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

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

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

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

[0005] For this purpose, the plasma process assembly may comprise an electrode to which a high-frequency power signal (referred to hereinafter as an HF power signal) for generating plasma is fed.

[0006] Generally, the plasma process assembly may be connected to a high-frequency power source (referred to hereinafter as an HF power source).

[0007] The HF power signal has a frequency of 4 MHz or more, and specifically 200 MHz or less. Commonly used frequencies are 13.56 MHz, 27 MHz, and 40 MHz.

[0008] US 6,673,724 B2 describes a plasma process system in which an electrode is 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 are explained in more detail below.

[0009] Plasma processes performed within plasma process assemblies generally face the problem that the electrical load impedance of the plasma process assembly generated during the process can vary significantly depending on the conditions within the plasma process assembly. Specifically, the characteristics of the workpiece, electrodes, and gas conditions must be taken into consideration.

[0010] Therefore, an impedance matching circuit is typically required to convert the load impedance to the nominal impedance of the HF power supply. Such an impedance matching circuit is usually located between the HF power supply and the plasma process assembly, and is typically located immediately adjacent to the plasma process assembly.

[0011] Impedance matching circuits and plasma process assemblies are typically connected via interconnects such as copper tabs, copper bars, or copper tubes.

[0012] Such interconnects exhibit parasitic inductance. These parasitic inductances increase the quality of the load impedance, which leads to a reduction in the possible bandwidth of the impedance matching circuit. Impedance quality is understood as a factor representing the ratio of stored energy to thermal energy loss during the next vibration period in a vibrating system. High quality in a system means that the system converts only a small amount of stored energy into thermal energy, resulting in only a small reduction in vibration. This increased quality, coupled with reduced bandwidth, diminishes the ability to transmit high-speed pulses to the plasma process assembly through the impedance matching circuit.

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

[0014] Therefore, the present invention is based on the objective of providing a plasma process supply system and a high-current coaxial line for a plasma process system that slightly increases or does not increase the quality of load impedance in a plasma process system. Another objective of the present invention is 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 objective is achieved by the low-impedance, high-current coaxial line described in independent claim 1, the plasma process supply system described in claim 7, the plasma process system described in claim 10, and / or the method described in claim 11. Advantageous further developments of the present invention will become apparent from the dependent claims and / or description.

[0016] According to the present invention, a low-impedance, high-current coaxial line for a plasma process system is provided, a) Specifically, a tubular thermally conductive electrical insulator made of ceramic, b) An electrical outer conductor arranged on the insulator in the form of an outer layer, c) Having an electrical internal conductor arranged in the form of an inner layer within the insulator, d) The inner and outer diameters of the insulator are sized to achieve a line impedance of 20 Ω or less. e) Low-impedance, high-current coaxial lines are designed to connect to impedance matching circuits and plasma process assemblies. f) A low-impedance, high-current coaxial line is proposed, which is designed to supply HF power to the plasma process assembly via an HF power supply.

[0017] In this way, the quality of the load impedance in the plasma process system can be slightly increased, or not increased at all, and may even be reduced. Specifically, this is possible without additional attenuation measures such as lossy resistors that negatively affect the efficiency of the plasma process system.

[0018] Using such low-impedance, high-current coaxial lines, inductive connections in plasma process systems can be replaced with coaxial lines. However, in this regard, the coaxial line is not a conventional line dimensioned for 50Ω. It is intentionally designed to closely approximate the impedance of the plasma process assembly in operation. This helps to reduce reflections.

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

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

[0021] For this purpose, possible electrodes in the plasma process assembly can be brought into contact with the internal conductor of a low-impedance, high-current coaxial line and connected to the signal in the impedance matching circuit. In connection with this, the external 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 to the housing ground of the impedance matching circuit. This ground can be connected to the ground of the plasma process assembly, specifically to the housing ground of the plasma process assembly.

[0022] The inner conductor is preferably applicable to the insulator, for example, as a copper coating and / or silver coating. Such a coating material can have a positive effect on electrical conductivity and thermal conductivity.

[0023] The tube wall thickness of the tubular thermally conductive electrical insulator may be 2 mm or less. This enables very good adjustment of impedance, and due to the good insulation properties of the insulator, it is possible to insulate high voltages with a relatively small thickness and prevent flashover, corona discharge, and / or partial discharge.

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

[0025] The electrical inner conductor can be arranged as an inner layer in the insulator so as to be firmly connected to the insulator, specifically by being applied in a galvanic process, a plasma deposition process or a sintering process. A highly reliable configuration can be achieved in this way.

[0026] The electrical outer conductor can be arranged as an outer layer on the insulator so as to be firmly connected to the insulator, specifically by being applied in a galvanic process, a plasma deposition process or a sintering process. A highly reliable configuration can be achieved in this way. In addition, the relative permeability of the conductor approximates 1, and there is no adverse effect on 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 may comprise ceramic, and is preferably made of ceramic. When ceramic is selected as the material, a thin insulating layer can be achieved due to the high dielectric strength of ceramic. Such a thin insulating layer also enables achievement of a particularly low characteristic impedance. Therefore, the impedance of the cable can be dimensioned 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 an impedance matching circuit and a plasma process assembly can be connected. In this regard, little or no increase in the quality of the load impedance occurs depending on the line impedance. This makes it possible to achieve 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. This advantageously allows the outer conductor to be connected to a plasma process assembly that is also normally connected to ground.

[0030] Furthermore, the outer conductor of the low-impedance high-current coaxial line can be integrated into a cooling device. Such a cooling device may preferably be a fluid cooling device made of copper. This enables reliable thermal and electrical connection of the low-impedance high-current coaxial line to the surrounding system.

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

[0032] Furthermore, 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 process assembly in the ignited plasma state. This makes the plasma process system more efficient overall. Here, "approximates impedance" means a distance where the absolute value is 10 ohms or less, specifically 5 ohms or less, and particularly preferably 2 ohms or less.

[0033] The cavity inside a low-impedance, high-current coaxial line can be filled with material, specifically an airtight and / or moisture-proof material. In this regard, only the entire cavity or only a portion thereof can be filled. Since there is no electric or magnetic field inside the cavity of a low-impedance, high-current coaxial line, there are only slight limitations on the choice of material. Filling the cavity of a low-impedance coaxial line makes it possible to achieve a vacuum-sealed connection of the low-impedance, high-current coaxial line to electrodes in a plasma process assembly. If the cavity is only partially filled with material, this results in material savings. Filling the entire cavity achieves high stability for the low-impedance, high-current coaxial line.

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

[0035] Advantageously, the low-impedance, high-current coaxial line is designed to supply pulsed HF power to the plasma process assembly, specifically pulsed HF power provided by an HF power supply, with a pulse frequency of 200 kHz or higher. 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 slight distortion due to the filtering effect of otherwise significantly mismatched connections. This significantly improves the sharpness of the pulse edges in the plasma process.

[0036] In a further embodiment, this objective can be achieved by a plasma process supply system having an impedance matching circuit and a low-impedance, high-current coaxial line as described above, which is 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 supply system and the plasma process assembly. In this way, HF power can be delivered to the plasma process assembly with low reflection.

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

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

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

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

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

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

[0043] In the drawing, [Figure 1a] This is a schematic cross-sectional view of a first embodiment of the low-impedance, high-current coaxial line according to the present invention. [Figure 1b] This is a schematic side view of a first embodiment of the low-impedance, high-current coaxial line according to the present invention. [Figure 2]This figure shows a low-impedance, high-current coaxial line placed in a plasma process system that does not have an HF power supply. [Figure 3] This figure shows a low-impedance, high-current coaxial line placed within a plasma process system with an HF power supply. [Figure 4a] This is a cross-sectional view of a low-impedance, high-current coaxial line integrated into a cooling device. [Figure 4b] This is a side view of a low-impedance, high-current coaxial line integrated into a cooling device. [Modes for carrying out the invention]

[0044] Figures 1a and 1b show a first embodiment of the 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 electrical inner conductor 4, and an electrical outer 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 connected to the insulator 2. The outer conductor 3 is applied as an outer layer on the outside of the insulator 2 and connected to the insulator 2. In Figure 1a, the low-impedance, high-current coaxial line 1 is shown in a cross-sectional view, and in Figure 1b, it is shown in a side view. The inner conductor 4 is shown protruding beyond the insulator 2 on one side. This is shown here for clarity, even though it is not often implemented in this manner. 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, for example, at high power levels or during ignition. This then allows for an increase in clearance distance and creepage distance. This can increase the dielectric strength.

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

[0047] Figure 2 shows an embodiment of the low-impedance, high-current coaxial line 1 according to the present invention, which is located within a plasma process system 10 that further includes a plasma process supply system 8 and a plasma process assembly 7.

[0048] The low-impedance, high-current coaxial line 1 also includes an insulator 2, an internal conductor 4, and an external 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 process assembly 7 via a low-impedance, high-current coaxial line 1.

[0050] As a result, the plasma process assembly 7 is connected to the plasma process supply system 8, and together they form the plasma process system 10.

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

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

[0053] The low-impedance, high-current coaxial line 1 is integrated into the cooling device 5. The cooling device 5 is directly connected to the outer conductor 3 and may preferably be a fluid cooling device having holes for fluid flow. Figure 4a shows a cross-sectional view of the low-impedance, high-current coaxial line 1 integrated into the cooling device 5, and Figure 4b shows a side view.

Claims

1. A low-impedance, high-current coaxial line (1) for a plasma process system (10), a) Specifically, a tubular thermally conductive electrical insulator (2) made of ceramic, b) An electrical outer conductor (3) arranged on the insulator in the form of an outer layer, c) comprising an electrical internal conductor (4) arranged within the insulator in the form of an inner layer, d) The inner and outer diameters of the insulator (2) are sized such that a line impedance of 20 Ω or less can be achieved. e) The low-impedance, high-current coaxial line (1) is designed to be connected to the impedance matching circuit (6) and the plasma process assembly (7), f) The low-impedance, high-current coaxial line (1) is designed to supply HF power to the plasma process assembly (7) by an HF power supply (9).

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), specifically a fluid cooling device made of copper.

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

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

5. The low-impedance, high-current coaxial line (1) according to claim 1 or 2, wherein the internal cavity of the low-impedance, high-current coaxial line (1) is partially filled with material.

6. The low-impedance, high-current coaxial line (1) according to claim 1 or 2, wherein the low-impedance, high-current coaxial line (1) is designed for pulsed plasma processing having a pulse frequency of 200 kHz or higher, specifically 400 kHz or higher.

7. A plasma process supply system (8) having an impedance matching circuit (6) and a low-impedance, high-current coaxial line (1) as described in claim 1, wherein the plasma process supply system (8) is connected to the impedance matching circuit (6) and is designed to be connected at the 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. Plasma process supply system (8) according to claim 7, comprising an HF power supply (9), wherein the impedance matching circuit (6) is electrically connected to the HF power supply (9) via the impedance matching circuit (6) and the low-impedance, high-current coaxial line (1) so that power supplied by the HF power supply (9) during operation can be supplied to the plasma process assembly (7).

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

10. A plasma process system (10) comprising a plasma process supply system (8) according to claim 7 and a plasma process assembly (7), wherein the low-impedance, high-current coaxial line (1) establishes a connection between the impedance matching circuit (6) and the plasma process assembly (7).

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

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

Images