Plasma area expansion device and method based on dual-frequency microwave feeding

Abstract

This invention provides a plasma area expansion device based on dual-frequency microwave feeding, comprising a three-segment resonant cavity and a dual-frequency microwave feed system. The three-segment resonant cavity includes a first cavity, a second cavity, and a third cavity connected sequentially. The second cavity is a sealed cavity. The first and third cavities are equipped with tuning structures to adjust the total length of the cavities, allowing standing waves excited by the first and second microwave sources to superimpose within the cavities to form a plasma excitation region. The dual-frequency microwave feed system includes a first microwave source and a second microwave source providing different frequencies. Microwaves generated by the first microwave source are fed into the first cavity, and microwaves generated by the second microwave source are fed into the third cavity. This invention can be widely applied in industrial fields requiring large-area uniform plasma, significantly improving processing efficiency and uniformity, and expanding the application scope of plasma technology.

Description

Technical Field

[0001] This invention relates to the field of microwave plasma technology, specifically a plasma area expansion device and method based on dual-frequency microwave feeding. Background Technology

[0002] Traditional single-frequency microwave plasma devices excite plasma within a resonant cavity using a single-frequency microwave source. Their structure primarily includes a coaxial feed antenna, a cylindrical resonant cavity, and gas inlets and outlets. In existing technologies, the fixed standing wave wavelength of single-frequency microwaves restricts plasma distribution to standing wave nodes, concentrating the excitation area at the cavity center and hindering its expansion over a large area. Furthermore, the shielding effect of high-density plasma on microwaves reduces energy transmission efficiency, further exacerbating the uniformity problem. Therefore, the single-frequency standing wave mode within the cavity is the core factor limiting plasma area expansion. Existing adjustment methods (such as cavity structure adjustments) can only achieve localized optimization and cannot overcome the standing wave node limitation. Therefore, a technical solution for achieving large-area uniform plasma excitation is urgently needed. Summary of the Invention

[0003] This invention provides a plasma area expansion device and method based on dual-frequency microwave feeding, aiming to solve the problems of limited area and insufficient uniformity when traditional single-frequency microwave plasma devices excite plasma.

[0004] The first aspect of this invention proposes a plasma area expansion device based on dual-frequency microwave feeding, comprising a three-segment resonant cavity and a dual-frequency microwave feed system; wherein,

[0005] The three-segment resonant cavity includes a first cavity, a second cavity, and a third cavity connected in sequence. The second cavity is a sealed cavity. The first cavity and the third cavity are provided with tuning structures to adjust the total length of the cavity, so that the standing waves excited by the first microwave source and the second microwave source are superimposed in the cavity to form a plasma excitation region.

[0006] The dual-frequency microwave feed system includes a first microwave source and a second microwave source providing different frequencies. The microwaves generated by the first microwave source are fed into the first cavity, and the microwaves generated by the second microwave source are fed into the third cavity.

[0007] As a preferred embodiment, the second cavity surface is provided with a first observation window, a second observation window, and a third observation window arranged axially.

[0008] As a preferred embodiment, the second cavity is provided with an air inlet and an air outlet for introducing the required process gas.

[0009] As a preferred option, the first observation window, the second observation window, and the third observation window all adopt a cutoff waveguide plus quartz window design.

[0010] As a preferred embodiment, the first microwave source is fed into the first cavity via a T-shaped coaxial probe; the second microwave source is fed into the third cavity via a T-shaped coaxial probe.

[0011] As a preferred embodiment, the first cavity, the second cavity, and the third cavity are cylindrical waveguides and are connected by threads.

[0012] As a preferred embodiment, the two sides of the second cavity are sealed with quartz plates.

[0013] As a preferred embodiment, the second cavity is made of a metal with high conductivity or the surface of the second cavity is silver-plated.

[0014] As a preferred embodiment, the first microwave source provides microwaves at a first frequency, and the second microwave source provides microwaves at a second frequency; the first frequency and the second frequency must be able to transmit within the same waveguide and have a fixed wavelength difference.

[0015] The second aspect of this invention proposes a plasma area expansion method based on dual-frequency microwave feeding, implemented using the plasma area expansion device based on dual-frequency microwave feeding described in the first aspect, comprising:

[0016] The second chamber was evacuated to 12 Pa, nitrogen was introduced and the pressure was kept stable.

[0017] Microwaves of the second frequency are fed into the third cavity through the second microwave source, and the length of the third cavity is adjusted until a strong plasma luminescence area appears on the right side of the third observation window.

[0018] Microwaves of the first frequency are fed into the first cavity through the first microwave source, and the length of the first cavity is adjusted so that the standing waves of the first and second frequencies are superimposed in the cavity, thereby completing the plasma area expansion.

[0019] Compared with existing technologies, the beneficial effects of adopting the above technical solution are as follows: the present invention can be widely applied in industrial fields that require large-area uniform plasma, and can significantly improve processing efficiency and uniformity, and expand the application scope of plasma technology. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the plasma area expansion device proposed in an embodiment of the present invention.

[0021] Figure 2 This is a schematic diagram of plasma area expansion in an embodiment of the present invention.

[0022] Figure label:

[0023] 100-Three-segment resonant cavity, 101-First cavity, 102-Second cavity, 103-Third cavity, 104-First observation window, 105-Second observation window, 106-Third observation window, 107-Quartz plate, 108-Air inlet, 109-Air outlet, 110-T-type coaxial probe;

[0024] 200 - First Microwave Source;

[0025] 300 - Second microwave source. Detailed Implementation

[0026] The embodiments of this application are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar modules or modules having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. Rather, the embodiments of this application include all variations, modifications, and equivalents falling within the spirit and scope of the appended claims.

[0027] To address the limitations in plasma area and insufficient uniformity of traditional single-frequency microwave plasma devices, this invention proposes a plasma area expansion device based on dual-frequency microwave feeding, achieving large-area uniform plasma excitation through a multi-frequency superposition mechanism. Specifically,

[0028] Please refer to Figure 1 The plasma area expansion device includes a three-segment resonant cavity 100 and a dual-frequency microwave feed system.

[0029] Specifically, the three-segment resonant cavity 100 includes a first cavity 101, a second cavity 102, and a third cavity 103 connected in sequence. The second cavity 102 is a sealed cavity. The first cavity 101 and the third cavity 103 are provided with tuning structures to adjust the total length of the cavity, so that the standing waves excited by the first microwave source 200 and the second microwave source 300 are superimposed in the cavity to form a plasma excitation region. The dual-frequency microwave feed system includes a first microwave source 200 and a second microwave source 300 providing different frequencies. The microwaves generated by the first microwave source 200 are fed into the first cavity 101, and the microwaves generated by the second microwave source 300 are fed into the third cavity 103.

[0030] To achieve adjacent standing wave antinodes of two frequencies at a certain position in the intermediate region (e.g., at Z = L / 2, where L is the cavity length), phase matching is required. For frequencies 1 and 2, the following applies:

[0031]

[0032] If both waves are antinodes at Z = L / 2, then the phase difference is 0 or an integer multiple of 2π, that is:

[0033] k1L / 2 = nπ, k2L / 2 = mπ (n, m are integers)

[0034]

[0035] Since the wavelengths of the two frequencies are different, it is impossible to find a satisfactory value of L. However, in the implementation process, a phase delay Δφ can be introduced at the feed end so that the phase difference is 0 at z = L / 2. Phase delays φ1 and φ2 are introduced for the two microwave sources respectively:

[0036]

[0037] Solving the above equation, we can obtain:

[0038]

[0039] Therefore, in the actual design, this embodiment designs the length parameter of the cavity as a tunable structure, and uses an adjustable length cavity to dynamically match the resonant length of the two frequencies so that the antinodes overlap in the middle.

[0040] With the cavity structure proposed in this embodiment, dual-frequency microwaves excite standing wave electric fields at different locations within the cavity (the left standing wave peak is closer to the left end, and the right standing wave peak is closer to the right end), which are superimposed to form an extended plasma excitation region.

[0041] It should be noted that in this embodiment, the first microwave source 200 and the second microwave source 300 are fed into the first cavity 101 and the third cavity 103 respectively through the T-shaped coaxial probe 110.

[0042] Preferably, the first cavity 101, the second cavity 102, and the third cavity 103 are cylindrical waveguides and are connected by threads. The two sides of the second cavity 102 are sealed with quartz plates 107.

[0043] To reduce microwave loss and improve excitation efficiency, the second cavity 102 can be made of a metal with high conductivity, or the surface of the second cavity 102 can be silver-plated.

[0044] As a preferred embodiment, the first microwave source 200 provides microwaves at a first frequency, and the second microwave source 300 provides microwaves at a second frequency; the first frequency and the second frequency must be able to transmit within the same waveguide and have a fixed wavelength difference. For example, the first microwave source 200 is a 2.35 GHz microwave source, and the second microwave source 300 is a 2.65 GHz microwave source. In practical applications, other dual-frequency combinations (such as 2.4 GHz and 2.7 GHz) can also be used, provided that both frequencies can transmit within the same waveguide and have a fixed wavelength difference to ensure effective complementarity in the standing wave peak region. The cavity length and radius need to be adjusted accordingly.

[0045] To better observe the formation of plasma within the cavity, in one embodiment, the surface of the second cavity 102 is provided with axially arranged first observation windows 104, second observation windows 105, and third observation windows 106. Simultaneously, the second cavity 102 also has an inlet 108 and an outlet 109 for introducing the required process gas. Preferably, the first observation window 104, second observation window 105, and third observation window 106 all employ a cutoff waveguide and quartz window design, with an overall diameter of 10 mm and a height of 30 mm. Of course, the dimensions of the observation windows can be adjusted to other radii and heights according to monitoring requirements, as long as the observation and spectral measurement requirements are met.

[0046] In this embodiment, two microwaves of different frequencies are fed into the cavity. Waves of different frequencies do not produce interference superposition effects within the cavity. Even if they superimpose in a certain region, it is an incoherent superposition. If the two standing waves of different frequencies are distributed adjacently in different regions (assuming region A and region B) without any electric field intersection, the electric field of the standing waves can be expressed as follows:

[0047]

[0048] Since the two standing waves are spatially complementary, the total field strength is a direct concatenation of the field strengths of the two regions, which can be expressed as:

[0049]

[0050] The corresponding instantaneous power density is:

[0051]

[0052] The plasma responds to its own standing wave power in different regions, and the overall response is the superposition of the two regions. Due to spatial separation, the power densities of the two standing waves do not modulate each other, and the plasma behavior is determined by the local field.

[0053] Regarding the plasma area expansion device based on dual-frequency microwave feeding proposed in the embodiments of the present invention, the embodiments of the present invention also provide a plasma area expansion method based on the device, including:

[0054] S1. Evacuate the second chamber 102 to 12Pa, introduce nitrogen gas and maintain stable gas pressure.

[0055] S2. Microwaves of the second frequency are fed into the third cavity 103 through the second microwave source 300, and the length of the third cavity 103 is adjusted until a strong plasma luminescence area appears on the right side of the third observation window 106.

[0056] S3. Microwaves of the first frequency are fed into the first cavity 101 through the first microwave source 200, and the length of the first cavity 101 is adjusted so that the standing waves of the first frequency and the second frequency are superimposed in the cavity, thereby completing the plasma area expansion.

[0057] Through the proposed plasma area expansion device and method, the original plasma generation region, which was only strongly distributed at the right observation window, was transformed into a strongly uniform distribution throughout the entire cavity. Figure 2 As shown, (a) is a single-port excitation schematic diagram with a first microwave source feeding 2.35 GHz microwaves, (b) is a single-port excitation schematic diagram with a second microwave source feeding 2.65 GHz microwaves, and (c) is a dual-port excitation schematic diagram with the first microwave source feeding 2.35 GHz microwaves and the second microwave source feeding 2.65 GHz microwaves. By detecting the spectral line intensity ratio, calculating the electron temperature distribution, and verifying the plasma distribution area using a spectrometer, it can be seen that the plasma distribution area expands to twice that of the single-frequency case. Specifically, as shown... Figure 2 As shown.

[0058] It should be noted that, in the description of the embodiments of the present invention, unless otherwise explicitly specified and limited, the terms "set" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the present invention based on the specific circumstances. The accompanying drawings in the embodiments are used to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0059] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A plasma area expansion device based on dual-frequency microwave feeding, characterized in that, It includes a three-section resonant cavity and a dual-frequency microwave feed system; among which, The three-segment resonant cavity includes a first cavity, a second cavity, and a third cavity connected in sequence. The second cavity is a sealed cavity. The first cavity and the third cavity are provided with tuning structures to adjust the total length of the cavity, so that the standing waves excited by the first microwave source and the second microwave source are superimposed in the cavity to form a plasma excitation region. The dual-frequency microwave feed system includes a first microwave source and a second microwave source providing different frequencies. The microwaves generated by the first microwave source are fed into the first cavity, and the microwaves generated by the second microwave source are fed into the third cavity.

2. The plasma area expansion device based on dual-frequency microwave feeding according to claim 1, characterized in that, The second cavity surface has a first observation window, a second observation window, and a third observation window arranged axially.

3. The plasma area expansion device based on dual-frequency microwave feeding according to claim 2, characterized in that, The second cavity has an air inlet and an air outlet for introducing the required process gas.

4. The plasma area expansion device based on dual-frequency microwave feeding according to claim 2, characterized in that, The first observation window, the second observation window, and the third observation window all adopt a cutoff waveguide plus quartz window design.

5. The plasma area expansion device based on dual-frequency microwave feeding according to claim 1, characterized in that, The first microwave source is fed into the first cavity through a T-shaped coaxial probe; the second microwave source is fed into the third cavity through a T-shaped coaxial probe.

6. The plasma area expansion device based on dual-frequency microwave feeding according to claim 1, characterized in that, The first cavity, the second cavity, and the third cavity are cylindrical waveguides and are connected by threads.

7. The plasma area expansion device based on dual-frequency microwave feeding according to claim 1, characterized in that, The second cavity is sealed on both sides with quartz plates.

8. The plasma area expansion device based on dual-frequency microwave feeding according to claim 1, characterized in that, The second cavity is made of a metal with high conductivity or the surface of the second cavity is silver-plated.

9. The plasma area expansion device based on dual-frequency microwave feeding according to claim 1, characterized in that, The first microwave source provides microwaves at a first frequency, and the second microwave source provides microwaves at a second frequency; the first frequency and the second frequency must be able to transmit within the same waveguide and have a fixed wavelength difference.

10. A plasma area expansion method based on dual-frequency microwave feeding, characterized in that, Based on the plasma area expansion device based on dual-frequency microwave feeding as described in any one of claims 3 to 9, it includes: The second chamber was evacuated to 12 Pa, nitrogen was introduced and the pressure was kept stable. Microwaves of the second frequency are fed into the third cavity through the second microwave source, and the length of the third cavity is adjusted until a strong plasma luminescence area appears on the left side of the third observation window. Microwaves of the first frequency are fed into the first cavity through the first microwave source, and the length of the first cavity is adjusted so that the standing waves of the first and second frequencies are superimposed in the cavity, thereby completing the plasma area expansion.

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