Surface chemical processes in chemical mechanical polishing relationship between silica material removal rate and the point of zero charge of the abrasive material

Chemical mechanical polishing (CMP) of a silica substrate is visualized as a two-step process involving release of substrate-derived species into solution (dissolution), followed by adsorption of these species by abrasive particles. The adsorption is quantified by treating it as a surface complexation process. Mass action equations are provided for the complex-formation reaction as well as protonation and deprotonation of surface hydroxyls present on the abrasive particles. By combining these equations with mass balances on surface sites and dissolved species, it is shown that the surface concentration of substrate-derived species (and, therefore, the material removal rate) goes through a maximum as the point of zero charge (pzc) of the abrasive particle increases. Further, it is shown that the surface concentration of substrate-derived species (and, therefore, the material removal rate) is highest for the abrasive material whose pzc coincides with the pH of the polishing slurry.