Analysis of effect of gate oxidation at SiC MOS interface on threshold-voltage shift using deep-level transient spectroscopy

In this study, we investigate the influence of wet oxidation after nitridation of a gate oxide on the interface states in SiC metal–oxide–semiconductor field-effect transistors (MOSFETs). We used deep-level transient spectroscopy (DLTS) to clarify the mechanism behind the positive shift in the threshold voltage after wet oxidation without any significant decrease in the mobility. We applied DLTS using a small pulse to obtain the depth profile of the states. We found that the density of deep-level states near the interface on the SiC side increased after wet oxidation at 600 and 800 °C, whereas the density of shallow states did not increase. This result indicates that the increase in the deep-level states is related to the threshold-voltage shift, and there is no degradation in the mobility.