Computer simulation of dry etching is used to explore line edge profiles obtained in IC processing. The model divides the process into isotropic or chemically reactive etching and directional or ion illuminated etching. The algorithm simulates the time evolution of the two dimensional profile by advancing nodes on a string according to the local anisotropic and isotropic rates. The accuracy of the model and its applicability to IC processing are illustrated through comparison with known mathematical cases and experimental results. Experiment and simulation are used to explore the residue left at a step with anisotropic etching and the amount of under cut necessary in producing stepped arsenic implanted polysilicon layers.