JP2804932B2 - Stereo image observation and photography device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention provides a scanning electron microscope (hereinafter referred to as an SEM) for observing a stereo image by tilting and vibrating a sample in synchronization with scanning of an electron beam. TECHNICAL FIELD The present invention relates to a stereoscopic image observation / photographing apparatus using a scanning electron microscope capable of performing the operation.

[Prior Art] Conventionally, two methods are known for obtaining a stereo image using an SEM.

The first method is a method of taking a photo with a different sample tilt angles to each other, first, a SEM image obtained by inclining angle theta ₁ with the sample and photographed, then another sample A photograph is taken of an SEM image obtained by inclining by the angle θ2 of the above, _two photographs thus obtained are arranged, and observed as a stereo image using stereo glasses or the like.

The second method is a method in which an electron beam for scanning a sample is tilted while the sample is fixed.
In Japanese Patent Application Laid-Open No. -1180, the direct current of + and-is superimposed on the scanning current supplied to the deflection coil, so that the electron beam 30 is incident on the sample 31 as shown in FIGS. Scanning is performed with the angles set to + α and −α, respectively, and as shown in FIG. 7C, the SEM images 34a and 34b obtained by the respective scans are arranged on a screen 33 of a cathode ray tube (hereinafter, referred to as a CRT). It is shown that the image is displayed, photographed, and a stereo image is observed with stereo glasses.

In addition, the method is the same in that two SEM images are obtained by inclining the electron beam. However, instead of taking a picture, two CRTs 35a and 35b are used as shown in FIG.
It is also known to display an image on 35a and another SEM image on 35b and observe these two images with stereo glasses 36.

[Problems to be Solved by the Invention] However, in the conventional method, there is a problem that the operation is troublesome in any of the methods. That is, in the first method described above, a stereo image can be observed only with a photograph, and photographing two photographs takes time and is very troublesome.

In the above-mentioned second method, photography is required only once, but it takes time since two images 35a and 35b are not obtained at a time, and correction of astigmatism is very difficult. It was troublesome and had a problem in operability. In other words, if the electron beam is scanned electromagnetically tilted, astigmatism will occur and the electron beam will be distorted, so the amount of astigmatism correction must be changed between when observing a normal SEM image and when observing a stereo image. Not only does it need to be performed, but strictly speaking, since the astigmatism is different between an electron beam with a sample incidence angle of + α and an electron beam with a sample incidence angle of −α, it is necessary to correct them independently and separately.
As described above, in observing a stereo image by tilting the electron beam, astigmatism correction, which is said to be the most difficult in the operation of the scanning electron microscope, must be performed, and there is a problem in operability. there were.

Although the one shown in FIG. 8 is advantageous in that a stereo image can be observed on a CRT screen, the use of two CRTs not only increases the size of the apparatus but also eliminates the hassle of astigmatism correction. That is not done.

The present invention solves the above-mentioned problems, and directly
It is an object of the present invention to provide a stereo image observation photographing apparatus which can observe a stereo image on a CRT screen and does not have to perform astigmatism correction.

[Means for Solving the Problems] In order to achieve the above object, a stereoscopic image observation and imaging apparatus according to the present invention uses a scanning electron microscope that scans a desired range of a sample surface two-dimensionally. The apparatus is characterized in that it comprises means for tilting and vibrating the sample in synchronization with the electron beam to be scanned, and display means for simultaneously displaying two scanned images having different tilt angles.

[Operation and Effect of the Invention] According to the present invention, two SEM images having different inclination angles are simultaneously displayed side by side on a CRT, so that a stereo image can be directly observed. It is good and not essential.

In addition, the present invention tilts the sample and does not tilt the electron beam, so once astigmatism correction is performed, a normal SEM image is observed and a stereo image is observed. Thus, it is not necessary to change the astigmatism correction, and the trouble of the astigmatism correction can be eliminated.

Further, the field of view can be easily corrected.

Embodiment Hereinafter, an embodiment will be described. First, the principle of the present invention will be described with reference to FIG. FIG. 1A is a diagram showing a tilt angle of a sample, FIG. 1B is a diagram showing a scanning line of an electron beam on a sample surface, and FIG. 1C is a diagram showing a raster on a CRT screen. .

Now, as shown in FIG. 1 (b), it is assumed that the electron beam 1 scans the surface of the sample 2 with n scanning lines, and when the first scanning line A1 to B1 is scanned, the sample is scanned. 2 is maintained at θ ₁ in FIG. 1 (a). The signal detected at this time is supplied to the CRT and displayed as A1'-B1 'in FIG. 1 (c). That is, when observing a stereo image, the scanning width of the raster of the CRT is reduced to half of that in a normal case. Then, in order to scan the next scanning line, the electron beam 1 is emitted from B1 of the sample 2
While returning to A2, the inclination angle of the sample 2 is done and theta _2, while scanning from A2 is the second scanning line to B2 is being performed is kept at this angle. Then, the signal obtained by the electron beam scanning is supplied to the CRT, and A2'-B shown in FIG.
As shown in 2 ', it is displayed in the other half of the CRT screen. Incidentally, the difference theta ₁ and theta ₂ are made with 5 ° to 10 °. Then, the sample 2 is taken until the electron beam 1 returns from B2 to A3.
Is again set to θ ₁ and is maintained at this angle while the scanning from A3 to B3, which is the third scanning line, is being performed. A signal obtained by the electron beam scanning is supplied to a CRT, and A1'-B3 'as shown at A3'-B3' in FIG.
It is displayed below 1 '.

By performing the above processing up to the order as soon as the n-th scan line, SEM image by odd-numbered scanning lines, i.e., a SEM image when the inclination angle of the sample is theta _1, SEM by even-numbered scanning lines
Image, i.e., the tilt angle of the sample and the SEM increase in case of theta ₂ at the same time
The images can be displayed side by side on a CRT screen, and if the screen is observed using stereo glasses or the like, a stereo image can be observed. Of course, in this case, the size of one screen is 1/2 of the normal size, and the number of scanning lines on one screen is 1/2 of that of the normal SEM image. Time is the same, so the CRT
Can be displayed within a time period in which the afterglow is maintained. In addition, although the resolution decreases due to the decrease in the number of scanning lines, the number of scanning lines of an SEM is usually about 1000, so even if the number of scanning lines is halved, the number of scanning lines of one image is 500
This is about the same as the number of scanning lines of a normal television, and it has been confirmed that there is no problem in observing a stereo image.

FIG. 2 is a diagram showing the overall configuration of a stereoscopic image observation and photographing apparatus according to the present invention, wherein 1 is an electron beam, 2 is a sample, 3 is a focusing lens, 4, 5 are scanning coils, and 6 is an objective. Lens, 7 is a field correction coil, 8 is an astigmatism correction coil, 9 is a collector, 10 is a photomultiplier tube, 11 is an amplifier, 12 is a CRT, 13
Is a scanning circuit, 14 is a mode / speed switching circuit, 15 is a display control circuit, 16 is a magnification control circuit, 17 is a magnification display circuit, 18 is a switch, 19 is a power supply, 20 is a motor drive synchronization circuit, and 21 is a motor control circuit. , 22 indicate a motor.

In the configuration shown in FIG. 2, an electron beam 1 emitted from a filament (not shown) is focused by a focusing lens 3, focused on the surface of the sample 2 by an objective lens 6, and scanned by the scanning coils 4, 5. As shown in FIG. 1B, the predetermined range is scanned two-dimensionally in the X and Y directions. At this time, the field of view of the electron beam 1 has been set in advance by the field-of-view correction coil 7 and the astigmatism correction coil 8, and the astigmatism has been corrected.

The scanning coils 4 and 5 are switched in mode and scanning speed by the mode / speed switching circuit 14, and
It is driven via a magnification control circuit 16 to define a scanning range. In this case, the set magnification is displayed on the magnification display circuit 17.

Secondary electrons generated from the surface of the sample 2 by the irradiation of the electron beam 1 are collected by a collector 9 and converted into an electric signal by a photomultiplier tube 10, and the signal converted by the photomultiplier tube 10 is amplified by an amplifier. 11 is applied to the grid of CRT 12.

The display control circuit 15 is a circuit that controls the raster scanning of the CRT 12, and displays a full screen in a normal case.
When the observation of the stereo image is instructed, the first signal is input based on the scanning signal of the electron beam 1 input from the scanning circuit 13.
A deflection signal for performing the raster scanning shown in FIG. 9C is generated and supplied to the deflection coil of the CRT 12. Accordingly, in the case of stereo image observation, the raster scanning of the CRT 12 is performed in synchronization with the scanning of the electron beam 1 on the surface of the sample 2, as shown in FIG. 1 (c).

The switch 18 has a normal (NOR) terminal connected to obtain a normal SEM image and a stereo (STEREO) terminal connected to obtain a stereo image. As shown in FIG. Side, the motor 22
The power supply to is stopped, and the raster scan on CRT12
It is performed on the entire screen to display a normal scanning image,
When connected to the STEREO side, the power supply 19 is connected to the motor control circuit 21 and the operation of the motor drive synchronization circuit 20 causes
The motor 22 is driven only during the return period of the electron beam 1, that is, the period indicated by the broken line in FIG. 1 (b), and the tilt angle of the sample 2 becomes θ for each scanning line in synchronization with the scanning of the electron beam 1. from ₁ to theta _2, or is changed from theta ₂ to the theta _1. At this time, CRT
The raster scanning width of 12 is interlocked with the switch 18 and becomes 1/2 of the normal case as shown in FIG.
The magnification is reduced to 1/2 compared to the OR state, and the display of the magnification display circuit 17 is also reduced to 1/2 in conjunction with the switch 18.

FIG. 3 shows one configuration example for changing the inclination angle of the sample 2. 3, the sample 2 is placed on a sample holder 25 supported by a bearing 26 and a gear 24, and the gear 24
Is in mesh with a gear 23 connected to the rotation shaft of the motor 22. Therefore, the motor 22 is turned by the motor control circuit 21 into an arrow 27.
Alternatively, when rotated by a predetermined angle in the direction of arrow 28, sample holder 25 rotates by an angle corresponding to the gear ratio of gears 23 and 24. Therefore, the gear ratio should be set so that the difference between the inclination angles θ ₁ and θ ₂ becomes a predetermined desired angle. Note that, as the motor 22, an appropriate motor such as a stepping motor can be used. In addition to the motor, for example, as shown in FIG. 4, a piezoelectric element 29 may be arranged at one end of the sample holder 25, and the piezoelectric element 29 may be expanded and contracted with the other end as a fulcrum. That is, it is clear that a predetermined inclination angle difference can be obtained by applying a predetermined voltage to the piezoelectric element 29 and expanding and contracting it in synchronization with the scanning of the electron beam.

In the present invention, since the electron beam scanning is performed in a state where the sample is tilted, it is conceivable that the focus is shifted. However, the focus shift due to the tilt of the sample causes the observation position on the sample and the tilt axis to coincide. This can be avoided by using a so-called eucentric stage that can perform electron beam scanning in a state. However, even when the eucentric stage is used, when observing at a high magnification, there is a possibility that the display positions of the two SEM images are shifted as shown in FIG. If such a shift in the display position, that is, a shift in the visual field occurs, the image cannot be observed as a stereo image on the CRT 12, so the display position needs to be corrected so that the two SEM images are aligned. The field-of-view correction coil 7 is provided to perform the correction, and the configuration is shown in FIG. The visual field correction circuit 27 determines the direction and magnitude of the current for performing the visual field correction according to the position of the visual field correction knob 28, and supplies the current to the visual field correction coil 7. Since the visual field correction needs to be performed only on one image, the visual field correction circuit 27 synchronizes with the scanning of the electron beam in a period of the odd-numbered scanning line of the electron beam 1 or in a period of the even-numbered scanning line. The operation state is set only during the period. It is convenient to use a joystick as the visual field correction knob 28. According to such a configuration, the operator, for example, an image of the specimen rotation angle theta ₂ CRT
The field of view can be easily corrected by tilting the joystick in the direction in which the SEM image is moved while observing on the 12, so that the two SEM images are correctly displayed side by side on the CRT 12.

If the two SEM images displayed in this way are observed with stereo glasses, a stereo image can be directly observed on a CRT.

It is obvious to those skilled in the art that a stereo image can be observed by taking a photograph of an image on a CRT.

[Brief description of the drawings]

FIG. 1 is a view for explaining the principle of a stereoscopic image observation and photographing apparatus according to the present invention, FIG. 2 is a view showing one configuration example of the stereoscopic image observation and photographing apparatus, and FIG.
FIG. 4 is a diagram showing a configuration example, FIG. 4 is a diagram showing another configuration example for tilting the sample, FIG. 5 is a diagram for explaining field deviation, FIG. 6 is a diagram for explaining field correction, FIG. 7 is a diagram for explaining a conventional example of a stereo image observation device, and FIG. 8 is a diagram for explaining another conventional example of a stereo image observation device. DESCRIPTION OF SYMBOLS 1 ... Electron beam, 2 ... Sample, 3 ... Focusing lens, 4,5 ... Scan coil, 6 ... Objective lens, 7 ... Field correction coil, 8 ...
Astigmatism correction coil, 9 ... Collector, 10 ... Photomultiplier tube, 11
... Amplifier, 12 CRT, 13 Scanning circuit, 14 Mode / speed switching circuit, 15 Display control circuit, 16 Magnification control circuit,
17: Magnification display circuit, 18: Switch, 19: Power supply, 20: Motor drive synchronization circuit, 21: Motor control circuit, 22: Motor.

Claims (1)

(57) [Claims] 1. A scanning electron microscope for two-dimensionally scanning a desired area of a sample surface, means for tilting and vibrating the sample in synchronization with an electron beam scanning the sample surface, and two means having different tilt angles from each other. A stereo image observation and photographing apparatus, comprising: display means for simultaneously displaying a scanned image.