The Effect of Doping Concentration and Conductivity Type on Preferential Etching of 4H-SiC by Molten KOH

Molten KOH etchings were implemented to delineate structural defects in the n- and ptype 4H-SiC samples with different doping concentrations. It was observed that the etch preference is significantly influenced by both the doping concentrations and the conductivity types. The p-type Si-face 4H-SiC substrate has the most preferential etching property, while it is least for n + samples. It has been clearly demonstrated that the molten KOH etching process involves both chemical and electrochemical processes, during which isotropic etching and preferential etching are competitive. The n + 4H-SiC substrate was overcompensated via thermal diffusion of boron to p-type and followed by molten KOH etching. Three kinds of etch pits corresponding to threading screw, threading edge, and basal plane dislocations are distinguishably revealed. The same approach was also successfully employed in delineating structural defects in ( 0001̅) C-face SiC wafers.