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, a nd liquid-nitrogen temperature is investigated by means of various compleme ntary techniques during and after thermal treatments. Thermal programmed de sorption was used to study the dissociation kinetics of helium from the def ects and to plan suitable heat treatments for the other techniques. The hel ium profiles were determined by 8 MeV N-15(2+) elastic recoil detection, qu antitative data on damage were obtained by channeling Rutherford backscatte ring spectrometry, double crystal x-ray diffraction, and positron annihilat ion spectroscopy. Isothermal treatments at 250 degrees C produce first heli um 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 highe r temperature treatments (2 h at 500 degrees C) the traps are almost emptie d and at 700 degrees C all vacancy-like defects are annealed out. No bubble s 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].