JPH0248494A - Method for preparing carbon - Google Patents

Abstract

PURPOSE:To efficiently obtain diamond granules by subjecting hydrogen, carbon dioxide and carbonized product gas to plasma vapor phase reaction using a microwave, etc. CONSTITUTION:A carbonized product gas, e. g., carbon-hydrogen compound such as methane is reacted with hydrogen and carbon dioxide in high-density plasma formed by electric field and magnetic field of microwave at 0.003-800Torr, preferably 0.1-30Torr to grow the diamond crystal on a substrate (heated at 400-900 deg.C).

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention uses a plasma gas phase reaction using microwaves or the like to efficiently form a solid object mainly composed of carbon, preferably diamond grains or a diamond film. It relates to a method of forming.

In the present invention, the plasma atmosphere is particularly high pressure of 0.03 to 800 torr, more preferably 400 torr.
It relates to a method of forming at a low temperature of ~900°C.

[Conventional technology]

Conventionally, as a means for forming thin films, ECR (electron cyclotron resonance) conditions, that is, lXl0-3 to IXl0-'tor
Under conditions of A film forming method using electron cyclotron resonance to form a film is known.

[Conventional problems]

However, if you try to make a carbon film at such low pressure,
The carbon contains a large amount of graphite and tends to have an amorphous structure, and Guyardondo's vapor phase growth has a low yield and has become too expensive for industrialization. For this reason, when trying to make diamond at a higher growth rate, the formation principle is to simultaneously grow the crystal and etch the amorphous carbon component using active hydrogen (H2).
Or use oxygen (0□). Furthermore, the growth rate is slow despite the high temperature of 800°C. In particular, even if a large amount of carbide gas is not introduced into the reaction chamber, the 10z~1
Because 0.3 times as much hydrogen is introduced, the mixing ratio of carbon compounds becomes a flow rate ratio of 1 to 0.1χ. It is not possible to flow large amounts of material (which becomes the material).

For this reason, while producing microcrystalline diamond (single crystal of carbon) (with SP' bonds and C-C bonds) using the gas phase method, relatively little gas such as hydrogen is used. It was impossible to efficiently grow a single crystal on the surface by introducing a large amount of carbide gas such as methane or ethylene (assuming the total flow rate was constant). It was difficult to form a film on metal.

In order to solve these problems, even if we try to form a film at a high pressure (hybrid resonance region) of 0.03 to 800 torr, especially 10 Lor or more (hybrid resonance region), which is outside the existing range of ECR, plasma will not be generated. It was considered impossible to use high-density plasma. However, the inventor has determined that the range is 0.03 to 800 tOrr, preferably 0.1
Even at high pressures of ~30 torr, a third gas is introduced in addition to a mixture of hydrogen and a carbonate gas, which is a non-oxygenate gas such as reactive gas methane, ethylene, or carbon fluoride. As a result, it is possible to create a high-density plasma, and such plasma is not ECR but a new mode (i.e., electrons in a pressure region where electrons cannot rotate once even if the resonance conditions are set to 2.45 GHz and 875 Gauss, for example). We have discovered that this is a resonance state in which ions, etc. are mixed, which is herein referred to as "hybrid resonance."

[Means to solve the problem]

The present invention uses such hybrid resonance and mixes carbon dioxide (Co□), which is a carbon oxygenate gas that is harmless to the human body, in addition to hydrogen, which is a gas that has etching properties. In addition, carbon reactive gases include not only carbon hydrides (compounds of carbon and hydrogen) but also carbon halides (compounds of carbon and halogen elements or compounds of carbon, halogen elements, and hydrogen). By mixing a carbon non-oxygenate gas with hydrogen (H2) and carbon dioxide gas (COz) at the same time, making them react with each other in a high-density plasma, and causing carbon atoms or molecules to fly in a radical state onto the upper surface of the substrate, hydrogen can be produced. The film formation rate is increased compared to the case of using only carbide gas, and the type of substrate on which the film is formed can be arbitrarily selected.
It is intended to produce a coating or grains whose main component is carbon containing diamond.

The present invention utilizes carbon hydride gases such as CH4, carbon dioxide (Co□), and hydrogen (th) under such high-density plasma conditions.
) and react with each other. Then CO□+ H2→
CO+ HzO(1) CH4+ 2CO→ 3C+2H
zO(2)CH4+ COz → 2G +2HzO
The reaction (3) occurs. In particular, according to equation (1), this atmosphere can produce carbon monoxide, which is a reducing agent.

This CO reduces and removes the natural oxide on the forming surface, resulting in improved adhesion to the diamond (
Diamond-like carbon or SP with SP3 bond below
Diamonds with only 3 bonds can be collectively called diamonds.

Carbon can also be produced as shown in formula (3) by directly reacting CH4 and CO2 with each other.

Furthermore, carbon monoxide, which is harmful to the human body, can be generated only when plasma is present, and carbon can be produced from equation (2). This prevents CO from leaking out of the reaction space and causing an accident.

This high-density plasma then generates 0.03~8.
High-density plasma is generated at a high pressure of 0.00 torr, preferably 0.1 to 30 torr, and SP co-bonded carbon crystals are grown on the substrate to form a diamond structure. In addition, graphite components that tend to have an amorphous structure (
The carbon (generally forming an alloy of carbon and hydrogen) (having an SP2 bond) is removed by etching with reducing CO or water (OH group or oxygen radical). This allows for faster and lower temperature growth of crystalline components.

In addition to these, the present invention further includes the addition of a catalyst agent. The activated carbide gas or its decomposition product comes into contact with the reduced nickel, manganese, or germanium decomposed products for catalysts, and by maintaining the excited state for a long time, diamond grains or diamond-containing carbon are formed on the surface to be formed. The purpose was to form a film at high speed.

These substrates to be formed are placed in the hybrid resonance space or a space apart from the hybrid resonance space that maintains an active state, and the reaction product is coated on the surface of the substrate. For this purpose,
A substrate having a surface to be formed is disposed in or near a region where the electric field strength of microwave power is maximum.

The abundance ratio of carbon in the product gas in this space (the ratio of carbide gas, which is a product gas, to hydrogen, H2O, or these radicals in the entire plasma space) and the concentration of product gas per unit space are The concentration is about 10" to 10S times higher than that of the conventional FiCRCVD method. This makes it possible to form a diamond film whose main component is carbon, which is a material that can only decompose or react for the first time under such high pressure. i.e. diamond, i
- Carbon (diamond with sp3 bonds or carbon coating with microcrystalline grains).

The formation mechanism of this diamond-containing carbon film is that carbon is pre-formed as a nucleus during the film formation process, and a positive reaction that produces crystal growth at or near this point (crystal growth occurs where carbon crystals are present) Diamonds can be grown by a reaction that facilitates the growth of diamonds. The dense constituents (e.g. crystalline parts) of this forming carbon are left behind and selectively grown there, and the coarse constituents (e.g. amorphous parts) are transformed into plasma of hydrogen, water or CO. The purpose is to remove it using radicals, that is, to perform etching. The purpose is to form a film having crystallinity on at least a portion of the formed film.

That is, in the present invention, the force of a magnetic field is added to the plasma CVD method using microwaves, and the interaction between the electric field and the magnetic field of the microwaves is used. Then, by utilizing the high energy state in the "hybrid resonance space" at a high pressure of 0.03 to 3QQ torr, for example, a large amount of activated carbon is generated, with excellent reproducibility,
Coatings with uniform thickness and homogeneous properties, such as diamond,
This makes it possible to form a film such as an i-carbon film. Furthermore, since the strength of the applied magnetic field can be changed arbitrarily, it is possible to set resonance conditions not only for electrons but also for specific ions.

Examples will be shown below to further explain the present invention.

〔Example〕

FIG. 1 shows a microwave plasma CVD apparatus capable of applying a magnetic field used in the present invention.

In the figure, this device includes a plasma generation space (1) that can be maintained in a reduced pressure state, an auxiliary space (2), electromagnets (5) and (5') that generate magnetic fields, and their electric! (25), microwave oscillator (4), turbo molecular pump (7) that constitutes the exhaust system, rotary pump (14L pressure regulating pulp (11), substrate holder (10'), film forming object (10)
), microwave introduction window (15), gas system (6),
(7), (8), water cooling system (18).

(1B'), halogen lamp (20), reflector (21)
, a heating space (3).

First, the thin film forming object (10) is placed on the substrate holder (10''), and the plasma generation space (10) is opened from the gate valve (16).
). In this example, a silicon wafer was used as the substrate. This substrate holder (10') was made of stainless steel so as not to disturb microwaves and electromagnetic fields as much as possible. It is effective to apply a bias voltage here to apply a positive voltage to increase the film formation speed.

As part of the fabrication process, the entire structure was first assembled using a turbo molecular pump (
17), 1× by rotary pump (14)
Evacuate to 10" btorr or less. Next, hydrogen (
6) is introduced into the plasma generation region (1) through the 11005CC gas system (7), and the pressure is set at 0.03 to 30 to
Let it be rr. A microwave with a frequency of 2.45 GHz is applied from the outside at a strength of IKW. Furthermore, a magnet (5).

(5") is water-cooled from (18) and (18°) while applying a Gaussian magnetic field to generate high-density plasma in the plasma generation space (1). High energy is generated from this high-density plasma region. The non-product gases or electrons that it carries reach onto the surface of the object (10) on the substrate holder (10') and clean the surface.

Next, a product gas (
CH4 and CO, which are the gases that constitute the decomposition/reaction postfix
□ and a flow rate ratio of 1:Hl:4 to 4:1), and the total flow rate is introduced at a flow rate of 10SCCH. The amount of carbide gas relative to hydrogen was 2 to 30%. This carbon hydride is acetylene (C, 1I2).

Ethylene (C2H4) and benzene (C6H6) may also be used. Also, as a carbon halide, CF4. CHJz,C
It may be zFz, CzF4°CzCIz, or C2Cl4. Then, in the method of the present invention, a non-oxide of carbon is used as the carbide gas, and since this and CO□ are used, methyl alcohol (C!(:+OH)) ethyl alcohol (CJs
It has the advantage of being able to control the amount of oxygen mixed in compared to OH).

In addition to this, the method of the present invention also uses nickel carbonyl (Ni).
(CO) 4) to ISCCM or to it
eH4).

Germanium fluoride (GeF4) was added at a concentration ratio of 25 CCM, ie 0.1-10% compared to the carbide gas.

In this way, highly energetically excited carbon atoms are produced,
This carbon is heated to 400-1000° C. by plasma or additionally a heater (20), and deposits on the object (10) (here a silicon substrate) on the substrate holder (10″), with a temperature of 0.1 It was possible to form a diamond particle size of ~100 urn or an i-carbon film with a thickness of 0.1-100 μm.

It is a reactive gas consisting only of CH, and hydrogen, and contains a catalyst (when not used, even at a high temperature of 800"C
Only a film with an average thickness of 0.75 μm was formed over time. However, in the method of the present invention, Cog/CH
4=1/1 C(h+cl14)/Hz = 6
Figure 4 shows the relationship between diamond growth rate and substrate temperature when Z is shown, and it has become possible to grow diamond as high as 4.2 μm in one hour at a low temperature of 800°C. In addition, in the conventional method, the film formed had severe irregularities, and the irregularities could be seen even when viewed with a metallurgical microscope (XLOOO). However, when the method of the present invention was used, it was possible to produce a film whose surface was relatively flat.

In Figure 1, the magnetic field is connected to two ring-shaped magnets (5).
, (5') was adopted. Furthermore, FIG. 2 shows the results of examining the strength of the electric and magnetic fields for the space (30) divided into four parts.

In Figure 2 (8), the horizontal axis (X-axis) is the horizontal direction of the space (30) (reactive gas release direction), and the vertical axis (R-axis)
indicates the diameter direction of the magnet. The curves in the drawings indicate equipotential surfaces of the magnetic field. The number shown on the line indicates the strength of the magnetic field obtained when the magnet (5) is about 2000 Gauss. By adjusting the strength of the magnet (5), the space (100) (875 Gauss ± 18
(within 5 Gauss), the strength of the magnetic field can be made approximately uniform over a wide area of the surface on which the substrate is formed. The drawing shows an isomagnetic scene, in particular the isomagnetic scene that gives rise to the conditions of resonance where the line (26) is 875 Gauss.

The space (100) that produces this resonance condition is designed to be a region where the electric field is maximum, as shown in FIG. 2(B). The horizontal axis in FIG. 2(B) indicates the direction in which the reactive gas flows, as in FIG. 2(A), and the vertical axis indicates the strength of the electric field (electric field strength).

Of course, if a donut-shaped coating is to be formed, this may be used.

There is also a region on the opposite side of the origin symmetrical to region (100) where the electric field is maximum and the magnetic field is constant over a wide region. When there is no need to heat the substrate, film formation in such a space is also effective. However, it is difficult to find a way to perform heating without disturbing the microwave electric field.

As a result, considering the ease of loading and unloading the substrate and the ease of heating, the area (100) in Figure 2 (A) is the most industrially mass-producible of the three areas in order to obtain a uniform and homogeneous coating. Estimated to be in an excellent location. .

As a result, in the present invention, when the substrate (1o) is disposed in the area (100), if this substrate is circular, the radius is 100.
It became possible to form a uniform and homogeneous film with a radius of up to 50 mm, preferably up to 50 mm.

For an even larger area, for example, to achieve the same uniform film thickness over an area four times larger than this, the frequency should be set to 2.45 GH.
If it is set to 1.225GH2 instead of z, the diameter of this space (direction R in FIG. 2(A)) can be doubled.

FIG. 3 is a diagram of equal magnetic fields and equal electric fields of the magnetic field (A) and electric field (B) in a circular space at the position of the substrate (10) in FIG. 2. FIG. As is clear from FIG. 3(B), it can be seen that the electric field can reach a maximum of 25 KV/m.

"Example 2" The apparatus of Example 1 was used. The results are shown in FIG. That is, (CH4+CO□)/H2=6χ (volume ratio),
The substrate temperature was 800°C. Then, the mixing ratio of CHa and CO□ was varied. Hydrogen was then formed by first flowing CH4 and CO2 in a mixing ratio of 1:2 or 2:1 into the reactor. The growth rate was determined by the conventional method, i.e. CH4+
Approximately 20 to 8
It's now four times bigger.

Furthermore, (CH4+CO□)/H2 was varied from 1 to 30%.

As this value increased, the film formation rate increased. However, when it exceeds 10%, the color of the polycrystal changes from transparent to yellowish. That is, it is presumed that graphite components have been mixed into the diamond.

As is clear from the present invention, diamond can be produced even when the reactive gas is CO□/UZ and the amount of methane mixed is zero. However, the film formation rate was as slow as 0.8 μ/hour. However, it was still possible to achieve a growth rate 60% higher than the method using only methane and hydrogen, which was superior to the conventional method.

Furthermore, CH4:CO2=2:1 (CO,/CH4=0.
In 5), the minimum temperature for forming a thin film containing diamond was 700° C. and the maximum pressure was 20 torr. However, if CHn:C0z-1:1, 650℃ (0,1
torr), maximum pressure is 50 torr (80 torr)
0°C), and when CH4:CO□- was set to 2, diamond crystals were observed even at a temperature of 650'C when the pressure was set to 1 Qtorr.

It was formed. As a result, it has become possible to form diamond in the form of a film not only on a silicon substrate but also on the surface of TiN, Mo, a metal cutting tool, or the like.

〔effect〕

In the present invention, diamond grains or a film are formed by diluting a carbide gas with a gas in which hydrogen and carbon dioxide gas are simultaneously mixed into a carbon reactive gas (non-oxide gas). As a result, it has become possible to form diamond in the form of a film not only on a silicon substrate but also on the surface of a TtN, Mo, metal cutting tool, or the like.

Furthermore, rather than mixing CO (-carbon oxide), which is extremely harmful to the human body, into hydrogen from a cylinder, the present invention uses CO□, which is safe for the human body, as the starting gas.

Therefore, it has an industrial feature of being safe even if gas leaks to the outside due to malfunction of the device. In addition, the film-forming speed was reduced by diluting the hydrocarbon gas with hydrogen, making it possible to produce diamonds 5 to 20 times faster.

Furthermore, the present invention is also effective when diamond-like carbon is produced using high-frequency plasma at room temperature or at a temperature of 300°C or less using hydrogen, carbon dioxide gas, and non-oxide carbonide gas such as methane or carbon fluoride. . In such a case, the formation method using only methane results in a yellow opaque film, and
Although the Vickers hardness is 2000-4000Kg/cm, the Vickers hardness is 5000-9000Kg.
/cm'' can now be produced.

For this reason, in the gas phase method, the production cost per duram is about 1000 times higher than that of diamond produced by the conventionally known high-pressure pressing method, but it has become possible to reduce the production cost to about 1000 times. Furthermore, since it is not possible to form a film using a high-pressure method, the present invention makes it possible to create a flat film for the first time, making it possible to expect new applications.

In the method of the present invention, when carbon is made, boron, nitrogen, phosphorus, etc. are added thereto to make it a P- or N-type semiconductor, and silicon is added to form 5ixC+□ on the surface to be formed. A carbon film may be formed on top to have a two-layer structure to further improve adhesion with the base material. GeF also has a catalytic effect during film formation.

It is effective to simultaneously mix nickel carbonyl gas and lower the mixed pressure for film formation.

[Brief explanation of the drawing]

FIG. 1 schematically shows a microwave CVD apparatus using magnetic field/electric field interaction used in the present invention. FIG. 2 shows the magnetic field and electric field characteristics by computer simulation. Figure 3 shows the characteristics of the magnetic field and electric field at a position where the electric field and magnetic field interact. Figures 4 and 5 show the growth rate characteristics of diamond made using the method of the present invention. 1... Plasma generation space 4... Microwave oscillator 5.5''... External magnetic field generator 17... Turbo molecular pump 10... Film forming object or substrate 10''...
・Substrate holder 20...Halogen lamp 21...Reflector 100...Space with maximum electric field Fig. 2 ÷ - 1

Claims (1)

[Claims] 1. A plasma gas phase reaction method, which involves introducing hydrogen, carbon dioxide gas, and carbonide gas into a plasma generation space to produce a diamond-like carbon or diamond-based object. Characteristic carbon production method. 2. In claim 1, diamond-like carbon or diamond is produced by simultaneously applying a magnetic field in addition to microwaves and generating plasma in a pressure range of 0.03 to 800 torr using the interaction of the electric and magnetic fields. A carbon production method characterized by producing an object whose main component is 3. In claim 1, 400 to 900°C
1. A carbon production method characterized by producing an object having diamond on a substrate at a substrate temperature of .