JPH0959091A - Diamond crystal and method for producing the same - Google Patents

Abstract

(57) Abstract: A hexahedron consisting of six (100) faces, that is, a dice-shaped diamond, and a manufacturing method thereof are provided. In a diamond crystal manufacturing method for synthesizing a diamond crystal on a substrate 10 that does not bind to carbon by a chemical vapor deposition method, a raw material gas in the chemical vapor deposition method contains at least carbon and hydrogen, and all molecules are included. The number of carbon atoms with respect to the number is 0.3% or less, and the temperature of the substrate 10 is set to 725 ° C. or higher to grow a diamond crystal.
A diamond crystal, which is a substantially hexahedral single crystal composed of the (0) plane, was manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diamond crystal having excellent characteristics for electronic materials, optical materials, tools, hardness measurement, etc., and a method for producing the same.

[0002]

2. Description of the Related Art Diamond has extremely high thermal conductivity, high hardness, high abrasion resistance, extremely high refractive index and reflectance, and electrical conductivity, and has a wide band gap, so that it can be used in ultraviolet light emitting devices and ultraviolet rays. Since it has unique characteristics such as being expected to be a laser, it is used not only as a decorative item but also for hardness meters, tools, abrasives, electronic materials, etc. Applications to materials and semiconductor materials are also being considered.

It is known that diamond has high crystallinity because the density of atoms and the arrangement of atoms are different depending on the crystal plane, and in particular, the (100) plane of diamond is difficult to contain impurities and crystal defects. There is. Therefore, it is expected that the diamond crystal composed of the (100) plane will exhibit the above-mentioned features of diamond more strongly than other planes.

By the way, in recent years, a chemical vapor deposition method (CVD method) for synthesizing diamond from a vapor phase at a low pressure has been studied,
Although developed and various CVD methods have been tried,
Considering the application as described above, it is necessary that the crystal orientation of diamond synthesized by the CVD method can be controlled arbitrarily. However, the crystal orientation of diamond obtained by the CVD method is usually random, and cannot be controlled.

Conventionally, there are a few known techniques for controlling the crystal orientation of diamond synthesized by the CVD method. One of them is the method disclosed in Japanese Patent Laid-Open No. 2-160695, in which a raw material gas containing an organic compound is activated on a copper single crystal substrate to grow a (111) plane parallel to the substrate. This is a method of depositing octahedral single crystal diamond. Another method is disclosed in Japanese Patent Laid-Open No. 5-2
In the method disclosed in Japanese Patent Publication No. 70977, the upper surface has a (111) plane or a (100) plane by reducing the nucleation density and setting an appropriate ratio of oxygen and carbon in the source gas. This is a method of depositing flat diamond.

[0006]

By the way, in order to make more effective use of the characteristics of the (100) plane of diamond as described above, a hexahedron composed of six (100) planes, that is, a dice-shaped diamond is used. preferable.

However, the above-mentioned Japanese Laid-Open Patent Publication No. 2-1606.
Japanese Patent Laid-Open No. 270977/1993.
With the method disclosed in the publication, it is not possible to control the diamond shape so that it has a dice shape. Also,
In the case of a flat plate diamond whose upper surface has a (100) plane as disclosed in Japanese Patent Laid-Open No. 270977/1993, the side surface portion is not necessarily composed of the (100) plane.

Considering optical applications such as an ultraviolet laser, a hexahedron composed of six (100) faces, that is, a dice-shaped diamond, has a higher light trapping efficiency than a flat diamond because of its shape. As expected, excellent properties can be expected.

The present invention has been made in view of the above points, and an object thereof is to provide a hexahedron consisting of six (100) faces, that is, a dice-shaped diamond, and a method for producing the same.

[0010]

In order to achieve the above object, the present invention provides a method for producing a diamond crystal by synthesizing a diamond crystal on a substrate which does not bond with carbon by a chemical vapor deposition method. The source gas in the phase growth method is a gas containing at least carbon and hydrogen, and the ratio of the number of carbon atoms to the total number of molecules is 0.3% or less,
By growing a diamond crystal at a substrate temperature of 725 ° C. or higher, a diamond crystal whose shape is a substantially hexahedral single crystal composed of six (100) faces was manufactured.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below with reference to the drawings.

The embodiment described below is an example of diamond synthesis by the microwave plasma CVD method, and FIG. 1 shows a microwave plasma CVD apparatus which is a diamond synthesis apparatus.

This apparatus has the same structure as that conventionally known, and 1 is a quartz reaction vessel for synthesizing diamond,
Reference numeral 2 is a substrate support provided in the reaction container 1, 3 is a reflecting plate for reflecting microwaves, 4 is a microwave oscillator as an excitation source, and 5 is the microwave generated by the microwave oscillator 4 in the reaction container 1 The waveguide 5 is provided with a power monitor 6 for monitoring the power supplied to the microwave oscillator 4.

In order to synthesize diamond with the above apparatus, the reaction vessel 1 is first evacuated to a high vacuum, and a hydrocarbon gas such as methane, ethane, propane, butane, ethylene and benzene is supplied from the gas inlet 1a as a source gas. A mixed gas of oxygen and hydrogen in a predetermined ratio is introduced into the reaction vessel 1, the microwave oscillator 4 is activated, the microwave is guided to the reaction field F of the reaction vessel 1 through the waveguide 5, and plasma is generated. To do. The pressure in the reaction vessel 1 is maintained at a predetermined pressure by introducing the mixed gas. After that, a substrate supporting base 2 on which a copper plate as a substrate 10 for depositing diamond is placed is put into the plasma formed in the reaction field F in the reaction vessel 1. At this time, the copper plate which is the substrate 10 is subjected to a diamond nucleation treatment. This nucleation treatment may be a conventionally known treatment such as a scratching treatment or a carbon ion implantation treatment. The periphery of the reaction field F of the reaction container 1 is cooled with cooling water. The concentration of the hydrocarbon gas in the source gas is set to a low concentration of 0.3% or less, and the temperature of the substrate 10 is 725 ° C.
Diamond crystals are deposited as described above. The diamond crystal obtained by this method has many (100) orientations, and its shape becomes dice-shaped isolated particles.

Next, a diamond synthesis experiment conducted by the inventors of the present invention will be described.

The microwave plasma CVD apparatus shown in FIG. 1 was used for the experiment. The oscillation frequency of the microwave oscillator 4 is 2450 MHz, and the output is 400 to 600 W. The raw material gas for diamond synthesis was a mixed gas of methane gas, oxygen and hydrogen, and the supply amount of all the raw material gas was constant at 100 ccm (cm ³ / min), and the supply amounts of methane and oxygen were changed. A copper plate was used as the substrate 10 for depositing diamond. The temperature of the copper plate or substrate 10 is 710
The temperature was from ℃ to 750 ℃. The substrate temperature was measured without contact using a radiation thermometer. The emissivity (ε) of the radiation thermometer is 1.0
And

Table 1 shows the results of the experiment.

[0018]

[Table 1] Supply amount (ccm) is shown for methane and oxygen,
Furthermore, the ratio of the number of carbon atoms in the source gas (methane concentration) CNR and the atomic number ratio of carbon and oxygen (C: O) are shown. In the present invention, "the ratio C of the number of carbon atoms C
“NR” is represented by Formula 1.

[0019]

## EQU1 ## Ratio of number of carbon atoms CNR (%) = (supply amount of carbon compound) × (number of carbon atoms in one molecule of carbon compound) / supply amount of source gas = (number of molecules of carbon compound) × ( (Number of carbon atoms in one molecule of carbon compound) / total number of molecules of raw material gas = number of carbon atoms / total number of molecules of raw material gas Next, the experimental results shown in Table 1 are summarized.

Experiment No. In 1, CNR is 0.2%,
The substrate temperature was set to about 750 ° C. The diamond crystals obtained in this experiment had many grains of (100) orientation, and the crystals had a dice shape with a large (100) plane.

Experiment No. In 2, CNR is 0.3%,
The substrate temperature was set to about 750 ° C. The diamond crystals obtained in this experiment consist of (100) oriented grains and (111) oriented grains.
The number of oriented particles is almost the same, and the crystal shape is (100).
It was a dice with a large surface.

Experiment No. In 3, set CNR to 1.0%,
The substrate temperature was set to about 750 ° C. The diamond crystals obtained in this experiment had many grains of (111) orientation, and the crystal shape was a hexaoctahedron in which (111) faces and (100) faces were approximately the same.

Experiment No. In 4, CNR is 2.0%,
The substrate temperature was set to about 750 ° C. The diamond crystals obtained in this experiment have a large number of grains with a (111) orientation, and the crystal shape is a hexaoctahedral with a (111) face and a (100) face that are approximately the same, and a large plate with a (111) face. It was a shape.

Experiment No. In 5, CNR is 0.4%,
The substrate temperature was set to approximately 710 to 720 ° C. The diamond crystal obtained in this experiment had many grains of (111) orientation, and the crystal shape was plate-like with a large (111) plane.

Experiment No. In 6, CNR is 1.0%,
The substrate temperature was set to approximately 710 to 720 ° C. The diamond crystal obtained in this experiment had many grains of (111) orientation, and the crystal shape was plate-like with a large (111) plane.

Experiment No. In 7, the CNR is 2.0%,
The substrate temperature was set to approximately 710 to 720 ° C. The diamond crystal obtained in this experiment had many grains of (111) orientation, and the crystal shape was plate-like with a large (111) plane.

Considering on the basis of the above experimental results, the concentration of the hydrocarbon gas in the raw material gas is set to a low concentration of 0.3% or less, and the substrate temperature exceeds 720 ° C., for example, 7.
It can be seen that when the temperature is 25 ° C. or higher, diamond crystals having a (100) orientation and a dice shape are deposited.
If the concentration of the hydrocarbon gas in the source gas is too low, the diamond nuclei formed on the substrate 10 are etched and the diamond is not deposited. Therefore, the concentration of the hydrocarbon gas should be low enough not to be etched. .

By the way, when the concentration of the hydrocarbon gas in the raw material gas is set to a low concentration of 0.3% or less to deposit the diamond, the growth rate of the diamond becomes very slow. Therefore, a method for solving this growth rate problem will be described below.

It is known that when a nucleus formed on a substrate made of a material which does not bond with carbon, for example, a copper plate is grown to deposit diamond, the diamond crystal moves, rotates, or tilts on the substrate. While the size of the diamond crystal is smaller than about 50 nm, movement on this substrate is active, and the size is about 500 n.
Almost no exercise occurs when the distance exceeds m. Therefore, if the above-mentioned concentration condition is maintained until the size of the diamond crystal exceeds about 50 nm, the crystal orientation hardly changes even if the concentration condition is changed thereafter, and the (100) orientation Diamond crystals can be obtained.

2 (a) to 2 (e) are views showing changes in the shape and orientation of diamond crystals in the method for producing diamond crystals of the present invention.

FIG. 2 (a) is a diagram showing a state in which diamond nuclei 11 are formed on the substrate 10, and in this state no orientation occurs. When the diamond deposition is performed under the concentration condition of reducing the concentration of the hydrocarbon gas as described above from the state shown in FIG. 2 (a) to a low concentration of 0.3% or less, FIG.
As shown in, the (100) plane is preferentially generated, and the diamond crystal becomes a hexahedron composed of six (100) planes. In this state, the size of diamond crystal is about 50n
Since it is less than m, the movement on the substrate is actively performed, but since the diamond crystal face is rotated and tilted so that the face having the largest area comes into contact with the substrate 10, FIG. (100) orientation as shown in ().

When the size of the diamond crystal exceeds about 50 nm, the movement of the diamond crystal on the substrate becomes inactive, so the hydrocarbon gas concentration is changed from a low concentration of 0.3% or less to 0.4 or less at this timing. Continue to deposit diamond while changing to a high concentration of 10% or more. Then, although the growth rate is increased, the (100) plane is already large and the movement of the diamond crystal on the substrate is not active, so that the diamond crystal continues to grow in the (100) orientation.
The diamond crystal thus grown to a desired size becomes a hexaoctahedral with some (111) faces, as shown in FIG. 2 (d).

Even this hexa-octahedral diamond crystal close to a dice has great potential for future use.
Further, in order to obtain a diamond crystal closer to a regular hexahedron, the concentration of the hydrocarbon gas is reduced again to a low concentration of 0.3% or less and diamond precipitation is continued. Then, Figure 2
As shown in (e), the (100) plane becomes larger and a dice diamond crystal closer to a regular hexahedron can be obtained.

The embodiment of the present invention has been described above. As the raw material gas for synthesizing diamond which can be used in the present invention, hydrocarbons such as methane, ethane, propane, butane, hexane, ethylene, benzene and acetylene are used. Mixed gas of hydrogen gas with hydrogen gas, mixed gas of oxygen gas or carbon dioxide, mixed gas of oxygen-containing organic compounds such as methanol, ethanol, acetone and hydrogen gas, carbon monoxide and hydrogen gas Mixed gas can be used. The carbon component which is a constituent component of the raw material gas used for the synthesis of diamond according to the present invention does not depend on the kind of the carbon compound.

Although a copper plate is used as the substrate in this embodiment, the reason why the diamond crystals are oriented is as described above, and therefore, a material having the same behavior at the time of orientation of the diamond crystals, that is, carbon and a bond, are bonded. If the substrate is made of a material (for example, platinum, gold, or silver), it can be used in place of the copper plate. Further, the substrate that can be used in the present invention is not only a solid metal material but also a material stable in an environment for synthesizing diamond such as silicon, silicon oxide, silicon nitride, silicon carbide, sapphire, molybdenum, and tungsten. PVD methods such as vapor deposition, sputtering, ion beam film formation and ion plating,
A thin film of copper, gold, silver, platinum or the like formed by the CVD method or plating may be used.

In the present embodiment, diamond is synthesized by the plasma CVD method using microwave plasma, but the present invention can utilize direct current discharge plasma, thermal plasma, high frequency thermal plasma, or hot filament CVD method. The electron impact CVD method, the arc jet method, etc. can also be used.

[0037]

As described above, according to the present invention,
It is possible to produce hexahedral or dice diamonds consisting of six (100) faces.

Further, according to the present invention, there is an effect that the time required to obtain a dice diamond can be shortened.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a microwave plasma CVD apparatus for producing a diamond crystal according to the present invention.

2 (a) to (e) are diagrams showing changes in the shape and orientation of a diamond crystal in the method for producing a diamond crystal of the present invention.

[Explanation of symbols]

 1 Reaction Vessel 2 Substrate Support 3 Reflector 4 Microwave Oscillator 5 Waveguide 6 Power Monitor 10 Substrate 11 Nuclear

Claims (9)

[Claims] 1. A (100) -oriented diamond crystal synthesized on a substrate by chemical vapor deposition, comprising:
A diamond crystal whose shape is a substantially hexahedral single crystal composed of six (100) faces. 2. A method for producing a diamond crystal, which comprises synthesizing a diamond crystal on a substrate which does not bind to carbon by a chemical vapor deposition method, wherein the source gas used in the chemical vapor deposition method contains at least carbon and hydrogen, and A gas having a ratio of the number of carbon atoms to the number of molecules of 0.3% or less is used, and the temperature of the substrate is set to 72.
The method for producing a diamond crystal according to claim 1, wherein the diamond crystal is produced by growing the diamond crystal at 5 ° C. or higher. 3. A method for producing a diamond crystal by synthesizing a diamond crystal on a substrate that does not bind to carbon by a chemical vapor deposition method, wherein the source gas in the chemical vapor deposition method contains at least carbon and hydrogen, and A gas having a ratio of the number of carbon atoms to the number of molecules of 0.3% or less is used, and the temperature of the substrate is set to 72.
At 5 ° C. or higher, the diamond crystal is grown until the diamond crystal does not actively move on the substrate, and then the ratio of the number of carbon atoms to the total number of molecules of the raw material gas is increased to grow the diamond crystal, Then, the ratio of the number of carbon atoms to the total number of molecules of the raw material gas is adjusted to 0.3% or less again to adjust the shape of the diamond crystal, thereby producing the diamond crystal according to claim 1. Diamond crystal manufacturing method. 4. The substrate according to claim 2, which is a copper plate.
The method for producing a diamond crystal according to 1. 5. The method for producing a diamond crystal according to claim 2, wherein the source gas contains methane gas. 6. The method for producing a diamond crystal according to claim 2, wherein the source gas contains oxygen, and the ratio of oxygen atoms to carbon atoms in the source gas is 1: 1. . 7. The method for producing a diamond crystal according to claim 1, wherein the source gas is activated by plasma having a high frequency, a direct current or a microwave as an excitation source. 8. The method for producing a diamond crystal according to claim 1, wherein the source gas is activated by a hot filament. 9. The method for producing a diamond crystal according to claim 1, wherein the source gas is activated by an arc jet.