Effects of dilution gas on characteristics of SiOC(H) films synthesized by atmospheric pressure plasma CVD

In this study, we synthesized SiOC(H) films by atmospheric pressure plasma enhanced CVD from trimethylsilane and oxygen gas diluted by helium, argon and nitrogen. We changed the oxygen flow rate and investigated the effect of dilution gas on the hardness of the films. The deposition rate for both helium and argon dilution increased with increasing the oxygen flow rate up to 100 ml/min. The hardness of the films diluted by argon gradually increased from 0.2 GPa to 1.1 GPa with an increase of oxygen flow rate while that of the films diluted by helium was hardly changed about 0.6 GPa. The films diluted by nitrogen exhibited high hardness at 2.3 GPa, which was highest value among the samples. The FT-IR spectra of the films showed the peaks corresponding to terminal methyl and hydroxyl bonds along with the stretching vibrations of SiOSi network bonding were observed and their intensities varied with the hardness of the films. As the oxygen flow rate increased, intensity of methyl bond decreased and that of hydroxyl bond was not increased different from the result of the films diluted by argon or helium gas. The methyl bonds are likely to prevent oxygen atom from forming SiOSi structures. The existence of terminated bonds such as methyl bond and hydroxyl bond lead to low hardness of the films. From the result of optical emission spectroscopy, peaks of nitrogen-oxygen radicals were observed at plasma diluted by nitrogen, while a large amount of oxygen radical were generated in the plasma diluted with noble gas.