Fabrication of EUVL micro-field exposure tools with 0.5 NA

In support of the Extreme Ultraviolet Lithography (EUV, EUVL) roadmap, a joint program between Zygo Corporation and SEMATECH is under way to develop 13.5 nm, 0.5NA R&D photolithography tools with small fields. Those tools are referenced as micro-field exposure tools, or METs . Previous papers 1,2,3 have focused on the design and theoretical performance and the fabrication and testing of the optical components. In this paper, results from the completed projection optic box (PO, POB) systems are presented. The achieved single pass transmitted wavefront (CA – 30 cycles/aperture) on the first two systems was better than 0.25nm RMS at the center of the field and The paper includes a presentation of results from the component mirror metrology, the multilayer coatings, and the system metrology. To support the tight specifications, the component and system metrology tests required test reproducibility on the order of <50pm. To achieve the high quality wavefront, the optic mounts had to produce very small surface deformation. Also, the precision and stability of the alignment had to be controlled to a few tens of nanometer. The mirror motion is controlled by a hexapod system and the processes and mechanics that were used to align the POB will be described. Results of alignment convergence, wavefront error at the center of the field and over the field, as well as reproducibility are presented.