Self-interstitials and substitutional C in silicon: Interstitial-trapping and C-clustering

The interactions between self-interstitials (I's) produced by 20 keV silicon implantation, and substitutional carbon in silicon have been studied using a Si1-yCy layer interposed between a near surface I source and a deeper B spike used as a marker for the I concentration. The Si1-yCy layer behaves as a filtering membrane for the interstitials flowing towards the bulk. This trapping ability is related to the total C amount in the Si1-yCy membrane. Substitutional carbon atoms interacting with self-interstitials are shown to trap I's, to be removed from their substitutional sites, and to precipitate into the C-rich region. After precipitation, C atoms are not able to further trap injected self-interstitials. The atomistic mechanism leading to Si-interstitial trapping has been investigated by developing a simulation code describing the migration of injected interstitials. By a comparison with the experimental data it was possible to derive quantitative indications on the trapping mechanism. It is shown that one Si-interstitial is able to deactivate about two C traps by means of interstitial trapping and C-clustering reactions.