Power converter, power supply system and high frequency plasma system

Abstract

To improve stability and tolerance to reflected power of an amplifier.SOLUTION: A power converter (3) configured to generate a high-frequency power signal comprises at least one amplification stage (40) having a first amplifier path (42) and a second amplifier path (43) each having an amplifier (42a, 43a). The first amplifier path (42) outputs a first amplifier path output signal and the second amplifier path (43) outputs a second amplifier path output signal that, with respect to the first amplifier path output signal, has a phase shift greater than 0° and less than 180°. The first amplifier path (42) and second amplifier path (43) are connected to a phase-shifting coupler (47) that is configured to couple the first amplifier path output signal and the second amplifier path output signal to form the high-frequency power signal. At least one amplifier (42a, 43a) of the first amplifier path (42) and second amplifier path (43) comprises an SiC-MOSFET.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a power converter, a power supply system for generating high-frequency power that can be supplied to a plasma process, and a high-frequency (HF) plasma system.

[0002] Power supply systems, particularly those producing more than 1 kW of power at frequencies greater than 300 kHz, are used in plasma processes such as plasma dry etching processes, plasma coating equipment, or the like.

[0003] US Patent Application Publication No. 2017 / 0064802 discloses a power supply system for a reactive gas generator, and proposes that metal oxide semiconductor field effect transistors, bipolar junction transistors, insulated gate bipolar transistors or silicon carbide (SiC) transistors be used in the power generation system.

[0004] In a power supply system for a plasma process, abrupt changes in the required power can occur, for example, when an arc occurs in the plasma chamber and the supplied power must be adapted accordingly. On the other hand, the power required to ignite the plasma can be different from the power required to operate the plasma process. When the plasma conditions change, the load impedance changes accordingly. This also results in abrupt changes in the load. Often, the impedance cannot be adjusted quickly enough, causing power to be reflected by the load. Furthermore, when multiple power sources with different frequencies are connected to a plasma process, such as a plasma dry etching process, the power reflected back to the power source can exhibit a wide variety of frequencies. Therefore, power with a wide variety of frequencies can be coupled back into the power source, and this power must be handled.

[0005] One object of the present invention is, inter alia, to improve stability and immunity to reflected power.

[0006] A power converter capable of generating a high frequency power signal for a plasma process may include at least one amplifier stage having a first amplifier path and a second amplifier path, each having an amplifier. The first amplifier path may output a first amplifier path output signal, and the second amplifier path may output a second amplifier path output signal having a phase shift greater than 0° and less than 180° relative to the first amplifier path output signal. The first amplifier path and the second amplifier path may be connectable to a phase shift coupler configurable to combine the first amplifier path output signal and the second amplifier path output signal to form a high frequency power signal. At least one amplifier in the first amplifier path and the second amplifier path may include a SiC MOSFET.

[0007] A phase-shift coupler is understood to be a unit that combines two input signals into an output signal that is phase-shifted relative to at least one input signal. A phase-shift coupler may include a coupler and, optionally, a phase-shift network for each of one or more amplifier paths, and during normal operation, the input signals of the coupler may have a phase position relative to each other that is neither 0° nor 180°, and in particular greater than 0° and less than 180°. For example, the input signals may be phase-shifted by 90°. The phase-shift coupler may be a 90° hybrid coupler or a 3dB coupler.

[0008] 3 dB couplers are also referred to as "hybrid couplers", and their behavior in the field of plasma power sources is described in U.S. Pat. No. 7,151,422, U.S. Pat. No. 7,477,114, U.S. Patent Application Publication No. 2018 / 0123212, U.S. Patent Application Publication No. 2013 / 0038226, EP 2,202,776, and U.S. Pat. No. 8,133,347, and for example, within the meaning of this specification, a 3 dB coupler behaves as described in these documents.

[0009] A phase shift coupler, in particular a 90° hybrid coupler or a 3 dB coupler, may have an impedance at its input and output ports in the range of 10Ω to 100Ω, in particular 30Ω to 60Ω.

[0010] In one embodiment of the present invention, the SiC MOSFET may be a high-voltage SiC MOSFET. The high-voltage SiC MOSFET is a new generation SiC (Silicon Carbide) MOSFET having a maximum rated voltage between drain and source of 1,500 V or higher, preferably 600 V or higher. Typical applications of SiC MOSFETs at present are, for example, solar inverters, DC / DC converters, switch-mode power supplies, induction heating, or motor drives.

[0011] High-voltage SiC MOSFETs often have timing characteristics with rise or fall times longer than 70 ns, which may imply that their use in high-frequency applications may be difficult. One embodiment of the present invention proposes combining at least one amplifier with a high-voltage SiC MOSFET with a phase-shift coupler that suppresses multiple reflections from a load, e.g., a plasma, to the amplifier. In such an embodiment, the high-voltage SiC MOSFET exhibits advantageous characteristics and has been found to be stable.

[0012] In one embodiment, at least one amplifier in the first amplifier path and the second amplifier path of the power converter may be a switch mode amplifier.

[0013] The first amplifier path and the second amplifier path of the power converter are connected to a phase-shift coupler, also known as a coupler configured to provide reflected power. This reflected power is conducted from a load, e.g., a plasma load, through the coupler and back to the amplifier out of phase, i.e., phase-shifted. The load may change its impedance over time. A condition in which the load impedance is not the same as the source impedance is called an "impedance mismatch" or "mismatch." In the case of a load impedance mismatch, a portion of the transmitted power is reflected back to the source. If the source is a power supply having a phase-shift coupler, e.g., a 90° hybrid coupler, the reflected power returned from the load may be phase-shifted by the coupler and divided between its two input connectors. The reflected power may then be phase-shifted and returned to the amplifier connected to the input connector.

[0014] The coupler changes the phase of the reflected power, so the amplifier is faced with a phase change in the reflected power. Switch-mode amplifiers can be designed to close the switch when the voltage across the switch output is zero or close to zero. This is then referred to as soft switching.

[0015] In power-reflected situations, phase changes caused by phase-shift couplers can cause these switches to switch when the voltage across their outputs is not zero. This is called hard switching and can be detrimental to the switches and risk damage. This is particularly important in plasma power supply systems where impedance changes frequently, rapidly, and significantly. This damage to the switches can occur especially in fast-switching MOSFETs, which are typically used at frequencies above 300 kHz. It has been found that using SiC MOSFETs in at least one amplifier of a power converter, or possibly in each amplifier, can improve the reliability of the power converter under these hard-switching conditions described above, even though these SiC MOSFETs have not been recommended for plasma power supplies in the past. This is likely due to their critical timing behavior at frequencies above 300 kHz. This improved reliability can be attributed to using at least one SiC MOSFET in at least one amplifier of a power converter.

[0016] In one embodiment of the present invention, the switch mode amplifier may be a class D or class E amplifier.

[0017] In one embodiment, the amplifier is a Class F or Inverse Class F -1 ) mode.

[0018] D, E, F or F -1 The basic circuit and function of a switch-mode amplifier such as a class E amplifier are described, for example, in EP 1601098, particularly in Figures 1 and 2A-2F and corresponding paragraphs 0006-0014. The use of SiC MOSFETs in these types of amplifiers allows for increased DC link voltages, which translates into increased power per transistor. This potentially extends the use of, for example, class E amplifiers.

[0019] In one embodiment of the present invention, the power converter is connected to a load, for example, a plasma load, and is capable of outputting a high frequency power signal to the load via an output connector. In particular, plasma processes above 1 kW have rapidly changing impedances, and the power supply must be resistant to reflected power.

[0020] The power supply system can be configured to generate power at frequencies above 300 kHz and below 10 MHz, in particular above 1 MHz and in particular below 5 MHz, in which range the advantages mentioned above are particularly evident.

[0021] In one embodiment of the present invention, the phase-shift coupler may have a connector connected to ground via an absorbing resistor. The absorbing resistor is configured to absorb a large amount of power, which may be at least 10% of the output power. The absorbing resistor may have a value in the range of 10Ω to 100Ω, in particular 30Ω to 60Ω. A phase-shift coupler may also be understood as a unit having a first input impedance at a first input connector and a second impedance at a second input connector, configured so that the input impedances are equal when no reflected output is passed to the input connector via the coupler and different when a reflected output is passed to the input connector via the coupler.

[0022] With a phase-shift coupler included in the power converter, the two amplifier paths connected to the coupler may have different impedances in the case of mismatch. Furthermore, in the case of mismatch, the power may not be reflected back into the amplifier path, but may instead dissipate into an absorbing resistor.

[0023] An amplifier, and in particular each amplifier, may have an output impedance at its output that may differ from the input impedance of the coupler. In this case, when power is reflected from the load, a large portion of the power conducted by the amplifier is reflected back to the coupler, which then conducts the power to the absorbing resistor. This improves the stability and reliability of the system.

[0024] For example, when multiple power sources having different frequencies are connected to a plasma process, such as a dry etching process, reflected power having a wide variety of frequencies may be coupled back into the power sources and power converters.

[0025] In one embodiment of the present invention, the power converter comprises a first circuit configured to perform a wideband measurement of a signal at an output connector of the power converter, which wideband measurement allows the measurement of frequencies different from those supplied by the power converter, such as frequencies reflected back from a load connectable to the output connector of the power converter.

[0026] One embodiment of the power converter may include a voltage source configured to supply voltage to a first amplifier path and a second amplifier path. A second circuit may be configured to control the voltage source and may be connected to a first circuit configured to perform wideband measurements of the output signal. The first circuit may include, for example, an analog-to-digital converter having a high sampling rate and may be connected to a high-speed digital evaluation unit, such as a programmable logic device (PLD). The second circuit may receive an output from the first circuit, the output having information related to the frequency, voltage, and current of the signal at the output of the power supply. The second circuit may then adjust the voltage supply to the first amplifier path and the second amplifier path in response to the signal received from the first circuit.

[0027] The power converter may further include a third circuit configured to measure data related to the absorption resistor.

[0028] In one embodiment of the present invention, the power converter may include an adjustable voltage source configured to supply a voltage to the at least one amplifier and a fourth circuit that measures a signal output by the adjustable voltage source.

[0029] In other embodiments of the invention, additional signals and values ​​within the power supply can be measured in response to and / or influenced by the signal output by the first circuit, such as DC link voltage, DC link current, DC link power, absorption resistor voltage, or temperature. The measured values ​​can be the basis for a learning process in which other values ​​are influenced, the results are measured, and the influence on these values ​​is then adjusted. This procedure can then resemble closed-loop control of the system. This learning process can be implemented by a neural network.

[0030] In other embodiments of the invention, additional communication channels external to the power supply may be provided, for example, to communicate the status of the power supply to an overall system controller and / or to other power supplies that may be present in the system.

[0031] One aspect of the present invention features a power supply system connectable to an electrode of a plasma process and configured to supply radio frequency power to the electrode of the plasma process. The power supply system may include a power converter with at least one amplification stage having a first amplifier path and a second amplifier path, each including an amplifier. The first amplifier path may output a first amplifier path output signal, and the second amplifier path may output a second amplifier path output signal that may have a phase shift relative to the first amplifier path output signal that is greater than 0° and less than 180°, e.g., 90°. The first amplifier path and the second amplifier path may be connectable to a phase shift coupler that may be configured to combine the first amplifier path output signal and the second amplifier path output signal to form a radio frequency power signal. At least one amplifier in the first amplifier path and the second amplifier path may include a SiC MOSFET.

[0032] One aspect of the invention features a radio frequency plasma system that may have a plasma chamber in which at least one electrode may be disposed, and a power supply system connected to the electrode and configurable to supply radio frequency power to the electrode.

[0033] In order that the features and advantages of the present invention may be better appreciated, several embodiments will now be described, by way of example only, with reference to the accompanying schematic drawings, in which: [Brief explanation of the drawings]

[0034] [Figure 1] 1 is a schematic diagram of a plasma system having a power supply system and a load. [Figure 2] FIG. 1 is a schematic diagram of a power converter having an amplifier and a coupler. [Figure 3] FIG. 1 is a schematic diagram of a power converter with an additional measurement circuit.

[0035] 1 shows a plasma system 1 with a power supply system 2. The power supply system 1 itself has a power converter 3 that can be connected to a voltage supply network 4. The power generated at the output of the power converter 3 is passed via an impedance matching network 5 to a load 6, which may be, for example, a plasma chamber, in which a plasma is generated that can be used for plasma processing in the plasma chamber. In particular, a workpiece can be etched or a material layer can be deposited on a substrate. The load 6 can also be a gas laser pump.

[0036] 2 is a highly schematic depiction of a power supply system 2. The power supply system 2 has a power converter 3 that generates output power that can be supplied to a load 6, for example, a plasma process or laser excitation. An impedance matching network 5 can be disposed between the load 6 and the power converter 3.

[0037] An analog output signal is generated by a digital-to-analog converter (DAC) 31. The generated analog signal is supplied to an amplifier stage 40, particularly a splitter 41 therein. The splitter 41 can be configured as a hybrid coupler that splits the analog signal into two phase-shifted signals, particularly signals phase-shifted by 90°. One signal emitted by the splitter 41 can be supplied to a first amplifier path 42, and the other signal emitted by the splitter 41 can be supplied to a second amplifier path 43. The amplifier paths 42, 43 each include at least one amplifier 42a, 43a, which can be configured as a push-pull amplifier and thus each include two transistors, particularly two SiC MOSFET transistors. A voltage source 44 supplies the amplifier paths 42, 43, and thus the amplifiers 42a, 43a and the transistors included therein. At the output of each amplifier path 42, 43, an output network 45, 46 is provided, which matches the output impedance of the amplifiers 42a, 43a to the input impedance of the phase-shift coupler 47, while filtering out unwanted harmonics. In the phase-shift coupler 47, the output signals of the amplifier paths 42, 43 are combined in a phase-dependent manner to form an output signal which is passed through a selective impedance matching network 5 and ultimately to a load 6. The phase-shift coupler 47 is connected to ground via an absorbing resistor 51. The phase-shift coupler 47 is preferably a 90° hybrid coupler.

[0038] The output power at the output of coupler 47 can be detected by a first circuit 48, for example, a suitable wideband measurement circuit. Dashed line 49 indicates that the wideband measurement circuit is connected to a second circuit 50, for example, a voltage control system, which itself operates voltage source 44. In particular, first circuit 48 can detect the power supplied to load 6 and also the power reflected by load 6. This detection can include, in particular, the voltage, current, and frequency of the signal supplied to and reflected by load 6. From these values, a signal indicative of the reflection of load 6 can be generated and used to influence the supplied voltage and other factors, as will be explained in connection with FIG. 3 .

[0039] 3 is a highly schematic diagram of a power converter 3 including a first amplifier path 42 and a second amplifier path 43 and a voltage source 44 that supplies voltage to the first amplifier path 42 and the second amplifier path 43 and the amplifiers contained therein. Instead of a single voltage source 44, two voltage sources can be used to supply voltage to the first amplifier path 42 and the second amplifier path 43, respectively. A phase-shift coupler 47 combines the output signals of the amplifier paths 42 and 43 to form a high-frequency power signal for the power converter 3. The phase-shift coupler 47 is connected to ground via an absorption resistor 51. The absorption resistor 51 can absorb power reflected by the load 6. The power converter 3 further includes a first circuit 48, a second circuit 50, a third circuit 55, and a fourth circuit 52.

[0040] The first circuit 48 is configured to measure the voltage and current of the output signal of the phase shift coupler 47 over a wide frequency range. In particular, the wide frequency range measured may include both one or more frequencies of the power converter 3 itself as well as a wide frequency range outside the frequency range of the power converter 3 itself. The first circuit 48 may include an analog-to-digital converter (ADC) with a high sampling rate and a fast evaluation unit, for example a PLD.

[0041] The first circuit 48 outputs a signal related to the measurement to a second circuit 50. The second circuit 50 is configured to control the voltage source 44. The second circuit 50 can control the voltage supplied to the amplifier paths 42, 43 via the voltage source 44. The second circuit can also be connected to a system controller 60.

[0042] The third circuit 55 is configured to measure data related to the absorbing resistor 51. Examples of measured data are the voltage across the absorbing resistor 51 and / or its temperature.

[0043] The fourth circuit 52 is configured to measure the voltage output by the voltage source 44. This measurement enables the fourth circuit 52 to feed back the voltage output by the voltage source 44 to the system controller 60.

[0044] The system controller 60 can use different types of measurements, such as, for example, DC link voltage, DC link current, DC link power, absorber resistor voltage, and / or absorber resistor temperature. The learning process can be performed within the system controller 60, and the system controller 60 can communicate with other power supplies and / or the entire plasma system controller. The data provided to the system controller 60 can be used to implement, for example, closed-loop control of the power converter and / or the plasma system.

Claims

1. A power converter (3) configured to generate a high frequency power signal for a plasma process, said power converter (3) comprising: at least one amplifier stage (40) having a first amplifier path (42) and a second amplifier path (43) each including an amplifier (42a, 43a), the first amplifier path (42) outputting a first amplifier path output signal and the second amplifier path (43) outputting a second amplifier path output signal having a phase shift with respect to the first amplifier path output signal that is greater than 0° and less than 180°; a voltage source (44) configured to supply a voltage to the first amplifier path (42) and the second amplifier path (43); an output connector configured to output the high frequency power signal to a plasma load (6) connected to the output connector; a first circuit (48) configured to perform a wideband measurement of the high frequency power signal at the output connector; a second circuit (50) configured to control the voltage source (44) in response to a signal received from the first circuit (48), the second circuit (50) being connected to the first circuit (48); an absorption resistor (51) through which the phase shift coupler (47) is connected to ground; a third circuit (55) configured to measure data related to said absorption resistor (51); and the first amplifier path (42) and the second amplifier path (43) are connected to the phase shift coupler (47) configured to combine the first amplifier path output signal and the second amplifier path output signal to form the high frequency power signal; At least one amplifier (42a, 43a) of the first amplifier path (42) and the second amplifier path (43) comprises a SiC MOSFET; At least one of the amplifiers (42a, 43a) has an output impedance at the output of the at least one amplifier (42a, 43a) that is different from the input impedance of the phase shift coupler (47). Power converter (3).

2. 2. The power converter (3) of claim 1, wherein at least one of the amplifiers (42a, 43a) has an output impedance at the output of the at least one amplifier (42a, 43a) in the case of mismatch that is different from the input impedance of the phase shift coupler (47).

3. each of the at least one amplifier (42a, 43a) having an output impedance at the output of the respective amplifier (42a, 43a) that is different from the input impedance of the phase shift coupler (47); A power converter (3) according to claim 1 or 2.

4. Power converter (3) according to any one of claims 1 to 3, characterized in that the SiC MOSFET is a high voltage SiC MOSFET.

5. 5. The power converter (3) according to claim 1, wherein at least one of the amplifiers (42a, 43a) of the first amplifier path (42) and the second amplifier path (43) is a switch-mode amplifier.

6. Power converter (3) according to claim 5, characterized in that the switch mode amplifier is a class D or class E amplifier.

7. 7. The power converter (3) according to any one of claims 1 to 6, characterized in that the SiC MOSFET is used for amplifying high frequency power signals having frequencies higher than 300 kHz and lower than 10 MHz.

8. A power converter (3) according to claim 7, characterized in that the high frequency power signal has a frequency higher than 1 MHz and lower than 5 MHz.

9. 9. The power converter (3) according to any one of claims 1 to 8, wherein the data relating to the absorption resistor (51) is the voltage across the absorption resistor (51) and / or the temperature of the absorption resistor (51).

10. 10. The power converter (3) of claim 1, further comprising an adjustable voltage source configured to supply a voltage to at least one of the amplifiers, and a fourth circuit (52) for measuring a signal output by the adjustable voltage source.

11. 11. A power supply system (2) connected to an electrode of a plasma process and configured to supply high frequency power to the electrode of the plasma process, characterized in that the power supply system (2) comprises a power converter (3) according to any one of claims 1 to 10.

12. A high frequency plasma system (1), comprising:

12. A radio frequency plasma system (1) comprising: a plasma chamber in which at least one electrode is arranged; and a power supply system (2) according to claim 11, connected to the electrode and configured to supply radio frequency power to the electrode.

13. 13. The radio frequency plasma system (1) of claim 12, further comprising a plurality of power sources having different frequencies connected to the plasma process, and wherein reflected power having the plurality of different frequencies is coupled back to the power supply system (2) and the power converter (3).

Images