An effort in planarising microwave plasma CVD grown polycrystalline diamond (PCD) coated 4in. Si wafers

Large area CVD grown diamond coatings should have very smooth surface in many of its applications, like microwave power transmission windows etc. Combination of mechanical and chemical forces during polishing helps to achieve desired surface roughness of the polycrystalline diamond (PCD) coatings. Authors report the variation of pressure, slurry feeding rate, addition of chemicals and the time of polishing to observe the efficiency of chemo-mechanical polishing (CMP) technique in planarising CVD diamond material grown over 100 mm diameter silicon wafers. PCD were found to be polished by bringing down the as-grown surface roughness from 1.62 µm to 46 nm at some points on large areas. One coherence scanning interferometer was used to check the roughness at different stages of CMP. Raman spectroscopy was used to evaluate the polished PCD samples in terms of their quality, internal stress at different positions on the same wafer surface after CMP process. It was found that the well polished regions were of better quality than the less polished regions on the same wafer surface. But due to coating non-uniformity of the deposited PCD grown by microwave plasma CVD over large area, CMP could not produce uniform surface roughness over the entire 100 mm diameter wafer surface. We concluded that CMP could effectively but differentially polish large area PCD surfaces, and further process improvements were needed.