Re-Oxidation-Induced Asymmetric Reliability in Annealed SiC MOS Devices

This study systematically investigates the impact of re-oxidation during post-oxidation annealing (POA) on 4H-SiC MOS device stability through breakdown and bias temperature instability (BTI) tests, comparing high-temperature N₂O annealing and low-temperature O₂ annealing. Both annealing methods reduce leakage current and improve dielectric breakdown strength, demonstrating that re-oxidation effectively suppresses electron traps at the SiO₂/SiC interface and increases the conduction band offset. Positive bias temperature instability (PBTI) results confirm improved positive bias temperature stability. However, negative bias temperature instability (NBTI) reveals degraded stability under negative bias, attributed to oxygen vacancy formation during unfavorable re-oxidation conditions, which introduces detrimental hole traps. These findings demonstrate that re-oxidation-based annealing adversely affects long-term high-temperature reliability, providing critical guidance for annealing process selection in SiC power devices.