Extreme ultraviolet lithography (EUVL) is a leading candidate for use in next-generation high volume manufacturing of
semiconductor chips that require feature sizes less than 32 nm. The essential requirement for enabling this technology
is to have a reliable, clean and powerful EUV source which efficiently emits light at a wavelength of 13.5 nm. Laser-produced
plasma EUV sources are strong candidates for use in EUVL light source systems. The development and
optimization of high-efficiency EUV sources requires not only well-diagnosed experiments, but also a good
understanding of the physical processes affecting the emitting plasma, which can be achieved with the help of accurate
numerical simulation tools. Here, we investigate the radiative properties of tin and tin-doped foam plasmas heated by
1.06 μm laser beams with 10 ns pulse widths. Results from simulations are compared with experimental conversion
efficiencies and emission spectra.
Tin-based laser-produced plasmas are attractive candidates as extreme ultraviolet light (EUV) sources for
lithography. The accurate simulation of the dynamics and spectral properties of plasmas used in radiation source
experiments plays a crucial role in analyzing and interpreting experimental measurements, and in optimizing the 13.5
nm radiation from the plasma source. We use HELIOS-CR, a 1-D radiation-magnetohydrodynamics code, along with a
detailed and comprehensive atomic database for tin, to simulate the properties and EUV emission from a plasma
produced by the interaction of 1.06 μm laser light and a tin-doped water droplet. Simulated spectra are shown to be in
good agreement with experimental results at a variety of laser intensities. Simulation results are also presented to
examine the ionization distribution for tin at the simulated temperatures and densities.
Laser-produced plasmas (LPPs) are being studied as potential extreme ultraviolet (EUV) and soft x-ray (SXR) sources for a wide variety of applications in commercial, defense, and medical research. For radiation sources to be of practical use in these systems, they must very efficiently emit light at the desired wavelength. EUV lithography, a viable approach in the manufacture of next-generation semiconductor chips, requires radiation sources that efficiently emit light at a wavelength of 13.5 nm, while producing relatively little radiation at other wavelengths in order to avoid damaging the wafer. Developing highly efficient plasma radiation sources requires a good understanding of critical physics issues that influence the plasma emission, including laser heating, plasma hydrodynamics, radiation transport, and atomic physics. We have developed a suite of well-tested plasma hydrodynamics, atomic physics, and plasma radiation simulation tools that are being used to simulate in detail the key physical processes in LPPs, and guide the development of higher efficiency plasma radiation sources. These tools include: 1-D and 2-D radiation-hydrodynamics codes, multidimensional spectral analysis tools, and a suite of atomic physics codes used to generate accurate atomic databases for radiation source simulations. Here, we discuss results from 2-D simulations of tin spherical droplets irradiated on one side by 0.35 μm laser beams. In particular, we examine the angular dependence of the 13.5 nm flux from the Sn plasma, and the sensitivity of the 13.5 nm conversion efficiency (CE) to the laser spot size and laser pulse width.
Tin, lithium, and xenon laser-produced plasmas are attractive candidates as light sources for extreme ultraviolet lithography (EUVL). Simulation of the dynamics and spectral properties of plasmas created in EUVL experiments plays a crucial role in analyzing and interpreting experimental measurements, and in optimizing the 13.5 nm radiation from the plasma source. Developing a good understanding of the physical processes in EUVL plasmas is challenging, as it requires accurate modeling for the atomic physics of complex atomic systems, frequency-dependent radiation transport, hydrodynamics, and the ability to simulate emergent spectra and images that can be directly compared with experimental measurements. We have developed a suite of plasma and atomic physics codes to simulate in detail the radiative properties of hot plasmas. HELIOS-CR is a 1-D radiation-magnetohydrodynamics code used to simulate the dynamic evolution of laser-produced and z-pinch plasmas. Multi-frequency radiation transport can be computed using either flux-limited diffusion or multi-angle models. HELIOS-CR also includes the capability to perform in-line non-LTE atomic kinetics calculations at each time step in the simulation. Energy source modeling includes laser energy deposition, radiation from external sources, and current discharges. The results of HELIOS-CR simulations can be post-processed using SPECT3D to generate images and spectra that include instrumental effects, and therefore can be directly compared with experimental measurements. Results from simulations of Sn laser-produced plasmas are presented, along with comparisons with experimental data. We discuss the sensitivity of the 13.5 nm conversion efficiency to laser intensity, wavelength, and pulse width, and show how the thickness of the Sn radiation layer affects the characteristics of the 13.5 nm emission.