A combined cross‐sectional and plan‐view transmission electron microscope study of residual defects in 110‐keV, 5×1015/cm2BF+2‐ implanted (001)Si has been carried out. Complete amorphization of the surface layer to a depth of about 1400 A˚ from the surface was found in as‐implanted samples. The general trends of the amorphous/crystalline (a/c) regrowth were found to be similar in 550–900 °C annealed samples. ‘‘Paired’’ dislocations were observed in the first ∼600 A˚ of regrown layers. A high density of twins was found subsequently as thea/cinterface advanced to the surface. Small defect clusters, irregular dislocations, equiaxial loops, and rodlike defects were observed to distribute in bands underneath the originala/cinterface. The regrown layers were found to be almost dislocation‐ and twin‐free in 1000–1100 °C annealed specimens. The regrown layer, however, contained a high density of fluorine bubbles. The bubbles were concentrated near the orignala/cinterface and the surface. Irregular dislocation networks were found to develop near the orignala/cinterface. The origins of residual defects and their possible influences on device applications are discussed.