Papers by Keyword: Proton Implantation

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 ΔV_F by 97% at 600A/cm². The implanted diode extended the safe operating current range to 1300A/cm², ~200A/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 11.4µm; however, the threshold hole density required for their activation remains approximately the same (~ 4×10¹⁶ cm^-3) [3].

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: 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: 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: Bipolar degradation is a well-known issue when using body diodes in SiC-MOSFETs. Recent studies suggest that H⁺ (proton) implantation can effectively inhibit this degradation, but demonstrations on its suppression are still limited. Therefore, in this study, we have experimentally demonstrated how the expansion of Shockley-type stacking faults (SSFs) is suppressed by proton implantation. We fabricated a vertical SiC-MOSFET, in which protons were implanted into the middle depth of the drift layer. We then subjected the body diode to continuous current stress and performed photoluminescence (PL) analysis. Detailed PL image and emission spectral analysis of SSFs revealed that the proton-implanted layer can function as a recombination-enhancing layer during bipolar operation. Furthermore, it can be formed at any depth within the drift layer by controlling the energy, offering a significant advantage in the design of SiC-MOSFETs.

Abstract: In this paper, a method for suppressing bipolar degradation through proton implantation was investigated. Previous work suggests implantation applied to the full thickness of the epi layer, which results in unwanted defects leading to a deterioration in performance. In this work, proton implantation to the buffer layer was successful in reducing the forward-voltage drift ΔV_F of the fabricated SiC PiN diode by 85% at a current density of 800A/cm², when applying room temperature (RT) proton irradiation at a dose of 1×10¹⁶ cm^-2. Irradiation solely to the buffer layer keeps the deterioration of forward current performance to a minimum, while the fabricated SiC PiN diodes are more robust against bipolar degradation at higher current density. In addition, RT proton irradiated PiN diodes show full recovery from their bipolar degraded characteristics within 2.5 h of annealing at 350 °C under vacuum. This indicates proton irradiation alters the crystal structure for the stacking fault (SF) to “shrink” back with ease to their initial basal plane dislocations (BPD) state.

Abstract: We investigated how proton implantation influences electrical characteristics of the 4H-SiC MOSFETs. Bipolar degradation in SiC is one of the key issues to be solved for utilizing the bipolar operation in SiC power devices. Its suppression with the proton implantation technique has recently been reported. If we can apply such a new technique being involved for realizing reliable SiC MOSFETs, it would give us great merit to take advantage of the body diode. However, few study has been reported of proton implanted SiC MOSFETs, to our knowledge. Thus, we fabricated 4,000 chips, applied current stress to their body diodes and subsequently evaluated them to verify statistically any effectiveness on the suppression of the bipolar degradation as well as on the electrical performance of MOSFET in order to consider its technological applicability to their mass production process. We found that proton implantation not only has little influence on the static electrical characteristics of the MOSFETs but also improves the switching characteristics.

Abstract: In this paper, Shockley-Read-Hall (SRH) lifetime depth profiles in the drift layer of 10 kV SiC PiN diodes are calculated after MeV proton implantation. It is assumed that the carbon vacancy will be the domination trap for charge carrier recombination and the SRH lifetime is calculated with defect parameters from the literature and proton-induced defect distributions deduced from SRIM calculations. The lifetime profiles are imported to Sentaurus TCAD and static and dynamic simulations using tailored lifetime profiles are carried out to study the electrical effect of proton implantation parameters. The results are compared to measurements, specializing on optimization of the trade off between on-state and turn-off losses, represented by the forward voltage drop, V_T, and reverse recovery charge, Q_rr, respectively. Both the simulated and measured IV characteristics show that increasing proton dose, or energy, has the effect on increasing forward voltage drop and on-state losses, while simultaneously, the localized SRH lifetime drop decreases the plasma level, increases the speed of recombination and decreases reverse recovery charge. Finally, TCAD simulations with different combinations of proton energies and fluences are used to optimize the trade-off between static and dynamic performances. Reverse recovery charge and forward voltage drops of these groups of diodes are plotted together, showing that a medium energy which induces the most defects in the depletion region relatively close to the anode gives the best dynamic performances, with a minimum cost of static performance.

Abstract: In this paper, proton implantation with different combinations of MeV energies and doses from 2×10⁹ to 1×10¹¹ cm^-2 is used to create defects in the drift region of 10 kV 4H-SiC PiN diodes to obtain a localized drop in the SRH lifetime. On-state and reverse recovery behaviors are measured to observe how MeV proton implantation influences these devices and values of reverse recovery charge Q_rr are extracted. These measurements are carried out under different temperatures, showing that the reverse recovery behavior is sensitive to temperature due to the activation of incompletely ionized p-type acceptors. The results also show that increasing proton implantation energies and fluencies can have a strong effect on diodes and cause lower Q_rr and switching losses, but also higher on-state voltage drop and forward conduction losses. The trade-off between static and dynamic performance is evaluated using Q_rr and forward voltage drop. Higher fluencies, or energies, help to improve the turn-off performance, but at a cost of the static performance.

Abstract: Two metastable defects with energy levels at Ec-0.28eV and Ec-0.37eV, which previously have been reported in proton implanted- and in proton implanted and annealed crystalline silicon are discussed. Recent results on the peculiar behavior of these defects upon periodical application of two different bias conditions during DLTS measurement are reviewed. Two specifically designed DLTS measurement sequences are proposed in order to further reveal the defects transformation rates and respective activation energies.