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We developed an in-operando x-ray topography method for dynamically visualizing single Shockley-type stacking fault (1SSF) expansion motions in silicon carbide (SiC) metal–oxide–semiconductor field-effect transistors (MOSFETs) during their operations and investigated the effect of the operating condition applied to the body diodes in SiC MOSFETs on dislocation glide velocity. In-operando x-ray topography observations were carried out in reflection geometry, and a high-resolution x-ray camera was used as a detector to record topographies dynamically. The sequence of 1SSF expansion motions in the SiC MOSFETs was observed at a high resolution of 1 s in x-ray topographies, which is sufficient to analyze the dislocation glide velocity of a 1SSF expansion. The observation results of changing the forward current density applied to the body diodes in SiC MOSFETs revealed that each triangular and bar-shaped 1SSF expands at different forward current densities. The 1SSF expansion timings also differed, even in the same chip under the same current density. The dislocation glide velocity of each expanded 1SSF in SiC MOSFETs was extracted, and it increased with the forward current density. Our method enables the dynamic visualization of bipolar degradation in SiC MOSFETs during their operations, and we can accurately obtain the information of when, where, and which 1SSF expands in a SiC MOSFET. [ABSTRACT FROM AUTHOR]

We investigated the nucleation sites of expanded single Shockley-type stacking faults (1SSFs) in a silicon carbide (SiC) metal–oxide–semiconductor field effect transistor (MOSFET) and demonstrated epitaxial layers designed for bipolar-degradation-free SiC MOSFETs. Since the sufficient hole density just below the basal plane dislocation (BPD)-threading edge dislocation (TED) conversion points induces 1SSF expansion, we derived the dependence of the nucleation depth on the applied current condition from the BPD-TED conversion points of 1SSFs. We first simulated and determined the three-step current conditions applied to a body diode in a SiC MOSFET so that a sufficient amount of holes would be supplied to the drift layer, to the buffer layer, and inside the substrate in the SiC MOSFET. An in operando x-ray topography analysis was conducted with the determined conditions for dynamically visualizing 1SSF expansion motions, and 1SSFs expanded at different forward current densities were successfully extracted. The depths of the BPD-TED conversion points of the extracted 1SSFs were analyzed, and it was experimentally clarified that these depths, i.e., the nucleation sites of expanded 1SSFs, became deeper with forward current densities. The bipolar degradation characteristics of SiC MOSFETs were evaluated as a function of the forward current density, and the validity of the simulation model was verified by experimental results. We also confirmed that bipolar degradation can be suppressed to some extent by using a substrate with a low BPD density, and SiC MOSFETs with a high-nitrogen-concentration epitaxial layer showed high reliability under bipolar operation. Depending on the application of SiC MOSFETs, the epitaxial layers should be designed to prevent the hole density inside the substrate from exceeding the threshold for 1SSF expansion. [ABSTRACT FROM AUTHOR]

When developing silicon carbide (SiC) devices, the reliability of the internal body diode is an important issue. Stacking faults (SFs) are expanded from basal plane defects by using a body diode. Although it is well known that ON-voltage degradation occurs due to SFs, their effects on dynamic reliability have not been studied well. Furthermore, including the effects of SFs, there are not many reports about the dynamic reliability of SiC-MOSFETs. In this paper, a double-pulse switching test using 3.3-kV SiC-MOSFETs was carried out to clarify the failure mechanism of the switching operation of SiC-MOSFETs and effects of SFs on the safe operation area (SOA). Before the switching test, current stress was applied to the body diode of the devices under test (DUTs) to expand the SFs. The circuit configuration was half-bridge type, and a double-pulse gate signal was applied to the lower arm DUT. The switching voltage was 1.8 kV, and the switching current increased at about 8-A steps to failure. As a result, reverse recovery SOA (RRSOA) reliability decreased depending on the amount of SFs in the SiC-MOSFET. Because RRSOA failure was caused by avalanche due to the hole concentration during reverse recovery and the SFs raised local current density, reverse bias SOA (RBSOA) hardly decreased even if SFs containing SiC-MOSFETs were used. This is because RBSOA failure was caused by degradation of the gate isolation layer due to overheating and the temperature coefficient of the SFs electric resistance indicated negative. [ABSTRACT FROM AUTHOR]

The SAGA Light Source provides X‐ray imaging resources based on high‐intensity synchrotron radiation (SR) emitted from the superconducting wiggler at beamline 07 (BL07). By combining quasi‐monochromatic SR obtained by the newly installed water‐cooled metal filter and monochromatic SR selected by a Ge double‐crystal monochromator (DCM) with high‐resolution lens‐coupled X‐ray imagers, fast and low‐dose micro‐computed tomography (CT), fast phase‐contrast CT using grating‐based X‐ray interferometry, and 2D micro‐X‐ray absorption fine structure analysis can be performed. In addition, by combining monochromatic SR obtained by a Si DCM with large‐area fiber‐coupled X‐ray imagers, high‐sensitivity phase‐contrast CT using crystal‐based X‐ray interferometry can be performed. Low‐temperature CT can be performed using the newly installed cryogenic system, and time‐resolved analysis of the crystallinity of semiconductor devices in operation can be performed using a time‐resolved topography system. The details of each instrument and imaging method, together with exemplary measurements, are presented. [ABSTRACT FROM AUTHOR]