JPH09202693A - Synthesis of diamond by chemical deposition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for synthesizing diamond by a chemical deposition method without using hydrogen which has been used as a gas having danger of explosion as a reaction gas.

SOLUTION: A mixture of two component gases is decomposed by a plasma formed under conditions at 150-900°C substrate temperature under 1-50Torr at 250-450W microwave output to deposit a diamond on the substrate. The mixture of two component gases is a hydrocarbon (CxHy) plus CO₂ having 0.2-0.8 flow rate ratio of CxHy to CO₂ or a gasified oxygen-containing liquid hydrocarbon (CxHyOz) plus CO₂ having 12-17 flow rate ratio of CxHyOz to CO₂. A high-quality diamond can be obtained at a low temperature of 180°C.

COPYRIGHT: (C)1997,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for synthesizing diamond by chemical vapor deposition, and more particularly to a method for synthesizing diamond which does not use explosion-hazardous hydrogen as a reactive gas and a temperature lower than 400.degree. On the method of synthesizing diamond at

[0002]

2. Description of the Related Art The hardest substance in the world (about Hv10,0
00 kg / mm ² ) diamond has very high thermal conductivity (about 24 W / ° C.-cm) and good insulation (about 10 ¹² to 10 ¹⁶ Ωcm / 15 ° C.). Furthermore,
It is transparent in the ultraviolet, visible and infrared spectra.
Diamond is also a material that has many properties not found in other materials, such as good resistance to chemical corrosion, low coefficient of friction, and high speed of sound propagation. For example, a diamond can be converted into a semiconductor by adding a small amount of phosphorus or boron. As a result, diamond has attracted attention as an important material in applications in the electronics and defense related industries. Conventionally, artificial synthetic diamonds have been used in the manufacture of tools. In the last few years, the manufacturing method of artificial diamond has been greatly improved, and optical instruments, semiconductor devices, VLS
The applications of synthetic diamond have been extended to industries such as heat sinks for I-integrated circuits, speaker diaphragms, anti-reflective films for solar cells and other mechanical tools.

[0003] Diamond thin films are usually synthesized from a mixture of a large amount of explosive hydrogen gas and a small amount of hydrocarbons, the typical synthesis temperature of which is 700-1000 ° C. However, GaAs, plastics, ZnS and M
Since many substrates materials, such as gF ₂ is unstable at high temperatures, in order to widen the further range of applications, it is important to synthesize diamond films at low temperatures (below 500 ° C.). Diamond synthesis at low temperatures can be performed by changing the synthesis method and reaction gas. For example,
Liou et al. Use microwave plasma enhanced chemical vapor deposition (MPCVD) to synthesize diamond. The reaction gas is _{H 2 / CH 4 / O 2} . 400 diamonds
Can be synthesized at temperatures higher than ℃ (Appl. Phy
s. Lett. 56 (5), p. 437 (1990)). Yasuchi et al. Also synthesize diamond by MPCVD. The reaction gas is CO / O ₂ / H _2. 400 ° C diamond
It has been confirmed that synthesis can be performed at higher temperature (Surf
ace and Coatings Technology, 47 (1991), 1). We
i et al. suggest that diamond thin films can be formed by ECR microwave plasma CVD with CH ₄ + CO ₂ / H ₂ at temperatures above 500 ° C. (Journal of C.
rystal Growth, 99 (1990), p. 1201).

[0004]

All of the above methods for synthesizing diamond involve a large amount of explosive H _2.
And has the common problem that it creates a possible danger. Another problem is that combining
The process must be performed at a temperature higher than ° C., which requires high energy and limits the usable substrate material.

[0005]

SUMMARY OF THE INVENTION The object of the present invention is as follows.
An object of the present invention is to solve the above problems and to provide a method for synthesizing high-quality diamond without using explosive gas, that is, hydrogen. It is another object of the present invention to provide a method for synthesizing high quality diamond at lower temperatures, i.e. below 400 <0> C. Also, the diamond formation rate is relatively fast.

In order to achieve the above object, the diamond synthesis method of the present invention uses a chemical vapor deposition method, which includes a substrate temperature of 150 ° C. to 900 ° C., a pressure of 1 to 50 Torr, and a micro pressure of 250 to 450 W. Under conditions of wave power,
Decompose the binary gas mixture by the generated plasma,
Depositing diamond on the substrate. The binary gas mixture contains 0.2 to 0.8 hydrocarbons (C
C with a flow rate ratio C _x H _y CO ₂ of the vaporized liquid oxygen-containing hydrocarbon plus CO ₂ or _{12~17 (C x H y O Z} ) having a flow ratio of CO _{2 x} H _y)
It may be _x H _y O _Z plus CO _2.

According to the present invention, a method for synthesizing diamond includes microwave plasma CVD, F. Plasma C
A chemical vapor deposition (CVD) method such as a VD method and a hot filament CVD method may be used.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following examples, a microwave plasma CVD method was used to synthesize diamond. FIG. 1 shows a schematic diagram of an apparatus for carrying out this method.
Shown in In this figure, the reaction chamber 1 is connected via a waveguide 2 to a microwave generator 3 and at the bottom to a vacuum system 4 and at the top via a gas supply line 5 to a gas supply system 8 and 9 is connected. The substrate holder 6 is disposed in the reaction chamber 1 and holds a substrate. The substrate holder 6 is cooled by a cooling system 7 connected to the reaction chamber 1. The reaction gases to be synthesized, for example CO ₂ and CH _4, are supplied from their respective gas supply systems 8 and 9 to the reaction chamber 1 via a flow controller 10.

[0009] Reactive gases suitable for use in the present invention are binary gas mixtures. The binary gas mixture may be hydrocarbon (C _x H _y ) plus CO ₂ or liquid hydrocarbon containing vaporized oxygen (C _x H _y O _Z ) plus CO ₂ . Examples of C _{x Hy} include CH ₄ , C ₂ H ₂ , C ₂
H _4, C ₃ H _8, is C ₄ H ₁₀ and C ₆ H _6. C _x H
Examples of _y O _Z include C ₃ H ₆ O ₃ , CH ₃ OH, CH ₃ CO
CH ₃ , CH ₃ COOCH ₃ , C ₂ H ₅ OH and C ₂ H
₅ OC ₂ H ₅ .

According to the present invention, the substrate temperature is 150 to 900.
℃ is controlled within the range of the pressure is adjusted in the range of 1～50Torr, microwave power is adjusted within the range of 250～450W, flow ratio C _x H _y of CO ₂ is from 0.2 to 0 It is adjusted within a range of .8, and C _x H _y O
Flow ratio of CO _{2 Z} is adjusted in the range of 12-17.

The substrate temperature is measured with a k-type thermocouple and an optical pyrometer in direct contact with the graphite substrate holder. In order to confirm the temperature of the surface of the synthetic substrate, lead (m.
p. = 335 ° C) and tin (mp = 243 ° C). The present inventors have found that the accurate substrate surface temperature is 65 ± 10 ° C. less than the thermocouple reading.
You can be convinced that it is high. The temperature values indicated in the present invention are true substrate surface temperatures.

The following specific examples are not intended to serve as limiting the scope of the invention, but are intended to more fully illustrate the invention, as numerous modifications and variations will be apparent to those skilled in the art. Things.

Example 1 In this example, the apparatus shown in FIG. 1 was used. A silicon wafer substrate (10 mm × 10 mm) was polished with diamond powder and then placed on a substrate holder 6 having a diameter of 15 mm, which was arranged in the center of a reaction chamber 1 having an outer diameter of 55 mm. During the production process, the substrate was heated to 850 ° C. by microwave plasma. The pressure in the reaction chamber 1 was maintained at 25 Torr, and the microwave output was 40
It was 0W. The reaction gas is CO ₂ -C ₂ H ₂ ,
The flow rates of O ₂ and C ₂ H ₂ were 30.0 ml / min and 14 ml / min, respectively. With a reaction time of 3 hours, about 2.
A 7 μm thick diamond thin film having good crystallinity was obtained. The formation rate of the diamond thin film was 0.9 μm / hour. FIG. 2 shows an SEM micrograph of this diamond thin film. In order to obtain a high quality diamond thin film, when maintaining the flow rate of CO ₂ at 30.0 ml / min,
The flow rate of C ₂ H ₂ is preferably 13.8～14.5Ml /
Keep within minutes.

Example 2 The reaction gases used were 30.0 ml / min and 2
Except were CO ₂ -CH ₄ having a flow rate of 1.1 ml / min, using the same apparatus and procedure as described in Example 1. With a reaction time of 3 hours, as shown in FIG.
A diamond thin film with good crystallinity having a thickness of μm was obtained. The formation rate of the diamond thin film was about 2.0 μm / hour. To obtain high quality diamond thin film,
When the flow rate of CO ₂ is maintained at 30.0 ml / min, CH 2
The flow rate of ₄ is preferably maintained in the range from 20.6 to 21.7 ml / min.

Example 3 Same as described in Example 1, except that the reaction gas used was CO ₂ -C ₃ H ₈ with a flow rate of 30.0 ml / min and 8.6 ml / min, respectively. Apparatus and methods were used. With a reaction time of 3 hours, a diamond thin film having good crystallinity and a thickness of about 6.0 μm was obtained as shown in FIG. The formation rate of the diamond thin film was 2 μm / hour. To obtain high quality diamond thin film,
When the flow rate of CO ₂ is maintained at 30.0 ml / min, C ₃
The flow rate of H ₈ is preferably maintained in the range of 7.9～9Ml / min.

Example 4 The reaction gases used were 1.35 ml / min and 2 respectively.
Except were CO ₂ -C ₃ H ₆ O ₃ having a flow rate of 0 ml / min, using the same apparatus and procedure as described in Example 1. With a reaction time of 3 hours, a diamond thin film having a good crystallinity and a thickness of about 11 μm was obtained as shown in FIG. The formation rate of diamond thin film is about 3.7μm
/ Hour. To obtain a high-quality diamond film, when maintaining the flow rate of the C ₃ H ₆ O ₃ in 20 ml / min, the flow rate of CO ₂ is preferably maintained in the range of 1.2～1.6Ml / min.

Example 5 The reaction gases used were 30.0 ml / min and 1
CO ₂ —CH ₄ with a flow rate of 8.0 ml / min,
Pressure is 25 Torr, microwave output is 290W
The same equipment and method as described in Example 1 was used, except that the substrate temperature was 340 ° C. and the reaction time was 24 hours. The formation rate of the diamond thin film was about 0.3 μm / hour, and the synthesis rate of diamond fine particles was 0.8 μm / hour. FIGS. 6a and 6b show SEM images of the surface morphology and cross section of the obtained diamond thin film, respectively. To obtain a high-quality diamond film, when maintaining the flow rate of CO ₂ in 30.0 ml / min, the flow rate of CH ₄ is preferably maintained in the range of 17～21Ml / min.

Example 6 The same equipment and method as described in Example 5 was used, except that the total reaction time was 4 hours. FIG. 7 shows an SEM image of the surface morphology of the obtained diamond thin film. This demonstrates that under these conditions only four hours are required to obtain high quality and continuous diamond films.

Example 7 The reaction gases used were 30.0 ml / min and 1
CO ₂ —CH ₄ with a flow rate of 7.0 ml / min,
Pressure is 10 Torr, microwave output is 290W
And the same equipment and method as described in Example 1 except that the substrate temperature was 270 ° C. and the total reaction time was 24 hours. The formation rate of the diamond thin film was about 0.2 μm / hour. FIG. 8 shows a cross-sectional view of the obtained diamond thin film. In order to obtain a high quality diamond thin film, the flow rate of CO ₂ was set to 30.0 ml /
When maintaining the minute, the flow rate of CH ₄ is preferably 16 to 2
Maintain within 0 ml / min.

Example 8 The reaction gases used were 30.0 ml / min and 1
CO ₂ —CH ₄ with a flow rate of 6.9 ml / min,
The same equipment and method as described in Example 1 was used, except that the pressure was 4 Torr, the microwave power was 290 W, the substrate temperature was 180 ° C., and the total reaction time was 24 hours. . The formation rate of the diamond thin film was 0.13 μm / hour. FIGS. 9A and 9B show SEM images of the surface morphology and cross section of the obtained diamond thin film, respectively. In order to obtain a high quality diamond thin film, when the CO ₂ flow rate is maintained at 30.0 ml / min, the CH ₄ flow rate is preferably 16-19.
Maintain within the ml / min range.

[0021]

According to the present invention, high quality diamond can be obtained even at a low temperature of 180 ° C.

[Brief description of drawings]

FIG. 1 is a schematic view of a microwave plasma CVD apparatus of the present invention.

FIG. 2 is an SEM micrograph showing the crystal structure of the diamond thin film obtained from Example 1.

FIG. 3 is a SEM micrograph showing a crystal structure of a diamond thin film obtained from Example 2.

FIG. 4 is an SEM micrograph showing the crystal structure of the diamond thin film obtained from Example 3.

FIG. 5 is an SEM micrograph showing a crystal structure of a diamond thin film obtained from Example 4.

6 (a) and (b) are SEMs of the surface morphology and cross section of the diamond thin film obtained from Example 5, respectively.
It is an image.

FIG. 7 is an SEM image of the surface morphology of the diamond thin film obtained from Example 6.

FIG. 8 is an SEM image of a cross section of the diamond thin film obtained from Example 7.

FIGS. 9A and 9B are SEMs of the surface morphology and cross section of the diamond thin film obtained from Example 8, respectively.
It is an image.

Claims (18)

[Claims] A substrate temperature of 150 ° C. to 900 ° C .;
Under the conditions of a pressure of 0 Torr and a microwave power of 250 to 450 W, the generated plasma decomposes the binary gas mixture and deposits diamond on the substrate, and the binary gas mixture is 0.2 to 0.2 W. C having a flow ratio of hydrocarbons (C _x H _y ) to CO ₂ of 0.8
selected from C _x H _y O _Z mixed gas of plus CO ₂ having a flow rate ratio _x H _y plus CO ₂ and 12 to 17 liquid hydrocarbons containing vaporized oxygen of CO ₂ (C _x H _y O _Z) A method of synthesizing diamond by chemical vapor deposition on a substrate using chemical vapor deposition (CVD). 2. The method according to claim 1, wherein the CVD method is a microwave plasma CVD method. 3. The method according to claim 1, wherein F. The method for synthesizing diamond by a chemical vapor deposition method according to claim 1, which is a plasma CVD method. 4. The method according to claim 1, wherein the CVD method is a hot filament CVD method. 5. A C _x H _{y is, CH 4, C 2 H 2} , C 2 H
_{4, C 3 H 8, C} 4 H 10 and method of synthesizing diamond by chemical vapor deposition method according to claim 1 selected from the group consisting of C ₆ H _6. 6. The method according to claim 5, wherein C _x H _y is C ₂ H ₂ . 7. The method according to claim 5, wherein C _x H _y is CH ₄ . 8. The method according to claim 5, wherein C _x H _y is C ₃ H ₈ . 9. C _x H _y O _Z is _{C 3 H 6 O 3, CH} 3 O
H, CH ₃ COCH ₃ , CH ₃ COOCH ₃ , C ₂ H ₅
Method of synthesizing diamond by chemical vapor deposition method according to claim 1 selected from the group consisting of OH and _{C 2 H 5 OC 2 H 5} . 10. A C _x H _y O _Z methods for synthesizing diamond by chemical vapor deposition method according to claim 9 is C ₃ H ₆ O _3. 11. A substrate temperature of 850 ° C. and a pressure of 2
5 Torr, a microwave output of 400 W,
The flow rates of CO ₂ and C ₂ H ₂ are 30 ml /
The method for synthesizing diamond by a chemical vapor deposition method according to claim 6, wherein the amount is 13.8 to 14.5 ml / min. 12. The substrate temperature is 850 ° C. and the pressure is 2
5 Torr, a microwave output of 400 W,
The method of synthesizing diamond by chemical vapor deposition method according to claim 7 flow rates of CO ₂ and CH ₄ are 30ml / min and 20.6～21.7Ml / min, respectively. 13. A substrate temperature of 340 ° C. and a pressure of 2
5 Torr, the microwave output is 290 W,
The method of synthesizing diamond by chemical vapor deposition method according to claim 7 flow rates of CO ₂ and CH ₄ are 30ml / min and 17～21Ml / min, respectively. 14. A substrate temperature of 300 ° C. and a pressure of 2 ° C.
5 Torr, the microwave output is 290 W,
The method of synthesizing diamond by chemical vapor deposition method according to claim 7 flow rates of CO ₂ and CH ₄ are 30ml / min and 16～20Ml / min, respectively. 15. A substrate temperature of 270 ° C. and a pressure of 1
0 Torr, the microwave output is 290 W,
The method of synthesizing diamond by chemical vapor deposition method according to claim 7 flow rates of CO ₂ and CH ₄ are 30ml / min and 16～20Ml / min, respectively. 16. A substrate temperature of 180 ° C. and a pressure of 4 ° C.
A Torr, a microwave output is 290W, and method of synthesizing diamond by chemical vapor deposition method according to claim 7 flow rates of CO ₂ and CH ₄ are 30ml / min and 16～19Ml / min, respectively. 17. A substrate temperature of 850 ° C. and a pressure of 2
5 Torr, a microwave output of 400 W,
The method of synthesizing diamond by chemical vapor deposition method according to claim 7 flow rates of CO ₂ and CH ₄ are 30ml / min and 7.9～9Ml / min, respectively. 18. A substrate temperature of 850 ° C. and a pressure of 2
5 Torr, a microwave output of 400 W,
The flow rates of CO ₂ and C ₃ H ₆ O ₃ are each 1.2.
The method for synthesizing diamond by a chemical vapor deposition method according to claim 10, wherein the concentration is from 1.6 ml / min to 20 ml / min.