Contact angles and liquid loss behavior 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. Due to their low surface tension to viscosity ratios, candidate high index fluids have an increased tendency to lose liquid from the underlens region during scanning. Since any residual liquid left on the wafer is a potential defect mechanism, the conversion to high index fluids may drastically reduce scanning speeds and chip throughput. The mechanism for liquid loss strongly depends on the behavior of the three-phase contact line, so this work focuses on the experimental study of the static and dynamic contact behavior of five high index fluids. Contact angle and critical liquid loss velocity data is compared to the critical velocity model we previously developed, and the liquid loss behavior is discussed.