Effect of slurry ionic salts at dielectric silica CMP

The effects of alkaline ionic salts on silica chemical mechanical polishing (CMP) have been studied. Particle size, zeta potential, and stability via turbidity tests have been characterized. Particle size and size distributions have been found to increase with ionic strength for three types of alkaline ionic salts due to the decrease in the magnitude of the zeta potential of silica slurry due to the addition of alkaline ionic salts. Slurry stability measured by turbidity tests showed two regimes of slurry stability (i.e., stable regime and unstable regime). For the stable slurry regime, the increase in ionic strength leads to an increase in friction force and material removal rate; however, for the unstable slurry regime, the addition of ionic salts results in a decrease in the measured friction force and material removal rate. Surface root-mean-square roughness and maximum depth of surface damage (R-max) are shown to increase with particle size and size distribution. Investigation into the effect of ionic salts on the polishing mechanism reveals both a chemical and mechanical aspect to polishing silica wafers with silica slurries containing alkaline ionic salts. (C) 2004 The Electrochemical Society.