Plasma processing supply system, low impedance high current coaxial line for a plasma processing system, and method for operating a plasma processing system

Abstract

The present invention relates to a low-impedance, high-current coaxial line (1) for a plasma processing system (10), comprising: a) a tubular, thermally conductive electrical insulator (2), e.g., made of ceramic; b) an electrical outer conductor (3) disposed on the insulator in the form of an outer layer; and c) an electrical inner conductor (4) disposed within the insulator in the form of an inner layer. d) the inner and outer diameters of the insulator (2) are sized to achieve a line impedance of 20 ohms or less. e) the low-impedance, high-current coaxial line (1) is designed to be connected to an impedance matching circuit (6) and a plasma processing assembly (7). f) the low-impedance, high-current coaxial line (1) is designed to supply HF power to the plasma processing assembly (7) via an HF power source (9).

Description

[Technical Field]

[0001] The present invention relates to a low impedance, high current coaxial line for a plasma processing supply system and a plasma processing system, and a method for operating a plasma processing system.

[0002] Such a plasma processing system may be, for example, a system in which power is supplied to a load, for example, a plasma processing assembly.

[0003] Such a plasma processing assembly may be, for example, a plasma processing chamber used for industrial plasma processes such as surface treatment of a workpiece, semiconductor manufacturing using plasma, or treatment of a workpiece using a gas laser.

[0004] In such applications, a plasma processing assembly is used to generate the plasma.

[0005] To this end, the plasma processing assembly may comprise an electrode to which a high frequency power signal (hereinafter referred to as HF power signal) is delivered to generate the plasma.

[0006] Typically, the plasma processing assembly can be connected to a radio frequency power source (hereinafter referred to as HF power source).

[0007] HF power signals have frequencies above 4 MHz and specifically below 200 MHz. Commonly used frequencies are 13.56 MHz, 27 MHz, and 40 MHz.

[0008] US 6,673,724 B2 describes a plasma processing system in which the electrodes are exposed to a pulsed RF signal as a so-called "RF pulse bias", the pulse frequency of which may range from 10 kHz to 1 MHz. Such a configuration is not easy to implement in practice for various reasons that will be explained in more detail below.

[0009] Plasma processes performed within a plasma processing assembly generally suffer from the problem that the electrical load impedance of the plasma processing assembly created during the process can vary significantly depending on the conditions within the plasma processing assembly, particularly the workpiece characteristics, electrode, and gas conditions that must be considered.

[0010] Therefore, an impedance matching circuit is typically required to transform the impedance of the load to the nominal impedance of the HF power source. Such an impedance matching circuit is typically located between the HF power source and the plasma processing assembly, and is typically located in close proximity to the plasma processing assembly.

[0011] The impedance matching circuit and the plasma processing assembly are typically connected via interconnects such as copper tabs, copper bars, or copper tubes.

[0012] Such interconnections exhibit parasitic inductances. These parasitic inductances increase the quality of the load impedance, which leads to a reduction in the possible bandwidth of the impedance matching circuit. The quality of the impedance is understood as a factor that represents the ratio of stored energy to thermal energy loss during the next oscillation period in the oscillating system. A high quality of the system means that the system converts less of the stored energy into thermal energy and the oscillations decrease less. The increased quality, combined with the reduced bandwidth, reduces the ability to transmit high-speed pulses through the impedance matching circuit to the plasma processing assembly.

[0013] In addition, the reactive current in the impedance matching circuit increases, thus reducing its efficiency. [Background technology]

[0014] The present invention is therefore based on the object of providing a plasma process supply system and a high current coaxial line for a plasma process system that increases the quality of the load impedance in the plasma process system little or not at all. It is also an object of the present invention to develop a plasma process supply system and a plasma process system having such a high current coaxial line, as well as a method for operating the plasma process system.

[0015] Summary of the Invention This object is achieved by a low impedance high current coaxial line according to independent claim 1, a plasma process supply system according to claim 7, a plasma process system according to claim 10 and / or a method according to claim 11. Advantageous further developments of the invention become apparent from the dependent claims and / or the description.

[0016] In accordance with the present invention, there is provided a low impedance, high current coaxial line for a plasma processing system, comprising: a) a tubular thermally conductive electrical insulator, specifically made of ceramic; b) an electrical outer conductor disposed on the insulator in the form of an outer layer; c) an electrical inner conductor disposed within the insulator in the form of an inner layer; d) The inner and outer diameters of the insulator are dimensioned to achieve a line impedance of 20 ohms or less; e) a low impedance, high current coaxial line is designed to connect to the impedance matching circuit and the plasma process assembly; f) A low impedance, high current coaxial line is proposed, which is designed to supply HF power to the plasma processing assembly by an HF power source.

[0017] In this way, the quality of the load impedance in the plasma processing system can be increased slightly or not at all, and may even be reduced, particularly without additional damping means such as lossy resistors that would adversely affect the efficiency of the plasma processing system.

[0018] Such low-impedance, high-current coaxial lines can be used to replace inductive connections in plasma processing systems. However, in this regard, the coaxial lines are not traditional lines sized for 50 ohms. They are intentionally designed to closely match the impedance of the operating plasma processing assembly. This helps reduce reflections.

[0019] Such a plasma processing system typically includes a plasma processing assembly as a load and an impedance matching circuit. Additionally, the plasma processing system may also include an HF power supply for supplying HF power.

[0020] A low impedance, high current coaxial line according to the present invention can interconnect the impedance matching circuit and the plasma processing assembly in such a plasma processing system.

[0021] For this purpose, a possible electrode in the plasma processing assembly can be in contact with the inner conductor of the low-impedance, high-current coaxial line and connected to a signal in the impedance matching circuit. In this regard, the outer conductor of the low-impedance, high-current coaxial line can be connected to ground. This ground can be connected to the ground of the impedance matching circuit, specifically the housing ground of the impedance matching circuit. This ground can be connected to the ground of the plasma processing assembly, specifically the housing ground of the plasma processing assembly.

[0022] The inner conductor may preferably be applied to the insulator as, for example, a copper and / or silver coating, which may have a positive effect on electrical and thermal conductivity.

[0023] The wall thickness of the tubular thermally conductive electrical insulator can be 2 mm or less, which allows for very good impedance control and the good insulating properties of the insulator allow it to insulate high voltages at a relatively small thickness and prevent flashover, corona discharge, and / or partial discharge.

[0024] The outer conductor can be preferably applied to the insulator as, for example, a copper and / or silver coating. Such coating materials can have a positive effect on electrical and thermal conductivity. In addition, the relative permeability of the conductor is close to 1, and there is no adverse effect on the skin effect.

[0025] The electrical inner conductor can be arranged as an inner layer within the insulator so as to be firmly connected to the insulator, in particular by application in a galvanic process, a plasma deposition process or a sintering process, thus achieving a highly reliable construction.

[0026] The electrical outer conductor can be applied as an outer layer on the insulator, specifically by a galvanic process, plasma deposition process, or sintering process, so that it is firmly connected to the insulator. In this way, a highly reliable construction can be achieved. In addition, the relative permeability of the conductor is close to 1, so there is no adverse effect of the skin effect.

[0027] By using a thermally conductive electrical insulator, the current-carrying capacity of a low-impedance, high-current coaxial line can be significantly increased by cooling. Specifically, the material of the electrical insulator can include, and preferably consists of, a ceramic. When ceramic is selected as the material, a thin insulating layer can be realized due to the ceramic's high dielectric strength. Such a thin insulating layer can also achieve a particularly low characteristic impedance. Therefore, the cable impedance can be sized by selecting the material of the insulator and the inner and outer diameters.

[0028] This provides a low impedance, high current coaxial line to which the impedance matching circuit and plasma processing assembly can be connected, with little or no increase in the quality of the load impedance depending on the line impedance, thereby enabling a higher possible bandwidth of the impedance matching circuit, better behavior at high pulse frequencies, and better efficiency in the impedance matching circuit.

[0029] The outer conductor of the low impedance, high current coaxial line can be designed to be connected to ground, which advantageously allows the outer conductor to be connected to a plasma processing assembly that is also typically connected to ground.

[0030] Furthermore, the outer conductor of the low-impedance, high-current coaxial line can be integrated into a cooling device, which can preferably be a fluid cooling device made of copper, allowing the low-impedance, high-current coaxial line to be reliably connected thermally and electrically to the surrounding system.

[0031] The low-impedance, high-current coaxial line can be designed so that the insulator protrudes beyond the outer conductor at one end. In other words, the outer conductor of the low-impedance, high-current coaxial line does not have the same length as the insulator, but can be designed so that it is slightly shorter at at least one end, and preferably both ends, of the insulator. This allows for larger creepage and clearance distances to be achieved, making the low-impedance, high-current coaxial line suitable for higher voltages, and therefore for greater power transmission, as well as for more reliable ignition.

[0032] Additionally, the inner and outer diameters of the insulator can be selected so that the impedance of the low-impedance, high-current coaxial line approximates the impedance of the plasma processing assembly under ignited plasma conditions, making the plasma processing system more efficient overall. Here, "approximating the impedance" refers to a distance that is 10 Ω or less, specifically 5 Ω or less, and most preferably 2 Ω or less, in absolute value.

[0033] The cavity inside the low-impedance, high-current coaxial line can be filled with a material, specifically an airtight and / or moisture-proof material. In this regard, the entire cavity or only a portion of it can be filled. Since no electric or magnetic field exists inside the cavity of the low-impedance, high-current coaxial line, there are only few restrictions on the choice of material. By filling the cavity of the low-impedance coaxial line, it is possible to achieve a vacuum-tight connection of the low-impedance, high-current coaxial line to an electrode in a plasma processing assembly. If the cavity is only partially filled with material, this saves material. By filling the entire cavity, high stability of the low-impedance, high-current coaxial line is achieved.

[0034] Additionally, low impedance, high current coaxial lines can be used in pulsed plasma processes with pulse frequencies up to 400 kHz.

[0035] Advantageously, the low-impedance, high-current coaxial line is designed to supply pulsed HF power, particularly provided by an HF power supply, to the plasma process assembly, particularly at a pulse frequency of 200 kHz or greater. The pulsed power can advantageously be 400 kHz. This allows the pulsed power to be coupled to the plasma process with low reflection and only minor distortion due to the filtering effect of otherwise significantly mismatched connections. This can significantly improve pulse edge steepness in the plasma process.

[0036] In a further embodiment, this object can be achieved by a plasma process delivery system having an impedance matching circuit and a low impedance, high current coaxial line as described above, connected to the impedance matching circuit and designed to be connected at the other end to a plasma process assembly, thereby establishing a connection between the plasma process delivery system and the plasma process assembly. In this way, HF power can be delivered to the plasma process assembly with low reflections.

[0037] In a further embodiment, the aforementioned plasma process supply system can include an HF power supply, and the impedance matching circuit is electrically connected to the HF power supply such that during operation, power supplied by the HF power supply can be supplied to the plasma process assembly via the impedance matching circuit and the low-impedance, high-current coaxial line. In this way, the HF power can be delivered to the plasma process assembly with particularly low reflection.

[0038] In a further embodiment, one of the aforementioned plasma process supply systems can be designed so that an impedance matching circuit is integrated into the HF power supply, thus achieving further improvement in the delivery of HF power to the plasma process assembly.

[0039] In a further embodiment, this object can be achieved by a plasma processing system having the plasma process supply system and plasma processing assembly described above, wherein a low impedance, high current coaxial line establishes a connection between the impedance matching circuit and the plasma processing assembly. In this way, further improvement in the delivery of HF power to the plasma processing assembly can be achieved.

[0040] When placed in a plasma processing system that may include an impedance matching circuit, a plasma processing assembly, and an HF power supply, the low impedance, high current coaxial line described above can interconnect the impedance matching circuit and the plasma processing assembly. The impedance matching circuit can be located within or integrated into the HF power supply.

[0041] This object is also achieved by a method for operating a plasma processing assembly having a plasma processing supply system as described above, wherein an HF power signal for generating a plasma in the plasma processing assembly is induced to the plasma processing assembly by a low impedance, high current coaxial line.

[0042] In one embodiment of a method for operating a plasma processing assembly, the HF power signal for generating a plasma in the plasma processing assembly is pulsed between different power levels, particularly at a pulse frequency of 200 kHz or greater, and particularly preferably at a pulse frequency of 400 kHz or greater. [Brief explanation of the drawings]

[0043] In the drawings, [Figure 1a] 1 is a schematic cross-sectional view of a first embodiment of a low impedance high current coaxial line according to the present invention; [Figure 1b] 1 is a schematic side view of a first embodiment of a low impedance high current coaxial line according to the present invention; [Figure 2]FIG. 1 illustrates a low impedance, high current coaxial line placed in a plasma processing system without an HF power source. [Figure 3] FIG. 1 illustrates a low impedance, high current coaxial line placed in a plasma processing system having an HF power source. [Figure 4a] FIG. 1 is a cross-sectional view of a low impedance high current coaxial line integrated into a cooling device. [Figure 4b] FIG. 1 is a side view of a low impedance, high current coaxial line integrated into a cooling device. DETAILED DESCRIPTION OF THE INVENTION

[0044] 1a and 1b show a first embodiment of a low impedance, high current coaxial line 1 according to the present invention. The low impedance, high current coaxial line 1 comprises an insulator 2, an inner electrical conductor 4 and an outer electrical conductor 3.

[0045] The insulator 2 is tubular and made of a thermally conductive and electrically insulating material. The inner conductor 4 is applied as an inner layer on the inside of the insulator 2 and is connected to the insulator 2. The outer conductor 3 is applied as an outer layer on the outside of the insulator 2 and is connected to the insulator 2. In Figure 1a, a low-impedance, high-current coaxial line 1 is shown in cross section, and in Figure 1b, in side view. The inner conductor 4 is shown protruding beyond the insulator 2 on one side. This is shown here for clarity, even though this is not often done this way. In this regard, the insulator 2 is also shown protruding beyond the outer conductor 3 on one side. This can be particularly advantageous when high voltages are expected, such as at high power levels or during ignition. This then allows clearance and creepage distances to be increased, which can increase the dielectric strength.

[0046] A low impedance, high current coaxial line 1 can be used to connect the impedance matching circuit 6 to the plasma processing assembly 7 .

[0047] FIG. 2 shows an embodiment of a low impedance, high current coaxial line 1 according to the present invention disposed in a plasma processing system 10 additionally having a plasma processing delivery system 8 and a plasma processing assembly 7 .

[0048] The low impedance, high current coaxial line 1 again includes an insulator 2, an inner conductor 4, and an outer conductor 3. In addition to the low impedance, high current coaxial line 1, the plasma process supply system 8 includes an impedance matching circuit 6.

[0049] The impedance matching circuit 6 is connected to the plasma processing assembly 7 via a low impedance, high current coaxial line 1 .

[0050] The plasma processing assembly 7 is thereby connected to a plasma processing delivery system 8 , which together form a plasma processing system 10 .

[0051] 3 shows an embodiment of a low-impedance, high-current coaxial line 1 according to the present invention disposed within the plasma processing system 10 described in the description of FIG. 2. In this case, the plasma processing system 10 accommodates an additional HF power source 9 for supplying HF power. The impedance matching circuit 6 is here disposed within or integrated into the HF power source 9. The impedance matching circuit 6 can also be disposed separately from the HF power source 9 in another configuration (not shown). This makes sense, in particular, when the HF power source 9 is too large or for other reasons cannot be disposed in close proximity to the plasma processing assembly 7, but the impedance matching circuit 6 can.

[0052] Figures 4a and 4b show an embodiment of a low impedance high current coaxial line 1 according to the invention, as described in the description of Figures 1a and 1b.

[0053] The low impedance high current coaxial line 1 is integrated into a cooling device 5. The cooling device 5 is directly connected to the outer conductor 3 and may preferably be a fluid cooling device with holes for fluid flow. In Figure 4a the low impedance high current coaxial line 1 integrated into the cooling device 5 is shown in cross section and in Figure 4b in side view.

Claims

1. A low impedance, high current coaxial line (1) for a plasma processing system (10), comprising: a) a tubular thermally conductive electrical insulator (2), in particular made of ceramic; b) an electrical outer conductor (3) disposed on said insulator in the form of an outer layer; c) an electrical inner conductor (4) disposed within the insulator in the form of an inner layer; d) the inner and outer diameters of the insulator (2) are dimensioned to achieve a line impedance of 20 ohms or less; e) the low impedance, high current coaxial line (1) is designed to be connected to an impedance matching circuit (6) and a plasma processing assembly (7); f) A low impedance, high current coaxial line (1), wherein said low impedance, high current coaxial line (1) is designed to supply HF power to said plasma process assembly (7) by an HF power source (9).

2. 2. The low impedance, high current coaxial line (1) according to claim 1, wherein the outer conductor (3) is integrated into a cooling device (5), in particular a fluid cooling device made of copper.

3. 3. A low impedance, high current coaxial line (1) according to claim 1 or 2, wherein the insulator (2) projects beyond the outer conductor (3) at one end.

4. 4. The low impedance, high current coaxial line (1) according to claim 1, wherein the inner and outer diameters of the insulator (2) are designed so that the line impedance approximates the impedance of the plasma process assembly (7) in an ignited plasma state.

5. A low impedance, high current coaxial line (1) according to any one of claims 1 to 4, wherein the internal cavity of the low impedance, high current coaxial line (1) is partially filled with a material.

6. The low impedance, high current coaxial line (1) according to any one of claims 1 to 5, wherein the low impedance, high current coaxial line (1) is designed for pulsed plasma processing having a pulse frequency of 200 kHz or more, in particular 400 kHz or more.

7. 1. A plasma process supply system (8) comprising an impedance matching circuit (6) and a low impedance, high current coaxial line (1) according to any one of claims 1 to 6, the plasma process supply system (8) being connected to the impedance matching circuit (6) and designed to be connected at its other end to a plasma process assembly (7), thereby establishing a connection between the plasma process supply system (8) and the plasma process assembly (7).

8. 8. The plasma process supply system (8) of claim 7, further comprising an HF power supply (9), wherein the impedance matching circuit (6) is electrically connected to the HF power supply (9) such that power supplied by the HF power supply (9) during operation can be supplied to the plasma process assembly (7) via the impedance matching circuit (6) and the low impedance, high current coaxial line (1).

9. 9. The plasma process supply system (8) of claim 8, wherein the impedance matching circuit (6) is integrated into the HF power supply (9).

10. 10. A plasma processing system (10) comprising the plasma processing supply system (8) of any one of claims 7 to 9 and a plasma processing assembly (7), wherein the low impedance, high current coaxial line (1) establishes a connection between the impedance matching circuit (6) and the plasma processing assembly (7).

11. A method for operating a plasma processing assembly (7) having a plasma processing supply system (8) according to any one of claims 7 to 9 or a plasma processing system (10) according to claim 10, wherein an HF power signal for generating a plasma in the plasma processing assembly (7) is induced to the plasma processing assembly (7) by the low impedance, high current coaxial line (1).

12. 12. The method for operating a plasma process assembly (7) according to claim 11, wherein the HF power signal for generating a plasma in the plasma process assembly (7) is pulsed between different power levels, in particular at a pulse frequency of 200 kHz or more, particularly preferably at a pulse frequency of 400 kHz or more.

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