Charged micelle halo mechanism for agglomeration reduction in metal oxide particle based polishing slurries

Abstract

A method for chemically stabilizing metal oxide polishing slurries to prevent their agglomeration while maintaining their surface activity is demonstrated experimentally. Negatively charged ceria, zirconia, and alumina particles are reversibly size-stabilized under low ionic strength conditions at and above their isoelectric points using anionic surfactants.Stability is imparted only at surfactant concentrations above the critical micelle concentration and when the particle and the micelle have like-signed charges. Zeta potential measurements demonstrate that little adsorption of anionic surfactant occurs under conditions where the particles are negatively charged. Changes to pH, hydrophobicity, and ionic strength disrupt the surfactant's ability to size-stabilize the slurries. These results suggest that the charged micelles electrosterically hinder the agglomeration of oxide particles.Because the stabilization method does not rely on adsorption, the particle surface remains accessible for chemical reactions, such as those involved in polishing. Metal oxide slurries stabilized by this method remove material at a rate comparable to that of unstabilized slurry. In addition, stabilized slurry is easier to filter, which improves the quality of the polished surface. Stabilizing colloids by this method may prove valuable for systems where particle surface functionality is important, such as those used in ceramics processing, optical polishing, and chemical-mechanical planarization.