Compositional and structural properties of deuterated plasma enhanced chemical vapour deposited silicon-carbon alloys

Hydrogenated and deuterated amorphous silicon carbon films were prepared by plasma enhanced chemical vapour deposition (PECVD) starting from silane an d deuterated methane gas mixtures. The gas percentages was varied in order to produce films with different carbon and silicon content. The elemental c omposition was determined by Rutherford backscattering and elastic recoil d etection analysis and the bonding structure by infrared spectroscopy. The h ydrogen plus deuterium atomic fraction, in the grown films, is about 0.36, almost independent of the film composition. However, the concentration of h ydrogen or deuterium depends on the carbon content. In silicon-rich samples both hydrogen and deuterium atoms are contained in the films, with increas ing carbon content, the hydrogen concentration decreases-and the deuterium concentration increases. At the highest carbon concentration (0.28) the res ulting films are fully deuterated with the deuterium atoms attached both to silicon and carbon. From infrared absorption analysis, information on plas ma chemistry and surface or bulk reactions during film growth was obtained. For the first time the experimental determination of the origin of the bon ded hydrogen in amorphous SiC:H films, grown by methane-silane PECVD, is re ported. Comparison of elemental composition and infrared spectra of films g rown from hydrogenated and deuterated methane shows that hydrogen exchange occurs between carbon and silicon atoms. Moreover, as the films approach st oichiometry the hydrogen incorporated into the sample originates mainly fro m methane gas.