Electron-Beam-Induced Carbon Contamination in STEM-in-SEM: Quantification and Mitigation

• Published in: Microscopy and microanalysis Vol. 29; no. 1; pp. 219 - 234
• Main Authors: Hugenschmidt, Milena, Adrion, Katharina, Marx, Aaron, Müller, Erich, Gerthsen, Dagmar
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 01.02.2023
• Subjects: Carbon; Contamination; Electron beams; Electron energy; Imaging; Microscopy; Scanning transmission electron microscopy; Thickness measurement; Thin films; Transmission electron microscopy
• ISSN: 1431-9276; 1435-8115
• DOI: 10.1093/micmic/ozac003

Contamination is an undesired side effect in many electron microscopy studies that covers structures of interest and degrades resolution. Although contamination has been studied for decades, open questions remain regarding favorable imaging conditions for contamination minimization and the efficiency of contamination-mitigation strategies. This work focuses on electron-beam-induced carbon contamination in scanning transmission electron microscopy at electron energies of 30 keV and below. A reliable method to measure contamination thicknesses was developed in this work and enables the identification of imaging conditions that minimize contamination. Thin amorphous carbon films were used as test samples. The variation of important imaging parameters shows that the contamination thickness increases with the reduction of the electron energy to about 1 keV but decreases below 1 keV. Contamination increases with the beam current but saturates at high currents. Applying a given dose with a high dose rate reduces contamination. Among the tested contamination-mitigation methods, plasma cleaning and beam showering are most effective. Most experiments in this work were performed with focused scanning illumination. Experiments were also carried out with a stationary defocused beam for comparison with a theoretical contamination model with good agreement between measured and calculated contamination thickness.