Fluorinated amorphous diamond-like carbon films deposited by plasma-enhanced chemical vapor deposition

Fluorinated amorphous diamond-like carbon films (a-C:F) have been prepared on room-temperature (100) Si substrates by using 13.56 MHz radio frequency plasma-enhanced chemical vapor deposition (rf PECVD), where methane (CH₄) and carbon tetrafluoride (CF₄) were used as gas precursors. The films were deposited as a function of the ratio of CF₄ to CH₄ flow rate (CF₄/CH₄) at 60 and 100 W rf power, respectively. During the film preparation, two processes, i.e., deposition coming from CH₄ and etching induced by CF₄, always coexist. The competition between both, mainly dependent on the CF₄/CH₄ ratio and the rf power, influenced the film surface, thickness, bonding states between C and F, microstructure, the incorporation level of F, and therefore the properties. The F content was found to rapidly increase to ∼12 at.% with the introduction of CF₄, leading to a sharp reduction in surface energy of the samples compared with that of diamond-like carbon (DLC) film. With increasing CF₄, the F content increased, concurrent with increase in - CF, appearance to increase in - CF₂ content, and variation from diamond-like to graphite-like in microstructure, as disclosed by X-ray photoelectron spectroscopy (XPS) and Raman analyses, respectively. Such change in the bonding configurations is also responsible for a continuing reduction in the film surface energy with increasing F incorporation.