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Thermal etching of hexagonal (4H-, 6H-, 8H- and 10H-), rhombohedral (15R- and 21R-), and cubic (3C-) SiC Si-faces was performed between 900 and 1000oC in a mixed gas of chlorine (Cl2) and oxygen (O2). In the case of well oriented Si-faces, the 3C-SiC (111) substrate was etched fastest in polytypes. The etching rate in the dislocation-free area depended on the hexagonality. Etch pits with definite shapes appeared, which depend on the type of dislocation and crystal structures. On the basis of these results, etching properties are discussed.

. 　 Crystallographically specific pyramidal planes in 4H-SiC could be naturally formed at mesa sidewalls by a thermal etching at 900oC in a chlorine (Cl2) based ambience. The mesa structures have been fabricated on the 4H-SiC C-face with 0-45o off-angle toward [11-20]. The etched surface was rather smooth, and bunched step structures on the specific pyramidal planes were not observed with atomic force and scanning electron microscopes. The formation mechanisms of the specific pyramidal planes at mesa sidewalls are discussed on the basis of these experimental results.

The shape control inside a trenched 4H-SiC by atmospheric-pressure chlorine (Cl2) etching has been investigated. The trench fabricated by a plasma process on the 4H-SiC(0001̄) C-face with 4°-off toward [112̄0] was used. The inside of the 4H-SiC trench was thermally etched in Cl2 ambience at 900 °C. The subtrenches intentionally formed by the plasma process were successfully eliminated along with thermal Cl2 etching. With further Cl2 etching, the 4°-off (0001̄) C-face at the trench bottom disappeared and the V-shaped bottom with a specific angle for the (0001̄) basal plane was formed. The mechanism underlying the change inside the trench shape is discussed in comparison with the off-angle dependence of Cl2 etching rate.