Methodology of stitching evaluation at NA 0.33 to enable high-NA assessment

With the currently used mask architecture and anamorphic projection optics of High NA EUVL scanner, stitching of two or more images is required to create a field (die) larger than 26x16.5 mm² at a wafer level. Therefore, the availability of a methodology to evaluate the performance of stitching is of paramount importance. In this report, we present a comprehensive methodology developed using a large set of data from stitching experiments conducted at imec using the ASML NXE:3400 scanner (NA = 0.33), on P28 lines-space pattern, that will be useful for later evaluation of stitching at NA=0.55. We will show that such methodology requires high density CD measurement, systematic sampling and statistical analysis (calculating means and variations), to build Mean CD, Global CD uniformity (GCDU) and Local CD uniformity (LCDU) profiles and extract stitching signature and performance metrics. The metrics will be used to evaluate the performance of stitching as compared to references.