Patent ID: 7324269
Filing Date: 2008-01-29
Classification: G02B,G03F

Abstract:
1. A projection optical system for projecting a pattern on an object plane onto an image plane in a reduced size, said projection optical system comprising six reflective surfaces that include, in order of reflecting light from the object plane, a first reflective surface, a second convex reflective surface, a third convex reflective surface, a fourth reflective surface, a fifth reflective surface and a sixth reflective surface, and an aperture stop along an optical path between the first and second reflective surfaces, wherein the six reflective surfaces are arranged so that radii of curvature of these six reflective surfaces are substantially aligned with a certain optical axis, wherein a surface apex is defined, with respect to each of the six reflective surfaces, as one of nodal points between an optical axis and an approximately spherical surface, which one is closest to a reflection point of the light on each of the six reflective surfaces, the approximately spherical surface having a center that is defined as a center of curvature of each of the six reflective surfaces, and a radius that is defined as a radius of curvature of each of the six reflective surfaces, and wherein the following condition is met, where L wherein 25°<θ where θ