Application of a slurry injection system to cobalt “buff step” chemical mechanical planarization

This study investigates the effects of a novel slurry injection system on the thermal, tribological, and kinetic aspects of new middle of the line cobalt “buff step” CMP process. The mean pad temperature, coefficient of friction (COF) and removal rate were higher when applying the slurry using the novel injection system compared to the standard point application method. By using the novel slurry injection system, the overall consumption of slurry could be reduced by 25 to 33% compared to the slurry consumed by the point application method, while still achieving similar removal rates. Our well-established modified two-step Langmuir-Hinshelwood model apparently failed when it was used to simulate the removal rates using the activation energy and optimized parameters from our previous work with the same slurry. By making a small alteration (e.g. by optimizing the pre-exponential factor for the Arrhenius chemical rate constant for each different flow rate and slurry application method) to account for slurry dilution by residual rinse water and spent slurry, the model was able to successfully simulate experimental removal rates.