Reactive magnetron sputtering of silicon to produce silicon oxide

Abstract

Well controlled silicon dioxide films with refractive index 1.400–1.490 have been deposited at rates of up to 0.85 nm/s from a 100 mm diameter polycrystalline silicon cathode, sputtered at 200 W of 40 kHz rectified AC power in a reactive environment. This frequency used with control of the partial pressure of the oxygen in the system from the cathode potential has demonstrated an ability to reactively sputter silicon oxide of high quality. Stress/stoichiometry curves showed a peak in stress at a refractive index of 1.460 indicating both a dense structure and optimised SiO 2. We have demonstrated a pulsing system for the admission of oxygen into the silicon sputtering system which is under the control of a signal derived from the voltage appearing on the cathode when sputtering at constant power. Such a signal indicates the sputtering status of the target as to the degree to which the cathode is covered with oxide i.e. poisoned. By varying combinations of reactive gas flow rate and switching levels, different film compositions could be reproducibly and reliably obtained. The growing films could be subjected to a externally-varied degree of argon-ion bombardment with a simple modification of the geometry of the unbalanced magnetron used for the sputtering. The amount of ion bombardment with such a system was also a function of the argon sputtering pressure that was used. Increased argon-ion bombardment resulted in more compressive stress in the film that was produced.