Si/SiO₂ etch properties using CF₄ and CHF₃ in radio frequency cylindrical magnetron discharges

Si/SiO₂ etch properties have been studied in CF₄ and CHF₃ cylindrical 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 Å widths and trenches deeper than 2 μm. Etch rates exceeding 2500 Å/min were obtained in a CF₄ plasma, with little or no radiation damage, and with minimum contamination of the surface.