JP2021044461A - Method of detecting alignment mark position and device for detecting alignment mark position - Google Patents

Abstract

PURPOSE: To provide a method that can accurately detect the position of an alignment mark using multi-electron beams.CONSTITUTION: A method of detecting an alignment mark position in an embodiment of the present invention comprises: a step of capturing an image of a concerned alignment mark using an optical camera; a step of detecting a first position of the concerned alignment mark using the captured optical image; a step of obtaining a first secondary electronic image of the concerned alignment mark using multi electron beams based on the detected first position; a step of detecting a second position of the concerned alignment mark using the obtained first secondary electronic image; a step of obtaining a second secondary electronic image of the concerned alignment mark using a prescribed electron beam in a state where the detected second position is aligned to a radiation range of the prescribed electron beam out of the multi electron beams; and a step of detecting using the obtained second secondary electronic image and outputting a third position of the concerned alignment mark.SELECTED DRAWING: Figure 5

Description

The present invention relates to a method for detecting an alignment mark position. For example, the present invention relates to a method for detecting an alignment mark position on a substrate using a multi-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.

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 it 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.

Defect inspection of semiconductor wafers and photomasks is required to detect defects of smaller sizes. Therefore, in recent inspection devices, the above-mentioned pattern inspection device includes a device that irradiates a substrate to be inspected with a laser beam and captures a transmitted image or a reflected image thereof, as well as a laser in order to improve the pixel resolution of the image. An inspection device that scans the inspection target substrate with an electron beam having a wavelength shorter than that of light, detects secondary electrons emitted from the inspection target substrate when the electron beam is irradiated, and acquires a pattern image. Development is also in progress. As for the inspection device using the electron beam, the development of the device using the multi-beam is also in progress.

When inspecting the pattern formed on the substrate to be inspected, it is first necessary to specify the reference alignment mark position. The substrate to be inspected is transported to the stage in the inspection room by the transport system. An error in position reproducibility in such transportation occurs on the order of several hundred μm. Therefore, even if the alignment mark on the substrate to be inspected is imaged with an optical camera, it is difficult to align in the nm order required for inspection accuracy because the division ability of the optical camera is about several μm. is there. On the other hand, the resolution of the scanned image with the electron beam is on the order of nm, but when the multi-electron beam is used, an error occurs between the electron beams, so it is desirable to image the alignment mark with the same specific beam. However, since the field of view of each beam of the multi-electron beam is smaller than the partitioning ability of the optical camera, it is difficult to align the field of view within the field of view of a specific beam. As a result, the measured alignment mark position becomes a value having an error between the electron beams.

Here, a method of measuring the position of an alignment mark by an optical camera and a single electron beam is disclosed (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2011-243957

Therefore, one aspect of the present invention provides a method capable of detecting the position of an alignment mark with high accuracy using a multi-electron beam and an apparatus therefor.

The method for detecting the alignment mark position according to one aspect of the present invention is as follows.
The process of imaging the alignment mark with an optical camera on the substrate on which the pattern having the alignment mark is formed, and
The process of detecting the first position of the alignment mark using the captured optical image, and
A step of acquiring a first secondary electron image of the alignment mark using a multi-electron beam based on the detected first position, and
A step of detecting the second position of the alignment mark using the acquired first secondary electron image, and
A step of acquiring a second secondary electron image of the alignment mark using a predetermined electron beam in a state where the detected second position is aligned with the irradiation region of the predetermined electron beam of the multi-electron beam.
A process of detecting and outputting the third position of the alignment mark using the acquired second secondary electronic image, and
It is characterized by being equipped with.

Further, it is preferable to use the central beam of the multi-electron beam as the predetermined electron beam.

Further, it is preferable that the first secondary electron image is acquired as an image having a coarser resolution than the second secondary electron image.

In addition, a plurality of chips are formed on the substrate,
Multiple chips each have multiple alignment marks
The first position of the alignment mark detected by using the optical image of the alignment mark of one of the plurality of chips, and the alignment mark of any of the alignment marks of the other one of the plurality of chips. It is preferable to further include a step of adjusting the arrangement angle of the substrate by using the first position of the alignment mark detected by using the optical image.

The alignment mark position detection device according to one aspect of the present invention is
An optical camera that captures the alignment mark on the substrate on which the pattern having the alignment mark is formed, and
A position detection unit that detects the first position of the alignment mark using the captured optical image, and
An image acquisition mechanism that acquires a first secondary electron image of the alignment mark using a multi-electron beam based on the detected first position, and an image acquisition mechanism.
With
The position detection unit detects the second position of the alignment mark using the acquired first secondary electronic image, and then detects the second position of the alignment mark.
The image acquisition mechanism uses the predetermined electron beam to capture the second secondary electron image of the alignment mark in a state where the detected second position is aligned with the irradiation region of the predetermined electron beam in the multi-electron beam. Acquired,
The position detection unit is characterized in that the third position of the alignment mark is detected by using the acquired second secondary electron image.

Further, it is preferable to use the central beam of the multi-electron beam as a predetermined electron beam.

Further, it is preferable that the first secondary electron image is acquired as an image having a coarser resolution than the second secondary electron image.

In addition, a plurality of chips are formed on the substrate,
Each of the plurality of chips has the plurality of alignment marks.
The first position of the alignment mark detected by using the optical image of the alignment mark of one of the plurality of chips, and the alignment mark of any of the alignment marks of the other one of the plurality of chips. It is preferable to further include an arrangement angle adjusting unit for adjusting the arrangement angle of the substrate by using the first position of the alignment mark detected by using the optical image.

According to one aspect of the present invention, the position of the alignment mark can be detected with high accuracy by using the multi-electron beam.

It is a block diagram which shows the structure of the inspection apparatus 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 flowchart which shows the main part process of the alignment mark position detection method in Embodiment 1. FIG. It is a figure for demonstrating the method of adjusting the arrangement angle of the substrate in Embodiment 1. FIG. It is a figure for demonstrating the detection method of the alignment mark position in Embodiment 1 in order. It is a conceptual diagram which shows the structure of the molded aperture array 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 for demonstrating the inspection process in Embodiment 1. FIG. It is a block diagram which shows an example of the structure in the comparison circuit in Embodiment 1. FIG.

Hereinafter, in the embodiment, a multi-electron beam inspection device will be described as an example of a device for detecting the alignment mark position. However, the device for detecting the alignment mark position is not limited to the inspection device, and may be any device that acquires an image by irradiating a multi-electron beam using an electron optical system.

Embodiment 1.
FIG. 1 is a configuration diagram showing a configuration of an 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 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, and a multi-detector 222 are arranged. Electron gun 201, electromagnetic lens 202, molded aperture array substrate 203, electromagnetic lens 205, batch blanking deflector 212, limiting aperture substrate 213, electromagnetic lens 206, electromagnetic lens 207 (objective lens), main deflector 208, and sub-deflection The primary electron optics system is composed of the instrument 209. Further, the secondary electron optical system is composed of the electromagnetic lens 207, the beam separator 214, the deflector 218, and the electromagnetic lens 224.

In the examination room 103, a stage 105 that can move at least in the XY direction is arranged. 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.

Further, in the examination room 103, an optical camera 219 that captures an image of the substrate 101 mounted on the stage 105 from above is arranged with the lens facing downward. Further, as shown in the example of FIG. 1, a part of the optical camera 219 may be arranged so as to protrude from the inside of the examination room 103 to the outside. Further, it is preferable that a white LED (not shown) is used as the illumination of the optical camera 219. As the optical camera 219, for example, a CCD (Charged-coupled devices) camera is preferably used. Further, the optical camera 219 has, for example, a field of view on the order of mm square and a resolution on the order of μm on the substrate 101. The optical camera 219 is connected to the detection circuit 131 outside the examination room 103.

Further, the multi-detector 222 is connected to the detection circuit 106 outside the electron beam column 102. The detection circuit 106 is connected to the chip pattern memory 123.

In the control system circuit 160, 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. It is connected to a control circuit 126, a deflection control circuit 128, a camera control circuit 130, a mark position detection circuit 132, an alignment circuit 134, a storage device 109 such as a magnetic disk device, a monitor 117, a memory 118, and a printer 119. 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 131 is connected to the camera control circuit 130.

Further, the chip pattern memory 123 is connected to the comparison circuit 108 and the mark position detection circuit 132. 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 be moved 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 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 of the multi-primary electron beam 20.

The electromagnetic lens 202, the electromagnetic lens 205, the electromagnetic lens 206, the electromagnetic lens 207 (objective lens), the electromagnetic lens 224, 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.

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 diagram showing an example of a plurality of chip regions formed on the semiconductor substrate according to the first embodiment. In FIG. 2, 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 mask pattern for one chip is generally composed of a plurality of graphic patterns. A plurality of alignment marks 27 are formed on each chip 332. In the example of FIG. 2, the case where the alignment marks 27 are arranged at the four corners of the region of each chip 332 is shown. As the alignment mark 27, it is preferable to use a pattern having edges (ends) in the x-direction and the y-direction.

In order to inspect the defects of the graphic pattern formed on each chip 332, it is necessary to measure the edge position of each graphic pattern with high accuracy. As described above, the error in the position reproducibility of the substrate 101 on the stage 105 of the inspection room 103 in the transport system is about several hundred μm. Therefore, it is necessary to configure a coordinate system based on a plurality of alignment marks 27 whose positions are measured with high accuracy for each chip 332. Therefore, the position accuracy of the plurality of alignment marks 27 is important. Therefore, even if the alignment mark on the substrate to be inspected is imaged with an optical camera, it is difficult to align in the nm order required for inspection accuracy because the division ability of the optical camera is about several μm. is there. Therefore, it is necessary to detect the alignment mark position in the secondary electron image by the electron beam having a resolution on the order of nm. However, since the field of view of each beam of the multi-electron beam is smaller than the partitioning ability of the optical camera, it is difficult to align the alignment mark within the field of view of a specific beam of the multi-electron beams. As a result, multiple alignment mark positions measured within the same chip may be detected from secondary electron images captured by different electron beams of the multi-electron beam, resulting in an error between the electron beams. It will be the value you have. Therefore, in the first embodiment, a plurality of alignment marks 27 in the same chip 332 can be imaged by the same specific electron beam among the multi-electron beams. Hereinafter, a specific description will be given.

FIG. 3 is a flowchart showing a main step of the alignment mark position detection method according to the first embodiment. In FIG. 3, the method of detecting the alignment mark position in the first embodiment carries out a series of steps. First, the arrangement angle of the substrate 101 conveyed to the stage 105 in the inspection room 103 is corrected.

As an alignment mark image acquisition step (S102) by an optical camera, the image acquisition mechanism 150 captures an optical image of any alignment mark 27 possessed by one chip of the plurality of chips 332. Similarly, the image acquisition mechanism 150 captures an optical image of any alignment mark 27 possessed by the other one of the plurality of chips 332.

FIG. 4 is a diagram for explaining a method of adjusting the arrangement angle of the substrate in the first embodiment. As shown in FIG. 4, by detecting the positions of the alignment marks 27 of at least two different chips 332, it is possible to correct the error of the arrangement angle of the substrate 101. In the example of FIG. 4, two chips 332 formed at both ends of one row of chips 332 arranged in the x direction of a plurality of chips 332 arranged in a two-dimensional array on the substrate 101 are selected. Then, one of the four alignment marks 27 arranged on each chip 332 is selected. For example, it is preferable to select the alignment marks 27 having the same positional relationship. Then, for each of the selected chips 332, the stage 105 is moved so that the selected alignment mark 27 is within the field of view of the optical camera 219. Then, the optical camera 219 controlled by the camera control circuit 130 images the selected alignment mark 27 for each of the selected chips 332. The captured data is output to the detection circuit 131. In the detection circuit 131, analog detection data is converted into digital optical image data by an A / D converter (not shown), and the optical image data is output to the mark position detection circuit 132 via the camera control circuit 130. To.

As the alignment mark position detection step (S104), the mark position detection circuit 132 detects the position of the selected alignment mark 27 for each selected chip 332 from the input optical image data. For example, the intersection of the center line of the pattern extending in the x direction and the center line of the pattern extending in the y direction is detected as the position of the alignment mark 27. The positional relationship between the optical axis of the optical camera 219 and the orbital center axis of the multi-primary electron beam 20 is measured in advance with high accuracy. Further, the relative positional relationship between the orbital central axis of the multi-primary electron beam 20 and the stage 105 is also measured with high accuracy in advance. Therefore, if the positional relationship between the optical axis of the optical camera 219 and the position of the alignment mark 27 can be detected, the positions of the alignment marks 27 of the two selected chips 332 on the stage 105 can be detected.

In the substrate arrangement angle adjustment step (S106), the stage control circuit 114 (arrangement angle adjustment unit) detects the alignment mark using an optical image of any of the alignment marks 27 possessed by one chip of the plurality of chips 332. The position of 27 (first position) and the position of the alignment mark (another first position) detected using an optical image of one of the alignment marks 27 possessed by the other one of the plurality of chips 332. ) To adjust the arrangement angle of the substrate 101. In other words, the stage control circuit 114 adjusts the arrangement angle of the substrate 101 on the stage 105 based on the positions of the alignment marks 27 of the two chips 332. For example, if the line connecting the two chips 332 arranged in the x direction is not parallel to the x direction of the stage coordinate system, the substrate placement angle is adjusted by rotating the stage position in the θ direction so as to be parallel. do it.

As described above, the arrangement angle of the substrate 101 is adjusted (coarse adjustment) with the accuracy of the resolution of the optical image obtained by the optical camera 219. Therefore, in order to inspect the graphic pattern in each chip 332, it is necessary to detect the positions of the plurality of alignment marks 27 in the chip 332 with high accuracy before acquiring the image to be inspected for each chip 332. is there. Hereinafter, a specific description will be given.

As an alignment mark image acquisition step (S110) by the optical camera, the image acquisition mechanism 150 uses the optical camera 219 for each alignment mark 27 with respect to the substrate 101 on which the pattern having the plurality of alignment marks 27 is formed. The alignment mark 27 is imaged. Here, with respect to the plurality of alignment marks 27 in the chip 332 to be inspected, the image acquisition mechanism 150 images the alignment marks 27 with the optical camera 219 for each alignment mark 27. Specifically, the stage 105 is moved so that the target alignment mark 27 is within the field of view of the optical camera 219. Then, the optical camera 219 controlled by the camera control circuit 130 images the target alignment mark 27. The captured data is output to the detection circuit 131. In the detection circuit 131, analog detection data is converted into digital optical image data by an A / D converter (not shown), and the optical image data is output to the mark position detection circuit 132 via the camera control circuit 130. To.

As the alignment mark position detection step (S112), the mark position detection circuit 132 (position detection unit) detects the position (first position) of the alignment mark 27 using the captured optical image. For example, the position on the stage 105 of the intersection of the center line of the pattern extending in the x direction and the center line of the pattern extending in the y direction is detected as the position of the alignment mark 27.

FIG. 5 is a diagram for sequentially explaining the method for detecting the alignment mark position in the first embodiment. As shown in FIG. 5, first, the position of the target alignment mark 27 is detected from the optical image taken by the above-mentioned optical camera 219. However, the position accuracy of the target alignment mark 27 obtained from the optical image obtained by the optical camera 219 is low. Therefore, a multi-beam image is used next.

As an alignment mark image acquisition step (S114) by the multi-beam, the image acquisition mechanism 150 uses the multi-primary electron beam 20 for each alignment mark 27 with reference to the detected position (first position). 27 secondary electronic images (first secondary electronic images) are acquired. Specifically, it operates as follows. The stage 105 is moved so that the position of the target alignment mark 27 obtained from the optical image is within the field of view of the multi-primary electron beam 20.

FIG. 6 is a conceptual diagram showing the configuration of the molded aperture array substrate according to the first embodiment. In FIG. 6, the molded aperture array substrate 203 has _{holes (openings) of two-dimensional horizontal (x direction) m 1} row × vertical (y direction) n ₁ step (m ₁ and n ₁ are integers of 2 or more). ) 22 are formed at a predetermined arrangement pitch in the x and y directions. In the example of FIG. 6, a case where a 23 × 23 hole (opening) 22 is formed is shown. Each hole 22 is formed by a rectangle having the same size and shape. Alternatively, it may be a circle having the same outer diameter. A part of the electron beam 200 passes through each of these plurality of holes 22, so that the multi-primary electron beam 20 is formed. Next, the operation of the image acquisition mechanism 150 in the case of acquiring a secondary electronic image 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. 6, 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.

The formed multi-primary electron beam 20 is refracted by the electromagnetic lens 205 and the electromagnetic lens 206, respectively, and the intermediate image plane (image plane) 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 conjugate position) and proceeds to the electromagnetic lens 207 (objective lens).

When the multi-primary electron beam 20 is incident on the electromagnetic lens 207 (objective lens), the electromagnetic lens 207 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 101 of each beam is deflected collectively. Each of the above irradiation positions 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 central hole of the limiting aperture substrate 213, and the multi-primary electrons are displaced by the limiting aperture substrate 206. The entire beam 20 is shielded. 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 206 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 206 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 image acquisition is formed by the beam group that has passed through the limiting aperture substrate 206 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.

FIG. 7 is a diagram for explaining a multi-beam scanning operation according to the first embodiment. In the example of FIG. 7, for example, the case of a 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). The irradiation region 34 becomes the field of view of the multi-primary electron beam 20. Then, each of the primary electron beams 10 constituting 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. , Scan (scan operation) in the sub-irradiation area 29. Each primary electron beam 10 is responsible for any of the sub-irradiation regions 29 that are 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.

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 the direction (center axis of the orbit) in which the central beam of the multi-primary electron beam 20 travels. 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 obliquely 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 lens 224. The multi-detector 222 detects the projected multi-secondary electron beam 300. The multi-detector 222 has, for example, a diode-type two-dimensional sensor (not shown). Then, at the diode-type two-dimensional sensor positions corresponding to each beam of the multi-primary electron beam 20, each secondary electron of the multi-secondary electron beam 300 collides with the diode-type two-dimensional sensor to generate electrons. Secondary electronic image data is generated for each pixel. The intensity signal detected by the multi-detector 222 is output to the detection circuit 106.

As described above, the secondary electron image is obtained by irradiating the multi-primary electron beam 20 with the multi-secondary electrons including backscattered electrons emitted from the substrate 101 due to the irradiation of the multi-primary electron beam 20. The beam 300 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 secondary electronic image data (data of the secondary electronic image 1) is output to the mark position detection circuit 132 together with the information indicating each position from the position circuit 107.

As the alignment mark position detection step (S116), the mark position detection circuit 132 uses the acquired secondary electronic image 1 (first secondary electronic image) for each alignment mark 27 to obtain the position of the alignment mark 27 (the first secondary electronic image). Second position) is detected. Since the field of view (sub-irradiation region 29) of each electron beam 10 of the multi-primary electron beam 20 is smaller than the division ability of the optical camera 219, the target alignment mark 27 is the multi-primary electron beam as shown in FIG. It is unknown at which position in the irradiation region 34 of 20 the image is taken. In the example of FIG. 5, for example, the image was taken within the field of view (sub-irradiation region 29) of the primary electron beam 10 in the second row from the right and the third stage from the bottom of the 5 × 5 multi-primary electron beam 20. Shows the case.

The target alignment mark 27 this time is imaged in the field of view of the primary electron beam 10 shown in FIG. 5 (sub-irradiation region 29 in the second row from the right and the third stage from the bottom), but is in the same chip 332. The alignment mark 27 is not always imaged within the same field of view of the primary electron beam 10 as this time (sub-irradiation region 29 in the second row from the right and the third stage from the bottom). Therefore, in the first embodiment, the operation is as follows.

As a specific beam alignment step (S118), the alignment circuit 134 sets the detected position (second position) for each alignment mark 27 to the same specific 1 set in advance in the multi-primary electron beam 20. It is adjusted to the irradiation position of the next electron beam 11. Specifically, it operates as follows. The alignment circuit 134 controls the stage control circuit 114, and the position (second position) of the detected target alignment mark 27 enters the field of view (sub-irradiation region 29) of the specific primary electron beam 11. The stage 105 is moved so as to. Alternatively, the alignment circuit 134 controls the deflection control circuit 128 to position the detected target alignment mark 27 (second position) within the field of view (sub-irradiation region 29) of the specific primary electron beam 11. The multi-primary electron beam 20 is collectively deflected by the main deflector 208 so that In the example of FIG. 5, the case where the central beam of the multi-primary electron beam 20 is used as the specific primary electron beam 11 is shown. The multi-primary electron beam 20 is affected by aberrations caused by the electron optical system and the like as the distance from the center increases. Therefore, by using the central beam, it is possible to acquire an image with higher accuracy than when other peripheral beams are used.

As an alignment mark image acquisition step (S120) using the specific beam, the image acquisition mechanism 150 sets the position (second position) of the detected target alignment mark 27 in the multi-primary electron beam 20 for each alignment mark 27. A secondary electron image (second 2) of the alignment mark 27 using the specific primary electron beam 11 in a state of being aligned with the preset field of view (sub-irradiation region 29) of the same specific primary electron beam 11. Next electronic image) is acquired. Specifically, it operates as follows. In the state of being aligned in the specific beam alignment step (S118), the image acquisition mechanism 150 again acquires the secondary electron image 2 of the target alignment mark 27 using the multi-primary electron beam 20. As described above, it is not necessary to take an image only with the specific primary electron beam 11, and the entire multi-primary electron beam 20 may be scanned again. This eliminates the need to arrange a beam selection mechanism that selects the primary electron beam so as to limit the primary electron beam that can reach the substrate 101. The method of acquiring the secondary electronic image is the same as the above-mentioned contents. The obtained secondary electronic image data (data of the secondary electronic image 1) is output to the mark position detection circuit 132 together with information indicating each position from the position circuit 107.

As the alignment mark position detection step (S122), the mark position detection circuit 132 produces a secondary electron image (second secondary electron image) acquired by using a specific primary electron beam 11 for each alignment mark 27. The position of the alignment mark 27 (third position) is detected by using the alignment mark 27. Specifically, it operates as follows. The imaged secondary electron image 2 contains image data obtained by the entire multi-primary electron beam 20. However, here, the secondary potential image data obtained by the specific primary electron beam 11 is required, and the image data obtained by the other primary electron beam 10 is not required. Therefore, the mark position detection circuit 132 has the secondary potential image obtained by the specific primary electron beam 11 among the secondary potential image data obtained by the entire multi-primary electron beam 20 as shown in FIG. Data (specific beam image) may be extracted to detect the position (third position) of the target alignment mark 27. As a result, the processing time required for data processing can be shortened. The detected position of the target alignment mark 27 (third position) is output to the comparison circuit 108. Alternatively, it is output to the storage device 109, the monitor 117, or the memory 118, or is output from the printer 119.

As a determination step (S130), the control computer 110 determines whether or not the position detection of all the alignment marks 27 in the chip 332 to be inspected has been completed. If there is an alignment mark 27 whose position has not been detected yet, the process returns to the alignment mark image acquisition step (S110) by the optical camera, and the optical method is performed until the position detection of all the alignment marks 27 in the chip 332 to be inspected is completed. Each step from the alignment mark image acquisition step (S110) to the alignment mark position detection step (S122) by the camera is repeated.

As described above, the positions of all the alignment marks 27 in the chip 332 to be inspected can be detected from the secondary electron image acquired by using the specific primary electron beam 11 of the multi-primary electron beam 20.

In the above-described example, the case of acquiring the secondary electron image 1 with high accuracy in the alignment mark image acquisition step (S114) by the multi-beam has been described, but the present invention is not limited to this. The secondary electron image 1 acquired in the alignment mark image acquisition step (S114) by the multi-beam is acquired as an image having a coarser resolution than the secondary electron image 2 acquired in the alignment mark image acquisition step (S120) by the specific beam. It is also preferable to configure the structure so as to be used. For example, when the secondary electron image of each sub-irradiation region 29 is composed of 1024 × 1024 pixels, in the alignment mark image acquisition step (S114) by the multi-beam, for example, one pixel is skipped in each of the x and y directions. An image may be created with 512 × 512 pixels. As a result, the amount of data can be reduced to 1/4, so that data processing can be speeded up. Alternatively, an image may be created with 256 × 256 pixels composed of, for example, three pixels skipped in each of the x and y directions. As a result, the amount of data can be reduced to 1/16, so that the data processing can be further speeded up. Even when the resolution is deteriorated to such a resolution, an image having a resolution sufficiently higher than that of the optical image can be obtained. In addition, the position of the target alignment mark 27 can be detected with higher accuracy than the field size of one electron beam.

After the positions of all the alignment marks 27 in the chip 332 to be inspected are completed, the process proceeds to the inspection process of the graphic pattern in the chip 332 to be inspected.

FIG. 8 is a diagram for explaining the inspection process according to the first embodiment. As shown in FIG. 8, the region of each chip 332 is divided into a plurality of stripe regions 32 with a predetermined width in the y direction, for example. 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.

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 example of FIG. 8, 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. Alternatively, it may be large. Then, each of the primary electron beams 10 constituting 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. , Scan (scan operation) in the sub-irradiation area 29. Then, when the scanning of one sub-irradiation region 29 is completed, the main deflector 208 moves to the adjacent rectangular 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 irradiated region 34 moves to the next striped region 32 by moving the stage 105 and / and batch deflection of the entire multi-primary electron beam 20 by the main deflector 208. As described above, by irradiating each of the primary electron beams 10, the scanning operation for each sub-irradiation region 29 and the acquisition of the secondary electron image are performed. By combining the secondary electron images for each of the sub-irradiation regions 29, a secondary electron image of the rectangular region 33, a secondary electron image of the stripe region 32, or a secondary electron image of the chip 332 is formed. Further, when actually performing image comparison, the sub-irradiation region 29 in each rectangular region 33 is further divided into a plurality of frame regions 30, and the frame images 31 for each frame region 30 are compared. The example of FIG. 8 shows a case where the sub-irradiation region 29 scanned by one primary electron beam 10 is divided into four frame regions 30 formed by dividing the sub-irradiation region 29 into two in the x and y directions, for example. ..

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.

As described above, the image acquisition mechanism 150 promotes the scanning operation for each stripe area 32. As described above, the multi-secondary electron beam 300 that irradiates the multi-primary electron beam 20 and contains backscattered electrons emitted from the substrate 101 due to the irradiation of the multi-primary electron beam 20 is a multi-detector 222. Is detected by. 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 comparison circuit 108 together with the information indicating each position from the position circuit 107.

FIG. 9 is a configuration diagram showing an example of the configuration in the comparison circuit according to the first embodiment. In FIG. 9, storage devices 50, 51, 52, 56 such as a magnetic disk device, a frame image creation unit 54, an alignment unit 57, and a comparison unit 58 are arranged in the comparison circuit 108. Each "-part" such as the frame image creation unit 54, 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, or a semiconductor. Devices and the like are 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 frame image creation unit 54, the alignment unit 57, and the comparison unit 58 are stored in a memory (not shown) or a memory 118 each time.

The measurement image data (beam image) transferred into the comparison circuit 108 is stored in the storage device 50. Further, the detected position data of each alignment mark 27 is stored in the storage device 51.

Then, the frame image creation unit 54 creates a frame image 31 for each frame region 30 of a plurality of frame regions 30 by further dividing the image data of the sub-irradiation region 29 acquired by the scanning operation of each primary electron beam 10. .. At that time, the frame image creation unit 54 sets each frame area 30 with reference to the position data of the four alignment marks 27 of the chip 332 to be inspected stored in the storage device 51. As a result, the position of each graphic pattern in the frame image 31 can be measured with reference to the positions of the four alignment marks 27 detected with high accuracy of the chip 332 to be inspected via the reference position of the frame area 30. .. Then, the frame area 30 is used as a unit area of the image to be inspected. It is preferable that the frame regions 30 are configured so that the margin regions overlap each other so that the image is not omitted. The created frame image 31 is stored in the storage device 56.

On the other hand, the reference image creation circuit 112 creates a reference image corresponding to the frame image 31 for each frame region 30 based on the design data that is the basis 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. Graphic 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 characteristic 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. The reference image data transferred into the comparison circuit 108 is stored in the storage device 52.

Next, the alignment unit 57 reads out the frame image 31 to be the image to be inspected and the reference image corresponding to the frame image 31, and aligns both images in units of sub-pixels smaller than pixels. For example, the alignment may be performed by the method of least squares.

Then, the comparison unit 58 compares the frame image 31 and the reference image for each 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 gradation value difference for each pixel is larger than the determination threshold value Th, it is determined as 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-mentioned example, the die-database inspection has been described, but the present invention is not limited to this. It may be the case of performing a die-die inspection. When performing a die-die inspection, between the target frame image 31 (die 1) and the frame image 31 (die 2) (another example of the reference image) in which the same pattern as the frame image 31 is formed. , The above-mentioned alignment and comparison processing may be performed.

As described above, according to the first embodiment, the position of the alignment mark can be detected with high accuracy by using the multi-electron beam.

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, camera control circuit 130, mark position detection circuit 132, and position. The matching circuit 134 may be composed of at least one processing circuit described above. For example, the processing in these circuits may be performed by the control computer 110.

The embodiment has been described above with reference to a specific example. 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 a single beam emitted from an electron gun 201 as one irradiation source, but the present invention is limited to this. is not it. A mode may be used in which the multi-primary electron beam 20 is formed by irradiating the primary electron beams from a plurality of irradiation sources.

In addition, 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 methods for detecting alignment mark positions 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 11 Specific primary electron beam 20 Multi-primary electron beam 22 Hole 27 Alignment mark 29 Sub-irradiation area 30 Frame area 31 Frame image 32 Stripe area 33 Rectangular area 34 Irradiation area 50, 51, 52, 56 Storage Device 54 Frame image creation unit 57 Alignment unit 58 Comparison unit 100 Inspection device 101 Board 102 Electronic 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 130 Camera control circuit 131 Detection circuit 132 Mark position detection circuit 134 Alignment circuit 142 Drive mechanism 144,146,148 DAC amplifier 150 Image acquisition mechanism 160 Control system circuit 201 Electronic gun 202 Electromagnetic lens 203 Molded aperture array substrate 205, 206, 207, 224,226 Electromagnetic lens 208 Main deflector 209 Sub-deflector 212 Collective blanking deflection Instrument 213 Restriction Aperture Board 214 Beam Separator 216 Mirror 218 Deflector 219 Optical Camera 222 Multi Detector 300 Multi Secondary Electronic Beam 330 Inspection Area 332 Chip

Claims (7)

The process of imaging the alignment mark with an optical camera on the substrate on which the pattern having the alignment mark is formed, and
The process of detecting the first position of the alignment mark using the captured optical image, and
A step of acquiring a first secondary electron image of the alignment mark using a multi-electron beam based on the detected first position, and
A step of detecting the second position of the alignment mark using the acquired first secondary electron image, and
A step of acquiring a second secondary electron image of the alignment mark using the predetermined electron beam in a state where the detected second position is aligned with the irradiation region of the predetermined electron beam in the multi-electron beam. When,
A process of detecting and outputting the third position of the alignment mark using the acquired second secondary electronic image, and
A method for detecting an alignment mark position. The method for detecting an alignment mark position according to claim 1, wherein the central beam of the multi-electron beam is used as the predetermined electron beam. The method for detecting an alignment mark position according to claim 1 or 2, wherein the first secondary electron image is acquired as an image having a coarser resolution than the second secondary electron image. A plurality of chips are formed on the substrate.
The plurality of chips each have the plurality of alignment marks.
The first position of the alignment mark detected by using the optical image of the alignment mark of one of the plurality of chips, and any of the other chips of the plurality of chips. Any of claims 1 to 3, further comprising a step of adjusting the arrangement angle of the substrate by using the first position of the alignment mark detected by using the optical image of the alignment mark. The method for detecting the position of the alignment mark described. An optical camera that captures the alignment mark on the substrate on which the pattern having the alignment mark is formed, and
A position detection unit that detects the first position of the alignment mark using the captured optical image, and
An image acquisition mechanism that acquires a first secondary electron image of the alignment mark using a multi-electron beam based on the detected first position, and an image acquisition mechanism.
With
The position detection unit detects the second position of the alignment mark by using the acquired first secondary electron image.
The image acquisition mechanism uses the predetermined electron beam to align the detected second position with the irradiation region of the predetermined electron beam in the multi-electron beam, and uses the predetermined electron beam to perform the second secondary of the alignment mark. Get an electronic image,
The position detection unit is an alignment mark position detection device, which detects the third position of the alignment mark using the acquired second secondary electron image. The alignment mark position detection device according to claim 5, wherein the central beam of the multi-electron beam is used as the predetermined electron beam. A plurality of chips are formed on the substrate.
The plurality of chips each have the plurality of alignment marks.
The first position of the alignment mark detected by using the optical image of the alignment mark of one of the plurality of chips, and any of the other chips of the plurality of chips. A fifth aspect of the present invention, further comprising an arrangement angle adjusting unit for adjusting the arrangement angle of the substrate by using the first position of the alignment mark detected by using the optical image of the alignment mark. 6 Alignment mark position detection device according to any one of the above.

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