JPH01308896A - Diamond and vapor synthesis thereof - Google Patents

Abstract

PURPOSE:To synthesize a uniform diamond film on a wide area at a high speed, by generating a plasma in the presence of a gaseous mixture of H2 gas, an inert gas and a carbon-containing compound at specific ratios. CONSTITUTION:A mixed gas is produced by mixing (A) H2 gas, (B) an inert gas (e.g., Ar) and (C) a carbon-containing compound gas (e.g., methanol) at ratios to satisfy the formulas 0.001<=B/A+B+C<=0.95 and 0.001<=C/A+B+C<=0.1. The mixed gas is introduced into a reaction vessel 2 through an inlet port 4. A DC or AC electromagnetic field having a frequency of >=1kHz is transmitted from a magnetron 6 through a wave guide 7 and applied to the mixed gas under a pressure of 5-760Torr to generate a plasma 5. A diamond film having a thickness (F) of >=5mum and satisfying the relationship of the formula (E is average particle diameter) can be synthesized on a substrate 1 by this process.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for rapidly synthesizing or coating high-quality diamond by chemical vapor phase synthesis, which has high thermal conductivity and low dielectric properties. It can be applied to fields that require high light transmittance, high pressure elasticity, high strength, wear resistance, etc., such as window materials, diaphragms, cutting tools, heat sinks, and IC bonders.

[Prior art] Diamond has traditionally been synthesized in a thermodynamic equilibrium state at high temperatures and high pressures, but in recent years diamond has also been synthesized by a gas phase synthesis method (CVD method) that actively utilizes non-equilibrium states. It is now possible to synthesize

As a method for vapor phase synthesis of diamond, a method has generally been proposed in which a hydrocarbon diluted with hydrogen at least 10 times (by volume) is used and the gas is excited with plasma or a hot filament. For example, in JP-A-58-91100, a mixed gas of hydrocarbon and hydrogen is preheated with a thermionic emitter heated to 1000°C or more, and then the mixed gas is introduced onto the heated substrate surface. A method for precipitating diamond by thermal decomposition of hydrocarbons was also disclosed in Japanese Patent Application Laid-Open No. 58-110494.
JP-A-59-3098 describes a method in which diamond is deposited in the same way by passing hydrogen gas through a microwave electrodeless discharge and then mixing it with hydrocarbons. There is a method in which microwaves are introduced into a gas mixture to generate microwave plasma, a substrate is placed in the plasma, and the substrate is heated at a temperature of 300 to 1,300°C to decompose hydrocarbons and precipitate diamonds. Are listed.

[Problems to be Solved by the Invention] Such conventional diamond vapor phase synthesis methods basically use only raw material gases containing hydrogen and carbon (e.g., carbon-hydrogen gases), so they cannot be used at temperatures up to about 50 Torr. Plasma could only be stably generated at extremely low pressures, and there were problems with constraints on diamond synthesis conditions, synthesis speed, synthesis area, etc., making it unsatisfactory in terms of application.

The present invention attempts to solve these problems.

[Means for Solving the Problems] As a result of examining various conditions for generating stable and highly active plasma, the present inventors found that extremely high speeds can be achieved when the mixed gas conditions are as follows. discovered that diamonds could be synthesized using

That is, a mixed gas containing hydrogen gas (A), inert gas (B) and organic compound gas (C) at a pressure of 5 to 760 Torr such that their molar ratio is 't+'4 plus (J:
More preferably, diamond synthesis is performed at a pressure of 30 to 600 Torr in the presence of a mixed gas containing three gases in a molar ratio such that the molar ratio of the three gases is satisfied, and an inert gas is not used. It has been found that diamond can be synthesized uniformly over a wide area (several tens of square millimeters) at a growth rate several hundred times faster (several tens of μx/h) than in the conventional method.

In the method of the present invention, the molar ratio of the three types of gases is: It is most preferable to satisfy the following conditions.

In the present invention, either a direct current or an alternating current electromagnetic field may be used as a plasma generation source, and in the latter case, high frequency waves or microwaves having a frequency of IKIlz or higher are preferable from the viewpoint of operability. More preferably, microwaves of 500 MHz or higher are used. Input power is generally 1'vV
/cm” 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 remains the same no matter which one is used.
Argon is preferred because it is available and inexpensive.

The carbon-containing compound gas may be a carbon-containing compound gas that is a gas under CVD conditions, for example an aliphatic hydrocarbon such as gaseous methane, ethane, or an aromatic hydrocarbon such as benzene, - Inorganic compounds such as carbon oxide and carbon dioxide, alcohol 1. It may also be an organic compound containing a small amount of a heteroatom such as oxygen, nitrogen, or sulfur in its molecule such as 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 under the usual conditions of several tens of W or more, the output can be as low as several tens of W or less. , several hundred Torr
It is possible to generate stable and highly active plasma even in the pressure range above, and it is possible to generate three-dimensional plasma that is difficult to coat diamond at an appropriate substrate temperature (700 to 1200℃) because the plasma is usually concentrated. Even basic substrates can be coated with diamond. The material of the base material is conventional CVD
similar to that used in the Act. Particularly preferred base materials include Si, Mo, 'vV, Ta5Nb, Zr5B, C
.

AI, SiC, S 13N4, MoC, MotC,
wc.

ILc, TaC, NbC, BN, B4C5AIN.

These include TiC, TiN, Ti, etc.

Further, within the condition range of the present invention, it is possible to grow diamond particles having a particle size of several hundred μm or more at high speed.

Here, highly active plasma can be confirmed by plasma emission spectroscopic analysis and visual observation of the plasma. In other words, according to optical emission spectroscopy, highly active plasmas are characterized by a relatively weak H2 continuous band intensity and strong hydrogen radicals such as I-I (α) and C7 and CI radicals. . Furthermore, by visual inspection, it is often observed that the luminescence has a greenish tinge due to C radicals (swan band).

From this phenomenon, it is considered that the raw material gas is decomposed more efficiently under the conditions of the present invention.

The effect of adding inert gas in the present invention is as follows: 5T
It appears in the pressure range from orr to 760 Torr.

Generally, when the pressure is low, the growth rate is slow, and when the pressure is high, the plasma shrinks significantly and the deposition area becomes narrow. Therefore, the preferable pressure range is 30 Torr or more and 60 Torr or more.
It is in the range of 0 Torr or less. In order to bring about the effect of increasing the degree of leaf formation with a practical precipitation area (several tens of square millimeters),
A pressure range of 60 Torr or more and 400 Torr or less is more preferable.

In addition to the essential components of hydrogen gas (A), inert gas (B), and carbon-containing compound gas (C), the raw material gas also contains doping gas (D), such as diborane (B, 11.), nitrogen (N
, ), the effect of adding an inert gas appears similarly. In such cases, hydrogen gas (A), inert gas (B), carbon-containing compound gas (C), and doping gas (D) are mixed in such a way that the molar ratio of each gas satisfies the conditions. is preferable.

The brightening effect becomes smaller.

In the vapor phase synthesis of diamond using plasma, the effects of the present invention can be achieved no matter what method is used, but as mentioned above, as a plasma generation source, 500 MI (
It is most preferable to use microwaves of z or higher.

Observation of the average crystal grain size (E) and grown film thickness (F) on the diamond film growth surface obtained by the method of the present invention using an optical microscope and a scanning electron microscope (SEM)1. As a result, the average grain size (E) was 1.5% of the grown film thickness (F). It was found that it is characterized by its relatively large size.

In diamond with such a relatively large crystal grain size, transmission electron microscopy (TEM) observation reveals that diamond crystals are thought to have many crystal defects such as dislocations and precipitation of non-diamond components such as amorphous carbon. It was found that the crystal has few grain boundaries and has low defects.

In addition, it was found to exhibit many properties inherent to diamond, such as high light transmittance based on transmission spectrum measurements in the ultraviolet to infrared region, and high thermal conductivity based on thermal conductivity measurements.

The effect of the crystal grain size is due to the film thickness (
F) is 5μ or higher, and the average crystal grain size (E) and film thickness (F)
This is a case where the following relationship is satisfied: 0.3≦E/E≦3.

E/IF < o, 3 or C3 < E/, ff
ノ[x[[c, the properties of the diamond described above deteriorate.

According to the method of the present invention, diamond in this range can be easily obtained.

The apparatus for diamond synthesis used in the present invention is shown in Figures 1-
It is shown in Figure 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 DC plasma CVD apparatus. In the figure, 1 is a base material, 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 Brantsya, 19 is an RF power source, IO is a DC power supply, II is a substrate support, 12 is an insulating seal, and 13 is a cathode. Generally, quartz tubes have a diameter of 50ix or more.

Next, the effects of the present invention will be specifically explained using Examples and Comparative Examples.

Example 1 Microwave plasma CVD as a diamond synthesis method
(hereinafter referred to as μ-PCVD), high-frequency plasma C
Either the VD method (hereinafter referred to as RF-PCVD) or the direct current plasma CVD method (hereinafter referred to as DC-PCVD) was used (see Tables 1 and 2).As the base material , 40×35Xl (L+!I!3) molybdenum plate was finally polished with 1600 diamond powder.

First, an inert gas was introduced into the quartz tube 2 shown in the drawing from the inlet 4, plasma 5 was generated by a plasma source using a pressure mold roller, and the molybdenum plate was cleaned with the plasma for 5 minutes. Thereafter, plasma CVD was performed under the conditions shown in Tables 1 and 2, and the molybdenum plate was coated with diamond synthesized in a vapor phase.

The surface temperature of the substrate during synthesis was measured using an optical pyrometer and was in the range of 800 to 1200°C.

In addition, regarding the diamond film formed by the plasma CVD method, surface observation and film thickness observation using a scanning electron microscope,
When the crystallinity was evaluated by X-ray diffraction and Raman scattering spectroscopy, the results shown in Tables 1 and 2 were obtained. In addition, in the table, rDiaJ stands for diamond, ra
-cl represents 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 1E force are within the condition range of the present invention, the diamond deposition rate can be increased to a very high rate of, for example, 400 μm/h. It is possible to do so.

On the other hand, outside the condition range of the present invention, even if you try to generate plasma at high pressure without adding an inert gas, plasma will not be generated stably, and even if plasma can be generated, the diamond film will be amorphous carbon. Moreover, the deposition rate is as slow as 2 μth order/h at the maximum.

In addition, when the thermal conductivities of samples No. 1 8 to 22 shown in Table 2 were measured using a thermal conductivity measuring device using a simple thermistor, it was found that the samples manufactured under the conditions of the present invention ranged from 2 W/cmK. A high thermal conductivity of 15 W/crttK was confirmed, whereas it was less than 2 W/cπ in the sample manufactured under comparative conditions.Example 2 A diamond plate (10X I OX 0.2gm3) 40x34xl
Placed on a molybdenum plate with Ox shoulder 3, microphone A wave output 80
Under the conditions of 0W, pressure 300 Torr, hydrogen flow fftl
Microwave plasma cV・D was performed for 3 hours while introducing 1000 scc, 7) L, Bonn flow fi 500 sccM, and ethanol flow rate 40 secM, and the diamond plate was grown to a thickness of 0.2 mm to 1 R true. This diamond plate, like the original sample No. 4 diamond plate, was found to be a (100) preferentially oriented diamond with good crystallinity by X-ray diffraction and Raman spectroscopy.

Example 3 Diameter: 40 mm and thickness: 20 mm. Five single-crystal diamond abrasive grains with a grain size of 25,071 m made by ultra-high pressure method were placed near the center of the dragon molybdenum plate, and an argon flow rate of 20,009 m was placed.
When microwave plasma CVD was performed for 5 hours under the conditions of CCM, hydrogen i1iftml OOosccM1 acetylene flow m20secM, microwave output soow, and pressure 500 Torr, five single crystal abrasive grains each having a diameter of 1 mm were obtained. It was confirmed by X-ray diffraction and Raman spectroscopy that it was a diamond with good crystallinity.

Example 4 A diamond single crystal grain with a diameter of 3 m11 created by an ultra-high pressure method was placed in the center of a 40 x 35 x 10 x m3 molybdenum plate, and a helium flow rate of 2000 SCCM and a hydrogen flow rate of 5 were placed.
009CCM, propane flow rate 20SCCM,? When microwave plasma CVD was performed for 5 hours under the conditions of microwave output 200 W and pressure 600 Torr, the diameter was 4 mm.
It was increasing.

The surface seemed to be slightly graphitized, but as the chromic acid treatment progressed, the euhedral shape of the diamond clearly appeared. This was confirmed to be diamond by X-ray diffraction and Raman spectroscopy.

Example 5 A #6 molybdenum plate with a diameter of 40mm and a thickness of 30Il1m
After polishing with 00 diamond grindstone, argon flowff
1200 S CCM, hydrogen flow ff1200sccM.

Methane flow ff14secM, microwave output 1.5KW
When microwave plasma CVD was performed for 1 hour under the conditions of a pressure cuff of 60 Torr, diamond particles with a diameter of 500 μm were grown in the center of the molybdenum plate. This was confirmed to be diamond by X-ray diffraction and Raman spectroscopy.

Cold storm 1 fight More preferred embodiments of the present invention are shown below.

1. To generate plasma, microwaves with a frequency of IKHz or higher, particularly 500MHz or higher, are used.

2. The carbon-containing compound gas to be used is at least one selected from gaseous aliphatic hydrocarbons, aromatic hydrocarbons, alcohols, thiols, ketones, ethers, carbon oxides, carbon dioxide, etc. under cVD conditions. using compounds.

3. At least one selected from l\\zolium neon, argon, krypton, and xenon is used as the inert gas.

4. Input power for plasma generation, 1w/cy,
' and the pressure is 60 to 400 Torr.

5. The diameter of the reaction tube is 50 JJI or more.

6. The flow rate of the mixed gas in the diamond production reaction section is 0.1 cttr/sec or more and 5 cx/see or less.

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≦
The following conditions are satisfied: □≦0.8 and A + B + C O,005≦□≦0,05 A+B+C.

[Effect of the invention] The method of the present invention has the following effects.

It is possible to synthesize diamond at very high speeds north of several hundred μx/h, and it is possible to synthesize diamond at high speeds of several tens of μm/h while suppressing the decrease in the precipitation area (several tens of square millimeters). can.

In addition, not only diamond film growth but also diamond particle growth1 is selectively stable and fast (several tens of μ71
/+1 or more).

Furthermore, it can be applied to diamond heat noncrite and diamond abrasive grains, which conventionally relied on high-pressure methods, and also has high thermal conductivity, low dielectricity, high light transmittance, high specific elasticity, high strength, and wear resistance. In fields where high performance is required, such as window materials, diaphragms, cutting tools, heat sinks, and IC bonders, diamond is used not only as a thin film (several μm or less) but also as a base material (several tens of μm or more). It becomes possible.

In addition, the method of the present invention can be easily applied to conventional equipment, and is superior in terms of stable operation, equipment cost, and raw material cost, compared to high-temperature plasma equipment that uses a plasma torch or the like.

[Brief explanation of the drawing]

Figure 1 is a microwave plasma CVD equipment, Figure 2 is a high frequency plasma CVD equipment, Figure 3 is a DC plasma CV
FIG. 3 is a schematic diagram of the D device. 1. Base material, 2: Quartz tube, 3: Vacuum exhaust port, 4: Supply gas inlet, 5: Generated plasma, 6 Magnetron, 7: Waveguide,
8 nib run gear, 9: RF power supply, IO: DC power supply, It/substrate support stand, 12: insulation seal, 13: cathode. Patent applicant Sumitomo Electric Industries, Ltd.

Claims (1)

[Claims] 1. Hydrogen gas (A), inert gas (B), and carbon-containing compound gas (C) in a molar ratio of 0.001≦B/(A+B+C)≦0.95 and 0 ．．
A mixed gas containing 001≦C/(A+B+C)≦0.1 is introduced into a reaction vessel, and a plasma is generated by a direct current or alternating current electromagnetic field under a pressure of 5 to 760 Torr to form diamonds on the substrate. A method of vapor phase synthesis of diamond characterized by the formation of . 2. Formed by vapor phase synthesis method, the average crystal grain size (E) and film thickness (F) of the surface diamond film are 0.3≦E/
A diamond that satisfies the relationship: √F≦3 and has a film thickness (F) of 5 μm or more.