It was shown that the thickness of ultrathin gate oxides measured with low energy O-2(+) SIMS shows linear relationships with medium energy ion scattering spectroscopy (MEIS) and HRTEM results in the range of 9-2.5 nm. For quantitative N depth profiling, N profiles in similar to3 nm Si oxynitrides were measured by low energy O-2(+) and Cs+ SIMS and calibrated with, MEIS analysis results of the thickness and the N areal density. N SIMS profiles observed for low energy O-2(+) and Cs+ SIMS showed some difference in the shape and distribution. (C) 2002 Elsevier Science B.V. All rights reserved.