Reactive ion etching of silicon dioxide and positive photoresist in CHF3–C2F6–O2–He plasma in a parallel‐plate etcher is studied using the response surface experimental design procedure. The experimental results are reproducible within 5%. Analytical expression for the dependence of the etch rates on the plasma parameters (oxygen concentration, pressure, rf power) are obtained. Detailed contour maps of the behavior of the etch rates as functions of the plasma parameters are prepared from the analytic expressions. Calculated etch rates are within 10% of the measured value at a large number of points in the range of the parameters explored. Using the results of this study it has been possible to etch contact holes with a variety of sidewall slopes. Predictability of the etch rates from the analytical expressions for resist and silicon dioxide also provided great flexiblity while planarizing a dielectric over patterned aluminum and etching of vias in the planarized but unevenly thick dielectric.