Plasma process supply systems, particularly for pulsed plasma processes, and methods for operating such plasma process supply systems.

Abstract

The present invention relates in particular to a plasma process supply system (100) for a pulsed plasma process, the plasma process supply system (100) comprising an RF generator (2) having 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), which is designed to set a target impedance (10) as the input impedance of the RF generator (2). The control device (1) is designed to set the target impedance (10) such that the trajectory (40) of the impedance curve of the input impedance during the settling period (41) extends from the starting impedance region (42) through the ignition impedance region (43) to the target impedance region (44), and the RF generator (2) delivers a power level higher in the ignition impedance region (43) than the target power level in the subsequent target impedance region (44).

Description

Technical Field

[0001] The present invention relates in particular to a plasma process supply system for a pulse plasma process, and a method for operating such a plasma process supply system.

[0002] The surface treatment of a workpiece using a plasma laser and a gas laser is specifically an industrial method in which plasma is generated using either a DC signal or an AC signal in the range of several tens of kHz to GHz in a plasma chamber.

[0003] The plasma chamber is connected to a high-frequency generator (RF (HF) generator) via additional electronic components such as a coil, a capacitor, a cable, or a transformer. These additional components can be an oscillation circuit, a filter, or an impedance matching circuit.

[0004] The plasma process is a load that is very likely to vary for a high-frequency generator depending on the conditions inside the plasma chamber. Specifically, the characteristics of the workpiece, the electrodes, and the gas conditions are taken into account.

[0005] The high-frequency generator has a limited operating region with respect to the impedance of the connected electrical load (= consumer part). If the load impedance deviates from the allowable region, the required energy / power level cannot be delivered to the consumer part. Damage to the RF generator can also occur.

[0006] Therefore, an impedance matching circuit (match box) is usually required to convert the impedance of the load to the nominal impedance of the generator output.

[0007] Various impedance matching circuits are known. An impedance matching circuit can be fixed and have a predetermined conversion effect; that is, an impedance matching circuit consists of electrical components that do not change during operation, specifically coils and capacitors. This is particularly useful for always consistent operation, such as with gas lasers. Furthermore, impedance matching circuits are known in which at least some of the components of the impedance matching circuit are mechanically variable. For example, a motor-driven rotary capacitor is known, whose capacitance can be changed by changing the arrangement of the capacitor plates relative to each other.

[0008] Plasma can be assigned to three impedance regions in a general sense. A very high impedance exists before ignition. A lower impedance exists during normal operation, i.e., during the intended operation using the plasma. Very low impedance can occur in the case of undesirable local discharges (arcs) or plasma fluctuations. In addition to these three identified impedance regions, other special conditions with other associated impedance values ​​may arise. If the load impedance changes suddenly and the load impedance or converted load impedance falls outside the acceptable impedance region, the RF generator or the transmission equipment between the RF generator and the plasma chamber may be damaged. Undesirable plasma stabilization states may also exist.

[0009] The impedance matching circuit is described, for example, in the document DE10 2009 001 355 A1.

[0010] Depending on the plasma process, the plasma can be operated with a pulsed or continuous RF signal, also known as a CW signal. Due to the high variability that can occur in plasma processes, reproducible plasma ignition is a critical issue for the safe operation of the plasma process. Reproducible ignition is less problematic with RF generators that provide a CW signal, because the impedance matching circuit can be configured first to ensure ideal ignition conditions (matching to the "cold" impedance). After ignition, the impedance matching circuit is adjusted so that matching occurs as quickly as possible. With a CW signal, there is ample time for this. However, reliable ignition is more problematic with RF generators that produce pulsed high-frequency signals. In pulsed operation, the impedance matching circuit is adjusted to the "burning position," which may not be optimal for ignition.

[0011] Therefore, an object of the present invention is to create a plasma process supply system that enables reliable ignition of the plasma at the start of each pulse, particularly in pulsed plasma processes.

[0012] The problem relates to a plasma process supply system achieved by claim 1, and to a method for operating such a plasma process supply system achieved by claim 19. Claims 2 to 18 explicitly state advantageous further developments of the plasma process supply system.

[0013] The plasma process supply system is particularly suitable for pulsed plasma processes. It features an RF (HF) generator with at least one amplifier circuit. Furthermore, the plasma process supply system includes an impedance matching circuit and a control device. The plasma process supply system can be connected to a plasma chamber. The RF generator is connected (galvanically) to the impedance matching circuit. The impedance matching circuit is designed to set the target impedance as the input impedance of the RF generator. Specifically, the target impedance is set at the 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 the trajectory of the impedance curve of the input impedance during the settling period extends from the starting impedance region through the ignition impedance region to the target impedance region, and the RF generator outputs a power level higher in the ignition impedance region than the target power level in the subsequent target impedance region. The target impedance is within the target impedance region. Amplifiers generally exhibit characteristic behavior with respect to the output power level depending on the load impedance. This behavior can also be described as the power contour of the RF amplifier. Selecting the correct target impedance has the significant advantage of exceeding the appropriate impedance at a speed that the controller cannot adjust within that time. This is especially true when using pulsed high-frequency signals where the controller needs to adjust each pulse individually. The target power level output from the RF generator can be the same across the entire impedance curve. In fact, a portion of the power level is always reflected in different impedance regions. Therefore, the trajectory is selected as expected in the ignition impedance region, where the reflected power level is lower than the target impedance region when the plasma is ignited.

[0014] Here, it is particularly advantageous that the trajectory, passing through various regions up to the target impedance region, is set by selecting the target impedance such that the RF generator passes through an ignition impedance region where a higher power level is delivered than in the later target impedance region. This higher power level (power peaking) ensures a short-term increase in the electric field strength within the plasma chamber, which more reliably ignites the plasma than conventional plasma process supply systems. Furthermore, it is particularly advantageous that the process cannot be regulated until the target impedance region of the trajectory curve is reached, which significantly simplifies operation. The fact that the RF generator does not immediately recognize the target impedance is due, among other things, to the fact that the impedance matching circuit has a high quality factor, and that the corresponding resonant circuit formed from, for example, capacitors and inductors, must first settle into a stable position. Passive components oscillate at least within the initial impedance region. Therefore, the impedance changes during the settling period described above. In addition to the impedance matching circuit, the consumption section also participates in the formation of the trajectory curve. The plasma impedance also changes during the settling period. Since there are various target impedances to achieve the desired target power level output from the RF generator, it is possible to select a target impedance through which the trajectory passes through the desired ignition impedance region, i.e., the region in which the power level output by the RF generator exceeds the target power level. In actual plasma processes, the elevated power level that may approach the ignition impedance region is often unnecessary, or the continuous use of this elevated power level is avoided for efficiency reasons.

[0015] In one embodiment, the settling period includes a time range from the start of the RF signal pulse until the impedance no longer changes, or until the change in impedance falls below a threshold. The impedance includes the impedance of impedance matching circuits (capacitors, coils) and plasma impedance.

[0016] In one embodiment, the amplifier circuit includes a balanced amplifier. The use of a balanced amplifier offers significant advantages in plasma applications because it delivers its maximum power level when it encounters an input impedance that matches the nominal impedance (e.g., 50 ohms). A balanced amplifier is also more robust and has a constant output resistance. If one problem arises when igniting the plasma, this problem can be solved by selecting a target impedance and thereby improving the trajectory curve. For this reason, the plasma process supply system allows the use of a balanced amplifier. The balanced amplifier is preferably sized such that its target power level is sufficient to operate the plasma process when the target impedance is present, and the increased power level in the matching region is used to ignite the plasma process.

[0017] A balanced amplifier preferably has two amplifier paths and preferably operates with a 90° phase shift. Such a balanced amplifier is described, for example, as a “power converter” in WO2015 / 091468A1. WO2015 / 091468A1 is incorporated in its entirety by reference.

[0018] A balanced amplifier preferably includes a 90° coupler for coupling the output signals of the amplifier path.

[0019] A balanced amplifier preferably features a hybrid coupler for coupling the output signals of the amplifier path.

[0020] A balanced amplifier preferably has a 3dB coupler for coupling the output signals of the amplifier path.

[0021] In one embodiment, the control device is designed to set a target impedance such that the RF generator delivers a preset target power level when a target impedance exists. As already described, there are various target impedances from which the RF generator delivers the same target power level output. The ability to specify the target power level is also advantageous.

[0022] In one embodiment, the control device includes a memory device. The memory device contains corresponding target impedances for different target power level outputs that can be delivered by the RF generator. For a given target power level, one target impedance or multiple target impedances can be defined. The data can be stored, for example, in the form of a lookup table.

[0023] In one embodiment, the control device is designed to set the target impedance to a value such that the trajectory passes through an ignition impedance region where the RF generator delivers a power level that is a quantity that can be presented above the target power level. Here again, it is advantageous that the size can be preset. The user can specify that the power level is, for example, 10% or 20% higher than the target power level in the ignition impedance region. Preferably, the ignition impedance region is closer to 50 ohms than the target impedance region in the Smith chart of the balanced amplifier.

[0024] In one embodiment, the plasma process supply system comprises an operating unit. A control unit is designed to receive user input from the operating unit. The user input is a target power level and / or a preset amount by which the power level exceeds the target power level in the ignition impedance region. It is particularly advantageous that the operator of the plasma process power supply only needs to specify the target power level and the increased power level in the ignition impedance region, thereby ensuring reliable ignition of the plasma process.

[0025] In one aspect, the control device is designed to set the target impedance to a value such that the locus passes through the ignition impedance region and the target impedance region, and the amplifier circuit, specifically the amplifier element of the amplifier circuit, has a power level loss below a threshold, thereby specifically minimizing the power level loss. By measuring the amplifier circuit, it is possible to determine a region where the efficiency exceeds the threshold or a region where the power level loss occurring in an individual amplifier element (e.g., a transistor) is below the threshold. Selecting the corresponding locus is particularly advantageous when using a balanced amplifier because the balanced amplifier does not operate by matching in the target impedance region, and thus the signal power level is reflected back from the impedance matching circuit to the RF amplifier.

[0026] In one aspect, the control device is designed to set the target impedance to a value such that the average value of the impedance curve corresponds to the nominal impedance of the RF generator, specifically 50 ohms. This improves the efficiency.

[0027] In one aspect, the control device is designed to measure the impedance curve of the locus and adjust the target impedance based on the measured impedance curve such that the locus exhibits an improved curve during a subsequent setting period. This has the advantage that the locus can be continuously adjusted to an optimal curve, particularly in pulsed plasma applications. When a repetition rate (pulse rate) of preferably 10 Hz or more and preferably less than 1 MHz is used, the desired locus is achieved very quickly.

[0028] In one aspect, this can improve the curve of the locus during a subsequent setting period with respect to the efficiency of the amplifier circuit, the achievable power level in the ignition impedance region, the average impedance during the setting period, and / or the achievable power level in the target impedance region.

[0029] In one aspect, the control device is designed to measure the trajectory during each setting period. This enables more precise adjustment of the target impedance and, at the same time, allows for checking whether the curve of the trajectory is improved in subsequent setting periods (e.g., the next pulse). At a high pulse repetition rate, it is not necessary to measure the trajectory during the setting period of each pulse. In this case, it is possible to measure the trajectory during the setting period of at least every nth pulse (where n = 2, 5, 10, 50, 100, 500, 1000, 5000, 10,000).

[0030] In one aspect, the RF generator is designed to pulse a high-frequency signal and output this pulsed high-frequency signal to an impedance matching circuit. The setting period extends over the duration of such a pulse. The pulse repetition rate can be in the range of about 10 Hz to 1 MHz. The pulse length can be in the range of 1 μs to 500 μs, particularly in the range of 100 μs to 500 μs, and most preferably 300 μs. The setting time can include any time range (e.g., 5% or more and 90% or less) of each pulse. Specifically, the setting time depends on the pulse length. When the pulse has a long pulse length, the setting time is shorter with respect to the pulse length compared to a pulse with a shorter length.

[0031] In one aspect, the control device is designed to measure the trajectory for each setting period, and thereby is designed to measure the trajectory for each pulse of the high-frequency signal. This allows for a particularly accurate adjustment of the target impedance. It is also conceivable that at least n pulses for which the trajectory is not measured follow after the measured trajectory of a pulse, where n > 2, 3, 5, 10, 15, 20, 50, 100, 500. When a high pulse rate, e.g., 1 MHz, is used, it is not necessary to measure the trajectory of each pulse.

[0032] In one embodiment, the control device comprises a measuring unit. The measuring unit comprises at least one directional coupler unit, or a current sensor and a voltage sensor, for measuring the power levels of forward and reverse high-frequency signals. The control device is designed to measure the impedance curve of the trajectory based on the measurement results of the directional coupler unit, or the current sensor and voltage sensor. In this way, the impedance curve of the trajectory can be measured very easily and very quickly.

[0033] In one embodiment, the voltage sensor of the measuring unit is a capacitive voltage divider, where the first capacitance is formed by a conductive ring or cylinder through which a cable carrying RF power levels can be routed. 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.

[0034] In one embodiment, the measurement unit is located between the RF generator and the impedance matching circuit. Preferably, the measurement unit is located closer to the impedance matching circuit than to the RF generator.

[0035] In one embodiment, the ignition impedance region is crossed by the trajectory faster than the trajectory remains within the target impedance region. The impedance (trajectory) recognized over time at the output of the RF generator crosses the ignition impedance region faster than it remains within the target impedance region. This enables a more reliable ignition and a more stable plasma process.

[0036] In one embodiment, the trajectory passes through the ignition impedance region for less than 30%, 20%, or 10% of the time spent in the target impedance region.

[0037] In one embodiment, a DC generator is provided that is designed to generate a DC signal, thereby supplying the DC signal to a plasma chamber in superposition with a high-frequency signal. The DC signal can be output by the DC generator in a constant or pulsed manner. An impedance matching circuit may have an additional input to which the DC generator is connected. A bias tee may also be connected between the impedance matching circuit and the plasma chamber, and the bias tee is designed to superimpose the high-frequency signal and the DC signal and transmit them to the plasma chamber.

[0038] In one embodiment, the impedance matching circuit comprises at least one adjustable reactance to vary the impedance conversion ratio between an input section to which an RF generator is connected and an output section to which a load, i.e., a plasma chamber, can be connected. The reactance is mechanically adjustable and / or electrically adjustable. This can be achieved, for example, by semiconductor switching elements such as transistors or PIN diodes. Additionally or alternatively, at least one varactor and / or at least one switchable inductor and / or capacitor may be used.

[0039] This method is used to operate a plasma process supply system. Specifically, this method can be used to operate a pulsed plasma process. The plasma process supply system comprises an RF generator with at least one amplifier circuit, an impedance matching circuit, and a control device. The plasma process supply system can be connected to a plasma chamber. In the first step of the process, the RF generator is connected to the impedance matching circuit. In the second step of the method, the target impedance is defined as the input impedance of the RF generator such that the trajectory of the impedance curve of the input impedance during the settling period extends from the starting impedance region through the ignition impedance region to the target impedance region. The RF generator outputs a power level in the ignition impedance region that is higher than the target power level in the subsequent target impedance region. In the third step of the method, the target impedance is set as the input impedance of the RF generator by the impedance matching circuit.

[0040] The present invention is depicted below purely as an example with reference to the drawings. [Brief explanation of the drawing]

[0041] [Figure 1] Figure 1 shows an exemplary embodiment of a plasma process supply system with a control device. [Figure 2] Figure 2 shows an exemplary embodiment of the amplifier circuit of an RF amplifier in a plasma process supply system. [Figure 3] Figures 3A, 3B, 3C, 3D, and 3E illustrate various examples of how the trajectory of the impedance curve of the input impedance during the settling period can extend. [Figure 4] Figures 4A and 4B show various curves of the output power level delivered by the RF generator. [Figure 5] Figures 5A and 5B show various exemplary embodiments of how impedance matching circuits can be constructed. [Figure 6] Figure 6 shows an exemplary embodiment of how the measuring unit can be configured to measure current and voltage. [Figure 7] Figure 7 shows an exemplary embodiment of how the measuring unit can be configured to measure current and voltage. [Figure 8] Figure 8 is a flowchart illustrating the operation of the control device.

[0042] Figure 1 shows a plasma process supply system 100 equipped with a control device 1. The plasma generation system 100 further comprises an RF generator 2, an impedance matching circuit 3, and at least one consumption unit 4 in the form of a plasma chamber. The RF (HF) generator 2 has a nominal power P Nenn The impedance matching circuit 3 is designed to supply a high-frequency signal having frequency f0, specifically in the form of a pulsed high-frequency signal, and to output it at output terminal 2a. The impedance matching circuit 3 includes an input terminal 3a, and the RF generator 2 is connected to the input terminal 3a via a first cable connection 5a. The impedance matching circuit 3 further includes an output terminal 3b. The output terminal 3b is connected to at least one consumption unit 4 via a second cable connection 5b. The first cable connection 5a and / or the second cable connection 5b may include, for example, one or more cables connected in series and / or in parallel. Preferably, coaxial cables are used.

[0043] The consumption unit 4, i.e., the plasma chamber, comprises at least one electrode 6 for generating 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, designed to monitor the plasma 7, is located inside the plasma chamber.

[0044] The control device 1 is preferably a processor and / or FPGA and / or microcontroller and / or ASIC. The control device 1 may also include a storage device 9.

[0045] The control device 1 is designed to control the RF generator 2, specifically by activating or deactivating it. Additionally or alternatively, the control device 1 is also designed to change the power level and / or frequency of the RF signal by correspondingly controlling the RF generator 2. Additionally or alternatively, the control device 1 is also designed to change the waveform of the high-frequency signal (type of high-frequency signal, modulation of the RF signal, pulse duration, pulse repetition rate) by correspondingly controlling the RF generator 2.

[0046] The control device 1 is also preferably designed to control the impedance matching circuit 3. Specifically, the control device 1 is designed to change the transformation ratio in the impedance matching circuit 3, or to specify a target impedance 10 that acts as the input impedance of the RF generator 2.

[0047] The control device 1 also includes a measuring unit 11. The measuring unit 11 is designed, in particular, to measure the impedance value at the input terminal 3a of the impedance matching circuit 3. The measuring unit 11 is preferably located between the RF generator 2 and the impedance matching circuit 3.

[0048] For this purpose, the measurement unit 11 includes a directional coupler unit. The measurement unit 11 can measure the power levels of the forward and reverse high-frequency signals on the first cable connection 5a via the directional coupler unit, from which the input impedance can be calculated. The measurement unit 11 may also optionally include a current sensor 16 and a voltage sensor 20. Designs with a current sensor 16 and a voltage sensor 20 are shown in Figures 6 and 7. The control device 1 is designed to calculate the impedance recognized by the RF generator 2 based on the measurement results of the directional coupler unit, or the current sensor 16 and voltage sensor 20.

[0049] The plasma generation system 100 also preferably comprises an operating unit 12. The operating unit 12 is preferably a screen, specifically a touch-sensitive screen. In addition to the screen, the operating unit 12 may also include input means such as a keyboard and / or mouse. The operating unit 12 may also be a web server that provides data and receives user input. The control unit 1 is designed to display the current settings of the RF generator 2 and / or impedance matching circuit 3 on the operating unit 12.

[0050] The control device 1 is preferably designed to receive, for example, a setpoint specification for the power level of a high-frequency signal, called the target power level. Furthermore, the frequency and / or waveform of the high-frequency signal and / or pulse rate and / or pulse duration of the high-frequency signal can be received by the operating unit 12. From this, corresponding control variables for the RF generator 2 and impedance matching circuit 3 can be generated and transferred thereto.

[0051] Figure 1 also shows the following: - An example of the curve of trajectory 40 in the Smith chart SD depicts the impedance curve of the input impedance 10 during the settling period 41, extending from the starting impedance region 42 through the ignition impedance region 43 to the target impedance region 44. This is depicted in detail below in Figure 3D. - The output power level P emitted by the RF generator 2 over time t during the settling period 41 L An example of the curve. This is shown in detail below with reference to Figure 4B.

[0052] Figure 2 shows an exemplary configuration of the amplifier circuit 30 of the RF amplifier 2. The amplifier circuit 30 includes a balanced amplifier. In principle, the amplifier circuit 30 can also include an unbalanced amplifier. The balanced amplifier specifically has a first 3dB coupler 31a and a second 3dB coupler 31b, which are designed as a hybrid coupler. The first input of the first 3dB coupler 31a is connected to a signal source 32. The signal source 32 is designed to generate a high-frequency signal (pulse signal). The second input of the first 3dB coupler 31a is connected to ground reference via a resistor 33. The first output of the first 3dB coupler 31a is specifically connected to a first amplifier 34a in the form of a transistor amplifier. The second output of the first 3dB coupler 31a is specifically connected to a second amplifier 34b in the form of a transistor amplifier. The first transistor amplifier 34a is connected to the first input of the second 3dB coupler 31b via its output. The output of the second transistor amplifier 34b is connected to the second input of the second 3dB coupler 31b. The first output of the second 3dB coupler 31b is connected to reference ground via resistor 35. In the case of intentionally induced mismatch, as described below, the mismatch depends on whether the power level reflected back to the RF amplifier 2 is converted into heat in resistor 35 or in the first transistor amplifier 34a and / or the second transistor amplifier 34b, depending on the target impedance 10. The purpose is to ensure that the power level reflected back is converted into heat in resistor 35, because this can be easily made to an appropriate magnitude. The second output of the second transistor amplifiers 34a and 34b can be output terminal 2a, which is connected to impedance matching circuit 3.

[0053] Figures 3A, 3B, 3C, 3D, and 3E illustrate various embodiments of how the trajectory 40 can extend in a Smith chart SD that plots the impedance curve of the input impedance 10 during a settling period 41. The trajectory 40 shows the impedance curve over time. Such a trajectory 40 is shown as a dashed line in the figures mentioned.

[0054] In Figure 3A, the trajectory 40 extends in the direction of a point on the Smith chart SD corresponding to a 50-ohm impedance during the settling period 41 (see Figures 4A and 4B). In this case, this impedance is the target impedance 10. In a balanced amplifier, the adjustment is made at this point, and the balanced amplifier delivers the maximum power level. The ignition behavior of the plasma 7 is the issue here. If maximum efficiency is not necessarily required here, it may be advantageous to select a target impedance 10 that is far from the nominal impedance. In this case, the mismatch is intentionally created. This is shown, for example, in Figures 3C and 3D.

[0055] Figure 3B illustrates that a balanced amplifier has different impedance regions that deliver the same power level. These regions have the same hatching in Figure 3B and extend in a nearly circular shape around the nominal impedance point. When a user specifies a target power level output, different target impedances 10 can be selected so that the RF amplifier 2 delivers the desired target power level output. Not all of these target impedances 10 are useful; for example, there are target impedances that allow the RF amplifier 2 to deliver the desired power level, but which allow individual transistor amplifiers 34a, 34b to receive different loads. The closer the hatched region is to the nominal impedance point, the higher the output power level that the RF amplifier 2 can provide.

[0056] Figure 3C shows the curve of the trajectory 40 in the direction of the target impedance 10. Due to the settling process in the impedance matching circuit 3 and the plasma chamber 4, the target impedance 10 is not reached immediately. Instead, the trajectory 40, i.e., the impedance curve over time, can be measured, and at its endpoint, the target impedance is reached. This means that the RF generator 2 does not immediately recognize the target impedance 10 at its output. In Figure 3C, the RF generator 2 provides the desired output power level (outermost circle) when it reaches the target impedance 10 at the endpoint of the trajectory 40. The problem is that until the target impedance 10 is reached, the RF generator 2 only recognizes impedances that do not provide the power level necessary to supply the high-frequency signal required for reliable ignition of the plasma 7.

[0057] According to the advanced configuration presented here, the control device 1 is designed to set the target impedance 10 such that the trajectory 40 extends from the starting impedance region 42 through the ignition impedance region 43 to the target impedance region 44, and the RF generator 2 delivers a power level higher than the target power level of the subsequent target impedance region 44 where the target impedance 10 is located to the ignition impedance region 43. This situation is illustrated in Figure 3D. In the target impedance region 44, the RF amplifier 2 outputs a high-frequency signal having approximately the same power level as the target impedance region 44 in Figure 3C. In Figure 3D, the trajectory 40 passes through the ignition impedance region 43, where there is an impedance that causes the RF amplifier 2 to output a power level higher than that of the subsequent target impedance region 44, resulting in more reliable ignition of the plasma 7. As described, the user can input a desired power level output from the RF amplifier 2 to the ignition impedance region 41.

[0058] A suitable target impedance 10 is selected according to a selected target power level that can be specified by the user and a desired power level in the ignition impedance region 43, which can also be specified by the user. The measurement unit 11 enables the control device 1 to continuously measure the impedance curve and adjust the target impedance 10 so that the trajectory 40 passes through the desired ignition impedance region 43. The storage device 9 can store the power level that the RF amplifier 2 can deliver when the target impedance 10 is reached, for each target impedance 10 that can be adjusted by the impedance matching circuit 2.

[0059] Figure 3E shows that there is a region 45 through which the trajectory 40 should not pass. This may be due to impedances that cause the transistor amplifiers 34a and 34b to be overloaded or unevenly and / or to be inefficient due to power levels that reflect back to the RF amplifier 2. Therefore, the task of the control device 1 is to ensure that the trajectory 40 does not pass through region 45, or passes through it only for a very short period within the settling period 41, by selecting a target impedance 10.

[0060] Figures 4A and 4B show the output power level P over time t, respectively. L This shows the curve.

[0061] Figure 4A shows the settling period 41 as seen in the trajectory 40 of Figure 3A. The target impedance in Figure 3A is the nominal impedance, in this case 50 ohms, and the amplifier circuit 30 is a balanced amplifier that delivers the maximum power level at the nominal impedance. Therefore, the power level output of the RF amplifier 2 in Figure 4A increases with increasing time within the settling period 41.

[0062] On the other hand, Figure 4B shows the settling period 41, for example, in the case of trajectory 40 in Figure 3D. Trajectory 40 extends from the starting impedance region 42 to the ignition impedance region 43, and then to the target impedance region 44. The power level output of RF amplifier 2 is higher in the ignition impedance region 43 than in the target impedance region 44. This results in more reliable ignition of the plasma 7. It is also clearly visible that the target impedance region 44 lasts the longest for the entire duration of the settling period 41. The ignition impedance region 43 lasts for a shorter period, preferably less than 30%, less than 20%, or less than 10% of the duration for which the target impedance region 44 persists.

[0063] 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. It can adjust the target impedance 10, preferably while the target power level (specified by the user) remains constant, in order to positively influence the curve of the trajectory 40, i.e., specifically to ensure that a sufficiently high power level is delivered by the RF generator 2 in the ignition impedance region 43.

[0064] To convert the plasma impedance to the input impedance of the RF generator 2, the impedance matching circuit 3 may comprise one or more (series-connected) conversion stages.

[0065] One such conversion stage is shown, for example, in Figures 5A and 5B. If the impedance matching circuit 3 includes multiple conversion stages, each conversion stage can be constructed according to the exemplary embodiments shown in Figures 5A and 5B. It will also be understood that the impedance matching circuit 3 can be designed differently from those shown in Figures 5A and 5B.

[0066] In Figure 5A, the input terminal 3a of the impedance matching circuit 3 is connected to a first coil 50 (first inductance) and a second coil 51 (second inductance). The first coil 50 and the second coil 51 are connected to a common node at their first terminals, thereby connecting to the input terminal 3a of the impedance matching circuit 3. The first coil 50 is connected to reference ground via a first capacitor 52 (first capacitance). The second coil 51 is connected to output terminal 3b via a second capacitor 53 (second capacitance). The first capacitor 52 and / or the second capacitor 53 are specifically adjustable components in the form of rotary capacitors, whose capacitance can be changed via a stepping motor. Alternatively, a solid switch can be used to add and remove capacitance as quickly as possible. Specifically, the plate spacing of the first capacitor 52 and the second capacitor 53 can be changed. The control device 1 is designed to control each stepping motor accordingly. The capacitances of the first capacitor 52 and the second capacitor 53 can be adjusted independently of each other. Preferably, the impedance matching circuit 3 does not include any additional components. Naturally, the positions of the first coil 50 and the first capacitor 52 can also be swapped. In this case, the first capacitor 52 is located at the input terminal 3a of the impedance matching circuit 3, and the first coil 50 is located at the reference ground. Additionally or alternatively, the positions of the second coil 51 and the second capacitor 53 can also be swapped. In this case, the second capacitor 53 is located at the input terminal 3a of the impedance matching circuit 3, and the second coil 51 is located at the output terminal 3b of the impedance matching circuit 3.

[0067] The input terminal 3a of the impedance matching circuit 3 is connected to the first capacitor 52 (first capacitance) in Figure 5B. 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 and 51 are connected. The first coil 50 is still connected to the reference ground. The second coil 51 is connected (in series) to the second capacitor 53 (second capacitance). The second capacitor 53 is connected to the output terminal 3b of the impedance matching circuit 3. The positions of the second coil 51 and the second capacitor 53 can also be reversed. In this case, the second capacitor 53 is connected to the common node and the second coil 51 is connected to the output terminal 3b of the impedance matching circuit 3. Preferably, the impedance matching circuit 3 does not include any additional components.

[0068] Figures 6 and 7 show exemplary embodiments of possible structures of the measurement unit 11. The measurement unit 11 is designed to measure voltage and current in a non-contact manner.

[0069] For this purpose, the measurement unit 11 includes a current sensor 16 and a voltage sensor 20.

[0070] It is preferable to measure the phase relationship between current and voltage so that the impedance can be calculated.

[0071] The current sensor 16 of the measuring unit 11 is specifically a coil 21 in the form of a Rogowski coil. The ends of the coil are preferably connected to each other via a shunt resistor 22. The voltage drop across the ends of the shunt resistor 22 can be digitized by the first A / D converter 23.

[0072] The voltage sensor 20 of the measurement unit 11 is preferably incorporated as a capacitive voltage divider. The first capacitor 24 is formed by a conductive ring 24. A conductive cylinder can also be used. The corresponding first cable connection 5a is guided through this conductive ring 24. The second capacitor 25 of the voltage sensor 20, which is constructed as a voltage divider, is connected to reference ground. The second A / D converter 26 is connected in parallel to the second capacitor 25 and is designed to detect and digitize the voltage drop across the second capacitor 25.

[0073] In principle, the measuring unit 11 can be placed on or incorporated into a (common) circuit board. The first capacitor 24 can be formed by coatings on a first side and a second side of the circuit board. In this case, the coatings on the first and second sides are electrically connected to each other by vias. The first cable connection 5a is guided through an opening in the circuit board. The second capacitor 25 can be formed by discrete components.

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

[0075] The shunt resistor 22 can also be placed on this circuit board. The same applies to the first A / D converter 23 and / or the second A / D converter 23.

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

[0077] In principle, the measurement unit 11 can also be placed 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 to measure current and voltage. Then, the input impedance can be calculated by considering the known transformation ratio of the impedance matching circuit 3.

[0078] Figure 8 illustrates the method used to operate the plasma process supply system 100. Specifically, this method can be used to operate a pulsed plasma process. The plasma process supply system 100 comprises an RF generator 2 having 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. In the joining method step S1, the RF generator 2 is connected to the impedance matching circuit 3. In the setting method step S2, the target impedance 10 is set as the input impedance of the RF generator 2 such that the trajectory 40 that draws the impedance curve of the input impedance during the settling period 41 extends from the starting impedance region 42 through the ignition impedance region 43 to the target impedance region 44. The RF generator 2 outputs a power level in the ignition impedance region 43 that is higher than the target power level in the subsequent target impedance region 44. In the setting method step S3, the impedance matching circuit 3 sets the target impedance 10 as the input impedance of the RF generator 2.

Claims

1. In particular, a plasma process supply system (100) for pulsed plasma processes, comprising an RF generator (2) with 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), - The RF generator (2) is connected to the impedance matching circuit (3), and the impedance matching circuit (3) is designed to set the target impedance (10) as the input impedance of the RF generator (2). - The control device (1) is designed to set the target impedance (10) such that the trajectory (40) that traces the impedance curve of the input impedance during the settling period (41) extends from the starting impedance region (42) through the ignition impedance region (43) to the target impedance region (44), and the RF generator (2) delivers a power level higher in the ignition impedance region (43) than the target power level in the subsequent target impedance region (44), wherein the plasma process supply system (100) is characterized in that

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

3. The plasma process supply system (100) according to claim 1 or 2, characterized in that the control device (1) is designed to set the target impedance (10) such that the RF generator (2) delivers a preset target power level when the target impedance (10) is present.

4. - The plasma process supply system (100) according to claim 3, characterized in that the control device (1) comprises a memory device (9) and the memory device (9) stores corresponding target impedances (10) for different target power level outputs that can be delivered by the RF generator (2), which must be set by the impedance matching circuit (3) for this purpose.

5. - The plasma process supply system (100) according to any one of claims 1 to 4, characterized in that the control device (1) is designed to set the target impedance (10) to a value such that the trajectory (40) passes through the ignition impedance region (43), and in the ignition impedance region (43), the RF generator (2) delivers a power level that exceeds the target power level by a preset amount.

6. - A feature is that an operating unit (12) is provided. - The control device (1) is designed to receive user input from the operating unit (12), and the user input is, a) The level of the target power level, and / or b) The plasma process supply system (100) according to claim 5, characterized by including the preset amount by which the power level in the ignition impedance region (43) exceeds the target power level.

7. - The control device (1) is designed to set the target impedance (10) to a value such that the trajectory (40) passes through the ignition impedance region (43) and the target impedance region (44), and the plasma process supply system (100) according to any one of claims 1 to 6 is characterized by the amplifier circuit (30), and in particular the amplifier elements (34a, 34b) of the amplifier circuit (30) having a power level loss below a threshold.

8. - The plasma process supply system (100) according to any one of claims 1 to 7, characterized in that the control device (1) is designed to set the target impedance (10) to a value such that the average value of the impedance curve over the settling period (41) corresponds to the nominal impedance of the RF generator (2), particularly 50 ohms.

9. A plasma process supply system (100) according to any one of claims 1 to 8, characterized in that the control device (1) is designed to measure the impedance curve of the trajectory (40) and adjust the target impedance (10) based on the measured impedance curve such that the trajectory (40) has an improved curve during the subsequent settling period (41).

10. - The curve of the trajectory (40) is, a) Efficiency of the amplifier circuit (30), b) Achievable power levels within the ignition impedance region (43), c) The average impedance during the settling period (41), and / or d) The plasma process supply system (100) according to claim 9, characterized by being in a subsequent settling period with respect to improving the achievable power level within the target impedance region (44).

11. A plasma process supply system (100) according to any one of claims 1 to 10, characterized by the fact that the control device (1) is designed to measure the trajectory (40) within each settling period (41) or within each nth settling period (41), wherein n = 2, 5, 10, 50, 100, 500, 1000, 5000, 10000.

12. - 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), - A plasma process supply system (100) according to any one of claims 1 to 11, characterized by the fact that the settling period (41) extends over a time length of such pulse or a portion thereof.

13. The plasma process supply system (100) according to claim 12, characterized in that the control device (1) is designed to measure the trajectory (40) for each settling period (41) and, consequently, for each pulse of the high-frequency signal.

14. - The control device (1) is characterized by comprising a measuring unit (11), - The measurement unit (11) is characterized by comprising a directional coupler unit for detecting the power levels of forward and reverse high-frequency signals, or a current sensor (16) and a voltage sensor (20), A plasma process supply system (100) according to any one of claims 1 to 13, characterized in that the control device (1) is designed to measure the impedance curve of the trajectory (40) based on the measurement results of the directional coupler unit, or the current sensor (16) and the voltage sensor (20).

15. - The plasma process supply system (100) according to any one of claims 1 to 14, characterized by the fact that the trajectory (40) crosses the ignition impedance region (43) faster in time than the trajectory remains in the target impedance region (44).

16. - The plasma process supply system (100) according to claim 15, characterized by the fact that the trajectory (40) passes through the ignition impedance region (43) for less than 50%, 40%, 30%, 20%, or 10% of the time the trajectory (40) remains in the target impedance region (44).

17. A plasma process supply system (100) according to any one of claims 1 to 16, characterized by the provision of a DC generator designed to generate a DC signal, the DC signal being supplied to the plasma chamber (4) in conjunction with a high-frequency signal.

18. - The impedance matching circuit (3) comprises at least one or more adjustable reactances (52, 53) to change the impedance conversion ratio between the input section (3a) to which the RF generator (2) is connected and the output section (3b) to which the plasma chamber (4) can be connected. A plasma process supply system (100) according to any one of claims 1 to 17, characterized in that the reactance (52, 53) is mechanically adjustable and / or electrically adjustable, and in particular is formed by at least one varactor and / or at least one switchable inductance and / or capacitance (52, 53) and / or at least one PIN diode.

19. A method for operating a plasma process supply system (100) for a pulsed plasma process, comprising an RF generator (2) having 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 the method is - Step (S) of connecting the RF generator (2) to the impedance matching circuit (3) １ ), - The step (S) of setting the target impedance (10) as the input impedance of the RF generator (2) such that the trajectory (40) that draws the impedance curve of the input impedance during the settling period (41) extends from the starting impedance region (42) through the ignition impedance region (43) to the target impedance region (44), and the RF generator (2) delivers a power level in the ignition impedance region (43) that is higher than the target power level in the subsequent target impedance region (44). ２ ), - The impedance matching circuit (3) sets the target impedance (10) as the input impedance of the RF generator (2) (S ３ Methods including ),

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