Patent ID: 6556648
Filing Date: 2003-04-29
Classification: G02B,G03F

Abstract:
A lithographic projection apparatus comprising:a radiation system to provide a projection beam of radiation; a support structure adapted to support patterning structure which can be used to pattern the projection beam according to a desired pattern; a substrate table to hold a substrate; a projection system to project the patterned beam onto a target portion of the substrate, wherein said projection system includes precisely four imaging mirrors in the optical path of the projection beam and has an incidence angle classification, C, of 2(âˆ’), 6(âˆ’), or 9(âˆ’), where: C=&Sum;i=14&it;ai&CenterDot;2(4-i)&it;(M&LeftBracketingBar;M&RightBracketingBar;)ai=1 if an angle of incidence of a chief ray at mirror i is negative, ai=0 if the angle of incidence of the chief ray at mirror i is positive, M is a magnification of the projection system, and the index i numbers the mirrors from object to image.