Dissolution dynamics of poly(4-hydroxystyrene) in potassium hydroxide (KOH) and sodium hydroxide (NaOH) aqueous solutions investigated by quartz crystal microbalance (QCM) method

Abstract The molecular size of an alkaline cation has been reported to affect the dissolution of resist film in an alkaline aqueous solution. However, the details are still unclear. In this study, the dissolution dynamics of poly(4-hydroxystyrene) (PHS) in potassium hydroxide (KOH) and sodium hydroxide (NaOH) aqueous solutions were investigated to clarify the effects of small alkaline cations on the dissolution dynamics of typical backbone polymer for chemically amplified resists by a quartz crystal microbalance (QCM) method. The temporal changes in the frequency and impedance of QCM substrates during development were measured. The maximum impedance reachable during development significantly exceeded that of the developer saturated with PHS, unlike the case of tetramethylammonium and tetraethylammonium cations. This means that the PHS matrix near the surface was swollen by decreasing the size of the alkaline cation. By either increasing or decreasing the size of the alkaline cation from tetramethylammonium and tetraethylammonium cations, the transient swelling layer became thick.