Plasma process supply system, in particular for pulsed plasma processes, and method for operating such a plasma process supply system

Abstract

The invention relates to a plasma process supply system (100), in particular for pulsed plasma processes, comprising an RF generator (2) which has at least one amplifier circuit (30), an impedance matching circuit (3), and a control device (1). The plasma process supply system (100) can be connected to a plasma chamber (4). The RF generator (2) is connected to the impedance matching circuit (3), the impedance matching circuit (3) being designed to set a target impedance (10) as an input impedance for the RF generator (2). The control device (1) is designed to set the target impedance (10) such that a trajectory (40), which describes an impedance curve for the input impedance in a settling period (41), runs from a starting impedance region (42) through an ignition impedance region (43) to a target impedance region (44), the RF generator (2) delivering, in the ignition impedance region (43), a power level which is higher than a target power level in the subsequent target impedance region (44).

Description

[0001] Plasma process supply system, in particular for pulsed plasma processes, and a method for operating such a plasma process supply system

[0002] The invention relates to a plasma process supply system, in particular for pulsed plasma processes, and a method for operating such a plasma process supply system.

[0003] The surface treatment of workpieces using plasma and gas lasers are industrial processes in which a plasma is generated, particularly in a plasma chamber, using direct current or a high-frequency alternating signal with an operating frequency in the range of a few 10 kHz up to the GHz range.

[0004] The plasma chamber is connected to a high-frequency generator (HF generator) via additional electronic components such as coils, capacitors, cables, or transformers. These additional components can represent resonant circuits, filters, or impedance matching circuits.

[0005] Plasma processes represent a highly variable load for the high-frequency generator, which depends on the conditions in the plasma chamber. In particular, the properties of the workpiece, electrodes, and gas conditions are important.

[0006] High-frequency generators have a limited operating range with respect to the impedance of the connected electrical load (= consumer). If the load impedance exceeds a permissible range, the required energy / power cannot be delivered to the consumer. Damage to the RF generator is also possible. For this reason, an impedance matching circuit (matchbox) is usually required to transform the load impedance to a nominal impedance of the generator output.

[0007] Various impedance matching circuits are known. Either the impedance matching circuits are fixed and have a predetermined transformation effect, i.e., they consist of electrical components, particularly coils and capacitors, that do not change during operation. This is particularly useful for constant operation, such as in a gas laser. Furthermore, impedance matching circuits are known in which at least some of the components of the impedance matching circuits are mechanically variable. For example, motor-driven variable capacitors are known, whose capacitance value can be changed by changing the arrangement of the capacitor plates relative to one another.

[0008] Roughly speaking, a plasma can be assigned three impedance ranges. Before ignition, very high impedances exist. During normal operation, i.e., when plasma is used as intended, lower impedances exist. In the case of unwanted local discharges (Ares) or plasma fluctuations, very low impedances can occur. In addition to these three identified impedance ranges, other special states with other associated impedance values ​​can occur. If the load impedance changes suddenly and the load impedance or the transformed load impedance moves out of a permissible impedance range, the RF generator or transmission equipment between the RF generator and the plasma chamber can be damaged. There are also stable plasma states that are undesirable.

[0009] An impedance matching circuit is described, for example, in DE 10 2009 001 355 A1. Depending on the plasma process, a plasma can be operated with a pulsed or a continuous RF signal, also called a CW signal. Due to the high variance that can occur in plasma processes, reproducible ignition of the plasma is an important issue for the safe operation of a plasma process. Reproducible ignition is less problematic with an RF generator that provides a CW signal because an impedance matching circuit can be initially configured to ensure ideal ignition conditions (matching to "cold" impedance). After ignition, the impedance matching circuit is then controlled to achieve matching as quickly as possible. With a CW signal, there is sufficient time for this. Reliable ignition, however, is more problematic with an RF generator that generates a pulsed high-frequency signal.In pulsed operation, the impedance matching circuit is set to the "burning position." However, this may not be optimal for ignition.

[0010] It is therefore the object of the present invention to provide a plasma process supply system which allows reliable ignition of the plasma at the beginning of each pulse, particularly in pulsed plasma processes.

[0011] The problem is solved with respect to the plasma process supply system by claim 1 and with respect to a method for operating such a plasma process supply system by claim 19. Advantageous developments of the plasma process supply system are specified in claims 2 to 18.

[0012] The plasma process supply system is particularly suitable for pulsed plasma processes. It comprises an RF generator that includes at least one amplifier circuit. Furthermore, the plasma process supply system comprises an impedance matching circuit and a control device. The plasma process supply system is connectable to a plasma chamber. The RF generator is (galvanically) connected to the impedance matching circuit. The impedance matching circuit is designed to set a target impedance as the input impedance for the RF generator. The target impedance is set, in particular, at an input of the impedance matching circuit, to which the RF generator is connected.The control device is designed to set the target impedance such that a trajectory describing an impedance curve for the input impedance in a transient response period runs from a starting impedance range through an ignition impedance range to a target impedance range, wherein the RF generator outputs a power in the ignition impedance range that is higher than a target power in the subsequent target impedance range. The target impedance lies within the target impedance range. Amplifiers generally exhibit a characteristic behavior with regard to the output power depending on the load impedance. This behavior can also be referred to as the power profile of an RF amplifier. The appropriate selection of the target impedance has the great advantage that the appropriate impedances are passed through at a speed that a controller could not compensate for in this time.This is especially true when using a pulsed high-frequency signal, for which a controller would have to adjust each pulse individually. The target power delivered by the RF generator can be the same across the entire impedance range. However, in reality, a portion of the power is always reflected in the various impedance ranges. Therefore, the trajectory is chosen so that less reflected power is expected in the ignition impedance range when the plasma is ignited than in the target impedance range.

[0013] It is particularly advantageous here that the trajectory, which passes through various ranges up to the target impedance range, is adjusted by selecting the target impedance such that it passes through an ignition impedance range in which the RF generator delivers a higher power than in the subsequent target impedance range. This higher power (power peaking) ensures a short-term increase in the field strength in the plasma chamber, which ignites the plasma more reliably than with conventional plasma process supply systems. Another particularly advantageous feature is that the progression of the trajectory until the target impedance range is reached can be uncontrolled, which significantly simplifies operation.The fact that the RF generator does not immediately detect the target impedance is due, among other things, to the high quality of the impedance matching circuit, which requires the corresponding resonant circuits, formed, for example, from capacitances and inductances, to first settle. Passive components oscillate at least in the initial impedance range. For this reason, the impedance changes during the aforementioned settling period. In addition to the impedance matching circuit, the load is also responsible for the formation of the trajectory. Thus, the plasma impedance also changes during the settling period.Since there are a variety of target impedances to achieve a desired target power output from the RF generator, the target impedance can be selected at which the trajectory passes through a desired ignition impedance range, i.e., a range in which the power delivered by the RF generator exceeds the target power. The increased power that can be accessed in the ignition impedance range is often not necessary for the actual plasma process, or the continuous access to this increased power is avoided for efficiency reasons.

[0014] In one aspect, the settling period comprises the time range from the beginning of a pulse of the RF signal to a point in time at which the impedances no longer change, or to the point in time at which a change in the impedances is smaller than a threshold value. The impedances include the impedances of the impedance matching circuit (capacitors, coils) as well as the plasma impedance.

[0015] In one aspect, the amplifier circuit comprises a balanced amplifier. The use of balanced amplifiers offers significant advantages in plasma applications because they deliver their maximum power when they encounter an input impedance that corresponds to the nominal impedance (e.g., 50 ohms). They are also more robust and have a constant output resistance. One problem arises when igniting the plasma, which is resolved by selecting the target impedance and thereby improving the trajectory. For this reason, the plasma process supply system allows the use of balanced amplifiers. The balanced amplifier is preferably dimensioned such that its target power is sufficient to operate the plasma process when the target impedance is present, with the increased power in the matching range being used to ignite the plasma process.

[0016] The balanced amplifier preferably has two amplifier paths, which are operated with a phase shift of preferably 90°. Such a balanced amplifier is described, for example, in WO2015 / 091468 A1 as a "power converter." WO2015 / 091468 A1 is hereby incorporated by reference in its entirety into this disclosure.

[0017] The balanced amplifier preferably has a 90° coupler for coupling the output signals of the amplifier paths.

[0018] The balanced amplifier preferably has a hybrid coupler for coupling the output signals of the amplifier paths.

[0019] The balanced amplifier preferably has a 3dB coupler for coupling the output signals of the amplifier paths.

[0020] In one aspect, the control device is configured to set the target impedance such that, when the target impedance is present, the RF generator delivers the preset target power. As already explained, there are a variety of target impedances at which the RF generator delivers the same target power. It is also advantageous that the target power can be specified.

[0021] In one aspect, the control device comprises a memory device. Corresponding target impedances are stored in the memory device for different target powers that can be delivered by the RF generator. One target impedance can be stored for a target power, or multiple target impedances can be stored. The storage can be in the form of a look-up table, for example.

[0022] In one aspect, the control device is configured to set the target impedance to a value for which the trajectory passes through the firing impedance range, at which the RF generator delivers a power that is higher than the target power by a presettable amount. Here, too, it is advantageous that the amount is presettable. Thus, a user can specify that the power in the firing impedance range should be, for example, 10% or 20% higher than the target power. Preferably, the firing impedance range in the Smith chart for a balanced amplifier is closer to 50 ohms than the target impedance range.

[0023] In one aspect, the plasma process supply system comprises an operating unit. The control device is configured to receive a user input from the operating unit. The user input is the level of the target power and / or the presettable value by which the power in the ignition impedance range exceeds the target power. It is particularly advantageous that the operator of the plasma process supply system only needs to specify the target power and the increased power in the ignition impedance range, thereby providing a reliably ignited plasma process.

[0024] In one aspect, the control device is configured to set the target impedance to a value for which the trajectory passes through the ignition impedance range and the target impedance range, wherein the amplifier circuit, and in particular amplifier elements of the amplifier circuit, have a power loss that is below a threshold value, thereby minimizing the power loss. By measuring the amplifier circuit, those regions can be determined in which the efficiency is above a threshold value or in which the power loss occurring in the individual amplifier elements (for example, in the transistors) is below a threshold value.The choice of a corresponding trajectory is particularly advantageous because when using a balanced amplifier, it is not operated with matching in the target impedance range and therefore a signal power is reflected back from the impedance matching circuit to the RF amplifier.

[0025] In one aspect, the control device is configured to set the target impedance to a value such that a mean value of the impedance curve corresponds to the nominal impedance of the RF generator, in particular 50 ohms. This improves efficiency.

[0026] In one aspect, the control device is configured to measure the impedance profile of a trajectory and to adjust the target impedance based on the measured impedance profile so that the trajectory exhibits an improved profile in a subsequent settling period. This has the advantage, particularly in pulsed plasma applications, that the trajectory can be successively adjusted to the optimal profile. If a repetition rate (pulse rate) of preferably more than 10 Hz to preferably less than 1 MHz is used, the desired trajectory is achieved very quickly.

[0027] In one aspect, the course of the trajectory in a subsequent settling period can thus be improved with regard to the efficiency of the amplifier circuit, the achievable power in the ignition impedance range, the averaged impedance in the settling period and / or the achievable power in the target impedance range.

[0028] In one aspect, the control device is configured to measure the trajectory in each settling period. This allows the target impedance to be adjusted more finely, while simultaneously checking whether the trajectory is improved in the subsequent settling period (e.g., in the subsequent pulse). With a high pulse repetition rate, it is not necessary to measure the trajectory in the settling period for each pulse. In this case, the trajectory for the settling period can be measured for at least every nth pulse, with n = 2, 5, 10, 50, 100, 500, 1000, 5000, 10000.

[0029] In one aspect, the RF generator is configured to pulse a high-frequency signal and output this pulsed high-frequency signal to the impedance matching circuit. The settling period extends over the temporal length of such a pulse. The repetition rate of the pulses may be approximately 10 Hz to 1 MHz. The pulse length may be in the range from 1 ps to 500 ps, ​​in particular in the range from 100 ps to 500 ps, ​​particularly preferably 300 ps. The settling time may comprise any desired time range of each pulse (e.g., 5% or more and 90% or less). The settling time depends in particular on the pulse length. If a pulse has a long pulse length, the settling time is shorter relative to the length of the pulse compared to a pulse with a shorter length.

[0030] In one aspect, the control device is configured to measure the trajectory for each settling period and thus for each pulse of the high-frequency signal. This allows for particularly fine adjustment of the target impedance. It is also conceivable that after a measured trajectory for a pulse, at least n pulses follow for which no trajectory is measured, with n > 2, 3, 5, 10, 15, 20, 50, 100, 500. If pulsing is carried out at a high pulse rate, e.g., 1 MHz, it is not necessary to measure the trajectory of each pulse.

[0031] In one aspect, the control device comprises a measuring unit. The measuring unit comprises at least one directional coupler unit for detecting the power of a forward and return high-frequency signal, or a current sensor and a voltage sensor. The control device is designed to measure the impedance curve of the trajectory based on the measurement result of the directional coupler unit, or the current sensor and the voltage sensor. In this way, the impedance curve of the trajectory can be measured very easily and very quickly. In one aspect, the voltage sensor of the measuring unit is a capacitive voltage divider, wherein a first capacitance is formed by an electrically conductive ring or cylinder through which a cable can be passed, over which the RF power can be transmitted. In addition, the current sensor of the measuring unit is a coil arranged around the conductive ring or cylinder.This design enables non-contact measurement of current and voltage.

[0032] In one aspect, the measuring unit is arranged between the RF generator and the impedance matching circuit. Preferably, the measuring unit is arranged closer to the impedance matching circuit than to the RF generator.

[0033] In one aspect, the trajectory passes through the ignition impedance range faster than it remains in the target impedance range. The impedance seen at the RF generator's output over time (trajectory) passes through the ignition impedance range faster than it remains in the target impedance range. This allows for a stable plasma process with more reliable ignition.

[0034] In one aspect, the trajectory traverses the ignition impedance range in less than 30%, 20%, or 10% of the time it remains in the target impedance range.

[0035] In one aspect, a DC generator is provided which is designed to generate a DC signal, wherein the DC signal can be fed to the plasma chamber in overlap with the high-frequency signal. The DC signal can be output constantly or pulsed by the DC generator. The impedance matching circuit can have a further input to which the DC generator is connected. A bias tee can also be connected between the impedance matching circuit and the plasma chamber, which bias tee is designed to overlap the high-frequency signal and the DC signal with each other and transmit them to the plasma chamber. In one aspect, the impedance matching circuit comprises at least one or more adjustable reactances in order to change the transformation ratio for the impedance between an input to which the RF generator is connected and an output to which a load, i.e. the plasma chamber, can be connected.The reactances can be adjusted mechanically and / or electrically. This can be achieved, for example, using semiconductor switching elements such as transistors or PIN diodes. Additionally or alternatively, at least one varactor and / or at least one switchable inductance and / or capacitor can be used.

[0036] The method serves to operate the plasma process supply system. In particular, pulsed plasma processes can be operated using the method. The plasma process supply system comprises an RF generator having at least one amplifier circuit, an impedance matching circuit, and a control device. The plasma process supply system is connectable to a plasma chamber. In a first method step, the RF generator is connected to the impedance matching circuit. In a second method step, a target impedance is defined as the input impedance for the RF generator, such that a trajectory describing an impedance curve for the input impedance in a transient response period runs from a starting impedance range via an ignition impedance range to a target impedance range. The RF generator outputs a power in the ignition impedance range that is higher than a target power in the subsequent target impedance range.In a third process step, a target impedance is set as the input impedance for the RF generator by the impedance matching circuit.

[0037] The development is described below purely by way of example with reference to the drawings. Figure 1 shows an embodiment of the plasma process supply system with a control device;

[0038] Figure 2: an embodiment of an amplifier circuit of an RF amplifier of the plasma process supply system;

[0039] Figures 3A, 3B, 3C, 3D, 3E: various examples of how a trajectory can proceed that describes an impedance curve for an input impedance in a settling period;

[0040] Figures 4A, 4B: different curves for output power delivered by the RF generator;

[0041] Figures 5A, 5B: various embodiments of how an impedance matching circuit can be constructed;

[0042] Figures 6, 7: embodiments of how a measuring unit for measuring a current and a voltage can be designed; and

[0043] Figure 8: a flowchart for a method explaining the operation of the control device.

[0044] Figure 1 shows a plasma process supply system 100, which comprises a control device 1. The plasma generation system 100 further comprises an RF generator 2, an impedance matching circuit 3, and at least one consumer 4, in particular in the form of a plasma chamber. The RF generator 2 is designed to provide a high-frequency signal, in particular in the form of a pulsed high-frequency signal, with a nominal power PNenn and a frequency fo and to output it at an output terminal 2a. The impedance matching circuit 3 comprises an input terminal 3a, wherein the RF generator 2 is connected to the input terminal 3a via a first cable connection 5a. The impedance matching circuit 3 further comprises an output terminal 3b. The output terminal 3b is connected to the at least one consumer 4 via a second cable connection 5b.The first and / or second cable connection 5a, 5b may comprise one or more cables, for example, connected in series and / or in parallel. Coaxial cables are preferably used.

[0045] The consumer 4, i.e., the plasma chamber, comprises at least one electrode 6 for generating a plasma 7. The electrode 6 is (galvanically) connected to the output terminal 3b of the impedance matching circuit 3. In this embodiment, a camera system 8 is also arranged in the plasma chamber, which is designed to observe the plasma 7.

[0046] The control device 1 is preferably a processor and / or FPGA and / or microcontroller and / or ASIC. The control device 1 can also include a memory device 9.

[0047] The control device 1 is designed to control the RF generator 2, in particular to activate or deactivate it. Additionally or alternatively, the control device 1 is also designed to change the power and / or frequency of the RF signal by appropriately controlling the RF generator 2. Additionally or alternatively, the control device 1 is designed to change the waveform (type of RF signal, modulation of the RF signal, pulse durations, pulse repetition rate) of the RF signal by appropriately controlling the RF generator 2.

[0048] The control device 1 is preferably also designed to control the impedance matching circuit 3. In particular, the control device 1 is designed to change the transformation ratio within the impedance matching circuit 3 or to specify a target impedance 10 that acts as the input impedance for the RF generator 2.

[0049] The control device 1 further comprises a measuring unit 11. The measuring unit 11 is designed to measure, among other things, the impedance value at the input terminal 3a of the impedance matching circuit 3. The measuring unit 11 is preferably arranged between the RF generator 2 and the impedance matching circuit 3.

[0050] For this purpose, the measuring unit 11 comprises a directional coupler unit. Using the directional coupler unit, the measuring unit 11 can measure the power of a forward and return high-frequency signal on the first cable connection 5a in order to calculate the input impedance therefrom. The measuring unit 11 can alternatively also comprise a current sensor 16 and a voltage sensor 20. A configuration with a current sensor 16 and a voltage sensor 20 is shown in Figures 6 and 7. The control device 1 is designed to calculate the impedance seen by the RF generator 2 based on the measurement result of the directional coupler unit or the current sensor 16 and the voltage sensor 20.

[0051] The plasma generation system 100 preferably also includes an operating unit 12. The operating unit 12 is preferably a screen, in particular a touch-sensitive screen. In addition to a screen, the operating unit 12 can also include input devices such as a keyboard and / or mouse. The operating unit 12 can also be a web server that provides data and receives user input. The control device 1 is designed to display current settings of the RF generator 2 and / or the impedance matching circuit 3 on the operating unit 12.

[0052] The control device 1 is preferably designed to receive setpoint specifications, for example, for the power of the high-frequency signal, the so-called target power. Furthermore, the frequency of the high-frequency signal and / or the waveform of the high-frequency signal and / or the pulse rate and / or the pulse duration for the high-frequency signal can be received by the control unit 12. From this, corresponding control variables for the RF generator 2 and the impedance matching circuit 3 can be generated and transmitted to them.

[0053] Fig. 1 also shows:

[0054] - An example of the course of a trajectory 40 in a Smith chart SD, which describes an impedance curve for an input impedance 10 in a settling period 41, which runs from a starting impedance range 42 via a firing impedance range 43 to a target impedance range 44. This is described in detail below in Fig. 3D.

[0055] - An example of the curve of an output power PL over time t, which an RF generator 2 delivers during a transient period 41. This is described in detail below in Fig. 4B.

[0056] Figure 2 shows an exemplary structure of an amplifier circuit 30 of the RF amplifier 2. The amplifier circuit 30 comprises a balanced amplifier. In principle, the amplifier circuit 30 could also comprise an unbalanced amplifier. The balanced amplifier has a first 3 dB coupler 31 a and a second 3 dB coupler 31 b, which are designed in particular in the form of a hybrid coupler. A first input of the first 3 dB coupler 31 a is connected to a signal source 32. The signal source 32 is designed to generate the high-frequency signal (pulsed). A second input of the first 3 dB coupler 31 a is connected to the reference ground via a resistor 33. A first output of the first 3 dB coupler 31 a is connected to a first amplifier 34 a, in particular in the form of a transistor amplifier. A second output of the first 3dB coupler 31a is connected to a second amplifier 34b, in particular in the form of a transistor amplifier.The first transistor amplifier 34a is connected by its output to a first input of the second 3dB coupler 31b. The second transistor amplifier 34b is connected by its output to a second input of the second 3dB coupler 31b. A first output of the second 3dB coupler 31b is connected to the reference ground via the resistor 35. In the case of a mismatch, which is deliberately induced as explained below, it depends on the target impedance 10 whether power reflected back into the RF amplifier 2 is converted into heat in the resistor 35 or in the first and / or second transistor amplifiers 34a, 34b. The goal is for power reflected back to be converted into heat in the resistor 35, because this can easily be dimensioned sufficiently.A second output of the second transistor amplifier 34a, 34b, which may be the output terminal 2a, is connected to the impedance matching circuit 3.

[0057] Figures 3A, 3B, 3C, 3D, and 3E show various examples of how a trajectory 40 can run in a Smith chart SD, which describes an impedance curve for an input impedance 10 during a settling period 41. A trajectory 40 describes an impedance curve over time. Such a trajectory 40 is shown in dashed lines in the figures mentioned.

[0058] In Figure 3A, the trajectory 40 runs during a settling period 41 (see Figures 4A, 4B) towards a point on a Smith chart SD that corresponds to an impedance of 50 ohms. In this case, this impedance is the target impedance 10. In a balanced amplifier, there is matching at this point and the balanced amplifier delivers maximum power. The ignition behavior of the plasma 7 is problematic here. If the efficiency does not absolutely have to be maximum here, it could be advantageous to choose a target impedance 10 that is far from the nominal impedance. In this case, a mismatch would be deliberately induced. This is shown, for example, in Figures 3C and 3D. Figure 3B explains that there are different impedance ranges in a balanced amplifier in which the balanced amplifier delivers the same power. These areas have the same hatching in Figure 3B and extend approximately circularly around the point of nominal impedance.If a user specifies a target power, different target impedances 10 can be selected so that the RF amplifier 2 actually delivers the desired target power. Not all of these target impedances 10 are appropriate; for example, there are target impedances at which the RF amplifier 2 delivers the desired power, but the individual transistor amplifiers 34a, 34b are loaded to different degrees. The closer the hatched areas are to the point of the nominal impedance, the higher the output power that the RF amplifier 2 can provide.

[0059] Figure 3C describes the course of a trajectory 40 toward the target impedance 10. Due to a transient process in the impedance matching circuit 3 and also in the plasma chamber 4, the target impedance 10 is not reached immediately. Instead, a trajectory 40, i.e., an impedance curve over time, can be measured, at the end of which the target impedance is reached. This means that the RF generator 2 does not immediately see the target impedance 10 at its output. In Figure 3C, the RF generator 2 provides the desired output power (outermost circle) upon reaching the target impedance 10, at the end of the trajectory 40. The problem is that until the target impedance 10 is reached, the RF generator 2 only sees impedances at which it cannot provide the required power for the high-frequency signal, which is necessary for reliable ignition of the plasma 7.

[0060] According to the present development, the control device 1 is now configured to determine the target impedance 10 such that a trajectory 40 runs from a starting impedance range 42 via an ignition impedance range 43 to the target impedance range 44, wherein the RF generator 2 in the ignition impedance range 43 outputs a power that is higher than the target power in the subsequent target impedance range 44, where the target impedance 10 is present. This situation is illustrated in Figure 3D. In the target impedance range 44, the RF amplifier 2 outputs a high-frequency signal with approximately the same power as in the target impedance range 44 of Figure 3C. In Figure 3D, the trajectory 40 passes through the ignition impedance range 43, in which impedances are present that cause the RF amplifier 2 to output a higher power than in the later target impedance range 44, which results in a more reliable ignition of the plasma 7.As explained, a user can enter what power he wants to have from the RF amplifier 2 in the ignition impedance range 41.

[0061] The appropriate target impedance 10 is selected depending on the selected target power, which can be specified by a user, and the desired power in the ignition impedance range 43, which can also be specified by a user. The measuring unit 11 enables the control device 1 to continuously measure the impedance curve and adjust the target impedance 10 such that the trajectory 40 passes through the desired ignition impedance range 43. For each target impedance 10, which can be set by the impedance adjustment circuit 2, a power can be stored in the memory device 9, which the RF amplifier 2 can deliver when the target impedance 10 is reached.

[0062] Figure 3E shows that there are regions 45 through which the trajectory 40 should not pass. This can be due, for example, to impedances present here that result in the transistor amplifiers 34a, 34b being excessively or one-sidedly loaded and / or insufficiently efficient due to power reflected back to the RF amplifier 2. It is therefore the task of the control device 1, by selecting the target impedance 10, to ensure that the trajectory 40 does not pass through the regions 45, or only for a very short period of time within the settling period 41.

[0063] Figures 4A and 4B each show a curve of the delivered power PL over time t. Figure 4A shows a settling period 41, such as that present in the trajectory 40 from Figure 3A. The target impedance in Figure 3A is at the nominal impedance, in this case 50 ohms, with the amplifier circuit 30 being a balanced amplifier that delivers maximum power at the nominal impedance. Therefore, the power delivered by the RF amplifier 2 in Figure 4A increases with increasing time in the settling period 41.

[0064] Figure 4B, on the other hand, shows a transient response period 41 such as that shown in trajectory 40 from Figure 3D. Trajectory 40 runs through a starting impedance range 42 to an ignition impedance range 43 and further to a target impedance range 44. The power delivered by RF amplifier 2 is higher in ignition impedance range 43 than in target impedance range 44. This results in more reliable ignition of plasma 7. It is also clearly visible that target impedance range 44 lasts the longest relative to the total duration of transient response period 41. Ignition impedance range 43 extends over a shorter period, preferably less than 30%, 20%, or less than 10% of the duration of target impedance range 44.

[0065] If the high-frequency signal is a pulsed high-frequency signal, the settling period 41 can be, for example, the pulse duration. In this case, the control device 1 is preferably designed to measure the trajectory 40 again for each pulse, i.e., for each new settling period 41. In doing so, it can adapt the target impedance 10, wherein the target power (specified by the user) preferably remains unchanged, in order to positively influence the course of the trajectory 40, i.e., in particular, to ensure that a sufficiently high power is delivered by the RF generator 2 in the ignition impedance range 43. In order to transform the plasma impedance to the input impedance of the RF generator 2, the impedance adaptation circuit 3 can comprise one or more (series-connected) transformation stages.

[0066] Such a transformation stage is shown, for example, in Figures 5A and 5B. If the impedance matching circuit 3 contains multiple transformation stages, each transformation stage can be constructed according to the embodiment of Figures 5A and 5B. It is clear that the impedance matching circuit 3 can also be constructed differently than shown in Figures 5A and 5B.

[0067] In Figure 5A, the input terminal 3a of the impedance matching circuit 3 is connected to a first coil 50 (first inductance) and to a second coil 51 (second inductance). The first terminals of the first and second coils 50, 51 are connected to a common node and thus to the input terminal 3a of the impedance matching circuit 3. The first coil 50 is connected to a reference ground via a first capacitor 52 (first capacitance). The second coil 51 is connected to the output terminal 3b via a second capacitor 53 (second capacitance). The first and / or second capacitors 52, 53 are adjustable components, in particular in the form of variable capacitors whose capacitance can be changed via stepper motors. Alternatively, solid-state switches can be used to switch capacitances on and off as quickly as possible. In particular, the plate spacing of the first and second capacitors 52, 53 can be changed.The control device 1 is designed to control the respective stepper motors accordingly. The capacitances of the first and second capacitors 52, 53 can be adjusted independently of one another. The impedance matching circuit 3 is preferably free of additional components. Of course, the position of the first coil 50 and the first capacitor 52 can also be swapped. In this case, the first capacitor 52 is arranged at the input terminal 3a of the impedance matching circuit 3, and the first coil 50 is arranged at the reference ground. Additionally or alternatively, the position of the second coil 51 and the second capacitor 53 can also be swapped. In this case, the second capacitor 53 is arranged at the input terminal 3a of the impedance matching circuit 3, and the second coil 51 is arranged at the output terminal 3b of the impedance matching circuit 3.

[0068] In Figure 5B, the input terminal 3a of the impedance matching circuit 3 is connected to the first capacitor 52 (first capacitance). The first capacitor 52 is connected to both the first coil 50 (first inductance) and the second coil 51 (second inductance). This is done via a common node to which both the first capacitor 52 and the first and second coils 50, 51 are connected. The first coil 50 is also connected to the reference ground. The second coil 51 is connected to the second capacitor 53 (second capacitance) (series connection). The second capacitor 53 is connected to the output terminal 3b of the impedance matching circuit 3. The position of the second coil 51 and the second capacitor 53 could also be reversed. In this case, the second capacitor 53 would be connected to the common node and the second coil 51 to the output terminal 3b of the impedance matching circuit 3.Preferably, impedance matching circuit 3 is free of additional components.

[0069] Figures 6 and 7 show an embodiment of a possible structure of the measuring unit 11. The measuring unit 11 is designed to measure a voltage and a current without contact.

[0070] For this purpose, the measuring unit 11 comprises a current sensor 16 and a voltage sensor 20.

[0071] Preferably, the phase relationship between current and voltage is measured so that the impedance can be calculated. The current sensor 16 of the measuring unit 11 is a coil 21, in particular in the form of a Rogowski coil. Both ends of the coil are preferably connected to each other via a shunt resistor 22. The voltage drop across the shunt resistor 22 can be digitized using a first A / D converter 23.

[0072] The voltage sensor 20 of the measuring unit 11 is preferably designed as a capacitive voltage divider. A first capacitance 24 is formed by an electrically conductive ring 24. An electrically conductive cylinder could also be used. The corresponding first cable connection 5a is routed through this electrically conductive ring 24. A second capacitance 25 of the voltage sensor 20, which is designed as a voltage divider, is connected to the reference ground. Connected in parallel to the second capacitance 25 is a second A / D converter 26, which is designed to detect and digitize the voltage drop across the second capacitance 25.

[0073] In principle, the measuring unit 11 can also be arranged or constructed on a (common) printed circuit board. The first capacitor 24 can be formed by a coating on a first and an opposite second side of the printed circuit board. In this case, the coatings on the first and second sides are electrically connected to one another by vias. The first cable connection 5a is routed through an opening in the printed circuit board. The second capacitor 25 can be formed by a discrete component.

[0074] The current sensor 16 in the form of the coil 21, in particular in the form of a Rogowski coil, is spaced further from the first cable connection 5a than the first capacitor 24. The coil can also be formed on the same circuit board by appropriate coatings and vias. The coil for current measurement and the first capacitor for voltage measurement preferably extend through a common plane. The shunt resistor 22 can also be arranged on this circuit board.

[0075] The same applies to the first and / or second A / D converter 23, 23.

[0076] The measuring unit 11 can also be designed as a directional coupler unit.

[0077] In principle, the measuring unit 11 can also be arranged between the impedance matching circuit 3 and the load in the form of the plasma chamber 4. In this case, the second cable connection 5b would be used for measuring current and voltage. The input impedance can then be calculated by taking into account a known transformation ratio of the impedance matching circuit 3.

[0078] Figure 8 describes the method used to operate the plasma process supply system 100. Pulsed plasma processes, in particular, can be operated using this method. The plasma process supply system 100 comprises an RF generator 2, which has at least one amplifier circuit 30, an impedance matching circuit 3, and a control device 1. The plasma process supply system 100 is connectable to a plasma chamber 4. In a connecting method step S1, the RF generator 2 is connected to the impedance matching circuit 3. In a setting method step S2, a target impedance 10 is set as the input impedance for the RF generator 2, so that a trajectory 40, which describes an impedance curve for the input impedance in a settling period 41, runs from a starting impedance range 42 via an ignition impedance range 43 to a target impedance range 44.The RF generator 2 outputs a power in the ignition impedance range 43 that is higher than a target power in the subsequent target impedance range 44. In a setting method step S3, a target impedance 10 is set as the input impedance for the RF generator 2 by the impedance matching circuit 3.

Claims

Claims 1. Plasma process supply system (100), in particular for pulsed plasma processes, with an RF generator (2) comprising at least one amplifier circuit (30), an impedance matching circuit (3) and a control device (1), wherein the plasma process supply system (100) is connectable to a plasma chamber (4), having the following features: - the RF generator (2) is connected to the impedance matching circuit (3), wherein the impedance matching circuit (3) is designed to set a target impedance (10) as input impedance for the RF generator (2); - the control device (1) is designed to determine the target impedance (10) in such a way that a trajectory (40) which describes an impedance curve for the input impedance in a transient response period (41) runs from a starting impedance range (42) via an ignition impedance range (43) to a target impedance range (44), wherein the RF generator (2) in the ignition impedance range (43) outputs a power which is higher than a target power in the subsequent target impedance range (44).

2. Plasma process supply system (100) according to claim 1, characterized by the following feature: - the amplifier circuit (30) comprises a balanced amplifier.

3. Plasma process supply system (100) according to claim 1 or 2, characterized by the following feature: - the control device (1) is designed to set the target impedance (10) in such a way that the RF generator (2) delivers the presettable target power when the target impedance (10) is present.

4. Plasma process supply system (100) according to claim 3, characterized by the following feature: - the control device (1) comprises a memory device (9), wherein corresponding target impedances (10) which must be set for this purpose by the impedance matching circuit (3) are stored in the memory device (9) for different target powers which can be delivered by the RF generator (2).

5. Plasma process supply system (100) according to one of the preceding claims, characterized by the following feature: - the control device (1) is designed to set the target impedance (10) to a value for which the trajectory (40) runs through the ignition impedance range (43) at which the RF generator (2) delivers a power which is higher than the target power by a presettable amount.

6. Plasma process supply system (100) according to claim 5, characterized by the following features: - an operating unit (12) is provided; - the control device (1) is designed to receive a user input from the operating unit (12), wherein the user input comprises: a) the level of the target power; and / or b) the presettable value by which the power in the ignition impedance range (43) is above the target power.

7. Plasma process supply system (100) according to one of the preceding claims, characterized by the following feature: - the control device (1) is designed to set the target impedance (10) to a value for which the trajectory (40) passes through the ignition impedance range (43) and the target impedance range (44), wherein the amplifier circuit (30) and in particular amplifier elements (34a, 34b) of the amplifier circuit (30) have a power loss which is below a threshold value.

8. Plasma process supply system (100) according to one of the preceding claims, characterized by the following feature: - the control device (1) is designed to set the target impedance (10) to a value such that an average value of the impedance curve over the settling period (41) corresponds to the nominal impedance of the RF generator (2), in particular 50 ohms.

9. Plasma process supply system (100) according to one of the preceding claims, characterized by the following feature: - the control device (1) is designed to measure the impedance curve of a trajectory (40) and to adapt the target impedance (10) on the basis of the measured impedance curve, so that the trajectory (40) has an improved curve in a subsequent settling period (41).

10. Plasma process supply system (100) according to claim 9, characterized by the following feature: - the course of the trajectory (40) is improved in a subsequent transient response period with respect to: a) efficiency of the amplifier circuit (30); b) achievable power in the ignition impedance range (43); c) averaged impedance in the transient response period (41); and / or d) achievable power in the target impedance range (44).

11. Plasma process supply system (100) according to one of the preceding claims, characterized by the following feature: - the control device (1 ) is designed to measure the trajectory (40) in each settling period (41 ) or within each n-th settling period (41 ), with n = 2, 5, 10, 50, 100, 500, 1000, 5000, 10000.

12. Plasma process supply system (100) according to one of the preceding claims, characterized by the following features: - the RF generator (2) is designed to pulse a high-frequency signal and output this pulsed high-frequency signal to the impedance matching circuit (3); - the settling period (41) extends over the temporal length of such a pulse or a part thereof.

13. Plasma process supply system (100) according to claim 12, characterized by the following feature: - the control device (1) is designed to measure the trajectory (40) for each settling period (41) and thus for each pulse of the high-frequency signal.

14. Plasma process supply system (100) according to one of the preceding claims, characterized by the following features: - the control device (1 ) comprises a measuring unit (11 ); - the measuring unit (11) comprises a directional coupler unit for detecting the power of a forward and return high-frequency signal or a current sensor (16) and a voltage sensor (20); - the control device (1) is designed to measure the impedance curve of the trajectory (40) based on the measurement result of the directional coupler unit or the current sensor (16) and the voltage sensor (20).

15. Plasma process supply system (100) according to one of the preceding claims, characterized by the following feature: - the ignition impedance range (43) is passed through by the trajectory (40) faster in time than it remains in the target impedance range (44).

16. Plasma process supply system (100) according to claim 15, characterized by the following feature: - the trajectory (40) passes through the ignition impedance range (43) in less than 50%, 40%, 30%, 20% or 10% of the time that the trajectory (40) remains in the target impedance range (44).

17. Plasma process supply system (100) according to one of the preceding claims, characterized by the following feature: - a DC generator is provided which is designed to generate a DC signal, wherein the DC signal can be fed to the plasma chamber (4) in overlap with the high-frequency signal.

18. Plasma process supply system (100) according to one of the preceding claims, characterized by the following feature: - the impedance matching circuit (3) comprises at least one or more adjustable reactances (52, 53) in order to change the transformation ratio for the impedance between an input (3a) to which the RF generator (2) is connected and an output (3b) to which the plasma chamber (4) can be connected; - the reactances (52, 53) are mechanically adjustable and / or electrically adjustable and are formed in particular by at least one varactor and / or at least one switchable inductance and / or capacitance (52, 53) and / or by at least one PIN diode.

19. A method for operating a plasma process supply system (100), in particular for pulsed plasma processes, with an RF generator (2) comprising at least one amplifier circuit (30), an impedance matching circuit (3) and a control device (1), wherein the plasma process supply system (100) is connectable to a plasma chamber (4) and wherein the method comprises the following method steps: - connecting (Si) the RF generator (2) to the impedance matching circuit (3); - defining (S2) a target impedance (10) as the input impedance for the RF generator (2), so that a trajectory (40) describing an impedance curve for the input impedance in a settling period (41) runs from a starting impedance range (42) via an ignition impedance range (43) to a target impedance range (44), wherein the RF generator (2) delivers a power in the ignition impedance range (43) that is higher than a target power in the subsequent target impedance range (44); - Setting (S3) the target impedance (10) as input impedance for the RF generator (2) by the impedance matching circuit (3).

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