The annealing effects on the structural and electrical properties of fluorinated amorphous carbon (a-C:F) thin films prepared from C6F6 and Ar plasma are investigated in a N-2 environment at 200 mTorr. The a-C:F films deposited at room temperature are thermally stable up to 250 degreesC, but as the annealing temperature is increased beyond 300 degreesC, the fluorine incorporation in the film is reduced. and the degree of crosslinking and graphitization in the film appears to be enhanced. At the annealing temperature of 250 degreesC, the chemical bond structures of the film are unchanged noticeably, but the interface trapped charges between the film and the silicon substrate are reduced significantly. The increased annealing temperature contributes the decrease of both the interface charges and the effective charge density in the a-C:F film. Higher self-bias voltage is shown to reduce the charge density in the film.