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`CLAIMS
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`1.
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`A measurement system, the measurement system comprising:
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`a sensor apparatus;
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`an illumination system arranged to illuminate the sensor apparatus with radiation, the sensor
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`apparatus comprising a patterned region arranged to receive a radiation beam and to form a plurality
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`of diffraction beams, the diffraction beams being separated in a shearing direction;
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`the sensor apparatus comprising a radiation detector;
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`wherein the patterned region is arranged such that at least some of the diffraction beams form
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`interference patterns on the radiation detector;
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`wherein the sensor apparatus comprises a plurality of patterned regions, and
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`whercin pitches of the patterned regionsare different in adjacent patterned regions.
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`2.
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`The measurement system of claim |, wherein the measurement system is arranged such that
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`the interference patterns from adjacent patterned regionsat least partially overlap at the radiation
`detector.
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`3.
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`The measurement systemof either of claims 1 or 2, wherein the pitches of alternating
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`patterned regions are the same.
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`4.
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`The measurement system of any preceding claim, wherein the pitches of the adjacent
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`patterned regions are not even numberinteger multiples.
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`10
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`15
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`20
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`5.
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`The measurement system of claim 4, wherein the pitches of the adjacent patterned regions are
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`25
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`not integer multiples.
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`6.
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`The measurement system of any preceding claim, wherein the plurality of patterned regions
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`comprise thirteen patterned regions.
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`7.
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`The measurement system of any preceding claim, wherein the plurality of patterned regions
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`are positioned at odd and evenfield point locations.
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`8.
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`The measurement system of any preceding claim, wherein the plurality of patterned regions
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`extend in an x direction and in a second direction orthogonal to the x direction.
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`35
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`9.
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`The measurement system of any preceding claim, the measurement system further
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`comprising:
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`WO 2022/100930
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`a patterning device;
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`wherein the illumination systemis arranged to illuminate the patterning device with radiation,
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`the patterning device comprising a first patterned region arranged to receive the radiation beam andto
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`form a plurality of first diffraction beams, the first diffraction beams being separated in the shearing
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`direction;
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`wherein the patterned region of the sensor apparatus comprises a second patterned region;
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`the projection system being configured to project the first diffraction beams onto the sensor
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`apparatus, the second patterned region being arranged to receive the first diffraction beams from the
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`projection system and to form a plurality of second diffraction beams from each ofthe first diffraction
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`10
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`beams suchthat the first and second patterned regions forma set;
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`wherein the first and second patterned regions in the set are matched by matching the pitches
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`of the first and sccond patterned regionsin the shearing direction such that at least some of the second
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`diffraction beams formed fromat least one of the first diffraction beams are spatially coherent with a
`second diffraction beam formed from at least one otherfirst diffraction beam to form interference
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`15
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`patterns on the radiation detector;
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`wherein the patterning device comprises a plurality of first patterned regions and the sensor
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`apparatus comprises a plurality of second patterned regions such that there is a plurality of sets, each
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`set comprising one ofthe plurality of first patterned regions and one of the plurality of second
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`patterned regions, and
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`wherein the pitches of the first patterned regions are different in adjacent scts and/or the
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`pitches of the second patterned regions are different in adjacent sets.
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`10.
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`The measurement system of claim 9, wherein the pitches of the first patterned regions and the
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`second patterned regionsin at least one of the plurality of sets are the same.
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`11.
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`The measurement system of either of claims 9 or 10, further comprising a positioning
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`apparatus configured to moveat least one of the patterning device and the sensor apparatus in the
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`shearing direction; and
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`a controller configured to:
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`control the positioning apparatus so as to moveat least one ofthe first patterning
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`device and the sensor apparatus in the shearing direction such that an intensity of radiation received
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`by each part of the radiation detector varies as a function of the movementin the shearing direction so
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`as to form oscillating signals corresponding to the different pitches of the first patterned regions in
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`adjacent sets and/or the different pitches of the second patterned regions in adjacentsets;
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`determine from the radiation detector phases of harmonicsofthe oscillating signals at
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`a plurality of positions on the radiation detector; and
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`25
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`determinea set of coefficients that characterize an aberration map of the projection
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`system fromthe phase of the harmonics of the oscillating signals at the plurality of positions on the
`radiation detector.
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`12.
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`The measurement system of claim 11, wherein the set of coefficients that characterize the
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`aberration map ofthe projection system are determined by equating the phases of the harmonicsof the
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`oscillating signals to a difference in the aberration map between positions in the pupil plane that are
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`separated in the shearing direction by twice a shearing distance which correspondsto the distance in
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`the pupil plane between two adjacentfirst diffraction beams and solving to find the set of coefficients.
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`13.
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`The measurement system of claim 12, wherein the set of coefficients that characterize the
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`aberration map ofthe projection system are determined by simultancously solving constraints for the
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`shearing direction and for a second, orthogonaldirection.
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`14.
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`The measurement system of any of claims 9-13, wherein the plurality of first patterned
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`regions andthe plurality of second patterned regionsare gratings.
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`15.
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`A lithographic apparatus comprising the measurement system of any one of claims 1 to 14.
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`16.
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`A method for measurement, the method comprising:
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`illuminating a sensor apparatus with radiation, wherein the sensor apparatus comprises a
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`patterned region arranged to receive at least a portion of the radiation and to form a plurality of
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`diffraction beams, the diffraction beams being separated in a shearing direction;
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`wherein the sensor apparatus comprises a radiation detector arranged to receive at least a
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`15
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`20
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`portion of the diffraction beams,
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`wherein the patterned region is arranged suchthat at least some ofthe diffraction beams form
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`interference patterns on the radiation detector;
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`wherein the sensor apparatus comprises a plurality of patterned regions, and
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`wherein pitches of the patterned regions are different in adjacent patterned regions.
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`17.
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`The method of claim 16, the method further comprising:
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`illuminating a patterning device with radiation, wherein the patterning device comprises a
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`first patterned region arranged to receive at least a portion of the radiation and to form a plurality of
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`first diffraction beams, the first diffraction beams being separated in the shearing direction;
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`projecting, with the projection system, at least part of the plurality of first diffraction beams
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`onto the scnsor apparatus comprising:
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`the patterned region comprising a second patterned region arranged to receive thefirst diffraction
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`beams fromthe projection system and to forma plurality of second diffraction beams from each of the
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`first diffraction beams; and
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`a radiation detector arranged to receive at least a portion of the second diffraction beams,
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`wherein the first and second patterned regionsin the set are matched by matching the pitches
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`of the first and second patterned regions in the shearing direction such that at least some of the second
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`diffraction beams formed from at least one of the first diffraction beams are spatially coherent with a
`second diffraction beam formed from at least one otherfirst diffraction beam to form interference
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`patterns on the radiation detector;
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`wherein the patterning device comprises a plurality of first patterned regions and the sensor
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`apparatus comprises a plurality of second patterned regions such that there is a plurality of sets, each
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`set comprising onc of the plurality of first patterned regions and oneof the plurality of second
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`patterned regions, and
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`wherein the pitches of the first patterned regions are different in adjacent sets and/or the
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`pitches of the second patterned regions are different in adjacent sets.
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`18.
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`The method of claim 17, further comprising moving at least one of the patterning device and
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`the sensor apparatus in the shearing direction such that an intensity of radiation received by eachpart
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`of the radiation detector varies as a function of the movement in the shearing direction so as to form a
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`plurality of oscillating signals corresponding to the different pitches of the first patterned regions in
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`adjacent sets and/or the different pitches of the second patterned regions in adjacentsets;
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`determining from the radiation detector phases of harmonics ofthe oscillating signals at a
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`plurality of positions on the radiation detector; and
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`determining a set of coefficients that characterize an aberration map of the projection system
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`from the phaseof the harmonics of the oscillating signals at the plurality of positions on the radiation
`detector.
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`19,
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`The method ofeither of claims 17 or 18, further comprising determining the set of
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`coefficients that characterize the aberration map of the projection system by equating the phases of the
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`harmonics of the oscillating signals to a difference in the aberration map between positions in the
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`pupil plane that are separated in the shearing direction by twice a shearing distance which corresponds
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`to the distance in the pupil plane between two adjacentfirst diffraction beams and solving to find the
`set of coefficients.
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`20.
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`The method of any of claims 17 to 19, further comprising determining the set of coefficients
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`that characterize the aberration map of the projection system by simultancously solving constraints for
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`the shearing direction and for a second, orthogonal direction.
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`21.
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`The method of any of claims 17 to 20, further comprising moving the at least one of the
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`patterning device and the sensor apparatus in the shearing direction in phase steps in a range of 4-9 to
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`form the plurality of oscillating signals.
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`22.
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`A computer readable medium carrying a computer program comprising computer readable
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`instructions configured to cause a computer to carry out a method according to any oneof claims 16
`to 21.
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`23.
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`A computer apparatus comprising:
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`a memory storing processor readable instructions, and
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`a processor arranged to read and cxccute instructions stored in said memory, whercin said
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`processor readable instructions comprise insiructions arranged to conirol the computer to carry out the
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`method according to any one of claims 16 to 21.
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