In the reference diode (no proton implantation), basal plane dislocation (BPD) expansion begins when the hole density exceeds the threshold of approximately 4×1016 cm−3 near the buffer/substrate interface. In contrast, the H+implanted diode exhibits a delayed activation, with the BPD expansion point shifting deeper into the epilayer, just beyond the implantation tail edge (~11.4μ m). This delay arises because the protoninduced damage region locally reduces carrier lifetime (from 181 ns to 23.5 ns ) [5,6], creating a lower-injection zone that temporarily suppresses the minority-carrier density below the critical threshold.

Depth-Resolved Electroluminescence Analysis and Experimental Correlation with Implantation Profile

The original version of this paper is available on https://www.scientific.net/MSF.1190.89.pdf

[picture]

Fig. 4. EL images of (a) reference diode and (b) H+- implanted diode stressed at an equivalent current density of J=1200 A/cm2

Fig. 4. EL images of (a) reference diode and (b) H + - implanted diode stressed at an equivalent current density of J = 1200 A / c m 2

After the comb-shaped PiN diode had been fabricated, a bias stress of 400−μs−long8.5 V voltage pulse, equivalent to stress-current density of J=1200 A/cm2, was injected at a frequency of 3.33pulses/s for 20 min to observe the stacking fault expansion. Once the initially expanded dark region was observed, the bias stress was switched to DC to capture the time-evolution EL images at a current density of J=200 A/cm2 for an additional 20 min . For the reference diode (Fig. 4 (a)), both triangle-shaped and bar-shaped SSFs (Shockley-type stacking faults) were seen expanding along the [ [ 100 ] direction. To estimate the depth of the most active basal-plane dislocations (BPDs), the measured maximum width of a single stacking fault ( W ) was used in the geometric relation: d=W·tanθ, where d is depth of the expansion point and θ is the actual off-cut angle. From the EL image in Fig. 4(a), a maximum stacking-fault width of approximately 160μ m was observed. This corresponds to a depth of about 11.15μ m, calculated using the wafer off-cut angle of 4∘. The proton-implantation energy of 170 keV was therefore chosen so that the hydrogen peak would appear at this depth, matching the
location of the most active basal-plane dislocations near the buffer/substrate interface. As shown in the fabrication sequence below, the proton implantation step was introduced after the buffer layer growth and before the epitaxial growth, enabling a sufficiently high implantation dose and penetration depth to reach the targeted BPD-active region. The effectiveness of this approach is evident in Fig. 4(b), where the implanted diodes show no stacking-fault expansion even under the same current density conditions.

[picture]

Fig. 5. (a) SIMS hydrogen (H+)depth profile for 170keV,1×1015 cm−2 implantation showing a peak concentration at 11.15μ m within the buffer/substrate interface region. (b) Proton implantation step integrated into the 4H−SiC PiN diode fabrication sequence, illustrating the buffer layer position and subsequent process flow

Fig. 5. (a) SIMS hydrogen ( H + ) depth profile for 170 k e V , 1 × 10 15 c m − 2 implantation showing a peak concentration at 11.15 μ m within the buffer/substrate interface region. (b) Proton implantation step integrated into the 4 H − S i C PiN diode fabrication sequence, illustrating the buffer layer position and subsequent process flow

Finally, although the proton-implanted diodes initially showed no stacking-fault expansion under equivalent current densities, expansion was eventually observed at higher stress levels and longer operation times. This behavior defines the limit of the effective bipolar-degradation suppression range and highlights the need to further investigate the safe operating window of proton-implanted SiC diodes, where the devices do not exhibit bipolar degradation due to dislocation pinning [7,8] and carrier-lifetime reduction, thereby ensuring long-term reliability.

[picture]

Fig. 6. Time evolution of electroluminescence microscopy images under bias stress in the protonimplanted 4H−SiC PiN diode. Abrupt bar-shaped stacking faults (SFs) emerge at higher stress levels ( J=1400 A/cm2 ), indicating the upper limit of the bipolar-degradation suppression window

Fig. 6. Time evolution of electroluminescence microscopy images under bias stress in the protonimplanted 4 H − S i C PiN diode. Abrupt bar-shaped stacking faults (SFs) emerge at higher stress levels ( J = 1400 A / c m 2 ), indicating the upper limit of the bipolar-degradation suppression window

To correlate the simulated carrier-density threshold with the experimental onset of stacking-fault expansion, electroluminescence (EL) imaging was performed under incremental current stress. The observed width of 163μ m in the fully expanded bar-shaped SSF in Fig. 6, image (j) suggests that SF expansion initiates just below the proton implantation tail depth of 11.4μ m. This unpinning is triggered when minority carrier injection becomes sufficient to overcome the reduced-lifetime region
introduced by the implantation damage. This release occurs abruptly above ~1400 A/cm2 with barshaped SFs appearing more frequently than the reference diode, indicating an explosive activation of BPDs once the proton-induced barrier, defined by an excess hole density threshold, is overcome.

[picture]

Fig. 7. (a) I−V characteristics of reference and (b) H+-implanted diodes. Reference diode shows ΔVF drift under stress ( J=1300 A/cm2 ), while H+-implanted diode remains stable (c) Summary of VF shift in reference and H+-implanted PiN diodes under various current stress

Fig. 7. (a) I − V characteristics of reference and (b) H + -implanted diodes. Reference diode shows Δ V F drift under stress ( J = 1300 A / c m 2 ), while H + -implanted diode remains stable (c) Summary of V F shift in reference and H + -implanted PiN diodes under various current stress

As shown in Fig. 7, room-temperature proton implantation ( 1×1016 cm−2 ) into the buffer reduced forward-voltage drift ΔVF by 97% at 600 A/cm2. Proton-implanted diode demonstrated an extended safe operating current range, withstanding up to 1300 A/cm2, an increase of 200 A/cm2 compared to the non-implanted reference diode.
These observations, together with the TCAD-extracted threshold hole density of 4×1016 cm−3, support a consistent mechanism: proton-induced lifetime reduction within the buffer region pins BPDs and keeps the local minority-carrier density below the threshold near the buffer/substrate interface, thereby delaying SF activation until regions deeper than the proton-implant tail ( ~11.4μ m ) under elevated stress. As a result, the implanted diodes exhibit stable forward characteristics and no EL-visible SF expansion up to ~1300 A/cm2; beyond this level, the abrupt emergence of bar-shaped SFs indicates barrier overrun and defines the upper limit of the safe operating window.

Summary

The original version of this paper is available on https://www.scientific.net/MSF.1190.89.pdf

Proton implantation suppresses BPD-driven bipolar degradation in 4H−SiC diodes by reducing carrier lifetime and pinning dislocations within the implanted profile region, thereby shifting SF activation deeper beyond the implant tail. TCAD fitted with literature-calibrated lifetimes ( τ=181 ns for the reference, τ=23.5 ns for 1×1016 cm−2 at 170 keV implantation) indicates that, although the implanted diode exceeds the SF threshold at the buffer/substrate interface, proton-induced pinning prevents expansion, delaying activation until deeper beyond the implant tail. Implanted diodes remained stable up to 1300 A/cm2(~200 A/cm2 higher than reference), with no ΔVF drift and no bar-shaped SFs observed in EL imaging. These results confirm that lifetime engineering via proton implantation selectively into the buffer layer is an effective approach to extend the safe-operating current density of 4H−SiC PiN diodes without significantly reducing minority-carrier injection or conduction efficiency.

Acknowledgements

The original version of this paper is available on https://www.scientific.net/MSF.1190.89.pdf

The authors of this paper would like to thank Nissin Ion Equipment Co. Ltd for their support in the implantation process.

References

The original version of this paper is available on https://www.scientific.net/MSF.1190.89.pdf

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A. Shimbori, R. Wada, N. Tokoro, T. Kuroi, H. Y. Wong, and A. Q. Huang, "Estimation of threshold hole density in single Shockley stacking fault expansion and its suppression through proton implantation in PiN diodes," 2025 Device Research Conference (DRC), Durham, NC, USA, 2025, pp. 1-2, doi: 10.1109/DRC66027.2025.11105740.

T. Kimoto et al., "Understanding and reduction of degradation phenomena in SiC power devices," 2017 IEEE International Reliability Physics Symposium (IRPS), Monterey, CA, USA, 2017, pp. 2A-1.1-2A-1.7, doi: 10.1109/IRPS.2017.7936253

S. Harada, T. Mii, H. Sakane, and M. Kato, "Suppression of stacking-fault expansion in a 4HSiC epitaxial layer by proton irradiation," Sci. Rep., vol. 12, art. no. 13542, 2022, doi: 10.1038/s41598-022-17060-y.

T. Mii, H. Sakane, S. Harada, and M. Kato, "Analysis of carrier lifetime in a drift layer of 1.2kV -class 4 H -SiC devices toward complete suppression of bipolar degradation," Mater. Sci. Semicond. Process., vol. 153, art. no. 107126, 2023, doi: 10.1016/j.mssp.2022.107126.

M. Kato, S. Harada, and H. Sakane, "Effects of proton implantation for expansion of basal plane dislocations in SiC toward suppression of bipolar degradation: Review and perspective," Jpn. J. Appl. Phys., vol. 63, no. 2, art. no. 020804, Jan. 2024, doi: 10.35848/1347-4065/ad1779.

T. Li, H. Sakane, S. Harada, and M. Kato, "Suppression of stacking-fault expansion in 4H-SiC diodes by helium implantation," Appl. Phys. Express, vol. 17, no. 8, p. 086503, Aug. 2024, doi: 10.35848/1882-0786/ad6be5.

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Keywords Index

#

1ssf Challenges in 1SSF Detection in 4H-SiC Epilayer and Related Failure

4 H -sic; Characterization; X-ray Topography; Defects Investigation of Spoke Pattern of Stacking Faults in 4H-SiC Wafers Grown by Physical Vapor Transport Method

4 H -silicon Carbide Synchrotron X-Ray Topography Analysis of Low Angle Grain Boundaries Induced by Growth Step Flow in PVT-Grown 4H-SiC Crystals

A

And Electroluminescence Depth-Dependent Suppression of Bipolar Degradation in 4H-SiC Diodes via Proton Implantation and Evaluation of Safe Operating Current Density Range

B

Basal Plane Dislocation Depth-Dependent Suppression of Bipolar Degradation in 4H-SiC Diodes via Proton Implantation and Evaluation of Safe Operating Current Density Range

Basal Plane Dislocation (bpd) Trial Implementation of Operando PL Spectrum Mapping Using a Mini-Spectrometer in EVC Screening of 4H-SiC Wafers

Bipolar Degradation Investigation on Bipolar Degradation Caused by In-Grown Stacking Fault in 3.3 kV SiC-MOSFET; Depth-Dependent Suppression of Bipolar Degradation in 4H-SiC Diodes via Proton Implantation and Evaluation of Safe Operating Current Density Range

Body Diode Investigation on Bipolar Degradation Caused by In-Grown Stacking Fault in 3.3 kV SiC-MOSFET

Bpd Investigation on Bipolar Degradation Caused by In-Grown Stacking Fault in 3.3 kV SiC-MOSFET; Challenges in 1SSF Detection in 4H-SiC Epilayer and Related Failure

Burger Vector Challenges in 1SSF Detection in 4H-SiC Epilayer and Related Failure

D

Defect Process-Dependent Photoluminescence Behavior Evolution of Stacking Faults in 4H-SiC

Defect Formation Polytype Transitions in Silicon Carbide: A Macroscopic View

Defects Micropipes in SiC die Observed by Molten KOH Etching

Device Degradation Polytype Transitions in Silicon Carbide: A Macroscopic View

Device Failure Process-Dependent Photoluminescence Behavior Evolution of Stacking Faults in 4H-SiC

E

Elfr Challenges in 1SSF Detection in 4H-SiC Epilayer and Related Failure

F

Failure Analysis Investigation on Bipolar Degradation Caused by In-Grown Stacking Fault in 3.3 kV SiC-MOSFET

Forward Voltage Drop Depth-Dependent Suppression of Bipolar Degradation in 4H-SiC Diodes via Proton Implantation and Evaluation of Safe Operating Current Density Range

I

Idss Challenges in 1SSF Detection in 4H-SiC Epilayer and Related Failure

In-grown Stacking Fault Investigation on Bipolar Degradation Caused by In-Grown Stacking Fault in 3.3 kV SiC-MOSFET

Ion Implant Process-Dependent Photoluminescence Behavior Evolution of Stacking Faults in 4H-SiC

K

Koh Etching Micropipes in SiC die Observed by Molten KOH Etching

L

Leakage Current Degradation Investigation on Bipolar Degradation Caused by In-Grown Stacking Fault in 3.3 kV SiC-MOSFET

Low-angle Grain Boundary Synchrotron X-Ray Topography Analysis of Low Angle Grain Boundaries Induced by Growth Step Flow in PVT-Grown 4H-SiC Crystals

M

Micro Photoluminescence Challenges in 1SSF Detection in 4H-SiC Epilayer and Related Failure

Micropipes Micropipes in SiC die Observed by Molten KOH Etching

Minority Carrier Lifetime Depth-Dependent Suppression of Bipolar Degradation in 4H-SiC Diodes via Proton Implantation and Evaluation of Safe Operating Current Density Range

N

Nonequilibriums State Polytype Transitions in Silicon Carbide: A Macroscopic View

P

Phase Transition Polytype Transitions in Silicon Carbide: A Macroscopic View

Photoluminescence Process-Dependent Photoluminescence Behavior Evolution of Stacking Faults in 4H-SiC

Photoluminescence (pl) Proton Implantation-Induced Reduction of SSF Width and Associated Adverse Effects in 4H-SiC Epitaxial Layers; Trial Implementation of Operando PL Spectrum Mapping Using a Mini-Spectrometer in EVC Screening of 4H-SiC Wafers

Physical Vapor Growth Synchrotron X-Ray Topography Analysis of Low Angle Grain Boundaries Induced by Growth Step Flow in PVT-Grown 4H-SiC Crystals

Pl Imaging Investigation on Bipolar Degradation Caused by In-Grown Stacking Fault in 3.3 kV SiC-MOSFET

Pl Mapping Trial Implementation of Operando PL Spectrum Mapping Using a Mini-Spectrometer in EVC Screening of 4H-SiC Wafers

Polytype Stability Polytype Transitions in Silicon Carbide: A Macroscopic View

Polytype Transition Polytype Transitions in Silicon Carbide: A Macroscopic View

Proton Implantation Proton Implantation-Induced Reduction of SSF Width and Associated Adverse Effects in 4H-SiC Epitaxial Layers; Trial Implementation of Operando PL Spectrum Mapping Using a Mini-Spectrometer in EVC Screening of 4H-SiC Wafers; Depth-Dependent Suppression of Bipolar Degradation in 4H-SiC Diodes via Proton Implantation and Evaluation of Safe Operating Current Density Range

S

Self-organization Polytype Transitions in Silicon Carbide: A Macroscopic View

Shockley-type Stacking Fault (ssf) Proton Implantation-Induced Reduction of SSF Width and Associated Adverse Effects in 4H-SiC Epitaxial Layers; Trial Implementation of Operando PL Spectrum Mapping Using a Mini-Spectrometer in EVC Screening of 4H-SiC Wafers

SiC Die Micropipes in SiC die Observed by Molten KOH Etching

SiC Pin Diode Depth-Dependent Suppression of Bipolar Degradation in 4H-SiC Diodes via Proton Implantation and Evaluation of Safe Operating Current Density Range

Stacking Fault Depth-Dependent Suppression of Bipolar Degradation in 4H-SiC Diodes via Proton Implantation and Evaluation of Safe Operating Current Density Range

Stacking Faults Process-Dependent Photoluminescence Behavior Evolution of Stacking Faults in 4H-SiC

Synchrotron X-ray Characterization Synchrotron X-Ray Topography Analysis of Low Angle Grain Boundaries Induced by Growth Step Flow in PVT-Grown 4H-SiC Crystals

T

Tcad Depth-Dependent Suppression of Bipolar Degradation in 4H-SiC Diodes via Proton Implantation and Evaluation of Safe Operating Current Density Range

Thermodynamics Polytype Transitions in Silicon Carbide: A Macroscopic View

U

Uv Irradiation Proton Implantation-Induced Reduction of SSF Width and Associated Adverse Effects in 4H-SiC Epitaxial Layers; Trial Implementation of Operando PL Spectrum Mapping Using a Mini-Spectrometer in EVC Screening of 4H-SiC Wafers

W

Wide-bandgap Materials Micropipes in SiC die Observed by Molten KOH Etching

Y

Yield Process-Dependent Photoluminescence Behavior Evolution of Stacking Faults in 4H-SiC

Authors Index

A

Adamo, S. Challenges in 1SSF Detection in 4H-SiC Epilayer and Related Failure

Alessandrino, M. Challenges in 1SSF Detection in 4H-SiC Epilayer and Related Failure

Amishiro, H. Investigation on Bipolar Degradation Caused by In-Grown Stacking Fault in 3.3 kV SiC-MOSFET

Anzalone, R. Micropipes in SiC die Observed by Molten KOH Etching

B

Bottari, C. Challenges in 1SSF Detection in 4H-SiC Epilayer and Related Failure

Bouch, C. Investigation of Spoke Pattern of Stacking Faults in 4H-SiC Wafers Grown by Physical Vapor Transport Method; Synchrotron X-Ray Topography Analysis of Low Angle Grain Boundaries Induced by Growth Step Flow in PVT-Grown 4H-SiC Crystals

C

Calabretta, C. Challenges in 1SSF Detection in 4H-SiC Epilayer and Related Failure; Micropipes in SiC die Observed by Molten KOH Etching

Carbone, B. Challenges in 1SSF Detection in 4H-SiC Epilayer and Related Failure

Chen, Z. Investigation of Spoke Pattern of Stacking Faults in 4H-SiC Wafers Grown by Physical Vapor Transport Method; Synchrotron X-Ray Topography Analysis of Low Angle Grain Boundaries Induced by Growth Step Flow in PVT-Grown 4H-SiC Crystals

D

Dudley, M. Investigation of Spoke Pattern of Stacking Faults in 4H-SiC Wafers Grown by Physical Vapor Transport Method; Synchrotron X-Ray Topography Analysis of Low Angle Grain Boundaries Induced by Growth Step Flow in PVT-Grown 4H-SiC Crystals

E

Erlbacher, T. Process-Dependent Photoluminescence Behavior Evolution of Stacking Faults in 4H-SiC

F

Faisal, F. Process-Dependent Photoluminescence Behavior Evolution of Stacking Faults in 4H-SiC

Fiorenza, P. Challenges in 1SSF Detection in 4H-SiC Epilayer and Related Failure

Fontana, E. Challenges in 1SSF Detection in 4H-SiC Epilayer and Related Failure

Fuchs, A. Process-Dependent Photoluminescence Behavior Evolution of Stacking Faults in 4H-SiC

H

Hu, S. Investigation of Spoke Pattern of Stacking Faults in 4H-SiC Wafers Grown by Physical Vapor Transport Method; Synchrotron X-Ray Topography Analysis of Low Angle Grain Boundaries Induced by Growth Step Flow in PVT-Grown 4H-SiC Crystals

Huang, A. Depth-Dependent Suppression of Bipolar Degradation in 4H-SiC Diodes via Proton Implantation and Evaluation of Safe Operating Current Density Range

I

Igarashi, Y. Proton Implantation-Induced Reduction of SSF Width and Associated Adverse Effects in 4H-SiC Epitaxial Layers; Trial Implementation of Operando PL Spectrum Mapping Using a Mini-Spectrometer in EVC Screening of 4H-SiC Wafers; Quantitative Analysis of Excess Minority Carrier Density and Critical Duration in UV Irradiation-Based Screening for Bipolar Degradation in 4H-SiC

K

Kagawa, Y. Investigation on Bipolar Degradation Caused by In-Grown Stacking Fault in 3.3 kV SiC-MOSFET

Kakushima, K. Exploring the Ion Implantation Mechanism for Suppressing Stacking Fault Expansion in 4H-SiC: A Fundamental Approach

Kallinger, B. Process-Dependent Photoluminescence Behavior Evolution of Stacking Faults in 4H-SiC

Kojima, J. Exploring the Ion Implantation Mechanism for Suppressing Stacking Fault Expansion in 4H-SiC: A Fundamental Approach

Kranert, C. Process-Dependent Photoluminescence Behavior Evolution of Stacking Faults in 4H-SiC

Kuroi, T. Depth-Dependent Suppression of Bipolar Degradation in 4H-SiC Diodes via Proton Implantation and Evaluation of Safe Operating Current Density Range

Kurtash, V. Polytype Transitions in Silicon Carbide: A Macroscopic View

Kölbel, N. Process-Dependent Photoluminescence Behavior Evolution of Stacking Faults in 4H-SiC

L

Li, Y. Investigation of Spoke Pattern of Stacking Faults in 4H-SiC Wafers Grown by Physical Vapor Transport Method; Synchrotron X-Ray Topography Analysis of Low Angle Grain Boundaries Induced by Growth Step Flow in PVT-Grown 4H-SiC Crystals

Liu, Y. Investigation of Spoke Pattern of Stacking Faults in 4H-SiC Wafers Grown by Physical Vapor Transport Method; Synchrotron X-Ray Topography Analysis of Low Angle Grain Boundaries Induced by Growth Step Flow in PVT-Grown 4H-SiC Crystals

M

Maira, G. Challenges in 1SSF Detection in 4H-SiC Epilayer and Related Failure

Matsushita, Y. Proton Implantation-Induced Reduction of SSF Width and Associated Adverse Effects in 4H-SiC Epitaxial Layers; Trial Implementation of Operando PL Spectrum Mapping Using a Mini-Spectrometer in EVC Screening of 4H-SiC Wafers; Quantitative Analysis of Excess Minority Carrier Density and Critical Duration in UV Irradiation-Based Screening for Bipolar Degradation in 4H-SiC

Morita, T. Proton Implantation-Induced Reduction of SSF Width and Associated Adverse Effects in 4H-SiC Epitaxial Layers; Trial Implementation of Operando PL Spectrum Mapping Using a Mini-Spectrometer in EVC Screening of 4H-SiC Wafers; Quantitative Analysis of Excess Minority Carrier Density and Critical Duration in UV Irradiation-Based Screening for Bipolar Degradation in 4H-SiC

Myalitsin, A. Exploring the Ion Implantation Mechanism for Suppressing Stacking Fault Expansion in 4H-SiC: A Fundamental Approach

Müller, S. Process-Dependent Photoluminescence Behavior Evolution of Stacking Faults in 4H-SiC

N

Nania, C. Micropipes in SiC die Observed by Molten KOH Etching

Neubert, F. Polytype Transitions in Silicon Carbide: A Macroscopic View

Niwa, H. Investigation on Bipolar Degradation Caused by In-Grown Stacking Fault in 3.3 kV SiC-MOSFET

O

Ohba, T. Exploring the Ion Implantation Mechanism for Suppressing Stacking Fault Expansion in 4H-SiC: A Fundamental Approach

Onda, S. Exploring the Ion Implantation Mechanism for Suppressing Stacking Fault Expansion in 4H-SiC: A Fundamental Approach

Oshiyama, A. Exploring the Ion Implantation Mechanism for Suppressing Stacking Fault Expansion in 4H-SiC: A Fundamental Approach

P

Pezoldt, J. Polytype Transitions in Silicon Carbide: A Macroscopic View

Philpott, R. Investigation of Spoke Pattern of Stacking Faults in 4H-SiC Wafers Grown by Physical Vapor Transport Method; Synchrotron X-Ray Topography Analysis of Low Angle Grain Boundaries Induced by Growth Step Flow in PVT-Grown 4H-SiC Crystals

Piluso, N. Challenges in 1SSF Detection in 4H-SiC Epilayer and Related Failure; Micropipes in SiC die Observed by Molten KOH Etching

R

Raciti, D. Micropipes in SiC die Observed by Molten KOH Etching

Raghothamachar, B. Investigation of Spoke Pattern of Stacking Faults in 4H-SiC Wafers Grown by Physical Vapor Transport Method; Synchrotron X-Ray Topography Analysis of Low Angle Grain Boundaries Induced by Growth Step Flow in PVT-Grown 4H-SiC Crystals

Roccaforte, F. Challenges in 1SSF Detection in 4H-SiC Epilayer and Related Failure

Russo, A. Challenges in 1SSF Detection in 4H-SiC Epilayer and Related Failure

S

Sano, M. Exploring the Ion Implantation Mechanism for Suppressing Stacking Fault Expansion in 4H-SiC: A Fundamental Approach

Schulze, J. Process-Dependent Photoluminescence Behavior Evolution of Stacking Faults in 4H-SiC

Schunemann, P. Investigation of Spoke Pattern of Stacking Faults in 4H-SiC Wafers Grown by Physical Vapor Transport Method; Synchrotron X-Ray Topography Analysis of Low Angle Grain Boundaries Induced by Growth Step Flow in PVT-Grown 4H-SiC Crystals

Severino, A. Challenges in 1SSF Detection in 4H-SiC Epilayer and Related Failure; Micropipes in SiC die Observed by Molten KOH Etching

Shimbori, A. Depth-Dependent Suppression of Bipolar Degradation in 4H-SiC Diodes via Proton Implantation and Evaluation of Safe Operating Current Density Range

Shiraishi, K. Exploring the Ion Implantation Mechanism for Suppressing Stacking Fault Expansion in 4H-SiC: A Fundamental Approach

Sugawara, K. Investigation on Bipolar Degradation Caused by In-Grown Stacking Fault in 3.3 kV SiC-MOSFET

T

Takano, K. Proton Implantation-Induced Reduction of SSF Width and Associated Adverse Effects in 4H-SiC Epitaxial Layers; Trial Implementation of Operando PL Spectrum Mapping Using a Mini-Spectrometer in EVC Screening of 4H-SiC Wafers; Quantitative Analysis of Excess Minority Carrier Density and Critical Duration in UV Irradiation-Based Screening for Bipolar Degradation in 4H-SiC

Tanaka, T. Investigation on Bipolar Degradation Caused by In-Grown Stacking Fault in 3.3 kV SiC-MOSFET

Tojima, K. Investigation on Bipolar Degradation Caused by In-Grown Stacking Fault in 3.3 kV SiC-MOSFET

Tokoro, N. Depth-Dependent Suppression of Bipolar Degradation in 4H-SiC Diodes via Proton Implantation and Evaluation of Safe Operating Current Density Range

Turchetti, S. Investigation of Spoke Pattern of Stacking Faults in 4H-SiC Wafers Grown by Physical Vapor Transport Method; Synchrotron X-Ray Topography Analysis of Low Angle Grain Boundaries Induced by Growth Step Flow in PVT-Grown 4H-SiC Crystals

V

Vento, F. Challenges in 1SSF Detection in 4H-SiC Epilayer and Related Failure; Micropipes in SiC die Observed by Molten KOH Etching

W

Wada, R. Depth-Dependent Suppression of Bipolar Degradation in 4H-SiC Diodes via Proton Implantation and Evaluation of Safe Operating Current Density Range

Wang, H. Investigation of Spoke Pattern of Stacking Faults in 4H-SiC Wafers Grown by Physical Vapor Transport Method

Watahiki, T. Investigation on Bipolar Degradation Caused by In-Grown Stacking Fault in 3.3 kV SiC-MOSFET

Wong, H. Depth-Dependent Suppression of Bipolar Degradation in 4H-SiC Diodes via Proton Implantation and Evaluation of Safe Operating Current Density Range

Y

Yoda, T. Exploring the Ion Implantation Mechanism for Suppressing Stacking Fault Expansion in 4H-SiC: A Fundamental Approach

Z

Zhang, J. Investigation of Spoke Pattern of Stacking Faults in 4H-SiC Wafers Grown by Physical Vapor Transport Method; Synchrotron X-Ray Topography Analysis of Low Angle Grain Boundaries Induced by Growth Step Flow in PVT-Grown 4H-SiC Crystals

Zhang, K. Investigation of Spoke Pattern of Stacking Faults in 4H-SiC Wafers Grown by Physical Vapor Transport Method