Contour quality assessment for OPC model calibration

Site-based SEM measurements produce accurate OPC models in 180nm to 65nm technology nodes, but the lack of 2D information has prompted for new calibration methods for sub 65nm designs. A hybrid technique using site-based SEM measurements together with SEM contours has been developed to produce more accurate OPC models. Contour samples account for 2D effects while CD sites provide high accuracy 1D measurements. SEM contours are prone to sampling and processing errors as well as extensive calibration run time. We develop a method to filter out inferior samples prior to model calibration to effectively decrease calibration runtime and increase model accuracy. Fitness and coverage metrics are used to assess the quality of the contour data in order to select the best subset of the calibration contours. Our results demonstrate a selection routine that consistently performs better than picking contours at random, and we discuss the trade-offs between coverage, accuracy and runtime with respect to model quality.