XPS Investigation of the Oxidation State of Different Ceria Powders for CMP Slurry

Ceria nanoparticles are used in chemical mechanical planarization (CMP) slurry for their selective removal of oxides over nitrides. This removal depends on the ratio of Ce
³⁺
/Ce
⁴⁺
ions on the surface of the particles. As this ratio increases, so does the interaction with the oxide surface, resulting in an increased removal rate.Most studies to date focus on how synthesis [1,2] and particle size [3–5] affect these ratios but ignore the changes that could arise when using the particles in an aqueous slurry environment.In this study, X-ray photoelectron spectroscopy (XPS) was used to measure the surface Ce
³⁺
concentration as a function of pH and oxidizing agent concentration [Figures 1&2] in the slurry. The effects of these properties were examined using three different sources for the ceria nanoparticles [Table 1].