As feature sizes below 0.25 micron are pursued deep-UV lithography at 193 nm is being investigated. This paper presents results from investigations into phase-shift mask issues for 193 nm excimer laser lithography. A small field refractive projection system for operation at the 193.3 nm wavelength of a spectrally narrowed ArF excimer laser has been constructed for lithographic research. The small field, 20X system operates with a variable objective lens numerical aperture from 0.30 to 0.60, variable partial coherence, and control over illumination fill. Through the use of attenuated and alternating phase-shifting techniques resolution can be pushed to the 0.2 micron range with depth of focus as large as 2 microns. Sensitivities to shifter deviations and resist interaction increase. Shifter etch influences on fused silica surface characteristics need to be addressed. Transmission affects of attenuating materials becomes increasingly important. Resist imaging and simulation results presented shed some light on the potential of phase-shift masking for 193 nm lithography, along with inherent difficulties.
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