A semi-empirical study into the effects of residual casting solvent on the lithographic properties of photoresist is described. Solvent content of a commercial i-line photoresist after postapply bake has been measured using a quartz crystal microbalance and using radio-labeled solvent with scintillation counting. Analysis of this data has led to a calibrated model of solvent diffusivity as a function of solvent content which can then predict solvent content as a function of depth into the photoresist for a given bake.