JP7576194B2 - Multi-beam image generating device and multi-beam image generating method - Google Patents

Description

The present invention relates to a multi-beam image generating device and a multi-beam image generating method that generate an image by scanning a sample with multiple primary electron beams.

Traditionally, the semiconductor industry has been supported by the improved device performance and cost benefits brought about by advances in microfabrication technology, famously known as Moore's Law, but the limits of microfabrication of semiconductor devices are determined by exposure technology. Semiconductor exposure technology consists of an original plate called a photomask for creating patterns, an exposure device, and a resist that forms the pattern. Currently, exposure devices use 4:1 reduction exposure technology, so a pattern structure that is four times the size of the pattern structure on the silicon wafer on which the semiconductor device is actually made is formed on the photomask.

The biggest challenge in exposure technology is how accurately the pattern created on the photomask based on semiconductor circuit design data can be transferred to the resist film pattern on the wafer surface. If there is an abnormality in the photomask, it will be transferred to the wafer surface by the exposure device, causing defects on the wafer.

To prevent exposure defects, it is necessary to at least inspect the entire photomask and correct it to create a perfect pattern as designed. The limit of fine processing is proportional to the wavelength of the light used for exposure, so the wavelength of the light used for exposure is becoming shorter and shorter with the times.

Since the end of the 20th century, laser light sources with a wavelength of 193 nm have been used as exposure light sources, and for a long time, patterns on photomasks have been inspected using optical mask pattern inspection equipment that uses laser light of 193 nm or the like as illumination light.

However, since 2019, exposure technology using EUV light with a short wavelength of 13.5 nm has been fully introduced, and the limit of microfabrication that can be exposed has become smaller. Patterns on photomasks have also become smaller, from the previous minimum pattern size of around 100 nm to 50 nm or less, making it no longer possible to adequately inspect with the previous 193 nm light.

On the other hand, there are also so-called actinic inspection devices that use a wavelength of 13.5 nm, which is the same wavelength as the exposure wavelength. However, because the wavelength is as short as 13.5 nm, it is almost entirely absorbed by air, so the inside of the inspection device must be evacuated, making it extremely complex compared to conventional devices that were implemented in the atmosphere. Also, because there are no optical lenses that can transmit 13.5 nm light, the optical system must be constructed entirely of reflective optical systems, which is also complex and inefficient. For example, EUV exposure devices that use a wavelength of 13.5 nm are so inefficient that they can only utilize about 1% of the total output of the light source.

The resolution of an optical device is proportional to the numerical aperture (NA). For example, in the case of an optical system using a wavelength of 193 nm, a large numerical aperture exceeding 1 can be achieved by using liquid immersion or oil immersion, so that a pattern of about 40 nm can be resolved in a single exposure despite the long wavelength of 193 nm. By using double patterning, it is even possible to create a pattern of about 20 nm.

On the other hand, when EUV light is used, only a small aperture ratio such as MA 0.33 can be achieved because a reflective optical system is used. Although the light source wavelength is one-tenth shorter than the conventional wavelength, only a resolution of about 13 nm can be obtained, and the performance improvement is small considering the shorter wavelength. In addition, for example, when the detection target is a particle, the reflected light weakens in proportion to the sixth power of the particle size, and the reflected light strengthens in proportion to the square of the wavelength. In other words, as the particle size becomes smaller, the signal strength rapidly weakens, and the defect detection sensitivity decreases dramatically. In this way, photomask inspection technology using optical technology has reached its technical limit. In addition, conventional devices using optical principles operated in the atmosphere, making them easy to manufacture and operate, but as the wavelength becomes shorter, they are absorbed by the air, requiring a large vacuum chamber, which eliminates the advantage in usability over electron beam devices.

On the other hand, electron microscopes are a technology that can achieve nanometer-order high resolution. Electron beam defect inspection technology using electron beams has been developed for over 30 years. Although it has been commercialized, the throughput is extremely low compared to optical methods, so it has not yet been put into practical use as a primary inspection device. However, because it can find electrical defects that cannot be found with optical methods, it is gradually becoming more widely used for developing new wafer processes.

Unlike laser light, electron beams do not have a source with high brightness and small energy dispersion like lasers. Furthermore, because electrons have a negative charge, when they are focused into a small spot using a lens or other device, they electrostatically repel each other. Therefore, when the large current required for high-speed inspection is passed, the minimum beam spot size becomes larger than the optical limit, and the resolution deteriorates. In other words, when a single electron beam is used, there is a very severe trade-off between resolution and inspection speed, so there is a fundamental flaw in that the speed becomes slower as miniaturization progresses.

For example, currently, the maximum inspection speed that can be achieved using one electron beam is at most several hundred megapixels per second. Since a photomask has a pattern written in an area of approximately 10 cm square, it is necessary to inspect the entire area. For example, in order to inspect the patterns on the most advanced photomasks at a resolution of 10 nm, which is sufficient to resolve the patterns on the photomask, it is necessary to acquire 10^14 pixels. For example, acquiring pixels at 100 megapixels per second requires 10^6 seconds. In other words, it takes 277 hours, or more than 10 days. In addition, multiple scans are required to obtain an image with an SNR of 10 or more, which is necessary for inspection. Conventional optical photomask inspection equipment can inspect one photomask in about two hours, so the electron beam type is 100 times slower than that and cannot be used in practice.

On the other hand, in order to improve the speed of electron beam inspection equipment, a method known as a multi-electron beam inspection equipment is being researched that performs high-speed inspections by irradiating a sample with multiple electron beams simultaneously in parallel. With this method, more than 100 small electron beams are irradiated simultaneously for scanning, making it possible to reduce the amount of current flowing through each beam, and it is said that the inspection speed can be made faster than when using a conventional single electron beam while maintaining high resolution without being affected by the electrostatic repulsion of the beam.

However, many companies have been developing various types of multi-beam inspection equipment, and although they are seen as very promising next-generation high-speed inspection equipment, they have not yet achieved the speed and resolution expected, and have not yet been commercialized as semiconductor inspection equipment.

The equipment used in the semiconductor industry is industrial measurement equipment, a type of mission-critical equipment that must operate 24 hours a day, 365 days a year without malfunction, so high robustness is essential. Unlike scientific equipment, which university professors and students can use occasionally to write papers, it is completely unusable for practical purposes. It is necessary for the equipment to withstand various measurement conditions, measurement targets, and changes in the equipment installation environment, and to maintain stable performance over the long term.

Conventional high-speed inspection equipment using a single beam method generally uses a continuous stage method, but multi-beam methods that simultaneously acquire two-dimensional images have adopted a step-and-repeat method that maximizes the area that can be acquired in one scan to increase speed. This causes the stage movement time to be dominant, making it impossible to increase speed.

In addition, there was a clear contrast difference due to the difference in sensitivity at the boundaries of the scanning area, making it difficult to use as an inspection image.

In addition, with the single beam system, since there is only one beam, it is easy to correct the irradiation position and irradiate the electron beam to the desired position. However, with the multi-beam system, multiple electron beams are irradiated simultaneously to acquire a two-dimensional image, so there is the problem that it is not easy to precisely control the irradiation position of each electron beam to the desired position. Furthermore, if the stage is moved while acquiring two-dimensional image information in order to increase speed, there is the problem that stage rotation, undulation, stage speed fluctuation, height fluctuation, vibration, etc. that occur during the movement affect the acquisition of two-dimensional images and reduce the quality of the images.

In addition, simply capturing an image in the same way as with a conventional single beam results in distorted or skipped images, making it impossible to capture an accurate image and making it unusable for inspection.

In order to solve the above-mentioned problems, the present invention generates multiple primary electron beams and irradiates the sample while moving the sample, and then separates the multiple secondary electron beams emitted at this time using a beam splitter, detects the image information of each beam using an electron detection device, and combines them into a single image, thereby achieving high-speed image acquisition.

Therefore, the present invention provides a multi-beam image generating device that generates an image by scanning a sample with a plurality of primary electron beams, the device comprising: a multiple beam generating device that generates a plurality of primary electron beams; a beam splitter that deflects the plurality of primary electron beams generated by the multiple beam generating device in two stages to cause them to be incident on the axis of an objective lens, and also deflects a secondary electron beam emitted from the sample in two stages in the opposite direction to the primary electron beams to cause them to be incident on the axis of a projection lens; an objective lens that narrows the primary electron beam that has been deflected in two stages by the beam splitter and incident on the axis; a deflection system that deflects the primary electron beam narrowed by the objective lens to scan it on a sample; and a beam splitter that narrows the primary electron beam that has been deflected in two stages by the beam splitter to cause it to be incident on the axis. It is equipped with a projection lens that focuses the secondary electron beam, which is deflected in two stages by the splitter and incident on the axis, on an electron detector, a stage that moves the sample at least in a fixed direction, and an interferometer that measures the position of the sample in the direction of movement and the position perpendicular to the direction in real time. The beam splitter deflects multiple primary electron beams generated by the multiple beam generating device to the axis of the objective lens, the objective lens irradiates the sample with a finely focused primary electron beam and scans it with a deflection system, and the beam splitter deflects the secondary electrons emitted from the sample to the axis of the projection lens, which then focuses the image on the electron detector to output image information of the multiple electron beams.

In this case, a synthesis means is provided to synthesize the image information from the multiple electron beams into a single image.

In addition, the amount of movement and rotation of the stage is corrected based on the image information of the multiple electron beams output and the real-time position of the sample in the movement direction and perpendicular direction output from the interferometer, or the image information is moved and rotated by an amount corresponding to the amount of movement and rotation of the stage.

In addition, the height of the stage is measured in real time and the stage height is corrected based on this, or corrected electromagnetically, for automatic focusing.

The multiple beam generating device also irradiates a single primary electron beam onto an aperture with multiple holes to generate multiple primary electron beams.

The beam splitter also has an electrostatic deflector in the first stage on the primary electron incidence side, and an electromagnetic deflector in the second stage, and the second stage electromagnetic deflector deflects the secondary electron beam emitted from the sample in the opposite direction to the primary electron beam to separate it.

In addition, a negative retarding voltage is applied to the sample to reduce the energy of the primary electron beam that irradiates and scans the sample while maintaining the high resolution, thereby reducing damage to the sample.

In addition, a deflection system for correcting the position of the secondary electron beam is provided before or after the projection lens.

The present invention generates multiple primary electron beams and irradiates the sample while moving the sample, and then separates the multiple secondary electron beams emitted at this time using a beam splitter, detects the image information of each beam using an electron detection device, and combines them into a single image, making it possible to acquire images at high speed.

In addition, by irradiating a sample with multiple primary electron beams and detecting multiple secondary electron beam images that are overlapped and combined into a single image, it was possible to reduce the occurrence of contrast differences at the boundaries.

In addition, by acquiring and registering in advance the irradiation positions of multiple primary electron beams on the sample, it is now possible to correct the center position of the secondary electron beam image and synthesize a precise image.

In addition, the position and rotation of the stage carrying the sample can be precisely measured and recorded in real time using a laser interferometer, allowing the amount of movement and rotation of the images of multiple secondary electron beams to be corrected, generating precise image information.

Figure 1 shows a structural diagram of one embodiment of the present invention.

In FIG. 1, the electron gun 1 is a known device that generates an electron beam, generating a primary electron beam accelerated to several hundred volts to several tens of kilovolts. The electron gun uses a thermionic electron source such as W or LaB6, a TFE using ZrO or a cold field emitter or a photocathode, and the electron gun chamber is kept at an ultra-high or extremely high vacuum of 10-8 Pa or higher using an ion pump or getter pump.

The blanking device 2 quickly turns the primary electron beam emitted from the electron gun 1 on or off, deflecting the primary electron beam by turning the voltage on or off to pass or block it.

The illumination lens 3 focuses the electron beam generated and accelerated by the electron gun 1 into a specified beam as shown in Figure 4, which will be described later.

The multi-beam aperture 3-1 splits the irradiated primary electron beam into multiple primary electron beams (for example, 100 splits).

The objective aperture 4 is used to pass the central portion of each of the multiple primary electron beams, and each of the primary electron beams is focused and irradiated onto the surface of the sample 8 by the objective lens 6, which will be described later.

The beam splitter 5 separates the primary electrons from the secondary electrons traveling in the opposite direction, and is composed of an electrostatic deflector 5-1 at the top and an electromagnetic deflector 5-2 at the bottom. The primary electron beam is deflected to the right by the electrostatic deflector 5-1 as shown in FIG. 1, and to the left by the electromagnetic deflector 5-2, and is deflected back onto the axis of the objective lens 6, which narrows the beam and focuses it onto the sample 8. The secondary electrons emitted from the sample 8 are deflected to the right by the electromagnetic deflector 5-2 as shown in FIG. 1, and to the left by the electrostatic deflector 5-1, and are deflected back onto the axis of the projection lens 12, which forms multiple secondary electron beams onto the electron detection device 14, and outputs multiple secondary electron images (secondary electron signals).

The electrostatic deflector 5-1 is the deflector that is closer to the electron gun 1 and that constitutes the beam splitter 5, and in this case is an electrostatic deflector.

The electromagnetic deflector 5-2 is the deflector that constitutes the beam splitter 5 and is located away from the electron gun 1, and in this case is an electromagnetic deflector.

The objective lens 6 narrows the multiple primary electron beams and irradiates them onto the sample 8.

The deflection device 7 scans the sample 8 with multiple primary electron beams, and typically scans the sample 8 at a constant speed in the perpendicular direction when the stage 9 is moved at a constant speed in a constant direction. Note that in addition to scanning in a constant direction (constant scanning in the X or Y direction or any arbitrary direction), planar scanning (XY scanning) is also possible.

Sample 8 is a specimen for which multiple images, such as a mask or wafer, are acquired and combined into a single image.

Mirror 8-1 is a reflector used to measure the position in real time using a laser interferometer.

The stage (XYZθ stage) 9 is a stage on which a sample can be mounted and which can move in XYZ and also θ (rotation), and is configured to be able to measure and record XYZ and θ in real time using an interferometer (not shown).

The vacuum chamber 10 is a container that can house the sample 8, stage 9, etc. and can be evacuated to a vacuum.

The vacuum pump 10-1 is used to evacuate the inside of the vacuum chamber 10, and is an oil-free pump that evacuates the air.

The alignment 11 aligns the axes of multiple secondary electron beams deflected onto the axis of the projection lens 12 by the electrostatic deflector 5-1 that constitutes the beam splitter 5.

The projection lens 12 images the multiple secondary electron beams emitted from the sample 8 onto the detection surface of the electron detection device 14.

The deflector 13 corrects (returns) the multiple secondary electron beams emitted when the multiple primary electron beams are narrowly focused and scanned over the sample 8 so that they remain within a specified area on the detection surface of the electron detection device 14.

The electron detection device 14 detects each of the multiple secondary electron beams emitted from the sample 8. For example, an avalanche photodiode, CCD, CMOS sensor, or TDI camera can be used. The electrons may first collide with a scintillator and be converted into light, which is then detected by the aforementioned device, or the electrons may be directly bombarded into the aforementioned device and detected. In any case, it is sufficient to be able to independently detect each of the multiple secondary electron beams that are each imaged within a specified area of the detection surface.

The operation of the structure of FIG. 1 will now be described.
(1) The primary electron beam emitted from the electron gun 1 irradiates the multi-beam aperture 3-1 to generate multiple primary electron beams. The generation of multiple primary electron beams is not limited to this method, and multiple electron emission sources may be provided on the surface of the emitter of the electron gun 1 to generate multiple corresponding primary electron beams.
(2) The multiple primary electron beams generated by being split by the beam aperture 3-1 each pass through the center portion of the objective aperture 4, and are deflected to the right by the upper electrostatic deflector 5-1 that constitutes the beam splitter 5, and to the left by the electromagnetic deflector 5-2, before entering the axis of the objective lens 6.
(3) The primary electron beams incident on the axis of the objective lens 6 are narrowed by the objective lens 6 and irradiate the surface of the sample 8, while the sample 8 moves in a constant direction at a constant speed and is electrostatically deflected by the deflection device 7 in a direction perpendicular to the moving direction, and the primary electron beams are scanned in a strip shape on the sample 8. As a result, the surface of the sample 8 is scanned with the primary electron beams in a region (strip-shaped region) having a width deflected by the electrostatic deflector 5-1 with respect to the moving direction of the stage 9. At this time, although not shown, a negative retarding voltage is applied to the sample 8, and the energy of the primary electron beams is set to, for example, 1 KV for irradiation (for example, a negative retarding voltage of 14 KV is applied to the energy of the primary electron beams of 15 KV to generate a primary electron beam of 1 KV for irradiation of the sample 8).
(4) Secondary electrons, reflected electrons, light, X-rays, etc. are emitted from the area of the multiple primary electron beams scanned in a strip shape in (3).
(5) The secondary electrons emitted in (4) travel in a spiral in the opposite direction on the axis of the objective lens 6 due to the magnetic field of the objective lens 6, are deflected to the right here (deflected in the opposite direction to the deflection of the multiple primary electron beams) by the lower electromagnetic deflector 5-2 that constitutes the beam splitter 5, are deflected to the left by the electrostatic deflector 5-1, and are incident on the axis of the projection lens 12.
(6) After being corrected by the alignment 11 as necessary on the axis of the projection lens 12, the multiple secondary electron beams emitted from the sample 8 are imaged on the electron detection device 14 and irradiated onto the imaging area of each of the multiple secondary electron beams of the electron detection device 14. If the multiple secondary electron beams go beyond the imaging area, the return deflector 13 synchronizes with the scanning (deflection) of the multiple primary electron beams on the sample 8 and supplies a voltage (or current) to the return deflector 13 to correct the multiple secondary electron beams so that they fall within the imaging area. Then, secondary electron images (secondary electron signals) detected by each of the multiple secondary electron beams are output from the electron detection device 14.

By the above, multiple primary electron beams are generated and narrowed by the objective lens 6 via the beam splitter 5, and the sample 8 is moved in a fixed direction on the stage 9 while the multiple primary electron beams are scanned in a perpendicular direction, repeatedly scanning the sample 8 in a rectangular area with the multiple primary electron beams. The multiple secondary electron beams emitted at this time are then separated via the beam splitter 5, and the multiple secondary electron beams are imaged on the respective detection surfaces of the electron detection device 14 by the projection lens 12, making it possible to output secondary electron images (secondary electron signals) of each of the multiple secondary electron beams.

Figure 2 shows an example of the type of multi-beam array of the present invention. This shows an example of the type of hole array of the multi-beam aperture 3-1 of Figure 1 described above. Note that in Figure 2, the holes are shown as being rectangular in shape, but in reality, circular holes are preferable.

Figure 2(a) shows an example of one row, Figure 2(b) shows an example of two rows, Figure 3(c) shows an example of two-row staggered pattern, and Figure 3(d) shows an example of nine-row staggered pattern.

Figure 2 (a) shows an example of one stage. This is a schematic diagram of an example in which holes as shown (in practice, round shapes are preferable) are provided in one stage in the aperture of the multi-beam aperture 3-1 in Figure 1 in the direction that coincides with the scanning direction of the primary electron beam. For example, if 100 holes are provided in one stage, 100 primary electron beams can be generated.

Figure 2(b) shows an example of two stages. This is a schematic diagram of an example in which holes (round shapes are preferable in practice) as shown in the figure are provided in two stages in the aperture of the multi-beam aperture 3-1 in Figure 1 in the direction that coincides with the scanning direction of the primary electron beam. For example, if 100 holes are provided in two stages, the second stage scan starts after the first stage with a delay of a distance equivalent to the distance difference between the first and second stages (the distance difference divided by the reduction ratio of the objective lens 6), and two secondary electron images can be obtained with one overall scan, and a secondary electron image (secondary electron signal) with double the signal strength, or a secondary electron image can be obtained at twice the speed if the signal strength is made equal, thereby reducing the acquisition time of the secondary electron image by half.

Figure 2(c) shows an example of a two-stage staggered arrangement. This is a schematic diagram of an example in which holes (round shapes are preferable in practice) as shown in the figure are provided in the aperture of the multi-beam aperture 3-1 in Figure 1 in two stages and staggered in the direction that coincides with the scanning direction of the primary electron beam. For example, if 100 holes are provided in a two-stage staggered arrangement, the second stage of staggered scanning begins after the first stage with a delay equivalent to the distance difference between the first and second stages (the distance difference divided by the reduction ratio of the objective lens 6), and two secondary electron images can be obtained with one overall scan, and a secondary electron image with double the signal strength, or a secondary electron image at twice the speed if the signal strength is reduced to one, can be obtained, and the acquisition time of the secondary electron image can be reduced by half.

Figure 2(d) shows an example of a nine-stage staggered arrangement. This is a schematic diagram of an example in which holes as shown (in practice, round shapes are preferable) are provided in the aperture of the multi-beam aperture 3-1 in Figure 1 in nine stages and staggered in the direction that coincides with the scanning direction of the primary electron beam. For example, if nine stages are provided in a staggered arrangement as shown, the staggered scanning of each stage begins with a delay equivalent to the distance difference between each stage (the distance obtained by dividing each distance difference by the reduction ratio of the objective lens 6), and nine secondary electron images can be obtained in one overall scan.

In addition, each multi-beam aperture 3-1 in Figure 2 (a) to (d) can be given the function of independently turning on and off each primary electron beam, and instead of preparing a large number of apertures with different physical arrangements as shown, they can be created so that only the electron beam at an arbitrary position selected from all the multi-beams can be controlled to reach the sample.

Figure 3 shows an example of a data table of the present invention. As already described and described later, in the structure of Figure 1, the position XYZ and rotation θ of stage 9 carrying sample 8 (e.g., a mask) are measured in real time using a laser interferometer, and the stage deviation amount, stage rotation amount, and stage height are recorded in association with the stage position when stage 9 is scanned in a certain direction.

In FIG. 3, the stage position indicates the position when the XYZθ stage (hereinafter referred to as stage) 9 carrying the sample 8 in FIG. 1 is scanned at a constant speed in a constant direction, and is measured in real time by a laser interferometer (described later). The stage position is measured and recorded in real time at steps (intervals) corresponding to the distance between pixels of the image to be acquired, for example. For example, when attempting to acquire an image of 1000 pixels x 1000 pixels for a 100 μm rectangular area, one entry of information (stage position, stage deviation amount, stage rotation amount, stage height) is measured and recorded in real time every 0.1 μm. Furthermore, it is also possible to measure and record in real time every 0.01 μm, which corresponds to a 10 μm or 1 μm rectangular area, or every 0.001 μm. Note that if the same value occurs consecutively, the difference may be recorded.

The stage deviation is the deviation in the stage position (deviation from the ideal position), and is the value measured in real time by a laser interferometer and recorded (described later).

The stage rotation amount is the amount of rotation at the stage position (the amount of rotation θ from the ideal no rotation), and is the amount of stage rotation measured in real time by a laser interferometer and recorded (described later).

The stage height is the height Z at the stage position (the deviation in the Z direction from the ideal height), and is the height deviation measured in real time by a laser interferometer and recorded (described below).

As described above, when the stage 9 in FIG. 1 is scanned at a constant speed in a constant direction (for example, in the stage movement direction in FIG. 2 described above), it is possible to precisely measure and record in real time using a laser interferometer the deviations (stage deviation (X.Y)), stage rotation θ, and stage height Z) from the ideal values of the stage 9. Then, by correcting the position of the stage 9 or correcting the acquired image in real time based on the recorded deviations, it is possible to correct errors associated with the scanning of the stage 9 and generate a single precise image by synthesizing the images of the multiple secondary electron beams acquired by irradiating the sample with multiple primary electron beams. The details are explained below in order.

Figure 4 shows an example of multi-beam creation according to the present invention. This Figure 4 is a schematic diagram showing an example of multi-beam creation using the multi-beam aperture 3-1 of Figure 1 described above.

In FIG. 4, the primary electron beam emitted from the electron gun 1 is projected by the illumination lens 3 so as to irradiate the multiple holes of the multi-beam aperture 3-1 as shown in the figure. The multiple primary electron beams (multi-electron beam 3-2) that are generated by passing through the multi-beam aperture 3-1 and splitting are narrowed down and irradiated onto the surface of the sample 8 by the objective lens 6 of FIG. 1, which is not shown in FIG. 4. Here, the sample 8 moves in a certain direction (here, perpendicular to the paper surface) with the stage movement, and the multi-electron beam 3-2 (six primary electron beams) are scanned in a single direction in the left-right direction of the paper surface, so that the surface of the sample 8 is scanned in a strip-like manner by the multi-electron beam 3-2 (six primary electron beams). Then, the six emitted secondary electron beams are detected by the electron detection device 14 of FIG. 1, six sets of secondary electron images are obtained, and these are combined into one (described later), making it possible to generate a secondary electron image of the sample 8.

Figure 5 shows an explanatory diagram of the multi-beam detection of the present invention. This shows a detailed explanatory diagram of the projection lens 12, the deflector 13, and the electronic detection device 14 of Figure 1.

In FIG. 5, multiple secondary electron beams emitted from the sample 8 are split by the beam splitter 5 and, when they are incident from the top to the bottom in FIG. 4, are imaged on the detection surface of the electron detection device 14 by the projection lens 12. At this time, the imaging area in which the multiple secondary electron beams are imaged is not a problem if it is within the imaging area of the sample itself, but if it extends beyond other areas, it will go undetected and the secondary image will be missing. To prevent this, the deflector 13 synchronizes with the scanning of the primary electron beam on the sample 8 (scanning by deflection of multiple primary electron beams by the deflection device 7) and corrects the deflection so that it falls within a specified imaging area, correcting it so that it falls within the imaging area of the sample itself.

As a result, each of the multiple secondary electron beams emitted from the sample 8 is imaged in each imaging area of the electron detection device 14, making it possible to reliably detect and output the secondary electron images of each of the multiple secondary electron beams.

Figure 6 shows an explanatory diagram (1st row) of multi-beam image acquisition and synthesis according to the present invention.

Figure 6 (a) shows an example of an image before synthesis. This is the case where the number of primary electron beams in Figure 2 (a) is one stage (one stage in the direction perpendicular to the stage movement (scanning) direction), and Figure 6 (a) shows a schematic diagram of a state in which four one-stage primary electron beams are used, and the sample 8 is moved (scanned) in a constant direction by the stage 9 at a constant speed while the four primary electron beams are repeatedly scanned in the perpendicular direction, and the four secondary electron beams emitted from the sample 8 at this time are each imaged on the electron detection device 14 by the projection lens 12 in Figure 1, and the four secondary electron images are generated as four strip-shaped images of swaths 1, 2, 3, and 4 shown in the figure. Here, the four strip-shaped secondary electron images of swaths 1, 2, 3, and 4 are partially overlapped (for example, overlapping by about 10%) with the primary electron beam as shown as overlap 1, 2, and 3 in order to be synthesized later. This eliminates missed scans and also creates a common image in adjacent swaths, so that the positional relationship between adjacent swaths can be corrected using position information obtained from a laser interferometer (see Figure 3) and pattern matching, etc., to create a single large image (see Figure 6 (b)).

Figure 6B shows an example of an image after synthesis. This is a single image obtained by synthesizing the four secondary electron images of swaths 1, 2, 3, and 4 in Figure 6A. In Figure 6B, overlaps 1, 2, and 3 (for example, about 10%) are used, and the images are synthesized into one image based on the various amounts of shear corresponding to the stage positions in Figure 3 described above. Here, the overlaps 1, 2, and 3 areas are scanned twice, so a high SNR can be obtained due to the image addition effect, and more accurate alignment can be achieved. For example, by aligning swaths 1, 2, 3, and 4 and synthesizing the images, one large image area is formed from the four independent swaths 1, 2, 3, and 4. The image processed in this way is output as a synthesized image and used as an inspection image. If the area to be inspected is formed without straddling each of swaths 1, 2, 3, and 4, inspection can be achieved using the area of one of the swaths, so it is not necessarily necessary to synthesize them into one image.

As described above, by repeatedly scanning the sample 9 with the single-stage primary electron beam of FIG. 2(a) while moving the sample 9 in the perpendicular direction on the stage 9 at a constant speed, it is possible to generate strip-shaped secondary electron images (FIG. 6(a)) shown in swaths 1, 2, 3, and 4, and to generate a single secondary electron image (FIG. 6(b)) by combining these images.

Figure 7 shows an explanatory diagram (two stages) of multi-beam image acquisition and synthesis according to the present invention.

Figure 7 (a) shows an example of an image before synthesis. This is the case where the number of primary electron beams in Figure 2 (b) is two stages (two stages in the direction perpendicular to the stage movement (scanning) direction), and Figure 6 (a) shows a schematic representation of the state in which four two-stage primary electron beams are used, and the sample 8 is moved (scanned) in a constant direction by the stage 9 at a constant speed, while the four two-stage primary electron beams are repeatedly scanned in the perpendicular direction, and the four two-stage secondary electron beams emitted from the sample 8 at that time are each imaged on the electron detection device 14 by the projection lens 12 in Figure 1, and the four two-stage secondary electron images are four strips of swaths 1, 2, 3, and 4 shown in the figure, and the first stage secondary electron image is generated by starting scanning from the left end of the scanning start point, and the second stage secondary electron image is generated a little later by overlapping and adding it. In this two-stage case, scanning is started with the first stage primary electron beam in FIG. 2B (four primary electron beams in FIG. 7A), and then, a little later, scanning is started with the second stage primary electron beam (four primary electron beams in FIG. 7A). As shown in the figure, the second stage secondary electron beam becomes an overlap-added secondary electron image, which has the advantage of generating a high SNR. Here, the four rectangular secondary electron images (overlap-added secondary electron images) of swaths 1, 2, 3, and 4 are partially overlapped (for example, overlapped by about 10%) with the primary electron beams for later synthesis, as shown as overlap 1, 2, and 3. This eliminates scanning omissions and at the same time allows common images to exist in adjacent swaths, so that the positional relationship of adjacent swaths can be corrected using position information obtained by a laser interferometer (see FIG. 3) and pattern matching, etc., to create one large image (see FIG. 7B).

Figure 7B shows an example of an image after synthesis. This is an image obtained by synthesizing four secondary electron images (overlap-added images) of swaths 1, 2, 3, and 4 in Figure 7A into one image. In Figure 7B, overlaps 1, 2, and 3 (for example, about 10%) are used, and the images are synthesized into one image based on various amounts of shear corresponding to the stage positions in Figure 3 described above. Here, overlaps 1, 2, and 3 are scanned twice, so a high SNR can be obtained due to the image addition effect, and more accurate alignment can be achieved. For example, by aligning swaths 1, 2, 3, and 4 and synthesizing the images, one large image area is formed from four independent swaths 1, 2, 3, and 4 in two stages. The image processed in this way is output as a synthesized image and used as an inspection image. If the area to be inspected is formed without straddling each of swaths 1, 2, 3, and 4, inspection can be realized using the area of one of the swaths, so it is not necessarily necessary to synthesize them into one image.

As described above, by repeatedly scanning the sample 9 with the two-stage primary electron beam of FIG. 2(b) while moving the sample 9 in the perpendicular direction on the stage 9 at a constant speed, it is possible to generate strip-shaped secondary electron images (FIG. 7(a), overlap-added images) shown in swaths 1, 2, 3, and 4, and then to generate a single secondary electron image (FIG. 7(b)) by combining these.

Figure 8 shows an explanatory diagram (staggered) of multi-beam image acquisition and synthesis according to the present invention.

Figure 8 (a) shows an example of an image before synthesis. This is the case where the number of primary electron beams in Figure 2 (c) is arranged in a staggered manner in two stages. Figure 8 (a) uses four staggered (two stages) primary electron beams, and while moving (scanning) the sample 8 at a constant speed in a fixed direction by the stage 9, the four two-stage staggered primary electron beams are repeatedly scanned in the perpendicular direction, and the four two-stage staggered secondary electron beams emitted from the sample 8 at that time are imaged on the electron detection device 14 by the projection lens 12 in Figure 1. Then, the four two-stage staggered secondary electron images imaged are staggered in two stages of four strips of swaths 1, 2, 3, and 4 shown in the figure, and the scanning is started from the left end of the scanning start point to generate the first stage secondary electron image, and a little later, the secondary electron image is overlapped and added downward in the figure for the second stage staggered amount. In the case of this two-stage staggered pattern, scanning is started with the first stage primary electron beam in FIG. 2C (four primary electron beams in FIG. 8A), and then, a little later, scanning is started with the second stage staggered primary electron beam (four primary electron beams in FIG. 8A, slightly lower position). As shown in the figure, the second stage secondary electron beam becomes an overlap-added secondary electron image, which has the advantage of generating a high SNR. Here, the four rectangular secondary electron images (overlap-added secondary electron images) of swaths 1, 2, 3, and 4 are partially overlapped (for example, overlapped by about 10%) with the primary electron beam for later synthesis, as shown as overlap 1, 2, and 3. This eliminates scanning omissions and at the same time allows common images to exist in adjacent swaths, so that the positional relationship of adjacent swaths can be corrected using position information obtained by a laser interferometer (see FIG. 3) and pattern matching, etc., to create one large image (see FIG. 8B).

Figure 8(b) shows an example of the image after synthesis. This is a synthesis of four staggered secondary electron images (overlapped and added images) of swaths 1, 2, 3, and 4 in Figure 8(a) into one image. In Figure 8(b), overlaps 1, 2, and 3 (for example, about 10%) are used, and the images are synthesized into one image based on the various amounts of shear corresponding to the stage positions in Figure 3 described above. Here, the overlaps 1, 2, and 3 areas are scanned twice, so a high SNR can be obtained due to the image addition effect, and more accurate alignment can be achieved. For example, by aligning swaths 1, 2, 3, and 4 and synthesizing the images, one large image area is formed from four independent swaths 1, 2, 3, and 4 in two stages. The image processed in this way is output as a synthesized image and used as an inspection image. If the area to be inspected is formed without spanning each of swaths 1, 2, 3, and 4, inspection can be performed using the area of one of the swaths, so it is not necessary to combine them into a single image.

As described above, by scanning the sample 9 with the staggered primary electron beam in two stages as shown in FIG. 2(c) while repeatedly moving the sample 9 in the perpendicular direction on the stage 9 at a constant speed, two stages of rectangular secondary electron images shown in swaths 1, 2, 3, and 4 (FIG. 8(a); the second stage is located slightly below) can be generated, and these can be combined to generate a single secondary electron image (FIG. 8(b)).

Note that Figure 8 shows an example in which the primary electron beams are arranged in an arbitrary staggered position, but even when the primary electron beams are arranged in an arbitrary position (staggered), alignment of multiple swaths is required to ultimately obtain a single image, so it is necessary to provide at least an area of overlap with the swaths created by adjacent primary electron beams. If there is an overlapping area, it becomes possible to precisely determine the relative positions of the swaths regardless of how they are arranged, and they can be combined into a single image. However, this has many disadvantages, such as the processing of the added image becoming more complicated, so it is desirable to use an arrangement that makes it easy to perform addition processing in advance, such as a simple row or staggered arrangement.

Figure 9 shows a flowchart explaining the operation of the present invention (obtaining the center coordinates of a multi-beam image).

In FIG. 9, S1 prepares a pattern with known spacing dimensions. This is a reference sample with precisely known pattern spacing and shape dimensions. A conductive photomask or silicon substrate with the same pattern fabricated in advance is preferable. The pattern size and spacing are measured in advance using a CDSEM or optical measurement device. To simplify the measurement, the electron beam deflection center coordinates are known in advance as design values, so calibration can be easily performed by using a reference sample in which a pattern is located at the designed deflection center coordinates, as shown in FIG. 10 described later. The pattern size is arbitrary, but a pattern that is symmetrical from left to right and up to down is desirable so that the center position can be accurately determined even if process variations occur.

S2 acquires an image while the stage is stopped. This involves scanning multiple primary electron beams over the substrate with the pattern prepared in S1 while the stage 9 in FIG. 1 is stopped, and acquiring an image of the pattern.

S3 compares the acquired image with the spacing dimension position pattern.

S4 calculates the central coordinates of each electron beam scan. S3 and S4 calculate the deviation of the central position by comparing the image acquired in S2 with a reference sample image or design data using pattern matching or the like. The deflection center coordinates of each of the multiple primary electron beams are calculated from the amount of position deviation and the design data of the reference sample.

This makes it possible to actually measure the scanning center coordinates (see FIG. 10, described later) of each of the multiple primary electron beams as they scan the surface of the sample 8 in FIG. 1.

Figure 10 shows an explanatory diagram of the operation of the present invention (multi-beam scanning direction and stage movement direction).

In FIG. 10, the electron beam scanning direction is the direction in which the multiple primary electron beams in FIG. 1 scan the surface of the sample 8 one-dimensionally.

The stage movement direction (constant speed) is the direction in which the stage 9 carrying the sample 8 in Figure 1 scans (moves) in a constant direction at a constant speed.

The first stage aperture is the first stage aperture (corresponding to the primary electron beam) in the two-stage case of Figure 2(b) described above.

The second stage aperture is the second stage aperture (corresponding to the primary electron beam) in the two-stage case of Figure 2(b) described above.

The deflection center corresponding coordinates of each beam indicate the center position coordinates corresponding to each aperture (each primary electron beam), as shown in the figure.
First stage aperture: (X1, Y1), (X2, Y1), (X3, Y1), (X4, Y1)
Second stage aperture: (X1, Y2), (X2, Y2), (X3, Y2), (X4, Y4)
It is written as follows.

As described above, in the case of the two-stage secondary electron beam of FIG. 2(b), in the case of two stages with four in each stage as shown in FIG. 10, the deflection center coordinates of the four primary electron beams in each of the two stages generated by the first stage aperture and the second stage aperture are defined as shown in the figure, and a pattern with known spacing dimensions is created according to the flowchart of FIG. 9 described above, and images of these patterns are acquired and compared, making it possible to actually measure and record the deflection center coordinates of the four primary electron beams in each of the two stages.

Figure 11 shows an explanatory diagram of the operation of the present invention (measuring the amount of deviation and rotation of the stage movement).

Figure 11 (a) shows an example of the positional relationship of the laser interferometer 31 for measuring XY positions, and Figure 11 (b) shows an example of the positional relationship of the laser interferometer 31 for measuring rotation.

In FIG. 11(a), the interferometer X1 is positioned as shown in the figure so that the distance of the position of the stage 9 in the X direction can be precisely measured, and a mirror is placed on the stage side.

Interferometer Y1 is positioned as shown in the figure so that it can precisely measure the distance to the Y-direction position of stage 9, and a mirror is placed on the stage side.

As described above, by arranging the interferometers X1 and Y1, it is possible to precisely measure and record the distance (position) of the stage 9 in the X and Y directions in real time (see Figure 3).

In FIG. 11(b), the interferometer X1 is positioned as shown in the figure so that the distance of the position of the stage 9 in the X direction can be precisely measured, and a mirror is also positioned on the stage side.

Interferometers Y1 and Y2 are positioned as shown in the figure so that the distance between the positions of stage 9 in the Y direction can be precisely measured, and a mirror is placed on the stage side so that the rotation angle can be measured.

As described above, by arranging interferometers X1, Y1, and Y2, it is possible to precisely measure the rotation of stage 9 in real time (see Figure 3).

Figure 12 shows an explanatory diagram of stage tilt correction of the present invention. This shows an example of stage 9 in Figure 1 already described, and shows an example of a three-point supported stage with stage Z1 (cone), stage Z2 (cone), and stage Z3 (flat). Each stage with three points of support is contracted by applying a voltage to the piezoelectric element, and can be adjusted to any distance from the outside.

In more detail, Figure 12 is composed of three independent piezoelectric actuators with the same performance, arranged to provide three-point support for the center of the sample.

One end of each of the three piezoelectric actuators has a support point on the movable surface of the XY stage, and the other end is connected to a holder that supports the sample. The connection is shaped to ensure accurate three-point support. For example, a ruby ball with a non-slip surface treatment can be used, or a metal or plastic material shaped into a cone. It is desirable to perform surface treatment to obtain the largest possible coefficient of friction. At least one of the three supports is conductive to form the circuit required to apply a bias voltage to the sample.

It has three independent control circuits to drive the three piezoelectric actuators, and the signals from the height sensors 151 and 152 are processed by a PC, and the processing results are used to give commands from the PC, etc., to change the desired distance and height. Each actuator has a built-in displacement sensor such as a capacitance sensor, and the actual amount of displacement is monitored and fed back, allowing the nonlinearity of the piezoelectric element to be corrected. Positional accuracy can be achieved to the order of nm (see Figure 190 described below).

The stroke required for Z-axis control ranges from a few microns to approximately 1000 microns. The Z-axis stage must also have high rigidity so that the sample does not vibrate when supported. The support system, which uses a piezoelectric actuator with a displacement magnification mechanism including the sample holder, combines a high response speed of ms with great mechanical rigidity, and has a high resonance frequency of several hundred Hz or more, preventing unnecessary vibrations. As a result, even heavy samples weighing nearly 1 kg, such as photomasks, can be kept horizontal instantly.

Figure 13 shows an explanatory diagram of the meandering of the stage of the present invention.

Figure 13(a) shows a schematic diagram of the stage without meandering, Figure 13(b) shows a schematic diagram of the stage with left meandering, and Figure 13(c) shows a schematic diagram of the stage with right meandering. Here, the vertical direction indicates the stage movement direction, and the horizontal direction indicates the electron beam scanning direction.

In FIG. 13(a), the stage 9 is shown diagrammatically in a state where there is no meandering in the direction of stage movement in a fixed direction (vertical direction), and no correction is required.

In FIG. 13(b), the stage 9 is shown as meandering to the left with respect to the stage movement direction, which is fixed (vertical direction), indicating a case in which correction is necessary. In this case, the meandering is corrected to the right (see the stage deviation in FIG. 3).

In FIG. 13(c), the stage 9 is shown as meandering to the right relative to the stage movement direction, which is fixed (vertical), indicating a case in which correction is necessary. In this case, the meandering is corrected to the left (see the stage deviation in FIG. 3).

XY stages generally combine direct motors, servo motors, stepping motors, ultrasonic motors, linear motors, etc., which have a large driving force and can move at high speeds of more than a micron, with piezoelectric actuators and brakes that allow fine movements on the order of nanometers or less.

The XY stage has the freedom of movement in the X and Y directions by combining an X-axis movement mechanism and a Y-axis movement mechanism that are independent of each other, and has the function of moving to a specified coordinate point. For example, suppose a movement command is given to the XY stage to move along the Y axis. A perfect stage would not move in the X direction, but only in the Y direction, but in an actual stage, movement also occurs in the X direction, as shown in Figure 13.

The guide rails that determine the accuracy of stage movement are made of ceramics and other materials, and although they are machined with extremely high precision, there is a mechanical precision error of the order of microns. For example, when the stage moves from (X1, Y1) to (X1, Y2) along the Y axis, the center coordinates of the stage meander left and right along the X axis during the stage movement. The multi-beam method uses a group of primary electron beams that are arranged in two dimensions with predetermined spacing between each electron beam. If the stage meanders during continuous inspections, the primary electron beams will irradiate different locations from the intended locations, resulting in uneven irradiation of the primary electron beams and defects in the inspection.

Figure 14 shows an explanatory diagram of the meandering correction of the stage of the present invention.

Figure 14(a) shows a schematic example of an image before correction, and Figure 14(b) shows a schematic example of an image after correction. Here, the vertical direction represents the stage movement direction, and the horizontal direction represents the scanning direction of the primary electron beam.

In FIG. 14(a), each image is a schematic representation of the image of the rectangular area shown meandering left and right with each snake of the stage.

In FIG. 14(b), each image is a schematic representation of the state after the image of the illustrated rectangular area has been corrected for each meander of the stage. There is no meandering in the image, and it can be seen that the image is scanned with the same width in the direction of stage movement.

As described above and explained in FIG. 13, if there is (is detected) meandering of the stage 9 (deviations in the direction perpendicular to the stage movement direction, and further deviations in the stage movement direction), a correction is made to move the stage (or move the detected image) by the amount of the meandering, making it possible to perform a correction so that there appears to be no meandering, as shown in FIG. 14(b).

Figure 15 shows an explanatory diagram of the stage rotation of the present invention.

Figure 15(a) shows a schematic diagram of the state without horizontal rotation, Figure 15(b) shows a schematic diagram of the state with horizontal rotation to the right, and Figure 15(c) shows a schematic diagram of the state with horizontal rotation to the left. Here, the vertical direction indicates the stage movement direction, and the horizontal direction indicates the electron beam scanning method.

In FIG. 15(a), the stage 9 is shown diagrammatically in a state where there is no horizontal rotation relative to the stage movement direction in a fixed direction (vertical direction), and no correction is required.

In FIG. 15(b), the stage 9 is shown as having a horizontal rotation to the right relative to the stage movement in a fixed direction (vertical direction), indicating a case in which correction is necessary. In this case, the horizontal rotation is corrected to the left (see the stage rotation amount in FIG. 3).

In FIG. 15(c), the stage 9 is shown as having a horizontal rotation to the left relative to the stage movement in a fixed direction (vertical direction), indicating a case in which correction is necessary. In this case, the horizontal rotation is corrected to the right (see the stage rotation amount in FIG. 3).

Generally, stage 9 is placed on two rails symmetrically, with the movable part in between. The characteristics of the left and right rails are not necessarily the same, and friction is also different, so when stage 9 is moved along the rails, the amount of movement differs between the left and right rails. As a result, the movable part of stage 9 rotates slightly in the XY plane. This is corrected in the present invention.

Figure 16 shows an explanatory diagram of the stage rotation correction of the present invention.

Figure 16(a) shows a schematic example of an image before correction, and Figure 16(b) shows a schematic example of an image after correction. Here, the vertical direction represents the stage movement direction, and the horizontal direction represents the scanning direction of the primary electron beam.

In FIG. 16(a), each image is a schematic representation of how the image in the illustrated rectangular area rotates left or right with each horizontal rotation of the stage.

In FIG. 16(b), each image is a schematic representation of the state after the image of the illustrated rectangular area has been corrected for each horizontal rotation of the stage. It can be seen that there is no horizontal rotation of the image, and it is scanned in the same direction as the stage movement.

As described above and explained in Figure 15, if there is (is detected) horizontal rotation of stage 9 (a deviation in the rotational direction relative to the stage movement direction), a correction is made to rotate the stage in the opposite direction (or rotate the detected image) by the amount of this horizontal rotation, making it possible to perform a correction so that there appears to be no horizontal rotation relative to the stage movement direction, as shown in Figure 16 (b).

Figure 17 shows an explanatory diagram of the stage tilt correction of the present invention (height control and automatic leveling using the Z stage).

Figure 17(a) shows a schematic diagram of the state before correction, and Figure 17(b) shows a schematic diagram of the state after correction. Here, the horizontal axis represents the stage movement direction Y1 to Y2, and the vertical axis represents the height Z at that time.

In FIG. 17(a), the convex curve shown is an example of a curve before correction, and shows a schematic diagram of how the coordinate of height Z changes when the stage 9 moves at a constant speed from coordinate Y1 to coordinate Y2. Here, it can be seen that the height Z changes in a convex shape (actually measured (see stage height in FIG. 3)).

In FIG. 17(b), the curve shown is an example of a corrected curve, showing the state after the height Z of the stage 9 has been corrected. Like the convex curve shown in FIG. 17(a) before correction, if the coordinate of height Z changes when the stage 9 moves from coordinate Y1 to coordinate Y2 at a constant speed (see stage height in FIG. 3), the height Z is automatically corrected in response to the height Z detected in real time.

As described above, when the stage 9 moves in a constant direction at a constant speed, it is possible to detect the height Z in real time and automatically correct the stage height by the change in height (see Figure 18 described later).

In addition, a method may be adopted in which automatic focus and automatic magnification correction is performed by controlling the objective lens 6 (or an auxiliary objective lens not shown) in response to movement of the stage 9 in the Z direction, without performing the Z direction correction of the stage 9 described above in FIG. 17.

Figure 18 shows an explanatory diagram of the stage height correction of the present invention.

Figure 18(a) shows a schematic diagram of the state without correction, and Figure 18(b) shows a schematic diagram of the state with correction. Here, the vertical direction is the electron beam scanning direction, and the horizontal direction is the direction of movement of the stage.

In FIG. 18(a), the images of the tip, center, and rear end without the illustrated correction are schematic representations of the blurring of the images that occurs with the change in height Z that occurs with the movement of the stage 9 (from coordinate Y1 (tip) to coordinate Y2 (rear end) in FIG. 17).

In FIG. 18(b), the images of the tip, center, and rear end in the case of the illustrated correction are schematic representations of images (without blur) after height correction has been performed in response to the change in height Z that occurs with the movement of stage 9 (from coordinate Y1 (tip) to coordinate Y2 (rear end) in FIG. 17).

As described above, it is possible to detect the height Z in real time and automatically correct the height of the stage 9 for the blurred image without correction in FIG. 18(a), thereby automatically correcting it to the corrected image in FIG. 17(b).

Figure 19 shows an explanatory diagram of the sample height and tilt correction of the present invention. This shows an example of a structural diagram of an embodiment in which the stage of Figure 17 is incorporated into the previously described Figure 1.

In FIG. 19, primary electron beam 1-1 represents multiple primary electron beams.

Secondary electron beam 1-2 represents multiple secondary electron beams emitted when multiple primary electron beams 1-1 are irradiated onto sample 51.

The height sensors 151 and 152 are devices that measure and output the height of the sample 51 in real time, such as a laser interferometer.

The sample holder 52 holds the sample 8.

Piezoelectric elements (Z1) 51, (Z2) 52, and (Z3) 55 correspond to stage Z1 (cone), stage Z2 (cone), and stage Z3 (flat) in FIG. 12, and support sample holder 52 at three points.

With the above structure, as explained in Figure 12, it is possible to automatically correct the height and inclination of the sample holder 52 to the desired height Z in real time and at ultra-high speed by applying a control voltage to any of the piezoelectric elements (Z1) 51, (Z2) 52, and (Z3) 55 that support the sample holder 52 at three points.

FIG. 1 is a structural diagram of an embodiment of the present invention. 2 is a diagram showing an example of a type of multi-beam array according to the present invention. 1 is an example of a data table according to the present invention. 1 is an example of creating a multi-beam according to the present invention. FIG. 2 is an explanatory diagram of multi-beam detection according to the present invention. FIG. 1 is an explanatory diagram (first row) of multi-beam image acquisition and synthesis according to the present invention. FIG. 2 is a diagram (two columns) for explaining multi-beam image acquisition and synthesis according to the present invention. FIG. 1 is an explanatory diagram (staggered) of multi-beam image acquisition and synthesis according to the present invention. 1 is a flowchart illustrating the operation of the present invention (obtaining the center coordinates of a multi-beam image). 1 is a diagram for explaining the operation of the present invention (multi-beam scanning direction and stage movement direction). 1A to 1C are diagrams for explaining the operation of the present invention (measurement of deviation amount and rotation amount of stage movement). FIG. 4 is an explanatory diagram of tilt correction of a stage according to the present invention. FIG. 4 is an explanatory diagram of the meandering of a stage according to the present invention. FIG. 4 is an explanatory diagram of meandering correction of a stage according to the present invention. FIG. 4 is an explanatory diagram of the rotation of a stage according to the present invention. FIG. 13 is an explanatory diagram of rotation correction of a stage according to the present invention. FIG. 4 is an explanatory diagram of stage tilt correction according to the present invention. FIG. 4 is an explanatory diagram of height correction of the stage of the present invention. FIG. 4 is an explanatory diagram of sample height and tilt correction according to the present invention.

1: Electron gun 2: Blanking device 3: Illumination lens 3-1: Multi-beam aperture 3-2: Multi-electron beam 4: Objective aperture 5: Beam splitter 5-1: Electrostatic deflector 5-2: Electromagnetic deflector 6: Objective lens 7: Deflection device 8: Sample 8-1: Mirror 9: XYZθ stage (stage)
10: Vacuum chamber 10-1: Vacuum pump 11: Alignment 12: Projection lens 13: Deflector 14: Electronic detector 52: Sample holder 53, 54, 55; Piezoelectric elements 151, 152: Height sensor

Claims (11)

1. A multi-beam imaging apparatus for scanning a sample with a plurality of primary electron beams to produce an image, comprising:
a multiple beam generating device for generating a plurality of primary electron beams;
a beam splitter that causes the multiple primary electron beams generated by the multiple beam generating device to be incident on an axis of an objective lens and causes the secondary electron beam emitted from a sample to be incident on an axis of a projection lens;
an objective lens for narrowing the primary electron beam;
a deflection system that deflects the primary electron beam narrowed by the objective lens to scan the beam on a sample;
a projection lens for forming an image of the secondary electron beam incident on the axis by the beam splitter on an electron detector;
a stage for at least moving the sample at a constant velocity;
an interferometer for measuring the position of the sample in the moving direction and the position perpendicular to the moving direction in real time;
a plurality of primary electron beams generated by the plurality of beam generating devices are incident on the axis of the objective lens by the beam splitter, the sample is irradiated with a narrowed primary electron beam by the objective lens and scanned by the deflection system, secondary electrons emitted from the sample are incident on the axis of the projection lens by the beam splitter, and an image is formed on an electron detector by the projection lens, and image information of the plurality of electron beams is output;
A multi-beam image generating device characterized in that the movement and rotation amounts of the stage are corrected based on the real-time position of the sample in the movement direction and the perpendicular position output from the interferometer, or the image is moved and rotated by an amount corresponding to the movement and rotation amounts of the stage based on the real-time position of the sample in the movement direction and the perpendicular position output from the interferometer and an image from the image information of the multiple electron beams output. The multi-beam image generating device according to claim 1, characterized in that the movement at least at a constant speed is movement at a constant speed and in a constant direction. The multi-beam image generating device according to any one of claims 1 to 2, characterized in that it is provided with a synthesis means for synthesizing the image information of the output multiple electron beams into one image. A multi-beam image generating device according to any one of claims 1 to 3, characterized in that the height of the stage is measured in real time and the height of the stage is corrected based on the measurement, or the height is corrected electromagnetically, and automatic focusing is performed. The multi-beam image generating device according to any one of claims 1 to 4, characterized in that the multiple beam generating device generates multiple primary electron beams by irradiating one primary electron beam onto an aperture having multiple holes. The multi-beam image generating device according to any one of claims 1 to 5, characterized in that the beam splitter has a first stage on the primary electron incidence side as an electrostatic deflector and a second stage as an electromagnetic deflector, and the second stage electromagnetic deflector deflects the secondary electron beam emitted from the sample in the opposite direction to the primary electron beam and separates it. 7. A multi-beam image generating device according to claim 1, characterized in that a negative retarding voltage is applied to the sample, thereby reducing the energy of the primary electron beam that is irradiated and scanned on the sample while maintaining high resolution, thereby reducing damage to the sample. The multi-beam image generating device according to any one of claims 1 to 7, characterized in that a deflection system for correcting the position of the secondary electron beam is provided before or after the projection lens. 1. A multi-beam imaging method for scanning a plurality of primary electron beams onto a sample to produce an image, comprising:
a multiple beam generating device for generating a plurality of primary electron beams;
a beam splitter that causes the multiple primary electron beams generated by the multiple beam generating device to be incident on an axis of an objective lens and causes the secondary electron beam emitted from a sample to be incident on an axis of a projection lens;
an objective lens for narrowing the primary electron beam;
a deflection system that deflects the primary electron beam narrowed by the objective lens to scan it on a sample;
a projection lens for forming an image of the secondary electron beam incident on the axis by the beam splitter on an electron detector;
a stage for at least moving the sample at a constant velocity;
an interferometer for measuring the position of the sample in the moving direction and the position perpendicular to the moving direction in real time;
a plurality of primary electron beams generated by the plurality of beam generating devices are incident on the axis of the objective lens by the beam splitter, the sample is irradiated with a narrowed primary electron beam by the objective lens and scanned by the deflection system, secondary electrons emitted from the sample are incident on the axis of the projection lens by the beam splitter, and an image is formed on an electron detector by the projection lens, and image information of the plurality of electron beams is output;
A multi-beam image generating method characterized in that the movement and rotation amounts of the stage are corrected based on the real-time position of the sample in the movement direction and the perpendicular position output from the interferometer, or the image is moved and rotated by an amount corresponding to the movement and rotation amounts of the stage based on the real-time position of the sample in the movement direction and the perpendicular position output from the interferometer and an image from the image information of the multiple electron beams output. The multi-beam image generating method according to claim 9, characterized in that the movement at least at a constant speed is movement at a constant speed and in a constant direction. The multi-beam image generating method according to any one of claims 9 to 10, further comprising a synthesis means for synthesizing the image information of the output multiple electron beams into one image.

Images