A double-shell structure radio frequency self-neutralizing plasma source

Abstract

The application belongs to the field of plasma, and discloses a double-layer shell structure radio frequency self-neutralization plasma source, which comprises a grounded shell, a radio frequency shell, a discharge chamber, a radio frequency coil and a grid system; the radio frequency coil is wound outside the discharge chamber; the discharge chamber is provided with an air inlet at an upstream and an outlet at a downstream, the outlet is connected with the grid system, the radio frequency shell is wrapped outside the discharge chamber and the radio frequency coil and is located inside the grounded shell; the grid system comprises a screen grid and an acceleration grid, the radio frequency shell is electrically connected with the screen grid, and the grounded shell is electrically connected with the acceleration grid. The application introduces the radio frequency shell between the discharge chamber and the grounded shell, improves the ratio of the screen grid direct current self-bias component and the screen grid radio frequency voltage component amplitude, and then improves the beam energy and the extraction efficiency of the radio frequency self-neutralization plasma source, so that the performance of the plasma source is improved.

Description

Technical Field

[0001] This invention belongs to the field of plasma and relates to a radio frequency self-neutralizing plasma source with a double-layer shell structure. Background Technology

[0002] A radio frequency plasma source is a device that uses an electromagnetic field generated by a radio frequency coil to ionize a working medium and produce plasma. It has advantages such as low discharge pressure, high plasma density, and simple structure. By adding a gate system downstream, a directional high-energy ion beam can be obtained. This device has been widely used in semiconductor etching, thin film deposition, and optical component shaping.

[0003] In a conventional grid-connected radio frequency plasma source, the radio frequency coil is located outside the discharge chamber and connected to the RF coil power supply. An alternating electromagnetic field is generated inside the discharge chamber to accelerate electrons, thereby producing plasma. A DC voltage is applied to the screen and accelerating grid downstream of the discharge chamber to extract and accelerate the ion beam. To improve the stability and collimation of the ion beam, a neutralizer is typically added downstream of the grid. The electrons emitted by this neutralizer compensate for the positive charge in the beam, thus reducing beam divergence caused by the space charge effect.

[0004] A radio frequency self-neutralizing plasma source is a plasma source capable of simultaneously extracting electrons and ions using a grid system. This concept was first proposed by École Polytechnique (Rafalskyi D and Aanesland A. Coincident ion acceleration and electron extraction for space propulsion using the self-bias formed on a set of RF biased grids bounding a plasma source). Journal of Physics D: Applied Physics (2014;47:495203.). Unlike conventional radio frequency plasma sources, this device utilizes a method where the grid is connected to the grid's radio frequency power supply via a DC blocking capacitor and the accelerating grid is grounded. This allows it to simultaneously extract electrons and ions within one grid radio frequency cycle, achieving a stable and highly collimated plasma beam without the need for a neutralizer. This method improves the efficiency and reliability of the plasma source while reducing the frequency and complexity of device maintenance.

[0005] However, in a radio frequency self-neutralizing plasma source, the energy of ions extracted from the beam is determined by the DC self-bias component of the grid across the DC blocking capacitor. Ideally, the DC self-bias component of the grid is comparable in amplitude to the RF voltage component of the grid; however, in practical applications, due to the influence of stray capacitance, the DC self-bias component of the grid is often significantly smaller than the RF voltage component, which limits the beam energy and extraction efficiency of the plasma source. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a double-shell structure radio frequency self-neutralizing plasma source, which improves the ratio of the amplitude of the DC self-bias component of the screen grid to the amplitude of the radio frequency voltage component of the screen grid, thereby improving the beam energy and extraction efficiency of the radio frequency self-neutralizing plasma source and realizing the improvement of plasma source performance.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] A dual-shell structure radio frequency self-neutralizing plasma source includes a grounded shell, a radio frequency shell, a discharge chamber, a radio frequency coil, and a gate system;

[0009] The radio frequency coil is wound around the outside of the discharge chamber; an air inlet is provided upstream of the discharge chamber and an outlet is provided downstream, with the outlet connected to the gate system; the radio frequency housing covers the discharge chamber and the radio frequency coil and is located inside the grounded housing;

[0010] The gate system includes a screen gate and an acceleration gate. The RF housing is electrically connected to the screen gate, and the ground housing is electrically connected to the acceleration gate.

[0011] Preferably, both the downstream axis of the grounding housing and the downstream axis of the radio frequency housing are provided with a downstream through hole not smaller than the discharge chamber outlet.

[0012] Preferably, both the upstream of the grounding housing and the upstream of the radio frequency housing are provided with upstream through holes for the discharge chamber air inlet and the radio frequency coil pins to be led out.

[0013] Preferably, the RF housing includes a grid extension, a radial cover, and an upstream cover, wherein the radial cover and the upstream cover are both connected to the grid extension via snap-fit ​​connections.

[0014] Preferably, there are three screen grid extension members arranged in a circular array between the discharge chamber and the screen grid, and the screen grid extension members are fan-shaped structures.

[0015] Preferably, the materials of the screen extension, radial covering and upstream cover are all metal.

[0016] Preferably, the gate system further includes a gate gap insulating pad and a ground housing insulating pad; the gate gap insulating pad is disposed between the screen gate and the acceleration gate, and the ground housing insulating pad is disposed downstream of the acceleration gate.

[0017] Preferably, the discharge chamber and the grounded outer casing insulating gasket are secured together by a tight clamping ring.

[0018] Preferably, the tightness ring is made of ceramic.

[0019] The radio frequency coil is connected with a radio frequency coil power supply V2, and the screen grid is connected with a screen grid radio frequency power supply V1 through a direct current blocking capacitor C1.

[0020] Compared with the prior art, the application has the following beneficial effects:

[0021] The application introduces a radio frequency shell between the discharge chamber and the ground shell, changes the stray capacitance between the plasma and each potential, reduces the potential difference between the plasma and the screen grid, and further improves the ratio of the screen grid direct current self-bias component to the screen grid radio frequency voltage component amplitude, improves the plasma source beam energy and extraction efficiency and other performance parameters; at the same time, the radio frequency coil and the discharge chamber are both arranged inside the radio frequency shell, the coupling relationship between the radio frequency coil and the plasma in the discharge chamber is unchanged, and the power transmission efficiency of the radio frequency coil is not affected; in addition, the ground shell is wrapped outside the radio frequency shell and maintains the ground potential, still has the radio frequency signal shielding function of the conventional radio frequency plasma source shell, and prevents the loss of radio frequency power. In summary, the double-shell structure radio frequency self-neutralizing plasma source effectively improves the performance indicators of the plasma source by changing the stray capacitance between the plasma and each potential without affecting the power transmission efficiency of the radio frequency coil and the shielding function of the ground shell. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is a schematic diagram of the principle of the double-shell structure radio frequency self-neutralizing plasma source of the embodiment;

[0023] Figure 2 It is a schematic diagram of the structure of the double-shell structure radio frequency self-neutralizing plasma source of the embodiment;

[0024] Figure 3 It is a schematic diagram of the radio frequency shell structure of the embodiment, wherein Figure 3 a in the figure is a radio frequency shell assembly view, Figure 3 b in the figure is a radio frequency shell explosion view;

[0025] Figure 4 It is an equivalent circuit diagram of the radio frequency component of the radio frequency self-neutralizing plasma source, wherein Figure 4 a in the figure corresponds to a conventional radio frequency self-neutralizing plasma source, Figure 4 b in the figure corresponds to a double-shell structure radio frequency self-neutralizing plasma source;

[0026] Figure 5 It is a radio frequency component waveform diagram of the voltage of the radio frequency self-neutralizing plasma source, wherein Figure 5 a in the figure corresponds to a conventional radio frequency self-neutralizing plasma source, Figure 5 b in the figure corresponds to a double-shell structure radio frequency self-neutralizing plasma source.

[0027] 1 - ground housing, 2 - RF housing, 21 - screen grid extension, 22 - radial cladding, 23 - upstream cover plate, 3 - discharge chamber, 4 - RF coil, 5 - screen grid, 6 - acceleration grid, 7 - grid gap insulating spacer, 8 - ground housing insulating spacer, 9 - compression ring, 10 - downstream cover plate, 11 - housing main body. DETAILED DESCRIPTION

[0028] In order to make the personnel in the technical field better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work should belong to the protection scope of the present application.

[0029] As shown in Figure 1 and Figure 2 , the RF self-neutralizing plasma source with a double-layer housing structure described in the present embodiment comprises a discharge chamber 3, an RF coil 4, a grid system and a double-layer housing.

[0030] The material of the discharge chamber 3 is a dielectric. The upstream of the discharge chamber 3 is provided with an air inlet, the air inlet is connected with an air path, and the downstream is provided with an outlet, the outlet is connected with the grid system. The RF coil 4 is wound outside the discharge chamber 3, and the plasma is generated in the discharge chamber 3 after the RF signal is applied.

[0031] The grid system comprises a screen grid 5, an acceleration grid 6, a grid gap insulating spacer 7 and a ground housing insulating spacer 8. The screen grid 5 and the acceleration grid 6 are both conductive materials. The screen grid 5 is close to the discharge chamber 3, and the acceleration grid 6 is away from the discharge chamber 3. The grid gap insulating spacer 7 is placed between the screen grid 5 and the acceleration grid 6, and the ground housing insulating spacer 8 is placed downstream of the acceleration grid 6.

[0032] The double-layer housing comprises an RF housing 2 and a ground housing 1. The RF housing 2 clads outside the discharge chamber 3 and the RF coil 4. The radius and length of the RF housing 2 are both greater than the external dimensions of the discharge chamber 3. The ground housing 1 clads outside the RF housing 2. The radius and length of the ground housing 1 are both greater than the external dimensions of the RF housing 2. The upstream of the ground housing 1 and the upstream of the RF housing 2 are both provided with upstream through holes for the air inlet of the discharge chamber 3 and the pin of the RF coil 4. The downstream axis of the ground housing 1 and the downstream axis of the RF housing 2 are both left with downstream through holes which are not less than the outlet of the discharge chamber 3.

[0033] The ground shell 1 is located outside the radio frequency shell 2, wherein the radio frequency shell 2 is located downstream between the discharge chamber 3 and the screen grid 5, the ground shell 1 is connected with the ground shell insulation pad 8 downstream, and the radio frequency coil 4, the radio frequency shell 2 and the ground shell 1 are all kept a certain insulation interval. The radio frequency coil 4 is connected with the radio frequency coil power supply V2, the screen grid 5 is connected with the screen grid radio frequency power supply V1 through the blocking capacitor C1, the screen grid radio frequency power supply V1 is connected with the ground potential, the radio frequency shell 2 and the screen grid 5 are electrically connected through close contact, and the ground shell 1 and the acceleration grid 6 are both connected with the ground potential.

[0034] The radio frequency shell 2 includes the screen grid extension 21, the radial cladding 22 and the upstream cover plate 23, the screen grid extension 21, the radial cladding 22 and the upstream cover plate 23 are all made of metal and are integrally cladded outside the discharge chamber 3 and the radio frequency coil 4, and the structure of the radio frequency shell 2 is shown in the a of Figure 3 and the b of Figure 3 The screen grid extension 21 is in a fan-shaped structure, the number of the screen grid extension 21 is three, the screen grid extension 21 is arranged at intervals of 120°, one side of the screen grid extension 21 is located between the discharge chamber 3 and the screen grid 5, and the other side of the screen grid extension 21 extends out a metal sheet with a protruding buckle; the radial cladding 22 and the upstream cover plate 23 are connected with the screen grid extension 21 through buckles.

[0035] The ground shell 1 includes the downstream cover plate 10 and the shell main body 11, the shell main body 11 is connected with the downstream cover plate 10 by using metal screws. The pressing ring 9 is made of ceramic, the downstream flange of the discharge chamber 3, the screen grid extension 21, the screen grid 5, the grid gap insulation pad 7, the acceleration grid 6 and the ground shell insulation pad 8 are sequentially located between the pressing ring 9 and the downstream cover plate 10 and are fixed with each other by using the metal screw pressing mode. The screen grid 5 and the acceleration grid 6 extend out wire connection holes in the radial direction, wherein the wire connection hole of the screen grid 5 is connected with the screen grid radio frequency power supply V1 through the blocking capacitor C1, and the wire connection hole of the acceleration grid 6 is grounded.

[0036] The screen grid extension 21 of the radio frequency shell 2 is pressed between the discharge chamber 3 and the screen grid 5, which not only extends the potential of the screen grid 5 to the outside of the grid system, but also provides a connection point with a certain mechanical strength for the radio frequency shell 2; the radial cladding 22 and the upstream cover plate 23 are connected with the screen grid extension 21 through buckles, and since the screen grid extension 21, the radial cladding 22 and the upstream cover plate 23 are all made of metal, the radio frequency shell 2 as a whole keeps the same potential as the screen grid 5.

[0037] The influence of stray capacitance on the screen-grid DC self-bias component is analyzed by using the RF component equivalent circuit of the RF self-neutralized plasma source. There is a sheath between the plasma and the screen-grid 5, which is represented by a parallel circuit of a current source, a diode and a sheath capacitance C3. The current source represents the ion current, the diode current represents the electron current, and the sheath capacitance C3 is directly represented by a capacitance element. Considering that the ion current is approximately direct current, and that the diode is almost non-conducting because the plasma sheath potential is positive at most times, the current source and the diode can be removed in the RF component equivalent circuit analysis of the RF self-neutralized plasma source.

[0038] The simplified RF component equivalent circuit of the RF self-neutralized plasma source is shown in Figure 4 a (conventional RF self-neutralized plasma source) and Figure 4 b (double-shell structure RF self-neutralized plasma source) in Figure 4 a and b, N1 is the plasma, N2 is the grid, and the stray capacitance between the plasma and the grounded shell 1 is represented by the stray capacitance C2 between the plasma and the ground potential. In the double-shell structure RF self-neutralized plasma source, the stray capacitance between the plasma and the RF shell 2 is represented by the stray capacitance C4 between the plasma and the screen-grid 5 potential, and because of the blocking of the RF shell 2, the positive area between the plasma and the grounded shell 1 is reduced, and the stray capacitance between the plasma and the grounded shell 1 is reduced. Therefore, the RF shell 2 not only reduces the capacitance of the stray capacitance C2 between the plasma and the ground potential, but also increases the capacitance of the stray capacitance C4 between the plasma and the screen-grid 5 potential, which helps to reduce the potential difference between the plasma and the screen-grid 5, thereby reducing the electron extraction difficulty and increasing the screen-grid DC self-bias component.

[0039] In the RF self-neutralized plasma source, the screen-grid voltage includes a screen-grid RF voltage component and a screen-grid DC self-bias component, where the screen-grid DC self-bias component is smaller than the amplitude of the screen-grid RF voltage component, and there is an interval where the screen-grid voltage is less than zero in the negative half cycle of the RF, and the screen-grid voltage is greater than zero at other times. In one RF period in the discharge chamber 3, heavy ions are difficult to respond to the change of the screen-grid RF voltage component and are almost only affected by the screen-grid DC self-bias component, and can be extracted throughout the RF period; small mass electrons can respond to the change of the screen-grid RF voltage component and can only be extracted when the screen-grid voltage is less than zero, and cannot be extracted at other times. Because the electron migration ability is much greater than that of the ion, the amount of electrons extracted only when the screen-grid voltage is less than zero can be comparable to the amount of ions extracted continuously in the RF period. When the amount of electrons extracted in one RF period is equal to the amount of ions extracted, the plasma source achieves self-neutralized extraction.

[0040] The length of time for the electrons in the discharge chamber 3 to be extracted is affected by the ratio of the DC self-bias component of the screen grid to the amplitude of the RF voltage component of the screen grid in one RF period: when the ratio is small, the time for the screen grid voltage to be less than zero is longer, and the time for the electrons to be extracted is correspondingly increased; when the ratio is large, the time for the screen grid voltage to be less than zero is shorter, and the time for the electrons to be extracted is correspondingly shortened. The DC self-bias component of the screen grid is automatically adjusted according to the operation of the plasma source, so as to ensure that the amount of electrons extracted by the grid is equal to the amount of ions in one RF period. Since the ions are almost only affected by the DC self-bias component of the screen grid to be extracted and accelerated, when the amplitude of the RF voltage component of the screen grid is the same, the larger the ratio of the DC self-bias component of the screen grid to the amplitude of the RF voltage component of the screen grid, the greater the ion extraction speed, and the indexes such as the beam energy and the extraction efficiency of the plasma source are increased.

[0041] Next, the RF component equivalent circuit of the RF self-neutralizing plasma source is quantitatively analyzed. Assuming that the plasma is uniformly distributed in the discharge chamber 3, the capacitance C3 of the sheath between the plasma and the screen grid 5 is C sh The following formula is obtained:

[0042]

[0043] wherein, ε 0 is the vacuum permittivity; S sh is the sheath area, which is equal to the internal cross-sectional area of the discharge chamber 3 in this case; d sh is the sheath thickness, which can be obtained by the Child-Langmuir law:

[0044]

[0045] wherein, V sh,dc is the DC component of the sheath voltage, e is the elementary charge, n e is the plasma density, T e is the electron temperature. Taking common plasma parameters as an example, it is assumed that V sh,dc = 30 V, n e = 5 × 10 17 m -3 , T e = 5 eV, then d sh = 1.6722 × 10 -4 m; further, it is assumed that the radius in the discharge chamber 3 is 1.5 cm, and the following can be obtained: C sh=37.428pF.

[0046] Let the radius of the grounding casing 1 be... r 1. Axial length is l 1; The radius of the RF housing 2 is r 2, axial length is l 2; The inner radius of discharge chamber 3 is r 3, axial length is l 3. In a conventional RF self-neutralizing plasma source, the capacitance of stray capacitance C2 between the plasma and the grounded casing 1. C 1,plas It can be obtained from the following formula:

[0047]

[0048] In the formula, C r,1 The capacitance between the plasma and the radial wall of the grounded casing 1. C z,1 The capacitance between the plasma and the upstream wall of the grounded casing 1.

[0049] Similarly, in a dual-shell structure RF self-neutralizing plasma source, the capacitance of stray capacitance C4 between the plasma and the RF shell 2 is... C 2,plas It can be obtained from the following formula:

[0050]

[0051] In the formula, C r,2 The capacitance between the plasma and the radial wall of the RF housing 2. C z,2 The capacitance between the plasma and the upstream wall of the RF housing 2.

[0052] Let the inner radius and length of discharge chamber 3 be 1.5cm and 5cm respectively, the radius and length of grounding outer shell 1 be 3cm and 7cm respectively, and the radius and length of radio frequency outer shell 2 be 2.5cm and 6cm respectively, then we have C 1,plas =4.3260pF, C 2,plas =6.0712pF. Assuming that in the dual-shell structure RF self-neutralizing plasma source, the RF shell 2 covers 90% of the discharge chamber 3, then the stray capacitance between the plasma and the grounded shell 1 can be considered to be 0.1 × 10⁻⁶ pF. C 1,plas =0.4326pF, the stray capacitance between the plasma and the RF housing 2 is 0.9× C 2,plas =5.4641pF.

[0053] In order to reduce the fluctuation of the screen-grid DC self-bias component, the capacitance of the direct-current blocking capacitor C1 is usually large, and in the embodiment, is set to 1 nF. The amplitude of the screen-grid RF power supply V1 is set to 400 V, and the frequency is 10 MHz. The above parameters are substituted into the RF self-neutralizing plasma source RF component equivalent circuit model of a in Figure 5 and b in Figure 5 , and the waveforms of the screen-grid RF voltage component, the plasma potential RF component and the sheath voltage RF component shown in a and b in Figure 5 can be obtained. The waveform of a in Figure 5 is a conventional RF self-neutralizing plasma source waveform. In the negative half cycle of the screen-grid RF power supply, the sheath voltage RF component reaches a maximum value of 41.269 V, at which time the electron extraction is difficult, resulting in a small ratio of the screen-grid DC self-bias component to the amplitude of the screen-grid RF voltage component. The waveform of b in Figure 5 is a double-shell structure RF self-neutralizing plasma source waveform. In the waveform, the plasma potential RF component is almost the same as the screen-grid RF voltage component, and the amplitude of the sheath voltage RF component is only 3.9724 V, so that the electron is more easily extracted, the ratio of the screen-grid DC self-bias component to the amplitude of the screen-grid RF voltage component is larger, and the performance parameters such as the beam energy and the extraction efficiency of the plasma source are better.

[0054] The double-shell structure RF self-neutralizing plasma source disclosed in the embodiment introduces the RF shell 2 between the discharge chamber 3 and the grounded shell 1, changes the stray capacitance between the plasma and each potential, reduces the potential difference between the plasma and the screen grid 5, and further improves the ratio of the screen-grid DC self-bias component to the amplitude of the screen-grid RF voltage component, and improves the performance parameters such as the beam energy and the extraction efficiency of the plasma source. At the same time, the RF coil 4 and the discharge chamber 3 are both arranged inside the RF shell 2, the coupling relationship between the RF coil 4 and the plasma in the discharge chamber 3 is unchanged, and the power transmission efficiency of the RF coil 4 is not affected. In addition, the grounded shell 1 is wrapped outside the RF shell 2 and maintains the ground potential, and still has the RF signal shielding function of the shell of the conventional RF plasma source, preventing the loss of RF power. In summary, the double-shell structure RF self-neutralizing plasma source does not affect the power transmission efficiency of the RF coil 4 and the shielding function of the shell, and effectively improves the performance parameters of the plasma source by changing the stray capacitance between the plasma and each potential.

[0055] The above-mentioned serial numbers of the embodiments of the present application only serve for description, and do not represent the advantages and disadvantages of the embodiments.

[0056] In the above-described embodiments of the present application, the description of each embodiment has its own emphasis, and the parts not described in detail in a certain embodiment can be referred to the relevant description of other embodiments.

[0057] In several embodiments provided in the present application, it should be understood that the disclosed technology can be implemented in other manners. The described embodiments of the device are merely illustrative, for example, the division of the units can be different, and each unit can be integrated or can not be integrated. In addition, the display or discussion of a coupling or direct coupling or communication connection between units can be indirect coupling or communication connection through some interface, and can be in electrical or other forms.

[0058] The units described as separated components can or can not be physically separated, and the components displayed as units can or can not be physical units, i.e., can be located in one place or can be distributed on multiple units. Some or all of the units can be selected according to actual needs to achieve the purposes of the embodiments of the present application.

[0059] The above description is merely preferred embodiments of the present application, and it should be pointed out that, for those skilled in the art, without departing from the principles of the present application, some improvements and refinements can be made, and these improvements and refinements should be regarded as the protection scope of the present application.

[0060] It should be understood that the above description is for illustration only and is not intended to be limiting. Many embodiments and many applications other than those described herein will be readily apparent to those skilled in the art from this description. The scope of the application should therefore not be determined with reference to the above description, but should instead be determined with reference to the appended claims and the full scope of equivalents to which such claims are entitled. The disclosures of all articles and references, including patent applications and publications, are incorporated by reference for all purposes. The omission of any aspect of the subject matter disclosed herein does not preclude coverage of that aspect, and the application should not be deemed forfeit of that aspect of the subject matter.

Claims

1. A radio frequency self-neutralizing plasma source with a double-layer shell structure, characterized in that, It includes a grounded housing (1), a radio frequency housing (2), a discharge chamber (3), a radio frequency coil (4), and a gate system; The radio frequency coil (4) is wound around the outside of the discharge chamber (3); an air inlet is provided upstream of the discharge chamber (3) and an outlet is provided downstream, and the outlet is connected to the gate system; the radio frequency housing (2) covers the discharge chamber (3) and the radio frequency coil (4) and is located inside the grounded housing (1); The gate system includes a screen gate (5) and an acceleration gate (6). The RF housing (2) is electrically connected to the screen gate (5), and the ground housing (1) is electrically connected to the acceleration gate (6). The grid (5) is connected to the grid RF power supply (V1) via the DC blocking capacitor (C1), and the grid RF power supply (V1) is connected to ground potential.

2. The double-layer shell structure radio frequency self-neutralizing plasma source according to claim 1, characterized in that, Both the downstream axis of the grounding housing (1) and the downstream axis of the radio frequency housing (2) are provided with a downstream through hole not smaller than the outlet of the discharge chamber (3).

3. The double-layer shell structure radio frequency self-neutralizing plasma source according to claim 1, characterized in that, Both the upstream of the ground housing (1) and the upstream of the radio frequency housing (2) are provided with upstream through holes for the air inlet of the discharge chamber (3) and the pin of the radio frequency coil (4).

4. The double-layer shell structure radio frequency self-neutralizing plasma source according to claim 1, characterized in that, The radio frequency housing (2) includes a grid extension (21), a radial cover (22) and an upstream cover (23), both of which are connected to the grid extension (21) by snap-fit.

5. The double-layer shell structure radio frequency self-neutralizing plasma source according to claim 4, characterized in that, There are three screen grid extensions (21) arranged in a circular array between the discharge chamber (3) and the screen grid (5). The screen grid extensions (21) are fan-shaped structures.

6. The double-layer shell structure radio frequency self-neutralizing plasma source according to claim 4, characterized in that, The materials of the screen extension (21), the radial cover (22) and the upstream cover (23) are all metal.

7. The double-layer shell structure radio frequency self-neutralizing plasma source according to claim 1, characterized in that, The gate system also includes a gate gap insulating pad (7) and a ground housing insulating pad (8); the gate gap insulating pad (7) is disposed between the screen gate (5) and the acceleration gate (6), and the ground housing insulating pad (8) is disposed downstream of the acceleration gate (6).

8. The double-layer shell structure radio frequency self-neutralizing plasma source according to claim 7, characterized in that, The discharge chamber (3), the grid extension (21), the grid (5), the grid gap insulating pad (7), the acceleration grid (6) and the ground housing insulating pad (8) are pressed and fixed together by a clamping ring (9).

9. The double-layer shell structure radio frequency self-neutralizing plasma source according to claim 8, characterized in that, The material of the tight ring (9) is ceramic.

10. The double-layer shell structure radio frequency self-neutralizing plasma source according to claim 1, characterized in that, The radio frequency coil (4) is connected to the radio frequency coil power supply (V2).

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