Patent ID: 7492509
Filing Date: 2009-02-17
Classification: G02B,G03F

Abstract:
1. A projection optical system for imaging a first object into a region of a second object using light of a wavelength shorter than 250 nm, the projection optical system comprising: a plurality of lenses disposed along an optical axis of the projection optical system; wherein the plurality of lenses is dividable into four non-overlapping groups of lenses, such that a total refractive power of a first group disposed closest to the first object is a negative refractive power, a total refractive power of a second group disposed directly adjacent to the first group is a positive refractive power, a total refractive power of a third group disposed directly adjacent to the second group is a negative refractive power, and a total refractive power of a fourth group disposed directly adjacent to the third group is a positive refractive power; and wherein the following relation is fulfilled: wherein: y is half a diameter in mm of a maximum image field imaged by the projection optical system, NA is a maximum numerical aperture on a side of the second object, φ k is a total number of lenses of the projection optical system, and wherein V