Advanced process control applied to 90-nm lithography and etch

In this paper, we demonstrate how understanding and controlling lithography through etch, using appropriate integrated metrology, can improve process results, reducing across-wafer CD variability. A spectroscopic CD tool was used to generate CD, profile, and film thickness information from wafers exposed on a 248 nm ASML track/scanner cluster. Using this data, detailed intrafield and interfiled wafermaps were generated. Based on this information, dose, focus, and intensity uniformity corrections were fed back to the track/scanner cluster as offsets for subsequent exposures. In parallel and as a complement to this control loop, CD and profile information was also fed forward to a Lam 2300 Versys Star silicon etch system as input for the etch process optimization step. Following etch, the wafers were moved into the integrated CD metrology module on the etch platform, whereupon post-etch CD/profile measurements were made to verify the effect of the lithography correction, effectiveness of optimized etch process parameters, and magnitude of the lithography-to-etch CD bias.