Evolution of nucleation sites and bubble precursors in silicon as a function of helium implanted dose

(111) oriented silicon samples were implanted at room temperature with 1.55 MeV He-3 ions in the dose range of 5x10(15) to 5x10(16)/cm(2). Cross-sectional transmission electron microscopy (XTEM) was used to study the evolution of bubbles and extended defects during subsequent thermal annealing at 800degreesC and 900degreesC for 30min. The He desorption from bubbles and bubble precursors was measured by means of nuclear reaction analysis (NRA). TEM observations show that no bubbles were observed in Si implanted at doses lower than 1x10(16)/cm(2), while a well-defined cavity band was formed after implantation at 5x10(16)/cm(2) and subsequent thermal annealing. At the intermediary dose of 2x10(16)/cm(2), however, the evolution of bubbles and extended defects is quite different. The bubbles prefer to nucleate in large planar clusters surrounded by a high density of dislocation loops emerging from them. The clusters of bubbles act as the sources of the dislocation loops. NRA measurements indicate that the He desorption behavior is also dose-dependent. The He desorption is achieved much faster in low dose implanted Si. The results are qualitatively discussed.