Boron profile narrowing in laser-processed silicon after rapid thermal anneal

Abstract

The narrowing or broadening of the boron profile during annealing of laser-processed samples is observed to occur depending on which of two competing mechanisms, uphill diffusion of boron due to a highly defective single-crystal layer near the surface or transient-enhanced diffusion due to end-of-range defects, dominates during the post-laser processing anneal. The results show that uphill diffusion of boron is found to dominate during annealing of a single-pulse laser-processed sample because the defects near the surface cannot be efficiently removed with a single laser pulse adjusted to a value that can melt the amorphous silicon but not the underlying crystalline substrate. Junctions thus become shallower with the post-laser processing anneal. However, with successive laser pulses, the dopants are observed to move deeper into the silicon with subsequent rapid thermal annealing cycles. This could be due to the reduced contribution of uphill boron diffusion when the defects near the surface decrease with successive pulses. The end-of-range defects, which cannot be sufficiently annealed because the melt depth is not beyond the amorphous layer, thus play the key role in broadening the boron concentration profile for multiple-pulse laser-annealed silicon. (C) 2003 The Electrochemical Society.