Effects of the plasma oxygen concentration on the formation of SiOxCy films by low temperature PECVD

Experiments were made to produce SiOxCy coatings by PECVD on polycarbonate substrates at a temperature below 80 °C, using a gaseous mixture of methyltrimethoxy-silane (MTMOS) [CH3Si(OCH3)3] with O2 and CH4. Under those conditions, the effects of the oxygen concentration in the plasma on the film thermal shock and long-term stability, hardness and growth rate were studied using Fourier transform infrared absorption spectrocopy (FTIR) and optical emission spectroscopy (OES). It is concluded that for given deposition conditions there is an optimum oxygen concentration in the plasma compatible with films presenting a best compromise in terms of the indicated properties, which is determined essentially by a competition between the reaction rates at the substrate surface for Si–O–Si formation and Si–OH elimination by dehydration reactions, and the deposition rate of silanol groups formed in the plasma phase. The overall results suggest that this competition is sensitive to the plasma electron temperature.