In this work, we study the thermal stability and interaction between SiOF and Cu. Blanket SiOF films with various F concentration were deposited by PE-CVD. A dielectric constant as low as 3.2 was obtained. Copper were deposited on these SiOF and a series of post-deposition anneal were performed. Dielectric constant of SiOF was measured after deposition and again after anneal. AES and SIMS depth profile are utilized to determine the interdiffusion between Cu and SiOF under different annealing conditions. Breakdown voltage and dielectric constant were determined form C-V and I-V measurement using a MIS ( Cu/ SiOF/ p-Si) diode. This results of leakage current measurement and flat band shift measurement suggest that the fluorine in the SiOF film will retard the cu diffusion.