Multibeam image generation apparatus and multibeam image generation method

Abstract

The present invention relates to a multibeam image generation apparatus and a multibeam image generation method. The objective is to generate multiple primary electron beams, irradiate a sample with them while moving the sample, detect the multiple electron beams emitted during this process, and combine them into a single image to achieve high-speed image acquisition. [Configuration] The system comprises means for scanning different locations on a sample with multiple primary electron beams and outputting multiple image information, a stage for moving the sample, and a laser interferometer that measures the position of the stage in the direction of movement and the position perpendicular to the direction of movement in real time. It has overlapping images between the multiple output image information, and is configured to correct the position of the stage or correct the position of the image information by an amount corresponding to the correction of the stage position based on the real-time position information of the stage and the overlapping images obtained by the laser interferometer, and then synthesize the corrected multiple image information to generate a single image.

Description

Technical Field

[0001] The present invention relates to a multi-beam image generation apparatus and a multi-beam image generation method for generating an image by scanning a plurality of primary electron beams on a sample.

Background Art

[0002] Conventionally, the semiconductor industry has been supported by the economy through the improvement of device performance and cost advantages brought about by the progress of microfabrication technology well-known as Moore's law. However, the microfabrication limit of semiconductor devices is determined by the lithography technology. The semiconductor lithography technology consists of a master plate called a photomask for creating a pattern, a lithography apparatus, and a resist for forming a pattern. Currently, since a 4-to-1 reduction lithography technology is used in the lithography apparatus, a pattern structure four times as large as the pattern structure on the silicon wafer where the semiconductor device is actually made is formed on the photomask.

[0003] The biggest issue in lithography technology is how to accurately transfer the pattern formed on the photomask based on semiconductor circuit design data 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 lithography apparatus and defects will occur on the wafer.

[0004] In order to prevent exposure failures, it is necessary to at least inspect the entire photomask, correct it to a proper state, and make it into a perfect pattern state as designed. Since the microfabrication limit is proportional to the wavelength of the light used for exposure, the wavelength of the light used for exposure has been continuously shortened over time.

[0005] Since a laser light source with a wavelength of 193 nm has been used as the exposure light source since the end of the 20th century, the pattern on the photomask has been inspected using an optical mask pattern inspection apparatus using a laser beam such as 193 nm as the illumination light over a long period of time.

[0006] However, since 2019, exposure technology using EUV light with a shorter wavelength of 13.5 nm has been fully introduced, further reducing the limit of microfabrication that can be exposed. The patterns on the photomask have also become smaller, from the conventional minimum pattern size of around 100 nm to less than 50 nm, making it impossible to perform sufficient inspection with conventional 193 nm light.

[0007] On the other hand, there are so-called actinic inspection devices 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 completely absorbed by the air, requiring a vacuum inside the inspection device, making it much more complex than conventional devices that were implemented in the atmosphere. Furthermore, since there are no optical lenses that can transmit 13.5 nm light, the entire optical system must be composed of reflective optics, which is also complex and inefficient. For example, EUV exposure devices that use a wavelength of 13.5 nm are so inefficient that they can only utilize about 1% of the total output of the light source.

[0008] The resolution of an optical device is proportional to its aperture ratio (NA). For example, in the case of an optical system using a wavelength of 193 nm, a large aperture ratio greater than 1 can be achieved by using methods such as liquid immersion or oil immersion. Therefore, even though the wavelength is long at 193 nm, it is possible to resolve a pattern of about 40 nm in a single exposure. Using double patterning, it is even possible to create a pattern of about 20 nm.

[0009] On the other hand, when using EUV light, a reflective optical system is used, so only small aperture ratios such as MA of 0.33 can be achieved. Despite the light source wavelength being one-tenth shorter than conventional wavelengths, a resolution of at most about 13 nm can be obtained, indicating that the performance improvement is small considering the shorter wavelength. Furthermore, for example, when the detection target is a particle, the reflected light weakens in proportion to the sixth power of the particle size and strengthens in proportion to the square of the wavelength. In other words, as the particle size decreases, the signal intensity weakens rapidly, and the defect detection sensitivity decreases drastically. Thus, photomask inspection technology using optical technology has reached its technical limits. In addition, conventional devices using optical principles operated in the atmosphere, making them easy to manufacture and operate, but as the wavelength shortens, it is absorbed by the air, requiring a large vacuum chamber, thus eliminating the advantage of usability compared to electron beam devices.

[0010] On the other hand, electron microscopes are a technology that can achieve high resolution on the nanometer order. Electron beam defect inspection technology has been under development for over 30 years. Although commercialization has been achieved, the throughput is extremely low compared to optical methods, so it has not yet been put into practical use as a primary inspection device. However, because it can detect electrical defects that optical methods cannot, it is gradually becoming more widespread for new wafer process development applications.

[0011] Unlike laser beams, electron beams lack a source with the low energy dispersion and high brightness of a laser. Furthermore, because electrons have a negative charge, focusing them into a small spot using lenses causes electrostatic repulsion between them. Therefore, when the large current required for high-speed inspection is applied, the minimum beam spot size becomes larger than the optical limit, degrading the resolution. In other words, when using a single electron beam, there is a very tight trade-off between resolution and inspection speed, resulting in a fundamental flaw where the speed slows down as miniaturization progresses.

[0012] For example, currently, the highest inspection speed achievable with a single electron beam is at most a few hundred megapixels per second. Since the pattern is drawn on a photomask in an area of ​​approximately 10 cm square, it is necessary to inspect the entire area. For example, to inspect the pattern on the most advanced photomask with a resolution of 10 nm, which is sufficient for resolution, it is necessary to acquire 10^14 pixels. If pixels are acquired at 100 megapixels per second, it will take 10^6 seconds. In other words, it will take 277 hours, or more than 10 days. Furthermore, it is necessary to scan the image many times to obtain an image with an SNR of 10 or higher, which is required for inspection. Conventional optical photomask inspection devices can inspect one photomask in about 2 hours, so the electron beam method is 100 times slower and is not practical for use.

[0013] On the other hand, in order to improve the speed of electron beam inspection equipment, a method called multi-electron beam inspection equipment is being researched, which uses multiple electron beams to simultaneously irradiate the sample in parallel for high-speed inspection. In this method, more than 100 small electron beams are irradiated and scanned simultaneously, making it possible to keep the amount of current flowing through each beam small. This is said to allow for a faster inspection speed compared to conventional methods using a single electron beam, while maintaining high resolution without being affected by electrostatic repulsion of the beams.

[0014] However, while many companies have developed various types of multi-beam inspection systems, and they are considered very promising as next-generation high-speed inspection devices, they have not yet achieved the speed and resolution that was initially expected, and have not yet been commercialized as semiconductor inspection devices.

[0015] The equipment used in the semiconductor industry is industrial measuring instrument, a type of mission-critical device that needs to operate continuously 24 hours a day, 365 days a year without malfunction, making high robustness essential. Unlike scientific instruments that can be used occasionally by university professors and students to write papers, such equipment is completely impractical. It needs to withstand various measurement conditions, measurement targets, and changes in the equipment's installation environment, and maintain stable performance over long periods. [Disclosure of the Invention] [Problems that the invention aims to solve]

[0016] While conventional single-beam high-speed inspection systems generally employ a continuous stage system, multi-beam systems that simultaneously acquire two-dimensional images have adopted a step-and-repeat system to maximize the area acquired in a single scan and achieve high speed. However, this system has the problem that stage movement time becomes dominant, preventing further speed improvements.

[0017] Furthermore, a clear contrast difference based on sensitivity differences occurred at the boundaries of the scanning area, which made the images unsuitable for use as inspection images.

[0018] Furthermore, in the single-beam system, since there is only one beam, it is easy to correct the irradiation position and irradiate the electron beam to the desired position. However, in the multi-beam system, since multiple electron beams are irradiated simultaneously to acquire a 2D image, there was a problem in that it was not easy to precisely control the irradiation position of each electron beam to the desired position. In addition, if stage movement is performed after acquiring 2D image information in order to further increase speed, the stage rotation, undulation, stage speed fluctuations, height fluctuations, and vibrations that occur during movement affect the acquisition of 2D images, resulting in a decrease in image quality.

[0019] Furthermore, simply acquiring images in the same way as with conventional single-beam systems resulted in distorted or distorted images, making accurate image acquisition impossible and unsuitable for inspection. [Means for solving the problem]

[0020] To solve the above-mentioned problems, the present invention generates multiple primary electron beams arranged in two dimensions, scans them when the sample stops, and then moves again, repeatedly separating the multiple secondary electron beams emitted at that time with a beam splitter, detecting the image information of each with an electron detection device, and combining them into a single image, thereby achieving high-speed image acquisition.

[0021] Therefore, the present invention relates to a multi-beam image generation apparatus that generates an image by scanning a sample with multiple primary electron beams, comprising: a multiple beam generation apparatus that generates multiple primary electron beams arranged in two dimensions; a beam splitter that deflects the multiple primary electron beams generated by the multiple beam generation apparatus in two stages and directs them onto the axis of the objective lens, and also deflects the secondary electron beam emitted from the sample in two stages in the opposite direction to the primary electron beam and directs it onto the axis of the projection lens; an objective lens that narrows the primary electron beam that has been deflected in two stages by the beam splitter and directed onto the axis; a deflection system that deflects the primary electron beam that has been narrowed by the objective lens and scans it on the sample; and the primary electron beam that has been deflected in two stages by the beam splitter and directed onto the axis. The system includes a projection lens that images the generated secondary electron beam onto an electron detector, a stage that repeatedly moves and stops the sample and acquires an image when it stops, and an interferometer that measures the position of the sample in the direction of movement and the position perpendicular to it in real time. Multiple primary electron beams generated by a multiple beam generator are deflected along the axis of the objective lens by a beam splitter, and the sample is irradiated with a narrowly focused primary electron beam by the objective lens and scanned by the deflection system. Secondary electrons emitted from the sample are deflected along the axis of the projection lens by the beam splitter, and the secondary electron beams corresponding to the two-dimensionally arranged multiple primary electron beams are imaged onto the electron detector by the projection lens, and image information of the multiple electron beams is output.

[0022] In this process, the system is equipped with a synthesis mechanism that combines the image information of multiple output electron beams into a single image.

[0023] Furthermore, the system corrects the stage's movement and rotation based on the image information of the multiple output electron beams and the real-time position of the sample in the direction of movement and perpendicular to it, or it corrects the image information by moving and rotating it by an amount corresponding to the stage's movement and rotation.

[0024] Also, the position of the stage in the height direction is measured in real time, and based on this, the height of the stage is corrected, or corrected electromagnetically, so as to perform automatic focusing.

[0025] Also, the plurality of beam generation devices irradiate a single primary electron beam onto an aperture having a plurality of two-dimensionally arranged holes to generate a plurality of primary electron beams.

[0026] Also, the beam splitter has an electrostatic deflector for the first stage on the incident side of the primary electrons and an electromagnetic deflector for the second stage, and deflects the secondary electron beam emitted from the sample by the electromagnetic deflector for the second stage in the opposite direction to the primary electron beam for separation.

[0027] Also, a negative retardation voltage is applied to the sample to reduce the energy while maintaining the high resolution of the primary electron beam irradiated on and scanned over the sample, thereby reducing damage to the sample.

[0028] Also, a deflection system for position correction of the secondary electron beam is provided in front of or behind the projection lens.

Advantages of the Invention

[0029] The present invention generates a plurality of primary electron beams arranged two-dimensionally, scans them when the sample stops, then repeats moving, and separates the plurality of secondary electron beams emitted at that time with a beam splitter, detects the respective image information with an electron detection device, and synthesizes it into one image, making it possible to acquire an image at high speed.

[0030] Also, when the images of the plurality of secondary electron beams scanned and detected by irradiating the sample with the plurality of primary electron beams arranged two-dimensionally are overlapped and detected and synthesized into one image, the occurrence of a contrast difference at the boundary can be reduced.

[0031] Furthermore, by pre-acquiring and registering the scanning positions of multiple primary electron beams arranged in a two-dimensional configuration onto the sample, it became possible to correct the central position of the secondary electron beam image and synthesize a precise image.

[0032] Furthermore, the position and rotation of the stage carrying the sample are precisely measured and recorded in real time using a laser interferometer. By correcting the movement and rotation amounts of multiple secondary electron beam images, it is now possible to generate precise image information.

[0033] As a result, in this invention, not only is the position control of each primary electron beam constituting the multi-beam system performed, but changes in the stage's attitude or velocity that occur during the stage's S&R movement are measured in real time by a stage position measuring means, and the stage is corrected in real time to control the positional relationship between the stage and the objective lens and the irradiation state of the primary electron beam to an ideal or reference state. Furthermore, by performing position correction processing between each scanned image at high speed using a computer, it becomes possible to obtain a single large, normalized image without boundary effects, which is considered ideal for inspection. Addition processing between arbitrary scanned images is possible, and the current value of each primary electron beam can be kept low, resulting in high S&R and high throughput with high resolution. The highest throughput can be achieved while operating in S&R mode. [Example 1]

[0034] First, as an example of the present invention, a multi-beam inspection system is characterized by increasing the inspection speed by simultaneously irradiating the sample with more than 100 primary electron beams and acquiring a two-dimensional secondary electron image. Each primary electron beam constituting the multi-beam system is made up of an electron beam generated by one electron gun that is divided by an aperture, and in order to achieve a small beam spot size, the amount of each primary electron beam is small compared to a single-beam system, for example, about 1 nA. However, since each primary electron beam is scanned at a speed of several tens of MHz or more, an overall detection speed of more than gigapixels per second can be achieved. The position of the primary electron beam irradiated onto the sample surface is determined by the relative motion of the stage movement and the irradiation of the multi-electron beam. Whether or not this relative motion can be ideally realized determines the performance of the high-speed inspection system.

[0035] Because it is relative motion, the irradiation position of the primary electron beam can be controlled by controlling the stage or by controlling the irradiation position of the primary electron beam using a primary electron beam deflection device. The primary electron beam deflection device can be implemented by using a two-stage deflection device, similar to a primary electron beam lithography device, to shift the primary electron beam in the XY horizontal plane while maintaining the irradiation angle. In the case of a multi-beam inspection system, individual deflection of each primary electron beam is not performed; instead, a uniform electric or magnetic field is applied to all primary electron beams to scan them simultaneously.

[0036] Generally, the stage has a large inertial mass, while the primary electron beam has almost no mass. Therefore, in terms of response speed, position correction using the deflection of the primary electron beam is faster and provides higher positional accuracy. On the other hand, slow vertical movement of the stage with a large time constant requires complex focus control if performed with the primary electron beam. However, if correction is performed using a Z-axis stage or similar to keep the height constant, the control can be simplified. The following will explain this in detail.

[0037] Figure 1 shows a structural diagram of one embodiment of the present invention.

[0038] In Figure 1, electron gun 1 is a known electron beam generator that produces a primary electron beam accelerated to several hundred volts or tens of kilovolts. The electron gun uses a thermionic source such as W or LaB6, or a TFE using ZrO, a cold-field emitter, or a photocathode. The electron gun chamber is maintained at an ultra-high vacuum of 10⁻⁸ Pa or higher using an ion pump or getter pump.

[0039] The blanking device 2 rapidly switches the primary electron beam emitted from the electron gun 1 ON or OFF, deflecting the primary electron beam to pass through or block it by switching the voltage ON or OFF.

[0040] The illumination lens 3 focuses the electron beam generated and accelerated by the electron gun 1, thereby focusing it into a predetermined beam as shown in Figure 4, which will be described later.

[0041] The multi-beam aperture 3-1 is generated by splitting the irradiated primary electron beam into multiple primary electron beams arranged in a two-dimensional configuration (for example, 100 divisions) (see Figure 2).

[0042] The objective aperture 4 is used to pass the central portion of each of the multiple primary electron beams through, and then, using the objective lens 6 (described later), narrowly focus each of the passed primary electron beams onto the surface of the sample 8 for irradiation.

[0043] The beam splitter 5 separates primary electrons from secondary electrons traveling in the opposite direction, and consists of an electrostatic deflector 5-1 in the upper section and an electromagnetic deflector 5-2 in the lower section. The primary electron beam is deflected to the right by the electrostatic deflector 5-1 as shown in Figure 1, deflected to the left by the electromagnetic deflector 5-2, and swung back onto the axis of the objective lens 6, where it is narrowly focused and imaged onto the sample 8 by the objective lens 6. The secondary electrons emitted from the sample 8 are deflected to the right by the electromagnetic deflector 5-2 as shown in Figure 1, deflected to the left by the electrostatic deflector 5-1, and swung back onto the axis of the projection lens 12, where the projection lens 12 images multiple secondary electron beams arranged two-dimensionally on the electron detection device 14, outputting multiple secondary electron images (secondary electron signals).

[0044] The electrostatic deflector 5-1 is the deflector closest to the electron gun 1 that constitutes the beam splitter 5, and in this case, it is an electrostatic deflector.

[0045] The electromagnetic deflector 5-2 is a deflector located away from the electron gun 1 that constitutes the beam splitter 5, and in this case, it is an electromagnetic deflector.

[0046] The objective lens 6 focuses multiple primary electron beams into a narrow beam and irradiates them onto the sample 8.

[0047] The deflection device 7 scans the surface of the sample 8 with multiple primary electron beams, and normally repeats two-dimensional scanning (scanning in the X and Y directions) with the stage 9 moved and stopped (see Figures 6 and 7, etc.).

[0048] Sample 8 is a sample for which multiple images, such as a mask and wafer, are acquired and combined into a single image.

[0049] Mirror 8-1 is a reflecting mirror used to measure position in real time with a laser interferometer.

[0050] Stage (XYZθ stage) 9 is a stage that can mount a sample and move in XYZ and θ (rotation). It is configured to measure and record XYZ and θ in real time using an interferometer (not shown), and to perform real-time correction.

[0051] The vacuum chamber 10 is a container that can house the sample 8, stage 9, etc., and is capable of being evacuated under vacuum.

[0052] The vacuum pump 10-1 is used to evacuate the inside of the vacuum chamber 10, and is an oil-free pump.

[0053] Alignment 11 is performed to align the axes of multiple secondary electron beams that are deflected from the electrostatic deflector 5-1, which constitutes the beam splitter 5, onto the axis of the projection lens 12.

[0054] The projection lens 12 images multiple secondary electron beams emitted from the sample 8 onto the detection surface of the electron detection device 14.

[0055] The reverse scanning device 13 reverses (swivels back or corrects) the multiple secondary electron beams emitted when multiple primary electron beams arranged in two dimensions are narrowly focused and scanned over the sample 8, so that each of them remains within a predetermined area on the detection surface of the electron detection device 14.

[0056] The electron detection device 14 detects each of the multiple secondary electron beams emitted from the sample 8. For example, an avalanche photodiode, CCD, CMOS sensor, or TDI camera can be used. The electrons may be first struck by a scintillator to convert them into light and then detected by the aforementioned device, or the electrons may be directly fired into the aforementioned device for detection. In any case, it is sufficient that each of the multiple secondary electron beams, each imaged within a predetermined area of ​​the detection surface, can be detected independently.

[0057] Next, we will explain the operation of the structure shown in Figure 1.

[0058] (1) The primary electron beam emitted from electron gun 1 is irradiated with multi-beam aperture 3-1 to generate multiple primary electron beams arranged in two dimensions (see Figure 2). The generation of multiple primary electron beams arranged in two dimensions is not limited to this method; multiple electron emission sources may be provided on the surface of the emitter of electron gun 1 to generate multiple primary electron beams arranged in two dimensions corresponding to these sources.

[0059] (2) The multiple primary electron beams, which are split and generated by the beam aperture 3-1 and arranged in a two-dimensional manner, pass through their respective central parts by the objective aperture 4, are deflected to the right by the upper electrostatic deflector 5-1 and to the left by the electromagnetic deflector 5-2 that constitute the beam splitter 5, and then incident on the axis of the objective lens 6.

[0060] (3) Multiple primary electron beams arranged in two dimensions and incident on the axis of the objective lens 6 are narrowed by the objective lens 6 and scan the surface of the sample 8 in two dimensions when the sample 8 moves and stops, and then move and stop again, and this process is repeated. As a result, when the movement of the sample 8 stops, the multiple primary electron beams arranged in two dimensions scan the surface of the sample 8 in a rectangular or other shape. At this time, although not shown in the figure, a negative retarding voltage is applied to the sample 8 to irradiate the sample 8 with the energy of the multiple primary electron beams set to, for example, 1KV (for example, a negative retarding voltage of 14KV is applied to the energy of the multiple primary electron beams of 15KV to make them 1KV primary electron beams and irradiate the sample 8).

[0061] (4) Secondary electrons, backscattered electrons, light, X-rays, etc. are emitted from multiple primary electron beam regions that have been scanned in a rectangular or similar shape in (3).

[0062] The secondary electrons emitted in (5)(4) travel in a spiral motion in the opposite direction along the axis of the objective lens 6 due to the magnetic field of the objective lens 6. Here, they are deflected to the right by the lower electromagnetic deflector 5-2 that constitutes the beam splitter 5 (deflected in the opposite direction to the deflection of the multiple primary electron beams), and then deflected to the left by the electrostatic deflector 5-1, before being incident on the axis of the projection lens 12.

[0063] (6) After correcting 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 onto the electron detector 14 and irradiated onto the imaging area of ​​each of the multiple secondary electron beams of the electron detector 14. If the beams extend beyond the imaging area, the reverse scanning device 13 is used to correct them so that they remain within the imaging area by supplying voltage (or current) to the reverse scanning device 13 in synchronization with the scanning (deflection) of the multiple primary electron beams on the sample 8. The electron detector 14 then outputs a secondary electron image (secondary electron signal) for each of the multiple secondary electron beams detected.

[0064] As described above, multiple primary electron beams arranged in two dimensions are generated, and these are narrowed by the objective lens 6 via the beam splitter 5. With the sample 8 stationary on the stage 9, a rectangular or other surface scan is performed, and this process is repeated, scanning the rectangular or other surface area with each of the multiple primary electron beams. The multiple secondary electron beams emitted at that time are then separated via the beam splitter 5, and the projection lens 12 images the multiple secondary electron beams onto the respective detection surfaces of the electron detection device 14, making it possible to output secondary electron images (secondary electron signals) for each of the multiple secondary electron beams.

[0065] Figure 2 shows a schematic arrangement example of the multibeam aperture of the present invention. This shows an example of the arrangement of holes in the multibeam aperture 3-1 of Figure 1 described above. Although the holes are schematically shown as rectangles in Figure 2, circular holes are actually preferable.

[0066] Figure 2(a) shows an example of a quadrilateral (rectangle), and Figure 2(b) shows an example of a hexagon.

[0067] Figure 2(a) shows an example of a quadrilateral (rectangle) shape. This schematically illustrates an example where the aperture of the multibeam aperture 3-1 in Figure 1 is provided with holes arranged in a two-dimensional array as shown (a circular shape is actually preferable). For example, if 9x9 holes are arranged in a quadrilateral (rectangle) shape, a total of 81 primary electron beams can be generated. As shown in the figure, the size of the holes is Ax×Ay, the distance between holes in the horizontal (X) direction is Sx, and the distance between holes in the vertical (Y) direction is Sy.

[0068] Figure 2(b) shows an example of a hexagon. This schematically shows an example in which the aperture of the multibeam aperture 3-1 in Figure 1 is provided with two-dimensionally arranged holes (circular shapes are actually preferable) as shown. For example, if holes are provided as shown, it will look like this, with a total of 73 holes.

[0069] ·First row: 5 pieces ·2nd row: 8 pieces ·3rd row: 9 pieces ·4th row: 10 pieces ·5th row: 9 pieces ·6th row: 10 pieces ·7th row: 9 pieces ·8th row: 8 pieces ·9th row: 5 pieces Total: 73 Therefore, a total of 73 primary electron beams can be generated. As shown in the figure, the hole size is Ax × Ay, the distance between holes in the horizontal (X) direction is Sx, and the distance between holes in the vertical (Y) direction is Sy, and they are arranged in a staggered pattern as shown in the figure.

[0070] Furthermore, each multibeam aperture 3-1 in Figure 2(a) to (b) has the function of independently turning on / off its respective primary electron beam. This allows for control so that only the electron beam at any selected position among all the multibeams reaches the sample, rather than having to prepare a large number of apertures with physically different arrangements as shown in the figure.

[0071] Figure 3 shows an example of a data table of the present invention (Figure 2). As described above and will be described later, under the structure of Figure 1, the position XYZ, rotation θ, etc. of the stage 9 on which the sample 8 (e.g., a mask) is mounted are measured in real time with a laser interferometer. The stage 9 is then stopped, the primary electron beam is scanned over the sample 8 to acquire a secondary electron image, and then the stage is moved again. The stage displacement, stage rotation, and stage height are recorded in correspondence with the stage position during this repeated process.

[0072] In Figure 3, the stage position indicates the position when the XYZθ stage (hereinafter referred to as the stage) 9, on which the sample 8 in Figure 1 is mounted, is moved and stopped, and the primary electron beam is scanned across the sample 8. This position is measured in real time using a laser interferometer (described later). 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 acquiring a 1000x1000 pixel image over a 100 μm rectangular area, one entry of information (stage position, stage displacement, stage rotation, stage height) is measured and recorded in real time every 0.1 μm. Furthermore, measurements are taken and recorded in real time every 0.01 μm, every 0.001 μm, etc., corresponding to 10 μm and 1 μm rectangular areas. If the same value is consecutive, the difference between them may be recorded. In addition, each stopping position of the stage 9 may be recorded.

[0073] The stage displacement is the amount of deviation in the stage position (deviation from the ideal position), and the value recorded is measured in real time using a laser interferometer (described later).

[0074] The stage rotation amount is the amount of rotation at the stage position (rotation amount θ from an ideal state of no rotation), and is a record of the stage rotation amount measured in real time by a laser interferometer (described later).

[0075] The stage height is the height Z at the stage position (the amount of deviation in the Z direction from the ideal height), and is a record of the height deviation measured in real time by a laser interferometer (described later).

[0076] As described above, when the stage 9 in Figure 1 is moved and stopped, it becomes possible to precisely measure and record in real time the deviations of the stage 9 from its ideal values ​​(stage deviation (XY)), stage rotation θ, and stage height Z) using a laser interferometer. Then, by correcting the position of the stage 9 or the acquired image in real time based on the recorded deviations, it becomes possible to correct errors associated with the movement of the stage 9 and synthesize multiple images of secondary electron beams acquired by irradiating the sample with multiple primary electron beams to generate a precise single image. This will be explained in detail below.

[0077] Figure 4 shows an example of multibeam fabrication according to the present invention. This Figure 4 schematically shows an example of multibeam fabrication using the multibeam aperture 3-1 of Figure 1 described above.

[0078] In Figure 4, the primary electron beam emitted from the electron gun 1 is projected by the illumination lens 3 so as to illuminate multiple holes (see Figure 2) arranged in a two-dimensional pattern in 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 narrowly focused and illuminate the surface of the sample 8 by the objective lens 6 (not shown in Figure 4, but shown in Figure 1). Here, since the sample 8 is scanned in a plane while it is stopped by the stage 9, the surface of the sample 8 is scanned in a plane such as a rectangle by the multi-electron beam 3-2. The emitted secondary electron beams are then detected by the electron detection device 14 (shown in Figure 1), and secondary electron images are acquired for each, which are then combined into a single image (see Figures 6 and 7) to generate a secondary electron image of the sample 8.

[0079] Figure 5 shows an explanatory diagram of the multibeam detection of the present invention. This shows a detailed explanatory diagram of the projection lens 12, inverse scanning device 13, and electronic detection device 14 of Figure 1.

[0080] In Figure 5, multiple secondary electron beams emitted from sample 8 are separated via beam splitter 5 and incident from top to bottom in Figure 4. The projection lens 12 then images each beam onto the detection surface of electron detector 14. At this time, the imaging region where the multiple secondary electron beams are imaged is fine as long as it is within its own imaging region. However, if they extend beyond other regions, they become undetected, resulting in a missing secondary image. To prevent this, the reverse scanning device 13 synchronizes with the scanning of the primary electron beam onto sample 8 (scanning by deflection of multiple secondary electron beams by the deflection device 7) to correct the deflection so that the beams remain within a predetermined imaging region, ensuring they stay within its own imaging region.

[0081] As a result, each of the multiple secondary electron beams emitted from sample 8 is imaged within each imaging region of the electron detection device 14, making it possible to reliably detect and output secondary electron images of each of the multiple secondary electron beams.

[0082] Figure 6 shows an explanatory diagram (quadrilateral) of the multibeam image acquisition and synthesis method of the present invention. Here, the horizontal direction represents the X direction, and the vertical direction represents the Y direction. The numbers 1, 2, 3, and 4 represent image 1, image 2, image 3, and image 4.

[0083] In Figure 6, Images 1, 2, 3, and 4 schematically show how multiple primary electron beams generated using the quadrilateral multi-beam aperture 3-1 in Figure 2(a) were irradiated onto a stationary sample 8, and then moved a predetermined distance, repeating this process four times. As shown in the figure, four images (secondary electron images) with adjacent portions overlapping were obtained, and these four images were then combined into a single image using known image synthesis software. A detailed explanation follows below.

[0084] (1) In Figure 6, each primary electron beam is applied in two dimensions in the XY direction on the surface of the sample 8, and the stage 9 moves by a predetermined distance in an arbitrary direction using S&R. The amount of stage movement corresponds to the width of the area that one scanning plane can cover. In reality, overlap areas are provided at the corners for alignment, so the stage instantaneously moves a distance less than the scanning plane width by the amount of overlap.

[0085] (2) The movement of the primary electron beam, the position of the stage, and the brightness information of the scan surface image are recorded. Multiple images of the scan surface are formed each time S&R is repeated. In order to scan sample 8 completely, the scan width of the scan surface is overlapped by about 5 to 10%. This eliminates scanning misses and, at the same time, creates a common image in the images of adjacent scan surfaces. Using position coordinates obtained from the laser interferometer and pattern matching, the positional relationship of the images of adjacent scan surfaces can be corrected to create one large image.

[0086] (3) Since the overlapping region is scanned twice, a high SNR can be obtained through the image addition effect, enabling more accurate alignment. For example, in the example in Figure 6, images 1, 2, 3, and 4 of each scanning plane are aligned and the images are combined to form a region of one large image from the images of the four independent scanning planes. The image processed in this way is used as the inspection image. If the object to be inspected is formed without spanning across the images of each scanning plane, inspection can be performed using the image of one scanning plane, so it is not always necessary to combine them into a single image.

[0087] Figure 7 shows an explanatory diagram (hexagon) of the multibeam image acquisition and synthesis method of the present invention. Here, the horizontal direction represents the X direction, and the vertical direction represents the Y direction. The numbers 1, 2, 3, and 4 represent image 1, image 2, image 3, and image 4.

[0088] In Figure 7, Images 1, 2, 3, and 4 schematically show how multiple primary electron beams generated using the hexagonal multi-beam aperture 3-1 in Figure 2(b) were irradiated onto a stationary sample 8, and then moved a predetermined distance, repeating this process four times. As shown in the figure, four images (secondary electron images) with adjacent portions overlapping were obtained, and these four images were then combined into a single image using known image synthesis software. A detailed explanation follows below.

[0089] Here, similar to (1) to (4) in the case of a quadrilateral, in the case of a hexagon in Figure 7, as shown in the examples of scan surface images 1, 2, 3, and 4 when a honeycomb-shaped aperture (Figure 2(b)) is provided, electron beam columns are generally cylindrical, and when the electron beam is scanned, its characteristics change or deteriorate in a concentric manner. Therefore, a honeycomb-shaped hexagon has the advantage of suppressing deterioration and allowing many images with the same characteristics to be acquired.

[0090] Similar to Figure 6, in Figure 7, the secondary electron images generated by scanning each primary electron beam are independent of each other; therefore, images 1, 2, 3, and 4 of each scanning plane are completely independent images. Since their relative positions are known, a single image can be obtained by performing image processing using these relative positions and superimposing the images from each scanning plane. Image superposition is achieved by pattern matching the overlapping areas.

[0091] As described above, when using the S&R method of the present invention, the same location can be scanned multiple times and images can be added together. Therefore, when the electron beam current is the same, an image with a higher SNR can be obtained than when scanning only once. In addition, there is an averaging effect of sampling due to the electron beam scanning slightly different locations.

[0092] Figure 8 shows a flowchart illustrating the operation of the present invention (acquisition of the center coordinates of a multibeam image).

[0093] In Figure 8, S1 prepares a pattern with known spacing dimensions. This involves preparing a reference sample with a pattern whose spacing and shape dimensions are precisely known. A conductive photomask or silicon substrate with the same pattern fabricated in advance is suitable. The size and spacing of the patterns are measured in advance using a CDSEM or optical measuring device. To simplify the measurement, the deflection center coordinates of the electron beam are known in advance as design values, so calibration can be easily performed by using a reference sample in which the pattern is placed at the location of the design deflection center coordinates. The pattern size is arbitrary, but a pattern that is symmetrical left-right and up-down is desirable so that the center position can be accurately determined even if process variations occur.

[0094] S2 acquires images with the stage stopped. This involves scanning the pattern prepared in S1 with multiple primary electron beams while the stage is stopped, and acquiring an image of each pattern.

[0095] S3 compares the acquired image with a pattern whose spacing dimensions are known.

[0096] S4 calculates the center coordinates for each electron beam scan. S3 and S4 compare the images acquired in S2 with the reference sample image (or design data) using pattern matching, etc., and S4 calculates the deviation of the center position for each. The deflection center coordinates of each primary electron beam are calculated and stored from the amount of center position deviation and the design data of the reference sample.

[0097] As described above, it becomes possible to calculate (measure) the center coordinates of each primary electron beam on sample 8 scanned by the multiple primary electron beams generated by being divided by the two-dimensionally arranged multi-beam aperture in Figure 2. Subsequently, based on the center coordinates of these multiple primary electron beams, it becomes possible to perform a planar scan on each and synthesize the acquired images to generate a single image. This will be explained in detail below.

[0098] Figure 9 shows a flowchart illustrating the operation (calibration) of the present invention. This shows an example of a procedure for automatically correcting errors (XY,Z) associated with the movement of Stage 9.

[0099] In Figure 9, S11 is set to the stage movement start position. This is set to the stage movement start position of Stage 9 in Figure 1, for example, the movement start position (home position) on Sample 8 where an image is to be acquired.

[0100] S12 moves the stage a desired distance and issues a stop command.

[0101] S13 feeds back the difference between the target position and the current position to the electron beam deflection device.

[0102] S14 aligns the center coordinates of the electron beam scan with the target position. S12, S13, and S14 move the stage 9 a predetermined distance from the stage movement start position set in S11 (for example, from the stage movement start position to the center position for acquiring an image, or from the center position of an already acquired image to the center position of the next image), issue a stop command, and stop the stage. Then, the difference (ΔX, ΔY) between the current position where the stage is stopped (the current position (X, Y) measured in real time by the laser interferometer described later) and the specified target position is fed back to the electron beam deflection device 7 in Figure 1 to correct the correction so that the stage 9 stops at the specified position (correcting the irradiation positions of multiple primary electron beams).

[0103] S15 adjusts the stage height to match the target value. Similarly, the height Z of stage 9 is corrected in real time so that it matches the current real-time measured height Z of stage 9 with the target height (see Figure 14, etc., described later).

[0104] S16 is for image acquisition. This is done after correcting the stage position and height in S11 to S15 to match the target position and height (this will be explained later using Figures 10 and 11).

[0105] As described above, by moving and stopping the stage 9, measuring its position and height in real time, and then correcting it to match the target position and height, it becomes possible to acquire images of each desired position (multibeam images). Then, the multiple acquired images are combined to generate a single image.

[0106] Figure 10 shows a flowchart illustrating the operation of the present invention (acquisition of a multi-beam image (quadrilateral)). This is a flowchart illustrating the operation when acquiring the quadrilateral multi-beam image shown in Figure 6.

[0107] In Figure 10, S21 acquires an image of the stage stop position. This acquires an image of the position where the stage 9 is stopped. For example, multiple primary electron beams divided by the quadrilateral multi-beam aperture in Figure 2(a) described above are irradiated onto the surface of the sample 8 while performing a surface scan, and the secondary electrons emitted at that time are detected by the electron detection device 14, and secondary electron images are acquired and combined to obtain a single image 1 as shown in Figure 6.

[0108] S22 moves the stage by the scanning plane width X minus the overlap width x. As shown in Figure 6, when moving from the position of image 1 acquired in S21 to the position of image 2, the stage 9 is moved to a position obtained by subtracting the overlap width x from the scanning plane width X.

[0109] S23 acquires an image. This involves moving the device with the overlap width x set in S22, stopping at the position, and acquiring image 2. As a result, there is an overlap width x between images 1 and 2 in Figure 6, and this overlapping portion can be used to accurately combine them into a single image.

[0110] S24 determines if the process is complete. If YES, proceed to S25. If NO, return to S22 and repeat.

[0111] S25 moves the stage by the scanning plane width Y minus the overlap width y. As shown in Figure 6, when moving from the position of image 2 (indicated by the illustration) to the position of image 4, the stage 9 is moved to a position obtained by subtracting the overlap width y from the scanning plane width Y.

[0112] S26 acquires an image. It stops at the downward position after moving with the overlap width y set in S25, and acquires image 4. As a result, there is an overlap width y between images 2 and 4 in Figure 6, and it is possible to accurately combine them into a single image using this overlapping portion.

[0113] S27 determines whether the process is finished. If YES, it finishes. If NO, it returns to S25 and repeats.

[0114] As described above, when generating multiple primary electron beams using the quadrilateral multi-beam aperture in Figure 2(a), and acquiring an image of the sample 8 by scanning the surface while irradiating it with these beams, as shown in Figure 6, by moving the stage so that there is overlap width x and y between the images, it is possible to generate partially overlapping images 1, 2, 3, 4, etc., and accurately and quickly combine these overlapping parts into a single image.

[0115] Figure 11 shows a flowchart illustrating the operation of the present invention (acquisition of a multi-beam image (hexagon)). This is a flowchart illustrating the operation when acquiring the hexagonal multi-beam image shown in Figure 7.

[0116] In Figure 11, S31 acquires an image of the stage stop position. This acquires an image of the position where the stage 9 is stopped. For example, multiple primary electron beams divided by the hexagonal multi-beam aperture in Figure 2(b) described above are irradiated onto the surface of the sample 8 while performing a surface scan, and the secondary electrons emitted at that time are detected by the electron detection device 14, and secondary electron images are acquired and combined to obtain a single image 1 as shown in Figure 7.

[0117] In S32, the stage is moved by the scanning plane width X minus the overlap width x. As shown in Figure 7, when moving from the position of image 1 acquired in S31 to the position of image 2, the stage 9 is moved to a position obtained by subtracting the overlap width x from the scanning plane width X.

[0118] S33 acquires an image. This involves moving the device with the overlap width x set in S32, stopping at the position, and acquiring image 2. As a result, there is an overlap width x between images 1 and 2 in Figure 7, and this overlapping portion can be used to accurately combine them into a single image.

[0119] S34 determines if the process is complete. If YES, proceed to S35. If NO, return to S32 and repeat.

[0120] S35 moves the stage by the scanning plane width Y minus the overlap width y. As shown in Figure 7, when moving from the position of image 2 to the position of image 4, the stage 9 is moved to a position obtained by subtracting the overlap width y from the scanning plane width Y.

[0121] S36 acquires an image. It stops at the downward position after moving with the overlap width y set in S35, and acquires image 4. As a result, there is an overlap width y between images 2 and 4 in Figure 7, and it is possible to accurately combine them into a single image using this overlapping portion.

[0122] S37 determines whether the process is finished. If YES, it finishes. If NO, it returns to S35 and repeats.

[0123] As described above, when generating multiple primary electron beams using the hexagonal multi-beam aperture in Figure 2(b), and acquiring an image of the sample 8 by scanning the surface while irradiating it with these beams, as shown in Figure 7, by moving the stage so that there is overlap width x and y between the images, it is possible to generate partially overlapping images 1, 2, 3, 4, etc., and accurately and quickly combine these overlapping parts into a single image.

[0124] Figure 12 shows an explanatory diagram of the operation of the present invention (measurement of the amount of displacement and rotation of the stage movement).

[0125] Figure 12(a) shows an example of the positional relationship of the laser interferometer 31 for XY position measurement, and Figure 12(b) shows an example of the positional relationship of the laser interferometer 31 for rotation measurement.

[0126] In Figure 12(a), the interferometer X1 is positioned as shown in the diagram to precisely measure the distance to the position of the stage 9 in the X direction, and a mirror is placed on the stage side.

[0127] The interferometer Y1 is positioned as shown in the diagram to precisely measure the distance to the stage 9 in the Y direction, and a mirror is placed on the stage side.

[0128] As described above, by arranging interferometers X1 and Y1, it becomes possible to precisely measure and record the distance (position) of stage 9 in the X and Y directions in real time (see Figure 3).

[0129] In Figure 12(b), the interferometer X1 is positioned as shown in the diagram so that the distance to the position of the stage 9 in the X direction can be precisely measured, and mirrors are placed on the stage side.

[0130] Interferometers Y1 and Y2 are positioned as shown in the diagram to precisely measure the distance to the stage 9 in the Y direction, and to measure the rotation angle, with mirrors placed on the stage side.

[0131] As described above, by arranging interferometers X1, Y1, and Y2, it becomes possible to precisely measure the rotation of stage 9 in real time (see Figure 3).

[0132] Figure 13 shows an explanatory diagram of the tilt correction of the stage according to the present invention. This shows an example of the stage 9 in Figure 1 described above, and shows an example of a three-point supported stage consisting of stage Z1 (cone), stage Z2 (cone), and stage Z3 (flat). Each of the three supported stages can be contracted by applying voltage to a piezoelectric element and adjusted to any distance from the outside.

[0133] More specifically, Figure 13 consists of three independent piezo actuators with identical performance, arranged to provide three-point support to the center of the sample.

[0134] One end of each of the three piezo 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 point is molded to ensure precise three-point support. Examples include using ruby ​​spheres with a non-slip surface, or using conical metal or plastic. It is desirable to surface treat the material to achieve the largest possible coefficient of friction. At least one of the three support points is conductive to form the circuit necessary to apply a bias voltage to the sample.

[0135] The system has three independent control circuits to drive the three piezoelectric actuators. Signals from height sensors 151 and 152 are processed by a PC, and the desired distance and height can be changed by issuing commands from the PC or other device based on the processing results. Each actuator has a built-in displacement sensor, such as a capacitive sensor, which monitors the actual displacement and provides feedback, thereby correcting the nonlinearity of the piezoelectric element. Positional accuracy can be achieved to the order of nanometers (see Figure 20 below).

[0136] The stroke required for Z-axis control ranges from a few microns to approximately 1000 microns. The Z-axis stage must also possess high rigidity to prevent sample vibration. A support system using a piezo actuator with a displacement amplification mechanism, including the sample holder, combines a high response speed of ms with high mechanical rigidity, resulting in a high resonant frequency of several hundred Hz or more, thus avoiding unwanted vibrations. Therefore, even heavy samples weighing nearly 1 kg, such as photomasks, can be instantly maintained horizontally.

[0137] Figure 14 shows an explanatory diagram of the meandering stage of the present invention.

[0138] Figure 14(a) schematically shows the stage without meandering, Figure 14(b) schematically shows the stage with meandering to the left, and Figure 14(c) schematically shows the stage with meandering to the right. Here, the vertical direction indicates the stage movement direction, and the horizontal direction indicates the electron beam scanning method.

[0139] In Figure 14(a), stage 9 is schematically shown as not meandering in a certain direction (vertical direction) of stage movement, indicating that no correction is necessary.

[0140] In Figure 14(b), stage 9 schematically shows a meandering to the left relative to the stage movement direction in a certain direction (vertical direction), indicating that correction is necessary. In this case, the meandering is corrected to the right (see the stage displacement amount in Figure 3).

[0141] In Figure 14(c), stage 9 schematically shows a meandering to the right relative to the stage movement direction in a certain direction (vertical direction), indicating that correction is necessary. In this case, the meandering is corrected to the left (see the stage displacement amount in Figure 3).

[0142] Generally, XY stages often combine direct motors, servo motors, stepping motors, ultrasonic motors, and linear motors—which require large driving forces to perform high-speed movements of microns or more—with piezo actuators and brakes that enable fine movements of nanometers or less.

[0143] The XY stage has the ability to move to a specified coordinate point by combining independent X-axis and Y-axis movement mechanisms, giving it degrees of freedom in the X and Y directions. For example, suppose a movement command is given to the XY stage to move along the Y-axis. A perfect stage would only move in the Y-axis direction and not in the X-axis direction, but as shown in Figure 14, in a real stage, movement also occurs in the X-axis direction.

[0144] The guide rails that define the movement accuracy of the stage are made of ceramic or similar material and are machined with extremely high precision, but there is a mechanical error of about a micron. If the stage moves, for example, along the Y axis from (X1, Y1) to (X1, Y2), the center coordinates of the stage meander left and right along the X axis during the stage movement. The multi-beam method uses a group of primary electron beams arranged in two dimensions with predetermined spacing between each electron beam. If the stage meanders during continuous inspection, the area irradiated by the primary electron beam will differ from the intended location, resulting in uneven irradiation and malfunctions in the inspection.

[0145] Figure 15 shows an explanatory diagram of the meandering correction of the stage according to the present invention.

[0146] Figure 15(a) schematically shows an example of an image before correction, and Figure 15(b) schematically shows an 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.

[0147] In Figure 15(a), each image schematically shows how the image in the rectangular area shown meanders from left to right with each meander of the stage.

[0148] In Figure 15(b), each image schematically shows the state of the rectangular area after correction for each meander of the stage. The image shows no meandering and appears to be scanned with the same width in the direction of stage movement.

[0149] As described above, and as explained in Figure 14, if there is (detects) meandering of stage 9 (amount of deviation perpendicular to the stage movement direction, and also amount of deviation in the stage movement direction), a correction is performed to move the stage (or move the detected image) by the amount of this meandering, making it possible to correct the image so that it appears as if there is no meandering, as shown in Figure 15(b).

[0150] Figure 16 shows an explanatory diagram of the stage rotation according to the present invention.

[0151] Figure 16(a) schematically shows the state without horizontal rotation, Figure 16(b) schematically shows the state with horizontal rotation to the right, and Figure 16(c) schematically shows the state with horizontal rotation to the left. Here, the vertical direction indicates the stage movement direction, and the horizontal direction indicates the electron beam scanning method.

[0152] In Figure 16(a), Stage 9 is schematically shown as having no horizontal rotation relative to a certain direction of stage movement (vertical direction), indicating that no correction is necessary.

[0153] In Figure 16(b), the stage 9 schematically shows a case where the horizontal rotation is to the right relative to the stage movement direction in a constant direction (vertical 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).

[0154] In Figure 16(c), Stage 9 schematically shows a case where the horizontal rotation is to the left relative to the stage movement direction in a constant direction (vertical 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).

[0155] Generally, Stage 9 rests on two rails symmetrically on either side of the movable part. The characteristics of the left and right rails are not necessarily the same, and their frictions differ. Therefore, when Stage 9 is moved along the rails, the amount of movement differs on the left and right rails. As a result, the movable part of Stage 9 experiences a slight rotational wobble in the XY plane. This invention corrects for this.

[0156] Figure 17 shows an explanatory diagram of the rotational correction of the stage according to the present invention.

[0157] Figure 17(a) schematically shows an example of an image before correction, and Figure 17(b) schematically shows an 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.

[0158] In Figure 17(a), each image schematically shows how the image in the rectangular area shown rotates left or right with each horizontal rotation of the stage.

[0159] In Figure 17(b), each image schematically shows the state 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 that it is scanned in the same direction in the direction of stage movement.

[0160] As described above, and as explained in Figure 16, if there is (detects) horizontal rotation of stage 9 (amount of deviation in the rotational direction relative to the stage movement direction), a correction is performed by rotating the stage in the opposite direction by the amount of this horizontal rotation (or rotating the detected image), making it possible to correct the image so that, as shown in Figure 17(b), there is no apparent horizontal rotation relative to the stage movement direction.

[0161] Figure 18 shows an explanatory diagram of the tilt correction of the stage according to the present invention (height control and automatic leveling by the Z-stage).

[0162] Figure 18(a) schematically shows the state before correction, and Figure 18(b) schematically shows the state after correction. Here, the horizontal axis represents the stage movement direction Y1 to Y2, and the vertical axis represents the height Z at that time.

[0163] In Figure 18(a), the convex curve shown is an example of the curve before correction, schematically illustrating the change in the height Z coordinate when Stage 9 moves from coordinate Y1 to coordinate Y2 at a constant speed. Here, it is found that the height Z changes in a convex shape (this is measured (see the stage height in Figure 3)).

[0164] In Figure 18(b), the curve shown is an example of a corrected curve, illustrating the state after correcting the height Z of the stage 9. This is because, as shown in the convex curve in Figure 18(a) before correction, if the coordinate of height Z changes when the stage 9 moves from coordinate Y1 to coordinate Y2 at a constant speed (see stage height in Figure 3), the height Z is automatically corrected in response to the height Z detected in real time.

[0165] As described above, when Stage 9 moves in a constant direction at a constant speed, its height Z can be detected in real time, and the height of the stage can be automatically corrected by the amount of that height change (see Figure 19, which will be described later).

[0166] Alternatively, instead of performing the Z-direction correction of stage 9 as described in Figure 18 above, a method may be adopted in which automatic focus and automatic magnification correction are performed by controlling the objective lens 6 (or an auxiliary objective lens not shown) in response to the movement of stage 9 in the Z direction.

[0167] Figure 19 shows an explanatory diagram of the stage height correction according to the present invention.

[0168] Figure 19(a) schematically shows the state without correction, and Figure 19(b) schematically shows the state with correction. Here, the vertical direction is the electron beam scanning direction, and the horizontal direction is the stage movement direction.

[0169] In Figure 19(a), the images of the front, middle, and rear ends without the illustrated correction schematically represent the blurring of the image caused by the change in height Z that occurred as the stage 9 moved (from coordinate Y1 (front end) to coordinate Y2 (rear end) in Figure 18).

[0170] In Figure 19(b), the images of the leading edge, middle section, and trailing edge with the illustrated correction applied schematically represent the images (without blur) after height correction has been applied to compensate for the change in height Z that occurred as a result of the movement of Stage 9 (from coordinate Y1 (leading edge) to coordinate Y2 (trailing edge) in Figure 18).

[0171] As described above, it is possible to automatically correct the uncorrected blurred image in Figure 19(a) to the corrected image in Figure 18(b) by detecting the height Z in real time and automatically correcting the height of the stage 9.

[0172] Figure 20 shows an explanatory diagram of sample height and tilt correction according to the present invention. This shows an example of an embodiment structure diagram in which the stage of Figure 13 is incorporated into Figure 1 as described above.

[0173] In Figure 20, primary electron beam 1-1 represents multiple primary electron beams.

[0174] Secondary electron beam 1-2 represents the multiple secondary electron beams emitted when multiple primary electron beams 1-1 were irradiated onto sample 51.

[0175] Height sensors 151 and 152 are devices that measure and output the height of sample 51 in real time, such as laser interferometers.

[0176] The sample holder 52 holds sample 8.

[0177] The piezoelectric elements (Z1) 51, (Z2) 52, and (Z3) 55 correspond to the stages Z1 (cone), Z2 (cone), and Z3 (flat) shown in Figure 12, and support the sample holder 52 with three-point support.

[0178] Under the above structure, as explained in Figure 13 above, by applying a control voltage to any of the three piezoelectric elements (Z1) 51, (Z2) 52, and (Z3) 55 that support the sample holder 52 at three points, it becomes possible to automatically correct the height and tilt of the sample holder 52 to a desired height Z in real time and at ultra-high speed. By correcting the tilt, the incident angle of the electron beam on the sample can be kept constant. [Brief explanation of the drawing]

[0179] [Figure 1] This is a structural diagram of one embodiment of the present invention. [Figure 2] This is an example of a schematic arrangement of the multibeam aperture of the present invention. [Figure 3] Figure 2 shows an example of a data table of the present invention. [Figure 4] This is an example of multibeam fabrication according to the present invention. [Figure 5] This is an explanatory diagram of the multi-beam detection method of the present invention. [Figure 6] This is an explanatory diagram (quadrilateral) of the multibeam image acquisition and synthesis method of the present invention. [Figure 7] This is an explanatory diagram (hexagon) for multibeam image acquisition and synthesis according to the present invention. [Figure 8] This is a flowchart illustrating the operation of the present invention (acquisition of the center coordinates of a multibeam image). [Figure 9] This is a flowchart (proofread) illustrating the operation of the present invention. [Figure 10] This is a flowchart illustrating the operation of the present invention (acquiring a multibeam image (quadrilateral)). [Figure 11] This is a flowchart illustrating the operation of the present invention (acquiring a multibeam image (hexagon)). [Figure 12] This is an explanatory diagram of the operation of the present invention (measurement of stage movement displacement and rotation). [Figure 13] This is an explanatory diagram for tilt correction of the stage according to the present invention. [Figure 14] This is an explanatory diagram of the meandering stage of the present invention. [Figure 15]This is an explanatory diagram for correcting the meandering of the stage in the present invention. [Figure 16] This is a diagram illustrating the rotation of the stage of the present invention. [Figure 17] This is an explanatory diagram for stage rotation correction in the present invention. [Figure 18] This is an explanatory diagram for tilt correction of the stage according to the present invention. [Figure 19] This is an explanatory diagram for stage height correction in the present invention. [Figure 20] This is an explanatory diagram for sample height and tilt correction of the present invention. [Explanation of Symbols]

[0180] 1: Electronic gun 1-1: Primary electron beam 1-2: Secondary electron beam 2: Blanking device 3: Illumination lens 3-1: Multibeam 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: Reverse scanning device 14: Electronic detector 52: Sample holder 53, 54, 55; Piezoelectric element 151, 152: Height sensor

Claims

1. In a multi-beam imaging device that generates an image by scanning a sample with multiple primary electron beams, A means for scanning different locations on a sample with multiple primary electron beams and outputting multiple image information, A stage for moving the aforementioned sample, The system includes a laser interferometer that measures the position of the stage in the direction of movement and the position perpendicular to the direction of movement in real time. The output image information includes overlapping images, and based on the real-time position information of the stage obtained by the laser interferometer and the overlapping images, the position of the stage is corrected, or the position of the image information is corrected to the extent corresponding to the correction of the stage position, and the corrected multiple image information is combined to generate a single image. A multibeam image generation device characterized by the following features.

2. The multi-beam image generation apparatus according to claim 1, characterized in that it corrects the amount of rotation based on the image information of the multiple electron beams output and the real-time position in the direction of movement of the stage output from the laser interferometer and the position perpendicular to the direction of movement, or corrects the image information by rotating it by an amount corresponding to the amount of rotation of the stage.

3. A multibeam image generation apparatus according to any one of claims 1 to 2, characterized in that it measures the position of the stage in the height direction in real time and corrects the height of the stage based on this, or corrects it electromagnetically and autofocuses.

4. The aforementioned multiple beam generation device is characterized in that it generates multiple primary electron beams by irradiating a single primary electron beam onto multiple apertures with holes arranged in a two-dimensional manner. A multibeam image generation apparatus according to any one of claims 3.

5. A multibeam image generation apparatus according to any one of claims 1 to 4, characterized in that a negative retarding voltage is applied to the sample, thereby reducing the energy of the primary electron beam irradiated onto and scanned by the sample while maintaining high resolution, and reducing damage to the sample.

6. In a multibeam image generation method that generates an image by scanning a sample with multiple primary electron beams, A means for scanning different locations on a sample with multiple primary electron beams and outputting multiple image information, A stage for moving the aforementioned sample, A laser interferometer is provided to measure the position of the stage in the direction of movement and the position perpendicular to the direction of movement in real time. The output image information includes overlapping images, and based on the real-time position information of the stage obtained by the laser interferometer and the overlapping images, the position of the stage is corrected, or the position of the image information is corrected to the extent corresponding to the correction of the stage position, and the corrected multiple image information is combined to generate a single image. A method for generating multibeam images characterized by the following:

Images