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Planarization of Wafer Edge Profile in Chemical Mechanical Polishing
박영봉,정해도,정호빈,최성하 한국정밀공학회 2013 International Journal of Precision Engineering and Vol.14 No.1
Within wafer non-uniformity (WIWNU), which significantly affects the yield of chip products, is mainly caused by non-uniform chemical mechanical polishing (CMP) at the wafer’s edge. This study investigates the origins of the non-uniformity and presents a process that uses an edge profile control ring (EPC ring) to solve the problem. The EPC ring is designed to be positioned between the wafer and the retaining ring and pressed at the same pressure as the wafer by a flexible membrane to reduce the pressure discontinuity between the center region and the edge region of the wafer. Experimental results show that for a WIWNU of 2%, the EPC ring makes it possible to shrink the edge exclusion region from 15 mm to 2 mm without any change in process conditions. This result suggests that the EPC ring is applicable to real fabrication.
박영봉,정해도,이현섭,이영균,박선준 한국정밀공학회 2013 International Journal of Precision Engineering and Vol. No.
This paper presents the effect of the contact angle between the retaining ring and the polishing pad in chemical mechanical polishing (CMP) on the profile of the material removal rate (MRR) around the wafer edge and on the within-wafer nonuniformity (WIWNU). This study demonstrates that the mechanical interaction among the polishing pad, wafer, and retaining ring influences the ability to achieve planarization from the CMP process. In particular, the purpose of this study is to understand the effect of the contact conditions between the retaining ring and the pad on the CMP process. In order to verify the mechanical aspects of the MRR near the wafer edge, retaining rings with different contact angles were prepared. Finite element analysis (FEA) verified the effect of the contact angle between the retaining ring and the polishing pad on the stress distribution around the edge of the wafer. The results of the analysis were corroborated by conducting CMP experiments with 200-mm blanket oxide wafers. As expected, the FEA results were in good agreement with the MRR profile around the edge area. Through simulations and experiments, we concluded that the contact angle is an important factor to achieve a flatter edge profile and the material removal profile around the edge of the wafer was optimum at a 0o contact angle. In particular the WIWNU was below 4% when a flat retaining ring was used. The results of this study make it possible to improve the yield of chip production by ensuring the retaining ring maintains perfect flatness without making any special design changes to the CMP equipment.