Improved fidelity to an integrated circuit pattern design in a semiconductor structure ultimately produced is achieved by modeling material removal and deposition processes in regard to materials, reactant, feature size, feature density, process parameters and the like as well as the effects of such parameters on etch and material deposition bias due to microloading and RIE lag (including inverse RIE lag) and using the models to work backward through the intended manufacturing method steps, including hard mask pattern decomposition, to morphologically develop feature patterns for use in most or all process steps which will result in the desired feature sizes and shapes at the completion of the overall process. Modeling of processes may be simplified through use of process assist features to locally adjust rates of material deposition and removal.