A new type of boron cluster is presented through the study of boron diffusion at high concentrations under predeposition conditions. Recent experimental results of boron predeposition give the opportunity to analyze, with the simulations, the behavior of the inactive part of the boron profile, found to increase dramatically with surface concentrations. After a rapid thermal annealing, the electrical activation appears to be extremely high due to the dissolution of the inactive part of the profile. The only way to reproduce the experimental observations has been to consider an inactive and mobile 2-atom boron cluster. A complete kinetic model, including the reactions between boron cluster, boron-interstitial pair, substitutional boron and point defects, is used in order to determine all the parameters characterizing this cluster. The diffusivity of the cluster is much less than the one of the boron-interstitial pair (about 40 times). It is suggested that the nature of this cluster may depend on the exact predeposition conditions. Finally, from a general point of view, the behavior of supersaturations of interstitials during predeposition as a function of surface concentration is presented, in order to understand the implication of each basic reaction involved in the kinetic model.

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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.

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