Astigmatism correction method, product, and apparatus for electron beam imaging systems
The method enhances astigmatism correction in electron beam imaging by adjusting lens current, calculating gradients, and using iterative search to optimize parameters, improving accuracy and efficiency in semiconductor manufacturing.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- DONGFANG JINGYUAN ELECTRON LTD
- Filing Date
- 2025-11-14
- Publication Date
- 2026-07-08
AI Technical Summary
Existing astigmatism correction methods for electron beam imaging devices in semiconductor manufacturing require high operator expertise, are labor-intensive, and suffer from inaccuracies due to reliance on sample selection and image binarization, leading to lower accuracy and efficiency in astigmatism correction.
A method that adjusts the objective lens current in electron beam imaging systems to collect multiple focused images, calculates gradients, and uses gradient consistency to determine astigmatism correction requirements, employing an iterative search method to optimize astigmatism parameters.
Improves astigmatism correction accuracy and efficiency by ensuring precise focusing and reducing the need for manual intervention, thereby enhancing the measurement accuracy of electron beam imaging devices.
Smart Images
Figure 2026114951000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of semiconductor manufacturing and detection, and particularly relates to a method for correcting spherical aberration of an electron beam imaging device, as well as products and devices.
Background Art
[0002] In the manufacture of integrated circuits, a charged particle beam imaging device controls the focusing state of charged particles to cause the charged particles to act on a sample, and images by capturing particle signals such as secondary particles and transmitted particles, thereby characterizing information such as the form, structure, and components of the sample. In the technical field of semiconductors, a charged particle beam imaging device includes a detection device for detecting surface defects of a wafer and an electron beam measurement device for detecting important dimensions of the wafer.
[0003] A scanning electron microscope (SEM), as a charged particle beam imaging device, is used for defect detection and measurement of critical dimensions in semiconductor manufacturing and other micro- and nano-fabrication fields. The device scans the surface of a sample with a high-energy electron beam, collecting and analyzing signals such as secondary electrons and backscattered electrons generated by the interaction between electrons and the sample, thereby enabling accurate measurement of the sample's surface morphology and dimensions. As a high-precision imaging device, SEMs must ensure stable imaging quality. During actual measurements, the SEM's state drifts somewhat over time to its optimal hardware parameters, requiring periodic correction of some hardware parameters. Astigmatism correction is a critical correction item, and its automation is particularly important. However, manual correction requires significant labor costs; therefore, automation of the astigmatism correction process is necessary. Automatic astigmatism correction analyzes the astigmatism characteristics of the image and automatically adjusts the orientation and size of the stigmator, thereby eliminating astigmatism in the image. Such automated processing not only improves imaging quality but also reduces the burden on operators, lowers the requirement for operator experience, significantly reduces labor and time costs, and indirectly improves the measurement efficiency of SEM equipment.
[0004] Conventional solutions for correcting astigmatism in images acquired by a scanning electron microscope (SEM) (i.e., SEM images) involve selecting an isotropic sample position to perform astigmatism correction, calculating spectral information of the sample pattern, and using the circularity and area characteristics of the spectral binary image to determine whether the current instrument needs to correct astigmatism. However, such solutions have problems such as limitations in sample selection, higher requirements for operator experience, the need for operators to thoroughly understand image characteristics, low diversity of application scenarios, and higher labor costs. Furthermore, such solutions rely on the circularity and area characteristics of the spectral binary image to determine whether the instrument needs to perform astigmatism correction, resulting in high requirements for SEM image quality and accuracy of the spectral image binarization results, lower noise tolerance of the algorithm, lower redundant search capability due to anomaly detection, lower algorithm operational efficiency, and lower accuracy of the astigmatism correction results.
[0005] Another solution for performing astigmatism correction adjustment on SEM images using conventional technology involves adjusting the distance from the electron microscope's imaging lens to the focal point based on the degree of image blurring. When the imaging lens is at the focal point, the sharpness of the focused image is described using two values: the local dispersion and the mean value of the local dispersion. The sharpness of the focused image is then used as the criterion for completing the adjustment of the astigmatism value. However, this solution has problems such as the unavoidable application of incorrect results because the overall automatic adjustment of astigmatism correction is directly checked after the astigmatism value has been adjusted, resulting in lower algorithm accuracy and the inability to ensure normal measurement of the instrument. [Overview of the Initiative] [Problems that the invention aims to solve]
[0006] In view of the above problems, the present invention provides an astigmatism correction method, product, and apparatus for an electron beam imaging apparatus that overcomes the above problems or solves them at least partially. [Means for solving the problem]
[0007] One objective of the present invention is to ensure the accuracy of astigmatism correction by providing a method for correcting astigmatism in an electron beam imaging apparatus.
[0008] A further object of the present invention is to further improve the accuracy of astigmatism correction by improving the accuracy of determining whether the astigmatism correction requirements are met.
[0009] Another further object of the present invention is to improve the efficiency of astigmatism correction.
[0010] In particular, the present invention provides a method for correcting astigmatism in an electron beam imaging apparatus, and this method is To search for the target astigmatism parameter of the astigmatism corrector in an electron beam imaging system, The preset objective lens current is gradually adjusted according to the set step size, and multiple precisely focused images corresponding to different objective lens currents are collected. Calculating the gradient in different coordinate axis directions of multiple precisely focused images, Based on the consistency of the gradient, it is determined whether the target astigmatism parameter meets the astigmatism correction requirements, This includes determining the target objective lens current of the electron beam imaging device based on the gradient, if the astigmatism correction requirements are met.
[0011] Optionally, the step of determining whether the target astigmatism parameter meets the astigmatism correction requirement based on gradient consistency is: Calculating the X-axis gradient score change curve and Y-axis gradient score change curve for multiple precisely focused images based on the gradient, To determine whether the axis of symmetry of the X-axis gradient score change curve coincides with the axis of symmetry of the Y-axis gradient score change curve, If they match, verify that the target astigmatism parameters meet the astigmatism correction requirements, If they do not match, this includes confirming that the target astigmatism parameters do not meet the astigmatism correction requirements.
[0012] Optionally, the step of determining the target objective lens current of the electron beam imaging device based on the gradient is: This includes setting the objective lens current value corresponding to the axis of symmetry as the target objective lens current.
[0013] The optional step of searching for the target astigmatism parameter of the astigmatism corrector in an electron beam imaging system is: The process involves gradually adjusting the astigmatism parameters according to the initial astigmatism step size to acquire multiple astigmatism comparison images, and The system searches for astigmatism parameters tuned based on the variance of multiple astigmatism comparison images, and uses this as an iterative search base. The process involves iteratively searching for tuned astigmatism parameters, reducing the astigmatism step size in each iteration, and stopping the iterations until the astigmatism step size becomes smaller than a preset search stop precision. Finally, this includes setting the tuned astigmatism parameter obtained through iterative searching as the target astigmatism parameter of the astigmatism corrector.
[0014] The optional step of searching for astigmatism parameters tuned based on the variance of multiple astigmatism comparison images is: The variance of each astigmatism comparison image is calculated and used as the sharpness score for each astigmatism comparison image. This includes comparing the sharpness scores of multiple astigmatism comparison images and setting the astigmatism parameter value corresponding to the astigmatism comparison image with the highest sharpness score as the tuned astigmatism parameter.
[0015] Optionally, before the step of searching for the target astigmatism parameter of the astigmatism corrector in the electron beam imaging system, the astigmatism correction method is: To retrieve the preset objective lens current of the electron beam imaging device, This further includes setting the objective lens current of the electron beam imaging device to a preset objective lens current.
[0016] Optionally, the step of searching for the preset objective lens current of the electron beam imaging device is: The initial objective lens current is gradually adjusted according to the preset current step size, and multiple coarse-focused images corresponding to different objective lens currents are acquired. Calculating the sharpness of multiple coarsely focused images, This includes searching for an objective lens current tuned based on the sharpness of multiple coarsely focused images, and setting the retrieved tuned objective lens current as the preset objective lens current.
[0017] Optionally, after the step of determining whether the target astigmatism parameter meets the astigmatism correction requirement based on gradient consistency, the astigmatism correction method is: If the astigmatism correction requirements are not met, the system further includes outputting a prompt indicating that astigmatism correction failed.
[0018] According to another aspect of the present invention, a computer program product is provided, the product comprising a computer program, which, when executed by a processor, realizes the steps in the astigmatism correction method for an electron beam imaging apparatus described in any one of the above paragraphs.
[0019] According to yet another aspect of the present invention, there is further provided a computer device, which includes a memory, a processor, and a computer program stored in the memory and executed by the processor. When the processor executes the computer program, the steps in the method for correcting the spherical aberration of the electron beam imaging device according to any one of the above items are realized.
Advantages of the Invention
[0020] The method for correcting the spherical aberration of the electron beam imaging device according to the present invention searches for the target spherical aberration parameters of the spherical aberration corrector in the electron beam imaging device, then gradually adjusts the preset objective lens current according to the set step size, and collects a plurality of precision focusing images corresponding to different objective lens currents, calculates the gradients in different coordinate axis directions of the plurality of precision focusing images, and determines whether the target spherical aberration parameters meet the spherical aberration correction requirements based on the consistency of the gradients, thereby realizing the evaluation of the spherical aberration correction effect. Therefore, the spherical aberration correction method of the present invention can effectively avoid the application of incorrect results, avoid the problem that the accuracy caused by incorrect spherical aberration correction results is lower and the normal measurement of the device cannot be ensured, improve the accuracy of spherical aberration correction, and thereby improve the measurement accuracy of the electron beam imaging device. In addition, when it is confirmed that the target spherical aberration parameters meet the spherical aberration correction requirements, the method for correcting the spherical aberration of the electron beam imaging device according to the present invention determines the target objective lens current of the electron beam imaging device based on the gradient, thereby realizing the readjustment of the objective lens current of the electron beam imaging device, improving the adjustment accuracy of the objective lens current, and further improving the accuracy of spherical aberration correction.
[0021] Furthermore, the method for correcting spherical aberration of the electron beam imaging apparatus according to the present invention calculates the X-axis gradient score change curve and the Y-axis gradient score change curve of a plurality of precision focusing images based on the gradient, and determines whether the symmetry axis of the X-axis gradient score change curve coincides with the symmetry axis of the Y-axis gradient score change curve, and determines whether the target spherical aberration parameter meets the spherical aberration correction requirement, thereby optimizing the evaluation criteria, improving the judgment accuracy of whether it meets the spherical aberration correction requirement, and further improving the accuracy of spherical aberration correction.
[0022] Furthermore, the method for correcting spherical aberration of the electron beam imaging apparatus according to the present invention gradually adjusts the spherical aberration parameter according to the initial spherical aberration step size to obtain a plurality of spherical aberration comparison images, searches for the tuned spherical aberration parameter based on the variance of the plurality of spherical aberration comparison images, uses this as the iterative search basis, iteratively searches for the tuned spherical aberration parameter, reduces the spherical aberration step size in each iteration, stops the iteration until the spherical aberration step size becomes smaller than the preset search stop accuracy, and finally uses the tuned spherical aberration parameter obtained by the iterative search as the target spherical aberration parameter of the spherical aberration corrector, thereby realizing the search for the target spherical aberration parameter in the inverse pyramid search method. Therefore, the method for correcting spherical aberration of the electron beam imaging apparatus according to the present invention searches for the target spherical aberration parameter in the inverse pyramid search method, thereby improving the search speed of the target spherical aberration parameter of the spherical aberration corrector, reducing the time complexity and space complexity of the search, improving the efficiency of spherical aberration correction, and ensuring the stability of the spherical aberration correction process.
[0023] Hereinafter, by referring to the drawings and describing the specific embodiments of the present invention in detail, those skilled in the art will understand the above and other objects, advantages and features of the present invention more clearly.
Brief Description of the Drawings
[0024] Hereinafter, with reference to the drawings, several specific embodiments of the present invention will be described in detail in an exemplary and non-limiting manner. In the drawings, the same reference numerals indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the drawings, [Figure 1] Figure 1 is a schematic diagram of one embodiment of astigmatism correction adjustment in the prior art. [Figure 2] Figure 2 is a schematic flowchart of an astigmatism correction method for an electron beam imaging apparatus according to one embodiment of the present invention. [Figure 3] Figure 3 is a schematic diagram of a precisely focused image in an astigmatism correction method for an electron beam imaging apparatus according to one embodiment of the present invention. [Figure 4] Figure 4 is a schematic diagram of the X-axis gradient score change curve and the Y-axis gradient score change curve of the precisely focused image shown in Figure 3. [Figure 5] Figure 5 is a schematic diagram of a precisely focused image in an astigmatism correction method for an electron beam imaging apparatus according to another embodiment of the present invention. [Figure 6] Figure 6 is a schematic diagram of the X-axis gradient score change curve and the Y-axis gradient score change curve of the precisely focused image shown in Figure 5. [Figure 7] Figure 7 is a schematic flowchart of an astigmatism correction method for an electron beam imaging apparatus according to another embodiment of the present invention. [Figure 8] Figure 8 is a schematic diagram of a computer program product according to one embodiment of the present invention. [Figure 9] Figure 9 is a schematic diagram of a computer device according to one embodiment of the present invention. [Modes for carrying out the invention]
[0025] Hereinafter, exemplary embodiments of the present invention will be described in more detail with reference to the drawings. Although exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be realized in various forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present invention to those skilled in the art.
[0026] Figure 1 is a schematic diagram of an embodiment of aberration correction adjustment in the prior art. In the existing quality evaluation method, the process of performing aberration correction adjustment on a SEM image includes: step 1 of selecting an isotropic sample position; step 2 of reading and recording the current value of the current objective lens (OL) and the numerical values of the aberration parameters; step 3 of collecting a SEM image I1 at the current OL current, calculating a SEM image spectrogram and a self-adaptive threshold binary image, and calculating the binary image area S1 and the major and minor axes a1 and b1 of the fitted ellipse; step 4 of adjusting the OL current value to collect a SEM image I2, calculating a SEM image spectrogram and a self-adaptive threshold binary image, and calculating the binary image area S2 and the major and minor axes a2 and b2 of the fitted ellipse; step 5 of determining whether it is necessary to adjust the focus and aberration based on the areas S1 and S2 and the roundness a1 / b1, a2 / b2, entering step 7 when S1 and S2 > Smin, and entering step 6 otherwise; step 6 of when the roundness > threshold, there is no need to adjust the aberration parameters, when the roundness < threshold, it is necessary to adjust the aberration parameters, and entering step 8; step 7 of changing the OL current value at a specific step size to collect N images, performing a sharpness evaluation on the images, calculating the optimal focus plane based on the sharpness curve of the images, completing the automatic focus, and entering step 8; step 8 of searching for the aberration value at the position of the minimum roundness a1 / b1 - a2 / b2 by changing the aberration value, taking this as the optimal aberration, and completing the automatic aberration correction, which may be included.
[0027] Hereinafter, the process steps of the aberration correction adjustment scheme in the prior art will be described with reference to Figure 1.
[0028] Step S1 Select a sample location where the image features are isotropic. Step S2 Read and record the initial parameters OL0, stigmationX0, and stigmationY0, where stigmationX0 refers to the initial X-direction astigmatism and stigmationY0 refers to the initial Y-direction astigmatism. Step S3: Acquire an SEM image I1 at the OL0 current, calculate the SEM image spectrogram and the self-adaptive thresholded binarized image, calculate the area S1 of the binarized image and the major and minor axes a1 and b1 of the fitted ellipse. Step S4 Adjust the OL current value to acquire the SEM image I2, and calculate the SEM image spectrogram and the self-adaptive thresholded binarized image, and calculate the area S2 of the binarized image and the major and minor axes a2 and b2 of the fitted ellipse. Step S5: Determine whether S1 and S2 are greater than Smin. If YES, proceed to Step S6; otherwise, proceed to Step S7. Step S6 determines whether a1 / b1 and a2 / b2 are greater than the threshold. If YES, proceed to step S9; otherwise, proceed to step S8. Step S7: The OL current value is varied in a specific step size to collect N images, the image clarity is evaluated, the optimal OL current value is calculated based on the image clarity curve, autofocus is completed, and the process proceeds to Step S8. Step S8: By changing the astigmatism value, the system searches for the astigmatism value where the minimum roundness a1 / b1-a2 / b2 is located, sets this as the optimal astigmatism, and completes the automatic astigmatism correction. This concludes the process. Step S9: Skip the focus and astigmatism adjustment step. This completes this process.
[0029] Using the above method presents several problems: limitations in sample selection, higher operator experience requirements, a need for operators to thoroughly understand image features, low versatility in application scenarios, and higher labor costs. Furthermore, the above solution relies on the circularity and area features of the spectral binary image to determine whether the device requires astigmatism correction, resulting in high requirements for SEM image quality and accuracy of spectral image binarization results. The algorithm also suffers from lower noise tolerance, lower redundant search capability due to anomaly detection, lower algorithm operating efficiency, and lower accuracy of astigmatism correction results.
[0030] To solve the above problems, an embodiment of the present invention provides an astigmatism correction method for an electron beam imaging apparatus. Figure 2 is a schematic flowchart of an astigmatism correction method for an electron beam imaging apparatus according to one embodiment of the present invention. As shown in Figure 2, the astigmatism correction method for an electron beam imaging apparatus according to this embodiment may generally include the following steps. Step S202: Search for the target astigmatism parameter of the astigmatism corrector in the electron beam imaging system. Step S204: The preset objective lens current is gradually adjusted according to the set step size, and multiple precision focus images corresponding to different objective lens currents are collected. Step S206: Calculate the gradient in different coordinate axis directions of multiple precisely focused images. Step S208: Based on the consistency of the gradient, determine whether the target astigmatism parameter meets the astigmatism correction requirement. If it does, perform step S210. Step S210: Determine the target objective lens current of the electron beam imaging device based on the gradient.
[0031] In this embodiment, the astigmatism parameters required for the astigmatism corrector may include X-direction astigmatism (which may be denoted as StigmationX) and Y-direction astigmatism (which may be denoted as StigmationY). Thus, the target astigmatism parameters of the astigmatism corrector include target X-direction astigmatism (which may be denoted as BestStigX) and target Y-direction astigmatism (which may be denoted as BestStigY). Correspondingly, the gradients in different coordinate axis directions of the precisely focused image may include the X-axis gradient and Y-axis gradient of the precisely focused image.
[0032] Furthermore, the objective lens (OL) is the final focusing lens in a scanning electron microscope (SEM), and its role is to focus the electron beam of the electron beam imaging device into an extremely small point, thereby forming a high-resolution image on the sample. By adjusting the objective lens current (which may also be referred to as the OL current), the magnetic field strength of the objective lens can be changed, thereby altering the focusing state of the electron beam and further affecting the magnification of the SEM image. Alternatively, the preset objective lens current (which may also be referred to as OL_opt) may be an objective lens current value obtained by searching during the preliminary coarse focusing step, which can provide a basic improvement in imaging quality.
[0033] The astigmatism correction method for an electron beam imaging apparatus according to the present invention involves searching for the target astigmatism parameter of the astigmatism corrector in the electron beam imaging apparatus, gradually adjusting the preset objective lens current according to a set step size, collecting multiple precisely focused images corresponding to different objective lens currents, calculating the gradients in different coordinate axis directions of the multiple precisely focused images, and determining whether the target astigmatism parameter meets the astigmatism correction requirements based on the consistency of the gradients, thereby realizing the evaluation of the astigmatism correction effect. Accordingly, the astigmatism correction method of the present invention can effectively improve the accuracy of the astigmatism correction results, improve the precision of astigmatism correction, and thereby improve the measurement accuracy of the electron beam imaging apparatus.
[0034] Furthermore, the astigmatism correction method for an electron beam imaging apparatus according to the present invention, when it is confirmed that the target astigmatism parameter meets the astigmatism correction requirements, determines the target objective lens current of the electron beam imaging apparatus based on the gradient, thereby readjusting the objective lens current of the electron beam imaging apparatus, improving the accuracy of the objective lens current adjustment, and thereby further improving the accuracy of astigmatism correction.
[0035] In some embodiments, after step S210, the astigmatism correction method for an electron beam imaging apparatus according to the present invention may further include a step of outputting a prompt indicating that astigmatism correction has failed if the astigmatism correction requirements are not met. That is, if the target astigmatism parameter does not meet the astigmatism correction requirements, a prompt indicating that astigmatism correction has failed is output, and the process is terminated.
[0036] As a result, the astigmatism correction method of the present invention can effectively avoid the application of erroneous results, avoid the problem of lower accuracy and inability to ensure normal measurement of the instrument caused by erroneous astigmatism correction results, and thereby further improve the accuracy of astigmatism correction, thereby improving the measurement accuracy of the electron beam imaging instrument.
[0037] In some embodiments, before step S202 above, the astigmatism correction method for an electron beam imaging apparatus according to the present invention may further include the steps of searching for a preset objective lens current of the electron beam imaging apparatus and setting the objective lens of the electron beam imaging apparatus to the preset objective lens current. That is, the astigmatism correction method of the present invention first searches for a preset objective lens current of the electron beam imaging apparatus, then sets the retrieved preset objective lens current to the objective lens current of the electron beam imaging apparatus, and searches for the target astigmatism parameter of the astigmatism corrector in the electron beam imaging apparatus based on this.
[0038] Furthermore, the above step of searching for the preset objective lens current of the electron beam imaging apparatus may include gradually adjusting the initial objective lens current according to the preset current step size, collecting multiple coarse-focused images corresponding to different objective lens currents, calculating the sharpness of the multiple coarse-focused images, searching for an objective lens current tuned based on the sharpness of the multiple coarse-focused images, and setting the searched and obtained tuned objective lens current as the preset objective lens current. It should be noted that the sharpness of the multiple coarse-focused images may include the sharpness curve gradient of the multiple coarse-focused images. In addition, the searched and obtained preset objective lens current is used in the subsequent process of searching for the target astigmatism parameter of the astigmatism corrector in the electron beam imaging apparatus. In other words, the astigmatism correction method for an electron beam imaging apparatus according to the present invention can roughly determine the position of the image focal plane by roughly adjusting the objective lens current (OL current).
[0039] In one specific embodiment, the step of searching for the preset objective lens current of the electron beam imaging apparatus may be performed as a step of constantly adjusting the OL current value and acquiring multiple images, a step of dynamically adjusting the search step size based on the sharpness curve gradient of the multiple coarse-focused images to quickly search to a sharper focal plane position and thereby achieve coarse focus, and a step of recording a more appropriate objective lens current OL_opt as the searched and acquired preset objective lens current. It should be noted that the relative sharpness may be determined by the step size value of the dynamic step size, and the larger the step size value, the lower the accuracy and the lower the relative sharpness. Therefore, by subsequently reducing the preset current step size to perform an accurate search within a narrow range, the relative sharpness of the coarse-focused image can be improved. In one selectable embodiment of the above embodiment, the stopping condition for quickly searching to a sharper focal plane position may be set such that the sharpness curve of the coarse-focused image exhibits a downwardly opening quadratic parabola. In another optional embodiment, the stop condition for quickly searching to a clearer focal plane position may be further set so that the number of searches exceeds a preset maximum number of searches.
[0040] As a result, the astigmatism correction method for electron beam imaging apparatus according to the present invention significantly improves imaging quality by performing initial focusing followed by astigmatism correction, ensuring basic image clarity and resolution, and improving the efficiency and accuracy of subsequent target astigmatism parameter search operations.
[0041] In some embodiments, step S202 may include gradually adjusting the astigmatism parameter according to the initial astigmatism step size to acquire multiple astigmatism comparison images; searching for a tuned astigmatism parameter based on the variance of the multiple astigmatism comparison images and using this as an iterative search base; iteratively searching for the tuned astigmatism parameter, reducing the astigmatism step size in each iteration, and stopping the iteration until the astigmatism step size becomes smaller than a preset search stop accuracy; and finally using the tuned astigmatism parameter obtained through the iterative search as the target astigmatism parameter of the astigmatism corrector. Thus, the astigmatism correction method for electron beam imaging apparatus according to the present invention realizes the searching of the target astigmatism parameter using an inverted pyramid search method. What needs to be explained is that the specific steps of the inverted pyramid search method may include, firstly, searching within a specific range with an initial step size to determine the optimal value B1; secondly, searching in the neighborhood of B1 with a reduced step size to determine the optimal value B2; and thirdly, repeating the process in the same manner until the step size satisfies the minimum set precision. The inverted pyramid search method can reduce search time.
[0042] As a result, the astigmatism correction method for electron beam imaging apparatus according to the present invention realizes the retrieval of the target astigmatism parameter using an inverted pyramid search method, thereby improving the retrieval speed of the target astigmatism parameter of the astigmatism corrector, reducing the temporal and spatial complexity of the search, improving the efficiency of astigmatism correction, and ensuring the stability of the astigmatism correction process.
[0043] In some embodiments, the variance of an astigmatism comparison image can reflect the degree of variance of the grayscale values of the astigmatism comparison image and may be used to evaluate the sharpness of the astigmatism comparison image. Specifically, a larger variance in an image indicates a larger grayscale difference in the image, i.e., a sharper image. Therefore, in one specific embodiment, the above step of searching for an astigmatism parameter tuned based on the variance of multiple astigmatism comparison images may include calculating the variance of each astigmatism comparison image and using this as the sharpness score of each astigmatism comparison image, comparing the magnitudes of the sharpness scores of multiple astigmatism comparison images, and using the astigmatism parameter value corresponding to the astigmatism comparison image with the highest sharpness score as the tuned astigmatism parameter. In another specific embodiment, the above step of searching for an astigmatism parameter tuned based on the variance of multiple astigmatism comparison images may be more specifically performed as a step of using the astigmatism parameter value corresponding to the astigmatism comparison image with the largest variance as the tuned astigmatism parameter.
[0044] As a result, the astigmatism correction method for electron beam imaging apparatus according to the present invention evaluates the clarity of the astigmatism comparison image by calculating the variance of the astigmatism comparison image, optimizes the image scoring criteria, and improves the accuracy of astigmatism correction.
[0045] In some embodiments, step S202 may include searching for BestStigX and BestStigY of the astigmatism correctors in the electron beam imaging apparatus using an inverted pyramid search method.
[0046] In one specific embodiment, the step of searching for BestStigX of an astigmatism corrector in an electron beam imaging device using an inverted pyramidal search method may be performed as follows: obtaining a preset search stop accuracy (which may be denoted as StigStopAccuracy) and search range (which may be denoted as StigRange); adjusting StigmationX within StigRange with a specific step size, and using the image variance as the image score, obtaining the optimal score in each layer search, searching the next layer again at the astigmatism position of the optimal score, and so on, repeating the process until the current step size in the pyramidal search becomes smaller than StigStopAccuracy, and recording the X-direction astigmatism value corresponding to the optimal score of the current layer as BestStigX.
[0047] Furthermore, the step of searching for BestStigY of the astigmatism corrector in an electron beam imaging device using an inverted pyramid search method may be performed as follows: acquiring a preset search stop accuracy (which may be referred to as StigStopAccuracy) and search range (which may be referred to as StigRange); adjusting StigmationY within StigRange with a specific step size, and using image dispersion as the image score, obtaining the optimal score in each layer search, performing the search for the next layer again at the astigmatism position of the optimal score, and repeating the process in the same manner until the current step size in the pyramid search becomes smaller than StigStopAccuracy, and recording the X-direction astigmatism value corresponding to the optimal score of the current layer as BestStigY.
[0048] As a result, the astigmatism correction method for the electron beam imaging apparatus according to the present invention searches for target X-direction astigmatism and target Y-direction astigmatism using an inverted pyramid search method, thereby improving the search speed of the target astigmatism parameter of the astigmatism corrector and ensuring the search accuracy of target X-direction astigmatism and target Y-direction astigmatism, and thereby further ensuring the stability of the astigmatism correction process.
[0049] In some embodiments, step S204 may be specifically performed as a step of gradually adjusting the OL current value around OL_opt according to a set step size, and collecting multiple high-precision focused images corresponding to different OL current values. It should be noted that the set step size may be a preset based on parameters such as the OL focal length of the electron beam imaging apparatus. In one specific embodiment, the set step size may be set such that the change in OL focal length after adjusting the OL current value by the set step size is 1 to 10 micrometers. This enables the astigmatism correction method for electron beam imaging apparatus according to the present invention to achieve fine adjustment of the OL focal length, thereby improving the accuracy and efficiency of image acquisition.
[0050] Figure 3 is a schematic diagram of a precisely focused image in an astigmatism correction method for an electron beam imaging apparatus according to one embodiment of the present invention, showing a single precisely focused image when the target astigmatism parameter meets the astigmatism correction requirements. Figure 4 is a schematic diagram of the X-axis gradient score change curve and Y-axis gradient score change curve of the precisely focused image shown in Figure 3, showing the shape and position of the axis of symmetry of the X-axis gradient score change curve and Y-axis gradient score change curve of the precisely focused image when the target astigmatism parameter meets the astigmatism correction requirements. Figure 5 is a schematic diagram of a precisely focused image in an astigmatism correction method for an electron beam imaging apparatus according to another embodiment of the present invention, showing a single precisely focused image when the target astigmatism parameter does not meet the astigmatism correction requirements. Figure 6 is a schematic diagram of the X-axis gradient score change curve and Y-axis gradient score change curve of the precisely focused image shown in Figure 5, illustrating the shape and position of the axis of symmetry of the X-axis gradient score change curve and Y-axis gradient score change curve of the precisely focused image when the target astigmatism parameter does not meet the astigmatism correction requirements.
[0051] As shown in Figures 3 to 6, in some embodiments, step S206 may include calculating the X-axis and Y-axis gradients of multiple precision-focused images. Furthermore, step S208 may include calculating X-axis gradient score change curves and Y-axis gradient score change curves of multiple precision-focused images based on the gradients, determining whether the axis of symmetry of the X-axis gradient score change curve coincides with the axis of symmetry of the Y-axis gradient score change curve, confirming that if they coincide, the target astigmatism parameter meets the astigmatism correction requirements, and confirming that if they do not coincide, the target astigmatism parameter does not meet the astigmatism correction requirements. Thus, the astigmatism correction method for electron beam imaging apparatus according to the present invention establishes a mechanism to ensure astigmatism correction, thereby avoiding correction failures due to abnormal conditions such as shaking or dropped image frames.
[0052] It should be explained that the astigmatism correction requirement may include the elimination or reduction of both X-direction astigmatism and Y-direction astigmatism within a specified range. If both X-direction astigmatism and Y-direction astigmatism are eliminated or reduced within a specified range, it should be confirmed that the target astigmatism parameter meets the astigmatism correction requirement.
[0053] Furthermore, the gradient score is an index that measures the rate at which an image changes in a particular direction. In the imaging system of an electron beam imaging device, the gradient score can reflect the sharpness and contrast of the image edges. If the gradient score in a particular direction of the image is relatively high, it is explained that the image edges in that direction are sharp and have high contrast; conversely, if the gradient score is high in that direction, it is explained that the image edges are blurred and have low contrast. Therefore, if both X-direction astigmatism and Y-direction astigmatism are eliminated or reduced to a predetermined range, the electron beam can be focused to a single point after passing through the imaging system, forming a sharp image. At this time, regardless of how the objective lens current (or working distance) changes, the gradient scores in the X-axis and Y-axis directions of the image should be maintained to be essentially the same.
[0054] Therefore, as shown in Figure 4, when the axis of symmetry of the X-axis gradient score change curve of the precisely focused image coincides with the axis of symmetry of the Y-axis gradient score change curve, it is explained that the gradient scores in the X-axis direction and the Y-axis direction of the precisely focused image are consistent at the optimal position at different WDs (Working Distances). This allows us to determine that both X-direction astigmatism and Y-direction astigmatism have been eliminated or reduced to a predetermined range, and furthermore, that the target astigmatism parameter meets the astigmatism correction requirements. In this case, as shown in Figure 3, when the target astigmatism parameter meets the astigmatism correction requirements, the precisely focused image is sharper.
[0055] Furthermore, as shown in Figure 6, if the axis of symmetry of the X-axis gradient score change curve of the precisely focused image does not coincide with the axis of symmetry of the Y-axis gradient score change curve, it is explained that the gradient scores in the X-axis direction and the Y-axis direction of the precisely focused image are inconsistent at the optimal position at different WDs (Working Distances). This allows us to determine that at least one of the X-direction astigmatism and Y-direction astigmatism has not been removed, and further confirms that the target astigmatism parameter does not meet the astigmatism correction requirements. In this case, as shown in Figure 5, if the target astigmatism parameter does not meet the astigmatism correction requirements, the precisely focused image is more blurred.
[0056] As a result, the astigmatism correction method for an electron beam imaging apparatus according to the present invention calculates X-axis gradient score change curves and Y-axis gradient score change curves of multiple precisely focused images based on the gradient, and determines whether the axis of symmetry of the X-axis gradient score change curve coincides with the axis of symmetry of the Y-axis gradient score change curve. By determining whether the target astigmatism parameter meets the astigmatism correction requirements, the evaluation criteria are optimized, the accuracy of determining whether the astigmatism correction requirements are met is improved, and thereby the accuracy of astigmatism correction is further improved.
[0057] In some embodiments, the above step of determining the target objective lens current of the electron beam imaging apparatus based on the gradient may include setting the objective lens current value corresponding to the axis of symmetry as the target objective lens current (which may be denoted as BestOL). That is, when the axis of symmetry of the X-axis gradient score change curve coincides with the axis of symmetry of the Y-axis gradient score change curve, i.e., when astigmatism correction is successful, the OL current value corresponding to the axis of symmetry is set as BestOL, thereby achieving precise focusing.
[0058] As a result, the astigmatism correction method for electron beam imaging apparatus according to the present invention achieves precise focusing by setting the objective lens current value corresponding to the axis of symmetry as the target objective lens current after successful astigmatism correction, thereby further improving imaging quality and the astigmatism correction effect.
[0059] Figure 7 is a schematic flowchart of an astigmatism correction method for an electron beam imaging apparatus according to another embodiment of the present invention. The process steps of this embodiment will be described in detail below with reference to Figure 7.
[0060] Step S702: Record the initial OL current value, StigmationX, and StigmationY.
[0061] Step S704 gradually adjusts the OL current value according to the preset current step size and collects multiple coarse-focused images corresponding to different OL currents.
[0062] Step S706: Calculate the sharpness of multiple coarsely focused images.
[0063] Step S708 searches for an OL current tuned based on the clarity of multiple coarsely focused images, and denotes the obtained tuned OL current as OL_opt. What should be explained is that through this step, a clearer focal plane position can be quickly found, thereby completing the coarse focusing process.
[0064] Step S710 sets the OL current value = OL_opt, and also sets StigStopAccuracy and StigRange.
[0065] Step S712 searches for the BestStigX and BestStigY astigmatism correctors based on the StigRange and inverted pyramid search strategies.
[0066] Step S714: Set StigmationX=BestStigX and StigmationY=BestStigY.
[0067] Step S716: The preset OL current is gradually adjusted according to the set step size, and multiple precision focus images corresponding to different OL currents are collected.
[0068] Step S718: Calculate the gradient in different coordinate axis directions of multiple precisely focused images.
[0069] Step S720: Calculate the X-axis gradient score change curve and the Y-axis gradient score change curve for multiple precisely focused images based on the gradient.
[0070] Step S722 determines whether the axis of symmetry of the X-axis gradient score change curve coincides with the axis of symmetry of the Y-axis gradient score change curve. If they coincide, step S724 is executed; otherwise, step S726 is executed.
[0071] Step S724: The OL current value corresponding to the axis of symmetry is set to BestOL. This completes the precision focusing process, and this process is finished.
[0072] Step S726 outputs a prompt indicating that astigmatism correction failed. This completes the evaluation process of the astigmatism correction effect, and the process ends.
[0073] What needs to be explained is that steps S702 to S726 above describe a single astigmatism correction process in the astigmatism correction method for an electron beam imaging apparatus according to the present invention. Subsequently, if an astigmatism correction command is received again, the current process can be restarted in response to the astigmatism correction command.
[0074] As a result, the astigmatism correction method for an electron beam imaging apparatus according to the present invention effectively avoids the application of erroneous results by adding an evaluation step of the astigmatism correction effect after searching for the target astigmatism parameter of the astigmatism corrector in the electron beam imaging apparatus, avoiding the problem of lower accuracy caused by erroneous astigmatism correction results that prevent normal measurement of the apparatus, thereby improving the accuracy of astigmatism correction and thus improving the measurement accuracy of the electron beam imaging apparatus. Furthermore, the astigmatism correction method for an electron beam imaging apparatus according to the present invention further improves the accuracy of astigmatism correction by determining the target objective lens current of the electron beam imaging apparatus based on the gradient after confirming that the target astigmatism parameter meets the astigmatism correction requirements, thereby readjusting the objective lens current of the electron beam imaging apparatus and improving the adjustment accuracy of the objective lens current.
[0075] Furthermore, the astigmatism correction method for an electron beam imaging apparatus according to the present invention calculates X-axis gradient score change curves and Y-axis gradient score change curves of multiple precisely focused images based on the gradient, and determines whether the axis of symmetry of the X-axis gradient score change curve coincides with the axis of symmetry of the Y-axis gradient score change curve. By determining whether the target astigmatism parameter meets the astigmatism correction requirements, the evaluation criteria are optimized, the accuracy of determining whether the astigmatism correction requirements are met is improved, and thereby the accuracy of astigmatism correction is further improved.
[0076] Furthermore, the astigmatism correction method for an electron beam imaging apparatus according to the present invention improves the search speed of the target astigmatism parameter of the astigmatism corrector by searching for the target astigmatism parameter using an inverted pyramid search method, reduces the temporal and spatial complexity of the search, improves the efficiency of astigmatism correction, and ensures the stability of the astigmatism correction process.
[0077] The present invention further provides computer program products and computer devices. Figure 8 is a schematic diagram of the structure of a computer program product 10 according to one embodiment of the present invention, and Figure 9 is a schematic diagram of the structure of a computer device 20 according to one embodiment of the present invention.
[0078] The computer program 11 is stored in the computer program product 10, and when the computer program 11 is executed by the processor, the astigmatism correction method described in any one of the above embodiments is realized.
[0079] The computer device 20 includes a memory 220, a processor 210, and a computer program 11 stored in the memory 220 and executed by the processor 210, and when the processor 210 executes the computer program 11, it realizes the astigmatism correction method described in any one of the above embodiments.
[0080] What needs to be explained is the logic and / or steps shown in the flowchart or otherwise described herein, which may be considered, for example, an ordered list of executable instructions for implementing a logical function, which may be implemented in any specific computer program product for use with, or in combination with, instruction execution systems, devices or equipment (e.g., computer-based systems, systems including processors, or other systems capable of reading instructions from instruction execution systems, devices or equipment and executing those instructions).
[0081] In this embodiment, the computer program product 10 may be any device capable of containing, storing, communicating, propagating, or transmitting a program for use by, or in combination with, an instruction execution system, device, or apparatus. More specific examples (not exhaustive) of the computer program product 10 include an electrical connection unit with one or more wires (electronic device), a portable computer disk cartridge (magnetic device), random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). The computer program product 10 may also be paper or other suitable medium on which the program can be printed, for example, by optically scanning the paper or other medium, then editing, interpreting, or processing it in any other suitable form to obtain the program electronically, and then storing it in computer memory.
[0082] It should be understood that each part of the present invention may be implemented by hardware, software, firmware, or a combination thereof. In the above embodiments, a plurality of steps or methods may be implemented by software or firmware stored in memory and executed by a suitable instruction execution system.
[0083] The computer device 20 may be, for example, a server, desktop computer, laptop computer, tablet computer, or smartphone. In some examples, the computer device 20 may be a cloud computing node. The computer device 20 may also be described in the general context of computer system executable instructions (e.g., program modules) executed by a computer system. Generally, a program module may include routines, programs, object programs, components, logic, data structures, etc., that perform a specific task or realize a specific abstract data type. The computer device 20 may be implemented in a distributed cloud computing environment where remote processing units connected via a communication network perform tasks. In a distributed cloud computing environment, program modules may reside on storage media of local or remote computing systems, including storage devices.
[0084] The computer device 20 may include a processor 210 suitable for executing stored instructions and a memory 220 that provides temporary storage space for the operation of the instructions during operation. The processor 210 may be a single-core processor, a multi-core processor, a computing cluster, or any number of other configurations. The memory 220 may include random-access memory (RAM), read-only memory, flash memory, or any other suitable storage system.
[0085] The flowchart relating to this embodiment is not intended to show that the operations of the method are performed in any particular order, or that all operations of the method are included in all situations. Furthermore, the method may include additional operations. Additional modifications can be made to the method described in this embodiment, within the scope of the technical concept relating to the method.
[0086] As will be understood by those skilled in the art, several exemplary embodiments of the present invention have been described in detail herein, but many other variations or modifications that conform to the principles of the present invention can still be directly determined or derived based on the content disclosed herein without departing from the spirit and scope of the invention. Accordingly, the scope of the present invention should be understood and recognized as encompassing all of these other variations or modifications.
Claims
1. A method for correcting astigmatism in an electron beam imaging apparatus, To search for the target astigmatism parameter of the astigmatism corrector in the electron beam imaging apparatus, The preset objective lens current is gradually adjusted according to the set step size, and multiple precisely focused images corresponding to different objective lens currents are collected. The process involves calculating the gradient in different coordinate axis directions of the aforementioned multiple precisely focused images, Based on the consistency of the gradient, it is determined whether the target astigmatism parameter meets the astigmatism correction requirements. A method for correcting astigmatism in an electron beam imaging apparatus, comprising determining the target objective lens current of the electron beam imaging apparatus based on the gradient if the requirements for astigmatism correction are met.
2. Based on the consistency of the gradient, the step of determining whether the target astigmatism parameter meets the astigmatism correction requirements is: Based on the aforementioned gradient, the X-axis gradient score change curve and the Y-axis gradient score change curve of the plurality of precisely focused images are calculated, To determine whether the axis of symmetry of the X-axis gradient score change curve coincides with the axis of symmetry of the Y-axis gradient score change curve, If they match, confirm that the target astigmatism parameter meets the astigmatism correction requirements, A method for correcting astigmatism in an electron beam imaging apparatus according to claim 1, comprising confirming, if they do not match, that the target astigmatism parameter does not meet the astigmatism correction requirements.
3. The step of determining the target objective lens current of the electron beam imaging apparatus based on the gradient is: A method for correcting astigmatism in an electron beam imaging apparatus according to claim 2, comprising setting the objective lens current value corresponding to the axis of symmetry as the target objective lens current.
4. The step of searching for the target astigmatism parameter of the astigmatism corrector in the electron beam imaging apparatus is: The process involves gradually adjusting the astigmatism parameters according to the initial astigmatism step size to acquire multiple astigmatism comparison images, and The system searches for astigmatism parameters tuned based on the variance of the aforementioned multiple astigmatism comparison images, and uses this as an iterative search base. The tuned astigmatism parameter is searched iteratively, and the astigmatism step size is reduced in each iteration until the astigmatism step size becomes smaller than a preset search stop accuracy, and the iteration is stopped. The astigmatism correction method for an electron beam imaging apparatus according to claim 1, further comprising setting the tuned astigmatism parameter obtained by the last iterative search as the target astigmatism parameter of the astigmatism corrector.
5. The step of searching for astigmatism parameters tuned based on the variance of the aforementioned multiple astigmatism comparison images is: The variance of each of the aforementioned astigmatism comparison images is calculated and this is used as the clarity score for each of the aforementioned astigmatism comparison images. A method for correcting astigmatism in an electron beam imaging apparatus according to claim 4, comprising: comparing the magnitude of the clarity scores of a plurality of astigmatism comparison images; and setting the astigmatism parameter value corresponding to the astigmatism comparison image with the highest clarity score as the tuned astigmatism parameter.
6. Before the step of searching for the target astigmatism parameter of the astigmatism corrector in the electron beam imaging apparatus, the astigmatism correction method is: To retrieve the preset objective lens current of the electron beam imaging apparatus, The astigmatism correction method for an electron beam imaging apparatus according to claim 1, further comprising setting the objective lens current of the electron beam imaging apparatus to the preset objective lens current.
7. The step of searching for the preset objective lens current of the electron beam imaging apparatus is: The initial objective lens current is gradually adjusted according to the preset current step size, and multiple coarse-focused images corresponding to different objective lens currents are acquired. The sharpness of the aforementioned multiple coarsely focused images is calculated, A method for correcting astigmatism in an electron beam imaging apparatus according to claim 6, comprising: searching for an objective lens current tuned based on the clarity of the plurality of coarsely focused images; and setting the tuned objective lens current obtained by the search as the preset objective lens current.
8. After determining whether the target astigmatism parameter meets the astigmatism correction requirements based on the consistency of the gradient, the astigmatism correction method: The astigmatism correction method for an electron beam imaging apparatus according to claim 1, further comprising outputting a prompt indicating that astigmatism correction failed if the astigmatism correction requirements are not met.
9. A computer program product, A computer program product that includes a computer program, which, when executed by a processor, realizes the steps in the astigmatism correction method for an electron beam imaging apparatus described in any one of claims 1 to 8.
10. A computer device, A computer device comprising memory, a processor, and a computer program stored in the memory and executed by the processor, wherein when the processor executes the computer program, it realizes the steps in the astigmatism correction method for an electron beam imaging apparatus according to any one of claims 1 to 8.