Nitrogen depth profiles in ultrathin silicon oxynitride films (similar to2.6 nm) are measured by secondary ion mass spectroscopy. The results are compared with the profiles measured by high-resolution Rutherford backscattering spectroscopy (HRBS) to see if SIMS can be accurate in the topmost 1-2 nm region. Using a constant relative sensitivity factor for SIMS analysis, agreement between SIMS and HRBS is not satisfactory. SIMS underestimates the nitrogen concentration at larger concentrations probably due to matrix effects. The empirical composition-dependent RSF is derived from the observed results. Correcting the SIMS result with the empirical RSF, the nitrogen depth profiles agree with the HRBS results reasonably well except for the very surface region (d < 0.3 M). (C) 2002 Elsevier Science B.V. All rights reserved.