JP3047486B2 - Diamond film production equipment - 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 for producing a diamond film, and more particularly to an apparatus 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 a method that can effectively utilize a source gas as proposed in Japanese Patent Application Laid-Open No. H10-201097 or Japanese Unexamined Patent Application Publication No. HEI 1-220107, gas plasma is generated by causing an arc discharge in an opposed electrode and passing the source gas through the arc discharge. A synthesis method is known in which this gas plasma is sprayed onto a substrate as a plasma jet gas by means of a throttle to deposit and form diamond on the substrate.

[0007]

However, this synthesis method also has a problem that it is insufficient in terms of gas decomposition (dissociation) near the substrate to which the source gas is blown.

That is, although the gas decomposition rate is significantly improved by using arc discharge, it is only in the vicinity of the arc discharge generating portion, and remarkably due to recombination reaction or the like in the vicinity of the substrate where plasma is sprayed onto the substrate as a plasma jet. Is declining. FIG. 3 shows a characteristic diagram in which the amount of hydrogen radicals (decomposed hydrogen) from the nozzle portion (plasma ejection port) of the plasma jet to the substrate is represented by the spectrum intensity of the hydrogen Balmer series emission spectrum Hβ. As is clear from FIG. 3, the gas decomposition rate decreases remarkably as the distance from the plasma outlet increases, that is, near the substrate.

Here, it is conceivable to perform the synthesis at a position where the gas decomposition rate is high by bringing the substrate closer to the plasma jetting port. However, this will increase the substrate temperature, and will increase the impurity carbon such as graphite other than diamond. There is a problem that generation is rapidly increased. This is because a substrate temperature of 600 to 1100 ° C. when diamond is synthesized is suitable, and 800 to 1000 ° C. is optimum for high purity synthesis.

Therefore, in order to synthesize diamond with higher efficiency, it is necessary to increase the gas decomposition rate near the substrate without increasing the substrate temperature. The present invention has been made in view of the above circumstances, and has as its object to provide a diamond film manufacturing apparatus capable of synthesizing a high-quality diamond film with high efficiency.

[0011]

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 an arc discharge, gas supply means for supplying a source gas containing at least hydrogen and carbon to the arc discharge to generate gas plasma, and a flow of the gas plasma. A diaphragm, a plasma jetting means for blowing the gas plasma as a plasma jet to a substrate arranged downstream thereof, and a position where the plasma jet has a maximum diameter between a region side where the gas plasma is generated and the substrate side or It is arranged in the vicinity thereof and is formed in a ring shape so that the plasma jet flows therethrough, and the ring A ring-shaped positive electrode whose diameter A is defined so as to satisfy a relationship of A ≦ 5B with respect to a throttle diameter B of the plasma jetting means; and a ring-shaped positive electrode for promoting decomposition of the source gas. And a plasma current power supply for flowing a current into the plasma jet.

[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
A ring-shaped insulator 40 made of boron nitride, a ring-shaped positive electrode 31 made of copper, a substrate 2 and a substrate support 3 made of copper are vacuum containers maintained at a predetermined pressure within a range of 5 Torr to 5 atm. 5.

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 (registered trademark), and a cylindrical electrode 10 made of copper are provided. The electrode cooling unit 8 and the cylindrical electrode 10 have hollow portions 108,
110 are provided. Then, the cylindrical electrode 10
The cooling water supplied from the cooling water pipe 14 connected to the cooling water pipe 1 extends from the hollow portion 110 of the cylindrical electrode 10.
Flows out to 4a. Similarly, the cooling water supplied from the cooling water pipe 15 connected to the electrode cooling unit 8 is supplied to the hollow portion 108 of the electrode cooling unit 8 and discharged from the cooling water pipe 15a connected to the electrode cooling unit 8. . 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. Gas inlet 9
Is provided with a raw material gas introduction pipe 16, and an opening for sending the gas supplied from the gas introduction pipe 16 to the tip 7 a of the rod-shaped electrode 7 is formed at one end of the rod-shaped electrode 7. Have been.

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 plasma jet port 18 for narrowing the gas plasma to be a plasma jet gas. Further, a ring-shaped insulator 40 and a ring-shaped positive electrode 31 which are connected to the plasma outlet 18 and constitute a plasma passage are provided. Further, a carbon source gas inlet 19 is provided in the plasma outlet 18.

The ring-shaped positive electrode 31 is arranged at or near the position where the plasma jet gas has the maximum diameter downstream of the plasma jet port 18, and the arrangement is determined by the length of the ring-shaped insulator 40. I have. The ring inner diameter of each of the ring-shaped insulator 40 made of boron nitride and the ring-shaped positive electrode 31 made of copper is set to be larger than the diameter of the plasma jet port 18. Plasma spout 18
Is determined so as to satisfy A ≦ 5B with respect to the inner diameter B. A power supply 21 for plasma current is provided between the rod-shaped electrode 7 and the ring-shaped positive electrode 31.
Is electrically connected. This is for applying an electric field between the rod-shaped electrode 7 and the ring-shaped positive electrode 31 so that a current flows from the ring-shaped positive electrode 31 to the rod-shaped electrode 7 through the plasma. The ring-shaped positive electrode 31 is provided with a hollow portion 112 which is hollow. Cooling water is supplied from the cooling water introduction pipe 32 to the hollow portion 112 so that the cooling water pipe 3
2a. The ring-shaped positive electrode 31 is cooled by the cooling water, and the heating of the ring-shaped positive electrode 31 by the current flowing between the rod-shaped electrode 7 and the ring-shaped positive electrode 31 is suppressed, and the ring-shaped positive electrode 31 is worn by the heating. Is prevented.

A substrate support 3 is set downstream of the plasma outlet 18 via the ring-shaped insulator 40 and the ring-shaped positive electrode 31, 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 18 reaches several thousands to tens of thousands of degrees, so that the substrate 2 is cooled in order to keep the substrate temperature at 600 to 1100 ° C., which is a diamond synthesis region. It is necessary to do it. The substrate support 3 is grounded, and the potential of the substrate 2 is set to the ground potential.

The distance between the ring-shaped positive electrode 31 and the substrate 2 is 10 to 100 mm, and the distance between the region where gas plasma is generated and the ring-shaped positive electrode 31 is 5 to 100 m.
m, it is possible to synthesize diamond. In this embodiment, the distance between the plasma outlet 18 and the substrate 2 is 40 mm, and the ring-shaped positive electrode 31 has a distance of 10 mm from the plasma outlet 18. Are installed on a concentric axis. In the present embodiment, the inner diameter of the plasma outlet 18 is 4 mm, and the inner diameter of the ring-shaped positive electrode 31 is 10 m.
m.

Next, a method for synthesizing the diamond film of the present embodiment will be described. First, after the inside of the vacuum vessel 5 is evacuated, argon as 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 40 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 order to generate an arc discharge, a high frequency may be superimposed between the rod-shaped electrode 7 and the cylindrical electrode 10 or a spark discharge may be generated by an igniter or the like, and then the arc discharge may be started. In this embodiment, the arc discharge is performed under the conditions of a voltage of 40 V and a current of 60 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 restriction of the plasma jet port 18 to form a plasma jet. From the carbon source gas inlet 19, methane gas 240 cc / min and hydrogen gas 60 cc / min
Is introduced. Here, the hydrocarbon gas as a carbon source gas represented by methane gas may be introduced from the gas introduction pipe 16, but since the tungsten electrode rod is carbonized, the discharge may not be stable for a long time.
It is desirable to provide a gas inlet downstream of the discharge part and to introduce the hydrocarbon gas therefrom. Then, the methane gas introduced from the carbon source gas inlet 19 is blown onto the plasma jet of the above-mentioned plasma source gas to be a plasma jet gas. Here, the pressure in the vacuum vessel 5 is set to 4
Exhaust is properly performed to maintain 0 Torr.

Here, the rod-shaped electrode 7 and the ring-shaped positive electrode 31
Between them, an electric field is applied by a plasma current power supply 21 which is a DC power supply. In this embodiment, the voltage is 60
V, a current value of 40 A, the substrate support 3 is grounded, and the potential of the substrate 2 is set to the ground 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 is used as the substrate 2, and its surface is finely scratched in advance by polishing so that a diamond film can be easily synthesized. Then, a Raman spectrometer and an electron microscope were used for observation of the deposit on the substrate 2. FIG.
(A) shows the relationship between the Raman shift and the peak height in the present embodiment. FIG. 2B shows the relationship between the Raman shift and the peak height when no electric field is applied by the plasma current power supply 21 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 is understood that a high-purity diamond film can be deposited and formed by applying an electric field from the power source 21 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. Is 10
It can be synthesized at a sufficiently high synthesis rate of 0 μm / h.

Next, as in the above embodiment, an electric field is applied between the rod-shaped electrode 7 and the ring-shaped positive electrode 31 by the plasma current power supply 21 to flow a current through the plasma, thereby producing a high-purity diamond. The reason why the film can be deposited and formed at a high synthesis rate will be described below based on the considerations of 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 the synthesis of diamond by plasma decomposition, graphite other than diamond, amorphous carbon, i-carbon and the like 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, the rod-shaped electrode 7 and the ring-shaped positive electrode 31
When an electric field is applied by the plasma current power supply 21 during this time, the electrons flowing in the gas plasma are accelerated toward the ring-shaped positive electrode 31, and the energy of the electrons increases. 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.

Here, the current flows in the plasma, and the larger the value, the higher the purity and the synthesis rate of the diamond film deposited and formed. 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, the reason why the substrate potential is set to the ground potential in this embodiment is to prevent the substrate temperature from rising due to the flow of the positive current from the substrate 2 to the ring-shaped positive electrode 31.

Next, in this embodiment, the ring-shaped positive electrode 3
The reason why the inner diameter A of the first ring is defined as A ≦ 5B with respect to the inner diameter B of the plasma ejection port 18 will be described. The ring-shaped positive electrode 31 is disposed at or near the position where the plasma jet column has the maximum diameter so that the plasma jet column of the source gas passes through the ring, and a large amount of electrons flow through the plasma jet column. The purpose is to do so.

The inventors of the present invention have repeated experimental considerations, and found that, when the inner diameter of the ring-shaped positive electrode 31 is changed with respect to the inner diameter of the plasma outlet 18, the synthesis speed of the diamond film synthesized and the heat of the film are increased. The inventors have found that the diffusivity changes, and found that the inner diameter of the ring-shaped positive electrode 31 is restricted. FIG. 5 is a characteristic diagram showing the relationship. As is clear from FIG. 5, when the inner diameter of the ring of the ring-shaped positive electrode 31 is larger than 5 times the inner diameter of the plasma outlet 18, the synthesis speed and thermal diffusivity of the synthesized diamond film (corresponding to the purity of the diamond film). Drops sharply. That is, there is a correlation between the ring inner diameter A of the ring-shaped positive electrode 31 and the inner diameter B of the plasma ejection port 18 that is suitable for flowing a large amount of electrons into the plasma, where A ≦ 5B. If the inner diameter of the ring of the ring-shaped positive electrode 31 is set to be larger than this correlation, it becomes difficult to flow electrons into the plasma. In this embodiment, the ring-shaped positive electrode 31 is provided to form a plasma jet column. It is considered that the purpose of flowing a large amount of electrons to promote the decomposition of the source gas cannot be achieved.

As described above, the present invention has been described using the first embodiment, but the present invention is not limited thereto, and various modifications can be made without departing from the spirit thereof. For example,
In the first embodiment, the negative (low) voltage of the plasma current power supply 21 is used.
Although the potential side is connected to the rod-shaped electrode 7, it may be connected to the cylindrical electrode 10. In the first embodiment, the ring-shaped positive electrode 31 is connected to the plasma jet gun 1 via the insulator 40. However, if the ring-shaped positive electrode 31 is insulated from the plasma jet port 18, Alternatively, the insulator 40 may be omitted, and the insulator 40 may be held in the space between the plasma outlet 18 and the substrate 2. Further, in the first embodiment, the substrate 2 is set at the ground potential. However, it is sufficient that the substrate temperature can be prevented from rising due to electrons reaching the substrate. A power source which has the same potential as the positive electrode or which has a lower potential than the ring-shaped positive electrode so that the ring-shaped positive electrode has a higher potential than the substrate may be connected to the substrate holder.

[0035]

As described above, according to the present invention, between the region where gas plasma is generated and the ring-shaped positive electrode above the substrate, the electrode side is set to a high potential so that electrons flow in the plasma. Therefore, the decomposition of the source gas can be remarkably improved, and the recombined source gas can be re-decomposed. Further, since the inner diameter A of the ring-shaped positive electrode is set so as to satisfy A ≦ 5B with respect to the aperture diameter B of the plasma ejection port, a large amount of electrons can easily flow in the plasma. An excellent effect is obtained in that the decomposition rate of gas in the vicinity can be sufficiently increased, the synthesis rate can be increased, and a high-quality diamond film can be synthesized with high efficiency.

[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 a distribution of hydrogen (H) radical spectrum intensity from a plasma ejection port toward a substrate.

FIG. 4 is a characteristic diagram showing a degree of dissociation of hydrogen with respect to a gas temperature.

FIG. 5 is a characteristic diagram showing changes in the synthesis rate and thermal diffusivity of a synthetic diamond film when the ring inner diameter of the ring-shaped positive electrode is changed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plasma jet gun 2 Substrate 3 Substrate support 5 Vacuum container 7 Bar electrode 10 Cylindrical electrode 16 Gas introduction pipe 17 Power supply for arc discharge 18 Plasma ejection port 19 Carbon source gas introduction port 21 Power supply for plasma current 31 Ring-shaped positive electrode 40 Ring insulator

──────────────────────────────────────────────────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-5-213694 (JP, A) JP-A-4- 295092 (JP, A) JP-A-4-295091 (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 (2)

(57) [Claims] 1. A vacuum vessel maintained at a predetermined degree of vacuum, a positive electrode and a negative electrode disposed in the vacuum vessel 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, gas supply means for supplying a source gas containing at least hydrogen and carbon to the arc discharge to generate a gas plasma, A plasma jetting means for blowing the gas plasma as a plasma jet to a substrate disposed downstream thereof, and the plasma jet having a maximum diameter between a region side where the gas plasma is generated and the substrate side. At or near a certain position, and is formed in a ring shape so that the plasma jet flows therethrough. A ring-shaped positive electrode whose inner diameter A is defined so as to satisfy a relationship of A ≦ 5B with respect to a throttle diameter B of the plasma jetting means, and a ring-shaped positive electrode for promoting decomposition of the source gas. An apparatus for producing a diamond film, comprising: a plasma current power supply for flowing a current into the plasma jet. 2. The diamond film manufacturing apparatus according to claim 1, wherein the potential of the ring-shaped positive electrode is the same as the potential of the substrate or higher than the potential of the substrate.