JPH04318172A - Method for synthesizing rigid carbon film and device therefor - Google Patents

Abstract

PURPOSE:To obtain a method and a device for synthesizing a rigid carbon film by which this rigid carbon film excellent in film quality is uniformly synthesized at high velocity. CONSTITUTION:A vessel 6 insulated from earth potential is arranged in a vacuum tank 11 and a heating filament 5 is provided therein. A meshy electrode 2 is provided to the opening part of the vessel. Plasma is generated in this vessel 6. Since the circumference of the vessel is interrupted from earth potential, plasma 4 is maintained at high density in an equilibrium state. Plasma density and electric potential are uniformed in the vicinity of the meshy electrode 2 faced with a base body 1. In this state, bias is impressed to the base body 1 and ions are accelerated by both plasma 4 and the electric potential of the base body 1. A rigid carbon film is synthesized on the base body 1.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for synthesizing hard carbon membranes.

0002

BACKGROUND OF THE INVENTION In recent years, hard carbon films with excellent wear resistance and lubricity have been actively researched, and attempts have been made to apply them as protective films for tools, sliding members, etc. A hard carbon film is also called a diamond-like thin film, and although it is amorphous, it contains many diamond bond (sp3) components and has a Knoop hardness of 3.
It has an excellent hardness of 000 to 10,000. Furthermore, because it exhibits physical properties such as electrical and optical properties that are close to those of crystalline diamond, it is a material that is expected to find application in a variety of fields.

[0003] As a method for synthesizing this diamond-like thin film, a method is generally known in which a carbon-containing gas is turned into plasma and the physical energy and chemical energy of the generated ions and radicals are utilized. for example,
JP-A-60-65796 discloses a method for synthesizing a hard carbon film by subjecting raw material gas to plasma decomposition using thermionic bombardment from a hot filament. Below, a description of the prior art using this method will be given.

FIG. 12 shows a schematic configuration of a conventional hard carbon film synthesis apparatus. There is a hot filament 5 as a plasma generation source inside the vacuum chamber 11, and a plasma discharge electrode 14 is installed above the hot filament 5. Furthermore, a substrate 1 on which a film is synthesized is installed above via a shutter. The plasma discharge electrode 14 and the base 1 are connected to external power supplies 9 and 10, and are configured to control their potentials. Furthermore, a permanent magnet 13 is installed at the bottom to increase plasma density.

Next, a procedure for synthesizing a hard carbon film using this conventional apparatus will be explained. First, the inside of the vacuum chamber 11 is evacuated, and then the hot filament 5 is heated with electricity. Ethylene as a raw material gas is introduced into the vacuum chamber 11 from the gas inlet 8. Next, when a positive voltage is applied to the plasma discharge electrode 14, the thermoelectrons emitted from the hot filament 5 are accelerated and plasma is generated. Furthermore, when a magnetic field is applied by the permanent magnet 13, the thermoelectrons perform a spiral motion, the number of collisions with ethylene molecules increases, and the plasma density increases. On the other hand, a negative bias is applied to the substrate 1 from the power supply 9,
It accelerates ions in plasma to synthesize a hard carbon film on a substrate.

[0006]

[Problems to be Solved by the Invention] However, when attempting to synthesize a hard carbon film using this conventional structure, the following problems occur.

That is, since the plasma generated by the hot filament 5 has a constant potential at the initial stage of generation, it discharges with low potential parts, particularly with the ground potential around the plasma. Therefore, a non-uniform potential gradient is formed within the plasma. As a result, the plasma state facing the substrate 1 forms a non-uniform potential distribution, and the abundance ratio of ions and radicals is also distributed depending on the location. Furthermore, since a high voltage is applied to the substrate 1, the plasma does not spread toward the substrate, but is discharged laterally and spread throughout the vacuum chamber. As a result, the plasma density decreases, and the decomposition efficiency and ionization rate of the source gas also decrease.

[0008] In the conventional method, since film synthesis is carried out under such conditions, it is difficult to obtain a hard carbon film of uniform quality and thickness on a substrate. Moreover, the plasma spreads throughout the vacuum chamber and the plasma density is reduced, which has a negative effect on film quality and film adhesion, and also causes problems such as slowing down the film formation rate.

As described above, according to the conventional method, it is not possible to generate uniform and high-density plasma, and as a result, the films synthesized by this method have problems in terms of uniformity, film quality, film formation speed, etc. .

0010

[Means for Solving the Problems] In order to solve the above problems, a container insulated from earth potential is placed in a vacuum chamber, plasma is generated inside the container, and a mesh is installed at the opening of the container. A mesh-shaped electrode is provided, and a base body is disposed outside the container at a position facing the mesh-shaped electrode. Then, the ions are accelerated by the potential difference between the plasma potential controlled by the mesh electrode and the potential of the substrate, and a membrane is synthesized on the substrate.

In this case, it is more preferable to surround the flight path of ions from the plasma to the substrate with a member insulated from the ground potential.

0012

[Operation] The operation of the above means is as follows.

That is, according to the above configuration, when a potential is applied to the mesh electrode, plasma is generated only in a limited area inside the container, and a high-density state can be maintained. Here, since the container is insulated from the ground potential, the plasma will not be discharged to the ground potential. In other words, the plasma has no discharge area other than the mesh electrode, and the electric field in the plasma is entirely directed toward the mesh electrode, thus maintaining this equilibrium state.

Furthermore, in the region near the mesh electrode facing the substrate, the plasma density and plasma potential are made uniform by the potential supplied to the electrode.

As a result, the density and potential of ions generated in this region are also uniform. In other words, the mesh electrode not only accelerates electrons and generates plasma, but also has the role of uniformizing and controlling the plasma potential.

[0016] Therefore, the hard carbon film synthesized in this state can achieve uniformity in film quality and film thickness, and can also realize an improvement in the film formation rate using high-density plasma. Also,
By freely controlling the plasma potential and the potential of the substrate, desired acceleration energy can be given to the ions, and a high quality hard carbon film can be obtained.

Furthermore, in this case, if the ion flight path is surrounded by a member insulated from the ground potential, the following effect can be obtained. In other words, by surrounding the flight path of these ions with a member insulated from earth potential,
It is possible to suppress the diffusion of ions from the plasma toward a direction other than the substrate.

That is, some ions are accelerated toward the substrate, while others fly in a direction other than the substrate. Ions accelerated in a direction other than the direction of the substrate are blocked from advancing by this member on the way.

At this time, since this member is insulated from the ground potential, the electric charge is stored as it is, and charge-up occurs. If the synthesis of the film continues, the ions will be repelled by the charged-up member and their flight direction will be corrected toward the substrate. As a result, ions are concentrated toward the substrate, increasing the synthesis rate and improving film quality.

[0020]

[Example] Next, an example of the present invention will be described.

FIG. 1 schematically shows the configuration of a first embodiment of the present invention. In the center of the vacuum chamber 11, a raw material gas inlet 8 is insulated from the ground potential, that is, electrically floating.
A container 6 directly connected to the container 6 was placed. A hot filament 5 was installed as a plasma generating means inside this container 6, and a mesh electrode 2 was installed above the container 6. A potential is applied to the mesh electrode 2 by a DC power supply 10 outside the vacuum container 11 . Furthermore, the substrate 1 was placed above it, and the substrate potential was controlled by an external DC power source 9.

Next, the procedure for synthesizing the membrane will be explained. First, the inside of the vacuum chamber 11 is evacuated to 10 −4 Torr using a vacuum pump. Next, Ar gas was introduced from the raw material gas inlet 8, and the gas pressure was adjusted to 10 −3 Torr by adjusting the gas flow rate. At the same time, the hot filament 5 is electrically heated and thermoelectrons are supplied into the container 6.

A positive potential of +90 V was applied to the mesh electrode 2 to generate Ar plasma. In this state, a negative voltage of 2000 V was applied to the substrate 1, and the surface of the substrate was cleaned by Ar ion sputtering for 20 minutes. After cleaning was completed, plasma discharge was stopped and Ar gas supply was stopped. Next, the supply of methane or benzene, which is a carbon raw material, was started, and the potential of the substrate was adjusted in the range of 0 to -5000V. FIG. 2A shows the normalized distribution of plasma density measured from the plasma emission intensity between A and A in FIG. 1 when plasma discharge is resumed and carbon film synthesis is started. At the center of the hot filament, the amount of thermoelectrons supplied is the largest and the density is high, but the distribution near the mesh electrode is almost average, and a uniform and high-density plasma is generated.

[0024] A hard carbon film was synthesized on a substrate by the operating procedure as described above. Next, the characteristics of the membrane synthesized on the substrate will be described.

First, the uniformity of the film synthesized in this example was
The uniformity of the film was compared with that of a film formed using a conventional method. Figure 3(a)
shows the film thickness distribution of the film synthesized in this example. In the film forming region corresponding to the opening of the container 6, the film thickness unevenness is ±2% or less, and the film is uniformly formed.

On the other hand, for comparison, the film thickness distribution when a film was formed on the same substrate as in this example using the conventional method is also shown in FIG. 3(a). In the conventional method, film thickness unevenness is large depending on the distribution of plasma density.

Next, membranes were synthesized using two types of raw material gases, methane and benzene, and comparative experiments were conducted. In addition,
The film forming conditions in this comparative experiment are as shown in Table 1.

[0028]

[Table 1] FIG. 4 shows the relationship between the potential difference between the mesh electrode 2 and the substrate 1 and the film hardness. No matter which raw material gas is used, 100
Although the hardness tends to peak at a relatively low potential difference value of 0 V or less, especially when benzene is used, the film shows a hardness of 6000 on the Knoop hardness, and the film quality is improved. However, when the potential difference is less than 100 V, the energy of the ions is too small and only a soft film is synthesized. Also, if the energy is too high, the film quality tends to deteriorate.
In particular, when the voltage exceeds 5000 V, high-energy ions are synthesized while damaging the substrate and the underlying layer of the film, resulting in a decrease in film quality.

Furthermore, FIG. 5 shows the relationship between the film formation rate and the potential difference when these samples were prepared. The film formation rate is constant with respect to the potential difference, and the film formation rate is particularly high when benzene is used. This means that at a constant gas pressure, benzene, which has a larger number of carbon atoms in one molecule,
The amount of carbon supplied also increases and the synthesis rate improves.

Furthermore, at a constant current density, the energy distributed per carbon atom is smaller in benzene. Therefore, it is possible to realize a hard carbon film that is less likely to damage the underlying layer. From these facts, it is possible to synthesize a hard carbon film with excellent hardness and film formation speed by using a material with a large number of carbon atoms contained in one molecule as a raw material.

Next, the ion current density was varied and the membrane properties were compared. The experimental conditions are shown in (Table 2).

[0032]

[Table 2] FIG. 6 shows the relationship between current density and film formation rate, and FIG. 7 shows the relationship between current density and film hardness. It can be seen that by increasing the current density, the film formation rate is improved while the film quality is maintained. However, when the current density was increased by 1.0 mA/cm2 or more, the adhesion of the film deteriorated due to electrolytic concentration due to ions, resulting in peeling. Also, 0.01mA/cm
When it was 2 or less, the film formation rate became very slow.

Next, the gas pressure in the vacuum chamber was varied depending on the flow rate of the raw material gas introduced, and the relationship with film quality was investigated. The experimental conditions are shown in (Table 3).

[0034]

[Table 3] Figure 8 shows the relationship between the gas pressure in the vacuum chamber and the Knoop hardness of the membrane.

FIG. 9 shows the relationship between the gas pressure and the ion ratio calculated from the amount of ions reaching the substrate.

Furthermore, FIG. 10 shows the relationship between gas pressure and film formation rate. These figures show that by changing the gas pressure, the ratio of ions and radicals reaching the substrate changes. That is, when the gas pressure is increased, the amount of radicals that reach the substrate 1 increases, and the film formation rate increases.

However, it can be seen that as the number of radicals increases, the ion ratio decreases and the hardness of the film also decreases. This means that a membrane of good quality can be obtained by configuring the membrane with a higher ion ratio, and the ion ratio is at least 50% or more.

Next, a second embodiment of the present invention will be described. FIG. 11 shows a schematic configuration of an apparatus according to a second embodiment of the present invention.

In FIG. 11, components having the same functions as those in FIG. 1 are given the same reference numerals as in FIG.

In the apparatus of this embodiment, a cylindrical tube 12 insulated from the ground potential was installed around the path through which ions fly from the plasma toward the substrate.

[0041] Using the apparatus of this example, an experiment was conducted to synthesize a hard carbon film. The membrane synthesis procedure is exactly the same as in the first example. The experimental conditions are shown in (Table 4).

[0042]

[Table 4] (Table 5) compares the case where this configuration is implemented and the case where the configuration of FIG. 1 is not implemented in terms of film formation rate, ion current density, and film hardness.

[0043]

[Table 5] According to the apparatus of this embodiment, ions in the plasma can be concentrated in the direction of the substrate and the current density can be increased. That is, some ions are accelerated toward the substrate, while others fly in a direction other than the substrate, and the ions accelerated in a direction other than the substrate are blocked from advancing by this member on the way.

At this time, since this member is insulated from the ground potential, the charges of the ions whose progress is blocked by this member are retained as they are, and charge-up occurs. If the membrane synthesis continues in this state, the ions will be repelled by the charged-up member and their flight direction will be corrected toward the substrate. As a result, ions are concentrated toward the substrate, increasing the synthesis rate and improving film quality. Moreover, it does not particularly affect the film quality.

Note that the present invention is not limited to the experimental conditions shown in the examples described above. Further, the container or member insulated from the earth potential described in the present invention may be made of metal or an insulating member.

[0046] Furthermore, an external magnetic field or an external electric field may be used to increase the density of plasma. Furthermore, the raw materials are not limited to methane and benzene, and auxiliary gases such as argon and nitrogen may be added.

[0047]

[Effects of the Invention] As is clear from the above examples, the present invention makes it possible to synthesize high-quality hard carbon films uniformly, stably, and at high speed, and enables devices to which carbon films are applied. , parts, etc. can be expanded to various fields, and it is also highly effective from an industrial perspective.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a first embodiment of the hard carbon film synthesis apparatus of the present invention.

[Fig. 2] (a) is a characteristic diagram of plasma density in the example device of Fig. 1; (b) is a sectional view of main parts of the example device to show the positional relationship of plasma density;

[Figure 3] (a) is a film thickness distribution characteristic diagram of a film-formed sample obtained using the same example apparatus; (b) is a cross-sectional view of the main part of the example apparatus to show the positional relationship of the film thickness distribution;

[Figure 4] Relationship diagram between the hardness and potential difference of the film obtained by the same example device

[Figure 5] Relationship diagram between film formation speed and potential difference in the same example device

[Figure 6] Relationship diagram between film formation speed and current density in the same example device

[Figure 7] Relationship diagram between hardness and current density in the same example device

[Fig. 8] Relationship diagram between film formation speed and gas pressure in the same example apparatus

[Figure 9] Relationship diagram between ion ratio and gas pressure in the same example device

[Figure 10] Relationship diagram between membrane hardness and gas pressure in the same example device

FIG. 11 is a configuration diagram of a device according to a second embodiment of the present invention.

[Figure 12
]Block diagram of a conventional hard carbon film synthesis device

[Explanation of symbols]

1 Base 2 Mesh electrode 3 Insulating material 4 Plasma 5 Filament 6 Container 7 Insulating material 8 Raw material gas inlet 9 DC power supply 10 DC power supply 11 Vacuum chamber 12 Cylindrical tube 13 Permanent magnet 14　Plasma discharge electrode

Claims (7)

[Claims] [Claim 1] Converting a raw material gas containing carbon into plasma,
In a method for synthesizing a carbon film that forms a thin film on a substrate, plasma generated by a hot filament is insulated from ground potential in a vacuum chamber, and the plasma potential of the plasma facing the substrate is controlled; A method for synthesizing a hard carbon film, characterized in that a potential is applied to opposing substrates, and ions in the plasma are accelerated and synthesized toward the substrate due to the potential difference between the plasma potential and the substrate potential. 2. The method for synthesizing a hard carbon film according to claim 1, wherein ions account for 50% or more of the particles irradiated onto the substrate. 3. The method for synthesizing a hard carbon film according to claim 1, wherein a carbon source containing at least a plurality of carbon atoms in one molecule is used as a raw material. 4. A current density of ions irradiated onto the substrate is in a range of 0.01 to 1.0 mA/cm2.
Synthesis method of hard carbon film described 5. The potential difference between the plasma and the substrate is 100
The method for synthesizing a hard carbon film according to claim 1, wherein the voltage is 5000V. 6. A container having a hot filament for turning raw material gas into plasma and a mesh electrode at the opening thereof and insulated from earth potential, and facing the opening of the container,
An apparatus for synthesizing a hard carbon film, comprising a vacuum chamber provided with a substrate and a holding means for holding the substrate, and an application means for applying a potential to the electrode and the substrate. 7. A container having a hot filament for turning source gas into plasma and a mesh electrode at the opening and insulated from earth potential, a substrate and a holding means for holding the substrate opposite the opening of the container. and a vacuum chamber whose periphery between the opening of the container and the substrate holder is surrounded by a member insulated from earth potential, and an applying means for applying a potential to the electrode and the substrate. A hard carbon film synthesis device featuring