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 x 15 mm(2)) is covered by a glass insulator layer. Power absorption, sustaining voltage (2 kV(pp)), gap voltage (700 V), current density ( similar to 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 +/- 3degrees. 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 x 10(11) to 5 x 10(11) 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. (C) 2002 Elsevier Science B.V. All rights reserved.