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.3044167114915

Semi-empirical modeling of the optical gap of amorphous hydrogenated nitrogenated carbon films

We report here results of modeling the optical gap of amorphous hydrogenated nitrogenated carbon films using semi-empirical methods. Parametric Method 3 (PM3) was used to optimize the geometry of oligomers. Using the PM3 geometrical data, Zerner's intermediate neglect of differential overlap calculations were carried out to simulate the absorption spectra of the films. We have analyzed the optical gap values as a function of the geometry and elemental composition of these materials. The theoretical results are contrasted with the experimental ones and used to estimate the actual conformations of the amorphous materials. The results indicate that this approach can be an efficient tool to analyze amorphous carbon films. (C) 2000 American Vacuum Society. [S0734-2101(00)08705-4].1852466247