A scanning electron microscope imaging correction method, device and computer equipment

Abstract

The application relates to a scanning electron microscope imaging correction method and device and a computer device. The scanning electron microscope comprises a double deflector, a movable diaphragm and an objective lens. The method comprises performing a single correction process as follows: obtaining an initial gain ratio of the double deflector; obtaining first scanning images corresponding to different gain ratios within a preset adjustment range of the initial gain ratio; determining a target gain ratio of the double deflector based on a variation coefficient of the first scanning images; obtaining second scanning images under different movable diaphragm positions in response to a movable diaphragm movement instruction; determining a target position of the movable diaphragm based on a variation coefficient of the second scanning images; obtaining third scanning images corresponding to different objective lens focus values in response to an objective lens focus value adjustment instruction; determining a target focus value of the objective lens based on a clear value of a central sub-region of the third scanning images; and obtaining a fourth scanning image, and ending the correction process if the variation coefficient of the fourth scanning image is less than a preset convergence threshold.

Description

Technical Field

[0001] This application relates to the field of charged particle microscopy imaging technology, and in particular to an imaging correction method, apparatus, and computer equipment for a scanning electron microscope. Background Technology

[0002] The spatial resolution of a scanning electron microscope (SEM), i.e., the smallest electron beam spot size focused on the sample surface, is its most critical performance indicator. However, when imaging samples such as semiconductor wafers with a large field of view, the resolution at the center point alone is insufficient to measure the quality of the entire image. The uniformity of the large field of view image, i.e., the consistency between the image center and edges in terms of sharpness, distortion, etc., has become a key indicator restricting the accuracy and reliability of measurements. When the scanning field of view is small, the off-axis distance of the electron beam is extremely short, and off-axis aberrations are negligible, resulting in uniform image quality. However, as the field of view increases, the sharpness of the image edges deteriorates significantly, creating a stark contrast with the center.

[0003] In related technologies, a dual-deflector system can be used to rotate the electron beam around the back focal plane of the objective lens by precisely adjusting the scanning gain and rotation angle of the upper and lower deflectors, thereby almost perfectly eliminating distortion and field curvature. However, it relies on the operator's experience and manually adjusts the image edge sharpness by visual observation, lacking an objective and unified evaluation standard. Summary of the Invention

[0004] Therefore, it is necessary to provide an imaging correction method, apparatus, and computer equipment for scanning electron microscopes to address the aforementioned technical problems.

[0005] In a first aspect, this application provides an imaging correction method for a scanning electron microscope, the scanning electron microscope comprising a dual deflector, a movable aperture, and an objective lens, the method comprising:

[0006] Perform the following single-treatment procedure:

[0007] Obtain the initial gain ratio of the dual deflectors;

[0008] Within the preset adjustment range of the initial gain ratio, the value of the gain ratio is adjusted sequentially based on a fixed step size to obtain the first scan image corresponding to different gain ratios;

[0009] The target gain ratio of the dual deflectors is determined based on the coefficient of variation of the first scanned image.

[0010] In response to the movement command of the movable aperture, second scan images are obtained at different positions of the movable aperture;

[0011] The target position of the movable aperture is determined based on the coefficient of variation of the second scanned image;

[0012] In response to the adjustment command of the objective lens focus value, a third scan image corresponding to different objective lens focus values ​​is obtained;

[0013] Based on the sharpness value of the central sub-region of the third scan image, the target focus value of the objective lens is determined;

[0014] After the target gain ratio of the dual deflectors, the target position of the movable aperture, and the target focus value of the objective lens are determined, a fourth scan image is acquired. If the coefficient of variation of the fourth scan image is less than a preset convergence threshold, the correction process ends.

[0015] In one embodiment, the process of obtaining the coefficient of variation includes:

[0016] Acquire a baseline image;

[0017] The coefficient of variation of the reference image is obtained based on the sharpness evaluation values ​​of the central and edge sub-regions of the reference image.

[0018] In one embodiment, the first scan image, the second scan image, the third scan image, and the fourth scan image are obtained by imaging a sample with periodically repeating microstructures.

[0019] In one embodiment, the arithmetic mean of the grayscale values ​​of the pixels across the entire image area of ​​the first scanned image, the second scanned image, the third scanned image, and the fourth scanned image is between 100 and 150, and the grayscale value of each pixel across the entire image area is greater than 0 and less than 255.

[0020] In one embodiment, the method further includes:

[0021] If the coefficient of variation of the fourth scan image is not less than the preset convergence threshold, the single correction process is repeated starting from the currently determined target gain ratio, target position and target focus value until the current coefficient of variation is less than the preset convergence threshold.

[0022] Secondly, this application also provides a scanning electron microscope, the scanning electron microscope comprising:

[0023] An electron emission source, wherein the electron emission source is used to emit an electron beam;

[0024] A dual deflector is disposed in the propagation path of the electron beam and is used to control the scanning of the electron beam;

[0025] An objective lens, positioned below the dual deflector, is used to focus an electron beam onto the sample surface;

[0026] A movable aperture is disposed on the propagation path of the electron beam;

[0027] Image detector, used to acquire scanned images;

[0028] A controller is communicatively connected to the dual deflectors, the objective lens, the movable aperture, and the image detector. The controller is used to execute the imaging correction method of the scanning electron microscope described in any of the above-mentioned embodiments.

[0029] Thirdly, this disclosure also provides an imaging correction device for a scanning electron microscope, the scanning electron microscope including a dual deflector, a movable aperture, and an objective lens, the device comprising:

[0030] The first adjustment module is used to perform the following single correction process:

[0031] Obtain the initial gain ratio of the dual deflectors;

[0032] Within the preset adjustment range of the initial gain ratio, the value of the gain ratio is adjusted sequentially based on a fixed step size to obtain the first scan image corresponding to different gain ratios;

[0033] The target gain ratio of the dual deflectors is determined based on the coefficient of variation of the first scanned image.

[0034] The second adjustment module is used to respond to the movement command of the movable aperture to obtain the second scan image at different movable aperture positions;

[0035] The target position of the movable aperture is determined based on the coefficient of variation of the second scanned image;

[0036] The third adjustment module is used to respond to the adjustment command of the objective lens focus value and obtain the third scan image corresponding to different objective lens focus values;

[0037] Based on the sharpness value of the central sub-region of the third scan image, the target focus value of the objective lens is determined;

[0038] The correction module is used to acquire a fourth scan image after the target gain ratio of the dual deflectors, the target position of the movable aperture, and the target focus value of the objective lens are determined. If the coefficient of variation of the fourth scan image is less than a preset convergence threshold, the correction process ends.

[0039] Fourthly, this disclosure also provides a computer device. The computer device includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the steps of an imaging correction method for a scanning electron microscope.

[0040] Fifthly, this disclosure also provides a computer-readable storage medium. The computer-readable storage medium stores a computer program thereon, which, when executed by a processor, implements the steps of an imaging correction method for a scanning electron microscope.

[0041] Sixthly, this disclosure also provides a computer program product. The computer program product includes a computer program that, when executed by a processor, implements the steps of an imaging correction method for a scanning electron microscope.

[0042] The imaging correction method for scanning electron microscopy described above has at least the following beneficial effects:

[0043] The embodiments provided in this disclosure optimize three sets of mutually coupled correction parameters—dual deflector gain ratio, movable aperture position, and objective lens focus value—in stages. First, the optimal deflection ratio is selected by traversing the gain ratio range to suppress barrel distortion, pincushion distortion, and field curvature off-axis aberration caused by electron beam deflection in a large field of view, thereby alleviating problems such as beam spot elongation and defocusing at the image edges. Then, based on the optimal gain ratio, the XY coordinates of the movable aperture are searched in two dimensions to accurately compensate for residual mechanical assembly eccentricity between the dual deflectors and the objective lens optical axis, eliminating asymmetric image sharpness attenuation caused by eccentric magnification in a large field of view and reducing the hardware dependence of the equipment on ultra-high precision machining and assembly. Finally, the objective lens focus is fine-tuned based on the sharpness of the image center sub-region as the single optimization benchmark, prioritizing the imaging resolution of the center of the field of view and avoiding sacrificing center imaging quality for global uniformity optimization.

[0044] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments or conventional technologies of this disclosure, the accompanying drawings used in the description of the embodiments or conventional technologies will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a schematic diagram of a scanning electron microscope in one embodiment of the present disclosure;

[0047] Figure 2 This is a schematic diagram of a single deflector scanning imaging method;

[0048] Figure 3 This is a schematic diagram of different distortion forms in one embodiment;

[0049] Figure 4 This is a flowchart illustrating an imaging correction method for a scanning electron microscope in one embodiment;

[0050] Figure 5 This is a schematic diagram of a scanned image before calibration in one embodiment;

[0051] Figure 6 This is a schematic diagram illustrating the sharpness of a scanned image before calibration in one embodiment;

[0052] Figure 7 This is a schematic diagram of a calibrated scanned image in one embodiment;

[0053] Figure 8 This is a schematic diagram illustrating the sharpness of a calibrated scanned image in one embodiment;

[0054] Figure 9 This is a structural block diagram of the imaging correction device for a scanning electron microscope in one embodiment;

[0055] Figure 10 This is an internal structural diagram of a computer device in one embodiment;

[0056] Figure 11 This is an internal structure diagram of a server in one embodiment. Detailed Implementation

[0057] To enable those skilled in the art to better understand the technical solutions of this disclosure, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings.

[0058] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this disclosure are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this disclosure described herein can be implemented in orders other than those illustrated or described herein. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this disclosure as detailed in the appended claims. The terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, product, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, product, or apparatus. Without further limitation, the presence of other identical or equivalent elements in a process, method, product, or apparatus that includes said elements is not excluded. For example, the use of terms such as "first," "second," etc., is to denote names and does not indicate any specific order.

[0059] This disclosure provides a scanning electron microscope. Figure 1This is a schematic diagram of a scanning electron microscope in one embodiment of the present disclosure.

[0060] Electron emission sources are used to release electrons from the filament material and accelerate them under the action of a strong electric field to form a stable, high-energy incident electron beam, which provides a light source for subsequent electron optical systems.

[0061] An electron beam emitted from an electron emission source is a straight beam that travels in a straight line. A deflector can move the electron beam along the sample surface in a certain pattern, changing the direction of electron beam propagation. Figure 2 This diagram illustrates a single-deflector scanning imaging method. With only one deflection coil or deflector, the electron beam is deflected and directly strikes the sample at a large angle (~5-10 degrees). As the scanning field of view increases, the beam spot at the edges becomes significantly elongated, defocused, and the image edge resolution drops sharply. The dual-deflector disclosed herein includes an upper deflector and a lower deflector. The upper deflector first deflects the electron beam in a certain direction at an angle, and the lower deflector then deflects the electron beam back in the opposite direction. This allows the electron beam to be translated a certain distance before still striking the sample in a direction approximately parallel to the optical axis. The electron beam achieves a large-scale translational scanning on the sample surface, but the beam spot shape remains essentially unchanged.

[0062] The electron beam is emitted from the electron emission source above and, after initial focusing by various condenser lenses, remains a relatively coarse beam. The objective lens forms an electron probe with an extremely small diameter. The diameter of the electron probe directly determines the spatial resolution of the scanning electron microscope; the finer the probe, the higher the resolution.

[0063] A movable aperture is an adjustable electron beam blocker that allows only the highest-mass electrons passing through the central aperture to pass through, blocking stray electrons generated by scattering or deviation from the optical axis.

[0064] An image detector is a hardware component in a scanning electron microscope (SEM) responsible for receiving sample signals and converting them into digital images. When a primary electron beam scans a location on the sample surface, it excites secondary electrons, which the detector receives. By scanning the waveform in the X and Y directions using deflectors, the detector records the signal intensity under different scanning voltage conditions. A two-dimensional grayscale image of the X and Y directions and their intensity can then be plotted, which is the scanning pattern of the electron microscope.

[0065] The controller is communicatively connected to the dual deflectors, the objective lens, the movable aperture, and the image detector to execute the imaging correction method of the scanning electron microscope.

[0066] When the scanning field of view is small, the off-axis distance of the electron beam is extremely short, and off-axis aberrations are negligible, resulting in uniform image quality across the entire image. However, when the field of view increases to 100μm × 100μm or larger, the sharpness of the image edges sometimes deteriorates significantly, becoming noticeably worse than the sharpness of the center. This phenomenon is mainly caused by two fundamental reasons:

[0067] Scanning aberrations (off-axis aberrations): As the scanning range of the electron beam increases, off-axis aberrations such as distortion and field curvature increase sharply, causing the beam spot to be elongated and defocused at the edges. Figure 3 This is a schematic diagram of different distortion forms in one embodiment. Ideal distortion-free image (left), barrel distortion (middle), and pincushion distortion (right) are typical distortion forms.

[0068] Amplification effect of coaxial misalignment: Even if the central optical path has been initially aligned, small residual misalignment will be amplified at large deflection angles, leading to deterioration of beam alignment.

[0069] In some embodiments of this disclosure, such as Figure 4 As shown, an imaging correction method for scanning electron microscopes is provided. In one specific embodiment, the method may include the following steps:

[0070] S402: Perform the following single correction process: obtain the initial gain ratio of the dual deflector; within the preset adjustment range of the initial gain ratio, adjust the value of the gain ratio sequentially based on a fixed step size to obtain the first scan image corresponding to different gain ratios; determine the target gain ratio of the dual deflector based on the coefficient of variation of the first scan image.

[0071] The dual-deflector system consists of upper and lower deflectors, controlled by independent drive voltages V1 and V2 respectively. The gain ratio K is defined as K = V2 / V1, where V1 is the scanning voltage amplitude of the upper deflector and V2 is the scanning voltage amplitude of the lower deflector. The initial gain ratio refers to the gain ratio value when the electron microscope is in its uncalibrated default state or in the state saved after the last calibration.

[0072] Centered on the initial gain ratio K0, the K value is gradually changed at fixed intervals within a pre-set adjustment range, iterating through all possible gain ratio values. Due to machining and assembly tolerances, a slight misalignment between the electromagnetic centers of the two deflectors and the optical axis of the objective lens is unavoidable. Ideally, K=1, but in practice, K needs to deviate from 1 to compensate for the misalignment. Different K values ​​need to be tried within a range near K0 to find the optimal compensation. Each time the gain ratio K is adjusted, the scanning electron microscope is controlled to perform a complete scan of the standard sample at the current K value, acquiring a digital image, i.e., the first scan image.

[0073] The coefficient of variation can be calculated by taking five sub-regions from the center and four corners of the first scan image, calculating the sharpness of each sub-region, and then calculating the coefficient of variation of these five sharpnesses to obtain the coefficient of variation of the first scan image. The smallest coefficient of variation means that the sharpness of the image center and the edges is closest at this gain ratio. The gain ratio K is a key parameter affecting this uniformity. By adjusting the ratio of the driving intensity of the upper and lower deflectors, the aberrations caused by mechanical eccentricity can be compensated. Finding the K value that optimizes uniformity means finding the most effective electrical compensation value for the current mechanical deviation of the electron microscope.

[0074] S404: In response to the movement command of the movable aperture, obtain second scan images at different movable aperture positions; determine the target position of the movable aperture based on the coefficient of variation of the second scan image.

[0075] The controller sends a position adjustment command to the drive mechanism of the movable aperture, causing the aperture to shift slightly in the X and / or Y directions perpendicular to the electron beam propagation direction. Each time the aperture position is changed, a scanned image, i.e., the second scanned image, is acquired at the current aperture position. The movement method can be as follows: first, fix the Y direction, then fine-tune within the X direction in steps of a certain size to find the X position that minimizes the coefficient of variation; then fix the X position, fine-tune within the Y direction in steps of a certain size to find the Y position that minimizes the coefficient of variation, and repeat this fine-searching process, alternating between the X and Y directions, until the coefficient of variation cannot be further reduced in either direction. Each second scanned image corresponds to an aperture position. The coefficient of variation represents the dispersion of the image center and edge sharpness at that position. The smaller the coefficient of variation, the better the image uniformity at that aperture position. The aperture position corresponding to the minimum coefficient of variation is selected as the target position.

[0076] S406: In response to the objective lens focus value adjustment command, obtain a third scan image corresponding to different objective lens focus values; determine the target focus value of the objective lens based on the sharpness value of the central sub-region of the third scan image.

[0077] The controller sends adjustment commands to the objective lens's power supply, changing the objective lens's focusing excitation value, i.e., the excitation current or voltage, thereby altering the objective lens's magnetic field strength and shifting the electron beam's focal point along the optical axis. Within a preset focusing value adjustment range, the focusing value is changed sequentially in fixed steps, acquiring one image at each focusing value, i.e., the third scan image. The Laplacian variance algorithm is used, calculating only the central sub-region; a higher sharpness value indicates sharper edges and better focus in the central region.

[0078] S408: After the target gain ratio of the dual deflectors, the target position of the movable aperture, and the target focus value of the objective lens are determined, a fourth scan image is acquired. If the coefficient of variation of the fourth scan image is less than a preset convergence threshold, the correction process ends.

[0079] By traversing the gain ratio range and using the minimum image uniformity variation coefficient as the criterion, the optimal voltage ratio Kopt that best compensates for scanning distortion and field curvature is selected. This parameter is responsible for correcting barrel or pincushion distortion and off-axis aberration caused by large-field-of-view electron beam deflection. With the optimal gain ratio fixed, the X / Y coordinates of the two-dimensional search aperture are used to compensate for the mechanical assembly misalignment between the dual deflectors and the objective lens optical axis, eliminating asymmetrical edge sharpness attenuation on the left or right or top and bottom of the image. This parameter addresses the amplification problem of residual alignment deviation. After fixing the first two sets of optimal parameters, the objective lens excitation is fine-tuned only to achieve the highest image center sharpness, ensuring the focus quality of the field of view center reference and avoiding global blur caused by focus shift. The above three sets of optimized parameters are simultaneously written into the scanning electron microscope control module, and a complete large-field-of-view image is re-captured under unified imaging conditions, i.e., the fourth scan image.

[0080] If the coefficient of variation of the fourth scan image is less than the preset convergence threshold, it means that the parameters optimized by the three sets of parameters have achieved the standard for the dispersion of the sharpness of the center and edges of the large field-of-view image. The entire correction process is then terminated, and the target gain ratio, aperture coordinates, and objective lens focus value are permanently saved to the device configuration file for subsequent large field-of-view imaging of the same specifications. If the coefficient of variation of the fourth scan image is greater than the preset convergence threshold, it indicates that the parameters optimized step-by-step have coupling interference, and a single correction cannot achieve the uniformity standard. In this case, the current set of optimal parameters can be used as a new iteration starting point to completely re-execute the single correction process.

[0081] In the aforementioned imaging correction method for scanning electron microscopes, this scheme optimizes three sets of mutually coupled correction parameters—dual deflector gain ratio, movable aperture position, and objective lens focusing value—in stages. First, it traverses the gain ratio range to screen for the optimal deflection ratio, suppressing barrel distortion, pincushion distortion, and field curvature off-axis aberration caused by large-field-of-view electron beam deflection at the source, thus alleviating the problems of beam spot elongation and defocusing at the image edges. Then, based on the optimal gain ratio, it searches the XY coordinates of the movable aperture in two dimensions to accurately compensate for the residual eccentricity of the mechanical assembly between the dual deflectors and the objective lens optical axis, eliminating the asymmetric image sharpness attenuation caused by eccentric magnification under a large field of view, and reducing the hardware dependence of the equipment on ultra-high precision machining and assembly. Finally, it fine-tunes the objective lens focusing based on the sharpness of the image center sub-region as the single optimization benchmark, prioritizing the imaging resolution of the center of the field of view and avoiding sacrificing the center imaging quality for global uniformity optimization.

[0082] In some embodiments of this disclosure, the process of obtaining the coefficient of variation includes:

[0083] Acquire a baseline image;

[0084] The coefficient of variation of the reference image is obtained based on the sharpness evaluation values ​​of the central and edge sub-regions of the reference image.

[0085] In the baseline image, five sub-regions are extracted, located at the image center and four corners. Each sub-region has a size ranging from 300 pixels × 300 pixels to 500 pixels × 500 pixels. For each sub-region, its sharpness evaluation value Qi (i = 1...5) is calculated using the Laplacian variance algorithm, defined as:

[0086]

[0087] Where Ri is the i-th sub-region, and N is the total number of pixels in the sub-region. This represents the Laplacian value of the image intensity at pixel (x, y). This algorithm is extremely sensitive to changes in the edge sharpness of the image and can accurately reflect the local focus quality.

[0088] A uniformity evaluation function H is constructed, defined as the coefficient of variation of the sharpness evaluation values ​​of the five sub-regions, i.e.:

[0089]

[0090] The function H is dimensionless, and the closer its value is to 0, the better the image uniformity. When H < 0.01, the image uniformity can be judged to have reached the preset excellent standard.

[0091] In some embodiments of this disclosure, the first scan image, the second scan image, the third scan image, and the fourth scan image are obtained by imaging a sample with a periodically repeating microstructure.

[0092] Set the scanning electron microscope to the preset large field-of-view imaging conditions, image a standard sample with repeating microstructures, and obtain a reference image.

[0093] The preferred settings for imaging conditions are:

[0094] Field of view (FOV): not less than 20μm × 20μm;

[0095] Image pixel count: not less than 1024×1024;

[0096] Sample characteristics: It has periodically distributed repeating units, and the characteristic size of a single repeating unit is no greater than 1 μm;

[0097] Image brightness and contrast: Adjusted until the arithmetic mean of the gray values ​​of all pixels in the image falls within the range of 100 to 150, and there are no overly dark or overexposed pixels with a gray value of 0 or 255.

[0098] Focusing state: Adjust the excitation current or voltage of the objective lens to bring the reference image into the optimal focusing state determined by visual observation or algorithm.

[0099] The periodic structure exhibits a completely consistent pattern in the center and four corners of the entire image, with identical texture features across all sub-regions. Therefore, the sharpness contrast is unaffected by differences in the sample pattern. However, if the structure varies across different parts of the sample, and the texture complexity of the sub-regions differs, these differences may be mistakenly identified as imaging uniformity defects, leading to errors in the optimization of correction parameters.

[0100] In some embodiments of this disclosure, the arithmetic mean of the grayscale values ​​of the pixels across the entire image area of ​​the first scanned image, the second scanned image, the third scanned image, and the fourth scanned image is 100 to 150, and the grayscale value of each pixel across the entire image area is greater than 0 and less than 255.

[0101] A grayscale value of 0 represents complete signal loss and no effective imaging information in the area. A grayscale value of 255 represents detector signal saturation, where microstructural edge details are completely smoothed out. If saturated pixels exist in a sub-region, the Laplacian operator cannot capture the true line brightness gradient, resulting in a significantly underestimated or distorted sharpness calculation. This leads to misjudging the degree of image blur and causing errors in the optimization parameters for gain ratio, aperture, and focus. The image grayscale range is 0-255. A mean value below 100 indicates an overall darker image, with pixel grayscale concentrated in the low-value range and weak gradient changes. A mean value above 150 indicates an overly bright image, with pixels concentrated in the high-saturation range and compressed texture contrast. A mean value of 100-150 falls within the medium brightness range, where the brightness and darkness of microstructural lines can be sufficiently differentiated by grayscale. The image retains a complete and continuous grayscale gradient, and the Laplacian variance can accurately capture edge sharpness, allowing the sharpness difference between the center and corner sub-regions to truly reflect the defocusing and distortion defects at the electron microscope edges, ensuring the reliability of the coefficient of variation evaluation.

[0102] In some embodiments of this disclosure, the method further includes:

[0103] If the coefficient of variation of the fourth scan image is not less than the preset convergence threshold, the single correction process is repeated starting from the currently determined target gain ratio, target position and target focus value until the current coefficient of variation is less than the preset convergence threshold.

[0104] If the coefficient of variation is greater than the preset convergence threshold, it means that the current set of correction parameters still results in a large gap between the image center and edge sharpness, and the uniformity is not up to standard. Instead of ending the correction directly, the target gain ratio, aperture target position, and objective lens target focus value obtained in this study are used as new starting points, and the single correction process is repeated. The gain ratio, movable aperture, and objective lens focus are readjusted, and a fourth scan image is taken for verification. This process is repeated multiple times until the coefficient of variation of the newly taken fourth scan image is less than 0.01, and the uniformity is qualified. Only then is the correction stopped.

[0105] In one embodiment of this disclosure, a scanning electron microscope (SEM) without homogeneity calibration is used, with a field of view (FOV) of 30 μm × 30 μm, an image size of 2048 × 2048 pixels, and a sample repeatability unit size of approximately 1 μm. Images are captured before and after calibration. Figure 5 This is a schematic diagram of the scanned image before calibration in one embodiment, and each of the four corners and the center of the image is cropped into an 800×800 pixel sub-region for analysis.

[0106] Figure 6 This is a schematic diagram of the image sharpness before calibration in one embodiment. Before calibration, the image center sharpness is normalized to 1.000, and the sharpness of the four corners (top left, bottom left, top right, and bottom right) are 1.001, 1.073, 0.963, and 1.047, respectively. The image uniformity evaluation function H = 0.0433 is calculated.

[0107] Figure 7 This is a schematic diagram of a calibrated scanned image in one embodiment. Uniformity calibration was completed by optimizing the dual deflector voltage gain ratio and the aperture alignment position. Figure 8 This is a schematic diagram of the sharpness of a calibrated scanned image in one embodiment. The center sharpness was measured again and normalized to 1.000, while the sharpness of the four corners were 1.007, 1.001, 1.008, and 0.999, respectively. The evaluation function H decreased to 0.0042. The results show that the method of the present invention can significantly improve the uniformity of the image edges and center under a large field of view, converging discrete sharpness differences to a nearly uniform level.

[0108] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0109] Based on the same inventive concept, this disclosure also provides an imaging correction device for a scanning electron microscope (SEM) for implementing the imaging correction method for an SEM described above. The solution provided by this device is similar to the solution described in the above method; therefore, the specific limitations in the embodiments of the imaging correction device for an SEM provided below can be found in the limitations of the imaging correction method for an SEM described above, and will not be repeated here.

[0110] The apparatus may include a system (including a distributed system), software (application), module, component, server, client, etc., that uses the methods described in the embodiments of this specification, combined with necessary hardware implementation. Based on the same innovative concept, the apparatuses in one or more embodiments provided in this disclosure are as described in the following embodiments. Since the implementation schemes and methods for solving the problem by the apparatus are similar, the implementation of the specific apparatus in the embodiments of this specification can refer to the implementation of the foregoing methods, and repeated details will not be repeated. As used below, the terms "unit" or "module" can refer to a combination of software and / or hardware that implements a predetermined function. Although the apparatuses described in the following embodiments are preferably implemented in software, hardware implementations, or a combination of software and hardware, are also possible and contemplated.

[0111] In one embodiment, such as Figure 9 As shown, an imaging correction device 900 for a scanning electron microscope is provided. This device can be the aforementioned server, or a module, component, device, or unit integrated into the server. The device 900 may include:

[0112] The first adjustment module 902 is used to perform the following single correction process:

[0113] Obtain the initial gain ratio of the dual deflectors;

[0114] Within the preset adjustment range of the initial gain ratio, the value of the gain ratio is adjusted sequentially based on a fixed step size to obtain the first scan image corresponding to different gain ratios;

[0115] The target gain ratio of the dual deflectors is determined based on the coefficient of variation of the first scanned image.

[0116] The second adjustment module 904 is used to obtain second scan images at different positions of the movable aperture in response to the movement command of the movable aperture;

[0117] The target position of the movable aperture is determined based on the coefficient of variation of the second scanned image;

[0118] The third adjustment module 906 is used to respond to the adjustment command of the objective lens focus value to obtain the third scan image corresponding to different objective lens focus values;

[0119] Based on the sharpness value of the central sub-region of the third scan image, the target focus value of the objective lens is determined;

[0120] The correction module 908 is used to acquire a fourth scan image after the target gain ratio of the dual deflectors, the target position of the movable aperture, and the target focus value of the objective lens are determined. If the coefficient of variation of the fourth scan image is less than a preset convergence threshold, the correction process ends.

[0121] Regarding the apparatus in the above embodiments, the specific manner in which each module performs its operation has been described in detail in the embodiments related to the method, and will not be elaborated upon here.

[0122] The modules in the aforementioned imaging correction device for scanning electron microscopes can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device, or stored in the memory of a computer device as software, so that the processor can call and execute the corresponding operations of each module.

[0123] In one embodiment, a computer device is provided, which may be a server, and its internal structure diagram may be as follows: Figure 10 As shown, the computer device includes a processor, memory, and a network interface connected via a system bus. The processor provides computational and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system, computer programs, and a database. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage media. The database stores scanned images. The network interface communicates with external terminals via a network connection. When the computer program is executed by the processor, it implements an imaging correction method for a scanning electron microscope.

[0124] In one embodiment, a computer device is provided, which may be a terminal, and its internal structure diagram may be as follows: Figure 11 As shown, the computer device includes a processor, memory, communication interface, display screen, and input devices connected via a system bus. The processor provides computing and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs stored in the non-volatile storage media. The communication interface is used for wired or wireless communication with external terminals; wireless communication can be achieved through Wi-Fi, mobile cellular networks, NFC (Near Field Communication), or other technologies. When the computer program is executed by the processor, it implements an imaging correction method for a scanning electron microscope. The display screen can be an LCD screen or an e-ink screen. The input devices can be a touch layer covering the display screen, buttons, a trackball, or a touchpad on the computer device's casing, or an external keyboard, touchpad, or mouse.

[0125] Those skilled in the art will understand that Figure 10 , Figure 11 The structure shown is merely a block diagram of a portion of the structure related to the present disclosure and does not constitute a limitation on the computer device to which the present disclosure is applied. A specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0126] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, implements the methods described in any embodiment of this disclosure.

[0127] In one embodiment, a computer program product is provided, including a computer program that, when executed by a processor, implements the methods described in any embodiment of this disclosure.

[0128] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, databases, or other media used in the embodiments provided in this disclosure can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM). The databases involved in the embodiments provided in this disclosure may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this disclosure may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0129] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0130] The embodiments described above are merely illustrative of several implementations of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent disclosure. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this disclosure should be determined by the appended claims.

Claims

1. An imaging correction method for a scanning electron microscope, characterized in that, The scanning electron microscope includes a dual deflector, a movable aperture, and an objective lens; the method includes: Perform the following single-treatment procedure: Obtain the initial gain ratio of the dual deflectors; Within the preset adjustment range of the initial gain ratio, the value of the gain ratio is adjusted sequentially based on a fixed step size to obtain the first scan image corresponding to different gain ratios; The target gain ratio of the dual deflectors is determined based on the coefficient of variation of the first scanned image. In response to the movement command of the movable aperture, second scan images are obtained at different positions of the movable aperture; The target position of the movable aperture is determined based on the coefficient of variation of the second scanned image; In response to the adjustment command of the objective lens focus value, a third scan image corresponding to different objective lens focus values ​​is obtained; Based on the sharpness value of the central sub-region of the third scan image, the target focus value of the objective lens is determined; After the target gain ratio of the dual deflectors, the target position of the movable aperture, and the target focus value of the objective lens are determined, a fourth scan image is acquired. If the coefficient of variation of the fourth scan image is less than a preset convergence threshold, the correction process ends.

2. The method according to claim 1, characterized in that, The process of obtaining the coefficient of variation includes: Acquire a baseline image; The coefficient of variation of the reference image is obtained based on the sharpness evaluation values ​​of the central and edge sub-regions of the reference image.

3. The method according to claim 1, characterized in that, The first scan image, the second scan image, the third scan image, and the fourth scan image are obtained by imaging a sample with a periodic repeating microstructure.

4. The method according to claim 1, characterized in that, The arithmetic mean of the grayscale values ​​of the pixels in the entire image area of ​​the first scanned image, the second scanned image, the third scanned image, and the fourth scanned image is between 100 and 150, and the grayscale value of each pixel in the entire image area is greater than 0 and less than 255.

5. The method according to claim 1, characterized in that, The method further includes: If the coefficient of variation of the fourth scan image is not less than the preset convergence threshold, the single correction process is repeated starting from the currently determined target gain ratio, target position and target focus value until the current coefficient of variation is less than the preset convergence threshold.

6. A scanning electron microscope, characterized in that, The scanning electron microscope includes: An electron emission source, wherein the electron emission source is used to emit an electron beam; A dual deflector is disposed in the propagation path of the electron beam, and the dual deflector is used to control the propagation direction of the electron beam; An objective lens, positioned below the dual deflector, is used to focus an electron beam onto the sample surface; A movable aperture is disposed on the propagation path of the electron beam; Image detector, used to acquire scanned images; A controller, which is communicatively connected to the dual deflectors, the objective lens, the movable aperture, and the image detector, is used to execute the imaging correction method of the scanning electron microscope according to any one of claims 1 to 5.

7. An imaging correction device for a scanning electron microscope, characterized in that, The scanning electron microscope includes a dual deflector, a movable aperture, and an objective lens. The apparatus includes: The first adjustment module is used to perform the following single correction process: Obtain the initial gain ratio of the dual deflectors; Within the preset adjustment range of the initial gain ratio, the value of the gain ratio is adjusted sequentially based on a fixed step size to obtain the first scan image corresponding to different gain ratios; The target gain ratio of the dual deflectors is determined based on the coefficient of variation of the first scanned image. The second adjustment module is used to respond to the movement command of the movable aperture to obtain the second scan image at different movable aperture positions; The target position of the movable aperture is determined based on the coefficient of variation of the second scanned image; The third adjustment module is used to respond to the adjustment command of the objective lens focus value to obtain the third scan image corresponding to different objective lens focus values; Based on the sharpness value of the central sub-region of the third scan image, the target focus value of the objective lens is determined; The correction module is used to acquire a fourth scan image after the target gain ratio of the dual deflectors, the target position of the movable aperture, and the target focus value of the objective lens are determined. If the coefficient of variation of the fourth scan image is less than a preset convergence threshold, the correction process ends.

8. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 5.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 5.

10. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 5.

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