Formation factors of watermark for immersion lithography

In the advanced lithography process, the immersion lithography technique has become important in order to achieve the high quality resist patterns less than 50nm. In this technique, some defects such as a watermark and a nanoscale bubble have been focused as the serious problems to be solved. In actual system of the immersion lithography, the micro droplets of the immersion liquid remains randomly on the resist surface after the wafer scan. In this study, in order to prevent the watermark formation, the in-situ observation of the drying behavior of the water drop is conducted. As the solid defects, polystyrene latex (PSL) particles were mixed with deionized (DI) water. As the formation factors of the watermark, we focused on liquid evaporation, Laplace force, viscosity of liquid, convection in liquid drop (Drelich et al., 2000), surface energy (Harazaki, 1977), and zeta potential and so on.