Boron-enhanced diffusion of boron: Physical mechanisms

Silicon layers containing B in excess of a few atomic percent create a supersaturation of Si self-interstitials in the underlying Si, resulting in enhanced diffusion of B in the substrate [boron-enhanced diffusion (BED)]. The temperature and time dependence of BED is investigated here. Evaporated boron 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 increasing temperature up to 1050 degrees C and then decreases. In contrast, simulations based on interstitial generation via the kick-out mechanism predict a decreasing dependence leading to the conclusion that the kick-out mechanism is not the dominant source of excess interstitials responsible for BED. The 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 samples, show a similar temperature dependence as seen for evaporated B, except that the maximum enhancement occurs at 1000 degrees C. The temperature-dependent behavior of BED supports the hypothesis that the source of excess interstitials is the formation of a silicon boride phase in the high-boron-concentration silicon layer. (C) 1999 American Institute of Physics. [S0003-6951(99)00316-2].