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International audience; This paper demonstrates that highly reflective Cr/B 4 C multilayer interference coatings with nano-metric layer thicknesses, designed to operate in the soft X-ray photon energy range, have stable reflective performance for a period of 3 years after deposition. The microstructure and chemical composition of layers and interfaces within Cr/B 4 C multilayers is also examined, with emphasis on the B 4 Con -Cr interface where a significant diffusion layer is formed and on the oxide in the top B 4 C layer. Multiple characterization techniques (X-ray reflectivity at different photon energies, X-ray pho-toelectron spectroscopy, transmission electron microscopy, electron diffraction and X-ray diffraction) are employed and the results reveal a consistent picture of the Cr/B 4 C layer structure.

This manuscript presents the structural characterization of Al/Sc-based periodic multilayer coatings for the extreme ultraviolet (EUV) spectral range. Based on transmission electron microscopy and electron diffraction as well as grazing-incidence and large-angle x-ray diffraction, a model for the layer structure and the interfacial effects of Al/Sc coatings is built. The onset of crystallization in nanoscale Al and Sc layers as a function of thickness is also revealed in these characterizations. The Al/Sc layer model is validated and further refined by fitting in-band and out-of-band EUV reflectance measurements across 5 orders of magnitude in an extended wavelength range from 17 to 80 nm. The same type of EUV reflectance measurements is used to test the Al/Sc aging properties and to demonstrate the spectral response of optimized two- and tri-material multilayers including Al/Sc, Al/Sc/SiC and Mo/Al/Sc.

We present an experimental, self-consistent determination of the optical constants (refractive index) of Pt using a combination of photoabsorption and reflectance data in the photon energy range 25–778 eV, which includes the N- and O-shell electronic absorption edges of Pt. We compare our new experimental values with Pt optical constant data sets from the literature. Our Pt optical constant values reveal highly resolved absorption-edge fine structure around the O2,3 and N6,7 edges in both the absorptive and dispersive portions of the refractive index, which were missing in the earlier literature.We present an experimental, self-consistent determination of the optical constants (refractive index) of Pt using a combination of photoabsorption and reflectance data in the photon energy range 25–778 eV, which includes the N- and O-shell electronic absorption edges of Pt. We compare our new experimental values with Pt optical constant data sets from the literature. Our Pt optical constant values reveal highly resolved absorption-edge fine structure around the O2,3 and N6,7 edges in both the absorptive and dispersive portions of the refractive index, which were missing in the earlier literature.

Efficient multilayer optics for radiation in the water window range are difficult to manufacture due to extremely small layer thicknesses and severe intermixing of elements between the layers. Therefore, adequate analytics and short feedback loops are of utmost importance for manufacturers to improve performance and efficiency. We show the possibility for non-destructive elemental depth profiling with commercial laboratory equipment using four real-life CrSc multilayer samples. Comparative measurements at the laboratory of PTB at the synchrotron radiation facility BESSY II confirm the results and prove the potential of laboratory equipment for the reliable analysis of stratified materials with sub-nanometer layer thicknesses.

International audience; The Kossel effect is the diffraction by a periodically structured medium, of the characteristic X-ray radiation emitted by the atoms of the medium. We show that multilayers designed for X-ray optics applications are convenient periodic systems to use in order to produce the Kossel effect, modulating the intensity emitted by the sample in a narrow angular range defined by the Bragg angle. We also show that excitation can be done by using photons (X-rays), electrons or protons (or charged particles), under near normal or grazing incident geometries, which makes the method relatively easy to implement. The main constraint comes from the angular resolution necessary for the detection of the emitted radiation. This leads to small solid angles of detection and long acquisition times to collect data with sufficient statistical significance. Provided this difficulty is overcome, the comparison or fit of the experimental Kossel curves, i.e., the angular distributions of the intensity of an emitted radiation of one of the element of the periodic stack, with the simulated curves enables getting information on the depth distribution of the elements throughout the multilayer. Thus the same kind of information obtained from the more widespread method of X-ray standing wave induced fluorescence used to characterize stacks of nanometer period, can be obtained using the Kossel effect.

In this Letter, we have developed new and highly efficient periodic multilayer mirrors Al/Sc, Al/Sc/SiC, and Mo/Al/Sc with optimized reflectance at wavelengths between 40 and 65 nm. We have reached record values in measured peak reflectance: 57.5% at 44.7 nm and 46.5% at 51 nm, with Al/Sc/SiC at near-normal incidence. Furthermore, to the best of our knowledge, we have achieved the largest reported bandwidth with Mo/Al/Sc at 57 nm and the narrowest bandwidth with Al/Sc at a 60 nm wavelength. These new and promising results demonstrate that Al/Sc-based multilayer coatings are excellent candidates for future generations of extreme ultraviolet (EUV) instruments for solar physics, EUV lasers, and attosecond science, in a wavelength range that has not been fully explored.

The thin film optical constants are key parameters to carry out optical simulation or optimization of multilayer mirrors with high efficiency. However, for most materials, different sets of optical constants can be found in the literature especially in the EUV range, as these parameters are not as well-known in the EUV as in the visible or wavelength range. In this work, we have used several reflectance and transmittance measurements in the wavelength range from 10 nm to 60 nm. Different optical constant files have been tested and compared with the IMD simulation software. We will present some experimental spectra and theoretical simulations to highlight the existing problem on the reliability of optical constants sets and to discuss potential solutions. We focus our research on a few materials of particular interest in the EUV range such as aluminum, aluminum oxide, molybdenum, zirconium, magnesium, silicon carbide, and boron carbide. These analyses lead us to select the most reliable and accurate optical constants set, or to create the best one from the concatenation of existing data for each material of interest.

International audience; Soft X-ray and Extreme Ultraviolet (EUV) radiation (defined as light with wavelength in the 1 to 100 nm range) has been playing a growing role in major scientific and industrial applications over the last 20 years: astrophysics and solar physics, materials sciences, biology, semiconductor industry, plasma diagnostics. Especially the emergence of novel EUV/X-ray sources with unprecedented brightness and coherence (4th generation synchrotrons, free-electron lasers, tabletop lasers, high-harmonic generation and attosecond sources) has ushered a new era in the fields of materials science, chemistry, plasma physics, biology and life sciences. Several scientific and technological breakthroughs have been achieved recently. X-ray radiation from the SPRING-8 synchrotron light source in Japan has been focused on a spot with diameter smaller than 10 nm; this constitutes the smallest spot of light ever produced and could enable studies with the most exquisite spatial resolution. The generation of ultrashort EUV pulses with a duration less than 0.1 femtosecond (= 100 attosec-onds) made it possible for the first time to observe electron orbitals in molecules. Photolithography scanners based on EUV light have entered the world of semiconductor manufacturing in order to produce the next generation of computer chips. In 2007, the EUV telescopes aboard NASA's Solar Terrestrial Relations Observatory (STEREO) mission provided the first 3D images of the solar corona with its protuberances. Furthermore, since 2010, the Solar Dynamics Observatory (SDO), NASA's most advanced solar mission , has been continuously transmitting full-disk images of the solar corona every 10 seconds, simultaneously at 7 EUV wavelengths with 1 arcsec resolution. Observing the Sun with such unprecedented temporal and spatial resolution has led to groundbreaking discoveries related to the Sun's extremely complex magnetic field and has led to better understanding of extreme events such as solar flares and coronal mass ejections, which can seriously affect earth and space environments. These breakthroughs have been enabled by the development of new optical components dedicated to the EUV/ X-ray spectral range. The main challenges in fabricating EUV/X-ray optics come from the properties of materials in this spectral range. With the refractive index of any material being very close to 1, the refractive phenomena at any interface are weak and the reflectivity of any single material at non-grazing incidence angles is near zero. Moreover, all materials strongly absorb X-rays, so the transmission of any component is almost zero. Multi-layer interference mirrors are enabling optical components in most EUV/X-ray optical systems. Demonstrated experimentally for the first time in the 1970s by E. Spiller, these mirrors consist of periodic or aperiodic structures of alternating thin film layers of 2 or more materials with nanometer-scale thickness, deposited on an optical sub-strate. The constructive interference between the layers results in efficient reflectance at EUV/X-ray wavelengths even at near-normal incidence angles thus enabling the operation of a wide range of optical components including imaging and illumination systems, reflective filters, grating spectrometers and polarizers. However, the fabrication of high-performance multi-layer coatings poses serious technical challenges. Multi-layer coatings need to obey several stringent (and often conflicting) requirements, including: (i) contain materials with good optical contrast in the wavelength region of operation (ii) contain tens or hundreds of layers with nanometer-scale thickness, where each layer is deposited with picometer-scale precision (iii) form stable layer interfaces with minimal interdiffusion and with smoothness on the order of the atomic dimension, (iv) have low thin film stress, (v) have stable reflective performance for periods up to 10 years, or even longer. This special section aims to provide a survey of current topics and major development lines in the very active research area of X-ray and EUV multilayer coating development. It gathers studies of the properties of these nanoscale structures (microstructure, mechanical stress, lifetime stability) with a focus on new promising material combinations and on short-period multilay-ers, with individual layer thicknesses around (or less than) 1 nm. Technological developments, new characterization 516

International audience; The Kossel interferences generated by characteristic x-ray lines produced inside a periodic multilayer have been observed upon proton irradiation, by submitting a Cr/B4C/Sc multilayer stack to 2 MeV protons and observing the intensity of the Sc and Cr Kα characteristic emissions as a function of the detection angle. When this angle is close to the Bragg angle corresponding to the emission wavelength and period of the multilayer, an oscillation of the measured intensity is detected. The results are in good agreement with a model based on the reciprocity theorem. The combination of the Kossel measurements and their simulation, will be a useful tool to obtain a good description of the multilayer stack and thus to study nanometer-thick layers and their interfaces.

International audience; We present an experimental study of the effect of layer interfaces on the x-ray reflectance in Cr/B4C multilayer interference coatings with layer thicknesses ranging from 0.7 nm to 5.4 nm. The multilayers were deposited by magnetron sputtering and by ion beam sputtering. Grazing incidence x-ray reflectometry, soft x-ray reflectometry, and transmission electron microscopy reveal asymmetric multilayer structures with a larger B4C-on-Cr interface, which we modeled with a 1–1.5 nm thick interfacial layer. Reflectance measurements in the vicinity of the Cr L2,3 absorption edge demonstrate fine structure that is not predicted by simulations using the currently tabulated refractive index (optical constants) values for Cr.

In this study, we determine with improved accuracy the complex index of refraction n = 1 − δ + iβ of sputtered chromium thin films for photon energies ranging from 25 eV to 813 eV. These data include the first absolute measurements of the absorption fine structure near the Cr-L edge. First, we verified by combining Rutherford Backscattering Spectrometry and grazing-incidence x-ray reflectometry that the sputtered thin films were pure Cr with a density consistent with tabulated values. Then, we demonstrated that the Cr surface oxide layer remains stable when the samples are exposed to air for up to 4 years. The Cr absorption coefficient β was determined from the transmittance of freestanding Cr thin films with various thicknesses, measured at the ALS synchrotron radiation source. A model is proposed to correct the transmittance data from the spectral contamination of the source. Finally, we used the new β values, combined with theoretical and tabulated data from the literature, in order to calculate the δ values by the Kramers-Kronig relation. The improvement in the accuracy of β values is demonstrated by the f-sum rule. An additional validation of the new Cr optical constants (δ, β) is performed by comparing the simulated and experimental reflectance of a Cr/B4C multilayer mirror near the Cr-L2,3 edge.

Nanometer-thick Al/SiC periodic multilayers, designed for the Extreme Ultra Violet (EUV) range, have been characterized by different techniques dedicated to such thin multilayers (each between 4 and 10 nm thick). In order to decrease the roughness and to improve the optical performances of the stacks, an ultrathin (2 nm) refractory metal layer has also been introduced, thus making Al/W/SiC and Al/Mo/SiC multilayer systems with three layers in period. The samples are deposited by magnetron sputtering. The stacks have a period ranging between 16 and 18 nm. Time-of-Flight SIMS (ToF-SIMS) is used here to determine the depth profiles of the different elements present within the multilayers. It is observed that the interfaces of the Al/W/SiC and Al/Mo/SiC multilayers are sharper than those of the Al/SiC system. X-ray emission spectroscopy (XES) is used to identify the chemical state of the Al and Si atoms within the multilayers and to check if there is any interfacial compound. The results show that there is no interaction between the Al and SiC layers leading to the formation of an interfacial compound. The results are confirmed by X-ray reflectivity (XRR) measurements. They show that the Al/SiC multilayers present large interfacial roughnesses, but the Al/W/SiC and Al/Mo/SiC multilayers have the lower roughness values. Copyright © 2010 John Wiley & Sons, Ltd.

International audience; We report on the development of multilayer optics for the extreme ultra-violet (EUV) range. The optical performance of Al-based multilayer mirrors is discussed with regard to promising reflectivity and selectivity characteristics and the problems of the interfacial roughness for this type of multilayers. We demonstrate a possibility to reduce the average roughness by introducing additional metal layer (W or Mo) rather than depositing a buffer layer at each interface. We have prepared and tested Al/SiC, Al/W/SiC and Al/Mo/SiC multilayers of various periods for the spectral range from 15 to 40 nm, which is the range of increasing interest for high-order harmonic generation, synchrotron radiation and astrophysics. The structure of the three-component systems has been optimized in order to obtain the best reflectivity for each wavelength within the spectral range. We have shown that introduction of refractory metal in Al-based periodic stack can improve the optical performance of multilayer reflecting coatings designed for the EUV applications.

The authors present an experimental study of Cr∕Sc multilayer mirrors optimized for the detection of the nitrogen Kα-emission line (λ=3.16nm) at a grazing incidence around 23°, for electron probe microanalysis applications. The multilayers were deposited onto silicon substrates using a dc magnetron sputtering system. They were characterized with grazing incidence copper Kα x-ray reflectometry and atomic force microscopy, as well as with at-wavelength reflectometry using synchrotron radiation. These various characterization methods pointed out that the interfacial roughness of these multilayers increases drastically with the number of bilayers. Growth parameters were then optimized, and it is shown that the structure and reflectivity of such multilayers can be considerably improved by optimizing the sputter gas pressure during the deposition process. Reflectivity higher than 37% were measured at 22.3° grazing angle for the nitrogen Kα-emission line.

We present recent advances in Al-based multilayer mirrors for EUV applications including high efficiency narrowband, dual-band and broadband mirrors. Applications to solar physics and to ultrafast dynamics with coherent EUV sources will be discussed.

International audience; We propose a new model enabling the extraction of the phase of a multilayer mirror from photocurrent measure- ments in the soft x rays. In this range, the effects of the mean free path of the electrons inside the stack can no longer be neglected, which prevents the phase reconstruction by conventional photocurrent measurements. The new model takes into account this phenomenon and thus extends up to the x rays the applicability range of the technique. This ap- proach has been validated through a numerical and exper- imental study of chromium/scandium multilayers used near 360 eV. To our knowledge, this work constitutes the first measurement of the phase of a multilayer mirror in the soft x-ray range.

After a brief description of the theoretical principles of multilayer mirrors, we present the state of the art of experimental results obtained in the XUV range. We then focus on the specificities of multilayer mirrors for pico- and femtosecond sources, in terms of reflectivity, selectivity and stability. Finally, we report the recent advances in the development of multilayer mirrors for attosecond sources, from the design of the mirror to the characterization of such a component.

International audience; We study Cr/Sc-based multilayer mirrors designed to work in the water window range using hard and soft x-ray reflectivity as well as x-ray fluorescence enhanced by standing waves. Samples differ by the elemental composition of the stack, the thickness of each layer, and the order of deposition. This paper mainly consists of two parts. In the first part, the optical performances of different Cr/Sc-based multilayers are reported, and in the second part, we extend further the characterization of the structural parameters of the multilayers, which can be extracted by comparing the experimental data with simulations. The methodology is detailed in the case of Cr/B4C/Sc sample for which a three-layer model is used. Structural parameters determined by fitting reflectivity curve are then introduced as fixed parameters to plot the x-ray standing wave curve, to compare with the experiment, and confirm the determined structure of the stack.

An alternate multilayer (AML) grating has been prepared by coating an ion etched lamellar grating with a B4C/Mo2C multilayer (ML) having a layer thickness close to the groove depth. Such a structure behaves as a 2D synthetic crystal and can reach very high efficiencies when the Bragg condition is satisfied. This AML coated grating has been characterized at the SOLEIL Metrology and Tests Beamline between 0.7 and 1.7 keV and at the four-crystal monochromator beamline of Physikalisch-Technische Bundesanstalt (PTB) at BESSY II between 1.75 and 3.4 keV. A peak diffraction efficiency of nearly 27% was measured at 2.2 keV. The measured efficiencies are well reproduced by numerical simulations made with the electromagnetic propagation code CARPEM. Such AML gratings, paired with a matched ML mirror, constitute efficient monochromators for intermediate energy photons. They will extend the accessible energy for many applications as x-ray absorption spectroscopy or x-ray magnetic circular dichroism experiments.

In this paper, we report on the design, synthesis and characterization of extreme ultraviolet interferential mirrors for solar imaging applications in the spectral range 17 nm–34 nm. This research is carried out in the context of the preparation of the European Space Agency Solar Orbiter mission. The purpose of this study consists in optimizing the deposition of Al-based multilayers by ion beam sputtering according to several parameters such as the ion beam current and the sputtering angle. After optimization of Al thin films, several kinds of Al-based multilayer mirrors have been compared. We have deposited and characterized bi-material and also tri-material periodic multilayers: aluminum/molybdenum [Al/Mo], aluminum/molybdenum/boron carbide [Al/Mo/B 4 C] and aluminum/molybdenum/silicon carbide [Al/Mo/SiC]. Best experimental results have been obtained on Al/Mo/SiC samples: we have measured reflectivity up to 48% at 17.3 nm and 27.5% at 28.2 nm on a synchrotron radiation source.

The present article reports a study of current–voltage (J–E) and capacitance–voltage (C–V) measurements on metal–insulator–semiconductor diodes, using SiNx:H as an insulator layer and Si or InP as semiconductors. We have deposited SiNx:H films by distributed electron cyclotron resonance plasma enhanced chemical vapor deposition at floating temperature, with physical properties similar to films prepared at 800 °C by low pressure chemical vapor deposition. Silane and nitrogen were used as the reactive gases. The experimental results show that the resistivity (ρ) and the critical field (EC) are a strong function of the dielectric composition. For films deposited under optimum conditions, ρ was equal to 1016 Ω cm and EC reached 3.65 or 4.5 MV/cm for Al/SiNx:H/Si and Al/SiNx:H/InP diodes, respectively. The dominant mode of electronic conduction appears to be the Poole–Frenkel emission. The postmetallization annealing (PMA) has no significant effect on these bulk properties (ρ, EC and electronic conduction). On...

International audience; Since more than 20 years, Laboratoire Charles Fabry and Institut d’Astrophysique Spatiale are involved in development of the EUV multilayer coating for solar imaging. Previous instruments, such as the SOHO EIT and STEREO EUVI telescopes, employed the Mo/Si multilayer coatings, which offered at that time the best efficiency and stability. We present here recent results of the development of highly efficient EUV multilayers coatings at 17.4 nm and 30.4 nm for the Solar Orbiter mission. New multilayer structures, based on a combination of three materials including aluminum, have been optimized both theoretically and experimentally. We have succeeded to reduce interfacial roughness of Albased multilayers down to 0.5 nm via optimization of the multilayer design and the deposition process. The EUV peak reflectance of Al/Mo/SiC and Al/Mo/B4C multilayer coatings reaches 56% at 17.4 nm, the highest value reported up to now for this wavelength. We have also optimized specific bi-periodic structures that possess two reflection bands in the EUV range with high spectral selectivity. The EUV reflectivity of these Al-based dual-band coatings are compared with the Si/Mo/B4C baseline coating for Solar Orbiter. Since the stability of reflecting multilayer coating is an important issue for space missions, we have also studied the temporal stability as well as the resistivity of the coatings to thermal cycling and to proton irradiation. Experimental results confirm that Al/Mo/SiC and Al/Mo/B4C multilayer coatings are good candidates for the Solar Orbiter EUV imaging telescopes.

International audience; This paper presents a study of B4C/Mo2C multilayers mirrors with the aim of using it in the achievement of Alternate MultiLayer (AML) grating. Such component allows a high efficiency in the 500-2500 eV energy range for the DEIMOS beamline. Multilayers were deposited on silicon substrate. They are characterized by reflectometry under grazing incidence. Numerical adjustments were performed with a model of two layers in the period without any interfacial. A prototype of AML grating was fabricated and characterized. The efficiency of the first order of diffraction was worth 15% at 1700 eV.

International audience; We present a comparative study of B4C/Mo and B4C/Mo2C periodic multilayer structures deposited by magnetron sputtering. The characterization was performed by grazing incidence X-ray reflectometry at two different energies and high resolution transmission electron microscopy. The experimental results indicate the existence of an interdiffusion layer at the B4C-on-Mo interface in the B4C/Mo system. Thus, the B4C/Mo multilayers were modeled by an asymmetric structure with three layers in each period. The thickness of B4C-on-Mo interfacial layer was estimated about 1.1 nm. The B4C/Mo2C multilayers present less interdiffusion and are well modeled by a symmetric structure without interfacial layers. This study shows that B4C/Mo2C structure is an interesting alternative to B4C/Mo multilayer for X-ray optic applications.

We will present recent advances in the design and deposition of EUV multilayer mirrors. Efficient control of the spectral shape has been achieved by using three material structures. Applications to dual-band and broadband mirrors will be discussed.

Membranes a few hundred nanometers thick are used in EUV optics to make, for example, beams splitters or passband filters. Despite their necessity in numerous applications these components are, because of their thinness, extremely fragile and their implementation in space instruments is always difficult. The authors are developing thin film filters for the Full Sun Imager, one of the EUV telescopes on board the Solar Orbiter mission with objectives of high optical efficiency and mechanical strength. These filters are specifically designed to isolate one or the other of the two passbands (17.4 and 30.4 nm) reflected by the telescope's dual band mirror coating. In this paper we present the optical properties of the prototype components.

13 pages; International audience; Nanometric Co/Mg, Co/Mg/B4C, Al/SiC and Al/Mo/SiC periodic multilayers deposited by magnetron sputtering are studied in order to correlate their optical performances in the extreme ultraviolet (EUV) range to their structural quality. To that purpose, our recently developed methodology based on high resolution x-ray emission spectroscopy (XES) and x-ray and EUV reflectometry is now extended to nuclear magnetic resonance (NMR) spectroscopy and time-of-flight secondary ions mass spectrometry (ToF-SIMS). The analysis of the Co Lalpha,beta and Mg Kbeta emission spectra shows that the Co and Mg atoms within the multilayers are in a chemical state equivalent to that of the atoms in the pure Co and Mg references respectively. But NMR spectra give evidence for a reaction between Co atoms and B and/or C atoms from B4C. The Al and Si Kbeta emission spectra do not reveal the formation of an interfacial compound in Al/SiC and Al/Mo/SiC. Only the roughness limits the optical quality of Al/SiC. The comparative analysis of the ToF-SIMS spectra of Al/SiC and Al/Mo/SiC indicates that the structural quality is enhanced when Mo is introduced within the stack.

International audience; We present the results of an optical and chemical, depth and surface study of Al/Mo/SiC periodic multilayers, designed as high reflectivity coatings for the extreme ultra-violet (EUV) range. In comparison to the previously studied Al/SiC system, the introduction of Mo as a third material in the multilayer structure allows us to decrease In comparison to the previously studied Al/SiC system with a reflectance of 37% at near normal incidence around 17 nm, the introduction of Mo as a third material in the multilayer structure allows us to decrease the interfacial roughness and achieve an EUV reflectivity of 53.4%, measured with synchrotron radiation. This is the first report of a reflectivity higher than 50% around 17 nm. Time-of-flight secondary ion mass spectrometry (ToFSIMS) and x-ray photoelectron spectroscopy (XPS) measurements are performed on the Al/Mo/SiC system in order to analyze the individual layers within the stack. ToF-SIMS and XPS results give evidence that the first SiC layer is partially oxidized, but the O atoms do not reach the first Mo and Al layers. We use these results to properly describe the multilayer stack and discuss the possible reasons for the difference between the measured and simulated EUV reflectivity values.

Recent extreme ultraviolet sources using high-harmonic generation in a rare gas make new optics developments necessary. We report on the study and development of multilayer structures with efficient reflectivity in the 35–75 eV energy range. We have optimized, deposited and characterized two aperiodic broadband mirrors consisting of a Mo, Si and B4C thin-film stack. We used the needle procedure in order to optimize mirror reflectivity. The magnetron sputter deposited multilayers have been calibrated and characterized using Cu K α grazing incidence X-ray reflectometry. Reflectivity measured at near-normal incidence on a synchrotron radiation source reaches 12% with a full width at half maximum of nearly 40 eV. Experimental results are compared with theoretical simulation using available optical constants for Mo, Si and B4C in this spectral range.

Through its participation to European programs, SAGEM has worked on the design and manufacturing of normal incidence collectors for EUV sources. By opposition to grazing incidence, normal incidence collectors are expected to collect more light with a simpler and cheaper design. Designs are presented for the two current types of existing sources: Discharge Produced Plasma (DPP) and Laser Produced Plasma (LPP). Collection efficiency is calculated in both cases. It is shown that these collectors can achieve about 10 % efficiency for DPP sources and 40 % for LPP sources. SAGEM works on the collectors manufacturability are also presented, including polishing, coating and cooling. The feasibility of polishing has been demonstrated with a roughness better than 2 angstroms obtained on several materials (glass, silicon, Silicon Carbide, metals...). SAGEM is currently working with the Institut d'Optique and the Laboratoire des Materiaux Avances on the design and the process of EUV coatings for large mirrors. Lastly, SAGEM has studied the design and feasibility of an efficient thermal control, based on a liquid cooling through slim channels machined close to the optical surface.

International audience; Scandium/silicon multilayers have been deposited by magnetron sputtering and characterized by several techniques. Experimental peak reflectances of 0.22 and 0.37 have been measured respectively at wavelengths of 40 nm and 46 nm, for 10 degrees incidence angle. The corresponding theoretical values for a perfect Sc/Si structure are respectively 0.38 and 0.57. In order to explain these differences between calculated and measured reflectivity, thin film and multilayer characterizations have been done. Effects of multilayer imperfections on the reflectivity have been estimated independently by means of simulation. Based on these results, a new design of Sc/Si multilayer is proposed with top layer thickness optimization. With this design, the experimental peak reflectance reaches 0.46 at a wavelength of 46 nm.

The development of new high power EUV sources and EUV space imaging requires optics having specific properties which depend on applications and operating conditions. These both applications are very different in the working multilayers environment. For the high power sources, multilayers are submitted to short pulses with high energy peak whereas, for the space imaging, multilayers are submitted to continuous flux with low level. Moreover photon energy and environment for both applications may be different. The environment may affect structure and top layer contamination when optics are stored, handled, mounted on the final device and finally operating. Main environmental parameters investigated are temperature and humidity variation. One objective is the optimisation of multilayer coatings to offer the highest resistance under photonic, ionic fluxes and temperature cycle. This means that interfacial diffusion between thin layers and degradation of the capping layers have to be avoided or reduced. The present study relies with designing, depositing and testing different structures of multilayer coatings in order to minimise the influence of the environment. Multilayer coatings based on molybdenum, silicon and silicon carbide materials have been deposited by magnetron sputtering on silicon and zerodur substrates. Samples were submitted to radiations emitted by an EUV source at wavelength closed to 13.5 nm. Furthermore they were also submitted to thermal cycles and annealing under warm humidity in the aim to simulate extremes storage or handling conditions as space mission's conditions. The damages and the performance of the multilayers were evaluated by using grazing incidence reflectometry at 0.154 nm and EUV reflectometry at the operating wavelength. After a presentation of the multilayer design, deposition and metrology tools, we will describe the different environmental effects on the coatings to take in care during EUV source exposure, handling and storage conditions. First results on multilayers performances to EUV source exposure and space specification tests are presented. Main damages studies were on annealing, thermal cycling and warm humidity.

An alternate multilayer (AML) grating is a 2 dimensional diffraction structure formed on an optical surface, having a 0.5 duty cycle in the in‐plane and in the in‐depth direction. It can be made by covering a shallow depth laminar grating with a multilayer stack. We show here that their 2D structure confer AML gratings a high angular and energetic selectivity and therefore enhanced diffraction properties, when used in grazing incidence. In the tender X‐ray range (500eV – 5000 eV) they behave much like blazed gratings. Over 15% efficiency has been measured on a 1200 lines/mm Mo/Si AML grating in the 1.2 – 1.5 keV energy range. Computer simulations show that selected multilayer materials such as Cr/C should allow diffraction efficiency over 50% at photon energies over 3 keV.

Silicon nitride films have been deposited on relaxed Si 0.83 Ge 0.17 films using distributed electron resonance plasma-enhanced chemical vapor deposition without intentional substrate heating. The electrical properties of metal–insulator–semiconductor structures have been investigated. The electrical properties are strong functions of the post-processing treatment. The hysteresis of C–V curves can be reduced significantly after 30 min post-metallization annealing at 450 °C in forming gas. The flat-band voltage is then very low, thereby indicating that positive charges retained in the silicon nitride films are compensated for by negative charges located at the interface with the SiGe alloy. Conduction properties have also been analyzed from I–V measurements. A critical field of ≈2 MV cm −1 and a high resistivity of ≈2×10 15 Ω cm have been obtained. For higher electric fields, the leakage current is governed by a Poole–Frenkel conduction mechanism.

We present an experimental study of aging and thermal stability of Sc/Si multilayers deposited by magnetron sputtering. These multilayers have been characterized by using hard X-ray grazing incidence reflectometry at 0.154 nm and synchrotron radiation reflectometry at near normal incidence. The reflectivity was found to be stable after one year. A maximum reflectivity of 46% has been measured at 46 nm. However a 20% relative decrease of the reflectivity have been observed after one hour thermal annealing at 200°C. In order to improve thermal stability, we studied two different barriers layers (B4C and ScN ). We compare the decrease of peak reflectivity and its wavelength shift after one hour annealing at 200°C under argon atmosphere. The best result was observed with the design using 0.3 nm B4C barrier layers. A relative decrease of 2% of the reflectivity peak has been observed with this design as compared to a 20% decrease without barrier layers.

Theoretically, periodic three component multilayers as B 4 C/Mo/Si allow an improvement of the reflectivity in the 25 nm-40 nm range as compared to two component multilayers as B 4 C/Si. Optimized B 4 C/Mo/Si and B 4 C/Si multilayers have been deposited by magnetron sputtering and ion beam sputtering. The multilayers have been characterized by x-ray grazing reflectometry (λ = 0.154 nm) and synchrotron radiation measurements at near normal incidence. The maximum experimental reflectivity for B 4 C/Si is 25% at 32 nm and 23% at 38 nm. For B 4 C/Mo/Si multilayers, we obtained an experimental reflectivity of 34% at 32 nm and 29% at 39.5 nm. Moreover the width of the Bragg peak is larger for B 4 C/Mo/Si than for B 4 C/Si. We have used these multilayers in a non periodical structure in order to produce broadband mirrors. It consists of the superposition of two periodic B 4 C/Mo/Si multilayers with different period thickness. Theoretical optimization of such structure by simulation is presented. Preliminary experimental results demonstrate the interest of such structure : two broadband mirrors have been deposited and measured over a wide wavelength range (12 nm to 45 nm). The first mirror presents a broadband spectrum centered at 32 nm with peak reflectivity of 22% and bandwidth larger than 9 nm. The second mirror has been optimized to produce theoretically an average reflectivity of 19% from 25 nm to 35 nm.

We study theoretically and experimentally the increase of normal incidence reflectivity generated by addition of a third material in the period of a standard periodic multilayer, for wavelengths in the range 20 to 40 nm. The nature and thickness of the three materials has been optimized to provide the best enhancement of reflectivity. Theoretical reflectivity of an optimized B4C/Mo/Si multilayer reaches 42% at 32 nm. B4C/Mo/Si multilayers have been deposited with a magnetron sputtering system and a reflectivity of 34% at 32 nm has been measured on a synchrotron radiation source.

Imaging of the solar corona by selecting Fe IX (λ=17.1nm,), Fe XII (λ=19.5nm), Fe XV (λ=28.4nm) and He II (λ=30.4nm) emission lines with a Ritchey-Chretien telescope requires to coat the optics with multilayers having a high accuracy in their layer thicknesses, a high reflectivity and an optimal bandpass. Multilayers were simulated in order to determine the most adequate formula for each wavelength channel. Mo/Si coatings were deposited by using the ion beam sputtering technique in a high vacuum chamber equipped with a micro balance and an in-situ reflectometer. The multilayers were studied by grazing angle reflectometry at 0.1541nm, and their reflectances around the operating wavelengths were measured on the SA62 IAS/LURE beam line of the SuperACO synchrotron facility located at Orsay. In addition, aging versus time and behavior of the multilayers under a rapid thermal annealing were investigated. Performances of the ion-beam deposited multilayers have been improved compared to the Mo/Si coatings obtained in the past by the e-beam evaporation technique for the SOHO mission Extreme UV Imaging Telescope (EIT). The EUVI telescopes for the STEREO mission are being proceduced by depositing these new generation of multilayers onto primary and secondary mirrors. The reflectivity measurements on a telescope are presented.

International audience; With the aim of realizing a Michelson interferometer working at 13.9 nm, we have developed a symmetrical beam splitter with multilayers deposited on the front and back sides of a silicon nitride membrane. On the basis of the experimental optical properties of the membrane, simulations have been performed to define the multilayer structure that provides the highest reflectivity-transmission product. Optimized Mo-Si multilayers have been successfully deposited on both sides of the membrane by use of the ion-beam sputtering technique, with a thickness-period reproducibility of 0.1 nm. Measurements by means of synchrotron radiation at 13.9 nm and at an angle of 45° provide a reflectivity of 14.2% and a transmission of 15.2% for a 60% s-polarized light, close to the simulated values. Such a beam splitter has been used for x-ray laser Michelson interferometry at 13.9 nm. The first interferogram is discussed.

Dielectric behavior of SiNx films, fabricated by microwave electron cyclotron resonance discharge, has been studied as a function of film thickness on the basis of the current–voltage and the capacitance–voltage characteristics. In the thickness range (20 nm,d,80 nm), the resistivity and the critical field for SiNx were found not to be sensitive to the film thickness ~d! and which was opposite to strong dependence of the dynamic dielectric constant e d on thickness. To explain the e d behavior as a function of d, a model based on trapped space charge effects is proposed. The dominant mode of electronic conduction, determined from J –E1/2 curves and Arrhenius plots of leakage current, appears to be Poole–Frenkel emission only for thicker films (d.20 nm). Finally, the spatial profile of fixed charges reveals that SiNx /Si interface has a much greater concentration of defects than the bulk film.

Silicon nitride films were deposited at floating temperature using distributed electron cyclotron resonance plasma enhanced chemical vapor deposition (DECR-PECVD) on Si and InP substrates. The deposition parameters studied included the nature of gases (SiH4–N2 or SiH4–NH3) and the gas phase composition (SiH4/N2 or SiH4/NH3). The experimental results establish that to obtain device quality Si3N4, it is desirable to use N2 instead of NH3 and a high diluted SiH4 gas phase. These process parameters yield to a high resistivity (1016 Ω cm) and a high critical field (4.5 MV/cm). These properties confirm that the DECR technique is well suited for processing III–V compound semiconductors. NH3 does not induce such promising characteristics in terms of electrical properties but silicon nitride deposited with this gas is particularly interesting for applications where no stress is required.

We present the design, fabrication and characterization of non-periodic multilayer mirrors for the compression of attosecond pulses in the XUV domain. We demonstrate that time domain optimization allows pulse compression down to sub-50 as duration.