# US 12,761,571 B2 · Overlay measurement apparatus and overlay measurement method > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,761,571 B2 - Document ID: US12761571B2 - Status: Granted - Kind: B2 - Application number: 18/434,204 - Filed: 2024-02-06 - Published: 2024-08-15 - Granted: 2026-10-13 - Earliest claimed: 2023-02-14 - Assignees: Auros Technology, Inc. - Applicants: AUROS Technology, Inc. - Inventors: Seong Yun Choi; Hyo Sik Ham - Web page: https://patentgrep.com/patent/US12761571B2 ## 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} - G03F 7/70666: {Aerial image, i.e. measuring the image of the patterned exposure light at the image plane of the projection system} - G03F 7/706837: {Data analysis, e.g. filtering, weighting, flyer removal, fingerprints or root cause analysis} - G03F 7/706849: {Irradiation branch, e.g. optical system details, illumination mode or polarisation control} - 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 Disclosed is an overlay measurement apparatus which may include: a light source unit configured to direct an illumination to an overlay measurement target formed in a wafer; a lens unit having an objective lens and a lens focus actuator; a detection unit acquiring a focus image at a measurement position; a stage on which the wafer is seated; and a control unit controlling the lens unit to acquire the overlay measurement target, processing a first sample image of the overlay measurement target detected by the detection unit and a second sample image rotated at 180 degrees based on the first sample image and detected, and calculating a difference between the processed images to calculate the difference as a correction image for correcting an image for which overlay is measured. ## Claims ### Claim 1 An overlay measurement apparatus comprising: a light source configured to direct illumination to an overlay measurement target formed in a wafer; a lens assembly including an objective lens configured to condense the illumination on a measurement position and a focus actuator configured to control a distance between the objective lens and the overlay measurement target; a detection circuit configured to acquire a focus image at the measurement position through a beam reflected on the measurement position; a stage on which the wafer is seated; and a control circuit configured to control the lens assembly to acquire the overlay measurement target, processing a first sample image detected by the detection circuit for the overlay measurement target and a second sample image detected by the detection circuit for the overlay measurement target rotated at 180 degrees relative to the first sample image, normalizing respective pixels of the first sample image to generate a first normalization image and normalizing respective pixels of the second sample image to generate a second normalization image, rotating one of the first normalization image or the second normalization image at 180 degrees, and calculating a difference between the first normalization image and the rotated second normalization image to produce a correction image for correcting an image for measuring overlay. ### Claim 2 (depends on 1) The overlay measurement apparatus of claim 1, wherein the control circuit acquires first image information including pixel information for the first sample image, and acquires a first normalization image by normalizing respective pixels for the first sample image for each pixel, and acquires second image information including pixel information for the second sample image, and acquires a second normalization image by normalizing respective pixels for the second sample image for each pixel. ### Claim 3 (depends on 1) The overlay measurement apparatus of claim 1, wherein the control circuit calculates a pixel-specific difference between the first normalization image acquired by processing the first sample image and the second normalization image acquired by processing the second sample image to produce the correction image. ### Claim 4 (depends on 1) The overlay measurement apparatus of claim 1, wherein the control circuit includes a storage circuit configured to store the first sample image and the second sample image of the overlay measurement target, a normalization processing circuit configured to normalize respective pixels forming the first sample image for each pixel to acquire the first normalization image, and normalizing respective pixels forming the second sample image for each pixel to acquire the second normalization image, an image comparison circuit configured to rotate any one of the first normalization image or the second normalization image at 180 degrees, and comparing the first normalization image and the second normalization image, and a correction image calculation circuit configured to calculate a difference of the respective pixels forming the first normalization image and the second normalization image, and calculating the difference as the correction image. ### Claim 5 (depends on 1) The overlay measurement apparatus of claim 1, wherein the control circuit controls a 1-1st to 1-nth sample images to be detected at first to nth measurement positions, respectively among the overlay measurement targets formed at the plurality of measurement positions, and normalizes respective pixels for the 1-1st to 1-nth sample images for each pixel to acquire 1-1st to 1-nth normalization images, controls a 2-1st to 2-nth sample images to be detected at the first to nth measurement positions, respectively, and normalizes respective pixels for the 2-1st to 2-nth sample images for each pixel to acquire 2-1st to 2-nth normalization images, and calculates differences of respective pixels corresponding to each other in respective pixels forming the 1-nth normalization image and respective pixels forming the 2-nth normalization image, and calculates a mean for n differences and stores the calculated mean as the correction image. ### Claim 6 (depends on 1) The overlay measurement apparatus of claim 1, wherein the control circuit includes a stage operation circuit configured to control rotation of the stage at 180 degrees to detect the second sample image, wherein the rotation of the stage is performed during acquisition of the second sample image, and rotation of the normalization image is performed after acquisition as part of image processing. ### Claim 7 (depends on 1) The overlay measurement apparatus of claim 1, wherein the control circuit includes a scale processing circuit configured to acquire a correction scale image by correcting a scale of the correction image so as to be the same as the scale of the measurement image detected by the detection unit in order to measure alignment of a first overlay key and a second overlay key formed in the wafer, and an image correction circuit configured to correct the measurement image by combining or deleting the correction scale image in units of pixels in the measurement image. ### Claim 8 An overlay measurement method comprising: a first normalization image acquiring step of detecting a first sample image for an overlay measurement target formed on a wafer through a detection unit, and normalizing each pixel of the first sample image for each pixel to acquire a first normalization image; a second normalization information acquiring step of detecting a second sample image for the overlay measurement target rotated at 180 degrees based on the first sample image, and normalizing respective pixels for the second sample image for each pixel to acquire second normalization information; and a correction image calculating step of calculating a difference between the first normalization image acquired by processing the first sample image and the second normalization image acquired by processing the second sample image to produce a correction image. ### Claim 9 (depends on 8) The overlay measurement method of claim 8, further comprising: before the second normalization information acquiring step, a wafer rotating step of rotating the stage at 180 degrees so as to detect the second sample image rotated at 180 degrees from the first sample image. ### Claim 10 (depends on 8) The overlay measurement method of claim 8, wherein the first normalization image acquiring step includes a first measurement step of detecting the first sample image at a first measurement position of the overlay measurement target, and a first normalization processing step of acquiring a first normalization image by normalizing respective pixels forming the first sample image for each pixel, and the second normalization image acquiring step includes a second measurement step of detecting the second sample image at the first measurement position, and a second normalization processing step of acquiring a second normalization image by normalizing respective pixels forming the second sample image for each pixel. ### Claim 11 (depends on 10) The overlay measurement method of claim 10, wherein in the first measurement step, a 1-1st sample image to a 1-nth sample image are detected at a first measurement position to an nth measurement position, respectively among the overlay measurement targets formed at a plurality of measurement positions, in the first normalization processing step, respective pixels for the 1-1st sample image to the 1-nth sample image are normalized for each pixel to acquire a 1-1st normalization image to a 1-nth normalization image, in the second measurement step, a 2-1st sample image to a 2-nth sample image are detected at the first measurement position to the nth measurement position, respectively, and in the second normalization processing step, respective pixels for the 2-1st sample image to the 2-nth sample image are normalized for each pixel to acquire a 2-1st normalization image to a 2-nth normalization image. ### Claim 12 (depends on 11) The overlay measurement method of claim 11, wherein in the correction image calculating step, the 1-nth normalization image and the 2-nth normalization image are compared, differences of respective pixels corresponding to each other in respective pixels forming the 1-nth normalization image and respective pixels forming the 2-nth normalization image are calculated, and a mean for n differences is calculated and stored as the correction image. ### Claim 13 (depends on 8) The overlay measurement method of claim 8, wherein in the correction image calculating step, any one of the first normalization image or the second normalization image is rotated at 180 degrees and the first normalization image and the second normalization image are compared, and a difference between respective pixels forming the first normalization image and the second normalization image is calculated and calculated as the correction image. ### Claim 14 (depends on 8) The overlay measurement method of claim 8, comprising: an image measuring step of detecting the measurement image by measuring the overlay measurement target by the detection unit in order to measure the alignment of the first overlay key and the second overlay key formed in the wafer; a scale processing step of acquiring a correction scale image by correcting a scale of the correction image so that the scale of the correction image is the same as the scale of the measurement image; and an image correcting step of correcting the measurement image by combining or deleting the correction scale image in units of pixels in the measurement image to acquire a measurement image from which noise is removed.