The distribution and annealing behavior of the vacancy-type defects and displaced Si atoms in crystal Si caused by 7 x 10(16) cm(-2), 140 keV He+ implantation have been studied by variable-energy positron annihilation technology, cross-sectional transmission electron microscopy and Rutherford backscattering and channel spectroscopy. It was found that in the as-implanted sample, a region 400 nm wide around the projected range was heavily damaged by the implantation and dense microbubbles with diameters of 1.5-6 nm were formed in this region, while the near surface region was slightly damaged and small vacancy clusters less than 1 nm in diameter and some microbubbles scattered in this region. The defects in the heavily damaged region were stable at temperature below 400 degrees C and began to recrystallize from the crystalline Si in the near surface layer by solid phase epitaxy at temperatures higher than 600 degrees C. High temperature (1100 degrees C) was needed to anneal out most of the defects in this heavily damaged layer. The small vacancy clusters in the near surface region become removable at 300 degrees C and could be removed at 700 degrees C by dissociation and diffusing both to the surface and to the heavily damaged region. The diameter of the microbubbles in the original heavily damaged region increased with the increasing of annealing temperature and their density decreased with the increasing of annealing temperature at temperatures above 700 degrees C. The annealing behavior of the vacancy clusters induced by Het implantation is discussed by thermodynamical process.