JPH048367B2 - - Google Patents

Description

[Detailed description of the invention]

<Technical Field of the Invention> The present invention is directed to the use of thermal decomposition CVD (chemical vapor deposition) at a relatively low temperature of around 1000°C or lower.
This paper relates to a method for producing highly oriented pyrolytic graphite with excellent anisotropy and a technology for controlling the anisotropy of the pyrolytic graphite, and has established extremely useful basic material technology for creating new functional devices. It has technical significance in this respect. <Conventional technology and its problems> Artificial synthesis of graphite, which is chemically stable, does not undergo phase transformation at temperatures above 3000°C, and has significant anisotropy in terms of thermal and electrical conductivity, usually requires a long period of time. A wide range of high-temperature, high-pressure manufacturing processes have been required. For example, when using methane as a starting material, high temperatures (approximately
Heat treatment at high temperature and pressure is used to thermally decompose the material (at temperatures above 2000°C) and further improve the orientation. Furthermore, a method of obtaining fibrous carbon by subjecting polymer fibers to high temperature treatment has been known for a long time. However, since these methods are processed at high temperatures, although they can be used as standardized structural materials, it is difficult to apply them to functional electronic materials with controlled anisotropy. On the other hand, as a method for obtaining pyrolytic graphite at relatively low temperatures, formation methods that use special organic compounds as starting materials and utilize dehydrogenation reactions, dehydrohalogenation reactions, decarbonization reactions, dehydration reactions, etc. are often used. However, there are no examples in which highly oriented carbon deposits have been achieved, and therefore, there are also no examples in which control of crystallinity (anisotropy) has been achieved. In order to realize functional materials or functional devices that utilize the anisotropy of graphite, it is necessary to establish new technologies such as increasing the orientation of pyrolytic graphite at low temperatures and controlling the anisotropy. <Object of the Invention> The present invention has been made in view of the above-mentioned current state of the art. The company has established a technology that makes it possible to control the anisotropy of pyrolytic graphite produced by pyrolytic graphite. The purpose is to provide a technology for controlling the anisotropy of decomposed graphite. <Summary of the Invention> The method for forming pyrolytic graphite of the present invention uses an aromatic compound or an unsaturated compound as a raw material, and when forming pyrolytic graphite on a substrate, it adheres to the wall of a reaction tube in a pyrolysis atmosphere. By introducing the effect of a carbon thin film, we can deposit pyrolytic graphite with excellent anisotropy at a low temperature of around 1000°C or lower, and by controlling the deposition rate of the pyrolytic graphite on the substrate, It is characterized by controlling the crystallinity and anisotropy of pyrolytic graphite. <Example> The drawing is a block diagram of a pyrolytic graphite production apparatus used in an example of the present invention. The hydrocarbon compounds used as starting materials are preferably aromatic or unsaturated compounds, which are thermally decomposed at temperatures around 1000° C. or lower. As the substrate on which pyrolytic graphite is formed, single crystals such as silicon, sapphire, silicon carbide (α-type and β-type), boron nitride, hard graphite, highly oriented graphite, or quartz glass are used. These must satisfy the condition that they do not deteriorate even at a reaction temperature of about 1000°C. A normal pressure bubbler method or a reduced pressure method is used to supply raw materials to the reaction tube. In either method, highly oriented pyrolytic graphite can be obtained by controlling the supply amount of raw materials and the deposition rate of graphite, as will be described later, and it is also possible to control anisotropy. In the normal pressure bubbler method, argon gas is used as a carrier gas. Although the drawing shows a device configuration that uses the normal pressure bubbler method, it is also possible to use the low pressure CVD method with this device. In this case, it is possible to achieve a more uniform graphite film thickness than in the normal pressure bubbler method. The manufacturing process will be explained below. An argon gas control system 2 is installed in a bubble container 1 containing benzene that has been purified by vacuum distillation.
Then, argon gas is supplied to bubble the benzene, and the benzene molecules are sent to the quartz reaction tube 4 through the Pyrex glass tube 3. At this time, the temperature of the liquid benzene in the bubble container 1 is kept constant, the argon gas flow rate is adjusted by the valve 5, and the amount of benzene molecules supplied into the reaction tube 4 is controlled to be constant at several mmol per hour. On the other hand, argon is flowed through the dilution line 6 to optimize the benzene molecule number density and flow rate fed to the reaction tube 4. The reaction tube 4 is equipped with a sample stage 7 on which the aforementioned growth substrate of silicon or the like is placed, and a thin carbon film is attached to the inner wall of the reaction tube around the sample stage 7. A heating furnace 8 is provided around the outer periphery of the reaction tube 4, and the growth substrate inside the reaction tube 4 is maintained at a temperature of about 1000° C. or lower by this heating furnace 8. Benzene molecules introduced into reaction tube 4 are at 1000℃
The material is thermally decomposed by being heated to a temperature higher than or equal to that temperature, and is sequentially grown and formed on a growth substrate. At this time, the pyrolytic graphite that is grown and formed becomes graphite with excellent anisotropy due to the effect of the carbon thin film attached to the reaction tube 4 in the reaction atmosphere, and is highly oriented at a lower temperature than before. is achieved. Furthermore, by changing the flow rate and concentration of benzene molecules introduced into the reaction tube 4, the deposition rate changes and the crystallinity changes accordingly, making it possible to easily control the anisotropy. The crystallinity or anisotropy of the pyrolytic graphite was evaluated by measuring the specific resistance of the obtained pyrolytic graphite in the C-axis direction and in a plane perpendicular to the C-axis. According to Table 1, the in-plane resistivity value of conventional low-temperature pyrolytic graphite (1~2×
10 ^-3 Ω・cm), the specific resistance value of the pyrolytic graphite obtained in the above example is about an order of magnitude lower,
This clearly shows that the crystallinity has improved. Furthermore, the crystallinity of pyrolytic graphite is significantly dependent on the deposition rate, and highly oriented pyrolytic graphite can be obtained at slow deposition rates. Table 1 shows the results of one example of the present invention, and the present invention is not limited to this in any way.

[Table] <Effects of the Invention> According to the method for forming pyrolytic graphite of the present invention, highly oriented pyrolytic graphite with excellent anisotropy can be produced at a temperature of around 1000°C or lower, which is lower than conventional methods, by incorporating the effect of the pyrolysis atmosphere. Obtained at low temperatures below. Furthermore, by controlling the deposition rate, it is also possible to control anisotropy, so it is expected that this will be used to promote application to functional electronic materials.

[Brief explanation of drawings]

The accompanying drawing is a block diagram of a pyrolytic graphite production apparatus for explaining one embodiment of the present invention. 1... Bubble container, 2... Argon gas control system, 3... Glass tube, 4... Reaction tube, 6... Dilution line, 7... Sample stand, 8... Heating furnace.

Claims (1)

[Scope of Claims] 1. An aromatic compound or an unsaturated compound is used as a starting material, the amount of the starting material is controlled and a constant amount is supplied to a reaction system every hour, and carbon is added to a transparent hollow inner wall as the reaction system. Using a reaction tube with a thin film attached, the deposition rate of graphite on the substrate was controlled at 1000℃.
A method for producing pyrolytic graphite, which comprises forming highly oriented graphite having anisotropy on a substrate by pyrolysis at a lower or lower temperature.