JP3974415B2 - Field emission electron microscope - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a field emission electron microscope.
[0002]
[Prior art]
The field emission electron gun has extremely high brightness compared to other types of electron guns that are generally known (10 + 9 A / cm ² str level, 100 times that of a normal electron gun such as LaB6). Because the light source is very small (several tens of nm level, usually 20 to 50 μm), it is highly excellent in coherence and a remarkably strong electron beam bundle can be obtained.
[0003]
Therefore, the field emission electron gun can obtain a very small first spot-like beam, for example, a sub-nanometer level beam (electron probe) on the sample. Its strength is also sufficient. Therefore, the field emission electron gun can perform elemental analysis and crystal structure analysis in a sub-nano-sized region on the sample, and a high-resolution image with little influence of aberration can be obtained.
[0004]
Therefore, field emission electron guns have great expectations, and in recent years their performance is stable and frequently used.
[0005]
However, the field emission electron gun has a problem due to its high coherence. For example, the contrast of the sample changes suddenly at the edge of the sample, where the thickness of the sample changes, where the crystal orientation changes, or where the amount of elements is different. Make fresnel fringes and fringes. Furthermore, sharp Fresnel fringes and interference fringes are created by electron beams transmitted by crystal diffraction and reflection and transmitted electron beams. This phenomenon does not change much even if the focus is changed greatly.
[0006]
For this reason, on the other hand, excellent coherence often disturbs observation of the true appearance of the sample on the other hand. In particular, due to the influence of spherical aberration, the diffracted wave by the crystal forms an image with a slight deviation from the original position, and a sharp interference image may be generated where it should not be. This phenomenon makes it easy to misinterpret the image.
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a field emission electron microscope capable of utilizing excellent coherence and reducing or eliminating the coherence as necessary.
[0008]
[Means for Solving the Problems]
Examples of the solving means of the present invention are as follows.
[0009]
(1) In a field emission electron microscope that emits an electron beam from a field emission electron gun and scans a beam of the electron beam on a sample,
A first spot-shaped scanning mode for scanning the first spot-shaped beam on the sample and a second spot-shaped scanning mode for scanning the second spot-shaped beam on the sample are set in advance. The spot-like scan mode and the second spot-like scan mode can be switched,
In the course of the electron beam reaches the specimen from the electron gun, by reducing or eliminating the interference of the electron beam, Ri beam shape of the electron beam on the specimen Do the second spot,
The second spot-like beam, a field emission electron microscope, characterized in Oh Rukoto in spot beam form spread than the first spot beam.
[0010]
(2) The field emission electron microscope described above, wherein a scanning signal is superimposed on a deflection power source .
[0011]
(3) The field emission electron microscope described above, wherein a signal from an oscillation circuit that varies the acceleration voltage is superimposed on the acceleration voltage power source .
[0012]
(4) In the scanning mode, the above-described electric field is characterized in that the deflection coil and the deflection power source are connected via a scanning signal circuit, and the scanning signal is superimposed on the deflection coil to swing the electron beam. Emission electron microscope.
[0013]
(5) An electric field including a field emission electron gun for emitting an electron beam, a deflection coil for deflecting the electron beam to scan a sample, and a deflection power source for supplying a deflection current to the deflection coil Field emission, characterized in that in an emission electron microscope, a switching means for superimposing a scanning signal to be scanned in a predetermined shape on a deflection current is provided, and the coherence of the electron beam is reduced or eliminated by vibrating the electron beam Type electron microscope.
[0014]
(6) In a field emission electron microscope including a field emission electron gun for emitting an electron beam and an acceleration voltage power source for supplying an acceleration voltage to the field emission electron gun, the acceleration voltage power source is varied. A field emission electron microscope comprising a switching means for superimposing a signal from an oscillation circuit, and reducing or eliminating the coherence of an electron beam by changing an acceleration voltage.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, for example, a plurality of modes are selectively used by the action of a switch. When it is desired to make the best use of the characteristics of the field emission electron gun, the field emission type configuration is used as it is, and the beam shape of the electron beam on the sample is set to the first spot shape . In addition, when high interference is greatly disturbing, the interference is lost or reduced, and the beam shape of the electron beam on the sample is a second spot shape (for example, circular or rectangular, but limited to these shapes). To be observed).
[0016]
In the field emission electron microscope of the present invention, an electron beam is emitted from a field emission electron gun, and a beam of the electron beam is scanned on the sample through a deflection coil and a focusing lens.
[0017]
At least two modes, for example, a first spot-like scanning mode in which the first spot-like beam is scanned on the sample and a second spot- like scanning mode in which the second spot- like beam is scanned on the sample in advance. Is set. Preferably, the first spot-like scanning mode and the second spot- like scanning mode can be switched by a switch.
[0018]
Preferably, the second spot shape on the sample in the second spot scanning mode is circular or rectangular.
[0019]
It is preferable that the mode of the electron beam on the sample is formed in a second spot shape by reducing or eliminating the coherence of the electron beam on the way from the electron gun to the sample.
[0020]
There are various ways to eliminate or reduce the coherence of electron beams. For example, there are a method of superimposing and superposing many electron beams whose phases are shifted by largely moving the light source, and a method of superimposing electron beams whose phases are shifted by changing the energy of the electron beams.
[0021]
A field emission electron microscope according to one embodiment of the present invention preferably includes a field emission electron gun for emitting an electron beam, a deflection coil for deflecting the electron beam to scan a sample, and a deflection And a deflection power source for supplying a deflection current to the coil. The deflection power supply is provided with switching means for superimposing a scanning signal for scanning in a predetermined shape on the deflection current, and the operation causes the electron beam to vibrate at least two-dimensionally, thereby reducing the coherence of the electron beam. Or disappear.
[0022]
A field emission electron microscope according to another preferred embodiment of the present invention includes a field emission electron gun for emitting an electron beam, an acceleration voltage power source for supplying an acceleration voltage to the field emission electron gun, and Is provided. Then, a switching means for superimposing a signal from an oscillation circuit for changing the acceleration power supply is provided to the acceleration voltage power supply, and operating it to reduce the coherence of the electron beam by changing the acceleration voltage or Disappear.
[0023]
The field emission electron microscope is preferably a transmission electron microscope equipped with a field emission electron gun.
[0024]
According to the present invention, it is possible to make use of the coherence of an electron beam, which is an excellent characteristic of a field emission electron gun, or to eliminate or reduce it as necessary.
[0025]
【Example】
Embodiments 1 and 2 of the present invention will be described with reference to the drawings.
[0026]
<First embodiment>
1 and 2 show a first embodiment of the present invention.
[0027]
As shown in FIGS. 1 and 2, the field emission electron microscope according to the present invention has at least two modes, namely, a first spot-like scanning mode (FIG. 1) and a second spot- like scanning mode (FIG. 2). These two modes can be switched by a switch.
[0028]
A field emission electron microscope according to the present invention includes a field emission electron gun 1 for emitting an electron beam and a sample 2, a deflection coil 3 for deflecting the electron beam and scanning the sample, and focusing. A lens 4 is provided. In addition, a deflection power source 5 for supplying a deflection current to the deflection coil 3 and an acceleration voltage power source 6 for supplying an acceleration voltage to the field emission electron gun 1 are provided.
[0029]
Switching means for superimposing a scanning signal for scanning the deflection power source 5 in a predetermined shape (circular or rectangular second spot shape) on the deflection current, for example, a switch 10 is provided, and the electron beam is two-dimensionally operated by the switching means. Vibrate to reduce or eliminate the coherence of the electron beam.
[0030]
The deflection coil 3 for axial alignment of the electron gun 1 is provided closer to the electron gun 1 than the sample 2. The deflection coil 3 may be an axial alignment coil incorporated in advance or may be newly provided. The circuit 13 is a circuit that puts a scanning signal on the deflection coil 3. The mode of FIG. 2 in which the light source 9 on the side of the electron gun 1 is scanned within a limited range by the switch 10 for switching, and the observation or shooting without the circuit 13 is observed. The mode of FIG. 1 for photographing can be arbitrarily switched and used. The scanning size, shape, and scanning speed can be arbitrarily changed.
[0031]
The standard mode of FIG. 1 is a mode in which the actual light source 9 is shown in a first spot shape at the electron gun 1. The switch 10 is in contact with the upper contact in FIG. 2, and a first spot-like mode (probe) is formed on the sample 2 corresponding to the first spot-like light source 9.
[0032]
In the scanning mode of FIG. 2, the switch 10 is in contact with the lower contact of FIG. 2 (shown by the solid line), and the deflection coil 3 and the deflection power source 5 are connected via the scanning signal circuit 13. They are connected so that the scanning signal is superimposed on the deflection coil 3 and the electron beam is shaken, so that the coherence is lost or reduced.
[0033]
In such a mode of FIG. 2, the shape of the apparent light source is the second spot shape (for example, a circle or a rectangle) on the electron gun 1 side, and the electron beam beam is spread on the sample 2 side, Corresponding to the shape of the light source, a second spot shape (circular or rectangular) is formed. On the sample 2, image observation is performed in a form in which the beam is expanded in a second spot shape. As a result, the coherence can be reduced or eliminated. In addition, although circular and a rectangle were mention | raise | lifted as an example of 2nd spot shape, it is not limited to this.
[0034]
The size of the light source 9 of the field emission electron gun 1 generally used is actually 20 to 50 nm, for example. On the other hand, in LaB6 electron gun 1, it is 20-50 micrometers. The size of the light source 9 of the field emission electron gun 1 is extremely small, 11/500 to 1/1000 times that of the LaB6 electron gun.
[0035]
Therefore, if the light source 9 of the field emission electron gun 1 is scanned within a range of about 500 × 500 to 1000 × 1000 times (points), the coherence of the electron beam at each point changes. Although they are not integrated, the coherence can be reduced or eliminated just like the LaB6 electron gun.
[0036]
It is possible to scan larger than this. For example, scanning (scanning) can be performed within a range of about 500 × 500 times to 10000 × 10000 times (points). Thereby, the coherence can be further reduced or eliminated as compared with the LaB6 electron gun.
[0037]
In the example of FIGS. 1 and 2, since there is no change in the total amount of electron beams when scanning is performed and when scanning is not performed, the brightness of the fluorescent screen and the shutter speed during photographing are affected. It is practical enough.
[0038]
Ideally, if the light source 9 is scanned as if it were circular, it would be ideal without the direction of information acquisition. However, even if it is simply scanned in a rectangular shape, the normal purpose is sufficiently achieved. The Therefore, there is almost no need to stick to the scanning shape.
[0039]
The higher the scanning speed, the better. However, at least, the object can be achieved by scanning once during one exposure at the time of photographing . For observation on a fluorescent screen, considering the afterglow of the fluorescent screen, it is practical if it is faster than 2 to 3 times / second. Since this method is hardly affected by aberrations, it is suitable for high-resolution observation.
[0040]
<Second embodiment>
3 to 4 show a second embodiment of the present invention.
[0041]
FIG. 3 shows an example of a related member of the electron gun 1. For example, the electron gun 1 includes an emitter 21, a suppressor 22, an extractor 23, an anode 24, a heating circuit 25 for the emitter 21, a voltage control circuit 26 for the suppressor 22, a voltage control circuit 27 for the extractor 23, and the like.
[0042]
As shown in FIG. 3, switching means, for example, a switch 12 for superimposing a signal from an oscillation circuit 11 that fluctuates the acceleration power supply is provided to the acceleration voltage power supply 6 and is operated to vary the acceleration voltage. As a result, the coherence of the electron beam is reduced or eliminated. The circuit 11 is an oscillation circuit that varies the acceleration voltage of the electron beam by a certain amount (not necessarily strict). As this oscillation circuit 11, a built-in circuit such as a voltage wobbler may be used. A changeover switch 12 is used to arbitrarily switch between a mode for observing and photographing while changing the acceleration voltage of the electron beam via the oscillation circuit 11 and a mode for observing and photographing without changing the circuit 11. . The amount and speed of the change can be arbitrarily changed.
[0043]
The voltage control circuit 27 of the extractor 23 is a means for controlling the voltage applied to the electron gun 1 in order to extract the electron beam.
[0044]
The heating circuit 25 of the emitter 21 is a circuit for heating the anode 24 (electrode) in order to generate an electron beam.
[0045]
As another method of greatly shifting the phase of the electron beam in order to reduce or eliminate the coherence, it is conceivable to increase the energy fluctuation of the electron beam. However, since this method causes axial chromatic aberration and off-axis chromatic aberration such as magnification and rotation, the image quality is greatly affected.
[0046]
When the acceleration voltage U (kV) and the energy fluctuation are ΔU (kV), an example of the magnitude of the fluctuation width is ΔU / U> = 0 to 2 × 10 ⁻⁴ . The range is not limited to this. Practically, it can be varied within a range of ΔU / U> = 0 to 2 × 10 ⁻³ . Outside this range, off-axis chromatic aberration generally becomes conspicuous, and the image quality at the central portion is also deteriorated due to the on-axis chromatic aberration, but image observation of the interface on the fluorescent screen is sufficiently possible. However, it varies greatly depending on the observation magnification. Therefore, it is practical enough if the magnitude of the fluctuation range can be varied by about ΔU / U> = 0 to 2 × 10 ⁻³ . The shape of the fluctuation may be any of rectangular wave, sawtooth wave, sine wave, and the like. Furthermore, the shape of the variation need not be periodic.
[0047]
The speed of fluctuation is not as fast as the scanning of a, but the object is achieved if it fluctuates at least once during one exposure. For observation, considering the afterglow of the fluorescent screen, it is practical if it is 2 to 3 times / second.
[0048]
FIG. 4 shows a detailed structure of a field emission type electron gun according to the second embodiment shown in FIG.
[0049]
In FIG. 4, an anode 24 is an electrode to which an acceleration voltage is applied. Such an electrode is generally called a Schottky field emission electron gun (also referred to as a field emission electron gun, or FE electron gun). , Brightness close to that of a cold field emission electron gun is obtained, the initial velocity energy width of the electron beam is not significantly different from that of a cold field emission electrode, and the stability is extremely high, and the vacuum is also higher than that of a cold field emission electrode. Since it is easy, it is used a lot. However, unlike a cold field emission electron gun, a Schottky field emission electron gun must be used by heating the tip of the tip of the electron gun to about 1700 ° C. Therefore, many thermoelectrons are generated in the vicinity of the heating circuit 25 of the emitter 21. The heating circuit 25 of the emitter 21 refers to a circuit for generating electrons. By applying a reverse voltage so that unnecessary things such as thermionic electrons do not jump out, the unnecessary things are confined inside. The reverse voltage applied to confine (suppress) unnecessary thermoelectrons is called a suppressor voltage, and this is controlled by the voltage control circuit 26 of the suppressor 22.
[0050]
The chip of the field emission electron gun 1 is arranged so as to slightly protrude by a suppressor 22 (suspessa). A strong electric field is applied by the extractor 23 ahead. As a result, a strong potential gradient is generated at the tip of the chip, and electrons jump out.
[0051]
The extractor voltage is a voltage applied to extract electrons generated by the emitter circuit 25. The electrode for applying the voltage is the extractor 23.
[0052]
For the field emission chip, tungsten crystals are usually used. A number of crystal planes are formed at the tip, and there are a plurality of crystal planes in which electrons are likely to jump out. Therefore, although a plurality of electron beams are generated, they are adjusted and used so that only the center of the electron beam comes to the lower lens system. It is preferable to obtain a nearly ideal electron beam by finely adjusting the chip temperature, suppressor voltage, extractor voltage, and the like. If the temperature of the chip is changed, the positional relationship between the chip and the suppressor changes due to thermal expansion or the like.
[0053]
In any of the above-described embodiments, when it is desired to make the best use of the coherence of the electron beam, the configuration is used as it is, and when the high coherence is greatly disturbed, the coherence is instantaneously reduced by a switch and observed. Can do.
[0054]
【The invention's effect】
According to the present invention, the excellent coherence can be fully utilized, and the disadvantages caused thereby can be solved.
[Brief description of the drawings]
FIG. 1 shows one mode of a field emission electron microscope according to a first embodiment of the present invention.
FIG. 2 shows another mode of the field emission electron microscope according to the first embodiment of the present invention.
FIG. 3 shows a configuration of an electron gun side of a field emission electron microscope according to a second embodiment of the present invention.
4 shows a detailed structure of a related member of the electron gun of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electron gun 2 Sample 3 Deflection coil 4 Focusing lens 5 Deflection power supply 6 Acceleration voltage power supply 9 Light source 10 Switch 11 Oscillation circuit 13 Circuit 21 Emitter 22 Suppressor 23 Extractor 24 Anode 25 Emitter 21 heating circuit 26 Suppressor 22 voltage control circuit 27 Voltage control circuit of extractor 23

Claims (3)

In a field emission electron microscope that emits an electron beam from a field emission electron gun and scans a beam of the electron beam on a sample,
A first spot-shaped scanning mode for scanning the first spot-shaped beam on the sample and a second spot-shaped scanning mode for scanning the second spot-shaped beam on the sample are set in advance. The spot-like scan mode and the second spot-like scan mode can be switched,
In the middle of the electron beam from the electron gun to the sample, by reducing or eliminating the coherence of the electron beam, the beam shape of the electron beam on the sample becomes a second spot shape,
A field emission electron microscope characterized in that the second spot-shaped beam is a spot-shaped beam which is wider than the first spot-shaped beam. A field emission electron having a field emission electron gun for emitting an electron beam, a deflection coil for deflecting the electron beam to scan a sample, and a deflection power source for supplying a deflection current to the deflection coil In the microscope,
A field emission electron microscope comprising a switching means for superimposing a scanning signal to be scanned in a predetermined shape on a deflection current, and reducing or eliminating the coherence of the electron beam by vibrating the electron beam. In a field emission electron microscope comprising a field emission electron gun for emitting an electron beam and an acceleration voltage power source for supplying an acceleration voltage to the field emission electron gun,
A field emission electron microscope comprising a switching means for superimposing a signal from an oscillation circuit for changing an acceleration voltage power source, and reducing or eliminating the coherence of an electron beam by changing the acceleration voltage.

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