JP3093402B2 - Carbon material production 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 producing a carbon material containing diamond or a diamond material, and more particularly to an improvement in a film forming speed, an increase in the area of a film formed, and a low temperature film forming.

[0002]

2. Description of the Related Art Due to its attractive properties such as high hardness and high thermal conductivity, diamond has been actively studied in various fields such as cutting tools and semiconductor materials. Material.

[0003] At present, there are roughly two methods for producing such a method. One is a method for obtaining a single crystal diamond under a high pressure, and the other is a method for forming a diamond thin film from a gas phase under a low pressure. is there.

Among them, a hot filament CVD (chemical vapor deposition) method is most often used as a method for forming a carbon material containing diamond or a diamond material using the chemical vapor deposition method. The method is, for example, as shown in FIG. 1, a reactive gas is introduced into a quartz reaction tube 1 from a gas inlet 2 and metal tungsten (or tantalum)
An electric current is passed through the filament 3 to make the filament 1500 ° C.
The substrate 4 is heated to 400 ° C. to 1300 ° C. by heating to 30003000 ° C. and emitting thermoelectrons. At the same time, the reactive gas is thermally decomposed by contact heating to form a carbon material containing diamond or a diamond material on a substrate. At this time, the pressure in the reaction vessel is 1 to 350 Torr
r is maintained. Therefore, hot filament CVD
The method is a cheap and easy method.

As another method for forming a carbon material containing diamond or a diamond material, microwave plasma C
There is a VD method. In this method, for example, as shown in FIG. 2, the quartz reaction tube 1 is inserted into a part of the microwave waveguide 6, a reaction gas is introduced from the upper portion of the quartz reaction tube, and vacuum evacuation is performed from the lower portion. The most frequently used microwave oscillation frequency is 2.45 GHz. The pressure in the reactor is maintained at 10-200 Torr.

As a method for forming a carbon material containing diamond and a diamond material by utilizing the interaction between a microwave and a magnetic field, a mixed cyclotron resin (MCR) which is a phenomenon that occurs when the reaction pressure is higher than 0.1 Torr.
There is a magnetic field microwave plasma CVD method using e) and an ECR plasma CVD method using ECR (Electron Cyclotron Resonance), which is a phenomenon that occurs when the reaction pressure is as low as 0.1 Torr or less.

FIG. 3 is a schematic diagram of an apparatus used in a magnetic field microwave plasma CVD method. By utilizing the interaction between the magnetic field generated by the magnetic field coil 7 and the microwave introduced from the microwave waveguide 6 into the reaction chamber, the reactive gas flowing from the gas inlet 2 is efficiently excited, and diamond is deposited on the substrate 4. Forming a carbon material or a diamond material. The substrate 4 is externally controlled by heating the substrate holding plate. Further, a floating electric field 8 can be applied to the substrate 4. As the reaction gas, a gas obtained by diluting a normally gaseous or liquid hydrocarbon with hydrogen, such as methane, carbon monoxide, ethylene, methanol, and ethanol, is used. Further, a gas to which a small amount of water, carbon dioxide, and oxygen are added is also used.

The shape of the apparatus used in the ECR plasma CVD method is almost the same as that of the magnetic field microwave CVD apparatus. However, since the reaction pressure is very low at 0.1 Torr or less, the plasma spreads and is larger than that of the magnetic field microwave CVD method. Area deposition is possible. For this reason, most ECR plasma CVD apparatuses are of a deposit-down type as shown in FIG. In a magnetic field microwave CVD apparatus as shown in FIG. 3, it is very inefficient to form a film on a large area inevitably due to the problem of the mass and operability of the reaction chamber. Generally, a reaction gas flows in from the gas inlet 2, but a method in which a diluent gas flows in from the gas inlet 2 and a raw material gas flows in from the gas inlet 9 or the gas inlet 10 is also used. Hydrogen is used as a diluting gas, and methane, acetylene, carbon monoxide, carbon dioxide, etc., which are usually present as gases, are used as raw material gases, and rarely, usually, methanol, ethanol, Acetone is used. By rotating the substrate holder, the film thickness and film quality of the carbon material containing diamond or the diamond material on the substrate 4 may be improved in some cases.

[0009]

However, the current methods have a number of problems.

For example, in hot filament CVD,
Since the vapor pressure of the filament material inevitably increases, there is a high possibility that the formed film is contaminated. In addition, since the life of the filament is short, the frequency of replacement has to be increased, and there is a drawback that the change with time, the uniformity of each batch, and the reproducibility are poor.

On the other hand, with respect to the film formation by the above-mentioned plasma CVD, it is inherently difficult to form a uniform film over a large area because it is directly connected to uniformly generating a large plasma, and the film forming speed is also low. 1μm by magnetic field microwave CVD
/ Hr or less, 0.3 μm in ECR plasma CVD
It also has a decisive disadvantage of being as low as m / hr or less.

To summarize these problems, in a conventional vacuum process, the concentration of the reactive gas is low, so that the film forming speed is inevitably reduced. Therefore, it is sufficient that a thin film of a carbon material containing diamond or a diamond material can be formed by a relatively low vacuum, desirably a normal pressure process, but it is impossible with conventional methane and methanol systems. . Certainly, the method of thermal spraying using a plasma jet exists as a normal pressure process, but it must be said that it is out of the problem in view of the film quality and uniformity.

[0013] In addition to the above-mentioned problem of the film forming speed, the lowering of the film forming temperature has not been achieved conventionally. If this is overcome, it becomes possible to produce diamond-containing carbon materials or diamond materials on heat-sensitive materials such as low-melting metals at low temperatures, further expanding the applications that are currently only throw-away tips etc. It is expected that there is a great industrial advantage. Further, in film formation at a high temperature, the carbon material containing diamond or the diamond material is likely to be separated due to cooling when the sample is taken out, which is also important in preventing this phenomenon.

[0014]

As described above, in order to solve the problem, a method capable of forming a thin film of a carbon material containing diamond or a diamond material by a low vacuum, preferably a normal pressure process is developed. In order to make it possible to lower the temperature of the film at the same time, it is necessary to consider a raw material (reactive gas) that can replace conventional methane-based and methanol-based systems.

Recently, Patterson et al. At Rice University reported that CF ₄
It is reported that lower temperatures can be achieved than conventional methane systems when using raw materials such as methane and hydrogen or CS ₂ and fluorine. They discuss the formation and stability of solid carbon from simple thermodynamic considerations of solid carbon formation. Specifically, during solid carbon formation, the change in free energy when removing all side chains and the like from the raw material is observed.When the change in free energy at 1000 ° C. is compared, that of methane alone is − 4.5KJ / mo
While no more than the l, while that of making the solid carbon from the CF ₄ and hydrogen orders of magnitude and -340.0KJ / mol greater, therefore that there is a possibility that the deposition of the diamond is easily performed.

However, in their consideration, the consideration of the activation energy is completely absent, and it is not enough to discuss the reactivity only with the free energy. Graphite is also formed, but their considerations were easy and their modeling was inadequate. However, it is interesting because it is relatively close to the model we were thinking of.

Here, our model will be described in more detail. We have focused on halogenated carbons that have the shape of a gas or liquid at room temperature and produce carbene represented by CX ₂ radical (X is a halogen element) or CH ₂ radical by 1.1-elimination reaction. Hydrogen. These CX ₂ radicals (X is a halogen element) or CH ₂ radicals include singlet and triplet. Among them, a triplet, that is, a diradical is considered to cause an insertion reaction between C and H, which may exert an effect on diamond film formation.
As for the singlet type, a model of epitaxial growth due to the approach of singlet radicals of SiH ₂ has been proposed for a cluster model of a hollow bridge site on the (001) plane of silicon, and the same contents can be applied to diamond. Is not considered to be so difficult.

[0018] to select the raw materials in accordance with our model, diamond was tried to film formation is deposited, diamond was tried to the additional test experiment with CF ₄ which is to say that Patterson is good is was not confirmed.

[0019] That is, specifically, a CX ₂ radical (X is a halogen element) or a halogenated hydrocarbon which produces a CH ₂ radical by a 1.1-elimination reaction of CHF ₃ , CH ₃ F, etc. It is possible to form a carbon material containing diamond or a thin film made of a diamond material at a relatively high speed in a low-vacuum (several hundred Torr), preferably at normal pressure, thermal CVD using a gas to which an active gas is added as a source gas. I have found something.

In the thermal CVD, a reaction region of a material gas and a film formation region on a substrate are divided, and the respective temperatures are independently controlled, and a precursor generated in the reaction region is efficiently formed on the substrate. By controlling the gas flow to reach, it is possible to form a thin film made of a carbon material containing diamond or a diamond material even at a relatively low substrate temperature of 100 to 400 ° C. It was also found that was possible.

It should be remembered that when a diamond thin film is prepared by the method of the present invention, hydrogen halide such as hydrogen fluoride is generated as a by-product, so that the chamber portion which comes into contact with these at a high temperature. Is that it is practically difficult to use quartz or stainless steel used in conventional semiconductors. Therefore, as a material of the chamber, a material having relatively low reactivity with hydrogen fluoride or the like and functioning as a structural material at a high temperature, specifically, a ceramic material such as alumina, sapphire, or SiC, and an oxidation-resistant material such as Monel. A metallic material was used. Among them,
With respect to SiC, when a material coated by CVD from above the sintered body was used, the concentration of impurities in the resulting film was low and was very excellent.

Hereinafter, the present invention will be described in more detail with reference to examples.

【Example】

Example 1 As a first step, thermal CVD was attempted in a CF ₄ + hydrogen system according to the model of Patterson et al. The conditions for film formation are as follows: chamber pressure is 760 torr
The concentration of CF ₄ is 1 to 5%, the temperature of the material gas in the reaction region is 880 ° C., the time required for the gas to pass through the reaction region is about 1 to 10 seconds, and the substrate temperature of the film formation region is 300 to 40
The test was performed under the conditions of 0 ° C. and a deposition time of 8 hours. The material of the chamber was Monel 400. In fact, these parameters were based on those of Rice University's Patterson et al.

FIG. 5 shows the configuration of the experimental apparatus used in this experiment.
Shown in Basically, it is a hot-wall type thermal CVD using an electric furnace as a heating source. By changing the temperature of the electric furnace and the length of the chamber inserted into the electric furnace, the temperature and the passage in the reaction region can be reduced. The time required can be adjusted. The temperature gradient was adjusted by the presence or absence of heat insulating material and the installation of cooling fans.
The experiment was performed by adjusting the temperature to be linear from 0 ° C. to room temperature.

Firstly, in the chamber, a portion corresponding to 400 to 200 DEG ° C., providing a substrate consisting of a chamber similar to Monel 400, then, the inside of the chamber at least 10 ^-3
Vacuum was pulled to below torr. The substrate was subjected to a scratching treatment with diamond powder just in case.

After the inside of the chamber was sufficiently evacuated, the temperature of the electric furnace was raised, and when it reached a steady state, a reaction gas was introduced to form a film. The temperature during the film formation could be measured in situ by the structure in the chamber as shown in FIG. 6, and therefore the substrate temperature could be accurately grasped.

After the completion of the film formation for 8 hours, the reaction gas is stopped, and a sufficient evacuation (at least 10 ⁻³ torr or less) is performed.
A sample was removed. Of course, care must be taken since exposure to the air when the substrate temperature is high will result in oxidation.

The film after film formation was measured for Raman spectroscopy and XRD. Unfortunately, however, no peaks attributed to diamond were identified.
After that, various parameters were changed and the deposition time was extended up to 40 hours, but the result was the same.

Next, according to our model, the raw materials were changed to CHF ₃ and hydrogen as halogenated hydrocarbons producing CX ₂ radicals (X is a halogen element) or CH ₂ radicals by 1.1-elimination reaction. Was conducted. Since the above experiment was a mere additional test, we used a Monel substrate, but we are thinking of applying it to a semiconductor process.This time, we cut a single crystal silicon wafer, which is normally used as a substrate material. What was used was used.

First, a substrate made of single crystal silicon was set in a portion corresponding to 400 to 200 ° C. in the chamber, and then the chamber was evacuated to at least 10 ⁻³ torr or less. In this case, the substrate was also subjected to a scratching treatment with diamond powder just in case. Other conditions are exactly the same as the above-mentioned method.

After the film formation was completed, the substrate was taken out and subjected to Raman spectroscopy. When the substrate temperature was high, all peaks were considered to be due to amorphous carbon.
In the part between 0 and 300 ° C, a broad peak of the amorphous carbon material exists around 1550 cm ^-1 ,
A sharp diamond peak was observed at 1332 cm ^-1 . Even if the laser output was changed, it was confirmed that the peak position did not shift, and this peak was identified as diamond. That is, it may be considered that the carbon film containing the diamond material is formed. The sensitivity of Raman spectroscopy is sharp for amorphous carbon, but not so high for diamond, which may be due to the difference in peak intensity.

According to Patterson's theory, CF ₄ is CH 2
And it would likely produce a diamond than F _3, inconsistent with this experimental result. In other words, Patterson et al.'S theory was inadequate, confirming that our model was more correct.

Example 2 In this experiment, Example 1 was used.
Shows an example in which the process is further optimized. That is, the raw materials are exactly the same CHF ₃ and hydrogen, and helium is added to reduce the concentration of CHF ₃ . Each parameter is C
HF ₃ concentration of 1 to 0.25%, temperature of 840 ° C. in the reaction zone of the material gas, the time required for passing through a gas reaction region of the aforementioned approximately 1-5 seconds, the substrate temperature in the deposition region is from 100 to 350
C. and a film formation time of 8 hours. The apparatus and the experimental method used in the experiment are the same as those in the first embodiment.

First, the results of Raman spectroscopy obtained when the CHF ₃ concentration is 1% are shown in FIG. Although peaks attributable to diamonds and diamonds have been confirmed, many other peaks have also been confirmed. These peaks are considered to be caused by amorphous carbon or a polymer of carbon, which were also confirmed in the conventional methane system, and are often confirmed when the concentration of the raw material gas is higher than an appropriate concentration. The results of Raman spectroscopy at a CHF ₃ concentration of 0.25% are shown in FIG. The film forming conditions other than the CHF ₃ concentration are exactly the same. From this result, it was confirmed that diamond was clearly formed. Depot rate is about 1 μm /
hr or more, the temperature of the material gas in the reaction zone is 880 ° C.
° C, which was clearly higher than in Example 1, and was very interesting in considering the film formation mechanism. Also, the uniformity of the film was very high.

Example 3 In this experiment, Example 2 was used.
An example in which the raw materials are changed in the process of (1) is shown. That is,
The raw materials were CH ₃ F and hydrogen, and helium was added for dilution. Each parameter is 0.25% CH ₃ F concentration,
The temperature of the material gas in the reaction zone is 840 ° C, the time required for the gas to pass through the above-mentioned reaction zone is about 1 to 5 seconds, the substrate temperature in the film formation area is 100 to 350 ° C, and the film formation time is 8 hours. Performed under conditions. The apparatus and the experimental method used in the experiment are the same as those in the second embodiment.

Measurement of the obtained thin film by Raman spectroscopy
Very clear and due to diamond
A peak was observed. However, regarding the film thickness, C
HF _ThreeClearly thinner than the result of the concentration of 0.25%,
It has been confirmed that the cost has decreased.

Example 4 In this experiment, Example 2 was used.
An example in which the raw materials are changed in the process of (1) is shown. That is,
The raw materials were CHCl ₃ and hydrogen, and helium was added for dilution. In Examples 1 to 3, there was no problem because the raw materials were all gases at room temperature, but there was no problem. However, since the raw materials were liquid at room temperature, an experiment was performed using a vapor source. Since hydrogen chloride was inevitably generated during film formation, the chamber was changed from a monel tube to an alumina tube. The parameters are as follows: CHCl ₃ concentration: 0.25%; temperature in the reaction region of the material gas: 820 ° C .; time required for the gas to pass through the above-mentioned reaction region; The film formation was performed at a temperature of 350 ° C. and a film formation time of 8 hours. The apparatus and the experiment method used in the experiment are the same as those in Example 2 except for the above-mentioned changes. Prior to the experiment, a scratched silicon substrate was installed in the chamber, and then the inside of the chamber was sufficiently evacuated. Then, a film was formed. Note that, when connected to a vapor source under reduced pressure, there was a problem that the concentration of CHCl ₃ temporarily increased.
₃ was introduced to form a film.

When the thin film obtained in this example was measured by Raman spectroscopy, a very clear peak due to diamond was confirmed. In addition, the film thickness was clearly thicker than the result of the CHF ₃ concentration of 0.25%, and it was confirmed that the deposit increased.

[0038]

According to the present invention, a thin film of a carbon material containing diamond or a diamond material can be formed by a low vacuum or normal pressure process. Also in this method, it is possible to form a film by the most conventional thermal CVD, and therefore, unlike plasma CVD and the like, it is easy to increase the area by considering only the gas flow. Also, in our experiments, the depot obtained a value higher than about 1 μm / hr, which is higher than that of a magnetic field plasma CVD or the like, and a higher depot can be obtained by optimizing the parameters.

In the thermal CVD, a reaction region of a material gas and a film formation region on a substrate are separated, and the respective temperatures are independently controlled, and a precursor generated in the reaction region is efficiently applied to the substrate. By controlling the gas flow to reach, it is possible to form a thin film made of a carbon material containing diamond or a diamond material even at a relatively low substrate temperature of 100 to 400 ° C.
That is, the temperature can be reduced. This makes it possible to form diamond on materials that were previously considered impossible, such as plastics, which could not withstand high-temperature processes and could only form amorphous carbon or the like with conventional methods. Applications are possible.

Therefore, the present invention is considered to be a very useful industrial patent.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a hot filament CVD apparatus.

FIG. 2 is a schematic view of a microwave CVD apparatus.

FIG. 3 is a schematic diagram of a magnetic field microwave CVD apparatus.

FIG. 4 is a schematic view of an ECR plasma CVD apparatus.

FIG. 5 is a schematic view of a thermal CVD apparatus using a halogenated hydrocarbon used in this experiment.

FIG. 6 is a schematic view of the inside of a chamber of a thermal CVD apparatus using a halogenated hydrocarbon used in this experiment.

FIG. 7 is a Raman spectrum of the diamond material obtained in the experiment of this example.

FIG. 8 is a Raman spectrum of the diamond material obtained in the experiment of this example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Quartz reaction tube 2, 9, 10, 14 Gas inlet 3 Filament 4 Substrate 5 Exhaust 6 Microwave waveguide 7 Magnetic field coil 8 Floating potential 11 Chamber 12 Electric furnace (heating source) 13 Vapor source 15 Thermocouple protection tube 16 Source gas 17 Substrate holding boat 18 Substrate 19 Reaction area 20 Mass flow controller

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Claims (3)

(57) [Claims] In a method for producing a carbon material containing diamond or a diamond material by a thermal CVD method, a halogenated hydrocarbon existing as a gas or a liquid at room temperature, hydrogen, or hydrogen and a diluent gas are used.
1.1-elimination reaction of the halogenated hydrocarbon
To produce ruben, carbon material containing diamond or
A method for producing a carbon material, comprising producing a diamond material . 2. The method according to claim 1, wherein the concentration of the halogenated hydrocarbon is 1% or less. 3. The method according to claim 1, wherein the halogenated hydrocarbon is CHF ₃ or CHCl ₃ .