Boron diffusion in Si in shallow pre-amorphization implants (SPAI) of different species, including F, Ge, GeF2, BF2, and their combination was studied. Results show that different species have different impact on B diffusion. In addition to the chemical effect, the interaction of SPAI species with B, leading to immobile B clustering, is another important cause for B diffusion reduction. Fluorine is more effective than Ge in the B diffusion reduction. Adding more F in the amorphous region results in more B diffusion reduction. Aside from the effect on the B diffusion, fluorine itself manifests a large amount of out-diffusion for the shallow F implant case and as F is implanted deeper, a bell-shaped F profile exists around the end-of-range damage. The out-diffusion of F is further enhanced by the implanted damage.