Extreme ultraviolet (EUV) radiation from laser-produced plasma (LPP) has been thoroughly studied for application in mass production of next-generation semiconductor devices. One critical issue for the realization of an LPP-EUV light source for lithography is the conversion efficiency (CE) from incident laser power to EUV radiation of 13.5-nm wavelength (within 2% bandwidth). Another issue is solving the problem of damage caused when debris reaches an EUV collecting mirror. Here, we present an improved power balance model, which can be used for the optimization of laser and target conditions to obtain high CE. An integrated numerical simulation code has been developed for the target design. The code agrees well with experimental results not only for CE but also for detailed EUV spectral structure. We propose a two-pulse irradiation scheme for high CE, and reduced ion debris using a carbon dioxide laser and a droplet or a punch-out target. Using our benchmarked numerical simulation code, we find a possibility to obtain CE up to 6–7%, which is more than twice that achieved to date. We discuss the reduction of ion energy within the two-pulse irradiation scheme. The mitigation of energetic ions by a magnetic field is also discussed, and we conclude that no serious instability occurs due to large ion gyroradius.
Phase diagram of a Lennard-Jones fluid at liquid-gas equilibrium is studied by molecular dynamics simulations. The problem of potential cut-off influence on the properties of the model system is investigated. For several values of the cut-off radius, the physical properties of coexisting phases and critical parameters are calculated. It is shown that the results obtained for various cut-offs scaled by the critical temperature and density coincide, which means that fluids described by different modifications of the Lennard-Jones potential are thermodynamically similar, i.e., obey a corresponding states law.
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