Method, product and equipment for evaluating astigmatism degree of electron beam

Abstract

The invention provides an astigmatism degree evaluation method of an electron beam, a product and equipment. The method comprises the following steps: acquiring a plurality of to-be-processed images in different focusing states in a to-be-imaged area of a target wafer; processing each to-be-processed image one by one to obtain corresponding edge contour images of the to-be-imaged area in different focusing states; selecting a feature region in each edge contour image, and taking the image of the feature region as a to-be-evaluated sub-image; and judging the astigmatism degree of the electron beam according to the image features of the plurality of to-be-judged sub-images. Through the method, the plurality of to-be-judged sub-images are comprehensively analyzed, the limitation that judgment is carried out only depending on a single image or a single feature is avoided, the astigmatism degree of the electron beam can be more comprehensively evaluated from multiple angles, and the accuracy of a judgment result is improved.

Description

Technical Field

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

[0002] In the current semiconductor manufacturing and testing field, the electron beam is accelerated to a very high speed by the electrons generated by the cathode in the electron gun under the high-voltage accelerating electric field between the cathode and the anode, and then forms a dense high-speed electron stream after being converged by the lens. However, the electron beam will produce a certain amount of astigmatism during the lens convergence process. The focusing ability of the electron beam after astigmatism is different in different directions, which will make the image clear in some directions and blurred in other directions, and the overall image quality will be reduced, making it difficult to distinguish the fine structure and features of the wafer. Therefore, a method for judging the degree of astigmatism of the electron beam is needed to determine whether the current electron beam is within an acceptable range. Summary of the invention

[0003] In view of the above problems, the present invention proposes a method, product and device for judging the degree of astigmatism of an electron beam, which overcomes the above problems or at least partially solves the above problems.

[0004] One object of the present invention is to judge whether the astigmatism of the electron beam is within an acceptable range;

[0005] A further object of the present invention is to improve the accuracy of the evaluation results.

[0006] In particular, the present invention provides a method for judging the degree of astigmatism of an electron beam, comprising:

[0007] Acquire a plurality of images to be processed in different focusing states in the area to be imaged of the target wafer;

[0008] Processing each image to be processed one by one to obtain edge contour images corresponding to the imaging area under different focusing states;

[0009] Select feature regions in each edge contour image respectively, and use the image of the feature region as the sub-image to be judged;

[0010] The astigmatism degree of the electron beam is judged according to the image features of the plurality of sub-images to be judged.

[0011] Optionally, the step of judging the degree of astigmatism of the electron beam according to the image features of the plurality of sub-images to be judged comprises:

[0012] Ellipse fitting is performed on multiple sub-images to be judged respectively, so as to obtain the fitted target parameters;

[0013] The degree of electron beam astigmatism is judged based on the target parameters.

[0014] Optionally, the target parameters include the major axis length and the minor axis length after ellipse fitting;

[0015] The steps of judging the astigmatism of the electron beam according to the target parameters include:

[0016] The ratio of the major axis to the minor axis is calculated according to the major axis length and the minor axis length in the target parameters;

[0017] Determine whether the ratio of the major axis to the minor axis is greater than a preset threshold;

[0018] When the major-minor axis ratios of all sub-images to be judged are greater than a preset threshold, it is determined that the astigmatism degree of the electron beam is within an acceptable range.

[0019] Optionally, the area to be imaged includes an area in the target wafer where contact holes are densely distributed;

[0020] The images to be processed include in-focus images, under-focus images, and over-focus images;

[0021] The step of acquiring a plurality of images to be processed in different focusing states in the area to be imaged of the target wafer comprises:

[0022] The electron gun objective lens current is adjusted in the imaged area to perform automatic focusing to obtain a focused image, and the objective lens current at the moment when the image is clear is recorded as the focused objective lens current;

[0023] Obtaining a preset focus offset, and determining an under-focus objective lens current and an over-focus objective lens current according to the preset focus offset and a positive-focus objective lens current;

[0024] The electron gun objective lens current is adjusted to be an under-focus objective lens current and an over-focus objective lens current respectively to image the area to be imaged to obtain an under-focus image and an over-focus image.

[0025] Optionally, the step of processing each image to be processed one by one to obtain edge contour images corresponding to the imaged area under different focusing states includes:

[0026] Binarization is performed on each image to be processed one by one to obtain a binary image;

[0027] The edge contour image corresponding to the area to be imaged is obtained in each binary image respectively.

[0028] Optionally, the step of selecting a feature region in each edge contour image and using the image of the feature region as a sub-image to be judged includes:

[0029] In the edge contour image, the area with the largest area within the image contour is selected as the feature area;

[0030] The image in the feature area is used as the sub-image to be judged.

[0031] Optionally, the step of performing binarization processing on each image to be processed one by one to obtain a binarized image includes:

[0032] Get the image to be processed;

[0033] Perform fast Fourier transform on the image to be processed to obtain a Fourier transform image;

[0034] Perform mean filtering on the Fourier transform image, and generate a target histogram according to the result of mean filtering;

[0035] The mean and standard deviation corresponding to the Fourier transform image are calculated according to the target histogram;

[0036] The brightness and contrast of the Fourier transform image are adjusted according to the mean and standard deviation to obtain a binary image.

[0037] Optionally, the step of adjusting the brightness and contrast of the Fourier transform image according to the mean and the standard deviation includes: adjusting the maximum and minimum values ​​corresponding to the brightness in the Fourier transform image according to a preset formula, thereby adjusting the contrast;

[0038] The default formula is:

[0039] Minimum=Maximum=Mean+3*Std Dev

[0040] Among them, Minimum represents the minimum value corresponding to the brightness, Maximum represents the maximum value corresponding to the brightness, Mean represents the mean, and Std Dev represents the standard deviation.

[0041] According to another aspect of the present invention, a computer program product is provided, which includes a computer program. When the computer program is executed by a processor, the steps of any one of the above-mentioned methods for judging the degree of astigmatism of an electron beam are implemented.

[0042] According to another aspect of the present invention, a computer device is provided, comprising a memory, a processor, and a machine executable program stored in the memory and running on the processor, and the processor implements the steps of any of the above-mentioned methods for judging the degree of astigmatism of an electron beam when executing the machine executable program.

[0043] The method for judging the degree of astigmatism of an electron beam of the present invention obtains a plurality of images to be processed in different focusing states in the area to be imaged of a target wafer; processes each image to be processed one by one to obtain an edge contour image corresponding to the area to be imaged in different focusing states; selects a feature area in each edge contour image, and uses the image of the feature area as a sub-image to be judged; and judges the degree of astigmatism of the electron beam according to the image features of the plurality of sub-images to be judged. Through this method, a comprehensive analysis is performed on the plurality of sub-images to be judged, avoiding the limitation of judging by relying on a single image or a single feature, and being able to more comprehensively evaluate the degree of astigmatism of the electron beam from multiple angles, thereby improving the accuracy of the judgment result.

[0044] Furthermore, in the electron beam astigmatism degree evaluation method of the present invention, the area to be imaged includes the contact hole densely distributed area in the target wafer, and the area with the largest area in the image contour is selected as the characteristic area in each edge contour image; the image of the characteristic area is used as the sub-image to be evaluated. In this way, the occurrence of regional charging phenomenon can be prevented, and errors caused by differences in a single contact hole can be avoided, thereby further improving the accuracy of the evaluation result.

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

[0046] Hereinafter, some specific embodiments of the present invention will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the accompanying drawings:

[0047] Figure 1 is a schematic flow chart of a method for judging the degree of astigmatism of an electron beam according to an embodiment of the present invention;

[0048] Figure 2 is a flow chart of a method for judging the degree of astigmatism of an electron beam according to another embodiment of the present invention;

[0049] Figure 3 is a schematic diagram of a computer program product according to an embodiment of the present invention;

[0050] Figure 4 is a schematic diagram of a computer-readable storage medium according to an embodiment of the present invention; and

[0051] Figure 5 is a schematic diagram of a computer device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0052] It should be understood by those skilled in the art that the embodiments described below are only some embodiments of the present invention, rather than all embodiments of the present invention, and these embodiments are intended to explain the technical principles of the present invention, rather than to limit the protection scope of the present invention. Based on the embodiments provided by the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should still fall within the protection scope of the present invention.

[0053] It should be noted that the logic and / or steps represented in the flowchart or described in other ways herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be specifically implemented in any computer-readable medium for use by an instruction execution system, device or equipment (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or equipment and execute instructions), or used in combination with these instruction execution systems, devices or equipment.

[0054] In the current semiconductor manufacturing and testing field, for the astigmatism of electron beams, the general astigmatism elimination solution usually uses a contact hole with a diameter of 250nm-500nm, and the field of view FOV (field of view) is generally 1μm or 1.5μm. The width of the side wall in the X and Y directions of the contact hole is manually measured, and the current value of the astigmatism elimination coil is adjusted after comparison to eliminate the astigmatism.

[0055] However, this astigmatism elimination solution has some disadvantages, including:

[0056] 1. The astigmatism elimination process is cumbersome and time-consuming. Each time the coil current value is adjusted, the width of the X&Y side wall needs to be measured;

[0057] 2. There is a lack of detailed quantitative methods in the adjustment process, that is, the adjustment of the coil current value, and the amount of adjustment each time needs to be judged based on experience;

[0058] 3. A single contact hole is greatly affected by the pattern, that is, if the position is not changed, multiple scans will cause serious charging in the area and lead to inaccurate side wall measurement. If the measurement position is changed, even if the same wafer is in the same area, due to the influence of key processes such as lithography and etching, the side wall conditions and widths of different contact holes are inconsistent, making it difficult to evaluate the astigmatism elimination results.

[0059] Based on the above situation, the method of the present invention proposes a method for judging the degree of astigmatism of an electron beam, so as to judge the degree of astigmatism of the electron beam more comprehensively. It should be noted that the method can not only judge whether the electron beam after astigmatism elimination is within the acceptable range, but also judge the degree of astigmatism of the electron beam in use at any time, so as to ensure the normal use of the electron beam.

[0060] Specifically, Figure 1 FIG. 1 is a flow chart of a method for judging the degree of astigmatism of an electron beam according to an embodiment of the present invention. Figure 1 As shown, the method for judging the degree of astigmatism of an electron beam at least includes the following steps S101 to S104.

[0061] Step S101, a plurality of images to be processed under different focusing states are acquired in the imaging area of ​​the target wafer. The equipment used for imaging can generally include a DRSEM (defect review scanning electron microscope) or a CDSEM (critical dimension measurement electron microscope) machine and other equipment, and those skilled in the art can select the detection equipment according to actual conditions.

[0062] In some optional embodiments, the area to be imaged generally includes an area where contact holes are densely distributed in the target wafer (i.e., a Dense area). For example, a Dense area with a Contact Hole diameter of 100 nm is selected as the area to be imaged. Selecting an area where contact holes are densely distributed can effectively avoid the occurrence of the Charging phenomenon. This is because during the electron beam scanning process, electrons are continuously injected into the contact holes and the surrounding areas, causing the area to accumulate charge, which will produce a Charging effect. This Charging phenomenon will seriously interfere with subsequent measurements, but selecting an area where contact holes are densely distributed can effectively prevent regional Charging. In addition, selecting an area where contact holes are densely distributed can also avoid errors caused by differences between different contact holes. At the same time, the reliability of the Dense area in the subsequent binarization analysis process is much greater than that of the Single (single contact hole) area.

[0063] Optionally, the image to be processed may generally include a focused image, an underfocused image, and an overfocused image. Among them, a focused image refers to an image formed when the imaging system (such as an optical microscope, an electron microscope, etc.) is accurately adjusted to focus the electron beam on the plane where the observed object is located. The image at this time is the clearest and most accurate image. Underfocus means that the focal point of the imaging system is located before the plane of the observed object, that is, the electron beam has not been fully focused on the object and has begun to form an image. This causes the formed underfocus image to present a specific blurred state. Overfocus means that the focal point of the imaging system is located after the plane of the observed object, that is, the electron beam has been overfocused before interacting with the object to form an image, which will also cause a significant change in image quality. Selecting the focused image, the underfocus image, and the overfocus image as the images to be processed for evaluation can greatly improve the accuracy of the evaluation of the degree of electron beam astigmatism.

[0064] Optionally, the steps of obtaining multiple images to be processed in different focusing states in the area to be imaged of the target wafer may generally include: adjusting the electron gun objective lens current in the area to be imaged to perform automatic focusing to obtain a focused image, and recording the objective lens current at the moment when the image is clear as the focused objective lens current; obtaining a preset focus offset, and determining an underfocus objective lens current and an overfocus objective lens current according to the preset focus offset and the focused objective lens current; respectively adjusting the electron gun objective lens current to the underfocus objective lens current and the overfocus objective lens current to image in the area to be imaged to obtain an underfocus image and an overfocus image. The method for selecting the preset focus offset is based on the image clarity, and those skilled in the art can determine the specific value of the focus offset according to actual needs.

[0065] Step S102 , processing each image to be processed one by one to obtain edge contour images corresponding to the imaged area under different focusing states.

[0066] In some optional embodiments, step S102 may generally include: performing binarization processing on each image to be processed one by one to obtain a binarized image; and obtaining an edge contour image corresponding to the area to be imaged in each binarized image. Binarization processing is an image preprocessing technology that aims to convert an image originally having rich grayscale or color information into a binarized image containing only two values ​​(usually 0 and 1, or black and white). The binarized image can be used to clearly obtain the contours of different contact holes of the target wafer in the area to be imaged.

[0067] Optionally, binarization is performed on each image to be processed one by one, and the steps of obtaining the binarized image may generally include: obtaining the image to be processed; performing fast Fourier transform (FFT, Fast Fourier Transform) on the image to be processed to obtain a Fourier transformed image; performing mean filtering on the Fourier transformed image, and generating a target histogram according to the result of mean filtering; calculating the mean and standard deviation corresponding to the Fourier transformed image according to the target histogram; adjusting the brightness and contrast of the Fourier transformed image according to the mean and standard deviation to obtain a binarized image. Among them, mean filtering generally requires selecting a filtering range, for example, 5 pixels (5 pixels) means that for each pixel point in the Fourier transformed image, a circular neighborhood with a radius of 5 pixels is taken as the center (similar to a circular area on a two-dimensional image plane). Then the average value of all pixel values ​​in this neighborhood is calculated, and the average value is used as the new pixel value of the center pixel after filtering.

[0068] Optionally, the step of adjusting the brightness and contrast of the Fourier transform image according to the mean and standard deviation may generally include: adjusting the maximum and minimum values ​​corresponding to the brightness in the Fourier transform image according to a preset formula, thereby adjusting the contrast. The preset formula is shown in Formula 1:

[0069] Minimum=Maximum=Mean+3*Std Dev Formula 1

[0070] Among them, Minimum represents the minimum value corresponding to brightness, Maximum represents the maximum value corresponding to brightness, Mean represents the mean, and Std Dev represents the standard deviation. Such a setting will make the pixels in the image with pixel values ​​lower than the brightness setting value turn black (usually represented as 0 value, corresponding to one state in the binary image), and the pixels with pixel values ​​higher than the brightness setting value turn white (usually represented as 1 value, corresponding to another state in the binary image), thereby converting the original image with rich gray levels into a binary image with only black and white colors, which is convenient for subsequent clearer and more explicit analysis and extraction of the shape, contour and other features of the target object in the image.

[0071] Step S103 , selecting a characteristic region in each edge contour image, and using the image of the characteristic region as a sub-image to be judged.

[0072] In some optional embodiments, step S103 may generally include: selecting the area with the largest area in the image contour in the edge contour image as the feature area; using the image of the feature area as the sub-image to be judged. Since the method of the present invention selects the contact hole densely distributed area (i.e., Dense area) in step S101, there will be multiple contact hole contour images in the edge contour image. At this time, it is necessary to select a representative contour for judgment. An optional solution is to select the area with the largest area in the image contour as the feature area. The area with the largest area in the image contour is also the contact hole with the largest area. Such feature areas are often more likely to completely contain the key features of the image and can reduce the amount of data that needs to be processed later, thereby improving processing efficiency.

[0073] Step S104: judging the degree of astigmatism of the electron beam according to the image features of the plurality of sub-images to be judged.

[0074] In some optional embodiments, step S104 may generally include: performing ellipse fitting on a plurality of sub-images to be judged, respectively, so as to obtain the fitted target parameters; judging the degree of astigmatism of the electron beam according to the target parameters. When the sub-images to be judged corresponding to the three types of images, namely, the in-focus image, the underfocus image, and the overfocus image, all meet the requirements, it can be determined that the degree of astigmatism of the electron beam is within an acceptable range.

[0075] Among them, ellipse fitting refers to trying to fit the shape of the area with an ellipse, and then obtaining parameters related to the fitted ellipse, such as the length of the major axis and minor axis of the ellipse. These parameters can reflect the shape characteristics of the target object from another perspective, which is helpful for comparing with the theoretical standard shape and judging whether there is shape deviation in the manufacturing process of the target object.

[0076] Optionally, the target parameters include the major axis length and the minor axis length after ellipse fitting. The step of judging the degree of astigmatism of the electron beam according to the target parameters may generally include: calculating the major-minor axis ratio according to the major axis length and the minor axis length in the target parameters; judging whether the major-minor axis ratio is greater than a preset threshold; and judging that the degree of astigmatism of the electron beam is within an acceptable range when the major-minor axis ratios corresponding to all sub-images to be judged are greater than the preset threshold.

[0077] Calculating the major-minor axis ratio (i.e., the ratio of the minor axis to the major axis) can reflect the image quality and whether there are problems such as astigmatism from the aspect of shape characteristics. This is because the contact holes of the target wafer used for measurement are generally circular, and in the process of imaging such contact holes by the electron beam, the electron beam itself has astigmatism, which will cause the image after imaging to be not the same circle as the contact hole. Therefore, after obtaining the sub-image to be judged, the method of the present invention can determine whether it is a circle by calculating its major-minor axis ratio (theoretically, the major-minor axis ratio is 1 when the image is completely free of astigmatism). In some optional embodiments, the preset threshold can generally be selected to be set to 0.85, and if the minor axis / major axis ratio is >0.85, it can generally be considered that the image astigmatism value is within an acceptable range for the astigmatism degree of the electron beam. Those skilled in the art can determine the specific value of the preset threshold according to the accuracy requirements of imaging.

[0078] Through this method, a comprehensive analysis of multiple sub-images to be judged is performed, avoiding the limitation of relying on a single image or a single feature for judgment. It can more comprehensively evaluate the degree of electron beam astigmatism from multiple angles and improve the accuracy of the judgment results.

[0079] Figure 2 FIG. 1 is a flow chart of a method for judging the degree of astigmatism of an electron beam according to another embodiment of the present invention. Figure 2 As shown, the method for judging the degree of astigmatism of an electron beam at least includes the following steps S201 to S213.

[0080] Step S201, determine the area to be imaged of the target wafer. The area to be imaged generally includes the area where the contact holes are densely distributed in the target wafer (i.e., the Dense area). Selecting the area where the contact holes are densely distributed can effectively avoid the occurrence of the Charging phenomenon. In addition, selecting the area where the contact holes are densely distributed can also avoid errors caused by the differences between different contact holes. At the same time, the reliability of the Dense area in the subsequent binary analysis process is much greater than that of the Single (single contact hole) area.

[0081] Step S202, adjusting the electron gun objective lens current in the area to be imaged to perform automatic focusing to obtain a focused image, and recording the objective lens current at the moment when the image is clear as the focused objective lens current.

[0082] Step S203, obtaining a preset focus offset, and determining an under-focus objective lens current and an over-focus objective lens current according to the preset focus offset and the positive-focus objective lens current.

[0083] Step S204, respectively adjust the electron gun objective lens current to an underfocus objective lens current and an overfocus objective lens current to image the area to be imaged to obtain an underfocus image and an overfocus image. The method of the present invention selects to detect the three types of images, namely, the focused image, the underfocus image and the overfocus image, together, thereby increasing the accuracy of determining the degree of electron beam astigmatism.

[0084] Step S205, performing binarization processing on each image to be processed one by one to obtain a binarized image.

[0085] Step S206 , obtaining edge contour images corresponding to the area to be imaged in each binary image.

[0086] Step S207, in the edge contour image, the area with the largest area within the image contour is selected as the feature area, and the image of the feature area is used as the sub-image to be judged. The area with the largest area within the image contour is also the contact hole with the largest area. Such feature areas are often more likely to completely contain the key features of the image, and can reduce the amount of data that needs to be processed later, thereby improving processing efficiency.

[0087] Step S208 , performing ellipse fitting on the multiple sub-images to be judged respectively, so as to obtain the fitted target parameters.

[0088] Step S209, calculate the ratio of the long axis to the short axis according to the long axis length and the short axis length in the target parameters. The ratio of the long axis to the short axis is calculated because the contact hole of the target wafer used for measurement is generally circular, and in the process of imaging such contact holes by the electron beam, the image after imaging is not the same circle as the contact hole due to the astigmatism of the electron beam itself. Therefore, after obtaining the sub-image to be judged, the method of the present invention can determine whether it is a circle by calculating its ratio of the long axis to the short axis (theoretically, the ratio of the long axis to the short axis is 1 when the image is completely free of astigmatism).

[0089] Step S210 , determining whether the major-minor axis ratios of all sub-images to be judged are greater than a preset threshold.

[0090] Step S211, if the judgment in step S210 is yes, it is determined that the astigmatism degree of the electron beam is within an acceptable range. In some optional embodiments, the preset threshold value can generally be selected to be set to 0.85, and if the short axis / long axis ratio is greater than 0.85, it can generally be considered that the image astigmatism value is within an acceptable range for the astigmatism degree of the electron beam. Those skilled in the art can determine the specific value of the preset threshold value according to the accuracy requirements of imaging.

[0091] Through this method, a comprehensive analysis of multiple sub-images to be judged is performed, avoiding the limitation of relying on a single image or a single feature for judgment. It can more comprehensively evaluate the degree of electron beam astigmatism from multiple angles and improve the accuracy of the judgment results.

[0092] In order to more clearly illustrate the execution process of the present method, an optional specific operation example is proposed. The example implements different operation steps in the present method through the functions carried by a device such as a DRSEM (defect review scanning electron microscope) or a CDSEM (critical dimension measurement electron microscope). The specific operation process is as follows:

[0093] First, the equipment used for imaging generally includes DRSEM (defect review scanning electron microscope) or CDSEM (critical dimension measurement electron microscope) equipment. Such equipment has an electron gun that can generate a corresponding electron beam, so this embodiment determines the degree of astigmatism of the electron beam generated by such equipment, thereby ensuring the accuracy of imaging of such equipment.

[0094] Step 1: Switch to the SEM (Scanning Electron Microscopy) mode on the defect review DRSEM or critical dimension measurement CDSEM machine, and select a dense area with a contact hole diameter of 100 nm as the area to be imaged.

[0095] Step 2: Adjust the electron gun objective current in the area to be imaged for automatic focusing. When the image is clearest, record the objective current at this time as Objective Current_In Focus (OL_IN). At the same time, record the objective current in the underfocus and overfocus states as OL_LESS OL_IN–Δ, OL_OVER=OL_IN+Δ, where Δ is the preset focus offset. The method for selecting the preset focus offset is based on the image clarity. Those skilled in the art can determine the specific value of the focus offset according to actual needs.

[0096] Step 3: After collecting In Focus, Less Focus and Over Focus images, perform binarization processing and analysis on the images. Optionally, the software for binarization processing may be Image J software.

[0097] The specific process of binarization processing and analysis is as follows:

[0098] 1. File / Open: Open the In Focus, Less Focus and Over Focus images in the software;

[0099] 2.Process / FFT / FFT: Perform FFT transformation on the above image to be processed to obtain Fourier transform image;

[0100] 3.Process / Filters / Mean / Radius: 5pixels Perform 5pixels area mean filtering on the Fourier transform image;

[0101] 4.Analyze / Histogram: Generate a target histogram based on the result of mean filtering, and calculate the mean (Mean) and standard deviation (Std Dev) values ​​corresponding to the Fourier transform image based on the target histogram;

[0102] 5. Image / Adjust / Brightness&Contrast: Adjust the brightness and contrast of the Fourier transform image according to the mean and standard deviation to obtain a binary image. The specific adjustment method is shown in Formula 1, where Minimum represents the minimum value corresponding to the brightness, Maximum represents the maximum value corresponding to the brightness, Mean represents the mean, and Std Dev represents the standard deviation.

[0103] 6.Process / Find Edges: Get the edge contour of the binary image;

[0104] 7. Execute Analyze-Analyze Particles in sequence, select "clear result" and "Add to manager". Selecting "clear result" is to clear the previous analysis result data before conducting a new analysis to avoid interference with the current analysis. The "Add to manager" option adds the relevant information about these "particles" obtained from the analysis to a special manager (usually ROI Manager, Region of Interest Manager), which facilitates the subsequent viewing, management and further processing of various parameters of different "particles".

[0105] 8. Select the serial number corresponding to the area with the largest area within the image outline, find the corresponding serial number in the ROI Manager (that is, the sub-image to be judged), and select Measure on the right (which means "measurement". In Image J software, it is used to obtain the selected area in the image);

[0106] 9. In Result, select "Result-Set measurement", check "Area" and "Fit ellipse". Area means that the actual area of ​​the sub-image to be judged will be measured and recorded, which is critical for understanding the size of the target object. Checking the "Fit ellipse" option will allow the software to try to fit the shape of the area with an ellipse, and then get the parameters related to the fitted ellipse, such as the length of the major axis and minor axis of the ellipse. These parameters can reflect the shape characteristics of the target object from another perspective, which is helpful for comparison with the theoretical standard shape.

[0107] Step 4: Determine the ratio of the major axis to the minor axis of the In Focus, Less Focus, and Over Focus images. After the "Fit ellipse" in the previous step, the lengths of the major axis and minor axis corresponding to each sub-image to be judged will be obtained. The ratio of the major axis to the minor axis is generally calculated as minor axis / major axis.

[0108] Step 5: If the minor axis / major axis > 0.85, the image astigmatism value is considered to be within the acceptable range for the electron beam DRSEM / CDSEM machine (theoretically, the major axis to minor axis ratio is 1 when the image is completely free of astigmatism).

[0109] Through this method, on the one hand, using a dense area contact hole instead of a single contact hole can effectively prevent regional charging and errors caused by the differences between different contact holes. At the same time, the reliability of the dense area binarization analysis is much greater than that of the single area. On the other hand, the final result can be quantified. The existing solution manually measures the side wall width in the X&Y direction, and the error is too large to control the accuracy.

[0110] The flow chart provided by the present embodiment is not intended to indicate that the operation of the method will be performed in any particular order, or that all operations of the method are included in all every case. In addition, the method may include additional operations. Within the scope of the technical thinking provided by the present embodiment method, additional changes may be made to the above method.

[0111] It should be understood that in some embodiments, each part can be implemented by hardware, software, firmware or a combination thereof. In the above embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system.

[0112] This embodiment also provides a computer program product 10 , a computer readable storage medium 20 , and a computer device 30 . Figure 3is a schematic diagram of a computer program product 10 according to an embodiment of the present invention, Figure 4 is a schematic diagram of a computer-readable storage medium 20 according to an embodiment of the present invention, Figure 5 is a schematic diagram of a computer device 30 according to an embodiment of the present invention. The computer program product 10 includes a computer program 11, which implements the steps of any of the above-mentioned methods for judging the degree of astigmatism of an electron beam when the computer program 11 is executed by a processor 32. The computer-readable storage medium 20 stores the above-mentioned computer program 11, which implements the steps of any of the above-mentioned methods for judging the degree of astigmatism of an electron beam when the computer program 11 is executed by the processor 32. The computer device 30 may include a memory 31, a processor 32, and the computer program 11 stored in the memory 31 and running on the processor 32.

[0113] The computer program 11 for performing the operation of the present invention may be an assembly instruction, an instruction set architecture (ISA) instruction, a machine instruction, a machine-related instruction, a microcode, a firmware instruction, a state setting data, a configuration data of an integrated circuit, or a source code or an object code written in any combination of one or more programming languages ​​and process programming languages. The computer program 11 may be executed entirely on the user's computer, partially on the user's computer, as an independent software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the latter case, the remote computer may be connected to the user's computer via any type of network (including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., using an Internet service provider via the Internet). In some embodiments, in order to perform various aspects of the present invention, an electronic circuit including, for example, a programmable logic circuit, a field programmable gate array (FPGA) or a programmable logic array (PLA) may execute computer-readable program instructions by utilizing the state information of the computer-readable program instructions to personalize the electronic circuit.

[0114] For the purposes of the description of the present embodiment, the computer program product 10 is a related product that includes the computer program 11. For the purposes of the description of the present embodiment, the computer readable storage medium 20 is a tangible device capable of retaining and storing the computer program 11, which may be any device that can contain, store, communicate, propagate or transmit the program 11 for use with or in conjunction with an instruction execution system, device or apparatus. More specific examples (a non-exhaustive list) of the computer readable storage medium 20 include the following: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, and any suitable combination of the foregoing.

[0115] The computer device 30 may be, for example, a server, a desktop computer, a notebook computer, a tablet computer, or a smart phone. In some examples, the computer device 30 may be a cloud computing node. The computer device 30 may be described in the general context of computer system executable instructions (such as program modules) executed by a computer system. Typically, a program module may include routines, programs, target programs, components, logic, data structures, etc. that perform specific tasks or implement specific abstract data types. The computer device 30 may be implemented in a distributed cloud computing environment where remote processing devices linked via a communication network perform tasks. In a distributed cloud computing environment, program modules may be located on a local or remote computing system storage medium including a storage device.

[0116] The computer device 30 may include a processor 32 adapted to execute stored instructions, and a memory 31 providing temporary storage space for the operation of the instructions during operation. The processor 32 may be a single-core processor, a multi-core processor, a computing cluster, or any number of other configurations. The memory 31 may include a random access memory (RAM), a read-only memory, a flash memory, or any other suitable storage system.

[0117] The computer device 30 may also include a network adapter / interface and an input / output (I / O) interface. The I / O interface allows data to be input and output with external devices that may be connected to the computer device. The network adapter / interface may provide communication between the computer device and a network, which is typically shown as a communication network.

[0118] At this point, those skilled in the art should recognize that, although multiple exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications that conform to the principles of the present invention can still be directly determined or derived based on the content disclosed in the present invention without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be understood and recognized as covering all these other variations or modifications.

Claims

1. A method for judging the degree of astigmatism of an electron beam, comprising: Acquire a plurality of images to be processed in different focusing states in the area to be imaged of the target wafer; Processing each of the to-be-processed images one by one to obtain edge contour images corresponding to the to-be-imaged area under different focusing states; Selecting feature regions in each of the edge contour images respectively, and using the images of the feature regions as sub-images to be judged; The astigmatism degree of the electron beam is judged according to the image features of the plurality of sub-images to be judged.

2. The method for judging the degree of astigmatism of an electron beam according to claim 1, wherein: The step of judging the astigmatism degree of the electron beam according to the image features of the plurality of sub-images to be judged comprises: Performing ellipse fitting on the plurality of sub-images to be judged respectively, so as to obtain fitted target parameters; The astigmatism degree of the electron beam is judged according to the target parameter.

3. The method for judging the degree of astigmatism of an electron beam according to claim 2, wherein: The target parameters include the major axis length and the minor axis length after the ellipse fitting; The step of judging the astigmatism degree of the electron beam according to the target parameter comprises: Calculate the major-minor axis ratio according to the major axis length and the minor axis length in the target parameter; Determine whether the major-minor axis ratio is greater than a preset threshold; When the major-minor axis ratios corresponding to all the sub-images to be judged are greater than the preset threshold, it is determined that the degree of astigmatism of the electron beam is within an acceptable range.

4. The method for judging the degree of astigmatism of an electron beam according to claim 1, wherein: The area to be imaged includes an area in the target wafer where contact holes are densely distributed; The images to be processed include in-focus images, under-focus images, and over-focus images; The step of acquiring a plurality of images to be processed in different focusing states in the area to be imaged of the target wafer comprises: Adjusting the electron gun objective lens current in the imaged area to perform automatic focusing to obtain the in-focus image, and recording the objective lens current at the moment when the image is clear as the in-focus objective lens current; Acquire a preset focus offset, and determine an under-focus objective lens current and an over-focus objective lens current according to the preset focus offset and the positive-focus objective lens current; The electron gun objective lens current is adjusted to be the under-focus objective lens current and the over-focus objective lens current respectively to image the area to be imaged to obtain the under-focus image and the over-focus image.

5. The method for judging the degree of astigmatism of an electron beam according to claim 1, wherein: The step of processing each of the to-be-processed images one by one to obtain edge contour images corresponding to the to-be-imaged area under different focusing states comprises: Performing binarization processing on each of the to-be-processed images one by one to obtain a binarized image; The edge contour image corresponding to the area to be imaged is obtained in each of the binarized images respectively.

6. The method for judging the degree of astigmatism of an electron beam according to claim 5, wherein: The step of selecting a feature area in each edge contour image and using the image of the feature area as a sub-image to be judged comprises: Selecting the region with the largest area within the image contour in the edge contour image as the feature region; The image of the feature area is used as the sub-image to be judged.

7. The method for judging the degree of astigmatism of an electron beam according to claim 5, wherein: The step of performing binarization processing on each of the to-be-processed images one by one to obtain a binarized image comprises: Acquire the image to be processed; Performing fast Fourier transform on the image to be processed to obtain a Fourier transform image; Performing mean filtering on the Fourier transform image, and generating a target histogram according to the result of the mean filtering; Calculating the mean and standard deviation of the Fourier transform image according to the target histogram; The brightness and contrast of the Fourier transform image are adjusted according to the mean and the standard deviation to obtain the binarized image.

8. The method for judging the degree of astigmatism of an electron beam according to claim 7, wherein: The step of adjusting the brightness and contrast of the Fourier transform image according to the mean and the standard deviation comprises: adjusting the maximum value and the minimum value corresponding to the brightness in the Fourier transform image according to a preset formula, thereby adjusting the contrast; The preset formula is: Minimum=Maximum=Mean+3*Std Dev Among them, the Minimum represents the minimum value corresponding to the brightness, the Maximum represents the maximum value corresponding to the brightness, the Mean represents the mean, and the Std Dev represents the standard deviation.

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

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

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