# US 2014/0192338 A1 · Diffraction Based Overlay Metrology Tool and Method of Diffraction Based Overlay Metrology > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0192338 A1 - Document ID: US20140192338A1 - Status: Published application - Kind: A1 - Application number: 14/202,825 - Filed: 2014-03-10 - Published: 2014-07-10 - Earliest claimed: 2007-12-17 - Assignees: ASML Netherlands B.V. - Applicants: ASML Netherlands B.V. - Inventors: Arie Jeffrey DEN BOEF - Web page: https://patentgrep.com/patent/US20140192338A1 ## CPC - G01N 21/95607: {using a comparative method} - G03F 7/7015: {Details of optical elements} - 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} - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) - G03F: PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR; (phototypographic composing devices B41B; photosensitive materials or processes for photographic purposes G03C; electrophotography, sensitive layers or processes therefor G03G) ## 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. ## Claims ### Claim 1 A method comprising: illuminating a composite grating on a surface of a substrate under a normal angle of incidence, the composite grating comprising first and second superimposed gratings with similar pitch; measuring, at an image plane, a first intensity of a first diffracted beam from the composite grating; and measuring a second intensity of a second diffracted beam from the composite grating at the image plane. ### Claim 2 (depends on 1) The method of 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. ### Claim 3 (depends on 1) The method of claim 1, wherein: measuring the first intensity comprises using pattern recognition to detect an image of the composite grating obtained by a positive first order diffracted beam, and measuring the second intensity comprises using pattern recognition to detect an image of the composite grating obtained by a negative first order diffracted beam. ### Claim 4 (depends on 3) The method of claim 3, further comprising: blocking diffraction orders other than the first diffraction order. ### Claim 5 (depends on 1) The method of claim 1, wherein: measuring the first intensity comprises using pattern recognition to detect an image of the composite grating obtained by a zero order diffracted beam, and measuring the second intensity comprises using pattern recognition to detect an image of the composite grating obtained by a zero order diffracted beam. ### Claim 6 (depends on 1) The method of claim 1, further comprising: illuminating an additional composite grating on the substrate under a normal angle of incidence, wherein: the additional composite grating is formed by positioning a third grating 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, 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. ### Claim 7 (depends on 6) The method of claim 6, further comprising: measuring, at the image plane, a third intensity of a third diffracted beam from the additional composite grating; and measuring a fourth intensity of a fourth diffracted beam from the additional composite grating at the image plane. ### Claim 8 A detection system comprising: an illumination source configured to direct an illumination beam to diffract from a composite grating on a surface of a substrate under a normal angle of incidence, the composite grating comprising first and second superimposed gratings having a similar pitch; an image detector configured to receive, at an image plane, a first diffracted beam and a second diffracted beam from the composite grating; a lens arranged along an optical path between the substrate position and the image detector; and an aperture stop. ### Claim 9 (depends on 8) The detection system of claim 8, wherein: the first diffracted beam comprises a positive first order diffracted beam and the second diffracted beam comprises a negative first order diffracted beam, and the image detector is configured to use pattern recognition to detect an image of the composite grating using the first order diffracted beam and the negative first order diffracted beam. ### Claim 10 (depends on 8) The detection system of claim 8, wherein the image detector is configured to use pattern recognition to detect an image of the composite grating using only a zero order diffraction beam. ### Claim 11 (depends on 8) The detection system of claim 8, wherein: the lens comprises an objective lens adjacent to the surface of the substrate and a projection lens adjacent to the image detector, the aperture stop is arranged along the optical path between the objective lens and the projection lens, and the objective lens has a first numerical aperture value and the aperture stop has a second numerical aperture value, the second numerical aperture value being smaller than the first numerical aperture value. ### Claim 12 (depends on 8) The detection system of claim 8, wherein the image detector is further configured to measure a first intensity of the first diffracted beam and a second intensity of the second diffracted beam. ### Claim 13 (depends on 8) The detection system of claim 8, wherein the image detector is further configured to determine an intensity difference between the first intensity and the second intensity, the intensity difference being proportional to an overlay error between the first grating and the second grating. ### Claim 14 A lithographic apparatus comprising a detection system, comprising: an illumination source configured to direct an illumination beam to diffract from a composite grating on a surface of a substrate under a normal angle of incidence, the composite grating comprising first and second superimposed gratings with similar pitch on a surface of a substrate; an image detector configured to receive, at an image plane, a first diffracted beam and a second diffracted beam from the composite grating; a lens arranged along an optical path between the substrate position and the image detector; and an aperture stop. ### Claim 15 (depends on 14) 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. ### Claim 16 (depends on 14) The lithographic apparatus according to claim 14, wherein: the first diffracted beam comprises a first order diffracted beam and the second diffracted beam comprises a negative first order diffracted beam, and the image detector is configured to detect an image of the composite grating using the first order diffracted beam and the negative first order diffracted beam by a pattern recognition method. ### Claim 17 (depends on 16) The lithographic apparatus according to claim 16, wherein the aperture stop is configured to block beams of diffraction order other than the first diffraction order and the negative first diffraction order. ### Claim 18 (depends on 14) The lithographic apparatus according to claim 14, wherein the image detector is configured to detect an image of the composite grating using only a zero order diffraction beam by a pattern recognition method. ### Claim 19 (depends on 14) The lithographic apparatus according to claim 14, wherein: the lens comprises an objective lens adjacent to the surface of the substrate and a projection lens adjacent to the image detector, the aperture stop is arranged along the optical path between the objective lens and the projection lens, and the objective lens has a first numerical aperture value and the aperture stop has a second numerical aperture value, the second numerical aperture value being smaller than the first numerical aperture value. ### Claim 20 (depends on 14) The lithographic apparatus according to claim 14, wherein image detector is further configured to: measure a first intensity of the first diffracted beam and a second intensity of the second diffracted beam; and determine an intensity difference between the first intensity and the second intensity, the intensity difference being proportional to an overlay error between the first grating and the second grating.