Diffraction based overlay metrology tool and method
First Claim
1. A method for determining an overlay error between a first pattern on a surface of a substrate and a second pattern superimposed on the first pattern, the first pattern comprising a first grating and the second pattern comprising a second grating on top of the first grating, the second grating having substantially identical pitch as the first grating, the second and first gratings forming a composite grating, the method comprising:
- providing a first illumination beam for illuminating at least the composite grating under an angle of incidence such that the first illumination beam propagates along a direction that has a component along a first horizontal direction along the surface of the substrate, the substrate being in a fixed position;
measuring, at an image plane, a first intensity of a diffracted beam from the composite grating;
providing a second illumination beam for illuminating at least the composite grating under the angle of incidence such that the second illumination beam propagates along a direction that has a component along a second horizontal direction along the surface of the substrate, wherein the second horizontal direction is opposite to the first horizontal direction, the substrate being in the fixed position; and
measuring a second intensity of a diffracted beam from the composite grating at the image plane.
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Accused Products
Abstract
Systems, methods, and apparatus are provided for determining overlay of a pattern on a substrate with a mask pattern defined in a resist layer on top of the pattern on the substrate. A first grating is provided under a second grating, each having substantially identical pitch to the other, together forming a composite grating. A first illumination beam is provided under an angle of incidence along a first horizontal direction. The intensity of a diffracted beam from the composite grating is measured. A second illumination beam is provided under the angle of incidence along a second horizontal direction. The second horizontal direction is opposite to the first horizontal direction. The intensity of the diffracted beam from the composite grating is measured. The difference between the diffracted beam from the first illumination beam and the diffracted beam from the second illumination beam, linearly scaled, results in the overlay error.
63 Citations
21 Claims
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1. A method for determining an overlay error between a first pattern on a surface of a substrate and a second pattern superimposed on the first pattern, the first pattern comprising a first grating and the second pattern comprising a second grating on top of the first grating, the second grating having substantially identical pitch as the first grating, the second and first gratings forming a composite grating, the method comprising:
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providing a first illumination beam for illuminating at least the composite grating under an angle of incidence such that the first illumination beam propagates along a direction that has a component along a first horizontal direction along the surface of the substrate, the substrate being in a fixed position; measuring, at an image plane, a first intensity of a diffracted beam from the composite grating; providing a second illumination beam for illuminating at least the composite grating under the angle of incidence such that the second illumination beam propagates along a direction that has a component along a second horizontal direction along the surface of the substrate, wherein the second horizontal direction is opposite to the first horizontal direction, the substrate being in the fixed position; and measuring a second intensity of a diffracted beam from the composite grating at the image plane. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A detection system configured to determine an overlay error between a first pattern on a surface of a substrate and a second pattern superimposed on the first pattern, the first pattern comprising a first grating and the second pattern comprising a second grating on top of the first grating, the second grating having substantially identical pitch as the first grating, the second and first gratings forming a composite grating, the system comprising:
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an illumination source configured to (a) form a first illumination beam for illuminating the composite grating on the substrate under an angle of incidence such that the first illumination beam propagates along a direction that has a component along a first horizontal direction along the surface of the substrate, the substrate being in a substrate position and (b) to form a second illumination beam for illuminating the composite grating on the substrate under an angle of incidence such that the second illumination beam propagates along a direction that has a component along a second horizontal direction along the surface of the substrate, wherein the second horizontal direction is opposite to the first horizontal direction, the substrate being in the substrate position; an image detector configured to receive, at an image plane, a diffracted beam from the composite grating; a plurality of lenses arranged along an optical path between the substrate position and the image detector; and an aperture stop. - View Dependent Claims (12, 13, 14, 15)
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16. A lithographic apparatus comprising a detection system configured to determine an overlay error between a first pattern on a surface of a substrate and a second pattern superimposed on the first pattern, the first pattern comprising a first grating and the second pattern comprising second grating on top of the first grating, the second grating having substantially identical pitch as the first grating, the second and first gratings forming a composite grating, the system comprising:
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an illumination source configured to (a) form a first illumination beam for illuminating the composite grating on the substrate under an angle of incidence such that the first illumination beam propagates along a direction that has a component along a first horizontal direction along the surface of the substrate, the substrate being in a substrate position and (b) to form a second illumination beam for illuminating the composite grating on the substrate under an angle of incidence such that the second illumination beam propagates along a direction that has a component along a second horizontal direction along the surface of the substrate wherein the second horizontal direction is opposite to the first horizontal direction, the substrate being in the substrate position; an image detector configured to receive, at an image plane, a diffracted beam from the composite grating; a plurality of lenses arranged along an optical path between the substrate position and the image detector; and an aperture stop. - View Dependent Claims (17, 18, 19, 20, 21)
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Specification