Vladimir Krivtsun

Infrared diffractive filtering for extreme ultraviolet multilayer Bragg reflectors

We report on the development of a hybrid mirror realized by integrating an EUV-reflecting multilayer coating with a lamellar grating substrate. This hybrid mirror acts as an efficient Bragg reflector for extreme ultraviolet (EUV) radiation at a given wavelength while simultaneously providing spectral-selective suppression of the specular reflectance for unwanted longer-wavelength radiation due to the grating phase-shift resonance. The test structures, designed to suppress infrared (IR) radiation, were fabricated by masked deposition of a Si grating substrate followed by coating of the grating with a Mo/Si multilayer. To give the proof of principle, we developed such a hybrid mirror for the specific case of reflecting 13.5 nm radiation while suppressing 10 μm light, resulting in 61% reflectance at the wavelength of 13.5 nm together with the 70 × suppression rate of the specular reflection at the wavelength of 10 μm, but the considered filtering principle can be used for a variety of applications that are based on utilization of broadband radiation sources.

Removal of amorphous C and Sn on Mo:Si multilayer mirror surface in Hydrogen plasma and afterglow

Removal of amorphous carbon and tin films from a Mo:Si multilayer mirror surface in a hydrogen plasma and its afterglow is investigated. In the afterglow, the mechanism of Sn and C films removal is solely driven by hydrogen atoms (radicals). Probabilities of Sn and C atoms removal by H atoms were measured. It was shown that the radical mechanism is also dominant for Sn atoms removal in the hydrogen plasma because of the low ion energy and flux. Unlike for Sn, the removal mechanism for C atoms in the plasma is ion-stimulated and provides a much higher removal rate.

Extreme ultraviolet (EUV) source and ultra-high vacuum chamber for studying EUV-induced processes

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

Calibration models for multi-component quantitative analyses of dairy with the use of two different types of portable near infrared spectrometer

Several partial least squares (PLS) calibration models were performed on spectra of standards of restored milk measured with two different types of near infrared spectrophotometers (800–1080 nm); the most reliable instrument was chosen using a self-made PLS program, ISCAP, the efficiency of which was evaluated with the Quant2 OPUS program. Then ISCAP was applied to develop and test a method of moisture prediction in milk powder based on diffuse reflection spectra received in a NIR spectrometer (1100–1700 nm) equipped with a remote fibre-optic probe The reference moisture was determined by thermo-gravimetric analysis.

High brightness EUV sources based on laser plasma at using droplet liquid metal target

We present the study of a source of extreme ultraviolet (EUV) radiation based on laser plasma generated due to the interaction of radiation from a nanosecond Nd : YAG laser with a liquidmetal droplet target consisting of a low-temperature eutectic indium–tin alloy. The generator of droplets is constructed using a commercial nozzle and operates on the principle of forced capillary jet decomposition. Long-term spatial stability of the centre-of-mass position of the droplet with the root-mean-square deviation of ~0.5 μm is demonstrated. The use of a low-temperature working substance instead of pure tin increases the reliability and lifetime of the droplet generator. For the time- and space-averaged power density of laser radiation on the droplet target 4 × 1011 W cm-2 and the diameter of radiating plasma ~80 μm, the mean efficiency of conversion of laser energy into the energy of EUV radiation at 13.5 ± 0.135 nm equal to 2.3% (2π sr)-1 is achieved. Using the doublepulse method, we have modelled the repetitively pulsed regime of the source operation and demonstrated the possibility of its stable functioning with the repetition rate up to 8 kHz for the droplet generation repetition rate of more than 32 kHz, which will allow the source brightness to be as large as ~0.96 kW (mm2 sr)-1.

Exploring the electron density in plasma induced by EUV radiation:II. Numerical studies in argon and hydrogen

We used numerical modeling to study the evolution of EUV-induced plasmas in argon and hydrogen. The results of simulations were compared to the electron densities measured by microwave cavity resonance spectroscopy. It was found that the measured electron densities can be used to derive the integral amount of plasma in the cavity. However, in some regimes, the impact of the setup geometry, EUV spectrum, and EUV induced secondary emission should be taken into account. The influence of these parameters on the generated plasma and the measured electron density is discussed.

Short wave near infrared spectrometry of back scattering and transmission of light by milk for multi-component analysis

Quality and authenticity of milk are usually defined by the content and composition of fat, proteins, total solids, somatic cells and other established indicators. Along with traditional reference methods for quantitative analysis, the use of near infrared (NIR) spectrometers and multivariate modelling is becoming more widely utilised. It would be useful to apply a spectrometer with a linear silicon CCD array as a rapid, portable and rather cheap supervising device. However, milk is a multiphase disperse system which includes a rough disperse phase of somatic cells and fatty globules, a thin phase of casein and whey proteins particles and the molecular solutions of lactose, salts, vitamins etc. in water. The scattering of incident light by particles of milk affect the signal of an NIR spectrometer significantly. The calibration of a spectrometer can be improved by considering the distinction between scattering by fatty globules and casein micelles. For this purpose, it is attractive to use the anisotropy of scattering by rough particles, in particular, by fatty globules. The comparative results for calibration models constructed with transmission and back scattering spectra of milk are presented in this paper. The spectra were acquired with a new two-channel short wave NIR spectrometer. Restored drinking milk has been modelled with a set of calibration samples, since the difference in the optical properties due to the globules and the micelles is significant and also because the reliable quality control of drinking milk using a simple spectrometer is a relevant practical problem. PLS models were constructed for the prediction of fat and protein and also of the fat-free total solids which serve as an indicator of authenticity for drinking milk. The results obtained demonstrate that a large reductions in errors is possible. The SEP value of not more than 0.08% wt was achieved when predicting the fat content of milk using a calibration based on the difference spectra of transmission and backscattering compared with a SEP of 0.21% wt for the model using transmission spectra only. For protein determination, the SEP was reduced from 0.25% wt to 0.12% wt if the calibration was based on the spectra of backscattering rather than on transmission.

Cavitation and spallation in liquid metal droplets produced by subpicosecond pulsed laser radiation

The deformation and fragmentation of liquid metal microdroplets by intense subpicosecond Ti:sapphire laser pulses is experimentally studied with stroboscopic shadow photography. The experiments are performed at a peak intensity of 10^{14}W/cm^{2} at the targets surface, which produces shock waves with pressures in the Mbar range. As a result of such a strong impact, the droplet is transformed into a complex-shaped hollow structure that undergoes asymmetrical expansion and eventually fragments. The hollow structure of the expanding target is explained by the effects of cavitation and spallation that follow the propagation of the laser-induced shock wave.

Stable droplet generator for a high brightness laser produced plasma extreme ultraviolet source

We present the results of the low-melting liquid metal droplets generation based on excited Rayleigh jet breakup. We discuss on the operation of the industrial and in-house designed and manufactured dispensing devices for the droplets generation. Droplet diameter can be varied in the range of 30-90 μm. The working frequency of the droplets, velocity, and the operating temperature were in the ranges of 20-150 kHz, 4-15 m/s, and up to 250 °C, respectively. The standard deviations for the droplet center of mass position both their diameter σ < 1 μm at the distance of 45 mm from the nozzle. Stable operation in the long-term (over 1.5 h) was demonstrated for a wide range of the droplet parameters: diameters, frequencies, and velocities. Physical factors affecting the stability of the generator operation have been identified. The technique for droplet synchronization, allowing using the droplet as a target for laser produced plasma, has been created; in particular, the generator has been successfully used in a high brightness extreme ultraviolet (EUV) light source. The operation with frequency up to 8 kHz was demonstrated as a result of the experimental simulation, which can provide an average brightness of the EUV source up to ∼1.2 kW/mm2 sr.

Loss of Hydrogen Atoms in H 2 Plasma on the Surfaces of Materials Used in EUV Lithography

Low-pressure hydrogen is an important component of the working medium in extreme ultraviolet (EUV) projection lithography. Under the action of EUV photons and fast secondary electrons on the gas medium, plasma and atomic hydrogen, actively interacting with the surface, are produced. This interaction is very important, because it largely determines the lifetime of the multilayered EUV optics. In this study, the loss of atomic hydrogen under the conditions of a low pressure (<10 Torr) RF plasma discharge on the surfaces of materials used in EUV lithography is investigated. The surface loss probabilities of H atoms on these materials are measured. It is shown that surface recombination of atomic hydrogen goes according to the Eley-Rideal mechanism via direct recombination of H atoms from the gas phase with chemically and physically adsorbed atoms. In this case, the surface recombination probability is mainly determined by the density of chemical adsorption sites. The density of adsorption sites and the desorption energy of H atoms are estimated. The desorption energy of physically adsorbed H atoms on pure metal surfaces (or surfaces exposed to plasma) is about 0.5 eV, and the density of sorption sites is close to the surface density of atoms. This results in a high loss probability of H atoms on metals (∼0.1). Therefore, to provide efficient transportation of hydrogen atoms, it is necessary to use materials with the lowest loss probability of H atoms, i.e., dielectrics.