JP2000123774A - Scanning tunneling electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To observe and record a scanned/transmitted image and an electron beam diffraction image with a simple structure without requiring a two-dimensional detector by scanning a sample with an electron beam focused below the sample, and providing a function for displaying the electron beam diffraction image of the sample with the electron beam. SOLUTION: When a sample 6 is scanned by an electron beam 5 for observing a scanned/transmitted image with an objective lens 4 strongly excited, an electron beam 17 transmitting the sample 6 invariably enters a detector 13, and the scanned/transmitted image of the sample 6 is observed on a CRT 9 scanned synchronously with electron beam scanning. The electron beam diffracted by the sample 6 does not enter the detector 13. A lens power supply 15 is controlled by a lens current controller 16 to weakly excite the objective lens 4 for displaying an electron beam diffraction image. The electron beam incidence angle is changed synchronously with the scanning of the incident electron beam 5 in this case, spots of the electron beam diffraction image enter the detector 13, and the electron beam diffraction image is displayed on the CRT 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a scanning transmission electron microscope, and more particularly to a scanning transmission electron microscope capable of observing and recording a scanning transmission image and an electron beam diffraction image of a sample with a simple structure.

[0002]

2. Description of the Related Art A scanning transmission electron microscope (STEM: Scanni)
When observing a scanning transmission image of a crystalline sample with an ng transmission electron microscope, an electron diffraction image is observed to align the crystal orientation with the optical axis of the STEM. In addition to aligning the sample, electron diffraction images
It is used for evaluation of crystal orientation, evaluation of the growth state of a film, evaluation of whether a portion of interest of a sample is amorphous or crystalline or the like.

Conventionally, two methods are known for observing an electron beam diffraction image using a STEM. One is JM Cowley, Ultramicroscopy 4, pp.435-450, "
Coherent interference in convergent-beam electron
as described in "Diffraction and shadow imaging"
This is a method in which an electron beam probe is stopped in a region where a diffraction pattern is desired to be obtained while a TEM image is viewed on a CRT, and a diffraction image formed below the sample is recorded at this time. For recording, a photographic film, a TV camera or the like is used.

Another method is called a beam locking method, in which an electron beam having an opening angle of about 0.1 mrad is incident on one point of a sample at different angles, and is placed on the optical axis below the sample. In this method, a detector having an opening angle of about 0.1 mrad is placed, and the detection intensity is displayed on a CRT in synchronization with the locking of the electron beam.

[0005]

However, in the case of the first method, since the observation and recording of the scanning transmission image and the electron beam diffraction image must be performed by completely different means, the operation becomes complicated. Further, when the scanning transmission image and the electron beam diffraction image are separately recorded, there is a possibility that the electron beam diffraction image corresponding to the scanning transmission image is mistaken. Furthermore, the method of using a two-dimensional detector such as a film or a TV camera for detecting an electron diffraction image has a problem that a complicated configuration such as a camera room for loading the film or a TV camera system is required. .

In both the first method and the second method, the direction of incidence of an electron beam when observing a scanning transmission image does not always coincide with the direction when observing an electron diffraction image. That is, when observing an electron beam diffraction image in any of the conventional methods, only the electron beam diffraction image at one point on the sample is observed, and the average electron beam diffraction image of the entire observation area of the scanning transmission image is observed. Not necessarily.
Therefore, for example, when the sample has distortion, if the orientation of the sample is adjusted based on the electron beam diffraction image obtained by irradiating the distorted portion with an electron beam, a scanning transmission image should be observed. The azimuth is adjusted not to the entire region but to the distorted local portion, and a desired scanning transmission image may not be obtained.

When the sample is tilted only for observing the electron beam diffraction image for alignment or the like, the field of view moves, and the crystal orientation to be aligned is different from the observation target region. Sometimes. In some cases, there is a problem that the observation field of view is lost. In order to prevent this, scanning transmission image observation and electron beam diffraction image observation must be repeated many times at short intervals, which requires time.

An object of the present invention is to provide a scanning transmission electron microscope capable of observing and recording a scanning transmission image and an electron beam diffraction image with a simple configuration without requiring a two-dimensional detector.
Another object of the present invention is to provide a scanning transmission electron microscope capable of simultaneously observing and recording a scanning transmission image and an electron beam diffraction image.

[0009]

The object of the present invention is attained by adding a function capable of displaying an electron diffraction image of an entire electron beam scanning area of a sample to a scanning transmission electron microscope. This function can be realized by a mechanism for switching the excitation current of the objective lens between when a scanning transmission image is obtained and when an electron beam diffraction image is obtained. Another object of the present invention is to provide a mechanism for interlocking the scanning of the electron beam and the switching of the excitation current of the objective lens, for example, a mechanism for switching the excitation current of the objective lens for each scan, and detection by the electron beam detector. This is achieved by providing a mechanism for displaying and recording a scanning transmission image and an electron diffraction image of a sample composed of signals on one or a plurality of display devices.

That is, the present invention provides a scanning transmission electron microscope which scans a sample with an electron beam converging on the sample and displays a scanning transmission image of the sample by the electron beam transmitted through the sample.
The sample is scanned with an electron beam that converges on the downstream side in the optical axis direction, that is, an electron beam that converges below the sample compared to when displaying the scanning transmission image, and an electron beam diffraction image of the sample is displayed by the electron beam diffracted by the sample. It has a function to perform.

According to the present invention, in a scanning transmission electron microscope for scanning a sample with a converged electron beam and displaying a scanning transmission image of the sample, an electron beam diffraction image of the sample is formed on a rear focal plane of the objective lens. As described above, the sample is scanned by the converged electron beam and has a function of displaying an electron beam diffraction image of the sample. The present invention also provides a scanning transmission electron microscope that scans a sample with a converged electron beam and displays a scanning transmission image of the sample with the electron beam that has passed through the sample. And a function of displaying a scanning transmission image of the sample and a function of displaying an electron beam diffraction image of the sample area corresponding to the scanning transmission image.

The present invention also provides an electron gun, a converging lens for converging an electron beam emitted from the electron gun, an objective lens for imaging the electron beam transmitted through the sample, and a scanning means for scanning the electron beam. In a scanning transmission electron microscope including detection means for detecting an electron beam transmitted through a sample and display means for displaying an image based on the output of the detection means, objective lens control means for switching an excitation current of the objective lens, It has a function of detecting an electron beam diffracted from the sample by the detecting means by scanning the electron beam with the objective lens being weakly excited by the objective lens control means and displaying an electron beam diffraction image of the sample on the display means. It is characterized by the following. When the objective lens control means weakly excites the objective lens compared to the scanning transmission image observation so that the electron beam diffraction image of the sample is formed on the back focal plane of the objective lens, the electron beam diffraction image of the sample is can get.

The scanning transmission electron microscope according to the present invention is characterized in that it has a function of simultaneously displaying a scanning transmission image and an electron beam diffraction image of a sample. The scanning transmission image and the electron beam diffraction image may be displayed individually on different regions of one display device, or may be superimposed on the same region, or may be displayed separately on different display devices. Is also good.

When a scanning transmission image and an electron beam diffraction image of a sample are displayed on one display device, it is advantageous to alternately display the scanning transmission image and the electron beam diffraction image. This is performed by, for example, assigning alternating fields to a scanning transmission image and an electron beam diffraction image in the case of interlaced scanning in which one frame image is composed of two fields. That is, if one field is scanned with an electron beam in a mode for acquiring a scan transmission image of the sample, the next field is switched to a mode for acquiring an electron beam diffraction image of the sample to perform electron beam scanning. Further, by switching between the display of the scanning transmission image and the display of the electron beam diffraction image each time one scanning line is scanned, the two images can be superimposed and displayed. When observing the scanning transmission image and the electron beam diffraction image while tilting the sample to align the orientation of the sample, the scanning speed for scanning the sample surface is 10 in order to observe the two images without time delay. It is preferably at least frames / sec.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a basic configuration diagram of an example of a scanning transmission electron microscope according to the present invention. The scanning transmission electron microscope includes an electron gun 1, a converging lens 2, a converging lens movable stop 3, an objective lens 4, a scanning coil 7 for scanning an incident electron beam 5 on the surface of a sample 6, a scanning circuit 8, and a display device such as a CRT. 9, a scanning image observation device 10, a projection lens 11, an aperture 12, and a detector 13. A lens power supply 15 is connected to each lens, and a control unit 16 for switching the lens current is connected to the lens current 15. The control unit 16 is also connected to the scanning circuit 8.

The electron beam 5 generated from the electron gun 1 is converged by the converging lens 2 and further converged on the surface of the sample 6 by the pre-magnetic field of the strongly excited objective lens 4. The narrowed electron beam probe 5 scans the surface of the sample 6 with the scanning coil 7. At this time, the electron beam 17 transmitted or scattered downward from each point of the sample 6 is focused on the detector 13 by the objective lens 4 and the projection lens 11. Projection lens 11
The aperture 12 limits the angle range of the transmitted electrons 17 incident on the detector 13. The electron beam 17 entering the detector 13 is
It is converted into a time-series electrical signal. The signal intensity amplified by the amplifier 14 is synchronized with the excitation of the
By inputting to T9, a scanning transmission image of the sample is displayed on CRT9.

When displaying an electron beam diffraction image, the control unit 1
6 controls the lens power supply 15 so that the objective lens 4 is weakly excited. The incident electron beam 5 does not converge to a single point on the sample surface due to the pre-magnetic field of the weakly excited objective lens 4, but enters the sample with a certain spread. The electron beam incident on the sample
An electron beam diffraction image is formed on the back focal plane of the back magnetic field of the objective lens 4. In other words, the objective lens 4 is formed such that an electron beam diffraction image of the sample is formed on the back focal plane of the back magnetic field of the objective lens 4.
Is changed from strong excitation to weak excitation.

When the objective lens 4 is weakly excited, the incident angle of the electron beam on the sample 6 increases with the distance from the center of the scanning area. Therefore, in synchronization with the scanning of the incident electron beam 5, the electron beam incident angle changes, each spot of the electron beam diffraction image enters the detector 13, and the electron beam diffraction image is displayed on the CRT 9. The scanning transmission image observation mode and the electron beam diffraction image observation mode which are switched by changing the excitation state of the objective lens will be described with reference to FIGS. FIG. 2 is a ray diagram of each observation mode when the electron beam for scanning the sample is near the center of the optical axis. FIG. 3 is a ray diagram of each observation mode when the electron beam for scanning the sample is away from the center of the optical axis. FIG.

First, a ray diagram at the time of observing the scanning transmission image shown in FIG. 2A and a ray diagram at the time of observing the electron diffraction image shown in FIG. 2B will be referred to. The solid line represents the optical path of the transmitted electron beam, and the dotted line represents the optical path of the diffracted electron beam. As shown in FIG. 2A, at the time of scanning transmission image observation, the incident electron beam 5
The electron beam is converged at a large irradiation angle α by the pre-magnetic field of the strongly excited objective lens 4 to form an electron beam probe on the surface of the sample 6. The electron beam 17 transmitted through the sample 6 is condensed by the rear magnetic field of the objective lens 4 and the projection lens 11, and a part thereof is detected by the detector 1.
3 is incident. When the sample 6 is crystalline, a part of the incident electron beam 5 is diffracted by the sample, and a wide disk-shaped diffraction spot is formed on the rear focal plane 18 of the objective lens 4 by the rear magnetic field of the objective lens 4. Is done. In the case of the figure, the electron beam 19 diffracted by the sample 6 does not enter the detector 13.

On the other hand, as shown in FIG. 2B, when observing the electron beam diffraction image, the electron beam 5 incident on the surface of the sample 6 is changed by changing the current value of the objective lens 4 to the weak excitation side. Scanning is performed not as a probe but as a spot spread on the surface of the sample 6. When the sample 6 is crystalline, the objective lens 4
The rear magnetic field also causes the rear focal plane 18 of the objective lens 4
An electron beam diffraction image is formed on the substrate. However, since the irradiation angle α ′ of the electron beam 5 with respect to the sample 6 is smaller than the irradiation angle α in the case of FIG. 2A, the diffraction spot becomes a spot having a smaller diameter. In the case of the figure, the main spot 21 is located on the optical axis and is projected on the detector 13. On the other hand, the diffraction spot 22 is located away from the optical axis, and the electron beam 19 diffracted by the sample does not enter the detector 13.

Next, FIG. 3A is a ray diagram when observing a scanning transmission image and a ray diagram when observing an electron diffraction image when the position of the electron beam scanning probe is apart from the center of the optical axis. Referring to FIG. 3B. At the time of scanning transmission image observation with the objective lens 4 strongly excited, as shown in FIG. 3A, even if the position of the electron beam scanning probe is far from the center of the optical axis, the main focus of the rear focal plane 18 of the objective lens 4 can be improved. The spot and the diffraction spot are always at the same position. As a result, as in the case of FIG. 2A in which the electron beam 5 for scanning the sample is near the center of the optical axis, part of the electron beam 17 transmitted through the sample 6 is detected by the detector 13.
The electron beam 19 diffracted by the sample is
No incidence on 3.

On the other hand, when observing an electron diffraction image with the objective lens 4 weakly excited, as shown in FIG. 3B, the incident angle of the electron beam 5 incident on the sample 6 increases with the distance from the center of the optical axis. The main spot 31 changes from the optical axis at the rear focal plane 18 of the objective lens 4, and the diffraction spot 32 is located on the optical axis at the rear focal plane 18 instead. As a result, in the state shown in FIG. 3B, the electron beam 17 transmitted through the sample does not enter the detector 13 but the electron beam 19 diffracted by the sample.
Is incident on the detector 13.

As will be understood from the above description, in the scanning transmission image observation mode in which the objective lens 4 is strongly excited, when the sample 6 is scanned with the electron beam 5, the sample 13 is always transmitted through the detector 13. The scanned electron beam 17 is incident on the CRT 9 shown in FIG. 1 scanned in synchronization with the electron beam scanning, and a scanning transmission image of the sample 6 is observed. Electron beam 19 diffracted by sample 6
Does not enter the detector 13. On the other hand, in the electron beam diffraction image observation mode in which the objective lens 4 is weakly excited, a diffraction spot 32 due to the electron beam 19 diffracted by the sample 6 is formed on the back focal plane 18 of the objective lens 4 and located on the optical axis. The diffracted electron beam 19 of the diffracting spot 32 enters the detector 13. When the electron beam 5 scans the sample 6, the diffracted electron beams having different diffraction angles successively form diffraction spots on the optical axis according to the electron beam irradiation position on the sample 6, so that the scanning circuit 8 (FIG. 1) CRT 9 scanned according to the scanning signal from
At the top, an electron beam diffraction image of the entire electron beam scanning area of the sample 6 is displayed.

FIG. 4 shows an example of a scanning transmission image and an electron beam diffraction image by the scanning transmission electron microscope shown in FIG. FIG.
3A is an example of a scanning transmission image corresponding to FIG. 3A at an extremely low magnification, that is, when the scanning range is larger than the aperture 12. FIG. 4B is an example of an electron beam diffraction image corresponding to FIG. 3B. As described above, the control unit 1
6. The excitation current of the objective lens 4 is switched by the
By electron beam scanning, display switching between a scanning transmission image and an electron beam diffraction image can be performed.

FIG. 4 shows an example in which a scanning transmission image and an electron beam diffraction image of an electron beam scanning area of a sample are switched and displayed on a display device.
An electron diffraction image of the same sample area can be displayed simultaneously. Scanning transmission image and electron beam diffraction image of sample
For simultaneous display on the RT 9, scanning of the electron beam 5 and switching of the excitation current of the objective lens 4 are linked.

For example, in the case of interlaced scanning in which one frame image is composed of two fields, one field constituting a frame is scanned with an electron beam in a scanning transmission image acquisition mode (objective lens strong excitation), and the other field is scanned. By scanning the field with the electron beam in the electron beam diffraction image acquisition mode (weak excitation of the objective lens), an image in which the scanning transmission image and the electron beam diffraction image overlap each other is obtained. When interlaced scanning is not performed, the lens current control unit 1 is synchronized with the signal of the scanning circuit 8.
6 controls the lens power supply 15 so that the excitation current of the objective lens 4 is changed for each scan of the electron beam 5, and switches between a scanning transmission image acquisition mode and an electron beam diffraction image acquisition mode, thereby allowing the CRT 9 to be scanned. An image in which the scanning transmission image and the electron beam diffraction image of the same area of the sample are superimposed is displayed. By performing the scanning at a speed of, for example, 10 frames / second or more, a scanning transmission image and an electron beam diffraction image are displayed on the CRT 9.

FIG. 5 is a diagram showing another example of a method for displaying a scanning transmission image and an electron beam diffraction image. When the scanning transmission image and the electron beam diffraction image are superimposed as described above, the electron beam diffraction image is superimposed and displayed at the center of the CRT 9. FIG. 5 shows that when the display of the scanning transmission image and the electron beam diffraction image are switched, the display area of the CRT 9 is changed, the display position of the electron beam diffraction image is moved to the corner of the CRT 9 screen, and the display size is reduced. Is displayed.

FIG. 6 is a diagram showing another example of a method for displaying a scanning transmission image and an electron beam diffraction image. In this example, the display screen of the CRT 9 is divided into two, and the scanning transmission image and the electron beam diffraction image are displayed in the display area divided into right and left. FIG. 7 is a basic configuration diagram of another example of the scanning transmission electron microscope according to the present invention. 7, the same functional parts as those in FIG. 1 are denoted by the same reference numerals as in FIG. The difference between the scanning transmission electron microscope shown in FIG. 7 and the scanning transmission electron microscope shown in FIG. 1 is that two CRTs 9a and 9
b is prepared. In the embodiment shown above, the scanning transmission image and the electron diffraction image are displayed on the same CRT 9 screen. However, if two CRTs are prepared as shown in FIG. An image can be displayed, and an electron diffraction image can be separately displayed on the other CRT 9b.

When aligning the orientation of a crystalline sample, first, an observation area of the sample is searched for by a scanning transmission image, and the orientation is adjusted by tilting the sample while observing an electron beam diffraction image of the observation area. When the sample is tilted during the alignment, the observation field of view often moves. The conventional scanning transmission electron microscope cannot confirm whether or not the electron beam diffraction image is of a desired region of the sample when observing the electron beam diffraction image. An electron beam diffraction image obtained by a conventional scanning transmission electron microscope was an electron beam diffraction image of a minute spot area on a sample. On the other hand, according to the scanning transmission electron microscope of the present invention, it is possible to simultaneously observe an electron diffraction image of the same sample region while observing a scanning transmission image. Also,
The electron beam diffraction image is not of a minute spot area of the sample, but of the entire area where the scanning transmission image of the sample is observed. According to the scanning transmission electron microscope of the present invention, operability greatly improved compared to the conventional scanning transmission electron microscope can be obtained due to these features.

[0030]

According to the present invention, observation and recording of a scanning transmission electron microscope image and an electron beam diffraction image of a sample can be performed with a simple structure, and the scanning transmission electron microscope image and the electron beam diffraction image can be obtained. Simultaneous display is possible. Since the visual field can be observed even when the sample is tilted, the crystal orientation of the sample can be easily adjusted without losing the visual field.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of an example of a scanning transmission electron microscope according to the present invention.

FIG. 2 is a ray diagram of each of two observation modes when an electron beam for scanning a sample is near the center of an optical axis.

FIG. 3 is a ray diagram of two observation modes when an electron beam for scanning a sample is located at a position away from the center of the optical axis.

FIG. 4 is an electron micrograph showing an example of a scanning transmission image and an electron beam diffraction image by the scanning transmission electron microscope of the present invention.

FIG. 5 is an electron micrograph showing another example of a method for displaying a scanning transmission image and an electron beam diffraction image by the scanning transmission electron microscope of the present invention.

FIG. 6 is an electron micrograph showing another example of a method for displaying a scanning transmission image and an electron beam diffraction image by the scanning transmission electron microscope of the present invention.

FIG. 7 is a basic configuration diagram of another example of the scanning transmission electron microscope according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electron gun, 2 ... Convergent lens, 3 ... Convergent lens movable diaphragm, 4 ... Objective lens, 5 ... Incident electron beam, 6 ... Sample, 7 ...
Scanning coil, 8: scanning circuit, 9: CRT, 10: scanning image observation device, 11: projection lens, 12: diaphragm, 13: detector, 14: amplifier, 15: lens power supply, 16: lens current control unit, 17 ... Electron beam transmitted through the sample, 18 ... Back focal plane of the objective lens, 19 ... Electron beam diffracted by the sample, 21
… Main spot, 22… diffraction spot, 31… main spot, 32… diffraction spot

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takahito Hashimoto 882-Chair, Oji-shi, Hitachinaka-shi, Ibaraki Pref., Ltd.Measurement Division, Hitachi, Ltd. (72) Inventor Mitsuru Konno 832-2 Nagakubo, Horiguchi, Hitachinaka-shi, Ibaraki 2 Hitachi, Ltd. Measurement Engineering Co., Ltd. (72) Inventor Takeo Ueno 832 Nagakubo, Horiguchi, Hitachinaka City, Ibaraki Prefecture 2 Hitachi Measurement Engineering Co., Ltd. (72) Adult, Sunakozawa, 882 Omo, Ichimo, Hitachinaka City, Ibaraki Measurement by Hitachi, Ltd. F-term (Reference) in the Equipment Division 5C033 DE02 SS01 SS03 SS07 UU06

Claims (8)

[Claims] 1. A scanning transmission electron microscope for scanning a sample with an electron beam converging on the sample and displaying a scanning transmission image of the sample with the electron beam transmitted through the sample, wherein the sample is conveyed by an electron beam converging below the sample. A scanning transmission electron microscope having a function of scanning and displaying an electron beam diffraction image of a sample by an electron beam diffracted by the sample. 2. A sample is scanned by a converged electron beam,
In a scanning transmission electron microscope that displays a scanning transmission image of a sample, the electron beam diffraction image of the sample is scanned by a converged electron beam so that the electron beam diffraction image of the sample is formed on the back focal plane of the objective lens. A scanning transmission electron microscope characterized by having a function of displaying. 3. A sample is scanned by a converged electron beam,
A scanning transmission electron microscope for displaying a scanning transmission image of a sample by an electron beam transmitted through the sample, comprising: means for switching an irradiation angle of an electron beam irradiating the sample; a function of displaying a scanning transmission image of the sample; A scanning transmission electron microscope having a function of displaying an electron beam diffraction image of a sample area corresponding to an image. 4. An electron gun, a converging lens for converging an electron beam emitted from the electron gun, an objective lens for forming an image of the electron beam transmitted through the sample, scanning means for scanning the electron beam, A scanning transmission electron microscope including detection means for detecting a transmitted electron beam and display means for displaying an image based on an output of the detection means, comprising: objective lens control means for switching an excitation current of the objective lens; By detecting the electron beam diffracted from the sample by the detection means by scanning the electron beam in a state where the objective lens is weakly excited by the objective lens control means,
A scanning transmission electron microscope having a function of displaying an electron diffraction image of a sample on the display means. 5. The scanning transmission electron microscope according to claim 4, wherein the objective lens control means is configured to form an electron beam diffraction image of a sample on a back focal plane of the objective lens when observing an electron beam diffraction image. A scanning transmission electron microscope characterized in that the objective lens is weakly excited as compared with the time of scanning image observation. 6. The scanning transmission electron microscope according to claim 1, wherein the scanning transmission electron microscope has a function of simultaneously displaying a scanning transmission image and an electron diffraction image of a sample. 7. The scanning transmission electron microscope according to claim 1, wherein the scanning transmission electron microscope has a function of alternately displaying a scanning transmission image and an electron beam diffraction image. 8. The scanning transmission electron microscope according to claim 1, wherein each time one scanning line is scanned,
A scanning transmission electron microscope characterized by switching between display of a scanning transmission image and display of an electron diffraction image.