Microwave plasma reactor

Abstract

A microwave plasma reactor for manufacturing synthetic diamond material. The microwave plasma reactor comprises a microwave generator configured to generate microwaves, a plasma chamber having interior walls comprising aluminum, a microwave coupling configuration for feeding microwaves from the microwave generator into the plasma chamber, a gas flow system for feeding process gases into the plasma chamber and removing them from the plasma chamber, a substrate holder arranged in the plasma chamber and comprising a support surface for supporting a substrate, and a corrosion-resistant cooling system in thermal contact with the plasma chamber, on which, in use, the synthetic diamond material will be deposited.

Description

Technical Field

[0001] This disclosure relates to the field of microwave plasma reactors, and particularly to microwave plasma reactors for manufacturing synthetic diamond materials. Background Technology

[0002] Chemical vapor deposition (CVD) processes for synthesizing diamond materials are well known in the art. Useful background information on CVD of diamond materials can be found in review articles such as those by RS Balmer et al., which provide a comprehensive overview of CVD diamond materials, technologies and applications (see “Chemical vapor deposition synthetic diamond: materials, technology and applications” J. Phys.: Condensed Matter, Vol. 21, No. 36 (2009) 364221).

[0003] Because diamond is located in a metastable region compared to graphite, the synthesis of diamond under CVD conditions is driven by surface dynamics rather than bulk thermodynamics. CVD diamond synthesis typically uses a small amount of carbon (usually <5%) as a carbon-containing gas in an excess of molecular hydrogen. Significant dissociation of atomic hydrogen occurs if the molecular hydrogen is heated to temperatures exceeding 2000 K. With the availability of a suitable substrate material, diamond materials can be deposited and synthesized.

[0004] Atomic hydrogen is essential for this process because it selectively etches away non-diamond carbon from the substrate, allowing diamond growth to occur. Various methods exist for heating carbon-containing gaseous substances and molecular hydrogen to generate the reactive carbon-containing radicals and atomic hydrogen required for CVD diamond growth; these methods include arc jetting, hot filament, DC arc, oxy-acetylene flame, and microwave plasma.

[0005] Electrode-based methods, such as DC arc plasma, can have drawbacks due to electrode corrosion and material bonding into the diamond. Combustion methods avoid the electrode corrosion problem but rely on relatively expensive feed gases that must be purified to levels consistent with high-quality diamond growth. Even when burning an oxygen-acetylene mixture, the flame temperature is insufficient to obtain a substantial proportion of atomic hydrogen in the gas stream, and the method relies on concentrating the gas flux in a localized area to achieve a reasonable growth rate. A major reason why combustion may not be widely used for bulk diamond growth is the cost of extractable energy (in kWh). High-purity acetylene and oxygen are expensive ways to generate heat compared to electricity. While hot-filament reactors appear simple on the surface, they are limited to use at lower gas pressures, which are necessary to ensure a relatively efficient delivery of their limited amount of atomic hydrogen to the growth surface.

[0006] Based on the above, it has been found that microwave plasma is an effective method for driving CVD diamond deposition in terms of the combination of power efficiency, growth rate, growth area, and available product purity.

[0007] Microwave plasma-activated CVD diamond synthesis systems typically include a plasma reactor vessel coupled to a source gas supply and a microwave power source. The plasma reactor vessel is configured to form a resonant cavity supporting standing-wave microwaves. A source gas comprising carbon and molecular hydrogen is supplied to the plasma reactor vessel and can be activated by a standing-wave microwave field to form a plasma in a high-field region. If a suitable substrate is provided near the plasma, reactive carbon-containing radicals can diffuse from the plasma to the substrate and deposit thereon. Atomic hydrogen can also diffuse from the plasma to the substrate and selectively etch away non-diamond carbon from the substrate, enabling diamond growth.

[0008] A range of possible microwave plasma reactors for the growth of synthetic diamond films using CVD processes are known in the art. These reactors have various designs. Common features include: a plasma chamber; a substrate holder disposed within the plasma chamber; a microwave generator for forming the plasma; a coupling structure for supplying microwaves from the microwave generator into the plasma chamber; a gas flow system for supplying process gases into and removing them from the plasma chamber; and a temperature control system for controlling the substrate temperature on the substrate holder.

[0009] Plasma chambers are typically made of stainless steel. A cooling system is crucial to prevent overheating of the plasma chamber. Cooling systems usually rely on a flow of water through the cooling system to remove heat from the plasma chamber.

[0010] For reasons of cost, ease of manufacture and thermal conductivity, it may be desirable to use aluminum plasma chambers, but this leads to the problem of managing corrosion of aluminum chambers when the cooling system is incorporated as part of the chamber. Summary of the Invention

[0011] The aim is to provide a microwave plasma reactor for manufacturing synthetic diamond, which has a plasma chamber made primarily of aluminum or aluminum alloys, while reducing corrosion-related problems.

[0012] According to a first aspect, a microwave plasma reactor is provided for manufacturing synthetic diamond materials via chemical vapor deposition. The microwave plasma reactor comprises:

[0013] A microwave generator, which is configured to produce microwaves;

[0014] A plasma chamber having an inner wall composed of aluminum;

[0015] A microwave coupling structure is used to supply microwaves from a microwave generator to a plasma chamber;

[0016] A gas flow system is used to supply process gases into and remove them from the plasma chamber.

[0017] A substrate holder, disposed in the plasma chamber and comprising a support surface for supporting a substrate on which the synthetic diamond material will be deposited during use;

[0018] A corrosion-resistant cooling system that is in thermal contact with the plasma chamber.

[0019] As a first choice, the corrosion-resistant cooling system includes channels for transporting cooling fluid within the plasma chamber walls, the inner surfaces of which are configured to contact the cooling fluid and comprise anodized aluminum.

[0020] As a second option, the corrosion-resistant cooling system includes a jacket that is in thermal contact with the outer wall of the plasma chamber and contains channels for transporting cooling fluid.

[0021] The second alternative channel optionally has an inner surface configured to contact the cooling fluid, the inner surface comprising corrosion-resistant steel.

[0022] For both the first and second options, the path length of each channel can optionally have a larger proportion than that following a non-linear path. This improves cleanliness, accessibility, and ease of maintenance.

[0023] Alternatively, a corrosion-resistant cooling system comprises multiple sub-cooling systems, each in thermal contact with a different part of the plasma chamber. This has the advantage of reducing the passageway around difficult or inaccessible areas and allows for the application of individual cooling methods to different parts of the plasma chamber.

[0024] Alternatively, the plasma chamber has an inner wall made of aluminum alloy.

[0025] According to a second aspect, a cooling system is provided for a microwave plasma reactor used to manufacture synthetic diamond materials via chemical vapor deposition. The cooling system includes a jacket configured to make thermal contact with the outer wall of the plasma chamber of the microwave plasma reactor during use, and the jacket includes channels for conveying cooling fluid. This allows the cooling system to be retrofitted to existing microwave plasma reactors.

[0026] Alternatively, the channel has an inner surface configured to contact the cooling fluid, which comprises corrosion-resistant steel.

[0027] Alternatively, the path length of each channel can be proportionally larger than that of a non-linear path.

[0028] Alternatively, the jacket may include multiple sub-cooling systems, each of which is in thermal contact with a different part of the plasma chamber.

[0029] According to a third aspect, a method for manufacturing a microwave plasma reactor is provided, the microwave plasma reactor being used to manufacture synthetic diamond materials via chemical vapor deposition, the method comprising:

[0030] Provide a microwave generator configured to generate microwaves;

[0031] Provide a plasma chamber having an inner wall comprising aluminum;

[0032] A microwave coupling structure is provided for supplying microwaves from a microwave generator to a plasma chamber;

[0033] A gas flow system is provided for supplying process gases into and removing process gases from the plasma chamber;

[0034] A substrate holder is provided, which is disposed in the plasma chamber and includes a support surface for supporting the substrate, on which synthetic diamond material will be deposited during use;

[0035] A corrosion-resistant cooling system is provided that is in thermal contact with the plasma chamber.

[0036] The method optionally includes providing a corrosion-resistant cooling system comprising channels for conveying cooling fluid within the walls of a plasma chamber, the inner surfaces of which are configured to contact the cooling fluid and comprise anodized aluminum.

[0037] Alternatively, the method includes providing a jacket that is in thermal contact with the outer wall of the plasma chamber, the jacket containing channels for conveying cooling fluid.

[0038] Alternatively, the path length of each channel can be proportionally larger than that of a non-linear path.

[0039] The method optionally includes providing multiple sub-cooling systems, each of which is in thermal contact with a different part of the plasma chamber.

[0040] Alternatively, the plasma chamber has an inner wall made of aluminum alloy.

[0041] According to the fourth aspect, the microwave plasma reactor described in the first aspect above is provided for use in the manufacture of synthetic diamond materials. Attached Figure Description

[0042] To better understand the present invention and illustrate how it can be implemented, embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0043] Figure 1 schematically shows a cross-sectional view of a microwave plasma reactor configured to deposit synthetic diamond materials using chemical vapor deposition (CVD) technology.

[0044] Figure 2 A cross-sectional view of the microwave plasma reactor shown in FIG1, which has a plasma chamber cooling system according to a first embodiment of the present invention, is schematically shown.

[0045] Figure 3 A cross-sectional view of the microwave plasma reactor shown in FIG1, which has a plasma chamber cooling system according to a second embodiment of the present invention, is schematically illustrated; and

[0046] Figure 4 It shows that it provides Figure 2 and 3 The flowchart shows the steps of the microwave plasma reactor.

[0047] The accompanying drawings are not to scale. Throughout the specification, similar parts are assigned the same reference numerals, and detailed descriptions have been omitted for brevity. Detailed Implementation

[0048] Figure 1 illustrates an embodiment of a microwave plasma reactor 1 according to an embodiment of the present invention. The microwave plasma reactor 1 comprises the following basic components: a plasma chamber 2; a substrate holder 4 disposed in the plasma chamber for holding a substrate 6; a microwave generator 8 for forming plasma 10 within the plasma chamber 2; a microwave coupling structure 12 for supplying microwaves from the microwave generator 8 into the plasma chamber 2; and a gas flow system comprising a gas inlet 13 and a gas outlet 16 for supplying process gases into and removing them from the plasma chamber 2.

[0049] It should also be noted that although the microwave plasma reactor 1 shown in Figure 1 has a separate substrate holder disposed within the plasma chamber, the substrate holder may be formed from the base of the plasma chamber. The term "substrate holder" is used to cover these variations. Furthermore, the substrate holder may comprise a flat support surface with the same diameter as the substrate (as shown) or larger than the substrate. For example, the substrate holder may form a large flat surface formed by the base of the chamber or a separate component disposed above the base of the chamber, and the substrate may be carefully positioned on the central region of the flat support surface. In one arrangement, the flat support surface may have additional elements, such as protrusions or grooves, to align and optionally hold the substrate. Alternatively, no such additional elements may be provided, such that the substrate holder only provides a flat support surface on which the substrate is disposed.

[0050] The microwave coupling structure 12 includes a coaxial waveguide 14 configured to supply microwaves from a rectangular waveguide 16 to an annular dielectric window 18. The coaxial waveguide 14 includes an inner conductor 20 and an outer conductor 22. In the illustrated embodiment, the inner conductor 20 is a floating pillar that is not attached to the upper wall of the rectangular waveguide 16, but terminates within the waveguide at the transition region between the rectangular waveguide 16 and the coaxial waveguide 14.

[0051] The annular dielectric window 18 is made of a microwave-permeable material such as quartz. It forms a vacuum-sealed annular window in the top of the plasma chamber 2. The microwave generator 8 and the microwave coupling structure 12 are configured to generate microwaves of a suitable wavelength and to inductively couple the microwaves into the plasma chamber 2 to form a standing wave within the plasma chamber 2, which has a high-energy antinode located directly above the substrate 6 in use.

[0052] During operation, plasma 10 generates a significant amount of heat, which must be managed. Therefore, plasma chamber 2 has a cooling system to cool it from the outside. The cooling system has an inlet 30 and an outlet 32 ​​to allow cooling fluid to flow through the cooling system 28 to dissipate heat from the walls of plasma chamber 2. Typically, water is used as the cooling fluid due to its availability and cost. As described below, the cooling system 28 may be in the form of a jacket surrounding at least a portion of the outer wall of plasma chamber 2, or it may be a series of cooling channels directly disposed within the walls of plasma chamber 2.

[0053] In the first implementation scheme, such as Figure 2 As shown, the plasma chamber 2 is made of aluminum or an aluminum alloy. It has a cooling system 28, which includes one or more channels located in the wall of the plasma chamber 2. The cooling system 28 has an inlet 30 and an outlet 32, and is configured to allow a cooling fluid such as water to flow through the first cooling system 28.

[0054] To mitigate corrosion of the channel, its inner surface is anodized. Anodizing of aluminum is a well-known method. In short, anodizing involves creating a controlled oxide layer on the surface of aluminum. This oxide layer protects the aluminum from corrosion. It can also be used to improve its surface hardness.

[0055] Before anodizing, the surface is cleaned to remove any contaminants such as dirt, oil, or grease. This cleaning process is necessary to ensure uniform anodizing and good adhesion of the oxide layer. In some cases, the aluminum surface may be chemically etched to remove any surface irregularities or to prepare it for better anodizing. The surface may also be rinsed, deoxidized, or subjected to other suitable chemical treatments to prepare a surface for anodizing.

[0056] The surface is then anodized using an acidic electrolyte solution, such as sulfuric acid, which acts as the medium for the anodizing process. The concentration and temperature of the electrolyte solution are carefully controlled. The aluminum is electrically connected to an external power source, allowing the aluminum component to act as the anode, while the cathode is immersed in the electrolyte solution. When current flows through the electrolyte solution, oxygen ions from the electrolyte react with the aluminum surface to form an aluminum oxide layer.

[0057] After obtaining the desired alumina layer thickness, the anodized aluminum parts are rinsed with water to remove any residual electrolyte solution. This rinsing step not only removes the electrolyte but also seals openings and improves corrosion resistance. Various sealing steps and chemical treatments can be performed at this stage. The alumina layer on the surface of cooling channels is more corrosion-resistant than that on aluminum or aluminum alloy surfaces.

[0058] It may be desirable to anodize only a portion of the surface. For example, only the inner surface around the cooling channel and other areas may be anodized. Those skilled in the art will understand that there are several ways to anodize only a portion of the surface. For example, the surface may be masked prior to anodizing, so only the portion exposed by the mask will be anodized. Alternatively, the entire surface may be anodized, and then the anodized surface on the portions that do not need anodizing may be removed by machining.

[0059] Now go to Figure 3 A second embodiment is shown, in which the plasma chamber 2 is also made of aluminum or an aluminum alloy. In this embodiment, a cooling jacket 34 serves as a cooling system. The cooling jacket is mounted on the outer surface of the plasma chamber 2 and is in thermal contact with the outer surface of the plasma chamber 2. The cooling jacket 34 is provided with one or more channels located within the cooling jacket 34. The cooling jacket 34 has an inlet 36 providing access to the cooling channels and an outlet 38 configured to allow cooling fluids such as water to flow through the first cooling system 28.

[0060] The cooling jacket 34 can be made of stainless steel alloy to provide corrosion resistance, or, similar to the first embodiment, can have channels with an inner surface covered with anodized aluminum.

[0061] The advantages of using the cooling jacket 34 include allowing the cooling system to be isolated from other parts of the plasma chamber (such as microwave and vacuum components) and ensuring that the cooling fluid does not come into contact with the plasma chamber at all. It can be used to improve existing reactors and can be easily removed for cleaning or maintenance.

[0062] The outer wall of plasma chamber 2 is typically cylindrical. For both embodiments, it is preferable that the majority of the cooling channel path length lies in a direction substantially parallel to the main axis of plasma chamber 2, rather than substantially circumferentially surrounding the walls of the plasma chamber. This ensures that the majority of the channel path length is linear, thus providing a greater linear portion within the cooling channel path length. This facilitates cleaning and maintenance.

[0063] Figure 4 It is a flowchart showing the provision Figure 2 and 3 The steps of the exemplary microwave plasma reactor are shown below. The following reference numerals correspond to... Figure 4 The label.

[0064] S1. Provides a microwave generator configured to produce microwaves. Various types of microwave generators exist, such as magnetrons or solid-state microwave generators.

[0065] S2. Provide a plasma chamber having an inner wall comprising aluminum or an aluminum alloy.

[0066] S3. Provides a microwave coupling structure for supplying microwaves from a microwave generator to a plasma chamber.

[0067] S4. Provide a gas flow system for supplying process gases into and removing them from the plasma chamber. Process gases may include, for example, carbon-containing gases, hydrogen, argon, and gases that allow the introduction of dopants into the grown diamond, such as nitrogen- or boron-containing gases.

[0068] S5. Provide a substrate holder disposed in the plasma chamber and including a support surface for supporting the substrate, on which the synthetic diamond material will be deposited during use.

[0069] S6. As described above, a corrosion-resistant cooling system is provided that is in thermal contact with the plasma chamber. For example, this can take the form of channels for transporting cooling fluid within the plasma chamber walls, the inner surfaces of which are configured to contact the cooling fluid and comprise anodized aluminum. Alternatively, it can take the form of a jacket in thermal contact with the outer walls of the plasma chamber, the jacket containing channels for transporting cooling fluid. As described above, preferably, the path length of each channel has a greater proportion following a linear path compared to a proportion following a non-linear path. Furthermore, the cooling system may include multiple sub-cooling systems in thermal contact with different portions of the plasma chamber.

[0070] Although the invention has been specifically shown and described with reference to embodiments, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.

Claims

1. A microwave plasma reactor for manufacturing synthetic diamond materials via chemical vapor deposition, the microwave plasma reactor comprising: A microwave generator, which is configured to produce microwaves; A plasma chamber having an inner wall composed of aluminum; A microwave coupling structure is used to supply microwaves from a microwave generator to a plasma chamber; A gas flow system is used to supply process gases into and remove them from the plasma chamber. A substrate holder, disposed in the plasma chamber and comprising a support surface for supporting a substrate on which the synthetic diamond material will be deposited during use; A corrosion-resistant cooling system that is in thermal contact with the plasma chamber.

2. The microwave plasma reactor of claim 1, wherein the corrosion-resistant cooling system comprises a channel for conveying cooling fluid in the wall of the plasma chamber, the inner surface of the channel being configured to contact the cooling fluid, the inner surface comprising anodized aluminum.

3. The microwave plasma reactor of claim 1, wherein the corrosion-resistant cooling system comprises a jacket in thermal contact with the outer wall of the plasma chamber, the jacket comprising channels for conveying cooling fluid.

4. The microwave plasma reactor of claim 3, wherein the channel has an inner surface configured to contact a cooling fluid, the inner surface comprising corrosion-resistant steel.

5. The microwave plasma reactor according to any one of claims 2 to 4, wherein the path length of each channel has a greater proportion of following a linear path compared to the proportion of following a nonlinear path.

6. The microwave plasma reactor according to any one of claims 1 to 5, wherein the corrosion-resistant cooling system comprises a plurality of sub-cooling systems, each sub-cooling system being in thermal contact with a different portion of the plasma chamber.

7. The microwave plasma reactor according to any one of claims 1 to 6, wherein the plasma chamber has an inner wall comprising an aluminum alloy.

8. A cooling system for a microwave plasma reactor used to manufacture synthetic diamond materials via chemical vapor deposition, the cooling system comprising: A jacket configured to make thermal contact with the outer wall of the plasma chamber of the microwave plasma reactor during use, the jacket including channels for conveying cooling fluid.

9. The cooling system of claim 8, wherein the channel has an inner surface configured to contact the cooling fluid, the inner surface comprising corrosion-resistant steel.

10. The cooling system of claim 8 or 9, wherein the path length of each channel has a greater proportion of following a linear path compared to the proportion of following a nonlinear path.

11. The cooling system according to any one of claims 8 to 10, wherein the jacket comprises a plurality of sub-cooling systems, each sub-cooling system being in thermal contact with a different portion of the plasma chamber.

12. A method for manufacturing a microwave plasma reactor, the microwave plasma reactor being used to manufacture synthetic diamond materials via chemical vapor deposition, the method comprising: Provide a microwave generator configured to generate microwaves; Provide a plasma chamber having an inner wall comprising aluminum; A microwave coupling structure is provided for supplying microwaves from a microwave generator to a plasma chamber; Provide a gas flow system for supplying process gases into and removing them from the plasma chamber; A substrate holder is provided, which is disposed in the plasma chamber and includes a support surface for supporting the substrate, on which the synthetic diamond material will be deposited during use; A corrosion-resistant cooling system is provided that is in thermal contact with the plasma chamber.

13. The method of claim 12, further comprising providing a corrosion-resistant cooling system including channels for conveying cooling fluid within the walls of the plasma chamber, the inner surface of the channels being configured to contact the cooling fluid, the inner surface comprising anodized aluminum.

14. The method of claim 12, further comprising providing a jacket in thermal contact with the outer wall of the plasma chamber, the jacket including channels for conveying cooling fluid.

15. The method of any one of claims 13 or 14, further comprising providing channels, wherein the path length of each channel has a greater proportion of following a linear path compared to the proportion of following a nonlinear path.

16. The method according to any one of claims 12 to 15, further comprising providing a plurality of sub-cooling systems, each sub-cooling system being in thermal contact with a different portion of the plasma chamber.

17. The method according to any one of claims 12 to 16, wherein the plasma chamber has an inner wall comprising an aluminum alloy.

18. Use of the microwave plasma reactor according to any one of claims 1 to 7 for the manufacture of synthetic diamond materials.

Images