We have investigated plasma fluorination of hydrocarbon polymer films spincoated onto silicon wafers. Fluorinated hydrocarbon polymers gave low dielectric constants of 2.0 – 2.4 which was close to that of PTFE. However, the thermal stability of these fluorinated polymers inferior to that of the non-fluorinated polymers. We believe that this is due to a decrease in the molecular weight resulting from C-C bond cleavage. We think that such a side reaction will be controlled by removing residual oxygen in a fluorination chamber. The molecular structures of the fluorinated polymers were analyzed by X-ray photo emission spectroscopy. Finally, we proposed direct patterning of interlayer dielectrics using plasma fluorination.