An oxide etching recipe including a heavy hydrogen-free fluorocarbon having F/C ratios less than 2, preferably C4F6, an oxygen-containing gas such as O2 or CO, a lighter fluorocarbon or hydrofluorocarbon, and a noble diluent gas such as Ar or Xe. The amounts of the first three gases are chosen such that the ratio (F—H)/(C—O) is at least 1.5 and no more than 2. Alternatively, the gas mixture may include the heavy fluorocarbon, carbon tetrafluoride, and the diluent with the ratio of the first two chosen such the ratio F/C is between 1.5 and 2.