Plasma power supply device for improving harmonic distortion under light-load conditions, and control method

Abstract

The present invention relates to a plasma power supply device for improving harmonic distortion under light-load conditions, and a control method, the device comprising: a power supply unit for supplying single-phase or three-phase alternating current power; a boost converter for controlling an input voltage; a bridge circuit, which receives the voltage controlled by the boost converter in order to provide output power; and a control unit for controlling the operation of the bridge circuit to operate in a first mode or a second mode according to load power required in a load electrically connected to the bridge circuit, wherein the control unit fixes a duty ratio of the first mode at a first load power so as to control the output power, controls the duty ratio of the first mode at a second load power, which is lower than the first load power, so as to control the output power, and switches to the second mode at a third load power, which is lower than the second load power, so as to control the bridge circuit.

Description

Plasma power supply and control method for improving harmonic distortion under light load conditions

[0001] The present invention relates to a plasma power supply and control method for improving harmonic distortion under light load conditions, and more specifically, to a plasma power supply and control method for improving harmonic distortion under light load conditions that can stably generate plasma by improving waveform quality through a half-bridge switching method to address the problem of power quality degradation caused by waveform distortion during PWM duty control required in a full-bridge-based RF power circuit environment.

[0002] As the circuit linewidth of semiconductors becomes finer, the importance of cleaning processes to remove contaminants remaining after deposition, etching, and other processes is increasing. These cleaning processes include wet processes using chemical solutions and dry processes using plasma. Since the wet process requires rinsing and drying the object to be cleaned and contaminants may remain on the surface, causing secondary contamination, dry cleaning processes using plasma are gaining attention. Methods for generating plasma for dry cleaning processes can be divided into Capacitively Coupled Plasma (CCP), Inductively Coupled Plasma (ICP), and Transformer Coupled Plasma (TCP).

[0003] Among these, TCP, as illustrated in Fig. 1, is a method of generating plasma by confining a magnetic field inside a ferrite core; it has the advantage of securing a high-density plasma compared to the CCP method and causing less shock to the wafer due to the magnetic field compared to the ICP method. To generate the plasma required for the TCP dry cleaning method, an RF generator is needed to supply power. The RF generator consists of an AC-DC converter, a DC-AC inverter, a transformer, and an output filter network to supply stable power to the plasma chamber. Therefore, the design of the output filter network and the control of the AC-DC converter and DC-AC inverter are important for supplying stable and high-quality power to the plasma chamber.

[0004] If the current waveform of the RF generator is distorted, the gas dissociation rate is low, which reduces radical generation and directly decreases cleaning efficiency; therefore, to generate a stable and high-quality plasma, a sinusoidal current with as little distortion as possible must be supplied to the chamber. Since the equivalent impedance of the plasma chamber load is highly variable depending on the gas ignition state, input, and pressure, the RF generator must use an output filter network with low Total Harmonic Distortion (THD) and constant current characteristics to maintain a stable plasma even when the equivalent impedance changes.

[0005] Furthermore, many methods are being studied to provide high-quality plasma to the TCP cleaning process in terms of output power control. In conventional methods, output power is controlled by controlling the input voltage supplied to the DC-AC inverter using a PFC boost converter; however, the DC output voltage of the PFC boost converter cannot be controlled to be lower than its AC input voltage. Consequently, if the output power is reduced by the duty cycle control method of the full-bridge inverter, it leads to waveform distortion caused by a certain level of duty cycle reduction, making it difficult to generate stable, high-quality plasma. Therefore, power quality degradation may occur in processes requiring low-power conditions.

[0006] An example of technology related to an RF generator for plasma generation is disclosed in the following patent documents 1 to 3, etc.

[0007] For example, the active PFC utilizing a full-bridge boost converter and the converter system to which it is applied according to Patent Document 1 (Korean Published Patent Application No. 10-2020-0022203 (published on March 3, 2020)) is equipped with an active PFC having a full-bridge DC-DC converter switch that performs DC-DC conversion as a full bridge in response to the rectified power of the AC power supply. Thus, it is disclosed that the switching operation of the full-bridge DC-DC converter switch itself is controlled by a separate PFC control unit in response to the rectified power according to the full-bridge boost.

[0008] In addition, Patent Document 2 (U.S. Published Patent Application No. 2017-0205287 (published July 20, 2017)) discloses a high-frequency power supply device having a plasma input power detection unit that can accurately control the plasma input power regardless of the state of the plasma generating gas or the analysis sample by directly detecting the plasma input power.

[0009] While the technology disclosed in the aforementioned patent documents describes techniques for improving the power factor for each power source according to the power required by the user or controlling the input power by monitoring the plasma input power, it does not describe half-bridge switching technology for providing stable and distortion-free power for output power control even over a wide load range.

[0010] Furthermore, conventional technology that controls output power by controlling the input voltage to a full-bridge inverter cannot control the output voltage of the PFC boost converter to be lower than the input voltage; therefore, the output power is controlled by PWM duty control of the gates in the low voltage range. However, the PWM duty control method has a problem in which power quality deteriorates as THD (Total Harmonic Distortion) increases as the duty cycle decreases.

[0011] Therefore, the objective of the present invention is to solve the problems described above by providing a plasma power supply and a control method for improving harmonic distortion under light load conditions, wherein the output power is controlled by adjusting the output voltage in a full-bridge type, and the total harmonic distortion can be reduced even under light load conditions and the quality of the output power can be improved by switching from a full-bridge type to a half-bridge type at the point where THD deteriorates.

[0012] Another objective of the present invention is to provide a plasma power supply and a control method for improving harmonic distortion under light load conditions, which can obtain a desired sinusoidal waveform by blocking the DC bias that may occur in the half-bridge type when switching from a full-bridge type to a half-bridge type.

[0013] Another objective of the present invention is to provide a plasma power supply and a control method for improving harmonic distortion under light load conditions, which can provide stable output power even under light load conditions that cannot be controlled by a PFC boost converter through mode switching, and improve the quality of output power compared to conventional technology because the output power is not controlled through a duty cycle.

[0014] To achieve the above objective, a plasma power supply for improving harmonic distortion under light load conditions according to an embodiment of the present invention comprises: a power supply unit for supplying single-phase or three-phase AC power; a boost converter for controlling an input voltage that is rectified and input from the AC power; a bridge circuit for receiving the voltage controlled by the boost converter and providing output power; and a control unit for controlling the operation of the bridge circuit to operate in a first mode or a second mode according to the load power required by a load electrically connected to the bridge circuit, wherein the control unit controls the output power by fixing the duty ratio of the bridge circuit operating in the first mode at the first load power, controls the output power by controlling the duty ratio of the bridge circuit operating in the first mode at a second load power lower than the first load power, and controls the bridge circuit by switching it to operate in the second mode at a third load power lower than the second load power.

[0015] In addition, according to the plasma power supply for improving harmonic distortion under light load conditions according to an embodiment of the present invention, the control unit is characterized by fixing the duty ratio of the bridge circuit operating in the second mode to reduce THD.

[0016] In addition, according to the plasma power supply for improving harmonic distortion under light load conditions according to an embodiment of the present invention, the bridge circuit is characterized by being implemented using four MOSFETs.

[0017] In addition, according to the plasma power supply for improving harmonic distortion under light load conditions according to an embodiment of the present invention, the first mode is a mode in which the bridge circuit operates as a full bridge circuit, and the second mode is a mode in which the bridge circuit operates as a half bridge circuit.

[0018] In addition, according to the plasma power supply for improving harmonic distortion under light load conditions according to an embodiment of the present invention, the bridge circuit is characterized by having a DC blocking part electrically connected to block the DC bias generated when operating in the half-bridge mode.

[0019] In addition, according to the plasma power supply for improving harmonic distortion under light load conditions according to an embodiment of the present invention, a transformer is electrically connected to the DC blocking section, and an LCL filter is electrically connected to the secondary side of the transformer to remove harmonic components of the transformer's secondary voltage and convert it into a sinusoidal form.

[0020] In addition, according to an embodiment of the present invention, a plasma power supply for improving harmonic distortion under light load conditions is characterized in that a line filter unit for removing noise generated in the power supply unit and a rectifier unit for full-wave rectifying an AC power waveform that has passed through the line filter unit into DC are electrically connected between the power supply unit and the boost converter.

[0021] In addition, according to the plasma power supply for improving harmonic distortion under light load conditions according to an embodiment of the present invention, the boost converter is characterized as being a PFC boost converter.

[0022] A control method for a plasma power supply device for improving harmonic distortion under light load conditions according to an embodiment of the present invention for achieving the above objective comprises: i) a step of supplying a single-phase or three-phase AC power from a power supply unit; ii) a step of rectifying the AC power into a DC voltage; iii) a step of controlling the DC voltage using a boost converter; and iv) a step of receiving the voltage controlled by the boost converter and controlling the output power by a bridge circuit, wherein v) the step of controlling the output power is characterized by controlling the operation of the bridge circuit to operate in a first mode or a second mode according to the load power required by a load electrically connected to the bridge circuit, controlling the output power by fixing the duty ratio of the bridge circuit operating in the first mode at the first load power, controlling the output power by controlling the duty ratio of the bridge circuit operating in the first mode at a second load power lower than the first load power, and controlling the bridge circuit by switching it to operate in the second mode at a third load power lower than the second load power.

[0023] In addition, according to the control method of a plasma power supply for improving harmonic distortion under light load conditions according to an embodiment of the present invention, the first mode is a mode in which the bridge circuit operates as a full bridge circuit, and the second mode is a mode in which the bridge circuit operates as a half bridge circuit.

[0024] In addition, according to the control method of a plasma power supply for improving harmonic distortion under light load conditions according to an embodiment of the present invention, controlling the bridge circuit by switching to the second mode is characterized by fixing the duty ratio of the second mode to reduce THD.

[0025] In addition, according to the control method of a plasma power supply for improving harmonic distortion under light load conditions according to an embodiment of the present invention, when the bridge circuit is switched to the second mode in step v), it is characterized by further including a blocking step for blocking the DC bias that occurs when operating in the half-bridge mode.

[0026] In addition, according to the control method of a plasma power supply for improving harmonic distortion under light load conditions according to an embodiment of the present invention, step ii) is characterized by including: a step of removing noise generated in the power supply unit with a line filter unit; and a step of full-wave rectifying the AC power waveform that has passed through the line filter unit into DC.

[0027] As described above, according to the plasma power supply and control method for improving harmonic distortion under light load conditions according to an embodiment of the present invention, the output power is controlled by adjusting the output voltage in the full bridge type, and by switching from the full bridge type to the half bridge type at the point where THD deteriorates, the total harmonic distortion can be reduced even under light load conditions, thereby achieving the effect of improving the quality of the output power.

[0028] In addition, according to the plasma power supply and control method for improving harmonic distortion under light load conditions according to an embodiment of the present invention, when switching from a full bridge type to a half bridge type, the DC bias that may occur in the half bridge type is blocked, thereby obtaining a desired sinusoidal waveform.

[0029] In addition, according to the plasma power supply and control method for improving harmonic distortion under light load conditions according to an embodiment of the present invention, stable output power is provided even under light load conditions that cannot be controlled by a PFC boost converter through mode switching, and since the output power is not controlled through a duty cycle, the quality of the output power can be improved compared to the prior art.

[0030] In addition, according to the plasma power supply and control method for improving harmonic distortion under light load conditions according to an embodiment of the present invention, the effect of maintaining a constant current even when the chamber impedance value changes is also obtained by designing an LCL filter having stable current output characteristics over a wide load range.

[0031]

[0032] Figure 1 is a conceptual diagram of a TCP method according to the prior art.

[0033] FIGS. 2a to 2c are drawings illustrating the configuration of a plasma power supply device according to an embodiment of the present invention.

[0034] FIG. 3a is a diagram illustrating a control method for a plasma power supply device according to an embodiment of the present invention.

[0035] FIG. 3b is a diagram showing the operation of a bridge circuit in a first mode according to an embodiment of the present invention.

[0036] FIG. 3c is a diagram showing the operation of a bridge circuit in a second mode according to an embodiment of the present invention.

[0037] Figure 4 is a diagram showing the equivalent impedance characteristics of a plasma chamber applied in an experimental example of the present invention.

[0038] Figure 5 is a diagram showing the output current characteristics of an LCL filter applied in an experimental example of the present invention.

[0039] Figure 6 is a circuit diagram for simulating an LCL filter designed according to an experimental example of the present invention.

[0040] Figure 7 is a diagram showing the size and phase characteristics of an LCL filter according to an experimental example of the present invention.

[0041] Figure 8 is a diagram for PLECS simulation of a bridge circuit according to an experimental example of the present invention.

[0042] FIGS. 9a and 9b are drawings for showing the output voltage and current waveforms of the secondary side of a transformer of a power supply according to the prior art.

[0043] FIGS. 10a and FIGS. 10b are drawings for showing the output voltage and current waveforms of the transformer secondary side of a power supply device according to an experimental example of the present invention.

[0044] Figure 11 is a graph showing a comparison of the simulated results of THD values ​​according to load power.

[0045] Figure 12 is a photograph showing an experimental example of a PCB manufactured according to the present invention.

[0046] FIG. 13a is a graph showing output voltage and current waveforms according to the prior art.

[0047] FIG. 13b is a graph showing output voltage and current waveforms according to an experimental example of the present invention.

[0048] Figure 14 is a graph showing a comparison of the output voltage waveforms illustrated in Figures 13a and 13b.

[0049] Figure 15 is a graph showing the experimental results of comparing the THD values ​​according to load power.

[0050] The above and other objects and novel features of the present invention will become more apparent from the description in this specification and the accompanying drawings.

[0051] The size and thickness of each component shown in the description and drawings of the present invention are depicted arbitrarily for convenience of explanation, and therefore the present invention is not necessarily limited to what is illustrated. Additionally, thicknesses have been enlarged in the drawings to clearly represent various layers and regions, and the thickness of some layers and regions has been exaggerated for convenience of explanation.

[0052] Meanwhile, in the description of the invention, when it is stated that a certain part "includes" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0053] The terms “part,” “module,” or “part” as used herein perform at least one function or operation and may be implemented as hardware or software consisting of mechanical or electrical / electronic configurations, or as a combination of hardware and software; and a plurality of “parts,” “modules,” or a plurality of “parts” may be integrated into at least one module and implemented by at least one processor, except for the “parts,” “modules,” or “parts” that need to be implemented in specific hardware.

[0054]

[0055] Hereinafter, an embodiment according to the present invention will be described with reference to the drawings.

[0056] FIGS. 2a to 2c are drawings illustrating the configuration of a plasma power supply device according to an embodiment of the present invention.

[0057] Referring to FIGS. 2a to 2c, a plasma power supply (100) according to an embodiment of the present invention may be a device for supplying high-quality alternating current voltage of 1 kV or higher and a frequency of 400 kHz to a plasma chamber to generate plasma required in a dry cleaning process. The power supply (100) may be a Transformer Coupled Plasma (TCP) device coupled with a transformer, and may be implemented to accommodate various frequencies and various functions as the pattern of the semiconductor circuit is miniaturized and formed into a 3D structure.

[0058] The above power supply unit (100) is configured to include a power supply unit (200), a power conversion system (300), a plasma chamber (400), and a control unit (500). The power supply unit (200) provides a single-phase or three-phase AC voltage to the power conversion system (300) to supply stable power to the plasma chamber (400) to generate high-quality plasma. Since the equivalent impedance of the plasma chamber (400) is variable depending on the ignition state, input, and pressure of the gas, the power supply unit (100) must maintain a low total harmonic distortion (THD) and constant current characteristics to maintain a stable plasma even if the equivalent impedance changes.

[0059] The above power conversion system (300) is configured to include a line filter section (310), a rectifier section (320), a boost converter (330), a bridge circuit (340), a DC blocking section (350), a transformer (360), and an LCL filter (370). The line filter section (310) is electrically connected to a power supply section (200) to remove electromagnetic waves and noise generated from the power supply section (200), and can be configured using various electrical components. In an embodiment of the present invention, the line filter section (310) can filter AC power by electrically connecting a coil to the power supply section (200).

[0060] The rectifier (320) rectifies the single-phase or three-phase AC power output from the line filter (310) into a DC voltage and provides it to the boost converter (330). The rectifier (320) can be configured using various electrical components, such as diodes.

[0061] The above boost converter (330) is used to improve the power factor and control the input voltage, and can generate a stable output voltage by converting the DC voltage input from the rectifier (320) into pulsed DC, boosting the voltage, and then converting it back into a DC voltage. In an embodiment of the present invention, the boost converter (330) can be used for improving the power factor and controlling the input voltage by using a PFC boost converter.

[0062] The bridge circuit (340) receives the voltage controlled by the boost converter (330) and provides output power to the transformer (360). The bridge circuit (340) operates in a first mode or a second mode according to the load power required by the load, for example, the plasma chamber (400), under the control of the control unit (500). The bridge circuit (340) can be implemented using four MOSFETs, but is not limited thereto and can be implemented by adopting various electrical and power devices.

[0063] The above control unit (500) may be implemented as a central processing unit of a computer, for example, a processor. The above control unit (500) controls the output power of the bridge circuit (340) by fixing the duty ratio of the bridge circuit (340) operating in a first mode at a first load power according to the equivalent impedance of the plasma chamber (400), controls the output power by controlling the duty ratio of the bridge circuit (340) operating in a first mode at a second load power lower than the first load power, and controls the bridge circuit (340) by switching to a second mode at a third load power lower than the second load power. The above control unit (500) can reduce THD by fixing the duty ratio of the bridge circuit (340) in the second mode.

[0064] When the bridge circuit (340) is implemented using four MOSFETs, the first mode is a mode in which the bridge circuit (340) operates as a full bridge circuit, and the second mode is a mode in which the bridge circuit (340) operates as a half bridge circuit. The first to third load powers may be referred to as a heavy load, an intermediate load, and a light load, respectively, including a maximum load, depending on the equivalent impedance of the plasma chamber (400), the pressure of the gas injected into the plasma chamber (400), and the input voltage.

[0065] A DC blocking unit (350) is electrically connected to the bridge circuit (340) to block the DC bias generated when the bridge circuit (340) operates in half-bridge mode under the control of the control unit (500). The DC blocking unit (350) can be implemented using an electrical component, for example, a capacitor. A transformer (360) for supplying power to a load is electrically connected to the DC blocking unit (350), and an LCL filter (370) for removing harmonic components of the transformer (360) secondary voltage and converting it into a sinusoidal form is electrically connected to the secondary side of the transformer (360).

[0066] Accordingly, the above power supply (100) can provide high-quality power by improving the THD of the power required by the load, i.e., the plasma chamber (400), and has the advantage of providing improved power compared to conventional technology, especially even under low load conditions.

[0067]

[0068] Next, a control method for a plasma power supply according to an embodiment of the present invention will be described with reference to FIG. 3. FIG. 3a is a diagram illustrating a control method for a plasma power supply according to an embodiment of the present invention, FIG. 3b is a diagram showing the operation of a bridge circuit in a first mode according to an embodiment of the present invention, and FIG. 3c is a diagram showing the operation of a bridge circuit in a second mode according to an embodiment of the present invention.

[0069] Referring to FIGS. 3a to 3c, a control method for a plasma power supply device according to an embodiment of the present invention includes a step (S10) of supplying a single-phase or three-phase AC power supply from a power supply unit (200). After step S10, the AC power is rectified into a DC voltage by the rectifier unit (320) (S20), and the DC voltage is controlled using a boost converter (S30). Step S20 includes removing noise generated in the power supply unit (200) by a line filter unit (310), and full-wave rectifying the AC power waveform that has passed through the line filter unit (310) into DC. The boost converter is used to improve the power factor and control the input voltage, and can generate a stable output voltage by converting the DC voltage input from the rectifier unit (320) into pulsed DC, boosting the voltage, and then converting it back into a DC voltage.

[0070] Next, after the above step (S30), the voltage controlled by the boost converter (330) is input, and the output power is controlled by the bridge circuit (340) (S40). In the above step S40, the bridge circuit (340) can operate by changing the mode according to the load power required by the load. The bridge circuit (340) operates in a first mode or a second mode according to the control of the control unit (500). The bridge circuit (340) can control the output power by fixing the duty cycle of the bridge circuit (340) operating in the first mode at the first load power, control the output power by controlling the duty cycle of the bridge circuit (340) operating in the first mode at a second load power lower than the first load power, and control the output power by switching the bridge circuit (340) operating in the second mode at a third load power lower than the second load power.

[0071] In this case, the first mode may be a mode operating as a full bridge circuit, and the second mode may be a mode operating as a half bridge circuit. Additionally, controlling the bridge circuit (340) by switching to the second mode may reduce the THD by fixing the duty cycle of the second mode. When the bridge circuit (340) is switched to the second mode in step (S40), a step to block the DC bias occurring when operating in half bridge mode may be further performed.

[0072]

[0073] Next, an experimental example of the present invention will be described in detail with reference to FIG. 2c and FIGS. 4 to 15.

[0074] FIG. 4 is a diagram showing the equivalent impedance characteristics of a plasma chamber applied in an experimental example of the present invention, FIG. 5 is a diagram showing the output current characteristics of an LCL filter applied in an experimental example of the present invention, FIG. 6 is a circuit diagram for simulating an LCL filter designed according to an experimental example of the present invention, FIG. 7 is a diagram showing the magnitude and phase characteristics of an LCL filter according to an experimental example of the present invention. FIG. 8 is a diagram for simulating PLECS of a bridge circuit according to an experimental example of the present invention, FIG. 9a and FIG. 9b are diagrams for showing the output voltage and current waveforms of the transformer secondary side of a power supply according to the prior art, FIG. 10a and FIG. 10b are diagrams for showing the output voltage and current waveforms of the transformer secondary side of a power supply according to an experimental example of the present invention.

[0075] FIG. 11 is a graph showing a comparison of the results of simulating THD values ​​according to load power, and FIG. 12 is a photograph showing an experimental example of a PCB manufactured according to the present invention. FIG. 13a is a graph showing output voltage and current waveforms according to the prior art, and FIG. 13b is a graph showing output voltage and current waveforms according to an experimental example of the present invention. FIG. 14 is a graph showing a comparison of the output voltage waveforms shown in FIG. 13a and FIG. 13b, and FIG. 15 is a graph showing a comparison of the results of simulating THD values ​​according to load power.

[0076] Referring to FIG. 2c, the main power circuit of the power supply (100) is a full-bridge circuit type with a switching frequency of 400 kHz, and power control can be performed using pulse width modulation (PWM). The main power section, called a power amplifier, can be implemented using four IMZA65R048M1H SiC MOSFETs, and since the turn-on delay time of the MOSFETs is 14.8 ns and the turn-off delay time is 17 ns, it can be very efficient. The full-bridge method uses four MOSFETs, and MOSFETs S1 and S4 or MOSFETs S2 and S3 alternately conduct and block the output. To improve the stability of the circuit, a transformer is used to deliver 400 kHz square wave power to the secondary side, and since the square wave power induced on the secondary side contains harmonic components, an LCL filter is added to generate a sinusoidal wave with the harmonic components removed.

[0077] Although actual products use several kilowatts of power, the experimental example of the present invention focuses on waveform distortion, so the experiment was conducted with a load reduced to a maximum of 110W.

[0078]

[0079] Half-bridge conversion control

[0080] In conventional control methods, output power is controlled by controlling the voltage input to the full-bridge inverter. However, since the output voltage of the PFC boost converter cannot be controlled to be lower than the input voltage of the PFC boost converter, the output power is controlled by PWM duty control of the gates in the low voltage range; nevertheless, the PWM duty control method has a problem in which power quality deteriorates as THD increases as the duty decreases. [Table 1] below shows the sequence of the conventional control method.

[0081] Input Voltage Range [V] Load Power [W] Control Method Duty THD 300 ~ 400 220~440 Full Bridge Fixed Good 300 205~220 Full Bridge Control Good 300 30~205 Full Bridge Control Poor

[0082]

[0083] This experimental example proposes a half-bridge switching method to address these issues. Initially, the output power is controlled by adjusting the output voltage of the PFC boost converter after setting the duty cycle to the maximum in a full-bridge type. At this stage, the THD remains in a good state because the output power is controlled with the duty cycle fixed at the maximum. Since control is not possible below the DC voltage supplied to the PFC boost converter, a PWM duty cycle control method is used to control the duty cycle to the point where no distortion occurs in the low-load range. At the point where the THD deteriorates, the system switches from a full-bridge type to a half-bridge type; as DC bias occurs in the half-bridge type, the DC is blocked using a DC blocking capacitor to obtain the desired sinusoidal waveform. Table 2 below shows the sequence of the half-bridge switching method.

[0084] Input Voltage Range [V] Load Power [W] Control Method Duty Cycle THD 300 ~ 400 220~440 Full Bridge Fixed Good 300 205~220 Full Bridge Control Good 300 ~ 400 30~205 Half Bridge Fixed Good

[0085]

[0086] Through the method presented in [Table 2] above (variable DC full bridge ⇒ fixed DC full bridge duty control ⇒ variable DC half bridge), load power that cannot be controlled by the PFC boost converter can be reduced, and since output power is not controlled via the duty ratio, the quality of output power can be improved compared to existing control methods.

[0087]

[0088] Transformer Design

[0089] The transformer must be designed to improve circuit stability by separating the full-bridge inverter and the filter. At 400 kHz, the copper penetration depth is 0.1 mm considering the skin effect, and 9 strands of 0.3 mm were selected to minimize the skin effect considering the AWG (American Wire Gauge) standard.

[0090] Since the above RF generator operates at high frequency, the design uses a PL-13 ferrite core with excellent characteristics. The characteristics of the PL-13 core are shown in [Table 3] below.

[0091]

[0092]

[0093] Ap, derived from [Equation 1] below for the core size, has an area of ​​0.89 cm² 4 The EE-6565S core is used. Next, [Equation 2] is used to derive a minimum primary rotational speed of 2.2 or higher, and the rotational speed is set to an integer of 4 to provide a margin.

[0094]

[0095]

[0096] (Here, A p : A value considering the window area and cross-sectional area of ​​the core, W a : Window area of ​​the core, A c : Cross-sectional area of ​​the core, P0: Output power, D cma : Current density, K t : Winding Factor, B max : Maximum magnetic flux density, f : Switching frequency)

[0097]

[0098]

[0099] (Here, N p : Minimum number of turns on the primary side of the transformer, V pri : Maximum voltage applied to the inverter, Ac : Cross-sectional area of ​​the core, f : Switching frequency, B max : Maximum magnetic flux density, K f : Form factor of a square wave)

[0100]

[0101] In the experimental example of the present invention, the rotation ratio is 1, so the secondary coil has the same number of rotations as the primary coil. The specifications of the actual constructed transformer are presented in [Table 4] below.

[0102] ParameterDesign valueNumber of turns4:4Magnetizing Inductance176μHLeakage Inductance1.06μH

[0103]

[0104] LCL filter network design

[0105] The output filter must remove harmonic components from the square wave transformer secondary voltage and convert it into a sinusoidal form. Additionally, constant current characteristics are required because the current can change rapidly as the chamber impedance fluctuates.

[0106] As shown in Fig. 4, the impedance of the plasma chamber is very high before ignition, drops immediately after ignition, and increases as the gas pressure increases. If a constant voltage is used in this process, the control speed cannot keep up with the drop in impedance immediately after ignition, causing overcurrent and potentially reducing the reliability and stability of the cleaning process.

[0107] As illustrated in Fig. 5, the LCL filter exhibits constant current characteristics and must maintain a stable current despite impedance fluctuations in the chamber; therefore, the filter must be designed so that its resonant frequency becomes Wr1 near the switching frequency of the DC-AC inverter. The maximum value of the transformer secondary rms voltage input to the LCL filter is derived as shown in [Equation 3] below, and the Q factor can be calculated as a function of the output current of the LCL filter using [Equation 4]. The calculated Q factor can be used to calculate L1, L2 can be calculated using γ, and the resonant frequency can be used to calculate C1.

[0108]

[0109]

[0110] (Here, V TR.s( RMS ) : Effective value of the fundamental wave input to the LCL filter, V TR.s(peak) : V TR.s(RMS) (maximum value of)

[0111]

[0112]

[0113] (Here, R o : Output resistance, I O ( RMS ) : Effective value of LCL filter output current, V TR.s( RMS ) : Effective value of the fundamental wave input to the LCL filter, ω n : Resonance frequency (ω o ) and switching frequency (ω s Normalized frequency (ω) according to ) n = ω s / ω o ), γ: Ratio of inverter-side inductor (L1) to chamber-side inductor (L2)

[0114]

[0115]

[0116] (Here, L1: LCL filter inverter side inductor, Q: Q-factor, W0: resonant frequency, R L : Output resistance)

[0117]

[0118]

[0119] (Here, L2: LCL filter chamber-side inductor, γ: ratio of inverter-side inductor (L1) to chamber-side inductor (L2), L1: LCL filter inverter-side inductor)

[0120]

[0121]

[0122] (Here, C1: filter capacitor, ω o : Resonance frequency, L1: LCL filter inverter side inductor)

[0123]

[0124]

[0125] (Here, f: resonant frequency, L1: LCL filter inverter side inductor, c: filter capacitor)

[0126]

[0127] Using the above mathematical formulas, VTR.s(RMS) was calculated to be 100V. The output current must be at least 1.5 Arms, and it was designed to output 2 Arms considering the overload rating. Since the switching frequency is 400kHz, it was set to 450kHz to ensure zero-voltage switching, and ZVS operation was ensured by designing the ratio of γ to 0.7, which is less than 1. Using the above design conditions, the required Q-factor is 1.13, and the parameters of the LCL filter calculated using the design formula are as shown in [Table 5] below. The schematic diagram and characteristics of the LCL filter simulated through the Advanced Design System (ADS) are shown in Figures 6 and 7.

[0128] ParameterDesign valueL120μHL216μHC16.2nF

[0129]

[0130] Simulation

[0131] As shown in Figure 8, a simulation was performed to verify the validity of the proposed design and control methods, and the simulation was conducted using PLECS to construct a complete circuit and controller using the design values ​​and control methods. In addition, the simulation was performed under conditions identical to the actual experiment by considering the leakage inductance and magnetization inductance of the transformer.

[0132] As illustrated in FIGS. 9a and 9b, the conventional method of controlling the output through PWM duty control results in distortion of the output voltage (Vo) as the duty of the transformer's secondary voltage (VTRS) decreases. On the other hand, as illustrated in FIGS. 10a and 10b, the proposed half-bridge switching method does not reduce the duty of the transformer's secondary voltage (VTRS), thereby minimizing distortion of the output voltage (Vo). At a load power of 15W, the THD of the conventional method is 5.82%, whereas the THD of the method according to the experimental example of the present invention is 2.92%, confirming that the present invention improves the THD by approximately 50% compared to the conventional method.

[0133] As shown in Figure 11, the simulation results according to the present experimental example show that the THD of the output voltage is significantly improved in the light load region when the half-bridge switching method is applied. Therefore, the effectiveness of the proposed control method has been verified through simulation.

[0134]

[0135] Experimental Results

[0136] As illustrated in Fig. 12, the validity of the proposed design and control methods was verified through actual experiments. Output power control was performed using a DSP (TMS320F28335) in the inverter circuit. Since the equivalent impedance of the plasma chamber load can be the same as a purely resistive load, a non-conductive resistor with no resistance change with frequency was used. The THD was derived by importing waveform data measured by an oscilloscope into MATLAB and performing an FFT calculation.

[0137] The experimental results showed that it operates stably across all load ranges. Tables 6 and 7 below show the experimental results for the conventional control method and the proposed control method. For the conventional control method, it can be seen that the THD becomes poor as the PWM duty cycle decreases at a load power of approximately 40W. At the minimum load of the conventional method, the THD is 5.55%, which leads to severe waveform distortion as shown in Figure 13a.

[0138]

[0139]

[0140]

[0141]

[0142] On the other hand, the THD of the proposed half-bridge switching method was 2.33% under the same light-load power conditions, which is an improvement of more than 58% compared to the existing method. The waveforms for the output voltage and current of the proposed method are shown in FIG. 13b, and a comparison of the output voltage waveforms of the conventional full-bridge method and the half-bridge switching method of the present experiment is shown in FIG. 14.

[0143] Figure 15 is a graph comparing the THD of the output voltage as a function of load size in an actual experiment, and the experimental example showed results similar to the simulation.

[0144]

[0145] Conclusion

[0146] The present invention presents a half-bridge switching method for improving the quality of RF power circuits for generating high-quality plasma in a dry cleaning method. Compared to conventional PWM duty control, applying the half-bridge switching method significantly reduces the waveform's THD and improves the output power quality in light-load regions without the addition or modification of hardware. This enables the generation of high-quality plasma in the plasma chamber, which is expected to improve the performance of the cleaning process.

[0147]

[0148] Although the invention made by the inventors has been specifically described according to the above embodiments, the invention is not limited to the above embodiments and can be modified in various ways without departing from the gist thereof.

[0149]

[0150] By using the plasma power supply and control method for improving harmonic distortion under light load conditions according to the present invention, the quality of the waveform can be improved, thereby enabling stable plasma generation.

Claims

1. In a plasma power supply for improving harmonic distortion under light load conditions, A power supply unit for supplying single-phase or three-phase AC power; A boost converter for controlling the input voltage input after the above AC power is rectified; A bridge circuit for receiving a voltage controlled by the above-mentioned boost converter and providing output power; and A control unit that controls the operation of the bridge circuit to operate in a first mode or a second mode according to the load power required by a load electrically connected to the bridge circuit, wherein The above control unit A plasma power supply characterized by controlling output power by fixing the duty ratio of the bridge circuit operating in the first mode at a first load power, controlling output power by controlling the duty ratio of the bridge circuit operating in the first mode at a second load power lower than the first load power, and controlling the bridge circuit by switching it to operate in the second mode at a third load power lower than the second load power.

2. In Paragraph 1, A plasma power supply characterized by the above-described control unit reducing THD by fixing the duty ratio of the bridge circuit operating in the second mode.

3. In Paragraph 1, A plasma power supply characterized by the above bridge circuit being implemented using four MOSFETs.

4. In Paragraph 1, A plasma power supply characterized in that the first mode is a mode in which the bridge circuit operates as a full bridge circuit, and the second mode is a mode in which the bridge circuit operates as a half bridge circuit.

5. In Paragraph 4, A plasma power supply characterized by having a DC blocking section electrically connected to the bridge circuit to block the DC bias generated when operating in the half-bridge mode.

6. In Paragraph 5, A plasma power supply characterized in that a transformer is electrically connected to the DC blocking section, and an LCL filter is electrically connected to the secondary side of the transformer to remove harmonic components of the transformer's secondary voltage and convert it into a sinusoidal form.

7. In Paragraph 1, Between the above power supply unit and the boost converter, a line filter unit for removing noise generated in the power supply unit; and A plasma power supply characterized by having a rectifier electrically connected to rectify an AC power waveform that has passed through the above-mentioned line filter section into DC.

8. In Paragraph 6, A plasma power supply characterized in that the above boost converter is a PFC boost converter.

9. A control method for a plasma power supply to improve harmonic distortion under light load conditions, i) A step of supplying single-phase or three-phase AC power from a power supply unit; ii) a step of rectifying the above AC power into a DC voltage; iii) a step of controlling the DC voltage using a boost converter; and iv) A step of receiving the voltage controlled by the boost converter above and controlling the output power by a bridge circuit, wherein v) The step of controlling the output power above The operation of the bridge circuit is controlled to operate in a first mode or a second mode according to the load power required by a load electrically connected to the bridge circuit, and A method for controlling a plasma power supply, characterized by controlling the output power by fixing the duty ratio of the bridge circuit operating in the first mode at a first load power, controlling the output power by controlling the duty ratio of the bridge circuit operating in the first mode at a second load power lower than the first load power, and controlling the bridge circuit by switching it to operate in the second mode at a third load power lower than the second load power.

10. In Paragraph 9, A control method for a plasma power supply device characterized in that the first mode is a mode in which the bridge circuit operates as a full bridge circuit, and the second mode is a mode in which the bridge circuit operates as a half bridge circuit.

11. In Paragraph 10, A control method for a plasma power supply device characterized by controlling the bridge circuit by switching to the second mode, thereby reducing THD by fixing the duty ratio of the second mode.

12. In Paragraph 10, A control method for a plasma power supply device characterized by further including a blocking step for blocking the DC bias that occurs when operating in the half-bridge mode when the bridge circuit is switched to the second mode in step v).

13. In Paragraph 9, The above step ii) is A step of removing noise generated in the above power supply unit using a line filter unit; and A control method for a plasma power supply device characterized by including a step of full-wave rectifying an AC power waveform that has passed through the above-mentioned line filter section into DC.

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