| CPC G01B 11/161 (2013.01) [G01B 9/02024 (2013.01); G01B 9/02041 (2013.01); G01B 11/167 (2013.01); G01B 11/2441 (2013.01); G01B 2290/30 (2013.01)] | 33 Claims |
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1. A system for measuring a target grating, comprising:
an illumination source;
a reference transmission grating, wherein the illumination source is disposed to generate an incident light beam that illuminates the reference transmission grating, and wherein the reference transmission grating splits the incident light beam into a plurality of diffraction orders;
a target grating, wherein the plurality of diffraction orders interrogates the target grating, wherein the target grating generates a plurality of backward diffraction beams comprising a plurality of first backward diffraction beams and a plurality of second backward diffraction beams, and wherein the reference transmission grating and the target grating are parallel;
a pupil filter member comprising a plurality of first pupil apertures aligned in a first direction and a plurality of second pupil apertures aligned in a second direction different from the first direction, wherein the plurality of diffraction orders from the target grating reach the pupil filter member via the reference transmission grating, wherein the plurality of first pupil apertures pass the plurality of first backward diffraction beams entering the pupil filter member, and wherein the plurality of second pupil apertures pass the plurality of second backward diffraction beams entering the pupil filter member; and
a detector, wherein the detector takes a measurement of the plurality of first backward diffraction beams and the plurality of second backward diffraction beams.
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