Quantification of secondary-ion-mass spectroscopy depth profiles using maximum entropy deconvolution with a sample independent response function

Abstract

We describe a new method for extracting the secondary-ion-mass spectroscopy response function from measured data for δ layers. The method was developed to reduce the danger of incorporating sample dependent behavior in the response, and is particularly appropriate for use with sub-keV profile energies where the depth resolution is so high that structure can be observed in layers with nm-scale thickness. We demonstrate this method on a system of variously spaced boron δ layers grown in silicon by molecular beam epitaxy. The deconvolved boron distributions for different primary ion beam energies, ranging from 500 eV to 6 keV, appear to be self-consistent and the corresponding depth resolutions are all increased significantly. Deltas with a 2 nm spacing are resolved without deconvolution using a normally incident 250 eV O2+ beam and the depth resolution (Rayleigh criterion) achievable under these conditions with deconvolution is <1 nm. Segregation of boron at the near surface side of the δ layers is clearly visible in these deconvolved data. These features would have been removed using an uncorrected response.