JPH03174397A - Method and device for synthesizing rigid substance - Google Patents

Abstract

PURPOSE:To generate high-density plasma in a high range and to synthesize rigid substance by vapor growth at the high growth velocity on a base plate having large area by parallel opposing plate electrodes vertically to the electric field of microwave and exciting plasma between the electrodes in the case of synthesizing rigid substance by a plasma CVD method. CONSTITUTION:At least two sheets of plate electrodes 17a, 17b (shared in a base material, >=5mm interval and wavelength or below of microwave) are parallel opposed vertically to the electric field (directions C shown in a figure) of microwave 18 in a reaction pipe 6 (quartz, alumina and boron nitride, etc., are preferably utilized). Plasma 11 is excited between the plate electrodes 17a, 17b. A gaseous raw material is supplied and rigid substance such as diamond and cubic boron nitride is synthesized.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method and apparatus for synthesizing hard materials such as diamond and cubic boron nitride used as tools, thermal conductors, semiconductors, etc. The present invention relates to a method and apparatus for uniformly vapor-phase synthesizing high-quality hard materials over a large area at high speed.

[Prior Art] Hard substances such as diamond, cubic boron nitride, and wurtzite boron nitride are widely used as tools such as cutting tools, wear-resistant parts, abrasive grains, etc. by taking advantage of their high hardness. On the other hand, taking advantage of the high thermal conductivity of these materials, they are also used as heat dissipation substrates for semiconductor devices. Furthermore, progress is being made in the development of optical elements and semiconductors that take advantage of their translucent properties.

These hard substances are high-pressure phase substances that are stable under high pressure, so they were initially synthesized artificially only under ultra-high pressure.
In recent years, various methods have been developed to synthesize diamond and other hard materials in the gas phase under reduced pressure. Among these vapor phase synthesis methods for hard materials, the microwave plasma CVD method, in which plasma is generated using microwaves to decompose gas and deposit hard materials on a substrate, is the most effective method for synthesizing high-purity hard materials. This is a great way to do it. Regarding the synthesis of hard materials using this microwave plasma CVD method,
JP-A-58-110494.

JP-A-59-3098, JP-A-59-63732
No. 4,434,188, etc.

FIG. 5 shows a conventional diamond vapor phase synthesis apparatus. This device is a technology that applies microwaves, and its outline is as follows.

Referring to FIG. 5, microwaves oscillated from a magnetron oscillator 1 pass through an isolator 2, a power monitor 3, a tuner 4, and a waveguide 5 to a substrate 8 placed on a support 7 within a reaction tube 6. irradiated. The raw material gas is, for example, methane gas, hydrogen, etc. mixed in a predetermined ratio, introduced from the gas inlet 9, and sucked and exhausted from the exhaust port 10 via a pump (not shown), and the exhaust amount is adjusted. The inside of the reaction tube 6 is maintained at a predetermined pressure. Plasma 11 is generated by the microwave energy, and diamond is formed on the substrate 8. Cooling water is supplied to the applicator 12 from a cooling water supply pipe 13 and discharged from a cooling water discharge pipe 14 to prevent the reaction tube 6 from being excessively heated.

The waveguide 5 achieves optimal matching conditions by moving the plunger 15 or adjusting the tuner 4 according to the wavelength of the introduced microwave.

In the figure, arrows A and B indicate the direction of introduction and exhaust of raw material gas, respectively.

A method for synthesizing cubic boron nitride using such a microwave plasma CVD apparatus has also been reported in Japanese Patent Application Laid-open No. 174378/1983.

Generally speaking, microwaves range from 300MHz to 30MHz.
It is an electromagnetic wave in the 0 GHz range. Electromagnetic waves in this frequency range are easily absorbed by molecules, and the wavelength is 1 m to 1 mm, which is short compared to the size of the reaction tube. Therefore, plasma can be efficiently generated in gases having a wide range of pressures. Also, microwaves in this frequency range are several 10
Efficiently with a practical size waveguide of less than cm.
Since power can be supplied, there are fewer problems with losses and leakage in the supply path, such as coaxial cables, as is the case at lower frequencies.

[Problems to be Solved by the Invention] However, the conventional method and apparatus for synthesizing hard substances using the conventional microwave plasma apparatus have the following problems.

Industrially, microwaves with a frequency of 2.45 GHz are widely used, but when such microwaves are confined in a reaction tube, a standing wave is generated with a period of half the wavelength, and this standing wave is Depending on the intensity distribution, there are places where plasma is generated and places where it is not. Therefore, it has been impossible to synthesize a hard material by uniformly generating plasma over a wide area.

Further, as a property of microwaves, the higher the frequency, the more stable plasma can be generated even at higher gas pressures, and the growth rate of hard substances can be improved.

However, when the frequency is increased, the wavelength becomes shorter and the area of the part where the amplitude of the standing wave is larger becomes smaller, which is a contradiction.

In order to improve the non-uniformity of growth in the vapor phase synthesis of hard materials, a method of controlling plasma streamlines by applying a DC magnetic field and a method of lowering the gas pressure in the reaction tube have been proposed in Japanese Patent Publication No. This is reported in Publication No. 107899/1983. However, in any of these methods, the mean free path of active molecular species and electrons in the plasma must be maintained for a long time. Therefore, the gas pressure inside the reaction tube was set to 10T.

It has to be kept low, below rr, and the growth rate of hard substances is 1
It was extremely low, less than μm/h.

For the reasons mentioned above, the conventional method of synthesizing hard materials such as diamond using plasma CvD is severely restricted in terms of growth area and growth rate, making it difficult to synthesize hard materials in large quantities. Ta.

In order to solve the above-mentioned conventional problems, the present invention makes it possible to generate high-density plasma over a wide range, and provides a method and apparatus for synthesizing hard materials such as diamond at a high growth rate on a large-area substrate. The purpose is to

[Means for Solving the Problems] The method for synthesizing a hard substance of the present invention supplies a raw material gas into a reaction tube, and applies microwaves of a predetermined frequency to a region in the reaction tube where a hard substance synthesis reaction is to occur. This method synthesizes hard materials in a vapor phase by introducing the material in the same direction and irradiating it with plasma. The present invention is characterized in that at least two plate electrodes are opposed in parallel perpendicular to the microwave electric field, and plasma is excited between these plate electrodes to perform vapor phase synthesis of a hard substance.

The hard substance synthesis apparatus of the present invention includes a reaction tube, a means for supplying a raw material gas into the reaction tube, and a plasma generator by introducing microwaves in a predetermined direction into the vicinity of the substrate on which the hard substance is deposited in the reaction tube. It is equipped with a means to generate Inside the reaction tube, at least two plate electrodes are disposed, which face each other in parallel and perpendicular to the electric field of the microwave, with a base material on which a hard substance is deposited sandwiched therebetween.

[Function] According to the hard substance synthesis method or synthesis apparatus of the present invention, high-power microwaves are introduced into the reaction tube through a waveguide with little loss, and a uniform and strong electric field is created between the opposing flat electrodes. can be stably distributed. The plasma generated by this electric field is stable even at high reaction pressures and is uniform over a wide area.

This method is similar to the configuration of a parallel plate electrode type plasma CVD apparatus that uses high frequencies lower than microwaves (for example, see US Pat. No. 4,414,085), but at frequencies lower than microwaves, l QTo r r It is difficult to stably generate strong plasma at such a relatively high pressure, and it is unsuitable for the synthesis of hard materials. Furthermore, when a frequency lower than that of microwaves is used, there are major problems such as loss in the introduction path such as a coaxial cable and pressure reflection due to impedance mismatch to the introduction port to the reaction tube.

The direction of the electric field and the magnetic field of microwaves guided by a waveguide are determined by the shape of the waveguide, but this counter electrode must be placed perpendicular to the direction of the electric field of the microwave. By arranging it like this,
A strong electric field can be generated between the electrodes. Further, the microwave must be incident so that the direction of propagation of the microwave is parallel to these electrodes.

More than two counter electrodes can be arranged. By arranging a large number of opposing electrodes and using these electrodes themselves as substrates for hard material growth, or by arranging a base material between each electrode, it is possible to grow a hard material over an even larger area. , the yield of hard materials can be increased. Further, powder can be placed between the opposing electrodes as a base material, thereby making it possible to easily synthesize hard substance abrasive grains.

The distance between each opposing electrode is preferably 5 mm or more in order to facilitate the flow of the reaction gas.

Further, it is desirable that the distance between the opposing electrodes does not exceed a distance equivalent to the wavelength of a microwave. This is because when the distance between the electrodes exceeds the wavelength of the microwave used, the vibration mode of the microwave changes and the plasma between the electrodes becomes non-uniform.

At least the reaction tube is preferably made of a material such as quartz, alumina, beryllia, or boron nitride, which has low microwave transmission loss. The electrodes placed in the reaction tube are preferably made of materials with high microwave reflectance and heat resistance.
3. Metal materials such as Mo and W are suitable. When a base material on which a hard substance is grown also serves as an electrode, a conductive material such as a metal or a semiconductor is used as the base material.

[Example] Hereinafter, an example of the present invention will be described based on FIGS. 1 to 4.

(Example ■) The gas phase synthesis of hard materials of the present invention is carried out using the basic apparatus shown in FIG. Referring to the figure, in this embodiment, microwaves first pass through a waveguide 5 into a reaction tube 6.
Two base materials 17a placed oppositely on the support stand 16 inside.
, 17b is irradiated. Although the details of the microwave generating means are omitted in the figure, the microwave 8 is oscillated by the magnetron oscillator 1, and the isolator 2. Power monitor 3. The structure introduced into the reaction tube 6 through the tuner 4 and the waveguide 5 is similar to the conventional device shown in FIG.

The two base materials 17a and 17b are both made of silicon, are arranged perpendicular to the electric field direction of the microwave 18 (direction of arrow C in the figure), and serve as counter electrodes. Plasma 11 is generated by introducing microwaves between the base materials 17a and 17b, and the raw material gas is synthesized in a vapor phase to form the base material 17a.

A hard material film is simultaneously formed on 17b. Cooling water is supplied to the applicator 12 from a cooling water supply pipe 13 and discharged from a cooling water drain pipe 14 to prevent the reaction tube 16 from being excessively heated. Note that arrows A and B in the figure indicate the direction of introduction and exhaust of raw material gas, respectively.

Using such an apparatus, diamond was synthesized under the following specific conditions. The inner diameter of the reaction tube 6 used was 60 mm, the base materials t7a and 17b were silicon disks with a diameter of 5 Q mm and a thickness of 3 mm, and the interval between the base materials 17a and 17b was 25 mm. H2 and CH4 were supplied as reaction gases to the reaction tube 6 at a ratio of 100:2, and the pressure inside the reaction tube 6 was set to 60 Torr by adjusting the exhaust volume. Further, the input power of the microwave was set to 600W.

As a result, both base materials 17a and 17b have a diameter of 49 mm.
A diamond film could be formed at a fast growth rate of 5 μm/h. This is an effect obtained by concentrating the plasma 11 between the base materials 17g and 17b.

Although silicon is used as the base materials 17a and 17b in this embodiment, the material that allows the base materials 17a and 17b to function as counter electrodes may be, for example, a carbon material, a conductive metal material, or SiC.

Semiconductor materials other than Si, such as Ge, may also be used.

Alternatively, the surface of an insulating material may be coated with these materials.

Hydrocarbons other than CH4, alcohols, and ketones can also be used as the carbon source gas as the reaction gas. Furthermore, solid carbon can be decomposed in a gas phase and supplied as a raw material.

(Example 2) The apparatus and specific conditions used in this example are almost the same as those in Example 1 above. The difference from Example 1 is that H2 and CH4 were supplied as reaction gases at a ratio of 100:2, Ar was added, the exhaust amount was adjusted, and the pressure inside the reaction tube 6 was raised to 100 Torr. It is.

As a result, it was possible to synthesize a diamond film at a growth rate of 10 μm/h.

Note that He and Ne are inert gases other than Ar.

A similar effect can be obtained by stabilizing the plasma by adding Kr, Xe, Rn, or the like.

(Example 3) In this example, as shown in FIG. 2, microwaves were supplied from two locations in one reaction tube 6, and the input power of the microwave was 600 W for each, and the other conditions were set as above. In the same manner as in Example 1, diamond was vapor-phase synthesized on a total of four base materials 17a and 17b, two for each location. As a result, each base material 17a, 17b has a diameter of 30 m.
A diamond film could be synthesized at an average growth rate of 5 μm/h over a range of 5 μm/h.

(Example 4) This example was carried out using the apparatus shown in FIG. Third
The apparatus shown in the figure has the same reaction tube 6 and microwave generation means as that used in Example 1 shown in FIG. In this embodiment, a quartz jig 20 having opposing electrodes 19a and 19b is installed without using the base material as the opposing electrode. The DD cross section of the quartz jig 20 has a small partition plate 21 inside, as shown in FIG. It can be stirred by rotating it in the direction of arrow E.

Using such an apparatus, diamond was vapor-phase synthesized under the same conditions as in Example 2 above. As a result, the diamond abrasive grains with a diameter of 100 μm in the quartz jig 27 became grains with a diameter of 200 μm after growing for one hour.

(Example 5) In this example, the same apparatus shown in FIG. 1 as in Example 1 was used, the reaction gas and microwave conditions were the same as in Example 1, and three silicon circles were used as the base material. Board (diameter 50m
m, thickness 3 mm) in the electric field direction of the microwave 18 (arrow C
direction). In addition, the plasma
Diamond was synthesized at a pressure of 20 Torr so as to cover the entire substrate.

As a result, 0. Diameter 5Qmm at growth rate of 2μm/h
Diamonds were formed on the entire surface of the base material.

Note that when the pressure was increased to 40 Torr, the average growth rate of diamond was 0.05 μm/h, and when the pressure was further increased to 50 Torr, diamond growth was observed only in a small portion of the base material.

According to this embodiment, even if three or more boards are placed, four
At a pressure of 0 Torr or less, a diamond film could be uniformly formed on all substrates, and the number of diamonds produced could be increased.

In addition, in each of the above embodiments, the case where a carbon source gas and hydrogen were added as the raw material gas, and the case where an inert gas was added thereto were described, but it is also possible to use a substance containing oxygen as the raw material gas, or It has been experimentally confirmed that the well-known fact that addition contributes to higher quality diamonds, such as by increasing the light transmittance of synthesized diamonds, is also effective in the present invention. Examples of substances containing oxygen include alcohols, ketones, ethers, 0°, H2O, Co, CO2, NO
2, NO, 03 etc. can be used.

(Example 6) Using the same synthesis apparatus as that used in Example 1, two Si substrates were placed in the same manner as in Example 1, and H2, Ar, N H3 were used as reaction gases. , B2H6, 1
Supply at a ratio of 00:40:10:3 and the pressure is 25To
I kept it at rr. When a microwave of 800 W was introduced into this reaction gas and the reaction was carried out for 20 hours, a hard substance was grown on both substrates within a diameter range of 25 mm. The thickness of the thickest central portion of this hard material was 7 μm.

When the crystal structure of this hard material was examined by X-ray diffraction, it was confirmed that it consisted of cubic boron nitride.

[Effects of the Invention] As described above, according to the present invention, hard materials such as diamond can be grown at a high growth rate not only on a plate-shaped base material but also when abrasive grains are used as the base material in a relatively large area. Can synthesize substances.

By increasing the growth rate and growth area of hard materials in this way, the cost of synthesizing hard materials will decrease, and the scope of application of hard materials by vapor phase synthesis will be greatly expanded, for example in fields such as tools and abrasives. It also becomes possible to apply it to

In addition, by introducing multiple counter electrodes arranged perpendicular to the electric field of the plasma, it is possible to stabilize and increase the density of the plasma. A thin film can be formed. Also,
By making the electric field uniform between the opposing electrodes, the hard substance can be grown uniformly on the base material.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view schematically showing a hard substance synthesis apparatus used in Example 1 of the present invention, and FIG. 2 is a schematic cross-sectional view showing the configuration of a hard substance synthesis apparatus used in Example 3 of the present invention. FIG. 3 is a cross-sectional view schematically showing the configuration of a hard substance synthesis apparatus used in Example 4 of the present invention, and FIG. 4 is a cross-sectional view taken along line DD. FIG. 5 is a cross-sectional view schematically showing a synthesis apparatus used in the conventional vapor phase synthesis of diamond. In the figure, 5 is a waveguide, 6 is a reaction tube, 11 is plasma, 17a and 17b are base materials, and 18 is a microwave. Note that parts with the same numbers or symbols in each figure indicate the same or equivalent elements. Hou 20 8: My Furomi Oijima 30 also 59

Claims (2)

[Claims] (1) A raw material gas is supplied into a reaction tube, and microwaves of a predetermined frequency are introduced in a predetermined direction into a region in the reaction tube where a synthesis reaction of hard materials is to occur to generate plasma, thereby converting the hard material into a gas phase. A synthesis method, characterized in that at least two plate electrodes are opposed in parallel perpendicular to the electric field of microwaves, and plasma is excited between these plate electrodes to perform vapor phase synthesis of hard substances. A method for synthesizing hard substances. (2) a reaction tube; a means for supplying raw material gas into the reaction tube; and a means for generating plasma by introducing microwaves in a predetermined direction into the vicinity of the base material on which the hard substance is deposited in the reaction tube. A hard substance synthesis apparatus comprising: at least two plate electrodes facing perpendicularly to the electric field of the microwave and parallel to each other with a substrate on which the hard substance is deposited in the reaction tube in between. A hard substance synthesis device characterized by: