JPS6144705A - Method for forming electrically conductive carbon film - Google Patents

Abstract

PURPOSE:To obtain easily an electrically conductive carbon film having improved stability, etc. and high electric conductivity, by irradiating the carbon film with ions. CONSTITUTION:A carbon film having 1nm-100mum film thickness is formed from amorphous carbon, graphite, etc. as a raw material by the sputtering, vacuum deposition, chemical vapor deposition (CVD) or physical vapor deposition (PVD) method, etc. The resultant carbon film is then placed in an ion irradiation device, and the vacuum degree is set within about 10<-4>-10<-8>Torr range to irradiate the film with ions selected from He, Ar, Ne, Kr, Xe, etc. to give the aimed electrically conductive carbon film. Ions are preferably accelerated in the ion irradiation device to give 100eV-100keV range kinetic energy of the ions to be irradiated.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a method for forming a conductive carbon film, and more particularly, to a method for forming a conductive carbon film that can easily form a carbon film having high conductivity. .

[Technical background of the invention and its problems] In recent years, conductive thin films made of organic substances have been found to have low decomposition temperatures, do not vaporize when oxidized by heating to high temperatures and leave no ash, and have low heat capacity. , heat mode (local heating method using irradiation with light, infrared rays, electron beams, etc.)
It is expected that this material will be able to achieve the formation of no-turns and the modulation of conductivity.

Conventionally, as such an organic conductive thin film, t±, TTF
(tetrathiofulvalene)-TCNQ (tetracyanoquinodimethane) charge transfer complex, or a conjugated polymer such as polyacetylene ((-(H)) or polyphenylene, with halogen or AsF
5, a polymer thin film made of a system in which a strong oxidizing agent such as PF6 is added and reacted, and a polymer thin film made of a system in which a strong reducing agent such as an alkali metal is added and reacted are known.

However, these organic conductive thin films have the following problems.

In other words, in the case of a charge transfer complex, when a molecule with a small ionization potential (donor) and a molecule with a large electron affinity (acceptor) are spatially close to each other, electrons are donated and accepted to form a stable complex. It is. These donors and acceptors themselves are molecules that are not very stable and are easily decomposed by light or heat. Furthermore, the charge transfer complex itself is unstable and easily decomposed by light or heat, since the stabilization energy required for complex formation is smaller than that of a chemical bond.

In this way, the donor, acceptor, and charge transfer complex have the disadvantage that they are easily decomposed by light and heat.
When forming conductive thin films using vapor deposition methods, it is necessary to strictly control the vapor deposition conditions such as the evaporation source temperature and substrate temperature in order to avoid the effects of heat. Forming a conductive thin film is not easy.

On the other hand, conjugated polymer thin films exhibiting conductivity have the following drawbacks. In other words, polyacetylene ((C1,)・A
Although the sF5 system is formed by a wet process, its structure is quite non-uniform, and as a result, an extremely large number of pinholes and the like occur in the thin film. Since such a thin film is easily oxidized and deteriorates when exposed to the atmosphere, there is a problem in that the thin film must be sealed with another oxidation-resistant protective film before use. In addition, other conjugated polymers/
Some oxidizing and reducing agent systems exist stably even when exposed to the atmosphere, but few of these exhibit high electrical conductivity.

Recently, a method has been reported to improve the conductivity of organic thin films made of polycyclic condensed aromatic compounds such as phthalocyanine and perylene by irradiating them with ion beams (
J, Appl, Phys, 55 (3)', 73
21984). It is predicted that this phenomenon of improved conductivity is due to the polycyclic condensed aromatic compound approaching a highly conductive graphite structure by ion irradiation, but the mechanism is not clear. Since the mechanism of conductivity improvement is unknown, the question of what kind of substances other than polycyclic condensed aromatic compounds improve conductivity by in-beam irradiation has not been clarified. In addition, it is predicted that this ion irradiation will cause molecular decomposition of the thin film material, but molecular decomposition does not necessarily have an effective effect on improving conductivity, and the ion irradiation conditions such as irradiation energy and dose Settings tended to be complicated.

[Objective of the Invention 1] The purpose of the present invention is to provide a method for forming a conductive carbon wave film that solves the above-mentioned problems and can easily form a carbon film that has the stability and high conductivity of graphite. shall be.

[Summary of the Invention] As a result of extensive research in order to solve the above-mentioned problems, the present inventors have found that by irradiating a substantially amorphous carbon film, which does not have a graphite structure, with an ion beam, a high They discovered that conductivity could be obtained and completed the present invention.

That is, the method for forming a conductive carbon film of the present invention is characterized by irradiating the carbon film with ions in a vacuum.

First, in the present invention, as a method for forming a carbon film to be converted into a conductive carbon film, there are 1 conventional thin film forming methods, such as vacuum evaporation, sputtering! , lng method, CV
Ion brating methods such as the D method, PCVD method, and cluster ion beam method are applicable.

When applying the various thin film forming methods described above, the vacuum evaporation method is used as the raw material for the carbon film.

In the case of the sputtering method, either amorphous carbon or graphite may be used as the evaporation source and sputtering target. Amorphous carbon and graphite have excellent heat resistance on their own, so unlike the vapor deposition of charge transfer complexes and compounds, there is no need to worry about thermal decomposition, and there is no need for delicate heating control, etc., and there is no need for strict conditions for film formation. .

On the other hand, in the case of the CVD method and the PCVD method, the thermal decomposition source gas may be acetylene, acetone, alcohols, etc., and in particular, most gases containing carbon atoms can be used as long as they do not contain nitrogen, sulfur, or metals.

Using the above raw materials, a carbon film is formed on a substrate by the various thin film forming methods described above.

When forming a carbon film, the thickness of the carbon film is 1n+s~+00
It is preferable to adjust the amount of raw materials, heating temperature, etc. so that the amount is within the range of 1 Lm. If the film is outside this range and the film thickness is less than 1 nm, the film becomes island-like and has many pinholes.
If this is exceeded, cracks and protrusions will increase and the membrane surface will become rough, both of which will cause inconvenience.

The structure of the formed carbon film is approximately amorphous, and therefore the electrical conductivity of this approximately amorphous carbon film is low.
0"4 to 10-1 Ω-1・c" is about 1.

Thus, in the present invention, when forming a carbon film, the carbon film may be amorphous (amorphous), and unlike conventional materials, there is no need to perform crystallization at the same time as forming the film, and therefore, There is no need to pay special attention to crystallization, and a carbon film can be easily and stably formed.

Next, the bare foot-shaped carbon film thus formed is irradiated with an ion beam using various ion irradiation devices in a vacuum.

The degree of vacuum at this time is preferably set in the range of lO''4 to 10'' Torr.

Rare gas ions are used as ions in the ion beam, and commercially available ion implanters, various ion guns, etc. can be used as ion irradiation equipment, and sputtering equipment, which is also a film forming equipment, can be used for convenience. Just use it.

As the ion species for this ion beam, rare gas ions, ie, He, Ne, Kr, and Xe can be used, and Ar is preferable. In addition, when the kinetic energy of a noble gas ion with a large atomic number is the same as that of an ion with a small atomic number, the momentum is greater than that of a small ion, so the conductive carbon film obtained as a result of ion irradiation conductivity increases.

However, on the other hand, the carbon on the resulting conductive carbon film is scattered due to sputtering, resulting in a thinner overall film thickness. Therefore, the ion species, their kinetic energy, and irradiation amount may be appropriately selected in consideration of the desired conductivity and film thickness.

Furthermore, in the method of the present invention, it is possible to control the depth at which conductivity is imparted by selecting the ion species to be irradiated.

For example, when Kr or Xe is selected as the ion species, the depth of the conductive layer can be made deeper than when He, Ne, or Ar is selected.

It is preferable to accelerate the ions using an ion irradiation device so that the kinetic energy of the ions is in the range of 100 eV to 100 keV.

When the kinetic energy of the ion falls outside this range, it becomes 100
In the case of eV non-vortex, the conductivity of the conductive carbon film does not increase significantly compared to when ions are not irradiated, and when it exceeds 100 keV, sputtering phenomenon becomes dominant and the film thickness becomes thin, which is not preferable. Furthermore, the conductivity of the conductive carbon film can also be changed by changing the value of the kinetic energy of the ions.

In addition, it is recommended that the ion irradiation amount be set to an areal density of 10 to 10"/cm2. Outside this range, 10/c+
If it is less than a2, the conductivity of the conductive carbon film will not improve significantly! If it exceeds 023/cI12, sputtering phenomenon becomes dominant and carbon on the film scatters, which is not preferable.

Under the above irradiation conditions, the portions of the substantially amorphous carbon film irradiated with ions have higher conductivity than the portions that are not irradiated with ions. That is, its conductivity is 103~lΩ-10
cm', which is about 3 orders of magnitude larger than the non-ion irradiated area.

In this way, the conductivity increases only in the ion irradiated area, so if you use an irradiation device with focusing and deflection functions to irradiate specific areas on the surface of the carbon film, you can see dots or lines on the carbon film. A desired pattern, such as a circuit, with high conductivity can be formed in a shape.

Since the method for forming the conductive carbon film of the present invention, which is formed as described above, uses only carbon and rare gas, there are no problems such as decomposition of molecules in the carbon film, and the conditions for forming the conductive carbon film are stable. It is easy to manufacture.

In addition, in the method for forming a conductive carbon film of the present invention, additives are added in a vacuum, such as the diffusion addition method of low molecules (for example, AsF5), which is used to improve the conductivity of polyacetylene (01:l) films. There is no risk of evaporation and loss, and it has excellent environmental resistance.

In addition, the carbon coating with improved conductivity is heat resistant.

It also has improved corrosion resistance and exhibits the stability of graphite.

[Examples of the Invention] Example 1 A carbon film was formed by a vacuum evaporation method. First, a pressure-molded pellet of amorphous carbon is put into the port, and the degree of vacuum is set to 1.
The amorphous carbon was vaporized by heating the port using a resistance heating method, and a carbon film was formed on the quartz glass substrate.The thickness of the obtained carbon film was 300 mm.
As a result of structural analysis of the carbon film using X-rays, it was confirmed that it was amorphous. The electrical conductivity of this carbon film was measured by a four-terminal method and was found to be 10Ω-1·cm′.

Next, this amorphous carbon film is stored in a vacuum chamber, and 10=
At a vacuum level of Torr, Ar ions with a kinetic energy of 10 keV were irradiated with lθ~10237C112 using an ion gun.
The carbon film was irradiated with an areal density of . The conductivity of the area irradiated with ions was as high as 102Ω4·Cm'.

Example 2 The carbon film was formed by sputtering.

A quartz glass substrate was used as the substrate, and a pressure-molded gelafite powder was used as the sputtering target.

Frequency 13.0 in an Ar atmosphere with a vacuum degree of 10' Torr.
Sputtering was performed using a high frequency discharge (RF discharge) of 58 MHz. As a result of structural analysis of the carbon film obtained on the substrate using X-rays, it was confirmed that it was amorphous.

The conductivity of the film was measured using the 4-terminal method and was 1O-2Ω.
It was 4.cs'. The film thickness was 1000 people.

Next, the substrate on which the carbon film has been formed is returned to the sputtering apparatus, and the electrical relationship between the substrate and the sputter target (the relationship between the positive electrode and the negative electrode) is reversed to perform so-called reverse sputtering.
A: “The ions bombarded the carbon film on the substrate.

The kinetic energy of Ar ions at this time was 3 keV.

The carbon film was scraped away by Ar ion sputtering and its film thickness became thinner, but when the film thickness reached 80% of the initial thickness, Ar sputtering was stopped. The conductivity of the conductive carbon film was 102Ω-1·C11-1.

Example 3 A carbon film was formed by a CVD method. A quartz plate was used as the substrate, butadiene was used as the pyrolysis source gas, argon was used as the carrier gas, the degree of vacuum in the reaction chamber was set to lw 10-'' Torr, and the reaction temperature was 500 to 1500. ℃.The thickness of the carbon film obtained on the substrate was 1000A, and as a result of structural analysis of the carbon film using X-rays, it was confirmed that it was amorphous.The conductivity of the carbon film The rate is 1O-2Ω-1・c
It was m'.

Next, this amorphous carbon film was irradiated with ions in the same manner as in Example 1. The ion species at this time was argon, the kinetic energy of the ions was 100 keV, and the ion irradiation amount was 10'-1020/cts2.

The conductivity of the conductive carbon film irradiated with ions was measured and found to be 102Ω-'e cr'te.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to easily obtain a highly conductive and stable conductive carbon film by simply irradiating a low conductivity carbon film with ions. can.

In addition, by specifying the ion irradiation conditions, it is possible to obtain the desired conductivity, and furthermore, by focusing and deflecting the ion beam to be irradiated, it is possible to form a pattern with the desired high conductivity. For example, an electric circuit can be formed from the carbon film. Furthermore, the method for producing it is easy, and its stability is of great industrial value.

Claims (1)

[Claims] 1. A method for forming a conductive carbon film, which comprises irradiating the carbon film with ions in a vacuum. 2. The kinetic energy of the ion is 100 eV or more
2. The method for forming a conductive carbon film according to claim 1, wherein the conductive carbon film has a voltage of keV or less. 3. The method for forming a conductive carbon film according to claim 1, wherein the ion is one selected from the group of He, Ar, Ne, Kr, and Xe. 4. The method for forming a conductive carbon film according to claim 1, wherein the conductive carbon film has a thickness in the range of 1 nm to 100 μm.