Defect distribution and evolution in He+ implanted Si studied by variable-energy positron beam

The distribution and annealing behavior of the vacancy-type defects and dis placed Si atoms in crystal Si caused by 7 x 10(16) cm(-2), 140 keV He+ impl antation have been studied by variable-energy positron annihilation technol ogy, cross-sectional transmission electron microscopy and Rutherford backsc attering and channel spectroscopy. It was found that in the as-implanted sa mple, a region 400 nm wide around the projected range was heavily damaged b y the implantation and dense microbubbles with diameters of 1.5-6 nm were f ormed in this region, while the near surface region was slightly damaged an d small vacancy clusters less than 1 nm in diameter and some microbubbles s cattered in this region. The defects in the heavily damaged region were sta ble at temperature below 400 degrees C and began to recrystallize from the crystalline Si in the near surface layer by solid phase epitaxy at temperat ures higher than 600 degrees C. High temperature (1100 degrees C) was neede d to anneal out most of the defects in this heavily damaged layer. The smal l vacancy clusters in the near surface region become removable at 300 degre es C and could be removed at 700 degrees C by dissociation and diffusing bo th to the surface and to the heavily damaged region. The diameter of the mi crobubbles in the original heavily damaged region increased with the increa sing of annealing temperature and their density decreased with the increasi ng of annealing temperature at temperatures above 700 degrees C. The anneal ing behavior of the vacancy clusters induced by Het implantation is discuss ed by thermodynamical process. (C) 1998 Elsevier Science S.A. All rights re served.