Near‐surface defects formed during rapid thermal annealing (950–1150 °C, 10 s) of preamorphized and BF+2‐implanted (100) Si have been studied by a combination of cross‐sectional transmission electron microscopy and secondary‐ion mass spectrometry. Two types of defects are identified: fine clusters (1.5–4 nm in diameter) are shown to be related to fluorine, and stacking faults are correlated with the presence of both excess boron above the solid solubility limit and fluorine. In addition, the peak fluorine concentration is found to be lower in samples which contain a high density (∼108cm−2) of ‘‘hairpin’’ dislocations, indicating that a pipe diffusion mechanism for the rapid out‐diffusion of fluorine may be operative.