Fluorinated amorphous carbon thin films (a-C:F) are deposited using inductively coupled plasma chemical vapor deposition with various flow-rare ratios of CH4:CF4 gases for ultralarge-scale integrated intermetal dielectric applications. The accurate composition of the thin films are quantitatively analyzed using elastic recoil detection-time of flight. The incorporation of fluorine is saturated at about 25 atom % by increasing the CF4 flow rate. The dielectric constant decreases to 2.4 and the refractive index of the film is reduced to 1.35 as the CF4 flow rate increases. Also, it is observed that the C-F bonding configuration changes from an unsaturated C-F bond to C-F-2 and C-F-3 bonds with growing CF4 flow rate. Thus, the reduction mechanism of the dielectric constant can be obtained by variation of the C-F, bonding configuration as well as the incorporation of fluorine.