An EUV source is a critical component for the industrial extension of EUVL to feature sizes of 45 nm and beyond. In the ITRS road map, the current specification requires an EUV source capable of producing inband radiation at 13.5 nm in excess of 115 W collectable over a 2% bandwidth at the intermediate focus (IF). This calls for extreme plasma parameters of unprecedented radiation efficiency.
DPPs, such as the hollow-cathode-triggered (HCT) Z-pinch, capillary discharge, and dense plasma focus (DPF), and also LPPs, are considered as possible candidates for the creation of a compact EUV radiation source. In plasma discharges, low-Z materials such as Li (Z = 3) or various high-Z materials such as Sn (Z = 50), In (Z = 49), or the gases Kr (Z = 36) and Xe (Z = 54), for instance, are considered for the generation of EUV radiation. The 5p-4f transitions in xenon ions Xe XI and 4d-4f resonances of a set of tin ions Xe V–XIV emit intensely in the 1.5-nm 2%-bandwidth spectral band. Knowledge of the behavior of discharge plasmas with low- and high-Z elements is critical for the study of DPP or LPP and is of vital importance in the design of EUV sources.
A suitable source of radiation in the case of a high-Z radiator is the radiating multicharged ion plasma heated up to tens of electron volts. In such sources the complicated atomic and plasma physics, the nonstationary, nonequilibrium ionization process, and the radiation transport and plasma dynamics with self-consistent electromagnetic field (for discharge plasmas) interact strongly with each other. In a DPP plasma, heating is effected through several physical mechanisms: Joule dissipation; viscous kinetic energy dissipation, driven by the magnetic j × B force, in compression waves; and P d V work of the preheated plasma. The energy deposition in the discharge often exceeds 10 keV per ion to create the highly charged ion plasma. The ionization degree may reach 10 or higher. A significant part of the deposited energy is radiated. Radiation may be partially trapped, especially in the most intense lines. Optical properties and the plasma equation of state (EOS) are, as a rule, in conditions far from local thermodynamic equilibrium (LTE), i.e., in a non-LTE state.
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