Measurement method, inspection apparatus, patterning device, lithographic system and device manufacturing method
A focus metrology target includes one or more periodic arrays of features. A measurement of focus performance of a lithographic apparatus is based at least in part on diffraction signals obtained from the focus metrology target. Each periodic array of features includes a repeating arrangement of first zones interleaved with second zones, a feature density being different in the first zones and the second zones. Each first zone includes a repeating arrangement of first features. A minimum dimension of each first feature is close to but not less than a resolution limit of the printing by the lithographic apparatus, so as to comply with a design rule in a given a process environment. A region of high feature density may further include a repeating arrangement of larger features.
1. A method comprising:
using a lithographic apparatus to print at least a first focus metrology target on a substrate, the printed focus metrology target including at least a first periodic array of features;
using inspection radiation to obtain one or more diffraction signals from the first periodic array in the printed focus metrology target; and
deriving a measurement of focus performance of the lithographic apparatus based at least in part on the diffraction signals,
wherein the first periodic array comprises a repeating arrangement of first zones interleaved with second zones in at least a first direction of periodicity, a feature density being different in the first zones and the second zones, and
wherein each of the first zones includes a repeating arrangement of first features, a minimum dimension of each first feature being close to but not less than a resolution limit of the printing step, and
wherein the first and second zones are arranged such that an illumination spot of the inspection radiation is arranged to illuminate both the first and second zones at a same time.
2. The method of claim 1 , wherein the first zones and second zones are interleaved only in the first direction of periodicity.
3. The method of claim 1 , wherein the focus metrology target further includes a second periodic array of features,
wherein the second periodic array comprises a repeating arrangement of third zones interleaved with fourth zones, a feature density being different in the third zones and the fourth zones,
wherein each of the third zones includes a repeating arrangement of third features, a minimum dimension of each third feature being close to but not less than a resolution limit of the printing step, and
wherein using the inspection radiation to obtain one or more diffraction signals further includes obtaining one or more diffraction signals from the second periodic array in the printed focus metrology target.
4. The method of claim 3 , wherein the third zones are interleaved with the fourth zones in a second direction of periodicity orthogonal to the first direction of periodicity.
5. The method of claim 3 , wherein the feature density in the first zones and third zones is the same, and the feature density in the second zones and fourth zones is the same.
6. The method of claim 5 , wherein the second periodic array is the same as the first periodic array but rotated ninety degrees.
7. The method of claim 3 , wherein the third zones are interleaved with the fourth zones in the first direction of periodicity, the first periodic arrangement of features and the second periodic arrangement of features differing in one or more design parameters.
8. The method of claim 1 , wherein the first features in the first zones comprise lines with a width corresponding to the minimum dimension and with a length longer than the minimum dimension.
9. The method of claim 8 , wherein the first features in the first zones comprise chopped lines, each first feature having a width corresponding to the minimum dimension and a length longer than the minimum dimension but less than one quarter of a period of the first periodic array.
10. The method of claim 1 , wherein the first features include line segments having a width corresponding to the minimum dimension and having different orientations.
11. A method of manufacturing devices wherein a device pattern is applied to a series of substrates using a lithographic process, the method including:
using the method of claim 1 to monitor the focus parameter, and
controlling the lithographic process in accordance with the determined focus parameter.
12. A patterning device for use in a lithographic apparatus, the patterning device comprising contrasting portions that when printed by the lithographic apparatus define features of one or more device patterns and one or more metrology patterns, the one or more metrology patterns including at least a first focus metrology target, the first focus metrology target including at least a first periodic array of features,
wherein the first periodic array comprises a repeating arrangement of first zones interleaved with second zones in at least a first direction of periodicity, a feature density being different in the first zones and the second zones, and
wherein each of the first zones includes a repeating arrangement of first features, a minimum dimension of each first feature being close to but not less than a resolution limit of the printing by the lithographic apparatus, and
wherein the first and second zones are arranged such that an illumination spot of inspection radiation is arranged to illuminate both the first and second zones at a same time.
13. The patterning device of claim 12 , wherein the first zones and second zones are interleaved only in the first direction of periodicity.
14. The patterning device of claim 12 , wherein the focus metrology target further includes a second periodic array of features,
wherein the second periodic array comprises a repeating arrangement of third zones interleaved with fourth zones, a feature density being different in the third zones and the fourth zones, and
wherein each of the third zones includes a repeating arrangement of third features, a minimum dimension of each third feature being close to but not less than a resolution limit of the printing by the lithographic apparatus.
15. The patterning device of claim 14 , wherein the third zones are interleaved with the fourth zones in a second direction of periodicity orthogonal to the first direction of periodicity.
16. The patterning device of claim 14 , wherein the feature density in the first zones and third zones is the same, and the feature density in the second zones and fourth zones is the same.
17. The patterning device of claim 16 , wherein the second periodic array is the same as the first periodic array but rotated ninety degrees.
18. The patterning device of claim 14 , wherein the third zones are interleaved with the fourth zones in the first direction of periodicity, the first periodic arrangement of features and the second periodic arrangement of features differing in one or more design parameters.
19. The patterning device of claim 12 , wherein the first zones and second zones are interleaved in the first direction of periodicity and in a second direction of periodicity orthogonal to the first direction of periodicity.
20. The patterning device of claim 12 , wherein the first features in the first zones comprise lines with a width corresponding to the minimum dimension and with a length longer than the minimum dimension.