Impact of Carbon Cap Defects on the Reliability of Automotive 1.2 kV SiC MOSFETs

To proactively identify and mitigate potential reliability issues in 1.2 kV SiC MOSFETs during electric vehicle (EV) traction inverter operation, extensive burn-in and reliability assessments were conducted on about 100,000 chips. A key observation was that certain half-bridge power modules passed the standard Module-level Burn-in (MLBI) yet failed under extended MLBI, with failures ultimately traced to chip defects. Through physical analysis and numerical simulation, the origin and failure mechanism of such defects have been identified. These defects originate from the carbon cap (C-cap) process step and their presence leads to abnormal gate oxide morphology in the JFET region as well as localized electric field peaks, which accelerate gate oxide degradation and then lead to failure under aging stress. Furthermore, the results of comparative experiments within the screening process suggest that the targeted unclamped inductive switching (UIS) test is essential for activating such defects, leading to early failure at the MLBI stage. Eventually, the full-process screening strategy for SiC MOSFET chips has been optimized, thus significantly enhancing the reliability of the final product.