Hydrogenated and nitrogenated amorphous carbon films, a-C:H and a-C:H:N, were elaborated by Plasma Enhanced Chemical Vapor Deposition (PECVD) in a dual Electron Cyclotron Resonance - Radio Frequency (ECR-RF) discharge of methane and/or nitrogen. The use of a low pressure plasma (2.6 mTorr) and a capacitive coupling of the substrate, separately from the electrical power of the ECR source, leads to reach new conditions of preparation. The ions and radicals fluxes, Φ_i and Φ_R, determined respectively from the Langmuir probe measurements and the Mass Spectrometry (MS) give a ratio Φ_R/Φ_i of order of 20. The CH_3 radicals were identified and their concentration was measured from the technique of threshold ionization. It is shown that, even at low pressure, numerous ion-molecule reactions take place in the gas phase which explain the formation of major ions CH_5~+ and C_2H_5~+. The plasma-surface interaction is studied by in-situ kinetic ellipsometry and by ex-situ X-ray Photoelectron Spectroscopy (XPS) measurements of deposited films. The role of the impact energy of ions, during the growth of films, is studied by Ultra-Violet-Visibte spectroscopic ellipsometry. A new technique of deposition by alternating sequences of ? CH_4 deposition - treatment by N_2 plasma ? is described in this paper. The resulted a-C:H:N films are compared to those elaborated from CH_4-N_2 plasmas. The aim of the discussion on the presented results is to better understand the mechanism of the growth of amorphous carbon films by PECVD.
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