Swelling and dissolution kinetics of poly(4-hydroxystyrene) in alkaline aqueous solution studied by quartz crystal microbalance (QCM) method

The dissolution (including the formation of transient swelling layer) of a resist polymer is key to the realization of ultrafine patterning. However, the details of the dissolution of resist polymers remain unclarified. In this study, the swelling and dissolution kinetics of poly(4-hydroxystyrene) (PHS) film in tetramethylammonium hydroxide (TMAH) and tetrabutylammonium hydroxide (TBAH) aqueous solutions were investigated. PHS is a typical backbone polymer (a dissolution agent) of chemically amplified resists. By changing the length of alkyl chains of tetraalkylammonium hydroxide, the swelling and dissolution kinetics of PHS were observed. Their dependences on the thickness of PHS film and the concentration of ammonium hydroxide were discussed.