Small-area depth profiling in a quadrupole based SIMS instrument

Abstract

The dynamic range, the erosion rate and the depth resolution achievable in small-area SIMS depth profiling has been studied using the quadrupole based ion microprobe ATOMIKA 4000. It was found that for a given object aperture of the oxygen or cesium ion gun the beam diameter is essentially independent of the beam energy (1.5–12 keV). Most of the results presented here relate to primary ion beams with a diameter between 25 and 30 μm. Dynamic ranges up to 10 6 were obtained with δ-doped and ion-implanted samples at raster sizes between 140 and 160 μm, even at the lowest beam energies. The excellent instrument performance was used to determine the energy dependence of the decay length for germanium in silicon. High speed depth profiling of thick layers or deep concentration distributions could be achieved with oxygen primary ions at 12 keV, in which case the mean current density in the raster scanned area was up to 3.5 mA cm −2. The advantages of small-area depth profiling are also illustrated for vacuum-sensitive impurities like carbon and oxygen, analyzed under cesium bombardment.