JP2836927B2 - Diamond synthesis method and diamond semiconductor manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for synthesizing diamond and a method for manufacturing a diamond semiconductor.

More specifically, the present invention relates to a method for synthesizing high-quality diamond useful as, for example, coating of various articles, electronic materials, and the like, and a method for manufacturing a diamond semiconductor useful as a semiconductor.

[Prior Art and Problems to be Solved by the Invention] Various methods have been proposed as methods for synthesizing diamond (diamond film) using various carbon sources by a gas phase method.

Since diamond formed by a gas phase synthesis method can be generally formed as a film having various thicknesses on an appropriate substrate, for example, a cutting tool, a hard metal such as a wear-resistant member,
Diamond tools and other diamond-coated members that are useful for coating the base material of ceramics, or as a protective material for various articles, and have excellent hardness, wear resistance, and chemical resistance. A wide range of applications are being developed.

In addition, in recent years, in the synthesis of diamond by a vapor phase synthesis method, a doping impurity component such as boron or phosphorus is added to the raw material carbon source gas to convert the diamond into a semiconductor and apply it as an electronic material. It has been noted.

For example, Japanese Patent Application Laid-Open No. 1-96094 discloses that a compound containing an impurity element for doping is dissolved in a liquid organic compound,
A method of vaporizing this and obtaining a diamond semiconductor by a CVD method is disclosed.

However, in such a conventional diamond synthesis method, there is a problem that it is difficult to obtain an n-type diamond semiconductor, and a solution has been desired.

Under these circumstances, the 37th Joint Lecture Meeting on Applied Physics [30a-ZB-9,10], Spring 1990: JNDFTX [Section 2]
-90], acetone was used as a raw material carbon source, and diphosphorus pentoxide (P
₂ O ₅ ), a method of synthesizing an n-type semiconductor diamond by a hot filament method, and a method of producing diamond PN
A method of manufacturing a junction diode has been proposed.

Thus, it is extremely important that not only p-type but also n-type diamond can be synthesized by using acetone as a raw material carbon source and adding an appropriate doping impurity.

However, in these conventional methods, the synthesis of diamond from acetone is performed by the hot filament method, so that it is not possible to avoid contamination by the filament, in which extra impurity elements generated from the filament are mixed into the obtained diamond. Further, there are disadvantages such as damage to the filament.

Electronic materials such as semiconductors generally require high-purity materials in the sense that they do not contain extra impurities other than predetermined impurities added as necessary such as doping impurity elements.

Therefore, the contamination of diamond by the above-mentioned filament is considered to be a very serious problem for a diamond material as an electronic material such as a semiconductor.

As a method of synthesizing high-purity diamond from ketones such as acetone, avoiding contamination by this filament,
For example, a microwave plasma CVD method can be considered.

However, in this microwave plasma CVD method, C
Diamond can be synthesized when a hydrocarbon such as O or methane is used as a carbon source, but good diamond cannot be obtained when a ketone such as acetone is used as a carbon source. [J.App.Phys., Vol.27, No.8, pp 1
397-1400 (1988)].

The present invention has been made based on the above facts.

An object of the present invention is to use a specific raw material gas containing a ketone such as acetone as a carbon source as a high-quality electronic material or a coating material such as a diamond semiconductor, which is free from contamination by extra impurities having a bad influence such as contamination by a filament. In particular, it is an object of the present invention to provide a practically useful diamond synthesis method which has an advantage that an excellent diamond can be obtained, and in particular, an n-type diamond semiconductor which has been difficult to synthesize by the conventional method can be obtained.

[Means for Solving the Problems] As a result of intensive studies to achieve the above object, the present inventor has used ketones such as acetone and hydrogen as main raw material gases, and added doping impurities as necessary. When synthesizing diamond such as a diamond semiconductor by incorporating the components, a method of adding a specific ratio of carbon dioxide gas to the raw material gas, and using a specific diamond forming technique called microwave plasma CVD method, The present inventors have found that the method is an extremely useful method that satisfies the above object, and have completed the present invention based on the findings.

That is, the invention according to claim 1 of the present application is a method for synthesizing diamond, which comprises contacting a base material with a plasma formed by irradiating a mixture of ketone, hydrogen, and carbon dioxide with microwaves, The invention according to claim 2 of the present application is the method for synthesizing diamond according to claim 1, wherein the molar ratio of carbon dioxide in the mixture to the ketone is 30 or more. The present invention is a method for producing a diamond semiconductor, wherein a plasma formed by irradiating a mixture of ketone, hydrogen, carbon dioxide and doping impurities with microwaves is brought into contact with a substrate.

Hereinafter, a method for synthesizing diamond and a method for manufacturing a diamond semiconductor according to the present invention will be described in detail.

Ketones used in any of the method of synthesizing diamond and the method of manufacturing diamond semiconductors (hereinafter, both methods may be abbreviated to the method of the present invention) are not particularly limited, and various compounds are used. However, ketones having about 3 to 10 carbon atoms, particularly 3 to 6 carbon atoms, can be used.
Slightly lower saturated ketones can be mentioned as preferred examples.

Specific examples of the ketones that can be particularly preferably used include, for example, acetone, methyl ethyl ketone, diethyl ketone, methyl n-propyl ketone, methyl isopropyl ketone, ethyl n-propyl ketone, ethyl isopropyl ketone, methyl butyl Ketone, cyclopentanone, cyclohexanone and the like can be mentioned.

Among them, acetone, methyl ethyl ketone, diethyl ketone and the like are preferable, and acetone is particularly preferable.

These ketones may be used alone or in combination of two or more.

The hydrogen and carbon dioxide are not particularly limited, and hydrogen and carbon dioxide produced by various methods can be used.

In the method for synthesizing diamond of the present invention, a mixture of the ketone, hydrogen, and carbon dioxide gas is used as a raw material gas, and the raw material gas is irradiated with microwaves to form plasma, and the plasma is applied to an appropriate base material. Contacting,
A desired diamond (diamond film) is formed on the surface of the substrate.

That is, in the method of the present invention, it is important to use a mixed gas composed of at least ketone, hydrogen and carbon dioxide gas as a raw material gas used in synthesizing diamond.

Without containing carbon dioxide gas in the raw material gas,
Even if a plasma is formed by irradiating a microwave to a raw material gas consisting only of ketone and hydrogen such as acetone, and the plasma is brought into contact with a base material, it is difficult to form a desired high-purity diamond. Non-diamonds such as glassy carbon (glassy carbon) are formed, and the object of the present invention cannot be achieved.

The amount of the carbon dioxide gas added, that is, the ratio of carbon dioxide contained in the raw material gas is not particularly limited, but is usually 30 mol or more, preferably 40 to 100 mol, per mol of the ketone used. Within range.

If the added amount of the carbon dioxide gas is too small, a desired high-purity diamond may not be formed.On the other hand, if the added amount is too large, the diamond forming rate cannot be sufficiently secured or the diamond is not formed. Inconveniences such as a decrease in efficiency may occur.

Since the ratio of ketone and hydrogen in the raw material gas varies depending on other conditions such as the type of ketone used, it cannot be determined uniformly, but the ratio of ketone such as acetone is usually Is less than 10% by volume, preferably 0.1 to 5% by volume.

In the method of the present invention, in the source gas containing the ketone, hydrogen and carbon dioxide gas, if necessary, additives such as doping impurities, other than the ketone, as long as the object of the present invention is not hindered. It may contain other components such as another carbon source gas component, a reducing gas component other than hydrogen, an oxidizing gas component, or an inert gas component.

In particular, when a source gas containing a doping impurity, that is, a ketone, hydrogen, carbon dioxide, and a source gas containing a doping impurity is used, a diamond semiconductor can be manufactured by the method of the present invention.

As the doping impurities, various known elements and the like can be used.

For example, to obtain an n-type diamond, for example,
Phosphorus compounds (preferably P ₂ O ₅ or phosphoric acid, particularly preferably P ₂ O ₅ ) and the like are suitably used. On the other hand, to obtain p-type diamond, for example, a boron compound (preferably B ₂ O ₃ or Boric acid, particularly preferably B ₂ O ₃ ), can be suitably used.

Here, it is used when obtaining an n-type diamond semiconductor.
Since the amount of the phosphorus compound such as P ₂ O ₅ and H ₃ PO ₄ depends on other conditions such as the type of the phosphorus compound or ketone used, the composition of the raw material gas, and the conditions for synthesizing diamond, it can be determined uniformly. can not, but typically, the proportion of phosphorus atoms in the phosphorus compound such as P ₂ O ₅ and H ₃ PO ₄ to carbon atoms of the ketone such as acetone to be used is, in molar ratio, in the range of about 10 to 10 ⁴ ppm Is adjusted as follows.

Further, B ₂ used for obtaining a p-type diamond semiconductor
The addition amount of the boron compound such as O ₃ cannot be uniformly determined because the type of the boron compound or ketone to be used depends on the composition of the raw material gas and other conditions such as diamond synthesis conditions. the proportion of boron atoms of the boron compound such as B ₂ O ₃ to carbon atoms ketones such as acetone which has a molar ratio, it is adjusted to the range of about 10 to 10 ⁴ ppm.

In the method of the present invention, in order to form a plasma by irradiating a microwave to the specific raw material gas (at least a raw material gas composed of ketone, hydrogen and carbon dioxide gas) in a diamond forming reaction, a microwave plasma is used. It is better to use the CVD method.

In this way, by using the specific source gas, and by using the microwave plasma CVD method, since the problem such as contamination by the filament which is a problem in the case of the hot filament method proposed as a conventional method is eliminated,
High-purity (high-quality) diamond (a diamond film or an n-type or p-type diamond semiconductor film) free from mixing of extraneous impurities having an adverse effect can be easily formed.

In the method of the present invention, a source gas having the specific composition (at least a source gas containing at least the ketone, hydrogen and carbon dioxide gas as a main component) is used as a source gas, and diamond or a diamond semiconductor is formed by a microwave plasma CVD method. Except for the synthesis, the conventional method for adjusting the composition of the source gas, the method for supplying the source gas, and the conditions for forming diamond or diamond semiconductor by the conventional microwave plasma CVD method can be employed as they are.

That is, in the method of the present invention, a method known as a microwave plasma CVD method may be appropriately employed, and if necessary, a magnetic field method, other methods that do not hinder the object of the present invention such as an ECR method. The methods can be used in combination.

The substrate temperature (T _s ) at the time of forming the diamond on the substrate can be appropriately selected usually from the range of 600 to 1,100 ° C.

When the substrate temperature is lower than 600 ° C., the deposition rate of the diamond film is significantly reduced. On the other hand, if the temperature is higher than 1,100 ° C., a corresponding effect may not be obtained, or diamond may be difficult to obtain.

In addition, if necessary, a positive or negative bias voltage can be applied to the base material.

The reaction pressure is usually 10 ^-6 to 10 ³ Torr, preferably 10 ^{-3 to} 5
It is appropriate to select within the range of 00 Torr.

The total flow rate of the source gas is usually 1 to 1,000 sccm,
Preferably, it is about 10 to 400 sccm.

The thickness of the diamond film formed on the base material in this way cannot be described unconditionally depending on what kind of application, but if it is used for cutting, a wear-resistant member, Usually, it is 200 μm or less, preferably 1 to 100 μm, and when it is formed as a diamond semiconductor for electronic materials, it is usually about 0.5 to 20 μm, preferably about 1 to 10 μm.

Ya P ₂ O ₅ is added according diamonds required concentration of each component of the raw material gas for forming (ketone and the rate and carbon dioxide gas of hydrogen and the ratio of acetone or these
The proportion of doping impurities such as B ₂ O ₃ ) may be appropriately selected from the above range as desired.

The diamond formed on the base material as described above can be used as it is with the base material, but can also be used after being separated from the base material as necessary. If necessary, the formed diamond may be subjected to various physical and / or chemical treatments, or may be appropriately processed such as further laminating a layer of a desired material on its surface. Can also.

The material and shape of the base material to be used are not particularly limited, and any material can be used as long as diamond (diamond film) can be formed on its surface. It can be appropriately selected according to the purpose from known base materials used in the gas phase synthesis method.

As the base material, for example, metals such as silicon, manganese, vanadium, thallium, aluminum, titanium, tungsten, molybdenum, germanium, chromium, oxides, nitrides, carbides, alloys thereof, and Al ₂ O ₃
-Fe system, TiC-Ni system, mention may be made of TiC-Co based, B ₄ C-Fe system or the like of the cermet such or hard metal and various ceramics.

Among these various substrates, for example, silicon,
Molybdenum or its alloys, tungsten or its alloys, silicon oxide, silicon nitride (for example, Si ₃ N
₄ ), SiAlON, alumina (Al ₂ O ₃ ), etc., or various cemented carbides used as a base material for cutting tools or wear-resistant members are preferred.

As a substrate on which a diamond semiconductor used for an electronic material is formed, for example, silicon is preferable.

As the silicon, any of single crystal silicon, polycrystalline silicon, amorphous silicon, and the like can be used. However, from the viewpoint of characteristics as an electronic material, single crystal silicon is usually preferably used.

In addition, these base materials may be appropriately formed or configured in advance into a laminate or an element material, or may be appropriately surface-treated as necessary (for example, surface treatment with diamond particles). , Patterning with a mask material, etc.).

Source gas supply methods such as a method for adjusting the concentration of source gas components such as the ketone, hydrogen, carbon dioxide gas and the doping impurities added thereto as necessary, and a method for controlling the flow rate of the source gas composed of these. There is no particular limitation, and any method may be used.

For example, the supply of ketone which is liquid at normal temperature can be performed according to the method for supplying a liquid organic compound described in JP-A-1-96094, or, for example,
Hydrogen or the like is used as a carrier gas, and the carrier gas is bubbled at a suitable temperature into a liquid ketone such as acetone put in a bubbler so that the ketone vapor has an appropriate concentration (for example, saturated vapor pressure). It is preferable to adopt a method in which hydrogen or carbon dioxide gas supplied from a separate line from the carrier gas is combined with the carrier gas and the concentration of each component and the supply amount of the raw material gas are adjusted. it can.

Here, when adding doping impurities such as a phosphorus compound such as P ₂ O ₅ or H ₃ PO ₄ or a boron compound such as B ₂ O ₃ , an appropriate amount of the predetermined compound is added to the acetone or the like. (E.g., by dissolving the ketone solution in a ketone solution of
Such a solution is added to a ketone liquid such as acetone) to contain the solution, and the vapor of the doping impurity is entrained in the carrier gas together with the vapor of ketone such as acetone. it can.

When adding P ₂ O ₅ , H ₃ PO ₄ or B ₂ O ₃ to a ketone solution such as acetone, for example, they are saturated with an appropriate amount (usually, a small amount) of a solvent such as methanol, and A method of adding to a ketone liquid such as acetone is preferably used.

As shown in FIG. 1, as a method for supplying a raw material gas by bubbling a carrier gas into a ketone liquid such as acetone and causing a predetermined ketone or a ketone and a predetermined doping impurity to accompany the carrier gas, as shown in FIG. The method shown can be suitably adopted.

FIG. 1 shows the method for synthesizing diamond of the present invention.
FIG. 1 is an explanatory diagram schematically showing an example of a method of adjusting the composition and supply flow rate of a source gas that can be suitably used and an example of a method of forming a diamond or a diamond semiconductor on a substrate by using the method. is there.

In the method shown in FIG. 1, hydrogen is used as a carrier gas, and the carrier hydrogen 1 is supplied at an appropriate flow rate into a bubbler 5 installed in a thermostat 4 at an appropriate temperature (T ° C.). Then, the bubbles are bubbled in the ketone liquid 6 in the bubbler 5. The ketone liquid 6 is a liquid containing an appropriate amount of doping impurities such as ketone, preferably acetone, or a methanol solution of P ₂ O ₅ (preferably a saturated solution). That is, by bubbling the carrier hydrogen 1 into the ketone liquid 6, a vapor of a ketone such as acetone (or, in some cases, a vapor of a predetermined doping impurity such as ketone and P ₂ O ₅ ) is introduced into the carrier hydrogen 1 by a predetermined amount. It is contained at a vapor pressure (usually a saturated vapor pressure).
And Here, when the ketone liquid 6 is used in a sufficient amount for contact with the carrier hydrogen 1, the hydrogen
The concentration (vapor pressure) of the ketone such as acetone in the medium can be stably maintained as the saturated vapor pressure at the set temperature (T ° C.). Similarly, the concentration of doping impurities such as P ₂ O ₅ in the vapor component-containing hydrogen 7 can be stably maintained at a predetermined concentration.

In this way, the concentration of the ketone or the concentration of the doping impurities such as P ₂ O ₅ and the ketone and the hydrogen containing the vapor component 7 are adjusted.
Is combined with separately controlled flow rates of hydrogen 2 and carbon dioxide gas 3 to obtain a raw material gas 8 having a predetermined composition,
This is circulated on a predetermined base material 10 installed in the reactor 9. On the other hand, the substrate 10 in the reactor 9 is controlled at a predetermined temperature (substrate temperature: T _S ° C), and a microwave is applied to a reaction system including the substrate 10 according to a known method or the like. The source gas 8 is excited, and a desired diamond (a diamond film or a diamond semiconductor film) is formed on the surface of the substrate 10 by a gas phase synthesis method by a so-called microwave plasma CVD method.

The method illustrated in FIG. 1 can be particularly preferably employed in the method of the present invention in that the composition of the raw material gas can be easily and stably maintained. It is not necessarily limited to the method illustrated in FIG.

As described above, according to the diamond synthesis method of the present invention, high-purity (high-quality) diamond free from contamination by filaments and the like and free from adverse effects due to extra impurities can be obtained. Also, depending on the purpose,
By adding doping impurities such as B ₂ O ₃ and P ₂ O ₅ , a high-quality p-type diamond semiconductor or n-type diamond semiconductor can be easily obtained.

The diamond obtained by the method of the present invention can be used, for example, for coating a base material of carbide tools such as cutting tools and polishing tools, or as a coating material such as a protective film for various articles, It can be advantageously used in a wide range of fields such as the field of electronic materials.

[Examples] Next, examples of the present invention and comparative examples are shown, and the present invention will be described more specifically.

(Examples 1 to 3) Using the raw material supply system shown in FIG.
Using pure acetone, and setting the temperature of the bubbler 5 to -2.
By controlling the temperature to 6.3 ° C., the vapor pressure of acetone contained in the carrier hydrogen 1 is set to 15 Torr (saturated vapor pressure).
A raw material gas having the composition and flow rate shown in the table was formed, and the raw material gas was supplied onto the base material. Under the synthesis conditions shown in Table 1, diamond was synthesized on the base material by the microwave plasma CVD method.

The microwave frequency was set to 2.45 GHz, and the microwave output was adjusted so that the temperature (Ts) of the base material became a predetermined temperature. As the base material, silicon surface-treated with diamond particles was used.

 The results are shown in Table 1.

(Example 4) In Example 2, a solution obtained by saturating P ₂ O ₅ with a small amount of methanol in place of pure acetone as the ketone solution 6 was prepared by adjusting the molar ratio of phosphorus atoms to carbon atoms of acetone (P /
P ₂ O ₅ added to acetone so that it becomes 100 ppm in C)
A diamond was synthesized in the same manner as in Example 2 except that the contained acetone solution was used.

In addition, it was confirmed that the diamond obtained by this method exhibited the properties of an n-type semiconductor.

(Comparative Example 1) Diamond synthesis was attempted in the same manner as in Example 1, except that a gas containing no carbon dioxide gas was used as a raw material gas (composition and flow rate are shown in Table 1).

As a result, as shown in Table 1, diamond (DIA)
Is not obtained, amorphous carbon material (glassy carbon)
Only generated.

Note that when not adding the carbon dioxide gas as a raw material gas in this way, the reaction pressure 15~80Torr, 850~1,000 ℃ substrate temperature (T _S), the ratio of hydrogen acetone
Attempts were made to synthesize diamond under various synthesis conditions by changing the range from 0.1 to 1% by volume, but no diamond was formed in any case, and only an amorphous carbon material (glassy carbon) was formed. It was confirmed.

[Effects of the Invention] According to the present invention, it is possible to synthesize high-purity (high-quality) diamond that is free from contamination by filaments, which is a problem in the conventional hot filament method, and free from impurities that have extra adverse effects. When a source gas contains a doping impurity, a diamond semiconductor can be produced. In particular, a high-quality n-type diamond semiconductor which has been difficult to synthesize by the conventional method can be easily produced. .

The diamond film produced by the method of the present invention is useful for a diamond semiconductor useful as a cutting tool or an electronic material.

[Brief description of the drawings]

FIG. 1 shows an example of a method for adjusting the composition and supply flow rate of a source gas which can be particularly preferably used in the diamond synthesis method of the present invention, and forming a diamond or diamond semiconductor on a substrate using the method. It is explanatory drawing which showed an example of the method schematically. 1 ... carrier gas, 2 ... hydrogen gas, 5 ... bubbler, 8 ... source gas, 9 ... reaction chamber, 10 ... base material.

Claims (3)

(57) [Claims] 1. A method for synthesizing diamond, wherein plasma formed by irradiating a mixture of ketone, hydrogen and carbon dioxide with microwaves is brought into contact with a substrate. 2. The method for synthesizing diamond according to claim 1, wherein the amount of carbon dioxide in said mixture is 30 or more in molar ratio to said ketone. 3. A method for producing a diamond semiconductor, comprising: contacting a base material with plasma formed by irradiating a mixture of ketone, hydrogen, carbon dioxide and doping impurities with microwaves.