A process for forming porous SiC from single-crystal SiC wafers has been demonstrated. Porous SiC can be fabricated by anodizing n-type 6H-SiC in HF under UV illumination. Transmission electron microscopy reveals pores of sizes 10–30 nm with interpore spacings ranging from ≊5 to 150 nm. This is the first reported direct observation of porous SiC formation.
A new photoelectrochemical etching process is described for n-type 6H-SiC, while dark electrochemistry has been used to pattern p-type material. In this two-step etching process, the SiC is first anodized to form a deep porous layer, and this layer is subsequently removed by thermal oxidation followed by an HF dip. Etch rates as high as 4000 A/min for n-SiC and 2.2 ~m/min for p-SiC have been obtained during the anodization, resulting in near mirror-like etched surfaces.
In this paper a nonthermal photoelectrochemical etching technique for [~-SiC is reported. The measured etch rates of 1-100 ~m/min in this process are much faster than other etching methods currently available for this material. UV radiation is necessary for efficient photogeneration of holes near the surface. These holes are transported in the presence of an external bias to the semiconductor/liquid interface, where dissolution occurs through the anodic oxidation of the SiC and the removal of the oxide by F-ions present in the electrolyte. The electrochemistry of B-SiC and the etching process variables are discussed.
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