Chemical bond structure of a-C:F films with a low dielectric constant deposited from CH4/CF4

Abstract

Fluorinated amorphous carbon thin films were deposited on p-type Si(100) substrates by using an inductively coupled plasma chemical vapor deposition (ICPCVD) system with a mixture of carbon tetrafluoride (CF4) and methane (CH4) gases. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy spectra showed that the film had C-F, C-F-2,GF(3), C=CF2, and CF=CF2 bonds. The C-CF bonds induced a re-arrangement of the chemical bonds with C-F and C-F-2 as the fluorine content was increased. The C-F and C-F-2 bonds of the annealed sample decreased at 400 degreesC. The dielectric constant of the a-C:F film depends on the concentrations of the C-F-2 and the C-F-3 bonds. In the sample annealed at 400 degreesC, the relative contents of the C-F-2 and the C-F-3 bonds decreased, and the relative contents of the C-CF bond increased. The lowest relative dielectric constant of as-deposited films with a CF4/(CH4 +CF4) flow rate ratio of 75 % was about 2.6, but the dielectric constant of the sample annealed at 400 degreesC was about 3.5. Therefore, a reduction of the dielectric constant can be obtained by varying the C-F,.,, bonding configuration, as well as by incorporating fluorine atoms.