JPH05209275A - Formation and device for carbonaceous material - Google Patents

Abstract

PURPOSE:To form a diamond thin film without pretreating a substrate and in high film forming speed by using a gaseous mixture of a halogenated hydrocarbon, hydrogen and a rare gas as raw materials at the case of forming the diamond thin film on the substrate by plasma CVD method. CONSTITUTION:The substrate for forming a diamond or diamond-contained carbonaceous thin film is placed in a vessel, the inner wall of which is made by alumina or the like having small reactivity with HF or the like, and the gaseous mixture of a halogenated carbide such as CF4, CHF3 or CH2F2, gaseous H2 and a rare gas such as He is supplied as the raw material into the vessel at <=100Torr pressure and, at the same time, the substrate excellent in oxidation resistance made of ceramics such as alumina, sapphire, SiC or monelmetal or the like is placed. The diamond or diamond-contained thin film is formed on the substrate in >=1mum film forming speed by introducing microwave into the vessel to make the raw gas plasma state. In this case, hydrogen conc. in the diamond film is freely regulated by regulating hydrogen gas conc. in the raw gas.

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 improving the film forming speed and simplifying the film forming step by omitting the substrate pretreatment step.

[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.

We have been studying the latter method for making a diamond film into a device or using it as a coating material. For example, as a method for forming a carbon material containing diamond or a diamond material by using thermal energy in a vapor phase growth method, a hot filament CV is used.
There is a D (chemical vapor deposition) method. The method is to heat the substrate to 400 ° C to 1300 ° C by applying an electric current to the filament made of metallic tungsten (or tantalum) to heat the filament to 1500 ° C to 3000 ° C, and to emit thermoelectrons, and at the same time, to increase the reactivity. The gas is pyrolyzed by contact heating,
It is a method of forming a carbon material containing diamond or a diamond material on a substrate.

However, in the above method, the vapor pressure of the filament material is inevitably high, so that the possibility of fouling the membrane is high. It also has the drawbacks that the life of the filament is shortened and the frequency of replacement is increased, and that the change over time and the uniformity and reproducibility between batches are poor.

The present invention relates to a process of forming plasma by using energy of an electromagnetic field to form active species and forming a film from them, instead of using the thermal energy as described above. Uniformity when considering industrial applications,
This is because a reproducible process is required. As a process using such plasma, there are a microwave plasma CVD method and a magnetic field plasma CVD method which are performed at a relatively low pressure, and there are DC plasma, arc plasma and combustion flame in a region where the pressure is higher (close to atmospheric pressure). And the like. As described above, the low pressure process is further divided into a film formation in a low pressure region (100 torr or less) and a film formation in a medium and low pressure region (100 torr to atmospheric pressure). The present invention relates to the former low pressure plasma CVD method. In the method, microwave is introduced into the reaction tube,
The structure is such that vacuum evacuation is carried out while introducing the reaction gas, and the reaction gas is excited to form active species to form a film. 2.45 GHz is the most commonly used microwave oscillation frequency. The pressure in the reaction vessel is maintained at 10 to 200 Torr.

The method of forming plasma using microwaves further utilizes the interaction between the microwave and the magnetic field depending on the conditions, and uses MCR (Mixed Cyclotron Resonance) which is a phenomenon that occurs when the reaction pressure is higher than 0.1 Torr. The magnetic field microwave plasma CVD method used and the reaction pressure
EC, which is a phenomenon that occurs when the value is 0.1 Torr or less
There is an ECR plasma CVD method using R (Electron Cyclotron Resonance).

[0008]

[Problems to be Solved by the Invention]

One of the problems in the diamond film formation in the plasma CVD method is the film formation speed problem. In the conventional vacuum process, the reactive gas concentration becomes low, so that the film formation rate inevitably decreases. . That is, in the vacuum process, the film formation rate is how efficiently active species can be formed and a film can be formed.

In addition, there is a troublesome process of pretreating the substrate. To briefly describe the pretreatment, for example, when a Si wafer is used as a substrate, ultrasonic treatment is performed in alcohol in which diamond powder is dispersed before film formation.
Due to the inclusion of this process, the reproducibility or uniformity of each batch becomes a problem as well as the complexity of film formation. However, if this pretreatment is omitted, nucleation is extremely delayed at the stage of nucleation at the initial stage of film formation, and film formation cannot be performed smoothly. A process that makes these both compatible has been desired.

Further, there is a problem of lowering the substrate temperature during film formation. This is because it is difficult to form a composite device with a conventional device (especially Si-based) when a film forming process with a high substrate temperature is entered into the manufacturing process.

The inclusion of impurities in the film, especially hydrogen, centering on the grain boundaries is also an important issue when considering the various applications of the diamond thin film. Although the mechanical strength has a great influence on the resistance value and the energy gap in the field of electronic materials, the method for controlling the impurity concentration during film formation has not yet been clarified. ..

[0013]

The process in the present invention solves the above problems. In the present invention, attention is paid to the fact that halogenated hydrocarbon is used as a material gas as such means.

[0014] 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
Although it is only l, it is an order of magnitude larger at -340.0 KJ / mol when solid carbon is made from CF ₄ and hydrogen, and therefore, diamond film formation may be easily performed.

However, in their consideration, the activation energy is not taken into consideration at all, and it is not sufficient to discuss the reactivity only with free energy. Graphite is also formed in the same way, but its consideration was easy and their modeling was insufficient. Their consideration, of course, is thermal energy and cannot be adapted to the plasma state. However, it is expected that the use of halogenated hydrocarbons will lead to the efficient formation of effective active species even in plasma. Therefore, when the film is formed by actually introducing it into the plasma reaction, good results can be obtained. It just happened.

[0016] That is, specifically, CF4, CHF₃, CH₂
F₂Halogenated hydrocarbons such as hydrogen and hydrogen, or as required
Gas with an inert gas added as a source gas
In the plasma CVD system, the substrate pretreatment is omitted and
Comparatively high speed (2 to several times faster than when using conventional materials)
Carbon material containing diamond at the above deposition rate or
It is possible to form a thin film of diamond material
And to adjust the concentration of the halogenated hydrocarbon
Allows adjustment of the impurity concentration in the film centered on hydrogen
It came to discover that.

We attribute this to the efficient formation of effective active species in the plasma from halogenated hydrocarbons mixed with hydrogen. It is conjectured, but unlike the Patterson model, I suspect that the diradical function is strong in plasma.
This is because diradical may cause an insertion reaction between C—H bonds.

According to our method, the substrate temperature can be lowered. As described below, the diamond peak could be observed even at a low substrate temperature of 100 ° C to 200 ° C. This is also because the active species necessary for film formation are efficiently formed.

We have also confirmed in the present invention that simultaneous implantation of hydrogen and halogen into diamond is possible. Implantation of such a foreign element may be effective for device fabrication together with the aforementioned impurity concentration adjustment.

By the way, when a diamond thin film is produced by the method of the present invention, hydrogen halide such as hydrogen fluoride is generated as a by-product. It is practically difficult to use the quartz and stainless steel used in. 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, as for 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.

The substrates used in connection with the present invention also have the above-mentioned restrictions on materials, and the substrates used are, for example, Si, sapphire, alumina, monel, tungsten carbide, and other oxidation resistant metal materials.
Hereinafter, the present invention will be described in more detail with reference to Examples.

[0022]

【Example】

Example 1 First, an example of microwave CVD will be described below. . We performed plasma CVD using CF ₄ + hydrogen system as a material. The film forming conditions are shown. The pressure in the chamber is 1 to 100 torr, preferably about 40 torr. The CF ₄ concentration is 10% or less, preferably 2-3% by hydrogen dilution. From the result of Raman measurement of the film, it was confirmed that the film quality was improved when the CF ₄ concentration was lowered, but when the concentration is low, the film formation rate becomes slow, and 2-3% is appropriate in our apparatus. Met.
The substrate temperature was 600 ° C to 900 ° C. According to Raman measurement of the formed film, the film quality was good at a substrate temperature of about 800 to 820 ° C. Alumina was used as the material of the chamber in consideration of resistance to halogen.

Microwave plasma C used in this experiment
The configuration of the VD experimental device is shown in FIG. Basically, it is a normal microwave plasma CVD method and microwaves are introduced into the chamber through the window 5. Output of microwave is 1
It is set to 00 to 800 W. Normally, it is operated at 400 to 600W. The substrate used Si, alumina, and monel. Here, the region 3 in FIG. 1 shows the distribution of plasma when the substrate 4 and the substrate holder 9 are not arranged. (It should be noted that the plasma distribution when the substrate is arranged is different from the plasma 3 in the figure.) The substrate was arranged at position 6 or position 7. No film formation was seen when the substrate was spaced too far from the substrate, such as position 8. The film forming rate was about 2 to 3 μm / hour.
When Raman spectroscopic measurement was performed after taking out the film from the chamber after the film formation time of 4 hours, the results shown in FIG. 2 are obtained. A diamond peak is seen around 1332 cm ^-1 . Although this is a film on the Si substrate arranged at the position 6 in FIG. 1, similar peaks were observed on other Monel and alumina substrates. Although there is a broad peak near 1500 cm ^-1 which is considered to be an amorphous carbon material, a sharp diamond peak can 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. 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.

When plasma emission analysis was carried out at the time of film formation, radicals such as CF ₃ and CF ₂ were found, but carbon completely dissociated from CF ₄ and CF radicals were not found. This indicates that there is an active species that is particularly effective for film formation in correlation with microwave power and other factors. In fact, in the latter plasma, where radical peaks are strong, only a film with poor film quality could be formed.

FIG. 3 shows the result of Raman measurement of the film in which the Si substrate was placed at the position 7 in FIG. Although the film quality was rather poor, a diamond peak was also observed.

Further, although it was shown above that the substrate temperature can be lowered according to our method, specifically, the substrate temperature is 100
The substrate temperature dependence was investigated in the range of ℃ to 900 ℃.
The substrate temperature is cooled by water because it has a heating effect by plasma. The substrate temperature is measured by installing a thermocouple on the back side of the substrate. A film having a substrate temperature of 400 ° C. or higher was formed at position 6 in FIG. 1, and a film having a substrate temperature lower than that was formed at position 7 in FIG. When Raman measurement of the formed film was performed, the peak of diamond was weak, but it could be confirmed even in the films at substrate temperatures of 100 ° C and 200 ° C.

Further, we performed SIMS analysis on the film formed at a substrate temperature of 750 ° C. The results showed that the concentration of halogen and hydrogen taken into the film changed by changing the concentration of halogenated hydrocarbon. Specifically, it was shown that the concentration of halogen and hydrogen in the film was increased by increasing the concentration of halogenated hydrocarbon. That is, according to the method of the present invention, the concentrations of halogen and hydrogen in the film could be controlled. Thereby, there is a sufficient possibility of manufacturing an electronic device using diamond or a carbon material containing diamond.

[Embodiment 2] In this embodiment, an example in which the material gas of Embodiment 1 is changed is shown. That is, the raw material is CHF ₃
And hydrogen, and helium was further added in order to lower the concentrations of CHF ₃ , two types were performed. For each parameter, the CHF ₃ concentration was 5 to 0.5%, the substrate temperature was 750 to 820 ° C., and the film formation time was 4 hours. The substrate uses Monel. The apparatus and others used in the experiment are the same as in Example 1.

In both cases where He was contained in the reaction gas and when He was not contained, a peak due to diamond was clearly confirmed from the results of Raman spectroscopy. Focusing on the film formation rate, the film formation rate in the case of using CHF ₃ was two to several times faster than that in the case of using CF ₄ . (However, the film formation rate with He was almost the same as that with CF _4. ) Specifically, when CF ₄ was used at a concentration of 2%, it was 2.5 to 3 μm / hour. When CHF ₃ was used, it was ₃ to 8 μm / hour. That is, in the case of our apparatus, CHF ₃ was more suitable for diamond film formation in the plasma CVD method. It should be noted that, since the film forming rate was 0.5 to 1 μm when a conventional material such as methane was used, it is understood that the use of halogenated hydrocarbon contributes to the improvement of the film forming rate.

[Example 3] In this experiment, in Example 1
An example in which the raw materials are changed in the above process is shown. That is,
CHCl ₃ , hydrogen and He were used as raw materials. In Examples 1 and 2, 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 vaporizer. Further, since hydrogen chloride is inevitably generated during film formation, the chamber naturally uses an alumina tube. Substrate temperature is 700-8
It was performed under the conditions of 00 ° C. and the film formation time of 8 hours. The apparatus and others used in the experiment are the same as in Example 1.

When the obtained thin film was measured by Raman spectroscopy, a very distinct peak due to diamond was confirmed. Regarding film thickness, CHF ₃ concentration 2
It was confirmed that the deposition rate was higher than that of the result of%.

[Embodiment 4] In this embodiment, an example of forming a film by a magnetic field microwave plasma CVD method will be described. The above method is effective for forming a large-area thin film, and it is possible to form a film even on a wafer of at least 4 inches and 6 inches or more. Although it corresponds to the microwave plasma method, it is also characterized in that it is possible to form a film having excellent film quality as compared with RF plasma or the like. A schematic diagram of the apparatus used in this example is shown in FIG. By utilizing the interaction between the magnetic field generated by the magnetic field coil and the microwave introduced into the reaction chamber from the microwave waveguide, the reactive gas introduced from the gas inlet 2 is efficiently excited, and carbon containing diamond is placed on the substrate 4. Form a material or diamond material. Board 4
Is externally controlled by heating the substrate holding plate. The stray electric field 13 can also be applied to the substrate 4. Usually, when forming diamond, a gas obtained by diluting a gas such as methane, carbon monoxide, ethylene, methanol, and ethanol or a liquid hydrocarbon with hydrogen is used as a reaction gas, and water, carbon dioxide, and oxygen are used. A gas added in a small amount may be used. We used CF ₄ and hydrogen as source gases. The vacuum degree is 0.02 to 5 tor when showing some parameters of film formation.
r preferably 0.1 to 2 torr, substrate temperature 700 to 800
C., microwave output 1-5 kw. The substrates used are Si, Monel and WC. Film formation was performed at position 6. The inner wall of the chamber was coated with SiC. The magnetic field was 200 to 2000 gauss. When the optimum conditions were obtained from Raman measurement with our apparatus, the magnetic field of 800 to 900 gauss was appropriate. At this time, the film forming rate was 3 μm / hour. Film formation was carried out for 4 hours with a magnetic field of 850 gauss and a CF ₄ concentration of 3%, and Raman measurement of the film was performed. As a result, a peak of an amorphous component and a peak of diamond were observed. Then CF ₄
When the film thickness was further reduced to 1.5% and the film was formed for 4 hours, the Raman peak of the formed film became clearer. From this fact, it is expected that the CF ₄ concentration during film formation also has a great influence on the film quality in this example.

Example 5 In this example, the microwave plasma CVD apparatus used in Example 1 was used to try to adjust the hydrogen concentration in the film. In our study, it was found that the hydrogen concentration in the film changed depending on the supply concentration of halogenated hydrocarbon. Therefore, in this example, an experiment was conducted to investigate the specific effect. The film forming conditions are as follows.
CF ₄ + hydrogen system was used as the reaction gas, and the pressure in the chamber was 40 Torr. The substrate was made of Si and heated to 800 ° C. to form a film.

The concentration of CF ₄ is set to 10% or less, 2.5%,
Film formation and hydrogen concentration measurement in the film by SIMS were performed at three points of 5.0% and 7.4%. As a result, 1.
0 × 10 ²¹ , 1.5 × 10 ²¹ , 1.7 × 10 ²¹ (atoms / c
m ³ ), indicating the hydrogen content, and the concentration of CF _{4 in} the reaction gas 2.
The hydrogen concentration changes in the order of 5% <5.0% <7.4%,
That is, it was found that the hydrogen concentration in the film can be changed by changing the halogenated hydrocarbon concentration.

Although this tendency could not be evaluated quantitatively, similar results were obtained with respect to the concentrations of fluorine and silicon. It is considered that the impurity content in the film can be controlled by examining other conditions, mainly the change in the concentration of halogenated hydrocarbon.

[0036]

As described above, in the plasma CVD, the film forming process without pretreatment is established and the film forming speed is improved. This is because halogenated hydrocarbons are used as a material, and by making a device to make it possible, it is possible to efficiently generate active species involved in film growth. It was also possible to obtain a value several times higher than the conventional film formation rate.
Moreover, it was clarified that the impurity concentration in the diamond thin film can be adjusted based on the adjustment of the amount of halogenated hydrocarbon added.

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

[Brief description of drawings]

FIG. 1 shows a microwave plasma CVD apparatus used in the present invention.

FIG. 2 shows an example of the results of Raman spectroscopy of a film formed according to the present invention.

FIG. 3 shows an example of the results of Raman spectroscopy of a film formed according to the present invention.

FIG. 4 is a magnetic field microwave plasma C used in the present invention.
3 shows a VD device.

[Explanation of symbols]

 1 Reaction Chamber 2 Gas Inlet 3 Plasma Region 4 Substrate 5 Window 6 Position 7 Position 8 Position 9 Substrate Holder 10 Waveguide 11 Exhaust 12 Magnetic Field Generation Coil 13 Stray Electric Field Generation Part

Claims (9)

[Claims] 1. A method for producing a carbon material containing diamond or a diamond material using plasma CVD, which comprises using a halogenated hydrocarbon and hydrogen or a raw material consisting of the halogenated hydrocarbon and hydrogen and a rare gas as a diluent gas. A method for producing a carbon material, characterized in that the pressure during film formation is 100 torr or less. 2. The method for producing a carbon material according to claim 1, comprising the step of forming a film by placing the raw material in a plasma state and disposing a substrate inside the plasma region or in contact with the plasma. 3. The method for producing a carbon material according to claim 1, wherein the film forming rate is 1 μm or more. 4. The method for producing a carbon material according to claim 1, wherein the film forming step does not include a step of pretreatment of the substrate. 5. The method for producing a carbon material according to claim 1, wherein a microwave plasma CVD method or a magnetic field microwave plasma CVD method is used as the plasma CVD method. 6. An apparatus for producing a carbon material containing diamond or a diamond material using plasma CVD, wherein the inner wall of a reaction chamber of the apparatus is a material having resistance to halogen, hydrogen halide, etc. and their plasma. An apparatus for producing a carbon material, comprising: 7. The carbon material manufacturing method according to claim 6, wherein the inner wall of the reaction chamber of the apparatus is made of any one of alumina, sapphire and SiC, or an oxidation resistant metal material or a coating film of the material. apparatus. 8. An apparatus for producing a carbon material containing diamond or a diamond material using plasma CVD, wherein the reaction chamber of the apparatus functions as a structural material at high temperature, and halogen, hydrogen halide, etc. A carbon material manufacturing apparatus, which is formed of a material having resistance to plasma. 9. A method for producing a carbon material containing diamond or a diamond material using plasma CVD, using a halogenated hydrocarbon and hydrogen or a raw material comprising the halogenated hydrocarbon and hydrogen and a rare gas as a diluent gas, A method for producing a carbon material, characterized in that the hydrogen concentration in a film is arbitrarily changed by adjusting the concentration of halogenated hydrocarbon.