O. Yakushev

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

Soft X-ray spectrum of laser-produced aluminum plasma

Soft X-ray spectra (30–70 Å) 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.

Crater formation in a target under the action of a high-power laser pulse

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.

Dynamics of the ion energy spectrum in EUV-induced hydrogen plasma

The dynamics of the ion energy spectrum in low-pressure (10–100 Pa) hydrogen plasma induced by extreme ultraviolet (EUV) pulses in the wavelength range of 10–20 nm was studied experimentally. The plasma was generated under cathode irradiation due to both direct gas ionization by EUV photons and impact ionization by high-energy secondary electrons. The dynamics of the spectra of ions incident on the cathode was measured using a time-resolved retarding field energy analyzer. It is shown that the ion spectrum dynamics is completely determined by the time evolution of the cathode sheath. At low gas pressures (<20 Pa), the ion spectrum at early moments after the EUV pulse has a peaked shape, typical of a collisionless plasma sheath, and is mainly determined by the cathode voltage. As the pressure increases, the peak broadens and low energy ions appear in the spectrum due to ion collisions in the cathode sheath. An increase in the role of collisions with decreasing plasma density is also observed in the time evolution of ion spectra.

New type of discharge-produced plasma source for extreme ultraviolet based on liquid tin jet electrodes

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.

Plasma-assisted oxide removal from ruthenium-coated EUV optics

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.

Debris free high brightness light source based on LPP for actinic EUV microscopy and metrology applications

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.

The image of a nanosecond laser plasma in its own optical radiation

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.

A compact centrifugal pump for transmitting molten metals and other liquids with an operating temperature of up to 380°C

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.