Image defocus monitoring method and system

Abstract

The invention relates to an image defocus monitoring method and system. The image defocusing monitoring method comprises the following steps: providing a target wafer, and obtaining an electron beam measurement image of the target wafer and a target gray value standard deviation of the electron beam measurement image; and when the standard deviation of the target gray value is smaller than an image defocusing threshold value, carrying out image defocusing early warning. According to the method and the device, the image defocusing problem is monitored based on the gray value standard deviation of the image, so that the error early warning rate of the wafer machine is reduced, and the image defocusing problem can be accurately monitored in real time.

Description

Technical Field

[0001] The present application relates to the field of semiconductor testing, and in particular to a method and system for monitoring image defocus. Background Art

[0002] In the current semiconductor testing field, the sharpness of the image to be tested is usually measured to monitor the image defocus in the wafer. For example, a lower limit value of sharpness is set; if the sharpness values ​​of multiple images to be tested in a wafer are lower than the lower limit value, it is determined that there is an image defocus problem in the wafer, and a wafer machine warning is issued.

[0003] However, in conventional image defocus monitoring methods, each image to be tested only outputs a single sharpness value (sharpness), which makes it difficult to eliminate measurement inaccuracies caused by environmental factors and other issues, thereby reducing the accuracy of monitoring image defocus problems. In addition, the setting of the lower limit of sharpness depends on human judgment, which can easily lead to image defocus misjudgment caused by inaccurate setting of the lower limit of sharpness; for example, if the lower limit of sharpness is set too high, the focused image will be misjudged as a defocused image, resulting in an excessively high warning rate for the wafer machine; if the lower limit of sharpness is set too low, the defocused image will be misjudged as a focused image, making it difficult to accurately monitor the image defocus problem, thereby reducing the accuracy of monitoring the image defocus problem. Summary of the invention

[0004] Based on this, an embodiment of the present application provides a method and system for monitoring image defocus, which monitors image defocus problems based on the standard deviation of the grayscale value of the image to reduce the false warning rate of the wafer machine, thereby facilitating accurate and real-time monitoring of image defocus problems.

[0005] In order to achieve the above-mentioned purpose, on the one hand, some embodiments of the present application provide a method for monitoring image defocus. The method for monitoring image defocus includes: providing a target wafer, obtaining an electron beam measurement image of the target wafer and a target grayscale value standard deviation of the electron beam measurement image; when the target grayscale value standard deviation is less than an image defocus threshold, performing an image defocus warning.

[0006] In some embodiments, before providing a target wafer and obtaining an electron beam measurement image of the target wafer and a target grayscale value standard deviation of the electron beam measurement image, the image defocus monitoring method also includes: providing a reference wafer and obtaining sampled images of multiple specified areas in the reference wafer; determining a reference image from multiple sampled images based on the clarity of each sampled image; obtaining a reference grayscale value standard deviation of the reference image, and determining an image defocus threshold based on the reference grayscale value standard deviation.

[0007] In some embodiments, a reference image is determined from a plurality of sampled images based on the clarity of each sampled image, including: setting a critical clarity index; comparing the clarity index of each sampled image with the critical clarity index, and determining the sampled image corresponding to the clarity index having the smallest difference with the critical clarity index among the clarity indexes as the reference image.

[0008] In some embodiments, the method of obtaining a baseline grayscale value standard deviation of a baseline image and determining an image defocus threshold based on the baseline grayscale value standard deviation includes: obtaining a first grayscale value histogram of the baseline image; calculating a baseline grayscale value standard deviation of the baseline image based on the first grayscale value histogram; and determining the image defocus threshold based on the baseline grayscale value standard deviation of the baseline image.

[0009] In some embodiments, the number of electron beam measurement images is greater than the number of sampled images; the image defocus monitoring method further includes: after measuring the target wafer, redetermining the reference image; and redetermining the image defocus threshold value according to the target gray value standard deviation of the redetermined reference image.

[0010] In some embodiments, after measuring the target wafer, the reference image is re-determined, including: after measuring the target wafer, the clarity index of the electron beam measurement image of the sampling image whose difference between the gray value standard deviation and the image defocus threshold is within a preset range is compared with the clarity critical index, and the electron beam measurement image corresponding to the clarity index with the smallest difference between the clarity critical index and the clarity critical index is re-determined as the reference image.

[0011] In some embodiments, the reference wafer comprises: a first wafer in a wafer batch.

[0012] In some embodiments, the target wafer also includes: other wafers other than the first wafer in the wafer batch; wherein, the judgment of the image defocus warning of other wafers is performed based on the re-determined image defocus threshold.

[0013] In some embodiments, the plurality of designated areas are evenly located on portions of the reference wafer in upper, middle, lower, left, and right directions.

[0014] In some embodiments, providing a target wafer, obtaining an electron beam measurement image of the target wafer and a target grayscale value standard deviation of the electron beam measurement image include: obtaining an electron beam measurement image of the target wafer; obtaining a second grayscale value histogram of the electron beam measurement image; and calculating the target grayscale value standard deviation of the electron beam measurement image according to the second grayscale value histogram.

[0015] On the other hand, the present disclosure also provides an image defocus monitoring system according to some embodiments; the monitoring system includes an image acquisition device, an image processing module, a threshold determination module and a controller; the image acquisition device is used to acquire sampling images of multiple specified areas in a reference wafer; and, is also used to acquire electron beam measurement images of a target wafer; the image processing module is connected to the image acquisition device, and is used to determine a reference image from multiple sampling images according to the clarity of each sampling image, and to acquire a reference grayscale value standard deviation of the reference image; and, is also used to acquire a target grayscale value standard deviation of the electron beam measurement image; the threshold determination module is connected to the image processing module, and is used to determine an image defocus threshold according to the reference grayscale value standard deviation; the controller is connected to the image processing module, the threshold determination module and the wafer machine, and is used to issue an image defocus warning and control the wafer machine to shut down when the target grayscale value standard deviation is less than the image defocus threshold.

[0016] In some embodiments, the image processing module includes a reference image determination unit; the reference image determination unit is connected to the image acquisition device and the threshold determination module; the reference image determination unit is used to compare the clarity index of each sampled image with the set clarity critical index, and determine the sampled image corresponding to the clarity index with the smallest difference between the clarity critical index and the clarity critical index as the reference image.

[0017] In some embodiments, the reference wafer includes the first wafer in the wafer batch, and the target wafer includes other wafers other than the first wafer in the wafer batch; the number of electron beam measurement images is greater than the number of sampling images; the reference image determination unit is also used to redetermine the reference image after measuring the target wafer; the threshold determination module is also used to redetermine the image defocus threshold based on the target grayscale value standard deviation of the redetermined reference image; the controller is also used to judge the image defocus warning of other wafers based on the redetermined image defocus threshold.

[0018] In some embodiments, the reference image determination unit is also used to compare the clarity index of the electron beam measurement image of the sampled image whose difference between the gray value standard deviation and the image defocus threshold is within a preset range with the clarity critical index after measuring the target wafer, and to re-determine the electron beam measurement image corresponding to the clarity index having the smallest difference with the clarity critical index among the clarity indicators as the reference image.

[0019] In some embodiments, the image processing module also includes an acquisition unit and a calculation unit; the acquisition unit is connected to the image acquisition device and the reference image determination unit; the acquisition unit is used to acquire a first grayscale value histogram of the reference image; and the acquisition unit is also used to acquire a second grayscale value histogram of the electron beam measurement image; the calculation unit is connected to the acquisition unit, the threshold determination module and the controller; the calculation unit is used to calculate the reference grayscale value standard deviation of the reference image based on the first grayscale value histogram; and the calculation unit is also used to calculate the target grayscale value standard deviation of the electron beam measurement image based on the second grayscale value histogram.

[0020] The embodiments of the present application may or at least have the following advantages:

[0021] In an embodiment of the present application, a target grayscale value standard deviation of an electron beam measurement image of a target wafer is obtained, and the target grayscale value standard deviation is compared with an image defocus threshold. Since the grayscale value standard deviation of an image is negatively correlated with its defocus degree, when the target grayscale value standard deviation is less than the image defocus threshold, it is determined that a defocused image has been monitored. In this way, the electron beam measurement image of the target wafer is monitored in real time, and an image defocus warning is promptly issued when the target grayscale value standard deviation is less than the image defocus threshold. This not only enables real-time monitoring of whether the electron beam measurement image is defocused, but also effectively reduces the false warning rate of the wafer machine, thereby achieving accurate monitoring of the image defocus condition, which is beneficial to improving the wafer product yield.

[0022] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 A schematic flow chart of a method for monitoring image defocus provided in some embodiments;

[0025] Figure 2 A schematic flow chart of another method for monitoring image defocus provided in some embodiments;

[0026] Figure 3 is a flow chart of step S220 provided in some embodiments;

[0027] Figure 4is a flow chart of step S230 provided in some embodiments;

[0028] Figure 5 A schematic flow chart of an optimization process of a method for monitoring image defocus provided in some embodiments;

[0029] Figure 6 is a flowchart of step S110 provided in some embodiments;

[0030] Figure 7 A schematic diagram of the structure of a reference wafer provided in some embodiments;

[0031] Figure 8 Figure (a) is a schematic diagram of multiple sample images provided in some embodiments. Figure 8 Figure (b) is a fitting curve of the standard deviation of the gray values ​​of multiple sampled images shown in Figure (a);

[0032] Fig. 9 Figure (a) is a schematic diagram of a reference image provided in some embodiments. Fig. 9 Figure (b) is a first gray value histogram of the reference image shown in Figure (a);

[0033] Fig.10 A fitting curve of target grayscale value standard deviations of a plurality of electron beam measurement images provided in some embodiments;

[0034] Fig.11 is a structural block diagram of an image defocus monitoring system provided in some embodiments;

[0035] Fig.12 is a structural block diagram of another image defocus monitoring system provided in some embodiments;

[0036] Fig.13 This is a structural block diagram of yet another image defocus monitoring system provided in some embodiments.

[0037] Description of reference numerals:

[0038] W1-reference wafer, A1, A2, A3, A4, A5-specified areas, E-sampling image, S-reference image, SPEC-image defocus threshold, 1-image acquisition device, 2-image processing module, 21-reference image determination unit, 22-acquisition unit, 23-calculation unit, 3-threshold determination module, 4-controller, 41-comparison unit, 42-image defocus warning unit, M-wafer machine, EAP-equipment automation system. DETAILED DESCRIPTION

[0039] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are given in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0041] It should be understood that when an element or layer is referred to as being "on," "adjacent to," or "connected to" other elements or layers, it may be directly on, adjacent to, connected to, or coupled to other elements or layers, or there may be intervening elements or layers. It should be understood that, although the terms first, second, third, etc. may be used to describe various elements, components, regions, layers, doping types, and / or portions, these elements, components, regions, layers, doping types, and / or portions should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, doping type, or portion from another element, component, region, layer, doping type, or portion. Therefore, without departing from the teachings of the present application, the first element, component, region, layer, doping type, or portion discussed below may be represented as a second element, component, region, layer, or portion.

[0042] When used herein, the singular forms "a", "an", and "said / the" may also include plural forms, unless the context clearly indicates otherwise. It should also be understood that when the terms "consisting of" and / or "comprising" are used in this specification, the presence of the features, integers, steps, operations, elements and / or parts can be determined, but the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups is not excluded. At the same time, when used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0043] Embodiments of the invention are described herein with reference to cross-sectional views that are schematic representations of idealized embodiments (and intermediate structures) of the present application, such that variations in the shapes shown due to, for example, manufacturing techniques and / or tolerances are anticipated. Embodiments of the present application should not be limited to the specific shapes of the regions shown herein, but include deviations in shapes due to, for example, manufacturing techniques. Therefore, the regions shown in the figures are schematic in nature, their shapes do not represent the actual shapes of the regions of the device, and do not limit the scope of the present application.

[0044] The embodiments of the present application provide a method and system for monitoring image defocus, which monitors image defocus problems based on the standard deviation of the grayscale value of the image to reduce the false warning rate of the wafer machine, thereby facilitating accurate and real-time monitoring of image defocus problems.

[0045] In some embodiments, see Figure 1 The image defocus monitoring method includes the following steps S110~S120.

[0046] S110, providing a target wafer, obtaining an electron beam measurement image of the target wafer and a target grayscale value standard deviation of the electron beam measurement image.

[0047] S120, when the target gray value standard deviation is less than the image defocus threshold, an image defocus warning is issued.

[0048] It should be noted that the image defocus threshold refers to the gray value standard deviation threshold used to determine whether the electron beam measurement image is defocused. For example, when the target gray value standard deviation is greater than or equal to the image defocus threshold, the corresponding electron beam measurement image is determined to be a focused image; when the gray value standard deviation is less than the image defocus threshold, the corresponding electron beam measurement image is determined to be a defocused image.

[0049] In an embodiment of the present application, a target grayscale value standard deviation of an electron beam measurement image of a target wafer is obtained, and the target grayscale value standard deviation is compared with an image defocus threshold value; since the grayscale value standard deviation of an image is negatively correlated with its defocus degree, when the target grayscale value standard deviation is less than the image defocus threshold value, it is determined that a defocused image has been monitored; in this way, the electron beam measurement image of the target wafer is monitored in real time, and an image defocus warning is issued when the target grayscale value standard deviation is less than the image defocus threshold value. Therefore, not only can the electron beam measurement image be monitored in real time to determine whether it is defocused, but the false warning rate of the wafer machine can also be effectively reduced, thereby achieving accurate monitoring of the image defocus condition, which is beneficial to improving the wafer product yield.

[0050] In some embodiments, see Figure 2 Before step S110, the image defocus monitoring method further includes the following steps S210 to S230.

[0051] S210, providing a reference wafer, and acquiring sampling images of a plurality of designated areas in the reference wafer.

[0052] S220: Determine a reference image from a plurality of sample images according to the clarity of each sample image.

[0053] S230, obtaining a reference gray value standard deviation of the reference image, and determining an image defocus threshold according to the reference gray value standard deviation.

[0054] In an embodiment of the present application, a reference image is determined from sampled images of multiple specified areas in a reference wafer, and an image defocus threshold is determined based on the standard deviation of a reference grayscale value of the reference image; the image defocus threshold can be determined based on the actual conditions of each wafer product or each layer structure in the wafer, thereby effectively eliminating the adverse effects of process differences and environmental factors on the accuracy of determining the image defocus threshold, thereby improving the accuracy of determining the image defocus threshold.

[0055] In some embodiments, see Figure 3 , step S220 includes the following steps S221~S222.

[0056] S221, setting a critical clarity index.

[0057] It should be noted that, in this step, the definition critical index may be a definition index corresponding to a critical situation where the visual effect is between clear and blurred in past experience.

[0058] For example, the clarity index includes resolution, contrast, bit rate and / or sharpness, etc.

[0059] S222, comparing the clarity index of each sampled image with the clarity critical index, and determining the sampled image corresponding to the clarity index having the smallest difference with the clarity critical index among the clarity indexes as the reference image.

[0060] In some embodiments, see Figure 4 , step S230 includes the following steps S231~S233.

[0061] S231, obtaining a first grayscale value histogram of the reference image.

[0062] S232: Calculate a reference grayscale value standard deviation of the reference image according to the first grayscale value histogram.

[0063] S233, determining an image defocus threshold according to a standard deviation of a reference grayscale value of the reference image.

[0064] In an embodiment of the present application, by calculating the standard deviation of the reference grayscale value based on the first grayscale value histogram of the reference image in the reference wafer, the image processing accuracy for the reference wafer is improved, making the determination of the standard deviation of the reference grayscale value more accurate, thereby improving the determination accuracy of the image defocus threshold.

[0065] In some embodiments, the number of electron beam metrology images is greater than the number of sampling images; see Figure 5 After step S110, the image defocus monitoring method further includes the following steps S310-S320.

[0066] S310 , after measuring the target wafer, re-determine the reference image.

[0067] In some embodiments, step S310 includes: after measuring the target wafer, comparing the clarity index of the electron beam measurement image of the sampled image whose difference between the gray value standard deviation and the image defocus threshold is within a preset range with the clarity critical index, and re-determining the electron beam measurement image corresponding to the clarity index with the smallest difference between the clarity critical index and the clarity critical index as the reference image.

[0068] S320, re-determine the image defocus threshold value according to the re-determined target gray value standard deviation of the reference image.

[0069] It should be noted that the judgment of the image defocus warning of other wafers in the wafer batch except the reference wafer is performed according to the re-determined image defocus threshold. In the embodiment of the present application, steps S310~S320 are the optimization process of the image defocus threshold, which re-determines the image defocus threshold according to the clarity of each electron beam measurement image corresponding to the target wafer in the wafer process, and makes the judgment of the image defocus warning of other wafers in the wafer process determined according to the re-determined image defocus threshold; in this way, the adverse effects of process differences and environmental factors on the accuracy of determining the image defocus threshold are effectively eliminated, the accuracy of determining the image defocus threshold is improved, and the false warning rate of the wafer machine is effectively reduced.

[0070] In some embodiments, see Figure 6 , step S110 includes the following steps S111~S113.

[0071] S111, acquiring an electron beam measurement image of a target wafer.

[0072] S112, obtaining a second grayscale value histogram of the electron beam measurement image.

[0073] S113, calculating the target gray value standard deviation of the electron beam measurement image according to the second gray value histogram.

[0074] In an embodiment of the present application, by calculating the target grayscale value standard deviation based on the second grayscale value histogram of each electron beam measurement image in the target wafer, the target grayscale value standard deviation is determined more accurately, thereby improving the image processing accuracy for the target wafer, thereby enabling more accurate real-time monitoring of the image defocus condition in the target wafer.

[0075] It should be understood that although Figure 1 to Figure 6The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. Moreover, Figure 1 to Figure 6 At least part of the steps may include multiple steps or multiple stages. These steps or stages are not necessarily performed at the same time, but can be performed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed in turn or alternately with other steps or at least part of the steps or stages in other steps.

[0076] In order to more clearly illustrate the image defocus monitoring method in some of the above embodiments, the following embodiments are combined with Figure 7~Figure 10 Understand.

[0077] In some embodiments, the method for monitoring image defocus includes steps S210 to S230.

[0078] In step S210, refer to Figure 7 , provide a reference wafer, and obtain sampling images E of multiple specified areas in the reference wafer.

[0079] In some embodiments, the reference wafer W1 includes: a first wafer in a wafer batch.

[0080] In some embodiments, the plurality of designated areas are evenly located on portions of the reference wafer W1 in upper, middle, lower, left, and right directions.

[0081] For example, the number of designated areas in the reference wafer W1 may be 3, 5, 7, 9, 10 or 12. Figure 7 The number of specified areas is 5 (such as Figure 7 It is illustrated by taking A1~A5 in the figure as an example, but it can be understood that the number of designated areas can also be other values, and this application does not limit this.

[0082] In some embodiments, each designated area includes a plurality of sample images E.

[0083] For example, the number of sampled images E in each designated area includes 2, 3, 4, 5, 6, 7, 8 or 9, etc.

[0084] In step S220, refer to Figure 8 In FIG. 5( a ), a reference image S is determined from a plurality of sample images E according to the clarity of each sample image E. As shown in FIG.

[0085] In some embodiments, step S220 includes steps S221-S222.

[0086] In step S221, a definition critical index is set.

[0087] It should be noted that the critical clarity index may be a clarity index corresponding to a critical situation where the visual effect is between clarity and blur in past experience.

[0088] For example, the clarity index includes resolution, contrast, bit rate and / or sharpness, etc.

[0089] In step S222, the definition index of each sampled image E is compared with the definition critical index, and the sampled image E (eg Figure 8 E4) in is determined as the reference image S.

[0090] For example, the definition of the reference image may be greater than or equal to a definition critical index.

[0091] In step S230, refer to Figure 8 In (b) of FIG. 1 , a reference gray value standard deviation of the reference image S is obtained, and an image defocus threshold SPEC is determined according to the reference gray value standard deviation.

[0092] In some embodiments, step S230 includes steps S231 to S233.

[0093] In step S231, refer to Fig. 9 In Figure (b), a first grayscale value histogram of the reference image S is obtained.

[0094] In step S232, a reference gray value standard deviation of the reference image S is calculated according to the first gray value histogram.

[0095] It should be noted that the gray value standard deviation refers to the deviation of the gray value of each pixel in the image from the average gray value, and is used to measure the dispersion of the gray value distribution of each pixel.

[0096] For example, the standard deviation of the reference gray value of the reference image can be determined according to the following calculation formula:

[0097] ;

[0098] Among them, S1 is the standard deviation of the reference gray value of the reference image, Xn is the gray value of the nth pixel in the reference image, is the first average grayscale value of each pixel in the reference image.

[0099] In step S233 , the image defocus threshold SPEC is determined according to the standard deviation of the reference gray value of the reference image.

[0100] For example, in step S233, the image defocus threshold SPEC is determined according to the standard deviation of the reference gray value of the reference image, and one of the following determination schemes may be adopted:

[0101] (1) The image defocus threshold SPEC is equal to the standard deviation of the reference grayscale value;

[0102] (2) The image defocus threshold SPEC is an integer value within the permissible range of the standard deviation of the reference gray value;

[0103] (3) Within the permissible range of the standard deviation of the reference grayscale value of the reference image, the optimal image defocus threshold SPEC is determined in combination with the historical empirical value of the image defocus threshold SPEC. For example, the optimal image defocus threshold may be the lower limit of the permissible range of the standard deviation of the reference grayscale value.

[0104] The permitted range may be 0 to 10% of the standard deviation of the reference gray value.

[0105] For example, see Figure 8 In Figure (b), the standard deviation of the reference grayscale value of the reference image S is 101.58. Taking the above-mentioned determination scheme (2) as an example to determine the image defocus threshold SPEC, the image defocus threshold SPEC can be an integer value within a range of 10% above and below the standard deviation of the reference grayscale value. For example, the value of the image defocus threshold SPEC can be specifically determined to be 90, 95, 100, 105 or 110, etc.

[0106] In step S110 , a target wafer is provided, and an electron beam measurement image of the target wafer and a target grayscale value standard deviation of the electron beam measurement image are obtained.

[0107] It should be noted that the target wafer includes but is not limited to the reference wafer, that is, the reference wafer and the target wafer can be the same wafer, or different wafers of the same batch and specification in the wafer manufacturing process.

[0108] In some embodiments, step S110 includes steps S111 - S112 .

[0109] In step S111 , an electron beam measurement image of a target wafer is acquired.

[0110] For example, the target wafer includes a plurality of designated areas, each of which includes a plurality of electron beam measurement images; and each of the designated areas is evenly located on the upper, middle, lower, left and right portions of the target wafer.

[0111] In step S112 , a second grayscale value histogram of the electron beam measurement image is obtained.

[0112] In step S113 , a target gray value standard deviation of the electron beam measurement image is calculated according to the second gray value histogram.

[0113] For example, the target grayscale value standard deviation of each electron beam measurement image can be determined according to the following calculation formula:

[0114] ;

[0115] Where S2 is the target grayscale value standard deviation of the electron beam measurement image, Xm is the grayscale value of the mth pixel in the electron beam measurement image, The second average gray value of each pixel in the electron beam measurement image.

[0116] In step S120, when the target gray value standard deviation is less than the image defocus threshold SPEC, an image defocus warning is issued.

[0117] It should be noted that the image defocus threshold SPEC refers to: a gray value standard deviation threshold used to determine whether the electron beam measurement image is defocused.

[0118] For example, when the target gray value standard deviation is greater than or equal to the image defocus threshold SPEC, the corresponding electron beam measurement image is determined as a focused image; when the gray value standard deviation is less than the image defocus threshold SPEC, the corresponding electron beam measurement image is determined as a defocused image.

[0119] For example, the value range of the image defocus threshold SPEC includes 90-110; the value of the image defocus threshold SPEC may be, for example, 90, 95, 100, 105 or 110.

[0120] Based on the above example, see Fig.10 Taking the number of electron beam measurement images obtained from the target wafer as 20 and the image defocus threshold SPEC as 100 as an example, in step S120, the target grayscale value standard deviation of each electron beam measurement image is compared with the image defocus threshold SPEC; wherein, if the target grayscale value standard deviation of the electron beam measurement images corresponding to n1~n19 is greater than or equal to the image defocus threshold SPEC, the electron beam measurement images corresponding to n1~n19 are determined as focused images; if the target grayscale value standard deviation of the electron beam measurement image corresponding to n20 is less than the image defocus threshold SPEC, the electron beam measurement image corresponding to n20 is determined as a defocused image.

[0121] It should be added that if the target grayscale value standard deviation of the current electron beam measurement image is less than the image defocus threshold SPEC, an image defocus warning is issued to control the wafer machine to stop, and the warning information is fed back to the feedback equipment automation system (Equipment Automation Programming, EAP for short) to remind the operator to check the current target wafer and the status of the wafer machine to eliminate the image defocus problem.

[0122] It should be noted that if the target grayscale value standard deviation of the current electron beam measurement image is greater than or equal to the image defocus threshold SPEC, it is necessary to return to step S111 to continue monitoring the image defocus problem of the next electron beam measurement image in the target wafer. If no defocused image appears in each electron beam measurement image in the target wafer, the next wafer in the wafer process is used as the new target wafer, and the process returns to step S110 to continue monitoring the image defocus problem of the next wafer in the wafer process.

[0123] In some embodiments, the target wafer includes a reference wafer; after step S110, the image defocus monitoring method further includes the following steps S310-S320.

[0124] In step S310 , after measuring the target wafer, the reference image S′ is re-determined.

[0125] In some examples, after measuring the target wafer, the clarity index of the electron beam measurement image of the sampled image whose difference between the gray value standard deviation and the image defocus threshold is within a preset range is compared with the clarity critical index, and the electron beam measurement image corresponding to the clarity index with the smallest difference with the clarity critical index among the clarity indexes is re-determined as the reference image S'. The preset range may be 5%, 10%, etc. of the image defocus threshold. For example, the image defocus threshold is 100, and the preset range is 5, that is, the clarity index of the electron beam measurement image of the sampled image whose gray value standard deviation is 95-105 is compared with the clarity critical index, and the electron beam measurement image corresponding to the clarity index with the smallest difference with the clarity critical index among the clarity indexes is re-determined as the reference image S'.

[0126] It should be noted that the reference image S′ re-determined in step S310 and the reference image S initially determined in step S222 may be the same image or different images, and the present disclosure does not impose any limitation on this.

[0127] It should be noted that the clarity index in step S310 can be set in step S221, or before step S221, according to the clarity index corresponding to the critical situation between clarity and blur in previous experience, and the present disclosure does not limit this.

[0128] For example, the clarity index includes resolution, contrast, bit rate and / or sharpness, etc.

[0129] In step S320, the image defocus threshold SPEC' is re-determined according to the re-determined target gray value standard deviation of the reference image S'.

[0130] In some examples, similar to the determination scheme of the image defocus threshold SPEC in step S233, in step S320, the image defocus threshold SPEC' is re-determined according to the target gray value standard deviation of the reference image after re-determination, and one of the following determination schemes may be adopted:

[0131] (1) The image defocus threshold SPEC' is equal to the standard deviation of the target grayscale value;

[0132] (2) The image defocus threshold SPEC' is an integer value within the permissible range of the target gray value standard deviation;

[0133] (3) Within the permissible range of the target gray value standard deviation of the reference image, combined with the historical empirical value of the image defocus threshold, determine the optimal image defocus threshold SPEC', which may be, for example, the lower limit of the permissible range of the target gray value standard deviation.

[0134] The permitted range may be 0 to 10% of the target gray value standard deviation.

[0135] It should be noted that since the number of electron beam measurement images is greater than the number of sampled images; after measuring the reference wafer, the reference image is re-determined based on the clarity of the electron beam measurement images with a larger number of samples, and the image defocus threshold is re-determined based on the re-determined reference image; in this way, in the embodiment of the present application, by collecting and calculating a large sample based on the electron beam measurement image, the accuracy of the image defocus threshold can be further improved, thereby improving the accuracy of the image defocus warning and reducing the false warning rate.

[0136] It needs to be explained that the target wafer includes a reference wafer, which means that the reference wafer and the target wafer can be the same wafer, or different wafers of the same batch and the same specification in the wafer manufacturing process.

[0137] For example, the target wafer may be the first wafer in a wafer batch; in addition, the target wafer may also include other wafers other than the first wafer in the wafer batch; wherein the judgment of the image defocus warning of other wafers is performed based on the re-determined image defocus threshold.

[0138] It is worth mentioning that, in some embodiments, the method for monitoring image defocus also includes the following steps: after performing image defocus measurement on each wafer in a wafer batch, performing sampling detection on the focused image and the defocused image determined in the measurement; wherein, if it is detected that an image with a clear visual effect is misjudged as a defocused image, the image defocus threshold is increased accordingly according to the target grayscale value standard deviation of the misjudged image; if it is detected that an image with a blurred visual effect is misjudged as a focused image, the image defocus threshold is lowered accordingly according to the target grayscale value standard deviation of the misjudged image.

[0139] For example, the adjusted (including increased or decreased) image defocus threshold in the above embodiment may be, for example, 0 to 10% of the standard deviation of the target grayscale value of the misjudged image.

[0140] In an embodiment of the present application, by sampling and detecting the focused image and the defocused image determined in the image defocus measurement of each wafer, and adjusting the value of the image defocus threshold accordingly, the image defocus threshold can be optimized piece by piece according to the actual measurement conditions of each wafer, so as to gradually improve the accuracy of determining the image defocus threshold, thereby improving the accuracy of the image defocus warning and reducing the false warning rate.

[0141] The present application also provides an image defocus monitoring system according to some embodiments, and the image defocus monitoring system can be used to execute the image defocus monitoring method in some of the above embodiments. The image defocus monitoring system also has the technical advantages of the above-mentioned image defocus monitoring method. It should be noted that the parts that are the same or corresponding to the above embodiments can refer to the corresponding description of the above embodiments, and will not be described in detail below.

[0142] In some embodiments, the image defocus monitoring system is connected to the wafer machine M; see Fig.11 The monitoring system includes an image acquisition device 1, an image processing module 2, a threshold determination module 3 and a controller 4. The image acquisition device 1 is used to acquire sampled images of multiple specified areas in a reference wafer; and the image acquisition device 1 is also used to acquire an electron beam measurement image of a target wafer; the image processing module 2 is connected to the image acquisition device 1; the image processing module 2 is used to determine a reference image from multiple sampled images according to the clarity of each sampled image, and to acquire a reference gray value standard deviation of the reference image; and the image processing module 2 is also used to acquire a target gray value standard deviation of the electron beam measurement image; the threshold determination module 3 is connected to the image processing module 2; the threshold determination module 3 is used to determine an image defocus threshold according to the reference gray value standard deviation; the controller 4 is connected to the image processing module 2, the threshold determination module 3 and the wafer machine M; the controller 4 is used to issue an image defocus warning and control the wafer machine M to stop when the target gray value standard deviation is less than the image defocus threshold.

[0143] By way of example, the image acquisition device 1 includes but is not limited to an Electrons Beam inspection (E-beam inspection, EBI for short) device.

[0144] In some embodiments, see Fig.13The controller 4 includes a comparison unit 41 and an image defocus warning unit 42; the comparison unit 41 is connected to the image processing module 2 and the threshold determination module 3; the comparison unit 41 is used to compare the target gray value standard deviation with the image defocus threshold and output the comparison result; the image defocus warning unit 42 is connected to the comparison unit 41 and the wafer machine M, and is used to output an image defocus warning signal to control the wafer machine M to stop when the comparison result is that the target gray value standard deviation is less than the image defocus threshold.

[0145] In some embodiments, please refer to Fig.13 The image defocus monitoring system also includes an equipment automation system EAP; the equipment automation system EAP is connected to the image defocus warning unit 42 and the wafer machine M; the equipment automation system EAP is used to receive the image defocus warning signal from the image defocus warning unit 42, and remind the operator to check the status of the current target wafer and the wafer machine M to eliminate the image defocus problem.

[0146] In some embodiments, see Fig.13 The image processing module 2 includes a reference image determination unit 21; the reference image determination unit 21 is connected to the image acquisition device 1 and the threshold determination module 3; the reference image determination unit 21 is used to compare the clarity index of each sampled image with the set clarity critical index, and determine the sampled image corresponding to the clarity index with the smallest difference between the clarity critical index and the clarity critical index as the reference image.

[0147] In some embodiments, the reference wafer includes the first wafer in the wafer batch, and the target wafer also includes other wafers other than the first wafer in the wafer batch; the number of electron beam measurement images is greater than the number of sampled images; the reference image determination unit 21 is also used to, after measuring the reference wafer, redetermine the reference image from multiple electron beam measurement images according to the clarity of each electron beam measurement image corresponding to the reference wafer; the threshold determination module 3 is also used to redetermine the image defocus threshold based on the target grayscale value standard deviation of the redetermined reference image; the controller is also used to judge the image defocus warning of other wafers based on the redetermined image defocus threshold.

[0148] In some embodiments, the reference image determination unit 21 is also used to redetermine the reference image after measuring the target wafer, that is, the reference image determination unit 21 is also used to compare the clarity index of the electron beam measurement image of the sampling image whose difference between the gray value standard deviation and the image defocus threshold is within a preset range with the clarity critical index after measuring the target wafer, and redetermine the electron beam measurement image corresponding to the clarity index having the smallest difference with the clarity critical index among the clarity indicators as the reference image.

[0149] In some embodiments, please refer to Fig.13 , the image processing module 2 also includes an acquisition unit 22 and a calculation unit 23. The acquisition unit 22 is connected to the image acquisition device 1 and the reference image determination unit 21; the acquisition unit 22 is used to acquire a first gray value histogram of the reference image; and the acquisition unit is also used to acquire a second gray value histogram of the electron beam measurement image; the calculation unit 23 is connected to the acquisition unit 22, the threshold determination module 3 and the controller 4; the calculation unit 23 is used to calculate the reference gray value standard deviation of the reference image according to the first gray value histogram; and the calculation unit is also used to calculate the target gray value standard deviation of the electron beam measurement image according to the second gray value histogram.

[0150] In addition, in the image defocus monitoring system provided in some of the above embodiments, the terms "module", "unit" and / or "system" used in this specification can be used to represent computer-related entities, hardware, firmware, a combination of hardware and software, software, or software in execution. For example, "module", "unit" and / or "system" can be but not limited to: a process running on a processor, a processor, an object, an executable file, an execution thread, a program and / or a computer. For example, "module", "unit" and / or "system" can be executed from various computer-readable media on which various data structures are stored. And, in the above embodiments provided in the present disclosure, it should be understood that the disclosed "module", "unit" and / or "system" can be implemented in other ways. For example, the device described above is only schematic. For example, the division of modules is only a division of a logical function, and there may be other division methods in actual implementation, such as multiple modules can be combined or integrated into another device, or some features can be ignored or not executed. The connection between each other described can be through some interfaces, indirect coupling or communication connection of modules, which can be electrical, mechanical or other forms. The modules described separately may or may not be physically separated. Some or all of the modules may be selected according to actual needs to achieve the purpose of the embodiments of the present disclosure.

[0151] In the description of this specification, the description with reference to the terms "some embodiments", "some examples", "exemplarily", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example.

[0152] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0153] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application.

Claims

1. A method for monitoring image defocus, characterized in that: include: Providing a target wafer, acquiring an electron beam measurement image of the target wafer and a target grayscale value standard deviation of the electron beam measurement image; When the target gray value standard deviation is less than the image defocus threshold, an image defocus warning is issued.

2. The method for monitoring image defocus according to claim 1, characterized in that: Before providing a target wafer and acquiring an electron beam measurement image of the target wafer and a target grayscale value standard deviation of the electron beam measurement image, the image defocus monitoring method further includes: Providing a reference wafer, and acquiring sampling images of a plurality of designated areas in the reference wafer; Determining a reference image from a plurality of the sampled images according to the clarity of each of the sampled images; A reference grayscale value standard deviation of the reference image is obtained, and the image defocus threshold is determined according to the reference grayscale value standard deviation.

3. The method for monitoring image defocus according to claim 2, characterized in that: The step of determining a reference image from a plurality of sample images according to the clarity of each sample image comprises: Set critical clarity indicators; The clarity index of each of the sampled images is compared with the clarity critical index, and the sampled image corresponding to the clarity index having the smallest difference with the clarity critical index among the clarity indexes is determined as the reference image.

4. The method for monitoring image defocus according to claim 2 or 3, characterized in that: The obtaining of a reference gray value standard deviation of the reference image and determining the image defocus threshold according to the reference gray value standard deviation includes: Acquire a first grayscale value histogram of the reference image; Calculating the reference gray value standard deviation of the reference image according to the first gray value histogram; The image defocus threshold is determined according to the reference gray value standard deviation of the reference image.

5. The method for monitoring image defocus according to claim 2, characterized in that: The number of the electron beam measurement images is greater than the number of the sampling images; the image defocus monitoring method further includes: After measuring the target wafer, re-determining the reference image; The image defocus threshold is re-determined according to the re-determined target gray value standard deviation of the reference image.

6. The method for monitoring image defocus according to claim 5, characterized in that: After measuring the target wafer, re-determining the reference image includes: After measuring the target wafer, the clarity index of the electron beam measurement image of the sampled image whose difference between the gray value standard deviation and the image defocus threshold is within a preset range is compared with the clarity critical index, and the electron beam measurement image corresponding to the clarity index with the smallest difference between the clarity critical index and the clarity critical index is re-determined as the reference image.

7. The method for monitoring image defocus according to claim 5, characterized in that: The reference wafer includes: a first wafer in a wafer batch.

8. The method for monitoring image defocus according to claim 5, characterized in that: The target wafers also include: other wafers other than the first wafer in the wafer batch; The judgment of the image defocus warning for the other wafers is performed based on the re-determined image defocus threshold.

9. The method for monitoring image defocus according to claim 2, characterized in that: The plurality of designated areas are evenly located on the upper, middle, lower, left and right portions of the reference wafer.

10. The method for monitoring image defocus according to claim 1, characterized in that: The providing of a target wafer, obtaining an electron beam measurement image of the target wafer and a target grayscale value standard deviation of the electron beam measurement image, comprises: Acquiring the electron beam measurement image of the target wafer; Acquire a second grayscale value histogram of the electron beam measurement image; The target gray value standard deviation of the electron beam measurement image is calculated according to the second gray value histogram.

11. An image defocus monitoring system, characterized in that: Connected to the wafer machine; the monitoring system includes: An image acquisition device is used to acquire sample images of a plurality of designated areas in a reference wafer; and is also used to acquire an electron beam measurement image of a target wafer; An image processing module, connected to the image acquisition device, for determining a reference image from a plurality of the sampled images according to the clarity of each of the sampled images, and obtaining a reference gray value standard deviation of the reference image; and also for obtaining a target gray value standard deviation of the electron beam measurement image; A threshold determination module, connected to the image processing module, for determining an image defocus threshold according to the standard deviation of the reference gray value; The controller is connected to the image processing module, the threshold determination module and the wafer machine, and is used to issue an image defocus warning and control the wafer machine to stop when the target gray value standard deviation is less than the image defocus threshold.

12. The image defocus monitoring system according to claim 11, characterized in that: The image processing module comprises: The reference image determination unit is connected to the image acquisition device and the threshold determination module, and is used to compare the clarity index of each sampled image with the set clarity critical index, and determine the sampled image corresponding to the clarity index with the smallest difference between the clarity critical index and the clarity critical index as the reference image.

13. The image defocus monitoring system according to claim 12, characterized in that: The reference wafer includes the first wafer in the wafer batch, and the target wafer includes other wafers in the wafer batch except the first wafer; the number of the electron beam measurement images is greater than the number of the sampling images; the reference image determination unit is also used to redetermine the reference image after measuring the target wafer; the threshold determination module is also used to redetermine the image defocus threshold according to the target gray value standard deviation of the redetermined reference image; the controller is also used to judge the image defocus warning of the other wafers according to the redetermined image defocus threshold.

14. The image defocus monitoring system according to claim 13, characterized in that: The reference image determination unit is also used to compare the clarity index of the electron beam measurement image of the sampled image whose difference between the gray value standard deviation and the image defocus threshold is within a preset range with the clarity critical index after measuring the target wafer, and to re-determine the electron beam measurement image corresponding to the clarity index having the smallest difference with the clarity critical index among the clarity indicators as the reference image.

15. The image defocus monitoring system according to claim 11, characterized in that: The image processing module also includes: an acquisition unit connected to the image acquisition device and the reference image determination unit, and configured to acquire a first grayscale value histogram of the reference image; and, further configured to acquire a second grayscale value histogram of the electron beam measurement image; A calculation unit is connected to the acquisition unit, the threshold determination module and the controller, and is used to calculate the reference gray value standard deviation of the reference image according to the first gray value histogram; and is also used to calculate the target gray value standard deviation of the electron beam measurement image according to the second gray value histogram.

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