Cobalt “buff step” chemical mechanical planarization

In this study, silicon dioxide wafers were polished as part of a cobalt “buff step” CMP using a novel and state-of-the-art application-specific slurry and pad combination to study the thermal, tribological, and kinetic attributes of the process. Removal rate and mean pad temperature showed increases with higher polishing pressures and sliding velocities, while coefficient of friction stayed relatively constant across all investigated conditions. Under all conditions, the process was tribologically robust as it remained in “boundary lubrication”. As the removal rate exhibited a non-Prestonian behavior, a well-established Langmuir-Hinshelwood model was used to simulate, for the first time for this process and this set of consumables, removal rate data such that chemical and mechanical rate constants could be extracted and understood in light of the process parameters chosen. Results indicated that the process was mechanically limited at nearly all combinations of pressure and velocity except at the highest values investigated, indicating that small deviations from set polishing power can greatly affect material removal rate.