Astigmatism eliminating method of electron beam imaging equipment, product and equipment

Abstract

The invention relates to the field of semiconductor manufacturing and detection, in particular to an anastigmatism method of electron beam imaging equipment, a product and the equipment. The anastigmatism method comprises the following steps: searching a target astigmatism parameter of an anastigmatism device in the electron beam imaging equipment; gradually adjusting the current of the preset objective lens according to a set step length, and collecting a plurality of fine focusing images corresponding to different objective lens currents; calculating gradients of the plurality of fine focusing images in different coordinate axis directions; judging whether the target astigmatism parameter meets the astigmatism elimination requirement or not according to the gradient consistency; and if yes, determining the target objective current of the electron beam imaging equipment according to the gradient. According to the anastigmatism method, after the target astigmatism parameter of the anastigmatism device is determined, the judgment operation on the target astigmatism parameter is executed, the anastigmatism accuracy is improved, the problem that the measurement accuracy is low due to the fact that a wrong anastigmatism result is applied is avoided, and therefore the measurement accuracy of the electron beam imaging device is improved.

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, allows charged particles to interact with samples, and captures particle signals such as secondary particles and transmitted particles for imaging, which can characterize the morphology, structure, composition and other information of samples. In the semiconductor field, charged particle beam imaging equipment includes detection equipment for detecting surface defects of wafers and electron beam measurement equipment for detecting critical dimensions of wafers.

[0003] Scanning Electron Microscope (SEM) is a charged particle beam imaging device used for defect detection and key dimension measurement in semiconductor manufacturing and other micro-nano processing fields. The device scans the sample surface with a high-energy electron beam, collects and analyzes signals such as secondary electrons and backscattered electrons generated by the interaction between electrons and samples, thereby achieving accurate measurement of the sample surface morphology and size. As a high-precision imaging device, the SEM device needs to ensure the stability of imaging quality. In actual measurement, the state of the SEM device will drift to a certain extent over time, so some hardware parameters need to be calibrated regularly. As an important calibration item, the automation of astigmatism calibration is particularly important. However, manual calibration requires and consumes a certain amount of manpower costs, so it is necessary to automate the astigmatism elimination process. Automatic astigmatism elimination calibration analyzes the astigmatism characteristics of the image and automatically adjusts the position and size of the stigmator to eliminate the astigmatism phenomenon in the image. 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, a solution for adjusting the image (i.e., SEM image) obtained by a scanning electron microscope (SEM) is to select an isotropic sample position for adjusting the astigmatism, 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 calibrate the astigmatism. However, this solution has certain limitations in the selection of samples, relatively high requirements for the operator's experience, and requires the actual operator to have a thorough understanding of the image characteristics. There are 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 calibrate the astigmatism. The method also has high requirements for the imaging quality of the SEM image and the accuracy of the spectrum image binarization result. There are 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 result.

[0005] In addition, another solution for adjusting the SEM image to eliminate astigmatism in the prior art is: adjusting the imaging lens of the electron microscope to the quasi-focus distance according to the defocus degree of the image, and when the imaging lens is at the quasi-focus distance, using the variance of the local variance and the mean of the local variance to compositely describe the clarity of the quasi-focus image, and using the clarity of the quasi-focus image as a judgment reference to complete the adjustment of the astigmatism value. However, this solution directly confirms the completion of the entire automatic astigmatism elimination adjustment after completing the adjustment of the astigmatism value, which cannot avoid the application of erroneous results, and there are problems such as low algorithm accuracy and inability to ensure normal measurement of the equipment. Summary of the invention

[0006] In view of the above problems, the present invention proposes an anti-astigmatism 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 an astigmatism elimination method for an electron beam imaging device to ensure the accuracy of astigmatism elimination.

[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 elimination.

[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 length, 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 according to 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 taken 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 comprises:

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

[0025] The astigmatism parameters are tuned and searched based on the variance of multiple astigmatism comparison images, which serves 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 by the last iterative search are used as the target astigmatism parameters of the astigmatism remover.

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

[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 stigmatizer in an electron beam imaging device, the stigmatism elimination 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 pre-adjusted objective lens current of the electron beam imaging device comprises:

[0035] The initial objective lens current is gradually adjusted according to the preset current step length, and a plurality of 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 judging whether the target astigmatism parameter meets the astigmatism elimination requirement according to the consistency of the gradient, the astigmatism elimination method further comprises:

[0039] If the astigmatism elimination requirement is not met, an astigmatism calibration failure prompt is 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 of 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 the processor implements the steps of any of the above-mentioned methods for eliminating stigmatism of an electron beam imaging device when executing the computer program.

[0042] The destigmatization method of the electron beam imaging device of the present invention, after searching for the target destigmatization parameter of the destigmatizer in the electron beam imaging device, gradually adjusts the pre-adjusted objective lens current according to the set step length, 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 destigmatization parameter meets the destigmatization requirement based on the consistency of the gradient, thereby achieving the judgment of the destigmatization effect. Therefore, the destigmatization 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 the error of the destigmatization result, improve the accuracy of destigmatization, and thus improve the measurement accuracy of the electron beam imaging device. In addition, the destigmatization method 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 when confirming that the target destigmatization parameter meets the destigmatization requirement. The re-adjustment of the objective lens current of the electron beam imaging device is achieved, the precision of the objective lens current adjustment is improved, and the accuracy of destigmatization is further improved.

[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 according to the gradient, and judges 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 judge whether the target astigmatism parameter meets the astigmatism elimination requirement, thereby optimizing the judgment standard, improving the accuracy of judging whether the astigmatism elimination requirement is met, and further improving the accuracy of astigmatism elimination.

[0044] Furthermore, the method for eliminating astigmatism of the electron beam imaging device of the present invention obtains multiple astigmatism comparison images by gradually adjusting the astigmatism parameters according to the initial image step length, searches and tunes the astigmatism parameters according to the variance of the multiple astigmatism comparison images and uses them as the basis for iterative search, iteratively searches and tunes the astigmatism parameters, reduces the image step length in each iteration, stops the iteration when the image step length is less than the preset search stop accuracy, and uses the tuned astigmatism parameters obtained by the last iterative search as the target astigmatism parameters of the astigmatism eliminator, thereby realizing the search for the target astigmatism parameters by the inverted pyramid search method. Therefore, the method for eliminating astigmatism of the electron beam imaging device of the present invention searches for the target astigmatism parameters by the inverted pyramid search method, accelerates the search speed of the target astigmatism parameters of the astigmatism eliminator, reduces the time complexity and space complexity of the search, improves the efficiency of eliminating astigmatism, and ensures 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-astigmatism adjustment in the prior art;

[0048] Figure 2 is a schematic flow chart of an astigmatism elimination method for 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 an astigmatism elimination method of 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 an astigmatism elimination method of 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 schematic flow chart of an astigmatism elimination method for 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 an embodiment of the present invention; and

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

[0056] The exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the 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. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present disclosure and to enable the scope of the present invention to be fully communicated 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 values of the astigmatism parameters; 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 major and minor 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 major and minor axes a2 and b2 of the fitted ellipse; Step 5: Determine whether to adjust the focus and astigmatism according to 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 parameters; when the roundness < threshold, the astigmatism parameters need 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 sharpness of the images, calculate the best focal plane according to the sharpness curve of the images, complete the autofocus, and go to Step 8;

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

[0059] The following combines Figure 1 to illustrate 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 major and minor 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 major and minor 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 value. If yes, proceed to step S9; if no, proceed to step S8.

[0066] Step S7: changing the OL current value with a certain step length and collecting N images, evaluating the clarity of the images, and determining the optimal OL current value according to the clarity curve of the images. Automatic focusing is completed, and the process proceeds to step S8;

[0067] Step S8: By changing the astigmatism value, the astigmatism value where the minimum roundness a1 / b1-a2 / b2 is located is searched, which is the optimal astigmatism, and the automatic astigmatism elimination is completed. At this point, this process ends.

[0068] Step S9: Skip the step of adjusting focus and astigmatism. At this point, this process ends.

[0069] From the perspective of sample selection, the above method has certain limitations in sample selection, and the requirements for operator experience are relatively high. The actual operator needs to have a thorough understanding of image features, and there are problems such as poor diversity of application scenarios and high labor costs. In addition, the above scheme uses the roundness and area characteristics of the spectral binary image to determine whether the equipment needs to calibrate the astigmatism. It also has high requirements for the imaging quality of the SEM image and the accuracy of the spectral image binarization results. There are 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.

[0070] In order to solve the above problem, an embodiment of the present invention provides an astigmatism elimination method for an electron beam imaging device. Figure 2 The figure is a flow chart of an astigmatism elimination method for 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 length, 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, if so, executing step S210.

[0076] Step S210, determining a target objective lens current of an 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 (which may be recorded as StigmationX) and Y-direction astigmatism (which may be recorded as StigmationY). Therefore, the target astigmatism parameters of the stigmator include target X-direction astigmatism (which may be recorded as BestStigX) and target Y-direction astigmatism (which may be recorded as BestStigY). Accordingly, the gradients of the fine focus image in different coordinate axis directions may include the X-axis gradient and the Y-axis gradient of the fine focus image.

[0078] In addition, the objective lens (OL) is the last focusing lens in the SEM, which is responsible for focusing the electron beam of the electron beam imaging device to a very small point in order to form a high-resolution image on the sample. Adjusting the objective lens current (which can be recorded as OL current) can change the magnetic field strength of the objective lens, thereby changing the focusing state of the electron beam, and further affecting the magnification of the SEM image. In addition, the pre-adjusted objective lens current (which can be recorded as OL_opt) can be the objective lens current value that can be searched in the pre-coarse focusing step to preliminarily improve the imaging quality.

[0079] The stigmatism elimination method of the electron beam imaging device of the present invention realizes the evaluation of the stigmatism elimination effect because after searching the target stigmatism parameter of the stigmatism elimination device in the electron beam imaging device, the pre-adjusted objective lens current is gradually adjusted according to the set step length, and multiple fine focus images corresponding to different objective lens currents are collected, the gradients of the multiple fine focus images in different coordinate axis directions are calculated, and whether the target stigmatism parameter meets the stigmatism elimination requirement is judged according to the consistency of the gradient. Therefore, the stigmatism elimination method of the present invention can effectively improve the correctness of the stigmatism elimination result, improve the accuracy of the stigmatism elimination, and thus improve 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 requirements of eliminating astigmatism, thereby realizing re-adjustment 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 eliminating astigmatism.

[0081] In some embodiments, after the above step S210, the method for eliminating astigmatism of an electron beam imaging device of the present invention may further include the following steps: if the astigmatism elimination requirement is not met, an astigmatism calibration failure prompt is output. That is, if the target astigmatism parameter does not meet the astigmatism elimination requirement, an astigmatism calibration failure prompt is output, and the current process is terminated.

[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 guarantee 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 electron beam imaging equipment.

[0083] In some embodiments, before the above step S202, the stigmation method of the electron beam imaging device of the present invention may further include the following steps: searching for a pre-adjusted objective lens current of the electron beam imaging device; setting the objective lens current of the electron beam imaging device to the pre-adjusted objective lens current. That is, the stigmation method of the present invention first searches for the pre-adjusted objective lens current of the electron beam imaging device, then uses the searched pre-adjusted objective lens current as the objective lens current of the electron beam imaging device, and searches for the target stigmation parameter of the stigmator in the electron beam imaging device on this basis.

[0084] Furthermore, the above-mentioned step of searching for the pre-adjustment 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-adjustment 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 searched tuned objective lens current as the pre-adjustment 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 searched pre-adjustment objective lens current is used in the subsequent process of searching for the target astigmatism parameter of the stigmatizer in the electron beam imaging device. That is to say, the stigmatism elimination 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 a specific embodiment, the step of pre-adjusting the objective lens current of the above-mentioned search electron beam imaging device can be specifically performed as the following steps: continuously adjusting the OL current value and collecting multiple images; dynamically adjusting the search step size according to the clarity curve gradient of multiple coarse focus images, and quickly searching to a relatively clear focal plane position to achieve coarse focus; recording the better 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 according to 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 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 stop condition for quickly searching to a relatively clear focal plane position can be set to the clarity curve of the coarse focus image presenting a quadratic parabola opening downward. In another optional implementation, the stop condition for quickly searching to a relatively clear focal plane position can also be set to the number of searches exceeding the 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, the above step S202 may include the following steps: gradually adjusting the astigmatism parameters according to the initial image step length to obtain multiple astigmatism comparison images; searching and tuning the astigmatism parameters according to the variance of the multiple astigmatism comparison images as the basis for iterative search; iteratively searching and tuning the astigmatism parameters, and reducing the image step length in each iteration until the iteration is stopped when the image step length is less than the preset search stop accuracy; using the tuned astigmatism parameters obtained from the last iterative search as the target astigmatism parameters of the astigmatism eliminator. So far, the astigmatism eliminator method of the electron beam imaging device of the present invention realizes the search for the target astigmatism parameters using an inverted pyramid search method. 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 by reducing the step length near B1 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 de-stigmatization method of the electron beam imaging device of the present invention realizes the search for the target de-stigmatization parameters by using the inverted pyramid search method, thereby improving the search speed of the target de-stigmatization parameters of the de-stigmatization device, reducing the time complexity and space complexity of the search, improving the de-stigmatization efficiency, and ensuring the stability of the de-stigmatization process.

[0089] In some embodiments, the variance of the astigmatism comparison image can reflect the degree of discreteness of the grayscale value of the astigmatism comparison image, and can be used for the clarity assessment 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 above-mentioned step of searching and tuning the astigmatism parameters according to the variance of multiple astigmatism comparison images may 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 above-mentioned step of searching and tuning the astigmatism parameters according to the variance of multiple astigmatism comparison images can also be specifically performed as: using the astigmatism parameter value corresponding to the astigmatism comparison image with the largest variance as the tuning astigmatism parameter.

[0090] Therefore, the method for eliminating astigmatism 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 BestStigX of the stigmator in the electron beam imaging device by 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 StigmationX with a certain step size within StigRange, and using the variance of the image as the image score, each layer of search can obtain the best score, and the next layer of search is performed 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 BestStigX.

[0093] In addition, the step of searching BestStigY of the stigmator in the electron beam imaging device by 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, each layer of search can get the best score, and the next layer of search is performed 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 destigmatization 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, which improves the search speed of the target astigmatism parameters of the destigmatizer while ensuring the search accuracy of the target X-direction astigmatism and the target Y-direction astigmatism, thereby further ensuring the stability of the destigmatization process.

[0095] In some embodiments, the above step S204 can be specifically performed as the following steps: taking OL_opt as the center, gradually adjusting the OL current value according to the set step length, and collecting multiple fine focus images corresponding to different OL current values. It should be noted that the set step length can be pre-set according to parameters such as the OL focal length of the electron beam imaging device. In a specific embodiment, the set step length can be set to a change in the focal length of the OL of 1 to 10 microns after adjusting the OL current value with the set step length. Therefore, the anti-astigmatism method of the electron beam imaging device of the invention 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 the target astigmatism parameter meets the astigmatism elimination requirement. 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 the 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 anti-astigmatism requirements. Figure 5 3 is a schematic diagram of a fine focus image in an stigmatism elimination method of 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 stigmatism 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 shown is used to illustrate 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 requirements of eliminating astigmatism.

[0097] like Figure 3 to Figure 6 In some embodiments, the above step S206 may include the following steps: calculating the X-axis gradient and the Y-axis gradient of multiple fine focus images. Further, the above step S208 may include the following steps: 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; 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; if they are consistent, confirming that the target astigmatism parameter meets the astigmatism elimination requirement; if they are inconsistent, confirming that the target astigmatism parameter does not meet the astigmatism elimination requirement. At this point, the astigmatism elimination method of the electron beam imaging device of the invention 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 anti-astigmatism requirement may include that both the X-direction astigmatism and the Y-direction astigmatism are successfully eliminated or reduced to a preset range. When both the X-direction astigmatism and the Y-direction astigmatism are successfully eliminated or reduced to a preset range, it is confirmed that the target astigmatism parameter meets the anti-astigmatism requirement.

[0099] In addition, the gradient score is an indicator to measure how fast 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. Otherwise, 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 a preset range, the electron beam will be able to focus on one point after passing through the imaging system to form 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. 1 , 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 score of the fine focus image in the X-axis direction and the gradient score in the Y-axis direction are consistent in the optimal position at different WDs (Working Distances), so it can be determined that both the X-direction astigmatism and the Y-direction astigmatism are successfully eliminated or reduced to a preset range, and then it is confirmed that the target astigmatism parameters meet the requirements of eliminating astigmatism. At this time, if Figure 3 As shown, 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. 1 , 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 gradient score of the fine focus image in the X-axis direction and the gradient score in the Y-axis direction are not consistent in the optimal position at different WD (Working Distance), 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 then it is confirmed that the target astigmatism parameter does not meet the astigmatism elimination requirements. At this time, if Figure 5 As shown in FIG. 1 , when the target astigmatism parameter does not meet the astigmatism elimination requirement, the fine focus image is relatively blurred.

[0102] Therefore, 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 according to the gradient, and judges 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 judge whether the target astigmatism parameter meets the astigmatism elimination requirement, optimizes the judgment standard, 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 according to the gradient may include the following steps: taking the objective lens current value corresponding to the symmetry axis as the target objective lens current (which may be recorded as BestOL). That is, when 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, that is, when the astigmatism calibration is successful, the OL current value corresponding to the symmetry axis is taken as BestOL, thereby achieving fine focusing.

[0104] Therefore, the method for eliminating astigmatism of the electron beam imaging device of the present invention realizes fine focusing by using the objective lens current value corresponding to the axis of symmetry 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 length, 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 focusing 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 to complete the coarse focusing 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 adjusting the preset OL current according to the set step length, and acquiring a plurality of fine focus images corresponding to different OL currents.

[0114] Step S718, calculating 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, 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, if consistent, execute step S724, if inconsistent, execute step S726.

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

[0118] Step S726: Output a prompt indicating that the astigmatism calibration has failed. At this point, the process of evaluating the astigmatism elimination 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 in the future, the current process can be restarted in response to the stigma elimination instruction.

[0120] Therefore, the stigmation method for the electron beam imaging device of the present invention adds a step of judging the stigmation effect after searching the target stigmation parameters of the stigmator in the electron beam imaging device, thereby effectively avoiding the application of erroneous results, avoiding the problem of low accuracy and inability to ensure normal measurement of the device due to erroneous stigmation results, improving the accuracy of stigmation, and thus improving the measurement accuracy of the electron beam imaging device. In addition, the stigmation method for the electron beam imaging device of the present invention also determines the target objective lens current of the electron beam imaging device according to the gradient when confirming that the target stigmation parameters meet the stigmation requirements, thereby realizing the 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 according to the gradient, and judges 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 judge whether the target astigmatism parameter meets the astigmatism elimination requirement, thereby optimizing the judgment standard, improving the accuracy of judging whether the astigmatism elimination requirement is met, and further improving the accuracy of astigmatism elimination.

[0122] Furthermore, the de-stigmatization method of the electron beam imaging device of the present invention searches for the target destigmatization parameters by an inverted pyramid search method, which speeds up the search speed of the target destigmatization parameters of the destigmatization device, reduces the time complexity and space complexity of the search, improves the efficiency of destigmatization, and ensures the stability of the destigmatization 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 an embodiment of the present invention, Fig. 9 is a schematic diagram of the structure 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, and 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, and the processor 210 implements the data processing method of any of the above embodiments when executing the computer program 11.

[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 equipment (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 equipment and execute instructions), or used in combination with these instruction execution systems, devices or equipment.

[0127] For the purposes of the description of this embodiment, the 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 (a non-exhaustive list) of the computer program product 10 include the following: an electrical connection with one or more wirings (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and editable read-only memory (EPROM or flash memory), a fiber optic device, and a portable compact disk read-only memory (CDROM). In addition, the computer program product 10 may even be paper or other suitable medium on which the program may be printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering or processing in other suitable ways 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 may be, for example, a server, a desktop computer, a notebook computer, a tablet computer, or a smart phone. In some examples, the computer device 20 may be a cloud computing node. The computer device 20 may be described in the general context of computer system executable instructions (such as program modules) executed by a computer system. Typically, a program module may include routines, programs, target programs, components, logic, data structures, etc. that perform specific tasks or implement specific abstract data types. The computer device 20 may be implemented in a distributed cloud computing environment where remote processing devices linked through a communication network perform tasks. In a distributed cloud computing environment, program modules may be located on a local or remote computing system storage medium including a storage device.

[0130] The computer device 20 may include a processor 210 adapted to execute stored instructions, and a memory 220 providing 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 a random access memory (RAM), a read-only memory, a flash memory, or any other suitable storage system.

[0131] The flow chart provided by the present embodiment is not intended to indicate that the operation 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 thinking provided by the present embodiment method, additional changes may be made to the above method.

[0132] At this point, those skilled in the art should recognize that, although multiple exemplary embodiments of the present invention have been shown and described in detail herein, 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 in 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 recognized as covering all these 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 length, 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; Judging whether the target astigmatism parameter meets the astigmatism elimination requirement according to the consistency of the gradient; If so, a target objective lens current of the electron beam imaging device is determined according to the gradient.

2. The method for eliminating astigmatism of an electron beam imaging device according to claim 1, wherein: The step of judging whether the target astigmatism parameter meets the astigmatism elimination requirement according to the consistency of the gradient comprises: Calculate 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; 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; If they are consistent, it is confirmed that the target astigmatism parameter meets the astigmatism elimination requirement; If they are inconsistent, it is confirmed that the target astigmatism parameter does not meet the astigmatism elimination requirement.

3. The method for eliminating astigmatism of an electron beam imaging device according to claim 2, wherein: The step of determining the target objective lens current of the electron beam imaging device according to the gradient comprises: The objective lens current value corresponding to the symmetry axis is used as the target objective lens current.

4. 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 parameter is 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 the tuning 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 by the last iterative search is used as the target astigmatism parameter of the astigmatism eliminater.

5. The method for eliminating astigmatism of an electron beam imaging device according to claim 4, 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 tuning astigmatism parameter.

6. 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 an stigmatism corrector in the electron beam imaging device, the stigmatism correcting method further comprises: searching 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.

7. The method for eliminating astigmatism of an electron beam imaging device according to claim 6, 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 length, and a plurality of 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 adjusted according to the clarity of the plurality of coarse focus images, and the objective lens current adjusted and adjusted obtained by the search is used as the pre-adjusted objective lens current.

8. The method for eliminating astigmatism of an electron beam imaging device according to claim 1, wherein: After the step of judging whether the target astigmatism parameter meets the astigmatism elimination requirement according to the consistency of the gradient, the astigmatism elimination method further includes: If the astigmatism elimination requirement is not met, an astigmatism calibration failure prompt is output.

9. A computer program product, comprising a computer program, wherein when the computer program is executed by a processor, the steps of the astigmatism elimination method for an electron beam imaging device according to any one of claims 1 to 8 are implemented.

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

Images