Edell, Shapiro & Finnan, LLC
Chromatically corrected objective with specifically structured and arranged dioptric optical elements and projection exposure apparatus including the same
An objective having a plurality of optical elements arranged to image a pattern from an object field to an image field at an image-side numerical aperture NA>0.8 with electromagnetic radiation from a wavelength band around a wavelength λ includes a number N of dioptric optical elements, each dioptric optical element i made from a transparent material having a normalized optical dispersion Δni=ni(λ0)−ni(λ0+1 pm) for a wavelength variation of 1 pm from a wavelength λ0. The objective satisfies the relation  for any ray of an axial ray bundle originating from a field point on an optical axis in the object field, where si is a geometrical path length of a ray in an ith dioptric optical element having axial thickness di and the sum extends on all dioptric optical elements of the objective. Where A=0.2 or below, spherochromatism is sufficiently corrected. 
CARL ZEISS SMT GMBH
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Alexander Heiko Hans-Juergen
Epple Feldmann Rostalski