Focal plane positioning method and device, related equipment and computer program product

Abstract

The invention discloses a focal plane positioning method and device, related equipment and a computer program product, and relates to the technical field of semiconductor manufacturing processes. The method comprises the following steps: acquiring interference light intensity of a camera at different preset sampling positions perpendicular to a focusing direction of a measured object; the light intensity of the interference light is the light intensity of an optical signal formed by combining two beams of reflected light, the two beams of reflected light are reflected light of a measured object and a reference mirror to light sources located in the focusing direction, the reference mirror is placed parallel to the light sources, and the distance between the reference mirror and the light sources is the optimal focusing distance of a camera; fitting the interference light intensity corresponding to all the preset sampling positions to obtain an interference light signal; and determining a zero optical path difference point from the interference light signal, and determining the zero optical path difference point as the optimal focal plane position of the camera. Therefore, the flexibility and accuracy of focal plane positioning are improved.

Description

Technical Field

[0001] This application relates to the field of semiconductor manufacturing process technology, and more specifically, to a focal plane positioning method, apparatus, related equipment, and computer program product. Background Technology

[0002] In semiconductor manufacturing, rapid measurement and accurate assessment of overlay errors are crucial for optimizing lithography machine operating parameters and managing process yield. Therefore, overlay error measurement equipment is typically used to measure the overlay errors generated during the lithography process. Its working principle primarily involves analyzing the reflection or diffraction of light on specific patterns on the semiconductor wafer surface to measure the overlay error. Understandably, a clear image is essential for accurate measurement of overlay errors. If the image is not clear enough, it will affect the accuracy of the measurement results, preventing proper compensation and correction of overlay errors, and ultimately leading to a decline in overall chip performance.

[0003] Because the front layer of the chip is covered by multiple thin films, the camera focal length needs to be continuously adjusted during error detection to obtain a sufficiently clear image. Currently, the focus detection method is mainly used for focusing. This method determines the optimal focal plane position by calculating the distance between the current image and the image at the optimal focal plane position. However, due to changes in the shooting environment, there will be an error between the actual optimal focal plane and the image at the set optimal focal plane position, resulting in lower accuracy in the final determined optimal focal plane.

[0004] Therefore, there is an urgent need for a focal plane positioning method to accurately locate the actual optimal focal plane. Summary of the Invention

[0005] In view of the above problems, this application is made to provide a text processing method, apparatus, related equipment, and computer program product to process reading comprehension tasks. The specific solution is as follows:

[0006] In a first aspect, this application provides a focal plane positioning method, including:

[0007] The intensity of interference light is obtained when the camera is at different preset sampling positions in the focusing direction perpendicular to the object under test; the intensity of interference light is the intensity of the light signal after the two reflected beams are combined, the two reflected beams are the reflected light of the object under test and the reference mirror respectively to the light source located in the focusing direction, the reference mirror is placed parallel to the light source, and the distance between the reference mirror and the light source is the optimal focusing distance of the camera.

[0008] The interference light intensity corresponding to all the preset sampling positions is fitted to obtain the interference light signal;

[0009] The zero optical path difference point is determined from the interference light signal, and the zero optical path difference point is determined as the optimal focal plane position of the camera.

[0010] In one possible design, in another implementation of the first aspect of the embodiments of this application, the process of determining the zero optical path difference point from the interfering optical signal includes:

[0011] The intensity of the interference light at each position point in the interference light signal is used as the weight value of that position point.

[0012] Based on the weight value of each position point, a weighted average is calculated for all position points in the interference optical signal to obtain the centroid position point of the interference optical signal.

[0013] The centroid position is determined as the zero optical path difference point of the interference optical signal.

[0014] In one possible design, in another implementation of the first aspect of the embodiments of this application, after the weighted average of all position points in the interference optical signal based on the weight value of each position point to obtain the centroid position point of the interference optical signal, the method further includes:

[0015] In the interference optical signal, the minimum points closest to the centroid position point are determined from the left and right sides of the centroid position point, respectively, to obtain the left minimum point and the right minimum point;

[0016] The target function is obtained by fitting the signal waveform between the left minimum point and the right minimum point in the interference optical signal using a preset function.

[0017] Based on the parameter values ​​corresponding to the preset parameter types in the objective function, the position points corresponding to the parameter values ​​are determined from the interference optical signal and used as the target centroid position points of the interference optical signal.

[0018] The process of determining the centroid position point as the zero optical path difference point of the interference optical signal includes: determining the target centroid position point as the zero optical path difference point of the interference optical signal.

[0019] In one possible design, in another implementation of the first aspect of the embodiments of this application, the preset function is a trigonometric function.

[0020] In one possible design, in another implementation of the first aspect of the embodiments of this application, the process of fitting the interference light intensity corresponding to all the preset sampling positions to obtain the interference light signal includes:

[0021] When the distribution of the preset sampling positions is not equidistant, all the preset sampling positions are interpolated at equal intervals according to the preset intervals to obtain a preset number of sampling positions with equal intervals and the interference light intensity corresponding to each sampling position.

[0022] The interference light intensity corresponding to all the sampling positions is fitted to obtain the interference light signal.

[0023] In one possible design, in another implementation of the first aspect of the embodiments of this application, after fitting the interference light intensity corresponding to all the preset sampling positions to obtain the interference light signal, the method further includes:

[0024] The interference light signal is filtered to obtain the filtered interference light signal;

[0025] Determining the zero optical path difference point from the interference optical signal includes: determining the zero optical path difference point from the filtered interference optical signal.

[0026] Secondly, this application provides a focal plane positioning device, including: a light source, a stage, a camera, a beam splitter, a reference mirror, a detector, and a processing module;

[0027] The camera is positioned directly above the placement platform, and the beam splitter is positioned between the camera and the placement platform, with a fixed distance between the beam splitter and the camera; the reference mirror is placed parallel to the beam splitter, and the distance between the reference mirror and the beam splitter is the optimal focusing distance of the camera;

[0028] The camera is used to respond to the movement command sent by the processing module, move to the preset sampling position, and drive the beam splitter and the reference mirror to move;

[0029] The beam splitter is used to split the light source into two beams, which are directed at the test object and the reference mirror placed on the stage, respectively, and reflect the reflected light from the light source by the test object and the reference mirror to the detector.

[0030] The detector is used to receive the reflected light from the light source by the object under test and the reference mirror respectively, and to detect the light intensity of the light signal after the two reflected lights are combined, so as to obtain the light intensity of the interference light corresponding to the preset sampling position of the camera, and transmit the light intensity of the interference light corresponding to the preset sampling position to the processing module.

[0031] The processing module is configured to receive the interference light intensity corresponding to different preset sampling positions of the camera, and process the interference light intensity according to the focal plane positioning method described in any of the first aspects of this application to obtain the optimal focal plane position of the camera.

[0032] Thirdly, this application provides an electronic device, including: a memory and a processor;

[0033] The memory is used to store programs;

[0034] The processor is configured to execute the program to implement the focal plane positioning method described in any of the first aspects of this application.

[0035] Fourthly, this application provides a readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the focal plane positioning method described in any of the first aspects of this application.

[0036] Fifthly, this application provides a computer program product, including a computer program that, when executed by a processor, implements the focal plane positioning method described in any of the first aspects of this application.

[0037] By employing the aforementioned technical solution, this application actually collects the interference light intensity at multiple preset sampling points along the focusing direction, adapting to variations in different test objects or shooting environments. This allows the fitted interference light signal to reflect the actual optical path difference between the camera at different positions and the optimal focusing distance, thereby improving the flexibility of focal plane positioning. Furthermore, by finding the position with zero optical path difference from the interference light signal, the optimal focal plane position of the camera in the current environment can be accurately located. Attached Figure Description

[0038] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0039] Figure 1 This is a schematic diagram of the structure of a focal plane positioning device provided in an embodiment of this application;

[0040] Figure 2 A schematic diagram of an implementation system architecture for the focal plane positioning method provided in this application embodiment;

[0041] Figure 3 A flowchart illustrating a focal plane positioning method provided in an embodiment of this application;

[0042] Figure 4 An example diagram of an interference optical signal provided in an embodiment of this application;

[0043] Figure 5Example diagram of sampling position interpolation provided in the embodiments of this application;

[0044] Figure 6 An example diagram of zero optical path difference positioning provided in this application embodiment;

[0045] Figure 7 An example diagram of a zero-order stripe provided for an embodiment of this application;

[0046] Figure 8 Another example diagram of zero optical path difference positioning provided in this application embodiment;

[0047] Figure 9 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application. Detailed Implementation

[0048] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0049] This application can be applied to the field of semiconductor manufacturing process technology. The following section will take the camera focal plane positioning process in the overlay measurement process as an example to introduce several application scenarios that have been implemented in products.

[0050] First, we introduce one possible application scenario for this application. The target autofocus technology mainly employs distance measurement and focus detection methods. Distance measurement focuses by pre-calculating the true position of the focal plane; however, ultrasonic and infrared ranging methods are easily affected by external factors such as temperature and humidity in the working environment, and have certain requirements for the focus detection beam, which is detrimental to the lightweighting of the imaging system. Triangulation requires an independent optical path structure, cannot directly provide a light source for camera photography, and increases the structural complexity of the overlay error measurement system. Focus detection methods establish a mathematical model of the optimal focal plane position image and the current image position; however, changes in the focus detection environment can cause errors in the ideal mathematical model itself, reducing measurement accuracy and making precise focus detection impossible.

[0051] To address the aforementioned problems, this application provides a focal plane positioning method, apparatus, related equipment, and computer program product. The following description, in conjunction with the accompanying drawings, details the focal plane positioning method, apparatus, related equipment, and computer program product according to embodiments of this application.

[0052] The focal plane positioning method provided in this application can be applied to, for example... Figure 1The processing template in the focal plane positioning device shown can be understood to also be used as an overlay measurement device for overlay measurement. Specifically, the focal plane positioning device may include: a light source, a stage 10, a camera, a beam splitter 20, a reference mirror 30, a detector, and a processing module.

[0053] The camera is positioned directly above the stage 10, and the beam splitter 20 is positioned between the camera and the stage, with a fixed distance between the beam splitter and the camera. The reference mirror 30 is placed parallel to the beam splitter 20, and the distance between the reference mirror 30 and the beam splitter 20 is the optimal focusing distance of the camera.

[0054] The camera responds to the movement command sent by the processing module, moves to the preset sampling position, and drives the beam splitter and reference mirror to move;

[0055] The beam splitter 20 is used to split the light source into two beams, which are directed at the object under test and the reference mirror 30 placed on the stage 10, respectively, and reflect the reflected light from the object under test and the reference mirror 30 to the detector.

[0056] The detector is used to receive the reflected light from the light source by the object under test and the reference mirror, and to detect the light intensity of the light signal after the two reflected lights are combined. The intensity of the interference light corresponding to the camera at the preset sampling position is obtained, and the intensity of the interference light corresponding to the preset sampling position is transmitted to the processing module.

[0057] The processing module is used to receive the interference light intensity corresponding to different preset sampling positions of the camera, and process the interference light intensity according to the focal plane positioning method to obtain the optimal focal plane position of the camera.

[0058] This application integrates an overlay measurement device with a Linnik-type interferometer to obtain a focal plane positioning device, which not only has the function of overlay measurement, but also the function of focal plane positioning using white light interferometry.

[0059] The camera, detector, and beam splitter belong to the same driving unit. That is, during focusing, a vertical displacement of the camera will cause the detector, beam splitter, and reference mirror to all move in the same vertical direction. The reference mirror is placed parallel to the light source (beam splitter), and the distance between the reference mirror and the light source is set to the camera's optimal focusing distance. This ensures that the reference optical path is in ideal focus, thus providing a benchmark for interferometric measurements. By recording the light intensity at different sampling positions, the sequence of interferometric light intensity changes with position can be captured.

[0060] The following example illustrates the testing method of this device by taking the process of acquiring the interference light intensity of the camera at a preset sampling position. First, the camera responds to the movement command of the processing module and moves to a preset sampling position. During the movement, the camera moves the beam splitter, reference mirror, and detector together, and the relative positional relationship between the camera, beam splitter, reference mirror, and detector does not change during the movement.

[0061] After the camera moves to the preset sampling position, the beam splitter splits the light emitted by the light source into two beams. One beam is focused onto the reference mirror through the microscope objective and reflected by the reference mirror. The other beam is focused onto the surface of the object being measured through another microscope objective and reflected by the surface of the object being measured. The reflected light then returns to the beam splitter through the same microscope objective.

[0062] The beams from the two light sources are reflected by the surface of the object under test and the reference mirror, respectively, and then combined into a single beam by a beam splitter. Since the two reflected beams satisfy the interference condition, interference occurs when they are combined, forming interference light. The beam splitter reflects this interference light to the detector, which detects the intensity of the interference light to obtain the intensity of the interference light at the current preset sampling position of the camera, and transmits it to the processing module.

[0063] After receiving the interference light intensity corresponding to different preset sampling positions, the processing module executes the deployed focal plane positioning method to process the interference light intensity corresponding to different preset sampling positions, thereby locating the optimal focal plane position. Based on this optimal focal plane position, a movement command is sent to the camera again, causing it to move to the optimal focal plane position to image the object under test, obtaining an image with the best focusing effect, thereby improving the accuracy of the overlay measurement results of the object under test.

[0064] In one possible implementation, the focal plane positioning method can also be applied to, for example... Figure 2 In the system architecture shown, the system may include a terminal 100 and a server 200, and the server 200 may include one or more servers. Figure 1 (This example uses a server as an illustration).

[0065] Either terminal 100 or server 200 can be used independently to execute the focal plane positioning method provided in the embodiments of this application. Alternatively, terminal 100 and server 200 can also be used collaboratively to execute the focal plane positioning method provided in the embodiments of this application. For example, terminal 100 collects the intensity of interference light from the camera at various preset sampling positions and uploads it to server 200. Server 200 processes the interference light intensity according to the deployed focal plane positioning method to obtain the optimal focal plane position of the camera, and then feeds it back to terminal 100. Terminal 100 then controls the camera to focus according to the optimal focal plane position.

[0066] In this application embodiment, the terminal 100 can be a mobile phone, tablet computer, teaching large screen, wearable device, vehicle-mounted device, conference terminal, augmented reality (AR) / virtual reality (VR) device, laptop computer, ultra-mobile personal computer (UMPC), netbook, personal digital assistant (PDA), etc., and this application embodiment does not impose any restrictions on it.

[0067] The product form of server 200 in this application embodiment may include, but is not limited to, cloud servers (running as virtual server instances on physical servers), micro servers (suitable for small office or home environments), storage servers (focused on data storage and management), GPU servers (equipped with graphics processing units, suitable for high-performance computing and graphics processing tasks), and modular servers (allowing flexible configuration and expansion of hardware components as needed).

[0068] Next, we will illustrate this with an example of applying the focal plane positioning method to computer equipment. (Refer to...) Figure 3 The present application provides a flowchart of a focal plane positioning method, which may include steps S100 to S120, and these steps are described in detail below.

[0069] Step S100: Obtain the intensity of interference light at different preset sampling positions of the camera in the focusing direction perpendicular to the object being measured.

[0070] Among them, the intensity of the interference light is the intensity of the light signal after the two reflected light beams are combined. The two reflected light beams are the reflected light from the object under test and the reference mirror to the light source located in the focusing direction, respectively. The reference mirror is placed parallel to the light source, and the distance between the reference mirror and the light source is the optimal focusing distance of the camera.

[0071] This step is the data acquisition stage. As mentioned above, the intensity of the interference light from the camera at different preset sampling positions can be uploaded by the terminal or obtained in real time through the focal plane positioning device.

[0072] Specifically, to achieve this acquisition process, an optical interference structure needs to be built, such as a Linnik interferometer (see the focal plane positioning device described above). The camera or the object under test is mounted on a precision moving platform and moves along the focusing direction in preset steps. At each sampling position, the camera or photodetector captures the intensity value of the interference light, usually through image acquisition or intensity reading. Throughout this process, the stability of the light source and the alignment of the optical components must be maintained to ensure data accuracy.

[0073] Understandably, this step, by sampling the camera at multiple positions, can capture the phase and amplitude changes of the interference light signal, thereby improving focusing accuracy and reliability. Furthermore, it allows for the acquisition of valid data even in non-ideal real-world shooting environments (such as uneven surfaces of the object being measured), enhancing the robustness of focal plane positioning.

[0074] Step S110: Fit the interference light intensity corresponding to all preset sampling positions to obtain the interference light signal.

[0075] The discrete interference light intensities obtained in step S100 are fitted to reconstruct the continuous interference light signal, with reference to... Figure 4 An example diagram of an interference optical signal is provided in the embodiments of this application.

[0076] In one possible implementation, the fitting in this step can be achieved using mathematical algorithms and software tools. First, the sequence of interference light intensity varying with position is imported into a processing environment such as MATLAB or Python. Then, fitting algorithms, such as least squares, Fourier transform, or Gaussian process regression, are applied to generate a smooth interference light signal curve. The model used for fitting can include, for example, a sine function, a polynomial, or a custom interference equation, to match the actual data trend. Finally, a continuous function or curve, i.e., the interference light signal, is output, representing the relationship between the interference light intensity and the camera position.

[0077] The embodiments of this application do not depend on the density of sampling positions, and can overcome the limitations of discrete sampling. By fitting the sequence of interference light intensity changes with position, the characteristics of interference light signals are revealed, thereby enabling more accurate identification of key points, such as zero optical path difference points. This reduces errors caused by sampling intervals or environmental fluctuations, thereby improving the accuracy of focal plane positioning.

[0078] Step S120: Determine the zero optical path difference point from the interference light signal and set the zero optical path difference point as the optimal focal plane position of the camera.

[0079] The zero optical path difference point is located in the fitted interference light signal. Here, "zero optical path difference" refers to the fact that the optical path difference between the reflected light from the light source by the object under test and the reflected light from the light source by the reference mirror is zero. In the interference light signal, the zero optical path difference point usually corresponds to the extreme value of light intensity (such as the maximum value, minimum value, etc.) or the zero phase point.

[0080] In this embodiment, the zero optical path difference point is interpreted as the optimal focal plane position of the camera because when the camera is at this position, the distance L1 between the object being measured and the beam splitter is equal to the distance L2 between the reference mirror and the beam splitter. Since the distance L2 between the reference mirror and the beam splitter is the optimal focusing distance of the camera, the distance L1 between the object being measured and the beam splitter is also the optimal focusing distance of the camera. Therefore, the zero optical path difference point is taken as the optimal focusing position of the camera.

[0081] Understandably, the distance L3 between the beam splitter and the camera is fixed, while the camera's focusing length is L = L1 + L3. The value of L1 is determined based on the difference between the camera's optimal focusing length and L3, and the position of the reference mirror is set based on L1. It should be noted that the reason this application specifies the camera's optimal focusing length but does not directly fix the camera position is because different objects have different thicknesses and surface roughnesses. Even if the camera's optimal focusing length remains unchanged, the camera's optimal focusing position will be different.

[0082] If a calibrated object is used as the reference mirror, and the distance between it and the camera is set as the optimal focusing length, the optimal focusing position of the camera is determined and fixed. However, since the thickness of the object being measured differs from that of the calibrated object, the fixed optimal focusing position is no longer suitable for the current object, and optimal focusing cannot be achieved. Therefore, this embodiment sets the distance between the reference mirror and the beam splitter as the optimal focusing distance (the difference between the optimal focusing length and L3), and uses interference light to locate the optimal focusing position of the camera.

[0083] In one possible implementation, locating the zero optical path difference point from the interferometric optical signal can include: first, identifying characteristic points on the interferometric optical signal curve, such as finding intensity peaks or valleys, or determining the zero-phase point through phase calculation. Then, mapping the coordinates of the point to the camera's focusing direction as the camera's optimal focal plane position.

[0084] In summary, this application, by actually collecting the interference light intensity at multiple preset sampling points along the focusing direction, adapts to changes in different test objects or shooting environments. This allows the fitted interference light signal to reflect the actual optical path difference between the camera at different positions and the optimal focusing distance, thereby improving the flexibility of focal plane positioning. Furthermore, by finding the position with zero optical path difference from the interference light signal, the optimal focal plane position of the camera in the current environment can be accurately located.

[0085] Furthermore, due to the short coherence of white light sources, the interference signal only produces an extremely sharp envelope peak when the optical path difference is nearly zero. This transforms the determination of the focal plane position from a relatively ambiguous optimization problem based on image quality into a problem of precise measurement of the absolute physical signal peak. Its axial resolution can reach the nanometer level, and its positioning accuracy is far superior to traditional focusing methods based on image sharpness evaluation functions. It also effectively avoids the phase ambiguity problem present in laser interferometry, thus providing a solid foundation for the ultra-precision measurement and inspection requirements of semiconductor manufacturing.

[0086] Next, other possible implementations of the focal plane positioning method provided in this application will be described in detail through the following embodiments.

[0087] It is understandable that during the fitting of the sequence of interference light intensity varying with position, if the preset sampling positions in the sequence are nonlinearly distributed at the beginning and end stages, such as due to non-uniform mechanical motion, uneven sensor response, or inconsistent data recording intervals, directly using the original sequence of interference light intensity varying with position will lead to inconsistent spatial sampling intervals, thus affecting the subsequent analysis results. For example, the fitted interference light signal curve may show stages of dense or sparse sampling, making it impossible to accurately locate the zero optical path difference point.

[0088] Based on the above considerations, in one possible implementation, the process of fitting the interference light intensity corresponding to all preset sampling positions to obtain the interference light signal includes: when the distribution of preset sampling positions is not equally spaced, performing equal-interval interpolation on all preset sampling positions according to a preset interval to obtain a preset number of equally spaced sampling positions and the interference light intensity corresponding to each sampling position; fitting the interference light intensity corresponding to all sampling positions to obtain the interference light signal.

[0089] Specifically, before fitting the sequence of interference light intensity varying with position, this embodiment first determines whether the distribution of the preset sampling positions in the interference light intensity sequence corresponding to all collected preset sampling positions is non-linear, i.e., the sampling positions are not equidistant in space. If the determination result is yes, i.e., the distribution of preset sampling positions is not equidistant, then before fitting, the interference light is interpolated according to equidistant positions to ensure the consistency of the spatial sampling interval of the sampling signal.

[0090] by Figure 5 The example diagram showing the sampling position interpolation is used as an illustration. Figure 5The left-hand image shows the original interference light intensity sequence as a function of position, with sampling points (i.e., preset sampling positions) at 1.0, 1.5, 2.3, and 2.6. Clearly, the sampling points are not evenly spaced. In this case, cubic splines and linear interpolation are used to insert new sampling points between the original data points. For example, the right-hand image shows two new sampling points at 2.0 and 2.5, forming an evenly spaced sampling sequence with all or some of the original sampling points. Further, the evenly spaced sampling sequence obtained after interpolation is fitted to obtain the interference light signal.

[0091] It is understandable that even if the main features of the interference light signal are extracted from the sequence of interference light intensity changing with position by fitting, noise in the original data (such as random noise, environmental interference, etc.) may still remain in the fitting residual. The presence of this noise will mask the details of the real signal, affect the signal-to-noise ratio, cause signal distortion or increase fitting error, and thus affect the final determination of the zero optical path difference point.

[0092] Based on this consideration, in one possible implementation, after fitting the interference light intensity corresponding to all preset sampling positions to obtain the interference light signal, the method further includes: filtering the interference light signal to obtain the filtered interference light signal; determining the zero optical path difference point from the interference light signal, including: determining the zero optical path difference point from the filtered interference light signal.

[0093] The fitted interference light signal can be filtered using methods such as Gaussian filtering, Butterworth filtering, and mean filtering. In this embodiment, Gaussian filtering of the interference light signal based on the following equation (1) is used as an example. The vertical distribution of the interference light signal is similar to a Gaussian-modulated cosine signal. Using Gaussian filtering can better preserve the details of the interference light signal while removing smooth noise.

[0094] (1)

[0095] Where π is a constant, approximately 3.14, σ is the standard deviation of the filter, and x and y are the abscissa and ordinate of the signal point in the interference light signal on the overall signal distribution, respectively. The abscissa is the signal sampling position, and the ordinate is the intensity of the interference light.

[0096] In this embodiment, filtering is used to optimize the fitted interference light signal, extract the effective signal, and thus improve the accuracy and reliability of the optimal focal plane positioning.

[0097] Furthermore, the zero optical path difference point is located on the interference light signal obtained above, thereby determining the optimal focal plane position of the camera in the current environment and achieving the positioning of the optimal focal plane.

[0098] In one possible implementation, the process of determining the zero optical path difference point from the interference optical signal includes: using the intensity of the interference light corresponding to each position point in the interference optical signal as the weight value of the position point; taking a weighted average of all position points in the interference optical signal based on the weight value of each position point to obtain the centroid position point of the interference optical signal; and determining the centroid position point as the zero optical path difference point of the interference optical signal.

[0099] Reference Figure 6 This application provides an example diagram for locating the zero optical path difference point. In physical space, the center of gravity is considered to be a point where the mass of an object is concentrated. Ideally, the white light interference signal is centrally symmetrical about the zero-order fringe (the small waveform segment where the zero optical path difference point is located). Therefore, the center position of the interference light signal should coincide with the center position of the fringe. Thus, the zero optical path difference point is determined by locating the center of the interference light signal.

[0100] Specifically, the zero optical path difference of the interference light signal is calculated using the centroid method of the following formula (2).

[0101] (2)

[0102] Where Centroid is the center of gravity, I i z represents the intensity of the interference light at the i-th position, n represents the total number of sampling positions, and z i This represents the i-th position.

[0103] The intensity value of the interference light at a given location is used as the weight value for that location. A weighted average is then calculated for all locations to obtain the centroid location, which is then used as the zero optical path difference point.

[0104] It is understandable that the symmetry of the actual signal may be disrupted due to factors such as noise and excessively large sampling step size, resulting in a certain error between the located centroid position and the actual zero optical path difference point. In another possible implementation, to improve the positioning accuracy of the zero optical path difference point, this embodiment, after obtaining the centroid position of the interference light signal by weighted averaging of all position points based on the weight value of each position point, further includes: determining the nearest minimum points to the centroid position point from both the left and right sides of the centroid position point in the interference light signal, obtaining the left minimum point and the right minimum point; fitting the signal waveform between the left minimum point and the right minimum point in the interference light signal using a preset function to obtain a target function; and determining the position point corresponding to the parameter value in the interference light signal based on the parameter value corresponding to the preset parameter type in the target function, as the target centroid position of the interference light signal. The process of determining the centroid position point as the zero optical path difference point of the interference light signal includes: determining the target centroid position point as the zero optical path difference point of the interference light signal.

[0105] Understandably, the centroid position point located above is used as a coarse positioning point. This coarse positioning point is used to determine a fringe period. Within this fringe period, the centroid method or extreme value method is applied again to reposition the center point within that fringe period, thus improving positioning accuracy. Specifically, refer to... Figure 7 The present application provides an example diagram of a zero-order fringe to illustrate this process in detail.

[0106] First, in the interferometric optical signal, starting from the centroid, we search for local minima in the signal waveform to its left and right, respectively, obtaining the left and right local minima. Using the nearest local minima to the left and right of the centroid, we can further define a relatively stable waveform region in the interferometric optical signal. This region contains the key signal at the actual zero optical path difference point.

[0107] Based on this, the waveform fringe data formed between the left and right minimum points is extracted. In this embodiment, the waveform fringe is called the zero-order fringe. According to the characteristics of the interference light signal, a preset function for fitting the zero-order fringe is selected, such as a Gaussian function or a polynomial function. This application takes a trigonometric function (such as the sine function y=Asin(Bx+C)+D or the cosine function y=Acos(Bx+C)+D) as an example to fit the zero-order fringe and obtain the target function of the following formula (3).

[0108] (3)

[0109] Among them, I bg Indicates background light intensity, and A represents signal replication. denoted as the center wavelength of the light source, z is the sampling position, I(z) is the signal light intensity corresponding to the sampling position z, and z0 is the target zero optical path difference point.

[0110] like Figure 8 Another example diagram of zero optical path difference point positioning provided in this application embodiment uses z0 in the fitted objective function as the target zero optical path difference point to locate the optimal focal plane position of the camera.

[0111] In summary, this application's embodiments effectively filter out noise introduced by factors such as stage vibration, irregular motion, and background light changes during the testing process by preprocessing the interference signal, such as fitting and noise filtering, thereby improving the signal-to-noise ratio and laying the foundation for improving the camera's focusing accuracy. Furthermore, by calculating the centroid of the interference signal, the optimal focal plane is obtained, allowing the camera to be adjusted to the optimal focusing position, saving computational resources and fully meeting the high-throughput requirements of actual overlay measurement scenarios. Based on this, this application performs iterative operations on the centroid and triangulation fitting of the interference signal, resulting in a more accurate and robust calculated focal plane, effectively avoiding the impact of outliers introduced by hardware devices causing focal plane deviation.

[0112] This application also provides an electronic device in its embodiments. (See reference...) Figure 9 The diagram illustrates a structural schematic suitable for implementing the electronic device in the embodiments of this application. The electronic device in the embodiments of this application may include, but is not limited to, fixed terminals such as mobile phones, tablets, large-screen teaching displays, wearable devices, etc. Figure 9 The electronic device shown is merely an example and should not impose any limitation on the functionality and scope of use of the embodiments of this application.

[0113] like Figure 9 As shown, the electronic device may include a processing unit (e.g., a central processing unit, a graphics processing unit, etc.) 1, which can perform various appropriate actions and processes according to a program stored in a read-only memory (ROM) 2 or a program loaded from a storage device 8 into a random access memory (RAM) 3, to implement the focal plane positioning method of the foregoing embodiments of this application. When the electronic device is powered on, the RAM 3 also stores various programs and data required for the operation of the electronic device. The processing unit 1, ROM 2, and RAM 3 are interconnected via a bus 4. An input / output (I / O) interface 5 is also connected to the bus 4.

[0114] Typically, the following devices can be connected to I / O interface 5: input devices 6 including, for example, touchscreens, touchpads, keyboards, mice, cameras, microphones, accelerometers, gyroscopes, etc.; output devices 7 including, for example, liquid crystal displays (LCDs), speakers, vibrators, etc.; storage devices 8 including, for example, memory cards, hard drives, etc.; and communication devices 9. Communication device 9 allows electronic devices to communicate wirelessly or wiredly with other devices to exchange data. Although Figure 9 Electronic devices with various devices are shown, but it should be understood that it is not required to implement or have all of the devices shown. More or fewer devices may be implemented or have instead.

[0115] This application also provides a computer program product including computer-readable instructions, which, when executed on an electronic device, cause the electronic device to implement any of the focal plane positioning methods provided in this application.

[0116] This application also provides a computer-readable storage medium that carries one or more computer programs. When the one or more computer programs are executed by an electronic device, the electronic device can implement any of the focal plane positioning methods provided in this application.

[0117] It should also be noted that the device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and 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. In addition, in the device embodiment drawings provided in this application, the connection relationship between modules indicates that they have a communication connection, which can be implemented as one or more communication buses or signal lines.

[0118] Through the above description of the embodiments, those skilled in the art can clearly understand that this application can be implemented by means of software plus necessary general-purpose hardware, or it can be implemented by special-purpose hardware including application-specific integrated circuits, special-purpose CPUs, special-purpose memory, special-purpose components, etc. Generally, any function performed by a computer program can be easily implemented by corresponding hardware, and the specific hardware structure used to implement the same function can also be diverse, such as analog circuits, digital circuits, or special-purpose circuits. However, for this application, software program implementation is more often the preferred implementation method. Based on this understanding, the technical solution of this application, 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 is stored in a readable storage medium, such as a computer floppy disk, USB flash drive, mobile hard disk, ROM, RAM, magnetic disk, or optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, training equipment, or network device, etc.) to execute the methods described in the various embodiments of this application.

[0119] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product.

[0120] The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this application are generated. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions may be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions may be transmitted from one website, computer, training device, or data center to another website, computer, training device, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium may be any available medium that a computer can store or a data storage device such as a training device or data center that integrates one or more available media. The available media may be magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g., DVDs), or semiconductor media (e.g., solid-state drives (SSDs)).

[0121] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The various embodiments can be combined as needed, and the same or similar parts can be referred to each other.

Claims

1. A focal plane positioning method, characterized in that, include: The intensity of interference light is obtained when the camera is at different preset sampling positions in the focusing direction perpendicular to the object under test; the intensity of interference light is the intensity of the light signal after the two reflected beams are combined, the two reflected beams are the reflected light of the object under test and the reference mirror respectively to the light source located in the focusing direction, the reference mirror is placed parallel to the light source, and the distance between the reference mirror and the light source is the optimal focusing distance of the camera. The interference light intensity corresponding to all the preset sampling positions is fitted to obtain the interference light signal; The zero optical path difference point is determined from the interference light signal, and the zero optical path difference point is determined as the optimal focal plane position of the camera.

2. The focal plane positioning method according to claim 1, characterized in that, The process of determining the zero optical path difference point from the interference optical signal includes: The intensity of the interference light at each position point in the interference light signal is used as the weight value of that position point. Based on the weight value of each position point, a weighted average is calculated for all position points in the interference optical signal to obtain the centroid position point of the interference optical signal. The centroid position is determined as the zero optical path difference point of the interference optical signal.

3. The focal plane positioning method according to claim 2, characterized in that, After obtaining the centroid position of the interference light signal by weighted averaging of all position points based on the weight value of each position point, the method further includes: In the interference optical signal, the minimum points closest to the centroid position point are determined from the left and right sides of the centroid position point, respectively, to obtain the left minimum point and the right minimum point; The target function is obtained by fitting the signal waveform between the left minimum point and the right minimum point in the interference optical signal using a preset function. Based on the parameter values ​​corresponding to the preset parameter types in the objective function, the position points corresponding to the parameter values ​​are determined from the interference optical signal and used as the target centroid position points of the interference optical signal. The process of determining the centroid position point as the zero optical path difference point of the interference optical signal includes: determining the target centroid position point as the zero optical path difference point of the interference optical signal.

4. The focal plane positioning method according to claim 3, characterized in that, The preset function is a trigonometric function.

5. The focal plane positioning method according to any one of claims 1-4, characterized in that, The process of fitting the interference light intensity corresponding to all the preset sampling positions to obtain the interference light signal includes: When the distribution of the preset sampling positions is not equidistant, all the preset sampling positions are interpolated at equal intervals according to the preset intervals to obtain a preset number of sampling positions with equal intervals and the interference light intensity corresponding to each sampling position. The interference light intensity corresponding to all the sampling positions is fitted to obtain the interference light signal.

6. The focal plane positioning method according to any one of claims 1-4, characterized in that, After fitting the interference light intensity corresponding to all the preset sampling positions to obtain the interference light signal, the method further includes: The interference light signal is filtered to obtain the filtered interference light signal; Determining the zero optical path difference point from the interference optical signal includes: determining the zero optical path difference point from the filtered interference optical signal.

7. A focal plane positioning device, characterized in that, include: Light source, stage, camera, beam splitter, reference mirror, detector, and processing module; The camera is positioned directly above the placement platform, and the beam splitter is positioned between the camera and the placement platform, with a fixed distance between the beam splitter and the camera. The reference mirror is placed parallel to the beam splitter, and the distance between the reference mirror and the beam splitter is the optimal focusing distance of the camera; The camera is used to respond to the movement command sent by the processing module, move to the preset sampling position, and drive the beam splitter and the reference mirror to move; The beam splitter is used to split the light source into two beams, which are directed at the test object and the reference mirror placed on the stage, respectively, and reflect the reflected light from the light source by the test object and the reference mirror to the detector. The detector is used to receive the reflected light from the light source by the object under test and the reference mirror respectively, and to detect the light intensity of the light signal after the two reflected lights are combined, so as to obtain the light intensity of the interference light corresponding to the preset sampling position of the camera, and transmit the light intensity of the interference light corresponding to the preset sampling position to the processing module. The processing module is used to receive the interference light intensity corresponding to different preset sampling positions of the camera, and process the interference light intensity according to the focal plane positioning method according to any one of claims 1-6 to obtain the optimal focal plane position of the camera.

8. An electronic device, characterized in that, include: Memory and processor; The memory is used to store programs; The processor is used to execute the program to implement each step of the focal plane positioning method as described in any one of claims 1 to 6.

9. A readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements each step of the focal plane positioning method as described in any one of claims 1 to 6.

10. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by the processor, it implements the various steps of the focal plane positioning method as described in any one of claims 1 to 6.

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