High contrast 3D imaging of surfaces near the wavelength limit using tabletop EUV ptychography

Abstract

Scanning electron microscopy and atomic force microscopy are well-established techniques for imaging surfaces with nanometer resolution. Here we demonstrate a complementary and powerful approach based on tabletop extreme-ultraviolet ptychography that enables quantitative full field imaging with higher contrast than other techniques, and with compositional and topographical information. Using a high numerical aperture reflection-mode microscope illuminated by a tabletop 30 nm high harmonic source, we retrieve high quality, high contrast, full field images with 40 nm by 80 nm lateral resolution (≈1.3 λ), with a total exposure time of less than 1 min. Finally, quantitative phase information enables surface profilometry with ultra-high, 6 Å axial resolution. In the future, this work will enable dynamic imaging of functioning nanosystems with unprecedented combined spatial (<10 nm) and temporal (<10 fs) resolution, in thick opaque samples, with elemental, chemical and magnetic sensitivity.

Quantitative Chemically Specific Coherent Diffractive Imaging of Reactions at Buried Interfaces with Few Nanometer Precision

“…The reflectivity of the gold mirror was taken to be 27.9% [36] with the surface roughness assumed to be that of sibling silicon substrates used in Ref. [17]. Then, in RAPTR-CDI, the probe is normalized to the measured power in each iteration.…”

“…2), the phase of the reconstructions contains both material and height information. By subtracting the phase of the complex reflectivity predicted by our modeled feature and substrate stacks (discussed below) from the reconstructed phase images, we can generate height maps showing the surface topography of the samples [16,17]. In the case of the coated sample, the phase of the exit surface wave accounts for phase changes within the stack, and the height map therefore shows the top surface topography as opposed to the buried surface.…”

“…In particular, by combining coherent, short-wavelength beams from either high harmonic generation (HHG) [10] or X-ray free electron lasers (XFELs) [11] with coherent diffractive imaging (CDI) [12][13][14][15], it is now possible to reach near-wavelength resolution imaging in the EUV and X-ray regions for the first time [16,17]. Accordingly, CDI has found a range of applications in transmission and reflection geometries [18][19][20] to investigate nanoscale strain [21,22], semiconductor structures [18], and for biological imaging [23][24][25].…”

Coherent Ptychographic Imaging Microscope With 17.5nm Spatial Resolution Employing 13.5nm High Harmonic Light

“…In particular, tabletop extreme ultraviolet (EUV) coherent diffractive imaging (CDI) techniques based on high harmonic generation (HHG) are ideal for investigating complex nanostructured systems, including their static and dynamic electronic, phononic and magnetic properties. Tabletop EUV CDI combines elemental and chemical selectivity with nanometer spatial resolution, with pulse durations in the femtosecond (fs)-toattosecond (as) range [1][2][3][4][5]. In this work, we use ptychographic CDI [6][7] with high-spatial-coherence 13.5nm tabletop HHG to obtain 17.5nm spatial resolution images of a zone plate.…”

“…These patterns are combined with a phase retrieval algorithm to reconstruct the complex profiles of the object and probe beam. Ptychography provides excellent image fidelity compared to other techniques such as scanning electron microscope (SEM) imaging [1,3,6], requires no contact with the sample, has a working distance of centimeters and does not suffer from adverse effects such as surface charging.We used an actively stabilized 13.5nm HHG source (KM Labs XUUS 4.0) driven by a 20fs, 2mJ, 3kHz, Ti:Sapphire laser centered at 785nm (KM Labs Dragon), and generated a flux which was 10 times higher than was previously possible using the same driving laser [2]. The HHG light was produced in a 150µm diameter waveguide filled with 500 Torr of He.…”