Planarization mechanism for 6H–SiC (0001) Si-faced surfaces using electrochemical reactions

We have developed a fast planarization method of 6H–SiC (0001) Si-faced surfaces using electrochemical reactions. In this method, a working electrode of a rotating Pt disc electrode is physically contacted with an SiC wafer immersed in an HF solution, and a potential of 2 or 3 V with respect to the Ag/AgCl reference electrode is applied to the Pt disk electrode. After the planarization process with the applied voltage of 3 V for 1 h, relatively flat surfaces with the 0.09 nm average roughness (Ra) value are obtained, but a 1 ∼ 2 nm carbon-rich layer is present on the surfaces. A subsequent planarization process with the applied voltage of 2 V for 1 h almost completely removes the carbon-rich layer, resulting in atomically flat surfaces with the 0.05 nm Ra value. Under the condition of the applied voltage of 2 V, the concentration of OH radicals generated during water electrolysis decreases to one-half of that generated under 3 V. The oxidation rate of C atoms is proportional to the concentration of OH radicals while that of Si atoms is proportional to the square of the concentration. Under the condition of the applied voltage of 2 V, therefore, oxidation of C atoms proceeds more dominantly than that of Si atoms, resulting in absence of the carbon-rich layer.