Patent ID: 8842272

Claim:
An apparatus for inspecting a photomask using extreme ultra-violet (EUV) light, the apparatus comprising: an illumination source for generating the EUV light which illuminates a target substrate; objective optics for receiving and projecting the EUV light which is reflected from the target substrate; and a sensor for detecting the EUV light which is projected by the objective optics, wherein the objective optics comprises a first mirror which is arranged to receive and reflect the EUV light which is reflected from the target substrate, an opening in the first mirror, a second mirror which is arranged to receive and reflect the EUV light which is reflected by the first mirror, a third mirror which is arranged to receive and reflect the EUV light which is reflected by the second mirror, wherein the light reflected by the second mirror passes through the opening in the first mirror in traveling to the third mirror, and a fourth mirror which is arranged to receive and reflect the EUV light which is reflected by the third mirror.