| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an EUV projection optical system operable at high numerical aperture having relatively large transmission, providing higher wafer throughput than conventional systems. <P>SOLUTION: An optical system has a plurality of elements arranged to image radiation, the elements include mirror elements having a reflective surface positioned at a path of radiation. At least one of the mirror elements is a pupil mirror having a pupil mirror surface arranged at or near to a pupil surface of the optical system. At least one of the remaining mirror elements is a highly loaded mirror arranged at a position where at least one of a largest value of a range of angles of incidence and a largest value of an average angle incidence of all remaining mirrors occurs. The pupil mirror surface is formed by a reflective coating designed as a one-dimensionally graded coating including a multilayer stack of layers of different materials, the layers having a geometrical layer thickness which varies according to a first grading function in a first direction of the coating and which is substantially constant in a second direction perpendicular to the first direction. The mirror surface of the highly loaded mirror is coated with a reflective mirror coating designed as a graded coating according to a second grading function. <P>COPYRIGHT: (C)2008,JPO&INPIT |
