The effect of a post plasma treatment on the dielectric properties and reliability of fluorine doped silicon oxide (SiOF) films deposited by electron cyclotron resonance chemical vapor deposition (ECRCVD) was studied. Also, the thermal stability of an electrodeposited Cu / sputtered Ta interconnect system with SiOF intermetal dielectrics was examined by annealing in a vacuum furnace. The stability of the dielectric constant of SiOF films was improved by O2 post plasma treatment. Surface modification by the plasma treatment was effective in prevention of water absorption. The Cu/Ta/SiOF/Si system was thermally stable at least up to 500°C for 3h. For the Cu/Ta/SiOF/Si multilayer structure, the plasma treatment seemed to play a big role in suppressing the interdiffusion between SiOF and metal interconnects. By C-V measurement, the electrical stability of the Cu/Ta/SiOF/Si multilayer structure was found to be stable up to 500°C for 2 h.