Improved control techniques for the reactive magnetron sputtering of silicon to produce silicon oxide and the implications for selected film properties

Silicon oxide films were reactively sputtered to give reproducibly controlled properties with refractive indices between 1.400 and 1.490. They were deposited at rates of up to 0.85 nm s(-1) from a 100 mm diameter polycrystalline silicon cathode, sputtered at 200 W, 40 kHz rectified a.c. power in a reactive environment. This frequency, combined with feedback control of the flow of reactive gas, achieved from a d.c. signal derived from the cathode potential, used directly or with a novel gas pulsing unit, has demonstrated that the process can be controlled with at least as much success as conventional optical emission feedback from the plasma. Stress-stoichiometry curves showed a peak in stress at a refractive index of 1.460 indicating both a dense structure and optimized SiO2. We have demonstrated a reactive-gas pulsing system which allows stable sputtering conditions to be easily established for the duration of the deposition, which gives rapid recovery from are disruptions and allows various combinations of reactive gas incorporation into the growing film.