Mirror-grinding of single-crystal diamond substrates with a rotary grinder

Single-crystal diamond substrates are required for realizing diamond semiconductor devices. These substrates require ultrasmooth (atomic-order) surface finishes. Previously reported methods for polishing single-crystal diamonds are based on pressure-control processes; these are capable of improving the quality of the surface, but are inefficient. To obtain high-precision surface smoothness with greater process efficiency, we have developed a method for diamond polishing that is based on a depth-control principle and employs an ordinary rotary grinder in which both the substrate and the grinding wheel are rotated simultaneously during the grinding. The resulting ground surface showed tiny crosshatch scratches. By progressively applying finer grinding wheels from #600 to #15000, the surface could be gradually improved, and finally a surface with a near-atomic-order surface roughness was obtained with the finest wheel (#15000); the average surface roughness was 0.13 nm for 5 × 5 μm2 area. The removal rate with the #15000 wheel was 0.04 μm/min, which was markedly higher than that achievable by other methods capable of producing an atomic-order surface roughness on single-crystal diamond. The depth of subsurface damage induced by the grinding process was reduced by using finer grinding wheels. However, a certain depth of damage appeared to remain on and near the surface, even for surfaces ground to near-atomic levels of roughness.