JP2022077421A - Electron beam inspection device and electron beam inspection method - Google Patents

Abstract

PURPOSE: To provide a device which can maintain the edge shape of a pattern and compare a measurement image with a reference image applied with correction processing of a corner part according to the characteristics of a beam used in acquisition of the measurement image.CONSTITUTION: An electron beam inspection device according to an embodiment of the present invention comprises: a reference image creation circuit 112 which creates a reference image corresponding to an electronic optical image created from design data being the source of a graphic pattern; a correction processing unit 68 which maintains the edge shape of the graphic pattern in the reference image by using an image processing filter depending on the intensity distribution of the electron beam used for acquiring the electronic optical image corresponding to the reference image and corrects the corner shape of the graphic pattern in the reference image; and a comparison unit 58 which compares the reference image in which the corner shape is corrected with the electronic optical image.SELECTED DRAWING: Figure 14

Description

One aspect of the present invention relates to an electron beam inspection device and an electron beam inspection method. For example, the present invention relates to an inspection device and a method for inspecting using a secondary electron image of a pattern emitted by irradiating a substrate with a multi-beam of an electron beam.

In recent years, with the increasing integration and capacity of large-scale integrated circuits (LSIs), the circuit line width required for semiconductor devices has become narrower and narrower. Further, improvement of the yield is indispensable for manufacturing LSI, which requires a large manufacturing cost. However, the patterns constituting the LSI are approaching the order of 10 nanometers or less, and the dimensions that must be detected as pattern defects are extremely small. Therefore, it is necessary to improve the accuracy of the pattern inspection device for inspecting the defects of the ultrafine pattern transferred on the semiconductor wafer. In addition, one of the major factors that reduce the yield is the pattern defect of the mask used when the ultrafine pattern is exposed and transferred on the semiconductor wafer by the photolithography technique. Therefore, it is necessary to improve the accuracy of the pattern inspection device for inspecting defects of the transfer mask used in LSI manufacturing.

As a defect inspection method, a measurement image obtained by imaging a pattern formed on a substrate such as a semiconductor wafer or a lithography mask using ultraviolet rays or an electron beam, a reference image based on design pattern data, or a reference image on the substrate. A method of performing an inspection by comparing with a measured image obtained by capturing the same pattern is known.

In particular, in die-database inspections that compare the measured image with the reference image based on the design pattern data, the contour line extracted from the reference image and the contour line extracted from the measured image are used to detect defects with high sensitivity. It is required that the degree of agreement with is high. On the other hand, in the SEM (Scanning Electron Microscope) image obtained by scanning a sample with an electron beam, the roundness of the pattern corner portion (corner portion) differs from that of the design pattern data due to the influence of the manufacturing process or electron optical conditions. It ends up. For example, an SEM image obtained by a beam having an intensity distribution in which the irradiation shape of the electron beam is not a rotation target has a blur of a non-rotation target, and has a corner shape corresponding to the blur. In particular, when a multi-beam is used, it tends to be a beam having an intensity distribution to be non-rotating except for a beam passing through the central axis of the orbit. Therefore, if the reference image is not corrected according to the characteristics of the beam used for acquiring the SEM image, pseudo defects will occur frequently.

Further, when the rounding process of the corner portion is performed by the filter process, not only the corner portion but also the edge shape of the pattern is corrected. As a result, the edge position of the pattern shifts. In this case, the difference between the extracted contour lines becomes large, and as a result, pseudo-defects occur. Therefore, it is required to maintain the edge shape of the pattern and perform the rounding process of the corner portion. If it is necessary to perform a resizing process that intentionally shifts the edge position of the pattern, it is required to perform the resizing process independently of the rounding process of the corner portion.

Here, in the inspection device that compares the contour lines, the non-linear portion is extracted from the contour line extracted from the measurement image instead of performing the corner rounding process for the corner portion that originally has a low degree of coincidence, and the design data is obtained. A method is disclosed in which the presence or absence of a non-linear portion existing within a certain range is detected for each point of a corner portion of the above, and a portion having no corresponding point is set as a defective portion (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2008-047664

One aspect of the present invention provides an apparatus and method that can be compared with a reference image in which the edge shape of the pattern is maintained and the corner portion is corrected according to the characteristics of the beam used for acquiring the measurement image.

The electron beam inspection device according to one aspect of the present invention is
A reference image creation unit that creates a reference image corresponding to an electro-optical image created from the design data that is the basis of the graphic pattern,
An image processing filter that depends on the intensity distribution of the electron beam used to acquire the electro-optical image corresponding to the reference image is used to maintain the edge shape of the graphic pattern in the reference image and the corners of the graphic pattern in the reference image. A correction processing unit that corrects the shape of the part, and a correction processing unit that corrects the shape of the part.
A comparison unit that compares the reference image with the corrected corner shape and the electro-optical image,
It is characterized by being equipped with.

Further, when the reference image is filtered by convolving the image processing filter while moving the target pixel, the filtered gradation value for the target pixel and the overlapping relationship between the image processing filter and the graphic pattern are obtained. Further, a corner determination unit for determining whether or not the target pixel is located in the corner portion is further provided by using a value determined accordingly.
It is preferable that the correction processing unit corrects the gradation value of the target pixel when it is determined that the target pixel is located at the corner portion.

In addition, an upper limit value and a lower limit value are set as values determined according to the overlapping relationship.
It is preferable that the corner determination unit determines that the target pixel is located in the corner portion when the filtered gradation value for the target pixel is between the upper limit value and the lower limit value.

Further, it is preferable that the upper limit value and the lower limit value change depending on the relative angle between the image processing filter and the edge of the graphic pattern.

The electron beam inspection method according to one aspect of the present invention is
The process of creating a reference image corresponding to an electro-optical image created from the design data that is the basis of the graphic pattern,
An image processing filter that depends on the intensity distribution of the electron beam used to acquire the electro-optical image corresponding to the reference image is used to maintain the edge shape of the graphic pattern in the reference image and the corners of the graphic pattern in the reference image. The process of correcting the shape of the part and
The process of comparing the reference image with the corrected corner shape and the electro-optical image and outputting the result,
It is characterized by being equipped with.

Further, when the reference image is filtered by convolving the image processing filter while moving the target pixel, the filtered gradation value for the target pixel and the overlapping relationship between the image processing filter and the graphic pattern are obtained. Further provided with a step of determining whether or not the target pixel is located in the corner portion by using a value determined accordingly and
It is preferable to correct the gradation value of the target pixel when it is determined that the target pixel is located at the corner portion.

In addition, an upper limit value and a lower limit value are set as values determined according to the overlapping relationship.
It is preferable to determine that the target pixel is located at the corner portion when the filtered gradation value for the target pixel is between the upper limit value and the lower limit value.

Further, it is preferable that the upper limit value and the lower limit value change depending on the relative angle between the image processing filter and the edge of the graphic pattern.

According to one aspect of the present invention, a reference image in which the edge shape of the pattern is maintained and the corner portion is corrected according to the characteristics of the beam used for acquiring the measurement image can be compared.

It is a block diagram which shows an example of the structure of the inspection apparatus in Embodiment 1. FIG. It is a conceptual diagram which shows the structure of the molded aperture array substrate in Embodiment 1. FIG. It is a figure which shows an example of the plurality of chip regions formed on the semiconductor substrate in Embodiment 1. FIG. It is a figure for demonstrating the scan operation of the multi-beam in Embodiment 1. FIG. It is a flowchart which shows the main part process of the inspection method in Embodiment 1. FIG. It is a figure which shows an example of the beam shape on the sample surface in Embodiment 1. FIG. It is a figure for demonstrating an example of the method of calculating the filter function in Embodiment 1. FIG. It is a figure which shows an example of the internal structure of the table making circuit in Embodiment 1. FIG. It is a figure which shows an example of the overlap relation between the filter function and the graphic pattern edge in Embodiment 1. FIG. It is a figure which shows another example of the overlap relation between the filter function and the graphic pattern edge in Embodiment 1. FIG. It is a figure which shows an example of the overlap relation between each edge of a rectangular pattern and a filter function in Embodiment 1. FIG. It is a figure which shows an example of the V1 and V2 tables in Embodiment 1. FIG. It is a figure which shows an example of the internal structure of the correction circuit in Embodiment 1. FIG. It is a figure for demonstrating the overlap relation between the filter function and the graphic pattern in Embodiment 1. FIG. It is a figure which shows an example of the pattern before and after the correction in Embodiment 1. FIG. It is a figure which shows an example of the internal structure of the comparison circuit in Embodiment 1. FIG. It is a figure which shows an example of the actual image contour line and the reference contour line in Embodiment 1. FIG.

Hereinafter, in the embodiment, an electron beam inspection device will be described as an example of the inspection device. Further, in the embodiment, an inspection device for acquiring an image by using a multi-beam of a plurality of electron beams will be described, but the present invention is not limited to this. It may be an inspection device that acquires an image by using a single beam with one electron beam.

Embodiment 1.
FIG. 1 is a configuration diagram showing an example of the configuration of the inspection device according to the first embodiment. In FIG. 1, the inspection device 100 for inspecting a pattern formed on a substrate is an example of a multi-electron beam inspection device. The inspection device 100 includes an image acquisition mechanism 150 (secondary electron image acquisition mechanism) and a control system circuit 160. The image acquisition mechanism 150 includes an electron beam column 102 (electron lens barrel) and an examination room 103. In the electron beam column 102, an electron gun 201, an electromagnetic lens 202, a molded aperture array substrate 203, an electromagnetic lens 205, a batch blanking deflector 212, a limiting aperture substrate 213, an electromagnetic lens 206, an electromagnetic lens 207 (objective lens), A main deflector 208, a sub-deflector 209, a beam separator 214, a deflector 218, an electromagnetic lens 224, an electromagnetic lens 226, and a multi-detector 222 are arranged. In the example of FIG. 1, an electron gun 201, an electromagnetic lens 202, a molded aperture array substrate 203, an electromagnetic lens 205, a batch blanking deflector 212, a limiting aperture substrate 213, an electromagnetic lens 206, an electromagnetic lens 207 (objective lens), and a main deflection. The device 208 and the sub-deflector 209 constitute a primary electron optical system that irradiates the substrate 101 with the multi-primary electron beam 20. The beam separator 214, the deflector 218, the electromagnetic lens 224, and the electromagnetic lens 226 constitute a secondary electron optical system that irradiates the multi-detector 222 with the multi-secondary electron beam 300.

In the examination room 103, a stage 105 that can move in the XY direction at least is arranged. A substrate 101 (sample) to be inspected is arranged on the stage 105. Here, the substrate 101 is supported by, for example, three-point support. The substrate 101 includes a mask substrate for exposure and a semiconductor substrate such as a silicon wafer. When the substrate 101 is a semiconductor substrate, a plurality of chip patterns (wafer dies) are formed on the semiconductor substrate. When the substrate 101 is an exposure mask substrate, a chip pattern is formed on the exposure mask substrate. The chip pattern is composed of a plurality of graphic patterns. By exposing and transferring the chip pattern formed on the exposure mask substrate to the semiconductor substrate a plurality of times, a plurality of chip patterns (wafer dies) are formed on the semiconductor substrate. Hereinafter, the case where the substrate 101 is a semiconductor substrate will be mainly described. The substrate 101 is arranged on the stage 105, for example, with the pattern forming surface facing upward. Further, on the stage 105, a mirror 216 that reflects the laser beam for laser length measurement emitted from the laser length measuring system 122 arranged outside the examination room 103 is arranged. The multi-detector 222 is connected to the detection circuit 106 outside the electron beam column 102.

In the control system circuit 160, the control computer 110 that controls the entire inspection device 100 uses the position circuit 107, the comparison circuit 108, the expansion circuit 111, the reference image creation circuit 112, the stage control circuit 114, and the lens control circuit via the bus 120. It is connected to 124, a blanking control circuit 126, a deflection control circuit 128, a correction circuit 132, a filter calculation circuit 134, a table creation circuit 136, a storage device 109 such as a magnetic disk device, a monitor 117, and a memory 118. Further, the deflection control circuit 128 is connected to a DAC (digital-to-analog conversion) amplifier 144, 146, 148. The DAC amplifier 146 is connected to the main deflector 208, and the DAC amplifier 144 is connected to the sub-deflector 209. The DAC amplifier 148 is connected to the deflector 218.

Further, the detection circuit 106 is connected to the chip pattern memory 123. The chip pattern memory 123 is connected to the comparison circuit 108 and the filter calculation circuit 134. Further, the stage 105 is driven by the drive mechanism 142 under the control of the stage control circuit 114. In the drive mechanism 142, for example, a drive system such as a three-axis (XY−θ) motor that drives in the X direction, the Y direction, and the θ direction in the stage coordinate system is configured, and the stage 105 is movable. .. The stage 105 can be moved in the horizontal direction and the rotational direction by the motor of each axis of XYθ. Then, the moving position of the stage 105 is measured by the laser length measuring system 122 and supplied to the position circuit 107. The laser length measuring system 122 measures the position of the stage 105 by the principle of the laser interferometry method by receiving the reflected light from the mirror 216. In the stage coordinate system, for example, the X direction, the Y direction, and the θ direction are set with respect to the plane orthogonal to the optical axis (electron orbit center axis) of the multi-first-order electron beam.

The electromagnetic lens 202, the electromagnetic lens 205, the electromagnetic lens 206, the electromagnetic lens 207 (objective lens), the electromagnetic lens 224, the electromagnetic lens 226, and the beam separator 214 are controlled by the lens control circuit 124. Further, the batch blanking deflector 212 is composed of electrodes having two or more poles, and is controlled by the blanking control circuit 126 via a DAC amplifier (not shown) for each electrode. The sub-deflector 209 is composed of electrodes having four or more poles, and each electrode is controlled by the deflection control circuit 128 via the DAC amplifier 144. The main deflector 208 is composed of electrodes having four or more poles, and each electrode is controlled by a deflection control circuit 128 via a DAC amplifier 146. The deflector 218 is composed of electrodes having four or more poles, and each electrode is controlled by a deflection control circuit 128 via a DAC amplifier 148.

A high-voltage power supply circuit (not shown) is connected to the electron gun 201, and another extraction electrode is applied along with the application of an acceleration voltage from the high-voltage power supply circuit between the filament (cathode) and the extraction electrode (anode) in the electron gun 201 (not shown). By applying a voltage of (Wenert) and heating the cathode at a predetermined temperature, a group of electrons emitted from the cathode is accelerated and emitted as an electron beam 200.

Here, FIG. 1 describes a configuration necessary for explaining the first embodiment. The inspection device 100 may usually have other configurations required.

FIG. 2 is a conceptual diagram showing the configuration of the molded aperture array substrate according to the first embodiment. In FIG. 2, on the molded aperture array substrate 203, one of the two-dimensional horizontal (x direction) m ₁ row × vertical (y direction) n ₁ step (m ₁ , n ₁ is an integer of 2 or more, and the other is Holes (openings) 22 (an integer of 1 or more) are formed at a predetermined arrangement pitch in the x and y directions. In the example of FIG. 2, a case where a hole (opening) 22 of 23 × 23 is formed is shown. Ideally, each hole 22 is formed by a rectangle having the same size and shape. Alternatively, it may ideally be a circle having the same outer diameter. When a part of the electron beam 200 passes through each of these plurality of holes 22, a multi-primary electron beam 20 of m ₁ × n ₁ (= N) is formed.

Next, the operation of the image acquisition mechanism 150 in the inspection device 100 will be described.

The electron beam 200 emitted from the electron gun 201 (emission source) is refracted by the electromagnetic lens 202 to illuminate the entire molded aperture array substrate 203. As shown in FIG. 2, a plurality of holes 22 (openings) are formed in the molded aperture array substrate 203, and the electron beam 200 illuminates a region including all the plurality of holes 22. Each part of the electron beam 200 irradiated to the positions of the plurality of holes 22 passes through the plurality of holes 22 of the molded aperture array substrate 203, respectively, thereby forming the multi-primary electron beam 20.

The formed multi-primary electron beam 20 is refracted by the electromagnetic lens 205 and the electromagnetic lens 206, respectively, and the crossover position (each beam) of each beam of the multi-primary electron beam 20 is repeated while repeating the intermediate image and the crossover. It passes through the beam separator 214 arranged at the intermediate image position) and proceeds to the electromagnetic lens 207 (objective lens). Then, the electromagnetic lens 207 focuses (focuses) the multi-primary electron beam 20 on the substrate 101. The multi-primary electron beam 20 focused (focused) on the surface of the substrate 101 (sample) by the objective lens 207 is collectively deflected by the main deflector 208 and the sub-deflector 209, and the substrate of each beam. Each irradiation position on 101 is irradiated. When the entire multi-primary electron beam 20 is collectively deflected by the batch blanking deflector 212, the position is displaced from the hole in the center of the limiting aperture substrate 213 and is shielded by the limiting aperture substrate 213. On the other hand, the multi-primary electron beam 20 not deflected by the batch blanking deflector 212 passes through the central hole of the limiting aperture substrate 213 as shown in FIG. By turning ON / OFF of the batch blanking deflector 212, blanking control is performed, and ON / OFF of the beam is collectively controlled. In this way, the limiting aperture substrate 213 shields the multi-primary electron beam 20 deflected so that the beam is turned off by the batch blanking deflector 212. Then, the multi-primary electron beam 20 for inspection (for image acquisition) is formed by the beam group that has passed through the restricted aperture substrate 213 formed from the time when the beam is turned on to the time when the beam is turned off.

When the multi-primary electron beam 20 is irradiated to a desired position of the substrate 101, it corresponds to each beam of the multi-primary electron beam 20 from the substrate 101 due to the irradiation of the multi-primary electron beam 20. , A bundle of secondary electrons including backscattered electrons (multi-secondary electron beam 300) is emitted.

The multi-secondary electron beam 300 emitted from the substrate 101 passes through the electromagnetic lens 207 and advances to the beam separator 214.

Here, the beam separator 214 generates an electric field and a magnetic field in a direction orthogonal to each other on a plane orthogonal to the direction in which the central beam of the multi-primary electron beam 20 travels (electron orbital central axis). The electric field exerts a force in the same direction regardless of the traveling direction of the electron. On the other hand, the magnetic field exerts a force according to Fleming's left-hand rule. Therefore, the direction of the force acting on the electron can be changed depending on the intrusion direction of the electron. The force due to the electric field and the force due to the magnetic field cancel each other out in the multi-primary electron beam 20 that enters the beam separator 214 from above, and the multi-primary electron beam 20 travels straight downward. On the other hand, in the multi-secondary electron beam 300 that invades the beam separator 214 from below, both the force due to the electric field and the force due to the magnetic field act in the same direction, and the multi-secondary electron beam 300 moves diagonally upward. It is bent and separated from the multi-primary electron beam 20.

The multi-secondary electron beam 300, which is bent diagonally upward and separated from the multi-primary electron beam 20, is further bent by the deflector 218 and projected onto the multi-detector 222 while being refracted by the electromagnetic lenses 224 and 226. To. The multi-detector 222 detects secondary electrons emitted from the substrate 101 by irradiation with the multi-primary electron beam 20. Specifically, the multi-detector 222 detects the projected multi-secondary electron beam 300. Backscattered electrons and secondary electrons may be projected onto the multi-detector 222, or the backscattered electrons may be diverged on the way and the remaining secondary electrons may be projected. The multi-detector 222 has a two-dimensional sensor. Then, each secondary electron of the multi-secondary electron beam 300 collides with the corresponding region of the two-dimensional sensor to generate electrons, and secondary electron image data is generated for each pixel. In other words, in the multi-detector 222, a detection sensor is arranged for each primary electron beam of the multi-primary electron beam 20. Then, the corresponding secondary electron beam emitted by the irradiation of each primary electron beam is detected. Therefore, each detection sensor of the plurality of detection sensors of the multi-detector 222 detects the intensity signal of the secondary electron beam for the image caused by the irradiation of the primary electron beam in charge of each. The intensity signal detected by the multi-detector 222 is output to the detection circuit 106.

FIG. 3 is a diagram showing an example of a plurality of chip regions formed on the semiconductor substrate according to the first embodiment. In FIG. 3, when the substrate 101 is a semiconductor substrate (wafer), a plurality of chips (wafer dies) 332 are formed in a two-dimensional array in the inspection region 330 of the semiconductor substrate (wafer). A mask pattern for one chip formed on an exposure mask substrate is transferred to each chip 332 by being reduced to, for example, 1/4 by an exposure device (stepper, scanner, etc.) (not shown). The region of each chip 332 is divided into a plurality of stripe regions 32 with a predetermined width, for example, in the y direction. The scanning operation by the image acquisition mechanism 150 is performed, for example, for each stripe region 32. For example, while moving the stage 105 in the −x direction, the scanning operation of the stripe region 32 is relatively advanced in the x direction. Each stripe region 32 is divided into a plurality of rectangular regions 33 in the longitudinal direction. The movement of the beam to the rectangular region 33 of interest is performed by batch deflection of the entire multi-primary electron beam 20 by the main deflector 208.

FIG. 4 is a diagram for explaining a multi-beam scanning operation according to the first embodiment. In the example of FIG. 4, the case of the multi-primary electron beam 20 having 5 × 5 rows is shown. The irradiation region 34 that can be irradiated by one irradiation of the multi-primary electron beam 20 is (the x-direction obtained by multiplying the x-direction beam-to-beam pitch of the multi-primary electron beam 20 on the substrate 101 surface by the number of beams in the x-direction. Size) × (size in the y direction obtained by multiplying the pitch between beams of the multi-primary electron beam 20 in the y direction on the surface of the substrate 101 by the number of beams in the y direction). It is preferable that the width of each stripe region 32 is set to the same size as the y-direction size of the irradiation region 34 or to be narrowed by the scan margin. In the example of FIG. 4, the case where the irradiation area 34 has the same size as the rectangular area 33 is shown. However, it is not limited to this. The irradiation area 34 may be smaller than the rectangular area 33. Or it may be large. Then, each beam of the multi-primary electron beam 20 is irradiated in the sub-irradiation region 29 surrounded by the inter-beam pitch in the x-direction and the inter-beam pitch in the y direction in which the own beam is located, and the sub-irradiation region 29 is irradiated. Scan inside (scan operation). Each of the primary electron beams 10 constituting the multi-primary electron beam 20 is in charge of any of the sub-irradiation regions 29 different from each other. Then, at each shot, each primary electron beam 10 irradiates the same position in the responsible sub-irradiation region 29. The movement of the primary electron beam 10 in the sub-irradiation region 29 is performed by batch deflection of the entire multi-primary electron beam 20 by the sub-deflector 209. This operation is repeated to sequentially irradiate the inside of one sub-irradiation region 29 with one primary electron beam 10. Then, when the scan of one sub-irradiation region 29 is completed, the irradiation position is moved to the adjacent rectangular region 33 in the same stripe region 32 by the collective deflection of the entire multi-primary electron beam 20 by the main deflector 208. This operation is repeated to irradiate the inside of the stripe region 32 in order. When the scan of one stripe region 32 is completed, the irradiation position is moved to the next stripe region 32 by the movement of the stage 105 and / or the collective deflection of the entire multi-primary electron beam 20 by the main deflector 208. As described above, the secondary electron image for each sub-irradiation region 29 is acquired by the irradiation of each primary electron beam 10. By combining these secondary electronic images for each sub-irradiation region 29, a secondary electronic image of the rectangular region 33, a secondary electronic image of the striped region 32, or a secondary electronic image of the chip 332 is configured.

As shown in FIG. 4, each sub-irradiation region 29 is divided into a plurality of rectangular frame regions 30, and a secondary electron image (image to be inspected) of 30 units of the frame region is used for inspection. In the example of FIG. 4, one sub-irradiation region 29 is divided into, for example, four frame regions 30. However, the number to be divided is not limited to four. It may be divided into other numbers.

It is also preferable that, for example, a plurality of chips 332 arranged in the x direction are grouped into the same group, and each group is divided into a plurality of stripe regions 32 with a predetermined width in the y direction, for example. The movement between the stripe regions 32 is not limited to each chip 332, and may be performed for each group.

Here, when the substrate 101 is irradiated with the multi-primary electron beam 20 while the stage 105 continuously moves, the main deflector 208 collectively deflects the irradiation position of the multi-primary electron beam 20 so as to follow the movement of the stage 105. Tracking operation is performed by. Therefore, the emission position of the multi-secondary electron beam 300 changes momentarily with respect to the orbital central axis of the multi-primary electron beam 20. Similarly, when scanning in the sub-irradiation region 29, the emission position of each secondary electron beam changes momentarily in the sub-irradiation region 29. The deflector 218 collectively deflects the multi-secondary electron beam 300 so that each secondary electron beam whose emission position has changed is irradiated into the corresponding detection region of the multi-detector 222.

FIG. 5 is a flowchart showing a main process of the inspection method according to the first embodiment. In FIG. 5, the inspection method according to the first embodiment is a representative pattern scanning step (S102), a representative pattern design image creating step (S104), a filter calculation step for each beam (S106), and each angle of each filter. Threshold V1, V2 calculation step (S108), V1, V2 table creation step (S110), scan step (S202), reference image creation step (S204), filter identification step (S206), and angle of each filter. The determination step (S208) and the threshold V1 and V2 extraction steps (S210). With the convolution calculation process (S220). A series of steps of an overlap determination step (S222), a correction step (S224), a contour line extraction step (S230), and a comparison step (S232) are carried out.

FIG. 6 is a diagram showing an example of the beam shape on the sample surface in the first embodiment. In the example of FIG. 6, a 3 × 3 multi-primary electron beam 20 is shown. Ideally, each beam of the multi-primary electron beam 20 is irradiated in a circular shape. However, by using an electron optical system such as an electromagnetic lens 202, an electromagnetic lens 205, an electromagnetic lens 206, and / or an electromagnetic lens 207, astigmatism may occur as shown in FIG. Therefore, as shown in FIG. 6, the focal position shifts in the quadratic direction in the x and y directions on the surface of the substrate 101 (sample), and the beam shape has a so-called elliptical intensity distribution of non-rotational symmetry. .. Therefore, an elliptical blur of each primary electron beam occurs in the irradiated beam. Therefore, even in the secondary electron image obtained by the primary electron beam, the corner shape corresponds to the elliptical blur. The direction of the astigmatism and the amount of misalignment that occur in the multi-primary electron beam 20 tend to be elliptical so as to extend radially from the center of the multi-primary electron beam 20, but they differ from beam to beam. Therefore, in order to match the shape of the corner portion of the reference image with the shape of the corner portion of the measurement image obtained by each beam, it is required to perform corner correction according to the beam intensity distribution on the substrate 101 of each beam. .. Therefore, in the first embodiment, a filter function corresponding to the intensity distribution of the beam is calculated for each beam.

As the representative pattern scanning step (S102), the image acquisition mechanism 150 acquires a secondary electronic image of the representative pattern. As the representative pattern, a preset pattern may be formed on the evaluation substrate, or a pattern formed in the representative region of the substrate 101 to be inspected may be diverted as a representative pattern.

First, the stage 105 is moved to a position where the stripe region 32 including the representative region of the substrate 101 can be scanned. Alternatively, or the evaluation substrate is placed on the stage 105, the stage 105 is moved to a position where the stripe region 32 including the region where the representative pattern is formed can be scanned. The image acquisition mechanism 150 acquires an image of the stripe region 32 including the representative region (representative pattern region) of the substrate 101 (or evaluation substrate) on which the representative pattern is formed. Here, for example, the multi-primary electron beam 20 is irradiated to the stripe region 32 including the representative region of the substrate 101, and the multi-secondary electron beam emitted from the substrate 101 due to the irradiation of the multi-primary electron beam 20. By detecting 300, a secondary electron image of the stripe region 32 including the representative region is acquired. As described above, backscattered electrons and secondary electrons may be projected onto the multi-detector 222, and the backscattered electrons are diverged on the way and the remaining secondary electrons (multi-secondary electron beam 300) are projected. May be done.

As described above, the multi-secondary electron beam 300 emitted from the substrate 101 due to the irradiation of the multi-primary electron beam 20 is detected by the multi-detector 222. The secondary electron detection data (measured image data: secondary electron image data: inspected image data) for each pixel in each sub-irradiation region 29 detected by the multi-detector 222 is output to the detection circuit 106 in the order of measurement. To. In the detection circuit 106, analog detection data is converted into digital data by an A / D converter (not shown) and stored in the chip pattern memory 123. Then, the obtained measurement image data is transferred to the filter calculation circuit 134 together with the information indicating each position from the position circuit 107. The measured image data is stored in a storage device (not shown) in the filter calculation circuit 134. As a result, the measured image data for each primary electron beam 10 can be obtained. In the example of FIG. 4, four (= 2 × 2) frame images 31 of the frame region 30 are obtained for each primary electron beam 10. Here, the frame image 31 of one frame area 30 out of the 2 × 2 frame areas 30 may be selected for each primary electron beam. The representative pattern for each of the primary electron beams 10 may be the same pattern, or may be a different pattern for each or a part of the primary electron beams 10.

As a representative pattern design image creation step (S104), first, the expansion circuit 111 (an example of the design image creation unit) is primary based on the design pattern data that is the basis of the representative pattern formation of the substrate 101 (or the evaluation substrate). For each electron beam 10, the design pattern data of the frame region corresponding to the obtained frame image 31 is expanded into an image to create a representative pattern design image (representative design image). Specifically, the design pattern data is read from the magnetic disk device 109 through the control computer 110, and each graphic pattern in the corresponding frame area defined in the read design pattern data is converted into binary or multi-valued image data. (Image development) to create a standard design image.

Here, the figure defined in the design pattern data is, for example, a basic figure of a rectangle or a triangle, for example, the coordinates (x, y) at the reference position of the figure, the length of the side, the rectangle, the triangle, or the like. Graphical data (vector data) that defines the shape, size, position, etc. of each pattern graphic is stored with information such as a graphic code that serves as an identifier that distinguishes graphic types.

When the information of the design pattern that becomes the graphic data is input to the expansion circuit 111, the data is expanded to the data for each graphic, and the graphic code indicating the graphic shape of the graphic data, the graphic dimension, and the like are interpreted. Then, binary or multi-valued design image data is developed and output as a pattern arranged in the squares having a grid of predetermined quantized dimensions as a unit. In other words, the design data is read, the occupancy rate of the figure in the design pattern is calculated for each cell created by virtually dividing the inspection area into cells with a predetermined dimension as a unit, and the n-bit occupancy rate data is obtained. Output. For example, it is preferable to set one cell as one pixel. Then, assuming that one pixel has a resolution of 1/28 ⁽ = 1/256), a small area of 1/256 is allocated to the area of the figure arranged in the pixel to determine the occupancy rate in the pixel. Calculate. Then, a representative design image of 8-bit occupancy rate data is created for each pixel. The data of the representative design image is output to the filter calculation circuit 134. The data of the reference design image for each primary electron beam 10 is stored in a storage device (not shown) in the filter calculation circuit 134.

As a filter calculation step (S106) for each beam, the filter calculation circuit 134 uses the measurement image and the representative design image of the representative pattern for the primary electron beam for each primary electron beam 10 of the multi-primary electron beam 10. Based on this, the filter function for filtering the representative design image or the coefficient of the filter function is calculated.

FIG. 7 is a diagram for explaining an example of a method for calculating a filter function in the first embodiment. For example, as shown in FIG. 7A, an unknown coefficient matrix a (u, v) composed of (2k + 1) × (2k + 1) elements smaller than the number of pixels in the frame area 30 (an example of a coefficient). Ask for. For example, a coefficient matrix a (u, v) of 15 × 15 is obtained for an image of a frame area 30 composed of 512 × 512 pixels. The sum of the products of the pixels of (2k + 1) × (2k + 1) pixels and the coefficient matrix a (u, v) is the pixel of interest d (i, j) centered on the pixel of interest d (i, j) of the representative design image. The coefficient matrix a (u, v) closer to the pixel r (i, j) of interest in the measurement image corresponding to is obtained. The relational expression (1) is shown below.

As shown in FIG. 7B, the relational expression (1) is calculated each time while moving the pixel of interest within the region of the representative design image 31. Then, the coefficient matrix a (u, v) that most satisfies the relational expression (1) defined by using the unknown coefficient matrix a (u, v) obtained for all the pixels in the reference design image 31. Ask for. The number of elements (2k + 1) × (2k + 1) of the coefficient matrix a (u, v) may be appropriately set. If it is too small, the accuracy will deteriorate, and if it is too large, the calculation time will be long. Further, when the pixel of interest moves within the region of the representative design image 31, if it is close to the end, the peripheral pixels on the end side may not exist as much as necessary, but in such a case, the peripheral pixels from which a value can be obtained are used. You just have to calculate.

Further, in the filter calculation circuit 134, when the center pixel of the (2k + 1) × (2k + 1) pixel and the center of gravity of the filter function are deviated from each other for each calculated filter function, the center pixel and the center of gravity of the filter function are deviated from each other. Correct the filter function so that it matches, for example, by translation.

As described above, a filter function (image processing filter) that depends on the intensity distribution of the primary electron beam can be acquired for each primary electron beam 10. The acquired filter function data for each primary electron beam 10 is output to the table creation circuit 136.

FIG. 8 is a diagram showing an example of the internal configuration of the table making circuit according to the first embodiment. In FIG. 8, a storage device 70, 71, 79 such as a magnetic disk device, an angle setting unit 72, a V1 calculation unit 74, a V2 calculation unit 76, and a table creation unit 78 are arranged in the table creation circuit 136. Each "-part" such as the angle setting unit 72, the V1 calculation unit 74, the V2 calculation unit 76, and the table creation unit 78 includes a processing circuit, which includes an electric circuit, a computer, a processor, a circuit board, and a quantum. A circuit, a semiconductor device, or the like is included. Further, a common processing circuit (same processing circuit) may be used for each "-part". Alternatively, different processing circuits (separate processing circuits) may be used. The input data or the calculated result required in the format angle setting unit 72, the V1 calculation unit 74, the V2 calculation unit 76, and the table creation unit 78 are stored in a memory (not shown) or a memory 118 each time.

The data of the filter function for each primary electron beam 10 input in the table creation circuit 136 is stored in the storage device 70. Further, the storage device 71 stores, for example, image data of a rectangular pattern having sides having a size larger than the size of the filter function (k × k pixels).

As a threshold value V1 and V2 calculation step (S108) for each angle of each filter, the table creation circuit 136 includes a filter function for the primary electron beam 10 and an edge of a graphic pattern in the image for each primary electron beam 10. The threshold values V1 and V2 that index the overlapping relationship for each relative angle are calculated. The threshold values V1 and V2 are values determined according to the overlapping relationship between the filter function and the graphic pattern in the image.

FIG. 9 is a diagram showing an example of the overlapping relationship between the filter function and the graphic pattern edge in the first embodiment. In the example of FIG. 9 (a), a non-zero value (for example, 1) is set in the pixel of the elliptical region in which the major axis is formed in the y direction, which depends on the intensity distribution of the predetermined primary electron beam. A filter function 12 of, for example, 11 × 11 pixels, in which zero is defined for the pixels in the region of, is shown. The example of FIG. 9A shows a case where a part of the filter function 12 overlaps with the rectangular pattern 16 across the edge of the rectangular pattern 16 having an edge (side) extending in the x direction.

In FIG. 9B, the filter function 12 overlaps across the upper (y-direction side) edge of the two edges extending in the x direction of the rectangular pattern 16, and the central pixel 14 of the filter function 12 overlaps. The overlapping relationship between the filter function 12 and the rectangular pattern 16 at the position where the rectangular pattern 16 is in contact with the outside is shown. In other words, there is a case where the entire area of the filter function 12 in the x direction and the area of about half the size in the y direction overlap with the rectangular pattern 16, and the edge is within the range where the central pixel 14 of the filter function 12 is not included in the rectangular pattern 16. It shows the overlapping relationship at the position where the center pixel 14 and the center pixel 14 are in contact with each other. The gradation value of the central pixel 14 after filtering by convolving the filter function 12 into the image in which the rectangular pattern 16 is arranged at this position is set as the threshold value V1. In other words, the threshold V1 is each of the elliptical regions in which the central pixel 14 shown in FIG. 9B is not included in the rectangular pattern 16 and overlaps with the rectangular pattern 16 in the overlapping positional relationship where the edge and the central pixel 14 are in contact with each other. The total value obtained by multiplying the element value of the pixel by the gradation value of the corresponding pixel of the rectangular pattern is shown. For example, the image is defined by 256 gradations from 0 to 255, the gradation value of the pixels in the rectangular pattern 16 is 255, and the gradation value of the pixels outside the rectangular pattern 16 is zero. Further, the element value of the pixel in the elliptical region of the filter function 12 is set to 1, for example, and the element value of the other pixels is set to zero. In such a case, when the filter function 12 is folded at this position, the gradation value after the filter of the center pixel 14 which is the pixel of interest is the number of pixels in the elliptical region overlapping the rectangular pattern 16 × the gradation value (here, the gradation value). For example, the value is 255). In the example of FIG. 9B, the threshold value V1 = 20 pixels × 255.

In FIG. 9C, the filter function 12 overlaps across the upper (y-direction side) edge of the two edges extending in the x direction of the rectangular pattern 16, and the central pixel 14 of the filter function 12 overlaps. The overlapping relationship between the filter function 12 and the rectangular pattern 16 at the position where the rectangular pattern 16 is in contact with the inside is shown. In other words, when the area of the filter function 12 having a size of about half in the x direction and about half in the y direction overlaps with the rectangular pattern 16, the edge is within the range in which the central pixel 14 of the filter function 12 is included in the rectangular pattern 16. It shows the overlapping relationship at the position where the center pixel 14 and the center pixel 14 are in contact with each other. The gradation value of the central pixel 14 after filtering by convolving the filter function 12 into the image in which the rectangular pattern 16 is arranged at this position is set as the threshold value V2. In other words, in the threshold value V2, the central pixel 14 shown in FIG. 9C is included in the rectangular pattern 16, and each of the elliptical regions overlapping the rectangular pattern 16 in the overlapping positional relationship where the edge and the central pixel 14 are in contact with each other. The total value obtained by multiplying the element value of the pixel by the gradation value of the corresponding pixel of the rectangular pattern is shown. In such a case, when the filter function 12 is folded at this position, the gradation value after the filter of the center pixel 14 which is the pixel of interest is the number of pixels in the elliptical region overlapping the rectangular pattern 16 × the gradation value (here, the gradation value). For example, the value is 255). In the example of FIG. 9C, the threshold value V2 = 27 pixels × 255.

In the example of FIG. 9A, for an image in which a pattern having an edge with an angle of 0 ° with respect to the x-axis is arranged, a case where a part of the filter function 12 overlaps the pattern across the edge is shown. However, the angle of the edge of the pattern is not limited to this.

FIG. 10 is a diagram showing another example of the overlapping relationship between the filter function and the graphic pattern edge in the first embodiment. In the example of FIG. 10A, the case where the filter function 12 shown in FIG. 9A overlaps with the rectangular pattern 16 having an edge extending in the direction of the angle θ1 with respect to the x-axis is shown. When the rectangular pattern 16 is arranged diagonally, the region of the entire filter function 12 that overlaps with the rectangular pattern 16 is different from that in FIG. 9A. Therefore, the threshold values V1 and V2 have an angle dependence. In other words, the thresholds V1 and V2 change depending on the relative angle between the filter function and the edge of the graphic pattern. Therefore, in the first embodiment, the filter function 12 and the rectangular pattern 16 are set in the direction opposite to the direction of the arrangement angle of the rectangular pattern 16 so that the direction in which the edge of the rectangular pattern 16 extends is apparently the x-axis. It is assumed that the rotation is performed by the angle θ1. At this angle, the threshold values V1 and V2 described above are calculated.

In FIG. 10B, the central pixel 14 of the filter function 12 rotated clockwise by an angle θ1 is the upper edge (y direction side) of the two edges extending in the x direction of the rectangular pattern 16 and the rectangular pattern 16. The overlapping relationship between the filter function 12 and the rectangular pattern 16 at the position where the filter function 12 is in contact with the outside of the above is shown. In other words, in the case where the entire area of the filter function 12 in the x direction and the area of about half the size in the y direction overlap with the rectangular pattern 16, the central pixel 14 of the filter function 12 is not included in the rectangular pattern 16, and the edges and the center are not included. It shows the overlapping positional relationship in which the pixel 14 is in contact with the pixel 14. When the filter function 12 is folded at this position, the gradation value after the filter of the central pixel 14 which is the pixel of interest is the value of the number of pixels in the elliptical region overlapping the rectangular pattern 16 × 255. In the example of FIG. 10B, the threshold value V1 = 21 pixels × 255.

In FIG. 10C, the central pixel 14 of the filter function 12 rotated clockwise by an angle θ1 is the upper edge (y direction side) of the two edges extending in the x direction of the rectangular pattern 16 and the rectangular pattern 16. The overlapping relationship between the filter function 12 and the rectangular pattern 16 at the position where the filter function 12 is in contact with the inside of the above is shown. In other words, in the case where the entire area of the filter function 12 in the x direction and the area of about half the size in the y direction overlap with the rectangular pattern 16, the central pixel 14 of the filter function 12 is included in the rectangular pattern 16 and the edge and the edge. The overlapping positional relationship in which the central pixel 14 is in contact is shown. When the filter function 12 is folded at this position, the gradation value after the filter of the central pixel 14 which is the pixel of interest is the value of the number of pixels in the elliptical region overlapping the rectangular pattern 16 × 255. In the example of FIG. 10C, the threshold value V2 = 28 pixels × 255.

As described above, the threshold values V1 and V2, which are indicators of the overlapping relationship between the filter function 12 and the rectangular pattern 16, depend on the arrangement angle of the rectangular pattern in the image.

FIG. 11 is a diagram showing an example of the overlapping relationship between each edge of the rectangular pattern and the filter function in the first embodiment. The example of FIG. 11 shows a case where each edge of the rectangular pattern 13 having an edge at an angle of 0 ° with respect to the x-axis overlaps with the filter function 12. When the filter function 12 straddles the upper edge extending in the x direction, the lower half area of the filter function 12 overlaps with the rectangular pattern. In this case, the angle θ = 0 °. When the filter function 12 straddles the left edge extending in the y direction, about half of the area on the right side of the filter function 12 overlaps with the rectangular pattern. In this case, the angle θ = 90 °. When the filter function 12 straddles the lower edge extending in the x direction, the upper half area of the filter function 12 overlaps with the rectangular pattern. In this case, the angle θ = 180 °. When the filter function 12 straddles the right edge extending in the y direction, about half of the area on the left side of the filter function 12 overlaps with the rectangular pattern. In this case, the angle θ = 275 °. The thresholds V1 and V2 may differ at each angle θ. Therefore, in the first embodiment, the threshold values V1 and V2 for each angle are calculated while changing the angle of the straddling edge for each filter function. Hereinafter, a specific description will be given.

First, the angle setting unit 72 sets the edge angle θ for each filter function. Next, the V1 calculation unit 74 calculates the threshold value V1 at the set angle θ. Next, the V2 calculation unit 76 calculates the threshold value V2 at the set angle θ. Hereinafter, the threshold values V1 and V2 are calculated each time while changing the angle θ. It is preferable to change the setting of the angle θ by, for example, 1 °. However, it is not limited to this. For example, the angle change width may be set to 5 °, 10 °, 22.5 °, 45 °, or 90 °. The smaller the angle change width, the more accurately the threshold values V1 and V2 can be calculated.

As a V1 and V2 table creation step (S110) of each filter, the table creation unit 78 creates V1 and V2 tables that define threshold values V1 and V2 for each angle for each filter function.

FIG. 12 is a diagram showing an example of the V1 and V2 tables in the first embodiment. In the example of FIG. 12, an example of the V1 and V2 tables that define the threshold values V1 and V2 at each angle from 0 ° to 359 ° is shown while shifting the angle by 1 °. The created V1 and V2 tables are stored in the storage device 79.

Prior to the inspection process, each of the above steps is performed as a pretreatment, and then the actual inspection process of the substrate to be inspected is started.

As a scanning step (S202), the image acquisition mechanism 150 acquires an electro-optical image (secondary electron image) by scanning the substrate 101 on which the graphic pattern is formed with an electron beam. Here, the substrate 101 on which a plurality of graphic patterns are formed is irradiated with the multi-primary electron beam 20, and the multi-secondary electron beam 300 emitted from the substrate 101 due to the irradiation of the multi-primary electron beam 20 is generated. By detecting, the secondary electron image of the substrate 101 is acquired. As described above, backscattered electrons and secondary electrons may be projected onto the multi-detector 222, and the backscattered electrons are diverged on the way and the remaining secondary electrons (multi-secondary electron beam 300) are projected. May be done.

As described above, the multi-secondary electron beam 300 emitted from the substrate 101 due to the irradiation of the multi-primary electron beam 20 is detected by the multi-detector 222. The detection data of the secondary electrons (measured image data: secondary electronic image data: inspected image data: electro-optical image data) for each pixel in each sub-irradiation region 29 detected by the multi-detector 222 is detected in the order of measurement. It is output to the circuit 106. In the detection circuit 106, analog detection data is converted into digital data by an A / D converter (not shown) and stored in the chip pattern memory 123. Then, the obtained measurement image data is transferred to the comparison circuit 108 together with the information indicating each position from the position circuit 107.

As the reference image creation step (S204), a reference image created from the design data that is the source of the graphic pattern and corresponding to the electro-optical image is created. This will be described in detail. First, the expansion circuit 111 (a part of the reference image creation unit) reads the design pattern data from the storage device 109 through the control computer 110, and converts each graphic pattern defined in the read design pattern data into binary or multi-value. Convert to image data of. It is preferable that the expansion circuit 111 creates a design image of the corresponding frame region 30 according to the acquisition order of the measurement images acquired in the scanning step.

As described above, the figure defined in the design pattern data is, for example, a rectangle or a triangle as a basic figure, for example, the coordinates (x, y) at the reference position of the figure, the length of the side, the rectangle, the triangle, or the like. Graphical data that defines the shape, size, position, etc. of each pattern graphic is stored with information such as a graphic code that serves as an identifier that distinguishes the graphic types of.

When the design pattern data to be the graphic data is input to the expansion circuit 111, the data is expanded to the data for each graphic, and the graphic code indicating the graphic shape of the graphic data, the graphic dimension, and the like are interpreted. Then, it is developed into binary or multi-valued design image data as a pattern arranged in the squares having a grid of predetermined quantized dimensions as a unit and output. In other words, the design data is read, the occupancy rate of the figure in the design pattern is calculated for each cell created by virtually dividing the inspection area into cells with a predetermined dimension as a unit, and the n-bit occupancy rate data is obtained. Output. For example, it is preferable to set one cell as one pixel. Then, assuming that one pixel has a resolution of 1/28 ⁽ = 1/256), a small area of 1/256 is allocated to the area of the figure arranged in the pixel to determine the occupancy rate in the pixel. Calculate. Then, it is created as 8-bit occupancy rate data. Such squares (inspection pixels) may be matched with the pixels of the measurement data.

Next, the reference image creation circuit 112 (another part of the reference image creation unit) uses a predetermined image processing filter for the design image corresponding to the target electro-optical image for each electro-optical image of the plurality of electro-optical images. By performing the filtering process, a reference image corresponding to the target electro-optical image is created. Thereby, the design image data in which the image intensity (shade value) is the image data on the design side of the digital value can be matched with the image generation characteristic obtained by the irradiation of the multi-primary electron beam 20. The image data of the created reference image is output to the correction circuit 132.

Here, the image processing filter applied to create the reference image does not depend on the intensity distribution for each primary electron beam 10. For example, it is created according to the beam characteristics of the central beam. Therefore, as it is, the reference image used for acquiring the SEM image is not matched to the characteristics of the beam having the beam intensity distribution of the non-rotating target individually. Therefore, the reference image does not have a corner shape corresponding to the blur of the non-rotating target that the SEM image has. Therefore, the reference image is individually corrected according to the characteristics of the beam obtained from the electro-optical image. At that time, devise not to change the edge shape. Hereinafter, a specific description will be given.

FIG. 13 is a diagram showing an example of the internal configuration of the correction circuit according to the first embodiment. In FIG. 13, storage devices 60, 61, 69 such as a magnetic disk device, a filter specifying unit 62, an angle determination unit 64, a V1, V2 extraction unit 65, a convolution calculation unit 66, and an overlap determination unit 67 are included in the correction circuit 132. , And the correction processing unit 68 are arranged. Each "-unit" such as the filter specifying unit 62, the angle determination unit 64, the V1, V2 extraction unit 65, the convolution calculation unit 66, the overlap determination unit 67, and the correction processing unit 68 includes a processing circuit, and the processing circuit includes a processing circuit. , Electrical circuits, computers, processors, circuit boards, quantum circuits, semiconductor devices and the like. Further, a common processing circuit (same processing circuit) may be used for each "-part". Alternatively, different processing circuits (separate processing circuits) may be used. The input data required in the filter specifying unit 62, the angle determination unit 64, the V1, V2 extraction unit 65, the convolution calculation unit 66, the overlap determination unit 67, and the correction processing unit 68, or the calculated result is a memory (not shown) each time. Alternatively, it is stored in the memory 118.

As a filter specifying step (S206), the filter specifying unit 62 specifies a primary electron beam 10 for acquiring an electro-optical image of the frame region for each frame region 30, and a filter function for the primary electron beam 10. To identify.

In the angle determination step (S208), the edge angle when the filter function straddles each edge of the graphic pattern arranged in the frame region is determined for each frame region 30. For example, in the case of a rectangular pattern having two edges extending along the x-axis, the upper edge has an angle θ = 0 °, and the lower edge has an angle θ = 180 °.

As the threshold value V1 and V2 extraction step (S210), the V1 and V2 extraction units 65 refer to the V1 and V2 tables and refer to the V1 and V2 tables for each edge of the graphic pattern and the threshold value V1 corresponding to the edge angle θ of the specified filter function. , V2 is extracted.

In the convolution calculation step (S220), the convolution calculation unit 66 convolves the specified filter function (image processing filter) with respect to the reference image in the frame area 30 while moving the target pixel. Perform processing.

As an overlap determination step (S222), the overlap determination unit 67 (corner determination unit) is a filter that convolves the specified filter function with respect to the reference image in the frame area 30 while moving the target pixel. Using the filtered gradation value C0 for the target pixel when processing is performed, and the thresholds V1 and V2 determined according to the overlapping relationship between the specified filter function and the graphic pattern, the target pixel is Determine if it is located in the corner.

FIG. 14 is a diagram for explaining the overlapping relationship between the filter function and the graphic pattern in the first embodiment. In the example of FIG. 14, the gradation value of the pixel with the pattern is 255, and the gradation value of the pixel without the pattern is zero. Further, in the filter function 12, a value other than zero (for example, 1) is set in the pixel of the elliptical region in which the major axis is formed in the y direction, and zero is set in the pixel of the other region, as shown in FIG. 9A. A defined filter function 12, for example, 11 × 11 pixels is shown. Further, here, the edge angle straddling is set to θ = 0 °. Therefore, for example, V1 = 20 × 255 and V2 = 27 × 255.

When the filter function 12 is at the position of the A part, the target pixel (the pixel at the same position as the center pixel of the filter function 12) is located outside the pattern, and the gradation value C0 after the filter of the target pixel becomes zero. Therefore, C0 <V1.

When the filter function 12 is at the position of the B portion, a part of the lower side of the filter function 12 (the elliptical region is equivalent to 8 pixels) overlaps with the pattern, and the target pixel (the pixel at the same position as the center pixel of the filter function 12). ) Is still outside the pattern, and the gradation value C0 = 8 × 255 after the filter of the target pixel. Therefore, C0 <V1 still holds.

When the filter function 12 is at the position of the C part, about half of the area of the filter function 12 (the elliptical area is equivalent to 20 pixels) overlaps with the pattern, and the target pixel (the pixel at the same position as the center pixel of the filter function 12). Is still outside the pattern, and the gradation value C0 = 20 × 255 after the filter of the target pixel. Therefore, C0 = V1.

On the other hand, when the filter function 12 is at the position of the D part, which is shifted by one pixel from the position of the C part, about half of the area of the filter function 12 (the elliptical area is 27 pixels) overlaps with the pattern, and the target pixel (the target pixel (the elliptical area is 27 pixels)). The pixel at the same position as the center pixel of the filter function 12) is located in the pattern, and the gradation value C0 = 27 × 255 after the filter of the target pixel. Therefore, C0 = V2.

When the filter function 12 is at the position of the E part, most of the area of the filter function 12 (the elliptical area is 27 pixels) overlaps with the pattern, and the target pixel (the pixel at the same position as the center pixel of the filter function 12) is , It is located in the pattern, and the gradation value C0 = 44 × 255 after the filter of the target pixel. Therefore, C0> V2.

As described above, when the gradation value C0 after the filter of the target pixel is not zero and C0≤V1 or C0≥V2, the filter function 12 overlaps the graphic pattern across one edge of the graphic pattern. It can be seen that there is a positional relationship. In other words, it can be determined that the target pixel is not a corner portion. Further, if the gradation value C0 is zero, it can be determined that the filter function 12 and the graphic pattern do not overlap in the first place.

On the other hand, when the filter function 12 is at the position of the F part (corner part), the target pixel (the pixel at the same position as the center pixel of the filter function 12) is located in the pattern, but the filter function overlaps with the pattern. The 12 regions are more than the C portion in the V1 state and less than the D portion in the V2 state. Therefore, the gradation value C0 = 21 × 255 after the filter of the target pixel. Therefore, V1 <C0 <V2. As described above, the threshold value V2 is the upper limit value and the threshold value V1 is the lower limit value as the values determined according to the overlapping relationship. Therefore, the overlap determination unit 67 determines that the target pixel is located at the corner portion when the gradation value C0 filtered for the target pixel is between the upper limit value and the lower limit value. In other words, the overlap determination unit 67 determines that the target pixel with V1 <C0 <V2 is located at the corner portion.

In the example of FIG. 14, for a pixel at a position (corner tip) displaced by 1 pixel in the + x direction from the position of the F portion, C0 <V1. Therefore, it is not determined that the target pixel is located at the corner portion, but F. Since V1 <C0 <V2 at a position shifted by one pixel in the −x direction from the position of the portion, it can be determined that most of the pixels in the corner portion are located in the corner portion.

As a correction step (S224), the correction processing unit 68 uses a filter function that depends on the intensity distribution of the primary electron beam 10 used to acquire the electro-optical image corresponding to the reference image, and uses a graphic pattern in the reference image. Maintains the edge shape of and corrects the corner shape of the graphic pattern in the reference image. Specifically, the correction processing unit 68 corrects the gradation value of the target pixel for each pixel of the reference image when it is determined that the target pixel is located at the corner portion. More specifically, the gradation value of the pixel for which C0 ≦ V1 is set to zero. The gradation value of the pixel for which C0 ≧ V2 is 255. Then, the pixel in which V1 <C0 <V2 corrects the gradation value to (C0-V1) / (V2-V1). Since the threshold values V1 and V2 are values that change depending on the intensity distribution of the primary electron beam, gradation correction can be performed depending on the intensity distribution of the primary electron beam.

Further, the edge portion has C0 ≦ V1 or C0 ≧ V2, and the pixel in which C0 ≦ V1 is found in the edge portion is located outside the pattern, so that the gradation value is originally zero. Since the pixel in which C0 ≧ V2 is located in the edge portion is located in the pattern, the gradation value is originally 255. Therefore, the edge shape of the graphic pattern can be kept unchanged. On the other hand, since the corner portion has V1 <C0 <V2, it can be corrected. In this way, the straight line portion is not gradation-corrected, and only the corner portion is gradation-corrected, so that it functions as a corner rounding process. The data of the reference image to which the corner rounding process has been corrected is stored in the storage device 69 and output to the comparison circuit 108.

FIG. 15 is a diagram showing an example of a pattern before and after correction in the first embodiment. FIG. 15A shows the pattern before correction. By performing the correction of the first embodiment on such a pattern, the corner rounding process can be performed without changing the shape of the edge portion of the straight line as shown in FIG. 15 (b).

FIG. 16 is a diagram showing an example of the internal configuration of the comparison circuit according to the first embodiment. In FIG. 16, storage devices 50 and 52 such as a magnetic disk device, contour line extraction units 54 and 56, and a comparison unit 58 are arranged in the comparison circuit 108. Each "-part" such as the contour line extraction unit 54, 56 and the comparison unit 58 includes a processing circuit, and the processing circuit includes an electric circuit, a computer, a processor, a circuit board, a quantum circuit, a semiconductor device, or the like. included. Further, a common processing circuit (same processing circuit) may be used for each "-part". Alternatively, different processing circuits (separate processing circuits) may be used. The input data or the calculated result required in the contour line extraction units 54 and 56 and the comparison unit 58 are stored in a memory (not shown) or a memory 118 each time.

The data of the electro-optical image for each sub-irradiation region 29 input in the comparison circuit 108 is stored in the storage device 50. Further, the data of the correction reference image to which the corner rounding processing correction is performed, which is input to the comparison circuit 108, is stored in the storage device 50. The comparison circuit 108 compares the image to be inspected, which is composed of at least a part of the secondary electron image for each sub-irradiation region 29, with the reference image. As the image to be inspected, for example, a secondary electronic image (electro-optical image) for each frame region 30 is used. For example, the sub-irradiation region 29 is divided into four frame regions 30. As the frame area 30, for example, an area of 512 × 512 pixels is used.

As the contour line extraction step (S230), the contour line extraction unit 54 extracts the contour line (actual image contour line) of the graphic pattern in the image for each electro-optical image (frame image 31) for each frame region 30. Further, the contour line extraction unit 56 extracts the contour line (reference contour line) of the graphic pattern in the image for each correction reference image for each frame area 30. The contour line extraction method may be the same as before. For example, it is preferable to extract the image by filtering it with a differential filter to emphasize the contour position.

As a comparison step (S232), the comparison unit 58 compares the corrected reference image whose corner shape has been corrected with the frame image 31.

FIG. 17 is a diagram showing an example of an actual image contour line and a reference contour line in the first embodiment. In FIG. 17, the comparison unit 58 calculates, for example, a position shift vector from the reference contour line to the actual image contour line, and is defective when the length of the position shift vector (distance between the contour lines) exceeds the determination threshold Th. Is determined. Then, the comparison result is output. The comparison result may be output to the storage device 109, the monitor 117, or the memory 118, or may be output from a printer (not shown).

As described above, according to the first embodiment, the reference image in which the edge shape of the pattern is maintained and the corner portion is corrected according to the characteristics of the beam used for acquiring the measurement image can be compared.

In the above description, the series of "-circuits" includes a processing circuit, and the processing circuit includes an electric circuit, a computer, a processor, a circuit board, a quantum circuit, a semiconductor device, and the like. Further, a common processing circuit (same processing circuit) may be used for each "-circuit". Alternatively, different processing circuits (separate processing circuits) may be used. The program for executing the processor or the like may be recorded on a recording medium such as a magnetic disk device, a magnetic tape device, an FD, or a ROM (read-only memory). For example, position circuit 107, comparison circuit 108, expansion circuit 111, reference image creation circuit 112, stage control circuit 114, lens control circuit 124, blanking control circuit 126, deflection control circuit 128, correction circuit 132, filter calculation circuit 134, And the table making circuit 136 may be composed of at least one processing circuit described above.

The embodiment has been described above with reference to specific examples. However, the present invention is not limited to these specific examples. The example of FIG. 1 shows a case where a multi-primary electron beam 20 is formed by a molded aperture array substrate 203 from a single beam emitted from an electron gun 201 as one irradiation source, but the present invention is limited to this. is not. A mode may be used in which the multi-primary electron beam 20 is formed by irradiating each of the primary electron beams from a plurality of irradiation sources.

Further, although the description of parts not directly required for the description of the present invention such as the device configuration and the control method is omitted, the required device configuration and the control method can be appropriately selected and used.

In addition, all electron beam inspection devices and electron beam inspection methods that include the elements of the present invention and can be appropriately redesigned by those skilled in the art are included in the scope of the present invention.

10 Primary electron beam 12 Filter function 13, 16 Rectangular pattern 14 Central pixel 20 Multi-primary electron beam 22 Hole 29 Sub-irradiation area 30 Frame area 31 Frame image 32 Stripe area 33 Rectangular area 34 Irradiation area 50, 52 Storage device 54, 56 Contour line extraction unit 58 Comparison unit 60, 61, 69 Storage device 62 Filter identification unit 64 Angle determination unit 65 V1, V2 Extraction unit 66 Folding calculation unit 67 Overlap determination unit 68 Correction processing unit 70, 71, 79 Storage device 72 Angle Setting unit 74 V1 calculation unit 76 V2 calculation unit 78 Table creation unit 100 Inspection device 101 Board 102 Electron beam column 103 Inspection room 105 Stage 106 Detection circuit 107 Position circuit 108 Comparison circuit 109 Storage device 110 Control computer 112 Reference image creation circuit 114 Stage Control circuit 117 Monitor 118 Memory 120 Bus 122 Laser length measurement system 123 Chip pattern memory 124 Lens control circuit 126 Blanking control circuit 128 Deflection control circuit 132 Correction circuit 134 Filter calculation circuit 136 Table creation circuit 142 Drive mechanism 144, 146, 148 DAC Amplifier 150 Image acquisition mechanism 160 Control system circuit 201 Electron gun 202 Electromagnetic lens 203 Molded aperture array board 205, 206, 207, 224,226 Electromagnetic lens 208 Main deflector 209 Sub-deflector 212 Collective blanking deflector 213 Limitation aperture board 214 Beam Separator 216 Mirror 218 Deflector 222 Multi Detector 300 Multi Secondary Electron Beam 330 Inspection Area 332 Chip

Claims (8)

A reference image creation unit that creates a reference image corresponding to an electro-optical image created from the design data that is the basis of the graphic pattern,
An image processing filter that depends on the intensity distribution of the electron beam used to acquire the electro-optical image corresponding to the reference image is used to maintain the edge shape of the graphic pattern in the reference image, and the said in the reference image. A correction processing unit that corrects the corner shape of the graphic pattern,
A comparison unit for comparing the reference image with the corrected corner shape and the electro-optical image, and a comparison unit.
An electron beam inspection device characterized by being equipped with. The filtered gradation value for the target pixel when the reference image is filtered by convolving the image processing filter while moving the target pixel, and the image processing filter and the graphic pattern. Further, a corner determination unit for determining whether or not the target pixel is located in the corner portion by using a value determined according to the overlapping relationship is further provided.
The electron beam inspection device according to claim 1, wherein the correction processing unit corrects the gradation value of the target pixel when it is determined that the target pixel is located at the corner portion. An upper limit value and a lower limit value are set as values determined according to the overlapping relationship.
The corner determination unit is characterized in that when the filtered gradation value for the target pixel is between the upper limit value and the lower limit value, the target pixel is determined to be located in the corner portion. The electron beam inspection apparatus according to claim 2. The electron beam inspection apparatus according to claim 3, wherein the upper limit value and the lower limit value change depending on the relative angle between the image processing filter and the edge of the graphic pattern. The process of creating a reference image corresponding to an electro-optical image created from the design data that is the basis of the graphic pattern,
An image processing filter that depends on the intensity distribution of the electron beam used to acquire the electro-optical image corresponding to the reference image is used to maintain the edge shape of the graphic pattern in the reference image, and the said in the reference image. The process of correcting the corner shape of the graphic pattern and
A step of comparing the reference image with the corrected corner shape and the electro-optical image and outputting the result.
An electron beam inspection method characterized by being equipped with. The filtered gradation value for the target pixel when the reference image is filtered by convolving the image processing filter while moving the target pixel, and the image processing filter and the graphic pattern. Further provided with a step of determining whether or not the target pixel is located at the corner portion by using a value determined according to the overlapping relationship.
The electron beam inspection method according to claim 5, wherein when it is determined that the target pixel is located at the corner portion, the gradation value of the target pixel is corrected. An upper limit value and a lower limit value are set as values determined according to the overlapping relationship.
The electron according to claim 6, wherein when the filtered gradation value for the target pixel is between the upper limit value and the lower limit value, it is determined that the target pixel is located at the corner portion. Beam inspection method. The electron beam inspection method according to claim 7, wherein the upper limit value and the lower limit value change depending on the relative angle between the image processing filter and the edge of the graphic pattern.

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