Plasma ion source

Abstract

The present invention relates to a plasma ion source that uses cyclotron resonance and inductive coupling between individual elements. The plasma ion source includes an excitable element, which is an emitter coil (5) that is excited by a high frequency signal generated by a high frequency signal source (1). The emitter coil (5) is inductively coupled with the interior of the chamber (2) or with coupling members (6) located inside the chamber (2).

Description

[0001] Plasma ion source

[0002] Field of Art

[0003] The invention relates to a plasma ion source using electron cyclotron resonance and inductive coupling between individual elements of the plasma ion source. The invention relates to a plasma ion source for use in particular in microscopy.

[0004] Background Art

[0005] Ion machining has a wide range of applications due to its ability to machine very precisely even very small structures. Ion machining therefore plays a key role, for example, in the production of microscopic structures, in the preparation of lamellae from samples for observation in transmission electron microscopes or in the analysis of defects in semiconductor devices and in many other applications.

[0006] One option for creating ions is the use of a plasma ion source. The plasma ion source can be the source disclosed in patent US8664862B2. This patent describes a plasma source with a first rod forming a quarter-wave antenna, which is surrounded by other rods forming coupling members together with the first rod. These rods are placed in a cylindrical cavity. The said rods are attached to one of the bases of the cylindrical cavity and in the other base there is an opening through which the ions formed in the cavity can escape. The rods forming the coupling members together with the rod forming the antenna are electrically conductively connected to the cavity. The rod forming the antenna passes through the base of the cavity and is separated from the cavity by an insulator. The plasma is generated with the greatest intensity at the unattached ends of these rods. For the most efficient generation of ions, a precise positioning of the rod forming the antenna relative to the opening in the base of the cavity is very important. At the same time, it is also very important that the rod forming the antenna has a certain length within the cavity. The disadvantage of this solution is the necessity of a very precise positioning of the rod forming the antenna, which is very difficult to achieve, because it is very complicated to measure the placement of the rod forming the antenna inside the cavity and, depending on the technical design, it may be difficult to position the rod in a defined manner.

[0007] It would therefore be desirable to provide a solution for a plasma source that would enable efficient generation of ions and at the same time easier production of such a source with lower demands on production accuracy. Summary of the invention

[0008] The above-mentioned aim is achieved by providing a plasma ion source comprising a source of high-frequency signal, a chamber, a magnetic field source located outside the chamber and surrounding the chamber, the magnetic field source being adapted to create a homogeneous magnetic field extending into the chamber and affecting the atoms of the gas supplied into the chamber, a gas supply system passing through the chamber wall, and an excitable element that is excited by a high-frequency signal generated by the high-frequency signal source, wherein the excitable element is an emitter coil inductively coupled with the chamber. The plasma ion source fulfills the above-mentioned objective by using an emitter coil as the excitable element. The advantage of using the emitter coil is that the coil is easier to manufacture, not requiring such precision in production, since the coil turns can be easily shaped into a shape suitable for a given application, and the dimensions of the coil turns can be easily determined. Furthermore, the advantage of using an emitter coil as the excitable element is simpler production of the plasma ion source, since placing the emitter coil in the desired position in the chamber is easier than in the case of an antenna.

[0009] In a preferred embodiment of the plasma ion source, at least one coupling member is placed in the chamber, wherein each coupling member is mechanically and electrically connected to the chamber and also is inductively coupled with the emitter coil. The advantage of this embodiment is the controllability of the location where the plasma is formed.

[0010] In a first variant of the plasma ion source, the emitter coil is located inside the chamber and is electrically connected to the chamber. In a preferred embodiment according to this variant, the emitter coil is galvanically separated from the high-frequency signal source. The advantage of such separation is that the high-frequency signal source does not need to be designed with regard to the optional potential of the chamber.

[0011] In a second variant of the plasma ion source, the emitter coil is located outside the chamber. The advantage of this variant is that the emitter coil is not located in the space where the plasma is generated and is therefore not exposed to the plasma's degrading effects. In this variant, the emitter coil is also galvanically separated from the chamber and does not need to be designed with regard to the optional potential of the chamber.

[0012] In a third variant of the plasma ion source, the emitter coil is located inside the chamber, and a receiving coil electrically connected to the emitter coil is also located inside the chamber, and a transmitting coil electrically connected to the high-frequency signal source and having an inductive coupling with the receiving coil is located outside the chamber. The advantage of this variant is that the emitter coil is galvanically separated from the chamber and it is not necessary to design it with respect to the optional potential of the chamber.

[0013] In a preferred embodiment, the profile of the coupling member has the shape of an annular sector with a sector central angle of 5° to 90°. The advantage of such an embodiment of the coupling member is easier machining when it is manufactured together with the chamber from a single blank.

[0014] Brief description of the Drawings

[0015] The invention is further explained by way of examples, which are described using the attached drawings, wherein:

[0016] Fig. 1 schematically shows an example of a first variant of an embodiment of a plasma ion source arrangement,

[0017] Fig. 2 schematically shows an example of a second variant of an embodiment of a plasma ion source arrangement,

[0018] Fig. 3 schematically shows an example of a third variant of an embodiment of a plasma ion source arrangement.

[0019] Examples of carrying out the Invention

[0020] The embodiments shown herein illustrate examples of embodiments of the invention, however, they should not be construed as limiting the scope of the protection.

[0021] Electrical connection means a physical connection using, for example, a class 1 conductor or a coaxial cable 9 capable of transmitting electrical energy.

[0022] Location at something means a location where one element touches the other or the distance between them is negligible compared to the dimensions of the relevant elements. A negligible distance can be a distance of up to approximately 5 mm.

[0023] An example of an embodiment of the invention is a plasma ion source shown in Figs. 1 to 3 containing a source 1 of a high-frequency signal. The high-frequency signal source 1 is a source enabling the generation of a signal in the range of 1 to 5.8 GHz, usually 2.2 to 2.8 GHz. The plasma ion source further comprises a chamber 2, a magnetic field source 3 adapted to generate a homogeneous magnetic field and located outside the chamber 2, a system 4 for supplying gas passing through the wall of the chamber 2 and at least one excitable element.

[0024] The excitable element is an emitter coil 5. The emitter coil 5 is a coil adapted to emit an alternating electric field. In one embodiment of the emitter coil 5, the emitter coil 5 is planar. In another embodiment of the emitter coil 5, the emitter coil 5 is a so-called magnetic loop. There is inductive coupling between the emitter coil 5 and the chamber 2. When the emitter coil 5 is excited by a high-frequency signal, plasma is formed between the chamber 2 and the emitter coil 5.

[0025] In one embodiment of the plasma ion source, further at least one coupling member 6 is located in the chamber 2, as shown in Fig. 2 and 3. The emitter coil 5 is inductively coupled to the coupling member 6; and when the emitter coil 5 is excited by a high-frequency signal, plasma is formed between the emitter coil 5 and the coupling member 6.

[0026] The chamber 2 has at least one side and two bases. In one base of the chamber 2, an opening is formed, said opening being adapted for discharging the generated ions, hereinafter this base will be referred to as the output base Ij.. The base of the chamber 2 opposite the output base 11 will be referred to as the source base 10. In an embodiment of the chamber 2, the output base 1 1 is an integral part of the chamber 2, as shown in Fig. 3. In another embodiment of the chamber 2, the output base 1 1 is made as a separate cover, as shown in Figs. 1 and 2, the cover being detachably or firmly connected to the chamber 2. In one of embodiment of the cover, the cover is conductive and is connected to the same potential as the potential of the chamber 2. In a first embodiment of the source base jO, as shown in Fig. 1 , the source base 10 is made of the same material as the rest of the chamber 2. In a second embodiment of the source base jO, as shown in Fig. 3, the entire source base 10 is made of any solid dielectric. In an embodiment of the chamber 2, as shown in Fig. 2, a part of the source base 10 is made of any solid dielectric and the remainder of the source base 10 is made of the same material as the remainder of the chamber 2, wherein the part made of the dielectric is understood to mean such part of the source base 10 that corresponds to the projection of the emitter coil 5 or the transmitter coil 7 or the receiver coil 8 into the plane of the source base O.

[0027] The chamber 2 is further adapted for receiving a supplied gas. A gas supply system 4 passes through the wall of the chamber. The gas supply system 4 includes at least one gas source and a gas line connected to the gas source at one end and at the other end opening into the chamber 2. The desired ions are subsequently formed from the gas supplied into the chamber 2. A magnetic field source 3 is located outside the chamber 2. The magnetic field source 3 is located outside the chamber 2 and configured so that the magnetic field generated by this source 3 extends into the space of the chamber 2 and influences the atoms of the gas supplied to the chamber 2. The magnetic field source 3 contains one or more elements capable of jointly creating a homogeneous magnetic field inside the chamber 2. The magnetic field source 3 is a permanent magnet or an electromagnet. Elements of the magnetic field source 3 may have a ring shape or a rectangular shape or any other shape, and such number of the elements may be provided that they are capable of creating a homogeneous magnetic field inside the chamber 2.

[0028] The coupling members 6 are mechanically connected to the chamber 2 and are also electrically connected to the chamber. In a first embodiment of the coupling members 6, the coupling members 6 and the chamber 2 are formed integrally as one part, i.e. they are made from one blank. In a second embodiment of the coupling members 6, the coupling members 6 are attached to the chamber 2 in a detachable or non-detachable manner, e.g. by screwing, pressing, or in any other way, as long as the mechanical and electrical connection is maintained. The coupling members 6 may have various shapes, for example a rod with a circular profile or a rod with a profile in the shape of an annulus sector with a sector central angle from 5° to 90°, or any other manufacturable shape that can be produced by subtractive or additive manufacturing technology and that is capable of performing the function of the coupling member 6 with the emitter coil 5.

[0029] The interior of the chamber 2, the emitter coil 5 and, if they are located in the chamber 2, the coupling members 6 have such a combination of dimensions and mutual location that allows resonance to be achieved at a selected frequency of the generated high-frequency signal. The parameters include, for example, the diameter of the thread of the emitter coil 5, the length of the coupling members 6, the shape of the interior of the chamber 2 and the chamber 2 dimensions, wherein when the chamber 2 is cylindrical, these dimensions are the internal diameter and height.

[0030] In a first embodiment of the arrangement of the plasma ion source, the emitter coil 5 is inside the chamber 2 at the source base 10 and is electrically connected to a galvanic isolation element 12. The galvanic isolation element 12 is located outside the chamber 2 and is, for example, a frequency pass filter with a resonant frequency equal to the plasma excitation frequency. The emitter coil 5 is further electrically connected to the chamber 2. The galvanic isolation element 12 is further electrically connected to the source 1 of the high-frequency signal.

[0031] In a second embodiment of the arrangement of the plasma ion source, the emitter coil 5 is inside the chamber 2 and there is also a receiving coil 8 inside the chamber 2, the coil 8 being located at the source base . The receiving coil 8 is electrically connected to the emitter coil 5. Outside the chamber 2, a transmitting coil 7 is located at the source base 1.0, the coil 7 being inductively connected to the receiving coil 8. The transmitting coil 8 is further electrically connected to the source 1 of the high-frequency signal. In this case, the emitter coil 5 is not electrically connected to the chamber 2, so it is galvanically separated from the chamber 2.

[0032] In a third embodiment of the arrangement of the plasma ion source, the emitter coil 5 is outside the chamber 2 at the source base 10 and is electrically connected to the source 1 of the high- frequency signal. In this case, the emitter coil 5 is not electrically connected to the chamber 2, i.e. it is galvanically separated from the chamber 2.

[0033] The chamber 2 is connected to a non-zero potential generated by a DC voltage source 13. The potential of the chamber 2 is in the range of more than 0 kV to 35 kV, inclusive.

[0034] In a first specific embodiment shown in Fig. 1 , according to the first embodiment of the plasma ion source arrangement, the emitter coil 5 is inside the chamber 2 and is electrically connected by means of a coaxial cable 9 to a galvanic isolation element 1.2, which is a frequency pass filter with a resonant frequency equal to the plasma excitation frequency located outside the chamber 2. The emitter coil 5 is located at the source base 10 and the electrical connection of the emitter coil 5 with the frequency pass filter passes through the source base 10 and is insulated from the source base . The frequency pass filter with a resonant frequency equal to the plasma excitation frequency is further connected to the high-frequency signal source 1. The frequency of the signal generated by the high-frequency signal source 1 and transmitted to the emitter coil 5 through the frequency pass filter is 2.4 GHz in this embodiment. The emitter coil 5 is further electrically connected to the chamber 2. The entire chamber 2, including both bases, is made of one material and is connected to a potential of 30 kV. In this specific embodiment, no coupling element 6 is located in the chamber 2. A magnetic field source 3 in the form of a permanent magnet with a ring shape is located outside the chamber 2. The emitter coil 5 is inductively connected to the interior of the chamber 2 and plasma is thus formed within the entire space of the chamber 2.

[0035] In the second specific embodiment shown in Fig. 2, according to the second embodiment of the plasma ion source arrangement, the emitter coil 5 is placed inside the chamber 2 and is electrically connected to the receiver coil 8. The receiver coil 8 is located at the source base , while the part of the source base 10 that corresponds to the projection of the receiver coil 5 to the plane of the source base 10 is made of ceramic. A transmitter coil 7 is located outside the chamber 2, at the source base 10. The transmitter coil 7 and the receiver coil 8 are connected by inductive coupling. The transmitter coil 7 is further electrically connected to the high-frequency signal source 1. The emitter coil 5 is not connected to the chamber 2. In this embodiment, the chamber 2 has an approximately cylindrical shape. A magnetic field source 3 in the form of four evenly spaced electromagnets having a rectangular shape is located outside the chamber 2. Around the emitter coil 5, three coupling members 6 are concentrically arranged, each mechanically and electrically connected at one end to the chamber 2. In this embodiment, the coupling member 6 has the form of a rod with a profile in the shape of a sector of an annulus with a sector central angle of 35°. There is inductive coupling between the emitter coil 5 and the coupling members 6. In this case, plasma is formed around the ends of the coupling members 6 not attached to the chamber 2.

[0036] In the third specific embodiment shown in Fig. 3, according to the third embodiment of the plasma ion source arrangement, the emitter coil 5 is located outside the chamber 2 at the source base . The source base 10 is made of ceramic in this embodiment. The output base 1 1 is part of the chamber in this embodiment. The emitter coil 5 is electrically connected to the high-frequency signal source 1. Three coupling members 6 are located in the chamber 2 and are mechanically and electrically connected thereto. The coupling members 6 are in this embodiment mechanically connected to the side walls of the chamber 2. The coupling members 6 have a circular profile in this embodiment. The emitter coil 5 is further inductively connected to the coupling members 6 in the chamber 2. The source base 10 is made of ceramic. The chamber 2 has an approximately cuboid shape in this embodiment. A magnetic field source 3 in the form of a coil wound around the chamber 2 is located outside the chamber 2.

[0037] The plasma ion source according to the above description can be used, for example, as an ion source for a focused ion beam device containing other elements known from the prior art.

[0038] List of reference signs:

[0039] 1 - High-frequency signal source

[0040] 2 - Chamber

[0041] 3 - Magnetic field source

[0042] 4 - Gas supply system

[0043] 5 - Emitter coil

[0044] 6 - Coupling member

[0045] 7 - Transmitter coil

[0046] 8 - Receiver coil

[0047] 9 - Coaxial cable

[0048] 10 - Source base

[0049] 1 1 - Output base 12 - Galvanic isolation element

[0050] 13 - DC voltage source

Claims

AMENDED CLAIMS received by the International Bureau on 26 May 2025 (26.05.2025)1. A plasma ion source comprising a high-frequency signal source (1 ), a chamber (2), a magnetic field source (3) located outside the chamber (2) and adapted to generate a homogeneous magnetic field extending into the internal space of the chamber (2) and influencing the atoms of a supplied gas, a gas supply system (4) passing through the wall of the chamber (2) and an excitable element that can be excited by the high- frequency signal generated by the high-frequency signal source (1 ), characterized in that the excitable element is an emitter coil (5) located inside the chamber (2) and is inductively coupled with the chamber (2).

2. A plasma ion source according to claim 1 , wherein at least one coupling member (6) is located in the chamber (2), each of the coupling members (6) being mechanically and electrically connected to the chamber (2) and also inductively coupled with the emitter coil (5).

3. Plasma ion source according to claim 1 or 2, wherein the emitter coil (5) is electrically connected to the chamber (2).

4. Plasma ion source according to claim 1 or 2, wherein the emitter coil (5) is located inside the chamber (2), and a receiving coil (8) is located inside the chamber (2) and electrically connected to the emitter coil (5), further there is a transmitting coil (7) located outside the chamber (2) and electrically connected to the high-frequency signal source (1 ) and inductively coupled with the receiving coil (8).

5. Plasma ion source according to claim 3, wherein the emitter coil (5) is galvanically isolated from the high-frequency signal source (1 ).

6. Plasma ion source according to any one of claims 2 to 5, wherein the profile of the coupling member (6) has the shape of a sector of an annulus with a sector central angle of 5° to 90°.

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