Comparison of copper disc and copper wafer polishing processes in terms of their kinetic, tribological, and thermal characteristics

Coefficients of friction, removal rate, and pad temperature analysis were used to compare chemical-mechanical polishing processes involving two substrates, copper discs and copper-deposited wafers with different grain sizes and degrees of flatness (i.e., concave or convex). The average coefficient of friction and the total mechanical energy of the processes (as measured by the spectral attributes of the raw frictional force) were higher for the copper-deposited wafers. This result is believed to be due to differences in the extent of convexity of the two types of substrates and the shapes of their bevels. Pad temperature transients as well as material removal rates were also slightly higher for the copper wafers, suggesting a thermally dependent removal mechanism. Grain sizes associated with the copper-deposited wafers used in this paper were larger compared to those of the copper discs. Grains are thought to have complex interactions with the chemical as well as mechanical attributes of the process, based on the fact that smaller grains led to greater chemical reaction rates, while they needed more mechanical force to abrade away. Based on these results, careful attention to copper grain size as well as deposited film and wafer geometry is recommended in experimental studies of copper polishing.