Optical element, and light source unit and exposure apparatus having the same

摘要

An optical element includes plural multilayer mirrors, and is characterised in that the multilayer mirrors are renewable. <??>The multilayer mirrors may comprise a substrate, a release layer and reflection multilayers, in which the release layer is much more soluble than the substrate. Alternatively, the reflection multilayers may be more soluble or more easily removed e.g. by reactive ion etching than the substrate or an intervening buffer layer. The reflection multilayers are removable so that the substrate can be recoated e.g. if the multilayers have been damaged by debris. The optical element may be used for reflecting extreme ultraviolet light in exposure apparatus for semiconductor device fabrication. <IMAGE>