JPH0794082A - Method for manufacturing cold cathode for electron emission - Google Patents

Abstract

(57) [Summary] [Purpose] To easily prepare a cold cathode for electron emission having a structure suitable for electron emission. [Structure] As shown in FIG. 3A, a conical electrode 9 is formed. The cone-shaped electrode 9 is a rough shape of the cold cathode to be finally formed, and has a substantially cone shape, but the tip portion is not sharp. The pyramidal electrode 9 is anodized to form an oxide film 9a on the surface as shown in FIG. The portion that was not oxidized remains as the internal electrode 9b, but this internal electrode 9b has a sharp tip. Therefore, by removing only the oxide film 9a and leaving the internal electrode 9b, the internal electrode 9b can be used as a cold cathode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a cold cathode for electron emission, and more particularly to a method for producing a cold cathode for electron emission used in vacuum micro devices and the like.

[0002]

2. Description of the Related Art With the spread of semiconductor devices, the vacuum tube technology has been forgotten, but in the last few years, the vacuum tube technology has regained attention. This is the development of so-called vacuum micro devices. This vacuum micro device is one in which fine vacuum tubes are integrated on the same substrate by utilizing the semiconductor fine processing technology cultivated in many years of research on semiconductor devices. That is, this element is provided with a cold cathode, an extraction electrode, and an anode, and an electron is extracted from the cold cathode by the extraction electrode and is emitted to the anode. By controlling the voltage applied to the extraction electrode, the amount of electrons emitted from the cold cathode can be controlled.

In a semiconductor device, since electrons move in a solid, the operating speed is governed by the mobility of electrons in the solid. On the other hand, in the vacuum micro device, since electrons move in the vacuum, it can operate at a very high speed as compared with the semiconductor device, and has attracted attention as a charge transport medium utilizing the advantages of the vacuum. Further, along with the research on this vacuum micro device, a cold cathode has been developed and is expected to be applied to a flat display and the like.

[0004]

As described above, the vacuum micro device is, in principle, the same as a vacuum tube, but its size is so small that it is incomparable to that of a vacuum tube, and its manufacture is difficult. Requires advanced microfabrication technology. In particular, the cold cathode needs to be processed into a surface shape that easily emits electrons, and such fine processing is extremely difficult. Conventionally, as materials for this cold cathode, W, Ta, M
A refractory metal such as o is used, and the tip of the electron emitting portion is processed to have a radius of curvature of 1 μm or less, and a strong electric field of about 10 ⁷ V / cm is concentrated on this tip to emit electrons. If there is a processing defect in the cold cathode, the operation of the vacuum micro device becomes unstable due to the processing defect.

However, in order to process the radius of curvature of the tip of the cold cathode to 1 μm or less, a very advanced fine processing technique is required. For example, when forming a cold cathode on a silicon substrate, it is common to perform etching using the difference in the etching rate of the plane orientation of silicon, but it is a very advanced technique for performing accurate processing. Is required. Further, in the case of forming a cold cathode on a glass substrate, a method of utilizing oblique vapor deposition is generally used, and for example, an English-language journal `` Journal of Applied Physics: Vol. 39,
No. 7, p3504-3505 (1968) ”introduces a method using such oblique deposition. However, the method using the oblique deposition also requires a high level of technical capability and know-how.

Therefore, an object of the present invention is to provide a method for easily producing a cold cathode for electron emission having a structure suitable for electron emission.

[0007]

[Means for Solving the Problems]

(1) The first invention of the present application is a method for producing a cold cathode used in an apparatus comprising a cold cathode, an extraction electrode, and an anode, wherein the extraction electrode draws electrons from the cold cathode and discharges the electrons to the anode. After forming the cone-shaped electrode, the surface of the cone-shaped electrode is oxidized to form an oxide film of a predetermined thickness, and the oxide film is removed to obtain a cone-shaped cold cathode having a sharp tip. It was done like this.

(2) A second invention of the present application is the manufacturing method according to the first invention, wherein the conical electrode is made of a metal material, and an oxide film is formed on the metal material by an anodic oxidation method. It is the one.

(3) The third invention of the present application is the manufacturing method according to the above-mentioned second invention, wherein the etching characteristics are different from each other and the respective oxides also have different etching characteristics from each other. The first metal material and the second metal material are prepared, the first metal material layer is formed on the substrate, the second metal material layer is formed on the first metal material layer, and the second metal material layer is formed. Secondly by etching the metal material layer
Forming a conical electrode made of the metal material described above and anodizing the exposed surface of the first metal material layer and the surface of the conical electrode to form the first metal material oxide film and the second metal material oxide film. A cold cathode made of the second metal material is obtained by forming and etching the second metal material oxide film, and the first metal material oxide film is used as an insulating layer between the cold cathode and the extraction electrode. It is intended to be used.

(4) A fourth invention of the present application is the manufacturing method according to the above-mentioned third invention, wherein a transparent substrate is used as the substrate.
Tantalum is used as the first metal material and aluminum is used as the second metal material, and anodic oxidation is performed under the condition that all the thickness portions in the exposed region of the tantalum layer are oxidized.

(5) The fifth invention of the present application is, in the manufacturing method according to each of the above-mentioned inventions, after obtaining a cone-shaped cold cathode having a sharp tip, a film made of a different material is formed on the surface of the cold cathode. Are formed.

[0012]

[Work]

(1) According to the first invention of the present application, an oxide film having a predetermined thickness is formed by oxidizing the surface of the conical electrode. In this way, when the surface is oxidized, the inside that has not been oxidized becomes a pyramidal electrode that is one size smaller than that before the oxidation. The inventor of the present application has found out that the tip portion of the conical electrode inside this is sharpened.
Therefore, if you remove the oxide film on the surface and leave only the conical electrodes inside, the size will be reduced by one size,
The tip is sharpened, and a cold cathode having a structure suitable for electron emission is obtained. According to this method, since the pyramidal electrode before oxidation does not need to have a sharp tip, a technique for highly sharpening is unnecessary.

(2) In the second invention of the present application, the conical electrode is made of a metal material, and its surface is oxidized by the anodic oxidation method. In the anodic oxidation method, a voltage (formation voltage) is applied to the metal to be oxidized, but the film thickness of the oxide film to be formed can be controlled by adjusting the formation voltage. Therefore, it becomes possible to easily manufacture a cold cathode having a desired structure.

(3) In the third invention of the present application, the first invention is formed on the substrate.
Is formed, and a conical electrode made of the second metal material is formed thereon. These two kinds of metal materials are simultaneously oxidized. At this time, the first metal material layer functions as a protective layer for the substrate surface. The oxide film formed on the surface of the conical electrode is removed and only the cold cathode with a sharp tip is left, but the oxide film of the first metal material is left as it is and the cold cathode and the extraction formed later. It is used as an insulating layer between the electrodes. Therefore, an electron-emitting device having a sufficient insulating layer can be easily manufactured.

(4) In the fourth invention of the present application, tantalum and aluminum are used as two kinds of metals. They have different etching properties, and these oxides also have different etching properties. Moreover, the tantalum oxide has a light-transmitting property. Therefore, if anodic oxidation is performed under the condition that all the thickness portions in the exposed region of the tantalum layer are oxidized and a transparent substrate is used, the cold cathode forming region is formed when the cold cathode is formed. It is possible to realize a transparent structure in all the parts except for it, and it becomes possible to use the patterning in which the back exposure is performed using the cold cathode as a mask in the process of forming the extraction electrode and the like later.

(5) In the fifth aspect of the present invention, different material films are formed on the surface of the cone-shaped cold cathode having a sharp tip. Such a material film can be used as a protective film when a material susceptible to oxidation or corrosion is used as the cold cathode.

[0017]

The present invention will be described below based on illustrated embodiments. First, the structure of a conventional general vacuum micro device will be described. FIG. 1 is a cross-sectional view showing a general structure of a vacuum micro device for driving a flat panel display. Here, for convenience of description, only the structure for driving one pixel of the display is shown, and the actual dimensional ratio of each part is ignored. The glass substrate 1 has a sufficient thickness to support this element, and the wiring layer 2 is formed thereon. A cold cathode 3 and an insulating layer 4 are formed on the wiring layer 2, and an extraction electrode 5 is formed on the insulating layer 4. The wiring layer 2 is for supplying a voltage to the cold cathode 3, and is made of a transparent conductive film such as ITO, ZnO: Al, Al, Au, W, Mo, Ti, Ta, N.
It is configured by forming a metal thin film of b, Cr or the like to a thickness of about 0.02 to 1.0 μm. The cold cathode 3 formed thereon is a conical electrode made of a high melting point metal such as W, Ta, Mo. The insulating layer 4 is
The extraction electrode 5 is a layer obtained by depositing SiO ₂ , Al ₂ O ₅ or the like to a thickness of about 0.5 to 3.0 μm, and the extraction electrode 5 includes Al, Au, W, Mo, Ti, Ta, Nb, or the like. The metal thin film is formed to a thickness of about 0.02 to 1.0 μm. The extraction electrode 5 is located at almost the same height as the height of the tip of the cold cathode 3.

On the other hand, the anode 7 and the phosphor layer 8 are formed on the lower surface of the other glass substrate 6. Anode 7
Is a transparent conductive film of ITO, ZnO: Al, etc.
The phosphor layer 8 is formed to have a thickness of about 1.0 μm, and the phosphor layer 8 is formed of a phosphor such as ZnO: Zn to have a thickness of about 10 μm. As shown in FIG. 1, the structure formed on the upper surface of the glass substrate 1 and the structure formed on the lower surface of the glass substrate 6 are arranged so as to face each other.
The gap between the two is kept in a vacuum state.

The vacuum micro device having such a structure operates as a vacuum tube. That is, the cold cathode 3 is a cathode, the anode 7 is an anode, the extraction electrode 5 is a grid,
As a result, if a predetermined voltage is applied to each electrode, electrons can be extracted from the cold cathode 3 and emitted to the anode 7,
The amount of emitted electrons can be controlled by the voltage applied to the extraction electrode 5. The phosphor layer 8 emits light in response to collision of electrons toward the anode 7. This light emission is observed from above the drawing through the anode 7 and the glass substrate 6.

Now, in manufacturing a vacuum micro device having such a structure, the most difficult process is to form the conical cold cathode 3. In order to enable the emission of electrons by a relatively low electric field, it is necessary to make the tip of the cold cathode 3 sharp, but such fine processing is very difficult. Moreover, FIG. 1 shows only the structure corresponding to one pixel of the flat panel display, but in reality, a large number of such structures are arrayed vertically and horizontally to improve the processing accuracy of each cold cathode 3. It is necessary to have almost the same precision. If the processing accuracy of the plurality of cold cathodes 3 arranged vertically and horizontally is uneven, the display screen becomes uneven. The present invention has been made to solve such a problem, and a cold cathode is manufactured by the following method.

First, the basic principle of the method of manufacturing the cold cathode for electron emission according to the present invention will be described with reference to FIG. First, as shown in FIG. 2A, the conical electrode 9 is formed. The cone-shaped electrode 9 is a rough shape of the cold cathode to be finally formed, and has a substantially cone shape, but the tip portion is not sharp. In the illustrated example, the conical electrode 9 has a so-called frustoconical shape, and the tip portion is circular with a diameter D. Thus, the conical electrode 9 having a conical structure with a flat tip can be formed relatively easily. This is because the shape of the tip does not require so high processing accuracy. In the present invention, after the conical electrode 9 having such a rough shape is formed, its surface is oxidized. Figure 2 (b)
FIG. 4 is a cross-sectional view of the surface thus oxidized. The oxide film 9a is formed in the hatched portion in the figure, and the portion which is not oxidized remains as the internal electrode 9b. The inventor of the present application found out that the internal electrode 9b thus formed has a conical structure having a sharp tip. That is, after the oxidation, only the oxide film 9a is removed and the internal electrode 9b is left, so that the internal electrode 9b can be used as a cold cathode. The cold cathode thus formed has a sharpened tip, and has a shape suitable for emitting electrons. The sharpening of the tip portion by this method is finer than the sharpening by the conventional etching method.

If the cold cathode is manufactured based on such a principle, it becomes possible to easily prepare the cold cathode for electron emission having a sharp tip structure suitable for electron emission. Even if a large number of cold cathodes are formed on the same substrate, it is possible to form a cold cathode having a substantially uniform tip structure by uniformly oxidizing the substrates. Here, the thickness of the oxide film 9a formed is determined by the conditions of the oxidation process. In particular, when a metal material is used as the conical electrode 9a and an oxidation process using an anodic oxidation method (an oxidation method performed while applying a positive voltage to the conical electrode 9) is performed, the thickness of the oxide film 9a becomes It can be controlled by (voltage applied to the conical electrode 9). Generally, when a certain layer is oxidized to form an oxide film, the thickness of this oxide film becomes larger than the thickness of the original layer. In other words, the oxidation causes the layer to swell in the thickness direction. That is, the oxidation will be performed both inward and outward. In FIG. 2 (b), the original conical electrode 9
The shape is indicated by a broken line, but the portion outside the contour indicated by the broken line is the portion that is oxidized outward, and the inside portion is the portion that is oxidized inward. Oxidation directed inward is responsible for sharpening the tip of the internal electrode 9b. Therefore, in this specification, the thickness portion of the oxide film 9a formed by the inward oxidation is referred to as an inward oxide film thickness d (see FIG. 2B). When the value of the inward oxide film thickness d exceeds a certain level, the tip of the internal electrode 9b is sharpened. As a general reference, a sufficiently sharpened internal electrode 9b can be obtained by performing oxidation under the condition that the inward oxide film thickness d = (conical electrode tip end diameter D) / 2 or so. it can.

Next, the manufacturing process of the cold cathode for electron emission based on the above-mentioned basic principle will be described with reference to the sectional views.
A detailed description will be given based on a more specific embodiment. In the following cross-sectional views, for convenience of illustration, the dimensional ratio of each part is neglected.

<First Embodiment> First, as shown in FIG. 3, a glass substrate 11 is prepared as a transparent insulating substrate, and an ITO layer 12 is formed thereon as a transparent conductive film. Further thereon, a tantalum layer 13 as a first metal material layer and an aluminum layer 14 as a second metal material layer.
Are respectively formed (the thickness of each layer will be described later). For forming each layer, for example, a sputtering method or a vacuum vapor deposition method may be used. Subsequently, a photoresist is applied on the aluminum layer 14 and patterned into a specific shape to form a resist layer 15 as shown in FIG. Since this example is an example of forming a conical cold cathode,
The resist layer 15 has a circular pattern in plan view, but if a pyramidal cold cathode is to be formed, it may have a polygonal pattern accordingly. Next, this resist layer 15
Using as a mask, the aluminum layer 14 is etched. In this example, an etching solution for aluminum (MR-ALE manufactured by Hishie Chemical Co., Ltd.) was used in about 4
Keep the whole substrate in this solution while keeping it heated to 0 ℃.
Etching was performed by immersing it for a minute. As a result, as shown in FIG. 5, a part of the aluminum layer 14 remains as the conical electrode 16. This conical electrode 1
Reference numeral 6 is a so-called frustoconical shape, which is a rough shape of the cold cathode to be manufactured. Then, the resist layer 15 is removed by sufficiently washing with water and then drying.

Subsequently, an oxidation step, which is a feature of the present invention, is performed. In this embodiment, the oxidization is performed by using the anodic oxidation method which can easily control the oxide film thickness. That is, a 5% (wt%) ammonium borate aqueous solution was prepared as an electrolyte solution, and the electrolyte solution was stirred,
The fully dried substrate is immersed. On the other hand, a platinum plate was similarly dipped as a counter electrode, a voltage was applied between the counter electrode and the conical electrode 16 so that the conical electrode 16 side became an anode, and a constant value of 0.5 mA / cm ² was obtained at room temperature. Oxidation was performed at a current density. The applied voltage was increased from 0 V to a predetermined formation voltage, and oxidation was performed until an oxide film having a predetermined film thickness described later was obtained. The electrolyte solution used for this anodic oxidation is not limited to the ammonium borate aqueous solution described above, and various other electrolyte solutions can be used. For example, as the solvent used for the electrolyte solution, various organic solvents (ethylene glycol, methanol, glycerin, propionic acid, etc.) can be used in addition to water, and as the solute, citric acid, adipic acid, boric acid, Neutral organic acids such as lactic acid and acrylic acid, borax, ammonium citrate, ammonium tartrate, ammonium dihydrogen phosphate, sodium phosphate, potassium phosphate, sodium sulfate, potassium sulfate,
A neutral, weakly acidic or weakly alkaline salt such as sodium carbonate or potassium carbonate can be used. Also,
Instead of platinum, aluminum, stainless steel, carbon or the like can be used as the counter electrode.

FIG. 6 is a cross-sectional view showing a state when the above-mentioned oxidation step is completed. An oxide film 16a (Al ₂ O ₃ ) is formed on the surface of the conical electrode 16 by oxidation,
The portion that was not oxidized remains as the internal electrode 16b. In addition, in the above-mentioned oxidation process, the conical electrode 16
At the same time, the exposed region of the tantalum layer 13 will also be oxidized. Therefore, the exposed region of the tantalum layer 13 becomes the oxide film 13a (Ta ₂ O ₅ ) and the non-exposed region remains as the tantalum layer 13b. The tantalum layer 13 is formed in order to protect the ITO layer 12 from being damaged by the above-described anodic oxidation process. The point to be noted here is that the exposed region of the tantalum layer 13 is
The point is that all the thickness parts are oxidized. In other words, the exposed area of the tantalum layer 13 is not limited to the surface,
Oxidation is carried out to the deep part, and all are oxide film 1
It has changed to 3a. This is the oxide of tantalum (Ta
₂ O ₅ ) pays attention to the property that ₂ O ₅ has a light-transmitting property, and is a consideration for enabling back exposure in a later step.
That is, since tantalum itself does not have a light-transmitting property, the exposed region of the tantalum layer 13 is oxidized over the entire thickness to be changed to the light-transmitting oxide film 13a in order to perform back exposure. It is necessary.

After the oxidation process is completed, the entire substrate is thoroughly washed with water and dried to remove the aluminum oxide film 16a. In this example, the stripping solution was 5% phosphoric acid + 2.
% Chromic acid aqueous solution was prepared, the aqueous solution was heated and maintained at about 85 ° C., and the entire substrate was immersed for about 15 minutes to perform peeling. As a result, as shown in FIG. 7, only the aluminum oxide film 16a is peeled and removed, and the exposed internal electrode 16b forms the cold cathode 17. In this peeling process, the tantalum oxide film 13a is not affected at all.

The above is the process of the method of manufacturing the cold cathode for electron emission according to the present invention. Next, the case of continuously forming the extraction electrode used for this cold cathode will be described. First, as shown in FIG. 8, a resist layer 18 is formed. The resist layer 18 needs to have a thickness such that at least the cold cathode 17 is completely covered. After applying the resist, pre-baking is performed, and back exposure is performed here. That is, the resist layer 18 is exposed to light from the bottom of the drawing. As described above, the glass substrate 11 and the ITO layer 12 are transparent, and
The tantalum oxide film 13a also has a light-transmitting property. Therefore, when backside exposure is performed from the backside of the substrate, the tantalum layer 1
3b and aluminum cold cathode 17 can be used as a mask for exposure, and by developing, as shown in FIG. 9, the resist layer 18 is formed only in the region where the cold cathode 17 is formed.
a can be left. Then, as shown in FIG.
The insulating layer 19 is formed on the entire surface of the substrate. As the insulating layer 19, for example, SiO ₂ , Al ₂ O ₃ , shot glass or the like may be formed by a sputtering method or a vacuum evaporation method. Further thereon, as shown in FIG. 11, a gate electrode layer 20 is formed. As the gate electrode layer 20, for example, Al, Au, W, Mo, Ti, Ta, N
A metal material such as b may be formed by a sputtering method or a vacuum evaporation method. Finally, the resist layer 18a is peeled off (so-called lift-off), followed by sufficient water washing and drying to obtain the structure shown in FIG. This structure is equivalent to the structure of the electron-emitting device shown in the lower part of FIG. For removing the resist layer 18a, for example, a removing liquid such as acetone may be used. Of course, any stripping solution may be used as long as it is capable of stripping the resist layer 18a without affecting other structural parts.

Next, the thickness of each layer and the conditions of anodic oxidation in the above steps will be examined. First, FIG.
Consider the thicknesses of the ITO layer 12, the tantalum layer 13, and the aluminum layer 14 in FIG. Since the ITO layer 12 is a conductive film that functions as a wiring layer for the cold cathode,
There is no particular limitation as long as the wiring layer has an appropriate thickness. In this embodiment, the ITO has a thickness of about 0.1 to 0.5 μm.
Layer 12 was formed. On the other hand, it is preferable that the tantalum layer 13 and the aluminum layer 14 have an optimum thickness determined in consideration of the size of the cold cathode 17 to be formed and the conditions of anodic oxidation. First, the thickness of the aluminum layer 14 is preferably about half the diameter of the cold cathode 17 to be formed. For example, if a conical cold cathode 17 having a diameter of 5 μm is formed (the diameter of the resist layer 15 is 5 μm).
m) and the thickness of the aluminum layer 14 is preferably about 2.5 μm. With such a thickness, the pyramidal electrode 16 having a pointed tip to some extent can be formed by etching as shown in FIG.

On the other hand, the thickness of the tantalum layer 13 needs to be determined based on the conditions of anodic oxidation. This is because, as described above, when the anodic oxidation is completed, the exposed region of the tantalum layer 13 needs to be oxidized for all the thickness portions (the reason is that all the exposed regions of the tantalum layer 13 must be oxidized so that the back surface exposure can be performed later). This is because it is necessary to change the thickness part of the oxide film to a translucent oxide film). By the way, the condition of the anodic oxidation should be determined based on the inward oxide film thickness d shown in FIG. 2 (b), and the value of this inward oxide film thickness d is the conical shape shown in FIG. 2 (a). The diameter D of the head portion of the electrode 9 should be taken into consideration (as described above, if d = D / 2 or so, an internal electrode 9b having a sufficiently sharp tip can be obtained).

Now, more specifically, the optimum conditions for anodic oxidation and the optimum value for the thickness of the tantalum layer 13 will be determined by taking as an example the case of forming a conical cold cathode 17 having a diameter of 5 μm. In FIG. 5, when etching is performed using the resist layer 15 having a circular pattern with a diameter of 5 μm,
The diameter D of the cutting head of the resulting conical electrode 16 is 0.24 μm.
It has been confirmed by experiments that it is about the same level. Therefore, the value of the inward oxide film thickness d shown in FIG.
It is preferably about 12 μm. Here, when the relationship between the formation voltage (voltage applied at the time of oxidation) and the film thickness of the oxide film to be formed in performing the anodic oxidation is determined, the relationship shown in the table of FIG. 13 is obtained. The formation voltage in this table indicates the voltage value applied to the conical electrode during the oxidation step, and the anodic oxide film thickness is the thickness of the oxide film obtained when each formation voltage is applied. And the inward oxide film thickness d.
Indicates the inward oxide film thickness of the aluminum oxide film obtained by oxidation.

As described above, when the circular pattern having the diameter of 5 μm is used, the value of the inward oxide film thickness d is 0.12 μm.
It is preferably about the same. Therefore, according to this table, it is understood that the anodic oxidation may be performed under the condition that the formation voltage is 150V. In this way, the optimum conditions for anodic oxidation can be determined. On the other hand, under the anodizing condition of the formation voltage of 150 V, the oxide film thickness of the tantalum layer is about 0.25 μm according to the table of FIG. 0.2 for tantalum
When an oxide film with a thickness of 5 μm is formed, this 0.25 μ
0.1 μm of m is the inward oxide film thickness. Therefore, it is understood that the original thickness of the tantalum layer 13 is preferably 0.1 μm.

<Second Embodiment> First, as shown in FIG. 14, an insulating substrate 21 is prepared, and a tantalum layer 2 is formed thereon.
2. A tungsten layer 23 and an aluminum layer 24 are formed respectively. As will be described later, part of the tungsten layer 23 will be used as a cold cathode. Therefore, if a cold cathode having a conical shape with a diameter of about 5 μm is formed, it is preferable that the thickness of the tungsten layer 23 is about 2.5 μm, which is half the thickness, as in the first embodiment. Further, in order to perform anodization suitable for forming a cold cathode on tungsten, the formation voltage is preferably set to about 140 V, and the inward oxide film thickness d of tantalum at this formation voltage is 0. Since it is about 09 μm, the tantalum layer 22 needs to have a thickness of at least about 0.1 μm. Further, since the aluminum layer 24 functions as a cap layer as described later,
The thickness is preferably about 0.5 μm. Note that each of these layers may be formed by a sputtering method or a vacuum evaporation method.

Subsequently, a photoresist is applied on the aluminum layer 24 and patterned into a specific shape, as shown in FIG.
A resist layer 25 as shown in 5 is formed. Since this embodiment is an example of forming a conical cold cathode, the resist layer 25 has a circular pattern in plan view, but if a pyramidal cold cathode is formed, a polygonal pattern is formed accordingly. And it is sufficient. Then, using the resist layer 25 as a mask, the aluminum layer 24 is etched. The etching method is the same as in the first embodiment.
As a result, as shown in FIG. 16, part of the aluminum layer 24 remains as the cap layer 24a. Therefore, the tungsten layer 23 is etched using the cap layer 24a as a mask. H ₂ O ₂ was used as an etching solution for tungsten. As a result, the conical electrode 26 made of tungsten as shown in FIG. 17 is obtained. The conical electrode 26 has a so-called truncated cone shape and is a rough shape of the cold cathode to be manufactured.

Then, as shown in FIG. 18, an insulating layer 27 is formed.
To form. As the insulating layer 27, for example, Si
O ₂ , Al ₂ O ₃ , shot glass, or the like may be formed by a sputtering method or a vacuum evaporation method. Further thereon, as shown in FIG. 19, a gate electrode layer 28 is formed. As the gate electrode layer 28, for example, Ta,
A metal material such as Nb or Cr may be formed by a sputtering method or a vacuum evaporation method. It is preferable that the total thickness of the insulating layer 27 and the gate electrode layer 28 be substantially equal to the height of the conical electrode 26. For example, when the pyramidal electrode 26 has a height of 2.5 μm, the insulating layer 27 has a thickness of 2.3 μm and the gate electrode layer 28 has a thickness of 2.3 μm.
Can have a thickness of 0.2 μm.

Next, the cap layer 24a is peeled off (so-called lift-off) to obtain the structure shown in FIG. Then, an oxidation process, which is a feature of the present invention, is performed to form the conical electrode 26.
Sharpen the tip of the. At this time, care should be taken not to apply a voltage to the gate electrode layer 28 while applying a voltage to the conical electrode 26 to perform anodization.
Otherwise, even the gate electrode layer 28 will be oxidized. As the electrolyte solution used for this anodic oxidation, 0.5 M phosphoric acid was used. However, the electrolyte solution used for this anodic oxidation is not limited to phosphoric acid, and various other electrolyte solutions can be used. For example, as the solvent used for the electrolyte solution, acetic acid and various organic solvents (ethylene glycol, methanol, glycerin, propionic acid, etc.) can be used in addition to water, and as the solute, citric acid, adipic acid,
A neutral organic acid such as boric acid, lactic acid or acrylic acid, or a neutral or weakly acidic salt such as borax, sodium phosphate, potassium phosphate, sodium sulfate, potassium sulfate or potassium carbonate can be used.

FIG. 21 is a sectional view showing a state when the above-mentioned oxidation step is completed. An oxide film 26a is formed on the surface of the conical electrode 26 by oxidation, and a portion that has not been oxidized remains as the internal electrode 26b.
In addition, in the above-mentioned oxidation step, the exposed region of the tantalum layer 22 is also oxidized together with the conical electrode 26. Therefore, the exposed region of the tantalum layer 22 becomes the oxide film 27a. Then, when the tungsten oxide film 26a is removed, the exposed internal electrode 26b forms the cold cathode 29, and the structure shown in FIG. 22 is obtained. The oxide film 26a may be removed by immersing it in a 5% (wt%) ammonium borate aqueous solution, for example.

When the formation voltage is 140 V and the anodic oxidation is performed, the inward oxide film thickness d of tungsten is about 0.07 μm. Therefore, if the diameter D of the cutting head of the conical electrode 26 is up to about 0.14 μm, the cold cathode having a sharp tip can be obtained by the oxidation under these conditions. When the diameter D is larger, theoretically, the formation voltage should be raised to increase the thickness of the inward oxide film, but in reality, in the anodization of tungsten,
If the formation voltage is increased to 140 V or higher, stable oxide film formation cannot be achieved. So in this case,
Anodization with a formation voltage of 140 V may be performed several times in succession, and the oxide film may be formed and removed (dissolved) repeatedly. Even if the formation of the oxide film by anodic oxidation and the dissolution thereof are repeatedly performed, the internal tungsten is not adversely affected.

<Third Embodiment> This third embodiment is a modification of the above-mentioned first embodiment. First, as shown in FIG. 23, a transparent glass substrate 11 is prepared, and on top of this,
A tantalum layer 13 is formed as a first metal material layer, and an aluminum layer 14 is formed as a second metal material layer.
This structure corresponds to the structure of the first embodiment shown in FIG.
The ITO layer 12 is omitted. Thus, the third
The embodiment is characterized in that the ITO layer 12 is unnecessary. The reason will be described later. Also, the tantalum layer 1
The thickness of 3 is also slightly different from that of the first embodiment. That is,
In the first embodiment, the thickness of the tantalum layer 13 is 0.1 μm.
However, in the third embodiment, this is 0.12
The thickness is set to about 0.125 μm and is set to be slightly thicker. The reason for this will be described later.

Then, a photoresist is applied on the aluminum layer 14 to perform patterning in a specific shape, and then, as shown in FIG.
4 is formed, the resist layer 15 is used as a mask, and the aluminum layer 14 is etched. As shown in FIG.
A structure with 6 is obtained. This step is exactly the same as the step of the first embodiment described above. After that, the point that the resist layer 15 is removed and anodization is performed is also the same as in the first embodiment described above. The condition of anodic oxidation is also the formation voltage 150V.
I set it to. However, the difference from the first embodiment is that
As described above, the thickness of the tantalum layer 13 is set to be slightly thick. Therefore, even if anodic oxidation is performed under the same conditions, in the third embodiment, the tantalum layer 1
No. 3 is not completely oxidized for the entire thickness, and a part of the substrate side remains as a layer that has not been oxidized. FIG. 26 shows a state after completion of this anodic oxidation. The tantalum layer 13 is formed on the non-exposed portion covered with the internal electrode 16b.
The point that b remains is the same as in the first embodiment, but in the other exposed portions, the surface side is oxidized to form the oxide film 13a, but the substrate side is not oxidized. It remains as the remaining tantalum layer 13c. In this example, the remaining tantalum layer 13c having a thickness of about 0.025 μm remained.

Next, as in the first embodiment, the aluminum oxide film 16a shown in FIG. 26 is peeled off and removed, and the aluminum oxide film 16a shown in FIG.
The cold cathode 17 is exposed as shown in FIG. And FIG.
As shown in FIG. 8, a resist layer 18 is formed on the entire surface, and a part of the resist layer 18 is exposed by backside exposure. However, the conditions for this backside exposure are slightly different from those in the first embodiment. In the first embodiment, the backside exposure is performed in the structure as shown in FIG. 8, and in this structure, ITO is used.
Since both the layer 12 and the oxide film 13a are transparent,
In the resist layer 18, the portion shaded by the tantalum layer 13b and the cold cathode 17 was the non-exposed portion, and the other portion was the exposed portion. However, in this third embodiment,
In the structure as shown in FIG. 28, the backside exposure is performed, and the portion to be originally exposed (of the resist layer 18,
The light irradiated on the portion other than the portion shaded by the tantalum layer 13b and the cold cathode 17 is the remaining tantalum layer 13
The light is shielded by c. Remaining tantalum layer 13
Since c is a metal layer of tantalum, it does not have a light-transmitting property like an oxide layer. However, as mentioned above, the thickness is 0.025
Since it is a very thin film of about μm, it does not have a perfect light shielding property. Therefore, although the area to be originally exposed is weaker than that in the first embodiment, the back exposure exposes the light. Therefore,
In the third embodiment, the back surface exposure time is set to be long so that the resist layer 18 is sufficiently exposed. Specifically, while the backside exposure in the first embodiment was several seconds, the backside exposure in the third embodiment allows sufficient exposure by taking about 3 minutes. did it.

When the back exposure of the resist layer 18 is completed in this way, it is developed to obtain the structure shown in FIG. The structure of FIG. 29 is the first
9 is equivalent to the structure shown in FIG. That is, the remaining tantalum layer 13c plays the role of the ITO layer 12 in the structure shown in FIG. In the first place, the reason why the ITO layer 12 is formed in the first embodiment is to make it function as a wiring layer for the cold cathode 17. However, in the third embodiment, the remaining tantalum layer 13c can function as a wiring layer for the cold cathode 17, so that it is not necessary to provide the ITO layer 12. After the structure of FIG. 29 is obtained, the insulating layer 19 and the gate electrode layer 20 are formed as in the first embodiment.

In summary, the feature of the third embodiment is that a part of the tantalum layer 13 on the substrate side is left as the remaining tantalum layer 13c without being oxidized, and the remaining tantalum layer 13c is left as the first tantalum layer 13c.
It is used as a substitute for the ITO layer 12 in the above embodiment. At this time, it is important to set the thickness of the remaining tantalum layer 13c. If the remaining tantalum layer 13c becomes too thick, the light transmittance will decrease, and it will be a problem that the resist layer 18 cannot be sufficiently exposed in the step of back exposure. On the other hand, if the remaining tantalum layer 13c becomes too thin, the resistivity of the conductive layer increases, which causes a problem in the function of the cold cathode 17 as a wiring layer. Therefore, when anodizing a tantalum layer having a thickness of 0.12 μm from the surface side, the formation voltage during anodization (this is a condition that affects the thickness of the remaining tantalum layer) and the transmittance of the remaining tantalum layer. I investigated the relationship with FIG. 30 is a graph showing the results of this experiment. The formation voltage is plotted on the horizontal axis and the transmittance is plotted on the vertical axis, and the respective relationships are shown. It can be seen that the higher the formation voltage, the higher the transmittance. This is because the higher the formation voltage is, the more the anodic oxidation progresses and the thickness of the remaining tantalum layer becomes smaller. The formation voltage during anodic oxidation in this example is 150 V. Oxidation under these conditions provides a residual tantalum layer 13c having a thickness that can sufficiently function as a wiring layer, and the residual tantalum layer 13c having this thickness has a rear surface. A transmittance that allows sufficient exposure to light is obtained.

<Other Embodiments> The present invention has been described with respect to three embodiments, but the present invention is not limited to these embodiments and can be implemented in various modes other than this. . For example, it is possible to form another metal film on the surface of the cold cathode produced by the above method by a sputtering method or a vacuum evaporation method. For example, when a cold cathode made of aluminum is formed, aluminum generally has a relatively low melting point and is easily oxidized, so that it is not necessarily a suitable material for a cold cathode for electron emission. Therefore, by forming a metal film such as tantalum on the surface of the aluminum cold cathode and using it as a protective film, a cold cathode more suitable for electron emission can be generated. If the thickness of this protective film is suppressed to about 0.05 μm, the sharpness of the tip portion of the cold cathode is not affected.

Tantalum layer 1 in the above-mentioned first embodiment
3 has two functions. The first function is to protect the ITO layer 12 during anodic oxidation, and the second function is to use the gate electrode layer 20 and the cold cathode 17 as the oxide film 13a.
It is a function to increase the insulation between and. However, the tantalum layer 13 is not an essential component in the present invention, and the present invention can be implemented without using the tantalum layer 13. Further, in the above-mentioned embodiments, the oxidation is performed by the anodic oxidation method, but another oxidation method such as thermal oxidation may be used.

[0046]

As described above, according to the present invention, a conical electrode whose tip is not sharpened is generated, and an oxide film is formed on the surface of the pyramidal electrode to remove it, thereby sharpening the tip. Therefore, the cold cathode having a sharp tip can be easily manufactured.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a structure of a conventional general vertical vacuum micro device.

FIG. 2 is a diagram showing a basic principle of a method for manufacturing a cold cathode for electron emission according to the present invention.

FIG. 3 is a cross-sectional view showing a state in which a three-layer structure is formed on a substrate in the first embodiment of the present invention.

4 is a cross-sectional view showing a state in which a resist layer 15 having a circular pattern is formed in the state shown in FIG.

5 is a cross-sectional view showing a state in which a pyramidal electrode 16 is formed by performing etching with the resist layer 15 as a mask in the state shown in FIG.

6 is a cross-sectional view showing a state where anodic oxidation is performed on the conical electrode 16 shown in FIG.

7 is a cross-sectional view showing a state in which oxide film 16a shown in FIG. 6 is removed.

8 is a cross-sectional view showing a state in which a resist layer 18 has been formed in the state shown in FIG.

9 is a cross-sectional view showing a state where back exposure is performed and a resist layer is patterned in the state shown in FIG.

10 is a cross-sectional view showing a state where an insulating layer 19 is further formed in the state shown in FIG.

11 is a cross-sectional view showing a state where a gate electrode layer 20 is further formed in the state shown in FIG.

FIG. 12 shows a resist layer 18 in the state shown in FIG.
It is sectional drawing which shows the state which peeled a.

FIG. 13 is a table showing various conditions for anodization (relationship between formation voltage and oxide film thickness).

FIG. 14 shows a second embodiment of the present invention in which 3 is formed on the substrate.
It is sectional drawing which shows the state which formed the layer structure.

15 is a cross-sectional view showing a state in which a resist layer 25 having a circular pattern is formed in the state shown in FIG.

16 is a view showing the resist layer 15 in the state shown in FIG.
FIG. 6 is a cross-sectional view showing a state in which a cap layer 24a is formed by performing etching with the mask as a mask.

FIG. 17 is a diagram showing the tungsten layer 23 shown in FIG.
FIG. 6 is a cross-sectional view showing a state in which a conical electrode 26 is formed by etching.

FIG. 18 further includes an insulating layer 27 in the state shown in FIG.
FIG. 6 is a cross-sectional view showing a state in which the formation has been performed.

19 is a cross-sectional view showing a state in which a gate electrode layer 28 is further formed in the state shown in FIG.

FIG. 20 shows the cap layer 24 in the state shown in FIG.
It is sectional drawing which shows the state which peeled a.

21 is a cross-sectional view showing a state where anodic oxidation is performed on the conical electrode 26 in the state shown in FIG.

22 is a cross-sectional view showing a state in which oxide film 26a is removed in the state shown in FIG.

FIG. 23 shows the second embodiment of the present invention, in which 2 is formed on the substrate.
It is sectional drawing which shows the state which formed the layer structure.

FIG. 24 is a cross-sectional view showing a state in which a resist layer 15 having a circular pattern is formed in the state shown in FIG.

FIG. 25 shows the resist layer 15 in the state shown in FIG.
FIG. 6 is a cross-sectional view showing a state in which a conical electrode 16 is formed by performing etching using the as a mask.

26 is a cross-sectional view showing a state in which the surface portions of the pyramidal electrode 16 and the tantalum layer 13 shown in FIG. 25 are anodized.

27 is a cross-sectional view showing a state in which oxide film 16a shown in FIG. 26 is removed.

FIG. 28 is a view showing the resist layer 18 in the state shown in FIG.
It is sectional drawing which shows the state which formed.

29 is a cross-sectional view showing a state where back exposure is performed and the resist layer is patterned in the state shown in FIG. 28. FIG.

FIG. 30 is a graph showing the relationship between the formation voltage of the tantalum layer during anodic oxidation and the transmittance of the remaining tantalum layer that has not been oxidized.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Glass substrate 2 ... Wiring layer 3 ... Cold cathode 4 ... Insulating layer 5 ... Extraction electrode 6 ... Glass substrate 7 ... Anode 8 ... Phosphor layer 9 ... Conical electrode 9a ... Oxide film 9b ... Internal electrode 11 ... Glass substrate 12 ... ITO layer 13 ... Tantalum layer 13a ... Tantalum oxide film 13b ... Tantalum layer 13c ... Remaining tantalum layer 14 ... Aluminum layer 15 ... Resist layer 16 ... Conical electrode 16a ... Aluminum oxide film 16b ... Internal electrode 17 ... Cold cathode 18 , 18a ... Resist layer 19 ... Insulating layer 20 ... Gate electrode layer 21 ... Insulating substrate 22 ... Tantalum layer 23 ... Tungsten layer 24 ... Aluminum layer 24a ... Cap layer 25 ... Resist layer 26 ... Conical electrode 26a ... Tungsten oxide film 26b ... Internal electrode 27 ... Insulating layer 27a ... Oxide film 28 ... Gate electrode layer 29 ... Cold cathode

Claims (5)

[Claims] 1. A method for producing a cold cathode used in an apparatus comprising a cold cathode, an extraction electrode, and an anode, wherein an electron is extracted from the cold cathode by the extraction electrode and emitted to the anode, wherein a conical electrode is formed. After that, the surface of the conical electrode is oxidized to form an oxide film having a predetermined thickness, and the oxide film is removed to obtain a conical cold cathode having a sharp tip. Manufacturing method of cold cathode for electron emission. 2. The method according to claim 1, wherein the conical electrode is made of a metal material, and an oxide film is formed on the metal material by an anodic oxidation method. Method. 3. The method according to claim 2, wherein the oxides have different etching characteristics, and the respective oxides also have different etching characteristics.
A metal material and a second metal material are prepared, a first metal material layer is formed on a substrate, a second metal material layer is formed on the first metal material layer, and the second metal material layer is formed. By etching the metal material layer to form a pyramidal electrode made of a second metal material and anodizing the exposed surface of the first metal material layer and the surface of the pyramidal electrode, Forming a metal oxide film and a second metal material oxide film, and removing the second metal material oxide film by etching to obtain a cold cathode made of the second metal material, and the first metal material. A method of manufacturing a cold cathode for electron emission, wherein the oxide film is used as an insulating layer between the cold cathode and the extraction electrode. 4. The method according to claim 3, wherein the substrate is a transparent substrate and the first metal material is tantalum.
Using aluminum as the second metal material,
A method of manufacturing a cold cathode for electron emission, characterized in that anodic oxidation is performed under conditions such that all the thickness portions in the exposed region of the tantalum layer are oxidized. 5. The method according to claim 1, wherein a cone-shaped cold cathode having a sharp tip is obtained,
A method of manufacturing a cold cathode for electron emission, characterized in that a film made of a different material is formed on the surface of the cold cathode.