The performance evaluation of at-resolution stitching on NXE

Abstract

As High NA extreme ultraviolet (EUV) lithography systems reduce image field sizes, in-die stitching becomes necessary for printing large dies. This study evaluates the performance of stitching of pitch 28 nm vertical line/space features using high-reflectivity (~13%) low-n masks on an ASML NXE:3400B scanner. To address imaging challenges in the double exposure region, sub-resolution gratings (SRGs) are employed to suppress reflectivity. Stitching is realized by overlapping line-ends from top and bottom masks, with a small design overlap. Critical dimension (CD) measurements are extracted from CD-SEM images using MXP software for contour-based metrology. Key performance indicators—mean CD, global CD uniformity (GCDU), and local CD uniformity (LCDU) are determined and compared between stitched and reference features. Results show that, in general, stitched features exhibit imaging performance comparable to the reference features. Still, there are distinct trends at the stitch for which we provide further insights. Mean CD profile at the stitch can be reproduced in simulations and is understood as the summation of aerial images of overlapped rectangular line-ends. GCDU elevation is explained by overlay variation across the wafer, while LCDU trends align with dose sensitivity, indicating increased image contrast at the stitch. While simulation results reproduce CD profiles and SRG-induced modulations, they diverge in contrast trends, suggesting further modeling is needed. To sum up, this work demonstrates the feasibility of atresolution stitching with low-n masks, explains imaging trends at stitch, and provides insights for future high-NA EUV stitching evaluations.