Stability of cavities formed by He + implantation in silicon

Abstract

Microscopic cavities are known to be efficient gettering sites for metallic impurities in silicon. In the present study, they were formed in 〈1 1 1〉 silicon by 40 keV room temperature He +implantation at doses of 5 × 10 16 and 10 17/cm 2, followed by a heat treatment in an N 2 atmosphere using either rapid thermal annealing or conventional furnace annealing. Helium desorption and cavity evolution were studied by non-Rutherford elastic scattering of protons and Rutherford backscattering/channeling analysis. Cavities and residual defects were observed by transmission electron microscopy (TEM). The retained fraction of helium was shown to depend on the manner of annealing and was found to decrease with annealing time much more slowly than the first order gas release model. TEM observations show that {3 1 1} defects and dislocations are also present close to the cavities. Channeling analysis shows that {3 1 1} defects dissolve during the first minutes of annealing at 800°C. It is assumed that the self-interstitials released from these defects are able to fill the smallest cavities, thus causing a rapid increase of the mean cavity radius. This variation, introduced in the desorption law, leads to reasonable agreement with the experimental results. For longer annealing time the total cavity surface decreases slowly with annealing duration.