Impact Analysis of Off-State Avalanche-Breakdown Stress on 650 V-Class Superjunction MOSFET

In this work, the reliability degradation of a 650 V-class superjunction (SJ) MOSFET under continuous violent OFF-state avalanche-breakdown stress is studied. Decreased threshold voltage and increasing saturation current have been observed which are attributed to the injection of hot holes below the trench bottom into the gate oxide layer. High-energy electrons and holes are generated under OFF-state avalanche stress leading to accelerated and violent collision ionization. The body diode suffers from severe avalanche breakdown leading to heat generation by collision ionization. In addition, the injection of hot holes is further enhanced with the assistance of the electrical field at the bottom of the gate. These phenomena are further analyzed by experimental characterizations and theoretical simulation using TCAD tools. Our comprehensive study on the reliability degradation behaviors of SJ devices under OFF-state avalanche-breakdown stress can be instructive in future device optimization and failure analysis.