Structural, mechanical, and nanoscale tribological properties of nitrogen-incorporated fluorine-carbon films

Nitrogen incorporation into hard fluorinated carbon films deposited by rf-plasma decomposition of CH4-CF4-N2 mixtures was studied as a function of the self-bias voltage. The self-bias voltage, Vb, which was controlled by the rf power input, ranged from −100 to −600 V. The structural and chemical characterization of the films was performed by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and ion beam analysis (IBA). The film hardness was measured by nanoindentation and the internal stress determined from the bending of the substrate. The friction behavior was investigated by atomic force microscopy in lateral force mode. The film composition and the chemical ambient of carbon and nitrogen atoms were independent of Vb as revealed by IBA and XPS, respectively. In particular, the absence of F-rich CFn groups, together with the low H and F content, suggests a high degree of interconnectivity of the film network in agreement with hardness and stress values. Raman results suggest that polymer-like films were obtained at −100 V and that more graphitic structures were obtained for films deposited at −600 V. The atomic density, hardness and internal stress are strongly dependent on the self-bias voltage, presenting a broad maximum in the range of −270 and −420 V. These results confirm the importance of the ion bombardment during film growth on the mechanical properties of the films. The friction coefficient was independent of the self-bias voltage.