JP3047485B2 - Apparatus and method for producing diamond film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for producing a diamond film, and more particularly to an apparatus and a method for vapor-phase synthesizing a diamond film using arc discharge.

[0002]

2. Description of the Related Art In recent years, various methods have been proposed as low-pressure vapor-phase synthesis methods for diamond films. First, there is a hot filament CVD method. In this method, a tungsten filament is provided directly above a substrate heated to 800 to 1000 ° C., the filament is heated to 2000 ° C. or higher, hydrogen and a hydrocarbon gas (eg, CH ₄ ) are blown through the filament to the substrate, and diamond is placed on the substrate. This is a method of growing a film.

[0003] Second, a microwave plasma CVD method is known. This is a method in which plasma is generated in a mixed gas gas of hydrogen and hydrocarbon gas by a microwave of several hundred watts, and diamond is grown on a substrate placed in the plasma.
The temperature is about 00 to 900 ° C.

[0004] In these two kinds of synthesis methods, atomic hydrogen promotes the decomposition of CH ₄ and further acts to selectively etch synthetic substances other than diamond such as amorphous carbon. Plays an important role. However, the hot filament CVD method in which the filament is heated to a high temperature has many problems that the filament is broken, and is not practical. Further, considering the melting point of tungsten, the temperature of the filament is about 2000 ° C., and if it is higher than that, there is a problem that disconnection is caused and sufficient decomposition of the raw material gas cannot be performed. In addition, in the synthesis method using microwave plasma, it is difficult to apply the method to a large-area sample because the size of the plasma chamber is restricted.
In particular, there is a problem that decomposition of hydrogen becomes insufficient.

A third method is a synthesis method using an ion beam. This is intended to grow a diamond film by applying a carbon ion beam to a substrate. However, there is a problem that the diamond contains a large amount of impurities such as amorphous.

Accordingly, for example, Japanese Patent Application Laid-Open No. 63-176399
As disclosed in Japanese Patent Application Laid-Open No. HEI 10-201097 or Japanese Patent Application Laid-Open No. Hei 1-201097, an arc discharge is generated in the opposed electrode, and the raw material gas is passed through the arc discharge to form a gas plasma. A synthesis method is known in which diamond is deposited and formed on a substrate by spraying the substrate with the plasma jet gas.

[0007]

However, according to this synthesis method, although the synthesis rate can be remarkably improved, in order to improve the purity of the diamond film, the concentration of the hydrocarbon to be introduced with respect to hydrogen must be reduced. There is a problem that the synthesis speed must be reduced, thereby decreasing the synthesis speed.

That is, as is apparent from the data shown in FIG. 7, when the hydrocarbon concentration is reduced, the thermal diffusivity (purity) of the synthetic diamond film is improved, but the synthesis rate is reduced.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an apparatus and a method for manufacturing a diamond film capable of forming a high-purity diamond film while increasing the synthesis speed. It is the purpose.

[0010]

In order to achieve the above object, a diamond film manufacturing apparatus according to the present invention has the following configuration. That is, a vacuum container maintained at a predetermined degree of vacuum, a positive electrode and a negative electrode disposed in the vacuum container so as to face each other, and electrically connected to the positive electrode and the negative electrode, and a space between the positive electrode and the negative electrode. An arc discharge power supply for supplying a predetermined electric power to cause arc discharge, and a source gas containing at least hydrogen and carbon for the arc discharge to generate a gas plasma, and the gas plasma is disposed downstream thereof. Gas supply means for spraying the substrate, a third electrode provided between the region where the gas plasma is generated and the substrate, and the positive electrode or the negative electrode from the third electrode via the gas plasma. A power supply for plasma current for flowing a current to the substrate and a third electrode having the same potential or the same potential as the third electrode for preventing a positive current from flowing from the substrate to the third electrode. From the foregoing substrate 3
Substrate electric potential setting means for setting the electric potential of the substrate so that the electrode has a high electric potential.

In the method for producing a diamond film according to the present invention, a gas plasma is generated by flowing a raw material gas containing at least hydrogen and carbon into an arc discharge.
In the method of depositing and forming a diamond film on a substrate by spraying the gas plasma on a substrate disposed downstream thereof, a third electrode is provided between a region where the gas plasma is generated and the substrate. And a third electrode for supplying a current between the third electrode and a region where the gas plasma is generated in a state where a positive current is prohibited from flowing from the substrate to the third electrode. Is characterized by applying an electric field that becomes a high potential.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to an embodiment shown in the drawings. FIG. 1 is a sectional structural view of a manufacturing apparatus according to a first embodiment of the present invention.

In FIG. 1, a plasma jet gun 1
And the substrate support 3 made of copper and 5 Torr to 5 Torr.
It is provided in a vacuum vessel 5 maintained at a predetermined degree of vacuum within the range of atmospheric pressure.

The plasma jet gun 1 has a rod-shaped electrode 7 made of tungsten formed at a tip 7a having an acute angle at one end and a flange 7b at the other end as an axis. A cooling section 8, a gas introduction section 9 made of Teflon, and a cylindrical electrode 10 made of copper are provided. The electrode cooling unit 8 and the cylindrical electrode 10 are provided with hollow portions 108 and 110 which are hollow. Then, the cooling water supplied from the cooling water pipe 14 connected to the cylindrical electrode 10 flows out of the hollow portion 110 of the cylindrical electrode 10 to the cooling water pipe 14a. Similarly, the cooling water pipe 1 connected to the electrode cooling unit 8
5 is supplied to the hollow portion 108 of the electrode cooling portion 8.
Water pipe 1 supplied to the electrode cooling unit 8
It is discharged from 5a. The cooling water prevents wear of both electrodes due to heat of arc discharge generated between the rod-shaped electrode 7 and the cylindrical electrode 10. The gas introduction section 9 is provided with a raw material gas introduction pipe 16. Further, an opening for sending the gas supplied from the gas introduction pipe 16 to the distal end portion 7 a of the rod-shaped electrode 7 is provided in the gas introduction section 9. It is configured on one end side.

Further, the rod-shaped electrode 7 and the cylindrical electrode 10
The rod electrode 7 and the cylindrical electrode 10 are connected to an arc discharge power source 17 in order to cause an arc discharge between the electrodes. The arc discharge power supply 17 has a sharply formed tip portion 7 for effectively generating arc discharge.
The rod-shaped electrode 7 having a is connected to a negative potential. Further, on the surface of the cylindrical electrode 10 opposite to the gas introduction portion 9, there is provided a throttle portion 18 using gas plasma as a plasma jet gas. And
The plasma jet gun 1 is provided with a third electrode 22 made of copper via an insulator 21 which communicates with the throttle portion 18 and has a plasma passage 24 having a diameter larger than that of the throttle portion 18. Further, a carbon source gas inlet 19 is provided in the throttle unit 18.

The third electrode 22 is formed in a ring shape, and the inside of the ring is communicated with the plasma passage 24 of the insulator 21 as a plasma outlet 25. And
A power supply 26 for plasma current is electrically connected between the rod-shaped electrode 7 and the third electrode 22. This is the rod-shaped electrode 7
And an electric field is applied between the third electrode 22 and the third electrode 2.
This is to allow current to flow from 2 to the rod-shaped electrode 7 through the plasma. The third electrode 22 is provided with a hollow portion 122 which is hollow. Cooling water is supplied from a cooling water introduction pipe 23 connected to the hollow portion 122, and discharged from a cooling water pipe 23a. The third cooling water
Is cooled, the heating of the third electrode 22 by the current flowing between the rod-shaped electrode 7 and the third electrode 22 is suppressed, and the wear of the third electrode 22 due to the heating is prevented.

A substrate support 3 is set downstream of the plasma outlet 25, and the substrate 2 is disposed on the substrate support 3. The substrate support 3 is hollow so that cooling water is supplied from a cooling water pipe 20 and is discharged from a cooling water pipe 20a to maintain the substrate at a predetermined temperature (about 800 ° C. in this embodiment). This is because the gas temperature of the plasma jet ejected from the plasma ejection port 25 reaches several thousands to tens of thousands of degrees, so that the substrate 2 is cooled in order to set the substrate temperature to 600 to 1100 ° C., which is a diamond synthesis region. It is necessary to do it.

A power supply 26 for plasma current is also electrically connected between the substrate support 3 and the rod-shaped electrode 7 so that the substrate support 3 has the same potential as the potential of the third electrode 22. . Note that the distance between the third electrode 22 and the substrate 2 is 1 to 10
If the distance is 0 mm and the distance between the region where the gas plasma is generated and the third electrode 22 is 5 to 100 mm, diamond can be synthesized. In this embodiment, the distance between the plasma jet port 25 and the substrate 2 can be increased. Is 18 mm.

Next, a method for synthesizing the diamond film of the present embodiment will be described. First, after evacuating the inside of the vacuum vessel 5, argon, which is a Group 0 gas having a high degree of ionization, is introduced into the plasma jet gun 1 from the gas introduction pipe 16, and the pressure inside the vacuum vessel 5 is set to 20 Torr. . Thereafter, an arc discharge is generated between the rod-shaped electrode 7 (negative electrode) and the cylindrical electrode 10 (positive electrode) by the arc discharge power supply 17. In this embodiment, the arc discharge is performed under the conditions of a voltage of 40 V and a current of 65 A.

When the discharge was stabilized, a mixed gas of 50 vol% of argon and 50 vol% of H _{2 was} supplied as a plasma source gas at a flow rate of 12 liters per minute from the gas introduction pipe 16 to the gas discharge to form a gas plasma. Is passed through the throttle unit 18 to form a plasma jet. Then, a mixed gas of methane gas 240 cc / min and hydrogen gas 60 cc / min is introduced from the carbon source gas inlet 19. Here, a hydrocarbon gas as a carbon source gas typified by methane gas may be introduced from the gas introduction pipe 16, but since the tungsten electrode rod may be carbonized and the discharge may not be stable for a long time, the carbonization may be performed. It is desirable to provide a gas inlet downstream of the discharge unit and introduce hydrogen gas from there. And this carbon source gas inlet 19
The introduced methane gas is blown to the plasma jet of the above-mentioned plasma source gas to obtain a plasma jet gas.
Here, evacuation is appropriately performed so that the pressure in the vacuum vessel 5 is maintained at 20 Torr.

Here, an electric field is applied between the rod-shaped electrode 7 and the third electrode 22 by a plasma current power supply 26 which is a DC power supply. In this embodiment, the voltage is 50
V, the current value is 40 A, and the potential on the third electrode 22 side is a positive potential. The positive potential of the plasma current power supply 26 is also applied to the substrate support 3, and the third electrode 22 and the substrate support 3 have the same potential.

In this state, a red-purple plasma jet gas is blown onto the substrate 2 to deposit and form diamond on the substrate 2. In this embodiment, the temperature at the center of the plasma is 3000 ° C. or higher, and the discharge portion inside the gun rises more.

A description will now be given of the evaluation results of the surface deposits on the substrate 2 which were actually synthesized for 30 minutes under the above conditions. In addition,
A tungsten metal plate was used as the substrate 2, and the surface of the substrate 2 was mirror-polished in advance so that the diamond film could easily adhere. In addition, a Raman spectrometer and an electron microscope were used for observation of the deposit on the substrate 2. FIG. 2A shows the relationship between the Raman shift and the peak height in this embodiment. 1B shows the relationship between the Raman shift and the peak height when no electric field is applied by the plasma current power supply 26 in the configuration shown in FIG. 1 for comparison.

From this Raman spectrum, FIG.
As shown in the figure, a Raman peak having a Raman shift around 1333 cm ^-1 indicating the presence of diamond was confirmed. In FIG. 2B, from this Raman spectrum, 1400 to 1600c indicating graphite amorphous carbon, i-carbon and the like are shown.
A broad peak at m ^-1 clearly appears. From the results shown in FIGS. 2A and 2B, it can be seen that a high-purity diamond film can be deposited and formed by applying an electric field from the power source 26 for plasma current. Note that a crystal particle image was also confirmed by observation with an electron microscope, and the crystal form showed the same form as the diamond particles synthesized by the microwave plasma CVD method.

The diamond film was synthesized at a rate of 0.3 μm / h in a diamond synthesis experiment performed using microwave plasma CVD, which was conventionally known. 75
The synthesis speed is μm / h, and synthesis can be performed at a sufficiently high speed.

Next, by applying an electric field between the rod-shaped electrode 7 and the third electrode 22 as in the above embodiment, a high-purity diamond film can be deposited and formed at a high synthesis rate. The reason will be described below based on the result of consideration by the present inventors.

The method of synthesizing a diamond film using arc discharge is a method of synthesizing a diamond film by sufficiently decomposing a gas by the heat energy of the arc discharge, and the gases used are generally hydrocarbons and hydrogen. Considering the role of gas, hydrocarbons are decomposed by plasma decomposition to produce diamond, graphite, amorphous carbon, and i-carbon. On the other hand, hydrogen is considered to be decomposed by plasma decomposition to become hydrogen radicals, hydrogen ions, and the like. Since the hydrogen radical has a large reducing power, it has a function of reducing carbon and evaporating it to methane or the like. That is, the hydrogen radicals reduce diamond, graphite, amorphous carbon, i-carbon, and the like, which are generated by hydrocarbon decomposition by plasma.

Here, the reducing ability of hydrogen radicals to the diamond, graphite, amorphous carbon and i-carbon, that is, the removing ability is different from each other, and the removing ability to diamond is other graphite, amorphous carbon and i-carbon. It is much lower than the removal ability for carbon. Therefore, in diamond synthesis by plasma decomposition, graphite, amorphous carbon, i-carbon, etc. other than diamond are apparently selectively removed by hydrogen radicals, and only diamond is synthesized.

Therefore, in order to improve the synthesis rate and purity of diamond, it is necessary not only to increase the amount of introduced hydrocarbons but also to improve the decomposition (dissociation) of hydrogen and hydrocarbons. For example, when the dissociation rate of hydrogen with respect to the gas temperature is calculated by statistical mechanics, a graph shown in FIG. 4 is obtained. According to this graph, hydrogen is not dissociated by several percent at about 2,000 and several hundreds K, for example, as in the hot filament method. In order to highly dissociate hydrogen, a gas temperature of at least 3,000 K is required. Here, the arc discharge is several To
It is a discharge that occurs in the pressure range of rr to several atmospheres and a high-density current flows in the space instead of the potential difference between the counter electrodes being as low as several tens of volts. Therefore, it is considered that hydrogen can be sufficiently dissociated.

Then, by applying an electric field between the rod-shaped electrode 7 and the third electrode 22, the electrons flowing in the gas plasma are accelerated toward the third electrode 22, and the energy of the electrons is increased. When the electrons collide with hydrogen and hydrocarbons, the energy is absorbed by hydrogen and hydrocarbons. As a result, the hydrogen and hydrocarbons are easily decomposed and dissociated. It is considered that precipitation can be formed.

FIG. 3 shows the relationship between the Raman shift and the peak height when the value of the current applied between the rod-shaped electrode 7 and the third electrode 22 is changed. As can be seen from FIG. 3, when the applied current is 20 A or more, 1400 to 1600 cm ⁻¹
Almost no broad peak appears, and a high-purity diamond film can be obtained.

Here, the current flows in the plasma, and if the value is 10 A or more, it is effective. Also, the larger the value, the higher the purity and the synthesis rate of the diamond film formed by deposition. However, the electrons accelerated by increasing the current flowing in the plasma reach the substrate 2 and increase the substrate temperature, so that the substrate temperature cannot be maintained at 600 to 1100 ° C., which is the above-described diamond synthesis region. It is possible. That is,
In the present embodiment, the third electrode 22 and the substrate support 3 are electrically connected to have the same potential because the current flows between the third electrode 22 and the substrate 2 and the substrate temperature rises. This is in order to prevent that.

FIG. 5 shows the relationship between the peak intensity of the hydrogen radical emission at 5 mm above the substrate 2 and the current flowing therethrough. It can be seen that the hydrogen radical abundance increases as the current increases. I understand. In other words, the amount of hydrogen dissociated near the substrate is increased by energizing gas plasma, and this increase in dissociated hydrogen improves the ability to remove non-diamond carbon such as graphite other than diamond, amorphous carbon, and i-carbon. Thereby, the purity of the diamond can be improved.

Next, a second embodiment of the present invention will be described with reference to FIG. Although the arc discharge plasma jet method is used in the first embodiment, the same effect as that of the first embodiment can be obtained by the arc discharge method having the structure shown in FIG. In other words, an arc discharge is generated between the opposed electrodes 210 and 207 by the arc discharge power supply 217, and a mixed gas of hydrogen, methane, and argon is used as a source gas containing a plasma source gas and a carbon source gas through the source gas introduction pipe 216. At the same ratio and the same flow rate as in the first embodiment. Then, an electric field is applied between the third electrode 222 and the electrode 207 (or the electrode 210) by a plasma current power supply 226 which is a DC power supply. The synthesis conditions were the same as those described in the first embodiment. As with the first embodiment, the synthesis of high-purity diamond was confirmed by the apparatus of the present embodiment.

As described above, the present invention has been described using the first and second embodiments. However, the present invention is not limited thereto, and various modifications can be made without departing from the spirit of the present invention.
For example, in the first embodiment, the negative (low) potential side of the plasma current power supply 26 is connected to the rod-shaped electrode 7, but may be connected to the cylindrical electrode 10. In the first embodiment, the third electrode 22 is integrated with the plasma jet gun 1 via the insulator 21. However, the third electrode 22 may be insulated from the diaphragm 18 if it is insulated. Alternatively, the insulator 21 may be omitted, and the third electrode 22 may be held in the space between the plasma outlet and the substrate 2 by using the throttle portion 18 as the plasma outlet of the gun 1. Furthermore, in the first and second embodiments, the substrate 2, 202 and the third electrode 22, 222 are made to have the same potential. Alternatively, a power supply that sets the substrate to a lower potential than the third electrode may be connected to the substrate holding base so that the third electrode has a higher potential than the substrate. Good.

[0036]

As described above, according to the present invention, an electric field in which the electrode side above the substrate has a high potential is applied between the region where the gas plasma is generated and the electrode above the substrate to generate a current in the plasma. By flowing the gas, the gas can be sufficiently decomposed near the substrate. And since the substrate potential is set to the same potential or a low potential as the electrode, the substrate temperature is prevented from rising due to the current flowing in the plasma,
Thus, an excellent effect is obtained in that a high-purity diamond film can be formed while increasing the synthesis speed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a diamond film manufacturing apparatus according to a first embodiment of the present invention.

FIGS. 2A and 2B are characteristic diagrams showing the relationship between Raman shift and peak height. FIG. 2A is a characteristic diagram of a sample synthesized according to the first embodiment, and FIG. FIG. 4 is a characteristic diagram of a sample synthesized when no current is passed from the electrode into the gas plasma.

FIG. 3 is a characteristic diagram showing the relationship between the Raman shift and the peak height of each synthesized sample when the magnitude of the current flowing from the third electrode into the gas plasma is changed in the first embodiment.

FIG. 4 is a graph showing the degree of dissociation of hydrogen with respect to gas temperature.

FIG. 5 is a graph showing the relationship between the current value applied to the plasma and the value of 5
4 is a graph showing the relationship between the amount of hydrogen dissociation at the position of mm.

FIG. 6 is a sectional view of a diamond film manufacturing apparatus according to a second embodiment of the present invention.

FIG. 7 is a graph showing the thermal diffusivity and synthesis rate of diamond with respect to the hydrocarbon concentration (CH ₄ / H ₂ ).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plasma jet gun 2 Substrate 3 Substrate support 5 Vacuum container 7 Rod electrode 10 Cylindrical electrode 16 Gas introduction pipe 17 Power supply for arc discharge 19 Carbon source gas introduction port 22 Third electrode 26 Power supply for plasma current

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tadashi Hattori 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Inside Denso Co., Ltd. (56) References JP-A-4-295092 (JP, A) JP-A-4- 295091 (JP, A) JP-A-4-295090 (JP, A) JP-A-3-131598 (JP, A) JP-A-3-88799 (JP, A) JP-A-1-201097 (JP, A) JP-A-63-176399 (JP, A) JP-A-64-65093 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C30B 1/00-35/00 CA (STN) Patent file (PATOLIS) WPI / L (QUESTEL)

Claims (4)

(57) [Claims] A vacuum container maintained at a predetermined degree of vacuum; a positive electrode and a negative electrode arranged in the vacuum container so as to face each other; and electrically connected to the positive electrode and the negative electrode, and between the positive electrode and the negative electrode. An arc discharge power supply for supplying a predetermined electric power to cause an arc discharge in the space, and supplying a raw material gas containing at least hydrogen and carbon to the arc discharge to generate a gas plasma; Gas supply means for spraying the arranged substrate; a third electrode provided between the region where the gas plasma is generated and the substrate; and a third electrode provided through the gas plasma from the third electrode. A plasma current power supply for flowing a current to a positive electrode or a negative electrode, and the substrate and the third electrode have the same potential to prevent a positive current from flowing from the substrate to the third electrode. Or a substrate potential setting means for setting a potential of the substrate such that the third electrode has a higher potential than the substrate. 2. The diamond film according to claim 1, wherein the third electrode has a ring shape, and the gas plasma containing a carbon source gas is blown to the substrate through the inside of the ring. Manufacturing equipment. 3. The gas plasma flows between the positive electrode or the negative electrode and the third electrode so that a current flows from the third electrode to the positive electrode or the negative electrode via the gas plasma. 3. The apparatus for producing a diamond film according to claim 1, wherein a surrounding insulator is provided. 4. A gas plasma is generated by flowing a raw material gas containing at least hydrogen and carbon into an arc discharge, and a diamond film is deposited on the substrate by spraying the gas plasma on a substrate disposed downstream thereof. In the forming method, a third electrode is provided between the region where the gas plasma is generated and the substrate, and in a state where a positive current is prohibited from flowing from the substrate to the third electrode, A method for producing a diamond film, characterized in that an electric field that causes the third electrode to have a high potential is applied in order to cause a current to flow between the third electrode and a region where the gas plasma is generated.