Grouping design method of catadioptric projection objective for deep ultraviolet lithography

Choosing an adequate initial design for optimization plays an important role in obtaining high-quality deep ultraviolet (DUV) lithographic objectives. In this paper, the grouping design method is extended to acquire initial configurations of catadioptric projection objective for DUV lithography. In this method, an objective system is first divided into several lens groups. The initial configuration of each lens group is then determined by adjusting and optimizing existing lens design according to respective design requirements. Finally, the lens groups are connected into a feasible initial objective system. Grouping design allocates the complexity of designing a whole system to each of the lens groups, which significantly simplifies the design process. A two-mirror design form serves as an example for illustrating the grouping design principles to this type of system. In addition, it is demonstrated that different initial designs can be generated by changing the design form of each individual lens group.