Off-axis projection optics and extreme ultraviolet lithography apparatus employing the same

Abstract

Off-axis projection optics that includes first and second mirrors positioned off-axis and sharing a confocal point that are arranged to reduce linear astigmatism. If a distance between an object plane and the first mirror is l1, an incident angle of light coming from the object plane to the first mirror is i1, a distance between the first mirror and the confocal point is l1′, a distance between the confocal point and the second mirror is l2, an incident angle of light coming from the first mirror to the second mirror is i2, and a distance between the second mirror and an image plane is l2′, the off-axis projection optics may satisfy the following equation: l 1 ′ + l 1 l 1 ⁢ tan ⁢ ⁢ i 1 = l 2 ′ + l 2 l 2 ⁢ tan ⁢ ⁢ i 2 .

Dependencies are inferred from the claim text.