Some variants of the composition of multilayer absorption film filters with a high transmittance in the spectral region of the "water window" (2.3-4.4 nm) have been considered. Having created an ultimate pressure difference between the sides of free-standing films at which they are damaged, we compared the strength of 100 nm thick Ti-based multilayer filters with Al, Be, C interlayers and 100 nm thick V-based multilayer filters with Al interlayers. Sc and Cr was also considered as interlayers. Among the tested periodic multilayer structures, the best strength characteristics were demonstrated by Ti/Be (with a fraction of Ti in a period of about 0.6) and V/Al (with a fraction of V in a period of about 0.4) multilayer filters. Despite the fact that Ti/Be and V/Al filters are inferior in strength to Ti and V monolayer filters of the same thickness, these multilayer filters may be of interest, since they have either a higher transmittance in the "water window" (Ti/Be) or more high level of blocking of visible radiation (V/Al). Keywords: spectral region of the "water window" multilayer free-standing filters, ultimate pressure difference, film filter strength, transmittance in the soft x-ray, visible light blocking level.

Using a multilayer mirror spectrometer of the extreme ultraviolet (EUV) range, the laser plasma emission spectra of bulk aluminum in the wavelength range of 8.0-18.0 nm were studied. Testing of thin film laser targets made of aluminum and comparative measurements of the intensity of EUV radiation of a film with a thickness of 100 nm and a bulk material target were carried out. Keywords: SXR and EUV radiation, thin film, laser plasma.

Knowledge of the emissivity and thermal conductivity of thin metal films used in conjunction with multilayer mirrors for the spectral selection of radiation in the extreme-ultraviolet- and “soft”-X-ray wavelength ranges is necessary in order to correctly calculate the heating of film elements at high heat loads. Heating is associated with absorption in the film of a significant fraction of the incident intensity, and the concept of a high heat load is somewhat arbitrary, since even at an absorbed intensity level on the order of 1 W/cm 2 a freestanding film can be heated in vacuum by several hundred degrees. In the first approximation, to estimate the thermal-conductivity coefficient, one could use tabular values for bulk samples of the corresponding metals or use the well-known Wiedemann-Franz law which links the thermal conductivity and the electrical resistivity of the sample; the latter is easier to measure. However, an analysis of the published data indicates significant errors that are possible when using any of these approaches. Therefore, in this work, we measure the thermal conductivity directly by processing the temperature distribution obtained by infrared (IR) pyrometry over a film sample mounted on a heated frame or heated by a flowing electric current. The thermophysical characteristics (thermal conductivity and emissivity) are determined for samples of film absorption filters based on Mo, Al, and Be of submicron thickness (from 100 nm), as well as for films of copper: a metal whose bulk samples have high thermal and electrical conductivity. As expected, significant differences are found between the thermal and electrical properties of the film materials and the properties of the same metals in monolithic samples.

Variants of the structures of free-standing films with a high transmittance coefficient at a wavelength of 13.5 nm, which were developed for use in the projection of extreme ultraviolet (EUV) lithography as protective and filtering elements, are considered. Our attention is focused on the most problematic—in terms of manufacturing and the requirements on their characteristics—ultrathin free-standing films (pellicles), which are installed in front of the mask (photomask) in modern EUV scanners and serve to protect the surface of the mask from contamination. The main approaches used to manufacture ultrathin free-standing large-aperture films are compared. A brief review of the research on the development of high transmittance pellicles at a wavelength of 11.2 nm, which may become an operating wavelength for future EUV lithography, is given.

We demonstrate the possibility of manufacturing Be-basedultrathin films with high transmission at wavelengths of 11.4 and 13.5 nm. For free-standing films of Be and Be-based multilayer structures (Si/Be,ZrSi2/Be, Be/BexNy, Zr/Be, Ru/Be, Mo/Be), we determine the thresholds of theabsorbed power at which over a short period (tens of minutes) of vacuumannealing, initially sagging free-standing films became visibly stretchedover the hole. Of the film structures tested here, the Be/BexNy structure(with beryllium nitride interlayers) showed the highest threshold for theabsorbed power (1 W/cm2). However, due to the low strength of thisstructure, ZrSi2/Be, Mo/Be, and Be films seem to be more promising for themanufacture of a full-size pellicle. Long-term vacuum annealing of Mo/Beand Be ultrathin films showed that they could withstand 24 hours of vacuumheating at an absorbed power density of 0.2 W/cm2 (film temperature 250oC)without noticeable changes in EUV transmission or sagging of films. Withcomparable transmission (~83% at 13.5 nm and ~88% at 11.4 nm), a multilayerMo/Be structure with a thickness of 30 nm appears to be preferable, as itshows less brittleness than a monolayer Be film with a thickness of 50 nm. Keywords: Be-based pellicle, multilayer thin film, EUV lithography,thermal stability\

The radiation spectra in the soft X-ray and extreme ultraviolet wavelength ranges of thin-film (0.15 microns thick) targets made of light materials (Si, C, Be) were studied when excited by a Nd:YAG laser pulse with a duration of 5.2 ns focused to an intensity of ~10^12 W/cm^2. Line spectra of BeIII, BeIV, CV, and SiV ions were recorded using a spectrometer based on a multilayer X-ray mirror. A comparison with the spectra of bulk solid-state targets of the same materials is carried out. In all cases, there was a decrease in the intensity of the lines of the soft X-ray spectrum of film targets compared to monolithic ones; the decrease was, depending on the material, from several tens of percent to several times, with more than an order of magnitude less mass of the vaporized substance.

Observation of a sample of Si/Al/Sc mirror with a MoSi2 protective cap layer, which was stored in air for 40 months, showed that the peak reflectivity at a wavelength of 58.4 nm during this period decreased from 32 % to 20.5 %, and over the last 20 months of observation-from 21.5 % to 20.5 %, which indicates a significant decrease in the rate of decline and almost stabilization of the peak reflectivity at the level of 20 %. The spectral reflection peak width of this mirror at half maximum has not changed over the past 20 months and amounted to 6.3 nm. The given data of secondary ion mass spectrometry and grazing incidence X-ray reflectometry show that the decrease in reflectance of Si/Al/Sc multilayer mirrors with a MoSi2 protective cap layer is mainly due to an increase in the amount of impurities (oxygen and carbon) in the structure and on the surface of the mirrors and, to a lesser extent, due to the broadening of the interlayer boundaries. Comparison of the rate of decrease in reflectance at 58.4 nm of Sc/Al mirrors with interlayers of silicon and nitride scandium and a MoSi2 cap layer indicates that neither the material and thickness of the interlayer nor the thickness of the protective MoSi2 cap layer within 3-6 nm have a significant effect on this rate.

Variants of the structures of freely hanging films with a high transmittance coefficient at a wave-length of 13.5 nm, which were developed for use in the projection of extreme ultraviolet (EUV) lithography as protective and filtering elements, are considered. Our attention is focused on the most problematic—in terms of manufacturing and the requirements on their characteristics—ultrathin freely hanging films (pelli-cles), which are installed in front of the mask (photomask) in modern EUV scanners and serve to protect the sur-face of the mask from contamination. The main approaches used to manufacture ultrathin freely hanging large-aperture films are compared. A brief review of the research on the development of high transmittance pellicles at a wavelength of 11.2 nm, which may become an operating wavelength for future EUV lithography, is given.

Some variants of the composition of multilayer absorption film filters with a high transmittance in the spectral region of the “water window” (2.3–4.4 nm) have been considered. Having created an ultimate pressure difference between the sides of free-standing films at which they are damaged, we compared the strength of 100 nm thick Ti-based multilayer filters with Al, Be, C interlayers and 100 nm thick V-based multilayer filters with Al interlayers. Sc and Cr was also considered as interlayers. Among the tested periodic multilayer structures, the best strength characteristics were demonstrated by Ti/Be (with a fraction of Ti in a period of about 0.6) and V/Al (with a fraction of V in a period of about 0.4) multilayer filters. Despite the fact that Ti/Be and V/Al filters are inferior in strength to Ti and V monolayer filters of the same thickness, these multilayer filters may be of interest, since they have either a higher transmittance in the “water window” (Ti/Be) or more high level of blocking of visible radiation (V/Al).

We demonstrate the possibility of manufacturing Be-based ultrathin films with high transmission at wavelengths of 11.4 and 13.5 nm. For free-standing films of Be and Be-based multilayer structures (Si/Be, ZrSi2/Be, Be/BexNy, Zr/Be, Ru/Be, Mo/Be), we determine the thresholds of the absorbed power at which over a short period (tens of minutes) of vacuum annealing, initially sagging free-standing films became visibly stretched over the hole. Of the film structures tested here, the Be/BexNy structure (with beryllium nitride interlayers) showed the highest threshold for the absorbed power (1 W/cm2). However, due to the low strength of this structure, ZrSi2/Be, Mo/Be, and Be films seem to be more promising for the manufacture of a full-size pellicle. Long-term vacuum annealing of Mo/Be and Be ultrathin films showed that they could withstand 24 hours of vacuum heating at an absorbed power density of 0.2 W/cm2 (film temperature ~250°C) without noticeable changes in EUV transmission or sagging of films. With comparable transmission (~83% at 13.5 nm and ~88% at 11.4 nm), a multilayer Mo/Be structure with a thickness of 30 nm appears to be preferable, as it shows less brittleness than a monolayer Be film with a thickness of 50 nm.

The use of field emission cathodes in X-ray tubes requires the placement of the cathode assembly with a small gap from the anode, and this hampers the output of radiation. The greatest difficulties arise in the generation of a relatively soft spectrum with wavelengths of 1–10 nm: in this case, the accelerating voltage does not exceed several kilovolts and the interelectrode gap does not exceed several hundred microns. In this work, the possibility of using submicron films based on beryllium as through-type anodes for emitting the BeKα line (λ = 11.4 nm) and the accompanying bremsstrahlung spectrum is experimentally demonstrated. In particular, the characteristic radiation of a tube with a field emission blade-type cathode and a Be-film anode, introduced into a grazing incidence grating spectrometer, was detected. The characteristics of beryllium films necessary for designing high-power X-ray tubes of this type are determined.

The use of field emission cathodes in the design of x-ray tubes requires the placement of a cathode assembly with a small distance from the anode, complicating the output of radiation. Most acute this problem occurs when generating a relatively soft spectrum with wavelengths of 1-10 nm: in this case, the accelerating voltage does not exceed several kilovolts, and the inter-electrode distance composes several hundred micrometers. In this work, we experimentally demonstrated the applicability of beryllium-based submicron films as “shot-through” anodes for generating the Be K line ( = 11.4 nm) and the associated bremsstrahlung spectrum. In particular, the characteristic radiation of a tube with a field emission blade cathode and a Be film anode was recorded within the scheme of a grazing incidence grating spectrometer. The characteristics of beryllium films necessary for the development of X-ray tubes of this type with a higher output power are determined.

The optical, mechanical, and thermal properties of freestanding films based on nitrided molybdenum and zirconium disilicides were investigated. It has been shown that nitriding of silicides leads to a significant increase in the thermal stability of the films. So, if crystallization of initially amorphous freestanding MoSi2 or ZrSi2 films is observed at temperatures of 330-370°C, the introduction of nitrogen into the film makes it possible to increase the temperature up to 600-700°С at which MoSi2Nx and ZrSi2Ny (at least for x ≥ 0.25, y ≥ 1.3) films can be used for many hours when heated under vacuum. The study of mechanical tensile strength showed that the ultimate strength is weakly dependent on the nitrogen content in MoSi2Nx films (0 ≤ x ≤ 0.55). Comparison of the properties of MoSi2Nx and ZrSi2Ny films obtained by the magnetron method at the same nitrogen partial pressure demonstrated that at similar values of the transmittance at 13.5 nm, nitrated ZrSi2 films are more effective as protective coatings (less susceptible to oxidation and more resistant to degradation at high temperatures).

The optical, mechanical, and thermal properties of free-standing structures based on nitrided molybdenum and zirconium silicides have been studied. It has been shown that silicide nitriding considerably improves the thermal stability of films. While as-prepared amorphous MoSi 2 and ZrSi 2 films crystallize in the interval 330–370°C, nitriding of films has made it possible to increase their working temperatures in vacuum to 600–700°C (at least, for x ≥ 0.25, y ≥ 1.3). Tensile tests have shown that the ultimate strength of MoSi 2 N x films (0 ≤ x ≤ 0.55) depends on nitrogen content only slightly. Comparison between the properties of MoSi 2 N x and ZrSi 2 N y films magnetron-sputtered at the same partial pressure of nitrogen has demonstrated that with transmission coefficients of films at a wavelength of 13.5 nm being close to each other, ZrSi 2 films are more effective as protection coatings (they are less prone to oxidation and more degradation-resistant).

Aluminum thin-film spectral filters are widely used in telescopes for space observations of the Sun in the extreme ultraviolet range of wavelengths. The main purpose of film filters is to block radiation in the IN, visible, and nearIR spectral ranges. In connection with the development of new projects for the observation of the Sun from close distances, the thermal stability of the entrance film filter is an important characteristic. In this paper, the thermal stability of Al films with 2.5 nm thick MoSi2 protective cap layers has been studied. MoSi2 was chosen as a coating material because MoSi2 caps effectively protect the Al film from oxidation and simultaneously increase the mechanical strength of the Al film. Vacuum annealing of MoSi2/Al/MoSi2 films was carried out at temperatures up to 300 degrees C. It has been demonstrated that at an annealing temperature of more than 200 degrees C for 24 h, a noticeable decrease in the blocking properties of the MoSi2/Al/MoSi2 film is observed in the visible wavelength range, which is caused by the appearance of semi-transparent crystalline silicon dendritic structures that are tens of micrometers in size in the film. In the annealed area of the film specimen, the intermetallic Al-12 Mo phase was detected by electron diffraction structure analysis, indicating a possible reason for the appearance of silicon atoms needed for dendrite growth as a result of the chemical interaction of Al and MoSi2. Due to the requirements for a high degree of visible radiation blocking (10(6) to 10(7) times), the appearance of even one dendritic structure significantly reduces the blocking properties of the film filter and is, therefore, not permissible. Based on the measurement of the transmission of MoSi2 -2.5 nm/AI-72 nm/MoSi2 -2.5 nm films at 633 nm for isothermal annealing at 200 degrees C-250 degrees C, the activation energy for the formation of dendritic structures (E = 1.55 +/- 0.1 eV) was measured and the maximum permissible film temperature (130 degrees C) at which dendritic structures did not appear during a 5-year mission was predicted. (C) 2018 Optical Society of America

In this paper we investigated the influence of thin nanometer cap layers of aluminum nitride (AlN) and molybdenum disilicide (MoSi2) on the temporal stability of transmission and the ultimate strength of aluminum (Al) film filters. An increase in the stability of the optical characteristics and in the mechanical strength of Al films both with AlN and MoSi2 cap layers are shown in comparison with a monolayer Al film. The greatest efficiency was demonstrated in the case of Al with MoSi2 cap layers. The obtained results show that the presence of MoSi2 cap layers 2.5 nm thick on each side of an Al film significantly reduces (for example, by >4 times at the wavelength of 30.4 nm) the rate of film transmission loss in the extreme ultraviolet (EUV) range. In addition, the presence of cap layers can lead to a significant increase in the film's strength: the results of pressure bulge tests show that the Al with MoSi2 cap layers film can withstand an ultimate load 1.5 times greater than an Al monolayer film of comparable thickness. The carried-out bulge tests indicate that an increase in the strength of the Al thin film in the presence of MoSi2 cap layers may be due to the cap layers hindering crack initiation, which allows Al film to be plastically deformed. Acoustic tests of Al with MoSi2 cap layers filters indicate the possibility of their use as entrance filters on a supporting mesh with a mesh size up to 10 mm in solar telescopes.

A real opportunity for applying traditional optical methods to soft X-ray and extreme UV (ultraviolet) radiation bands has appeared thanks to recent successes in the area of multilayer-mirror deposition and procedures for fabricating supersmooth and highly precise substrates of mirrors. The implementation of this opportunity opens up fundamentally new prospectss in the nanodiagnostics of substances, micro-and nanoelectronics, microbiology, solar astronomy and other applications. The main directions in multilayer X-ray optics developed at the Institute for the Physics of Microstructures, Russian Academy of Sciences, are presented and the aspects of the use thereof in science and technology are considered. The main problems arising during the fabrication of multilayer interference structures for the soft X-ray and extreme UV bands are discussed. The main results obtained recently in the scope of each direction of investigation are presented. Plans for the future development of these directions are discussed.

The paper describes a technique for manufacturing of sub-micron metal membranes based on magnetron deposition of multilayer structures. Tensile stress, biaxial elastic modulus and mechanical strength of 25–50nm thick multilayer Mo/ZrSi2 membranes were measured, and the behavior of these parameters before and after vacuum heating of samples at the level of heat loads up to 1W/cm2 was studied. The elastic properties were obtained from measurements of deformation dependence of the round membranes on the applied pressure differential. A rapid increase in tensile stress of a 25nm thick Mo/ZrSi2 film was observed at a uniform heat load of 0.25W/cm2 which was probably caused by desorption of water molecules from the membrane surface.

Al, with a passband in the wavelength range of 17-60 nm, and Zr, with a passband in the wavelength range of 6.5-17 nm, thin films on a support grid or support membrane are frequently used as UV, visible, and near-IR blocking filters in solar observatories. Although they possess acceptable optical performance, these filters also have some shortcomings such as low mechanical strength and low resistance to oxidation. These shortcomings hinder meeting the requirements for filters of future telescopes. We propose multilayer thin film filters on the basis of Al, Zr, and other materials with improved characteristics. It was demonstrated that stretched multilayer films on a support grid with a mesh size up to 5 mm can withstand vibration loads occurring during spacecraft launch. A large mesh size is preferable for filters of high-resolution solar telescopes, since it allows image distortion caused by light diffraction on the support grid to be avoided. We have investigated the thermal stability of Al/Si and Zr/Si multilayers assuming their possible application as filters in the Intergelioprobe project, in which the observation of coronal plasma will take place close to the Sun. Zr/Si films show high thermal stability and may be used as blocking filters in the wavelength range of 12.5-17 nm. Al/Si films show lower thermal stability: a significant decrease in the film's transmission in the EUV spectral range and an increase in the visible spectrum have been observed. We suppose that the low thermal stability of Al/Si films restricts their application in the Intergelioprobe project. Thus, there is a lack of filters for the wavelength range of λ>17  nm. Be/Si and Cr/Si filters have been proposed for the wavelength range near 30.4 nm. Although these filters have lower transparency than Al/Si, they are superior in thermal stability. Multilayer Sc/Al filters with relatively high transmission at a wavelength of 58.4 nm (HeI line) and simultaneously sufficient rejection in the wavelength range near 30.4 nm (HeII line) have been fabricated. They are planned to be used in the project KORTES, whose telescopes will have an EUV channel at 58.4 nm.