Structural and optical properties of amorphous hydrogenated fluorinated carbon films produced by PECVD

Fluorinated films were deposited from radiofrequency discharges of toluene/trifluorotoluene and toluene/sulfur hexafluoride mixtures. Actinometric optical emission spectroscopy was used to determine trends in the concentrations of the plasma species H, CH, and F as a function of the partial pressure of trifluorotoluene or sulfur hexafluoride present (expressed as a percentage of the total chamber pressure) designated R-T and R-s, respectively. Transmission infrared spectrophotometry and electron spectroscopy for chemical analysis revealed that the films contain various fluorine-containing functionalities and that the degree of fluorination increases as R-T or R-s is increased. Ultraviolet-visible spectrophotometry of films deposited at various values of R-T and of R-s allowed the determination of the absorption coefficients ct of the films. From plots of ct as a function of photon energy it was possible to calculate the optical gap (E-04). An intriguing result was a decline and subsequent rise in E-04 as R-s was increased. Molecular modelling using ZINDO/PM3 calculations provided a semi-quantitative explanation of the dependence of E-04 on R-s. (C) 1997 Elsevier Science S.A.