Colloids and surfaces in chemical-mechanical polishing: An adsorptive model for abrasive particle/oxide substrate interactions

Using silica (glass) as a model material, an approach is presented whereby chemical-mechanical polishing (CMP) of oxide substrates may be visualized as an adsorptive removal process. The adsorption of substrate-derived species is quantified by treating it as a surface complexation reaction. Mass action equations are derived for the relevant surface reactions (complex formation, and protonation/deprotonation of surface hydroxyls). 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.