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The effects of F on B diffusion and activation have been studied by implanting various doses of F/sup +/ followed by Si/sup +/ preamorphization and B/sup +/ implant. In B tail region, the activation of B is suppressed with increasing F concentration, and B diffusion is also suppressed when F concentration exceeds a critical level, 1/spl times/10/sup 18/ cm/sup -3/, which was confirmed from the experiments using BDSL (Boron delta doped superlattice) implanted with F/sup +/. The fact that F atoms remain in silicon after annealing at 820/spl deg/C has been investigated. The experiments of a subamorphous threshold Si/sup +/ dose at high energy reveal that F atoms remain at excess vacancy region extending from the surface to about 0.8 R/sub p/ of the implanted Si profile.