Design of an extreme ultraviolet lithography objective system based on off-axis conic surfaces including a starting...

In this paper, we propose a design method for an extreme ultraviolet lithography (EUVL) objective system based on off-axis conic surfaces and a visualized full-field aberration correction derived from nodal aberration theory. We divide the entire system into three groups with different combinations of off-axis conic surfaces. A starting point with no ray obstruction and zero image telecentricity is established by ideal object-image transformation with off-axis conic surfaces for each group. By analyzing the relationships between specific freeform terms and primary aberrations, targeted terms are utilized to efficiently correct aberrations. Then, an EUVL objective system with a NA of 0.33 is designed. The maximum RMS wavefront error is 0.015 λ, and the average RMS wavefront error is smaller than 0.01 λ. The EUVL objective system can maintain performance with relaxed tolerance requirements, with 97% of the cases exhibiting RMS wavefront error below 0.03 λ. This study provides an EUVL objective system that achieves both high optical performance and good manufacturability, providing a valuable reference for the design and optimization of multi-mirror optical systems.