Film growth and relationship between microstructure and mechanical properties of a-C:H:F films deposited by PECVD

Results of a systematic investigation on the effects of some deposition parameters (partial pressure of CF, and self-bias voltage) on the microstructure, mechanical and tribological properties of a-C:H:F films are presented. The films were deposited by r.f.-PECVD using CH4-CF4 mixtures. The film composition was measured by ion beam analysis and, combining these results with the film thickness, the film density was determined. The structural arrangement was probed by Raman spectroscopy and the chemical bonding was investigated by infrared absorption and X-ray photoelectron spectroscopies. The hardness was measured by microindentation and the internal stress was determined by measuring the changing of the substrate curvature after the film deposition. The friction coefficient was measured by lateral force microscopy. The results indicate that the properties of a-C:H:F films are controlled by the ionic bombarding during the film growth. For a fixed self-bias, the increase of the CF, partial pressure leads to a transition from diamond-like to a polymer-like structure, to a higher fluorine incorporation and to a decrease of both hardness and internal stress. The friction coefficient decreases too. The fluorine incorporation also increases with the increase of the self-bias and was associated to higher plasma decomposition. Fluorine-poor polymer-like films were deposited at low self-bias (-50 V). In both situations, fluorine incorporation occurs at the expenses of the hydrogen content and the reduction of the energy of the bombarding species results in less dense and soft films with a polymer-like structure. (C) 2001 Elsevier Science B.V. All rights reserved.