Dissolution kinetics of poly(4-hydroxystyrene) with different molecular weight distributions in alkaline aqueous solution

A poly(4-hydroxystyrene) (PHS) backbone polymer and a tetramethylammoniumhydroxide (TMAH) aqueous developer are typically combined to form a positive chemically amplified resist. We investigated the dissolution kinetics of PHS with different molecular weights and molecular weight dispersions and different concentrations of TMAH by quartz crystal microbalance (QCM) measurement. QCM graphs showed different dissolution rates and forms for different concentrations. We attempted to explain the dissolution kinetics by introducing a dissolution index calculated from swelling and dissolving factors. These factors were calculated using a penetrating factor (water or TMAH molecules) and a disentanglement factor. It is considered that the dissolution index depends on the molecular weight distribution because polymers with different molecular weight distributions have different voids in their bulk and different tendencies of disentanglement. Our results suggest that dissolution can be controlled by adjusting the molecular weight distribution, which will lead to reduced defect generation during the fabrication of fine structures.