The chemical bond structure and electrical properties of a-C:F films by post-annealing treatment

Fluorinated amorphous carbon films (a-C:F) were deposited on a p-type Si (100) substrate 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 spectra showed that the film has C-F, C-F2, C-F3, C=CF2 and C-F2 bonds. The C-CF and C-CF2 bonding modes increased as the fluorine content was increased. The C-F and C-F2 bonds of the annealed sample decreased at 400 deg.C. The dielectric constant of the a-C:F film depends on the concentration of C-F2 and C-F3. In the sample annealed at 400 deg. C., the relative contents of the C-F2 and the C-F3 bonds decreased. The lowest dielectric constant of as-deposited films with a CF4/(CH4+CF4) flow rate ratio of 83% was about 2.43, but the dielectric constant of the sample annealed at 400 deg.C was about 3.5. Therefore, a reduction of the dielectric constant can be obtained by varying the C-Fx bonding configurations, as well as by incorporating fluorine atoms. (author)