Boron-enhanced diffusion of boron from ultralow-energy ion implantation

We have investigated the diffusion enhancement mechanism of boron-enhanced diffusion (BED), wherein boron diffusivity is enhanced four to five times over the equilibrium diffusivity at 1050 degrees C in the proximity of a silicon layer containing a high boron concentration. It is demonstrated that BED is driven by excess interstitials injected from the high boron concentration layer during annealing. For evaporated layers, BED is observed above a threshold boron concentration between 1% and 10%, though it appears to be closer to 1% for B-implanted layers. For sub-keV B implants above the threshold, BED dominates over the contribution from transient-enhanced diffusion to junction depth. For 0.5 keV B, this threshold implantation dose lies between 3 x 10(14) and 1 x 10(15) cm(-2). It is proposed that the excess interstitials responsible for BED are produced during the formation of a silicon boride phase in the high B concentration layers. (C) 1999 American Institute of Physics. {[}S0003-6951(99)02117-8].