Helium-implanted silicon: A study of bubble precursors

The interaction of helium atoms with the radiation damage imparted to (100) silicon single crystal by He+ implantation at 5 x 10(15) cm(-2), 20 keV, and liquid-nitrogen temperature is investigated by means of various complementary techniques during and after thermal treatments. Thermal programmed desorption was used to study the dissociation kinetics of helium from the defects and to plan suitable heat treatments for the other techniques. The helium profiles were determined by 8 MeV N-15(2+) elastic recoil detection, quantitative data on damage were obtained by channeling Rutherford backscattering spectrometry, double crystal x-ray diffraction, and positron annihilation spectroscopy. Isothermal treatments at 250 degrees C produce first helium redistribution and trapping in vacancy-like defects, rather than helium desorption from traps. The process is thermally activated with an effective activation energy, dispersed in a band from 1.1 to about 1.7 eV. For higher temperature treatments (2 h at 500 degrees C) the traps are almost emptied and at 700 degrees C all vacancy-like defects are annealed out. No bubbles or voids are observed by transmission electron microscopy, either in the as-implanted or in annealed samples. (C) 1999 American Institute of Physics. [S0021-8979(99)00903-2].