Investigation of Failure Mechanisms of 1200 V Rated Trench SiC MOSFETs Under Repetitive Avalanche Stress

Abstract

In this article, the repetitive avalanche ruggedness of silicon carbide metal-oxide-semiconductor field-effect transistors (MOSFETs) with asymmetric trench (AT) and double trench (DT) structure is investigated experimentally. The different failure mechanisms, i.e., thermal-induced fatigue or field oxide breakdown for AT-MOSFET and electric field induced gate oxide degradation or breakdown for DT-MOSFET, are verified by device decapsulation and TCAD simulation. Different from the transient failure in single-pulse avalanche test, the degradation and failure under repetitive avalanche stress are related to the accumulation of gate oxide traps or thermal stress. Under high energy ratio condition, DT-MOSFET fails with shorted gate-drain terminal after only 2k unclamped inductive switching (UIS) cycles. Microscopic failure analysis shows an obvious crack through the bottom gate oxide to N-drift layer, whereas the electrical parameters of AT-MOSFET remain stable during 12k UIS cycles until gate leakage current of 10 mA exceeds the failure threshold of devices. The thermal-induced field oxide breakdown is found upon polysilicon gate in AT-MOSFET. Under low energy ratio condition, over 5% reduction of threshold voltage and on-state resistance is observed in DT-MOSFET due to hot holes injection in gate oxide. However, the threshold voltage of AT-MOSFET is almost constant and an approximately 10% increase of on-state resistance caused by thermal fatigue is observed.