Catadioptric system design for ArF excimer laser lithography

Abstract

A catadioptric system for ArF excimer laser lithography has been designed, and its performance has been assessed. The structure of the designed system was based upon the Schwarzschild system, and corrector lenses were introduced to correct the residual aberrations. This catadioptric system is suggested as a solution to the problem of lack of refracting materials because of its large absorption at a 193-nm wavelength. It may be used to explore the exposure characteristics of a photoresist and to develop lithography processes. Its specifications are a NA (numerical aperture) of 0.5, a reduction ratio of 1/5, a field size of Phi 3 mm, a working distance of about 14 mm, and a total conjugate length of 293.16 mm. The MTF (modulation transfer function) value at 1,000 cycles/mm is 50% and at 2,000 cycles/mm is 25%. Distortion is suppressed within 0.023 mu m. The notable advantage of this system is its broad band aspect. It can use a bandwidth of 800 pm because it obtain the most of refractive power from the reflections and because the chromatic aberration is suppressed to a low level even though it uses only one refracting material.