Microlithography 1998
Conference paper

Probabilistic model for the mechanism of phenolic polymer dissolution

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A probabilistic model for polymer dissolution was recently presented that aims to provide a fully molecular explanation for the complex dissolution behavior of phenolic polymers such as novolac in aqueous developers. It is based on the hypothesis that a phenolic polymer, which is below the entanglement molecular weight, becomes appreciably soluble only when a certain fraction of its phenol groups are deprotonated. If the rate of dissolution of the polymer is limited by this solubility criterion rather than by mass transfer, then the dissolution rate of the polymer may be predicted from the probability of deprotonation. This hypothesis has been supported by laboratory measurements that tested the model's predictions for the effect of polymer molecular weight on the minimum base concentration for development and by combinatory potentiometric and turbidimetric titrations. The model can adequately account for the observed effects of residual casting solvent and novolac/inhibitor interactions and the differential dissolution behavior between novolac and poly(hydroxystyrene). No other model for phenolic polymer dissolution predicts all of these behaviors. This evidence suggests that even in a primitive form, the probabilistic model captures the important physical elements affecting the dissolution process that are absent from models based solely on diffusion theory. ©2003 Copyright SPIE - The International Society for Optical Engineering.