JPS6079636A - Thermoelectric field emission cathode and applied device - Google Patents

Abstract

PURPOSE:To obtain a plurality of electric field emission beams having high luminance and high stability simultaneously from a single electric field emission chip, by taking out a plurality of electric field emission beams with restricted, radiant angle of W(100) plane from a single sharp needle. CONSTITUTION:A wire of W having axial bearings <110> of such as 0.1- 0.15mm. in diameter is spot welded to the top end of a heating element 11 of W formed to V-shape, and the tip of the wire is sharp-pointed by electrolytic grinding by using such as aqueous solution of KOH to make a sharp needle 12. Subsequently, Ti is adhered to the V-shaped tip of the heating element 11 and a Ti supply source 13 is formed by passing a heating current to the heating element 11 in a vacuum. At the tip of the sharp needle 12, atmospheric oxygen is taken in and an absorption layer of Ti and oxygen is formed thereon. When a high voltage is applied to an opposing anode 14 in this condition, the work function on the (100) crystal plane of the sharp needle 12 of W having axial bearings of <100> decreases, and two electric field emission beams 15a, 15b having high luminance with restricted radiant angles to bearings of <100> are obtained.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a field emission cathode, and particularly to a thermal field emission cathode ('l) suitable for simultaneously obtaining a plurality of high-brightness and highly stable electron beam sources. 'hermal pield En1issi
onCath□de (hereinafter referred to as TFE cathode).

[Background of the invention]

As an electron beam source, there is a thermal pole that uses thermionic electrons emitted from the surface of a metal etc. heated to a high temperature, and a tunnel effect that applies a strong electric field to a needle-shaped tip with a radius of curvature of a ladle angstrom. Field emission cathodes can be broadly divided into field emission cathodes that utilize electrons emitted from the cathode surface. As a hot cathode,
Barium-strotium oxide cathodes and barium dispenser cathodes, which can operate at low temperatures and at high current densities, are known as electron beam sources for electron tubes. Furthermore, in recent years, lanthanum hexaboride has been put into practical use as a high-brightness electron beam source, but the brightness of these hot cathodes is about 10 h/c4 Sr. On the other hand, field radiation can be roughly divided into cold field radiation where the chip temperature is near room temperature.
sion (hereinafter referred to as CFE) and TFE.

In order to operate CFE stably, the space where the emitter is located must be 10-I0' in order to reduce gas adsorption to the emitter tip and eliminate damage to the emitter due to ion bombardment.
It is required to maintain an ultra-high vacuum of less than L'orr, and the emission current for stable operation should be less than 10μ8.

Also, the brightness is about 10'A/c+MS r. on the other hand,
TFE is fired by heating the emitter tip to a temperature range that does not generate thermoelectrons, and then applying a strong electric field to draw out the emissions. In particular, Wolfe et al.
According to the method proposed in Patent No. 3,814,975), a stable emission current with high brightness can be obtained even in a vacuum of about 10 −7 Torr. That is, 1 in an 02 gas atmosphere of about 10-7T□rr.
When the emitter is heated between 750 and 18501 and zirconium (Zr) is adsorbed at the tip, an adsorption state of Zr0-W is formed at the emitter tip, and w < t.
o o ) surface work per night J number is 2.6 to 2.8 e V
decreases to As a result, a large emission current from the emitter tip can be selectively obtained from the W (100) plane, which is what is called the angular distribution restriction of the emission current. Similar effects can be seen in titanium (Tim), hafnium (H
f).

Niobium (Nb), ) Lium (Tll), Magnesium (
It can also be obtained from Mg) and cerium (Ce). In particular, when Ti is used as an adsorbent for the emitter, the emitter temperature can be lowered to 1000 to 1200 t:', the oxygen partial pressure can be as low as 10-9 Torr, and the amplitude is 10' to 10'.
High performance of 1010A/crrl Sr can be obtained.

Now, field emission cathodes have high brightness and a small spread of the energy width of emitted electrons, and can be used in high-resolution electron microscopes, scanning electron microscopes (SEM), Auger electron analyzers (AES),
It is used as an electron beam source for X-micro analyzers (XMA) and the like.

In particular, in analyzers such as AES and XMA, in addition to high-resolution image observation and analysis, electron beam current is There is a demand for increased use of . In order to increase the electron beam current, it is necessary to increase the field emission voltage, and to increase the aperture diameter of the electron optical system, that is, to increase the angle of incidence on the beam spot, it is necessary to As shown in the figure, as the beam current increases, the sbot diameter increases and the resolution decreases. Therefore, in conventional AES and XMA, for example, the electron beam current is lowered to observe the image of the surface of the analysis sample, and the electron beam current is increased during analysis at the expense of resolution. It was necessary to adjust the electron optical system each time observation and analysis were performed.

In addition, in conventional electron tubes, etc., multiple, for example, 3
As shown in Figure 2, if you need several electron beam sources,
Three separate cans are arranged and used. Now, the case of color display in an electron tube will be explained. As an electron beam source, red (几), green CG), i%
'(E) Three individual cathodes 1 are used, each corresponding to a color. Electrons generated from the cathode 1 pass through a hole in the control electrode 2, and this electron beam 3 is projected onto a converging screen 5 by a converging lens 4. The screen is coated with phosphors that emit light in the colors B, G, and B, respectively. The intensity of the 83 electron beams 3 is changed by controlling the potential of the cathode, and the amount of light emitted by the phosphors on the screen 5 changes accordingly, emitting various colors. Furthermore, the electron beam 3 can be moved to any desired location by means of the deflection coil 6.

Now, in recent years, with the advancement of high-definition electron tubes, etc., it has become possible to use a
High-brightness electron beam sources are now being sought after. but,
Until now, there has been no practical electron beam source that meets these requirements.

[Purpose of the invention]

An object of the present invention is to provide a thermal field emission cathode that can simultaneously obtain a plurality of high-intensity and highly stable field emission beams from a single field emission chip, and an electron beam device using this cathode. be.

[Summary of the invention]

The field emission cathode of the present invention is composed of a large sword with a sharp tip, a heating element that heats the large sword, an adsorbent that is attracted to the large needle, and a supply source that stores the same, and at the tip of the large needle,
By forming a monatomic adsorption layer of adsorbent and oxygen, for example, W (
100) A small amount of oxygen is required to lower the work function of the surface and emit electrons with a limited radiation angle. Conventionally, in physical and chemical instruments such as electron microscopes, it is sufficient to have a single light source, so for example, the axis direction (100) (
7) Single crystal tungsten (W) with a direct ff of 10.1 to 0.15 ntrn is used. Further, it is desirable that the heating element has high electrical resistance, high high temperature strength, and low reactivity with the supply source. Mainly tungsten (W).

Molybdenum (Mol, rhenium (lLe), tantalum (Ta), and alloys thereof are used. As a supply source,
Zr+ Ti, I4f, Nb, Th+ Mg and oxides thereof are used. As described above, since a single electron beam source is sufficient as a conventional electron beam source for physical and chemical equipment, a large needle made of W single crystal with an axial orientation of <100> satisfies the requirements.

On the other hand, an object of the present invention is to provide an electron beam device that can simultaneously provide a plurality of electron beam sources, for example, three electron beam sources, and easily obtain a high current density. Now, referring to the tungsten lattice model in Figure 3, if a crystal with an axial direction W (111) is used as a large needle, three (100
) are arranged in a triangular shape. Now, when electric field emission is performed using the large needle 12 with the axial direction W<111>, a field emission image lO corresponding to each crystal plane of the large needle 12 is projected onto the anode 14, as shown in FIG. be done. Next, for example, the large needle 12
Illi supply source 13 by heating to about 1ioot:'
When replenishing the tip of the large needle 12 and forming a monatomic adsorption layer of If i and oxygen at the tip of the large needle 12, W(
100), (010), and (001) planes have work functions of approximately 2.
．． 66-V (the work function of W is about 4,56 V), w(ioo), (oio).

A large emission current flows selectively from the (001) plane, making it possible to obtain three high-brightness electron beam sources.

Furthermore, if a tip with the axial direction W<tto> is used as the large needle, two high-intensity electron beam sources can be obtained in the same way.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail by way of examples.

Embodiment 1 An embodiment of an electron beam apparatus using a plurality of thermal field emission cathodes of the present invention will be described with reference to FIG. First, a tungsten (W) heating element 11 having a diameter of 0.1 to 0.15 mm and having a diameter of 0.1 to 0.1511 O++ and an axial direction (110), for example, is fabricated at the tip of a tungsten (W) heating element 11 formed in a figure 7 shape.

Next, titanium (Ti) is attached to the V-shaped tip of the heating element 11, and the heating element 11 is heated with electricity in a vacuum to
A replenishment source 13 is formed, and a thermal field emission cathode consisting of the large needle 12, the heating weight 1, and the replenishment source 13 is manufactured. This thermal field emission cathode is heated by applying electricity to the heating element ii in a vacuum of 10"9 to 10-"l"orr, and the supply source 13 and the large needle 12 are
When heated to ~1500C, Ti is supplied from the replenishment source 13 to the tip of the large needle 12 due to thermal diffusion. At the tip of the large needle 12, oxygen in the atmosphere is taken in, and an adsorption layer of Tl and oxygen is formed. When a high voltage is applied to the opposing anode 14 in this state, the tungsten large needle 12 with the axial direction <110>
The work function of the (100) crystal plane of
Two high-intensity field emission electron beams 15a and 15b whose radiation angles are limited in direction can be obtained. These 2
The two electron beams isa and isb are connected to each convergent lens 16.
a, 16b, passes through the slit 17, and is projected onto a point on the sample surface 18. Electron beam 15a, 1
5b can scan the surface of the sample 18 using the deflection coil 19. Further, a deflection plate 20 is provided in the path of the electron beam 15b, and the deflection voltage can be turned on and off as necessary to turn off the irradiation of the electron beam 15b onto the sample 20. The operation will be explained using an example in which the electron beam device having this configuration is applied to AES. When applied to AES, a secondary electron detector 2 is used to observe the secondary electron image of the sample surface.
1 and Auger electrons are detected and set up. First, in high-resolution SEM image observation and AES image observation, the deflection plate 20
The electron beam 15b is blocked by acting on the electron beam 15a, and only the narrowly focused electron beam 15a is made to act on the electron beam 15b. Also, A
In ES analysis, it is known that by increasing the electron beam current irradiated onto the sample 18, the S/N of the detected Auger electron signal also improves. During analysis, the electron beam current on the sample 18 can be easily increased by stopping the action of the deflection plate 20 and irradiating the electron beam 15b to the same position as the spot of the electron beam 15H. Also,
The amount of current of the electron beam 15b can be increased or decreased by arbitrarily selecting the diameter of the slit 17. That is, according to the electron beam device with this configuration, by effectively utilizing two electron beams, it is possible to easily observe and analyze high-resolution anal images, and to perform high-sensitivity analysis with good S/N. can be done.

The large needle 12 of the thermal field emission cathode of this configuration has an axial direction <
In addition to tungsten with an axial orientation of <111>, tungsten with an axial orientation of <111> may be used. In addition to AES, XM
It may be applied to A and similar analyzers.

Example 2 An example in which the thermal field emission cathode of the present invention is applied to an electron tube will be explained with reference to FIG. As the large needle 12, the axial direction (111)
Using a tungsten wire, a monatomic adsorption layer of 1゛i and oxygen is formed at the tip of the large needle 12 by the same method as in Example 1, and a high voltage is applied between the large needle 12 and the anode 31. , the work function of the (100) crystal plane of the cusp *t i 2 decreases, and three field emission electron beams 32 whose radiation angle is restricted to the <100> direction can be obtained. If an anode 31 with holes corresponding to the emission positions of the three electron beams 32 is used as the anode facing the large needle 12, each of the three electron beams will be displayed in red in a color display electron tube or the like.

It can correspond to the three electron beams 32 of green and evening. Further, behind the anode 31, a converging lens 4. By arranging the deflection coil 6 and the screen 5 coated with phosphors that emit red, green, and evening light, it was possible to project a high-intensity color spot anywhere on the screen 5.

〔Effect of the invention〕

As described above, according to the present invention, multiple high-intensity electron beams can be obtained simultaneously from a single large needle using a field emission cathode capable of low-vacuum operation, and multiple electron beams can be simultaneously generated. By focusing the electron beam on a single point, it is possible to achieve a current density that is more than twice that of a single electron beam.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the relationship between electron beam current and spot diameter, Fig. 2 is an explanatory diagram of a conventional color display electron tube, Fig. 3 is a tungsten lattice model diagram, and Fig. 4 is an explanatory diagram of a conventional color display electron tube. FIG. 5 is an explanatory diagram showing an image of emitted electrons from a thermal field emission cathode, FIG. 5 is an explanatory diagram of Example 1 of the present invention, and FIG. 6 is an explanatory diagram of Example 2 of the present invention. 1... Cathode, 2... Control electrode, 3, 15a, 1
5b. 32... Electron beam, 4, 16a, 16b... Converging lens, 5... Screen, 6.19... Deflection coil, 10... Field emission image, 11... Heating element, 12...
... large needle, 13... supply source, 14.31... anode,
417... Slit, 18... Sample, 20... Deflection plate, 21... Secondary electron 1st and 2nd figure Rod 3rd figure

Claims (1)

[Claims] 1. A large needle made of tungsten with a needle-like tip, a heating element for heating the large needle, and at least one of titanium, zirconium, hafnium, niobium, and magnesium. In a field emission cathode which is composed of an adsorbent and which is used by adsorbing the adsorbent and oxygen at the tip of the large needle, a plurality of electric fields are generated from the single large needle by reducing the radiation angle of the w(ioo) plane. A thermal field radiation cathode characterized in that it extracts a radiation beam. 2. The thermal field radiation cathode according to claim 1, wherein the large sword is a W tip with an axial direction (111:). Cathode. 3. The thermal field emission cathode according to claim 1, wherein the large needle is a W tip with an axial direction (110). 4. The large needle is made of tungsten and has a needle-like tip; , comprising a heating element that heats the large needle, and an adsorbent made of at least one of titanium, zirconium, hafnium, niobium, thorium, and magnesium, and adsorbs the adsorbent and oxygen at the tip of the large needle, A field emission cathode extracts a plurality of field emission beams with a W (100) plane having a reduced radiation angle from a large needle, and a plurality of electron beams emitted from the field emission cathode are placed at respective predetermined positions.