The development of a source bright enough for EUVL, possessing the required long-term stability within a reasonable cost, is forcing plasma physicists to address issues associated with dense plasmas that have up until now received scant attention. With both discharge plasmas and laser plasmas, addressing these issues has stimulated many new ideas and concepts for source design and measures associated with them. Although these new developments are currently directed toward satisfying the needs of next-generation lithography (NGL), it is likely they will also open new fields of application in the years ahead.
Early on in the development of EUVL sources, when the required source power (2π sr, 2% bandwidth) was ∼10 W, we speculated that the so-called debris problem would be the most difficult to overcome. It was for this reason that we proposed the notion of the mass-limited target for the laser plasma source. In this scenario, the material supplied to the source should consist only of a mass sufficient to provide the minimum required number of atomic radiators.
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