In SiC MOSFETs, low channel mobility caused by defects at the SiO₂/SiC interface remains a critical issue. While post-oxidation annealing in NO is commonly used to improve interface properties,[1] concerns remain regarding reliability degradation associated with the progression of nitridation.[2] Furthermore, it has been reported that surface conditioning of SiC, including the removal of native oxide residues, plays a crucial role in determining the resulting MOS interface quality.[3,4] Therefore, in this study, as an oxidation-free approach, we propose a fabrication process for SiC MIS structures based on direct deposition of an SiN film using N₂-based PECVD, and subsequent CO₂ annealing.

Samples were prepared by depositing 20-nm-thick SiN films onto a 4H-SiC(0001) substrate, with optional CF₄ plasma pre-treatment. For comparison, a control sample with a deposited SiO₂ film was also prepared, and all samples were subjected to CO₂ annealing at 1100ºC for 30 min. Electrical characterization revealed that the SiN-deposited samples processed via CO₂ annealing exhibited steeper capacitance-voltage (C-V) characteristics (Fig. 1) and significantly lower interface state densities (Dit) compared to the SiO₂-deposited controls, with CF₄ plasma pre-treatment providing further improvement (Fig. 2), confirming the successful formation of a high-quality SiON/SiC interface.

1. G. Y. Chung et al., IEEE Electron Dev. Lett. 22, 176 (2001), DOI: 10.1109/55.915604
2. J. Rozen et al., J. Appl. Phys. 105, 124506 (2009), DOI: 10.1063/1.3131845
3. K. Tachiki et al., Appl. Phys. Express 14, 031001 (2021), DOI: 10.35848/1882-0786/abdcd9
4. T. Kobayashi et al., Appl. Phys. Express 18, 081002 (2025), DOI: 10.35848/1882-0786/adf6ff