Static and dynamic contact angles of water on photoresist

Fluid management issues in an immersion lithography system include the retention of the liquid (i.e., prevention of residual liquid on the wafer) and the possible entrainment of gas bubbles within the immersion fluid. Three key parameters strongly influence the control of fluid within the lens gap: the static liquid/resist contact angle, the contact angle hysteresis, and the dynamic contact angle characteristics. This article presents a comprehensive set of data for these parameters on silicon wafers coated with six different photoresists and describes the experimental apparatus and data reduction techniques used to collect the data. Measurements for six candidate photoresists, one with a top-coat, indicate that air entrainment due to contact line motion is highly unlikely for typical immersion lithography systems. However, significant contact angle hysteresis does exist that may lead to meniscus failure and to the deposition of droplets at low to moderate wafer velocities. In addition, the receding dynamic contact angle can approach zero on some surfaces, leading to liquid film deposition.