Microwave resonant cavity and microwave plasma chemical vapor deposition device

Abstract

The application discloses a microwave resonance cavity and a microwave plasma chemical vapor deposition device, wherein a convex top cover is arranged in a deposition chamber, and the convex top cover is arranged as a V-shaped convex platform or a W-shaped convex platform towards a deposition table, so that the microwave electromagnetic field in the resonance cavity can be improved, the electric field intensity at the top cover can be eliminated, plasma at the top cover can be avoided, the adverse effect of secondary plasma on diamond film growth can be eliminated, and the deposition of the diamond film is facilitated; and the resonance cavity with the conical deposition table can increase the electric field intensity and area on the tray, improve the microwave electromagnetic field in the resonance cavity, and then increase the plasma, improve the microwave energy utilization rate, and increase the deposition area and deposition speed of the diamond film.

Description

Technical Field

[0001] This invention belongs to the field of microwave plasma chemical vapor deposition technology, and specifically relates to a microwave resonant cavity and a microwave plasma chemical vapor deposition device. Background Technology

[0002] Microwave plasma chemical vapor deposition (MPCVD) is a process in which microwaves generated by a microwave generator are introduced into a deposition chamber via a waveguide and an isolator. Under the excitation of the microwaves, the gas molecules in the deposition chamber are ionized to generate plasma, which is then deposited on a substrate to obtain a diamond film.

[0003] This technology offers high controllability during diamond film deposition, and the diamond films prepared using this method are characterized by excellent quality and high color clarity. The most critical part of this technology is the design of the microwave resonant cavity. To date, MPCVD diamond film deposition devices have evolved from quartz tube type, quartz bell jar type, cylindrical resonant cavity type, loop antenna type, ellipsoidal resonant cavity type to dish cavity type. In the past few decades, MPCVD technology has made great strides and significant progress, and the MPCVD microwave resonant cavity has also been thoroughly studied, with its internal structure undergoing substantial improvements.

[0004] Based on the cylindrical resonant cavity type, ellipsoidal and dish-shaped cavity types have emerged in the industry. The dish-shaped cavity type has gradually become the optimal choice in the industry due to its stability, ease of fabrication, and high power. However, different devices have some common problems: secondary plasma is easily generated under high microwave input power conditions inside the cavity, microwave energy utilization efficiency is low, and the deposition area is small.

[0005] Currently, traditional dish-cavity MPCVD devices generally adopt a flat-top cover structure. This method easily generates secondary plasma at the top cover. The secondary plasma produces amorphous carbon that adheres to the top cover. When there is enough amorphous carbon, it will fall off the top cover and contaminate the diamond film on the tray substrate, which is not conducive to the normal growth of the diamond film.

[0006] However, the problem of secondary plasma, which is prevalent in the industry, persists and severely affects diamond growth. This issue has become a key and challenging problem hindering the industry's development. Research on how to eliminate secondary plasma has stalled. Secondary plasma is generated by microwave electromagnetic fields, and weakening the electric field strength at the location of secondary plasma would mean eliminating it. Therefore, weakening the electric field strength at the location of secondary plasma has become a common goal for the industry. Electromagnetic fields are invisible and intangible, and microwave resonant cavities have irregular structures, making it difficult to improve the distribution of electromagnetic fields within the microwave resonant cavity, weaken the electric field strength at the location of secondary plasma, and eliminate secondary plasma. Thanks to the development of computer simulation technology in recent years, this research has become possible.

[0007] Therefore, in order to eliminate secondary plasma, a microwave resonant cavity and microwave plasma chemical vapor deposition device are provided for conventional flat-top MPCVD devices, which can improve the microwave electromagnetic field and eliminate secondary plasma. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of the prior art by providing a microwave resonant cavity and a microwave plasma chemical vapor deposition apparatus to eliminate secondary plasma, thereby eliminating polycrystalline carbon adhering to the top cover, which is beneficial for the growth of diamond films.

[0009] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0010] A microwave resonant cavity includes a deposition chamber consisting of a cavity cover and a cavity base plate, and a coaxial waveguide connected to the deposition chamber from top to bottom. The deposition chamber is provided with a deposition stage and a protruding top cover. The protruding top cover is arranged as a V-shaped protrusion or a W-shaped protrusion facing the deposition stage. The deposition stage is connected to the cavity base plate through a quartz window.

[0011] The top of the cavity cover has an inlet for introducing the reaction gas, while the bottom plate of the cavity has an outlet for connecting to a vacuum pump and a main hole for connecting to a coaxial waveguide.

[0012] The deposition platform is a conical deposition platform, with the side away from the bottom plate of the cavity being the short end and the side closer to the bottom plate of the cavity being the long end.

[0013] The upper surface of the cavity bottom plate and the lower surface of the deposition stage are respectively provided with rectangular grooves, and rubber pads are provided in the rectangular grooves. The quartz window is sandwiched in the rubber pads located in the rectangular grooves.

[0014] The coaxial waveguide is connected to the cavity base plate and placed below the main hole, and is also connected to the mode converter.

[0015] The joint between the cavity bottom plate and the cavity cover is sealed with a rubber ring.

[0016] A tray is placed above the deposition stage.

[0017] A microwave plasma chemical vapor deposition apparatus, comprising a microwave system, a vacuum system, a gas supply system, and a microwave resonant cavity.

[0018] The microwave system includes a microwave generator, an isolator, a three-pin connector, and a rectangular waveguide connected in sequence. The outlet of the rectangular waveguide is connected to the inlet flange of the mode converter, and the microwave transmitted through the rectangular waveguide enters the mode converter.

[0019] The right end of the mode converter is connected to a short-circuit piston, which can slide left and right for adjustment.

[0020] The beneficial effects of this invention are:

[0021] (1) The microwave resonant cavity and microwave plasma chemical vapor deposition apparatus, by setting a protruding top cover in the deposition chamber, and the protruding top cover is arranged as a V-shaped protrusion or a W-shaped protrusion facing the deposition stage, can improve the microwave electromagnetic field in the resonant cavity, eliminate the electric field intensity at the top cover, and thus prevent plasma from being generated at the top cover, thereby eliminating the adverse effects of secondary plasma on diamond film growth and facilitating the deposition of diamond film.

[0022] (2) The resonant cavity with a conical deposition stage of the present invention can increase the electric field strength and area on the tray, improve the microwave electromagnetic field in the resonant cavity, thereby increasing the plasma, improving the microwave energy utilization rate, increasing the deposition area and deposition rate of the diamond film; the deposition stage is set as a conical deposition stage, which can improve the microwave energy utilization rate and thus increase the deposition area of ​​the diamond film.

[0023] (3) The microwave resonant cavity and microwave plasma chemical vapor deposition device designed in this invention were verified by computer simulation technology. The microwave resonant cavity and MPCVD device with V-shaped or W-shaped protrusions on the top cover can change the distribution of electromagnetic field in the microwave resonant cavity, weaken the electric field intensity at the secondary plasma, eliminate the secondary plasma, and solve the key and difficult problems that restrict the development of the industry. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the MPCVD device with a W-shaped top cover according to the present invention;

[0025] Figure 2 This is a schematic diagram of the MPCVD device with a V-shaped top cover according to the present invention;

[0026] Figure 3This is a schematic diagram of the MPCVD apparatus with a conical deposition stage according to the present invention.

[0027] Figure 4 This is a flowchart simulating the electric field distribution inside a microwave resonant cavity;

[0028] Figure 5 This is a flowchart of the microwave resonant cavity design;

[0029] Figure 6 This is a cloud map showing the distribution of the electromagnetic field inside the resonant cavity of a traditional dish-cavity MPCVD device.

[0030] Figure 7 This is a cloud map showing the distribution of the electromagnetic field inside the resonant cavity of an MPCVD device with a W-shaped top cover.

[0031] Figure 8 This is a cloud map showing the distribution of the electromagnetic field inside the resonant cavity of an MPCVD device with a V-shaped top cover.

[0032] Figure 9 This is a cloud map showing the distribution of the electromagnetic field inside the resonant cavity of an MPCVD device with a conical deposition stage. Detailed Implementation

[0033] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0034] This invention provides a microwave resonant cavity and a microwave plasma chemical vapor deposition apparatus, such as... Figures 1 to 9 As shown.

[0035] The microwave resonant cavity includes a deposition chamber 15 consisting of a cavity cover 16 and a cavity base plate 8, and a coaxial waveguide 7 connected to the deposition chamber 15 from top to bottom. The deposition chamber 15 is provided with a deposition stage 13 and a protruding top cover 18. The protruding top cover 18 is arranged with a V-shaped protrusion or a W-shaped protrusion facing the deposition stage. The deposition stage 15 is connected to the cavity base plate 8 through a quartz window 11. The top of the cavity cover 16 has an inlet 17 for introducing reactive gas, and the cavity base plate 8 has an outlet 9 for connecting to a vacuum pump and a main hole for communicating with the coaxial waveguide 7.

[0036] The deposition stage 13 is a conical deposition stage, with a short end on the side away from the bottom plate 8 of the cavity and a long end on the side closer to the bottom plate 8 of the cavity. A tray 14 is provided above the deposition stage 13. The tray 14 is located directly above the deposition stage 13 and can hold diamond seed crystals. Hydrogen, methane and other reactive gases enter the deposition chamber 15 through the air inlet 17. The air inlet system connected to the air inlet 17 and the air outlet system connected to the air outlet 9 are linked to maintain a negative pressure environment in the deposition chamber 15.

[0037] The upper surface of the cavity bottom plate 8 and the lower surface of the deposition stage 13 are respectively provided with rectangular grooves, and rubber pads 12 are provided in the rectangular grooves. The quartz window 11 is sandwiched in the rubber pads 12 located in the rectangular grooves.

[0038] The coaxial waveguide 7 is connected to the cavity base plate 8 and placed below the main hole, and the coaxial waveguide 7 is connected to the mode converter 5; the joint between the cavity base plate 8 and the cavity cover 16 is sealed with a rubber ring 10.

[0039] A microwave plasma chemical vapor deposition (PCCVD) apparatus includes a microwave system, a vacuum system, a gas supply system, and a microwave resonant cavity. The microwave system comprises a microwave generator 1, an isolator 2, a three-pin connector 3, and a rectangular waveguide 4 connected in sequence. The outlet of the rectangular waveguide 4 is connected to the inlet flange of a mode converter 5, and the microwaves transmitted through the rectangular waveguide 4 enter the mode converter 5. A short-circuit piston 6 is connected to the right end of the mode converter 5, and the short-circuit piston 6 is adjustable left and right.

[0040] The following describes the specific embodiments in further detail:

[0041] Example 1

[0042] First, the power supply provides power to the microwave generator 1, which generates and emits microwaves. The microwaves pass through the isolator 2. The inlet of the isolator 2 is bolted to the outlet flange of the microwave generator 1, and the outlet of the isolator 2 is bolted to the three-pin flange 3. The function of the isolator 2 is to absorb the microwaves reflected from the microwave resonant cavity and protect the microwave generator 1 from damage caused by the reflected waves.

[0043] The microwave enters the three pins 3. After adjustment of the three pins, the entire microwave system achieves impedance matching, which can reduce microwave reflection power. The outlet of the three pins 3 is bolted to the inlet flange of the rectangular waveguide 4. After transmission through the rectangular waveguide, the microwave enters the mode converter 5. The outlet of the rectangular waveguide is bolted to the inlet flange of the mode converter 5.

[0044] The mode converter 5 converts the TE mode microwaves transmitted in the rectangular waveguide 4 into the TEM mode transmitted in the coaxial waveguide 7, so that the microwaves propagate upward along the coaxial waveguide 7, pass through the quartz window 11 and enter the deposition chamber 15, where the microwaves are converted back into the TM mode; the right end of the mode converter 5 is connected to the short-circuit piston 6, so that as much microwave energy as possible enters the deposition chamber 15.

[0045] Microwaves propagate upwards along the coaxial waveguide 7, which is bolted to the cavity base plate 8. The cavity base plate 8 has a dovetail groove for placing the rubber ring 10. The cavity cover 16 covers the cavity base plate 8, and they are sealed with a rubber ring. The air outlet 9 is located on the cavity base plate 8 and is connected to the external air outlet system. The air inlet 17 is located on the top of the cavity cover 16 and is connected to the external air inlet system. The air inlet system and the air outlet system are linked to maintain a negative pressure environment inside the deposition chamber 15.

[0046] The upper surface of the cavity base plate 8 is also provided with a rectangular groove for placing the rubber pad 12. The lower surface of the deposition stage 13 is also provided with a rectangular groove for placing the rubber pad 12. A quartz window 11 is sandwiched between the two rubber ring pads 12. The quartz window 11 can allow microwaves to pass through without loss, and can also work together with the cavity base plate 8, the rubber ring pads 12, and the deposition stage 13 to provide a vacuum seal.

[0047] The tray 14 is located directly above the deposition stage 13. Diamond seed wafers can be placed in the tray 14. Hydrogen, methane and other reactive gases enter the deposition chamber 15 through the inlet 17. The inlet system connected to the inlet 17 and the outlet system connected to the outlet 9 are linked to maintain a negative pressure environment in the deposition chamber 15. Microwaves also enter the deposition chamber 15 through the microwave generator 1, isolator 2, three pins 3, rectangular waveguide 4, mode converter 5, short-circuit piston 6, coaxial waveguide 7 and quartz window 11. The microwave energy excites the reactive gases in the deposition chamber 15 under negative pressure, which will form plasma directly above the tray 14. The plasma will deposit down and fall on the diamond seed wafers in the tray 14. The seed wafers will grow and thicken to form large diamond particles.

[0048] In this embodiment, the protruding top cover adopts a W-shaped top cover. If a flat-top MPCVD device is used, the microwave will not only have a strong electromagnetic field on the tray 14, but also a strong electromagnetic field at the top cover. The strong electromagnetic field will excite the reactive gas to generate plasma. Therefore, in a flat-top MPCVD device, there will be two plasmas: the main plasma located above the tray 14 and the secondary plasma located below the top of the cavity cover 16. The secondary plasma is harmful. However, the W-shaped top cover used in this embodiment can eliminate the electromagnetic field intensity at the top cover, thereby eliminating the secondary plasma. Therefore, the adverse effects of the secondary plasma on the growth of the diamond film can be eliminated.

[0049] The working principle and method of the microwave resonant cavity and microwave plasma chemical vapor deposition device are as follows:

[0050] Microwaves are emitted by the microwave generator, passing through isolator 2, three pins 3, and rectangular waveguide 4 into the microwave resonant cavity. They then pass through mode converter 5, short-circuit piston 6, coaxial waveguide 7, and quartz window 11 before entering the deposition chamber. Reactive gas enters the deposition chamber 15 through inlet 17, and outlet 9 is connected to a vacuum pump to expel reactive waste gas, maintaining a low-pressure environment in deposition chamber 15. Under microwave excitation, plasma is generated above tray 14, ionizing gas molecules to obtain active molecular groups, which deposit a diamond film on the tray substrate.

[0051] The method for calculating microwave electromagnetic fields is as follows:

[0052] The microwave electric field distribution of the MPCVD device can be obtained by solving Maxwell's equations:

[0053]

[0054] In the formula It is an electric field. and Microwave angular frequency and wavenumber, It is the vacuum permittivity. , and These are the material's relative permeability, relative permittivity, and conductivity, respectively. It is the imaginary part unit. In the region of undischarged gas... , Quartz glass area , For the discharge gas region, the conductivity is given by the following formula:

[0055]

[0056] In the formula, and These are the charge and mass of an electron, respectively. It is electron density. This refers to the electron-neutral particle collision frequency of the plasma. Alternatively, the relative permittivity of the plasma can be defined as follows:

[0057]

[0058] In calculations, plasma can be considered as having an electrical conductivity of [missing value]. A conductor, or a conductor with a relative permittivity of The dielectric material.

[0059] After solving the microwave electric field equations, the absorbed power of the plasma can be obtained from the following equations:

[0060]

[0061] In the formula This indicates finding the real part of the expression. yes The complex conjugate of the plasma. Alternatively, the plasma absorptivity can be written as a function of electron density:

[0062]

[0063] Microwave electromagnetic field simulation has been widely and successfully applied to various aspects of electromagnetic performance prediction and design. The electromagnetic field simulation software used in this paper is a numerical simulation software based on the finite element method to calculate electromagnetic fields. The electromagnetic field simulation software can divide the entire model into a finite number of independent elements for solution, and then combine the results after solution into the final result. The accuracy of electromagnetic field simulation has been recognized by the industry. Through electromagnetic field simulation software, the distribution cloud map of electromagnetic field inside microwave resonant cavity can be obtained.

[0064] The design process for a microwave resonant cavity is as follows:

[0065] First, use simulation software to perform microwave electromagnetic field simulation analysis on the microwave resonant cavity, obtain the electric field intensity cloud map, save it, and use it as the original size simulation result for comparative analysis.

[0066] Second, modify the model dimensions using the controlled variable method, changing only one dimension at a time. Then, perform electromagnetic field simulation analysis and observe the electric field contour plot results. If the results are better than those with the original dimensions, retain them as a comparison result; if they are worse, discard them, and use the original dimensions as the comparison result. Changes to a single dimension, whether increasing or decreasing, should be done slowly. Repeat the above process until the optimal result for that dimension is obtained. Similarly, based on this dimension, change all other dimensions until the optimal dimensions of the resonant cavity are obtained.

[0067] Third, plasma simulation analysis is performed on the optimal model obtained by microwave electromagnetic field simulation. If the electric field strength, temperature field, and electron density meet the requirements, the cavity size can be determined, and then physical manufacturing and physical model verification tests can be carried out.

[0068] The electromagnetic field of the microwave resonant cavity inside the W-shaped top cover of this embodiment was verified by a three-dimensional model using electromagnetic field simulation software. The verification results are as follows: Figure 7 As shown in the figure. Electromagnetic field simulation of a three-dimensional model was also performed inside the microwave resonant cavity with a flat-top cover. The verification results are as follows. Figure 6 As shown.

[0069] By comparison Figure 6 and Figure 7It can be found that the W-shaped top cover can eliminate the electric field intensity at the top cover, thereby preventing the generation of plasma at the top cover and thus eliminating the adverse effects of secondary plasma on the growth of diamond films.

[0070] Example 2

[0071] Based on Example 1, the protruding top cover adopts a V-shaped top cover. Electromagnetic field simulation software was used to perform a three-dimensional electromagnetic field simulation verification of the microwave resonant cavity inside the V-shaped top cover of this example. The verification results are as follows: Figure 8 As shown.

[0072] By comparison Figure 6 and Figure 8 It can be observed that the V-shaped top cover can eliminate the electric field intensity at the top cover, thereby preventing the generation of plasma at the top cover and eliminating the adverse effects of secondary plasma on the growth of diamond films.

[0073] Example 3

[0074] Based on Example 1 or Example 2, a microwave resonant cavity and MPCVD device with a conical deposition stage are proposed. In this example, electromagnetic field simulation software is used to simulate and verify the structure of the MPCVD device with the conical deposition stage and the traditional planar deposition stage.

[0075] In this embodiment, electromagnetic field simulation software was used to perform a three-dimensional electromagnetic field simulation of the microwave resonant cavity, verifying the effectiveness of the device of the present invention. The verification results are as follows: The distribution cloud map of the electromagnetic field inside the resonant cavity of a traditional dish-cavity MPCVD device is shown in the figure below. Figure 6 As shown, the electromagnetic field distribution cloud map inside the resonant cavity of the MPCVD device with a conical deposition stage is as follows. Figure 9 As shown.

[0076] By comparison Figure 6 and Figure 9 It can be observed that the red area of ​​the electromagnetic field above the tray inside the resonant cavity with the conical deposition stage is larger, which means that the electromagnetic field intensity in the area above the tray is higher. Therefore, the area of ​​plasma generated by the ionization of the reactive gas by the electromagnetic field is larger. It can be seen that the conical deposition stage can improve the microwave electromagnetic field in the resonant cavity, improve the microwave energy utilization rate, and thus increase the deposition area of ​​the diamond film.

[0077] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection of this invention is defined by the appended claims and their equivalents.

[0078] In the description of this invention, it should be understood that the terms "front", "rear", "left", "right", "center", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only used to facilitate the description of this invention and to simplify the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of this invention.

Claims

1. A microwave resonant cavity, characterized in that: It includes a deposition chamber consisting of a cavity cover and a cavity bottom plate, and a coaxial waveguide connected to the deposition chamber from top to bottom. The deposition chamber is equipped with a deposition stage and a protruding top cover. The protruding top cover is arranged as a V-shaped protrusion or a W-shaped protrusion facing the deposition stage. The deposition stage is connected to the cavity bottom plate through a quartz window. The top of the cavity cover has an inlet for introducing the reaction gas, while the bottom plate of the cavity has an outlet for connecting to a vacuum pump and a main hole for connecting to a coaxial waveguide. The deposition platform is a conical deposition platform, with the side away from the bottom plate of the cavity being the short end and the side closer to the bottom plate of the cavity being the long end. The upper surface of the cavity bottom plate and the lower surface of the deposition stage are respectively provided with rectangular grooves, and rubber pads are provided in the rectangular grooves. The quartz window is sandwiched in the rubber pads located in the rectangular grooves.

2. A microwave resonant cavity according to claim 1, characterized in that: The coaxial waveguide is connected to the cavity base plate and placed below the main hole, and is also connected to the mode converter.

3. A microwave resonant cavity according to claim 1, characterized in that: The connection between the cavity bottom plate and the cavity cover is sealed with a rubber ring.

4. A microwave resonant cavity according to claim 1, characterized in that: A tray is placed above the deposition stage.

5. A microwave plasma chemical vapor deposition apparatus, characterized in that: The microwave plasma chemical vapor deposition apparatus includes a microwave system, a vacuum system, a gas supply system, and a microwave resonant cavity as described in any one of claims 1-4.

6. The microwave plasma chemical vapor deposition apparatus according to claim 5, characterized in that: The microwave system includes a microwave generator, an isolator, a three-pin connector, and a rectangular waveguide connected in sequence. The outlet of the rectangular waveguide is connected to the inlet flange of the mode converter, and the microwave transmitted through the rectangular waveguide enters the mode converter.

7. The microwave plasma chemical vapor deposition apparatus according to claim 6, characterized in that: The right end of the mode converter is connected to a short-circuit piston, which can slide left and right for adjustment.

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