Structure characterization of carbon and fluorine-doped silicon oxide films with low dielectric constant

Carbon and fluorine-doped silicon oxide (SiO2:C,F) films with low dielectric constant have been deposited from tetraethoxysilane (TEOS), C4F8 and Ar using plasma enhanced chemical vapor deposition (PECVD) method. X-ray diffraction (XRD) analysis shows that SiO2:C,F film is amorphous. Fourier transform infrared (FTIR) spectra illustrate that the intense absorption band between l000 and 1300 cm−1 becomes broader with increasing C4F8 flow rate which indicates that the amount of fluorocarbon compound incorporated into the film increases. C 1s X-ray photoelectron spectrum reveals that the fluorocarbon compound has a high degree of cross-linked structure because of the existence of only C–F bonds. By fitting the absorption band of Si–Fn at about 940 cm−1 and Si 2p X-ray photoelectron spectrum using Gaussian profile, we can consider that there are (O–)2Si(–F)2 and (O–)3Si–F groups in the deposited films, and the former is less than the latter. The measurements of capacitance–voltage (C–V) characteristics of the films indicate that the dielectric constant of the deposited film decreased with increasing C4F8 flow rate which is in accord with the increase in the frequency of Si–O stretching mode. When the flow rate ratio of C4F8 to TEOS is equal to 1.8, the dielectric constant of the film amounts to 2.35 at 1 MHz.