Synthesis and characterization of inorganic silicon oxycarbide glass thin films by reactive rf-magnetron sputtering

Silicon oxycarbide glasses have been of interest because of the potential range of properties they might exhibit through a change in carbon-to-oxygen ratio. They are metastable materials and, as such, their structures and properties are very dependent upon the synthesis method. Silicon oxycarbide bonding has been seen in materials made by melting, oxidation, polycarbosilane or sol/gel pyrolysis, and chemical vapor deposition. In this work, the radio-frequency reactive sputtering of silicon carbide targets was explored for synthesis of amorphous silicon oxycarbide thin films. Si O(2-2x) Cx films, with a continuous range of compositions where 0≤x≤1, were deposited by controlling the amount of oxygen present in the plasma with a SiC target. This resulted in a density range from 1.9 to 2.8 g cm3 and a range of refractive indexes from 1.35 to 2.85. Analysis of the film compositions, structures, and properties were performed using x-ray photoelectron spectroscopy, infrared spectroscopy, nuclear magnetic resonance, profilometry, electron microscopy, grazing incidence x-ray reflectivity, and UV-visible transmission and reflection. The compositional range obtainable by this rf sputtering method is much wider than that of other synthesis methods. It is shown here that for oxygen-to-carbon ratios between ∼0.10 and 10.0, silicon oxycarbide bonding comprises 55%-95% of the material structure. These sputter-deposited materials were also found to have significantly less free carbon as compared to those produced by other methods. Thus, the unique properties for these novel oxycarbide materials can now be established.