WO2021205728A1 - Multielectron beam inspection device and multielectron beam inspection method - Google Patents

Abstract

A multielectron beam inspection device (100) of an embodiment of the present invention is characterized by being provided with: a secondary-electron image acquisition mechanism (150) for irradiating a sample (101) having a pattern formed thereon with a multi-primary-electron beam (20), detecting a multi-secondary-electron beam (300) emitted due to the irradiation of the sample with the multi-primary-electron beam, and acquiring a secondary-electron image containing a crosstalk component; a correction circuit (132) for generating a corrected secondary-electron image obtained by removing the crosstalk component from the secondary-electron image by using preset gain information with which to remove the crosstalk component from the secondary-electron image; and a comparison circuit (108) for comparing the corrected secondary-electron image with a predetermined image (123).

Description

Multi-electron beam inspection device and multi-electron beam inspection method

This application is an application claiming priority based on JP2020-068595 (application number) filed in Japan on April 6, 2020. The content described in JP2020-068595 will be incorporated into this application.

The present invention relates to a multi-electron beam inspection device and a multi-electron beam inspection method. For example, the present invention relates to an inspection device that inspects using a secondary electron image of a pattern emitted by irradiating a multi-beam with 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 elements has become narrower and narrower. Further, improvement of the yield is indispensable for manufacturing an LSI, which requires a large manufacturing cost. However, as represented by 1-gigabit class DRAM (random access memory), the patterns constituting the LSI are on the order of submicron to nanometer. In recent years, with the miniaturization of LSI pattern dimensions formed on semiconductor wafers, the dimensions that must be detected as pattern defects have become extremely small. Therefore, it is necessary to improve the accuracy of the pattern inspection apparatus for inspecting the defects of the ultrafine pattern transferred on the semiconductor wafer. In addition, one of the major factors for reducing the yield is a pattern defect of a mask used when exposing and transferring an ultrafine pattern on a semiconductor wafer by photolithography technology. Therefore, it is required to improve the accuracy of the pattern inspection apparatus for inspecting defects of the transfer mask used in LSI manufacturing.

As an inspection method, a method of inspecting 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. It has been known. For example, as a pattern inspection method, "die to die inspection" in which measurement image data obtained by imaging the same pattern in different places on the same substrate are compared with each other, or a design image based on pattern-designed design data. There is a "die to database (die database) inspection" that generates data (reference image) and compares this with the measurement image that is the measurement data obtained by imaging the pattern. The captured image is sent to the comparison circuit as measurement data. In the comparison circuit, after the images are aligned with each other, the measurement data and the reference data are compared according to an appropriate algorithm, and if they do not match, it is determined that there is a pattern defect.

The pattern inspection device described above includes a device that irradiates a substrate to be inspected with laser light to image a transmitted image or a reflected image, and scans the substrate to be inspected with a primary electron beam. Development of an inspection device that acquires a pattern image by detecting secondary electrons emitted from the substrate to be inspected with irradiation of the secondary electron beam is also in progress. As for the inspection device using the electron beam, the development of the device using the multi-electron beam is also in progress. In an inspection device using a multi-electron beam, a sensor for detecting secondary electrons caused by irradiation of each beam of the multi-primary electron beam is arranged to acquire an image for each beam. However, since the multi-primary electron beams are simultaneously irradiated, there is a problem that secondary electrons of other beams are mixed in the sensor for each beam, that is, so-called crosstalk occurs. Crosstalk becomes a noise factor and deteriorates the image accuracy of the measured image, which in turn deteriorates the inspection accuracy. In order to avoid crosstalk, it is necessary to reduce the electron energy of the primary electron beam on the sample surface, but this reduces the number of secondary electrons generated. Therefore, it is necessary to lengthen the irradiation time in order to obtain the number of secondary electrons required for the desired image accuracy, and the throughput deteriorates.

Here, a method is disclosed in which the distance between the primary electron beams is made larger than the aberration of the secondary optical system in order to eliminate the crosstalk between the plurality of secondary electron beams (see, for example, Patent Document 1). ..

Japanese Unexamined Patent Publication No. 2002-260571

Therefore, one aspect of the present invention provides an inspection device and method capable of inspecting with high accuracy even when so-called crosstalk occurs in which secondary electrons of other beams are mixed in the sensor for each beam.

The multi-electron beam inspection apparatus according to one aspect of the present invention is
The sample in which the pattern is formed is irradiated with the multi-primary electron beam, and the multi-secondary electron beam emitted due to the multi-primary electron beam irradiating the sample is detected, and the crosstalk component is generated. A secondary electron image acquisition mechanism that acquires the included secondary electron image,
A correction circuit that generates a corrected secondary electronic image in which the crosstalk component is removed from the secondary electronic image by using preset gain information for removing the crosstalk component from the secondary electronic image.
A comparison circuit that compares the corrected secondary electronic image with a predetermined image,
It is characterized by being equipped with.

The multi-electron beam inspection method according to one aspect of the present invention is
The sample in which the pattern is formed is irradiated with the multi-primary electron beam, the multi-secondary electron beam emitted due to the irradiation of the sample with the multi-primary electron beam is detected, and the crosstalk component is contained. Obtained the secondary electron image
Using the preset gain information for removing the crosstalk component from the secondary electron image, a corrected secondary electronic image in which the crosstalk component is removed from the secondary electronic image is generated.
The corrected secondary electronic image is compared with a predetermined image, and the result is output.
It is characterized by that.

According to one aspect of the present invention, even when so-called crosstalk occurs in which secondary electrons of other beams are mixed in the sensor for each beam, inspection can be performed with high accuracy.

It is a block diagram which shows an example of the structure of the pattern 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 scanning operation of the multi-beam in Embodiment 1. FIG. It is a figure which shows an example of the spread of the secondary electron beam per primary electron 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 for demonstrating the scanning of the sub-irradiation region and the measured secondary electron intensity in Embodiment 1. FIG. It is a figure which shows an example of the secondary electron intensity map in Embodiment 1. FIG. It is a figure which shows an example of the gain matrix in Embodiment 1. FIG. It is a figure which shows an example of the structure of each gain value in Embodiment 1. FIG. It is a figure which shows the relational expression of the secondary electron image P'which contains the crosstalk image component, the gain matrix G, and the secondary electron image P which does not contain a crosstalk image component in Embodiment 1. FIG. It is a figure which shows an example of the gain inverse matrix in Embodiment 1. FIG. It is a figure which shows the relational expression of the secondary electron image P'which contains the crosstalk image component, the gain inverse matrix G-1, and the secondary electron image P which removed the crosstalk image component in Embodiment 1. FIG. It is a block diagram which shows an example of the structure in the comparison circuit in Embodiment 1. FIG.

[Embodiment 1]
FIG. 1 is a configuration diagram showing an example of the configuration of the pattern 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 electronic 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, a beam selection aperture substrate 219, an electromagnetic lens 205, a batch blanking deflector 212, a limiting aperture substrate 213, an electromagnetic lens 206, and an electromagnetic lens. 207 (objective lens), main deflector 208, sub-deflector 209, beam separator 214, deflector 218, electromagnetic lens 224, electromagnetic lens 226, and 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, a beam selection aperture substrate 219, an electromagnetic lens 205, a batch blanking deflector 212, a limiting aperture substrate 213, an electromagnetic lens 206, and an electromagnetic lens 207 ( The objective lens), the main deflector 208, and the sub-deflector 209 constitute a primary electron optics system that irradiates the substrate 101 with a multi-primary electron beam. 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 a multi-secondary electron beam.

A stage 105 that can move at least in the XYZ direction is arranged in the inspection room 103. A substrate 101 (sample) to be inspected is arranged on the stage 105. The substrate 101 includes an exposure mask substrate 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 reference image creation circuit 112, the stage control circuit 114, the lens control circuit 124, and the blanking via the bus 120. Control circuit 126, deflection control circuit 128, secondary electron strength measurement circuit 129, gain calculation circuit 130, correction circuit 132, inverse matrix calculation circuit 134, storage device 109 such as magnetic disk device, monitor 117, memory 118, and printer 119. It is connected to the. 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 and the secondary electron intensity measurement circuit 129. The chip pattern memory 123 is connected to the comparison circuit 108. 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 can move in the XYθ direction. It has become. As these X motors, Y motors, and θ motors (not shown), for example, step motors can be used. The stage 105 can be moved in the horizontal direction and the rotational direction by a motor of each axis of XYθ. Further, in the drive mechanism 142, for example, a piezo element or the like is used to control the stage 105 so as to be movable in the Z direction (height direction). 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-primary 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 each electrode is controlled by a blanking control circuit 126 via a DAC amplifier (not shown). 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.

Further, in the beam selection aperture substrate 219, for example, a passage hole through which one beam can pass is formed in the central portion, and a direction orthogonal to the orbital central axis (optical axis) of the multi-primary electron beam is provided by a drive mechanism (not shown). It is configured to be movable in the (two-dimensional direction).

A high-voltage power supply circuit (not shown) is connected to the electron gun 201, and an acceleration voltage from the high-voltage power supply circuit is applied between the filament (cathode) and the extraction electrode (anode) in the electron gun 201 (not shown), and another extraction electrode is used. 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 apparatus 100 may usually have other necessary configurations.

FIG. 2 is a conceptual diagram showing the configuration of the molded aperture array substrate according to the first embodiment. In FIG. 2, in 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 23 × 23 hole (opening) 22 is formed is shown. Ideally, each hole 22 is formed by a rectangle having the same dimensions and shape. Alternatively, ideally, it may 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 an area including all the plurality of holes 22. The multi-primary electron beam 20 is formed by each part of the electron beam 200 irradiated to the positions of the plurality of holes 22 passing through the plurality of holes 22 of the molded aperture array substrate 203. At the time of normal image acquisition, the beam selection aperture substrate 219 is retracted to a position where it does not interfere with 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 is arranged at the crossover position of each beam of the multi-primary electron beam 20 while repeating the intermediate image and the crossover. It passes through the beam separator 214 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 electromagnetic lens 207 (objective lens) is collectively deflected by the main deflector 208 and the sub-deflector 209. Each beam is irradiated to each irradiation position on the substrate 101. When the entire multi-primary electron beam 20 is collectively deflected by the batch blanking deflector 212, the position is deviated from the central hole 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 limiting 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 proceeds 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 (the central axis of the electron orbit). 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 invasion direction of the electron. The force due to the electric field and the force due to the magnetic field cancel each other out to the multi-primary electron beam 20 that invades 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 is obliquely 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. NS. 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 described later. 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, the primary electron beam 10i of the multi-primary electron beam 20 (i indicates an index. If the multi-primary electron beam 20 has 23 × 23, i = 1 to 529. ), A detection sensor is arranged. Then, the corresponding secondary electron beam emitted by the irradiation of each primary electron beam 10i 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 10i 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) (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 frame regions 33 in the longitudinal direction. The movement of the beam to the target frame region 33 is performed by the collective 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 in a 5 × 5 row 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 in the y direction of the multi-primary electron beam 20 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 a size similar to the y-direction size of the irradiation region 34 or narrowed by the scan margin. In the examples of FIGS. 3 and 4, the case where the irradiation region 34 has the same size as the frame region 33 is shown. However, it is not limited to this. The irradiation area 34 may be smaller than the frame area 33. Alternatively, 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 scanning of one sub-irradiation region 29 is completed, the main deflector 208 moves to the adjacent frame region 33 in the stripe region 32 having the same irradiation position by the collective deflection of the entire multi-primary electron beam 20. This operation is repeated to irradiate the inside of the stripe region 32 in order. After scanning one striped region 32 is complete, the irradiation position is moved to the next striped region 32 by moving the stage 105 and / or batch deflection of the entire multi-primary electron beam 20 by the main deflector 208. As described above, the secondary electron images for each sub-irradiation region 29 are acquired by irradiating each of the primary electron beams 10i. By combining the secondary electron images for each of the sub-irradiation regions 29, a secondary electron image of the frame region 33, a secondary electron image of the stripe region 32, or a secondary electron image of the chip 332 is formed.

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 every moment with respect to the orbital central axis of the multi-primary electron beam 20. Similarly, when scanning the inside of the sub-irradiation region 29, the emission position of each secondary electron beam changes every moment 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 diagram showing an example of the spread of the secondary electron beam per primary electron beam in the first embodiment. In the example of FIG. 5, the case of the multi-primary electron beam 20 in a 5 × 5 row is shown. In the multi-detector 222, a plurality of detection sensors 223 corresponding to the number of multi-primary electron beams 20 are arranged two-dimensionally. In the plurality of detection sensors 223, among the multi-secondary electron beams 300 emitted as a result of the multi-primary electron beam 20 irradiating the substrate 101, each preset primary electron beam 10 is the substrate 101. It is a sensor for detecting the secondary electron beam 12 emitted due to being irradiated with. However, in order to obtain a desired throughput for the inspection process using the inspection device 100, it is necessary to irradiate the substrate 101 with electronic energy corresponding to the throughput. In this case, there is a problem that secondary electrons of other primary electron beams 10 are mixed in the detection sensor 223 for each primary electron beam 10, that is, so-called crosstalk occurs. In the example of FIG. 5, the secondary electron beam 12 scheduled to be incident on the detection sensor 223 in the second row from the left and the fourth stage from the bottom causes some secondary electrons to be mixed in the other detection sensors 223 in the vicinity. Indicates the state. Although most of the secondary electron beams 12 caused by the irradiation of the primary electron beam 10 are incident on the detection sensor 223 preset for the primary electron beam 10, some secondary electrons are emitted from other surroundings. It is incident on the detection sensor 223 for the beam. The larger the electron energy on the substrate 101 of the multi-primary electron beam 20, the wider the distribution of secondary electrons. In the scanning operation with the multi-beam, since the multi-primary electron beam 20 is simultaneously irradiated, the secondary electron data detected by the detection sensor 223 for each beam is caused by the irradiation of the other primary electron beam2. The secondary electronic information is also included. Such crosstalk becomes a noise factor and deteriorates the image accuracy of the measured image.

On the other hand, the reference image to be compared used when inspecting the measurement image is created based on, for example, the design data that is the basis of the graphic pattern formed on the substrate 101. Therefore, when comparing the measurement image containing the crosstalk image (image to be inspected: secondary electron image) with the reference image created based on the design data, there is a difference in the image even though it is not a defect. Therefore, a so-called pseudo-defect, which is determined as a defect, may occur. In this way, crosstalk deteriorates the inspection accuracy. In order to avoid crosstalk, it is necessary to reduce the electron energy of the primary electron beam 10 on the surface of the substrate 101, but this reduces the number of secondary electrons generated. Therefore, it is necessary to lengthen the irradiation time in order to obtain the number of secondary electrons required for the desired image accuracy, and the throughput deteriorates. Therefore, in the first embodiment, the gain matrix of the crosstalk component is obtained, and the inverse matrix of the gain is calculated in advance to correct the scanned image with the inverse matrix and remove the crosstalk component. Hereinafter, a specific description will be given.

FIG. 6 is a flowchart showing a main process of the inspection method according to the first embodiment. In FIG. 6, the inspection method according to the first embodiment is a secondary electron intensity measurement step (S102), a gain calculation step (S104), an inverse matrix calculation step (S108), and a secondary electronic image acquisition step (S110). , An image correction step (S112), a reference image creation step (S114), an alignment step (S120), and a comparison step (S122).

As the secondary electron intensity measuring step (S102), the secondary electron intensity measuring circuit 129 is a secondary electron intensity measuring circuit 129 detected by each detection sensor 223 in the multi-detector 222 for each primary electron beam 10 of the multi-primary electron beam 20. Measure the electron strength. Specifically, it operates as follows. First, the beam selection aperture substrate 219 is moved to select one primary electron beam 10 that passes through the passage hole of the beam selection aperture substrate 219 from among the multi-primary electron beams 20. The other primary electron beam 10 is shielded by the beam selection aperture substrate 219. Then, the inside of the sub-irradiation region 29 of the evaluation substrate is scanned using the single primary electron beam 10. In the scanning method, as described above, the irradiation positions (pixels) of the primary electron beam 10 are sequentially moved by the deflection by the sub-deflector 209. Here, since it is only necessary to know the difference in the secondary electron intensity detected by each detection sensor 223 by irradiating the same primary electron beam, for example, the primary electron beam 10 is irradiated to the evaluation substrate 1 in which the pattern is not formed. do it. By using the evaluation substrate on which the pattern is not formed in this way, the effect that the characteristics of each sub-irradiation region become uniform can be obtained. However, the evaluation substrate 2 on which the evaluation pattern is formed may be used.

FIG. 7 is a diagram for explaining the scanning of the sub-irradiation region and the measured secondary electron intensity in the first embodiment. FIG. 7 shows, for example, a case where the beam 1 scans the inside of the sub-irradiation region 29 among the N × N multi-primary electron beams 20. The sub-irradiation region 29 is composed of, for example, a size of n × n pixels. For example, it is composed of 1000 × 1000 pixels. It is preferable that the pixel size is configured to be about the same size as the beam size of the primary electron beam 10, for example. However, it is not limited to this. The pixel size may be smaller than the beam size of the primary electron beam 10. Alternatively, the resolution of the image is lowered, but the pixel size may be larger than the beam size of the primary electron beam 10. When each pixel is irradiated with the beam 1 in order, the secondary electron beam caused by the irradiation of the beam 1 with the beam 1 is sequentially detected by the detection sensor 223 for the beam 1 of the multi-detector 222. If the distribution of the secondary electron beam is wider than the region of the detection sensor 223 for the target beam as shown in FIG. 5, it can be detected in order by the detection sensors 223 for other beams at the same time. The intensity signals detected by the multi-detector 222 are output to the detection circuit 106 in the order of measurement. In the detection circuit 106, analog detection data is converted into digital data by an A / D converter (not shown) and output to the secondary electron intensity measurement circuit 129. The secondary electron intensity measurement circuit 129 uses the input intensity signal to form a secondary electron intensity map having secondary electron intensity i (1,1) to i (n, n) of each pixel as elements. I (1,1) is measured. (A, b) of the secondary electron intensity i (a, b) of each pixel indicates the coordinates of each pixel. It becomes any value of a = 1 to n and b = 1 to n.

FIG. 8 is a diagram showing an example of a secondary electron intensity map according to the first embodiment. In FIG. 8, A of the secondary electron intensity I (A, B), which is an element of the secondary electron intensity map, indicates a beam number, and B indicates a detection sensor number. Any value of A = 1 to N and B = 1 to N. The secondary electron intensities I (1,1) to I (1,N) can be measured by scanning the sub-irradiation region 29 for the beam 1 with the beam 1. By moving the beam selection aperture substrate 219 and selecting the target primary electron beams 10 in order, for example, the secondary electron intensities I (2,1) to I (2, N) can be obtained by using the beam 2. It can be measured, and the secondary electron intensities I (3,1) to I (3,N) can be measured using the beam 3. Similarly, by measuring using each of the primary electron beams 10, the secondary electron intensity measuring circuit 129 has secondary electron intensity I (1,1) to I in the sub-irradiation region 29 units (primary electron beam unit). (N, N) can be measured. The measured secondary electron intensity I (1,1) to I (N, N) information is output to the gain calculation circuit 130.

As a gain calculation step (S104), the gain calculation circuit 130 calculates a gain value for each detection sensor 223 and for each primary electron beam 10. Specifically, the gain calculation circuit 130 determines the gain value of the primary electron beam 10 detected by the detection sensor 223 for detecting the secondary electron beam 12 caused by the irradiation of the primary electron beam 10. The ratio of the intensity value of the secondary electron beam 12 due to another primary electron beam 10 detected by the same detection sensor 223 to the intensity value of the secondary electron beam 12 due to irradiation is calculated.

FIG. 9 is a diagram showing an example of the gain matrix according to the first embodiment. In FIG. 9, A of the gain value G (A, B), which is each element of the gain matrix G, indicates a beam number. B indicates the detection sensor number. Any value of A = 1 to N and B = 1 to N. The gain value G (m, k) of the beam m (primary electron beam) in the detection sensor k for the beam k (primary electron beam) is defined by the following equation (1).
(1) G (m, k) = I (m, k) / I (k, k)

By calculating the gain value for each detection sensor 223 and for each primary electron beam 10, gain values G (1,1) to G (N, N) can be obtained as shown in FIG. Then, a gain matrix having such gain values G (1,1) to G (N, N) as elements can be created. It should be noted that the gain values G (1,1), G (2,2), ..., G (N, N) having the same beam number and detection sensor number are any of them, as is clear from the equation (1). Is also 1, so the calculation may be omitted.

FIG. 10 is a diagram showing an example of the configuration of each gain value in the first embodiment. As shown in FIG. 7, the secondary electron intensities I (1,1) to I (N, N) are the secondary electron intensities i (1,1) to i (n, n) of each pixel, respectively. Since the map is composed of elements, as shown in FIG. 10, the gain values g (1,1) to g (1) to g (for each gain value G (1,1) to G (N, N)) of each pixel are also formed. It is composed of maps having n, n) as elements. In other words, the gain value may differ from pixel to pixel. The information of the created gain matrix G is stored in the storage device 109.

FIG. 11 is a diagram showing the relational expressions of the secondary electron image P'including the crosstalk image component, the gain matrix G, and the secondary electron image P not including the crosstalk image component according to the first embodiment. .. In FIG. 11, the set P'= (P1', P2', ..., PN') of the secondary electron images including the crosstalk image component for each sub-irradiation region 29 of each primary electron beam 10 is The product of the gain matrix G and the set P = (P1, P2, ..., PN) of the secondary electron images that do not include the crosstalk image component for each sub-irradiation region 29 of each primary electron beam 10. Can be defined. Briefly, the relationship between the secondary electron image P'containing the crosstalk image component, the gain matrix G, and the secondary electron image P not including the crosstalk image component is defined by the following determinant (2). can.
(2) P'= GP

^{Therefore, by obtaining the gain inverse matrix G -1} , which is the inverse matrix of the gain matrix G, the crosstalk image is taken from the secondary electron image P'containing the crosstalk image component as shown in the following equation (3). A secondary electron image P that does not contain a component can be obtained.
(3) P = G ^-1・ P'

In the inverse matrix calculation step (S108), the inverse matrix calculation circuit 134 (inverse matrix calculation unit) provides gain information for each sensor of the plurality of sensors and for each primary electron beam of the multi-primary electron beam. From the gain matrix G shown in FIG. 9 having the above as an element, the gain inverse matrix G ^-1 (gain information), which is the inverse matrix of the gain matrix G, is calculated. As the method of inverse matrix operation, a conventional method may be used.

FIG. 12 is a diagram showing an example of the gain inverse matrix G- ^{1 in the first embodiment.} In FIG. 12, A of the inverse gain value G ^-1 (A, B), which is each element of the gain inverse matrix G ^{-1, indicates a beam number.} B indicates the detection sensor number. Any value of A = 1 to N and B = 1 to N. By this calculation, as shown in FIG. 12, the gain inverse with the inverse gain values G ^-1 (1, 1) to G ^-1 (N, N) for each detection sensor 223 and each primary electron beam 10 as elements. The matrix G- ¹ can be obtained. The gain information of the calculated gain inverse matrix G- ¹ is stored in the memory 118 or the storage device 109.

After performing the above steps as pretreatment, the substrate 101 to be inspected is placed on the stage 105, and the actual inspection process is performed.

As a secondary electronic image acquisition step (S110), the image acquisition mechanism 150 (secondary electronic image acquisition mechanism) irradiates the substrate 101 on which a plurality of graphic patterns are formed with the multi-primary electron beam 20 to perform multi-primary. The multi-secondary electron beam 300 emitted due to the electron beam 20 irradiating the substrate 101 is detected, and a secondary electron image including a crosstalk component for each sub-irradiation region 29 is acquired. As described above, backscattered electrons and secondary electrons may be projected onto the multi-detector 222, or the backscattered electrons may be diverged in the middle and the remaining secondary electrons may be projected.

To acquire the image, as described above, the multi-primary electron beam 20 is irradiated, and the multi-secondary electron beam 300 containing backscattered electrons emitted from the substrate 101 due to the irradiation of the multi-primary electron beam 20 is used. It 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. NS. 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 correction circuit 132 together with the information indicating each position from the position circuit 107. Needless to say, the secondary electron image data for each pixel obtained here still contains the crosstalk image component.

As the image correction step (S112), the correction circuit 132 (correction unit) uses the gain information (gain inverse matrix G- ¹ ) stored in the memory 118 and the storage device 109 in advance in the inverse matrix calculation step (S108). A corrected secondary electronic image in which the crosstalk component is removed from the secondary electronic image is generated. Specifically, the correction circuit 132 multiplies the acquired secondary electron image including the crosstalk image component for each sub-irradiation region 29 by the gain inverse matrix G- ^{1 read from the memory 118 or the storage device 109.} As a result, a corrected secondary electron image for each sub-irradiation region 29 from which the crosstalk component is removed is generated.

FIG. 13 shows the relational expressions of the secondary electron image P'including the crosstalk image component, the gain inverse matrix G- ¹ , and the secondary electron image P from which the crosstalk image component is removed according to the first embodiment. It is a figure. In FIG. 13, the set P = (P1, P2, ..., PN) of the secondary electron images from which the crosstalk image component for each sub-irradiation region 29 of each primary electron beam 10 is removed is the gain inverse matrix G. ^-1 and a set of secondary electron images P'= (P1', P2', ..., PN') including a crosstalk image component for each sub-irradiation region 29 of each primary electron beam 10. Can be defined as a product. Briefly, the corrected secondary electron image P from which the crosstalk image component has been removed is obtained from the gain inverse matrix G ^-1 and the secondary electron image P'containing the crosstalk image component according to the equation (3). Can be sought. The image data of the corrected secondary electron image P 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 (S114), the reference image creation circuit 112 creates a reference image corresponding to the mask die image based on the design data that is the source of the plurality of graphic patterns formed on the substrate 101. Specifically, it operates as follows. First, the design pattern data is read from the storage device 109 through the control computer 110, and each graphic pattern defined in the read design pattern data is converted into binary or multi-valued image data.

As described above, 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 or the triangle, etc. 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 reference image creation circuit 112, it is expanded to the data for each graphic, and the graphic code, the graphic dimension, etc. indicating the graphic shape of the graphic data are interpreted. Then, it is developed into binary or multi-valued design pattern image data as a pattern arranged in a grid having a grid of predetermined quantization dimensions as a unit and output. In other words, the design data is read, the inspection area is virtually divided into squares with a predetermined dimension as a unit, the occupancy rate of the figure in the design pattern is calculated for each square, and the n-bit occupancy rate data is obtained. Output. For example, it is preferable to set one square as one pixel. Then, when to have a resolution of 1/2 8 ^{(= 1/256)} to 1 pixel, the occupancy rate of the pixel allocated the small area region amount corresponding 1/256 of figures are arranged in a pixel Calculate. Then, it becomes 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 filters the design image data of the design pattern, which is the image data of the figure, by using a predetermined filter function. 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 characteristics obtained by the irradiation of the multi-primary electron beam 20. The image data for each pixel of the created reference image is output to the comparison circuit 108.

FIG. 14 is a configuration diagram showing an example of the configuration in the comparison circuit according to the first embodiment. In FIG. 14, storage devices 52 and 56 such as a magnetic disk device, an alignment unit 57, and a comparison unit 58 are arranged in the comparison circuit 108. Each "-unit" such as the alignment unit 57 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. 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 necessary input data or the calculated result in the alignment unit 57 and the comparison unit 58 is stored in a memory (not shown) or a memory 118 each time.

In the first embodiment, the sub-irradiation region 29 acquired by the scanning operation of one primary electron beam 10i is further divided into a plurality of mask die regions, and the mask die region is used as a unit region of the image to be inspected. It is preferable that the mask die regions are configured so that the margin regions overlap each other so that the image is not omitted.

In the comparison circuit 108, the transferred corrected secondary electronic image data is temporarily stored in the storage device 56 as a mask die image (image to be inspected) for each mask die area. Similarly, the transferred reference image data is temporarily stored in the storage device 52 as a reference image for each mask die area.

As the alignment step (S120), the alignment unit 57 reads out a mask die image to be an image to be inspected and a reference image corresponding to the mask die image, and aligns both images in sub-pixel units smaller than pixels. For example, the alignment may be performed by the method of least squares.

As the comparison step (S122), the comparison unit 58 compares the mask die image (corrected secondary electronic image) with the reference image (an example of a predetermined image). In other words, the comparison unit 58 compares the reference image data with the corrected secondary electronic image data from which the crosstalk image component has been removed, pixel by pixel. The comparison unit 58 compares the two for each pixel according to a predetermined determination condition, and determines the presence or absence of a defect such as a shape defect. For example, if the difference in gradation value for each pixel is larger than the determination threshold value Th, it is determined to be a defect. 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 the printer 119.

In the above example, the case of performing die database inspection was explained, but it is not limited to this. Since the crosstalk image component is removed from the image to be inspected, a die-die inspection may be performed. A case of performing a die-die inspection will be described.

In the alignment step (S120), the alignment unit 57 reads out the mask die image of the die 1 (corrected inspected image) and the mask die image of the die 2 in which the same pattern is formed (corrected inspected image) from the pixels. Align both images in small sub-pixel units. For example, the alignment may be performed by the method of least squares.

As a comparison step (S122), the comparison unit 58 compares the mask die image of the die 1 (corrected inspected image) with the mask die image of the die 2 (corrected inspected image). The comparison unit 58 compares the two for each pixel according to a predetermined determination condition, and determines the presence or absence of a defect such as a shape defect. For example, if the difference in gradation value for each pixel is larger than the determination threshold value Th, it is determined to be a defect. Then, the comparison result is output. The comparison result is output to the storage device 109, the monitor 117, or the memory 118.

As described above, according to the first embodiment, even when so-called crosstalk occurs in which secondary electrons of other beams are mixed in the sensor for each beam, inspection can be performed with high accuracy.

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, reference image creation circuit 112, stage control circuit 114, lens control circuit 124, blanking control circuit 126, deflection control circuit 128, secondary electron intensity measurement circuit 129, gain calculation circuit 130, The correction circuit 132 and the inverse matrix calculation circuit 134 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. In the example of FIG. 1, a case is shown in which a multi-primary electron beam 20 is formed by a molded aperture array substrate 203 from one beam emitted from an electron gun 201 as one irradiation source, but the present invention is limited to this. is not it. The multi-primary electron beam 20 may be formed by irradiating the primary electron beams from a plurality of irradiation sources.

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

In addition, all multi-electron beam inspection devices and multi-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.

Regarding multi-electron beam inspection equipment and multi-electron beam inspection method. For example, it can be used as an inspection device that inspects using a secondary electron image of a pattern emitted by irradiating a multi-beam with an electron beam.

10 Primary electron beam 12 Secondary electron beam 20 Multi-primary electron beam 22 Hole 29 Sub-irradiation area 32 Stripe area 33 Frame area 34 Irradiation area 52, 56 Storage device 57 Alignment unit 58 Comparison unit 100 Inspection device 101 Board 102 Electronics 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 119 Printer 120 Bus 122 Laser length measurement system 123 Chip pattern memory 124 Lens Control circuit 126 Blanking control circuit 128 Deflection control circuit 129 Secondary electron intensity measurement circuit 130 Gain calculation circuit 132 Correction circuit 134 Inverse matrix calculation circuit 142 Drive mechanism 144, 146, 148 DAC amplifier 150 Image acquisition mechanism 160 Control system circuit 200 Electronic Beam 201 Electron gun 202 Electron lens 203 Molded aperture array substrate 205, 206, 207, 224,226 Electromagnetic lens 208 Main deflector 209 Sub-deflector 212 Collective blanking deflector 213 Limitation aperture substrate 214 Beam separator 216 Mirror 218 Deflector 219 Beam selection aperture board 222 Multi detector 223 Detection sensor 300 Multi secondary electron beam 330 Inspection area 332 Chip

Claims (10)

1. A sample in which a pattern is formed is irradiated with a multi-primary electron beam, and a multi-secondary electron beam emitted due to the irradiation of the sample with the multi-primary electron beam is detected, and a crosstalk component is detected. A secondary electronic image acquisition mechanism that acquires a secondary electronic image containing
   A correction circuit that generates a corrected secondary electronic image in which the crosstalk component is removed from the secondary electronic image by using preset gain information for removing the crosstalk component from the secondary electronic image.
   A comparison circuit for comparing the corrected secondary electron image with a predetermined image,
   A multi-electron beam inspection device characterized by being equipped with.
2. In the secondary electron image acquisition mechanism, among the multi-secondary electron beams emitted due to the irradiation of the sample with the multi-primary electron beam, preset primary electron beams are used for the sample. It has a multi-detector in which multiple sensors are arranged to detect the secondary electron beam emitted due to the irradiation of the electrons.
   The 1 detected by the sensor for detecting the secondary electron beam caused by the irradiation of the primary electron beam for each sensor of the plurality of sensors and for each primary electron beam of the multi-primary electron beam. A gain calculation circuit that calculates the ratio of the intensity value of the secondary electron beam caused by another primary electron beam detected by the same sensor to the intensity value of the secondary electron beam caused by the irradiation of the secondary electron beam as the gain value. The multi-electron beam inspection apparatus according to claim 1, further comprising.
3. As the gain information, an inverse matrix calculation circuit for calculating the inverse matrix of the gain matrix having the gain value for each sensor of the plurality of sensors and each primary electron beam of the multi-primary electron beam as an element is further provided.
   The multi-electron beam inspection apparatus according to claim 2, wherein the correction circuit generates a corrected secondary electron image from which the crosstalk component is removed by multiplying the acquired secondary electron image by the inverse matrix. ..
4. The multi-electron beam inspection apparatus according to claim 1, further comprising a beam selection aperture substrate that selects one primary electron beam from the multi-primary electron beam.
5. The multi-electron beam inspection apparatus according to claim 3, wherein the gain matrix includes a plurality of elements having a gain value of 1.
6. A sample in which a pattern is formed is irradiated with a multi-primary electron beam, and a multi-secondary electron beam emitted due to the irradiation of the sample with the multi-primary electron beam is detected, and a crosstalk component is detected. Acquires a secondary electronic image containing
   Using the preset gain information for removing the crosstalk component from the secondary electronic image, a corrected secondary electronic image in which the crosstalk component is removed from the secondary electronic image is generated.
   The corrected secondary electronic image is compared with a predetermined image, and the result is output.
   A multi-electron beam inspection method characterized by this.
7. Of the multi-secondary electron beams emitted due to the irradiation of the sample with the multi-primary electron beam, each preset primary electron beam is irradiated to the sample. A secondary electron beam caused by irradiation of the primary electron beam is detected for each sensor of a plurality of sensors for detecting the emitted secondary electron beam and for each primary electron beam of the multi-primary electron beam. Of the intensity value of the secondary electron beam due to another primary electron beam detected by the same sensor with respect to the intensity value of the secondary electron beam due to the irradiation of the primary electron beam detected by the sensor. The multi-electron beam inspection method according to claim 6, wherein the ratio is calculated as a gain value.
8. As the gain information, the inverse matrix of the gain matrix having the gain value for each sensor of the plurality of sensors and for each primary electron beam of the multi-primary electron beam as an element is calculated.
   The multi-electron beam inspection method according to claim 7, wherein the corrected secondary electron image from which the crosstalk component is removed is generated by multiplying the acquired secondary electron image by the inverse matrix.
9. The multi-electron beam inspection method according to claim 6, wherein one primary electron beam is selected from the multi-primary electron beams using a beam selection aperture substrate.
10. The multi-electron beam inspection method according to claim 8, wherein the gain matrix includes a plurality of elements having a gain value of 1.
    

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