Mitigation of fast ions from laser-produced Sn plasma for an extreme ultraviolet lithography source

The authors present evidence of the reduction of fast ion energy from laser-produced Sn plasma by introducing a low energy prepulse. The energy of Sn ions was reduced from more than 5keV to less than 150eV nearly without loss of the in-band conversion from laser to 13.5nm extreme ultraviolet (EUV) emission as compared with that of a single pulse. The reason may come from the interaction of the main pulse with preplasma instead of the full density solid surface. This makes it possible to use the full density Sn target in the practical EUV lithography source.