Patent Application
20190346769
This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2018-092777 filed on May 14, 2018 in Japan, the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to a pattern inspection apparatus and a pattern inspection method. For example, the embodiments described herein relate generally to a method for inspecting an image for inspection acquired by using an electron beam.
Recently, with an increase in the degree of integration and an increase in the capacity of a large-scale integrated circuit (LSI), a circuit line width required for a semiconductor element decreases. Further, improvement of a yield is indispensable for manufacturing the LSI requiring a large manufacturing cost. However, as represented by a 1-Gbit random access memory (DRAM), patterns configuring the LSI are on the order of submicron to nanometer. In recent years, with the miniaturization of a dimension of an LSI pattern formed on a semiconductor wafer, a dimension to be detected as a pattern defect is also extremely small. Therefore, it is necessary to improve accuracy of a pattern inspection apparatus for inspecting a defect of an ultrafine pattern transferred to the semiconductor wafer. As one of major factors decreasing the yield, there is a pattern defect of a mask used at the time of exposing and transferring an ultrafine pattern on the semiconductor wafer by photolithography technology. For this reason, it is necessary to improve the accuracy of the pattern inspection apparatus for inspecting a defect of a transfer mask used for manufacturing the LSI.
As an inspection method, a method of performing inspection by comparing a measurement image obtained by imaging a pattern formed on a substrate, such as a semiconductor wafer or a lithography mask, with design data or a measurement image obtained by imaging the same pattern on the substrate is known. For example, as a pattern inspection method, there are a “die to die inspection” for comparing measurement image data obtained by imaging the same patterns at different places on the same substrate with each other and a “die to database inspection” for generating design image data (reference image) on the basis of pattern-designed design data and comparing the design image data with a measurement image to be measurement data obtained by imaging a pattern. The imaged image is sent as the measurement data to a comparison circuit. In the comparison circuit, after positions of the images are adjusted, the measurement data and the reference data are compared according to an appropriate algorithm. When the measurement data and the reference data are not matched, it is determined that there is a pattern defect.
In the pattern inspection apparatus, in addition to development of an apparatus that irradiates an inspection target substrate with a laser beam and images a transmitted image or a reflected image, development of an inspection apparatus that scans the inspection target substrate with an electron beam, detects secondary electrons emitted from the inspection target substrate according to irradiation of the electron beam, and acquires a pattern image is also advanced. In the inspection apparatus using the electron beam, development of an apparatus using multiple beams is also advanced. Since the number of secondary electrons in the case of acquiring an image using an electron beam is smaller than the number of photons in the case of acquiring an image by using a laser beam such as ultraviolet rays, an amount of information is small, and in image data obtained by using the electron beam, a ratio of noise relatively increases and an influence of the noise is greatly received. For this reason, so-called pseudo defects that are unnecessary for detection may occur frequently. For example, in a scanning electron microscope (SEM) or the like, filter processing such as a Gaussian filter is used for noise reduction (for example, refer to JP 2829968 B2). However, in an average filter, a Gaussian filter, or a median filter to be conventionally used, it is difficult to avoid an influence of large noise generated randomly such as shot noise. In addition, from the viewpoint of improving the throughput of the inspection apparatus, it is also difficult to perform complicated digital filter processing requiring a large number of calculations.
According to one aspect of the present invention, a pattern inspection apparatus includes:
According to another aspect of the present invention, a pattern inspection apparatus includes:
According to yet another aspect of the present invention, a pattern inspection method includes:
According to yet another aspect of the present invention, a pattern inspection apparatus includes:
According to yet another aspect of the present invention, a pattern inspection apparatus includes:
In the following embodiments, an apparatus and a method capable of reducing occurrence of pseudo defects that are unnecessary for detection even where large noise such as shot noise occurs when a defect inspection is performed using an image acquired by using an electron beam will be described.
In the inspection chamber 103, an XY stage 105 to be movable on at least an XY plane is disposed. On the XY stage 105, a substrate 101 (target object) to be inspected is disposed. The substrate 101 includes a mask substrate for exposure and a semiconductor substrate such as a silicon wafer. When the substrate 101 is the semiconductor substrate, a plurality of chip patterns (wafer dies) are formed on the semiconductor substrate. When the substrate 101 is the mask substrate for exposure, a chip pattern is formed on the mask substrate for exposure. The chip pattern is configured by a plurality of figure patterns. A plurality of chip patterns (wafer dies) are formed on the semiconductor substrate by exposing and transferring the chip pattern formed on the mask substrate for exposure to the semiconductor substrate a plurality of times. Hereinafter, the case where the substrate 101 is the semiconductor substrate will be mainly described. The substrate 101 is disposed on the XY stage 105 with a pattern formation surface oriented upward, for example. Further, a mirror 216 for reflecting a laser beam for laser length measurement emitted from the laser length measurement system 122 disposed outside the inspection chamber 103 is disposed on the XY stage 105. The multi-detector 222 is connected to the detection circuit 106 outside the electron beam column 102. The detection circuit 106 is connected to the chip pattern memory 123.
In the control system circuit 160, a control computer 110 for controlling the entire inspection apparatus 100 is connected to a position circuit 107, a comparison circuit 108, a reference image generation circuit 112, a stage control circuit 114, a lens control circuit 124, a blanking control circuit 126, a deflection control circuit 128, a contour data generation circuit 130, a defect selection circuit 132, a storage device 109 such as a magnetic disk drive, a monitor 117, a memory 118, and a printer 119 via a bus 120. Further, the deflection control circuit 128 is connected to a digital-analog conversion (DAC) amplifiers 144 and 146. The DAC amplifier 144 is connected to the main deflector 208 and the DAC amplifier 146 is connected to the sub-deflector 209.
Further, the chip pattern memory 123 is connected to the comparison circuit 108. Further, the XY stage 105 is driven by the stage drive mechanism 142 under the control of the stage control circuit 114. In the stage drive mechanism 142, for example, a drive system such as three-axis (X-Y-θ) motors driven in an X direction, a Y direction, and a θ direction in a stage coordinate system is configured and the XY stage 105 is movable. For these X-axis motor, Y-axis motor, and θ-axis motor not shown in the drawings, for example, step motors can be used. The XY stage 105 is movable in a horizontal direction and a rotational direction by the motors of the X, Y, and θ axes. In addition, a movement position of the XY stage 105 is measured by the laser length measurement system 122 and is supplied to the position circuit 107. The laser length measurement system 122 receives reflected light from the mirror 216 and measures a position of the XY stage 105 by the principle of a laser interference method. In the stage coordinate system, for example, an X direction, a Y direction, and a θ direction are set with respect to a plane orthogonal to an optical axis of multiple primary electron beams.
A high-voltage power supply circuit not shown in the drawings is connected to the electron gun assembly 201 and an electron group emitted from a cathode is accelerated by application of an acceleration voltage from the high-voltage power supply circuit between a filament and an extraction electrode not shown in the drawings in the electron gun assembly 201, application of a voltage of a predetermined extraction electrode (Wehnelt), and heating of a cathode at a predetermined temperature and becomes an electron beam 200. As the illumination lens 202, the reduction lens 205, the objective lens 207, and the projection lenses 224 and 226, for example, electromagnetic lenses are used. These lenses are controlled by the lens control circuit 124. The beam separator 214 is also controlled by the lens control circuit 124. Each of the collective blanking deflector 212 and the deflector 228 is configured by an electrode group of at least two poles and is controlled by the blanking control circuit 126. The main deflector 208 is configured by an electrode group of at least four poles and is controlled by the deflection control circuit 128 via the DAC amplifier 144 disposed for each electrode. Similarly, the sub-deflector 209 is configured by an electrode group of at least four poles and is controlled by the deflection control circuit 128 via the DAC amplifier 146 disposed for each electrode.
Here, in
The image acquisition mechanism 150 acquires an inspected image of a figure pattern from the substrate 101 on which the figure pattern has been formed by using the multiple beams 20 based on the electron beam. Hereinafter, an operation of the image acquisition mechanism 150 in the inspection apparatus 100 will be described.
The electron beam 200 emitted from the electron gun assembly 201 (emission source) illuminates the entire shaping aperture array substrate 203 substantially vertically by the illumination lens 202. As shown in
The formed multiple beams 20a to 20d form a crossover (C.O.) and passes through the beam separator 214 disposed at a crossover position of each beam of the multiple beams 20. Then, the multiple beams 20a to 20d are reduced by the reduction lens 205 and travels toward a center hole formed in the limitation aperture substrate 206. Here, when the entire multiple beams 20a to 20d are collectively deflected by the collective blanking deflector 212 disposed between the shaping aperture array substrate 203 and the reduction lens 205, positions of the multiple beams 20a to 20d deviate from the center hole of the limitation aperture substrate 206 and the multiple beams 20a to 20d are shielded by the limitation aperture substrate 206. On the other hand, the multiple beams 20a to 20d that are not deflected by the collective blanking deflector 212 pass through the center hole of the limitation aperture substrate 206 as shown in
The multiple secondary electron beams 300 emitted from the substrate 101 are refracted to the center side of the multiple secondary electron beams 300 by the objective lens 207 and travel toward the center hole formed in the limitation aperture substrate 206. The multiple secondary electron beams 300 that have passed through the limitation aperture substrate 206 are refracted substantially parallel to an optical axis by the reduction lens 205 and travel to the beam separator 214.
Here, the beam separator 214 generates an electric field and a magnetic field in directions orthogonal to each other on a plane orthogonal to a traveling direction (optical axis) of the multiple beams 20. The electric field exerts a force in the same direction regardless of the traveling direction of electrons. Meanwhile, the magnetic field exerts a force according to the Fleming's left-hand rule. Therefore, it is possible to change the direction of the force acting on the electrons depending on a penetration direction of the electrons. The force due to the electric field and the force due to the magnetic field cancel each other in the multiple beams 20 (primary electron beams) penetrating the beam separator 214 from the upper side and the multiple beams 20 go straight downward. On the other hand, in the multiple secondary electron beams 300 penetrating the beam separator 214 from the lower side, both the force due to the electric field and the force due to the magnetic field act in the same direction and the multiple secondary electron beams 300 are bent obliquely upward.
The multiple secondary electron beams 300 bent obliquely upward are projected onto the multi-detector 222 while being refracted by the projection lenses 224 and 226. The multi-detector 222 detects the projected multiple secondary electron beams 300. The multi-detector 222 has, for example, a diode type two-dimensional sensor not shown in the drawings. At a position of the diode type two-dimensional sensor corresponding to each beam of the multiple beams 20, each secondary electron of the multiple secondary electron beams 300 collides with the diode type two-dimensional sensor, generates electrons, and generates secondary electron image data for each pixel to be described later. Further, since scanning is performed while the XY stage 105 is continuously moved, the tracking deflection is performed as described above. The deflector 228 deflects the multiple secondary electron beams 300 to irradiate a desired position on a light reception surface of the multi-detector 222 in accordance with the movement of the deflection position associated with the tracking deflection.
In a scanning operation in the first embodiment, scanning is performed for each mask die 33. In the example of
As described above, in the entire multiple beams 20, the mask die 33 is scanned as the irradiation region 34. However, each beam scans one corresponding sub-irradiation region 29. If scanning of one mask die 33 is completed, a next adjacent mask die 33 moves to become the irradiation region 34 and the next adjacent mask die 33 is scanned (scanned). This operation is repeated and scanning of each chip 332 is progressed. A secondary electron beam is emitted from the measurement pixel 36 irradiated with the beam every time the shot of the multiple beams 20 is performed and is detected by the multi-detector 222. The multi-detector 222 detects the secondary electron beam 11 emitted upward from each measurement pixel 36 for each measurement pixel 36 (or for each sub-irradiation region 29).
As described above, by performing scanning using the multiple beams 20, a scanning operation (measurement) can be performed at a higher speed than in the case of performing scanning with a single beam. Each mask die 33 may be scanned by a step and repeat operation or each mask die 33 may be scanned while the XY stage 105 is continuously moved. When the irradiation region 34 is smaller than the mask die 33, the scanning operation may be performed while the irradiation region 34 is moved in the mask die 33.
Here, the case of scanning the sub-irradiation region 29 in which an inter-beam pitch size becomes rectangular with one beam has been shown as an example. However, the present disclosure is not limited thereto. The sub-irradiation region 29 may be scanned with a plurality of beams. In any case, each pixel in the inspection region may be irradiated with any beam of the multiple beams 20 so that there is no irradiation leak.
When the substrate 101 is a mask substrate for exposure, a chip region of one chip formed on the mask substrate for exposure is divided into a plurality of stripe regions in the form of a strip with the size of the mask die 33 described above. For each stripe region, each mask die 33 may be scanned with the same scanning as the operation described above. Since the size of the mask die 33 in the mask substrate for exposure is a size before transferring, the size becomes four times larger than that of the mask die 33 of the semiconductor substrate. Therefore, when the irradiation region 34 is smaller than the mask die 33 in the mask substrate for exposure, the scanning operation for one chip increases (for example, four times). However, since a pattern for one chip is formed on the mask substrate for exposure, the number of scans can be smaller than that of a semiconductor substrate on which more chips than four chips are formed.
As described above, the image acquisition mechanism 150 scans the inspected substrate 101 on which the figure pattern has been formed by using the multiple beams 20 and detects the multiple secondary electron beams 300 emitted from the inspected substrate 101 due to irradiation of the multiple beams 20. Detection data of the secondary electrons (secondary electron image: measurement image: inspected image) from each measurement pixel 36 detected by the multi-detector 222 are output to the detection circuit 106 in order of measurement. In the detection circuit 106, analog detection data is converted into digital data by an A/D converter not shown in the drawings and is stored in the chip pattern memory 123. In this way, the image acquisition mechanism 150 acquires a measurement image of a pattern formed on the substrate 101. For example, when the detection data for one chip 332 is accumulated, the detection data is transferred to the comparison circuit 108 together with information showing each position from the position circuit 107 as chip pattern data.
In the line pattern image shown in
In the inspected image acquisition step (S102), the inspected image acquisition mechanism 150 acquires an inspected image of the figure pattern formed on the substrate 101 (inspection target object), using the multiple beams 20 (electron beams). The operation for acquiring a measurement image of the pattern formed on the substrate 101 is as described above.
In the reference image generation step (S104), the reference image generation circuit 112 (reference image generation unit) generates a reference image corresponding to the inspected image. The reference image generation circuit 112 generates a reference image for each frame region, on the basis of design data to be a basis for forming the pattern on the substrate 101 or design pattern data defined in exposure image data of the pattern formed on the substrate 101. For example, it is preferable to use the mask die 33 as the frame region. Specifically, the following operation is executed. First, the design pattern data is read from the storage device 109 through the control computer 110 and each figure pattern defined in the read design pattern data is converted into binary or multi-valued image data.
Here, in the figure defined in the design pattern data is, for example, a rectangle or a triangle is used as a basic figure. For example, diagram data in which a form, a size, a position, and the like of each pattern figure are defined by information such as the coordinates (x, y) at a reference position of the figure, a length of a side, and a figure code to be an identifier to distinguish a figure type such as the rectangle or the triangle is stored.
If the design pattern data to be the figure data is input to the reference image generation circuit 112, the data is expanded into data of each figure and a figure code showing the figure shape of the figure data, a figure dimension, and the like are interpreted. In addition, the data is expanded into binary or multi-valued design pattern image data as a pattern disposed in a square having a grid of a predetermined quantization size as a unit and is output. In other words, the design data is read, an occupation ratio occupied by the figure in the design pattern is operated for each square formed by virtually dividing the inspection region as a square with a predetermined dimension as a unit, and n-bit occupation ratio data is output. For example, it is preferable to set one square as one pixel. Assuming that one pixel has a resolution of 1/28 (=1/256), a small region of 1/256 is allocated by the region of the figure disposed in the pixel to calculate the occupation ratio in the pixel. In addition, the data is output to the reference image generation circuit 112 as 8-bit occupation ratio data. The square (inspection pixel) may be matched with the pixel of the measurement data.
Next, the reference image generation circuit 112 performs appropriate filter processing on the design image data of the design pattern to be image data of the figure. Since optical image data as the measurement image is in a state in which the filter is operated by an optical system, in other words, in an analog state which continuously changes, the filter processing is performed on the design image data in which the image intensity (gray value) is image data on the design side of a digital value, so that the data can be matched with the measurement data. The image data of the generated reference image is output to the comparison circuit 108.
In the comparison circuit 108, the transferred stripe pattern data (or the chip pattern data) is temporarily stored in the storage device 50 together with information showing each position from the position circuit 107. Further, the transferred reference image data is temporarily stored in the storage device 52.
Next, the inspected image generation unit 54 generates a frame image (inspected image) for each frame region (unit inspection region) of a predetermined size, using the stripe pattern data (or the chip pattern data). Here, for example, an image of the mask die 33 is generated as the frame image. However, the size of the frame region is not limited thereto. The generated frame image (for example, the mask die image) is stored in the storage device 56.
In the position adjustment step (S110), the position adjustment unit 57 reads the wafer die image to be the inspected image and the reference image corresponding to the wafer die image and adjusts positions of both the images in a unit of a sub-pixel smaller than the pixel 36. For example, the position adjustment may be performed by a method of least squares.
In the comparison step (S112), the comparison unit 58 compares the wafer die image (inspected image) with the reference image. The comparison unit 58 compares both the images for each pixel 36 according to a predetermined determination condition and determines presence or absence of a defect such as a shape defect, for example. For example, when a gray value difference for each pixel 36 is larger than a determination threshold Th, the defect is determined. In addition, a comparison result is output. The comparison result is output to the storage device 109 and is output to the defect selection circuit 132. As described above, at this stage, a large number of pseudo defects caused by the shot noise or the like are generated.
In the contour data generation step (S120), the contour data generation circuit 130 (contour data generation unit) generates contour data defining the contour line of the figure pattern. Specifically, the following operation is executed. The contour data generation circuit 130 reads the design pattern data to be a basis for generating the comparison target reference image stored in the storage device 109 and generates contour data defining the contour line of the figure pattern for each figure pattern. The generated contour data is output to the storage device 109 and is output to the defect selection circuit 132.
In the defect selection step (S130), the defect selection circuit 132 (defect selection unit) selects a defect within a range preset on the basis of the contour line of the figure pattern as a valid defect, from at least one defect determined to be the defect by the comparison, using the contour data.
In the search step (S10), the search unit 63 searches for the contour line closest to the defect position determined to be the defect, using the contour data.
In the shortest distance calculation step (S12), the distance calculation unit 64 calculates the shortest distance from the defect position to the contour line. In principle, the distance calculation unit 64 calculates the distance (normal distance) in the normal direction with respect to the contour line from the defect position to the searched contour line as the shortest distance. As shown in the example of
In the determination step (S14), the determination unit 65 determines whether the shortest distance from the defect position to the contour line is within a preset valid distance, for each detected defect. A parameter (masking parameter) showing the valid distance is stored in advance in the storage device 66. Hereinafter, it will be specifically described.
If the shortest distance from the defect position to the contour line is smaller than the preset valid distance (if the defect position is close to the contour line), the determination unit 65 stores the data of the defect as a valid defect in the storage device 67. If the shortest distance from the defect position to the contour line is larger than the preset valid distance (if the defect position is not close to the contour line), the determination unit 65 stores the data of the defect as an invalid defect in the storage device 68. By the above determination processing, a valid defect within a range preset on the basis of the contour line of the figure pattern is selected from at least one defect detected. In addition, a selection result is output. The selection result may be output to the storage device 109, the monitor 117, or the memory 118 or may be output from the printer 119.
As described above, by narrowing down the defects to the defects within the valid distance on the basis of the contour line inside and outside the figure pattern, the defect data of the region unnecessary for the inspection is eliminated. As a result, the pseudo defects caused by the shot noise and the like can be greatly reduced. Particularly, as shown in
In the above example, as shown in
The contents of the inspected image acquisition step (S102) are the same as those described above. In the die to die inspection, frame images of the die on which the same pattern is formed are compared. Therefore, a mask die image of a region of a part of the chip (wafer die) 332 to be a die (1) and a mask die image of a corresponding region of another chip (wafer die) 332 to be a die (2) are used.
In the position adjustment step (S110), the position adjustment unit 57 reads the wafer die image of the die (1) and the wafer die image of the die (2) to be the inspected images and adjusts positions of both the images in a unit of a sub-pixel smaller than the pixel 36. For example, the position adjustment may be performed by a method of least squares.
In the comparison step (S112), the comparison unit 58 compares the wafer die image of the die (1) with the wafer die image of the die (2). Here, one of the wafer die image of the die (1) and the wafer die image of the die (2) becomes the reference image (for example, the die (1)) and the other becomes the inspected image (for example, the die (2)). A comparison method may be the same as that in the case of the die to database inspection. In addition, a comparison result is output. The comparison result is output to the storage device 109 and is output to the defect selection circuit 132. As described above, at this stage, a large number of pseudo defects caused by the shot noise or the like are generated.
In the contour data generation step (S122), the contour data generation circuit 130 (contour data generation unit) generates contour data defining the contour line of the figure pattern. Specifically, the following operation is executed. In the case of performing the die to die inspection, the design pattern data often does not exist. Therefore, the contour data generation circuit 130 reads the wafer die image of the die (1) used as the reference image from the storage device 56 in the comparison circuit 108 and extracts the figure pattern. In addition, the contour data generation circuit 130 generates contour data defining the contour line of the figure pattern, for each extracted figure pattern. As shown in
The contents of the defect selection step (S130) are the same as those described above. As such, defect selection using the contour line can also be applied to the die to die inspection.
As described above, according to the first embodiment, even in the case where the large noise such as the shot noise occurs when the defect inspection is performed using the image acquired by using the electron beam, occurrence of the pseudo defects that are unnecessary for detection can be reduced.
In the first embodiment, the configuration in which a region of a valid defect is limited after a defect is detected has been described. In a second embodiment, a configuration in which an inspection is performed after an inspection region is limited will be described. Points not specifically described below may be the same as those of the first embodiment.
The contents of each step of the inspected image acquisition step (S102), the reference image generation step (S104), and the contour data generation step (S120) are the same as those in the first embodiment. However, in the inspected image acquisition step (S102), for example, at a stage where detection data for one chip 332 is accumulated, the detection data is transferred to the image processing circuit 134 together with information showing each position from a position circuit 107 as chip pattern data. Further, in the reference image generation step (S104), the generated reference image is transferred to the image processing circuit 134. Further, the generated contour data is output to a storage device 109 and is output to the image processing circuit 134.
In the data processing step (S140), the image processing circuit 134 (image processing unit) processes the inspected image and the reference image using the contour data.
In the image processing circuit 134, the input contour data is stored in the storage device 70. Further, transferred stripe pattern data (or chip pattern data) is temporarily stored in the storage device 71 together with information showing each position from the position circuit 107. Further, the transferred reference image data (reference image (a)) is temporarily stored in the storage device 72. Further, a parameter (masking parameter) showing the valid distance is stored in advance in the storage device 83.
Next, the inspected image generation unit 81 generates a frame image (inspected image) for each frame region (unit inspection region) of a predetermined size, using the stripe pattern data (or the chip pattern data). Here, for example, an image of the mask die 33 is generated as the frame image. However, the size of the frame region is not limited thereto. The generated frame image (for example, the mask die image) (inspected image (a)) is stored in the storage device 82.
In the contour line extraction step, the contour line extraction unit 73 refers to the contour data to extract a contour line 10 of a figure pattern to be disposed in the target reference image (a) (before data processing) for each reference image (a).
In the inspection region setting step, the inspection region setting unit 75 sets a valid inspection region 1 between the contour line 10 of the figure pattern and an outer circumferential line 12 separated by a valid distance A shown by a masking parameter in a normal direction of the contour line 10 along the contour line 10 of the figure pattern and a valid inspection region 2 between the contour line 10 of the figure pattern and an inner circumferential line 14 separated by a valid distance B in a normal direction of the contour line 10 along the contour line 10 of the figure pattern, for each figure pattern.
In the reference image data processing step (S142), the image processing unit 78 generates a reference image (b) by processing a pixel value of a region deviated from the valid inspection regions 1 and 2 of the target reference image (a) with a predetermined value, for each reference image (a) (image before data processing). A pixel value of the region deviated from the valid inspection regions 1 and 2 is set to zero, for example. Data of the processed reference image (b) is stored in the storage device 80 and is output to a comparison circuit 108.
In the inspected image data processing step (S144), the image processing unit 77 generates an inspected image (b) by processing a pixel value of a region deviated from the valid inspection regions 1 and 2 of the target inspected image (a) with a predetermined value, for each inspected image (a) (image before data processing). A pixel value of the region deviated from the valid inspection regions 1 and 2 is set to zero, for example. Data of the processed inspected image (b) is stored in the storage device 79 and is output to the comparison circuit 108. Here, a difference value between the pixel value of the reference image (b) and the pixel value of the inspected image (b) may be set to zero, for the region deviated from the valid inspection regions 1 and 2.
In the comparison circuit 108, the processed reference image (b) is stored in a storage device 52. Further, the processed inspected image (b) is stored in a storage device 56.
Here, in the second embodiment, since the inspected image (a) is generated in the image processing circuit 134, a storage device 50 and an inspected image generation unit 54 in the comparison circuit 108 in
In the position adjustment step (S150), a position adjustment unit 57 reads a wafer die image to be the inspected image (b) and the reference image (b) corresponding to the wafer die image and adjusts positions of both the images in a unit of a sub-pixel smaller than a pixel 36. For example, the position adjustment may be performed by a method of least squares.
In the comparison step (S112), a comparison unit 58 compares the wafer die image (inspected image (b)) with the reference image (b). The comparison unit 58 compares both the images for each pixel 36 according to a predetermined determination condition and determines presence or absence of a defect such as a shape defect, for example. For example, when a gray value difference for each pixel 36 is larger than a determination threshold Th, the defect is determined. In addition, a comparison result is output. The comparison result may be output to the storage device 109, a monitor 117, or the memory 118 or may be output from a printer 119.
As described above, by narrowing down the inspection regions to the regions (valid inspection regions 1 and 2) within the valid distance on the basis of the contour line inside and outside the figure pattern, defect data of the region unnecessary for the inspection is eliminated. As a result, the pseudo defects caused by the shot noise and the like can be greatly reduced. Particularly, as shown in
Here, in the above example, as shown in
The contents of the inspected image acquisition step (S102) are the same as those described above. However, in the inspected image acquisition step (S102), for example, at a stage where detection data for one chip 332 is accumulated, the detection data is transferred to the image processing circuit 134 together with information showing each position from a position circuit 107 as chip pattern data.
In the image processing circuit 134, the transferred stripe pattern data (or the chip pattern data) is temporarily stored in the storage device 71 together with information showing each position from the position circuit 107. Further, a parameter (masking parameter) showing the valid distance is stored in advance in the storage device 83.
Next, the inspected image generation unit 81 generates a frame image (inspected image) for each frame region (unit inspection region) of a predetermined size, using the stripe pattern data (or the chip pattern data). Here, for example, an image of the mask die 33 is generated as the frame image. However, the size of the frame region is not limited thereto. The generated frame image (for example, the mask die image) (inspected image (a)) is stored in the storage device 82.
In the die to die inspection, frame images of the die on which the same pattern is formed are compared. Therefore, a mask die image of a region of a part of the chip (wafer die) 332 to be a die (1) and a mask die image of a corresponding region of another chip (wafer die) 332 to be a die (2) are used.
In the contour data generation step (S122), the contour data generation circuit 130 (contour data generation unit) generates contour data defining the contour line of the figure pattern. Specifically, the following operation is executed. In the case of performing the die to die inspection, the design pattern data often does not exist. Therefore, the contour data generation circuit 130 reads the wafer die image (die (1) image (a)) of the die (1) used as the reference image (a) from the storage device 82 in the image processing circuit 134 and extracts a figure pattern. In addition, the contour data generation circuit 130 generates contour data defining the contour line of the figure pattern, for each extracted figure pattern. As shown in
In the image processing circuit 134, the input contour data is stored in the storage device 70.
In the data processing step (S140), the image processing circuit 134 (image processing unit) processes the wafer die image (die (2) image (a)) of the die (2) to be the inspected image and the wafer die image (die (1) image (a)) of the die (1) to be the reference image, using the contour data.
In the contour line extraction step, the contour line extraction unit 73 refers to the contour data to extract a contour line 10 of a figure pattern to be disposed in the target reference image (a) (before data processing) for each reference image (a).
In the inspection region setting step, the inspection region setting unit 75 sets a valid inspection region 1 between the contour line 10 of the figure pattern and an outer circumferential line 12 separated by a valid distance A shown by a masking parameter in a normal direction of the contour line 10 along the contour line 10 of the figure pattern and a valid inspection region 2 between the contour line 10 of the figure pattern and an inner circumferential line 14 separated by a valid distance B in a normal direction of the contour line 10 along the contour line 10 of the figure pattern, for each figure pattern.
In the reference image data processing step (S142), the image processing unit 78 generates a die (1) image (b) by processing a pixel value of a region deviated from the valid inspection regions 1 and 2 of the target die (1) image (a) with a predetermined value, for each wafer die image (die (1) image (a)) of the die (1) to be the reference image. A pixel value of the region deviated from the valid inspection regions 1 and 2 is set to zero, for example. Data of the processed die (1) image (b) is stored in the storage device 80 and is output to the comparison circuit 108.
In the inspected image data processing step (S144), the image processing unit 77 generates a die (2) image (b) by processing a pixel value of a region deviated from the valid inspection regions 1 and 2 of the target die (2) image (a) with a predetermined value, for each wafer die image (die (2) image (a)) of the die (2) to be the inspected image. A pixel value of the region deviated from the valid inspection regions 1 and 2 is set to zero, for example. Data of the processed die (2) image (b) is stored in the storage device 79 and is output to the comparison circuit 108. Here, a difference value between the pixel value of the reference image (b) (die (1) image (b)) and the pixel value of the inspected image (b) (die (2) image (b)) may be set to zero, for the region deviated from the valid inspection regions 1 and 2.
In the comparison circuit 108, the processed reference image (b) (die (1) image (b)) is stored in the storage device 52. Further, the processed inspected image (b) (die (2) image (b)) is stored in the storage device 56.
The contents of the position adjustment step (S150) and the comparison step (S152) are the same as those in the case of the die to database inspection. As such, defect selection using the contour line can also be applied to the die to die inspection.
As described above, according to the second embodiment, even in the case where the large noise such as the shot noise occurs when the defect inspection is performed using the image acquired by using the electron beam, occurrence of the pseudo defects that are unnecessary for detection can be reduced.
In the second embodiment, the case where a region simply deviated from a valid distance is excluded from an inspection region has been described. However, the present disclosure is not limited thereto. There are cases where it is desired to detect a large defect at a position in the vicinity deviated outward from an outer circumferential line 12. There are cases where it is desired to detect a large defect at a position in the vicinity deviated inward from an inner circumferential line 14. However, if all defects deviated from valid inspection regions 1 and 2 are detected, pseudo defects frequently occur. Therefore, in a third embodiment, a configuration capable of detecting large defects in the vicinity of the outer circumferential line 12 and in the vicinity of the inner circumferential line 14 while reducing pseudo defects at positions deviated from the valid inspection regions 1 and 2 will be described. In the third embodiment, the concept of the second embodiment in which an inspection region is narrowed down on the basis of a contour line 10 is combined with the concept of weighting according to a distance from the contour line 10.
A configuration of an inspection apparatus 100 in the third embodiment is the same as that of
In a data processing step (S140), an image processing circuit 134 (image processing unit) processes an inspected image (a) and a reference image (a) using contour data to weight data of the inspected image (a) and data of the reference image (a), according to a distance from the contour line 10.
In a reference image data processing step (S142), an image processing unit 78 generates the reference image (b) by executing filter processing (data processing) on all data of the target reference image (a), using a filter function in which the weight becomes zero at the distance n in the normal direction from the position of the contour line with the primary proportion, for each reference image (a) (image before data processing). Data of the processed reference image (b) is stored in the storage device 80 and is output to a comparison circuit 108.
In an inspected image data processing step (S144), an image processing unit 77 generates the inspected image (b) by executing filter processing (data processing) on all data of the target inspected image (a), using a filter function in which the weight becomes zero at the distance n in the normal direction from the position of the contour line with the primary proportion, for each inspected image (a) (image before data processing). Data of the processed inspected image (b) is stored in the storage device 79 and is output to the comparison circuit 108.
In the reference image data processing step (S142), the image processing unit 78 generates the reference image (b) by executing filter processing (data processing) on all data of the target reference image (a), using a filter function in which the weight becomes zero at the distance n in the normal direction from the position of the contour line with the secondary proportion, for each reference image (a) (image before data processing). Data of the processed reference image (b) is stored in the storage device 80 and is output to a comparison circuit 108.
In the inspected image data processing step (S144), the image processing unit 77 generates the inspected image (b) by executing filter processing (data processing) on all data of the target inspected image (a), using a filter function in which the weight becomes zero at the distance n in the normal direction from the position of the contour line with the secondary proportion, for each inspected image (a) (image before data processing). Data of the processed inspected image (b) is stored in the storage device 79 and is output to the comparison circuit 108.
In the reference image data processing step (S142), the image processing unit 78 generates the reference image (b) by executing filter processing (data processing) on all data of the target reference image (a), using a filter function in which the weight becomes zero at the distance n in the normal direction from the position of the contour line along the normal distribution, for each reference image (a) (image before data processing). Data of the processed reference image (b) is stored in the storage device 80 and is output to a comparison circuit 108.
In the inspected image data processing step (S144), the image processing unit 77 generates the inspected image (b) by executing filter processing (data processing) on all data of the target inspected image (a), using a filter function in which the weight becomes zero at the distance n in the normal direction from the position of the contour line along the normal distribution, for each inspected image (a) (image before data processing). Data of the processed inspected image (b) is stored in the storage device 79 and is output to the comparison circuit 108.
In the reference image data processing step (S142), the image processing unit 78 generates the reference image (b) by executing filter processing (data processing) on all data of the target reference image (a), using a filter function in which the weight 1 (100%) is set from the contour line 10 to the valid distance m and the weight becomes zero at the distance n in the normal direction from the position of the contour line with the primary proportion from the valid distance m, for each reference image (a) (image before data processing). Data of the processed reference image (b) is stored in the storage device 80 and is output to a comparison circuit 108.
In the inspected image data processing step (S144), the image processing unit 77 generates the inspected image (b) by executing filter processing (data processing) on all data of the target inspected image (a), using a filter function in which the weight 1 (100%) is set from the contour line 10 to the valid distance m and the weight becomes zero at the distance n in the normal direction from the position of the contour line with the primary proportion from the valid distance m, for each inspected image (a) (image before data processing). Data of the processed inspected image (b) is stored in the storage device 79 and is output to the comparison circuit 108.
Here, the valid distance m is preferably set to a distance A from the edge (contour line) of the figure pattern described in
The other steps are the same as those in the second embodiment.
As described above, according to the third embodiment, it is possible to detect large defects in the vicinity of the outer circumferential line 12 and in the vicinity of the inner circumferential line 14 while reducing pseudo defects at positions deviated from the valid inspection regions 1 and 2.
In a fourth embodiment, a configuration in which a filter function according to the third embodiment is further improved will be described. A configuration of an inspection apparatus 100 in the fourth embodiment is the same as that of
Further, a gray value (pixel value) O(p) after filter processing of each pixel by the contour line distance combination filter is defined by a value obtained by dividing a sum of products of a pixel I(p) of k×k pixels (for example, 5×5 pixels) around a target pixel and coefficient matrixes (p,q)·fr(I(p), I(q))·ft′(U(p),U(q)) by a sum K of coefficient matrixes fs(p,q)·fr(I(p), I(q))·ft(U(p),U(q)), as shown in
In the example of
In a data processing step (S140), an image processing circuit 134 (image processing unit) processes an inspected image (a) and a reference image (a), using the contour line distance combination filter function obtained by combining the contour line distance filter kernel ft(U(p),U(q)) weighting data of the inspected image (a) and data of the reference image (a) according to a distance from the contour line 10 with the kernel of the bilateral filter.
In a reference image data processing step (S142), an image processing unit 78 generates a reference image (b) by executing filter processing (data processing) on all data of the target reference image (a), using the contour line distance combination filter function in which the contour line distance filter kernel ft(U(p),U(q)) performing weighting according to a distance from the contour line 10 is combined, for each reference image (a) (image before data processing). Data of the processed reference image (b) is stored in the storage device 80 and is output to a comparison circuit 108.
In an inspected image data processing step (S144), an image processing unit 77 generates an inspected image (b) by executing filter processing (data processing) on all data of the target inspected image (a), using the contour line distance combination filter function in which the contour line distance filter kernel ft(U(p),U(q)) performing weighting according to a distance from the contour line 10 is combined, for each inspected image (a) (image before data processing). Data of the processed inspected image (b) is stored in the storage device 79 and is output to the comparison circuit 108.
The other steps are the same as those in the second embodiment.
As described above, according to the fourth embodiment, it is possible to detect large defects in the vicinity of an outer circumferential line 12 and in the vicinity of an inner circumferential line 14 while reducing pseudo defects at positions deviated from valid inspection regions 1 and 2 and it is possible to reduce noise of an image in the valid inspection regions 1 and 2.
In the above description, a series of “circuits” includes a processing circuit and an electric circuit, a computer, a processor, a circuit board, a quantum circuit, or a semiconductor device is included in the processing circuit. Further, a common processing circuit (same processing circuit) may be used for each “circuit”. Alternatively, a different processing circuit (separate processing circuit) may be used. A program for executing a processor or the like may be recorded on a record carrier body such as a magnetic disk drive, a magnetic tape device, an FD, or a read only memory (ROM). For example, the position circuit 107, the comparison circuit 108, the reference image generation circuit 112, the contour data generation circuit 130, the defect selection circuit 132, and the image processing circuit 134 may be configured by at least one processing circuit described above.
The embodiments have been described with reference to the specific examples. However, the present disclosure is not limited to these specific examples.
Further, descriptions of parts and the like that are not directly necessary for explanation of the present disclosure, such as the apparatus configuration and the control method, are omitted. However, the necessary apparatus configuration and control method can be appropriately selected and used.
Further, all pattern inspection apparatuses and pattern inspection methods including the elements of the present disclosure and capable of being appropriately designed and changed by those skilled in the art are included in the scope of the present disclosure.
Additional advantages and modification will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-092777 | May 2018 | JP | national |
