A composite plasma source and method of operation thereof

Abstract

This invention provides a composite plasma source and its operation method, which combines microwave plasma and transformer-coupled plasma mechanisms to form a composite plasma source for gas dissociation and chemical activation. The reaction chamber of the composite plasma source consists of two microwave resonant cavities and multiple sets of hollow metal tubes. After generating plasma using a high-intensity electric field generated by the microwave resonant cavities, the high-efficiency coupling mechanism of the transformer-coupled plasma generates high-power and high-density plasma, which can significantly improve gas conductivity. At the same time, each set of hollow metal tubes is driven by a ferrite transformer core to disperse power, thereby reducing the energy density of each hollow metal tube and decreasing the occurrence of plasma transitioning from diffusion mode to contraction mode, thus further improving the operable gas flow rate.

Description

A composite plasma source and its operation method Technical Field

[0001] This invention relates to a plasma source, and more particularly to a composite plasma source and its operation method. Background Technology

[0002] Plasma is widely used in semiconductor manufacturing and other industrial processes. Its advantage lies in its ability to decompose gas molecules, generating a highly reactive mixture of neutral free radicals, ions, atoms, electrons, and excited molecules to provide the various physical and chemical reactions required for the process. Many different mechanisms exist for generating plasma, one of which uses a ferrite transformer core to generate inductively coupled plasma discharge. The main mechanism, as shown in Figure 1, utilizes a ferrite transformer core 502 to generate an induced electric field within a toroidal vacuum chamber 500, thereby discharging the gas. One end of the toroidal vacuum chamber 500 is the gas inlet 506, and the other end is the gas outlet 508. This method is similar to the principle of a transformer; the power supply is connected to the primary side of the ferrite transformer core 502, while the plasma becomes the secondary side of a single turn, connected by magnetic flux to form a good coupling efficiency. The induced electric field in the plasma drives electron drift current to flow along the vacuum chamber 500 in a closed path; therefore, this mechanism is also called Transformer Coupled Plasma (TCP). In conventional technology, the ferrite transformer core 502 connected to the driving AC power supply can generate an induced electric field within the annular vacuum cavity 500 to excite current in the plasma. However, the structure of the annular vacuum cavity 500 must provide an electrically isolated region with ceramic annular plates 504; otherwise, it will cause a short circuit to the ferrite transformer core 502, preventing the generation of an induced electric field in the annular vacuum cavity 500. Moreover, the electrically isolated region must be small enough to generate a sufficiently strong electric field to excite and maintain a stable plasma. However, the strong electric field generated by the ferrite transformer core 502, under the influence of the metal structure of the annular vacuum cavity 500, will concentrate in the electrically isolated region formed by the ceramic annular plates 504. Sometimes, this can cause regional discharge, resulting in the ceramic annular plates 504 breaking and destroying the electrically isolated region. It can even cause back discharge, damaging the driving power supply, or causing the protective coating of the reaction cavity to peel off.

[0003] Anderson described this method in U.S. Patents 3,500,118 and 3,987,334. U.S. Patent 4,180,763 proposed the application of ferrite core TCP in lighting applications. Reinberg et al. proposed the application of plasma to remove photoresist in semiconductor processes in U.S. Patent 4,431,898. This TCP technology has been used to provide plasma sources with high activation rates for dissociated gases. In some high-pressure, high-flow-rate applications, high-power-density plasmas are required to chemically activate or alter the properties or composition of the working gas, which can then be sent to a vacuum processing system. Such applications are referred to as “remote plasma processing” and include: (1) remote chamber cleaning; (2) remote chamber ashing of polymer surfaces; and (3) downstream pre-cleaning and post-treatment gas reduction in vacuum pre-line systems. Many of these applications involve high flow rates (greater than 1 slm) of electronegative plasma discharge gases (such as O2, NF3, SF6) and relatively high gas pressures (greater than 1 Torr). Therefore, high power density is typically required to achieve the high dissociation and activation of the working gas. Under high-pressure, high-flow operating conditions, similar to many inductively coupled plasma (TCP) source devices, the intensity of the induced electromagnetic field in TCP is insufficient to ignite plasma discharge. Other methods must be employed to introduce a high-intensity electric field into the vacuum reaction chamber to trigger plasma discharge, such as adding high-voltage electrodes or introducing a high AC voltage into electrically isolated sections of the chamber to generate localized radio frequency glow discharge. However, the lifespan and reliability of high-voltage discharge devices are limited. For example, some literature has proposed adding a resonant circuit to generate high voltage (1-10kV) to effectively generate regional discharge and thus plasma. However, if the same voltage is used after plasma generation, it will generate an extremely large current, damaging power components. Therefore, a high-voltage relay must be added to the circuit to quickly switch the power circuit to a non-resonant circuit after plasma generation to reduce voltage and avoid damage from large currents. However, if the relay fails or the control signal is delayed and cannot be activated immediately, it will damage the power components. On the other hand, using high voltage can easily damage the insulating components of the vacuum chamber, causing electrical short circuits. It can also cause the plating on the chamber walls to peel off and flow into the process chamber, resulting in particulate contamination. In some applications, such as panel display manufacturing, the large volume of the process system necessitates the use of large amounts of gas (>30 slm) to meet process requirements. Therefore, in the existing annular vacuum chamber structure, the operating gas pressure and power density must be significantly increased.However, under these conditions, the diameter of the cylindrical plasma column within the vacuum chamber can decrease due to limitations in ion and electron collisions, ambipolar diffusion, and heat dissipation efficiency. This causes the plasma to transition from diffusion mode to contraction mode, preventing it from completely filling the vacuum chamber. Consequently, some gas fails to react via the plasma, reducing the overall gas activation rate and failing to meet process requirements. In severe cases, plasma instability can even occur, leading to plasma failure and eventual shutdown. Therefore, improving the existing annular vacuum chamber structure to ensure plasma stability is a crucial problem that must be overcome to further increase gas flow rate. Summary of the Invention

[0004] In view of the problems of the prior art, the purpose of this invention is to improve upon the shortcomings of the existing TCP plasma technology and to provide a solution for further increasing the working gas flow rate. The main technologies are: (1) Combining the mechanisms of microwave plasma and TCP plasma to form a composite plasma source, using a microwave resonant cavity to generate a high-intensity electric field to generate plasma, and then using the efficient energy coupling mechanism of TCP to plasma to generate high-power and high-density plasma. This eliminates the shortcomings of high-voltage ignition devices, and since microwaves are responsible for exciting and maintaining the initial plasma, the shortcomings of TCP weak electric field can be solved to improve plasma stability. (2) The reaction chamber is composed of two microwave resonant cavities and multiple sets of hollow metal tubes. Compared with the existing toroidal vacuum chamber, the gas conduction can be greatly improved, so that the gas pressure can be maintained in the range of several Torr under high gas flow. At the same time, because the power of each set of hollow metal tubes is dispersed, the energy density of each hollow tube is reduced, reducing the occurrence of plasma changing from diffusion mode to contraction mode.

[0005] To achieve the aforementioned objectives, this invention proposes a composite plasma source comprising a reaction chamber and at least one ferrite transformer core. The reaction chamber includes a first microwave resonant cavity, a second microwave resonant cavity, and at least one pair of hollow metal tubes. The two ends of the pair of hollow metal tubes are respectively connected to the first microwave resonant cavity and the second microwave resonant cavity. At least one microwave is introduced into the reaction chamber to excite a working gas within the reaction chamber into a plasma. The ferrite transformer core includes a ferrite core with two hollow regions respectively fitted onto the pair of hollow metal tubes, an induction coil wound around the ferrite core through the two hollow regions, and a driving power supply electrically connected to the induction coil. This generates an induced electric field within the pair of hollow metal tubes of the reaction chamber. The induced electric field excites the plasma, thereby forming a current with a closed path within the reaction chamber, further ionizing the working gas to increase the plasma density.

[0006] The current circulates through the first microwave resonant cavity, the pair of hollow metal tubes, and the second microwave resonant cavity to form the closed path.

[0007] It further includes at least one microwave source disposed on the first microwave resonant cavity, the second microwave resonant cavity, or the first microwave resonant cavity and the second microwave resonant cavity of the reaction cavity, for introducing the microwave into the reaction cavity.

[0008] The microwave source includes a magnetron, a central metal rod, and a cylindrical outer tube arranged coaxially. The central metal rod is located in the cylindrical outer tube. One end of the central metal rod is connected to an output antenna of the magnetron, and the other end of the central metal rod extends into the reaction cavity, so as to guide the microwave generated by the magnetron into the reaction cavity through the central metal rod and the cylindrical outer tube.

[0009] The microwave source further includes a microwave matching element to reduce the amount of reflection when the microwaves generated by the magnetron are introduced into the reaction cavity through the central metal rod and the cylindrical outer tube, so that the microwaves enter the reaction cavity.

[0010] The microwave matching element includes a metal coaxial tube horizontally disposed on the cylindrical outer tube. The metal coaxial tube has a horizontal tube, a metal plate and a crossbar arranged coaxially. The horizontal tube is horizontally disposed on the cylindrical outer tube, the crossbar extends from the cylindrical outer tube into the horizontal tube, and the metal plate is disposed on the crossbar.

[0011] The metal plate is movably mounted on the crossbar to perform impedance matching and improve the amount of microwave reflection.

[0012] The output antenna and the central metal rod have a diameter gradient region to reduce the amount of reflection when the microwave generated by the magnetron is conducted from the output antenna to the central metal rod.

[0013] The cylindrical outer tube is made of ceramic.

[0014] The cylindrical outer tube is a sealed vacuum tube.

[0015] The two ends of the pair of hollow metal tubes are respectively connected to the first microwave resonant cavity and the second microwave resonant cavity via at least one electrical barrier region, so as to prevent short circuit between the reaction cavity and the ferrite transformer core.

[0016] The electrical barrier region is a ceramic ring-shaped sheet.

[0017] The first microwave resonant cavity and the second microwave resonant cavity are hollow cylinders.

[0018] The working gas has a pressure greater than 1 Torr and a flow rate greater than 10 slm.

[0019] The number (and / or diameter) of the pair of hollow metal tubes increases in response to the increase in the flow rate of the working gas, thereby ensuring the stability of the plasma in the pair of hollow metal tubes and increasing gas conductivity.

[0020] The power density of the plasma corresponds to the number of hollow metal tubes in the pair.

[0021] The ferrite transformer has two sets of magnetic cores, and the induction coil is connected in parallel to the drive power supply for power supply.

[0022] The electric field generated by the ferrite transformer core is perpendicular to a central metal rod that guides the microwaves into the reaction cavity, so as to avoid interfering with the microwave source that generates the microwaves.

[0023] The driving power supply can be an AC power supply, a DC power supply, or a pulse power supply.

[0024] The first microwave resonant cavity has a gas inlet, and the second microwave resonant cavity has a gas outlet.

[0025] To achieve the aforementioned objectives, the present invention further proposes a method for operating a composite plasma source, characterized in that a working gas is first formed into a plasma by a microwave electric field, and then energy is coupled to the plasma with high efficiency by a transformer-coupled plasma technology, thereby further increasing the plasma density and generating an activated gas with a high degree of dissociation.

[0026] As described above, the composite plasma source and operating method of the present invention may have one or more of the following advantages:

[0027] (1) A composite plasma source is formed by combining the mechanisms of microwave plasma and TCP plasma. (2) After generating plasma by using a microwave resonant cavity to generate a high-intensity electric field, the energy is effectively coupled by the TCP mechanism to generate high-power and high-density plasma. (3) The disadvantages of high-voltage ignition devices can be eliminated. At the same time, since microwaves are responsible for exciting and maintaining the initial plasma, the disadvantages of weak electric fields in TCP can be solved to improve plasma stability. (4) Utilizing the strong electric field characteristics of the reaction cavity, a certain plasma density can still be maintained even when the process conditions are adjusted. Even when the gas pressure is 1 Torr to 5 Torr, a high-intensity electric field can still be effectively excited to meet the requirements for stable plasma generation. (5) The number of hollow metal tubes can be increased to disperse the flow rate according to the gas flow rate of the working gas, which can not only ensure the stability of the plasma but also increase the gas conductivity. (6) Since the plasma of the present invention is excited by microwaves, the electrical barrier region of the present invention can be wider, which is beneficial to the extension of service life and the stability of the system. (7) Under the condition of large gas flow, the gas pressure can be maintained in the range of several Torr. (8) Because the power of each hollow metal tube is dispersed, the energy density of each hollow tube decreases, reducing the occurrence of plasma transitioning from diffusion mode to contraction mode. (9) This invention utilizes a high-intensity electric field in the reaction chamber to excite a stable plasma under high pressure and high gas flow rate, providing sufficient free electrons. Driven and accelerated by the electric field induced by the ferrite transformer core, a closed-path electron drift current is formed in the reaction chamber, further effectively ionizing the gas to generate high-density plasma.

[0028] To enable you to have a better understanding of the technical features and effects of this invention, preferred embodiments and detailed descriptions are provided below. Attached Figure Description

[0029] Figure 1 is a cross-sectional schematic diagram of the annular vacuum cavity of a conventional annular low-electric-field plasma source.

[0030] Figure 2 is a cross-sectional schematic diagram of the composite plasma source of the present invention.

[0031] Figure 3 is a schematic diagram of the operation of the composite plasma source of the present invention from another perspective.

[0032] Figure 4 is a cross-sectional schematic diagram of the microwave source of the composite plasma source of the present invention.

[0033] Figure 5 is a cross-sectional schematic diagram of the ferrite transformer core of the composite plasma source of the present invention.

[0034] Explanation of reference numerals in the attached figures:

[0035] 10: Reaction chamber; 24: Central metal rod; 56: Induction coil

[0036] 11: Gas inlet; 25: Diameter gradient zone; 58: Drive power supply

[0037] 12: First microwave resonant cavity; 26: Cylindrical outer tube; 100: Composite plasma source.

[0038] 14: Second microwave resonant cavity; 30: Microwave matching element; 200: Working gas.

[0039] 15: Gas outlet 32a: Horizontal tube 300: Microwave electric field

[0040] 16: Hollow metal tube; 32b: Metal plate; 400: Induced electric field

[0041] 17: Electrically isolated region 32c: Crossbar 500: Vacuum chamber

[0042] 20: Microwave source; 50: Ferrite transformer core; 502: Ferrite transformer core

[0043] 22: Magnetron; 52: Ferrite core; 504: Ceramic toroidal plate.

[0044] 23: Output antenna; 54: Hollow region; 506: Gas inlet

[0045] 508: Gas outlet Detailed Implementation

[0046] To facilitate understanding of the technical features, content, advantages, and effects of this invention, the invention is described in detail below with reference to accompanying drawings and embodiments. The drawings used are for illustrative and supplementary purposes only and may not represent the actual scale and precise configuration of the invention in practice. Therefore, the scale and configuration of the accompanying drawings should not be used to interpret or limit the scope of the invention in actual implementation. Furthermore, for ease of understanding, the same elements in the following embodiments are indicated by the same symbols.

[0047] Furthermore, unless otherwise specified, the terms used throughout this specification and the claims generally have their ordinary meaning in the context of the art, the disclosure, and the specific content. Certain terms used to describe the invention will be discussed below or elsewhere in this specification to provide additional guidance to those skilled in the art in describing the invention.

[0048] The use of terms such as "first," "second," and "third" in this article does not specifically refer to order or sequence, nor is it intended to limit this work; it is merely to distinguish components or operations described using the same technical terminology.

[0049] Secondly, when this article uses terms such as "contains", "includes", "has", or "contains", these are all open-ended terms, meaning that they include but are not limited to.

[0050] This invention discloses a composite plasma source and its operation method, combining microwave plasma and transformer-coupled plasma (TCP) technologies to form a composite plasma source for working gas dissociation and chemical activation, thereby generating high-power and high-density plasma under high gas pressure and high gas flow rate. The invention first uses microwaves to generate a high-intensity electric field (microwave electric field) in a microwave resonant cavity, causing the working gas to form plasma. Then, transformer-coupled plasma technology effectively couples the energy, causing the plasma to discharge and generate electron drift current, further effectively ionizing the working gas to produce high-power and high-density plasma.

[0051] Please refer to FIGS. 2 to 5. The present invention discloses a composite plasma source 100 including a reaction chamber 10 and at least one ferrite transformer core 50. The reaction chamber 10 includes a first microwave resonance chamber 12, a second microwave resonance chamber 14, and at least a pair of hollow metal tubes 16. The two ends of the hollow metal tubes 16 are respectively connected to the first microwave resonance chamber 12 and the second microwave resonance chamber 14. In the reaction chamber 10, a microwave is first used to form plasma from the working gas 200, and the ferrite transformer core 50 generates an induced electric field 400 (which is a TCP induced electric field) to excite the plasma so that plasma discharge generates a current. As shown in FIG. 2, the first microwave resonance chamber 12 and the second microwave resonance chamber 14 are, for example, horizontally lying hollow cylinders, and the above-mentioned pair of hollow metal tubes 16 are respectively connected to the bodies of the first microwave resonance chamber 12 and the second microwave resonance chamber 14 and are spaced apart from each other by a distance. The above-mentioned ferrite transformer core 50 includes a ferrite core 52, an induction coil 56, and a driving power supply 58. The ferrite core 52 has at least two hollow regions 54 respectively sleeved on the pair of hollow metal tubes 16 of the reaction chamber 10. The ferrite core 52 is, for example, in the shape of a Chinese character 'Ri' (日). The induction coil 56 winds around the ferrite core 52 using the above two hollow regions 54, for example, winds around the middle crossbar of the 'Ri'-shaped ferrite core 52, and the driving power supply 58 is, for example, electrically connected to both ends of the induction coil 56 via wires, so as to generate an induced electric field 400 in the reaction chamber 10 (for example, in the hollow metal tube 16). This induced electric field 400 can excite stable plasma to provide sufficient free electrons, and is driven and accelerated by the electric field induced by the ferrite core 52. Therefore, a closed-path current (for example, an electron drift current) can be formed in the reaction chamber 10, and further effectively ionize the gas to generate high-density plasma. The above-mentioned electron drift current circulates through the first microwave resonance chamber 12, the hollow metal tube 16, and the second microwave resonance chamber 14 in the reaction chamber 10 to form a closed path, so as to further ionize the working gas 200 to increase the density of the plasma. Among them, the type of the working gas 200 of the present invention is not particularly limited. Any gas as long as it can be used to generate plasma is suitable as the working gas 200 of the present invention. The size of the reaction chamber 10 and the spacing and pipe diameter of the hollow metal tubes 16 can be determined according to actual needs, so it is not limited to the above examples.

[0052] The composite plasma source of this invention utilizes the high-intensity electric fields in the first microwave resonant cavity 12 and the second microwave resonant cavity 14 of the reaction chamber 10 to excite a stable plasma under high pressure and high gas flow rate (pressure > 1 Torr, gas flow rate > 1 slm), providing sufficient free electrons. Driven and accelerated by the electric field induced by the ferrite transformer core 50, a closed-path electron drift current is formed within the reaction chamber 10, further effectively ionizing the gas to generate high-density plasma. While transformer coupling technology can very effectively transfer energy to the plasma, like many inductively coupled plasma devices, the intensity of the induced electromagnetic field (10 V / cm) is insufficient to break down the working gas 200, especially under high pressure and high gas flow rate. Although a high-voltage device can be used to generate an initial discharge in the reaction chamber 10 (vacuum chamber) to achieve the goal of plasma generation, the lifespan and reliability of the high-voltage discharge device are limited, and it is highly susceptible to damage to the cavity of the reaction chamber 10. Transformer-coupled plasma (TCP), in particular, is a low-field mechanism, and is prone to instability or even extinction when there are disturbances in gas pressure or airflow, such as during process changes in working gas flow. This invention utilizes the strong microwave electric field 300 of the first microwave resonant cavity 12 and the second microwave resonant cavity 14 of the reaction chamber 10, which can maintain a certain plasma density even when process conditions are adjusted, thus overcoming this drawback.

[0053] On the other hand, under high pressure, high flow rate, and high power density, the cylindrical plasma column within the existing annular vacuum cavity is prone to shrinkage due to ion and electron collisions and the limitation of ambipolar diffusion. This prevents the plasma from filling the vacuum cavity completely and can even lead to plasma instability. Furthermore, the power density and gas pressure flow rate that existing annular vacuum cavities using a single metal tube can withstand are limited. In contrast, this invention uses a larger microwave resonant cavity and a combination of multiple metal tubes to disperse the working gas flow rate, while simultaneously reducing the power density within each metal tube using a grouped power supply approach, thus achieving the goal of high pressure and high flow rate operation.

[0054] Specifically, one side of the above-described first microwave resonance cavity 12 has a gas inlet 11 for introducing a working gas 200, and one side of the second microwave resonance cavity 14 has a gas outlet 15 for discharging the working gas 200. The installation positions of the gas inlet 11 and the gas outlet 15 are, for example, located on the opposite sides of the first microwave resonance cavity 12 and the second microwave resonance cavity 14 respectively. The first microwave resonance cavity 12 and the second microwave resonance cavity 14 are hollow cylinders. The hollow metal tubes 16 are preferably arranged in pairs so that the working gas 200 can flow symmetrically through the hollow metal tubes 16. The number of the hollow metal tubes 16 can be one pair, or for example, two pairs or more. The hollow metal tubes 16 are preferably spaced apart from each other by a distance. The two ends of the hollow metal tubes 16 are, for example, respectively connected to the opposite sides of the first microwave resonance cavity 12 and the second microwave resonance cavity 14. Since many applications involve the generation of high-flow corrosive activated particles (such as NF3, SF6 plasma), the interior of the metal reaction chamber 10 must be protected. Therefore, the present invention can selectively anodize the aluminum reaction chamber 10 (including the first microwave resonance cavity 12, the second microwave resonance cavity 14, and the hollow metal tubes 16) to form a protective film.

[0055] The present invention further includes at least one microwave source 20 for generating microwaves and introducing the microwaves into the reaction chamber 10. The resonance frequency is 2.45 GHz, and the power is, for example, between 800 W and 1000 W. The resonance mode is TE 111 mode, so as to use the high-intensity microwave electric field 300 of the first microwave resonance cavity 12 and the second microwave resonance cavity 14 to excite the working gas 200 in the reaction chamber 10 into plasma. Among them, the number of the above-described microwave sources 20 can be one, which is used to be arranged on the first microwave resonance cavity 12 or the second microwave resonance cavity 14 of the reaction chamber 10, for example, on the side (as shown in FIG. 2) or on the top side, and the conduction direction of the microwaves generated by the microwave source 20 is preferably perpendicular to the arrangement direction of the hollow metal tubes 16. In addition, the number of the microwave sources 20 can also be, for example, two or more, which are used to be arranged on the first microwave resonance cavity 12 and the second microwave resonance cavity 14 of the reaction chamber 10 at the same time. As shown in FIG. 5, the present invention takes four hollow metal tubes 16 and two microwave sources 20 as an example, but is not limited thereto. In addition, since the number of the hollow regions 54 of the ferrite cores 52 corresponds to the hollow metal tubes 16, the present invention takes two sets of ferrite transformer cores 50 as an example, in a "field" shape. The two induction coils 56 of the two sets of ferrite transformer cores 50 respectively wind the two ferrite cores 52 by using the two pairs of hollow regions 54, and the two induction coils 56 are, for example, connected in parallel to the driving power supply 58 to supply power to the induction coils 56.

[0056] In detail, as shown in Figure 4, the microwave source 20 of the present invention is, for example, a coaxial magnetron microwave source, which includes a coaxially arranged magnetron 22, a central metal rod 24, and a cylindrical outer tube 26. The magnetron 22 is disposed on the reaction chamber 10. One end of the central metal rod 24 is connected to the output antenna 23 of the magnetron 22, and the other end of the central metal rod 24 extends into the reaction chamber 20. The central metal rod 24 is located in the cylindrical outer tube 26, thereby allowing the microwaves generated by the magnetron 22 to be introduced into the reaction chamber 20 via the central metal rod 24 and the cylindrical outer tube 26. Preferably, the cylindrical outer tube 26 is a sealed vacuum tube, which, in addition to maintaining a vacuum, also prevents direct contact between the plasma and the central metal rod 24. Its material can be, for example, ceramic, and preferably alumina ceramic. The diameter of the output antenna 23 and the central metal rod 24 can be, for example, the same. In addition, if the output antenna 23 and the central metal rod 24 have different diameters, for example, one has a larger diameter and the other has a smaller diameter, then the output antenna 23 and the central metal rod 24 used in this invention may selectively have a diameter transition region 25, with one end having a larger diameter and the other end having a smaller diameter, thereby reducing the amount of microwaves generated by the magnetron 22 reflected when they are conducted from the output antenna 23 to the central metal rod 24. This diameter transition region 25 may be located at the end of the output antenna 23 or at the end of the central metal rod 24; any location that achieves the effect of reducing microwave reflection is suitable for this invention.

[0057] Furthermore, the microwave source 20 used in this invention may optionally include a microwave matching element 30 to reduce the amount of microwave reflection when it is introduced into the reaction cavity 10 via the central metal rod 24 and the cylindrical outer tube 26, thereby enabling the microwave to be effectively transmitted into the reaction cavity 10. The microwave matching element 30, for example, includes a metal coaxial tube laterally disposed on the cylindrical outer tube 26. The metal coaxial tube has a coaxially disposed transverse tube 32a, a metal plate 32b, and a crossbar 32c. The transverse tube 32a is laterally disposed on the cylindrical outer tube 26, and the crossbar 32c extends from the cylindrical outer tube 26 into the transverse tube 32a. The metal plate 32b is disposed on the crossbar 32c. The metal plate 32b is movably disposed on the crossbar 32c. By adjusting the position of the metal plate 32b for impedance matching, the amount of microwave reflection can be improved, allowing the microwave to be effectively transmitted into the first microwave resonant cavity 12 and the second microwave resonant cavity 14 of the reaction cavity 10. The quality factor of the first microwave resonant cavity 12 and the second microwave resonant cavity 14 can exceed 2,000, thus effectively exciting a high-intensity electric field to achieve the requirement of stable plasma generation at pressures of 1 Torr to 5 Torr. On the other hand, generally speaking, the collision frequency between free electrons and neutral gas molecules is about several GHz / Trr. This collision frequency is close to the microwave frequency of 2.45 GHz in the pressure range of several Torr, which is beneficial for microwave to excite plasma in the pressure range above 1 Torr.

[0058] As shown in Figure 2, the first microwave resonant cavity 12 and the second microwave resonant cavity 14 of the reaction cavity 10 are connected by hollow metal tubes 16. The diameter of the hollow metal tubes 16 is, for example, 2.5 cm, and the number and / or diameter of the hollow metal tubes 16 can be increased according to the increase in the flow rate of the working gas 200. That is, according to the gas flow rate of the working gas 200, the present invention can increase the number of hollow metal tubes 16 to disperse the flow rate, which not only ensures the stability of the plasma in the hollow metal tubes 16 but also increases the gas conductance. At the same time, the diameter of the gas outlet 15 of the reaction cavity 10 can be increased to 5 cm. This diameter is smaller than the cut-off diameter of 2.45 GHz microwaves, so microwaves cannot be transmitted and have little impact on the characteristics of the second microwave resonant cavity 14. However, compared with the prior art of 2.5 cm, the gas conductance of the system of the present invention is greatly increased, thereby reducing the pressure of the reaction cavity 10, which is beneficial to the efficiency of the microwave resonant cavity in exciting high gas flow plasma. Furthermore, multiple hollow metal tubes 16 can constructively increase the power density within the hollow metal tubes 16 and the microwave resonant cavity. That is, the power density of the plasma corresponds to the number of hollow metal tubes 16, so as to achieve a very high-density plasma state under relatively high vacuum pressure and high gas flow rate (>1 Torr, >10 slm) and achieve the function of activating gas.

[0059] Furthermore, as shown in Figures 3 and 5, this set of hollow metal tubes 16 passes through a pair of central hollow regions 54 of the ferrite core 52 of the ferrite transformer core 50. The ferrite transformer core 50, when connected to an AC drive power supply 58, can generate an induced electric field 400 within the reaction chamber 10 to excite current in the plasma. However, the structure of the reaction chamber 10 must be electrically isolated; otherwise, it will cause a short circuit to the ferrite transformer core 50, preventing the generation of the induced electric field 400 within the reaction chamber 10. In this invention, this electrical isolation is achieved using a ceramic ring at the connection between the hollow metal tubes 16 and the first microwave resonant cavity 12 and the second microwave resonant cavity 14. The electric field excited by the ferrite transformer core 50, under the influence of the metal structure of the reaction chamber 10, will concentrate in the electrically isolated region 17 formed by the ceramic ring. In conventional technologies, the electrical barrier region must be small enough to generate a sufficiently strong electric field to excite and maintain a stable plasma. However, strong electric fields can sometimes cause regional discharges, leading to the cracking of the ceramic ring and damaging the electrical barrier, or even reverse discharge damaging the drive power supply, or causing the protective coating of the reaction chamber to peel off. In contrast, since the plasma of this invention is already excited by the first microwave resonant cavity 12 and the second microwave resonant cavity 14, the electric field strength of the electrical barrier region is not a critical parameter. Therefore, the electrical barrier region of this invention can be wider, thus reducing the disadvantages of the conventional technology and contributing to extended service life and system stability.

[0060] As shown in Figure 5, the present invention can also employ multiple hollow metal tubes 16 and two or more associated ferrite cores 52, which are powered in parallel with a separate primary current source (i.e., drive power supply 58) to support the induced electron drift current of the plasma in the hollow metal tubes 16. Figure 5 shows how the induced electron drift current of the plasma in the multiple hollow metal tubes 16 works collaboratively in the plasma of the reaction chamber 10 (first microwave resonant cavity 12, second microwave resonant cavity 14, and hollow metal tubes 16). On the other hand, since the electric field induced by the ferrite transformer core 50 is at a 90-degree angle to the central metal rod 24 inserted into the reaction chamber 10, it does not interfere with the microwave source 20.

[0061] Figure 5 further illustrates the power supply circuit for driving the TCP plasma of the present invention, which consists of a drive power supply 58, a ferrite transformer core 50, and plasma. The present invention uses the drive power supply 58 as an example of an AC power supply, the frequency of which is appropriately selected to suit the driving plasma, the voltage and current withstand capability of the power components, and the losses of the ferrite core 52, and is approximately between 100 kHz and approximately 500 kHz. The AC power supply can operate at constant power or constant current. The output voltage is approximately 250V to 350V, and the maximum power is 10kW. In the prior art, the load impedance of the AC power supply changes drastically during plasma excitation, from low-density plasma to stable high-density plasma, posing a significant challenge to the power components. In contrast, in the present invention, because the microwave resonant cavity has already excited a certain density of plasma in the initial stage, the dynamic changes in load impedance can be significantly reduced, lowering the probability of problems with the power components. Furthermore, the driving power supply 58 of the driving microwave source 20 of the present invention can be DC or pulsed. For example, it can be boosted to about 1kV by a high-voltage transformer via a switching circuit, and then driven by a voltage multiplier circuit to drive the magnetron, with an operating power of 50W-1000W. With the specifications of existing magnetrons, it can withstand almost total internal reflection, thus being advantageous for exciting initiation plasma.

[0062] In summary, the composite plasma source and its operation method of the present invention have the following advantages: (1) The composite plasma source is composed of the mechanisms of microwave plasma and TCP plasma. (2) After generating plasma by generating a high-intensity electric field using a microwave resonant cavity, the energy is effectively coupled by the TCP mechanism to generate high-power and high-density plasma. (3) The disadvantages of high-voltage ignition devices can be eliminated. At the same time, since microwaves are responsible for exciting and maintaining the initial plasma, the disadvantages of weak electric fields in TCP can be solved to improve plasma stability. (4) Utilizing the characteristic of a strong electric field in the reaction cavity, a certain plasma density can still be maintained even when the process conditions are adjusted. Even when the gas pressure is 1 Torr to 10 Torr, a high-intensity electric field can still be effectively excited to meet the requirements for stable plasma generation. (5) The number of hollow metal tubes can be increased to disperse the flow rate according to the gas flow rate of the working gas, which can not only ensure the stability of the plasma but also increase the gas conductivity. (6) Since the plasma of the present invention is excited by microwaves, the electrical barrier region of the present invention can be wider, which is beneficial to the extension of service life and the stability of the system. (7) Under high gas flow conditions, the gas pressure can be maintained in the range of several Torr. (8) Because the power of each hollow metal tube is dispersed, the energy density of each hollow tube decreases, reducing the occurrence of plasma transitioning from diffusion mode to contraction mode. (9) This invention utilizes the high-intensity electric field in the reaction chamber to excite a stable plasma under high gas pressure and high gas flow rate, providing sufficient free electrons. Driven and accelerated by the electric field induced by the ferrite transformer core, a closed-path electron drift current is formed in the reaction chamber, further effectively ionizing the gas to generate high-density plasma.

[0063] The above description is merely illustrative and not restrictive. Any equivalent modifications or alterations made without departing from the spirit and scope of this invention should be included within the scope of the appended claims.

Claims

1. A composite plasma source, characterized in that, The device comprises: a reaction chamber including a first microwave resonant cavity, a second microwave resonant cavity, and at least a pair of hollow metal tubes, the two ends of which are respectively connected to the first microwave resonant cavity and the second microwave resonant cavity, wherein at least one microwave is introduced into the reaction chamber to excite a working gas in the reaction chamber into a plasma; and at least one ferrite transformer core, the ferrite transformer core comprising a ferrite core having two hollow regions respectively fitted onto the pair of hollow metal tubes, an induction coil wound around the ferrite core through the two hollow regions, and a driving coil. The source is electrically connected to the induction coil to generate an induced electric field in the pair of hollow metal tubes in the reaction chamber. The induced electric field excites the plasma to form a current with a closed path in the reaction chamber, thereby further ionizing the working gas to increase the plasma density. The current circulates through the first microwave resonant cavity, the pair of hollow metal tubes and the second microwave resonant cavity to form the closed path. The pair of hollow metal tubes disperse the flow rate of the working gas and reduce the energy density in the pair of hollow metal tubes, thereby reducing the occurrence of the plasma changing from the diffusion mode to the contraction mode.

2. The composite plasma source as described in claim 1, characterized in that: The first microwave resonant cavity and the second microwave resonant cavity are hollow cylinders, and the two ends of the pair of hollow metal tubes are respectively connected to the cylinder of the first microwave resonant cavity and the second microwave resonant cavity.

3. The composite plasma source as described in claim 1, characterized in that: It further includes at least one microwave source disposed on the first microwave resonant cavity, the second microwave resonant cavity, or the first microwave resonant cavity and the second microwave resonant cavity of the reaction cavity, for introducing the microwave into the reaction cavity.

4. The composite plasma source as described in claim 3, characterized in that: The microwave source includes a magnetron, a central metal rod, and a cylindrical outer tube arranged coaxially. The central metal rod is located in the cylindrical outer tube. One end of the central metal rod is connected to an output antenna of the magnetron, and the other end of the central metal rod extends into the reaction cavity, so as to guide the microwave generated by the magnetron into the reaction cavity through the central metal rod and the cylindrical outer tube.

5. The composite plasma source as described in claim 4, characterized in that: The microwave source further includes a microwave matching element to reduce the amount of reflection when the microwaves generated by the magnetron are introduced into the reaction cavity through the central metal rod and the cylindrical outer tube, so that the microwaves enter the reaction cavity.

6. The composite plasma source as described in claim 5, characterized in that: The microwave matching element includes a metal coaxial tube horizontally disposed on the cylindrical outer tube. The metal coaxial tube has a horizontal tube, a metal plate and a crossbar coaxially disposed on the cylindrical outer tube. The horizontal tube is horizontally disposed on the cylindrical outer tube, the crossbar extends from the cylindrical outer tube into the horizontal tube, and the metal plate is disposed on the crossbar.

7. The composite plasma source as described in claim 6, characterized in that: The metal plate is movably mounted on the crossbar to perform impedance matching and improve the amount of microwave reflection.

8. The composite plasma source as described in claim 4, characterized in that: The output antenna and the central metal rod have a diameter gradient region to reduce the amount of reflection when the microwave generated by the magnetron is conducted from the output antenna to the central metal rod.

9. The composite plasma source as described in claim 4, characterized in that: The cylindrical outer tube is made of ceramic.

10. The composite plasma source as described in claim 4, characterized in that: The cylindrical outer tube is a sealed vacuum tube.

11. The composite plasma source as described in claim 1, characterized in that: The two ends of the pair of hollow metal tubes are respectively connected to the first microwave resonant cavity and the second microwave resonant cavity via at least one electrical barrier region, thereby preventing a short circuit between the reaction cavity and the ferrite transformer core.

12. The composite plasma source as described in claim 11, characterized in that: The electrical barrier region is a ceramic ring-shaped sheet.

13. The composite plasma source as described in claim 1, characterized in that: The first microwave resonant cavity and the second microwave resonant cavity are hollow cylinders.

14. The composite plasma source as described in claim 1, characterized in that: The working gas has a pressure greater than 1 Torr and a flow rate greater than 10 slm.

15. The composite plasma source as described in claim 1, characterized in that: The number and / or diameter of the pair of hollow metal tubes increase in response to the increase in the flow rate of the working gas, thereby ensuring the stability of the plasma in the pair of hollow metal tubes and increasing gas conductivity.

16. The composite plasma source as described in claim 1, characterized in that: The power density of the plasma corresponds to the number of hollow metal tubes in the pair.

17. The composite plasma source as described in claim 1, characterized in that: The ferrite transformer has two sets of magnetic cores, and the induction coil is connected in parallel to the drive power supply for power supply.

18. The composite plasma source as described in claim 1, characterized in that: The electric field generated by the ferrite transformer core is perpendicular to a central metal rod that guides the microwaves into the reaction cavity, so as to avoid interfering with a microwave source that generates the microwaves.

19. The composite plasma source as described in claim 1, characterized in that: The power supply can be an AC power supply, a DC power supply, or a pulse power supply.

20. The composite plasma source as described in claim 1, characterized in that: The first microwave resonant cavity has a gas inlet, and the second microwave resonant cavity has a gas outlet.

21. A method for operating a composite plasma source, characterized in that... First, a working gas is used to form a plasma in the composite plasma source described in any one of claims 1 to 20 using a microwave electric field. Then, energy is coupled to the plasma with high efficiency using a transformer-coupled plasma technology, thereby further increasing the plasma density and generating an activated gas with a high degree of dissociation.

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