Improved model for liquid loss at a dynamic contact line including behaviors of high-index fluids

Abstract

To achieve the numerical aperture required for the next generation of immersion lithography, water may be replaced with a high index liquid as the immersion fluid. Because of their low surface tension to viscosity ratios, candidate high index fluids have an increased tendency to lose liquid from the under-lens region during scanning. Because any residual liquid left on the wafer is a potential defect mechanism, the conversion to high index fluids may drastically reduce scanning speeds and wafer throughput. The mechanism for liquid loss strongly depends on the behavior of the three-phase contact line; thus, this work focuses on the experimental study of the static and dynamic contact line behavior of five high index fluids. Contact angle and critical liquid loss velocity data is compared to the current model, which has been updated to better fit this new range of fluids. Liquid loss behaviors and their implications to the immersion lithography industry are discussed.