Nanotech 2010

Molecular Dynamics Investigation on Tin

M. Masnavi, H. Parchamy Araghy, M. Nakajima, K. Horioka
Tokyo Institute of Technology, JP

Keywords: molecular dynamics, extreme ultraviolet (EUV) lithography, laser ablation, laser-produced plasmas


Laser-produced tin (Sn) plasma has been considered as one of main candidates for extreme ultraviolet (EUV) light source used in EUV lithography due to its high conversion efficiency and scalability to high EUV power. The Sn target could be either solid or liquid droplet. In order to increase conversion efficiency and to mitigate energetic ions and neutral from laser-produced Sn plasma, fundamental investigation is necessary. Theoretical study by means of hydrodynamic simulation is expected to guide us to optimize Sn target and pumping conditions. Equation of state of materials is an inevitable ingredient of all hydrodynamic simulations. However, the early stages of the laser-matter interaction process, equation of state at phase transition, for example, liquid-vapor transition, and the ejection of particles are remain unexplored. Investigations of these early stages are essential in order to understand the dynamics of fundamental mechanisms. Although theoretical models in this regard exist, they are mostly based on questionable thermodynamic equilibrium concepts and have been insufficiently verified by measurements. The question of the behavior of Sn properties under either rapid heating/cooling is still open. The aim of this research is to report the simulated properties of Sn over wide physical conditions by means of Materials Studio code and a 3D homemade molecular dynamics code developed for this purpose. In particular, we are interested to investigate the behavior of physical parameters of Sn in transient situation relevant to conditions in laser-produced EUV sources. Results showed transient effects on the phase transitions. The simulation results are compared to experimental data obtained on pulsed laser ablation of Sn. Velocity distributions of evaporated particles from the Sn are discussed as a function of laser fluence. Also, the equation of state has been derived in warm dense region of Sn. This research is supported by Gigaphoton Inc.
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