JPS61151095A - Synthesis of diamond - Google Patents

Abstract

PURPOSE:A base plate on which fine particles of diamond is deposited in dispersion by the vapor-phase method is placed in the diamond synthesis system to give diamond particles of good quality with relatively large diameters and narrow particle size distribution. CONSTITUTION:A base plate with scratch lines in an equal interval is heated up to 700-1,000 deg.C and the system is irradiated with microwaves of 30MHz-10 GHz in an atmosphere containing hydrocarbons under reduced pressure of 10-50Torr for 30-60min to generate plasma state whereby fine particles of diamond of 0.5-1mum diameter are formed on the base plate. The resultant base plate is laminated with a thin film of a diamond synthesis catalyst such Fe, Co, Ni, Cr and another thin film of carbon, then placed in a high- temperature and high-pressure system. The temperature of 1,400-2,000 deg.C and the pressure of 50-60kb are applied to synthesize diamond, then metals are dissolved off with an acid and the unreacting carbon is removed with nitric acid or aqua regia.

Description

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

Conventional diamond synthesis methods include 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 gas phase method, in which hydrocarbon gas is brought into a plasma state using high frequency waves, microwaves, etc., and diamond is deposited on a substrate. (
There is a method using CVD). 110 generally yields granular diamonds or diamond sintered bodies, while the latter generally yields diamond-shaped diamonds.

For granular diamonds, it is desirable to have large grains, and the grain size should be as uniform as possible.There is a method of placing diamond seeds in the synthesis system to increase the size of diamond grains, and there is also a method of placing diamond seeds in the synthesis system to make the grain size uniform. It has also been proposed to arrange them regularly (Japanese Patent Application Laid-Open No. 113-1983)
9994). The regular arrangement is, for example, a method in which small holes are made at predetermined intervals in a nickel plate serving as a catalyst, seeds are charged into the holes, and a large number of these and carbon plates are laminated. This method yields relatively large diamonds with uniform grains, but requires one seed;
If the seeds are large, there will be a problem with heat resistance strength due to the consistency at the interface between the seeds and the growth layer, and if the seeds are made fine, there will be no problem in terms of strength, but special operations are required to arrange the fine seeds. The problem is what you need.

Problems to be Solved by the Invention The present invention solves the problems listed in L when diamond seeds are placed in the synthesis system in diamond synthesis using the hydrostatic method, and has good quality (euhedral) and narrow particle size range. The objective is to obtain diamond grains with a relatively large grain size.

The uninvented means of solving the problem is a combination of 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, and at this time, preferably, they are deposited regularly at predetermined intervals. This is a method in which diamond is precipitated and then used as a seed to synthesize diamond from carbon (non-diamond carbon, graphite, hereinafter referred to as "carbon") and a diamond synthesis catalyst using a hydrostatic 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 was discovered that when a small scratch was made on this silicon wafer, a diamond nucleus was first formed at the scratch, which then gradually grew.

This means that diamond particles can be deposited at desired positions on the plate.

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 apply any of these known methods, but 1
As an example, in an embodiment using a microwave method, methane, ethane, propane, ethylene, benzene, etc. can be used as the hydrocarbon, and 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 diamonds, but in the present invention, it is sufficient to attach fine diamond particles to the substrate, so the substrate is 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 metals such as nickel, chromium, cobalt, or alloys thereof.

For example, the point where you want to deposit diamond fine particles on the substrate is
Make a scratch with a diamond needle. 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 300 MHz to 10 G&, vacuum 10
-50 Torr, and the substrate temperature is suitably in the range of 700-1000°C. In the present invention, the time required for precipitation 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 scratches on the substrate from being deposited outside the background and in consideration of economic efficiency. In this way, fine particles of diamond of about 0.5 p.m to 1 tile m 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 diamond synthesis catalyst is layered on the diamond fine 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. high temperature,
Load it into a 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, nitrogen, chromium, tantalum, etc. and alloys can be used, and the temperature is 1400~1400~
A temperature of 2000° C. and a pressure of 50 to 80 Kb are suitable.

After synthesis, metals are dissolved and removed using acids, etc., and unreacted graphite is removed by treatment with sulfur, 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 the deposition of diamond by the vapor phase method, by controlling the deposition conditions, the diamond crystal plane can be selectively grown in 1R. That is, if the substrate temperature is set high, the grains will grow fp first on the (III) plane of the diamond crystal, and on the other hand, if the substrate temperature is set low, the grains will grow preferentially on the (100) plane. If diamond is synthesized by the static pressure method using a diamond precipitation substrate on which these crystal planes have grown, grains will similarly be obtained in which the crystal planes described above have grown preferentially. That is, the method of the present invention has the advantage that a specific crystal plane of diamond can be selectively torsionally grown.

EXAMPLE Dotted scratches were made with a diamond needle on the mirror surface of a silicon wafer having a diameter of 25 mm and a thickness of 0.1 mm at intervals of 0.5+ sm in length and width. The damage is 100% from a height of 10cm.
It is sufficient to use the same force as when a diamond grain of g is dropped.

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

Pressure: 30 Torr Gas composition: CH, 1%, H2 99% (volume) Substrate temperature = 850°C Microwave: 2.450 Time: Approximately 0.5 p-tn on the wafer surface taken out after 30 minutes of reaction
A diamond grain of size 2 ~
Five pieces were precipitated.

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

A Ni-Fe alloy (Ni 30% by weight) plate with a diameter of 25 mm and a thickness of 0.25 a+m is used as a catalyst, and this is stacked on the diamond precipitation surface side of the silicon wafer, and a plate with a diameter of 25+5I11 and a thickness of 1. On+m graphite plates were stacked. 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 the pressure was set to 52 Kb, the temperature was raised to 1450°C and held for 2 minutes. Thereafter, the pressure was gradually increased to 5aKb over 30 minutes. Thereafter, the temperature was lowered to atmospheric pressure and the product was taken out.

Diamonds were extracted from the product using tap water, sulfur and nitric acid according to a conventional method. In addition, when the product is crushed before processing and the state of diamond dispersion in the laminated cross section is observed under a microscope, many particles are present at intervals of about 0.5 mm.
It seems that the fine particles that were precipitated in advance grew. These diamond particles have a small dot (approximately 5 µl) in the center, have a smooth surface, are well-shaped, and have an average particle size of 350JL111. Most of them are 300-4
It was in the range of 00 pi, and the variation was small compared to the conventional method. The point clusters present in these particles are thought to be diamond seeds precipitated by the vapor phase method, and as mentioned above, 2 to 1 seeds were present at the scratch position of the silicon wafer, but in the static pressure method synthesis, these seeds were not found. It seems that either there was one body, or one of them grew preferentially.

Example 2 Example 1 except that the substrate temperature was slightly lowered to 820-830°C.
In the same manner as above, five diamonds were deposited at predetermined positions on a silicon wafer.

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.

The synthesis conditions were 55Kb, held at 1500℃ for 2 minutes, and then
The pressure was increased to 58 Kb in 0 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 200 g rr.
r, and the majority were in the range of 150-250μ layers.

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.
11) A diamond crystal with developed surfaces was obtained.

Using this substrate, Ni-Cr alloy (Ni80
A laminate was constructed in the same manner as in Example 1 except that % by weight) was used.

The diamond synthesis conditions were 53 Kb, held at 1480° C. for 2 minutes, and then raised to 57 Kb in 30 minutes. As a result of extracting diamond in the same manner as in Example 1, an oct-hexahedral diamond with a predominant (+11) plane was obtained. Its average particle size is 280 g m, mostly 250 g m
~300 p-m, with narrow variation.

Effects of the Invention According to the present invention, placement of seeds in diamond synthesis,
In particular, it is easy to arrange the diamond grains regularly, which results in relatively large and uniform diamond grains.

Claims (1)

[Claims] A method for synthesizing diamond from carbon and a diamond synthesis catalyst at high temperature and high pressure, comprising dispersing and precipitating diamond fine particles on a substrate by a vapor phase method, and placing this substrate in the diamond synthesis system. A diamond synthesis method featuring