Polishing of Sapphire with Colloidal Silica

The polishing of sapphire with colloidal silica has been studied. Stock removal rates have been found to vary with the solids content in the polishing fluid and the temperature on the polishing pad. The p H of the polishing fluid has also been found to be a factor influencing removal rate. Because concentrated silica solutions are unstable at high temperatures, a compromise between temperature and concentration must be made. Still, practical removal rates over 25 μ/hr have been achieved. Work damage, an important factor in polishing operations, has been found to extend about 1.0–1.5 mils into the surface of commercially available sawn or ground sapphire blanks. When all embedded diamond from the slicing and grinding operations is removed prior to polishing, a scratch‐free, featureless surface is produced on which high quality, epitaxial silicon films can be deposited. C‐MOS devices built into the films without the use of any specific processing technique to minimize the effect of the interface showed n‐channel leakage of with negligible wafer‐to‐wafer variations (1). The polishing of sapphire by colloidal silica is believed to follow a chemical reaction leading to aluminum silicate dihydrate as described in previous literature. For the reaction an activation energy of 14.6 kcal/mole has been calculated from the temperature dependency of the removal rate.