Low-temperature PECVD of transparent SiOxCyHz thin films

Hybrid organic/inorganic SiOxCyHz thin films are prepared on Cu, Si(100), and SiO2 substrates by plasma-enhanced (PE)CVD using tetramethoxysilane (TMOS) as the precursor compound. Depositions are performed from Ar plasmas at temperatures as low as 60 °C, avoiding the use of oxidizing reagents in view of possible film application as protective coatings against substrate oxidation. In situ monitoring of deposition processes is performed using laser reflection interferometry (LRI), which provides valuable information on the growth rate as a function of the adopted synthesis conditions. The obtained film thickness values are confirmed by scanning electron microscopy (SEM), which is also used to investigate the film morphology and its adhesion to the substrate. The chemical structure and composition are investigated in detail by a combined use of energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Glancing incidence X-ray diffraction (GIXRD) and UV-vis spectroscopy are used for the study of the structural and optical properties of the system. Finally, nanoindentation measurements permit the evaluation of the hardness of the synthesized coatings. Amorphous layers with a silica-like network incorporating covalently bonded methyl and methoxy groups are obtained under very mild synthesis conditions. Furthermore, the coatings are characterized by good substrate conformal coverage and remarkable optical transparency.