Patent ID: 6353470
Filing Date: 2002-03-05
Classification: G02B,G03F

Abstract:
A projection objective for use in short wavelength microlithography, comprising;six mirrors (a first mirror (S1), a second mirror (S2), a third mirror (S3), a fourth mirror (S4), a fifth mirror (S5) disposed closest to an object to be illuminated and a sixth mirror (S6)) arranged such that an image-side numerical aperture (NA) is NA&gE;0.15, and wherein said fifth mirror is positioned such that at least one of the following conditions is satisfied: an image-side optical free working distance is greater than or equal to a used diameter D of the fifth mirror; the image-side optical free working distance is greater than or equal to a sum of one-third of the used diameter of the fifth mirror and a length between 20 mm and 30 mm; and the image-side optical free working distance is at least 50 mm.