Advanced testing requirements of diffractive optical elements for off-axis illumination in photolithography

The progress of immersion lithography toward the 22nm production node is putting more stringent requirements on the diffractive optics that are used for off-axis illumination. Tighter tolerances on pole balance, stray light, zeroth order, optical transmission, and matching of the far field output pattern to the design specification are in-turn requiring more accurate and repeatable optical testing. This paper will report on preliminary results from Tessera's new excimer diffractive optics test stand, including gauge capability and sources of variation, ending with a comparison of measurement capability to the required specifications.