Analysis of Gate Oxide Degradation Induced by Heavy Ion in SiC Power MOSFETs

Recent research has revealed that SiC power MOSFETs can experience failures at remarkably low gate stress after heavy ion irradiation, even though no discernible degradation in gate leakage current can be measured during irradiation. However, the damage structure has yet to be precisely analyzed. In this article, the nanoscale structure and element distribution of the degradation site in gate leakage current failure devices after post-irradiation gate stress (PIGS) tests were investigated. A gate leakage current failure occurred in PIGS tests of a 1200 V SiC power MOSFET with only 50 V drain bias during irradiation. Further failure analysis using transmission electron microscope (TEM) and energy dispersive X-ray (EDX) revealed a 50-nm wide structural defect in the gate oxide layer directly above the JFET region, which was mainly filled with polysilicon. Suspected latent damage was also observed adjacent to the damaged region. Besides the gate oxide damage, defects were observed on the SiC surface and the polysilicon gate. Through the internal physical response simulation, the picosecond short response time of the electric field in the gate oxide layer can be highly destructive and a critical factor contributing to potential failures at lower drain bias. The diffusion of holes on SiC surfaces causes an extension of the degradation region where the electric field changes.