Effects of photoacid generator decomposition on dissolution kinetics of poly(4-hydroxystyrene) in tetraalkylammonium hydroxide aqueous solutions

For the advancement of lithography, the resist materials and processes are the most critical factors. In particular, the process of developing resist materials is important in reducing the line width roughness and stochastic defects. In this study, a quartz crystal microbalance method was used to investigate the dissolution dynamics of poly(4-hydroxystyrene) (PHS) films containing triphenylsulfonium nonaflate (TPS-nf) in tetraalkylammonium hydroxide (TAAH) aqueous solutions. The time required for dissolution increased with the alkyl chain length of TAAH. The dissolution rate of PHS films increased with UV irradiation dose for tetramethylammonium hydroxide and tetraethylammonium hydroxide developers, whereas the dissolution time increased for the tetrabutylammonium hydroxide developer. For the tetrapropylammonium hydroxide developer, the dissolution time of PHS films without postexposure baking (PEB) slightly decreased with UV irradiation, whereas that with PEB increased. Both the surface free energy of PHS films and the molecular size of TAAH are considered to affect dissolution kinetics.