Internal r.f. plasma parameters correlated with structure and properties of deposited hydrocarbon films

Hydrogenated amorphous carbon films (a-C:H) have been prepared by r.f. plas ma deposition from a C3H8-Ar gas mixture. Visible, infrared and Raman spect roscopy as well as electrical measurements are reported and used to charact erize the bonding and electronic properties of these films. The gas phase d ischarge has been investigated by Langmuir probe and by optical emission sp ectroscopy diagnostics. Under constant self-bias voltage and total pressure , variations in the propane partial pressure brought into evidence the infl uence of gas phase scission of hydrocarbon bonds on the growth process and the layer composition. The change appears with the increase of the: propane partial pressure, which leads to a decrease of both electron temperature a nd electron density. Simultaneously, CH optical emission increases with res pect to the carbon emission. The decrease in the electron temperature resul ts in a decrease of the discharge efficiency to break CW and carbon bonds, and thus, in a decrease of carbon atom production in the gas phase. The for mation of more hydrogenated radical precursors, as a consequence of the abo ve, enhances the plasma polymerization process with respect to graphitic nu cleation. Films deposited at high electron temperatures were found to conta in a large amount of graphite, while those prepared at lower temperatures w ere found to be polymer-like, with a high hydrogen content. (C) 2000 Elsevi er Science S.A. All rights reserved.