Metrology method, target and substrate
A diffraction measurement target that has at least a first sub-target and at least a second sub-target, and wherein (1) the first and second sub-targets each include a pair of periodic structures and the first sub-target has a different design than the second sub-target, the different design including the first sub-target periodic structures having a different pitch, feature width, space width, and/or segmentation than the second sub-target periodic structure or (2) the first and second sub-targets respectively include a first and second periodic structure in a first layer, and a third periodic structure is located at least partly underneath the first periodic structure in a second layer under the first layer and there being no periodic structure underneath the second periodic structure in the second layer, and a fourth periodic structure is located at least partly underneath the second periodic structure in a third layer under the second layer.
1. A method comprising:
illuminating a measurement target on a substrate with radiation, wherein:
the measurement target comprises at least a first sub-target and a second sub-target,
each of the first sub-target and the second sub-target has a first periodic structure having features extending in a first direction and a second periodic structure having features extending in a second different direction,
the first sub-target at least partly overlays a third sub-target and the second sub-target at least partly overlays a fourth sub-target, and
the first sub-target has a different design than the third sub-target and/or the second sub-target has a different design than the fourth sub-target; and
detecting radiation scattered by at least the first and second sub-targets to obtain for the measurement target a measurement representing a parameter of a lithographic process.
2. The method of claim 1 , wherein the first sub-target has a different pitch, feature width, or space width than the third sub-target and/or the second sub-target has a different pitch, feature width, or space width than the fourth sub-target.
3. The method of claim 1 , wherein the first sub-target has a different design than the second sub-target.
4. The method of claim 3 , wherein the first sub-target has a different pitch, feature width, or space width than the second sub-target.
5. The method of claim 1 , wherein the third sub-target has a different design than the fourth sub-target.
6. The method of claim 5 , wherein the third sub-target has a different pitch, feature width, or space width than the fourth sub-target.
7. The method of claim 1 , wherein the first and second periodic structures of the second sub-target meet at a center of the measurement target and the first and second periodic structures of the first sub-target are arranged around a periphery of the first and second periodic structures of the second sub-target.
8. The method of claim 7 , wherein a length and width of each of the first and second periodic structures of the first sub-target is substantially the same as a length and width of each of the first and second periodic structures of the second sub-target.
9. The method of claim 1 , wherein the first direction and the second different direction are substantially perpendicular.
10. The method of claim 1 , wherein the parameter of the lithographic process is overlay.
11. The method of claim 1 , wherein a bias difference is provided between the first sub-target and the second sub-target.
12. The method of claim 1 , wherein the illuminating comprising illuminating a measurement spot on the measurement target that covers at one time at least part of each of the first and second periodic structures of the first sub-target and the first and second periodic structures of the second sub-target.
13. The method of claim 1 , wherein the third and fourth sub-targets each comprise periodic structures.
14. The method of claim 1 , wherein the detecting comprises detecting radiation scattered by at least the first, second, third and fourth sub-targets to obtain for the measurement target a measurement representing the parameter of the lithographic process.
15. The method of claim 1 , wherein the detecting radiation comprises forming a dark field image of at least the first and second sub-targets.
16. A non-transitory computer program product comprising machine-readable instructions therein, the instructions, upon execution by a computer system, configured to cause the computer system to at least cause performance of the method of claim 1 .
17. A non-transitory computer program product comprising machine-readable instructions therein, the instructions, upon execution by a computer system, configured to cause the computer system to at least:
obtain a result from detection of radiation scattered by a measurement target on a substrate, wherein:
the measurement target comprises at least a first sub-target and a second sub-target,
each of the first sub-target and the second sub-target has a first periodic structure having features extending in a first direction and a second periodic structure having features extending in a second different direction,
the first sub-target at least partly overlays a third sub-target and the second sub-target at least partly overlays a fourth sub-target, and
the first sub-target has a different design than the third sub-target and/or the second sub-target has a different design than the fourth sub-target; and
determine, from the result and for the measurement target, a measurement representing a parameter of a lithographic process.
18. A measurement target for determination of a parameter of a lithographic process, the target comprising:
at least a first sub-target and a second sub-target, wherein:
each of the first sub-target and the second sub-target has a first periodic structure having features extending in a first direction and a second periodic structure having features extending in a second different direction,
the first sub-target at least partly overlays a third sub-target and the second sub-target at least partly overlays a fourth sub-target, and
the first sub-target has a different design than the third sub-target and/or the second sub-target has a different design than the fourth sub-target.
19. The target of claim 18 , wherein the first sub-target and/or second sub-target has a different pitch, feature width, or space width than the third sub-target and/or fourth sub-target.
20. The target of claim 18 , wherein the first sub-target has a different design than the second sub-target.
21. The target of claim 18 , wherein the target is a dark-field image-based target.
22. A substrate comprising the target of claim 18 .