Stability of cavities formed by He+ implantation in silicon

Microscopic cavities are known to be efficient gettering sites for metallic impurities in silicon. In the present study, they were formed in [111] sil icon by 40 keV room temperature He+ implantation at doses of 5x10(16) and 1 0(17)/cm(2), followed by a heat treatment in an N-2 atmosphere using either rapid thermal annealing or conventional furnace annealing. Helium desorpti on and cavity evolution were studied by non-Rutherford elastic scattering o f protons and Rutherford backscattering/channeling analysis. Cavities and r esidual defects were observed by transmission electron microscopy (TEM), Th e retained fraction of helium was shown to depend on the manner of annealin g and was found to decrease with annealing time much more slowly than the f irst order gas release model. TEM observations show that {311} defects and dislocations are also present close to the cavities. Channeling analysis sh ows that {311} defects dissolve during the first minutes of annealing at 80 0 degrees C. It is assumed that the self-interstitials released from these defects are able to fill the smallest cavities, thus causing a rapid increa se of the mean cavity radius. This variation, introduced in the desorption law, leads to reasonable agreement with the experimental results. For longe r annealing time the total cavity surface decreases slowly with annealing d uration. (C) 1999 Elsevier Science B.V. All rights reserved.