JP3079086B2 - Method for manufacturing field emission electron source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a field emission type electron source which emits an electron beam by field emission using a semiconductor material.

[0002]

2. Description of the Related Art Conventionally, as a field emission type electron source, there is a so-called Spindt electrode disclosed in, for example, US Pat. No. 3,665,241. This Spindt-type electrode has a substrate on which a number of minute triangular pyramid-shaped emitter chips are arranged, a gate layer having a radiation hole for exposing the tip of the emitter chip, and being arranged insulated from the emitter chip. And applying a high voltage with the emitter tip as a negative electrode to the gate layer in a vacuum to emit an electron beam from the tip of the emitter tip through a radiation hole.

However, the Spindt-type electrode has a complicated manufacturing process, and it is difficult to accurately form a large number of triangular pyramid-shaped emitter chips. For example, the Spindt-type electrode has a large area when applied to a flat light emitting device or a display. There was a problem that was difficult. In the Spindt-type electrode, the electric field is concentrated at the tip of the emitter tip, so if the degree of vacuum around the tip of the emitter tip is low and residual gas is present, the emitted gas turns the residual gas into positive ions. Since the ions are ionized and the positive ions collide with the tip of the emitter tip, the tip of the emitter tip is damaged (for example, damage due to ion bombardment), and the current density and efficiency of emitted electrons become unstable. There is a problem that the life of the chip is shortened. Therefore, in the Spindt-type electrode, in order to prevent this kind of problem from occurring, a high vacuum (10 ⁻⁵ Pa to 10 ⁻⁵ Pa) is used.
^-6 Pa), which is disadvantageous in that the cost increases and the handling becomes troublesome.

In order to improve this kind of problem, MIM
(Metal Insulator Metal) method and MOS (Metal Oxid
e Semiconductor) type field emission electron sources have been proposed. The former is a flat field emission type electron source having a metal-insulating film-metal structure, and the latter is a metal-oxide film-semiconductor stacked structure. However, in order to increase the emission efficiency of electrons in this type of field emission type electron source (to emit many electrons), it is necessary to reduce the thickness of the insulating film and the oxide film. If the thickness of the insulating film or the oxide film is too thin, dielectric breakdown may occur when a voltage is applied between the upper and lower electrodes of the laminated structure. Since the thickness of the insulating film or the oxide film is limited, the electron emission efficiency (drawing efficiency) cannot be increased.

In recent years, Japanese Patent Application Laid-Open No. 8-250766
As disclosed in Japanese Patent Application Laid-Open Publication No. H10-209, a porous semiconductor layer (for example, a porous silicon layer) is formed by using a single crystal semiconductor substrate such as a silicon substrate and anodizing one surface of the semiconductor substrate. A field emission type electron source (semiconductor cold electron emission device) has been proposed in which a metal thin film is formed on the porous semiconductor layer, and a voltage is applied between the semiconductor substrate and the metal thin film to emit electrons. ing.

[0006]

However, in the field emission type electron source described in JP-A-8-250766, since the substrate is limited to a semiconductor substrate, it is difficult to increase the area and reduce the cost. There is. In the field emission type electron source described in Japanese Patent Application Laid-Open No. 8-250766, a so-called popping phenomenon tends to occur during electron emission, and the amount of emitted electrons tends to be uneven. There is a problem that unevenness occurs.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing a low-cost field emission electron source capable of stably and efficiently emitting electrons.

[0008]

According to a first aspect of the present invention, there is provided a semiconductor device comprising: a conductive substrate; an oxidized porous polysilicon layer formed on one surface of the conductive substrate; Manufacturing a field emission type electron source that emits an electron beam through the metal thin film by applying a voltage with the metal thin film as a positive electrode to the conductive substrate, comprising a metal thin film formed on the porous polysilicon layer. Forming a polysilicon layer on a conductive substrate, making the polysilicon layer porous, and lamp annealing the porous polysilicon layer.
Oxidized by rapid heating method using the device, forming an electrode made of a thin metal film oxidized porous polysilicon layer characterized by complex structures and fabrication processes, such as a conventional Spindt type electrode It is possible to provide a low-cost field emission electron source that can stably and efficiently emit electrons from the surface of the metal thin film in a direction substantially orthogonal to the metal thin film by a relatively simple manufacturing process without requiring Further, a large-area field emission electron source can be provided. Therefore, in the display device using the field emission type electron source manufactured by the manufacturing method of the first aspect of the present invention, it is not necessary to provide an electron converging lens, and it is possible to easily realize a high definition and a large number of pixels of the display device. can do. Further, in the flat light emitting device using the field emission type electron source manufactured by the manufacturing method of the first aspect of the present invention, it is not necessary to provide a focusing electrode, so that the structure can be simplified and the thickness can be easily reduced. it can. Further, in a solid-state vacuum device using a field emission electron source manufactured by the manufacturing method of the first aspect of the invention as a cold cathode, a heating means is used as in a conventional solid-state vacuum device having a hot cathode utilizing thermionic emission. There is no need to provide
It is possible to reduce the size, suppress evaporation and deterioration of the cathode material, and extend the life.

[0009] The invention of claim 2 is the invention according to claim 1.
Thus, the porous polysilicon layer is formed on a conductive substrate.
Layers with different porosity in the thickness direction are alternately laminated
Characterized in that it is a layer. The invention according to claim 3, in the invention of claim 1 or claim 2, upper Symbol lamp Annie
When the oxidation is rapid heating method using the Le device, dry <br/>燥酸to not 800 ° C. The oxidation temperature at Motochu 900 ° C., 30 minutes to an oxidation time and characterized in that a 120 min, preferred embodiments It is.

[0010]

FIG. 1 is a schematic structural view of a field emission type electron source 10, and FIGS. 2 and 3 are sectional views showing main steps in a method of manufacturing the field emission type electron source 10. As shown in FIG. In this embodiment, an n-type silicon substrate 1 (a (100) substrate having a resistivity of about 0.1 Ωcm) is used as the conductive substrate.

As shown in FIG. 1, a field emission type electron source 10 has a polysilicon layer 5 formed by rapid thermal oxidation on a main surface of an n-type silicon substrate 1 and a rapid thermal oxidation on the polysilicon layer 5. An oxidized porous polysilicon layer 6 is formed,
A gold thin film 7 as a metal thin film is formed on the porous polysilicon layer 6. An ohmic electrode 2 is formed on the back surface of the n-type silicon substrate 1. Here, the rapidly thermally oxidized porous polysilicon layer 6 has a high porosity rapidly thermally oxidized porous polysilicon layer 6b and a low porosity rapidly thermally oxidized polysilicon layer 6a alternately stacked. Layer.

In the present embodiment, the n-type silicon substrate 1 is used as the conductive substrate. The conductive substrate constitutes the negative electrode of the field emission electron source 10 and is thermally oxidized in a vacuum. The porous polysilicon layer 6 is supported and electrons are injected into the porous polysilicon layer 6. Therefore, the conductive substrate is not limited to the n-type silicon substrate 1 as long as it can constitute the negative electrode of the field emission type electron source 10 and support the porous polysilicon layer 6, and is not limited to the n-type silicon substrate 1. The substrate may be used, or a conductive film may be formed on one surface of a substrate such as glass. In the case where a substrate in which a conductive film is formed on one surface of a glass substrate is used, the area and cost of the electron source can be increased as compared with the case where a semiconductor substrate is used.

The thermally oxidized porous polysilicon layer 6 is a layer into which electrons are injected when a voltage is applied between the conductive substrate and the metal thin film.

In the present embodiment, the gold thin film 7 is used as the metal thin film. The metal thin film constitutes the positive electrode of the field emission type electron source 10 and is made of porous polysilicon which is thermally oxidized. An electric field is applied to the layer 6.
Electrons that have reached the surface of the porous polysilicon layer 6 thermally oxidized by the application of the electric field are emitted from the surface of the metal thin film by a tunnel effect. Therefore, the energy obtained by subtracting the work function of the metal thin film from the energy of the electron obtained by the DC voltage applied between the conductive substrate and the metal thin film becomes the ideal energy of the emitted electrons.
The smaller the work function of the metal thin film, the better. In this embodiment, gold is used as the material of the metal thin film.
The material of the metal thin film is not limited to gold, but may be any metal having a small work function, for example, aluminum,
Chromium, tungsten, nickel, platinum or the like may be used. Here, the work function of gold is 5.10 eV, the work function of aluminum is 4.28 eV, the work function of chromium is 4.50 eV, and the work function of tungsten is 4.55 eV.
The work functions of V and nickel are 5.15 eV, and the work functions of platinum are 5.65 eV.

Hereinafter, the manufacturing method will be described with reference to FIG.

First, an ohmic electrode 2 is formed on the back surface of an n-type silicon substrate 1, and then a non-doped polysilicon layer 3 having a thickness of about 1.5 μm is formed on the surface of the n-type silicon substrate 1 as shown in FIG. A structure as shown in FIG. The polysilicon layer 3 is formed by the LPCVD method under the conditions of a vacuum degree of 20 Pa and a substrate temperature of 64.
At 0 ° C., the flow rate of the monosilane gas was set at 600 sccm.
Note that the polysilicon layer 3 may be formed by an LPCVD method or a sputtering method when the conductive substrate is a semiconductor substrate, or by performing an annealing process after forming an amorphous silicon film by a plasma CVD method. Thus, the film may be crystallized to form a film. When the conductive substrate is a glass substrate on which a conductive thin film is formed,
The amorphous silicon may be formed on the conductive thin film by the CVD method, and then the polysilicon layer may be formed by annealing with an excimer laser. Further, the method of forming a polysilicon layer on a conductive thin film is not limited to the CVD method. For example, a CGS (Continuous Grai
n Silicon) method or catalytic CVD method. Further, in this embodiment, the metal thin film is formed by vapor deposition, but the method of forming the metal thin film is not limited to vapor deposition, and for example, a sputtering method may be used.

After the non-doped polysilicon layer 3 is formed, a platinum electrode (not shown) is connected to a negative electrode using an electrolytic solution consisting of a mixture of a 55 wt% aqueous solution of hydrogen fluoride and ethanol at a ratio of about 1: 1. Using the n-type silicon substrate 1 (ohmic electrode 2) as a positive electrode, anodizing is performed at a constant current while irradiating the polysilicon layer 3 with light. Here, the anodic oxidation treatment was performed in the following procedure. The anodizing treatment conditions were the first condition that the current density was constant at ^2.5 mA / cm ² and the anodizing time was 4 seconds.
A / cm ² constant and anodizing time of 5 seconds were set as the second condition, and as shown in FIG. 4, the anodizing process under the first condition and the anodizing process under the second condition were performed. Was alternately repeated three times. However, during the anodization, the surface was irradiated with light by a 500 W tungsten lamp.
Here, when the anodic oxidation under the first condition is completed,
A porous polysilicon layer 4a having a low porosity (hereinafter referred to as a PPS layer 4a) is formed on the surface side of the polysilicon layer 3, and a structure as shown in FIG. 2B is obtained. Then the second
When the anodic oxidation under the conditions of the above is completed, the PP is placed closer to the n-type silicon substrate 1 than the porous polysilicon layer 4a.
Porous polysilicon layer 4b having higher porosity than S layer 4a
(Hereinafter, referred to as PPS layer 4b) is formed, and a structure as shown in FIG. 2C is obtained. However, at the time when the anodic oxidation under the first condition and the second condition is completed three times, P
FIG. 3 in which PS layers 4a and PPS layers 4b are alternately stacked
The structure shown in (a) is obtained. In the present embodiment,
The thickness of the porous polysilicon layer having a laminated structure of the PPS layer 4a and the PPS layer 4b was approximately 1 μm. In this embodiment, a part of the polysilicon layer 3 is made porous, but the entire polysilicon layer 3 may be made porous.

Next, rapid thermal oxidation (RTO: Rapid Therm)
al Oxidation) technology (rapid heating method)
By performing rapid thermal oxidation of the PS layers 4a and 4b and the polysilicon layer 3, the structure shown in FIG. 3B is obtained. Here, in FIG. 3B, reference numeral 5 denotes a rapidly thermally oxidized polysilicon layer, and reference numeral 6a denotes a low-porosity rapidly thermally oxidized porous polysilicon layer (hereinafter referred to as an RTO-PPS layer 6a).
6b indicates a porous polysilicon layer having high porosity and rapid thermal oxidation (hereinafter, referred to as an RTO-PPS layer 6b). As a condition of the rapid heating method, a lamp annealing apparatus is used, and the oxidation temperature is set to 800 ° C. to 900
C. and the oxidation time was 30 minutes to 120 minutes. In this embodiment, since the PPS layers 4a and 4b and the polysilicon layer 3 are oxidized by rapid thermal oxidation, the temperature can be raised to the oxidation temperature in a few seconds. Entrapment oxidation at the time of furnace entry, which is a problem in the apparatus, can be suppressed.

Thereafter, a gold thin film 7 as a metal thin film is formed on the uppermost RTO-PPS layer 6a by, for example, vapor deposition to obtain the field emission type electron source 10 having the structure shown in FIG. Here, in the present embodiment, the thickness of the gold thin film 7 is set to approximately 10 nm, but this thickness is not particularly limited. The field emission electron source 10 has a diode in which the gold thin film 7 is used as a positive electrode (anode) of the electrode and the ohmic electrode 2 is used as a negative electrode (cathode). Further, in the present embodiment, the metal thin film is formed by vapor deposition.
The method of forming the metal thin film is not limited to vapor deposition,
For example, a sputtering method may be used.

Hereinafter, the characteristics of the field emission type electron source 10 manufactured by setting the oxidation time by the rapid heating method to 60 minutes will be described.

The above-mentioned field emission type electron source 10 is introduced into a vacuum chamber (not shown), and a collector electrode 21 (radiation electron collection electrode) is arranged at a position facing the gold thin film 7 as shown in FIG. And reduce the degree of vacuum in the vacuum chamber to about 5 × 10 ^−5.
As Pa, a DC voltage Vps is applied between the gold thin film 7 and the ohmic electrode 2, and a DC voltage Vc is applied between the collector electrode 21 and the gold thin film 7. Between the collector electrode 21 and the gold thin film 7 due to the diode current Ips flowing between the collector electrode 21 and the electron e ⁻ (the dashed line in FIG. 5 indicates the emitted electron flow) emitted from the field emission type electron source 10 through the gold thin film 7. FIG. 6 shows the result of measurement of the emission electron current Ie flowing between. Here, the gold thin film 7 is connected to the ohmic electrode 2 (that is, n
A DC voltage Vps is applied as a positive electrode to the silicon substrate 1), and a DC voltage Vc is applied to the collector electrode 21 as a positive electrode to the thin gold film 7.

The horizontal axis of FIG. 6 shows the value of the DC voltage Vps, and the vertical axis shows the current density.
ps, and b (●) in the figure indicates the emission electron current Ie. Note that the DC voltage Vc was kept constant at 100V.

As can be seen from FIG. 6, the emission electron current I
e is observed only when the DC voltage Vps is positive.
As the value of ps was increased, both the diode current Ips and the emission electron current Ie increased. For example, when the DC voltage Vps is 15 V, the current density of the diode current Ips is approximately 1 mA / cm ² , and the current density of the emission electron current Ie is approximately 4 μA.
/ Cm ² , and the value of the emission electron current Ie is determined by making the surface of a single-crystal silicon substrate porous as described in the conventional example, a field emission type electron source (JP-A-8-2507).
For example, according to ED96-141, P41-46 of the Institute of Electronics, Information and Communication Engineers, when the DC voltage Vps is 15 V, the current density of the diode current Ips is approximately 40 mA / cm. ^2. Emission electron current Ie
Is about 1 μA / cm ² ), indicating that the field emission electron source of the present embodiment has a high electron emission efficiency.

FIG. 7 shows data on the emission electron current Ie and the DC voltage Vps by Fowler-Nordhei.
The result of m (Fowler-Nordheim) plot is shown. From FIG. 7, since each data is on a straight line, it is inferred that this emission electron current Ie is a current due to emission of electrons based on the quantum tunnel effect.

FIG. 8 shows a field emission type electron source 10 according to this embodiment.
Is a graph showing the time-dependent changes of the diode current Ips and the emission electron current Ie of FIG. 3, where the horizontal axis represents time and the vertical axis represents current density.
B in the figure indicates the emission electron current Ie. In addition, FIG.
The results are obtained when the DC voltage Vps is constant at 21 V and the DC voltage Vc is constant at 100 V. As can be seen from FIG. 8, no popping phenomenon is observed in both the diode current Ips and the emission electron current Ie, and the diode current Ips and the emission electron current Ie can be maintained substantially constant over time. Such a stable characteristic of the emission electron current Ie with little change with time is a characteristic that cannot be obtained by a conventional MIM method or a field emission electron source realized by making the surface of a single crystal silicon substrate porous. And the characteristics obtained by employing the structure of the present invention.

Next, rapid thermal oxidation (RT)
The result of examining the dependence of the electron emission efficiency on the oxidation temperature (thermal oxidation temperature) with the oxidation time of O) set to 60 minutes and the DC voltage Vps fixed at 16 V will be described with reference to FIG. The horizontal axis in FIG. 9 is the thermal oxidation temperature, and the vertical axis is the electron emission efficiency (Ie / Ips × 100).
Is shown. As is clear from FIG.
By changing the electron emission efficiency by 100 ° C. in the range of 100 ° C. to 1000 ° C., the electron emission efficiency changes as the thermal oxidation temperature increases in the range of 600 ° C. to 900 ° C., but the electron emission efficiency increases at 1000 ° C. About 1% when the thermal oxidation temperature is 800 ° C. and 900 ° C., respectively.
It can be seen that a high electron emission efficiency is obtained.
This result is considered to be because, when the thermal oxidation temperature is increased to 1000 ° C., the grain size of the crystal grains (polycrystalline columns) constituting the thermally oxidized porous polysilicon layer 6 becomes too large. It is considered that when the oxidation temperature is lower than 800 ° C., the rate of thermal oxidation is reduced and thermal oxidation becomes insufficient. Therefore, the thermal oxidation temperature is 800 ° C.
To 900 ° C.

Next, regarding the thermal oxidation temperature of 900 ° C. at which the highest electron emission efficiency was obtained in FIG. 9 (that is, the thermal oxidation temperature was fixed at 900 ° C.), the dependence of the electron emission efficiency on the oxidation time with the DC voltage Vps was determined. The result of the examination will be described with reference to FIG. The horizontal axis in FIG. 10 shows the voltage Vps, and the vertical axis shows the electron emission efficiency (Ie / Ips × 100).
When the oxidation time was 10 minutes, ● was 30 minutes, Δ was 60 minutes, Δ was 90 minutes, Δ
Indicates a case of 120 minutes, and ▼ indicates a case of 180 minutes. As is clear from FIG. 10, the electron emission efficiency changes depending on the oxidation time.
It can be seen that a high electron emission efficiency of 1% is obtained when the voltage Vps is in the range of 10 V to 25 V by setting the time to 0 minute, 90 minutes, and 120 minutes. In particular, an oxidation time of 90
In this case, when the voltage Vps is 18 V, about 4
%, A very high electron emission efficiency was obtained. The electron emission efficiency of about 0.1% is obtained when the oxidation time is set to 10 minutes or 180 minutes. However, when the thermal oxidation temperature is 900 ° C., the oxidation time is set to 30 minutes. Or 1
Desirably, it is 20 minutes.

From the results of FIGS. 9 and 10 described above, in order to obtain an electron emission efficiency of about 1% or more, the oxidation temperature is set to 800 ° C. to 900 ° C. and the oxidation time is set to 30% in the oxidation by the rapid heating method. Minutes to 120 minutes.

In this embodiment, the n-type silicon substrate 1 ((100) substrate having a resistivity of about 0.1 Ωcm) is used as the conductive substrate, but the conductive substrate is limited to the n-type silicon substrate. Instead, for example, a transparent conductive thin film (for example, ITO: Indium) is formed on a metal substrate, a glass substrate, or the like.
A substrate on which a conductive film such as Tin Oxide or Platinum or Chromium is formed may be used, and the area and cost can be reduced as compared with the case where a semiconductor substrate such as an n-type silicon substrate is used.

[0030]

According to the first to third aspects of the present invention, there is provided a conductive substrate, an oxidized porous polysilicon layer formed on one surface side of the conductive substrate, and an upper surface of the porous polysilicon layer. A field emission type electron source that emits an electron beam through the metal thin film by applying a voltage with the metal thin film as a positive electrode to the conductive substrate, the method comprising: Form a polysilicon layer on top,
The polysilicon layer is porous, the polysilicon layer made porous is oxidized by rapid heating method using a lamp annealing apparatus, an electrode made of a thin metal film oxidized porous polysilicon layer This eliminates the need for complicated structures and manufacturing processes like conventional Spindt-type electrodes, and stably and efficiently emits electrons from the surface of the metal thin film in a direction almost perpendicular to the metal thin film by a relatively simple manufacturing process. It is possible to provide an inexpensive field emission type electron source and to provide a large area field emission type electron source. Therefore, in the display device using the field emission type electron source manufactured by the manufacturing method of the first aspect of the present invention, it is not necessary to provide an electron converging lens, and it is possible to easily realize a high definition and a large number of pixels of the display device. can do. Further, in the flat light emitting device using the field emission type electron source manufactured by the manufacturing method of the first aspect of the present invention, it is not necessary to provide a focusing electrode, so that the structure can be simplified and the thickness can be easily reduced. it can. Further, in a solid-state vacuum device using a field emission electron source manufactured by the manufacturing method of the first aspect of the invention as a cold cathode, a heating means is used as in a conventional solid-state vacuum device having a hot cathode utilizing thermionic emission. Since there is no need to provide such a structure, the size can be reduced, and the evaporation and deterioration of the cathode material can be suppressed, and the life can be extended.

[0031] The invention of claim 3 is claim 1 or claim 1.
In 2 of the invention, when the oxidation by rapid <br/> speed heating method using the above SL lamp annealing apparatus, to not 800 ° C. The oxidation temperature in dry燥酸Motochu 900 ° C., was 30 minutes to an oxidation time was 120 minutes Therefore, there is an effect that higher efficiency of electron emission can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment.

FIG. 2 is a main process sectional view for explaining the manufacturing process of the above.

FIG. 3 is a cross-sectional view showing main processes for describing a manufacturing process of the above.

FIG. 4 is an explanatory diagram of conditions for anodizing treatment in the above.

FIG. 5 is an explanatory diagram of a principle of measuring emitted electrons according to the embodiment.

FIG. 6 is a voltage-current characteristic diagram of the above.

FIG. 7 shows the data of FIG. 5 as Fowler-Nordhei.
It is a graph which plotted m.

FIG. 8 is a graph showing a temporal change of the current in the above.

FIG. 9 is a graph showing the dependence of electron emission efficiency on the oxidation temperature.

FIG. 10 is a graph showing voltage dependence of electron emission efficiency with the oxidation time as a parameter.

[Explanation of symbols]

 Reference Signs List 1 n-type silicon substrate 2 ohmic electrode 5 rapidly thermally oxidized polysilicon layer 6 rapidly thermally oxidized porous polysilicon layer 7 gold thin film 10 field emission electron source

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-10-269932 (JP, A) JP-A-10-312740 (JP, A) JP-A-9-259795 (JP, A) 59th Applied Physics Proceedings 17a-A-9 (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01J 1/30 H01J 9/02 H01J 31/12 H01L 33/00

Claims (3)

(57) [Claims] A conductive substrate, an oxidized porous polysilicon layer formed on one surface side of the conductive substrate, and a metal thin film formed on the porous polysilicon layer;
A method for manufacturing a field emission type electron source that emits an electron beam through a metal thin film by applying a voltage with the metal thin film as a positive electrode to a conductive substrate, comprising forming a polysilicon layer on the conductive substrate, The silicon layer is made porous, and the porous polysilicon layer is made using a lamp annealing device.
It was oxidized by rapid heating method, oxidized method of manufacturing a field emission electron source, which comprises forming a porous polysilicon formed of a metal thin film on the layer electrode. 2. The porous polysilicon layer,
Layers with different porosity alternate in the thickness direction of conductive substrate
2. The method for manufacturing a field emission electron source according to claim 1, wherein the layers are stacked . 3. A rapid heating method using the lamp annealing apparatus.
When oxidizing by the thermal method, the oxidation temperature is set in dry oxygen.
800 ° C to 900 ° C, oxidation time 30 minutes to 12
3. The method according to claim 1, wherein the time is 0 minutes.
Of manufacturing the field emission type electron source described above.