Structural and mechanical characterization of fluorinated amorphous-carbon films deposited by plasma decomposition of CF4–CH4 gas mixtures

Abstract

Fluorinated amorphous-carbon films $\mathrm{(a-}\mathrm{C:F:H})$ were deposited by low-power rf capacitively coupled plasma-enhanced chemical-vapor deposition using ${\mathrm{CH}}_{\mathrm{4}}{\mathrm{–CF}}_{\mathrm{4}}$ gas mixtures. Different series of films were deposited, changing one parameter at a time: the ${\mathrm{CF}}_{\mathrm{4}}$ partial pressure from 0% to 100%, the self-bias voltage from −50 to −700 V, and the total deposition pressure from 5 to 15 Pa. The composition was determined by ion-beam analysis (IBA): Rutherford backscattering spectrometry, elastic recoil detection analysis, and nuclear reaction analysis. The atomic density of the films was evaluated by combining the IBA results with the thickness value measured by stylus profilometry. Film structure was investigated by infrared transmission and Raman scattering spectroscopies. The internal stress and Vickers hardness were also measured. For a fixed self-bias, the increase of the ${\mathrm{CF}}_{\mathrm{4}}$ partial pressure leads to a higher fluorine incorporation and the decrease of both hardness and internal stress. The film microstructure changes from diamond-like to a polymer-like structure. The fluorine incorporation also increases with the self-bias, and fluorine-poor polymer-like films are deposited at low-bias voltage. Fluorine incorporation occurs at the expense of the hydrogen content in both cases, i.e., increasing the ${\mathrm{CF}}_{\mathrm{4}}$ partial pressure or the self-bias. Finally, the role of ion bombardment during film growth on the mechanical and structure properties of the films is discussed.