Low-impedance high-current coaxial line for plasma process supply system, plasma process system and method for operating plasma process system

Abstract

The invention relates to a low-impedance high-current coaxial line (1) for a plasma process system (10), comprising: a) a tubular heat-conducting electrical insulator (2), for example made of ceramic, b) an electrical outer conductor (3), which is arranged on the insulator in the form of an outer layer, and c) an electrical inner conductor (4), which is arranged in the insulator in the form of an inner layer, the inner diameter and the outer diameter of the insulator (2) are dimensioned in such a way that a line impedance of < = 20 Omega can be achieved, e) wherein the low-impedance high-current coaxial line (1) is designed to be connected to the impedance adaptation circuit (6) and the plasma process component (7), and f) wherein the low-impedance high-current coaxial line (1) is designed to supply HF power to the plasma process component (7) by means of 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. Background Art

[0002] Such a plasma processing system may be, for example, a system that supplies electrical power to a load such as a plasma processing assembly.

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

[0004] In such applications, plasma processing components are used to generate plasma.

[0005] For this purpose, the plasma process component can have an electrode which is supplied with a high-frequency power signal, hereinafter referred to as an HF power signal, for generating the plasma.

[0006] Typically, the plasma process assembly may be connected to a high frequency power supply, hereinafter referred to as HF power supply.

[0007] The HF power signal has a frequency greater than or equal to 4 MHz, in particular less than or equal to 200 MHz. Frequencies commonly used are 13.56 MHz, 27 MHz, and 40 MHz.

[0008] US Pat. No. 6,673,724 B2 describes a plasma processing system in which the electrodes are additionally exposed to a pulsed RF signal as a so-called "RF pulse bias," wherein the pulse frequency may be in the range of 10 kHz to 1 MHz. For various reasons, such an arrangement is not easy to implement in practice, as will be described in more detail below.

[0009] Plasma processes performed in a plasma process assembly often suffer from the problem that the electrical load impedance of the plasma process assembly occurring during the process depends on the conditions in the plasma process assembly and can vary significantly. In particular, the characteristics of the workpiece, electrodes, and gas conditions must be taken into account.

[0010] Therefore, an impedance adaptation circuit is usually required to convert the impedance of the load to the nominal impedance of the HF power supply. Such an impedance adaptation circuit is usually arranged between the HF power supply and the plasma process component, usually in close proximity to the plasma process component.

[0011] The impedance matching circuit and the plasma process components are typically connected via interconnects such as copper sheets, copper bars, or copper tubes.

[0012] Such interconnections exhibit parasitic inductances. These parasitic inductances increase the mass of the load impedance, which reduces the possible bandwidth of the impedance adaptation circuit. Impedance mass is understood as a factor that represents the ratio of energy stored in an oscillating system to energy lost as heat during subsequent oscillation cycles. A high-quality system means that the system converts stored energy into heat only to a small extent, and the oscillations are only slightly reduced. The combination of increased mass and reduced bandwidth reduces the ability to transmit fast pulses to plasma process components via the impedance adaptation circuit.

[0013] In addition, the reactive current in the impedance adaptation circuit increases, thereby reducing its efficiency.

[0014] Purpose of the Invention

[0015] The present invention is therefore based on the object of providing a high-current coaxial line for a plasma process supply system and a plasma process system that increases the mass of the load impedance in the plasma process system only slightly or not at all. It is also an object 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 a plasma process system. Summary of the Invention

[0016] 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 emerge from the dependent claims and / or the description.

[0017] According to the present invention, a low-impedance, high-current coaxial line for a plasma process system is proposed. The low-impedance, high-current coaxial line has:

[0018] a) a tubular thermally conductive electrical insulator, in particular made of ceramic,

[0019] b) an electrical outer conductor, which is arranged in the form of an outer layer on the insulating body,

[0020] c) an electrical inner conductor, which is arranged in the form of an inner layer in the insulation,

[0021] d) wherein the inner and outer diameters of the insulator are dimensioned such that a line impedance of ≤ 20Ω can be achieved,

[0022] e) wherein the low impedance, high current coaxial line is designed to be connected to the impedance matching circuit and the plasma process component,

[0023] f) wherein the low-impedance, high-current coaxial line is designed to supply HF power to the plasma process component by means of an HF power supply.

[0024] In this way, the mass of the load impedance in the plasma process system can be increased only slightly or not at all, and in particular can even be reduced. And in particular, this can be achieved without additional damping measures such as lossy resistors, which would have a negative impact on the efficiency of the plasma process system.

[0025] Utilizing such low-impedance, high-current coaxial lines, inductive connections within plasma processing systems can be replaced by coaxial lines. However, in this context, the coaxial lines are not conventional 50Ω wires. Instead, they are intentionally designed to more closely match the impedance of plasma processing components during operation. This helps reduce reflections.

[0026] Such a plasma process system usually has an impedance adaptation circuit and a plasma process component as a load. In addition, the plasma process system may also have an HF power supply for providing HF power.

[0027] The low-impedance, high-current coaxial line according to the present invention can interconnect the impedance adaptation circuit and the plasma process components in such a plasma process system.

[0028] To this end, a potential electrode in the plasma process assembly can be in contact with the inner conductor of a low-impedance, high-current coaxial line and connected to a signal in the impedance adaptation circuit. In this context, 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 adaptation circuit, in particular to its housing ground. This ground can be connected to the ground of the plasma process assembly, in particular to its housing ground.

[0029] The inner conductor can preferably be applied to the insulation as a coating of, for example, copper and / or silver. Such coating materials can have a positive influence on electrical and thermal conductivity.

[0030] The wall thickness of the tubular thermally conductive electrical insulator can be ≤2 mm. This allows the impedance to be well adjusted, and thanks to the good insulating properties of the insulator, the relatively thin thickness can still isolate high voltages and prevent flashover, corona discharge and / or partial discharge.

[0031] The outer conductor can preferably be applied to the insulator as a coating, for example, of copper and / or silver. Such a coating material can have a positive effect on electrical and thermal conductivity. In addition, the relative magnetic permeability of the conductor is close to 1 and there is no negative impact on the skin effect.

[0032] The electrical inner conductor can be arranged as an inner layer in the insulation so that it is firmly connected to the insulation, in particular by being applied in a galvanic process, a plasma deposition process or a sintering process. In this way, a very reliable arrangement can be achieved.

[0033] The electrical outer conductor can be arranged as an outer layer on the insulator so that it is firmly connected to the insulator, in particular by being applied in an electroplating process, a plasma deposition process, or a sintering process. This makes it possible to achieve a very reliable arrangement. In addition, the relative magnetic permeability of the conductor is close to 1 and there is no negative impact on the skin effect.

[0034] By using thermally conductive electrical insulators, the current-carrying capacity of low-impedance, high-current coaxial cables can be significantly improved through cooling. In particular, the electrical insulator material can include, or preferably consist of, ceramic. Choosing ceramic as the material allows for a thin insulation layer due to its high dielectric strength. Such a thin insulation layer can also achieve a particularly low characteristic impedance. Therefore, the impedance of the cable can be determined by the choice of the insulator material, as well as the inner and outer diameters.

[0035] This provides a low-impedance, high-current coaxial line to which the impedance adaptation circuit and plasma process components can be connected with little or no increase in the mass of the load impedance, depending on the line impedance in that regard. This enables a higher possible bandwidth of the impedance adaptation circuit, better behavior at high pulse frequencies, and better efficiency of the impedance matching circuit.

[0036] The outer conductor of the low impedance high current coaxial line can be designed to be connected to ground. This enables it to be advantageously connected to plasma process components which are also typically connected to ground.

[0037] Furthermore, the outer conductor of the low-impedance, high-current coaxial line can be integrated into a cooling device, preferably a fluid cooling device made of copper. This enables the low-impedance, high-current coaxial line to be reliably connected thermally and electrically to the surrounding system.

[0038] The low-impedance, high-current coaxial cable 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 cable is not the same length as the insulator, but is slightly shortened at at least one end, and preferably at both ends, of the insulator. This enables greater creepage and clearance distances, making the low-impedance, high-current coaxial cable suitable for higher voltages and, therefore, greater power transmission, while also providing more reliable ignition.

[0039] Furthermore, the inner and outer diameters of the insulator can be selected such that the impedance of the low-impedance, high-current coaxial line approaches the impedance of the plasma processing component in the ignited plasma state. This makes the plasma processing system more efficient overall. "Approximate impedance" here means a difference of less than or equal to 10Ω, particularly less than or equal to 5Ω, and particularly preferably less than or equal to 2Ω in absolute terms.

[0040] The cavity within the low-impedance, high-current coaxial line can be filled with a material, particularly an airtight and / or moisture-proof material. The entire cavity can be filled, or only a portion. Since no electric or magnetic fields exist within the cavity of the low-impedance, high-current coaxial line, the material selection is minimally limited. By filling the cavity of the low-impedance, high-current coaxial line, a vacuum-tight connection between the low-impedance, high-current coaxial line and an electrode in a plasma process assembly can be achieved. If the cavity is only partially filled with material, this can save material. By filling the entire cavity, high stability of the low-impedance, high-current coaxial line is achieved.

[0041] Additionally, low impedance, high current coaxial lines can be used in pulsed plasma processing where the pulse frequency is as high as 400 kHz.

[0042] Advantageously, the low-impedance, high-current coaxial line is designed to supply pulsed HF power to the plasma process components, in particular at a pulse frequency of greater than or equal to 200 kHz, wherein the pulsed HF power is provided, in particular, by an HF power source. Advantageously, the pulse power can be 400 kHz. This allows the pulse power to be coupled into the plasma process with low reflectivity and only slight distortion due to filtering effects of otherwise significantly mismatched connections. Consequently, the edge steepness of the pulses in the plasma process can be significantly improved.

[0043] In another embodiment, this object can be achieved by a plasma process supply system having an impedance matching circuit and the previously described low-impedance, high-current coaxial line. The low-impedance, high-current coaxial line is connected to the impedance matching circuit and is designed to be connected to the plasma process component at its other end, thereby establishing a connection between the plasma process supply system and the plasma process component. In this way, HF power can be delivered to the plasma process component with low reflection.

[0044] In another embodiment, the aforementioned plasma process supply system may include an HF power supply, wherein an impedance adaptation circuit is electrically connected to the HF power supply, such that power supplied by the HF power supply during operation can be supplied to the plasma process component via the impedance adaptation circuit and a low-impedance, high-current coaxial line. In this manner, the HF power can be delivered to the plasma process component with particularly low reflection.

[0045] In a further embodiment, one of the aforementioned plasma process supply systems can be designed such that the impedance adaptation circuit is integrated into the HF power supply. In this way, a further improved delivery of HF power to the plasma process component can be achieved.

[0046] In another embodiment, this object can be achieved by a plasma process system having the aforementioned plasma process supply system and a plasma process component, wherein a low-impedance, high-current coaxial line establishes a connection between the impedance adaptation circuit and the plasma process component. In this manner, further improved HF power delivery to the plasma process component can be achieved.

[0047] In a plasma process system including an impedance adaptation circuit, a plasma process component, and an HF power supply, the previously described low-impedance, high-current coaxial line can interconnect the impedance adaptation circuit and the plasma process component. The impedance adaptation circuit can be arranged inside the HF power supply or integrated into the HF power supply.

[0048] The object is also achieved by a method for operating a plasma process component using the previously described plasma process supply system, wherein an HF power signal for generating a plasma in the plasma process component is guided to the plasma process component by means of a low-impedance, high-current coaxial line.

[0049] In one aspect of the method for operating a plasma process component, an HF power signal for generating a plasma in the plasma process component is pulsed between different power levels, in particular at a pulse frequency greater than or equal to 200 kHz, particularly preferably at a pulse frequency greater than or equal to 400 kHz. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In the attached figure:

[0051] Figure 1a A schematic cross-sectional view showing a first embodiment of a low-impedance, high-current coaxial line according to the present invention

[0052] Figure 1b A schematic side view showing a first embodiment of a low-impedance, high-current coaxial line according to the present invention

[0053] Figure 2 Shows a low impedance, high current coaxial line arranged in a plasma process system without an HF power supply

[0054] Figure 3 Shows a low impedance, high current coaxial line arranged in a plasma process system with an HF power supply

[0055] Figure 4a Cross-sectional view showing the integration of low impedance, high current coaxial lines into a cooling device

[0056] Figure 4b Side view showing low impedance, high current coaxial line integrated into cooling device DETAILED DESCRIPTION

[0057] Figure 1a and Figure 1b A first embodiment of a low-impedance, high-current coaxial line 1 according to the present invention is shown. The low-impedance, high-current coaxial line 1 comprises an insulator 2 , an electrical inner conductor 4 and an electrical outer conductor 3 .

[0058] 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 to the inner side of the insulator 2 and connected thereto. The outer conductor 3 is applied as an outer layer to the outer side of the insulator 2 and connected thereto. Figure 1a In FIG. 1 , a low impedance, high current coaxial line 1 is shown in cross section, and in FIG. Figure 1b A low-impedance, high-current coaxial line 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 typically implemented this way. In this respect, 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 allows for increased air and creepage distances, which can improve dielectric strength.

[0059] The low-impedance, high-current coaxial line 1 can be used to connect the impedance adaptation circuit 6 to the plasma process component 7 .

[0060] Figure 2 An embodiment of a low-impedance, high-current coaxial line 1 according to the invention is shown, which is arranged in a plasma process system 10 , which additionally has a plasma process supply system 8 and a plasma process component 7 .

[0061] Here, the low-impedance, high-current coaxial line 1 further comprises 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 further comprises an impedance adaptation circuit 6.

[0062] The impedance adaptation circuit 6 is connected to the plasma process component 7 via the low-impedance, high-current coaxial line 1 .

[0063] The plasma process assembly 7 is thus connected to a plasma process supply system 8 , together forming a plasma process system 10 .

[0064] Figure 3 The arrangement according to the present invention is shown in FIG. Figure 2An embodiment of a low-impedance, high-current coaxial line 1 in a plasma process system 10 is described in the description of FIG. In this case, the plasma process system 10 includes an additional HF power supply 9 for supplying HF power. The impedance adaptation circuit 6 is arranged in or integrated into the HF power supply 9. In another arrangement (not shown), the impedance adaptation circuit 6 can also be arranged separately from the HF power supply 9. This is particularly useful in situations where the HF power supply 9 is too large or cannot be arranged in close proximity to the plasma process component 7 for other reasons, but the impedance adaptation circuit 6 can be arranged in close proximity to the plasma process component.

[0065] Figure 4a and Figure 4b It shows that according to the present invention Figure 1a and Figure 1b An embodiment of the low-impedance, high-current coaxial line 1 is described in the description.

[0066] 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 can preferably be a fluid cooling device with holes for fluid flow. Figure 4a In FIG. 1 , a cross-sectional view is shown in which a low-impedance, high-current coaxial line 1 is integrated into a cooling device 5 and in FIG. Figure 4b FIG. 4 shows a side view of a low-impedance, high-current coaxial line 1 integrated into a cooling device 5 .

Claims

1. A low-impedance, high-current coaxial line (1) for a plasma process system (10), the low-impedance, high-current coaxial line having: a) a tubular thermally conductive electrical insulator (2), in particular made of ceramic, b) an electrical outer conductor (3) arranged in the form of an outer layer on the insulation, c) an electrical inner conductor (4), which is arranged in the form of an inner layer in the insulating body, d) wherein the inner and outer diameters of the insulator (2) are dimensioned such that a line impedance of ≤ 20Ω can be achieved, e) Among them, The low-impedance, high-current coaxial line (1) is designed to be connected to an impedance adaptation circuit (6) and a plasma process component (7). f) Among them, The low-impedance, high-current coaxial line (1) is designed to supply HF power to the plasma process component (7) by means of 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), in particular into a fluid cooling device made of copper.

3. The low-impedance, high-current coaxial line (1) according to any one of the preceding claims, wherein: The insulator (2) protrudes beyond the outer conductor (3) at one end.

4. The low-impedance, high-current coaxial line (1) according to any one of the preceding claims, wherein: The inner diameter and outer diameter of the insulator (2) are designed so that the line impedance is close to the impedance of the plasma process component (8) in the ignition plasma state.

5. The low-impedance, high-current coaxial line (1) according to any one of the preceding claims, wherein: The inner 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 any one of the preceding claims, wherein: The low-impedance, high-current coaxial line (1) is designed for pulse plasma processing at a pulse frequency greater than or equal to 200 kHz, in particular greater than or equal to 400 kHz.

7. A plasma process supply system (8), comprising an impedance adaptation circuit (6) and a low-impedance, high-current coaxial line (1) according to any one of the preceding claims, wherein the low-impedance, high-current coaxial line is connected to the impedance adaptation circuit (6) and is designed to be connected to a plasma process component (7) with its other end, thereby establishing a connection between the plasma process supply system (8) and the plasma process component (7).

8. The plasma process supply system (8) according to claim 7, comprising an HF power supply (9), wherein: The impedance adaptation circuit (6) is electrically connected to the HF power supply (9) so that the power supplied by the HF power supply (9) during operation can be supplied to the plasma process component (7) via the impedance adaptation circuit (6) and the low-impedance high-current coaxial line (1).

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

10. A plasma process system (10) comprising a plasma process supply system (8) and a plasma process component (7) according to any one of claims 7 to 9, wherein: The low-impedance, high-current coaxial line (1) establishes a connection between the impedance adaptation circuit (6) and the plasma process component (7).

11. A method for operating a plasma process component (7) using a plasma process supply system (8) according to any one of claims 7 to 9 or using a plasma process system (10) according to claim 10, wherein: An HF power signal for generating plasma in the plasma process component (7) is guided to the plasma process component (7) by means of the low-impedance, high-current coaxial line (1).

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

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