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

Hydrogenated and deuterated amorphous silicon carbon films were prepared by plasma enhanced chemical vapour deposition (PECVD) starting from silane and deuterated methane gas mixtures. The gas percentages was varied in order to produce films with different carbon and silicon content. The elemental composition was determined by Rutherford backscattering and elastic recoil detection analysis and the bonding structure by infrared spectroscopy. The hydrogen plus deuterium atomic fraction, in the grown films, is about 0.36, almost independent of the film composition. However, the concentration of hydrogen or deuterium depends on the carbon content. In silicon-rich samples both hydrogen and deuterium atoms are contained in the films; with increasing carbon content, the hydrogen concentration decreases and the deuterium concentration increases. At the highest carbon concentration (0.28) the resulting films are fully deuterated with the deuterium atoms attached both to silicon and carbon. From infrared absorption analysis, information on plasma chemistry and surface or bulk reactions during film growth was obtained. For the first time the experimental determination of the origin of the bonded hydrogen in amorphous SiC:H films, grown by methane-silane PECVD, is reported. Comparison of elemental composition and infrared spectra of films grown from hydrogenated and deuterated methane shows that hydrogen exchange occurs between carbon and silicon atoms. Moreover, as the films approach stoichiometry the hydrogen incorporated into the sample originates mainly from methane gas.