Effect of retaining ring slot designs and polishing conditions on slurry flow dynamics at bow wave

The effect of retaining ring slot design and polishing conditions on slurry flow dynamics at the bow wave was investigated. An ultraviolet enhanced fluorescence technique was employed to measure the slurry film thickness at the bow wave for two polyetheretherketone (PEEK) retaining rings with different slot designs. Multiple sliding velocities, slurry flow rates and ring pressures were investigated. Results showed that the retaining ring with the sharp angle slot design (PEEK-1) generated significantly thicker slurry films at the bow wave than PEEK-2 which had a rounded angle slot design. For PEEK-1, film thickness at the bow wave increased with increasing flow rate and ring pressure and decreased with increasing sliding velocity. On the other hand, film thickness at bow wave did not change significantly for the PEEK-2 ring at different polishing conditions indicating an apparent robustness of the PEEK-2 design to various operating conditions. With retaining rings having different designs, and all else being the same, a thinner bow wave was preferred since it was indicative of a ring design that allowed more slurry to flow into the pad-wafer interface. Therefore, the work underscored the importance of optimizing retaining ring slot design and polishing conditions for efficient slurry utilization.