Nitric acid oxidation method to form SiO2/3C-SiC structure at 120 °C

3C-SiC(0 0 1) surfaces are considerably rough with the roughness root mean square value (R_ms) of 1.3 nm, but the surfaces become considerably smooth (i.e., R_ms of 0.5 nm) by heat treatment in pure hydrogen at 400 °C. Two-step nitric acid (HNO₃) oxidation (i.e., immersion in ∼40 wt% HNO₃ followed by that in 68 wt% HNO₃) performed after the hydrogen treatment can oxidize 3C-SiC at extremely low temperature of ∼120 °C, forming thick SiO₂ (e.g., 21 nm) layers. With no hydrogen treatment, the leakage current density of the 〈Al/SiO₂/3C-SiC〉 metal-oxide-semiconductor (MOS) diodes is high, while that for the MOS diodes with the hydrogen treatment is considerably low (e.g., ∼10⁻⁶ A/cm² at the forward gate bias of 1 V) due to the formation of uniform thickness SiO₂ layers. The MOS diodes with the hydrogen treatment show capacitance-voltage curves with accumulation, depletion, and deep-depletion characteristics.