Device and method for generating ions using a plasma

Abstract

A device provides a simple and safe way of generating ions. The ions generated can be mixed and/or neutralized simply and without many additional parts and equipment. The device (10) required for this purpose is very compact and inexpensive since only one excitation system (44) is required for two spatially and/or electrically separated regions (24, 26) of a plasma vessel (20). In this way, at least one complete excitation system can be dispensed with, resulting in additional space and more degrees of freedom (e.g. in the movement of the device itself). The device (10) can be used both as an ion engine and for material processing, and is therefore universally applicable, it being possible to precisely adjust the kinetic energy via the grid system (28, 30) and the current density via the gas flow and the power of the plasma excitation.

Claims

1.-10. (canceled)

11. A device (10) for generating ions by a plasma, comprising: a first chamber (24) which serves for ion extraction and which is surrounded by an induction coil (46) for generating the plasma; and a second chamber (26) which serves for extraction of further charged particles which have been generated by a further plasma, the second chamber (26) also being surrounded by the induction coil (46), wherein the induction coil (46) feeds both the plasma in the first chamber (24) and the further plasma in the second chamber (26), and wherein the first chamber (24) and the second chamber (26) are arranged inside the induction coil (46).

12. The device (10) according to claim 11, wherein the first chamber (24) is arranged concentrically around the second chamber (26).

13. The device (10) according to claim 11, wherein the first chamber (24) is electrically insulated from the second chamber (26).

14. The device (10) according to claim 13, wherein the first chamber (24) and/or the second chamber (26) has an electrically insulating wall material (22).

15. The device (10) according to claim 14, wherein the electrically insulating wall material (22) is a ceramic material.

16. The device (10) according to claim 11, wherein the first chamber (24) and/or the second chamber (26) have an extraction opening (27, 40).

17. The device (10) according to claim 16, wherein the extraction opening (27) has at least one aperture (32).

18. The device (10) according to claim 16, wherein at least one grid (28, 30) is arranged in the extraction opening (27).

19. The device (10) according to claim 16, wherein a grid system is arranged in the extraction opening (27).

20. The device according to claim 19, wherein the grid system has a bias grid (28) and an extraction grid (30).

21. The device according to claim 19, wherein the grid system has a bias grid (28) in form of a molybdenum foil, an extraction grid (30), and one or more further grids.

22. The device (10) according to claim 19, wherein the second chamber (26) serves for electron extraction and thereby forms a neutralizer for the ions generated, or wherein the second chamber (26) serves for further ion extraction.

23. The device (10) according to claim 11, wherein the second chamber (26) is arranged in the first chamber (24).

24. A method for generating ions by a plasma, comprising: providing a first chamber (24) which serves for ion extraction and which is surrounded by and arranged inside an induction coil (46); and generating and extracting further charged particles in a second chamber (26), wherein the further charged particles are generated by a further plasma, and wherein the induction coil (46) feeds both the plasma in the first chamber (24) and the further plasma in the second chamber (26).

25. The method according to claim 24, wherein the plasma is generated by applying a frequency from 0.9 to 100 MHz to the induction coil (46).

26. The method according to claim 24, further comprising generating electrons in the second chamber (26) and extracting the electrons from the second chamber (26) to neutralize ions generated in the first chamber (24).

27. The method according to claim 26, further comprising using neutralized ions in an ion beam source for material processing or in an ion engine.

28. The method according to claim 24, further comprising generating further ions in the second chamber (26), extracting the further ions from the second chamber (26), and mixing the further ions with the ions generated in the first chamber (24).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 shows the device for ion generation according to a preferred configuration in a perspective view from the front,

[0030] FIG. 2 shows the device according to FIG. 1 in a perspective view from behind,

[0031] FIG. 3 shows the device according to FIG. 1 in plan view from the front and

[0032] FIG. 4 shows the device according to FIG. 1 in a sectional view.

DETAILED DESCRIPTION

[0033] FIGS. 1 to 4 show the device 10 for generating ions according to a preferred configuration in various views.

[0034] As can be seen, the device 10 has a housing 12 which comprises a front 14, a rear wall 16 and struts 18 connecting them. A plasma vessel 20 is arranged between the front 14 and the rear wall 16. The front 14 forms the end of the plasma vessel 20 and centres and fixes it.

[0035] The plasma vessel 20 is integrally connected to a coaxial wall formation 22 which encloses a first discharge chamber 24 in a first annular section and encloses a second discharge chamber 26 in a second cylindrical section. These discharge chambers 24, 26 are thus spatially separated from each other.

[0036] Preferably, the discharge chambers 24, 26 are approximately 40 mm in length, the first discharge chamber 24 is 40 mm in diameter and the second discharge chamber 26 is 14 mm in diameter.

[0037] The first discharge chamber 24 has an extraction opening 27 which is defined by the wall 22 and the front 14 and which is closed by a perforated foil 28 acting as a screen grid, which is preferably a molybdenum foil. This perforated foil 28 is preferably 0.2 mm thick. This perforated foil 28 is kept at a potential of 1.4 to 1.5 keV and thus draws a beam current of approximately 20 mA. This perforated foil 28 thus acts as a bias grid.

[0038] The wall formation 22 preferably consists of an insulator, in particular of a ceramic, so that the two discharge chambers 24, 26 are electrically insulated from one another.

[0039] An extraction grid 30 having numerous apertures 32 is arranged in front of the perforated foil 28 at a small distance of, for example, 0.5 mm. This extraction grid 30 is preferably made of graphite and is 1 mm thick. It is at a potential of approximately 400 eV, the ions generated thereby being extracted and accelerated through the apertures 32.

[0040] The connections 28a, 30a are provided for applying the respective potential to the perforated foil 28 and the grid 30.

[0041] The second discharge chamber 26 is closed by the rear cover 34, in which the central gas inlet 36 for the second discharge chamber 26 and the gas inlet 38 for the first discharge chamber 24 are located. The gas inlet 36 for the second discharge chamber is designed to be electrically conductive so that a potential could be applied to it. This allows the positive charges to be discharged during the extraction of electrons. In addition, the electrons generated in the second discharge chamber 26 could thereby be accelerated if necessary.

[0042] At the front, there is a hole 40 that is 0.5 mm in diameter in the wall formation 22. The electrons generated in the second chamber 26 are extracted through this hole 40. No separate grid is required for this because the ions generated in the first chamber 24 build up a space charge zone, that latter pulling the electrons generated in the second chamber 26 out through the hole 40 via a plasma bridge. Very high currents of approximately 20 mA flow here. This corresponds to the beam current drawn off via the foil 28, so that the total charge is balanced again. The design of the device 10 thus guarantees that the same amount of current of ions and electrons is generated. The electrons extracted from the hole 40 neutralize the ions extracted from the first chamber 24.

[0043] In principle, all typical working gases, that is to say all ionizable gaseous species such as noble gases, oxygen, nitrogen and reactive gases, can be used as working gases for ion generation. As far as an ion engine is concerned, xenon and krypton are usually used. The electrons can be generated using the same working gas or a different one, for example a lighter one in space travel, because this gas does not have to be used for thrust and therefore weight could be saved.

[0044] Instead of a single hole 40, several holes could also be used. Alternatively or additionally, an accelerating grid for the electrons could be used.

[0045] Windings 44 of an induction coil 46 are placed around the outer wall shape 22 in corresponding recesses 42, which serve to generate plasma in the two chambers 24, 26. Since both chambers 24, 26 are located within the induction coil 46, both discharges are fed by a single excitation, these being are operated independently of each other due to the electrical insulation. A high frequency, preferably in the range from 0.9 to 100 MHz, is applied to the induction coil 46 via the electrical connection 48a, 48b. Thus, due to the spatial arrangement of the two plasma spaces in the chambers 24, 26, only one induction coil 46 and one high frequency supply (not shown) are required to excite both discharges, which considerably reduces the complexity of the system. In addition to the common coil geometries such as cylinder, cone and planar coils, other cross-sectional shapes such as rectangles, trapezoids or any round and n-sided shapes are also possible, it being possible for the geometric dimensions thereof also to vary along the longitudinal axis L of the device 10.

[0046] The device for generating ions has been explained above using an example in which the second chamber 26 is arranged coaxially within the first chamber 24. The first chamber could also be arranged coaxially within the second chamber. In addition, any other arrangements and geometries of the two chambers could be used, two or more first chambers and/or two or more second chambers could also be used. These first and second chambers could each generate different charged particles. It is essential that the first chamber and the second chamber have separate discharges, but are fed by the same excitation.

[0047] Furthermore, the device has been described using an example in which the ions generated in the first chamber 24 are neutralized by electrons generated in the second chamber 26.

[0048] Alternatively, ions could likewise also be generated in the second chamber, it being possible for these to be a different ion species.

[0049] In addition, there could be several different first chambers in which different ion species are generated and there could be one or more second chambers for generating electrons for their neutralization.

[0050] It is clear from the above that the present disclosure provides a simple and safe way to generate ions. The ions generated can be mixed and/or neutralized simply and without many additional parts and equipment. The device required for this purpose is very compact and inexpensive since only one excitation system is required for two spatially and/or electrically separated regions 24, 26 of a plasma vessel 20. In this way, at least one complete excitation system can be dispensed with, resulting in additional space and more degrees of freedom (e.g. in the movement of the device itself). The device 10 can be used both as an ion engine and for material processing, and is therefore universally applicable, it being possible to precisely adjust the kinetic energy via the grid system 28, 30 and the current density via the gas flow and the power of the plasma excitation.

[0051] When used as an ion engine, the device 10 simultaneously generates a beam of positive ions and electrons neutralizing them, the current intensity thereof being identical in magnitude. Due to the law of conservation of momentum, the ion beam generates the necessary thrust for the missile and the electrons carry away the excess negative charges created by the ion generation in the plasma, thus preventing the missile from becoming charged. Since the electron beam largely exits in the direction of the ion beam, a good coupling between ions and electrons and a continuous beam neutralization is achieved.

[0052] When used as an ion source in the processing of materials, the device 10 likewise simultaneously generates a beam of positive and negative charge carriers. These can then be used on electrically insulating materials (substrates or targets). They are incident on the surface there and lead to interaction processes, such as material removal, layer and surface modification and, as a side effect, to layer growth. Because the same number of positive and negative charge carriers are incident on the material, charging of the material is avoided, which in the case of electrically insulating materials would otherwise lead to repulsion of the ions and consequently to an unstable process.

[0053] Individual features from the description of an exemplary embodiment do not necessarily have to be combined with one or more or all of the other features specified in the description of that exemplary embodiment; in this regard, each sub-combination is expressly also disclosed. In addition, physical features of a device can also be reformulated and used as process features, and process features can be reformulated and used as physical features of a device. Such a reformulation is therefore automatically also disclosed.

LIST OF REFERENCE SYMBOLS

[0054] 10 Device for generating ions according to a preferred configuration [0055] 12 Housing [0056] 14 Front [0057] 16 Rear wall [0058] 18 Struts [0059] 20 Plasma vessel [0060] 22 Wall formation [0061] 24 First discharge chamber, first chamber [0062] 26 Second discharge chamber, second chamber [0063] 27 Opening in first discharge chamber 24, extraction opening [0064] 28 Perforated foil, bias grid or screen grid [0065] 28a Connection for perforated foil 28 [0066] 30 Extraction grid [0067] 30a Connection for extraction grid 30 [0068] 32 Apertures [0069] 34 Cover [0070] 36 Central gas inlet for the second discharge chamber 26 [0071] 38 Gas inlet for the first discharge chamber 24 [0072] 40 Hole in second discharge chamber 26, extraction opening [0073] 42 Recesses in the outer wall shape 22 [0074] 44 Windings [0075] 46 Induction coil [0076] 48a, 48b High frequency electrical connection of the induction coil 46 [0077] L Longitudinal axis of the device 10