Role of oxygen in surface kinetics of SiO2 growth on single crystal SiC at elevated temperatures

Understanding surface kinetics of SiO₂ growth on single crystal SiC at elevated temperatures is crucial to fabricate high-performance SiC-based devices. However, the role of oxygen in the evolution mechanism of SiC surface at atomic scale has not been comprehensively elaborated. Here, we reveal the manipulation effect of oxygen on the competitive growth of thermal oxidation SiO₂ (TO-SiO₂) and thermal chemical vapor deposition SiO₂ (TCVD-SiO₂) on the 4H-SiC substrate at 1500 °C. TO-SiO₂ is formed by the thermal oxidation of SiC, in which the substrate undergoes layer-by-layer oxidation, resulting in an atomically flat SiC/TO-SiO₂ interface. TCVD-SiO₂ growth includes the sublimation of Si atoms, the reaction between sublimated Si atoms and reactive oxygen, and the adsorption of gaseous Si_xO_y species. A relatively high sublimation rate of Si atoms at SiC atomic steps causes the transverse evolution of the nucleation sites, leading to the formation of nonuniform micron-sized pits at the SiC/TCVD-SiO₂ interface. The low oxygen concentration favors TCVD-SiO₂ growth, whose crystal quality is much better than that of TO-SiO₂ due to the high surface mobility in the thermal CVD process. We further achieve the epitaxial growth of graphene on 4H-SiC in an almost oxygen-free reaction atmosphere. Additionally, ReaxFF reactive molecular dynamic simulation results illustrate that the decrease in oxygen concentration can promote the growth kinetics of SiO₂ on single crystal SiC from being dominated by thermal oxidation to being dominated by thermal CVD.