JPS62260061A - Formation of amorphous carbon film - Google Patents

Abstract

PURPOSE:To form an amorphous carbon film having excellent characteristics on a substrate with relatively simple constitution by introducing a gaseous raw material contg. gaseous hydrocarbon into a reduced vessel in which a high voltage is impressed between a cathode and anode to generate plasma and impressing a magnetic field to said plasma. CONSTITUTION:The inside of a chamber 1 is evacuated 10 to <=10Torr and thereafter the gaseous HC of the raw material is introduced 8 into the chamber. The system is kept under the specified pressure by controlling a discharge side valve 10 and the DC voltage is impressed between the cathode 3 and the anode 2. The pressure during this time is kept under 2X10<-2>-10Torr and the impressed voltage is 500-5,000V. The magnetic field of 100-800 gauss magnetic flux density generated by a magnet 5 is impressed to the plasma generated between the cathode and the anode and the generated ions or radicals are deposited on a substrate 4. The deposition time in this case is 1-3hr and the film is formed to 0.5-3mum thickness. The film forming speed is 0.5-1mum/h and the substrate temp. is <=200 deg.C.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for forming an amorphous carbon film, and since this amorphous carbon film has a diamond shape, it can be used as a surface protective coating layer or for its thermal conductivity. ,
It is effective for use in insulating heat dissipation layers for IC circuits, etc., taking advantage of its good insulation properties.

[Conventional technology]

Diamond is a crystal made of carbon bonded together through SP3 bonds, and has unique mechanical, electrical, and optical properties that cannot be obtained from other solid materials. The so-called high-pressure method, in which carbon raw materials are converted into diamond under ultra-high pressure and ultra-high temperature, has traditionally been known as an artificial synthesis method for diamond crystals, but it is difficult to implement because it requires expensive and special equipment. I don't get it. Furthermore, when considering applications to semiconductors and sliding materials, a thin film is preferable, but granular diamond synthesized using a high-pressure method can be sliced into pieces.
It has the disadvantage that it is difficult to make into pieces or into arbitrary shapes, and it is not possible to make large-area pieces. If a thin film of diamond of any shape could be easily synthesized, it could be used to make high-density integrated circuits by taking advantage of its hardness and making it a hard, covering, or sliding material on metal or resin surfaces, or by using its high electrical resistance and thermal conductivity. It can be considered to be used as an insulating heat dissipation layer, etc. Against this background, the creation of diamond-like amorphous carbon films by low-pressure synthesis from the gas phase has been studied in recent years.

[Problem that the invention seeks to solve]

Low-pressure vapor phase synthesis methods that have been implemented so far include thermal filament CVD, microwave plasma CVD, and R
There are F glow discharge plasma CVD methods, electron beam CVD methods, and ionization vapor deposition methods, each of which requires a temperature-controlled heating furnace and microwave oscillator.

Those that require expensive and special equipment such as a high-frequency oscillator, those that use filaments have problems with low reproducibility due to changes in the shape of the filament during film formation, and those that require heating the substrate to high temperatures. For this reason, it has the disadvantage that it cannot be deposited on substrates with low heat resistance. The DC glow discharge plasma CVD method, which uses only a DC power source, is a method that can perform low-temperature synthesis using simple equipment, but the simple DC method, which applies a DC voltage between parallel plate electrodes, has low plasma density and sufficient characteristics. It has the disadvantage that it is difficult to obtain a thin film.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for solving the above-mentioned drawbacks and producing an amorphous carbon film having satisfactory characteristics using a simple DC glow discharge method.

[Means for solving problems]

In order to achieve the above object, the present invention generates plasma by applying a high voltage between a cathode and an anode facing each other in a reduced pressure container and introducing a raw material gas containing hydrocarbon gas into the reduced pressure container. The present invention employs a method of forming an amorphous carbon film in which a film is formed on a substrate placed in the plasma while applying a magnetic field to the plasma.

[Effect]

By the above means, 1) the plasma generated by glow-discharging hydrocarbon gas contains neutral radicals at a high ratio of about ions:radicals-1=6, and has a long life. These radicals are normal molecules that are decomposed by colliding with energetic particles in plasma, and have unpaired electrons. Having unpaired electrons can be thought of as a small magnet, and in a magnetic field it receives a force that orients it in the direction of the magnetic field lines, resulting in an amorphous carbon film with more short-range order than in the case without a magnetic field. Therefore, although it is amorphous, it has a structure similar to that of diamond when viewed microscopically, and its properties are improved.

2) When positive ions collide with the cathode, electrons are ejected from the cathode surface. This electron moves toward positive (1) and collides with other particles on the way, causing them to be excited.

At this time, if a magnetic field is applied to the plasma, the electrons, which are charged particles, move spirally around the magnetic lines of force and move toward the anode, so the distance of movement is longer than when there is no Luho field, which moves in a straight line. The collision probability increases, and as a result, the ionization rate of the plasma increases and the plasma density increases, which can compensate for the drawback of the DC glow method, which has a low plasma density.

〔Example〕

An experimental apparatus used in the method of forming an amorphous carbon film of the present invention is shown in FIGS. 1 and 2. The names and functions of each part will be explained in FIGS. 1 and 2. Reference numeral 1 is a glass chamber that is transparent so that the discharge state can be observed from the outside. Reference numerals 2 and 3 are an anode and a cathode for discharge, respectively, and the material used is graphite or stainless steel, which is less affected by sputtering. Reference numeral 4 designates a substrate on which a carbon film is to be deposited, and Si single crystal was mainly used, but a metal substrate or a resin substrate may also be used. 5 is a hollow cylindrical permanent magnet, and when it is arranged so that both poles are included in the magnetic field as shown in Figure 1, and
As shown in the figure, an arrangement was made in which only the cathode was included in the magnetic field, but in any case, the arrangement was such that a relatively uniform magnetic field was applied to the vicinity of the cathode on which the substrate 4 was placed. 6 is a glass container that houses the magnet 5. 7 is a raw material gas supply cylinder, which mainly uses methane, but also ethane and propane.

A hydrocarbon gas such as ethylene or acetylene or a mixed gas of these and hydrogen may be used. 8 is a needle valve that adjusts the flow rate of the raw material gas. 9 is an exhaust pipe to an exhaust pump (not shown), and a valve 10 adjusts the pressure within the system. 11 is a DC power supply for applying a DC voltage between the two electrodes.

Next, the formation method of the present invention using the above device will be explained.
First, open the valve 10 of the exhaust pipe connected to the vacuum pump to exhaust the inside of the chamber 1 to a pressure of 10-5 Torr or less, and then supply the raw material gas from the needle valve 8 to the cylinder 7.
Introduced via. The discharge side valve 10 was adjusted to maintain the system at a specified pressure, and a DC voltage was applied between both electrodes by a DC power supply 11. The pressure is 2 x 10-2 to 10 TOrr,
Below 2 x 10-" Torr, glow discharge cannot be maintained, and above 1 Q Torr, the discharge state becomes unstable, resulting in uneven film quality and furthermore, the substrate temperature rises too much, causing residual stress to occur in the film and resulting in peeling. This is not preferable because it causes
Glow discharge cannot be maintained below 00V, and
If it is more than V, sputtering of the cathode will occur violently, which is not preferable. Of course, the higher the pressure, the more glow discharge can be maintained even with a lower voltage, and when the pressure is lower, a higher voltage is required.

The magnetic flux density generated by the magnet 5 is 100 to 800 Ga
If it is less than 100 Gauss, the magnet has no effect, and if it is more than 800 Gauss, the plasma will gather in the center and the film will become non-uniform. The distance between the electrodes is 30 to 1,001 mm for an electrode with a diameter of 25 mm, and discharge is difficult to occur when the distance is less than 30 m or more than 100 mm. However, between the electrode area (S), electrode spacing (d), and pressure (P), S and d
Since there is a relationship that the discharge voltage does not change even if P is multiplied by n and P is set to 1/n, the optimum range is determined automatically. Under the above conditions, a DC glow discharge is performed to generate plasma, and the ions and radicals generated therein are deposited on the substrate 4. The deposition time is 1 to 3 hr, the thickness of the produced film is 0.5 to 3 μm, depending on the pressure and applied voltage, and the film formation rate is 0.5 to 1 μm/hr. Note that under the conditions of this experiment, the substrate temperature was 200° C. or less, making it possible to form a film even on a substrate with low heat resistance, such as a resin.

[Example 1] In a glass chamber 1 with a diameter of 100 mm and a height of 1501 mm, a Si single crystal was used as the substrate 4, and while supplying methane gas as a raw material gas at lcc/min, the system pressure was increased to 5×.
10～” Maintain magnetic flux density at 50Q Gauss,
Deposition was performed for 3 hours at an applied voltage of 2000V. Si substrate 4
A thin film with a thickness of 2 μm that was visually smooth to the naked eye was obtained on top. When this film was analyzed using a laser Raman spectrometer, it was found that it had a peak of 158 Qcm-' which is unique to carbon, as shown in FIG. Furthermore, when X-ray diffraction was performed, no sharp peaks indicating crystals appeared.
Also, observation using a scanning electron microscope revealed that both the surface and the inside of the film were smooth and homogeneous, and it was therefore possible to identify that this film was an amorphous carbon film. The properties of this film were measured for hardness, electrical resistance, and thermal conductivity. The hardness was measured using a micro Vickers hardness tester made by Akashi Seisakusho under a load of 25 g, and the Vickers hardness was 3000 kg/mu. carbon film + Si substrate)
The resistance was measured, and the resistance of only the Si substrate was subtracted from it, and it was found to be 1010 Ω·cm. Also heat (
Yunsen uses AC using a light irradiation type heat diffusion meter manufactured by Shinku Riko.
The thermal diffusivity of (carbon film + Si substrate) was measured by the calorimetry method, and based on the value, calculations were made taking into account specific heat and density, and a thermal conductivity of 1450 kcal/m, hr''C was obtained.

The results obtained by slightly changing the conditions from those of the above example are shown in Table 1 along with the results of the conventional simple direct current glow discharge method that does not use a magnet.

(Hereinafter, blank space) Although the substrate 4 was placed on the cathode 3 in the above embodiment, the substrate 4 is not necessarily limited to this, and may be held separately by an appropriate holding means. Furthermore, it goes without saying that the magnet 5 may be an electromagnet instead of a permanent magnet.

〔Effect of the invention〕

As described above, the present invention can provide a method for forming an amorphous carbon film with excellent characteristics using a relatively simple configuration in which a magnetic field is applied to plasma generated by glow discharge.

[Brief explanation of drawings]

1 and 2 are schematic cross-sectional views showing the structure of an apparatus used in the method of the present invention, and FIG. 3 is a characteristic diagram showing Raman spectrum data of the amorphous carbon film formed. 1...Glass chamber, 2...Anode, 3...
cathode. 4... Board, 5... Magnet, 7... Cylinder, 11...
...DC power supply.

Claims (3)

[Claims] (1) Plasma is generated by applying a high voltage between a cathode and an anode facing each other in a reduced pressure container and introducing a raw material gas containing hydrocarbon gas into the reduced pressure container, and a magnetic field is applied to the plasma. A method for forming an amorphous carbon film, in which the film is formed on a substrate placed in the plasma while applying an amorphous carbon film. (2) The method for forming an amorphous carbon film according to claim 1, wherein the substrate is placed on a cathode, and the magnetic field is applied in a perpendicular direction to the substrate. (3) The method for forming an amorphous carbon film according to claim 1, wherein the magnetic flux density of the magnetic field is 100 to 800 Gauss.