Method for depositing single-crystal artificial diamond films

Abstract

To provide a method for easily depositing a diamond film on the surface of a single-crystal diamond substrate using a single-crystal artificial diamond film deposition method. [Solution] The method includes the step of introducing a carbon-containing gas into a vacuum chamber when the plasma is rising inside the vacuum chamber and the surface temperature of the single-crystal diamond substrate is below a predetermined temperature, thereby forming a diamond film on the surface of the single-crystal diamond substrate.

Description

Technical Field

[0001] The present invention relates to a method for forming a diamond film on the surface of a single-crystal artificial diamond substrate by a CVD synthesis method using a microwave plasma CVD apparatus.

Background Art

[0002] Synthetic diamonds are industrially used as processing tool materials and abrasive grains, and most of them have been manufactured by the high-temperature and high-pressure synthesis method. In recent years, however, the use of the CVD synthesis method for vapor-phase synthesis using a microwave plasma CVD apparatus has become popular.

[0003] In the CVD synthesis method, microwaves are introduced into the vacuum chamber of the apparatus together with raw material gases for film formation mainly composed of methane gas and hydrogen gas to plasmaize the raw material gases, thereby forming a diamond film on a single-crystal diamond substrate.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the former high-temperature and high-pressure synthesis method, the film-forming environment is a high-temperature and high-pressure environment, so it is not easy to form a diamond film. On the other hand, in the latter CVD synthesis method, it is easier to form a diamond film because it is not under a high-temperature and high-pressure environment.

[0006] The main objective of the present invention is to provide a novel method for depositing a single-crystal artificial diamond film on the surface of a single-crystal diamond substrate. [Means for solving the problem]

[0007] The present invention relates to a method for forming a single-crystal artificial diamond by introducing microwaves into a vacuum chamber in which a single-crystal diamond substrate, which is a seed crystal to be used as a raw material for single-crystal artificial diamond, is installed, thereby generating plasma, and forming a diamond film on the single-crystal diamond substrate by CVD synthesis. The present invention is characterized by including a film deposition step of introducing a carbon-containing gas and a hydrogen gas into the vacuum chamber when the inside of the vacuum chamber is in the plasma rise state and the surface temperature of the single-crystal diamond substrate is below a predetermined temperature, thereby depositing a diamond film on the surface of the single-crystal diamond substrate.

[0008] According to the present invention, since a diamond film is formed on the surface of a single-crystal diamond substrate by introducing a carbon-containing gas and a hydrogen gas into a vacuum chamber, the formation of a diamond film on the surface of a single-crystal diamond substrate is easy.

[0009] In the present invention, in a preferred embodiment, the carbon-containing gas in the film formation step is obtained by gasifying hair, bone meal of animals or fish, or other fixed carbon powders.

[0010] In the present invention, in a preferred embodiment, the carbon-containing gas includes CO2 formed by placing solid carbon (hair, bone meal of animals or fish, etc.) at high temperature and in oxygen. [Effects of the Invention]

[0011] According to the present invention, since the materials used to form the diamond film are a carbon-containing gas and a hydrogen gas, it is easy to form a diamond film on the surface of a single-crystal diamond substrate. [Brief explanation of the drawing]

[0012] [Figure 1]Figure 1 is a schematic diagram of a microwave plasma CVD apparatus used to carry out a film deposition method according to an embodiment of the present invention. [Figure 2] Figure 2 is a schematic diagram showing the carbon-containing gas generation apparatus, including the microwave plasma CVD (MPCVD) apparatus, in a block-like manner. [Modes for carrying out the invention]

[0013] The film deposition method according to an embodiment of the present invention will be described below with reference to the attached Figure 1. The figure is a configuration diagram of a microwave plasma CVD apparatus (MPCVD). CVD is an abbreviation for Chemical Vapor Deposition, and it is a method of depositing a diamond film on the surface of a single-crystal diamond substrate by decomposing a raw material gas and hydrogen gas on a substrate using plasma. The single-crystal diamond substrate has a seed crystal formed on it, which will be the raw material for single-crystal artificial diamond.

[0014] In Figure 1, 100 represents a microwave plasma CVD apparatus. In this microwave plasma CVD apparatus 100, 1 is a depressurization chamber that reduces the pressure to a near-vacuum level for plasma processing, 2 is a depressurization chamber bottom plate that constitutes the bottom plate of the depressurization chamber 1, and 3 is a vacuum chamber that can be opened and closed relative to the depressurization chamber bottom plate 2 and, in its closed position, forms the depressurization chamber 1 together with the depressurization chamber bottom plate 2. 4 is a metal stage provided above the depressurization chamber bottom plate 2 when placed inside the vacuum chamber 3, 5 is a metal substrate holder, such as molybdenum, which is placed on the stage 4 with a single-crystal diamond substrate 6 set on it, 7 is the plasma generated in the depressurization chamber 1, 8 is a gas introduction section to the depressurization chamber 1, 9 is a gas discharge section from the depressurization chamber 1, and 10 is a microwave waveguide section that introduces microwaves into the depressurization chamber 1. Furthermore, 11 is an annular dielectric window made of quartz or similar material that blocks the passage of gas but allows microwaves to pass through, 12 is a central axial tube section with a vacuum path and a coolant circulation path, and 13 is a downward biasing mechanism for the stage 4 and the central axial tube section 12.

[0015] The vacuum chamber 3 is made of aluminum, for example, and its lower edge is in close contact with the decompression chamber bottom plate 2 to form the decompression chamber 1 together with the decompression chamber bottom plate 2, and it is switchable between a closed state and a state in which it is separated from the decompression chamber bottom plate 2 to open the decompression chamber 1. The stage 4 and the central shaft tube section 12 are fixedly connected and are configured to move up and down together as a single unit. An annular dielectric window 11 is interposed between the lower surface of the stage 4 and the upper surface of the decompression chamber bottom plate 2, and the downward biasing mechanism 13 biases the stage 4 downward via the central shaft tube section 12, causing the dielectric window 11 to be in close contact with the stage 4 and the decompression chamber bottom plate 2. This close contact prevents gas in the decompression chamber 1 from leaking to the microwave waveguide section 10. Note that while the central shaft tube section 12 moves up and down, the decompression chamber bottom plate 2 and the microwave waveguide section 10 fixedly connected to it are, in principle, fixed in position.

[0016] The central axial tube section 12 is inserted through a coaxial microwave coaxial conduit 2a formed in the decompression chamber bottom plate 2. The microwave waveguide section 10 has a horizontal waveguide section 10a and a vertical waveguide section 10b. The vertical waveguide section 10b is fixed to the lower surface of the decompression chamber bottom plate 2 with the central axial tube section 12 inserted through it. A coaxial microwave guidance passage 10c is formed between the inner circumferential surface of the vertical waveguide section 10b and the outer circumferential surface of the central axial tube section 12.

[0017] The microwave induction passage 10c communicates with the microwave coaxial conduit 2a formed in the depressurization chamber bottom plate 2, and as a result, microwaves are introduced to the underside of the stage 4. The microwaves introduced to the underside of the stage 4 then pass through the dielectric window 11, wrap around from the edge of the stage 4 to the top surface of the stage 4, and propagate to its top surface and the space above it. In this case, the microwaves propagate from the edge to the central area of ​​the top surface of the stage 4, and the energy of the microwaves causes a gas discharge above the stage 4 to generate plasma.

[0018] The propagation pattern of such microwaves is in a circumferentially uniform distribution state around the central axis. And in the space above the central area of stage 4, plasma 7 is generated by the interaction between the microwaves propagated as described above and the introduced hydrogen gas.

[0019] Regarding the propagation pattern of microwaves in the vacuum chamber 3 from the microwave induction path 10c through the lower space of stage 4 and further through the dielectric window 11, it is in a circumferentially uniform distribution state around the central axis.

[0020] Note that 14 is a gas introduction path, 2a is a microwave coaxial conduit, 10a is a horizontal waveguide, 10b is a vertical waveguide, 24b is a vertical pipe, and 24d is an L-shaped pipe.

[0021] Note that the description of other configurations of the apparatus 100 in FIG. 1 is omitted.

[0022] In this embodiment, in the microwave plasma CVD apparatus having the above configuration, a carbon-containing gas and hydrogen are introduced into the vacuum chamber 3 from the gas introduction unit 8, and plasma is generated on the single-crystal diamond substrate 6 set on stage 4 to form a diamond film on the single-crystal diamond substrate 6. Note that 9 discharges the used gas from the vertical pipe 24b of the gas discharge unit 9, and at the same time, a pressure gauge is set on the L-shaped pipe 24d to control the pressure in the vacuum chamber 3.

[0023] In the present invention, it includes a film-forming step of introducing a carbon-containing gas and a hydrogen gas into the vacuum chamber 3 from the gas introduction unit 8 to form a diamond film on the surface of the single-crystal diamond substrate 6 when the inside of the vacuum chamber 3 is in a plasma rising state and the surface temperature of the single-crystal diamond substrate 6 is at a predetermined temperature.

[0024] Here, the carbon-containing gas in the film-forming step is obtained, for example, by gasifying solid carbon powder obtained by burning bones such as those of animals and fish.

[0025] The following steps are included as pre-processing steps in the above film deposition process.

[0026] (Washing process) The cleaning process involves cleaning the single-crystal diamond substrate 6.

[0027] This cleaning process consists of the following first to third cleaning steps, which are performed in this order.

[0028] In the first cleaning step, the single-crystal diamond substrate 6 is immersed in pure water containing ultrapure water, acetone, and ethanol, respectively, and cleaned for several minutes, for example 5 minutes, using ultrasonic waves at 20-50 kHz, preferably 45 kHz. Pure water includes distilled water, demineralized water, and purified water, and is water with few impurities. Acetone and ethanol are used for the decomposition of organic matter.

[0029] In the second cleaning step, after the first cleaning step, the single-crystal diamond substrate 6 is acid-washed for a predetermined time, for example, 60 minutes, in a solution containing nitric acid (HNO3) and sulfuric acid (H2SO4) in equal proportions at a predetermined temperature, for example, 250°C, and then acid-washed again for a predetermined time, for example, 20 minutes, in perchloric acid (HClO4).

[0030] The second cleaning step is to remove various metals and graphite SP2 that remain on the surface of the single-crystal diamond substrate during polishing.

[0031] In the third cleaning step, after the second cleaning step, the single-crystal diamond substrate 6 is cleaned in pure water, and then ultrasonically cleaned in a solution of acetone and ethanol.

[0032] (drying process) After the cleaning step, the single-crystal diamond substrate 6 is dried in a drying step.

[0033] In the drying process, the single-crystal diamond substrate 6 is dried in a nitrogen gas atmosphere.

[0034] (Depressurization process) After the drying process, the single-crystal diamond substrate 6 is placed on the substrate holder 5 inside the vacuum chamber 3 during the depressurization process, and the inside of the vacuum chamber 3 is depressurized.

[0035] In this depressurization process, the internal pressure of vacuum chamber 3 is reduced to 1 Pa.

[0036] (Hydrogen gas introduction process) After the depressurization process, hydrogen gas is introduced into the vacuum chamber 3 under a predetermined reduced pressure. In the hydrogen gas introduction process, hydrogen gas is introduced using an MFC (mass flow meter).

[0037] (Plasma startup process) In the hydrogen gas process, when the vacuum chamber 3 contains a predetermined flow rate of hydrogen gas (10 sccm) and the internal pressure of the chamber 3 reaches 10 Torr, a plasma is generated inside the vacuum chamber 3.

[0038] As the plasma starts to rise, the microwave power is increased from 1kW to 4-6kW. In this process, the hydrogen gas is set to 100sccm-500sccm and the chamber pressure is set to 70-150 Torr. For example, the pressure inside chamber 3 is set to 70-150 Torr. The relationship between microwave power and chamber pressure is as follows: for example, when the pressure inside chamber 3 is 10 Torr, the microwave power is 1kW; when the pressure inside chamber 3 is 15 Torr, the microwave power is 1.5kW; when the pressure inside chamber 3 is 20 Torr, the microwave power is 2kW; and when the pressure inside chamber 3 is 30 Torr, the microwave power is 3kW.

[0039] When the microwave power is 4-6 kW, the surface temperature of the single-crystal diamond substrate is set to 900-1100°C.

[0040] (Film forming process) Once the surface temperature of the single-crystal diamond substrate reaches the above temperature, 300-500 sccm of hydrogen gas, 10-50 sccm of methane gas, and 0-5 sccm of oxygen are flowed through the chamber, and 5-50 sccm of carbon-containing gas is introduced into the vacuum chamber 3 to begin film deposition.

[0041] Under these deposition conditions, the deposition rate is 5-15 μm / hour.

[0042] The thickness of the deposited diamond film is set to the width of the single-crystal diamond substrate × 0.7. For example, when depositing a diamond film on a 10 × 10 mm single-crystal diamond substrate, the thickness is almost always 7 mm. In this case, it is necessary to adjust the height of the substrate holder 5 during film deposition. The substrate holder 5 is lowered while the film is being deposited. The lowering speed and the film deposition speed are set to be the same. When the film deposition speed reaches the substrate width × 0.7, the deposition of the diamond film is complete.

[0043] The carbon-containing gas may be obtained by gasifying fixed carbon powder. The fixed carbon powder can include hair, bone meal from animals or fish, or other carbon powders.

[0044] Next, the carbon-containing gas generator 200 will be described with reference to Figure 2.

[0045] The carbon-containing gas generator 200 is a device that generates a carbon-containing gas and introduces the generated carbon-containing gas from the gas introduction section 8 of the microwave plasma CVD apparatus 100 into the vacuum chamber 3. The carbon-containing gas generator 200 will be described with reference to Figure 2.

[0046] In the carbon-containing gas generator 200, 30 is the first valve, 31 is the flow meter (MFC), 32 is the quartz tube, 33 is the heating coil, 34 is the second valve, 35 is the vacuum pump, 36 is the vacuum gauge, and 37 is the third valve.

[0047] The flow meter 31 measures the flow rates of oxygen and hydrogen gases introduced through the first valve 30.

[0048] The quartz tube 32 has hair, bone meal from animals or fish, and other solid carbon powders 201-203 placed near the center of its interior.

[0049] The heating coil 33 is positioned around the quartz tube 32 to heat the quartz tube 32.

[0050] In the carbon-containing gas generator 200 configured as described above, the vacuum pump 35 is activated, and after approximately 5 seconds have elapsed since the start of operation, the second valve 34 is opened to create a vacuum inside the quartz tube 32, and when the internal pressure falls below 1 Pa, the second valve 34 is closed.

[0051] Next, the heating coil 533 is energized to heat the solid carbon powders 201-203 to a constant temperature, for example 900°C, inside the quartz tube 32, thereby decomposing them.

[0052] Subsequently, the first valve 30 is opened, and oxygen and hydrogen gases are introduced into the quartz tube 32 from one side through the first valve 30.

[0053] This process gasifies the decomposed solid carbon powder to generate a carbon-containing gas. This generated carbon-containing gas is then introduced into the microwave plasma CVD (MPCVD) apparatus 100 by opening the third valve 37. [Explanation of symbols]

[0054] 100 Microwave Plasma CVD Apparatus 1. Decompression chamber 2. Decompression chamber bottom plate 3. Vacuum Chamber 4 stages 5. Circuit board holder 7 Plasma 8. Gas inlet 9. Gas discharge section 10 Microwave Navigator 11 Dielectric window 12 Center axis tube section 13 Downward bias mechanism 200 Carbon-containing gas generator 30. Valve No. 1 31 Flowmeter (MFC) 32 Quartz tube 33 Heating coil 34. Second valve 35 Vacuum pump 36 Vacuum Gauge 37 Third valve

Claims

1. A method for forming a single-crystal artificial diamond, comprising introducing microwaves into a vacuum chamber in which a single-crystal diamond substrate, which is a seed crystal to be used as the raw material for single-crystal artificial diamonds, is installed, generating plasma on the single-crystal diamond substrate, and forming a diamond film on the single-crystal diamond substrate by a CVD synthesis method, When the vacuum chamber is in the plasma rise state and the surface temperature of the single-crystal diamond substrate is below a predetermined temperature, a film deposition process is performed in which a carbon-containing gas and hydrogen gas are introduced into the vacuum chamber to deposit a diamond film on the surface of the single-crystal diamond substrate. A method for forming a single-crystal artificial diamond film, characterized by including [a specific component].

2. The carbon-containing gas is a gas produced by gasifying solid carbon powder, such as hair, bone meal from animals or fish, or other carbon powders. The method for forming a single-crystal artificial diamond film according to claim 1.

3. The carbon-containing gas includes methane gas and oxygen. The method for forming a single-crystal artificial diamond film according to claim 2.

4. As a step preceding the aforementioned film formation process, A cleaning step of ultrasonically cleaning the single-crystal diamond substrate, After the cleaning step, a drying step is performed to dry the single-crystal diamond substrate. After the drying step, the single-crystal diamond substrate is placed on a substrate holder in the vacuum chamber and the vacuum chamber is depressurized in a depressurization step, After the depressurization step, a hydrogen gas introduction step is performed in which hydrogen gas is introduced while the internal pressure of the vacuum chamber is under a predetermined reduced pressure. When the vacuum chamber reaches a predetermined pressure with a predetermined flow rate of hydrogen gas in the hydrogen gas process, a plasma rise-up process is performed to start up plasma in the vacuum chamber. Features including, A method for forming a single-crystal artificial diamond film according to any one of claims 1 to 3.

5. The aforementioned cleaning step is The first cleaning step involves ultrasonically cleaning the single-crystal diamond substrate while it is immersed in pure water containing ultrapure water, acetone, and ethanol for a predetermined time. After the first cleaning step, a second cleaning step is performed in which the single-crystal diamond substrate is cleaned for a predetermined time in a liquid containing nitric acid and sulfuric acid in a predetermined ratio at a predetermined temperature. The process includes, after the second cleaning step, a third cleaning step in which the single-crystal diamond substrate is cleaned in pure water and then ultrasonically cleaned in a solution of acetone and ethanol. The method for forming a single-crystal artificial diamond film according to claim 4.

6. The aforementioned drying process is The process includes drying the single-crystal diamond substrate in a nitrogen gas atmosphere. A method for forming a single-crystal artificial diamond film according to any one of claims 1 to 5.

7. The aforementioned depressurization process is The process includes reducing the pressure inside the vacuum chamber to 1 Pa, A method for forming a single-crystal artificial diamond film according to any one of claims 2 to 6.

8. The hydrogen gas introduction process is as follows: This includes a process of controlling the introduction of hydrogen gas by mass flow rate control. A method for forming a single-crystal artificial diamond film according to any one of claims 2 to 7.

9. The aforementioned plasma start-up process is: The process includes setting the hydrogen gas level to 100 sccm to 500 sccm and setting the internal pressure of the chamber to 70 to 130 Torr. A method for forming a single-crystal artificial diamond film according to any one of claims 2 to 8.

10. The aforementioned film formation process is, The process includes flowing methane gas at a rate of 10 to 50 sccm and oxygen at a rate of 0 to 5 sccm into the vacuum chamber. A method for forming a single-crystal artificial diamond film according to any one of claims 1 to 9.

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