In this work we investigate the promising properties of F in helping the B confinement in pre-amorphized Si, looking into the physical mechanisms acting. We studied also the effect of F on the electrical activity of B-doped junctions in pre-amorphized Si. The carrier dose, measured by four-point probe and Hall effect techniques, lowers because of F, with respect to the sample implanted only with B. To explain the measured B deactivation we employed scanning probe microscopy that allowed to verify a significant F-donor behaviour. Our results clarifies that the physical reason for the lost of holes dose in junctions co-implanted with B and F is not due to a chemical interaction between dopants and F, but simply to a dopant compensation effect.