Mechanism of the interaction between Al2O3 and SiO2 during the chemical-mechanical polishing of sapphire with silicon dioxide

Chemical-mechanical polishing of sapphire with colloidal silicon dioxide has been studied with X-ray photoelectron spectroscopy. It has been found that aluminum silicate with the composition Al₂SiO₅ is formed on the polished crystal surface. The silicon-containing layer thickness reaches 20.5 nm. Its value decreases in the sequence of samples with (0001), ((10[`1]bar 12), and (11[`2]bar 20) and orientations. A mechanism by which Al₂O₃ reacts with SiO₂ has been proposed. It has been revealed that sapphire samples with different crystallographic orientations exhibit an anisotropic rate of material removal. The anisotropy can be explained by a difference in the rate of the formation of intermediate products during chemical interaction between aluminum and silicon oxides on different planes.