Materials Science Forum Vol. 1190

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 (350 keV, 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 30 μm 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 drift-layer 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 implantation-induced degradation.

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 (V_DSon) and leakage current (I_DSX) degradation. A high current stress was applied to over 1,500 chips, resulting in 72 degraded devices, with 45 exhibiting notable I_DSX degradation. A detailed analysis revealed that most I_DSX 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 I_DSX degradation, indicating the need for further research to elucidate the mechanisms behind this degradation in SiC-MOSFETs.

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.

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.

Abstract: Ultraviolet (UV) irradiation on 4H-SiC epitaxial wafers, conducted prior to metalized circuit formation, is widely used to reveal whether BPD (basal plane dislocation) induced nucleation and expansion of a single Shockley stacking fault (1SSF) occurs or not 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,” t_crit. Notably, t_crit shows only weak dependence on the bulk carrier lifetime (τ_b), offering a practical route to determine pulsed UV irradiation conditions that faithfully emulate forward bias stress, even when τ_b is unknown.

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.

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 (V_c) generated by high-energy proton implantation are found to play a significant role in suppressing the expansion of 1SSFs.

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.

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 high-performance 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.