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

Abstract

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.

Practical applications of SiC-MOSFETs and further developments

“…The wet oxidation is performed at a relative low temperature from 800 °C to 900 °C. The low temperature wet oxidation induces deep level states at the MOS interface which was investigated by DLTS measurement [13]. The deep states at around 0.68 eV contribute to the elevation of the threshold voltage and do not lower channel mobility.…”

Accuracy of the Energy Distribution of the Interface States at the SiO₂/SiC Interface by Conductance Method

“…Accurate analysis of the D it at the SiO 2 /SiC interface is essential for correctly evaluating the oxide quality, which is related to the electrical characteristics of SiC MOSFETs. Several techniques [1][2][3][4] have been applied to evaluate the interface states at the SiO 2 /SiC interface experimentally by using MOS capacitor. Conductance method at lower temperature is used for quantitatively evaluating the energy distribution of the D it at MOS interface closer to the conduction band edge [5][6][7][8].…”