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We present the results of an experimental study of soft X-ray (SXR) and extreme ultraviolet emission spectra of the plasma produced by exposing a plane solid beryllium target to laser radiation with broad frequency and angular spectra. SXR lines up to 1s – 9p of Be IV as well as the plasma continuum are recorded for a laser focal-spot intensity of 5.3 × 1013 W cm−2. To model the SXR beryllium plasma spectra, simulations are carried out using the INDHAUS programme and the FLYCHK code in the framework of local thermodynamic equilibrium model, which agree nicely with experimentally obtained results.

We present performance metrics for the commercially available TEUS product line. TEUS-S is a high-brightness EUV LPP light source based on a fast rotating liquid metal target with EUV collection angle of 0.05sr. The TEUS-S100 and S400 models employing 100W and 400W of average laser power respectively have been characterized wi0th particular attention to the collector optics lifetime. It is estimated that 10% mirror reflectivity degradation will occur after 2 years for the TEUS-S100 and after 0.5 year for the TEUS-S400 in 24/7operation mode. The TEUS-S400 source provides more than 30 mW of in-band (±1%) EUV radiation after the debris mitigation system.

The results of a laser—matter interaction experiment are presented in the paper. Low-density volume-structured material (cellulose triacetate) is used as a target in the experiments. Low-density materials are of interest for both fundamental and applied research. The information on how the parameters of the target and laser radiation influence the penetration of laser radiation through the generated plasma layer is generalized. The energy, spatial, spectral, and temporal characteristics of the plasma of low-density cellulose triacetate targets are analyzed.

A sealed compact system based on two series-connected magnetohydrodynamic pumps for pumping liquid metal media with an operating temperature as high as 450°C is described. The system is designed to produce a renewable target in the form of a liquid lithium jet in a pulsed-repetition rate source of extreme ultraviolet (EUV) radiation based on laser plasma. The system provides a head pressure of 2 bar and a flow rate of up to 80 cm3/s and is characterized by reliability, simplicity of design, the absence of moving parts, convenient handling, and the ability to pump aggressive conductive liquids. The system is easily scalable in both the head pressure and the flow rate. The long-term operation of the system has been demonstrated in a laser-produced plasma EUV source, where it provided a jet velocity of up to 22 m/s.

The energy spectrum and the distribution of the total charge over the ion energy are studied for plasma produced by partially coherent radiation of the neodymium glass laser with a power density of ~1013 W/cm2 in the focusing spot incident on continuous gadolinium (Gd) and aluminum(Al) plates. The spectra of plasma ions for gadolinium and aluminumtargets are presented at laser radiation energies of 2, 7, 20 J and 1 J, respectively. For the gadolinium target, an increase in the peak amplitudes in ion spectra with increasing influencing radiation energy and manifestations of higher-energy ions are observed. The difference in the ion emission for gadolinium and aluminum targets is also recorded at close radiation energies of 2 and 1 J, respectively.

The results of experimental measurements of the hydrodynamic efficiency of laser plasma for aluminum and copper targets are presented. The studies were performed on the “Kanal-2” laser setup system using the ballistic pendulum method. The pressure in the interaction chamber was 10−4 Torr, the pendulum length was 145 mm, the mass of the pendulum with a target was 7.2 g. At the half-height pulse duration of 2.5 ns, the power density on the target surface was ∼1013 W/cm2. In the case of aluminum target, the hydrodynamic efficiency coefficient increased from 1.5% to 4.5% with increasing laser pulse energy from 5 J to 10 J, whereas it remained at the level of 5% for the copper target.

Dynamics and spectral transmission of Al plasma produced by extreme ultraviolet (EUV) irradiation of 0.75-μm thick Al foil is investigated. The EUV radiation with the peak power density in the range of 0.19–0.54 TW/cm2 is provided by Z-pinch formed by W multiwire array implosion in the Angara-5-1 facility. Geometry of the experiment ensures that there are no plasma fluxes from the pinch toward the Al foil and plasma. The same EUV source is used as a back illuminator for obtaining the absorption spectrum of Al plasma in the wavelength range of 5–24 nm. It comprises absorption lines of ions Al4+, Al5+, Al6+, Al7+. Analysis of relative intensities of the lines shows that those ions are formed in dense Al plasma with a temperature of ∼20 eV. Dynamics of Al plasma has been investigated with transverse laser probing. We have also performed radiation-gas-dynamics simulations of plasma dynamics affected by external radiation, which includes self-consistent radiation transport in a plasma shell. The simulations show good agreement with an experimental absorption spectrum and with experimental data concerning plasma dynamics, as well as with the analysis of line absorption spectrum. This confirms the correctness of the physical model underlying these simulations.

The effect of induced transparency of thin Al foils radiatively heated by intense extreme ultraviolet (EVU) radiation has been observed. The radiation of the plasma of Z-pinches appearing under the compression of tungsten liners at the Angara-5-1 facility has been used as the radiation that heats the Al foil (peak illumination on the foil ~0.55 TW/cm2) and is transmitted through it. The photoabsorption has been studied in the formed aluminum plasma at temperatures of ~10–30 eV in the density range of ~1–20 mg/cm3 in the wavelength range of ~5–24 nm. Absorption lines of Al4+...7+ ions have been identified in the experimental spectrum. In addition, radiative gas-dynamic simulations of the foil heating and expansion have been performed taking into account radiation transfer processes.

In this paper, we explore the possibility of using free standing thin films from single walled carbon nanotube SWCNT material in optics of the extreme ultraviolet EUV range. Test samples were fabricated using an aerosol chemical vapor deposition method. Synchrotron radiation was used to record the transmittance spectra of samples in the EUV range. The measured transmittance for a film 40 amp; 8239;nm thick almost monotonously increases from 76 at a wavelength of 20 amp; 8239;nm 99 at a wavelength of 1 amp; 8239;nm. The measured stress strain curve for the test samples shows that the SWCNT based thin films have rather high ductility as opposite to fragile films made of conventional solid state materials. We use numerical simulations to demonstrate that the film strain occurs mainly by straightening and sliding of the nanotubes past each other without forming of strain localization responsible for fragile behavior. The combination of high radiation transmittance and unique mechanical properties makes the SWCNT based thin films very promising for use in the EUV optics. In particular, such films can be used to protect delicate optical elements for EUV lithography from their contamination with debris particles

The progress of EUVL and the introduction of HVM scanners demands advanced actinic metrology especially for the EUV mask supply chain. For stand alone field use reliable metrology sources for EUV inband emission around 13.5 nm are critically needed. For nanometer resolution the effective “inband brightness” is extremely important. Laser produced EUV sources (LPP) are cost effective with efficient energy use thus providing a reliable approach for real-life industrial applications. However, apart from the Cymer/ASML LPP scanner source no such source is available. One reason is that realizing a reliable tin droplet target is beyond the technical and financial scope of a metrology source. In this paper, we propose a path to make industrial laser produced plasma based EUV sources reliable and with easy renewable targets a reality.

Characteristics of a source of laser-induced radiation in the extreme ultraviolet (EUV) range, obtained in a discharge between two jets of liquid tin, are investigated. The possibility of designing a high-brightness EUV source on this basis for employing in mask inspection techniques in projection EUV lithography is demonstrated. The average efficiency of converting the electric energy to radiation in the spectral range of 13.5 ± 0.135 nm is approximately 2%/2π sr with the size of emitting plasma 0.2 ± 0.35 mm. The possibility of producing a EUV source with a brightness of about 200 W (mm2 sr)-1 is demonstrated.

A centrifugal pump for transmitting molten metals and other liquids with a working temperature as high as 380°C is described. The pump ensures a head pressure of up to 9 atm and a flow rate of up to 1 m3/h. A rotary torque is transmitted from the electric motor to the turbine of the pump by means of the alternatingpole magnetic coupling. The compactness of the design is ensured by a vacuum gap between the “hot” inner and “cold” outer half-couplings. The pump is applied in high-power X-ray and extreme ultraviolet sources for forming liquid tin jets used as updated electrodes (in sources based on a discharge plasma) or a updated target (in sources based on a laser plasma), where it ensures velocities of tin jets of up to 15 m/s.

Soft X-ray spectra (30–70 A) of aluminum plasma have been measured in experiments carried out at the Kanal-2 laser facility at laser intensities of (1–7) × 1013 W/cm2. It is shown that the measured spectra satisfactory agree with those calculated using the RADIAN numerical code.

The results of the study of laser plasma generated by nanosecond laser radiation with controlled spatial coherence incident on various targets containing gadolinium are presented. X-ray radiation of such plasma is studied using an X-ray diagnostic system developed and fabricated by the authors. Metal gadolinium, gadolinium oxide, gadolinium and aluminum alloy, and aluminum were used as targets. The electron temperature of generated plasma and the efficiency of laser-to-X-ray radiation conversion are estimated; the emitting region sizes are determined. Particular attention is paid to the study of laser plasma spectra in the X-ray region near the wavelength of 6.7 nm.

We use the two-dimensional particle-in-cell model with Monte Carlo collisions to study the plasma induced in hydrogen by short pulses of extreme ultraviolet (EUV) radiation at wavelengths in the range 10–20 nm with a pulse duration of about 40 ns (FWHM). This plasma is formed via both photoionization by the high-energy EUV photons and by the secondary photoelectrons emitted from the hydrogen molecules and the irradiated surface. The latter process can be enhanced by the external electric field that accelerates the electrons. In order to establish a base for our model so as to obtain accurate results, we record a temporally-resolved series of current–voltage characteristics for a small probing electrode inserted into EUV-induced hydrogen plasma. We then resort to simulating this plasma in the same geometry with the probe in our model which we validate by matching its results to the experimentally measured dynamics of the probe current–voltage curves. Having validated the model this way, we use this model as an independent instrument capable of obtaining the spatiotemporal picture of EUV-induced plasma evolution. We use this instrument to study the plasma formation during the EUV pulse and point out the processes that take part in forming this plasma, such as impact ionization and direct ionization by EUV photons.

Experimental results on the spatial distribution of X-ray radiation of the plasma generated by nanosecond laser radiation incident on a target made of carbon nanotubes are presented and compared with the results obtained for solid-state magnesium targets.

A comparison method of high-temperature plasma diagnostics, developed by Shevelko [Quantum Electron. 41, 726 (2011)] and Shevelko et al. [Plasma Phys. Rep. 34, 944 (2008)], is modified and applied for Mo laser-produced plasma analyses. This method consists in determining the electron temperature Te of the studied plasmas by comparing the spectra of the investigated radiation source with the spectra of well-diagnosed laser-produced plasmas recorded at different Te. The modified comparison method includes the theoretical modeling of X-ray spectra of laser-produced plasmas of different elements. The most complete correspondence between the structure of the theoretical spectrum and the experimental one is achieved by changing the single parameter in theoretical calculations—the electron temperature Te. Such a method made it possible to describe in detail the structure of the X-ray spectra of multiply charged Mo ions, improve the accuracy of measurements, and justify the methods used. In particular, for Mo laser plasma (3-2 transitions in Mo31+-Mo34+ ions), the electron temperatures determined experimentally by the comparison method (Te = 685 ± 55 eV) and calculated theoretically (Te = 650 eV) are in a very good agreement.

We investigate the spectral characteristics of new focusing multilayer structures used as dispersive elements in a high-transmission X-ray spectrometer with cylindrical geometry (Hamos scheme): W/B4C structures in a wavelength range of λ = 8.0−9.5 A and Cr/Sc structures in a range of λ = 30−40 A (the range is not accessible for natural crystals). The results of demonstration experiments on laser-produced plasma spectra recording are considered. It is shown that the luminosity of a Hamos spectrometer with multilayer dispersive elements is an order of magnitude higher than the luminosity of grazing-incidence grating spectrographs with a comparable spectral resolution.

An experimental study of oxide reduction at the surface of ruthenium layers on top of multilayer mirrors and thin Ru/Si films is presented. Oxidation and reduction processes were observed under conditions close to those relevant for extreme ultraviolet lithography. The oxidized ruthenium surface was exposed to a low-temperature hydrogen plasma, similar to the plasma induced by extreme ultraviolet radiation. The experiments show that hydrogen ions are the main reducing agent. Furthermore, the addition of hydrogen radicals increases the reduction rate beyond that expected from simple flux calculations. We show that low-temperature hydrogen plasmas can be effective for reducing oxidized top surfaces. Our proof-of-concept experiments show that an in situ, EUV-generated plasma cleaning technology is feasible.

An experimental setup that directly reproduces extreme ultraviolet (EUV) lithography relevant conditions for detailed component exposure tests is described. The EUV setup includes a pulsed plasma radiation source, operating at 13.5 nm; a debris mitigation system; collection and filtering optics; and an ultra-high vacuum experimental chamber, equipped with optical and plasma diagnostics. The first results, identifying the physical parameters and evolution of EUV-induced plasmas, are presented. Finally, the applicability and accuracy of the in situ diagnostics is briefly discussed

The formation of craters in targets of various materials under the action of a high-power neodymium-laser pulse at radiation intensities from 1010 to 1014 W/cm2 was studied experimentally and theoretically. The interaction between the laser beam and solid targets is investigated to determine the efficiency of the ablation loading of various materials and the transformation of the laser energy into the energy of a shock wave.

The results of investigation of a capillary discharge plasma, used as a source of intense VUV radiation and soft X-rays, are presented. The plasma was generated during the discharge of low-inductance condensers in a gas-filled ceramic capillary. Intense line radiation was observed in a broad spectral range (30-400 A) in various gases (CO2, Ne, Ar, Kr, Xe). The absolute radiation yield for the xenon discharge was ~5 mJ (2π sr)-1 pulse-1 within a spectral band of width 9 A at 135 A. Such a radiation source can be used for various practical applications, such as EUV projection lithography, microscopy of biological objects in a 'water window', reflectometry, etc.

Molecular contamination of a grazing incidence collector for extreme ultraviolet (EUV) lithography was experimentally studied. A carbon film was found to have grown under irradiation from a pulsed tin plasma discharge. Our studies show that the film is chemically inert and has characteristics that are typical for a hydrogenated amorphous carbon film. It was experimentally observed that the film consists of carbon (~70 at. %), oxygen (~20 at. %) and hydrogen (bound to oxygen and carbon), along with a few at. % of tin. Most of the oxygen and hydrogen are most likely present as OH groups, chemically bound to carbon, indicating an important role for adsorbed water during the film formation process. It was observed that the film is predominantly sp3 hybridized carbon, as is typical for diamond-like carbon. The Raman spectra of the film, under 514 and 264 nm excitation, are typical for hydrogenated diamond-like carbon. Additionally, the lower etch rate and higher energy threshold in chemical ion sputtering in H2 plasma, compared to magnetron-sputtered carbon films, suggests that the film exhibits diamond-like carbon properties., 18 pages, 10 figures

The results of experiments on the interaction of nanosecond laser radiation (wavelength of 1.06 μm and a radiation power density of 1012–1013 W/cm2) with targets from various materials (Cu, (C2H4)n, TAC) are presented in the paper. In the experiments images of the plasma in own optical radiation in the wavelength range 0.4–1.1 μm were obtained. In one shot of laser images at wavelengths corresponding to the radiation of the harmonics 2ω 0, 3/2ω 0, 5/2ω 0, and at the frequency of laser radiation ω 0 were recorded. Using the obtained images the spatial characteristics of the radiating regions of the plasma, as well as the radiated energy for each of the harmonics, were estimated.

The spectra of a laser plasma in the soft x-ray (0.8–0.95 nm) and vacuum ultraviolet (3–4 nm) ranges are recorded with the use of new focusing multilayer structures. It is demonstrated that the electron temperature of the light-element plasma produced by a laser pulse with an energy of ∼1 mJ can be measured by using the relative intensities of the satellites and the lines of ions with different charges.

Cleaning of contamination of optical surfaces by amorphous carbon (a-C) is highly relevant for extreme ultraviolet (EUV) lithography. We have studied the mechanisms for a-C removal from a Si surface. By comparing a-C removal in a surface wave discharge (SWD) plasma and an EUV-induced plasma, the cleaning mechanisms for hydrogen and helium gas environments were determined. The C-atom removal per incident ion was estimated for different sample bias voltages and ion fluxes. It was found that H2 plasmas generally had higher cleaning rates than He plasmas: up to seven times higher for more negatively biased samples in EUV-induced plasma. Moreover, for H2, EUV-induced plasma was found to be 2-3 times more efficient at removing carbon than the SWD plasma. It was observed that carbon removal during exposure to He is due to physical sputtering by He+ ions. In H2, on the other hand, the increase in carbon removal rates is due to chemical sputtering. This is a new C cleaning mechanism for EUV-induced plasma, which we call 'EUV-reactive ion sputtering'. © 2014 IOP Publishing Ltd.

Modified comparison method is developed. In this method detailed theoretical calculations of spectra of heavy elements is conducted varying one parameter ( Te ) in order to find the most complete matching of the structure of the theoretical and the experimental Mo spectra in laser-produced plasmas.

A new approach for discharge-produced plasma (DPP) extreme ultraviolet (EUV) sources based on the usage of two liquid metallic alloy jets as discharge electrodes has been proposed and tested. Discharge was ignited using laser ablation of one of the cathode jets. A system with two jet electrodes was tested at a repetition rate of 1 to 5 kHz with dissipated electrical power up to 20 kW. Radiating spectra, time characteristics, and conversion efficiency are similar to conventional DPP schemes with rotating wheels. In the first experiments, the Ga:Sn eutectic alloy, which is liquid at room temperature, was circulating in a closed loop. The high velocity of the jets (30 m/s 30 m/s ) ensures a renewed electrode surface for every shot, for a repetition rate frequency of up to 30 to 50 kHz, and provides effective heat transportation from the discharge zone. Modeling and experiments demonstrate that the proposed scheme is able to dissipate up to 200 kW of electrical power without overheating the nozzles and tin surface. It was found that the flexible electrode configuration allows the channeling of essential parts of debris plasma in directions opposite to the EUV collector.

Emission of radiation at short wavelengths demands hot plasmas, which are readily produced by the pinch effect. This term describes the self-constriction accompanied by heating of discharges by the magnetic field B of the current I in a discharge plasma. Pinching starts when the magnetic field pressure B2∕2μ0 exceeds the plasma particle pressure p, and it stops when the two are equal; this condition describes a magnetically confined plasma column. There are two complementary geometries: the linear, or Z, pinch and the Θ pinch (Fig. 6.1). Both are axially symmetric. In the Z pinch the current flows along the axis (Z direction) and the plasma is confined by the azimuthal magnetic field of the current. In the second arrangement an azimuthal current (in the Θ direction) is induced in the plasma column by a rapidly varying current in a single-turn coil around the discharge vessel, and the confining magnetic field is parallel to the axis. Both discharges are operated in a pulsed mode, since the high currents required can conveniently be supplied only by discharging properly designed capacitor banks. Operation in pulsed mode is useful also for other reasons: the lifetime of hot plasma columns is limited by plasma losses at the ends of the column on the one hand, and on the other hand these plasmas are prone to hydromagnetic instabilities, which are extremely serious in the case of the Z pinch. However, the transformation of electrical energy into plasma is rather inefficient in Θ-pinch devices of short length; thus nearly all discharge-based EUV sources employ the linear geometry. A typical Z-pinch discharge proceeds as follows: high voltage is applied to the electrodes of the discharge tube, and after breakdown the current starts to flow in a thin cylindrical low-temperature plasma shell adjacent to the insulating wall. This current produces a corresponding magnetic field outside the shell, which accelerates the plasma like a piston or a slug toward the axis till it stagnates on the axis. For rough estimates, modeling of the compression employing a simple “snowplow” model suffices, although a detailed description of the plasma state requires solving MHD equations combined with kinetic codes for ionization and population of the atomic species, taking into account also radiative transport. A cylindrical shock wave running ahead of the piston is characteristic of fast discharges. Several calculations are presented in this book; see, for example, Chapter 11. In this chapter we focus on the development of a magnetically confined plasma cylinder consisting of strongly radiating ions after it has been formed on the axis. In this state, energy is transferred to the plasma mainly by Joule heating.

Laser superradiance was achieved for the first time as a result of an electronic transition in a diatomic heteronuclear molecule as a result of direct optical pumping. This superradiance was observed in the region of 670 nm due to a transition to the ground stated X 1Σ + of the intermetallic alkali molecule NaRb pumped by radiation from a pulsed copper vapor laser (λ =510.6 nm).

Pulsed lasing was obtained for the first time from Li2 molecules by optical pumping with radiation from a pulsed copper vapor laser (578.2 nm, pulse repetition frequency 5 kHz). The laser transitions, with wavelengths in the range 867–907 nm, belong to the electronic A1Σu+–X1Σg+ system. With a pump power of 190 mW, an average output power of 8 mW was achieved with an efficiency for the conversion of the optical pumping energy of 7%. A number of Li2 laser emission lines were observed in the superradiant regime.

A pulsed copper vapor laser emitting the 578.2 nm line was used as the pump source in achieving stimulated emission as a result of the electronic A1?+u?X1?+gtransitions in the Na2 molecule in the spectral range 0.765?0.804 ?. The average power of all the emission lines was 10 mW when the pulsed pump power was 150 W and the efficiency of conversion of the optical pump energy was about 3%. The pulse repetition frequency was 3.3 kHz. Violet diffuse radiation of the Na2 molecules, generated by pumping with the copper vapor laser, was observed. The superradiance regime was found for some of the lines.

Pulsed stimulated emission at a repetition frequency of 7 kHz was obtained as a result of B3Iu–X1Σg+ transitions in the I2 molecule pumped optically with radiation from a copper vapor laser emitting in the yellow and green parts of the spectrum. Metal vapor lasers capable of ensuring both high peak and average powers were found to be convenient sources for pumping the diatomic molecules. The iodine molecules were excited in five channels. The most efficient were the transitions to the levels (υ' = 14, J' = 52) and (υ' = 16, J' = 30) of the state B, pumped by the yellow line at 578.2 nm. The molecular stimulated emission spectrum consisted of characteristic doublets in the 1.016–1.34 μ range. When the energy conversion efficiency was 1%, the total peak power output from iodine was 30 W.