The reduction of the dielectric constant of the inter-metal dielectric is a key task for realizing high performances IC devices. In this work ion implantation is proposed as a novel method to reduce the dielectric properties of SiO2. Thermally grown SiO2 on silicon was implanted by Xe at 300 keV and a fluence of 5× 1016 at/cm2. The dielectric constant of the obtained structure, measured by means of the CV method and Infrared measurements, was shown to strongly decrease. From the IR reflection spectra, a hypothesis of the implantation defects involved in lowering the ionic contribution to the dielectric constant will be proposed.