Beryllium-based multilayer X-ray optics Polkovnikov, V N; Salashchenko, N N; Svechnikov, M V ...
Physics Uspekhi,
01/2020, Letnik:
63, Številka:
1
Journal Article
Recenzirano
The article provides a review of the current state of affairs in the field of physics and technology of multilayer beryllium-containing mirrors intended for projection lithography and solar corona ...studies in the extreme ultraviolet (EUV) region. The methods of synthesizing and studying beryllium-containing multilayer mirrors are described. The results of recent studies on the internal structure and EUV reflection coefficients are given for Mo/Be, Mo/Si, Be/Al, and Be/Mg multilayer mirrors. The effect of Si and Be interlayers on the reflectivity is explained. Avenues for further research on beryllium-containing mirrors are discussed.
A comparative study was carried out of the structure and reflection performance of four types of multilayer mirror for extreme ultraviolet lithography at 11.2 nm; these were a pure Mo/Be structure ...and three Mo/Be-based structures with thin B
C, C and Si interlayers. It was demonstrated that Mo/Be mirrors show maximum reflectance at normal incidence, while maximum structural perfection is shown by Mo/Be/Si mirrors. The introduction of B
C and C layers into the structure increases the interlayer roughness and reduces the sharpness of the interfaces, adversely affecting the target coating characteristics. Results are presented for studies using four techniques: X-ray reflectometry, small-angle X-ray scattering, atomic force microscopy, and transmission electron microscopy.
The structural inhomogeneities of silicon films embedded within W/Si multilayer mirrors were studied by X‐ray reflection, grazing‐incidence small‐angle X‐ray scattering (GISAXS) and X‐ray ...photoelectron spectroscopy (XPS). In the diffuse scattering spectra, evidence of laterally and vertically ordered in‐layer inhomogeneities was consistently observed. In particular, specific substructures resonant in nature (named here `ridges') were detected. The properties of the ridges were similar to the roughness determined by quasi‐Bragg peaks of scattering, which required a high interlayer correlation of particles. The XPS showed the nanocrystalline nature of the Si particles in the amorphous matrix. The geometric characteristics and in‐layer and inter‐layer correlations of the nanoparticles were determined. In GISAXS imaging, the unusual splitting of the waists between the Bragg sheets into filament structures was observed, whose physical nature cannot yet be explained.
The nature of the observed bulk inhomogeneities in the silicon layers in W/Si multilayers is established. In the diffuse scattering spectra, specific substructures, which are clearly resonant in nature, are observed. The physical nature of some of them is not established.
The influence of Mo interlayers on the microstructure of films and boundaries, and the reflective characteristics of Ru/Be multilayer mirrors (MLM) were studied by X-ray reflectometry and ...diffractometry, and secondary ion mass spectrometry (SIMS). An increase in the reflection coefficients of MLM at a wavelength of 11.4 nm to record values of R = 72.2% and FWHM to Δλ
= 0.38 nm is shown. The effect of interlayers on the structural and reflective characteristics of MLM is explained by the barrier properties of the Mo layers, which prevent the mutual mixing of the Ru and Be layers, which leads to the formation of beryllides and a decrease in the X-ray optical contrast at the boundaries.
In a condensed matter system, phonons and plasmons are well-known quasiparticles that represent unusual dispersion behavior of energy and momentum at nanoscales. In a nanoscale Mo/Si multilayer ...structure, phonon modes in Raman scattering indicated the coexistence of crystalline Si (c-Si) nanoclusters within an amorphous silicon (a-Si) matrix. The TO mode was red-shifted with a decrease in the nanocluster size of Si in nanolayer films. This was associated with the momentum of phonons and it is fundamentally correlated to phonon confinement. The correlation length of the Si network was significantly smaller in a-Si and the TO mode broadened asymmetrically and red-shifted due to localized phonon density of state. Consequently, with a decrease in the thickness of the Si layer, blue shifts of plasmon energy for Mo 3d, Mo 4p, and Si 2p spectra were observed in X-ray photoelectron spectroscopy. Plasmon energy of the c-Si nanocluster was related to the forbidden gap, which increased with a decrease in cluster size. The concept of quantum confinement of phonon and electron states was used to determine the size of the c-Si nanoclusters in the a-Si matrix.
The results of an investigation on oxidation processes in Mo/Be multilayer nanofilms are presented. The films annealed both in ambient atmosphere and in vacuum. The extreme ultraviolet (EUV) and ...X-ray reflectivity of the samples at 11.34 and at 0.154 nm respectively were measured before and after the treatment. No noticeable changes in film thicknesses and boundaries were observed during the annealing at temperatures up to 300°C. An oxidation mechanism of the nanofilms Mo/Be is established and the activation energy of the oxidation process is estimated to be 38 kJ/mol. To determine an absolute quantity of oxygen in the oxidized layers, a simple technique based on the EUV reflectivity data is proposed, and the range of its applicability is subsequently analysed.
A round-robin characterization is reported on the sputter depth profiling of 60×(3.0nm Mo/0.3nm B4C/3.7nm Si) and 60×(3.5nm Mo/3.5nm Si) stacks deposited on Si(111). Two different commercial ...secondary ion mass spectrometers with time-of-flight and magnetic-sector analyzers, a pulsed radio frequency glow discharge optical emission spectrometer, and a home-built time-of-flight low-energy ion scattering and quadrupole-based secondary ion mass spectrometer were used. The influence of the experimental conditions, especially the type and energy of sputter ions, on the depth profiles of Mo/Si nanostructures with and without B4C barrier layers is discussed in terms of depth resolution, modulation factor and rapidity of analysis. The pros and cons of each instrumental approach are summarized.
•Sputter depth profiling of thin 60 layer periods Mo/Si and Mo/B4C/Si X-ray mirrors•Different commercial and home-built instruments were used.•0.3nm B4C layers suppress the profile degradation for glow discharge spectrometer.
Microstructural investigation of the Mo/Si nanoscale multilayers (MLs) is essential to design high-reflective nanomirrors. Raman spectroscopy showed existence of silicon layer in the amorphous ...structure. Small fraction of the nanocrystalline silicon (nc-Si) phase was found to be embedded in the amorphous silicon (a-Si) matrix. The disorder in a-Si is increased with the decrease in the thickness of silicon layer in the Mo/Si MLs, determined by the increased bond-angle deviation (ΔΘ) of the Si–Si network. The MLs exposed to high-temperature (HT) showed a decrease in the ΔΘ value, which signifies the relaxation of both molecular disorder and residual stress. X-ray diffraction analysis confirmed the polycrystalline bcc phase of Mo and the formation of intermetallic t-Mo5Si3 phase in the interfaces. This phase is more prominent for higher value of β (thickness ratio of high atomic weight (z) layer to ML period d, i.e. β = dMo/d). Intensity of the Mo (110) plane is decreased for the sample annealed at HT, which is directly related to the degree of amorphization and the formation of intermetallic phases. However, HT annealed Mo/Si showed the growth of Mo (220) planes for higher β value of MLs. Current findings revealed that the disorder in the a-Si and microstructure of the Mo and intermetallic phase depend on the annealing temperature and the β value. The analysis of the intermetallic phase is critical for the development of high reflective mirrors.
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•Magnetron sputtered deposited highly reflective Mo/Si multilayer nanomirror films.•Investigation of microscopic phase-structure and intermetallic compounds.•Molecular structure of silicon nanolayers and thermal stability of the intermetallic interfaces.
We have developed the design and experimentally studied aperiodic and stack broadband Mo/Si mirrors for the purposes of the KORTES project, optimised for uniform reflection in the 17 - 21 nm ...wavelength range. It is shown that stack structures with an insignificant loss in the reflection coefficient are much more preferable from the point of view of manufacturing and certification, which, in turn, makes it possible to correct the deposition process and to reach the calculated parameters of a multilayer mirror in a small number of iterations.
The article is devoted to the development of an EUV microscope using a wavelength of 13.84 nm. Due to the use of a mirror lens with a large numerical aperture, NA = 0.27, and a short depth of focus, ...it has been possible to carry out z-tomography of bio-samples for the first time with this type of microscope. A 3D image was reconstructed, and a pixel resolution of 140 nm was obtained. A new simple algorithm for the 3D reconstruction of absorption images from z-tomography data has been proposed that takes into account lens aberrations and a point spread function. The algorithm reduces the inverse absorption task to the corresponding well-studied task of fluorescence microscopy, with an error of 10% for cells up to 10 µm thick.
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