The interaction of He atoms, with the radiation damage of (100) single crystals which was caused by 20keV He+ implantation to 5 x 1015/cm2 at liquid-N temperatures, was investigated during and after heat treatment. Thermal programmed desorption was used to study the dissociation kinetics of He from the defects and to plan suitable heat treatments. The He profiles were determined by 8MeV 15N2+ elastic recoil detection, and quantitative data concerning damage were obtained by means of channelling Rutherford back-scattering spectrometry, double-crystal X-ray diffraction and positron annihilation spectroscopy. Isothermal treatment at 250C first led to He redistribution and trapping in vacancy-like defects, rather than He desorption from traps. The process was thermally activated, with an effective activation energy of between 1.1 and 1.7eV. At higher temperatures (500C, 2h), the traps were almost emptied and, at 700C, all vacancy-like defects annealed out. No bubbles or voids were observed in as-implanted or annealed samples.

Helium-implanted silicon F.Corni, G.Calzolari, S.Frabboni, C.Nobili, G.Ottaviani, R.Tonini, G.F.Cerofolini, D.Leone, M.Servidori, R.S.Brusa, G.P.Karwasz, N.Tiengo, A.Zecca: Journal of Applied Physics, 1999, 85[3], 1401-8