Nitrogen doped fluorinated amorphous carbon thin films for low dielectric constant interlayer dielectrics have been investigated. The films were deposited with a parallel-plate plasma enhanced chemical vapor deposition. Source gases were CH4, CF4, and N2. The thermal stability of the films can be improved by the addition of N2. X-ray photoelectron spectroscopy (XPS) measurement revealed that the C-N bonds were formed in the films with the addition of N2. The dielectric constant of the films was increased from 2.1 to 2.4 at the nitrogen concentration of 10%.