JPH10316491A - High purity diamond synthesis method - Google Patents

Abstract

(57) Abstract: A reaction gas obtained by diluting a carbon-containing organic gas, an inorganic gas, or a mixed gas of the organic gas and the inorganic gas with a hydrogen gas is used as a reaction gas. In a method for synthesizing diamond by a gas phase synthesis method used as
When an oxygen-containing gas is added to the reaction gas to remove non-diamond components, high-purity diamond is difficult to obtain because of impurities such as nitrogen contained in the oxygen-containing gas. SOLUTION: When diamond is synthesized on the surface of a silicon substrate 1 by a gas phase synthesis method, CH _{4 is used} as a reaction gas.
And a mixed gas to which oxygen gas is added in addition to H ₂ .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing diamond suitable for use as a new material in fields such as environment-resistant semiconductors and optical coatings by a gas phase synthesis method, and more particularly to a high-purity diamond containing few impurities. To a gas phase synthesis method.

[0002]

2. Description of the Related Art Diamond has the best physical properties of being the hardest of all materials, having the best thermal conductivity, and having the fastest sound transmission. For example, diamond is used for hard tools, wear-resistant coatings, heat sinks and speakers. Applications to diaphragms, high-frequency filters, etc. are being considered. Furthermore, it has various characteristics such as a wide band gap, high electron mobility, excellent transparency from ultraviolet to infrared, and chemical stability, making use of these excellent physical properties. Environment-resistant devices, light-emitting / receiving devices in the ultraviolet region, microwave power devices, and optical materials
A wide range of applications such as optical components are considered, and are expected as next-generation materials beyond silicon. In recent years, it has become possible to synthesize diamond under extremely low temperature and pressure by a gas phase synthesis method. This vapor-phase synthetic diamond has high hardness, high thermal conductivity, high corrosion resistance and high insulation like natural diamond, and can be operated at high temperature by controlling impurities. Materials are known for their usefulness.

[0003] In the vapor phase synthesis method of diamond, a reaction gas obtained by diluting a carbon-containing gas with hydrogen gas is decomposed by plasma, heat, or the like, and is further excited to grow diamond on a substrate. At this time, only diamond can be grown on the substrate by removing simultaneously grown non-diamond components with hydrogen that has been turned into an atomic state by plasma, heat, or the like. However, when diamond is formed by a gas phase synthesis method, plasma, heat, and the like are used, and therefore, contamination of impurities from the inner wall of the chamber, the base, the filament, and the like is inevitable. Even if the amount of these impurities is very small, they have a great effect on the electrical properties and thermal conductivity of diamond. Therefore, when diamond is used as a semiconductor material or its related material, it has become a serious problem.

For example, when diamond is synthesized on a silicon substrate by a plasma CVD method using a mixed gas of methane and hydrogen as a reaction gas, silicon as a substrate material is mixed into a diamond film [J. Rua
n, W. J. Choyke and W.C. D. Part
low, Appl. Phys. Lett. 58, 295
(1991)]. On the other hand, for the purpose of increasing the growth rate and improving the crystallinity,
A technique in which an oxygen-containing gas such as carbon dioxide is introduced into a reaction gas is disclosed in JP-A-63-117996. In this technique, a proper amount of carbon dioxide is added to a reaction gas in which hydrocarbon and hydrogen are mixed, so that non-hydrogen is deposited simultaneously with diamond in a gas phase synthesis method as compared with a case where only hydrogen is mixed with hydrocarbon. By removing the diamond component more effectively, the crystallinity is improved and the growth rate can be increased.

[0005]

However, a gas containing a component other than oxygen, such as carbon dioxide, generally contains nitrogen as an impurity in the gas production process.
It significantly reduces the crystallinity of diamond. In addition, if you try to use diamond as a semiconductor material,
Since nitrogen becomes a dopant for diamond, it has a problem in that it has a great effect on electrical properties such as electrical conductivity, making it extremely difficult to use.

[0006]

According to a first aspect of the present invention, there is provided a method for synthesizing a high-purity diamond, comprising the steps of: providing an organic gas containing carbon, an inorganic gas, or the organic gas; In a method for synthesizing diamond by a vapor phase synthesis method using a gas obtained by diluting a mixed gas of hydrogen and an inorganic gas with a hydrogen gas as a reaction gas, an oxygen gas is added to the reaction gas. Therefore, when diamond is formed by the vapor phase synthesis method, contamination of the diamond with impurities can be prevented and high purity can be achieved.

According to a second aspect of the present invention, there is provided a method for synthesizing a high-purity diamond, comprising the steps of:
The ratio of the number of carbon atoms in the reaction gas to the number of carbon atoms is 1, and the number of oxygen atoms is 0.001 or more and 0.1 or less. Therefore, the allowable range of the ratio of the added oxygen gas to the number of carbon atoms in the reaction gas can be widened.

[0008] The method of synthesizing high-purity diamond according to the invention of claim 3 is characterized in that the amount of oxygen gas added to the reaction gas is different at least between the initial stage and the final stage. Therefore, the amount of oxygen added can be varied in any way during the synthesis. For example, it is possible to freely change the combination, for example, by setting the amount of oxygen to be added to be small at the beginning of growth, and then increasing the amount in a stepwise manner, or vice versa.

The method of synthesizing high-purity diamond according to the invention of claim 4 is characterized in that the amount of oxygen gas added at the beginning of synthesis is smaller than the amount of oxygen gas at the end of synthesis. Therefore, when only the vicinity of the diamond surface is to be highly purified, the ratio of the number of oxygen atoms / the number of carbon atoms is reduced in the initial stage of growth, or the synthesis is performed at a sufficiently high growth rate without adding oxygen. However, the effect of oxygen addition can be obtained even if the ratio of the number of oxygen atoms / the number of carbon atoms is made larger than 0.1 by, for example, increasing the amount of added oxygen stepwise during the growth. .

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a method for synthesizing high-purity diamond according to the present invention will be described below with reference to the drawings.

[Embodiment 1] This embodiment is an example in which a diamond thin film is formed on a silicon substrate by microwave plasma CVD. As a pretreatment of the silicon substrate, the silicon substrate is immersed in an ethanol suspension of diamond powder having a particle size of ４ μm, and stirred by ultrasonic waves for 30 minutes. This is to improve the nucleation density by making fine scratches on the nanometer scale on the surface of the substrate.
After degreased cleaning with ethanol, the silicon substrate 1 was placed on the substrate holder 2 of the microwave plasma CVD apparatus shown in FIG.
Attach. Next, the pressure inside the chamber 5 was reduced to 2 × 10 ⁻⁷ Torr by the vacuum pump 7, and CH ₄ was supplied at ₃ scc.
m, H ₂ are set to 300 sccm and O ₂ is set to 0.3 sccm, respectively, and introduced into the chamber 5 from the gas inlet 4, and the reaction pressure is maintained at 50 Torr. The substrate temperature was set to 850 ° C. by the substrate heater 3 and the microwave generator 6
To generate plasma with a microwave power of 1.3 kW.

The synthesis is carried out for 4 hours while fixing the above conditions.
As a result, a high-purity diamond thin film having a thickness of about 1.2 μm was obtained. FIG. 2 shows a photoluminescence spectrum of the formed high-purity diamond thin film. The measurement was performed using a spectroscope in the range of 5000 to 9000 ° using a laser beam having a wavelength of 4880 ° by an argon laser as an excitation light source. Only a broad emission band with a sharp peak at about 5220 ° due to diamond and a peak at about 6000 ° is observed. From the above, contamination from a silicon substrate can be prevented by using a mixed gas of CH ₄ , H ₂ , and O ₂ as a reaction gas, and high purity without impurities can be obtained by a microwave plasma CVD method. It can be seen that a diamond thin film of

Comparative Example 1 This comparative example is an example in which a diamond thin film is formed on a silicon substrate by a microwave plasma CVD method without adding oxygen to a reaction gas. The conditions and apparatus for pretreatment of the silicon substrate are the same as those in the first embodiment. A mixed gas of CH ₄ and H ₂ was used as a reaction gas, and gas flow rates were ₃ sccm for CH _{4 and} 300 sccm for H ₂ .
The substrate temperature is set to 850 ° C., the above conditions are fixed, the reaction pressure is set to 50 Torr, and the synthesis is performed for 4 hours. As a result, a diamond thin film having a thickness of about 0.9 μm was obtained.
FIG. 3 shows the photoluminescence spectrum of the formed diamond thin film.

The measurement conditions are the same as in the first embodiment. 600
In addition to the broad emission band with a peak near 0 °, 73
An emission peak is observed at 70 °. This emission peak is attributed to the silicon of the substrate mixed into the film, which is described in the literature [J. Ru-an, W.M. J. Choyke and
W. D. Partlow, Appl. Phys. Let
t. 58, 295 (1991)]. From Example 1 and Comparative Example 1, it can be seen that by adding oxygen gas to the reaction gas, contamination from the silicon substrate can be prevented, and a high-purity diamond thin film can be obtained.

[Embodiment 2] This embodiment is an example in which a diamond thin film is formed on a silicon substrate by ECR microwave plasma CVD. First, the silicon substrate 11
Is mounted on the substrate holder 12 of the ECR microwave plasma CVD apparatus shown in FIG. Next, the pressure inside the chamber 15 was reduced to 1 × 10 ⁻⁶ Torr by the vacuum pump 17, and then ₂ sccm of CH ₄ and 100 of H ₂ were used as reaction gases.
It is set to sccm, and the chamber 1
And maintain the reaction pressure at 0.1 Torr. The substrate temperature is heated to 600 ° C. by the substrate heating heater, a DC voltage of −100 V is applied to the silicon substrate 11, and the silicon substrate 11 is set at a position under the ECR condition. A microwave power of 5.0 kW was applied by the microwave oscillator 16, and a current of 300 A was applied by the magnetic coil 18, and the maximum magnetic field was 13
00 Gauss, the silicon substrate 11
Is 875 Gauss, which satisfies the ECR condition. In this way, plasma is generated.

Nucleation is carried out for 10 minutes while fixing the above conditions. Next, the reaction gas was a mixed gas of CH ₄ , H ₂ , and O _2, and the gas flow rates were 1 sccm for CH _{4 and} 100 gas for H _2.
sccm, O ₂ 0.1 sccm, substrate temperature 650 ° C.
And a DC voltage of +150 V is applied to the substrate. A microwave power is set to 5 kW, a magnetic field is applied by the magnetic coil 18, and the substrate is set at a position under ECR conditions. With the above conditions fixed, the reaction pressure is set to 0.1 Torr, and growth is performed for 2 hours.

As a result, a high-purity diamond thin film having a thickness of about 0.3 μm was obtained. FIG. 5 shows a photoluminescence spectrum of the formed high-purity diamond thin film.
The measurement was performed using a spectroscope in the range of 5000 to 9000 ° using a laser beam having a wavelength of 4880 ° by an argon laser as an excitation light source. Only a broad emission band having a sharp peak due to the Raman line of diamond near 5220 ° and a peak near 6000 ° is observed.

Comparative Example 2 This comparative example is an example in which a diamond thin film is formed on a silicon substrate by ECR microwave plasma CVD. The conditions for nucleation are the same as in Example 2. After performing nucleation, the reaction gas is CH ₄ and H ₂
, A gas flow rate of 1 sccm for CH ₄ and H ₂
Is set to 100 sccm, the substrate temperature is set to 650 ° C., and a DC voltage of +150 V is applied to the silicon substrate. Next, a magnetic field is applied by the magnetic coil 18 with a microwave power of 5 kW, and the substrate is set at a position under ECR conditions. With the above conditions fixed, the reaction pressure is set to 0.1 Torr, and growth is performed for 2 hours. The formed diamond thin film had a thickness of about 0.2 μm.

FIG. 6 shows the photoluminescence spectrum of this diamond thin film. The measurement conditions are the same as in Example 2. In addition to a broad emission band having a peak near 6000 °, an emission peak is observed at 7370 °. This emission peak is attributed to the silicon of the substrate mixed into the film, which is described in the literature [J. Ruan, W.C. J. Choyk
e and W. D. Partlow, Appl. Ph
ys. Lett. 58 , 295 (1991)]. From Example 2 and Comparative Example 2, even in the ECR microwave plasma CVD method, contamination from the silicon substrate can be prevented by adding oxygen gas to the reaction gas, and a high-purity diamond thin film can be obtained. It is understood that it is possible.

[Embodiment 3] In this embodiment, a diamond thin film is formed on a molybdenum substrate by a hot filament CVD method. As a pretreatment of the molybdenum substrate 21, the molybdenum substrate 21 is immersed in an ethanol suspension of diamond powder having a particle size of 10 μm, and stirred by ultrasonic waves for one hour. After degreased and washed with ethanol, it is mounted on the substrate holder 22 of the hot filament CVD apparatus shown in FIG. After reducing the pressure to 8 × 10 ⁻⁷ Torr by the vacuum pump 27,
As a reaction gas, a mixed gas of C ₂ H ₅ and H _{2 to} which O ₂ is added is used, and the gas flow rate is ₅ sccm of C ₂ H ₅ and H _{2.
2 is set} to 500 sccm and O _{2 is set} to 1 sccm, and introduced into the chamber 25 from the gas inlet 24. If the temperature of the tungsten filament 23 is 2000 ° C. and the distance between the filament 23 and the molybdenum substrate 21 is 8 mm, the substrate temperature rises to 800 ° C. due to the radiant heat of the filament.

The reaction pressure is set to 20 Torr and the synthesis is performed for 3 hours. As a result, a high-purity diamond thin film having a thickness of about 2.5 μm was obtained. FIG. 8 shows a photoluminescence spectrum of the formed high-purity diamond thin film.
The measurement was performed using a spectroscope in the range of 5000 to 9000 ° using a laser beam having a wavelength of 4880 ° by an argon laser as an excitation light source. Only a sharp peak due to the Raman line of diamond is observed around 5220 °.

[Comparative Example 3] This comparative example uses hot filament C
This is an example in which a diamond thin film is formed on a molybdenum substrate by a VD method. Substrate pretreatment conditions and apparatus were as in Example 3.
Is the same as A mixed gas of C ₂ H ₅ and H ₂ was used as a reaction gas, and the gas flow rates were 5 sccm for C ₂ H _{5 and} 500 for H _2.
The synthesis was performed in the same manner as in Example 3 except for the sccm and the other conditions. The formed diamond thin film had a thickness of about 2 μm. FIG. 9 shows the photoluminescence spectrum of this diamond thin film. The measurement conditions are the same as in Example 3. A sharp peak of diamond near 7220 ° and 72
A broad emission band having a peak near 40 ° is observed. This broad light emission band is due to the tungsten of the filament mixed in the film.

From Comparative Example 3 and Example 3, contamination of tungsten from the filament can be prevented by adding oxygen gas to the reaction gas in the hot filament CVD method, and a high-purity diamond thin film can be obtained. It is understood that it is possible.

Table 1 summarizes the synthesis conditions and measurement results of the above Examples and Comparative Examples.

[0025]

[Table 1]

In the present invention, high-purity diamond is grown by vapor phase synthesis by adding oxygen gas to the reaction gas. The added oxygen gas is decomposed by plasma, a hot filament, or the like, as in other reaction gases, and becomes an excited state. The oxygen in the excited state reacts with the impurity element to prevent these impurities from being mixed into diamond, and as a result, high-purity diamond can be obtained. The amount of oxygen gas at which the above-described effects can be obtained is not particularly limited. However, considering the growth rate, purity, and the like, the ratio of the number of oxygen atoms to the number of carbon atoms [O] / [C] is set to 0. .00
It is preferable to set it to 1 or more and 0.1 or less. [O] /
When [C] is larger than 0.1, high-purity diamond can be obtained, but the growth rate is low, and the growth time is extremely long, which is not practical. On the other hand, [O] / [C]
Is less than 0.001, the growth rate does not decrease, but the purity is low because the effect of adding oxygen cannot be sufficiently obtained.

As described above, by setting the ratio of the number of oxygen atoms to the number of carbon atoms [O] / [C] to be 0.001 or more and 0.1 or less, it is possible to sufficiently produce diamond with extremely high purity as compared with the prior art. Can be obtained at high growth rates. In the case where only the vicinity of the surface of the diamond thin film is made highly pure depending on the use, [O] / [C] is 0.001 in the initial stage of growth.
Keep it smaller or do not add oxygen,
Even when [O] / [C] is larger than 0.1 by synthesizing at a sufficiently high growth rate and increasing the amount of oxygen added stepwise during the growth, the effect of oxygen addition can be reduced. Obtainable.

[0028]

According to the method for synthesizing diamond by a gas phase synthesis method using a reaction gas obtained by diluting a carbon-containing gas with hydrogen gas, impurities mixed into diamond are removed by introducing oxygen gas into the reaction gas. High purity.

[Brief description of the drawings]

FIG. 1 shows a microwave plasma CVD apparatus used in Example 1 and Comparative Example 1 of the present invention.

FIG. 2 is a photoluminescence spectrum of the high-purity diamond thin film obtained in Example 1.

FIG. 3 is a photoluminescence spectrum of the diamond thin film obtained in Comparative Example 1.

FIG. 4 shows ECs used in Example 2 and Comparative Example 2 of the present invention.
R microwave plasma CVD device.

FIG. 5 is a photoluminescence spectrum of the high-purity diamond thin film obtained in Example 2.

FIG. 6 is a photoluminescence spectrum of the diamond thin film obtained in Comparative Example 2.

FIG. 7 is a hot filament CVD apparatus used in Example 3 and Comparative Example 3 of the present invention.

FIG. 8 is a photoluminescence spectrum of the high-purity diamond thin film obtained in Example 3.

FIG. 9 is a photoluminescence spectrum of the diamond thin film obtained in Comparative Example 3.

[Explanation of symbols]

 Substrates 2, 12, 22; Substrate holders 3, 13; Heaters for substrate heating 4, 14, 24; Gas inlets 5, 15, 25; Chambers 6, 16; Microwave generators 7, 17 , 27; vacuum pump 18; magnet coil 23; filament

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshio Hata 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Teiko Takagi 22-22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka In the company

Claims (4)

[Claims] A gas phase synthesis method using a gas obtained by diluting a carbon-containing organic gas, an inorganic gas, or a mixed gas of the organic gas and the inorganic gas with a hydrogen gas as a reaction gas. A method for synthesizing high-purity diamond, comprising adding oxygen gas to the reaction gas. 2. The number of oxygen atoms in the oxygen gas to be added,
2. The high-purity diamond according to claim 1, wherein the ratio of the number of carbon atoms in the reaction gas to the number of carbon atoms is 1 and the number of oxygen atoms is 0.001 or more and 0.1 or less. Synthesis method. 3. The method for synthesizing high-purity diamond according to claim 1, wherein the amount of oxygen gas added to the reaction gas is different at least between the initial stage and the final stage. 4. The method for synthesizing high-purity diamond according to claim 1, wherein the amount of oxygen gas added at the beginning of the synthesis is smaller than the amount of oxygen gas at the end of the synthesis.