Optical design of high-efficiency ripple plate illuminator for EUV lithography

A high-efficiency ripple plate illumination system for extreme ultraviolet (EUV) lithography is proposed. A cylindrical mirrors array is used as ripple plate mirror to simplify the system. By analyzing the characteristics of reflection on ripple plate, we design a relay system with a modified compound parabolic concentrator and two conic mirrors to reduce the efficiency loss caused by excessive number of reflective mirrors. Compared with the traditional EUV lithography illumination system, it greatly improves the system' s efficiency. A design example for a numerical aperture (NA) 0.33 projection objective is given and the efficiency of the illuminator is 39.7% while the slit non-uniformity of the scanning energy distribution is 2.7% in a prescribed arc area, which proves the feasibility of the design.