Analysis of Parameters Affecting the Surface Roughness in Sapphire Wafer Polishing Using Nanocrystalline–Microcrystalline Multilayer Diamond CVD Pellets

To reduce the processing cost and to polish high hardness substrates, a change from the currently used slurry process to the process using fixed abrasive grain is required. Therefore, studying the fixed abrasive tool to improve yield and process stability is important. In this study, a chemical vapor deposition (CVD) diamond pellet with an artificially controlled contact area was applied to replace the slurry polishing process. The CVD diamond pellets were prepared by depositing a microcrystalline diamond on silicon nitride ceramic substrates using a hot filament CVD technique and preparing a multi-layered pellet in which a nanocrystalline diamond (NCD) was deposited. The influences of the real contact area of CVD diamond on the surface roughness and material removal rate were studied using scanning electron microscopy, a stylus profilometer, atomic force microscopy, and Raman spectroscopy before and after polishing. In addition, the polishing effect of the sapphire wafer was analyzed and predicted by modeling the roughness and the real contact area of the diamond CVD pellet. To analyze the polishing characteristics according to changes in the area, the surface roughness of the NCD was varied from 65 to 115 nm, and the polishing was evaluated. The results showed that compared with the process using diamond slurry, the multilayer diamond pellet had a higher material removal rate and the same surface roughness and total thickness variation.