A 157-nm immersion microstepper

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.