Predicting variations of critical dimensions (CDs) during a dry etching process is highly desirable in order to reduce cost and shorten fabrication time. Microloading and macroloading effects contribute to CD variation. Variation of pattern density and plasma distribution over the photomask are the main reasons for variation of etch rates. Pattern dependent error is the most important. TRAVIT is a dry etch simulation tool that has been developed to simulate etch profiles, etched linewidths, and CD variations resulting from dry etching. The software takes a GDSII pattern and determines if the CD variation is within the prescribed tolerance or if the pattern needs additional correction, and to what degree. In this way, an expensive writing of a high end mask, its dry etch, and metrology can be replaced by a simulation to avoid actual fabrication of a mask. Examples of simulations including variable ICP power, physical and chemical etch components, and optimization of a sidewall, bias, and CD variation are presented.