Influence of plasma source frequency on composition and density of fluorinated amorphous carbon thin films

Different types of fluorinated amorphous carbon (a-C:H:F) thin films were grown from CH(4)/CF(4)/Ar mixtures using a 13.56 MHz radiofrequency and a 13.56 MHz radiofrequency-2.45 GHz microwave hybrid plasma source. Comparison of X-ray photoelectron spectroscopy (XPS) and X-ray reflectivity (XRR) allowed us to determine the film hydrogen concentration, which depends on the plasma source used, and showed that, independently of the plasma source employed, the fluorine incorporation occurs at the expenses of the hydrogen content. Moreover, films with lower fluorine content were deposited from the radiofrequency-microwave hybrid technique. XRR measurements suggested that with increasing fluorine content, the film density changes indicating a phase transition towards an open and less cross-linked structure. For a fixed gas mixture composition, the deposition of less dense films grown by radiofrequency-microwave hybrid plasma source is probably associated to a different plasma decomposition and lower energy of the bombarding species.