Patent ID: 8592787

Claim:
An EUV light source for generating an EUV light for an exposure device, the EUV light source comprising: a chamber; a target supply device configured for supplying a target into the chamber; an optical system for introducing laser light from a driver laser into the chamber and irradiating the target with the laser light to turn the target into plasma from which EUV light is emitted; and an EUV collector mirror in the chamber, the EUV collector mirror comprising a multilayered reflecting surface with grooves and including an aperture through which the laser light from the driver laser propagates toward the target, the EUV collector mirror being configured for collecting the EUV light from the plasma to a focal spot, the grooves being arranged in a concentric fashion, wherein the grooves are configured for diffracting at least light at a wavelength which is the same as that of the laser light from the driver laser.