Properties of fluorinated amorphous diamond like carbon films by PECVD

Fluorinated amorphous diamond-like carbon films (a-DLC:F) were prepared on room-temperature Si(1 0 0) substrates using radio frequency plasma enhance chemical vapor deposition (rf PECVD) by varying the ratio of carbon tetrafluoride and methane (CF ₄ :CH ₄ ). The films formed were investigated in terms of the surface morphology, chemical composition, microstructure, mechanical properties, and surface free energy by means of atomic force microscopy (AFM), X-ray photoelectron spectrum (XPS), micro-scratch test, nano-indenter test and contact angle measurement. Emphasis was placed on investigation of the factors affecting the film surface energy, which was calculated from three methods (the harmonic mean equation, the geometric mean equation and acid-base equation). It was observed that with increasing CF ₄ :CH ₄ , the roughness and F content of the a-DLC:F films increased while the hardness, Young's modulus and surface energy decreased. The films also became more graphitized. The reduction of the film surface energy with varying F content is believed to be mainly due to the change of bonds in the film, i.e. the decrease of -C-CF bond and corresponding increase of -CF, -CF ₂ . The roles of the roughness and the microstructure in affecting the film surface energy were negligible.