We present a comprehensive secondary ion mass spectrometry (SIMS) study performed at ultralow energies using both oxygen and cesium primary ions, in positive and negative SIMS for silicon depth pro. ling, respectively. Variations in surface transient widths and depth resolution are reported as a function of primary ion energy (250 eV-1 keV) over a wide range of incidence angles (0-70 degrees). The instrument used is the Atomika 4500 SIMS depth profiler and the sample was Si with 10 delta-layers of Si0.7Ge0.3. Optimum pro. ling conditions are found that are useful for silicon ultrashallow profiling. (C) 2008 Elsevier B. V. All rights reserved.