Modeling high-concentration boron diffusion under amorphization conditions

A study of high-concentration boron diffusion using a precipitation model is presented in this paper. Recent experimental results on the annealing of boron implanted in preamorphized silicon give the opportunity to analyze, with the help of simulations, the precipitation kinetics and the effect of dislocation loops existing at the amorphous/crystalline interface. A nonequilibrium point-defect diffusion model is used throughout the study, including explicitly the equations describing the kinetics of precipitation. The initial conditions take into account the high level of activation observed experimentally after the solid-phase epitaxy. This influences both the sheet resistance and the doping profile shape at the end of the process. In addition, it is shown that a proper modeling of these diffused profiles includes the effect of the dislocation loops at the amorphous/crystalline interface, acting as a sink term for the interstitials. A more classical formulation of the diffusion equation does not require the modeling of such phenomena since the equilibrium concentration of the point defects is implicitly assumed. Finally, other applications to high-concentration boron diffusion are presented, demonstrating the range of validity of the involved parameters.