Fluorinated silicon oxide films were prepared in a plasma enhanced chemical vapor deposition reactor using TEOS, O2, and either C2F6 or NF3. Properties such as deposition rate, film refractive index, dielectric constant, density, and fluorine concentration were investigated as a function of experimental conditions. Based on nuclear reaction analysis (NRA) and Fourier Transform Infrared (FTIR) measurements, no single linear relationship was found between fluorine concentration or film density and dielectric constant. Special attention was paid to the interaction of fluorine with metals. NRA and X-ray photoelectron spectroscopy (XPS) depth profiles showed that fluorine diffuses rapidly through aluminum and piles up at the free surface. The effect of various plasma treatments was investigated to passivate the surface of fluorinated silicon oxide. CF4 - O2 plasma treatment of the fluorinated oxide before aluminum deposition produced significant improvement in inhibiting fluorine diffusion into aluminum without increasing the dielectric constant.