Surface transient effects in ultralow-energy O2+ sputtering of silicon

It is known that by lowering the impact energy the sputter rate and surface transient width in SIMS will be reduced. However, few studies have been done at ultralow energies over a wide range of impact angles. This study examines the dependence of sputter rate and transient width as a function Of O-2(+) primary ion energy (E-p = 250 eV, 500 eV and 1 keV) and incidence angles of 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. We observed that the lowest transient width of 0.7 nm is obtainable at normal and near-normal incidence with E-p similar to 250 eV and E-p similar to 500 eV. There is no significant improvement in transient width going down in energy from E-p similar to 500 to similar to 250 eV. The onset of roughening is also not obvious at E-p similar to 250 eV over the whole angular range studied. Although the sputter rate during the surface transient is normally different from that at steady state, only at E-p similar to 250 eV was it observed that the sputter rate remained fairly independent of depth. We conclude that the best working ranges to achieve a narrow transient width and accurate depth calibration are at E-p similar to 250 eV/0 degrees < theta < 20 degrees and 500 eV/0 degrees < theta < 10 degrees. Copyright (c) 2005 John Wiley & Sons, Ltd.