Sheet substrate surface topography measurement device and method based on metasurface holographic imaging

Abstract

The application provides a sheet substrate surface topography measuring device and method based on metasurface holographic imaging. The topography measuring device comprises an air floating bearing platform, a metasurface holographic projection unit, a high-precision displacement device, an image acquisition unit, an image processing unit and a controller; a regular micrometer-level dot array structure light field is projected to a sample surface by using a metasurface, a distorted light field modulated by the sample is captured by an imaging system, and a micro three-dimensional topography and thickness distribution of a large-area region are reconstructed synchronously and non-contactly by combining an image processing algorithm. The method avoids mechanical contact and optical damage, is not sensitive to changes in material optical properties, has the advantages of full-field, rapidness and high resolution, and is suitable for high-precision online detection of the surface topography of a sheet substrate.

Description

Technical Field

[0001] This invention belongs to the field of optical measurement and non-destructive testing technology, specifically relating to a sheet substrate surface morphology measurement device based on metasurface holographic imaging technology and a method for morphology measurement using the device. Background Technology

[0002] In the production and application of large-area sheet-type transparent substrates (such as polymer sheets like acrylic, specialty glass, and optical films), thickness uniformity and surface warpage are key parameters determining their optical performance, mechanical strength, and subsequent processing quality. These materials are widely used in aerospace, high-end display devices, precision instruments, and specialized building curtain walls. Therefore, developing rapid, high-precision, and non-contact large-area microstructure inspection technologies is of great significance for product quality control and process optimization.

[0003] Currently, the main methods for measuring the thickness and warpage of sheet-like substrates are laser triangulation and contact probe methods. However, both of these existing technologies have inherent limitations: Firstly, laser triangulation is susceptible to changes in the reflectivity and refractive index of the tested material, requiring frequent calibration in actual testing. Furthermore, this method often employs single-point or line scanning, resulting in low detection efficiency and complex system integration, making it difficult to meet the demands of batch and rapid testing. Secondly, contact probe methods, requiring physical contact with the tested substrate, pose a risk of scratching or damaging the surface, making them particularly unsuitable for optical-grade or soft thin-film materials. Additionally, the probe method has limited spatial resolution and a slow scanning speed, making it difficult to simultaneously achieve non-destructive, high-resolution, and rapid testing. Summary of the Invention

[0004] The purpose of this invention is to address the significant limitations of existing technologies in achieving rapid, non-contact, and high-precision detection of thickness uniformity and warpage in large-area transparent sheet-like substrates. This invention provides a device and method for measuring the surface morphology of sheet-like substrates based on metasurface holographic imaging. The invention utilizes a metasurface to generate a regular micron-scale lattice structured light field that is projected onto the sample surface. An imaging system captures the distorted light field modulated by the sample, and combined with image processing algorithms, synchronously and non-contactly reconstructs the microscopic three-dimensional morphology and thickness distribution of a large area. This invention avoids mechanical contact and optical damage, is insensitive to changes in the optical properties of the material, and offers advantages such as full-field, rapid, and high-resolution detection, making it suitable for high-precision online detection of the surface morphology of sheet-like substrates.

[0005] To achieve the above objectives, the technical solution provided by this invention is:

[0006] A sheet-type substrate surface morphology measurement device based on metasurface holographic imaging includes an air-bearing support platform, a metasurface holographic projection unit, a high-precision displacement device, an image acquisition unit, an image processing unit, and a controller;

[0007] The metasurface holographic projection unit includes a light source, a front lens group, and a transmissive metasurface device. The light source emits an illumination beam. The front lens group is positioned in the optical path between the light source and the transmissive metasurface device to guide and shape the illumination beam before it is incident on the transmissive metasurface device. The transmissive metasurface device modulates the phase or amplitude of the incident light wavefront after it has been shaped by the front lens group to form a regularly arranged dot matrix holographic image on or near the surface of the substrate under test located below it.

[0008] The image acquisition unit includes a rear lens group and a CCD image acquisition unit; the rear lens group is disposed in the optical path between the substrate under test and the CCD image acquisition unit, and is used to collect the deformed holographic dot matrix image after being acted upon by the substrate under test, and to image it onto the CCD image acquisition unit; the CCD image acquisition unit is used to convert the optical signal of the received deformed holographic dot matrix image into an image signal and output it.

[0009] The image processing unit is electrically connected to the CCD image acquisition unit to receive image signals and calculate the three-dimensional morphology information of the surface of the substrate under test by analyzing the geometric deformation and relative position changes of the deformed holographic dot matrix image.

[0010] The metasurface holographic projection unit and the image acquisition unit are respectively mounted on a high-precision displacement device. The high-precision displacement device is used to support and drive the metasurface holographic projection unit and / or the image acquisition unit to perform three-dimensional motion in order to realize the positioning, scanning and focusing adjustment of the measurement area.

[0011] An air-bearing support platform is positioned below the metasurface holographic projection unit to support and horizontally move the substrate to be tested, thereby enabling continuous measurement of different regions on it.

[0012] The controller is electrically connected to the high-precision displacement device, the air-bearing platform, and the image acquisition unit. The controller is configured to automatically control the linkage movement of the air-bearing platform and the high-precision displacement device according to the preset measurement area plan, so that the substrate under test is sequentially positioned to each preset measurement point, and the image acquisition unit is automatically triggered to acquire images at each measurement point.

[0013] Furthermore, the light source is a low-power laser source in the visible light band, with an output power of 0.1–3 mW.

[0014] Furthermore, the front lens group includes an aperture, a collimating lens, and a first polarization control element arranged along the optical path, used to shape, collimate, and adjust the polarization state of the received illumination beam to optimize the beam quality incident on the metasurface device to achieve a Gaussian distribution; the rear lens group includes an objective lens, a second polarization control element, and a convex lens arranged along the optical path.

[0015] Furthermore, the transmissive metasurface device includes a transparent substrate and an array of micro / nano structures fabricated on its surface; the micro / nano structures are nanorods, frustums, squares, pores, or crosses, and the size of a single micro / nano structure is 300–800 nm; the arrangement period of the micro / nano structure array is set so that the micro / nano structures can modulate the wavefront of incident light in a specific wavelength band to form a micron-scale dot matrix holographic image.

[0016] Furthermore, the image processing unit is configured to: receive the image signal of a dot matrix holographic image acted upon by the substrate under test; identify the positional offset of feature points in the dot matrix holographic image by running an image analysis algorithm, and calculate the surface gradient, three-dimensional height distribution, local thickness, and surface warpage of the substrate under test based on the positional offset.

[0017] Furthermore, the high-precision displacement device includes a multi-axis electrically controlled moving platform, with the metasurface holographic projection unit and image acquisition unit independently mounted on different moving parts of the multi-axis electrically controlled moving platform.

[0018] Furthermore, the multi-axis electrically controlled moving platform includes an X-axis moving platform, a Z-axis moving platform, and two Y-axis moving platforms;

[0019] Two Y-axis moving platforms are slidably set at the upper and lower ends of the Z-axis moving platform, respectively, and are used to independently adjust the position of the metasurface holographic projection unit and the image acquisition unit in the Y-axis; the moving range of the Y-axis moving platform is 0 to 50 cm, the moving step is 1 to 1000 μm, and the moving speed is 1 to 100000 μm / s.

[0020] The Z-axis moving platform is used to adjust the relative position between the two Y-axis moving platforms respectively; the moving range of both the X-axis and Z-axis moving platforms is 0 to 100 cm, the moving step length is 1 to 1000 μm, and the moving speed is 1 to 100000 μm / s.

[0021] Furthermore, the air-bearing support platform is used to provide air-bearing support to maintain the horizontal stability of the platform. It includes a first air-bearing support platform and a second air-bearing support platform that are vertically arranged on both sides of the high-precision displacement device, and a first moving roller assembly and a second moving roller assembly that are respectively arranged on the top of the first air-bearing support platform and the second air-bearing support platform. The first moving roller assembly and the second moving roller assembly are used to jointly support and horizontally move the test substrate located on it.

[0022] This invention also provides a method for measuring the surface morphology of sheet-like substrates based on metasurface holographic imaging, implemented using the sheet-like substrate surface morphology measuring device designed above; including the following steps:

[0023] Step 1: Initialize the sheet substrate surface morphology measurement device, including initializing the air-bearing platform, the high-precision displacement equipment control system, and the image processing unit;

[0024] Step 2: Preset measurement parameters based on the optical properties of the substrate to be tested, including the material refractive index and measurement distance; pre-plan the measurement area using the controller; start the light source and adjust its wavelength and power;

[0025] Step 3: Acquire a dot matrix holographic image of a high-flatness reference piece or a sample in a known flat area as a reference holographic dot matrix image, and use the center coordinates of each feature point on it as the reference coordinates;

[0026] Step 4: Place the substrate to be tested on the air-floating support platform. The controller automatically controls the air-floating support platform and the high-precision displacement device to move together, so that the substrate to be tested is sequentially positioned to each preset measurement point. At each measurement point, the image acquisition unit is automatically triggered to acquire the holographic image modulated on the surface of the substrate to be tested, and obtain a deformed holographic dot matrix image with geometric deformation and positional offset.

[0027] Step 5: Analyze the pixel offset of each feature point in the deformed holographic dot matrix image relative to the reference coordinates using the image processing unit, and calculate the three-dimensional morphology information of the substrate to be tested by combining it with the preset optical measurement model.

[0028] Furthermore, in step 5, the preset optical measurement model calculates the three-dimensional morphology information of the substrate to be tested using the following method:

[0029] (1) Based on the pixel offset , and the refractive index of the substrate to be tested Calculate the surface gradient:

[0030]

[0031]

[0032] in, This represents the surface gradient of the front surface of the substrate along the x-direction; This represents the surface gradient of the front surface of the substrate along the y-direction; The physical size of a unit pixel in a CCD image acquisition device; The vertical distance from the holographic projection dot matrix to the front surface of the substrate; , , Used as the reference coordinates; The coordinates of the pixel points of the feature points of the deformation lattice to be measured;

[0033] (2) The surface gradient field is integrated in two dimensions to reconstruct the three-dimensional height distribution of the front surface of the substrate. :

[0034]

[0035] (3) Calculate the local thickness and thickness uniformity of the substrate according to the following formula:

[0036]

[0037] in, The local thickness of the substrate represents the height difference between the rear surface and the front surface of the substrate. Distribution on the back surface of the substrate; It is distributed on the front surface of the substrate;

[0038]

[0039] in, Indicates thickness uniformity; , These represent the maximum and minimum values ​​of the substrate thickness within the measurement area, respectively. The average thickness of the substrate;

[0040] (4) Define the surface warpage by the difference between the maximum and minimum height of the substrate surface within the measurement area. :

[0041]

[0042] in, , These represent the maximum and minimum surface heights within the measurement area, respectively.

[0043] The advantages of this invention are:

[0044] 1. This invention utilizes metasurface holography to project a high-density, regular dot matrix light field covering a certain area in a single operation, and simultaneously acquires the image using a CCD image acquisition device, thereby achieving rapid acquisition and measurement of the surface morphology of sheet-like substrates and avoiding the risks of mechanical scanning and contact damage.

[0045] 2. To address the issue that traditional laser methods are susceptible to variations in material reflectivity and refractive index, requiring frequent calibration, this invention employs a visual computation method based on the spatial location and deformation analysis of feature points. This method detects the geometric distortion of the structured light field caused by the physical morphology of the sample, rather than relying on the absolute value of light intensity. Therefore, this method exhibits greater adaptability and robustness to substrates with different materials, surface treatments, or transparency, facilitating stable and high-precision measurements, and improving testing accuracy to the micrometer level; experimental verification shows a minimum measurement accuracy of 15 micrometers.

[0046] 3. This invention organically combines an air-bearing platform, a metasurface holographic projection unit, a high-precision displacement device, an image acquisition unit, and an image processing unit. The high-precision displacement device enables flexible positioning and scanning of the metasurface holographic projection unit and the image processing unit. The air-bearing platform supports the stable and continuous feeding of large substrates, making the measuring device of this invention not only suitable for fixed-point accuracy testing in the laboratory, but also compatible with production line environments, achieving high-efficiency, automated, continuous, multi-point measurement of large-size sheet substrates, meeting the needs of industrial quality control.

[0047] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0048] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0049] Figure 1 This is an overall schematic diagram of the sheet-type substrate surface morphology measurement device based on metasurface holographic imaging according to the present invention;

[0050] Figure 2 A schematic diagram of the layout of the optical detection section in this invention; the optical detection section includes a metasurface holographic projection unit, an imaging acquisition unit, and an optical imaging area;

[0051] Figure 3 This is a scanning electron microscope schematic diagram of the transmission metasurface device used in this invention;

[0052] Figure 4 This is a micron-scale dot matrix spatial holographic image photograph obtained by a transmissive metasurface device in this invention;

[0053] Figure 5 This is a one-dimensional side view of the dot matrix changes during the testing process in an application example of this invention;

[0054] Figure 6 This is a schematic diagram of the warped sheet substrate structure in an application example of the present invention; wherein Figure 6(a) is a schematic diagram of sheet warping; (b) is a schematic diagram of the displacement change of the test points on the surface of the warped sheet during the test.

[0055] Figure 7 This is a schematic diagram of the test results of the glass substrate in an application example of the present invention, wherein... Figure 7 (a) is the displacement field diagram; (b) is the surface gradient diagram; (c) is the reconstructed surface morphology diagram; and (d) is the warping distribution diagram.

[0056] In the figure: 1-First air-bearing support stage, 2-First moving roller assembly, 3-Substrate to be tested, 4-Metasurface holographic projection unit, 401-Light source, 402-Aperture, 403-Collimating lens, 404-First polarization control element, 405-Transmissive metasurface device, 5-Upper Y-axis moving axis, 6-Upper Y-roller, 7-Upper Y-support plate, 8-X-roller, 9-X-axis moving axis, 10-Z-axis moving axis, 11-Second moving roller assembly, 12-Second air-bearing support stage, 13-Image acquisition unit, 1301-Objective lens, 1302-Second polarization control element, 1303-Convex lens, 1304-CCD image acquisition device, 14-Lower Y-roller, 15-Lower Y-axis moving axis, 16-Image processing unit, 17-Optical imaging area, 1701-Holographic dot matrix image. Detailed Implementation

[0057] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0058] Reference Figure 1 and Figure 2 This invention provides a sheet-type substrate surface morphology measurement device based on metasurface holographic imaging, comprising an air-floating support platform, a high-precision displacement device, a metasurface holographic projection unit, an image acquisition unit 13, an image processing unit 16, and a controller (not shown in the figure). The controller is electrically connected to the high-precision displacement device, the air-floating support platform, and the image acquisition unit. The controller has a built-in storage unit for storing the planning information of the preset measurement area, including at least the scanning path, measurement point coordinates, and focusing parameters, and automatically generates control commands based on the planning information to coordinate the linkage movement of each actuator.

[0059] The high-precision displacement device is used to support and drive the metasurface holographic projection unit and / or image acquisition unit in three-dimensional space for independent or coordinated fixed motion. Its movement range, step accuracy, and speed are adjustable to achieve positioning, focusing, and scanning of the measurement area, and to adapt to the measurement needs of samples of different sizes. The high-precision displacement device includes a multi-axis electrically controlled moving platform. The metasurface holographic projection unit and image acquisition unit can be independently mounted on different moving parts of the multi-axis electrically controlled moving platform. The multi-axis electrically controlled moving platform includes an X-axis moving platform, a Z-axis moving platform, and two Y-axis moving platforms.

[0060] Two Y-axis moving platforms are defined as an upper Y-axis moving platform and a lower Y-axis moving platform. These platforms are slidably positioned above and below the Z-axis moving platform, respectively. The positions of the metasurface holographic projection unit and the image acquisition unit in the Y-axis can be independently adjusted by controlling the movement of the upper and lower Y-axis moving platforms. The upper Y-axis moving platform includes an upper Y-axis moving shaft 5, an upper Y-axis roller 6, and an upper Y-axis support plate 7. One end of the upper Y-axis moving shaft 5 is fixedly connected to the roller at the upper end of the Z-axis moving shaft 10, and moves synchronously up and down along the Z-axis with the roller. The upper Y-axis moving shaft 5 extends along the Y-axis, and the upper Y-axis roller 6 is mounted on it, forming a rolling engagement with the shaft, allowing it to reciprocate along the Y-axis. The upper Y-axis support plate 7 is a rigid connecting plate; its upper end is fixedly connected to the upper Y-axis roller 6, and its lower end is used to mount the metasurface holographic projection unit 4. The upper Y-axis moving axis 5 has a built-in drive motor, which is electrically connected to the controller. It can drive the upper Y-axis roller 6 to move along the upper Y-axis moving axis 5 according to the control command received from the controller, thereby driving the upper Y-axis support plate 7 and the metasurface holographic projection unit 4 installed on it to move along the Y-axis direction, thereby realizing the positioning of the metasurface holographic projection unit in the Y-axis direction.

[0061] The lower Y-axis 15 and the upper Y-axis 5 are independently arranged vertically, with one end fixedly connected to a roller at the lower end of the Z-axis 10. The lower Y-axis 15 also extends along the Y-axis, and the lower Y-axis roller 14 is mounted on it, forming a rolling engagement, allowing it to reciprocate along the Y-axis. The image acquisition unit 13 is fixedly connected to the top of the lower Y-axis roller 14 via a connecting bracket. The lower Y-axis 15 has a built-in drive motor, which is electrically connected to the controller. Based on the received commands from the controller, the drive motor can drive the lower Y-axis roller 14 to move along the lower Y-axis 15, thereby moving the image acquisition unit 13 along the Y-axis, thus achieving the positioning of the image acquisition unit 13 in the Y-axis direction. In this embodiment, the movement range of both the upper Y-axis 5 and the lower Y-axis 15 is 0–50 cm, the movement step length is 1–1000 μm, and the movement speed is 1–100000 μm / s.

[0062] The aforementioned X-axis, Z-axis, upper Y-axis, and lower Y-axis drive motors are all electrically connected to the controller. The controller, based on a preset measurement area plan, synchronously or independently controls the movement of each drive motor, enabling the metasurface holographic projection unit 4 and the image acquisition unit 13 to move independently or in conjunction in three-dimensional space, thus completing the positioning, scanning, and focusing adjustment of the measurement area.

[0063] The X-axis moving platform includes X-axis rollers 8 and an X-axis moving shaft 9. The X-axis moving shaft 9 is a long guide rail that spans above the air-bearing platform, with its top ends fixed to the two ends of a gantry (not shown in the figure) to form a stable beam structure. The X-axis rollers 8 are mounted on the bottom of the X-axis moving shaft 9 and form a rolling engagement with it, allowing them to reciprocate along the X-axis. The X-axis moving shaft 9 has a built-in drive motor, which is electrically connected to a controller and can drive the X-axis rollers 8 to move along the X-axis moving shaft 9 according to the controller's instructions.

[0064] The Z-axis moving platform includes a Z-axis moving shaft 10, which is a vertically arranged guide rail. Its upper end is fixedly connected to an X-axis roller 8, and it moves synchronously with the X-axis roller 8 along the X-axis direction. A Z-axis roller, capable of moving up and down along the Z-axis, is mounted on the Z-axis moving shaft 10, forming a rolling engagement with the Z-axis moving shaft 10. The Z-axis moving shaft 10 has a built-in drive motor, which is electrically connected to a controller. This drive motor can drive the Z-axis roller to rise and fall along the Z-axis moving shaft 10 according to commands from the controller, thereby adjusting the positions of the upper and lower Y-axis moving platforms in the Z-axis direction. In this embodiment, the movement range of both the X-axis and Z-axis moving platforms is 0–100 cm, the step size is 1–1000 μm, and the movement speed is 1–100000 μm / s.

[0065] An air-bearing platform is positioned below the metasurface holographic projection unit 4 to support and horizontally move the sheet-like substrate under test, enabling continuous measurement of different areas on it. In this invention, the air-bearing platform includes a first air-bearing support platform 1 and a second air-bearing support platform 12 vertically positioned on either side of the high-precision displacement device, and a first moving roller assembly 2 and a second moving roller assembly 11 respectively positioned on top of the first and second air-bearing support platforms. The first and second moving roller assemblies jointly support and horizontally move the sheet-like substrate under test located on them. The two moving roller assemblies are driven by motors and electrically connected to a controller, automatically conveying the substrate to each measurement point according to control commands output by the controller. The air-bearing platform is designed to effectively isolate environmental vibrations and ensure the stability of the mounting platform. Furthermore, the first and second moving roller assemblies 2 and 11, positioned on it as substrate conveying devices, enable stable and continuous horizontal transport of large sheet-like substrates, facilitating large-area, multi-point measurement. Specifically, the bottom of the two air-bearing support platforms is integrated with an air-bearing device to provide air-bearing support to maintain the horizontal stability of the platform, so as to meet the requirements of microscopic optical measurement for the reference surface; in this embodiment, the height of the air-bearing support platform is 80cm and the levelness is 0.02~0.05mm.

[0066] Reference Figure 1 and Figure 2 The metasurface holographic projection unit 4 includes a light source 401, a front lens group, and a transmissive metasurface device 405. The light source emits an illumination beam; the front lens group is disposed in the optical path between the light source and the transmissive metasurface device, guiding and shaping the illumination beam before it is incident on the transmissive metasurface device; the transmissive metasurface device modulates the phase or amplitude of the wavefront of the incident light after it has been shaped by the front lens group, so as to form a regularly arranged dot matrix holographic image on or near the surface of the substrate under test located below it. Specifically, in this embodiment, the light source 401 is a low-power laser source in the visible light band, whose wavelength can be modulated from 300 to 800 nm, and whose power is adjustable from 0.1 to 3 mW. The front lens group includes an aperture 402, a collimating lens 403, and a first polarization control element 404 arranged along the optical path. These elements are used to shape, collimate, and adjust the polarization state of the received illumination beam in sequence to optimize the beam quality incident on the metasurface device, i.e., to achieve a Gaussian distribution. In this embodiment, the first polarization control element is a quarter-wave plate.

[0067] The transmissive metasurface device 405 includes a transparent substrate and an array of micro / nanostructures fabricated on its surface. The micro / nanostructures can be nanorods, frustums, squares, apertures, or crosses, with individual micro / nanostructures ranging in size from 300 to 800 nm. By designing the periodic arrangement of the micro / nanostructures, the transmissive metasurface device can generate electromagnetic resonance with incident light of a specific wavelength band, thereby achieving phase modulation of the incident light wavefront and forming a micrometer-scale lattice-type holographic image. (Refer to...) Figure 3 In this embodiment of the invention, the transmissive metasurface device is an α-Si nanorod array constructed by vapor deposition. The nanorods have a length of 300–800 nm, a width of 50–200 nm, and a height of 500–3000 nm. By designing the periodic arrangement of the nanorods, the transmissive metasurface device 405 can perform phase modulation on the incident light wavefront, thereby generating a regularly arranged micron-scale lattice holographic image on or near the surface of the substrate under test. Figure 4 As shown. By adjusting the size of the metasurface nanorods, the minimum size of the holographic lattice can reach 10 μm, and the projection distance is adjustable within the range of 0–10 cm.

[0068] The image acquisition unit 13 includes a rear lens group and a CCD image acquisition unit 1304. The rear lens group is disposed in the optical path between the substrate under test and the CCD image acquisition unit 1304, and is used to collect multiple deformed holographic dot matrix images after being acted upon by the substrate under test, and to image them onto the CCD image acquisition unit. The CCD image acquisition unit is used to convert the light signals of the received deformed holographic dot matrix images into image signals and output them. Specifically, the rear lens group includes an objective lens 1301, a second polarization control element 1302, and a convex lens 1303 disposed along the optical path. When the incident light passes through the transmissive metasurface device 405, the generated holographic dot matrix image 1701 is projected onto or near the surface of the transparent substrate. The holographic image carrying surface morphology information is obtained by modulation on the substrate surface, and after passing through the objective lens 1301, the second polarization control element 1302, and the convex lens 1303 in sequence, it is imaged onto the photosensitive surface of the CCD image acquisition unit 1304. In this embodiment, the second polarization control element is a quarter-wave plate. In this embodiment, the CCD image acquisition device 1304 has a light response range of 300–1100 nm, a pixel size of less than 10 μm, and a transmission rate of 20–60 ms. The CCD image acquisition device 1304 transmits the acquired image signal to the image processing unit 16.

[0069] The image processing unit 16 is electrically connected to the CCD image acquisition unit and is capable of receiving image signals output by the CCD image acquisition unit. The image processing unit 16 is configured to: run an image recognition and analysis algorithm based on Matlab programming, automatically identify the center coordinates of each feature point in the spatial dot matrix in the image through the software, and calculate the pixel offset and image distortion information of each feature point by comparing it with a reference image acquired from a standard plane; and calculate the surface morphology information of the sheet substrate.

[0070] Figure 5 This is a one-dimensional side view schematic diagram illustrating the lattice changes during testing, representing an application example of the present invention. The curves in the diagram represent the surface contour of the sheet-like substrate along a certain direction; the horizontal axis represents the horizontal position, and the vertical axis represents the relative height. , These are the maximum (peak) and minimum (valley) values ​​of the surface height within the measurement area, respectively. The vertical distance between the peak and valley values ​​can be represented as the warp of the profile. Figure 6 This is a schematic diagram of the warped sheet substrate structure and a schematic diagram of the displacement change at the test points in an example of the present invention. Figure 6 (a) shows the structure of the substrate under test with warping deformation, where L represents the side length of the substrate under test; Figure 6 In (b), the grid points represent the test points of the holographic dot matrix, the arrows indicate the direction and magnitude of the lateral and longitudinal displacements of each point caused by the warping of the substrate, and the displacement vectors point to the valley or peak direction of the warping.

[0071] Based on the above principle, when the surface of the sheet-like substrate has warping or uneven thickness, the holographic dot array projected onto its surface will shift spatially with the change in surface morphology. The image processing unit can extract the shift and combine it with a preset optical measurement model to calculate the three-dimensional morphology, thickness uniformity, and surface warping of the substrate surface. The specific calculation process is as follows:

[0072] (1) Surface gradient calculation

[0073] Based on the pixel offset , and the refractive index of the substrate to be tested Calculate the surface gradient:

[0074]

[0075]

[0076] in, This represents the surface gradient of the front surface of the substrate along the x-direction; This represents the surface gradient of the front surface of the substrate along the y-direction; The physical size of a unit pixel in a CCD image acquisition device; The vertical distance from the holographic projection dot matrix to the front surface of the substrate; , , Used as the reference coordinates; The coordinates of the pixel points of the feature points of the deformation lattice to be measured are given.

[0077] (2) Calculate the height of the three-dimensional surface

[0078] By performing a two-dimensional integral on the surface gradient field, the three-dimensional height distribution of the front surface of the substrate can be reconstructed. :

[0079]

[0080] In this embodiment of the invention, the Fourier integral method is preferably used to quickly solve the height field: First, a two-dimensional Fourier transform is performed on the surface gradient field. After the height is calculated in the frequency domain, the three-dimensional surface height data in the spatial domain is obtained by inverse Fourier transform.

[0081] (3) Calculation of local thickness and thickness uniformity of substrate

[0082] By adjusting the focal length of the metasurface holographic projection unit, the projected holographic dot matrix is ​​made to clearly image or produce specific deformations on the front and back surfaces of the substrate under test in sequence, thereby separating and obtaining the height distribution of the two surfaces. Based on the difference between the two height distributions, the local thickness of the substrate is obtained. ;in, The local thickness of the substrate represents the height difference between the rear surface and the front surface of the substrate. Distribution on the back surface of the substrate; It is distributed on the front surface of the substrate.

[0083] After obtaining the local thickness distribution, the range method is used to characterize the thickness uniformity: The formula for calculating the thickness uniformity coefficient is: .in, Due to extremely poor thickness, Indicates the thickness uniformity coefficient. , These represent the maximum and minimum values ​​of the substrate thickness within the measurement area, respectively. The average thickness of the substrate.

[0084] (4) Surface warpage

[0085] Surface warpage is defined as the difference between the maximum and minimum height of the substrate surface within the measurement area. : ,in , These represent the maximum and minimum surface heights within the measurement area, respectively.

[0086] Through the above calculations and the fitting of data from multiple measurement areas, the three-dimensional morphology, thickness uniformity, and warpage distribution of the sheet substrate surface can be accurately obtained.

[0087] This invention also provides a method for measuring the surface morphology of sheet-like substrates based on metasurface holographic imaging. The following describes in detail the specific operational steps for surface morphology detection using the device of this invention, taking a glass sheet-like substrate as an example:

[0088] Step 1: System Initialization: The controller starts the air-floating support platform, making the platform stably suspended and ensuring that the level accuracy of the platform is better than 0.05mm; initializes the air-floating support platform, the high-precision displacement equipment control system and the image processing unit; puts the high-precision displacement equipment at the zero point position; and loads the preset measurement area planning parameters.

[0089] Step 2: Parameter setting: The operator sets the material parameters and measurement parameters of the substrate to be tested through the human-machine interface of the controller. The material parameters are determined according to the optical characteristics of the substrate to be tested, such as the refractive index of the material. The measurement parameters include the measurement distance D, the scanning area and the sampling interval, etc.

[0090] In this embodiment, the substrate material is soda-lime glass with a refractive index of 1.52; the vertical distance D from the holographic projection dot matrix to the front surface of the substrate is set to 1500mm; and the camera parameters are set, including a high-speed shutter of 1 / 1000s, a high ISO of 800, and a short focal length with a wide angle; these parameters will be used in subsequent morphology calculation formulas.

[0091] Turn on the light source and adjust its wavelength and power. Adjust the wavelength to the visible light range that matches the design wavelength of the transmissive metasurface device. In this example, the wavelength is 530nm, and the power is adjusted to 0.5mW to avoid thermal effects on the glass sample.

[0092] Step 3: Using a high-flatness reference sheet or a known flat area of ​​the substrate to be tested, acquire a reference holographic dot matrix image unaffected by deformation, and record the center coordinates of each feature point as the reference coordinates. Then, place the glass substrate to be tested stably on the air-floating support platform. Drive the high-precision displacement device to move the metasurface holographic projection unit and image acquisition unit above the measurement starting position, and use the high-precision displacement device to perform Z-axis focusing, so that the projected dot matrix image is clearly imaged on the sample surface.

[0093] Step 4: Automatic scanning and data collection.

[0094] The substrate to be tested is placed on the air flotation support platform, and the controller executes the following processes sequentially according to the preset scanning path:

[0095] Step 4.1: Drive the roller assembly of the air flotation support platform to move the substrate to be tested to a predetermined measurement point.

[0096] Step 4.2: Drive the high-precision displacement device to automatically adjust the focus position of the metasurface holographic projection unit and the image acquisition unit until the transmissive metasurface device projects a clear, regularly arranged dot matrix holographic image on or near the surface of the substrate to be tested.

[0097] Step 4.3: Trigger the image acquisition unit to acquire a dot matrix holographic image of the current measurement point modulated on the surface of the substrate to be tested, obtain a deformed holographic dot matrix image with geometric deformation and positional offset, and record the pixel center coordinates of the dot matrix. .

[0098] Step 4.4: Using a high-precision displacement device, the air-floating support platform moves the substrate to be tested to the next preset measurement point. Repeat the image projection, autofocus, and image acquisition steps of steps 4.1-4.3 until the scanning of all preset measurement areas is completed, and the deformed holographic dot matrix image of each measurement point is obtained.

[0099] Step 5: The image processing unit runs an image recognition and analysis algorithm based on Matlab to automatically identify and extract the center coordinates of each feature point of the holographic dot matrix in each acquired image. The system calculates the pixel offset of feature points relative to the reference coordinates in the deformed holographic dot matrix image of each measurement point, and combines this with a preset optical measurement model to calculate parameters such as the surface three-dimensional morphology, thickness uniformity, and surface warpage of the substrate under test. A visualized report is generated, including a surface three-dimensional morphology cloud map, contour map, cross-sectional profile curve, and quantitative data such as flatness and warpage. The inspection results of the glass substrate in the application example are as follows: Figure 7 As shown, where:

[0100] Figure 7 (a) is a displacement field diagram. The diagram shows the lateral displacement of each light point in the holographic array before and after passing through the glass in the form of vector arrows, with the unit being millimeters. The direction and length of the arrows represent the displacement direction and magnitude, respectively. This diagram intuitively reflects the light deflection effect caused by the local tilt of the glass surface and is the direct input for subsequent gradient calculations.

[0101] Figure 7 (b) is a schematic diagram of the surface gradient field. Based on the glass thickness and refractive index, the displacement field is converted into the slope distribution of the glass surface along the X and Y directions, showing the magnitude and direction of the normal tilt at each point on the surface. It is a key intermediate quantity connecting displacement observation and morphology reconstruction.

[0102] Figure 7Image (c) shows the reconstructed surface topography, a three-dimensional surface plot obtained by numerically integrating the gradient field (in this embodiment, the Poisson equation is used for solving). The coordinate axes represent spatial positions in millimeters; the height axis represents the relative height of the glass surface in millimeters. This image fully presents the overall surface topography features of the inspected glass, including depressions, convexities, and wavy deformations. The inspection area exhibits slight warping deformation, with the peak value located at coordinates (350.5 mm, 156.0 mm) and a height of +0.0064 mm; the valley value located at (185.9 mm, 96.8 mm) and a height of -0.0048 mm. The overall topography shows a distribution characteristic of slight concavity in the center and local convexity at the edges.

[0103] Figure 7 Image (d) shows the reconstructed surface topography. This image uses a pseudo-color two-dimensional plot to display the planar projection of the same height data. The color from blue to red represents a monotonically increasing height from negative to positive. The image directly reveals the peak and valley locations and the overall warping symmetry, and the root mean square (RMS) value is calculated accordingly as a basis for quantitatively assessing the warping level. The quantitative calculation results are shown in Table 1.

[0104] Table 1. Three-dimensional topography information

[0105]

[0106] The above results verify the micron-level accuracy of the device of the present invention in detecting the surface morphology and thickness uniformity of glass substrates. It can output multi-dimensional detection results such as displacement field map, surface gradient field map, reconstructed surface morphology map and warpage distribution map, providing comprehensive data support for the quality assessment of glass substrates.

[0107] The device of this invention is not limited to the detection of the aforementioned glass substrates, but can also be applied to the surface morphology detection of various transparent or semi-transparent sheet-type substrates such as quartz substrates and ultra-thin polymer film materials. Because this invention is based on a geometric analysis method of feature point spatial position offset, it does not depend on the intensity of reflected light from the surface of the material being tested, thus exhibiting good adaptability to materials with different optical properties.

[0108] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention.

Claims

1. A sheet-type substrate surface morphology measurement device based on metasurface holographic imaging, characterized in that, It includes an air-bearing platform, a metasurface holographic projection unit, a high-precision displacement device, an image acquisition unit, an image processing unit, and a controller; The metasurface holographic projection unit includes a light source, a front lens group, and a transmissive metasurface device; the light source is used to emit an illumination beam; the front lens group is disposed in the optical path between the light source and the transmissive metasurface device, and is used to guide and shape the illumination beam before it is incident on the transmissive metasurface device; The transmissive metasurface device is used to modulate the phase or amplitude of the incident light wavefront after it has been shaped by the front lens group, so as to form a regularly arranged dot matrix holographic image on the surface of the substrate under test or in the space near it. The image acquisition unit includes a rear lens group and a CCD image acquisition device; the rear lens group is disposed in the optical path between the substrate under test and the CCD image acquisition device, and is used to collect the deformed holographic dot matrix image after being acted upon by the substrate under test, and to image it onto the CCD image acquisition device; the CCD image acquisition device is used to convert the optical signal of the received deformed holographic dot matrix image into an image signal and output it. The image processing unit is electrically connected to the CCD image acquisition unit and is used to receive the image signal and calculate the three-dimensional morphology information of the surface of the substrate under test by analyzing the geometric deformation and relative position change of the deformed holographic dot matrix image. The metasurface holographic projection unit and the image acquisition unit are respectively mounted on the high-precision displacement device. The high-precision displacement device is used to support and drive the metasurface holographic projection unit and / or the image acquisition unit to perform three-dimensional motion, so as to realize the positioning, scanning and focusing adjustment of the measurement area. The air-bearing support platform is located below the metasurface holographic projection unit and is used to support and horizontally move the substrate to be tested, so as to realize continuous measurement of different areas on it. The controller is electrically connected to the high-precision displacement device, the air-bearing platform, and the image acquisition unit. The controller is configured to automatically control the linkage movement of the air-bearing platform and the high-precision displacement device according to the preset measurement area plan, so that the substrate under test is sequentially positioned to each preset measurement point, and the image acquisition unit is automatically triggered to acquire images at each measurement point.

2. The sheet-type substrate surface morphology measuring device according to claim 1, characterized in that, The light source is a low-power laser source in the visible light band, with an output power of 0.1 to 3 mW.

3. The sheet-type substrate surface morphology measuring device according to claim 2, characterized in that, The front lens group includes an aperture, a collimating lens, and a first polarization control element arranged along the optical path, used to shape, collimate, and adjust the polarization state of the received illumination beam to optimize the beam quality incident on the metasurface device to achieve a Gaussian distribution; the rear lens group includes an objective lens, a second polarization control element, and a convex lens arranged along the optical path.

4. The sheet-type substrate surface morphology measuring device according to claim 1, characterized in that, The transmissive metasurface device includes a transparent substrate and an array of micro / nano structures fabricated on its surface; the micro / nano structures are nanorods, frustums, squares, pores, or crosses, and the size of a single micro / nano structure is 300–800 nm; the arrangement period of the micro / nano structure array is set so that the micro / nano structures can modulate the wavefront of incident light in a specific wavelength band to form a micron-scale dot matrix holographic image.

5. The sheet-type substrate surface morphology measuring device according to claim 1, characterized in that, The image processing unit is configured to: receive the image signal of a dot matrix holographic image acted upon by the substrate under test; identify the positional offset of feature points in the dot matrix holographic image by running an image analysis algorithm, and calculate the surface gradient, three-dimensional height distribution, local thickness and surface warpage of the substrate under test based on the positional offset.

6. The sheet-type substrate surface morphology measuring device according to claim 1, characterized in that, The high-precision displacement device includes a multi-axis electrically controlled moving platform, and the metasurface holographic projection unit and the image acquisition unit are independently installed on different moving parts of the multi-axis electrically controlled moving platform.

7. The sheet-type substrate surface morphology measuring device according to claim 6, characterized in that, The multi-axis electrically controlled moving platform includes an X-axis moving platform, a Z-axis moving platform, and two Y-axis moving platforms; The two Y-axis moving platforms are respectively slidably disposed at the upper and lower ends of the Z-axis moving platform, and are used to independently adjust the position of the metasurface holographic projection unit and the image acquisition unit in the Y-axis; the moving range of the Y-axis moving platform is 0-50cm, the moving step length is 1-1000μm, and the moving speed is 1-100000μm / s; The Z-axis moving platform is used to adjust the relative position between the two Y-axis moving platforms respectively; the moving range of the X-axis moving platform and the Z-axis moving platform is 0-100cm, the moving step length is 1-1000μm, and the moving speed is 1-100000μm / s.

8. The sheet substrate surface morphology measuring device according to claim 7, characterized in that, The air-bearing support platform is used to provide air-bearing support to maintain the horizontal stability of the platform. It includes a first air-bearing support platform and a second air-bearing support platform that are vertically arranged on both sides of the high-precision displacement device, and a first moving roller assembly and a second moving roller assembly that are respectively arranged on the top of the first air-bearing support platform and the second air-bearing support platform. The first moving roller assembly and the second moving roller assembly are used to jointly support and horizontally move the substrate to be tested located on it.

9. A method for measuring the surface morphology of a sheet-like substrate based on metasurface holographic imaging, implemented using the sheet-like substrate surface morphology measuring device according to any one of claims 1 to 8, characterized in that, Includes the following steps: Step 1: Initialize the sheet-type substrate surface morphology measurement device, including initializing the air-bearing platform, the high-precision displacement equipment control system, and the image processing unit; Step 2: Preset measurement parameters based on the optical properties of the substrate to be tested, including the material refractive index and measurement distance; preset the measurement area using the controller; start the light source and adjust its wavelength and power; Step 3: Acquire a dot matrix holographic image of a high-flatness reference piece or a sample in a known flat area as a reference holographic dot matrix image, and use the center coordinates of each feature point on it as the reference coordinates; Step 4: Place the substrate to be tested on the air-floating support platform. The controller automatically controls the air-floating support platform and the high-precision displacement device to move together, so that the substrate to be tested is sequentially positioned to each preset measurement point. At each measurement point, the image acquisition unit is automatically triggered to acquire the holographic image modulated on the surface of the substrate to be tested, and a deformed holographic dot matrix image with geometric deformation and positional offset is obtained. Step 5: Analyze the pixel offset of each feature point in the deformed holographic dot matrix image relative to the reference coordinates using the image processing unit, and calculate the three-dimensional morphology information of the substrate to be tested by combining it with the preset optical measurement model.

10. The method for measuring the surface morphology of a sheet-type substrate according to claim 9, characterized in that, In step 5, the preset optical measurement model calculates the three-dimensional morphology information of the substrate to be tested using the following method: (1) Based on the pixel offset , and the refractive index of the substrate to be tested Calculate the surface gradient: in, This represents the surface gradient of the front surface of the substrate along the x-direction; This represents the surface gradient of the front surface of the substrate along the y-direction; The physical size of a unit pixel in a CCD image acquisition device; The vertical distance from the holographic projection dot matrix to the front surface of the substrate; , , Used as the reference coordinates; The coordinates of the pixel points of the feature points of the deformation lattice to be measured; (2) The surface gradient field is integrated in two dimensions to reconstruct the three-dimensional height distribution of the front surface of the substrate. : (3) Calculate the local thickness and thickness uniformity of the substrate according to the following formula: in, The local thickness of the substrate represents the height difference between the rear surface and the front surface of the substrate. Distribution on the back surface of the substrate; Distribution on the front surface of the substrate; in, Indicates thickness uniformity; , These represent the maximum and minimum values ​​of the substrate thickness within the measurement area, respectively. The average thickness of the substrate; (4) Define the surface warpage by the difference between the maximum and minimum height of the substrate surface within the measurement area. : in, , These represent the maximum and minimum values ​​of the surface height within the measurement area, respectively.

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