Quantitative Thin-Film X-Ray Microanalysis by STEM/HAADF: Statistical Analysis for Precision and Accuracy Determination

Silicon-germanium thin films have been analysed by EDS microanalysis in a FEG-STEM equip-ped with a high angular dark-field detector (STEM/HAADF). Several spectra have been acquired in the same homogeneous area of the cross-sectioned sample by drift-corrected linescan acquisitions. The Ge concentrations and the local film thickness have been obtained by using a previously described Monte-Carlo based `2 tilt-angle' method. While the concentrations are in excellent agreement with the known values, the resulting confidence intervals are not as good as expected from the precision in beam positioning and tilt angle position and read out offered by our state-of-the-art microscope. The Gaussian shape of the SiK_alpha and GeK_alpha X-ray intensities allows one to use the parametric bootstrap method of statistics, whereby it becomes possible to perform the same quantitative analysis in sample regions of different composition and thickness, but by doing only one measurement at the two angles.