Fluorinated amorphous carbon (a-C:F) thin films were prepared using CH, and CF, gases by plasma chemical vapor deposition (CVD) method. The basic properties of these films were investigated by electron spin resonance (ESR), infrared (IR) absorption, optical absorption, X-ray photoelectron spectroscopy (XPS) and dielectric constant measurements. XPS measurement revealed that the fluorine concentration of the CVD film increased to approximately 67 at.%. In one film, the CF, mode appeared in the IR spectrum and the hydrogen-related modes disappeared. The dielectric constant of the film was estimated to be 2.2 at 1 MHz. The ESR spectra revealed that the carbon dangling bond density and the line width increased with increasing fluorine concentration. The increase in the dangling bond density and the larger line width of the ESR spectrum are attributed to the larger atomic radius of fluorine compared to that of hydrogen and to the hyperfine interaction between the dangling bonds and the fluorine nucleus, respectively. On the other hand, the g-value and the optical band gap remained unchanged with increasing fluorine concentration. This result is consistent with the fact that the g-value is dominated by the band state. We also discuss the effect of deposition temperature on the film properties. (C) 1998 Elsevier Science B.V. All rights reserved.