Vladimir Titov

Erosion and degradation of EUV lithography collector mirrors under particle bombardment

In extreme ultraviolet lithography (EUVL) environments both laser produced plasma (LPP) and gas discharge produced plasma (GDPP) configurations face serious issues regarding components lifetime and performance under particle bombardment, in particular collector mirrors. For both configurations debris, fast ions, fast neutrals, and condensable EUV radiator fuels (Li, Sn) can affect collector mirrors. In addition, collector mirrors are exposed to impurities (H,C,O,N), off-band radiation (depositing heat) and highly-charged ions leading to their degradation and consequently limiting 13.5 nm light reflection intensity. The IMPACT (Interaction of Materials with charged Particles and Components Testing) experiment at Argonne studies radiation-induced, thermodynamic and kinetic mechanisms that affect the performance of optical mirror surfaces. Results of optical component interaction with singly-charged inert gases (Xe) and alternate radiators (e.g. Sn) are presented for glancing incidence mirrors (i.e., Ru, Pd) at bombarding energies between 100-1000 eV at room temperature. Measurements conducted include: In-situ surface analysis: Auger electron spectroscopy, X-ray photoelectron spectroscopy, direct recoil spectroscopy and low-energy ion scattering spectroscopy; Ex-situ surface analysis: X-ray reflectivity, X-ray diffraction, atomic force microscopy and at-wavelength EUV reflectivity (NIST-SURF).

Study of brittle destruction and erosion mechanisms of carbon-based materials during plasma instabilities

Abstract Erosion damage due to plasma instabilities such as hard disruptions, edge-localized modes, and vertical displacement events remains a major obstacle to successful realization of the tokamak-reactor concept. As a result of these plasma instabilities, intense plasma energy that is deposited during short periods can cause severe erosion, structural damage, and surface modifications of the plasma-facing materials. Experimental work is being carried out at the high-power VIKA-93 plasma-gun facility in the Efremov Institute, Russia. Interesting results were obtained during preliminary heating of the samples (to 1200°C) and use of maximum plasma gun parameters, i.e., E in =30 MJ/m 2 , τ=360 μ s. In all samples, a large increase in weight loss (up to 80%) was observed during plasma bombardment when preheating was used. Scanning electron microscope investigations have demonstrated a considerable evolution of surface recrystallization processes, especially for preheated CFC materials. Significant differences among various carbon materials are found for specimens with and without preliminary heating.

Effect of xenon bombardment on ruthenium-coated grazing incidence collector mirror lifetime for extreme ultraviolet lithography

The effect of energetic xenon ion bombardment on the extreme ultraviolet (EUV) reflectivity performance of mirrors is of vital importance for the performance of discharge- and laser-produced plasma extreme ultraviolet lithography sources. To study these effects, we measured absolute and relative reflectivities at the National Institute of Standards and Technology and the Interaction of Materials with Particles and Components Testing facility to quantify the effects of singly ionized Xe ion bombardment on the reflectivity of Ru EUV collector mirrors. Results show that unity sputtering is reached at Xe+ energies near 400–500eV. The Xe+-induced sputter yield decreases an order of magnitude with only a 60% decrease in energy. Incident angle-dependent data of Xe+ bombardment show that the sputter yield is weakly dependent on angle at energies near 1keV. Dynamic measurements of in situ EUV reflectivity during Xe+ irradiation show that the oxygen state of the reflecting mirror has a significant effect on reflect...

Experimental simulation of plasma high heat flux - materials interaction during ITER disruption

The main parameters of test facilities based on high-current coaxial plasma accelerators developed at the Efremov Institute to study PFC candidate material damage under high heat plasma fluxes with a specific energy close to the PFC ITER disruptive load are given. The extremely high values of plasma heat flux density (up to 110 MJ m−2) and dynamic plasma pressure (up to 15 MPa) are unique features of these facilities. Research on parameters of plasma shielding layer (SL) formed during plasma-material interaction has shown that they are close to the SL parameters predicted for short (τd < 1 ms) disruptions in ITER. That gives grounds for obtaining reliable results on PFC material damage in model experiments with such a disruption simulator. The test material research on the VIKA facility has shown, in particular, that the main mechanism of metal damage is the melt layer movement due to high SL plasma pressure.

Effect of charged-particle bombardment on collector mirror reflectivity in EUV lithography devices

EUV metallic light radiators such as Sn or Li used for lithography will limit the lifetime of collector optics in source devices by both contamination and irradiation. Generation of EUV light requires the use of hot, dense plasma. Pinch dynamics generates fast ions and atoms, such as metallic sources (Sn, Li) with energies ranging from 100 eV up to several keV. The expanding Sn plasma will thermalize and condense in nearby components, including the debris shield and collector optics. The incident distribution of debris onto the collector optics will likely include Sn fast ions. Sn contamination will lead to two different mechanisms. One is condensation and Sn thin-film buildup on the reflective optics surface (i.e., Ru or Pd mirror) from the thermalized Sn plasma. This mechanism will lead to performance failure after about 1-2 nm build up of Sn thin film whereby the at-wavelength EUV reflectivity will decrease 20% in magnitude for grazing incident angles less than 20-degrees. The second mechanism is more complex. Fast Sn ions generated at the pinch will reach the collector optics and induce mixing, sputtering, and implant at depths between 3 and 5 monolayers on the Ru or Pd surface. EUV light can also induce ionization in background Ar or He gas used for debris mitigation. Low-energy Ar or He ions therefore impinge on the collector mirror surface at threshold-level energies between 40 and 100 eV. A steady-state Sn surface concentration will be attained after a given fluence of both Sn debris and low-energy Ar ions. The amount of Sn implanted or deposited will affect EUV reflectivity as a function of ion and/or atom fluence. Sn contamination mechanisms, as well as threshold-level sputtering from inert ion species, are studied in the IMPACT (Interaction of Materials with charged Particles and Components Testing) experiment. Sn exposure conditions include incident singly charged particles between 500 and 1000 eV, oblique incidence and incident fluxes ranging from 1011 to 1014 ions/cm2/s. In-situ surface metrology includes sputter yield diagnosis, Auger electron spectroscopy, X-ray photoelectron spectroscopy, direct recoil spectroscopy and low-energy ion scattering spectroscopy, and at-wavelength EUV reflectivity.

Material response due to simulated plasma disruption loads

Abstract The paper is focused on the problem of understanding key items of high heat flux plasma-material interaction during abnormal events: the net power flux that reached the target surface and the nature of the target erosion. As to first the results of direct measurements of visible radiation (Δ λ =400–800 nm) flux on the target surface are presented. It is shown that visible radiation power flux emitted inside spectral range Δ λ =400–700 nm can be characterised by the level of P R ≤1 GW/m 2 typical of experiments performed at the VIKA facility during irradiation power of P irr ∼80 GW/m 2 . It is also shown that the existence of the strong guide magnetic field of B ∼2 T results in a change in the behaviour and microstructure of the (Al) metal melt layer.

Plasma‐material Interaction Studies On Lithium And Lithiated Substrates During Compact Tokamak Operation

The role of lithium on the modification of recycling regimes in fusion reactors has renewed interest of previous lithium supershot experiments carried out in TFTR. There is a need to understand the interaction between edge plasmas and lithiated plasma‐facing components (PFCs), which have the potential of enabling fusion reactors to operate at low‐recycling regimes. The Interaction of Materials with Particles and Components Testing (IMPACT) facility at Argonne National Laboratory is currently collaborating with Princeton Plasma Physics Laboratory (PPPL) to conduct lithiated surface studies for the National Spherical Tokamak Experiment (NSTX) and the Current Drive eXperiment — Upgrade (CDX‐U). IMPACT has the necessary tools to perform experiments that diagnose the surface dynamics of lithium thin films on metallic and non‐metallic substrates, and can be monitored with multiple in‐situ techniques (LEISS, AES, QMS and XPS) capturing real‐time surface dynamics. Therefore, these techniques are available during ...

Study of material response in disruption simulation experiments with variable irradiation duration

Abstract Collection of data on response of materials, and especially metals, to ITER plasma disruption-like loads remains an actual problem, in spite of a considerable volume of research. Some data on materials (Al, Cu, SS, W, graphites) responses to plasma load in disruption simulation experiments at the VIKA facility are given in this paper. Plasma heat flux specific values (w=7.5; 10; 15; 30 MJ m−2), pulse duration (τρ=0.09; 0.18; 0.27; 0.36 ms) and, in some experiments also, initial sample temperature (TS=RT-1100°C) were varied. The dynamics of material response was studied in the mode of operation with a fixed level of irradiation power (∼100 GW m−2) at pulse duration variation. It was confirmed that total mass losses (erosion depth) under plasma irradiation is determined mainly by melt layer dynamics for Be-like metal (Al). The absorbed energy coefficient for all materials decreases with both time of irradiation and the growth of plasma load. It is shown that preheating of irradiated W and graphite samples does not result in a reduction of mass losses values, but suppresses significantly cracking intensity for W.

Experimental study of radiation power flux on the target surface during high heat plasma irradiation

Abstract Some new data of the experimental study of visible radiation from the plasma shielding layer (SL) on the target surface during high heat plasma–material interaction are given in the report. The experiments were performed on the VIKA facility. Long pulse ( τ p =0.36 ms) high power ( P irr ∼100 GW m −2 plasma streams were used for irradiation of graphite and tungsten samples. The target inclination ( α =0° normal irradiation; 45°; 70°) and magnetic field ( B =0 to 3 T) were varied in experiments. It is shown that the values of ( Δλ ≈400 to 700 nm) visible radiation power flux (VRPF) on the target surface can be characterised by the level of P R ∼1 GW m −2 for normal irradiation in the presence of a magnetic field B =2 to 3 T. Inclination of targets leads to the reduction of this flux in conformity with the corresponding decrease of the irradiation power. The material of the target does not influence sufficiently on the level of the incident radiation power flux in the performed experiments.

Study of shielding layer plasma parameters in experiments on intensive plasma stream-material interaction

Abstract Some results of a study of the plasma shielding layer (SL) which appears near the surface of a material irradiated by a plasma high heat flux (wp ≥ 10 MJ m−2) are presented. Analysis of the SL radiation in the visible and UV regions of the spectrum and also data on probing the laser beam absorption have made it possible to estimate the values of plasma density (Ne ≤ 3 × 1024 m−3) and electron temperature (Te = 3−8 eV) and have revealed that the SL plasma is optically thick for visible radiation.