Etching of a patterned semiconductor surface in a plasma depends strongly on the transport of ion and neutral species between the features. Factors altering ion scattering at the sidewalls of high aspect ratio features, such as ion temperature, mask erosion, and charging, influence significantly the final profile shape. Models to describe the inelastic and reactive scattering at various surfaces, coupled to ion trajectory calculations in the sheath and between features, are used to illustrate the contribution of these factors to microtrenching and sidewall bowing. A transition in the profile shape from exhibiting microtrenching to having a rounded bottom is predicted as a result of plasma-induced charging in very high aspect ratio insulating masks.