Time-Dependent Dielectric Breakdown of 4H-SiC MOS Capacitors and DMOSFETs

Time-dependent dielectric breakdown measurements were performed at 200 degC on 4H-SiC MOS capacitors and vertical DMOSFETs with 50-nm-thick nitrided oxides in order to better understand the physical mechanisms of failure and to predict the component reliability. Oxide breakdown locations are shown to have no correlation to defects in the SiC epitaxial layer. Characterization of the electric-field acceleration of failures indicates that failure modes differ at low and high electric fields. Specifically, extrapolations from measurements at electric fields greater than 8.5 MV/cm predict anomalously high reliability at normal operating fields. Thus, we have shown that SiC MOS reliability characterization must ensure that electric field stresses be performed at low electric fields in order to accurately predict failure times.