Plasma area expansion device and method based on double-frequency microwave feed-in

Abstract

The invention provides a plasma area expansion device based on double-frequency microwave feed-in. The plasma area expansion device comprises a three-section resonant cavity and a double-frequency microwave feed source system, wherein the three-section resonant cavity comprises a first cavity, a second cavity and a third cavity which are connected in sequence, the second cavity is a sealed cavity, and the first cavity and the third cavity are provided with tuning structures used for adjusting the total length of the cavities. Standing waves excited by the first microwave source and the second microwave source are superposed in the cavity to form a plasma excitation area; the double-frequency microwave feed source system comprises a first microwave source and a second microwave source which provide 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. The method can be widely applied to the industrial field needing large-area uniform plasma, the processing efficiency and uniformity can be remarkably improved, and the application range of the plasma technology is expanded.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave plasma, and particularly to a plasma area expansion device and method based on dual-frequency microwave feeding. Background Art

[0002] Traditional single-frequency microwave plasma devices excite plasma in a resonant cavity through a single-frequency microwave source. Its structure mainly includes a coaxial feed antenna, a cylindrical resonant cavity, and a gas inlet and outlet. In the existing technology, the standing wave wavelength of single-frequency microwaves is fixed, resulting in the plasma distribution being restricted by the standing wave nodes, and the excitation area is concentrated in the center of the cavity, which is difficult to expand to a large area. In addition, the shielding effect of high-density plasma on microwaves will reduce the energy transmission efficiency and further aggravate the uniformity problem. Therefore, the single-frequency standing wave mode in the cavity is the core factor limiting the expansion of the plasma area. The existing adjustment means (such as cavity structure adjustment) can only achieve local optimization and cannot break through the standing wave node limitation. Therefore, there is an urgent need for a technical solution to achieve large-area uniform plasma excitation. Summary of the Invention

[0003] The present 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 a traditional single-frequency microwave plasma device excites plasma.

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

[0005] The three-section resonant cavity includes a first cavity, a second cavity, and a third cavity connected in sequence, wherein the second cavity is a sealed cavity, and the first cavity and the third cavity are provided with a tuning structure for adjusting 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 feeding 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 solution, a first observation window, a second observation window and a third observation window arranged axially are provided on the surface of the second cavity.

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

[0009] As a preferred solution, 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 solution, 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.

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

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

[0013] As a preferred solution, 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 solution, the first microwave source provides microwaves of a first frequency, and the second microwave source provides microwaves of a second frequency; the first frequency and the second frequency must be able to be transmitted in the same waveguide and have a fixed wavelength difference.

[0015] A second aspect of the present invention provides a plasma area expansion method based on dual-frequency microwave feeding, which is implemented based on the plasma area expansion device based on dual-frequency microwave feeding described in the first aspect, and includes:

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

[0017] Feeding microwaves of a second frequency from the third cavity through a second microwave source, and adjusting the length of the third cavity until a strong plasma luminous area appears on the right side of the third observation window;

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

[0019] Compared with the existing technology, the beneficial effects of adopting the above technical solution are: the present invention can be widely used in industrial fields that require large-area uniform plasma, can significantly improve processing efficiency and uniformity, and expand the application scope of plasma technology. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0021] Figure 2 Schematic diagram of plasma area expansion in an embodiment of the present invention.

[0022] Reference numerals:

[0023] 100 - three-section 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 DESCRIPTION

[0026] The embodiments of the present application are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar modules or modules with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application and are not to be construed as limiting the present application. On the contrary, the embodiments of the present application include all changes, modifications, and equivalents that fall within the spirit and scope of the appended claims.

[0027] In order to solve the problem of limited area and insufficient uniformity when exciting plasma in traditional single-frequency microwave plasma devices, the embodiment of the present invention proposes a plasma area expansion device based on dual-frequency microwave feeding, which realizes 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-section resonant cavity 100 and a dual-frequency microwave feeding system.

[0029] Specifically, the three-section resonant cavity 100 comprises a first cavity 101, a second cavity 102, and a third cavity 103, which are connected in sequence. The second cavity 102 is a sealed cavity. The first and third cavities 101 and 103 are equipped with tuning structures to adjust the total cavity length, so that the standing waves excited by the first and second microwave sources 200 and 300 overlap within 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 the two frequencies’ standing wave antinodes adjacent to each other at a certain position in the middle region (such as Z = L / 2, where L is the cavity length), phase matching must be satisfied. For frequency 1 and frequency 2, respectively:

[0031]

[0032] If the two waves are both 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 L value. 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 to the two microwave sources respectively:

[0036]

[0037] Solving the above formula, we can get:

[0038]

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

[0040] Through the cavity structure proposed in this embodiment, dual-frequency microwaves excite standing wave electric fields at different positions in the cavity (the left standing wave peak is close to the left end, and the right standing wave peak is close to the right end), forming an extended plasma excitation area through superposition.

[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. Both sides of the second cavity 102 are sealed with quartz plates 107 .

[0043] In order 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 of a first frequency, and the second microwave source 300 provides microwaves of a second frequency. The first and second frequencies must be capable of being transmitted within the same waveguide with 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 substituted. It is required that both frequencies can be transmitted within the same waveguide with a fixed wavelength difference to ensure effective complementarity of the standing wave peak regions. The cavity length and radius need to be adjusted accordingly.

[0045] To better observe the formation of plasma in the cavity, in one embodiment, the surface of the second cavity 102 is provided with a first observation window 104, a second observation window 105, and a third observation window 106 arranged axially. Furthermore, the second cavity 102 is provided with an air inlet 108 and an air outlet 109 for admitting the required process gases. Preferably, the first observation window 104, the second observation window 105, and the third observation window 106 all utilize a cutoff waveguide plus quartz window design, with an overall size of 10 mm in diameter and 30 mm in height. Of course, the observation window dimensions can also be adjusted to other radii and heights based on monitoring needs, as long as they meet the observation and spectral measurement requirements.

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

[0047]

[0048] Since the two standing waves complement each other in space, the total field strength is the direct concatenation of the field strengths in the two regions, which can be expressed as:

[0049]

[0050] The corresponding instantaneous power density is:

[0051]

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

[0053] With respect to the plasma area expansion device based on dual-frequency microwave feeding proposed in an embodiment of the present invention, an embodiment of the present invention also provides a plasma area expansion method based on the device, including:

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

[0055] S2, feeding microwaves of a second frequency from the third cavity 103 through the second microwave source 300, and adjusting the length of the third cavity 103 until a strong plasma luminous area appears on the right side of the third observation window 106;

[0056] S3. Feed microwaves of the first frequency from the first cavity 101 through the first microwave source 200, and adjust the length of the first cavity 101 so that standing waves of the first frequency and the second frequency are superimposed in the cavity, thereby completing the expansion of the plasma area.

[0057] Through the proposed plasma area expansion device and method, the original plasma generation area is changed from being strongly distributed only at the right observation window to being uniformly distributed throughout the entire cavity. Figure 2 As shown, (a) is a schematic diagram of a single-port excitation in which the first microwave source feeds 2.35 GHz microwaves, (b) is a schematic diagram of a single-port excitation in which the second microwave source feeds 2.65 GHz microwaves, and (c) is a schematic diagram of a dual-port excitation in which the first microwave source feeds 2.35 GHz microwaves and the second microwave source feeds 2.65 GHz microwaves. By detecting the spectral line intensity ratio, calculating the electron temperature distribution, and verifying the plasma distribution area through a spectrometer, it can be seen that the plasma distribution area is expanded to twice that of the single-frequency case, as shown in FIG. Figure 2 shown.

[0058] It should be noted that, in the description of the embodiments of the present invention, unless otherwise clearly specified and limited, the terms "setting" and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances; the 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 part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings herein can be arranged and designed in various different configurations.

[0059] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present 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 feeding system; wherein, The three-section resonant cavity includes a first cavity, a second cavity, and a third cavity connected in sequence, wherein the second cavity is a sealed cavity, and the first cavity and the third cavity are provided with a tuning structure for adjusting 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 feeding 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 surface of the second cavity is provided with 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 is provided with an air inlet and an air outlet for introducing 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 design of a cutoff waveguide plus a quartz window.

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; and 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: Both sides of the second cavity are sealed 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 of a first frequency, and the second microwave source provides microwaves of a second frequency; the first frequency and the second frequency must be able to be transmitted in the same waveguide and have a fixed wavelength difference.

10. A plasma area expansion method based on dual-frequency microwave feeding, characterized in that: The plasma area expansion device based on dual-frequency microwave feeding according to any one of claims 3 to 10 is implemented, comprising: The second chamber was evacuated to 12 Pa, nitrogen was introduced and the pressure was maintained stable; Feeding microwaves of a second frequency from the third cavity through a second microwave source, and adjusting the length of the third cavity until a strong plasma luminous area appears on the left side of the third observation window; The microwave of the first frequency is fed into the first cavity by the first microwave source, and the length of the first cavity is adjusted so that the first frequency The standing wave of the first and second frequencies is superimposed in the cavity to complete the expansion of the plasma area.

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