Analysis of Photoelectrochemical Processes in α-SiC Substrates with Atomically Flat Surfaces

The etching of alpha(4H,6H)-SiC{0001} substrates by a photoelectrochemical method using HF (0.015-4.5wt%) and HF + HNO3 (0.006 -1.2 wt %) electrolytes was studied. The dependences of etching rate oil polytype, polarity, and pH were measured. In the case of the HF electrolyte, an etching rate of 15-27nm/min was achieved over a pH range from 0.5 to 4.5 under a photocurrent density of 1 mA/cm(2). By optimizing etching conditions, the surface roughness of the Si face could be improved to 0.9 nm (4H) and 0.4 nm (6H) compared with the initial surface roughnesses of 4H (8.9 nm) and 6H-SiC (6.5 nm). In the case of the HF + HNO3 electrolyte, a thin oxide film 2-3 mu m thick was formed after 60 min. The oxidized layer was two orders of magnitude thicker than that obtained using the thermal method. The pH of the electrolyte decreased after the electrochemical process, indicating an increase in the concentration of H+ ions. Therefore, holes and H2O have a strong influence on the rate of oxidation reactions in electrochemical methods. Electrochemical etching proceeds by the competitive processes of formation and removal of oxide films.