The continuing shrinkage of device size will result in stringent demands on high precision CD control. For example, at 0.13um technology node a typical poly gate size variation should be controlled within +/- 8nm or even smaller. This tight CD budget includes all possible variations which can be from different modules of resist coating track, optical and mechanical parts of exposure tool, non-uniformity of wafer substrate, CD metrology, mask making and so on. Particularly, the residual swing effect after applying an inorganic anti-reflection layer (SiON) still can claim a significant CD budget if not properly optimized. Therefore, how to minimize the residual swing effect still plays important role in CD control. Simulation of reflectivity is considered analytically rigorous and is therefore frequently employed to aid in process development. However, since in manufacturing environments people usually pay more attention to the repeatability of optical metrology tools rather than their accuracies, it is not surprising if some significant discrepancies exist between theoretical and experimental results. Instead of discussing the detail error sources and the tool calibrations, a quick and convenient experimental methodology is introduced to account for such differences and to optimize the film stack composition effectively. In this paper, with the CD variations on metal and poly substrates as examples, an effective combination between the calculations and the experiments is presented in order to minimize the CD swing. We also demonstrate that with the "single wafer swing curve" technique, the residual swing effect can be easily detected and minimized. This methodology provides a possibility to determine the best anti-reflection layer not only from theoretical but also from experimental point of view in manufacturing environments. Since the residual swing effect is a common issue, the results of this paper can be widely used in either manufacturing fabs or experimental labs.