Method, product and apparatus for stigmation of an electron beam imaging device

Abstract

The present application relates to the field of semiconductor manufacturing and detection, in particular to a method, product and device for stigmation of an electron beam imaging device. The method comprises: searching for a target stigmation parameter of a stigmator in the electron beam imaging device; adjusting a pre-adjusted objective lens current step by step according to a set step size, and collecting multiple fine focus images corresponding to different objective lens currents; calculating gradients of the multiple fine focus images in different coordinate axis directions; judging whether the target stigmation parameter meets the stigmation requirement according to the consistency of the gradients; and if yes, determining a target objective lens current of the electron beam imaging device according to the gradients. The method for stigmation of the present application performs a judgment operation on the target stigmation parameter after determining the target stigmation parameter of the stigmator, thereby improving the accuracy of stigmation, avoiding the problem of low measurement accuracy caused by application of incorrect stigmation results, and improving the measurement accuracy of the electron beam imaging device.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing and detection, and in particular to an astigmatism elimination method, product and equipment for electron beam imaging equipment. Background Art

[0002] In integrated circuit manufacturing, charged particle beam imaging equipment controls the focusing state of charged particles, allowing them to interact with samples and capture particle signals such as secondary particles and transmitted particles for imaging. This allows characterization of the sample's morphology, structure, and composition. In the semiconductor field, charged particle beam imaging equipment includes equipment for detecting wafer surface defects and electron beam metrology equipment for measuring critical wafer dimensions.

[0003] A scanning electron microscope (SEM), a charged particle beam imaging device, is used for defect detection and critical dimension measurement in semiconductor manufacturing and other micro-nanofabrication fields. It scans the sample surface with a high-energy electron beam, collecting and analyzing signals such as secondary electrons and backscattered electrons generated by the interaction between the electrons and the sample, enabling precise measurement of the sample's surface topography and dimensions. As a high-precision imaging device, the SEM must maintain stable imaging quality. In actual measurements, the optimal hardware parameters of the SEM device drift over time, necessitating regular calibration of certain hardware parameters. Astigmatism calibration is a crucial calibration step, and automation is particularly important. Manual calibration consumes significant labor costs, necessitating automation of the stigmator process. Automatic stigmator calibration analyzes the astigmatism characteristics of the image and automatically adjusts the position and size of the stigmator to eliminate astigmatism. This automated processing not only improves imaging quality, but also reduces the burden on operators, lowers the requirements for operator experience, greatly reduces labor costs and time costs, and indirectly improves the measurement efficiency of SEM equipment.

[0004] In the prior art, one solution for adjusting the astigmatism of images obtained by a scanning electron microscope (SEM) (i.e., SEM images) is to select an isotropic sample position for astigmatism adjustment, calculate the spectrum information of the sample pattern, and use the roundness and area characteristics of the spectrum binary image to determine whether the current device needs to be calibrated for astigmatism. However, this solution has certain limitations in sample selection, requires relatively high operator experience, and requires the actual operator to have a relatively thorough understanding of the image characteristics. It also has problems such as poor diversity of application scenarios and high labor costs. In addition, this solution uses the roundness and area characteristics of the spectrum binary image to determine whether the device needs to be calibrated for astigmatism, and has high requirements for the imaging quality of the SEM image and the accuracy of the spectrum image binarization results. It has problems such as relatively poor algorithm noise resistance, low redundant search caused by abnormal judgment, low algorithm operation efficiency, and low accuracy of the astigmatism elimination results.

[0005] Another existing approach to adjusting SEM images for astigmatism is to adjust the electron microscope's imaging lens to a near-focus distance based on the image's defocus level. When the imaging lens is at the near-focus distance, the variance of the local variance and the mean of the local variance are used to compositely describe the sharpness of the in-focus image. This astigmatism value is then adjusted based on the sharpness of the in-focus image. However, this approach directly confirms the completion of the automatic astigmatism adjustment after the astigmatism value adjustment, inevitably leading to the application of erroneous results. This leads to problems such as low algorithm accuracy and inability to guarantee proper equipment measurement. Summary of the Invention

[0006] In view of the above problems, the present invention proposes an astigmatism elimination method, product and device for an electron beam imaging device that overcomes the above problems or at least partially solves the above problems.

[0007] An object of the present invention is to provide a method for eliminating astigmatism in an electron beam imaging device to ensure the accuracy of eliminating astigmatism.

[0008] A further object of the present invention is to improve the accuracy of determining whether the astigmatism elimination requirement is met, so as to further improve the accuracy of astigmatism elimination.

[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 eliminating astigmatism of an electron beam imaging device, comprising:

[0011] Searching for target astigmatism parameters of an stigmator in an electron beam imaging device;

[0012] The preset objective lens current is gradually adjusted according to the set step size, and multiple fine focus images corresponding to different objective lens currents are collected;

[0013] Calculate the gradients of multiple fine-focus images in different coordinate axis directions;

[0014] Judging whether the target astigmatism parameters meet the requirements of eliminating astigmatism based on the consistency of the gradient;

[0015] If so, a target objective lens current of the electron beam imaging device is determined according to the gradient.

[0016] Optionally, the step of judging whether the target astigmatism parameter meets the astigmatism elimination requirement according to the consistency of the gradient includes:

[0017] Calculate the X-axis gradient score change curve and the Y-axis gradient score change curve of the multiple fine focus images according to the gradient;

[0018] Determine whether the symmetry axis of the X-axis gradient score change curve is consistent with the symmetry axis of the Y-axis gradient score change curve;

[0019] If they are consistent, it is confirmed that the target astigmatism parameters meet the astigmatism elimination requirements;

[0020] If they are inconsistent, it is confirmed that the target astigmatism parameters do not meet the astigmatism elimination requirements.

[0021] Optionally, the step of determining a target objective lens current of the electron beam imaging device according to the gradient includes:

[0022] The objective lens current value corresponding to the symmetry axis is used as the target objective lens current.

[0023] Optionally, the step of searching for a target astigmatism parameter of an stigmator in an electron beam imaging device includes:

[0024] The astigmatism parameters are gradually adjusted according to the initial image step length to obtain multiple astigmatism comparison images;

[0025] The astigmatism parameters are tuned based on the variance of multiple astigmatism comparison images as the basis for iterative search;

[0026] Iteratively search and tune the astigmatism parameters, and in each iteration, reduce the image step length until the image step length is less than the preset search stop accuracy and the iteration is stopped;

[0027] The tuned astigmatism parameters obtained from the last iterative search are used as the target astigmatism parameters of the astigmatism canceller.

[0028] Optionally, the step of searching and tuning the astigmatism parameter according to the variance of the plurality of astigmatism comparison images includes:

[0029] Calculate the variance of each astigmatism comparison image as the clarity score of each astigmatism comparison image;

[0030] The clarity scores of the multiple astigmatism comparison images are compared, and the astigmatism parameter value corresponding to the astigmatism comparison image with the highest clarity score is used as the tuning astigmatism parameter.

[0031] Optionally, before the step of searching for a target astigmatism parameter of an stigmator in the electron beam imaging device, the stigmator method further comprises:

[0032] Search for preset objective lens currents in electron beam imaging equipment;

[0033] The objective lens current of the electron beam imaging device is set to the preset objective lens current.

[0034] Optionally, the step of searching for a preset objective lens current of the electron beam imaging device includes:

[0035] The initial objective lens current is gradually adjusted according to the preset current step size, and multiple coarse focus images corresponding to different objective lens currents are collected;

[0036] Calculate the clarity of multiple coarse focus images;

[0037] The objective lens current is searched and tuned according to the clarity of a plurality of coarse focus images, and the searched tuned objective lens current is used as the pre-adjusted objective lens current.

[0038] Optionally, after the step of determining whether the target astigmatism parameter meets the astigmatism elimination requirement based on the gradient consistency, the astigmatism elimination method further includes:

[0039] If the astigmatism correction requirement is not met, an astigmatism calibration failure prompt will be output.

[0040] According to another aspect of the present invention, a computer program product is provided, comprising a computer program, which implements the steps of any one of the above-mentioned methods for eliminating astigmatism in an electron beam imaging device when executed by a processor.

[0041] According to another aspect of the present invention, a computer device is provided, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, and when the processor executes the computer program, the steps of any of the above-mentioned methods for eliminating astigmatism of an electron beam imaging device are implemented.

[0042] The stigmation elimination method for an electron beam imaging device of the present invention, after searching for the target stigmation parameter of the stigmator in the electron beam imaging device, gradually adjusts the pre-adjusted objective lens current according to a set step size, collects multiple fine focus images corresponding to different objective lens currents, calculates the gradients of the multiple fine focus images in different coordinate axis directions, and judges whether the target stigmation parameter meets the stigmation elimination requirements based on the consistency of the gradients, thereby achieving an evaluation of the stigmation elimination effect. Therefore, the stigmation elimination method of the present invention can effectively avoid the application of erroneous results, avoid the problem of low accuracy and inability to ensure normal measurement of the device due to erroneous stigmation results, improve the accuracy of stigmation elimination, and thus improve the measurement accuracy of the electron beam imaging device. In addition, the stigmation elimination method of the electron beam imaging device of the present invention determines the target objective lens current of the electron beam imaging device based on the gradient after confirming that the target stigmation parameter meets the stigmation elimination requirements. This achieves the re-adjustment of the objective lens current of the electron beam imaging device, improves the precision of the objective lens current adjustment, and further improves the accuracy of stigmation elimination.

[0043] Furthermore, the method for eliminating astigmatism of the electron beam imaging device of the present invention calculates the X-axis gradient score change curve and the Y-axis gradient score change curve of multiple fine focus images based on the gradient, and determines whether the symmetry axis of the X-axis gradient score change curve is consistent with the symmetry axis of the Y-axis gradient score change curve to determine whether the target astigmatism parameter meets the astigmatism elimination requirement. This optimizes the evaluation criteria and improves the accuracy of judging whether the astigmatism elimination requirement is met, thereby further improving the accuracy of astigmatism elimination.

[0044] Furthermore, the present invention provides a method for eliminating astigmatism for an electron beam imaging device by gradually adjusting the astigmatism parameter according to an initial image step length to obtain multiple astigmatism comparison images. The astigmatism parameter is then searched and tuned based on the variance of the multiple astigmatism comparison images and used as the basis for an iterative search. The astigmatism parameter is iteratively searched and tuned, and the image step length is reduced at each iteration until the image step length is less than a preset search stop accuracy. The tuned astigmatism parameter obtained from the last iterative search is used as the target astigmatism parameter of the astigmatism eliminator, thereby implementing an inverted pyramid search method for searching the target astigmatism parameter. Therefore, the present invention provides a method for eliminating astigmatism for an electron beam imaging device by searching the target astigmatism parameter using an inverted pyramid search method, thereby accelerating the search speed for the target astigmatism parameter of the astigmatism eliminator, reducing the time and space complexity of the search, improving the efficiency of the astigmatism elimination, and ensuring the stability of the astigmatism elimination process.

[0045] Based on the following detailed description of specific embodiments of the present invention in conjunction with the accompanying drawings, those skilled in the art will become more aware of the above and other objects, advantages and features of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Hereinafter, some specific embodiments of the present invention will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings 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 accompanying drawings:

[0047] Figure 1 is a schematic diagram of an embodiment of an anti-stigmation adjustment in the prior art;

[0048] Figure 2 is a schematic flow chart of a method for eliminating astigmatism in an electron beam imaging device according to an embodiment of the present invention;

[0049] Figure 3 is a schematic diagram of a finely focused image in a method for eliminating astigmatism in an electron beam imaging device according to an embodiment of the present invention;

[0050] Figure 4 yes Figure 3 Schematic diagram of the X-axis gradient score change curve and the Y-axis gradient score change curve of the fine focus image shown;

[0051] Figure 5 is a schematic diagram of a finely focused image in a method for eliminating astigmatism in an electron beam imaging device according to another embodiment of the present invention;

[0052] Figure 6 yes Figure 5 Schematic diagram of the X-axis gradient score change curve and the Y-axis gradient score change curve of the fine focus image shown;

[0053] Figure 7 is a flow chart of a method for eliminating astigmatism in an electron beam imaging device according to another embodiment of the present invention;

[0054] Figure 8 is a schematic diagram of a computer program product according to one embodiment of the present invention; and

[0055] Figure 9 is a schematic diagram of a computer device according to one embodiment of the present invention. DETAILED DESCRIPTION

[0056] Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided 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.

[0057] Figure 1It is a schematic diagram of an embodiment of astigmatism adjustment in the prior art. In the existing quality evaluation method, the process of astigmatism adjustment for SEM images may include the following steps: Step 1: Select a sample position with isotropy; Step 2: Read and record the current objective lens (OL) current value and the numerical value of the astigmatism parameter; Step 3: Acquire SEM image I1 at the current OL current, calculate the SEM image spectrogram and the adaptive threshold binary image, calculate the area S1 of the binary image and the long and short axes a1 and b1 of the fitted ellipse; Step 4: Adjust the OL current value and acquire SEM image I2, calculate the SEM image spectrogram and the adaptive threshold binary image, calculate the area S2 of the binary image and the long and short axes a2 and b2 of the fitted ellipse; Step 5: Determine whether to adjust focus and astigmatism based on the areas S1 and S2 and the roundness a1 / b1, a2 / b2. When S1 and S2 > Smin, go to Step 7; otherwise, go to Step 6; Step 6: When the roundness > threshold, there is no need to adjust the astigmatism parameter; when the roundness < threshold, the astigmatism parameter needs to be adjusted, and go to Step 8; Step 7: Change the OL current value in a certain step and acquire N images, evaluate the clarity of the images, calculate the best focal plane according to the clarity curve of the images, complete autofocus, and go to Step 8;

[0058] Step 8: Search for the astigmatism value corresponding to the minimum roundness a1 / b1 - a2 / b2 by varying the astigmatism value, which is the optimal astigmatism, and complete automatic astigmatism correction.

[0059] The following will describe Figure 1 the process steps of an astigmatism adjustment scheme in the prior art.

[0060] Step S1: Select a sample position where the image features are isotropic;

[0061] Step S2: Read and record the initial parameters OL0, stigmationX0, and stigmationY0; where stigmationX0 refers to the initial X-axis astigmatism and stigmationY0 refers to the initial Y-axis astigmatism;

[0062] Step S3: Acquire SEM image I1 at the OL0 current, calculate the SEM image spectrogram and the adaptive threshold binary image, calculate the area S1 of the binary image and the long and short axes a1 and b1 of the fitted ellipse;

[0063] Step S4: Adjust the OL current value and acquire SEM image I2, calculate the SEM image spectrogram and the adaptive threshold binary image, calculate the area S2 of the binary image and the long and short axes a2 and b2 of the fitted ellipse;

[0064] Step S5: Determine whether S1 and S2 are greater than Smin. If so, proceed to step S6; if not, proceed to step S7.

[0065] Step S6: Determine whether a1 / b1 and a2 / b2 are greater than a threshold. If so, proceed to step S9; if not, proceed to step S8.

[0066] Step S7: Change the OL current value in a certain step size and collect N images, evaluate the image clarity, and determine the optimal OL current value based on the image clarity curve. Automatic focusing is completed and the process proceeds to step S8;

[0067] Step S8: By changing the astigmatism value, the astigmatism value with the minimum roundness a1 / b1-a2 / b2 is searched, which is the optimal astigmatism, and the automatic astigmatism elimination is completed. This process ends here.

[0068] Step S9: Skip the step of adjusting focus and astigmatism. This completes the process.

[0069] The above method has certain limitations in terms of sample selection and requires relatively high operator experience, requiring a thorough understanding of image features. This leads to limited application diversity and high labor costs. Furthermore, the above solution, which uses the circularity and area characteristics of spectral binary images to determine whether the device requires astigmatism calibration, places high demands on the SEM image quality and the accuracy of the spectral image binarization results. This leads to relatively poor algorithm noise immunity, low redundant search capabilities due to abnormal judgments, low algorithm efficiency, and low accuracy of astigmatism elimination results.

[0070] To solve the above problem, an embodiment of the present invention provides a method for eliminating astigmatism in an electron beam imaging device. Figure 2 FIG. 4 is a flow chart of a method for eliminating astigmatism in an electron beam imaging device according to an embodiment of the present invention.

[0071] like Figure 2 As shown, the method for eliminating astigmatism of the electron beam imaging device of this embodiment may generally include:

[0072] Step S202 : searching for target astigmatism parameters of an stigmator in an electron beam imaging device.

[0073] Step S204 : gradually adjusting the preset objective lens current according to the set step size, and collecting a plurality of fine focus images corresponding to different objective lens currents.

[0074] Step S206 , calculating the gradients of the multiple fine-focus images in different coordinate axis directions.

[0075] Step S208 , judging whether the target astigmatism parameter meets the astigmatism elimination requirement according to the consistency of the gradient, and if so, executing step S210 .

[0076] Step S210 , determining a target objective lens current of the electron beam imaging device according to the gradient.

[0077] In this embodiment, the astigmatism parameters that need to be adjusted in the stigmator may include X-direction astigmatism (denoted as StigmationX) and Y-direction astigmatism (denoted as StigmationY). Therefore, the target astigmatism parameters of the stigmator include target X-direction astigmatism (denoted as BestStigX) and target Y-direction astigmatism (denoted as BestStigY). Accordingly, the gradients of the fine focus image along different coordinate axes may include the X-axis gradient and the Y-axis gradient of the fine focus image.

[0078] The objective lens (OL) is the final focusing lens in the SEM, responsible for focusing the electron beam from the electron beam imaging device to a very small point, thereby forming a high-resolution image on the sample. Adjusting the objective lens current (also known as the OL current) can change the magnetic field strength of the objective lens, thereby changing the focusing state of the electron beam and, in turn, affecting the magnification of the SEM image. Furthermore, the preset objective lens current (also known as OL_opt) can be the objective lens current value found in the previous coarse focusing step to initially improve image quality.

[0079] The stigmation elimination method for an electron beam imaging device of the present invention, after searching for the target astigmatism parameter of the stigmator in the electron beam imaging device, gradually adjusts the pre-adjusted objective lens current according to a set step size, collects multiple fine-focus images corresponding to different objective lens currents, calculates the gradients of the multiple fine-focus images in different coordinate axis directions, and determines whether the target astigmatism parameter meets the stigmation elimination requirements based on the consistency of the gradients, thereby achieving an assessment of the stigmation elimination effect. Therefore, the stigmation elimination method of the present invention can effectively improve the correctness of the stigmation elimination results and the accuracy of the stigmation elimination, thereby improving the measurement accuracy of the electron beam imaging device.

[0080] In addition, the method for eliminating astigmatism of the electron beam imaging device of the present invention determines the target objective lens current of the electron beam imaging device according to the gradient after confirming that the target astigmatism parameters meet the astigmatism elimination requirements, thereby achieving a readjustment of the objective lens current of the electron beam imaging device, improving the fineness of the objective lens current adjustment, and further improving the accuracy of astigmatism elimination.

[0081] In some embodiments, after step S210, the method for eliminating astigmatism in an electron beam imaging device of the present invention may further include the following step: if the astigmatism elimination requirements are not met, outputting an astigmatism calibration failure notification. In other words, if the target astigmatism parameters do not meet the astigmatism elimination requirements, an astigmatism calibration failure notification is output, and the process ends.

[0082] Therefore, the stigmation elimination method of the present invention can effectively avoid the application of erroneous results, avoid the problem of low accuracy and inability to ensure normal measurement of the equipment due to erroneous stigmation results, thereby further improving the accuracy of stigmation elimination and thus improving the measurement accuracy of the electron beam imaging equipment.

[0083] In some embodiments, before step S202, the stigmation correction method for an electron beam imaging device of the present invention may further include the following steps: searching for a preset objective lens current for the electron beam imaging device; and setting the objective lens current of the electron beam imaging device to the preset objective lens current. In other words, the stigmation correction method of the present invention first searches for the preset objective lens current for the electron beam imaging device, then uses the searched preset objective lens current as the objective lens current for the electron beam imaging device, and based on this, searches for a target astigmatism parameter of the stigmator in the electron beam imaging device.

[0084] Furthermore, the above-mentioned step of searching for the pre-adjusted objective lens current of the electron beam imaging device may include the following steps: gradually adjusting the initial objective lens current according to the pre-adjusted current step size, and collecting multiple coarse focus images corresponding to different objective lens currents; calculating the clarity of the multiple coarse focus images; searching for the tuned objective lens current according to the clarity of the multiple coarse focus images, and using the tuned objective lens current obtained by the search as the pre-adjusted objective lens current. It should be noted that the clarity of the multiple coarse focus images may include the clarity curve gradient of the multiple coarse focus images. In addition, the pre-adjusted objective lens current obtained by the search is used in the subsequent process of searching for the target astigmatism parameter of the stigmator in the electron beam imaging device. That is to say, the stigmation method of the electron beam imaging device of the present invention can roughly determine the position of the image focal plane by roughly adjusting the objective lens current (OL current).

[0085] In one specific embodiment, the above-mentioned step of searching for the pre-adjusted objective lens current of the electron beam imaging device can be specifically performed as follows: continuously adjusting the OL current value and capturing multiple images; dynamically adjusting the search step size based on the clarity curve gradient of the multiple coarse focus images to quickly search for a relatively clear focal plane position to achieve coarse focus; and recording the optimal objective lens current OL_opt as the pre-adjusted objective lens current obtained by the search. It should be noted that the relative clarity can be determined based on the step size value of the dynamic step size. The larger the step size value, the lower the accuracy and the lower the relative clarity. Therefore, if the pre-adjusted current step size is subsequently reduced to perform a precise search within a small range, the relative clarity of the coarse focus image can be improved. In an optional implementation of the above embodiment, the stopping condition for the rapid search to a relatively clear focal plane position can be set to when the clarity curve of the coarse focus image presents a quadratic parabola opening downward. In another optional implementation, the stopping condition for the rapid search to a relatively clear focal plane position can also be set to when the number of searches exceeds a preset maximum number of searches.

[0086] Therefore, the method for eliminating astigmatism of the electron beam imaging device of the present invention significantly improves the imaging quality by first performing preliminary focusing and then performing astigmatism calibration, ensures the basic clarity and resolution of the image, and improves the efficiency and accuracy of subsequent operations of searching for target astigmatism parameters.

[0087] In some embodiments, step S202 may include the following steps: gradually adjusting the astigmatism parameter according to the initial image step length to obtain multiple astigmatism comparison images; searching and tuning the astigmatism parameter based on the variance of the multiple astigmatism comparison images as a basis for iterative search; iteratively searching and tuning the astigmatism parameter, and reducing the image step length at each iteration until the iteration stops when the image step length is less than a preset search stop accuracy; and using the tuned astigmatism parameter obtained from the last iterative search as the target astigmatism parameter of the stigmatizer. Thus, the astigmatism elimination method for an electron beam imaging device of the present invention implements the use of an inverted pyramid search method to search for the target astigmatism parameter. It should be noted that the specific steps of the inverted pyramid search method may include: 1. searching within a certain range of initial step lengths to determine the optimal value B1; 2. searching near B1 by reducing the step length to determine the optimal value B2; 3. and so on until the step length meets the minimum set accuracy. The inverted pyramid search method can speed up the search time.

[0088] Therefore, the aberration elimination method of the electron beam imaging device of the present invention realizes the search for the target aberration parameter by using the inverted pyramid search method, thereby improving the search speed of the target aberration parameter of the aberration eliminater, reducing the time complexity and space complexity of the search, improving the efficiency of aberration elimination, and ensuring the stability of the aberration elimination process.

[0089] In some embodiments, the variance of the astigmatism comparison image can reflect the degree of discreteness of the grayscale values ​​of the astigmatism comparison image and can be used to evaluate the clarity of the astigmatism comparison image. Specifically, the larger the variance of the image, the greater the grayscale difference in the image, that is, the clearer the image. Therefore, in a specific embodiment, the step of searching and tuning the astigmatism parameter based on the variance of multiple astigmatism comparison images can include the following steps: calculating the variance of each astigmatism comparison image as the clarity score of each astigmatism comparison image; comparing the clarity scores of multiple astigmatism comparison images, and using the astigmatism parameter value corresponding to the astigmatism comparison image with the highest clarity score as the tuning astigmatism parameter. In another specific embodiment, the step of searching and tuning the astigmatism parameter based on the variance of multiple astigmatism comparison images can also be specifically performed as follows: using the astigmatism parameter value corresponding to the astigmatism comparison image with the largest variance as the tuning astigmatism parameter.

[0090] Therefore, the astigmatism elimination method of the electron beam imaging device of the present invention evaluates the clarity of the astigmatism comparison image by calculating the variance of the astigmatism comparison image, optimizes the image scoring standard, and improves the accuracy of astigmatism correction.

[0091] In some embodiments, the above step S202 may include searching BestStigX and BestStigY of the stigmator in the electron beam imaging device by using an inverted pyramid search method.

[0092] In a specific embodiment, the step of searching for the BestStigX of the stigmatism eliminater in the electron beam imaging device using an inverted pyramid search method can be specifically performed as follows: obtaining a preset search stop accuracy (which can be recorded as StigStopAcuuracy) and a search range (which can be recorded as StigRange); adjusting StigmationX with a certain step size within StigRange, and using the variance of the image as the image score. The best score can be obtained for each search layer, and the next layer is searched again at the best score astigmatism position, and so on, ..., until the current pyramid search step size is less than StigStopAcuuracy, then the iteration is stopped, and the X-direction astigmatism value corresponding to the best score of the current layer is recorded as BestStigX.

[0093] In addition, the step of searching for the BestStigY of the stigmator in the electron beam imaging device using the inverted pyramid search method can be specifically performed as follows: obtaining a preset search stop accuracy (which can be recorded as StigStopAcuuracy) and a search range (which can be recorded as StigRange); adjusting StigmationY with a certain step size within StigRange, and using the image variance as the image score. The best score can be obtained for each search layer, and the next layer is searched again with the best score astigmatism position, and so on, ..., until the current pyramid search step size is less than StigStopAcuuracy, the iteration is stopped, and the X-direction astigmatism value corresponding to the best score of the current layer is recorded as BestStigY.

[0094] Therefore, the stigmation elimination method of the electron beam imaging device of the present invention searches for the target X-direction astigmatism and the target Y-direction astigmatism respectively through an inverted pyramid search method, thereby improving the search speed of the target astigmatism parameters of the stigmator while ensuring the search accuracy of the target X-direction astigmatism and the target Y-direction astigmatism, thereby further ensuring the stability of the stigmation elimination process.

[0095] In some embodiments, step S204 can be specifically implemented as follows: With OL_opt as the center, the OL current value is gradually adjusted according to a set step size, and multiple fine-focus images corresponding to different OL current values ​​are acquired. It should be noted that the set step size can be pre-set based on parameters such as the OL focal length of the electron beam imaging device. In one specific embodiment, the set step size can be set so that the change in the OL focal length after adjusting the OL current value according to the set step size is 1 to 10 microns. Thus, the invented method for eliminating astigmatism in an electron beam imaging device can achieve fine adjustment of the OL focal length, thereby improving the accuracy and efficiency of image acquisition.

[0096] Figure 3 3 is a schematic diagram of a fine focus image in an astigmatism elimination method for an electron beam imaging device according to an embodiment of the present invention, which shows a fine focus image when target astigmatism parameters meet the astigmatism elimination requirements. Figure 4 yes Figure 3 The schematic diagram of the X-axis gradient score change curve and the Y-axis gradient score change curve of the fine focus image is shown, which shows the shape and position of the symmetry axis of the X-axis gradient score change curve and the Y-axis gradient score change curve of the fine focus image when the target astigmatism parameters meet the aberration elimination requirements. Figure 5 3 is a schematic diagram of a fine focus image in an stigmation elimination method for an electron beam imaging device according to another embodiment of the present invention, which shows a fine focus image when the target astigmatism parameter does not meet the stigmation elimination requirement. Figure 6 yes Figure 5The schematic diagram of the X-axis gradient score change curve and the Y-axis gradient score change curve of the fine focus image is shown, which shows the shape and position of the symmetry axis of the X-axis gradient score change curve and the Y-axis gradient score change curve of the fine focus image when the target astigmatism parameters do not meet the aberration elimination requirements.

[0097] like Figures 3 to 6 In some embodiments, step S206 may include the following steps: calculating the X-axis gradient and Y-axis gradient of the multiple fine-focus images. Furthermore, step S208 may include the following steps: calculating the X-axis gradient fraction change curve and the Y-axis gradient fraction change curve for the multiple fine-focus images based on the gradients; determining whether the axis of symmetry of the X-axis gradient fraction change curve is consistent with the axis of symmetry of the Y-axis gradient fraction change curve; if they are consistent, confirming that the target astigmatism parameters meet the astigmatism elimination requirements; if they are inconsistent, confirming that the target astigmatism parameters do not meet the astigmatism elimination requirements. Thus, the invented astigmatism elimination method for electron beam imaging equipment establishes a guarantee mechanism for astigmatism elimination calibration, thereby avoiding calibration failures caused by abnormal conditions such as jitter or image frame loss.

[0098] It should be noted that the astigmatism elimination requirement may include that both X-direction astigmatism and Y-direction astigmatism are successfully eliminated or reduced to within a preset range. If both X-direction astigmatism and Y-direction astigmatism are successfully eliminated or reduced to within a preset range, it is confirmed that the target astigmatism parameters meet the astigmatism elimination requirement.

[0099] In addition, the gradient score is an indicator that measures how quickly an image changes in a certain direction. In the imaging system of an electron beam imaging device, the gradient score can reflect the clarity and contrast of the image edge. When the gradient score of an image in a certain direction is high, it means that the image edge in that direction is clear and the contrast is high. Conversely, it means that the image edge is blurred and the contrast is low. Therefore, when both the X-direction astigmatism and the Y-direction astigmatism are successfully eliminated or reduced to within a preset range, the electron beam will be able to focus on one point after passing through the imaging system, forming a clear image. At this point, no matter how the objective lens current (or working distance) changes, the gradient scores of the image in the X-axis and Y-axis directions should remain basically consistent.

[0100] Therefore, if Figure 4 As shown in FIG, the symmetric axis of the X-axis gradient score change curve of the fine focus image is consistent with the symmetric axis of the Y-axis gradient score change curve, which means that the gradient scores of the fine focus image in the X-axis direction and the gradient scores in the Y-axis direction are consistent in their optimal positions at different WDs (Working Distances), thereby confirming that both the X-direction astigmatism and the Y-direction astigmatism have been successfully eliminated or reduced to within the preset range, and further confirming that the target astigmatism parameters meet the astigmatism elimination requirements. At this time, if Figure 3 As shown in the figure, when the target astigmatism parameters meet the requirements of eliminating astigmatism, the fine focus image is clearer.

[0101] In addition, if Figure 6 As shown in FIG, the symmetric axis of the X-axis gradient score change curve of the fine focus image is inconsistent with the symmetric axis of the Y-axis gradient score change curve, which means that the optimal positions of the gradient scores of the fine focus image in the X-axis direction and the gradient scores in the Y-axis direction at different WD (Working Distance) are inconsistent, so it can be determined that at least one of the X-direction astigmatism and the Y-direction astigmatism has not been successfully eliminated, and further confirming that the target astigmatism parameters do not meet the astigmatism elimination requirements. At this time, if Figure 5 As shown in FIG, when the target astigmatism parameters do not meet the astigmatism elimination requirements, the fine focus image is relatively blurred.

[0102] Therefore, the method for eliminating astigmatism of the electron beam imaging device of the present invention determines whether the target astigmatism parameter meets the astigmatism elimination requirement by calculating the X-axis gradient score change curve and the Y-axis gradient score change curve of multiple fine focus images according to the gradient, and judging whether the symmetry axis of the X-axis gradient score change curve is consistent with the symmetry axis of the Y-axis gradient score change curve. This optimizes the evaluation criteria, improves the accuracy of judging whether the astigmatism elimination requirement is met, and thus further improves the accuracy of astigmatism elimination.

[0103] In some embodiments, the step of determining the target objective lens current of the electron beam imaging device based on the gradient may include the following steps: using the objective lens current value corresponding to the symmetry axis as the target objective lens current (which may be denoted as BestOL). In other words, when the symmetry axis of the X-axis gradient fraction variation curve coincides with the symmetry axis of the Y-axis gradient fraction variation curve, that is, when astigmatism calibration is successful, the OL current value corresponding to the symmetry axis is used as BestOL, thereby achieving fine focusing.

[0104] Therefore, the method for eliminating astigmatism of the electron beam imaging device of the present invention achieves fine focusing by using the objective lens current value corresponding to the symmetry axis as the target objective lens current after the astigmatism calibration is successful, thereby further improving the imaging quality and further improving the astigmatism elimination effect.

[0105] Figure 7 FIG. 1 is a flow chart of a method for eliminating astigmatism of an electron beam imaging device according to another embodiment of the present invention. Figure 7 The process steps of this embodiment are described in detail.

[0106] Step S702 , recording the initial OL current value, StigmationX, and StigmationY.

[0107] Step S704 : gradually adjusting the OL current value according to the preset current step size, and acquiring a plurality of coarse focus images corresponding to different OL currents.

[0108] Step S706 , calculating the clarity of the multiple coarsely focused images.

[0109] Step S708: Search and tune the OL current according to the clarity of the multiple coarse focus images, and use the searched tuned OL current as OL_opt. It should be noted that after this step, a relatively clear focal plane position can be quickly searched, completing the coarse focus process.

[0110] Step S710 , setting the OL current value=OL_opt, and setting StigStopAcuuracy and StigRange.

[0111] Step S712 , searching BestStigX and BestStigY of the stigmator according to StigRange and the inverted pyramid search strategy.

[0112] Step S714, set StigmationX=BestStigX, StigmationY=BestStigY.

[0113] Step S716 : gradually adjust the pre-adjusted OL current according to the set step size, and collect multiple fine-focus images corresponding to different OL currents.

[0114] Step S718: Calculate the gradients of the multiple fine-focus images in different coordinate axis directions.

[0115] Step S720, calculating an X-axis gradient score change curve and a Y-axis gradient score change curve of the plurality of fine focus images according to the gradient;

[0116] Step S722 , determining whether the symmetry axis of the X-axis gradient score change curve is consistent with the symmetry axis of the Y-axis gradient score change curve. If they are consistent, executing step S724 ; if not, executing step S726 .

[0117] In step S724, the OL current value corresponding to the symmetry axis is used as BestOL. At this point, the fine focusing process is completed and this process ends.

[0118] Step S726: Outputting a prompt indicating that the astigmatism calibration has failed. Thus, the process of evaluating the astigmatism correction effect is completed, and this process ends.

[0119] It should be noted that the above steps S702 to S726 describe a single stigma elimination process of the stigma elimination method for the electron beam imaging device of the present invention. If a stigma elimination instruction is received again later, the current process can be restarted in response to the stigma elimination instruction.

[0120] Thus, the stigmation method for an electron beam imaging device of the present invention adds a step of evaluating the stigmation effect after searching for the target stigmation parameters of the stigmator in the electron beam imaging device. This effectively avoids the use of erroneous results, avoids the problem of low accuracy and inability to ensure normal measurement of the device due to erroneous stigmation results, improves the accuracy of stigmation, and thus improves the measurement accuracy of the electron beam imaging device. In addition, the stigmation method for an electron beam imaging device of the present invention further determines the target objective lens current of the electron beam imaging device based on the gradient after confirming that the target stigmation parameters meet the stigmation requirements, thereby achieving re-adjustment of the objective lens current of the electron beam imaging device, improving the precision of the objective lens current adjustment, and further improving the accuracy of stigmation.

[0121] Furthermore, the method for eliminating astigmatism of the electron beam imaging device of the present invention calculates the X-axis gradient score change curve and the Y-axis gradient score change curve of multiple fine focus images based on the gradient, and determines whether the symmetry axis of the X-axis gradient score change curve is consistent with the symmetry axis of the Y-axis gradient score change curve to determine whether the target astigmatism parameter meets the astigmatism elimination requirement. This optimizes the evaluation criteria and improves the accuracy of judging whether the astigmatism elimination requirement is met, thereby further improving the accuracy of astigmatism elimination.

[0122] Furthermore, the aberration elimination method of the electron beam imaging device of the present invention searches for the target aberration parameters through an inverted pyramid search method, thereby accelerating the search speed of the target aberration parameters of the aberration eliminater, reducing the time complexity and space complexity of the search, improving the efficiency of aberration elimination, and ensuring the stability of the aberration elimination process.

[0123] The present invention also provides a computer program product and a computer device. Figure 8 is a schematic diagram of the structure of a computer program product 10 according to one embodiment of the present invention, Figure 9 FIG. 2 is a schematic structural diagram of a computer device 20 according to an embodiment of the present invention.

[0124] The computer program product 10 stores a computer program 11 thereon. When the computer program 11 is executed by a processor, the data processing method of any of the above embodiments is implemented.

[0125] The computer device 20 may include a memory 220, a processor 210, and a computer program 11 stored in the memory 220 and running on the processor 210. When the processor 210 executes the computer program 11, the data processing method of any of the above embodiments is implemented.

[0126] It should be noted that the logic and / or steps represented in the flowchart or described in other ways herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be specifically implemented in any computer program product for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or used in combination with these instruction execution systems, devices or apparatuses.

[0127] For the purposes of the present description, computer program product 10 may be any device that can contain, store, communicate, propagate, or transmit a program for use with or in conjunction with an instruction execution system, device, or apparatus. More specific examples (not an exhaustive list) of computer program product 10 include the following: an electrical connection having one or more wires (electronic device), a portable computer disk cartridge (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), a fiber optic device, and a portable compact disc read-only memory (CDROM). In addition, computer program product 10 may even be paper or other suitable medium on which the program is printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering, or otherwise processing in a suitable manner as necessary, and then stored in a computer memory.

[0128] It should be understood that each part of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system.

[0129] The computer device 20 can be, for example, a server, a desktop computer, a laptop computer, a tablet computer, or a smartphone. In some examples, the computer device 20 can be a cloud computing node. The computer device 20 can be described in the general context of computer system executable instructions (such as program modules) executed by a computer system. Generally, program modules can include routines, programs, object programs, components, logic, data structures, etc. that perform specific tasks or implement specific abstract data types. The computer device 20 can be implemented in a distributed cloud computing environment where remote processing devices linked via a communication network perform tasks. In a distributed cloud computing environment, program modules can be located on local or remote computing system storage media, including storage devices.

[0130] The computer device 20 may include a processor 210 adapted to execute stored instructions, and a memory 220 that provides temporary storage for 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.

[0131] The flowchart provided in this embodiment is not intended to indicate that the operations of the method will be performed in any particular order, or that all operations of the method are included in all every case. In addition, the method may include additional operations. Within the scope of the technical ideas provided by the method of this embodiment, additional changes can be made to the above method.

[0132] At this point, those skilled in the art will recognize that, although a number of exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications consistent with the principles of the present invention may be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be understood and deemed to cover all such other variations or modifications.

Claims

1. A method for eliminating astigmatism of an electron beam imaging device, comprising: searching for a target astigmatism parameter of an stigmator in the electron beam imaging device; The preset objective lens current is gradually adjusted according to the set step size, and multiple fine focus images corresponding to different objective lens currents are collected; Calculating the gradients of the plurality of fine-focus images in different coordinate axis directions; Calculating an X-axis gradient score change curve and a Y-axis gradient score change curve of the plurality of fine focus images according to the gradient; Determining whether the symmetry axis of the X-axis gradient score change curve is consistent with the symmetry axis of the Y-axis gradient score change curve; If they are consistent, it is confirmed that the target astigmatism parameter meets the astigmatism elimination requirement, and the objective lens current value corresponding to the symmetry axis is used as the target objective lens current of the electron beam imaging device; If they are inconsistent, it is confirmed that the target astigmatism parameter does not meet the astigmatism elimination requirement.

2. The method for eliminating astigmatism of an electron beam imaging device according to claim 1, wherein: The step of searching for a target astigmatism parameter of an stigmator in the electron beam imaging device comprises: The astigmatism parameters are gradually adjusted according to the initial image step length to obtain multiple astigmatism comparison images; Search and tune the astigmatism parameters according to the variance of the multiple astigmatism comparison images as a basis for iterative search; Iteratively searching for the tuned astigmatism parameter, and reducing the image step length in each iteration until the iteration is stopped when the image step length is less than a preset search stop accuracy; The tuned astigmatism parameter obtained from the last iterative search is used as the target astigmatism parameter of the stigmator.

3. The method for eliminating astigmatism of an electron beam imaging device according to claim 2, wherein: The step of searching and tuning the astigmatism parameters according to the variance of the multiple astigmatism comparison images comprises: Calculating the variance of each of the astigmatism comparison images as the clarity score of each of the astigmatism comparison images; The clarity scores of the multiple astigmatism comparison images are compared, and the astigmatism parameter value corresponding to the astigmatism comparison image with the highest clarity score is used as the tuned astigmatism parameter.

4. The method for eliminating astigmatism of an electron beam imaging device according to claim 1, wherein: Before the step of searching for a target astigmatism parameter of the stigmator in the electron beam imaging device, the stigmation elimination method further includes: searching for the preset objective lens current of the electron beam imaging device; The objective lens current of the electron beam imaging device is set to the preset objective lens current.

5. The method for eliminating astigmatism of an electron beam imaging device according to claim 4, wherein: The step of searching for the pre-adjusted objective lens current of the electron beam imaging device comprises: The initial objective lens current is gradually adjusted according to the preset current step size, and multiple coarse focus images corresponding to different objective lens currents are collected; Calculating the clarity of the multiple coarsely focused images; The objective lens current is searched and tuned according to the clarity of the multiple coarse focus images, and the tuned objective lens current obtained by the search is used as the pre-adjusted objective lens current.

6. The method for eliminating astigmatism of an electron beam imaging device according to claim 1, wherein: After the step of confirming that the target astigmatism parameter does not meet the astigmatism elimination requirement, the astigmatism elimination method further includes: Outputs a prompt indicating that astigmatism calibration failed. 7 . A computer program product, comprising a computer program, wherein when the computer program is executed by a processor, the computer program implements the steps of the astigmatism elimination method for an electron beam imaging device according to claim 1 .

8. A computer device comprising a memory, a processor, and a computer program stored in the memory and running on the processor, wherein when the processor executes the computer program, the steps of the astigmatism elimination method for an electron beam imaging device according to any one of claims 1 to 6 are implemented.

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