Apparatus and methods for determining overlay of structures having rotational or mirror symmetry

• US 20070008533A1
• Filed: 09/14/2005
• Published: 01/11/2007
• Est. Priority Date: 08/30/2000
• Status: Active Grant

• Current Assignee: Kla-Tencor Technologies Corporation (KLA Corporation)
• Original Assignee: Kla-Tencor Technologies Corporation (KLA Corporation)
• Inventors: Ghinovker, Mark
• Granted Patent: US 7,541,201 B2
• Time in Patent Office: Days
• US Class Current: 356/401
• CPC Class Codes: G01B 11/272 using photoelectric detection means
• CPC Class Codes: G01N 21/4785 Standardising light scatter apparatus; Standards therefor
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G03F 7/70633 Overlay, i.e. relative alignment between patterns printed by separate exposures in different layers, or in the same layer in multiple exposures or stitching
• CPC Class Codes: H01L 21/68 for positioning, orientation or alignment
• CPC Class Codes: H01L 21/682 Mask-wafer alignment in general G03F7/70, G03F9/70
• CPC Class Codes: H01L 23/544 Marks applied to semiconductor devices or parts, e.g. registration marks, alignment structures, wafer maps test patterns for characterising or monitoring manufacturing processes H01L22/00
• CPC Class Codes: Y10S 438/975 Substrate or mask aligning feature

Abstract

Disclosed are overlay targets having flexible symmetry characteristics and metrology techniques for measuring the overlay error between two or more successive layers of such targets. In one embodiment, a target includes structures for measuring overlay error (or a shift) in both the x and y direction, wherein the x structures have a different center of symmetry (COS) than the y structures. In another embodiment, one of the x and y structures is invariant with a 180° rotation and the other one of the x and y structures has a mirror symmetry. In one aspect, the x and y structures together are variant with a 180° rotation. In yet another example, a target for measuring overlay in the x and/or y direction includes structures on a first layer having a 180 symmetry and structures on a second layer having mirror symmetry. In another embodiment, a target for determining overlay in the x and/or y direction includes structures on a first layer and structures on a second layer, wherein the structures on the first layer have a COS that is offset by a known amount from the COS of the structures on the second layer. In a specific implementation, any of the disclosed target embodiments may take the form of device structures. In a use case, device structures that have an inherent 180° rotational symmetry or a mirror symmetry in each of the first and second layers are used to measure overlay in a first layer and a second layer. Techniques for imaging targets with flexible symmetry characteristics and analyzing the acquired images to determine overlay or alignment error are disclosed.

Claims

1. A semiconductor target for determining a relative shift between two or more successive layers of a substrate or between two or more separately generated patterns on a single layer of a substrate, the target comprising:

a plurality of first structures having a first center of symmetry (COS) or first line of symmetry (LOS) and being arranged to determine the relative shift in an x direction by analyzing an image of the first structures; and

a plurality of second structures having a second COS or second LOS and being arranged to determine the relative shift in an x direction by analyzing an image of the second structures,

wherein the first COS or LOS has a different location than the second COS or LOS.

2. The target of claim 1, wherein

the first structures have a first LOS about which the first structures have a mirror symmetry or the first structures have a 180°

rotational symmetry with respect to the first COS, and

the second structures have a first LOS about which the second structures have a mirror symmetry or the second structures have a 180°

rotational symmetry with respect to the second COS.

3. The target of claim 1, wherein the first and second structures are in the form of device structures.

4. The target of claim 2, wherein a one of the first or second structures has a 180°

rotational symmetry with respect to its COS and the other one of the first or second structures'"'"' has a mirror symmetry with respect to its LOS.

5. The target of claim 4, wherein the first structures and the second structures together are variant with a 180°

rotational asymmetry or together have a mirror asymmetry.

6. A semiconductor target for determining an overlay error between two or more successive layers of a substrate, the target comprising:

a plurality of first structures formed in a first semiconductor layer and having a first center of symmetry or first line of symmetry (LOS); and

a plurality of second structures formed in a second semiconductor layer and having a second COS OR LOS,

wherein the first COS OR LOS is designed to have a known offset from the second COS or LOS so that the overlay error can be determined by acquiring an image of the first and second structures and then analyzing a shift between the first and second COS'"'"'s or LOS'"'"'s in the image and comparing the shift to the known offset.

7. The target of claim 6, wherein

the first structures have a first LOS about which the first structures have a mirror symmetry or the first structures have a 180°

rotational symmetry with respect to the first COS, and

the second structures have a first LOS about which the second structures have a mirror symmetry or the second structures have a 180°

rotational symmetry with respect to the second COS.

8. The target of claim 6, wherein the first and second structures are in the form of device structures.

9. The target of claim 7, wherein a one of the first or second structures has a 180°

rotational symmetry with respect to its COS and the other one of the first or second structures'"'"' has a mirror symmetry with respect to its LOS.

10. The target of claim 9, wherein the first structures and the second structures together are variant with a 180°

rotational asymmetry or together have a mirror asymmetry.

11. A method for determining the relative shift between two or more successive layers of a substrate or between two or more separately generated patterns on a single layer of a substrate, the method comprising:

acquiring a first image of a plurality of first structures having a first center of symmetry (COS) or first line of symmetry (LOS) and being arranged to determine the relative shift in an x direction by analyzing an image of the first structures; and

acquiring a first image of a plurality of second structures having a second COS or second LOS and being arranged to determine the relative shift in an x direction by analyzing an image of the second structures,

wherein the first COS or LOS has a different location than the second COS or LOS.

analyzing the first image of the first structures'"'"' COS to determine whether the first structures have a shift in the x direction that is out of specification; and

analyzing the second image of the second structures'"'"' COS to determine whether the second structures have a shift in the y direction that is out of specification.

12. A method as recited in claim 11, wherein the first and second images are acquired together in a same field of view.

13. A method as recited in claim 11, wherein analyzing the first image comprises:

when it is determined that the first structures fail to have a 180 rotational or mirror symmetry, determining that the first structures are out of specification; and

when it is determined that the second structures fail to have a 180 rotational or mirror symmetry, determining that the second structures are out of specification.

14. A method as recited in claim 13, wherein analyzing the first image and analyzing the second image each includes (i) using outside edges of each region of interest of the first or second image to determine a COS or LOS for a first set of substructures and a COS or LOS for a second set of substructures, and (ii) when the COS or LOS of the first set of substructures differs from the COS or LOS of the second set of substructures by more than a predetermined amount, determining that the corresponding structures are out of specification.

15. A method as recited in claim 14, wherein the first set of substructures are formed from a first layer and the second set of substructures are formed from a second layer.

16. A method as recited in claim 13, wherein analyzing the first image and analyzing the second image each includes (i) for a first set of substructures, selecting an initial COS or LOS between a plurality of regions of interest, (ii) for the first set of substructures, automatically placing its 180 degree or mirror counterpart based on the initial COS or LOS, respectively, for each of the first and second images, (iii), for the first set of substructures, continuing to move the initial COS or LOS until a best correlation is found between the first substructures and their counterpart, (iv) repeating operations (i) through (iii) for a second set of substructures, (v) when a best correlation is found for both the first and second substructures and when the COS or LOS of the first set of substructures differs from the COS or LOS of the second set of substructures by more than a predetermined amount, determining that the corresponding first structures are out of specification.

17. A method as recited in claim 16, wherein the first set of substructures are formed from a first layer and the second set of substructures are formed from a second layer.

18. A method for determining the overlay error between two or more successive layers of a substrate, the method comprising:

acquiring an image of a plurality of first structures formed in a first semiconductor layer and having a first center of symmetry (COS) or line of symmetry (LOS) and a plurality of second structures formed in a second semiconductor layer and having a second COS or LOS,

wherein the first COS or LOS is designed to have a known offset from the second COS or LOS so that the overlay error can be determined by acquiring an image of the first and second structures and then analyzing a shift between the first and second COS'"'"'s or LOS'"'"'s in the image and comparing the shift to the known offset; and

analyzing the image of the first and second structures'"'"' COS or LOS to determine whether there is an overlay error between the first and second structures that is out of specification.

19. The method of claim 18, wherein

the first structures have a first LOS about which the first structures have a mirror symmetry or the first structures have a 180°

rotational symmetry with respect to the first COS, and

the second structures have a first LOS about which the second structures have a mirror symmetry or the second structures have a 180°

rotational symmetry with respect to the second COS.

20. The method of claim 18, wherein the first and second structures are in the form of device structures.

21. The method of claim 19, wherein a one of the first or second structures has a 180°

rotational symmetry with respect to its COS and the other one of the first or second structures'"'"' has a mirror symmetry with respect to its LOS.

22. The method of claim 21, wherein the first structures and the second structures together are variant with a 180°

rotational asymmetry or together have a mirror asymmetry.