Importance

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Abstract

Single-stage projection systems typically have a twice-folded optical path, with mask leg, crossover, 1:1 projection lens system, and substrate leg. They offer seamless patterning of large microlithographic substrates by overlapping complementary small-field scanning. A reverser maintains mask/substrate pattern congruence despite optical reversal, but presents the requirement of large working distance to permit access to the scanning stage. The required working distance demands large-diameter lens elements which are expensive in materials, grinding and assembly. A high-resolution 1:1 projection lens, for high-fluence laser light, adds extreme expense. Dividing the projection lens into two distributed-part-lenses, in mask and substrate legs, maintains satisfactory working distance, minimizes lens diameter requirements, and thus cuts cost. The aperture stop is positioned at the midpoint of the optical path, preferably at the time of manufacture, by an auxiliary stage. The aperture stop is physically asymmetrical because of the optical path length inherent in the reverser.

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First Claim