JP3350992B2 - Diamond synthesis method - Google Patents

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, and more particularly to a method for synthesizing a relatively large diamond single crystal used for cutting tools, wear-resistant tools, precision tools, semiconductor materials, electronic parts, optical parts and the like. Things.

[0002]

2. Description of the Related Art Diamond has high hardness, high thermal conductivity,
Since it has many excellent properties such as transparency, it is widely used as a material for various tools, optical components, semiconductors, electronic components and the like, and it is considered that its importance will further increase in the future.

[0003] Diamond has the highest hardness among substances known so far, is a very good insulator electrically, has a high thermal conductivity, and is about five times as high as copper at high temperatures. It also has excellent properties such as showing value.

[0004] Also, diamond has characteristics such as good light transmittance over a wide wavelength range of ultraviolet, visible, and infrared except for a part of the infrared region, and further, it becomes a semiconductor by adding impurities.

Utilizing these properties, diamond has already been applied to coatings on tool surfaces, electronic materials, and particularly to heat sinks such as LSIs used in high-power semiconductor lasers. Further, application of diamond as a high-temperature semiconductor operable even in a high-temperature region has been considered.

In the past, diamonds produced naturally have been used for industrial purposes in the past, but now diamonds are mainly artificially synthesized.

[0007] At present, all single crystals of diamond are synthesized under a pressure of tens of thousands of atmospheres or more at which they are stable. Ultrahigh pressure vessels that generate such large pressures are very expensive and have a limited internal volume. For this reason, it is very difficult to grow a large-area diamond single crystal, which is a cause that single-crystal diamond cannot be supplied at low cost.

[0008] On the other hand, diamonds having a relatively large area have been artificially manufactured using a vapor phase synthesis method, but these are all made of a polycrystalline thin film and have a good quality of a thickness of several tens μm or more. No crystalline diamond has been obtained.

Usually, when a diamond thin film is formed by vapor phase synthesis, the substrate is often scratched in advance by diamond grains. It is understood that the effect of promoting the growth of the diamond thin film by the scratching is because diamond small crystal fragments remain on the substrate and the diamond is grown using this as a seed crystal. (S. Iijima, Y. Aikawa and
K. Baba: Appl. Phys. Lett. 57
(1990) 2646. ). Since the diamond small crystal pieces left on the substrate after the scratching are mixed with those oriented in various directions, the diamond thin film grown as a seed crystal using this becomes a polycrystalline film.

However, it is indispensable to use single-crystal diamond having a uniform crystal orientation for ultra-precision tools, optical parts, semiconductors, and the like that require a particularly smooth surface among diamond applications. Therefore, conditions for epitaxially growing a large and single crystal diamond by a vapor phase synthesis method have been studied.

However, hitherto, a method of heteroepitaxially growing diamond on a heterogeneous substrate by a vapor phase synthesis method has not been successful. This is due to the fact that the lattice constant and the thermal expansion coefficient of the diamond and the dissimilar substrate are different, so that distortion is likely to occur and only a single crystal having many defects can be obtained. Therefore, a technique for homoepitaxially growing diamond on the same type of diamond substrate by a vapor phase synthesis method has been studied.

For example, as disclosed in Japanese Patent Application Laid-Open No. Hei 2-131994, a single crystal diamond of mm order obtained by a high-pressure synthesis method is arranged in a uniform crystal orientation to form a substrate, and an integrated single crystal is formed on the substrate surface. There is a way to get a diamond.

[0013]

However, in such a method, a crystal plate is cut out of a single crystal diamond so that a desired crystal orientation is a growth surface, and the side surface is polished so as to be perpendicular to the growth surface. Were arranged side by side and used as a substrate, the crystal orientation in a plane parallel to the growth plane of the adjacent diamond crystal plate was likely to vary, and it was difficult to align the crystal orientation in the substrate in one direction. .

For this reason, if a diamond layer is homoepitaxially grown on the substrate surface by vapor phase synthesis to obtain an integrated diamond alone, a polycrystalline component may be formed at the junction of the grown layers on each diamond crystal plate. In addition, problems such as twins and defects increase.

Therefore, it has been an important issue how to minimize the deviation of the crystal orientation between diamond crystal plates.

The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to provide a method for synthesizing a diamond capable of obtaining a homogeneous and large-sized single crystal diamond by vapor phase synthesis. I do.

[0017]

A method for synthesizing diamond according to the present invention is a method for synthesizing diamond in a vapor phase, wherein a diamond crystal exhibiting an automorphic shape grown under high pressure is grown on a growth surface during growth under high pressure. A plurality of diamond crystals are produced by cutting parallel to one of the diamond crystals, and the diamond crystals are brought into contact with each other on the respective self-formed surfaces to form a plurality of diamond crystals. Appearing and forming an aggregated surface in which multiple surfaces parallel to one of the growth surfaces and exhibiting almost the same crystal orientation are connected in a plane, and diamond is vapor-phase grown on the aggregated surface to obtain an integrated diamond film It is characterized by.

In the present invention, “a diamond crystal having an automorphic shape” means that when diamond grows freely without being hindered by external conditions, it is completely formed by a unique crystal plane governed by the symmetry of the crystal structure. Can be defined as a diamond crystal having a crystal form surrounded by.

In the present invention, the diamond crystal having an automorphic shape grown under a high pressure includes a natural diamond crystal and a diamond crystal artificially synthesized under a pressure of 50,000 atm or more according to an ordinary ultra-high pressure synthesis method. Either one can be preferably used.

Usually, a diamond crystal exhibiting an automorph is:
For example, as shown in FIG. 1 or FIG.
It is considered to have a polyhedral structure composed of a (0) plane and eight (111) planes (referred to as a hexahedron in the present invention).

In the present invention, one of the growth surfaces during growth under high pressure is (10) as shown in the following examples.
It is most preferable to select the 0) plane.

(10)
The 0) plane has the simplest structure, and has relatively good workability. Therefore, by selecting this surface as one of the growth surfaces, there is an advantage that the production of a plurality of diamond crystals by cutting can be facilitated. In addition, by selecting the (100) plane as one of the growth planes, a plurality of planes appearing on the surfaces of the plurality of diamond crystals, respectively, and being parallel to one of the growth planes and having substantially the same crystallographic orientation [100] are planar. An aggregated surface connected in a shape can be formed. Thereby, a diamond layer having a relatively smooth surface can be grown on the collecting surface by vapor phase growth.

As one of the growth surfaces of the diamond single crystal, the (111) plane can be selected in addition to the (100) plane.

In the present invention, a hexahedral diamond crystal as shown in FIG. 1 is one of the growth surfaces (100).
When a plurality of diamond crystals having a shape as shown in FIG. 2 are manufactured by cutting parallel to the plane, for example, as shown in FIG. By making contact with one (111) of the self-shaped planes formed on the surface, a plurality of planes each appearing on the surface of a plurality of diamond crystals and showing substantially the same crystal orientation [100] are connected in a plane. An assembly surface can be formed.

On the other hand, by cutting a hexahedral diamond crystal as shown in FIG. 5 in parallel with the (100) plane which is one of the growth surfaces, a plurality of diamonds having a shape as shown in FIG. When a crystal is manufactured, for example, as shown in FIG. 7, a plurality of diamond crystals are brought into contact with each other at one (100) of the self-shaped surfaces formed on the respective surfaces, thereby forming a plurality of diamond crystal surfaces. , And a plurality of planes each having substantially the same crystal orientation [100] are connected in a plane to form an aggregated plane.

In the present invention, as a method for growing diamond by vapor phase, for example, thermal CVD, plasma C
Examples include a CVD method such as a VD method, a microwave CVD method, an optical CVD method, and a laser CVD method, sputtering, and an ion beam evaporation method.

More specifically, the method of decomposing and exciting the source gas to vapor-grow the diamond on the collecting surface is as follows. For example, (1) Thermionic emission material is heated to a temperature of 1500 K or more to convert the source gas. Activation method, (2)
There are a method using a discharge by a DC wave, an AC wave or a microwave electric field, (3) a method using ion bombardment, (4) a method of irradiating light such as a laser, and (5) a method of burning a source gas. .

A carbon-containing compound is generally used as a raw material used for vapor-phase growth of diamond.
This carbon-containing compound is preferably used in combination with hydrogen gas. If necessary, an oxygen-containing compound and / or an inert gas may be added to the source gas.

Examples of the carbon-containing compound include paraffinic hydrocarbons such as methane, ethane, propane and butane, olefinic hydrocarbons such as ethylene, propylene and butylene, acetylene hydrocarbons such as acetylene and allylene, and butadiene. Diolefinic hydrocarbons, alicyclic hydrocarbons such as cyclopropane, cyclobutane, cyclopentane and cyclohexane, aromatic hydrocarbons such as cyclobutadiene, benzene, toluene, xylene and naphthalene, ketones such as acetone, diethyl ketone and benzophenone , Alcohols such as methanol and ethanol, amines such as trimethylamine and triethylamine, carbon dioxide and carbon monoxide. One of these can be used alone, or two or more can be used in combination. Further, the carbon-containing compound may be a substance consisting only of a carbon raw material such as graphite, coal, coke and the like.

As the oxygen-containing compound to be added to the raw material gas, hydrogen, water, carbon monoxide, carbon dioxide, or hydrogen peroxide is preferable because it can be easily obtained.

As the inert gas that can be added to the source gas, for example, argon, helium, neon, krypton, xenon, or radon can be used.

[0032]

In a diamond crystal exhibiting an automorphic shape grown under high pressure, microscopic defects such as steps at the atomic level are slightly present particularly on a low-index growth surface such as a (100) plane or a (111) plane. However, there is almost no deviation in the plane orientation.

Therefore, in the method for synthesizing diamond according to the present invention, a diamond crystal exhibiting an automorphic shape grown under high pressure is first replaced with one of the low-index growth surfaces such as (100) plane during growth under high pressure. By cutting the diamond crystal in parallel to, a plurality of diamond crystals with little deviation of the plane orientation are manufactured.

The plurality of diamond crystals thus obtained respectively appear on the surface of the diamond crystal, and are parallel to one of the growth surfaces and have substantially the same crystal orientation [1].
00].

Next, a plurality of diamond crystals are aligned with each other in a crystallographic orientation [100] which is parallel to substantially one of the automorphic planes, ie, one of the growth planes or one of the growth planes formed on the plurality of diamond crystals. By making contact on surfaces other than the plurality of surfaces shown, almost the same crystal orientation [10
[0] can be obtained.

Since the plurality of diamond crystals constituting the substrate are stably arranged by surface contact on a self-shaped surface having a uniform plane orientation, the relative positions of the plurality of diamond crystals are relatively small when the diamond is vapor-phase grown. There is almost no displacement or the like, whereby the displacement of the crystal orientation in the collective plane can be kept extremely small.

Therefore, if diamond is epitaxially grown on the gathering surface by vapor phase synthesis, a large single crystal diamond film having only small-angle grain boundaries can be integrally formed.

[0038]

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 In this example, a hexaoctahedral Ib type diamond single crystal 1 prepared by high-pressure synthesis as shown in FIG. 1 was prepared. The diamond single crystal 1 was grown on its (100) plane 1
Sliced in parallel to a, and as shown in FIG.
m diamond crystal plate 2 was obtained. The deviation between the plane orientation of the cut surface of the obtained diamond crystal plate 2 and [100] is as follows:
It was confirmed by X-ray diffraction that it was within 0.05 degrees.

Two diamond crystal plates 2 having the (100) plane 1a and the cut surface mirror-polished are prepared, and one of the diamond crystal plates is turned over, and as shown in FIG. Were arranged so as to be in contact with each other on the (111) plane to obtain a substrate 3 for vapor phase growth.

By a known microwave plasma CVD method, methane 3%, hydrogen 71%, oxygen 1%, argon 25
% And the gas pressure is 80To.
A diamond thin film was grown on the substrate 3 under the conditions of rr and a substrate temperature of 900 ° C. for 500 hours.

After the diamond was grown, the substrate 3 was taken out and examined. The thickness of the substrate 3 was about 500 μm.
Diamond thin film was growing.

When the misalignment between the plane orientations of the two diamond crystal plates 2 and 2 'arranged by using a measuring method utilizing electron beam diffraction was examined, the deviation was suppressed to within 0.05 degrees. .

The growth surface of the integrated diamond thin film was mirror-polished, and the substrate 3 was removed by polishing to obtain an integrated single diamond 4 having a thickness of 450 μm as shown in FIG. Observation with the naked eye revealed no particularly strong reflection or the like at the joint surface of the diamond thin films grown on the two diamond crystal plates 2, 2 '.

Further, the surface of the sample composed of the diamond alone 4 was polished and the surface was observed by STM (scanning tunneling electron microscope). As a result, although a small-angle grain boundary was present at the junction of the grown diamond layer, polycrystal was found. It was confirmed that no component or amorphous component was present.

Example 2 In this example, a hexaoctahedral Ib type diamond single crystal 5 prepared by high-pressure synthesis as shown in FIG. 5 was prepared. The diamond single crystal 5 is grown on its (100) plane 5
Sliced in parallel to a, and as shown in FIG.
m diamond crystal plate 6 was obtained. The deviation between the plane orientation of the cut surface of the obtained diamond crystal plate 6 and [100] is as follows:
It was confirmed by X-ray diffraction that it was within 0.1 degree.

Nine diamond crystal plates 6 having the (100) plane 5a and the cut surface mirror-polished are prepared, and the diamond crystal plates 6 are arranged so as to be in contact with the (111) plane as shown in FIG. A growth substrate 7 was obtained.

By a known microwave plasma CVD method, methane 5%, hydrogen 69%, oxygen 1%, argon 25
% And a gas pressure of 75To.
A diamond thin film was grown on the substrate 7 for 500 hours under the conditions of rr and a substrate temperature of 1050 ° C.

After the diamond was grown, the substrate 7 was taken out and examined.
m of diamond thin film had been grown.

When the displacement between the plane orientations of the nine diamond crystal plates 6 arranged was examined by a measurement method utilizing electron beam diffraction, it was found to be as small as 0.2 degrees at the maximum.

The growth surface of the integrated diamond thin film was mirror-polished, and the substrate 7 was removed by polishing to obtain an integrated diamond single piece having a thickness of 800 μm.
Observation with the naked eye revealed no particularly strong reflection or the like at the joint surface of the diamond thin films grown on the nine diamond crystal plates 6.

Further, when the surface of the sample consisting of diamond alone was polished and observed by STM, a small angle grain boundary was present at the joint of the grown diamond layer.
It was confirmed that there was no polycrystalline component or amorphous component.

Comparative Example In the comparative example, as shown in FIG. 8, natural diamond was grown on the (100) plane and the side face was almost (110).
Four commercially available diamond substrates 8 were formed and polished to a size of 3 mm long × 3 mm wide × 1 mm thick so as to form a surface.

The plane orientation of the diamond substrate 8 and [10
0] was confirmed by X-ray diffraction to be about 3 degrees.

As shown in FIG. 9, four diamond substrates 8 were arranged in two rows each in the vertical and horizontal directions so as to be almost in contact with each other on the (110) plane.

By a known microwave plasma CVD method, methane 3%, hydrogen 71%, oxygen 1
%, And the raw material gas is supplied so as to be 25% argon.
At a gas pressure of 100 Torr and a substrate temperature of 900 ° C., a diamond thin film was grown on the substrate 9 for 500 hours.

After the diamond was grown, the substrate 9 was taken out and examined.
Diamond thin film was growing.

The displacement between the plane orientations of the four placed diamond substrates 8 was measured using a measuring method utilizing electron beam diffraction, and was about 3 degrees.

The growth surface of the integrated diamond thin film was mirror-polished, and the substrate 9 was removed by polishing to obtain an integrated single diamond having a thickness of 400 μm.
Observation with the naked eye revealed that a brown layer was formed at the joint surface of the diamond layers grown on the four diamond substrates 8.

Further, a part of the sample composed of diamond alone was sliced by polishing and ion milling, and the joint was observed by a TEM (transmission electron microscope).
It was confirmed that an amorphous layer having a thickness of nm to 1 μm was formed.

[0061]

As described above, according to the present invention, a diamond is formed by using a plurality of diamond crystals cut parallel to one another on a growth surface from a diamond crystal having an automorphic shape grown under high pressure. By bringing the crystals into contact with each other on an automorphic plane, the misorientation in the plane of aggregation consisting of multiple planes can be kept extremely small. Although a field exists, it does not contain any polycrystalline component, and it is possible to easily obtain a single diamond of good quality and large area, which is homogeneously fused with each other on the gathering surface and integrated as a whole.

In the present invention, since diamond is synthesized by vapor phase synthesis, the growing diamond crystal can be easily doped with impurity elements such as boron and nitrogen. Therefore, the present invention can be widely applied to the production of various diamonds applicable to applications such as precision tool cutting edges, wear-resistant tools, heat-resistant tools, semiconductor substrates, heat-radiating substrates, high-pressure semiconductor materials, optical materials, and acoustic diaphragms. .

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a diamond crystal having a self-form grown under high pressure conditions.

FIG. 2 is a schematic view showing a diamond crystal cut from the diamond crystal shown in FIG.

FIG. 3 is a schematic view showing a substrate for vapor phase synthesis composed of the diamond crystal shown in FIG.

FIG. 4 is a schematic diagram showing a single diamond synthesized on the substrate for vapor phase synthesis shown in FIG.

FIG. 5 is a schematic diagram showing another example of a diamond crystal exhibiting an automorphic shape grown under high-pressure synthesis.

FIG. 6 is a schematic diagram showing a diamond crystal cut from the diamond crystal shown in FIG.

FIG. 7 is a schematic diagram showing a substrate for vapor phase synthesis made of the diamond crystal shown in FIG.

FIG. 8 is a schematic diagram showing a diamond crystal cut from a natural diamond crystal grown under high pressure conditions according to a conventional method.

FIG. 9 is a schematic diagram showing a substrate for vapor phase synthesis composed of the diamond crystal shown in FIG. 8 according to a conventional method.

[Explanation of symbols]

 1,5 diamond single crystal 1a, 5a (100) plane 2,2 ', 6 diamond crystal plate 3,7 vapor growth substrate 4 diamond alone Note that in each figure, the same reference numerals indicate the same or corresponding parts.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-1399091 (JP, A) JP-A-3-75298 (JP, A) JP-A-4-89393 (JP, A) JP-A-1- 103994 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C30B 29/04

Claims (1)

(57) [Claims] 1. A method for synthesizing diamond in a gas phase, comprising cutting a diamond crystal having a self-form grown under high pressure in parallel with one of the growth surfaces during the growth under high pressure. By fabricating a plurality of diamond crystals, by bringing the plurality of diamond crystals into contact with each other on a self-formed surface, each appears on the surface of the plurality of diamond crystals, and is parallel to one of the growth surfaces. A plurality of surfaces exhibiting substantially the same crystal orientation are connected in a plane to form an aggregated surface, and diamond is vapor-phase grown on the aggregated surface to obtain an integrated diamond film. Method.