WO2022230338A1 - 欠陥を検出するシステム、及びコンピュータ可読媒体 - Google Patents
欠陥を検出するシステム、及びコンピュータ可読媒体 Download PDFInfo
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Definitions
- the present disclosure relates to a method, system, and computer-readable medium for detecting defects, and in particular, a method, system, and computer-readable medium for detecting with high accuracy the occurrence of minute pattern defects that occur stochastically very rarely. Regarding.
- Patent Literature 1 discloses an autoencoder in which a three-layer neural network undergoes supervised learning using the same data for the input layer and the output layer. explained.
- Patent Document 2 an original image is divided into grids of small areas, model learning is performed using an autoencoder for each small area, and an inspection model generated by the model learning is used to divide an image as an inspection target. It is described that anomaly detection processing is performed for each data to specify an anomalous location in units of small regions.
- image (or data) augmentation is performed using multiple images generated by cutting out portions of one image and performing various different processing. commonly known.
- Patent Documents 1 and 2 describe generating an estimation model for each small area and using the model to detect anomalies in each small area. Such a technique is effective when the pattern (geometric shape) contained in the image is a relatively simple shape.
- a method, system, and computer readable method for generating a reference image based on an appropriate model and inspecting defects using the reference image, even for a sample including a large number of patterns, such as a semiconductor device, will be described below. Describe the medium.
- a system, method, and computer readable medium for detecting defects on a semiconductor wafer, such as by identifying one or more defects contained in an input image received.
- the one or more computer systems comprise a learner including an autoencoder trained in advance by inputting a plurality of images at different positions included in the training images, and the one or more computer systems proposes a system or the like that divides the input image, inputs it to the autoencoder, and compares the output image output from the autoencoder with the input image.
- FIG. 4 is a flow chart showing the procedure of a defect detection method;
- FIG. 10 is a diagram showing an example of the frequency distribution of the degree of divergence between input and output of an autoencoder;
- FIG. 4 is a diagram showing an example of the arrangement of sub-images for inspection;
- FIG. 2 is a diagram showing an example of a design pattern of wiring layers of a typical logic semiconductor integrated circuit;
- FIG. 4 is a diagram showing an overview of the relationship between circuit design patterns and sub-images;
- FIG. 4 is a diagram showing an overview of the relationship between patterns transferred onto a wafer and sub-images;
- FIG. 4 is a timing chart showing the relationship between an imaging process in a scanning electron microscope and an image analysis process in a computer system;
- FIG. 10 is a diagram for explaining the principle of improving the accuracy rate by providing a superimposed region in a sub-image region;
- FIG. 4 is a diagram showing inspection processes of a semiconductor device manufacturing department and a design department;
- abnormality determination is performed by comparing the pattern image to be inspected with the external normal pattern image.
- a normal pattern image is an image of the same pattern created separately (for example, at a different position on the same wafer), or a composite image of a plurality of images of the same pattern (often called a golden image), a design pattern, or a simulation image generated from the design pattern. , etc. are used.
- golden images and design data are not prepared for each design pattern, it may be difficult to conduct proper inspections.
- machine learning using deep neural networks and the like has been developed, and attempts have been made to detect defects using this.
- this method is applied to inspect random patterns of semiconductor integrated circuits, the scale of the network becomes unrealistically large, as will be explained later.
- by embedding normal pattern information in a neural network of a realistic scale defect inspection and defect judgment of wafers with patterns of arbitrary design shapes without using golden images and design data.
- FIG. 1 is a flow chart for explaining the process of generating an autoencoder based on acquisition of an original image for learning and performing serial defect detection using the autoencoder.
- FIG. 2 is an image for learning an autoencoder.
- 4 is a flow chart for explaining a process of acquiring an inspection image in parallel and detecting a defect included in the inspection image.
- an image original image for learning
- an image original image for learning
- a scanning electron microscope SEM
- the image includes a minimum dimension pattern defined by the layout design rule and is obtained for a pattern created under optimum conditions of the lithography or etching process.
- a plurality of sub-images for learning are cut out at different positions in the original image for learning.
- a plurality of original images for learning are prepared, a plurality of sub-images for learning are cut out from each of them.
- the angle of view of the sub-image for learning (for example, the length of one side of the sub-image) may be about F to 4F, where F is the resolution of the lithography or etching process or the minimum dimension of the layout design rule. preferable.
- one autoencoder is generated using the plurality of cut-out learning sub-images as teacher data.
- one autoencoder is generated from a plurality of sub-images cut out from different positions of the sample (wafer). This means that instead of generating an autoencoder for each of the multiple subimages at different positions, we generate one autoencoder using the subimages at different positions. It does not mean that the number of autoencoders generated is limited to one. For example, semiconductor devices including a plurality of types of circuits, which will be described later, may have different circuit performances, and it may be desirable to generate an autoencoder in each circuit.
- each circuit uses a plurality of sub-images at different positions to generate an autoencoder for each circuit.
- a plurality of autoencoders may be generated according to the optical conditions of the SEM, the manufacturing conditions of the semiconductor device, and the like.
- a sub-image is a small region image cut out from different shapes or different positions, and generates one autoencoder based on the input of these images.
- the small area image includes the background, pattern, and edge of the semiconductor device, and the number of included patterns or background is preferably one.
- the sample image is generated in layers, and so on.
- the set of all sub-images for learning may be divided into a teacher data set and a test data set, and the autoencoder may be trained using the image data of the teacher data set while verifying the accuracy with the data of the test data set.
- the autoencoder uses normal data as teacher data to learn an hourglass-shaped neural network as shown in FIG. That is, the network is trained so that when normal data is input, the input data itself is output.
- an hourglass-shaped neural network the amount of information is suppressed to a level necessary for reproducing normal data as normal data in the constricted portion of the network. Therefore, if data other than normal data is input, it cannot be reproduced correctly. Therefore, it is known that normality or abnormality can be determined by taking the difference between the input and the output.
- An autoencoder consists of an encoder (compressor) and a decoder (demodulator), the encoder compresses the input data into an intermediate layer called the hidden layer vector, and the decoder extracts the hidden layer vector from which the output data is as close as possible to the original input data. generated to be Since the dimension of the hidden layer vector is smaller than the dimension of the input vector, it can be regarded as a compressed form of the information of the input data.
- the autoencoder is trained using normal data as teacher data. At this time, when normal data is input, the autoencoder outputs output data that is as close to normal data as possible. is known to be difficult. Therefore, there is known a method of determining whether or not there is an abnormality in the input data by comparing the input and the output and seeing if they match within a certain allowable range.
- a fully-connected multi-perceptron a feedforward neural network (FNN), a convolutional neural network (CNN), or the like can be used.
- FNN feedforward neural network
- CNN convolutional neural network
- the number of layers, the number of neurons in each layer or the number of CNN filters, network configuration such as activation function, loss function, optimization method, mini-batch size, learning methods such as number of epochs are generally known.
- the inventor made use of the characteristics of the autoencoder and studied an appropriate method, system, and non-transitory computer-readable medium for defect inspection of semiconductor devices.
- the inventors found that the shape of a semiconductor device included in an image obtained by an electron microscope or the like is complex in a wide area, but simple in a narrow area, and can be regarded as a simple shape. , the image area is reduced, and if the narrow area image is used as an input to the autoencoder, defect inspection based on high-precision comparison image generation becomes possible.
- the curvature r of the pattern edge included in a certain narrow image area, the intersection (x1, y1, x2, y2) of the frame of the narrow image area, and the boundary (edge) between the inside of the pattern and the background portion is 4.
- the curvature r of the pattern edge included in a certain narrow image area, the intersection (x1, y1, x2, y2) of the frame of the narrow image area, and the boundary (edge) between the inside of the pattern and the background portion is 4.
- the area that can be inspected is extremely large with respect to the size of the pattern that needs to be inspected (for example, the line width).
- a pattern that can be inspected corresponds to one branch of a tree. That is, for example, when performing a full-surface inspection, it is necessary to capture an image with a resolution that enables recognition of a single tree branch over the entire island.
- an image obtained by capturing a semiconductor device is mainly divided into narrow regions that can be regarded as a simple shape as described above, and the divided image is input to an autoencoder.
- a method, system, and non-transitory computer-readable medium are described for performing defect inspection by comparing autoencoder output images.
- the pattern to be inspected which is designed according to the layout design rules and transferred onto the wafer using the lithography or etching process, is imaged with an SEM to obtain an inspection image (original image for inspection).
- a plurality of sub-images for inspection are cut out from the original image for inspection with the same angle of view as the sub-image for learning, and are input to the autoencoder to obtain an output image (first image) for inspection.
- Defects are detected from the difference between sub-images (second images).
- a detection method for example, for each of a plurality of inspection sub-images, the degree of divergence between the input and the output is calculated, a histogram as shown in FIG.
- the value is A sub-image exceeding a certain threshold is output as an image with a high possibility of having a defect.
- a value obtained by summing the squares of the differences in the luminance values of corresponding pixels in the input and output images for all pixels can be used.
- another method of obtaining the difference between the input and the output based on the comparison between the input and the output may be used.
- the shape of the histogram showing the frequency for each degree of difference will change. For example, even if sub-images exceeding the above threshold are not detected in a specific image to be inspected, if the extrapolated value of the frequency of appearance near the divergence threshold increases due to, for example, the tail of the histogram extending, the inspection point It is expected that defects will be detected by increasing the inspection image in the vicinity. Even if defects do not occur, the shape of the histogram is very sensitive to changes in process conditions. can be prevented. Therefore, the shape change itself can be used as an index of the normality of the process. As an index of shape change, numerical values such as the mean value, standard deviation, skewness, kurtosis, and higher-order moment of histogram distribution may be used.
- the computer system is configured to display, on the display device, a frequency histogram for each degree of divergence (difference information) extracted from a plurality of sub-images, as illustrated in FIG. Additionally, the computer system may be configured to evaluate the shape of the histogram using the index. At least one of a past image of a semiconductor wafer manufactured under the same manufacturing conditions, a histogram extracted from the image, and shape data thereof is used as reference data (first data) to evaluate changes in the process state. , and compared with a newly extracted histogram or its shape data (second data), it is possible to monitor changes over time in the process conditions.
- the change over time of the skewness (index value of shape change) with respect to the original histogram shape may be graphed and displayed or output as a report. Further, as illustrated in FIG. 4, a plurality of histograms extracted from semiconductor wafers with the same manufacturing conditions but with different manufacturing timings may be displayed together. Furthermore, an alarm may be issued when the skewness or the like exceeds a predetermined value.
- a learning device that learns data sets such as information on changes in frequency information for each difference information (change in histogram shape over time, etc.), causes of abnormalities, amount of adjustment of semiconductor manufacturing equipment, timing of adjustment of semiconductor manufacturing equipment, etc. as teacher data. , and inputting frequency information for each difference information to the learning device, thereby estimating the cause of an abnormality or the like.
- the plurality of inspection sub-images cover the entire area of the inspection original image.
- the plurality of test sub-images preferably have overlapping areas in common with adjacent test sub-images. For example, when cutting out sub-images for inspection from the inspection image, as shown in FIG. If a defect is detected in two or more adjacent sub-images, it may be determined that there is a high probability that the defect is present. In this way, the region is set so that a plurality of sub-image regions straddle the same location, and if a defect is found in a plurality of sub-image regions in which some regions overlap, the region is a region where a defect occurs with a high probability. may be defined as
- FIG. 13 shows an example in which a plurality of sub-image areas 1302 are set in an image acquisition area 1301 while providing, for example, an overlapping area 1303 .
- sub-areas 1302 are set at four locations around the superimposed area 1303.
- the four sub-image areas are set so as to partially overlap other sub-areas, and the four sub-areas are superimposed in an overlapping area 1303 .
- Areas 1306 and 1307 are similar.
- An area 1305 shows an example in which a sub-area 1308 located in the lower right of the area is extracted as an area with a large divergence.
- the shaded area is extracted as an area with a large degree of divergence.
- the upper left, upper right, and lower right sub-image areas are extracted, and in the area 1307, the upper left and lower right sub-image areas are extracted as areas with a large divergence degree. Since it is considered that the larger the number of sub-regions with a large degree of deviation, the higher the probability of defect occurrence, the identification display according to the number of regions with a large degree of deviation per unit area should be performed on the map that defines the sample coordinates.
- the defect existence probability can be displayed as a distribution.
- FIG. 13 shows an example of displaying a bar graph 1304 that increases and decreases according to the number of areas with large degrees of deviation.
- weighting according to the degree of divergence may be performed, for example.
- identification display may be performed according to the statistic of the degree of divergence of a plurality of sub-regions.
- the defect existence probability may be obtained according to the number of superimposed regions per unit area or the density of regions with a large divergence.
- the sub-image position for example, the center coordinates of the sub-image
- the degree of divergence By plotting the relationship between the sub-image position (for example, the center coordinates of the sub-image) and the degree of divergence, it is possible to know the distribution of defect positions within the original image area.
- the above positional distribution is useful for inferring the mechanism of defect generation.
- by outputting an enlarged SEM image around the position of the sub-image having a large degree of divergence it is possible to directly confirm an abnormality such as a defect shape.
- a bar graph 1304 as exemplified in FIG. 13 on the GUI screen and displaying the image of the area 1305 according to the selection, visual confirmation corresponding to the defect existence probability becomes possible.
- An autoencoder trains an hourglass-shaped neural network using normal data as teacher data so that input data itself is output when normal data is input. If data other than normal data is input, it cannot be reproduced correctly. Therefore, by taking the difference between the input and the output, it can be applied to abnormality detection for determining normality or abnormality. Therefore, it is conceivable to apply the method to the inspection SEM image of the pattern of the semiconductor integrated circuit, and to apply it to the detection of abnormalities in the pattern.
- FIG. 1 An example of a wiring layer pattern of a typical logic semiconductor integrated circuit is shown in FIG.
- Such circuit patterns are usually designed according to certain layout design rules, and in many cases simply consist of pattern areas (lines) and non-pattern areas (intervals (white areas)) that extend in the vertical and horizontal directions and are larger than the minimum dimensions. .
- an area with a certain limited angle of view is cut out from an arbitrary layout design pattern.
- the pattern (object) included in the clipped angle of view varies depending on the positional relationship between the target pattern and the clipped region. , the included pattern is reduced to a relatively simple pattern.
- FIG. 7(b) shows how the sub-image changes when the pattern is cut by changing the position of the sub-region with respect to the corner. For example, if the sub-region is completely outside the pattern as shown in the left of FIG. 7(a), the sub-image does not include the pattern region (corresponding to the lower left of FIG. 7(b)). As shown in the left part of FIG. 7(a), when the sub-area is at the edge of the pattern corner, the pattern area appears in the lower left corner of the sub-image (corresponding to the upper right part in FIG. 7(b)).
- the sub-region is a square whose side is the minimum dimension in the layout design rule, and an arbitrary position of an arbitrary design pattern is cut out with this square, at most one pattern region and one non-pattern region are cut out. only included. If the pattern is limited to the vertical and horizontal directions, the variation is, as shown in FIG. It is defined by how to allocate each of the defined four areas A, B, C, and D to pattern areas or non-pattern areas.
- lithographic processes can be thought of as low-pass filters for spatial frequencies in a two-dimensional plane.
- the size of the sub-image to be cut out is assumed to be a square with one side having the minimum design dimension, but this is an assumption for the sake of simplicity of explanation, and in reality it is not limited to this.
- the length of one side of the sub-image is preferably 2 to 4 times the minimum dimension of the design pattern or 2 to 4 times less than the resolution critical dimension of the lithography or etching process used for transfer.
- the resolution limit dimension W is determined by the wavelength ⁇ of light used in lithography, the numerical aperture NA of the optical system, the proportional constant k1 depending on the illumination method and resist process, and the spatial frequency magnification amplification factor Me of the etching process.
- Me is 1 when etching a pattern formed by lithography as it is, 1/2 for the so-called SADP (Self-Aligned Double Patterning) or LELE (Litho-Etch-Litho-Etch) process, and 1/2 for the LELELE process. 3. 0.25 for SAQP (Self-Aligned Quadruple Patterning) process.
- SADP Self-Aligned Double Patterning
- LELE Litho-Etch-Litho-Etch
- LELELE Low-Etch-Litho-Etch
- SAQP Self-Aligned Quadruple Patterning
- formula 2 is stored in the storage medium of the computer system, and the appropriate size of the sub-image is selected by inputting necessary information from an input device or the like. You can make it work.
- M is a multiple (for example, 2 ⁇ multiple ⁇ 4) of the minimum dimension of the pattern as described above. Note that it is not always necessary to enter all values. For example, if the wavelength of light used for exposure is fixed, treat it as already entered information and enter other information, Alternatively, the size of the sub-image may be obtained. Further, as described above, the size SI (length of one side) of the sub-region may be calculated based on the input of the dimensions of the layout pattern.
- the variation can be covered by cutting out images of various transferred patterns, including patterns designed with minimum allowable dimensions, at various different positions. For example, as shown in FIG. 8(b), by cutting out a rectangular pattern with rounded corners by changing the position of the window indicated by the dotted line in various ways, variations for learning as shown in FIG. 8(c) can be obtained. Sub-images can be generated. Also, patterns cut at various different angles may be added.
- the relative positional relationship between the angle of view and the pattern changes in various ways depending on the positioning accuracy of the wafer stage. Therefore, the relative positional relationship between the angle of view of the sub-image acquired from the SEM image and the pattern included therein also varies.
- a normal pattern must be judged normal for these various relative positional relationships. Variations within these normal ranges can be covered by cutting different patterns of the same or similar designs at different locations.
- the autoencoder is configured and learned so that the degree of divergence between the input and output of the autoencoder with respect to normal patterns is kept small while the degree of divergence with respect to abnormal patterns is maximized. .
- a patterned area or non-patterned area may exist at the edge of the field of view (FOV) of the sub-image and may be detected as an abnormality without being reproduced by the autoencoder.
- FOV field of view
- the adjacent sub-image is also detected as abnormal.
- the width of the patterned area or the non-patterned area with a normal width is within the normal range, no abnormality is detected in the adjacent sub-image. Therefore, as shown in FIG. 5, the feed pitch of the detection sub-region is set smaller than the angle of view of the sub-region, and the case where an abnormality is simultaneously detected in adjacent sub-images is determined to be a true abnormality. rate improves.
- FIG. 14 is a diagram explaining the principle of improving the accuracy rate by providing a superimposed area in the sub-image area (setting the feed pitch of the sub-image area to be smaller than the angle of view).
- the feed pitch of the sub-image areas (1401 to 1404) on the image acquisition area 1301 is half that of the sub-image area.
- FIG. 14 shows an example in which an abnormality is detected in sub-image areas 1401, 1403, and 1404 included in areas 1305 and 1307, and no abnormality is detected in a sub-image area 1402.
- FIG. As described above, no abnormality is detected in the sub-image area 1402 adjacent to the sub-image area 1401 in which an abnormality has been detected in the area 1305 . By including such a determination procedure, it is possible to quantitatively evaluate an improvement in the accuracy rate of anomalies and the probability of anomalies.
- the system consists of a scanning electron microscope and one or more computer systems for storing and processing image data output therefrom.
- the computer system is configured to read a program stored in a predetermined computer-readable medium and execute defect detection processing as described later.
- a computer system is configured to communicate with the scanning electron microscope.
- the computer system may be remote from the scanning electron microscope, connected to the scanning electron microscope by one or more transmission media, or may be a module of the scanning electron microscope.
- the scanning electron microscope captures the wafer pattern created under optimal conditions and transfers the image data to the computer system.
- a computer system stores the images as training images and generates an autoencoder from the training images.
- the scanning electron microscope then images the wafer pattern under inspection and transfers the image data to a computer system.
- the computer system stores the image as inspection image data, and detects defects from the inspection image data using the autoencoder.
- the computer system outputs a signal for displaying at least one of inspection results, inspection conditions, electron microscope images, etc. on the display device.
- the display device displays necessary information based on the signal.
- pipeline processing and parallel computation may be combined. That is, the scanning electron microscope captures an image of a specified position on the inspection wafer according to an imaging recipe. Immediately after each position is captured, each image is transferred to the computer system, and an image of the next specified position is captured according to the imaging recipe. The computer system generates a plurality of sub-images from the sequentially transferred images and calculates the degree of divergence for each sub-image. Here, the degree of divergence calculation for a plurality of sub-images may be processed in parallel.
- an electron beam 803 is extracted from an electron source 801 by an extraction electrode 802 and accelerated by an acceleration electrode (not shown).
- the accelerated electron beam 803 is condensed by a condenser lens 804 which is one form of a focusing lens, and then deflected by a scanning deflector 805 .
- the electron beam 803 scans the sample 809 one-dimensionally or two-dimensionally.
- An electron beam 803 incident on a specimen 809 is decelerated by a decelerating electric field formed by applying a negative voltage to an electrode incorporated in a specimen stage 808 and focused by the lens action of an objective lens 806 to reach the specimen 809 . surface is irradiated.
- a vacuum is maintained inside the sample chamber 807 .
- Electrons 810 (secondary electrons, backscattered electrons, etc.) are emitted from the irradiated location on the sample 809 .
- Emitted electrons 810 are accelerated toward the electron source 801 by the acceleration action based on the negative voltage applied to the electrodes built in the sample stage 808 .
- Accelerated electrons 810 collide with conversion electrodes 812 to generate secondary electrons 811 .
- Secondary electrons 811 emitted from the conversion electrode 812 are captured by a detector 813, and the output I of the detector 813 changes depending on the amount of captured secondary electrons.
- the output I changes, the brightness of the display device changes. For example, when forming a two-dimensional image, the deflection signal to the scanning deflector 805 and the output I of the detector 813 are synchronized to form an image of the scanning area.
- the SEM illustrated in FIG. 811 shows an example in which the electrons 810 emitted from the sample 809 are once converted into secondary electrons 811 at the conversion electrode 812 and detected, but the configuration is of course limited to such a configuration. Instead, for example, a configuration in which an electron multiplier or a detection surface of a detector is arranged on the trajectory of accelerated electrons may be adopted.
- a controller 814 supplies necessary control signals to each optical element of the SEM according to an operation program for controlling the SEM called an imaging recipe.
- the image processing unit 816 generates an integrated image by integrating signals obtained by a plurality of scans on a frame-by-frame basis, if necessary.
- an image obtained by scanning the scanning area once is called an image of one frame.
- an integrated image is generated by averaging signals obtained by 8 times of two-dimensional scanning on a pixel-by-pixel basis. It is also possible to scan the same scanning area multiple times and generate and store multiple one-frame images for each scan.
- the generated image is transferred to an external data processing computer at high speed by an image transfer device. As described above, image transfer may be performed in parallel with imaging in a pipeline fashion.
- a work station 820 controls the entire system having a storage medium 819 for storing the measured values of each pattern and the luminance value of each pixel. , GUI).
- the image memory stores the output signal of the detector (the signal proportional to the amount of electrons emitted from the sample) in synchronization with the scanning signal supplied to the scanning deflector 805, and stores the corresponding address (x, y).
- the image processing unit 816 generates a line profile from the luminance values stored in the memory as needed, identifies edge positions using a threshold method or the like, and functions as an arithmetic processing unit that measures dimensions between edges. also works.
- FIG. 16 shows an example of a GUI screen for setting learning conditions (training conditions).
- the GUI screen shown in FIG. 16 is provided with a setting field 1601 for setting a file name or a folder name in which training images and metadata attached to each image are placed.
- the computer system stores image data and metadata or reads them from an external storage medium, and displays them in the attached information display field 1606 and the SEM image display field 1607, respectively.
- a setting field 1602 for setting the dimension Lsub (angle of view) of the sub-image is provided. Note that the minimum size F of the pattern included in the image and the coefficient n using this as a unit may be input from the setting field 1602 .
- an input field may be used in which at least 1 of the number of pixels Npxl (the number of pixels in at least one of the vertical and horizontal directions, or the total number of pixels) of the sub-image can be input.
- One or more of a plurality of parameters relating to sub-image dimensions, such as dimensions, minimum pattern dimensions, and number of pixels, may be selectable.
- the GUI screen illustrated in FIG. 16 further includes a setting field 1603 for setting the pitch Ps between sub-images.
- the same parameters as those in the setting field may be input, or the exclusion area width Wexcl around the sub-images (interval width between sub-images not acquired as sub-images) may be input. You can do it. Also, a plurality of parameters may be input together.
- a setting field 1604 is provided for setting the number of sub-images to be selected from the sub-images cut out under the conditions set in the setting fields 1601 to 1603 and the like.
- the number of sub - images to be used for learning is set. length of one side), the computer system notifies that or sets the maximum number of samples that can be set. It is also possible to take training time into account and not use all the data.
- a setting field 1605 for setting the type of neural network is provided.
- Neural networks that can be set in the setting field 1605 include, for example, Auto Encoder (AE), Convolutional Auto Encoder (CAE), Variational Auto Encoder (VAE), and Convolutional Variational Auto Encoder (CVAE). These modules are built into or stored in the computer system.
- parameters related to neural network configuration such as latent dimension, encoding dimension, number of stages, number of neurons (or filters) in each stage, activation function, mini-batch size, number of epochs, loss function, optimization method, number of training data and
- a setting column may be provided in which optimization parameters such as the ratio of the number of verification data can be set.
- a setting column may be provided for setting the model configuration and network weighting coefficient storage file name and folder name.
- a display column on the GUI screen that allows the training results to be visually determined. Specifically, it is a histogram of the degree of divergence and an in-plane distribution of the degree of divergence of each image for training. These information may be displayed by selecting tags 1608 and 1609, for example. Furthermore, as supplementary information, the model configuration and network weighting coefficient storage file or folder name may be displayed together.
- FIG. 16 has been described as a GUI for setting learning conditions
- the GUI screen for setting inspection conditions also includes folders in which images to be inspected and metadata attached to each image are placed, sampling pitch Ps of sub-images, image It is desirable to be able to set the surrounding exclusion area width Wexcl, the model configuration used for inspection, the file name of the network weight coefficient, the deviation threshold used for defect determination, the file name for saving inspection result data, the folder name, etc. .
- a wiring layer pattern of a logic LSI semiconductor integrated circuit
- logic circuits and SRAMs is formed on a predetermined base layer for EUV by using an exposure apparatus with NA of 0.33 and a resist processing apparatus using EUV light with a wavelength of 13.5 nm.
- a wafer coated with a resist was exposed to light to form a resist pattern.
- Predetermined optimum conditions were used for exposure amount, focus, resist processing conditions, and the like.
- the logic circuit section and the SRAM section are imaged using an SEM such as that shown in FIG. saved.
- the pixel size of the original image for learning was 1 nm, and the FOV was 2048 nm (length of one side).
- 39601 50 nm-square sub-images for learning were cut out from each of all the acquired original images for learning at a feed pitch of 10 nm in the vertical and horizontal directions.
- the input is a vector with a length of 2500, which is a one-dimensional version of the two-dimensional image data in which the luminance value (gray level) of the image pixel is the value of each element.
- the final output was a vector of length 2500, the same as the input.
- ReLU was used as the activation function for each layer except for the final layer.
- 80% of the sub-images for learning were selected at random as teacher data, and learning was performed.
- Mean square error was used as the loss function, and RMSProp was used as the optimization algorithm. Note that the pixel size, original image size, sub-image size, network configuration, learning method, etc. are not limited to those shown above.
- the original image for inspection of the pattern including the minimum dimension was acquired at the periphery of the wafer.
- an FEM (Focus Exposure Matrix) wafer for inspection was created using the same materials and process equipment, and original images for inspection of patterns including the minimum dimensions formed under various exposure and focus conditions that deviated from the predetermined optimal conditions were obtained. .
- An FEM wafer is a chip that has been exposed and transferred on the wafer under various conditions of focus and exposure. From each of these inspection original images, 9801 inspection sub-images of 50 nm square were cut out at a feed pitch of 20 nm in the vertical and horizontal directions. Each of these test sub-images was input into the autoencoder and the output was calculated. The degree of divergence between the input vector and the output vector was calculated by summing the squares of the deviations of the corresponding elements of the input vector and the output vector. A histogram of the degree of divergence of all the sub-images for inspection was created, and the sub-images for inspection whose degree of divergence was equal to or greater than the threshold value were extracted.
- an SEM capable of relatively large beam deflection is used as the imaging device.
- the pixel size of the original image for learning and the original image for inspection was set to 2 nm, and the FOV size was set to 4096 nm.
- 163,216 learning sub-images of 48 nm square were cut out at a feed pitch of 10 nm in the vertical and horizontal directions.
- 113,569 learning sub-images of 48 nm square were cut out at a feed pitch of 12 nm in the vertical and horizontal directions.
- 40,804 sub-images for learning of 48 nm square were cut out from each image at a feed pitch of 20 nm in the vertical and horizontal directions.
- a convolutional neural network (CNN) is used for the autoencoder.
- the input is two-dimensional image data (30 ⁇ 30 two-dimensional array) with each pixel luminance value (gray level) as an element.
- Nine layers of 12, 12, 12, 12, 12, 1 were used, and the size of the convolution filter was 3 ⁇ 3.
- Each convolution in the first half has a 3x3 max pooling layer, each convolution in the following two layers has a 3x3 max pooling layer, and each convolution in the latter two layers has a 2x2 max pooling layer.
- a 3 ⁇ 3 up-sampling layer was provided after the up-sampling layer and each subsequent convolution of the two layers.
- an activation function ReLU is provided after the max pooling layer and up sampling layer.
- the network was trained using the sigmoid function as the activation function of the final layer, binary_crossentropy as the loss function, and Adam as the optimization algorithm.
- the same defect inspection as in the first application example could be performed for a wide range of patterns in a short period of time.
- the imaging conditions, image cropping method, autoencoder network configuration, learning method, and the like in this embodiment are not limited to those described above.
- a variational autoencoder, a convolutional variational autoencoder, or the like may be used.
- the inspection as described in the first application example and the second application example does not require design data unlike the Die to data base inspection method.
- the judgment work is usually performed in a circuit design department, a yield control department, or the like, not in the manufacturing process of the integrated circuit where the inspection by this method is performed. Therefore, the in-wafer in-chip coordinates and the image data of the abnormal pattern extracted in the manufacturing process by this method may be transmitted to the circuit design department or the yield control department holding the design data.
- the circuit design department, yield management department, or the like determines whether the detected abnormality is acceptable in terms of circuit performance and function based on the above coordinates and images, and if it is not acceptable, takes necessary measures. By doing so, in this method, yield management based on design data can be performed without holding design data in the manufacturing process.
- a semiconductor wafer pattern is usually generated by lithography or the like using a photomask created based on design data designed by a design department (step 1501).
- the resist pattern and the like are evaluated by measurement and inspection equipment such as a CD-SEM to determine whether manufacturing is being performed under appropriate conditions.
- measurement and inspection equipment such as a CD-SEM to determine whether manufacturing is being performed under appropriate conditions.
- an SEM image is obtained for a semiconductor device pattern manufactured in a manufacturing department (step 1502), a sub-image is cut out, and an inspection using an autoencoder is performed (step 1503).
- the manufacturing department conducts inspections using an autoencoder, and selectively transmits image data that captures patterns that can be considered abnormal to the design department and yield management department.
- the design department reads the image data transmitted from the manufacturing department (step 1505), designs the semiconductor device at the time of designing, and executes a comparison inspection with the held design data (step 1506).
- the design data is diagrammed as layout data. Also, pattern edges included in the image data are thinned (contoured).
- the design department will decide whether to consider a design change based on the above comparative inspection, or whether to continue manufacturing without making a design change by reviewing the manufacturing conditions.
- the computer system on the manufacturing department side executes an inspection using an autoencoder and creates a report to the design department based on the inspection results (step 1504).
- the report to the design department includes, for example, the coordinate information of the position where the abnormality was found, the SEM image, and may also include manufacturing conditions, SEM apparatus conditions (observation conditions), and the like. Further, the report may include information such as the frequency distribution of the degree of deviation as illustrated in FIG. 4 and the probability of occurrence of defects in the surroundings.
- the computer system on the design department side executes a comparative inspection and creates a report based on the inspection results (step 1508).
- the report may include the results of the comparison inspection, and may also include the defect types specified as a result of the comparison inspection, inspection conditions, and the like.
- the computer system of the design department may include a learner such as a DNN trained by a data set of comparative inspection results and past feedback history (whether the design was changed or the manufacturing conditions were adjusted, etc.). .
- comparison inspection results difference information of corresponding positions of outline data and layout data, etc.
- correction of design data, policy of correction, policy of correction of manufacturing conditions, etc. are output (step 1507).
- the learner can be replaced with a database that stores the relationship between the comparison test results and the feedback policy.
- Application Example 3 Using an exposure apparatus with an NA of 0.33 and a resist processing apparatus using EUV light with a wavelength of 13.5 nm, a DRAM word line layer mask is exposed onto a wafer having a predetermined base layer coated with an EUV resist, and a resist pattern is formed. formed. Predetermined optimum conditions were used for exposure amount, focus, resist processing conditions, and the like.
- the memory cell portion was imaged using a wide FOV compatible SEM in the same manner as in Application Example 2 at a plurality of locations within the wafer surface, avoiding the wafer peripheral portion, transferred to a data processing computer, and stored as original images for learning. After that, learning sub-images were generated in the same manner as in Application Example 2, and an autoencoder was created using these sub-images.
- a wafer is extracted at a predetermined frequency, inspection images are acquired at a plurality of predetermined positions within the wafer surface, and are obtained in the same size as the learning sub-images.
- a test sub-image was generated.
- the inspection sub-image was input to the autoencoder, and the degree of divergence from the output was calculated. When the locations with high possibility of defects were extracted from the degree of divergence and their distribution in the inspection image was obtained, two cases of defects that appeared randomly and defects that were concentrated in a linear distribution were found.
- the learning pattern and the pattern to be inspected are fixed to the specific process layer pattern of the specific LSI.
- an autoencoder that determines normal dimensional variation and LER (Line Edge Roughness) within the allowable range.
- a wafer prepared in the same manner as the wafer for acquiring the original image for learning in Application Example 1 is inspected using an optical defect inspection apparatus for patterned wafers to identify possible defect positions. output.
- a pattern observation image was captured using a review SEM centering on the output in-plane position of the wafer, and defects were detected using the autoencoder produced in Application Example 1.
- FIG. A difference image between the input image and the output image of the autoencoder was output for the sub-image of the portion where the defect was detected.
- various defects are local (point-like) protrusions or recesses, linear protrusions or recesses across patterns, and along pattern edges.
- the unevenness was classified into linear protrusions or recesses, unevenness along the pattern edge, fine unevenness spreading over the entire image, gentle unevenness spreading over the entire image, and the like. These in turn suggest, for example, micro-foreign particles, bridges between patterns or separation of patterns, pattern edge shifts, pattern edge roughness, image noise, image brightness shifts.
- a defect inspection was performed by the method shown in Application Example 2 for the estimated area with a high risk of defect occurrence.
- ADC Auto Defect Classification
- Defect types include bridging between pattern lines, breakage of pattern lines, disappearance of isolated patterns, excess of LER tolerance, local undulation of pattern lines, other pattern size and shape variations, various foreign matter defects, etc. did.
- pattern abnormalities can be extracted at high speed without using a golden image, design information, or the like.
- the autoencoder is used to extract defects concerns.
- the ADC is selectively used to classify and determine the defect in the pattern image near the defect concern point.
- a combination of an image analysis method and machine learning such as SVM (support vector machine), or various techniques such as supervised machine learning (deep learning using CNN) can be used.
- SVM support vector machine
- supervised machine learning deep learning using CNN
- One or more computer systems are equipped with a module that includes an ADC module and an autoencoder, so that parts that can be candidates for defects can be extracted at high speed, and the work up to defect classification can be made more efficient. becomes.
- one defect classification neural network as shown in FIG. 12(b) perform defect classification and judgment.
- the defect classification neural network shown in FIG. 12(b) is composed of an autoencoder section and a comparative classification section. A large number of sub-images are generated from the SEM image of the inspection target as described in Application Examples 1 to 7, and each sub-image is input to the defect classification network of FIG. 12(b). In the network, first, each sub-image is input to an autoencoder section, and then the obtained autoencoder output and the original subimage are simultaneously input to a comparison and classification section.
- the comparison/classification unit is, for example, a neural network such as a multiperceptron or a CNN that receives the combined vector or matrix of the autoencoder output and the original sub-image, and outputs the probability that the input sub-image is defect-free or contains various defects.
- a neural network such as a multiperceptron or a CNN that receives the combined vector or matrix of the autoencoder output and the original sub-image, and outputs the probability that the input sub-image is defect-free or contains various defects.
- the learning of the above defect classification network is performed as follows. First, as described in Application Examples 1 to 7, the autoencoder is trained to reproduce and output the input as much as possible when sub-images generated from patterns in the normal range are input. Next, a large number of images including defects are input to the autoencoder section to create teacher data of defect images.
- the teacher data may be created by another method without referring to the autoencoder output. Next, a large number of images containing the defects are input to the entire defect classification network, and learning is performed using the teacher data. However, at this time, the network of the autoencoder section is fixed, and only the network of the comparison classification section is learned. Even with this method, bridges between pattern lines, breakage of pattern lines, disappearance of isolated patterns, exceeding the allowable value of LER, local undulations of pattern lines, other pattern size and shape variations, various foreign matter defects, etc. could be determined. .
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Abstract
Description
発明者はオートエンコーダの特徴を活かして、半導体デバイスの欠陥検査を行う適切な方法、システム、及び非一時的コンピュータ可読媒体について検討を行った。その結果、発明者は電子顕微鏡等で取得された画像に含まれる半導体デバイスの形状は、広域であれば複雑であるが、狭域で見れば単純な形状であり、単純形状として捉えられる程度まで、画像領域を縮小し、その狭域画像をオートエンコーダの入力とすれば、高精度な比較画像生成に基づく欠陥検査が可能となるという考えに至った。
試料室807内部は真空が保たれている。
波長13.5nmのEUV光を用いたNA0.33の露光装置とレジスト処理装置により、ロジック回路及びSRAM等を含むロジックLSI(半導体集積回路)の配線層パターンを、所定の下地層上にEUV用レジストを塗布したウエハに露光して、レジストパターンを形成した。露光量、フォーカス、レジスト処理条件等に関し、あらかじめ求めた所定の最適条件を用いた。ウエハ周辺部を避けたウエハ面内の複数個所で、ロジック回路部、及びSRAM部を、図11に例示するようなSEMを用いて撮像し、データ処理用コンピュータに転送して学習用元画像として保存した。
本実施例では、第1実施例においてパターンの撮像に用いたSEMに代えて、相対的に大きなビームの偏向(走査)が可能なSEMを撮像デバイスとして用いた。学習用元画像及び検査用元画像のピクセルサイズは2nm、FOVサイズは4096nmとした。学習用元画像の各々において、縦横方向に10nmの送りピッチで、48nm角の学習用サブ画像を163,216個切り出した。同様にして、縦横方向に12nmの送りピッチで、48nm角の学習用サブ画像を113,569個切り出した。検査用サブ画像については、画像毎に、縦横方向に20nmの送りピッチで、48nm角の学習用サブ画像を40,804個切り出した。
波長13.5nmのEUV光を用いたNA0.33の露光装置とレジスト処理装置により、DRAMのワード線層マスクを所定の下地層上にEUV用レジストを塗布したウエハに露光して、レジストパターンを形成した。露光量、フォーカス、レジスト処理条件等に関し、あらかじめ求めた所定の最適条件を用いた。ウエハ周辺部を避けたウエハ面内の複数個所で、メモリセル部を、適用例2と同様に広FOV対応SEMを用いて撮像し、データ処理用コンピュータに転送、学習用元画像として保存した。しかる後、適用例2と同様に学習用サブ画像を生成し、これを用いてオートエンコーダを作成した。
適用例1で学習用元画像取得のためのウエハを準備した際と同様の方法により作成したウエハを、パターン付きウエハ用光学式欠陥検査装置を用いて検査して、欠陥可能性のある位置を出力した。出力されたウエハ面内位置を中心に、レビューSEMを用いてパターン観察像を撮像し、適用例1で作成したオートエンコーダを用いて欠陥検出を行った。上記欠陥検出された箇所のサブ画像に対して、オートエンコーダの入力画像と出力画像の差分画像を出力した。その結果、様々な欠陥は、上記差分の元画像の画角内における分布において、局所的な(点状の)凸部又は凹部、パターン間にまたがる線状の凸部又は凹部、パターンエッジに沿った線状の凸部又は凹部、パターンエッジに沿った凹凸、画像全体に広がる細かい凹凸、画像全体に広がるなだらかな凹凸、等に分類された。これらは順に例えば、微小異物、パターン間のブリッジ又はパターンの分離、パターンエッジのシフト、パターンエッジのラフネス、画像のノイズ、画像輝度のシフトを示唆する。
適用例3で学習用元画像取得のためのウエハを準備した際と同様の方法により作成したウエハに対し、そのウエハ全面のDRAMメモリセル領域を、パターン付きウエハ用光学式欠陥検査装置を用いて検査して、ヘイズレベルのウエハ面内分布を計測した。ヘイズレベルが所定の閾値より高い領域に対して、適用例2に示した方法で欠陥検査を行った。
適用例1で学習用元画像取得のためのウエハを準備した際と同様の方法により作成したウエハに対して、パターン設計情報、上記情報に基づくパターンシミュレーション、露光装置等のプロセス装置からのフォーカスマップ等の出力情報、又は、ウエハ形状等の各種計測機の出力等から、欠陥発生の危険領域をあらかじめ推定した。推定された欠陥発生危険度の高い領域に対して、適用例2に示した方法で欠陥検査を行った。
適用例1から適用例6において、欠陥検査により抽出された欠陥懸念点座標を含むパターン画像から、所謂ADC(Auto Defect Classification)を用いて欠陥の判定及びその種類を分類した。欠陥の種類としては、パターン線間のブリッジ、パターン線の破断、孤立パターンの消失、LERの許容値越え、パターン線の局所的なうねり、その他のパターン寸法形状変動、各種異物欠陥、等を判定した。オートエンコーダを用いた検査法によれば、パターンの異常を、ゴールデン画像や設計情報等を用いることなく高速に抽出することができる。これをADC等の他の方法と組み合わせることにより、抽出された欠陥を分類・解析して、欠陥発生の原因解析と対策を行うことができる。
適用例1等で説明したように、オートエンコーダを用いた検査は、正常パターンからの逸脱を、ゴールデン画像や設計情報等を用いることなく高速に抽出する。即ち、図12(a)に示すように、検査画像から切り出したサブ画像をオートエンコーダに入力し、その出力と上記入力を比較判別することにより、上記サブ画像の欠陥・無欠陥を判別する。
Claims (15)
- 半導体ウエハ上の欠陥を検出するように構成されたシステムであって、
当該システムは、受け取った入力画像に含まれる欠陥を特定する1以上のコンピュータシステムを備え、前記1以上のコンピュータシステムは、学習用画像に含まれる異なる位置の複数の画像の入力によって予め学習が施されたオートエンコーダを含む学習器を備え、前記1以上のコンピュータシステムは、前記入力画像を分割して、前記オートエンコーダに入力し、当該オートエンコーダから出力される出力画像と、前記入力画像を比較するように構成されているシステム。 - 請求項1において、
前記1以上のコンピュータシステムは、前記入力画像を複数のサブ画像に分割し、当該分割された複数のサブ画像に基づいて1のオートエンコーダを学習させるように構成されているシステム。 - 請求項1において、
前記1以上のコンピュータシステムは、学習用の入力画像の入力に基づいて前記オートエンコーダを学習させ、当該学習が施された前記オートエンコーダに、検査用の複数のサブ画像の入力することによって画像に含まれる欠陥を検出するように構成されているシステム。 - 請求項1において、
前記異なる位置の複数の画像に対応する前記半導体ウエハ上の大きさは、当該複数の画像内に含まれるオブジェクトの最小寸法の1倍より大きく、4倍より小さいシステム。 - 請求項1において、
前記1以上のコンピュータシステムは、前記入力画像を、重畳領域を設けつつ複数のサブ画像に分割するように構成されているシステム。 - 請求項1において、
前記1以上のコンピュータシステムは、前記入力画像と出力画像の乖離度を評価するように構成されているシステム。 - 請求項6において、
前記1以上のコンピュータシステムは、前記乖離度の頻度分布または半導体ウエハ上の分布を表示装置に表示させるように構成されているシステム。 - 請求項6において、
前記1以上のコンピュータシステムは、前記入力画像を、重畳領域を設けつつ、複数のサブ画像に分割し、当該分割された入力画像と出力画像の乖離度を評価し、前記重畳領域を構成するサブ画像の内、前記乖離度が所定値以上のサブ画像の数に応じた識別情報を表示装置に表示させるように構成されているシステム。 - 半導体ウエハ上の欠陥を検出するコンピュータ実装方法を実行するためにコンピュータシステム上で実行可能なプログラム命令を記憶する非一時的コンピュータ可読媒体であって、前記コンピュータ実装方法は、学習用画像に含まれる異なる位置の複数の画像の入力によって予め学習が施されたオートエンコーダを含む学習器を備え、前記1以上のコンピュータシステムは、前記入力画像を分割して、前記オートエンコーダに入力し、当該オートエンコーダから出力される出力画像と、前記入力画像を比較する非一時的コンピュータ可読媒体。
- 半導体ウエハへのビーム照射に基づいて得られる画像信号を処理するシステムであって、
当該システムは、第1の画像データと第2の画像データとの間の差分情報を演算する1以上のコンピュータシステムを備え、前記1以上のコンピュータシステムは、前記第1の画像データと第2の画像データ間の差分の程度毎の頻度を演算するように構成されているシステム。 - 請求項10において、
前記1以上のコンピュータシステムは、前記第1の画像データと第2の画像データの画素毎の乖離度の程度毎の頻度を示すヒストグラムを生成するように構成されているシステム。 - 請求項11において、
前記1以上のコンピュータシステムは、前記ヒストグラムの形状を評価するように構成されているシステム。 - 請求項11において、
前記1以上のコンピュータシステムは、異なる製造タイミングで製造された異なる半導体ウエハで得られた異なる前記ヒストグラムを表示装置に表示させるように構成されているシステム。 - 請求項10において、
前記1以上のコンピュータシステムは、学習用画像に含まれる異なる位置の複数の画像の入力によって予め学習が施されたオートエンコーダを含む学習器を備え、前記1以上のコンピュータシステムは、前記第2の画像を分割して、前記オートエンコーダに入力し、当該オートエンコーダから出力される第1の画像と、前記第2の画像を比較するように構成されているシステム。 - 請求項10において、
前記1以上のコンピュータシステムは、前記第1の画像と第2画像の画素毎の乖離度を評価するように構成されているシステム。
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