Characteristics of a minimum-debris optimum conversion efficiency tin-based LPP source

The conversion efficiency and potential for debris of planar and spherical targets of laser-produced tin-plasmas for use in a high-volume manufacturing EUVL source collector module are computationally examined. A Nd:YAG laser beam is used to irradiate the targets under different irradiances and pulse durations. A two-dimensional/axisymmetric hydrodynamic code, an atomic physics code and an analytical model are used to perform simulations of the laser-plasma processes. The predicted conversion efficiencies are in good agreement with data reported from experiments. The optimum laser parameters yield maximum conversion efficiencies of 1.86% and 1.45%, respectively for the planar and spherical targets. However, the spherical target is best suited for low cost-of-ownership, as it has significantly lower neutral debris compared to the planar target. The key finding of this work is that the laser produced plasmas of both planar and spherical targets are non-uniform. These non-uniformities must be accounted for in the design of collection optics and debris mitigation schemes.

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