JP6192097B2 - Photocathode type electron beam source, method for producing the same, and photocathode type electron beam source system - Google Patents

Description

  The present invention relates to a photocathode type electron beam source, a method for producing the same, and a photocathode type electron beam source system.

  An electron beam source is a device that takes out electrons in a solid into space. Depending on the difference in electrode structure, there is an emitter type or a cathode type. Further, there are a thermionic emission type in which electrons are emitted by thermal energy, a field emission type in which electrons are extracted into space by a quantum mechanical tunnel effect, etc.

The electrons emitted from the electron beam source to the space are accelerated by an electric field and converged and irradiated in the form of a beam by an electron lens, and are used in high-resolution electron microscopes, electron beam drawing apparatuses, and the like.
However, even with the various types of electron beam sources, there has been a problem that, for example, sufficient luminance has not been obtained as a high-resolution electron beam source of a transmission electron microscope (TEM).

  The present inventor has so far continued research on a photocathode type electron beam source (Patent Documents 1 to 6). The photocathode type electron beam source is an electron beam source that is connected to or integrated with a cathode and can emit electrons by an external photoelectric effect.

Based on those studies, as materials that emit electrons by external photoelectric effect, quantum efficiency of Cs ₃ Sb, K ₃ Sb, Rb ₃ Sb, etc. (the proportion of photoelectrons emitted by the photoelectric effect of one photon It was conceived that by using a substance having a very high index), sufficient luminance could be obtained as a high-resolution electron beam source for a transmission electron microscope (TEM).

As expected, photocathodes using high quantum efficiency materials such as Cs ₃ Sb, K ₃ Sb, Rb ₃ Sb showed high quantum efficiency. However, the high quantum efficiency material is chemically extremely active, and has a crystal structure due to oxidation of H ₂ O (water vapor) or O ₂ adhering to the surface or evaporation of alkali metal in vacuum even in a high vacuum. As a result of deterioration, the quantum efficiency is lowered, and the lifetime as a photocathode is lowered.

Japanese Patent No. 3567747 Japanese Patent No. 3577718 Japanese Patent No. 3833766 Japanese Patent No. 5071699 Japanese Patent No. 4915786 Dutch Patent No. 1002246

  The present invention can generate an electron beam with significantly higher brightness than a conventional electron beam source, and can significantly increase the lifetime, "a photocathode type electron beam source, a method for producing the same, and a photocathode type electron beam source system" It is an issue to provide.

The present inventor originally thought that the lifetime can be improved by forming a W film or a Cr film that does not cause a chemical reaction with Sb and Cs on the surface of a high quantum efficiency material such as Cs ₃ Sb. A photoelectron emission experiment was conducted by forming a protective film of a W film or a Cr film. However, the life improvement effect was not obtained. However, by repeating the trial and error of the experiment, the quantum efficiency is reduced by forming a protective treatment layer made of a passive film by oxidizing the W film or Cr film so as not to interfere with the emission of photoelectrons. In this way, oxidation due to a chemical reaction between a high quantum efficiency substance and H ₂ O (water vapor) or O ₂ (oxygen molecules) in a vacuum can be suppressed, and a decrease in quantum efficiency due to evaporation of Cs can be prevented. The present invention has been completed by discovering that it can be lengthened.
The present invention has the following configuration.

(1) A photocathode type electron beam source formed on a tip surface of a cathode tip, a bonding layer formed on the tip surface, a photoelectron emission layer formed on one surface of the bonding layer, and the photoelectron emission A protective treatment layer formed on one surface of the layer, wherein the bonding layer is made of a material that does not react with the cathode tip and does not react with the material that constitutes the photoelectron emitting layer. The photocathode-type electron beam source is characterized in that the protective treatment layer is formed of a passive film made of a substance that does not react with the substance constituting the photoelectron emission layer.

(2) The photoelectron emission layer is any selected from the group consisting of Cs ₃ Sb, K ₃ Sb, Rb ₃ Sb, Na ₂ KSb, (Cs) Na ₂ KSb, K ₂ CsSb, Cs ₂ Te, and GaAs (Cs) And the substance constituting the photoelectron emitting layer is selected from the group consisting of alkali metals of Cs, Rb, K, and Na, group III metals of Ga, and metalloids of any of Sb, Te, and As. The photocathode type electron beam source according to (1), which is any one or more selected elements.

(3) The photocathode electron beam source according to (2), wherein the thickness of the photoelectron emission layer is equal to or greater than the longest penetration depth of the photons to be irradiated.
(4) The photocathode electron beam source according to (1), wherein the substance that does not react with the substance constituting the photoelectron emitting layer is W or Cr.
(5) The photocathode electron beam source according to (1), wherein the substance that does not react with the cathode and does not react with the element constituting the photoelectron emitting layer is W or Cr. .
(6) The photocathode type electron beam source according to (1), wherein the passive film is made of a metal oxide of WO ₃ or Cr ₂ O ₃ .

(7) A step of forming a bonding layer made of W or Cr on the tip surface of the cathode tip by a dry film formation method, and Cs ₃ Sb, K ₃ Sb, Rb _{3 on} one surface of the bonding layer by a dry film formation method. Forming a photoelectron emission layer made of any one compound selected from the group consisting of Sb, Na ₂ KSb, (Cs) Na ₂ KSb, K ₂ CsSb, Cs ₂ Te, and GaAs (Cs); Forming a protective treatment layer comprising a passive film of a substance that does not react with a substance constituting the photoelectron emitting layer on one surface of the layer. A method for producing a photocathode type electron beam source, comprising:

(8) The step of forming the photoelectron emitting layer includes a first constituent element layer made of a half metal of Sb, Te, or As, an alkali metal of any of Cs, Rb, K, or Na, or III of Ga. A second constituent element layer made of any one of group metals is alternately stacked to form a multilayer film having one or more unit layers made up of the first constituent element layer, the second constituent element layer, and the first constituent element layer The method for producing a photocathode type electron beam source according to (7), characterized by comprising the steps of: and a step of making the multilayer film into a single layer by heating.

(9) The step of forming the protective treatment layer includes a step of forming a substance that does not react with a substance constituting the photoelectron emission layer on one surface of the photoelectron emission layer by a dry film forming method, and a change of a vacuum environment. The method according to (7) or (8), further comprising: oxidizing a substance that does not react with the substance constituting the photoelectron emitting layer to form a passive film made of the oxide film. A method for producing a photocathode type electron beam source.
(10) The method for producing a photocathode electron beam source according to (9), wherein the photocathode electron beam source is continuously irradiated with a laser while changing the vacuum environment.

(11) The photocathode electron beam source according to any one of (1) to (6), a light source capable of irradiating light to the photocathode electron beam source, and emitted from the photocathode electron beam source A photocathode-type electron beam source system comprising: a photoelectron capturing section capable of attracting photoelectrons.

The photocathode type electron beam source of the present invention is a photocathode type electron beam source formed on the tip surface of the cathode tip, and is formed on the one surface of the bonding layer formed on the tip surface and the bonding layer. A substance comprising a photoelectron emission layer and a protective treatment layer formed on one surface of the photoelectron emission layer, wherein the bonding layer is a substance that does not react with the cathode tip, and constitutes the photoelectron emission layer The protective treatment layer is composed of a passive film of a substance that does not react with the substance constituting the photoelectron emission layer, so that it is thin and strong in a range that does not hinder the emission of photoelectrons. the protective treatment layer, without reducing the electron beam generated by the photoelectric effect from the high quantum efficiency materials such as Cs 3 _Sb, it is possible to emit photoelectrons, by increasing the photocurrent value, the quantum efficiency based on the photoelectric conversion It is possible to increase the, Cs 3 and high quantum efficiency materials such as _Sb, it is possible to suppress chemical reaction of water and oxygen to trace amounts present even in a vacuum, to increase the life of the photocathode electron beam source Can do.

The method for producing a photocathode type electron beam source of the present invention comprises a step of forming a bonding layer made of W or Cr on the tip surface of the cathode tip by a dry film forming method, and a surface of the bonding layer by a dry film forming method. A photoelectron composed of any one compound selected from the group consisting of Cs ₃ Sb, K ₃ Sb, Rb ₃ Sb, Na ₂ KSb, (Cs) Na ₂ KSb, K ₂ CsSb, Cs ₂ Te, and GaAs (Cs) Since the structure has a step of forming an emission layer and a step of forming a protective treatment layer made of a passive film of a substance that does not react with a substance constituting the photoelectron emission layer on one surface of the photoelectron emission layer, quantum efficiency is improved. A photocathode type electron beam source that is high, can have a large photocurrent value, and has a long lifetime can be easily produced.

The photocathode electron beam source system of the present invention is a photocathode electron beam source described above, a light source capable of irradiating the photocathode electron beam source, and the photocathode electron beam source emitted from the photocathode electron beam source. Since it has a photoelectron capturing section that can attract photoelectrons, it emits light from the light source to the photocathode-type electron beam source, efficiently emits photoelectrons, and generates an electron beam with a high photocurrent value. In addition, the electron beam can be attracted to the photoelectron capture portion with a high yield. In addition, since the protective treatment layer is formed, (1) high quantum efficiency materials such as Cs ₃ Sb and high quantum efficiency materials by reaction with H ₂ O and O ₂ that exist in a very small amount even in a vacuum. Deterioration of the crystal structure of the high quantum efficiency material due to oxidation and (2) loss due to evaporation of constituent atoms (Cs, etc.) of the high quantum efficiency material into a vacuum can be suppressed, and the lifetime of the photocathode type electron beam source Can be lengthened. As described above, it can be used for an electron beam source for a next-generation transmission electron microscope (TEM) having higher functions.

It is a cross-sectional schematic diagram which shows an example of the photocathode type electron beam source system which is embodiment of this invention. It is a figure which shows an example of the photocathode type | mold electron beam source which is embodiment of this invention. It is a flowchart figure which shows an example of the production method of the photocathode type | mold electron beam source which is embodiment of this invention. It is a figure which shows another example of the photocathode type | mold electron beam source which is embodiment of this invention. It is a schematic diagram of the preparation / evaluation apparatus of a photocathode type electron beam source. It is a creation process figure of a photocathode type electron beam source. It is a graph which shows the measurement result of the time change of the common logarithm of the normalized value of the photocurrent from the photocathode type electron beam source of test example 1-1. It is a graph which shows the measurement result of the time change of the common logarithm of the normalized value of the photocurrent from the photocathode type electron beam source of test example 1-2. It is a graph which shows the measurement result of the time change of the common logarithm of the normalized value of the photocurrent from the photocathode type electron beam source of Test example 1-3. It is a graph which shows the measurement result of the time change of the common logarithm of the normalized value of the photocurrent from the photocathode type electron beam source of Test example 1-3. It is a graph which shows the measurement result of the time change of the common logarithm of the normalized value of the photocurrent from the photocathode type electron beam source of Test example 1-3.

(Embodiment of the present invention)
Hereinafter, a photocathode type electron beam source, a method for producing the same, and a photocathode type electron beam source system according to embodiments of the present invention will be described with reference to the accompanying drawings.

<Photocathode electron beam source system>
First, a photocathode electron beam source system according to an embodiment of the present invention will be described. FIG. 1 is a schematic sectional view showing an example of a photocathode type electron beam source system according to an embodiment of the present invention.
As shown in FIG. 1, a photocathode electron beam source system 51 according to an embodiment of the present invention includes a photocathode electron beam source 11, a light source 33 capable of irradiating the photocathode electron beam source 11, and a photo A photoelectron capturing section 35 capable of attracting photoelectrons 42 emitted from the cathode type electron beam source 11 is schematically configured.

  An example of the light source 33 is a laser light source. If a pulse laser light source is used, a pulsed electron beam can be obtained, and the application range of the apparatus can be expanded. The wavelength of the laser is not particularly limited, and examples thereof include 405 nm and 488 nm.

The photocathode type electron beam source system 51 includes a vacuum chamber 31 that can be evacuated.
A photoelectron trap 35 made of a Faraday cup is disposed in the vacuum chamber 31. A mirror 36 is provided inside the photoelectron trap 35.

A lens 34 is incorporated in one side surface of the vacuum chamber 31, and a photoelectron capturing unit 35 receives laser light 41 emitted from the tip of an optical fiber 32 connected to a light source 33 disposed outside through the lens 34. The mirror 36 is irradiated inside, and the reflected light can be irradiated to the tip side of the rod-like cathode 20 attached to the cathode support portion 19.
The photoelectron capturing unit 35 is connected to an external ammeter 37 via a wiring 38, and a photocurrent obtained by an electron beam 42 made of photoelectrons captured by the photoelectron capturing unit 35 can be measured.

A cathode support portion 19 is disposed in the vacuum chamber 31. A cathode tip 20 having a sharp tip is attached to the cathode support portion 19.
A photocathode electron beam source is formed on the tip surface of the cathode tip 20.

<Photocathode type electron beam source>
Next, a photocathode electron beam source that is an embodiment of the present invention will be described.
FIG. 2 is a diagram showing an example of a photocathode type electron beam source according to an embodiment of the present invention, and is a plan view (a) and a cross-sectional view taken along line AA ′ of FIG. 2 (a). is there.
As shown in FIG. 2, a photocathode electron beam source 11 according to an embodiment of the present invention is a photocathode electron beam source formed on the tip surface 20a of the cathode tip 20, and is formed on the tip surface 20a. The bonding layer 21, the photoelectron emission layer 22 formed on the one surface 21 a of the bonding layer 21, and the protective treatment layer 23 formed on the one surface 22 a of the photoelectron emission layer 22 are schematically configured.

The bonding layer 21 is made of a material that does not react with the cathode tip 20 and that does not react with the material that constitutes the photoelectron emission layer 22.
For example, when the cathode tip 20 is Ni, Ni causes a chemical reaction with Sb and Cs. Therefore, as shown in FIG. 2B, first, for example, Ni that is a substance constituting the cathode tip, a photoelectron emission layer, or the like. Cr, which is known not to chemically react with Sb or Cs constituting the slag, is coated.
The protective treatment layer 23 is made of a passive film made of a substance that does not react with the substance constituting the photoelectron emission layer 22. Since the passive film has a very dense crystal structure, it can effectively prevent oxidation even if it is a very thin film.

The photoelectron emission layer 22 is any one selected from the group consisting of Cs ₃ Sb, K ₃ Sb, Rb ₃ Sb, Na ₂ KSb, (Cs) Na ₂ KSb, K ₂ CsSb, Cs ₂ Te, and GaAs (Cs). Can be mentioned. By using these compounds, quantum efficiency can be improved.
The substance constituting the photoelectron emitting layer 22 is any one selected from the group consisting of alkali metals of Cs, Rb, K, and Na, group III metals of Ga, and semimetals of any of Sb, Te, and As. Or 2 or more elements can be mentioned.

It is preferred maximum penetration depth of photons thickness t ₂₂ is irradiated with light emission layer 22 (when in Cs 3 _Sb of visible light irradiation is about 30 nm) is more thick. This is because some photons penetrate the photoelectron emission layer 22 below this thickness, and the photoelectric effect due to some of these photons does not occur. Maximum photon efficiency is obtained by stopping all photons and producing a photoelectric effect.

Examples of the substance that does not react with the substance constituting the photoelectron emission layer 22 include W or Cr metal.
Examples of the passive film include WO _3, Cr ₂ O ₃ , and Al ₂ O ₃ . For example, when Al, Fe, Ni, Cr is added to concentrated nitric acid or hot concentrated sulfuric acid, it becomes passive and does not dissolve in these solutions. This is because a passive film (very thin oxide film) is formed on the surface. As metals to be passivated, Fe, Ni, Co, Ti, Nb, Ta, Al and the like are well known, but it is also known that their alloys are passivated.

Thickness t ₂₃ of the protective treatment layer 23 in the above thickness of the lattice constant, and it is desirable photoelectrons emitted from a high quantum efficiency material is less capable of transmitting thick. Thick optoelectronic than permeable layer thickness of t ₂₃ photoelectrons is because not emitted into the vacuum.
For example, in the case of a WO ₃ film, the thickness is 0.56 to 1.11 nm.
In the case of a Cr ₂ O ₃ film, the thickness is 0.93 nm.
These thicknesses do not hinder the emission of photoelectrons.

The cathode tip 20 is a solid material that can be energized. Ni etc. can be mentioned.
The tip of the cathode tip with a metal Ni tip sharpened to a diameter of 0.2 mm is coated with Cs ₃ Sb to form a photocathode type electron beam source, which can be easily used for an electron microscope. it can.

<Method of creating a photocathode type electron beam source>
Next, a method for producing a photocathode electron beam source according to an embodiment of the present invention will be described.
FIG. 3 is a flowchart showing an example of a method for producing a photocathode electron beam source according to an embodiment of the present invention.
As shown in FIG. 3, the photocathode-type electron beam source production method according to the embodiment of the present invention includes a bonding layer forming step S1, a photoelectron emitting layer forming step S2, and a protective treatment layer forming step S3. Thus, it is schematically configured.

(Junction layer forming step S1)
The bonding layer forming step S1 is a step of forming a bonding layer made of W or Cr on the tip surface of the cathode tip by a dry film forming method.
Examples of the dry film forming method include a vapor deposition method and a sputtering method.

(Photoelectron emission layer forming step S2)
In the photoelectron emission layer forming step S2, Cs ₃ Sb, K ₃ Sb, Rb ₃ Sb, Na ₂ KSb, (Cs) Na ₂ KSb, K ₂ CsSb, Cs ₂ Te are formed on one surface of the bonding layer by a dry film forming method. , A step of forming a photoelectron emission layer made of any one compound selected from the group of GaAs (Cs).
The photoelectron emission layer forming step S2 includes, for example, a multilayer film forming step S21 and a multilayer film single layer forming step S22.

((Multilayer film forming step S21))
The multilayer film forming step S21 includes a first constituent element layer made of a semimetal of Sb, Te, or As, an alkali metal of any of Cs, Rb, K, or Na, or a group III metal of Ga. The second constituent element layer is alternately laminated to form a multilayer film having one or more unit layers composed of the first constituent element layer, the second constituent element layer, and the first constituent element layer.

((Multilayer single layer process S22))
The multilayer film single layer forming step S22 is a step of forming the multilayer film into a single layer by heating. The multilayer film forming step S21 is performed in a temperature environment of −20 ° C., and the temperature environment is set to, for example, + 13 ° C. in the multilayer film single layer forming step S22.

(Protective treatment layer forming step S3)
The protective treatment layer forming step S3 is a step of forming a protective treatment layer made of a passive film of a substance that does not react with a substance constituting the photoelectron emission layer on one surface of the photoelectron emission layer.
The process S3 for forming the protective treatment layer includes, for example, an inert material film forming process S31 and a passive film forming process S32.

((Inert Material Film Formation Step S31))
This is a step of forming a substance that does not react with a substance constituting the photoelectron emission layer on one surface of the photoelectron emission layer by a dry film forming method.
A substance (inert material) that does not react with the elements constituting the photoelectron emission layer 22 is deposited and formed.
Examples of the substance that does not react with the elements constituting the photoelectron emission layer 22 include W or Cr.

More specifically, for example, a W film is formed with a thickness of 0.32 to 0.63 nm. Even if it is thicker than 0.63 nm, the effect can be expected. However, if the thickness is less than 0.32 nm, that is, if the thickness is less than the lattice constant, the passive film is incomplete and the effect is expected to decrease.
Further, instead of the W film, a Cr film may be formed with a thickness of 0.43 nm.

((Passive film forming step S32))
This is a step of oxidizing a substance that does not react with the substance constituting the photoelectron emission layer by changing the vacuum environment to form a passive film composed of the oxide film.
The change in the vacuum environment includes not only changing the degree of vacuum from a high vacuum to a low vacuum, but also changing the amount of water and oxygen present in the vacuum by changing the exhaust method. For example, when the main pump for evacuation is changed from a cryopump to a turbo molecular pump (TMP), in addition to the degree of vacuum, the amount of H ₂ O and O ₂ present in a very small amount in the vacuum also changes.

By changing from a cryopump to a turbo molecular pump (TMP), a substance that does not react with the substance constituting the photoelectron emission layer can be oxidized to form a passive film made of the oxide film.
In the case of the W film, a passive film of WO ₃ having a thickness of 0.56 to 1.11 nm is formed.
Further, in the case of a Cr film, a passive film of Cr ₂ O ₃ having a thickness of 0.93 nm is formed.
These passive film, Cs 3 _Sb surface can protect a, Cs 3 with the oxidation of _Sb can be suppressed, it is possible to prevent evaporation of Cs, Cs 3 time of light amount of emitted electrons from _Sb Slowing down significantly. Thereby, the lifetime of the photocathode type electron beam source can be extended.

  While changing the vacuum environment, the photocathode electron beam source may be continuously irradiated with a laser. Thereby, a passive film can be stabilized.

FIG. 4 is a diagram showing another example of the photocathode type electron beam source according to the embodiment of the present invention.
As shown in FIG. 4, the tip surface of the cathode tip may be a curved surface instead of a flat surface. Even with a curved surface, a photocathode-type electron beam source having a layer structure corresponding to the shape can be formed, and since it is provided with a protective treatment layer made of a passive film, it is thin enough to prevent emission of photoelectrons. The robustly formed protective treatment layer can emit photoelectrons from a high quantum efficiency material such as Cs ₃ Sb without reducing the electron beam generated by the photoelectric effect, increasing the photocurrent value, It is possible to increase the quantum efficiency based on photoelectric conversion, and to suppress a chemical reaction between a high quantum efficiency material such as Cs ₃ Sb and H ₂ O and O ₂ that exist in a very small amount even in a vacuum. The lifetime of the electron beam source can be extended.

A photocathode type electron beam source 11 according to an embodiment of the present invention is a photocathode type electron beam source formed on a tip surface 20a of a cathode tip 20, and a bonding layer 21 formed on the tip surface 20a, The bonding layer 21 includes a photoelectron emission layer 22 formed on one surface 21 a of the layer 21 and a protective treatment layer 23 formed on one surface 22 a of the photoelectron emission layer 22, and the bonding layer 21 is a substance that does not react with the cathode tip 20. In addition, since the protective layer 23 is composed of a passive film of a substance that does not react with the substance constituting the photoelectron emission layer 22, the photoelectron emission is performed. thin it does not inhibit a durably by formed protective treatment layer without reducing the electron beam generated by the photoelectric effect with high quantum efficiency materials such as Cs 3 _Sb, this to emit photoelectrons Can be, by increasing the photocurrent value, chemistry it is possible to increase the quantum efficiency based on photoelectric conversion, and a high quantum efficiency materials such as Cs 3 _Sb, water and oxygen are also trace amounts present in the vacuum The reaction can be suppressed, and the life of the photocathode type electron beam source can be extended.

In the photocathode electron beam source 11 according to the embodiment of the present invention, the photoelectron emission layer 22 has Cs ₃ Sb, K ₃ Sb, Rb ₃ Sb, Na ₂ KSb, (Cs) Na ₂ KSb, K ₂ CsSb, Cs _2. It is composed of any one compound selected from the group of Te and GaAs (Cs), and the elements constituting the photoelectron emitting layer are any one of alkali metals of Cs, Rb, K and Na, Group III metal of Ga, Sb , Te and As, any one or two or more elements selected from the group of semimetals can be used, so that the quantum efficiency is high and the photocurrent value can be increased.

In the photocathode type electron beam source 11 according to the embodiment of the present invention, the photoelectron emission layer 22 has a film thickness (47 nm) of about the longest penetration depth of irradiated photons (Cs ₃ Sb in the case of visible light irradiation). Since the thickness is 30 nm or more, the quantum efficiency is high and the photocurrent value can be increased.

The photocathode type electron beam source 11 according to the embodiment of the present invention has a configuration in which the material that does not react with the material constituting the photoelectron emission layer 22 is W or Cr. Therefore, the constituent atoms of the high quantum efficiency material such as Cs ₃ Sb are used. A photoelectron emission layer can be formed without reacting with Ni or the like, the quantum efficiency is high, and the photocurrent value can be increased. In addition, a strong protective treatment layer can be formed.

  Since the photocathode electron beam source 11 according to the embodiment of the present invention is a substance that does not react with the cathode tip 20 and does not react with the substance that constitutes the photoelectron emission layer 22, the structure is W or Cr. The photoelectron emission layer can be formed without causing the cathode tip and the photoelectron emission layer to react with each other, the quantum efficiency is high, and the photocurrent value can be increased.

In the photocathode type electron beam source 11 according to the embodiment of the present invention, the passive film is composed of a metal oxide of WO ₃ or Cr ₂ O ₃ , so that the quantum efficiency is high and the photocurrent value is kept large. Long life can be achieved.

The method for producing the photocathode electron beam source 11 according to the embodiment of the present invention includes a step of forming a bonding layer 21 made of W or Cr on the tip surface 20a of the cathode tip 20 by a dry film forming method, and a dry film forming method. The surface 21a of the bonding layer 21 is selected from the group of Cs ₃ Sb, K ₃ Sb, Rb ₃ Sb, Na ₂ KSb, (Cs) Na ₂ KSb, K ₂ CsSb, Cs ₂ Te, and GaAs (Cs). Forming a photoelectron emission layer 22 made of any one of the compounds, and forming a protective treatment layer 23 made of a passive film of a substance that does not react with the substance constituting the photoelectron emission layer 22 on one surface 22a of the photoelectron emission layer 22 Therefore, a photocathode type electron beam source with high quantum efficiency, high photocurrent value, and long life can be easily produced.

  In the method for producing the photocathode-type electron beam source 11 according to the embodiment of the present invention, the step of forming the photoelectron emission layer 22 includes a first constituent element layer made of a semimetal of Sb, Te, or As, and Cs. , Rb, K, and Na, and second constituent element layers made of any one of Ga group III metals are alternately stacked to form a first constituent element layer, a second constituent element layer, and a first constituent element. Since it is composed of a step of forming a multilayer film having one or more unit layers composed of elemental layers and a step of forming the multilayer film into a single layer by heating, a desired photoelectron emission layer can be easily formed, A photocathode-type electron beam source having high quantum efficiency and a large photocurrent value can be easily produced.

  In the method for producing the photocathode type electron beam source 11 according to the embodiment of the present invention, the step of forming the protective treatment layer 23 comprises forming the photoelectron emission layer 22 on the one surface 22a of the photoelectron emission layer 22 by a dry film forming method. A step of forming a substance that does not react with the element, a step of oxidizing the substance that does not react with the substance constituting the photoelectron emission layer 22 by changing the vacuum environment, and forming a passive film made of the oxide film; Therefore, a photocathode type electron beam source with high quantum efficiency, a large photocurrent value, and a long lifetime can be easily produced.

  The method for producing the photocathode type electron beam source 11 according to the embodiment of the present invention is configured to change the vacuum environment and continuously irradiate the photocathode type electron beam source with a laser. The photocathode type electron beam source having a long lifetime can be easily produced.

A photocathode type electron beam source system 51 according to an embodiment of the present invention includes a photocathode type electron beam source 11, a light source 33 capable of irradiating the photocathode type electron beam source 11, and the photocathode type electron beam source 11. Since the photoelectron capturing section 35 is capable of attracting the emitted photoelectrons, the photocathode-type electron beam source is irradiated with light from the light source to efficiently emit photoelectrons, and an electron beam having a high photocurrent value. And the electron beam can be attracted to the photoelectron capture portion with high yield. In addition, since the protective treatment layer is formed, it is possible to suppress a chemical reaction between a high quantum efficiency material such as Cs ₃ Sb and H ₂ O or O ₂ that exists in a trace amount even in a vacuum, and photocathode-type electrons The life of the radiation source can be extended. As described above, it can be used as an electron beam source for a more advanced next-generation transmission electron microscope (TEM).

  The photocathode type electron beam source, the method for producing the photocathode type electron beam source, and the photocathode type electron beam source system according to the embodiment of the present invention are not limited to the above embodiment, and various types are possible within the scope of the technical idea of the present invention. It can be changed and implemented. Specific examples of this embodiment are shown in the following examples. However, the present invention is not limited to these examples.

(Test Example 1-1)
<Preparation of photocathode electron beam source and measurement of photoemission characteristics>
FIG. 5 is a schematic diagram of a photocathode-type electron beam source creation / evaluation apparatus.
The apparatus is divided into “upper vacuum chamber”, “intermediate vacuum chamber”, and “lower vacuum chamber”.
Since the upper vacuum chamber is evacuated by a “cryo pump” having an extremely high evacuation speed, it is in a high vacuum. Both the lower vacuum chamber and the intermediate vacuum chamber are evacuated by a “turbo molecular pump”, and the degree of vacuum is medium. The upper vacuum chamber and the intermediate vacuum chamber are separated to some extent by a narrow passage (“narrow tube”), and an “open / close valve” that can be operated remotely is provided between the intermediate vacuum chamber and the lower vacuum chamber. ing.

  Although a vapor deposition boat is disposed in the lower vacuum chamber, the degree of vacuum during heating of the vapor deposition boat is significantly reduced. During deposition on the “cathode tip” of Sb, Cs, etc., the open / close valve is opened, but the upper chamber is evacuated by a cryopump with an extremely high exhaust speed, and the vacuum due to the presence of narrow tubes and intermediate chambers. Due to the differential evacuation effect, the degree of vacuum can be maintained at 1000 times higher than the degree of vacuum in the lower vacuum chamber. Five vapor deposition boats are movably attached to the lower vacuum chamber, and powder materials containing Cr, Sb, Cs, W, and the like are sealed therein and heated by an “electron beam heating device”.

  A “crystal oscillator” is housed in the intermediate vacuum chamber, and is used to measure the thickness of the deposited film. From the thickness, the thickness of the deposited film at the cathode tip can be calculated.

  In the upper vacuum chamber, a “cathode unit” having a Ni cathode tip with a tip sharpened to a diameter of 0.2 mm is detachably installed. The reason why the tip is sharpened to 0.2 mm is to avoid a decrease in emission current due to the space electron effect. The cathode tip can be cooled to about −20 ° C. using a “Peltier cooling device”, and can be heated to about 200 ° C. using a “ceramic heating device”.

A “diaphragm” having a microhole at the center is positioned just below the cathode tip so as to be three-dimensionally movable by a “three-dimensional operation tool”, and a minute region (diameter: 1 to 70) at the center of the cathode tip. “Evaporated matter” such as Sb, Cs, Cr, etc. can be deposited in a limited manner. This is because the “telescope” is used to observe the tip surface of the cathode tip and the microhole of the diaphragm using the “one-dimensional operation tool”, and the diameter of the center of the microhole of the diaphragm and the diameter of the cathode tip using the three-dimensional operation tool. This is possible by aligning the center of 0.2 mm.
The “photoelectrons” that have jumped out of the cathode tip into the vacuum due to the photoelectric effect are accelerated by the “anode plate” that can be two-dimensionally controlled by the “two-dimensional operation tool” and controlled one-dimensionally by the one-dimensional operation tool. It jumps into a possible "Faraday cup" and is detected as a current.

  The “laser” emitted from the optical fiber is introduced from the window of the upper vacuum chamber, reflected by the atmospheric lens and the 45 ° rod mirror housed in the Faraday cup, and applied to the tip surface of the cathode tip. The center of the 45 ° rod mirror has a 1.5 mm hole, and the Faraday cup has a 2 mm hole in the bottom. Therefore, in order to improve quantum efficiency in the Faraday cup arrangement of FIG. The amount of photoelectrons emitted can be measured while performing additional deposition of Cs.

After depositing Cr as a bonding layer on the tip of the cathode to form Cs ₃ Sb and forming a passive film of WO ₃ or Cr ₂ O ₃ having a thickness of about the lattice constant, using a three-dimensional operation tool After the aperture is retracted, the “lid” is pressed against the cathode unit using the “operation bar”.
Thereafter, “argon gas” is introduced into the upper vacuum chamber at about 1 atm, and the O-ring attached to the lid is pressed by the pressure so that the cathode tip is sealed in vacuum by the lid and the O-ring. Thus, with the cathode tip kept in a vacuum atmosphere, the cathode unit is removed from the photocathode-type electron beam source creation / evaluation apparatus, and the cathode tip is exposed to the TEM so that the cathode tip is not exposed to the atmosphere (water vapor or oxygen molecules) at all. Install. A TEM or the like needs to have a structure in which a cathode unit can be mounted so that the cathode tip is not exposed to the atmosphere.

FIG. 6 is a production process diagram of a photocathode type electron beam source.
As shown in FIG. 6, the photocathode type electron beam source is formed at the tip end made of metallic Ni.
First, after making a high vacuum of 1 × 10 ⁻⁷ Pa, in order to completely remove dirt on the tip surface of the cathode tip, the cathode tip was heated to 200 ° C. and held for 2 hours using a ceramic heating device and baked. .
Thereafter, the temperature of the cathode tip was set to room temperature.
Next, Cr was formed to a thickness of 8 nm on the flat surface of the cathode tip.
Next, in order to completely remove dirt on the surface of the deposited Cr, the cathode tip was heated to 200 ° C. and held for 2 hours using a ceramic heating device, and baked.
Next, the cathode tip was cooled to −15 ° C. using a Peltier cooling device.
Next, an Sb film having a thickness of 4 nm was formed on the Cr film.
Next, a Cs film having a thickness of 93 nm was formed on the Sb film.
Next, an Sb film having a thickness of 4 nm was formed on the Cs film.
Thus, the Sb / Cs / Sb sandwich structure shown in FIG.
As a method for forming Cs ₃ Sb, there is also a method in which the cathode tip is heated at a high temperature and Sb and Cs are frequently deposited alternately. Compared to this method, the operation of the “sandwich method” employed in this example is simpler, and FIG. 5 shows that “Cs ₃ Sb can be formed in a minute region, so that frequent alternating deposition is difficult”. The present sandwich method was suitable for the deposition apparatus shown.

In the formation of Cs ₃ Sb, the minimum necessary Cs film thickness is 60 nm, whereas the Sb layer has a total film thickness of 8 nm. However, in consideration of experimental errors, the actual deposition thickness of the actual Cs film was intentionally increased to 93 nm. Cs corresponding to the excess of about 33 nm was dissipated into the vacuum without adversely affecting the formation of Cs ₃ Sb.

Next, the temperature of the cathode tip was heated to 13 ° C.
Thus, as shown in FIG. 6 (b), the Sb / Cs / Sb sandwich structure was _Cs 3 Sb layer having a thickness of 47 nm.
This formed a photoelectron emitting layer made of Cs 3 _Sb layer is a high quantum efficiency material.

The cooling of the cathode tip was stopped 63 minutes after the formation of the Sb / Cs / Sb sandwich structure, but the temperature after 66 minutes became 0 ° C.
The quantum efficiency was found to be 1.113% from the detection result of the photoelectron amount by 405 nm laser irradiation performed 64 minutes after the completion of the sandwich structure formation. In the measurement of quantum efficiency, the voltage applied to the anode was 1 kV in this and all the following.
From the 488 nm laser irradiation experiment 66 minutes after the formation of the sandwich structure, it was found that the quantum efficiency was 0.263%, which was smaller than that of the 405 nm laser irradiation.

After 66 minutes from the end of the formation of the sandwich structure, an experiment was conducted in which Cs was additionally deposited on Cs ₃ Sb formed at the cathode tip in order to increase the quantum efficiency. The cathode tip temperature in this experiment was varied between 13 and 120 ° C.
Due to the deposition of additional Cs, the quantum efficiency under the laser irradiation of 488 nm showed a maximum value of 0.474% after 187 minutes from the end of the formation of the sandwich structure. Thus, the addition deposition of Cs, the quantum efficiency of _Cs 3 Sb was found to increase.

After the Cs additional vapor deposition experiment was completed, an experiment (life test) was started to investigate the temporal change in the amount of photoelectrons emitted at a cathode tip temperature of 13 ° C. This life test was performed 233 minutes after the completion of the sandwich structure formation.
As shown in FIG. 7, a W film was formed with a thickness of 0.32 nm (one atomic layer) at a temperature that remained at 13 ° C. 214.5 hours after the start of the life test (FIG. 6C). .

Next, after 312.5 hours from the start of the life test and 98 hours after the end of the deposition of W, the main vacuum exhaust in the upper vacuum chamber where the cathode tip is present is converted from a cryopump to a turbo molecular pump (TMP). Te, by varying the vacuum environment, and the protection processing layer comprising a W film from W0 ₃ film having a thickness of 0.56 nm (FIG. 6 (d)).

Even after the formation of the photoelectron emission layer composed of the Cs ₃ Sb layer, a laser is emitted from the optical fiber while the vacuum degree of the upper vacuum chamber is set to 1 × 10 ⁻⁷ Pa, and the photoelectron emission layer is passed through the lens and the mirror. The photoelectrons emitted from the photoelectron emission layer were captured by a Faraday cup to generate a photocurrent, and the photocurrent value was measured. Two types of lasers were used: a laser with a wavelength of 405 nm and a laser with a wavelength of 488 nm.
Unless otherwise specified, the laser was irradiated only for 10 seconds or less only during photocurrent measurement, and the shortest irradiation time interval in the experiment was 1 hour. This is because irradiation within 10 seconds per hour has the same effect on the time change of quantum efficiency as if irradiation was not performed for one hour.

FIG. 7 is a graph showing the measurement result of the time change of the common logarithm of the normalized value of the photocurrent from the photocathode type electron beam source of Test Example 1-1.
In FIG. 7, the photocurrent value is normalized by the value at time 0, and the measurement result of the time change of the common logarithm is shown. The quantum efficiency of Cs ₃ Sb at time 0 was 1.293% for the 405 nm laser and 0.212% for the 488 nm laser.

  As shown in FIG. 7, between the time 0 hour and the time 100 hours, the common logarithm of the normalized photoelectron emission amount suddenly decreases nonlinearly with time, but from the time 100 hours to the time 312.5 hours. During the period, it decreased almost linearly. This indicates that in the steady state, the amount of emitted photoelectrons decreases almost exponentially with time. The rate of decrease in the common logarithm of the normalized photoelectron emission amount was slower in the 405 nm laser irradiation than in the 488 nm laser irradiation.

The W film was deposited at the time of 214.5 hours. Regardless of which laser was used, the common logarithm of the standard value of the photocurrent value was changed with time in the range up to the time of 312.5 hours. The previous period from 100 hours to 214.5 hours is the same. From this, it was found that the deposition of a single atomic W film does not affect the rate of exponential decrease in photoelectron emission from Cs ₃ Sb, that is, its lifetime.
The rate at which the common logarithm of the normalized photoelectron emission amount decreases with time was 0.00208 (/ h) in the case of laser irradiation at 405 nm.

From the time of 312.5 hours when the main vacuum exhaust pump of the upper vacuum chamber was changed from a cryopump to a turbo molecular pump (TMP) and the degree of vacuum was changed from 1 × 10 ⁻⁷ Pa to 1.6 × 10 ⁻⁷ Pa The rate of decrease in the common logarithm of the normalized photoelectron emission amount increased rapidly. The rate of decrease from 312.5 hours to 331 hours is 0.0917 (/ h), which is approximately 44 times the rate of decrease from 100 hours to 312.5 hours. Became faster.

By converting the main vacuum exhaust pump in the upper vacuum chamber from a cryopump to a turbo molecular pump, the degree of vacuum is reduced by about 1.6 times from 1 × 10 ⁻⁷ Pa to 1.6 × 10 ⁻⁷ Pa. However, the quality of the vacuum was also changing.
Before and after the conversion, the ratio of the partial pressure of oxygen molecules (O ₂ ) to the whole is approximately the same from about 1.45% to about 1.47%, and the partial pressure of O ₂ in vacuum is 1.3 × 10 ^{− It} increases only about 1.62 times from ⁹ Pa to 2.3 × 10 ⁻⁹ Pa. However, the ratio of the partial pressure of H ₂ O to the whole has increased from about 6.45% to about 25.1%, and the partial pressure of water vapor is from 6.45 × 10 ⁻⁹ Pa to 4. This is an increase of about 6.23 times to 02 × 10 ⁻⁸ Pa.
H ₂ O is more likely to adhere to the surface of the material than O ₂ , and it is considered that O (oxygen atom) separated from the attached H ₂ O enters Cs ₃ Sb and oxidizes it. Therefore, it is considered that the oxidation is rapidly accelerated when the amount of H ₂ O in the vacuum is increased. For this reason, the increase in the concentration of H ₂ O in the vacuum is considered to be the cause of the rapid increase in the speed of 44 times as described above.

As shown in FIG. 7, the common logarithm of the normalized photoelectron emission amount slightly increased after the time 331 hours. That is, the value was −2.930 at 331 hours, but slightly increased to −2.790 at 356 hours.
Furthermore, the rate of decrease of the common logarithm of the photoelectron emission amount between time 356 hours and time 504 hours was extremely slow as 0.000667 (/ h). This continues until time 655.4 hours, when a measure for further reducing the degree of vacuum is performed.

Such a gradual change in the common logarithm of the photoelectron emission amount between 331 hours and 645.5 hours is that the W film having a thickness of one atomic layer is in a vacuum from time 312.5 to time 331 hours. This is because the passivation film WO ₃ was formed by oxidation due to an increase in H ₂ O. That is, H ₂ O in vacuum adheres to the W film deposited on the surface of Cs ₃ Sb, gradually oxidizes W, and the formation of the passive film WO ₃ is completed at time 331 hours. passivating film WO ₃ is due to prevent evaporation of the Cs from oxidation and _Cs 3 Sb of _Cs 3 Sb. Cs ₃ evaporation of the Cs from oxidation and _Cs 3 Sb and Sb is to degrade the crystal structure of _Cs 3 Sb, but not to promote the reduction in the light amount of emitted electrons, between time 331 hours Time 645.5 hours The reason is that the passive film WO ₃ having a lattice constant thickness protected the surface of Cs ₃ Sb and extended its life.

In FIG. 7, the temperature of the cathode is always maintained at 13 ° C., but at the time of 650 hours, the way of evacuating the upper vacuum chamber is changed, and the degree of vacuum is from 1.6 × 10 ⁻⁷ Pa to 2.8 × 10 8. ^Since the protective function of Cs ₃ Sb by the passive film WO ₃ was lost because the pressure decreased to ⁻⁷ Pa and the quality of the vacuum deteriorated, the logarithm of the normalized photoelectron emission amount suddenly decreased again. Since the thickness of the passive film WO ₃ is too thin, about the lattice constant, there is a possibility that the film was destroyed by further deterioration of the degree of vacuum.

(Test Example 1-2)
During the life test, the photocathode type of Test Example 1-2 was substantially the same as Test Example 1-1 except that a W film was deposited with a thickness of 0.63 nm (2 atomic layers) as the material for the protective treatment layer. An electron beam source was created. The temperature at the tip of the cathode during the life test was performed at 13 ° C. as in Test Example 1-1.
FIG. 8 is a graph showing the measurement result of the time change of the common logarithm of the normalized value of the photocurrent from the photocathode type electron beam source of Test Example 1-2.
FIG. 8 shows the result of measurement (life test) of the time change of the common logarithm of the value obtained by normalizing the amount of emitted photoelectrons with the value at time 0 hour.
The life test was started 173 minutes after the end of the formation of the Sb / Cs / Sb sandwich structure, but the quantum efficiency at time 0 was 1.842% under 405 nm laser irradiation, and under 488 nm laser irradiation. 0.910%.

As shown in FIG. 8, when a 405 nm laser was used, the common logarithm of the normalized photoelectron emission amount decreased at a substantially constant rate with time in the range from time 0 hours to time 211 hours. During this time, the laser was irradiated continuously all the time, not only during photocurrent measurement.
Between the time 117 hours and the time 211 hours, the common logarithm of the normalized photoelectron emission amount decreases almost linearly at a rate of 0.0144 (/ h) with time.

  In Test Example 1-1, as shown in FIG. 7, between the time 100 hours and the time 312 hours when the cathode was irradiated with a 405 nm laser only at the time of photocurrent measurement at the same vacuum degree and temperature, The rate of decrease is more moderate at 0.00208 (/ h).

By performing continuous irradiation, the rate of decrease in the common logarithm of the photoelectron emission amount was as fast as 6.9 times. This means that continuous irradiation of the laser with the laser tip has the same effect as lowering the degree of vacuum. That is, it shows that the laser irradiation itself promotes the oxidation of Cs ₃ Sb. This is consistent with a phenomenon generally known as laser irradiation induced oxidation.

As shown in FIG. 8, when the continuous irradiation of the laser was stopped at the time of 211 hours, the temporal change in the common logarithm of the normalized photoelectron emission amount became moderate. When continuous laser irradiation was resumed at time 286 hours, the reduction rate of the common logarithm of the photoelectron emission amount again increased.
In FIG. 8, the range indicated as “Laser: ON” or “ON” at the top of the graph indicates the time range during which the laser was continuously irradiated. The range described as “On + e ⁻ ” indicates a time range in which photoelectrons are continuously emitted while continuously irradiating a laser. The range described as “OFF” indicates a time range during which continuous laser irradiation was not performed.

When the W film was formed with a thickness of 0.63 nm (2 atomic layers) at the time of 311.5 hours while continuing the continuous irradiation of the laser, the value of the common logarithm of the photoelectron emission amount increased in a short time. The value began to decrease again at the same rate as before the W film was formed. The cause of the temporary increase in the amount of photoelectron emission during the deposition of the W film is not clear, but the H ₂ O film that probably adhered to the surface of Cs ₃ Sb and hindered the emission of photoelectrons was repelled by the collision of W. Maybe because

At time 357 hours, the main evacuation pump in the upper vacuum chamber was changed from a cryopump to a turbo molecular pump, and the degree of vacuum was changed from 0.9 × 10 ⁻⁷ Pa to 1.6 × 10 ⁻⁷ Pa. It was. At time 357 hours, continuous laser irradiation was stopped at the same time, but the time of the common logarithm value of the photoelectron emission amount was reached between time 357 hours and time 383 hours, even though the degree of vacuum decreased. The change was almost zero.

In Test Example 1-1, as shown in FIG. 7, from the time of 312.5 hours to the time of 331 hours under the same vacuum degree, temperature, and laser irradiation conditions before the formation of the passive film of WO ₃ The rate of decrease between them was 0.0917 (/ h), indicating a rapid decrease.
Comparison with the results of this test example 1-1, in the test example 1-2, the W film is oxidized during the period from the time 311.5 hrs with a deposit of W film to the time 357 hours, not of WO ₃ It can be reasonably estimated that a dynamic film has been formed.

Between time 357 hours and time 383, the passive film of WO ₃ acts as a protective film for Cs ₃ Sb, and as shown in FIG. 8, the temporal change in the value of the common logarithm of the photoelectron emission amount is almost zero. It was concluded that Laser irradiation-induced oxidation is generally known, but in this test as well, continuous laser irradiation from time 311.5 hours to time 357 hours promoted the oxidation of the W film in the diatomic layer. is there.

At the time of 383 hours, the vacuum pump is again evacuated by the cryopump and the degree of vacuum is changed from 1.6 × 10 ⁻⁷ Pa to 0.9 × 10 ⁻⁷ Pa. Continuous laser irradiation resumed. Thereby, from time 383 hours, the common logarithm of the photoelectron emission amount increased again with time, and the decrease rate was 0.00781 (/ h). This rate is 0.54 times the decrease rate 0.0144 (/ h) between time 117 hours and time 211 hours before the formation of the passive film of WO ₃ under the same conditions. It was late. This is also due to the protective effect of the passive film of WO ₃ .

In order to investigate the influence of the degree of vacuum during continuous irradiation with a 405 nm laser, at 455.5 hours, the main vacuum exhaust pump in the upper vacuum chamber was changed again from a cryopump to a turbo molecular pump, and the degree of vacuum was reduced to 0. There was no significant change in the rate of decrease in the common logarithm of the normalized photoelectron emission amount even when it was reduced from 1.9 × 10 ⁻⁷ Pa to 1.6 × 10 ⁻⁷ Pa. This is because the effect of oxidation by continuous laser irradiation is greater than the effect of oxidation caused by a decrease in the degree of vacuum or the quality of the vacuum, specifically, the concentration of H ₂ O increased by about 6.23 times. It is shown that.

At the time of 529 hours, the laser was continuously irradiated and the method of evacuation of the upper vacuum chamber was changed again, and the degree of vacuum was changed from 1.6 × 10 ⁻⁷ Pa to 3.4 × 10 ⁻⁷ Pa. changed. As a result, the reduction rate of the common logarithm of the photoelectron emission amount was remarkably increased to 0.229 (/ h). This is about 29 times the previous decrease rate of 0.00781 (/ h), and it is estimated that the protective effect of the passive film of WO ₃ has disappeared due to the decrease in the degree of vacuum.

(Test Example 1-3)
Cs ₃ Sb is formed on the cathode tip from the sandwich structure, and a Cr film is deposited as a protective treatment layer with a thickness of 0.43 nm (1.5 atomic layers) during the life test after the investigation experiment of additional deposition of Cs. The photocathode type electron beam source of Test Example 1-3 was produced in substantially the same manner as Test Example 1-1 and Test Example 1-2.

FIGS. 9-11 is a graph which shows the measurement result of the time change of the common logarithm of the normalized value of the photocurrent from the photocathode type electron beam source of Test Example 1-3. Since the test time was as long as 1121 hours, it was divided into three graphs. FIG. 10 shows a time change from FIG. 9 and FIG. 11 shows a time change from FIG.
9 to 11 show the measurement results of the time change of the common logarithm of the value obtained by normalizing the photoelectron emission amount by the value at time 0.

  The life test was started 233 minutes after the end of the formation of the Sb / Cs / Sb sandwich structure, but the quantum efficiency at time 0 hours in FIG. Under laser irradiation, it was 0.342%.

As shown in FIG. 9, the temperature at the cathode tip was −20 ° C. from time 0 hour to time 356 hour, and 13 ° C. from time 356 hour. Further, the vacuum degree of the upper vacuum chamber from time 0 hour to time 281 hours was 0.9 × 10 ⁻⁷ Pa, but the vacuum degree from time 281 hours was 1.6 × 10 ⁻⁷ Pa. In the time range shown in FIG. 9, continuous laser irradiation is not performed.

At the time of 142 hours, a Cr film having a thickness of 0.43 nm (1.5 atomic layer) was deposited on the surface of Cs ₃ Sb. Before and after that, the rate of decrease in the common logarithm of the normalized photoelectron emission amount was somewhat It was increasing.

The rate of decrease between the time 142 hours and the time 281 hours is 0.00516 (/ h), and during the 405 nm laser irradiation in Test Example 1-1 shown in FIG. (Temperature 13 ° C., degree of vacuum 1 × 10 ⁻⁷ Pa), the rate of decrease is about 2.5 times the rate of 0.00208 (/ h). Since the conditions are the same except for the temperature, reducing the cathode temperature to −20 ° C. is the cause of the reduction rate of about 2.5 times. When the temperature is −20 ° C. than when the temperature is 13 ° C., H ₂ O in the vacuum is more likely to adhere to the surface of Cs ₃ Sb, and the oxidation is further promoted, which is the cause of the increase in the decrease rate. Can be guessed.

At the time of 281.5 hours, the degree of vacuum in the upper vacuum chamber was changed from 0.9 × 10 ⁻⁷ Pa to 1.6 × 10 ⁻⁷ Pa by the same method as described above. The rate of decrease of the common logarithm of the normalized photoelectron emission amount became extremely rapid.
The speed was 0.281 (/ h), approximately 54.5 times under the same 405 nm laser irradiation from 282 hours to 286 hours. In Test Example 1-1, when the vacuum degree was reduced to 1.6 × 10 ⁻⁷ Pa after 312.5 hours (temperature 13 ° C.), the rate of decrease 0.0917 (/ h) under 405 nm laser irradiation It is estimated that this is because the influence of a decrease in the degree of vacuum becomes more remarkable because of the low temperature of -20 ° C.
However, as shown in FIG. 9, the rate of decrease gradually and gradually decreased with time.

In the vicinity of time 286 hours, the rate of decrease is moderate from 0.281 (/ h) to 0.0375 (/ h), and in the vicinity of time 292 hours, 0.0375 (/ h) to 0.00759 (/ h). )
Furthermore, with the passage of time, the rate of decrease of the normalized logarithm of the normalized photoelectron emission amount continued to decrease stepwise, and the rate became almost zero between time 339 hours and time 356 hours. This was because the vacuum degree was reduced to 1.6 × 10 ⁻⁷ Pa, so that the concentration of H ₂ O in the vacuum increased to about 6.23 times and was formed on the surface of Cs ₃ Sb. It can be reasonably estimated that this is because the Cr film having a thickness of 0.43 nm (1.5 atomic layer) was oxidized to become a passive film Cr ₂ O ₃ and protected Cs ₃ Sb. The rate of decrease in the common logarithm of the amount of electron emission decreased stepwise means that the passive film Cr ₂ O ₃ was strengthened stepwise over time.

When the temperature of the cathode tip is increased from −20 ° C. to 13 ° C. at time 356 hours, as shown in FIG. 9, the common logarithm of the photoelectron emission amount normalized under the laser irradiation of 405 nm is −4. It increased rapidly from 222 to -3.699.
This sharp rise may not understand, or elevated itself temperature increased emission of photoelectrons, H _{2 O} of the film to the film thickness of the H _{2 O} which has been deposited is reduced to passive film Cr ₂ O ₃ It is presumed that the effect of preventing the escape of photoelectrons into the vacuum due to the thickness was reduced.

It was examined how the effect of the passivation film Cr ₂ O ₃ protecting Cs ₃ Sb changed with the temperature while keeping the degree of vacuum at 1 × 10 ⁻⁷ Pa. Although continuous laser irradiation accelerates the decrease in photoelectron emission, this accelerated test effect was used. That is, from time 476 hours, continuous irradiation with a 405 nm laser is performed intermittently, and the temperature at the cathode tip is 13 ° C, 20 ° C, 30 ° C, 40 ° C, 50 ° C, 60 ° C, 70 ° C, 80 ° C, 90 ° C. The rate of decrease in the common logarithm of the normalized photoelectron emission amount under continuous laser irradiation was investigated by changing to 100 ° C., 100 ° C., 110 ° C., 120 ° C., 130 ° C. and 140 ° C.

10 and 11 show the results. Since it is presumed that the reduction rate of the common logarithm of the photoelectron emission amount under continuous laser irradiation is affected by the intensity of the laser to be irradiated, it was examined at temperatures of 80 ° C. and 130 ° C.
Further, the difference in the reduction rate of the common logarithm of the photoelectron emission amount between continuous irradiation and non-continuous irradiation of the laser was examined at 40 ° C., but details of those results are omitted.
However, the effect of the laser intensity under the continuous irradiation of the laser on the rate of decrease of the common logarithm of the photoelectron emission amount is based on the evaluation of the temperature effect of the effect that the passive film Cr ₂ O ₃ protects Cs ₃ Sb. It was reflected in.
10 and FIG. 11, the time change of the degree of vacuum is indicated by numerical values and arrows at the top of the graph. In the lower row, the temperature change at the cathode tip is indicated by a numerical value and an arrow. Further, at the bottom, the range of the time of continuous laser irradiation is indicated by a mark with a numerical value of the laser intensity at the cathode tip.

From the results shown in FIG. 10, the reduction rate of the common logarithm of the normalized photoelectron emission amount under continuous irradiation of the laser is the fastest when the cathode temperature is 13 ° C., and the cathode temperature is 20 ° C. to 30 ° C., 40 ° C. It turned out that it becomes slow, so that it heats up with 50 degreeC, 60 degreeC, 70 degreeC, 80 degreeC, and 90 degreeC.
Further, from the results shown in FIG. 11, from the comparison under the same laser irradiation intensity, the standardized photoemission is increased as the temperature of the cathode is increased from 90 ° C. to 100 ° C., 110 ° C., 120 ° C., 130 ° C. The rate of decline of the common logarithm of the quantity was faster.
However, the rate of decrease at a temperature of 140 ° C. was slower than the rate of decrease at a temperature of 130 ° C. This is because some crystal structure change occurred in the passive film Cr ₂ O _{3 due} to continuous laser irradiation at a temperature of 130 ° C. with an extremely weak laser irradiation intensity of 0.10 W / cm ^2. There is a possibility that it is caused by.

Summarizing the above results, it was speculated that the effect of protecting the passive film Cr ₂ O ₃ on Cs ₃ Sb would be greatest at a temperature of 90 ° C.
The more intense the laser beam is irradiated, the more photoelectrons are emitted, but the temperature at the cathode tip is increased by laser irradiation, but the protective effect of the passive film Cr ₂ O ₃ at a relatively high temperature of 90 ° C. It is advantageous to maximize the.

When the test results shown in FIG. 10 and FIG. 11 are summarized, it can be inferred that the passive film Cr ₂ O ₃ protects Cs ₃ Sb at the highest temperature at the cathode tip of about 90 ° C. .
The more intense the laser beam is irradiated, the more photoelectrons are emitted, but the temperature at the cathode tip is increased by laser irradiation, but the protective effect of the passive film Cr ₂ O ₃ at a relatively high temperature of 90 ° C. It is advantageous to maximize the.
The experimental results are summarized in Table 1. In this table, “the maximum quantum efficiency detected during the experiment” and “a value indicating the detection time as the elapsed time (minutes) from the end of the second deposition of Sb” are for reference. It was described in. It can be seen that a predetermined quantum efficiency was also obtained in the formation of Cs ₃ Sb from the “Sb / Cs / Sb sandwich structure” employed in the examples. By the way, after forming Cs ₃ Sb by this method, it is possible to obtain a quantum efficiency higher than the maximum quantum efficiency shown in this table by holding the cathode tip at a high temperature and optimally depositing Cs. It is.

(Test Example 1-4)
The ratio of the partial pressure of H ₂ O and O ₂ , which are extremely small even in vacuum, to the total partial pressure of the main vacuum exhaust pump in the upper vacuum chamber (cryopump (measurement points P1, P2) and turbo molecule The pump (measurement points P3, P4, P5)) and how it changes depending on the degree of vacuum was examined. The measurement point P7 is a measurement in a state in which the vacuum evacuation by the turbo molecular pump from the side of the upper vacuum chamber is stopped and the vacuum evacuation is performed by the turbo molecular pump through only the narrow tube between the intermediate vacuum chamber. The measurement times of P1 to P7 are indicated by marks with respective numbers in FIGS. 10 and 11.
Table 2 shows the result of the partial pressure measurement.

As shown in Table 2, when the upper vacuum chamber was mainly evacuated with a cryopump (P1, P2), only a very small amount of both H ₂ O and O ₂ was present.
On the other hand, when the upper vacuum chamber is mainly evacuated with a turbo molecular pump (P3, P4, P5), the degree of vacuum is 1.6 to 1 compared with when the upper vacuum chamber is evacuated with a cryopump (P1, P2). .8 times lower. With this change, the partial pressure of O ₂ (or the number in vacuum) increased only 1.62 times, but the partial pressure of H ₂ O increased 6.35 times. The partial pressure of H ₂ O at a vacuum degree of 1.6 × 10 ⁻⁸ Pa was 5.7 times the partial pressure of O ₂ .

  The photocathode type electron beam source of the present invention can generate an electron beam with much higher luminance than a conventional electron beam source, and the service life as a photocathode type electron beam is much longer than before. can do. If the electron beam emitted from this photocathode type electron beam source is used for a transmission electron microscope (TEM) and a scanning electron microscope (SEM) as a high-intensity electron beam source, their performance can be dramatically improved. It can contribute to the discovery of new materials that can contribute to industrial development. It can also be used as a high-intensity electron beam source for electron beam accelerators, and promotes the development of the medical industry, science and technology industry, etc. by radiation therapy. Furthermore, it may be used in various electron beam apparatus industries. For example, if it is applied to a system that exposes a target pattern by irradiating a mask blank through an electron lens, an aperture, a deflector, etc. while finely controlling an XYZ stage, an electron beam processing apparatus, an electron beam ( EB) There is a possibility of application to an exposure apparatus, an electron beam (EB) drawing apparatus, and the like.

DESCRIPTION OF SYMBOLS 11 ... Photo cathode type electron beam source, 19 ... Cathode support part, 20 ... Cathode tip, 20a ... Tip surface, 21 ... Bonding layer, 21a ... One side, 22 ... Photoelectron emission layer, 22a ... One side, 23 ... Protection treatment layer, DESCRIPTION OF SYMBOLS 31 ... Vacuum chamber, 32 ... Optical fiber, 33 ... Light source, 34 ... Lens, 35 ... Faraday cup (photoelectron capture part), 36 ... Mirror, 37 ... Ammeter, 38 ... Wiring, 41 ... Laser, 42 ... Electron beam, 51 ... Photo cathode type electron beam source system.

Claims (9)

A photocathode type electron beam source formed on the tip surface of the cathode tip,
A junction layer made of W or Cr is formed on the tip surface,
A photoelectron emission layer formed on one surface of the bonding layer;
A protective treatment layer formed on one surface of the photoelectron emission layer,
The photocathode type electron beam source, wherein the protective treatment layer is made of a passive film in which W or Cr is oxidized . The photoelectron emitting layer is any one selected from the group consisting of Cs ₃ Sb, K ₃ Sb, Rb ₃ Sb, Na ₂ KSb, (Cs) Na ₂ KSb, K ₂ CsSb, Cs ₂ Te, and GaAs (Cs). Consisting of compounds,
The material constituting the photoelectron emitting layer is any one selected from the group consisting of an alkali metal of any one of Cs, Rb, K, and Na, a group III metal of Ga, and a semimetal of any of Sb, Te, and As, or The photocathode type electron beam source according to claim 1, wherein the photocathode type electron beam source is two or more elements.   3. The photocathode electron beam source according to claim 2, wherein the thickness of the photoelectron emission layer is equal to or greater than a longest penetration depth of the photons to be irradiated. _{2. The} photocathode type electron beam source according to claim 1, wherein the passive film is made of a metal oxide of WO ₃ or Cr ₂ O ₃ . A method for producing a photocathode type electron beam source according to claim 1,
Forming a bonding layer made of W or Cr on the tip surface of the cathode tip by a dry film forming method;
From the group of Cs ₃ Sb, K ₃ Sb, Rb ₃ Sb, Na ₂ KSb, (Cs) Na ₂ KSb, K ₂ CsSb, Cs ₂ Te, GaAs (Cs) on one surface of the bonding layer by a dry film forming method. Forming a photoelectron emitting layer comprising any one of the selected compounds;
Forming a protective treatment layer made of a passive film in which W or Cr is oxidized on one surface of the photoelectron emission layer, and a method for producing a photocathode type electron beam source. The step of forming the photoelectron emitting layer includes a first constituent element layer made of a semimetal of Sb, Te, or As, an alkali metal of Cs, Rb, K, or Na, or a group III metal of Ga. Forming a multilayer film having one or more unit layers each composed of a first constituent element layer, a second constituent element layer, and a first constituent element layer by alternately laminating any second constituent element layer; The method for producing a photocathode type electron beam source according to claim 5 , further comprising: a step of making the multilayer film into a single layer by heating. The step of forming the protective treatment layer, the dry film forming method, forming a film made of W or Cr on a surface of the photoelectron emitting layer, by varying the vacuum environment, consisting of pre-Symbol W or Cr The method for producing a photocathode type electron beam source according to claim 5 or 6, comprising the step of oxidizing the film to form a passive film composed of the oxide film. The method for producing a photocathode type electron beam source according to claim 7 , wherein the photocathode type electron beam source is continuously irradiated with a laser while changing a vacuum environment. The photocathode type electron beam source according to any one of claims 1 to 4 ,
A light source capable of irradiating light to the photocathode-type electron beam source;
A photocathode-type electron beam source system, comprising: a photoelectron capturing section capable of attracting photoelectrons emitted from the photocathode-type electron beam source.