Abstract: i-line wafer steppers are evolving as establishedproduction tools, and it is evident that they will beused to realize features in the sub-half-micron region.Consequently, i-line steppers can be expected to be theequipment of choice for volume production of 16 MBitDRAMs and possibly the first generation of 64 Mbitdevices, before the introduction of DUV lithography.However, for this sub-half-micron resolution, lenseswith higher apertures and large field sizes will berequired. In this paper a new family of wafer steppersis introduced, with a new mechanical frame design andmodular architecture which can accommodate a family oflarge field i-line and deep UV lenses. Results from thefirst lens type with NA$EQ@0.54 and a field diameter of25.5 mm are described. To overcome the anticipateddepth of focus problems on production wafers, afield-by-field leveling system is introduced, ensuringoptimum focus over the whole image field. A challengingproblem of wafer steppers using this option is thealignment accuracy during stepping of stage and activeleveling of the wafer chuck. The stepper conceptintroduced here is able to realize the field-by-fieldleveling without the need for the throughput consumingfield-by-field alignment. For that purpose a waferstage with a new metrology system and improved accuracyhas been designed, resulting in an overlay accuracybetter than 85 nm in the global alignment mode.Simultaneously a throughput of more than 80 150 mmwafers per hour is realized. Along with the new lensand metrology concept, the stepper contains localenvironmental control systems performing better thanclass 1, to ensure clean handling of 8-inch waferswithout the need for space consuming environmentalenclosures. This paper reports practical results fromthe new stepper, including resist features below 0.4$mu@m, overlay measurements, particle control, as wellas a general description of the new stepperarchitecture.!
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