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In this paper, an experimental measurement of the diffusion constant of hydrogen in ruthenium is presented. By using a hydrogen indicative Y layer, placed under the Ru layer, the hydrogen flux through Ru was obtained by measuring the optical changes in the Y layer. We use optical transmission measurements to obtain the hydrogenation rate of Y in a temperature range from room temperature to 100 °C. We show that the measured hydrogenation rate is limited mainly by the hydrogen diffusion in Ru. These measurements were used to estimate the diffusion coefficient, D, and activation energy of hydrogen diffusion in Ru thin films to be D = 5.9 × 10−14 m2/s ∙ exp (-0.33 eV/kBτ), with kB the Boltzmann constant and τ the temperature.

In this work, we investigated the influence of composition on the polycrystalline structure, elastic properties and fracture strength, of ZrxSi1-x, NbxSi1-x, and MoxSi1-x free-standing thin films that were deposited by magnetron sputtering and subsequently annealed at 500 °C. Despite deviations from the stoichiometric composition, the crystalline structure of all films, except for the most Zr-rich ZrxSi1-x, corresponded to their respective stoichiometric disilicide structures, without the formation of a second-phase. Off-stoichiometry was found to be accompanied by the presence of lattice defects and a decrease of the grain size, which bring about a lower tensile stress in the films. The dependence of the fracture strength on the composition was remarkably similar for the three silicides, with the lowest and highest strength values occurring for samples with 30% and 37–40% of metal content, respectively. The observed dependence of strength on composition was attributed to the combination of the Hall-Petch effect, changes in the morphology and strength of grain boundaries, and the enhancement of crystal plasticity due to lattice defects induced by off-stoichiometry.

Following the recent demonstration of the sensitivity of grazing-incidence X-ray fluorescence to the lateral structure of periodic nano-patterned devices, a computational scheme for the simulation of experimental data is presented. This can be used for the element-selective analysis of 3D atomic distributions in nano-patterned structures., Following the recent demonstration of grazing-incidence X-ray fluorescence (GIXRF)-based characterization of the 3D atomic distribution of different elements and dimensional parameters of periodic nanoscale structures, this work presents a new computational scheme for the simulation of the angular-dependent fluorescence intensities from such periodic 2D and 3D nanoscale structures. The computational scheme is based on the dynamical diffraction theory in many-beam approximation, which allows a semi-analytical solution to the Sherman equation to be derived in a linear-algebraic form. The computational scheme has been used to analyze recently published GIXRF data measured on 2D Si3N4 lamellar gratings, as well as on periodically structured 3D Cr nanopillars. Both the dimensional and structural parameters of these nanostructures have been reconstructed by fitting numerical simulations to the experimental GIXRF data. Obtained results show good agreement with nominal parameters used in the manufacturing of the structures, as well as with reconstructed parameters based on the previously published finite-element-method simulations, in the case of the Si3N4 grating.

We present a general method for designing XUV aperiodic multilayer mirrors that can mimic a given target spectrum, specifically, the spectral transmission of an XUV optical system. The method is based on minimizing a merit function and using fidelity parameters that quantify the matching of the multilayer reflectivity spectrum with that of the target spectrum. To assess the feasibility of fabricating such a system, we show how to reduce the layer-to-layer thickness variations throughout the aperiodic layer stack. We demonstrate the design method using an example of an EUV optical system composed of 12 identical Mo/Si multilayer mirrors having a reflectivity peak at 13.5 nm. We found that the target spectrum can be mimicked with high fidelity either with a single reflection at an aperiodic multilayer mirror combined with standard absorbing filters or, if required, with two subsequent reflections at a mimic mirror. These examples demonstrate the applicability for metrology at XUV sources, including spectrally proper source imaging. Because our approach is of general applicability, the process can be used to mimic any other narrowband, single-peaked target spectrum in the XUV region.

Transition metals used in semiconductor, photolithography and fusion applications interact with low energy oxygen ions. Understanding erosion, the nature of the formed oxide and depth of oxygen transport is necessary in mitigating unexpected performance of sensors, optics or plasma facing components. Oxide formation is governed by both the ion–target combination and the incident ion energy. We study the interaction of the transition metals molybdenum, ruthenium, palladium and tungsten, with oxygen ions in the energy region of 50–500 eV. Near-threshold sputtering of metals was experimentally measured and compared to predictions by the Monte Carlo code TRIDYN. Compositional changes and oxide thicknesses following sputtering were measured using Angle resolved X-ray photoelectron spectroscopy and subsequently compared to limiting oxide formed by atomic oxygen exposures. Sputter yields in some cases (ruthenium) were found to be sensitive to ion beam impurities such as ozone ( 1% of background gas) leading to chemical sputtering. Ion induced oxide thicknesses (for molybdenum and tungsten) were found to be larger than those predicted by ballistic transport where sputtering is balanced by implantation. It is hypothesized that radiation enhanced diffusion of free oxygen leads to thicker oxide films at low ion energies.

In this work, a technique for hydrogen diffusion measurements through thin films is proposed and demonstrated. A yttrium film, which changes its refractive index upon hydrogen absorption, is used as an optical sensor to detect hydrogen. The yttrium sensor is coated with a thin (up to 12 nm) layer of test material and exposed to atomic hydrogen. To ensure that the calculated diffusion constant is not artificially changed by surfaces processes, the test layer is coated with palladium. Hydrogen diffusion through test layers of Si, Al, Ag, Ru, Mo, Al2O3 and SiO2 were measured and compared with existing data. The hydrogenation time (time to form YH2) was found to exponentially scale with the enthalpy of hydrogen solution in the test material. Comparison between measured diffusion coefficients for different film thicknesses, as well as previously reported results, highlights the strong dependence of the diffusion constant on sample fabrication conditions, and hydrogen exposure conditions. It is concluded that diffusion through thin films can be reliably compared only when specimen form and exposure conditions are the same. The relevance of this study for applications is discussed.

X-ray W/B multilayer mirrors with a period of 2.5 nm were deposited by dc magnetron sputtering and studied in comparison with W/Si multilayer systems of the same period. Transmission electron microscopy, grazing incidence X-Ray reflectivity, and x-ray photoelectron spectroscopy analysis revealed that the layer quality and interfaces of the W/B multilayers are not better than those of the W/Si multilayers. Strong intermixing between W and B is present, which leads to compound formation with little or no pure W left after the interaction: an optically unfavorable boride formation and an increased roughness result in a reduced reflectivity. The deposited W/B multilayer mirrors showed a reflectivity of 34.5% at 0.84 nm and angle of incidence 9.7°, compared to 40% obtained for W/Si multilayers. Ion polishing applied on the boron layers did not result in improvements of the reflectivity.

Transition metal surfaces exposed to low-energy reactive ions undergo dynamic changes in composition and density due to implantation and compound formation. We report measurements of nitrogen ion induced sputter yields for transition metals relevant to fusion and optics applications. Thin films of molybdenum, ruthenium, palladium and tungsten are bombarded by nitrogen ions of kinetic energies in the range of 50–500 eV at steady state fluences (1 × 10 18 ions / cm 2 ). Measured sputter yields are explained through energy and momentum transfer under the binary collision approximation using the Monte Carlo code TRIDYN. X-ray Photoelectron spectroscopy (XPS) studies showed the nitrogen content in the films at the end of ion exposure is independent of incoming ion energy. This occurs due to competing implantation and preferential surface nitrogen sputtering processes within the XPS probing depth. All metals investigated showed evidence of a nitride formed due to energetic nitrogen impact. The combination of XPS and TRIDYN simulations were applied to extract effective reaction cross-sections for each metal.

We performed combined experimental and computational research on damage processes in ruthenium thin films induced by femtosecond lasers with various photon energies. We present an experiment with an optical laser at normal incidence conditions and compare it with previously reported experiments at grazing incidence conditions with XUV and hard X-ray photons, covering a large range of photon energies. Analysis of ablation craters in Ru shows very similar crater morphology and depth of about 10–20 nm for all considered irradiation conditions. Simulations of light-matter interactions are performed with our combined Monte Carlo and two-temperature hydrodynamics approach. The simulation results show that the primal cause of eventual ablation is Auger decay of core-shell holes created after absorption of XUV and hard X-ray photons in the vicinity of ruthenium surface. They lead to the creation of many low-energy electrons which consequently release the absorbed energy near the surface, resembling the optical irradiation case. Similar absorbed energy distributions in the top part of ruthenium induce a similar thermo-mechanical response and, therefore, similar ablation process. Our results suggest that such mechanism is universal in a wide range of photon energies at grazing incidence conditions, when the photon absorption depth is smaller than the photoelectrons range.

Applied surface science 528, 146952 - (2020). doi:10.1016/j.apsusc.2020.146952, The dynamics of a thin ruthenium film irradiated by femtosecond extreme UV laser pulses is studied with a hybrid computational approach, which includes Monte Carlo, two-temperature hydrodynamics and molecular dynamics models. This approach is capable of accurate simulations of all stages of material evolution induced by extreme UV or X-ray photons: from nonequilibrium electron kinetics till complete lattice relaxation. We found that fast energy deposition in a subsurface layer leads to a two-level ablation: the top thin layer is ablated as a gas–liquid mixture due to expansion of overheated material at near and above critical conditions, whereas a thicker liquid layer below is ablated via a cavitation process. The latter occurs due to a thermo-mechanically induced tensile pressure wave. The liquid ablating layer exhibits unstable behaviour and disintegrates into droplets soon after detachment from the rest of the target. Our simulations reveal basic processes leading to formation of specific surface morphologies outside and inside the damage craters. The calculated ablation threshold, crater depth and morphological features are in quantitative agreement with the experimental data, which justifies the applicability of our hybrid model to study laser-induced material damage., Published by Elsevier, Amsterdam

We studied the formation of interfaces in W/Si multilayer structures deposited by magnetron sputtering. In vacuo Low Energy Ion Scattering Spectroscopy was used to determine the materials growth profile with a close to atomic resolution. For that purpose, bi-layer structures, W-on-Si and Si-on-W were grown, with Si being deposited using Ar as the sputter gas and W being deposited in either Ar or Kr. The measurements revealed strongly asymmetric interfaces, with W-on-Si being significantly broader than Si-on-W. However, no difference was found in the W-on-Si interface width depending on the sputter gas, Ar or Kr, used for W deposition, suggesting that it is not a ballistic effect of the backscattered gas ions that is responsible for the wider W-on-Si interface. However, strong surface segregation of Si atoms upon the deposition of W in Kr on Si was observed. Mechanisms responsible for the observed effects are discussed.

We studied a possibility of fabricating LaN/B grazing incidence multilayer mirrors for 6.

In this study, the density and oxygen content of Mo thin films were varied by changing the deposition conditions, in order to understand their influence on the catalytic activity of Mo2C for the synthesis of multi-layer graphene (MLG). Structural and morphological analysis of Mo2C in relation to its catalytic activity indicate that the density of Mo plays a more critical role on MLG synthesis than the oxygen content. Results show that the pinholes present in relatively low density Mo layers act as catalytically active defect sites, promoting MLG synthesis.

The adsorption and dissociation of carbon dioxide on a Ru(0001) single crystal surface was investigated by reflection–absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption (TPD) spectroscopy for CO2 adsorbed at 85 K. RAIRS spectroscopy shows that the adsorption of CO2 on a Ru(0001) single crystal is partially dissociative, resulting in CO2 and CO. The CO vibrational mode was also observed to split into two distinct modes, indicating two general populations of CO present at the surface. Furthermore, a time-dependent blue-shift is observed, which is characteristic of increasing CO surface coverage. TPD showed that coverages of up to 0.3 ML were obtained, and no evidence for chemisorption of oxygen on ruthenium was found.

Freestanding silicon nitride membranes with thicknesses down to a few tens of nanometers find use as TEM windows or soft X-ray spectral purity filters. As the thickness of a membrane decreases, emissivity vanishes, which limits radiative heat emission and resistance to heat loads. We show that thin metal layers with thicknesses in the order of 1 nm enhance the emissivity of thin membranes by two to three orders of magnitude close to the theoretical limit of 0.5. This considerably increases thermal load capacity of membranes in vacuum environments. Our experimental results are in line with classical theory in which we adapt thickness dependent scattering terms in the Drude and Lorentz oscillators., Comment: 5 pages, 5 figures

The substantially increased effort on multilayer coating technology, as motivated currently by the application of Mo/Si coatings in Extreme UV lithography, is expected to have a beneficial effect on the technology for multilayer optics in the XUV wavelength range in general. Some examples of new usage of multilayer structures in XRL research are given.

An analysis is made of the state of the art of x-ray lithography and x-ray optics. The principles of design and configurations of projection x-ray lithographic systems are considered. An analysis is made of the main trends of research on these topics proceeding in the laboratories in the Soviet Union, USA, Japan, and Great Britain. The problems encountered in the development of multilayer normal-incidence x-ray mirrors are described.

The latest generation of 193nm immersion lithography optics, with a numerical aperture (NA) of 1.35 and ultra pure water as immersion fluid serves the 45nm node on the ITRS roadmap. The potential solutions for the next step, the 32nm node, as presented in December 2007 by the ITRS are: 193nm double patterning / exposure, 193nm with 2nd generation fluid and EUVL. The performance of such next generation lithography optics is increasingly driven by the coating performance. For 193nm the performance of the antireflection and high reflection coatings is driven by the increasing NA, which requires the control of polarisation effects and transmission uniformity over light incidence angles. For EUV only high reflection coatings are needed and the NA is comparatively small. But the performance is limited by higher absorption and lower refractive index contrasts of the applicable coating materials at 13.5nm with respect to 193nm. In this talk we discuss and compare the different requirements and challenges in coating material, design, process, lifetime and accuracy for next generation lithography optics.

A Particle-in-Cell Monte Carlo model is used to simulate extreme ultraviolet driven plasma. In an extreme ultraviolet lithography tool, photons of a pulsed discharge source will ionize a low pressure argon gas by photoionization. Together with the photoelectric effect, this results in a strongly time dependent and low density plasma, which is potentially dangerous to the optical elements, the collector in particular. Plasma sheaths will develop and ions are accelerated towards the collector, which might lead to sputtering. A spherical geometry is used to study the plasma between the point source and collector. Simulations are performed to study the in.uence of background pressure and source intensity on the damage to the collector by sputtering.

Summary form only given. Plasmas with densities in the range 10 24-1025 m-3 have been created by making use of capillary discharges. These capillary discharges are low-current (300-800 A) discharges produced in hydrogen filled alumina capillaries of 0.3-0.5 mm diameter with a lifetime of a few hundred nanoseconds. The plasma channel produced in such a discharge has a hollow electron density profile. The minimum electron density results in a maximum refractive index in the centre which makes such a plasma suitable as a waveguide for intense laser light. When the plasma channel is used to guide a high-power (TW) intense laser pulse, it can be used as an accelerator for injected electron bunches. Such a laser pulse creates a wakefield in the plasma that in turn accelerates the electrons to energies of several hundreds MeV. Creating a lower density plasma channel with a density around 1023 m-3 is rather attractive due to the simpler synchronization of the injection of the electron bunch and the created wakefield by the high power laser pulse. A serious experimental problem in creating a capillary plasma with a low density can be the desorption of the hydrogen from the capillary walls. Desorption of one monolayer of hydrogen can give a density around 1024 m-3. Our experimental results show that if there would be any desorption, the contribution is less than 1022 m-3. Experimental results show a more fundamental problem for creating a suitable low density capillary plasma for wakefield acceleration of electrons. This is the relatively large matched spot size at lower pressures. That means that only large focused laser spot sizes can be guided properly resulting in lower energy density in the spot. This gives a weaker wakefield which in turn results in a smaller energy gain for the accelerated electrons. This problem can be solved by decreasing the capillary diameter, increasing the current (voltage) and using an axial magnetic field, resulting in a smaller matched spot size

We survey several research themes and experimental results of an initial collaborative development programme in Europe on Extreme Ultraviolet Lithography (EUVL).

Radiative characteristics of laser-plasma soft x-ray sources are reviewed. The dependence of the main plasma parameters on the heating laser wavelength is discussed, as well as the use of application-specific excimer lasers. A comparison is given with other soft x-ray sources like electron storage rings. Examples of the application of normal-incidence multilayer x-ray optics, e.g. to collimate the laser-plasma radiation or for soft x-ray projection lithography, are given.

The increasing reflectivity of multilayer mirrors has made the use of reflective soft x-ray optical systems, e.g. in soft x-ray microscopy and soft x-ray projection lithography [1,2] possible. However, the use of multi-mirror systems [3] in industrial applications can only be successful if such a system has sufficient throughput. It is therefore necessary to optimize the reflectivity to the highest value possible.

We developed an optical system for soft x-ray projection lithography [1] with a laser plasma x-ray source. In the optical system Mo/Si multilayer mirrors are used for near normal incidence reflectivity. High reflectivity of each multilayer is mandatory because in the optical system four reflecting surfaces are used. A reliable tool for characterisation of multilayers is needed in the process of determining the optimum parameters for the production of high reflectivity multilayer mirrors. Therefore we developed software to analyse the hard x-ray reflectivity measurements. With this software, that is based on a fast Fourier transform (FFT) of the Bragg peaks, a distinction between interface-roughness and layer-thickness errors can be made. These two parameters have considerable influence on the near normal incidence reflectivity. Furthermore, reflectivity measurements are done at various wavelengths to find the material densities. These are also important parameters for the near normal incidence reflectivity. This article will restrict itself to the analysis Mo/Si multilayers deposited at 36°C and 215°C with or without ion etching. These multilayers are made for a wavelength of 13.5 nm at normal incidence.

The rapid development of high average power excimer lasers pushes the potential of a laser plasma x-ray source for SXPL. Now that the problem of debris production is solved at least at the prototype level [1] the source might be a candidate for operation in an industrial environment. The development of high reflectivity multilayer coatings for soft x-rays at normal incidence makes it possible to produce a demagnifying x-ray optical system. Together with an x-ray reflection mask all ingredients to develop a SXPL system are present. A cooperation of research institutes, semiconductor industry, resist and laser manufacturers has been set up to develop the process technology required.

A soft-x-ray projection system has been designed, which consists of spherical components to be coated with multilayer reflection coatings. In the design, a two-mirror system and a spherical reflection mask, the optical aberrations were minimized. The design enables a resolution of sub-100 nm over a circular image field with a diameter of 4 mm at a wavelength of 10.5 nm. The assembly tolerances of the system and the fabrication tolerances of the substrates have been calculated. The surface roughness determined from our superpolished quartz substrates amounts to 0.3 nm, which is sufficient to meet the required specifications.

We report on design and development activities of an integrated soft-X-ray projection system, consisting of all-reflective multilayer optics and a repetitive laser plasma soft-X-ray source.