Surface transient effects in ultralow-energy Cs+ sputtering of Si

Abstract

This study examines the dependence of the sputter rate and the transient width (ztr) as a function of Cs+ primary ion energy (impact energy (Ep) = 320 eV, 500 eV and 1 keV) and incident angles between 0 and 70°. The instrument used was the ATOMIKA 4500 SIMS depth profiler and the sample was Si with ten delta layers of Si0.7 Ge 0.3. We observed the narrowest transient widths of between 1.4 and 2.0 nm apparent depth. This was achieved at incident angles (θ) of 30-50°. An extended transient effect was observed when profiled at θ > 50°. Below this incident angle, the transient width is less than twice the penetration depth (ztr < 2Rnorm). At minimum z tr, ztr ≈ Rnorm. The detection sensitivity is best achieved at θ ≈ 30° for all energies investigated. The sputter rate is lowest at normal incidence, rising gradually to a maximum at θ ≈ 50-60°. This is similar to that observed with ultralow-energy O2 + primary ion beams.1 At ultralow energies, reducing Ep does not have a significant effect in reducing z tr. We conclude that for Ep < 1 keV, the optimum condition to achieve minimum ztr while maintaining good sensitivity and high sputter rate is at θ ≈ 30°. Copyright © 2007 John Wiley & Sons, Ltd.