CONTROL DEVICE AND METHOD FOR CONTROLLING IMPEDANCE MATCHING CIRCUIT FOR A PLASMA GENERATION SYSTEM, AND PLASMA GENERATION SYSTEM - Patent application

Abstract

The control device 1 is used to control an impedance matching circuit 50 for a plasma generation system 100, the impedance matching circuit 50 having an input terminal 50a and an output terminal 50b. The impedance matching circuit 50 is connected between an HF generator 60 and a load 70. The control device 1 is configured to determine an impedance target value at the input terminal 50a of the impedance matching circuit 50 based on a) a pre-determinable operating frequency of the HF generator 60, b) a pre-determinable target power of the HF generator 60, and c) model parameters of the HF generator 60, the impedance target value having a value different from the nominal impedance in order to achieve improved operating characteristics, in particular efficiency, of the HF generator 60 at the pre-determinable operating frequency and the pre-determinable target power.

Description

[Technical Field]

[0001] The present invention relates to a control device for controlling an impedance matching circuit for a plasma generation system, a method for controlling an impedance matching circuit for a plasma generation system, and a plasma generation system equipped with such a control device. [Background technology]

[0002] Surface treatment of workpieces using plasma and gas lasers is an industrial process in which plasma is generated, particularly in a plasma chamber, using direct current or high-frequency alternating current signals with operating frequencies in the range of several tens of kHz to GHz.

[0003] The plasma chamber is then connected to a high frequency generator (HF generator) via further electronic components such as coils, capacitors, wires or transformers, which may function as resonant circuits, filters or impedance matching.

[0004] A problem with plasma processing is that the electrical load impedance of the plasma generated in the plasma chamber during the process varies greatly depending on the conditions within the plasma chamber. This is particularly affected by the characteristics of the workpiece, electrode, and gas conditions. A characteristic of such large load fluctuations is that they can occur faster than the load matching achieved by controlled impedance matching. In particular, the load fluctuations can occur within the period of the fundamental wave, i.e., within the period of the HF power signal that activates the plasma. In this case, not only the power of the fundamental wave but also the power components of the harmonics, or so-called harmonic waves, are reflected.

[0005] High frequency generators have a limited operating range related to the impedance of the electrical load (= consumer) to which they are connected. If the load impedance exceeds the allowable range, the HF generator can be damaged or destroyed. For example, if the reflected power, voltage, or reflected energy is too great for the HF generator, it can often be damaged due to the reflected power.

[0006] This usually requires an impedance matching circuit (matchbox) to transform the impedance of the load to the nominal impedance of the generator output.

[0007] Various impedance matching circuits are known. Impedance matching circuits are configured with electrical components, in particular coils and capacitors, that have a fixed and predetermined transformation function and therefore do not change during operation. This is particularly useful for constant operation, such as in gas lasers. Furthermore, impedance matching circuits are also known in which at least some of the components of the impedance matching circuit are mechanically variable. For example, motor-driven rotating capacitors are known, whose capacitance value is variable by changing the arrangement of the capacitor plates relative to each other.

[0008] Generally, three impedance ranges can be assigned to a plasma. Before ignition, a relatively high real impedance exists. During normal operation, i.e., during the intended operation of the plasma, a relatively low real impedance exists. In the event of an undesired local discharge (arc) or plasma fluctuation, a relatively small impedance value may occur. In addition to these three specified impedance ranges, other special situations may occur in which other impedance values are assigned. If the load impedance changes suddenly and the load impedance or the transformed load impedance falls outside the allowable impedance range, damage to the HF generator or the transmission device between the HF generator and the plasma chamber may occur. Furthermore, undesired plasma stable states may also exist. Therefore, for example, stable plasma may form in undesired areas within the plasma chamber, for example, in the surrounding area rather than at the target.

[0009] An impedance matching circuit is described in, for example, Patent Document 1.

[0010] It is also known that plasma processes require relatively large powers and / or energies, often greater than 1 kW, which nowadays play an increasingly important role.

[0011] The HF generator and the impedance matching circuit each operate at an efficiency that varies depending on several parameters. As the power and / or energy in the plasma process increases, efficiency becomes increasingly important. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] German Patent Application Publication No. 102009001355A1 Summary of the Invention [Problem to be solved by the invention]

[0013] Therefore, an object of the present invention is to establish a low-loss, energy-saving plasma process. [Means for solving the problem]

[0014] This problem is solved according to the invention by a control device according to independent claim 1, a plasma generation system according to independent claim 18 and a method according to independent claim 29.

[0015] The controller is used to control an impedance matching circuit for a plasma generation system, the impedance matching circuit including an input terminal and an output terminal, and connectable between the HF generator and a load, which may be, in particular, at least one electrode at which plasma is generated in a plasma chamber.

[0016] The control device a) the pre-settable operating frequency of the HF generator; b) a pre-settable target power of the HF generator, and c) HF generator model parameters The control device is configured to determine an impedance target value at the input terminals of the impedance matching circuit based on the impedance target value, which has a value different from the nominal impedance of the HF generator in order to achieve improved operating characteristics of the HF generator at a pre-determinable operating frequency and a pre-determinable target power. The operating characteristics of the HF generator are preferably the efficiency of the HF generator. In this case, the control device can be configured to receive, store internally, and / or otherwise access the pre-determinable operating frequency, the pre-determinable target power, and the model parameters of the HF generator. To this end, the control device can receive them, for example, by transmission via an interface, for example, via an electronic data interface. The control device can store them, for example, in an internal electronic data storage device. The control device can also determine them, for example, itself, from other sources or data or a combination thereof.

[0017] It is particularly preferred that the impedance target value at the input terminal of the impedance matching circuit is variable. An HF generator can be connected to the input terminal. If this impedance target value differs from the nominal impedance, the HF generator will be mismatched to the input terminal. In this case, the HF generator operates at an operating point different from the operating point at which it can output maximum power. Instead, an operating point is set at which the HF generator's operable efficiency is improved. This improved efficiency significantly reduces the energy consumption of the HF generator, making the plasma process more energy-efficient. Tests have shown that the maximum power that the HF generator can deliver is rarely required in plasma processes. The HF generator can deliver this maximum power when adapted, i.e., when the impedance target value is set to the HF generator's nominal impedance. However, in this operating state, the HF generator requires the most energy.

[0018] The operating frequency of the HF generator is preferably freely adjustable. The HF generator is specifically designed for plasma processes and is preferably designed to generate and output high frequency signals in the range of 1 MHz to 200 MHz, preferably in the range of 3 MHz to 100 MHz, more preferably in the range of 12 MHz to 50 MHz. More preferably, the HF generator is designed to generate HF signals having frequencies of 13.56 MHz, 27 MHz, and / or 40 MHz.

[0019] Basically, it is conceivable that an HF generator can be designed to modulate the HF signal.

[0020] "Efficiency" is preferably understood as the power (especially the active power) coupled to the load relative to the power (especially the active power) consumed by the generator.

[0021] In a preferred embodiment, the operating characteristics are the following characteristics of the HF generator: a) efficiency, b) temperature, in particular limits on the maximum permissible temperature of certain components, such as transistors, capacitors, inductors, couplers, matching circuits; c) voltages, in particular limits on the maximum permissible voltages on certain components, such as transistors, capacitors, inductors, couplers, matching circuits; d) Limitations of currents, in particular the maximum allowable currents in certain components, such as transistors, capacitors, inductors, couplers, matching circuits; The characteristics of the HF generator related to temperature, voltage and current may also affect the efficiency. A limit on the maximum allowable temperature may be related to the maximum allowable energy consumption. Similarly, a limit on the maximum allowable voltage or current may be related to the maximum allowable energy consumption.

[0022] In a preferred embodiment, the configurable target power is an active power. The target power is rarely the power supplied to the load, because the impedance matching circuit may have an active power loss, which may further depend on the setting of the impedance matching circuit. However, because the active power loss in the impedance matching circuit is reproducible, this does not pose much of a problem for the efficiency of the plasma process. Therefore, a plasma process that operates at a predetermined target power can be guaranteed to continue to function in the future.

[0023] In a further preferred embodiment, the control device is configured to control the impedance matching circuit to set the impedance at the input terminals of the impedance matching circuit to a target impedance value. This can be done before starting the HF generator or while the HF generator is operating. The control device is configured to continuously adjust or change the target impedance value while the HF generator is operating.

[0024] In a further preferred embodiment, the nominal impedance is 50 ohms. This is a standardized value to which most cables and connectors are designed. The output impedance of an HF generator is usually designed to a nominal impedance, so that no reflections are generated by components.

[0025] In a further preferred embodiment, the control device is configured to select an impedance target value that improves efficiency compared to the efficiency at the nominal impedance, preferably an impedance target value that improves efficiency by at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or at least 45% compared to the efficiency at the nominal impedance.

[0026] In a further preferred embodiment, the model parameters of the HF generator include impedance target values corresponding to different predefined target powers, at which the efficiency reaches its maximum value or deviates from its maximum value by a maximum of 10%. The model parameters can be stored, for example, in a look-up table. Corresponding model parameters exist for different operating frequencies. Preferably, a separate look-up table exists for each operating frequency, or alternatively, one look-up table is valid for one or more operating frequencies or for a frequency range. It is also conceivable to calculate the look-up table using appropriate conversion factors (values or functions), so that the look-up table can be used at different operating frequencies depending on the conversion factor. This reduces memory requirements. For storing the look-up table, the control device preferably includes a memory device. More preferably, the look-up table stores impedance target values corresponding to different target powers at which the efficiency reaches its maximum value or deviates from its maximum value by a maximum of 10%.

[0027] In a further preferred embodiment, the different target powers are located on one curve or on one family of curves. When one curve is used, the maximum efficiency is preferably achieved. When one family of curves is used, the target powers are preferably located within 10% of the maximum efficiency. This allows the user to visualize the process, which in turn supports the user in setting up the plasma process, in particular allowing the user to set up the plasma process in accordance with the above criteria.

[0028] In a further preferred embodiment, the control device is configured to store impedance target values for adjacent target powers on the curve or on the family of curves, such that minimal mechanical adjustment of the impedance matching circuit requires successive recall of the impedance target values. For example, the target powers can be stored with a resolution of 0.1 in ten. In this case, adjacent target powers would be, for example, 49 dBm and 49.1 dBm. This allows for the selection of an impedance target value that achieves optimal efficiency while minimizing the mechanical adjustment (mechanical range) of the capacitors and / or inductors. This can protect the motor and / or gearing of the impedance matching circuit.

[0029] In a further preferred embodiment, the control device is configured to additionally take into account model parameters of the cable impedance of the connecting cable between the HF generator and the impedance matching circuit. The cable impedance is also frequency-dependent, so that different cable impedances are taken into account for different operating frequencies. This allows the efficiency of the HF generator to be set more accurately.

[0030] In a further preferred embodiment, the control device is configured to read the cable impedance from a storage device, where the cable impedance can be stored, for example, in the same storage device in which the look-up table is stored.

[0031] In a further preferred embodiment, the control device is configured to calculate the cable impedance using first and second measuring units. The first measuring unit can be arranged between the HF generator and the connecting cable. The second measuring unit can be arranged between the connecting cable and the impedance matching circuit or between the impedance matching circuit and the load. Therefore, the first measuring unit can be arranged, in particular, in the region of the output terminal of the HF generator, and the second measuring unit can be arranged, in particular, in the region of the input or output terminal of the impedance matching circuit. Therefore, the control device is configured to determine the current cable impedance of the connecting cable before operating the HF generator and / or to detect changes in the cable impedance of the connecting cable during operation. Therefore, the correct value of the cable impedance is automatically used when connecting another connecting cable. If the second measuring unit is arranged after the impedance matching circuit and before the load, model parameters, in particular the Z parameters of the impedance matching circuit, must also be taken into account. However, these are known for the current state of the impedance matching circuit. The cable impedance can also be referred to as a model parameter of the connecting cable. Therefore, it can be said that the control device is configured to take into account the model parameters of the connecting cable.

[0032] In a further preferred embodiment, the control device includes different model parameters corresponding to different operating frequencies of the HF generator.

[0033] In a further preferred embodiment, the input terminal of the impedance matching circuit is arranged on the case of the impedance matching circuit. However, it is also conceivable that the HF generator can be connected to the impedance matching circuit via a connecting cable. In this case, a first end of the connecting cable can be connected to the HF generator, and a second end of the connecting cable can be connected to the impedance matching circuit, and the input terminal is arranged at the first end of the connecting cable, i.e., at the HF generator. In this case, the input terminal is not arranged directly on the case of the impedance matching circuit. This makes it possible to take the connecting cable into account and it becomes clear that the control device is configured to set the impedance target value acting on the HF generator directly at the output of the HF generator.

[0034] In a further preferred embodiment, the control device is configured to determine different impedance target values at the input terminals of the impedance matching circuit for different pulses during pulsed operation of the HF generator, in which pulses with different amplitudes and preferably also with pulse rest times are generated, thereby maximizing efficiency.

[0035] In a further preferred embodiment, the control device is configured to determine a target impedance value at the input terminals of the impedance matching circuit, the target impedance value being selected so that the HF generator can deliver the target power for the entire envelope of the generated signal. This means that the power of the HF generator must be sufficient to completely track the amplitude of the generated signal. Therefore, the HF generator must be able to deliver sufficient power even for the peaks of the generated signal. In this case, the target impedance value is selected so that the HF generator can deliver the required maximum power.

[0036] The plasma generation system according to the invention comprises a suitable control device as described in the introduction. Furthermore, the plasma generation system comprises an HF generator and an impedance matching circuit. The output terminal of the HF generator is connected to the input terminal of the impedance matching circuit. Preferably, the output terminal of the impedance matching circuit is connected to a load, in particular to at least one electrode in the plasma chamber.

[0037] In a further embodiment, the impedance matching circuit is integrated into the HF generator. This has the advantage that the impedance matching circuit does not need to take into account the cable impedance, which is preferably 50 ohms. This makes it easier to convert, for example, a transistor impedance of 5 ohms into a plasma impedance, which is preferably 2 ohms, because fewer adjustments of the components (e.g., capacitors, inductors) of the impedance matching circuit are required.

[0038] In a further preferred embodiment, the control device is configured to take into account the cable impedance of the connecting cable between the HF generator and the impedance matching circuit when determining the impedance target value at the input terminals of the impedance matching circuit. Preferably, the cable impedance is measured continuously (for example several times per second), so that if the cable impedance changes, the impedance matching circuit is adjusted during operation so that the desired impedance target value is continuously achieved.

[0039] In a further preferred embodiment, the plasma generation system includes first and second measuring units. The control device is configured to calculate the cable impedance of a connecting cable between the HF generator and the impedance matching circuit using the first and second measuring units. The first measuring unit is arranged between the HF generator and the connecting cable. The first measuring unit is arranged closer to the HF generator and the second measuring unit is arranged closer to the impedance matching circuit. The second measuring unit is arranged between the connecting cable and the impedance matching circuit or between the impedance matching circuit and the load.

[0040] In a further preferred embodiment, the first measurement unit is a directional coupler. Additionally or alternatively, the second measurement unit is a directional coupler. Additionally or alternatively, the first measurement unit includes a current sensor and a voltage sensor. Additionally or alternatively, the second measurement unit includes a current sensor and a voltage sensor. These sensors can be used to calculate the cable impedance of the connecting cable.

[0041] The voltage sensor of the first measuring unit has a capacitive voltage divider, and the first capacitor is formed by a conductive ring or cylinder, through which a connecting cable is routed between the HF generator and the impedance matching circuit. The current sensor of the first measuring unit includes a coil arranged around the conductive ring or cylinder. This allows for a compact design. Additionally or alternatively, the voltage sensor of the second measuring unit includes a capacitive voltage divider, and the first capacitor is formed by a conductive ring or cylinder. Through which a connecting cable is routed between the HF generator and the impedance matching circuit or between the impedance matching circuit and the load. The current sensor of the second measuring unit includes a coil arranged around the conductive ring or cylinder. This allows for a particularly compact design.

[0042] In a further preferred embodiment, the control device is configured to vary the power of the HF generator by varying the input power of the amplifier of the HF generator and / or by varying the supply voltage of the amplifier of the HF generator, thereby allowing the HF generator to be precisely adjusted with further improved efficiency.

[0043] In a further preferred embodiment, the first connecting cable includes at least two parallel-connected cables, thereby reducing the impedance of the connecting cable. In this case, the ends of the two inner conductors are electrically connected to each other, particularly by soldering. A 25-ohm cable is created from two 50-ohm cables. In this case, the nominal impedance of the system is 25 ohms. This measure ensures that the transition from the HF generator's transistor impedance of approximately 5 ohms to the 25-ohm cable impedance and the plasma impedance of approximately 2 ohms is smaller than the transition from 5 ohms to the standardized 50-ohm cable impedance and the plasma impedance of approximately 2 ohms. This further reduces losses.

[0044] In a further preferred embodiment, the impedance matching circuit includes one or more capacitors, at least one of which has a variable capacitance value during operation. This can be achieved by a rotating capacitor, in particular a vacuum rotating capacitor, driven by a motor, in particular a stepping motor. A gear mechanism is also preferably provided. Instead of a motor, a switch, in particular a semiconductor switch (solid-state switch), can be used to increase or decrease the capacitance. In particular, a plurality of such switched capacitors can be provided to allow a plurality of different capacitance values to be set. In this case, the impedance target value can be set particularly quickly, in particular faster than a motor-driven capacitor adjustment, preferably within 100 ms, 50 ms, 10 ms, or 1 ms or less. This is particularly useful when using pulsed signals, in order to allow a fast reaction to different pulse heights.

[0045] The method according to the invention is used to control an impedance matching circuit for a plasma generation system, the impedance matching circuit having an input terminal connected to the output terminal of an HF generator and an output terminal connected to the input of a load, the method being suitable for setting an input impedance at the input terminal in the event of a varying output impedance at the output terminal, The target impedance value at the input terminal is a) a pre-settable operating frequency of the HF generator; b) a pre-settable target power of the HF generator; c) determining based on model parameters of the HF generator, wherein the impedance target value has a value different from the nominal impedance in order to achieve improved operating characteristics, in particular improved efficiency, of the HF generator at a pre-determinable operating frequency and at a pre-determinable target power.

[0046] Various embodiments of the present invention will now be described, by way of example only, with reference to the drawings, in which like reference numerals refer to like objects and corresponding figures of the drawings showing their details. [Brief explanation of the drawings]

[0047] [Figure 1] FIG. 1 illustrates an embodiment of a plasma generation system including an HF generator, an impedance matching circuit, a controller, and a plasma chamber. [Figure 2A] FIG. 1 is a diagram illustrating an example of an impedance matching circuit. [Figure 2B] FIG. 10 is a diagram illustrating another embodiment of an impedance matching circuit. [Figure 3] FIG. 2 shows an embodiment of a first and / or second measuring unit for contactlessly measuring voltage and current. [Figure 4] 1 is a Smith chart showing how an HF generator transitions from maximum power to maximum efficiency depending on the impedance target value. [Figure 5]10 is a graph showing the progression of efficiency at a particular target power in relation to a required impedance target value. [Figure 6] 10 is a flowchart illustrating a method for controlling the impedance matching circuit. DETAILED DESCRIPTION OF THE INVENTION

[0048] FIG. 1 shows a plasma generation system 100, which is particularly useful for surface treatment of workpieces.

[0049] The plasma generation system 100 comprises a control device 1, an impedance matching circuit 50, an HF generator 60, and a plasma chamber 70 as a load. The HF generator 60 is electrically connected to the impedance matching circuit 50. This connection is preferably made via a connecting cable 2a, in particular a first connecting cable 2a, which is at least a first coaxial cable 2a. The first connecting cable 2a is connected to an output terminal 60a of the HF generator 60 and an input terminal 50a of the impedance matching circuit 50. The impedance matching circuit 50 is further electrically connected to the plasma chamber 70. This connection is preferably made via a second connecting cable 2b, in particular a second coaxial cable 2b. The impedance matching circuit 50 is often arranged close to the plasma chamber 70, in particular at a distance of 10 cm or less, preferably directly to the plasma chamber 70. This allows the second connecting cable 2b to be made correspondingly short and to have only a few mechanical parts, such as plugs and / or cable connectors. The second connection cable 2b is connected to the output terminal 50b of the impedance matching circuit 50 and to the input of the plasma chamber 70. Preferably, the second connection cable 2b is connected to an electrode in the plasma chamber 70.

[0050] The first connecting cable 2a is longer than the second connecting cable 2b, preferably 2 times, 3 times, 4 times, 5 times, 6 times, 7 times or at least 8 times longer than the second connecting cable 2b.

[0051] The first connecting cable 2a can include at least two parallel-connected cables to reduce the overall impedance of the connecting cable. In this case, the ends of the two inner conductors are electrically connected, in particular soldered, to each other. Thus, one 25-ohm cable is created from two 50-ohm cables. This reduces the transition from the transistor impedance of the HF generator 60, which is about 5 ohms, to the cable impedance of 25 ohms and the plasma impedance, which is about 2 ohms. In this case, the nominal impedance is 25 ohms.

[0052] The plasma generation system 100 preferably includes an input / output device 80, which is preferably a touch screen in particular. A keyboard and / or a mouse and a monitor may also be considered as input / output device 80.

[0053] The plasma chamber 70 can be considered a consumer (load). Depending on the application, one or more electrodes 3 can be provided in the plasma chamber 70, for example, at least one of which is connected to the second connecting cable 2b. In Figure 1, the plasma 4 in the plasma chamber 70 is indicated by a dot.

[0054] Preferably, the plasma generation system 100 also includes an optical device 90. The optical device 90 is more preferably disposed within the plasma chamber 70 and configured to visually detect the plasma 4 and, therefore, the plasma state. The optical device 90 may be, for example, a photoconductor such as glass fiber. A camera may also be used, but for cost reasons, a camera is often omitted. Furthermore, lenses and other protective glass may quickly become fogged by the plasma 4.

[0055] The control device 1 is preferably a processor (eg a microcontroller) and / or a programmable logic device, eg an FPGA (Field Programmable Gate Array).

[0056] The control device 1 is used for controlling the impedance matching circuit 50. The control device 1 is configured to determine an impedance target value at the input terminal 50a based on a pre-determinable operating frequency of the HF generator 60, a pre-determinable target power of the HF generator 60, and model parameters of the HF generator 60. In this case, the impedance target value has a value different from the nominal impedance (usually 50 ohms), so that improved operating characteristics, in particular efficiency, of the HF generator 60 are achieved for the pre-determinable operating frequency and the pre-determinable target power.

[0057] The model parameters of the HF generator 60 include impedance target values corresponding to different pre-settable target powers, at which the efficiency reaches its maximum value or deviates from the maximum value by a maximum of 10%. These target powers can be entered by a user, for example, via the input / output device 80. These target powers can also be stored in the control device 1 for a given plasma process. When the user selects a given plasma process, the target powers stored for this plasma process are fetched and the corresponding impedance target values are loaded.

[0058] A look-up table 9 is preferably stored in the storage device 8, in which impedance target values corresponding to different target powers are stored, at which impedance target values the efficiency is at its maximum or is at most 10% away from its maximum.

[0059] 1, the input terminal 50a of the impedance matching circuit 50 is depicted directly on the case of the impedance matching circuit 50. In principle, the input terminal 50a can also be located at the end of the first connecting cable 2a, at which the first connecting cable 2a is connected to the HF generator 60. This still takes into account the cable impedance of the first connecting cable 2a. In this case, the HF generator 60 directly sees the impedance target value, which is not distorted by the first connecting cable 2a.

[0060] As mentioned above, the control device 1 is preferably configured to further take into account model parameters of the cable impedance of the first connecting cable 2a between the HF generator 60 and the impedance matching circuit 50. The model parameters of the cable impedance can be stored in the memory device 8. These model parameters are frequency dependent, and different cable impedances are loaded depending on the operating frequency of the HF generator 60.

[0061] The control device 1 can also be configured to calculate the cable impedance of the first connecting cable by means of first and second measuring units 5, 6. In this case, the first measuring unit 5 is arranged between the HF generator 60 and the first connecting cable 2a, and the second measuring unit 6 is arranged between the first connecting cable 2a and the impedance matching circuit 50 or between the impedance matching circuit 50 and the load 70. Two second measuring units 6 are shown in Figure 1. If the second measuring unit 6 is arranged between the impedance matching circuit 50 and the load 70, the control device 1 is further configured to take into account model parameters of the impedance matching circuit 50.

[0062] 2A and 2B show different examples of the impedance matching circuit 50. In Fig. 2A, the impedance matching circuit 50 is L-shaped. In Fig. 2B, the impedance matching circuit 50 is T-shaped.

[0063] In FIG. 2A, the input terminal 50a of the impedance matching circuit 50 is connected to a first coil 10 (first inductor) and a second coil 11 (second inductor). The first and second coils 10, 11 are connected by their first terminals to a common node, which is then connected to the input terminal 50a of the impedance matching circuit 50. The first coil 10 is connected to a reference ground via a first capacitor 12 (first capacitor). The second coil 11 is connected to an output terminal 50b via a second capacitor 13 (second capacitor). The first and second capacitors 12, 13 are adjustable components, particularly in the form of rotary capacitors, whose capacitance can be changed by stepping motors. Alternatively, solid-state switches can be used to increase or decrease the capacitance more quickly. In particular, the electrode plate spacing of the first and second capacitors 12, 13 can be changed. The control device 1 is configured to appropriately control the respective stepping motors. Essentially, the control device 1 can perform the control. The capacitances of the first and second capacitors 12, 13 can be adjusted independently of each other. Preferably, the impedance matching circuit 50 does not include any additional components. Of course, the positions of the first coil 10 and the first capacitor 12 can be interchanged. In this case, the first capacitor 12 is arranged at the input terminal 50a of the impedance matching circuit 50, and the first coil 10 is arranged at the reference ground. Additionally or alternatively, the positions of the second coil 11 and the second capacitor 13 can also be interchanged. In this case, the second capacitor 13 is arranged at the input terminal 50a of the impedance matching circuit 50, and the second coil 11 is arranged at the output terminal 50b.

[0064] In FIG. 2B, the input terminal 50a of the impedance matching circuit 50 is connected to a first capacitor 12 (first capacitor). The first capacitor 12 is connected to both a first coil 10 (first inductor) and a second coil 11 (second inductor). This is done via a common node to which the first capacitor 12 and both the first and second coils 10, 11 are connected. The first coil 10 is also connected to a reference ground. The second coil 11 is connected (series) to a second capacitor 13 (second capacitor). The second capacitor 13 is connected to an output terminal 50b of the impedance matching circuit 50. The positions of the second coil 11 and the second capacitor 13 may be interchanged. In this case, the second capacitor 13 is connected to the common node, and the second coil 11 is connected to the output terminal 50b of the impedance matching circuit 50. Preferably, the impedance matching circuit 50 does not include any additional components.

[0065] 3 shows an example of a possible configuration of the first and / or second measuring unit 5, 6. In this example, the first and / or second measuring unit 5, 6 is configured to measure voltage and current contactlessly.

[0066] To that end, the first and / or second measuring unit 5 , 6 comprises a current sensor 15 and a voltage sensor 16 .

[0067] Preferably, however, the phase relationship between current and voltage is measured, thereby allowing the impedance to be calculated.

[0068] The current sensor 15 of the first and / or second measuring unit 5, 6 comprises a coil, in particular in the form of a Rogowski coil.

[0069] The two ends of the coil are preferably connected together via a shunt resistor 17. The voltage dropped across the shunt resistor 17 can be digitized by a first A / D converter (analog-to-digital converter) 18.

[0070] The voltage sensor 16 of the first and / or second measuring unit 5, 6 is preferably configured as a capacitive voltage divider. A first capacitor 19 is formed by a conductive ring 19. A conductive cylinder can also be used. The corresponding first or second connecting cable 2a, 2b is routed through this conductive ring 19. A second capacitor 20 of the voltage sensor 16 configured as a voltage divider is connected to the reference ground. A second A / D converter 21 is connected in parallel to the second capacitor 20 and is configured to detect and digitize the voltage drop across the second capacitor 20.

[0071] Basically, the first measuring unit 5 and the second measuring unit 6 can also be arranged or formed on a (common) circuit board. The first capacitor 19 can be formed by coating a first surface and an opposing second surface of the circuit board. In this case, the coatings on the first and second surfaces are electrically connected to each other by through holes. The first and second connecting cables 2a, 2b are routed through openings in the circuit board. The second capacitor 20 can be formed by separate components.

[0072] The current sensor 15 in the form of a coil, in particular a Rogowski coil, is further from the first and second connecting cables 2a, 2b than the first capacitor 19. The coils can also be formed on the same circuit board by suitable coatings and through-holes. The coil for measuring the current and the first capacitor for measuring the voltage preferably run on a common plane.

[0073] The shunt resistor 17 may also be placed on this circuit board, as may the first and / or second A / D converters 18, 21.

[0074] When the first and second measurement units 5, 6 are arranged on the first connecting cable 2a, they are spaced apart from each other so that mutual interference is reduced to such an extent that it plays only a minor role in terms of the desired measurement accuracy. The first measurement unit 5 is arranged in the area of the HF generator 60, and the second measurement unit 6 is arranged in the area of the impedance matching circuit 50.

[0075] The second measuring unit 6 can also be arranged at the output terminal 50b of the impedance matching circuit 50, while the first measuring unit 5 is further arranged in the area of the HF generator 60, thereby being able to detect the cable impedance of the first connecting cable 2a.

[0076] The first and / or second measuring unit 5, 6 may also be formed as a directional coupler.

[0077] FIG. 4 shows a Smith chart demonstrating how the HF generator 60 transitions from maximum power to maximum efficiency depending on the impedance target.

[0078] In the Smith chart of FIG. 4, six exemplary impedance curves, P1, P2, P3, P4, P5, and P6, are shown. Each impedance target value on the impedance curve indicates that the HF generator 60 has the same output power. This means that the same output power can be achieved from the HF generator 60 at different impedance target values on the same impedance curve. Different impedance curves result in different output powers from the HF generator 60. The HF generator 60 generates different output powers when the impedance target value on the impedance curve P1 is compared to the impedance target value on the impedance curve P2.

[0079] 4 shows only six impedance curves P1, P2, P3, P4, P5, and P6 by way of example, although there may be more than six.

[0080] The Smith chart of FIG. 4 exemplarily shows six additional impedance curves E1, E2, E3, E4, E5, and E6. Each impedance target value located on one of these additional impedance curves means that the HF generator 60 has the same efficiency. This means that the same efficiency can be achieved for an HF generator 60 with different impedance target values. The different impedance curves result in different efficiencies for the HF generator 60. The HF generator 60 operates at different efficiencies when comparing the impedance target value on the impedance curve E1 with the impedance target value on the impedance curve E2.

[0081] For clarity of explanation, some example values are given below.

[0082] [Table 1]

[0083] It can be seen that for the maximum achievable power at the impedance target value on the impedance curve P1, only an efficiency of E6=72% is obtained, whereas at a lower power P2=47.0 dBm an efficiency of E3=84.0% is possible.

[0084] Furthermore, one further curve 30 is also shown, which connects the impedance curve P1 for the maximum possible power with the impedance curve E1 for the maximum possible efficiency.

[0085] On the curve 30, different impedance target values are located for different target powers, and the HF generator 60 then provides the target power at which the efficiency is maximized for each impedance target value. If a user requires a power of P=44.5 dBm, the user moves along the curve 30 to the desired target power. For this target power, the corresponding impedance target value at which the efficiency is maximized is stored. This impedance target value is then set by the impedance matching circuit 50.

[0086] In principle, a family of curves can be plotted, with each impedance target value producing an efficiency that preferably deviates from its maximum by no more than 10%. The use of such a family of curves is advantageous, for example, because it allows the use of impedance targets that minimize the need for mechanical adjustment of the impedance matching circuit 50.

[0087] Preferably, the curve 30, i.e. the relationship between target power, target impedance and optional efficiency, is stored in a look-up table 9. Furthermore, it is clear that for different operating frequencies of the HF generator 60, there may be different extensions of the curve 30.

[0088] 5 is a graph showing the progression of efficiency at a given target power in relation to the required impedance target value. It can be seen that the efficiency decreases as the target power increases. It also shows which efficiency or target power is achievable for which impedance target value. For this purpose, a curve 30 is plotted in FIG. 5, with a first end of the curve 30 corresponding to maximum efficiency and a second end of the curve 30 corresponding to maximum power.

[0089] 6 shows a flowchart illustrating a method for controlling the impedance matching circuit 50. In method step S1, an impedance target value at the input terminal 50a of the impedance matching circuit 50 is determined based on a presettable operating frequency of the HF generator 60, a presettable target power of the HF generator 60, and model parameters of the HF generator 60. The impedance target value differs from the nominal impedance in order to improve the operating characteristics of the HF generator 60, in particular the efficiency of the HF generator 60. In method step S2, the determined impedance target value is set by the impedance matching circuit 50.

[0090] The invention is not limited to the described embodiments: within the scope of the invention, all features described and / or illustrated can be combined in any way. [Explanation of symbols]

[0091] 1. Control device 2a First connecting cable 2b Second connecting cable 5 First measuring unit 6 Second measuring unit 8 Storage device 9. Lookup Tables 15 Current Sensor 16 Voltage Sensor 19 Conductive ring or conductive cylinder (first capacitor) 30 curves 50 Impedance matching circuit 50a input terminal 50b output terminal 60 HF generator 70 load 100 Plasma Generation System

Claims

1. A control device (1) for controlling an impedance matching circuit (50) for a plasma generation system (100), the impedance matching circuit (50) having an input terminal (50a) and an output terminal (50b) and connected between an HF generator (60) and a load (70); The control device (1) a) a pre-settable operating frequency of said HF generator (60); b) a pre-determinable target power of the HF generator (60); and c) model parameters of said HF generator (60); The impedance matching circuit (50) is configured to determine a target impedance value at the input terminal (50a) based on the The control device (1) is characterized in that the impedance target value has a value different from a nominal impedance in order to achieve improved operating characteristics, in particular improved efficiency, of the HF generator (60) at the pre-settable operating frequency and at the pre-settable target power.

2. The operating characteristics include the following characteristics of the HF generator (60): a) efficiency, b) temperature, in particular the limits on the maximum allowable temperature of certain components, such as transistors, capacitors, inductors, couplers, matching circuits; c) voltages, in particular limits on the maximum allowable voltages on certain components, such as transistors, capacitors, inductors, couplers, matching circuits; d) Limitations of currents, in particular the maximum allowable currents in certain components, such as transistors, capacitors, inductors, couplers, matching circuits; 2. A control device (1) according to claim 1, characterized in that it comprises one or more of the following:

3. The control device (1) according to claim 1 or 2, characterized in that the control device (1) is configured to control the impedance matching circuit (50) so as to set the impedance at the input terminal (50a) to the impedance target value.

4. Control device (1) according to any one of claims 1 to 3, characterized in that the nominal impedance is 50 ohms.

5. The control device (1) according to any one of claims 1 to 4, characterized in that the control device (1) is configured to select the impedance target value at which efficiency is improved compared to the efficiency at the nominal impedance.

6. 6. The control device (1) according to claim 1, wherein the model parameters of the HF generator (60) comprise the impedance target values corresponding to different pre-settable target powers, for which the efficiency reaches its maximum value or deviates from its maximum value by a maximum of 10%.

7. 7. Control device (1) according to claim 6, characterized in that the different target powers lie on one curve (30) or on one family of curves.

8. 8. The control device (1) according to claim 7, characterized in that the control device (1) is configured to store the impedance target values for adjacent target powers on the curve (30) or on the family of curves, and a minimum of mechanical adjustment of the impedance matching circuit (50) requires successive recalls of the impedance target values.

9. The control device (1) comprises a memory device (8) having a look-up table (9), The control device (1) according to any one of claims 6 to 8, characterized in that in the look-up table (9) impedance target values corresponding to the different target powers are stored, for which impedance target values the efficiency reaches its maximum value or deviates from its maximum value by a maximum of 10%.

10. The control device (1) according to any one of claims 1 to 9, characterized in that the control device (1) is configured to further take into account model parameters of the cable impedance of the connection cable (2a) between the HF generator (60) and the impedance matching circuit (50).

11. the control device (1) is configured to read the cable impedance from a storage device (8), or 11. The control device (1) according to claim 10, characterized in that the control device (1) is configured to calculate the cable impedance using first and second measuring units (5, 6), wherein the first measuring unit (5) can be arranged between the HF generator (60) and the connecting cable (2a), and the second measuring unit (6) can be arranged between the connecting cable (2a) and the impedance matching circuit (50) or between the impedance matching circuit (50) and the load (70).

12. The control device (1) according to any one of claims 1 to 11, characterized in that the control device (1) is further formed to take into account model parameters of the impedance matching circuit (50).

13. The control device (1) according to any one of claims 1 to 12, characterized in that the control device (1) comprises different model parameters corresponding to different operating frequencies of the HF generator (60).

14. The control device (1) according to any one of claims 1 to 13, characterized in that the input terminal (50a) is arranged on a case of the impedance matching circuit (50).

15. The HF generator (60) is connectable to the impedance matching circuit (50) via a connecting cable (2a), a first end of the connection cable (2a) connectable to the HF generator (60); a second end of the connection cable (2a) connectable to the impedance matching circuit (50); Control device (1) according to any one of claims 1 to 13, characterized in that the input terminal (50a) is arranged at the first end of the connecting cable (2a).

16. The control device (1) according to any one of claims 1 to 15, characterized in that during pulse operation of the HF generator (60) in which pulses of different amplitudes are generated, the control device (1) is configured to determine different impedance target values at the input terminal (50a) of the impedance matching circuit (50) for different pulses.

17. The control device (1) is configured to determine an impedance target value at the input terminal (50a) of the impedance matching circuit (50), Control device (1) according to any one of the preceding claims, characterized in that the impedance target value is selected so that the HF generator (60) is able to deliver a target power for the entire envelope of the generated signal.

18. A plasma generation system (100) comprising: A control device (1) according to any one of claims 1 to 17, HF generator (60) and an impedance matching circuit (50); A plasma generation system (100) in which the output terminal (60a) of the HF generator (60) is connected to the input terminal (50a) of the impedance matching circuit (50).

19. 20. The plasma generation system (100) of claim 18, wherein the impedance matching circuit (50) is integrated into the HF generator (60).

20. 19. The plasma generation system (100) according to claim 18, characterized in that the impedance matching circuit (50) is connected to the HF generator (60) via a connecting cable (2a).

21. 21. The plasma generation system (100) according to claim 20, characterized in that the connection cable (2a) comprises at least two cables connected in parallel to reduce the impedance of the connection cable (2a).

22. 22. The plasma generation system (100) according to claim 20 or 21, characterized in that the control device (1) is configured to take into account the cable impedance of the connection cable (2a) between the HF generator (60) and the impedance matching circuit (50) when determining the impedance target value at the input terminal (50a) of the impedance matching circuit (50).

23. 23. The plasma generation system (100) according to claim 22, characterized in that the control device (1) is configured to take into account the cable impedance of the connection cable (2a) between the HF generator (60) and the impedance matching circuit (50) and to continuously determine it anew during operation of the plasma generation system (100).

24. First and second measuring units (5, 6) are provided, the control device (1) is configured to calculate a cable impedance of the connection cable (2 a) using the first and second measuring units (5, 6); The first measuring unit (5) a) between the HF generator (60) and the connecting cable (2a), and / or b) located in the area of the output terminal (60a) of said HF generator (60); The second measuring unit (6) a) between the connecting cable (2a) and the impedance matching circuit (50) and / or in the area of the input terminal (50a) of the impedance matching circuit (50), or b) the plasma generation system (100) according to any one of claims 20 to 23, arranged between the impedance matching circuit (50) and a load (70).

25. the first measuring unit (5) comprises a directional coupler, and / or the second measuring unit (6) comprises a directional coupler, and / or 25. The plasma generation system (100) according to claim 24, characterized in that the first measurement unit (5) comprises a current sensor (15) and a voltage sensor (16) and / or the second measurement unit (6) comprises a current sensor (15) and a voltage sensor (16).

26. the voltage sensor (16) of the first measuring unit (5) comprises a capacitive voltage divider, a first capacitor being formed by a conductive ring (19) or cylinder through which the connecting cable (2a) is routed in the area of the output terminal (60a) of the HF generator (60) and in the area of the impedance matching circuit (50); the current sensor (15) of the first measuring unit (5) comprises a coil arranged around the conductive ring (19) or cylinder; and / or The voltage sensor (16) of the second measuring unit (6) comprises a capacitive voltage divider, in which a first capacitor is formed by a conductive ring (19) or cylinder through which a) the connection cable (2a) is wired within the area of the input terminal (50a) of the impedance matching circuit (50), or b) a connecting cable (2b) is wired between the impedance matching circuit (50) and the load (70); 26. The plasma generation system (100) according to claim 25, characterized in that the current sensor of the second measuring unit (6) comprises a coil arranged around the conductive ring (19) or cylinder.

27. The control device (1) is configured to vary the power of the HF generator (60), A plasma generation system (100) according to any one of claims 18 to 26, characterized in that the power change is made by changing the input power of the amplifier of the HF generator (60) and / or by changing the supply voltage of the amplifier of the HF generator (60).

28. The plasma generation system (100) according to any one of claims 18 to 27, characterized in that the impedance matching circuit (50) comprises one or more capacitors, the capacitance value of at least one of the capacitors being variable during operation.

29. 1. A method of controlling an impedance matching circuit (50) for a plasma generation system (100), the impedance matching circuit (50) having an input terminal (50a) connected to an output terminal (60a) of an HF generator (60) and an output terminal (50b) connected to an input of a load (70), A method suitable for setting an input impedance at the input terminal (50a) in the event of a varying output impedance at the output terminal (50b), comprising: The impedance target value at the input terminal (50a) is a) a pre-settable operating frequency of said HF generator (60); b) a pre-determinable target power of said HF generator (60); c) determining based on model parameters of the HF generator (60), The method is characterized in that the impedance target value has a value different from a nominal impedance in order to achieve improved operating characteristics, in particular improved efficiency, of the HF generator (60) at the pre-settable operating frequency and at the pre-settable target power.

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