High efficient polishing of sliced 4H-SiC (0001) by molten KOH etching

Single-crystal silicon carbide (4H-SiC) is a promising third-generation semiconductor material because of its excellent electrical, mechanical and chemical properties. However, the high hardness of 4H-SiC makes it a typical difficult-to-machine material, which greatly restricts the development of SiC devices. In this work, molten KOH etching was first used to polish SiC. The perfect crystal surface and dislocation spots were studied separately. For the perfect crystal surface, a typical isotropic etching polishing behavior was observed. The speed of the polishing process was closely correlated with the temperature. An ultrafast polishing of sliced SiC was achieved, reducing the roughness from 246.5 nm to 16.06 nm within 2 min at 800 degrees C, and all subsurface damage was removed, as demonstrated by TEM. For the dislocation spot, a relationship between the etch pits angle and temperature was found, making it possible to remove the influence of the dislocation spot by increasing the etch pits angle to approach 180 degrees. This study shows that molten KOH etching could be a very promising SiC polishing method and deserves further research. We anticipate that this approach will be applicable to ultrafast polishing of SiC at the industrial scale.