White light interference measurement method based on out-of-focus degree guidance and related device

Abstract

The invention discloses a white light interference measurement method based on out-of-focus guide and a related device, and relates to the technical field of precision optical measurement. On the basis of white light interference measurement, a structured light out-of-focus measurement method is introduced, a nonlinear mapping relation between the out-of-focus and height is established based on structured light, and the out-of-focus degree of the white light interference measurement is obtained. Global morphology priori information of the measured workpiece is obtained; white light interference measurement is guided through global morphology prior information to directly skip a non-feature region position, interference fringe scanning is performed on a key feature position, and efficient scanning of a measured element is realized, so that the global three-dimensional morphology of a measured workpiece is established, the scanning time of the non-feature region is greatly shortened, and the measurement efficiency is improved. And thus, the efficiency and robustness of white light interference measurement are improved.

Description

Technical Field

[0001] This invention relates to the field of precision optical measurement technology, and in particular to a white light interferometry measurement method and related apparatus based on defocus guidance. Background Technology

[0002] With the rapid development and widespread application of precision micro-optical components, semiconductor devices, and other microstructured workpieces, the requirements for surface micro-morphology are becoming increasingly stringent. Therefore, corresponding high-precision advanced detection technologies are becoming increasingly important, and white light interferometry is an important non-contact micro-morphology measurement technique. This measurement technique utilizes the short coherence length characteristic of broadband light sources (such as white LEDs) to determine the height of standard samples by vertically scanning to find clear interference fringes at the zero optical path difference position, achieving non-destructive nanometer-level precision detection of precision components. However, due to its short coherence length and position-by-position interference fringe scanning mechanism, white light interferometry requires a relatively long time to determine the height range by scanning position by position when measuring components with unknown morphology or multi-scale microstructure features, resulting in low workpiece measurement efficiency. Summary of the Invention

[0003] This invention provides a white light interferometry measurement method and related apparatus based on defocus guidance, which solves the technical problem that existing white light interferometry requires a long time to scan position by position to determine the height range of unknown morphological elements and cross-scale microstructure features, resulting in low measurement efficiency of workpieces.

[0004] This invention provides a white light interferometry measurement method based on defocus guidance, the method comprising:

[0005] Multiple sets of binary fringe patterns are projected onto the workpiece under test using a structured light defocusing measurement system, and actual binary fringe images obtained from multiple sets of reflections are acquired based on the defocusing effect.

[0006] Based on multiple sets of actual binary fringe images, the defocus degree of each pixel in the camera of the structured light defocus measurement system is calculated; based on the preset defocus degree-height mapping relationship, the corresponding reconstruction height is determined according to the defocus degree of each pixel in the camera, thereby establishing the global morphological prior information of the workpiece to be measured.

[0007] The height distribution of the global topographic prior information is fitted using peak detection and Gaussian fitting algorithms to obtain the scanning planning area.

[0008] Based on the scanning planning area, the motion platform guides the workpiece to be measured to the field of view of the white light interferometry system.

[0009] The scanning area of ​​the workpiece under test is scanned by a white light interferometry system to obtain multiple sets of interferometric images; the global three-dimensional shape of the workpiece under test is reconstructed from the multiple sets of interferometric images based on the white light interferometric phase-shifting method.

[0010] Optionally, the step of calculating the defocus degree of each pixel in the camera of the structured light defocus measurement system based on multiple sets of actual binary fringe images includes:

[0011] The corresponding fringe modulation degree is calculated based on multiple sets of actual binary fringe images.

[0012] Based on the least squares method, the defocus of each pixel in the camera of the structured light defocus measurement system is calculated according to the fringe modulation degree corresponding to multiple sets of actual binary fringe images.

[0013] Optionally, before the step of projecting multiple sets of binary fringe patterns onto the workpiece under test using a structured light defocus measurement system and acquiring multiple sets of actual binary fringe images obtained from reflections based on the defocus effect, the method further includes:

[0014] Determine whether the structured light defocusing measurement system and the white light interferometry measurement system have completed height calibration;

[0015] If not, select a standard sample and place it on the motion platform; obtain the measurement height result of the standard sample through a white light interferometry system, and use the measurement height result as the height reference;

[0016] The standard sample is translated into the structured light defocusing measurement system, and the motion platform is driven so that the standard sample is on the reference plane at different height positions.

[0017] At different height positions, multiple sets of binary fringe patterns are projected onto the standard sample, and multiple sets of actual binary fringe images of the sample obtained by reflection are acquired based on the defocus effect.

[0018] Based on the actual binary stripe images of multiple sets of samples, the defocus of each pixel of the camera at different height positions is calculated, thereby establishing a preset defocus-height mapping relationship for each pixel in the camera.

[0019] Based on the height reference and the preset defocus degree-height mapping relationship, the height of the structured light defocus measurement system and the white light interferometry measurement system is unified in the same platform coordinate system, thereby completing the height calibration.

[0020] Optionally, the process of constructing the preset defocus-height mapping relationship includes:

[0021] Based on multiple sets of actual binary fringe images of the samples, the defocusing degree of each pixel in the camera of the structured light defocusing measurement system corresponding to different height positions is calculated.

[0022] By combining the defocus values ​​corresponding to all different height values, a quadratic function of initial defocus - height is constructed;

[0023] Based on the fitting relationship between the initial defocus-height quadratic function and the reconstructed height, the fitted preset defocus-height mapping relationship is obtained.

[0024] Optionally, the step of fitting the height distribution of the global topographic prior information based on peak detection and Gaussian fitting algorithms to obtain the scan planning region includes:

[0025] Establish a height histogram of the global topographic prior information;

[0026] The height distribution characteristics of the height histogram are fitted using peak detection and Gaussian fitting algorithms to determine the feature regions and non-feature regions in the height histogram.

[0027] The feature region is used as the scanning planning area for the workpiece to be tested.

[0028] Optionally, the step of moving the workpiece to be measured to the field of view position of the white light interferometry system based on the scanning planning area guided motion platform includes:

[0029] Based on the homography transformation relationship between the field of view of the structured light defocus measurement system and the white light interferometry measurement system, and the coordinate data of the scanning planning area under the structured light defocus measurement system, the displacement required by the motion platform is calculated.

[0030] According to the displacement, the motion platform is controlled to move the workpiece to be measured to the field of view position of the white light interferometry system.

[0031] Optionally, the step of reconstructing the global three-dimensional shape of the workpiece under test based on the multiple sets of interference images using the white light interferometry phase-shifting method includes:

[0032] Based on the white light interferometry phase-shifting method, the light intensity of each pixel in each interferometric image is calculated using a sliding sampling window based on the multiple sets of interferometric images;

[0033] Determine the maximum intensity regime of each pixel in the interference image and extract the phase value of the pixel with the maximum intensity regime;

[0034] The global three-dimensional shape of the workpiece under test is reconstructed based on the phase values ​​of all pixels at the maximum light intensity level and the preset wavelength.

[0035] The present invention also provides a white light interferometry measurement device based on defocus guidance, the device comprising:

[0036] The binary fringe projection module is used to project multiple sets of binary fringe patterns onto the workpiece under test through a structured light defocusing measurement system, and acquire multiple sets of actual binary fringe images obtained by reflection based on the defocusing effect.

[0037] The global topography prior information calculation module is used to calculate the defocus degree of each pixel in the camera of the structured light defocus measurement system based on multiple sets of actual binary fringe images; and to determine the corresponding reconstruction height based on the defocus degree of each pixel in the camera, thereby establishing the global topography prior information of the workpiece to be measured.

[0038] The scanning planning region determination module is used to fit the height distribution of the global topographic prior information based on peak detection and Gaussian fitting algorithms to obtain the scanning planning region.

[0039] The field-of-view switching module is used to guide the motion platform to move the workpiece to be measured to the field-of-view position of the white light interferometry system based on the scanning planning area.

[0040] The global 3D topography establishment module is used to scan the scan planning area of ​​the workpiece under test through a white light interferometry system to obtain multiple sets of interferometric images; and to reconstruct the global 3D topography of the workpiece under test based on the multiple sets of interferometric images using the white light interferometric phase-shifting method.

[0041] The present invention also provides a computer-readable storage medium having a computer program or instructions stored thereon, which, when executed by a processor, implement the steps of the white light interferometry method based on defocus guidance as described above.

[0042] The present invention also provides a computer program product, including a computer program or instructions, characterized in that, when the computer program or instructions are executed by a processor, they implement the steps of the white light interferometry method based on defocus guidance as described above.

[0043] As can be seen from the above technical solutions, the present invention has the following advantages:

[0044] This invention provides a white light interferometry measurement method and related apparatus based on defocus guidance. The method includes: projecting multiple sets of binary fringe patterns onto the workpiece under test using a structured light defocus measurement system; acquiring multiple sets of actual binary fringe images obtained from reflection based on the defocus effect; calculating the defocus degree of each pixel in the camera of the structured light defocus measurement system based on the multiple sets of actual binary fringe images; determining the corresponding reconstruction height based on the defocus degree of each pixel in the camera according to a preset defocus degree-height mapping relationship, thereby establishing prior global topographic information of the workpiece under test; fitting the height distribution of the prior global topographic information based on peak detection and Gaussian fitting algorithms to obtain a scanning planning area; guiding a motion platform to move the workpiece under test to the field of view position of the white light interferometry measurement system based on the scanning planning area; scanning the scanning planning area of ​​the workpiece under test using the white light interferometry measurement system to obtain multiple sets of interferometric images; and reconstructing the global three-dimensional topography of the workpiece under test based on the multiple sets of interferometric images using the white light interferometric phase-shifting method.

[0045] This invention introduces a structured light defocus measurement method based on white light interferometry. It establishes a nonlinear mapping relationship between defocus degree and height based on structured light to obtain prior information on the global morphology of the workpiece under test. By using the prior information on the global morphology, the white light interferometry is guided to directly skip the position of featureless region and perform interference fringe scanning on the key feature position, thereby achieving efficient scanning of the measured component, significantly reducing the scanning time of featureless region, and thus improving the efficiency and robustness of white light interferometry. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 A flowchart illustrating the steps of a white light interferometry measurement method guided by defocus, provided in an embodiment of the present invention;

[0048] Figure 2 A schematic diagram of the structure of a system for white light interferometry based on defocus guidance provided in an embodiment of the present invention;

[0049] Figure 3 This is a schematic diagram of the height calibration of the structured light defocusing measurement system and the white light interferometry measurement system provided in an embodiment of the present invention;

[0050] Figure 4 This is a schematic diagram illustrating the identification of the scanning planning area provided in an embodiment of the present invention;

[0051] Figure 5 A schematic diagram of a white light interferometry measurement device based on defocus guidance provided in an embodiment of the present invention;

[0052] The attached figures are labeled as follows: projector 1, first industrial camera 2, infinity imaging objective lens 3, first tube mirror 4, second industrial camera 5, interference objective lens 6, second tube mirror 7, Z-axis precision scanning motion platform 8, tilting stage 9, Z-axis vertical motion platform 10, horizontal motion platform 11, marble stage 12, air-bearing vibration isolation platform 13, personal computer 14, and piezoelectric controller 15. Detailed Implementation

[0053] This invention provides a white light interferometry measurement method and related apparatus based on defocus guidance, which solves the technical problem that existing white light interferometry requires a long time to scan position by position to determine the height range of unknown morphological elements and cross-scale microstructure features, resulting in low measurement efficiency of workpieces.

[0054] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0055] Please see Figure 1 This invention provides a white light interferometry measurement method based on defocus guidance, the method comprising:

[0056] Step 101: Project multiple sets of binary fringe patterns onto the workpiece under test using a structured light defocusing measurement system, and acquire multiple sets of actual binary fringe images obtained from reflections based on the defocusing effect.

[0057] It should be noted that this invention applies to a system for white light interferometry based on defocus guidance; please refer to [link to relevant documentation]. Figure 2 The system for white light interferometry guided by defocus includes a structured light defocus measurement system, a white light interferometry system, a horizontal motion platform 11, a piezoelectric controller 15, a personal computer 14, a marble stage 12, and an air-bearing vibration isolation platform 13. The structured light defocus measurement system is used to quickly acquire prior global topographic information of the workpiece under test to guide the white light interferometry system to perform efficient scanning. The white light interferometry system is used to achieve high-precision global three-dimensional topographic measurement and reconstruction of the workpiece under test based on the prior global topographic information.

[0058] The structured light defocus measurement system includes a projector 1, an infinity optical path structure, a first industrial camera 2 (CMOS), and a Z-axis vertical motion platform 10. The projector 1 is used to project a phase-modulated binary fringe pattern onto the surface of a standard sample. The infinity optical path structure includes an infinity imaging objective lens 3 and a first tube lens 4, which provides the imaging optical path for defocus measurement. The first industrial camera 2 is used to acquire the actual binary fringe image based on the reflection of the defocus effect. The Z-axis vertical motion platform 10 is used for focus adjustment and provides reference planes at different heights.

[0059] The white light interferometry system includes a white light broadband light source, an interference optical path structure, a second industrial camera 5, and a Z-axis precision scanning motion platform 8. The white light broadband light source provides broadband illumination to the workpiece under test, generating white light interference with a short coherence length. The interference optical path structure includes an interference objective lens 6 and a second tube lens 7, which provides an interference imaging optical path to form interference fringes. The second industrial camera 5 is used to acquire interference images. The tilting stage 9 is used to adjust the overall posture of the workpiece under test. The Z-axis precision scanning motion platform 8 is used to achieve nanometer-level precision scanning in the vertical direction to find the zero optical path difference position.

[0060] The horizontal motion platform 11 is used to switch the field of view between the structured light defocus measurement system and the white light interferometry system; the piezoelectric controller 15 is used to control the motion state of the Z-axis vertical motion platform 10 and the Z-axis precision scanning motion platform 8; the personal computer 14 is used to perform calculations based on the measurement data of the structured light defocus measurement system and the white light interferometry system; the marble stage 12 is set on the air-bearing vibration isolation platform 13 to provide a stable mounting base for components such as the structured light defocus measurement system and the white light interferometry system, while the air-bearing vibration isolation platform 13 reduces the impact of external vibration and other noise.

[0061] In this embodiment, the height information of the workpiece surface is inferred by utilizing the defocusing characteristics of the projector in the structured light defocusing measurement system and the blurring degree of the fringe pattern. The projector projects a phase-modulated binary fringe pattern (binary coded fringe) onto the surface of the workpiece. It can be represented as follows:

[0062] (1)

[0063] (2)

[0064] In the formula: Represents pixel coordinates, For the nth sine stripe pattern In pixel coordinates The light intensity value below; Indicates the maximum brightness of the stripe; i is the index of the Fourier series summation, from 1 to infinity; s is the phase parameter, and s is the phase shift parameter. N is the total number of projected patterns, and n is the sequence number; For the nth ideal binary stripe pattern In pixel coordinates The light intensity value under the condition is obtained by thresholding. Obtained by modulation.

[0065] Since the projector's optical system is not ideally focused, the projected binary fringe pattern will be blurred. In this case, the defocusing effect of the projected fringes can be approximated by Gaussian filtering. The convolution of the image with the Gaussian kernel in the spatial domain is equivalent to multiplying the Fourier transforms of the two in the frequency domain. Therefore, equation (1) can also be expressed as shown in equation (5). The defocused fringe pattern introduces a modulation attenuation coefficient. As shown in equation (4):

[0066] (3)

[0067] (4)

[0068] (5)

[0069] In the formula: These are binary fringes after defocusing. Gaussian filtering was applied. Defocus, representing the standard deviation of the point spread function. Proportional to the radius R of the discrete circle, representing the degree of defocus of the projector; T is the width of the projected stripes; For Fourier transform operators; This is the convolution operator; to determine the extent to which the defocus effect affects the fringe contrast, this embodiment introduces a modulation attenuation coefficient. ; The binary stripes after defocusing at pixel coordinates The light intensity value below.

[0070] Combining equations (2), (3), and (4), we can obtain the theoretical expression for the defocused fringes (i.e., equation (5)). Thus, by analyzing the modulation changes of the defocused fringes, we can infer the height information of the object's surface.

[0071] The actual binary fringe image obtained after projection defocusing, object reflection, and camera response can be represented as:

[0072] (6)

[0073] In the formula, Actual binary fringe image obtained by camera based on defocus effect reflection. In pixel coordinates The light intensity value below, For the stripes at pixel coordinates The adjustment system; External light intensity, For DC signal response, For the response of harmonic signals, The random noise of the camera, its value conforms to , This represents the variance of the random noise.

[0074] In this embodiment, a projector of a structured light defocusing measurement system projects multiple sets of binary fringe patterns of different widths onto the surface of the workpiece under test. Because the projector's optical system is in a defocused state, the fringes projected onto the uneven surface will undergo local blurring and deformation. At this time, a camera synchronously acquires these actual binary fringe images obtained from the deformed reflections due to surface topography modulation. These multiple sets of actual binary fringe images carry fringe intensity data for each pixel on the surface of the workpiece under test at different degrees of blur, providing a data foundation for subsequent accurate calculation of the defocus degree of that point and reconstruction of its height information, thereby improving the preliminary measurement efficiency and accuracy of the overall topography of the workpiece under test.

[0075] Step 102: Based on multiple sets of actual binary fringe images, calculate the defocus degree of each pixel in the camera of the structured light defocus measurement system; based on the preset defocus degree-height mapping relationship, determine the corresponding reconstruction height according to the defocus degree of each pixel in the camera, thereby establishing the global morphological prior information of the workpiece to be measured.

[0076] It should be noted that when the projector projects a striped pattern onto the surface of the workpiece, the light, after being reflected by a physical point on the workpiece surface, enters the camera lens and is imaged onto a specific pixel on the camera sensor. Throughout the measurement process, this correspondence between physical points and pixels remains constant. Therefore, this embodiment calculates the defocus degree of each pixel in the camera of the structured light defocus measurement system based on the actual binary striped image; then, using a preset defocus degree-height mapping relationship, it determines the corresponding reconstruction height based on the defocus degree of each pixel in the camera, thereby establishing prior information on the global topography of the workpiece.

[0077] The preset defocus-height mapping relationship is the mapping relationship between pixels and reconstructed height. The global topography prior information refers to the preliminary three-dimensional topography data of the workpiece under test, which includes the reconstructed height information of all major features (such as protrusions, pits, and slopes) on the surface of the workpiece. The global topography prior information of the workpiece under test can guide the white light interferometry system to perform accurate measurements.

[0078] In one specific implementation, the step of calculating the defocus degree of each pixel in the camera of the structured light defocus measurement system based on multiple sets of actual binary fringe images may include:

[0079] S21. Calculate the corresponding stripe modulation degree based on multiple sets of actual binary stripe images;

[0080] S22. Based on the least squares method, the defocus of each pixel in the camera of the structured light defocus measurement system is calculated according to the fringe modulation degree corresponding to multiple sets of actual binary fringe images.

[0081] It should be noted that by combining equations (4) and (6), the fringe modulation of the actual binary fringe image can be obtained, that is:

[0082] (7)

[0083] To calculate the defocus more accurately, this specific embodiment calculates multiple sets of fringe modulation degrees by projecting multiple sets of binary fringe pattern sequences with different fringe spacings, as shown below:

[0084] (8)

[0085] In the formula: This represents the stripe spacing of multiple sets of stripes with different widths; A is the first coefficient matrix; F is the second coefficient matrix. The stripe pitch is the stripe spacing corresponding to the width of the j-th stripe group.

[0086] Based on the least squares method and considering the fringe spacing and modulation of multiple sets of different fringe widths, the defocus of each pixel in the camera of the structured light defocus measurement system is calculated, as shown below:

[0087] (9)

[0088] Therefore, the fringe tone of binary fringe patterns with different fringe widths is calculated according to equation (8); and the final defocus of each pixel in the camera is calculated according to multiple sets of fringe spacing and fringe tone with different fringe widths using equation (9), thereby determining the corresponding reconstruction height.

[0089] It is important to note that the structured light defocus measurement system and the white light interferometry system have independent height measurement references. Therefore, before actually measuring the workpiece, it is necessary to determine whether the height measurement references of the structured light defocus measurement system and the white light interferometry system are consistent and related, that is, whether the structured light defocus measurement system and the white light interferometry system have completed height calibration.

[0090] In one specific implementation, the height calibration process of the structured light defocus measurement system and the white light interferometry system may include the following steps:

[0091] S31. Select a standard sample and place it on the motion platform; obtain the measurement height result of the standard sample through a white light interferometry system, and use the measurement height result as the height reference;

[0092] S32. Move the standard sample to the structured light defocusing measurement system and drive the motion platform so that the standard sample is on the reference plane at different height positions.

[0093] S33. At different height positions, project multiple sets of binary fringe patterns onto the standard sample and acquire multiple sets of actual binary fringe images of the sample obtained by reflection based on the defocus effect.

[0094] S34. Based on the actual binary stripe images of multiple sets of samples, calculate the defocus of each pixel of the camera at different height positions, thereby establishing a preset defocus-height mapping relationship for each pixel in the camera.

[0095] S35. Based on the height reference and the preset defocus degree-height mapping relationship, the height of the structured light defocus measurement system and the white light interferometric measurement system is unified in the same platform coordinate system, thereby completing the height calibration.

[0096] Specifically, before performing measurements with two measurement systems, it is necessary to determine whether the relative relationship between the two systems in the height direction has been calibrated. To obtain the relative positional relationship between the two systems in the height direction and to calibrate this height direction, a suitable standard block needs to be selected as a standard sample, and the height measurement result of the white light interferometry system needs to be used as the height reference.

[0097] Then, the horizontal motion platform is controlled to translate the standard sample under the structured light defocus measurement system. Defocus measurement is then performed on the standard sample within the structured light system to obtain a set of correspondences between the height and defocus degree of each reference plane, maintaining parallelism with the standard sample in the white light interferometry system. By fitting the functional relationship between defocus degree and the height of the reference planes, a defocus degree-height mapping relationship for the standard sample is constructed, achieving calibration and alignment of the two systems in the height direction.

[0098] In structured light defocusing measurement systems and white light interferometry systems, the core of achieving coordinate system unification lies in establishing a precise reference standard. For example... Figure 3As shown, the specific process for unifying the reference is as follows: First, based on the defocus measurement height calculation method, the spatial position of the reference plane in the platform coordinate system of the structured light measurement system is accurately calibrated. Then, in the white light interferometry system, the absolute height value relative to the platform zero point position is obtained by collecting platform displacement data. Finally, the white light interferometry result is used as the sole height reference of the system, and the coordinate unification of the two measurement modes is achieved using the position information of the nanometer displacement stage, thus obtaining the measurement area distribution relationship between the structured light defocus measurement system and the white light interferometry system. Figure 3 In For standard samples, The height distribution of the measurement area in the structured light defocusing measurement system. The height distribution of the measurement area in the white light interferometry system.

[0099] In one specific implementation, the process of establishing the preset defocus-height mapping relationship may include:

[0100] S41. Based on the actual binary fringe images of multiple samples, calculate the defocusing degree of each pixel in the camera of the structured light defocusing measurement system corresponding to different height positions.

[0101] S42. Combine the defocus values ​​corresponding to all different height values ​​to construct a quadratic function of initial defocus value minus height;

[0102] S43. Based on the fitting relationship between the quadratic function of initial defocus degree-height and the reconstructed height, the fitted preset defocus degree-height mapping relationship is obtained.

[0103] To establish a quantitative relationship between defocus and the surface height of the measured object, a Z-axis vertical motion platform is used to drive the stage within the measurement range to provide... There are 10 reference planes, and the height positions (i.e., height values) of these planes are recorded as follows: ;

[0104] Projection at various height values Binary fringe patterns of different widths were collected and analyzed, and the defocusing results of the standard sample at different height values ​​were measured; therefore, for each pixel, a value with... The defocus distribution results of each element.

[0105] By combining the defocus distribution results at all different height positions, it can be found that the defocus is minimal at the focal position, while it gradually increases and exhibits a symmetrical distribution as it moves away from the projector's focal position. Based on this pattern, this specific embodiment uses a quadratic function to describe the defocus relationship at different height positions, obtaining a quadratic function of initial defocus - height, as shown below:

[0106] (10)

[0107] In the formula, For pixel coordinates, , and These are quadratic fitting coefficients; where the height in the quadratic function of initial defocus - height refers to the height value of the reference plane.

[0108] For each pixel, a quadratic function is used to fit the curve of its defocus as a function of the reference platform height. During the solution process, it is found that the height corresponding to the peak of the curve is the reconstructed height of that pixel. Therefore, based on the fitting relationship between the initial defocus-height quadratic function and the reconstructed height, the fitted preset defocus-height mapping relationship can be obtained, i.e.:

[0109] (11)

[0110] In the formula: This represents the measured height value when the defocus reaches its minimum value. , and with These are known quadratic fitting coefficients. Therefore, when calculating the defocus of each pixel, the corresponding reconstructed height can be obtained by matching the preset defocus-height mapping relationship. The relative height value of the workpiece under test (i.e., the reconstructed height) can be indirectly reconstructed using this principle.

[0111] Step 103: Based on the peak detection and Gaussian fitting algorithm, the height distribution of the global topographic prior information is fitted to obtain the scanning planning area.

[0112] To improve measurement efficiency and accuracy, after obtaining the global topographic prior information, the height distribution of the global topographic prior information is fitted using peak detection and Gaussian fitting algorithms to obtain the scanning planning area, thereby determining the scanning area of ​​the white light interferometry system.

[0113] In one specific embodiment, step 103 may include the following steps:

[0114] S51. Establish a height histogram of the prior information of global topography.

[0115] S52. Based on peak detection and Gaussian fitting algorithms, the height distribution characteristics of the height histogram are fitted to determine the feature regions and non-feature regions in the height histogram.

[0116] S53. Use the feature region as the scanning planning area for the workpiece to be tested.

[0117] Understandably, after obtaining the height distribution of a standard sample of the workpiece under defocus measurement, it is necessary to divide the surface morphology into height sections to determine the measurement location area. The height distribution histogram is a graphical representation obtained through statistical analysis of the workpiece surface height data. It reflects the height distribution characteristics of the workpiece surface; the peak values ​​of the histogram represent the height range of characteristic areas, while the valley values ​​represent non-characteristic areas.

[0118] Based on the characteristics of histogram distribution, peak detection and Gaussian fitting algorithms can be used to process the height distribution of a region. Based on the fitting results, using... As the height range for determining the feature region, This represents the mean, corresponding to the peak position. The standard deviation corresponds to the width of the peak value. It is a constant. Based on the characteristic height range, the length of the coherence region is further extended upwards and downwards to determine the planning area for white light interferometry. Among them, the feature region highly identifiable range of the histogram is as follows: Figure 4 As shown.

[0119] Based on the height range corresponding to the peak values, the workpiece under test is divided into characteristic regions and non-characteristic regions. Assume the histogram contains... Each peak, respectively The corresponding height range for each peak is:

[0120] (12)

[0121] in, This represents the pixel result of the height distribution region after segmentation. This represents the height value of one pixel. This represents the non-featured regions after partitioning. This represents the segmented feature regions. The height threshold is obtained from the mean and standard deviation after fitting.

[0122] Step 104: Based on the scanning planning area, guide the motion platform to move the workpiece to be measured to the field of view position of the white light interferometry system.

[0123] In this embodiment, the motion platform guided by the scanning planning area moves the workpiece to be measured to the field of view of the white light interferometry system, avoiding the white light interferometry system from scanning featureless areas and greatly improving the overall measurement efficiency. Here, the field of view of the white light interferometry system refers to the scanning range of the camera of the white light interferometry system.

[0124] In one specific implementation, step 104 may include the following steps:

[0125] S61. Based on the homography transformation relationship between the field of view of the structured light defocus measurement system and the white light interferometry measurement system, and the coordinate data of the scanning planning area under the structured light defocus measurement system, the displacement required by the motion platform is calculated.

[0126] S62. According to the displacement, control the motion platform to move the workpiece to be measured to the field of view position of the white light interferometry system.

[0127] In this specific embodiment, a dual-optical-path system is used, and a precision motion platform is employed to move the field of view between the systems. To achieve high-precision switching of the field of view across measurement systems, the homography transformation relationship between the field of view of the structured light defocus measurement system and the white light interferometry measurement system can be obtained in advance using a checkerboard calibration plate. The homography transformation relationship reflects the spatial positional relationship between the field of view of the structured light defocus measurement system and the white light interferometry measurement system. Under the homography transformation relationship, the required displacement of the motion platform is calculated based on the coordinate data of the scanning planning area under the structured light defocus measurement system. According to the displacement, the motion platform can be precisely controlled to move the workpiece to be measured to the field of view position of the white light interferometry measurement system.

[0128] Among them, the checkerboard calibration plate serves as a tool for calibrating the relative relationship between the two fields of view. Therefore, the process of establishing the homography transformation relationship between the fields of view of the structured light defocus measurement system and the white light interferometry measurement system includes:

[0129] The checkerboard calibration plate is rigidly fixed to the motion platform, and the precision horizontal motion platform is driven to perform position-by-position displacement along the X-axis. At each displacement point, the camera is triggered to acquire images of the calibration plate. The corner detection algorithm is used to extract the corner points of the field of view and establish a set of matching point pairs.

[0130] Based on the coplanar constraint, the homography transformation model from the white light interferometry field of view (i.e., camera A in white light interferometry) to the defocus measurement field of view (i.e., camera B in the structured light defocus measurement system) is established as follows:

[0131] (13)

[0132] in, The homography matrix to be determined is... This is the platform displacement. The angle between the displacements is the angle of motion. The coordinates of the feature corner points identified under the field of view of white light interferometry. The coordinates of the feature corner points identified under the defocus measurement field of view are used; a multi-displacement joint optimization function is constructed:

[0133] (14)

[0134] The Levenberg-Marquardt optimization algorithm can iteratively solve for a higher accuracy homography matrix and the angle between the motion displacements. At this point, the homography matrix... It reflects the relative position and attitude relationship between the two cameras, and is used to help calculate the spatial position relationship of objects from different viewpoints.

[0135] In actual measurement, the coordinate data of the scanning planning area under the structured light defocusing measurement system is converted into the coordinate data under the white light interferometry measurement system by the calibrated homography matrix in the homography transformation relationship. Then, the displacement required by the motion platform can be calculated according to equation (13).

[0136] Thus, by obtaining the morphological information of the standard sample under the structured light defocusing measurement system, the amount of platform movement corresponding to the spatial position of the coherent measurement region of the white light interferometer system can be calculated. Then, the moving platform is switched to the planned position, thereby guiding the moving platform to move the workpiece to be measured to the field of view position of the white light interferometer system.

[0137] Step 105: Scan the planned area of ​​the workpiece under test using a white light interferometry system to obtain multiple sets of interferometric images; reconstruct the global three-dimensional shape of the workpiece under test based on the multiple sets of interferometric images using the white light interferometric phase-shifting method.

[0138] After the motion platform moves the workpiece to be measured to the field of view of the white light interferometry system, the system scans the planned scanning area of ​​the workpiece to obtain multiple sets of interferometric images. Based on the white light interferometric phase-shifting method, the global three-dimensional morphology of the workpiece is reconstructed from the acquired interferometric images. The global three-dimensional morphology refers to the complete and high-precision distribution information of the workpiece surface in three-dimensional space, which can accurately reflect the surface features of the workpiece, such as microscopic features like steps and holes.

[0139] Among them, the white light interferometry phase-shifting method is a high-precision surface topography measurement technique based on the principle of monochromatic light phase-shifting interference. Its core lies in establishing the correspondence between phase difference and surface height difference by analyzing the phase distribution of interference fringes, thereby quantitatively characterizing three-dimensional topography features.

[0140] In one specific implementation, the process of reconstructing the global three-dimensional shape of the workpiece under test based on multiple sets of interference images using the white light interferometry phase-shifting method may include the following steps:

[0141] S71. Based on the white light interference phase-shifting method, the light intensity intensity of each pixel in each interference image is calculated by using a sliding sampling window based on multiple sets of interference images;

[0142] S72. Determine the maximum intensity degree of each pixel in the interference image and extract the phase value of the pixel with the maximum intensity degree;

[0143] S73. Based on the phase values ​​of all pixels at the maximum light intensity level and the preset wavelength, the global three-dimensional shape of the workpiece under test is reconstructed.

[0144] Suppose there are five consecutive sampling points within the sliding sampling window ( The phase shift between ) is We can establish the corresponding set of interference light intensity equations, namely:

[0145] (15)

[0146] According to equation (15), the formula for calculating the light intensity regime M is as follows:

[0147] (16)

[0148] After sequentially sliding the sampling window and calculating the intensity of light at each pixel location, phase extraction is performed at the point of maximum modulation, as shown below:

[0149] (17)

[0150] Obtain the position of maximum modulation and its corresponding phase value. Then, three-dimensional topography reconstruction can be completed based on wavelength and phase values, that is:

[0151] (18)

[0152] In the formula: For in pixels ( The height after reconstruction The number of frames corresponding to the maximum modulation. The scan step size, The center wavelength is .

[0153] In this specific embodiment, the white light interference phase-shifting algorithm is used to process the interference image, calculate the phase and height of each pixel, and finally reconstruct a high-precision global three-dimensional shape of the key feature area of ​​the workpiece under test.

[0154] In this invention, a structured light defocusing measurement system with a large-scale 3D topography measurement capability is used to initially determine the height of the workpiece under test using the defocusing measurement results. Combined with the three-dimensional coordinates of each feature position under defocusing measurement, the relative position of the sample surface under white light interferometry is calculated. Based on the calculation results, a motion platform is guided to the planned position. At the planned position, a piezoelectric motion platform is used to scan and reconstruct the data, thus completing efficient data acquisition and reconstruction. This method establishes a nonlinear relationship between defocus and height in structured light defocusing measurement to obtain global topographic prior information. Based on peak detection and Gaussian fitting algorithms, the height distribution of the surface under test and its extended target height region are obtained for scanning position planning. This enables efficient guided measurement of key areas in white light interferometry, providing a new measurement method for efficient, nanometer-precision measurement of surface features of complex parts and multi-scale microstructures.

[0155] This invention provides a white light interferometry measurement method based on defocus guidance, which has the following advantages:

[0156] 1. Existing white light interferometry rapid measurement methods use coarse focusing with a large step size to quickly determine the focusing height of the device under test. However, when the coarse focusing step interval is too large, it will either miss the clear fringes that exist after the height change, resulting in the loss of key fringe signals, or it will cross the transition zone at the edge of the change, failing to capture the gradual change of the fringes from clear to attenuated, ultimately causing the coarse focusing scan to generate height profile distortion.

[0157] This invention utilizes structured light defocus measurement technology to project phase-modulated binary coded stripes onto the sample surface using a projector. It captures height correlation information using pixel synchronization, calculates the defocus degree using the least squares method, and finds the height of the measured point corresponding to the minimum defocus degree by fitting a curve, thereby eliminating the risk of missed sampling due to "excessive step interval skipping key areas" from a mechanism perspective.

[0158] This invention determines the height position of the measured element by structured light defocus measurement, effectively overcoming the problem that traditional white light interferometric rapid measurement methods are prone to missing data in regions of abrupt height changes, expanding the height measurement range and eliminating the need for a complex calibration process.

[0159] 2. Existing white light interferometry rapid measurement methods are all based on white light interferometry point-by-point or region-by-region scanning modes. The scanning speed is limited by its passive measurement principle. In contrast, structured light defocus measurement adopts an active projection coded fringe method, which maps three-dimensional topographic information into the phase change of the fringe image, resulting in high scanning efficiency.

[0160] This invention proposes a rapid white-light interferometry scanning mechanism based on structured light-guided positioning. By establishing a nonlinear relationship between defocus and height, prior information on the global topography is obtained. Peak detection and Gaussian fitting algorithms are introduced to guide the white-light interferometry to directly skip featureless regions and perform interference fringe scanning on key feature locations, thus achieving efficient guided scanning of key areas in white-light interferometry measurements. This method effectively resolves the contradiction between measurement efficiency and accuracy in traditional techniques.

[0161] The following describes the white light interferometry measurement device based on defocus guidance provided in the embodiments of this application. The white light interferometry measurement device based on defocus guidance described below and the white light interferometry measurement method based on defocus guidance described above can be referred to in correspondence with each other.

[0162] Please see Figure 5 The present invention also provides a white light interferometry measurement device based on defocus guidance, the device comprising:

[0163] Binary fringe projection module 201 is used to project multiple sets of binary fringe patterns onto the workpiece under test through a structured light defocus measurement system, and acquire multiple sets of actual binary fringe images obtained by reflection based on the defocus effect.

[0164] The global topography prior information calculation module 202 is used to calculate the defocus degree of each pixel in the camera of the structured light defocus measurement system based on multiple sets of actual binary fringe images; and to determine the corresponding reconstruction height based on the preset defocus degree-height mapping relationship, thereby establishing the global topography prior information of the workpiece to be measured.

[0165] The scanning planning region determination module 203 is used to fit the height distribution of the global topographic prior information based on peak detection and Gaussian fitting algorithm to obtain the scanning planning region.

[0166] The field-of-view switching module 204 is used to guide the motion platform to move the workpiece to be measured to the field-of-view position of the white light interferometry system based on the scanning planning area.

[0167] The global three-dimensional shape establishment module 205 is used to scan the scanning planning area of ​​the workpiece under test through a white light interferometry system to obtain multiple sets of interferometric images; and to reconstruct the global three-dimensional shape of the workpiece under test based on the white light interferometric phase shift method according to the multiple sets of interferometric images.

[0168] The present invention also provides a computer-readable storage medium having a computer program or instructions stored thereon, wherein the computer program or instructions, when executed by a processor, implement the steps of any of the above-described defocus-guided white light interferometry methods.

[0169] The present invention also provides a computer program product, including a computer program or instructions, characterized in that, when the computer program or instructions are executed by a processor, they implement the steps of any of the above-mentioned defocus-guided white light interferometry methods.

[0170] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0171] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between apparatuses or units through some interfaces, and may be electrical, mechanical, or other forms.

[0172] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0173] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0174] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0175] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A white light interferometry measurement method based on defocus guidance, characterized in that, The method includes: Multiple sets of binary fringe patterns are projected onto the workpiece under test using a structured light defocusing measurement system, and actual binary fringe images obtained from multiple sets of reflections are acquired based on the defocusing effect. Based on multiple sets of actual binary fringe images, the defocus degree of each pixel in the camera of the structured light defocus measurement system is calculated; based on the preset defocus degree-height mapping relationship, the corresponding reconstruction height is determined according to the defocus degree of each pixel in the camera, thereby establishing the global morphological prior information of the workpiece to be measured. The height distribution of the global topographic prior information is fitted using peak detection and Gaussian fitting algorithms to obtain the scanning planning area. Based on the scanning planning area, the motion platform guides the workpiece to be measured to the field of view of the white light interferometry system. The scanning area of ​​the workpiece under test is scanned by a white light interferometry system to obtain multiple sets of interferometric images; the global three-dimensional shape of the workpiece under test is reconstructed from the multiple sets of interferometric images based on the white light interferometric phase-shifting method.

2. The white light interferometry measurement method based on defocus guidance according to claim 1, characterized in that, The step of calculating the defocus degree of each pixel in the camera of the structured light defocus measurement system based on multiple sets of actual binary fringe images includes: The corresponding fringe modulation degree is calculated based on multiple sets of actual binary fringe images. Based on the least squares method, the defocus of each pixel in the camera of the structured light defocus measurement system is calculated according to the fringe modulation degree corresponding to multiple sets of actual binary fringe images.

3. The white light interferometry measurement method based on defocus guidance according to claim 1, characterized in that, Before the step of projecting multiple sets of binary fringe patterns onto the workpiece under test using a structured light defocus measurement system and acquiring multiple sets of actual binary fringe images obtained from reflections based on the defocus effect, the following is also included: Determine whether the structured light defocusing measurement system and the white light interferometry measurement system have completed height calibration; If not, select a standard sample and place it on the motion platform; obtain the measurement height result of the standard sample through a white light interferometry system, and use the measurement height result as the height reference; The standard sample is translated into the structured light defocusing measurement system, and the motion platform is driven so that the standard sample is on the reference plane at different height positions. At different height positions, multiple sets of binary fringe patterns are projected onto the standard sample, and multiple sets of actual binary fringe images of the sample obtained by reflection are acquired based on the defocus effect. Based on the actual binary stripe images of multiple sets of samples, the defocus of each pixel of the camera at different height positions is calculated, thereby establishing a preset defocus-height mapping relationship for each pixel in the camera. Based on the height reference and the preset defocus degree-height mapping relationship, the height of the structured light defocus measurement system and the white light interferometry measurement system is unified in the same platform coordinate system, thereby completing the height calibration.

4. The white light interferometry measurement method based on defocus guidance according to claim 3, characterized in that, The process of constructing the preset defocus-height mapping relationship includes: Based on multiple sets of actual binary fringe images of the samples, the defocusing degree of each pixel in the camera of the structured light defocusing measurement system corresponding to different height positions is calculated. By combining the defocus values ​​corresponding to all different height values, a quadratic function of initial defocus - height is constructed; Based on the fitting relationship between the initial defocus-height quadratic function and the reconstructed height, the fitted preset defocus-height mapping relationship is obtained.

5. The white light interferometry measurement method based on defocus guidance according to claim 1, characterized in that, The step of fitting the height distribution of the global topographic prior information to obtain the scan planning region based on peak detection and Gaussian fitting algorithm includes: Establish a height histogram of the global topographic prior information; The height distribution characteristics of the height histogram are fitted using peak detection and Gaussian fitting algorithms to determine the feature regions and non-feature regions in the height histogram. The feature region is used as the scanning planning area for the workpiece to be tested.

6. The white light interferometry measurement method based on defocus guidance according to claim 1, characterized in that, The step of moving the workpiece to be measured to the field of view of the white light interferometry system based on the scanning planning area guided motion platform includes: Based on the homography transformation relationship between the field of view of the structured light defocus measurement system and the white light interferometry measurement system, and the coordinate data of the scanning planning area under the structured light defocus measurement system, the displacement required by the motion platform is calculated. According to the displacement, the motion platform is controlled to move the workpiece to be measured to the field of view position of the white light interferometry system.

7. The white light interferometry measurement method based on defocus guidance according to claim 1, characterized in that, The step of reconstructing the global three-dimensional shape of the workpiece under test based on the multiple sets of interference images using the white light interferometry phase-shifting method includes: Based on the white light interferometry phase-shifting method, the light intensity of each pixel in each interferometric image is calculated using a sliding sampling window based on the multiple sets of interferometric images; Determine the maximum intensity regime of each pixel in the interference image and extract the phase value of the pixel with the maximum intensity regime; The global three-dimensional shape of the workpiece under test is reconstructed based on the phase values ​​of all pixels at the maximum light intensity level and the preset wavelength.

8. A white light interferometric measurement device based on defocus guidance, characterized in that, The device includes: The binary fringe projection module is used to project multiple sets of binary fringe patterns onto the workpiece under test through a structured light defocusing measurement system, and acquire multiple sets of actual binary fringe images obtained by reflection based on the defocusing effect. The global topography prior information calculation module is used to calculate the defocus degree of each pixel in the camera of the structured light defocus measurement system based on multiple sets of actual binary fringe images; and to determine the corresponding reconstruction height based on the defocus degree of each pixel in the camera, thereby establishing the global topography prior information of the workpiece to be measured. The scanning planning region determination module is used to fit the height distribution of the global topographic prior information based on peak detection and Gaussian fitting algorithms to obtain the scanning planning region. The field-of-view switching module is used to guide the motion platform to move the workpiece to be measured to the field-of-view position of the white light interferometry system based on the scanning planning area. The global 3D topography establishment module is used to scan the scan planning area of ​​the workpiece under test through a white light interferometry system to obtain multiple sets of interferometric images; and to reconstruct the global 3D topography of the workpiece under test based on the multiple sets of interferometric images using the white light interferometric phase-shifting method.

9. A computer-readable storage medium having a computer program or instructions stored thereon, characterized in that, When the computer program or instructions are executed by the processor, they implement the steps of the white light interferometry method based on defocus guidance as described in any one of claims 1-7.

10. A computer program product, comprising a computer program or instructions, characterized in that, When the computer program or instructions are executed by the processor, they implement the steps of the white light interferometry method based on defocus guidance as described in any one of claims 1-7.

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