Use of organosilicate precursors for transparent coatings on organic substrates by plasma CVD

This work discusses the production of transparent coatings of SiOxCy on substrates polycarbonated by PECVD at temperatures below 80oC, with a gaseous mixture using different precursors with which, in similar processes produced the same results with respect to the coating obtained, with the same excellent quality and in accordance with international standards for optic coatings. Chlorinated precursors were excluded because they are highly corrosive as well as those with operating risks (toxic or explosive). The precursors used were tetraethyl orthosilicate (TEOS), tetramethylsilanete (TMS,) tetramethoxy silane (TMOS), hexamethyldisilizane (HMDS), and methyltrimethoxysilane (Z6070), with the contribution of O2 and methane as reactive gases. Fourier transform infrared spectroscopy (FTIR) was used as well as X-ray generated photoelectron spectroscopy (XPS/ESCA). The functional groups were studied together with the film elements and its mechanical properties, transparency and refraction index. Irregardless of the precursor used, by properly modifying the process variables (pressure of the gaseous mixture, radio frequency power, relationship of processing gases and their flow), similar coatings can be chemically obtained, having the same morphology and, therefore, with identical adherence, structural and optic properties. None of the works consulted refer to the possibility of the indistinct use of different precursors for obtaining the same coating. These results are relevant when considering the difference in costs and their market availability. The influence of the addition of methane was studied in two processing variants, a) with oxygen and methane and b) with oxygen alone. For all the precursors used and with identical processing conditions, the carbon contributed by the addition of methane increased the concentration of carbon compounds, considerably reducing the presence of silanol, which being absorbent produces structural instability and cracking of the coating, noticeably improving the properties of the coating obtained. The use of methane as a reactive gas is also not mentioned in the works consulted (CW)