Structural and optical properties of r.f.-sputtered SixC1 − x:O films

Oxygenated silicon-carbon alloy (Si x C 1 − x :O) films have been prepared by reactive r.f. sputtering. These films were deposited, in a gas mixture of argon and oxygen, from a composite target consisting of a silicon disc on which graphite chips had been placed. The structural and optical properties have been investigated using infrared (IR) spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and visible-near-infrared optical absorption. XPS as well as IR measurements show that the films are essentially composed of silicon, carbon and oxygen as expected. The atomic fractions of these elements, deduced from quantitative XPS analysis, are of the order of 50%, 28% and 22% for Si, C and O atoms respectively. A study of the chemical shifts of C 1 s and Si 2p core level spectra reveals that the films contain not only Si atoms bound to C and O but also free silicon and free carbon clusters. The Raman spectroscopy results confirm the presence of free silicon and indicate that the films are amorphous. The optical gap of these films is around 1.3 eV and the refractive index is found to follow the Sellmeier law with a value of about 2.05 at λ = 2 μm.