AbstractFluorinated amorphous carbon (a-C:F) thin films were deposited by inductively coupled plasma enhanced chemical vapor deposition (ICP-CVD) with increasing CF4:CH4 gas flow rate ratio, and then annealed with increasing annealing temperature (100, 200, 300, and 400.). We have found the reduction mechanism of the dielectric constant and the thermally stable condition for the a-C:F films. On the basis of the results, the optimal condition to satisfy both the low dielectric constant and the thermal stability is followed as; the a-C:F films have to have the compatible F content to make a compromise between the two properties; the C-Fx bonding configuration has to exist as a form of C-F2 & C-F3 instead of C-F; The films should be somewhat cross-linked structure.