Modeling and Characterization of Tungsten Chemical and Mechanical Polishing Processes

Due to the complexity of chemical mechanical polishing (CMP) in general and metal CMP in particular, modeling of CMP processes has been pursued only minimally in the literature. A fundamental understanding of these metal CMP processes is needed to minimize manufacturing and development costs that will continue to escalate as more devices migrate to subhalf-micrometer technologies where metallization schemes are more complicated. In this work, we have used two different models to characterize the tungsten CMP process. While the chemical Preston model is used to explain the effect of process parameters on the mean polish rate, the slurry transport model is useful in explaining the within wafer uniformity for the polishing process. We successfully validated the chemical Preston model using design of experiment (DOE) data and demonstrated the importance of slurry transport and the pad to wafer gap, to the within wafer uniformity for the embossed and regular politex polishing pads. We showed that better uniformity is obtained throughout the wafer with the embossed politex than the regular politex pad due to the presence of grooves in the embossed pad, which allow for better slurry transport across the pad. We effectively characterized the process and studied the effects of changing the various tool and process parameters on process performance.