An experimental stitching study on the eve of High NA EUV

The combination of High NA EUV anamorphic projection optics and unchanged mask-blank size result in a "High NA field" with a maximum size of 26x16.5 mm(2) at wafer level. Therefore, to create a die larger than the High NA full field, two images are stitched together. So-called in-die stitching is enabled by a combination of design, mask, OPC, process, and scanner solutions. We present an overview of our learnings about at-resolution stitching based on a representative experimental study at NA=0.33, in preparation for tomorrow's NA=0.55.For a pitch 28nm vertical line-space, optimum conditions are confirmed experimentally to create a robust stitch. A P28 LS is measured post-stitching utilizing either a Ta absorber or a low-n absorber. For the latter, the higher reflectivity is experimentally mitigated by using sub-resolution-gratings. We also quantify the imaging impact of the transition between the absorber and the black border in the stitching region.