Origin of Etch Hillocks Formed on On-Axis SiC(0001) Surfaces by Molten KOH Etching

Molten KOH etching of 6H- and 4H-SiC0001 on-axis substrates was investigated. After molten KOH etching, etch pits originating from threading dislocations (TDs) and basal-plane dislocations (BPDs) were observed on (0001) surfaces. On the other hand, large and small hillocks were observed on (0001) surfaces. The etch hillocks consist of SiC, indicating slower etching at TDs. By comparing the (0001) side and (0001) side of the same substrate, it was found that large hillocks correspond to edge-type TDs, while small hillocks correspond to screw-type TDs.