Multilayer Mirrors Research Articles

Ultrafast Laser Material Damage Simulation-A New Look at an Old Problem.

The chirped pulse amplification technique has enabled the generation of pulses of a few femtosecond duration with peak powers multi-Tera and Peta–Watt in the near infrared. Its implementation to realize even shorter pulse duration, higher energy, and higher repetition rate laser systems relies on overcoming the limitations imposed by laser damage of critical components. In particular, the laser damage of coatings in the amplifiers and in post-compression optics have become a bottleneck. The robustness of optical coatings is typically evaluated numerically through steady-state simulations of electric field enhancement in multilayer stacks. However, this approach cannot capture crucial characteristics of femtosecond laser induced damage (LID), as it only considers the geometry of the multilayer stack and the optical properties of the materials composing the stack. This approach neglects that in the interaction of an ultrashort pulse and the materials there is plasma generation and associated material modifications. Here, we present a numerical approach to estimate the LID threshold of dielectric multilayer coatings based on strong field electronic dynamics. In this dynamic scheme, the electric field propagation, photoionization, impact ionization, and electron heating are incorporated through a finite-difference time-domain algorithm. We applied our method to simulate the LID threshold of bulk fused silica, and of multilayer dielectric mirrors and gratings. The results are then compared with experimental measurements. The salient aspects of our model, such as the implementation of the Keldysh photoionization model, the impact ionization model, the electron collision model for ‘low’-temperature, dense plasma, and the LID threshold criterion for few-cycle pulses are discussed.

Design of an efficient illuminator for partially coherent sources in the extreme ultraviolet.

In this paper, the design of an efficient illuminator for extreme ultraviolet (EUV) applications such as photolithography, metrology, and microscopy is investigated. Illuminators are arrangements of optical components that allow us to tailor optical parameters to a targeted application. For the EUV spectral range, illuminators are commonly realized by an arrangement of several multilayer mirrors. Within this publication, design methods are developed to tailor optical parameters such as the intensity distribution, the spatial coherence, and the spectral bandwidth by using only one multilayer mirror. For the demonstration of the methods, an illuminator is designed for a compact in-lab EUV interference lithography system that is suited for industrial EUV resist qualification and large-area nanopatterning. The designed illuminator increases the wafer-throughput and improves the imaging quality.

Raman scattering studies of the ambient atmospheric thermal stability of Be in periodic Be/Mo and Be/W multilayer mirrors

The ambient atmospheric thermal stability of beryllium (Be) layers in Be/Mo and Be/W multilayer mirrors was investigated by Raman scattering. The physical characteristic of the transverse optical (TO) mode was considered for structural analysis of the Be layers in the multilayers. With an increase in thermal annealing temperature, two important modifications of this mode were noticed: the TO mode of Be was found to shift to a lower frequency and the peak width became wider. These two facts are related to the deterioration of the crystalline quality of the Be layers upon thermal annealing. The TO mode of the crystalline Be phase completely vanished and high-intensity peaks at the shoulder were detected for the Be/Mo multilayer thermally annealed at 723 K. This evidence is associated with the transformation of polycrystalline into an oxidized amorphous Be phase. In this case, the diffusion of oxygen to the inner period and the destruction of the modulation of the periodic structure of the multilayer was investigated by a secondary ion mass spectrometer. However, the TO mode of Be embedded within W in Be/W multilayers was stable in similar annealing conditions, which revealed the thermal stability.

A ReaxFF Molecular Dynamics Study of Hydrogen Diffusion in Ruthenium-The Role of Grain Boundaries.

Ruthenium (Ru) thin films are used as protective caps for the multilayer mirrors in extreme ultraviolet lithography machines. When these mirrors are exposed to atomic hydrogen (H), it can permeate through Ru, leading to the formation of hydrogen-filled blisters on the mirrors. H has been shown to exhibit low solubility in bulk Ru, but the nature of H diffusion through Ru and its contribution to the mechanisms of blistering remain unknown. This work makes use of reactive molecular dynamics simulations to study the influence of imperfections in a Ru film on the behavior of H. For the Ru/H system, a ReaxFF force field which reproduces structures and energies obtained from quantum-mechanical calculations was parametrized. Molecular dynamics simulations have been performed with the newly developed force field to study the effect of tilt and twist grain boundaries on the overall diffusion behavior of H in Ru. Our simulations show that the tilt and twist grain boundaries provide energetically favorable sites for hydrogen atoms and act as sinks and highways for H. They therefore block H transport across their planes and favor diffusion along their planes. This results in the accumulation of hydrogen at the grain boundaries. The strong effect of the grain boundaries on hydrogen diffusion suggests tailoring the morphology of ruthenium thin films as a means to curb the rate of hydrogen permeation.

High-dispersive mirror for pulse stretcher in femtosecond fiber laser amplification system

We present a high-dispersive multilayer mirror for pulse stretching in a femtosecond fiber laser amplification system. The designed mirror contains 54 layers with a total physical thickness of 7.3 μm, which can provide a positive group delay dispersion (GDD) of 600 fs2 and a high reflectance over 99.9% from 1010 to 1070 nm. The samples were prepared by dual ion beam sputtering. The measured transmittance matches well with the theoretical result. The GDD characteristics of samples were tested by home-made white light interferometer. The measured GDD is higher than the design results, an average GDD of +722 fs2 from 1010 nm to 1070 nm. The mirrors were employed in a Yb-doped large-mode-area photonic crystal fiber amplification system. An input pulse compressed by the gratings with autocorrelation function of 83 fs is obtained with a stretched FWHM of 1.29 ps after 28 bounces between the dispersive mirrors. The results show that the multilayer dispersive mirror could be an effective and promising technique for pulse stretching in femtosecond amplification systems.

Broadband Tamm Plasmons in Chirped Photonic Crystals for Light-Induced Water Splitting.

An electrode of a light-induced cell for water splitting based on a broadband Tamm plasmon polariton localized at the interface between a thin TiN layer and a chirped photonic crystal has been developed. To facilitate the injection of hot electrons from the metal layer by decreasing the Schottky barrier, a thin n-Si film is embedded between the metal layer and multilayer mirror. The chipping of a multilayer mirror provides a large band gap and, as a result, leads to an increase in the integral absorption from 52 to 60 percent in the wavelength range from 700 to 1400 nm. It was shown that the photoresponsivity of the device is 32.1 mA/W, and solar to hydrogen efficiency is 3.95%.

Development of a quasi-coaxis dual-energy flat spectral response X-ray imaging instrument for measuring hotspot electron temperature.

The measurement of hotspot electron temperature is a paramount technique of implosion physics research in inertial confinement fusion. This study proposes a novel quasi-coaxis dual-energy flat spectral response high-resolution X-ray imaging instrument comprising a dual-channel total-reflection Kirkpatrick-Baez microscope and two flat non-periodic multilayer mirrors, which can image at 6.4 ± 0.5 and 9.67 ± 0.5 keV simultaneously. Various theoretical simulations were performed to verify the performance and feasibility of the imaging instrument, which was assembled and characterized in a laboratory. Experimental results show that the imaging instrument could achieve a high spatial resolution of 5 µm in a ± 150 µm field of view (FOV), the root mean square(RMS) deviation values of the measured reflection efficiency are 1.71% and 1.82% for the 6.4 keV and 9.67 keV imaging channels, respectively, in the ± 150 µm FOV.

ID23-2: an automated and high-performance microfocus beamline for macromolecular crystallography at the ESRF.

ID23-2 is a fixed-energy (14.2 keV) microfocus beamline at the European Synchrotron Radiation Facility (ESRF) dedicated to macromolecular crystallography. The optics and sample environment have recently been redesigned and rebuilt to take full advantage of the upgrade of the ESRF to the fourth generation Extremely Brilliant Source (ESRF-EBS). The upgraded beamline now makes use of two sets of compound refractive lenses and multilayer mirrors to obtain a highly intense (>1013 photons s-1) focused microbeam (minimum size 1.5 µm × 3 µm full width at half-maximum). The sample environment now includes a FLEX-HCD sample changer/storage system, as well as a state-of-the-art MD3Up high-precision multi-axis diffractometer. Automatic data reduction and analysis are also provided for more advanced protocols such as synchrotron serial crystallographic experiments.

Evaluation of Hydrogen-Induced Blistering of Mo/Si Multilayers with a Capping Layer

Mo/Si multilayer mirrors are used for extreme ultraviolet (EUV) lithography. The formation of hydrogen-induced blisters in the Mo/Si multilayer is a problem that reduces the reflectance of the mirror. To evaluate the blister-resistance of EUV mirrors, the blister formation processes of Mo/Si multilayers with a capping layer were investigated using a high-frequency hydrogen plasma system as a hydrogen ion source under varying hydrogen ion exposure conditions. As a result, it was observed that blister formation by low-energy hydrogen ion irradiation of about 10 eV increases the blister-occupied area, depending on the amount of the ion dose. Furthermore, the sample was heated to promote the diffusion of hydrogen atoms, and the activation energy of blister formation was examined using the Arrhenius plot of the ion dose required for blister formation with respect to the heating temperature. The analysis showed that when the ion flux is known, the blister formation time can be predicted.

Design of a broadband reflection mirror for the water window region using a stacked multilayer with optimized structure

A broadband reflection mirror that can realize maximum uniform reflectivity is an important optical element in the water window region. In this paper, a stacked multilayer (SM) mirror with optimized structure for achieving broadband reflection in the water window region is presented. A genetic algorithm with a two-parametric merit function is employed to achieve maximum uniform reflection in the desired spectral band. A 4.90% average reflectivity with 0.25% root-mean-square deviation in the range of 370–390 eV is achieved by a Cr/Sc SM with 40 periodic multilayer structures. Compared with aperiodic multilayers, proposed SMs exhibit better optimization efficiency, design robustness, and thickness error tolerance. This research provides an efficient method for designing broadband reflection mirrors in the water window region, and may be helpful for steering broadband water window sources, such as high order harmonics and attosecond pulse.

Manufacturing and research of mirrors with a wide bandwidth for synchrotron applications

The work is devoted to the development, fabrication and analysis of broadband W / Si multilayer mirrors for a broadband monochromator, calculated for the spectral range of 7-10 keV. The possibility of using the stacking approach to obtain multilayer mirrors with a reflection coefficient of about 30% and a spectral bandwidth Delta E/E of about 20% is shown. The results of measurements of the angular and spectral reflection curves of the mirror obtained on a laboratory diffractometer and on a synchrotron in Novosibirsk are presented. Keywords: hard X-ray range, monochromator, synchrotron radiation, broadband mirrors, stack structures, multilayer X-ray mirrors.

Prospective wavelengths for projection lithography uing synchrotron radiation

Promising wavelengths for next-generation lithography with a wavelength shorter than 13.5 nm based on a synchrotron X-ray source are discussed. Theoretical and experimental values of the reflection coefficients of multilayer X-ray mirrors providing the maximum reflectivity in the range of 11.4-3.1 nm are presented. The theoretical efficiency of multilayer optics is compared for different wavelengths. Keywords: X-ray lithography, multilayer X-ray optics, multilayer X-ray mirrors.

Project of a two-mirror monochromator for the photon energy range 8-36 keV for the "SKIF" synchrotron

A project of an X-ray monochromator for the "SKIF" synchrotron based on two flat mirrors with multilayer reflective coatings is reported. The concept of the monochromator is based on the absence of precision mechanical systems and feedthroughs in vacuum, which significantly reduces mirror surface contamination and increases scanning accuracy. In addition, the overall structure of the device is greatly simplified in this way, which in turn leads to a significant reduction in the total cost and labor for manufacturing. The grazing angle of incidence of radiation on the mirrors in the process of scanning by photon energy varies within 0.5-1.3o. The length of the mirrors is 120 mm, the assumed size of the input beam is 1x1 mm2. A wide operating energy range, 8-36 keV, is achieved through the use of 3 strip-mirrors with coatings of different chemical composition, namely: Mo/B4C, W/B4C and Cr/Be. The article presents the X-ray optical scheme, the expected reflection coefficients and spectral selectivity of the monochromator, the results of the calculation of thermally induced surface deformations and the corresponding slope errors of the first mirror. Keywords: synchrotron radiation, multilayer mirror, monochromator, surface.

Ru/Sr multilayer mirrors for the spectral range 9-12 nm

The results of studies of Ru/Sr multilayer mirrors optimized for the working wavelength range of 9-12 nm are presented in the paper. Within the framework of the presented article the strontium based multilayer structures with stable over time reflective characteristics were obtained for the first time. It is shown that Ru/Sr mirrors have the highest reflectance of all known reflective coatings, with the exception of beryllium-containing, in the spectral range of 9-12 nm. Keywords: multilayer X-ray mirrors, X-ray lithography, X-ray radiation.

Перспективные длины волн для проекционной литографии с использованием синхротронного излучения

Promising wavelengths for next-generation lithography with a wavelength shorter than 13.5 nm based on a synchrotron X-ray source are discussed. Theoretical and experimental values of the reflection coefficients of multilayer X-ray mirrors providing the maximum reflectivity in the range of 11.4-3.1 nm are presented. The theoretical efficiency of multilayer optics is compared for different wavelengths.

Research and creation of broadband X-ray mirrors with a spectral transmission band coinciding with emission lines and the possibility of filtering

The article considers broadband multilayer X-ray mirrors based on Mo/Be and Mo/Si structures with a transmission band coinciding with the Si Lα (13.5 nm) and Sn (13.5 nm) emission lines. The described structures are of great interest for the currently developed liquid source of EUV radiation, since they make it possible to increase the efficiency of the source-X-ray optical system due to the "complete" capture of emission lines. Keywords: extreme ultraviolet radiation, emission spectrum, laser spark, multilayer X-ray mirror.

Алмаз-карбид-кремниевый композит "скелетон" как перспективный материал для подложек рентгенооптических элементов

The paper proposes the use of diamond-carbide-silicon composite "Skeleton"® coated with amorphous silicon as substrates for multilayer X-ray mirrors for powerful synchrotron radiation sources (3rd+ and 4th generation). The surfaces with the following parameters were obtained using standard deep polishing methods: flatness at the level of RMS90%=54.2 nm; effective roughness sigmaeff~1.0 nm; high-frequency roughness sigma2х2~0.1 nm.

Исследование и создание широкополосных рентгеновских зеркал со спектральной полосой пропускания, совпадающей с эмиссионными линиями и возможностью фильтрации

The article considers broadband multilayer X-ray mirrors based on Mo/Be and Mo/Si structures with a transmission band coinciding with the Si Lα (13.5 nm) and Sn (13.5 nm) emission lines. The described structures are of great interest for the currently developed liquid source of EUV radiation, since they make it possible to increase the efficiency of the source-X-ray optical system due to the “complete” capture of emission lines.

Система визуализации плазменного факела бетатронного источника рентгеновского излучения

The paper describes the design of a microscope for studying a betatron radiation source based on the PEARL femtosecond laser complex in the SXR and EUV wavelength range. The main optical element of the microscope is a spherical Schwarzschild objective a x5 magnification. The device allows to study the size and spatial structure of the interaction area of laser radiation with matter, at a selected wavelength in the EUV or SXR range with a resolution of δx = 2.75 microns. The operation wavelength (=13.5 nm) is set by multilayer X-ray mirrors. Thin-film absorption filters are used to suppress the background component of the signal.

Diamond-carbide-silicon composite "skeleton" as a promising material for X-ray optical substrates

The paper proposes the use of diamond-carbide-silicon composite "Skeleton"oledR coated with amorphous silicon as substrates for multilayer X-ray mirrors for powerful synchrotron radiation sources (3+ and 4th generation). The surfaces with the following parameters were obtained using standard deep polishing methods: flatness at the level of RMS90%=54.2 nm; effective roughness sigmaeff~1.0 nm; high-frequency roughness sigma2x2~0.1 nm. Keywords: x-ray optics, x-ray mirrors, substrates for x-ray mirrors, roughness.