JP7657706B2 - Electron guns and devices - Google Patents

Description

The present invention relates to an electron gun and device.

Electron guns are used in electron microscopes such as scanning electron microscopes and transmission electron microscopes. One such electron gun that has attracted attention is the nanotip electron gun, which uses nanotips such as tungsten nanowires to emit electrons from single atoms.

In an electron gun, electrons are extracted from the emitter by the electric field created by the extraction electrode, passing through the electrode and aperture to reach the sample. The emission current, which is the amount of electron current emitted from the electron gun, can be determined, for example, by measuring the amount of electron current that hits the electrode or aperture. In Patent Document 1, the emission current is measured by measuring the amount of electron current that hits the aperture.

JP 2013-258030 A

For example, in an electron gun with a small light source such as a nanotip electron gun, the emission current is a small value of 100 nA or less. In an electron gun with such a small emission current, unless the leakage current between the emitter and the extraction electrode is reduced, the leakage current will become larger than the emission current, and the emission current may not be measured accurately.

One aspect of the electron gun according to the present invention is
An emitter that emits electrons;
an extraction electrode for extracting electrons from the emitter;
a support member for supporting the emitter and the extraction electrode;
Including,
The support member is
a first portion having the emitter attached thereto;
a second portion to which the extraction electrode is attached;
a third portion provided between the first portion and the second portion; and
Including,
The electrical conductivity of the third portion is higher than the electrical conductivity of the first portion and the electrical conductivity of the second portion.

In such an electron gun, the support member includes a third portion, which prevents leakage current from flowing from the extraction electrode to the emitter, thereby reducing leakage current between the emitter and the extraction electrode.

One aspect of the device according to the present invention is
The electron gun includes the above.

1 is a cross-sectional view showing a schematic configuration of an electron gun according to an embodiment of the present invention; 1 is a cross-sectional view showing a schematic configuration of an electron gun according to an embodiment of the present invention; 1 is a circuit diagram showing an electron gun according to an embodiment of the present invention; FIG. 4 is a diagram for explaining a method for detecting an emission current. FIG. 4 is a diagram for explaining leakage current between an emitter and an extraction electrode. FIG. 11 is a circuit diagram showing an electron gun according to a comparative example. FIG. 1 is a diagram showing the configuration of an electron microscope according to an embodiment of the present invention.

Below, preferred embodiments of the present invention are described in detail with reference to the drawings. Note that the embodiments described below do not unduly limit the content of the present invention described in the claims. Furthermore, not all of the configurations described below are necessarily essential components of the present invention.

1. Configuration of the Electron Gun First, an electron gun according to an embodiment of the present invention will be described with reference to the drawings. Figures 1 and 2 are cross-sectional views that show a schematic view of an electron gun 100 according to an embodiment of the present invention. Figures 1 and 2 show an X-axis, a Y-axis, and a Z-axis as three mutually orthogonal axes.

As shown in Figures 1 and 2, the electron gun 100 includes an emitter 10, a suppressor 20, an extraction electrode 30, a terminal 40a, a terminal 40b, a conductive member 42a, a conductive member 42b, a conductive member 44, a conductive member 46, a conductive member 48, a support member 50, and a holder 60.

The emitter 10 (filament) emits electrons. For example, a nanotip with a tip diameter on the order of nanometers can be used as the emitter 10. In an electron gun using a nanotip as the emitter 10, electrons can be emitted from a single atom or from several atoms. As a result, the size of the light source can be reduced to a few nm or less, and high brightness can be achieved. For example, a metal nanowire such as a tungsten nanowire, or a carbon nanotube can be used as the nanotip.

The emitter 10 is not limited to a nanotip. For example, a tungsten single crystal coated with zirconium oxide may be used as the emitter 10.

The emitter 10 is supported by a support member 50. In the illustrated example, the emitter 10 is supported by the support member 50 via terminals 40a, 40b, conductive members 42a, and conductive members 42b. The emitter 10 is attached to terminals 40a and 40b fixed to the base 12. The terminal 40a is connected to the conductive member 42a, and the terminal 40b is connected to the conductive member 42b. The conductive members 42a and 42b are attached to the support member 50.

The suppressor 20 is arranged to surround the terminals 40a and 40b. In the electron gun 100, the tip of the emitter 10 is disposed outside the space surrounded by the suppressor 20. The suppressor 20 is given a negative potential with respect to the emitter 10. This allows it to block the thermoelectrons emitted from the emitter 10. The suppressor 20 is supported by a support member 50.

The extraction electrode 30 is an electrode for extracting electrons from the emitter 10. A positive high voltage (extraction voltage) is applied between the emitter 10 and the extraction electrode 30 to create a strong electric field on the surface of the emitter 10.

The extraction electrode 30 is disposed behind the emitter 10. The extraction electrode 30 is supported by a support member 50. The extraction electrode 30 has a hole 32 that allows electrons emitted from the emitter 10 to pass through.

The terminals 40a and 40b are connected to the emitter 10. The terminals 40a and 40b are fixed to the insulating base 12. The terminal 40a is connected to the conductive member 42a, and the terminal 40b is connected to the conductive member 42b.

One end of the conductive member 44 is connected to the suppressor 20. A predetermined voltage is applied to the suppressor 20 via the conductive member 44. One end of the conductive member 46 is connected to the extraction electrode 30. A predetermined voltage is applied to the extraction electrode 30 via the conductive member 46.

One end of the conductive member 48 is connected to the third portion 56 of the support member 50. A predetermined voltage is applied to the third portion 56 of the support member 50 via the conductive member 48.

The support member 50 supports the emitter 10, the suppressor 20, and the extraction electrode 30. The support member 50 includes a first portion 52, a second portion 54, and a third portion 56. The third portion 56 is disposed between the first portion 52 and the second portion 54. That is, the first portion 52 and the second portion 54 are connected via the third portion 56 and are not in contact with each other. The second portion 54 is cylindrical, and the third portion 56 is provided on the inner surface of the second portion 54. The first portion 52 passes through the inside of the second portion 54. The first portion 52 and the third portion 56 are in contact with each other, and the second portion 54 and the third portion 56 are in contact with each other.

The electrical conductivity of the third portion 56 is higher than the electrical conductivity of the first portion 52 and the electrical conductivity of the second portion 54. The third portion 56 is connected to the conductive member 48.

The support member 50 is, for example, an insulating insulator with a guard ring embedded in it. The first part 52 and the second part 54 are the insulators, and the third part 56 is the guard ring. The insulator is made of a material such as porcelain, glass, or resin. The guard ring is made of a material such as metal.

The emitter 10 and the suppressor 20 are attached to the first portion 52 of the support member 50. The conductive member 42a, the conductive member 42b, and the conductive member 44 are further attached to the first portion 52 of the support member 50. The conductive member 42a passes through the first portion 52 and is connected to the terminal 40a. The conductive member 42b passes through the first portion 52 and is connected to the terminal 40b. The conductive member 44 passes through the first portion 52 and is connected to the suppressor 20.

The extraction electrode 30 is attached to the second portion 54 of the support member 50. The conductive member 46 is further attached to the second portion 54 of the support member 50. The conductive member 46 passes through the second portion 54 and is connected to the extraction electrode 30.

By providing the third portion 56 on the support member 50, it is possible to reduce leakage current between the emitter 10 attached to the first portion 52 and the extraction electrode 30 attached to the second portion 54. The reason for this will be explained later.

The support member 50 is attached to the holder 60. The holder 60 is cylindrical, and the conductive members 42a, 42b, 44, 46, and 48 pass through the internal space.

The electron gun 100 may have other electrodes (lenses), apertures, etc., which are not shown.

Figure 3 is a circuit diagram showing the electron gun 100. For convenience, the suppressor 20 is not shown in Figure 3.

As shown in FIG. 3, the electron gun 100 includes a deflection electrode 70 (an example of an electrode), a high-voltage power supply 80 (an example of a second power supply), a filament power supply 82, an extraction electrode power supply 84 (an example of a first power supply), a deflection electrode power supply 86, and a detection resistor 90 (an example of a detector).

The deflection electrode 70 is disposed after the extraction electrode 30. That is, in the electron gun 100, the extraction electrode 30 (first anode) and the deflection electrode 70 (second anode) are disposed in this order from the emitter 10 side. There is a predetermined potential difference between the extraction electrode 30 and the deflection electrode 70. The extraction electrode 30 and the deflection electrode 70 form an electrostatic lens.

The deflection electrode 70 has a hole 72 for passing electrons. The diameter of the hole 72 of the deflection electrode 70 is smaller than the diameter of the hole 32 of the extraction electrode 30, for example. The deflection electrode 70 is supported by the support member 50. The deflection electrode 70 is attached to the second part 54 in the same manner as the extraction electrode 30.

The filament power supply 82 supplies current to the emitter 10 to heat it.

The high-voltage power supply 80 supplies a negative high voltage HT to the emitter 10. The negative terminal of the high-voltage power supply 80 is electrically connected to the emitter 10 via the detection resistor 90. The positive terminal of the high-voltage power supply 80 is connected to ground.

The negative terminal of the high voltage power supply 80 is electrically connected to the negative terminal of the extraction electrode power supply 84. The positive terminal of the extraction electrode power supply 84 is electrically connected to the extraction electrode 30. The extraction electrode power supply 84 superimposes a positive voltage on the negative high voltage HT supplied by the high voltage power supply 80. The positive voltage superimposed by the extraction electrode power supply 84 is, for example, about several kV. Therefore, an extraction voltage of about several kV is applied between the emitter 10 and the extraction electrode 30. The negative terminal of the extraction electrode power supply 84 is also electrically connected to the third part 56 of the support member 50.

The negative terminal of the high-voltage power supply 80 is electrically connected to the negative terminal of the deflection electrode power supply 86. The positive terminal of the deflection electrode power supply 86 is electrically connected to the deflection electrode 70. The deflection electrode power supply 86 superimposes a positive voltage on the negative high voltage HT supplied by the high-voltage power supply 80. Therefore, the deflection electrode 70 has a predetermined potential difference with respect to the extraction electrode 30, and an electrostatic lens is formed between the extraction electrode 30 and the deflection electrode 70. The negative terminal of the deflection electrode power supply 86 is also electrically connected to the third part 56 of the support member 50.

The negative terminal of the high-voltage power supply 80 is also electrically connected to the third portion 56. As a result, the potential of the third portion 56 is the same as the high voltage HT. Therefore, the potential difference between the emitter 10 and the third portion 56 is smaller than the potential difference between the extraction electrode 30 and the third portion 56.

2. Operation In the electron gun 100, when a current is supplied from the filament power supply 82 to the emitter 10 and the emitter 10 is heated, electrons are extracted from the emitter 10 by a strong electric field created by the extraction electrode 30 on the surface of the emitter 10. At this time, the thermal electrons emitted from the emitter 10 are shielded by the suppressor 20 and are not emitted from the electron gun 100. The electrons extracted from the emitter 10 pass through the hole 32 in the extraction electrode 30, are focused by the electrostatic lens created by the extraction electrode 30 and the deflection electrode 70, and pass through the hole 72 in the deflection electrode 70. The electrons that have passed through the deflection electrode 70 pass through electrodes, apertures, etc. (not shown) and are then emitted from the electron gun 100.

In a transmission electron microscope equipped with an electron gun 100, electrons emitted from the electron gun 100 pass through an optical system and reach a fluorescent screen 102. The fluorescent screen 102 is for visualizing, for example, a transmission electron microscope image or an electron diffraction pattern. Note that a digital camera for photographing a transmission electron microscope image or an electron diffraction pattern may be used instead of the fluorescent screen 102. The fluorescent screen 102 is connected to ground.

Figure 4 is a diagram to explain the method of detecting emission current.

When electrons emitted from the emitter 10 hit the fluorescent screen 102, a current I2 corresponding to the electrons that hit the fluorescent screen 102 flows through the detection resistor 90. Therefore, the emission current can be measured by detecting the current I2 with the detection resistor 90. Here, the amount of current of electrons that are emitted from the emitter 10 and reach the fluorescent screen 102 can be measured as the emission current.

Figure 5 is a diagram for explaining leakage current between the emitter 10 and the extraction electrode 30. Figure 6 is a circuit diagram showing an electron gun 1 according to a comparative example. Figure 6 shows, as an electron gun 1 according to a comparative example, an electron gun in which the support member 50 does not have a third portion 56 (guard ring) and the first portion 52 and the second portion 54 are composed of an integrated insulator.

The potential difference (extraction voltage) between the emitter 10 and the extraction electrode 30 is about several kV. Therefore, if the emitter 10 and the extraction electrode 30 are connected via an insulator as shown in FIG. 6, a large leakage current I0 occurs even if the resistance 2 of the insulator is large. This leakage current I0 flows through the detection resistor 90, so the emission current cannot be measured accurately.

For example, even if the resistance 2 of the insulator is several hundred gigaΩ, if the potential difference between the emitter 10 and the extraction electrode 30 is 1 kV, the leakage current I0 will be several tens of nA. If the emitter 10 is a nanotip, the emission current is 100 nA or less, and the effect of the leakage current I0 is large.

In contrast, in the electron gun 100, as shown in FIG. 5, a third portion 56 (guard ring) is provided on the support member 50. The third portion 56 is connected to the negative terminal of the high-voltage power supply 80, and the potential of the third portion 56 is the same as the potential of the high voltage HT. Therefore, the potential difference between the emitter 10 and the third portion 56 is small. Therefore, the leakage current flowing between the emitter 10 and the third portion 56 can be made extremely small.

For example, the voltage supplied by the filament power supply 82 to the emitter 10 is about 1 V. Therefore, the potential difference between the emitter 10 and the third portion 56 is about 1 V, and even if the resistance of the first portion 52 is 10 GΩ, the leakage current between the emitter 10 and the third portion 56 is about 0.1 nA. In this way, by providing the third portion 56 in the electron gun 100, the leakage current flowing between the emitter 10 and the third portion 56 can be made extremely small. Therefore, in the electron gun 100, the leakage current flowing between the emitter 10 and the extraction electrode 30 can be reduced. As a result, the emission current can be accurately measured.

Here, when an extraction voltage is applied between the emitter 10 and the extraction electrode 30, a leakage current I0 flows between the third portion 56 and the extraction electrode 30, but this leakage current I0 does not flow through the detection resistor 90.

Specifically, leakage current I0 flows through resistor 4 (resistance component of second portion 54) between third portion 56 and extraction electrode 30, and through third portion 56, and returns to extraction electrode power supply 84. Since detection resistor 90 does not exist in the path of this leakage current I0, leakage current I0 does not contribute to the detection result of detection resistor 90. Therefore, the electron gun 100 can accurately measure the emission current.

In the above, the leakage current between the emitter 10 and the extraction electrode 30 has been described, but the same applies to the leakage current between the emitter 10 and the deflection electrode 70. That is, in the electron gun 100, the deflection electrode 70 is attached to the second part 54 of the support member 50 in the same way as the extraction electrode 30, so by providing the third part 56 on the support member 50, the leakage current between the emitter 10 and the deflection electrode 70 can be reduced.

In addition, instead of the deflection electrode 70, an aperture for cutting off a portion of the electrons emitted from the emitter 10 may be attached to the second portion 54. Even in this case, the leakage current between the emitter 10 and the aperture can be reduced, as in the case of the extraction electrode 30.

3. Effects The electron gun 100 includes an emitter 10 that emits electrons, an extraction electrode 30 that extracts electrons from the emitter 10, and a support member 50 that supports the emitter 10 and the extraction electrode 30. In the electron gun 100, the support member 50 includes a first portion 52 to which the emitter 10 is attached, a second portion 54 to which the extraction electrode 30 is attached, and a third portion 56 provided between the first portion 52 and the second portion 54, and the electrical conductivity of the third portion 56 is higher than the electrical conductivity of the first portion 52 and the electrical conductivity of the second portion 54.

In this way, in the electron gun 100, the third portion 56 is provided between the emitter 10 and the extraction electrode 30, so that leakage current can be prevented from flowing from the extraction electrode 30 to the emitter 10, and the leakage current between the emitter 10 and the extraction electrode 30 can be reduced.

In the electron gun 100, the positive terminal of the extraction electrode power supply 84 is connected to the extraction electrode 30, and the negative terminal of the extraction electrode power supply 84 is connected to the third part 56. The electron gun 100 also includes a high-voltage power supply 80 that supplies a high voltage HT to the emitter 10, and a detection resistor 90 for detecting the emission current. In the electron gun 100, the negative terminal of the high-voltage power supply 80 is connected to the emitter 10 via the detection resistor 90, and the third part 56 is connected to the negative terminal of the high-voltage power supply 80.

Therefore, in the electron gun 100, the potential of the third portion 56 can be made the same as the potential of the high voltage HT, and the potential difference between the emitter 10 and the third portion 56 can be reduced. This makes it possible to reduce the leakage current between the emitter 10 and the third portion 56 even when an extraction voltage is applied between the emitter 10 and the extraction electrode 30. Therefore, in the electron gun 100, the leakage current between the emitter 10 and the extraction electrode 30 can be reduced. Furthermore, in the electron gun 100, although a leakage current flows between the extraction electrode 30 and the third portion 56, this leakage current does not flow through the detection resistor 90. Therefore, in the electron gun 100, the emission current can be accurately measured.

In the electron gun 100, the emitter 10 is a nanotip. When a nanotip is used as the emitter 10, the emission current is 100 nA or less. In the electron gun 100, the leakage current between the emitter 10 and the extraction electrode 30 can be reduced, so that an emission current of 100 nA or less can be accurately measured.

In the electron gun 100, the second portion 54 is provided with a deflection electrode 70. Therefore, in the electron gun 100, leakage current between the emitter 10 and the deflection electrode 70 can be reduced.

As described above, the electron gun 100 can accurately measure the emission current, so even in an electron gun with a small emission current, such as a nanotip electron gun that uses a nanotip as the emitter 10, the emission current can be automatically controlled based on the measurement results of the emission current.

4. Electron Microscope Next, an electron microscope according to an embodiment of the present invention will be described with reference to the drawings. Fig. 7 is a diagram showing the configuration of an electron microscope 200 according to an embodiment of the present invention. The electron microscope 200 includes an electron gun 100. Furthermore, the electron microscope 200 includes an illumination system 210, a sample stage 220, an imaging system 230, and a fluorescent screen 240.

The electron microscope 200 is a transmission electron microscope (TEM). In the electron microscope 200, an electron beam is emitted from the electron gun 100 and accelerated by an accelerating tube (not shown). The irradiation system 210 focuses the electron beam and irradiates the focused electron beam onto a sample S supported on a sample stage 220. The imaging system 230 forms a transmission electron microscope image with the electron beam that has passed through the sample S. The transmission electron microscope image is visualized by a fluorescent screen 240.

The irradiation system 210 includes, for example, a condenser lens 212. The irradiation system 210 may also include an aperture for cutting out unnecessary electron beams.

The imaging system 230 includes an objective lens 232, an intermediate lens 234, and a projection lens 236. The objective lens 232 is the first lens for forming a transmission electron microscope image with the electron beam transmitted through the sample S. The intermediate lens 234 and the projection lens 236 further enlarge the image formed by the objective lens 232 and form an image on the fluorescent screen 240.

The fluorescent screen 240 visualizes the transmission electron microscope image. In the fluorescent screen 240, the fluorescent material applied thereto is excited by the collision of electrons, and the emitted visible light creates light and dark areas corresponding to the intensity of the electrons. As a result, the transmission electron microscope image is visualized. Note that, instead of visualizing the transmission electron microscope with the fluorescent screen 240, an image may be acquired with a digital camera such as a CCD camera. As described above, the fluorescent screen 240 is also used to detect the emission current.

Note that, although a transmission electron microscope equipped with an electron gun 100 has been described here as an example of the device according to the present invention, the device according to the present invention may be various devices capable of mounting an electron gun. For example, the device according to the present invention may be a scanning electron microscope, a scanning transmission electron microscope, an Auger microprobe, an electron probe microanalyzer, an electron beam drawing device, etc.

The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, the present invention includes configurations that are substantially the same as the configurations described in the embodiments. Substantially the same configurations are, for example, configurations that have the same functions, methods, and results, or configurations that have the same purpose and effect. The present invention also includes configurations in which non-essential parts of the configurations described in the embodiments are replaced. The present invention also includes configurations that have the same effects as the configurations described in the embodiments, or that can achieve the same purpose. The present invention also includes configurations in which publicly known technology is added to the configurations described in the embodiments.

Reference Signs List 1 electron gun, 2 resistor, 4 resistor, 10 emitter, 12 base, 20 suppressor, 30 extraction electrode, 32 hole, 40a terminal, 40b terminal, 42a conductive member, 42b conductive member, 44 conductive member, 46 conductive member, 48 conductive member, 50 support member, 52
...first part, 54...second part, 56...third part, 60...holder, 70...deflection electrode, 72...hole, 80...high voltage power supply, 82...filament power supply, 84...extraction electrode power supply, 86...deflection electrode power supply, 90...detection resistor, 100...electron gun, 102...fluorescent screen, 200...electron microscope, 210...irradiation system, 212...condenser lens, 220...sample stage, 230...imaging system, 232...objective lens, 234...intermediate lens, 236...projection lens, 240...fluorescent screen

Claims (8)

An emitter that emits electrons;
an extraction electrode for extracting electrons from the emitter;
a support member for supporting the emitter and the extraction electrode;
Including,
The support member is
a first portion having the emitter attached thereto;
a second portion to which the extraction electrode is attached;
a third portion provided between the first portion and the second portion; and
Including,
The third portion has a higher electrical conductivity than the first portion and the second portion. In claim 1,
an electron gun, wherein a potential difference between the emitter and the third portion is smaller than a potential difference between the extraction electrode and the third portion. In claim 1 or 2,
a first power supply that applies an extraction voltage between the emitter and the extraction electrode to extract electrons;
One end of the first power source is connected to the extraction electrode,
The other end of the first power supply is connected to the third portion. In any one of claims 1 to 3,
a second power supply for supplying a predetermined voltage to the emitter;
a detector for detecting the emission current;
Including,
one end of the second power source is connected to the emitter via the detector;
The third portion is connected to one end of the second power supply. In any one of claims 1 to 4,
An electron gun, wherein the emitter is a nanotip. In any one of claims 1 to 5,
the first portion and the second portion are insulators,
The electron gun, wherein the third portion is a guard ring. In any one of claims 1 to 6,
An electron gun including an electrode attached to the second portion. An apparatus including an electron gun according to any one of claims 1 to 7.

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