Fluorinated amorphous carbon films (a-F : C) were deposited by high-density plasma-chemical vapor deposition (HDP-CVD) using C 4 F 8 and CH 4 as precursors. The deposition process was performed at two temperatures: $200 and $3508C. In order to study the thermal stability of the films, the samples were annealed at 400 or 5008C for 30 min in an N 2 ambience. We have found that the films deposited at $3508C were more thermally stable than those deposited at $2008C. Both deposition conditions produced a-F : C films with a C : F ratio of 1.7 and a very low content of H; The bonding types identified by XPS were C-C/C-H, C-CF, CF-CF and C-F in all the a-F : C films and in addition CF 2 bond was found in the as-deposited films deposited at $2008C. The films' composition was maintained after annealing at 4008C. However, after 5008C annealing, in the low-temperature deposited films, F out-diffusion was observed in large amounts compared to the very small changes observed in the high-temperature films. The a-F : C films remained amorphous at least up to 5008C. The dielectric constant of the low-temperature deposited films was $2.7 after 4008C annealing, and increased after 5008C anneal to $9.3. The high-temperature deposited films had a higher dielectric constant of $2.7-3, remaining stable after the various thermal treatments employed. These results indicate a trade-off between thermal stability and lowering the dielectric constant.