Study of an atmospheric pressure glow discharge (APG) for thin film deposition

We studied a homogeneous atmospheric pressure dielectric barrier discharge in helium with small admixtures (<10−3) of hexamethyldisiloxane (HMDSO) vapor for the deposition of thin silicon organic films on a technical aluminum sheet metal. The powered (100 kHz) plane electrode (80×15 mm2) is covered by a glass insulator layer. Power absorption, sustaining voltage (2 kVpp), gap voltage (700 V), current density (∼20 mA cm−2), and total light emission are monitored to characterize the discharge in the gap (1–1.5 mm). The gas composition of the exhaust gas is studied by mass spectrometry. During discharge operation a decrease of the precursor concentration is observed, due to dissociation and thin film deposition. Typical deposition rates range from approximately 0.2 to 2.0 nm s−1, as measured by substrate weighing. The films display water contact angles of 63±3°. A protection of the Al sheet metal against 0.1n-NaOH for 3 min is observed. FT–IR (dominant SiOSi band) and XPS (low C content) measurements both reveal the dominance of non-organic components in the film. The spatially averaged electron concentration (2×1011 to 5×1011 cm−3) is experimentally determined by heterodyne interferometry. Discharge properties and thin film deposition are discussed in relation to the ionization rate of the precursor molecules and the current density.