Metrology targets and methods with oblique periodic structures
Metrology targets, design methods and measurement methods thereof are provided with periodic structure(s) which are oblique with respect to orthogonal production axes X and Y of the lithography tool—enabling more accurate overlay measurements of devices having diagonal (oblique, tilted) elements such as DRAM devices. One or more oblique periodic structure(s) may be used to provide one- or two-dimensional signals, with respect to one or more layers, possibly providing overlay measurements for multiple steps applied to one layer. The oblique periodic structure(s) may be used to modify current metrology target designs (e.g., imaging targets and/or scatterometry targets) or to design new targets, and measurement algorithms may be adjusted respectively to derive signals from the oblique periodic structure(s) and/or to provide pre-processed images thereof. The disclosed targets are process compatible and reflect more accurately the device overlays with respect to various process steps.
1. A metrology target comprising a plurality of periodic structures that have a long dimension and a short dimension, wherein at least a first of the periodic structures is oblique with respect to a second of the periodic structures, wherein one of the first of the periodic structures and the second of the periodic structures is disposed as an inner periodic structure of the metrology target and another of the first of the periodic structures and the second of the periodic structures is disposed as an outer periodic structure of the metrology target, and wherein a plurality of the first of the periodic structures and a plurality of the second of the periodic structures are arrayed around a center of the metrology target such that the inner periodic structure is closer to the center than the outer periodic structure and such that the plurality of periodic structures of the inner periodic structure are arrayed with the long dimension extending in two orthogonal directions relative to the center.
2. The metrology target of claim 1 , wherein the metrology target is configured as an imaging target, wherein the imaging target includes at least one target layer having the plurality of periodic structures, wherein the plurality of periodic structures are configured to be non-parallel.
3. The metrology target of claim 2 , further comprising at least three target layers, wherein the each of the periodic structures is disposed within one of the target layers.
4. The metrology target of claim 1 , wherein the metrology target is configured as a Moiré-effect-based target.
5. The metrology target of claim 4 , wherein the Moiré-effect-based target includes at least one target layer having the plurality of periodic structures, wherein the plurality of periodic structures are configured to be non-parallel.
6. The metrology target of claim 1 , wherein the metrology target has one measurement direction oblique to the second of the periodic structures, wherein the plurality of periodic structures are of two types differing in pitch and/or critical dimension.
7. The metrology target of claim 1 , wherein each of the periodic structures is configured to fill rectangles having sides along X and Y axes of the metrology target.
8. The metrology target of claim 1 , wherein each of the periodic structures is configured to fill a specified space, wherein the specified space is designed according to an available space on a wafer.
9. The metrology target of claim 1 , wherein each of the periodic structures is configured to fill a convex quadrilateral, wherein the convex quadrilateral is designed according to an available space on a wafer.
10. The metrology target of claim 1 , wherein the metrology target is a configured as a scanning electron microscopy target, the scanning electron microscopy target having two partly overlapping, alternating periodic structures, wherein the two partially overlapping, alternating periodic structures are oblique with respect to the second of the periodic structures.
11. The metrology target of claim 1 , wherein each of the periodic structures includes one or more elements, wherein each of the elements has a segmentation.
12. The metrology target of claim 11 , wherein the segmentation of each of the elements is two-dimensional.
13. The metrology target of claim 11 , wherein a pitch of the segmentation of each of the elements is one fifth or less of a pitch of its corresponding periodic structure.
14. The metrology target of claim 11 , wherein the segmentation of each of the elements is rectangular.
15. The metrology target of claim 1 , wherein each of the first periodic structures form angles of between 20° and 70° with respect to the second of the periodic structures.
16. The metrology target of claim 1 , wherein the metrology target further comprises at least one intermediate layer having assist features between two of the periodic structures.
17. The metrology target of claim 16 , wherein the assist features are oblique with respect to the second of the periodic structures.
18. The metrology target of claim 1 , wherein at least two of the periodic structures are placed side-by-side.
19. A target design file comprising the metrology targets of claim 1 .
20. A target design method comprising configuring at least a first periodic structure of a metrology target to be oblique with respect to a second periodic structure of the metrology target, wherein the first periodic structure and the second periodic structure have a long dimension and a short dimension, wherein one of the first of the periodic structures and the second of the periodic structures is disposed as an inner periodic structure of the metrology target and another of the first of the periodic structures and the second of the periodic structures is disposed as an outer periodic structure of the metrology target, and wherein a plurality of the first of the periodic structures and a plurality of the second of the periodic structures are arrayed around a center of the metrology target such that the inner periodic structure is closer to the center than the outer periodic structure and such that the plurality of periodic structures of the inner periodic structure are arrayed with the long dimension extending in two orthogonal directions relative to the center.
21. The target design method of claim 20 , further comprising:
identifying, in a device design, oblique structures that are oblique with respect to the second periodic structure; and
configuring the first periodic structure to be disposed within a same layer and at a same angle to the X and Y axes as the identified oblique structures.
22. A method of measuring metrology targets comprising:
performing, using a processor and image processing and/or signal modelling, a metrology measurement of a metrology target to derive corresponding signals from oblique periodic structures;
wherein the metrology target comprises a plurality of periodic structures that have a long dimension and a short dimension, wherein at least a first of the periodic structures is oblique with respect to a second periodic structure, wherein one of the first of the periodic structures and the second of the periodic structures is disposed as an inner periodic structure of the metrology target and another of the first of the periodic structures and the second of the periodic structures is disposed as an outer periodic structure of the metrology target, and wherein a plurality of the first of the periodic structures and a plurality of the second of the periodic structures are arrayed around a center of the metrology target such that the inner periodic structure is closer to the center than the outer periodic structure and such that the plurality of periodic structures of the inner periodic structure are arrayed with the long dimension extending in two orthogonal directions relative to the center.