Secondary-ion mass spectrometry (SIMS) with an ultralow energy primary ion beam was used to profile ultrashallow arsenic implants in silicon. Such shallow profiles are necessary for the formation of shallow junctions in future generations of transistors. A 750 eV Cs primary provides the best resolution in both dosimetry and depth profiling. However, even under these optimal conditions SIMS has limited resolution. We used high resolution X-ray photoelectron spectroscopy and monolayer chemical oxidation and etching of silicon to investigate the abruptness resolution of SIMS and to obtain the impulse response of the instrument. Using this technique, we found that a 1 keV, 1 x 10(15)/cm(2) arsenic implant is more abrupt than the SIMS resolution. The impulse response of SIMS under these conditions was obtained via deconvolution. This impulse response can be used to correct the SIMS results. Also, the more accurate profile can be used to improve the calibration of simulation tools, which up to now have been calibrated to fit SIMS profiles.