Mechanism of molten KOH etching of SiC single crystals: Comparative study with thermal oxidation

The etching mechanism of SiC single crystals by molten KOH has been investigated. The etching process is significantly affected by the etching ambience: the etching rate is greatly reduced by a nitrogen gas purge. This result clearly suggests an essential role of dissolved oxygen in the melt. SiC{0001} surfaces show a large surface polarity dependence, where the etching rate of SiC(000 (1) over bar)C is about four times larger than that of SiC(0001)Si. The etching rate of SiC(000 (1) over bar)C exhibits an Arrhenius type temperature dependence with an activation energy of 15-20 kcal/mol. The obtained activation energy and selectivity between the (000 (1) over bar)C and the (0001)Si surfaces are quite similar to those for thermal oxidation, which implies that the surface oxidation process occurs during molten KOH etching of SiC and is the rate-limiting step for the etching. We have conducted a comparative study of molten KOH etching with thermal oxidation in regard to the crystal orientation, polytype and carrier concentration dependence.