Focusing method, device and equipment of scanning electron microscope, medium and product

Abstract

The invention discloses a focusing method, device and equipment of a scanning electron microscope, a medium and a product, and is applied to the field of semiconductor manufacturing. The method comprises the steps of obtaining a first image and image definition based on a plurality of first focal lengths, and predicting a first target focal length with the highest image definition; then, determining a plurality of second focal lengths based on the first target focal length, respectively obtaining a second image and image definition, and carrying out secondary prediction to obtain a second target focal length with the highest image definition; therefore, high-precision automatic focusing is realized. According to the scheme, high-precision real-time focusing can be realized through two times of focal length prediction in one focusing process, and particularly, under the condition of high magnification, the focusing precision can be improved while real-time focusing is ensured. For a scanning electron microscope, the performance can be improved; for scanning electron beam equipment, the throughput of the equipment can be greatly improved, and the performance competitiveness of the equipment is improved.

Description

Technical Field

[0001] The present application belongs to the field of semiconductor manufacturing, and in particular, relates to a focusing method, device, equipment, medium and product of a scanning electron microscope. Background Art

[0002] In electron beam equipment, the automatic focusing process is required when the sample is collected at different focal lengths. Therefore, the automatic focusing process of the electron microscope is one of the processes that has the greatest impact on throughput. The depth of field of the scanning electron microscope is short at high magnification. During the operation of the equipment, it is easily affected by various factors such as the equipment platform and the sample, resulting in defocus. Therefore, there is an urgent need for real-time high-precision automatic focusing function. The traditional focusing process is as follows: First, according to the setting conditions of the scanning electron microscope, set the appropriate focusing step length, collect focusing data according to the process, and find the best focus focal length under the process by evaluating the focusing data; if the magnification is high, the focal length at this time does not reach the actual best because the depth of field is too small. It is necessary to adjust the focusing step length to a finer value, continue to collect focusing data according to the process, and then find the best focus focal length by evaluating the focusing data.

[0003] However, under general high magnification conditions, at least two focusing processes are required to obtain the optimal focal length. In this process, dozens of focusing adjustments and dozens of focusing signals need to be collected, which is time-consuming and reduces the online operation time of the equipment. Summary of the invention

[0004] The embodiments of the present application provide a focusing method, device, equipment, medium and product for a scanning electron microscope, which can reduce the focusing time of the scanning electron microscope and ensure the focusing accuracy.

[0005] On the one hand, an embodiment of the present application provides a focusing method of a scanning electron microscope, comprising:

[0006] Determining a plurality of first focal lengths based on an original focal length of the scanning electron microscope;

[0007] Acquire a corresponding first image and a corresponding definition at each of the first focal lengths of the scanning electron microscope;

[0008] Inputting each of the first focal lengths and the clarity of each of the first images into a first prediction model to predict a first target focal length; the first target focal length is a focal length corresponding to an extreme point in a clarity curve constructed by the first prediction model;

[0009] Based on the first target focal length, determining a plurality of second focal lengths; the second focal lengths at least include at least one focal length greater than the first target focal length and at least one focal length less than the first target focal length;

[0010] Acquire corresponding second images and corresponding sharpness at each of the second focal lengths of the scanning electron microscope;

[0011] Inputting each of the second focal lengths and the clarity of each of the second images into a second prediction model to predict a second target focal length; the second target focal length is the focal length corresponding to the extreme point in the clarity curve constructed by the second prediction model;

[0012] Based on the second target focal length, the scanning electron microscope is adjusted to obtain a target focal length.

[0013] On the other hand, determining a plurality of first focal lengths based on the original focal length of the scanning electron microscope comprises:

[0014] Determining a first step length based on a current target depth of field of the scanning electron microscope;

[0015] The original focal length is adjusted according to the first step to obtain at least one third focal length smaller than the original focal length and at least one fourth focal length larger than the original focal length;

[0016] A plurality of first focal lengths are determined according to the original focal length, at least one of the third focal lengths and at least one of the fourth focal lengths.

[0017] On the other hand, determining a plurality of second focal lengths based on the first target focal length includes:

[0018] Acquire a first focal length difference between the third focal length and the first target focal length, and a second focal length difference between the fourth focal length and the first target focal length;

[0019] Determining at least one fifth focal length that is smaller than the first target focal length based on the first focal length difference and the second focal length difference;

[0020] Determining at least one sixth focal length greater than the first target focal length based on the first focal length difference and the second focal length difference;

[0021] A plurality of the second focal lengths are determined based on the first target focal length, at least one of the fifth focal lengths, and at least one of the sixth focal lengths.

[0022] On the other hand, the fifth focal length and the sixth focal length are symmetrically distributed on both sides of the first target focal length.

[0023] On the other hand, determining the first step length based on the current target depth of field of the scanning electron microscope includes:

[0024] The target depth of field is multiplied by a preset multiple to obtain the first step length.

[0025] On the other hand, before multiplying the target depth of field by a preset multiple to obtain the first step length, the method further includes:

[0026] Obtaining a current target magnification of the scanning electron microscope;

[0027] The target depth of field is determined based on the target magnification and a corresponding relationship between the depth of field and the magnification of the scanning electron microscope.

[0028] On the other hand, adjusting the scanning electron microscope based on the second target focal length to obtain the target focal length includes:

[0029] determining a plurality of seventh focal lengths based on the second target focal length;

[0030] Acquire a corresponding third image and a corresponding definition at each of the seventh focal lengths of the scanning electron microscope;

[0031] Comparing the clarity of each of the third images to obtain a target image corresponding to the highest clarity;

[0032] Determine the seventh focal length corresponding to the target image as the target focal length;

[0033] The scanning electron microscope was adjusted to the target focus.

[0034] On the other hand, determining a plurality of seventh focal lengths based on the second target focal length includes:

[0035] Based on the target depth of field, determining a second step length;

[0036] determining, based on the second step length, at least one eighth focal length that is greater than the second target focal length;

[0037] determining, based on the second step length, at least one ninth focal length that is smaller than the second target focal length;

[0038] The second target focal length, at least one of the eighth focal lengths, and at least one of the ninth focal lengths are determined as the seventh focal length.

[0039] On the other hand, the first prediction model and the second prediction model are Gaussian models or quadratic curve models.

[0040] In another aspect, an embodiment of the present application provides a focusing device for an electron microscope, comprising: a processor and a memory storing computer program instructions;

[0041] When the processor executes the computer program instructions, the focusing method of the electron microscope as described above is implemented.

[0042] On the other hand, an embodiment of the present application provides a computer-readable storage medium, on which computer program instructions are stored. When the computer program instructions are executed by a processor, the focusing method of the electron microscope as described above is implemented.

[0043] On the other hand, an embodiment of the present application provides a computer program product. When instructions in the computer program product are executed by a processor of an electronic device, the electronic device executes the focusing method of the electron microscope as described above.

[0044] The focusing method of the scanning electron microscope provided in the embodiment of the present application obtains the first image and the image clarity respectively based on multiple first focal lengths determined by the original focal length of the scanning electron microscope. Because the image clarity of different focal lengths changes according to a rule, a clarity curve can be constructed to obtain the first target focal length corresponding to the extreme point of the curve. The first target focal length is the focal length with the highest image clarity predicted by the model. Then, based on the multiple second focal lengths determined by the first target focal length, the second image and the image clarity are obtained respectively, and the clarity curve is constructed again based on the model to obtain the second target focal length corresponding to the extreme point; finally, high-precision automatic focusing is achieved. This solution can achieve high-precision real-time focusing by predicting the focal length twice in one focusing process, especially under high magnification conditions, while ensuring real-time focusing, it can improve focusing accuracy. For scanning electron microscopes, it can improve performance; for scanning electron beam equipment, it can greatly improve equipment throughput and enhance equipment performance competitiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solution of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0046] Figure 1 A schematic flow chart of a focusing method for a scanning electron microscope provided in one embodiment of the present application is shown;

[0047] Figure 2 A schematic flow chart of a complete focusing method provided by an embodiment of the present application is shown;

[0048] Figure 3 A schematic diagram of a clarity curve predicted by a first prediction model provided in one embodiment of the present application is shown;

[0049] Figure 4 A schematic diagram of a clarity curve of a second prediction model provided by an embodiment of the present application is shown;

[0050] Figure 5A schematic structural diagram of a focusing device for a scanning electron microscope provided in an embodiment of the present application is shown;

[0051] Figure 6 A schematic diagram of the hardware structure of a focusing device for a scanning electron microscope provided in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0052] The features and exemplary embodiments of various aspects of the present application will be described in detail below. In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, rather than to limit the present application. For those skilled in the art, the present application can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present application by illustrating the examples of the present application.

[0053] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "include..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0054] In the field of semiconductor manufacturing, with the continuous iteration of technology, the urgent market demand for high-end semiconductor equipment and the continuous pursuit of manufacturing yield, the market share of electron beam equipment has gradually increased. In electron beam equipment, automatic focusing process is required when collecting images at different positions of the sample. In order to meet the increasingly high requirements of the key dimensions of integrated circuits, the accuracy requirements of electron beam automatic focusing are also higher, and the demand for improving equipment throughput has risen sharply.

[0055] Traditional focusing solutions require multiple focusing steps based on different step lengths under high magnification conditions, from coarse focusing to fine focusing, to finally obtain the best focusing conditions. This process requires more focusing steps, and it is also necessary to collect multiple images to judge the clarity, which is time-consuming. Moreover, the step length of each focusing adjustment is difficult to determine, which places high demands on equipment users, especially at high magnifications and when the scanning electron microscope setting parameters change. Users need to conduct repeated tests to find the appropriate focusing step length, which is time-consuming and labor-intensive, and reduces the online operation time of the equipment.

[0056] In order to solve the problems of the traditional solution, the embodiment of the present application provides a focusing method, device, equipment, medium and product of a scanning electron microscope. The focusing method of the scanning electron microscope provided by the embodiment of the present application is first introduced below. Figure 1 FIG. 1 is a flow chart of a focusing method for a scanning electron microscope provided by an embodiment of the present application. Figure 1 As shown, the method comprises the following steps:

[0057] S101: Determine a plurality of first focal lengths based on an original focal length of a scanning electron microscope.

[0058] In electron beam equipment, when collecting images at different positions of the sample, the scanning electron microscope needs to be automatically focused. Before focusing, the original focal length of the scanning electron microscope needs to be known first, and then the focal length can be adjusted based on the original focal length, and finally the focal length of the scanning electron microscope is adjusted to the target focal length.

[0059] After obtaining the original focal length, it is necessary to determine multiple first focal lengths based on the original focal length. The selection method of the first focal length is not limited. The first focal length is used to preliminarily predict the focal length corresponding to the image with the highest definition. The original focal length and multiple focal lengths near it can be selected as the first focal length.

[0060] In practical applications, each first focal length needs to be adjusted once and the image and its clarity need to be obtained. Therefore, in order to reduce the duration of the entire focusing process, the number of first focal lengths can be reduced; but in order to ensure the accuracy of the first target focal length obtained by the preliminary prediction, the number of first focal lengths needs to be increased. Therefore, the number of first focal lengths can be selected according to actual conditions, but at least two first focal lengths are required to construct a clarity curve.

[0061] Because the image can be directly acquired at the original focal length, the time of focusing is saved, so the original focal length can be used as a first focal length. In order to ensure the accuracy of the constructed clarity curve and avoid the problem of taking too much time to acquire too many images, the original focal length and two focal lengths close to the original focal length on both sides can be used as the first focal length. For example, based on the predetermined first step length, the focal length of the first step length is increased and decreased on the basis of the original focal length, thereby obtaining two first focal lengths on both sides of the original focal length. Here, the first step length can be determined based on the depth of field of the scanning electron microscope, so that the spacing between the first focal lengths is more reasonable, thereby better constructing the clarity curve.

[0062] S102: Acquire corresponding first images and corresponding sharpness at respective first focal lengths of the scanning electron microscope.

[0063] After determining multiple first focal lengths in the above steps, it is necessary to adjust the scanning electron microscope to the corresponding first focal length, and then obtain the first image at the first focal length, and simultaneously obtain the clarity of the first image. When obtaining the image clarity, Fourier transform can be used to evaluate the image clarity by calculating the image kurtosis and skewness in the frequency domain; the secondary electron signal intensity or image sharpness of the image can also be collected for evaluation. There is no specific limitation here, and it can be selected according to the actual situation. The same is true for the evaluation of image clarity below.

[0064] In addition, because the scanning electron microscope needs to be adjusted to the corresponding focal length to acquire an image, there is a problem of the adjustment order between different focal lengths. In the specific implementation process, the adjustment order of each focal length is not limited, and the next focal length can be selected based on the distance between the current focal length and other focal lengths.

[0065] S103: Inputting each first focal length and the clarity of each first image into a first prediction model to predict a first target focal length.

[0066] Because the image clarity of the scanning electron microscope changes regularly according to different focal lengths, after obtaining at least two first focal lengths and corresponding image clarity, the image clarity curve of the scanning electron microscope at each focal length can be constructed through the first prediction model.

[0067] The clarity curve of a scanning electron microscope is similar to a Gaussian curve and a quadratic curve, so the first prediction model can be a Gaussian model or a quadratic curve model. The purpose of building a model is to predict the focal length corresponding to the highest image clarity of the scanning electron microscope. Therefore, the clarity curve can be built through the first prediction model, and the extreme point of the clarity curve can be found. The focal length corresponding to the extreme point is the predicted first target focal length.

[0068] S104: Determine a plurality of second focal lengths based on the first target focal length.

[0069] The first target focal length predicted in S103 is only the focal length corresponding to the highest image clarity obtained by preliminary prediction, and its accuracy is limited. This is because the reference information is limited when selecting the first focal length, and taking too many first focal lengths will lead to too long focusing time.

[0070] The purpose of the preliminary prediction of the first target focal length in the embodiment of the present application is to quickly obtain more information, that is, to roughly determine the central symmetric point (first target focal length) of the clarity curve, so as to re-take multiple second focal lengths based on the first target focal length to perform focal length prediction again. Although the accuracy of the preliminary predicted first target focal length is limited, it is sufficient as a reference point for taking the second focal length. Through the first target focal length, multiple points evenly distributed on the clarity curve of the scanning electron microscope can be found, thereby achieving a more accurate secondary prediction.

[0071] The selection of the second focal length is not specifically limited, and a point can be selected according to the actual situation. In order to ensure that the selection of the second focal length is more referenceable, so as to construct a more accurate clarity curve, at least one focal length greater than the first target focal length and at least one focal length less than the first target focal length are selected as the second focal length. And the first target focal length, as the central symmetric point of the initially predicted curve, can also be used as the second focal length.

[0072] Because the second prediction needs to obtain a more accurate focal length corresponding to the highest image clarity, the number of selected second focal lengths is generally greater than the number of first focal lengths. In addition, since the image and its clarity at the first focal length have been obtained, in order to save focusing time, the information obtained at the first focal length can be reused in the second prediction. And because the first focal length may be distributed on one side of the central symmetric point of the clarity curve, in order to construct the curve more accurately, the first target focal length can be used as the central symmetric point, and the focal lengths symmetrical to the first focal length can be taken, and these focal lengths can also be used as the second focal length.

[0073] S105: Acquire corresponding second images and corresponding sharpness at each second focal length of the scanning electron microscope.

[0074] After the second focal length is determined, the image clarity can be evaluated by calculating the image kurtosis and skewness in the frequency domain, collecting the secondary electron signal intensity of the image, or calculating the image sharpness. If the second focal length overlaps with the first focal length, the information of the first focal length can be directly reused.

[0075] S106: Input each second focal length and the clarity of each second image into a second prediction model to predict a second target focal length.

[0076] The second prediction is similar to the initial prediction. The second prediction model can be a Gaussian model or a quadratic curve model, that is, a clarity curve is constructed based on a Gaussian curve or a quadratic curve. A more accurate clarity curve can be constructed through a suitable model. The structure of the second prediction model may be the same as the first prediction model; however, since the second focal length taken in the second prediction is usually greater than the first focal length, the structure of the second prediction model needs to be adjusted accordingly.

[0077] The second prediction model constructs a clarity curve through each second focal length and the clarity of each second image, and the second target focal length is the focal length corresponding to the extreme point in the clarity curve constructed by the second prediction model.

[0078] S107: Based on the second target focal length, the scanning electron microscope is adjusted to obtain the target focal length.

[0079] Through the secondary prediction, a relatively accurate second target focal length has been obtained. The second target focal length can be directly used as the target focal length corresponding to the highest image clarity of the scanning electron microscope, and the scanning electron microscope can be adjusted to the second target focal length.

[0080] In some embodiments, in order to further improve the accuracy of autofocus, the image clarity of the second target focal length and its nearby focal lengths can be obtained, and the focal length corresponding to the highest image clarity can be found by comparing the image clarity, and used as the final target focal length, and then the scanning electron microscope is adjusted to obtain the target focal length.

[0081] The focusing method of the scanning electron microscope provided in the embodiment of the present application obtains the first image and the image clarity respectively based on multiple first focal lengths determined by the original focal length of the scanning electron microscope. Because the image clarity of different focal lengths changes according to a rule, a clarity curve can be constructed to obtain the first target focal length corresponding to the extreme point of the curve. The first target focal length is the focal length with the highest image clarity predicted by the model. Then, based on the multiple second focal lengths determined by the first target focal length, the second image and the image clarity are obtained respectively, and the clarity curve is constructed again based on the model to obtain the second target focal length corresponding to the extreme point; finally, high-precision automatic focusing is achieved. This solution can achieve high-precision real-time focusing by predicting the focal length twice in one focusing process, especially under high magnification conditions, while ensuring real-time focusing, it can improve focusing accuracy. For scanning electron microscopes, it can improve performance; for scanning electron beam equipment, it can greatly improve equipment throughput and enhance equipment performance competitiveness.

[0082] In the above embodiments, it is mentioned that the present application does not limit the selection scheme of the first focal length, but an unreasonable selection method will not only increase the focusing time, but also affect the focusing accuracy. Therefore, this embodiment provides a specific scheme, based on the original focal length of the scanning electron microscope, to determine multiple first focal lengths, including:

[0083] First, based on the current target depth of field of the scanning electron microscope, the first step length is determined; for example, the target depth of field can be multiplied by a preset multiple to obtain the first step length; the preset multiple is determined according to actual needs and is generally not less than 2. Then, the original focal length is adjusted according to the first step length to obtain at least one third focal length less than the original focal length and at least one fourth focal length greater than the original focal length; for example, the first step length can be reduced from the original focal length to obtain the third focal length, and the first step length can be increased from the original focal length to obtain the fourth focal length. Finally, multiple first focal lengths are determined based on the original focal length, at least one third focal length, and at least one fourth focal length.

[0084] The embodiment of the present application selects focal lengths on both sides of the original focal length, and then combines the original focal lengths and inputs them into the first prediction model, so that a sharpness curve can be initially constructed more accurately by selecting a smaller number of first focal lengths, thereby saving the focusing time and ensuring the focusing accuracy. In addition, the embodiment also determines a more appropriate first focal length by the depth of field, ensuring that the selection of the first focal length and the second focal length is more reasonable.

[0085] Similar to the scheme for determining the first focal length, the embodiment of the present application also does not limit the scheme for determining the second focal length. The embodiment of the present application provides an implementation method for determining multiple second focal lengths based on the first target focal length, including:

[0086] First, a first focal length difference between the third focal length and the first target focal length, and a second focal length difference between the fourth focal length and the first target focal length are obtained. Then, based on the first focal length difference and the second focal length difference, at least one fifth focal length that is smaller than the first target focal length is determined; and based on the first focal length difference and the second focal length difference, at least one sixth focal length that is larger than the first target focal length is determined. Finally, multiple second focal lengths are determined based on the first target focal length, at least one fifth focal length, and at least one sixth focal length.

[0087] There are three size relationships between the third focal length and the fourth focal length and the first target focal length. Relationship 1: both the third focal length and the fourth focal length are greater than the first target focal length; Relationship 2: both the third focal length and the fourth focal length are less than the first target focal length; Relationship 3: one of the third focal length and the fourth focal length is greater than the first target focal length, and the other is less than the second target focal length.

[0088] One of the second focal length determination schemes is that the fifth focal length and the sixth focal length are symmetrically distributed on both sides of the first target focal length. The fifth focal length and the sixth focal length are symmetrically distributed on both sides of the first target focal length, and the points for constructing the clarity curve are evenly distributed, which can construct a more accurate clarity, thereby improving the accuracy of focusing. For example, the third focal length, the fourth focal length and the first target focal length are directly used as the second focal length; then the first target focal length is used as the central symmetry point, and the focal lengths symmetrical to the third focal length and the fourth focal length are taken, and these focal lengths are also used as the second focal length. In actual application, it can be achieved by calculating the difference, that is, after obtaining the first focal length difference and the second focal length difference, the first target focal length is increased and decreased by the first focal length difference and the second focal length difference, that is, the above-mentioned second focal lengths are obtained.

[0089] The embodiment of the present application determines multiple second focal lengths by preliminarily predicting the first target focal length, so that the second focal lengths are distributed on both sides of the first target focal length, ensuring the rationality of the focal lengths, so that a more accurate clarity curve can be constructed by acquiring only a few images, thereby improving the accuracy of focusing.

[0090] In the specific implementation process, after obtaining the second target focal length, the second target focal length can be directly used as the final target focal length. However, in actual applications, the determined second target focal length may still have deviations. Therefore, the embodiment of the present application provides an implementation scheme that can further improve the focusing accuracy.

[0091] First, based on the second target focal length, multiple seventh focal lengths are determined; the seventh focal length is generally a focal length near the second target focal length, and the actual value can be determined based on the specific focal length range of the scanning electron microscope. Then, at each seventh focal length of the scanning electron microscope, the corresponding third image and the corresponding clarity are obtained; by comparing the clarity of each third image, the target image corresponding to the highest clarity is obtained. Finally, the seventh focal length corresponding to the target image is determined as the target focal length, and the scanning electron microscope is adjusted to the target focal length.

[0092] After determining the second target focal length, the embodiment of the present application has roughly obtained the range of the optimal focal length. By comparing the clarity of images corresponding to multiple focal lengths within this focal length range, a better focal length can be found, further improving the focusing accuracy.

[0093] As mentioned above, the first step length can be obtained by multiplying the current target depth of field of the scanning electron microscope by the preset magnification. The preset magnification can be selected according to the actual situation, and the current target depth of field of the scanning electron microscope is related to its current target magnification. In order to obtain the first step length, it is necessary to first obtain the current target magnification of the scanning electron microscope; then, based on the target magnification and the corresponding relationship between the depth of field and magnification of the scanning electron microscope, the target depth of field is determined.

[0094] The embodiment of the present application utilizes the correspondence between the depth of field and the magnification of the scanning electron microscope to accurately determine the target depth of field, and combines the depth of field, magnification and focusing process together, thereby achieving high-precision adaptive focusing.

[0095] The above embodiment mentioned that it is necessary to determine multiple seventh focal lengths based on the second target focal length. The seventh focal length is to further improve the focusing accuracy. Selecting too many seventh focal lengths will increase the focusing time. Therefore, in order to improve efficiency, generally only a small number of seventh focal lengths are selected. In the case of a small number, in order to ensure the focusing effect, a more appropriate selection method needs to be adopted. A specific implementation scheme is provided below.

[0096] Because the second target focal length is the focal length corresponding to the highest definition obtained by the second prediction, the second target focal length can be directly used as the seventh focal length. Then, based on the target depth of field, the second step length is determined, and based on the second step length, at least one eighth focal length greater than the second target focal length is determined; and based on the second step length, at least one ninth focal length less than the second target focal length is determined; finally, the second target focal length, at least one eighth focal length, and at least one ninth focal length are determined as the seventh focal length.

[0097] For example, the target depth of field determined in the foregoing may be directly used as the second step length, and then the second target focal length may be increased by the second step length to obtain an eighth focal length, and the second target focal length may be reduced by the second step length to obtain a ninth focal length.

[0098] The embodiment of the present application selects a reasonable second step length through the depth of field, and selects multiple focal lengths on both sides of the second target focal length, so as to efficiently find a focal length with higher image clarity.

[0099] The focusing method of the present application is described below in conjunction with a specific embodiment. Figure 2 FIG. 1 is a flow chart of a complete focusing method provided by an embodiment of the present application; Figure 2 As shown, the following steps are included:

[0100] S201: Construct a mathematical model between the depth of field and magnification of a scanning electron microscope.

[0101] First, the corresponding relationship between the depth of field and the magnification is determined according to the properties of the scanning electron microscope itself, so as to construct a mathematical model between the depth of field and the magnification. The mathematical model is as follows:

[0102]

[0103] β is the divergence of the electron beam of the SEM, and M is the current magnification of the SEM.

[0104] S202: Adaptively adjust the focus according to the magnification, collect images and their clarity, and use the Gaussian model to make a preliminary focal length prediction.

[0105] Determine the depth of field of the scanning electron microscope under the current conditions based on the magnification After that, the first step length Δd in the focusing process is further determined, as shown in formula (2);

[0106]

[0107] The preset magnification n is set according to the stability of the focal length of the device platform and is generally required to be greater than or equal to 2.

[0108] Figure 3 FIG. 4 shows a schematic diagram of a clarity curve predicted by a first prediction model provided in an embodiment of the present application; Figure 3 As shown, a Gaussian regression model is used as the first prediction model to obtain the image clarity at the first focal lengths d, d1, and d2, and then input into the Gaussian regression model to predict the corresponding clarity curve, and then preliminarily predict the first target focal length μ. The following is an explanation with reference to a specific formula.

[0109] According to the determined first step length Δd, the focal length of the scanning electron microscope is adjusted by the following formula: d1=d+Δd and d2=d-Δd, d is the current original focal length, three first images are correspondingly collected at focal lengths d, d1, and d2, and the clarity of the first images is evaluated.

[0110] According to the image clarity evaluation results, the Gaussian model is used to predict the first target focal length μ.

[0111]

[0112] is the distance between the original focal length and the predicted first target focal length, f(x) is the image clarity at focal length x, and σ is the parameter of the Gaussian model.

[0113] S203: Adaptive focusing is performed again according to the information obtained from the preliminary prediction, the image and its clarity are collected, and a second focal length prediction is performed using the Gaussian model.

[0114] Based on the preliminary predicted first target focal length, the second focal length d3=μ is determined. and Three second images are collected accordingly, and then the image clarity is evaluated. In addition, d1 and d2 are also used as the second focal length, and the corresponding images are also second images.

[0115] Based on the clarity evaluation results of the five second images, the second target focal length d6 is predicted using a Gaussian regression model.

[0116] S204: Adaptively change the focus step size using the depth of field, focus again near the secondary predicted focal length, and determine the final target focal length.

[0117] Figure 4 FIG. 4 shows a schematic diagram of a clarity curve of a second prediction model provided by an embodiment of the present application; Figure 4 As shown in the figure, the horizontal axis is the focal length and the vertical axis is the clarity index. By obtaining the image clarity corresponding to the five second focal lengths, the Gaussian regression model is used as the second prediction model to construct the clarity curve. Finally, the second target focal length is predicted.

[0118] According to the depth of field determined above, the second step length in the adaptive focus adjustment process is determined. Then determine the three seventh focal lengths: d6, d7 and d8; d7 = d6-Δd1, d8 = d6+Δd1, collect three third images accordingly, and evaluate the image clarity. Find the focal length corresponding to the clearest third image as the final target focal length of the scanning electron microscope.

[0119] The embodiment of the present application proposes a real-time focusing method for a scanning electron microscope, which can achieve faster focusing while ensuring high precision at high magnification. First, a mathematical model between the depth of field and magnification of the scanning electron microscope is constructed, and the focus is adaptively adjusted according to the magnification. Focusing data is collected twice, and then the focal plane is predicted using a Gaussian model; then the focusing step is adaptively adjusted according to the magnification, and images are collected under multiple predicted scanning electron microscope conditions. The focal plane is finally accurately located using a Gaussian regression model based on the image clarity evaluation data. In a focusing process, this scheme combines the magnification, depth of field and focusing process of the electron scanning microscope by constructing a mathematical model between the depth of field and magnification of the scanning electron microscope, and realizes adaptive change of the focusing step, thereby improving focusing accuracy while focusing in real time at high magnification.

[0120] In order to solve the above technical problems, the present application also provides a focusing device for a scanning electron microscope. Figure 5 FIG. 1 is a schematic diagram showing the structure of a focusing device for a scanning electron microscope provided in an embodiment of the present application. Figure 5 As shown, the device includes the following modules:

[0121] A first determination module 501 is used to determine a plurality of first focal lengths based on an original focal length of the scanning electron microscope;

[0122] A first acquisition module 502 is used to acquire corresponding first images and corresponding sharpness at each first focal length of the scanning electron microscope;

[0123] The first prediction module 503 is used to input each first focal length and the clarity of each first image into a first prediction model to predict a first target focal length; the first target focal length is the focal length corresponding to the extreme point in the clarity curve constructed by the first prediction model;

[0124] A second determination module 504 is used to determine a plurality of second focal lengths based on the first target focal length; the second focal lengths at least include at least one focal length greater than the first target focal length and at least one focal length less than the first target focal length;

[0125] A second acquisition module 505 is used to acquire corresponding second images and corresponding sharpness at each second focal length of the scanning electron microscope;

[0126] The second prediction module 506 is used to input each second focal length and the clarity of each second image into a second prediction model to predict a second target focal length; the second target focal length is the focal length corresponding to the extreme point in the clarity curve constructed by the second prediction model;

[0127] The adjustment module 507 is used to adjust the scanning electron microscope based on the second target focal length to obtain the target focal length.

[0128] In some embodiments, the first determining module is specifically configured to:

[0129] Determine the first step length based on the current target depth of field of the SEM;

[0130] The original focal length is adjusted according to the first step to obtain at least one third focal length smaller than the original focal length and at least one fourth focal length larger than the original focal length;

[0131] A plurality of first focal lengths are determined based on the original focal length, at least one third focal length, and at least one fourth focal length.

[0132] In some embodiments, the second determining module is specifically configured to:

[0133] Obtaining a first focal length difference between the third focal length and the first target focal length, and a second focal length difference between the fourth focal length and the first target focal length;

[0134] Determining at least one fifth focal length that is smaller than the first target focal length based on the first focal length difference and the second focal length difference;

[0135] Determining at least one sixth focal length greater than the first target focal length based on the first focal length difference and the second focal length difference;

[0136] A plurality of second focal lengths are determined based on the first target focal length, at least one fifth focal length, and at least one sixth focal length.

[0137] In some embodiments, the fifth focal length and the sixth focal length are symmetrically distributed on both sides of the first target focal length.

[0138] In some embodiments, the first determination module is specifically configured to multiply the target depth of field by a preset multiple to obtain the first step length.

[0139] In some embodiments, the focusing device of the electron microscope further includes:

[0140] A third acquisition module is used to acquire the current target magnification of the scanning electron microscope before multiplying the target depth of field by a preset multiple to obtain the first step length;

[0141] The third determination module is used to determine the target depth of field based on the target magnification and the corresponding relationship between the depth of field and the magnification of the scanning electron microscope.

[0142] In some embodiments, the adjustment module is specifically configured to:

[0143] determining a plurality of seventh focal lengths based on the second target focal length;

[0144] Acquire a corresponding third image and a corresponding definition at each seventh focal length of the scanning electron microscope;

[0145] Comparing the clarity of each third image to obtain a target image corresponding to the highest clarity;

[0146] The seventh focal length corresponding to the target image is determined as the target focal length;

[0147] Adjust the scanning electron microscope to the target focus.

[0148] In some embodiments, the adjustment module is specifically configured to:

[0149] Based on the target depth of field, determine the second step length;

[0150] determining, based on the second step length, at least one eighth focal length that is greater than the second target focal length;

[0151] determining, based on the second step length, at least one ninth focal length that is smaller than the second target focal length;

[0152] The second target focal length, at least one eighth focal length, and at least one ninth focal length are determined as the seventh focal length.

[0153] In some embodiments, the first prediction model and the second prediction model are Gaussian models or quadratic curve models.

[0154] The device provided in the embodiment of the present application is the same as the method in the above embodiment, so both have the same embodiments and beneficial effects, which will not be repeated here.

[0155] Figure 6 FIG. 1 is a schematic diagram showing the hardware structure of a focusing device for a scanning electron microscope provided in an embodiment of the present application. Figure 6 As shown, the focusing device of the scanning electron microscope may include a processor 601 and a memory 602 storing computer program instructions.

[0156] Specifically, the processor 601 may include a central processing unit (CPU), or an application specific integrated circuit (ASIC), or may be configured to implement one or more integrated circuits of the embodiments of the present application.

[0157] The memory 602 may include a large capacity memory for data or instructions. By way of example and not limitation, the memory 602 may include a hard disk drive (HDD), a floppy disk drive, a flash memory, an optical disk, a magneto-optical disk, a magnetic tape, or a universal serial bus (USB) drive or a combination of two or more of these. In appropriate cases, the memory 602 may include a removable or non-removable (or fixed) medium. In appropriate cases, the memory 602 may be inside or outside the integrated gateway disaster recovery device. In a specific embodiment, the memory 602 is a non-volatile solid-state memory.

[0158] The memory 602 may include a read-only memory (ROM), a random access memory (RAM), a magnetic disk storage medium device, an optical storage medium device, a flash memory device, an electrical, optical or other physical / tangible memory storage device. Therefore, generally, the memory includes one or more tangible (non-transitory) computer-readable storage media (e.g., a memory device) encoded with software including computer-executable instructions, and when the software is executed (e.g., by one or more processors), it is operable to perform the operations described with reference to the method according to one aspect of the present disclosure.

[0159] The processor 601 reads and executes the computer program instructions stored in the memory 602 to implement any one of the focusing methods for the scanning electron microscope in the above embodiments.

[0160] In one example, the focusing device of the scanning electron microscope may further include a communication interface 603 and a bus 604. The processor 601, the memory 602, and the communication interface 603 are connected via the bus 604 and communicate with each other.

[0161] The communication interface 603 is mainly used to implement communication between various modules, devices, units and / or equipment in the embodiments of the present application.

[0162] The bus 604 includes hardware, software, or both, coupling the components of the focusing device of the scanning electron microscope to each other. By way of example and not limitation, the bus may include an Accelerate Graphical Port (AGP) or other graphics bus, an Enhanced Industry Standard Architecture (EISA) bus, a Front Side Bus (FSB), a Hyper Transport (HT) interconnect, an Industry Standard Architecture (ISA) bus, an InfiniBand interconnect, a Low Pin Count (LPC) bus, a Memory bus, a Micro Channel Architecture (MCA) bus, a Peripheral Component Interconnect (PCI) bus, a PCI-Express (PCI-X) bus, a Serial Advanced Technology Attachment (SATA) bus, a Video Electronics Standards Association Local Bus (VLB) bus, or other suitable buses or a combination of two or more of the above. Where appropriate, the bus 604 may include one or more buses. Although embodiments of the present application describe and illustrate a particular bus, the present application contemplates any suitable bus or interconnect.

[0163] In addition, in combination with the focusing method of the scanning electron microscope in the above embodiment, the embodiment of the present application can provide a computer storage medium for implementation. The computer storage medium stores computer program instructions; when the computer program instructions are executed by the processor, any one of the focusing methods of the scanning electron microscope in the above embodiment is implemented.

[0164] An embodiment of the present application also provides a computer program product, including a computer program, which, when processed and executed, implements any one of the focusing methods for a scanning electron microscope in the above-mentioned embodiments.

[0165] It should be clear that the present application is not limited to the specific configuration and processing described above and shown in the figures. For the sake of simplicity, a detailed description of the known method is omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present application is not limited to the specific steps described and shown, and those skilled in the art can make various changes, modifications and additions, or change the order between the steps after understanding the spirit of the present application.

[0166] The functional blocks shown in the block diagram above can be implemented as hardware, software, firmware or a combination thereof. When implemented in hardware, it can be, for example, an electronic circuit, an ASIC, appropriate firmware, a plug-in, a function card, etc. When implemented in software, the elements of the present application are programs or code segments used to perform the required tasks. The program or code segment can be stored in a machine-readable medium, or transmitted on a transmission medium or a communication link by a data signal carried in a carrier wave. "Machine-readable medium" can include any medium capable of storing or transmitting information. Examples of machine-readable media include electronic circuits, semiconductor memory devices, ROM, flash memory, erasable ROM (Erasable ROM, EROM), floppy disks, compact disc read-only memory (Compact Disc Read-Only Memory, CD-ROM), optical discs, hard disks, optical fiber media, radio frequency (Radio Frequency, RF) links, etc. Code segments can be downloaded via computer networks such as the Internet, intranets, etc.

[0167] It should also be noted that the exemplary embodiments mentioned in this application describe some methods or systems based on a series of steps or devices. However, this application is not limited to the order of the above steps, that is, the steps can be performed in the order mentioned in the embodiment, or in a different order from the embodiment, or several steps can be performed simultaneously.

[0168] Aspects of the present disclosure are described above with reference to the flowcharts and / or block diagrams of the focusing method, device, equipment, medium and product of a scanning electron microscope according to an embodiment of the present disclosure. It should be understood that each box in the flowchart and / or block diagram and the combination of each box in the flowchart and / or block diagram can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device to produce a machine so that these instructions executed by the processor of the computer or other programmable data processing device enable the implementation of the functions / actions specified in one or more boxes of the flowchart and / or block diagram. Such a processor can be, but is not limited to, a general-purpose processor, a special-purpose processor, a special application processor or a field programmable logic circuit. It can also be understood that each box in the block diagram and / or flowchart and the combination of boxes in the block diagram and / or flowchart can also be implemented by dedicated hardware that performs a specified function or action, or can be implemented by a combination of dedicated hardware and computer instructions.

[0169] The above contents are only specific implementation methods of the present application. Those skilled in the art can clearly understand that for the convenience and simplicity of description, the specific working processes of the systems, modules and units described above can refer to the corresponding processes in the aforementioned method embodiments, and will not be repeated here. It should be understood that the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application.

Claims

1. A focusing method for a scanning electron microscope, characterized in that: include: Determining a plurality of first focal lengths based on an original focal length of the scanning electron microscope; Acquire a corresponding first image and a corresponding definition at each of the first focal lengths of the scanning electron microscope; Inputting each of the first focal lengths and the clarity of each of the first images into a first prediction model to predict a first target focal length; the first target focal length is a focal length corresponding to an extreme point in a clarity curve constructed by the first prediction model; Based on the first target focal length, determining a plurality of second focal lengths; the second focal lengths at least include at least one focal length greater than the first target focal length and at least one focal length less than the first target focal length; Acquire corresponding second images and corresponding sharpness at each of the second focal lengths of the scanning electron microscope; Inputting each of the second focal lengths and the clarity of each of the second images into a second prediction model to predict a second target focal length; the second target focal length is the focal length corresponding to the extreme point in the clarity curve constructed by the second prediction model; Based on the second target focal length, the scanning electron microscope is adjusted to obtain a target focal length.

2. The focusing method of an electron microscope according to claim 1, characterized in that: The step of determining a plurality of first focal lengths based on an original focal length of the scanning electron microscope comprises: Determining a first step length based on a current target depth of field of the scanning electron microscope; The original focal length is adjusted according to the first step to obtain at least one third focal length smaller than the original focal length and at least one fourth focal length larger than the original focal length; A plurality of first focal lengths are determined according to the original focal length, at least one of the third focal lengths and at least one of the fourth focal lengths.

3. The focusing method of an electron microscope according to claim 2, characterized in that: The determining a plurality of second focal lengths based on the first target focal length comprises: Acquire a first focal length difference between the third focal length and the first target focal length, and a second focal length difference between the fourth focal length and the first target focal length; Determining at least one fifth focal length that is smaller than the first target focal length based on the first focal length difference and the second focal length difference; Determining at least one sixth focal length greater than the first target focal length based on the first focal length difference and the second focal length difference; A plurality of the second focal lengths are determined based on the first target focal length, at least one of the fifth focal lengths, and at least one of the sixth focal lengths.

4. The focusing method of an electron microscope according to claim 3, characterized in that: The fifth focal length and the sixth focal length are symmetrically distributed on both sides of the first target focal length.

5. The focusing method of an electron microscope according to claim 2, characterized in that: The step of determining the first step length based on the current target depth of field of the scanning electron microscope comprises: The target depth of field is multiplied by a preset multiple to obtain the first step length.

6. The focusing method of an electron microscope according to claim 5, characterized in that: Before multiplying the target depth of field by a preset multiple to obtain the first step length, the method further includes: Obtaining a current target magnification of the scanning electron microscope; The target depth of field is determined based on the target magnification and a corresponding relationship between the depth of field and the magnification of the scanning electron microscope.

7. The focusing method of an electron microscope according to claim 6, characterized in that: The step of adjusting the scanning electron microscope based on the second target focal length to obtain a target focal length includes: determining a plurality of seventh focal lengths based on the second target focal length; Acquire a corresponding third image and a corresponding definition at each of the seventh focal lengths of the scanning electron microscope; Comparing the clarity of each of the third images to obtain a target image corresponding to the highest clarity; Determine the seventh focal length corresponding to the target image as the target focal length; The scanning electron microscope was adjusted to the target focus.

8. The focusing method of an electron microscope according to claim 7, characterized in that: The step of determining a plurality of seventh focal lengths based on the second target focal length comprises: Based on the target depth of field, determining a second step length; determining, based on the second step length, at least one eighth focal length that is greater than the second target focal length; determining, based on the second step length, at least one ninth focal length that is smaller than the second target focal length; The second target focal length, at least one of the eighth focal lengths, and at least one of the ninth focal lengths are determined as the seventh focal length.

9. The focusing method of an electron microscope according to any one of claims 1 to 8, characterized in that: The first prediction model and the second prediction model are Gaussian models or quadratic curve models.

10. A focusing device for an electron microscope, characterized in that: include: a processor and a memory storing computer program instructions; When the processor executes the computer program instructions, the focusing method of the electron microscope as described in any one of claims 1 to 9 is implemented.

11. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer program instructions, and when the computer program instructions are executed by a processor, the focusing method of an electron microscope as described in any one of claims 1 to 9 is implemented.

12. A computer program product, characterized in that When the instructions in the computer program product are executed by a processor of an electronic device, the electronic device executes the focusing method of an electron microscope as described in any one of claims 1 to 9.

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