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

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 O-2(+) primary ions at an ultralow-energy (E-p) of 250 eV and incidence angles (theta) between 0 and 70 degrees 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, theta - 0 degrees provides the narrowest surface transient (z(tr)) Of 0.7 nm, which is marginally better than at 0 similar to 40 degrees with z(tr), of 1.0 nm. The depth resolution denoted by the full width at half maximum (FWHM) of the Ge-70(+) peaks is comparable for both theta similar to 0 and 40 degrees at 1.6 and 1.4 nm, respectively. However, in the case of MQW profiling, whereby the quantum wells are normally located deeper, theta similar to 40 degrees 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 theta similar to 0 degrees and a better depth resolution with decay length (lambda(d)) of 0.64 nm compared to 0.92 nm at theta similar to 0 degrees. Moreover, the dynamic range possible is also better at theta similar to 40 degrees. theta similar to 60 degrees 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. (c) 2006 Elsevier B.V. All rights reserved.