Optimization of EUV/SXR plasma radiation source characteristics

Abstract

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.