Failure mechanism of 4H-SiC junction barrier Schottky diodes under harsh thermal cycling stress

The concern in the long-term reliability of the SiC power devies is raised lately in power electronic field due to its brief history and limited data. In this work, discrete 1200 V/20A SiC JBS diodes have been intensively investigated by HTRB, HAST, and TCT. 2 % samples have failed in the harsh thermal cycling test, showing that the failure mechanism is attributed to field-oxide cracking. The electrical and physical failure analysis pointed out that a gradual degradation occurred at the termination structure, causing non-recoverable damages and provoking a significant increase in the leakage current. The FIB cut and SEM analysis showed the delamination existence between field oxide layer and silicon carbide layer in the degraded devices. The observed leakage current after the TCT could be well correlated with the formation of the delamination, which created a current leaking path between active and termination region. These findings emphasize the importance of SiO2/SiC interface quality in the long-term highly reliable SiC power devices, and indicate further optimized design of SiO2 passivation layer or other alternative materials is urgently needed to overcome this structural weakness.