US Patent 7834979 Off-axis catadioptric projection optical system for lithography

An off-axis catadioptric projection optical systems for use in lithography tools for processing modulated light used to form an image on a substrate is provided. The optical system includes an off-axis mirror segment, a fold mirror, a relay, an aperture stop and a refractive lens group. Modulated light is transmitted through the system to form an image on a substrate. The projection system includes an off-axis mirror segment, an aperture stop and a refractive lens group. Alternatively, the projection system includes an off-axis mirror segment, a negative refractive lens group, a concave mirror, a relay, an aperture stop, and a refractive lens group.