The behaviors of nitrogen during Czochralski (CZ) silicon crystal growth have been investigated in this paper. It is found that the nitrogen impurities in silicon mainly exist as nitrogen pair and nitrogen-oxygen complex. The nitrogen concentration can be exactly determined by Fourier transformed infrared spectroscopy (FTIR) after eliminating the thermal donors. Above a critical concentration of 4 x 10(15)/cm(3), the nitrogen impurities easily form Si(3)N(4) particles, causing the dislocations, grain boundary and cellular structure in the crystal. Meanwhile, with a nitrogen-doped seed, the dislocations due to thermal shocking during the dipping process can be effectively suppressed at the seed/crystal interface, which will allow growing a crystal without a Dash neck. These results are of interest for the CZ silicon crystal growth in semiconductor industry. (C) 2010 Elsevier B.V. All rights reserved.