Diffraction Based Overlay Metrology Tool and Method

• US 20100328655A1
• Filed: 12/09/2009
• Published: 12/30/2010
• Est. Priority Date: 12/17/2007
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Den Boef, Arie Jeffrey
• Granted Patent: US 8,339,595 B2
• Time in Patent Office: Days
• US Class Current: 356/237.5
• CPC Class Codes: G01N 21/95607 using a comparative method
• CPC Class Codes: G03F 7/7015 Details of optical elements
• 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

Abstract

A method for determining overlay between a first grating (110) and a second grating (120) on a substrate (100), the second grating (120) on top of the first grating (110), the second grating (120) having substantially identical pitch (P1) as the first grating (110), the second and first gratings forming a composite grating (110,120), the method including providing a first illumination beam (IB) for illuminating the composite grating (110,120) under an angle of incidence (β) along a first horizontal direction (D1) along the surface of the substrate, and measuring a first intensity (i+) of a first order diffracted beam (B+) from the composite grating (110,120); providing a second illumination beam for illuminating the composite grating (11θ!i2O) under the angle of incidence (−β) along a second horizontal direction (D2) along the surface of the substrate, wherein the second horizontal direction (D2) is opposite to the first horizontal direction (DI)1 and measuring a second intensity (i−) of a minus first order diffracted beam (B−) from the composite grating (110,120).

Claims

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 a first intensity of a first order 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 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 minus first order diffracted beam from the composite grating.

2. The method according to claim 1, further comprising:

determining an intensity difference between the first intensity and the second intensity, the intensity difference being proportional to the overlay error between the first grating and the second grating.

3. The method according to claim 1, wherein the first and second illumination beams are portions of a common illumination beam.

4. The method according to claim 3, wherein the common illumination beam has an annular cross-section.

5. The method according to claim 1, wherein the angle of incidence is oblique relative to the surface of the substrate, a diffraction angle of the first and the minus first diffraction beam relative to the normal of the surface being smaller than the angle of incidence.

6. The method according to claim 1, wherein the angle of incidence is substantially perpendicular to the surface of the substrate, the method comprising:

using the first illumination beam as the second illumination beam,

wherein the measuring of the first intensity of the first order diffracted beam from the composite grating and the measuring of the second intensity of the first order diffracted beam from the composite grating are performed consecutively during provision of the first illumination beam.

7. The method according to claim 1, comprising:

blocking beams of diffraction order other than the first diffraction order when providing the first illumination beam; and

blocking beams of diffraction order other than the minus first diffraction order when providing the second illumination beam.

8. The method according to claim 1, wherein measuring the first intensity of the first order diffracted beam from the composite grating comprises:

detecting an image of the composite grating obtained by only the first order diffracted beam by pattern recognition, and

wherein measuring the second intensity of the composite grating obtained by only the minus first order diffracted beam from the composite grating comprises;

detecting an image of the composite grating obtained by only the minus first order diffracted beam by pattern recognition.

9. The method according to claim 1, further comprising

providing an additional composite grating on the substrate, the additional composite grating formed by a third grating in the first pattern and a fourth grating on top of the first grating, the third grating and the fourth grating having a substantially identical pitch as the first and the second grating, wherein the composite grating is biased with a first shift in a shift direction along the grating direction and the additional composite grating is biased with a second shift in the shift direction along the grating direction, the first shift being different from the second shift;

providing the first illumination beam for illuminating the additional composite grating under the angle of incidence such that the first illumination beam propagates along a direction that has a component along the first horizontal direction along the surface of the substrate, the substrate being in the fixed position;

measuring a first intensity of a first order diffracted beam from the second composite grating;

providing the second illumination beam for illuminating the additional composite grating under the angle of incidence such that the second illumination beam propagates along a direction that has a component along the second horizontal direction along the surface of the substrate; and

measuring a second intensity of a minus first order diffracted beam from the second composite grating.

10. 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:

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 the 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 a substrate position;

an image detector configured to receive a minus first order 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.

11. The detection system according to claim 10, wherein the image detector is configured to detect an image of the composite grating using only first order diffraction beam and the minus first order diffraction beam by a pattern recognition method.

12. The detection system according to claim 10, wherein the aperture stop of the detection system is configured to block beams of diffraction order other than the first diffraction order when forming the first illumination beam, and to block beams of diffraction order other than the minus first diffraction order when forming the second illumination beam.

13. The detection system according to claim 10, wherein the plurality of lenses comprises at least an objective lens adjacent to the surface of the substrate and a projection lens adjacent to the image detector, the aperture stop arranged along the optical path between the objective lens and the projection lens, and

wherein the objective lens has a first numerical aperture value and the aperture stop has a second numerical aperture value, the second numerical aperture value smaller than the first numerical aperture value.

14. 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:

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 the 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 a substrate position;

an image detector configured to receive a minus first order 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.

15. The lithographic apparatus according to claim 14, further comprising

an illumination system configured to condition a beam of radiation;

a patterning device support configured to hold a patterning device, the patterning device configured to pattern the beam of radiation to form a patterned beam of radiation;

a substrate table configured to hold the substrate; and

a projection system configured to projected the patterned beam of radiation onto the substrate.

16. The lithographic apparatus according to claim 14, wherein the image detector is configured to detect an image of the composite grating using only first order diffraction beam and the minus first order diffraction beam by a pattern recognition method.

17. The lithographic apparatus according to claim 14, wherein the aperture stop of the detection system is configured to block beams of diffraction order other than the first diffraction order when forming the first illumination beam, and to block beams of diffraction order other than the minus first diffraction order when forming the second illumination beam.

18. The lithographic apparatus according to claim 14, wherein the plurality of lenses comprises at least an objective lens adjacent to the surface of the substrate and a projection lens adjacent to the image detector, the aperture stop arranged along the optical path between the objective lens and the projection lens, and

wherein the objective lens has a first numerical aperture value and the aperture stop has a second numerical aperture value, the second numerical aperture value smaller than the first numerical aperture value.