A method including providing a present wafer to be processed by a photolithography tool, selecting a processed wafer having a past chip design from a plurality of processed wafers, the processed wafer being previously processed by the photolithography tool, selecting a plurality of critical dimension (CD) data points extracted from a plurality of fields on the processed wafer, modeling the plurality of CD data points with a function relating CD to position on the processed wafer, creating a field layout on the present wafer for a new chip design, creating an initial exposure dose map for the new chip design using the function and the field layout, and controlling the exposure of the photolithography tool according to the initial exposure dose map to form the new chip design on the present wafer.