Carbon-doped SiO 2 :F films were deposited by adding CH 4 gas to SiH 4 /O 2 /CF 4 gas mixtures using a plasma-enhanced chemical vapor deposition method. As CH 4 is added increasingly, the dielectric constants, ε s , of the films decreased and were stabilized as manifested by a decreased change in ε 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 CH 3 bonds in SiO 2 :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.