EUV optical design for a 100 nm CD imaging system

The imaging specifications for extreme ultraviolet lithography (EUVL) projection optics parallel those of other optical lithographies. Specifications are scaled to reflect the 100 nm critical dimension for the first generation EUVL systems. The design being fabricated for the Engineering Test Stand, an EUVL alpha tool, consists of a condenser with six channels to provide an effective partial coherence factor of 0.7. The camera contains four mirrors; three of the mirrors are aspheres and the fourth is spherical. The design of the optical package has been constrained so that the angles of incidence and the variations in the angle of incidence of all rays allow for uniform multilayer coatings. The multilayers introduce a slight shift in image position and magnification. We have shown that a system aligned with visible light is also aligned at 13.4 nm, Each mirror must be fabricated with an RMS figure error of less than 0.25 nm and better than 0.2 nm RIMS roughness. Optical surfaces that exceed each of these specifications individually have been fabricated. The success of EUVL requires that these specifications be met simultaneously.