Progress toward a comprehensive, chemically detailed, mesoscale photoresist simulation with predictive capability is reported. The semiconductor industry has developed a need for mechanistically detailed simulations capable of studying photoresist performance at nanometer dimensions. The nanometer-scale dimensional tolerances on photoresist features are becoming increasingly difficult to meet and expensive to produce in high-volume manufacturing processes. A mesoscale Monte Carlo simulation for processing of positive tone, chemically amplified photoresists has been developed to enable detailed study of photoresist performance as a function of formulation and processing variables. In this model, the molecular components of the photoresist material are included explicitly within a three-dimensional lattice framework. Molecular level models for each processing step have been derived from experimental studies and are implemented in the simulation modules for the several photoresist processing steps. Simulation input variables are fundamental and measurable material properties and processing parameters. Empirical calibrations to expensive lithography experiments are not used. The mesoscale nature of the simulation offers the ability to study the stochastic processes that contribute to resist feature roughness, while the chemical detail included in the models enables investigation of the wide photoresist formulation variable space. This suite of programs provides a unique tool to guide the rational design of new photoresist materials. (C) 2004 The Electrochemical Society.