JPH07335172A - Scanning transmission electron microscope - Google Patents

Abstract

PURPOSE:To produce a distinct image even when a specimen in which change in the spatial distribution of the electromagnetic field differs largely, is to be observed by combining a slit for separating the interferential striation with a sensor to sense the position and intensity of an electron beam having passed the surface of the specimen. CONSTITUTION:An electron beam 4 fed from an electron source 1 under a vacuum is converged on the surface 6 of a specimen by an irradiation lens 5 and deflected into a scan using a deflecting coil 3. The deflection is made by receiving a Rolents force with the electromagnetic field of the specimen. The deflecting amount is sensed by a sensor 10, and the position and intensity of the deflection are calculated by a signal calculation circuit 12. On the basis of the obtained deflection signal 13, a computer 17 determines the magnetism distribution image. Thereby a scanning transmissive electron microscope is used in the scanning Rorents electron microscopic mode. When this is to be used in the scanning interferential electron microscopic mode, a switch 16 of a by-prism 2 is turned on through a control circuit 15, and a slit 9 is inserted to the electron path 11. Thereby the electron beam 2 is separated into two pieces, and the sensor 10 performs sensing upon formation of an interferential striation after passage of the specimen surface 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning transmission electron microscope used for evaluating the magnetic characteristics and magnetization state of minute regions inside and outside a magnetic material.

[0002]

2. Description of the Related Art Many attempts have been made to evaluate the magnetic characteristics of a minute region using an electron beam. As one of the methods, the deflection received by the electron beam due to the electromagnetic field inside and outside the sample is detected by a detector (phase difference contrast detector) which is divided into four or more parts and a signal can be taken out independently from each divided part. There is a scanning Lorentz electron microscope (a phase contrast mode of a scanning transmission electron microscope) for displaying an image. The electromagnetic field measurement principle of this microscope is as follows. First, an electron beam extracted from an electron source is converged on a sample by a lens and scanned. Then, the deflection due to the Lorentz force applied while the electron beam is passing through the sample is detected by the phase difference contrast detector, and this is displayed as the electromagnetic field distribution in the sample. This measurement method is, for example, ultramicroscopy, 3, 1
1978, p. 203 (Ultramicroscope
y, 3 (1978) 203).

Another method is a scanning interference electron microscope. The electromagnetic field measurement principle of this microscope is as follows. A biprism is provided between the electron source and a deflector that performs electron beam scanning, and the biprism divides the electron beam that converges on the sample. The divided electron beams pass through the sample and then overlap with each other to form intensity interference fringes. The position of this interference fringe changes depending on the electromagnetic field that the divided electron beam experiences. Therefore, the electromagnetic field inside and outside the sample is detected by detecting the position change of the interference fringes, and the electromagnetic field distribution is displayed as an image. This microscope is described in JP-A-3-81939.

All of these microscopes use a focused electron beam. Therefore, the spatial resolution is high, and moreover,
Since the magnetic information can be imported directly into the computer,
It has the feature that signals can be handled easily. Furthermore, it has the feature that it can be combined with other measurement functions such as elemental analysis.

[0005]

However, each microscope has the following problems.

First, since the contrast of the scanning Lorentz electron microscope is linear with respect to the intensity of the electromagnetic field, when the electromagnetic field being observed is changing spatially gently, the contrast is correspondingly gentle. There is a problem that only a change is shown and a clear image is difficult to obtain. For example,
When simultaneously observing the magnetization distribution inside the magnetic material and the leakage magnetic field distribution leaking from the magnetic material, there is a problem in that the leakage magnetic field has almost no contrast when an image with a clear contrast of magnetization is obtained.

On the other hand, in the scanning interference electron microscope, the contrast becomes periodic with respect to the change in the intensity of the electromagnetic field. Therefore, even when the gradually changing leak magnetic field is observed, the change can be displayed as a clear contrast. However, when observing the magnetization distribution of a magnetic material that changes drastically, the contrast becomes too complicated, and the image becomes unclear.

An object of the present invention is to provide a microscope capable of obtaining a clear image even when observing a sample in which the spatial distribution of the electromagnetic field changes greatly.

[0009]

In order to achieve the object of the present invention, a scanning Lorentz electron microscope and a measurement mode as a scanning interference electron microscope are incorporated in one electron microscope, and these modes can be switched instantaneously. I chose

[0010]

As described above, the scanning Lorentz electron microscope has a linear contrast with respect to the intensity of the electromagnetic field. Therefore, when the electromagnetic field under observation is drastically changed spatially like the magnetization state inside the magnetic thin film, the contrast is drastically changed accordingly. Therefore, the obtained image has a clear contrast.

On the other hand, in the scanning interference electron microscope, the contrast becomes periodic with respect to the change in the intensity of the electromagnetic field. Therefore, even when an electromagnetic field that changes gently, such as the distribution of the leakage magnetic field leaking from the magnetic thin film, is observed, the change changes periodically, and a clear contrast can be displayed.

As described above, according to the present invention, a scanning Lorentz electron microscope is used for observing a portion where the spatial distribution of the electromagnetic field changes drastically, and a scanning interference is used for observing a portion where the change is gentle. A clear image can be obtained by observing with an electron microscope and displaying them together. Since the switching of the observation mode is performed in the same microscope, the observation area does not shift.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic explanatory view when the scanning transmission electron microscope according to the present invention is used in the scanning Lorentz electron microscope mode. The electron microscope shown in the present embodiment is configured by adding a biprism, a magnetic field-free and electric field-free sample chamber, an electron beam deflection detector, and a slit to a normal scanning transmission electron microscope. First, by turning off the switch 16 by the control circuit 15 controlled by the computer 17, the voltage application to the biprism 2 is stopped and the slit 9 is retracted. In this case, the electron beam 4 emitted from the electron source 1 and accelerated to 200 kV is converged by the irradiation lens 5 to a point on the sample surface 6 including the sample. The convergence point is scanned by the deflection coil 3. The electron beam 4 that has passed through the inside of the sample or has passed outside the sample is deflected by the Lorentz force due to the electromagnetic field of the sample. By the way, this deflection amount is about 10 microradians, although it varies depending on the sample. This deflection is detected by the detector 10. In the case of the present embodiment, as the detector 10, a microchannel plate having an anode divided into five was used. If the electron beam 4 is not deflected, adjustment is made so that the same intensity is incident on the four outer divided portions. When the electron beam 4 is deflected, the signal balance of the intensity of the electron beam entering each part is lost, and the difference and the direction of the deflection can be obtained by calculating the difference between them. The signal from one anode in the middle is used to obtain a bright field image. Further, the detector 10 is rotatable, and the direction in which the deflection of the electron beam 4 is detected can be arbitrarily changed.

FIG. 2 shows an embodiment in which the scanning transmission electron microscope according to the present invention is used in the scanning interference electron microscope mode. In this case, the control circuit 15 turns on the switch 16 to apply a voltage to the biprism 2,
The slit 9 is inserted and used. The electron beam 4 emitted from the electron source 1 and accelerated to 200 kV is first split into two by the biprism 2. The two electron beams 4 are made to scan by the deflection coil 3 while being converged at two points on the sample surface 6 by the irradiation lens 5. The two electron beams 4 that have separated and passed through the position of the sample surface 6 overlap again and form interference fringes 8. Since these two electron beams undergo a phase change due to the electromagnetic field when passing through the sample surface 6, the position of the interference fringe 8 changes depending on the strength of the electromagnetic field at the position of the sample surface 6. This is rotatable slit 9 and detector 10
Detect with a combination of (micro channel plate).
If the direction and the interval of the interference fringe 8 are adjusted to the direction and the interval of the slit 9 by adjusting the magnification of a magnifying lens system (not shown) and rotating the slit, the transmitted intensity changes depending on the position of the interference fringe 8. . If the direction of the interference fringe 8 and the direction of the slit 9 that are overlapped by the biprism 2 are aligned once,
There is no need for readjustment during subsequent observations. The intensity change of the transmitted electron beam can be obtained by calculating the sum of the signals from the respective anodes of the microchannel plate by the signal calculation circuit 12. The direction of the electromagnetic field to be detected is perpendicular to the electron beam separation direction. Therefore, by rotating the biprism 2 provided with the rotation mechanism and the slit 9 by 90 degrees, it is also possible to detect the orthogonal component.

With the two microscope modes described above,
To observe the part where the spatial distribution of the electromagnetic field differs greatly,
Do the following: First, the slit 9 is retracted, and the scanning Lorentz electron microscope mode is set without applying a voltage to the biprism 2. In this mode, the image of the entire observation visual field is captured and stored in the memory on the computer 17. At this time, the signal calculation circuit 12 calculates the difference signal 13,
The deflection of the electron beam 4 is detected. Next, the slit 9 is inserted and a voltage is applied to the biprism 2 to set the scanning interference electron microscope mode. In this mode, the same place as that observed with the scanning Lorentz electron microscope is observed, and this is also stored in the memory on the computer 17. At this time, the signal calculation circuit 12 calculates the sum signal 14, and the slit 9
The intensity of the electron beam 4 transmitted through is detected. After observing in two microscope modes, the images stored in the memory are processed to combine the two images and each clear portion is displayed as an image. The images can be taken in the reverse order, of course.

In this way, the voltage application to the biprism 2,
Instantaneous switching is possible only by inserting the slit 9 and changing the calculation method of the signal calculation circuit 12. Therefore,
The same location of the sample can be observed with two microscopes.

The image display method described above is not limited to this. For example, for each pixel to be measured, two microscope modes may be switched to, two images may be acquired at a time, and then processed and displayed. Alternatively, once an image is acquired in one of the microscope modes, only the part where the contrast is not clear may be observed in another mode. Moreover, especially when observing a sample having a large contrast distribution inside and outside the sample, first, acquire a transmission electron microscope image, determine the inside or outside of the sample from the signal intensity, and switch the measurement mode accordingly. You can In this way, the sample boundary portion is strictly determined, and the position at which the microscope mode is switched can be accurately determined.

FIG. 3 shows a schematic diagram of an image observed by the present invention, and FIG. 4 shows a schematic diagram of an image observed only by a conventional scanning Lorentz electron microscope. Both of these are images of the recording bit recorded on the magnetic thin film and the leakage magnetic field leaking from the recording bit. The upper part of FIG. 3 shows the distribution of the leakage magnetic field observed by the scanning interference electron microscope, and the lower part of FIG. 3 shows the magnetization distribution image inside the film observed by the scanning Lorentz electron microscope. In this way, even when observing samples with greatly different magnetic field distributions,
Observed with clear contrast. On the other hand, in FIG. 4, the leakage magnetic field distribution cannot be observed with sufficient contrast.

Although the present invention has been described with reference to the embodiments, a detector that can be used in the present invention is a detector that can detect the deflection of an electron beam and the intensity of an electron beam that passes through a slit. Needless to say, if something other than a micro channel plate is available, it can be used.
For example, a semiconductor detector divided into four or more may be used. In this case, the size of the detector can be reduced, and it is not necessary to apply a high voltage.

Further, in the above embodiment, the switching of whether or not the biprism is activated is controlled by the application of voltage.
It is not limited to this. For example, the structure may be such that the biprism can be retracted from the electron beam path, and the biprism may be inserted and removed. By doing so, it is possible to avoid the influence of the shadow of the biprism that appears when a voltage is not applied with the biprism inserted.

[0022]

As described above, according to the present invention, one scanning transmission electron microscope can be selectively used as a scanning Lorentz electron microscope and a scanning interferometric electron microscope, so that the same field of view can be used. Even if the spatial variation of the electromagnetic field distribution is remarkably different, it is possible to observe each part with a suitable contrast.

Since the same visual field can be observed in two different modes, the reliability of the measurement result can be improved by comparing the observation results in both modes with each other.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram of an electron beam path when an embodiment of a scanning transmission electron microscope according to the present invention is used as a scanning Lorentz electron microscope.

FIG. 2 is a schematic explanatory diagram of an electron beam path when an embodiment of a scanning transmission electron microscope according to the present invention is used as a scanning interference electron microscope.

FIG. 3 is a schematic diagram of a magnetic field distribution of magnetic recording bits observed by a scanning transmission electron microscope of the present invention.

FIG. 4 is a schematic diagram of a magnetic field distribution of a magnetic recording bit observed by a conventional scanning Lorentz electron microscope.

[Explanation of symbols]

1 ... Electron source, 2 ... Biprism, 3 ... Deflection coil, 4 ...
Electron beam, 5 ... Irradiation lens, 6 ... Sample surface, 7 ... Imaging lens, 8 ... Interference fringe, 9 ... Slit, 10 ... Detector, 11 ...
Electron beam path, 12 ... Signal operation circuit, 13 ... Difference signal, 14
... sum signal, 15 ... control circuit, 16 ... switch, 17 ... calculator.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhiro Kuroda 1-280, Higashi-Kengikubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd.

Claims (5)

[Claims] 1. An electron beam extracted from an electron source in a vacuum,
In a scanning transmission electron microscope provided with a means for separating into two or more, a means for converging the separated electron beams on the sample surface, a means for scanning the converged electron beams, and a means for detecting the electron beams passing through the sample surface. A scanning transmission electron microscope, characterized in that the means for detecting the electron beam is constituted by a combination of a slit and a detector having a function capable of detecting the position and intensity of the electron beam. 2. A scanning transmission electron microscope according to claim 1, further comprising means for separating the electron beam and means for retracting or invalidating the slit. 3. The detector for detecting the intensity and deflection of the electron beam is divided so that four or more signals can be independently taken out, and the deflection of the electron beam is detected by calculating the signal from each divided portion. The scanning transmission electron microscope according to claim 1, wherein the scanning transmission electron microscope is a detector configured to. 4. The scanning transmission electron microscope according to claim 3, wherein the detector is a microchannel plate in which an anode is divided into four or more. 5. The scanning transmission electron microscope according to claim 3, wherein said detector is composed of four or more divided semiconductor detectors.