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

Abstract

PURPOSE: To provide a multi-beam image generating device and a multi-beam image generating method, which generates multiple primary electron beams, irradiates a sample with these while moving the sample, detects the multiple electron beams emitted at this time, and combines them into a single image, thereby quickly acquiring images.CONSTITUTION: A system includes a multiple beam generating device, means for irradiating a sample with multiple primary electron beams, means for detecting electrons emitted or reflected from the sample and outputting multiple electron beam images, a stage for acquiring images by repeatedly moving and stopping the sample, and an interferometer for measuring in real time the position of the stage in the direction of movement and the position perpendicular to the direction, and is configured to combine image information of the multiple output electron beams into a single image on the basis of position information obtained by a laser interferometer of a common image that overlaps between the image information.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Traditionally, the semiconductor industry 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, multiple electron beams are irradiated at the same time to acquire a 2D image, so 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 after acquiring 2D image information to further increase 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 arranged in a two-dimensional array, scans these with the sample when it is stopped, and then moves, repeating this process, and 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 that generates 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 arranged two-dimensionally, 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 beam to cause it to be incident on the axis of a projection lens, an objective lens that narrows the primary electron beam that has been deflected in two stages by the beam splitter and incident on the axis, a deflection system that deflects the primary electron beam narrowed by the objective lens to scan it on a sample, and the beam splitter that deflects the primary electron beam in two stages to cause it to be incident on the axis. The system is equipped with 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 the direction in real time.The multiple primary electron beams generated by the multiple beam generator are deflected by a beam splitter onto the axis of an objective lens, the objective lens irradiates the sample with the finely focused primary electron beam and scans it with a deflection system, the secondary electrons emitted from the sample are deflected by the beam splitter onto the axis of the projection lens, and the projection lens forms an image of a secondary electron beam corresponding to the multiple primary electron beams arranged two-dimensionally on an electron detector, outputting image information of the multiple electron beams.

[0022] At this time, 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 a plurality of holes arranged two-dimensionally to generate a plurality of 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 generates multiple primary electron beams arranged in a two-dimensional array, scans these with the sample when it is stopped, and then moves, repeating this process. The multiple secondary electron beams emitted during this process are separated by a beam splitter, and the respective image information is detected by an electron detection device and combined into a single image, making it possible to acquire images at high speed.

[0030] In addition, by scanning a sample with multiple primary electron beams arranged in two dimensions and detecting multiple secondary electron beam images that are 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 scanning positions of multiple two-dimensionally arranged primary electron beams on the sample, it is possible to correct the center position of the secondary electron beam image and synthesize a precise image.

[0032] In addition, the position and rotation of the stage carrying the sample as it moves can be precisely measured and recorded in real time using a laser interferometer, and the amount of movement and rotation of the images of multiple secondary electron beams can be corrected to generate precise image information.

[0033] As a result, in the present invention, not only the position control of each primary electron beam constituting the multi-beam, but also the posture or speed change of the stage that occurs while the stage moves for S&R is measured in real time by the 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, and further, by performing position correction processing between each scanned image at high speed by a computer, a normalized large image without boundary effects that is ideal for inspection can be obtained.Addition processing between any scanned images is possible, and the current value of each primary electron beam can be kept small, resulting in high S&R and high throughput with high resolution. The highest throughput can be achieved even with S&R operation. Example 1

[0034] First, as an example of the present invention, a multi-beam inspection device is characterized by increasing the inspection speed by irradiating a sample with 100 or more primary electron beams at the same time and acquiring a two-dimensional secondary electron image. Each primary electron beam constituting the multi-beam is formed by dividing an electron beam generated by one electron gun with an aperture, and a small beam spot size is realized. Therefore, the amount of one primary electron beam is, for example, about 1 nA, which is small compared to the single-beam method, but each primary electron beam is scanned at a speed of several tens of MHz or more, so that an overall detection speed of more than gigapixels per second can be realized. The position of the primary electron beam irradiated on the sample surface is determined by the relative movement between the stage movement and the multi-electron beam irradiation. Whether or not this relative movement can be ideally realized determines the performance of the high-speed inspection device.

[0035] Because it is a relative motion, the irradiation position of the primary electron beam can be controlled either by controlling the stage or by using a primary electron beam deflection device. For the primary electron beam deflection device, for example, a two-stage deflection device can be used, as in a primary electron beam drawing device, to shift the primary electron beam within the XY horizontal plane while maintaining its irradiation angle. In the case of a multi-beam inspection device, each primary electron beam is not deflected individually, but instead, a uniform electric or magnetic field is applied to all the primary electron beams to scan them all at once.

[0036] Generally, a stage has a large inertial mass, whereas a primary electron beam has almost no mass, so position correction using deflection of the primary electron beam provides faster response speed and higher position accuracy. On the other hand, slow vertical fluctuations of a stage with a large time constant make focus control complicated when performed with the primary electron beam, but control can be simplified by using a Z-axis stage or other means to correct so that the height is always constant. Details will be explained below.

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

[0038] 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.

[0039] 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.

[0040] 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.

[0041] The multi-beam aperture 3-1 splits the irradiated primary electron beam into a plurality of primary electron beams arranged two-dimensionally (for example, 100 splits) (see FIG. 2).

[0042] 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 the sample 8 by the objective lens 6 described below.

[0043] 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, which forms an image of multiple secondary electron beams arranged two-dimensionally on the electron detection device 14, and outputs multiple secondary electron images (secondary electron signals).

[0044] 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.

[0045] 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.

[0046] The objective lens 6 narrows the primary electron beams and irradiates them onto the sample 8 .

[0047] The deflection device 7 scans a plurality of primary electron beams over the surface of a sample 8, and typically repeats two-dimensional scanning (scanning in the X and Y directions) while moving and stopping a stage 9 (see Figures 6, 7, etc.).

[0048] The sample 8 is a specimen such as a mask or wafer, from which multiple images are acquired and synthesized into a single image.

[0049] The mirror 8-1 is a reflecting mirror for measuring the position in real time by a laser interferometer.

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

[0051] The vacuum chamber 10 is a container that can accommodate the sample 8, the stage 9, etc. and can be evacuated to a vacuum.

[0052] The vacuum pump 10-1 evacuates the inside of the vacuum chamber 10 and is an oil-free pump.

[0053] 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 .

[0054] 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 .

[0055] The inverse scanning device 13 inversely scans (reverses or corrects) the multiple secondary electron beams emitted when multiple two-dimensionally arranged primary electron beams are narrowed and scanned over the sample 8 so that each of the secondary electron beams remains within a specified 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, 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.

[0057] Next, the operation of the structure of FIG. 1 will be described.

[0058] (1) The primary electron beam emitted from the electron gun 1 irradiates the multi-beam aperture 3-1 to generate multiple primary electron beams arranged in a two-dimensional array (see FIG. 2). The generation of multiple primary electron beams arranged in a two-dimensional array 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 primary electron beams arranged in a two-dimensional array corresponding to the multiple electron emission sources.

[0059] (2) The multiple primary electron beams split and generated by the beam aperture 3-1 and arranged in two dimensions 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.

[0060] (3) The two-dimensionally arranged multiple primary electron beams incident on the axis of the objective lens 6 are narrowed by the objective lens 6, and two-dimensionally scan the surface of the sample 8 when the sample 8 moves and stops, and then move and stop repeatedly. As a result, when the movement of the sample 8 stops, the two-dimensionally arranged multiple primary electron beams are surface-scanned in a rectangular shape or the like on the sample 8. At this time, although not shown, a negative retarding voltage is applied to the sample 8, and the energy of the multiple 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 multiple primary electron beams of 15 KV to generate a 1 KV primary electron beam for irradiating the sample 8).

[0061] (4) Secondary electrons, reflected electrons, light, X-rays, etc. are emitted from the area of ​​the multiple primary electron beams scanned in a rectangular shape, etc. in (3).

[0062] 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.

[0063] (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 reverse scanning device 13 synchronizes with the scanning (deflection) of the multiple primary electron beams on the sample 8 and supplies a voltage (or current) to the reverse scanning device 13 to correct the multiple secondary electron 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.

[0064] As a result of the above, a plurality of two-dimensionally arranged primary electron beams are generated, which are narrowed by objective lens 6 via beam splitter 5, and with sample 8 stopped on stage 9, surface scanning is performed in a rectangular shape or the like, and then the sample moves again, and this process is repeated to scan a rectangular or other surface area with the plurality of primary electron beams. Then, the plurality of secondary electron beams emitted at this time are separated via beam splitter 5, and the plurality of 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 plurality of secondary electron beams.

[0065] Fig. 2 shows an example of a schematic arrangement of the multibeam aperture of the present invention. This shows an example of the arrangement of holes in the multibeam aperture 3-1 of Fig. 1. Note that, although the holes are shown in Fig. 2 as a schematic rectangular shape, in practice, the holes (circular holes) are preferable.

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

[0067] Figure 2(a) shows an example of a square (rectangle). This is a schematic diagram of an example in which holes are arranged two-dimensionally as shown (in practice, round shapes are better) in the aperture of multi-beam aperture 3-1 in Figure 1. For example, if 9 x 9 holes are arranged in a square (rectangle), a total of 81 primary electron beams can be generated. As shown in the figure, the size of the holes is Ax x Ay, the spacing between holes in the horizontal (X) direction is Sx, and the spacing between holes in the vertical (Y) direction is Sy.

[0068] Figure 2(b) shows an example of a hexagon. This is a schematic diagram of an example in which holes (round shapes are preferable in practice) arranged two-dimensionally as shown in the figure are provided in the aperture of the multi-beam aperture 3-1 in Figure 1. For example, if holes are provided as shown in the figure, there will be a total of 73 holes, as shown below.

[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 pieces Therefore, a total of 73 primary electron beams can be generated. As shown in the figure, the size of the holes is Ax × Ay, the spacing between holes in the horizontal (X) direction is Sx, and the spacing between holes in the vertical (Y) direction is Sy, and they are arranged in a staggered pattern as shown in the figure.

[0070] Each of the multi-beam apertures 3-1 in Figures 2(a) to 2(b) may be provided with a function for independently turning on / off each primary electron beam, and instead of preparing a large number of apertures with different physical arrangements as shown in the figure, 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.

[0071] Fig. 3 shows an example of the data table (Fig. 2) of the present invention. As already described and described later, Fig. 3 shows the stage displacement amount, stage rotation amount, and stage height recorded in association with the stage position when the position XYZ and rotation θ of the stage 9 carrying the sample 8 (e.g., a mask) are measured in real time by a laser interferometer under the structure of Fig. 1, the stage 9 is stopped, the sample 8 is scanned with a primary electron beam to obtain a secondary electron image, and then the stage is moved repeatedly.

[0072] 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 moved and stopped, and the primary electron beam is surface-scanned on the sample 8, 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 measured and recorded in real time every 0.01 μm corresponding to 10 μm and 1 μm rectangular areas, every 0.001 μm, etc. Note that if the same value is repeated, the difference may be recorded. Also, each stop position of the stage 9 may be recorded.

[0073] 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).

[0074] 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).

[0075] 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).

[0076] As described above, when the stage 9 in Fig. 1 is moved and stopped, it is possible to precisely measure and record in real time the deviations of the stage 9 from the ideal values ​​(stage deviation (XY)), stage rotation amount θ, and stage height Z) 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 movement 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.

[0077] Fig. 4 shows an example of the creation of multiple beams according to the present invention, which is a schematic diagram showing an example of the creation of multiple beams using the multibeam aperture 3-1 shown in Fig. 1 described above.

[0078] In FIG. 4, the primary electron beam emitted from the electron gun 1 is projected by the illumination lens 3 so as to irradiate a plurality of holes (see FIG. 2) arranged two-dimensionally in the multi-beam aperture 3-1 as shown in the figure. A plurality of primary electron beams (multi-electron beams 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 planar scanning is performed when the sample 8 is stopped by the stage 9, so that the surface of the sample 8 is planarly scanned by the multi-electron beam 3-2 on a plane such as a rectangular shape. Then, the emitted secondary electron beams are detected by the electron detection device 14 of FIG. 1, and secondary electron images are acquired and synthesized into one (see FIG. 6 and FIG. 7), making it possible to generate a secondary electron image of the sample 8.

[0079] 5 shows a diagram illustrating the multi-beam detection of the present invention, which shows a detailed diagram of the projection lens 12, the inverse scanning device 13, and the electronic detection device 14 of FIG.

[0080] 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 reverse scanning device 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.

[0081] 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.

[0082] 6 shows an explanatory diagram (rectangle) of the multi-beam image acquisition and synthesis 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 Fig. 6, images 1, 2, 3, and 4 are schematic diagrams showing how a plurality of primary electron beams generated using the rectangular multi-beam aperture 3-1 in Fig. 2(a) are irradiated onto a stationary sample 8, which is then moved a predetermined distance, and four images (secondary electron images) in which adjacent portions overlap as shown in the figure are obtained, and how these four images are synthesized into one image using a known synthesis software. A detailed explanation will be given below.

[0084] (1) In Fig. 6, each primary electron beam is directed two-dimensionally in the XY directions onto the surface of the sample 8, and the stage 9 moves a set distance in any direction by S&R. The amount of stage movement corresponds to the width of the area that can be covered by one scanning surface. In reality, an overlapping area is provided at the corner for alignment, so the stage instantaneously moves a distance that is less than the scanning surface width by the amount of overlap.

[0085] (2) The amount of movement of the primary electron beam, the position of the stage, and brightness information of the image of the scanning surface are recorded. Each time S&R is repeated, multiple images of the scanning surface are formed. In order to scan the sample 8 without leaving anything behind, the scanning surfaces are overlapped by about 5 to 10% of the scanning width. This eliminates scanning omissions and also results in a common image being present in the images of adjacent scanning surfaces. Therefore, the positional relationship of the images of adjacent scanning surfaces can be corrected and combined into a single large image using the position coordinates obtained by the laser interferometer and pattern matching, etc.

[0086] (3) Because the overlapping area is scanned twice, a high SNR can be obtained due to 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 single large image area from the images of the four independent scanning planes. The image processed in this way is used as the inspection image. If the inspection object is formed without spanning the images of each scanning plane, inspection can be achieved using the image of one scanning plane, so it is not necessarily necessary to combine them into a single image.

[0087] 7 shows an explanatory diagram (hexagonal) of the multi-beam image acquisition and synthesis 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 Fig. 7, images 1, 2, 3, and 4 are schematic diagrams showing how a plurality of primary electron beams generated using the hexagonal multi-beam aperture 3-1 in Fig. 2(b) are irradiated onto a stationary sample 8, which is then moved a predetermined distance, and four images (secondary electron images) in which adjacent portions overlap as shown in the figure are obtained, and these four images are synthesized into one image using a known synthesis software. A detailed explanation will be given below.

[0089] Here, similarly to (1) to (4) in the case of a square in Figure 6, in the case of a hexagon in Figure 7, as shown in the examples of images 1, 2, 3, and 4 of the scanning surface generated when an aperture arranged in a honeycomb pattern (Figure 2 (b)) is provided, an electron beam column is generally cylindrical, and when the electron beam is scanned, the characteristics change or deteriorate in a concentric manner. Therefore, by using a hexagon in a honeycomb pattern, deterioration is suppressed and many images with the same characteristics can be obtained.

[0090] As in the case of Figure 6, in Figure 7, the secondary electron images generated by scanning each primary electron beam are independent of each other, so images 1, 2, 3, and 4 of each scanning plane are completely independent images. Since the relative positions of each are known, image processing is performed using that relative position to obtain a single image by superimposing the images of each scanning plane. The image superimposition is achieved by pattern matching the overlapping parts.

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

[0092] FIG. 8 is a flowchart illustrating the operation of the present invention (acquiring the central coordinates of a multi-beam image).

[0093] In FIG. 8, S1 prepares a pattern with known spacing dimensions. This is a reference sample with a pattern whose pattern spacing and shape dimensions are precisely known. A conductive photomask or silicon substrate with the same pattern fabricated in advance is good. The pattern size and spacing are measured in advance using a CDSEM or optical measurement 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 with a pattern located at the designed deflection center coordinates. 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.

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

[0095] S3 compares the acquired image with a pattern of known interval dimensions.

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

[0097] As a result of the above, it is possible to calculate (measure) the central coordinates on sample 8 scanned by the multiple primary electron beams split and generated by the two-dimensionally arranged multi-beam aperture in Fig. 2. Thereafter, based on the central coordinates of these multiple primary electron beams, each is subjected to planar scanning, and the acquired images are synthesized to generate a single image. This will be explained in detail below.

[0098] 9 is a flowchart explaining the operation (calibration) of the present invention. This shows an example of a procedure for automatically correcting errors (XY, Z) that accompany the movement of the stage 9.

[0099] 9, S11 is set to the stage movement start position. This is set to the stage movement start position of the stage 9 in FIG. 1, for example, the movement start position (home position) on the sample 8 from which 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] In step S14, the center coordinates of the electron beam scanning are made to coincide with the target position. These steps S12, S13, and S14 move the stage 9 a predetermined distance from the stage movement start position set in step S11 (for example, move from the stage movement start position to the center position where an image is acquired, or move from the center position of an image that has already been acquired to the center position of the next image), issue a stop command, and stop the stage 9. Then, the difference (ΔX, ΔY) between the current position where the stage 9 has been stopped (the current position (X, Y) measured in real time by a laser interferometer described later) and the specified target position is fed back to the electron beam deflection device 7 in FIG. 1 so as to correct the difference, and the stage 9 is corrected so as to stop at the specified position (the irradiation positions of the multiple primary electron beams are corrected).

[0103] In step S15, the stage height is adjusted to match the target value. Similarly, the height Z of the stage 9 measured in real time is corrected in real time so that the height Z of the stage 9 matches the target height (see FIG. 14, etc., described later).

[0104] In step S16, an image is acquired after the stage position and height are corrected to match the target position and height in steps S11 to S15 (described later with reference to FIGS. 10 and 11).

[0105] As described above, the position and height of the stay 9 are measured in real time while the stage 9 is moved and stopped, and after matching (correcting) it to the target position and height, images are acquired, making it possible to accurately acquire images (images by multi-beams) at the desired positions. Then, the acquired multiple images are synthesized to generate a single image.

[0106] 10 shows a flowchart for explaining the operation of the present invention (acquiring a multi-beam image (square)). This is a flowchart for explaining the operation when acquiring the square multi-beam image of FIG.

[0107] In Fig. 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 split by the rectangular multi-beam aperture in Fig. 2(a) described above are irradiated onto the surface of the sample 8 while scanning the surface, and secondary electrons emitted at this time are detected by the electron detection device 14, and secondary electron images are acquired and synthesized to acquire, for example, one image 1 shown in Fig. 6.

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

[0109] S23 acquires an image. It stops at the position where it moved with the overlap width x of S22 and acquires image 2. As a result, there is an overlap width x between images 1 and 2 in Figure 6, and it is possible to accurately combine them into one image using this overlap portion.

[0110] In S24, it is determined whether the process is finished. If the result is YES, the process proceeds to S25. If the result is NO, the process returns to S22 and is repeated.

[0111] S25 moves the stage by the scan plane width Y-overlap width y. As shown in Fig. 6, when moving from the image 2 shown in the image acquisition to the position of image 4, the stage 9 is moved to a position obtained by subtracting the "overlap width y" from the "scan plane width Y".

[0112] S26 acquires an image. This stops at the position moved downward with the overlap width y of S25, and acquires image 4. As a result, there is an overlap width y between images 2 and 4 in FIG. 6, and it is possible to accurately combine them into one image using this overlap portion.

[0113] In step S27, it is determined whether the process is to end. If the result is YES, the process ends. If the result is NO, the process returns to step S25 and is repeated.

[0114] As described above, when multiple primary electron beams are generated using the rectangular multi-beam aperture in Figure 2(a) and these are irradiated onto the surface of a sample 8 while performing a surface scan to obtain an image of the sample 8, by moving the stage so that there is an overlap width x, y between the images as shown in Figure 6, partially overlapping images 1, 2, 3, 4, etc. can be generated and these overlapping portions can be used to accurately and quickly combine into a single image.

[0115] 11 shows a flowchart for explaining the operation of the present invention (acquiring a multi-beam image (hexagonal)). This is a flowchart for explaining the operation when acquiring the hexagonal multi-beam image of FIG.

[0116] In Fig. 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 split by the hexagonal multi-beam aperture in Fig. 2(b) described above are irradiated onto the surface of the sample 8 while surface scanning, and secondary electrons emitted at this time are detected by the electron detection device 14, and secondary electron images are acquired and synthesized to acquire, for example, one image 1 shown in Fig. 7.

[0117] S32 moves the stage by the scan plane width X-overlap width x. As shown in Fig. 7, when moving from image 1 acquired in S31 to the position of image 2, the stage 9 is moved to a position obtained by subtracting "overlap width x" from "scan plane width X".

[0118] S33 acquires an image. It stops at the position where it moved with the overlap width x of S32 and acquires image 2. As a result, there is an overlap width x between images 1 and 2 in FIG. 7, and it is possible to accurately combine them into one image using this overlap portion.

[0119] In step S34, it is determined whether the process is to end. If the result is YES, the process proceeds to step S35. If the result is NO, the process returns to step S32 and is repeated.

[0120] S35 moves the stage by the scan plane width Y-overlap width y. As shown in Fig. 7, when moving from the position of image 2 where an image was acquired to the position of image 4, the stage 9 is moved to a position obtained by subtracting "overlap width y" from "scan plane width Y".

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

[0122] In step S37, it is determined whether the process is to end. If the result is YES, the process ends. If the result is NO, the process returns to step S35 and is repeated.

[0123] As described above, when multiple primary electron beams are generated using the hexagonal multi-beam aperture in Figure 2(b) and these are irradiated onto the surface of a sample 8 while performing a surface scan to obtain an image of the sample 8, by moving the stage so that there is an overlap width x, y between the images as shown in Figure 7, partially overlapping images 1, 2, 3, 4, etc. can be generated and these overlapping portions can be used to accurately and quickly combine into a single image.

[0124] FIG. 12 is a diagram illustrating the operation of the present invention (measurement of deviation amount and rotation amount of stage movement).

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

[0126] In FIG. 12(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.

[0127] 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.

[0128] 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).

[0129] In FIG. 12(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.

[0130] 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.

[0131] 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).

[0132] Fig. 13 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 contracts by applying a voltage to the piezoelectric element, and the structure allows it to be arbitrarily adjusted from the outside to any distance.

[0133] In detail, FIG. 13 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.

[0134] 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.

[0135] 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. Position accuracy can be achieved on the order of nm (see Figure 20 below).

[0136] 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.

[0137] FIG. 14 is an explanatory diagram of the meandering of the stage of the present invention.

[0138] Fig. 14(a) shows a schematic diagram of the stage without meandering, Fig. 14(b) shows a schematic diagram of the stage with left meandering, and Fig. 14(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.

[0139] FIG. 14(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.

[0140] In (b) of Fig. 14, 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 amount in Fig. 3).

[0141] 14(c) shows a schematic diagram of the stage 9 wobbling to the right with respect to the stage movement direction in a fixed direction (vertical direction), indicating 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).

[0142] 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.

[0143] 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 14.

[0144] 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.

[0145] FIG. 15 is an explanatory diagram of meandering correction of the stage of the present invention.

[0146] Fig. 15(a) shows a schematic example of an image before correction, and Fig. 15(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.

[0147] In FIG. 15(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.

[0148] In Fig. 15(b), each image is a schematic diagram of the state after the image of the illustrated rectangular area is corrected for each meandering of the stage. It can be seen that there is no meandering in the image, and that the scanning is performed with the same width in the direction of stage movement.

[0149] As described above with reference to Figure 14, 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 15(b).

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

[0151] Fig. 16(a) shows a schematic diagram of the state without horizontal rotation, Fig. 16(b) shows a schematic diagram of the state with horizontal rotation to the right, and Fig. 16(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.

[0152] FIG. 16(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.

[0153] In (b) of Figure 16, the stage 9 is shown to be rotated to the right 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 left (see the stage rotation amount in Figure 3).

[0154] In Fig. 16(c), 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 Fig. 3).

[0155] 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.

[0156] FIG. 17 is a diagram illustrating the rotation correction of the stage according to the present invention.

[0157] Fig. 17(a) shows a schematic example of an image before correction, and Fig. 17(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.

[0158] In FIG. 17(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.

[0159] In Fig. 17(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.

[0160] As described above in FIG. 16, 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. 17(b).

[0161] FIG. 18 is an explanatory diagram of stage tilt correction of the present invention (height control and automatic leveling by the Z stage).

[0162] Fig. 18(a) shows a schematic diagram of the state before correction, and Fig. 18(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.

[0163] 18(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)).

[0164] In (b) of Fig. 18, 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. 18 before correction, if 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.

[0165] 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. 19 described later).

[0166] 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. 18 with respect to the movement of the stage 9 in the Z direction.

[0167] FIG. 19 is an explanatory diagram of the height correction of the stage of the present invention.

[0168] Fig. 19(a) shows a schematic diagram of a state without correction, and Fig. 19(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.

[0169] In FIG. 19(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. 18).

[0170] In FIG. 19(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. 18).

[0171] As described above, for the uncorrected blurred image in FIG. 19(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. 18(b).

[0172] Fig. 20 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. 13 is incorporated into the already described Fig. 1.

[0173] In FIG. 20, a primary electron beam 1-1 represents a plurality of primary electron beams.

[0174] 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.

[0175] 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.

[0176] The sample holder 52 holds the sample 8 .

[0177] 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.

[0178] 13, it is possible to automatically correct the height and tilt of sample holder 52 to the desired height Z in real time at ultra-high speed by applying a control voltage to any of the piezoelectric elements (Z1) 51, (Z2) 52, (Z3) 55 that support sample holder 52 at three points. By correcting the tilt, the incidence angle of the electron beam with respect to the sample can be kept constant. [Brief description of the drawings]

[0179] [Figure 1] FIG. 1 is a structural diagram of an embodiment of the present invention. [Diagram 2] 2 is a schematic example of a multi-beam aperture arrangement according to the present invention. [Diagram 3] 2 is an example of a data table of the present invention (FIG. 2). [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 (square shape) of multi-beam image acquisition and synthesis according to the present invention. [Figure 7] FIG. 1 is an explanatory diagram (hexagonal) of multi-beam image acquisition and synthesis according to the present invention. [Figure 8] 1 is a flowchart illustrating the operation of the present invention (obtaining the center coordinates of a multi-beam image). [Figure 9] 4 is a flowchart illustrating the operation (calibration) of the present invention. [Figure 10] 1 is a flowchart illustrating the operation of the present invention (acquiring a multi-beam image (quadrilateral)). [Figure 11] 1 is a flowchart illustrating the operation of the present invention (acquiring a multi-beam image (hexagonal)). [Figure 12] 1A to 1C are diagrams for explaining the operation of the present invention (measurement of deviation amount and rotation amount of stage movement). [Figure 13] FIG. 4 is an explanatory diagram of tilt correction of a stage according to the present invention. [Figure 14] FIG. 4 is an explanatory diagram of the meandering of a stage according to the present invention. [Figure 15]FIG. 4 is an explanatory diagram of meandering correction of a stage according to the present invention. [Figure 16] FIG. 4 is an explanatory diagram of the rotation of a stage according to the present invention. [Figure 17] FIG. 13 is an explanatory diagram of rotation correction of a stage according to the present invention. [Figure 18] FIG. 4 is an explanatory diagram of stage tilt correction according to the present invention. [Figure 19] FIG. 4 is an explanatory diagram of height correction of the stage of the present invention. [Figure 20] FIG. 4 is an explanatory diagram of sample height and tilt correction according to the present invention. [Explanation of symbols]

[0180] 1: Electron gun 1-1: Primary electron beam 1-2: Secondary electron beam 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: Reverse scanning device 14: Electronic detector 52: Sample holder 53, 54, 55; Piezoelectric element 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 two-dimensionally arranged primary electron beams; a means for irradiating a sample with a plurality of primary electron beams generated by the multiple beam generating device; means for detecting electrons emitted or reflected from the sample to produce an image of the multiple electron beams; a stage for acquiring images of the sample while repeatedly moving and stopping the sample; A laser interferometer that measures the position in the moving direction and the position perpendicular to the moving direction of the stage in real time; Equipped with The overlapping common image between the output image information of the multiple electron beams is The position information of the stage obtained by the laser interferometer is combined into a single image. A multi-beam image generating device comprising:

2. 2. The multi-beam image generating device according to claim 1, wherein the amount of movement and rotation of the stage is corrected based on the image information of the output multiple electron beams and the real-time position of the stage in the movement direction and the perpendicular direction output from the laser interferometer, or the image information is moved and rotated by an amount corresponding to the amount of movement and rotation of the stage.

3. 3. A multi-beam image generating device as described in claim 1, characterized in that the height of the stage is measured in real time, and the height of the stage is corrected based on the measured height, or electromagnetically corrected, and automatic focusing is performed.

4. 2. The multiple beam generating device according to claim 1, wherein the multiple beam generating device generates multiple primary electron beams by irradiating a single primary electron beam onto a plurality of apertures having holes arranged two-dimensionally.

4. A multi-beam image generating device according to claim 3.

5. 5. 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.

6. 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 two-dimensionally arranged primary electron beams; a means for irradiating a sample with a plurality of primary electron beams generated by the plurality of beam generating devices; means for detecting electrons emitted or reflected from the sample to produce an image of the multiple electron beams; a stage for acquiring images of the sample while repeatedly moving and stopping the sample; A laser interferometer that measures the position in the moving direction and the position perpendicular to the moving direction of the stage in real time; Established The overlapping common image between the output image information of the multiple electron beams is A multi-beam image generating method characterized by combining multiple beams into a single image based on stage position information obtained by a laser interferometer.

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