Compact laser plasma soft x-ray sources are under serious consideration for projection lithography. Current baseline designs for soft x-ray projection lithography systems place stringent performance and cost requirements on a laser plasma soft x-ray source. The x-ray source must meet specific criteria relating to x-ray fluence in the 13 nm region, the wavelength of preference for projection lithography, to output stability at high (kHz) repetition- rates, to continuous long term operation and to operating costs. Moreover the source must operate in a vacuum enclosure in close proximity to costly x-ray and optical elements which must remain in pristine condition, free from degradation by particulate and plasma emission emanating from the source. We discuss these requirements, and review experiments leading to the optimal design of a laser plasma soft x-ray source.
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