Lattice damages induced by BF2+ ion implantation in single-crystalline silicon have been analyzed using secondary-ion mass spectrometry, ion channeling technique in Rutherford backscattering spectroscopy, and transmission electron microscopy. Concentration depth profiles of boron and fluorine showed the same values of projection range 400 angstrom at all doses for 50-keV energy. A considerable amount of damage was formed in the silicon lattice and the surface region of the substrate was amorphized when the dosage exceeded a critical value, which was determined to be 8.0 x 10(14)/cm2 experimental dose. The amorphized layer showed a clear boundary to the crystalline silicon, which contains severly damaged regions identified to be microamorphous clusters. He2+ ion channeling data revealed that the integrated damage in implanted layers increases linearly with dosage up to the critical dose and increases with a much smaller rate with further increase in the dosage. It is suggested that the integrated damage shows a smaller damage rate once the surface was amorphized because there can be no further increase of lattice damage in the amorphous layer. The calculated values of the integrated damage based on a model for damage formation agree well with the measured ones.