Ion Beam Reactive Sputter-Deposition of Silicon and Zirconium Oxides.
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Oxides of silicon and zirconium have been deposited onto silicon, carbon and aluminium substrates by reactive sputtering using a I keV argon ion beam and a controlled partial pressure of oxygen. Using RBS, film composition was determined for a given partial pressure of oxygen and different Si or Zr deposition rates. There is evidence of retained argon in the film which is primarily due to argon ions reflected from the sputtered target. Cross-sectional TEM was used to examine the film microstructure and morphology. Both silica films and sub-stoichiometric zirconia films were found to be amorphous,whereas stoichiometric zirconia films were found to be polycrystalline with grain sizes in the range 10-20nm. A model has been developed to predict the composition of deposited films. INTRODUCTION. Reactive sputtering is a widely used technique for the deposition of compound thin films. Films may be reactively sputtered using ion beam, magnetron or RF diode sputtering; ion beam reactive sputtering being conceptually less complicated than plasma-based systems. In general the main applications of reactive sputtering use oxides and nitrides of single metal elements, however, carbides, borides, and many other compounds may be deposited including multi-elemental/multi-gas compounds. Over the past 20 years there have been many attempts to model reactive sputtering"4 . Most of the models proposed have been applied to metalnitride systems and assume that the system is in dynamic equilibrium. This type of process has been shown to be very difficult to control' because metallic atoms getter the reactive gas and an altered layer of the compound forms on the target. The deposition process itself generally switches from metallic film deposition to compound deposition, the latter usually at a considerably lower rate, making it difficult to examine in any detail what is occurring at the substrate. To study reactive sputtering in depth it is desirable to reduce the effect of gettering by using a less reactive target material. The data reported by T.W. Barbee et al' have shown that the silicon-oxygen system may be such a system. In this work both silicon oxygen and zirconium-oxygen systems were studied since silica/zirconia multilayers have important application as anti-reflective coatings. EXPERIMENTAL PROCEDURE The films were deposited by ion beam reactive sputtering using a pure Zr target (99.999% Goodfellow Metals Ltd) or a Si target formed from standard wafers. The deposition system has been described in detail elsewhere6 . The films were deposited on to Si, NaCl, Al or C substrates located at four different positions on the sample holder. In the case of the silica films this allowed the arrival rates to be varied by a factor of 2.3 so that the effect of deposition rate on the composition could be investigated. The chamber was evacuated to a pressure of better than 10' Pa using a diffusion pump. Prior to deposition the target was sputter cleaned using I keV Ar' in an oxygen free environment for at least 20 minutes, during which the sam
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