CONTROL DEVICE AND METHOD FOR CONTROLLING AN IMPEDANCE ADJUSTING CIRCUIT FOR A PLASMA GENERATION SYSTEM AND SUCH A PLASMA GENERATION SYSTEM

Description

[0001] The 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 such a plasma generation system with such a control device.

[0002] Surface treatment of workpieces using plasma and gas lasers are industrial processes in which, particularly in a plasma chamber, a plasma is generated with direct current or with a high-frequency alternating signal with a working frequency in the range of a few tens of kHz to the GHz range.

[0003] The plasma chamber can be connected to a high-frequency generator (HF generator) via additional electronic components such as coils, capacitors, wires, or transformers. These additional components can function as resonant circuits, filters, or impedance matching devices.

[0004] The plasma process has the problem that the electrical load impedance of the plasma in the plasma chamber, which arises during the process, depends on the conditions in the plasma chamber and can vary considerably. In particular, the properties of the workpiece, electrodes, and gas conditions play a role. A further challenge with such highly variable loads is that these load changes can occur faster than a controlled impedance matching system can adjust the load. Specifically, a load change can even occur within a single period of the fundamental frequency, i.e., the RF power signal that drives the plasma. In such cases, not only is power reflected at the fundamental frequency, but also power components at overtones, the so-called harmonics.

[0005] High-frequency generators have a limited operating range with respect to the impedance of the connected electrical load. If the load impedance deviates from a permissible range, the RF generator can be damaged or even destroyed. In most cases, this is due to reflected power, which can damage the generator. e.g. the reflected power, voltage, or energy becomes too large for the RF generator.

[0006] For this reason, an impedance matching circuit (matchbox) is usually required, which transforms the impedance of the load to a nominal impedance of the generator output.

[0007] Various impedance matching circuits are known. Some impedance matching circuits are fixed and have a predetermined transformation effect, meaning they consist of electrical components, particularly inductors and capacitors, that are not changed during operation. This is especially useful for applications with constant operation, such as a gas laser. Other impedance matching circuits are known in which at least some of the components are mechanically variable. For example, motor-driven variable capacitors are known whose capacitance can be changed by altering the arrangement of the capacitor plates relative to each other.

[0008] A plasma can be broadly categorized into three impedance ranges. Before ignition, impedances with a relatively high real part are present. During normal operation, i.e., during intended operation with plasma, impedances with a relatively lower real part are present. Relatively low impedance values ​​can occur during unwanted local discharges (arcs) or plasma fluctuations. In addition to these three identified impedance ranges, other special states with different associated impedance values ​​can occur. If the load impedance changes abruptly and, consequently, the load impedance and thus also the transformed load impedance, falls outside a permissible impedance range, the RF generator or transmission equipment between the RF generator and the plasma chamber can be damaged. There are also stable plasma states that are undesirable. For example,in a plasma chamber, a stable plasma forms in an area where it is not desired, e.g. in a peripheral area instead of at the target.

[0009] An impedance matching circuit is described, for example, in DE 10 2009 001 355 A1.

[0010] US Patent 2019 / 272306 A1 describes systems and methods for the stepwise tuning of an impedance matching network. By stepwise tuning the impedance matching network, instead of directly aiming for optimal values ​​of a high frequency and a combined variable capacitance, it becomes possible to process a wafer with the tuned optimal values.

[0011] US Patent 2022 / 139674 A1 describes a power supply system for a plasma processing system and the associated methods. The power supply system comprises a generator with a frequency-tuning subsystem, a match network coupled between the plasma processing chamber and the generator, and a means for adjusting the impedance of the match network, such that the frequency-tuning subsystem adjusts the frequency of the power applied by the generator to a target frequency, while the match network presents a desired impedance to the generator in response to variations in the impedance of a plasma in a plasma processing chamber.

[0012] US 2016 / 322207 A1 describes systems and methods for using multiple devices and efficiency to determine fixed parameters of a matching network model. An efficiency value measured with a network analyzer is compared to a predicted efficiency value determined using the corresponding network model. This comparison determines whether the fixed parameters should be assigned to the matching network model.

[0013] US Patent 6,291,999 B1 describes a plasma monitoring device for monitoring the plasma state of a plasma load to which current is supplied from a high-frequency current source via an impedance match. This involves several calculations of impedances at the input and output of the impedance match.

[0014] It is also known that plasma processes require relatively high power, often one or more kW, and / or energy, which is playing an increasingly important role nowadays.

[0015] An RF generator and an impedance matching circuit each operate with variable efficiency depending on several parameters. As the power and / or energy in the plasma process increases, efficiency becomes increasingly important.

[0016] The object of the invention presented here is therefore to establish a low-loss, energy-saving plasma process.

[0017] The problem is solved by the control device according to independent claim 1, as well as by the plasma generation system according to independent claim 16, and by the method according to independent claim 29.

[0018] The control device is used to control an impedance matching circuit for a plasma generation system. The impedance matching circuit comprises an input terminal and an output terminal and can be connected between an RF generator and a load. The load can be, in particular, at least one electrode at which a plasma is generated, especially in a plasma chamber.

[0019] The control device is designed to use the following: a) a predefinable operating frequency of the RF generator; b) a predefinable target power of the RF generator; and c) model parameters of the RF generator; to determine a target impedance value for the input of the impedance matching circuit, wherein the target impedance value differs from the nominal impedance of the RF generator, in order to increase the operating characteristic of the RF generator for the specified operating frequency and target power. The operating characteristic of the RF generator is preferably its efficiency. The control device can be configured to receive and / or internally store the specified operating frequency, target power, and model parameters of the RF generator and / or have access to them in another way. For example, it can receive them via an interface, such as an electronic data interface. It can store them in an internal electronic data memory.determine this yourself from other sources or data, or a combination thereof.

[0020] It is particularly preferred that the target impedance value for the input terminal of the impedance matching circuit is adjustable. The RF generator can be connected to this input terminal. If this target impedance value deviates from the nominal impedance, the RF generator is mismatched to the input terminal. The RF generator then operates at a different operating point than the one at which it can deliver its maximum power. Instead, an operating point is set at which the efficiency of the RF generator is increased. This increased efficiency significantly reduces the energy consumption of the RF generator, and the plasma process becomes more energy-efficient. Studies have shown that the maximum power output of the RF generator is rarely required in a plasma process.The RF generator can provide such maximum power when impedance matching is achieved, i.e., when the target impedance is set to the RF generator's nominal impedance. However, the RF generator also requires the most energy in this operating state.

[0021] The operating frequency of the RF generator is preferably freely adjustable. The RF generator is designed, particularly for plasma processes, to generate and output RF signals in the range of preferably 1 MHz to 200 MHz, more preferably in the range of 3 MHz to 100 MHz, and more preferably in the range of 12 MHz to 50 MHz. More preferably, the RF generator is configured to generate RF signals with frequencies of 13.56 MHz, 27 MHz, and / or 40 MHz.

[0022] In principle, it is conceivable that the RF generator could be designed to modulate the RF signal.

[0023] The term "efficiency" is preferably understood to mean the power coupled into the load (especially active power) in relation to the power (especially active power) absorbed by the generator.

[0024] In a preferred embodiment, the operating characteristic includes one or more of the following properties of the RF generator: a) Efficiency; b) Temperature, in particular the limitation to a maximum permissible temperature, in certain components, e.g. transistors, capacitors, inductors, couplers, matching circuits; c) Voltage, in particular the limitation to a maximum permissible voltage, in certain components, e.g. transistors, capacitors, inductors, couplers, matching circuits; d) Current, voltages, in particular the limitation to a maximum permissible current, in certain components, e.g. transistors, capacitors, inductors, couplers, matching circuits.

[0025] The characteristics of the RF generator, relating to temperature, voltage, and current, can also influence its efficiency. Limiting the operating temperature to a maximum permissible temperature can correlate with a maximum permissible energy consumption. Similarly, limiting the voltage or current to a maximum permissible voltage or current can also correlate with a maximum permissible energy consumption.

[0026] In a preferred embodiment, the adjustable target power is active power. The target power is rarely the same as the power delivered to the load, because an impedance matching circuit can exhibit active power losses, which can also depend on the impedance matching circuit's setting. However, this is less of a hindrance to the efficiency of the plasma process because the active power losses in the impedance matching circuit are reproducible. This ensures that a plasma process that functions at a specific target power will continue to function in the future.

[0027] In another preferred embodiment, the control device is configured to control the impedance matching circuit such that it adjusts the impedance of the input terminal of the impedance matching circuit to the target impedance value. This can be done before activating the RF generator or during operation of the RF generator. The control device is also configured to continuously adjust, i.e., change, the target impedance values ​​during operation of the RF generator.

[0028] In another preferred embodiment, the nominal impedance is 50 ohms. This is a standardized value, and most cables and connectors are designed for it. The output impedance of the RF generator is typically designed to match the nominal impedance to prevent reflections from the components.

[0029] In a further preferred embodiment, the control device is configured to select the target impedance value for which the efficiency is improved compared to the efficiency at nominal impedance. Preferably, the target impedance value is selected for which the efficiency is improved by at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or at least 45% compared to the efficiency at nominal impedance.

[0030] In another preferred embodiment, the model parameters of the RF generator for various predefined target power outputs include corresponding target impedance values. For the respective target impedance values, the efficiency reaches its maximum or is at most 10% away from its maximum. The model parameters can be stored, for example, in a lookup table. Corresponding model parameters exist for the different operating frequencies. Preferably, there is a separate lookup table for each operating frequency, or a single lookup table is valid for one or more operating frequencies or a frequency range. It is also conceivable that a lookup table is processed with a corresponding conversion factor (value or function) so that this lookup table can be used for different operating frequencies depending on the conversion factor. This reduces the required memory space.The control device preferably includes a storage device for storing the look-up table. More preferably, the look-up table stores corresponding impedance target values ​​for various target power outputs, for which the efficiency reaches its maximum or is at most 10% away from its maximum.

[0031] In another preferred embodiment, the various target performance levels lie on a curve or a family of curves. Using a single curve preferably achieves maximum efficiency. Using a family of curves, the target performance levels can preferably be 10% or less away from the maximum efficiency. This allows the user to visualize the process, thus supporting them in setting up the plasma process, and in particular, making it possible for them to set the process according to the aforementioned criteria.

[0032] In another preferred embodiment, the control device is configured to store, for adjacent target power levels on the curve or family of curves, those impedance target values ​​whose successive recall requires minimal mechanical adjustment of the impedance matching circuit. For example, the target power levels can be stored with a resolution of one-tenth (0.1). Adjacent target power levels would then be, for example, 49 dBm and 49.1 dBm. Those impedance target values ​​could then be selected for which the correspondingly increased efficiency is achieved, while keeping the mechanical adjustment (the mechanical travel distance) of capacitors and / or inductors to a minimum. This protects the motor and / or the gearbox of the impedance matching circuit.

[0033] In a further preferred embodiment, the control device is designed to additionally take into account the model parameters of a cable impedance of a cable connection between the RF generator and the impedance matching circuit. The cable impedance is also frequency-dependent, so different cable impedances are considered for different operating frequencies. This allows the efficiency of the RF generator to be adjusted more precisely.

[0034] In another preferred embodiment, the control device is configured to load the cable impedance from a storage device. In this case, the cable impedance could, for example, be stored in the same storage device in which the look-up table is also stored.

[0035] In a further preferred embodiment, the control device is configured to calculate the cable impedance using a first and a second measuring unit. The first measuring unit can be arranged between the RF generator and the cable connection. The second measuring unit can be arranged between the cable connection and the impedance matching circuit or between the impedance matching circuit and the load. The first measuring unit can therefore be arranged, in particular, in the region of the output terminal of the RF generator, and the second measuring unit can therefore be arranged, in particular, in the region of the input terminal or the output terminal of the impedance matching circuit. The control device is thus configured to determine the current cable impedance of the cable connection before the RF generator is activated and / or to detect a change in the cable impedance of the cable connection during operation.When a different cable connection is used, the correct cable impedance values ​​are automatically applied. If the second measuring unit is located after the impedance matching circuit and before the load, the model parameters, particularly 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 considered a model parameter for the cable connection. Therefore, the control device is also designed to consider the model parameters for the cable connection.

[0036] In another preferred embodiment, the control device for different operating frequencies of the RF generator comprises different model parameters.

[0037] In another preferred embodiment, the input terminal of the impedance matching circuit is located on the housing of the impedance matching circuit. However, it would also be conceivable for the RF generator to be connected to the impedance matching circuit via a cable connection, wherein a first end of the cable connection can be connected to the RF generator and a second end of the cable connection can be connected to the impedance matching circuit, with the input terminal located at the first end of the cable connection and thus on the RF generator. In this case, the input terminal is not located directly on the housing of the impedance matching circuit. This clarifies that the cable connection can be taken into account and that the control device is configured to set a target impedance value directly at the output of the RF generator, which acts on the RF generator.

[0038] In a further preferred embodiment, the control device is designed to determine different target impedance values ​​for the input terminal of the impedance matching circuit for the different pulses during pulsed operation of the RF generator, in which pulses with different amplitudes and preferably also with pulse pauses are generated. This allows efficiency to be maximized.

[0039] In another preferred embodiment, the control device is configured to determine target impedance values ​​for the input of the impedance matching circuit, wherein the target impedance values ​​are selected such that the RF generator can provide a corresponding target power for the entire envelope of a generated signal. This means that the power of the RF generator is sufficient to fully reproduce the amplitude of the generated signal. The RF generator should also be able to provide sufficient power for the peaks of the generated signal. In this case, the target impedance value must be selected such that the RF generator can still generate the necessary maximum power.

[0040] The plasma generation system according to the invention comprises a corresponding control device as described above. Furthermore, the plasma generation system comprises an RF generator and an impedance matching circuit. The output terminal of the RF generator is connected to the input terminal of the impedance matching circuit. Preferably, an output terminal of the impedance matching circuit is connected to a load, in particular at least one electrode in a plasma chamber.

[0041] In another embodiment, the impedance matching circuit is integrated into the RF generator. This has the advantage that the impedance matching circuit does not have to take the cable impedance, which is preferably 50 ohms, into account. For example, the transformation of the transistor impedance, which is 5 ohms, to the plasma impedance, which is preferably 2 ohms, is easier to accomplish because the components of the impedance matching circuit (e.g., capacitors, inductors) require less adjustment.

[0042] In a further preferred embodiment, the control device is designed to take into account the cable impedance of the cable connection between the RF generator and the impedance matching circuit when determining the target impedance value at the input terminal of the impedance matching circuit. Preferably, the cable impedance is measured continuously (e.g., several times per second) so that if the cable impedance changes, the impedance matching circuit is adjusted during operation to ensure that the desired target impedance value is still achieved.

[0043] In a further preferred embodiment, the plasma generation system comprises a first and a second measuring unit. The control device is configured to calculate the cable impedance of the cable connection between the RF generator and the impedance matching circuit using the first and second measuring units. The first measuring unit is arranged between the RF generator and the cable connection. The first measuring unit is arranged closer to the RF generator, and the second measuring unit is arranged closer to the impedance matching circuit. The second measuring unit is arranged between the cable connection and the impedance matching circuit or between the impedance matching circuit and the load.

[0044] In another preferred embodiment, the first measuring unit is a directional coupler. Additionally or alternatively, the second measuring unit is also a directional coupler. Additionally or alternatively, the first measuring unit comprises a current sensor and a voltage sensor. Additionally or alternatively, the second measuring unit comprises a current sensor and a voltage sensor. The cable impedance of the cable connection can be calculated using these sensors.

[0045] In a further preferred embodiment, the voltage sensor of the first measuring unit comprises a capacitive voltage divider, wherein a first capacitance is formed by an electrically conductive ring or cylinder through which the cable connection between the RF generator and the impedance matching circuit is routed. The current sensor of the first measuring unit comprises 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 comprises a capacitive voltage divider, wherein a first capacitance is formed by an electrically conductive ring or cylinder. The cable connection between the RF generator and the impedance matching circuit, or the cable connection between the impedance matching circuit and the load, is routed through the cylinder.The current sensor of the second measuring unit comprises a coil arranged around the conductive ring or cylinder. This allows for a particularly compact design.

[0046] In another preferred embodiment, the control device is configured to change the power output of the RF generator, whereby this is achieved by changing the input power of an amplifier of the RF generator and / or by changing the supply voltage of an amplifier of the RF generator. This allows the RF generator to be tuned even more precisely for further improved efficiency.

[0047] In a further preferred embodiment, the first cable connection comprises at least two cables connected in parallel to reduce the impedance of the cable connection. In this case, the ends of the two inner conductors are electrically connected to each other, in particular by soldering. Two 50-ohm cables would thus be combined to create a 25-ohm cable. In this case, the nominal impedance of the system would be 25 ohms. This measure results in a lower transition from the transistor impedance of the RF generator (approximately 5 ohms) to the cable impedance of 25 ohms and then to the plasma impedance of approximately 2 ohms than the transition from 5 ohms to the cable impedance (the standard 50 ohms) and then to the plasma impedance of approximately 2 ohms. This further reduces losses.

[0048] In a further preferred embodiment, the impedance matching circuit comprises one or more capacitors, wherein the value of at least one capacitor is variable during operation. This change can be achieved by controlling a variable capacitor, particularly a vacuum variable capacitor, by means of a motor, particularly a stepper motor. Preferably, a gearbox is also provided. Instead of a motor, a switch, particularly in the form of a solid-state switch, can also be used to switch capacitors on and / or off. In particular, several such switched capacitors can be provided to enable the setting of multiple different capacitance values. In this case, the target impedance value can be set particularly quickly, especially faster than with a motor-driven capacitor adjustment, preferably in less than 100 ms, 50 ms, 10 ms, or less than 1 ms.This is particularly useful when using a pulsed signal, in order to be able to react quickly to different pulse heights.

[0049] The method according to the invention serves to control an impedance matching circuit for a plasma generation system with an input terminal connected to an output terminal of an RF generator and an output terminal connected to the input of a load. The method is suitable for adjusting the input impedance at the input terminal when the output impedance at the output terminal is variable, using the following steps: Determining a target impedance value for the input connection based on: a) a predefined operating frequency of the RF generator; b) a predefined target power of the RF generator; and c) model parameters of the RF generator; wherein the target impedance value differs from the nominal impedance in order to achieve an increase in an operating characteristic of the RF generator, in particular the efficiency, for the specified operating frequency and the specified target power.

[0050] Various embodiments of the invention are described below by way of example with reference to the drawings. Identical objects have the same reference numerals. The corresponding figures in the drawings show in detail: Figure 1: An embodiment of a plasma generation system comprising an RF generator, an impedance matching circuit, a control device, and a plasma chamber; Figures 2A, 2B: Various embodiments of the impedance matching circuit; Figure 3: An embodiment of a first and / or second measuring unit for non-contact voltage and current measurement; Figure 4: A Smith chart illustrating how the RF generator transitions from maximum power to maximum efficiency depending on the target impedance value; Figure 5: A diagram showing the efficiency curve for specific target powers in relation to the required target impedance values; and Figure 6: A flowchart describing a method for controlling the impedance matching circuit.

[0051] The Figure 1 shows a plasma generation system 100, which is used, among other things, for the surface treatment of workpieces.

[0052] The plasma generation system 100 comprises a control device 1, an impedance matching circuit 50, an RF generator 60, and a plasma chamber 70 as a load. The RF generator 60 is electrically connected to the impedance matching circuit 50. This connection is made via a cable 2a, which is preferably a first cable 2a, in particular at least one first coaxial cable 2a. The first cable 2a is connected to an output terminal 60a of the RF generator 60 and to 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 further, in particular a second, cable 2b, which is preferably a second coaxial cable 2b.The impedance matching circuit 50 is often located close to the plasma chamber 70, particularly at a distance of 10 cm or less, preferably directly adjacent to it, so that the second cable connection 2b is also correspondingly short and has only a few mechanical parts, such as plugs and / or connectors. The second cable connection 2b is connected to an output terminal 50b of the impedance matching circuit 50 and to an input of the plasma chamber 70. Preferably, the second cable connection 2b is connected to an electrode inside the plasma chamber 70.

[0053] The first cable connection 2a is longer than the second cable connection 2b. Preferably, the first cable connection 2a is longer than the second cable connection 2b by a factor of 2, 3, 4, 5, 6, 7 or at least by a factor of 8.

[0054] The first cable connection 2a can also include at least two cables connected in parallel to reduce the overall impedance of the cable connection. In this case, the ends of the two inner conductors are electrically connected to each other, in particular by soldering. Two 50-ohm cables would thus be combined to create a 25-ohm cable. This reduces the transition from the transistor impedance of the RF generator 60 (approximately 5 ohms) to the cable impedance of 25 ohms and then to the plasma impedance of approximately 2 ohms. In this case, the nominal impedance would be 25 ohms.

[0055] The plasma generation system 100 preferably comprises an input and output device 80, which is preferably a screen, in particular one that is touch-sensitive. A keyboard and / or a mouse and a monitor can also be considered an input and output device 80.

[0056] The plasma chamber 70 can be considered a load. Depending on the application, one or more electrodes 3 can be provided in the plasma chamber 70, at least one of which is connected to the second cable connection 2b. A plasma 4 is in Figure 1 within the plasma chamber 70, shown as dotted lines.

[0057] Preferably, the plasma generation system 100 also includes an optical device 90. The optical device 90 is further preferably arranged in the plasma chamber 70 and configured to visually detect the plasma 4 and thus the plasma state. The optical device 90 can, for example, be an optical conductor such as a fiber optic cable. Cameras can be used, but are often omitted for cost reasons. Furthermore, lenses and other protective glass can quickly become cloudy due to the plasma 4.

[0058] The control device 1 is preferably a processor (for example, a microcontroller) and / or a programmable logic module, e.g., an FPGA (Field Programmable Gate Array).

[0059] The control device 1 serves to control the impedance matching circuit 50. The control device 1 is designed to determine a target impedance value for the input terminal 50a based on a predefinable operating frequency of the RF generator 60, a predefinable target power of the RF generator 60 and based on model parameters of the RF generator 60, wherein the target impedance value has a value that differs from the nominal impedance (usually 50 ohms) in order to thereby increase an operating characteristic of the RF generator 60, in particular to increase the efficiency, for the predefinable operating frequency and the predefinable target power.

[0060] The model parameters of the RF generator 60 include corresponding impedance target values ​​for various predefined target powers, at which efficiency reaches its maximum or is at most 10% away from its maximum. These target powers can be entered, for example, by a user via the input / output device 80. They can also be stored in the control device 1 for a specific plasma process. If a user selects a specific plasma process, a target power stored for that plasma process is retrieved and a corresponding impedance target value is loaded.

[0061] Preferably, a look-up table 9 is stored in the storage device 8, in which corresponding impedance target values ​​are stored for various target powers, for which the efficiency reaches its maximum or is at most 10% away from its maximum.

[0062] In Figure 1The input terminal 50a of the impedance matching circuit 50 is shown directly on the housing of the impedance matching circuit 50. In principle, this terminal could also be connected to the end of the first cable connection 2a where the first cable connection 2a is connected to the RF generator 60. This would take the cable impedance of the first cable connection 2a into account. In this case, the RF generator 60 directly sees the target impedance value, which is not distorted by the first cable connection 2a.

[0063] As already explained, it is preferred that the control device 1 is configured to additionally take into account the model parameters of a cable impedance of the first cable connection 2a between the RF generator 60 and the impedance matching circuit 50. The model parameters for the cable impedance can be stored in a memory device 8. These model parameters are frequency-dependent, and different cable impedances are loaded depending on the operating frequency of the RF generator 60.

[0064] The control device 1 could also be configured to calculate the cable impedance of the first cable connection by means of a first and second measuring unit 5, 6, wherein the first measuring unit 5 is arranged between RF generator 60 and the first cable connection 2a, and wherein the second measuring unit 6 is arranged between the first cable connection 2a and impedance matching circuit 50 or between the impedance matching circuit 50 and the load 70. Figure 1 A second measuring unit 6 is shown. In the case that the second measuring unit 6 is arranged between the impedance matching circuit 50 and the load 70, the control device 1 is designed to additionally take into account the model parameters of the impedance matching circuit 50.

[0065] The Figures 2A, 2B Various embodiments of the impedance matching circuit 50 are shown. Figure 2A The impedance matching circuit is L-shaped (50). Figure 2BThe impedance matching circuit is T-shaped (50).

[0066] The input terminal 50a of the impedance matching circuit 50 is in Figure 2AThe circuit is connected to a first coil 10 (first inductor) and a second coil 11 (second inductor). The first terminals of the first and second coils 10 and 11 are connected to a common node, and thus 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 capacitance). The second coil 11 is connected to the output terminal 50b via a second capacitor 13 (second capacitance). The first and second capacitors 12 and 13 are adjustable components, specifically variable capacitors, whose capacitance can be changed by stepper motors. Alternatively, solid-state switches can be used to enable faster switching of the capacitances. In particular, the plate separation of the first and second capacitors 12 and 13 can be changed.The plasma ignition detection device 1 is designed to control the respective stepper motors accordingly. The processing unit 7 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 is free of other components. Of course, the positions of the first coil 10 and the first capacitor 12 can also be reversed. In this case, the first capacitor 12 is connected to the input terminal 50a of the impedance matching circuit 50, and the first coil 10 is connected to ground. Additionally or alternatively, the positions of the second coil 11 and the second capacitor 13 can also be reversed. In this case, the second capacitor 13 is connected to the input terminal 50a of the impedance matching circuit 50, and the second coil 11 is connected to ground.

[0067] The input terminal 50a of the impedance matching circuit 50 is in Figure 2BThe first capacitor 12 (first capacitance) is connected to both the first coil 10 (first inductance) and the second coil 11 (second inductance). This connection is made via a common node to which both the first capacitor 12 and the first and second coils 10 and 11 are connected. The first coil 10 is also connected to ground. The second coil 11 is connected to the second capacitor 13 (second capacitance) in series. The second capacitor 13 is connected to the output terminal 50b of the impedance matching circuit 50. The positions of the second coil 11 and the second capacitor 13 could also be reversed. In this case, the second capacitor 13 would be connected to the common node and the second coil 11 to the output terminal 50b of the impedance matching circuit 50. Preferably, the impedance matching circuit 50 is free of other components.

[0068] Figure 3 Figure 1 shows an embodiment of a possible setup of the first and / or second measuring unit 5, 6. In this embodiment, the first and / or second measuring unit 5, 6 are designed to measure voltage and current without contact.

[0069] For this purpose, the first and second measuring units 5 and 6 comprise a current sensor 15 and a voltage sensor 16.

[0070] However, it is still preferred to measure the phase relationship between current and voltage so that the impedance can be calculated.

[0071] 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.

[0072] Both ends of the coil are preferably connected to each other via a shunt resistor 17. The voltage drop across the shunt resistor 17 can be digitized by means of a first A / D converter (analog-to-digital converter) 18.

[0073] 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 an electrically conductive ring 19. An electrically conductive cylinder could also be used. The corresponding first or second cable connection 2a, 2b is routed through this electrically 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. This converter is designed to detect and digitize the voltage drop across the second capacitor 20.

[0074] In principle, the first measuring unit 5 and the second measuring unit 6 can also be arranged or built on a (shared) printed circuit board. The first capacitance 19 can be formed by a coating on a first and an opposite second side of the printed circuit board. In this case, the coatings on the first and second sides are electrically connected to each other by vias. The first and second cable connections 2a and 2b, respectively, are routed through an opening in the printed circuit board. The second capacitance 20 can be formed by a discrete component.

[0075] The current sensor 15, in the form of a coil, particularly a Rogowski coil, is located further away from the first and second cable connections 2a and 2b, respectively, than the first capacitor 19. The coil can also be formed on the same circuit board by means of appropriate coatings and vias. The coil for current measurement and the first capacitor for voltage measurement preferably lie in a common plane.

[0076] The shunt resistor 17 can also be arranged on this circuit board. The same applies to the first and / or second A / D converters 18, 21.

[0077] If the first and second measuring units 5, 6 are arranged at the first cable connection 2a, they are spaced apart from each other to such an extent that mutual interference is reduced to a minor degree with regard to the desired measurement accuracy. The first measuring unit 5 is located in the area of ​​the RF generator 60, and the second measuring unit 6 is located in the area of ​​the impedance matching circuit 50.

[0078] The second measuring unit 6 could also be arranged at the output terminal 50b of the impedance matching circuit 50, with the first measuring unit 5 still being arranged in the area of ​​the RF generator 60 in order to be able to detect a cable impedance of the first cable connection 2a.

[0079] The first and / or second measuring unit 5, 6 could also be designed as a directional coupler.

[0080] Figure 4shows a Smith chart, which illustrates how the RF generator 60 transitions from maximum power to maximum efficiency depending on the target impedance value.

[0081] In the Smith diagram from Figure 4 Six impedance curves, P1, P2, P3, P4, P5, and P6, are shown as examples. Each target impedance value that lies on a given impedance curve means that the RF generator 60 has the same output power. This means that the same output power of the RF generator 60 can be achieved with different target impedance values ​​that lie on the same impedance curve. Different impedance curves result in different output powers of the RF generator 60. The RF generator 60 produces a different output power when it encounters a target impedance value that lies on impedance curve P1 compared to a target impedance value that lies on impedance curve P2.

[0082] In Figure 4The six impedance curves shown are merely examples: P1, P2, P3, P4, P5, P6. There may be more than six.

[0083] In the Smith diagram from Figure 4 Six additional impedance curves, E1, E2, E3, E4, E5, and E6, are shown as examples. Each target impedance value that lies on one of these additional impedance curves means that the RF generator 60 has the same efficiency. This means that the same efficiency can be achieved for the RF generator 60 with different target impedance values. Different impedance curves result in different efficiencies for the RF generator 60. The RF generator 60 operates at a different efficiency when it sees a target impedance value that lies on impedance curve E1 compared to a target impedance value that lies on impedance curve E2.

[0084] The following are some example values ​​to illustrate the representation. Performance Efficiency P1 = 47.7 dBm E 1 = 91, 5 % P2 = 47.0 dBm E 2 = 88, 0 % P3 = 46.0 dBm E 3 = 84, 0 % P4 = 45.0 dBm E 4 = 80,0 % P 5 = 44.0 dBm E 5 = 76, 0 % P 6 = 43.0 dBm E 6 = 72,0 %

[0085] It can be seen that for the maximum possible power achievable for target impedance values ​​lying on the impedance curve P1, an efficiency of only E6 = 72% is possible. In contrast, for a lower power P2 = 47.0 dBm, an efficiency of E3 = 84.0% is possible.

[0086] Another curve, 30, is also shown. Curve 30 connects the impedance curve P1 for the maximum possible power with the impedance curve E1 for the maximum possible efficiency.

[0087] Curve 30 displays different target impedance values ​​for various target power levels. For each target impedance value, the RF generator 60 provides a target power level at which the efficiency reaches its maximum. If the user requires a power level of P = 44.5 dBm, they move along curve 30 until they reach the desired target power level. A corresponding target impedance value is stored for this target power level, at which the efficiency is at its maximum. This target impedance value is then set by the impedance matching circuit 50.

[0088] In principle, a family of curves could also be plotted, with the respective target impedance values ​​then yielding an efficiency that is preferably no more than 10% away from its maximum. Using a family of curves would then have advantages because, for example, target impedance values ​​could be used that require minimal mechanical adjustment of the impedance matching circuit 50.

[0089] Preferably, curve 30, i.e., the relationship between target power, target impedance values, and optionally efficiency, is stored in look-up table 9. It is also clear that different curve 30 profiles can exist for different operating frequencies of the RF generator 60.

[0090] Figure 5 The diagram shows the efficiency curve for specific target performance levels in relation to the required impedance target values. It can be seen that efficiency decreases as target performance levels increase. The diagram also shows which efficiency levels or target performance levels are achievable for which impedance target values. Curve 30 is still in use here. Figure 5 plotted, with a first end of curve 30 corresponding to maximum efficiency and a second end of curve 30 corresponding to maximum power.

[0091] Figure 6Figure 1 shows a flowchart describing a procedure for controlling the impedance matching circuit 50. In procedure step S1, a target impedance value for the input terminal 50a of the impedance matching circuit 50 is determined based on a predefined operating frequency of the RF generator 60, a predefined target power of the RF generator 60, and model parameters of the RF generator 60. The target impedance value deviates from a nominal impedance in order to increase an operating characteristic of the RF generator 60, in particular to increase its efficiency. In procedure step S2, the determined target impedance value is set by the impedance matching circuit 50.

[0092] The invention is not limited to the described embodiments. Within the scope of the invention, all described and / or drawn features can be combined with one another as desired. The invention is defined by the claims.

Claims

1. A control device (1) for actuating an impedance matching circuit (50) for a plasma generation system (100), with an input terminal (50a) and an output terminal (50b) for connection between an RF generator (60) and a load (70), characterized in that the control device (1) is designed, on the basis of: a) a predefinable operating frequency of the RF generator (60); b) a predefined target power of the RF generator (60); and c) model parameters of the RF generator (60); to ascertain a target impedance value for the input terminal (50a) of the impedance matching circuit (50), wherein the target impedance value has a value that deviates from the nominal impedance in order to achieve an increase in a characteristic operating value of the RF generator (60), in particular the efficiency, for the predefinable operating frequency and the predefinable target power.

2. The control device (1) according to claim 1, with the following features: - the characteristic operating value includes one or more of the following characteristics of the RF generator (60): a) efficiency; b) temperature, in particular the limitation to a maximum permissible temperature, in certain components, for example transistors, capacitors, inductors, couplers, matching circuits; c) voltage, in particular the limitation to a maximum permissible voltage, in certain components, for example transistors, capacitors, inductors, couplers, matching circuits; d) current, voltages, in particular the limitation to a maximum permissible current, in certain components, for example transistors, capacitors, inductors, couplers, matching circuits.

3. The control device (1) according to any one of the previous claims, with the following feature: - for different predefinable target powers, the model parameters of the RF generator (60) include corresponding target impedance values for which the efficiency reaches its maximum or is at most 10% away from its maximum.

4. The control device (1) according to any one of the previous claims, with the following feature: - the control device (1) is designed, in addition, to take the model parameters of a cable impedance of a cable connection (2a) between the RF generator (60) and the impedance matching circuit (50) into account.

5. The control device (1) according to any one of the previous claims, with the following feature: - the control device (1) is designed, in addition, to take the model parameters of the impedance matching circuit (50) into account.

6. The control device (1) according to any one of the previous claims, with the following feature: - the control device (1) is designed, in a pulsed operation of the RF generator (60) in which pulses of different amplitudes are generated, to ascertain, for the different pulses, different target impedance values for the input terminal (50a) of the impedance matching circuit (50).

7. The control device (1) according to any one of the previous claims, with the following feature: - the control device (1) is designed to ascertain target impedance values for the input terminal (50a) of the impedance matching circuit (50), wherein the target impedance values are selected such that the RF generator (60) can provide a corresponding target power for the entire envelope of a generated signal.

8. A plasma generation system (100) with a control device (1) according to any one of the previous claims, an RF generator (60) and an impedance matching circuit (50), wherein an output terminal (60a) of the RF generator (60) is connected to the input terminal (50a) of the impedance matching circuit (50).

9. The plasma generation system (100) according to claim 8, with the following feature: - the control device (1) is designed to take the cable impedance of the cable connection (2a) between the RF generator (60) and the impedance matching circuit (50) into account when the target impedance value at the input terminal (50a) of the impedance matching circuit (50) is ascertained.

10. The plasma generation system (100) according to claim 9, with the following feature: - the control device (1) is designed to take the cable impedance of the cable connection (2a) between the RF generator (60) and the impedance matching circuit (50) into account and to continuously re-determine it during operation of the plasma generation system (100).

11. The plasma generation system (100) according any one of claims 8 to 10, with the following features: - a first and a second measuring unit (5, 6) are provided; - the control device (1) is designed to calculate the cable impedance of the cable connection (2a) by means of the first and the second measuring unit (5, 6), wherein the first measuring unit (5) is arranged: a) between the RF generator (60) and the cable connection (2a); and / or b) in the region of the outlet terminal (60a) of the RF generator (60); and wherein the second measuring unit (6) is arranged: a) between the cable connection (2a) and the impedance matching circuit (50) and / or in the region of the input terminal (50a) of the impedance matching circuit (50); or b) between the impedance matching circuit (50) and the load (70).

12. The plasma generation system (100) according to claim 11, with the following features: - the first measuring unit (5) has a directional coupler and / or the second measuring unit (6) has a directional coupler; and / or - the first measuring unit (5) includes a current sensor (15) and a voltage sensor (16) and / or the second measuring unit (6) includes a current sensor (15) and a voltage sensor (16).

13. The plasma generation system (100) according to claim 12, with the following features: - the voltage sensor (16) of the first measuring unit (5) has a capacitive voltage divider, wherein a first capacitance is formed by an electrically conductive ring (19) or cylinder through which the cable connection (2a) is routed in the region of the output terminal (60a) of the RF generator (60) and the impedance matching circuit (50); and - the current sensor (15) of the first measuring unit (5) has a coil arranged around the conductive ring (16) or cylinder; and / or - the voltage sensor (16) of the second measuring unit (6) has a capacitive voltage divider, wherein a first capacitance is formed by an electrically conductive ring (19) or cylinder, through which: a) the cable connection (2a) is routed in the region of the input terminal (50a) of the impedance matching circuit (50); or b) the cable connection (2b) is routed between the impedance matching circuit (50) and the load (70); and - the current sensor of the second measuring unit (6) has a coil arranged around the conductive ring (19) or cylinder.

14. The plasma generation system (100) according to any one of claims 8 to 13, with the following feature: - the control device (1) is designed to change the power of the RF generator (60), wherein this takes place due to a change in an input power of an amplifier of the RF generator (60) and / or due to a change in a supply voltage of an amplifier of the RF generator (60).

15. A method for actuating an impedance matching circuit (50) for a plasma generation system (100), said circuit having an input terminal (50a) connected to an output terminal (60a) of an RF generator (60) and an output terminal (50b) connected to an input of a load (70), wherein the method is suitable for adjusting the input impedance at the input terminal (50a) when the output impedance at the output terminal (50b) changes, characterized in that the method has the following method step: - ascertaining a target impedance value for the input terminal (50a) on the basis of: a) a predefinable operating frequency of the RF generator (60); b) a predefined target power of the RF generator (60); and c) model parameters of the RF generator (60); wherein the target impedance value has a value that deviates from the nominal impedance in order to achieve an increase in a characteristic operating value of the RF generator (60), in particular the efficiency, for the predefinable operating frequency and the predefinable target power.