The correlation between atomic structure and the electrical properties of thermally grown SiO2/4H-SiC(0001) interfaces was investigated by synchrotron x-ray photoelectron spectroscopy together with electrical measurements of SiC-MOS capacitors. We found that the oxide interface was dominated by Si-O bonds and that there existed no distinct C-rich layer beneath the SiC substrate despite literature. In contrast, intermediate oxide states in Si core-level spectra attributable to atomic scale roughness and imperfection just at the oxide interface increased as thermal oxidation progressed. Electrical characterization of corresponding SiC-MOS capacitors also indicated an accumulation of both negative fixed charges and interface defects, which correlates well with the structural change in the oxide interface and provides insight into the electrical degradation of thermally grown SiC-MOS devices.

An alternative and effective method to perform interface nitridation for 4H-SiC metal-oxide-semiconductor (MOS) devices was developed. We found that the high-temperature post-oxidation annealing (POA) in N2 ambient was beneficial to incorporate a sufficient amount of nitrogen atoms directly into thermal SiO2/SiC interfaces. Although N2-POA was ineffective for samples with thick thermal oxide layers, interface nitridation using N2-POA was achieved under certain conditions, i.e., thin SiO2 layers (< 15 nm) and high annealing temperatures (>1350°C). Electrical characterizations of SiC-MOS capacitors treated with high-temperature N2-POA revealed the same evidence of slow trap passivation and fast trap generation that occurred in NO-treated devices fabricated with the optimized nitridation conditions.

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Unusual behavior of bias-temperature instabilities in SiC metal-oxide-semiconductor (MOS) devices is studied. Electrical measurements of SiC-MOS capacitors are used to investigate details of self-generated mobile ions in thermal oxides on 4H-SiC(0001) substrates, such as their polarity, density, distribution, and impact on interface properties. It is found that positive bias-temperature stress (BTS) accumulates self-generated positive mobile ions at the bottom SiO2/SiC interface with an areal density of several 1012 cm−2, and that they induce additional electron trap formation at the interface. Using this knowledge, we demonstrate effective removal of the positive mobile ions with a combination of negative BTS and subsequent etching of the oxide surface.

Significant improvement of bias-temperature instability characteristics in SiC-based metal-oxide-semiconductor (MOS) devices was demonstrated with high-permittivity aluminum oxynitride (AlON) dielectrics deposited on thin thermal oxides. AlON/SiO2 stacked dielectrics were found to be beneficial not only for reducing gate leakage current but also for suppressing diffusion of positively charged ions, leading to stable SiC-MOS characteristics even under strong electric fields and high temperatures. Unlike the prompt electric-field-induced ion migration in thermally grown and sputter-deposited SiO2 dielectrics, the ion drift for the stacked gate dielectrics was confined within the thin SiO2 underlayers owing to low ion diffusivity in AlON layers. Impacts of mobile ions on interface properties of SiC-MOS devices and effects of intentional ion trapping within the AlON layers were also systematically investigated.