Enhancement of immersion lens stability using vapor-driven solutal Marangoni effect

In the semiconductor industry, water-based immersion lithography has been adopted to achieve O(10 nm) spatial resolution. One of the difficulties remaining in immersion lithography is to avoid the formation of residual droplets after the main lens while increasing the relative speed of the silicon wafer with respect to the main lens for a high production rate. The critical condition for the lens breakdown is highly related to the design of the immersion hood. To prevent its unstable mode, it has been suggested to apply strong shear stress using the air curtain along the immersion drop surface. However, the shear flow can also make the lens unstable due to the relatively high surface tension of the immersion liquid where the working fluid is water. Therefore, the shear and capillary flow should be controlled simultaneously. To solve this problem, we propose the volatile vapor knife to use the vapor-driven solutal Marangoni effect, which requires only a little amount of vapors to effectively alter the local capillary effect. We develop a new type of immersion hood by modifying the vapor inlet and outlet instead of the air curtain system. During the talk, experimental and theoretical findings about the improvement of immersion lens stability and wafer speed will be discussed.