A white light interference scanning interval fast automatic positioning system and method

Abstract

The application discloses a white light interference scanning interval fast automatic positioning system and method, which comprises an illumination unit, a differential confocal positioning unit, a white light interference data acquisition unit and an electric displacement control unit. The target area required to be observed by the measured sample is placed in the field of view of the camera. The measured sample is coarsely positioned and scanned to obtain a first absolute zero position as an upper surface and a second absolute zero position as a lower surface, and the corresponding light intensity value is recorded. The electric angular stage is driven to complete the tilt positioning. The interference region length of the interference fringe picture is determined. The piezoelectric ceramic is moved along the z-axis for variable speed scanning according to the first absolute zero position, the second absolute zero position and the interference region length. The interference fringe picture is collected in real time through the camera after the tilt positioning. The interference fringe picture with the interference fringe is screened out to complete the scanning interval positioning, so that the three-dimensional reconstruction can be carried out, and the measurement precision and efficiency of the measured sample are improved.

Description

Technical Field

[0001] This invention belongs to the field of optical measurement technology, specifically relating to a rapid automatic positioning system and method for white light interferometric scanning intervals. Background Technology

[0002] With the increasing demand for miniaturization, integration, and functional applications of measurement systems, the size of micro- and nano-structure units is becoming smaller, with higher precision and complexity. The spacing between adjacent units has reached the sub-micrometer level, and the high-precision measurement and characterization of their morphology is crucial to ensuring the quality of micro- and nano-materials.

[0003] White light interferometry, as a non-contact measurement method, can achieve precise three-dimensional measurement of submicron and even nanometer-scale microstructures, and is widely used in the field of precision measurement. However, during measurement, the interference fringes cause interference with image grayscale, making the single-peak nature of autofocus algorithms prone to failure, significantly reducing focus search accuracy. Existing white light interferometry systems often require manual adjustment of scanning parameters, using human visual observation to determine the positions where interference fringes appear and disappear to establish the upper and lower boundaries of the scan. However, white light interferometry systems use broadband light sources, resulting in short coherence lengths, typically only a few micrometers, limiting the visible range of interference fringes. Furthermore, the limited depth of field of the interferometric objective lens poses a significant challenge to traditional manual focusing, making precise focusing difficult. In addition, in the measurement of large-scale structural components—those with large vertical or horizontal dimensions—the measured object has height variations of tens or even hundreds of micrometers. Traditional white light interferometry systems maintain a fixed step size during scanning, resulting in a significant portion of the defocused signals being acquired without interference fringes. These defocused signals are background noise and do not contain information about the true height of the object, which limits the measurement efficiency of this scanning mode. At the same time, the reconstruction efficiency is also reduced due to the large number of redundant images involved in the reconstruction. Summary of the Invention

[0004] The purpose of this invention is to address the above-mentioned problems by proposing a rapid automatic positioning system and method for white light interferometric scanning intervals, which helps to improve the measurement accuracy and efficiency of the tested samples.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] This invention proposes a rapid automatic positioning system for white light interferometric scanning intervals, comprising:

[0007] The illumination unit includes a low-coherence light source, a first beam splitter, and a first lens group arranged sequentially along the first optical path. The first beam splitter is used to transmit the light emitted by the low-coherence light source through the first lens group to the third beam splitter.

[0008] The differential confocal positioning unit includes a second beam splitter, a rear focal detector, and a front focal detector. The rear focal detector and the front focal detector are located on adjacent sides of the second beam splitter, respectively. The first beam splitter is used to transmit the light reflected back from the third beam splitter to the rear focal detector and reflect it to the front focal detector through the second beam splitter.

[0009] The white light interferometric data acquisition unit includes a camera, a second lens group, a third beam splitter, a piezoelectric ceramic, and an interferometric objective lens arranged sequentially along the second optical path. The second optical path is perpendicular to the first optical path. The third beam splitter reflects the received light to the piezoelectric ceramic and then through the interferometric objective lens to illuminate the sample under test. The light reflected back from the sample under test passes through the interferometric objective lens and the piezoelectric ceramic in sequence to the third beam splitter. After being transmitted by the third beam splitter, the light passes through the second lens group to the camera to acquire interference fringe images, and after being reflected, it passes through the first lens group to the first beam splitter.

[0010] The electric displacement control unit includes an electric angular stage and an electric three-dimensional platform. The electric angular stage is used to drive the sample under test to adjust the rotation angle around the x-axis, y-axis and z-axis, and the electric three-dimensional platform is used to drive the electric angular stage to move along the x-axis, y-axis and z-axis.

[0011] Preferably, the differential confocal positioning unit further includes a first pinhole aperture and a second pinhole aperture, the first pinhole aperture being located between the second beam splitter and the back focus detector, and the second pinhole aperture being located between the second beam splitter and the front focus detector.

[0012] Preferably, both the first lens group and the second lens group include at least one lens.

[0013] A method for rapid automatic localization of a white light interferometric scanning interval, based on any of the above-mentioned rapid automatic localization systems for white light interferometric scanning intervals, includes the following steps:

[0014] S1. Drive the electric three-dimensional platform to move along the x and y axes, placing the target area of ​​the sample to be observed within the camera's field of view;

[0015] S2. After coarse positioning of the sample by moving it along the z-axis, the first absolute zero point position Z1 is obtained by scanning along the z-axis using a piezoelectric ceramic as the upper surface of the sample, and the second absolute zero point position Z2 is obtained as the lower surface of the sample. The light intensity value I at the first absolute zero point position Z1 is recorded by a camera. focus1 And the light intensity value I at the second absolute zero position Z2 focus2 The front focal intensity values ​​I1 and I3 of the upper and lower surfaces of the sample are recorded by the front focal detector, and the back focal intensity values ​​I2 and I4 of the upper and lower surfaces of the sample are recorded by the back focal detector.

[0016] S3. Drive the electric angle stage to adjust the tilt angle of the sample under test until the number of interference fringes on the interference fringe image observed by the camera is less than or equal to the preset value to complete the tilt positioning.

[0017] S4. Determine the length of the interference region of the interference fringe image. Based on the first absolute zero position Z1, the second absolute zero position Z2 and the length of the interference region, move the piezoelectric ceramic along the z-axis to perform variable speed scanning, and acquire the interference fringe image in real time through the camera. The length of the interference region is min(DOF,ΔL), where ΔL is the coherence length of the low coherence light source and DOF is the depth of field of the interference objective.

[0018] S5. Select interference fringe images to complete the scanning interval positioning for 3D reconstruction, that is, record the light intensity value I of the interference fringe image at scanning position Z. Z Interference fringe images are compared with a first threshold η1 and a second threshold η2 respectively. Images greater than or equal to either the first threshold η1 or the second threshold η2 are retained, while images less than either the first threshold η1 or the second threshold η2 are filtered out. The first threshold η1 = min(I... focus1 -I1,I focus1 -I2), the second threshold η2=min(I focus2 -I3,I focus2 -I4).

[0019] Preferably, the process for obtaining the positions of each absolute zero point is as follows:

[0020] S21. Observe the camera and drive the electric three-dimensional platform to move along the z-axis. Adjust the sample to be tested to a preset position near the corresponding focal plane to achieve coarse positioning. The focal plane is the absolute zero point position.

[0021] S22. Taking the position of the piezoelectric ceramic when the coarse positioning is completed as the starting position, scan the piezoelectric ceramic upward or downward along the z-axis according to the preset scanning step size, and obtain the corresponding differential confocal axial response intensity value I to determine the corresponding absolute zero point position. The formula for the judgment condition value ID of the absolute zero point position is as follows:

[0022]

[0023] Where Ia is the front focal light intensity value of the sample under test at the current scanning position corresponding to the focal plane, Ib is the back focal light intensity value of the sample under test at the current scanning position corresponding to the focal plane, max(·) represents taking the maximum value, min(·) represents taking the minimum value, and Δ represents the minimum value approaching 0.

[0024] Right now

[0025]

[0026] When ID = 0 or ID transitions between -1 and 1, it indicates the existence of a focal plane, meaning the current z-axis position of the piezoelectric ceramic is obtained as the corresponding absolute zero position.

[0027] Preferably, the number of interference fringes in the interference fringe image is obtained by binarizing the interference fringe image.

[0028] Preferably, the coherence length ΔL of the low-coherence light source is given by the following formula:

[0029]

[0030] The depth of field (DOF) of an interference lens is calculated using the following formula:

[0031]

[0032] Where λ0 represents the center wavelength of the low-coherence light source, Δλ represents the wavelength range of the low-coherence light source, and NA represents the numerical aperture of the interference objective.

[0033] Preferably, the piezoelectric ceramic is moved along the z-axis for variable-speed scanning based on the first absolute zero position Z1, the second absolute zero position Z2, and the length of the interference region, as follows:

[0034] S41. Perform a fine scan downwards along the z-axis within the actual interference region [Z1-d1, Z1+d2] of the first absolute zero position Z1. The ideal interference interval of the first absolute zero position Z1 is [Z1-d, Z1+d]. Wherein, the lower limit of the adjustment threshold d1 of the first absolute zero position Z1 is d ± n1·ΔZ, the upper limit of the adjustment threshold d2 of the first absolute zero position Z1 is d ± n2·ΔZ, the ideal adjustment threshold d = min(DOF, ΔL) / 2, n1 is the number of steps relative to the scan position Z1-d, and n2 is... The number of steps relative to the scanning position Z1+d, ΔZ is the preset fine scanning step size, Z1-d1 is the actual position where the interference fringes appear at the first absolute zero position Z1, which is calculated by moving the piezoelectric ceramic up or down along the z-axis relative to the scanning position Z1-d to determine the d1 value when the interference fringes appear, Z1+d2 is the actual position where the interference fringes disappear at the first absolute zero position Z1, which is calculated by moving the piezoelectric ceramic up or down along the z-axis relative to the scanning position Z1+d to determine the d2 value when the interference fringes disappear, and n1 and n2 may be equal or unequal;

[0035] S42. Continue to perform accelerated scanning downwards along the z-axis until the actual interference region of the second absolute zero position Z2 is reached. The scanning step size of the accelerated scanning is greater than the preset fine scanning step size ΔZ.

[0036] S43. Perform a fine scan downwards along the z-axis within the actual interference region [Z2-d3, Z2+d4] of the second absolute zero position Z2. The ideal interference interval range of the second absolute zero position Z2 is [Z2-d, Z2+d]. Here, the lower limit of the adjustment threshold for the second absolute zero position Z2 is d3 = d ± n3 · ΔZ, and the upper limit of the adjustment threshold for the second absolute zero position Z2 is d4 = d ± n4 · ΔZ. n3 is the number of movement steps relative to the scan position Z2-d, and n4 is the number of steps relative to the scan position Z2-d. The number of steps to move at position Z2+d, Z2-d3 is the actual position where the interference fringes appear at the second absolute zero position Z2, which is calculated by moving the piezoelectric ceramic relative to the scanning position Z2-d along the z-axis to determine the d3 value when the interference fringes appear, and Z2+d4 is the actual position where the interference fringes disappear at the second absolute zero position Z2, which is calculated by moving the piezoelectric ceramic relative to the scanning position Z2+d along the z-axis to determine the d4 value when the interference fringes disappear, and n3 and n4 may be equal or unequal.

[0037] Preferably, the method for rapid automatic positioning of the white light interferometric scanning range further includes:

[0038] S6. The selected interference fringe images are reconstructed in three dimensions using the coherence peak sensing algorithm.

[0039] Preferably, the coherence peak sensing algorithm is an improved centroid method, and the formula is as follows:

[0040] m(Z)=(I Z -I Z-ΔZ ) 2

[0041]

[0042] Among them, I Z I represents the light intensity value of the interference fringe image recorded at scanning position Z. Z-ΔZ denoted as the light intensity value of the interference fringe image recorded at the scanning position Z-ΔZ, where ΔZ is the preset fine scanning step size, m(Z) is the light intensity difference, and h is the height of the sample being tested.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] The technical solution of this invention includes an illumination unit, a differential confocal positioning unit, a white light interferometric data acquisition unit, and an electric displacement control unit. It enables multi-degree-of-freedom adjustment of the sample under test to collect light intensity signals at different optical axis positions, acquires the confocal axial response intensity curve to determine the absolute zero point position, accurately positions the upper and lower focal planes of the sample under test, and obtains high-quality interference fringe images in real time. This avoids errors caused by manual operation and human eye judgment, and can be used for scanning large-scale structural components, improving measurement efficiency and accuracy. Furthermore, it limits the length of the fine scanning area by selecting a smaller value between the coherence length of the low-coherence light source and the depth of field of the interferometric objective. The first absolute zero point is located in the middle of the fine scanning area on the upper surface, and the second absolute zero point is located in the middle of the fine scanning area on the lower surface. This determines the scanning range of different speeds and further corrects the corresponding interference region range. The piezoelectric ceramic is driven to scan within the interference region range, and a series of interference fringe images are recorded by the camera for three-dimensional reconstruction. Compared with the traditional fixed step size scanning method, the variable speed scanning method proposed in this invention, combined with the use of a differential confocal positioning unit to capture front focal intensity maps and back focal intensity maps for subsequent selection of interference fringe images, can reduce the subsequent white light interference reconstruction time and greatly improve the measurement efficiency and accuracy of the tested sample. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the structure of the white light interferometric scanning interval rapid automatic positioning system of the present invention;

[0046] Figure 2 This is a flowchart of the rapid automatic positioning method for white light interferometric scanning interval of the present invention;

[0047] Figure 3 This is a graph showing the axial response intensity of the differential confocal circuit of the present invention.

[0048] Figure 4 This is a schematic diagram illustrating the variable speed scanning principle of the present invention.

[0049] Explanation of reference numerals in the attached figures: 1. Low coherence light source; 2. First beam splitter; 3. First lens group; 4. Second beam splitter; 5. First pinhole aperture; 6. Back focus detector; 7. Second pinhole aperture; 8. Front focus detector; 9. Camera; 10. Second lens group; 11. Third beam splitter; 12. Piezoelectric ceramic; 13. Interferometer objective lens; 14. Sample under test; 15. Motorized angular stage; 16. Motorized three-dimensional platform; 17. Illumination unit; 18. Differential confocal positioning unit; 19. White light interferometric data acquisition unit; 20. Motorized displacement control unit. Detailed Implementation

[0050] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0051] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the application.

[0052] Example 1:

[0053] like Figure 1 As shown, a rapid automatic positioning system for a white light interferometric scanning range includes:

[0054] The illumination unit 17 includes a low coherence light source 1, a first beam splitter 2 and a first lens group 3 arranged sequentially along the first optical path direction. The first beam splitter 2 is used to transmit the light emitted by the low coherence light source 1 through the first lens group 3 to the third beam splitter 11.

[0055] The differential confocal positioning unit 18 includes a second beam splitter 4, a rear focal detector 6, and a front focal detector 8. The rear focal detector 6 and the front focal detector 8 are located on adjacent sides of the second beam splitter 4, respectively. The first beam splitter 2 is used to transmit the light reflected back from the third beam splitter 11 through the second beam splitter 4 to the rear focal detector 6 and reflect it to the front focal detector 8, respectively.

[0056] The white light interferometric data acquisition unit 19 includes a camera 9, a second lens group 10, a third beam splitter 11, a piezoelectric ceramic 12, and an interferometric objective lens 13 arranged sequentially along the second optical path. The second optical path is perpendicular to the first optical path. The third beam splitter 11 is used to reflect the received light to the piezoelectric ceramic 12 and then through the interferometric objective lens 13 to illuminate the sample 14 under test. The light reflected back from the sample 14 under test passes through the interferometric objective lens 13 and the piezoelectric ceramic 12 in sequence to reach the third beam splitter 11. After being transmitted by the third beam splitter 11, the light passes through the second lens group 10 to reach the camera 9 to realize the acquisition of interference fringe images and after being reflected, it passes through the first lens group 3 to reach the first beam splitter 2.

[0057] The electric displacement control unit 20 includes an electric angle stage 15 and an electric three-dimensional platform 16. The electric angle stage 15 is used to drive the sample 14 to adjust the rotation angle around the x-axis, y-axis and z-axis, and the electric three-dimensional platform 16 is used to drive the electric angle stage 15 to move along the x-axis, y-axis and z-axis.

[0058] In one embodiment, the differential confocal positioning unit 18 further includes a first pinhole aperture 5 and a second pinhole aperture 7. The first pinhole aperture 5 is located between the second beam splitter 4 and the back focus detector 6, and the second pinhole aperture 7 is located between the second beam splitter 4 and the front focus detector 8.

[0059] In one embodiment, both the first lens group 3 and the second lens group 10 include at least one lens.

[0060] like Figure 1 As shown, a white light interferometric scanning interval rapid automatic positioning system is described. The light emitted by the low coherence light source 1 of the illumination unit 17 passes through the first beam splitter 2, is collimated by the first lens group 3, and enters the third beam splitter 11 of the white light interferometric data acquisition unit 19. After being reflected by the third beam splitter 11, the light enters the interferometric objective lens 13 and illuminates the sample 14 under test. The light reflected back from the sample 14 returns to the first beam splitter 2 along the original path, and is then reflected into the differential confocal positioning unit 18. It is then split into two beams by the second beam splitter 4. The reflected beam is detected by the front focal detector 8 through the second pinhole aperture 7, and the corresponding front focal intensity map is recorded to obtain the front focal light intensity value. The transmitted beam is detected by the rear focal detector 6 through the first pinhole aperture 5, and the corresponding rear focal intensity map is recorded to obtain the rear focal light intensity value. The light reflected back from the sample 14 also passes sequentially through the interferometric objective lens 13, the piezoelectric ceramic 12, the third beam splitter 11, and the second lens group 10 to reach the camera 9 to acquire the interference fringe image. Interference objective 13 can be a Mirau interferometer objective, and back focus detector 6 and front focus detector 8 can be cameras, etc. The x-axis, y-axis, and z-axis form a rectangular coordinate system. For example, the first optical path direction is parallel to the y-axis direction, and the second optical path direction is parallel to the z-axis direction. This is for ease of understanding only, and the specific orientation can be adjusted according to actual needs. This system enables control over the spatial placement of the sample 14 under test, and can continuously perform high-precision nanoscale scanning through the piezoelectric ceramic 12, while the camera 9 simultaneously and continuously acquires interference fringe images.

[0061] During operation, the target area of ​​the sample 14 to be observed is placed within the field of view of the camera 9 by adjusting the movement of the electric three-dimensional platform 16 along the x and y axes. Then, the sample 14 is moved along the z axis to achieve coarse positioning (and the first absolute zero point position Z1 is taken as the upper surface of the sample 14, and the second absolute zero point position Z2 is taken as the lower surface of the sample 14, and the corresponding light intensity values ​​are recorded. For example, the coarse positioning positions are near the upper and lower surfaces of the sample 14, respectively. The piezoelectric ceramic 12 can be scanned near the upper surface (including scanning the piezoelectric ceramic 12 upward or downward along the z axis according to the preset scanning step size) to obtain the front focal light intensity value and back focal light intensity value of the corresponding scanning position. The first absolute zero point position is determined by using the front focal intensity value and the back focal intensity value, which is the upper surface of the sample 14 under test. The above process is repeated to scan the piezoelectric ceramic 12 near the lower surface to determine the second absolute zero point position, which is the lower surface of the sample 14 under test. The rotation angle around the x-axis, y-axis and z-axis is adjusted by the electric angle stage 15 to ensure that the number of interference fringes on the interference fringe image observed by the camera 9 meets the requirements to complete the tilt positioning, which is conducive to accurate scanning positioning. The light reflected back from the sample 14 under test is also directly transmitted through the third beam splitter 11 and focused onto the camera 9 by the second lens group 10. The camera 9 records a series of interference fringe images at the Z-axis position for subsequent three-dimensional reconstruction.

[0062] Example 2:

[0063] like Figures 2-4 As shown, a method for rapid automatic positioning of a white light interferometric scanning interval, based on the rapid automatic positioning system for a white light interferometric scanning interval in Example 1, includes the following steps:

[0064] S1. Drive the electric 3D platform 16 to move along the x and y axes, placing the target area of ​​the sample 14 to be observed within the field of view of the camera 9. It should be noted that for large-scale structural components, the target area to be observed can be acquired in portions each time, and then the images can be stitched together for subsequent processing.

[0065] S2. After coarse positioning of the sample 14 by moving it along the z-axis, the piezoelectric ceramic 12 is used to scan along the z-axis to obtain the first absolute zero point position Z1 as the upper surface of the sample 14 and the second absolute zero point position Z2 as the lower surface of the sample 14. The light intensity value I at the first absolute zero point position Z1 is recorded by the camera 9. focus1 And the light intensity value I at the second absolute zero position Z2 focus2The front focal intensity value I1 of the upper surface of the sample 14 and the front focal intensity value I3 of the lower surface of the sample 14 are recorded by the front focal detector 8, and the back focal intensity value I2 of the upper surface of the sample 14 and the back focal intensity value I4 of the lower surface of the sample 14 are recorded by the back focal detector 6.

[0066] In one embodiment, the process of obtaining the absolute zero point positions is as follows:

[0067] S21. Observe the camera 9 and drive the electric three-dimensional platform 16 to move along the z-axis, and adjust the sample 14 to the preset position near the corresponding focal plane to achieve coarse positioning. The focal plane is the absolute zero point position.

[0068] S22. Taking the position of the piezoelectric ceramic 12 when the coarse positioning is completed as the starting position, scan the piezoelectric ceramic 12 upward or downward along the z-axis according to the preset scanning step size, and obtain the corresponding differential confocal axial response intensity value I to determine the corresponding absolute zero point position. The formula for the judgment condition value ID of the absolute zero point position is as follows:

[0069]

[0070] Where Ia is the front focal light intensity value of the sample 14 at the current scanning position corresponding to the focal plane, Ib is the back focal light intensity value of the sample 14 at the current scanning position corresponding to the focal plane, max(·) represents taking the maximum value, min(·) represents taking the minimum value, and Δ represents the minimum value approaching 0.

[0071] Right now

[0072]

[0073] When ID = 0 or ID transitions between -1 and 1, it indicates the existence of a focal plane, meaning the current z-axis position of the piezoelectric ceramic 12 is obtained as the corresponding absolute zero position.

[0074] This embodiment specifically performs the following operations:

[0075] 1) Observe the camera 9 and drive the electric three-dimensional platform 16 to move along the z-axis, and adjust the sample 14 to the preset position near the first focal plane to achieve coarse positioning. The first focal plane is the first absolute zero position Z1.

[0076] 2) The tested sample 14 is currently located in an approximately linear region AB on the differential confocal axial response intensity curve. Point O is the first absolute zero point position Z1 to be obtained, as shown below. Figure 3As shown. Taking the current position of the piezoelectric ceramic 12 as the starting position, the preset fine scanning step size of the piezoelectric ceramic 12 is set to ΔZ = 100nm. Assuming that the sample 14 under test is located below the first absolute zero position Z1, when the piezoelectric ceramic 12 scans upward along the z-axis from the starting position by one step each time, the rear focal detector 6 and the front focal detector 8 each correspond to a light intensity value. The intensity response curve of the axial distance-light intensity relationship is plotted, as shown. Figure 3 As shown, the front focus detector 8 records the front focus light intensity value I1 on the upper surface of the sample 14, and the rear focus detector 6 records the rear focus light intensity value I2 on the upper surface of the sample 14. Then, the differential confocal axial response intensity value I is obtained as I = I1 - I2. Based on the absolute zero-point position judgment condition value ID, the first absolute zero-point position is found and denoted as Z1. The formula for the absolute zero-point position judgment condition value ID is as follows:

[0077]

[0078] Where max(·) represents taking the maximum value, min(·) represents taking the minimum value, and Δ represents the minimum value approaching 0, which can be ignored and is used to prevent the occurrence of 0 / 0.

[0079]

[0080] The ID value is used to determine the relationship between the current Z-axis position of the piezoelectric ceramic 12 and the focal plane position of the sample 14 under test. -1 indicates that the current Z-axis position of the piezoelectric ceramic 12 is lower than the focal plane position, 1 indicates that the current Z-axis position of the piezoelectric ceramic 12 is higher than the focal plane position, and 0 indicates that the current Z-axis position of the piezoelectric ceramic 12 is the focal plane position. At this time, the camera 9 displays the clearest focused image. In actual operation, due to the influence of the surrounding environment and noise, the interference fringes fluctuate. Under the same defocus amount, the light intensity values ​​of the front focal point and the back focal point will always have a deviation. The case of ID=0 is basically impossible. Therefore, when ID transitions between -1 and 1, the current Z-axis position of the piezoelectric ceramic 12 represents the focal plane position. Assuming that the detection position is the upper surface of the sample 14 under test, and the Z-axis position of the piezoelectric ceramic 12 is Z1, the camera 9 records the light intensity value I at the first absolute zero point position Z1. focus1 .

[0081] 3) When the height difference between the upper and lower surfaces of the sample 14 exceeds the depth of field of the objective lens, it indicates that there are two focal planes. In this case, two positioning operations are required. After finding the first absolute zero point position Z1, continue to adjust the piezoelectric ceramic 12 downward along the Z-axis and repeat the above operation. That is, continue to observe the camera 9 and drive the electric three-dimensional platform 16 to move along the Z-axis to adjust the sample 14 to a preset position near the second focal plane to achieve coarse positioning. The second focal plane is the second absolute zero point position Z2. Find the front focal intensity value I3 and the back focal intensity value I4 of the lower surface of the sample 14. Obtain the second absolute zero point position Z2 according to the judgment condition value ID of the absolute zero point position. The formula is as follows:

[0082]

[0083] At this point, when ID = 0 or ID transitions between -1 and 1, the z-axis position of the piezoelectric ceramic 12 is the second absolute zero position Z2, which is the lower surface of the sample 14 under test. The camera 9 records the light intensity value I at the second absolute zero position Z2. focus2 .

[0084] S3. Drive the electric angle stage 15 to adjust the tilt angle of the sample 14 under test until the number of interference fringes on the interference fringe image observed by the camera 9 is less than or equal to the preset value, and the tilt positioning is completed.

[0085] In one embodiment, the number of interference fringes on the interference fringe image is obtained by binarizing the interference fringe image.

[0086] Specifically, after determining the focal plane position, it is necessary to determine the appropriate number of interference fringes. This can be done by binarizing the interference fringe image to calculate the number of fringes. Generally, 3 to 5 interference fringes are suitable. This avoids the problem that the interference fringes become blurry when the coherence length of the white light is short and exceeds a certain range. Fewer than 5 interference fringes can ensure clarity and high contrast within the coherence length, and the tilt angle is relatively small. Set the target number of interference fringes and the tilt angle of the motorized angle stage 15 until the appropriate number of interference fringes appears, then stop the motorized angle stage 15.

[0087] S4. Determine the length of the interference region of the interference fringe image. Based on the first absolute zero position Z1, the second absolute zero position Z2 and the length of the interference region, move the piezoelectric ceramic 12 along the z-axis to perform variable speed scanning, and acquire the interference fringe image in real time through the camera 9. The length of the interference region is min(DOF,ΔL), where ΔL is the coherence length of the low coherence light source 1 and DOF is the depth of field of the interference objective lens 13.

[0088] In one embodiment, the coherence length ΔL of the low-coherence light source 1 is given by the following formula:

[0089]

[0090] The depth of field (DOF) of interference objective 13 is calculated using the following formula:

[0091]

[0092] Where λ0 represents the center wavelength of the low-coherence light source 1, Δλ represents the wavelength range of the low-coherence light source 1, and NA represents the numerical aperture of the interference objective 13.

[0093] In one embodiment, the piezoelectric ceramic 12 is moved along the z-axis for variable-speed scanning based on the first absolute zero position Z1, the second absolute zero position Z2, and the length of the interference region, as follows:

[0094] S41. Within the actual interference region [Z1-d1, Z1+d2] of the first absolute zero position Z1, perform a fine downward scan along the z-axis (region S1). The ideal interference interval of the first absolute zero position Z1 is [Z1-d, Z1+d]. Here, the lower limit of the adjustment threshold for the first absolute zero position Z1 is d1 = d ± n1·ΔZ, the upper limit of the adjustment threshold for the first absolute zero position Z1 is d2 = d ± n2·ΔZ, and the ideal adjustment threshold is d = min(DOF, ΔL) / 2. n1 is the number of steps relative to the scan position Z1-d, and n2 is... The number of steps relative to the scanning position Z1+d, ΔZ is the preset fine scanning step size, Z1-d1 is the actual position where the interference fringes appear at the first absolute zero position Z1, which is calculated by moving the piezoelectric ceramic 12 up or down along the z-axis relative to the scanning position Z1-d to determine the d1 value when the interference fringes appear, and Z1+d2 is the actual position where the interference fringes disappear at the first absolute zero position Z1, which is calculated by moving the piezoelectric ceramic 12 up or down along the z-axis relative to the scanning position Z1+d to determine the d2 value when the interference fringes disappear, and n1 and n2 may be equal or unequal;

[0095] S42. Continue to accelerate the scan downward along the z-axis (S2 region) until the actual interference region range of the second absolute zero position Z2 is reached. The scanning step size of the accelerated scan is greater than the preset fine scan step size ΔZ.

[0096] S43. Within the actual interference region [Z2-d3, Z2+d4] of the second absolute zero position Z2, perform a fine downward scan along the z-axis (region S3). The ideal interference range of the second absolute zero position Z2 is [Z2-d, Z2+d]. Here, the lower limit of the adjustment threshold for the second absolute zero position Z2 is d3 = d ± n3·ΔZ, and the upper limit of the adjustment threshold for the second absolute zero position Z2 is d4 = d ± n4·ΔZ. n3 is the number of movement steps relative to the scanning position Z2-d, and n4 is the number of steps relative to the scanning position Z2-d. The number of steps to move at position Z2+d, Z2-d3 is the actual position where the interference fringes appear at the second absolute zero position Z2, which is calculated by moving the piezoelectric ceramic 12 up or down along the z-axis relative to the scanning position Z2-d to determine the d3 value when the interference fringes appear, and Z2+d4 is the actual position where the interference fringes disappear at the second absolute zero position Z2, which is calculated by moving the piezoelectric ceramic 12 up or down along the z-axis relative to the scanning position Z2+d to determine the d4 value when the interference fringes disappear. n3 and n4 may be equal or unequal.

[0097] Specifically, since the optical path structure of the white light interferometric scanning interval rapid automatic positioning system is determined, the low coherence light source 1 used is also determined. The length of the region where interference fringes appear on the upper and lower surfaces of the sample 14 under test is fixed and its value depends on the smaller of the coherence length ΔL of the low coherence light source 1 and the depth of field DOF of the interferometric objective lens 13. Therefore, the length of the interference region is min(DOF,ΔL).

[0098] like Figure 4As shown, the positive direction of the z-axis is downward, that is, from the first absolute zero position Z1 to the second absolute zero position Z2. Ideally, a fine scan is performed within the range of the lower limit Z1-d and the upper limit Z1+d of the first interference region (the actual interference region range of the first absolute zero position Z1), where d=min(DOF,ΔL) / 2. In actual operation, due to the susceptibility to environmental influences, the interference fringes no longer present a symmetrical distribution centered on the optimal interference position, and the upper and lower limits of the actual interference region also change. If the fine scanning step size is set to ΔZ = 100 nm, the focal intensity map taken during the process of finding the first absolute zero position Z1 in step S2 can be used to further verify the location of the interference fringes. The lower limit Z1-d becomes Z1-d1, where d1 = min(DOF,ΔL) / 2 ± n1·ΔZ, n1 is the number of steps relative to the scanning position Z1-d, and Z1-d1 may be above or below Z1-d. That is, Z1-d is the ideal location of the interference fringes in the first interference region, and Z1-d1 is the actual location of the interference fringes in the first interference region. The sign of d1 indicates that Z1-d1 may be above or below Z1-d. Its positive or negative value is determined by the actual location of the interference fringes determined when the piezoelectric ceramic 12 moves upward or downward along the z-axis relative to the scanning position Z1-d. If the location of the interference fringes is verified directly using the focal intensity map taken during the process of finding the first absolute zero position Z1 in step S2, there is no need to repeat the search. Similarly, using the step The back focal intensity map taken during the search for the first absolute zero position Z1 in step S2 further verifies the location where the interference fringes disappear. The upper limit Z1+d becomes Z1+d2, where d2=min(DOF,ΔL) / 2±n2·ΔZ, n2 is the number of steps moved relative to the scanning position Z1+d. Z1+d2 may be above or below Z1+d, that is, Z1+d is the ideal location where the interference fringes of the first interference region disappear, and Z1+d2 is the actual location where the interference fringes of the first interference region disappear. The sign of d2 indicates that Z1+d2 may be above or below Z1+d. Its positive or negative value is determined by the actual location where the interference fringes disappear when the piezoelectric ceramic 12 moves up or down along the z-axis relative to the scanning position Z1+d. If the back focal intensity map taken during the search for the first absolute zero position Z1 in step S2 is used directly to verify the location where the interference fringes disappear, there is no need to search again. n1 and n2 are not necessarily equal, depending on the specific situation. d1 and d2 are not much different from d.

[0099] like Figure 4 As shown, after passing through the first interference region, the scanning continues downward along the z-axis to enter the background signal region without interference fringes. The piezoelectric ceramic 12 is then subjected to a large-step accelerated scan, with the step size set to ΔZ. a =1000nm.

[0100] After passing through the accelerated scanning area, a fine scan is performed within the lower limit Z2-d and upper limit Z2+d of the second interference area (the actual interference area range of the second absolute zero position Z2). Similarly, in actual operation, due to the susceptibility to environmental influences, the interference fringes no longer present a symmetrical distribution centered on the optimal interference position, and the upper and lower limits of the actual interference area also change. If the fine scanning step size is set to ΔZ = 100nm, the focal intensity map taken during the process of finding the second absolute zero position Z2 in step S2 can be used to further verify the location of the interference fringes. The lower limit Z2-d becomes Z2-d3, where d3 = min(DOF,ΔL) / 2 ± n3·ΔZ, n3 is the number of steps relative to the scanning position Z2-d. Z2-d3 may be above or below Z2-d, that is, Z2-d is the ideal location of the interference fringes in the second interference region, and Z2-d3 is the actual location of the interference fringes in the second interference region. The sign of d3 indicates that Z2-d3 may be above or below Z2-d. Its positive or negative value is determined by the actual location of the interference fringes determined when the piezoelectric ceramic 12 moves upward or downward along the z-axis relative to the scanning position Z2-d. If the focal intensity map taken during the process of finding the second absolute zero position Z2 in step S2 is used directly to verify the location of the interference fringes, there is no need to repeat the search. Similarly, using the step The back focal intensity map taken during the search for the second absolute zero position Z2 in step S2 further verifies the location where the interference fringes disappear. The upper limit Z2+d becomes Z2+d4, where d4=min(DOF,ΔL) / 2±n4·ΔZ, n4 is the number of steps moved relative to the scanning position Z2+d. Z2+d4 may be above or below Z2+d, that is, Z2+d is the ideal location where the interference fringes of the second interference region disappear, and Z2+d4 is the actual location where the interference fringes of the second interference region disappear. The sign of d4 indicates that Z2+d4 may be above or below Z2+d. Its positive or negative value is determined by the actual location where the interference fringes disappear when the piezoelectric ceramic 12 moves upward or downward along the z-axis relative to the scanning position Z2+d. If the back focal intensity map taken during the search for the second absolute zero position Z2 in step S2 is used directly to verify the location where the interference fringes disappear, there is no need to search again. n3 and n4 are not necessarily equal, depending on the specific situation. d3 and d4 are not much different from d.

[0101] By selecting the smaller value between the coherence length ΔL of the low coherence light source 1 and the depth of field DOF of the interferometer 13 as the limit for the length of the fine scanning area, the first absolute zero point is located in the middle of the fine scanning area on the upper surface, and the second absolute zero point is located in the middle of the fine scanning area on the lower surface. This determines the scanning range for different speeds, and by further correcting the corresponding interference area range, it helps to improve positioning efficiency and positioning accuracy.

[0102] S5. Select interference fringe images to complete the scanning interval positioning for 3D reconstruction, that is, record the light intensity value I of the interference fringe image at scanning position Z. Z Interference fringe images are compared with a first threshold η1 and a second threshold η2 respectively. Images greater than or equal to either the first threshold η1 or the second threshold η2 are retained, while images less than either the first threshold η1 or the second threshold η2 are filtered out. The first threshold η1 = min(I... focus1 -I1,I focus1 -I2), the second threshold η2=min(I focus2 -I3,I focus2 -I4).

[0103] Specifically, since true height information exists only in the interference fringes, signals without interference fringes are considered background noise. After determining the scanning boundary position and scanning step size, the interference process is recorded from Z1-d1 to Z2+d4. To verify the existence of interference fringes, verification conditions are set to exclude interference fringe images without interference fringes from subsequent reconstruction processes, thus reducing white light interference reconstruction time.

[0104] That is, when the current z-axis position of the piezoelectric ceramic 12 is Z1-d1, the camera 9 displays interference fringes; when the current z-axis position of the piezoelectric ceramic 12 is Z1, the interference fringes displayed by the camera 9 are most distinct; and when the current z-axis position of the piezoelectric ceramic 12 is Z1+d2, the interference fringes displayed by the camera 9 disappear. The judgment can be made simultaneously with the acquisition, based on the light intensity value of Z1 obtained in step S2 (including the light intensity value I at the first absolute zero position Z1). focus1 The judgment threshold is calculated using the front focal light intensity value I1 and the back focal light intensity value I2 of the upper surface of the sample 14 under test. The first threshold η1 is set as min(I1, I2, I3, I4, I5, I6, I7, I8, I9, I1, I2, I2, I3, I4, I9, I2, I2, I3, I4 ... focus1 -I1,I focus1 -I2) is used as a condition to determine the existence of interference fringes. The light intensity value I of the interference fringe image recorded at the scanning position Z is used. Z Compared with the first threshold η1, the expression is as follows:

[0105]

[0106] Among them, I Z In the case of ≥η1, the interference fringe image will be preserved for reconstruction, I Z In the case of <η2, the green fringes in the interference fringe image will be coarse and will not be included in the reconstruction.

[0107] When the current z-axis position of the piezoelectric ceramic 12 is Z2-d3, the camera 9 displays the interference fringes reappearing; when the current z-axis position of the piezoelectric ceramic 12 is Z2, the camera 9 displays the interference fringes with the most obvious contrast; when the current z-axis position of the piezoelectric ceramic 12 is Z2+d4, the camera 9 displays the interference fringes disappearing again. This can be determined simultaneously with the data acquisition, based on the light intensity value of Z2 obtained in step S2 (including the light intensity value I at the second absolute zero position Z2). focus2 The judgment threshold is calculated using the front focal light intensity value I3 and the back focal light intensity value I4 of the lower surface of the tested sample (14). The second threshold is set as η2 = min(I3, I4, I5). focus2 -I3,I focus2 -I4) is used as a condition to determine the existence of interference fringes. The light intensity value I of the interference fringe image recorded at the scanning position Z is used. Z Compared with the second threshold η2, the following expression shows:

[0108]

[0109] Among them, I n In the case of ≥η2, the interference fringe image is preserved for reconstruction, I n If the value is less than η2, the interference fringe image will be filtered out and not included in the reconstruction.

[0110] In one embodiment, the rapid automatic positioning method for white light interferometric scanning intervals further includes:

[0111] S6. The selected interference fringe images are reconstructed in three dimensions using the coherence peak sensing algorithm.

[0112] In one embodiment, the coherence peak sensing algorithm is an improved centroid method, and the formula is as follows:

[0113] m(Z)=(I Z -I Z-ΔZ ) 2

[0114]

[0115] Among them, I Z I represents the light intensity value of the interference fringe image recorded at scanning position Z. Z-ΔZ The light intensity value of the interference fringe image recorded at the scanning position Z-ΔZ is denoted as ΔZ, where ΔZ is the preset fine scanning step size, m(Z) is the light intensity difference, and h is the height of the sample 14 being tested.

[0116] Based on the operations of steps S1 to S6 above, the spatial position of the sample 14 under test can be quickly and accurately located and three-dimensionally reconstructed to complete the measurement, thereby improving the measurement accuracy and efficiency.

[0117] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0118] The embodiments described above are merely specific and detailed examples of the embodiments described in this application, and should not be construed as limiting the scope of the application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the appended claims.

Claims

1. A white light interferometry scanning interval fast auto-positioning system, characterized in that: The white light interference scanning interval fast automatic positioning system comprises: An illumination unit (17) comprising a low coherence light source (1), a first beam splitter (2) and a first lens group (3) arranged in sequence along a first light path direction, the first beam splitter (2) being used for transmitting light emitted by the low coherence light source (1) to a third beam splitter (11) through the first lens group (3); A differential confocal positioning unit (18) comprising a second beam splitter (4), a back focal detector (6) and a front focal detector (8), the back focal detector (6) and the front focal detector (8) being located on two adjacent sides of the second beam splitter (4) respectively, the first beam splitter (2) being used for transmitting light reflected by the third beam splitter (11) to the back focal detector (6) and the front focal detector (8) through the second beam splitter (4) respectively; A white light interference data acquisition unit (19) comprising a camera (9), a second lens group (10), the third beam splitter (11), a piezoelectric ceramic (12) and an interference objective lens (13) arranged in sequence along a second light path direction, the second light path direction being perpendicular to the first light path direction, the third beam splitter (11) being used for reflecting received light to the piezoelectric ceramic (12) and transmitting the light through the interference objective lens (13) to irradiate a measured sample (14), light reflected by the measured sample (14) again sequentially transmitting through the interference objective lens (13), the piezoelectric ceramic (12) to reach the third beam splitter (11), and being transmitted by the third beam splitter (11) to reach the camera (9) through the second lens group (10) to realize interference fringe picture acquisition and being reflected to reach the first beam splitter (2) through the first lens group (3); An electric displacement control unit (20) comprising an electric angle table (15) and an electric three-dimensional platform (16), the electric angle table (15) being used for driving the measured sample (14) to adjust rotation angles around x, y and z axes, and the electric three-dimensional platform (16) being used for driving the electric angle table (15) to move along x, y and z axes.

2. The white light interferometry scanning interval fast autopositioning system of claim 1, wherein: The differential confocal positioning unit (18) further comprises a first pinhole diaphragm (5) and a second pinhole diaphragm (7), the first pinhole diaphragm (5) being located between the second beam splitter (4) and the back focal detector (6), and the second pinhole diaphragm (7) being located between the second beam splitter (4) and the front focal detector (8).

3. The white light interferometry scanning interval fast autopositioning system of claim 1, wherein: The first lens group (3) and the second lens group (10) each comprise at least one lens.

4. A method for fast automatic positioning of a white light interferometry scanning interval, based on the system for fast automatic positioning of a white light interferometry scanning interval according to any one of claims 1 to 3, characterized in that: The white light interference scanning interval fast automatic positioning method comprises the following steps: S1, driving the electric three-dimensional platform (16) to move along x and y axes to place a target region required to be observed by the measured sample (14) in a field of view of the camera (9); S2, after the z-axis movement of the measured sample (14) to achieve coarse positioning, the first absolute zero position Z1 and the second absolute zero position Z2 are obtained by moving the piezoelectric ceramic (12) along the z-axis to scan, and the light intensity value I of the first absolute zero position Z1 and the light intensity value I of the second absolute zero position Z2 are recorded by the camera (9) corresponding to the upper surface of the measured sample (14) focus1 and the second absolute zero position Z2 focus2 , the front focal light intensity value I1 of the upper surface of the measured sample (14) and the front focal light intensity value I3 of the lower surface of the measured sample (14) are recorded by the front focal detector (8) corresponding, and the back focal light intensity value I2 of the upper surface of the measured sample (14) and the back focal light intensity value I4 of the lower surface of the measured sample (14) are recorded by the back focal detector (6) corresponding; S3, driving the electric angle table (15) to adjust an inclination angle of the measured sample (14) until the number of interference fringes on an interference fringe picture observed by the camera (9) is less than or equal to a preset value to complete inclination positioning. S4, determining the interference region length of the interference fringe picture, moving the piezoelectric ceramic (12) along the z-axis for variable speed scanning according to the first absolute zero position Z1, the second absolute zero position Z2 and the interference region length, and collecting the interference fringe picture in real time through the camera (9), the interference region length being min (DOF, AL), wherein AL is the coherence length of the low coherence light source (1), and DOF is the depth of field of the interference objective (13); S5, screening out the interference fringe pictures with interference fringes to complete the scanning interval positioning for three-dimensional reconstruction, that is, recording the light intensity value I of the interference fringe picture at the scanning position Z Z The interference fringe pictures greater than or equal to the first threshold η1 or the second threshold η2 are reserved, and the interference fringe pictures less than the first threshold η1 or the second threshold η2 are filtered out by comparison with the first threshold η1 and the second threshold η2 respectively, wherein the first threshold η1 = min(I focus1 -I1,I focus1 The second threshold η2 = min(I focus2 -I3,I focus2 -I4).

5. The method of claim 4, wherein: the white light interferometry scan interval fast auto-positioning method further comprises: determining a position of the reference surface based on the reference surface position data; and determining a position of the sample surface based on the sample surface position data. The acquisition process of each absolute zero position is as follows: S21, observing the camera (9) and driving the motorized three-dimensional platform (16) to move along the z-axis, adjusting the measured sample (14) to the preset adjacent position of the corresponding focal plane to realize coarse positioning, and the focal plane is the absolute zero position; S22, taking the position of the piezoelectric ceramic (12) when the coarse positioning is completed as the starting position, scanning the piezoelectric ceramic (12) upward or downward along the z-axis according to the preset scanning step length, acquiring the corresponding differential confocal axial response intensity value I to determine the corresponding absolute zero position, and the judgment condition value ID of the absolute zero position is as follows: Wherein, Ia is the front focal light intensity value of the measured sample (14) at the corresponding focal plane at the current scanning position, Ib is the back focal light intensity value of the measured sample (14) at the corresponding focal plane at the current scanning position, max (·) represents taking the maximum value, min (·) represents taking the minimum value, and delta represents an extremely small value approaching 0; That is When ID = 0 or ID realizes the transition between-1 and 1, it indicates that there is a focal plane, that is, the current z-axis position of the piezoelectric ceramic (12) is the corresponding absolute zero position.

6. The method of claim 4, wherein: the white light interferometry scan interval fast auto-positioning method further comprises: determining a position of the reference surface based on the reference surface position data; and determining a position of the sample surface based on the sample surface position data. The number of interference fringes on the interference fringe picture is obtained by binarizing the interference fringe picture.

7. The method of claim 4, wherein: the white light interferometry scan interval fast auto-positioning method further comprises: determining a position of the reference surface based on the reference surface position data; and determining a position of the sample surface based on the sample surface position data. The coherence length AL of the low coherence light source (1) is as follows: The depth of field DOF of the interference objective (13) is as follows: Wherein, lambda0 represents the center wavelength of the low coherence light source (1), delta lambda represents the wavelength range of the low coherence light source (1), and NA represents the numerical aperture of the interference objective (13).

8. The method of claim 4, wherein: the white light interferometry scan interval fast auto-positioning method further comprises: determining a position of the reference surface based on the reference surface position data; and determining a position of the sample surface based on the sample surface position data. The piezoelectric ceramic (12) is moved along the z-axis for variable speed scanning according to the first absolute zero position Z1, the second absolute zero position Z2 and the interference region length, and the specific process is as follows: S41, fine scanning is performed downward along the z-axis within the actual interference region range [Z1-d1, Z1+d2] of the first absolute zero position Z1, the ideal interference interval range of the first absolute zero position Z1 is [Z1-d, Z1+d], wherein the lower limit d1 of the adjustment threshold of the first absolute zero position Z1 is d±n1·ΔZ, the upper limit d2 of the adjustment threshold of the first absolute zero position Z1 is d±n2·ΔZ, the ideal adjustment threshold d is min(DOF, ΔL) / 2, n1 is the number of moving steps relative to the scanning position Z1-d, n2 is the number of moving steps relative to the scanning position Z1+d, ΔZ is a preset fine scanning step length, Z1-d1 is the actual appearance position of the interference fringes of the first absolute zero position Z1, which is calculated by moving the piezoelectric ceramic (12) upward or downward along the z-axis relative to the scanning position Z1-d to determine the d1 value when the interference fringes appear, Z1+d2 is the actual disappearance position of the interference fringes of the first absolute zero position Z1, which is calculated by moving the piezoelectric ceramic (12) upward or downward along the z-axis relative to the scanning position Z1+d to determine the d2 value when the interference fringes disappear, and n1 and n2 are equal or unequal; S42, accelerated scanning is continuously performed downward along the z-axis until the actual interference region range of the second absolute zero position Z2 is reached, and the scanning step length of the accelerated scanning is greater than the preset fine scanning step length ΔZ; S43, fine scanning is performed downward along the z-axis within the actual interference region range [Z2-d3, Z2+d4] of the second absolute zero position Z2, the ideal interference interval range of the second absolute zero position Z2 is [Z2-d, Z2+d], wherein the lower limit d3 of the adjustment threshold of the second absolute zero position Z2 is d±n3·ΔZ, the upper limit d4 of the adjustment threshold of the second absolute zero position Z2 is d±n4·ΔZ, n3 is the number of moving steps relative to the scanning position Z2-d, n4 is the number of moving steps relative to the scanning position Z2+d, Z2-d3 is the actual appearance position of the interference fringes of the second absolute zero position Z2, which is calculated by moving the piezoelectric ceramic (12) upward or downward along the z-axis relative to the scanning position Z2-d to determine the d3 value when the interference fringes appear, Z2+d4 is the actual disappearance position of the interference fringes of the second absolute zero position Z2, which is calculated by moving the piezoelectric ceramic (12) upward or downward along the z-axis relative to the scanning position Z2+d to determine the d4 value when the interference fringes disappear, and n3 and n4 are equal or unequal.

9. The method of claim 4, wherein: the white light interferometry scan interval fast auto-positioning method further comprises: determining a position of the reference surface based on the reference surface position data; and determining a position of the sample surface based on the sample surface position data. The white light interference scanning interval rapid automatic positioning method further comprises: S6, a coherent peak perception algorithm is used for three-dimensional reconstruction of the screened interference fringe pictures.

10. The method of claim 9, wherein: the white light interferometry scan interval fast auto-positioning method further comprises: determining a position of the reference surface based on the reference surface position data; and determining a position of the sample surface based on the sample surface position data. The coherent peak perception algorithm is an improved barycenter method, and the formula is as follows: m(z) = (i Z -I Z-ΔZ ) 2 where I Z is the light intensity value of the interference fringe picture recorded at the scanning position Z, Z-ΔZ is the light intensity value of the interference fringe picture recorded at the scanning position Z-ΔZ, ΔZ is a preset fine scanning step, m(Z) is the light intensity value difference, and h is the height of the sample (14) being measured.

Images