Fourier transform infrared spectroscopy studies of water-polymer interactions in chemically amplified photoresists

Abstract

Fourier-transform infrared absorption spectroscopy is implemented to measure the infrared spectrum of water absorbed by the poly(t-butoxycarbonylstyrene) and the ketal-protected poly(hydroxystyrene) polymer photoresists. The shape and intensity of the OH stretching band of the water spectrum is monitored in a variety of humidity conditions in order to obtain information on the hydrogen-bonding interactions between the water and the polymer chains. The band is deconvoluted into four subbands, which represent four types of water molecules in different environments. Because of the hydrophilicity of the polymers studied, a large portion of the sorbed water molecules is believed to be strongly bound to the polar sites of the polymer. The ratios of each type of water are found to be dependent on the humidity conditions to which the sample was exposed. At higher humidities, there is an increase in the fraction of free and weakly bound water molecules. These findings are used to explain the humidity dependence of the deprotection reaction rates, since certain types of water may slow transport of reactive species within the polymer network.