Communication-Tribology of retaining rings in chemical mechanical planarization

Stribeck and Stribeck+ curves helped determine the tribological mechanisms in the ring-slurry-pad interface. Both methods gave consistent results with the lubrication mechanism starting at “boundary lubrication” and transitioning to “mixed lubrication” as pseudo-Sommerfeld numbers increased. COF for PPS rings were higher than PEEK. They were also higher for inter-level dielectric (ILD) processes as compared to copper. Stribeck curves were used to infer wear rate information about the ring, which in conjunction with Stribeck+ curves could help choose process parameters that balanced wafer removal with ring wear. Data cluster shapes were shown to be due to shear and normal force fluctuations.