The soluble site density (SSD) model assumes that changes, in SSD account for changes in dissolution rate for negative and positive chemically amplified resists with reaction rate dependent dissolution mechanisms. In this context, the image mechanism in negative resists can,be explained by removal of soluble, sites instead of increase of molecular weight. Under identical initial conditions this model predicts that acid diffuses faster in negative resists than in equivalent positive resists. Application of this model helps explain why negative resists consistently exhibit less contrast than positive resists. Permeable resist surfaces and the depth dependence in resist energy absorption create a non-uniform depth profile of SSD, which can cause a decrease in sensitivity in ultrathin resist film's (< 150 nm thick). Simulations of resist gratings using the SSD model have been compared to experimental results with qualitatively good agreement in sidewall roughness. Spatial fluctuations of the SSD arise from the acid generation statistics during exposure, aerials image contrast, electron scattering, acid diffusion, and localization of catalytic events. These fluctuations modify the interaction of the resist with the developer, which. contributes to sidewall roughness. (C) 2003 American Vacuum Society.