Fei LIU and Yanqiu LI^*

Key Laboratory of Photoelectron Imaging Technology and System of Ministry of Education, School of Optoelectronics, Beijing Institute of Technology, Beijing 100081, P. R. China

(Received August 15, 2012; Accepted December 2, 2012)

We develop a new method for multi-mirror optics design. The system includes several mirror groups that will be designed separately to fulfil the designer's needs. The elements of individual mirror group are all spherical mirrors. The radii and separations of the all spherical mirror groups can be calculated by three conditions: the pupil-stop condition, the non-obstruction condition and the conjugate condition. The connected mirror groups could be optimized as a whole optics by gradual optimization process, and the final optics includes high order aspheric mirrors. The all sphere structure design method is effective to reduce the load of calculation and evaluation of the configurations. The gradual optimization method can help the objective achieve high imaging performance smoothly. Finally we got a NA 0.3 EUVL objective, and the mean wavefront error of 0.0287λ (RMS) is reached.

Key words: EUV lithography, optical design, multi-mirror optics, high-NA, ring field

^*E-mail address: liyanqiu@bit.edu.cn