Profile evolution of trenches and lines, both nested and isolated, during etching with Cl-2, HBr, and HCl plasmas in a high density, commercial etch tool was investigated. Features patterned with and without an insulating SiO2 mask layer produced similar profiles with Cl-2 and HCl plasma etching, but markedly different profiles with HBr plasma etching. The contribution of the SiO2 mask material to sidewall passivation is discussed. Under certain plasma conditions without a SiO2 mask, severe facets on the silicon lines were observed. The importance' and relevance of this facet formation to the profile evolution process is reviewed. Profile evolution with increasing reactor pressure was identical during etching with HBr and Cl-2 plasma etching, although the profiles etched in either gas at the same pressure were markedly different. These experimental results are compared to plasma etching models and molecular beam experiments reported in the literature, and the contribution of these data to feature profile evolution simulators is presented.