JPS62185879A - Formation of amorphous carbon film - Google Patents

Abstract

PURPOSE:To obtain a homogeneous amorphous carbon film of a large area by placing a high frequency electrode opposite to a substrate and applying bias voltage to the electrode to cause electric discharge in gaseous hydrocarbon under a prescribed pressure. CONSTITUTION:A high frequency electrode 4 is placed opposite to a substrate 5 placed on a grounded electrode 2. Positive DC bias voltage is applied to the electrode 4 from a power source 3 to cause electric discharge in an atmosphere of gaseous hydrocarbon under <=20 Pa pressure. The gaseous hydrocarbon may be mixed with an inert gas. An amorphous carbon film is formed by the electric discharge.

Description

[Detailed Description of the Invention] [1M Industrial Application Field] The present invention relates to a method for forming a highly hard amorphous carbon film.

[Prior art] Amorphous carbon films have various excellent properties such as high hardness, itching resistance, high thermal conductivity, and high chemical resistance. It is wide-ranging.

For this reason, various methods for forming an amorphous carbon film have been devised, and the methods can be broadly classified as follows.

■ Sputtering method As shown in FIG.
3, H2 gas to which Ar gas has been added is introduced, a graphite targeter (106) is provided on the electrode 105 side connected to the high frequency power source 104, and a discharge is caused between it and the ground electrode 107 to cause a reaction in the H2 atmosphere. The carbon atoms of the graphite target 107 are released by natural sputtering, and a carbon film is formed on the substrate 108 provided on the ground electrode 107 side.

■Ion Beam Method As shown in Figure 7, solid carbon or hydrocarbon gas (methane, butane, benzene, etc.) is used as the ion source 109, and a carbon film is formed on the substrate 110 to which a negative high voltage is applied. It is something to do.

■Plasma CVD method (a) Substrate electrode type As shown in FIG. 8, air is removed from the exhaust port Ill, and hydrocarbon gas is introduced from the gas inlet 113 into the reduced pressure chamber 112, which is made into a high vacuum. installed electrode 115
is used as a high-frequency electrode, glow discharge is generated between the electrode 116 and one electrode 116, hydrocarbons are dissociated by glow discharge decomposition method, and a carbon film is formed on the substrate 114. At this time, a negative high voltage is applied to the substrate side electrode 115.

(b) Probe electrode type As shown in FIG. 9, air is removed from the exhaust port 116, and hydrocarbon gas is introduced from the gas inlet 118 into the decompression chamber 117, which has been made into a high vacuum. A probe electrode 120 for applying a positive voltage is provided, and while a high negative voltage is applied to the electrode 122 on which the substrate 121 is installed, the emission of thermionic electrons supplied from the filament 119 is utilized.Glow discharge decomposition method A carbon film is formed on the substrate 121 by a method of dissociating hydrocarbons.

[Problems to be Solved by the Invention] However, the following technical problems have been pointed out in the above-mentioned prior art.

That is, the sputtering method, the ion beam method, and the above-mentioned plasma CVD method can all form a film with uniform quality over a small area.

For example, in the sputtering method, the range in which a uniform I& film can be formed is about 1/2 of the target area, and considerable effort is required to uniformly form a film over a large area.

In addition, in each of the above methods, it is necessary to apply a high voltage to the substrate side, so it is difficult to transport or rotate the substrate for the purpose of forming a film on a large area substrate. This method becomes complicated and is not suitable for configuring a film forming line.

SUMMARY OF THE INVENTION Therefore, the present invention aims to provide a film forming method that can form a uniform high-hardness amorphous carbon film over a large area using a relatively small electrode, and also allows the substrate to be transported and rotated relatively easily. created for a purpose.

[Means to solve the problem] Unexploded IJJ uses hydrocarbon gas as a raw material and plasma C
In a method of forming an amorphous carbon film by the VD method, a high frequency electrode to which a positive DC bias voltage is applied is arranged opposite to a substrate placed on the ground electrode side,
The present invention relates to a method for forming an amorphous carbon film characterized by performing discharge in a hydrocarbon gas atmosphere of Pa or less.

The basic principle of the method of forming an amorphous carbon film of the present invention is shown in FIG.

1 is a decompression chamber provided with an exhaust port 1a and a gas inlet 1b, and in the same chamber 1, a ground electrode 2 and an electrode 4 connected to a power source 3 for applying a positive DC bias voltage and a high frequency voltage are placed facing each other. A substrate 5 is installed on the ground electrode z side.

Here, air is first removed from the decompression chamber 1 through the exhaust port 1a to create a high vacuum state, and then hydrocarbons are supplied from the gas inlet 1b to maintain the inside of the decompression chamber 1 at 20 Pa or less. Then, when a positive DC bias voltage and a high frequency voltage are applied from the power supply 3 to the electrode 4, glow discharge occurs between the earth electrode 2 and the electrode 4, and the hydrocarbon gas in the decompression chamber 1 is decomposed into plasma by glow discharge decomposition. The plasma species are then dissociated and adhere to the surface of the substrate 5 on the ground electrode z side, forming an amorphous carbon film.

In the present invention, the discharge is performed in a hydrocarbon atmosphere of 20 Pa or less as described above, but an inert gas such as Ne, Ar, or Kr may also be added to the hydrocarbon gas.

Furthermore, as shown in FIG. 2, the side of the space 6 facing the substrate 5 and the electrode 4 connected to the power supply 3 that applies a positive DC bias voltage and high frequency voltage may be covered with a smesh 7. This is effective in forming a uniform film.

[Function] In the present invention, in addition to a high frequency voltage, a positive bias voltage is applied to the electrode 4, and discharge is performed under a low gas pressure of 20 Pa or less, so that radicals (active species) incident on the substrate 5 are energy increases, making it possible to form a highly hard amorphous carbon film. By the way, as a general tendency, the higher the DC bias voltage, the higher the film hardness, but if the voltage is too high, arc discharge occurs and the discharge becomes unstable, making it impossible to obtain a uniform film formation. The lower the pressure, the higher the film hardness; however, if the pressure is too low, the discharge becomes unstable or stops, while if the gas pressure is too high, the film hardness decreases.

Based on such characteristics, film hardness can be controlled over a wide range by appropriately changing the DC bias voltage and gas pressure.

Further, when an inert gas is added to the hydrocarbon gas, the discharge becomes stable, and a uniform film can be obtained.

Furthermore, if the sides of the opposing space 6 between the substrate 5 and the electrode 4 are covered with earth mesh, the plasma between the substrate 5 and the electrode 4 can be concentrated in the opposing space 6, and the substrate 5 can be Even if the area is large, it is possible to form a film uniformly over almost the entire surface.

This is based on the following reasons.

Under low gas pressure, according to Pfzien's law, the discharge will be stable at a point where the distance from the electrode 4 is large, but generally the distance between the electrode 4 and the inner wall of the decompression chamber 1 is longer than the distance between the electrode 4 and the substrate 5. Since the pressure is also large, a dense plasma will be generated between the electrode 4 and the inner wall of the decompression chamber l. When Paschen's law is plotted on a graph, the area indicated by 8 in Figure 3 is the film formation area, so it is necessary to maximize the distance between the electrode 4 and the substrate 5 in the discharge system. plays a role in realizing this, and can uniformly concentrate the plasma in the opposing space 6.

[Example] Next, an example of the present invention will be described using FIGS. 4 and 5.

FIG. 4 shows a schematic diagram of a flat plate type amorphous carbon membrane tr and membrane apparatus for carrying out the method of the present invention, and 11 is a decompression chamber provided with an exhaust port 11a and a gas inlet port 11b; Inside, an earth electrode 12 and an electrode 17 connected to a DC power supply 14 that applies a positive DC bias voltage via a filter circuit 13 and a high frequency power supply 16 that applies a high frequency voltage via a matching circuit 15 are arranged facing each other. A substrate 18 is installed on the ground electrode 12 side.

Here, first, air is extracted from the decompression chamber 11 through the exhaust port 11a, and a high vacuum state is created.C2H4 gas is supplied from the gas inlet port 11b, and the pressure inside the decompression chamber 11 is 5 Pa.
is maintained. Then, when a positive DC bias voltage of 200 V and high frequency power ioow are applied to the electrode 17.

A glow discharge occurs between the earth electrode 12 and the electrode 17,
The C2Ha gas in the decompression chamber 11 is dissociated into plasma seeds by glow discharge decomposition, and the plasma seeds adhere to the surface of the substrate 18 on the ground electrode 12 side, forming an amorphous carbon film. That is, when an amorphous carbon film was formed under the conditions shown in Table 1 below, an extremely uniform and hard amorphous film was formed over a substrate size of 240 mm in diameter, with a Mohs hardness of 7.5 or more and a film thickness uniformity of ±5% or less. A carbon film was obtained.

Table 1 FIG. 5 shows a schematic diagram of a film forming equipment for an amorphous carbon film for a cylindrical substrate in which the method of the present invention is carried out, and 21 is a reduced pressure chamber provided with an exhaust port 21a and a gas inlet 21b. In the same room zl, there are a DC power supply 25 and a matching circuit 2 that apply a positive DC bias voltage around the substrate heater 22 via a cylindrical substrate 23 and a filter circuit 24.
Cylindrical electrodes 28 connected to a high-frequency power source 27 for applying a high-frequency voltage through the electrodes 6 are arranged concentrically. still.

In this embodiment, the exhaust port 21b is guided to the outside of the decompression chamber 21 as a pipe installed on the side of the electrode 28, and the intervening pipe is used as a connection. Furthermore, in this embodiment, 7-smesh 30 are provided at both ends of the electrode 28 so as to cover the opposing space 29 between the electrode 28 and the substrate 23 from the sides.

First, air is removed from the decompression chamber 21 through the exhaust port 21a to create a high vacuum state.Next, the substrate 23 is heated by the substrate heater 22 and kept at a constant temperature, and Ar gas is added from the gas inlet 21b. The C2H4 gas is supplied, and the inside of the decompression chamber 21 is maintained at 10 Pa. Then, when a positive DC bias voltage of 160 V and a high frequency power of 100 W are applied to the electrode 28.

Glow discharge occurs between the substrate 23 and the electrode 28, the gas in the reduced pressure chamber 21 is dissociated into plasma seeds by glow discharge decomposition, and the plasma seeds adhere to the surface of the substrate 23 to form an amorphous carbon film. It turns out. That is, when an amorphous carbon film was formed under the conditions shown in Table 2 below, an extremely uniform and hard amorphous carbon film was formed over the entire length of the substrate 23 with a Mohs hardness of 7.5 or more and a film thickness uniformity of ±5% or less. was gotten.

Table 2 In addition, as raw material gas, methane CHa, ethane C2H6,
Even if common hydrocarbons such as propane C3Ha and acetylene C2H are used, the Mohs hardness is 7.5 or higher in all cases.
An extremely uniform and hard amorphous carbon film with a uniform thickness of 5% or less was obtained.

As a result of experiments based on the above examples, the following conclusion was reached as a suitable or optimal range of film-forming conditions for an amorphous carbon film.

Preferred range> DC bias voltage: 50-3000V Gas pressure: 0.1-50Pa High frequency electric crab 10-2000W Distance between electrode substrates GL: 20-500 without earth mesh
mm Optimum range: 10-500 mm with earth mesh DC bias voltage: 100-500 V Gas pressure: 5-20 Pa High frequency electric crab 50-500 W Electrode-substrate pressure GL: 40--100 without earth mesh
mm With earth mesh 20 to 100 mm [Effects of the Invention] As described above, the present invention has the following advantages:
It is possible to uniformly form an amorphous carbon film over a large area.

In this way, since the application of a low voltage is sufficient, the equipment becomes simple, making it easy to transport and rotate the substrate for the purpose of depositing a film on a large area substrate, and making it possible to configure the deposition line. This will be convenient for the occasion.

Furthermore, by arranging the earth mesh on the side of the space where the electrode and the substrate face each other, we have succeeded in concentrating the discharge energy, greatly expanding the area of uniform film thickness, and improving the I&, lI2 speeds.

[Brief explanation of drawings]

Figures 1 and 2 are diagrams showing the basic principle of the present invention;
The figure is a graph of Paschen's law with (gas pressure) x (electrode spacing) plotted on the horizontal axis and discharge voltage plotted on the vertical axis. Schematic diagram: FIG. 5 is a schematic diagram of an apparatus for forming an amorphous carbon film for a cylindrical substrate according to an embodiment. 6 to 9 are diagrams showing the concept of the prior art,
6 shows the sputtering method, FIG. 7 shows the ion beam method, FIG. 8 shows the plasma CVD method (substrate electrode type), and FIG. 9 shows the plasma CVD method (probe electrode type). 1... Decompression chamber, la... Exhaust port, lb... Gas inlet, 2... Earth electrode, 3... Power source for applying positive DC bias voltage and high frequency voltage, 4... Electrode, 5.
. . . Substrate, 6. Opposing space for electrodes, 7. Earth mesh, 8. Film formation region, 11. Decompression chamber. 11a...Exhaust port, 11b...Gas inlet port, 12.
...Earth electrode, 13...Filter circuit, 14...
・DC power supply, 15...Matching circuit, 16...High frequency power supply, 17...Electrode, 18...Substrate, 21...
- Decompression chamber, 21a... Exhaust port, 21b... Gas inlet, 22... Substrate heating heater, 23... Substrate, 2
4... Filter circuit, 25... DC power supply, 26.
...Matching circuit, 27...High frequency power supply, 28...
・Electrode, 29...Opposing space between electrode and substrate, 30...
Earth mesh, 31... board extension! -1...
・Decompression chamber 1a...Suction hole 1b...Suction hole 2
...Earth electrode 3...Power source for applying positive DC bias voltage and high frequency voltage 4...Electrode 5...Substrate 6...Space facing electrode 7...Earth mesh 8...Film formation Area Figure 5 Figure 8 Figure 9

Claims (3)

[Claims] (1) In a method of forming an amorphous carbon film by plasma CVD using hydrocarbon gas as a raw material,
A method for forming an amorphous carbon film characterized by disposing a high frequency electrode to which a positive DC bias voltage is applied facing a substrate placed on the ground electrode side, and discharging in a hydrocarbon gas atmosphere of 20 Pa or less. . (2) The method for forming an amorphous carbon film according to claim (1), wherein an inert gas is added to the hydrocarbon gas to cause discharge. (3) Claim (1) or Claim 1 in which the side part of the opposing space between the substrate installed on the earth electrode side and the high frequency electrode to which a positive DC bias voltage is applied is covered with an earth mesh to cause a discharge. (2) The method for forming an amorphous carbon film described in section (2).