Boron-enhanced diffusion of boron: Physical mechanisms

Silicon layers containing B in excess of a few atomic percent create a supe rsaturation of Si self-interstitials in the underlying Si, resulting in enh anced diffusion of B in the substrate [boron-enhanced diffusion (BED)]. The temperature and time dependence of BED is investigated here. Evaporated bo ron as well as ultralow energy 0.5 keV B-implanted layers were annealed at temperatures from 1100 to 800 degrees C for times ranging from 3 to 3000 s. Isochronal 10 s anneals reveal that the BED effect increases with increasi ng temperature up to 1050 degrees C and then decreases. In contrast, simula tions based on interstitial generation via the kick-out mechanism predict a decreasing dependence leading to the conclusion that the kick-out mechanis m is not the dominant source of excess interstitials responsible for BED. T he diffusivity enhancements from the combined effects of BED and transient- enhanced diffusion, measured in 2 x 10(15) cm(-2), 0.5 keV B-implanted samp les, show a similar temperature dependence as seen for evaporated B, except that the maximum enhancement occurs at 1000 degrees C. The temperature-dep endent behavior of BED supports the hypothesis that the source of excess in terstitials is the formation of a silicon boride phase in the high-boron-co ncentration silicon layer. (C) 1999 American Institute of Physics. [S0003-6 951(99)00316-2].