Selective electrochemical mechanical polishing of 4H–SiC surface employing porous material impregnated with electrolyte

Slurryless electrochemical mechanical polishing (ECMP) is a high-efficiency and high-precision method that can be applied to SiC wafers. However, this method has not been used on curved surfaces because it is difficult to realize selective ECMP due to electrolyte liquidity. In this study, a novel selective ECMP method using porous material impregnated with electrolyte was proposed, and its feasibility was verified using porous quartz glass. In addition, the effects of porous material pore size, applied voltage, current density, and oxidation time on the selective anodic oxidation performance were investigated and clarified. A porous material with a larger pore size exhibited a higher anodic oxidation rate, but the oxidation area was more difficult to control. A large electrical field and the hydrophilicity of the oxide layer facilitated electrolyte exudation from the porous material. Moreover, selective ECMP was conducted on the 4H–SiC (0001) surface, porous quartz glass showed poor polishing performance and could not remove the oxidized layer. Selective ECMP using a ceria grinding wheel obtained a material removal rate of 4.5 μm/h and significantly decreased the surface roughness from 79.219 to 2.166 nm Sq in 20 min, showing great application potential. This study provided a novel polishing method for difficult-to-machine curved surfaces.