Fluorinated Amorphous Carbon Thin Films: Analysis of the Role of the Plasma Excitation Mode on the Structural and Mechanical Properties

The effects of pulsed plasma enhanced chemical vapor deposition on the thermally induced gas effusion characteristics of fluorinated amorphous carbon thin films are investigated. The main contributions to the effusion spectra are found to come from hydrogen, hydrocarbons, and CF4 . With a plasma excitation frequency of 1023 s, the film produced is relatively compact and the effusion of hydrogen-related species dominate. A strong change in the effusion characteristics for the highest on-time plasma excitation (1021 s) indicates that an interconnected network of voids is present. Strong effusion of CF4 related species is in fact found to be consistent with a surface desorption process and can only be observed when the void network dimensions are large enough. Nanoindentation measurements showed increased elasticity of the film, as well as increased hardness upon reduction of the plasma excitation period. Raman spectroscopy was applied to corroborate the effusion results, indicating a structural transition from diamond-like to polymer-like film with an increase in the plasma excitation period. Finally the microtribological properties of such types of films are presented and discussed.