We have designed and constructed a microstepper for 157 nm immersion lithography. The lens, designed and fabricated at Newport, provides a numerical aperture of 1.3 and a field size of 60 μm with immersion liquids of index n=1.38. Because of a lack of system interferometer, final alignment has been ongoing in the field using actuators incorporated into the lens design. Lithography down to 250 nm has been demonstrated but lens alignment has proved difficult. We are currently implementing an image monitoring system to provide real-time feedback on lens performance and to allow expedited alignment.
High performance optical systems can be very labor intensive and costly to fabricate and assemble by traditional methods. With the advent of modern diamond turning methods and other key technologies, more deterministic methods of manufacturing optomechanical assemblies that require extremely tight tolerances have been developed. High numerical aperture lenses that must approach diffraction-limited performance at deep ultraviolet (DUV) wavelengths represent some of the most difficult optical systems to manufacture. Modern diamond turning equipment and advanced assembly techniques have been applied to produce a DUV microlithographic lens assembly that features both precision machined subcells and internal compensators for the correction of residual optical aberrations. The details of this process are described in this paper
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