We have studied, by means of B diffusion analyses, the effect of F on the point defect density in preamorphized Si. Through molecular beam epitaxy (MBE) Si samples containing a special B multi-spike were grown. These samples were amorphized to a depth of 550 nm by implanting Si at liquid nitrogen temperature and then enriched with F at different energies (65–150 keV) and fluences (0.7–5 × 1014/cm2). After solid phase epitaxy (SPE) of the samples, we induced, by thermal annealing at 850 °C, the emission of Si self-interstitials (Is) from the end-of-range (EOR) defects. We studied the diffusion of the B spikes, demonstrating that F effectively reduces the B diffusion. This reduction is shown to be caused not by a direct B–F chemical interaction, but by a F interaction with point defects. In particular, F is able to reduce the density of Is, which are responsible for the B diffusion. Still, we showed that F does not …