Method for monitoring image defocus and system therefor

Abstract

The application relates to an image defocus monitoring method and system. The image defocus monitoring method comprises the following steps: providing a target wafer, acquiring an electron beam measurement image of the target wafer and a target gray value standard deviation of the electron beam measurement image; when the target gray value standard deviation is less than an image defocus threshold value, an image defocus early warning is performed. The application monitors the image defocus problem based on the gray value standard deviation of the image, so as to reduce the false early warning rate of the wafer machine, and is beneficial to realizing accurate and real-time monitoring of the image defocus problem.

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

[0002] In the current field of semiconductor testing, the sharpness of the images to be measured is usually measured to monitor the image defocus in the wafer. For example, a lower limit of sharpness is set. If the sharpness of a plurality of images to be measured in the wafer is lower than the lower limit of sharpness, it is determined that the image defocus problem occurs in the wafer, and a wafer machine is warned.

[0003] However, in the conventional method for monitoring image defocus, each image to be measured only outputs a single sharpness value, which is difficult to exclude the measurement inaccuracy caused by environmental factors and other problems, and reduces the monitoring accuracy of the image defocus problem. In addition, the setting of the lower limit of sharpness depends on human judgment, which is easy to cause the misjudgment of the image defocus problem caused by the inaccurate setting of the lower limit of sharpness. For example, if the set lower limit of sharpness is too high, the focused image will be misjudged as a defocused image, which will cause the high warning rate of the wafer machine. If the set lower limit of sharpness is too low, the defocused image will be misjudged as a focused image, which is difficult to achieve accurate monitoring of the image defocus problem, thereby reducing the monitoring accuracy of the image defocus problem. SUMMARY

[0004] Therefore, the embodiments of the present application provide a method and system for monitoring image defocus, which monitors the image defocus problem based on the standard deviation of the gray value of the image, so as to reduce the false warning rate of the wafer machine, and is beneficial to realize the accurate real-time monitoring of the image defocus problem.

[0005] In order to achieve the above-mentioned purpose, in one aspect, some embodiments of the present application provide a method for monitoring image defocus. The method for monitoring image defocus comprises: providing a target wafer, 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 target gray value standard deviation is less than an image defocus threshold, performing image defocus warning.

[0006] In some embodiments, before the providing a target wafer, obtaining an electron beam measurement image of the target wafer and a target gray value standard deviation of the electron beam measurement image, the method for monitoring image defocus further comprises: providing a reference wafer, obtaining sampling images of a plurality of specified regions in the reference wafer; determining a reference image from the plurality of sampling images according to the sharpness of each sampling image; 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.

[0007] In some embodiments, the determining the reference image from the plurality of sampling images according to the sharpness of each sampling image comprises: setting a sharpness threshold; comparing the sharpness threshold with the sharpness index of each sampling image, and determining the sampling image corresponding to the sharpness index having the smallest difference with the sharpness threshold as the reference image.

[0008] In some embodiments, the obtaining the reference gray value standard deviation of the reference image and determining the image out-of-focus threshold according to the reference gray value standard deviation comprises: obtaining a first gray value histogram of the reference image; calculating the reference gray value standard deviation of the reference image according to the first gray value histogram; and determining the image out-of-focus threshold according to the reference gray value standard deviation of the reference image.

[0009] In some embodiments, the number of e-beam measurement images is greater than the number of sampling images; and the monitoring method of image out-of-focus further comprises: after measuring the target wafer, re-determining the reference image; and re-determining the image out-of-focus threshold according to the target gray value standard deviation of the re-determined reference image.

[0010] In some embodiments, after measuring the target wafer, the re-determining the reference image comprises: after measuring the target wafer, comparing the sharpness index of the e-beam measurement image of the sampling image having the difference between the gray value standard deviation and the image out-of-focus threshold within a preset range with the sharpness threshold, and re-determining the e-beam measurement image corresponding to the sharpness index having the smallest difference with the sharpness threshold 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 further comprises: a wafer other than the first wafer in the wafer batch; and wherein the determining the image out-of-focus early warning of the wafer is performed according to the re-determined image out-of-focus threshold.

[0013] In some embodiments, the plurality of specified regions are uniformly located on the upper, middle, lower, left and right portions of the reference wafer.

[0014] In some embodiments, the providing the target wafer, obtaining the e-beam measurement image of the target wafer and the target gray value standard deviation of the e-beam measurement image comprises: obtaining the e-beam measurement image of the target wafer; obtaining a second gray value histogram of the e-beam measurement image; and calculating the target gray value standard deviation of the e-beam measurement image according to the second gray value histogram.

[0015] In another aspect, the present disclosure also provides, according to some embodiments, an image defocus monitoring system; the monitoring system comprises an image acquisition device, an image processing module, a threshold value determination module and a controller; the image acquisition device is configured to acquire sample images of a plurality of designated regions in a reference wafer; and is further configured to acquire electron beam metrology images of a target wafer; the image processing module is connected to the image acquisition device, and is configured to determine a reference image from the plurality of sample images according to the sharpness of each sample image, and acquire a reference gray value standard deviation of the reference image; and is further configured to acquire a target gray value standard deviation of the electron beam metrology image; the threshold value determination module is connected to the image processing module, and is configured to determine an image defocus threshold value according to the reference gray value standard deviation; the controller is connected to the image processing module, the threshold value determination module and a wafer machine, and is configured to perform image defocus early warning and control the wafer machine to stop when the target gray value standard deviation is less than the image defocus threshold value.

[0016] In some embodiments, the image processing module comprises a reference image determination unit; the reference image determination unit is connected to the image acquisition device and the threshold value determination module; the reference image determination unit is configured to compare the sharpness indicators of each sample image with a set sharpness critical indicator, and determine the sample image corresponding to the sharpness indicator with the smallest difference from the sharpness critical indicator as the reference image.

[0017] In some embodiments, the reference wafer comprises a first wafer in a wafer batch, and the target wafer comprises other wafers in the wafer batch except the first wafer; the number of electron beam metrology images is greater than the number of sample images; the reference image determination unit is further configured to re-determine the reference image after measuring the target wafer; the threshold value determination module is further configured to re-determine the image defocus threshold value according to the target gray value standard deviation of the re-determined reference image; and the controller is further configured to perform image defocus early warning judgment for other wafers according to the re-determined image defocus threshold value.

[0018] In some embodiments, the reference image determination unit is further configured to compare the sharpness indicators of the electron beam metrology images of the sample images with the difference between the gray value standard deviation and the image defocus threshold value within a preset range with the sharpness critical indicator after measuring the target wafer, and re-determine the electron beam metrology image corresponding to the sharpness indicator with the smallest difference from the sharpness critical indicator as the reference image.

[0019] In some embodiments, the image processing module further comprises an acquisition unit and a calculation unit; the acquisition unit is connected with the image acquisition device and the reference image determination unit; the acquisition unit is configured to acquire a first gray value histogram of the reference image; and the acquisition unit is further configured to acquire a second gray value histogram of the electron beam metrology image; the calculation unit is connected with the acquisition unit, the threshold determination module and the controller; the calculation unit is configured to calculate a reference gray value standard deviation of the reference image according to the first gray value histogram; and the calculation unit is further configured to calculate a target gray value standard deviation of the electron beam metrology image according to the second gray value histogram.

[0020] The embodiments of the present application can have / at least have the following advantages:

[0021] In the embodiments of the present application, the target gray value standard deviation of the electron beam metrology image of the target wafer is acquired, and the target gray value standard deviation is compared with the image defocus threshold; since the gray value standard deviation of the image is negatively correlated with the defocus degree, when the target gray value standard deviation is less than the image defocus threshold, it is determined that the defocus image is monitored; in this way, the electron beam metrology image of the target wafer is monitored in real time, and the image defocus early warning is performed in time when the target gray value standard deviation is less than the image defocus threshold, which not only can monitor whether the electron beam metrology image appears defocus, but also can effectively reduce the false alarm rate of the wafer machine, realizes the accurate monitoring of the image defocus, and thus is beneficial to improving the yield of wafer products.

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

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort.

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

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

[0026] Figure 3 A flowchart of step S220 provided in some embodiments;

[0027] Figure 4A flowchart of a process of step S230 provided in some embodiments;

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

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

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

[0031] Figure 8 (a) of FIG. 1 is a schematic diagram of a plurality of sampling images provided in some embodiments, Figure 8 (b) of FIG. 1 is a fitting curve of standard deviations of gray values of the sampling images shown in (a) of FIG. 1;

[0032] Figure 9 (a) of FIG. 2 is a schematic diagram of a reference image provided in some embodiments, Figure 9 (b) of FIG. 2 is a first histogram of gray values of the reference image shown in (a) of FIG. 2;

[0033] Figure 10 A fitting curve of standard deviations of target gray values of a plurality of e-beam measurement images provided in some embodiments;

[0034] Figure 11 A block diagram of a monitoring system of image defocus provided in some embodiments;

[0035] Figure 12 A block diagram of another monitoring system of image defocus provided in some embodiments;

[0036] Figure 13 A block diagram of yet another monitoring system of image defocus provided in some embodiments.

[0037] Explanation of reference numerals:

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

[0039] For the purposes of the present application, a more complete description of which will follow, reference will be made to the accompanying drawings referenced below. The drawings illustrate preferred embodiments of the application. However, the application can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and fully convey the scope of the application to those skilled in the art.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for describing particular embodiments only and is not intended to be limiting of the application.

[0041] It will be understood that when an element or layer is referred to as being "on" or "adjacent" or "connected" or "coupled" to another element or layer, it can be directly on, adjacent, connected or coupled to the other element or layer or one or more intervening elements or layers can be present. In addition, it will be understood that, although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present application.

[0042] As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. It should also be understood that the term "comprising" as used herein is intended to denote the presence of stated features, integers, steps, operations, elements, or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or groups thereof. In addition, as used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0043] Embodiments of the application are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of the application. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and / or tolerances, are to be expected. Embodiments of the application should not be construed as limited to the particular shapes of the regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the application.

[0044] The embodiment of the present application provides a kind of image defocus monitoring method and system thereof, by the standard deviation of the gray value of image, the monitoring of image defocus problem is carried out, to reduce the false alarm rate of wafer machine, it is favorable to realize the accurate real-time monitoring of image defocus problem.

[0045] In some embodiments, referring to Figure 1 , the monitoring method of image defocus includes steps S110-S120.

[0046] S110, provides target wafer, obtains the electron beam measurement image of target wafer and the target gray value standard deviation of electron beam measurement image.

[0047] S120, when target gray value standard deviation is less than image defocus threshold, image defocus early warning is carried out.

[0048] It should be noted that image defocus threshold refers to the gray value standard deviation threshold for judging whether electron beam measurement image is out of focus.Exemplarily, when target gray value standard deviation is greater than or equal to image defocus threshold, the corresponding electron beam measurement image is determined as focus image; when gray value standard deviation is less than image defocus threshold, the corresponding electron beam measurement image is determined as out-of-focus image.

[0049] In the embodiment of the present application, the target gray value standard deviation of the electron beam measurement image of the target wafer is obtained, and the target gray value standard deviation is compared with the image defocus threshold; since the gray value standard deviation of image is negatively correlated with its defocus degree, when target gray value standard deviation is less than image defocus threshold, it is determined that out-of-focus image is monitored; in this way, the electron beam measurement image of target wafer is monitored in real time, and image defocus early warning is carried out when target gray value standard deviation is less than image defocus threshold, so that not only whether electron beam measurement image appears out-of-focus condition can be monitored in real time, but also the false alarm rate of wafer machine can be effectively reduced, the accurate monitoring of image defocus condition is realized, thereby it is favorable to improve wafer product yield.

[0050] In some embodiments, referring to Figure 2 , before step S110, the monitoring method of image defocus further includes steps S210-S230.

[0051] S210, provides reference wafer, obtains the sampling image of multiple specified areas in reference wafer.

[0052] S220, according to the distinctness of each sampling image, determine reference image from multiple sampling images.

[0053] S230, obtains the reference gray value standard deviation of reference image, and determines image defocus threshold according to reference gray value standard deviation.

[0054] In the embodiment of the present application, the reference image is determined from the sampling images of the plurality of specified regions in the reference wafer, and the image defocus threshold is determined based on the reference gray value standard deviation of the reference image; so that the image defocus threshold can be determined according to the actual situation of each wafer product or each layer structure in the wafer, effectively eliminating the adverse effects of process differences and environmental factors on the determination accuracy of the image defocus threshold, and improving the determination accuracy of the image defocus threshold.

[0055] In some embodiments, referring to Figure 3 , step S220 includes steps S221-S222.

[0056] S221, set the sharpness critical index.

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

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

[0059] S222, compare the sharpness index of each sampling image with the sharpness critical index, and determine the sampling image corresponding to the sharpness index with the smallest difference value from the sharpness critical index as the reference image.

[0060] In some embodiments, referring to Figure 4 , step S230 includes steps S231-S233.

[0061] S231, obtain the first gray value histogram of the reference image.

[0062] S232, calculate the reference gray value standard deviation of the reference image according to the first gray value histogram.

[0063] S233, determine the image defocus threshold according to the reference gray value standard deviation of the reference image.

[0064] In the embodiment of the present application, the calculation of the reference gray value standard deviation is based on the first gray value histogram of the reference image in the reference wafer, which improves the image processing accuracy for the reference wafer, makes the determination of the reference gray value standard deviation more accurate, and thus improves the determination accuracy of the image defocus threshold.

[0065] In some embodiments, the number of e-beam measurement images is greater than the number of sampling images; referring to Figure 5 , after step S110, the image defocus monitoring method further includes steps S310-S320.

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

[0067] In some embodiments, step S310 comprises: after measuring the target wafer, comparing the sharpness indicators of the e-beam measurement images of the sampling images, whose difference between the gray value standard deviation and the image out-of-focus threshold value is within the preset range, with the sharpness critical indicator, and re-determining the e-beam measurement image corresponding to the sharpness indicator with the smallest difference between the sharpness indicator and the sharpness critical indicator as the reference image.

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

[0069] It should be noted that the determination of the image out-of-focus early warning of the wafers other than the reference wafer in the wafer batch is based on the re-determined image out-of-focus threshold value. In the embodiments of the present application, steps S310-S320 are the optimization process of the image out-of-focus threshold value, the image out-of-focus threshold value is re-determined according to the sharpness of each e-beam measurement image corresponding to the target wafer in the wafer process, and the determination of the image out-of-focus early warning of other wafers in the wafer process is determined according to the re-determined image out-of-focus threshold value; in this way, the adverse effects of process differences and environmental factors and the like on the accuracy of the determination of the image out-of-focus threshold value are effectively eliminated, the determination accuracy of the image out-of-focus threshold value is improved, and the false early warning rate of the wafer machine is effectively reduced.

[0070] In some embodiments, referring to Figure 6 , step S110 comprises steps S111-S113.

[0071] S111, obtain the e-beam measurement image of the target wafer.

[0072] S112, obtain the second gray value histogram of the e-beam measurement image.

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

[0074] In the embodiments of the present application, the target gray value standard deviation is calculated based on the second gray value histogram of each e-beam measurement image in the target wafer, so that the determination of the target gray value standard deviation is more accurate, the image processing accuracy for the target wafer is improved, and thus the image out-of-focus condition in the target wafer can be more accurately monitored in real time.

[0075] It should be understood that, although Figures 1 to 6The steps in the flowchart are shown in sequence according to the arrows, but the steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified herein, the steps are not strictly limited in sequence, and the steps can be executed in other sequences. Moreover, Figures 1 to 6 At least some of the steps in the flowchart can include multiple steps or multiple stages, which are not necessarily executed at the same time, but can be executed at different times, and the execution sequence of the steps or stages is not necessarily sequential, but can be alternately or alternately executed with other steps or steps in other steps or stages.

[0076] In order to more clearly illustrate the image defocus monitoring method in some embodiments described above, the following embodiments are understood in conjunction with Figures 7 to 10 .

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

[0078] In step S210, referring to Figure 7 , a reference wafer is provided, and sample images E of a plurality of specified regions in the reference wafer are obtained.

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

[0080] In some embodiments, the plurality of specified regions are uniformly located on the upper, middle, lower, left and right parts of the reference wafer W1.

[0081] For example, the number of specified regions in the reference wafer W1 includes 3, 5, 7, 9, 10 or 12, etc. It should be noted that Figure 7 In some embodiments, the number of specified regions is 5 (as shown in Figure 7 A1-A5), but it can be understood that the number of specified regions can also be other values, and the present application does not limit this.

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

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

[0084] In step S220, referring to Figure 8 (a) figure, according to the clarity of each sample image E, a reference image S is determined from the plurality of sample images E.

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

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

[0087] It should be noted that the criticality index of definition can be an index of definition corresponding to a critical situation in which the visual effect is between clear and blurred in the past experience.

[0088] For example, the index of definition includes resolution, contrast, code rate, and / or sharpness, etc.

[0089] In step S222, the index of definition of each sample image E is compared with the criticality index of definition, and the sample image E (for example, E4 in Figure 8 ) corresponding to the index of definition with the smallest difference from the criticality index of definition is determined as the reference image S.

[0090] For example, the definition of the reference image can be greater than or equal to the criticality index of definition.

[0091] In step S230, referring to (b) of FIG. 2 in Figure 8 , a reference gray value standard deviation of the reference image S is obtained, and an image out-of-focus threshold SPEC is determined according to the reference gray value standard deviation.

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

[0093] In step S231, referring to (b) of FIG. 2 in Figure 9 , a first gray value histogram of the reference image S is obtained.

[0094] In step S232, the 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, which is used to measure the dispersion degree of the distribution of the gray value of each pixel.

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

[0097] ;

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

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

[0100] For example, in step S233, the image defocus threshold SPEC is determined based on the standard deviation of the reference grayscale values ​​of the reference image. One of the following determination schemes can be adopted:

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

[0102] (2) The image defocus threshold SPEC is an integer value taken 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 gray value of the reference image, the optimal image defocus threshold is determined by combining the historical experience value of the image defocus threshold SPEC. For example, it can be the lower limit of the permissible range of the standard deviation of the reference gray value.

[0104] The permissible range can be 0 to 10% above or below the standard deviation of the baseline grayscale value.

[0105] For example, please refer to Figure 8 In Figure (b), the standard deviation of the baseline gray value of the baseline image S is 101.58. Taking the determination of the image defocus threshold SPEC using the above-mentioned determination scheme (2) as an example, the image defocus threshold SPEC can be an integer value within a range of 10% above or below the standard deviation of the baseline gray value. For example, the specific value of the image defocus threshold SPEC can be determined as 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 the standard deviation of the target grayscale value 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 they can be different wafers of the same batch and specifications in the wafer fabrication process.

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

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

[0110] For example, the target wafer includes multiple designated regions, each of which includes multiple electron beam measurement images; and each designated region is uniformly located on the upper, middle, lower, left, and right sides of the target wafer.

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

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

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

[0114]

[0115] wherein S2 is the target gray value standard deviation of the electron beam measurement image, Xm is the gray value of the mth pixel in the electron beam measurement image, and is 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 performed.

[0117] It should be noted that the image defocus threshold SPEC refers to a gray value standard deviation threshold for determining whether the electron beam measurement image is out of focus.

[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 to be a focus image; and when the gray value standard deviation is less than the image defocus threshold SPEC, the corresponding electron beam measurement image is determined to be an out-of-focus image.

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

[0120] According to the above example, please refer to Figure 10 For example, when the target gray value standard deviation is less than the image defocus threshold SPEC, an image defocus warning is performed to control the wafer machine to stop, and the warning information is fed back to the feedback equipment automation system (Equipment Automation Programming, EAP) to remind the operator to check the current target wafer and the state of the wafer machine to eliminate the image defocus problem.

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

[0122] It is to be noted that if the target gray value standard deviation of the current e-beam metrology 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 e-beam metrology image in the target wafer. If no defocus image occurs in each e-beam metrology image in the target wafer, the next wafer in the wafer process is taken as a new target wafer, and step S110 is returned 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 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 sharpness indicators of the e-beam metrology images of the sampling images whose difference between the gray value standard deviation and the image defocus threshold is within a preset range are compared with the sharpness critical indicator, and the e-beam metrology image corresponding to the sharpness indicator with the smallest difference from the sharpness critical indicator is re-determined as the reference image S'. The preset range can 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 sharpness indicators of the e-beam metrology images of the sampling images whose gray value standard deviation is 95-105 are compared with the sharpness critical indicator, and the e-beam metrology image corresponding to the sharpness indicator with the smallest difference from the sharpness critical indicator is re-determined as the reference image S'.

[0126] It is to be noted that the reference image S' re-determined in step S310 and the reference image S initially determined in step S222 can be the same image or different images, which is not limited by the present disclosure.

[0127] It is to be noted that the sharpness indicators in step S310 can be set in step S221, or can be set before step S221 according to the sharpness indicators corresponding to the critical situation in which the visual effect is between clear and blurred in the past experience, which is not limited by the present disclosure.

[0128] For example, the sharpness indicators include resolution, contrast, code rate, and / or sharpness, etc.

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

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

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

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

[0133] (3) Within the permitted range of the target gray value standard deviation of the reference image, the optimal image defocus threshold SPEC' is determined in combination with the historical experience value of the image defocus threshold, which can be, for example, the lower limit value of the permitted range of the target gray value standard deviation.

[0134] The permitted range can be 0-10% floating up and down 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 sampling images, after measuring the reference wafer, the reference image is re-determined based on the clarity of the larger number of electron beam measurement images, and the determination of the image defocus threshold is re-performed according to the re-determined reference image. In this way, by collecting and calculating a large sample based on electron beam measurement images in the embodiments of the present application, the accuracy of the image defocus threshold can be further improved, thereby improving the accuracy of the image defocus early warning and reducing the false alarm rate.

[0136] It should be explained that the target wafer includes the 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 specification in the wafer process.

[0137] For example, the target wafer can be the first wafer in the wafer batch. In addition, the target wafer also includes other wafers in addition to the first wafer in the wafer batch. The image defocus early warning of the other wafers is determined according to the re-determined image defocus threshold.

[0138] It is worth mentioning that in some embodiments, the image defocus monitoring method further includes the following steps: after measuring the image defocus of each wafer in the wafer batch, sampling detection is performed on the focused images and defocused images determined in the measurement; if an image with clear visual effect is misjudged as a defocused image, the image defocus threshold is increased according to the target gray value standard deviation of the misjudged image; if an image with blurred visual effect is misjudged as a focused image, the image defocus threshold is decreased according to the target gray value standard deviation of the misjudged image.

[0139] For example, the image defocus threshold value adjusted (including increased or decreased) in the above embodiments can be 0-10% of the standard deviation of the target gray value of the misjudged image.

[0140] In the embodiments of the present application, by sampling and detecting the in-focus image and the out-of-focus image determined in the image defocus measurement of each wafer, and adjusting the value of the image defocus threshold value accordingly, the image defocus threshold value can be optimized according to the actual measurement of each wafer, so as to gradually improve the determination accuracy of the image defocus threshold value, thereby improving the accuracy of the image defocus early warning and reducing the false alarm rate.

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

[0142] In some embodiments, the image defocus monitoring system is connected to the wafer machine M. Please refer to Figure 11 , the monitoring system includes an image acquisition device 1, an image processing module 2, a threshold value determination module 3, and a controller 4. The image acquisition device 1 is used to acquire sample images of a plurality of specified regions 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 a plurality of sample images according to the clarity of each sample image, and 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 value determination module 3 is connected to the image processing module 2; the threshold value determination module 3 is used to determine an image defocus threshold value according to the reference gray value standard deviation; the controller 4 is connected to the image processing module 2, the threshold value determination module 3, and the wafer machine M; the controller 4 is used to perform image defocus early warning and control the wafer machine M to stop when the target gray value standard deviation is less than the image defocus threshold value.

[0143] For example, the image acquisition device 1 includes but is not limited to an electron beam inspection (E-beam inspection, EBI for short) device.

[0144] In some embodiments, please refer to Figure 13, the controller 4 comprises a comparison unit 41 and an image defocus early warning unit 42; the comparison unit 41 is connected with the image processing module 2 and the threshold value determination module 3; the comparison unit 41 is used for comparing the target gray value standard deviation with the image defocus threshold value, and outputting a comparison result; the image defocus early warning unit 42 is connected with the comparison unit 41 and the wafer machine M, and is used for outputting an image defocus early warning signal when the comparison result is that the target gray value standard deviation is less than the image defocus threshold value, so as to control the wafer machine M to stop.

[0145] In some embodiments, please refer to Figure 13 , the image defocus monitoring system further comprises an equipment automation system EAP; the equipment automation system EAP is connected with the image defocus early warning unit 42 and the wafer machine M; the equipment automation system EAP is used for receiving the image defocus early warning signal from the image defocus early warning unit 42, and reminding an operator to check the current target wafer and the state of the wafer machine M, so as to exclude the image defocus problem.

[0146] In some embodiments, please refer to Figure 13 , the image processing module 2 comprises a reference image determination unit 21; the reference image determination unit 21 is connected with the image acquisition device 1 and the threshold value determination module 3; the reference image determination unit 21 is used for comparing the sharpness indicators of the sampling images with a set sharpness critical indicator, and determining the sampling image corresponding to the sharpness indicator with the minimum difference from the sharpness critical indicator as the reference image.

[0147] In some embodiments, the reference wafer comprises a first wafer in a wafer batch, and the target wafer further comprises 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 21 is further used for, after measuring the reference wafer, determining the reference image from the plurality of electron beam measurement images according to the sharpness of each electron beam measurement image corresponding to the reference wafer; the threshold value determination module 3 is further used for determining the image defocus threshold value according to the target gray value standard deviation of the re-determined reference image; and the controller is further used for determining the image defocus early warning of the other wafers according to the re-determined image defocus threshold value.

[0148] In some embodiments, the reference image determination unit 21 is further used for, after measuring the target wafer, re-determining the reference image, that is, the reference image determination unit 21 is further used for, after measuring the target wafer, comparing the sharpness indicators of the electron beam measurement images of the sampling images with the difference between the gray value standard deviation and the image defocus threshold value within a preset range and the sharpness critical indicator, and re-determining the electron beam measurement image corresponding to the sharpness indicator with the minimum difference from the sharpness critical indicator as the reference image.

[0149] In some embodiments, please refer toFigure 13 The image processing module 2 further comprises an acquisition unit 22 and a calculation unit 23. The acquisition unit 22 is connected with the image acquisition device 1 and the reference image determination unit 21; the acquisition unit 22 is configured to acquire a first gray value histogram of the reference image; and the acquisition unit is further configured to acquire a second gray value histogram of the electron beam measurement image; the calculation unit 23 is connected with the acquisition unit 22, the threshold value determination module 3 and the controller 4; the calculation unit 23 is configured to calculate a reference gray value standard deviation of the reference image according to the first gray value histogram; and the calculation unit is further configured to calculate a 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 by some of the above embodiments, the terms "module", "unit" and / or "system" and the like used in the specification can be used to represent computer-related entities, hardware, firmware, combinations of hardware and software, software, or software in execution. For example, "module", "unit" and / or "system" can be, but are not limited to, a process running on a processor, a processor, an object, an executable, an execution thread, a program and / or a computer. For example, "module", "unit" and / or "system" can be executed from various computer readable media having various data structures stored thereon. Moreover, in the above embodiments provided by the present disclosure, it should be understood that the disclosed "module", "unit" and / or "system" can be implemented in other ways. For example, the above-described devices are only schematic. For example, the division of the modules is only a logical function division, and actual implementation can have another division manner, for example, a plurality of modules can be combined or integrated into another device, or some features can be ignored or not executed. The connection between the described ones can be through some interfaces, indirect coupling or communication connection between modules, which can be electrical, mechanical or other forms. The modules described separately can be or can not be physically separated. Some or all of the modules can be selected according to actual needs to achieve the purpose of the embodiments of the present disclosure.

[0151] In the description of the present specification, the description of the terms "some embodiments", "some examples", "exemplarily" and the like means that the specific features, structures, materials or characteristics described in conjunction with the embodiments or examples are contained in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example.

[0152] The technical features of the above embodiments can be combined in any way. In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described, but as long as the combination of the technical features does not exist, it should be considered as the scope of the present disclosure.

[0153] The above embodiments only express several implementation ways of the present application, and the description is more specific and detailed, but it should not be understood as a limitation to the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are all within the scope of protection of the present application.

Claims

1. A method for monitoring image defocus, characterized in that, include: Provide a reference wafer and acquire sampled images of multiple specified regions in the reference wafer; A reference image is determined from the plurality of sampled images based on the sharpness of each of the sampled images; Obtain the standard deviation of the reference gray value of the reference image, and determine the image defocus threshold based on the standard deviation of the reference gray value; Provide a target wafer, and obtain an electron beam measurement image of the target wafer and the standard deviation of the target grayscale value of the electron beam measurement image; When the standard deviation of the target gray value is less than the image defocus threshold, an image defocus warning is issued.

2. The image defocus monitoring method according to claim 1, characterized in that, The step of determining a reference image from multiple sampled images based on the sharpness of each sampled image includes: Set a resolution threshold; The sharpness index of each sampled image is compared with the sharpness threshold index, and the sampled image corresponding to the sharpness index with the smallest difference from the sharpness threshold index is determined as the reference image.

3. The image defocus monitoring method according to claim 1 or 2, characterized in that, The step of obtaining the standard deviation of the reference grayscale value of the reference image and determining the defocus threshold of the image based on the standard deviation of the reference grayscale value includes: Obtain the first grayscale histogram of the reference image; The standard deviation of the reference gray value of the reference image is calculated based on the first gray value histogram; The image defocus threshold is determined based on the standard deviation of the reference grayscale value of the reference image.

4. The image defocus monitoring method according to claim 1, characterized in that, 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, the reference image is redefined; The image defocus threshold is redefined based on the standard deviation of the target grayscale value of the redefined reference image.

5. The image defocus monitoring method according to claim 4, characterized in that, After measuring the target wafer, the reference image is redefined, including: After measuring the target wafer, the sharpness 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 sharpness critical index, and the electron beam measurement image corresponding to the sharpness index with the smallest difference from the sharpness critical index is re-determined as the reference image.

6. The image defocus monitoring method according to claim 4, characterized in that, The reference wafer includes the first wafer in a wafer batch.

7. The image defocus monitoring method according to claim 4, characterized in that, The target wafer also includes: other wafers besides the first wafer in the wafer batch; The determination of image defocus warning for the other wafers is based on the redefined image defocus threshold.

8. The image defocus monitoring method according to claim 1, characterized in that, The specified regions are uniformly located on portions of the reference wafer in the upper, middle, lower, left, and right directions.

9. The image defocus monitoring method according to claim 1, characterized in that, The step of providing a target wafer and acquiring an electron beam measurement image of the target wafer and the standard deviation of the target grayscale value of the electron beam measurement image includes: Acquire the electron beam measurement image of the target wafer; Obtain the second grayscale histogram of the electron beam measurement image; The standard deviation of the target gray value of the electron beam measurement image is calculated based on the second gray value histogram.

10. An image defocus monitoring system, characterized in that, Connected to the wafer fabrication equipment; the monitoring system includes: An image acquisition device is used to acquire sampled images of multiple designated regions in a reference wafer; and also to acquire electron beam measurement images of a target wafer; An image processing module, connected to the image acquisition device, is used to determine a reference image from multiple sampled images based on the sharpness of each sampled image, and to obtain the reference grayscale standard deviation of the reference image; and is also used to obtain the target grayscale standard deviation of the electron beam measurement image. A threshold determination module, connected to the image processing module, is used to determine the image defocus threshold based on the standard deviation of the reference gray value. The controller, connected to the image processing module, the threshold determination module, and the wafer frame, is used to provide an image defocus warning and control the wafer frame to stop when the standard deviation of the target gray value is less than the image defocus threshold.

11. The image defocus monitoring system according to claim 10, characterized in that, The image processing module includes: The reference image determination unit, connected to the image acquisition device and the threshold determination module, is used to compare the sharpness index of each sampled image with a set sharpness threshold index, and determine the sampled image corresponding to the sharpness index with the smallest difference from the sharpness threshold index as the reference image.

12. The image defocus monitoring system according to claim 11, characterized in that, The reference wafer includes the first wafer in a wafer batch, and the target wafer includes other wafers in the wafer batch besides the first wafer; the number of electron beam measurement images is greater than the number of sampled images; the reference image determination unit is further configured to re-determine the reference image after measuring the target wafer; the threshold determination module is further configured to re-determine the image defocus threshold based on the standard deviation of the target grayscale value of the re-determined reference image; the controller is further configured to determine the image defocus warning of other wafers based on the re-determined image defocus threshold.

13. The image defocus monitoring system according to claim 12, characterized in that, The reference image determination unit is further configured to, after measuring the target wafer, compare the sharpness index of the electron beam measurement image of the sampled image whose difference between the grayscale value standard deviation and the image defocus threshold is within a preset range with the sharpness critical index, and re-determine the electron beam measurement image corresponding to the sharpness index with the smallest difference from the sharpness critical index among the sharpness indices as the reference image.

14. The image defocus monitoring system according to claim 10, characterized in that, The image processing module further includes: The acquisition unit, connected to the image acquisition device and the reference image determination unit, is used to acquire a first grayscale histogram of the reference image; and is also used to acquire a second grayscale histogram of the electron beam measurement image. The calculation unit, connected to the acquisition unit, the threshold determination module, and the controller, is used to calculate the standard deviation of the reference gray value of the reference image based on the first gray value histogram; and is also used to calculate the standard deviation of the target gray value of the electron beam measurement image based on the second gray value histogram.

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