Source d’ions

Abstract

Ion source The present description relates to a charge separation ion source device (100) comprising:- a cyclotron resonance electron source (110);- an electron impact source (130). Figure for abstract: Fig. 1A

Description

Title of the invention: Ion source Technical field

[0001] The present description relates generally to ion sources and more particularly to charge-separated ion sources.

[0002] The present description applies to all technical fields in which charge-separated ion sources are likely to be used, including applications involving neutralization, electron chemistry, high-power electron beams, etching, sputtering, surface activation, beam lines, accelerators, mass spectroscopy, surface figuring, surface modification, etc. Prior art

[0003] There are electron beam ion sources, or electron impact ion sources, which are supplied with electrons by emissive filaments, or cathodes, under vacuum. Documents US10176977B2, US6717155B1, US11004649B2 describe electron impact ion sources. Summary of the invention

[0004] There is a need for improvement of electron beam ion sources.

[0005] One embodiment overcomes all or part of the drawbacks of known ion sources.

[0006] One embodiment provides a charge-separated ion source device comprising: - a cyclotron resonance electron source; - an electronic impact source.

[0007] One embodiment provides a method for generating ions using a charge-separated ion source device comprising: - a cyclotron resonance electron source; - an electronic impact source.

[0008] The following embodiments may be applied to the device and / or the method.

[0009] According to one embodiment, the outer diameter of the electron source is less than the inner diameter of the electron impact source, at least in portions of the electron source and the electron impact source facing each other.

[0010] According to one embodiment, the difference between the inner diameter of the electron impact source and the outer diameter of the electron source is such that one end of the electron source penetrates into the electron impact source.

[0011] According to one embodiment: - the electron source and the electron impact source are arranged along an axis of circulation of an electron beam coming from the electron source; - the electron source comprises a microwave cavity around the axis and a first set of magnets positioned around the microwave cavity, the first set of magnets being configured to generate a resonant magnetic field, for example an axial magnetic field; and - the electron impact source comprises an ionization chamber around the axis and a second set of magnets positioned around the ionization chamber, the second set of magnets being configured to generate a magnetic field for compressing the electron beam around the axis, for example an axial magnetic field.

[0012] According to one embodiment, the first set of magnets comprises a plurality of magnets, for example permanent magnets, circumferentially spaced from each other around the microwave cavity and / or the second set of magnets comprises a plurality of magnets, for example permanent magnets, circumferentially spaced from each other around the ionization chamber.

[0013] According to one embodiment, an axial end of the first set of magnets penetrates an axial end of the second set of magnets.

[0014] According to one embodiment, the resonance magnetic field has, in the electron source, a first axial orientation, and the compression magnetic field has, in the electron impact source, a second axial orientation opposite the first axial orientation.

[0015] According to one embodiment, the relative axial positioning of the first set of magnets and the second set of magnets is defined so that a leakage field of the resonance magnetic field and the compression magnetic field are oriented in the same direction, for example in an area between the electron source and the electron impact source.

[0016] According to one embodiment, a multipolar field is superimposed on the compression magnetic field, for example so as to inject into the electron beam a mirror field superimposed on the multipolar field, or a minimum B.

[0017] According to one embodiment, the microwave cavity is adapted to be polarized at a first voltage and the ionization chamber is adapted to be polarized at a second voltage.

[0018] According to one embodiment, the first voltage is lower than the second voltage.

[0019] According to one embodiment, the ion source device further comprises an electron extractor between the electron source and a first end of the electron impact source, the electron extractor being adapted to be biased at a third voltage, the electron extractor being for example included in the electron source.

[0020] According to one embodiment, the third voltage is defined to accelerate electrons, or to decelerate electrons and deplete ions.

[0021] According to one embodiment, the ion source device further comprises an ion extractor positioned at a second end of the electron impact source opposite the first end, the ion extractor being adapted to be biased at a fourth voltage, the ion extractor being for example included in the electron impact source.

[0022] According to one embodiment, the fourth voltage is lower than the first voltage. Brief description of the drawings

[0023] These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments given without limitation in relation to the attached figures among which:

[0024] [Fig.1A] is a longitudinal sectional view schematically showing an ion source device according to one embodiment;

[0025] [Fig.lB] is a longitudinal sectional view showing details of the ion source device of [Fig.lA];

[0026] [Fig.2A] is a three-dimensional view showing an exemplary embodiment of an ion source device according to one embodiment;

[0027] [Fig.2B] is a three-dimensional longitudinal sectional view of the ion source device of [Fig.2A];

[0028] [Fig.2C] is a longitudinal sectional view of the ion source device of [Fig.2A];

[0029] [Fig.3] schematically illustrates an example of implementation of an ion source device according to one embodiment, as well as a trajectory of an electron beam in this ion source device;

[0030] [Fig.4A], [Fig.4B] and [Fig.4C] schematically illustrate alternative electron beam trajectories in an ion source device according to one embodiment, such as the ion source device of [Fig.3], in different configurations;

[0031] [Fig.5] schematically illustrates another electron beam trajectory in an ion source device according to one embodiment, such as the ion source device of [Fig.3];

[0032] [Fig.6A] shows graphs illustrating axial profiles of the axial magnetic field in an ion source device according to one embodiment in two different configurations corresponding to Figures 4B and 4C;

[0033] [Fig.6B] represents graphs illustrating axial profiles of the intensity of the magnetic field respectively in the electron source (resonance magnetic field) and in the electron impact source (compressing axial magnetic field);

[0034] [Fig.7A], [Fig.7B] and [Fig.7C] schematically illustrate examples of operation of an ion source device according to one embodiment, such as the ion source device of [Fig.3], according to different operating parameters; and

[0035] [Fig.8A] and [Fig.8B] schematically illustrate examples of charge separation in an ion source device according to one embodiment, such as the ion source device of [Fig.3], according to different operating parameters. Description of the embodiments

[0036] The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

[0037] For the sake of clarity, only the steps and elements useful for understanding the embodiments described have been represented and are detailed.

[0038] Unless otherwise specified, when referring to two elements connected to each other, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") to each other, this means that these two elements can be connected or be connected by means of one or more other elements.

[0039] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures or to an ion source device in a normal position of use.

[0040] Unless otherwise specified, the expressions "about", "approximately", "substantially", and "of the order of" mean to within 10% or 10°, preferably to within 5% or 5°.

[0041] In the following description, when referring to an axial magnetic field, reference is made to the axial component of the magnetic field, i.e., the component in the direction of the axis of the ion source device. This axial direction corresponds to the direction X identified in FIGS. 1A to 2C.

[0042] In the following description, a length corresponds to a dimension taken in the axial direction.

[0043] There are electron beam ion sources, or electron impact ion sources, in which an ionization chamber is supplied with electrons by a vacuum electron source comprising a cathode, for example an emissive filament, which is heated to emit electrons. The emitted electrons are then collimated and accelerated into an electron beam and attracted into the ionization chamber under the influence of a potential difference imposed between the cathode and an anode positioned at the entrance to the ionization chamber.

[0044] This ion source technology induces limitations, in particular by the need to have a vacuum, with a pressure generally having to be less than or equal to 10 4 mbar. This upper limit of the pressure can have the consequence of limiting the ionization rate of the gas in the ionization chamber.

[0045] An electron beam ion source is therefore sought which can operate at lower pressures, typically greater than 10 4 mbar, for example between 10 2 mbar and 10 1 mbar. More generally, an electron beam ion source is sought which can operate over a wide pressure range.

[0046] Advantageously, the ion sources in question must be able to operate with low energy electrons, for example an energy of between 10 eV and 1000 eV.

[0047] One of the objectives pursued by the embodiments is to increase the sensitivity, intensity and brightness of the ions produced in an ion source.

[0048] [Fig.lA] is a longitudinal sectional view schematically showing an ion source device 100 according to one embodiment. [Fig.lB] is a longitudinal sectional view showing details of the ion source device of [Fig.lA],

[0049] The ion source device 100 has an overall geometry or configuration arranged about an axis 102. In operation, the ion source device 100 produces a beam of electrons El, as well as ions II, along the axis 102.

[0050] The device 100 comprises an electron source 110, an electron extraction zone 120, an electron impact source 130 including an ionization chamber 135, an ion extraction and electron repulsion zone 140, referred to for short as the "ion extraction zone", and an ion exit zone 150.

[0051] The electron source 110 is of the electron cyclotron resonance type. Electron cyclotron resonance (ECR) can be referred to as cyclotron resonance. Cyclotron resonance is defined as the movement of an electron in a magnetic field, synchronous with the frequency of an electromagnetic wave.

[0052] In practice, generally, a static magnetic field and a high-frequency electromagnetic field are superimposed at the resonance frequency of the electron cyclotron. In a known manner, for an electromagnetic field of frequency 2.45 GHz, the resonance condition is fulfilled when the intensity of the magnetic field is equal to 0.0875 Tesla (T).

[0053] The electron source ECR 110 comprises a coupling antenna in an enclosure 115, designated cavity or microwave cavity (antenna not shown in FIGS. 1A and 1B but visible in FIGS. 2B and 2C). The coupling antenna is excited by a high-frequency electromagnetic field, and is connected to a microwave power injector 113. A gas inlet 112 allows the introduction of gas into the cavity 115 for the generation of gas or metal vapor plasma, for example rare gas, oxygen, or cesium vapor.

[0054] A set of magnets 111 (first set of magnets) is arranged around the cavity 115. The set of magnets 111 is configured to generate a resonance magnetic field B1 in the cavity 115. Preferably, the magnetic field B1 is axial, and has at least in certain axial positions, an intensity corresponding substantially to the electron cyclotron resonance, for example an intensity of 0.0875 T for a frequency of 2.45 GHz.

[0055] The pressure PI inside the cavity 115 of the electron source ECR 110 may, for example, be between 105 and 10 1 mbar, or even between 10 4 and 10 1 mbar. Unlike a heated filament electron source, it is not necessary for the electron source ECR to be in a high vacuum below 10 4 mbar. In some cases, the cavity 115 may be connected to a vacuum pump 104, to obtain a vacuum preferably above 10 4 mbar. In other cases, a pump connected to the ionization chamber 135 is sufficient to create the required vacuum level in the cavity 115.

[0056] The cavity 115 has a length L1 along the axis 102. As a non-limiting example, the length L1 of the cavity 115 is equal to approximately 3 cm.

[0057] The cavity 115 is connected to a voltage source to be biased to a voltage Veiec (first voltage).

[0058] The electron extraction zone 120 is provided at the exit of the electron source 110 in the direction of the axis 102 and is adapted to extract an electron beam El from the electron source 110 and direct it towards the ionization chamber 135.

[0059] The electron extraction zone 120 may comprise an electron extraction electrode 121, or electron extractor. The electron extraction electrode 121 may also form an ion repeller, for example in the case of backscattering of ions from the ionization chamber 135 to the electron source 110, to repel the ions towards the ionization chamber 135. The electron extraction electrode 121 is connected to a voltage source to be biased at a voltage Vrepei (third voltage) corresponding to an electron extraction voltage, or an ion repulsion voltage.

[0060] The electron extraction zone 120 may comprise another electrode 122, which may be designated as the inlet electrode of the ionization chamber, for short, inlet electrode.

[0061] Each electrode, which may be in the form of a wall or a plate, comprises an orifice or a slot for the passage of the electron beam in the direction of the axis 102.

[0062] The electron extraction electrode 121 may be included in the electron source 110. Alternatively, the electron extraction electrode 121 may be positioned after the output of the electron source 110.

[0063] The input electrode 122 is generally included in the ionization chamber 135, for example it forms an input diaphragm of the ionization chamber 135. The input electrode 122 is generally polarized at the ionization voltage Vion of the ionization chamber 135.

[0064] The electrodes 121 and 122 may form an electron beam collimator and / or a pressure regulator between the microwave cavity 115 and the ionization chamber 135.

[0065] In some cases, electrode 121 and / or electrode 122 may be omitted, as seen in [Fig.lB] where both electrodes are omitted.

[0066] The ionization chamber 135 is positioned at the outlet of the electron extraction zone 120 along the axis 102. The ionization chamber 135 has a length L2 along the axis 102 from a first end 135A to a second end 135B. The length L2 of the ionization chamber 135 is generally determined as a function of the gas introduced and the efficiency of the desired ionization. A compromise between the pressure P3 in the ionization chamber 135, its length L2 and the energy of the electrons can be determined in order to optimize the probability of ionization of a gas. given. As a non-limiting example, the length L2 of the ionization chamber 135 is greater than or equal to 5 cm, for example equal to approximately 8 cm.

[0067] The ionization chamber 135 has an inlet at its first end 135A through which the electron beam E1 enters the ionization chamber during operation of the device. This inlet generally corresponds to the orifice, or slot, 122A of the input electrode 122. The ionization chamber 135 has an outlet at its second end 135B through which an ion beam II, generally trapped in the electron beam E1, exits the ionization chamber 135 along the axis 102 during operation of the device. This outlet may correspond to the orifice, or slot, 141A of the ion extraction electrode 141 described later. An electron beam E2 can also exit the ionization chamber 135, but it is then decelerated and repelled by the effect of the polarization of other electrodes, as explained later.

[0068] The ionization chamber 135 is part of the electron impact source 130 which comprises a set of magnets 131 (second set of magnets) positioned around the ionization chamber 135, for example in a substantially coaxial manner. The set of magnets 131 is configured to generate a substantially axial, possibly uniform, magnetic field B3 in the ionization chamber 135, so as to focus and compress the electron beam El along the axis 102.

[0069] Thus, the ionization chamber 135 can be subjected to a magnetic field mainly parallel to the initial velocity of the electrons.

[0070] The magnetic field B3 is adapted to magnetically constrain the electron beam so that the electron beam is radially compressed around the axis 102. Thus, the magnetic field B3 can be referred to as the axial compression magnetic field, for short, the axial compression field, or the compression magnetic field. The ion beam II can also be compressed to the extent that it is trapped inside the electron beam before the charge separation between the ions and the electrons.

[0071] Optionally, a multipolar field can be superimposed on the compression magnetic field, for example so as to inject the electron beam into a so-called "minimum B" magnetic field (mirror field superimposed on the multipolar field).

[0072] The set of magnets 131 has a length L3 along the axis 102, which is advantageously greater than the length L2 of the ionization chamber 135. By way of non-limiting example, the length L3 of the set of magnets 131 is equal to approximately 10 cm.

[0073] The electron impact source 130 further comprises a gas inlet 132 allowing the introduction of a gas of a chosen species into the ionization chamber. 135. The molecules of the gas form the parent species of the ions whose formation is intended during the operation of the ion source device 100, and no other restrictions on the nature of the gas used apply.

[0074] The pressure P3 inside the ionization chamber 135 may, for example, be between 107 and 10 1 mbar. For example, a high pressure may be preferred to allow the presence of a large number of gas molecules inside the ionization chamber during operation of the device. In order to maintain the pressure P3 in the ionization chamber 135, the latter may be sealed using sealing means such as O-rings of appropriate dimensions and shapes. Furthermore, the ionization chamber 135 is preferably connected to a vacuum pump 103 to adjust this pressure.

[0075] The ionization chamber 135 is connected to a voltage source to be polarized to an ionization voltage Vion (second voltage).

[0076] Each set of magnets 111, 131 may comprise permanent magnets. Alternatively, at least one of the sets of magnets 111, 131 may comprise electromagnets, for example electromagnetic coils.

[0077] The ion extraction zone 140 is located near the second end 135B of the ionization chamber 135, and comprises a set of electrodes 14. All or part of the electrodes 141, 142, 143 of this set of electrodes 14 can form an element for focusing the ion beam, in particular a geometry known as an "Einzel lens".

[0078] The ion extraction zone 140 may at least partly be included in the electron impact source 130, for example in the ionization chamber 135. For example, the second end 135B of the ionization chamber may include all or part of the electrode assembly 14. Thus, the ionization chamber may be equipped with one or more electrodes.

[0079] The electrode assembly 14 is configured, among other things, to direct the ion beam II out of the ionization chamber 135 along the axis 102 and to replenish the electron beam E2 which leaves the ionization chamber 135 in order to return it towards the electron source 110. The ions and the electrons can thus be separated (charge separation).

[0080] For this purpose, the electrode assembly 14 preferably comprises a plurality of electrodes which can be independently polarized by voltage sources, an electrode of this electrode assembly being able to be grounded.

[0081] In the embodiment illustrated, by way of non-limiting example, the set of electrodes 14 comprises in order between the inlet and the outlet of the ion extraction zone 140: - an ion extraction electrode 141, or ion extractor, connected to a voltage source to be polarized at an extraction voltage Vextract corresponding to an ion extraction voltage (fourth voltage); - an electrode 142, which can be designated a focusing electrode, connected to a voltage source to be polarized at a focusing voltage Vfocus of the ion beam; - an electrode 143 which is connected to ground, which can be designated ground electrode.

[0082] The focusing electrode 142 may be omitted, as can be seen in [Fig.lB]. The ground electrode 143 may also be omitted.

[0083] The ion extraction electrode 141 may also form an electron repulsor. Thus, the extraction voltage VeXtract may also be an electron repulsion voltage to return an electron beam E3 towards the electron source 110.

[0084] Each electrode, which may be in the form of a wall or a plate, comprises an orifice or a slot for the passage of an ion beam or an electron beam in the direction of the axis 102.

[0085] The ion exit zone 150 is located at the exit of the ion extraction zone 140 along the axis 102. Downstream of the ion exit zone 150, the extracted ion beam II can be introduced into a downstream device, such as a processing or analysis device, for example mass spectroscopy, implantation, secondary ion spectroscopy (SIMS) or focused ion beam (FIB) systems.

[0086] An example of a method for implementing the ion source device 100 is described below. This example is non-limiting and the person skilled in the art will be able to adapt the method of implementation, and in particular the different polarization voltages.

[0087] To produce positively charged ions, a positive voltage +Veiec is applied to the microwave cavity 115 and a positive voltage +Vion is applied to the ionization chamber 135, +Veiec being less than +Vion. Thus, the extraction of electrons is done using a positive voltage +Veiec but less than the polarization voltage +Vion of the ionization chamber.

[0088] The electron energy is determined by the difference between Vion and Veiec to the extent that this difference is significantly greater than the self-energy dispersion of the electrons in the ECR plasma of the electron source (generally of the order of a few eV).

[0089] The electron source 110 may use so-called "accel-decel" extraction using the electron extraction electrode 121 biased at the voltage Vrepei which can be set to accelerate the electrons (accel), or to decelerate the electrons (decel) so as to deplete ions. To do this, we can apply a positive voltage +Vrepei greater than +Vion and a positive voltage +Vrepei greater than +Veiec-

[0090] To control the quantity of extracted ions, and thus the ionic intensity produced, one can act on the extraction voltage Vextract. For example, if one applies a positive voltage +Vextract lower than +VeieC, the voltage +Vion is higher than +Vextract: the electrons can be repulsed in the gap gl between the ionization chamber 135 and the ion extraction electrode 141. On the other hand, if one applies a positive voltage +Vextract higher than +VeieC, the voltage +Vion being lower than +Vextract, the ions can be partially repulsed in the gap gl (one can thus measure the extracted ions by returning a portion of the ion beam towards the electron source), then the electrons can be repulsed in the gap g2 between the ion extraction electrode 141 and the ground electrode 143, but accelerated in the gap gl.

[0091] The ion source device 100 is also adapted to produce and extract negative ions. In this case, a negative voltage -Veiec is applied to the microwave cavity 115 and a negative voltage -Vion is applied to the ionization chamber 135, -Veiec being less than -Vion. The ionization chamber 135 then becomes a charge exchange zone.

[0092] More generally, it is possible to act on the differences between the different voltages VeieC, Vion , Vextract, or even Vrepei so that the ion beam II is directed at the output of the electron impact source 130, and so that the electron beam El, after its extraction from the electron source 110 in the ionization chamber 135 and after separation with the ion beam II, is repelled towards the electron source 110.

[0093] For example, the bias voltage Vextract (extraction voltage) of the ion extraction electrode 141 can be set around the bias voltage Veiec of the electron source 110. This allows the location of the electron / ion separation zone to be controlled.

[0094] In the ion source device 100 of FIGS. 1A and 1B, the magnet assembly 131 of the electron impact source 130 at least partially surrounds the electron source 110 (cover portion LR described later). As explained later, this allows continuity of the axial magnetic field intensity between the microwave cavity 115 (resonance magnetic field B1) and the ionization chamber 135 (axial compression field B3).

[0095] [Fig.2A] is a three-dimensional view showing an exemplary embodiment of an ion source device according to one embodiment. [Fig.2B] is a three-dimensional longitudinal sectional view of the ion source device of [Fig.2A]. [Fig.2C] is a longitudinal sectional view of the ion source device of [Fig.2A].

[0096] The ion source device 100 of FIGS. 2A to 2C is similar to that of FIGS. 1A and 1B which are schematic and simplified figures, and it retains the same reference. The elements common to all these figures also retain the same references.

[0097] [Fig.2A] shows in a little more detail the gas inlets 112 and 132 respectively of the electron source 110 and the electron impact source 130, as well as the sources of the voltages VeieC, Vion, VeXtract respectively of the microwave cavity 115, the ionization chamber 135 and the ion extraction electrode 141. Optionally, voltage sources (not shown) can be provided to also allow the generation of the voltage Vfocus of the focusing electrode 142 and the voltage Vrepei of the electron extraction electrode 121. [Fig.2A] also shows the microwave power injector 113.

[0098] Figures 2B and 2C show the interior of the electron source 110 with the microwave cavity 115 in which the coupling antenna 116 is arranged. The coupling antenna 116 comprises an end 116A stopping before the entrance to the ionization chamber 135, i.e. before the first end 135A of the ionization chamber.

[0099] The electron source 110 further comprises a coupler 114 connected to the microwave power injector 113, the coupling antenna 116 extending inside the coupler 114. The coupler is adapted to transfer the high frequency electromagnetic field into the microwave cavity 115, and it can be designated an isolator coupler insofar as it can isolate the coupling antenna 116 from the high voltage.

[0100] Figures 2B and 2C also show the interior of the electron impact source 130, with the ionization chamber 135 surrounded by the magnet assembly 131.

[0101] In the exemplary embodiment of Figures 2B and 2C, the set of magnets 131 comprises a plurality of magnets 231 spaced circumferentially from each other around the ionization chamber 135, for example regularly spaced. The magnets 231 are arranged substantially symmetrically with respect to the axis 102. Furthermore, the magnets 231 extend substantially parallel to the axis 102. Other arrangements of magnets around the ionization chamber and / or other types of magnets may be envisaged.

[0102] Figures 2B and 2C also show the interior of the ion extraction zone 140 with the electrodes 141, 142, 143 included in the electron impact source 130 and positioned at the second end 135B of the ionization chamber 135.

[0103] As in Figures 1A and 1B, it is seen that one end of the electron impact source 130, in particular one end of the magnet assembly 131, surrounds one end of the electron source 110, forming a covering portion LR. Thus, in this configuration, and at least in the covering portion LR, the external diameter DI of the electron source 110, i.e. the external diameter of the magnet assembly 111, is smaller than the internal diameter D3 of the electron impact source 130, i.e. the internal diameter of the magnet assembly 131. This difference in diameters in the covering portion LR allows the end of the electron source 110 to penetrate inside the electron impact source 130. For example, the electron extraction zone 120 is positioned in the covering portion LR. An advantage of this configuration is explained later in the description in connection with [Fig.6A].

[0104] In Figures 3, 4A to 4C and 5 which follow, the electron beam trajectories are generated by simulation software.

[0105] [Fig. 3] schematically illustrates an exemplary implementation of an ion source device according to one embodiment, as well as a trajectory of an electron beam in this ion source device. More particularly, [Fig. 3] illustrates an exemplary arrangement of magnets around the cavity in the electron source and around the ionization chamber in the electron impact source.

[0106] The ion source device 100 of [Fig. 3] may be similar to the device of Figures 1A and 1B, and it retains the same reference. The elements common to all these figures retain the same references.

[0107] As in Figures 2B and 2C, [Fig.3] illustrates the plurality of magnets 231 spaced circumferentially, for example regularly spaced, from each other around the ionization chamber 135. The magnets 231 are arranged substantially symmetrically with respect to the axis 102.

[0108] [Fig. 3] also illustrates that the set of magnets 111 of the electron source 110 may comprise a plurality of magnets 211 spaced circumferentially, for example regularly spaced, from each other around the cavity 115. The magnets 211 are arranged substantially symmetrically with respect to the axis 102.

[0109] Each magnet 211, 231 shown is a permanent magnet. Alternatively, each magnet could be an electromagnet, for example a core surrounded by a coil.

[0110] It can be seen that the trajectory of the electron beam El is indeed compressed radially around the axis 102 in the ionization chamber 135 under the effect of the axial compression field generated by the set of magnets 131. Furthermore, it can be seen that the electrons are slowed down then repelled at the exit of the ionization chamber 135 at the level of the ion extraction zone 140.

[0111] As an example, the voltage Veiec is set at 7990V, the ionization voltage Vion at 8000V (electrons at 10 eV) and the extraction voltage Vextract at 8200V.

[0112] [Fig.4A], [Fig.4B] and [Fig.4C] schematically illustrate alternative electron beam trajectories in an ion source device according to one embodiment, such as the ion source device of [Fig.3], in different configurations.

[0113] [Fig.4A] shows a trajectory of an electron beam E4 without the influence of the axial compression field. It can be seen that the electron beam E4 extracted from the electron source 110 in the electron extraction zone 120 widens in the ionization chamber 135. It is therefore not compressed radially around the axis 102.

[0114] [Fig.4B] shows a trajectory of an electron beam E5 under the influence of the axial compression field, but with a large distance DF between the magnet assembly 111 of the electron source 110 and the magnet assembly 131 of the electron impact source 130, so that the electron extraction zone 120 does not penetrate inside the electron impact source 130. It can be seen that the electron beam E4 extracted from the electron source 110 in the electron extraction zone 120 initially widens at the entrance to the ionization chamber 135 before being radially compressed around the axis 102. This can create a dispersion of the electron trajectories, and thus a total or partial loss of the electron beam.

[0115] [Fig.4C] corresponds substantially to [Fig.3] and shows a trajectory of an electron beam El with the influence of the axial compression field, with a very small distance DN between the magnet assembly 111 of the electron source 110 and the magnet assembly 131 of the electron impact source 130, so that the electron extraction zone 120 penetrates into the electron impact source 130 (overlapping portion LR). It can be seen that the electron beam El extracted from the electron source 110 is already compressed radially around the axis 102 in the electron extraction zone 120 under the effect of the axial compression field, and then remains compressed in the ionization chamber 135.

[0116] It is noted that, in [Fig. 4C], the magnet assembly 111 of the electron source 110 does not have one end that fits inside one end of the magnet assembly 131 of the electron impact source 130, unlike what is shown in FIGS. 1A, 1B, 2A to 2C. In the case of [Fig. 4C], the overlap portion LR corresponds to the overlap of the electron extraction zone 120 by the electron impact source 130. The configuration of FIGS. 1A, 1B, 2A to 2C is particularly advantageous, but the configuration of [Fig. 4C] with the electron extraction zone 120 that penetrates inside the electron impact source 130 is also advantageous.

[0117] [Fig.5] schematically illustrates another electron beam trajectory in an ion source device according to one embodiment, such as the ion source device of [Fig.3].

[0118] In [Fig. 5], arrows in both directions along the axis 102 represent the path of the electron beam E1 directed from the electron source 110 to, and into, the exit of the ionization chamber 135, and the path of the electron beam E3 slowed down then repelled at the ion extraction zone 140, then returned to the electron source 110 where the electrons are decelerated. For example, the voltage Veiec was set at 5850V, the ionization voltage Vion at 6000V and the extraction voltage Vextract at 5800V.

[0119] [Fig.6A] shows graphs illustrating axial profiles of the axial magnetic field in an ion source device according to one embodiment, in two configurations, corresponding respectively to [Fig.4C] and [Fig.4B]. More particularly, each graph of [Fig.6A] shows a magnetic flux density in relative value at the axis of the ion source device as a function of axial position.

[0120] Separations between the different sources 110, 130 and zones 120, 140, 150 are marked by vertical lines.

[0121] The solid line graph 610 shows an axial profile of the axial magnetic field in the configuration of [Fig.4C], and the dotted line graph 620 shows an axial profile of the axial magnetic field in the configuration of [Fig.4B].

[0122] In the electron source 110, the magnetic field shown corresponds mainly to the resonance magnetic field B1. The band between the horizontal lines 601 and 603 defines an operating range, in terms of frequency of the electromagnetic field, of the electron source ECR 110. This operating range is for example between 1.3 and 5.8 GHz. Point 604 corresponds to a cyclotron resonance point at 2.45 GHz, with a magnetic field at 0.0875 T, which is represented by an intersection between a horizontal line 602 at 2.45 GHz and each of the graphs 610, 620.

[0123] As the axial position increases in the electron source 110 to the level of the electron extraction zone 120, the magnetic field rises until it becomes positive.

[0124] Preferably, the resonance magnetic field B1 in the electron source 110 has a direction opposite to the direction of the axial compression field B3 in the electron impact source 130. For example, as also seen in [Fig.lA] by dotted arrows, the resonance magnetic field B1 in the electron source 110 is negative, i.e. it is oriented in the opposite direction to the ionization chamber 135, while the axial compression field B3 is positive, i.e. that is to say that it is oriented towards the extraction and exit zones of the ions 140, 150. This allows that the leakage field of the resonance magnetic field Bl, which is in the opposite direction to the resonance magnetic field Bl, can be in the same direction as the axial compression field B3, and that the two fields can thus accumulate.

[0125] In the configuration of [Fig.4C] represented by graph 610, the magnetic field continues to increase until a first maximum 611 is reached. The extracted electrons can thus be compressed from the electron extraction zone 120. This is in particular due to the fact that the magnet assembly 131 of the electron impact source 130 is arranged around the electron extraction zone 120 (small distance DN of [Fig.4C]) and that thus the axial compression field B3 already contributes in the electron extraction zone 120 to the magnetic field represented, in addition to the leakage field of the resonance magnetic field B1. Thus, the intensity of the axial magnetic field has a continuous positive gradient between the microwave cavity 115 (resonance magnetic field) and the ionization chamber 135 (axial compression field).

[0126] In the electron impact source 130, the magnetic field shown corresponds mainly to the axial compression field B3 and maintains a relatively high positive value. Then a second maximum 612 of the magnetic field is found at the entrance to the ion extraction zone 140. In the ion extraction zone 140, the magnetic field decreases, and it decreases again in the ion extraction zone 150 where there is practically no longer any influence of the set of magnets 131. It is advantageous for the electron reflection / repulsion zone to be located in a maximum magnetic field zone in order to maintain the compression of the electrons, the ions being little or not at all magnetized.

[0127] In the configuration of [Fig.4B] represented by graph 620, the magnetic field decreases in the electron extraction zone 120 before rising again under the influence of the axial compression field B3. In this configuration, the intensity of the axial magnetic field has a discontinuous gradient (positive, negative then positive) between the microwave cavity 115 (resonance magnetic field) and the ionization chamber 135 (axial compression field). The magnetic field then continues to increase until it reaches a first maximum 621 in the electron impact source 130. The extracted electrons are therefore not compressed from the electron extraction zone 120, but only in the ionization chamber 135. This is due to the fact that the set of magnets 131 of the electron impact source 130 is arranged at too great a distance (distance DF of [Fig.4B]) of the electron source 110, and that thus the axial compression field B3 does not yet contribute to the magnetic field in the electron extraction zone. 120. In the electron extraction zone 120, it is mainly the leakage field that contributes to the magnetic field, and this leakage field contributes less and less as the axial position increases.

[0128] In the electron impact source 130, the magnetic field shown corresponds mainly to the axial compression field B3 and maintains a relatively high positive value. Then a second maximum 622 of the magnetic field is found at the entrance to the ion extraction zone 140. In the ion extraction zone 140, the magnetic field decreases, and it decreases further in the ion exit zone 150 where there is practically no longer any influence of the set of magnets 131.

[0129] Advantageously, the passages, or gaps, for extracting electrons and ions are placed in the vicinity of the first maximum and the second maximum of the axial magnetic field present in the ionization chamber, respectively.

[0130] Advantageously, the electron extraction electrode 121 can be positioned in the vicinity of the first maximum of the magnetic field. Advantageously, the ion extraction electrode 141 can be positioned in the vicinity of the second maximum of the magnetic field.

[0131] It can be seen that the distance between the set of magnets 131 of the electron impact source 130 and the set of magnets 111 of the electron source 110 can be adjusted, advantageously minimized, for example so that the electron extraction zone 120 is surrounded at least partially by the set of magnets 131 of the electron impact source 130, forming the covering portion LR. Furthermore, at least in the covering portion LR, the external diameter DI of the electron source 110 is preferably less than the internal diameter D3 of the electron impact source 130.

[0132] More generally, the relative axial positioning of the magnet assembly 111 of the electron source 110 and the magnet assembly 131 of the electron impact source 130 is preferably determined so that the resonance magnetic field B1 and the axial compression magnetic field B3 can be oriented in the same direction in an area between the electron source 110 and the electron impact source 130, so as to have a continuous magnetic field between the electron source 110 and the electron impact source 130. For example, the electron source can be moved axially until a maximum of the total magnetic field is observed in the area between the electron source 110 and the electron impact source 130.

[0133] [Fig.6B] shows graphs illustrating axial profiles of the magnetic field intensity respectively in the electron source (resonance magnetic field) and in the electron impact source (compressing axial magnetic field).

[0134] In [Fig.6B], it will be noted that the magnetic fields all have an orientation reversed with respect to [Fig.6A], that is to say that the resonance magnetic field B1 is positive in the electron source, the leakage field B2 is therefore negative, and the axial compression magnetic field B3 is negative in the electron impact source. In other words, between Figures 6A and 6B, the graphs of the magnetic fields are reversed with respect to the horizontal axis X. This is a matter of another orientation convention, the reasoning described below applying similarly for the convention of [Fig.6A]. In both conventions, the resonance magnetic field B1 in the electron source has a direction opposite to the direction of the axial compression field B3 in the electron impact source 130.

[0135] The intensity of the resonance magnetic field B1 has a central part in the shape of a Gaussian with a maximum. Each end of the Gaussian extends to a minimum B0_elec whose value is negative, then the intensity of the magnetic field rises from each minimum B0_elec, corresponding to the leakage field B2 of the magnetic field of the electron source. We are interested in the minimum point B0_elec which corresponds to the largest abscissa Xelec, which is located on the side of the electron impact source.

[0136] The axial compression magnetic field B3 has a central part in the form of an inverted double Gaussian with two minima B0_ion. Each end of the Gaussian extends to a maximum whose value is positive, then the intensity of the magnetic field decreases again. We are interested in the minimum point B0_ion which corresponds to the smallest abscissa Xion, which is located on the side of the electron source.

[0137] To be able to combine the intensities of the leakage field B2 and the axial compression field B3, and in particular to avoid drops in magnetic field intensity between the electron source and the electron impact source, it is understood from [Fig.6B] that it is advantageous for the abscissa Xelec to coincide substantially with the abscissa Xion. This is illustrated by the axial displacement of the graph of the magnetic field B1 of the electron source (in dotted lines).

[0138] [Fig.7A], [Fig.7B] and [Fig.7C] schematically illustrate examples of operation of an ion source device according to one embodiment, such as the ion source device of [Fig.3], according to different operating parameters.

[0139] More particularly, Figures 7A to 7C illustrate examples of operation of the electron source of the ion source device, the ionization chamber being grounded, i.e. without polarization of the ionization chamber. Ions are not generated in the ionization chamber. On the other hand, a compression magnetic field is generated around the ionization chamber. Each of Figures 7A to 7C represents on the left an electron beam trajectory E1 in the device ion source, the trajectory being generated by simulation software, and on the right an image of the trajectory of the electron beam leaving the electron impact source (zone 150).

[0140] Figures 7A, 7B, 7C differ from each other by the bias voltage Veiec of the electron source 110, so that the electron beam can have different energies. [Fig.7A] corresponds to a bias voltage Veiec of 250V (electron energy of 250 eV). [Fig.7B] corresponds to a bias voltage Veiec of 500V (electron energy of 500 eV). [Fig.7C] corresponds to a bias voltage Veiec of 1000V (electron energy of 1000 eV). It can therefore be seen that low-energy electron beams can be generated which pass through the ion source device while being compressed around the axis 102.

[0141] [Fig.8A] and [Fig.8B] schematically illustrate examples of charge separation in an ion source device according to one embodiment, such as the ion source device of [Fig.3], according to different operating parameters.

[0142] More particularly, Figures 8A and 8B illustrate examples of operation of the electron source with polarization of the ionization chamber. Ions are generated in the ionization chamber. As in Figures 7A to 7C, a compression magnetic field is generated around the ionization chamber. Each of Figures 8A and 8B represents on the left an electron beam trajectory in the ion source device, the trajectory being generated by simulation software, and on the right an image of the trajectory of the electron beam and an ion beam at the output of the electron impact source (area 150).

[0143] In [Fig.8A], the bias voltage Veiec of the electron source 110 is 1000 V and the bias voltage Vion (ionization voltage) of the ionization chamber 135 is 1500 V (electrons at 500 eV). It can be seen in the image that the electron beam El is stopped at the exit of the ionization chamber at a 1000 V equipotential line and that at this level, an ion beam II emerges from the electron beam EL. The 1000 V equipotential line corresponds to a charge separation zone.

[0144] In [Fig.8B], the bias voltage Veiec of the electron source 110 is 1000 V and the voltage Vion (ionization voltage) of the ionization chamber 135 is 2000 V (electrons at 1000 eV). It can be seen in the simulated electron trajectory and in the image that the electron beam El is stopped at the exit of the ionization chamber at a 1000 V equipotential line and that at this level, an ion beam II emerges from the electron beam EL. The 1000 V equipotential line corresponds to a charge separation zone.

[0145] It is apparent from the description that the ion source device according to embodiments can be implemented at different orders of magnitude of pressure thanks to the introduction of an ECR electron source with a microwave cavity which can operate independently of the nature of the gas and the pressure in the ionization chamber.

[0146] By introducing an electron source insensitive to the pressure and the nature of the gas into the ionization chamber, the ion source device can be operated at 102 mbar or more, or even at 10 1 mbar or more, if the operating voltages allow it. But the ion source device can also be operated at less than 102 mbar or more, or even less than 10 4 mbar, depending on the intended operating modes.

[0147] Indeed, in certain applications, it is necessary to be able to freely choose the pressure of the ionization chamber, in particular to maximize the ionization rate of the gas in the ionization chamber. One may want a very low pressure, for example a pressure less than or equal to 107 mbar, for example in an electron beam ion source (EBIS) operation dedicated to the production of multicharged ions. One may also want a higher pressure, for example a pressure greater than or equal to 102 mbar, for example in a plasma source type operation with damping of the electron beam in the gas. Thus, the embodiments make it possible to have a wide pressure range in the ionization chamber.

[0148] Furthermore, the microwave cavity electron source makes it possible to deliver extremely high current densities, including with very low energy electrons, for example of the order of 10 eV, which is extremely beneficial for the ionization of molecular species, for example in the field of mass spectroscopy. The microwave cavity electron source makes it possible to obtain electron beams of intensity adapted to ionization, including for reduced extraction dimensions, typically with a diameter of less than 0.5 mm, and thus to ensure electrostatic confinement of the ions inside the electron beam over reduced dimensions (brightness control).

[0149] The embodiments thus allow: - to control the current extracted from an ion source over several orders of magnitude n (for example n greater than 5) without physical modification of the ion source, by filtering the ions trapped in the electron beam, in particular by varying the value of the extraction voltage Vextract in particular in relation to the ionization voltage V- • ' ion 9 - to extract ions trapped inside an electron beam of minimal radial dimension without the extraction process modifying the dimension of the electron beam.

[0150] Furthermore, by varying the relative axial positioning of the electron source and the electron impact source, the resonance magnetic field and the axial compression magnetic field can be combined and the magnetic field can be continuous between the electron source and the electron impact source, so that the electron beam can be compressed between the electron source and the electron impact source and then all along the electron impact source.

[0151] The ECR electron source may be a microwave plasma source.

[0152] Various embodiments and variations have been described. The person skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art.

[0153] Finally, the practical implementation of the embodiments and variants described is within the reach of those skilled in the art from the functional indications given above.

Claims

Claims

1. A charge separation ion source device (100) comprising: - a cyclotron resonance electron source (110); - an electron impact source (130).

2. A method for generating ions using a charge separation ion source device (100) comprising: - a cyclotron resonance electron source (110); - an electron impact source (130).

3. A device according to claim 1 or a method according to claim 2, wherein the outer diameter (D1) of the electron source (110) is smaller than the inner diameter (D3) of the electron impact source (130), at least in portions of the electron source and the electron impact source facing each other.

4. The device or method of claim 3, wherein the difference between the inner diameter (D3) of the electron impact source (130) and the outer diameter (D1) of the electron source (110) is such that one end of the electron source penetrates the electron impact source.

5. Device according to any one of claims 1, 3, 4, or method according to any one of claims 2 to 4, wherein: - the electron source (110) and the electron impact source (130) are arranged along an axis (102) of circulation of an electron beam (El) coming from the electron source; - the electron source (110) comprises a microwave cavity (115) around the axis (102) and a first set of magnets (111) positioned around the microwave cavity, the first set of magnets being configured to generate a resonance magnetic field (Bl), for example an axial magnetic field;and - the electron impact source (130) comprises an ionization chamber (135) around the axis (102) and a second set of magnets (131) positioned around the ionization chamber, the second set of magnets being configured to generate a compression magnetic field (B3) of the electron beam (El) around the axis (102), for example an axial magnetic field.;

6. The apparatus or method of claim 5, wherein the first set of magnets (111) comprises a plurality of magnets (211), e.g. permanent magnets, circumferentially spaced from each other around the microwave cavity (115) and / or the second set of magnets (131) comprises a plurality of magnets (231), e.g. permanent magnets, circumferentially spaced from each other around the ionization chamber (135).

7. A device or method according to claim 5 or 6, wherein an axial end of the first set of magnets (111) penetrates an axial end of the second set of magnets (131).

8. Device or method according to any one of claims 5 to 7, wherein the resonance magnetic field (B1) has, in the electron source (110), a first axial orientation, and the compression magnetic field (B3) has, in the electron impact source (130), a second axial orientation opposite to the first axial orientation.

9. A device or method according to any one of claims 5 to 8, wherein the relative axial positioning of the first set of magnets (111) and the second set of magnets (131) is defined so that a leakage field (B2) of the resonance magnetic field (B1) and the compression magnetic field (B3) are oriented in the same direction, for example in an area between the electron source (110) and the electron impact source (130).

10. A device or method according to any one of claims 5 to 9, wherein a multipole field is superimposed on the compression magnetic field, for example so as to inject into the electron beam a mirror field superimposed on the multipole field, or a minimum B.

11. A device or method according to any one of claims 5 to 10, wherein the microwave cavity (115) is adapted to be polarized at a first voltage (Veiec) and the ionization chamber (135) is adapted to be polarized at a second voltage (Vion).

12. A device or method according to claim 11, wherein the first voltage (Veiec) is lower than the second voltage (Vion).

13. A device according to any one of claims 1, 3 to 11, or a method according to any one of claims 2 to 11, the ion source device further comprising an extractor of electrons (121) between the electron source (110) and a first end of the electron impact source (130), the electron extractor being adapted to be polarized at a third voltage (Vrepei ) the electron extractor being for example included in the electron source.

14. A device or method according to claims 13, wherein the third voltage (Vrepei) is set to accelerate electrons, or to decelerate electrons and deplete ions.

15. A device according to any one of claims 1, 3 to 14, or a method according to any one of claims 2 to 14, the ion source device further comprising an ion extractor (141) positioned at a second end of the electron impact source (130) opposite the first end, the ion extractor being adapted to be biased to a fourth voltage (Vextract), the ion extractor being for example included in the electron impact source (130).

16. Device or method according to claims 12 and 15, wherein the fourth voltage (Vextract) is lower than the first voltage (Veiec)-

Images