This article describes the mechanical planarization machining of SiC substrates involving the Si face (0001) and C face ($000\overline{1}$ ) of N-type (doping nitrogen) 4H-SiC, N-type 6H-SiC, and V-type (doping vanadium) 6H-SiC with a sol–gel polishing pad. The polishing results indicate that the C face, which has a surface roughness of less than 2 nm, is smoother than the Si face (>10 nm), and the material removal rate of the C face is higher than that of the Si face. The removal mechanism of SiC substrates was investigated with regard to the wear debris and subsurface structure through transmission electron microscopy, and instrumented nanomechanical tests were performed to further reveal the removal mechanism by nanoindentation and nanoscratching. The analysis results demonstrate that the difference in the material removal rates of the Si face and C face depends on the material removal scale together with the mechanical properties of SiC substrates. The processing of SiC substrates is dominated by the mechanical removal of SiC material during mechanical planarization machining.

Sapphire substrates with different crystal orientations are widely used in optoelectronic applications. In this work, focused ion beam (FIB) milling of single-crystal sapphire with A-, C-, and M-orientations was performed. The material removal rate (MRR) and surface roughness (Sa) of sapphire with the three crystal orientations after FIB etching were derived. The experimental results show that: The MRR of A-plane sapphire is slightly higher than that of C-plane and M-plane sapphires; the Sa of A-plane sapphire after FIB treatment is the smallest among the three different crystal orientations. These results imply that A-plane sapphire allows easier material removal during FIB milling compared with C-plane and M-plane sapphires. Moreover, the surface quality of A-plane sapphire after FIB milling is better than that of C-plane and M-plane sapphires. The theoretical calculation results show that the removal energy of aluminum ions and oxygen ions per square nanometer on the outermost surface of A-plane sapphire is the smallest. This also implies that material is more easily removed from the surface of A-plane sapphire than the surface of C-plane and M-plane sapphires by FIB milling. In addition, it is also found that higher MRR leads to lower Sa and better surface quality of sapphire for FIB etching.

Material removal mechanisms of abrasives for SiC and sapphire in nanoscale polishing.

Reactivity between nano-sized abrasives and sapphire wafer has been studied by interfacial solid state reaction during polishing process, and the abrasive with the highest reactivity has been selected from magnesium oxide, silicon dioxide and ferric oxide. Using the Sol-Gel polishing films, sapphire wafers were polished in the form of wet and dry mechanical chemical polishing respectively. The Raman spectra and Grazing incidence X-ray diffraction records show that aluminum silicate with the composition mullite was formed on the polished wafer surface, and silicon dioxide has the highest reactivity than other oxide abrasives under the same conditions during polishing the sapphire substrates.