A method and device for measuring a mirror surface topography based on projection imaging contrast

Abstract

The application discloses a mirror surface topography measurement method and device based on projection imaging contrast, wherein the imaging plate in the device is parallel to the mirror surface placed at the measured point, and the optical axis of the camera is perpendicular to the imaging plate; the projection device is used for projecting the speckle picture to the measured mirror surface; the camera is used for collecting the speckle image reflected to the imaging plate by the measured mirror surface as a change image; the reference image is stored in the processor, and the reference image is the image collected by the camera when the reference flat mirror is placed at the measured point; the processor is further used for determining the three-dimensional topography of the measured mirror surface according to the displacement change amount of the speckle based on the reference image and the change image. The topography of the measured mirror surface is measured through the projection light reflection angle change principle, the defocus problem caused by the fact that the camera directly faces the mirror surface is avoided, the measurement accuracy of the warping deformation can reach the micron level, the detection efficiency is high, and the method is suitable for large batch rapid detection of actual production lines.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optical measurement, and more particularly, relates to a mirror surface topography measurement method and device based on projection imaging contrast. BACKGROUND

[0002] As an important material for manufacturing chips, the semiconductor polished wafer such as monocrystalline silicon wafer has very strict requirements on surface shape and size precision, and the precision even needs to reach nanometer level. If the appearance of such material is excessively warped and deflected, it will affect the subsequent production process flow, and even cause the final chip product to be unusable. In order to timely find out whether the semiconductor polished wafer in the actual production process is qualified, the detection process for its size and appearance is essential. However, the surface roughness of the polished silicon wafer, wafer and the like is very low, close to an optical mirror, and the conventional optical measurement technology cannot complete the detection.

[0003] For the size and appearance measurement of such a mirror, the interferometric measurement method and the phase deflection method are commonly used in industrial detection. The interferometric measurement method uses the interference phenomenon of waves to represent the appearance information of the object by interference fringes, and realizes the appearance measurement through phase calculation. This method has high measurement precision, but has limitations on the size of the mirror to be measured, has strict requirements on the measurement environment, and has a complex structure and high cost of the interferometer, so it is not suitable for actual industrial occasions. The phase deflection measurement system is composed of a fringe display screen, a mirror to be measured and a camera and the like. In the system, the fringe pattern on the display screen is reflected by the mirror to be measured, and is deformed by the modulation of the surface geometry, the phase information of the object surface is obtained according to the deformed fringe, and the object surface gradient is calculated from the phase information, and finally the mirror object appearance is constructed. Some researchers use a random speckle pattern instead of the fringe pattern on the display screen, match the speckle pattern in the picture collected by the camera, calculate the normal vector of each point of the mirror, obtain the mirror object surface gradient, and finally construct the mirror object appearance.

[0004] However, in the phase deflection measurement system, the camera is directly against the mirror, and since the depth of field of the imaging lens is limited, the display screen and the mirror to be measured cannot be clearly imaged at the same time. In addition, when the depth or curvature of the measured mirror object is large, the camera receives the reflected pattern through the mirror, and cannot guarantee that all the reflected patterns collected by the camera are within the depth of field, so that the image in some areas is out of focus, the image contrast is reduced, and the gradient calculation of some mirror range is greatly affected, which brings errors to the appearance measurement. In addition, the pattern of the display screen is reflected to the camera through the mirror, which causes the picture collected by the camera to be seriously disturbed by the ambient light. At the same time, the existing method needs to collect multiple images when measuring the mirror appearance, and the detection efficiency is low. SUMMARY

[0005] In view of the above defects or improvement needs of the prior art, the present application provides a mirror surface topography measurement method and device based on projection imaging contrast, thereby solving the problem of out-of-focus of camera image acquisition caused by large depth of the mirror surface topography to be measured in phase deflectometry.

[0006] To achieve the above object, according to a first aspect of the present application, a mirror surface topography measurement device based on projection imaging contrast is provided, comprising: an imaging plate, a camera, a projection device and a processor; wherein the imaging plate is parallel to the mirror surface placed at a measurement point, and the optical axis of the camera is perpendicular to the imaging plate;

[0007] The projection device is used for projecting a speckle picture to the mirror surface to be measured, and the camera is used for collecting the speckle image reflected by the mirror surface to be measured to the imaging plate as a change image;

[0008] The processor stores a reference image, which is an image collected by the camera when a reference flat mirror is placed at the measurement point; the processor is further used for determining the displacement change amount of the speckle of each sub-domain of the change image relative to each sub-domain of the reference image, to obtain the reflection angle change amount of each sub-domain of the mirror surface to be measured relative to each sub-domain of the reference flat mirror to the projection light, so as to obtain the tangential slope of each sub-domain of the mirror surface to be measured, to reconstruct the three-dimensional topography of the mirror surface to be measured.

[0009] According to a second aspect of the present application, a mirror surface topography measurement method based on projection imaging contrast is provided, applied to the measurement device of the first aspect, comprising:

[0010] S1, projecting a speckle picture to the mirror surface to be measured by the projection device, and collecting the speckle image reflected by the mirror surface to be measured to the imaging plate by the camera as a change image;

[0011] S2, determining the displacement change amount of the speckle of each sub-domain of the change image relative to each sub-domain of the reference image, to obtain the reflection angle change amount of each sub-domain of the mirror surface to be measured relative to each sub-domain of the reference flat mirror to the projection light, so as to obtain the tangential slope of each sub-domain of the mirror surface to be measured, to reconstruct the three-dimensional topography of the mirror surface to be measured; wherein the reference image is an image collected by the camera when a reference flat mirror is placed at the measurement point.

[0012] According to a third aspect of the present application, a mirror surface topography measurement system based on projection imaging contrast is provided, comprising: a computer readable storage medium and a processor;

[0013] The computer readable storage medium is used for storing executable instructions;

[0014] The processor is used for reading the executable instructions stored in the computer readable storage medium, and executing the measurement method as described in the first aspect.

[0015] According to a fourth aspect of the present application, a computer readable storage medium is provided, which stores computer instructions for causing a processor to perform the measurement method according to the first aspect.

[0016] Overall, compared with the prior art, the above technical solutions conceived by the present application can achieve the following beneficial effects:

[0017] 1、The mirror surface topography measurement method and device provided by the present application based on projection imaging contrast, the projected speckle is clearly imaged on the imaging plane after being reflected by the mirror surface to be measured, and the camera optical axis is perpendicular to the imaging plane for image acquisition; even if the mirror surface has a large depth or produces a large deformation, the speckle on the imaging plate is always within the camera depth of field range, ensuring that the camera can still acquire a clear image, and the image will not be blurred due to the object image being outside the camera depth of field range, thereby affecting the topography measurement. In addition, compared with the display screen display pattern used in conventional methods, the present application uses a high-contrast and high-brightness projection pattern, which is less affected by environmental light and can significantly reduce the interference of the external environment.

[0018] 2、The conventional phase deflection method requires precise adjustment of the angle between the camera, the mirror surface to be measured, and the display screen, while the mirror surface topography measurement method and device provided by the present application can arbitrarily adjust the position and angle of the projection device, as long as the mirror surface object to be measured and the reference flat mirror are both arranged parallel to the imaging plate, and the projector can form a complete image on the imaging plate, which can effectively improve the flexibility of system construction and be applied to various measurement scenarios. The reliability of the measurement results is ensured, and the mirror surface topography measurement precision is improved.

[0019] 3、The conventional method must change the phase image on the screen or move the display screen during measurement, and the camera acquires multiple images, which is complex to operate; while the mirror surface topography measurement method and device provided by the present application only needs to acquire one image for processing after calibration, and the entire topography can be obtained, which improves the detection efficiency and is suitable for rapid detection on actual production lines. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A structure schematic diagram of the mirror surface topography measurement device provided by the embodiment of the present application;

[0021] Figure 2 A flowchart of the mirror surface topography measurement method provided by the embodiment of the present application;

[0022] Figure 3 A calculation schematic diagram of the projection light reflection angle change of the (m, n) sub-domain of the mirror surface to be measured in the xoz plane of the camera coordinate system provided by the embodiment of the present application;

[0023] Figure 4 (a), (b), (c), and (d) in the figure are respectively the slope distribution diagrams along the horizontal and vertical directions of the silicon wafer surface, the three-dimensional topography diagram constructed from the slope, and the contour diagram obtained by cutting the measured three-dimensional topography of the silicon wafer along the x-direction.

[0024] Figure 5 (a) and (b) in the figure are schematic diagrams of the measurement principle of the existing phase deflection method and the mirror morphology provided in the embodiment of the present invention, respectively.

[0025] In all the accompanying drawings, reference numerals are used to denote elements or structures in the system, wherein:

[0026] 1-Imaging plate; 2-Reference flat mirror; 3-Camera; 4-Mirror to be tested; 5-Projection device; 6-Base; 7-Guide rail. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0028] This invention provides a specular topography measurement device based on projection imaging comparison, such as... Figure 1 As shown, it includes: an imaging plate 1, a camera 3, a projection device 5, and a processor; wherein, the imaging plate is parallel to the mirror surface placed at the point to be measured, and the optical axis of the camera is perpendicular to the imaging plate;

[0029] The projection device 5 is used to project the speckle image onto the mirror 4 to be tested, and the camera 3 is used to collect the speckle image reflected by the mirror 4 to be tested onto the imaging plate 1 as a change image.

[0030] The processor stores a reference image, which is an image captured by the camera 3 when the reference flat mirror 2 is placed at the test point. The processor is also used to determine the displacement change of speckle in each sub-domain of the changed image relative to each sub-domain of the reference image, so as to obtain the change of the reflection angle of the projected light in each sub-domain of the test mirror relative to each sub-domain of the reference flat mirror, thereby obtaining the slope of each sub-domain of the test mirror to reconstruct the three-dimensional morphology of the test mirror.

[0031] Furthermore, the change in displacement and the change in reflection angle satisfy the following relationship:

[0032]

[0033]

[0034] wherein, respectively, are the corresponding mirror subdomains B m，n to be measured corresponding to A m，n respectively, are the corresponding reference flat mirror subdomains D m，n respectively, are the corresponding reference flat mirror subdomains D m，n are the change amounts of the reflection angles of the projection light on the xoz plane and the yoz plane of the camera coordinate system, L d , L p respectively, are the distances between the imaging plate, the projection device and the reference flat mirror, respectively, are the light path lengths of the projection light on the xoz plane of the camera coordinate system, from the projection device to the reference flat mirror and from the reference flat mirror to the imaging plate, respectively, are the light path lengths of the projection light on the yoz plane of the camera coordinate system, from the projection device to the reference flat mirror and from the reference flat mirror to the imaging plate; Δx m，n , Δy m，n respectively, are the displacement change amounts of the speckles of B m，n relative to the speckles of A m，n on the x and y axes of the camera coordinate system, A m，n is the mth row n column subdomain obtained by dividing the reference image A, B m，n is the subdomain corresponding to A m，n in the change image B, obtained by searching in the change image through a two-dimensional digital image correlation algorithm;

[0035] The reflection angle change amount and the slope satisfy the following relationship:

[0036]

[0037] wherein, is the tangential slope of C m，n on the xoz plane and the yoz plane of the camera coordinate system.

[0038] It can be understood that, is actually the change amount of the tangential slope of C m，n relative to the tangential slope of D m，n on the xoz plane and the yoz plane of the camera coordinate system, since the tangential slopes of D m，n on the xoz plane and the yoz plane of the camera coordinate system are both 0, the change amount is the tangential slope of C m，n on the xoz plane and the yoz plane.

[0039] The three-dimensional topography of the mirror to be measured is represented by the height of the center point of each mirror subdomain to be measured, and the slope and the height of the mirror subdomain to be measured satisfy the following relationship:

[0040]

[0041] wherein, x m，n , y m，n , z m，n are the coordinates of the center point of the mth row and nth column sub-domain C m，n of the mirror surface to be measured in the camera coordinate system.

[0042] Further, the measuring device further comprises a base 6, and the imaging plate, the camera and the projection device are placed on the base, and the point to be measured is arranged on the base.

[0043] Further, the measuring device further comprises a guide rail 7 arranged on the base, and the point to be measured is arranged on the guide rail.

[0044] Specifically, the projection device 5 is fixed on the base 6 to project speckles in the direction of the mirror surface, the imaging plate 1 is fixed vertically to the base 6, the speckles projected by the projector are reflected by the mirror surface (a reference flat mirror or a mirror surface to be measured) and then imaged on the surface, the camera 3 collects images at a position directly opposite to the imaging plate 1, i.e., directly in front of the imaging plate, and the optical axis of the camera 3 is perpendicular to the imaging plate 1; the reference flat mirror is placed in front of the imaging plate and is parallel to the imaging plate; after the parameters of the projector and the camera are calibrated and a reference image is obtained, the reference image is stored in the processor, then the reference flat mirror is removed, the mirror surface to be measured is placed at the same position (i.e., the position of the reference flat mirror on the base), and the camera collects images again to obtain a change image.

[0045] Since the topography of the mirror surface object 4 to be measured is different from that of the reference flat mirror 2, the projection reflection angle changes, and the speckle pattern on the imaging plate 1 also changes accordingly, and the camera 3 collects the speckle image at this time as a change image; the processor determines the displacement change of the speckle of each sub-domain of the change image relative to the reference image to obtain the reflection angle change of each sub-domain of the mirror surface to be measured relative to each sub-domain of the reference flat mirror, so as to obtain the tangential slope of each sub-domain of the mirror surface to be measured, so as to reconstruct the three-dimensional topography of the mirror surface to be measured.

[0046] The mirror surface object to be measured refers to a kind of object with high reflectivity of rear surface, such as semiconductor silicon wafer, wafer, lens lens, etc.; the reference flat mirror is used as a measurement reference of the mirror surface to be measured, and generally has a flatness less than 1 μm and a surface roughness Ra value less than 0.01 μm, and has a high flatness requirement.

[0047] The embodiment of the present application provides a mirror surface topography measurement method based on projection imaging contrast, which is applied to the measuring device in any of the above embodiments, as shown in FIG. Figure 2 , and comprises:

[0048] S1, projecting a speckle picture to the mirror to be measured by the projection device, and collecting a speckle image reflected by the mirror to be measured to the imaging plate by the camera as a change image.

[0049] Further, before step S1, further comprising:

[0050] Calibrating internal parameters, distortion parameters of the projection device and the camera respectively, and a spatial pose relationship between the projection device and the camera.

[0051] S2, determining displacement change amounts of speckles of each sub-domain of the change image relative to each sub-domain of the reference image, to obtain reflection angle change amounts of each sub-domain of the mirror to be measured relative to each sub-domain of the reference flat mirror to the projection light, so as to obtain a tangential slope of each sub-domain of the mirror to be measured, to reconstruct a three-dimensional topography of the mirror to be measured; wherein the reference image is an image collected by the camera when the reference flat mirror is placed at the measurement point.

[0052] Further, step S2 comprises:

[0053] S21, dividing the reference image A to obtain a plurality of sub-domains A m，n , searching for a change image sub-domain B m，n corresponding to each reference image sub-domain in the change image B by using a two-dimensional digital image correlation algorithm;

[0054] S22, calculating displacement change amounts Δx m，n , Δy m，n of speckles of B m，n relative to speckles of A m，n in x, y axis directions of the camera coordinate system respectively, to determine reflection angle change amounts of the projection light on the xoz plane, yoz plane of the camera coordinate system respectively, of a mirror to be measured sub-domain C m，n corresponding to B m，n relative to a reference flat mirror sub-domain D m，n corresponding to A m，n , so as to obtain tangential slopes of a center point of C m，n on the xoz plane, yoz plane of the camera coordinate system.

[0055]

[0056]

[0057]

[0058] S23, reconstructing the three-dimensional topography of the mirror to be measured according to the formula .

[0059] wherein x m，n , y m，n , z m，n are the coordinates of the center point of the mth row and nth column sub-domain C m，n of the mirror surface to be measured in the camera coordinate system, L d , L p are the distances between the imaging plate, the projection device and the reference flat mirror, respectively, are the optical path lengths of the projection of the speckle pattern from the projection device to the reference flat mirror and the reflection of the speckle pattern from the reference flat mirror to the imaging plate in the xoz plane of the camera coordinate system, respectively, are the optical path lengths of the projection of the speckle pattern from the projection device to the reference flat mirror and the reflection of the speckle pattern from the reference flat mirror to the imaging plate in the yoz plane of the camera coordinate system, respectively.

[0060] Specifically, a random speckle pattern is designed in advance, the speckle pattern is embedded in the projection device 5 or the projection device 5 is connected to a computer for projection by the computer; then the speckle is projected to the surface of the reference flat mirror 2, and the speckle is imaged on the imaging plate 1 after being reflected by the mirror. At the same time, the reference flat mirror 2 is located at a certain position in front of the imaging plate 1 and is ensured to be parallel to the imaging plate 1. The camera 3 is fixed in position and its optical axis is ensured to be perpendicular to the imaging plate 1, and the projection device 5 and the camera 3 are calibrated.

[0061] The internal parameter matrices M p , M c , the distortion parameter matrices K p , K c and the spatial pose relationship between them, i.e. the coordinate system rotation matrix R and the translation matrix T, are obtained through the calibration process described above, by which the coordinate positions of the center points of each speckle sub-domain on the imaging plane of the imaging plate 1 in the plane are calculated; at the same time, the distance L d between the imaging plate 1 and the reference flat mirror 2, the distance L p between the projection device 5 and the reference flat mirror 2, and the position of the imaging plane in the camera coordinate system, i.e. the coordinate of the imaging plane in the z-axis direction of the camera coordinate system, are also obtained.

[0062] The projected speckle pattern can be any pattern that meets the requirements of digital image correlation calculation, and the projection device 5 is adjusted so that the speckle is clearly imaged on the imaging plate 1 and the appropriate projection picture size is ensured.

[0063] In addition, when determining the position of the camera 3, it should be ensured that the field of view of the camera 3 can cover the entire speckle area reflected by the mirror to be measured or the reference mirror to the imaging plate 1.

[0064] After calibration, the camera 3 collects the speckle image reflected by the reference flat mirror 2 to the imaging plate 1 as a reference image. The reference flat mirror 2 is removed, and the measured mirror object 4 is moved to the same position by the guide rail 7. Since the topography of the measured mirror object 4 is different from that of the reference flat mirror 2, the projection reflection angle changes, and the speckle pattern on the imaging plate 1 also changes accordingly. The camera 3 collects the speckle image at this time as a change image; by comparing the reference image and the change image, the speckle region of the reference image is divided into multiple subdomains, and the displacement of the speckle of B m，n relative to the speckle of A m，n is calculated according to the two-dimensional digital image correlation algorithm.

[0065] The subdomain C m，n of the measured mirror corresponding to B m，n is calculated according to the speckle displacement relative to the subdomain D i of the reference flat mirror corresponding to A m，n The reflection angle change value of the speckle picture along the horizontal and vertical directions The slope of each subdomain of the measured mirror is calculated again and the three-dimensional topography of the measured mirror object 4 is constructed from the slope.

[0066] As shown in Figure 3 , taking the light reflection calculation of a single subdomain in the xoz plane as an example, the speckle reflected by the reference flat mirror 2 falls on the initial point P, and after being replaced by the measured mirror 4, the reflection angle changes, and the position of the speckle changes to the current point P'. Through the parameters obtained in the calibration process, the initial reflection angle θ x of the speckle passing through the flat mirror subdomain in the xoz plane is calculated as follows: wherein represents the optical path length of the projection speckle reflected by the flat mirror and projected to the imaging plate 1 in the xoz plane, and the related parameters of the projector and the camera are obtained by the above calibration.

[0067] When the reflection angle changes, the angle α x between the reflected light in the xoz plane and the central axis is calculated as follows:

[0068] Then the reflection angle change value of the subdomain along the horizontal direction is Similarly, the reflection angle change value of the subdomain along the vertical direction is

[0069] Therefore, the horizontal projection light reflection angle change is calculated as shown in formula (1),

[0070]

[0071] wherein m and n represent the horizontal and vertical numbers of the measured mirror subdomain, and Δxm，n The lateral displacement of the speckle on the imaging plate 1, calculated using digital image correlation, represents the difference between the reference image and the changed image; the longitudinal reflection angle change... The derivation formula is similar to the above formula; simply change Δx. m，n Replace with Δy m，n ,Will Replace with That's all. This indicates the length of the optical path on the yoz plane after the projected speckle is reflected by the flat mirror and projected onto the imaging plate 1.

[0072] Then, the slope is calculated based on the change of the reflection angle of the projected light in each subdomain, as shown in formula (2).

[0073]

[0074] Then, using the least squares integral method based on finite difference, the relationship between the height z and slope of each subdomain of the mirror is calculated by formula (3), thereby constructing the three-dimensional shape W of the mirror to be tested.

[0075]

[0076] The measurement results of the morphology of the semiconductor silicon wafer after deformation are as follows: Figure 4 As shown in (a), (b), (c), and (d), the slope distribution along the transverse and longitudinal directions of the silicon wafer surface is as follows: Figure 4 As shown in (a) and (b) in the figure, the three-dimensional morphology constructed by the slope is as follows Figure 4 As shown in (c) in the figure, Figure 4 In the figure, (d) is the contour image obtained by cutting the measured three-dimensional shape of the silicon wafer along the x-direction.

[0077] like Figure 5 As shown in (a), in existing phase-deflection techniques, the camera directly captures the stripes or speckle patterns on the display screen through the mirror under test. Since the mirror under test may have significant depth or be distorted, it cannot be guaranteed that all reflected patterns captured by the camera are within the camera's depth of field. Once the image is outside the camera's depth of field, the image contrast in the out-of-focus area decreases, thus affecting the morphology measurement results. Figure 5 As shown in (b) of the present invention, the measuring device provided in this embodiment of the invention uses projected speckle to clearly image the image on the imaging surface 1 after reflection by the mirror to be measured. The camera 3 is directly facing the imaging surface 1 to collect the image. Even if the mirror has a large depth or produces a large deformation, the camera 3 can still collect a clear image without affecting the measurement result, and has high reliability and high precision.

[0078] This invention provides a mirror topography measurement system based on projection imaging comparison, comprising: a computer-readable storage medium and a processor;

[0079] The computer readable storage medium is configured to store executable instructions.

[0080] The processor is configured to read the executable instructions stored in the computer readable storage medium, and execute the measurement method according to any one of the above embodiments.

[0081] An embodiment of the present application provides a computer readable storage medium, which stores computer instructions, and the computer instructions are configured to make a processor execute the measurement method according to any one of the above embodiments.

[0082] Those skilled in the art can easily understand that the above description is only the preferred embodiment of the present application, and is not used to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A specular surface topography measuring apparatus based on projection imaging contrast, characterized by The method comprises the following steps: An imaging plate, a camera, a projection device and a processor are provided, wherein the imaging plate is parallel to a mirror placed at a measurement point, and the optical axis of the camera is perpendicular to the imaging plate; The projection device is used for projecting a speckle picture to the measured mirror, and the camera is used for collecting a speckle image reflected by the measured mirror to the imaging plate as a change image; A reference image is stored in the processor, and the reference image is an image collected by the camera when a reference flat mirror is placed at the measurement point; the processor is further used for determining a displacement change amount of speckles of each sub-domain of the change image relative to each sub-domain of the reference image, so as to obtain a reflection angle change amount of each sub-domain of the measured mirror relative to each sub-domain of the reference flat mirror, and thus to obtain a tangential slope of each sub-domain of the measured mirror, so as to reconstruct a three-dimensional topography of the measured mirror; The displacement change amount and the reflection angle change amount satisfy the following relationship: ； ； in, To and Corresponding mirror subdomain to be tested Compared to Corresponding reference flat mirror subdomain For the projection light in the camera coordinate system The change in the reflection angle on the surface, To and Corresponding mirror subdomain to be tested Compared to Corresponding reference flat mirror subdomain For the projection light in the camera coordinate system The change in the reflection angle on the surface, , These represent the distances between the imaging plate, the projection device, and the reference flat mirror, respectively. In the camera coordinate system On the surface, the projection device projects projection light onto a reference flat mirror, and the reference flat mirror reflects the projection light onto the imaging plate. (The optical path length is missing from the original text.) In the camera coordinate system On the surface, the projection device projects the projection light onto the reference flat mirror, and the reference flat mirror reflects the projection light onto the imaging plate. , They are respectively speckle relative to The displacement changes of the speckle along the x and y axes of the camera coordinate system. This refers to the subfield in the m-th row and n-th column obtained by dividing the reference image A. For the changing image B and The corresponding subdomain; The reflection angle change amount and the slope satisfy the following relationship: ， ； wherein is the tangent slope in the camera coordinate system of the plane The slope and the height of the sub-domain of the measured mirror satisfy the following relationship: ； in, , , These are the subfields in the m-th row and n-th column of the mirror to be tested. The center point is located in the camera coordinate system.

2. The measuring device of claim 1, wherein, A base is further provided, and the imaging plate, the camera and the projection device are placed on the base, and the measurement point is arranged on the base.

3. The measuring device of claim 2, wherein, A guide rail is further provided on the base, and the measurement point is arranged on the guide rail.

4. A method for specular surface topography measurement based on projection imaging contrast, applied to the measurement device according to any one of claims 1-3, characterized in that, The method comprises the following steps: S1, projecting a speckle picture to a measured mirror by the projection device, and collecting a speckle image reflected by the measured mirror to the imaging plate as a change image by the camera; S2, determining a displacement change amount of speckles of each sub-domain of the change image relative to each sub-domain of a reference image, so as to obtain a reflection angle change amount of each sub-domain of the measured mirror relative to each sub-domain of the reference flat mirror, and thus to obtain a tangential slope of each sub-domain of the measured mirror, so as to reconstruct a three-dimensional topography of the measured mirror; wherein the reference image is an image collected by the camera when a reference flat mirror is placed at the measurement point.

5. The method of measuring of claim 4, wherein, Step S2 comprises: S21, dividing the reference image A to obtain a plurality of sub-domains , using a two-dimensional digital image correlation algorithm to search for a change image sub-domain corresponding to each reference image sub-domain in the change image B ; S22, respectively calculate the displacement variation of the speckle of in the x, y axis direction of the camera coordinate system , to determine the to-be-measured mirror sub-domain corresponding to the displacement variation of the projection light in the x, y axis direction of the camera coordinate system , respectively the reflection angle of the plane, the reflection angle of the plane , so as to obtain the tangential slope of the center point of the plane, the plane, the plane in the camera coordinate system ;​ wherein , ； ， ； S23, according to the formula reconstructing the three-dimensional topography of the mirror to be measured; wherein, , , are the coordinates of the center point of the mth row and nth column sub-domain of the mirror surface to be measured in the camera coordinate system, , , are the distances between the imaging plate, the projection device and the reference flat mirror, respectively, are the optical path lengths of the projection device projecting the speckle picture to the reference flat mirror and the reference flat mirror reflecting the speckle picture to the imaging plate on the plane of the camera coordinate system, respectively, are the optical path lengths of the projection device projecting the speckle picture to the reference flat mirror and the reference flat mirror reflecting the speckle picture to the imaging plate on the plane of the camera coordinate system, respectively.

6. The method of claim 4 or 5, wherein, Before step S1, the following steps are further included: The internal parameters, distortion parameters of the projection device and the camera, and the spatial pose relationship between the projection device and the camera are calibrated.

7. A specular surface topography measurement system based on projection imaging contrast, characterized by The method comprises the following steps: A computer readable storage medium and a processor are provided; The computer readable storage medium is used for storing executable instructions; The processor is used for reading the executable instructions stored in the computer readable storage medium, and executing the measurement method according to any one of claims 4-6.

8. A computer-readable storage medium, characterized in that, The computer readable storage medium stores computer instructions, and the computer instructions are used for making the processor execute the measurement method according to any one of claims 4-6.

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