Controlling the Cerium Oxidation State During Silicon Oxide CMP to Improve Material Removal Rate and Roughness

Abstract

Knowledge obtained on the mechanism for altering the Ce3+% on the ceria surface was used to create ceria slurries that polished thermal oxide with higher material removal rate (MRR) and lower post-polish roughness than slurries that are currently being used in industry. As described by the tooth-comb model, oxide removal occurs easiest at sites with fewer surface bonds. This allows for slurries to be prepared with particles of large size (68 nm) that have high MRR while obtaining roughness values that are equal to those of much smaller particles (5 nm). The addition of hydrogen peroxide initially increases the Ce3+% concentration on the particle surface, then decreases it. This trend is replicated by both MRR and roughness with improvements initially, until a threshold is reached, after which all of the metrics got worse. The effect of pH was more complex, as it impacts the polishing process in two ways, by governing the rate of the chemical reaction with ceria and also the rate at which silica hydrolyzes, which in turn determines the ease with which both chemical and mechanical removal occurs.