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

Fluorinated hydrogenated amorphous carbon films were grown by plasma-enhanc ed 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-B while the CF4 partial pressure in CH4/CF4 gas mixtures was change d from 0 to 80%. For the second one, a fixed 2:1 CF4/CH4 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 pro bed by Raman spectroscopy, The increase of both the CF4 partial pressure an d the \V-B\ leads to an increase of the fluorine concentration within the h im, 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 va lues investigated. In particular, the C-F-n band grows for higher CF4 parti al pressures, while it is negligible in the self-bias study. The analysis o f the Raman spectra shows that a progressive structural modification from a diamond-like towards a polymer-like material occurs for higher CF4 partial pressures as well as for lower \V-B\. This trend is accompanied by a notic eable broadening of the Cls WS peak on the side of lower binding energies. (C) 2001 Elsevier Science B.V. All rights reserved.