Two-Step Chemical Mechanical Polishing of Sapphire Substrate

Chemical mechanical polishing (CMP), as a widely used planarization technology, requires high removal rate and low surface roughness generally. However, it is difficult to meet these requirements in a single-step polishing process. To get an ultrasmooth surface of the sapphire substrate, we investigated a two-step CMP of the sapphire substrate using ultrafine α-alumina-based slurry and nanoscale silica-based slurry. Also, in situ coefficient of friction (COF) measurements were conducted. The results show that during the first-step polishing in the alumina-based slurry, the COF decreases with polishing time first and then tends to be a constant; a relatively high material removal rate was reached, and the root-mean-square (rms) roughness value of the polished surface can be decreased from 968.9–21.98 Å. In the second-step CMP, the nanoscale silica slurry was adopted; the COF increased in the first minute of polishing and then became stable too, and the rms roughness of the sapphire substrate surfaces can be further reduced to 6.83 Å by using the optimized process parameters. In addition, the CMP mechanism of sapphire using the above two slurries was deduced and documented preliminarily.