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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.

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In recent years, reaction-sintered silicon carbide (RS-SiC) has been of interest in many engineering fields because of its excellent properties, such as its light weight, high rigidity, high heat conductance and low coefficient of thermal expansion. However, RS-SiC is difficult to machine owing to its high hardness and chemical inertness and because it contains multiple components. To overcome the problem of the poor machinability of RS-SiC in conventional machining, the application of atmospheric-pressure plasma chemical vaporization machining (AP-PCVM) to RS-SiC was proposed. As a highly efficient and damage-free figuring technique, AP-PCVM has been widely applied for the figuring of single-component materials, such as Si, SiC, quartz crystal wafers, and so forth. However, it has not been applied to RS-SiC since it is composed of multiple components. In this study, we investigated the AP-PCVM etching characteristics for RS-SiC by optimizing the gas composition. It was found that the different etching rates of the different components led to a large surface roughness. A smooth surface was obtained by applying the optimum gas composition, for which the etching rate of the Si component was equal to that of the SiC component.

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