JP3436219B2 - Carbon material, method for producing the same, and field emission cold cathode using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon material and a field emission cold cathode, and more particularly to a field emission cold cathode having an emitter that emits electrons, and an electric field having an emitter using a carbon film. A method for forming a needle-like structure in an emissive cold cathode.

[0002]

2. Description of the Related Art A field-emission cold cathode has recently been attracting attention in display applications and the like as an electron gun capable of emitting electrons in a vacuum by applying an electric field to the emitter, instead of a hot cathode. In particular, attention has been paid to a cone-shaped emitter having a minute shape and a method of using diamond as the emitter. This is because the emitter having a minute cone shape can be processed to a size of a micron or less due to the progress of the fine processing technology of semiconductor elements, and thus it becomes possible to easily form a minute electron source. In addition, diamond has high hardness, is chemically stable, and has an advantageous characteristic as an electron-emitting device such as a negative electron affinity in which the energy level of the conductor surface is lower than the energy level of vacuum. Have When the electron has a property of negative electron affinity, electrons are supplied to the conductor of diamond, and when the electron reaches the diamond surface, the electron can be emitted into a vacuum.

Therefore, a technique of utilizing diamond as an emitter material has been proposed so far. For example, there is a method of thinly coating a carbon film of diamond or diamond-like carbon on the surface of a cone-shaped micro electron source. This is a cone-type field emission cold cathode with a CVD (Chemical Vap)
or Deposition method etc., there is an advantage that it can be formed only by adding a step of depositing a diamond thin film on the tip of the cone. Also, a method of etching the diamond film itself has been reported, which is disclosed in, for example, JP-A-6-
It is disclosed in Japanese Patent No. 132254.

This method is a method in which a mask material such as aluminum is formed on the surface of the diamond film and the diamond film is selectively plasma-etched using a mixed gas of argon gas and oxygen gas. According to this method, it is possible to increase the selection ratio between the mask material and diamond, and there is an advantage that the fine workability of diamond is improved. When plasma etching is performed on diamond with oxygen gas in this method, the selectivity with respect to the mask material is further increased, but the flatness of the diamond surface deteriorates and
It has been reported that a columnar structure of 50 nm is formed.

Further, there is a method of forming diamond on the tip of a protruding emitter, which is disclosed in Japanese Patent Laid-Open No. 9-265892.

FIG. 9 is a schematic sectional view showing a conventional field emission cold cathode and its manufacturing process. As shown in FIG. 9E, a protruding conductive material 28 made of, for example, silicon is formed on the substrate electrode 21 made of, for example, a silicon substrate, and a diamond 26 is formed at the tip thereof. The manufacturing method will be described in the order of steps. First, FIG.
As shown in (a), a diamond film 26 is formed on the substrate electrode 21 made of silicon by a vapor phase epitaxy method. Next, as shown in FIG. 9B, an aluminum layer 27 serving as a mask for processing diamond is formed by a vacuum evaporation method.
Next, as shown in FIG. 9C, the resist is processed into a desired pattern having a diameter of 5 microns and a spacing of 20 microns by photolithography, and the aluminum layer 27 is patterned using the resist as a mask. Next, as shown in FIG. 9D, the diamond 26 is patterned by reactive ion etching using oxygen gas using the aluminum layer 27 as a mask. Next, as shown in FIG. 9E, after removing the aluminum layer 27, the diamond 2
Using 6 as a mask, the substrate electrode 21 is etched by reactive ion etching to form a conductive material 28 having a protruding structure. As described above, it is possible to form the field emission cold cathode having the emitter in which the diamond 26 is formed on the conductive material 28 having the protruding structure. In this way diamond 26
Is formed only on the tip of the emitter, and the projection structure is formed of the conductive material 28 that is easily etched, so that it is easy to process.

As another method, Applied Physics Letters (Applied Physics) is used.
Letters) Volume73, Number1
5, 1998, pages 2119-2121, which form selectively grown graphite nanofibers. This is a method in which fibrous graphite grows from the substrate by performing a plasma assisted CVD method on a substrate made of nickel in nitrogen and acetylene gas. This method has been reported to form nanofibers of 30 to 100 nm.

[0008]

The first problem of the prior art shown in FIG. 9 is that the method of coating a carbon film such as diamond after forming a cone-type emitter has a large radius of curvature at the emitter tip. It is a disadvantage for electron emission. Generally, the field emission characteristics largely depend on the radius of curvature of the tip of the emitter material and the work function. Therefore,
Even if a material such as diamond that is easily emitted is coated on the surface of the cone-shaped emitter, the radius of curvature of the tip is increased by the coating film thickness. As a result, even if the coating material facilitates emission, there is a possibility that the radius of curvature of the tip becomes large and the characteristics are not necessarily significantly improved.

The second problem of the prior art shown in FIG. 9 is that
The fact that oxygen gas is mainly used as the etching gas for diamond facilitates oxygen termination on the diamond surface. Oxygen gas has a high etching rate with respect to diamond, and has an advantage of having a high selectivity with respect to a mask material such as aluminum. However, when oxygen gas is used for etching diamond, the structure in which the diamond surface is terminated by oxygen does not provide the negative electron affinity characteristics obtained when hydrogen-terminated, and the problem of emission deterioration occurs. there were. Furthermore, it was easy to supply electrons that contribute to emission to the emitter tip by increasing the surface conductivity of diamond when it is hydrogen-terminated, but through the bulk of diamond, which has low conductivity, when it is oxygen-terminated. Since electrons are supplied to the tip of the emitter, it is disadvantageous to obtain a high emission current when the emitter is formed only by diamond.

The third problem of the prior art shown in FIG. 9 is that
When oxygen is used as the main etching gas to process diamond, a high selection ratio with respect to the mask material can be obtained, but on the other hand, the columnar structure makes it difficult for an electric field to be applied to the protruding emitter tips. As described above, the emission characteristic greatly depends on the radius of curvature of the tip of the emitter, and therefore, it is advantageous to improve the emission characteristic by making the shape with a sharp tip radius of curvature small. However, in the case of etching using oxygen, a columnar structure is formed, so that the tip has a flat shape, which is disadvantageous for emission.

The fourth problem of the prior art shown in FIG. 9 is that
The method of forming a projection-shaped emitter with a material that can form the emitter shape relatively easily and forming a diamond at the tip is determined by the photolithography that forms the diamond at the tip. Is difficult to reduce. Generally, when photolithography is used, it is considered that the diameter of about submicron and the distance between patterning are the limits. Therefore, the tip radius of curvature is 10 nm, which is formed by a cone-shaped micro emitter.
This is disadvantageous for emission because it can only obtain a radius of curvature that is 10 times larger than the degree. Further, as the number of emitters increases, emission is more likely to be obtained, but the distance between emitters is also limited, so there is a limit to improvement of emissions by increasing the number of emitters.

Further, the fifth problem of the prior art shown in the above-mentioned document is that the needle-like emitter formed by the method of forming nanofibers becomes graphite fiber, so that the film quality is graphite-like. This means that the film is limited, and the negative electron affinity characteristic obtained with diamond may not be obtained. Further, since the shape is limited to the fiber structure, the diameter of the tip is about 30 nm at the minimum, but the diameter is mainly 60 to 70 nm, and there is a limit to the miniaturization of the tip.

An object of the present invention is to provide a field emission cold cathode in which a large number of emitters made of a carbon film such as diamond can be sharply formed to improve emission points and emission characteristics and to obtain high current emission at low voltage. is there.

[0014]

The present invention is a carbon material characterized in that the surface of a carbon film is covered with a needle-like protrusion structure made of carbon, and a field emission cold cathode using the same. .

Further, such a carbon material can be obtained by plasma-treating a carbon film in hydrogen gas to form a needle-shaped carbon film on the surface of the carbon film. Here, a needle-like carbon film may be formed by etching the carbon film by plasma treatment, and at this time, a desired shape is obtained by forming materials having different etching rates in or on the surface of the carbon film. be able to. Sp2 is used as a material with different etching rates
A carbon film in which the structure and the sp3 structure are mixed is conceivable.

According to the present invention, the emitter made of the carbon film has a needle-like shape with a plurality of sharpened tips, so that the electric field strength to the tip of the emitter is increased and many emission points can be formed. for,
It is possible to provide a high-performance field emission cold cathode capable of obtaining a high current value with a low emission current.

Further, in the structure of the present invention, by using as the emitter material a carbon film in which a diamond film having a high emission property, that is, a carbon film having an sp3 structure and a graphite film having a high conductivity, that is, a carbon film having an sp2 structure are combined. It is possible to provide a field emission cold cathode having high conductivity and high emission characteristics. In this structure, the emission characteristics can be further improved by disposing the carbon film having the sp3 structure at the tip of the emitter.

Further, according to the present invention, a method of manufacturing a field emission type cold cathode capable of easily forming a plurality of sharp needle-like emitters simultaneously by subjecting a carbon film to plasma treatment in hydrogen. Can be provided.

In the manufacturing method of the present invention, by mixing materials having different etching rates during hydrogen plasma in the carbon film or on the surface thereof, a material having a slow etching rate is masked when the carbon film is etched. Therefore, it becomes possible to form a needle-shaped emitter in a self-aligned manner.

Therefore, when a carbon film having a high sp2 structure and a carbon film having a low etching speed are simultaneously formed by the hydrogen plasma treatment when the carbon film is formed, the carbon film and the emitter are formed by the same film forming apparatus. It becomes possible to form a mask material. Furthermore, since carbon of sp3 structure having a high emission characteristic can be formed at the tip of the emitter in a self-aligned manner, the emission characteristic can be improved at the same time.

Further, the hydrogen plasma treatment is performed by ECR (Ele
ctron Cyclotron Resonance)
By using plasma, a high plasma property can be obtained, and a sharp needle-shaped emitter can be easily formed.

Further, the field emission type cold cathode having high conductivity can be formed by covering the needle-shaped emitter surface with an amorphous carbon film or a conductive film preferably made of carbon of sp2 structure by hydrogen plasma treatment.

Further, by adopting a structure in which the needle-shaped emitter reaches the lower substrate electrode, a field emission type cold cathode having higher conductivity can be formed.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a field emission cold cathode and a method for manufacturing the same according to a first embodiment of the present invention. In the first embodiment of the present invention, as shown in FIG. 1 (c), a carbon film 2 whose upper surface is covered with a sharp needle-like protrusion structure is formed on a substrate electrode 1 serving as a conductive cathode electrode. It has been configured. The needle-shaped protrusion structure has a conical or pyramidal shape with a bottom width of several nm to 200 nm and a height of approximately 10 nm to 1 μm.
They are arranged at the same pitch as the width of the bottom surface, which is m.
With such a structure in which the emitters made of needle-like carbon film with sharp tips are densely present, the sharpness of the tips of the emitters increases the amount of current that can be obtained from each emitter. The amount of emission current that is obtained is large due to the fact that they are densely arranged and the number is large. Further, by using a film having a high sp3 property as the carbon film, the characteristics of diamond are obtained and the emission characteristics are further improved. By adopting a structure in which the surface is individually hydrogen-terminated, the electric conduction on the diamond surface is improved and the emission current is more easily obtained.

Next, the manufacturing method will be described. Figure 1
In (a), for example, an n-type silicon substrate is prepared as the substrate electrode 1. In this example, it is a silicon substrate,
The present invention is not limited to this, and for example, for display applications, a substrate electrode made of a metal formed on a glass substrate may be used.

Next, as shown in FIG. 1B, a carbon film 2 is deposited on the substrate electrode 1 by a hot filament CVD method of about 5 μm. An example of the conditions for forming the carbon film is as follows: scratch treatment is performed on the substrate electrode 1 with diamond powder having a particle size of approximately 1 μm to attach the diamond powder to the substrate electrode surface, and then approximately 1.33 × 10 6 in a hot filament CVD chamber. ^-4 Pa (Pascal) (approximately 10 ^-6 Torr) is exhausted and, for example, methane / hydrogen is approximately 5 sccm (Standard cubic center).
imager per minute) / approximately 500sc
Flowing at a flow rate of cm, approximately 2.66 × 10 ³ Pa (approximately 20T
orr). At this time, the filament temperature is about 2200 ° C. and the substrate temperature is about 800 ° C. It is known from Raman evaluation that a polycrystalline carbon film having a high sp3 property is thus formed. In this example, the diamond powder was adhered to the substrate electrode by scratching before the film formation, but the diamond powder may be adhered by another method or may be formed without being adhered. Furthermore, although the film was formed by hot filament CVD this time, it may be formed by another method, for example, a microwave plasma CVD method, a DC arc method, or a combustion flame method.

Next, as shown in FIG. 1 (c), hydrogen is added to about 40%.
Introduce about 0.013 to 0.133 Pa (about 1)
Under a pressure of 0 ⁻⁴ to 10 ⁻³ Torr), a magnetic field of about 850 to 900 G and a microwave of about 2.5 GHz are applied to the ECR ion source to generate ECR plasma with an output of about 500 W. As a result, a needle-like structure is densely formed on the surface state of the carbon film. This is because the structure of the carbon film by the ECR plasma treatment, or the deposited material on the surface, or the regrown substance during the plasma treatment serves as a mask material when the carbon film is etched by the plasma treatment, or the plane orientation and the multiple orientations of the carbon film are increased. A needle-like structure is formed by a phenomenon in which the shape is locally changed due to a difference in etching rate between grains of a crystal structure, or singly or in combination.

In the present invention, since argon gas, which has an etching rate regardless of the material, is not the main component of etching, the mask material is not rapidly removed by etching, which has the advantage that protrusions having a high aspect ratio can be formed. is there. Also, since oxygen gas, which has a high selectivity, is not the main component, it does not have a columnar structure instead of a needle-like structure, and the etching rate is not as high as that of oxygen, so the carbon film is removed by etching before the needle-like structure is formed. It will not be done. FIG. 10 shows a photograph of the carbon film after etching.

Next, a second embodiment of the present invention will be described. FIG. 2 is a schematic sectional view showing a field emission type cold cathode according to a second embodiment of the present invention and a manufacturing process thereof. The second form of the present invention is as shown in FIG.
A carbon film 2 having an upper surface covered with a protrusion structure is formed on a substrate electrode 1 serving as a conductive cathode electrode, and carbon 3 of sp3 structure is formed in a sharp shape at the tip of the carbon film 2. Has become. The protrusion structure is in the shape of a cone or a pyramid having a bottom width of several nm to 200 nm, and the height is approximately 10 nm to 1 μm. In this way, diamond-like emission characteristics can be obtained by using the carbon film of sp3 structure at the tip of the acicular structure. The curvature of the carbon 3 of this sp3 structure is about 10
It is 0 nm or less, preferably about 10 nm. This is because the emission characteristics of the needle-shaped emitter largely depend on the radius of curvature of the tip. Further, the carbon film 2 is sp2
The structure gives low resistance graphite-like characteristics,
This is more advantageous in supplying current to the tip of the needle-like structure, which is an emission point, than forming the entire carbon film with diamond of sp3 structure.

Next, the manufacturing process of the second embodiment will be described. In FIG. 2A, a carbon film 2 having a thickness of about 5 μm is formed on a substrate electrode 1 made of, for example, a silicon substrate by a hot filament CVD method, for example. Next, as shown in FIG. 2B, granular carbon 3 having an sp3 structure is formed on the surface of the carbon film 2 by, for example, scratching diamond. After that, as shown in FIG. 2C, ECR using hydrogen gas
The carbon film 2 is etched by plasma treatment using the carbon 3 having the sp3 structure as a mask. By making the carbon film 2 a graphite film having an sp2 structure in this step, an appropriate selection ratio with respect to the carbon film having the sp3 structure on the surface is obtained, and the carbon film 2 is etched in the depth direction, and at the same time, the sp3 of the mask is The carbon film 3 having the structure is also etched and becomes smaller, so that a needle-like shape and a shape in which the carbon 3 having the sp3 structure remains at the tip can be obtained.

In this method, the carbon 3 having the sp3 structure at the tip can be removed by further lengthening the ECR plasma treatment. Thereby, the field emission cold cathode of the first embodiment can also be formed. As described above, in the present embodiment, it becomes possible to easily selectively form the diamond of the sp3 structure having a high emission characteristic at the tip of the needle-shaped emitter having a uniform height.
In addition, although the example in which the carbon film 3 having the sp3 structure is formed by the scratch process is shown in the present embodiment, the present invention is not limited to this, and instead, for example, hot filament CVD.
When the carbon film is formed on the surface of the carbon film 2 by the method at a substrate temperature of about 600 ° C., a carbon film having a mixture of sp2 and sp3 structures is formed. The carbon of sp3 structure in this film can also be used as a mask. in this way,
It is possible to control the particle size of carbon having an sp3 structure depending on the film forming conditions, and it is possible to control a finer diameter than that performed by scratching. Further, since it can be formed continuously with the carbon film 2, there is also an advantage that the process can be simplified.

Next, a third embodiment of the present invention will be described. FIG. 3 is a schematic sectional view showing a field emission cold cathode according to a third embodiment of the present invention and a manufacturing process thereof. The third mode of the present invention is as shown in FIG.
The structure is such that the upper surface is covered with a protruding structure and a carbon film 2 containing carbon 3 of sp3 structure is formed in the film on a substrate electrode 1 serving as a conductive cathode electrode. Furthermore, as shown in the figure, the tip of the needle-like protrusion that becomes the emitter is sp
You may arrange | position the carbon 3 of 3 structure. The number of protrusions is n
They have a conical or pyramidal shape with a bottom width of m to 200 nm and a height of approximately 10 nm to 1 μm, and are arranged at the same pitch as the bottom width. The carbon film 2 is a cathode material that emits electrons, and the carbon film 2 is composed of sp2 structure carbon 2a and sp3 structure carbon 3. The carbon film 2 preferably has a structure mainly composed of the sp2 structure 2a. Thus, s
By forming the carbon film 2 having the p2 structure as a main structure, it is possible to form a protrusion having a needle-like structure which is advantageous for supplying an emission current having a low resistance. Further, diamond-like emission characteristics can be obtained by forming the sp3 structure carbon film at the tip of the acicular structure.

Next, the manufacturing process of the third embodiment will be described. FIG. 3A shows a carbon film containing sp3 structure carbon 3 on a substrate electrode 1 made of, for example, a silicon substrate, and having a faster etching rate in a hydrogen plasma treatment process than sp3 structure carbon, for example, a sp2 structure-based carbon film. 2 is formed to a thickness of about 5 μm by, for example, a hot filament CVD method. Next, as shown in FIGS. 3B to 3C, the carbon film 2 is etched by ECR plasma treatment using hydrogen gas. The shape during the ECR plasma process is shown in Fig. 3.
As shown in (b), the carbon film 2 is etched, but if the carbon 3 of the sp3 structure in the film is exposed, the etching rate is slow and the film becomes a mask to form a needle-like protrusion structure. E so that a proper selection ratio can be obtained
When CR plasma conditions or film characteristics are set, the carbon film 2 is etched in the depth direction and at the same time sp
The carbon 3 having the three structure is also etched and becomes smaller, whereby a needle-like shape and a shape in which the carbon film 3 having the sp3 structure remains at the tip can be obtained. Further, when the ECR plasma treatment is performed, as shown in FIG. 3C, the carbon 3 having the sp3 structure formed deep in the carbon film 2 is exposed, and this serves as a new mask to form needle-like protrusions. As a result, although the heights are different, the needle-shaped protrusions are formed in the entire surface.

In this method, the carbon film 3 having the sp3 structure at the tip can be removed by further lengthening the ECR plasma treatment. Moreover, the height of the needle-like protrusion structure can be adjusted by adding oxygen plasma treatment. Incidentally, it is desirable that the particle size of the carbon 3 having the sp3 structure in the carbon film is finally set to about 10 nm or less in order to determine the diameter of the tip of the emitter. To form a needle-shaped protrusion structure having an aspect ratio of about 10 or more, a selection ratio of about 10 is required. In this case, if the carbon 3 having the sp3 structure is isotropically etched by the ECR plasma treatment, the grain size needs to be a selection ratio times the emitter tip diameter. Therefore, it is desirable that the thickness is approximately 100 nm.

This method has an advantage that the carbon 3 having the sp3 structure, which serves as a mask for forming needle-like protrusions in the carbon film 2 at the time of forming the carbon film 2, can be simultaneously formed and the process can be simplified. Furthermore, since the carbon 3 having the sp3 structure in the film is used as a mask, it is possible to arrange the carbon film 3 having the sp3 structure having high emission characteristics in a self-aligned manner at the tip of the needle-shaped protrusion, that is, the emitter. Further, since the carbon 3 having the sp3 structure is arranged in the depth direction of the carbon film 2 to serve as a mask for forming needle-like protrusions, needle-like protrusions are formed between the needle-like protrusions. With such a structure, the in-plane density of the needle-shaped protrusions can be greatly improved.

Next explained is the fourth embodiment of the invention. FIG. 4 is a sectional view of the fourth embodiment of the present invention. As shown in FIG. 4, a carbon film 2 whose upper surface is covered with a protrusion structure having a height of about 1 μm, for example, is formed on a substrate electrode 1 serving as a conductive cathode electrode. 2 through the insulating film 4
The gate electrode 5 made of a metal film having a thickness of 00 nm is formed. In this example, the structure of the carbon film 3 having the needle-shaped protrusions that serve as the emitter is the same as the first embodiment of the present invention.
However, the present invention is not limited to this, and the emitter according to the second or third embodiment of the present invention may be used. The fourth embodiment of the present invention has a structure in which the gate electrode 5 is arranged in the vicinity of the emitter, and it is possible to apply a desired electric field to the tip of the emitter at a low voltage and easily obtain high emission characteristics. Is possible.

Next explained is the fifth embodiment of the invention. FIG. 5D is a sectional view of a field emission cold cathode device according to the fifth embodiment of the present invention. The substrate electrode 1 is a substance that becomes a base during deposition of the cold cathode material, and also serves as a lower electrode. The substrate electrode 1 may be any semiconductor material or conductor, for example Si, Mo, F
e, Ni, Pt and the like. Alternatively, a metal film may be attached to an insulating substrate such as glass, or one obtained by vapor deposition or deposition may be used as the substrate electrode. The carbon film 2 serving as a cold cathode material is a material that causes electron emission. The surface of the carbon film 2 has a needle-like protrusion structure. The surface conductive film 9 is a carbon film containing sp2.
The electric conductivity is higher than that of, and the thickness is approximately 10 nm or less, and the surface resistivity is approximately 10 ⁵ Ωcm or less. Surface conductive film 9
Since it is a part of the electron supply path, its resistance is preferably low, and is preferably about 10 ⁵ Ωcm or less.
The insulating film 4 is an insulating material that electrically separates the carbon film 2 and the gate electrode 5, and is mainly formed of an oxide film or the like. The gate electrode 5 is an electrode for extracting electrons by the carbon film 2, and is composed of a metal thin film.

FIG. 5 is a sectional view showing the manufacturing process of the fifth embodiment of the present invention. As shown in FIG. 5A, an n-type silicon substrate electrode was used as the substrate electrode 1. Next in FIG.
As shown in (b), a polycrystalline diamond film was formed as a carbon film 2 on the substrate electrode 1 by the CVD method, and the film thickness at this time was set to about 5 μm. afterwards,
As shown in FIG. 5C, the surface of the carbon film 2 was exposed to hydrogen plasma. This hydrogen plasma treatment was generated by ECR. At this time, impurities and minute defects existing in the CVD polycrystalline diamond film are selectively etched to form a needle-shaped protrusion structure. This method does not require a lithographic step to process the cold cathode material itself. Further, since hydrogen plasma treatment damages the carbon film 2 in the etching process, the surface of the carbon film 2 and the surface of the needle-like protrusion structure are formed of an amorphous carbon film, or preferably a surface conductive film made of a carbon film containing an sp2 structure. The film 9 is formed. Next, as shown in FIG. 5D, after depositing the insulating film 4 and a metal film to be the gate electrode 5, the insulating film 4 and the gate electrode 5 are processed into arbitrary shapes by a lithography process. Although the needle-shaped protrusion structure is formed only by the hydrogen plasma treatment in this embodiment, the hydrogen plasma treatment may be performed after the oxygen plasma treatment is performed in advance. By performing the oxygen plasma treatment, the thickness of the carbon film 2 can be thinned and the needle-like protrusion structure can be formed by the hydrogen plasma treatment. Therefore, it is possible to easily form the needle-like protrusion structure from the substrate electrode 2. There is. The insulating film 4 and the gate electrode 5 were formed after the carbon film 2 was formed into a needle-like projection structure by hydrogen plasma treatment. The insulating film 4 and the gate electrode 5 were formed first, and then the carbon film 9 was formed by hydrogen plasma treatment. There is no problem even if the is processed into a needle-shaped protrusion structure. Further, in this embodiment, the carbon film 2 under the insulating film 4 is used.
Although an example in which the needle-like shape is formed as is shown in FIG. 4, the needle-like shape of the carbon film 2 under the insulating film 4 is removed by a method such as oxygen plasma etching in advance and flattened, as shown in FIG. 4 may be formed.

Next, the operation of the field emission type cold cathode device according to the fifth embodiment of the present invention will be described in detail with reference to FIG. In order to operate the field emission type cold cathode device of this embodiment, a negative bias is applied to the substrate electrode 1 or a positive bias is applied to the gate electrode 5. Then, electric field concentration occurs at the tip of the carbon film 2 whose surface has a needle-like protrusion structure, so that the voltage applied to the substrate electrode 1 or the gate electrode 5 can be lowered. In Table 1 below,
A diamond film in an as-grown state before hydrogen plasma treatment (sample 1), a diamond film whose surface has a needle-like protrusion structure and whose surface is covered with a diamond film containing an sp2 structure by hydrogen plasma treatment (sample 2), The respective threshold electric field intensities of the diamond film (Sample 3) obtained by removing the carbon film containing the sp2 structure by the oxidizing agent or oxygen plasma treatment are shown. The determination current density at this time is 10 μA / cm ² . From the results in Table 1, it was found that the threshold electric field strength of Sample 2 was the highest and the field electron emission characteristics were improved.

[0040]

[Table 1]

Next explained is the sixth embodiment of the invention. FIG. 6D is a sectional view of a field emission type cold cathode device according to the sixth embodiment of the present invention. The substrate electrode 1 is a lower electrode. The substrate electrode 1 may be any semiconductor material or conductor, such as Si, Mo,
Fe, Ni, Pt and the like can be mentioned. The carbon film 2 is a cathode material that emits electrons, and preferably contains carbon having an sp3 structure. Also, this carbon film 2
The surface of the has a needle-like protrusion structure. The surface conductive film 9 is an amorphous carbon film, or preferably a carbon film containing an sp2 structure, has higher conductivity than the carbon film 2 and has a thickness of about 10 nm or less and a surface resistivity of about 10 ⁵ Ωcm or less. is there. Since the surface conductive film 9 is a part of the electron supply path, it is preferable that its resistance is low.
It is preferably 0 ⁵ Ωcm or less. The insulating film 4 is an insulating material that electrically separates the carbon film 2 and the gate electrode 5, and is mainly formed of an oxide film or the like. The gate electrode 5 is an electrode for extracting electrons by the carbon film 2, and is composed of a metal thin film. The support substrate 10 is a portion that serves as a base of the field emission cold cathode device, and is made of an insulating material such as glass, plastic, or ceramic material.

FIG. 6 is a cross-sectional view showing the manufacturing process of the sixth embodiment of the present invention. In FIG. 6A, the substrate electrode 1 has M
Using o, a carbon film 2 containing, for example, polycrystalline diamond is formed as a cold cathode material on the substrate electrode 1 by the CVD method. At this time, the thickness of the carbon film 2 is approximately 5 μm.
And Next, an oxide film to be the insulating film 4 and a metal film to be the gate electrode 5 are deposited. Next, as shown in FIG. 6B, the insulating film 4 and the gate electrode 5 are processed into arbitrary shapes by a lithography process. Then, as shown in FIG. 6C, the surface of the carbon film 2 was exposed to hydrogen plasma. At this time, impurities and minute defects existing in the CVD polycrystalline diamond film are selectively etched to form a needle-shaped protrusion structure. At this time, the needle-like protrusion structure has a carbon film 2.
The structure is such that the surface of the substrate electrode 1 reaches the surface of the substrate electrode 1. The structure may be such that a part of the surface of the substrate electrode 1 is etched by overetching.
Further, by setting the hydrogen plasma treatment condition in the etching process to damage the carbon film 2,
On the surface of the carbon film 2 and the surface of the needle-like protrusion structure, an amorphous carbon film or a surface conductive film 9 preferably made of a carbon film containing an sp2 structure is formed. In this embodiment, after the insulating film 4 and the gate electrode 5 are formed on the carbon film 2, the carbon film 2 is subjected to hydrogen plasma treatment to form a needle-shaped protrusion structure. There is no problem even if the insulating film 4 and the gate electrode 5 are formed after forming the protruding structure having a circular shape. Finally, as shown in FIG. 6D, the support substrate 10 serving as a support base is formed by adhering it to the back surface of the substrate electrode 1.

Next, the operation of the field emission type cold cathode device according to the sixth embodiment of the present invention will be described in detail with reference to FIG. 6 (d). In order to operate the field emission type cold cathode device of this embodiment, a negative bias is applied to the substrate electrode 1 or a positive bias is applied to the gate electrode 5. Then, electric field concentration occurs at the tip of the carbon film 2 whose surface has a needle-like protrusion structure, and the needle-like protrusion reaches the substrate electrode 1, so that electrons can be easily supplied from the substrate. , Substrate electrode 1
Alternatively, the voltage applied to the gate electrode 5 can be lowered.

Next explained is the seventh embodiment of the invention. FIG. 7D is a sectional view of a field emission type cold cathode device according to the seventh embodiment of the present invention. The substrate electrode 1 is a substance that becomes a base during deposition of the cold cathode material, and also serves as a lower electrode. The substrate electrode 1 may be any semiconductor material or conductor, for example Si, Mo, F
e, Ni, Pt and the like. Alternatively, a metal film may be attached to an insulating substrate such as glass, or one obtained by vapor deposition or deposition may be used as the substrate electrode. The carbon film 2 serving as a cold cathode material is a material that causes electron emission. The carbon film 2 is a cathode material that emits electrons, and the carbon film 2 is composed of sp2 structure carbon 2a and sp3 structure carbon. The surface of the carbon film 2 has a needle-like protrusion structure. The surface conductive film 9 is an amorphous carbon film or, preferably, a carbon film containing an sp2 structure, has higher conductivity than the carbon film 2 and has a thickness of about 10 nm or less and a surface resistivity of about 1.
It is 0 ⁵ Ωcm or less. Since the surface conductive film 9 is a part of the path of electron supply, it is preferable that the resistance thereof is low.
It is preferably ⁵ Ωcm or less. The insulating film 4 is an insulating material that electrically separates the carbon film 2 and the gate electrode 5, and is mainly formed of an oxide film or the like. The gate electrode 5 is an electrode for extracting electrons by the carbon film 2, and is composed of a metal thin film.

FIG. 7 is a sectional view showing a manufacturing process of the seventh embodiment of the present invention. As shown in FIG. 7A, an n-type silicon substrate was used for the substrate electrode 1. Next, FIG.
As shown in (b), the carbon film 2 is formed on the substrate electrode 1 by the CVD method or the sputtering method. In this example, a diamond-like carbon film was formed on the substrate electrode 1 as the carbon film 2 of the cold cathode material, and the film thickness at this time was set to about 3 μm. This carbon film 2 is a film in which carbon 3 of sp3 structure is interspersed with carbon 2a of sp2 structure. Then, as shown in FIG. 7C, the surface of the carbon film 2 was exposed to hydrogen plasma treatment. At this time sp
The carbon 3 of 3 structure serves as a mask, and the carbon 2a of sp2 structure is selectively etched to form a needle-shaped protrusion structure. This is because the sp3 structure has a stronger bonding force than the sp2 structure, so that selective etching occurs. By setting so that the hydrogen plasma damages the carbon film 2 in the etching process,
A surface conductive film 9 made of an amorphous carbon film or a carbon film containing an sp2 structure is formed on the surface of the carbon film 2 and the surface of the needle-like protrusion structure. Next, FIG.
As shown in (d), the insulating film 4 and the gate electrode 5 are selectively formed. The insulating film 4 is the carbon film 2 and the gate electrode 5.
It is an insulating material that electrically separates and, and is mainly formed of an oxide film or the like. The gate electrode 5 is an electrode for extracting electrons from the carbon film 2, and is composed of a metal thin film. In this embodiment, the needle-like protrusion structure of the carbon film 2 is the carbon film 2.
Although the shape is left on the base, a needle-like protrusion structure may be formed directly from the substrate electrode 1 as shown in FIG.

Next, the operation of the field emission type cold cathode device according to the seventh embodiment of the present invention will be described in detail with reference to FIG. In order to operate the field emission type cold cathode device of this embodiment, a negative bias is applied to the substrate electrode 1 or a positive bias is applied to the gate electrode 5. Then, electric field concentration occurs at the tip of the carbon film 2 whose surface has a needle-like protrusion structure, and since the surface of the needle-like protrusion is covered with the upper surface conductive film 9, electrons are supplied from the substrate. It becomes easier and the voltage applied to the substrate electrode 1 or the gate electrode 5 can be lowered.

Next explained is the eighth embodiment of the invention. FIG. 8D is a sectional view of a field emission cold cathode device according to the eighth embodiment of the present invention. The substrate electrode 1 is a lower electrode and may be any semiconductor material or conductor, and examples thereof include Si, Mo, Fe, Ni and Pt. The carbon film 2 is a cathode material that emits electrons, and the carbon film 2 is composed of sp2 structure carbon 2a and sp3 structure carbon. The surface of the carbon film 2 has a needle-like protrusion structure. The surface conductive film 9 is a carbon film containing an sp2 structure, has a higher conductivity than the carbon film 2, a thickness of about 10 nm or less, and a surface resistivity of about 10 ⁵ Ωcm or less. Since the surface conductive film 9 is a part of the path for supplying electrons, the resistance thereof is preferably low, and is preferably about 10 ⁵ Ωcm or less. Therefore, an amorphous carbon film is preferable to a carbon film having an sp3 structure, and further, a carbon film having a low resistance sp2 structure is more preferable. The insulating film 4 is an insulating material that electrically separates the carbon film 2 and the gate electrode 5, and is mainly formed of an oxide film or the like. The gate electrode 5 is an electrode for extracting electrons by the carbon film 2, and is composed of a metal thin film. The support substrate 10 is a portion that serves as a base of the field emission cold cathode device, and is made of an insulating material such as glass, plastic, or ceramic material.

FIG. 8 is a sectional view showing the manufacturing process of the eighth embodiment of the present invention. As shown in FIG. 8A, glass was used for the supporting substrate 10, and Mo to be the substrate electrode 1 was deposited thereon by sputtering. Next, FIG.
As shown in (b), the carbon film 2 is formed on the substrate electrode 1 by the CVD method or the sputtering method. In this example, a diamond-like carbon film was formed as a cold cathode material on the substrate electrode 1, and the film thickness at this time was set to about 3 μm. This carbon film 2 is a film in which carbon 3 of sp3 structure is interspersed with carbon 2a of sp2 structure. Then, as shown in FIG. 8C, after depositing an oxide film to be the insulating film 4 and a metal film to be the gate electrode 5, the insulating film 4 and the gate electrode 5 are processed into arbitrary shapes by a lithography process. To do. After that, as shown in FIG. 8D, the surface of the cold cathode material 2 was exposed to hydrogen plasma. At this time sp3
The carbon 3a of the structure serves as a mask, and the carbon 2a of the sp2 structure is selectively etched to form a needle-shaped protrusion structure. Further, by setting the condition that hydrogen plasma damages the carbon film 2 in the etching process, the surface conductivity of the carbon film including the sp2 structure on the surface of the carbon film 2 and the surface of the needle-like protrusion structure is set. The film 9 is formed.

Next, the operation of the field emission type cold cathode device according to the eighth embodiment of the present invention will be described in detail with reference to FIG. In order to operate the field emission type cold cathode device of this embodiment, a negative bias is applied to the substrate electrode 1 or a positive bias is applied to the gate electrode 5. Then, electric field concentration occurs at the tip of the carbon film 2 whose surface has a needle-like protrusion structure, and the needle-like protrusion reaches the substrate electrode 1, so that electrons can be easily supplied from the substrate. , Substrate electrode 1
Alternatively, the voltage applied to the gate electrode 4 can be lowered.

[0050]

As described above, the field emission cold cathode of the present invention has an effect of easily realizing high emission current characteristics at a low voltage.

This is because by forming the emitter made of a carbon film into a needle-like shape having a plurality of sharpened tips, the electric field strength to the tip of the emitter is increased and many emission points can be formed. .

Further, by using as the emitter material, a carbon film in which a diamond film having a high emission property, that is, carbon having an sp3 structure and a graphite film having high conductivity, that is, a carbon film having an sp2 structure are combined, is used.
High conductivity and high emission characteristics.

Further, by disposing the carbon film having the sp3 structure at the tip of the emitter, there is an effect that the emission characteristic can be further improved.

Further, according to the present invention, it is possible to provide a method of manufacturing a field emission cold cathode which can easily realize high emission current characteristics. This is because it is possible to easily form a plurality of sharp needle-shaped emitters at the same time by subjecting the carbon film to plasma treatment in hydrogen.

In particular, by mixing materials having different etching rates in the carbon film or on the surface during hydrogen plasma, when the carbon film is etched, the material having a slow etching rate serves as a mask to self-align the needles. There is an effect that it is possible to form the emitter of.

Further, by simultaneously forming the carbon of sp2 structure having a high etching rate and the carbon film having a slow etching rate at the time of forming the carbon film by the hydrogen plasma treatment, the carbon film and the emitter can be formed by the same film forming apparatus. It is also possible to form a mask material.

In particular, by treating the carbon film containing sp3 structure or sp3 with hydrogen plasma, there is an effect that the surface of the cold cathode material can be finely processed by using the lithography technique. The reason is that minute defects, impurities, or sp2 structure portions are selectively etched, and the sp3 structure portions serve as masks to form needle-like protrusion structures.

Furthermore, sp3 having a high emission characteristic
Since carbon having a structure can be formed at the tip of the emitter in a self-aligned manner, the emission characteristics can be improved at the same time.

In particular, when the surface shape of the carbon film containing the sp3 or sp3 structure has a needle-like protrusion structure, a high current characteristic can be realized in a low electric field. The reason is that the cold cathode material surface and the needle-like protrusion structure enhance the effect of electric field concentration.

Further, by performing the hydrogen plasma treatment with ECR plasma, a high plasma property can be obtained, and a sharp needle-shaped emitter can be easily formed.

Further, at the time of forming the needle-like protrusion structure, the surface of the needle-like structure is covered with the amorphous carbon film or the film of sp2 structure due to damage by hydrogen plasma, so that high current electron emission can be realized. . The reason is that it becomes easy to supply electrons to the tip of the acicular structure of the sp2 structure film.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a field emission cold cathode according to a first embodiment of the invention and a manufacturing process thereof.

FIG. 2 is a schematic cross-sectional view showing an example of a field emission cold cathode according to a second embodiment of the invention and a manufacturing process thereof.

FIG. 3 is a schematic cross-sectional view showing an example of a field emission cold cathode according to a third embodiment of the invention and a manufacturing process thereof.

FIG. 4 is a schematic sectional view of a field emission cold cathode according to a fourth embodiment of the present invention.

FIG. 5 is a schematic cross-sectional view showing an example of a field emission cold cathode according to a fifth embodiment of the invention and a manufacturing process thereof.

FIG. 6 is a schematic sectional view showing an example of a field emission cold cathode according to a sixth embodiment of the present invention and a manufacturing process thereof.

FIG. 7 is a schematic sectional view showing an example of a field emission cold cathode according to a seventh embodiment of the present invention and a manufacturing process thereof.

FIG. 8 is a schematic sectional view of a field emission type cold cathode according to an eighth embodiment of the present invention.

FIG. 9 is a schematic cross-sectional view showing a conventional field emission cold cathode and its manufacturing process.

FIG. 10 is a photograph of a carbon film having a needle-shaped protrusion structure formed by ECR plasma treatment obtained according to the first embodiment of the present invention.

[Explanation of symbols]

1 substrate electrode 2 carbon film 2a sp2 structure carbon Carbon with 3 sp3 structure 4 insulating film 5 Gate electrode 6 diamonds 7 Aluminum layer 8 Conductive material 9 Surface conductive film 10 Support substrate

─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Masayuki Yoshiki 5-7-1 Shiba, Minato-ku, Tokyo Inside NEC Corporation (56) Reference JP-A-9-45215 (JP, A) JP-A-2 -239192 (JP, A) JP-A-8-236010 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01J 1/304 C01B 31/00-31/36 C23C 16/00 -16/56 C30B 1/00-35/00 H01J 9/02

Claims (22)

(57) [Claims] 1. A surface of a carbon film is covered with a needle-like protrusion structure made of carbon, and the surface of the needle-like protrusion structure is sp.
A carbon material characterized by being covered with a conductive film having two structures. 2. The carbon material according to claim 1, wherein the carbon film is diamond. 3. The carbon material according to claim 1, wherein the carbon film is diamond-like carbon. 4. The carbon film has a structure in which an sp2 structure and an sp3 structure are combined.
The listed carbon material. 5. The carbon material according to claim 1, wherein the conductive film covering the surface of the needle-like protrusion structure is amorphous carbon. 6. The carbon material according to claim 1, wherein the thickness of the conductive film covering the surface of the needle-shaped protrusion structure is about 10 nm or less. 7. The carbon material according to claim 1, wherein the resistivity of the conductive film covering the surface of the needle-like protrusion structure is about 10 5 Ωcm or less. 8. The carbon material according to claim 1, wherein at least a tip portion of the needle-like protrusion structure has an sp3 structure. 9. The curvature of the tip of the needle-like protrusion structure is 1
The carbon material according to claim 1, wherein the carbon material has a thickness of -100 nm. 10. The carbon material according to claim 1, wherein the needle-shaped protrusion structure has a conical or pyramidal shape and a height of 10 nm to 1 μm. 11. A field emission cold cathode, comprising the carbon material according to claim 1 as an emitter. 12. The field emission cold cathode according to claim 11, wherein at least the lower layer of the carbon material has an sp3 structure. 13. The field emission cold cathode according to claim 12, wherein the needle-like protrusion structure of the carbon material reaches the lower substrate electrode. 14. A method for producing a carbon material, comprising the step of forming a needle-like carbon film on the surface of the carbon film by plasma-treating the carbon film in hydrogen gas. 15. A method for producing a carbon material, comprising a step of performing plasma treatment in oxygen gas before or after the step of performing plasma treatment in the hydrogen gas. 16. The method for producing a carbon material according to claim 14, further comprising the step of forming a needle-shaped carbon film by etching the carbon film in the plasma treatment. 17. The method for producing a carbon material according to claim 16, further comprising the step of forming materials having different etching rates in or on the surface of the carbon film. 18. The carbon film has an sp2 structure and an sp3 structure.
The method for producing a carbon material according to claim 17, further comprising a step of forming the carbon material so that the structure and the structure are mixed. 19. The method for producing a carbon material according to claim 14, wherein the plasma treatment is performed by ECR plasma. 20. The method for producing a carbon material according to claim 19, wherein the ECR plasma treatment is performed by applying a bias to an ECR device substrate. 21. A method of manufacturing a field emission cold cathode, comprising a step of forming a needle-shaped protrusion structure which becomes an emitter by the method of manufacturing a carbon material according to claim 14. . 22. A field emission type device comprising a step of forming a carbon film on a substrate electrode and subjecting the carbon film to plasma treatment in hydrogen gas to form a needle-like carbon film on the surface of the substrate electrode. Cold cathode manufacturing method.