Effect of Copper Film Surface Properties on CMP Removal Rate
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Effect of Copper Film Surface Properties on CMP Removal Rate Yuchun Wang, Rajeev Bajaj, Gary Lam, Yezdi Dordi, Doyle Bennet, Fritz Redeker Applied Materials, CMP division, Santa Clara, CA 95054 Summary It has been observed that CMP removal rate of copper varies for films from different sources. While the film hardness and static wet etch rate in the absence of inhibitors are similar for various films, the static etch rate in the presence of inhibitors is significantly different. Analysis by AFM, XPS, and ion beam sputtering showed the film roughness and surface composition were different for different Cu films within 160 angstroms of the surface. Thus the different in Cu CMP removal rates can be explained by a synergetic effect of copper film roughness (grain size), surface composition, and effective adsorption of inhibitors. This explanation suggests that if polishing is initiated by an aggressive polishing step, removal rate of the remaining bulk copper films become more consistent. Based on these findings, the polishing slurry and process were further optimized. 1. Introduction Copper CMP is a critical step in copper damascene patterning. We have observed a removal rate variance of copper films from different sources that the same slurry produced different Cu CMP rate for films from different sources. In Cu CMP process flow, the CMP rate variance would affect throughput and dishing in clearing copper as well as the barrier layer. Several mechanisms can cause copper CMP removal rate variation (1-4): film deposition (electroplating), annealing of the film (either at high temperature or room temperature self annealing), and further surface oxidation in the environment. However, few papers have sought to explain the phenomenon (5,6). In this study, we attempted to understand the relationship between the film surface properties (microstructure, composition) and Cu CMP process. Although we found the removal rates showed sensitivity to film sources for various types of slurries commercially available, we present this work with a particular non-selective, copper and barrier removal slurry (ElectraPolishTM slurry from Applied Materials) on different types of copper films which exhibited low and high removal rates. The slurry had 10% silica with alkaline pH. Based on the findings, the slurry composition was optimized to extend the process window. 2. Experimental All wafers were 8 inch (200 mm) diameter copper plated on tantalum on silicon. They were supplied from 3 to 4 different vendors for removal rate comparison. Wafers were polished for 1 minute for removal rate on Applied Materials Mirra polisher using ElectraPolishTM slurry. The head membrane pressure was fixed at 3psi. The platen and head speed was 103 rpm and 97 rpm, respectively. Polishing pad was IC1010, wide grooved polyurethane on Suba IV from Rodel. Slurry flow rate was 200 ml/min unless M3.2.1
otherwise stated. Cu removal rate was calculated from the film thickness difference before and after the polishing, measured by sheet resistance (RS 75 from KLA-Tenc
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