The process parameter space for fluorocarbon plasmas (C2F6/CHF3and CF4/CHF3, with and without He) which are used to etch SiO2has been examined with a Lam Research Autoetch 580 parallel plate, single‐wafer etching system by response‐surface methodology. The response or behavior of the plasmas differs very significantly with reactor pressure, etch gas mixture, and He addition. In particular, substantially higher SiO2etch rates are obtained with C2F6/CHF3plasmas than with CF4/CHF3plasmas at an equivalent radio frequency power density for similar gas flow rates at significantly different reactor pressures: ∼2500 Å/min at ∼400 mTorr with C2F6/CHF3mixtures and ∼750 Å/min at ∼1500 mTorr with CF4/CHF3mixtures. Upon addition of He to the plasmas, the SiO2etch rate maximum for the C2F6‐based plasma shifts to ∼800 mTorr and declines to ∼2000 Å/min, while that for the CF4‐based plasma remains near 1400 mTorr and increases to ∼1000 Å/min. Whereas the addition of He sharply degrades the etching uniformity with C2F6/CHF3mixtures, it has no apparent effect on the etching uniformity with CF4/CHF3mixtures, which is high with or without the addition of He over the parameter space which was explored. For the C2F6/CHF3plasma, the etch selectivity to silicon is highest at 700–1100 mTorr, while for the CF4/CHF3plasma the selectivity is highest at 1100–1500 mTorr. Although addition of He substantially improves the selectivity with the CF4/CHF3plasmas, it has no effect on selectivity with the C2F6/CHF3plasma. These detailed characterizations of process parameter space have led to a uniform and selective SiO2sidewall spacer etching process which may be readily extended to other SiO2etching processes with this equipment and these gas mixtures.