Atmospheric pressure plasma deposition of thin films by Townsend dielectric barrier discharge

The aim of this study is to contribute to the understanding of the thin film growth mechanism using an Atmospheric Pressure Townsend-like Discharge (APTD). Films obtained in dielectric barrier discharges fed with N2 and small admixtures of hexamethyldisiloxane (HMDSO) and nitrous oxide (N2O) as oxidizer gas have been investigated. Results are compared to those obtained with SiH4, in similar conditions. The discharge dissipated power and the feed composition ([N2O]/[HMDSO] ratio) on film properties have been investigated by means of Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS) and Ellipsometry. The film thickness homogeneity and deposition rate have been measured by means of a profilometer and an ellipsometer at the same time. Then silicon oxide thin film properties obtained with SiH4 and HMDSO containing APTD are compared. Concerning chemical composition results are similar. In the two cases, a rather low adding of N2O allows to get SiOx layer without N and C incorporation. Si–OH bounds are always observed. The relative contribution of homogeneous and heterogeneous growth mechanisms is very dependent on the nature of the precursor. Because of its high reactivity, SiH4 induces particles formation in the plasma. These particles are efficiently included in the coating, decreasing drastically the layer density. Thin films made with HMDSO are always dense.