Fluid-photoresist interactions and imaging in high-index immersion lithography

Abstract

Optical immersion lithography using fluids with refractive indi- ces greater than that of water 1.436 can enable numerical apertures of 1.55 or above for printing sub-45-nm lines. Two second-generation im- mersion fluid candidates, IF132 and IF169, both have indices above 1.64 and have been optimized to absorb less than 0.1 cm 1 at 193.4 nm. These fluids, although meeting the requirements of index and absorp- tion, must also be compatible with current resists and processes to im- age the required fine line patterns. Results of fluid-resist interactions, with water and high-index fluids on four commercial resists, are shown. Photoacid generator PAG leaching measurements reveal much less leaching into both high-index fluids than into water, and in two water- immersion dedicated resists, no leaching is detected with the high-index immersion fluids. Little resist thickness change and swelling is detected by a quartz crystal microbalance QCM on contact with the fluids. Resist profile and line height changes due to pre- and postexposure fluid con- tact varies from one resist to the next, but overall the changes are mini- mal. Misting defects from high-index fluid-resist contact show lower counts than for water, and imaging on an immersion interference printer produces 36-nm half-pitch lines. We find no serious impediments to the use of high-index liquids based on these results. © 2009 Society of Photo-