The effect of humidity on water sorption in photoresist polymer thin films

A quartz crystal microbalance technique has been utilized to measure water sorption and desorption in three photoresist polymers: poly(p-hydroxystyrene), novolac, and bis-triflouromethyl carbinol substituted poly(norbornene). The humidity of the sample environment was varied to determine the rate and amount of water absorbed into the photoresist thin films as a function of local environmental conditions. At 100% absolute humidity, the polymers were found to absorb 9.8, 2-3, and 5-8 wt%, respectively. The sorption and diffusion of water into the polymer thin films was observed to initially follow Fickian behavior in the low fractional mass uptake regions (M_t/M_∞<0.6), but concentration dependent diffusion behavior was seen at higher levels of water uptake. All films sorbed and desorbed water rapidly with the majority of the water uptake or loss occurring in the first few seconds of exposure.