Material-specific imaging of nanolayers using extreme ultraviolet coherence tomography

Abstract

Scientific and technological progress depend substantially on the ability to image on the nanoscale. In order to investigate complex, functional, nanoscopic structures like, e.g., semiconductor devices, multilayer optics, or stacks of 2D materials, the imaging techniques not only have to provide images but should also provide quantitative information. We report the material-specific characterization of nanoscopic buried structures with extreme ultraviolet coherence tomography. The method is demonstrated at a laser-driven broadband extreme ultraviolet radiation source, based on high-harmonic generation. We show that, besides nanoscopic axial resolution, the spectral reflectivity of all layers in a sample can be obtained using algorithmic phase reconstruction. This provides localized, spectroscopic, material-specific information of the sample. The method can be applied in, e.g., semiconductor production, lithographic mask inspection, or quality control of multilayer fabrication. Moreover, it paves the way for the investigation of ultrafast nanoscopic effects at functional buried interfaces.

Photon counting of extreme ultraviolet high harmonics using a superconducting nanowire single-photon detector

“…Thus, a straightforward way to improve the resolution is to decrease the wavelength of the light. Using light in the extreme ultraviolet (10-124 nm wavelength) and soft X-ray range (1-10 nm) for microscopy enables nanoscale resolution and exhibits an unique high elemental contrast combined with the ability to penetrate a few micrometer into solid samples [1,2]. However, the technical realization of such microscopes is extremely demanding in every aspect starting from the light source via the available optics to the detection of the radiation.…”

All-Optical Experimental Control of High-Harmonic Photon Energy

“…In this way the central wavelength of the highorder harmonics is fixed, and their spectral positions are defined by the generating laser source. The simple spectral tunability of these harmonic peaks can significantly widen the range of applications of these XUV sources [12], e.g., in chemical composition mapping [13,14], transient absorption spectroscopy [15][16][17][18], or XUV coherence tomography [19][20][21].…”

Optical Shock-Enhanced Self-Photon Acceleration

“…Such sources have thus far been limited to wavelengths > 100 nm, due to a lack of dispersion control and strong absorption in the extreme ultraviolet (λ = 10 nm − 100 nm). Extending coherent broadband sources into the extreme ultraviolet would open new wavelength regimes for spectroscopy and increase the achievable spatial and temporal resolution for applications including single-shot spectral interferometry [8], transient spectroscopy [9], and coherence tomography [10].…”

“…Such a pulse could be useful for enabling a single-shot version of the coherence tomography application discussed in Ref. [10] and providing sub-fs time resolution to observe transient effects. A photon accelerator based on SFF driven plasma could be optimized further to deliver higher frequencies, shorter pulses and better efficiency.…”