JP2000011853A - Electron gun, its service life extending method and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prolong the service life of an electron gun by arranging a generating member which generates at least one of atoms forming a single crystal molecular structure near a cathode member formed of a single crystal of a molecule consisting of a specified atom. SOLUTION: A cathode member 13 is formed of a single crystal of LaB6, and a polycrystalline body 15 of LaB6 that is a generating member is arranged in the terminal part of the cathode member 13, and a graphite heater 12 is placed facing the cathode member 13 through the polycrystalline body 15. The surface of the body part 15 of a metallic aperture 14 is covered with a protecting film 17 consisting of a boride of a rare earth element having conductivity. When a negative charge is applied to the cathode member 13 having terminal part heated by the graphite heater 12 from the outside, thermoelectrons are released from the tip of the cathode member, and the polycrystalline body 15 is also overheated at this time to generate La atom or B atom. Accordingly, the La atom or B atom separated from the cathode member 13 is replenished with the La atom or B atom generated from the polycrystalline body 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electron gun for emitting thermoelectrons from a cathode member, a method for extending the life of the electron gun,
The present invention relates to an electronic device provided with the electron gun of the present invention.

[0002]

2. Description of the Related Art Generally, SEM (Scanning Electron M)
icroscope), AES (Auger Electron Spectroscopy), E
2. Description of the Related Art Electronic devices such as a B (Electron Beam) exposure machine have an electron gun, and are formed in a structure in which the electron gun is arranged inside a vacuum container.

As shown in FIG. 3, such an electron gun 1 includes a graphite heater 2 as a heating member, a cathode member 3, and a metal aperture 4 as an anode member.
For example, a pair of graphite heaters 2 are mounted on both sides of the end of the cathode member 3, and the metal aperture 4 is opposed to the tip of such a cathode member 3.

In the electron gun 1 having the above-described structure, the cathode member 3 is heated by the graphite heater 2, and a negative charge is externally applied to the cathode member 3. At the same time, a positive charge is applied to the metal aperture 4 to emit thermoelectrons from the cathode member 3 and limit the expansion of the electron beam by the metal aperture 4.

The above-described cathode member 3 of the electron gun 1 is generally formed of a single crystal of a molecule consisting of specific atoms.
Some are made of aB6 polycrystal. When these are compared, LaB6 has a small work function (W = 4.55 (eV), LaB6).
= 2.55 (eV)), and the emission efficiency of thermoelectrons is good.

[0006] emission during thermal electrons by the electron gun 1 is described by the equation of Richaradson-Dushman as ^{J = AT 2 exp (-eΦ /} K B T). Note that “J” is the current density due to emission of thermoelectrons,
“A” is Richardson's constant, “T” is absolute temperature,
"E" is the elementary charge, [Phi work function, K _B is the Boltzmann constant.

From the above-mentioned Ricardadson-Dushman equation, it is clear that the efficiency of thermionic emission depends on the temperature and the work function of the material. For example, the operating temperature at which a sufficient electron current can be obtained is about 2700 (K) for W, but La
In B6, it is about 1700 (K). The reason that LaB6 can emit sufficient electrons even at a temperature lower than W is that its work function is small.

[0008]

SUMMARY OF THE INVENTION As described above, the electron gun 1
The generated electron current depends on the temperature and work function of the cathode member 3, and therefore, if the work function of the cathode member 3 increases due to a change with time, the same electron current cannot be generated at the same temperature.

In view of the fact that an electron gun actually manufactured is considered, the life of a cathode member formed of a LaB6 single crystal is about 1000 (h) at 1500 (° C.). This is due to the fact that B atoms are desorbed from the cathode member as negative ions.
It is assumed that the crystal structure of aB6 is disturbed and the work function increases.

That is, as shown in FIG. 4, the crystal structure of LaB6 is a cubic system, with La atoms located at the center of the unit cell and B atoms at the vertices of the octahedral unit cell. When the LaB6 having such a structure is heated, the lattice vibration between atoms is intensified, and as shown in FIG.

The B atoms diffuse inside the crystal.
As shown in (b), the crystal surface moves easily on the crystal surface which is easy to diffuse. However, the B atoms moving on the crystal surface in this manner are desorbed to the space with a predetermined probability as shown in FIG.

When the B atoms are successively eliminated as described above,
Since the crystal structure of LaB6 is disturbed and the work function is increased, the electron gun 1 cannot generate the same electron current from the cathode member 3 at the same temperature. In this case, the cathode member 3 is determined to have reached the end of its life and is replaced.

Further, about 10% of the B atoms desorbed from the cathode member 3 as described above are boron ions B- of the negative electrode, and as shown in FIG. And collides with the metal aperture 4 to generate positive metal ions. Since the metal ions of the positive electrode are attracted to the cathode member 3 due to the potential difference, the cathode member 3 is contaminated with the aperture metal.

For example, when the metal layer contaminating the tip of the cathode member 3 is extremely thin, the work function of the cathode member 3 is reduced by making the surface potential a positive electrode. However, when observing an actual product, metal contamination having a layer thickness of about 2 to 3 (nm) accumulates on the surface of the LaB6 cathode member 3.

In this case, the cathode member 3 does not function as LaB6 due to a change in the crystal structure due to the bulk. As a result, the work function increases, and the cathode member 3 may generate the same electron current at the same temperature. It is no longer possible, and this is determined to be the end of life and will be replaced.

If the B atoms are successively eliminated as described above, the crystal structure of LaB6 cannot be maintained, and La
Atoms will also be eliminated. That is, the cathode member 3 made of LaB6 single crystal is worn out, which also causes the life of the cathode member 3 to be shortened.

When the life of the cathode member 3 is determined as described above, the whole of the cathode member 3 and the electron gun 1 is exchanged. Because it is used internally, its replacement is not easy. In particular,
When the electronic device requires a high vacuum, it is not easy to return the inside of the vacuum container, which has been brought to the atmospheric pressure for replacing the electron gun 1, to the high vacuum.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an electron gun having a long life by reducing an increase in the work function of a cathode member, a method of extending the life of such an electron gun, It is an object to provide an electronic device using a simple electron gun.

[0019]

A general electron gun to which the present invention is applied has a heating member, a cathode member, and an anode member. In such an electron gun, a negative charge is applied to a cathode member heated by a heating member to emit thermoelectrons, and expansion of the thermoelectrons is limited by an anode member to which a positive charge is applied.

In the first aspect of the above-described electron gun, the cathode member is formed of a single crystal of a molecule composed of a specific atom, and at least one of the atoms forming the molecular structure of the single crystal is used. A generating member for generating is arranged near the cathode member. Therefore, in the electron gun of the present invention,
Even if a specific atom is desorbed from the single crystal of the cathode member, the atom is replenished with an atom generated from a generation member arranged in the vicinity, so that a change in the crystal structure of the cathode member is reduced.

In the second aspect of the above-described electron gun, the cathode member is formed of a single crystal of LaB ₆ ,
A generating member for generating at least B atoms is arranged near the cathode member. Therefore, in the electron gun of the present invention,
Even if B atoms are desorbed from the LaB ₆ single crystal of the cathode member, the B atoms are replenished with B atoms generated from the nearby generation member, so that the change in the crystal structure of the cathode member is reduced.

In the third aspect of the above-mentioned electron gun, the cathode member is formed of a single crystal of LaB ₆ ,
A generating member for generating La atoms and B atoms is arranged near the cathode member. Therefore, in the electron gun of the present invention, even if La atoms or B atoms are desorbed from the LaB ₆ single crystal of the cathode member, they are replenished with La atoms or B atoms generated from the nearby generating member. In addition, the change in the crystal structure of the cathode member is reduced.

In the above-described electron gun, the generating member is made of LaB ₆ polycrystal. In this case, the LaB6 polycrystal generally generates atoms more favorably than the single crystal. Therefore, before the desorption of La atoms and B atoms at the cathode member starts, the La atoms and B atoms at the generation member start. Is started.

In the above-described electron gun, the heating member heats both the cathode member and the generating member.
In this case, the cathode member heated by the heating member emits thermoelectrons and the generation member generates atoms, and the heating member for heating the cathode member also heats the generation member,
There is no need for a dedicated member for heating the generating member.

In the above-described electron gun, the heat-generating member is opposed to the end of the cathode member that emits thermoelectrons from the tip via the generating member. In this case, the generating member is heated by the heat generating member, and the end of the cathode member is heated via the generating member, so that the thermoelectrons are emitted from the tip of the cathode member whose end is heated. Since the cathode member is heated after the generation member is heated, the generation of atoms in the generation member is started before the desorption of atoms in the cathode member is started.

In the above-described electron gun, the anode member is formed of a metal aperture, and a protective film for preventing emission of metal ions of the positive electrode is formed on the surface of the metal aperture. In this case, even if atoms generated from the cathode member or the generating member become negative ions and collide with the metal aperture, the protective film prevents the metal ions of the positive electrode from desorbing from the metal aperture due to the collision of the negative ions. You.

In the above-described electron gun, the protective film is made of a rare earth boride having conductivity. In this case, since the protective film of the metal aperture is made of a rare earth boride having conductivity, B atoms are also generated from this protective film.

In an electronic apparatus according to the present invention, the electron gun according to the present invention is disposed inside a vacuum vessel. Therefore, in the electronic device of the present invention, the electron gun disposed inside the vacuum vessel emits thermoelectrons into a vacuum. Although the entirety and parts of the electron gun disposed inside the vacuum vessel are not easy to replace, the frequency of replacement is reduced because the electron gun of the present invention has a long life.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a schematic perspective view showing the structure of the electron gun according to the present embodiment, and FIG.
It is a schematic diagram which shows the crystal structure of aB6.

As shown in FIG. 1, the electron gun 11 of the present embodiment also has a graphite heater 12 as a heat-generating member, a cathode member 13 made of a single crystal of LaB ₆ , similarly to the electron gun 1 of a conventional example. A metal aperture 14 serving as an anode member is provided, and the metal aperture 14 faces a tip end of a cathode member 13 in which a pair of graphite heaters 12 are arranged on both sides of a terminal end.

However, unlike the conventional electron gun 1 of the prior art, the electron gun 11 of the present embodiment has a LaB ₆
Is provided, and the polycrystal 15 is disposed near the cathode member 13. More specifically,
Since the above-described polycrystalline body 15 is mounted on the end of the cathode member 13, the graphite heater 12 faces the cathode member 13 via the polycrystalline body 15.

Further, in the electron gun 11 of the present embodiment, the main body portion 16 of the metal aperture 14 is formed of Fe similarly to the electron gun 1 of one conventional example. The surface of the portion 16 is covered with a protective film 17 with a rare earth boride having conductivity.

Note that the electron gun 11 of the present embodiment is actually used in an electronic device such as an SEM, and in such an electronic device, the electron gun 11 is disposed inside a vacuum vessel ( Not shown).

In the above-described configuration, also in the electron gun 11 of the present embodiment, a negative charge is applied from the outside to the cathode member 13 whose end portion is heated by the graphite heater 12, and at the same time, a positive charge is applied to the metal aperture from the outside. Is applied. Then, thermoelectrons are emitted from the tip of the cathode member 13, and expansion of the electron beam is restricted by the metal aperture 14.

At this time, the cathode member 13 which is also heated
La and B atoms are desorbed from the LaB ₆ single crystal of
The polycrystal 15 is similarly heated to generate La atoms and B atoms. For this reason, as shown in FIG. 2, La atoms and B atoms detached from the cathode member 13 are supplemented by La atoms and B atoms generated from the polycrystalline body 15, and the crystal structure of the cathode member 13 is reduced. Change has been reduced.

That is, even if the operation of the electron gun 11 is performed for a long time, the work function of the cathode member 13 does not easily increase, so that the deterioration of the performance of the cathode member 13 with time is reduced. For this reason, the electron gun 11 of the present embodiment has a long life and does not need to frequently replace the whole or parts, and does not need to frequently change the internal pressure of the vacuum container of the electronic device.

In particular, in the electron gun 11 of the present embodiment, the polycrystal 15 is formed of LaB ₆ polycrystal.
aB6 polycrystals generate atoms better than single crystals. Therefore, before the desorption of atoms from the cathode member 13 is started,
Generation of atoms in the polycrystalline body 15 can be started;
Atoms desorbed from cathode member 13 can be favorably replenished with atoms generated from polycrystal 15.

In addition, as described above, the polycrystal 15
Since both atoms and B atoms are generated, both the desorbed La atoms and B atoms of the cathode member 13 can be replenished. As described above, the LaB6 single crystal desorbs B atoms at first, and when the desorption of B atoms becomes large and the crystal structure cannot be maintained, La atoms are also desorbed.

That is, if B atoms can be sufficiently replenished in the cathode member 13, there is no need to replenish La atoms. In such a case, the polycrystal 15 can be made of boron crystal. However, in fact, it is difficult to completely replenish all the B atoms desorbed from the cathode member 13 and, as a result, it is assumed that La atoms are also desorbed. It is preferable to replenish both to reduce the wear of the cathode member 13.

Further, in the electron gun 11 of the present embodiment,
The graphite heater 12 includes a cathode member 13 and a polycrystalline body 15.
Since both are heated, it is not necessary to provide a dedicated member for heating the polycrystalline body 15, and it is possible to generate the B atoms and the like by heating the polycrystalline body 15 with a simple structure.

In particular, since the graphite heater 12 is disposed via the polycrystalline body 15 at the end of the cathode member 13 which emits thermoelectrons from the tip, the graphite heater 1
2, the cathode member 13 is heated after the polycrystalline body 15 is heated. Therefore, the generation of atoms in the polycrystalline body 15 can be started before the desorption of the atoms in the cathode member 13 is started. Can be satisfactorily replenished with atoms generated from.

Further, in the electron gun 11 of the present embodiment,
Since the protective film 17 made of a conductive rare earth boride is formed on the surface of the metal aperture 14, B atoms and the like generated from the cathode member 13 and the polycrystalline body 15 become negative ions and form on the metal aperture 14. Even in the case of collision, the metal ions of the positive electrode do not desorb from the metal aperture 14 due to the collision of the negative ions.

For this reason, the cathode member 13 is not contaminated with Fe of the metal aperture 17, and the life of the cathode member 13 is extended from this viewpoint. In particular, since the protection film 17 of the metal aperture 14 is made of boride as described above, B atoms are also generated from the protection film 17 and the cathode member 1 is formed.
3 and the life of the cathode member 13 is further extended.

The present invention is not limited to the above-described embodiment, but allows various modifications without departing from the scope of the invention. For example, in the above embodiment, the cathode member 13 is made of a single crystal of LaB6, and the polycrystal 15 is correspondingly made of LaB6.
It is exemplified that it is composed of a polycrystal. However, various materials can be used as the above-described cathode member, and accordingly, the material of the generating member can be variously modified.

[0045]

Since the present invention is configured as described above, it has the following effects.

In the first electron gun of the present invention, even if a specific atom is desorbed from the single crystal of the cathode member, it is replenished with atoms generated from a generating member arranged in the vicinity, thereby forming the cathode member. Since the change in the crystal structure can be reduced, the deterioration over time of the performance can be reduced and the life of the electron gun can be extended.

In the second electron gun of the present invention, the cathode member L
Even if B atoms are desorbed from the single crystal of aB ₆ , changes in the crystal structure of the cathode member can be reduced by replenishment of the B atoms with B atoms generated from a generation member arranged in the vicinity. Aging can be reduced and the life of the electron gun can be extended.

In the third electron gun of the present invention, the cathode member L
Even if La atoms or B atoms are desorbed from the single crystal of aB ₆ , La atoms or B atoms generated from a generating member arranged in the vicinity are generated.
Since the change in the crystal structure of the cathode member can be reduced by being replenished with atoms, the deterioration of the performance over time and the wear can be reduced, and the life of the electron gun can be extended.

In the above-described electron gun, by forming the generating member from LaB ₆ polycrystal, before the desorption of La atoms and B atoms from the cathode member is started, the generating member can be used. Since the generation of La atoms and B atoms can be started, the atoms desorbed from the cathode member can be satisfactorily replenished with the atoms generated from the generation member.

Further, the cathode member heated by the heating member emits thermoelectrons, and the generating member generates atoms,
Since the heat generating member for heating the cathode member also heats the generating member, a dedicated member for heating the generating member is not required, so that the generating member can be heated with a simple structure.

Further, since the heat generating member is opposed to the end portion of the cathode member which emits thermoelectrons from the front end portion via the generation member, the cathode member is heated after the generation member is heated. The generation of atoms in the generating member can be started before the desorption of the atoms in the member is started,
Atoms desorbed from the cathode member can be satisfactorily replenished with atoms generated from the generating member.

Further, since the protective film for preventing the release of the metal ions of the positive electrode is formed on the surface of the metal aperture, the protective film prevents the metal ions of the positive electrode from desorbing from the metal aperture due to the collision of the negative ions. Therefore, the cathode member can be prevented from being contaminated with metal ions, and the life of the electron gun can be extended.

Further, since the protective film of the metal aperture is made of a conductive rare earth boride, B atoms can also be generated from the protective film and replenished to the cathode member. Can be

According to the electronic apparatus of the present invention, since the electron gun of the present invention is disposed inside the vacuum container, the electron gun disposed inside the vacuum container can emit thermoelectrons into a vacuum. Since the electron gun, which is arranged inside the vacuum vessel and is not easy to replace, has a long life, it has good long-term maintainability.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing an electron gun according to an embodiment of the present invention.

FIG. 2 is a schematic view showing a state in which atoms are desorbed and replenished at the same time in a LaB6 single crystal.

FIG. 3 is a schematic perspective view showing a conventional electron gun.

FIG. 4 is a schematic view showing a crystal structure of LaB6.

FIG. 5 is a schematic view showing a process in which B atoms are desorbed from a single crystal of LaB6.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Electron gun 12 Graphite heater which is a heat generating member 13 Cathode member 14 Metal aperture which is an anode member 15 Polycrystalline body which is a generating member 17 Protective film

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H01J 37/06 H01J 37/06 Z

Claims (12)

[Claims] 1. A heat-generating member that generates heat, a cathode member that is heated by the heat-generating member and receives a negative charge from the outside to emit thermoelectrons, and a positive charge is applied from the outside and is emitted from the cathode member. An anode member that limits expansion of thermoelectrons, wherein the cathode member is formed of a single crystal of a molecule composed of a specific atom, and an atom that forms a molecular structure of the single crystal. An electron gun, wherein a generating member for generating at least one of the above is disposed near the cathode member. 2. A heating member that generates heat, a cathode member that is heated by the heating member and receives a negative charge from the outside to emit thermoelectrons, and a positive charge is applied from the outside and is released from the cathode member. An anode member for limiting the expansion of thermoelectrons, wherein the cathode member is formed of LaB ₆ single crystal, and at least a generating member for generating B atoms is in the vicinity of the cathode member. Electron gun that is located in the. 3. A heat-generating member that generates heat, a cathode member that is heated by the heat-generating member and receives a negative charge from the outside to emit thermoelectrons, and a positive charge is applied from the outside and is emitted from the cathode member. An anode member that limits expansion of thermoelectrons, wherein the cathode member is formed of a single crystal of LaB ₆ , and the generating member that generates La atoms and B atoms is the cathode member. An electron gun arranged near the member. 4. The electron gun according to claim 3, wherein said generating member is made of LaB ₆ polycrystal. 5. The electron gun according to claim 1, wherein said heat generating member heats both said cathode member and said generating member. 6. The electron gun according to claim 5, wherein said heat generating member is opposed to an end portion of said cathode member which emits thermoelectrons from a front end portion via said generating member. 7. The electron gun according to claim 1, wherein the anode member is formed of a metal aperture, and a protective film for preventing the release of metal ions of the positive electrode is formed on the surface of the metal aperture. 8. The electron gun according to claim 7, wherein said protective film is made of a rare earth boride having conductivity. 9. A heating member that generates heat, and a cathode member that is formed of a single crystal of a molecule composed of a specific atom, is heated by the heating member, and emits thermoelectrons when a negative charge is applied from the outside. An anode member to which a positive charge is applied from the outside to limit expansion of thermoelectrons emitted from the cathode member, wherein at least one of atoms forming the molecular structure of the single crystal is A method for extending the life of an electron gun which is generated near a cathode member. 10. A heating member that generates heat, a cathode member that is formed of a single crystal of LaB ₆ and is heated by the heating member and receives a negative charge from outside to emit thermoelectrons, and a positive charge from outside. An anode member that limits expansion of thermoelectrons that are applied and emitted from the cathode member; and a method for extending the life of the electron gun, wherein at least B atoms are generated near the cathode member. . 11. A heating member that generates heat, a cathode member that is formed of LaB ₆ single crystal and is heated by the heating member and receives a negative charge from outside to emit thermoelectrons, and a positive charge from outside. An anode member for limiting expansion of thermoelectrons applied and emitted from the cathode member, wherein the length of the electron gun is such that La atoms and B atoms are generated near the cathode member. Life extension method. 12. Electronic equipment wherein the electron gun according to claim 1 is arranged inside a vacuum vessel.