Multi-beam image generating device and multi-beam image generating method

Abstract

PURPOSE: To acquire image information by irradiating a sample with a plurality of primary electron beams, to synthesize the image information into one image, and to acquire the image at high speed, in a multibeam image generation device and a multibeam image generation method.CONSTITUTION: This device is provided with an interferometer for measuring the position in the moving direction and the position in the orthogonal direction of a sample in real time, a correcting means for correcting the moving amount and the rotating amount of a stage on which the sample is mounted based on the output of the interferometer, and a synthesizing means for irradiating the sample with a plurality of secondary electron beams and synthesizing one image based on acquired image information.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a multi-beam image generating device and a multi-beam image generating method for generating an image by scanning a sample with a plurality of primary electron beams. [Background technology]

[0002] Traditionally, the semiconductor industry's economy has been supported by improvements in device performance and cost benefits brought about by advances in microfabrication technology, famously known as Moore's Law. However, 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 a 4:1 reduction exposure technology, which means that pattern structures formed on the photomask are four times larger than the pattern structures on the silicon wafers where the semiconductor devices are actually made.

[0003] 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.

[0004] To prevent exposure defects, it is necessary to inspect the entire surface of the photomask and correct it to achieve 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 with the times.

[0005] 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.

[0006] 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 impossible to adequately inspect them with the previous 193 nm light.

[0007] 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 the wavelength is so short as 13.5 nm, it is almost entirely absorbed by air, so the inspection system must be evacuated, making it much more complex than conventional systems implemented in air. Furthermore, because there are no optical lenses that can transmit 13.5 nm light, the optical system must be entirely reflective, which is also complex and inefficient. For example, EUV exposure systems using a 13.5 nm wavelength are so inefficient that they can only utilize about 1% of the total light source output.

[0008] 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, making it possible to resolve a pattern of about 40 nm in a single exposure, despite the long wavelength of 193 nm. Using double patterning, it is even possible to create a pattern of about 20 nm.

[0009] On the other hand, EUV light, due to the use of reflective optics, can only achieve a small aperture ratio, such as an MA of 0.33. 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 detecting particles, 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 techniques is reaching its technical limits. Furthermore, while conventional optical systems 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 compared to electron beam systems.

[0010] 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 popular for use in developing new wafer processes.

[0011] 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 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 applied, the minimum beam spot size becomes larger than the optical limit, degrading resolution. In other words, when using a single electron beam, there is a very severe trade-off between resolution and inspection speed, which means that the speed becomes slower as miniaturization progresses, which is a fundamental flaw.

[0012] For example, the maximum inspection speed currently achievable using a single electron beam is only a few hundred megapixels per second. Because photomasks have patterns written over an area roughly 10 cm square, it is necessary to inspect the entire area. For example, to inspect the patterns on state-of-the-art 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 systems can inspect one photomask in approximately two hours, making electron beam systems 100 times slower than conventional systems, making them impractical.

[0013] Meanwhile, in order to improve the speed of electron beam inspection equipment, a method called a multi-electron beam inspection equipment is being researched, in which multiple electron beams are irradiated simultaneously in parallel onto a sample to perform high-speed inspection. 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 this method can achieve faster inspection speeds than when using a single electron beam, while maintaining high resolution without being affected by electrostatic repulsion of the beams.

[0014] 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.

[0015] 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 is only occasionally used by university professors and students to write papers, it is completely unusable for practical use. It must be able to withstand various measurement conditions, measurement targets, and changes in the equipment installation environment, and maintain stable performance over the long term. DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0016] 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 one scan to increase speed. However, this has led to the problem that the stage movement time is dominant and speed cannot be increased.

[0017] Furthermore, there is a problem in that a clear contrast difference due to a difference in sensitivity occurs at the boundary of the scanning area, making it difficult to use as an inspection image.

[0018] Furthermore, with the single-beam system, since 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 2D 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 2D image information to further increase speed, stage rotation, undulation, stage speed fluctuations, height fluctuations, and vibrations that occur during movement can affect 2D image acquisition and reduce image quality.

[0019] Furthermore, simply acquiring an image in the same way as with a conventional single beam results in distorted or skipped images, making it impossible to acquire an accurate image and making it unusable for inspection. [Means for solving the problem]

[0020] In order 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, 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.

[0021] Therefore, the present invention provides a multi-beam image generating device for generating an image by scanning a sample with a plurality of primary electron beams, the device comprising: a multiple beam generating device for generating a plurality of primary electron beams; a beam splitter for deflecting the plurality of 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 for deflecting a secondary electron beam emitted from the sample in two stages in the direction opposite to the primary electron beams to make it incident on the axis of a projection lens; an objective lens for narrowing the primary electron beam that has been deflected in two stages by the beam splitter and is incident on the axis; a deflection system for deflecting the narrowed primary electron beam by the objective lens to scan it on a sample; The system is equipped with a projection lens that focuses the secondary electron beam, which has been deflected two times 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 a 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 of the multiple electron beams.

[0022] In this case, a synthesis means is provided for synthesizing the image information of the outputted multiple electron beams into one image.

[0023] 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.

[0024] Furthermore, the height of the stage is measured in real time and corrected based on this, or electromagnetically corrected, for automatic focusing.

[0025] Furthermore, the multiple beam generating device generates multiple primary electron beams by irradiating one primary electron beam onto an aperture with multiple holes.

[0026] The beam splitter has an electrostatic deflector at the first stage on the primary electron incident side, and an electromagnetic deflector at 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.

[0027] 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 high resolution, thereby reducing damage to the sample.

[0028] In addition, a deflection system for correcting the position of the secondary electron beam is provided before or after the projection lens. [Effects of the Invention]

[0029] The present invention generates multiple primary electron beams and irradiates them onto a sample while the sample is moved, and then separates the multiple secondary electron beams emitted at this time using a beam splitter, detects the image information from each beam using an electron detection device, and combines them into a single image, making it possible to acquire images at high speed.

[0030] Furthermore, by irradiating a sample with multiple primary electron beams and detecting the images of multiple secondary electron beams, the contrast differences at the boundaries were reduced when the images were combined into a single image by overlapping them.

[0031] Furthermore, by acquiring and registering the irradiation positions of multiple primary electron beams on the sample in advance, it is possible to correct the center position of the secondary electron beam image and synthesize a precise image.

[0032] 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, and the amount of movement and rotation of the images of multiple secondary electron beams can be corrected to generate precise image information. Example 1

[0033] FIG. 1 shows a structural diagram of one embodiment of the present invention.

[0034] 1, electron gun 1 is a well-known device for generating 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, or the like.

[0035] The blanking device 2 quickly turns on or off the primary electron beam emitted from the electron gun 1, and deflects the primary electron beam by turning on or off a voltage to pass or block the primary electron beam.

[0036] The illumination lens 3 focuses the electron beam generated and accelerated by the electron gun 1 into a predetermined beam shown in FIG. 4, which will be described later.

[0037] The multi-beam aperture 3-1 splits the irradiated primary electron beam into a plurality of primary electron beams (for example, 100 splits).

[0038] The objective aperture 4 is used to pass the central portion of each of the multiple primary electron beams, and to narrow each of the passed primary electron beams and irradiate them onto the surface of the sample 8 using the objective lens 6 described below.

[0039] 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 on the upper stage and an electromagnetic deflector 5-2 on the lower stage. The primary electron beam is deflected to the right by the electrostatic deflector 5-1, and to the left by the electromagnetic deflector 5-2, as shown in Figure 1, and is deflected back onto the axis of the objective lens 6, which then focuses the beam into a fine image on 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 Figure 1, and to the left by the electrostatic deflector 5-1, and are deflected back onto the axis of the projection lens 12, which then focuses multiple secondary electron beams onto the electron detection device 14, outputting multiple secondary electron images (secondary electron signals).

[0040] The electrostatic deflector 5-1 is a deflector that constitutes the beam splitter 5 and is closer to the electron gun 1, and is an electrostatic deflector in this case.

[0041] The electromagnetic deflector 5-2 is a deflector that constitutes the beam splitter 5 and is located on the side farther from the electron gun 1, and is an electromagnetic deflector in this case.

[0042] The objective lens 6 narrows the primary electron beams and irradiates them onto the sample 8 .

[0043] The deflection device 7 scans a plurality of primary electron beams across the sample 8, and typically scans the sample 8 at a constant speed in a perpendicular direction when the stage 9 is moved at a constant speed in a constant direction. Note that planar scanning (XY scanning) is also possible in addition to scanning in a constant direction (constant scanning in X, Y, or any arbitrary direction).

[0044] The sample 8 is a specimen such as a mask or wafer, from which multiple images are acquired and synthesized into one image.

[0045] The mirror 8-1 is a reflecting mirror for measuring the position in real time using a laser interferometer.

[0046] The stage (XYZθ stage) 9 is a stage that can mount a sample and move in XYZ and also θ (rotation), and is configured so that XYZ and θ can be measured and recorded in real time using an interferometer not shown.

[0047] The vacuum chamber 10 is a container that can accommodate the sample 8, the stage 9, etc. and can be evacuated.

[0048] The vacuum pump 10-1 is an oil-free pump that evacuates the inside of the vacuum chamber 10 to a vacuum.

[0049] The alignment 11 aligns the axes of a plurality of secondary electron beams deflected onto the axis of the projection lens 12 by the electrostatic deflector 5 - 1 that constitutes the beam splitter 5 .

[0050] The projection lens 12 forms an image of the multiple secondary electron beams emitted from the sample 8 onto the detection surface of the electron detection device 14 .

[0051] The deflector 13 corrects (returns) the multiple secondary electron beams emitted when the multiple primary electron beams are narrowed and scanned on the sample 8 so that they remain within a predetermined area on the detection surface of the electron detection device 14.

[0052] The electron detector 14 detects each of the multiple secondary electron beams emitted from the sample 8. For example, an avalanche photodiode, a CCD, a CMOS sensor, or a TDI camera can be used. The electrons may be first collided with a scintillator to be converted into light, and then detected by the device described above, or the electrons may be directly incident on the 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 predetermined area on the detection surface.

[0053] 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 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 in a direction perpendicular to the direction of movement by the deflection device 7, 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). The secondary electrons emitted in (5)(4) travel in a spiral in the opposite direction along 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 alignment 11 as necessary on the axis of projection lens 12, the multiple secondary electron beams emitted from sample 8 are imaged on electron detection device 14 and irradiated onto the imaging area of ​​each of the multiple secondary electron beams of electron detection device 14. If any of the beams goes outside the imaging area, a voltage (or current) is supplied to return deflector 13 in synchronization with the scanning (deflection) of the multiple primary electron beams on sample 8 to correct the beam so that it fits within the imaging area. Then, secondary electron images (secondary electron signals) detected by each of the multiple secondary electron beams are output from electron detection device 14.

[0054] As described above, a plurality of primary electron beams are generated, which are 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 sample 8 is scanned with the plurality of primary electron beams in perpendicular directions, thereby repeatedly scanning a strip-shaped area with the plurality of primary electron beams. The plurality of secondary electron beams emitted at this time are then separated by the beam splitter 5, and the plurality of 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 plurality of secondary electron beams.

[0055] 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 already shown in Figure 1. Note that although the holes are shown in Figure 2 as a schematic rectangle, in practice, circular holes are preferable.

[0056] FIG. 2(a) shows an example of one row, FIG. 2(b) shows an example of two rows, FIG. 3(c) shows an example of two-row staggered, and FIG. 3(d) shows an example of nine-row staggered.

[0057] Figure 2(a) shows an example of one stage. This is a schematic diagram of an example in which holes (round shapes are preferable in practice) as shown 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.

[0058] Figure 2(b) shows an example of a two-stage configuration. 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 in a direction that coincides with the scanning direction of the primary electron beam. For example, if 100 holes are arranged in two stages, the second stage scan will start after the first stage with a delay equivalent to the difference in distance between the first and second stages (the distance obtained by dividing the difference in distance by the reduction ratio of the objective lens 6). This means that two secondary electron images can be acquired in one full scan, and a secondary electron image (secondary electron signal) with double the signal strength can be acquired, or a secondary electron image can be acquired at twice the speed by reducing the signal strength to one, thereby halving the time required to acquire the secondary electron image.

[0059] Figure 2(c) shows an example of a two-stage staggered arrangement. This is a schematic diagram of an example in which holes (round holes are preferable in practice) as shown in the aperture of the multi-beam aperture 3-1 in Figure 1 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 will begin after the first stage, with a delay 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 means that two secondary electron images can be acquired in one full scan, and secondary electron images with double the signal strength can be acquired, or secondary electron images can be acquired at twice the speed if the signal strength is reduced to one, thereby halving the time required to acquire the secondary electron images.

[0060] Figure 2(d) shows an example of a nine-stage staggered arrangement. This is a schematic illustration of an example in which holes (round shapes are preferable in practice) as shown are provided in the aperture of the multi-beam aperture 3-1 in Figure 1 in a staggered pattern of nine stages in the direction that coincides with the scanning direction of the primary electron beam. For example, if nine stages are provided in a staggered pattern 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.

[0061] Each multi-beam aperture 3-1 in Figures 2(a) to 2(d) may be provided with a function to independently turn on / off each primary electron beam, so that it is possible to control only the electron beam at an arbitrary position selected from all the multi-beams to reach the sample, without having to prepare a large number of apertures with physically different arrangements as shown in the figure.

[0062] Fig. 3 shows an example of a data table of the present invention. As already described and will be described later, Fig. 3 shows the stage displacement, stage rotation, and stage height recorded in association with the stage position when the stage 9 is scanned in a certain direction, after measuring the XYZ position, rotation θ, and other parameters of the stage 9 carrying the sample 8 (e.g., a mask) in real time using a laser interferometer based on the structure of Fig. 1.

[0063] In Figure 3, the stage position indicates the position when the XYZθ stage (hereinafter referred to as the 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.

[0064] The stage deviation is the deviation in the stage position (deviation from the ideal position), and is a recorded value measured in real time by a laser interferometer (described later).

[0065] The stage rotation amount is the amount of rotation at the stage position (amount of rotation θ from an ideal no rotation), and is the amount of stage rotation measured in real time by a laser interferometer and recorded (described later).

[0066] 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 later).

[0067] 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 of the stage 9 from the ideal values ​​(stage deviations (XY)), the stage rotation amount θ, and the stage height Z). Then, by correcting the position of the stage 9 or correcting the acquired images in real time based on the recorded deviations, it is possible to correct errors associated with the scanning of the stage 9, and to generate a single precise image by combining the images of the multiple secondary electron beams acquired by irradiating the sample with multiple primary electron beams. This will be explained in detail below.

[0068] 4 shows an example of the creation of multi-beams according to the present invention, which is a schematic diagram of an example of the creation of multi-beams using the multi-beam aperture 3-1 of FIG.

[0069] In FIG. 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 of the multi-beam aperture 3-1 as shown in the figure. The multiple primary electron beams (multi-electron beam 3-2) generated after 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 (not shown in FIG. 1) in FIG. 4. Here, the sample 8 moves in a certain direction (here, perpendicular to the paper surface) as the stage moves, and the multi-electron beam 3-2 (six primary electron beams) are scanned in a linear fashion in the left-right direction of 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 (FIG. 1), obtaining six sets of secondary electron images. These are then combined into a single image (described below), enabling the secondary electron image of the sample 8 to be generated.

[0070] 5 shows an explanatory diagram of the multi-beam detection of the present invention, which shows a detailed explanatory diagram of the projection lens 12, the deflector 13, and the electron detector 14 of FIG.

[0071] In Figure 5, multiple secondary electron beams emitted from sample 8 are split by beam splitter 5 and incident from top to bottom in Figure 4, and are then imaged by projection lens 12 on the detection surface of electron detection device 14. At this time, there is no problem with the imaging area where the multiple secondary electron beams are imaged if they are within their own imaging area, but if they extend beyond other areas, they will not be detected and the secondary image will be missing. To prevent this, a deflection deflector 13 synchronizes with the scanning of the primary electron beam on sample 8 (scanning by deflection of multiple primary electron beams by deflection device 7) and corrects and deflects the beam so that it falls within a predetermined imaging area, thereby correcting it to ensure that it falls within its own imaging area.

[0072] As a result of the above, 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.

[0073] FIG. 6 shows an explanatory diagram (first stage) of multi-beam image acquisition and synthesis according to the present invention.

[0074] 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 stage (one stage 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) a sample 8 in a fixed direction at a constant speed using a stage 9, while repeatedly scanning the four primary electron beams in the direction perpendicular to the direction. 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 (for example, overlapping by about 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. Therefore, using the position information obtained from the laser interferometer (see Figure 3) and pattern matching, the positional relationship between adjacent swaths can be corrected to create a single large image (see Figure 6(b)).

[0075] 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). In Figure 6(b), overlaps 1, 2, and 3 (e.g., approximately 10%) are used, and the composite image is based on the various shear amounts corresponding to the stage positions in Figure 3. Here, the overlaps 1, 2, and 3 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 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, it is not necessary to combine the images into a single image.

[0076] As a result of the above, by repeatedly scanning the sample 9 using the single-stage primary electron beam of (a) in Figure 2 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 ((a) in Figure 6) shown in swaths 1, 2, 3, and 4, and then to generate a single secondary electron image ((b) in Figure 6) by combining these.

[0077] FIG. 7 shows an explanatory diagram (two rows) of multi-beam image acquisition and synthesis according to the present invention.

[0078] Fig. 7(a) shows an example of an image before synthesis. This is for the case where the number of primary electron beams in Fig. 2(b) is two (two in the direction perpendicular to the stage movement (scanning) direction), and Fig. 6(a) shows a schematic representation of the situation in which four two-stage primary electron beams are used, and sample 8 is moved (scanned) at a constant speed in a fixed direction by stage 9, while the four two-stage primary electron beams are repeatedly scanned in the direction perpendicular to the direction, and the four two-stage secondary electron beams emitted from sample 8 at this time are each imaged on electron detection device 14 by projection lens 12 in Fig. 1, and the four two-stage secondary electron images are generated in four strip-shaped swaths 1, 2, 3, and 4 shown in the figure, with scanning starting from the left end of the scanning start point to generate a first-stage secondary electron image, and then a short time later, a second-stage secondary electron image is generated by overlapping and adding them. 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 by the second-stage primary electron beam (four primary electron beams in Figure 7(a)) a short time later. As shown in the figure, 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%) by the primary electron beams, as shown in the figure 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)).

[0079] 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) of swaths 1, 2, 3, and 4 in Figure 7(a). In Figure 7(b), overlaps 1, 2, and 3 (e.g., approximately 10%) are used, and the composite image is based on the various shear amounts corresponding to the stage positions in Figure 3. Here, the overlaps 1, 2, and 3 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 swaths (1, 2, 3, and 4) in two rows. 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 span swaths 1, 2, 3, and 4, inspection can be performed using the area of ​​one of the swaths; therefore, it is not necessary to combine the images into a single image.

[0080] As a result of the above, by repeatedly scanning the sample 9 using the two-stage primary electron beams of 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.

[0081] FIG. 8 shows an explanatory diagram (staggered) of multi-beam image acquisition and synthesis according to the present invention.

[0082] 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) a sample 8 at a constant speed in a fixed direction using a stage 9, the four two-stage staggered primary electron beams are repeatedly scanned in a direction perpendicular to the moving direction. 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 generated in a manner that starts scanning from the left end of the scanning start point and generates a first-stage secondary electron image, and then a short time later, the second-stage staggered secondary electron image is overlapped and added 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 by a short delay with 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%) by the primary electron beams, as shown in the figure, 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 8(b)).

[0083] Figure 8(b) shows an example of a composite image. This is a single image created by combining four staggered, two-stage secondary electron images (overlap-added images) of swaths 1, 2, 3, and 4 in Figure 8(a). In Figure 8(b), overlaps 1, 2, and 3 (e.g., approximately 10%) are used, and the images are combined into a single image based on the various shear amounts corresponding to the stage positions in Figure 3. 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 way 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 necessarily necessary to combine them into a single image.

[0084] 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 a 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 to generate a single secondary electron image (Figure 8(b)) by combining these.

[0085] 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 overlapping area with the swaths created by adjacent primary electron beams. If there is an overlapping area, regardless of the arrangement, it is possible to precisely determine the relative positions of the swaths, allowing them to be combined into a single image. However, this has many disadvantages, such as the complexity of processing the added image, 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.

[0086] FIG. 9 is a flowchart illustrating the operation of the present invention (acquiring the center coordinates of a multi-beam image).

[0087] 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 ideal. 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.

[0088] S2 acquires images 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 Figure 1 is stopped, and acquiring images of the pattern.

[0089] S3 compares the acquired image with the pattern of the interval dimension positions.

[0090] S4 calculates the central coordinates of each electron beam scan. S3 and S4 compare the image acquired in S2 with the reference sample image or design data using pattern matching or the like to calculate the deviation of 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.

[0091] As a result of the above, it becomes possible to actually measure the scanning center coordinates (see FIG. 10 described later) of each of the multiple primary electron beams scanning the surface of the sample 8 in FIG.

[0092] FIG. 10 is a diagram illustrating the operation of the present invention (multi-beam scanning direction and stage movement direction).

[0093] In FIG. 10, the electron beam scanning direction is the direction in which the multiple primary electron beams in FIG. 1 one-dimensionally scan the surface of the sample 8 here.

[0094] The stage movement direction (constant speed) is the direction in which the stage 9 carrying the sample 8 in FIG. 1 scans (moves) in a constant direction at a constant speed.

[0095] The first stage aperture is the first stage aperture (corresponding to the primary electron beam) in the two-stage case of FIG. 2(b) described above.

[0096] The second stage aperture is the second stage aperture (corresponding to the primary electron beam) in the two-stage case of FIG. 2(b) described above.

[0097] 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. 1st 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.

[0098] As described above, in the case of the two-stage secondary electron beams of FIG. 2(b), in the case of two stages with four beams per 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 FIG. 10, and patterns with known spacing dimensions are created according to the flowchart of FIG. 9 described above, and images of these patterns are acquired and compared, thereby making it possible to actually measure and record the deflection center coordinates of the four primary electron beams in each of the two stages.

[0099] FIG. 11 is a diagram illustrating the operation of the present invention (measurement of the amount of deviation and rotation of the stage movement).

[0100] FIG. 11(a) shows an example of the positional relationship of the laser interferometer 31 for measuring XY positions, and FIG. 11(b) shows an example of the positional relationship of the laser interferometer 31 for measuring rotation.

[0101] In FIG. 11(a), the interferometer X1 is arranged as shown in the figure so that the distance of the position of the stage 9 in the X direction can be measured with precision, and a mirror is arranged on the stage side.

[0102] The interferometer Y1 is arranged as shown in the figure so that the distance of the position of the stage 9 in the Y direction can be measured with precision, and a mirror is also arranged on the stage side.

[0103] As described above, by arranging the interferometers X1 and Y1, it becomes possible to precisely measure and record the distance (position) of the stage 9 in the X and Y directions in real time (see FIG. 3).

[0104] In FIG. 11(b), the interferometer X1 is arranged 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 arranged on the stage side.

[0105] Interferometers Y1 and Y2 are arranged at a distance from each other so that the rotation angle can be measured accurately, and a mirror is arranged on the stage side, as shown in the figure, so that the distance between the positions of the stage 9 in the Y direction can be measured accurately.

[0106] As described above, by arranging the interferometers X1, Y1, and Y2, it becomes possible to precisely measure the rotation of the stage 9 in real time (see FIG. 3).

[0107] 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.

[0108] More specifically, FIG. 12 is composed of three independent piezo actuators with the same performance, and is arranged so as to provide three-point support with respect to the center of the sample.

[0109] 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 can be used. It is desirable to treat the surface to have as large a coefficient of friction as possible. At least one of the three supports is conductive to form the circuit necessary to apply a bias voltage to the sample.

[0110] It has three independent control circuits to drive the three piezo actuators, and the signals from height sensors 151 and 152 are processed by a PC, and the height can be changed to the desired distance by issuing a command from the PC using the processed results. 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 piezo element to be corrected. Positioning accuracy can be achieved on the order of nanometers (see Figure 190 below).

[0111] 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 and includes 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 allows even heavy samples, such as photomasks, weighing nearly 1 kg, to be kept horizontal in an instant.

[0112] FIG. 13 is an explanatory diagram of the meandering of the stage of the present invention.

[0113] 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.

[0114] FIG. 13(a) shows a schematic diagram of the stage 9 not meandering in the direction of stage movement in a fixed direction (vertical direction), and shows a case where no correction is required.

[0115] 13(b), the stage 9 is shown as having a meandering motion to the left relative to the direction of stage movement in a fixed direction (vertical direction), indicating that correction is necessary. In this case, the meandering motion is corrected to the right (see the stage deviation amount in FIG. 3).

[0116] 13(c) shows a schematic diagram of the stage 9 meandering to the right relative to the direction of stage movement in a fixed direction (vertical direction), indicating a case where correction is necessary. In this case, the meandering is corrected to the left (see the stage deviation amount in FIG. 3).

[0117] Generally, XY stages are often made up of a combination of 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, and piezoelectric actuators and brakes, which allow for fine movements on the order of nanometers or less.

[0118] An XY stage has the ability to move to a specified coordinate point with 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. For example, suppose you give an XY stage a movement command to move along the Y axis. A perfect stage would only move in the Y axis direction and not in the X direction, but in an actual stage, movement in the X direction also occurs, as shown in Figure 13.

[0119] The guide rails that determine the movement accuracy of the stage 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 of the primary electron beam and defects in the inspection.

[0120] FIG. 14 is an explanatory diagram of the meandering correction of the stage of the present invention.

[0121] 14(a) shows a schematic example of an image before correction, and FIG. 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.

[0122] In FIG. 14(a), each image is a schematic representation of the image of the rectangular area shown meandering left and right as the stage meanders.

[0123] In Figure 14(b), each image shows the state after the image of the rectangular area shown has been corrected for each meander of the stage. There is no meandering in the image, and it can be seen that the scanning is performed with the same width in the direction of stage movement.

[0124] As described above and explained in Figure 13, if there is (is detected) meandering of the stage 9 (a deviation in the direction perpendicular to the stage movement direction, and also a deviation 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 a correction so that there is no apparent meandering, as shown in Figure 14(b).

[0125] FIG. 15 is an explanatory diagram of the stage rotation of the present invention.

[0126] 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.

[0127] FIG. 15(a) shows a schematic diagram of the stage 9 when there is no rotation in the horizontal direction relative to the stage movement direction in a fixed direction (vertical direction), and shows a case where no correction is required.

[0128] In Figure 15(b), the stage 9 is shown as being rotated to the right in the horizontal direction 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).

[0129] In Figure 15(c), the stage 9 is shown as being rotated to the left in the horizontal direction 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).

[0130] Generally, the 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 the friction is also different, so when the stage 9 moves along the rails, the amount of movement differs between the left and right rails. As a result, the movable part of the stage 9 rotates slightly within the XY plane. This is corrected in the present invention.

[0131] FIG. 16 is an explanatory diagram of the stage rotation correction of the present invention.

[0132] 16(a) shows a schematic example of an image before correction, and FIG. 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.

[0133] In FIG. 16(a), each image is a schematic representation of the image in the rectangular area rotating left or right with each horizontal rotation of the stage.

[0134] In Figure 16(b), each image is a schematic representation of the rectangular area 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.

[0135] As described above and explained in Figure 15, if there is (is detected) 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 make a correction so that there is no apparent horizontal rotation relative to the stage movement direction, as shown in Figure 16 (b).

[0136] FIG. 17 is an explanatory diagram of stage tilt correction according to the present invention (height control and automatic leveling by the Z stage).

[0137] 17(a) shows a schematic diagram of the state before correction, and FIG. 17(b) shows a schematic diagram of the state after correction, where the horizontal axis represents the stage movement direction Y1 to Y2, and the vertical axis represents the height Z at that time.

[0138] In Figure 17(a), the convex curve shown is an example of a curve before correction, and is a schematic representation 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 is clear that the height Z changes in a convex shape (actually measured (see the stage height in Figure 3)).

[0139] In (b) of Figure 17, 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. Like the convex curve shown in (a) of Figure 17 before correction, if the coordinate of the height Z changes when the stage 9 moves from coordinate Y1 to coordinate Y2 at a constant speed (see the stage height in Figure 3), the height Z is automatically corrected in accordance with the height Z detected in real time.

[0140] 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 height of the stage can be automatically corrected by the amount of the height change (see FIG. 18 described later).

[0141] Furthermore, 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) without performing the Z-directional correction of the stage 9 described above in Figure 17 when the stage 9 moves in the Z direction.

[0142] FIG. 18 is an explanatory diagram of the stage height correction of the present invention.

[0143] 18(a) shows a schematic diagram of the state without correction, and FIG. 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.

[0144] In (a) of FIG. 18, the images of the front, center, and rear end portions without correction shown in the figure 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 (front end) to coordinate Y2 (rear end) in FIG. 17).

[0145] In (b) of FIG. 18, the images of the front, center, and rear end portions with the illustrated correction are schematic representations of images (without blur) after height correction has been performed in accordance with the change in height Z that occurs with the movement of the stage 9 (from coordinate Y1 (front end) to coordinate Y2 (rear end) in FIG. 17).

[0146] As described above, it is possible to detect the height Z in real time for the blurred image without correction in (a) of Figure 18, automatically correct the height of the stage 9, and automatically correct it to the corrected image in (b) of Figure 17.

[0147] 19 is an explanatory diagram of sample height and tilt correction according to the present invention, showing an example of a structural diagram of an embodiment in which the stage shown in FIG. 17 is incorporated into the previously described FIG.

[0148] In FIG. 19, a primary electron beam 1-1 represents a plurality of primary electron beams.

[0149] The secondary electron beam 1-2 represents a plurality of secondary electron beams emitted when the sample 51 is irradiated with the plurality of primary electron beams 1-1.

[0150] The height sensors 151 and 152 are devices that measure and output the height of the sample 51 in real time, and are laser interferometers or the like.

[0151] The sample holder 52 holds the sample 8 .

[0152] 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 described above, and support the sample holder 52 at three points.

[0153] With the above structure, as explained in Figure 12, it is possible to automatically correct the height and tilt of 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 sample holder 52 at three points. [Brief explanation of the drawings]

[0154] [Figure 1] FIG. 1 is a structural diagram of an embodiment of the present invention. [Figure 2] 1 shows an example of a type of multi-beam array according to the present invention. [Figure 3] 1 is an example of a data table according to the present invention. [Figure 4] 10 is an example of creating a multi-beam according to the present invention. [Figure 5] FIG. 1 is an explanatory diagram of multi-beam detection according to the present invention. [Figure 6] FIG. 1 is a diagram (first row) illustrating multi-beam image acquisition and synthesis according to the present invention. [Figure 7] FIG. 1 is a diagram (two rows) illustrating multi-beam image acquisition and synthesis according to the present invention. [Figure 8] FIG. 1 is an explanatory diagram (staggered) of multi-beam image acquisition and synthesis according to the present invention. [Figure 9] 10 is a flowchart illustrating the operation of the present invention (acquiring the center coordinates of a multi-beam image). [Figure 10] 1 is a diagram illustrating the operation of the present invention (multi-beam scanning direction and stage movement direction). [Figure 11] 10A and 10B are explanatory diagrams of the operation of the present invention (measurement of deviation amount and rotation amount of stage movement). [Figure 12] 10A and 10B are explanatory diagrams illustrating tilt correction of a stage according to the present invention. [Figure 13] FIG. 10 is an explanatory diagram of the meandering of the stage of the present invention. [Figure 14] 10A and 10B are explanatory diagrams illustrating meandering correction of a stage according to the present invention. [Figure 15] FIG. 10 is an explanatory diagram of the rotation of the stage of the present invention. [Figure 16] FIG. 10 is an explanatory diagram of rotation correction of the stage according to the present invention. [Figure 17] FIG. 10 is an explanatory diagram of stage tilt correction according to the present invention. [Figure 18] 10A and 10B are explanatory diagrams illustrating height correction of a stage according to the present invention. [Figure 19] FIG. 10 is an explanatory diagram of sample height and tilt correction according to the present invention. [Explanation of symbols]

[0155] 1: Electron gun 2: Blanking device 3: Lighting 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: Swing-back deflector 14: Electronic detection device 52: Sample holder 53, 54, 55; Piezoelectric elements 151, 152: Height sensor

Claims

1. 1. A multi-beam imaging device that irradiates a sample with a plurality of primary electron beams to acquire image information, an interferometer for measuring the position of the sample in the direction of movement and the position perpendicular to the direction of movement in real time; a correction means for correcting the amount of movement and rotation of a stage carrying the sample based on the output of the interferometer; a synthesizing means for irradiating the sample with a plurality of secondary electron beams and synthesizing the beams into a single image based on the acquired image information; A multi-beam image generating device comprising:

2. 2. The multi-beam image generating device according to claim 1, wherein the correction means has a stage control means that corrects the movement direction and rotation angle of the stage based on the output of the interferometer, and controls the operation of the stage in synchronization with the operation of the combining means.

3. 3. The multi-beam image generating device according to claim 1, wherein the interferometer comprises a plurality of interferometers arranged at different positions on the stage, and calculates the direction of movement and amount of rotation of the stage based on outputs from the plurality of interferometers.

4. 4. The multibeam image generating device according to claim 1, wherein the combining means performs combining by correcting the coordinates of each of the image information in accordance with a correction amount based on the output of the interferometer.

5. 5. A multi-beam image generating device according to claim 1, wherein the correction means corrects the speed of the stage based on the output of the interferometer to control its movement, and corrects the readout timing of the image information in accordance with the amount of speed correction.

6. 1. A multi-beam imaging method for acquiring image information by irradiating a sample with a plurality of primary electron beams, comprising: 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 correction step of correcting the amount of movement and amount of rotation of a stage carrying the sample based on the output of the interferometer; a synthesis step of irradiating the sample with a plurality of secondary electron beams and synthesizing the obtained image information into a single image; A multi-beam image generating method comprising:

Images