Insights into the Atmospheric Pressure Plasma- Enhanced Chemical Vapor Deposition of Thin Films from Methyldisiloxane Precursors

his work describes the plasma-enhanced chemical vapor deposition of thin films at atmospheric pressure using dielectric barrier discharges fed with argon, oxygen and different methyldisiloxanes, i.e., hexamethyldisiloxane, pentamethyldisiloxane, and 1,1,3,3-tetramethyldisiloxane. The influence of the methyldisiloxane chemical structure and of the oxygen/methyldisiloxane feed ratio is investigated in order to provide insights into the organosilicon plasma chemistry at atmospheric pressure. As expected the FT-IR and XPS analyses show that the carbon content of the coatings depends on the number of methyl groups in the precursor molecule; in the case of coatings obtained with PMDSO and TMDSO carbon removal seems to be further enhanced by the presence of Si-H bonds. Gaschromatography-mass spectrometry analyses of the exhaust gas allow to assess the precursor depletion and to perform the quali-quantitative determination of by-products (e.g., silanes, siloxanes, silanols) formed by plasma activation. The results are exploited to rise hypotheses on the contribution of the different reaction pathways on the deposition mechanism.