OFF-AXIS PROJECTION OPTICS SYSTEM AND EXTREME ULTRA VIOLET LITHOGRAPHY APPARATUS APPLYING THE SAME

摘要

Example embodiments are directed to an off-axis projection optical system including first and second mirrors that are off-axially arranged. The tangential and sagittal radii of curvature of the first mirror may be R_1t and R_1s, respectively. The tangential and sagittal radii of curvature of the second mirror may be R_2t and R_2s, respectively. The incident angle of the beam from an object point to the first mirror 10 may be i₁, and an incident angle of the beam reflected from the first mirror 10 to the second mirror 30 is i₂. The values of R_1t, R_1s, R_2t, R_2s, i₁ and i₂ may satisfy the following Equation R_1t cos i₁=R_2t cos i₂ R_1s=R_1t cos²i₁ R_2s=R_2t cos²i₂.