White light interference scanning interval rapid automatic positioning system and method

Abstract

The invention discloses a white light interference scanning interval rapid automatic positioning system and method, and the system comprises an illumination unit, a differential confocal positioning unit, a white light interference data collection unit and an electric displacement control unit, and a to-be-observed target area of a detected sample is placed in a view field of a camera; performing coarse positioning and scanning on the tested sample to obtain a first absolute zero position as an upper surface and a second absolute zero position as a lower surface, and correspondingly recording a light intensity value; the electric angle table is driven to complete inclined positioning; determining the interference area length of the interference fringe picture, enabling the piezoelectric ceramic to move along the z axis according to the first absolute zero point position, the second absolute zero point position and the interference area length so as to carry out variable-speed scanning, and collecting the interference fringe picture in real time through the obliquely positioned camera; and the interference fringe pictures with the interference fringes are screened out to complete scanning interval positioning for three-dimensional reconstruction, so that the measurement precision and efficiency of the measured sample can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of optical measurement, and in particular relates to a system and method for rapid automatic positioning of a white light interference scanning interval. Background Art

[0002] With the demand for further miniaturization, integration and functional application of measurement systems, the size of micro-nano structural units has become smaller, with higher precision and complexity, and the spacing between adjacent units has reached the submicron level. High-precision measurement and characterization of their morphology is crucial to ensure the quality of micro-nano materials.

[0003] As a non-contact measurement method, white light interferometry can achieve accurate three-dimensional measurement of submicron or even nanoscale microstructures, and is widely used in the field of precision measurement. During measurement, the interference fringes on the grayscale of the image cause the unimodality of the autofocus algorithm to fail easily, and the accuracy of the focus search is greatly reduced. Existing white light interferometry systems often require manual adjustment of the configuration scanning parameters, and the positions where the interference fringes appear and disappear are determined by human visual observation to establish the upper and lower boundaries of the scan. However, the white light interferometry system uses a broadband light source, resulting in a short coherence length, generally only a few microns, which limits the visible range of the interference fringes, and the limited depth of field of the interference objective lens poses a major challenge to traditional manual focusing, making it difficult to accurately focus. In addition, in the measurement of large-scale structural parts, which refers to structural parts with large vertical dimensions or large horizontal dimensions, the object being measured has ups and downs of tens or even hundreds of microns. The traditional white light interferometry system maintains a fixed step size during the scanning process, resulting in a considerable portion of the defocused signal acquisition without interference fringes. These defocused signals are background noise, that is, they do not contain the true height information of the object, which makes this scanning mode limit the measurement efficiency. At the same time, due to the participation of a large number of redundant images in reconstruction, the reconstruction efficiency is also reduced. Summary of the invention

[0004] The purpose of the present invention is to address the above-mentioned problems and to provide a system and method for rapid automatic positioning of a white light interference scanning interval, which is helpful to improve the measurement accuracy and efficiency of the measured sample.

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

[0006] The present invention provides a white light interference scanning interval rapid automatic positioning system, comprising:

[0007] An illumination unit, comprising a low-coherence light source, a first beam splitter and a first lens group, which are sequentially arranged along a first light path direction, wherein the first beam splitter is used to transmit light emitted by the low-coherence light source to a third beam splitter through the first lens group;

[0008] A differential confocal positioning unit comprises a second beam splitter, a back-focus detector and a front-focus detector, wherein the back-focus detector and the front-focus detector are respectively located on two adjacent sides of the second beam splitter, and the first beam splitter is used to transmit the light reflected back by the third beam splitter to the back-focus detector and reflect it to the front-focus detector through the second beam splitter;

[0009] A white light interference data acquisition unit comprises a camera, a second lens group, a third beam splitter, a piezoelectric ceramic and an interference objective lens which are sequentially arranged along a second optical path direction, wherein the second optical path direction is perpendicular to the first optical path direction, and the third beam splitter is used to reflect the received light to the piezoelectric ceramic and irradiate the light to the sample under test through the interference objective lens, and the light reflected back by the sample under test sequentially passes through the interference objective lens and the piezoelectric ceramic to reach the third beam splitter, and is respectively transmitted by the third beam splitter and then reaches the camera through the second lens group to realize interference fringe image collection, and then reaches the first beam splitter through the first lens group after reflection;

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

[0011] Preferably, the differential confocal positioning unit further comprises a first pinhole diaphragm and a second pinhole diaphragm, the first pinhole diaphragm is located between the second beam splitter and the rear focus detector, and the second pinhole diaphragm is located between the second beam splitter and the front focus detector.

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

[0013] A white light interference scanning interval rapid automatic positioning method, based on any of the above white light interference scanning interval rapid automatic positioning systems, comprises the following steps:

[0014] S1, driving the electric three-dimensional platform to move along the x-axis and y-axis, and placing the target area of ​​the sample to be tested in the field of view of the camera;

[0015] S2, after the sample is roughly positioned by moving the z-axis, the piezoelectric ceramic is scanned along the z-axis to obtain the first absolute zero position Z1 as the upper surface of the sample, and the second absolute zero position Z2 as the lower surface of the sample, and the light intensity value I of the first absolute zero position Z1 is recorded by the camera. focus1 and the light intensity value I at the second absolute zero position Z2 focus2 , correspondingly recording the front focus light intensity value I1 of the upper surface of the measured sample and the front focus light intensity value I3 of the lower surface of the measured sample through the front focus detector, and correspondingly recording the back focus light intensity value I2 of the upper surface of the measured sample and the back focus light intensity value I4 of the lower surface of the measured sample through the back focus detector;

[0016] S3, driving the electric angle stage to adjust the tilt angle of the sample to be measured until the number of interference fringes on the interference fringes image observed by the camera is less than or equal to a preset value to complete the tilt positioning;

[0017] S4, determining the interference area length of the interference fringe image, moving the piezoelectric ceramic along the z-axis for variable speed scanning according to the first absolute zero point position Z1, the second absolute zero point position Z2 and the interference area length, and collecting the interference fringe image in real time through the camera, the interference area length 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 lens;

[0018] S5, filter out the interference fringe image with interference fringes to complete the scanning interval positioning for three-dimensional reconstruction, that is, the light intensity value I of the interference fringe image recorded at the scanning position Z Z The interference fringe images with values ​​greater than or equal to the first threshold η1 or the second threshold η2 are retained, and the interference fringe images with values ​​less than the first threshold η1 or the second threshold η2 are filtered out, wherein 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 of obtaining each absolute zero point position is as follows:

[0020] S21, observing the camera and driving the electric three-dimensional platform to move the z-axis, adjusting the sample to be tested to a preset adjacent position corresponding to the focal plane to achieve rough positioning, and the focal plane is the absolute zero point position;

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

[0022]

[0023] Wherein, Ia is the front focal light intensity value of the sample under test corresponding to the focal plane at the current scanning position, Ib is the back focal light intensity value of the sample under test corresponding to the focal plane at the current scanning position, max(·) indicates the maximum value, min(·) indicates the minimum value, and Δ indicates the minimum value close to 0;

[0024] Right now

[0025]

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

[0027] Preferably, the number of interference fringes on 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 expressed as follows:

[0029]

[0030] The depth of field DOF of the interference objective lens is given by the following formula:

[0031]

[0032] Wherein, λ0 represents the central 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 to perform variable speed scanning according to the first absolute zero point position Z1, the second absolute zero point position Z2 and the length of the interference region, as follows:

[0034] S41. Perform fine scanning downward along the z-axis within the actual interference area 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 of the adjustment threshold of the first absolute zero position Z1 is d1=d±n1·ΔZ, the upper limit of the adjustment threshold of the first absolute zero position Z1 is d2=d±n2·ΔZ, the ideal adjustment threshold d=min(DOF,ΔL) / 2, n1 is the number of moving steps relative to the scanning position Z1-d, and n2 is The number of moving steps relative to the scanning position Z1+d, ΔZ is the preset fine scanning step length, Z1-d1 is the actual appearance position of the interference fringes at the first absolute zero position Z1, which is obtained by calculating the d1 value when the interference fringes appear by moving the piezoelectric ceramic upward or downward along the z-axis relative to the scanning position Z1-d, Z1+d2 is the actual disappearance position of the interference fringes at the first absolute zero position Z1, which is obtained by calculating the d2 value when the interference fringes disappear by moving the piezoelectric ceramic upward or downward along the z-axis relative to the scanning position Z1+d, and n1 and n2 are equal or unequal;

[0035] S42, continue to perform accelerated scanning downward along the z-axis until reaching the actual interference region range of the second absolute zero position Z2, and the scanning step length of the accelerated scanning is greater than the preset fine scanning step length ΔZ;

[0036] S43, perform fine scanning downward along the z-axis within the actual interference area range [Z2-d3, Z2+d4] of the second absolute zero position Z2, and the ideal interference interval range of the second absolute zero position Z2 is [Z2-d, Z2+d], wherein the lower limit of the adjustment threshold of the second absolute zero position Z2 is d3=d±n3·ΔZ, the upper limit of the adjustment threshold of the second absolute zero position Z2 is d4=d±n4·ΔZ, n3 is the number of moving steps relative to the scanning position Z2-d, and n4 is the number of moving steps relative to the scanning position Z2-d. The number of moving steps of position Z2+d, Z2-d3 is the actual appearance position of the interference fringes at the second absolute zero point position Z2, which is obtained by calculating the d3 value when the interference fringes appear by moving the piezoelectric ceramic upward or downward along the z-axis relative to the scanning position Z2-d, Z2+d4 is the actual disappearance position of the interference fringes at the second absolute zero point position Z2, which is obtained by calculating the d4 value when the interference fringes disappear by moving the piezoelectric ceramic upward or downward along the z-axis relative to the scanning position Z2+d, and n3 and n4 are equal or different.

[0037] Preferably, the white light interference scanning interval rapid automatic positioning method further includes:

[0038] S6. Use the coherence peak sensing algorithm to perform three-dimensional reconstruction on the selected interference fringe images.

[0039] Preferably, the coherent peak perception 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 is the light intensity value of the interference fringe image recorded at scanning position Z, I Z-ΔZ is the light intensity value of the interference fringe image recorded at the scanning position Z-ΔZ, ΔZ is the preset fine scanning step, m(Z) is the light intensity difference, and h is the height of the sample being measured.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] The technical solution of the present invention includes an illumination unit, a differential confocal positioning unit, a white light interference data acquisition unit and an electric displacement control unit, which can realize multi-degree-of-freedom adjustment of the sample to be tested to collect light intensity signals of the sample to be tested at different optical axis positions, obtain the confocal axial response intensity curve to realize the determination of the absolute zero point position to accurately locate the upper and lower focal planes of the sample to be tested and obtain high-quality interference fringe images in real time, avoid errors caused by manual operation and human eye judgment, and can be used for scanning large-scale structural parts, thereby improving measurement efficiency and accuracy; and by selecting a smaller value between the coherence length of the low-coherence light source and the depth of field of the interference objective lens as the length limit of the fine scanning area The first absolute zero point position is located in the middle of the fine scanning area of ​​the upper surface, and the second absolute zero point position is located in the middle of the fine scanning area of ​​the lower surface, thereby determining the scanning intervals of different speeds, and further correcting the corresponding interference area range, driving the piezoelectric ceramic to scan in the interference area range, and the camera records a series of interference fringe images for three-dimensional reconstruction. Compared with the traditional fixed-step scanning method, the variable speed scanning method proposed in the present invention is combined with the use of a differential confocal positioning unit to shoot the front focus intensity map and the back focus intensity map for subsequent screening of interference fringe images. The judgment can reduce the subsequent white light interference reconstruction time and greatly improve the measurement efficiency and accuracy of the measured sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a structural schematic diagram of the white light interference scanning interval rapid automatic positioning system of the present invention;

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

[0047] Figure 3 This is a curve diagram of the differential confocal axial response intensity of the present invention;

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

[0049] Explanation of the accompanying drawings: 1. low coherence light source; 2. first beam splitter; 3. first lens group; 4. second beam splitter; 5. first pinhole diaphragm; 6. back focus detector; 7. second pinhole diaphragm; 8. front focus detector; 9. camera; 10. second lens group; 11. third beam splitter; 12. piezoelectric ceramics; 13. interference objective lens; 14. measured sample; 15. electric angle stage; 16. electric three-dimensional platform; 17. illumination unit; 18. differential confocal positioning unit; 19. white light interferometry data acquisition unit; 20. electric displacement control unit. DETAILED DESCRIPTION

[0050] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work 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 those commonly understood by those skilled in the art in the technical field of this application. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0052] Embodiment 1:

[0053] like Figure 1 As shown, a white light interference scanning interval rapid automatic positioning system comprises:

[0054] The lighting unit 17 comprises a low-coherence light source 1, a first beam splitter 2 and a first lens group 3 which are sequentially arranged along a first optical path direction, wherein the first beam splitter 2 is used for transmitting the light emitted by the low-coherence light source 1 to the third beam splitter 11 through the first lens group 3;

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

[0056] The white light interference data acquisition unit 19 comprises a camera 9, a second lens group 10, a third beam splitter 11, a piezoelectric ceramic 12 and an interference objective lens 13 which are sequentially arranged along a second optical path direction, wherein the second optical path direction is perpendicular to the first optical path direction, and the third beam splitter 11 is used to reflect the received light to the piezoelectric ceramic 12 and irradiate the light to the sample 14 through the interference objective lens 13, and the light reflected back by the sample 14 sequentially passes through the interference objective lens 13 and the piezoelectric ceramic 12 to reach the third beam splitter 11, and is respectively transmitted by the third beam splitter 11 and then reaches the camera 9 through the second lens group 10 to realize the collection of interference fringe images, and then reaches the first beam splitter 2 through the first lens group 3 after being reflected;

[0057] The electric displacement control unit 20 includes an electric angle table 15 and an electric three-dimensional platform 16. The electric angle table 15 is used to drive the measured 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 table 15 to move around 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 , wherein the first pinhole aperture 5 is located between the second beam splitter 4 and the rear 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, the first lens group 3 and the second lens group 10 each include at least one lens.

[0060] like Figure 1 As shown, a white light interference scanning interval rapid automatic positioning system, wherein 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 interference data acquisition unit 19, is reflected by the third beam splitter 11 and enters the interference objective lens 13 to irradiate the sample 14 to be tested, the light reflected back by the sample 14 to be tested returns to the first beam splitter 2 through the original path, is then reflected into the differential confocal positioning unit 18, and is divided into two light beams by the second beam splitter 4, the reflected light beam passes through the second pinhole diaphragm 7 and is detected by the front focus detector 8, and the corresponding front focus intensity map is recorded to obtain the front focus light intensity value, the transmitted light beam passes through the first pinhole diaphragm 5 and is detected by the back focus detector 6, and the corresponding back focus intensity map is recorded to obtain the back focus light intensity value, and the light reflected back by the sample 14 to be tested also passes through the interference objective lens 13, the piezoelectric ceramic 12, the third beam splitter 11, and the second lens group 10 in sequence to reach the camera 9 to realize the interference fringe image collection. The interference objective lens 13 may be a Mirau interference objective lens, and the back focus detector 6 and the front focus detector 8 may be cameras. The x-axis, y-axis and z-axis form a rectangular coordinate system, such as 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, which is only for ease of understanding, and the specific orientation can also be adjusted according to actual needs. The system realizes the control of the spatial placement position of the sample 14 under test, and can continuously perform high-precision nanometer-level scanning through the piezoelectric ceramic 12, and the camera 9 continuously collects interference fringe images at the same time.

[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 moving and adjusting the electric three-dimensional platform 16 in the x-axis and y-axis directions, and then the sample 14 to be tested is moved in the z-axis to achieve rough positioning (and scan and obtain the first absolute zero point position Z1 as the upper surface of the sample 14 to be tested, and the second absolute zero point position Z2 as the lower surface of the sample 14 to be tested and record the corresponding light intensity values. If the positions of the rough positioning are respectively near the upper surface and the lower surface of the sample 14 to be tested, 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 a preset scanning step length) to obtain the front focus light intensity value and the back focus light intensity value of the corresponding scanning position The first absolute zero point is determined by using the front focus light intensity value and the back focus light intensity value, which is the upper surface of the sample 14 to be tested. The above process is repeated to make the piezoelectric ceramic 12 scan near the lower surface to determine the second absolute zero point, which is the lower surface of the sample 14 to be tested. The electric angle table 15 is then used to adjust the rotation angle around the x-axis, y-axis and z-axis to ensure that the number of interference fringes on the interference fringes image observed by the camera 9 meets the requirements to complete the tilt positioning, which is conducive to accurate scanning and positioning. The light reflected back by the sample 14 to be tested is also directly transmitted through the third beam splitter 11 and focused by the second lens group 10 onto the camera 9. The camera 9 records a series of interference fringes images at the Z-axis position for subsequent three-dimensional reconstruction.

[0062] Embodiment 2:

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

[0064] S1, driving the electric three-dimensional platform 16 to move along the x-axis and the y-axis, and 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 the sample of the large-scale structural parts to be observed, it is also possible to complete image stitching and perform subsequent processing after collecting a partial area of ​​the target area to be observed each time.

[0065] S2, after the measured sample 14 is roughly positioned by moving the z-axis, the piezoelectric ceramic 12 is moved and scanned along the z-axis to obtain the first absolute zero point position Z1 as the upper surface of the measured sample 14, and the second absolute zero point position Z2 as the lower surface of the measured sample 14, and the camera 9 is used to record the light intensity value I of the first absolute zero point position Z1 focus1 and the light intensity value I at the second absolute zero position Z2 focus2, the front focus light intensity value I1 of the upper surface of the measured sample 14 and the front focus light intensity value I3 of the lower surface of the measured sample 14 are recorded correspondingly through the front focus detector 8, and the back focus light intensity value I2 of the upper surface of the measured sample 14 and the back focus light intensity value I4 of the lower surface of the measured sample 14 are recorded correspondingly through the back focus detector 6.

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

[0067] S21, observing the camera 9 and driving the electric three-dimensional platform 16 to move the z-axis, adjusting the sample 14 to a preset adjacent position corresponding to the focal plane to achieve rough positioning, the focal plane being the absolute zero position;

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

[0069]

[0070] Wherein, Ia is the front focal light intensity value of the measured sample 14 corresponding to the focal plane at the current scanning position, Ib is the back focal light intensity value of the measured sample 14 corresponding to the focal plane at the current scanning position, max(·) indicates the maximum value, min(·) indicates the minimum value, and Δ indicates the minimum value close to 0;

[0071] Right now

[0072]

[0073] When ID=0 or ID realizes a transition between -1 and 1, it indicates that a focal plane exists, that is, 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 in the z-axis, and adjust the sample 14 to a preset position adjacent to the first focal plane to achieve rough positioning. The first focal plane is the first absolute zero position Z1.

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

[0077]

[0078] Among them, max(·) means taking the maximum value, min(·) means taking the minimum value, and Δ means the minimum value close to 0, which can be ignored to prevent the occurrence of 0 / 0.

[0079]

[0080] The relationship between the current Z-axis position of the piezoelectric ceramic 12 and the focal plane position of the sample 14 to be tested is determined based on the ID value. -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, there is always a deviation between the front focus light intensity value and the back focus light intensity value. The situation where ID=0 is basically impossible to occur. Therefore, in fact, when the ID transitions between -1 and 1, the current z-axis position of the piezoelectric ceramic 12 indicates the focal plane position. Assuming that the detection position is the upper surface of the sample 14 to be tested at this time, the Z-axis position of the piezoelectric ceramic 12 is Z1, and the camera 9 records the light intensity value I of the first absolute zero position Z1. focus1 .

[0081] 3) When the height difference between the upper and lower surfaces of the sample 14 under test exceeds the depth of field of the objective lens, it means that there are two focal planes. At this time, two positionings are required. After finding the first absolute zero position Z1, continue to adjust the piezoelectric ceramic 12 downward along the Z axis, repeat the above operation, that is, continue to observe the camera 9 and drive the electric three-dimensional platform 16 to move the Z axis, adjust the sample 14 under test to the preset adjacent position of the second focal plane to achieve rough positioning, the second focal plane is the second absolute zero position Z2, find the front focal intensity value I3 of the lower surface of the sample 14 under test and the back focal intensity value I4 of the lower surface of the sample 14 under test, and obtain the second absolute zero position Z2 according to the judgment condition value ID of the absolute zero position, the formula is as follows:

[0082]

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

[0084] S3, driving the electric angle stage 15 to adjust the tilt angle of the sample 14 to be tested until the number of interference fringes on the interference fringes image observed by the camera 9 is less than or equal to a preset value to complete the tilt positioning.

[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, such as calculating the number of fringes by binarizing the interference fringe image. Generally, 3 to 5 interference fringes are more appropriate, which avoids the problem that the white light coherence length is short and the interference fringes become blurred after exceeding a certain range. Interference fringes below 5 can ensure clarity within the coherence length, with high contrast and a relatively small inclination angle. The target number of interference fringes and the inclination angle of the electric angle stage 15 are set until the appropriate number of interference fringes appears and the electric angle stage 15 stops moving.

[0087] S4. Determine the interference area length of the interference fringe image, and move the piezoelectric ceramic 12 along the z-axis for variable speed scanning according to the first absolute zero point position Z1, the second absolute zero point position Z2 and the interference area length, and collect the interference fringe image in real time through the camera 9. The interference area length 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 expressed as follows:

[0089]

[0090] The depth of field DOF of the interference objective lens 13 is given by the following formula:

[0091]

[0092] Wherein, λ0 represents the central 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 lens 13 .

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

[0094] S41. Finely scan downward along the z axis within the actual interference area range [Z1-d1, Z1+d2] of the first absolute zero position Z1 (S1 area). The ideal interference interval range of the first absolute zero position Z1 is [Z1-d, Z1+d], where the lower limit of the adjustment threshold of the first absolute zero position Z1 is d1=d±n1·ΔZ, the upper limit of the adjustment threshold of the first absolute zero position Z1 is d2=d±n2·ΔZ, the ideal adjustment threshold d=min(DOF,ΔL) / 2, n1 is the number of moving steps relative to the scanning position Z1-d, and n2 is The number of moving steps relative to the scanning position Z1+d, ΔZ is the preset fine scanning step length, Z1-d1 is the actual appearance position of the interference fringes at the first absolute zero position Z1, which is obtained by calculating the d1 value when the interference fringes appear by moving the piezoelectric ceramic 12 upward or downward along the z-axis relative to the scanning position Z1-d, Z1+d2 is the actual disappearance position of the interference fringes at the first absolute zero position Z1, which is obtained by calculating the d2 value when the interference fringes disappear by moving the piezoelectric ceramic 12 upward or downward along the z-axis relative to the scanning position Z1+d, and n1 and n2 are equal or unequal;

[0095] S42, continue to accelerate scanning downward along the z-axis (S2 area) until reaching the actual interference area range of the second absolute zero position Z2, and the scanning step length of the accelerated scanning is greater than the preset fine scanning step length ΔZ;

[0096] S43, perform a fine scan downward along the z-axis within the actual interference region range [Z2-d3, Z2+d4] of the second absolute zero position Z2 (S3 region), and the ideal interference region range of the second absolute zero position Z2 is [Z2-d, Z2+d], wherein the lower limit of the adjustment threshold of the second absolute zero position Z2 is d3=d±n3·ΔZ, the upper limit of the adjustment threshold of 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 movement steps relative to the scanning position Z2-d. The number of moving steps of position Z2+d, Z2-d3 is the actual appearance position of the interference fringes at the second absolute zero point position Z2, which is obtained by calculating the d3 value when the interference fringes appear by moving the piezoelectric ceramic 12 upward or downward along the z-axis relative to the scanning position Z2-d, Z2+d4 is the actual disappearance position of the interference fringes at the second absolute zero point position Z2, which is obtained by calculating the d4 value when the interference fringes disappear by moving the piezoelectric ceramic 12 upward or downward along the z-axis relative to the scanning position Z2+d, and n3 and n4 are equal or different.

[0097] Specifically, since the optical path structure of the white light interference scanning interval rapid automatic positioning system is determined, the low coherence light source 1 used is also determined. The length of the area 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 value of the coherence length ΔL of the low coherence light source 1 and the depth of field DOF of the interference objective lens 13. Therefore, the length of the interference area 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, the first interference area (the actual interference area range of the first absolute zero position Z1) is finely scanned within the range of the lower limit Z1-d and the upper limit Z1+d, where d=min(DOF,ΔL) / 2. In actual operation, due to the susceptibility to environmental influences, the interference fringes are no longer symmetrically distributed around the optimal interference position, and the actual upper and lower limits of the interference area also change. If the fine scanning step is set to ΔZ=100nm, the position where the interference fringes appear can be further verified by using the fore-focus intensity map taken during the process of finding the first absolute zero position Z1 in step S2, and the lower limit Z1-d becomes Z1-d1, where d1=min(DOF,ΔL) / 2±n1·ΔZ, n1 is the number of moving 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 position where the interference fringes appear in the first interference area, and Z1-d1 is the actual position where the interference fringes appear in the first interference area. The positive and negative signs of d1 indicate that Z1-d1 may be above Z1-d or below Z1-d, and its positive and negative values ​​are determined by the actual position where the interference fringes appear when the piezoelectric ceramic 12 moves upward or downward along the z-axis relative to the scanning position Z1-d. For example, the position where the interference fringes appear can be verified directly by using the fore-focus intensity map taken during the process of finding the first absolute zero position Z1 in step S2, without repeated searching. Similarly, using step The back focus intensity map captured during the process of searching for the first absolute zero point position Z1 in S2 further verifies the position where the interference fringes disappear, and the upper limit Z1+d becomes Z1+d2, where d2=min(DOF,ΔL) / 2±n2·ΔZ, n2 is the number of moving steps relative to the scanning position Z1+d, and Z1+d2 may be above or below Z1+d, that is, Z1+d is the ideal disappearance position of the interference fringes in the first interference area, and Z1+d2 is the actual disappearance position of the interference fringes in the first interference area. The positive and negative signs of d2 indicate that Z1+d2 may be above Z1+d or below Z1+d, and its positive and negative values ​​are determined by the actual disappearance position 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. For example, the back focus intensity map captured during the process of searching for the first absolute zero point position Z1 in step S2 can be directly used to verify the position where the interference fringes disappear, without repeated searching. 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 scan continues downward along the z-axis and enters the background signal region without interference fringes, and the piezoelectric ceramic 12 is made to perform large-step accelerated scanning, and the step length of the accelerated scanning is set to ΔZ a =1000nm.

[0100] After the accelerated scanning area, 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 point position Z2) are determined for fine scanning. Similarly, in actual operation, due to the susceptibility to environmental influences, the interference fringes are no longer symmetrically distributed with the optimal interference position as the center, and the actual upper and lower limits of the interference area also change. If the fine scanning step is set to ΔZ=100nm, the position where the interference fringes appear can be further verified by using the fore-focus intensity map taken during the process of finding the second absolute zero position Z2 in step S2, and the lower limit Z2-d becomes Z2-d3, where d3=min(DOF,ΔL) / 2±n3·ΔZ, n3 is the number of moving steps relative to the scanning position Z2-d, and Z2-d3 may be above or below Z2-d, that is, Z2-d is the ideal position where the interference fringes in the second interference area appear, and Z2-d3 is the actual position where the interference fringes in the second interference area appear. The positive and negative signs of d3 indicate that Z2-d3 may be above Z2-d or below Z2-d, and its positive and negative values ​​are determined by the actual position where the interference fringes appear when the piezoelectric ceramic 12 moves upward or downward along the z-axis relative to the scanning position Z2-d. For example, the position where the interference fringes appear can be verified directly by using the fore-focus intensity map taken during the process of finding the second absolute zero position Z2 in step S2, without repeated searching. Similarly, using step The back focus intensity map captured during the search for the second absolute zero position Z2 in S2 further verifies the position where the interference fringes disappear, and the upper limit Z2+d becomes Z2+d4, where d4=min(DOF,ΔL) / 2±n4·ΔZ, n4 is the number of moving steps relative to the scanning position Z2+d, and Z2+d4 may be above or below Z2+d, that is, Z2+d is the ideal disappearance position of the interference fringes in the second interference area, and Z2+d4 is the actual disappearance position of the interference fringes in the second interference area. The positive and negative signs of d4 indicate that Z2+d4 may be above Z2+d or below Z2+d, and its positive and negative values ​​are determined by the actual disappearance position 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. For example, the position where the interference fringes disappear can be verified directly using the back focus intensity map captured during the search for the second absolute zero position Z2 in step S2, without repeated search, and n3 and n4 are not necessarily equal, depending on the specific situation. d3 and d4 are not much different from d.

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

[0102] S5, filter out the interference fringe image with interference fringes to complete the scanning interval positioning for three-dimensional reconstruction, that is, the light intensity value I of the interference fringe image recorded at the scanning position Z Z The interference fringe images with values ​​greater than or equal to the first threshold η1 or the second threshold η2 are retained, and the interference fringe images with values ​​less than the first threshold η1 or the second threshold η2 are filtered out, wherein 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 the true height information only exists in the interference fringes, the signal without interference fringes is regarded as background noise. After determining the scanning boundary position and the scanning step length, the interference process is recorded from Z1-d1 to Z2+d4. In order to verify whether the interference fringes exist, the verification conditions are set, and the interference fringes images without interference fringes are screened out and do not participate in the subsequent reconstruction process, thereby reducing the white light interference reconstruction time.

[0104] That is, when the current z-axis position of the piezoelectric ceramic 12 is Z1-d1, the interference fringes displayed by the camera 9 appear, when the current z-axis position of the piezoelectric ceramic 12 is Z1, the interference fringes displayed by the camera 9 are most obvious, 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 while collecting, according to the light intensity value of Z1 obtained in step S2 (including the light intensity value I of the first absolute zero position Z1) focus1 , the front focal intensity value I1 of the upper surface of the sample 14, the back focal intensity value I2 of the upper surface of the sample 14) calculate the judgment threshold, and set the first threshold η1=min(I focus1 -I1,I focus1 -I2) as the condition for judging whether interference fringes exist, the light intensity value I of the interference fringes image recorded when the scanning position is Z Z Compared with the first threshold η1, it is shown in the following expression:

[0105]

[0106] Among them, I Z In the case of ≥η1, the interference fringe image is retained for reconstruction, I Z When <η2, the interference fringe image will be green and thick and will not be involved in the reconstruction.

[0107] When the current z-axis position of the piezoelectric ceramic 12 is Z2-d3, the interference fringes displayed by the camera 9 appear again; when the current z-axis position of the piezoelectric ceramic 12 is Z2, the interference fringes displayed by the camera 9 are most obvious again; when the current z-axis position of the piezoelectric ceramic 12 is Z2+d4, the interference fringes displayed by the camera 9 disappear again; judgment can be made while collecting, according to the light intensity value of Z2 obtained in step S2 (including the light intensity value I of the second absolute zero position Z2) focus2 , the front focal light intensity value I3 of the lower surface of the measured sample (14), the back focal light intensity value I4 of the lower surface of the measured sample (14)) calculate the judgment threshold, and set the second threshold value to η2=min(I focus2 -I3,I focus2 -I4) as the condition for judging whether interference fringes exist, the light intensity value I of the interference fringes image recorded when the scanning position is Z Z Compared with the second threshold η2, it is shown in the following expression:

[0108]

[0109] Among them, I n In the case of ≥η2, the interference fringe image is retained for reconstruction, I n When <η2, the interference fringe image is filtered out and does not participate in the reconstruction.

[0110] In one embodiment, the white light interference scanning interval rapid automatic positioning method further includes:

[0111] S6. Use the coherence peak sensing algorithm to perform three-dimensional reconstruction on the selected interference fringe images.

[0112] In one embodiment, the coherent peak perception 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 is the light intensity value of the interference fringe image recorded at scanning position Z, I Z-ΔZ is the light intensity value of the interference fringe image recorded at the scanning position Z-ΔZ, ΔZ is the preset fine scanning step, m(Z) is the light intensity value difference, and h is the height of the sample 14 under test.

[0116] Based on the operations of the above steps S1 to S6, the spatial position of the sample 14 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-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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 above-described embodiments only express the more specific and detailed embodiments described in this application, but they cannot be understood as limiting the scope of the application. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of this application, which all belong to the protection scope of this application. Therefore, the protection scope of this application shall be based on the attached claims.

Claims

1. A white light interference scanning interval rapid automatic positioning system, characterized in that: The white light interference scanning interval rapid automatic positioning system comprises: An illumination unit (17) comprises 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, wherein the first beam splitter (2) is used to transmit light emitted by the low-coherence light source (1) to the third beam splitter (11) via the first lens group (3); A differential confocal positioning unit (18), comprising a second beam splitter (4), a back-focus detector (6) and a front-focus detector (8), wherein the back-focus detector (6) and the front-focus detector (8) are respectively located on two adjacent sides of the second beam splitter (4), and the first beam splitter (2) is used to transmit the light reflected by the third beam splitter (11) to the back-focus detector (6) and reflect it to the front-focus detector (8) through the second beam splitter (4); A white light interference data acquisition unit (19) comprises a camera (9), a second lens group (10), a third beam splitter (11), a piezoelectric ceramic (12) and an interference objective lens (13) which are sequentially arranged along a second light path direction, wherein the second light path direction is perpendicular to the first light path direction, the third beam splitter (11) is used to reflect received light to the piezoelectric ceramic (12) and irradiate the light to a sample (14) through the interference objective lens (13), the light reflected back by the sample (14) sequentially passes through the interference objective lens (13) and the piezoelectric ceramic (12) to reach the third beam splitter (11), and is respectively transmitted by the third beam splitter (11) and then reaches the camera (9) through the second lens group (10) to realize interference fringe image acquisition, and is reflected and then reaches the first beam splitter (2) through the first lens group (3); The electric displacement control unit (20) comprises an electric angle table (15) and an electric three-dimensional platform (16), wherein the electric angle table (15) is used to drive the sample to be measured (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 table (15) to move around the x-axis, y-axis and z-axis.

2. The white light interference scanning interval rapid automatic positioning system according to claim 1, characterized in that: The differential confocal positioning unit (18) further comprises a first pinhole diaphragm (5) and a second pinhole diaphragm (7), wherein the first pinhole diaphragm (5) is located between the second beam splitter (4) and the rear focus detector (6), and the second pinhole diaphragm (7) is located between the second beam splitter (4) and the front focus detector (8).

3. The white light interference scanning interval rapid automatic positioning system as claimed in claim 1, characterized in that: The first lens group (3) and the second lens group (10) each include at least one lens.

4. A white light interference scanning interval rapid automatic positioning method, based on the white light interference scanning interval rapid automatic positioning system according to any one of claims 1 to 3, characterized in that: The white light interference scanning interval rapid automatic positioning method comprises the following steps: S1, driving the electric three-dimensional platform (16) to move along the x-axis and the y-axis, and placing the target area of ​​the sample to be tested (14) to be observed within the field of view of the camera (9); S2, after the sample (14) to be tested is roughly positioned by moving along the z-axis, the piezoelectric ceramic (12) is moved and scanned along the z-axis to obtain a first absolute zero point position Z1 as the upper surface of the sample (14) to be tested, and a second absolute zero point position Z2 as the lower surface of the sample (14) to be tested, and a light intensity value I of the first absolute zero point position Z1 is correspondingly recorded by a camera (9). focus1 and the light intensity value I at the second absolute zero position Z2 focus2 , correspondingly recording a front focus light intensity value I1 of the upper surface of the measured sample (14) and a front focus light intensity value I3 of the lower surface of the measured sample (14) through a front focus detector (8), and correspondingly recording a back focus light intensity value I2 of the upper surface of the measured sample (14) and a back focus light intensity value I4 of the lower surface of the measured sample (14) through a back focus detector (6); S3, driving the electric angle stage (15) to adjust the tilt angle of the sample (14) to be tested until the number of interference fringes on the interference fringes image observed by the camera (9) is less than or equal to a preset value, thereby completing the tilt positioning; S4, determining the interference region length of the interference fringe image, moving the piezoelectric ceramic (12) along the z-axis for variable speed scanning according to the first absolute zero point position Z1, the second absolute zero point position Z2 and the interference region length, and collecting the interference fringe image in real time through the camera (9), wherein the interference region length is min(DOF, ΔL), wherein 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); S5, filter out the interference fringe image with interference fringes to complete the scanning interval positioning for three-dimensional reconstruction, that is, the light intensity value I of the interference fringe image recorded at the scanning position Z Z The interference fringe images with values ​​greater than or equal to the first threshold η1 or the second threshold η2 are retained, and the interference fringe images with values ​​less than the first threshold η1 or the second threshold η2 are filtered out, wherein the first threshold η1 = min(I focus1 -I1,I focus1 -I2), the second threshold η2 = min(I focus2 -I3,I focus2 -I4).

5. The white light interference scanning interval rapid automatic positioning method according to claim 4, characterized in that: The process of obtaining the absolute zero position is as follows: S21, observing the camera (9) and driving the electric three-dimensional platform (16) to move along the z-axis, adjusting the sample to be tested (14) to a preset adjacent position corresponding to the focal plane to achieve rough positioning, wherein the focal plane is the absolute zero position; S22, taking the position of the piezoelectric ceramic (12) when the rough positioning is completed as the starting position, scanning the piezoelectric ceramic (12) upward or downward along the z-axis according to a preset scanning step length, and obtaining the corresponding differential confocal axial response intensity value I to determine the corresponding absolute zero point position, wherein the judgment condition value ID formula of the absolute zero point position is as follows: Wherein, Ia is the front focal light intensity value of the measured sample (14) corresponding to the focal plane at the current scanning position, Ib is the back focal light intensity value of the measured sample (14) corresponding to the focal plane at the current scanning position, max(·) represents the maximum value, min(·) represents the minimum value, and Δ represents the minimum value approaching 0; Right now When ID=0 or ID achieves a transition between -1 and 1, it indicates that a focal plane exists, that is, the current z-axis position of the piezoelectric ceramic (12) is obtained as the corresponding absolute zero point position.

6. The white light interference scanning interval rapid automatic positioning method according to claim 4, characterized in that: The number of interference fringes on the interference fringe image is obtained by binarizing the interference fringe image.

7. The white light interference scanning interval rapid automatic positioning method according to claim 4, characterized in that: The coherence length ΔL of the low coherence light source (1) is expressed as follows: The depth of field DOF of the interference objective lens (13) is expressed as follows: Wherein, λ0 represents the central 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 lens (13).

8. The white light interference scanning interval rapid automatic positioning method according to claim 4, characterized in that: The piezoelectric ceramic (12) is moved along the z-axis to perform variable speed scanning according to the first absolute zero point position Z1, the second absolute zero point position Z2 and the length of the interference region, specifically as follows: S41. Perform fine scanning downward along the z-axis within the actual interference area 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 of the adjustment threshold of the first absolute zero position Z1 is d1=d±n1·ΔZ, the upper limit of the adjustment threshold of the first absolute zero position Z1 is d2=d±n2·ΔZ, the ideal adjustment threshold d=min(DOF,ΔL) / 2, n1 is the number of movement steps relative to the scanning position Z1-d, and n2 is the number of movement steps relative to the scanning position Z1-d. The number of moving steps of the scanning position Z1+d, ΔZ is a preset fine scanning step length, Z1-d1 is the actual appearance position of the interference fringes at the first absolute zero point position Z1, which is obtained by calculating the d1 value when the interference fringes appear by moving the piezoelectric ceramic (12) upward or downward along the z-axis relative to the scanning position Z1-d, Z1+d2 is the actual disappearance position of the interference fringes at the first absolute zero point position Z1, which is obtained by calculating the d2 value when the interference fringes disappear by moving the piezoelectric ceramic (12) upward or downward along the z-axis relative to the scanning position Z1+d, and n1 and n2 are equal or different; S42, continue to perform accelerated scanning downward along the z-axis until reaching the actual interference region range of the second absolute zero position Z2, wherein the scanning step length of the accelerated scanning is greater than the preset fine scanning step length ΔZ; S43, perform fine scanning downward along the z-axis within the actual interference area range [Z2-d3, Z2+d4] of the second absolute zero position Z2, and the ideal interference interval range of the second absolute zero position Z2 is [Z2-d, Z2+d], wherein the lower limit of the adjustment threshold of the second absolute zero position Z2 is d3=d±n3·ΔZ, the upper limit of the adjustment threshold of the second absolute zero position Z2 is d4=d±n4·ΔZ, n3 is the number of moving steps relative to the scanning position Z2-d, and 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 at the second absolute zero point position Z2, which is obtained by calculating the d3 value when the interference fringes appear by moving the piezoelectric ceramic (12) upward or downward along the z-axis relative to the scanning position Z2-d, Z2+d4 is the actual disappearance position of the interference fringes at the second absolute zero point position Z2, which is obtained by calculating the d4 value when the interference fringes disappear by moving the piezoelectric ceramic (12) upward or downward along the z-axis relative to the scanning position Z2+d, and n3 and n4 are equal or different.

9. The white light interference scanning interval rapid automatic positioning method according to claim 4, characterized in that: The white light interference scanning interval rapid automatic positioning method also includes: S6. Use the coherence peak sensing algorithm to perform three-dimensional reconstruction on the selected interference fringe images.

10. The white light interference scanning interval rapid automatic positioning method according to claim 9, characterized in that: The coherent peak perception algorithm is an improved centroid method, and the formula is as follows: m(Z)=(I Z -I Z-ΔZ ) 2 Among them, I Z is the light intensity value of the interference fringe image recorded at scanning position Z, I Z-ΔZ is the light intensity value of the interference fringe image recorded at the scanning position Z-ΔZ, ΔZ is the preset fine scanning step, m(Z) is the light intensity value difference, and h is the height of the sample (14) under test.

Images