JPH08337497A - Vapor phase synthesis of diamond thin film - Google Patents

Abstract

PURPOSE: To efficiently form high-quality-diamond by generating peak current having an instantaneously high peak at the time of rising of the electric discharge between electrodes, thereby omitting the pretreatment of a substrate and increasing the decomposition rate of gaseous raw materials. CONSTITUTION: An anode 8 installed in a reaction chamber 1 internally contains a heater 10 and thermocouples 9 and is so constituted that a base material 7 installed on the anode 8 can be heated. The anode 8 internally has a water cooling part 13 to allow the cooling of the base material 7. The base material 7 is heated by electron bombardment at the time of electric discharge and is, therefore, set at an arbitrary substrate temp. by commonly using the heating with heater and water cooling. Gaseous CH4 diluted with H2 is used for the gaseous raw material and is introduced into the reaction chamber after its flow rate is controlled by a mass flow controller 2. The inside of the chamber is evacuated by a vacuum pump 5 and the pressure is regulated to an arbitrary reaction pressure by the conductance of a discharge valve 4.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for depositing a diamond thin film from a gas phase on a substrate.

[0002]

2. Description of the Related Art In recent years, a vapor phase synthesis technique for diamond thin films has progressed, and various methods for producing diamond thin films have been proposed. The purpose of putting this production method into practical use is coating on a carbide cutting tool as an application utilizing the hardness of diamond, and manufacturing a diaphragm of a speaker as an application utilizing the high Young's modulus.
As a method for producing such a diamond thin film, decomposition of a hydrocarbon gas or a hydrocarbon oxygen gas is utilized under a reduced pressure environment of hydrogen gas, and the following methods have been conventionally known.

(1) The hot filament CVD method is a method of decomposing gas by thermoelectrons emitted from a tungsten filament to form a diamond thin film on a substrate. (2) The microwave plasma CVD method is a method of decomposing gas by a high electron temperature in microwave plasma to form a diamond thin film on a substrate. (3) ECR (electron cyclotron resonance) plasma CV
The D method is to generate microwave plasma in a magnetic field to generate ECR.
Is a method of generating high-density plasma to generate a diamond thin film on the substrate. (4) In the DC plasma CVD method, 1 kV to 10
It is a method of decomposing a gas and depositing a diamond film on a substrate by high electron temperature and electron density in an arc plasma generated by a direct current having a high voltage of kV.

[0004]

The conventional vapor phase synthesis method for diamond thin films is as described above, but each has the following problems. (1) In the hot filament CVD method, since the tungsten heater is heated to about 2000 ° C., the vapor pressure of the tungsten itself becomes high, and there is a problem that the tungsten is consumed in a short time or evaporated tungsten is mixed into diamond. is there. Further, when processing a plurality of base materials or processing a large-area substrate, the tungsten heater must be stretched into a complicated shape, which makes handling and condition setting difficult. Furthermore, when forming a diamond film on the surface of the substrate, diamond nuclei will not be generated sufficiently and the diamond film will not be formed unless the substrate surface is pre-treated and damaged by ultrasonic vibration using diamond powder in a solvent. It is difficult to synthesize into a shape.

(2) In the microwave plasma CVD method,
As a general apparatus, a structure in which a quartz tube is penetrated in a microwave waveguide is used. Here, the range in which the microwave enters the reaction tube is limited by the cross-sectional size of the waveguide, and in the 2.45 GHz band which is usually used, the diameter of the reaction tube can only be about 60 mm or less. Also, a method of expanding the end portion of the waveguide into a horn shape and injecting microwaves into a quartz bell jar with a large volume has been studied, but the actual diamond synthesis reaction is performed under a pressure condition of about several tens Torr, and plasma is generated. Pinch to a diameter of 10 to 20 mm. Therefore, 1
A diamond film can be formed only in an area having a diameter of about 20 mm per batch. In addition, since it is necessary to perform a treatment (pretreatment) on the surface of the substrate, it can be said that it is not practically suitable.

(3) The ECR plasma CVD method uses 1 × 1
Since the plasma is generated in a high vacuum region of about 0 ^-4 Torr, the plasma can be spread at a higher plasma density than the normal microwave plasma, but a large magnetic field is generated over a large area, so that a large-scale device can be used. It is not suitable for practical use, because it is necessary and the surface of the substrate needs to be damaged.

(4) In the DC plasma CVD method,
An electron impact is applied to the anode on which the substrate is placed from the opposite cathode, whereby the diamond film can be formed without damaging the substrate (pretreatment). However, since a high voltage is constantly applied between the electrodes, when a plurality of randomly shaped base materials etc. are installed on the anode,
The arc is concentrated on a specific substrate or the discharge becomes unstable, which makes it difficult to form a film on a plurality of substrates. In addition, since the arc discharge is unstable and is interrupted, the decomposition rate of the raw material gas cannot be increased and non-diamond carbon is generated. Therefore, it is not practically suitable.

The present invention is intended to solve such a conventional problem, and it is possible to efficiently prepare a high-quality diamond film by omitting the pretreatment of the substrate and increasing the decomposition rate of the raw material gas. An object of the present invention is to provide a practical method for producing a diamond thin film.

[0009]

In order to achieve the above object, in the first invention, a variable transformer and a fixed transformer are provided in a method of forming a diamond thin film by a direct current plasma CVD method using parallel plate electrodes. A rectifier is connected in series to form a power supply circuit to the discharge electrode, and the power supply circuit intermittently supplies the discharge electrode with applied power for plasma generation, and a capacitor is inserted in parallel with the rectifier. By doing so, a peak current having a momentary high peak is generated at the time of rising of discharge between the electrodes.

Further, according to the second aspect of the present invention, in the method of forming a diamond thin film by the direct current plasma CVD method using parallel plate electrodes, a variable transformer, a full wave rectifier, a switching element, a fixed transformer and a rectifying device are connected in series. By connecting to form a power supply circuit to the discharge electrodes and supplying the discharge electrodes with applied power for plasma generation in the form of a pulsed waveform, a capacitor is inserted in parallel with the rectifier to discharge between the electrodes. It is characterized in that a peak current with an instantaneously high peak is generated at the time of rising.

[0011]

In the present invention, in the method of forming a diamond thin film by the direct current plasma CVD method using the parallel plate electrodes, the variable electrode, the fixed transformer and the rectifier are connected in series to the discharge electrode formed. Discharge formed by intermittently supplying applied power for plasma generation to the discharge electrode in the power supply circuit, or by connecting a variable transformer, a full-wave rectifier, a switching element, a fixed transformer, and a rectifying device in series. The power supply circuit for the electrodes supplies the applied power for plasma generation to the discharge electrodes as a pulsed waveform, and by inserting a capacitor in parallel with the rectifier, the instantaneous high voltage at the start of discharge between the electrodes Since a peak current with a peak is generated, it is not possible with a normal discharge in the plasma generated between the electrodes due to this peak current. It is possible to generate high electron temperature and electron density that is not a raw material gas efficiently to the fast excitation and decompose, it is possible to deposit a high-quality diamond film.

Here, the electric power supplied to the electrodes may be, for example, a half-wave rectified commercial power supply having a frequency of 50 to 60 Hz and an intermittent half-wave waveform, or 50 to 50 formed by a pulse oscillation circuit. A square wave pulse between 1000 Hz may be used. Also, as a capacitor to be inserted in parallel with the rectifying device, it is small enough that the rectified waveform is not smoothed according to the frequency, and large enough that a peak of the peak current occurs at the moment of rising of discharge between the electrodes due to charging and discharging. A high-voltage capacitor having a capacitance value is preferable.

Since the method of the present invention is basically a direct current plasma, it has the following effects. Introducing a hydrocarbon or a mixed gas of hydrocarbon oxygen and hydrogen into a vacuum reaction vessel, glow discharge generated between electrodes in an atmosphere of about several tens to 100 Torr becomes a thermal plasma state as the current increases, If the substrate has a current density of 0.5 A / cm ² or more, it is sufficiently 700-80 without heating with a heater.
Plasma heated to 0 ° C. In particular, when it is necessary to form a film at a low temperature, the anode can be water-cooled, and conversely, when the heat capacity of the substrate is large, it can be adjusted to an arbitrary reaction temperature by auxiliary heating with a heater. Further, during this glow discharge, electron impact on the base material or substrate is strong, so normally, pretreatment of the substrate surface at the time of performing microwave plasma CVD or hot filament CVD, that is, scratch treatment with diamond powder or the like is required. Nonetheless, diamond can be sufficiently nucleated.

Further, the DC plasma is an intermittent or pulsed discharge, and a high-voltage capacitor having an appropriate capacitance value is inserted in parallel with the rectifier in the power supply circuit, which has the following effect. For normal half-wave rectification,
After the AC power is rectified by the rectifying element, a capacitor having a sufficiently large capacitance value is inserted between the capacitor and the ground potential, so that the intermittent half-wave rectification waveform is sufficiently charged and discharged by the capacitor. As shown in (A), the waveform is smoothed and a stable DC voltage is obtained. Therefore, when a power source having a capacitor having a sufficiently large capacitance value is used, the discharge current becomes constant in the state where the discharge between the electrodes is stable, and therefore the discharge current is constant as shown in FIG. 11 (B). It becomes a direct current plasma through which a discharge current flows.

On the other hand, when this capacitor is not provided or when the electrostatic capacitance value is sufficiently small, the charging / discharging action disappears and the half-wave rectified waveform is applied to the electrodes, so that the discharge between the electrodes is intermittent. The discharge current does not flow until the discharge starts in one cycle, and the half-wave waveform voltage starts rising as shown in FIG. 12 (A), but at the same time when the discharge starts, the discharge current is as shown in FIG. 12 (B). Then, the voltage starts to flow in accordance with the half-wave waveform and the voltage drops. That is, in the case of half-wave rectification, an intermittent half wave is output, and in the case of using a pulse oscillator, a pulse waveform is output as it is, and intermittent plasma or pulse plasma is generated. In this case, the crystallinity of the diamond thin film formed can be improved by the action of afterglow that occurs during intermittent or pulsed discharge, as compared with direct current discharge. However, since the peak value of the discharge current is not much different from that in the case of DC discharge, there is no significant difference in the energy in the plasma.

Further, according to the present invention, the capacitance value inserted into the output of the power supply is small enough not to smooth the rectified waveform according to the frequency, but high enough to permit charging and discharging to some extent. If you insert a capacitor,
As shown in FIG. 13 (A), it is similar to the case where the capacitance value is small until the start of discharge, but as shown in FIG. 13 (B), a transiently high peak occurs due to the charge / discharge action of the capacitor as the discharge starts. A peak current flows between the electrodes, causing a discharge (tp) to rise, after which the discharge current flows in accordance with the half-wave waveform. Therefore, in the intermittent or pulsed discharge, a state in which both the electron temperature and the electron density in the plasma are significantly high immediately after the start of discharge is generated instantaneously, and it is more efficient than ordinary DC discharge, intermittent discharge or pulsed discharge. The raw material gas can be dissociated and reacted with high energy, and a diamond film with good crystallinity can be synthesized. For example, comparing the case of using a commercial power supply with a frequency of 50 Hz with a high-voltage capacitor with a sufficiently large capacitance value for direct current discharge and the case of intermittent discharge with the capacitance value of 0.5 μF, plasma The average measured values of the electron temperature and the electron density in the inside are as shown in Table 1. The electron temperature is slightly increased by intermittent discharge, but the electron density is almost the same.

◆

[Table 1]

However, when the changes in the electron temperature and the electron density with time in the intermittent discharge are compared, there are instantaneous peaks of the electron temperature and the electron density corresponding to the peaks of the peak waveform as shown in FIG. Electron temperature of normal DC discharge or intermittent discharge in the part is 8 to 11 eV, electron density is 1.0
〜1.2 × 10 ¹² cm ^-3 , the electron temperature is about 3 instantaneously.
A very high energy state of 00 eV and an electron density of 100 to 200 × 10 ¹² cm ⁻³ is generated. It should be noted that the capacitance value required for the charging / discharging action changes depending on the frequency of the rectified waveform, and the higher the frequency, the smaller the capacitance. However, as the frequency becomes higher, the electrostatic capacity becomes smaller and the charging / discharging time becomes shorter, so that the peak current becomes smaller and the effect of the present invention is hard to be obtained. According to an experiment using a variable frequency pulse oscillation circuit, at a frequency between 100 and 1000 Hz, a low frequency has good crystallinity but a low growth rate, and a high frequency has low crystallinity but a low growth rate. A fast tendency appeared, and it was confirmed that the crystallinity and the growth rate were in the most balanced state near the frequency of 500 Hz. Including the case where half-wave rectification of a commercial power source having a frequency of 50 Hz is also included, a diamond thin film having good crystallinity at a frequency of 50 to 1000 Hz can be practically formed depending on the use of the diamond thin film.

[0019]

EXAMPLE 1 FIG. 1 is a block diagram of a direct current plasma CVD apparatus used in the vapor phase synthesis method of a diamond thin film of the present invention, in which a commercial power source having a frequency of 50 to 60 Hz is boosted and half-wave rectified power is applied to intermittent discharge. Is used. Reaction chamber
The anode (8) installed in (1) has a heater (10) and a thermocouple (9) built therein so that the base material (7) installed on the anode (8) can be heated. . Further, the anode (8) has a water cooling part (13) inside so that the base material (7) can be cooled. Since the base material (7) is also heated by electron impact at the time of discharge, it is set to an arbitrary substrate temperature by heating with a heater or cooling with water. Raw material gas introducing CH ₄ gas diluted with H ₂ to the reaction chamber by a flow rate controlled by the mass flow controller (2), and evacuated by a vacuum pump (5),
The reaction pressure is adjusted to an arbitrary value by the conductance of the exhaust valve (4).

As electric power for generating plasma,
The commercial power source (200 V) (19) with a frequency of 50 to 60 Hz is adjusted with the primary voltage 200 V: the slide regulator (18) with a secondary voltage of 0 to 240 V, and the primary voltage 240
V: boosted by a high voltage transformer of secondary voltage 6000V, half-wave rectified by a high voltage rectifying element (16) to a negative voltage, 0.5-2.
It is applied to the cathode (6) through a series resistor (14) in parallel with a 0 μF high voltage capacitor (15).

With this device configuration, a pressure of 150 Torr, a substrate temperature of 700 ° C., and CH ₄ / CH ₄ are used in the case of DC discharge in which the half-wave rectified waveform is smoothed and in the case of intermittent discharge according to this embodiment.
A comparison was made under the conditions where the H ₂ ratio was 1% and 3%. 2 shows the case where the CH ₄ / H ₂ ratio (Cm) is 1%, and FIG. 3 shows CH ₄ / H ₂
The case where the ratio (Cm) is 3% is shown. And in each figure
(a) is an SEM photograph of a diamond thin film produced by intermittent discharge, and (b) is an SEM photograph of a diamond thin film produced by direct current discharge. CH ₄ / H ₂
When the ratio is 1%, the crystallinity grows with good intermittent or direct current discharge, but when the CH ₄ / H ₂ ratio becomes 3%, the self-form of the crystal is broken in the direct current discharge. On the other hand, it is understood that the intermittent discharge is a polycrystalline thin film having a good self-shape. This is clear compared to the Raman spectrum,
When the CH ₄ / H ₂ ratio shown in FIG. 4 is 1%, the intermittent discharge (a) and the direct current discharge (b) are both 1333 cm ^−1.
A clear diamond spectrum appears in the vicinity. However, when the CH ₄ / H ₂ ratio shown in FIG. 5 is 3%, a clear diamond spectrum is observed in the case of intermittent discharge (a), but no diamond spectrum is observed in the case of direct current discharge (b). It is clear. In addition, the broad peaks seen around 1500 cm ^-1 in both cases of DC discharge at 1% and 3% are small in the case of intermittent discharge. This means that the amount of amorphous carbon in the film is small in the intermittent discharge.

As described above, according to the present embodiment, since a state in which the electron temperature and the electron density are extremely high is instantaneously generated in the plasma, hydrocarbon or oxygen (C in this embodiment is C
H ₄ ) and hydrogen molecules are dissociated with high efficiency, the etching action of the synthetic film by the generated atomic hydrogen is promoted, and the bonded state of graphite can be removed to form a diamond thin film with good crystallinity. Therefore, it is apparent that the diamond thin film having good crystallinity can be formed by the intermittent discharge according to this example.

[0023]

[Embodiment 2] FIG. 6 is a block diagram of a direct current plasma CVD apparatus used in the vapor phase synthesis method of a diamond thin film according to the present invention.
This is a pulse plasma CVD apparatus in which a switching circuit incorporating a pulse oscillating circuit that can be changed at an arbitrary cycle between 00 and 1000 Hz is configured and pulse power is used as plasma generation power.

As in Example 1, the anode (8) installed in the reaction chamber (1) has a heater (10) and a thermocouple (9) inside,
The base material (7) placed on the anode (8) can be heated. Further, the anode (8) has a water cooling part (13) inside, and can also cool the substrate (7). Since the base material (7) is also heated by electron impact at the time of discharge, it is set to an arbitrary substrate temperature by heating with a heater or cooling with water. Source gas mass flow controllers to CH ₄ gas diluted with H ₂ (2)
It is introduced into the reaction chamber (1) by controlling the flow rate by means of the vacuum pump (5), exhausted by the vacuum pump (5), and adjusted to an arbitrary reaction pressure by the conductance of the exhaust valve (4). As electric power for generating plasma, a pulse oscillation circuit (21) oscillates an arbitrary pulse having a period of 1 to 10 ms, the driver circuit (22) amplifies the pulse, and a commercial power supply (19) is used as a slide regulator (18). ) And a bridge diode (20) rectify any DC voltage and a high voltage transformer (17) and a switching transistor.
It is generated as a high voltage pulse by the switching circuit according to (23). This is half-wave rectified to a negative voltage by a high voltage rectifying element (16) and applied to a cathode (6) in parallel with a high voltage capacitor (15) of 0.02 to 2.0 μF via a series resistor (14).

With this device configuration, a pressure of 150 Torr, a substrate temperature of 600 ° C., and a CH _{4 of 4}
The comparison was made under the condition that the / H ₂ ratio was 3%. FIG.
(a) is the case of using pulse discharge, (b) is the case of using direct current discharge, SEM of the diamond thin film that was respectively prepared
It is a photograph. Here, the pulse discharge according to the present embodiment grows with better crystallinity than the direct current discharge. The Raman spectrum at this time is shown in FIG. In case of pulse discharge
Comparing (a) and (b) in the case of DC discharge, both are 13
The diamond spectrum is found around 33 cm ^-1, but the broad peak around 1600 cm ^-1 seen in the case of DC discharge (b) is 15 in the case of pulse discharge (a).
It has shifted to around 00 cm ^-1 . This is because the ratio of SP ³ bonds occupied by the pulse discharge becomes high in the mixed state of the SP ³ bond which is the bond state of diamond and the SP ² bond which is the bond state of graphite in the amorphous carbon component mixed in the film. It indicates that

That is, according to this embodiment, since a state in which the electron temperature and the electron density are extremely high is generated instantaneously in the plasma, hydrocarbon or oxygen (C in this embodiment is C
H ₄ ) and hydrogen molecules are dissociated with high efficiency, the etching action of the synthetic film by the generated atomic hydrogen is promoted, and the bonded state of graphite can be removed to form a diamond thin film with good crystallinity.

With this device configuration, the frequency is (a) 100 Hz, making the best use of the characteristics under the above-mentioned preparation conditions.
The SEM photograph of FIG. 9 and the Raman spectrum of FIG. 10 are compared by changing (b) 500 Hz and (c) 1000 Hz. Here, as seen in the SEM photograph, film growth with the best crystallinity is seen at 500 Hz. According to the Raman spectrum, the peak of diamond at around 1333 cm ^-1 is the most clear, and the broad peak is shifted to the peak of diamond at 100 Hz. According to the SEM photograph, the crystallinity is good but the crystal is good. However, it takes time to grow into a film. That is, it can be seen that when the frequency of the pulse discharge is low, the crystallinity is good but the growth rate is slow, and when the frequency is high, the crystallinity is poor but the growth rate is high.

Therefore, according to this embodiment, the film quality can be controlled by setting the frequency of the pulse discharge.
In addition, the frequency of intermittent discharge of the present embodiment and the first embodiment is 50 Hz.
It can be said that the diamond thin film having particularly good crystallinity can be formed in the frequency range of intermittent discharge or pulse discharge of 50 to 500 Hz.

[0029]

According to the present invention, the following effects can be expected. (1) The diamond thin film can be formed by omitting the pretreatment of the substrate. (2) A diamond film can be formed by efficiently decomposing and reacting a raw material gas. (3) It is possible to suppress the mixture of graphite and amorphous carbon and to form a high quality diamond film. (4) Frequency of intermittent discharge or pulse discharge 50 to 500
It can be said that a diamond thin film having particularly good crystallinity can be formed in the range of Hz.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a DC plasma CVD apparatus used for a vapor phase synthesis method of a diamond thin film.

FIG. 2 is a SEM photograph at a methane concentration of 1%,
(a) shows intermittent discharge, and (b) shows direct current discharge.

FIG. 3 is an SEM photograph at a methane concentration of 3%,
(a) shows intermittent discharge, and (b) shows direct current discharge.

FIG. 4 is a Raman spectrum at a methane concentration of 1%.

FIG. 5 is a Raman spectrum at a methane concentration of 3%.

FIG. 6 is a configuration diagram of a direct current plasma CVD apparatus of another embodiment used in a vapor phase synthesis method of a diamond thin film.

FIG. 7 is an SEM photograph at a methane concentration of 3%,
(a) shows intermittent discharge, and (b) shows direct current discharge.

FIG. 8 is a Raman spectrum at a methane concentration of 3%.

FIG. 9 is an SEM photograph with the frequency changed,
(a) is 100Hz, (b) is 500Hz, (c) is 1
000 Hz is shown.

FIG. 10 is a Raman spectrum diagram with the frequency changed.

FIG. 11 is a state diagram of voltage and current when the capacitance of the capacitor is large.

FIG. 12 is a state diagram of voltage and current when the capacitance of the capacitor is small.

FIG. 13 is a state diagram of voltage and current when a capacitor having an appropriate capacitance is used.

FIG. 14 is a graph showing changes in electron temperature and electron density. 1 ... Reaction chamber, 2 ... Mass flow controller, 3 ... Raw material gas introduction valve, 4 ... Exhaust valve, 5 ... Vacuum pump, 6
... cathode, 7 ... substrate or base material, 8 ... anode, 9 ... thermocouple,
10 ... Heater, 11 ... Heater power supply, 12 ... Temperature monitor,
13 ... Anode water cooling part, 14 ... Series resistance, 15 ... High voltage condenser,
16 ... High voltage rectifier, 17 ... High voltage transformer, 18 ... Slide regulator, 19 ... Commercial power supply, 20 ... Bridge diode,
23 ... Switching transistor, 21 ... Pulse oscillation circuit,
22 ... Driver circuit, 23 ... Switching transistor.

Claims (10)

[Claims] 1. A direct current plasma C using parallel plate electrodes.
In the production of a diamond thin film by the VD method, a power supply circuit to the discharge electrode is formed by connecting a variable transformer, a fixed transformer and a rectifying device in series, and the applied power for generating plasma is intermittently applied to the discharge electrode. And a capacitor is inserted in parallel with the rectifier to generate a peak current with an instantaneously high peak at the rise of discharge between the electrodes. Phase synthesis method. 2. The method for producing a diamond thin film according to claim 1, wherein the applied power applied to the discharge electrode has a high current density of 1.0 A / cm ² or more with respect to the electrode area or the substrate area. 3. The method for producing a diamond thin film according to claim 1, wherein the frequency of the applied power applied to the discharge electrode is set to 50 to 1000 Hz. 4. The method for producing a diamond thin film according to claim 1, wherein the applied power applied to the discharge electrode is rectified by using this as a negative voltage. 5. The applied power applied to the discharge electrode is a reaction pressure of 100 to 200 Torr and a methane gas concentration of 1 in hydrogen gas.
The method for producing a diamond thin film according to claim 1, wherein discharge is performed between electrodes in a gas phase of up to 5%. 6. A direct current plasma C using parallel plate electrodes.
In the production of diamond thin film by VD method, the power supply circuit to the discharge electrode, variable transformer, full-wave rectifier,
A switching element, a fixed transformer, and a rectifying device are connected in series to form a pulsed waveform of applied power for plasma generation to the discharge electrode, and a capacitor is inserted in parallel with the rectifying device to form an electrode. A method for vapor phase synthesis of a diamond thin film, which is characterized in that a peak current having a momentary high peak is generated at the time of the rise of the discharge between the two. 7. The method for producing a diamond thin film according to claim 6, wherein the electric power applied to the discharge electrode has a high current density of 1.0 A / cm ² or more with respect to the electrode area or the substrate area. 8. The method for producing a diamond thin film according to claim 6, wherein the frequency of the applied power applied to the discharge electrode is set to 50 to 1000 Hz. 9. The method for producing a diamond thin film according to claim 6, wherein the applied power applied to the discharge electrode is rectified by using this as a negative voltage. 10. The electric power applied to the discharge electrode is discharged between electrodes in a gas phase having a reaction pressure of 100 to 200 Torr and a methane gas concentration of 1 to 5% in hydrogen gas. Method for making diamond thin film.