2018P00159USO01
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`- 28 -
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`CLAIMS
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`1.
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`A target formed on a substrate, the target comprising:
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`a first pair of sub-targets comprising:
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`a first sub-target; and
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`a second sub-target; and
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`a secondpair of sub-targets comprising:
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`a third sub-target; and
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`a fourth sub-target,
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`wherein the first and second sub-targets are arranged adjacent to each other and the third
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`and fourth sub-targets are arranged on opposite sides ofthe first and second sub-targets,
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`wherein each sub-target comprises an overlay grating with a top layer and a bottom layer
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`with different pitches, and
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`wherein the target comprises a continuousvariation of bias values across each sub-target.
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`2.
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`Thetarget of claim 1, wherein:
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`features in a top layer of the first sub-target are arranged withafirst pitch;
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`features in a bottom layerof the first sub-target are arranged with a secondpitch; and
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`the first pitch is larger than the second pitch.
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`3.
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`Thetarget of claim 1, wherein:
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`features in a top layer of the second sub-target are arranged withafirst pitch;
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`features in a bottom layer of the second sub-target are arranged with a second pitch; and
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`the first pitch is smaller than the secondpitch.
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`4.
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`The target of claim 1, wherein the continuous variation of bias values across each sub-
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`target is associated with an asymmetry-related property of the target.
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`5.
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`The target of claim 1, wherein the sub-targets in the first and second pairs have equal and
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`opposite bias variations.
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`Atty. Dkt. No. 2857.8570003
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`2018P00159USO01
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`- 29 -
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`6.
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`The target of claim 1, wherein the first and second sub-targets have a sameorientation
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`that is opposite to an orientation of the third and fourth sub-targets.
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`7.
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`The target of claim 1, wherein the sub-targets of the first and second pairs are
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`rectangular.
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`8.
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`A patterning device for use in a lithographic apparatus, the patterning device comprising:
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`portions that define one or more device patterns; and
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`portions that define one or more metrology patterns,
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`wherein the one or more metrology patterns comprisea target, the target comprising:
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`a first pair of sub-targets comprising:
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`a first sub-target; and
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`a second sub-target; and
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`a secondpair of sub-targets comprising:
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`a third sub-target; and
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`a fourth sub-target,
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`wherein the first and second sub-targets are arranged adjacent to each other and
`
`the third and fourth sub-targets are arranged on opposite sides of the first and second sub-targets,
`
`wherein each sub-target comprises an overlay grating with a top layer and a
`
`bottom layer with different pitches, and
`
`wherein the target comprises a continuous variation of bias values across each
`
`sub-target.
`
`9.
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`The patterning device of claim 8, wherein:
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`features in a top layer of the first sub-target are arranged withafirst pitch;
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`features in a bottom layerof the first sub-target are arranged with a secondpitch; and
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`the first pitch is larger than the second pitch.
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`10.—_The patterning device of claim 8, wherein:
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`features in a top layer of the second sub-target are arranged withafirst pitch;
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`Atty. Dkt. No. 2857.8570003
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`2018P00159USO01
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`- 30-
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`features in a bottom layer of the second sub-target are arranged with a second pitch; and
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`the first pitch is smaller than the secondpitch.
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`11.
`
`The patterning device of claim 8, wherein the continuous variation of bias values across
`
`each sub-target is associated with an asymmetry-related property of the target.
`
`12.
`
`The patterning device of claim 8, wherein the sub-targets in the first and second pairs
`
`have equal and opposite bias variations.
`
`13.
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`The patterning device of claim 8, wherein the first and second sub-targets have a same
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`orientation that is opposite to an orientation of the third and fourth sub-targets.
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`14.
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`‘The patterning device of claim 8, wherein the sub-targets of the first and second pairs are
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`rectangular.
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`15.
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`A metrology apparatus comprising:
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`an illumination system configured to illuminate with radiation a target formed on a substrate; and
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`a detection system configured to detect scattered radiation arising from illumination ofthe target,
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`the target comprising:
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`a first pair of sub-targets comprising:
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`a first sub-target; and
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`a second sub-target; and
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`a secondpair of sub-targets comprising:
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`a third sub-target; and
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`a fourth sub-target,
`
`wherein the first and second sub-targets are arranged adjacent to each other and the third
`
`and fourth sub-targets are arranged on opposite sides ofthe first and second sub-targets,
`
`wherein each sub-target comprises an overlay grating with a top layer and a bottom layer
`
`with different pitches, and
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`Atty. Dkt. No. 2857.8570003
`
`
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`2018P00159USO01
`
`-31-
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`wherein the target comprises a continuousvariation of bias values across each sub-target,
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`and
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`wherein the metrology apparatus is configured to:
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`obtain a plurality of asymmetry measurements from locations on thetarget;
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`fit the plurality of asymmetry measurements to at least one expected relationship
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`between asymmetry and a performance parameter, based on a bias variation between the
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`locations on the target; and
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`derive a measure of the performance parameter from thefitting.
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`16.
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`The metrology apparatus of claim 15, wherein:
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`features in a top layer of the first sub-target are arranged withafirst pitch;
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`features in a bottom layerof the first sub-target are arranged with a secondpitch; and
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`the first pitch is larger than the second pitch.
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`17.
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`The metrology apparatus of claim 15, wherein:
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`features in a top layer of the second sub-target are arranged withafirst pitch;
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`features in a bottom layer of the second sub-target are arranged with a second pitch; and
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`the first pitch is smaller than the secondpitch.
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`18.
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`The metrology apparatus of claim 15, wherein the continuous variation of bias values
`
`across each sub-target is associated with an asymmetry-related property of the target.
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`19.
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`The metrology apparatus of claim 15, wherein the sub-targets in the first and secondpairs
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`have equal and opposite bias variations.
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`20.
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`The metrology apparatus of claim 15, wherein the first and second sub-targets have a
`
`same orientation that is opposite to an orientation of the third and fourth sub-targets.
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`Atty. Dkt. No. 2857.8570003
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