JPH0578194A - Preparation of graphite crystal - Google Patents

Abstract

PURPOSE:To improve crystallinity and readily control the crystal size and shape by depositing carbon dissolved in a metal onto a graphite seed crystal. CONSTITUTION:A metallic lump 4 is set through a carbon base material 6 on a heat insulator 2 provided on a supporting rod 1 and a contact part of the carbon base material 6 with the metallic lump 4 is irradiated with high- output laser beams 5 from a CO2 laser to dissolve the carbon base material 6 in the metallic lump 4. A graphite seed crystal 3 is then brought into contact with the metallic lump 4 to deposit carbon dissolved in the metal onto the seed crystal 3.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to the production of high quality graphite crystals having excellent crystallinity, by which the size and shape of the crystals can be easily controlled and the mass productivity can be improved. Regarding the method.

[0002]

2. Description of the Related Art Graphite is also called graphite and forms one of allotropes of carbon with amorphous carbon and diamond, and its crystal structure is as shown in FIG. It is a well-known substance from ancient times, and is used as a material for sliding parts by utilizing its excellent surface lubricity, or as a refractory material and reactor material by utilizing its excellent heat resistance. Films have been used as circuit materials such as resistors.

However, these applications were developed before the rise of the electronics industry represented by integrated circuits, LSIs, etc., and viewed from the level of material control technology of electronic materials used for microelectronics in recent years. ,
It remains in a state of pre-modern technical level. One of the reasons for this is that it is difficult to obtain high quality crystals even though carbon is a material that has been known for a long time. As expected from the Periodic Table, carbon is the element with the strongest covalent bond among the group IV elements, and because the bond between atoms is strong and the directionality is strong, the mobility of atoms is small and a stable crystal. It is difficult to move individual atoms because the lattice is formed. further,
Unlike Si and Ge, carbon does not liquefy in the atmosphere even when trying to melt and solidify to crystallize, but it sublimes as the temperature rises, and under the extreme conditions of several thousand atmospheric pressure or more. It has a troublesome property that it can only be liquefied. Due to such inherent properties of carbon, it is difficult to obtain high-quality crystalline carbon, and it has not been possible to play a leading role in the electronics industry until now.

On the other hand, the crystallinity of pyrolytic graphite is said to be relatively excellent. This substance is obtained by introducing a hydrocarbon-based gas onto a substrate heated to a high temperature and thermally decomposing the gas on the substrate to deposit carbon. However, in this case, although a coating film having a graphite-like structure can be obtained, its crystallinity is not high quality when viewed from the level required by the electronics industry, and it is suitable for use as an electronic material. Not a thing.

[0005]

As described above, in the prior art, there were various problems in using graphite as a material for electronics. However, as estimated from the structure of FIG. 2, the characteristic of graphite is that it exhibits strong anisotropy. That is, there is a contrast between the strong covalent bond in the ab axis two-dimensional plane and the weak van der Waals bond in the c axis direction. From this fact, the electric resistance in the ab axis plane is larger than that in the c axis direction. Is several orders of magnitude smaller, and the thermal conductivity in the ab axis plane direction is about 100 times greater than in the c axis direction. If it is possible to control these characteristic properties in the production of high-quality graphite crystals, the industrial application of graphite will be extremely widespread, and it will revolutionize the material technology for electronics.

Under these circumstances, interest in graphite crystal production technology is currently increasing, and there is a long-felt need for technical elucidation and breakthrough.

An object of the present invention is to solve the problems of the above-mentioned prior art, to provide a high-quality graphite crystal having excellent crystallinity, while simply controlling the size and shape of the crystal, and It is intended to provide a method for producing a graphite crystal that can be produced with high mass productivity.

[0008]

The above object can be achieved by dissolving carbon in a metal using carbon as a base material and precipitating the carbon dissolved in the metal on a graphite seed crystal. The contents will be described below in more detail. That is, first, if the carbon base material and the metal are brought into contact with each other and heated to a temperature equal to or higher than the melting point of the metal, it is possible to dissolve the carbon atom in the molten metal. Here, a graphite seed crystal is arranged at one end of the molten metal, and a temperature gradient is applied to the carbon base material-metal-seed crystal system, and the contact surface between the carbon base material and the metal is heated to a high temperature. By maintaining the contact surface with the seed crystal at a relatively low temperature, carbon atoms that have become supersaturated in the metal can precipitate on the seed crystal at the metal-seed crystal contact surface and grow as a graphite single crystal. it can.

[0009]

A laser beam is used as a heat source that sufficiently heats the carbon base material-metal-seed crystal system, realizes a necessary temperature gradient with good controllability, and does not cause contamination due to contamination with impurities. Is preferably used. When using the above method, the heating temperature must be at least 1000 ° C or higher, but a high-power laser such as a CO ₂ laser is optimal as a heat source for achieving such a high temperature with a temperature gradient. is there.

When heating the above carbon base material-metal-seed crystal system, the base material and the seed crystal are opposed to each other, and a metal is placed between them to control the positional relationship between the base material and the seed crystal. However, by moving these, it becomes possible to control the shape and size of the graphite crystal grown on the seed crystal.

[0011]

EXAMPLES The method for producing the graphite crystal of the present invention will be specifically described below with reference to examples.

[0012]

Example 1 FIG. 1 is a diagram showing a configuration of a main part of a graphite crystal producing apparatus used for carrying out the method of the present invention, in which a metal mass 4 is placed on a carbon base material 6 and further on the metal mass 4. Seed crystal 3
It shows that it is composed of. In this example, high-purity iron (Fe) was used as the metal block 4.

In the above structure, the high-power laser beam 5 from the CO ₂ laser was irradiated from the outer peripheral portion, and the laser beam intensity was adjusted to be the highest at the contact portion between the carbon base material 6 and the metal block 4. Here, the laser light intensity is set to 10 kW / cm ^2, and the speed of the seed crystal 3 is set to 1 at the time when the metal melts and the temperature gradient becomes uniform.
mm / hr, the velocity of the carbon base material 6 was moved upward at 0.5 mm / hr.

After the above operation was carried out for 10 hours, the operation was stopped, the seed crystal was taken out after cooling, and it was confirmed that graphite having a diameter of about 1 mm and a length of about 10 mm was grown on the seed crystal 3. .. Further, when the crystallinity of the graphite was examined by X-ray diffraction and electron beam diffraction, it was confirmed that the graphite was a very high quality single crystal. The results of composition analysis of the obtained crystals, only incorporation of some Fe in the crystal surface is observed, it can be seen that the extremely high purity graphite crystals is obtained, heating by CO ₂ laser contamination It has been confirmed that it works as a heat source that does not cause

According to thermal calculations, the temperature during crystal growth is about 1800 ° C. at the carbon base material-metal contact surface and about 1550 ° C. at the metal-seed crystal contact surface, and the difference in the solubility of carbon due to the temperature difference is Is suspected to have been sufficient for the purposes of the present invention.

[0016]

Example 2 Using the same apparatus as in Example 1, the same experiment was conducted using nickel (Ni) and cobalt (Co) and their alloys instead of the metal ingot Fe in Example 1. It was Since these metals have different melting points, it is necessary to perform the experiment by changing the laser light intensity, but as in the case of Example 1, extremely high quality and high purity graphite crystals could be obtained.

[0017]

[Example 3] In the same experiment as in Example 1, an experiment was conducted by changing the moving speed of the carbon base material in the range of 0.1 to 1 mm / hr and the moving speed of the seed crystal in the range of 0.4 to 4 mm / hr. By the way
The outer diameter of the obtained graphite single crystal depends on the square root of the ratio of the moving speeds of the seed crystal and the carbon base material, and the outer diameter of the carbon base material was set to 2 mm, and the speed ratio was fixed to 1: 4. In this case, a graphite single crystal having a diameter of about 1 mm was obtained in the above speed range, and it was found that its reproducibility was also good. Therefore, it is understood that the method of the present invention can obtain a single crystal having a size as designed by setting the conditions.

In the above embodiments, an example in which a CO ₂ laser is used as a heat source has been described, but as the light source, another laser such as a ruby laser may be used as long as it is capable of continuous oscillation with a large output. However, similar results can be obtained with essentially no change.

Further, the physical properties of the graphite crystal produced by the above method were measured, and it was confirmed that both the electrical resistance and the thermal conductivity had extremely large anisotropy in the ab axis in-plane direction and the c axis direction.

[0020]

As described above, by adopting the method for producing a graphite crystal as the method of the present invention,
A method capable of solving the problems of the prior art and producing a high-quality graphite crystal with excellent crystallinity while easily controlling the size and shape of the crystal and with good mass productivity. Could be provided.

Further, the structure of the device used for carrying out the method of the present invention is simple in principle, and it can be developed as a mass-producible device in view of controllability and cost due to the progress of the device technology. It is possible, and the graphite production method of the present invention is a method in which prospects for mass production are easy, and it can be applied to processes in the field of the electronics industry in the future.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a main part of a graphite manufacturing apparatus used for carrying out a method of the present invention.

FIG. 2 is a diagram showing a crystal structure of a graphite crystal.

[Explanation of symbols]

1 ... Support rod, 2 ... Heat insulator, 3 ... Seed crystal, 4 ... Metal lump,
5 ... Laser light, 6 ... Carbon base material, 7 ... Metal lump support rod.

Claims (5)

[Claims] 1. A method for producing a graphite crystal, which comprises dissolving carbon in a metal using carbon as a base material and then depositing the carbon dissolved in the metal on a graphite seed crystal. 2. As a metal for dissolving the carbon, iron (F
e), a transition metal such as nickel (Ni) or cobalt (Co), or an alloy thereof is used.
A method for producing a graphite crystal as described. 3. The method for producing a graphite crystal according to claim 1, wherein a laser beam is used as a heat source for heating the carbon base material, the metal and the graphite seed crystal. 4. When depositing graphite on the graphite seed crystal, the carbon base material and the graphite seed crystal are opposed to each other, and a metal is arranged between them, so that both of the carbon base material and the graphite seed crystal or The method for producing a graphite crystal according to claim 1, 2, or 3, wherein the size of the precipitated graphite crystal is controlled by moving either one and adjusting the moving speed. 5. The method for producing a graphite crystal according to claim 3, wherein a CO ₂ laser is used as a light source of the laser beam.