Thermally grown SiO2 was implanted at room temperature with 220 keV Kr in order to generate bubbles/cavities in the sample. The formation and thermal stability of these bubbles/cavities is studied in this work. Transmission Electron Microscopy (TEM), Rutherford Backscattering Spectrometry (RBS) and Positron Annihilation Spectroscopy (PAS) were used to provide a comprehensive characterisation of defects (bubbles, vacancy, Kr and other types of defects) created by Kr implantation in SiO2 layer. These measurements suggest that the bubbles observed with TEM were a consequence of the interaction between Kr and vacancies (V), with VnXem complexes created in the whole of implanted zone. After annealing, bubbles/cavities disappear from SiO2 due to the strongly desorption of Kr and the decrease in vacancy concentration.