Krypton as stopper for ions and small debris in laser plasma sources

A preliminary theoretical and experimental demonstration of the successful use of krypton as stopper for ions and small debris (Φ < 1 μm) in laser plasma sources is discussed. In particular, for applications to projection micro-lithography at h ν = 60-90 eV, an ions rejection by almost 2 orders of magnitude is obtained at a Kr pressure compatible for more than 80% transmission of the EUV radiation.