Improving the accuracy of overlay measurement through wafer sampling map rearrangement

Abstract

In this study, different sampling methods for alignment and overlay measurement were compared. Several types of wafer map, such as symmetry, asymmetry, and random were tested. In order to characterize the performance of each sampling plan, criteria including the alignment error, overlay measurement data and the final registration result after adjusting stepper parameters were examined. The compensation value for exposure systems control was calculated from measurement data by using overlay software. The distribution and numbers of sampling sites have crucial effect to the accuracy of measurement and the alignment site should be uniform for better exposure tool control. Also the measurement sites should be selected to match with stepper alignment mark location so that a more accurate result could be acquired. By using a well arranged sampling sites, systematic error result from the matching between production tool and measurement tool could be further reduced. After rearrangement, the closely matched sampling map could increase accuracy for production line with overlay feedback control system.