Bulk crystals of n-type 6H-material were etched electrochemically, using an aqueous KOH solution as an electrolyte. After etching, using a 50wt%KOH solution at room temperature, the samples exhibited pits which were always pairs of a crescent- or circle- shaped pit plus a triangle-shaped pit. The paired pits were aligned in a radial direction from the wafer center, and the triangle pits were on the wafer perimeter; with their bases facing the perimeter. By comparing optical microscopic observations and molten-KOH etching data, it was concluded that the causes of the electrochemically formed etch pits were not only micro-pipes but also some other type of defect; probably screw dislocations.

Etch Pit Observation for 6H-SiC by Electrochemical Etching Using an Aqueous KOH Solution. M.Kato, M.Ichimura, E.Arai, P.Ramasamy: Journal of the Electrochemical Society, 2003, 150[4], C208-11