Si/SiO2etch properties have been studied in CF4and CHF3cylindrical magnetron rf discharges as a function of magnetic field strength. As the magnetic field strength increases from 0 to 250 G, radical densities continuously increase and dc bias voltages exponentially decrease. The maximum etch rates of Si and SiO2, however, occur at an intermediate value of magnetic field strength which corresponds to the self‐bias voltage being between 25 and 50 V. Using magnetic field strengths near the maximum etch rate, we obtained vertical features having <2000 A˚ widths and trenches deeper than 2 &mgr;m. Etch rates exceeding 2500 A˚/min were obtained in a CF4plasma, with little or no radiation damage, and with minimum contamination of the surface.