T. Sizyuk

The effect of excitation wavelength on dynamics of laser-produced tin plasma

We investigated the effect of the excitation wavelength on the density evolution of laser-produced tin plasmas, both experimentally and numerically. For producing plasmas, Sn targets were excited with either 10.6 μm CO2 laser or 1.06 μm Nd:yttrium aluminum garnet laser; both are considered to be potential excitation lasers for extreme ultraviolet lithography laser-produced plasma light sources. The electron density of the plasma during the isothermal expansion regime was estimated using an interferometric technique. The Stark broadening of isolated singly-ionized emission was employed for deducing the density during the plasma adiabatic expansion regime. Our results indicate that the excitation source wavelength determines the initial density of the plasma, as well the plume expansion dynamics. Numerical simulation using HEIGHTS simulation package agrees well with the experimentally measured density profile.

Efficient laser-produced plasma extreme ultraviolet sources using grooved Sn targets

An efficient extreme ultraviolet (EUV) generation method has been developed with the use of a CO2 laser-produced plasma from a grooved target. A ∼5% conversion efficiency from laser to 13.5 nm photons was obtained with the use of grooves in a tin target or by repeated laser pulse shots at the same target position. Modeling studies proved that the groove target controls the hydrodynamic expansion of the plasma leading to confinement which prevents the plasma escaping from the EUV production zone.

Hollow laser self-confined plasma for extreme ultraviolet lithography and other applications

Laser-produced plasma ~LPP! devices are being developed as a light source for the extreme ultraviolet ~EUV! lithography applications. One concern of such devices is to increase the conversion efficiency of laser energy to EUV light. A new idea based on the initiation and confinement of cumulative plasma jet inside a hollow laser beam is developed and simulated. The integrated computer model ~HEIGHTS!was used to simulate the plasma behavior and the EUV radiation output in the LPP devices. The model takes into account plasma heat conduction and magnetohydrodynamic processes in a two-temperature approximation, as well as detailed photon radiation transport in 3D Monte Carlo model. The model employs cylindrical 2D version of a total variation-diminishing scheme ~for the plasma hydrodynamics! and an implicit scheme with the sparse matrix linear solver ~to describe heat conduction!. Numerical simulations showed that the EUV efficiency of the proposed hollow-beam LPP device to be higher than the current standard devices.

Three-dimensional simulation of laser-produced plasma for extreme ultraviolet lithography applications

Laser-produced plasma (LPP) from a tin target is being considered as the light source for the next generation of extreme ultraviolet (EUV) lithography. An integrated model was developed to simulate the plasma behavior and the EUV radiation output in LPP devices. The model includes plasma heat conduction and hydrodynamic processes in a two-temperature approximation, as well as detailed photon radiation transport using Monte Carlo methods. Multiple laser beams incident on a single target have been simulated in full three-dimensional geometry, using the total variation-diminishing scheme for the plasma hydrodynamics and an implicit scheme for heat conduction processes. Numerical simulations showed that EUV conversion efficiency increases for multiple-beam devices with specific optimum laser locations and direction compared to a single-beam device.

Effects of plasma spatial profile on conversion efficiency of laser-produced plasma sources for EUV lithography

Extreme ultraviolet (EUV) lithography devices that use laser-produced plasma (LPP), discharge-produced plasma (DPP), and hybrid devices need to be optimized to achieve sufficient brightness with minimum debris generation to support the throughput requirements of high-volume manufacturing lithography exposure tools with a long lifetime. Source performance, debris mitigation, and reflector system are all critical to efficient EUV collection and component lifetime. Enhanced integrated models continue to be developed using the High Energy Interaction with General Heterogeneous Target Systems (HEIGHTS) computer package to simulate EUV photon emission, debris generation, and transport in both single and multiple laser beam interaction systems with various targets. A new Center for Materials under Extreme Environments (CMUXE) was recently established to benchmark HEIGHTS models for various EUV-related issues. The models being developed and enhanced were used to study the effect of plasma hydrodynamics evolution on the EUV radiation emission for planar and spherical geometry of a tin target and explain the higher conversion efficiency of a planar target in comparison to a spherical target. HEIGHTS can study multiple laser beams, various target geometries, and pre-pulses to optimize EUV photon production. Recent CMUXE and other experimental results are in good agreement with HEIGHTS simulation.

Numerical Simulation of Laser-Produced Plasma Devices for EUV Lithography Using the Heights Integrated Model

ABSTRACT Laser-produced plasma (LPP) devices have been modeled as the light source for extreme ultraviolet (EUV) lithography. A key challenge for LPP is achieving sufficient brightness to support the throughput requirements of high-volume manufacturing. An integrated model (HEIGHTS) was applied to simulate the environment of EUV sources and optimize their output. The model includes plasma evolution and magnetohydrodynamic processes in a two-temperature approximation, as well as photon radiation transport determined by the Monte Carlo method. It uses the total variation diminishing scheme for the description of magnetic compression and diffusion in a cylindrical 2-D geometry for the target. Generation of the internal magnetic field with nonparallel density and temperature gradients was also considered. Preliminary results from numerical simulation in hydrodynamics and line radiation output of xenon and tin plasmas are presented for planar and droplet targets.

Plasma-facing material alternatives to tungsten

Tungsten is the leading high-Z candidate surface material for magnetic fusion reactor plasma-facing components, however, there are specific performance concerns for tungsten, and a general major concern about relying on one material. To broaden the options for fusion development we identified and examined five potential alternative high-Z plasma-facing materials: zirconium, niobium, molybdenum, hafnium and tantalum. We assess these materials from three standpoints: neutron-induced activation, sputter erosion/redeposition and plasma transient response. This initial analysis is encouraging showing (1) environmentally attractive activation properties with minimum waste disposal, for a tokamak reactor divertor, using advanced recycling techniques, (2) acceptable sputtering erosion/redeposition performance, similar to a tungsten divertor, and (3) concerns about the transient response of the alternative materials, but not fundamentally different than concerns for tungsten. We identify work needed to advance the qualification of these materials.

Analysis, simulation, and experimental studies of YAG and CO2 laser- produced plasma for EUV lithography sources

Efficient laser systems are essential for the realization of high volume manufacturing in extreme ultraviolet lithography (EUVL). Solid-state Nd:YAG lasers usually have lower efficiency and source suppliers are alternatively investigating the use of high power CO2 laser systems. However, CO2 laser-produced plasmas (LPP) have specific characteristics and features that should be taken into account when considering them as the light source for EUVL. The analysis of recent experimental and theoretical work showed significant differences in the properties of plasma plumes produced by CO2 and the Nd:YAG lasers including EUV radiation emission, source formation, debris generation, and conversion efficiency. The much higher reflectivity of CO2 laser from liquid, vapor, and plasma of a tin target results in the production of optically thinner plumes with higher velocity and in a better formation of plasma properties (temperature and density values) towards more efficient EUV source. However, the spikes in the temporal profiles of current CO2 laser will additionally affect the properties of the produced plasma. We have developed unique combination of state-of-the-art experimental facilities (CMUXE Laboratory) and advanced computer simulation (HEIGHTS) package for studying and optimizing various lasers, discharge produced plasmas (DPP), and target parameters as well as the optical collection system regarding EUV lithography. In this work, detailed characteristics of plasmas produced by CO2 and Nd:YAG lasers were analyzed and compared both experimentally and theoretically for optimizing EUV from LPP sources. The details of lower overheating of plasma produced by CO2 laser are given with time and explain how to utilize the high reflectivity of such lasers in plasmas produced in different target geometries to significantly enhance the conversion efficiency of EUV radiation.

Comprehensive simulation of vertical plasma instability events and their serious damage to ITER plasma facing components

Safe and reliable operation is still one of the major challenges in the development of the new generation of ITER-like fusion reactors. The deposited plasma energy during major disruptions, edge-localized modes (ELMs) and vertical displacement events (VDEs) causes significant surface erosion, possible structural failure and frequent plasma contamination. While plasma disruptions and ELM will have no significant thermal effects on the structural materials or coolant channels because of their short deposition time, VDEs having longer-duration time could have a destructive impact on these components. Therefore, modelling the response of structural materials to VDE has to integrate detailed energy deposition processes, surface vaporization, phase change and melting, heat conduction to coolant channels and critical heat flux criteria at the coolant channels. The HEIGHTS 3D upgraded computer package considers all the above processes to specifically study VDE in detail. Results of benchmarking with several known laboratory experiments prove the validity of HEIGHTS implemented models. Beryllium and tungsten are both considered surface coating materials along with copper structure and coolant channels using both smooth tubes with swirl tape insert. The design requirements and implications of plasma facing components are discussed along with recommendations to mitigate and reduce the effects of plasma instabilities on reactor components.

Simulation and optimization of DPP hydrodynamics and radiation transport for EUV lithography devices

Discharge produced plasma (DPP) devices are being used as a light source for Extreme Ultraviolet (EUV) Lithography. A key challenge for DPP is achieving sufficient brightness to support the throughput requirements of exposure tools for high-volume manufacturing lithography. An integrated model is being developed to simulate the environment of the EUV source and optimize the output of the source. The model describes the hydrodynamic and optical processes that occur in DPP devices. It takes into account plasma evolution and magnetohydrodynamic processes as well as detailed photon radiation transport. The total variation diminishing scheme in the Lax-Friedrich formulation for the description of magnetic compression and diffusion in a cylindrical geometry is used. Several models are being developed for opacity calculations: a collisional radiation equilibrium model, a self-consistent field model with Auger processes, and a non-stationary kinetic model. Radiation transport for both continuum and lines with detailed spectral profiles is taken into account. The developed models are being integrated into the HEIGHTS-EUV computer simulation package. Preliminary results of a numerical simulation of xenon gas hydrodynamics and EUV radiation output are presented for various plasma conditions.