Current status of 157-nm lithography using a full-field scanner

In July 2004, the third FPA-5800 FS1 157-nm full-field scanner, developed by Canon Inc., was shipped to Selete. The scanner has an exposure field of 22 x 26 mm with a five-times reduction ratio. The numerical aperture is 0.80, which is the highest among all 157-nm scanners. We are now investigating tool performance, illumination uniformity, and imaging performance under various exposure conditions. In this paper, we will report our findings, focusing on the applicability of 157-nm dry lithography for the half-pitch 65-nm-node. We have obtained a resolution limit of 55-nm line-and-space (L&S) patterns with an alternating phase shifting mask. This corresponds to a 0.28 k1 factor. The depth of focus for these patterns at lens-center was 0.30 μm. For an attenuating PSM (Att-PSM) with annular illumination, the resolution limit was 65-nm L&S, which corresponds to 0.33 k1. The line width uniformity of 65-nm L&S with an Att-PSM was 15.0 nm. The dense-hole resolution was 80 nm. However, lens flare had a considerable effect on resist profiles, viewed as a difference between dark and bright field patterns. In addition, with the application of gate etching processes, the fabrication of a 40-nm line/120-nm pitch gate pattern was achieved. Improvement in the line width roughness (8.3 nm) is needed and should be attainable.