Patent attributes
A projection optical system for performing reduction projection of a pattern of a reticle onto a projection plane. The system includes a first mirror having a concave reflective surface, a second mirror having a reflective surface, a third mirror having a convex reflective surface, a fourth mirror having a concave reflective surface, a fifth mirror having a convex reflective surface, and a sixth mirror having a concave reflective surface. The reflective surface of the fourth mirror has a curvature radius of not less than 400 mm and not more than 800 mm in absolute value. The reflective surface of the sixth mirror has a curvature radius of not less than 400 mm and not more than 600 mm in absolute value, and the reflective surfaces of the first, second, third, fourth, fifth and sixth mirrors have curvatures of not more than 1500 mm in absolute value, respectively.
