Optical imaging detection device and autofocusing method thereof
By setting a common light source for the focusing mark area and imaging field of view in the optical imaging detection equipment, the problem of inconsistent light source wavelengths in the autofocus system is solved, and the imaging system and the focusing system achieve co-illumination and co-imaging, which improves the stability and accuracy of the focusing system and ensures high-precision detection of the sample under test.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANGHAI JINGJI SEMICON TECH CO LTD
- Filing Date
- 2024-12-25
- Publication Date
- 2026-06-26
Smart Images
Figure CN122284079A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of optical imaging technology, and in particular to an optical imaging detection device and its automatic focusing method. Background Technology
[0002] Defect detection is an essential part of semiconductor manufacturing. Commonly used optical inspection equipment employs the imaging principle of a microscope in conjunction with a high-sensitivity camera to acquire high-resolution images. To obtain high-resolution images, high-NA objectives must be used, which results in an object-side depth of focus of around 100 nanometers. Therefore, autofocus technology is indispensable to maintain clear imaging.
[0003] In existing optical inspection equipment, a separate autofocus optical path is typically required. The wavelength of the light source used for autofocus is inconsistent with that of the uniform light source used for imaging. The focusing system needs to be equipped with projection and detection slits, which must be precisely aligned. Furthermore, since focusing systems are based on energy detection, they are sensitive to energy fluctuations, affecting the autofocus performance. Summary of the Invention
[0004] This invention provides an optical imaging detection device and its automatic focusing method. By setting a field stop with a focus marking area, the focusing optical path is coupled into the optical imaging detection device. The focusing optical path and the imaging optical path use the same light source, which improves focusing stability and ensures detection effect.
[0005] In a first aspect, embodiments of the present invention provide an optical imaging detection device, comprising:
[0006] The worktable is used to hold the sample to be tested and to allow for multi-degree-of-freedom movement;
[0007] A light source, used to emit and transmit incident light beams;
[0008] The field stop includes a light-transmitting imaging field of view and a light-transmitting focus mark area. The incident beam forms a first incident sub-beam through the imaging field of view and a second incident sub-beam through the focus mark area.
[0009] The objective lens unit is used to converge the first incident sub-beam and the second incident sub-beam onto the sample under test, and to collect the first reflected sub-beam of the first incident sub-beam reflected by the surface of the sample under test and the second reflected sub-beam of the second incident sub-beam reflected by the surface of the sample under test.
[0010] A baffle unit is used to block part of the second incident sub-beam to adjust the numerical aperture of the second incident beam as it is focused onto the sample under test by the objective lens unit.
[0011] The first detection unit is used to receive the first reflective sub-beam to generate a detection image of the sample to be tested;
[0012] The second detection unit is used to receive the second reflective sub-beam and obtain the imaging position of the focus mark area;
[0013] The control unit acquires the focus signal calibration relationship of the sample under test based on multiple detection images, the imaging position acquired synchronously with the multiple detection images, and the corresponding position of the stage. Based on the imaging position acquired in real time during the detection process and the focus signal calibration relationship, the control unit adjusts the position of the stage so that the test area of the sample under test is located on the focal plane of the objective lens unit. The control unit then detects the sample under test based on the detection image when the test area of the sample under test is located on the focal plane.
[0014] In a second aspect, embodiments of the present invention provide an autofocus method, applied to the optical imaging detection device described in any one of the first aspects, comprising:
[0015] The control stage moves the sample to be tested along a direction perpendicular to the plane of the stage. The first detection unit acquires the detection images of the sample to be tested at different positions of the stage, and the second detection unit simultaneously acquires the imaging position of the focus mark area at different positions of the stage. During the movement of the stage, the corresponding detection images include a process of change from blurry to clear and then back to blurry.
[0016] Based on the acquired multiple detection images, the position of the worktable corresponding to the detection image with the clearest image and the imaging position of the focus mark area corresponding to the detection image with the clearest image are marked as the zero point position of the focus signal.
[0017] Based on the zero-point position, the defocusing amount of the test area of the sample under test and the relative value of the imaging position are obtained when the stage is in different positions;
[0018] Mathematical fitting is performed on the relative values of multiple defocus amounts and corresponding imaging positions to establish the focus signal calibration relationship of the sample under test.
[0019] Based on the relative value of the imaging position collected in real time during the detection process and the calibration relationship of the focus signal, the real-time defocus amount of the test area of the sample to be tested is obtained.
[0020] The stage is adjusted based on the real-time defocusing amount so that the test area of the sample is located on the focal plane.
[0021] The technical solution of this invention provides an optical imaging detection device. By setting a light-transmitting imaging field of view and a light-transmitting focus mark area in the field of view aperture, the light emitted from the light source forms a first incident sub-beam for imaging the sample under test through the imaging field of view and a second incident sub-beam for focusing through the focus mark area. This achieves shared illumination and imaging optical path for the imaging system and the focusing system, eliminating the need for an additional focusing system and saving space and cost. Simultaneously, the shared light source effectively avoids the deviation between the zero plane of the focusing system and the zero plane of the imaging system caused by chromatic aberration. It also avoids the need for precise matching steps between the projection slit and the detection slit in an independent focusing system, reducing system integration difficulty, ensuring the stability of the focusing system, and guaranteeing accurate detection of the sample under test. Furthermore, the optical imaging detection device utilizes a baffle unit to reduce the numerical aperture of the second incident sub-beam emitted through the focus mark area, which is then converged to the sample under test by the objective lens unit. This improves the accuracy of obtaining the imaging position of the focus mark area, thereby achieving precise focusing and ensuring the subsequent detection effect of the sample under test.
[0022] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description
[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0024] Figure 1 This is a schematic diagram of the structure of an optical imaging detection device provided in an embodiment of the present invention;
[0025] Figure 2 This is a schematic diagram of the structure of a field stop provided in an embodiment of the present invention;
[0026] Figure 3 This is a schematic diagram of another optical imaging detection device provided in an embodiment of the present invention;
[0027] Figure 4 This is a schematic diagram of another field stop provided in an embodiment of the present invention;
[0028] Figure 5 This is a schematic diagram of another field stop provided in an embodiment of the present invention;
[0029] Figure 6This is a schematic diagram of another field stop provided in an embodiment of the present invention;
[0030] Figure 7 This is a schematic diagram of another optical imaging detection device provided in an embodiment of the present invention;
[0031] Figure 8 This is a schematic diagram of the structure of a cylindrical mirror unit provided in an embodiment of the present invention;
[0032] Figure 9 This is a schematic diagram of another cylindrical mirror unit provided in an embodiment of the present invention;
[0033] Figure 10 This is a schematic diagram of another optical imaging detection device provided in an embodiment of the present invention;
[0034] Figure 11 This is a flowchart illustrating an autofocus method provided in an embodiment of the present invention.
[0035] Figure 12 This is a graph illustrating the calibration relationship of a focus signal, provided as an embodiment of the present invention. Detailed Implementation
[0036] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.
[0037] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.
[0038] Figure 1 This is a schematic diagram of the structure of an optical imaging detection device provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of the structure of a field stop provided in an embodiment of the present invention, as shown below. Figure 1 and Figure 2 As shown, the optical imaging detection device includes: a stage 110 for carrying the sample 111 to be tested and performing multi-degree-of-freedom motion; a light source (not shown) for emitting an incident light beam; a field stop 202, including a light-transmitting imaging field of view 1a and a light-transmitting focusing mark area 3a, wherein the incident light beam forms a first incident sub-beam through the imaging field of view 1a and a second incident sub-beam through the focusing mark area 3a; an objective lens unit 112 for converging the first and second incident sub-beams onto the sample 111 to be tested, and collecting the first reflected sub-beam of the first incident sub-beam reflected from the surface of the sample 111 and the second reflected sub-beam of the second incident sub-beam reflected from the surface of the sample 111; and a baffle unit 203 for blocking part of the second incident sub-beam to adjust the second incident sub-beam. The numerical aperture of the sample 111 is converged by the objective lens unit 112; the first detection unit 115 is used to receive the first reflector beam to generate a detection image of the sample 111; the second detection unit 303' is used to receive the second reflector beam and obtain the imaging position of the focus mark area 3a; the control unit 400 obtains the focus signal calibration relationship of the sample 111 based on multiple detection images, the imaging position obtained synchronously with the multiple detection images and the corresponding position of the stage 110, adjusts the position of the stage 110 based on the imaging position and the focus signal calibration relationship acquired in real time during the detection process, so that the test area of the sample 111 is located on the focal plane of the objective lens unit 112, and detects the sample 111 based on the detection image when the test area of the sample 111 is located on the focal plane.
[0039] The light source can be a point source, a line source, or a surface source. The incident beam emitted from the light source can be polychromatic or monochromatic light. The field stop 202 has a first region 202a corresponding to the effective field of view of the objective lens 112. A light-transmitting imaging field of view region 1a and a light-transmitting focus mark region 3a are configured within the first region 202a. For example, the imaging field of view region 1a can be set as an inscribed rectangle of the first region 202a to ensure the maximum field of view corresponding to the first detection unit 115. One or more focus mark regions 3a can be set, and the shape of the focus mark region 3a can be selected according to actual design requirements. This embodiment of the invention does not impose specific limitations. The imaging field of view region 1a and the focus mark region 3a are isolated by a non-transparent area. The imaging field of view 1a of the field stop 202, the objective lens unit 112, and the first detection unit 115 can form an imaging system. Specifically, when the imaging system detects and images the sample 111 to be tested, the incident light beam emitted from the light source forms a first incident sub-beam through the imaging field of view 1a. The first incident light beam is converged onto the sample 111 to be tested by the objective lens unit 112 and reflected by the surface of the sample 111 to form a first reflected sub-beam. The first reflected sub-beam is then collected by the objective lens unit 112 and received by the first detection unit 115 to generate a detection image of the sample 111 to be tested. The focusing mark area 3a of the field stop 202, the objective lens unit 112, and the second detection unit 303' can form a focusing system. Specifically, the focusing optical path of the focusing system is as follows: the incident light beam emitted from the light source passes through the focusing mark area 3a to form a second incident sub-beam; the second incident light beam is converged by the objective lens unit 112 onto the sample 111 to form the focusing mark area projection 3a'; the focusing mark area projection 3a' is reflected by the sample 111 to form a second reflected sub-beam; the second reflected sub-beam is then collected by the objective lens unit 112 and received by the second detection unit 303'. The second detection unit 303' includes an image sensor or an energy sensor. The photosensitive surface of 03' forms an image of the second reflective sub-beam (focus mark area image 3a") or spot energy, and then calculates the imaging position of the focus mark area 3a for subsequent autofocusing. In this embodiment, the incident beam of the imaging optical path and the incident beam of the focusing optical path are generated by the same light source, avoiding the deviation between the zero plane of the focusing system and the zero plane of the imaging system caused by chromatic aberration; the entire focusing optical path only sets the focus mark area 3a in the field stop 202, and there is no need to make a receiving mark area at the second detection unit 303', so there is no problem of precise alignment between the projection slit and the detection slit, reducing the integration difficulty, improving the stability of the focusing system, and ensuring the focusing effect.
[0040] The optical imaging detection device also includes a baffle unit 203, which is positioned on the side of the field stop 202 away from the light source to block part of the second incident beam. For example... Figure 1As shown, the edges corresponding to the second incident sub-beam emitted from the focus mark area 3a of the field stop 202 are denoted as 3a0 and 3a2. After the baffle unit 203 blocks part of the light from the second incident sub-beam, part of the beam between edge line 3a0 and edge line 3a1 is blocked. The remaining beam between edge line 3a1 and edge line 3a2 is incident on the objective lens unit 112. After passing through the objective lens unit 112, edge lines 3a1 and 3a2 are denoted as aperture edge lines 3a1' and 3a2', respectively. After being reflected by the sample 111 and collected by the objective lens unit 112, aperture edge lines 3a1' and 3a2' are denoted as aperture edge lines 3a1' and 3a2', respectively. Aperture edge lines 3a1' and 3a2' constitute the aperture angle of the focus mark area 3a. The angle between the aperture edge 3a2' and the normal of the sample 111 is the outer aperture angle θ of the objective lens unit 112, representing the outermost angle of the numerical aperture of the objective lens unit 112. The angle between the aperture edge 3a1' and the normal of the sample 111 represents the inner aperture angle of the projection of the focus mark area 3a' onto the sample 111. Thus, with the help of the baffle unit 203, the numerical aperture of the second incident sub-beam emitted through the focus mark area 3a and converged to the sample 111 by the objective lens unit 112 is reduced, ensuring clear imaging of the focus mark area 3a on the second detection unit 303' and achieving precise focusing.
[0041] The optical imaging inspection equipment also includes a control unit 400, which is connected to the first detection unit 115, the second detection unit 303', and the stage 110. To ensure accurate focusing and inspection of the sample 111 under test, the control unit 400 controls the stage 110 to move the sample 111 under test in multiple degrees of freedom. The control unit 400 records the position of the stage 110, and correspondingly enables the first detection unit 115 to acquire multiple inspection images of the sample 111 under test, and the second detection unit 303' to simultaneously acquire the corresponding imaging position of the focus mark area 3a. During the inspection process, the stage 110 carries the sample 111 under test and achieves multi-degree-of-freedom movement to perform image acquisition of the sample 111 under test at different positions, thereby completing the inspection of the sample 111 under test. As the sample 111 moves vertically, the imaging position of the focus mark area 3a on the second detection unit 303' changes. The control unit 400, based on multiple detection images, synchronously acquired imaging positions, and the corresponding position of the stage 110, obtains the focus signal calibration relationship of the sample 111. This calibration relationship is the correspondence between the defocus amount of the test area of the sample 111 and the relative value of the imaging position of the focus mark area 3a when the stage 110 is in different positions. The imaging position of the focus mark area 3a is directly measured by the second detection unit 303', making it insensitive to energy fluctuations caused by the light source or sample surface pattern, thus improving process adaptability and the stability of the focusing system. The control unit 400 adjusts the position of the stage 110 based on the real-time acquired imaging positions and the focus signal calibration relationship during the detection process, ensuring that the test area of the sample 111 is located on the focal plane of the objective lens unit 112, guaranteeing that the first detection unit 115 acquires a high-resolution detection image of the test area of the sample 111. The area to be detected in the sample 111 is located on the surface of the sample 111, and the area to be detected in the sample 111 can be determined according to the actual detection requirements. The control unit 400 detects the sample 111 based on the detection image when the area to be detected in the sample 111 is located on the focal plane, so as to ensure the detection accuracy of the sample 111.
[0042] Based on the principle of optical imaging, by controlling the position of the baffle unit 203 to adjust the amount of light blocking, the aperture angle of the second incident sub-beam emitted through the focus mark region 3a can be adjusted, so that the numerical aperture NAx' of the focus mark region projection 3a' in the focus detection direction, such as the X direction of the object plane, is much smaller than the numerical aperture NA of the objective lens unit 112. Preferably, controlling the numerical aperture NAx' to within 6° can make NAx' / NA ≤ 0.2. When the target condition is met, a small defocusing amount of the sample 111 can cause a significant change in the imaging position of the focus mark region 3a. The numerical aperture NAx” of the focus mark region 3a in the image side is even smaller, satisfying: NAx” = NAx' / β, where β is the system magnification. Therefore, when the sample 111 defocuses, it has virtually no impact on the clarity of the projection 3a' of the focus mark region in the X direction, which is beneficial for the edge extraction accuracy of the image 3a” of the focus mark region in the measurement section direction, thus improving the defocusing measurement accuracy. This invention does not control NAy' in the Y direction of the object plane. Since this direction is not within the focusing measurement section and is a non-measurement direction, the clarity of the image in this direction has no impact on the focusing measurement accuracy. At the same time, the large numerical aperture in this direction ensures sufficient light energy to reach the second detection unit 303', which is beneficial for obtaining a stable measurement signal.
[0043] The optical imaging inspection device also includes an imaging relay unit 114. Taking an optical imaging inspection device that meets the following conditions as an example: the magnification β of the system composed of the objective lens unit 112 and the imaging relay unit 114 is 50, the numerical aperture NA of the objective lens unit 112 is 0.9, and the external aperture angle θ of the objective lens unit 112 is 64°, where NA = n*sinθ, and n is the refractive index of the medium between the objective lens unit 112 and the sample 111 to be tested. Correspondingly, when the baffle unit 203 is not added, the angle between the aperture edge 3a2' and the normal of the sample 111 to be tested, or the angle between the aperture edge of the imaging field region 1a and the normal of the sample 111 to be tested, is the external aperture angle θ of the objective lens, and the numerical aperture NAx' of the projection of the focusing mark region 3a' is 0.9. This invention adjusts the baffle 203a so that the numerical aperture NAx' of the projection 3a' of the focus mark area meets the aforementioned target range. At this point, the movement of the image 3a" of the focus mark area in the second detection unit 303' is Z' = δz * 2 * β * tanθ. According to the aforementioned formula, when the vertical defocusing amount δz of the sample 111 under test is 0.1 μm, the movement of the image 3a" of the focus mark area in the second detection unit 303' is approximately 20.5 μm, and the numerical aperture NAx" of the image 3a" on the image side is 0.002, i.e., 0.1 / 50. Clearly, relative to the 0.1 μm defocusing amount of the sample 111 under test, the focusing signal detected by this invention, i.e., the displacement of 20.5 μm, achieves a signal amplification effect of 205 times. Therefore, it can detect the vertical displacement of the sample 111 under test with extremely high sensitivity. Meanwhile, since the numerical aperture NAx” of the focus mark area image 3a” is very small, the focus mark area image 3a” will have a sufficient range of clear imaging. That is, the defocus amount of the sample 111 under test has basically no effect on the clarity of the focus mark area image 3a” formed by the projection 3a’ of the focus mark area in the second detection unit 303’, thereby greatly improving the position detection accuracy of the sample 111 under test and realizing high-precision focusing of the sample 111 under test.
[0044] This invention, through the setting of an imaging field of view and a focus mark area within the field of view aperture, allows the light emitted from the light source to pass through the imaging field of view to form a first incident sub-beam for imaging the sample under test, and through the focus mark area to form a second incident sub-beam for focusing. This achieves shared illumination and imaging optical paths for the imaging and focusing systems, eliminating the need for an additional focusing system and saving space and cost. Simultaneously, the shared light source effectively avoids deviations between the zero plane of the focusing system and the zero plane of the imaging system caused by chromatic aberration. It also avoids the need for precise matching steps between the projection slit and the probe slit in independent focusing systems, reducing system integration difficulty, ensuring the stability of the focusing system, and guaranteeing accurate detection of the sample under test. Furthermore, the optical imaging detection device utilizes a baffle unit to reduce the numerical aperture of the second incident sub-beam emitted through the focus mark area, which is then converged to the sample under test by the objective lens unit. This improves the accuracy of acquiring the imaging position of the focus mark area, thereby achieving precise focusing and ensuring the subsequent detection effect of the sample under test.
[0045] Optional, see reference Figure 1 and Figure 2 An imaging field of view region 1a and a focus mark region 3a are configured within the first region 202a of the field of view aperture 202. The imaging field of view region 1a is located in the central region of the field of view aperture 202, corresponding to the effective field of view that the first detection unit 115 can acquire. The focus mark region 3a is located outside the imaging field of view region 1a, corresponding to the effective field of view that the second detection unit 303' can acquire. The focus mark region 3a and the imaging field of view region 1a are isolated by a non-transparent area.
[0046] Optional, continue to refer to Figure 2 The focus mark area 3a can be a light-transmitting area of any shape. For example, the focus mark area 3a can be any shape such as a rectangle, square, circle, ellipse, triangle, or irregular shape; this embodiment of the invention does not impose specific limitations. In this embodiment, the focus mark area 3a is shown as a rectangle.
[0047] Optional, see reference Figure 1 The optical imaging detection device also includes an illumination relay mirror unit 201 and a beam splitter unit 113. The illumination relay mirror unit 201 is used to collimate the first incident sub-beam and the second incident sub-beam. The beam splitter unit 113 is used to coaxially couple the collimated first incident sub-beam with the first reflected sub-beam and the collimated second incident sub-beam with the second reflected sub-beam. The first incident sub-beam is incident on the sample 111 to be tested through the illumination relay mirror unit 201, the beam splitter unit 113 and the objective lens unit 112 in sequence to form the first reflected sub-beam. The second incident sub-beam is incident on the sample 111 to be tested through the illumination relay mirror unit 201, the beam splitter unit 113 and the objective lens unit 112 in sequence to form the second reflected sub-beam.
[0048] The propagation paths of the first and second incident sub-beams emitted through the field stop 202 are further provided with an illumination relay mirror unit 201 and a beam splitter unit 113. After being collimated by the illumination relay mirror unit 201, the first incident sub-beam is incident on the beam splitter unit 113. The beam splitter unit 113 reflects the first incident sub-beam and incident on the objective lens unit 112. The objective lens unit 112 converges the beam onto the sample 111 to be tested, and the first reflected sub-beam is generated by reflection from the surface of the sample 111. The first reflected sub-beam is collected by the objective lens unit 112 and emitted on the beam splitter unit 113. The beam splitter unit 113 coaxially couples the collimated first incident sub-beam with the first reflected sub-beam and incident on the first detection unit 115. The second incident sub-beam is collimated by the illumination relay mirror unit 201 and then incident on the beam splitting unit 113. The beam splitting unit 113 reflects the second incident sub-beam and incident on the objective lens unit 112. The objective lens unit 112 converges the beam onto the sample 111 to be tested, and the second reflected sub-beam is generated by reflection from the surface of the sample 111. The reflected sub-beam is collected by the objective lens unit 112 and emitted to the beam splitting unit 113. The beam splitting unit 113 coaxially couples the collimated second incident sub-beam with the second reflected sub-beam and then incident on the second detection unit 303'.
[0049] Optional, see reference Figure 1 The baffle unit 203 is located between the illumination repeater unit 201 and the field stop 202, or between the light source and the field stop 202. For example, the baffle unit 203 is positioned between the illumination repeater unit 201 and the field stop 202. The incident light beam emitted from the light source exits through the focusing mark area 3a with a certain aperture angle in the field stop 202. Part of the light from the second incident sub-beam is blocked by the baffle unit 203 to reduce the aperture angle of the second incident sub-beam incident on the illumination repeater unit 201, ensuring that the second incident sub-beam meets the preset target aperture angle, thereby guaranteeing clear imaging of the adjusted second incident sub-beam on the second detection unit 303'.
[0050] In addition, the baffle unit 203 can be placed between the light source and the field stop 202. The baffle unit 203 adjusts the aperture angle of the incident beam emitted from the light source, reducing the aperture angle of the incident beam incident on the focus mark area 3a of the field stop 202, thereby reducing the aperture angle of the second incident sub-beam emitted through the focus mark area 3a, so that the second incident sub-beam meets the preset target aperture angle, thereby ensuring clear imaging of the adjusted second incident sub-beam on the second detection unit 303'.
[0051] Optional, see reference Figure 1The optical imaging detection device also includes an imaging relay unit 114. The first reflector beam passes through the objective lens unit 112 and the beam splitter unit 113 in sequence, and is then amplified by the imaging relay unit 114. After that, it is received by the first detection unit 115 to generate a detection image. The second reflector beam passes through the objective lens unit 112 and the beam splitter unit 113 in sequence, and is then amplified by the imaging relay unit 114. After that, it is received by the second detection unit 303' to obtain the imaging position of the focus mark area 3a.
[0052] An imaging relay unit 114 is also provided on the propagation path of the first and second reflective sub-beams. The first and second reflective sub-beams, which are emitted sequentially from the objective lens unit 112 and the beam splitter unit 113, are incident on the imaging relay unit 114. The imaging relay unit 114 amplifies the first reflective sub-beam and emits it to the first detection unit 115. The first detection unit 115 receives the amplified first reflective sub-beam to generate a detection image of the sample 111 to be tested, ensuring the clarity of the detection image. The imaging relay unit 114 amplifies the second reflective sub-beam and emits it to the second detection unit 303'. The second detection unit 303' receives the amplified second reflective sub-beam to obtain the imaging position of the focus mark area 3a, ensuring the accurate acquisition of the imaging position of the focus mark area 3a.
[0053] Optionally, the focus mark region 3a can be configured as one or more. When the focus mark region 3a is configured as one, both the baffle unit 203 and the second detection unit 303' are configured as one. When the focus mark region 3a is configured as multiple, both the baffle unit 203 and the second detection unit 303' are configured as multiple, and each focus mark region 3a is configured with one baffle unit 203 and one second detection unit 303'. Each baffle unit 203 is used to block part of the light of the second incident sub-beam formed by the corresponding focus mark region 3a, and each second detection unit 303' is used to receive the second reflected sub-beam formed by the corresponding focus mark region 3a to obtain the imaging position of the corresponding focus mark region 3a.
[0054] The focus mark area 3a is configured as one or more, and each focus mark area 3a is correspondingly configured with a baffle unit 203 and a second detection unit 303', for example, as shown in the figure. Figure 2As shown, a focus mark area 3a can be set in the field stop 202, and a baffle unit 203 and a second detection unit 303' are set accordingly. The incident beam emitted from the light source passes through the focus mark area 3a to form a second incident sub-beam. The baffle unit 203 blocks part of the light of the second incident sub-beam, and the remaining second incident sub-beam is collimated by the illumination relay mirror unit 201 and then incident on the beam splitting unit 113. The beam splitting unit 113 reflects the collimated second incident sub-beam and incident on the objective lens unit 112. The objective lens unit 112 converges the beam onto the sample 111 to form a focus mark area projection 3a'. The focus mark area projection 3a' reflects to form a second reflective sub-beam. The second reflective sub-beam is then collected by the objective lens unit 112, the beam splitting unit 113 and the imaging relay unit 114 and received by the corresponding second detection unit 303' to generate the imaging position of the focus mark area 3a.
[0055] For example, Figure 3 This is a schematic diagram of another optical imaging detection device provided in an embodiment of the present invention. Figure 4 This is a schematic diagram of another field stop structure provided in an embodiment of the present invention, as shown below. Figure 3 and Figure 4As shown, the field stop 202 has two focus marking areas, including a first focus marking area 3a1 and a second focus marking area 3a2 spaced apart along the Z direction. The first direction is the Z direction. Correspondingly, there are two baffle units, namely 203a and 203b, and two second detection units, namely 303a and 303b. The focusing system includes a first focusing system and a second focusing system. The first focusing system includes the first focus marking area 3a1, the first baffle unit 203a, the objective lens unit 112, and the first sub-detection unit 303a; the second focusing system includes the second focus marking area 3a2, the second baffle unit 203, the objective lens unit 112, and the second sub-detection unit 303b. The incident light beam emitted from the light source passes through the first focusing mark area 3a1 to form a first beam of the second incident sub-beam. The first baffle unit 203a blocks part of the light from the first beam of the second incident sub-beam. The first beam of the second incident sub-beam is collimated by the illumination relay mirror unit 201 and then incident on the beam splitting unit 113. The beam splitting unit 113 reflects the collimated first beam of the second incident sub-beam and incident on the objective lens unit 112. The objective lens unit 112 converges the first beam of the second incident sub-beam onto the sample 111 to be tested, and generates a first beam of the second reflected sub-beam through reflection from the surface of the sample 111. The first beam of the second reflected sub-beam passes through the objective lens unit 112 and the beam splitting unit 113 in sequence and is incident on the imaging relay unit 114. The first beam of the second reflected sub-beam is magnified and then incident on the first sub-detection unit 303a. The first sub-detection unit 303a receives the magnified first beam of the second reflected sub-beam and obtains the imaging position of the first focusing mark area 3a1.
[0056] Synchronously, the incident beam emitted from the light source passes through the second focusing mark area 3a2 to form a second incident sub-beam. The second baffle unit 203 blocks part of the light from the second incident sub-beam. The second incident sub-beam is collimated by the illumination relay mirror unit 201 and then incident on the beam splitting unit 113. The beam splitting unit 113 reflects the collimated second incident sub-beam and incident on the objective lens unit 112. The objective lens unit 112 focuses the second incident sub-beam onto the sample 111 to be tested, and generates a second reflected sub-beam through reflection from the surface of the sample 111. The second reflected sub-beam passes through the objective lens unit 112 and the beam splitting unit 113 in sequence and is incident on the imaging relay unit 114. The second reflected sub-beam is magnified and then incident on the second sub-detection unit 303b. The second sub-detection unit 303b receives the magnified second reflected sub-beam and obtains the imaging position of the second focusing mark area 3a2.
[0057] By utilizing the first baffle unit 203a, the numerical aperture of the projected first focusing mark area 3a1 is less than 0.1, and by utilizing the second baffle unit 203, the numerical aperture of the projected second focusing mark area 3a2 is less than 0.1. This ensures the imaging clarity of the first focusing mark area 3a1 in the first sub-detection unit 303a and the imaging clarity of the second focusing mark area 3a2 in the second sub-detection unit 303b. At this time, the first focusing mark area 3a1 and the second focusing mark area 3a2 are arranged along the Z direction and will image at the sample 111 under test along the X direction. Based on the imaging process, two height data in the X direction can be obtained, enabling detection of the sample 111 under test in the RY direction. That is, the difference between the two height distances in the X direction can be calculated, and the offset in the RY direction can be calculated based on the difference and the ratio of the actual distances of the first focusing mark area 3a1 and the second focusing mark area 3a2. This enables detection of the sample 111 under test in the RY direction, and the offset is combined to improve compensation accuracy and detection accuracy.
[0058] Or, for example, Figure 5 This is a schematic diagram of another field stop structure provided in an embodiment of the present invention, as shown below. Figure 5 As shown, the field stop 202 has two focus mark areas, a third focus mark area 3a3 and a fourth focus mark area 3a4 spaced apart along the Y direction. The second direction is the Y direction, and correspondingly, two baffle units and two second detection units are provided. The focusing system includes a third focusing system and a fourth focusing system. The third focusing system includes the third focus mark area 3a3, a third baffle unit, an objective lens unit 112, and a third sub-detection unit; the fourth focusing system includes the fourth focus mark area 3a4, a fourth baffle unit, an objective lens unit 112, and a fourth sub-detection unit. The incident beam emitted from the light source forms a third beam of the second incident sub-beam through the third focusing mark area 3a3. The third baffle unit blocks part of the light of the third beam of the second incident sub-beam. The third beam of the second incident sub-beam is collimated by the illumination relay mirror unit 201 and then incident on the beam splitting unit 113. The beam splitting unit 113 reflects the collimated third beam of the second incident sub-beam and incident on the objective lens unit 112. The objective lens unit 112 focuses the third beam of the second incident sub-beam onto the sample 111 to be tested, and generates a third beam of the second reflected sub-beam through the reflection of the surface of the sample 111. The third beam of the second reflected sub-beam is incident on the imaging relay unit 114 through the objective lens unit 112 and the beam splitting unit 113 in sequence. After being magnified, the third beam of the second reflected sub-beam is incident on the third sub-detection unit. The third unit 303c receives the magnified third beam of the second reflected sub-beam and obtains the imaging position of the third focusing mark area 3a3.
[0059] Synchronously, the incident beam emitted from the light source passes through the fourth focusing mark area 3a4 to form the fourth beam of the second incident sub-beam. The fourth baffle unit blocks part of the light of the fourth beam of the second incident sub-beam. The fourth beam of the second incident sub-beam is collimated by the illumination relay mirror unit 201 and then incident on the beam splitting unit 113. The beam splitting unit 113 reflects the collimated fourth beam of the second incident sub-beam and incident on the objective lens unit 112. The objective lens unit 112 focuses the fourth beam of the second incident sub-beam onto the sample 111 to be tested, and generates the fourth beam of the second reflection sub-beam by reflection from the surface of the sample 111. The fourth beam of the second reflection sub-beam passes through the objective lens unit 112 and the beam splitting unit 113 in sequence and is incident on the imaging relay unit 114. The fourth beam of the second reflection sub-beam is magnified and then incident on the fourth sub-detection unit. The fourth sub-detection unit receives the magnified fourth beam of the second reflection sub-beam and obtains the imaging position of the fourth focusing mark area 3a4.
[0060] By utilizing the third baffle unit, the numerical aperture of the projected third focusing mark area 3a3 is made less than 0.1, and by utilizing the fourth baffle unit, the numerical aperture of the projected fourth focusing mark area 3a4 is made less than 0.1. This ensures the imaging clarity of the third focusing mark area 3a3 in the third sub-detection unit and the imaging clarity of the fourth focusing mark area 3a4 in the fourth sub-detection unit. At this time, the third focusing mark area 3a3 and the fourth focusing mark area 3a4 are arranged along the Y direction and will image at the test sample 111 along the Y direction. Based on the imaging process, two height data in the Y direction can be obtained, enabling the detection of the test sample 111 in the RX direction. That is, the difference between the two height distances in the Y direction can be calculated, and the offset in the RX direction can be calculated based on the difference and the ratio of the actual distances of the third focusing mark area 3a3 and the fourth focusing mark area 3a4. This enables the detection of the test sample 111 in the RX direction, and the offset is combined to improve compensation accuracy and detection accuracy.
[0061] Similarly, in Figure 3 , Figure 4 and Figure 5 On this basis, Figure 6 This is a schematic diagram of another field stop structure provided in an embodiment of the present invention, as shown below. Figure 6As shown, the field stop 202 is provided with four focusing mark areas, including a first focusing mark area 3a1 and a second focusing mark area 3a2 spaced apart along the Z direction, and a third focusing mark area 3a3 and a fourth focusing mark area 3a4 spaced apart along the Y direction. Correspondingly, four baffle units and four second detection units are provided. The first focusing mark area 3a1 and the second focusing mark area 3a2 are arranged along the Z direction. The incident beam emitted from the light source passes through the first focusing mark area 3a1 to form a first beam of the second incident sub-beam, and the incident beam emitted from the light source passes through the second focusing mark area 3a1 to form a second beam of the second incident sub-beam. The first beam of the second incident sub-beam and the second beam of the second incident sub-beam will image at the sample 111 to be tested along the X direction. The corresponding control unit 400 can obtain two height data in the X direction to realize the detection of the sample 111 to be tested in the RY direction. The third focusing mark region 3a3 and the fourth focusing mark region 3a4 are arranged along the Y direction. The incident beam emitted from the light source forms a third beam of the second incident sub-beam through the third focusing mark region 3a3, and the incident beam emitted from the light source forms a fourth beam of the second incident sub-beam through the fourth focusing mark region 3a4. The third and fourth beams of the second incident sub-beams image the sample 111 under test along the Y direction. The corresponding control unit 400 can obtain two height data in the Y direction, realizing the detection of the sample 111 under test in the RX direction. The control unit 400 can also calculate the defocus amount of the sample 111 under test by averaging the four height data, reducing the influence of the pattern and local surface shape of the sample 111 under test on the measurement, realizing the detection of the sample 111 under test in the Z direction, RX, and RY, realizing tilt measurement and compensation, and further improving the compensation accuracy and detection accuracy.
[0062] Optional, Figure 7 This is a schematic diagram of another optical imaging detection device provided in an embodiment of the present invention. Figure 8 This is a schematic diagram of the structure of a cylindrical mirror unit provided in an embodiment of the present invention. Figure 9 This is a schematic diagram of another cylindrical mirror unit provided in an embodiment of the present invention, as shown below. Figure 7 , Figure 8 and Figure 9 As shown, the optical imaging detection device also includes a cylindrical mirror unit 304', which is disposed in front of the receiving surface of the second detection unit 303'. The cylindrical mirror unit 304' includes at least one cylindrical mirror for compressing the second reflector beam to improve the illuminance of the second reflector beam.
[0063] Among them, a cylindrical mirror unit 304' is also provided in front of the receiving surface of the second detection unit 303', such as Figure 7As shown, 304a' is the projection of cylindrical mirror unit 304' onto the XY plane. Cylindrical mirror unit 304' can compensate for insufficient energy of the second reflector beam under a small numerical aperture. Since the direction of the detected defocus is in the Z direction, compression in the Y direction will not affect the detection sensitivity. For example, as... Figure 8 As shown, the cylindrical mirror unit 304' may include a cylindrical mirror to compress the second reflector beam in the Y direction, thereby increasing the illuminance of the second reflector beam and thus improving the energy utilization rate and the detection sensitivity of the second detection unit 303'. For example, as... Figure 9 As shown, the cylindrical mirror unit 304' may also include three cylindrical mirrors 304a to form a cylindrical mirror array, which compresses and divides the second reflector beam in the Y direction, forming three images or spot energies on the receiving surface of the second detection unit 303', i.e., forming three measurement points. Then, by averaging the defocusing amount of the three measurement points, the influence of local topography on the measurement is reduced, and the vertical detection accuracy is improved.
[0064] In addition, Figure 3 Based on this, it can also be combined with cylindrical mirror unit 304'. Figure 10 This is a schematic diagram of another optical imaging detection device provided in an embodiment of the present invention, as shown below. Figure 10 As shown, when the focus mark area 3a includes a first focus mark area 3a1 and a second focus mark 3a2, the cylindrical lens unit 304' includes a first cylindrical lens unit 304a and a second cylindrical lens unit 304b. Both the first cylindrical lens unit 304a and the second cylindrical lens unit 304b can include multiple cylindrical lenses. The cylindrical lenses are arranged along the Y direction, compressing the first and second beams of the second reflective sub-beams in the Y direction to improve illumination. Similarly, when the focus mark area 3a includes a third focus mark area 3a3 and a fourth focus mark 3a4, the cylindrical lens unit 304' includes a third cylindrical lens unit and a fourth cylindrical lens unit. Both the third and fourth cylindrical lens units can include multiple cylindrical lenses, arranged along the X direction, compressing the third and fourth beams of the second reflective sub-beams in the X direction to improve illumination. Similarly, when the focus mark area 3a includes the first focus mark area 3a1, the second focus mark 3a2, the third focus mark area 3a3, and the fourth focus mark 3a4, cylindrical mirrors are arranged along the X and Y directions respectively to increase the illumination of the first second reflective sub-beam, the second second reflective sub-beam, the third second reflective sub-beam, and the fourth second reflective sub-beam. At the same time, the original four measurement points are divided into twelve measurement points by multiple cylindrical mirrors, which can further improve the vertical fitting accuracy of the entire surface.
[0065] In addition, refer to Figure 1The optical imaging detection device also includes a reflection unit 301', which is located between the second detection unit 303' and the imaging relay unit 114. The reflection unit 301' reflects the second reflective sub-beam emitted from the imaging relay unit 114, adjusts the propagation direction of the second reflective sub-beam, and ensures that the second reflective sub-beam is received by the second detection unit 303', thereby ensuring the subsequent focusing effect.
[0066] Based on the same inventive concept Figure 11 This is a flowchart illustrating an autofocus method provided in an embodiment of the present invention, as shown below. Figure 11 As shown, the autofocus method is applied to the optical imaging detection device described in any of the above embodiments. This method can be executed by a control unit, which can be implemented in hardware and / or software. The autofocus method includes:
[0067] S101, control the stage to move the sample to be tested along the plane perpendicular to the stage, acquire the detection image of the sample to be tested at different positions of the stage through the first detection unit, and simultaneously acquire the imaging position of the focus mark area at different positions of the stage through the second detection unit. During the movement of the stage, the corresponding detection image includes the process of change from blurry to clear and then back to blurry.
[0068] The worktable carries the sample to be tested and moves along a direction perpendicular to the plane on which the worktable is located. The first detection unit acquires the detection images of the sample to be tested in real time at different positions of the worktable, while the second detection unit simultaneously acquires the imaging position of the focus mark area at different positions of the worktable. The detection images of the sample to be tested and the imaging position of the focus mark area are acquired at different positions of the worktable. For example, when the worktable moves from positive defocus to negative defocus or from negative defocus to positive defocus, the acquired detection images include a process of change from blurry to clear and then back to blurry. That is, the acquired detection images of the sample to be tested include the clearest detection image and some blurry detection images.
[0069] S102, based on the acquired multiple detection images, the position of the worktable corresponding to the detection image with the clearest image and the imaging position of the focus mark area corresponding to the detection image with the clearest image are calibrated as the zero point position of the focus signal.
[0070] The process involves analyzing and processing the detection images of multiple samples to be tested, selecting the clearest image, and extracting the corresponding stage position and the imaging position of the focus mark area based on the clearest image. These positions are then calibrated as the zero-point position of the focus signal. If multiple focus mark areas are configured, the average of the imaging positions of these areas is calculated and combined with the corresponding stage position to determine the zero-point position of the focus signal.
[0071] S103, based on the zero-point position, obtains the defocus amount of the test area of the sample and the relative value of the imaging position when the stage is in different positions.
[0072] Specifically, the difference between the zero point position and the position of the worktable is used to calculate the defocus amount of the test area of the sample under test when the worktable is in different positions, and the relative value of the imaging position of the focus mark area is obtained accordingly.
[0073] S104 performs mathematical fitting on the relative values of multiple defocus amounts and corresponding imaging positions to establish the focus signal calibration relationship of the sample under test.
[0074] in, Figure 12 A graph illustrating the calibration relationship of a focus signal is provided in an embodiment of the present invention, such as... Figure 12 As shown, the horizontal axis represents the defocus amount δz, and the vertical axis represents the relative value of the imaging position Z'. The control unit performs linear fitting on multiple defocus amounts and relative values of multiple imaging positions of the test area of the sample under test when the stage is in different positions, thus obtaining the focus signal calibration relationship of the test sample. The position range of the stage corresponding to the linear region near the zero point position can ensure that the test area of the sample is always in the focal plane. In addition, the marking for each optical imaging detection device only needs to be done once and stored as a system constant.
[0075] S105 obtains the real-time defocus amount of the test area of the sample based on the relative value of the imaging position acquired in real time during the detection process and the focus signal calibration relationship.
[0076] In the actual testing process, the stage moves the sample to be tested, and the second detection unit collects the relative value of the imaging position of the focus mark area in real time. Combined with the focus signal calibration relationship, the real-time defocus amount of the sample area to be tested, which is deviated from the optimal focal plane, is obtained.
[0077] S106 is based on a real-time defocus control stage to ensure that the test area of the sample is located on the focal plane.
[0078] Specifically, the position of the worktable is adjusted according to the real-time defocus amount of the test area of the sample, and the worktable is controlled to perform defocus compensation to achieve real-time and accurate focus control. This ensures that the test area of the sample is located on the focal plane, so that the first detection unit can acquire the clearest detection image during the test of the sample, thus ensuring the detection effect.
[0079] This invention calibrates an optical imaging detection device to obtain a focus signal calibration relationship; based on the relative value of the imaging position collected in real time during the detection process and the focus signal calibration relationship, it obtains the real-time defocus amount of the test area of the sample; and adjusts the stage based on the real-time defocus amount to ensure that the test area of the sample is located on the focal plane, thereby achieving real-time and precise focus control and ensuring the detection accuracy of the test sample detection process.
[0080] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.
Claims
1. An optical imaging detection device, characterized in that, include: The worktable is used to hold the sample to be tested and to allow for multi-degree-of-freedom movement; A light source, used to emit and transmit incident light beams; The field stop includes a light-transmitting imaging field of view and a light-transmitting focus mark area. The incident beam forms a first incident sub-beam through the imaging field of view and a second incident sub-beam through the focus mark area. The objective lens unit is used to converge the first incident sub-beam and the second incident sub-beam onto the sample under test, and to collect the first reflected sub-beam of the first incident sub-beam reflected by the surface of the sample under test and the second reflected sub-beam of the second incident sub-beam reflected by the surface of the sample under test. A baffle unit is used to block part of the second incident sub-beam to adjust the numerical aperture of the second incident beam as it is focused onto the sample under test by the objective lens unit. The first detection unit is used to receive the first reflective sub-beam to generate a detection image of the sample to be tested; The second detection unit is used to receive the second reflective sub-beam and obtain the imaging position of the focus mark area; The control unit acquires the focus signal calibration relationship of the sample under test based on multiple detection images, the imaging position acquired synchronously with the multiple detection images, and the corresponding position of the stage. Based on the imaging position acquired in real time during the detection process and the focus signal calibration relationship, the control unit adjusts the position of the stage so that the test area of the sample under test is located on the focal plane of the objective lens unit. The control unit then detects the sample under test based on the detection image when the test area of the sample under test is located on the focal plane.
2. The optical imaging detection device according to claim 1, characterized in that, The field stop has a first region corresponding to the effective field of view of the objective lens unit. The imaging field of view region and the focus mark region are arranged in the first region. The focus mark region is located outside the imaging field of view region, and the focus mark region and the imaging field of view region are isolated by a non-transparent region.
3. The optical imaging detection device according to claim 2, characterized in that, The focus marking area can be a light-transmitting area of any shape.
4. The optical imaging detection device according to claim 1, characterized in that, It also includes an illumination relay mirror unit and a beam splitter unit; The illumination relay mirror unit is used to collimate the first incident sub-beam and the second incident beam; The beam splitting unit is used to coaxially couple the collimated first incident sub-beam and the first reflected sub-beam, and the collimated second incident beam and the second reflected beam. The first incident sub-beam is incident on the sample under test through the illumination relay mirror unit, the beam splitter unit and the objective lens unit in sequence to form the first reflected sub-beam; The second incident sub-beam is incident on the sample under test through the illumination relay mirror unit, the beam splitter unit and the objective lens unit in sequence to form the second reflective sub-beam.
5. The optical imaging detection device according to claim 4, characterized in that, The baffle unit is located between the illumination relay mirror unit and the field stop, or between the light source and the field stop.
6. The optical imaging detection device according to claim 4, characterized in that, It also includes an imaging relay unit, whereby the first reflective sub-beam passes sequentially through the objective lens unit and the beam splitter unit, is then amplified by the imaging relay unit, and is subsequently received by the first detection unit to generate the detection image; The second reflector beam passes sequentially through the objective lens unit and the beam splitter unit, is amplified by the imaging relay unit, and is then received by the second detection unit to obtain the imaging position of the focus mark area.
7. The optical imaging detection device according to any one of claims 1-6, characterized in that, The focus marking area is configured as one or more; When the focus marking area is configured as one, both the baffle unit and the second detection unit are configured as one. When multiple focus mark areas are configured, multiple baffle units and multiple second detection units are also configured, and each focus mark area is correspondingly configured with one baffle unit and one second detection unit. Each baffle unit is used to block part of the light of the second incident sub-beam formed by the corresponding focus mark area, and each second detection unit is used to receive the second reflected sub-beam formed by the corresponding focus mark area to obtain the imaging position of the corresponding focus mark area.
8. The optical imaging detection device according to claim 7, characterized in that, It also includes a cylindrical mirror unit disposed in front of the receiving surface of the second detection unit. The cylindrical mirror unit includes at least one cylindrical mirror for compressing the second reflector beam to improve the illuminance of the second reflector beam.
9. The optical imaging detection device according to claim 7, characterized in that, When multiple focus mark areas are configured, the focus mark areas include a first focus mark area and a second focus mark area, and the first focus mark area and the second focus mark area are spaced apart along a first direction; And / or, the focusing field of view includes a third focusing mark area and a fourth focusing mark area, the third focusing area and the fourth focusing area being spaced apart along a second direction; Wherein, the first direction is perpendicular to the second direction, the first direction is perpendicular to the plane where the worktable is located, and the second direction is parallel to the light-emitting surface of the light source.
10. An autofocus method, applied to the optical imaging detection device according to any one of claims 1-9, comprising: The control stage moves the sample to be tested along a direction perpendicular to the plane of the stage. The first detection unit acquires the detection images of the sample to be tested at different positions of the stage, and the second detection unit simultaneously acquires the imaging position of the focus mark area at different positions of the stage. During the movement of the stage, the corresponding detection images include a process of change from blurry to clear and then back to blurry. Based on the acquired multiple detection images, the position of the worktable corresponding to the detection image with the clearest image and the imaging position of the focus mark area corresponding to the detection image with the clearest image are marked as the zero point position of the focus signal. Based on the zero-point position, the defocusing amount of the test area of the sample under test and the relative value of the imaging position are obtained when the stage is in different positions; Mathematical fitting is performed on the relative values of multiple defocus amounts and corresponding imaging positions to establish the focus signal calibration relationship of the sample under test. Based on the relative value of the imaging position collected in real time during the detection process and the calibration relationship of the focus signal, the real-time defocus amount of the test area of the sample to be tested is obtained. The stage is adjusted based on the real-time defocusing amount so that the test area of the sample is located on the focal plane.