JPH05155686A - Production of carbon material - Google Patents

Abstract

PURPOSE:To easily obtain a large-area thin film by heating prescribed raw materials under a reaction region to change the raw materials to active species, then transporting the active species to a heated film forming region and forming the film on a substrate. CONSTITUTION:The raw materials consisting of hydrocarbon halide, hydrogen, diluting gas, etc., are introduced from a gas introducing port 2 into a quartz reaction tube 1. The inside of the reaction tube 1 is then set at about 760Torr and is heated by a filament 3 to 800 to 900 deg.C to form the reaction region. The gases are passed in the region for the required time from 1 to 10sec to form the active species. After the active species are transferred to a film forming region kept at 100 to 400 deg.C, the film is formed on the substrate 4 consisting of single crystal silicon by a chemical vapor growth method, by which the objective carbon material incorporating diamond having a granular or thin-film shape is produced.

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 film formation rate, an increase in film area, and a low temperature film formation.

[0002]

2. Description of the Related Art Due to its attractive properties such as hardness and high thermal conductivity, diamond has been actively researched in various fields such as cutting tools or semiconductor materials. It is a material.

At present, there are roughly two manufacturing methods, one is a method for obtaining a single crystal diamond under high pressure, and the other is a method for forming a diamond thin film from a vapor phase under low pressure. is there.

Among them, the hot filament CVD (chemical vapor deposition) method is most widely used as a method for forming a carbon material containing diamond or a diamond material by 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 through a gas inlet 2 and metal tungsten (or tantalum) is supplied.
An electric current is applied to the filament 3 to make the filament 1500 ° C.
The substrate 4 is heated to 400 ° C. to 1300 ° C. by heating to ˜3000 ° 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 the substrate. At this time, the pressure in the reaction vessel is 1 to 350 Tor.
maintained at r. Therefore, hot filament CVD
The method is an inexpensive and easy method.

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

As a method of forming a carbon material containing diamond and a diamond material by utilizing the interaction between a microwave and a magnetic field, MCR (Mixed Cyclotron Resonanc) 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 shows a schematic view of an apparatus used in the magnetic field microwave plasma CVD method. 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 introduced from the gas introduction port 2 is efficiently excited and diamond is deposited on the substrate 4. A carbon material or a diamond material containing is formed. The substrate 4 is externally controlled by heating the substrate holding plate. The stray electric field 8 can also be applied to the substrate 4. As the reaction gas, a gas such as methane, carbon monoxide, ethylene, methanol or ethanol, which is usually a gas or liquid hydrocarbon diluted with hydrogen, is used. Moreover, a gas to which a small amount of water, carbon dioxide, or oxygen is 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, but since the reaction pressure is as low as 0.1 Torr or less, the plasma spreads wider than the magnetic field microwave CVD method. Area film formation is possible. Therefore, most ECR plasma CVD apparatuses are of the depot down type, as shown in FIG. In the magnetic field microwave CVD apparatus as shown in FIG. 3, it is very inefficient to form a film over a large area inevitably due to the problems of mass and operability of the reaction chamber. Generally, the reaction gas is introduced through the gas introduction port 2, but a method in which the diluent gas is introduced through the gas introduction port 2 and the source gas is introduced through the gas introduction port 9 or the gas introduction port 10 is also used. Hydrogen is used as the diluent gas, and methane, acetylene, carbon monoxide, carbon dioxide, and the like, which are usually present as a gas, are used as the raw material gas, and methanol, ethanol, which is very rarely present as a liquid, are used. Acetone or the like is used. The uniformity of the film thickness and film quality of the carbon material containing diamond or the diamond material on the substrate 4 may be improved by rotating the substrate holder.

[0009]

However, there are a number of problems with the presently practiced methods.

For example, in hot filament CVD,
Since the vapor pressure of the filament material is inevitably high, there is a high possibility of contaminating the formed film. Further, since the life of the filament is short, it is inevitable that the filament will be replaced frequently, and there is a drawback that it is poor in temporal change, uniformity in each batch, and reproducibility.

On the other hand, regarding the film formation by the above-mentioned plasma CVD, it is essentially difficult to form a large-area film uniformly because it is directly connected to the uniform generation of a large-sized plasma, and the film forming rate is also high. 1 μm by magnetic field microwave CVD method
/ Hr or less, 0.3μ in ECR plasma CVD method
It also has a decisive drawback of being as low as m / hr or less.

Summarizing these problems, in the conventional vacuum process, the reactive gas concentration becomes low, so that the film formation rate inevitably decreases. Therefore, it would be sufficient if a thin film of a carbon material containing diamond or a diamond material can be formed by a relatively low vacuum, preferably an atmospheric pressure process, but it was not possible in a conventional methane system and methanol system. .. Certainly, a method of thermal spraying using a plasma jet also exists as an atmospheric pressure process, but it must be said that it is out of the problem considering the film quality and uniformity.

Further, in addition to the above-mentioned problem of the film forming rate, the lowering of the film forming temperature has not been conventionally achieved. If this is overcome, it becomes possible to fabricate a carbon material containing diamond or a diamond material at a low temperature on a heat-sensitive substance such as a low-melting point metal, which further expands the applications currently only for throw-away chips. It is expected that there will be a great industrial advantage. Further, in film formation at a high temperature, peeling of a carbon material containing diamond or a diamond material is likely to occur due to cooling when a 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 in a low vacuum, preferably atmospheric pressure process is developed. At the same time, in order to make it possible to lower the temperature of the film formation at the same time, it was necessary to consider a raw material (reactive gas) instead of the conventional methane-based or methanol-based.

[0015] Recently, Rice University of Patterson et al., CF ₄
It has been reported that the use of a raw material gas such as hydrogen or CS ₂ and fluorine can lower the temperature compared to the conventional methane system. They discuss solid carbon formation and stability from a simple thermodynamic study of solid carbon formation. Specifically, when forming solid carbon, we are looking at the change in free energy when all side chains are removed from the raw material.When we compare the change in free energy at 1000 ° C, that of methane alone is − 4.5KJ / mo
While it is only l, it is an order of magnitude larger than -340.0 KJ / mol when solid carbon is made from CF ₄ and hydrogen, and therefore they are likely to form diamond film easily. That.

However, in their consideration, the activation energy is not taken into consideration at all, and it is insufficient to discuss the reactivity only by the free energy. Graphite is also formed in the same way, but its consideration was easy and their modeling was insufficient. However, it is interesting because it is relatively close to the model we were thinking of.

Let us now describe our model in more detail. We focused on molecules with low molecular symmetry and dipole moments, among which halogenated hydrocarbons. The reason for having a dipole moment is that the charge is more reactive when the charge is biased. In addition, having halogens is considered to be advantageous in increasing the dipole moment in view of electronegativity, and the stability of hydrogen halides, such as HF, generated when hydrogen is extracted. Because it is highly probable, it was expected from the viewpoint of free energy.

When a raw material was selected according to our model and a film was formed, a diamond film was formed, and when a follow-up experiment was conducted with CF ₄ , which is said to have a good Patterson, no diamond was confirmed.

[0019] That is, specifically, a low vacuum (several hundred Torr) using a halogenated hydrocarbon and hydrogen having a dipole moment such as CHF ₃ , CH ₂ F ₂ or the like, or a gas to which an inert gas is added as necessary as a raw material gas. It has been found that it is possible to form a thin film of a carbon material containing diamond or a diamond material at a relatively high speed, preferably by thermal CVD under normal pressure.

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

It should be remembered that when a diamond thin film is produced by the method of the present invention, a hydrogen halide such as hydrogen fluoride is generated as a by-product, so that the chamber portion that comes into contact with these at a high temperature. It is practically difficult to use quartz or stainless steel used in conventional semiconductors and the like. Therefore, as a material of the chamber, a material having relatively low reactivity with hydrogen fluoride and 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 these,
Regarding SiC, when a material obtained by performing CVD coating on the sintered body was used, the concentration of impurities in the finished film was low and it was very excellent.

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

【Example】

Example 1 First, as the first step, it was decided to try thermal CVD with CF ₄ + hydrogen system according to the model of Patterson et al. The film formation condition is that the chamber pressure is 760 torr.
, The CF ₄ concentration is 1 to 5%, the temperature in the reaction region of the material gas 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 in the film formation region is 300 to 40
The film formation was performed under conditions of 0 ° C. and a film formation time of 8 hours. The chamber material used was Monel 400. In fact, these parameters were in accordance with the experimental parameters of Rice-Patterson et al.

The configuration of the experimental apparatus used in this experiment is shown in FIG.
Shown in. Basically, it is a hot wall type thermal CVD using an electric furnace as a heating source, and by changing the temperature of the electric furnace and the length of the chamber inserted in the electric furnace, the temperature and the passage in the reaction region can be controlled. It is possible to adjust the time required. The temperature gradient is adjusted by adjusting the presence or absence of heat insulating materials and installing a cooling fan.
The experiment was conducted by adjusting the temperature to be linear from 0 ° C to room temperature.

First, a substrate made of Monel 400, which is similar to the chamber, is placed in a portion of the chamber corresponding to 400 to 200 ° C., and thereafter, the inside of the chamber is at least 10 ^−3.
The vacuum was pulled to below torr. The substrate was scratched 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 a steady state was reached, a reaction gas was introduced to form a film. The temperature during the film formation can be measured in situ by the structure inside the chamber as shown in FIG. 6, and therefore the substrate temperature could be accurately grasped.

After completion of film formation for 8 hours, the reaction gas was stopped, and after sufficiently evacuation (at least 10 ⁻³ torr or less),
The sample was removed. Of course, it is necessary to be careful because it will be oxidized if exposed to the atmosphere when the substrate temperature is high.

Raman spectroscopic measurement and XRD measurement were performed on the film after film formation. However, unfortunately, no peak that could be attributed to diamond was confirmed.
After that, various parameters were changed and the film formation time was extended up to 40 hours, but the result was the same.

Then, according to our model, CHF ₃ was obtained as a halogenated hydrocarbon having a large dipole moment.
And the same experiment was conducted by changing the raw material to hydrogen. Since the above experiment was just a follow-up experiment, we used a Monel substrate, but we are considering application to a semiconductor process,
This time, we used a cut single crystal silicon wafer, which is normally used as a substrate material.

First, a substrate made of single crystal silicon was placed in a portion of the chamber corresponding to 400 to 200 ° C., and then the chamber was evacuated to at least 10 ⁻³ torr or less. In this case, the substrate was also scratched 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 spectroscopic measurement. As a result, the peak at the portion where the substrate temperature was high was thought to be attributable to the amorphous carbon.
Regarding the part of 0 to 300 ℃, a broad peak of the amorphous carbon material exists near 1550 cm ^-1 ,
A sharp peak of diamond could be confirmed 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 a carbon film containing a diamond material is formed. The sensitivity of Raman spectroscopy is sharp for amorphous carbon but not so much for diamond, which is considered to be caused by the difference in peak intensity.

According to Patterson's theory, CF ₄ is CH
It should be easier to make diamond than F _3, which contradicts the experimental results of this time. That is, it was confirmed that the theory of Patterson et al. Was insufficient and that our model was more correct.

Example 2 In this experiment, Example 1 was used.
An example in which the process is further optimized is shown below. 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
The HF ₃ concentration is 1 to 0.25%, the temperature in the reaction region of the material gas is 840 ° C., the time required for the gas to pass through the reaction region is about 1 to 5 seconds, and the substrate temperature in the film formation region is 100 to 350.
The film formation was carried out under the conditions that the film formation time was 8 ° C. The apparatus used in the experiment, the experiment method, and the like are the same as in Example 1.

First, FIG. 7 shows the results of Raman spectroscopy obtained when the CHF ₃ concentration was 1%. This is the substrate temperature
It was formed at a very low temperature of 130 ° C.
Clearly, the peaks caused by diamond are confirmed, but many other peaks are also confirmed. It is considered that these are peaks caused by amorphous carbon or carbon polymer, which has been confirmed even in the conventional methane system, and are often confirmed when the source gas is higher than the proper concentration. Therefore, the concentration is further reduced and the result of Raman spectroscopy at a CHF ₃ concentration of 0.25% is 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. The deposition rate was about 1 μm / hr or more, which was significantly higher than that in Example 1 in which the temperature in the reaction region of the material gas was 880 ° C., which was very interesting in considering the film formation mechanism. Also, the uniformity of the film was very high.

[Embodiment 3] In this experiment, Embodiment 2 is used.
An example in which the raw materials are changed in the above process is shown. That is,
CH ₃ F and hydrogen were used as raw materials, and helium was added for dilution. Each parameter has a CH ₃ F concentration of 0.25%,
The temperature of the material gas in the reaction region is 840 ° C, the time required for the gas to pass through the reaction region is about 1 to 5 seconds, the substrate temperature in the film forming region is 100 to 350 ° C, and the film forming time is 8 hours. I went under the conditions. The apparatus used in the experiment, the experiment method, and the like are the same as in Example 2.

When the obtained thin film was measured by Raman spectroscopy, a peak due to diamond was confirmed very clearly. However, regarding the film thickness, C
It was confirmed that the HF ₃ concentration was 0.25%, which was clearly thinner than the result, and the deposition rate was lowered.

Example 4 In this experiment, Example 2 was used.
An example in which the raw materials are changed in the above process is shown. That is,
CHCl ₃ and hydrogen were used as raw materials, and helium was added for dilution. In Examples 1 to 3, there was no problem because all the raw materials were gases at room temperature, but since the raw materials this time were liquid at room temperature, experiments were conducted using a vapor sauce. Also, since hydrogen chloride is 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 is 0.25%, temperature in material gas reaction region is 820 ° C., time required for gas to pass through the reaction region is about 1 to 5 seconds, and film formation region substrate temperature is 100. It was carried out under the conditions that the film formation time is 8 hours at 350 ° C. The apparatus used for the experiment, the experiment method, and the like are the same as in Example 2 except for the above-mentioned changes. Prior to the experiment, a scratched silicon substrate was placed in the chamber, and after the chamber was sufficiently evacuated, the temperature of the electric furnace was raised and the reaction gas was introduced when it reached a steady state. Then, a film was formed. When connecting to a vapor source in a depressurized state, there was a problem that the concentration of CHCl ₃ temporarily increased, so first set the chamber to 760 torr with hydrogen and helium, and then CHCl 3.
₃ was introduced to form a film.

When the thin film obtained in this example was measured by Raman spectroscopy, a very distinct peak due to diamond was confirmed. Moreover, regarding the film thickness, it is clearly thicker than the result of CHF ₃ concentration of 0.25%,
It was confirmed that the deposit rate was rising.

[0038]

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

Further, in the thermal CVD, the reaction region of the material gas and the film formation region on the substrate are separated, the respective temperatures are independently controlled, and the precursor generated in the reaction region is efficiently generated 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.
That is, the temperature can be lowered. This makes it possible to form diamond even on materials that could not be formed in the past, such as plastic, which cannot withstand high temperature processes and in which only amorphous carbon etc. could be formed by the conventional method. Applications are possible.

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

[Brief description of drawings]

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

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

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

FIG. 4 is a schematic diagram 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]

 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 Raw material gas 17 Substrate holding boat 18 Substrate 19 Reaction region 20 Mass flow controller

Claims (3)

[Claims] 1. A method for producing a carbon material containing diamond or a diamond material using a thermal CVD method, comprising a halogenated hydrocarbon and hydrogen, or a raw material comprising the halogenated hydrocarbon and hydrogen and a rare gas as a diluent gas. And having a step of converting the raw material into an active species in a reaction zone heated to a temperature of 800 to 900 ° C., and heating to a temperature of 100 to 400 ° C. provided in connection with the reaction zone. A step of transporting the active species to a film formation region,
A method for producing a carbon material, comprising a step of forming a film of active species carried in a film forming region heated to a temperature of 100 to 400 ° C. on a desired substrate. 2. The method for producing a carbon material according to claim 1, wherein the produced carbon material containing diamond or the diamond material has a particle shape or a thin film shape. 3. The method for producing a carbon material according to claim 1, wherein the time required for the raw material to pass through the reaction region is 1 to 10 seconds.