Model Friction Studies of Chemical Mechanical Planarization using a Pin-on-Disk Tribometer

Chemical mechanical planarization (CMP) uses polyurethane polishing pads and highly engineered slurries to planarize, or polish, silicon wafers for semiconductor manufacturing. Friction is present as a critical aspect of this complex process, and is a function of pH, isoelectric point of the slurry particles, particle concentration, pad design, and other variables. Despite the connection of friction with CMP outcomes, detailed studies of friction and polishing are lacking due to the expense and difficulty of modifying commercial equipment to make precise tribology measurements. A pin-on-disk tribology attachment for the Anton-Paar MCR-502 rheometer can simulate a commercial polisher, to condition the pad in-situ and then polish the Si wafer. We measure both friction and the z-displacement, or change in gap, at realistic downpressures (1-5 psi) and sliding velocities (up to 1 m/s), which allows careful study of lubrication mechanisms, pad wear and slurry performance. The friction and z-displacement results for water at different pH’s are consistent with some mechanistic models used to represent surface and colloidal forces in these systems.