| 摘要 |
Spectral-purity filters (SPFS) are disclosed that produce a stream of "SPF gas" through which a beam of light, particularly a beam including extreme ultraviolet (EUV) light, is allowed to pass. The SPF can be located in a system that receives a beam of EUV-containing light from a source and delivers the beam to a downstream EUV-optical system, wherein the beam from the source passes through the SPF to the optical system. The gaseous SPF is formulated and configured to enrich the beam in at least one EUV wavelength as the beam passes through the gaseous SPF. For enrichment of EUV wavelengths, an exemplary SPF gas is ZrCl4. The stream of SPF gas can be sheathed in an inert "sheath gas." The gaseous SPF is usable in a vacuum environment, in which used SPF gas, and sheath gas if used, is collected.
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