Overlay measurement apparatus and method

Abstract

To provide an overlay measurement apparatus and an overlay measurement method for correcting a pixel which becomes noise in actual measurement from pattern noise information created from an image of an overlay measurement target.SOLUTION: An overlay measurement apparatus includes: a light source unit 100 which illuminates an overlay measuring target T; a lens unit 200 in which a lens focal point actuator 220 for adjusting distance between an object lens 210 and the overlay measuring target T is formed; a detection unit 300 which acquires a focus image at a measurement position through a beam reflected from a measuring point; a stage 500 on which a wafer W is seated; and a control unit which controls the lens unit 200 to acquire the overlay measurement target T, processing a first sample image of the overlay measurement target T detected by the detection unit 300 and a second sample image rotated at 180 degrees based on the first sample image and detected with respect to the overlay measurement target T, and calculating difference between the processed images.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to wafer overlay metrology, and to an overlay metrology apparatus and an overlay metrology method. [Background technology]

[0002] Generally, as technology advances, the size of semiconductor devices decreases and the density of integrated circuits on a wafer increases. In order to form integrated circuits on a wafer, the wafer must undergo a number of manufacturing steps to sequentially form desired circuit structures and elements at specific locations. The manufacturing steps sequentially produce patterned layers on the wafer.

[0003] Through such repeated stacking processes, electrically activated patterns are produced in the integrated circuit. If the respective structures are not aligned within an allowable error range during the manufacturing process, interference occurs between the electrically activated patterns, which can cause problems in the performance and reliability of the manufactured circuit. In order to measure and verify the alignment error between the layers, a metrology tool is used to find the position of the focus through the contrast or phase difference in the image of the wafer.

[0004] In this case, measurement errors occur due to the inability to precisely align the optical device and the stage vertically, or due to structural defects in the optical device, such as optics alignment, lens quality, and stage leveling. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made to solve various problems including those mentioned above, and an object of the present invention is to provide an overlay measurement apparatus and an overlay measurement method capable of calculating pattern noise information created from an image of an overlay measurement target and correcting pixels that become noise in actual measurement using the calculated pattern noise information. However, these problems are merely examples and the scope of the present invention is not limited thereto. [Means for solving the problem]

[0006] According to an embodiment of the present invention, there is provided an overlay measurement apparatus, which may include a light source unit configured to direct illumination onto an overlay measurement target formed on a wafer, a lens unit having an objective lens for focusing the illumination onto a measurement position at any point on the overlay measurement target and a lens focus actuator for adjusting a distance between the objective lens and the overlay measurement target, a detector unit for acquiring a focused image at the measurement position through a beam reflected from the measurement position, a stage on which the wafer is seated, and a controller for controlling the lens unit so that the overlay measurement target can be acquired, processing a first sample image of the overlay measurement target detected by the detector unit and a second sample image of the overlay measurement target rotated 180 degrees with respect to the first sample image, calculating a difference between the processed images, and calculating the difference as a correction image for correcting an image for measuring an overlay.

[0007] According to one embodiment of the present invention, the control unit may obtain first image information including pixel information for the first sample image, normalize each pixel for the first sample image on a pixel-by-pixel basis to obtain a first normalized image, obtain second image information including pixel information for the second sample image, and normalize each pixel for the second sample image on a pixel-by-pixel basis to obtain a second normalized image.

[0008] According to an embodiment of the present invention, the control unit may calculate, as the corrected image, a pixel-by-pixel difference between a first normalized image obtained by processing the first sample image and a second normalized image obtained by processing the second sample image.

[0009] According to an embodiment of the present invention, the control unit may include a storage unit that stores the first sample image and the second sample image of the overlay measurement target; a normalization processing unit that normalizes each pixel forming the first sample image per pixel to obtain a first normalized image and normalizes each pixel forming the second sample image per pixel to obtain a second normalized image; an image comparison unit that rotates either the first normalized image or the second normalized image by 180 degrees and compares the first normalized image with the second normalized image; and a correction image calculation unit that calculates a difference for each pixel forming the first normalized image and the second normalized image to obtain the correction image.

[0010] According to an embodiment of the present invention, the control unit may control the overlay measurement targets formed at a plurality of measurement positions to detect 1-1 to 1-n sample images at a first to n-th measurement positions, normalize each pixel of the 1-1 to 1-n sample images for each pixel to obtain 1-1 normalized images to 1-n normalized images, control the control unit to detect 2-1 to 2-n sample images at the first to n-th measurement positions, normalize each pixel of the 2-1 to 2-n sample images for each pixel to obtain 2-1 normalized images to 2-n normalized images, calculate differences between corresponding pixels from each pixel forming the 1-n normalized image and each pixel forming the 2-n normalized image, calculate an average of n differences, and store the average as the corrected image.

[0011] According to an embodiment of the present invention, the control unit includes a stage operating unit that rotatably controls the stage, and the second sample image can be detected by rotating the stage 180 degrees.

[0012] According to an embodiment of the present invention, the control unit may include a scale processing unit that corrects a scale of the correction image to obtain a corrected scale image so that the scale is the same as that of a measurement image detected by the detection unit in order to measure alignment of a first overlay key and a second overlay key formed on the wafer; and an image correction unit that corrects the correction scale image by combining or deleting it from the measurement image on a pixel basis.

[0013] According to an embodiment of the present invention, there is provided an overlay measurement method, which may include: detecting a first sample image of 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 obtain a first normalized image; detecting a second sample image for the overlay measurement target rotated 180 degrees with respect to the first sample image, and normalizing each pixel of the second sample image for each pixel to obtain second normalized information; and calculating a correction image by calculating a difference between the first normalized image obtained by processing the first sample image and the second normalized image obtained by processing the second sample image as a correction image.

[0014] According to one embodiment of the present invention, the method may further include, prior to the second normalization information acquisition step, rotating the stage 180 degrees so as to detect the second image rotated 180 degrees from the first sample image.

[0015] According to one embodiment of the present invention, the first normalized image acquisition step may include 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 normalizing each pixel forming the first sample image on a pixel-by-pixel basis to obtain a first normalized image; and the second normalized image acquisition step may include a second measurement step of detecting the second sample image at the first measurement position; and a second normalization processing step of normalizing each pixel forming the second sample image on a pixel-by-pixel basis to obtain a second normalized image.

[0016] According to an embodiment of the present invention, in the first measurement step, among the overlay measurement targets formed at a plurality of measurement positions, 1-1 sample images to 1-n sample images are detected from the first measurement position to the nth measurement position, respectively, and in the first normalization processing step, each pixel of the 1-1 sample images to the 1-n sample images is normalized for each pixel to obtain 1-1 normalized images to 1-n normalized images, respectively. In the second measurement step, 2-1 sample images to 2-n sample images are detected from the first measurement position to the nth measurement position, respectively, and in the second normalization processing step, each pixel of the 2-1 sample images to the 2-n sample images is normalized for each pixel to obtain 2-1 normalized images to 2-n normalized images, respectively.

[0017] According to an embodiment of the present invention, in the corrected image calculation step, the 1-n normalized image and the 2-n normalized image are compared to calculate differences between corresponding pixels of each pixel forming the 1-n normalized image and each pixel forming the 2-n normalized image, and an average of n pixels is calculated and stored as the corrected image.

[0018] According to an embodiment of the present invention, in the corrected image calculation step, either the first normalized image or the second normalized image may be rotated 180 degrees, the first normalized image and the second normalized image may be compared, and a difference between each pixel forming the first normalized image and the second normalized image may be calculated to calculate the corrected image.

[0019] According to an embodiment of the present invention, in order to measure alignment of a first overlay key and a second overlay key formed on the wafer, the method may include an image measurement step of measuring the overlay measurement target with the detection unit to detect a measurement image; a scale processing step of correcting a scale of the corrected image to obtain a corrected scale image so that the scale of the corrected image is the same as that of the measurement image; and an image correction step of correcting the measurement image by combining or deleting the corrected scale image on a pixel basis to obtain a measurement image from which noise has been removed. Effect of the Invention

[0020] According to some embodiments of the present invention configured as described above, a corrected image can be calculated through pixel-by-pixel normalization and applied to a measurement image to calculate an accurate measurement image, thereby increasing measurement accuracy and enabling consistent results to be derived through automatic optimization based on the corrected image data.

[0021] In addition, the present invention has an advantage that the correction value can be calculated by modifying the processor without adding or modifying a separate structure in an existing overlay measurement device, and the error occurring for each overlay measurement device and wafer can be automatically calculated and reflected in the actual overlay measurement to optimize the measurement recipe. Of course, the scope of the present invention is not limited by such advantages. [Brief description of the drawings]

[0022] [Figure 1]1 is a schematic diagram illustrating an overlay metrology apparatus according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a diagram illustrating a control unit of the overlay measurement apparatus of the present invention. [Diagram 3] 1 is a flowchart illustrating an overlay metrology method according to an embodiment of the present invention. [Figure 4] 1 is a flowchart illustrating an overlay metrology method according to an embodiment of the present invention. [Diagram 5] 1 is a flowchart illustrating an overlay metrology method according to an embodiment of the present invention. [Figure 6] 1 is a flowchart illustrating an overlay metrology method according to an embodiment of the present invention. [Figure 7] 1 is a flowchart illustrating an overlay metrology method according to an embodiment of the present invention. [Figure 8] FIG. 13 illustrates a corrected image according to an embodiment of the present invention. [Figure 9] 13A and 13B are diagrams comparing measurement images with and without application of a correction image according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, some preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0024] The embodiments of the present invention are provided to more completely explain the present invention to those having ordinary skill in the art, and the following embodiments can be modified into various other forms, and the scope of the present invention is not limited to the following embodiments. Rather, these embodiments are provided to make the present disclosure more faithful and complete, and to fully convey the spirit of the present invention to those skilled in the art. Note that the thickness and size of each layer in the drawings are exaggerated for convenience and clarity of explanation.

[0025] Hereinafter, embodiments of the present invention will be described with reference to the drawings that show an ideal embodiment of the present invention. In the drawings, for example, variations in the illustrated shapes can be expected depending on manufacturing techniques and / or tolerances. Therefore, the embodiments of the present invention should not be interpreted as being limited to the specific shapes of regions shown in the specification, but should include, for example, variations in shapes that occur during manufacturing.

[0026] The overlay metrology system is a system that measures an error between a first overlay key and a second overlay key formed on different layers of a wafer W.

[0027] For example, the first overlay key may be an overlay mark formed in a previous layer, and the second overlay key may be an overlay mark formed in a current layer. The overlay marks are formed in a scribe line simultaneously with forming a layer for forming a semiconductor device in a die region. For example, the first overlay key may be formed together with an insulating film pattern, and the second overlay key may be formed together with a photoresist pattern formed on the insulating film pattern. In this case, the second overlay key is exposed to the outside, but the first overlay key is hidden by a photoresist layer, and may be made of an oxide having optical properties different from those of the second overlay key made of a photoresist material.

[0028] Also, the physical locations of the first overlay key and the second overlay key are different from each other, but the focal planes may be the same or different.

[0029] FIG. 1 is a diagram illustrating an overlay measurement apparatus according to an embodiment of the present invention, and FIG. 2 is a diagram illustrating a control unit 400 of the overlay measurement apparatus of the present invention.

[0030] First, an overlay measurement apparatus according to an embodiment of the present invention may broadly include a light source unit 100 , a lens unit 200 , a detection unit 300 , a control unit 400 and a stage 500 .

[0031] 1, illumination may be directed from at least one illumination source to an overlay measurement target T. Specifically, the light source unit 100 may be configured to direct illumination to the overlay measurement target T where a first overlay key formed in a first layer and a second overlay key formed in a second layer stacked above the first layer are located.

[0032] For example, the light source unit 100 may be formed of a halogen lamp, a xenon lamp, a supercontinuum laser, a light emitting diode, a laser induced lamp, etc., and may include various wavelengths such as ultraviolet (UV), visible light, or infrared (IR), but is not limited thereto.

[0033] An overlay metrology apparatus according to one embodiment of the present invention may include an aperture 110 , a spectral filter 120 , a polarizing filter 130 , and a beam splitter 140 .

[0034] The aperture 110 may be formed of an opaque plate having an aperture through which light passes, and may change the beam emitted from the light source unit 100 into a form suitable for photographing the overlay measurement target T.

[0035] The aperture 110 may include one or more of an aperture stop that adjusts the amount of light and a field stop that adjusts the range at which an image is focused, and may be formed between the light source unit 100 and the beam splitter 140 as shown in FIG. 1, or may be formed between the beam splitter 140 and the lens unit 200, although not shown.

[0036] The spectral filter 120 can adjust the center wavelength and bandwidth of the beam emitted from the light source unit 100 to suit image acquisition of the overlay metrology target T. For example, the spectral filter 120 can be formed from at least one of a filter wheel, a linear translation device, a flipper device, and combinations thereof.

[0037] The beam splitter 140 transmits a part of the beam that has left the light source unit 100 and passed through the aperture 110 and reflects a part of the beam, thereby splitting the beam from the light source unit 100 into two beams.

[0038] As shown in FIG. 1, the lens unit 200 may be formed with an objective lens 210 that focuses the illumination at a measurement position at any point on the overlay measurement target T, and a lens focus actuator 220 that adjusts the distance between the objective lens 210 and the overlay measurement target T.

[0039] The objective lens 210 can focus the beam reflected from the beam splitter 140 onto a measurement position on the wafer W where the overlay measurement target T is formed, and collect the reflected beam.

[0040] The objective lens 210 may be mounted on a lens focus actuator 220 .

[0041] The lens focus actuator 220 can adjust the distance between the objective lens 200 and the wafer W so that the focal plane is located at an optimal area of ​​the overlay metrology target T.

[0042] The lens focus actuator 220 can adjust the focal length by moving the objective lens 200 vertically in the direction of the wafer W under the control of the controller 400 .

[0043] In this case, the measurement position may be formed at least at any point of the overlay measurement target T. Also, the measurement position may include a plurality of measurement positions according to the driving of the lens unit 200 and the detection unit 300, and may include a plurality of measurement regions and focal depths according to the driving of the lens focus actuator 220.

[0044] As shown in FIG. 1, the detection unit 300 can obtain a focused image at the measurement position through a beam reflected from the measurement position.

[0045] The detection unit 300 can capture the beam reflected from the overlay measurement target T and passing through the beam splitter 140 to obtain an image of the overlay measurement target T.

[0046] The detection unit 300 may include an optical detector capable of measuring the beam reflected from the overlay measurement target T. For example, the optical detector may include a charge-coupled device (CCD) that converts light into an electric charge to extract an image, a complementary metal-oxide-semiconductor (CMOS) sensor, which is an integrated circuit, a photomultiplier tube (PMT) that measures light, an avalanche photodiode (APD) array as a photodetector, or various sensors that generate or capture images.

[0047] The detector 300 may include filters, polarizers, beam blocks, and may further include any collection optical components (not shown) for collecting the illumination collected by the objective lens 210.

[0048] 1, the control unit 400 can control the direction of illumination emitted from the light source unit 100, can control the lens unit 200 to focus the illumination on the overlay measurement target T and collect a reflected beam, and can control the detection unit 300 to obtain a focused image measured through the reflected beam collected from the lens unit 200. For example, the control unit 400 can control the light source unit 100, the lens unit 200, and the detection unit 300 to change the measurement area, the measurement position, or the focal depth according to a preset setting value of the overlay measurement target T, and can obtain an image for each position and depth of the overlay measurement target T.

[0049] When detecting a measurement image from the overlay measurement target T, the control unit 400 calculates a correction value to correct structural errors caused by the influence of optics alignment, lens quality, stage leveling, etc., and applies the correction value to the measurement image to calculate an accurate measurement image, thereby enabling overlay measurement through the more accurate measurement image.

[0050] The control unit 400 of the overlay measurement apparatus according to an embodiment of the present invention processes a first sample image of the overlay measurement target T detected by the detection unit 300 and a second sample image detected by rotating 180 degrees based on the first sample image, calculates a difference between the processed images, and calculates a correction image for correcting the image for measuring the overlay.

[0051] Specifically, the control unit 400 can obtain first image information including pixel information for a first sample image, and normalize each pixel for the first sample image on a pixel-by-pixel basis to obtain a first normalized image, and can obtain second image information including pixel information for a second sample image, and normalize each pixel for the second sample image on a pixel-by-pixel basis to obtain a second normalized image.

[0052] In this case, a pixel is a rectangular dot having color information as the smallest unit constituting an image, and an image is composed of a set of pixels.

[0053] Then, the control unit 400 may calculate a pixel-by-pixel difference between a first normalized image obtained by processing the first sample image and a second normalized image obtained by processing the second sample image as a correction image.

[0054] For example, the control unit 400 may include a light source operating unit 410 , a lens operating unit 420 , a stage operating unit 430 , a storage unit 440 , a normalization processing unit 450 , an image comparison unit 460 and a corrected image calculation unit 470 .

[0055] As shown in FIG. 2, the light source operating unit 410 can control the direction of the illumination emitted from the light source unit 100, and the lens operating unit 420 can control the operation of the lens focus actuator 220 so that the illumination is focused on the overlay measurement target T and images are obtained for the measurement position, the measurement area, and the focal depth.

[0056] As shown in FIG. 2, the storage unit 430 may store the first and second sample images of the overlay measurement target T acquired by the detection unit 300 .

[0057] For example, in the lens operation unit 420, an image can be measured at a preset measurement position of the objective lens 210 and the overlay measurement target T and stored in the storage unit 430 as a first sample image, and an image of the overlay measurement target T rotated 180 degrees from the first measurement position can be measured and stored in the storage unit 430 as a second sample image.

[0058] At this time, the stage operating unit 430 can control the stage 500 to rotate 180 degrees to detect the second sample image. Also, the detection unit 300 can be rotated 180 degrees from an existing position to measure the overlay measurement target T, and the second sample image rotated 180 degrees from the first sample image can be detected.

[0059] The normalization processor 450 may calculate the mean and standard deviation of the sample images and normalize them so that noise can be calculated by comparing the sample images.

[0060] In this case, the normalization may include Min-Max Normalization, which sets the minimum value of all data to 0, the maximum value to 1, and scales the remaining values ​​to values ​​between 0 and 1 by adding up the ratios; Standardization; and Z-Score Normalization, which divides the standard deviation from the mean to re-adjust the data to have the attributes of a standard normal distribution.

[0061] That is, the normalization processor 450 is a program that processes an image so that all pixel points of the sample image are reflected at the same scale, and the normalization processor 450 can be expressed as follows:

[0062]

number

[0063] (Here, Imgf : normalized image, RealImg: sample image, σ: standard deviation)

[0064] That is, the normalization processing unit 450 divides the sample image RealImg by the standard deviation to obtain a normalized image Img that has been normalized for each pixel. f can be obtained.

[0065] For example, the normalization processing unit 450 may apply Equation 1 to the first sample image to normalize each pixel on a pixel-by-pixel basis to obtain a first normalized image, and may normalize each pixel forming the second sample image on a pixel-by-pixel basis to obtain a second normalized image.

[0066] The image comparison unit 460 is a program that compares sample images measured at the same measurement position. Specifically, it can rotate either the first normalized image or the second normalized image by 180 degrees and compare the first normalized image with the second normalized image.

[0067] For example, the stage 500 may be rotated 180 degrees and a second normalized image obtained from a second sample image may be rotated 180 degrees in the same orientation as the first normalized image to compare corresponding pixels at the same locations.

[0068] The corrected image calculation unit 470 is a program that compares identical images to calculate noise. Specifically, it calculates the difference between corresponding pixels of a first normalized image and a second normalized image rotated 180 degrees in the same direction as the first normalized image, and calculates the corrected image from the average value.

[0069] In this case, the corrected image calculation unit 470 can be expressed as Equation 2. In this case, the first normalized image is the 0 degree normalized image Img f0 and the second normalized image is the 180 degree normalized image Imgf 180 It could be.

[0070]

number

[0071] (Here, Img diff : Correction image, Img f0 :0 degree normalized image, Img f180 : 180 degree normalized image)

[0072] That is, the corrected image calculation unit 470 calculates the first normalized image Img f0 and the second normalized image Img f180 A corrected image can be obtained by dividing the difference between the measured values ​​by the average, 2. At this time, the corrected image can be stored in the storage unit 440, and the measured image can be corrected by applying the corrected image during overlay measurement.

[0073] According to another embodiment of the present invention, the control unit 400 may control the correction image to be calculated from images measured at a plurality of measurement positions.

[0074] Specifically, the control unit 400 controls the detection of the 1-1 sample image to 1-n sample image at the 1st measurement position to the nth measurement position of the overlay measurement target T formed at a plurality of measurement positions, and normalizes each pixel of the 1-1 sample image to the 1-n sample image on a pixel basis to obtain the 1-1 normalized image to 1-n normalized image.

[0075] In addition, the control unit 400 may control the detection of the 2-1st to 2-nth sample images at the 1st to nth measurement positions, respectively, and may normalize each pixel of the 2-1st to 2-nth sample images on a pixel-by-pixel basis to obtain the 2-1st to 2-nth normalized images.

[0076] Next, the control unit 400 may calculate the difference between corresponding pixels between each pixel forming the 1-n normalized image and each pixel forming the 2-n normalized image, calculate the average of n pixels, and store the average as the corrected image.

[0077] For example, the detection unit 300 measures a first image at each of the first and second measurement positions and stores a 1-1 sample image and a 1-2 sample image in the storage unit 440, and the stage operation unit 430 controls the stage 500 to rotate 180 degrees, and then the detection unit 300 searches for and moves to the first and second measurement positions to measure each image a second time, and stores a 2-1 sample image and a 2-2 sample image in the storage unit 440.

[0078] In the normalization processing unit 450, the 1-1 sample image, the 1-2 sample image, the 2-1 sample image, and the 2-2 sample image can be applied to [Equation 1] to obtain respective normalized images, i.e., the 1-1 normalized image, the 1-2 normalized image, the 2-1 normalized image, and the 2-2 normalized image.

[0079] The image comparison unit 460 may compare the 1-1 normalized image with the 2-1 normalized image, and may compare the 2-1 normalized image with the 2-2 normalized image.

[0080] Therefore, the corrected image calculation unit 470 can calculate a first correction value based on a difference between corresponding pixels in the 1-1 normalized image and the 2-1 normalized image, calculate a second correction value based on a difference between corresponding pixels in the 1-2 normalized image and the 2-2 normalized image, and calculate a corrected image based on an average of the first correction value and the second correction value.

[0081] That is, the reliability of the correction can be further improved by calculating a corrected image from images measured at a plurality of measurement positions.

[0082] According to one embodiment of the present invention, a scale processing unit 480 and an image correction unit 490 may be included to apply the correction image stored in the storage unit 400 to the measurement image detected to measure the alignment of the overlay measurement target T.

[0083] In order to measure the overlay of the wafer W, the detector 300 can measure an image to detect a measurement image. In this case, in order to correct structural errors included in the measurement image caused by the influence of optics alignment, lens quality, stage leveling, etc., the correction image calculated as described above is applied to the measurement image to correct the structural errors, and the overlay is measured from the corrected measurement image.

[0084] In this case, the scale processor 480 may perform correction so that the pixel scales of the corrected image and the measurement image are the same so that the corrected image is applied to the measurement image.

[0085] Specifically, the scale processor 480 is a program that corrects the scale so that the pixel scale of the corrected image is the same as the pixel scale of the measurement image.

[0086] The image corrector 490 may correct the measurement image by combining or deleting the correction scale image in pixel units. real Corrected scale image Img diff* σ real Image after removing the measurement save can be calculated.

[0087] For example, as shown in [Equation 3], the corrected image Img diff Measure the image scale standard deviation σ real Apply the correction scale to the image Img diff* σ real The measurement image Img can be calculated. real Corrected scale image Img diff* σ real Delete and save the measurement image Img save can be calculated.

[0088]

number

[0089] (Here, Img save : Measurement image, Img real : Measurement image, Img diff : Corrected image, σ real : Scale of measured image (standard deviation)

[0090] In addition, the control unit 400 may include a display unit (not shown) for allowing a user to monitor a series of processes performed by the control unit 400, and may also include an input unit (not shown) that the user can directly control.

[0091] That is, through the display unit, the user can check the sample image and measurement image stored in the storage unit 440, the normalized image obtained by the normalization processing unit 450, the corrected image calculated by the image comparison unit 460 and the corrected image calculation unit 470, and the measurement image calculated by the scale processing unit 480 and the image correction unit 490. Through the input unit, the user can directly control the light source operation unit 410, the lens operation unit 420, and the stage operation unit 430, or directly select, change, and calculate pixel information representing the normalized image, the corrected image, the scale corrected image, etc.

[0092] The control unit 400 may include an ARO (Auto Recipe Optimization) program that automatically optimizes an overlay measurement recipe using image correction information, filter optimization information, aperture optimization information, focus optimization information, and pinhole optimization information.

[0093] In addition, the overlay measurement apparatus may include a memory that stores commands, programs, logic, etc. that allow the control unit 400 to control the operation of each component of the overlay measurement apparatus, and components may be added, modified, or deleted as necessary.

[0094] That is, the overlay measurement apparatus of the present invention can calculate a correction image for correcting structural errors that occur due to the influence of optics alignment, lens quality, stage leveling, etc., and the correction image can be applied to a measurement image to calculate an accurate measurement image in which the structural errors are corrected, thereby enabling more accurate overlay measurement.

[0095] 3 to 7 are flowcharts showing an overlay measurement method according to one embodiment of the present invention.

[0096] The overlay measurement method according to an embodiment of the present invention may include a first normalized image acquisition step S100, a second normalized image acquisition step S200, and a corrected image calculation step S300.

[0097] The first normalized image acquisition step S100 is a step of detecting a first sample image of an overlay measurement target T formed on a wafer via the detection unit 300, and normalizing each pixel of the first sample image on a pixel-by-pixel basis to acquire a first normalized image.

[0098] Specifically, as shown in FIG. 5, the first normalized image acquisition step S100 may include a first measurement step S110 and a first normalization processing step S120.

[0099] The first measurement step S110 is a step of detecting a first sample image at a first measurement position of the overlay measurement target T via the detection unit 300, and the first normalization processing step S120 is a step of normalizing each pixel forming the first sample image on a pixel-by-pixel basis to obtain a first normalized image.

[0100] Specifically, the first normalization process step S120 is a step of dividing the first sample image by the standard deviation to obtain a normalized image that has been normalized for each pixel. For example, the first normalization process step S120 may apply the first sample image to Equation 1 to normalize each pixel to obtain the first normalized image.

[0101]

number

[0102] (Here, Img f : normalized image, RealImg: sample image, σ: standard deviation)

[0103] As shown in FIGS. 1 and 5, the second normalized image acquisition step S200 is a step of detecting a second sample image detected by rotating 180 degrees based on the first sample image, and normalizing each pixel of the second sample image on a pixel-by-pixel basis to obtain second normalized information.

[0104] Specifically, as shown in FIG. 5, the second normalized image acquisition step S200 may include a second measurement step S210 and a second normalization processing step S220.

[0105] The second measurement step S210 is a step of detecting a second sample image at a first measurement position, which is the same position where the first sample image was detected through the detection unit 300, and the second normalization processing step S220 is a step of normalizing each pixel forming the second sample image on a pixel-by-pixel basis to obtain a second normalized image.

[0106] Specifically, the second normalization process step S220 is a step of obtaining a normalized image that has been normalized for each pixel by dividing the second sample image by the standard deviation in the same manner as the first normalization process step S120. That is, the second sample image is applied to Equation 1 to normalize each pixel to obtain a second normalized image.

[0107] In this case, in the first normalized image obtaining step S100 and the first normalized image obtaining step S200, the sample image is measured at a plurality of measurement positions, and a corrected image, which will be described later, can be calculated.

[0108] As shown in FIG. 6, the first measurement step S110 is a step of detecting sample images 1-1 to 1-n at the first to n-th measurement positions of the overlay measurement target T formed at a plurality of measurement positions.

[0109] For example, in the first measurement step S110, a primary image may be measured at each of the first and second measurement positions, and a 1-1 sample image and a 1-2 sample image may be stored in the storage unit 440.

[0110] In this case, the first normalization processing step S120 is a step of normalizing each pixel of the 1-1th to 1-nth sample images to obtain the 1-1th to 1-nth normalized images.

[0111] For example, in the first normalization processing step S120, the 1-1 sample image and the 1-2 sample image stored in the first measurement step S110 can be applied to the above-mentioned [Equation 1] to obtain respective normalized images, i.e., the 1-1 normalized image and the 1-2 normalized image.

[0112] Also, as shown in FIG. 6, the second measurement step S210 is a step of detecting 2-1 to 2-n sample images at the first to n-th measurement positions, respectively.

[0113] For example, in the second normalized image acquisition step S200, the detection unit 300 may be moved to search for the first measurement position and the second measurement position, and the images at each of the first measurement position and the second measurement position may be measured a second time, and the 2-1 sample image and the 2-2 sample image may be stored in the storage unit 440.

[0114] Specifically, in the second normalization process step S220, each pixel of the 2-1th to 2-nth sample images may be normalized pixel by pixel to obtain the 2-1th to 2-nth normalized images.

[0115] For example, in the second normalization processing step S220, the 2-1 sample image and the 2-2 sample image stored in the second measurement step S210 can be applied to the above-mentioned [Equation 1] to obtain respective normalized images, i.e., the 2-1 normalized image and the 2-2 normalized image.

[0116] As shown in FIG. 4, before the second normalized image acquisition step S200, a wafer rotation step S400 may be further included in which the stage 500 is rotated 180 degrees so that a second image rotated 180 degrees from the first sample image can be detected.

[0117] In wafer rotation step S400, the stage 500 rotates 180 degrees to rotate the second normalized image obtained from the second sample image 180 degrees in the same direction as the first normalized image, so that corresponding pixels at the same positions can be compared.

[0118] In addition, when measuring sample images at multiple measurement positions, the wafer rotation step S400 may measure each primary image at the first measurement position and the second measurement position in the detection unit 300, and then the stage 500 may rotate 180 degrees in the stage operation unit 430, and then locate and move to the first measurement position and the second measurement position to measure each image a second time, thereby measuring the 2-1 sample image and the 2-2 sample image.

[0119] Alternatively, the wafer rotation step S400 may involve rotating the stage 500, but rather rotating the detection unit 300 180 degrees from an existing position so that the rotated image of the wafer W can be measured, measuring the overlay measurement target T of the rotated wafer W as viewed from the detection unit 300, and measuring a second sample image rotated 180 degrees from the first sample image.

[0120] As shown in FIGS. 3 to 7, the corrected image calculation step S300 is a step of calculating a difference between a first normalized image obtained by processing a first sample image and a second normalized image obtained by processing a second sample image as a corrected image.

[0121] Specifically, the corrected image calculation step S300 rotates either the first normalized image or the second normalized image by 180 degrees, compares the first normalized image with the second normalized image, and calculates the difference between each pixel forming the first normalized image and the second normalized image to calculate the corrected image.

[0122] For example, in the corrected image calculation step S300, the second normalized image is rotated 180 degrees in the same direction as the first normalized image, and the difference between corresponding pixels at the same positions is calculated, and the corrected image can be calculated from the average value.

[0123] In this case, the corrected image calculation step S300 calculates the first normalized image Img as shown in [Equation 2]. f0 and the second normalized image Img f180 The difference between these can be divided by 2, which is the average, to obtain a corrected image.

[0124]

number

[0125] (Here, Img diff : Correction image, Img f0 :0 degree normalized image, Img f180 : 180 degree normalized image)

[0126] In addition, when a sample image is measured at a plurality of measurement positions, in the corrected image calculation step S300, the 1-n normalized image and the 2-n normalized image are compared to calculate the difference between corresponding pixels from each pixel forming the 1-n normalized image and each pixel forming the 2-n normalized image, and the average of n pixels is calculated and stored as the corrected image.

[0127] For example, in the corrected image calculation step S300, a first correction value is calculated based on the difference between corresponding pixels from the 1-1 normalized image and the 2-1 normalized image, a second correction value is calculated based on the difference between corresponding pixels from the 1-2 normalized image and the 2-2 normalized image, and a corrected image is calculated based on the average of the first correction value and the second correction value, thereby further improving the correction reliability.

[0128] For example, a corrected image may be calculated by calculating a pixel difference between a first normalized image and a second normalized image as shown in Fig. 8. However, Fig. 8 is a diagram for illustrating the corrected image, and the corrected image may be formed in various shapes, patterns, and sizes according to the image of the overlay measurement target T without being limited thereto.

[0129] An overlay measurement method according to an embodiment of the present invention may include an image measurement step S500, a scale processing step S600, and an image correction step S700.

[0130] The image measuring step S500 is a step of measuring an overlay measurement target T by the detector 300 to detect a measurement image in order to measure the alignment of the first overlay key and the second overlay key formed on the wafer W.

[0131] As shown in FIG. 7, the scale processing step S600 is a step of obtaining a corrected scaled image by correcting the scale of the corrected image so that the scale of the corrected image is the same as that of a measurement image.

[0132] Specifically, the scale processing step S600 scales the corrected image Img so that the pixel scales of the corrected image and the measured image are the same. diff Measure the image scale standard deviation σ real Apply the correction scale to the image Img diff* σ real This is the stage where the following is calculated:

[0133] As shown in FIG. 7, the image correction step S700 is a step of correcting the measurement image by combining or deleting the corrected scale image in pixel units from the measurement image to obtain a measurement image from which noise has been removed.

[0134] For example, as shown in [Equation 3], in the scale processing step S600, the corrected scaled image Img diff* σ real Calculate the measured image Img in the image correction step S700. realCorrected scale image Img diff* σ real Delete and save the measurement image Img save can be calculated.

[0135]

number

[0136] (Here, Img save : Measurement image, Img real : Measurement image, Img diff : Corrected image, σ real : Scale of measured image (standard deviation)

[0137] For example, (a) and (b) of FIG. 9 are diagrams comparing measurement images with and without the application of the correction image according to an embodiment of the present invention.

[0138] As shown in Fig. 9(a), the correction scale image can be combined or removed pixel by pixel from the measurement image to obtain a measurement image with noise removed and uniform pixel shading across the image. On the other hand, the uncorrected measurement image in Fig. 9(b) may not have uniform pixel shading across the image compared to the image with the correction image applied in Fig. 9(a).

[0139] Specifically, when comparing the contrast difference between the left and right sides of one pattern in region A in Figure 9(a) with the contrast difference between the left and right sides in region B in Figure 9(b), the contrast difference in region A is smaller than the contrast difference in region B, and the contrast difference in region B is more clearly noticeable than the contrast difference in region A.

[0140] Figures 9 (a) and (b) are diagrams illustrating a measurement image with a correction image applied and a measurement image without a correction image applied, and can be formed in various shapes, patterns, and sizes without being limited thereto depending on the image of the overlay measurement target T.

[0141] When detecting a measurement image from an overlay measurement target T, the overlay measurement method of the present invention calculates a correction image to correct structural errors caused by the influence of optics alignment, lens quality, stage leveling, etc., and applies the correction image to the measurement image to calculate an accurate measurement image, thereby improving measurement accuracy and enabling consistent results to be derived through automatic optimization based on the correction image data.

[0142] In particular, the error occurring for each overlay measurement device and wafer W can be automatically calculated and reflected in the actual overlay measurement, thereby optimizing the measurement recipe.

[0143] The present invention has been described with reference to the embodiments shown in the drawings, but these are merely illustrative, and those skilled in the art will appreciate that various modifications and equivalent embodiments are possible. Therefore, the true technical scope of the present invention should be determined by the technical ideas of the appended claims. [Explanation of symbols]

[0144] T ···Overlay measurement target W: Wafer 100...Light source section 110 Aperture 120 Spectral Filter 140 ···Beam splitter 200 ···Lens section 210 Objective lens 220 Lens focus actuator 300 Detector 400 Control unit 500 Stages

Claims

1. a light source configured to direct illumination onto an overlay metrology target formed on the wafer; an objective lens for focusing the illumination onto a measurement position of any one of the overlay measurement targets; and a lens unit having a lens focus actuator for adjusting a distance between the objective lens and the overlay measurement target; a detection unit that obtains a focus image at the measurement position through a beam reflected from the measurement position; a stage on which the wafer is seated; and a control unit that controls the lens unit to acquire the overlay measurement target, processes a first sample image of the overlay measurement target detected by the detection unit and a second sample image detected for the overlay measurement target rotated 180 degrees with respect to the first sample image, calculates a difference between the processed images, and calculates the difference as a correction image for correcting an image for measuring an overlay; Including, The control unit is a scale processing unit that acquires a corrected scale image by correcting a scale of the corrected image so that the scale of the corrected image is the same as that of a measurement image detected by the detection unit in order to measure alignment of a first overlay key and a second overlay key formed on the wafer; and an image correcting unit for correcting the measurement image by combining or deleting the correction scale image in pixel units; 1. An overlay metrology apparatus comprising:

2. The control unit is obtaining first image information including pixel information for the first sample image; normalizing each pixel for the first sample image on a pixel-by-pixel basis to obtain a first normalized image; 2. The overlay measurement apparatus of claim 1, further comprising: acquiring second image information including pixel information for the second sample image; and normalizing each pixel for the second sample image on a pixel-by-pixel basis to acquire a second normalized image.

3. The control unit is 2. The overlay measurement apparatus of claim 1, wherein the corrected image is calculated by calculating a pixel-by-pixel difference between a first normalized image obtained by processing the first sample image and a second normalized image obtained by processing the second sample image.

4. The control unit is a storage unit for storing the first sample image and the second sample image of the overlay measurement target; a normalization processing unit that normalizes each pixel forming the first sample image on a pixel-by-pixel basis to obtain a first normalized image, and normalizes each pixel forming the second sample image on a pixel-by-pixel basis to obtain a second normalized image; an image comparison unit that rotates either the first normalized image or the second normalized image by 180 degrees and compares the first normalized image with the second normalized image; and a corrected image calculation unit for calculating a difference between each pixel forming the first normalized image and the second normalized image, and calculating the corrected image; The overlay metrology apparatus of claim 1 , comprising:

5. The control unit is control the detection of 1-1 sample images to 1-n sample images at a first measurement position to an n-th measurement position among the overlay measurement targets formed at a plurality of measurement positions, and normalize each pixel of the 1-1 sample images to the 1-n sample images to obtain 1-1 normalized images to 1-n normalized images; controlling the detection of 2-1 sample images to 2-n sample images at the first measurement position to the nth measurement position, respectively; normalizing the pixels of the 2-1 sample images to 2-n sample images for each pixel to obtain 2-1 normalized images to 2-n normalized images; 2. The overlay measurement apparatus of claim 1, further comprising: calculating a difference between corresponding pixels from each pixel forming the first-n normalized image and each pixel forming the second-n normalized image; calculating an average of n pixels; and storing the average as the corrected image.

6. The control unit is 2. The overlay measurement apparatus according to claim 1, further comprising: a stage operating unit that rotatably controls the stage, wherein the second sample image is detected by rotating the stage by 180 degrees.

7. detecting a first sample image of an overlay measurement target formed on the wafer through a detector, and normalizing each pixel of the first sample image to obtain a first normalized image; detecting a second sample image for the overlay measurement target rotated 180 degrees with respect to the first sample image, and normalizing each pixel of the second sample image to obtain a second normalized image; a correction image calculating step of calculating a difference between a first normalized image obtained by processing the first sample image and a second normalized image obtained by processing the second sample image as a correction image; an image measuring step of measuring the overlay measurement target with the detector to detect a measurement image in order to measure alignment of a first overlay key and a second overlay key formed on the wafer; a scale processing step of obtaining a corrected scaled image by correcting the scale of the corrected image so that the scale of the corrected image is the same as that of the measurement image; and an image correction step of correcting the measurement image by combining or deleting the corrected scale image in pixel units from the measurement image to obtain a noise-free measurement image; An overlay metrology method comprising:

8. Prior to said second normalized image acquisition step, a wafer rotating step of rotating a stage on which the wafer is seated by 180 degrees so that the second sample image rotated by 180 degrees from the first sample image can be detected; The overlay metrology method of claim 7 , further comprising:

9. The first normalized image acquisition step includes: a first measurement step of detecting the first sample image at a first measurement location of the overlay metrology target; and a first normalization process for normalizing each pixel forming the first sample image to obtain a first normalized image; Including, The second normalized image acquisition step includes: a second measurement step of detecting the second sample image at the first measurement location; and a second normalization step of normalizing each pixel forming the second sample image to obtain a second normalized image; The overlay metrology method of claim 7 , comprising:

10. In the first measurement step, Detecting 1-1 sample images to 1-n sample images from the 1st measurement position to the nth measurement position among the overlay measurement targets formed at a plurality of measurement positions; In the first normalization step, normalizing each pixel of the 1-1 sample image to the 1-n sample image to obtain a 1-1 normalized image to a 1-n normalized image; In the second measurement step, detecting 2-1 sample images through 2-n sample images from the first measurement position through the nth measurement position, respectively; In the second normalization process, 10. The overlay measurement method of claim 9, further comprising: normalizing each pixel of the 2-1 sample image to the 2-n sample image to obtain 2-1 normalized images to 2-n normalized images.

11. In the step of calculating the corrected image, 11. The overlay measurement method of claim 10, further comprising: comparing the first-n normalized image and the second-n normalized image; calculating differences between corresponding pixels of each pixel forming the first-n normalized image and each pixel forming the second-n normalized image; calculating an average of n pixels; and storing the average as the corrected image.

12. In the step of calculating the corrected image, 8. The overlay measurement method of claim 7, further comprising: rotating one of the first normalized image or the second normalized image by 180 degrees, comparing the first normalized image with the second normalized image, and calculating a difference for each pixel forming the first normalized image and the second normalized image to calculate a corrected image.

Images