We implanted 300keV Xenon in silicon oxide at doses ranging from 1x1016 to 5x1016/cm2. For the first time, we reported the formation and the thermal evolution of bubbles/cavities in SiO2. Characterization by cross-section transmission electron microscopy (XTEM) and Rutherford backscattering spectrometry (RBS) showed that bubbles/cavities remain present even after a 1100°C annealing, while Xe strongly desorbs out at that temperature. Our measurements provides unexpected dielectric constant (k) lower than 1.6. These results make this technique very attractive for low-k applications in Si technology. Keywords: low-k dielectric, rare gas implantation, silicon oxid.