Method for supplying power to a laser or plasma and plasma or laser system

Abstract

A method for supplying a laser or a processing plasma in a discharge chamber (30) with electrical power comprises: a. providing power from an output terminal (24) of a balanced amplifier (12) to the discharge chamber (30), wherein the balanced amplifier (12) comprises at least two amplifier paths (14, 16), each of which delivers a signal to a coupler (22), wherein the coupler (22) has an output terminal (24) and an isolation terminal (26) and is configured such that it combines the signals depending on the phase relationship thereof and delivers power to the output terminal (24) and / or the isolation terminal (26), b. setting a first phase relationship of the signals for a predefined time in order to trigger the laser or ignite the plasma, c. setting a second phase relationship, different from the first phase relationship, in order to operate a laser or to maintain a plasma in the discharge chamber (30).

Description

[0001] Method for supplying a laser or plasma with power and plasma or laser system

[0002] The invention relates to a method for supplying electrical power to a laser or a processing plasma in a discharge chamber. Furthermore, the invention relates to a plasma or laser system comprising a discharge chamber and a balanced amplifier.

[0003] A processing plasma, i.e. a plasma for processing workpieces, for example for etching or coating workpieces in an industrial plasma system, particularly for the production of semiconductors, is often excited with high-frequency energy with frequencies greater than or equal to 2 MHz and high power, e.g. greater than or equal to 3 kW in a discharge chamber, also called a plasma chamber. To ignite the plasma, it is known to apply the full operating power with an increased voltage to the plasma system in order to achieve the fastest possible ignition of the plasma. In a similar way, such high-frequency energy is used to supply a laser in a discharge chamber. Such lasers are used, for example, for cutting and welding metal, glass, semiconductors and also for generating EUV light sources for lithography in semiconductor production.

[0004] To generate high-frequency energy, amplifiers or inverters are used. These are operated with transistors to amplify a high-frequency signal. Amplifiers here are understood to be amplifiers that operate predominantly in the linear range and partially in compression, typically those in operating mode A, AB, B, or C. Inverters here are understood to be inverters that operate predominantly in switching mode, typically those in operating mode D, E, F, inverse F (also abbreviated to F). -1) or similar. Since amplifiers or inverters are often used to generate high-frequency energy, which operate like an amplifier in the low power range and like an inverter in the high power range, the term "amplifier" is used below for both types, inverter and amplifier. Since the required power is often higher than the power that can be generated with a transistor, a pair of transistors, or even four transistors connected together to form a full bridge, several amplifiers are often connected together via a coupler, which couples the power of the individual amplifiers together. This is often done using power combiners with special properties, so-called 3dB couplers, also called 90° couplers, quadrature couplers or hybrid couplers.

[0005] Such arrangements are characterized by the fact that the amplifiers whose power is coupled together operate with a phase shift of 90° during normal operation. The coupler is therefore designed such that it couples power to the output precisely when the power signals at the coupling inputs are 90° out of phase. Amplifiers coupled in this way are usually referred to as 'balanced amplifiers'. If the power signals at the input of such a coupler are not 90° out of phase, a significant proportion of the power applied to the inputs of the coupler, depending on the phase position, is passed to a balancing resistor connected via a fourth terminal, also called a load balancing resistor, terminating resistor, balancing load or power dissipation device, where this leads to losses and heat generation.

[0006] A problem with such balanced amplifiers often arises when attempting to ignite the gas discharge. In a balanced amplifier, the output power is flat, essentially constant, across the complex load plane. Peaking power for ignition is difficult to generate. Until now, pseudo-peaking could only be achieved by selecting a higher DC supply voltage. However, generating a higher DC supply voltage for the power peak is very complex.

[0007] DE202017103327U describes an ignition method in which a higher power output is achieved for ignition by setting the 90° condition of the quadrature coupler only for ignition. The amplifier, actually configured as a "balanced amplifier," is only truly operated as a "balanced amplifier" with a 90° phase shift in ignition mode and is operated with a different phase position in normal operation. In this operating mode, this results in only a portion of the power applied to the inputs being coupled to the output, while the remaining portion is coupled via the isolation connection of the balanced amplifier into the balancing resistor, where it is converted into heat. This has proven to be a very lossy method. In particular, deliberately controlled energy loss during normal operation, i.e., during working mode, has a very negative impact on efficiency. This is not an acceptable method, especially for higher power levels.

[0008] The object of the present invention is to provide a method and a device with which a reliable ignition of a laser or plasma can be achieved when using a balanced amplifier and at the same time the efficiency can be kept high during normal operation.

[0009] This object is achieved according to the invention by a method for supplying a laser or a processing plasma in a discharge chamber with electrical power, the method comprising: a. providing power from an output terminal of a balanced amplifier to the discharge chamber, the balanced amplifier comprising at least two amplifier paths, each supplying a signal to a coupler, the coupler having an output terminal and an isolation terminal and being configured to combine the signals depending on their phase relationship and supply power to the output terminal and / or the isolation terminal depending on the phase relationship of the signals, b. setting a first phase relationship of the signals for a predetermined time in order to ignite the laser or the plasma, c.Setting a second phase relationship different from the first phase relationship in order to operate a laser or to maintain a plasma in the discharge chamber i. wherein the second phase relationship is set such that the coupler supplies substantially all of the power to the output terminal and supplies substantially no power to the isolation terminal, or ii. the first phase relationship is set such that the power reflected from the discharge chamber to the balanced amplifier is reflected back from the balanced amplifier to the discharge chamber to a proportion sufficient for ignition.

[0010] By 'essentially' we mean here that, within the tolerances of the coupler and the phase setting, everything reasonable is done to achieve these values. In this case, 5 - 10% of the power can certainly be fed to the isolation terminal if a better setting cannot reasonably be achieved within the amplifier. According to the invention, two different phase relationships can be set between the signals fed to the coupler. A first setting serves to ignite the plasma or laser, and the second setting serves to maintain the laser or plasma. The first setting can advantageously be shorter in time than the second. A phase relationship is the phase position or phase difference between the phases of two signals.Changing a phase relationship can, for example, be achieved by altering the phase of one or more signals, so that the phase relationship between two signals is different than before. In particular, the amplifier can be operated as or like an unbalanced amplifier by using the first adjustment described above in combination with the mismatch during laser or plasma ignition.

[0011] In the event of a mismatch in the second setting, i.e. with a balanced amplifier operated with a 90° phase shift, the power reflected from the discharge chamber is fed back into the amplifiers via the coupler's output connection. The majority of this is reflected back. Due to the reversed phase position, however, this reflected power is not fed back to the output connection and thus to the discharge chamber, but via the isolation connection to the compensating resistor connected there. This prevents power peaks on the line and at the plasma. This is very desirable for normal operation and is why balanced amplifiers operated in discharge chambers, with their typically very high tendency for rapid, unpredictable changes in impedance and thus with relatively high proportions of reflected power, especially in pulsed operation, are very popular with operators of processing plasma or lasers.

[0012] However, if the phase offset is adjusted in the event of a mismatch, e.g. to 45°, the power reflected back from the amplifiers and the power generated by the amplifiers can add up and, for certain mismatches, power peaks can occur. This is initially undesirable as it can lead to instabilities in discharge operation. However, these power peaks can be advantageously used for ignition. It is therefore advantageous for this process if the unignited state is detected or anticipated. The phase is then adjusted accordingly for the detected or anticipated duration of this state so that the discharge is ignited. This is because for this period of time, a proportion of the power reflected from the discharge chamber to the balanced amplifier can be reflected back from the balanced amplifier to the discharge chamber that is sufficiently large for ignition.As a disadvantage, some of the generated power is conducted via the insulation terminal to the compensating resistor connected here and converted into heat. However, this setting and thus this state can be kept very short, so that the energy loss can be kept low. In a subsequent, much longer-lasting state, the phase can then be set to normal operation, namely 90°, in which the coupler supplies essentially the entire power to the output terminal and thus to the discharge chamber, and essentially no power to the insulation terminal. Power is then only supplied to the output terminal during the first state for ignition, which is much more economical than the solution proposed, for example, in DE 20 2017 103327 U.

[0013] This method is particularly advantageous in pulsed operation with pulse frequencies from 10 kHz to 500 kHz. Since the plasma in the discharge chamber often completely extinguishes during pulse pauses, the discharge must be reignited with each new pulse. This can be advantageously achieved using the method described above.

[0014] The signals may have frequencies in the range from 1 MHz to 4,000 MHz, in particular from 1 MHz to 200 MHz. Furthermore, they may have power levels in the range greater than or equal to 1 kW, in particular from 1 kW to 3,000 kW, preferably from 1 to 3 kW.

[0015] The first phase relationship can be selected such that a mismatch occurs between the balanced amplifier and the plasma or laser or discharge chamber. In this case, the power reflected from the discharge chamber is also reflected by the switching or amplifying element(s), particularly transistor(s), of the amplifier and is largely dissipated by a resistor connected to the isolation terminal. In this case, by adjusting the first phase relationship, a superposition of the reflected power and the power generated by the amplifier can be created. This makes it possible to generate power that is greater than that normally generated at a 50 ohm load. This power can be used to ignite the plasma or laser.

[0016] The second phase relationship can be selected so that more than 50% of the combined power, especially more than 80% of the combined power, goes to the output terminal. This corresponds to normal operation, where the phase relationship of the signals is adjusted to deliver as much power as possible to the output terminal.

[0017] The specified time can be set in the range 0.1–10,000 ps, ​​preferably in the range 1–1,000 ps. The first phase relationship can therefore only be set for a relatively short period of time. This is sufficient to ignite the plasma or laser.

[0018] As previously mentioned, the power peaks achievable with the method can occur particularly at very specific reflection factors. Reflection factors are generally complex and have a real and imaginary component. They can be represented, for example, in a Smith chart. A reflection factor is transformed along the length of a line. This is shown graphically, for example, in the displacement in the Smith chart. Thus, the length of the line between the balanced amplifier and the discharge chamber or an impedance matching device, which can be located upstream of the discharge chamber, can be used to positively influence firing at certain phase angles between the amplifier paths and certain reflections in the unfired state.The length of the line between the balanced amplifier and the discharge chamber or an impedance matching device, which may be located upstream of the discharge chamber, can be adjusted so that the reflection factor of the unignited plasma or laser discharge is transformed so that the reflection factor seen by the balanced amplifier comes close to a power peak, in particular coincides with it.

[0019] A 3dB coupler, particularly a 90° hybrid coupler, can be used as a coupler. A 3dB coupler can combine two input signals that are 90° out of phase, so that the combined power is output at the output terminal and no power is output at the isolation terminal. The amplifier paths generating the signals can be decoupled and do not influence each other. A 3dB coupler itself can ideally be lossless. This means that the power of both amplifier paths can be fully supplied to the load (plasma or laser) connected to the output terminal.

[0020] To maintain the plasma or laser, a phase angle of 90° between the signals can be set. This allows maximum power to be delivered to the plasma or laser, especially in conjunction with a 3 dB coupler.

[0021] To ignite the plasma or laser, a phase angle other than 90° can be set between the signals, preferably a phase angle in the range of 5° to 85° or 95° to 175°, preferably in the range of 40° to 50° or in the range of 130° to 140°, most preferably 45° or 135°. A power peak can be generated particularly at phases of 45° and 135°. These power peaks occur, for example, at a reflection factor greater than 0.8 and at a reflection factor phase of -90° and 90°.

[0022] Also within the scope of the invention is a plasma or laser system comprising: a. a discharge chamber, b. a balanced amplifier connected to the discharge chamber, which comprises a coupler and at least two amplifier paths, each supplying a signal to the coupler, wherein the coupler has an output terminal and an isolation terminal and is configured to combine the signals depending on their phase relationship and supply power to the output terminal and / or the isolation terminal, c. a controller which is configured to control the amplifier paths to set a first phase relationship of the signals for igniting the plasma or the laser in the discharge chamber and to set a second phase relationship of the signals for maintaining the plasma or the laser.

[0023] With such a system it is possible to ignite a plasma or a laser, even when using a balanced amplifier.

[0024] An impedance matching device can be arranged between the discharge chamber and the balanced amplifier, wherein the impedance matching device is connected to the output terminal via a line having a length such that the load angle in the unignited state is close to, and in particular coincides with, the voltage peaks. This measure can support the rapid ignition of the laser or plasma.

[0025] The coupler can be designed as a 3dB coupler, particularly a 90° hybrid coupler. Such a coupler is also known as a quadrature coupler. Such a coupler can operate with particularly low losses and combine multiple input signals into an output signal with a higher power than any individual input signal.

[0026] At least one amplifier path can have a phase adjustment device, in particular a DDS (Direct Digital Synthesis) component or an FPGA with a digital-to-analog converter (DAC) for adjusting the phase of the signal output by the amplifier path. This allows a phase relationship between the signals to be adjusted in a particularly simple manner.

[0027] The amplifier paths can also receive their signals to be amplified via a splitter that sets the phase angle to 90°. This can be, for example, a 90° 3 dB splitter. In this case, a phase adjustment device can also be provided in at least one amplifier path for phase adjustment.

[0028] The amplifiers can deliver signals at frequencies from 2 MHz to 60 MHz, especially from 10 MHz to 16 MHz. This firing behavior can be tuned particularly well within this range.

[0029] The amplifier paths can in particular each comprise a class D, a push-pull, and / or a class F or an inverse class F (F -1 -) inverters. Such an inverter can, in particular, comprise LDMOS transistors as switching and / or amplifying transistors. Inverters of this class(es) and / or with such transistors have proven particularly suitable for such ignition operation and, at the same time, operate very stably and economically during normal operation.

[0030] Further features and advantages of the invention will become apparent from the following detailed description of exemplary embodiments of the invention, with reference to the figures of the drawing, which illustrate details essential to the invention, and from the claims. The various features can be implemented individually or in combinations in variants of the invention.

[0031] Embodiments of the invention are shown in the schematic drawing and explained in the following description.

[0032] They show:

[0033] Fig. 1 is a schematic representation of a plasma system or a laser system;

[0034] Fig. 2 shows the output characteristics of a balanced amplifier across the load level in normal operation;

[0035] Fig. 3 shows the output characteristics of the output power of an amplifier when a first phase relationship is set.

[0036] Figure 1 shows a plasma or laser system 10. The plasma or laser system 10 comprises a balanced amplifier 12, which has a first amplifier path 14 and a second amplifier path 16. The output signals of the first and second amplifier paths 14, 16 are applied to the input terminals 18, 20 of a coupler 22. The first and second amplifier paths 14, 16 are thus connected to the input terminals 18, 20 of the coupler 22. The coupler 22 has an output terminal 24 and an isolation terminal 26, to which a resistor 27 is connected. The resistor 27 is also referred to as a balancing resistor. A discharge chamber 30 is connected to the output terminal 24 via a line 28. The length of the line 28 can be adjusted. An impedance matching device 32 is arranged directly at the discharge chamber 30.In the illustrated embodiment, the discharge chamber 30 is connected to the balanced amplifier 12 via the line 28 and the impedance matching device. Such amplifier topologies with this type of coupler are described, for example, in the following publications: US7512387B2, US7452443B, US7745955B2, US10026593B2, DE 20 2017 103327 U, W02011 / 110652 A1, DE 10 2011 086557 B4.

[0037] In particular, in US10026593B2 and the corresponding DE10 2013 226537 A1, Fig. 9 shows the difference in measured output power versus the complex reflection coefficient for an unbalanced amplifier (non-phase-shifting coupler unit, upper graph) and for a balanced amplifier (with 90° hybrid coupler, lower graph). It is clearly visible in the lower graph that the maximum power is delivered at the 50° point in the middle of the graph, and that the power slowly decreases as the reflection coefficient increases. In contrast, the upper graph of the unbalanced amplifier shows that the maximum power is not delivered at the 50° point in the middle of the graph. In the case of a mismatch in the direction of cp = lln / 6, a significantly higher power is delivered. This results in a power peak.This is similar to what is achieved in this application with a balanced amplifier, i.e. with a 90° hybrid coupler but with a changed phase position between the amplifier paths.

[0038] Therefore, it is also mentioned here that the amplifier is operated as or like an unbalanced amplifier due to the described first setting in combination with the mismatch when igniting the laser or the plasma.

[0039] In particular, DE 10 2011 086557 B4 and WO2011 / 110652 A1 show how more than two amplifier paths can be interconnected to form particularly high-performance arrangements. It is not absolutely necessary for all couplers to be designed as 90° hybrid couplers, as shown in WO2011 / 110652 A1. An arrangement such as that shown in Fig. 4 or Fig. 5 of WO2011 / 110652 A1 has proven particularly advantageous.

[0040] The coupler 22 is configured to couple the signals arriving at the inputs 18, 20 to one another depending on their phase relationship and to supply them to the output terminal 24 and / or the isolation terminal 26. For normal operation, i.e., to maintain a plasma or a laser in the discharge chamber 30, a phase relationship is set between the signals arriving at the inputs 18, 20, which results in the signals being coupled by the coupler 22 such that maximum power is output at the output terminal 24 and, ideally, no power is output at the isolation terminal 26. This is typically 90°.

[0041] The amplifier paths 14, 16 can be controlled via a controller 34. In particular, the controller 34 can adjust the phase and / or amplitude of the signals output by the amplifier paths 14, 16. Thus, a phase relationship between the signals can be adjusted.

[0042] It is conceivable that additional amplifier paths 14, 16 are present, which are connected to the coupler 22. In the illustrated embodiment, the amplifier path 14 itself has additional amplifier paths 36, 38, whose output signals are combined by the coupler 40. The output signal of the coupler 40 corresponds to the output signal of the amplifier path 14.

[0043] Each of the amplifier paths 16, 36, 38 can in turn be constructed analogously to amplifier path 14. Only some amplifier paths can also be constructed like amplifier path 14. The amplifier paths 14, 16, 36, 38 can be controlled by the controller 34. In particular, the amplifier paths 14, 16, 36, 38 can have phase adjustment means, for example, a DDS component or an FPGA with a downstream DAC, by which the phase of the output signal of the respective amplifier path 14, 16, 36, 38 can be adjusted.

[0044] Figure 2 shows the load plane 50 in the form of a Smith chart. The real part of the reflection coefficient is plotted on the x-axis, and the imaginary part of the reflection coefficient is plotted on the y-axis. The output power is shown on the z-axis. Here, it can be seen that the output power at the output terminal 24 is almost constant. This results in a flat output power characteristic across the load plane 50. In particular, no power peaks can be seen. The output characteristic shown corresponds to the characteristic of a balanced amplifier in which a phase relationship between the input signals is set that leads to maximum power coupling at the output terminal 24. The figure shown was generated using a balanced amplifier that has a 3 dB coupler as the coupler and in which the input signals are phase-shifted by 90°. This corresponds to the setting of a second phase relationship for normal operation, i.e.to maintain a plasma or operate a laser.

[0045] Figure 3 shows the output power characteristic across load plane 50 when a first phase or amplitude relationship is set between the input signals that deviates from the setting during normal operation to maintain the plasma or laser. It can be seen that a substantially flat power distribution was not achieved, but rather that power peaks occur in region 52. In particular, a maximum power of more than 3200 W could be generated here, for example, with a reflection factor of approximately 0.8 and a reflection factor angle of approximately 110°. In the previous example, with a 50 ohm load, a power of approximately 2300 W was generated, and a maximum power of over 2400 W with a reflection factor of approximately 0.8 and a reflection factor angle of approximately 105°.

[0046] The power peaks in range 52 can be used to ignite the plasma or laser.

Claims

Claims: A method for supplying electrical power to a laser or a processing plasma in a discharge chamber (30), the method comprising: a. providing power from an output terminal (24) of a balanced amplifier (12) to the discharge chamber (30), the balanced amplifier (12) comprising at least two amplifier paths (14, 16) each supplying a signal to a coupler (22), the coupler (22) having an output terminal (24) and an isolation terminal (26) and being configured to combine the signals depending on their phase relationship and supply power to the output terminal (24) and / or the isolation terminal (26) depending on the phase relationship of the signals, b. setting a first phase relationship of the signals for a predetermined time to trigger the laser or plasma, c.Setting a second phase relationship different from the first phase relationship to operate a laser or to maintain a plasma in the discharge chamber (30), wherein i. the second phase relationship is set such that the coupler (22) delivers substantially all of the power to the output terminal (24) and delivers substantially no power to the isolation terminal (26), or ii. the first phase relationship is set such that a proportion of the power reflected from the discharge chamber (30) to the balanced amplifier (12) is reflected back from the balanced amplifier (12) to the discharge chamber (30) sufficiently to ignite the laser. A method according to claim 1, characterized in that the first phase relationship is selected such that there is a mismatch between the balanced amplifier (22) and the discharge chamber (30). A method according to any of the preceding claims, characterized in that the second phase relationship is selected such that more than 50% of the combined power, in particular more than 80% of the combined power, is delivered to the output terminal (24). A method according to any of the preceding claims, characterized in that the predetermined time is in the range of 0.1–10,000 microseconds, preferably in the range of 1–1,000 microseconds. A method according to any of the preceding claims, characterized in that a 3 dB coupler, in particular a 90° hybrid coupler, is used as the coupler (22). A method according to any of the preceding claims, characterized in that a phase angle of 90° between the signals is set to maintain the plasma.A method according to one of the preceding claims, characterized in that a phase angle other than 90° between the signals is set to ignite the plasma, preferably a phase angle in the range of 5°-85° or 95°-175°, preferably in the range of 40°-50° or in the range of 130°-140°, most preferably of 45° or 135°. Plasma or laser system (10) comprising a. a discharge chamber (30). b. a balanced amplifier (12) connected to the discharge chamber (30), comprising a coupler (22) and at least two amplifier paths (14, 16), each supplying a signal to the coupler (22), the coupler (22) having an output terminal (24) and an isolation terminal (26) and being configured to combine the signals depending on their phase relationship and supply power to the output terminal (24) and / or the isolation terminal (26), c. a controller (34) configured to drive the amplifier paths (14, 16) to set a first phase relationship of the signals for igniting the plasma or laser in the discharge chamber (30) and to set a second phase relationship of the signals for maintaining the plasma or laser. Plasma system according to claim 8, characterized in that the coupler (22) is configured as a 3dB coupler, in particular a 90° hybrid coupler.Plasma system according to one of the preceding claims 8 or 9, characterized in that at least one amplifier path (14, 16) has a phase adjustment means, in particular a DDS chip or FPGA with downstream DAC, for phase adjustment of the phase of the signal output by the amplifier path (14, 16).