A test method is needed to determine nitrogen lower than 1E15 atoms/cm(3) in silicon crystals very accurately. In order to determine the concentration, it is necessary to subtract the contribution of background nitrogen properly. The "raster changing" method with Cameca instruments has an advantage for determining the background. We performed experiments using this method, and we indicate this method is a promising technique for quantifying low concentration of nitrogen in silicon. (C) 2002 Elsevier Science B.V. All rights reserved.