Illumination system, particularly for EUV lithography

摘要

There is provided an illumination system for light having wavelengths <=193 nm. The system includes (a) a first raster element for receiving a first diverging portion of the light and directing a first beam of the light, (b) a second raster element for receiving a second diverging portion of the light and directing a second beam of the light, where the first raster element is oriented at an angle with respect to the second raster element to cause a center ray of the first beam to intersect with a center ray of the second beam at an image plane, and (c) an optical element for imaging secondary sources of the light in an exit pupil, where the optical element is situated in a path of the light after the first and second raster elements and before the image plane.