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

Abstract

PURPOSE: To relate to a multi-beam image generating device and a multi-beam image generating method that rapidly acquire images by generating multiple primary electron beams while maintaining a sample in a horizontal position, irradiating the sample with these beams while moving the sample, separating the multiple secondary electron beams with a beam splitter, detecting information on respective images with an electron detection device to synthesize a single image.CONSTITUTION: A multi-beam image generating device includes a multiple beam generating device, a beam splitter, an objective lens, a deflection system, a projection lens, a stage, and height measuring means, and is configured to make multiple primary electron beams incident on the axis of the objective lens via the beam splitter while the stage is maintained horizontal on the basis of the sample height output from the height measuring means, radiate the finely focused primary electron beam and scan with the deflection system, make secondary electrons emitted from the sample incident on the axis of the projection lens via the beam splitter, and form images to output image information of the multiple electron beams.SELECTED DRAWING: Figure 19

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

[0003] The biggest challenge in exposure technology is how accurately the pattern created on the photomask based on the 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] In order to prevent exposure defects, it is necessary to at least inspect the entire surface of the photomask and correct it to the correct state to create a perfect pattern as designed. Since the limit of fine processing is proportional to the wavelength of the light used for exposure, 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 the exposure light source, and for a long time, patterns on photomasks have been inspected using optical mask pattern inspection equipment that uses laser light of 193 nm or the like as illumination light.

[0006] However, since 2019, exposure technology using EUV light with a short wavelength of 13.5 nm has been fully introduced, which has narrowed 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 so-called actinic inspection tools that use a wavelength of 13.5 nm, which is the same wavelength as the exposure wavelength. However, because the wavelength is as short as 13.5 nm, it is almost entirely absorbed by air, so the inside of the inspection tool must be evacuated, which makes it much more complicated than conventional tools that are implemented in the atmosphere. In addition, because there are no optical lenses that can transmit 13.5 nm light, the optical system must be entirely made up of reflective optical systems, which also makes it complicated and inefficient. For example, EUV exposure tools that use a wavelength of 13.5 nm 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, so that a pattern of about 40 nm can be resolved in one exposure despite the long wavelength of 193 nm. By using double patterning, it is even possible to create a pattern of about 20 nm.

[0009] On the other hand, when EUV light is used, only a small aperture ratio such as MA 0.33 can be achieved because of the use of a reflective optical system. Although the wavelength of the light source is one-tenth shorter than that of conventional wavelengths, only a resolution of about 13 nm can be obtained, and the performance improvement is small considering the shorter wavelength. In addition, for example, when the detection target is a particle, the reflected light weakens in proportion to the sixth power of the particle size, and the reflected light strengthens in proportion to the square of the wavelength. In other words, as the particle size becomes smaller, the signal strength rapidly weakens, and the defect detection sensitivity decreases dramatically. Thus, photomask inspection technology using optical technology has reached its technical limit. In addition, conventional devices using optical principles operated in the atmosphere, making them easy to manufacture and operate, but as the wavelength becomes shorter, they are absorbed by air, requiring a large vacuum chamber, which eliminates the advantage of ease of use over electron beam devices.

[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, the throughput is extremely low compared to optical types, so it has not been put to practical use as a primary inspection tool. However, because it can find electrical defects that cannot be found with optical types, it is gradually becoming more popular for use in developing new wafer processes.

[0011] Unlike laser light, electron beams do not have a source with high brightness and small energy dispersion like lasers. Furthermore, because electrons have a negative charge, when they are focused into a small spot using a lens or other device, they electrostatically repel each other. Therefore, when a large current is applied, which is necessary for high-speed inspection, the minimum beam spot size becomes larger than the optical limit, and the resolution deteriorates. In other words, when a single electron beam is used, there is a very severe trade-off between resolution and inspection speed, and so there is a fundamental flaw in that the speed becomes slower as miniaturization progresses.

[0012] For example, currently, the maximum inspection speed that can be achieved using a single electron beam is at best several hundred megapixels per second. Since a photomask has a pattern written in an area of ​​approximately 10 cm square, it is necessary to inspect the entire area. For example, in order to inspect the patterns on the most advanced photomasks at a resolution of 10 nm, which is sufficient to resolve the patterns on the photomasks, it is necessary to acquire 10^14 pixels. For example, acquiring pixels at 100 megapixels per second requires 10^6 seconds. In other words, it takes 277 hours, or more than 10 days. In addition, multiple scans are necessary to obtain an image with an SNR of 10 or more, which is necessary for inspection. Conventional optical photomask inspection equipment can inspect one photomask in about two hours, so the electron beam type is 100 times slower than conventional optical photomask inspection equipment and is therefore not practical.

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

[0014] However, although many companies have developed various types of multi-beam inspection equipment and these are seen as very promising next-generation high-speed inspection equipment, they have not yet achieved the speed and resolution that were initially expected, and they 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 24 hours a day, 365 days a year without malfunction, so high robustness is essential. Unlike scientific equipment, it is completely unusable for practical use if university professors and students use it occasionally to write papers. It is necessary for the equipment to withstand various measurement conditions, measurement targets, and changes in the equipment installation environment, and to maintain stable performance over the long term. DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0016] Conventional high-speed inspection equipment using a single beam system generally uses a continuous stage system, but multi-beam systems that simultaneously acquire two-dimensional images have adopted a step-and-repeat system that increases speed by increasing the area that can be acquired in one scan as much as possible. However, this system has the problem that the stage movement time is dominant and it is not possible to increase speed.

[0017] In addition, 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] In addition, in the case of the single beam method, since there is only one beam, it is easy to correct the irradiation position and the electron beam can be irradiated to the desired position. However, in the case of the multi-beam method, since multiple electron beams are irradiated simultaneously to acquire a 2D image, there is a problem that it is not easy to precisely control the irradiation position of each electron beam to the desired position. Furthermore, if the stage is moved while acquiring 2D image information in order to increase the speed, there is a problem that the stage rotation, undulation, stage speed fluctuation, height fluctuation, vibration, etc. that occur during the movement affect the acquisition of 2D images and reduce the quality of the images.

[0019] Furthermore, simply acquiring an image in the same way as with a conventional single beam results in a distorted or skipped image, 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 the sample while moving the sample, separates the multiple secondary electron beams emitted at this time using a beam splitter, detects the respective image information 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 multi-beam generating device generating a plurality of primary electron beams, a beam splitter that deflects the plurality of primary electron beams generated by the multiple beam generating device in two stages to cause them to be incident on the axis of an objective lens, and also deflects a secondary electron beam emitted from the sample in two stages in the opposite direction to the primary electron beams to cause them to be incident on the axis of a projection lens, an objective lens that narrows down the primary electron beam that has been deflected in two stages by the beam splitter and incident on the axis, a deflection system that deflects the narrowed primary electron beam by the objective lens to scan it on a sample, and a beam splitter that narrows down the primary electron beam that has been deflected in two stages by the beam splitter to scan it on a sample. The system is equipped with a projection lens that focuses the secondary electron beam, which has been deflected in two stages 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 in real time the position of the sample in the direction of movement and its position perpendicular to the direction.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 a finely focused primary electron beam and scans it with a deflection system, and the secondary electrons emitted from the sample are deflected by the beam splitter to the axis of the projection lens, which then focuses the beam on the electron detector to output image information of the multiple electron beams.

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

[0023] In addition, the amount of movement and rotation of the stage is corrected based on the image information of the multiple electron beams output and the real-time position of the sample in the movement direction and perpendicular direction output from the interferometer, or the image information is moved and rotated by an amount corresponding to the amount of movement and rotation of the stage.

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

[0025] Moreover, the multiple beam generating device irradiates one primary electron beam onto an aperture having multiple holes to generate multiple primary electron beams.

[0026] In addition, the beam splitter has an electrostatic deflector in the first stage on the primary electron entrance side, and an electromagnetic deflector in the second stage, and the second stage electromagnetic deflector deflects the secondary electron beam emitted from the sample in the opposite direction to the primary electron beam to separate it.

[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 the 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. Effect of the Invention

[0029] The present invention makes it possible to generate multiple primary electron beams and irradiate 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 for each beam using an electron detection device, and combines them into a single image, thereby enabling high-speed image acquisition.

[0030] In addition, by irradiating a sample with multiple primary electron beams and detecting multiple secondary electron beam images that are then overlapped and synthesized into a single image, it was possible to reduce the occurrence of contrast differences at the boundaries.

[0031] In addition, by acquiring and registering in advance the irradiation positions of multiple primary electron beams on the sample, it is possible to correct the center position of the image of the secondary electron beam 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 movement and rotation amounts 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 known device for generating an electron beam, which generates a primary electron beam accelerated to several hundred V to several tens of KV. The electron gun uses a thermionic electron source such as W or LaB6, a TFE or cold field emitter using ZrO or the like, or a photocathode, and the electron gun chamber is kept at an ultra-high or extremely high vacuum of 10-8 Pa or more by using an ion pump, getter pump, etc.

[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 a voltage on or off to pass or block it.

[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 intended to pass a central portion of each of the multiple primary electron beams and to focus each of the primary electron beams so as to be irradiated onto the surface of a sample 8 by an objective lens 6, which will be described later.

[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 at the top and an electromagnetic deflector 5-2 at the bottom. The primary electron beam is deflected to the right by the electrostatic deflector 5-1 as shown in Fig. 1, and to the left by the electromagnetic deflector 5-2, and is deflected back onto the axis of the objective lens 6, which narrows the beam and forms an 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 Fig. 1, and to the left by the electrostatic deflector 5-1, and are deflected back onto the axis of the projection lens 12, and the projection lens 12 forms an image of multiple secondary electron beams on 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 embodiment.

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

[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 over the sample 8, and typically scans the sample 8 at a constant speed in a perpendicular direction repeatedly when the stage 9 is moved at a constant speed in a constant direction. Note that the deflection device 7 may not only scan in a constant direction (constant scanning in X, Y, or any arbitrary direction), but may also perform planar scanning (XY scanning).

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

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

[0046] The stage (XYZθ stage) 9 is a stage that can mount a sample and move in XYZ and further θ (rotation), and is configured to be able to measure and record XYZ and θ 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 to a vacuum.

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

[0049] The alignment unit 11 aligns the axes of a plurality of secondary electron beams deflected onto the axis of a projection lens 12 by an electrostatic deflector 5 - 1 constituting 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 over the sample 8 so that they remain within a specified area on the detection surface of the electron detection device 14.

[0052] The electron detection device 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 collided with a scintillator to be converted into light and then detected by the aforementioned device, or the electrons may be directly bombarded into the aforementioned device and detected. In any case, it is sufficient to be able to independently detect each of the multiple secondary electron beams that are each imaged within a 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 multiple corresponding primary electron beams. (2) The multiple primary electron beams generated by being split by the beam aperture 3-1 each pass through the center 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 primary electron beams incident on the axis of the objective lens 6 are narrowed by the objective lens 6 and irradiate the surface of the sample 8, while the sample 8 moves in a constant direction at a constant speed and is electrostatically deflected by the deflection device 7 in a direction perpendicular to the moving direction, and the primary electron beams are scanned in a strip shape on the sample 8. As a result, the surface of the sample 8 is scanned with the primary electron beams in a region (strip-shaped region) having a width deflected by the electrostatic deflector 5-1 in the moving direction of the stage 9. At this time, although not shown, a negative retarding voltage is applied to the sample 8, and the energy of the primary electron beams is set to, for example, 1 KV for irradiation (for example, a negative retarding voltage of 14 KV is applied to the energy of the primary electron beams of 15 KV to generate a primary electron beam of 1 KV for irradiation of the sample 8). (4) Secondary electrons, backscattered electrons, light, X-rays, etc. are emitted from the area of ​​multiple primary electron beams scanned in a rectangular shape 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 being corrected by the alignment 11 as necessary on the axis of the projection lens 12, the multiple secondary electron beams emitted from the sample 8 are imaged on the electron detection device 14 and irradiated onto the imaging area of ​​each of the multiple secondary electron beams of the electron detection device 14. If the multiple secondary electron beams go beyond the imaging area, the return deflector 13 synchronizes with the scanning (deflection) of the multiple primary electron beams on the sample 8 and supplies a voltage (or current) to the return deflector 13 to correct the beams so that they fall within the imaging area. Then, the electron detection device 14 outputs secondary electron images (secondary electron signals) that detect each of the multiple secondary electron beams.

[0054] As a result of the above, multiple primary electron beams are generated and narrowed by objective lens 6 via beam splitter 5, and the sample 8 is moved in a fixed direction on stage 9 while the multiple primary electron beams are scanned in a perpendicular direction, repeatedly scanning the sample 8 with the multiple primary electron beams in a rectangular area. The multiple secondary electron beams emitted at this time are then separated via beam splitter 5, and the multiple secondary electron beams are imaged on the respective detection surfaces of electron detection device 14 by projection lens 12, making it possible to output secondary electron images (secondary electron signals) of each of the multiple secondary electron beams.

[0055] Figure 2 shows an example of the type of multi-beam array of the present invention. This shows an example of the type of hole arrangement of the multi-beam aperture 3-1 of Figure 1. Note that, although the holes are shown in Figure 2 as a schematic rectangular shape, in reality, the holes (circular holes) are preferable.

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

[0057] Figure 2(a) shows an example of one stage. This is a schematic diagram of an example in which holes as shown in the figure (in practice, round shapes are preferable) are provided in one stage in the aperture of the multi-beam aperture 3-1 in Figure 1 in the direction that coincides with the scanning direction of the primary electron beam. For example, if 100 holes are provided in one stage, 100 primary electron beams can be generated.

[0058] Fig. 2(b) shows an example of two stages. This is a schematic diagram of an example in which holes (round shapes are preferable in practice) as shown in the figure are provided in two stages in the aperture of the multi-beam aperture 3-1 in Fig. 1 in the direction that coincides with the scanning direction of the primary electron beam. For example, if 100 holes are provided in two stages, the second stage scan starts after the first stage with a delay of a distance equivalent to the distance difference between the first and second stages (the distance obtained by dividing the distance difference by the reduction ratio of the objective lens 6), and two secondary electron images can be obtained in one overall scan, and 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 set to 1, can be obtained, and the acquisition time of the secondary electron image can be reduced by half.

[0059] Fig. 2(c) shows an example of a two-stage staggered arrangement. This is a schematic diagram of an example in which holes (round shapes are preferable in practice) as shown in the figure are provided in the aperture of the multi-beam aperture 3-1 in Fig. 1 in two stages and in a staggered arrangement in the direction coinciding with the scanning direction of the primary electron beam. For example, if 100 holes are provided in a staggered arrangement in two stages, the second stage of staggered scanning starts after the first stage with a delay equivalent to the distance difference between the first and second stages (the distance difference divided by the reduction ratio of the objective lens 6), and two secondary electron images can be obtained in one overall scan, and a secondary electron image with double the signal strength, or a secondary electron image at twice the speed can be obtained by making the signal strength equal to one, thereby reducing the acquisition time of the secondary electron images by half.

[0060] Figure 2(d) shows an example of a nine-stage staggered arrangement. This is a schematic diagram of an example in which holes as shown (in practice, round shapes are preferable) are provided in the aperture of the multi-beam aperture 3-1 in Figure 1 in nine stages and in a staggered pattern 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 in the figure, 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 of the multi-beam apertures 3-1 in Figures 2(a) to 2(d) may be provided with a function for independently turning on and off each primary electron beam, and instead of preparing a large number of apertures with different physical arrangements as shown in the figures, the apertures may be created so that only the electron beam at an arbitrary position selected from all the multi-beams can be controlled to reach the sample.

[0062] Fig. 3 shows an example of a data table of the present invention. As described above and below, Fig. 3 shows the stage displacement amount, stage rotation amount, and stage height recorded in association with the stage position when the stage 9 is scanned in a certain direction, after measuring the position XYZ, rotation θ, etc. of the stage 9 on which the sample 8 (e.g., a mask) is mounted in real time using a laser interferometer in the structure of Fig. 1.

[0063] In FIG. 3, the stage position indicates the position when the XYZθ stage (hereinafter referred to as stage) 9 carrying the sample 8 in FIG. 1 is scanned at a constant speed in a constant direction, and is measured in real time by a laser interferometer (described later). The stage position is measured and recorded in real time at steps (intervals) corresponding to the distance between pixels of the image to be acquired, for example. For example, when an image of 1000 pixels x 1000 pixels is to be acquired for a 100 μm rectangular area, one entry of information (stage position, stage deviation amount, stage rotation amount, stage height) is measured and recorded in real time every 0.1 μm. Furthermore, it is also possible to measure and record in real time every 0.01 μm corresponding to a 10 μm or 1 μm rectangular area, or every 0.001 μm. If the same value occurs consecutively, the difference between the values ​​may be recorded.

[0064] The stage deviation is the deviation in the stage position (deviation from an ideal position), and is a value measured in real time by a laser interferometer and recorded (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 the deviations (stage deviations (XY)), the stage rotation amount θ, and the stage height Z) of the stage 9 from the ideal values ​​by the laser interferometer. Then, by correcting the position of the stage 9 in real time based on the recorded deviations or correcting the acquired image, it is possible to correct errors associated with the scanning of the stage 9 and generate a single precise image by synthesizing the images of the multiple secondary electron beams acquired by irradiating the sample with multiple primary electron beams. This will be described in detail below.

[0068] Fig. 4 shows an example of the creation of multiple beams according to the present invention. Fig. 4 is a schematic diagram showing an example of the creation of multiple beams using the multibeam aperture 3-1 of Fig. 1 described above.

[0069] In FIG. 4, the primary electron beam emitted from the electron gun 1 is projected by the illumination lens 3 so as to irradiate the holes of the multi-beam aperture 3-1 as shown in the figure. The multiple primary electron beams (multi-electron beam 3-2) generated by passing through the multi-beam aperture 3-1 and splitting are narrowed down and irradiated onto the surface of the sample 8 by the objective lens 6 of FIG. 1, not shown in FIG. 4. Here, the sample 8 moves in a certain direction (here, perpendicular to the paper surface) with the stage movement, and the multi-electron beam 3-2 (six primary electron beams) are scanned in a unidirectional manner in the left-right direction of the paper surface. As a result, the surface of the sample 8 is scanned in a strip-like manner by the multi-electron beam 3-2 (six primary electron beams). Then, the six emitted secondary electron beams are detected by the electron detection device 14 of FIG. 1, six sets of secondary electron images are acquired, and these are combined into one (described later), making it possible to generate a secondary electron image of the sample 8.

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

[0071] In Fig. 5, multiple secondary electron beams emitted from the sample 8 are split by the beam splitter 5 and enter from the top to the bottom in Fig. 4, and are imaged by the projection lens 12 on the detection surface of the 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, the deflector 13 synchronizes with the scanning of the primary electron beam on the sample 8 (scanning by deflection of multiple primary electron beams by the deflection device 7) and corrects and deflects the beam so that it falls within a specified imaging area, correcting it so that it falls reliably 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 (1st row) of multi-beam image acquisition and synthesis according to the present invention.

[0074] FIG. 6(a) shows an example of an image before synthesis. This is the case where the number of primary electron beams in FIG. 2(a) is one stage (one stage in the direction perpendicular to the stage movement (scanning) direction), and FIG. 6(a) shows a schematic diagram of a state in which four one-stage primary electron beams are used, a sample 8 is moved (scanned) in a constant direction by a stage 9 at a constant speed, and the four primary electron beams are repeatedly scanned in the direction perpendicular to the direction, and four secondary electron beams emitted from the sample 8 at this time are imaged on the electron detection device 14 by the projection lens 12 in FIG. 1, and the four secondary electron images are generated as four strip-shaped images of swaths 1, 2, 3, and 4 shown in the figure. Here, the four strip-shaped secondary electron images of swaths 1, 2, 3, and 4 are partially overlapped (for example, overlapped by about 10%) by the primary electron beams as shown in the figure as overlaps 1, 2, and 3 in order to be synthesized later. This eliminates scanning omissions and also ensures that a common image exists in adjacent swaths. Using the position information obtained from the laser interferometer (see Figure 3) and pattern matching, etc., the positional relationship between adjacent swaths can be corrected to create a single large image (see Figure 6 (b)).

[0075] FIG. 6B shows an example of an image after synthesis. This is a single image obtained by synthesizing the four secondary electron images of swaths 1, 2, 3, and 4 in FIG. 6A. In FIG. 6B, overlaps 1, 2, and 3 (for example, about 10%) are used, and the images are synthesized into one image based on the various shear amounts corresponding to the stage positions in FIG. 3 described above. Here, the overlaps 1, 2, and 3 areas are scanned twice, so a high SNR can be obtained by the image addition effect, and more accurate alignment can be achieved. For example, by aligning swaths 1, 2, 3, and 4 and synthesizing the images, one large image area is formed from the four independent swaths 1, 2, 3, and 4. The image processed in this way is output as a synthesized image and used as an inspection image. If the area to be inspected is formed without straddling each of swaths 1, 2, 3, and 4, inspection can be realized using the area of ​​one of the swaths, so it is not necessarily necessary to synthesize them into one image.

[0076] As a result of the above, by repeatedly scanning the sample 9 using the single-stage primary electron beam of 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)) as shown in swaths 1, 2, 3, and 4, and to generate a single secondary electron image (Figure 6(b)) 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 the case where the number of primary electron beams in Fig. 2(b) is two stages (two stages in the direction perpendicular to the stage movement (scanning) direction), and Fig. 6(a) shows a schematic diagram of a state in which four two-stage primary electron beams are used, and while moving (scanning) the sample 8 at a constant speed in a constant direction by the stage 9, the four two-stage primary electron beams are repeatedly scanned in the direction perpendicular to the stage 9, and the four two-stage secondary electron beams emitted from the sample 8 at this time are imaged on the electron detection device 14 by the projection lens 12 in Fig. 1, and the four two-stage secondary electron images are generated in four strips of swaths 1, 2, 3, and 4 shown in the figure, with the first stage secondary electron image generated by starting scanning from the left end of the scanning start point, and the second stage secondary electron image generated a little later by overlapping and adding them. In this two-stage case, scanning is started with the first stage primary electron beam in Fig. 2(b) (four primary electron beams in Fig. 7(a)), and then, a little later, scanning is started with the second stage primary electron beam (four primary electron beams in Fig. 7(a)). As shown in the figure, the second stage secondary electron beam becomes an overlap-added secondary electron image, which has the advantage of generating a high SNR. Here, the four rectangular secondary electron images (overlap-added secondary electron images) of swaths 1, 2, 3, and 4 are partially overlapped (for example, overlapped by about 10%) with the primary electron beam, as shown as overlap 1, 2, and 3, in order to be synthesized later. This eliminates scanning omissions and at the same time, common images exist in adjacent swaths, so that the positional relationship of adjacent swaths can be corrected using position information obtained by a laser interferometer (see Fig. 3) and pattern matching, etc., to create one large image (see Fig. 7(b)).

[0079] FIG. 7B shows an example of an image after synthesis. This is a synthesis of four secondary electron images (overlap-added images) of swaths 1, 2, 3, and 4 in FIG. 7A into one image. In FIG. 7B, overlaps 1, 2, and 3 (for example, about 10%) are used, and the images are synthesized into one image based on various shear amounts corresponding to the stage positions in FIG. 3 described above. Here, the overlaps 1, 2, and 3 areas are scanned twice, so a high SNR can be obtained by the image addition effect, and more accurate alignment can be achieved. For example, by aligning swaths 1, 2, 3, and 4 and synthesizing the images, one large image area is formed from four independent swaths 1, 2, 3, and 4 in two stages. The image processed in this way is output as a synthesized image and used as an inspection image. If the area to be inspected is formed without straddling each of swaths 1, 2, 3, and 4, inspection can be realized using the area of ​​one of the swaths, so it is not necessarily necessary to synthesize them into one image.

[0080] As a result of the above, by repeatedly scanning the sample 9 using the two-stage primary electron beam 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 each of the strip-shaped secondary electron images shown in swaths 1, 2, 3, and 4 (Figure 7(a), overlap-added images), and to generate a single secondary electron image by combining these (Figure 7(b)).

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

[0082] Fig. 8(a) shows an example of an image before synthesis. This is an example in which the number of primary electron beams in Fig. 2(c) is arranged in a staggered manner in two stages, and Fig. 8(a) shows a schematic representation of a state in which four staggered (two stages) primary electron beams are used, and while moving (scanning) a sample 8 at a constant speed in a fixed direction by a stage 9, the four staggered primary electron beams are repeatedly scanned in a direction perpendicular to the sample 8, and the four staggered secondary electron beams emitted from the sample 8 at this time are imaged on the electron detection device 14 by the projection lens 12 in Fig. 1. The four staggered secondary electron images are generated in a two-stage staggered manner in four rectangular swaths 1, 2, 3, and 4 shown in the figure, and the first stage secondary electron image is generated by starting scanning from the left end of the scanning start point, and a little later, the secondary electron image for the second stage is overlapped and added downward in the figure. In the case of this two-stage staggered pattern, scanning is started with the first stage primary electron beam in Fig. 2(c) (four primary electron beams in Fig. 8(a)), and then, a little later, scanning is started with the second stage staggered primary electron beam (four primary electron beams in Fig. 8(a) at a slightly lower position). As shown in the figure, the second stage secondary electron beam becomes an overlap-added secondary electron image, which has the advantage of generating a high SNR. Here, the four rectangular secondary electron images (overlap-added secondary electron images) of swaths 1, 2, 3, and 4 are partially overlapped (for example, overlapped by about 10%) with the primary electron beams in order to be synthesized later, as shown as overlap 1, 2, and 3. This eliminates scanning omissions and at the same time allows common images to exist in adjacent swaths, so that the positional relationship of adjacent swaths can be corrected and one large image can be created using position information obtained by a laser interferometer (see Fig. 3) and pattern matching, etc. (see Fig. 8(b)).

[0083] FIG. 8(b) shows an example of the image after synthesis. This is a single image obtained by synthesizing four staggered secondary electron images (overlapped and added images) of swaths 1, 2, 3, and 4 in FIG. 8(a) into one image. In FIG. 8(b), overlaps 1, 2, and 3 (for example, about 10%) are used, and the images are synthesized into one image based on various shear amounts corresponding to the stage positions in FIG. 3 described above. Here, the overlaps 1, 2, and 3 areas are scanned twice, so that a high SNR can be obtained by the image addition effect, and more accurate alignment can be achieved. For example, by aligning swaths 1, 2, 3, and 4 and synthesizing the images, one large image area is formed from four independent swaths 1, 2, 3, and 4 in two stages. The image processed in this way is output as a synthesized image and used as an inspection image. If the area to be inspected is formed without spanning each of swaths 1, 2, 3, and 4, inspection can be achieved using the area of ​​one of the swaths, so it is not necessary to combine them into a single image.

[0084] As a result of the above, by repeatedly scanning the sample 9 using a 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 rectangular 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 by combining these (Figure 8(b)).

[0085] In addition, Fig. 8 shows an example in which the primary electron beams are arranged in an arbitrary position, called a staggered arrangement, but even when the primary electron beams are arranged in an arbitrary position (staggered), alignment of multiple swaths is required to obtain a single final 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, 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 complicated, 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 central coordinates of a multi-beam image).

[0087] In FIG. 9, S1 prepares a pattern with known spacing dimensions. This is a reference sample with precisely known pattern spacing and shape dimensions. A conductive photomask or silicon substrate with the same pattern fabricated in advance is preferable. The pattern size and spacing are measured in advance using a CDSEM or optical measurement device. To simplify the measurement, the electron beam deflection center coordinates are known in advance as design values, so calibration can be easily performed by using a reference sample in which a pattern is located at the designed deflection center coordinates, as shown in FIG. 10 described later. The pattern size is arbitrary, but a pattern that is symmetrical from left to right and up to down is desirable so that the center position can be accurately determined even if process variations occur.

[0088] S2 acquires images while the stage is stopped. This is done by scanning multiple primary electron beams on the substrate with the pattern prepared in S1 while the stage 9 in Fig. 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 a 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 position deviation amount and the design data of the reference sample.

[0091] In this manner, 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) 2nd 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 beam of FIG. 2(b), in the case of two stages with four in each stage as shown in FIG. 10, the deflection center coordinates of the four primary electron beams in each of the two stages generated by the first stage aperture and the second stage aperture are defined as shown in 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 obtained 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.

[0099] FIG. 11 is a diagram illustrating the operation of the present invention (measurement of deviation amount and rotation amount of 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 disposed as shown in the figure so as to be able to precisely measure the distance of the position of the stage 9 in the X direction, and a mirror is disposed on the stage side.

[0102] The interferometer Y1 is disposed as shown in the figure so as to be able to precisely measure the distance of the position of the stage 9 in the Y direction, and a mirror is also disposed 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 disposed as shown in the figure so as to be able to precisely measure the distance of the position of the stage 9 in the X direction, and a mirror is also disposed on the stage side.

[0105] Interferometers Y1 and Y2 are arranged at a distance from each other so that the rotation angle can be actually measured, 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 precisely measured.

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

[0107] Fig. 12 is an explanatory diagram of stage tilt correction of the present invention. This shows an example of stage 9 in Fig. 1 already described, and shows an example of a three-point supported stage: stage Z1 (cone), stage Z2 (cone), and stage Z3 (flat). Each stage with three support points is contracted by applying a voltage to the piezoelectric element, and the structure allows it to be arbitrarily adjusted from the outside to any distance.

[0108] In detail, FIG. 12 is composed of three independent piezoelectric actuators having 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 ​​ball with a non-slip surface treatment or a metal or plastic cone 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 required to apply a bias voltage to the sample.

[0110] It has three independent control circuits to drive three piezoelectric actuators, and the signals from the height sensors 151 and 152 are processed by a PC, and the desired distance height can be changed by issuing a command from the PC using the processed results. Each actuator has a built-in displacement sensor such as a capacitance sensor, and the actual amount of displacement is monitored and fed back, allowing the nonlinearity of the piezoelectric element to be corrected. Positioning accuracy can be achieved on the order of nm (see Figure 190 described later).

[0111] The stroke required for Z-axis control ranges from a few microns to about 1000 microns. The Z-axis stage must also have high rigidity to prevent the sample from vibrating when supported. The support system using a piezoelectric actuator with a displacement magnification mechanism, including the sample holder, combines a high response speed of ms with high mechanical rigidity, and has a high resonance frequency of several hundred Hz or more, preventing unnecessary vibrations. As a result, even heavy samples weighing nearly 1 kg, such as photomasks, can be instantly maintained horizontally.

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

[0113] Fig. 13(a) shows a schematic diagram of the stage without meandering, Fig. 13(b) shows a schematic diagram of the stage with left meandering, and Fig. 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 stage movement direction in a fixed direction (vertical direction), and shows a case where no correction is required.

[0115] In (b) of Fig. 13, the stage 9 is shown to be wobbling to the left with respect to the stage movement direction in a fixed direction (vertical direction), indicating a case in which correction is required. In this case, the wobbling is corrected to the right (see the stage deviation in Fig. 3).

[0116] In (c) of Fig. 13, the stage 9 is shown to be wobbling to the right with respect to the stage movement direction in a fixed direction (vertical direction), showing a case in which correction is necessary. In this case, the wobbling is corrected to the left (see the stage deviation amount in Fig. 3).

[0117] Generally, XY stages often combine direct motors, servo motors, stepping motors, ultrasonic motors, linear motors, etc., which have a large driving force and can perform movements of microns or more at high speed, with piezoelectric actuators and brakes that allow fine movements on the nanometer order or less.

[0118] The XY stage has the freedom of movement in the X and Y directions by combining an X-axis movement mechanism and a Y-axis movement mechanism that are independent of each other, and has the function of moving to a specified coordinate point. For example, suppose you give an XY stage a movement command to move along the Y axis. A perfect stage would not move in the X direction, but only in the Y direction, but in an actual stage, movement also occurs in the X direction, as shown in Figure 13.

[0119] The guide rails that determine the accuracy of stage movement are made of ceramics and other materials, and although they are machined with extremely high precision, there is still a mechanical accuracy error of the order of microns. For example, when the stage moves from (X1,Y1) to (X1,Y2) along the Y axis, the center coordinates of the stage will meander left and right along the X axis during the stage movement. The multi-beam method uses a group of primary electron beams that are arranged in two dimensions with predetermined intervals between each electron beam. If the stage meanders during continuous inspections, the primary electron beam will irradiate different locations 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 meandering correction of the stage of the present invention.

[0121] Fig. 14(a) shows a schematic example of an image before correction, and Fig. 14(b) shows a schematic example of an image after correction, where 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 state in which the image of the illustrated rectangular area meanders left and right with each meander of the stage.

[0123] In Fig. 14(b), each image is a schematic diagram of the state after the image of the rectangular area shown in the figure has been corrected for each meandering of the stage. It can be seen that there is no meandering in the image, and that the image is scanned with the same width in the direction of stage movement.

[0124] As described above with reference to Figure 13, if there is (is detected) meandering of stage 9 (deviation in the direction perpendicular to the stage movement direction, and further 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 stage rotation according to the present invention.

[0126] Fig. 15(a) shows a schematic diagram of the state without horizontal rotation, Fig. 15(b) shows a schematic diagram of the state with horizontal rotation to the right, and Fig. 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 state in which the stage 9 does not rotate in the horizontal direction relative to the stage movement direction in a fixed direction (vertical direction), and shows a case in which no correction is required.

[0128] In (b) of Figure 15, the stage 9 is shown to be rotated to the right in the horizontal direction relative to the stage movement direction in a fixed direction (vertical direction), indicating a case in which correction is required. In this case, the horizontal rotation is corrected to the left (see the stage rotation amount in Figure 3).

[0129] In (c) of Figure 15, the stage 9 is shown to be rotated to the left in the horizontal direction relative to the stage movement in a fixed direction (vertical direction), indicating a case in which correction is required. In this case, the horizontal rotation is corrected to the right (see the stage rotation amount in Figure 3).

[0130] Generally, stage 9 is placed on two rails symmetrically with a movable part in between. The characteristics of the left and right rails are not necessarily the same, and the friction is also different, so when stage 9 is moved along the rails, the amount of movement differs between the left and right rails. As a result, the movable part of stage 9 generates slight rotational vibration within the XY plane. This is corrected in the present invention.

[0131] FIG. 16 is a diagram illustrating the rotation correction of the stage according to the present invention.

[0132] Fig. 16(a) shows a schematic example of an image before correction, and Fig. 16(b) shows a schematic example of an image after correction, where 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 state in which the image in the illustrated rectangular area rotates left or right with each rotation of the stage in the horizontal direction.

[0134] In Fig. 16(b), each image is a schematic diagram of the state after the image of the illustrated rectangular area is corrected for each horizontal rotation of the stage. It can be seen that there is no horizontal rotation of the image, and it is scanned in the same direction as the stage movement.

[0135] As described above in FIG. 15, when there is (is detected) horizontal rotation of stage 9 (a deviation in the rotational direction relative to the stage movement direction), a correction is performed to rotate the stage in the opposite direction (or rotate the detected image) by the amount of this horizontal rotation, making it possible to perform a correction so that there appears to be no horizontal rotation relative to the stage movement direction, as shown in FIG. 16(b).

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

[0137] Fig. 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 moving direction of the stage from Y1 to Y2, and the vertical axis represents the height Z at that time.

[0138] 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 stage 9 moves at a constant speed from coordinate Y1 to coordinate Y2. Here, it is clear that height Z changes in a convex shape (actually measured (see stage height in FIG. 3)).

[0139] In (b) of Fig. 17, the curve shown is an example of a corrected curve, and shows the state after the height Z of the stage 9 has been corrected. Like the convex curve shown in (a) of Fig. 17 before correction, when the coordinate of the height Z changes when the stage 9 moves from the coordinate Y1 to the coordinate Y2 at a constant speed (see the stage height in Fig. 3), the height Z is automatically corrected in response to the height Z detected in real time.

[0140] As described above, when the stage 9 moves in a constant direction at a constant speed, it is possible to detect the height Z in real time and automatically correct the height of the stage by the amount of change in height (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 in the Z direction as described above in FIG. 17 with respect to the movement of the stage 9 in the Z direction.

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

[0143] Fig. 18(a) shows a schematic diagram of a state without correction, and Fig. 18(b) shows a schematic diagram of a 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 FIG. 18(a), the images of the tip, center, and rear end without the illustrated correction are schematic representations of the blurring of the images due to the change in height Z that occurs with the movement of the stage 9 (from coordinate Y1 (tip) to coordinate Y2 (rear end) in FIG. 17).

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

[0146] As described above, for the uncorrected blurred image in FIG. 18(a), it is possible to detect the height Z in real time and automatically correct the height of the stage 9 to produce a corrected image in FIG. 17(b).

[0147] Fig. 19 is 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 Fig. 17 is incorporated into the already described Fig. 1.

[0148] In FIG. 19, 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 (cone), stage Z2 (cone), and stage Z3 (flat) in FIG. 12 described above, and support the sample holder 52 at three points.

[0153] With the above structure, as explained in FIG. 12, it is possible to automatically correct the height and inclination of sample holder 52 to the desired height Z in real time at ultra-high speed by applying a control voltage to any one of piezoelectric elements (Z1) 51, (Z2) 52, (Z3) 55 that support sample holder 52 at three points. [Brief description of the drawings]

[0154] [Figure 1] FIG. 1 is a structural diagram of an embodiment of the present invention. [Diagram 2] 2 is a diagram showing an example of a type of multi-beam array according to the present invention. [Diagram 3] 1 is an example of a data table according to the present invention. [Figure 4] 1 is an example of creating a multi-beam according to the present invention. [Diagram 5] FIG. 2 is an explanatory diagram of multi-beam detection according to the present invention. [Figure 6] FIG. 1 is an explanatory diagram (1st row) of multi-beam image acquisition and synthesis according to the present invention. [Figure 7] FIG. 2 is an explanatory diagram (two columns) of 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] 1 is a flowchart illustrating the operation of the present invention (obtaining the center coordinates of a multi-beam image). [Figure 10] 1 is a diagram for explaining the operation of the present invention (multi-beam scanning direction and stage movement direction). [Figure 11] 1A to 1C are diagrams for explaining the operation of the present invention (measurement of deviation amount and rotation amount of stage movement). [Figure 12] FIG. 4 is an explanatory diagram of tilt correction of a stage according to the present invention. [Figure 13] FIG. 4 is an explanatory diagram of the meandering of a stage according to the present invention. [Figure 14] FIG. 4 is an explanatory diagram of meandering correction of a stage according to the present invention. [Figure 15] FIG. 4 is an explanatory diagram of the rotation of a stage according to the present invention. [Figure 16] FIG. 13 is an explanatory diagram of rotation correction of a stage according to the present invention. [Figure 17] FIG. 4 is an explanatory diagram of stage tilt correction according to the present invention. [Figure 18] FIG. 4 is an explanatory diagram of height correction of the stage of the present invention. [Figure 19] FIG. 4 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 detector 52: Sample holder 53, 54, 55; Piezoelectric elements 151, 152: Height sensor

Claims

1. 1. A multi-beam imaging apparatus for scanning a sample with a plurality of primary electron beams to produce an image, comprising: a multiple beam generating device for generating a plurality of primary electron beams; a beam splitter that causes the multiple primary electron beams generated by the multiple beam generating device to be incident on an axis of an objective lens and causes the secondary electron beam emitted from a sample to be incident on an axis of a projection lens; an objective lens for narrowing the primary electron beam; a deflection system that deflects the primary electron beam narrowed by the objective lens to scan it on a sample; a projection lens for forming an image of the secondary electron beam incident on the axis by the beam splitter on an electron detector; A stage for moving the sample; a sample height measuring means for measuring the height of the sample in real time; while maintaining the stage horizontal based on the height of the sample output from the sample height measuring means, a plurality of primary electron beams generated by the plurality of beam generating devices are incident on the axis of the objective lens by the beam splitter, the sample is irradiated with a finely focused primary electron beam by the objective lens and scanned by the deflection system, secondary electrons emitted from the sample are incident on the axis of the projection lens by the beam splitter, and an image is formed on an electron detector by the projection lens to output image information of the plurality of electron beams. A multi-beam image generating device comprising:

2. 2. The multi-beam image generating device according to claim 1, wherein the sample is moved at a constant speed and in a constant direction.

3. A synthesizing means for synthesizing the image information of the outputted multiple electron beams into one image.

3. The multi-beam image generating device according to claim 1, further comprising:

4. 4. A multi-beam image generating device as claimed in claim 1, further comprising: a step of measuring the height of the stage in real time; correcting the height of the stage based on the measured height; or performing electromagnetic correction; and performing automatic focusing.

5. 5. The multi-beam image generating device according to claim 1, wherein the multiple beam generating device generates a plurality of primary electron beams by irradiating one primary electron beam onto an aperture having a plurality of holes.

6. 6. A multi-beam image generating device according to claim 1, wherein the beam splitter has a first stage on the incident side of the primary electrons as an electrostatic deflector and a second stage as an electromagnetic deflector, and the secondary electron beam emitted from the sample is deflected in a direction opposite to that of the primary electron beam by the second stage electromagnetic deflector to separate the secondary electron beam.

7. 7. A multi-beam image generating device according to claim 1, characterized in that a negative retarding voltage is applied to the sample, thereby reducing the energy of the primary electron beam that is irradiated and scanned on the sample while maintaining high resolution, thereby reducing damage to the sample.

8. 8. A multi-beam image generating apparatus according to claim 1, further comprising a deflection system for correcting the position of the secondary electron beam provided before or after said projection lens.

9. 1. A multi-beam imaging method for scanning a plurality of primary electron beams onto a sample to produce an image, comprising: a multiple beam generating device for generating a plurality of primary electron beams; a beam splitter that causes the multiple primary electron beams generated by the multiple beam generating device to be incident on an axis of an objective lens and causes the secondary electron beam emitted from a sample to be incident on an axis of a projection lens; an objective lens for narrowing the primary electron beam; a deflection system that deflects the primary electron beam narrowed by the objective lens to scan it on a sample; a projection lens for forming an image of the secondary electron beam incident on the axis by the beam splitter on an electron detector; A stage for 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 maintaining the stage horizontal, a plurality of primary electron beams generated by the multiple beam generating device are made to enter the axis of the objective lens by the beam splitter, the sample is irradiated with a finely focused primary electron beam by the objective lens and scanned by the deflection system, secondary electrons emitted from the sample are made to enter the axis of the projection lens by the beam splitter, and an image is formed on an electron detector by the projection lens, thereby outputting image information of the plurality of electron beams. A multi-beam image generating method comprising:

10. 10. The method for generating a multi-beam image according to claim 9, wherein the sample is moved at a constant speed and in a constant direction.

11. A synthesizing means for synthesizing the image information of the outputted multiple electron beams into one image.

11. The multi-beam image generating method according to claim 9, further comprising:

Images