Suppression or stimulation of B diffusion and activation in Si (coimplanted with F) has been investigated by anneals in a N-2 ambient enriched with H-2 or O-2. The H-2 rich ambient leads to B desorption and therefore stimulated diffusion toward the surface, thus effectively reducing indiffusion. Annealing in an O-2 rich ambient promotes deeper B diffusion by injection of Si interstitials. The impact of these ambients can further be modulated by combining the B implant with a shallow or deep F coimplant acting as Si interstitial trap. Deep F coimplant and H-2 rich ambient offer attractive B diffusion and activation.