Dissolution Kinetics of Poly(4-hydroxystyrene) Film in Ethanol/water Mixture

Dissolution of polymer films is a key process in lithography. However, details of the dissolution mechanism remain unclear. In this study, the dissolution kinetics of a poly(4-hydroxystyrene) (PHS) film in an ethanol/water mixture were investigated using a quartz crystal microbalance to obtain the fundamental knowledge of dissolution kinetics. As the water content (a poor solvent of PHS) increased, the intrinsic viscosity and hydrodynamic radius of the PHS molecules decreased, whereas the Huggins coefficient and developer viscosity increased. The dissolution was delayed by the increase in the developer viscosity and Huggins coefficient upon water addition, whereas the dissolution rates did not differ significantly. Two reasons are considered. First, the hydrodynamic radius decreased with the addition of water. Second, the penetration of water into the PHS film was probably faster than that of ethanol owing to the smallness of water molecule and the weak interaction between water and PHS molecules.