JPH0917365A - Field emission type electron gun - Google Patents

Abstract

PURPOSE: To provide a field emission type electron gun which can substantially dispense with an axial adjustment between an emitter and a pullout electrode and can eliminate generation of microscopic discharge and can generate a stable electron beam. CONSTITUTION: An emitter 15, a stem 16, an emitter base 17 and a metallic holder 18 are previously integrally constituted, and the emitter 15 is axially adjusted in order of several ten μm to the metallic holder 18. Work is performed on the extraction electrode 19 in a tolerance of several ten μm. After such previous highly accurate assembling and work, when the metallic holder 18 is installed in a step part 19a of the extraction electrode 19, as a result, since axial adjustment accuracy of the emitter 15 and the pullout electrode 19 can be maintained in order of several ten μm, there is no need to adjust a position of the extraction electrode 10 relative to the emitter 15 after it is assembled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field emission electron gun for a scanning electron microscope or the like, which does not require axial alignment between an emitter and an extraction electrode.

[0002]

2. Description of the Related Art FIG. 1 shows a conventional cold cathode type field emission electron gun. 1 is a field emission emitter formed of tungsten or the like, and the emitter 1 is attached to an emitter base 2. The base 2 is fixed to the emitter mounting electrode 3, and the emitter mounting electrode 3 is mounted on the extraction electrode base 5 via the insulator 4.

A lead-out electrode base 5 is attached to a lead-out electrode 6 having a cylindrical shape with a bottom. An electron-beam passage hole 7 is provided at the bottom of the tip of the lead-out electrode 6, and the lead-out electrode 6 An exhaust hole 8 for exhausting the inside of the cylindrical extraction electrode is provided on the side of 6. Below the extraction electrode 6,
An anode 9 having a ground potential is arranged. An acceleration voltage is applied from the acceleration voltage power supply 10 between the emitter 1 and the anode 9, and an extraction voltage is applied from the extraction voltage power supply 11 between the emitter 1 and the extraction electrode 6.

With the above-mentioned structure, the field emission type electron gun is evacuated to an ultrahigh vacuum, and then the power source 10 causes the emitter 1
An acceleration voltage is applied between the anode 1 and the anode 9, and an extraction voltage is applied from the power supply 11 between the emitter 1 and the extraction electrode 6.
As a result, electrons are extracted from the tip of the emitter 1, and the extracted electrons are accelerated by the anode 9 to obtain a high-luminance electron beam.

[0005]

In the above-mentioned structure, when the acceleration voltage or the extraction voltage is changed, the position of the tip of the emitter and the center of the electron beam passage hole 7 of the extraction electrode 6 do not coincide with each other. A phenomenon occurs in which the axis of the obtained electron beam shifts. In order to obtain a stable electron beam in which the axis is not displaced, it is necessary to align the emitter 1 and the extraction electrode 6 with high accuracy of several tens of μm.

In the conventional configuration shown in FIG. 1, the emitter 1
Is an emitter base 2, an emitter mounting member 3, and an insulator 4
The extraction electrode 6 is attached to the extraction electrode base 5 via. For this reason, the axes of the electron beam passage hole 7 of the extraction electrode 6 and the emitter 1 inevitably deviate by several hundred μm due to assembly and processing tolerances of several parts therebetween.

Therefore, although not shown, an axial alignment mechanism is provided between the extraction electrode 6 and the extraction electrode base 5, and this mechanism is operated using a stereoscopic microscope to adjust the position of the extraction electrode 6. Thus, the axis alignment between the emitter 1 and the extraction electrode 6 is performed. Therefore, in the conventional configuration, a mechanism for performing axis alignment is required, and a skillful axis alignment work is indispensable.

In the case of a thermionic gun, a Wehnelt electrode is provided close to the filament to control the electrons generated from the filament. Since a voltage of negative polarity is applied to the filament to the Wehnelt electrode, the Wehnelt electrode is not irradiated with the electron beam. Therefore, backscattered electrons are not generated from the Wehnelt electrode, and there is no fear that the insulator or the like supporting the filament is charged.

On the other hand, in the field emission type electron gun as shown in FIG. 1, since a voltage having a positive polarity with respect to the emitter 1 is applied to the extraction electrode 6, the extraction electrode 6 emits from the emitter 1. Electrons collide with each other, and reflected electrons are generated from the extraction electrode 6. The reflected electrons are directed to an insulating member supporting the emitter 1 and cause a charging phenomenon. Therefore, a minute discharge is generated in the charged portion, which hinders stable generation of the electron beam.

Further, when the extraction electrode 6 has a negative polarity with respect to the ground potential, an electric field enters the extraction electrode 6 through the exhaust hole 8 of the extraction electrode 6, and the secondary electrons generated in the extraction electrode 6 reach the anode 9. Pour in. Further, when the accelerating voltage is changed, the distribution of the electric field entering from the exhaust hole 8 of the extraction electrode 6 changes, and the electric field applied to the tip of the emitter 1 changes accordingly. Due to such a phenomenon, the current of the electrons emitted from the emitter 1 changes, and a stable electron beam cannot be obtained.

The present invention has been made in view of the above circumstances, and an object thereof is to substantially eliminate the need for axial alignment between the emitter and the extraction electrode, and further to prevent the occurrence of micro-discharge and to stabilize the discharge. To realize a field emission type electron gun capable of generating various electron beams.

[0012]

A field emission electron gun according to the present invention has a field emission emitter, an insulating base member supporting the emitter and held by a metal holder, and an electron beam passage hole. And a metal holder aligned with the emitter. The metal holder is attached to the extraction electrode.

A field emission type electron gun according to a second aspect of the invention is characterized in that the base member has a step portion substantially parallel to the optical axis. The field emission electron gun according to the invention of claim 3 is characterized in that a ring-shaped projection is provided in the vicinity of the electron beam passage hole of the extraction electrode so as to surround the emitter.

The field emission type electron gun according to the invention of claim 3 is characterized in that the leading end portion of the extraction electrode is formed in a cylindrical shape.

[0015]

The field emission type electron gun according to the first aspect of the invention is
A field emission emitter, an insulating base member supporting the emitter and held by a metal holder, and an extraction electrode having an electron beam passage hole are provided, and the metal holder aligned with the emitter can be attached to the extraction electrode. It is not necessary to adjust the position of the extraction electrode.

In the field emission type electron gun according to the second aspect of the present invention, the base member is provided with a step portion substantially parallel to the optical axis to prevent charging. In the field emission electron gun according to the invention of claim 3, a ring-shaped projection is provided in the vicinity of the electron beam passage hole of the extraction electrode so as to surround the emitter, and a stable electron beam is generated.

In the field emission type electron gun according to the third aspect of the present invention, the leading end portion of the extraction electrode is formed in a cylindrical shape to generate a stable electron beam.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 shows a field emission type electron gun according to the present invention, and 15 is an electron emission emitter formed of tungsten or the like. The emitter 15 is supported by a stem 16, and the stem 16 is attached to an emitter base 17 made of an insulating material. The emitter base 17 is stepped, and has a portion 17a horizontal to the optical axis O.
have.

The emitter base 17 is attached to a ring-shaped metal holder 18. The emitter 15, the stem 16, the emitter base 17, and the ring-shaped metal holder 18 are integrally formed in advance, and the emitter 15 is axially aligned with the metal holder 18 in the order of several tens of μm. .

Reference numeral 19 is a bottomed cylindrical extraction electrode to which the metal holder 18 is directly attached, and an electron beam passage hole 20 is provided in the bottom portion of the tip of the extraction electrode 19. Further, an exhaust hole 21 for exhausting the inside of the extraction electrode 19 is provided on the side portion of the extraction electrode 19. In addition,
Reference numeral 22 denotes an electron gun support to which the extraction electrode 19 is attached, which is provided to insulate the voltage applied to the extraction electrode 19 from the ground potential.

Below the extraction electrode 19, an anode 23 having a ground potential is arranged. Further, a protrusion 24 facing the direction of the emitter 15 is provided in a cylindrical shape at the bottom of the extraction electrode 19. The extraction electrode 19 to which the emitter 15 is attached is mechanically aligned with the anode 23. The operation of such a configuration will now be described.

With the above structure, the emitter 15 and the stem 1
6, the emitter base 17, and the metal holder 18 are integrally configured in advance, and the emitter 15 is axially aligned with the metal holder 18 in the order of several tens of μm. Further, the extraction electrode 19 is processed with a tolerance of several tens of μm. In particular, the processing accuracy of the step portion 19a of the extraction electrode 19 to which the metal holder 18 is attached is high.

After such assembly and processing with high precision in advance, the metal holder 18 is attached to the stepped portion 19a of the extraction electrode 19.
As a result, the alignment accuracy of the emitter 15 and the extraction electrode 19 can be maintained on the order of several tens of μm, and it is not necessary to adjust the position of the extraction electrode 19 with respect to the emitter 15 after assembly. . Therefore, the position adjusting mechanism of the extraction electrode 19 is not necessary.

The emitter base 17 is provided with a step, and the portion 17a near the emitter 15 is parallel to the optical axis O. Here, a part of the electrons emitted from the emitter 15 is applied to the emitter base 17 as reflected electrons from the extraction electrode 19. However, since the reflected electrons are not irradiated to the portion 17a substantially parallel to the optical axis O, the insulation failure of the emitter base 17 does not occur, and the minute discharge that propagates on the surface of the emitter base 17 does not occur.

In the embodiment shown in FIG. 2, the extraction electrode 19 is provided with an exhaust hole 21, and the electric field from the anode 23 enters the extraction electrode 19 through this exhaust hole. When the accelerating voltage is changed, not only the amount of entry of this electric field is changed and the electron emission characteristic from the emitter 15 is changed, but also secondary electrons generated at the extraction electrode 19 pass through the exhaust hole 21 and the anode 23 by the electric field. Is irradiated.

The anode 23 releases gas from the anode 23 due to electron impact energy caused by irradiation of electrons, which deteriorates the vacuum of the electron gun portion. Therefore, in the embodiment of FIG. 2, a ring-shaped protrusion 24 is provided around the emitter 15 so as to surround the emitter 15 inside the extraction electrode 19 so that the electric field from the exhaust hole 21 is applied to the emitter 15.
And the influence of the extraction electrode 19 on the electron-irradiated portion is extremely reduced.

That is, even if the accelerating voltage is changed, there is almost no change in the electric field at the tip of the emitter 15, and a stable electron beam can be generated. In addition, secondary electrons generated by irradiation of the extraction electrode 19 around the electron beam passage hole 20 with the electron beam are generated by the projections 24 in the anode 23.
Heading to is prevented.

FIG. 3 shows another embodiment of the present invention.
In this embodiment, the shape of the extraction electrode 19 is different from that of the embodiment shown in FIG. The tip of the extraction electrode 19 is provided with a ring-shaped protrusion 24 in the embodiment of FIG. 2, but in the embodiment of FIG. 3, the shape of the inner portion 25 at the tip of the extraction electrode 19 is replaced by a cylindrical shape. I am in a state. The inside portion (inner wall) 25 of the cylindrical extraction electrode is configured to surround the tip end portion of the emitter 15 so as to prevent the influence of the electric field of the anode entering from the exhaust hole 21.

[0029]

As described above, the field emission electron gun according to the invention of claim 1 has a field emission emitter, an insulating base member supporting the emitter and held by a metal holder, and an electron beam passage hole. And a metal holder aligned with the emitter are attached to the extraction electrode. Therefore, the position adjustment of the extraction electrode is unnecessary.

In the field emission type electron gun according to the second aspect of the present invention, since the base member is provided with the step portion substantially parallel to the optical axis, it is possible to prevent charging due to backscattered electrons and prevent generation of minute discharge. it can.

In the field emission type electron gun according to the third aspect of the present invention, since the ring-shaped projection is provided in the vicinity of the electron beam passage hole of the extraction electrode so as to surround the emitter, secondary electrons generated from the extraction electrode are generated. In addition to the effect of preventing emission from the exhaust hole to the anode, it is possible to prevent the electric field from the exhaust hole from affecting the emitter even if the acceleration voltage is changed. Therefore, a stable electron beam can be generated.

In the field emission electron gun according to the third aspect of the present invention, since the inner shape of the leading end of the extraction electrode is formed in a cylindrical shape, secondary electrons generated from the extraction electrode are not emitted from the exhaust hole to the anode. In addition to the above effect, it is possible to prevent the electric field from the exhaust hole from affecting the emitter even if the acceleration voltage is changed. Therefore, a stable electron beam can be generated.

[Brief description of the drawings]

FIG. 1 is a diagram showing a conventional field emission electron gun.

FIG. 2 is a diagram showing a field emission electron gun according to an embodiment of the present invention.

FIG. 3 is a diagram showing another embodiment of the present invention.

[Explanation of symbols]

 15 Emitter 16 Stem 17 Emitter Base 18 Metal Holder 19 Extraction Electrode 20 Electron Beam Passage Hole 21 Exhaust Hole 22 Electron Gun Support 23 Anode 24 Protrusion

Claims (4)

[Claims] 1. A field emission emitter, an insulating base member supporting the emitter and held by a metal holder, and an extraction electrode having an electron beam passage hole, and a metal holder aligned with the emitter. A field emission electron gun configured to be attached to an extraction electrode. 2. The field emission electron gun according to claim 1, wherein the base member has a step portion substantially parallel to the optical axis. 3. A ring-shaped projection is provided near the electron beam passage hole of the extraction electrode so as to surround the emitter.
2. The field emission electron gun according to 2. 4. The field emission type electron gun according to claim 1, wherein a ring-shaped projection is provided so as to surround the emitter whose inner shape of the leading end of the extraction electrode is cylindrical.