A methodology for doing process control by using a heating apparatus comprising heating zones is revealed. First, a target CD (critical dimension) map is assigned. A baseline CD map corresponding to a substrate processed with the heating apparatus at a baseline setting is also obtained. An original CD map corresponding to a substrate processed at an original setting is obtained. For each heating zone, a perturbed CD map corresponding to a substrate processed at a perturbed setting is also obtained. The temperature distribution of the heating apparatus is adjusted according to the error CD map defined by the baseline CD map and the target CD map, basis functions defined by the original CD map and perturbed CD maps, and expansion coefficients expanding the error CD map with basis functions.