Carbon-doped SiO2:F films were deposited by adding CH4 gas to SiH4/O-2/CF4 gas mixtures using a plasma-enhanced chemical vapor deposition method. As CH4 is added increasingly, the dielectric constants, epsilon(s), of the films decreased and were stabilized as manifested by a decreased change in epsilon(s) after air exposure for 1 week, indicating a significant improvement in the water resistivity of the films. It is proposed that the improved water resistivity is correlated with a decrease in the peak frequency of the Si-O stretching absorption and with formation of Si-CH3 bonds in SiO2:F:C films, along with an increase in the film density. These dielectric and vibrational properties were analyzed in terms of a difference in the electronegativity of the constituent atoms.