APPARATUS AND METHODS FOR DETERMINING OVERLAY OF STRUCTURES HAVING ROTATIONAL OR MIRROR SYMMETRY

• US 20090224413A1
• Filed: 03/24/2009
• Published: 09/10/2009
• Est. Priority Date: 08/30/2000
• Status: Active Grant

• Current Assignee: KLA-Tencor Corporation
• Original Assignee: Kla-Tencor Technologies Corporation (KLA Corporation)
• Inventors: Ghinovker, Mark
• Granted Patent: US 8,138,498 B2
• Time in Patent Office: Days
• US Class Current: 257/797
• 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.

structures together are variant with a 180°

rotational asymmetry or together have a mirror asymmetry.