Fluorine incorporation into amorphous hydrogenated carbon films deposited by plasma-enhanced chemical vapor deposition: structural modifications investigated by X-ray photoelectron spectrometry and Raman spectroscopy

Abstract

Fluorinated hydrogenated amorphous carbon films were grown by plasma-enhanced chemical vapor deposition (PECVD). Two sets of films were deposited. For the first set, the self-bias voltage ( V B) was kept constant and equal to −350 V, while the CF 4 partial pressure in CH 4/CF 4 gas mixtures was changed from 0 to 80%. For the second one, a fixed 2:1 CF 4/CH 4 proportion in the precursor atmosphere was employed while V B was varied from −50 V to −500 V. The carbon chemical environment was investigated by X-ray photoelectron spectroscopy (XPS), while structural changes in the carbon matrix were probed by Raman spectroscopy. The increase of both the CF 4 partial pressure and the | V B| leads to an increase of the fluorine concentration within the film. While in the first case the increase of the fluorine content leads to a relative increase of the CF n XPS bands, in the second one the relative intensity of the CF n bands are nearly the same within the range of V B values investigated. In particular, the CF 2 band grows for higher CF 4 partial pressures, while it is negligible in the self-bias study. The analysis of the Raman spectra shows that a progressive structural modification from a diamond-like towards a polymer-like material occurs for higher CF 4 partial pressures as well as for lower | V B|. This trend is accompanied by a noticeable broadening of the C1s XPS peak on the side of lower binding energies.