Tribological, Thermal, Kinetic, and Pad Micro-Textural Studies Using Polyphenylene Sulfide Retaining Rings in Interlayer Dielectric Chemical Mechanical Planarization

Abstract

We compared the long-term wear performance of 2 different PPS retaining ring materials (E-PPS and O-PPS) provided by 2 different suppliers. After 4 h of wear, O-PPS resulted in higher values of mean pad summit height as compared to E-PPS (26.4 ± 1 vs 23.9 ± 1 μm, respectively). We believed this was due to excessive pad fragment generation (confirmed by its associated higher level of pore obscuration) which caused the asperities to artificially appear taller. Regarding mean summit curvature, O-PPS did not sharpen the asperity tips beyond what had already been achieved through conditioning (341 ± 50 vs 352 ± 50 per μm2, respectively). On the other hand, E-PPS caused the tips to sharpen significantly (508 ± 50 per μm2). The pad-slurry-ring coefficient of friction (COF) was higher for E-PPS (0.69 vs 0.65). This was consistent with the higher observed pad surface temperature for E-PPS and its associated sharper pad asperities. Both rings showed similar tribological behaviors, and the contact mechanism was one of “boundary lubrication.” Both rings caused the pad to wear at comparable rates, but regarding ring wear rate, E-PPS seemed to wear about 30 percent faster than O-PPS. This was deemed to be inconsequential in IC manufacturing due to the estimated excessive life of the ring (regardless of which type of PPS material was used) compared to the useful life of the pad and other consumables such as filters and discs.