Highly selective etching of SiO2 with respect to silicon and resist is obtained by reactive ion etching in CF4 + H2. The maximum etch rate ratio depends in a sensitive way on gas residence time with etch rate ratio increasing with decreasing residence time. The reproducibility of high etch rate ratios was found to decrease with increasing pressure. The cleanliness of etching is determined by the material of the electrode and the electrode to wall area ratio. A process was developed by optimizing etching conditions and reactor design and then was tested electrically. Contact holes were etched to 0.25 jim junctions using full RIE in CF4 + H2 and buffered HF. The same low junction leakage and contact resistivity, 10–9 amps/cm2 and 10−6 Ω-em2, were measured for both. Implications for scaling CF4 + H2 RIE into larger etching reactors as well as its use to pattern features at 1 μ.m ground rules are discussed. © 1982, The Electrochemical Society, Inc. All rights reserved.