JPH07300394A - Diamond and its vapor-phase synthesis - Google Patents

Abstract

PURPOSE:To improve the thermal conductivity of a diamond by generating a plasma under a prescribed pressure in a gaseous mixture of H2 gas, an inert gas and a carbon-containing compound gas having a molar ratio satisfying a specific condition, thereby forming a diamond film on a substrate. CONSTITUTION:An inert gas such as Ar is introduced into a quartz tube 2 having a diameter of about <=50mm and evacuated through an evacuation port 3 and a plasma is generated in the tube to clean a substrate 1 made of Mo, etc. A mixed gas containing H2 gas (A), an inert gas (B) and a carbon-containing compound gas (C) such as methane gas at a molar ratio satisfying the conditions of 0.001 <=B/(A+B+C) <=0.95 and 0.001 <=C/(A+B+C) $0.1 is introduced into the tube through an introducing port 4. A plasma 5 is generated with microwave having a frequency of >=1 kHz, especially 2500MHz under a pressure of 5-760 Torr to deposit a diamond film having a film thickness of >=5mum and satisfying the formula 0.3<=E/sq. rt. F<=3 (E is average crystal particle diameter and F is film thickness) on a substrate 1 heated at about 700-1200 deg.C.

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 or coating high quality diamond at a high speed by a chemical vapor phase synthesis method, which has a high thermal conductivity, a low dielectric property, a high translucency and a high transparency. Fields requiring specific elasticity, high strength, wear resistance, etc., such as window materials, diaphragms, cutting tools, heat sinks, I
It can be applied to C bonders and the like.

[0002]

2. Description of the Related Art Conventionally, diamond has been synthesized in a thermodynamic equilibrium state under high temperature and high pressure, but in recent years, a synthesis method from a vapor phase (CVD) which positively utilizes a non-equilibrium state.
Method) has also made it possible to synthesize diamond. As a vapor phase synthesis method of diamond, a method in which a hydrocarbon diluted with 10 times (volume) or more of hydrogen is generally used and a gas is excited by plasma or a hot filament has been proposed. For example, in JP-A-58-91100,
A method in which a mixed gas of hydrocarbon and hydrogen is preheated by a thermoelectron emitting material heated to 1000 ° C. or higher, and then the mixed gas is introduced to a heated substrate surface to deposit diamond by thermal decomposition of hydrocarbon, In addition, JP-A-58-11049
No. 4 discloses a method in which hydrogen gas is passed through a microwave electrodeless discharge and then mixed with hydrocarbon to deposit diamond in the same manner. A method in which microwaves are introduced into a mixed gas with an active gas to generate microwave plasma, a substrate is placed therein, and heating is performed at a temperature of 300 to 1300 ° C. to decompose hydrocarbons and deposit diamond. Is listed.

[0003]

Since such a conventional diamond vapor phase synthesis method basically uses only a raw material gas containing hydrogen and carbon (for example, a carbon hydrogen gas),
The plasma can be stably generated only at a relatively low pressure up to about 50 Torr, and there is a problem that the synthesis conditions, the synthesis rate, the synthesis area, etc. of diamond are limited, and it was insufficient in terms of application. The present invention is intended to solve these problems.

[0004]

As a result of studying various conditions for generating stable and highly active plasma, the inventors of the present invention have found that when the conditions of the mixed gas are as follows, extremely high speed is achieved. It was found that diamond can be synthesized with. That is, at a pressure of 5 to 760 Torr, hydrogen gas (A), inert gas (B) and organic compound gas (C)
More preferably in the presence of a mixed gas containing them such that the molar ratios thereof are 0.001 ≦ B / (A + B + C) ≦ 0.95 and 0.001 ≦ C / (A + B + C) ≦ 0.1. Satisfies the condition that the molar ratio of the three kinds of gas at a pressure of 30 to 600 Torr is 0.01 ≦ B / (A + B + C) ≦ 0.95 and 0.002 ≦ C / (A + B + C) ≦ 0.08. When plasma is generated in the presence of a mixed gas containing, and diamond synthesis is performed, the growth rate is several hundred times (several tens of μm / h) compared with the case where no inert gas is used, and a large area ( It has been found that diamonds can be synthesized on the surface of tens of square millimeters). In the method of the present invention, the molar ratios of the above-mentioned three kinds of gas satisfy the following conditions: 0.05 ≦ B / (A + B + C) ≦ 0.8 and 0.005 ≦ C / (A + B + C) ≦ 0.05. Most preferred.

In the present invention, either a direct current or an alternating current electromagnetic field may be used as the plasma generation source,
In the latter case, more than the high-frequency or microwave frequency 1 kH _Z is preferred in view of operability. More preferably 5
00MH _Z above using microwaves. Input power is generally 1 W / cm ² or more. The type of inert gas used in the present invention may be helium, neon, argon, krypton, xenon, or a mixture thereof, and the effect is the same regardless of which is used, but argon is preferable because it is inexpensive and easily available.

The carbon-containing compound gas may be a compound gas containing carbon which is a gas under CVD conditions, for example, gaseous methane, ethane or other aliphatic hydrocarbons or benzene or other aromatic hydrocarbons. It may be an inorganic compound such as carbon oxide or carbon dioxide, or an organic compound containing a small amount of a hetero atom such as oxygen, nitrogen or sulfur in the molecule such as alcohol, thiol, ketone or ether. In the present invention, since an inert gas such as argon is present in the plasma generation atmosphere, even if the plasma output is not a normal condition of tens of watts or more, the output is as low as tens of watts or less. , It is possible to stably generate plasma with high activity even in a pressure region of several hundred Torr or more, and it is difficult to coat diamond at an appropriate substrate temperature (700 to 1200 ° C.) because plasma is usually concentrated. It is possible to coat even a three-dimensional substrate with diamond. The material of the base material is the same as that used in the conventional CVD method. Particularly preferred substrates are Si, Mo, W, Ta, Nb, Zr,
B, C, Al, SiC, Si ₃ N ₄ , MoC, Mo ₂ C,
WC, W ₂ C, TaC, NbC, BN, B ₄ C, AlN,
TiC, TiN, Ti and the like.

Further, within the condition range of the present invention, the particle size is several hundred μm.
It is also possible to grow the above diamond particles at a high speed. Here, the highly active plasma can be confirmed by optical emission spectroscopic analysis of the plasma and visual observation of the plasma. That is, according to the emission spectroscopic analysis, the intensity of the H ₂ continuous band is relatively weak in the plasma having high activity, and the intensity of hydrogen radicals such as H (α) and C ₂ and CH radicals is strong. . In addition, it is often observed visually that the C ₂ radical (swan band) emits greenish light. From such a phenomenon, it is considered that the raw material gas is decomposed more efficiently under the conditions of the present invention.

The effect of adding the inert gas of the present invention appears in the pressure range from 5 Torr to 760 Torr as described above. In general, lower pressure will result in slower growth rate,
When the pressure is high, the shrinkage of plasma becomes remarkable and the deposition area becomes narrow. Therefore, the preferable pressure range is 30 Torr.
The above range is 600 Torr or less. The pressure range of 60 Torr or more and 400 Torr or less is more preferable in order to bring about the effect of increasing the deposition rate in a practical deposition area (several tens of square millimeters). In addition to the essential components of the hydrogen gas (A), the inert gas (B) and the carbon-containing compound gas (C), the source gas is a doping gas (D) such as diborane (B).
₂ H _6), even when containing nitrogen (N _2), the addition effect of the inert gas emerges in the same manner. In such a case, hydrogen gas (A), inert gas (B), carbon-containing compound gas (C)
It is preferable to mix and use each gas so that the molar ratio of the doping gas (D) is D / (A + B + C + D) ≦ 0.4. Under the condition of 0.4 <D / (A + B + C + D), the effect of the present invention becomes small. Incidentally, in the vapor phase synthesis of diamond using a plasma, but also it appears the effect of the present invention using any like technique, as described above, using a microwave over 500 mH _Z is as a source of plasma Is most preferred.

The average crystal grain size (E) and the grown film thickness (F) of the growth surface of the diamond film obtained by the method of the present invention
When observed with an optical microscope and a scanning electron microscope (SEM), it was found that the average crystal grain size (E) was relatively large with respect to the grown film thickness (F).
In a diamond having such a relatively large crystal grain size, it is considered that crystal defects such as dislocations and precipitation of non-diamond components such as amorphous carbon are often observed by observation with a transmission electron microscope (TEM). It was found that there were few grain boundaries and the crystals had low defects.
It was also found that the diamond exhibits many original characteristics such as a high light-transmittance measured by a transmission spectrum in the ultraviolet to infrared region and a high thermal conductivity measured by a thermal conductivity measurement.

The effect of this crystal grain size is that the average crystal grain size (E) is obtained when the film thickness (F) is 5 μm or more.
And the film thickness (F) satisfy the relation of 0.3 ≦ E / √F ≦ 3. E / √F <0.3 or 3
In the range of <E / √F, the characteristics of the diamond are deteriorated. According to the method of the present invention, diamond in this region can be easily obtained.

An apparatus for synthesizing diamond used in the present invention is shown in FIGS. 1 to 3. FIG. 1 is a schematic diagram of a microwave plasma CVD apparatus, FIG. 2 is a schematic diagram of a high frequency plasma CVD apparatus, and FIG. 3 is a schematic diagram of a direct current plasma CVD apparatus. In the figure, 1 is a substrate, 2 is a quartz tube, 3 is a vacuum exhaust port, 4
Is a supply gas inlet, 5 is a generated plasma, 6 is a magnetron, 7 is a waveguide, 8 is a plunger, 9 is an RF power source, 1
0 is a DC power supply, 11 is a substrate support, 12 is an insulating seal,
13 is a cathode. Generally, the quartz tube has a diameter of 50 mm or more. Next, the effects of the present invention will be specifically described with reference to Examples and Comparative Examples.

[0012]

【Example】

(Example 1) As a diamond synthesis method, a microwave plasma CVD method (hereinafter, referred to as μ-PCVD), a high frequency plasma CVD method (hereinafter, referred to as RF-PCVD), a direct current plasma CVD method (hereinafter, DC-PCVD).
Say. ) Was used (see Tables 1 and 2). As the base material, 40 × 35 × 10 mm
A molybdenum plate of No. ³ was finally polished with # 600 diamond powder and used. First, an inert gas was introduced into the quartz tube 2 shown in the drawing through the inlet 4, a plasma 5 was generated by a plasma generation source at a pressure of 1 Torr, and the molybdenum plate was cleaned with the plasma for 5 minutes.

After that, plasma CVD was performed under the conditions shown in Tables 1 and 2, and the molybdenum plate was coated with vapor phase synthesized diamond. When the surface temperature of the base material during synthesis was measured by an optical pyrometer, it was 800 to 12
It was in the range of 00 ° C. The diamond film formed by the plasma CVD method was subjected to surface observation and film thickness observation by a scanning electron microscope, and crystallinity evaluation by X-ray diffraction and Raman scattering spectroscopy. The results shown in are obtained. In the table, "Dia"
Indicates diamond, and “ac” indicates amorphous carbon. If the molar ratio of the inert gas to the total gas, the molar ratio of the carbon-containing compound gas to the total gas and the reaction pressure are within the conditions of the present invention, the deposition rate of diamond is
For example, it is possible to achieve a very high speed of 400 μm / h.

On the other hand, outside the conditions of the present invention, even if an attempt is made to generate plasma at a high pressure without adding an inert gas, the plasma is not stably generated, and even if the plasma can be generated, the diamond film is not formed. It is an inferior material containing amorphous carbon, and the vapor deposition rate is 2 μm at maximum.
/ H becomes slower. In addition, the sample No. shown in Table 2 was used. 18-2
When the thermal conductivity of 2 was measured by a thermal conductivity measuring device using a simple thermistor, it was confirmed that the samples manufactured under the conditions of the present invention had high thermal conductivity of 2 W / cmK to 15 W / cmK. On the other hand, it was less than 2 W / cmK in the sample manufactured under the comparative conditions.

[0015]

[Table 1]

[0016]

[Table 2]

(Example 2) Sample No. 1 shown in Table 1 Four
Diamond plate peeled from (10 x 10 x 0.2 mm
³ ) is placed on a 40 × 34 × 10 mm ³ molybdenum plate,
Microwave output 800W, pressure 300 Torr, hydrogen flow 1000SCCM, argon flow 500S
When microwave plasma CVD was carried out for 3 hours while introducing CCM and ethanol at a flow rate of 40 SCCM, the thickness of the diamond plate grew from 0.2 mm to 1 mm. This diamond plate is the original sample No. As with the 4 diamond plate, it was found by X-ray diffraction and Raman spectroscopy that the diamond had good crystallinity and had a (100) preferred orientation.

Example 3 Diameter 40 mm and thickness 20
In the vicinity of the center of the mm-mm molybdenum plate, 5 diamond single crystal abrasive grains having a grain size of 250 μm prepared by the ultra-high pressure method were placed, and the argon flow rate was 2000 SCCM and the hydrogen flow rate was 1000.
When microwave plasma CVD was performed for 5 hours under the conditions of SCCM, acetylene flow rate 20 SCCM, microwave output 800 W, and pressure 500 Torr, 5 single crystal abrasive grains with a diameter of 1 mm were obtained. It was confirmed by X-ray diffraction and Raman spectroscopy that the diamond had good crystallinity.

Example 4 A center of a 40 × 35 × 10 mm ³ molybdenum plate having a diameter of 3 formed by an ultra-high pressure method
mm diamond single crystal grains are placed and the helium flow rate is 20
00SCCM, hydrogen flow rate 500SCCM, propane flow rate 20SCCM, microwave output 200W, pressure 600T
When microwave plasma CVD was performed for 5 hours under the condition of orr, the diameter increased to 4 mm. Although the surface seemed to be a little graphitized, diamond automorphism appeared clearly as the chromic acid treatment proceeded. It was confirmed to be diamond by X-ray diffraction and Raman spectroscopy.

Example 5 Diameter 40 mm and thickness 30
After polishing a mm-mm molybdenum plate with a # 600 diamond grindstone, the flow rate of argon is 200 SCCM and the flow rate of hydrogen is 20.
When microwave plasma CVD was performed for 1 hour under the conditions of 0 SCCM, methane flow rate 4 SCCM, microwave output 1.5 KW, and pressure 760 Torr, diamond particles having a diameter of 500 μm were grown in the center of the molybdenum plate. It was confirmed to be diamond by X-ray diffraction and Raman spectroscopy.

(Embodiment) A more preferred embodiment of the present invention will be described below. 1. Frequency is 1 due to plasma generation
A microwave of KH _Z or higher, particularly 500 MH _Z or higher is used. 2. As the carbon-containing compound gas to be used, at least one compound selected from aliphatic hydrocarbons, aromatic hydrocarbons, alcohols, thiols, ketones, ethers, carbon monoxide, carbon dioxide, etc., which is gaseous under CVD conditions, is used. . 3. At least one selected from helium, neon, argon, krypton, and xenon is used as the inert gas. 4. Input power for plasma generation is 1
It is W / cm ² or more and the pressure is 60 to 400 Torr. 5. The diameter of the reaction tube is 50 mm or more. 6. The flow rate of the mixed gas in the diamond formation reaction part is 0.1.
It is not less than cm / sec and not more than 5 cm / sec. 7. The molar ratio of the mixed gas consisting of hydrogen gas (A), inert gas (B), and carbon-containing compound gas (C) is 0.05 ≦ B / (A + B + C) ≦ 0.8 and 0.005 ≦ C / ( The condition of A + B + C) ≦ 0.05 is satisfied.

[0022]

The method of the present invention has the following effects. It is possible to synthesize diamond at a very high speed of several hundreds μm / h or more, and even in a state where the reduction of the deposition area is suppressed (tens of square millimeters), diamond can be synthesized at a high speed of several tens μm / h. Further, not only the diamond film growth but also the growth of diamond particles can be selectively and stably performed at a high speed (several tens μm / h or more). Furthermore, it can be applied to diamond heat sinks and diamond abrasive grains that have hitherto depended on the high-pressure method, and also has high thermal conductivity, low dielectric properties, high translucency, high specific elasticity, high strength, wear resistance, etc. Areas where is required, such as window materials, diaphragms, cutting tools, heat sinks, IC bonder thin films (less than a few μm)
Not only can diamond be provided as a base material (several tens of μm or more). In addition, the method of the present invention comprises
Compared to a high temperature plasma device using a plasma torch and the like, it can be easily applied to conventional devices and is excellent in stable operation, equipment cost, and raw material cost.

[Brief description of drawings]

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

FIG. 2 is a schematic view of a high frequency plasma CVD apparatus.

FIG. 3 is a schematic diagram of a DC plasma CVD apparatus.

[Explanation of symbols]

 1: Base material 2: Quartz tube 3: Vacuum exhaust port 4: Supply gas inlet port 5: Generated plasma 6: Magnetron 7: Waveguide 8: Plunger 9: RF power source 10: DC power source 11: Substrate support 12: Insulation seal 13: Cathode

Claims (2)

[Claims] 1. A hydrogen gas (A), an inert gas (B) and a carbon-containing compound gas (C) having a molar ratio of 0.001 ≦ B / (A + B + C) ≦ 0.95 and 0.001 ≦. A mixed gas containing C / (A + B + C) ≦ 0.1 is introduced into a reaction vessel, and plasma is generated by a DC or AC electromagnetic field under a pressure of 5 to 760 Torr to form diamond on a substrate. A vapor phase synthesis method of diamond characterized by: 2. The average crystal grain size (E) and the film thickness (F) of the surface diamond film formed by the vapor phase synthesis method satisfy the relationship of 0.3 ≦ E / √F ≦ 3, and the film thickness (F) is 5 μm or more, a diamond.