JPH1112735A - Production of diamond-like thin carbon film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rapidly form a thin carbon film with stability at a low temp. by producing plasma by setting a solid dielectric on an opposed plane of at least either of counter electrodes and applying a pulsed electric field between the electrodes under an atmosphere containing carbon and oxygen and/or hydrogen under a pressure in the vicinity of atmospheric pressure. SOLUTION: Under a pressure of 100 to 800 Torr in the vicinity of atmospheric pressure, a solid dielectric of plastic, glass, etc., is set on one counter electrode plane, and, a pulsed electric field is applied between the counter electrode planes in a gaseous atmosphere containing carbon, oxygen, hydrogen, etc., to carry out electric discharge and produce plasma. In this case, the discharge current density between the counter electrodes is regulated to (0.2 to 300) mA/cm<2> , and (1 to 100) kv/cm electric field intensity is applied. Further, frequency and pulse duration at this time are regulated to 1 to 100 kHz and 1 to 1000 μs, respectively, by which the thin film can be easily formed on a base-material plane of the surface of the solid dielectric.

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 diamond-like carbon thin film on the surface of a substrate by using discharge plasma under a pressure near atmospheric pressure.

[0002]

2. Description of the Related Art Diamond-like carbon thin films have excellent physical properties such as hardness, high refractive index, and electrical conductivity, and are being used in a wide range of applications as coating materials for decoration, tools, electronic devices, and the like. .

Conventionally, as a method for producing a diamond-like carbon thin film, a thermal CVD method, a plasma CVD method, an ion beam method, an ion plating method, and the like have been known.
For example, Japanese Patent Application Laid-Open No. 58-91100 discloses thermal CVD.
A method for forming a diamond-like carbon thin film using a carbon-containing gas and a hydrogen gas by a plasma method is described in Japanese Patent Application Laid-Open No. 64-31974. A method for forming a film by using is described.

However, in the thermal CVD method and the plasma CVD method, since a film is formed in a low vacuum state, the activated carbon-containing active species collide with each other before the generated carbon-containing active species reach the substrate surface. , A different kind of active species is produced, a pure diamond-like carbon thin film is not formed, and
Because of the high temperature of 00 ° C. or higher, there was a drawback that a film could be formed only on a specific substrate. In addition, thin film synthesis under low pressure conditions requires vacuum equipment, does not increase plasma density, and is slow in film formation. Since these are industrially disadvantageous in cost, they are applied only to expensive processed products such as electronic components and optical components.

[0005] For this reason, a method of generating discharge plasma at a pressure close to the atmospheric pressure has been proposed.
Japanese Patent No. 48626 discloses a method of performing a treatment in a helium atmosphere, and Japanese Patent Application Laid-Open No. 4-74525 discloses a method of performing a treatment in an atmosphere comprising argon, acetone and / or helium. Have been.

However, all of the above methods generate plasma in a gas atmosphere containing helium or acetone, and the gas atmosphere is limited. Under these gas atmospheres, a diamond-like carbon thin film is formed. Cannot obtain a sufficient electron density. Therefore, no attempt has been made to form a diamond-like carbon thin film under a pressure near atmospheric pressure.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and it is intended to generate a uniform and high electron density discharge plasma under a pressure near the atmospheric pressure. And a method for producing a diamond-like carbon thin film on a substrate surface at high speed and at low temperature.

[0008]

The method for producing a diamond-like carbon thin film according to the first aspect of the present invention (hereinafter referred to as the first invention) is a method for producing at least one of the opposite electrodes under a pressure near atmospheric pressure. Discharge plasma is generated by placing a solid dielectric on the facing surface and applying a pulsed electric field between the facing electrodes in a gas atmosphere containing carbon and oxygen and / or hydrogen. .

The invention described in claim 2 of the present application (hereinafter referred to as “second
The method for producing a diamond-like carbon thin film of the invention)
In the first invention, the discharge current density between the opposed electrodes is 0.2
It is characterized by utilizing discharge plasma of up to 300 mA / cm ² .

[0010] The invention described in claim 3 of the present application (hereinafter referred to as "third")
The method for producing a diamond-like carbon thin film of the invention)
In the first invention or the second invention, the rise time and / or
Alternatively, a pulse electric field with a fall time of 40 ns to 100 μs and an electric field intensity of 1 to 100 kV / cm is applied.

The invention described in claim 4 of the present application (hereinafter referred to as the fourth
The method for producing a diamond-like carbon thin film of the invention)
In the first, second, or third invention, the frequency of the pulsed electric field is 1 to 100 kHz, and the pulse duration is 1 to 1000 μs.

In the above inventions, the first invention to the fourth invention are mutually related inventions, so these are collectively referred to as the present invention and will be described below.

In the present invention, the term "under atmospheric pressure" refers to a pressure of 100 to 800 Torr. The pressure is preferably in the range of 700 to 780 Torr, which facilitates pressure adjustment and makes the apparatus simple.

[0014] The plasma generation method of the present invention is performed in an apparatus having a pair of opposing electrodes, and a solid dielectric placed on at least one of the opposing surfaces of the electrodes. The portion where plasma is generated is between the solid dielectric and the electrode when a solid dielectric is installed on one of the electrodes, and between the solid dielectrics when the solid dielectric is installed on both of the electrodes. Space.

Examples of the electrodes include those made of a simple metal such as copper and aluminum, alloys such as stainless steel and brass, and intermetallic compounds. It is preferable that the counter electrode has a structure in which the distance between the counter electrodes is substantially constant in order to avoid occurrence of arc discharge due to electric field concentration. Examples of an electrode structure that satisfies this condition include a parallel plate type, a cylindrical opposed plate type, a spherical opposed plate type, a hyperboloid opposed plate type, and a coaxial cylindrical structure.

The solid dielectric is provided on one or both of the opposing surfaces of the electrode. At this time, the electrode on the side on which the solid dielectric is placed is in close contact with the electrode, and the opposing surface of the contacting electrode is completely covered. This is because if there is a portion where the electrodes directly face each other without being covered by the solid dielectric, an arc discharge occurs therefrom.

Examples of the solid dielectric include plastics such as polytetrafluoroethylene and polyethylene terephthalate, glass, metal oxides such as silicon dioxide, aluminum oxide, zirconium dioxide and titanium dioxide, and double oxides such as barium titanate. No.

The solid dielectric may be in the form of a sheet or a film, but preferably has a thickness of 0.05 to 4 mm. If the thickness is too large, a high voltage is required to generate discharge plasma. If the thickness is too small, dielectric breakdown occurs when a voltage is applied, and arc discharge occurs.

The distance between the electrodes is determined by the thickness of the solid dielectric,
It is determined in consideration of the magnitude of the applied voltage, the purpose of utilizing the plasma, and the like, and is preferably 1 to 50 mm.
If it is less than 1 mm, it is not enough to place the electrodes at intervals. If it exceeds 50 mm, it is difficult to generate uniform discharge plasma.

FIG. 1 shows an example of a pulse voltage waveform. Waveforms (A) and (B) are impulse waveforms, waveform (C) is a square wave waveform, and waveform (D) is a modulation waveform. Although FIG. 1 shows a case where the voltage application is repeated positive and negative, a pulse of a type that applies a voltage to either the positive or negative polarity side may be used.

The pulse voltage waveform in the present invention is not limited to the above-mentioned waveforms, but the shorter the rise time and the fall time of the pulse, the more efficient the ionization of the gas during plasma generation.

In particular, the rise time and / or fall time of the pulse is preferably 40 ns to 100 μs, more preferably 50 ns to 5 μs. 40
If it is less than ns, it is not realistic, and if it exceeds 100 μs, the discharge state easily shifts to an arc and becomes unstable. Here, the rise time refers to the time during which the voltage change is continuously positive, and the fall time refers to the time during which the voltage change is continuously negative.

Further, modulation may be performed using pulses having different pulse waveforms, rise times, and frequencies. Such modulation is suitable for high-speed continuous manufacturing.

The frequency of the pulse electric field is 1 kHz to 100
Preferably, it is kHz. If it is less than 1 kHz, it takes too much time for the treatment, and if it exceeds 100 kHz, arc discharge is likely to occur.

The pulse duration is 1 μs to 1000 μs.
μs, more preferably 3 μs to 2 μs.
00 μs. If it is less than 1 μs, the discharge becomes unstable, and if it exceeds 1000 μs, it is easy to shift to arc discharge. Here, the above pulse duration is
Although an example is shown in FIG. 2, it refers to the time during which a pulse is continuous in a pulse electric field composed of repetition of ON and OFF. In the case of the intermittent pulse as shown in FIG. 2A, the pulse duration is equal to the pulse width time, but in the case of the pulse having the waveform as shown in FIG. The time included.

Further, in order to stabilize the discharge, it is preferable to have an OFF time lasting at least 1 μs within a discharge time of 1 ms.

The discharge is performed by applying an electric field.
Although the magnitude of the electric field is determined as appropriate, in the present invention,
It is preferable that the electric field strength between the electrodes is in a range of 1 to 100 kV / cm. If the electric field strength is less than 1 kV / cm, it takes too much time to form a diamond thin film,
If it exceeds kV / cm, arc discharge is likely to occur.
In applying the pulse voltage, a direct current may be superimposed.

FIG. 3 shows a block diagram of a power supply when such a pulsed electric field is applied. FIG. 4 shows an equivalent circuit diagram of the power supply. In FIG. 4, SW is a semiconductor element functioning as a switch. By using a semiconductor element having a turn-on time and a turn-off time of 500 ns or less as the switch, the electric field strength as described above is 1 to 100 kV / cm, and the rise time and fall time of the pulse are 40 ns to 10 ns.
A high-voltage and high-speed pulse electric field of 0 μs can be realized.

Hereinafter, the principle of the power supply will be briefly described with reference to the equivalent circuit diagram of FIG. + E is a positive DC voltage supply unit, and -E is a negative DC voltage supply unit. SW1
Reference numerals 4 to 4 denote switch elements composed of the high-speed semiconductor elements as described above. D1 to D4 indicate diodes. I _{1 to} I ₄ indicate the direction of current flow.

[0030] First, SW1 is when ON, the positive load is charged in the flow direction current I _1. Then, the SW1 is turned OFF, by turning ON the SW2 instantaneously, the electric charge charged is charged in the direction of I ₃ through SW2 and D4. Next, when the switch SW3 is turned on after the switch SW2 is turned off, the load having the negative polarity causes the current I ₂
Charge in the direction of flow. Next, the SW3 is turned OFF, by turning ON the SW4 instantaneously, the electric charge charged is charged in the direction of I ₄ through SW4 and D2. By repeating the above series of operations, the output pulse of FIG. 5 can be obtained. Table 1 shows this operation table.

[0031]

[Table 1]

The advantage of this circuit is that even if the load impedance is high, the charged electric charge can be reliably discharged by operating SW2 and D4 or SW4 and D2, and high-speed operation. High-speed charging can be performed using SW1 and SW3, which are turn-on switch elements. Therefore, a pulse signal having a very fast rise time and fall time as shown in FIG. 5 can be obtained.

In the discharge obtained by the above method,
The discharge current density between the counter electrodes is 0.2 to 300 mA / c.
m ² is preferred.

The above-mentioned discharge current density is a value obtained by dividing a current value flowing between electrodes by discharge by an area in a direction orthogonal to a current flow direction in a discharge space. When used, it corresponds to a value obtained by dividing the current value by the facing area. In the present invention, a pulsed electric current flows to form a pulsed electric field between the electrodes. In this case, the maximum value of the pulse current, that is, the peak current
It means a value obtained by dividing the peak value by the above area.

In a glow discharge under a pressure near the atmospheric pressure,
It has been revealed by the present inventors that the discharge current density reflects the plasma density and is a value that influences the production of the diamond-like carbon thin film. By setting the range to 300 mA / cm ² , discharge plasma having a uniform and high electron density is generated, and a good production result of a diamond-like carbon thin film can be obtained.

In the present invention, carbon, oxygen and / or
Alternatively, discharge plasma is generated in an atmosphere of a gas containing hydrogen (hereinafter, referred to as a source gas). The source gas may be present as a separate compound, for example,
A compound containing carbon and oxygen, a compound containing carbon and hydrogen, or a compound containing carbon, oxygen, and hydrogen may be used.

As a specific example of the raw material gas, methano-
Alcohol-based gases such as toluene and ethanol; alkane-based gases such as methane, ethane, propane, butane, pentane and hexane; alkene-based gases such as ethylene, propylene, butene and pentene; pentadiene and butadiene Alkadiene-based gases, acetylene, alkyne-based gases such as methylacetylene, benzene, toluene, xylene, indene, naphthalene, aromatic hydrocarbon-based gases such as phenanthrene, cyclopropane, cycloalkane-based gases such as cyclohexane, Examples thereof include cycloalkene-based gases such as cyclopentene and cyclohexene, and oxygen-containing carbon compound-based gases such as carbon monoxide and carbon dioxide. At least one of these gases can be used.

When two or more of the above-mentioned carbon-containing gases are used, it is preferable to use carbon dioxide gas as one component, and the ratio is determined by the mixture ratio of carbon-containing gas other than carbon dioxide gas / carbon dioxide gas. As
It is preferably 1/3 (vol ratio). When the ratio of the carbon dioxide gas is in the above range, it is advantageous in improving the formation rate of the diamond-like carbon thin film.

The concentration of the carbon-containing gas in the gas atmosphere is preferably from 2 to 80 vol%. When the concentration is less than 2 vol%, the formation rate of the diamond-like carbon thin film decreases, and when it exceeds 80 vol%, the obtained thin film becomes graphite-like.

Oxygen and hydrogen become atomic during discharge, and have the effect of selectively removing graphite produced simultaneously with diamond. In order to make oxygen or hydrogen exist in the gas atmosphere, oxygen gas (O ₂ ) or hydrogen gas (H ₂ ) may be used in addition to the above-mentioned organic compound gas. When oxygen gas or hydrogen gas is used, the concentration of oxygen gas or hydrogen gas in the gas atmosphere is 70 vol.
% Is preferably not exceeded. On the other hand, if it exceeds 70 vol%, the obtained thin film becomes graphite-like.

The source gas may be diluted with a gas other than a gas containing carbon and oxygen and / or hydrogen. The use of a diluting gas is particularly preferable from the viewpoint of safety. Examples of the diluent gas used in the present invention include a gas of an element belonging to Group 0 of the periodic table and a nitrogen gas, and at least one of them can be used. To give a concrete example,
Examples include helium, argon, neon, xenon, and nitrogen gas. The concentration of the dilution gas in the gas atmosphere is preferably 20 to 90 vol%. When the concentration is 20
If it is less than vol%, the resulting thin film will be graphite-like, and if it exceeds 90 vol%, the formation rate of the diamond-like carbon thin film will decrease.

Further, diborane (B
By adding a gas containing a boron element such as H ₃ BH ₃ ) or phosphine (PH ₃ , CH ₃ PH ₂ ) or a phosphorus element to form a thin film, characteristics as a semiconductor can be improved.

Hereinafter, a method for producing a diamond-like carbon thin film on a substrate surface will be described in detail. The method of the present invention is directed to an apparatus having a pair of opposed electrodes, wherein a solid dielectric is provided on at least one of the opposed surfaces of the electrodes. When a solid dielectric is installed in both the electrode and the space between the dielectric and the electrode, the base material is installed in the space between the solid dielectrics, and the surface of the base material is treated by discharge plasma generated in the space. Things.

The substrate used in the present invention includes plastics such as polyethylene, polypropylene, polystyrene, polycarbonate, polyethylene terephthalate, polyphenylene sulphite, polyether ether ketone, polytetrafluoroethylene, and acrylic resin, glass, ceramic, and metal. And the like. The shape of the substrate is not particularly limited, and can be applied to substrates having a plate shape, a film shape, and various three-dimensional shapes.

FIG. 6 shows an example of an apparatus for performing the manufacturing method of the present invention. In this device, a solid dielectric 16 is provided on a lower electrode 15, and discharge plasma is generated in a space between the solid dielectric 16 and the upper electrode 14. Container 12
Is a gas inlet pipe 18, a gas outlet 20, and a gas outlet 2
The source gas is supplied to the discharge plasma generation space 13 from the gas introduction pipe 18. In the present invention,
Since a diamond-like carbon thin film is formed at a position in contact with the generated discharge plasma, the thin film is formed on the upper surface of the substrate 17 in the example of FIG. When it is desired to apply the thin film on both surfaces of the base material, the base material may be set up in the discharge plasma generation space 13 so as to float.

It is preferable that the atmospheric gas is uniformly supplied to the plasma generation space. When performing the discharge plasma treatment in an atmosphere gas composed of a mixed gas of a raw material gas and a diluent gas, since the difference in specific gravity is large, it is likely to be uneven at the time of supply,
It is preferable that the device is designed so as to avoid this. In the example shown in the apparatus of FIG.
Is connected to the upper electrode 14 having a porous structure, and the raw material gas is mixed by a gas mixer (not shown) and then supplied to the plasma generation space 13 from above the substrate through the hole of the upper electrode 14. . The dilution gas is separately supplied through a dilution gas introduction pipe 19. The structure is not limited to such a structure as long as the gas can be supplied uniformly, and a means such as stirring or blowing the gas at a high speed may be used.

The material of the container 12 includes, for example, resin and glass, but is not particularly limited. Metals such as stainless steel and aluminum can also be used as long as they have a structure insulated from the electrodes.

[0048]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the method of the present invention will be described in more detail with reference to examples. The power source is the power source according to the equivalent circuit diagram of FIG. 4 (made by Heiden, semiconductor device: manufactured by IXYS, model number TO-247AD).
Was used. The method for evaluating the obtained diamond-like carbon thin film is as follows.

Evaluation method (1) Identification of film Raman spectrometer (manufactured by Nicolet, Raman 9)
50), the obtained thin film was subjected to Raman spectroscopic analysis, and the presence or absence of a peak value (1332 / cm) of the Raman spectrum attributed to diamond was confirmed. Something has been identified. (2) Properties of Film The crystal grain size of the obtained film was observed and evaluated with a scanning electron microscope (EP-2000, manufactured by Hitachi, Ltd.).

Example 1 The discharge plasma processing apparatus shown in FIG. 6 was used. The chamber had an internal volume of 10 liters and was made of a stainless steel container 12. The lower electrode 15 has a diameter of 140 mm.
The surface is made of a zirconium oxide dielectric 16 having a relative dielectric constant of 16
, And a silicon substrate 17 was disposed thereon. The upper electrode 14 was arranged 2 mm above the substrate surface. The upper electrode 14 had a diameter of 80 mm, and holes with a diameter of 1 mm were arranged thereon at intervals of 5 mm. The surface was covered with a zirconium oxide dielectric having a relative dielectric constant of 16.

Using the oil rotary pump, the inside of the discharge plasma processing apparatus was evacuated until the pressure reached 0.1 Torr.
Nitrogen gas was supplied from the dilution gas introduction pipe 19 to the inside of the device at 760T.
orr. Thereafter, while a mixed gas of acetylene 2 sccm and nitrogen gas 998 sccm is introduced from the gas introduction pipe 18 connected to the upper electrode, a peak value of 18 kV, a frequency of 8 kHz, a rising speed of 500 ns is applied between the upper electrode 14 and the lower electrode 15. A pulse electric field having a pulse duration of 20 μs was applied, discharge was performed for 3 minutes, and a diamond-like carbon thin film was formed. The discharge current density was 60 mA / cm ² and the substrate temperature during film formation was 100
° C.

As a result of evaluating the obtained thin film by the method described above, a peak attributed to 1333 / cm diamond was confirmed by Raman spectroscopy, and a particle size of 0.3 to 1 μm was observed by scanning electron microscope. Was observed in a crystal state of diamond in which the particles were lined up all over the surface. When the film thickness was measured from the cross-section observation, it was 0.5 μm on average at five points. Therefore, the deposition rate at this time was 1 μm / hour.

Example 2 A diamond-like carbon thin film was formed in the same manner as in Example 1, except that 25 sccm of ethyl alcohol was used as the carbon-containing gas. As a result of evaluating the obtained thin film, peaks attributed to 1333 / cm diamond were confirmed by Raman spectroscopy, and diamond particles having a particle diameter of 0.3 to 1 μm were lined up in a scanning electron microscope. A crystalline state was observed. The deposition rate was 0.8 μm / hour.

Example 3 A diamond-like carbon thin film was formed in the same manner as in Example 1 except that the substrate was a soda glass substrate. As a result of evaluating the obtained thin film, the result of Raman spectroscopy was 1333 / c.
The peak attributed to the diamond of m was confirmed, and in a scanning electron microscope observation, a crystal state in which particles having a particle size of 0.3 to 1 μm were arranged on one surface was observed. The film forming speed was 1 μm / hour.

Comparative Example 1 The same gas mixture as in Example 1 was applied to the substrate at a frequency of 15 kHz.
A sine wave of 150 W was applied to try to form a diamond-like carbon thin film. Although discharge occurred, no change was observed on the substrate even after 1 hour of discharge, peaks attributed to diamond were not obtained by Raman spectroscopic analysis, and a special electron beam was observed on the substrate surface by scanning electron microscope observation. No precipitation of particles was observed.

[0056]

According to the manufacturing method of the present invention, as described above, a diamond-like carbon thin film can be formed on a substrate at a low temperature and a high speed near the atmospheric pressure. Therefore, it can be applied to a substrate having lower heat resistance than before, and at around atmospheric pressure,
Since surface treatment can be performed at high speed and economically, the range of application is widened, and for example, it is suitably used for transparent daylighting materials, transparent conductive materials, surface protection layers of cutting tools, optical materials, electronic materials, chemical industrial materials, and the like. .

[0057]

[Brief description of the drawings]

FIG. 1 is a voltage waveform diagram showing an example of a pulse electric field.

FIG. 2 is an explanatory diagram of a pulse duration.

FIG. 3 is a block diagram of a power supply that generates a pulse electric field.

FIG. 4 is an equivalent circuit diagram of a power supply that generates a pulse electric field.

FIG. 5 is a diagram of an output pulse signal corresponding to an operation table of a pulse electric field.

FIG. 6 is an example of a glow discharge plasma processing apparatus of the present invention.

[Explanation of symbols]

 11-1 High-voltage pulse power supply (AC power supply) 11-2 DC power supply 12 Stainless steel container 13 Discharge plasma generation space 14 Upper electrode 15 Lower electrode 16 Solid dielectric 17 Base material 18 Gas introduction pipe (carbon-containing gas) 19 Diluent gas Inlet pipe 20 Gas outlet 21 Exhaust port

Claims (4)

[Claims] At least one opposing surface of a counter electrode is provided with a solid dielectric at a pressure close to the atmospheric pressure, and a pulse is applied between the counter electrodes under a gas atmosphere containing carbon and oxygen and / or hydrogen. A method for producing a diamond-like carbon thin film, comprising generating discharge plasma by applying a converted electric field. 2. The discharge current density between the opposed electrodes is 0.2 to 3
The method for producing a diamond-like carbon thin film according to claim 1, wherein a discharge plasma having a current of 00 mA / cm ² is used. 3. A rise time and / or a fall time of 40 ns to 100 μs and an electric field intensity of 1 to 100 kV.
The method for producing a diamond-like carbon thin film according to claim 1 or 2, wherein a pulse electric field of / cm is applied. 4. The pulsed electric field has a frequency of 1 to 100 kHz and a pulse duration of 1 to 1000 μs.
The method for producing a diamond-like carbon thin film according to claim 1, 2 or 3, wherein: