Grating ruler pitch ultra-high precision measurement method, device and system

Abstract

The invention provides a grating scale pitch ultrahigh precision measurement method, device and system, and relates to the technical field of precision optical measurement, and the method comprises the steps: obtaining the three-dimensional shape data, collected by an optical contourgraph, of the surface of a grating scale; carrying out tilt correction on the three-dimensional shape data to obtain corrected data, and carrying out grid line direction identification on the corrected data based on a rotation search and frequency spectrum amplitude maximization principle to obtain an accurate period direction of the grating ruler; and based on the accurate period direction, rotating the corrected data and superposing and averaging a plurality of rows of signals to obtain a one-dimensional average signal, processing the obtained one-dimensional average signal by adopting a weighted spectrum analysis algorithm, and calculating to obtain the grating scale pitch. According to the ultrahigh-precision measurement method, device and system for the grating scale pitch, the grating scale pitch can be used as an independent parameter, the measurement method for rapid, automatic and ultrahigh-precision calibration is carried out, and the bottlenecks of low efficiency, difficulty in decoupling and dependence on manpower in the prior art are fundamentally solved.

Description

Technical Field

[0001] This application relates to the field of precision optical measurement technology, and in particular to a method, device and system for ultra-high precision measurement of grating ruler pitch. Background Technology

[0002] As a core sensor in modern ultra-precision displacement measurement, the accuracy of the grating pitch (i.e., the nominal distance between grating lines) directly determines the benchmark for displacement measurement. Tiny deviations in the grating pitch can be amplified by the measurement system, ultimately introducing a non-negligible proportional error, which seriously affects the positioning accuracy of high-end equipment such as lithography machines and coordinate measuring machines.

[0003] In related technologies, there is still a lack of perfect and efficient measurement methods for the accuracy testing of the grating line direction of two-dimensional planar gratings. The directional error between the grating line and the mechanical reference, especially the non-orthogonality between the two grating line directions, directly leads to Abbe error and cosine error in displacement measurement, which seriously restricts the further improvement of the positioning accuracy of ultra-precision worktables.

[0004] Therefore, independent, accurate, and efficient measurement and calibration of the grating pitch of the grating ruler is a key prerequisite for ensuring its metrological performance and traceability. Summary of the Invention

[0005] The purpose of this application is to provide a method, device and system for ultra-high precision measurement of grating ruler pitch, which can use the grating ruler pitch as an independent parameter for rapid, automatic and ultra-high precision calibration, fundamentally solving the bottlenecks of low efficiency, difficulty in decoupling and reliance on manual labor in the existing technology.

[0006] In a first aspect, this application provides a method for ultra-high precision measurement of grating ruler pitch, including: The three-dimensional topographic data of the grating ruler surface collected by the optical profilometer are acquired; the three-dimensional topographic data is tilted and corrected to obtain corrected data; based on the principle of rotation search and spectral amplitude maximization, the grating line direction is identified in the corrected data to obtain the precise periodic direction of the grating ruler; based on the precise periodic direction, the corrected data is rotated and averaged by superimposing multiple lines of signals to obtain a one-dimensional mean signal; and the one-dimensional mean signal is processed by a weighted spectrum analysis algorithm to calculate the grating ruler pitch.

[0007] Optionally, the step of tilt correction of the three-dimensional topography data to obtain corrected data includes: performing first-order plane fitting on the three-dimensional topography data using the least squares method to obtain a fitting plane; and performing Z-axis tilt correction on the three-dimensional topography data based on the fitting plane to obtain corrected data.

[0008] Optionally, the step of identifying the grating line direction of the corrected data based on the principle of rotation search and spectral amplitude maximization to obtain the precise periodic direction of the grating ruler includes: finding the rotation angle that makes the multi-line signals present the best periodicity in the superimposed average direction by rotating the corrected data, and taking the found rotation angle as the precise periodic direction of the grating ruler.

[0009] Optionally, the step of finding the optimal rotation angle for the multi-row signals to exhibit optimal periodicity in the superimposed averaging direction by rotating the corrected data, and using the found rotation angle as the precise periodic direction of the grating ruler, includes: setting an angle search range and a search step; within the angle search range, rotating the data matrix corresponding to the corrected data sequentially at intervals of the search step, and superimposing and averaging the data at each rotation angle along the column direction to obtain the corresponding one-dimensional mean signal; performing a fast Fourier transform on each one-dimensional mean signal and recording the corresponding spectral main frequency amplitude, until all rotation angles have been traversed, and using the target rotation angle as the precise periodic direction of the grating ruler; wherein, the target rotation angle is the rotation angle corresponding to the maximum spectral main frequency amplitude.

[0010] Optionally, the step of rotating and averaging the corrected data based on the precise periodic direction to obtain a one-dimensional mean signal includes: rotating the corrected data to the target rotation angle and averaging the multiple lines of signals to obtain a one-dimensional mean signal with optimal signal-to-noise ratio.

[0011] Optionally, the step of processing the obtained one-dimensional mean signal using a weighted spectrum analysis algorithm to accurately calculate the grating ruler pitch includes: performing a fast Fourier transform on the one-dimensional mean signal to obtain a discrete spectrum, and identifying peak spectral lines and adjacent spectral lines in the discrete spectrum; the adjacent spectral lines include: a left adjacent spectral line and a right adjacent spectral line; calculating a positive frequency deviation based on the peak spectral line and the right adjacent spectral line, and calculating a negative frequency deviation based on the peak spectral line and the left adjacent spectral line; weighting and fusing the positive frequency deviation and the negative frequency deviation according to the amplitude of the adjacent spectral lines to obtain weighted spectrum interpolation coefficients; calculating the normalized digital frequency of the one-dimensional mean signal based on the weighted spectrum interpolation coefficients, and calculating the grating ruler pitch based on the normalized digital frequency.

[0012] Optionally, the step of weighting and fusing the positive frequency deviation and the negative frequency deviation based on the amplitudes of the adjacent spectral lines to obtain weighted spectral interpolation coefficients includes: calculating the ratio of the amplitudes of two spectral lines in the adjacent spectral lines, and determining the weights corresponding to the left adjacent spectral line and the right adjacent spectral line based on the ratio; determining the weights corresponding to the left adjacent spectral line and the right adjacent spectral line based on the ratio, and performing a weighted average of the positive frequency deviation and the negative frequency deviation to obtain the weighted spectral interpolation coefficients.

[0013] Secondly, this application also provides an ultra-high precision measuring device for grating ruler pitch, comprising: The data acquisition module is used to acquire three-dimensional topographic data of the grating ruler surface collected by the optical profilometer; the tilt correction module is used to perform tilt correction on the three-dimensional topographic data to obtain corrected data; the grating line direction recognition module is used to identify the grating line direction of the corrected data based on the principle of rotation search and spectral amplitude maximization to obtain the precise periodic direction of the grating ruler; the grating pitch calculation module is used to rotate and average the corrected data based on the precise periodic direction to obtain a one-dimensional mean signal, and to process the obtained one-dimensional mean signal using a weighted spectrum analysis algorithm to calculate the grating pitch of the grating ruler.

[0014] Optionally, the tilt correction module is specifically used to perform first-order plane fitting on the three-dimensional topography data using the least squares method to obtain a fitting plane; the tilt correction module is also specifically used to perform Z-axis tilt correction on the three-dimensional topography data based on the fitting plane to obtain corrected data.

[0015] Optionally, the grating line direction recognition module is specifically used to find the rotation angle that makes the multi-line signals present the best periodicity in the superimposed average direction by rotating the corrected data, and to use the found rotation angle as the precise periodic direction of the grating ruler.

[0016] Optionally, the grating line direction recognition module is specifically used to set the angle search range and search step; the grating line direction recognition module is further used to rotate the data matrix corresponding to the corrected data sequentially within the angle search range, with the search step as the interval, and to superimpose and average the data under each rotation angle along the column direction to obtain the corresponding one-dimensional mean signal; the grating line direction recognition module is further used to perform a fast Fourier transform on each one-dimensional mean signal and record the corresponding spectral main frequency amplitude value, until all rotation angles are traversed, and the target rotation angle is taken as the precise periodic direction of the grating ruler; wherein, the target rotation angle is: the rotation angle corresponding to the maximum spectral main frequency amplitude value.

[0017] Optionally, the grating pitch calculation module is specifically used to rotate the corrected data to the target rotation angle and perform multi-line signal superposition and averaging to obtain a one-dimensional mean signal with optimal signal-to-noise ratio.

[0018] Optionally, the grating pitch calculation module is specifically used to perform a fast Fourier transform on the one-dimensional mean signal to obtain a discrete spectrum, and identify the peak spectral line and adjacent spectral lines in the discrete spectrum; the adjacent spectral lines include: a left adjacent spectral line and a right adjacent spectral line; the grating pitch calculation module is further used to calculate a positive frequency deviation based on the peak spectral line and the right adjacent spectral line, and to calculate a negative frequency deviation based on the peak spectral line and the left adjacent spectral line; the grating pitch calculation module is further used to perform weighted fusion of the positive frequency deviation and the negative frequency deviation according to the amplitude of the adjacent spectral lines to obtain weighted spectral interpolation coefficients; the grating pitch calculation module is further used to calculate the normalized digital frequency of the one-dimensional mean signal based on the weighted spectral interpolation coefficients, and to calculate the grating pitch of the grating ruler based on the normalized digital frequency.

[0019] Optionally, the grating pitch calculation module is further configured to calculate the ratio of the amplitudes of two spectral lines in the adjacent spectral lines, and determine the weights corresponding to the left adjacent spectral line and the right adjacent spectral line based on the ratio; the grating pitch calculation module is further configured to determine the weights corresponding to the left adjacent spectral line and the right adjacent spectral line based on the ratio, and perform a weighted average of the positive frequency deviation and the negative frequency deviation to obtain the weighted spectral interpolation coefficients.

[0020] Thirdly, this application also provides an ultra-high precision measurement system for grating ruler pitch, including an optical profilometer and a processing unit; the optical profilometer is used to acquire three-dimensional topographic data of the surface of the grating ruler; the processing unit is used to perform the steps of the ultra-high precision measurement method for grating ruler pitch as described in the first aspect above based on the acquired three-dimensional topographic data.

[0021] Fourthly, this application also provides a computer program product, including a computer program / instructions that, when executed by a processor, implement the steps of the ultra-high precision measurement method for grating ruler pitch as described above.

[0022] Fifthly, this application also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the ultra-high precision measurement method for grating ruler pitch as described above.

[0023] Sixthly, this application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the ultra-high precision measurement method for grating ruler pitch as described above.

[0024] The ultra-high precision measurement method, apparatus, and system for grating ruler pitch provided in this application first acquire three-dimensional topographic data of the grating ruler surface collected by an optical profilometer; then, the three-dimensional topographic data is tilt-corrected to obtain corrected data, and based on the principle of rotation search and spectral amplitude maximization, the grating line direction is identified in the corrected data to obtain the precise periodic direction of the grating ruler; finally, based on the precise periodic direction, the corrected data is rotated and averaged by superimposing multiple lines of signals to obtain a one-dimensional mean signal, and a weighted spectral analysis algorithm is used to process the obtained one-dimensional mean signal to calculate the grating ruler pitch. This provides a rapid, automatic, and ultra-high precision measurement method for grating ruler pitch as an independent parameter, fundamentally solving the bottlenecks of low efficiency, difficulty in decoupling, and reliance on manual labor in existing technologies. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in this application 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 some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the structure of the non-contact optical profilometer provided in this application; Figure 2 This is a flowchart illustrating the ultra-high precision measurement method for grating ruler pitch provided in this application; Figure 3 This is a schematic diagram of Z-axis surface fitting provided in this application; Figure 4 This is a schematic diagram of the precise periodic direction step search of the grating ruler provided in this application; Figure 5 This is a schematic diagram of the grating frequency domain after FFT transformation provided in this application; Figure 6 This is a schematic diagram of the structure of the ultra-high precision grating ruler pitch measuring device provided in this application; Figure 7 This is a schematic diagram of the structure of the electronic device provided in this application. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and the number of objects is not limited; for example, a first object can be one or more. Furthermore, "and / or" in the specification and claims indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship. All actions involving the acquisition of signal information or data in this application are performed in accordance with the relevant data protection laws and policies of the country where the application is located and with authorization from the owner of the relevant device.

[0029] In related technologies, the high-precision measurement methods for grating ruler pitch mainly fall into the following categories: 1. Atomic force microscopy This method utilizes a nanoscale probe of an atomic force microscope to scan the surface morphology of a grating point-by-point, directly calculating the grating pitch by analyzing the scanned images. Its advantage lies in obtaining true morphology at nanoscale resolution and good measurement repeatability. However, this method is essentially a point or line contact / near-field scan, resulting in extremely slow measurement speed. For example, for an area of ​​1 mm... 2 Performing high-resolution scanning over such a large area can take hundreds of hours, and the measurement range is limited by the probe scanning stroke. Therefore, this method is difficult to apply to rapid, full-field grating pitch calibration and inspection of large-size grating rulers in industrial settings.

[0030] 2. Optical diffraction method This method is based on the grating equation and indirectly calculates the grating pitch by precisely measuring the beam angle of a specific diffraction order produced by the incident light passing through the grating. Optical diffraction has the advantages of being non-contact and highly accurate. However, its limitations are twofold: firstly, the measurement relies on a high-precision mechanical turntable and a complex optical alignment system, making it extremely sensitive to environmental vibrations and assembly stability; secondly, this method typically only allows sampling measurements at discrete points or small local areas, making it difficult to quickly obtain grating pitch distribution information along the entire length of the grating ruler, thus failing to achieve efficient full-field measurement.

[0031] 3. Laser interferometer comparison method This method mounts the grating ruler and laser interferometer on the same motion stage, and calculates the average grating pitch by directly comparing the displacement signals of the two instruments simultaneously. This method offers good traceability. However, in practical systems, the laser interferometer measurement system itself contains multiple error sources, including optical nonlinearity, environmental errors, and Abbe errors. The grating ruler measurement system is also affected by factors such as installation offset and deformation. These complex system errors are coupled with each other, making it difficult for this method to clearly separate and independently calibrate the inherent parameter of the "grating ruler pitch" from the overall error of the measurement system.

[0032] In summary, the above technical solutions mainly suffer from the following common defects: low measurement efficiency and accuracy, and difficulty in using the grid pitch as a parameter independent of the measurement system for high-precision decoupling and calibration.

[0033] In response to the existing technical solutions in related technologies, this application provides a method for ultra-high precision measurement of grating ruler pitch. This method can perform ultra-high precision measurement of grating ruler pitch based on profilometer scanning and weighted spectrum analysis. It not only decouples grating ruler pitch measurement but also enables rapid, automatic, and ultra-high precision calibration.

[0034] like Figure 1 As shown, this embodiment of the present application provides a non-contact optical profilometer structure, including: a base, a vibration isolator, and a profilometer (e.g., a ZYGO Nexview™ 650 profilometer). This profilometer, as the core measuring device, rapidly acquires three-dimensional topographic data of the grating ruler surface using white light scanning interferometry.

[0035] The ultra-high precision measurement method for grating ruler pitch provided in this application will be described in detail below with reference to the accompanying drawings, through specific embodiments and application scenarios.

[0036] like Figure 2 As shown in the embodiment of this application, a method for ultra-high precision measurement of grating ruler pitch is provided. This method may include the following steps 201 to 203: Step 201: Obtain the three-dimensional topographic data of the grating ruler surface collected by the optical profilometer.

[0037] Exemplary, in the embodiments of this application, the following is adopted: Figure 1 The optical profilometer shown is the core strategic device, which quickly acquires the three-dimensional topographic data of the grating ruler surface through white light scanning interferometry.

[0038] It should be noted that a grating ruler, also known as a grating ruler displacement sensor, is a measurement feedback device that works using the optical principle of a grating. Grating rulers are frequently used in closed-loop servo systems of CNC machine tools for detecting linear or angular displacement. Their output signal is a digital pulse, characterized by a large detection range, high accuracy, and fast response speed. For example, in CNC machine tools, they are often used to detect the coordinates of the tool and workpiece to observe and track tool travel errors, thus compensating for tool movement errors. The grating pitch is the smallest and most fundamental unit for displacement measurement using a grating ruler. All measured displacement values ​​are essentially integer or fractional multiples of the grating pitch. If the basic scale of the grating pitch itself is inaccurate, all subsequent displacement measurements will have proportional errors (or scaling errors).

[0039] Step 202: The three-dimensional topography data is tilted to obtain the corrected data. Based on the principle of rotation search and spectral amplitude maximization, the corrected data is used to identify the grating line direction to obtain the precise periodic direction of the grating ruler.

[0040] For example, to eliminate the Z-axis tilt introduced by assembly and adjustment errors, the least squares method is used to perform a first-order plane fitting on the three-dimensional surface data, resulting in the following: Figure 3 The fitted plane is shown, and the tilt correction is achieved by subtracting the fitted plane from the corrected data.

[0041] Specifically, step 202 above, the step of tilt correction of the three-dimensional topography data, may further include step 202, and may further include step 202a1 and step 202a2: Step 202a1: Perform first-order plane fitting on the three-dimensional topography data using the least squares method to obtain the fitting plane.

[0042] For example, due to the assembly and adjustment error between the grating ruler and the profilometer measurement platform, the acquired 3D topographic data is not an ideal plane, but rather exhibits an overall tilt. To eliminate the macroscopic tilt component introduced by the assembly and adjustment, and thus correct the data reference plane to be parallel to the XY plane of the measurement coordinate system, allowing subsequent analysis to focus only on the periodic micro-topography of the grating itself, a fitted plane obtained by plane fitting using the least squares method is the best approximation plane for all data points along the Z direction (height direction). This plane precisely represents the overall, linearly varying tilt trend (first-order component) in the data. Therefore, the fitted plane itself is a mathematical representation of the "Z-direction tilt".

[0043] Step 202a2: Perform Z-axis tilt correction on the three-dimensional topography data based on the fitting plane to obtain the corrected data.

[0044] For example, a data correction method could be to subtract the Z value of the fitted plane at that point from the Z value (height value) of the original data point at the same spatial coordinates (x, y).

[0045] Specifically, step 202 above, which involves identifying the grating line direction of the corrected data to obtain the precise periodic direction of the grating ruler, may further include the following step 202a: Step 202a: By rotating the corrected data, find the rotation angle that makes the multi-line signals present the best periodicity in the superposition average direction, and use the found rotation angle as the precise periodic direction of the grating ruler.

[0046] For example, the gate line direction recognition in this application embodiment is essentially to rotate the data to a state where the gate line is parallel to the processing direction (such as the column direction), at which point the periodicity of the signal is most obvious.

[0047] Specifically, step 202a above may also include steps 202a1 to 202a3: Step 202a1: Set the angle search range and search step.

[0048] Step 202a2: Within the angle search range, the data matrix corresponding to the corrected data is rotated sequentially at the interval of the search step, and the data under each rotation angle is superimposed and averaged along the column direction to obtain the corresponding one-dimensional mean signal.

[0049] Step 202a3: Perform a fast Fourier transform on each one-dimensional mean signal and record the corresponding spectrum main frequency amplitude value until all rotation angles have been traversed, and then use the target rotation angle as the precise periodic direction of the grating ruler.

[0050] The target rotation angle is the rotation angle that maximizes the amplitude of the main frequency of the spectrum.

[0051] For example, based on the principles of rotation search and spectral amplitude maximization, the precise periodic direction of the grating ruler is automatically identified. Specifically: the angle search range and step are set, and the data matrix is ​​rotated; the data at each rotation angle are superimposed and averaged along the column direction to obtain a one-dimensional mean signal; this signal is then subjected to FFT, and the dominant frequency amplitude is recorded; such as... Figure 4 As shown, after traversing all angles, the rotation angle that maximizes the main frequency amplitude is the precise periodic direction of the grating ruler.

[0052] Step 203: Based on the precise periodic direction, rotate the corrected data and average the multiple lines of signals to obtain a one-dimensional mean signal. Then, use a weighted spectrum analysis algorithm to process the obtained one-dimensional mean signal and calculate the grating ruler pitch.

[0053] For example, after obtaining the precise correction angle, the corrected data is rotated to that angle and averaged again to obtain a one-dimensional mean signal with the optimal signal-to-noise ratio. The grating pitch of the grating ruler is then accurately calculated based on this one-dimensional mean signal. The grating pitch is either a one-dimensional grating ruler or a two-dimensional planar grating ruler, i.e., the technical solution in this application, which can measure the grating pitch of a one-dimensional grating ruler or a two-dimensional planar grating ruler.

[0054] Specifically, step 203 above, which involves rotating the corrected data and averaging multiple rows of signals to obtain a one-dimensional mean signal, may further include step 203a: Step 203a: Rotate the corrected data to the target rotation angle and perform multi-line signal superposition and averaging to obtain a one-dimensional mean signal with optimal signal-to-noise ratio.

[0055] For example, based on rotation search and automatic identification of grating line direction to maximize spectral amplitude, the grating ruler achieves accurate and automatic identification of grating line direction by searching for the rotation angle that maximizes the amplitude of the main frequency of the spectrum after superimposing multiple lines of signals, effectively overcoming the adjustment error.

[0056] Specifically, step 203 above, which involves processing the obtained one-dimensional mean signal to accurately calculate the grating ruler pitch, may further include steps 203b1 to 203b4: Step 203b1: Perform a fast Fourier transform on the one-dimensional mean signal to obtain a discrete spectrum, and identify the peak spectral lines and adjacent spectral lines in the discrete spectrum; the adjacent spectral lines include: the left adjacent spectral line and the right adjacent spectral line.

[0057] Step 203b2: Calculate the positive frequency deviation based on the peak spectral line and the right adjacent spectral line, and calculate the negative frequency deviation based on the peak spectral line and the left adjacent spectral line.

[0058] Step 203b3: Weight the positive frequency deviation and the negative frequency deviation according to the amplitude of the adjacent spectral lines to obtain the weighted spectral interpolation coefficients.

[0059] Step 203b4: Calculate the normalized digital frequency of the one-dimensional mean signal based on the weighted spectrum interpolation coefficients, and calculate the grating pitch of the grating ruler based on the normalized digital frequency.

[0060] For example, to overcome the "pick-up fence effect" of FFT, a spectral correction algorithm based on three-spectral-line weighted interpolation is adopted: such as Figure 5As shown, the peak spectral line of the FFT spectrum and its left and right adjacent spectral lines are located; the positive and negative frequency deviations are calculated using the peak spectral line and the right and left adjacent spectral lines respectively; the amplitudes of the adjacent spectral lines on both sides are weighted and fused to obtain the final weighted spectrum interpolation coefficients; the true normalized digital frequency of the signal is calculated using these coefficients, and then the grating pitch of the grating ruler is accurately calculated.

[0061] For example, the aforementioned three-spectral-line weighted interpolation spectrum correction algorithm is used to overcome the FFT picket fence effect in the precise measurement of grating pitch by grating rulers. This enables a fully automated measurement system that integrates tilt correction, orientation recognition, and grating pitch calculation.

[0062] The ultra-high precision measurement method for grating ruler pitch provided in this application employs a non-contact profilometer to rapidly acquire three-dimensional topographic data. Combined with a fully automated algorithm process, it significantly improves measurement efficiency. It enables direct and accurate separation and calibration of the grating ruler pitch as an independent parameter, overcoming the drawbacks of time-consuming methods such as AFM and the difficulty in decoupling system errors in laser interferometer comparison methods, allowing for independent measurement of the grating ruler pitch. A complete solution from data acquisition, preprocessing, orientation alignment to parameter calculation is constructed, achieving "one-click" measurement and reducing reliance on operator experience. This method is applicable not only to two-dimensional planar grating rulers but also to one-dimensional grating ruler systems, and has been successfully applied and validated in high-end equipment such as DUV lithography machine workpiece stages and mask stages.

[0063] The ultra-high precision measurement method for grating ruler pitch provided in this application first acquires three-dimensional topographic data of the grating ruler surface collected by an optical profilometer. Then, the three-dimensional topographic data is tilt-corrected to obtain corrected data. Based on the principles of rotation search and spectral amplitude maximization, the corrected data is used to identify the grating line direction to obtain the precise periodic direction of the grating ruler. Finally, based on the precise periodic direction, the corrected data is rotated and averaged using multi-line signal superposition to obtain a one-dimensional mean signal. A weighted spectral analysis algorithm is then used to process the obtained one-dimensional mean signal to calculate the grating ruler pitch. This method enables rapid, automatic, and ultra-high precision calibration of the grating ruler pitch as an independent parameter, fundamentally solving the bottlenecks of low efficiency, difficulty in decoupling, and reliance on manual labor in existing technologies.

[0064] It should be noted that the ultra-high precision measurement method for grating ruler pitch provided in this application can be executed by an ultra-high precision grating ruler pitch measuring device, or a control module within that device for executing the method. This application uses the execution of the ultra-high precision grating ruler pitch measurement method by the ultra-high precision grating ruler pitch measuring device as an example to illustrate the ultra-high precision grating ruler pitch measuring device provided in this application.

[0065] It should be noted that, in the embodiments of this application, the ultra-high precision measurement methods of grating ruler pitch shown in the accompanying drawings are all illustrated by way of example with reference to one accompanying drawing in the embodiments of this application. In specific implementation, the ultra-high precision measurement methods of grating ruler pitch shown in the accompanying drawings of the above methods can also be implemented in conjunction with any other accompanying drawings shown in the above embodiments, which will not be elaborated here.

[0066] The ultra-high precision measuring device for grating ruler pitch provided in this application is described below. The ultra-high precision measuring method for grating ruler pitch described below can be referred to in correspondence with the method described above.

[0067] Figure 6 This is a schematic diagram of the structure of the ultra-high precision grating ruler pitch measuring device provided in the embodiments of this application, as shown below. Figure 6 As shown, it specifically includes: The data acquisition module 601 is used to acquire the three-dimensional topography data of the grating ruler surface collected by the optical profilometer; the tilt correction module 602 is used to perform tilt correction on the three-dimensional topography data to obtain the corrected data; the grating line direction recognition module 603 is used to perform grating line direction recognition on the corrected data based on the principle of rotation search and spectral amplitude maximization to obtain the precise periodic direction of the grating ruler; the grating pitch calculation module 604 is used to rotate and average the corrected data based on the precise periodic direction to obtain a one-dimensional mean signal, and to process the obtained one-dimensional mean signal using a weighted spectrum analysis algorithm to calculate the grating pitch of the grating ruler.

[0068] Optionally, the tilt correction module 602 is specifically used to perform first-order plane fitting on the three-dimensional topography data using the least squares method to obtain a fitting plane; the tilt correction module 602 is also specifically used to perform Z-axis tilt correction on the three-dimensional topography data based on the fitting plane to obtain corrected data.

[0069] Optionally, the grating line direction recognition module 603 is specifically used to find the rotation angle that makes the multi-line signals present the best periodicity in the superimposed average direction by rotating the corrected data, and to use the found rotation angle as the precise periodic direction of the grating ruler.

[0070] Optionally, the grating line direction recognition module 603 is specifically used to set the angle search range and search step; the grating line direction recognition module 603 is further used to rotate the data matrix corresponding to the corrected data sequentially within the angle search range, with the search step as the interval, and to superimpose and average the data under each rotation angle along the column direction to obtain the corresponding one-dimensional mean signal; the grating line direction recognition module 603 is further used to perform a fast Fourier transform on each one-dimensional mean signal and record the corresponding spectral main frequency amplitude value, until all rotation angles are traversed, and the target rotation angle is taken as the precise periodic direction of the grating ruler; wherein, the target rotation angle is: the rotation angle corresponding to the maximum spectral main frequency amplitude value.

[0071] Optionally, the grating pitch calculation module 604 is specifically used to rotate the corrected data to the target rotation angle and perform multi-line signal superposition and averaging to obtain a one-dimensional mean signal with optimal signal-to-noise ratio.

[0072] Optionally, the grating pitch calculation module 604 is specifically used to perform a fast Fourier transform on the one-dimensional mean signal to obtain a discrete spectrum, and identify the peak spectral line and adjacent spectral lines in the discrete spectrum; the adjacent spectral lines include: a left adjacent spectral line and a right adjacent spectral line; the grating pitch calculation module 604 is further used to calculate a positive frequency deviation based on the peak spectral line and the right adjacent spectral line, and to calculate a negative frequency deviation based on the peak spectral line and the left adjacent spectral line; the grating pitch calculation module 604 is further used to perform weighted fusion of the positive frequency deviation and the negative frequency deviation according to the amplitude of the adjacent spectral lines to obtain weighted spectrum interpolation coefficients; the grating pitch calculation module 604 is further used to calculate the normalized digital frequency of the one-dimensional mean signal based on the weighted spectrum interpolation coefficients, and to calculate the grating pitch of the grating ruler based on the normalized digital frequency.

[0073] Optionally, the grating pitch calculation module 604 is further configured to calculate the ratio of the amplitudes of two spectral lines in the adjacent spectral lines, and determine the weights corresponding to the left adjacent spectral line and the right adjacent spectral line based on the ratio; the grating pitch calculation module 604 is further configured to determine the weights corresponding to the left adjacent spectral line and the right adjacent spectral line based on the ratio, and perform a weighted average of the positive frequency deviation and the negative frequency deviation to obtain the weighted spectral interpolation coefficients.

[0074] The ultra-high precision measurement device for grating ruler pitch provided in this application first acquires three-dimensional topographic data of the grating ruler surface collected by an optical profilometer; then, it performs tilt correction on the three-dimensional topographic data to obtain corrected data, and based on the principle of rotation search and spectral amplitude maximization, identifies the grating line direction of the corrected data to obtain the precise periodic direction of the grating ruler; finally, based on the precise periodic direction, it rotates the corrected data and averages multiple lines of signals to obtain a one-dimensional mean signal, and processes the obtained one-dimensional mean signal using a weighted spectrum analysis algorithm to calculate the grating ruler pitch. This provides a rapid, automatic, and ultra-high precision measurement method for grating ruler pitch as an independent parameter, fundamentally solving the bottlenecks of low efficiency, difficulty in decoupling, and reliance on manual labor in existing technologies.

[0075] Figure 7 An example is a schematic diagram of the physical structure of an electronic device, such as... Figure 7 As shown, the electronic device may include a processor 710, a communication interface 720, a memory 730, and a communication bus 740, wherein the processor 710, the communication interface 720, and the memory 730 communicate with each other through the communication bus 740. The processor 710 can call logic instructions in the memory 730 to execute a method for ultra-high precision measurement of the grating ruler pitch. This method includes: first, acquiring three-dimensional topographic data of the grating ruler surface collected by an optical profilometer; then, performing tilt correction on the three-dimensional topographic data to obtain corrected data, and based on the principle of rotation search and spectral amplitude maximization, identifying the grating line direction of the corrected data to obtain the precise periodic direction of the grating ruler; finally, based on the precise periodic direction, rotating and averaging the corrected data using multi-line signal superposition to obtain a one-dimensional mean signal, and processing the obtained one-dimensional mean signal using a weighted spectrum analysis algorithm to calculate the grating ruler pitch. Thus, a measurement method that enables rapid, automatic, and ultra-high precision calibration of the grating ruler pitch as an independent parameter fundamentally solves the bottlenecks of low efficiency, difficulty in decoupling, and reliance on manual labor in existing technologies.

[0076] Furthermore, the logical instructions in the aforementioned memory 730 can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a portion 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 this application. 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.

[0077] On the other hand, this application also provides a computer program product, which includes a computer program stored on a computer-readable storage medium. The computer program includes program instructions, which, when executed by a computer, enable the computer to perform the ultra-high precision measurement method for grating ruler pitch provided by the above-described methods. This method includes: first, acquiring three-dimensional topographic data of the grating ruler surface collected by an optical profilometer; then, performing tilt correction on the three-dimensional topographic data to obtain corrected data, and based on the principle of rotation search and spectral amplitude maximization, identifying the grating line direction of the corrected data to obtain the precise periodic direction of the grating ruler; finally, based on the precise periodic direction, rotating and averaging the corrected data using multi-line signal superposition to obtain a one-dimensional mean signal, and processing the obtained one-dimensional mean signal using a weighted spectral analysis algorithm to calculate the grating ruler pitch. Thus, a measurement method that allows the grating ruler pitch to be used as an independent parameter for rapid, automatic, and ultra-high precision calibration fundamentally solves the bottlenecks of low efficiency, difficulty in decoupling, and reliance on manual labor in existing technologies.

[0078] Furthermore, this application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, performs the aforementioned ultra-high precision measurement methods for grating ruler pitch. The method includes: first, acquiring three-dimensional topographic data of the grating ruler surface collected by an optical profilometer; then, performing tilt correction on the three-dimensional topographic data to obtain corrected data, and based on the principle of rotation search and spectral amplitude maximization, identifying the grating line direction of the corrected data to obtain the precise periodic direction of the grating ruler; finally, based on the precise periodic direction, rotating and averaging the corrected data using multi-line signal superposition to obtain a one-dimensional mean signal, and processing the obtained one-dimensional mean signal using a weighted spectral analysis algorithm to calculate the grating ruler pitch. Thus, a measurement method that allows for rapid, automatic, and ultra-high precision calibration of the grating ruler pitch as an independent parameter is provided, fundamentally solving the bottlenecks of low efficiency, difficulty in decoupling, and reliance on manual labor in existing technologies.

[0079] The device embodiments described above are merely illustrative. 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 modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0080] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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 this application.

Claims

1. A method for ultra-high precision measurement of grating ruler pitch, characterized in that, include: Acquire the three-dimensional topographic data of the grating ruler surface collected by the optical profilometer; The three-dimensional topography data is tilted to obtain corrected data. Based on the principle of rotation search and spectral amplitude maximization, the corrected data is used to identify the grating line direction to obtain the precise periodic direction of the grating ruler. Based on the precise periodic direction, the corrected data is rotated and averaged by superimposing multiple lines of signals to obtain a one-dimensional mean signal. The one-dimensional mean signal is then processed using a weighted spectrum analysis algorithm to calculate the grating ruler pitch.

2. The method according to claim 1, characterized in that, The process of tilt correction of the three-dimensional topography data to obtain corrected data includes: The three-dimensional topography data were fitted with a first-order plane using the least squares method to obtain the fitted plane. Based on the fitting plane, the three-dimensional topography data is subjected to Z-axis tilt correction to obtain the corrected data.

3. The method according to claim 1, characterized in that, The method of identifying the grating line direction based on the principle of rotation search and spectral amplitude maximization to obtain the precise periodic direction of the grating ruler includes: By rotating the corrected data, the rotation angle that makes the multi-line signals exhibit optimal periodicity in the superimposed average direction is found, and the found rotation angle is used as the precise periodic direction of the grating ruler.

4. The method according to claim 3, characterized in that, The step of finding the optimal rotation angle that makes the multi-line signals exhibit optimal periodicity in the superposition and averaging direction by rotating the corrected data, and using the found rotation angle as the precise periodic direction of the grating ruler, includes: Set the angle search range and search step; Within the angle search range, the data matrix corresponding to the corrected data is rotated sequentially with the search step as the interval, and the data under each rotation angle is superimposed and averaged along the column direction to obtain the corresponding one-dimensional mean signal. Perform a fast Fourier transform on each one-dimensional mean signal and record the corresponding spectral main frequency amplitude value until all rotation angles have been traversed. Then, take the target rotation angle as the precise periodic direction of the grating ruler. The target rotation angle is the rotation angle that maximizes the amplitude of the main frequency of the spectrum.

5. The method according to claim 4, characterized in that, The step of rotating and averaging the corrected data based on the precise periodic direction to obtain a one-dimensional mean signal includes: The corrected data is rotated to the target rotation angle, and multiple lines of signals are superimposed and averaged to obtain a one-dimensional mean signal with the optimal signal-to-noise ratio.

6. The method according to claim 1 or 5, characterized in that, The process of using a weighted spectrum analysis algorithm to process the obtained one-dimensional mean signal and accurately calculate the grating ruler pitch includes: A fast Fourier transform is performed on a one-dimensional mean signal to obtain a discrete spectrum, and peak spectral lines and adjacent spectral lines in the discrete spectrum are identified; the adjacent spectral lines include: left adjacent spectral lines and right adjacent spectral lines; The positive frequency deviation is calculated based on the peak spectral line and the right adjacent spectral line, and the negative frequency deviation is calculated based on the peak spectral line and the left adjacent spectral line. The positive frequency deviation and the negative frequency deviation are weighted and fused based on the amplitude of the adjacent spectral lines to obtain weighted spectral interpolation coefficients; The normalized digital frequency of the one-dimensional mean signal is calculated based on the weighted spectral interpolation coefficients, and the grating pitch of the grating ruler is calculated based on the normalized digital frequency.

7. The method according to claim 6, characterized in that, The step of weighting and fusing the positive frequency deviation and the negative frequency deviation based on the amplitude of the adjacent spectral lines to obtain weighted spectral interpolation coefficients includes: Calculate the ratio of the amplitudes of the two spectral lines in the adjacent spectral lines, and determine the weights corresponding to the left adjacent spectral line and the right adjacent spectral line based on the ratio; Based on the ratio, the weights corresponding to the left adjacent spectral line and the right adjacent spectral line are determined, and the positive frequency deviation and the negative frequency deviation are weighted and averaged to obtain the weighted spectral interpolation coefficients.

8. The method according to claim 1, characterized in that, The optical profilometer is a white light scanning interferometric profilometer; the grating pitch of the grating ruler is: a one-dimensional grating ruler, or the grating pitch of a two-dimensional planar grating ruler.

9. A high-precision measuring device for grating ruler pitch, characterized in that, The device includes: The data acquisition module is used to acquire the three-dimensional topographic data of the grating ruler surface collected by the optical profilometer; The tilt correction module is used to perform tilt correction on the three-dimensional topography data to obtain the corrected data. The grating line orientation identification module is used to identify the grating line orientation of the corrected data based on the principles of rotation search and spectral amplitude maximization, so as to obtain the precise periodic orientation of the grating ruler. The grating pitch calculation module is used to rotate and average the corrected data based on the precise periodic direction to obtain a one-dimensional mean signal, and then use a weighted spectrum analysis algorithm to process the obtained one-dimensional mean signal to calculate the grating pitch of the grating ruler.

10. A high-precision measurement system for grating ruler pitch, characterized in that, It includes an optical profilometer and a processing unit; the optical profilometer is used to acquire three-dimensional topographic data of the surface of the grating ruler; the processing unit is used to perform the steps of the ultra-high precision measurement method of the grating ruler pitch as described in any one of claims 1 to 8.

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