Modeling inactive boron during predeposition processes

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Abstract
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.