Radio frequency ion source equipment for optical polishing

Abstract

The utility model discloses radio frequency ion source equipment for optical polishing, which belongs to the technical field of ion beam processing equipment, solves the problems of complicated structure and limited use caused by the separation design of a neutralizer in the conventional radio frequency ion source equipment, and comprises an ion source shell, the ion source comprises an ion source shell, a tuning excitation mechanism, a discharge chamber and a grid system are installed in the ion source shell, the tuning excitation mechanism is connected with the discharge chamber, the grid system is installed on the end face, away from the tuning excitation mechanism, of the discharge chamber, one end of the ion source shell is connected with a neutralizer shell, and an annular neutralizer is installed in the neutralizer shell. According to the radio frequency ion source used for optical polishing processing, structure recombination is carried out based on a wide beam ion source excitation principle, a low-potential electric field is locally arranged so as to obtain a low-energy ion beam, and the discharge chamber, the accelerating electric field and the neutralizer are all embedded in the ion source, so that the structure of the ion source is more compact.

Description

Technical Field

[0001] The utility model belongs to the technical field of ion beam processing equipment, and in particular relates to a radio frequency ion source device used for optical polishing. Background Art

[0002] In recent years, with the continuous development of optical polishing technology, polishing methods have become more diversified, and polishing equipment has emerged one after another. Fluid polishing and non-contact polishing technology have become important means of ultra-precision optical polishing, and non-contact polishing uses ion beam polishing as the main surface finishing method.

[0003] The hot filament excitation source (Kaufman type) was the original design standard for the ion source. This ion source is easy to use, but requires frequent maintenance and is greatly limited in use in reactive gases. Therefore, researchers developed a radio frequency source (hereinafter referred to as "RF", Radio Frequency abbreviation) with filamentless plasma excitation, which better extends the service life and has better performance in reactive gases.

[0004] For micro or special-shaped optical parts, we need to remove the surface material of the component efficiently in a shorter time. Therefore, a wide beam RF source is the best. Inductively coupled plasma (ICP) or transformer coupled plasma heating (TCP) in the RF field is a very effective electrode-free excitation principle. RF power is transmitted to the plasma through the primary RF coil, and the plasma acts as the secondary part of the transformer.

[0005] In the field of ion beam processing, wide beam ion sources are usually used, such as ion beam etching (IBE), ion beam sputtering (IBS), ion beam implantation (IBI) and ion beam cleaning (IBC). Ion beam polishing is a processing form of ion sputtering. When processing ultra-precision optical components, the required surface accuracy is λ / 200 (λ=632.8nm) and the required surface roughness is 1nm. Therefore, a wide beam and low-energy RF ion source is required. The ion beam energy is 500eV~1500eV for the best. Too low ion beam energy will not achieve efficient surface removal, and too high ion beam energy will lead to secondary ion implantation.

[0006] Based on the characteristics of ion beam processing, this equipment requires a smaller ion source body as a "tool" to remove materials to achieve non-contact precision removal. The traditional RF ion source generates plasma through a discharge chamber, which is then accelerated by an accelerating electric field. A neutralizer is provided at the emission end to neutralize the electrons in the beam. Both discharge and neutralization require gas to enter. Therefore, the ion source body and the neutralizer are designed separately, with a complex structure and many restrictions on usage conditions. Utility Model Content

[0007] The purpose of the utility model is to:

[0008] In order to solve the problem that the existing radio frequency ion source equipment has a complex structure and limited use due to the separate design of the neutralizer, a radio frequency ion source equipment for optical polishing is provided. The structure is reorganized based on the excitation principle of a wide beam ion source, a low potential electric field is locally set to obtain a low energy ion beam, and the discharge chamber, the accelerating electric field and the neutralizer are all embedded in the ion source, making the structure of the ion source more compact.

[0009] The technical solution adopted by the utility model is as follows:

[0010] A radio frequency ion source device for optical polishing comprises an ion source housing, wherein a tuning excitation mechanism, a discharge chamber and a grid system are installed in the ion source housing, wherein the tuning excitation mechanism is connected to the discharge chamber, wherein the grid system is installed on an end face of the discharge chamber away from the tuning excitation mechanism, wherein one end of the ion source housing is connected to a neutralizer housing, wherein an annular neutralizer is installed in the neutralizer housing.

[0011] Furthermore, the neutralizer shell is a metal cylinder, a neutralizer cover is installed on the end face of the neutralizer shell, and the annular neutralizer includes a graphite ring connected to the inner wall of the neutralizer shell, a plurality of conductive columns are connected to the graphite ring, and a tungsten wire is connected to the conductive column.

[0012] Furthermore, a mounting flange is connected between the annular neutralizer and the neutralizer housing.

[0013] Furthermore, the tuning excitation mechanism includes an RF tuning unit and an RF excitation coil connected to each other, the RF tuning unit includes a matching capacitor connected to the inner wall of the ion source housing, the matching capacitor includes a ceramic shell on the outer surface and an internal copper electrode, the ceramic shell is connected to a capacitor device, the capacitor device is connected to a water-cooled copper plate, a permanent magnet is also connected to the end face of the ceramic shell, and an iron core is installed in the permanent magnet.

[0014] Furthermore, the capacitor device is connected to a radio frequency excitation coil, which is a copper coil spirally wound around the outer surface of the discharge chamber. The copper coil is wound around a hollow copper tube, and the cavity inside the copper coil is set as a cooling water flow cavity. The permanent magnet is installed on the periphery of the radio frequency excitation coil and the discharge chamber.

[0015] Furthermore, the discharge chamber includes a ceramic seat connected to the tuning excitation mechanism, a ceramic cavity is arranged in the ceramic seat, an auxiliary anode is installed at the center of the ceramic seat, and a part of the auxiliary anode extends to the inner wall of the ceramic cavity.

[0016] Furthermore, the grid system includes a shielding grid, an accelerating grid and a grounding grid arranged in sequence from the inside of the ceramic cavity to the outside of the ceramic cavity. The shielding grid, the accelerating grid and the grounding grid are connected to the inner wall of the ceramic cavity by bolts at intervals. The inner wall of the ceramic cavity is provided with an installation groove for installing the grid system.

[0017] Furthermore, annular insulating nets are respectively connected between the shielding grid, the accelerating grid and the grounding grid and the inner wall of the ceramic cavity, and ceramic balls are installed between adjacent insulating nets.

[0018] Furthermore, flange adjustment holes are provided on the shielding grid, the accelerating grid and the grounding grid, the ceramic balls are installed in the flange adjustment holes, and six ceramic balls are arranged between adjacent insulating nets.

[0019] In summary, due to the adoption of the above technical solution, the beneficial effects of the utility model are:

[0020] The utility model reorganizes the structure based on the excitation principle of a wide beam ion source, locally sets a low potential electric field to obtain a low energy ion beam, and embeds the discharge chamber, the accelerating electric field and the neutralizer inside the ion source, making the structure of the ion source more compact and more convenient for the extension of modern processing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the overall structure diagram of the radio frequency ion source device of the utility model;

[0022] Figure 2 It is a structural diagram of the tuning excitation mechanism of the utility model;

[0023] Figure 3 This is a structural diagram of the annular neutralizer of the utility model;

[0024] Figure 4 This is a schematic diagram of the overall structure and voltage of the discharge chamber of the utility model;

[0025] Figure 5 This is a structural diagram of the grid system and the ceramic seat of the utility model;

[0026] Figure 6 The utility model is a circuit structure diagram of the annular neutralizer.

[0027] Markings in the figure: 1-discharge chamber, 2-grid system, 3-RF excitation coil, 4-ceramic seat, 5-ceramic cavity, 6-auxiliary anode, 7-shielding grid, 8-acceleration grid, 9-grounding grid, 10-insulating mesh, 11-ceramic ball, 12-ion source housing, 13-tuning excitation mechanism, 14-neutralizer housing, 15-annular neutralizer, 16-graphite ring, 17-conductive column, 18-tungsten wire, 19-matching capacitor, 20-permanent magnet.

[0028] U BEA - beam voltage, U rf -RF voltage, U acc -acceleration gate voltage;

[0029] Neutralizer supply-neutralizer;

[0030] I fu - filament current;

[0031] U fu - Filament voltage;

[0032] U dis - Transmitter ring voltage;

[0033] I emi - emission current;

[0034] U bod - Voltage to ground. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the utility model more clear, the utility model is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the utility model and are not used to limit the utility model.

[0036] A radio frequency ion source device for optical polishing comprises an ion source housing 12, in which a tuning excitation mechanism 13, a discharge chamber 1 and a grid system 2 are installed, the tuning excitation mechanism 13 is connected to the discharge chamber 1, and the grid system 2 is installed on an end surface of the discharge chamber 1 away from the tuning excitation mechanism 13; one end of the ion source housing 12 is connected to a neutralizer housing 14, and an annular neutralizer 15 is installed in the neutralizer housing 14.

[0037] The neutralizer shell 14 is a metal cylinder, and a neutralizer cover is installed on the end surface of the neutralizer shell 14. The annular neutralizer 15 includes a graphite ring 16 connected to the inner wall of the neutralizer shell 14, and a plurality of conductive columns 17 are connected to the graphite ring 16, and a tungsten wire 18 is connected to the conductive column 17.

[0038] The neutralizer is set up so that when processing insulating samples, electrons need to be added to the electron beam to ensure current neutralization at the target. The neutralizer is heated by a dedicated DC power supply with a V-shaped tungsten filament 18 with a diameter of 0.5 mm and a total length of about 40 mm. Electrons are emitted from the filament and accelerated toward the neutralizer housing 14 by a discharge potential that is positive to the filament. The movement of gas in the neutralizer excites gas discharge, and some electrons are emitted through the 1 mm central aperture at the front end of the neutralizer. In order to provide sufficient electron emission, when in use, the voltage Ubod is set to a negative potential relative to the ground relative to the housing of the neutralizer.

[0039] Preferably, the annular neutralizer 15 can be designed to be directly installed internally or flange-mounted. The internal installation enables the ion source to have a more compact structural design, while the flange installation facilitates the replacement of the tungsten filament 18 .

[0040] The tuning excitation mechanism 13 includes an RF tuning unit and an RF excitation coil 3 connected to each other. The RF tuning unit includes a matching capacitor 19 connected to the inner wall of the ion source housing 12. The matching capacitor 19 includes a ceramic shell on the outer surface and an internal copper electrode. The ceramic shell is connected to a capacitor device, and the capacitor device is connected to a water-cooled copper plate. A permanent magnet 20 is also connected to the end face of the ceramic shell, and an iron core is installed in the permanent magnet 20.

[0041] The matching capacitor 19 provides impedance transformation between the RF generator and the electrical load through the power supply. The RF tuning unit consists of two very precise capacitors forming a capacitor device, which together with the RF excitation coil 3 forms an oscillation circuit. Through the installation of the capacitor, the power supply is supplied through the RF excitation coil 3 and connected to the insulated RF feed line.

[0042] The capacitor device is connected to the RF excitation coil 3, which is a copper coil spirally wound on the outer surface of the discharge chamber 1. The copper coil is wound by a hollow copper tube. The cavity inside the copper coil is set as a cooling water flow cavity. The permanent magnet 20 is installed on the periphery of the RF excitation coil 3 and the discharge chamber 1.

[0043] When the RF power source ionizes the gas to form plasma with different trajectories, divergent plasma is also generated, thereby reducing the ion density and affecting the focal plane energy of the final ion beam. Therefore, it is necessary to add a permanent magnet 20 with an iron core for superimposing the weak magnetic field of 0.15mT with the discharge device. The static magnetic field has a cylindrical geometry and causes the electrons in the discharge chamber 1 to perform cyclotron motion. This static magnetic field extends the electron path in the discharge and increases the ionization probability, which plays a vital role in the discharge process.

[0044] Both the capacitors and coils in the matching network require water cooling. For the capacitors, cooling is necessary to ensure extreme accuracy of the capacitance. The RF excitation coil 3 is not allowed to come into direct contact with the discharge plasma. RF power transfer is achieved by driving the secondary transformer current in the discharge. The spiral coil design is very susceptible to resistive heating, and to prevent this heating and thermal runaway, the mechanism is cooled by water flowing through the coil itself. Otherwise, if the coil becomes hot, its resistance increases, which will absorb more RF power and affect the fixed RF tuning.

[0045] The discharge chamber 1 includes a ceramic base 4 connected to the tuning excitation mechanism 13, a ceramic cavity 5 is arranged in the ceramic base 4, an auxiliary anode 6 is installed at the center of the ceramic base 4, and a part of the auxiliary anode 6 is extended to the inner wall of the ceramic cavity 5. The grid system 2 includes a shielding grid 7, an accelerating grid 8 and a grounding grid 9 arranged in sequence from the inside of the ceramic cavity 5 to the outside of the ceramic cavity 5, and the shielding grid 7, the accelerating grid 8 and the grounding grid 9 are connected to the inner wall of the ceramic cavity 5 by bolts in an interval shape, and the inner wall of the ceramic cavity 5 is provided with a mounting groove for mounting the grid system 2.

[0046] Annular insulating nets 10 are respectively connected between the shielding grid 7, the accelerating grid 8 and the grounding grid 9 and the inner wall of the ceramic cavity 5, and ceramic balls 11 are installed between adjacent insulating nets 10. Flange adjustment holes are provided on the shielding grid 7, the accelerating grid 8 and the grounding grid 9, and the ceramic balls 11 are installed in the flange adjustment holes. Six ceramic balls 11 are arranged between adjacent insulating nets 10.

[0047] The ceramic discharge chamber 1 is the main part of the ion source. In addition to containing the discharge plasma, the discharge chamber 1 is also used to provide gas supply and electrical contact, and to install the grid system 2. The permanent magnets 20 placed around the discharge chamber 1 ensure the electron confinement of the ionization, thereby reducing the operating pressure of the ion source and achieving a higher plasma density.

[0048] A planar auxiliary anode 6 made of graphite is mounted on the back of the cylindrical discharge chamber 1. The purpose of this anode is to fix the plasma potential, thereby controlling the energy of the generated ions and to evenly distribute the process gas in the discharge chamber 1.

[0049] The self-aligning grid system 2 is directly mounted on the ceramic cavity 5. Different grid series can be applied to achieve the best beam profile and the best grid life for each process. The grid system 2 is connected in a special groove at the front end of the ceramic cavity 5. The shielding grid 7 mesh is directly bolted to the ceramic cavity 5. The accelerating grid 8 mesh is suspended above the shielding grid 7 mesh, and a group of ceramic balls 11 are placed between the shielding grid 7 mesh and the accelerating grid 8 mesh. The ceramic balls 11 play the role of electrical insulation and mechanical adjustment between the grids. For proper power supply operation, such as low accelerator current, stable beam profile and low grid erosion rate, precise grid adjustment is required. Preferably, the grid system 2 of the RF ion source uses 6 ceramic balls 11 for self-alignment, and the ceramic balls 11 have two standard diameters Dsp=3.175mm (1 / 8") and Dsp=3.969mm (5 / 32"). The ceramic balls 11 are placed in the flange adjustment hole with a grid diameter dad=1.95mm. Furthermore, when a standard ball is used, the distances between the grids are fixed, dgr = 1.00 mm and dgr = 1.96 mm, respectively.

[0050] Depending on the total grid voltage applied, a spacing of 0.5 mm should be used as a minimum, otherwise charge shocks may form between the grids, with a maximum distance of 2 mm for the grid shocks. The distance between the grids affects the resulting beam performance.

[0051] Three bolts are required between the grids for fixing (two fixing bolts and one contact bolt). Two of the fixing bolts mount the grids on the ceramic cylinder. The last contact bolt is connected to the external cable and passes through the larger hole without contacting the internal grid. The contact bolt is fixed in the radial hole of the ceramic shell by a carbon roller.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A radio frequency ion source device for optical polishing, characterized in that: The invention comprises an ion source housing (12), wherein a tuning excitation mechanism (13), a discharge chamber (1) and a grid system (2) are installed in the ion source housing (12); the tuning excitation mechanism (13) is connected to the discharge chamber (1); the grid system (2) is installed on an end surface of the discharge chamber (1) away from the tuning excitation mechanism (13); one end of the ion source housing (12) is connected to a neutralizer housing (14); and an annular neutralizer (15) is installed in the neutralizer housing (14).

2. The radio frequency ion source device for optical polishing according to claim 1, characterized in that: The neutralizer shell (14) is a metal cylinder, a neutralizer cover is installed on the end surface of the neutralizer shell (14), and the annular neutralizer (15) comprises a graphite ring (16) connected to the inner wall of the neutralizer shell (14), a plurality of conductive columns (17) are connected to the graphite ring (16), and a tungsten wire (18) is connected to the conductive column (17).

3. A radio frequency ion source device for optical polishing according to claim 1 or 2, characterized in that: A mounting flange is connected between the annular neutralizer (15) and the neutralizer housing (14).

4. The radio frequency ion source device for optical polishing according to claim 1, characterized in that: The tuning excitation mechanism (13) comprises a radio frequency tuning unit and a radio frequency excitation coil (3) connected to each other, the radio frequency tuning unit comprises a matching capacitor (19) connected to the inner wall of the ion source housing (12), the matching capacitor (19) comprises a ceramic shell on the outer surface and a copper electrode inside, the ceramic shell is connected to a capacitor device, the capacitor device is connected to a water-cooled copper plate, and a permanent magnet (20) is also connected to the end surface of the ceramic shell, and an iron core is installed in the permanent magnet (20).

5. The radio frequency ion source device for optical polishing according to claim 4, characterized in that: The capacitor device is connected to a radio frequency excitation coil (3); the radio frequency excitation coil (3) is a copper coil wound in a spiral shape on the outer surface of a discharge chamber (1); the copper coil is wound by a hollow copper tube; the cavity inside the copper coil is set as a cooling water flow cavity; the permanent magnet (20) is installed on the periphery of the radio frequency excitation coil (3) and the discharge chamber (1).

6. The radio frequency ion source device for optical polishing according to claim 1, characterized in that: The discharge chamber (1) comprises a ceramic base (4) connected to a tuning excitation mechanism (13), a ceramic cavity (5) being arranged in the ceramic base (4), an auxiliary anode (6) being installed at the center of the ceramic base (4), and a part of the auxiliary anode (6) extending to the inner wall of the ceramic cavity (5).

7. The radio frequency ion source device for optical polishing according to claim 6, characterized in that: The grid system (2) comprises a shielding grid (7), an accelerating grid (8) and a grounding grid (9) which are arranged in sequence from the inside of the ceramic cavity (5) to the outside of the ceramic cavity (5); the shielding grid (7), the accelerating grid (8) and the grounding grid (9) are connected to the inner wall of the ceramic cavity (5) by bolts at intervals; and a mounting groove for mounting the grid system (2) is provided on the inner wall of the ceramic cavity (5).

8. The radio frequency ion source device for optical polishing according to claim 7, characterized in that: The shielding grid (7), the accelerating grid (8) and the grounding grid (9) are respectively connected to the inner wall of the ceramic cavity (5) with an annular insulating net (10), and ceramic balls (11) are installed between adjacent insulating nets (10).

9. The radio frequency ion source device for optical polishing according to claim 8, characterized in that: The shielding grid (7), the accelerating grid (8) and the grounding grid (9) are provided with flange adjustment holes, the ceramic balls (11) are installed in the flange adjustment holes, and six ceramic balls (11) are arranged between adjacent insulating nets (10).

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