Nitrogen incorporation into hard amorphous carbon films obtained by RF plasma decomposition of CH4-N-2 gas mixtures

Recent results on the incorporation of nitrogen into amorphous hydrogenated carbon films (a-CNx:H) are reviewed. The films are deposited onto silicon substrates by rf plasma decomposition of methane-nitrogen mixtures. The samples are characterized by a combination of analytical techniques: nuclear techniques (RES, NRA, and ERDA), SIMS, infrared absorption, Raman scattering, and positron annihilation spectroscopy (Doppler broadening method). The Vickers hardness and the internal stress of the films are also determined. The results indicate that the incorporation of nitrogen increases the density of voids and induces a progressive graphitization of the films. The incorporation of nitrogen up to 11 at% reduces the internal stress of the films without significant modification of the film hardness. Results on the thermal stability of a-CNx:H films are also presented: for annealing temperatures higher than 300 degrees C, hydrogen and nitrogen losses occur as well as the graphitization of the films.