A novel mechanical stress related failure mechanism of the state-of-the-art SiC double trench MOSFET under surge current stress

In this paper, the surge reliability of the state-of-the-art reinforced double trench silicon carbide (SiC) metal-oxide-semiconductor field effect transistors (RDT-MOSFETs) featuring the deep source trench is investigated. A previously unreported failure mechanism is identified, which leads to the short circuit between the drain and source terminals. After microcosmic failure analysis, a 10 μm-long crack connecting the poly Si in source trench and the SiC in drift region is found. The device-level electro-thermal-mechanical analysis is employed to explain the formation of the crack. The results indicate that a novel mechanical stress concentration is introduced by the deep source trench and primarily focuses at its corner. Once the crack forms, expansion occurs easily due to the inherently low fracture toughness of SiC. This failure mechanism highlights the necessity for device designers to carefully consider reliability risk related to mechanical stress.