JPH03174398A - Diamond synthesizing device - Google Patents

Abstract

PURPOSE:To stably control vapor phase epitaxial synthesis and to contrive cost reduction by providing a means for circulating a gaseous raw material in a sealed state to a reaction pipe for vapor phase epitaxial synthesis of diamond which is equipped with a plasma generating means and intermittently or continuously supplying the gaseous raw material to this circulation system. CONSTITUTION:A reaction pipe 3 for forming a circulation system 12 and the inside of a gas storing vessel 13 are vacuumized and exhausted by, closing the valve 2 of a gaseous raw material supplying system 1 and opening the valve 4 of an exhausting system 5. Then both a gaseous carbon source such as gaseous methane and a gaseous medium such as hydrogen are supplied at the prescribed flow rate by closing the valve 4 and opening the valve 2. Thereafter the valves 2, 4 and a valve 15 for supplying the gaseous carbon source are wholly closed and the circulation system 12 is made to a sealed system. The gaseous raw material is circulated through this circulation system 12 by a circulation pump 16. Successively plasma is generated by a plasma generating means 6 constituted of a microwave oscillator 7 and a waveguide 8 and diamond is synthesized in vapor growth. The necessary gaseous raw material is intermittently or continuously supplied according to reduction of the raw material.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a diamond synthesis apparatus, and particularly relates to a diamond synthesis apparatus that provides vapor phase synthesis technology for inexpensively producing high quality diamond in microwave plasma. .

[Prior art] Diamond vapor phase synthesis technology was developed by Derj in 1956.
aguin (USSRInv, Cert tl,;N
o, 339134.1958), Eve in 1958
rsole (USP; No, 3030187.303
0188) and Matsumoto et al. (Jap
anes Journal of Applie
d Physics Vo 1.21.1982. L1
Since the research of 83-L185), active development has been carried out.

Among these, the microwave plasma method, in which diamond synthesis is performed in plasma by microwave excitation, was first described in 1983 by Kamo et al.
Growth; 62.1983, p642-p644)
Based on the recognition that impurity-free films can be obtained due to electrodeless discharge, efforts have been made to reduce costs by expanding the formation area and increasing the growth rate.

Such conventional vapor phase synthesis of diamond in microwave plasma has basically been carried out using a so-called open type apparatus in which source gas is not circulated, as shown in FIG. To synthesize diamond using such an apparatus, refer to FIG.
A raw material gas, which is a mixture of approximately 1 to 2% carbon source gas and nearly 99% medium gas, is supplied into the reaction tube 3 through the raw material gas supply valve 2 . Carbon source gases include methane,
Hydrocarbons such as ethane, propane, acetylene and benzene, alcohols such as methanol, ethanol and propatool, organic acids such as acetic acid, ketones such as acetone, esters such as methyl acetate, carbon oxide, carbon dioxide, etc. is used. Hydrogen or oxygen is used as the medium gas.

Diamond is synthesized by flowing these gases and reacting in plasma, but only about 1 to 2% of the carbon source gas used here actually becomes diamond. All of the raw material gas used in the reaction, including unreacted carbon raw gas, is exhausted by the exhaust system 5 via the exhaust valve 4. In addition, the pressure adjustment of the vacuum container is
This is done by controlling the raw material gas supply system 1 and the exhaust system 5. Plasma generation within the reaction tube 3 is performed by plasma generation means 6. This plasma generating means 6
mainly consists of a microwave oscillator 7 and a waveguide 8. The microwave oscillated by the microwave oscillator 7 is generally 2.45 GHz in the case of diamond synthesis, and in order to match the frequency of this microwave, it is monitored by the power monitor 9 and the waveguide is 8 is adjusted by a tuner 10 and a plunger 11.

In diamond vapor phase synthesis, especially in the microwave plasma CVD method, by limiting the synthesis conditions,
It has been confirmed that high-quality film-like and lamellar diamonds with performance equivalent to bulk diamonds produced by natural or ultra-high-pressure synthesis methods can be obtained. Specifically, it has a Vickers hardness of 10,000, which is the same hardness as a single crystal diamond.
are obtained. In addition, the thermal conductivity is 16W
/ cm -K, which is sufficiently comparable to the diamond single crystal type IIa which has a power of 22 W/cm and the type Ia which has a power of 11 W/cm. Further, the heat sink, rear part, etc. are used in the form of a plate or a film on a base material. Therefore, according to the vapor phase synthesis method, in which the film is already in the form of a film or plate having a thickness of several μm to several 100 μm at the time of film formation, the processing effort can be considerably reduced.

On the other hand, when using single-crystal diamond, a process such as laser cutting is required to cut it into a plate shape.

However, at present, diamond produced by vapor phase synthesis has not achieved sufficient results due to cost issues. Therefore, cost reduction is being considered in various fields. The methods include expanding the formation area and increasing the growth rate. In the microwave plasma method, various methods of generating plasma have been studied in order to expand the formation area.

There are two types of conventional means for expanding the formation area: The first method is to use an apparatus using a large-diameter microwave plasma method as shown in FIG. With this means, the introduced microwave is expanded by the tapered waveguide 21, and the expanded microwave generates plasma 23 in the bell jar 22, and the rotating mechanism 22
A diamond film is vapor-phase synthesized on a wafer 26 on a holder 25 which is rotated by 4. In this method, a 4-inch diameter silicon substrate is used as a wafer,
Growth rate is 0. It is about 2 μm/hr. The second is
This method uses an apparatus using the ECR plasma method shown in FIG. In this method, a magnetic field is applied by an electromagnetic coil 33 to a microwave that is expanded from a waveguide 31 having a small cross-sectional area and a rectangular cross section to a trapezoidal cylindrical waveguide 32 . As a result, ECR plasma 36 is generated near the surface of the substrate 35 heated by the heater 34, and a diamond film is synthesized on the surface of the substrate 35 in a vapor phase. When using this method, a 2-inch diameter silicon substrate is used as the substrate 35, and the growth rate of the diamond film is 0. 1μ
It is about m/hr.

[Problems to be Solved by the Invention] However, when the conventional open-type gas phase synthesis apparatus described above is used, both of the means shown in FIGS. 4 and 5 for expanding the film formation area do not improve the film quality. resulting in significant deterioration of In particular, attempts have been made to increase the pressure and fuel gas concentration to increase the growth rate, but these efforts have been unsuccessful due to instability of the plasma and precipitation of non-diamond components such as graphite. I haven't.

Attempts have been made to rotate the substrate in order to make the plasma uniform, but the relatively good quality film parts overlap with the defective parts, resulting in a decline in film quality as a whole.

Furthermore, the film quality tends to deteriorate as the distance from the center of the plasma increases. These methods are still in the development stage;
The current situation is that there is not much progress.

With these means, typically 1 μm at a pressure of 40 TOrr.
/hr is the limit for growth. There is no limit to the development of large-area and high-speed film formation.
It is said that approximately μm/hr is preferable, and it can be said that the conventional open type does not come close to this.

Other problems with conventional open type vapor phase synthesis equipment in diamond vapor phase synthesis are listed below.

Only a few percent of the supplied carbon raw gas is subjected to the reaction, and the rest is discharged from the system without reaction. Further, the medium gas, which is required for nearly 99% of the total raw material gas, is ultimately discharged unchanged without reacting. That is, a raw material gas that is 5000 times larger than the carbon source gas that actually becomes diamond is required. For this reason, raw material costs account for a large proportion of the cost of vapor-phase synthetic diamonds, which have relatively low equipment costs. In other words, the challenge is to effectively utilize raw material gas and reduce raw material costs.

On the other hand, it has been confirmed that fluctuations in pressure and fluctuations in raw material composition have a negative impact on the synthesis of high-quality membranes, but pulp operations in the supply system and exhaust system to adjust them are also complicated, and long-term operation is difficult. It is difficult to stabilize the conditions. For this purpose, it is necessary for an operator to be present to make fine adjustments to the pulp, which is also a factor in increasing costs. Furthermore, if an attempt is made to automate this pressure adjustment, equipment costs will increase significantly, leading to an increase in costs. That is, it is also a challenge to realize automated or unmanned device operation by simplifying pulp operation and pressure adjustment.

As a means to solve these problems, it has been proposed to use the reactor as a sealed system to circulate the raw material gas and supply only the amount of carbon source gas consumed for diamond synthesis, thereby making effective use of the raw material. It will be done. In addition, in a sealed system, since the reaction space is sealed, there is no need for pressure adjustment, and it is thought that pulping operations can be simplified. However, in a reaction in which a carbon source gas is decomposed in plasma to produce diamond, for example, when the carbon source gas is a hydrocarbon, the reaction expressed by the following formula (1) proceeds.

CxHy-I-xC+y/2H2... (1) Due to this reaction, except for the case where y=2, the pressure inside the sealed reaction vessel increases due to the generated hydrogen gas, which affects the plasma state and reduces the film quality. resulting in deterioration. In addition, the carbon raw gas itself also multimerizes as shown in equation (2) below, causing a similar problem.

nCx Hv →Cn x Hn y −a+α/2H
2...(2) In this way, by simply performing gas phase synthesis with the reaction tube 3 in a sealed state in a conventional open-type device, it is difficult to stably control the raw material gas concentration or suppress the pressure increase. be.

In order to solve the above-mentioned conventional problems, an object of the present invention is to provide a diamond synthesis apparatus that realizes stable control of vapor phase synthesis of diamond in a sealed system and a reduction in cost.

[Means for Solving the Problems] The diamond synthesis apparatus of the present invention includes a reaction tube in which a diamond gas phase synthesis reaction is carried out, a plasma generation means for generating a predetermined microwave plasma in the reaction tube, and a reaction tube. A gas storage container is connected to the reaction tube and forms a circulation system together with the reaction tube. In addition, a means for exhausting air in this circulation system and a means for circulating the raw material gas, which is a compound containing carbon, in the circulation system in a sealed state are provided. It is equipped with a raw material gas supply means for supplying raw material gas to

[Function] According to the present invention, the raw material gas is circulated in a sealed state in the circulation system, and only the raw material gas that is required as the raw material decreases is supplied intermittently or continuously, and the raw material gas is By carrying out vapor phase synthesis of diamond, pressure fluctuations and composition fluctuations accompanying reactions and gas addition can be minimized, and diamond vapor phase synthesis can be carried out within an extremely limited gas composition and pressure range.

Furthermore, since vapor phase synthesis is performed in a closed circulation system, the consumption of raw material gas is significantly reduced, and the amount of raw material gas used can be reduced to 2% or less compared to a conventional open system.

In addition, since the circulation system includes a gas storage container, the gas concentration inside the reaction tube changes extremely slowly and smoothly when gas is supplied. Even if gas is supplied to the film, it will not affect the film quality.

[Embodiment] The second embodiment of the present invention will be described below with reference to FIG. In this embodiment, referring to the figure, first, the raw material gas supply pulp 2 of the raw material gas supply system is closed, the exhaust pulp 4 of the exhaust system 5 is opened, and the reaction tube 3 forming the circulation system 12 and the gas storage The inside of the container 13 is evacuated. Next, the exhaust pulp 4 is closed, the raw material gas supply valve 2 is opened, and the raw material gas is supplied until a predetermined pressure is reached. As this raw material gas, a carbon source gas and a medium gas are supplied at a predetermined flow rate.

Further, the pressure within the circulation system 12 is adjusted by controlling the raw material gas supply system 1 and the exhaust system 5. The gas storage container 13 is connected to a carbon source gas supply system 14, and carbon source gas is supplied as needed through the carbon source gas supply pulp 15. When the raw material gas supply valve 2, exhaust pulp 4 and carbon source gas supply pulp 15 are all closed, the circulation system 12
A sealed system is formed in which gas is blocked from entering and leaving the outside, and the raw material gas sealed within the circulation system 12 is circulated within the circulation system 12 by a circulation pump 16 .

Plasma generation within the reaction tube 3 is performed by plasma generation means 6. The plasma generating means 6 mainly consists of a microwave oscillator 7 and a waveguide 8, and the microwave oscillated by the microwave oscillator 7 generally has a frequency of 2.45 GHz. The waveguide 8 is adjusted by the tuner 10 and the plunger 11 while being monitored by the power monitor 9 so as to match the frequency of this microwave.

Using the apparatus of this example, diamond was vapor-phase synthesized under the following specific conditions. First, after evacuation, open the raw material gas supply valve 2 and supply methane gas for 10 minutes.
m1/min, hydrogen gas is supplied into the reaction tube 3 at a rate of 10,100 O/min, and the inside of the circulation system 12 is set at 40 Torr.
After filling up to r, the raw material gas supply valve 4 was closed to make the circulation system 12 a sealed system. As the reaction tube 3, a cylindrical quartz tube with an inner diameter of 40 mm was used. Further, the microwave output was approximately 400W. This microwave output is generally in the range of aoow to 500W, but is not limited thereto. The optimum film forming conditions cannot be determined uniquely because they may be affected by factors such as the positional relationship between the substrate and the plasma. Regarding the relationship between the shape of the reaction tube and the microwave output, the thicker the reaction tube, the higher the output required, but due to problems such as microwave leakage, the limit for the device of this example is 40 mm to 60 mm. it is conceivable that.

Next, the plasma generating means 6 was activated to generate plasma in the reaction tube 3, and synthesis of diamond was started. Thereafter, the carbon source gas supply pulp 15 was opened every hour to intermittently introduce methane gas.

The amount of intermittent introduction of methane gas was determined based on experimentally determined changes in methane gas concentration within the circulation system 12.

As a result of synthesizing diamond in this way, the pressure in the system after 50 hours from the start of vapor phase synthesis was 41.
It was 5 Torr. The reason why the pressure inside the circulation system 12 changed from 40 Gorr to 41°5 Torr was that as the diamond film was being formed, the raw material methane gas was decomposed and multimerized as described above.
This is because hydrogen is generated at that time and pressure rises.

After that, the plasma was stopped, the sample was taken out after evacuation, and
As a result of SEM observation and Raman spectroscopy, it was found that diamonds were synthesized using a conventional open-type gas-phase synthesis apparatus, with no difference at all compared to diamonds synthesized using an operator who adjusted the pulp. It was confirmed that there is.

The deterioration of the film quality can be clearly observed by the collapse of the diamond crystal shape in SEM observation. Diamonds usually have a hexahedral shape or a 6-octahedral shape, and high-quality diamonds have flat faces and clear straight edges. However, when the film quality deteriorates, the surfaces and edges become rounded and sagging.

In addition, as a result of trial calculation of the raw material gas used, it was found that the raw material gas of 1°4% in the case of an open system is the same amount, that is, 1Q mm square x 5
Diamonds with a thickness of approximately 0 μm were synthesized.

Note that the problem of pressure fluctuation in this embodiment is considered as follows. First, in the conventional method, pressure is controlled by controlling the supply amount of raw material gas and hydrogen gas using a mass flow controller and controlling the amount of exhaust gas by controlling the pulp on the vacuum pump side. Therefore, it can be said that compositional fluctuations are extremely unlikely. On the other hand, although it depends on the pulp and the performance of the vacuum pump, the pressure fluctuation is usually about ±2.5%. In contrast, in the method of this example, pressure fluctuations and composition fluctuations are
As mentioned above, the cause is the generation of hydrogen gas due to the decomposition of the raw material gas. This fluctuation range is determined by the amount of diamond produced and the capacity of the reservoir tank. If the amount of diamond produced is approximately 10 mm square x 50 μm pressure as described above, and approximately the same amount of carbon is decomposed and precipitated on the base support material and the inner wall of the reaction tube, the capacity of the reservoir tank is 1.
00 liters, the pressure fluctuation is 40 Torr.
The temperature increases from 41.8 Torr to 41.8 Torr. As a composition change, when only the amount of consumed methane gas is added, the concentration of methane gas changes from 1% to 0.96%. That is,
The fluctuation range has been suppressed to 4.5%. This pressure fluctuation needs to be suppressed within ±5%. If more fluctuation occurs, the plasma state and substrate temperature will change and deviate from the optimum conditions, resulting in deterioration of film quality.

Compositional fluctuations do not lead to deterioration of film quality when the concentration of source gas such as methane decreases, but they cause a decrease in the film formation rate. On the other hand, when the concentration of the source gas increases, even if the increase is small, it causes deterioration of the film quality. Empirically, it is necessary to suppress pressure fluctuations within a range of 0% to 0% per step.

As described above, according to this embodiment, by using the circulation system 12 consisting of the reaction tube 3 and the gas storage container 13 as a sealed system to circulate the raw material gas and perform vapor phase synthesis in the plasma, the consumption of the raw material gas can be reduced. is significantly reduced, and costs can be reduced.

In addition, since the raw material gas is circulated in a sealed system that is easy to maintain a constant pressure and a trace amount of methane gas is intermittently supplied, pressure fluctuations and composition fluctuations associated with reactions and gas addition are minimized and extremely limited. High-quality diamond, which can be synthesized within a specified gas composition and pressure range, can be automatically and stably synthesized without the need for manual adjustments such as pulp adjustment.

Next, a second embodiment of the present invention will be described based on FIG.

The apparatus of this embodiment is similar to the first embodiment in that it includes a raw material gas supply system, an exhaust system 5, a circulation system 12, and a carbon source gas supply system 14. This embodiment differs from the first embodiment in that in the circulation system 12, a plurality of reaction tubes 3 and plasma generation means 6 are arranged in parallel. In this case, one plasma generating means 6 is disposed in each reaction chamber 3, similarly to the apparatus shown in FIG. In FIG. 2, the plasma generating means 6 is shown as the plasma generating means 6 shown in FIG. 1 viewed from the right side.

Using the apparatus of this example, diamond was synthesized under the same specific conditions as in the first example. Note that the intermittent supply amount of methane gas in this example was controlled and regulated by a gas supply mass flow controller.

As a result of synthesizing diamond in this way, the pressure in the circulatory system 12 after 50 hours from the start of synthesis was 41
．． It was 7 Torr. Then stop the plasma and
After evacuation, the sample was taken out and subjected to SEM observation and Raman spectroscopy. The results showed that diamonds were synthesized with no difference at all compared to those synthesized using a conventional open-system device with a worker adjusting the valves. It was confirmed that Further, as a result of trial calculation of the amount of raw material gas used, it was found that the same amount of diamond was synthesized with 1.78% of the raw material gas in the case of an open system.

Raman spectroscopy revealed a sharp diamond peak at 1333 cm-', a gradual amorphous carbon signal from 1500 to 170Q (m-'!), and relatively broad graphite peaks appearing at 1360 cm-1 and 1600 cm-'. is observed.A film in which only diamond peaks appear in Raman spectroscopy can be said to be a good quality film.If an amorphous or graphite signal appears, it means that the film quality has deteriorated. do.

As described above, according to this embodiment, the relatively expensive raw material gas supply system 1. It is possible to increase only the number of reaction tubes 3 and plasma generation means while leaving one exhaust system 5 and one circulation system 12 each, and it is possible to significantly reduce equipment costs.

[Effects of the Invention] As described above, according to the present invention, the reaction tube and the gas storage container are connected to form a circulation system, and the raw material gas is circulated in this circulation system in a sealed state, and the raw material gas is Since it is equipped with a means for supplying gas intermittently or continuously, the following effects are achieved.

First, because the circulation system includes a gas storage container, even if raw material gas is supplied intermittently, fluctuations in gas pressure and gas composition can be suppressed to the extent that it does not affect the quality of the diamond film produced. Therefore, high-quality diamond can be synthesized by simply controlling the flow rate of the raw material gas. Therefore, there is no need for manual pressure adjustment, and unmanned operation is possible through automation.

In addition, in the circulation system in a sealed state, by appropriately replenishing only the reduced amount of raw material gas, it is possible to significantly reduce the consumption of raw material gas.

Furthermore, the supply system, exhaust system and circulation system remain as one,
By increasing the number of reaction tubes and plasma generation means, the volume for gas phase reaction can be expanded without significantly increasing equipment costs.

In summary, by using the apparatus of this embodiment, it is possible to significantly reduce the cost of diamond vapor phase synthesis.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing the configuration of a diamond synthesis apparatus according to a first embodiment of the present invention, and FIG.
FIG. 2 is a diagram schematically showing the configuration of a diamond synthesis apparatus in an example. FIG. 3 is a diagram schematically showing the configuration of a conventional open system diamond synthesis apparatus. FIG. 4 is a sectional view showing a conventional diamond synthesis apparatus using a large-diameter microwave plasma method, and FIG. 5 is a sectional view showing a diamond synthesis apparatus using an ECR plasma method. In the figure, 1 is a raw material gas supply system, 3 is a reaction tube, 1 is an exhaust system, 6 is a plasma generation means, 12 is a circulation system, 13 is a gas storage container, 14 is a carbon source supply system, and 16 is a circulation pump. In addition, parts given the same number in each figure indicate the same or equivalent elements. Yu 3 figure 4

Claims (1)

[Scope of Claims] A reaction tube in which a diamond vapor phase synthesis reaction is carried out; plasma generation means for generating a predetermined microwave plasma in the reaction tube; and plasma generation means connected to the reaction tube and circulating together with the reaction tube. a gas storage container forming a system; a means for evacuating the circulation system; a means for circulating a raw material gas, which is a carbon-containing compound, in a sealed state within the circulation system; A diamond synthesis apparatus comprising a raw material gas supply means that supplies the raw material gas intermittently or continuously.