High research costs and difficult technical challenges make simulation an important tool for sub-250nm lithography development. Resists can no longer be represented by smooth surfaces, however, because pattern edge roughness occurs due to the underlying base polymer structure and the distribution of cross-linking and dissolution inhibiting materials in the resist. To model effects of importance in semiconductor manufacturing, a new simulation method has been developed. The method begins with a resist material representation based on the base polymer resin and proceeds with algorithms for post-exposure bake processes and alteration of the structure upon contact with developer. The model has been successfully applied to proximity X-ray, projection extreme-UV, and electron beam lithography with chemical amplification resists. Measured 3σ fluctuation often approaches 25nm, limiting 10% fluctuation control to 250nm linewidths.