JPH0782803B2 - Thermal field emission cathode and its application equipment - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a field emission cathode, and particularly to a thermal field emission cathode (Thermal Field Cathode) suitable for obtaining a plurality of electron beam sources with high brightness and high stability at the same time. Emission Cathode (hereinafter referred to as TFE cathode)).

[Background of the Invention]

As an electron beam source, a hot cathode that utilizes thermoelectrons emitted from the surface of metal or the like heated to a high temperature, and a strong electric field is applied to a needle-shaped chip with a tip radius of curvature of about 1,000 angstroms to produce the tunnel effect. Therefore, it can be roughly classified into a field emission cathode utilizing electrons emitted from the cathode surface. As a hot cathode,
A barium-strotium oxide cathode and a barium-dispenser cathode capable of operating at a low current and a high current density are known as electron beam sources for electron tubes. In recent years, lanthanum hexaboride has been put to practical use as a high-brightness electron beam source, but the brightness of these hot cathodes is at most about 10 ⁷ A / cm ² Sr. On the other hand, field emission is roughly classified into cold field emission (CFE), which has a chip temperature near room temperature, and TFE. In order to operate the CFE stably, the space with the emitter is 10 ^-10 T in order to reduce the gas adsorption to the tip of the emitter and to eliminate the damage of the emitter due to ion impact.
It is required to maintain an ultrahigh vacuum of orr or less, and the emission current for stable operation is 10 μA or less. The brightness is about 10 ⁸ A / cm ² Sr. On the other hand, in TFE, the tip of the emitter is heated in a temperature range where thermoelectrons are not generated,
This is a method of applying a strong electric field to draw out the emission. In particular, according to the method proposed by Wolfe et al. (US Patent 3,814,975), it is possible to obtain a stable emission current with high brightness even in a vacuum of about 10 ^-7 Torr. That is,
When the emitter is heated to 1750 to 1850K in an O ₂ gas atmosphere of about 10 ^-7 Torr and zirconium (Zr) is adsorbed at the tip, an adsorption state of Zr-OW is formed at the tip of the emitter, and W ( The work function of the (100) plane drops to 2.6 to 2.8 eV. As a result, the emission current from the tip of the emitter can selectively obtain a large current from the W (100) plane, which makes it possible to limit the angular distribution of the emission current. Similar effects can be obtained with titanium (Ti), hafnium (Hf), niobium (Nb), thorium (Th), magnesium (Mg), and cerium (Ce). In particular, when Ti is used as the adsorbent for the emitter, the emitter temperature can be lowered to 1000 to 1200 ° C., the oxygen partial pressure can be set to 10 ⁻⁹ Torr, and the brightness can be set to 10 ⁹
High performance of up to 10 ¹⁰ A / cm ² Sr can be obtained.

By the way, the field emission cathode has high brightness and a small spread of the energy width of radiated electrons, and has high resolution such as electron microscope, scanning electron microscope (SEM), Auger electron analyzer (AES), and X-ray micro analyzer (XMA). It is used as an electron beam source. In particular, in the case of analyzers such as AES and XMA, in addition to high-resolution image observation and analysis, electron beam current is used to improve analysis sensitivity and signal-to-noise ratio (S / N) of analysis signals. There is a demand to increase and use. To increase the electron beam current, the field emission voltage is increased, or the aperture diameter of the electron optical system is increased, that is, the incident angle to the beam spot is increased.
As shown in the figure, as the beam current increases, the spot diameter increases and the resolution decreases. Therefore, for example, conventional AE
With S and XMA, the electron beam current is reduced when observing the image of the sample surface, and the electron beam current is increased at the expense of resolution during analysis. Adjustment of the electron optical system was required.

In addition, in conventional electron tubes and the like, a plurality of electron tubes, such as 3
When individual electron beam sources are required, as shown in FIG.
Three cathodes 1 which are separated from each other are arranged and used. Now, the case of color display in the electron tube will be described. As the electron beam source, three individual cathodes 1 corresponding to red (R), green (G) and blue (B) colors are used. The electrons generated from the cathode 1 pass through the hole of the control electrode 2, and this electron beam 3 is converged by the converging lens 4 and projected on the screen 5. The screen is coated with phosphors that emit R, G, and B, respectively. R,
The intensities of the G, B3 electron beams 3 are changed by controlling the electrons of the cathode 1, and in response to this, the emission amount of the phosphor on the screen 5 is changed to emit various colors. Further, the electron beam 3 can be moved to an arbitrary place by the deflection coil 6.

Now, with the increase in definition of electron tubes and the like in recent years, the power consumption is lower than that of conventional electron beam sources (mainly oxide cathodes).
There is a demand for a high-intensity electron beam source that is more than twice as high. However, there has been no practical electron beam source that satisfies these requirements.

[Object of the Invention]

An object of the present invention is to provide a thermal field emission cathode and an electron beam apparatus using the cathode capable of simultaneously obtaining a plurality of high-intensity and highly stable field emission beams from a single field emission chip. is there.

[Outline of Invention]

The field emission cathode of the present invention is composed of a sharp needle having a sharp tip, a heating element for heating the sharp needle, an adsorbent adsorbed to the sharp needle and a replenishment source for storing the same, and at the distal end of the sharp needle,
For example, W (10
A small amount of oxygen is required to lower the work function of the (0) plane and perform electron emission with a limited emission angle. Conventionally, in physics and chemistry equipment such as electron microscopes, a single light source is sufficient, so as a pointed needle, for example, a diameter of 0.1 in the axial direction <100> is used.
A single crystal tungsten (W) of 0.15 mm is used. Also,
It is desirable that the heating element has high electric resistance, high temperature strength, and low reactivity with the replenishment source. Mainly tungsten (W), molybdenum (Mo), rhenium (Re),
Tantalum (Ta) and alloys of these are used. As a supply source, Zr, Ti, Hf, Nb, Th, Mg and oxides thereof are used. As described above, since the conventional electron beam source for physics and chemistry equipment may be a single electron beam source, the W of axial direction <100>
The demand was met with a single crystal needle.

On the other hand, it is an object of the present invention to provide a plurality of electron beam sources, for example, three electron beam sources at the same time, and to provide an electron beam apparatus which is easy to obtain a high current density. Now, referring to the tungsten lattice model in FIG. 3, if a crystal with an axis direction W <111> is used as a pointed needle, three (100) planes are arranged in close proximity to each other in a triangular shape. Now, the needle 12 with the axis direction W <111>
When the field emission is performed using, as shown in Fig. 4,
The field emission image 10 corresponding to each crystal plane of the needle 12 is the anode 14
Projected on. Next, for example, by heating the needle 12 to about 1100 ℃, to reinforce the tip of the needle 12 from the Ti replenishment source 13, to form a monoatomic adsorption layer of Ti and oxygen at the tip of the needle 12, W (100), (010), (001) plane work function is about 2.6
eV (work function of W is about 4.5 eV) is reduced to W (100),
A large emission current selectively flows from the (010) and (001) planes, and three high-brightness electron beam sources can be obtained.

Further, if a chip having an axis direction W <110> is used as a pointed needle, two high-intensity electron beam sources can be obtained in the same manner.

Example of Invention

 Hereinafter, the present invention will be described in detail with reference to examples.

Example 1 An example of an electron beam apparatus using the multi-element thermal field emission cathode 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 0.15 mm is spot-welded with a tungsten wire having a diameter of 0.1 to 0.15 mm and having an axial orientation <110>, and the tip thereof is potassium hydroxide. (KO
H) A sharp needle 12 is made by sharpening sharply by electric field polishing using an aqueous solution or the like. Next, the titanium (T
i) is attached and the heating element 11 is electrically heated in a vacuum to form a Ti replenishing source 13, and a thermoelectric field emission cathode composed of the pointed needle 12, the heating element 11 and the replenishing source 13 is produced. This thermal field emission cathode 10
^The heating element 11 is electrically heated in a vacuum of ^-9 to 10 ^-7 Torr to generate a replenishment source.
When 13 and the needle 12 are heated to 1000 to 1500 ° C., Ti is supplied from the supply source 13 to the tip of the needle 12 by thermal diffusion. Pointed needle 12
At the tip of, the oxygen in the atmosphere is taken in and an adsorption layer of Ti and oxygen is formed. When a high voltage is applied to the opposing anode 14 in this state, (1
00) Two high-intensity field emission electron beams whose work function on the crystal plane is lowered and the emission angle is limited to the <100> direction.
You can get a, 15b. These two electron beams 15
The a and 15b are converged by the respective converging lenses 16a and 16b, pass through the slit 17, and are projected onto one point on the sample surface 18. The electron beams 15a and 15b can scan the surface of the sample 18 using the deflection coil 19. In addition, the deflection plate 20 is provided in the passage of the electron beam 15b.
Is provided, the deflection voltage can be turned on and off as necessary, and the irradiation of the electron beam 15b onto the sample 20 can be turned on and off. The operation of the electron beam apparatus of this configuration will be described by an example applied to AES. When applied to AES, a secondary electron detector 21 for observing a secondary electron image on the sample surface and an energy analyzer 22 for detecting and analyzing energy of Auger electrons.
To provide. First, in high-resolution SEM image observation and AES image observation, the deflection plate 20 is actuated to block the electron beam 15b, and only the finely converged electron beam 15a is acted. Further, in the AES analysis, it is known that the S / N of the detected Auger electron signal is improved by increasing the electron beam current with which the sample 18 is irradiated. In the AES analysis, the action of the deflection plate 20 is stopped and the electron beam 15b is irradiated to the same position as the spot of the electron beam 15a, whereby the electron beam current on the sample 18 can be easily increased. Also the electron beam
The current amount of 15b can be increased or decreased by arbitrarily selecting the diameter of the slit 17. That is, according to the electron beam apparatus of this configuration, it is possible to easily perform high-resolution image observation and analysis, and high-sensitivity analysis with a good S / N by effectively using the two electron beams. it can.

The point 12 of the thermal field emission cathode of this configuration has an axial orientation of <11.
In addition to tungsten of 0>, tungsten of axial direction <111> may be used. The electron beam apparatus using the thermal field emission cathode of the present invention may be applied to XMA and similar analyzers in addition to AES.

Example 2 An example in which the thermal field emission cathode of the present invention is applied to an electron tube will be described with reference to FIG. As the pointed needle 12, a tungsten wire having an axial orientation <111> is used, and a monoatomic adsorption layer of Ti and oxygen is formed at the tip of the pointed needle 12 by the same method as in Example 11 above.
When a high voltage is applied between the needle 12 and the anode 31, the work function of the (100) crystal plane of the needle 12 lowers and three field emission electron beams 32 with the emission angle limited to the <100> direction are obtained. be able to. Now, if an anode 31 having a hole at a position corresponding to the emission position of the above-mentioned three electron beams 32 is used as the anode corresponding to the pointed needle 12, in a color display electron tube or the like, red, green, and blue are respectively provided. It can correspond to the electron beam 32. Further, by arranging the converging lens 4, the deflection coil 6, and the screen 5 coated with phosphors that emit red, green, and blue light behind the anode 31, a high-intensity color can be placed anywhere on the screen 5. I was able to project spots.

〔The invention's effect〕

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

[Brief description of drawings]

FIG. 1 is an illustration of the relationship between electron beam current and spot diameter, FIG. 2 is an illustration of a conventional color display electron tube, and FIG.
FIG. 4 is a diagram of a tungsten lattice model, FIG. 4 is an explanatory diagram showing an electron emission image from a thermal field emission cathode of the present invention, FIG. 5 is an explanatory diagram of Example 1 of the present invention, and FIG. FIG. 5 is an explanatory diagram of Example 2 of the present invention. 1 ... Cathode, 2 ... Control electrode, 3,15a, 15b, 32 ... Electron beam, 4, 16a, 16b ... Converging lens, 5 ... Screen, 6,19 ... Deflection coil, 10 ... Electric field Radiation image, 11 ... Heating element, 12 ... Needle, 13 ... Reinforcing source, 14, 31 ... Anode, 17
…… Slit, 18 …… Sample, 20 …… Deflector, 21 …… Secondary electron detector, 22 …… Energy analyzer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-56-59422 (JP, A) JP-A-56-61733 (JP, A) JP-A-57-185647 (JP, A)

Claims (2)

[Claims] 1. A tip comprising a needle-shaped tungsten needle, a heating element for heating the needle, and an adsorbent made of at least one of titanium, zirconium, hafnium, niobium, thorium and magnesium. In the field emission cathode used by adsorbing the adsorbent and oxygen at the tip of the needle, the axis direction of the needle is <111> or <110>.
The W field of the present invention, wherein a plurality of field emission beams are extracted from a plurality of W (100) planes of the apex needle. 2. A tip is made of a needle-shaped tungsten needle, a heating element for heating the needle, and an adsorbent made of at least one of titanium, zirconium, hafnium, niobium, thorium, and magnesium. , The adsorbent and oxygen are adsorbed at the tip of the needle, and the axis direction is <11.
Multiple W of a pointed needle that is a W tip of 1> or <110>
Heat having a field emission cathode for extracting a plurality of field emission beams from the (100) plane, and means for converging a plurality of electron beams emitted from the field emission cathode at predetermined positions. Field emission cathode application device.