JP2005209360A - Manufacturing method of needle carbon film, needle carbon film, and field emission structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method forming a needle carbon film by a chemical vapor phase growth method without passing work for forming a substrate or a carbon film in a needle shape. <P>SOLUTION: Potential of a wall surface 2b of the substrate 2 facing voids 3 having a width W of 10 mm or less is made equipotential. Pulse voltage is applied to atmosphere containing raw gas containing a carbon source to produce discharge plasma 1, and the needle carbon film 7 having an aspect ratio of diameter and length of 1 or more is formed on the wall surface 2b. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing an acicular carbon film, an acicular carbon film, and a field emission structure.

Field emission-type cold cathodes have recently attracted attention for display applications and the like. As an emitter material, for example, there is a method of thinly coating a diamond-like carbon film on the surface of a minute electron source formed in a cone shape. This is a method in which a diamond thin film is deposited on the cone tip by a CVD method on a cone-type field emission cold cathode. As a method for forming a needle-like carbon film by this, a method is known in which a diamond-like carbon film is formed on a flat surface and then made into a needle-like shape by a plasma etching technique (Patent Document 1). Further, a method is known in which a substrate is processed into a needle shape before forming a carbon film, and then a diamond-like carbon film is formed on the needle-like processed surface (Patent Documents 2, 3, 4, 5).
JP 2000-215788 A JP-A-8-306300 JP-A-9-63460 Japanese Patent Laid-Open No. 9-185942 Japanese Patent Laid-Open No. 2002-117753

  However, in any of the manufacturing methods described above, in order to obtain a needle-like diamond-like carbon film, it is necessary to perform a number of processes such as a photolithography process, an etching process, a resist stripping process, and a cleaning process. The nature is low.

  An object of the present invention is to provide a method for forming a needle-like carbon film by chemical vapor deposition without undergoing processing for making the substrate or the carbon film into a needle shape.

In the present invention, acicular potential is applied to the wall surface of a substrate facing a gap having a width of 10 mm or less, and a discharge voltage is generated by applying a pulse voltage to an atmosphere containing a carbon source, whereby acicular carbon is formed on the wall surface of the substrate. The present invention relates to a method for producing a needle-like carbon film characterized by forming a film.
The present invention also relates to the acicular carbon film produced by the above method.

Further, the present invention is an acicular carbon film having an aspect ratio of diameter to length of 1 or more, and a peak of 1300 to 1580 cm ^{−1 and} a peak of about 2250 m ⁻¹ are observed in Raman spectroscopic measurement. This relates to a needle-like carbon film.

  According to the present invention, it is possible to provide a method for forming a needle-like carbon film by chemical vapor deposition without undergoing processing for making the substrate or the carbon film into a needle-like shape.

In addition, the needle-like carbon film according to the present invention has an aspect ratio of 1 or more in diameter and length, and in Raman spectroscopy, in addition to a normal diamond-like carbon peak of 1300 to 1580 cm ⁻¹ , about 2250 m ^−1. The peak is observed. It has been found that such a needle-like carbon film exhibits electron emission characteristics when used as a cold cathode.

In the present invention, an acicular potential is applied to the wall surface facing the gap of the substrate provided with a gap of 10 mm or less in width, and a gas containing discharge plasma is caused to flow on the wall surface, thereby forming the acicular carbon film on the wall surface. Can be generated.
For example, as schematically shown in FIG. 1, the base 2 is provided with a gap 3 having a width W of 10 mm or less. A predetermined carbon source gas is caused to flow in the space 4 on the upper surface 2a of the substrate 2 and an electric field is applied as indicated by an arrow A to generate plasma 1. The plasma generation gas 1 flows into the gap 3. At this time, it was found that a substantially smooth film 6 was formed on the upper surface 6 and, at the same time, a needle-like carbon film 7 was formed on at least a part of the inner wall surface 2b facing the void. Thus, a technique for forming a needle-like carbon film on a flat wall surface only by a chemical vapor deposition process is provided for the first time.

  Here, it is necessary to provide a gap having a width of 10 mm or less in the substrate and to flow a plasma gas in the gap. The shape of the substrate and the shape of the gap are not particularly limited. In one embodiment, the substrate is a single piece, and one or more voids are formed in the substrate. The void is preferably a through-hole through which gas can pass, but need not be a through-hole. The shape of the void is not particularly limited. The shape of the cross section of the gap may be, for example, a perfect circle, an ellipse, a curve, a triangle, a square, a rectangle or a groove, or a polygon such as a hexagon.

  For example, FIG. 2A is a plan view showing the base 2A, and FIG. 2B is a cross-sectional view of the base 2A. A plurality of through holes 3A are formed in the base 2A. In this example, the planar shape of each through-hole 3A is substantially square. The width W of each through-hole 3A is 10 mm or less. Using this substrate, a plasma generating gas is allowed to flow from the upper surface 2a side of the substrate to form a needle-like carbon film 7 on the wall surface 2b facing the through hole 3A as shown in FIG.

Alternatively, voids can be formed between the plurality of substrates. In this case, it is possible to simultaneously form the acicular carbon film on each wall surface of the plurality of substrates. This can be exemplified by the following types.
(1) Parallel plate type Two flat substrates are installed in parallel at regular intervals. Flat plate-shaped gaps at regular intervals are formed between the pair of substrates.
For example, in the example schematically shown in FIG. 4A, a pair of flat bases 2B are installed so as to be parallel to each other, and the pair of bases 2B are connected to the power source 10 to have the same potential. The space 3B between the base bodies 2B is a flat space having a constant width W, and the width W is 10 mm or less. According to the above-described method, the acicular carbon film 7 is formed on the inner wall surface 2b of each substrate 2B.
(2) Coaxial cylindrical opposed flat plate type Two cylindrical substrates are installed coaxially. Cylindrical voids with a constant interval are formed between the pair of substrates.
For example, in the example schematically shown in FIG. 4B, a pair of cylindrical base bodies 2C are installed coaxially, and the pair of base bodies 2C are connected to the power source 10 to have the same potential. A cylindrical gap 3C is generated between the base bodies 2C. The gap 3C is a space having a constant width W, and the width W is 10 mm or less. According to the above-described method, the acicular carbon film 7 is formed on the inner wall surface 2b of each base 2C.
(3) Sphere-facing flat plate type Two spherical substrates are installed in parallel at regular intervals. Spherical voids at regular intervals are formed between the pair of substrates.

  The size of the gap is 10 mm or less, but is preferably 2 mm or less, and more preferably 1 mm or less from the viewpoint of forming a needle-like carbon film. The lower limit of the size of the void is not particularly limited, but if the void is too small, the plasma generating gas is difficult to flow in. Therefore, the size of the void is preferably 1 μm or more, and more preferably 5 μm or more.

  Examples of the material of the substrate include plastics such as polyethylene, polypropylene, polystyrene, polycarbonate, polyethylene terephthalate, polyphenylene sulfite, polyether ether ketone, polytetrafluoroethylene, and acrylic resin, glass, ceramic, and metal. The form of the substrate is not particularly limited, and may be a plate shape, a film shape, or various three-dimensional shapes.

In the present invention, a pulse voltage is applied between the electrodes.
At this time, one or both of the electrodes can be covered with a solid dielectric. Examples of the solid dielectric include plastics such as polytetrafluoroethylene and polyethylene terephthalate, glass, metal dioxide such as silicon dioxide, aluminum oxide, zirconium dioxide, and titanium dioxide, and composite oxide such as barium titanate.

  The waveform of the pulse voltage is not particularly limited, and may be any of an impulse type, a square wave type (rectangular wave type), and a modulation type. A DC bias voltage can be applied simultaneously.

  In a preferred embodiment, the pulse width of the pulse voltage is preferably 0.01 to 1000 μsec. By setting the pulse width to 1000 μsec or less, the quality of the thin film is improved. From this point of view, the pulse width is preferably 500 μsec or less, and more preferably 300 μsec or less. Moreover, it is not realistic to set the pulse width to less than 0.01 μsec.

The pulse period of the pulse voltage is preferably 0.1 to 100 kHz. If it is less than 0.1 kHz, the process takes too much time, and if it exceeds 100 kHz, arc discharge tends to occur.
Although the magnitude | size of an electric field is not specifically limited, For example, it is preferable that the electric field strength between opposing electrodes shall be 0.1-100 kV / cm.

The pulse voltage as described above can also be applied by a steep pulse generating power source. As such a power source, a power source using an electrostatic induction thyristor element that does not require a magnetic compression mechanism, a thyratron equipped with a magnetic compression mechanism, a gap switch, an IGBT element, a MOF-FET element, or an electrostatic induction thyristor element is used. An example of a power supply that has been used.
Although the atmospheric pressure in this invention is not limited, Preferably it is 0.05-100 Pa.

During chemical vapor deposition, a source gas containing a carbon source is used. The following can be illustrated as a carbon source.
Alcohols such as methanol and ethanol Alkanes such as methane, ethane, propane, butane, pentane and hexane Alkenes such as ethylene, propylene, butene and pentene Pentadiene, alkadienes such as butadiene, alkynes such as methylacetylene,
Aromatic hydrocarbons such as benzene, toluene, xylene, indene, naphthalene and phenanthrene Cycloalkanes such as cyclopropane and cyclohexane Cycloalkenes such as cyclopentene and cyclohexene

In addition to the carbon source, at least one of the following gases can be used in combination.
(A) Oxygen gas (b) Hydrogen gas Oxygen or hydrogen becomes atomic during discharge and has the effect of removing graphite that is generated simultaneously with diamond.
(C) Carbon monoxide, carbon dioxide (d) Diluting gas (e) Gas for adding silicon (monosilane, dichlorosilane, silicon tetrachloride, tetramethylsilane, trimethylsilane, etc.)

When a carbon source and carbon dioxide gas are used, it is preferable that the mixing ratio of carbon source gas / carbon dioxide gas is 1/1 to 1/3 (vol ratio).
The concentration of the carbon source in the source gas atmosphere is preferably 2 to 80 vol%.
The concentration of oxygen gas or hydrogen gas in the gas atmosphere is preferably 70 vol% or less.

  Examples of the dilution gas include group 8 element gas and nitrogen gas, and at least one of them can be used, and examples include helium, argon, neon, and xenon. The concentration of the dilution gas in the source gas atmosphere is preferably 20 to 90 vol%.

Furthermore, boron elements such as diborane (BH ₃ BH ₃ ), trimethylboron (B (CH ₃ ) ₃ ), phosphine (PH ₃ ), and methylphosphine (CH ₃ PH ₂ ) are contained in the gas atmosphere during discharge. Gas and nitrogen gas can also be added.

By the above method, a needle-like carbon film having a diameter-length aspect ratio of 1 or more can be generated. A typical diamond-like carbon film has a smooth surface with a center line average surface roughness Ra = 0.1 nm or less.
In the acicular carbon film of the present invention, a peak of 1300 to 1580 cm ^{−1 and} a peak of about 2250 m ⁻¹ are observed in Raman spectroscopic measurement.
The particle size (diameter) of the acicular carbon film particles is not particularly limited, but is preferably 1 nm to 1000 nm.

Moreover, it turned out that the acicular carbon film of this invention has an electron emission characteristic as an emitter. For example, when a needle-like carbon film was used as an emitter, an emission current of about 1 × 10 ⁻⁷ A was possible at 300 V or less at a gap distance (emitter-collector distance) of 10 μm.

  As long as the acicular carbon film of the present invention is used as an emitter, the specific form of the field emission structure is not particularly limited. As an example, in the field emission structure shown in FIG. 5, a needle-like carbon film 7 is formed on a substrate 17 to be a conductive cathode electrode. The substrate 17 also serves as a lower electrode. The acicular carbon film 7 is a material that causes electron emission. The insulating film 18 is an insulating material that electrically separates the acicular carbon film 7 and the gate electrode 19 and is mainly formed of an oxide film or the like. The gate electrode 19 is an electrode for extracting electrons from the acicular carbon film 7 and is formed of a metal thin film.

(Generation of acicular carbon film)
A diamond-like carbon film was formed by the pulse plasma CVD method as described above. As a power source, a general DC pulse power source was used. The chamber is made of stainless steel. A substrate 2A having a configuration as shown in FIGS. 2 and 3 was placed on the electrode. The width W of the gap 3A was 1 mm, and the depth H was 15 mm. The material of the base 2A was a silicon wafer.

  Using an oil rotary pump, evacuation was performed until the pressure in the chamber reached 0.1 Torr. Subsequently, argon was supplied from the dilution gas supply hole at 3.5 sccm until the pressure in the chamber reached 3 Pa. Next, a pulse voltage was applied between the upper electrode and the lower electrode while introducing acetylene gas at a flow rate of 25 sccm. The peak value of the pulse voltage is −8 kV, the frequency is 5 kHz, and the pulse width is 20 μsec. The pulse voltage was applied to discharge for 10 minutes to form a needle-like carbon film 7.

About the obtained film | membrane, the film | membrane surface was image | photographed with the scanning electron microscope (10000 times and 40000 times magnification). 6 and 7 show surface photographs at different locations. It can be clearly seen that a needle-like carbon film is formed. The film was subjected to Raman spectroscopic analysis using a Raman spectroscopic device (“NRS-1000” manufactured by JASCO Corporation). The result is shown in FIG. As a result, a main peak of 1300 to 1580 cm ⁻¹ and a shoulder peak of about 2250 m ⁻¹ were observed.

(Field emission characteristics)
Using the apparatus schematically shown in FIG. 9, the field emission characteristics of the acicular carbon film were tested. In the internal space 15 of the chamber 14, a sample 12 in which the acicular carbon film 7 was formed on the substrate 17 was placed on the lower electrode 11. A collector 13 made of a tungsten needle (diameter 2 mm) was fixed in the space above the sample 12. The gap between the surface of the sample 12 and the collector 13 was 10 μm. The pressure in the internal space 15 was set to 1 × 10 ⁻⁸ Torr, and the voltage from the power source 10 was changed to 0 to 1000 V. As a result, field emission characteristics as shown in FIG. 10 were obtained.

As can be seen from this result, the current value increased rapidly at a voltage of 250 volts or more, and a discharge current of 1 × 10 ⁻⁷ A or more was possible at 300 V or less.

It is a schematic diagram for demonstrating the manufacturing process of the acicular carbon film in this invention. (A) is a top view which shows 2 A of base | substrates, (b) is sectional drawing which shows 2 A of base | substrates. It is a top view which shows the state by which the acicular carbon film 3A was formed into the wall surface 2b of 2 A of base | substrates. (A) is a top view which shows typically the state by which the acicular carbon film 3B was formed in the base | substrate 2B, (b) is the state in which the acicular carbon film 3C was formed in the base | substrate 2C typically. FIG. 2 is a schematic cross-sectional view showing an example of a field emission structure 12. FIG. It is a photograph of the surface of an acicular carbon film. It is a photograph of the surface of an acicular carbon film. It is a graph which shows the Raman spectrum of an acicular carbon film. It is a schematic diagram which shows the measurement system of a field emission characteristic. It is a graph which shows the field emission characteristic of an acicular carbon film.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Discharge plasma 2, 2A, 2B, 2C base | substrate 2b Wall surface facing the space | gap of a base | substrate 3, 3A, 3B, 3C space | gap 7 Needle-like carbon film 10 Power supply W Width | variety width

Claims (6)

  A needle-like carbon film is formed on the wall surface by generating an electric discharge plasma by applying a pulse voltage to an atmosphere containing a carbon source by setting the potential of the wall surface of the substrate facing a gap having a width of 10 mm or less to an equipotential. A method for producing a needle-like carbon film, wherein   2. The method according to claim 1, wherein the acicular carbon film is made of diamond-like carbon.   The method according to claim 1, wherein the acicular carbon film has a field emission characteristic.   An acicular carbon film produced by the method according to any one of claims 1 to 3. An acicular carbon film having an aspect ratio of a diameter to a length of 1 or more and having a peak of 1300 to 1580 cm ^{−1 and} a peak of about 2250 m ⁻¹ observed by Raman spectroscopy.   A field emission structure comprising the acicular carbon film according to claim 4 as an emitter.

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