Fundamental study on dissolution kinetics of poly(4-hydroxystyrene) for development of high-resolution resists

We investigated the dissolution kinetics of poly(4-hydroxystyrene) (PHS) in an alkali developer with tetramethylammoniumhydroxide (TMAH). Experiments using PHS with different molecular weights and molecular weight dispersions and developer with different concentrations of TMAH led to the clarification of the dissolution behavior. Not only a change in the dissolution time but also a change in the dissolution behavior was observed upon changing the concentration of the developer. The dissolution behavior depends on an index calculated from values indicating the effects of swelling and dissolving. The dissolution occurred through the swelling of the polymer bulk and the subsequent diffusion of polymer chains into the solution bulk. The development using the alkali aqueous solution system was complex. The swelling rate should not be much larger than the dissolving rate for the development of high-resolution resists because a high swelling rate causes the generation of defects during the fabrication of fine structures.