JP3047487B2 - 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. 8, when the hydrocarbon concentration is reduced, the thermal diffusivity (purity) of the synthetic diamond film is improved, but the synthesis speed is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been made to increase the synthesis speed, form a high-purity diamond film, and reduce the synthesis speed and purity of a predetermined portion of a diamond film on a substrate. It is an object of the present invention to provide an apparatus and a method for producing a diamond film that can be improved.

[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 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, at least one pair of opposed electrodes arranged between the region side where the gas plasma is generated and the substrate side so as to sandwich the flow of the gas plasma toward the substrate, A power source for plasma current for flowing a current in the gas plasma in a direction intersecting the flow of the gas plasma by applying an electric field between the electrodes. It is characterized in that it comprises.

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 gas flowing toward the substrate is provided between the region where the gas plasma is generated and the substrate. At least one pair of opposing electrodes is provided so as to sandwich the flow of plasma, and an electric field is applied between the opposing electrodes to flow a current in the gas plasma in a direction intersecting with the flow of the gas plasma. And

[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 (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 which narrows the gas plasma to form a plasma jet. Further, a carbon source gas inlet 19 is provided in the plasma outlet 18.

A substrate support 3 is set downstream of the plasma outlet 18, 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.

In the space between the plasma jet 18 and the substrate 2, the plasma jet 1 on a plane parallel to the surface of the substrate 2.
And a pair of opposing electrodes 21 and 22 opposing each other with the plasma jet from 8 interposed therebetween.
A plasma current power supply 23 is electrically connected to the power supply terminals 1 and 22. This is because an electric field is applied between the opposing electrodes 21 and 22 so that a current flows between the opposing electrodes 21 and 22 through the plasma. The counter electrode 21 on the negative electrode side is made of tungsten having one end formed at an acute angle, while the counter electrode 22 on the positive electrode side is made of copper, and the inside thereof is hollowed by the hollow portion 122. ing. A cooling water pipe 24 is connected to the counter electrode (positive) 22, and cooling water supplied from the cooling water pipe 24 is discharged from a hollow portion 122 of the counter electrode (positive) 22 to a cooling water pipe 24 a. The counter electrode (positive) 22 is cooled by the cooling water, thereby preventing the electrode from being worn from heat generated by a current flowing between the counter electrode (positive) 22 and the counter electrode (negative) 21.

The distance between the opposing electrodes 21 and 22 is set to be smaller than the diameter of the plasma jet. As a result, the electrodes 21 and
22 is inserted, and it becomes easier to energize the plasma jet (FIG. 1 is a schematic diagram, and the actual distance relationship is different from the diagram). Further, the counter electrodes 21 and
2 is 2 to 50 mm, and the substrate 2 and the counter electrodes 21 and
If the distance from the mounting surface of the substrate 2 is 1 to 100 mm, diamond can be synthesized. In this embodiment, the distance between the counter electrodes 21 and 22 is 15 mm,
The distance between the installation surfaces of the plasma injection nozzles 1 and 22 is 20 mm, and the distance between the plasma injection port 18 and the substrate 2 is 40 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 converted into a plasma jet by the restriction of the plasma injection port 18. 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 rod-shaped electrode 7 made of tungsten 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 2
Exhaust is properly performed to maintain 0 Torr.

Here, an electric field is applied between the counter electrode (positive) 22 and the counter electrode (negative) 21 by a plasma current power supply 23 which is a DC power supply. In this embodiment, the voltage is 100 V and the current value is 20 A.

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 the surface of the substrate 2 is finely polished in advance so that a diamond film can be easily synthesized. Also, the substrate 2
A Raman spectrometer and an electron microscope were used for observation of the upper deposit. FIG. 2A shows the relationship between the Raman shift and the peak height in this 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 23 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 23 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 50
The synthesis speed is μm / h, and synthesis can be performed at a sufficiently high speed.

Next, as in the above embodiment, the counter electrode 2
The reason why a high-purity diamond film can be deposited and formed at a high synthesis rate by applying an electric field between 1 and 22 will be described below based on the results 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 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.

When an electric field is applied between the two opposing electrodes 21 and 22, electrons flowing in the gas plasma are accelerated toward the positive opposing electrode 22, 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.

FIG. 3 shows the relationship between the Raman shift and the peak height when the value of the current flowing between the opposite electrodes 21 and 22 is changed. As can be seen from FIG.
At 0 A or more, a broad peak of 1400 to 1600 cm ^-1 hardly appears, and a high-purity diamond film can be obtained.

Here, the electric current flows in the plasma, and if the value is 1 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. Even if the current flowing through the plasma is increased, the direction of acceleration of the electrons is perpendicular to the plasma flow because the installation surfaces of both the counter electrodes 21 and 22 are parallel to the substrate 2. There is no inconvenience that the electrons that have reached the substrate 2 raise the substrate temperature from the above-mentioned range of synthesis of diamond, 600 to 1100 ° C. Further, it is considered that the counter electrodes 21 and 22 are exposed in the plasma, respectively, and the dissociation of the hydrogen and hydrocarbon source gases is mainly performed mainly on a straight line connecting the two electrodes. That is, especially on the substrate 2 located immediately downstream of the linear region connecting the electrodes 21 and 22 of the plasma jet, the synthesis speed and purity of the diamond film are improved.

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. In the first embodiment, a DC power source is used as the plasma current power source 23 between the counter electrodes 21 and 22. However, in the present embodiment, an AC power source is used as the plasma current power source 223 as shown in FIG. Used, both opposing electrodes 22
An AC electric field is applied between 1 and 222. In FIG. 6, the same reference numerals are given to the same or corresponding components as those in the first embodiment. Also, the inside of the electrode 221 side is hollow like the electrode 222, and the cooling water pipe 225,
Cooling water is supplied by 225a.

As in the present embodiment, the power source 22 for the plasma current
Even if an AC power source is used as 3 and an AC electric field is applied between the opposite electrodes 221 and 222, electrons are accelerated between the two electrodes and hydrogen and hydrocarbons are easily dissociated. That is, the present embodiment also provides the same effects as the first embodiment.

When a diamond film was actually synthesized using the apparatus of this embodiment, it was confirmed that a high-purity diamond film was synthesized as in the first embodiment. The conditions for synthesizing the diamond film were the same as in the first embodiment, the distance between the opposing electrodes 221 and 222 was 8 mm, and the current flowing through the plasma was 10 A.

Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 7 is a schematic diagram for explaining the arrangement of the counter electrode for flowing a current in the plasma in the present embodiment, and is a view from above of the counter electrode installation surface parallel to the substrate surface on which the diamond film is synthesized. . In the first and second embodiments, the pair of counter electrodes is used, but in this embodiment, two pairs of counter electrodes are arranged in parallel. That is, a pair of opposing electrodes 321 supplied with power from the first plasma current power supply 323a
a, 322a and a pair of opposed electrodes 321b, 322b supplied with power from a second plasma current power supply 323b.

By causing the current to flow in the plasma at a plurality of locations as described above, a large amount of dissociation of the source gas occurs at the plurality of locations in the plasma jet. The synthesis speed and purity of the diamond film in the specific region can be improved. As a result of actually synthesizing a diamond film with this configuration, it was confirmed that a high-purity diamond film was synthesized at a specific portion of the substrate as in the first and second embodiments. The conditions for synthesizing the diamond film were the same as in the first embodiment, and the distance between the positive and negative electrodes of each counter electrode was 1
The synthesis was performed by setting the distance between the pair of opposing electrodes to 5 mm and the flow of DC 5A into the plasma.

Although the present invention has been described with reference to the first to third embodiments, the present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the present invention.
For example, in the above-described various embodiments, the counter electrode for flowing a current in the plasma is fixedly installed. However, for example, the counter electrode may be moved in the vertical direction. Further, the counter electrode may be rotatable around the gas plasma flow. Thereby, the synthesis speed and purity of the predetermined portion can be improved over a wider area on the substrate. Further, the installation surface of these counter electrodes may not only be parallel to the substrate surface but may be inclined at a certain angle with respect to the substrate surface, and the angle may be arbitrarily changed. In short, it is necessary to apply an electric field to the gas plasma to flow a current.

[0040]

As described above, according to the present invention, a gas can be sufficiently decomposed in the vicinity of a substrate by flowing an electric current into a plasma, and a high-purity diamond film can be obtained at a high synthesis rate. Can be formed.

When a current is passed through the plasma,
Since at least one pair of opposed electrodes arranged so as to sandwich the gas plasma is used, on a straight line connecting the electrodes, and on the substrate located downstream of the plasma flow, the synthesis speed and the other regions are compared. There is an excellent effect that a diamond film having improved purity can be formed.

With this, corresponding to a predetermined portion on the substrate or a peripheral shape of the substrate (for example, a rectangle, an ellipse, etc.),
A diamond film having a partially improved synthesis rate and purity can be formed.

[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. 6 is a characteristic diagram of a sample synthesized when no current is supplied to the sample.

FIG. 3 is a characteristic diagram showing a relationship between a Raman shift and a peak height of each synthesized sample when the magnitude of a current flowing in 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 schematic diagram illustrating an arrangement of a counter electrode for flowing a current into plasma in a third embodiment of the present invention.

FIG. 8 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 Bar electrode 10 Cylindrical electrode 16 Gas introduction pipe 17 Power supply for arc discharge 19 Carbon source gas inlet 21 Counter electrode (negative electrode) 22 Counter electrode (positive electrode) 23 Plasma current Power supply

──────────────────────────────────────────────────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-4-295090 (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 (6)

(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, and a source gas containing at least hydrogen and carbon for the arc discharge to generate a gas plasma, and the gas plasma is supplied downstream thereof. Gas supply means for spraying the arranged substrate, and at least one pair of opposed electrodes arranged so as to sandwich the flow of the gas plasma toward the substrate between the region where the gas plasma is generated and the substrate. A current for flowing a current in a direction intersecting the flow of the gas plasma into the gas plasma by applying an electric field between the opposed electrodes. And a source. 2. The apparatus according to claim 1, wherein the position of the counter electrode is variable with respect to the substrate with the flow of the gas plasma as an axis. 3. The diamond film manufacturing apparatus according to claim 1, wherein each electrode surface of the counter electrode is exposed in the flow of the gas plasma. 4. The diamond film manufacturing apparatus according to claim 1, wherein said plasma current power supply is a DC power supply for applying a DC electric field between said opposed electrodes. 5. The diamond film manufacturing apparatus according to claim 1, wherein the power source for plasma current is an AC power source for applying an AC electric field between the opposed electrodes. 6. A gas plasma is generated by flowing a source 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, at least one pair of counter electrodes is provided between the substrate side and the region where the gas plasma is generated so as to sandwich the flow of the gas plasma toward the substrate, and the gas plasma is included in the gas plasma. Wherein an electric field is applied between the opposed electrodes in order to flow a current in a direction intersecting the flow of the diamond film.