Investigation into the Effect of CMP Slurry Chemicals on Ceria Abrasive Oxidation State using XPS

The ratio of Ce3+/Ce4+ on the surface of ceria CMP slurry abrasives was maximized by altering the slurries' chemical environment. Maximizing this ratio increases the proportion of active Ce3+ sites which participate in removal reactions, leading to increased removal rates. Small amounts of peroxide and surfactant were added to three ceria slurries at varying pH values to determine how these chemicals affected the different particle surfaces. The effects of these chemicals on the oxidation ratio were determined through XPS analysis of the Ce 3d spectrum. The addition of surfactants to ceria slurry, while necessary to increase particle dispersibility, decreased the Ce3+/Ce4+ ratio and therefore limited chemical removal. Of the conditions tested, pH had no effect, surfactants decreased the ratio, and peroxide could either increase or decrease the ratio based on concentration. Understanding these interactions will help to inform the design of future ceria CMP slurries to maximize their effectiveness.