JP2002008527A - Field radiation type electron source and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a field radiation electron source that has a high electron emission efficiency and little changes by the lapse of time of its electron emission efficiency and its manufacturing method. SOLUTION: The intense-field drift layer 6 is formed after the surface of multi-crystal silicon which is formed on the n-type silicon substrate 1 is made porous by the positive electrode oxidization treatment, and then oxidized electrochemically in the electrolyte. In the oxidization process, the counter electrode is made negative electrode and the n-type silicon substrate 1 (ohmic electrode) is made positive electrode and electric current is conducted between the positive electrode and the negative electrode. In this current conduction, firstly, electric current of a constant formation current density is flown continuously and after the voltage between the positive electrode and the negative electrode has increased by a specified amount, the voltage between the positive electrode and the negative electrode is maintained at the increased voltage, and when the formation current density has decreased to the prescribed value, the electric current conduction is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[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, the Spindt-type electrode needs to be used in a high vacuum (about 10 ^-5 Pa to about 10 ^-6 Pa) in order to prevent such a problem from occurring, which increases the cost and complicates handling. There was a problem.

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. H10-260, a porous semiconductor layer (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 electron source (semiconductor cold electron emission device) has been proposed in which a metal thin film is formed on a porous semiconductor layer, and a voltage is applied between the semiconductor substrate and the metal thin film to emit electrons. I have.

[0006] However, the above-mentioned Japanese Patent Application Laid-Open No. Hei 8-2507 has been disclosed.
In the field emission electron source described in Japanese Patent Publication No. 66, since the substrate is limited to a semiconductor substrate, there is a problem that it is difficult to increase the area and reduce the cost. In addition, Japanese Patent Application Laid-Open No. 8-25076
In the field emission type electron source described in Japanese Patent Application Publication No. 6 (1995) -76, a so-called popping phenomenon easily occurs during electron emission, and the amount of emitted electrons tends to be uneven. There is.

Therefore, the present inventors have filed Japanese Patent Application No. Hei.
No. 72340, Japanese Patent Application No. 10-272342, Japanese Patent Application No. 1
No. 0-271876, a porous polycrystalline silicon layer which is a porous layer is oxidized by a rapid thermal oxidation (Rapid Thermal Oxidation (RTO) technique) to form a conductive substrate (for example, metal). A field emission type electron source was proposed, in which a strong electric field drift layer was formed between the thin film and the conductive thin film and in which electrons injected from the conductive substrate drifted.

An example of a method for manufacturing the field emission type electron source 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 polycrystalline silicon layer 3 having a thickness of about 1.5 μm is formed on the surface of the n-type silicon substrate 1.
Is formed by the LPCVD method to form FIG.
A structure as shown in FIG.

After the non-doped polycrystalline silicon layer 3 is formed, an anodizing tank containing an electrolytic solution comprising a mixture of a 55 wt% aqueous solution of hydrogen fluoride and ethanol in a ratio of about 1: 1 is used. A platinum electrode (not shown) is connected to the negative electrode, n
Type silicon substrate 1 (ohmic electrode 2) as a positive electrode
By performing anodic oxidation at a constant current while irradiating the polycrystalline silicon layer 3 with light, a porous polycrystalline silicon layer 4 is formed, and a structure as shown in FIG. 11B is obtained.

Next, the porous polycrystalline silicon layer 4 is oxidized by a rapid thermal oxidation method to form a strong electric field drift layer 6 ', and a structure as shown in FIG. 11C is obtained. The conditions for oxidizing the porous polycrystalline silicon layer 4 by the rapid thermal oxidation method are as follows: a lamp annealing apparatus is used, and the oxidation temperature is set to 800 ° C. to 90 ° C. in dry oxygen.
Oxidation time is set within the temperature range of 0 ° C. and the oxidation time is 30 minutes to 120 minutes.
Set within minutes.

After forming the strong electric field drift layer 6 ', a conductive thin film 7 made of a gold thin film is formed on the strong electric field drift layer 6' by a vapor deposition method, so that the electric field emission of the structure shown in FIG. A type electron source 10 "is obtained.

In the field emission type electron source 10 ″, the electron emission characteristics have a small dependence on the degree of vacuum, and electrons can be stably emitted without generating a popping phenomenon during electron emission. In addition to a semiconductor substrate such as a single crystal silicon substrate, a conductive film (eg,
Since it is possible to use a substrate on which an ITO film is formed, a larger area of the electron source can be achieved compared with a conventional case where a porous semiconductor layer in which a semiconductor substrate is made porous or a Spindt-type electrode is used. Cost reduction becomes possible. When a display device is configured using such a field emission electron source, it is necessary to pattern a metal thin film into a predetermined shape.

By the way, the above-mentioned strong electric field drift layer 6 '
As shown in FIG. 12, at least a columnar polycrystalline silicon (grain) 61, a thin silicon oxide film 62 formed on the surface of the polycrystalline silicon 61, and a nanometer order It is considered to be composed of a microcrystalline silicon layer 63 and a silicon oxide film 64 formed on the surface of the microcrystalline silicon layer 63 and having a thickness smaller than the crystal grain size of the microcrystalline silicon layer 63. . That is, it is considered that the strong electric field drift layer 6 'has a porous surface at each grain and maintains a crystalline state at the center of each grain. Therefore, most of the electric field applied to the strong electric field drift layer 6 ′ is applied to the silicon oxide film 64, and the injected electrons are accelerated by the strong electric field applied to the silicon oxide film 64 and travel between the polysilicon 61 toward the surface. 12 (in the upward direction in FIG. 12), the electron emission efficiency can be improved.

However, the aforementioned Japanese Patent Application No. 10-272 is disclosed.
340, Japanese Patent Application No. 10-272342, Japanese Patent Application No. 10-272
In the field emission type electron source proposed in 271876, the oxidation temperature of rapid thermal oxidation cannot be increased to a temperature higher than the allowable temperature limit of the conductive substrate.
There is a problem that the material of the ITO film is limited, and the increase in the diameter (larger area) of the substrate is restricted.

In addition, the porous semiconductor layer (porous polycrystalline silicon layer or porous silicon layer) formed by the anodic oxidation treatment as described above is used as an electrolyte in the anodic oxidation treatment with a hydrogen fluoride aqueous solution and ethanol. Is used, the silicon atoms are terminated by hydrogen atoms. For this reason, the above-mentioned Japanese Patent Application No. 10-2723 is disclosed.
No. 40, Japanese Patent Application No. 10-272342, Japanese Patent Application No. 10-2
When an oxide film is grown by performing rapid thermal oxidation on a porous semiconductor layer formed by anodic oxidation treatment as disclosed in Japanese Patent No. 71876, hydrogen atoms may remain in the oxide film or Si-OH bonds may occur. As a result, there is a problem that a dense oxide film having a structure of SiO ₂ is hardly formed and the withstand voltage is lowered. In addition, the content of hydrogen in the strong electric field drift layer becomes relatively large, and the distribution of hydrogen in the strong electric field drift layer changes with time (for example, hydrogen atoms are desorbed from the surface of the strong electric field drift layer). In addition, there is a possibility that the stability of electron emission efficiency over time is deteriorated.

Also, the aforementioned Japanese Patent Application No. 10-272340.
No., Japanese Patent Application No. 10-272342, Japanese Patent Application No. 10-271
In the field emission type electron source proposed in US Pat.
Although the cost can be reduced and the electrons can be stably emitted with high efficiency as compared with the field emission type electron source disclosed in Japanese Patent No. 250766, it is desired to further increase the electron emission efficiency. It is rare.

Therefore, in the manufacturing method described with reference to FIG. 11, instead of oxidizing the porous polycrystalline silicon layer 4 by a rapid thermal oxidation method, the porous polycrystalline silicon layer 4 is electrochemically immersed in an electrolyte solution. It has been proposed to oxidatively oxidize. In this oxidation, an acid (for example, approximately 10% diluted nitric acid) is used as an electrolyte solution, and a porous polycrystalline silicon layer is formed using a platinum electrode (not shown) as a negative electrode and an n-type silicon substrate 1 (ohmic electrode 2) as a positive electrode. 4 is oxidized. However, in this oxidation, a current is caused to flow at a constant formation current density between the positive electrode and the negative electrode, and the current is stopped when the voltage between the positive electrode and the negative electrode rises to a predetermined voltage.

As described above, by oxidizing the porous polycrystalline silicon layer 4 electrochemically in an electrolyte solution,
The porous polycrystalline silicon layer 4 is oxidized by a rapid thermal oxidation method to form a strong electric field drift layer (the inventors of the present invention disclosed in Japanese Patent Application Nos. 10-272340 and 10-272342;
The process temperature is lower than that in the case proposed in Japanese Patent Application No. 10-271876), the restriction on the material of the conductive substrate is reduced, and the field emission type electron can be made large in area and low in cost. Sources can be provided. In addition, since the porous polycrystalline silicon layer 4 can be oxidized by wet processing subsequent to the anodic oxidation processing, the process can be simplified as compared with the case where oxidation is performed by rapid thermal oxidation after the anodic oxidation processing.

By the way, when the porous polycrystalline silicon layer 4 is oxidized with diluted nitric acid as described above, if the holes are h ⁺ and the electrons are e ⁻ , the following reactions are considered to have occurred. Negative electrode side: HNO ₃ + 3H ⁺ → NO + 2H ₂ O
+ 3h ⁺ positive electrode side: 3h ⁺ + Si + 2H ₂ O → SiO ₂ + 4H
⁺ + E ^- The process in which the strong electric field drift layer 6 is formed by this reaction will be described with reference to the schematic diagram shown in FIG. 13. When the above reaction occurs, the porous polycrystalline silicon layer 4 as shown in FIG. The generated holes h ⁺ move to the surface of the polycrystalline silicon 61 of the porous polycrystalline silicon layer 4 (that is, the inner surfaces of the fine holes formed in the porous polycrystalline silicon layer 4), and FIG. Silicon oxide film 6 as thin as
2 are formed, and the surface of the polycrystalline silicon 61 is covered with the thin silicon oxide film 62 as shown in FIG.

[0021]

However, when the porous polycrystalline silicon layer 4 is electrochemically oxidized in an electrolyte solution as described above, the conductive substrate is moved from the side closer to the conductive substrate in the thickness direction. Oxidation proceeds to the far side (oxidation progresses from the lower side to the upper side in FIG. 13A), so that a current flows at a constant formation current density and the voltage between the positive electrode and the negative electrode becomes a predetermined voltage. When the power supply is stopped at the time of rising, the oxide layer (silicon oxide layer) formed on the side farther from the conductive substrate than the oxide layer (silicon oxide films 62 and 64) formed on the side closer to the conductive substrate. Oxide films 62, 6
4) the film thickness is too thin or insufficiently dense,
It was difficult to form a dense oxide layer over the entire region of the strong electric field drift layer 6. For this reason, in the field emission type electron source manufactured by this manufacturing method, the energy of the drifting electrons is reduced due to scattering in an oxide layer having poor density, and sufficient electron emission efficiency cannot be obtained. Insufficient withstand voltage could be obtained due to the defect described above and the presence of an oxide layer having poor density, and there was a possibility that the stability over time would be deteriorated.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a field emission electron source having a high electron emission efficiency and a small change with time in the electron emission efficiency, and a method of manufacturing the same. .

[0023]

According to the first aspect of the present invention, there is provided a conductive substrate, a strong electric field drift layer formed on one surface side of the conductive substrate, and the strong electric field drift layer. A conductive thin film formed on the layer, and the electron injected from the conductive substrate drifts through the strong electric field drift layer by applying a voltage with the conductive thin film as a positive electrode with respect to the conductive substrate. A field emission type electron source emitted through the substrate, wherein the strong electric field drift layer includes a oxidizing step of forming an oxide layer by arranging a porous semiconductor layer to face a counter electrode in an electrolytic solution and flowing a current. In the oxidation step, the voltage between the conductive substrate and the counter electrode increases after the voltage between the conductive substrate and the counter electrode increases by a specified amount while the current continues to flow at a constant formation current density. Keeping the voltage at the later It is characterized in that the current is stopped when the flow density decreases to a predetermined value, and the strong electric field drift layer is formed by arranging the porous semiconductor layer in the electrolytic solution so as to face the counter electrode and flowing a current. Formed by a process including an oxidation step of forming an oxide layer, wherein the oxidation step
After the current continues to flow at a constant formation current density and the voltage between the conductive substrate and the counter electrode increases by a specified amount, the formation current is maintained by maintaining the voltage between the conductive substrate and the counter electrode at the increased voltage. When the density decreases to the specified value, the current is stopped, so
The process temperature is lower than in the case of forming a strong electric field drift layer by oxidizing the porous semiconductor layer only by the rapid thermal oxidation method, and the restriction of the conductive substrate is reduced, and the area and cost are reduced. It becomes easier, and the denseness of the oxide layer formed in the strong electric field drift layer is improved, so that energy loss due to scattering in the oxide layer is reduced, the electron emission efficiency is improved, and the withstand voltage is further improved. As a result, the stability of electron emission efficiency over time is improved.

According to a second aspect of the present invention, in the first aspect of the present invention, since the electrolytic solution is composed of an organic solvent and an electrolytic solution, the amount of gas generated during chemical formation is extremely small, and the pin caused by the gas is reduced. Since the generation of holes and the like is reduced and a more stable oxide layer can be formed, the stability over time is further improved.

According to a third aspect of the present invention, in the first or second aspect of the present invention, since the salt of the electrolyte solution is an organic salt, an alkali metal or the like contained in the salt is formed as a residue as a strong electric field drift layer. The alkali metal does not remain in the conductive layer and does not diffuse into the oxide layer when a voltage is applied between the conductive substrate and the conductive thin film. In addition, the stability over time is further improved.

According to a fourth aspect of the present invention, in the first to third aspects of the present invention, since the pH of the electrolytic solution is in the range of 6 to 8, a conductive material is provided on one surface of the insulating substrate as the conductive substrate. In the case where a conductive layer is formed, the conductive layer can be prevented from being corroded by the electrolytic solution, and the yield can be improved.

According to a fifth aspect of the present invention, in the first to fourth aspects of the present invention, since the porous semiconductor layer has a substantially uniform in-plane thickness of the porous region, the conductive thin film can be electrically conductive. When a voltage is applied as a positive electrode to the conductive substrate, the electric field acts almost uniformly on the porous region, so that the equipotential surface in the strong electric field drift layer becomes almost parallel to the conductive substrate, and Variations in the emission direction and unevenness in the amount of emitted electrons can be reduced.

According to a sixth aspect of the present invention, in the first to fifth aspects of the present invention, since the porous semiconductor layer is made of porous polycrystalline silicon, the dependence of the electron emission characteristics on the degree of vacuum is small and the electron emission characteristics are small. Occasionally, electrons can be stably emitted with high efficiency without occurrence of a popping phenomenon.

According to a seventh aspect of the present invention, there is provided a conductive substrate comprising: a conductive substrate; a strong electric field drift layer formed on one surface side of the conductive substrate; and a conductive thin film formed on the strong electric field drift layer. A method for manufacturing a field emission type electron source in which electrons injected from a conductive substrate are drifted through a strong electric field drift layer and emitted through the conductive thin film by applying a voltage with the conductive thin film as a positive electrode to a conductive substrate. In forming the strong electric field drift layer, an oxide layer is formed by arranging a porous semiconductor layer formed on one surface side of the conductive substrate so as to face a counter electrode in an electrolytic solution and flowing a current. An oxidation step is provided, wherein the oxidation step continues to flow a current at a constant formation current density, and after the voltage between the conductive substrate and the counter electrode increases by a specified amount, increases the voltage between the conductive substrate and the counter electrode. Maintain at increased voltage The method is characterized in that the current is stopped when the current density decreases to a predetermined value, and the process temperature is lower than in the case where the porous semiconductor layer is oxidized only by the rapid thermal oxidation method to form a strong electric field drift layer. Therefore, the restriction on the conductive substrate is reduced, the area and the cost are easily reduced, and the density of the oxide layer formed in the strong electric field drift layer is improved. It is possible to provide a field emission type electron source in which the emission efficiency has little change with time.

According to an eighth aspect of the present invention, in the invention of the seventh aspect, since the electrolytic solution is composed of an organic solvent and an electrolytic solution, the amount of gas generated during chemical formation is very small, and Since generation of holes and the like is reduced and a more stable oxide layer can be formed, a field emission electron source with further improved temporal stability can be provided.

According to a ninth aspect of the present invention, in the invention of the seventh or eighth aspect, since the salt of the electrolyte solution is an organic salt, the alkali metal or the like contained in the salt is formed as a residue as a strong electric field drift layer. Since it does not remain in the inside, it is possible to provide a field emission type electron source with further improved temporal stability.

According to a tenth aspect of the present invention, in the invention of the seventh to ninth aspects, since the pH of the electrolytic solution is in the range of 6 to 8, a conductive material is provided on one surface of the insulating substrate as the conductive substrate. When the conductive layer is formed, the conductive layer can be prevented from being corroded by the electrolytic solution, and the yield can be improved, so that the cost can be reduced.

According to an eleventh aspect of the present invention, in the method of the seventh to tenth aspects, when forming the porous semiconductor layer, the porous semiconductor layer is formed such that the thickness of a region to be made porous is substantially uniform. Since an anodic oxidation process step of forming a layer is provided, the thickness of the porous region of the porous semiconductor layer becomes substantially uniform, and the oxidation by the oxidation process proceeds almost uniformly in the plane. Are hardly left, and a field emission type electron source with further improved stability over time can be provided.

According to a twelfth aspect of the present invention, in accordance with the seventh to eleventh aspects of the present invention, since the porous semiconductor layer is made of porous polycrystalline silicon, the strong electric field drift layer is made of Si.
Provided is a field emission type electron source having an oxide film having a high density close to the structure of O2 or SiO2, improving the density and film quality of the oxide film, and improving the electron emission efficiency and the withstand voltage. can do.

[0035]

FIG. 1 is a schematic sectional view of a field emission type electron source 10 according to this embodiment, and FIGS. 2 (a) to 2 (d) are sectional views showing main steps in a method of manufacturing the field emission type electron source 10. Is shown. In this embodiment, a single-crystal n-type silicon substrate 1 having a resistivity relatively close to that of a conductor is used as a conductive substrate.
((100) substrate having a resistivity of about 0.1 Ωcm) is used.

In the field emission type electron source 10 of the present embodiment, as shown in FIG. 1, a non-doped polycrystalline silicon layer 3 is formed on the main surface of an n-type silicon substrate 1. A strong electric field drift layer 6 is formed, and a conductive thin film 7 made of a gold thin film is formed on the strong electric field drift layer 6. An ohmic electrode 2 is formed on the back surface of the n-type silicon substrate 1.

In this 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 has the above-mentioned strong electric field drift in vacuum. It supports the layer 6 and injects electrons into the strong electric field drift layer 6. Therefore, the conductive substrate is used for the field emission type electron source 10.
7 is not limited to the n-type silicon substrate, and may be a metal substrate such as chromium, as shown in FIG.
As shown in FIG. 1, a conductive layer (for example, IT
(O film) 12 may be formed. When a substrate having the conductive layer 12 formed on one surface of the insulating substrate 11 is used, compared with a case where a semiconductor substrate is used,
The area and cost of the electron source can be reduced.

The above-mentioned strong electric field drift layer 6 is formed by electrochemically oxidizing porous polycrystalline silicon in an electrolytic solution described later. This is a layer into which electrons are injected when a voltage is applied between them. The strong electric field drift layer 6 is a polycrystalline body composed of a large number of grains, and each grain has a structure having an oxide film on a nanometer unit (hereinafter, referred to as a nanostructure). In order for electrons injected into the strong electric field drift layer 6 to reach the surface of the strong electric field drift layer 6 without colliding with the nanostructure (that is, without electron scattering), the size of the nanostructure must be a single crystal. It must be smaller than about 50 nm, the mean free path of electrons in silicon. Specifically, the size of the nanostructure is preferably smaller than 10 nm, and more preferably smaller than 5 nm.

In this embodiment, a gold thin film is used as the conductive thin film 7. The conductive thin film 7 constitutes the positive electrode of the field emission type electron source 10 and has a strong electric field drift layer 6. To apply an electric field. The electrons that reach the surface of the strong electric field drift layer 6 by the application of the electric field are emitted from the surface of the conductive thin film 7 by a tunnel effect. Therefore, the energy obtained by subtracting the work function of the conductive thin film 7 from the energy of the electron obtained by the DC voltage applied between the conductive substrate and the conductive thin film 7 becomes the ideal energy of the emitted electrons. It is desirable that the work function of the conductive thin film 7 be as small as possible. In the present embodiment, gold is used as the material of the conductive thin film 7. However, the material of the conductive thin film 7 is not limited to gold, and may be any material having a small work function. ,
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.

Although the conductive thin film 7 is a single layer of a gold thin film, it may be composed of at least two thin film layers stacked in the thickness direction. When the conductive thin film 7 is composed of two thin film layers, for example, gold or the like can be used as the material of the upper thin film layer. Further, as a material of the lower thin film layer (the thin film layer on the strong electric field drift layer 6 side), for example, chromium, nickel, platinum, titanium, iridium and the like can be used.

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

First, after an ohmic electrode 2 is formed on the back surface of the n-type silicon substrate 1, a non-doped polycrystalline silicon layer 3 having a thickness of about 1.5 μm is formed on the surface of the n-type silicon substrate 1.
Is formed, a structure as shown in FIG. 2A is obtained. The polycrystalline silicon layer 3 is formed by the LPCVD method under the conditions of a vacuum of 20 Pa, a substrate temperature of 640 ° C., and a monosilane gas flow rate of 0.6 L under standard conditions.
/ Min (600 sccm). Note that the polycrystalline silicon layer 3 may be formed by a 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. Crystallization may be performed to form a film. In addition, when the conductive substrate is a substrate in which a conductive thin film is formed on a glass substrate, a polycrystalline silicon layer is formed by forming an amorphous silicon film on the conductive thin film by a CVD method and then annealing with an excimer laser. May be. Further, the method of forming a polycrystalline silicon layer on a conductive thin film is not limited to the CVD method. For example, CGS (Continuous Grain Silicon)
Alternatively, a catalytic CVD method or the like may be used.

After the non-doped polycrystalline silicon layer 3 is formed, an anodizing tank containing an electrolytic solution comprising a mixture of a 55 wt% aqueous solution of hydrogen fluoride and ethanol in a ratio of about 1: 1 is used. A platinum electrode (not shown) is connected to the negative electrode, n
Type silicon substrate 1 (ohmic electrode 2) as a positive electrode
By performing anodic oxidation at a constant current while irradiating the polycrystalline silicon layer 3 with light, a porous polycrystalline silicon layer 4 is formed, and a structure as shown in FIG. 2B is obtained.
In this embodiment, the conditions of the anodic oxidation treatment are as follows: the current density is constant at 10 mA / cm ² , the anodic oxidation time is 30 seconds, and the surface of the polycrystalline silicon layer 3 is anodically oxidized by a 500 W tungsten lamp. Light irradiation was performed. As a result, in the present embodiment, a porous polycrystalline silicon layer 4 having a thickness of about 1 μm was formed. In the present embodiment, a part of the polycrystalline silicon layer 3 is made porous, but the entire polycrystalline silicon layer 3 may be made porous.

After the above-described anodic oxidation treatment is completed, cleaning is performed, and then the porous polycrystalline silicon layer 4 is electrochemically oxidized in an electrolytic solution to form a strong electric field drift layer 6. The structure shown in FIG. 2C is obtained. This oxidation step is performed using the apparatus shown in FIG. That is, a 9: 1 mixture of ethylene glycol as an organic solvent and a 3% aqueous solution of ammonium tartrate as an electrolyte solution was mixed.
The object 30 on which the porous polycrystalline silicon layer 4 is formed is put into a processing tank 31 containing an electrolyte solution having an H of about 7, and the porous polycrystalline silicon layer 4 is arranged to face the counter electrode 33 which is a platinum electrode. Then, a current is applied between the positive electrode and the negative electrode, with the counter electrode 33 serving as the negative electrode and the n-type silicon substrate 1 (the ohmic electrode 2) serving as the positive electrode. In this energization, first, a current having a constant formation current density is kept flowing, and after the voltage between the positive electrode and the negative electrode has increased by a specified amount, the voltage between the positive electrode and the negative electrode is maintained at the increased voltage. When the current density decreases to a predetermined value, the energization is stopped. That is, in this oxidation step, the formation current density changes as shown by the solid line in FIG. 4 with the passage of time from the start of energization, and the voltage between the positive electrode and the negative electrode becomes one point in FIG. It changes as shown by the chain line. The energization pattern between the positive and negative electrodes is a galvanostat 36
Is controlled by In the present embodiment, the constant formation current density is set to ^2.5 mA / cm ^2, and the voltage between the positive electrode and the negative electrode is increased by a specified amount to 20 V. Was stopped at a point of time when the formation current density was reduced to 0.01 mA / cm ² while maintaining the voltage at 20 V. In this oxidation step, it is desirable to control the temperature of the electrolytic solution by placing the treatment tank 31 in a constant temperature water tank 32.

As shown in FIG. 5, the strong electric field drift layer 6 has at least a columnar polycrystalline silicon 61.
(Grain), a thin silicon oxide film 62 formed on the surface of the polycrystalline silicon 61, a microcrystalline silicon layer 63 interposed between the columnar polycrystalline silicons, and silicon formed on the surface of the microcrystalline silicon layer 63. It is considered to be composed of the oxide film 64.

After the strong electric field drift layer 6 is formed, a conductive thin film 7 made of a gold thin film is formed on the strong electric field drift layer 6 by, for example, vapor deposition to obtain a structure shown in FIG. 2D (FIG. 1). Is obtained. Here, in the present embodiment, the thickness of the conductive thin film 7 is set to about 10 n.
m, but this film thickness is not particularly limited. The field emission electron source 10 has a diode in which the conductive 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). In the present embodiment, the conductive thin film 7 is formed by vapor deposition, but the method of forming the conductive thin film 7 is not limited to vapor deposition.
For example, a sputtering method may be used.

In the field emission type electron source 10 of this embodiment,
It is considered that electron emission occurs in the following model. That is, as shown in FIG. 6, a collector electrode 21 is arranged at a position facing the conductive thin film 7, and a DC voltage Vps is applied between the conductive thin film 7 and the ohmic electrode 2;
DC voltage Vc between collector electrode 21 and conductive thin film 7
When the DC voltage applied to the conductive thin film 7 as a positive electrode with respect to the n-type silicon substrate 1 reaches a predetermined value (critical value), heat is applied to the strong electric field drift layer 6 from the n-type silicon substrate 1 side. Electrons e ^- are injected by the mechanical excitation. On the other hand, since the electric field applied to the strong electric field drift layer 6 is almost applied to the silicon oxide film 64 (see FIG. 5), the injected electrons are accelerated by the strong electric field applied to the silicon oxide film 64, and 6 drifts toward the surface in the direction of arrow A in FIG. 5 (toward the upward direction in FIG. 5), through the oxide layer on the outermost surface of the strong electric field drift layer 6. Then, the conductive thin film 7 is tunneled and released into a vacuum.

The field emission electron source manufactured by the above-described manufacturing method is disclosed by the present inventors in Japanese Patent Application No. 10-272340,
Japanese Patent Application No. 10-272342, Japanese Patent Application No. 10-27187
As in the field emission type electron source proposed in No. 6, the electron emission characteristic has a small dependence on the degree of vacuum and can stably emit electrons without popping phenomenon at the time of electron emission. In addition to a semiconductor substrate such as a single crystal silicon substrate, a conductive film (for example, ITO
It is possible to use a substrate on which a film has been formed.
Compared with the Spindt-type electrode, the area of the electron source can be increased and the cost can be reduced.

In the present embodiment, the strong electric field drift layer 6 is formed by an oxidizing step of forming an oxide layer by arranging the porous polycrystalline silicon layer 4 so as to face a counter electrode in an electrolytic solution and flowing a current. Therefore, the porous polycrystalline silicon layer 4 is oxidized by a rapid thermal oxidation method to form a strong electric field drift layer (the present inventors have filed Japanese Patent Application No. 10-272340).
No., Japanese Patent Application No. 10-272342, Japanese Patent Application No. 10-271
876), the process temperature is lower than in the case described above, the material of the conductive substrate is less restricted,
It is possible to provide a field emission type electron source capable of increasing the area and reducing the cost. In addition, since the porous polycrystalline silicon layer 4 can be oxidized by wet processing subsequent to the anodic oxidation processing, the process can be simplified as compared with the case where oxidation is performed by rapid thermal oxidation after the anodic oxidation processing.

Further, in the oxidizing step, the voltage between the conductive substrate and the counter electrode is increased after the voltage between the conductive substrate and the counter electrode increases by a specified amount while the current continues to flow at a constant formation current density. Since the current is stopped when the formation current density decreases to a predetermined value while maintaining the voltage after the increase, the oxide layer (silicon oxide films 62, 6) formed in the strong electric field drift layer 6
Since the denseness of 4) is improved (dense SiO ₂ is formed), energy loss due to scattering or the like in the oxide layer (silicon oxide film 64) is reduced, and the electron emission efficiency is improved. And the temporal stability of the electron emission efficiency is improved.

By the way, the pH of the above-mentioned electrolyte is not limited to 7, but if it is in the range of 6 to 8, a conductive layer is provided on one surface of the insulating substrate 11 such as a glass substrate. In the case where the conductive layer 12 is formed, the conductive layer 12 can be prevented from being corroded by the electrolytic solution, and the yield can be improved.

The organic solvent is not limited to the above-mentioned ethylene glycol, but may be one or more of ethylene glycol, γ-butyl lactone, methoxyethanol, glycerin, polyethylene glycol, polycarbonate and dimethylformamide. May be used. Further, an organic salt which is a compound of another organic acid and ammonia may be used as the electrolyte solution,
Examples of the organic acid include carbonic acid, oxalic acid, malonic acid,
It may be selected from saturated or unsaturated fatty acids such as adipic acid, caprylic acid, pelargonic acid, palmitic acid, and oleic acid. The pH of the electrolyte solution is adjusted to 6 to 8 with an aqueous ammonium solution. In addition, it is also possible to use a potassium salt or a sodium salt in addition to the ammonium salt. The mixing ratio between the organic solvent and the electrolyte solution is not limited to the above ratio, and the ratio between the organic solvent and the electrolyte solution may be appropriately selected in the range of 5: 5 to 100: 1. The formation current density is 0.01 to 100 m.
It may be appropriately selected in the range of A / cm ^2, anodizing current density when stopping the energization may be suitably set in the range of from 50 to 0.001% for a fixed anodizing current density immediately after the start of energization.

When the solvent of the electrolytic solution is composed of an organic solvent, the amount of gas generated during chemical formation is very small, the generation of pinholes and the like due to the gas is reduced, and a more stable oxide layer can be formed. Therefore, the field emission electron source 10 with further improved stability over time can be provided.
Further, when the salt of the electrolyte solution is mainly composed of an organic salt, alkali metal contained in the salt does not remain in the strong electric field drift layer as a residue, so that the stability over time is further improved. Field emission type electron source can be provided.

Further, in this embodiment, the porous polycrystalline silicon layer 4 is formed halfway in the thickness direction of the polycrystalline silicon layer 3, but the porous polycrystalline silicon layer 4 is formed so as to reach the n-type silicon substrate 1. The layer 4 may be formed. In this case, the strong electric field drift layer 6 is formed on the n-type silicon substrate 1 without interposing the polycrystalline silicon layer 3 as shown in FIG. Further, as shown in FIG. 9, instead of the n-type silicon substrate 1 as the conductive substrate, a substrate having a conductive layer 12 formed on one surface of an insulating substrate 11 such as a glass substrate is used. The strong electric field drift layer 6 may be formed without the polycrystalline silicon layer 3 interposed.

In this embodiment, a porous polycrystalline silicon layer is used as the porous semiconductor layer, but porous single crystal silicon may be used.

When the strong electric field drift layer 6 is formed from the porous semiconductor layer (porous polycrystalline silicon layer 4),
An auxiliary oxidation step may be provided at least before or after the oxidation step. As such an auxiliary oxidation step, a step of irradiating ultraviolet light in a gas atmosphere containing at least one of oxygen (O ₂ ) and ozone (O ₃ ) to oxidize the porous polycrystalline silicon layer 4; Oxidizing the porous polycrystalline silicon layer 4 by exposing it to plasma in a gas atmosphere containing at least one of the following: heating the porous polycrystalline silicon layer 4 at 100 to 600 ° C. in a gas atmosphere containing at least ozone; A step of oxidizing the layer 4, a step of irradiating ultraviolet light and heating at 100 to 600 ° C. to oxidize the porous polycrystalline silicon layer 4, and a step of oxidizing the porous polycrystalline silicon layer 4 by a rapid thermal oxidation method.
Oxidizing the porous polycrystalline silicon layer 4 with an acid, or oxidizing the porous polycrystalline silicon layer 4 with an oxidizing solution. The conditions of the rapid thermal oxidation method include, for example,
The oxidation temperature may be 600 ° C. to 900 ° C. and the oxidation time may be 30 minutes to 120 minutes in dry oxygen using a lamp annealing apparatus. The conditions for the oxidation with an acid include a treatment tank containing an acid (eg, HNO ₃ , H ₂ SO ₄ , aqua regia, etc.) (the treatment tank used for the anodic oxidation treatment is used as the treatment tank). A predetermined current may be passed using a platinum electrode (not shown) as a negative electrode and an n-type silicon substrate 1 (ohmic electrode 2) as a conductive substrate as a positive electrode. As the oxidizing solution, it is desirable to use one or more oxidizing agents selected from the group consisting of nitric acid, sulfuric acid, hydrochloric acid, and hydrogen peroxide.

By adding such an auxiliary oxidation step, the electron emission efficiency can be further increased.

In the anodic oxidation treatment, a treatment tank 31 in which an etchant in which a proper amount of hydrofluoric acid, ethanol and water are mixed is put into a constant temperature water tank 32 to control the temperature of the electrolytic solution, and the conductive substrate is charged. The object 30 on which the crystalline silicon layer 3 is formed and the counter electrode 33 which is a platinum electrode are immersed in an electrolytic solution, and electricity is supplied between the conductive substrate and the counter electrode 33. During this time, the exposed portion of the polycrystalline silicon layer 3 is irradiated with light from the lamp 34. The current pattern flowing between the conductive substrate and the counter electrode 33 is controlled by the function generator 35 and the galvanostat 36. That is, the function generator 35 controls the polarity and duration of the current flow, and the galvanostat 36 controls the current value of the current flow. In the current pattern in the present embodiment, a period in which the p-type silicon substrate 16 is a positive electrode and a period in which the p-type silicon substrate 16 is a negative electrode are alternately provided, and a pulse-like current is supplied in each period.

Here, the porosity progresses during a period in which the conductive substrate is used as a positive electrode, and a current easily flows in the porous region. On the other hand, during the period in which the conductive substrate is used as the negative electrode, gas by electrolysis is generated in the vicinity of the region where the porous substrate has been made porous, and when the conductive substrate is subsequently used as the positive electrode, the formation of porous material is suppressed. In other words, the portion where the progress of porosity is fast during the period in which the conductive substrate is used as the positive electrode is restrained from progressing in the next porosity. By repeating such an operation, the porous region has a substantially uniform thickness.

The energizing period (ie, pulse width) per pulse current and the current density per pulse are appropriately set according to the composition of the electrolytic solution and the temperature of the electrolytic solution.
That is, the amount of charge at the time of anodizing treatment is adjusted by the composition of the electrolytic solution and the temperature of the electrolytic solution. In addition, when using an electrolytic solution in which hydrofluoric acid, ethanol, and water are mixed as described above, the temperature of the electrolytic solution is controlled in a temperature range from 0 ° C. to room temperature.

[0061]

According to a first aspect of the present invention, there is provided a conductive substrate, a strong electric field drift layer formed on one surface side of the conductive substrate, and a conductive thin film formed on the strong electric field drift layer. ,
A field emission type electron source in which electrons injected from the conductive substrate are drifted through the strong electric field drift layer and emitted through the conductive thin film by applying a voltage with the conductive thin film as a positive electrode with respect to the conductive substrate, The strong electric field drift layer is formed by a process including an oxidation step of forming an oxide layer by arranging a porous semiconductor layer in the electrolytic solution so as to face a counter electrode and passing a current, and the oxidation step includes a constant formation current. After the current continues to flow at the density and the voltage between the conductive substrate and the counter electrode increases by a specified amount, the voltage between the conductive substrate and the counter electrode is maintained at the increased voltage and the formation current density becomes a predetermined value. The strong electric field drift layer forms an oxide layer by arranging the porous semiconductor layer in the electrolytic solution so as to face the counter electrode and causing a current to flow therethrough. Oxidation process The oxidizing step includes a step of continuously supplying a current at a constant formation current density, and after the voltage between the conductive substrate and the counter electrode increases by a specified amount, the voltage between the conductive substrate and the counter electrode. Is maintained at the increased voltage, and the current is stopped when the formation current density decreases to a predetermined value, so that the porous semiconductor layer is oxidized only by the rapid thermal oxidation method to form a strong electric field drift layer. Process temperature is low, the restriction on the conductive substrate is reduced, and the area and cost can be easily reduced.
Since the denseness of the oxide layer formed in the strong electric field drift layer is improved, energy loss due to scattering and the like in the oxide layer is reduced, thereby improving electron emission efficiency. Has the effect of improving the stability over time.

According to a second aspect of the present invention, in the first aspect of the present invention, since the electrolytic solution is composed of an organic solvent and an electrolytic solution, the amount of gas generated during chemical formation is very small, and Since the generation of holes and the like is reduced and a more stable oxide layer can be formed, there is an effect that the stability over time is further improved.

According to a third aspect of the present invention, in the first or second aspect of the present invention, since the salt of the electrolyte solution is an organic salt, alkali metal or the like contained in the salt is converted into a strong electric field drift layer as a residue. The alkali metal does not remain in the conductive layer and does not diffuse into the oxide layer when a voltage is applied between the conductive substrate and the conductive thin film. In addition, there is an effect that the stability over time is further improved.

According to a fourth aspect of the present invention, in the first to third aspects of the present invention, since the pH of the electrolytic solution is in the range of 6 to 8, a conductive material is provided on one surface of the insulating substrate as the conductive substrate. In the case where a conductive layer is formed, the conductive layer can be prevented from being corroded by the electrolytic solution, and the yield can be improved.

According to a fifth aspect of the present invention, in the first to fourth aspects of the present invention, since the thickness of the porous region in the porous semiconductor layer is substantially uniform in the plane, the conductive thin film can be electrically conductive. When a voltage is applied as a positive electrode to the conductive substrate, the electric field acts almost uniformly on the porous region, so that the equipotential surface in the strong electric field drift layer becomes almost parallel to the conductive substrate, and There is an effect that variations in the emission direction and unevenness in the amount of emitted electrons can be reduced.

According to a sixth aspect of the present invention, in the first to fifth aspects of the present invention, the porous semiconductor layer is made of porous polycrystalline silicon. There is an effect that electrons can be stably emitted with high efficiency without the occurrence of a popping phenomenon.

According to a seventh aspect of the present invention, there is provided a conductive substrate comprising: a conductive substrate; a strong electric field drift layer formed on one surface side of the conductive substrate; and a conductive thin film formed on the strong electric field drift layer. A method for manufacturing a field emission type electron source in which electrons injected from a conductive substrate are drifted through a strong electric field drift layer and emitted through the conductive thin film by applying a voltage with the conductive thin film as a positive electrode to a conductive substrate. In forming the strong electric field drift layer, an oxide layer is formed by arranging a porous semiconductor layer formed on one surface side of the conductive substrate so as to face a counter electrode in an electrolytic solution and flowing a current. An oxidation step is provided, wherein the oxidation step continues to flow a current at a constant formation current density, and after the voltage between the conductive substrate and the counter electrode increases by a specified amount, increases the voltage between the conductive substrate and the counter electrode. Maintain at increased voltage The method is characterized in that the current is stopped when the current density decreases to a predetermined value, and the process temperature is lower than in the case where the porous semiconductor layer is oxidized only by the rapid thermal oxidation method to form a strong electric field drift layer. Therefore, the restriction on the conductive substrate is reduced, the area and the cost are easily reduced, and the density of the oxide layer formed in the strong electric field drift layer is improved. There is an effect that it is possible to provide a field emission type electron source in which the emission efficiency has little change with time.

According to an eighth aspect of the present invention, in the invention of the seventh aspect, since the electrolytic solution is composed of an organic solvent and an electrolytic solution, the amount of gas generated during chemical formation is very small, and Since the generation of holes and the like is reduced and a more stable oxide layer can be formed, there is an effect that a field emission electron source with further improved temporal stability can be provided.

According to a ninth aspect of the present invention, in the invention of the seventh or eighth aspect, since the salt of the electrolyte solution is an organic salt, alkali metal or the like contained in the salt is formed as a residue as a strong electric field drift layer. Since it does not remain inside, there is an effect that a field emission type electron source with further improved stability over time can be provided.

According to a tenth aspect of the present invention, in the invention of the seventh to ninth aspects, since the pH of the electrolytic solution is in the range of 6 to 8, the conductive substrate is provided on one surface of an insulating substrate. When a conductive layer is used, the conductive layer can be prevented from being corroded by the electrolytic solution, and the yield can be improved, so that the cost can be reduced. .

According to an eleventh aspect of the present invention, in the method of the seventh to tenth aspects, when forming the porous semiconductor layer, the porous semiconductor layer is formed such that the thickness of the region to be made porous is substantially uniform. Since an anodic oxidation process step of forming a layer is provided, the thickness of the porous region of the porous semiconductor layer becomes substantially uniform, and the oxidation by the oxidation process proceeds almost uniformly in the plane. Are less likely to remain, and an effect is provided that a field emission electron source with further improved stability over time can be provided.

According to a twelfth aspect of the present invention, in the seventh to eleventh aspects of the present invention, since the porous semiconductor layer is made of porous polycrystalline silicon, the strong electric field drift layer is made of Si.
A field emission type electron source having an oxide film having a high density close to the structure of O ₂ or SiO ₂ , thereby improving the density and film quality of the oxide film, and improving the electron emission efficiency and the withstand voltage. There is an effect that can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a first embodiment.

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

FIG. 3 is a schematic configuration diagram of a manufacturing apparatus of the above.

FIG. 4 is an explanatory diagram of oxidation conditions using the above manufacturing apparatus.

FIG. 5 is a diagram illustrating the principle of the electron emission mechanism of the above.

FIG. 6 is an explanatory view of the operation principle of the embodiment.

FIG. 7 is a schematic sectional view of another configuration example of the above.

FIG. 8 is a schematic sectional view of another configuration example of the above.

FIG. 9 is a schematic sectional view of another configuration example of the above.

FIG. 10 is a schematic configuration diagram of a manufacturing apparatus of the above.

FIG. 11 is a main process sectional view for explaining a conventional manufacturing process.

FIG. 12 is a diagram illustrating the principle of an electron emission mechanism according to the embodiment.

FIG. 13 is an explanatory diagram schematically illustrating the oxidation process of the above.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 n-type silicon substrate 2 ohmic electrode 3 polycrystalline silicon layer 6 strong electric field drift layer 7 conductive thin film 10 field emission electron source

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) (72) Inventor Takuya Komoda 1048 Odakadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Works, Ltd. (72) Inventor Yoshiaki Ta, Kazuma, Kazuma, Osaka 1048, Matsushita Electric Works Co., Ltd. Matsushita Electric Works Co., Ltd. 1048 Okadoma Matsushita Electric Works Co., Ltd. (72) Inventor Kondo Yukihiro 1048 Ojido Kazuma Kadoma City, Osaka Pref.

Claims (12)

[Claims] 1. A conductive substrate comprising: a conductive substrate; a strong electric field drift layer formed on one surface side of the conductive substrate; and a conductive thin film formed on the strong electric field drift layer. A field emission type electron source in which electrons injected from the conductive substrate are drifted through the strong electric field drift layer and emitted through the conductive thin film by applying a voltage as a positive electrode to the substrate, and the strong electric field drift layer is The porous semiconductor layer is formed by a process including an oxidation step of forming an oxide layer by arranging a porous semiconductor layer to face a counter electrode in an electrolyte and causing a current to flow, wherein the oxidation step continues to flow a current at a constant formation current density. After the voltage between the conductive substrate and the counter electrode increases by a specified amount, the voltage between the conductive substrate and the counter electrode is maintained at the increased voltage, and the current is applied when the formation current density decreases to a predetermined value. Feature to stop Field emission type electron source. 2. The field emission type electron source according to claim 1, wherein the electrolyte comprises an organic solvent and an electrolyte solution. 3. The field emission electron source according to claim 2, wherein the salt of the electrolyte solution comprises an organic salt. 4. The field emission type electron source according to claim 1, wherein the pH of the electrolyte is in the range of 6 to 8. 5. The field emission type device according to claim 1, wherein the porous semiconductor layer has a region in which the porous region is made to have a substantially uniform thickness in a plane. Electron source. 6. The field emission type electron source according to claim 1, wherein the porous semiconductor layer is made of porous polycrystalline silicon. 7. A conductive substrate comprising: a conductive substrate; a strong electric field drift layer formed on one surface of the conductive substrate; and a conductive thin film formed on the strong electric field drift layer. A method for manufacturing a field emission type electron source in which electrons injected from a conductive substrate are drifted through a strong electric field drift layer and emitted through a conductive thin film by applying a voltage as a positive electrode to the substrate, comprising: In forming the drift layer, the method includes an oxidizing step of forming an oxide layer by arranging a porous semiconductor layer formed on one surface side of the conductive substrate so as to face a counter electrode in an electrolytic solution and flowing a current, In the oxidation step, after the voltage between the conductive substrate and the counter electrode is increased by a specified amount by continuously flowing a current at a constant formation current density, the voltage between the conductive substrate and the counter electrode is increased to the increased voltage. Keep the formation current density at the specified value A method for manufacturing a field emission type electron source, comprising: stopping the energization when the power source has decreased to a level lower than the maximum. 8. The method according to claim 7, wherein the electrolyte comprises an organic solvent and an electrolyte solution. 9. The method according to claim 8, wherein the salt of the electrolyte solution is an organic salt. 10. The method according to claim 7, wherein the pH of the electrolyte is in the range of 6 to 8. 11. The method of forming a porous semiconductor layer according to claim 11, further comprising an anodic oxidation step of forming the porous semiconductor layer such that the thickness of a region to be made porous is substantially uniform. A method for manufacturing a field emission electron source according to any one of claims 7 to 10. 12. The method according to claim 7, wherein the porous semiconductor layer is made of porous polycrystalline silicon.