Control device and method for actuating impedance matching circuit of plasma generation system, and such plasma generation system

Abstract

A control device (1) of a plasma generation system (100) is used to control an impedance matching circuit (50) having an input terminal (50a) and an output terminal (50b). An impedance matching circuit (50) is coupled between the HF generator (60) and the load (70). The control device (1) is designed to: as a function of a) a predeterminable operating frequency of the HF generator (60); b) a predeterminable target power of the HF generator (60); and c) model parameters of the HF generator (60); according to the invention, a target impedance value of the input connection (50a) of the impedance matching circuit (50) is determined, said target impedance value having a value that deviates from the target impedance, in order to achieve an increase in the operating characteristic value of the HF generator (60), in particular an increase in the efficiency, for a predeterminable operating frequency and a predeterminable target power.

Description

Technical Field

[0001] The invention relates to a control device for controlling an impedance matching circuit of a plasma generation system, a method for controlling an impedance matching circuit of a plasma generation system, and a plasma generation system of this type having such a control device. Background Art

[0002] Surface treatment of workpieces by means of plasma and gas lasers is an industrial processing method in which a plasma is generated, in particular in a plasma chamber, with direct current or with high-frequency alternating current signals with an operating frequency in the range of a few 10 kHz to GHz.

[0003] In this case, the plasma chamber can be connected to a high-frequency generator (HF generator) via further electronic components, such as coils, capacitors, lines or transformers. These further components can act as resonant circuits, filters or impedance matching.

[0004] A problem with plasma processes is that the electrical load impedance of the plasma in the plasma chamber that occurs during the process depends on the conditions in the plasma chamber and can vary greatly. In particular, the properties of the workpiece, the electrode and the gas conditions must be taken into account. Such strongly varying loads can also be characterized in that these load changes occur faster than the adjusted impedance matching can perform load matching. In particular, load changes can also occur within the period of the fundamental wave, i.e. the HF power signal that operates the plasma. As a result, power is reflected not only in the fundamental wave, but also in the higher-order waves, i.e. the so-called harmonics, power components are also reflected.

[0005] High-frequency generators have a limited operating range with respect to the impedance of the connected electrical load (=consumer). If the load impedance is outside the permissible range, the HF generator may be affected or even destroyed. In most cases, the cause is reflected power, which may be damaged if the reflected power, voltage or reflected energy is too high for the HF generator.

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

[0007] Different impedance matching circuits are known. Impedance matching circuits are either fixed and have a predetermined transformation effect, i.e. they consist of electrical components, in particular coils and capacitors, which do not change during operation. This is of interest for continuous operation, for example for gas lasers. In addition, impedance matching circuits are known in which at least some of the components of the impedance matching circuit can be changed mechanically. For example, motor-driven variable capacitors are known, the capacitance value of which can be changed by changing the arrangement of the capacitor plates relative to one another.

[0008] Roughly speaking, three impedance ranges can be assigned to the plasma. Before ignition, the impedance has a relatively high real part. During normal operation, i.e. when the plasma is used as expected, the impedance has a relatively low real part. In the case of undesired partial discharges (arcs) or in the case of plasma fluctuations, relatively small impedance values ​​may occur. In addition to these three confirmed impedance ranges, other special states with other assigned impedance values ​​may also occur. If the load impedance changes suddenly and in this case the load impedance and therefore also the transformed load impedance fall outside the allowed impedance range, the HF generator or also the transmission device between the HF generator and the plasma chamber may be damaged. There are also undesired stable states for plasma. Therefore, for example, in the plasma chamber, a stable plasma can be formed in an area where a stable plasma is not desired, for example in the edge area instead of at the target.

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

[0010] It is also known that plasma processes require relatively high power (typically one kilowatt or more) and / or energy, which is becoming increasingly important today.

[0011] HF generators and impedance matching circuits each operate with variable efficiency depending on a number of parameters. With increasing power and / or energy in plasma processes, efficiency plays an increasingly important role. Summary of the invention

[0012] Therefore, the object of the present invention is to establish a low-loss, energy-saving plasma process.

[0013] This object is achieved by a control device according to the invention as claimed in independent claim 1 , by a plasma generation system according to the invention as claimed in independent claim 16 , and by a method according to independent claim 29 .

[0014] The control device is used to control an impedance matching circuit of a plasma generation system. The impedance matching circuit comprises an input terminal and an output terminal and can be connected between an HF generator and a load. The load can be, in particular, at least one electrode on which plasma is generated, in particular in a plasma chamber.

[0015] The control device is designed to:

[0016] a) a predeterminable operating frequency of the HF generator;

[0017] b) a predeterminable target frequency of the HF generator; and

[0018] c) Model parameters of HF generator;

[0019] An impedance target value is determined for the input terminals of the impedance matching circuit, wherein the impedance target value has a value that deviates from a nominal impedance of the HF generator in order to achieve an increase in an operating characteristic value of the HF generator for a predeterminable operating frequency and a predeterminable target power. The operating characteristic value of the HF generator is preferably the efficiency of the HF generator.

[0020] In this case, the control device can be designed to provide a predeterminable operating frequency, a predeterminable target power and model parameters of the HF generator and / or store them internally and / or access them in another way. Thus, the control device can transmit them, for example, via an interface such as an electronic data interface. For example, the control device can store them in an internal electronic data memory. For example, the control device can obtain them itself from other sources or data or a combination thereof.

[0021] Particularly preferably, the impedance target value of the input terminal of the impedance matching circuit is variable. The HF generator can be connected to the input terminal. If the impedance target value deviates from the rated impedance, the HF generator is not matched to the input terminal. Here, the operating point at which the HF generator operates is different from the operating point at which it can provide the maximum power. On the contrary, such an operating point is set, that is, under this operating point, the efficiency of the HF generator can be improved. The increase in efficiency significantly reduces the energy consumption of the HF generator, and the operation process of the plasma process is more energy-efficient. Studies have shown that in plasma processes, the maximum power that the HF generator can provide is rarely needed. The HF generator can only provide such a maximum power when matched, that is, when the impedance target value is set to the rated impedance of the HF generator. However, in this operating state, the HF generator also requires the most energy.

[0022] The operating frequency of the HF generator is preferably freely adjustable. The HF generator is designed, in particular in a plasma process, to generate and output an HF signal in a range of preferably 1 MHz to 200 MHz, preferably in a range of 3 MHz to 100 MHz and more preferably in a range of 12 MHz to 50 MHz. More preferably, the HF generator is designed to generate an HF signal with a frequency of 13.56 MHz, 27 MHz and / or 40 MHz.

[0023] In principle, it is conceivable that the HF generator can be designed to modulate the HF signal.

[0024] “Efficiency” is preferably understood as the power (especially active power) coupled into the load relative to the power (especially active power) absorbed by the generator.

[0025] In a preferred embodiment, the operating characteristic value comprises one or more of the following characteristics of the HF generator:

[0026] a) Efficiency;

[0027] b) the temperature in certain components, such as transistors, capacitors, inductors, couplers, matching circuits, in particular the limitation of the maximum permissible temperature;

[0028] c) voltages in certain components, such as transistors, capacitors, inductors, couplers, matching circuits, in particular the limitation of the maximum permissible voltage;

[0029] d) Limitation of currents and voltages in certain components, such as transistors, capacitors, inductors, couplers, matching circuits, in particular the limitation of the maximum permissible current.

[0030] The temperature-, voltage- and current-dependent properties of the HF generator can also influence the efficiency. The limitation of the maximum permissible temperature can be related to the maximum permissible energy consumption. In a similar manner, the limitation of the maximum permissible voltage or the maximum permissible current can also be related to the maximum permissible energy consumption.

[0031] In a preferred embodiment, the settable target power is the active power. In this case, the target power is rarely the power delivered to the load, since the impedance matching circuit may have an active power loss which can also be set depending on the impedance matching circuit. However, this is not much of an obstacle for the efficiency of the plasma process, since the active power loss in the impedance matching circuit is reproducible. This ensures that the plasma process suitable for the determined target power continues to function in the future.

[0032] In another preferred embodiment, the control device is designed to control the impedance matching circuit in such a way that the control device adjusts the impedance of the input terminal of the impedance matching circuit to an impedance target value. This can be done before activating the HF generator or during operation of the HF generator. The control device is also designed to continuously adjust the impedance target value, i.e. continuously change the impedance target value, during operation of the HF generator.

[0033] In another preferred embodiment, the nominal impedance is 50 Ohm. This is a standardized size and most cables or plugs are designed for this. The output impedance of the HF generator is usually designed to the nominal impedance so that no reflections occur in the components.

[0034] In another preferred embodiment, the control device is designed to select an impedance target value with improved efficiency compared to the efficiency of the rated impedance. Preferably, an impedance target value with improved efficiency of at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40% or at least 45% compared to the efficiency of the rated impedance is selected.

[0035] In another preferred embodiment, the model parameters of the HF generator include impedance target values ​​corresponding thereto for different predeterminable target powers. For the corresponding impedance target values, the efficiency reaches its maximum value or differs from its maximum value by at most 10%. In this case, the model parameters can be stored in a lookup table, for example. There are corresponding model parameters for each different operating frequency. Preferably, there is a lookup table for each operating frequency, or a lookup table is applicable to one or more operating frequencies or a certain frequency range. It is also conceivable that the lookup table is converted with a corresponding conversion factor (value or function) so that the lookup table can be used for different operating frequencies according to the conversion factor. Thus, the storage space can be reduced. In order to store the lookup table, the control device preferably includes a storage device. More preferably, in the lookup table, corresponding impedance target values ​​are stored for different target powers, for which the efficiency reaches its maximum value or differs from its maximum value by at most 10%.

[0036] In another preferred embodiment, the different target powers are located on a curve or a family of curves. When using the curve, preferably the maximum efficiency is achieved. When using the family of curves, the target power can preferably differ from the maximum efficiency by 10% or less. This allows the user to visualize and thus supports the user when setting the plasma process, in particular, the setting can only be implemented for him if the above-mentioned criteria are met.

[0037] In another preferred embodiment, the control device is designed to store the following impedance target values ​​for adjacent target powers on a curve or a family of curves: the successive call of the impedance target values ​​requires a minimum mechanical adjustment of the impedance matching circuit. For example, the target powers can be stored with a resolution of one tenth (0.1). In this case, the adjacent target powers are then, for example, 49 dBm and 49.1 dBm. Then, those impedance target values ​​can be selected that achieve a correspondingly increased efficiency, wherein the mechanical adjustment (mechanical travel) of the capacitors and / or inductors is kept to a minimum. As a result, the motor and / or the transmission can be protected by the impedance matching circuit.

[0038] In a further preferred embodiment, the control device is designed to additionally take into account the model parameters of the cable impedance of the cable connection between the HF generator and the impedance matching circuit. The cable impedance is also frequency-dependent, so that different cable impedances are taken into account for different operating frequencies. This makes it possible to set the efficiency of the HF generator more precisely.

[0039] In another preferred embodiment, the control device is designed to load the cable impedance from a storage device. In this case, the cable impedance can be stored in the same storage device in which the lookup table is stored, for example.

[0040] In another preferred embodiment, the control device is designed to calculate the cable impedance by means of a first measuring unit and a second measuring unit. The first measuring unit can be arranged between the HF 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 HF 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. Therefore, the control device is designed to determine the current cable impedance of the cable connection before activating the HF generator and / or to detect changes in the cable impedance of the cable connection during operation. Therefore, when connecting another cable connection, the correct value of the cable impedance will be automatically considered. For the case where the second measuring unit is arranged after the impedance matching circuit and before the load, model parameters, especially the Z parameters of the impedance matching circuit, must also be considered. However, these parameters are all known for the current state of the impedance matching circuit. The cable impedance can also be referred to as the model parameter of the cable connection. Therefore, it can be said that the design of the control device also takes into account the model parameters of the cable connection.

[0041] In a further preferred embodiment, the control device includes different model parameters for different operating frequencies of the HF generator.

[0042] In another preferred embodiment, the input terminal of the impedance matching circuit is arranged on the housing of the impedance matching circuit. However, it is also conceivable in principle that the HF generator can be connected to the impedance matching circuit via a cable connection, wherein the first end of the cable connection can be coupled to the HF generator, and wherein the second end of the cable connection can be coupled to the impedance matching circuit, wherein the input terminal is arranged at the first end of the cable connection and thus on the HF generator. In this case, the input terminal is not arranged directly on the housing of the impedance matching circuit. This clearly shows that the cable connection can also be taken into account and the control device is configured to set the impedance target value acting on the HF generator directly at the output of the HF generator.

[0043] In another preferred embodiment, the control device is designed to determine different impedance target values ​​for the input terminals of the impedance matching circuit for different pulses during pulse operation of the HF generator, which generates pulses of different amplitudes and preferably also with pulse intervals. This makes it possible to maximize efficiency.

[0044] In a further preferred embodiment, the control device is designed to determine an impedance target value for the input terminals of the impedance matching circuit, wherein the impedance target value is selected such that the HF generator can provide the corresponding target power for the entire envelope of the generated signal. This means that the power of the HF generator is sufficient to fully reproduce the amplitude of the generated signal. Therefore, the HF generator should also be able to provide sufficient power for the peak values ​​of the generated signal. In this case, the impedance target value must be selected in such a way that the HF generator can always still generate the required maximum power.

[0045] The plasma generation system according to the invention comprises a corresponding control device as described in the opening paragraph. In addition, the plasma generation system comprises an HF generator and an impedance matching circuit. Here, the output terminals of the HF generator are connected to the input terminals of the impedance matching circuit. Preferably, the output terminals of the impedance matching circuit are connected to a load, in particular to at least one electrode in the plasma chamber.

[0046] In another embodiment, the impedance matching circuit is integrated in the HF generator. This has the advantage that the impedance matching circuit does not have to take into account the cable impedance of preferably 50 Ohm. Thus, for example, a switch from a transistor impedance of 5 Ohm to a plasma impedance of preferably 2 Ohm is easier to achieve, since the elements of the impedance matching circuit (e.g. capacitors, inductors) do not have to be adjusted to a large extent.

[0047] In a further preferred embodiment, the control device is designed to take into account the cable impedance of the cable connection 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) so that in the event of a change in the cable impedance, the impedance matching circuit is adjusted during operation so that the desired impedance target value is still achieved.

[0048] In another preferred embodiment, the plasma generation system comprises a first measuring unit and a second measuring unit. The control device is designed to calculate the cable impedance of the cable connection between the HF generator and the impedance matching circuit by means of the first measuring unit and the second measuring unit. The first measuring unit is arranged between the HF generator and the cable connection. The first measuring unit is arranged closer to the HF generator, while 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.

[0049] In another preferred embodiment, the first measuring unit is a directional coupler. Supplementarily or alternatively, the second measuring unit is a directional coupler. Supplementarily or alternatively, the first measuring unit comprises a current sensor and a voltage sensor. Supplementarily or alternatively, the second measuring unit comprises a current sensor and a voltage sensor. With the aid of these sensors, the cable impedance of the cable connection can be calculated.

[0050] In another preferred embodiment, the voltage sensor of the first measuring unit comprises a capacitive voltage divider, wherein the first capacitance is formed by a conductive ring or cylinder, through which the cable connection between the HF generator and the impedance matching circuit is led. The current sensor of the first measuring unit comprises a coil arranged around the conductive ring or cylinder. This allows a compact structure to be achieved. Supplementarily or alternatively, the voltage sensor of the second measuring unit comprises a capacitive voltage divider, wherein the first capacitance is formed by a conductive ring or cylinder. The cable connection between the HF generator and the impedance matching circuit or the cable connection between the impedance matching circuit and the load is led through the cylinder. The current sensor of the second measuring unit comprises a coil arranged around the conductive ring or cylinder. This allows a particularly compact structure to be achieved.

[0051] In a further preferred embodiment, the control device is designed to vary the power of the HF generator, wherein this is achieved by varying the input power of the amplifier of the HF generator and / or by varying the supply voltage of the amplifier of the HF generator. This allows a more precise fine-tuning of the HF generator to further increase the efficiency.

[0052] In another preferred embodiment, the first cable connection comprises at least two cables connected in parallel, in order to thereby reduce the impedance of the cable connection. In this case, the ends of the two inner conductors are respectively electrically connected to each other, in particular welded. Thus, a 25 Ohm cable can be formed from two 50 Ohm cables. In this case, the nominal impedance of the system will be 25 Ohm. By this measure, the transition from the transistor impedance of the HF generator of approximately 5 Ohm to the cable impedance of 25 Ohm and then to the plasma impedance of approximately 2 Ohm is smaller than the transition from 5 Ohm to the standardized cable impedance of 50 Ohm and then to the plasma impedance of approximately 2 Ohm. This further reduces losses.

[0053] In another preferred embodiment, the impedance matching circuit includes one or more capacitors, wherein the value of at least one capacitor is variable during operation. The change can be achieved by manipulating a variable capacitor (especially a vacuum variable capacitor) by means of a motor (especially a stepper motor). Preferably, a transmission device is also provided. Instead of a motor, a switch, especially a switch in the form of a semiconductor switch (solid-state switch) can also be used to connect and / or disconnect the capacitor. In particular, a plurality of such switched capacitors can be provided so that a plurality of different capacitance values ​​can be set. In this case, the setting speed of the impedance target value can be particularly fast, especially faster than the motor-driven capacitor adjustment, preferably set in less than 100ms, 50ms, 10ms or less than 1ms. This is particularly useful when using a pulse signal so as to be able to react quickly to different pulse heights.

[0054] The method according to the invention is used to control an impedance matching circuit of a plasma generation system, the impedance matching circuit having an input terminal connected to an output terminal of an HF generator and an output terminal connected to an input of a load. The method is suitable for setting an input impedance at the input terminal when the output impedance at the output terminal can be changed, and the method has the following method steps:

[0055] -The target impedance value of the input terminal is obtained based on the following items:

[0056] a) a predeterminable operating frequency of the HF generator;

[0057] b) a predeterminable target power of the HF generator; and

[0058] c) Model parameters of HF generator;

[0059] The impedance target value has a value that deviates from the nominal impedance in order to achieve an increase in operating characteristics of the HF generator, in particular an increase in the efficiency, for a predeterminable operating frequency and a predeterminable target power. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Different embodiments of the present invention are described below with reference to the accompanying drawings. The same objects have the same reference numerals. In the corresponding figures of the accompanying drawings, specifically:

[0061] Figure 1 : shows an embodiment of a plasma generation system, the plasma generation system comprising an HF generator, an impedance matching circuit, a control device and a plasma chamber;

[0062] Figure 2A , Figure 2B : Different embodiments of impedance matching circuits are shown;

[0063] Figure 3 : An embodiment of a first measuring unit and / or a second measuring unit for contactless measurement of voltage and current is shown;

[0064] Figure 4 : shows a Smith chart illustrating how an HF generator changes from maximum power to maximum efficiency depending on an impedance target value;

[0065] Figure 5 : a graph showing a curve of efficiency variation of a determined target power in relation to a required impedance target value; and

[0066] Figure 6 : A flow chart describing a method for operating an impedance matching circuit is shown. DETAILED DESCRIPTION

[0067] Figure 1 A plasma generating system 100 is shown, which is particularly useful for surface treatment of a workpiece.

[0068] 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 is achieved by a cable connection 2a, which is preferably a first cable connection 2a, in particular at least one first coaxial cable 2a. The first cable connection 2a is connected to an output terminal 60a of the HF generator 60 and an input terminal 50a of the impedance matching circuit 50. The impedance matching circuit 50 is also electrically connected to the plasma chamber 70. This is preferably achieved via another, in particular a second cable connection 2b, which is preferably a second coaxial cable 2b. The impedance matching circuit 50 is usually arranged close to the plasma chamber 70, in particular at a distance of 10 cm or less than 10 cm therefrom, preferably directly arranged at the plasma chamber, so that the second cable connection 2b is also designed to be correspondingly short and has only a small number of mechanical components, for example, with a plug and / or a line connector. The second cable connection portion 2b is connected to the output terminal 50b of the impedance matching circuit 50 and to the input end of the plasma chamber 70. The second cable connection portion 2b is preferably connected to an electrode within the plasma chamber 70.

[0069] The first cable connection portion 2a is longer than the second cable connection portion 2b. Preferably, the length of the first cable connection portion 2a is 2, 3, 4, 5, 6, 7 or at least 8 times that of the second cable connection portion 2b.

[0070] The first cable connection 2a can also comprise at least two cables connected in parallel in order to reduce the overall impedance of the cable connection. In this case, the ends of the two inner conductors are respectively electrically connected to each other, in particular welded. Thus, a 25 Ohm cable can be formed from two 50 Ohm cables. As a result, the transition from the transistor impedance of the HF generator 60 of approximately 5 Ohm to the cable impedance of 25 Ohm and then to the plasma impedance of approximately 2 Ohm is small. In this case, the nominal impedance would be 25 Ohm.

[0071] The plasma generation system 100 preferably comprises an input and output device 80 , which is preferably a screen, in particular a touch-sensitively controllable screen. A keyboard and / or a mouse as well as a monitor can also be considered as an input and output device 80 .

[0072] The plasma chamber 70 can be regarded as a consumer (load). Depending on the application, one or more electrodes 3 can be arranged in the plasma chamber 70, at least one of which is connected to the second cable connection 2b. Figure 1 In FIG. 7 , the plasma 4 is shown in dot form within the plasma chamber 70 .

[0073] The plasma generation system 100 preferably also includes an optical device 90. More preferably, the optical device 90 is arranged in the plasma chamber 70 and is designed to visually detect the plasma 4 and thus the plasma state. The optical element 90 can be, for example, a light conductor such as a glass fiber. Although a camera can be used, it is often omitted for cost reasons. In addition, the plasma 4 may quickly obscure lenses and other protective glass.

[0074] The control device 1 is preferably a processor (eg a microcontroller) and / or a programmable logic module, such as an FPGA (Field Programmable Gate Array).

[0075] The control device 1 is used to control the impedance matching circuit 50. The control device 1 is designed to determine an impedance target value for the input terminal 50a as a function of a predeterminable operating frequency of the HF generator 60, a predeterminable target power of the HF generator 60 and as a function of model parameters of the HF generator 60, wherein the impedance target value has a value that deviates from the nominal impedance, which is typically 50 Ohm, in order to thereby achieve an increase in the operating characteristic value of the HF generator 60 for the predeterminable operating frequency and the predeterminable target power, in particular in order to thereby achieve an increase in efficiency.

[0076] The model parameters of the HF generator 60 include, for different predeterminable target powers, corresponding impedance target values ​​for which the efficiency reaches its maximum value or differs from its maximum value by at most 10%. For example, these target powers can be input by the user via the input and output device 80. They can also be stored in the control device 1 for a specific plasma process. If the user selects a specific plasma process, the target power stored for this plasma process is retrieved and the corresponding impedance target value is loaded.

[0077] Preferably, a lookup table 9 is stored in the storage device 8, in which corresponding impedance target values ​​are stored for different target powers, for which the efficiency reaches its maximum value or differs from its maximum value by at most 10%.

[0078] exist Figure 1 , the input terminal 50a of the impedance matching circuit 50 is directly indicated on the housing of the impedance matching circuit 50. In principle, the input terminal can also be in contact with the end of the first cable connection 2a, by which the first cable connection 2a is connected to the HF generator 60. The cable impedance of the first cable connection 2a is thus also taken into account. In this case, the HF generator 60 directly seeks an impedance target value that is not distorted by the first cable connection 2a.

[0079] As already explained, the control device 1 is preferably designed to additionally take into account model parameters of the cable impedance of the first cable connection 2a between the HF generator 60 and the impedance matching circuit 50. The model parameters of the cable impedance can be stored in the memory device 8. These model parameters are frequency-dependent and different cable impedances are applied depending on the operating frequency of the HF generator 60.

[0080] The control device 1 can also be designed to calculate the cable impedance of the first cable connection by means of a first measuring unit and a second measuring unit 5, 6, wherein the first measuring unit 5 is arranged between the HF generator 60 and the first cable connection 2a, and wherein the second measuring unit 6 is arranged between the first cable connection 2a and the impedance matching circuit 50 or between the impedance matching circuit 50 and the load 70. Figure 1 . In the case where 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 .

[0081] Figure 2A , Figure 2B Different embodiments of the impedance matching circuit 50 are shown. Figure 2A In FIG. 5 , the impedance matching circuit 50 is L-shaped. Figure 2B In the embodiment, the impedance matching circuit 50 is T-shaped.

[0082] exist Figure 2A, the input terminal 50a of the impedance matching circuit 50 is connected to the first coil 10 (first inductor) and to the second coil 11 (second inductor). The first and second coils 10, 11 are attached to a common node with their first terminals and therefore to the input terminal 50a of the impedance matching circuit 50. The first coil 10 is connected to the reference ground via the first capacitor 12 (first capacitance). The second coil 11 is connected to the output terminal 50b via the second capacitor 13 (second capacitance). The first and second capacitors 12, 13 are adjustable elements, especially adjustable elements in the form of variable capacitors, whose capacitance can be changed via a stepper motor. Alternatively, a solid-state switch can be used to switch the capacitor on and off more quickly. In particular, the plate spacing of the first and second capacitors 12, 13 can be changed. The plasma ignition identification device 1 is designed to control the respective stepper motors accordingly. In principle, the processing unit 7 can perform the control. The capacities of the first and second capacitors 12, 13 can be adjusted independently of each other. Preferably, the impedance matching circuit 50 has no other elements. Of course, the positions of the first coil 10 and the first capacitor 12 may also be interchanged. In this case, the first capacitor 12 is arranged at the input terminal 50a of the impedance matching circuit 50, and the first coil 10 is arranged at the reference ground. Complementarily or alternatively, the positions of the second coil 11 and the second capacitor 13 may also be interchanged. In this case, the second capacitor 13 is arranged at the input terminal 50a of the impedance matching circuit 50, and the second coil 11 is arranged at the reference ground.

[0083] exist Figure 2B , the input terminal 50a of the impedance matching circuit 50 is connected to the first capacitor 12 (first capacitance). The first capacitor 12 is connected not only to the first coil 10 (first inductor) but also to the second coil 11 (second inductor). This is achieved by connecting the first capacitor 12 and the common node connected to the first and second coils 10, 11. The first coil 10 is still connected to the reference ground. The second coil 11 is connected (connected in series) to the second capacitor 13 (second capacitance). 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 can also be interchanged. In this case, the second capacitor 13 will be connected to the common node and the second coil 11 will be connected to the output terminal 50b of the impedance matching circuit 50. Preferably, the impedance matching circuit 50 has no other elements.

[0084] Figure 3 An exemplary embodiment is shown of a possible design of the first measuring unit and / or the second measuring unit 5 , 6 . In this exemplary embodiment, the first measuring unit and / or the second measuring unit 5 , 6 is designed for contactless voltage measurement and contactless current measurement.

[0085] For this purpose, the first or second measuring unit 5 , 6 comprises a current sensor 15 and a voltage sensor 16 .

[0086] However, it is preferred to also measure the phase relationship between current and voltage so that the impedance can be calculated.

[0087] 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.

[0088] The two ends of the coil are preferably connected to one another via a shunt resistor 17. With the aid of a first A / D converter (analog-to-digital converter) 18, the voltage dropped across the shunt resistor 17 can be digitized.

[0089] The voltage sensor 16 of the first measuring unit and / or the second measuring unit 5, 6 is preferably configured as a capacitive voltage divider. The first capacitor 19 is formed by a conductive ring 19. A conductive cylinder can also be used. The corresponding first cable connection or second cable connection 2a, 2b is guided through the conductive ring 19. The second capacitor 20 of the voltage sensor 16 configured as a voltage divider is connected to the reference ground. Connected in parallel with the second capacitor 20 is a second A / D converter 21, which is designed to detect the voltage dropped on the second capacitor 20 and digitize it.

[0090] In principle, the first measuring unit 5 and the second measuring unit 6 can also be arranged or constructed on a (common) circuit board. The first capacitor 19 can be formed by a coating on a first side and an opposite second side of the circuit board. In this case, the coatings on the first side and the second side are electrically connected to each other via plated through holes. The first cable connection or the second cable connection 2a, 2b passes through an opening in the circuit board. The second capacitor 20 can be formed by discrete components.

[0091] The current sensor 15 in the form of a coil, in particular a Rogowski coil, is spaced further from the first or second cable connection 2a, 2b than the first capacitor 19. The coils can also be formed on the same circuit board by corresponding coatings and plated-through holes. The coil for current measurement and the first capacitor for voltage measurement preferably pass through a common plane.

[0092] The shunt resistor 17 may also be arranged on the circuit board. Anything else does not apply to the first A / D converter and / or the second A / D converter 18, 21.

[0093] In the case where the first and second measuring units 5, 6 are arranged on the first cable connection 2a, they are arranged spaced apart from one another, in particular arranged such that the influence of mutual interference is reduced to such an extent that, in view of the required measurement accuracy, this influence plays only a minor role. The first measuring unit 5 is arranged in the region of the HF generator 60 and the second measuring unit 6 is arranged in the region of the impedance matching circuit 50.

[0094] The second measuring unit 6 can also be arranged at the output terminal 50 b of the impedance matching circuit 50 and the first measuring unit 5 still arranged in the region of the HF generator 60 , in order to thereby be able to detect the cable impedance of the first cable connection 2 a .

[0095] The first measuring unit and / or the second measuring unit 5 , 6 can also be designed as a directional coupler.

[0096] Figure 4 A Smith chart is shown which illustrates how the HF generator 60 transitions from maximum power to maximum efficiency depending on an impedance target value.

[0097] exist Figure 4 In the Smith chart of FIG. 1 , six impedance variation curves P1, P2, P3, P4, P5, and P6 are exemplarily shown. Any impedance target value on one impedance variation curve means that the HF generator 60 has the same output power. This means that the same output power of the HF generator 60 can be achieved using different impedance target values ​​on the same impedance variation curve. Different impedance variation curves result in different output powers of the HF generator 60. Compared with the impedance target value on the impedance variation curve P2, when the HF generator 60 seeks the impedance target value on the impedance variation curve P1, the HF generator generates a different output power.

[0098] Figure 4 Only six impedance variation curves P1, P2, P3, P4, P5, and P6 are shown in FIG. 1 , but there may be more than six impedance variation curves.

[0099] exist Figure 4 In the Smith chart of FIG. 1 , six other impedance variation curves E1, E2, E3, E4, E5, E6 are shown by way of example. Any impedance target value located on one of these other impedance variation curves means that the HF generator 60 has the same efficiency. This means that the same efficiency of the HF generator 60 can be achieved with different impedance target values. Different impedance variation curves result in different efficiencies of the HF generator 60. When the HF generator 60 seeks an impedance target value located on the impedance variation curve E1, the HF generator generates different efficiencies compared to the impedance target value located on the impedance variation curve E2.

[0100] Some values ​​are shown below as examples to illustrate the representation.

[0101]

[0102]

[0103] It can be seen that for the maximum possible power achievable for the impedance target value on the impedance variation curve P1, only an efficiency of E6 = 72% can be achieved, whereas for a lower power P2 = 47.0 dBm, an efficiency of E3 = 84.0% can be achieved.

[0104] A further 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.

[0105] On the curve 30, there are different impedance target values ​​for different target powers, wherein for each impedance target value of the HF generator 60 a target power is provided at which the efficiency has a corresponding maximum value. If the user requires a power of P=44.5 dBm, he will move along the curve 30 until the required target power. For this target power, the corresponding impedance target value is stored at which the efficiency has its maximum value. This impedance target value is then set by the impedance matching circuit 50.

[0106] In principle, a family of curves can also be plotted, wherein the corresponding impedance target values ​​then produce efficiencies which preferably differ by at most 10% from their maximum value. The use of a family of curves is then advantageous because, for example, impedance target values ​​which require minimal mechanical adjustment of the impedance matching circuit 50 can be used.

[0107] The curve 30 , ie the relationship between the target power, the impedance target value and the optional efficiency, is preferably stored in a look-up table 9 . It is also clear that different profiles of the curve 30 may exist for different operating frequencies of the HF generator 60 .

[0108] Figure 5 A diagram is shown which shows the curve of the efficiency of a determined target power in relation to the desired impedance target value. It can be seen that as the target power increases, the efficiency decreases. It is also shown which efficiencies or which target powers can be achieved for which impedance target values. For this purpose, Figure 5 Also shown in FIG. 3 is a curve 30 , wherein a first end of the curve 30 is associated with maximum efficiency and wherein a second end of the curve 30 is associated with maximum power.

[0109] Figure 6A flow chart describing a method for controlling an impedance matching circuit 50 is shown. In method step S1, an impedance target value for an input terminal 50a of the impedance matching circuit 50 is determined as a function of a predeterminable operating frequency of the HF generator 60, a predeterminable target power of the HF generator 60, and model parameters of the HF generator 60. The impedance target value deviates from the nominal impedance in order to thereby increase the operating characteristic value of the HF generator 60, in particular to thereby increase the efficiency of the HF generator 60. In method step S2, the determined impedance target value is set by the impedance matching circuit 50.

[0110] The invention is not limited to the described embodiments. Within the scope of the invention, all described and / or illustrated features can be combined in any desired manner.

Claims

1. A control device (1) for controlling an impedance matching circuit (50) of a plasma generation system (100), the impedance matching circuit comprising an input terminal (50a) and an output terminal (50b) for connection between an HF generator (60) and a load (70), characterized in that: The control device (1) is designed to: a) a predeterminable operating frequency of the HF generator (60); b) a predeterminable target power of the HF generator (60); and c) model parameters of the HF generator (60); An impedance target value is determined for an input terminal (50a) of the impedance matching circuit (50), wherein the impedance target value has a value that deviates from a nominal impedance in order to achieve an improvement in operating characteristic values, in particular an increase in efficiency, of the HF generator (60) for the predeterminable operating frequency and the predeterminable target power.

2. The control device (1) according to claim 1, characterized by the following features: The operating characteristic value comprises one or more of the following characteristics of the HF generator (60): a) Efficiency; b) the temperature in certain components, such as transistors, capacitors, inductors, couplers, matching circuits, in particular the limitation of the maximum permissible temperature; c) voltages in certain components, such as transistors, capacitors, inductors, couplers, matching circuits, in particular the limitation of the maximum permissible voltage; d) Limitation of currents and voltages in certain components, such as transistors, capacitors, inductors, couplers, matching circuits, in particular the limitation of the maximum permissible current.

3. The control device (1) according to claim 1 or 2, characterized by the following features: The control device (1) is designed to control the impedance matching circuit (50) in such a way that the control device adjusts the impedance of the input terminal (50a) to the impedance target value.

4. The control device (1) according to any one of the preceding claims, characterized by the following features: - The nominal impedance is 50Ohm.

5. The control device (1) according to any one of the preceding claims, characterized by the following features: The control device (1) is designed to select an impedance target value for which the efficiency is improved compared to the efficiency of the nominal impedance.

6. Control device (1) according to any of the preceding claims, characterized by the following features: The model parameters of the HF generator (60) include, for different predeterminable target powers, corresponding impedance target values ​​for which the efficiency reaches its maximum value or deviates from its maximum value by at most 10%.

7. The control device (1) according to claim 6, characterized by the following features: The different target powers are located on a curve (30) or a family of curves.

8. The control device (1) according to claim 7, characterized by the following features: The control device (1) is designed to store the following impedance target values ​​for adjacent target powers on the curve (30) or on the family of curves: the successive recall of the impedance target values ​​requires minimal mechanical adjustment of the impedance matching circuit (50).

9. The control device (1) according to any one of claims 6 to 8, characterized by the following features: - The control device (1) comprises a storage device (8), wherein the storage device (8) has a lookup table (9), in which impedance target values ​​corresponding to different target powers are stored, for which the efficiency reaches its maximum value or differs from its maximum value by at most 10%.

10. The control device (1) according to any one of the preceding claims, characterized by the following features: The control device (1) is designed to additionally take into account model parameters of the cable impedance of the cable connection (2a) between the HF generator (60) and the impedance matching circuit (50).

11. The control device (1) according to claim 10, characterized by the following features: - the control device (1) is designed to load the cable impedance from a storage device (8); or The control device (1) is designed to calculate the cable impedance by means of a first measuring unit and a second measuring unit (5, 6), wherein the first measuring unit (5) can be arranged between the HF generator (60) and the cable connection (2a), and wherein the second measuring unit (6) can be arranged between the cable connection (2a) and the impedance matching circuit (50) or between the impedance matching circuit (50) and the load (70).

12. Control device (1) according to any of the preceding claims, characterized by the following features: The control device (1) is designed to additionally take into account model parameters of the impedance matching circuit (50).

13. Control device (1) according to any of the preceding claims, characterized by the following features: The control device (1) includes different model parameters for different operating frequencies of the HF generator (60).

14. Control device (1) according to any of the preceding claims, characterized by the following features: - The input terminal (50a) is arranged on the housing of the impedance matching circuit (50).

15. The control device (1) according to any one of claims 1 to 13, characterized by the following features: The HF generator (60) can be connected to the impedance matching circuit (50) via a cable connection (2a), wherein a first end of the cable connection (2a) can be connected to the HF generator (60), and wherein a second end of the cable connection (2a) can be connected to the impedance matching circuit (50), wherein the input terminal (50a) is arranged at the first end of the cable connection (2a).

16. Control device (1) according to any of the preceding claims, characterized by the following features: The control device (1) is designed to determine different impedance target values ​​for the input terminal (50a) of the impedance matching circuit (50) for different pulses during a pulse operation of the HF generator (60) in which pulses of different amplitudes are generated.

17. Control device (1) according to any of the preceding claims, characterized by the following features: The control device (1) is designed to determine an impedance target value for an input terminal (50a) of the impedance matching circuit (50), wherein the impedance target value is selected such that the HF generator (60) can provide a corresponding target power for the entire envelope of the generated signal.

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

19. The plasma generation system (100) of claim 18, characterized by the following features: - The impedance matching circuit (50) is integrated in the HF generator (60).

20. The plasma generating system (100) of claim 18, characterized by the following features: The impedance matching circuit (50) is connected to the HF generator (60) via a cable connection (2a).

21. The plasma generation system (100) of claim 20, characterized by the following features: - The cable connection part (2a) comprises at least two cables connected in parallel so as to reduce the impedance of the cable connection part (2a).

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

23. The plasma generation system (100) of claim 22, characterized by the following features: The control device (1) is designed to take into account and continuously redetermine the cable impedance of the cable connection (2a) between the HF generator (60) and the impedance matching circuit (50) during operation of the plasma generating system (100).

24. The plasma generating system (100) according to any one of claims 20 to 23, characterized by the following features: - provided with a first measuring unit and a second measuring unit (5, 6); The control device (1) is designed to calculate the cable impedance of the cable connection (2a) by means of the first measuring unit and the second measuring unit (5, 6), wherein the first measuring unit (5): a) is arranged between the HF generator (60) and the cable connection (2a); and / or b) is arranged in the region of an output terminal (60a) of the HF generator (60); and Wherein, the second measuring unit (6): a) arranged between the cable connection portion (2a) and the impedance matching circuit (50) and / or arranged in the region of an input terminal (50a) of the impedance matching circuit (50); or b) arranged between the impedance matching circuit (50) and the load (70).

25. The plasma generation system (100) of claim 24, characterized by 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) comprises a current sensor (15) and a voltage sensor (16), and / or the second measuring unit (6) comprises a current sensor (15) and a voltage sensor (16).

26. The plasma generation system (100) of claim 25, characterized by the following features: the voltage sensor (16) of the first measuring unit (5) has a capacitive voltage divider, wherein the first capacitance is formed by a conductive ring (19) or a cylinder, through which the cable connection (2a) in the region of the output terminal (60a) of the HF generator (60) and the impedance matching circuit (50) is led; as well as The current sensor (15) of the first measuring unit (5) has a coil arranged around a conductive ring (16) or a cylinder; and / or The voltage sensor (16) of the second measuring unit (6) comprises a capacitive voltage divider, wherein the first capacitor is formed by a conductive ring (19) or a cylinder, wherein: a) the cable connection (2a) in the region of the input terminal (50a) of the impedance matching circuit (50) is led through the conductive ring or cylinder; or b) the cable connection portion (2b) between the impedance matching circuit (50) and the load (70) is guided through the conductive ring or cylinder; as well as The current sensor of the second measuring unit (6) has a coil which is arranged around a conductive ring (19) or cylinder.

27. The plasma generating system (100) according to any one of claims 18 to 26, characterized by the following features: The control device (1) is designed to change the power of the HF generator (60), wherein this is achieved by changing the input power of an amplifier of the HF generator (60) and / or by changing the supply voltage of the amplifier of the HF generator (60).

28. The plasma generating system (100) according to any one of claims 18 to 27, characterized by the following features: - The impedance matching circuit (50) comprises one or more capacitors, wherein the value of at least one capacitor is variable during operation.

29. A method for operating an impedance matching circuit (50) of a plasma generation system (100), the impedance matching circuit having an input terminal (50a) connected to an output terminal (60a) of an HF generator (60) and an output terminal (50b) connected to an input of a load (70), wherein: The method is applicable to setting the input impedance at the input terminal (50a) when the output impedance at the output terminal (50b) is changeable, and is characterized in that the method comprises the following method steps: - Obtaining the impedance target value of the input terminal (50a) according to the following: a) a predeterminable operating frequency of the HF generator (60); b) a predeterminable target power of the HF generator (60); and c) model parameters of the HF generator (60); The impedance target value has a value that deviates from the nominal impedance in order to achieve an increase in operating characteristic values, in particular an increase in efficiency, of the HF generator (60) for a predeterminable operating frequency and a predeterminable target power.

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