Tribological, thermal and kinetic attributes of copper and silicon dioxide CMP processes

Experimental and numerical analyses of the tribological, thermal and kinetic attributes of silicon dioxide and copper CMP processes are presented in this study. Real-time friction forces are measured to determine the lubrication mechanism during copper polishing. Pad temperatures are simultaneously measured by an infrared camera and are shown to correlate with the copper removal rates. Different platen temperatures are applied during silicon dioxide polishing, ranging from 10 to 45°C. Silicon dioxide removal rates are found to increase with the platen temperature and exhibit highly non-Prestonian behavior. Lim-Ashby plots, which show the separate effects of polishing pressure and wafer-pad sliding velocity, are used to describe the non-Prestonian copper and silicon dioxide removal rates. Assuming the chemical reaction temperature is determined by transient flash heating, a two-step modified LangmuirHinshelwood model is found to describe the copper and silicon dioxide removal rates well for the slurries used in this study. Extracted chemical and mechanical rate constants indicate that silicon dioxide removal can span a range of regimes from mechanically-limited to nearly equal balance between mechanical and chemical mechanisms; while for copper CMP, extracted mechanical rate constants exceed the chemical rate constants, suggesting that copper polishing is more chemically controlled.