# US 10,481,506 B2 · Method of measuring a structure, inspection apparatus, lithographic system and device manufacturing method > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,481,506 B2 - Document ID: US10481506B2 - Status: Granted - Kind: B2 - Application number: 15/967,861 - Filed: 2018-05-01 - Published: 2018-11-08 - Granted: 2019-11-19 - Earliest claimed: 2017-05-08 - Assignees: ASML Netherlands B.V. - Applicants: ASML Netherlands B.V. - Inventors: Murat Bozkurt; Maurits Van Der Schaar; Patrick Warnaar; Martin Jacobus Johan Jak; Mohammadreza Hajiahmadi; Grzegorz Grzela; Lukasz Jerzy Macht - Web page: https://patentgrep.com/patent/US10481506B2 ## CPC - 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 21/4788: {Diffraction (for sizing particles G01N15/0205)} - G01N 21/9501: {Semiconductor wafers (manufacturing processes per se of semiconductor devices implementing a measuring step H10P74/20)} - G01N 21/956: Inspecting patterns on the surface of objects {(contactless testing of electronic circuits G01R31/308; testing currency G07D; manufacturing processes per se of semiconductor devices implementing a measuring step H10P74/20)} - G03F 7/70616: {Monitoring the printed patterns} - G03F 7/70683: {Mark designs} - G03F 7/7085: {Detection arrangement, e.g. detectors of apparatus alignment possibly mounted on wafers, exposure dose, photo-cleaning flux, stray light, thermal load} - 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) - 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) ## Abstract An overlay metrology target (600, 900, 1000) contains a plurality of overlay gratings (932-935) formed by lithography. First diffraction signals (740(1)) are obtained from the target, and first asymmetry values (As) for the target structures are derived. Second diffraction signals (740(2)) are obtained from the target, and second asymmetry values (As′) are derived. The first and second diffraction signals are obtained using different capture conditions and/or different designs of target structures and/or bias values. The first asymmetry signals and the second asymmetry signals are used to solve equations and obtain a measurement of overlay error. The calculation of overlay error makes no assumption whether asymmetry in a given target structure results from overlay in the first direction, in a second direction or in both directions. With a suitable bias scheme the method allows overlay and other asymmetry-related properties to be measured accurately, even in the presence of two-dimensional overlay structure. ## Claims ### Claim 1 A method of determining overlay performance of a lithographic process, the method comprising: (a) directing radiation at a plurality of target structures that have been formed by the lithographic process, each target structure comprising a set of first features arranged periodically in at least a first direction and a set of second features arranged periodically in at least the first direction and being subject to overlay error associated with the second features relative to the first features, (b) using a detection system to detect first diffraction signals comprising selected portions of the radiation diffracted by at least a subset of the plurality of target structures; (c) using the detection system to detect second diffraction signals comprising selected portions of the radiation diffracted by at least a subset of the plurality of target structures; and (d) processing asymmetry information derived from the first diffraction signals and the second diffraction signals to calculate at least a measurement of the overlay error in at least the first direction, wherein said target structures have been formed with programmed offsets in the placement of the second features relative to the first features in addition to said overlay error, the programmed offsets within each subset differing in both the first direction and in a second direction, the first and second directions being non-parallel, wherein the calculation of overlay error in step (d) combines said asymmetry information with knowledge of the programmed offsets while making no assumption whether asymmetry in a given target structure results from relative displacement of the second features in the first direction, in the second direction or both directions, and wherein in step (b) said first diffraction signals for said plurality of target structures are captured using the detection system to form one or more first images of the plurality of target structures, wherein in step (c) said second diffraction signals for the plurality of target structures are captured using the detection system to form one or more second images of the plurality of target structures, and wherein in step (d) a first asymmetry value for each target structure is derived from intensity values in respective portions of the first image or images and a second asymmetry value is derived from intensity values in respective portions of the second image or images. ### Claim 2 (depends on 1) The method of claim 1, wherein the first diffraction signals are captured in step (b) under first capture conditions and the second diffraction signals are captured in step (c) under second capture conditions different from the first capture conditions. ### Claim 3 (depends on 2) The method of claim 2, wherein said first capture conditions and said second capture conditions differ in one or more of wavelength, polarization, and angular distribution of radiation used for illumination and/or detection of the target structures. ### Claim 4 (depends on 1) The method of claim 1, wherein the first diffraction signals captured in step (b) comprise radiation diffracted by the first subset of target structures and the second diffraction signals captured in step (c) comprise radiation diffracted by a second subset of target structures different from the first subset of target structures. ### Claim 5 (depends on 4) The method of claim 4, wherein the target structures of the first subset and the target structures of the second subset differ in one or more of pitch, feature size, relative placement, and segmentation in the second direction. ### Claim 6 (depends on 1) The method of claim 1, wherein each of the first features and said second features comprises an elongate feature extending transverse to the first direction and being segmented periodically in the second direction. ### Claim 7 (depends on 6) The method of claim 6, wherein the segmentation of the elongate first and second features has a period different to a period of spacing of the first and second features. ### Claim 8 (depends on 1) The method of claim 1, wherein the calculation of overlay error in step (d) derives from the first diffraction signals a first asymmetry value for each of at least four target structures and derives from the second diffraction signals a second asymmetry value for each of at least four target structures, and uses at least the derived first and second asymmetry values to solve equations in more than four unknowns, one of the unknowns being the measurement of overlay error in the first direction. ### Claim 9 (depends on 8) The method of claim 8, wherein the calculation of overlay error in step (d) calculates a measurement of overlay error in the second direction. ### Claim 10 (depends on 1) The method of claim 1, further comprising a step: using the detection system to capture third diffraction signals comprising selected portions of radiation diffracted by at least a subset of the plurality of target structures, and wherein the step (d) includes processing asymmetry information derived from the first diffraction signals, the second diffraction signals, and the third diffraction signals to calculate a measurement of the overlay error in at least the first direction. ### Claim 11 (depends on 10) The method of claim 10, wherein the calculation of overlay error in step (d) uses the first diffraction signals to derive an asymmetry value for each of at least four target structures, uses the second diffraction signals to derive an asymmetry value for each of at least four target structures, and uses the third diffraction signals to derive an asymmetry value for each of at least three target structures, and uses more than eight of the derived asymmetry values to solve equations in more than eight unknowns, one of the unknowns being the measurement of overlay error in the first direction. ### Claim 12 (depends on 1) The method of claim 1, wherein each of the first and second images contains complementary portions that are images of the same plurality of target structures formed using opposite diffraction orders of radiation diffracted in the first and second directions. ### Claim 13 A method of determining overlay performance of a lithographic process, the method comprising: (a) directing radiation at a plurality of target structures that have been formed by the lithographic process, each target structure comprising a set of first features arranged periodically in at least a first direction and a set of second features arranged periodically in at least the first direction and being subject to overlay error associated with the second features relative to the first features, (b) using a detection system to detect first diffraction signals comprising selected portions of the radiation diffracted by at least a subset of the plurality of target structures; (c) using the detection system to detect second diffraction signals comprising selected portions of the radiation diffracted by at least a subset of the plurality of target structures; and (d) processing asymmetry information derived from the first diffraction signals and the second diffraction signals to calculate at least a measurement of the overlay error in at least the first direction, wherein said target structures have been formed with programmed offsets in the placement of the second features relative to the first features in addition to said overlay error, the programmed offsets within each subset differing in both the first direction and in a second direction, the first and second directions being non-parallel, wherein the calculation of overlay error in step (d) combines said asymmetry information with knowledge of the programmed offsets while making no assumption whether asymmetry in a given target structure results from relative displacement of the second features in the first direction, in the second direction or both directions, and wherein in steps (b) and (c) said diffraction signals are captured while illuminating the target structures using a segmented illumination profile having illuminated regions and dark regions, each illuminated region being symmetrically opposite a dark region, when reflected in the first direction and when reflected in the second direction. ### Claim 14 (depends on 13) The method of claim 13, wherein said segmented illumination profile has four quadrants, said illuminated regions falling only within two quadrants diametrically opposite one another. ### Claim 15 (depends on 13) The method of claim 13, wherein the first diffraction signals are captured in step (b) under first capture conditions and the second diffraction signals are captured in step (c) under second capture conditions different from the first capture conditions. ### Claim 16 (depends on 13) The method of claim 13, wherein said first capture conditions and said second capture conditions differ in one or more of wavelength, polarization, and angular distribution of radiation used for illumination and/or detection of the target structures. ### Claim 17 (depends on 13) The method of claim 13, wherein the first diffraction signals captured in step (b) comprise radiation diffracted by the first subset of target structures and the second diffraction signals captured in step (c) comprise radiation diffracted by a second subset of target structures different from the first subset of target structures. ### Claim 18 (depends on 17) The method of claim 17, wherein the target structures of the first subset and the target structures of the second subset differ in one or more of pitch, feature size, relative placement, and segmentation in the second direction. ### Claim 19 (depends on 13) The method of claim 13, wherein the first features and said second features comprise respective first and second elongate features extending transverse to the first direction and being segmented periodically in the second direction. ### Claim 20 (depends on 19) The method of claim 19, wherein the segmentation of the first and second elongate features has a period different to a period of spacing of the first and second features. ### Claim 21 (depends on 13) The method of claim 13, wherein the calculation of overlay error in step (d) derives from the first diffraction signals a first asymmetry value for each of at least four target structures and derives from the second diffraction signals a second asymmetry value for each of at least four target structures, and uses at least the derived first and second asymmetry values to solve equations in more than four unknowns, one of the unknowns being the measurement of overlay error in the first direction. ### Claim 22 (depends on 21) The method of claim 21, wherein the calculation of overlay error in step (d) calculates a measurement of overlay error in the second direction. ### Claim 23 (depends on 13) The method of claim 13, further comprising: using the detection system to capture third diffraction signals comprising selected portions of radiation diffracted by at least a subset of the plurality of target structures, and wherein the step (d) includes processing asymmetry information derived from the first diffraction signals, the second diffraction signals, and the third diffraction signals to calculate a measurement of the overlay error in at least the first direction. ### Claim 24 (depends on 23) The method of claim 23, wherein the calculation of overlay error in step (d) uses the first diffraction signals to derive an asymmetry value for each of at least four target structures, uses the second diffraction signals to derive an asymmetry value for each of at least four target structures, and uses the third diffraction signals to derive an asymmetry value for each of at least three target structures, and uses more than eight of the derived asymmetry values to solve equations in more than eight unknowns, one of the unknowns being the measurement of overlay error in the first direction.