A process for controlling the plasma etch of a silicon dioxide layer at a high etch rate and high selectivity with respect to silicon nitride, particularly in a multilayer structure, by (1) maintaining various portions of the etch chamber at elevated temperatures, and/ox (2) using an etch chemistry having a fluorohydrocarbon gas containing at least as many hydrogen atoms as fluorine atoms, preferably CH₂F₂ or CH₃F.