Narrow surface transient and high depth resolution SIMS using 250 eV O2 +

Abstract

Ultrashallow junctions in semiconductors and multi-quantum wells (MQW) in lasers demand high depth resolution for accurate depth profiling. SIMS has been widely used in depth profiling and the use of ultralow-energy SIMS has demonstrated a narrower surface transient and an improvement in depth resolution. In this work, we use an ATOMIKA 4500 SIMS depth profiler with O2 + primary ions at an ultralow-energy (Ep) of 250 eV and incidence angles (θ) between 0 and 70° without oxygen flooding. A sample with 10 delta layers of Si0.7Ge0.3 nominally grown 11 nm apart is used. We observe that for applications like characterizing ultrashallow junctions, θ ∼ 0° provides the narrowest surface transient (ztr) of 0.7 nm, which is marginally better than at θ ∼ 40° with ztr of 1.0 nm. The depth resolution denoted by the full width at half maximum (FWHM) of the 70Ge+ peaks is comparable for both θ ∼ 0 and 40° at 1.6 and 1.4 nm, respectively. However, in the case of MQW profiling, whereby the quantum wells are normally located deeper, θ ∼ 40° is preferable. At this angle, the average sputter rate of 47 nm min-1 nA-1 cm-2 is significantly higher, more than double that at θ ∼ 0° and a better depth resolution with decay length (λd) of 0.64 nm compared to 0.92 nm at θ ∼ 0°. Moreover, the dynamic range possible is also better at θ ∼ 40°. θ ∼ 60ο is not ideal, even though there is no sign of the onset of roughening. Although the higher sputter rate is an advantage, the depth resolution deteriorates as the profile gets deeper. © 2006 Elsevier B.V. All rights reserved.