Improved near surface characterization of shallow arsenic distribution by SIMS depth profiling

Abstract

Accurate depth profile analyses of distributions created by ultra low energy (ULE) ion implantation and annealing in Si has been difficult because the implanted element distribution often is mainly within the surface oxide and spans the oxide interface. Although negative ions have the best sensitivity for As in Si, quantification of the negative ion intensities in ULE As distributions near the surface oxide is difficult due to large ion yield changes. The use of an oxidizing ambient and positive ion detection has poor sensitivity. Furthermore, the oxidizing ambient causes profile distortion due to As migration during the depth profile. Therefore, we focused our attention to Cs bombardment analyses. We investigated ULE As ion implanted samples with oxide thicknesses of 1–5 nm. Using the doses calibrated by RBS and oxide thicknesses measured by XPS, we formulated RSF and sputter rate changes across the oxide/Si interface. The resulting depth profiles dramatically improve the dose accuracy and profile shape in samples with oxides thicker than 1 nm, which is especially important in annealed samples for which most of the As is near the surface.