Two Mechanisms of Charge Accumulation in Edge Termination of 4H-SiC Diodes Caused by High-Temperature Bias Stress and High-Temperature and High-Humidity Bias Stress

High-temperature reverse bias (HTRB) and high-humidity HTRB (H3TRB) tests were carried out on 4H-SiC diodes to investigate the mechanism of charge accumulation at the SiO2/SiC interface in the edge termination area, which causes breakdown voltage instability. A differentiated capacitance-reverse voltage method was used to analyze the charge distribution. With HTRB, the charge accumulation occurred in the edge termination area with a passivation of O2oxidation film and the one with a NO oxidation film. In contrast, no charge accumulation occurred in the edge termination area without SiO2as a passivation film. With H3TRB, however, the charge accumulation took place not only in the edge of termination area with O2oxidation but also in the edge termination area without SiO2. The results of two tests revealed that the edge termination area without SiO2has little tolerance to charge accumulation in a high-humidity and high-temperature atmosphere, although it has tolerance in a high-temperature atmosphere. The difference of tolerance depending on stress condition suggests that there are two mechanisms of charge accumulation, one related to the SiO2/SiC interface and triggered by applying temperature and voltage stress without humidity and the other does not related to the interface and triggered by applying temperature and voltage stress with humidity.