A continuous and general model for boron diffusion during post-implant annealing including damaged and amorphizing conditions

Abstract

A model is presented for boron diffusion after ion implantation. The aim is to derive a formulation valid for a large range of implantation doses and annealing temperatures. In particular, it allows for the first time a continuous simulation of the transition between amorphizing and nonamorphizing conditions. Transient-enhanced diffusion and activation aspects are addressed through a physical approach. This includes a point-defect based formulation with a special emphasis on the initial conditions in order to reproduce the effects of damaging or amorphizing implants, with, in the latter case, solid-phase epitaxy. It is then shown that the initial level of activation is one of the most important parameters in such an analysis, in some cases overriding the influence of the initial amount of point-defects. On the other hand, a precipitation model describes the evolution of the active boron concentrations during the diffusion steps. The calculation results are compared satisfactorily with numerous experimental profiles, suggesting that the overall approach enables a correct modeling of the involved phenomena, without an explicit formulation of the extended defects kinetics. Finally, the model is validated through the simulation of the emitter/base region of PNP devices, with the emitter formed by various BF/sub 2/ implant doses.