Diffusion of the Diboron Pair in Silicon

We propose a novel mechanism for the diffusion of a diboron pair in Si, based on first principles density functional theory. We find a reaction pathway along which the boron pair diffuses from one lowest energy configuration of [Formula presented] to an equivalent structure at an adjacent equivalent site through three local minimum states denoted as [Formula presented], [Formula presented], and [Formula presented]. The activation energy for the diffusion is estimated to be 1.81 eV in the generalized gradient approximation. A kinetic model suggests that the diboron diffusion plays an important role in determining diffusion profiles during ultrashallow junction processing (which requires high boron-dopant concentration as well as high annealing temperature).