Patent ID: 6122037
Filing Date: 2000-09-19
Classification: G03F

Abstract:
An optical system for forming an image of a pattern on a wafer comprising:a light source for generating an initial optical beam;a beamsplitter for dividing said initial optical beam into first and second incident beams travelling on first and second beam legs and for combining first and second return beams from said first and second beam legs;a mirror disposed on a first one of said beam legs and oriented to reflect said first incident beam back toward said beamsplitter as said first return beam;a reflective surface having said pattern thereon, disposed in a second one of said beam legs, said pattern comprising first and second phase areas formed thereon for impressing said pattern on said second incident beam and for reflecting a patterned beam back toward said beamsplitter as said second return beam, said second return beam comprising first and second sub-beams differing in phase,where a first phase difference between said first return beam and said first sub-beam of said second return beam is substantially 2n.PI. radians and a second phase difference between said first return beam and said second sub-beam of said second return beam is (2n+1).PI. radians, where n is an integer; anda lens disposed to intercept a combined beam formed in said beamsplitter from said first and second return beams, for focusing said combined beam on said wafer, whereby areas of said wafer exposed to said first sub-beam receive radiation of exposing intensity from said first return beam and said first sub-beam and areas exposed to said second sub-beam receive substantially zero radiation, thereby forming an image of said pattern on said wafer.