Dependence of humidity-stress impact on passivation film for edge termination area in 4H-SiC diodes

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. To analyze the distribution of charge density during these tests, a differentiated capacitance-reverse-voltage method was used. From comparing the results of the HTRB and H³TRB tests, it was clarified that the H³TRB test induces a negative charge at the SiO₂/SiC interface but induces a positive charge at the polyimide/SiC interface. We concluded that the origin of the increase in charge density induced by high-humidity stress is the corrosion of the anode metal, which depends on the surface film of the SiC in the termination area, namely, the SiO₂/SiC or polyimide/SiC interface. The induced charge mechanism can become a guideline for designing highly reliable SiC power devices against humidity stress. (author)