We report experimental results on the formation of He bubbles in Cz grown (100) Si crystals implanted with 40 keV He + ions to a fluence of 1x10 1 6 cm - 2 at distinct implantation temperatures within the 373=<T i =<573 K range, and upon 600 s post-implantation thermal annealings at temperatures from 673 to 1073 K. The samples were analyzed by Rutherford backscattering/channeling spectrometry, elastic recoil detection analysis and transmission electron microscopy. The results obtained show that the microstructure characteristics of the bubble systems, as well as their thermal evolution behavior, depend significantly on the implantation temperature. A correlation between the dynamic annealing behavior and the bubble formation process is proposed.