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In this paper, we present the experimental results on wafer-to-wafer and within-wafer critical dimension (CD) control. It is known that photoresist thickness affects CD. In this paper, we control photoresist thickness to control CD. As opposed to run-to-run control where information from the previous wafer or batch is used for control of the current wafer or batch, the approach here is real time and makes use of the current wafer information for control of the current wafer CD. The experiments demonstrate that such an approach can reduce CD nonuniformity wafer to wafer and within wafer.