Surface Modification and Microstructuring of 4H-SiC(0001) by Anodic Oxidation with Sodium Chloride Aqueous Solution.

Anodic oxidation is a promising surface modification technique for the manufacture of SiC wafers owing to its high oxidation rate. It is also possible to fabricate porous SiC by anodic oxidation and etching owing to the material properties of SiC. In this study, the anodic oxidation of a 4H-SiC(0001) surface was investigated by performing repeated anodic oxidation and hydrofluoric acid etching on a 4H-SiC(0001) surface, during which the formation of porous SiC was observed and studied. Anodic oxidation is very effective for removing the surface damage formed by mechanical polishing, and the surface after removing the surface damage can be oxidized uniformly and has a higher oxidation rate than a surface newly finished by chemical mechanical polishing (CMP). We proposed a model based on the electrochemical impedance method to explain the difference in the oxidation between an as-CMP-finished surface and an oxidized/etched surface. Porous SiC was obtained in this study, which was due to the anisotropy of the SiC crystal. The structure of the porous SiC was significantly dependent on the etch pits generated at the beginning of anodic oxidation and can be controlled via anodic oxidation parameters. Anodic oxidation and hydrofluoric acid etching cannot remove porous SiC owing to the anisotropic oxidation of the SiC surface and the difficulty of anodizing SiC fibers. This study shows that anodic oxidation is a promising technique for the modification of SiC surfaces and the fabrication of porous SiC.