JP7624541B2 - Multi-beam image generating device and multi-beam image generating method - Google Patents

Description

The present invention relates to a multi-beam image generating device and a multi-beam image generating method that generate an image by scanning a sample with multiple primary electron beams.

Traditionally, the semiconductor industry has been supported by the improved device performance and cost benefits brought about by advances in microfabrication technology, famously known as Moore's Law, but the limits of microfabrication of semiconductor devices are 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 4:1 reduction exposure technology, so a pattern structure that is four times the size of the pattern structure on the silicon wafer on which the semiconductor device is actually made is formed on the photomask.

The biggest challenge in exposure technology is how accurately the pattern created on the photomask based on semiconductor circuit design data can be transferred to the resist film pattern on the wafer surface. If there is an abnormality in the photomask, it will be transferred to the wafer surface by the exposure device, causing defects on the wafer.

To prevent exposure defects, it is necessary to at least inspect the entire photomask and correct it to create a perfect pattern as designed. The limit of fine processing is proportional to the wavelength of the light used for exposure, so the wavelength of the light used for exposure is becoming shorter and shorter with the times.

Since the end of the 20th century, laser light sources with a wavelength of 193 nm have been used as exposure light sources, and for a long time, patterns on photomasks have been inspected using optical mask pattern inspection equipment that uses laser light of 193 nm or the like as illumination light.

However, since 2019, exposure technology using EUV light with a short wavelength of 13.5 nm has been fully introduced, and the limit of microfabrication that can be exposed has become smaller. Patterns on photomasks have also become smaller, from the previous minimum pattern size of around 100 nm to 50 nm or less, making it no longer possible to adequately inspect with the previous 193 nm light.

On the other hand, there are also so-called actinic inspection devices 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 device must be evacuated, making it extremely complex compared to conventional devices that were implemented in the atmosphere. Also, because there are no optical lenses that can transmit 13.5 nm light, the optical system must be constructed entirely of reflective optical systems, 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.

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 a single exposure despite the long wavelength of 193 nm. By using double patterning, it is even possible to create a pattern of about 20 nm.

On the other hand, when EUV light is used, only a small aperture ratio such as MA 0.33 can be achieved because a reflective optical system is used. Although the light source wavelength is one-tenth shorter than the conventional wavelength, 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. In this way, 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 the air, requiring a large vacuum chamber, which eliminates the advantage in usability over electron beam devices.

On the other hand, electron microscopes are a technology that can achieve nanometer-order high resolution. Electron beam defect inspection technology using electron beams has been developed for over 30 years. Although it has been commercialized, 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 find electrical defects that cannot be found with optical methods, it is gradually becoming more widely used for developing new wafer processes.

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 the large current required for high-speed inspection is passed, 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, so there is a fundamental flaw in that the speed becomes slower as miniaturization progresses.

For example, currently, the maximum inspection speed that can be achieved using one electron beam is at most 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 photomask, 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 required 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 that and cannot be used in practice.

On the other hand, in order to improve the speed of electron beam inspection equipment, a method known as a multi-electron beam inspection equipment is being researched that performs high-speed inspections 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.

However, many companies have been developing various types of multi-beam inspection equipment, and although they are seen as very promising next-generation high-speed inspection equipment, they have not yet achieved the speed and resolution expected, and have not yet been commercialized as semiconductor inspection equipment.

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, which university professors and students can use occasionally to write papers, it is completely unusable for practical purposes. 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.

Conventional high-speed inspection equipment using a single beam method generally uses a continuous stage method, but multi-beam methods that simultaneously acquire two-dimensional images have adopted a step-and-repeat method that maximizes the area that can be acquired in one scan to increase speed. This causes the stage movement time to be dominant, making it impossible to increase speed.

In addition, there was a clear contrast difference due to the difference in sensitivity at the boundaries of the scanning area, making it difficult to use as an inspection image.

In addition, with the single beam system, 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, with the multi-beam system, multiple electron beams are irradiated simultaneously to acquire a two-dimensional image, so there is the 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 two-dimensional image information in order to further increase speed, there is the problem that stage rotation, undulation, stage speed fluctuation, height fluctuation, vibration, etc. that occur during movement affect the acquisition of the two-dimensional image and reduce the quality of the image.

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

In order to solve the above-mentioned problems, the present invention generates multiple primary electron beams arranged in a two-dimensional manner, scans the sample when it is stopped, and then moves, repeating this process, and then splitting the multiple secondary electron beams emitted at this 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.

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 device comprising: a multiple beam generating device that generates 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 the secondary electron beam emitted from the sample in two stages in the opposite direction to the primary electron beam to cause them 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 over a sample; and a 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 secondary electron beams generated by the multiple beam generator onto an electron detector, a stage that repeatedly moves and stops the sample and captures an image when the sample stops, and an interferometer that measures the position of the sample in the moving direction and the perpendicular direction in real time. The multiple primary electron beams generated by the multiple beam generator are deflected to the axis of the objective lens by a beam splitter, the objective lens irradiates the sample with a finely focused primary electron beam and scans it with a deflection system, the secondary electrons emitted from the sample are deflected to the axis of the projection lens by a beam splitter, and the projection lens images a secondary electron beam corresponding to the multiple two-dimensionally arranged primary electron beams on the electron detector, outputting image information of the multiple electron beams.

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

In addition, the amount of 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.

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

The multiple beam generating device also irradiates a single primary electron beam onto an aperture with multiple holes arranged in a two-dimensional manner to generate multiple primary electron beams.

The beam splitter also has an electrostatic deflector in the first stage on the primary electron incidence 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.

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.

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

The present invention generates multiple primary electron beams arranged in two dimensions, scans 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 image information of each is detected by an electron detection device and combined into a single image, making it possible to acquire images at high speed.

In addition, by 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.

In addition, by acquiring and registering in advance the scanning positions of multiple two-dimensionally arranged primary electron beams on the sample, it is now possible to correct the center position of the secondary electron beam image and synthesize a precise image.

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

As a result, in this invention, not only is the position of each primary electron beam that constitutes the multi-beam controlled, but the stage position or speed change that occurs while the stage is moving in S&R is measured in real time by the stage position measurement 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 a computer is further used to perform high-speed position correction processing between each scanned image, thereby making it possible to obtain a single large normalized image without boundary effects, which is ideal for inspection. 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.

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 in order to realize a small beam spot size, the amount of one primary electron beam is, for example, about 1 nA, which is small compared to the single-beam method. However, 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.

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. The primary electron beam deflection device can be realized by shifting the primary electron beam within the XY horizontal plane while maintaining the irradiation angle by using a two-stage deflection device, for example, as in a primary electron beam drawing device. 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.

Generally, a stage has a large inertial mass, whereas the primary electron beam has almost no mass, so position correction using deflection of the primary electron beam provides faster response speed and higher positional accuracy. On the other hand, slow up and down stage fluctuations with a large time constant make focus control complicated when performed with the primary electron beam, but control can be simplified by correcting so that the height is always constant using a Z-axis stage, etc. These will be explained in detail below.

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

In FIG. 1, the electron gun 1 is a known device that generates an electron beam, generating a primary electron beam accelerated to several hundred volts to several tens of kilovolts. The electron gun uses a thermionic electron source such as W or LaB6, a TFE using ZrO or a cold field emitter or a photocathode, and the electron gun chamber is kept at an ultra-high or extremely high vacuum of 10-8 Pa or higher using an ion pump or getter pump.

The blanking device 2 quickly turns the primary electron beam emitted from the electron gun 1 on or off, deflecting the primary electron beam by turning the voltage on or off to pass or block it.

The illumination lens 3 focuses the electron beam generated and accelerated by the electron gun 1 into a specified beam as shown in Figure 4, which will be described later.

The multi-beam aperture 3-1 splits the irradiated primary electron beam into multiple primary electron beams arranged in two dimensions (e.g., 100 splits) (see Figure 2).

The objective aperture 4 is used to pass the central portion of each of the multiple primary electron beams, and each of the primary electron beams is focused and irradiated onto the surface of the sample 8 by the objective lens 6, which will be described later.

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 focuses it onto 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).

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

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

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

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

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

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

The stage (XYZθ stage) 9 is a stage on which a sample can be mounted and which can 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.

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

The vacuum pump 10-1 is used to evacuate the inside of the vacuum chamber 10, and is an oil-free pump that evacuates the air.

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

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

The inverse scanning device 13 performs inverse scanning (reversing or correcting) so that the multiple secondary electron beams emitted when multiple two-dimensionally arranged primary electron beams are narrowly focused and scanned on the sample 8 each remain within a specified area on the detection surface of the electron detection device 14.

The electron detection device 14 detects each of the multiple secondary electron beams emitted from the sample 8. For example, an avalanche photodiode, CCD, CMOS sensor, or TDI camera can be used. The electrons may first collide with a scintillator and be converted into light, which is 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 specified area of the detection surface.

Next, we will explain the operation of the structure in Figure 1.

(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. It is also possible to provide multiple electron emission sources on the surface of the emitter of the electron gun 1 and generate multiple primary electron beams arranged in a two-dimensional array corresponding to these.

(2) The two-dimensionally arranged multiple primary electron beams split and generated by the beam aperture 3-1 pass through the center of the objective aperture 4, are deflected to the right by the upper electrostatic deflector 5-1 that constitutes the beam splitter 5, and are deflected to the left by the electromagnetic deflector 5-2, and are incident on the axis of the objective lens 6.

(3) The 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).

(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 or the like in (3).

(5) The secondary electrons emitted in (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 (opposite the direction of the deflection of the multiple primary electron beams) by the lower stage electromagnetic deflector 5-2 that constitutes the beam splitter 5, are deflected to the left by the electrostatic deflector 5-1, and are incident on the axis of the projection lens 12.

(6) After correction by the alignment 11 as necessary on the axis of the projection lens 12, the multiple secondary electron beams emitted from the sample 8 are imaged on the electron detection device 14 and irradiated onto the imaging area of each of the multiple secondary electron beams of the electron detection device 14. If 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 to 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.

By the above, multiple primary electron beams arranged in two dimensions are generated, which are narrowed by the objective lens 6 via the beam splitter 5, and the sample 8 is stopped on the stage 9 and surface-scanned in a rectangular shape or the like, and then the process is repeated to scan each rectangular or other surface area with the multiple primary electron beams. The multiple secondary electron beams emitted at this time are then separated via the beam splitter 5, and the multiple secondary electron beams are imaged on the respective detection surfaces of the electron detection device 14 by the projection lens 12, making it possible to output secondary electron images (secondary electron signals) of each of the multiple secondary electron beams.

Figure 2 shows an example of a schematic arrangement of the multibeam aperture of the present invention. This shows an example of the type of arrangement of holes in the multibeam aperture 3-1 of Figure 1 described above. Note that in Figure 2, the holes are shown as being typically rectangular, but in practice, circular holes are preferable.

Figure 2(a) shows an example of a quadrangle (rectangle), and Figure 2(b) shows an example of a hexagon.

Figure 2(a) shows an example of a square (rectangle). This is a schematic diagram of an example in which holes (circular shapes are preferable in practice) are arranged two-dimensionally as shown 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, 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.

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) are arranged two-dimensionally as shown in the aperture of multi-beam aperture 3-1 in Figure 1. For example, if holes are arranged as shown in the figure, the total number of holes will be 73, as shown below.

・1st 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 the holes in the horizontal (X) direction is Sx, and the spacing between the holes in the vertical (Y) direction is Sx. The interval between the electrodes is Sy, and the electrodes are arranged in a staggered pattern as shown in the figure.

In addition, each multi-beam aperture 3-1 in Figures 2(a) and 2(b) can be given the function of independently turning on and off each primary electron beam, and instead of preparing a large number of apertures with different physical arrangements as shown, they can 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.

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

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.

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

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

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).

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 using a laser interferometer the deviations from the ideal values of the stage 9 (stage deviation (X.Y)), the stage rotation amount θ, and the deviations of the stage height Z). 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. The details are explained below in order.

Figure 4 shows an example of creating a multi-beam according to the present invention. This Figure 4 is a schematic diagram showing an example of creating a multi-beam using the multi-beam aperture 3-1 of Figure 1 described above.

In FIG. 4, the primary electron beam emitted from the electron gun 1 is projected by the illumination lens 3 so as to irradiate the multiple holes (see FIG. 2) arranged two-dimensionally in the multi-beam aperture 3-1 as shown in the figure. The multiple primary electron beams (multi-electron beams 3-2) that are 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 in FIG. 1, which is not shown in FIG. 4. Here, the sample 8 is planar-scanned while stopped by the stage 9, so that the surface of the sample 8 is planar-scanned by the multi-electron beam 3-2 on a rectangular or other plane. The emitted secondary electron beams are then detected by the electron detection device 14 in FIG. 1, and secondary electron images are obtained and combined into one (see FIG. 6 and FIG. 7), making it possible to generate a secondary electron image of the sample 8.

Figure 5 shows an explanatory diagram of the multi-beam detection of the present invention. This shows a detailed explanatory diagram of the projection lens 12, the inverse scanning device 13, and the electronic detection device 14 of Figure 1.

In FIG. 5, multiple secondary electron beams emitted from the sample 8 are split by the beam splitter 5 and, when they are incident from the top to the bottom in FIG. 4, they are each imaged on the detection surface of the electron detection device 14 by the projection lens 12. At this time, the imaging area in which the multiple secondary electron beams are imaged is not a problem if they are within the imaging area of the sample itself, 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.

As a result, 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.

Figure 6 shows an explanatory diagram (square) 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.

In Figure 6, images 1, 2, 3, and 4 are schematic diagrams showing how a stationary sample 8 is irradiated with multiple primary electron beams generated using the rectangular multi-beam aperture 3-1 in Figure 2(a), and then moved a predetermined distance, four times to obtain four images (secondary electron images) in which adjacent portions overlap each other as shown, and how these four images are then synthesized into one image using known synthesis software. A detailed explanation is given below.

(1) In Figure 6, each primary electron beam is directed two-dimensionally in the X and Y 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.

(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 ensures that images of adjacent scanning surfaces have a common image. 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.

(3) Because the overlapping areas are scanned twice, a high SNR can be obtained due to the image addition effect, allowing for more accurate alignment. For example, in the example of 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 manner 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.

Figure 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.

In Figure 7, images 1, 2, 3, and 4 are schematic diagrams showing how a stationary sample 8 is irradiated with multiple primary electron beams generated using the hexagonal multi-beam aperture 3-1 in Figure 2(b), and then moved a predetermined distance, four times to obtain four images (secondary electron images) in which adjacent portions overlap each other as shown, and how these four images are then synthesized into one image using known synthesis software. A detailed explanation is provided below.

As in the case of a square in Figure 6 (1) to (4), 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 that are generated when an aperture arranged in a honeycomb pattern (Figure 2 (b)) is provided, electron beam columns are generally cylindrical, and when the electron beam is scanned, the characteristics change or deteriorate in a concentric manner. Therefore, a honeycomb hexagon has the advantage that deterioration is suppressed and many images with the same characteristics can be obtained.

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 surface are completely independent images. Since their relative positions are known, image processing can be performed using those relative positions to overlay the images of each scanning surface to obtain a single image. The images are overlaid by pattern matching the overlapping parts.

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, so for the same electron beam current, an image with a higher SNR can be obtained than when scanning only once. In addition, there is an averaging effect of sampling by having the electron beam scan very slightly different locations.

Figure 8 shows a flowchart explaining the operation of the present invention (obtaining the center coordinates of a multi-beam image).

In FIG. 8, S1 prepares a pattern with known spacing dimensions. This is a reference sample having 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 preferable. 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 in which a pattern is 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.

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

S3 compares the acquired image with a pattern of known spacing dimensions.

S4 calculates the central coordinates of each electron beam scan. S3 and S4 compare the images acquired in S2 with the image of a 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 amount of deviation of the central position and the design data of the reference sample, and are saved.

By the above steps, it is possible to calculate (measure) the central coordinates on the sample 8 scanned by the multiple primary electron beams generated by splitting them using the two-dimensionally arranged multi-beam aperture in Figure 2. Thereafter, based on the central coordinates of these multiple primary electron beams, it is possible to perform planar scanning on each of them and synthesize the acquired images to generate a single image. This will be explained in detail below.

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

In FIG. 9, S11 sets the stage movement start position. This is 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.

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

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

S14 matches the central coordinates of the electron beam scan with the target position. S12, S13, and S14 move the stage 9 a specified distance from the stage movement start position set in S11 (for example, move from the stage movement start position to the central position where an image is acquired, or move from the central position of an image that has already been acquired to the central position of the next image), issue a stop command, and stop it. Then, feedback is given to the electron beam deflection device 7 in FIG. 1 to correct the difference (ΔX, ΔY) between the current position where the stage 9 was stopped (the current position (X, Y) measured in real time by a laser interferometer described later) and the specified target position, and the stage 9 is corrected so that it stops at the specified position (correcting the irradiation positions of the multiple primary electron beams).

S15 matches the stage height to the target value. Similarly, the height Z of stage 9 is corrected in real time so that the current height Z of stage 9 measured in real time matches the target height (see FIG. 14, etc., described later).

In step S16, an image is acquired. This is done by correcting the stage position and height to match the target position and height in steps S11 to S15, and then acquiring the image (described later with reference to Figures 10 and 11).

As described above, the position and height of the stay 9 is measured in real time while the stage 9 is moved and stopped, and then the image is acquired after matching (correcting) it to the target position and height. This makes it possible to accurately acquire images (multi-beam images) of the desired positions. The acquired multiple images are then synthesized to generate a single image.

Figure 10 shows a flowchart explaining the operation of the present invention (obtaining a multi-beam image (square)). This is a flowchart explaining the operation when obtaining the square multi-beam image of Figure 6.

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 the 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 as shown in FIG. 6.

S22 moves the stage by the scan surface width X minus the 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 the "overlap width x" from the "scan surface width X."

S23 acquires an image. It stops at the position moved with 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 this overlapping portion can be used to accurately combine them into a single image.

S24 determines whether to end. If YES, proceed to S25. If NO, return to S22 and repeat.

S25 moves the stage by the scan plane width Y minus the overlap width y. As shown in FIG. 6, when moving from the position of the captured image 2 to the position of the image 4, the stage 9 is moved to a position obtained by subtracting the "overlap width y" from the "scan plane width Y".

S26 acquires an image. It stops at the position moved downward with overlap width y of S25, and acquires image 4. As a result, there is an overlap width y between images 2 and 4 in Figure 6, and this overlapping portion can be used to accurately combine them into a single image.

S27 determines whether to end. If YES, end. If NO, return to S25 and repeat.

As described above, when multiple primary electron beams are generated using the rectangular multi-beam aperture in Figure 2(a) and the surface of the sample 8 is irradiated with these beams 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, it is possible to generate partially overlapping images 1, 2, 3, 4, etc., and to accurately and quickly combine these overlapping portions into a single image.

Figure 11 shows a flowchart explaining the operation of the present invention (obtaining a multi-beam image (hexagonal)). This is a flowchart explaining the operation when obtaining the hexagonal multi-beam image of Figure 7.

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 of FIG. 2(b) described above are irradiated onto the surface of the sample 8 while scanning the surface, and the 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 as shown in FIG. 7.

S32 moves the stage by the scan surface width X minus the 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 the "overlap width x" from the "scan surface width X."

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

S34 determines whether to end. If YES, proceed to S35. If NO, return to S32 and repeat.

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 the image was acquired 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".

S36 acquires an image. It stops at the position moved downward with overlap width y of S35, and acquires image 4. As a result, there is an overlap width y between images 2 and 4 in Figure 7, and this overlapping portion can be used to accurately combine them into a single image.

S37 determines whether to end. If YES, end. If NO, return to S35 and repeat.

As described above, when multiple primary electron beams are generated using the hexagonal multi-beam aperture in Figure 2(b) and the surface of the sample 8 is irradiated with these beams while scanning the surface 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, it is possible to generate partially overlapping images 1, 2, 3, 4, etc., and to accurately and quickly combine these overlapping portions into a single image.

Figure 12 shows an explanatory diagram of the operation of the present invention (measuring the amount of deviation and rotation of the stage movement).

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

In FIG. 12(a), the interferometer X1 is positioned as shown in the figure so that the distance of the position of the stage 9 in the X direction can be precisely measured, and a mirror is placed on the stage side.

Interferometer Y1 is positioned as shown in the figure so that it can precisely measure the distance to the Y-direction position of stage 9, and a mirror is placed on the stage side.

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

In FIG. 12(b), the interferometer X1 is positioned as shown in the figure so that the distance of the position of the stage 9 in the X direction can be precisely measured, and a mirror is also positioned on the stage side.

Interferometers Y1 and Y2 are positioned as shown in the figure so that the distance between the positions of stage 9 in the Y direction can be precisely measured, and a mirror is placed on the stage side so that the rotation angle can be measured.

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

Figure 13 shows an explanatory diagram of stage tilt correction of the present invention. This shows an example of stage 9 in Figure 1 already described, and shows an example of a three-point supported stage with stage Z1 (cone), stage Z2 (cone), and stage Z3 (flat). Each stage with three points of support is contracted by applying a voltage to the piezoelectric element, and the structure allows it to be arbitrarily adjusted from the outside to any distance.

In more detail, Figure 13 is composed of three independent piezoelectric actuators with the same performance, arranged to provide three-point support for the center of the sample.

One end of each of the three piezoelectric actuators has a support point on the movable surface of the XY stage, and the other end is connected to a holder that supports the sample. The connection is shaped to ensure accurate three-point support. For example, a ruby ball with a non-slip surface treatment can be used, or a metal or plastic material shaped into a cone. It is desirable to perform surface treatment to obtain the largest possible coefficient of friction. At least one of the three supports is conductive to form the circuit required to apply a bias voltage to the sample.

It has three independent control circuits to drive the three piezoelectric actuators, and the signals from the height sensors 151 and 152 are processed by a PC, and the processing results are used to give commands from the PC, etc., to change the desired distance and height. 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. Positional accuracy can be achieved to the order of nm (see Figure 20 described below).

The stroke required for Z-axis control ranges from a few microns to approximately 1000 microns. The Z-axis stage must also have high rigidity so that the sample does not vibrate when supported. The support system, which uses a piezoelectric actuator with a displacement magnification mechanism including the sample holder, combines a high response speed of ms with great mechanical rigidity, 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 kept horizontal instantly.

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

Figure 14(a) shows a schematic diagram of the stage without meandering, Figure 14(b) shows a schematic diagram of the stage with left meandering, and Figure 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.

In FIG. 14(a), the stage 9 is shown diagrammatically in a state where there is no meandering in the direction of stage movement in a fixed direction (vertical direction), and no correction is required.

In FIG. 14(b), the stage 9 is shown as meandering to the left with respect to the stage movement direction, which is fixed (vertical direction), indicating a case in which correction is necessary. In this case, the meandering is corrected to the right (see the stage deviation in FIG. 3).

In FIG. 14(c), the stage 9 is shown as meandering to the right relative to the stage movement direction, which is fixed (vertical), indicating a case in which correction is necessary. In this case, the meandering is corrected to the left (see the stage deviation in FIG. 3).

XY stages generally combine direct motors, servo motors, stepping motors, ultrasonic motors, linear motors, etc., which have a large driving force and can move at high speeds of more than a micron, with piezoelectric actuators and brakes that allow fine movements on the order of nanometers or less.

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 a movement command is given to the XY stage 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.

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 a mechanical precision 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 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 spacing between each electron beam. If the stage meanders during continuous inspections, the primary electron beams will irradiate different locations from the intended locations, resulting in uneven irradiation of the primary electron beams and defects in the inspection.

Figure 15 shows an explanatory diagram of the meandering correction of the stage of the present invention.

Figure 15(a) shows a schematic example of an image before correction, and Figure 15(b) shows a schematic example of an image after correction. Here, the vertical direction represents the stage movement direction, and the horizontal direction represents the scanning direction of the primary electron beam.

In FIG. 15(a), each image is a schematic representation of the image of the rectangular area shown meandering left and right with each snake of the stage.

In FIG. 15(b), each image is a schematic representation of the state after the image of the illustrated rectangular area has been corrected for each meander of the stage. It can be seen that there is no meandering in the image, and that the image is scanned with the same width in the direction of stage movement.

As described above and explained in FIG. 14, if there is (is detected) meandering of the stage 9 (deviations in the direction perpendicular to the stage movement direction, and further deviations in the stage movement direction), a correction is made to move the stage (or move the detected image) by the amount of the meandering, making it possible to perform a correction so that there appears to be no meandering, as shown in FIG. 15(b).

Figure 16 shows an explanatory diagram of the stage rotation of the present invention.

Figure 16(a) shows a schematic diagram of the state without horizontal rotation, Figure 16(b) shows a schematic diagram of the state with horizontal rotation to the right, and Figure 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 method.

In FIG. 16(a), the stage 9 is shown diagrammatically in a state where there is no horizontal rotation relative to the stage movement direction in a fixed direction (vertical direction), and no correction is required.

In FIG. 16(b), the stage 9 is shown as having a horizontal rotation to the right relative to the stage movement in a fixed direction (vertical direction), indicating a case in which correction is necessary. In this case, the horizontal rotation is corrected to the left (see the stage rotation amount in FIG. 3).

In FIG. 16(c), the stage 9 is shown as having a horizontal rotation to the left relative to the stage movement in a fixed direction (vertical direction), indicating a case in which correction is necessary. In this case, the horizontal rotation is corrected to the right (see the stage rotation amount in FIG. 3).

Generally, stage 9 is placed on two rails symmetrically, with the movable part in between. The characteristics of the left and right rails are not necessarily the same, and 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 rotates slightly in the XY plane. This is corrected in the present invention.

Figure 17 shows an explanatory diagram of the stage rotation correction of the present invention.

Figure 17(a) shows a schematic example of an image before correction, and Figure 17(b) shows a schematic example of an image after correction. Here, the vertical direction represents the stage movement direction, and the horizontal direction represents the scanning direction of the primary electron beam.

In FIG. 17(a), each image is a schematic representation of how the image in the illustrated rectangular area rotates left or right with each horizontal rotation of the stage.

In FIG. 17(b), each image is a schematic representation of the state after the image of the illustrated rectangular area has been 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.

As described above and explained in Figure 16, if 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 Figure 17 (b).

Figure 18 shows an explanatory diagram of the stage tilt correction of the present invention (height control and automatic leveling using the Z stage).

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

In FIG. 18(a), the convex curve shown is an example of a curve before correction, and shows a schematic diagram of how the coordinate of height Z changes when the stage 9 moves at a constant speed from coordinate Y1 to coordinate Y2. Here, it can be seen that the height Z changes in a convex shape (actually measured (see stage height in FIG. 3)).

In FIG. 18(b), the curve shown is an example of a corrected curve, showing the state after the height Z of the stage 9 has been corrected. Like the convex curve shown in FIG. 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 FIG. 3), the height Z is automatically corrected in response to the height Z detected in real time.

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 stage height by the change in height (see Figure 19 described later).

In addition, a method may be adopted in which automatic focus and automatic magnification correction is performed by controlling the objective lens 6 (or an auxiliary objective lens not shown) in response to movement of the stage 9 in the Z direction, without performing the Z direction correction of the stage 9 described above in FIG. 18.

Figure 19 shows an explanatory diagram of the stage height correction of the present invention.

Figure 19(a) shows a schematic diagram of the state without correction, and Figure 19(b) shows a schematic diagram of the state with correction. Here, the vertical direction is the electron beam scanning direction, and the horizontal direction is the direction of movement of the stage.

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 that occurs with 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).

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 response to 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).

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

Figure 20 shows an explanatory diagram of the sample height and tilt correction of the present invention. This shows an example of a structural diagram of an embodiment in which the stage of Figure 13 is incorporated into the already described Figure 1.

In FIG. 20, primary electron beam 1-1 represents multiple primary electron beams.

Secondary electron beam 1-2 represents multiple secondary electron beams emitted when multiple primary electron beams 1-1 are irradiated onto sample 51.

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

The sample holder 52 holds the sample 8.

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

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

FIG. 1 is a structural diagram of an embodiment of the present invention. 2 is a schematic example of a multi-beam aperture arrangement according to the present invention. 3 is an example of a data table of the present invention (FIG. 2). 1 is an example of creating a multi-beam according to the present invention. FIG. 2 is an explanatory diagram of multi-beam detection according to the present invention. FIG. 1 is an explanatory diagram (square) of multi-beam image acquisition and synthesis according to the present invention. FIG. 2 is an explanatory diagram (hexagonal) of multi-beam image acquisition and synthesis according to the present invention. 1 is a flowchart illustrating the operation of the present invention (obtaining the center coordinates of a multi-beam image). 4 is a flowchart illustrating the operation (calibration) of the present invention. 1 is a flowchart illustrating the operation of the present invention (acquiring a multi-beam image (quadrilateral)). 1 is a flowchart illustrating the operation of the present invention (acquiring a multi-beam image (hexagonal)). 1A to 1C are diagrams for explaining the operation of the present invention (measurement of deviation amount and rotation amount of stage movement). FIG. 4 is an explanatory diagram of tilt correction of a stage according to the present invention. FIG. 4 is an explanatory diagram of the meandering of a stage according to the present invention. FIG. 4 is an explanatory diagram of meandering correction of a stage according to the present invention. FIG. 4 is an explanatory diagram of the rotation of a stage according to the present invention. FIG. 13 is an explanatory diagram of rotation correction of a stage according to the present invention. FIG. 4 is an explanatory diagram of stage tilt correction according to the present invention. FIG. 4 is an explanatory diagram of height correction of the stage of the present invention. FIG. 4 is an explanatory diagram of sample height and tilt correction according to the present invention.

1: Electron gun 1-1: Primary electron beam 1-2: Secondary electron beam 2: Blanking device 3: Illumination lens 3-1: Multi-beam aperture 3-2: Multi-electron beam 4: Objective aperture 5: Beam splitter 5-1: Electrostatic deflector 5-2: Electromagnetic deflector 6: Objective lens 7: Deflection device 8: Sample 8-1: Mirror 9: XYZθ stage (stage)
10: Vacuum chamber 10-1: Vacuum pump 11: Alignment 12: Projection lens 13: Reverse scanning device 14: Electronic detector 52: Sample holder 53, 54, 55; Piezoelectric elements 151, 152: Height sensor

Claims (6)

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 repeatedly moving and stopping the sample and acquiring an image when the sample stops;
a laser interferometer for measuring the position of the stage in the moving direction and the position perpendicular to the moving direction in real time;
A multi-beam image generating device characterized by combining the overlapping common images between the output image information of the multiple electron beams into a single image based on the stage position information obtained by the laser interferometer. 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. A multi-beam image generating device according to any one of claims 1 to 2, 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 the height is corrected electromagnetically, and automatic focusing is performed. The multi-beam image generating device according to any one of claims 1 to 3, characterized in that the multiple beam generating device generates multiple primary electron beams by irradiating a single primary electron beam onto an aperture with multiple holes arranged in a two-dimensional manner. The multi-beam image generating device 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 that is irradiated and scanned on the sample while maintaining high resolution, thereby reducing damage to the sample. 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 multiple beam generating device; a means for detecting electrons emitted or reflected from the sample and outputting an image of the plurality of electron beams;
a stage for repeatedly moving and stopping the sample and acquiring an image when the sample stops;
a laser interferometer for measuring the position of the stage in the moving direction and the position perpendicular to the moving direction in real time;
A multi-beam image generating method characterized by combining the image information of the multiple output electron beams into a single image based on stage position information obtained by a laser interferometer of the overlapping common image between the image information of the multiple output electron beams.

Images