A novel mechanism was proposed for the diffusion of a di-B pair in Si, based on first principles density functional theory. A reaction pathway was found, along which the B pair diffused from one lowest energy configuration of [B-B]s-<001> to an equivalent structure at an adjacent equivalent site through 3 local minimum states; denoted by [B-B]s-<111>, Bs-Bi and Bs-Bs-Sii. The activation energy for diffusion was estimated to be 1.81eV in the generalized gradient approximation. A kinetic model suggested that di-boron diffusion played an important role in determining diffusion profiles during ultra-shallow junction processing - which required high B-dopant concentrations as well as high annealing temperatures.

Diffusion of the Diboron Pair in Silicon. G.S.Hwang, W.A.Goddard: Physical Review Letters, 2002, 89[5], 055901