Control device and method for controlling an impedance matching circuit for a plasma generation system, and plasma generation system

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 including such a control device.

Background Art

[0002] Surface treatment of a workpiece using plasma and gas lasers is an industrial process, and in this process, plasma is generated using a DC or high-frequency AC signal having an operating frequency in the range of several tens of kHz to GHz, particularly in a plasma chamber.

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

[0004] The plasma process has the problem that the electrical load impedance of the plasma in the plasma chamber, which occurs during the process, depends on the state in the plasma chamber and varies greatly. In particular, the characteristics of the workpiece, electrodes, and gas conditions have a great influence. A characteristic when such load fluctuations are large is that this load fluctuation may occur faster than the load matching by the controlled impedance matching. In particular, the load fluctuation may occur within the period of the fundamental wave, that is, within the period of the HF power signal for operating the plasma. In this case, not only the power of the fundamental wave but also the so-called harmonic power portion of the harmonics is reflected.

[0005] High-frequency generators have a limited operating range related to the impedance of the connected electrical load (consumer). If the load impedance exceeds the acceptable range, the HF generator may be damaged or destroyed. For example, if the reflected power, voltage, or reflected energy is too high for the HF generator, the generator may be damaged, often due to the reflected power.

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

[0007] Various impedance matching circuits are known. Impedance matching circuits consist of electrical components that are fixed and set, and have a predetermined conversion function, and therefore do not change during operation, particularly coils and capacitors. This is particularly effective for constant operation, such as in a gas laser. 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, a motor-driven rotary capacitor is known, whose capacitance value is variable by changing the relative positions of the capacitor electrode plates.

[0008] Generally speaking, three impedance ranges can be assigned to a plasma. Before ignition, a relatively high impedance in the real part exists. Under normal operation, i.e., when the plasma is operating as intended, a relatively low impedance in the real part exists. If undesirable local discharges (arcs) or plasma fluctuations occur, relatively small impedance values ​​may occur. In addition to these three specified impedance ranges, special conditions may occur to which other impedance values ​​are assigned. If the load impedance changes abruptly and the load impedance or converted load impedance falls outside the acceptable impedance range, the HF generator or the transmission equipment between the HF generator and the plasma chamber may be damaged. Furthermore, undesirable plasma stable states also exist. For example, a stable plasma may form in an undesirable region within the plasma chamber, such as a peripheral region rather than the target.

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

[0010] Furthermore, plasma processes require relatively large amounts of power and / or energy, often exceeding 1 kW, and it is known that this plays an increasingly important role today.

[0011] HF generators and impedance matching circuits operate at efficiencies that vary depending on several parameters. As power and / or energy increases in plasma processes, efficiency becomes increasingly important. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] German Patent Application Publication No. 102009001355A1 Specification [Overview of the Initiative] [Problems that the invention aims to solve]

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

[0014] This problem is solved by the control device described in independent claim 1 of the present invention, the plasma generation system described in independent claim 18 of the present invention, and the method described in independent claim 29.

[0015] The control unit is used to control the impedance matching circuit for the plasma generation system. The impedance matching circuit includes input and output terminals and can be connected between the HF generator and the load. The load can be, in particular, at least one electrode where plasma is generated within the plasma chamber.

[0016] The control device is a) Pre-settable operating frequencies of the HF generator, b) The preset target power of the HF generator, and c) Model parameters of the HF generator Based on this, the control unit is configured to determine the impedance target value at the input terminal of the impedance matching circuit, and the impedance target value 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 preset operating frequency and a preset target power. The operating characteristics of the HF generator are preferably the efficiency of the HF generator. In this case, the control unit may be configured to obtain the preset operating frequency, preset target power, and model parameters of the HF generator by being supplied and / or stored internally and / or accessible by other means. Thus, the control unit may obtain them by being transmitted, for example, via an interface, for example, via an electronic data interface. The control unit may store them, for example, in an internal electronic data storage device. The control unit may determine them, for example, from other sources or data or a combination thereof.

[0017] It is particularly preferable 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 with the input terminal. In this case, the HF generator will operate 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 operating efficiency of the HF generator 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 supply in the plasma process is hardly required. The HF generator can supply such maximum power when matched, i.e., when the impedance target value is set to the nominal impedance of the HF generator. 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 designed particularly for plasma processes and is preferably designed to generate and output a high-frequency signal in the range from 1 MHz to 200 MHz, preferably in the range from 3 MHz to 100 MHz, more preferably in the range from 12 MHz to 50 MHz. Even more preferably, the HF generator is designed to generate an HF signal having a frequency of 13.56 MHz, 27 MHz, and / or 40 MHz.

[0019] Basically, it is conceivable that the 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 with respect 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, especially the limitation of the maximum allowable temperature in certain components, such as transistors, capacitors, inductors, couplers, matching circuits, c) Voltage, especially the limitation of the maximum allowable voltage in certain components, such as transistors, capacitors, inductors, couplers, matching circuits, d) Current, especially the limitation of the maximum allowable current in certain components, such as transistors, capacitors, inductors, couplers, matching circuits, including one or more of the above. The characteristics of the HF generator related to temperature, voltage, and current may also affect the efficiency. The limitation of the maximum allowable temperature may be related to the maximum allowable energy consumption. Similarly, the limitation of the maximum allowable voltage or the maximum allowable current may be related to the maximum allowable energy consumption.

[0022] In a preferred embodiment, the settable target power is the active power. It is rare that the target power is the power supplied to the load at that time. This is because the impedance matching circuit may have an active power loss, and the loss may further depend on the setting of the impedance matching circuit. However, since the active power loss in the impedance matching circuit is reproducible, this does not pose much of an obstacle to the efficiency of the plasma process. Therefore, a plasma process that functions at a predetermined target power is guaranteed to continue to function in the future.

[0023] In a more preferred embodiment, the control device is configured to control the impedance matching circuit to set the impedance at the input terminal of the impedance matching circuit to an impedance target 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, i.e., change, the impedance target value while the HF generator is operating.

[0024] In a further preferred embodiment, the nominal impedance is 50 ohms. This is a standardized value, and most cables and connectors are designed to match this. The output impedance of the HF generator is usually designed to be the nominal impedance, so that no reflection occurs due to the components.

[0025] In a further preferred embodiment, the control device is configured to select an impedance target value at which the efficiency is improved compared to the efficiency at the nominal impedance. Preferably, an impedance target value at 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 the nominal impedance is selected.

[0026] In a further preferred embodiment, the model parameters of the HF generator include impedance target values ​​corresponding to different preset target powers. For these impedance target values, the efficiency reaches its maximum value or deviates by no more than 10% from its maximum value. The model parameters can be stored, for example, in a lookup table. For different operating frequencies, there are corresponding model parameters. Preferably, there is a separate lookup table for each operating frequency, or there is a single lookup table that is valid for one or more operating frequencies or for one frequency range. Alternatively, the lookup table may be calculated using an appropriate conversion factor (value or function), thereby making this lookup table usable at different operating frequencies depending on the conversion factor. This can reduce memory capacity. For storing the lookup table, the control device preferably includes a memory device. More preferably, the lookup table stores impedance target values ​​corresponding to different target powers where the efficiency is maximized or deviates by no more than 10% from its maximum value.

[0027] In a further preferred embodiment, different target powers are located on one curve or on a group of curves. When using one curve, preferably, the maximum efficiency is achieved. When using a group of curves, the target powers are preferably located within 10% of the maximum efficiency. This allows for visualization for the user, and as a result, the user is supported when setting up the plasma process, in particular, enabling the user to set up the plasma process according to the above criteria.

[0028] In a further preferred embodiment, the control device is configured to store impedance target values ​​for adjacent target powers on its curve or on a group of curves, so that minimal mechanical adjustment of the impedance matching circuit requires continuous recall of these impedance target values. For example, the target powers can be stored with a resolution of 1 / 10 (0.1). In this case, adjacent target powers would be, for example, 49 dBm and 49.1 dBm. Thus, an impedance target value can be selected that achieves appropriately enhanced efficiency, while minimizing the mechanical adjustment (mechanical range of motion) of the capacitor and / or inductor. This protects the motor and / or gear device of the impedance matching circuit.

[0029] In a further preferred embodiment, the control device is configured to further consider model parameters of the cable impedance of the connecting cable between the HF generator and the impedance matching circuit. Since the cable impedance is also frequency-dependent, different cable impedances are considered for different operating frequencies. This allows for more precise setting of the efficiency of the HF generator.

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

[0031] In a further preferred embodiment, the control unit is configured to calculate the cable impedance using first and second measurement units. The first measurement unit can be placed between the HF generator and the connecting cable. The second measurement unit can be placed between the connecting cable and the impedance matching circuit, or between the impedance matching circuit and the load. Thus, the first measurement unit can be particularly placed in the area of ​​the output terminals of the HF generator, and the second measurement unit can be particularly placed in the area of ​​the input or output terminals of the impedance matching circuit. Thus, the control unit 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. Thus, when connecting another connecting cable, the correct value of the cable impedance is automatically used. If the second measurement unit is placed after the impedance matching circuit and before the load, model parameters, in particular the Z parameter of the impedance matching circuit, must be further considered. However, these are known for the current state of the impedance matching circuit. Cable impedance can also be considered a model parameter of the connecting cable. Thus, it can be said that the control unit 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 terminals of the impedance matching circuit are located 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 is connectable to the HF generator, and a second end of the connecting cable is connectable to the impedance matching circuit, with the input terminals located on the first end of the connecting cable, i.e., on the HF generator. In this case, the input terminals are not located directly on the case of the impedance matching circuit. This allows for the consideration of a connecting cable, and it becomes clear that the control device is configured to set an impedance target value acting directly on the HF generator at the output section 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 an impedance matching circuit for different pulses during pulse operation of an HF generator, which generates pulses having different amplitudes and preferably also having pulse stop times. This can maximize efficiency.

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

[0036] The plasma generation system according to the present invention includes a suitable control device, as described at the beginning. Furthermore, the plasma generation system includes 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 consider the cable impedance, which is preferably 50 ohms. Therefore, it becomes easier to convert, for example, a transistor impedance of 5 ohms to a plasma impedance of preferably 2 ohms, because fewer adjustments are needed to the components of the impedance matching circuit (e.g., capacitors, inductors).

[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 terminal of the impedance matching circuit. Preferably, the cable impedance is measured continuously (e.g., several times per second). Thereafter, if the cable impedance changes, the impedance matching circuit is adjusted during operation, and as a result, 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 unit is configured to use the first and second measuring units to calculate the cable impedance of the connecting cable between the HF generator and the impedance matching circuit. The first measuring unit is located between the HF generator and the connecting cable. The first measuring unit is located closer to the HF generator, and the second measuring unit is located closer to the impedance matching circuit. The second measuring unit is located 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 measuring unit is a directional coupler. Additionally or alternatively, the second measuring unit is a directional coupler. Additionally or alternatively, the first measuring unit includes a current sensor and a voltage sensor. Additionally or alternatively, the second measuring 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, where the first capacitor is formed by a conductive ring or cylinder, and a connecting cable is routed through the ring or cylinder 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 enables a compact configuration. Additionally or alternatively, the voltage sensor of the second measuring unit includes a capacitive voltage divider, where the first capacitor is formed by a conductive ring or cylinder. A connecting cable between the HF generator and the impedance matching circuit, or between the impedance matching circuit and the load, is routed through the cylinder. The current sensor of the second measuring unit includes a coil arranged around the conductive ring or cylinder. This enables a particularly compact configuration.

[0042] In a further preferred embodiment, the control device is configured to change the power of the HF generator, which is done by changing the input power of the HF generator amplifier and / or by changing the supply voltage of the HF generator amplifier. This allows the HF generator to be precisely tuned to a further improved efficiency.

[0043] In a further preferred embodiment, the first connecting cable includes at least two cables connected in parallel, thereby reducing the impedance of the connecting cable. In this case, the ends of the two internal conductors are electrically connected to each other, in particular 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 makes the transition from the transistor impedance of approximately 5 ohms in the HF generator to the cable impedance of 25 ohms and then to the plasma impedance of approximately 2 ohms smaller than the transition from 5 ohms to a standardized 50-ohm cable impedance and then to 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, the capacitance value of at least one capacitor being variable during operation. This modification can be achieved by driving a rotating capacitor, such as a vacuum rotating capacitor, particularly by a motor, such as a stepping motor. Preferably, a gear mechanism is also provided. Instead of a motor, a switch, such as a semiconductor switch (solid-state switch), can be used to switch the capacitance up or down. In particular, multiple such switching capacitors can be provided to allow setting multiple different capacitance values. In this case, the impedance target value can be set particularly quickly, particularly faster than motor-driven capacitor adjustment, preferably in 100ms, 50ms, 10ms, or 1ms or less. This is particularly useful when using pulsed signals to allow for quick response to different pulse heights.

[0045] The method according to the present 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. This method is suitable for setting the input impedance at the input terminal when the output impedance at the output terminal is fluctuating. The target impedance value at the input terminal is a) The preset operating frequencies of the HF generator, b) The preset target power of the HF generator, c) The step includes determining the model parameters of the HF generator, where the impedance target value is different from the nominal impedance in order to achieve improved operating characteristics of the HF generator, particularly improved efficiency, at a preset operating frequency and a preset target power.

[0046] Hereinafter, various embodiments of the present invention will be described illustratively with reference to the drawings. The same reference numerals are used for the same components. Corresponding figures in the drawings illustrate their details. [Brief explanation of the drawing]

[0047] [Figure 1] This figure shows one embodiment of a plasma generation system comprising an HF generator, an impedance matching circuit, a control device, and a plasma chamber. [Figure 2A] This figure shows an example of an impedance matching circuit. [Figure 2B] This figure shows another embodiment of an impedance matching circuit. [Figure 3] This figure shows an embodiment of a first and / or second measuring unit for non-contact measurement of voltage and current. [Figure 4] This is a Smith chart showing how an HF generator transitions from maximum power to maximum efficiency depending on the impedance target value. [Figure 5]This graph shows the trend of efficiency at a specific target power level related to the required impedance target value. [Figure 6] This flowchart shows the control method for an impedance matching circuit. [Modes for carrying out the invention]

[0048] Figure 1 shows a plasma generation system 100, which is used particularly 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, particularly a first connecting cable 2a which is at least a first coaxial cable 2a. The first connecting cable 2a is connected to the output terminal 60a of the HF generator 60 and to the 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, preferably a second coaxial cable 2b. The impedance matching circuit 50 is often located near the plasma chamber 70, particularly at a distance of 10 cm or less, preferably directly on the plasma chamber 70. As a result, the second connecting cable 2b is also made shorter accordingly and has only a few mechanical parts, such as plugs and / or cable connectors. The second connecting cable 2b is connected to the output terminal 50b of the impedance matching circuit 50 and the input section of the plasma chamber 70. Preferably, the second connecting cable 2b is connected to an electrode inside the plasma chamber 70.

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

[0051] The first connecting cable 2a may include at least two cables connected in parallel to reduce the overall impedance of the connecting cable. In this case, the ends of the two inner conductors are electrically connected to each other, in particular by soldering. Thus, one 25-ohm cable is made from two 50-ohm cables. This reduces the change from the transistor impedance of the HF generator 60, which is about 5 ohms, to the cable impedance of 25 ohms, and then to the plasma impedance of 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 touchscreen in particular. A keyboard and / or mouse and monitor can also be considered as the input / output device 80.

[0053] The plasma chamber 70 can be considered a consuming component (load). Depending on the application, one or more electrodes 3 can be provided inside 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 inside the plasma chamber 70 is shown as a dot.

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

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

[0056] The control device 1 is used to control the impedance matching circuit 50. The control device 1 is configured to determine the impedance target value at the input terminal 50a based on the preset operating frequency of the HF generator 60, the preset target power of the HF generator 60, and the 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), thereby improving the operating characteristics of the HF generator 60, particularly its efficiency, with respect to the preset operating frequency and preset target power.

[0057] The model parameters of the HF generator 60 include impedance target values ​​corresponding to different preset target powers, where the efficiency reaches its maximum value or is no more than 10% away from its maximum value. These target powers can be input by the 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 read.

[0058] Preferably, a lookup table 9 is stored in the memory device 8, and within the lookup table 9, impedance target values ​​corresponding to different target powers are stored. At the impedance target value, the efficiency is either at its maximum value or within a maximum of 10% of that maximum value.

[0059] In Figure 1, the input terminal 50a of the impedance matching circuit 50 is drawn directly on the case of the impedance matching circuit 50. Essentially, the input terminal 50a can also be located at the end of the first connecting cable 2a on the side where it connects to the HF generator 60. In this case, the cable impedance of the first connecting cable 2a is still considered. In this case, the HF generator 60 directly recognizes the impedance target value that is not distorted by the first connecting cable 2a.

[0060] As described above, preferably, the control device 1 is configured to further consider 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 storage device 8. These model parameters are frequency-dependent, and different cable impedances are read according to 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 connection cable using first and second measurement units 5 and 6. In this case, the first measurement unit 5 is placed between the HF generator 60 and the first connection cable 2a, and the second measurement unit 6 is placed between the first connection cable 2a and the impedance matching circuit 50, or between the impedance matching circuit 50 and the load 70. Figure 1 shows two second measurement units 6. When the second measurement unit 6 is placed between the impedance matching circuit 50 and the load 70, the control device 1 is further configured to take into account the model parameters of the impedance matching circuit 50.

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

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

[0064] In Figure 2B, the input terminal 50a of the impedance matching circuit 50 is connected to the first capacitor 12. The first capacitor 12 is connected to both the first coil 10 (first inductor) and the 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 and 11 are connected. The first coil 10 is further connected to a reference ground. The second coil 11 is connected to the second capacitor 13 (second capacitor) (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 may be swapped. 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 further components.

[0065] Figure 3 shows one possible configuration of the first and / or second measuring units 5 and 6. In this embodiment, the first and / or second measuring units 5 and 6 are configured to measure voltage and current non-contact.

[0066] To this end, the first and / or second measuring units 5, 6 include a current sensor 15 and a voltage sensor 16.

[0067] However, preferably, the phase relationship between current and voltage is measured, thereby enabling the calculation of impedance.

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

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

[0070] The voltage sensors 16 of the first and / or second measuring units 5, 6 are preferably configured as capacitive voltage dividers. The first capacitor 19 is formed by a conductive ring 19. A conductive cylinder can also be used. The corresponding first or second connection cables 2a, 2b are wired through this conductive ring 19. The second capacitor 20 of the voltage sensor 16, configured as a voltage divider, is connected to a reference ground. The second A / D converter 21 is connected in parallel to the second capacitor 20 and is configured to detect and digitize the voltage dropping 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 and 2b are wired 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, particularly a Rogowski coil, is located further away from the first and second connecting cables 2a and 2b than the first capacitor 19. The coils can also be formed on the same circuit board by appropriate coating and through-holes. The coil for current measurement and the first capacitor for voltage measurement preferably pass through a common plane.

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

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

[0075] The second measurement unit 6 can also be placed at the output terminal 50b of the impedance matching circuit 50, in which case the first measurement unit 5 is further placed in the area of ​​the HF generator 60, thereby enabling the detection of the cable impedance of the first connection cable 2a.

[0076] The first and / or second measuring units 5, 6 can also be formed as directional couplers.

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

[0078] In the Smith chart of Figure 4, six impedance curves, P1, P2, P3, P4, P5, and P6, are shown exemplarily. Each impedance target value on the impedance curve means 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 for the HF generator 60. The HF generator 60 produces different output powers when comparing the impedance target value on impedance curve P1 with the impedance target value on impedance curve P2.

[0079] Figure 4 shows only six impedance curves P1, P2, P3, P4, P5, and P6 as an example. There may be more than six.

[0080] The Smith chart in Figure 4 illustrates 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 the HF generator 60 with different impedance target values. 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 impedance curve E1 with the impedance target value on impedance curve E2.

[0081] To clarify the explanation, some example values ​​are shown below.

[0082] [Table 1]

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

[0084] Furthermore, another curve 30 is also shown. This curve 30 connects the impedance curve P1 for maximum possible power and the impedance curve E1 for maximum possible efficiency.

[0085] On the curve 30, different impedance target values ​​are located for different target powers, and the HF generator 60 provides the target power at which the efficiency is maximized for each impedance target value. If the user requires power P=44.5dBm, 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 further set by the impedance matching circuit 50.

[0086] Basically, a set of curves can be drawn, in which case each impedance target value preferably produces an efficiency that is no more than 10% away from its maximum value. The use of such a set of curves has advantages, for example, because it allows the use of impedance target values ​​that minimize the mechanical adjustment of the impedance matching circuit 50.

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

[0088] Figure 5 is a graph showing the trend of efficiency at a given target power in relation to the required impedance target value. It can be seen that 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, the curve 30 is drawn in Figure 5, where the first end of the curve 30 is associated with maximum efficiency and the second end is associated with maximum power.

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

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

[0091] 1. Control device 2a First connection cable 2b Second connection cable 5. First measurement unit 6. Second measurement unit 8 Storage device 9 Look-up Table 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), wherein the impedance matching circuit (50) has an input terminal (50a) and an output terminal (50b) and is connected between an HF generator (60) and a load (70), The control device (1) is a) The preset operating frequency of the HF generator (60), b) The preset target power of the HF generator (60), and c) Model parameters of the HF generator (60), Based on this, the impedance matching circuit (50) is configured to determine the impedance target value at the input terminal (50a), The model parameters are data including an impedance target value at the input terminal (50a) corresponding to the operating frequency or the target power. The control device (1) is characterized in that the impedance target value has a value different from the nominal impedance at the operating frequency and target power, so as to improve the operating characteristics of the HF generator (60) compared to when the nominal impedance (50 ohms) is set at the input terminal (50a).

2. The aforementioned operating characteristics are the following characteristics of the HF generator (60): a) Efficiency showing the power coupled to the load (70) relative to the power consumed by the HF generator (60), b) Limitations on the maximum permissible temperature in transistors, capacitors, inductors, couplers, or matching circuits. c) Limitation of the maximum allowable voltage in transistors, capacitors, inductors, couplers, or matching circuits. d) Limitation of the maximum allowable current in transistors, capacitors, inductors, couplers, or matching circuits. The control device (1) according to claim 1, characterized by including one or more of the following.

3. The control device (1) according to claim 1 or 2 is characterized in that it 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. The control device (1) according to claim 2, characterized in that the control device (1) is configured to select an impedance target value that improves efficiency compared to the efficiency at the nominal impedance.

5. The control device (1) according to claim 2, wherein the model parameters of the HF generator (60) include the impedance target values ​​corresponding to different preset target powers, and with respect to the impedance target values, the efficiency reaches its maximum value or is at most 10% away from its maximum value.

6. The control device (1) according to claim 5, characterized in that the different target powers lie on a curve (30) or group of curves in a Smith chart that connects the impedance curve for the maximum achievable power and the impedance curve for the maximum achievable efficiency.

7. The control device (1) according to claim 6, wherein the control device (1) is configured to store the impedance target values ​​for adjacent target powers on the curve (30) or on the group of curves, and minimal mechanical adjustment of the impedance matching circuit (50) requires continuous recall of the impedance target values.

8. The control device (1) includes a storage device (8) having a lookup table (9), The control device (1) according to claim 2, wherein the lookup table (9) stores impedance target values ​​corresponding to the different target powers as part of the model parameters, and the efficiency reaches its maximum value or is no more than 10% away from its maximum value for that impedance target value.

9. The control device (1) according to claim 1 or 2, characterized in that the control device (1) is configured to further consider model parameters of the cable impedance of the connecting cable (2a) between the HF generator (60) and the impedance matching circuit (50).

10. The control device (1) is configured to read the cable impedance from the storage device (8), or The control device (1) is configured to calculate the cable impedance using first and second measurement units (5, 6), wherein the first measurement unit (5) can be positioned between the HF generator (60) and the connecting cable (2a), and the second measurement unit (6) can be positioned between the connecting cable (2a) and the impedance matching circuit (50), or between the impedance matching circuit (50) and the load (70), as described in claim 9.

11. The control device (1) according to claim 1 or 2, further characterized in that the control device (1) is configured to take into account the model parameters of the impedance matching circuit (50).

12. The control device (1) according to claim 1 or 2, characterized in that it includes different model parameters, including the impedance target values ​​corresponding to different operating frequencies of the HF generator (60).

13. The control device (1) according to claim 1 or 2, characterized in that the input terminal (50a) is located in the case of the impedance matching circuit (50).

14. The HF generator (60) can be connected to the impedance matching circuit (50) via the connecting cable (2a). The first end of the connecting cable (2a) is connectable to the HF generator (60), The second end of the connecting cable (2a) is connectable to the impedance matching circuit (50), The control device (1) according to claim 1 or 2, characterized in that the input terminal (50a) is located at the first end of the connecting cable (2a).

15. The control device (1) according to claim 1 or 2, characterized in that, when the HF generator (60) generates pulses of different amplitudes, it determines different impedance target values ​​at the input terminal (50a) of the impedance matching circuit (50) for different pulses.

16. The control device (1) is configured to determine the impedance target value at the input terminal (50a) of the impedance matching circuit (50), The control device (1) according to claim 1 or 2, characterized in that the impedance target value is selected so that the HF generator (60) can supply the target power to the entire envelope of the generated signal.

17. Plasma generation system (100), The control device (1) according to claim 1, HF generator (60) and The system includes 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).

18. The plasma generation system (100) according to claim 17, characterized in that the impedance matching circuit (50) is integrated into the HF generator (60).

19. The plasma generation system (100) according to claim 17, characterized in that the impedance matching circuit (50) is connected to the HF generator (60) via a connecting cable (2a).

20. The plasma generation system (100) according to claim 19, characterized in that the connecting cable (2a) includes at least two cables connected in parallel in order to reduce the impedance of the connecting cable (2a).

21. The plasma generation system (100) according to claim 19 or 20, characterized in that the control device (1) is configured to take into account the cable impedance of the connecting 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).

22. The plasma generation system (100) according to claim 21, characterized in that the control device (1) is formed to take into consideration the cable impedance of the connecting cable (2a) between the HF generator (60) and the impedance matching circuit (50), and to continuously determine the cable impedance during the operation of the plasma generation system (100).

23. First and second measuring units (5, 6) are provided. The control device (1) is configured to calculate the cable impedance of the connecting cable (2a) using the first and second measurement units (5, 6), The first measurement unit (5) is a) Between the HF generator (60) and the connecting cable (2a), and / or b) Located in the area of ​​the output terminal (60a) of the HF generator (60), The second measurement unit (6) is a) Between the connecting cable (2a) and the impedance matching circuit (50), and / or within the area of ​​the input terminal (50a) of the impedance matching circuit (50), b) The plasma generation system (100) according to claim 19 or 20, characterized in that it is located between the impedance matching circuit (50) and the load (70).

24. The first measuring unit (5) has a directional coupler, and / or the second measuring unit (6) has a directional coupler, and / or The plasma generation system (100) according to claim 23, characterized in that 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).

25. The voltage sensor (16) of the first measuring unit (5) has a capacitive voltage divider, and the first capacitor is formed by a conductive ring (19) or cylinder, and the connecting cable (2a) is wired through the ring or cylinder within the area of ​​the output terminal (60a) of the HF generator (60) and within the area of ​​the impedance matching circuit (50). The current sensor (15) of the first measuring unit (5) has a coil arranged around the conductive ring (19) or cylinder, and / or The voltage sensor (16) of the second measuring unit (6) has a capacitive voltage divider, and the first capacitor is formed by a conductive ring (19) or cylinder, and through the ring or cylinder, a) The connecting cable (2a) is wired within the area of ​​the input terminal (50a) of the impedance matching circuit (50), or b) The connecting cable (2b) is wired between the impedance matching circuit (50) and the load (70), The plasma generation system (100) according to claim 24, characterized in that the current sensor of the second measuring unit (6) has a coil arranged around the conductive ring (19) or cylinder.

26. The control device (1) is configured to change the power of the HF generator (60), The plasma generation system (100) according to claim 17 or 18, characterized in that this power change is performed 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).

27. The plasma generation system (100) according to claim 17 or 18, characterized in that the impedance matching circuit (50) includes one or more capacitors, and the capacitance value of at least one capacitor is variable during operation.

28. A method for controlling an impedance matching circuit (50) for a plasma generation system (100), wherein the impedance matching circuit (50) has an input terminal (50a) connected to the output terminal (60a) of an HF generator (60) and an output terminal (50b) connected to the input section of a load (70), This is a method for controlling the input impedance set at the input terminal (50a) when the output impedance at the output terminal (50b) fluctuates. The impedance target value at the input terminal (50a) is a) The preset operating frequency of the HF generator (60), b) The preset target power of the HF generator (60), c) The model parameters of the HF generator (60) are determined based on the following steps: The model parameters are data including an impedance target value at the input terminal (50a) corresponding to the operating frequency or the target power. The method is characterized in that the impedance target value has a value different from the nominal impedance at the operating frequency and target power, so as to improve the operating characteristics of the HF generator (60) compared to when the nominal impedance (50 ohms) is set at the input terminal (50a).

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