Thermal oxidation polishing of pressureless sintered silicon carbide

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Pressureless sintered silicon carbide (PS–SiC) is a promising material for mirrors used in short-wavelength optical systems. However, due to its intrinsic hardness and multiphase nature, achieving atomic and close-to-atomic scale (ACS) polishing to meet the stringent requirements of the optical systems is challenging. In this study, a thermal oxidation polishing method is employed to achieve ACS polishing of PS-SiC. This method converts the hard heterogeneous SiC phase and Si phase into the “softer” homogeneous SiO2 via thermal oxidation, followed by polishing using silica sol, resulting in a finished surface roughness of 0.55 nm in Ra within 15 min. Molecular dynamics simulations are also conducted to study the thermal oxidation process of PS-SiC. The results show that SiC and Si phases oxidize at different rates, leading to roughness deterioration after thermal oxidation. This also causes unevenness in the SiC and Si phases beneath the oxidized layer. Therefore, it is necessary to control the polishing time to avoid over-polishing and potential exposure of the underlying uneven SiC and Si phases.