Abstract
We demonstrate the first (to our knowledge) general purpose full-field reflection-mode extreme ultraviolet (EUV) microscope based on coherent diffractive imaging. This microscope is capable of nanoscale amplitude and phase imaging of extended surfaces at an arbitrary angle of incidence in a noncontact, nondestructive manner. We use coherent light at 29.5 nm from high-harmonic upconversion to illuminate a surface, directly recording the scatter as the surface is scanned. Ptychographic reconstruction is then combined with tilted plane correction to obtain an image with amplitude and phase information. The image quality and detail from this diffraction-limited tabletop EUV microscope compares favorably with both scanning electron microscope and atomic force microscope images. The result is a general and completely extensible imaging technique that can provide a comprehensive and definitive characterization of how light at any wavelength scatters from a surface, with imminent feasibility of elemental imaging with
Highlights
Dramatic advances in coherent diffractive imaging (CDI) using light in the extreme ultraviolet (EUV) and X ray regions of the spectrum over the past 15 years have resulted in near diffraction-limited imaging capabilities using both large and small scale light sources [1, 2]
Reflection ptychography produces surface images containing quantitative amplitude and phase information about the sample that are in excellent agreement with atomic force microscopy (AFM) and scanning electron microscopy (SEM) images, and removes all negative effects of non-uniform illumination of the sample or imperfect knowledge of the sample position as it is scanned
Because we use a tabletop high harmonic generation (HHG) 30 nm source [14], in the future it will be possible to image energy, charge and spin transport with nm spatial and fs temporal resolution on nanostructured surfaces or buried interfaces, which is a grand challenge in nanoscience and nanotechnology [15, 16]
Summary
A height map of the sample could be produced by assuming that 2π should be added to any part of the reconstruction that exhibited an amplitude above 25% of the maximum (based on the relative reflectivities of titanium and silicon, as discussed above) The result of this analysis is displayed, and represents a significant improvement in image quality compared with all tabletop coherent reflective imaging to date. None of the EUV work was done in a cleanroom environment The reason these are not visible in the CDI height map (Fig. 3a) is that the 3D information relies on the phase difference of light reflecting from the substrate versus the features (at 45◦) and not on the absolute height difference. This is significant for dynamic studies, since in contrast to ptychography CDI which requires overlapping diffraction patterns, keyhole CDI needs only one diffraction pattern, and requires no scanning of the sample
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