Retaining Ring Design Impact on CMP Process Stability and Optimization
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1249-E02-01
Retaining Ring Design Impact on CMP Process Stability and Optimization Joseph E. Smith1, Christopher Wargo1, Raghava Kakireddy1, Rakesh Singh1, Andrew Galpin1, Ara Philipossian2, Xiaomin Wei2, Karim Bennedine3, Claude Reversat3, Alain Chabourel3, 1 - Entegris Inc., 129 Concord Road Billerica, MA 01821 2 -Department of Chemical and Environmental Engineering, University of Arizona, Tuscon, Arizona, 85721 3- STMicroelectronics, Rousset SAS, France
ABSTRACT The focus of this work is wafer retaining rings and their impact on chemical mechanical planarization (CMP) process stability, yield, and overall cost of ownership (CoO). The study looks at various CMP retaining ring materials and processing methods. Tribological investigations as well as wafer processing are critical to understand the retaining ring and polishing pad environment. Interactions at the ring/pad interface have a major effect on the planarization and defectivity of a polished wafer. Shear and normal forces at this interface, as well as temperature and lubrication regimes, were monitored to establish an empirical model. All process conditions equal, the material properties of retaining rings govern the coefficient of friction (COF) in the ring and pad contact area. Present study demonstrates a lower COF to be an indicator of extended ring lifetime, decreasing WTWNU and removal rate (RR) variation. The study correlates the findings on wafer level data from high volume manufacturing fabs with empirical data generated using applications lab tribological equipment to understand the onwafer performance as a function of retaining ring material. The study’s further aim is to understand for specific applications, the material interactions on-wafer using various retaining ring materials. CMP process optimization can be attained with a better understanding of retaining ring design and material characteristics, as well as polishing head and slurry parameters. INTRODUCTION In any manufacturing environment it is desirable to have flexibility in the selection and use of process components. The CMP retaining ring is one of the many components in the CMP process that has been evolved and compensated for in myriad process corrections over time. The most common material for retaining rings is polyphenylene sulfide (PPS), compression molded or polymer blend in a one piece retaining ring or incorporating a stainless steel backing plate in a two piece configuration. Many applications use polyetheretherketone (PEEK™), which offers a slightly different set of material characteristics. Entegris manufactures Planaredge® CMP retaining rings from injection molded PEEK. The resulting molded ring is then machined to final shape, polished and cleaned for use. In order to better serve the customer and knowledge base, a thorough understanding of the collateral effects of an alternate retaining ring material is beneficial to moving up the compensation curve and closing in on a ‘drop in’ replacement. This paper presents results of an ongoing study to improve our understandin
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