Silicon wafers were annealed in pure and low-purity nitrogen gas at temperatures from 800 to 1200 degreesC. The surfaces of the annealed samples were investigated by means of X-ray photoelectron spectroscopy and optical microscopy. It was found that silicon wafers could react with nitrogen molecules to form silicon nitride films at temperatures higher than 1100 degreesC in pure nitrogen atmosphere. The thickness of the silicon nitride films thermally grown in pure nitrogen gas at I 100 and 1200 T for up to 4 h was measured. The maximum thickness was about 50 nm, and the growth kinetics of direct thermal nitridation at 1100 and 1200 degreesC was obtained. (C) 2004 Elsevier B.V. All rights reserved.