JP7770511B2 - 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 multiple primary electron beams on a sample.

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

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 equipment, causing defects on the wafer.

To prevent exposure defects, it is necessary to at least inspect the entire photomask and correct it to ensure 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 light used for exposure is becoming shorter over time.

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 similar as illumination light.

However, since 2019, exposure technology using EUV light with a short wavelength of 13.5 nm has been fully introduced, further reducing the limit of microfabrication that can be exposed. 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 them using the previous 193 nm light.

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

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 of over 1 can be achieved by using liquid immersion or oil immersion, making it possible to resolve patterns of around 40 nm with a single exposure, despite the long wavelength of 193 nm. Using double patterning, it is even possible to create patterns of around 20 nm.

On the other hand, when EUV light is used, only a small aperture ratio, such as an MA of 0.33, can be achieved due to the use of a reflective optical system. Despite the light source wavelength being one-tenth that of conventional wavelengths, a resolution of only about 13 nm can be achieved, resulting in a small performance improvement despite the shorter wavelength. Furthermore, when the detection target is a particle, for example, the reflected light weakens in proportion to the sixth power of the particle size and increases in proportion to the square of the wavelength. In other words, as particle size decreases, the signal strength rapidly weakens, dramatically reducing defect detection sensitivity. Thus, photomask inspection technology using optical technology is reaching its technological limits. Furthermore, while conventional devices using optical principles operated in the atmosphere, making them easy to manufacture and operate, shorter wavelengths are absorbed by air, requiring a large vacuum chamber, eliminating the ease of use advantage 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, its throughput is extremely low compared to optical methods, so it has not yet been put into practical use as a primary inspection tool. However, because it can find electrical defects that cannot be found with optical methods, it is gradually becoming more widely used in developing new wafer processes.

Unlike laser beams, electron beams do not have a source with the same small energy dispersion and high brightness as lasers. Furthermore, because electrons have a negative charge, when they are narrowed down to a small spot using a lens or other device, they electrostatically repel each other. As a result, when the large current required for high-speed inspection is passed, the minimum beam spot size becomes larger than the optical limit, degrading resolution. In other words, when using a single electron beam, there is an extremely severe trade-off between resolution and inspection speed, which means that the speed becomes slower as miniaturization progresses, resulting in a fundamental flaw.

For example, currently, the maximum inspection speed achievable using a single electron beam is at most a few hundred megapixels per second. Because photomasks have patterns written over an area of approximately 10 cm square, it is necessary to inspect that entire area. For example, to inspect the patterns on cutting-edge photomasks at a resolution of 10 nm, which is sufficient to resolve them, it is necessary to acquire 10^14 pixels. Acquiring pixels at 100 megapixels per second requires 10^6 seconds. In other words, this takes 277 hours, or more than 10 days. Furthermore, multiple scans are required to obtain images with an SNR of 10 or higher, which is necessary for inspection. Conventional optical photomask inspection equipment can inspect one photomask in approximately two hours, making electron beam systems 100 times slower than this to be practically usable.

Meanwhile, in order to improve the speed of electron beam inspection equipment, a method known as a multi-electron beam inspection system is being researched, in which multiple electron beams are irradiated simultaneously in parallel onto a sample to perform high-speed inspections. 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. This is said to enable faster inspection speeds than when using a single electron beam, while maintaining high resolution without being affected by electrostatic repulsion of the beams.

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 initially 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 without malfunction 24 hours a day, 365 days a year, so high robustness is essential. Unlike scientific equipment, which university professors and students may use occasionally to write papers, it is completely unusable for practical purposes. It must be able to withstand a variety of measurement conditions, measurement targets, and changes in the equipment installation environment, and maintain stable performance over the long term.

Conventional single-beam high-speed inspection equipment generally uses a continuous stage system, but multi-beam systems that simultaneously acquire two-dimensional images have adopted a step-and-repeat system that maximizes the area that can be acquired in a single scan to increase speed. However, this has led to the problem that the stage movement time is dominant and speed cannot be increased.

Another problem was that there were clear contrast differences due to differences in sensitivity at the boundaries of the scanned area, making it difficult to use as an inspection image.

Furthermore, with the single-beam system, because there is only one beam, the irradiation position can be easily corrected and the electron beam can be irradiated at the desired position. However, with the multi-beam system, multiple electron beams are irradiated simultaneously to acquire a two-dimensional image, which poses the problem of not being able 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, stage rotation, undulation, stage speed fluctuations, height fluctuations, and vibrations that occur during movement can affect the acquisition of two-dimensional images and reduce image quality.

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

To solve the above-mentioned problems, the present invention generates multiple primary electron beams and irradiates them onto a sample while the sample is moved. The multiple secondary electron beams emitted at this time are separated by a beam splitter, and the image information from each is detected by an electron detection device and combined 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 multiple primary electron beams, comprising: a multiple beam generating device that generates multiple primary electron beams; a beam splitter that deflects the multiple primary electron beams generated by the multiple beam generating device in two stages to make them 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 make them 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 is incident on the axis; a deflection system that deflects the narrowed primary electron beam by the objective lens to scan it on the sample; The system is equipped with a projection lens that focuses the secondary electron beam, which has been deflected twice by a beam splitter and is incident on the axis, onto an electron detector; a stage that moves the sample in at least a fixed direction; and an interferometer that measures the position of the sample in the direction of movement and in the perpendicular direction in real time. The multiple primary electron beams generated by the multiple beam generator are deflected by the beam splitter onto the axis of the objective lens, the objective lens irradiates the sample with the narrowed primary electron beam and scans it with the deflection system, and the secondary electrons emitted from the sample are deflected by the beam splitter onto the axis of the projection lens, which then focuses the beam on the electron detector, outputting image information from the multiple electron beams.

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

In addition, the amount of stage movement and rotation 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 stage movement and rotation.

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

In addition, the multiple beam generating device generates multiple primary electron beams by irradiating a single primary electron beam onto an aperture with multiple holes.

The beam splitter also has an electrostatic deflector in the first stage on the primary electron incident side, and an electromagnetic deflector in the second stage, with the second stage electromagnetic deflector deflecting 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, reducing the energy of the primary electron beam that irradiates and scans the sample while maintaining 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.

This invention generates multiple primary electron beams and irradiates them onto a sample while the sample is moved. The multiple secondary electron beams emitted at this time are separated by a beam splitter, and the image information from each is detected by an electron detection device and combined 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 in an overlapping manner, the contrast differences at the boundaries when the images were combined into a single image were reduced.

In addition, by acquiring and registering the irradiation positions of multiple primary electron beams on the sample in advance, 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 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 Figure 1, electron gun 1 is a well-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 maintained at an ultra-high or extremely high vacuum of 10-8 Pa or higher using an ion pump, getter pump, etc.

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 allow it to pass or block it.

The illumination lens 3 focuses the electron beam generated and accelerated by the electron gun 1 into the specified beam 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 allows the central portion of each of the multiple primary electron beams to pass through, and each of the passed primary electron beams is focused by the objective lens 6, which will be described later, and irradiated onto the surface of the sample 8.

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

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

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 multiple primary electron beams across the sample 8, 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. In addition to scanning in a constant direction (constant scanning in X, Y, or any direction), planar scanning (XY scanning) is also possible.

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

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

The stage (XYZθ stage) 9 is a stage that can mount a sample and move in XYZ and θ (rotation), and is configured to measure and record XYZ and θ in real time using an interferometer (not shown).

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

Vacuum pump 10-1 evacuates the inside of vacuum chamber 10 and is an oil-free pump.

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

The projection lens 12 focuses 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 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 to be converted into light, which is then detected by the aforementioned device, or the electrons may be directly incident on the aforementioned device and detected. In either 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 on the detection surface.

Next, the operation of the structure of FIG. 1 will 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 corresponding multiple primary electron beams.
(2) The multiple primary electron beams split and generated by the beam aperture 3-1 pass through the center of the objective aperture 4, are deflected to the right by the upper electrostatic deflector 5-1 that constitutes the beam splitter 5, and are deflected to the left by the electromagnetic deflector 5-2, and are incident on the axis of the objective lens 6.
(3) The multiple 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 is repeatedly moved in a constant direction at a constant speed and electrostatically deflected by the deflection device 7 in a direction perpendicular to the direction of movement, causing the multiple primary electron beams to scan in a strip-like pattern on the sample 8. As a result, an area (strip-like area) of the surface of the sample 8 whose width is deflected by the electrostatic deflector 5-1 in the direction of movement of the stage 9 is surface-scanned by the multiple primary electron beams. At this time, although not shown, a negative retarding voltage is applied to the sample 8, and the multiple primary electron beams are irradiated with an energy of, for example, 1 KV (for example, a negative retarding voltage of 14 KV is applied to the multiple primary electron beams with an energy of 15 KV, thereby generating a 1 KV primary electron beam and irradiating the sample 8).
(4) Secondary electrons, backscattered electrons, light, X-rays, etc. are emitted from the area of the multiple primary electron beams scanned in strips 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 correction 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 any of the secondary electron beams extend beyond the imaging area, a voltage (or current) is supplied to the return deflector 13 in synchronization with the scanning (deflection) of the multiple primary electron beams on the sample 8 to correct the beams so that they fit 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.

As a result of the above, multiple primary electron beams are generated and narrowed by the objective lens 6 via the beam splitter 5. The sample 8 is then moved in a fixed direction on the stage 9 while the multiple primary electron beams are scanned in perpendicular directions, repeatedly scanning a strip-shaped 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) for each of the multiple secondary electron beams.

Figure 2 shows examples of the types of multi-beam arrays of the present invention. These show examples of the types of hole arrangements of the multi-beam aperture 3-1 of Figure 1 mentioned above. Note that while the holes in Figure 2 are schematically shown as rectangular, in practice, 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 a single stage. This is a schematic diagram of an example in which holes (round shapes are preferable in practice) as shown are provided in a single 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 a two-stage example. This is a schematic diagram of an example in which holes (round shapes are preferable in practice) as shown are arranged in two stages in the aperture of the multi-beam aperture 3-1 in Figure 1, aligned in the direction of the primary electron beam scan. For example, if 100 holes are arranged in two stages, the second stage scan will begin after the first stage, a distance equivalent to the difference in distance between the first and second stages (the distance difference divided by the reduction ratio of the objective lens 6). This allows two secondary electron images to be acquired in one full scan, resulting in a secondary electron image (secondary electron signal) with double the signal strength, or a secondary electron image at twice the speed if the signal strength is kept the same, thereby halving the time required to acquire the secondary electron image.

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

Figure 2(d) shows an example of a nine-stage staggered pattern. This is a schematic illustration of an example in which holes (round shapes are preferable in practice) as shown are arranged in nine stages and staggered in the direction that coincides with the scanning direction of the primary electron beam in the aperture of the multi-beam aperture 3-1 in Figure 1. For example, if nine stages are staggered 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 acquired in one overall scan.

Furthermore, each multi-beam aperture 3-1 in Figures 2(a) to 2(d) can be given the function of independently turning on/off each primary electron beam, so that it is possible to create an aperture with a physically different arrangement as shown, but instead control it so that only the electron beam at an arbitrary position selected from all the multi-beams reaches the sample.

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

In Figure 3, the stage position indicates the position when the XYZθ stage (hereinafter referred to as "stage") 9 carrying the sample 8 in Figure 1 is scanned at a constant speed in a constant direction, and is measured in real time using a laser interferometer (described below). The stage position is measured and recorded in real time at steps (intervals) corresponding to the distance between pixels in the image to be acquired. For example, when attempting to acquire an image of 1000 pixels x 1000 pixels over a 100 μm rectangular area, one entry of information (stage position, stage deviation, stage rotation, stage height) is measured and recorded in real time every 0.1 μm. Furthermore, real time measurements may be recorded 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 repeatedly, 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 using a laser interferometer and recorded (described below).

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 recorded as the amount of stage rotation measured in real time by a laser interferometer (described below).

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 using a laser interferometer and recorded (described below).

As described above, when the stage 9 in Figure 1 is scanned at a constant speed in a fixed direction (for example, in the stage movement direction in Figure 2 described above), the deviations of the stage 9 from its ideal value (stage deviation (X, Y)), stage rotation θ, and stage height Z) can be precisely measured and recorded in real time using a laser interferometer. Then, by correcting the position of the stage 9 or correcting the acquired image in real time based on the recorded deviations, errors associated with the scanning of the stage 9 can be corrected, and multiple images of multiple secondary electron beams acquired by irradiating the sample with multiple primary electron beams can be synthesized to generate a single precise image. This will be explained in detail below.

Figure 4 shows an example of multi-beam generation according to the present invention. This Figure 4 is a schematic diagram of an example of multi-beam generation using the multi-beam aperture 3-1 shown in Figure 1.

In Figure 4, the primary electron beam emitted from the electron gun 1 is projected by the illumination lens 3 so as to illuminate the multiple holes in the multi-beam aperture 3-1, as shown. The multiple primary electron beams (multi-electron beam 3-2) generated after passing through the multi-beam aperture 3-1 and splitting are focused and irradiated onto the surface of the sample 8 by the objective lens 6 (not shown in Figure 4) (Figure 1). As the sample 8 moves in a fixed direction (here, perpendicular to the paper surface) with the stage, the multi-electron beam 3-2 (six primary electron beams) are scanned in a linear fashion across the paper surface. As a result, the surface of the sample 8 is scanned in a strip-like fashion by the multi-electron beam 3-2 (six primary electron beams). The six emitted secondary electron beams are then detected by the electron detection device 14 (Figure 1), obtaining six sets of secondary electron images. These are then combined into a single image (described below) 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. It shows a detailed diagram of the projection lens 12, deflector 13, and electron detector 14 shown in Figure 1.

In Figure 5, multiple secondary electron beams emitted from the sample 8 are split by the beam splitter 5 and, when incident from top to bottom in Figure 4, are each imaged on the detection surface of the electron detection device 14 by the projection lens 12. At this time, the imaging area where the multiple secondary electron beams are imaged is not a problem if it is within its own imaging area, but if it extends beyond other areas, it will not be detected and the secondary image will be missing. To prevent this, the return 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 the specified imaging area, correcting it to ensure that it falls within its own imaging area.

As a result, each of the multiple secondary electron beams emitted from the sample 8 is imaged within 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 (first row) of multi-beam image acquisition and synthesis in accordance with the present invention.

Figure 6(a) shows an example of an image before synthesis. This is for the case where the number of primary electron beams in Figure 2(a) is one (one in the direction perpendicular to the stage movement (scanning) direction). Figure 6(a) shows a schematic diagram of four single-stage primary electron beams used to move (scan) the sample 8 in a fixed direction at a constant speed using the stage 9, while repeatedly scanning the four primary electron beams in the direction perpendicular to the stage. 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, swaths 1, 2, 3, and 4, as shown. Here, the four strip-shaped secondary electron images of swaths 1, 2, 3, and 4 are partially overlapped (e.g., overlapping by approximately 10%) by the primary electron beams, as shown as overlaps 1, 2, and 3, for later synthesis. This eliminates missed scans and also creates a common image in adjacent swaths, so 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 6(b) shows an example of a composite image. This is a single image created by combining the four secondary electron images of swaths 1, 2, 3, and 4 in Figure 6(a). Figure 6(b) uses overlaps 1, 2, and 3 (e.g., approximately 10%) and combines them into a single image based on the various shear amounts corresponding to the stage positions in Figure 3 described above. Here, the overlaps 1, 2, and 3 areas are scanned twice, resulting in a high SNR due to the image addition effect, enabling more accurate alignment. For example, by aligning swaths 1, 2, 3, and 4 and combining the images, a single 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 composite image and used as an inspection image. If the area to be inspected does not straddle 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 a result of the above, by repeatedly scanning the sample 9 using the single-stage primary electron beam shown in Figure 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 (Figure 6(a)) shown in swaths 1, 2, 3, and 4, and then to generate a single secondary electron image (Figure 6(b)) by combining these.

Figure 7 shows a diagram (two rows) explaining multi-beam image acquisition and synthesis in accordance with the present invention.

Figure 7(a) shows an example of an image before synthesis. This is for the case where the number of primary electron beams in Figure 2(b) is two (two in the direction perpendicular to the stage movement (scanning) direction). Figure 6(a) shows a schematic representation of the situation in which four two-stage primary electron beams are used, with the sample 8 moved (scanned) at a constant speed in a fixed direction by the stage 9, while the four two-stage primary electron beams are repeatedly scanned in the direction perpendicular to the stage 9. The four two-stage 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 two-stage secondary electron images are generated in four strips, swaths 1, 2, 3, and 4 shown in the figure. The first secondary electron image is generated by starting scanning from the left edge of the scanning start point, and then the second secondary electron image is generated a short time later by overlapping and adding the images. In this two-stage system, scanning begins with the first-stage primary electron beam (four primary electron beams in Figure 7(a)) in Figure 2(b), followed a short time later by the second-stage primary electron beam (four primary electron beams in Figure 7(a)). As shown, the second-stage secondary electron beam forms 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 (e.g., about 10% overlap) by the primary electron beams, as shown as overlap 1, 2, and 3, for later synthesis. This eliminates scanning omissions and ensures that adjacent swaths share a common image. Therefore, the positional relationship between adjacent swaths can be corrected using position information obtained by a laser interferometer (see Figure 3) and pattern matching to combine them into a single large image (see Figure 7(b)).

Figure 7(b) shows an example of a composite image. This is a single image created by combining four secondary electron images (overlap-added images) from swaths 1, 2, 3, and 4 in Figure 7(a). Figure 7(b) uses overlaps 1, 2, and 3 (e.g., approximately 10%) and combines them into a single image based on the various shear amounts corresponding to the stage positions in Figure 3 described above. Here, the overlaps 1, 2, and 3 areas are scanned twice, resulting in a high SNR due to the image addition effect, enabling more accurate alignment. For example, by aligning swaths 1, 2, 3, and 4 and combining the images, a single large image area is formed from four independent, two-tiered swaths 1, 2, 3, and 4. The image processed in this manner is output as a composite image and used as an inspection image. If the area to be inspected does not span swaths 1, 2, 3, and 4, inspection can be performed using the area of one of the swaths; therefore, combining them into a single image is not necessary.

As a result of the above, by repeatedly scanning the sample 9 using the two-stage primary electron beams shown in Figure 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 (Figure 7(a), overlap-added images) shown in swaths 1, 2, 3, and 4, and then to generate a single secondary electron image (Figure 7(b)) by combining these.

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

Figure 8(a) shows an example of an image before synthesis. This is the case when the number of primary electron beams in Figure 2(c) is staggered in two stages. Figure 8(a) shows four staggered (two-stage) primary electron beams. While moving (scanning) the sample 8 at a constant speed in a fixed direction using the stage 9, the four two-stage staggered primary electron beams are repeatedly scanned perpendicularly. The four two-stage staggered 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 of Figure 1. The four two-stage staggered secondary electron images thus imaged are then schematically shown as being generated by starting scanning from the left end of the scanning start point to generate the first stage secondary electron image, followed a short time later by overlapping and adding the second stage staggered secondary electron image downward in the figure. In this two-stage staggered configuration, scanning begins with the first stage primary electron beam (four primary electron beams in Figure 8(a)) in Figure 2(c), followed a short time later by the second stage staggered primary electron beam (four primary electron beams in Figure 8(a) at a slightly lower position). As shown, the second stage secondary electron beam forms an overlap-summed secondary electron image, which has the advantage of generating a high SNR. Here, the four rectangular secondary electron images (overlap-summed secondary electron images) of swaths 1, 2, 3, and 4 are partially overlapped (e.g., about 10% overlap) by the primary electron beams for later synthesis, as shown as overlap 1, 2, and 3. This eliminates scanning omissions and ensures that adjacent swaths share a common image. Therefore, the positional relationship between adjacent swaths can be corrected using position information obtained by a laser interferometer (see Figure 3) and pattern matching to combine them into a single large image (see Figure 8(b)).

Figure 8(b) shows an example of a composite image. This is a single image created by combining four two-stage staggered secondary electron images (overlap-added images) of swaths 1, 2, 3, and 4 in Figure 8(a). Figure 8(b) uses overlaps 1, 2, and 3 (e.g., approximately 10%) and combines the images into a single image based on the various shear amounts corresponding to the stage positions in Figure 3 described above. Here, the overlaps 1, 2, and 3 areas are scanned twice, resulting in a high SNR due to the image addition effect, enabling more accurate alignment. For example, by aligning swaths 1, 2, 3, and 4 and combining the images, a single large image area is formed from the four independent, two-stage swaths 1, 2, 3, and 4. The image processed in this manner is output as a composite 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 a result of the above, by repeatedly scanning the sample 9 using the staggered primary electron beam in two stages as shown in Figure 2(c) while moving the sample 9 in the perpendicular direction on the stage 9 at a constant speed, it is possible to generate two stages of strip-shaped secondary electron images shown in swaths 1, 2, 3, and 4 (Figure 8(a); the second stage is located slightly below), and then to generate a single secondary electron image (Figure 8(b)) by combining these.

Note that Figure 8 shows an example in which the primary electron beams are arranged in an arbitrary staggered position, but even when arranging the primary electron beams 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 where the swaths created by adjacent primary electron beams overlap. 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 complex, so it is preferable 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 Figure 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 pre-fabricated is preferable. The pattern size and spacing are measured in advance using a CDSEM or optical measurement device. To simplify 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 with a pattern placed at the designed deflection center coordinates, as shown in Figure 10, which will be described later. The pattern size is arbitrary, but a pattern that is symmetrical left and right and top and bottom is desirable so that the center position can be accurately determined even if process variations occur.

S2 acquires images while the stage is stationary. This involves scanning multiple primary electron beams over the substrate with the pattern prepared in S1 while the stage 9 in Figure 1 is stationary, and acquiring images 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 compare the image acquired in S2 with a reference sample image or design data using pattern matching or the like to calculate the deviation in the central position. The deflection center coordinates of each of the multiple primary electron beams are calculated from the amount of positional deviation and the design data of the reference sample.

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

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

In Figure 10, the electron beam scanning direction is the direction in which the multiple primary electron beams in Figure 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 shown in Figure 2(b) above.

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

The deflection center corresponding coordinates of each beam indicate the center position coordinates corresponding to each aperture (each primary electron beam), and 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 Figure 2(b), where there are four beams in each stage as shown in Figure 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 Figure 10, and patterns with known spacing dimensions are created according to the flowchart of Figure 9 described above. Images of these patterns are then 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 position, and Figure 11(b) shows an example of the positional relationship of the laser interferometer 31 for measuring rotation.

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

Interferometer Y1 is positioned as shown in the figure to enable precise measurement of the distance in the Y direction of stage 9, and a mirror is placed on the stage side.

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

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

Interferometers Y1 and Y2 are positioned as shown in the figure to allow precise measurement of the distance between the positions of stage 9 in the Y direction and to allow actual measurement of the rotation angle, and a mirror is placed on the stage side.

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 is an explanatory diagram of stage tilt correction according to the present invention. This shows an example of the stage 9 in Figure 1, which is supported at three points: stage Z1 (conical), stage Z2 (conical), and stage Z3 (flat). Each stage, which is supported at three points, contracts by applying a voltage to the piezoelectric element, allowing it to be externally adjusted to any desired distance.

In more detail, Figure 12 is composed of three independent piezoelectric actuators with the same performance, arranged to provide three-point support relative to 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 sphere with a non-slip surface can be used, or a conical metal or plastic material can be used. It is desirable to treat the surface to achieve as high a coefficient of friction as possible. At least one of the three support parts is conductive to form the circuit necessary to apply a bias voltage to the sample.

It has three independent control circuits to drive the three piezoelectric actuators, and the signals from height sensors 151 and 152 are processed by a PC, and the processing results are used to issue commands from the PC, etc., allowing the desired distance and height to be changed. Each actuator has a built-in displacement sensor, such as a capacitance sensor, which monitors the actual amount of displacement and provides feedback, allowing the nonlinearity of the piezoelectric elements to be corrected. Positioning accuracy can be achieved on the order of nanometers (see Figure 190, described below).

The stroke required for Z-axis control ranges from a few microns to approximately 1000 microns. Supporting the sample on the Z-axis stage requires high rigidity to prevent it from vibrating. 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, resulting in a high resonance frequency of several hundred Hz or more, which prevents unnecessary vibration. This means that 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 representation of the stage without meandering, Figure 13(b) shows a schematic representation of the stage with left-side meandering, and Figure 13(c) shows a schematic representation of the stage with right-side meandering. Here, the vertical direction indicates the stage movement direction, and the horizontal direction indicates the electron beam scanning direction.

Figure 13(a) shows a schematic diagram of the stage 9 not meandering in the direction of stage movement in a fixed direction (vertical direction), indicating that no correction is required.

In Figure 13(b), the stage 9 is shown schematically as meandering to the left relative to the fixed (vertical) stage movement direction, indicating that correction is necessary. In this case, the meandering is corrected to the right (see the stage deviation in Figure 3).

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

XY stages generally combine direct motors, servo motors, stepping motors, ultrasonic motors, linear motors, etc., which have a large driving force and are capable of high-speed movements of microns or more, with piezoelectric actuators and brakes that allow for fine movements of the order of nanometers or less.

By combining independent X-axis and Y-axis movement mechanisms, the XY stage has the freedom of movement in the X and Y directions and the ability to move 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 only move in the Y axis direction and not in the X direction, but as shown in Figure 13, in an actual stage, movement also occurs in the X direction.

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

Figure 14 shows an explanatory diagram of the stage meandering correction 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 Figure 14(a), each image is a schematic representation of the image of the rectangular area shown snaked left and right as the stage snaked.

In Figure 14(b), each image shows a schematic representation of the rectangular area image after correction for each stage meander. 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 Figure 13, if there is (or is detected to be) meandering of the stage 9 (deviations in the direction perpendicular to the stage movement direction, and also 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 make corrections so that there is no apparent meandering, as shown in Figure 14 (b).

Figure 15 shows an explanatory diagram of stage rotation in 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 direction.

Figure 15(a) shows a schematic diagram of the stage 9 moving in a fixed direction (vertical direction) without any horizontal rotation, indicating that no correction is required.

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

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

Generally, stage 9 is mounted on two rails symmetrically, with the movable part sandwiched between them. The characteristics of the left and right rails are not necessarily the same, and friction is also different, so when stage 9 moves 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 within the XY plane. This is corrected by the present invention.

Figure 16 shows an explanatory diagram of stage rotation correction according to 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 Figure 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 Figure 16(b), each image is a schematic representation of the image of the rectangular area shown after correction 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 (or is detected to be) horizontal rotation of the 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 correct so that there is no apparent 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 representation of the state before correction, and Figure 17(b) shows a schematic representation 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 Figure 17(a), the convex curve shown is an example of a curve before correction, and is a schematic representation of how the height Z coordinate 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 Figure 3)).

In Figure 17(b), the curve shown is an example of a post-correction curve, showing the state after the height Z of the stage 9 has been corrected. This means that if the coordinate of height Z changes when the stage 9 moves at a constant speed from coordinate Y1 to coordinate Y2 (see stage height in Figure 3), as in the convex curve shown in Figure 17(a) before correction, the height Z is automatically corrected in accordance with the height Z detected in real time.

As described above, when the stage 9 moves in a fixed direction at a fixed speed, its height Z can be detected in real time and the stage height can be automatically corrected by the amount of the change in height (see Figure 18, described below).

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) when the stage 9 moves in the Z direction, without performing the Z direction correction of the stage 9 described above in Figure 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 stage movement.

In Figure 18(a), the images of the front, center, and rear end without correction shown in the figure are a schematic representation of the blurring of the images that occurs due to the change in height Z that occurs as the stage 9 moves (from coordinate Y1 (front end) to coordinate Y2 (rear end) in Figure 17).

In Figure 18 (b), the images of the front, center, and rear end with correction shown are schematic representations of images (without blur) after height correction has been performed in response to the change in height Z that occurs as the stage 9 moves (from coordinate Y1 (front end) to coordinate Y2 (rear end) in Figure 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 uncorrected image in Figure 18(a), thereby automatically correcting it to the corrected image in Figure 17(b).

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

In Figure 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.

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

The sample holder 52 holds the sample 8.

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

With the above structure, as explained in Figure 12, it is possible to automatically correct the height and tilt 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.

1 is a structural diagram of an embodiment of the present invention; 1 shows 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. 10 is an example of creating a multi-beam according to the present invention. FIG. 1 is an explanatory diagram of multi-beam detection according to the present invention. FIG. 1 is a diagram (first row) illustrating multi-beam image acquisition and synthesis according to the present invention. 1 is a diagram (two rows) illustrating 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. 10 is a flowchart illustrating the operation of the present invention (obtaining the center coordinates of a multi-beam image). 1 is a diagram illustrating the operation of the present invention (multi-beam scanning direction and stage movement direction). 10A and 10B are explanatory diagrams of the operation of the present invention (measurement of deviation amount and rotation amount of stage movement). 10A and 10B are explanatory diagrams illustrating tilt correction of a stage according to the present invention. FIG. 10 is an explanatory diagram of the meandering of the stage of the present invention. 10A and 10B are explanatory diagrams illustrating meandering correction of a stage according to the present invention. FIG. 10 is an explanatory diagram of the rotation of the stage of the present invention. FIG. 10 is an explanatory diagram of rotation correction of the stage according to the present invention. FIG. 10 is an explanatory diagram of stage tilt correction according to the present invention. 10A and 10B are explanatory diagrams illustrating height correction of a stage according to the present invention. FIG. 10 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: Return deflector 14: Electronic detector 52: Sample holder 53, 54, 55; Piezoelectric elements 151, 152: Height sensor

Claims (11)

1. A multi-beam imaging device for generating an image by scanning a plurality of primary electron beams onto a sample, comprising:
a multiple beam generating device for generating multiple primary electron beams;
a beam splitter that causes the multiple primary electron beams generated by the multiple beam generating device to be incident on the axis of an objective lens and causes the secondary electron beam emitted from the sample to be incident on the 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 that forms an image on an electron detector of the secondary electron beam incident on the axis of the projection lens by the beam splitter;
a stage for continuously moving the sample;
a sample height measuring means for measuring the height of the sample in real time;
Based on the height of the sample output from the sample height measuring means, while continuously moving the stage, the stage is supported at three points by three independent piezo actuators and kept horizontal in real time, and the multiple primary electron beams generated by the multiple beam generating device are made incident on the axis of the objective lens by the beam splitter, the objective lens irradiates the sample with the narrowed primary electron beam and scans it by the deflection system, and secondary electrons emitted from the sample are made incident on the axis of the projection lens by the beam splitter, and the projection lens forms an image on an electron detector, outputting image information of the multiple electron beams.
A multi-beam image generating device characterized by: The multi-beam image generating device described in claim 1, characterized in that the sample is moved at a constant speed and in a constant direction. A multi-beam image generating device according to any one of claims 1 and 2, characterized in that it is equipped with a synthesis means for synthesizing the image information of the output multiple electron beams into a single 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 corrected based on this, or electromagnetically corrected, to perform automatic focusing. A 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 a single primary electron beam onto an aperture with multiple holes. A multi-beam image generating device as described in any one of claims 1 to 5, characterized in that the beam splitter has an electrostatic deflector in the first stage on the primary electron incident side and an electromagnetic deflector in the second stage, and the second stage electromagnetic deflector deflects and separates the secondary electron beam emitted from the sample in the opposite direction to the primary electron beam. A multi-beam image generating device according to any one of claims 1 to 6, characterized in that a negative retarding voltage is applied to the sample, thereby reducing the energy of the primary electron beam irradiated onto and scanning the sample while maintaining high resolution, thereby reducing damage to the sample. A 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 sample with multiple primary electron beams to generate an image, comprising:
a multiple beam generating device for generating multiple primary electron beams;
a beam splitter that causes the multiple primary electron beams generated by the multiple beam generating device to be incident on the axis of an objective lens and causes the secondary electron beam emitted from the sample to be incident on the 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 that forms an image on an electron detector of the secondary electron beam incident on the axis of the projection lens by the beam splitter;
a stage for continuously moving the sample;
a sample height measuring means for measuring the height of the sample in real time;
Based on the height of the sample output from the sample height measuring means, while continuously moving the stage, the stage is supported at three points by three independent piezo actuators and maintained horizontally in real time, and in this state, the multiple primary electron beams generated by the multiple beam generating device are made incident on the axis of the objective lens by the beam splitter, the objective lens irradiates the sample with the narrowed primary electron beam and scans it by the deflection system, and secondary electrons emitted from the sample are made incident on the axis of the projection lens by the beam splitter, and the projection lens forms an image on an electron detector, outputting image information of the multiple electron beams.
A multi-beam image generating method comprising: The multi-beam image generation method described in claim 9, characterized in that the sample is moved at a constant speed and in a constant direction. A multi-beam image generation method according to any one of claims 9 to 10, characterized in that it comprises a synthesis means for synthesizing the image information of the output multiple electron beams into a single image.