Effects of Hydroxyethyl Cellulose and Colloidal Silica Abrasive on the Hydrophilicity of Polished Si Wafer Surfaces

Abstract

Final polishing processes are important to produce a clean surface in Si semiconductor wafers. Final polishing is carried out using a slurry that typically comprises colloidal silica, alkaline and a water-soluble polymer. Hydroxyethyl cellulose (HEC) has been widely used as a water-soluble polymer to impart hydrophilic properties to the polished wafer surface in order to reduce defects. In this study, we examined the effects of HEC concentration on the hydrophilicity of the polished wafer surface. We show correlations between the free HEC concentration in slurry liquid phase, friction during polishing, and hydrophilicity of the polished wafer surface. Furthermore, we show that the residual silica abrasive on the wafer enhances its hydrophilicity. These results show that HEC in the slurry not only acts as a hydrophilizing agent but also as an adsorptive medium between the wafer and silica. Silica has a highly hydrophilic surface owing to the presence of Si-O− groups on its surface. Therefore, a highly hydrophilic surface of polished wafer is achieved by adsorptive HEC as well as silica adsorbed on the wafer, bound by HEC. This mechanism is useful to develop new final polishing slurries to produce ultra-clean Si wafers.