Excimer laser based lithography: a deep-ultraviolet wafer stepper for VLSI processing

A deep-ultraviolet step-and-repeat system, operating at 248.4 nm, has been developed by retrofitting a commercial lithography tool with a KrF excimer laser and custom designed, fused silica condenser and projection optics. It is a reduction system with a field size of 14.5 mm and a variable numerical aperture of 0.20 to 0.38. Resolution of 0.5 µm features over the full field is obtained with routine use, and 0.35 µm resolution is attainable under more limited conditions. This paper describes the development and testing of the system, including recent modifications, and discusses some of the technical issues associated with short wavelength excimer laser based lithography.