JPH0480876B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for synthesizing diamonds used for abrasive materials, cutting materials, etc., and particularly to a method for synthesizing diamonds with uniform particle size.

Conventional technology The diamond synthesis method consists of the so-called static pressure method, in which carbon and a catalyst are synthesized at high temperatures and high pressures in the diamond stability range, and the so-called gaseous method, in which hydrocarbon gas is brought into a plasma state using radio frequency waves, microwaves, etc., and diamond is deposited on a substrate. There is a method using phased method (CVD). The former generally yields granular diamonds or diamond sintered bodies, and the latter generally yields film-like diamonds.

For granular diamonds, large grains are desirable, and grain sizes are preferably as uniform as possible. There is a method of arranging diamond seeds in a synthesis system in order to increase the size of diamond grains, and it has also been proposed to arrange seeds regularly in order to make the grain size uniform (Japanese Patent Application Laid-Open No. 169994/1983). The regular arrangement is, for example, a method in which small holes are made at predetermined intervals on a nickel plate serving as a catalyst, seeds are charged into the holes, and a large number of these and carbon plates are stacked one on top of the other. Although this method yields relatively large diamonds with uniform grains, it requires seeds, and large seeds pose problems in terms of heat resistance and strength due to the consistency at the interface between the seeds and the growth layer. Also, if fine seeds are used, the problem in terms of strength disappears, but there is a problem in that special operations are required to arrange the fine seeds.

Problems to be Solved by the Invention The present invention solves the above-mentioned problems when diamond seeds are placed in the synthesis system in diamond synthesis using the hydrostatic method. The objective is to obtain diamond grains with a large target grain size.

Means for Solving Problems The present invention combines a diamond synthesis method using a gas phase method and a static pressure method.First, fine particles such as diamond nuclei are precipitated in a dispersed manner on a substrate by the gas phase method, preferably in a predetermined manner. This is a method in which diamond is precipitated at intervals, and then using this seed as a seed, diamond is synthesized from carbon (non-diamond carbon, graphite, hereinafter referred to as "carbon") and a diamond synthesis catalyst using a hydrostatic pressure method.

In diamond synthesis using the vapor phase method, for example, a silicon wafer is used as a substrate, hydrocarbons are brought into a plasma state using microwaves, etc., and diamond is deposited on the substrate.However, if the silicon wafer is in a mirror-like state, most diamonds are deposited. do not. However, it has been discovered that when a small scratch is made on this silicon wafer, diamond nuclei are first formed at the scratch, and these diamond nuclei gradually grow.
This means that diamond particles can be deposited at desired locations on the substrate.

The present invention takes advantage of this phenomenon. First, a large number of scratches are made on a substrate, diamond synthesis is performed using a vapor phase method, fine particles such as diamond nuclei are precipitated at predetermined points, and these are used as seeds to synthesize diamond using a static pressure method. This method uses diamond synthesis to grow seeds.

As described in Japanese Patent Application Laid-Open No. 59-3098, vapor phase diamond synthesis combines the thermal decomposition of hydrocarbons under reduced pressure, arc discharge, and sputtering techniques to generate a positive carbon ion beam. Ion beam method in which diamond is precipitated by collision with a substrate; Microwave method and plasma in which diamond is precipitated on a heated substrate by turning a mixed gas containing hydrocarbon and hydrogen gas into a plasma state using microwaves or high frequency waves. The law is known.

The present invention can be applied to any of these known methods, but in an embodiment using a microwave method as an example, methane, ethane, propane, ethylene, benzene, etc. can be used as the hydrocarbon.
These are used diluted with hydrogen or hydrogen and an inert gas. Usually, silicon wafers are often used as substrates when forming diamond films because their coefficient of thermal expansion is close to that of diamond, but in the present invention, it is sufficient to attach fine diamond particles to the substrate, so the substrate It's not limited to silicon. However, to make it easier to control nucleation, it is best to use a single crystal with a mirror finish.
Since the substrate is then used for diamond synthesis using the hydrostatic method, the substrate itself may be made of a diamond synthesis catalyst, such as a metal such as nickel, chromium, cobalt, or an alloy thereof.

The substrate is scratched with a diamond needle, for example, at the point where the diamond fine particles are to be deposited. The scratches may be made randomly at appropriate intervals, but preferably they should be at equal intervals, and the intervals should be within the range where each particle does not come into contact with each other when the diamond is grown using the static pressure method in the next step, i.e., the grown diamond particles. The diameter should be greater than or equal to the diameter of The scratches can be made by tapping lightly with a diamond needle, or in the case of random scratches, by projecting fine particles of abrasive material, and it is effective if the scratches are only slightly visible under a microscope.

In order to deposit diamond fine particles onto this substrate using microwaves, the hydrocarbon-containing gas is used, the gas is brought into a plasma state under reduced pressure, and the substrate is heated. Microwave ranges from 300MHz to 10GHz, vacuum ranges from 10 to 50Torr, substrate temperature from 700 to 1000
A range of ℃ is appropriate. In the present invention, it is sufficient that the precipitation time is 30 minutes or more, since it is sufficient to precipitate the fine particles that serve as the core. The upper limit is not particularly limited, but it is preferably 1 hour or less in order to prevent precipitation on areas other than scratches on the substrate and in consideration of economic efficiency. In this way, fine diamond particles of about 0.5 μm to 1 μm are precipitated.

Next, using this substrate, diamond is synthesized by the static pressure method. For synthesis, when using a substrate other than a diamond synthesis catalyst such as a silicon wafer, a thin plate of the diamond synthesis catalyst is layered on the diamond particle side of the substrate, and a thin plate of carbon is layered on top of that, and a large number of these are stacked. It is carried out by loading it into a high-temperature, high-pressure device. In this case, the catalytic metal and carbon may be powdered and mixed to form a molded body, and a large number of molded bodies may be laminated alternately with the substrate. Further, in the case of a diamond catalyst metal plate on which diamond fine particles are deposited, a large number of such plates and carbon plates may be stacked alternately. As the synthesis catalyst, known iron, cobalt, nickel, chromium, tantalum, etc. and alloys can be used, and the temperature is 1400 to 2000℃ and the pressure is 50℃.
A range of ~60Kb is suitable.

After synthesis, metals are dissolved and removed using acids, etc., and unreacted graphite is removed by treatment with sulfuric acid, nitric acid, aqua regia, etc., according to conventional methods.

In the present invention, since fine diamond particles that have been dispersed in advance are mainly grown, the growth is easy and the structure is more uniform than that of coarse seeds, especially when the fine particles are regularly arranged. This tendency is strong.

In diamond precipitation using the vapor phase method, by controlling the precipitation conditions, it is possible to selectively grow diamond crystal planes. That is, if the substrate temperature is set high, grains will grow preferentially on the (111) plane of the diamond crystal, and on the other hand, if the substrate temperature is set low, grains will grow preferentially on the (100) plane.
If diamond is synthesized by the static pressure method using a diamond-precipitating substrate on which these specific planes have grown, grains will similarly be obtained in which the crystal planes mentioned above have grown preferentially.
That is, the method of the present invention has the advantage that a specific crystal face of diamond can be selectively grown.

Example Dotted scratches were made on the mirror surface of a silicon wafer with a diameter of 25 mm and a thickness of 0.1 mm at intervals of 0.5 mm in the vertical and horizontal directions using a diamond needle. The damage is 100μ from a height of 10cm.
It is sufficient to use the same force as when a diamond grain falls.

Using this substrate, diamond was deposited using microwaves under the following conditions.

Pressure: 30 Torr Gas composition: CH ₄ 1%, H ₂ 99% (volume) Substrate temperature: 850°C Microwave: 2.45 GHz Time: 30 minutes Diamond particles of approximately 0.5 μm in size are on the wafer surface taken out after the reaction. Two to five particles were precipitated at the scratched points on the substrate.

Using this wafer, diamond was synthesized by the static pressure method as follows.

A Ni-Fe alloy (30% by weight Ni) plate with a diameter of 25 mm and a thickness of 0.25 mm was used as a catalyst, and this was stacked on the diamond precipitation side of the silicon wafer, and a graphite plate with a diameter of 25 mm and a thickness of 1.0 mm was further placed on top of it. Layered. Twenty-six sets of these three-layer structures were stacked and loaded into a belt-type high-pressure device.

The synthesis conditions were as follows: After setting the pressure to 52 Kb, the temperature was raised to 1450°C and held for 2 minutes. After that, the pressure was gradually increased to 58Kb over 30 minutes. Thereafter, the temperature was lowered to atmospheric pressure and the product was taken out.

The product is made using aqua regia, sulfur and nitric acid, and according to the usual method,
Extracted diamonds. In addition, when the product is crushed before processing and the dispersion state of diamond in the laminated cross section is observed with a microscope, most of the particles are about 0.5 mm.
They are present at intervals of , and are thought to have grown from fine particles that had been precipitated in advance. This diamond particle has a minute lump (approximately 5μ) in the center,
Most of the particles had a smooth surface and a regular shape, and the average particle size was 350 μm, most of which was in the range of 300 to 400 μm, with less variation than in conventional methods. The dots present in these particles are thought to be diamond seeds deposited by the vapor phase method. Place 2 to 5 seeds at the scratch location on the silicon wafer as described above.
However, in the hydrostatic synthesis, it is thought that either they became one, or one of them grew preferentially.

Example 2 Diamond was deposited on a silicon wafer in the same manner as in Example 1, except that the substrate temperature was slightly lowered to 820-830°C. Two to five diamond crystals of approximately 0.5 μm in which rectangular (100) planes grew preferentially were precipitated at predetermined positions.

Using this wafer, the wafer, cobalt plate, and graphite plate were stacked in the same manner as in Example 1 except that the catalyst was replaced with cobalt.

Synthesis conditions were 55Kb, held at 1500℃ for 2 minutes,
Boosted to 58Kb in minutes. Diamond particles were extracted in the same manner as in Example 1. The resulting diamond was a crystal with (100) and (111) planes grown, and because the synthesis time was short, the average grain size was approximately
The diameter was 200 μm, and most of the particles were in the range of 150 to 250 μm.

Example 3 Diamond was deposited in the same manner as in Example 1 except that the substrate temperature was slightly higher at 870 to 880°C, and diamond crystals with developed (111) planes were obtained.

Using this substrate, a laminate was constructed in the same manner as in Example 1, except that a Ni--Cr alloy (80% by weight Ni) was used as a catalyst.

The diamond synthesis conditions were 53Kb, held at 1480°C for 2 minutes, and then increased to 57Kb in 30 minutes. Example 1
The result of extracting diamonds in the same way as (111)
An 8-hexahedral Brodsky diamond with predominant faces was obtained. The average particle size was 280 μm, with most of the particles falling within the range of 250 to 300 μm, with narrow variation.

Effects of the Invention According to the present invention, seed arrangement, particularly regular arrangement, is easy in diamond synthesis, and as a result, diamond grains having relatively large and uniform grain sizes can be obtained.

Claims (1)

[Claims] 1. A method for synthesizing diamond from carbon and a diamond synthesis catalyst under high temperature and high pressure, characterized in that diamond fine particles are dispersed and precipitated on a substrate by a vapor phase method, and this substrate is placed in the diamond synthesis system. Synthesis method.