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Quantitative thin-film x-ray microanalysis by STEM/HAADF: statistical analysis for precision and accuracy
Aldo Armigliato1, Roberto Balboni, Rodolfo Rosa
1Consiglio Nazionale delle Ricerche, Istituto per la Microelettronica e i Microsistemi (CNR-IMM), Sezione di Bologna, Via P. Gobetti 101, 40129 Bologna, Italy. aldo.armigliato@imm.cnr.it
Summary
This study analyzes silicon-germanium thin films using electron microscopy. A new statistical method improves accuracy for determining film composition and thickness, even with varying sample properties.
Area of Science:
- Materials Science
- Physics
- Chemistry
Background:
- Silicon-germanium (SiGe) thin films are crucial in semiconductor technology.
- Accurate characterization of SiGe film composition and thickness is essential for device performance.
- Advanced electron microscopy techniques are employed for nanoscale material analysis.
Purpose of the Study:
- To quantitatively analyze silicon-germanium thin films using energy-dispersive X-ray (EDS) microanalysis.
- To evaluate the effectiveness of a Monte Carlo-based "two tilt angles" method for determining Ge concentrations and film thickness.
- To explore statistical methods for improving the accuracy of quantitative analysis in scanning transmission electron microscopy (STEM).
Main Methods:
- Utilized a field emission gun scanning transmission electron microscope (FEG-STEM) with a high angular dark-field (STEM/HAADF) detector.
- Performed drift-corrected linescan acquisitions on cross-sectioned SiGe samples.
- Applied a Monte Carlo-based "two tilt angles" method for quantitative analysis.
- Investigated the parametric bootstrap method for statistical analysis of X-ray intensities.
Main Results:
- Ge concentrations determined by the "two tilt angles" method showed excellent agreement with known values.
- Confidence intervals for the quantitative analysis were not as precise as expected, despite state-of-the-art instrumentation.
- The Gaussian shape of SiKalpha and GeKalpha X-ray intensities enabled the application of the parametric bootstrap method.
- The parametric bootstrap method allows quantitative analysis in regions with varying composition and thickness from a single two-angle measurement.
Conclusions:
- The "two tilt angles" method provides accurate Ge concentration in SiGe films.
- Statistical improvements are needed to enhance the precision of quantitative analysis in STEM-EDS.
- The parametric bootstrap method offers a robust approach for quantitative analysis of SiGe thin films, simplifying the measurement process.