A radio frequency inductively coupled plasma neutralizer

Abstract

The present invention belongs to the technical field of low-temperature plasma, and particularly relates to a radio-frequency inductively coupled plasma neutralizer. The present invention includes a plasma discharge chamber for accommodating a discharge plasma, a high-voltage insulating gas path device, a radio-frequency coupling antenna, a cathode for collecting ions and shielding radio-frequency capacitive coupling, a shielding housing, and an anode for extracting an electron beam from the plasma discharge chamber. On the one hand, the structure of the radio-frequency inductively coupled plasma neutralizer can effectively shield the capacitive coupling between the radio-frequency coupling antenna and the discharge plasma, reduce the sputtering of the inner wall of the plasma discharge chamber caused by the radio-frequency capacitive coupling effect, reduce the impurity contamination in the discharge plasma, and at the same time can also effectively reduce the contamination on the ceramic insulating parts of the radio-frequency inductively coupled plasma neutralizer, improve the service life and stability of the radio-frequency inductively coupled plasma neutralizer, and has the advantages of simple structure, no electrode contamination, clean extraction of the electron beam, long service life, stable operation, easy control of the beam current intensity and energy, etc.

Description

Technical Field

[0001] The present invention belongs to the technical field of low-temperature plasma, and particularly relates to a radio-frequency inductively coupled plasma neutralizer. Background Art

[0002] A neutralizer is a device for generating electron beams. As a core key component of systems such as ion sources and electric thrusters, it is widely used in modern thin-film material preparation, material surface modification, very large scale integrated circuits, microfabrication of high-precision large optical elements, space electric propulsion systems, and active potential control of spacecraft. Neutralizers can be classified into three types according to their working methods: immersion hot cathode neutralizers, external hot cathode neutralizers, and plasma bridge neutralizers. The immersion hot cathode neutralizer places the hot cathode inside the ion beam, such as Figure 1 , and emits electrons when it is heated to a temperature above 2200 - 2300 °C. During the operation of the ion source, due to the very high temperature of the neutralization cathode and the strong sputtering effect of the ion beam, the cathode is consumed quickly, has a short lifespan, needs to be replaced frequently, and there is also a problem of impurity contamination. If the cathode is used in a reactive gas atmosphere, the consumption is even faster, and its application range is greatly limited. The external cathode neutralizer places the cathode outside the ion beam and uses the strong coupling voltage between the neutralizer and the ion beam to attract the electrons emitted by the cathode into the ion beam, thereby neutralizing the ion beam. It mainly includes two types: external hot cathode neutralizers and external field emission cathode neutralizers. For example, the external cathode neutralizer applicable to the fields of ion beam thin-film deposition and ion beam material surface modification disclosed in the publication number CN1917131A is as Figure 2。Although this hot cathode avoids the direct sputtering of ion beams, it is still limited by the thermal evaporation of the hot cathode material, resulting in a relatively short service life. In addition, the strong coupling voltage affects the performance of the ion beam. At the same time, the hot cathode is sensitive to the working atmosphere, which limits its application in some fields with high requirements for pollution control, such as the ion beam processing fields of high-purity optical components and semiconductor wafers. The external field emission cathode neutralizer applies a high-intensity electric field on the surface of metals or semiconductors, and electrons enter the vacuum through the tunnel effect. Compared with thermionic emission, the cold cathode of field emission has the advantages of low power consumption and fast response speed. It can obtain an emission current with a current density of up to more than 107 A / cm2, and there is no time delay in emission. The disadvantage is that when it is exposed to an environment above 10-8 Torr, ion sputtering and surface corrosion limit the life of the field emission cathode. The plasma bridge neutralizer uses a hollow cathode, radio frequency and other discharge methods to generate discharge plasma. Under the action of a bias voltage, the electrons and some ions generated by the discharge are transported to the ion beam. Some of the ions generated by the discharge play a "bridging" role for the electrons to enter the ion beam, so as to reduce the coupling voltage and allow the neutralizer to be located farther from the ion beam. The currently commonly used plasma bridge neutralizer is the hollow cathode neutralizer. For example, the publication number CN195626410A discloses a hollow cathode neutralizer suitable for use in a space electric propulsion system, and the publication number CN103770953A discloses a device and method for actively controlling the spacecraft structure potential using a hollow cathode. The hollow cathode mainly consists of a cathode tube, a top plate, an emitter, a heater, a holding electrode, etc. Among them, emitter poisoning and heater failure are the key factors restricting the performance of the hollow cathode. This is because when the emitter is exposed to the atmosphere, its surface will adsorb impurities such as oxygen and water vapor; when the emitter is heated, the impurities react with the emitter, resulting in the failure of the emitter, a decrease in the ability to emit electrons or the loss of the emission ability. At the same time, the insulation layer coating-sintering process of the hollow cathode heater is cumbersome, affected by human factors, the recrystallization phenomenon of the heating wire is serious, and the heating wire is prone to brittle fracture. To solve these problems, the publication number CN103762134A discloses a structure of a hollow cathode thermal shielding assembly, the publication number CN105006412A discloses a ceramic assembly structure of a hollow cathode heater, and the publication number CN104780631A discloses a heating device for a hollow cathode neutralizer, etc. After years of research, although the technical indicators such as the life and performance of the hollow cathode have been greatly improved, due to the high cathode temperature, cathode consumption during operation, and the reduction of performance with cathode consumption, sensitivity to the oxygen content in the working environment, large pollution, and high manufacturing cost, its application is limited. The radio frequency plasma neutralizer is a new type of neutralizer proposed in recent years. According to different discharge methods, it is divided into a radio frequency capacitive coupling plasma neutralizer and a radio frequency inductive coupling plasma neutralizer.Among them, the radio frequency capacitive coupling plasma neutralizer generates plasma through capacitive coupling discharge between radio frequency electrodes, and there are problems such as electrode sputtering and impurity pollution. The radio frequency inductive coupling plasma neutralizer maintains plasma discharge through electromagnetic induction coupling effect, has no electrode pollution, high plasma density, and can work stably in the reaction gas for a long time, but there are problems such as difficult discharge ignition and sputtering pollution of the discharge cavity. Summary of the Invention

[0003] The purpose of the present invention is to provide a radio frequency inductive coupling plasma neutralizer in view of the above-mentioned defects existing in the prior art.

[0004] The technical solution of the present invention is as follows:

[0005] A radio frequency inductive coupling plasma neutralizer, comprising: a plasma discharge cavity for accommodating discharge plasma, a high-voltage insulating gas path device, a radio frequency coupling antenna, a cathode for collecting ions and shielding radio frequency capacitive coupling, a shielding housing, and an anode for extracting an electron beam from the plasma discharge cavity. The plasma discharge cavity is of a hollow structure, with an air inlet provided at its upper end and an electron beam extraction hole provided at its lower end. The plasma discharge cavity is installed inside the shielding housing, and a fixed flange is fixedly installed at the middle position inside the shielding housing. The plasma discharge cavity is installed on the fixed flange;

[0006] The upper end of the plasma discharge cavity is provided with a gas inlet, and the lower end is provided with an electron beam outlet. The upper end of the shielding housing is provided with a gas inlet, whose position corresponds to the position of the gas inlet at the upper end of the plasma discharge cavity. A gas path is provided between the gas inlet at the upper end of the shielding housing and the air inlet at the upper end of the plasma discharge cavity, and a high-voltage insulating gas path device is installed on the part of the gas path between the gas inlet at the upper end of the shielding housing and the air inlet at the upper end of the plasma discharge cavity;

[0007] The outer wall of the cylindrical ceramic plasma discharge cavity is processed with a spiral groove for installing the radio frequency coupling antenna, and at the same time, the insulation strength between each turn of the radio frequency coupling antenna is improved. A lead pipe is provided at the annular groove at the lower end of the outer wall of the plasma discharge cavity. The lead pipe passes through the fixed flange and then through the shielding housing, so that the radio frequency power supply is connected to the radio frequency coupling antenna through a matching network;

[0008] The cathode is located inside the plasma discharge cavity, and there is a narrow slit in the transverse cutting direction of the winding direction of the radio frequency coupling antenna. A discharge trigger needle is provided at the narrow slit of the cathode;

[0009] The cathode and the anode located at the lower end of the plasma discharge cavity in the plasma discharge cavity constitute an extraction system for the electron beam of the radio frequency inductive coupling plasma neutralizer. The anode is provided with an extraction hole, and the extraction hole is aligned with the extraction hole at the lower end of the plasma discharge cavity. A positive bias voltage of 0 - 30V is applied between the anode and the cathode through an anode power supply, and a negative bias voltage of 0 - 70V is applied between the cathode and the ground through a cathode power supply.

[0010] A radio frequency inductively coupled plasma neutralizer, wherein the plasma discharge chamber is made of an insulating medium with low dielectric loss, preferably ceramic.

[0011] A radio frequency inductively coupled plasma neutralizer, wherein the cathode is cylindrical.

[0012] A radio frequency inductively coupled plasma neutralizer, wherein the cathode is closely attached to the inner wall of the plasma discharge chamber.

[0013] A radio frequency inductively coupled plasma neutralizer, wherein a discharge trigger pin 11 is arranged at the narrow slit of the cathode, and the radio frequency power supply, the matching network, the radio frequency coupling antenna, the plasma discharge chamber, the cathode and the high-voltage insulating gas path device together constitute a plasma discharge starting and maintaining system.

[0014] A radio frequency inductively coupled plasma neutralizer, wherein the plasma discharge chamber can be a hollow cuboid structure or a hollow cylinder structure.

[0015] A radio frequency inductively coupled plasma neutralizer, wherein two groups of corresponding gas inlets are arranged on the shielding outer shell and the plasma discharge chamber, and the number of gas paths arranged between the shielding outer shell and the plasma discharge chamber is two.

[0016] A radio frequency inductively coupled plasma neutralizer, characterized in that a plurality of groups of corresponding lead-out holes are opened at the lower ends of the anode and the plasma discharge chamber.

[0017] The beneficial effects of the present invention are as follows:

[0018] Compared with other structural neutralizers, on the one hand, the structure of this radio frequency inductively coupled plasma neutralizer can effectively shield the capacitive coupling between the radio frequency coupling antenna and the discharge plasma, reduce the sputtering of the inner wall of the plasma discharge chamber caused by the radio frequency capacitive coupling effect, reduce the impurity pollution in the discharge plasma, and at the same time can also effectively reduce the pollution on the ceramic insulating parts of the radio frequency inductively coupled plasma neutralizer, improve the service life and stability of the radio frequency inductively coupled plasma neutralizer, and has the advantages of simple structure, no electrode pollution, clean electron beam extraction, long service life, stable operation, easy control of beam current intensity and energy. And, a discharge trigger pin is arranged at the narrow slit of the cathode, and a strong electric field is generated between the trigger pins by using the inductive coupling effect between the cathode and the radio frequency coupling antenna to ionize the gas and start the discharge, making the start-up discharge of the radio frequency inductively coupled plasma neutralizer easier and more reliable. Description of the Drawings

[0019] Figure 1 is a schematic diagram of the structure of an existing ion source and an immersion cathode neutralizer;

[0020] Figure 2Schematic diagram of an existing ion source and an external cathode neutralizer;

[0021] Figure 3 Schematic diagram of an existing ion source and a hollow cathode plasma bridge neutralizer;

[0022] Figure 4 Schematic diagram of the specific embodiment 1 of a radio frequency inductively coupled plasma neutralizer provided by the present invention;

[0023] Figure 5 is from Figure 1 A diagram showing an example of the measurement result of the electron energy distribution emitted from the radio frequency inductively coupled plasma neutralizer shown;

[0024] Figure 6 Schematic diagram of the specific embodiment 2 of a radio frequency inductively coupled plasma neutralizer provided by the present invention.

[0025] In the figure: 1, plasma discharge chamber; 2, high-voltage insulating gas path device; 3, cathode; 4, radio frequency coupling antenna; 5, matching network; 6, radio frequency power supply; 7, anode; 8, anode power supply; 9, cathode power supply; 10, shielding housing; 11, trigger pin; 12, fixed flange. Specific embodiment

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] As Figure 4 shown, a radio frequency inductively coupled plasma neutralizer includes: a plasma discharge chamber 1 for accommodating discharge plasma, a high-voltage insulating gas path device 2, a radio frequency coupling antenna 4, a cathode 3 for collecting ions and shielding radio frequency capacitive coupling, a shielding housing 10, and an anode 7 for extracting an electron beam from the plasma discharge chamber 1.

[0028] The plasma discharge chamber 1 is a hollow cylindrical structure, made of an insulating medium with low dielectric loss. It is provided with an air inlet at the upper end and an electron beam extraction hole at the lower end. The plasma discharge chamber 1 is installed inside the shielding housing 10. A fixed flange 12 is fixedly installed at the middle position inside the shielding housing 10, and the plasma discharge chamber 1 is installed on the fixed flange 12;

[0029] The upper end of the plasma discharge chamber 1 is provided with a gas inlet, and the lower end is provided with an electron beam outlet. The upper end of the shielding housing 10 is provided with a gas inlet, whose position corresponds to the gas inlet position at the upper end of the plasma discharge chamber. There is a gas path between the gas inlet at the upper end of the shielding housing 10 and the air inlet at the upper end of the plasma discharge chamber. A high-voltage insulating gas path device 2 is installed on the part of the gas path between the gas inlet at the upper end of the shielding housing 10 and the air inlet at the upper end of the plasma discharge chamber;

[0030] The outer wall of the cylindrical ceramic plasma discharge chamber 1 is machined with a spiral groove for installing the radio frequency coupling antenna 4, and at the same time, the insulation strength between each turn of the radio frequency coupling antenna 4 is improved. A lead pipeline is arranged at the annular groove at the lower end of the outer wall of the plasma discharge chamber 1. The lead pipeline passes through the fixed flange 12 and then passes through the shielding shell 10, so that the radio frequency power supply 6 is connected to the radio frequency coupling antenna 4 through the matching network 5.

[0031] The cathode 3 is located inside the plasma discharge chamber 1, is cylindrical, and has a narrow slit in the direction transverse to the winding direction of the radio frequency coupling antenna 4. A discharge trigger pin 11 is arranged at the narrow slit of the cathode 3, and the cathode 3 is closely attached to the inner wall of the plasma discharge chamber 1.

[0032] The cathode 3 in the plasma discharge chamber 1 and the anode located at the lower end of the plasma discharge chamber 1 form an extraction system for the radio frequency inductively coupled plasma neutralizer electron beam. The anode 7 is provided with an extraction hole, and the extraction hole is aligned with the extraction hole at the lower end of the plasma discharge chamber 1. A positive bias voltage of 0 - 30V is applied between the anode 7 and the cathode 3 through the anode power supply 8, and a negative bias voltage of 0 - 70V is applied between the cathode 3 and the ground through the cathode power supply 9.

[0033] In order to facilitate the ignition of the radio frequency inductively coupled neutralizer, a discharge trigger pin 11 is arranged at the narrow slit of the cathode 3. The radio frequency power supply 6, the matching network 5, the radio frequency coupling antenna 4, the plasma discharge chamber 1, the cathode 3 and the high - voltage insulation gas path device 2 together form a plasma discharge ignition and maintenance system. The inductive coupling effect between the cathode 3 and the radio frequency coupling antenna 4 is used to generate a strong electric field between the trigger pins 11 to ionize the gas for ignition. This structure makes the ignition discharge of the radio frequency inductively coupled plasma neutralizer easier and more reliable. After ignition, energy is transferred between the radio frequency antenna and the plasma through the electromagnetic induction coupling effect to maintain the plasma discharge.

[0034] This structure of the radio frequency inductively coupled plasma neutralizer can, on the one hand, effectively shield the capacitive coupling between the radio frequency coupling antenna 4 and the discharge plasma, reduce the sputtering of the inner wall of the plasma discharge chamber 1 by the radio frequency capacitive coupling effect, reduce the impurity contamination in the discharge plasma, and at the same time, can also effectively reduce the contamination on the ceramic insulating parts of the radio frequency inductively coupled plasma neutralizer, improving the life and stability of the radio frequency inductively coupled plasma neutralizer.

[0035] The working process is as follows: When the gas working medium enters the discharge chamber through the high - voltage insulation gas path device 2, the radio frequency power supply 6 sends radio frequency energy to the radio frequency antenna 4 through the matching box 5. The inductive electric field is generated between the trigger pins 11 by using the Faraday electromagnetic induction coupling effect to ionize the gas working medium for ignition discharge. After ignition, the radio frequency antenna 4 maintains the plasma discharge through the electromagnetic induction coupling effect. The cathode absorbs ions by applying a negative bias voltage through the DC power supply 9, and a positive bias voltage is applied to the anode 7 through the DC power supply 8 to extract the electron beam.

[0036] The radio frequency inductively coupled plasma neutralizer has a radio frequency power range of 40 - 150 W, a frequency of 13.56 MHz, and an electron beam current intensity of 50 - 2000 mA. This neutralizer has the characteristics of low maintenance rate, simple structure, easy disassembly and maintenance, long service life, and good energy singularity of the extracted electron beam, such as Figure 5 and can achieve reliable and consistent operation in both inert and oxidizing environments.

[0037] Example 2

[0038] such as Figure 6 shown, a radio frequency inductively coupled plasma neutralizer includes: a plasma discharge chamber 1 for accommodating discharge plasma, a high - voltage insulating gas path device 2, a radio frequency coupling antenna 4, a cathode 3 for collecting ions and shielding radio frequency capacitive coupling, a shielding housing 10, and an anode 7 for extracting an electron beam from the plasma discharge chamber 1.

[0039] Its plasma discharge chamber 1 is a hollow cuboid structure, made of an insulating medium with low dielectric loss. It is provided with an air inlet at the upper end and an electron beam extraction hole at the lower end. The plasma discharge chamber 1 is installed inside the shielding housing 10 and fixed to the bottom end of the shielding housing 10. The upper end of the plasma discharge chamber is provided with a gas inlet, and the lower end is provided with an electron beam outlet. A high - voltage insulating gas path device 2 is installed on the gas path between the shielding housing 10 and the air inlet of the upper end of the plasma discharge chamber 1. To improve the uniformity of plasma in the discharge chamber, two gas supply systems are configured, and the flow rate of each gas inlet can be controlled independently. The radio frequency coupling antenna 4 is wound around the outer side wall of the plasma discharge chamber 1 and is connected to a radio frequency power supply 6 through a matching network 5.

[0040] The cathode 3 is located inside the plasma discharge chamber 1, is rectangular, and has a narrow slit in the direction transverse to the winding direction of the radio frequency coupling antenna 4. The cathode 3 is closely attached to the inner wall of the plasma discharge chamber 1. A discharge trigger pin 11 is provided at the narrow slit of the cathode 3. The radio frequency power supply 6, the matching network 5, the radio frequency coupling antenna 4, the plasma discharge chamber 1, the cathode 3, and the high - voltage insulating gas path device 2 together constitute a plasma discharge ignition and maintenance system. A strong electric field is generated between the trigger pins 11 by the inductive coupling effect between the cathode 3 and the radio frequency coupling antenna 4 to ionize the gas and cause ignition.

[0041] The cathode 3 inside the plasma discharge chamber 1 and the anode located at the lower end of the plasma discharge chamber 1 constitute an extraction system for the electron beam of the radio frequency inductively coupled plasma neutralizer. Multiple groups of corresponding extraction holes are opened between the anode 7 and the plasma discharge chamber 1. A positive bias voltage of 0 - 30 V is applied between the anode 7 and the cathode 3 through an anode power supply 8, and a negative bias voltage of 0 - 70 V is applied between the cathode 3 and the ground through a cathode power supply 9.

Claims

1. A radio frequency inductively coupled plasma neutralizer, comprising: a plasma discharge chamber (1) for accommodating a discharge plasma, a high-voltage insulating gas path device (2), a radio frequency coupling antenna (4), a cathode (3) for collecting ions and shielding radio frequency capacitive coupling, a shielding housing (10), and an anode (7) for extracting an electron beam from the plasma discharge chamber (1), characterized in that: the plasma discharge chamber (1) is of a hollow structure, having an air inlet at its upper end and an electron beam extraction hole at its lower end. The plasma discharge chamber (1) is installed inside the shielding housing (10). A fixed flange (12) is fixedly installed at the middle position inside the shielding housing (10), and the plasma discharge chamber (1) is installed on the fixed flange (12). The upper end of the plasma discharge chamber (1) has a gas inlet, and the lower end has an electron beam outlet. The upper end of the shielding housing (10) is provided with a gas inlet, corresponding to the position of the gas inlet at the upper end of the plasma discharge chamber. There is a gas path between the gas inlet at the upper end of the shielding housing (10) and the air inlet at the upper end of the plasma discharge chamber. A high-voltage insulating gas path device (2) is installed on the part of the gas path between the gas inlet at the upper end of the shielding housing (10) and the air inlet at the upper end of the plasma discharge chamber; the outer wall of the cylindrical ceramic plasma discharge chamber (1) is machined with a spiral groove for installing the radio frequency coupling antenna (4), and at the same time, the insulation strength between each turn of the radio frequency coupling antenna (4) is improved. A lead pipe is provided at the annular groove at the lower end of the outer wall of the plasma discharge chamber (1). The lead pipe passes through the fixed flange (12) and then through the shielding housing (10), so that the radio frequency power supply (6) is connected to the radio frequency coupling antenna (4) through the matching network (5); the cathode (3) is located inside the plasma discharge chamber (1). There is a narrow slit in the direction of the winding of the radio frequency coupling antenna (4) in the transverse section. A discharge trigger needle (11) is provided at the narrow slit of the cathode (3). The cathode uses the inductive coupling effect with the radio frequency coupling antenna to provide the voltage for ionizing the gas to start glow for the trigger needle; the cathode (3) inside the plasma discharge chamber (1) and the anode located at the lower end of the plasma discharge chamber (1) constitute an extraction system for the electron beam of the radio frequency inductively coupled plasma neutralizer. The anode (7) is provided with an extraction hole, and this extraction hole is aligned with the extraction hole at the lower end of the plasma discharge chamber (1). A positive bias voltage is applied between the anode (7) and the cathode (3) through the anode power supply (8), and a negative bias voltage is applied between the cathode (3) and the ground through the cathode power supply (9); the plasma discharge chamber (1) is made of an insulating medium with low dielectric loss; the cathode (3) is in a cylindrical shape.

2. A radio frequency inductively coupled plasma neutralizer according to claim 1, characterized in that: the cathode (3) is closely attached to the inner wall of the plasma discharge chamber (1).

3. A radio frequency inductively coupled plasma neutralizer according to claim 1, characterized in that: The discharge trigger needle (11) is arranged at the narrow slit of the cathode (3). The radio frequency power supply (6), the matching network (5), the radio frequency coupling antenna (4), the plasma discharge chamber (1), the cathode (3) and the high-voltage insulating gas path device (2) together constitute a plasma discharge starting and maintaining system.

4. A radio frequency inductively coupled plasma neutralizer according to claim 1, characterized in that: The plasma discharge chamber (1) can be a hollow cuboid structure or a hollow cylinder structure.

5. A radio frequency inductively coupled plasma neutralizer according to claim 1, characterized in that: Two groups of corresponding gas inlets are provided on the shielding outer shell (10) and the plasma discharge chamber (1), and the number of gas paths provided between the shielding outer shell (10) and the plasma discharge chamber (1) is two.

6. A radio frequency inductively coupled plasma neutralizer according to claim 1, characterized in that: Multiple groups of corresponding lead-out holes are provided at the lower ends of the anode (7) and the plasma discharge chamber (1).

7. A radio frequency inductively coupled plasma neutralizer according to claim 1, characterized in that: A positive bias voltage of 0 - 30V is applied between the anode (7) and the cathode (3) through the anode power supply (8).

8. A radio frequency inductively coupled plasma neutralizer according to claim 1, characterized in that: A negative bias voltage of 0 - 70V is applied between the cathode (3) and the ground through the cathode power supply (9).

Images