EUV ptychography: Material-Specific Imaging at the Nanoscale

EUV ptychography combines high resolution, strong material contrast, reasonable penetration depth, and easy sample preparation. It thus has the potential to bridge the gap between visible light and electron microscopy. In this contribution, we present recent results on table-top ptychographic EUV microscopy. The experimental setup relies on a high photon flux 13.5 nm wavelength high-order harmonic source [1]. A simple amplitude mask upstream of the sample tailors the illumination. The sample is scanned by piezo-driven stages. Finally, far-field diffraction patterns are recorded by an EUV detector and fed into a ptychographic iterative engine to retrieve both the illumination and the sample transmission in amplitude and phase. The resolution of the EUV microscope (16 nm) was characterized using a Siemens star test sample. In the next step, a thin lamella of an integrated circuit was investigated. The resulting EUV images exhibit a rich diversity in amplitude and phase. We analyzed that the relative amplitude precision is better than 4% and the absolute phase precision as good as ~ 20 mrad. In this way, the microscope provides excellent input data for further analysis of the material composition. For this purpose, the projected scattering quotient is calculated from the reconstructed phase and amplitude and compared to tabulated material parameters. Here, materials like Al, Si3N4, and SiO2 were determined with high sensitivity. Finally, biological samples, namely germlings of the filamentous fungus Aspergillus nidulans were investigated. A similar scattering quotient analysis allowed us to clearly distinguish regions with low- and high lipid and phospholipid concentrations.