SIMS is one of the tools available for the analysis of gate dielectric materials such as thin silicon oxynitride (SiON) and high-k films and it is especially useful method to investigate the distribution of N in these thin films. When measuring thin films by SIMS, high depth resolution is needed to see slight differences between samples. Here we have tried to improve the depth resolution by using backside SIMS. Samples for this analysis were prepared by using a SOI wafer, on which SiON and poly-Si films were deposited. Profiles of N, O and Si in the SiON layer and those of boron diffused from the upper poly-Si into the SiON layer have been acquired. Furthermore, by combining the profiles of conventional SIMS from the surface side with those of backside SIMS, we have tried to obtain a correct profile. In the interpretation of the depth profiles in and around the SiON film, changes in detection sensitivity are a difficult problem. We examined the effect of ion yield changes in the different matrices of poly-Si/SiON/Si by monitoring several different secondary ions. (C) 2004 Elsevier B.V. All rights reserved.