The formation behavior of grown-in voids during crystal growth as investigated for nitrogen-doped Czochralski silicon crystals by means of a new quantitative defect evaluation method using a bright-field infrared-laser interferometer. Crystal quenching techniques were employed to study void formation and it was found that in crystals grown without nitrogen doping, the total amount of vacancies composing the voids did not change during the crystal growth halt. In nitrogen-doped crystals, however. the total amount of vacancies composing the voids increased during the crystal growth halt. These results indicate that nitrogen makes excess vacancies remain after void formation in crystals grown without a growth halt. (C) 2002 Elsevier Science B.V. All rights reserved.