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Emission of particle debris from the target of laser pumped plasma (LPP) extreme ultra-violet (EUV) light source is of the interest because that causes the contamination of the collector mirrors [1]. More recently, a high output power and efficiency has been achieved using the double pulse technique. Firstly, by irradiating the target with a short (ps) pre-pulse laser, a cloud of particles is produced. Secondly, the particles are irradiated by main CO2 laser, which absorb the energy efficiently to produce plasmas with an appropriate density and temperature for the EUV emission [2].
We develop a hydrodynamics simulation code based on the Lagrangian grid. We develop algorithms of reorganization of mesh dynamically according to the distribution of the material. The method allows one to calculate the dynamics of gas bubbles in the liquid phase and clusters in gas phase with a macroscopic scale (>100nm) [3]. Furthermore, the liquid-to-gas transition are taken into account and the ratio between liquid and gas phase for given temperature and density of the material are reproduced based on the Van-der-waals equation of state [4].
We investigated the temporal evolution of the density of a tin cylinder heated by a rate of 2.5 and 6 x 1012 W/mol. A critical heating rate is suggested below which the emission of particle debris takes place. It is shown that in the case of small heating rate, initially small bubbles appear, which grow in numbers and sizes, and eventually break the target into particles. In the case of large heating rate, target expands uniformly because the temperature of the target increases rapidly above the critical temperature.
References
[1] V. Bakshi, et., EUV Sources for Lithography (SPIE press, 2005).
[2] A. Endo, proceedings of the 2012 EUV source workshop,
http://www.euvlitho.com.
[3] K. Tomita, et al., Appl. Phys. Express, 8, 126101 (2015).
[4] D. A. Young, Phys. Rev. A, 3 364 (1971).
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