Gas laser device and method for manufacturing electronic device

Abstract

A gas laser device according to one aspect of the present disclosure is provided with: a laser chamber in which a laser gas containing fluorine gas is sealed; a main electrode disposed inside the laser chamber; a preionization electrode disposed inside the laser chamber; a power supply device that supplies power to the main electrode and the preionization electrode; and a processor that controls the power supply device to execute a first discharge control for discharging the preionization electrode and the main electrode, and a second discharge control for discharging only the preionization electrode without discharging the main electrode.

Description

Technical Field

[0001] The present disclosure relates to a gas laser device and a method for manufacturing an electronic device. Background Art

[0002] In recent years, semiconductor exposure equipment has been required to improve resolution as semiconductor integrated circuits become increasingly miniaturized and highly integrated. Consequently, there has been a trend toward shortening the wavelength of light emitted by exposure light sources. For example, gas laser devices used for exposure include KrF excimer lasers, which output laser light with a wavelength of approximately 248 nm, and ArF excimer lasers, which output laser light with a wavelength of approximately 193 nm.

[0003] The spectral line width of the natural oscillation light of KrF excimer laser devices and ArF excimer laser devices is as wide as 350pm to 400pm. Therefore, if the projection lens is made of a material that allows ultraviolet rays such as KrF and ArF lasers to pass through, chromatic aberration may sometimes occur. As a result, the resolution may be reduced. Therefore, it is necessary to narrow the spectral line width of the laser output from the gas laser device to a level where chromatic aberration can be ignored. Therefore, in order to narrow the spectral line width, a narrowing module (Line Narrowing Module: LNM) containing narrowing elements (etalon, grating, etc.) is sometimes provided in the laser resonator of the gas laser device. Hereinafter, a gas laser device with a narrowed spectral line width is referred to as a narrowed gas laser device.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 11-135858 Summary of the Invention

[0007] A gas laser device according to one aspect of the present disclosure comprises: a laser chamber in which laser gas containing fluorine gas is sealed; a main electrode arranged inside the laser chamber; a preionization electrode arranged inside the laser chamber; a power supply device that supplies power to the main electrode and the preionization electrode; and a processor that controls the power supply device to execute a first discharge control for causing the preionization electrode and the main electrode to discharge, and a second discharge control for causing only the preionization electrode to discharge without causing the main electrode to discharge.

[0008] A method for manufacturing an electronic device according to one aspect of the present disclosure is a method for manufacturing an electronic device, comprising the following steps: generating laser light by a gas laser device; outputting the laser light to an exposure device; and exposing the laser light on a photosensitive substrate in the exposure device to manufacture the electronic device, wherein the gas laser device comprises: a laser chamber in which laser gas containing fluorine gas is sealed; a main electrode disposed inside the laser chamber; a pre-ionization electrode disposed inside the laser chamber; a power supply device that supplies power to the main electrode and the pre-ionization electrode; and a processor that controls the power supply device to execute a first discharge control for causing the pre-ionization electrode and the main electrode to discharge, and a second discharge control for causing only the pre-ionization electrode to discharge without causing the main electrode to discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Hereinafter, several embodiments of the present disclosure will be described with reference to the accompanying drawings, merely as examples.

[0010] Figure 1 It is a side view schematically showing the structure of a gas laser device according to a comparative example.

[0011] Figure 2 It is a cross-sectional view schematically showing the structure of a gas laser device according to a comparative example.

[0012] Figure 3 This is a circuit diagram schematically showing the configuration of a power supply device according to a comparative example.

[0013] Figure 4 This is a flowchart showing the flow of processing executed by the processor of the first embodiment.

[0014] Figure 5 This is a circuit diagram schematically showing the configuration of a power supply device according to a second embodiment.

[0015] Figure 6 Graphs showing simulation results of various voltages applied to the power supply device according to the second embodiment.

[0016] Figure 7 This is a circuit diagram schematically showing the configuration of a power supply device according to a third embodiment.

[0017] Figure 8 Graphs showing simulation results of various voltages applied to the power supply device according to the third embodiment.

[0018] Figure 9 This is a circuit diagram schematically showing the configuration of a power supply device according to a fourth embodiment.

[0019] Figure 10 Graphs showing simulation results of various voltages applied to the power supply device according to the fourth embodiment.

[0020] Figure 11 This is a circuit diagram schematically showing the configuration of a power supply device according to a fifth embodiment.

[0021] Figure 12 It is a diagram schematically showing a configuration example of an exposure apparatus. DETAILED DESCRIPTION

[0022] <Content>

[0023] 1. Comparative Example

[0024] 1.1 Gas laser device

[0025] 1.1.1 Structure

[0026] 1.1.2 Action

[0027] 1.2 Power supply device

[0028] 1.2.1 Structure

[0029] 1.2.2 Action

[0030] 1.3 Topics

[0031] 2. First Implementation

[0032] 2.1 Structure

[0033] 2.2 Action

[0034] 2.3 Effect

[0035] 3. Second Implementation

[0036] 3.1 Structure

[0037] 3.2 Action

[0038] 3.3 Effect

[0039] 4. Third Implementation

[0040] 4.1 Structure

[0041] 4.2 Action

[0042] 4.3 Effect

[0043] 5. Fourth Implementation

[0044] 5.1 Structure

[0045] 5.2 Action

[0046] 5.3 Effect

[0047] 6. Fifth Implementation

[0048] 6.1 Structure

[0049] 6.2 Action

[0050] 6.3 Effect

[0051] 7. Modifications

[0052] 8. Method for manufacturing electronic devices

[0053] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The embodiments described below represent several examples of the present disclosure and do not limit the content of the present disclosure. In addition, the structures and actions described in the embodiments may not all be required as the structures and actions of the present disclosure. In addition, the same reference numerals are given to the same components, and repeated descriptions are omitted.

[0054] 1. Comparative Example

[0055] First, comparative examples of the present disclosure will be described. The comparative examples of the present disclosure are methods that the applicant recognizes as being known only to the applicant and are not publicly known examples that the applicant recognizes.

[0056] 1.1 Gas laser device

[0057] 1.1.1 Structure

[0058] use Figure 1 as well as Figure 2 The structure of a gas laser device 2 according to a comparative example will be described. Figure 1 The structure of the gas laser device 2 is schematically shown. Figure 2 Observed from the Z direction Figure 1 1 is a cross-sectional view of a gas laser device 2. The gas laser device 2 is a discharge-excitation type gas laser device that excites laser gas by discharge, and is, for example, an excimer laser device.

[0059] exist Figure 1 In the figure, the direction of travel of the pulsed laser light PL output from the gas laser device 2 is defined as the Z direction. The discharge direction, described later, is defined as the Y direction. Furthermore, the direction perpendicular to the Z and Y directions is defined as the X direction. The pulsed laser light PL is an example of a "laser" in the technology disclosed herein.

[0060] exist Figure 1 In the figure, the gas laser device 2 includes a laser chamber 10, a charger 11, a pulse power module (PPM) 12, a pulse energy measurement unit 13, a processor 14, a pressure sensor 17, and a laser resonator. The laser resonator is composed of a narrowband module 15 and an output coupling mirror (OC) 16. The charger 11 is an example of the "first power supply" of the disclosed technology. The PPM 12 is an example of the "power generation circuit" of the disclosed technology.

[0061] The laser chamber 10 is a metal container formed of aluminum metal with nickel plating on the surface, for example. Figure 1 and Figure 2 As shown, a main electrode 20, a ground plate 21, wiring 22, a fan 23, a heat exchanger 24, a preionization electrode 19, an electrically insulating guide 28, and a metal damper 29 are provided inside the laser chamber 10. The preionization electrode 19 includes a preionization outer electrode 19a, a dielectric tube 19b, and a preionization inner electrode 19c.

[0062] A laser gas containing fluorine as a laser medium is enclosed in the laser chamber 10. The laser gas contains, for example, rare gases such as argon, krypton, and xenon, buffer gases such as neon and helium, and halogen gases such as fluorine and chlorine.

[0063] An opening is formed in the laser chamber 10. An electrical insulating plate 26 with a feedthrough 25 embedded therein is attached to the laser chamber 10 via an O-ring (not shown) to block the opening. The PPM 12 is placed on the electrical insulating plate 26. The laser chamber 10 is grounded.

[0064] PPM 12 includes a charging capacitor C0 (described later) connected to main electrode 20 via feedthrough 25. PPM 12 includes switch SW1 for discharging main electrode 20. Charger 11 is connected to charging capacitor C0 of PPM 12. Hereinafter, the discharge generated at main electrode 20 is referred to as main discharge. Switch SW1 is an example of the "first switch" in the disclosed technology.

[0065] The main electrode 20 is composed of a cathode electrode 20a and an anode electrode 20b. The cathode electrode 20a and the anode electrode 20b are arranged within the laser chamber 10 with their discharge surfaces facing each other. The space between the discharge surface of the cathode electrode 20a and the discharge surface of the anode electrode 20b is referred to as the discharge space 27. The surface of the cathode electrode 20a opposite the discharge surface is supported by an electrically insulating plate 26 and connected to the feedthrough 25. The surface of the anode electrode 20b opposite the discharge surface is supported by a ground plate 21.

[0066] The ground plate 21 is connected to the laser chamber 10 via the wiring 22. The laser chamber 10 is grounded. Therefore, the ground plate 21 is grounded via the wiring 22. The end portion of the ground plate 21 in the Z direction is fixed to the laser chamber 10.

[0067] The fan 23 is a cross-flow fan for circulating the laser gas in the laser chamber 10 and is arranged on the opposite side of the discharge space 27 from the ground plate 21. The laser chamber 10 is connected to a motor 23a for rotationally driving the fan 23.

[0068] Laser gas blown out from fan 23 flows into discharge space 27. The flow direction of the laser gas flowing into discharge space 27 is substantially parallel to the X direction. The laser gas flowing out of discharge space 27 can be sucked into fan 23 via heat exchanger 24. Heat exchanger 24 performs heat exchange between the refrigerant supplied to the interior of heat exchanger 24 and the laser gas.

[0069] Electrically insulating guide 28 is disposed on the surface of electrically insulating plate 26 on the discharge space 27 side, sandwiching cathode electrode 20a. Electrically insulating guide 28 is shaped to guide the flow of laser gas so that the laser gas from fan 23 flows efficiently between cathode electrode 20a and anode electrode 20b. Electrically insulating guide 28 and electrically insulating plate 26 are formed, for example, from a ceramic such as alumina (Al2O3) that has low reactivity with fluorine gas.

[0070] The metal damper 29 is disposed on the surface of the ground plate 21 on the discharge space 27 side so as to sandwich the anode electrode 20b. The metal damper 29 is formed of, for example, porous nickel metal having low reactivity to fluorine gas.

[0071] Laser chamber 10 is connected to a laser gas supply device 18a and a laser gas exhaust device 18b. Laser gas supply device 18a includes a valve and a flow control valve and is connected to a gas cylinder containing laser gas. Laser gas exhaust device 18b includes a valve and an exhaust pump.

[0072] Windows 10a and 10b for emitting light generated in the laser chamber 10 to the outside are provided at the ends of the laser chamber 10. The laser chamber 10 is arranged so that the optical path of the optical resonator passes through the discharge space 27 and the windows 10a and 10b.

[0073] The bandwidth narrowing module 15 includes a prism 15a and a grating 15b. The prism 15a allows light emitted from the laser chamber 10 through the window 10a to pass therethrough with a widened beam width toward the grating 15b.

[0074] Grating 15b is arranged in a Littrow configuration, where the incident angle and diffraction angle are equal. Grating 15b is a wavelength-selective element that selectively extracts light near a specific wavelength based on the diffraction angle. The spectral linewidth of the light returning from grating 15b to laser chamber 10 via prism 15a is narrowed.

[0075] The output coupling mirror 16 transmits a portion of the light emitted from the laser chamber 10 through the window 10b and reflects the other portion to return it to the laser chamber 10. The surface of the output coupling mirror 16 is coated with a partial reflection film.

[0076] Light emitted from the laser chamber 10 reciprocates between the bandwidth narrowing module 15 and the output coupling mirror 16, and is amplified each time it passes through the discharge space 27. A portion of the amplified light is output as pulsed laser light PL via the output coupling mirror 16.

[0077] The pulse energy measurement unit 13 is arranged on the optical path of the pulse laser light PL outputted via the output coupling mirror 16. The pulse energy measurement unit 13 includes a beam splitter 13a, a focusing optical system 13b, and a photosensor 13c.

[0078] Beam splitter 13a transmits pulsed laser light PL with high transmittance and reflects a portion of the pulsed laser light PL toward focusing optical system 13b. Focusing optical system 13b focuses the light reflected by beam splitter 13a onto the light-receiving surface of optical sensor 13c. Optical sensor 13c measures the pulse energy of the light focused on the light-receiving surface and outputs the measured value to processor 14.

[0079] Pressure sensor 17 detects the pressure in laser chamber 10 and outputs the detected value to processor 14. Processor 14 determines the pressure of the laser gas in laser chamber 10 based on the detected pressure value and charging voltage Vhv of charger 11.

[0080] The charger 11 is a high voltage power source that supplies a charging voltage Vhv to the charging capacitor C0 included in the PPM 12. The switch SW1 of the PPM 12 is controlled by the processor 14. When the switch SW1 is turned from off to on, the PPM 12 generates a high voltage pulse based on the electric energy stored in the charging capacitor C0 and applies it to the main electrode 20. Figure 3 As will be described later, the charger 11 and the PPM 12 are included in a power supply device 30 that supplies power to the pre-ionization electrode 19 and the main electrode 20 .

[0081] The processor 14 is a processing device that transmits and receives various signals to and from the exposure device controller 110 provided in the exposure device 100. For example, the target pulse energy Et of the pulsed laser light PL to be output to the exposure device 100, an oscillation trigger signal, and the like are transmitted from the exposure device controller 110 to the processor 14.

[0082] The processor 14 centrally controls the operation of each component of the gas laser device 2 based on various signals sent from the exposure device controller 110 , the measured value of pulse energy, the detected value of gas pressure, and the like.

[0083] The processor 14 functions as a controller for the gas laser device 2. For example, the processor 14 is a processing device including a storage device storing a control program and a CPU (Central Processing Unit) that executes the control program. The processor 14 is specifically configured or programmed to perform the various processes included in the present disclosure. The storage device is a computer-readable, non-transitory storage medium, and includes, for example, a memory as a primary storage device and a storage device as an auxiliary storage device. Alternatively, the storage device may be a semiconductor memory, a hard disk drive (HDD), a solid-state drive (SSD), or a combination thereof.

[0084] 1.1.2 Action

[0085] Next, the operation of the comparative example gas laser device 2 will be described. First, the processor 14 controls the laser gas supply device 18a to supply laser gas into the laser chamber 10 and drives the motor 23a to rotate the fan 23. This circulates the laser gas in the laser chamber 10.

[0086] The processor 14 receives the target pulse energy Et and the oscillation trigger signal transmitted from the exposure device controller 110. The oscillation trigger signal is a signal instructing the gas laser device 2 to output the pulsed laser light PL for one pulse.

[0087] The processor 14 sets a charging voltage Vhv corresponding to the target pulse energy Et for the charger 11. The processor 14 operates the switch SW1 of the PPM 12 in synchronization with the oscillation trigger signal.

[0088] When switch SW1 of PPM 12 is switched from off to on, voltage is applied between preionization inner electrode 19c and preionization outer electrode 19a, and between cathode electrode 20a and anode electrode 20b of preionization electrode 19. This generates corona discharge at preionization electrode 19, generating UV (Ultraviolet) light. UV light is irradiated onto the laser gas in discharge space 27, preionizing the laser gas.

[0089] Then, when the voltage between cathode electrode 20a and anode electrode 20b reaches the dielectric breakdown voltage, a main discharge occurs in discharge space 27. If the discharge direction of the main discharge is defined as the direction of electron flow, the discharge direction is from cathode electrode 20a toward anode electrode 20b. When the main discharge occurs, the laser gas in discharge space 27 is excited, emitting light.

[0090] Metal damper 29 prevents acoustic waves generated by the main discharge from being reflected and returning to discharge space 27. Furthermore, by circulating the laser gas in laser chamber 10, discharge products generated in discharge space 27 move downstream.

[0091] The light emitted from the laser gas is reflected by the band-narrowing module 15 and the output coupling mirror 16 and reciprocates within the laser resonator, thereby performing laser oscillation. The light narrowed by the band-narrowing module 15 is output from the output coupling mirror 16 as pulsed laser light PL.

[0092] A portion of the pulse laser light PL output from the output coupling mirror 16 enters the pulse energy measurement unit 13 . The pulse energy measurement unit 13 measures the pulse energy E of the incident pulse laser light PL and outputs the measured value to the processor 14 .

[0093] The processor 14 calculates a difference ΔE between the measured value of the pulse energy E and the target pulse energy Et. The processor 14 performs feedback control on the charging voltage Vhv based on the difference ΔE so that the measured value of the pulse energy E becomes the target pulse energy Et.

[0094] When the charge voltage Vhv exceeds the maximum value within the allowable range, the processor 14 controls the laser gas supply device 18a to supply laser gas into the laser chamber 10 until the pressure reaches a predetermined level. Furthermore, when the charge voltage Vhv falls below the minimum value within the allowable range, the processor 14 controls the laser gas exhaust device 18a to exhaust the laser gas from the laser chamber 10 until the pressure reaches a predetermined level.

[0095] The gas laser device 2 is not necessarily limited to a narrowband laser device, and may be a laser device that outputs natural oscillation light. For example, a high-reflection mirror may be provided instead of the narrowband module 15.

[0096] In addition, Figure 1 as well as Figure 2 In the figure, an excimer laser device is illustrated as the gas laser device 2 , but the gas laser device 2 may be an F 2 laser device or the like using a laser gas containing fluorine gas and a buffer gas.

[0097] 1.2 Power supply device

[0098] 1.2.1 Structure

[0099] Figure 3 The structure of a power supply device 30 of a comparative example is schematically shown. The power supply device 30 includes a charger 11, a PPM 12, and a voltage divider circuit 31. Based on control from the processor 14, the power supply device 30 supplies power to the preionization electrode 19 and the main electrode 20, thereby causing the preionization electrode 19 and the main electrode 20 to discharge.

[0100] A voltage divider circuit 31 and the main electrode 20 are connected in parallel to the output terminal of the PPM 12. The voltage divider circuit 31 is connected to the pre-ionization electrode 19.

[0101] PPM 12 includes the aforementioned switch SW1, transformer TC1, magnetic switches MS1, MS2, and MS3, a charging capacitor C0, and capacitors C1, C2, and C3. Charging capacitor C0 is connected to charger 11, which is a DC charger. Switch SW1 is a semiconductor switching element such as an IGBT (Insulated Gate Bipolar Transistor). Switch SW1 switches on and off based on a control signal from processor 14. Transformer TC1 is an example of the "first transformer" in the disclosed technology.

[0102] Magnetic switches MS1, MS2, MS3 and capacitors C1, C2 form a magnetic pulse compression circuit that compresses the pulse width of the current flowing from transformer TC1 to capacitor C3. Capacitor C3 is an example of a "peak capacitor" in the technology disclosed herein.

[0103] Switch SW1 is provided between charging capacitor C0 and the primary side of transformer TC1. Magnetic switch MS1 is provided between the secondary side of transformer TC1 and capacitor C1. Magnetic switch MS2 is provided between capacitor C1 and capacitor C2. Magnetic switch MS3 is provided between capacitor C2 and capacitor C3.

[0104] The primary and secondary sides of transformer TC1 are electrically insulated. Furthermore, the windings on the primary and secondary sides of transformer TC1 are in opposite directions, known as additive polarity. Having the windings on the primary and secondary sides in the same direction is known as subtractive polarity.

[0105] The voltage divider circuit 31 is formed by connecting the inductor L0 and the capacitor C 11 and capacitor C 12 The capacitor C is connected in series to prevent insulation breakdown caused by excessive voltage applied to the pre-ionization electrode 19. 11 With capacitor C 12 The connection point of the capacitor C is connected to the pre-ionization inner electrode 19c of the pre-ionization electrode 19. 12 It functions as a pre-ionization capacitor for applying a voltage to the pre-ionization electrode 19 .

[0106] 1.2.2 Action

[0107] Next, the operation of the power supply device 30 will be described. First, the charger 11 sets the charging voltage Vhv via the processor 14. The charger 11 then charges the charging capacitor C0 based on the set charging voltage Vhv.

[0108] In the PPM 12 , when a control signal is sent from the processor 14 to the switch SW1 , the switch SW1 is closed, and current flows from the charging capacitor C0 to the primary side of the transformer TC1 .

[0109] In transformer TC1, current flows into the primary side of transformer TC1, causing current to flow in the opposite direction on the secondary side of transformer TC1 through electromagnetic induction. The electromotive force generated by the current flowing through the secondary side of transformer TC1 closes magnetic switch MS1, causing current to flow from the secondary side of transformer TC1 to capacitor C1, charging capacitor C1.

[0110] As capacitor C1 is charged, magnetic switch MS2 is closed, and current flows from capacitor C1 to capacitor C2, charging capacitor C2. At this time, capacitor C2 is charged with a pulse width smaller than the pulse width of the current when charging capacitor C1.

[0111] As capacitor C2 is charged, magnetic switch MS3 is closed, and current flows from capacitor C2 to capacitor C3, charging capacitor C3. At this time, capacitor C3 is charged with a pulse width smaller than the pulse width of the current when charging capacitor C2.

[0112] In this way, as the current flows through the capacitor C1, the capacitor C2, and the capacitor C3 in sequence, the pulse width of the current is compressed, and the charge is charged into the capacitor C3.

[0113] Then, a voltage is applied from the capacitor C3 to the voltage divider circuit 31. The voltage divider circuit 31 divides the applied voltage. 12 The voltage is applied to the pre-ionization electrode 19 to generate a corona discharge, and a voltage is applied from the capacitor C3 to the main electrode 20 to generate a main discharge.

[0114] 1.3 Topics

[0115] In the gas laser device 2 of the comparative example, main discharge is generated at the main electrode 20 in conjunction with generation of corona discharge at the preionization electrode 19 , and this main discharge excites the laser gas, thereby generating pulsed laser light PL.

[0116] The laser gas contains carbon components derived from carbon adhering to the inner walls of the laser chamber 10 or O-rings. The main discharge causes the carbon components in the laser gas to react with fluorine, generating carbon fluoride (CF4). This carbon fluoride is believed to be decomposed and removed to a certain extent by the pulsed laser light PL generated by the main discharge and the main discharge. However, since the amount generated exceeds the amount removed, the concentration of carbon fluoride in the laser gas increases with repeated main discharges. Since carbon fluoride absorbs pulsed laser light PL, repeated main discharges reduce the pulse energy of the pulsed laser light PL output from the gas laser device 2.

[0117] 2. First Implementation

[0118] 2.1 Structure

[0119] The gas laser device 2 of the first embodiment of the present disclosure has the same configuration as the gas laser device 2 of the comparative example, except for the processing executed by the processor 14. In this embodiment, the configuration of the power supply device 30 is the same as that of the comparative example.

[0120] In this embodiment, the processor 14 controls the charging voltage of the charger 11 to execute a first discharge control in which the preionization electrode 19 and the main electrode 20 are discharged, and a second discharge control in which only the preionization electrode 19 is discharged. In this embodiment, the processor 14 executes the first and second discharge controls by changing the charging voltage.

[0121] As a first discharge control, the processor 14 sets a first charging voltage Vhv1 for the charger 11. After the charging capacitor C0 is charged, the processor 14 turns on the switch SW1. As in the comparative example, the first charging voltage Vhv1 is a voltage corresponding to the target pulse energy Et and is a voltage above the dielectric breakdown voltage that causes dielectric breakdown in the discharge space 27. For example, the dielectric breakdown voltage is 10 kV. In other words, the first charging voltage Vhv1 is 10 kV or higher. When the first charging voltage Vhv1 is set for the charger 11, the preionization electrode 19 and the main electrode 20 discharge.

[0122] As a second discharge control, processor 14 sets a second charging voltage Vhv2, which is lower than first charging voltage Vhv1, for charger 11. After charging capacitor C0 is charged, processor 14 turns on switch SW1. Second charging voltage Vhv2 is a voltage lower than the dielectric breakdown voltage. For example, second charging voltage Vhv2 is within a range of 4 kV to 9 kV. When second charging voltage Vhv2 is set for charger 11, only preionization electrode 19 discharges.

[0123] 2.2 Action

[0124] Next, the operation of the gas laser device 2 according to the first embodiment will be described. Figure 4 The flow of processing executed by the processor 14 in the first embodiment is shown.

[0125] First, in step S10, the processor 14 determines whether it has received an oscillation trigger signal transmitted from the exposure device controller 110. When the processor 14 determines that it has received an oscillation trigger signal (step S10: YES), the process proceeds to step S11.

[0126] In step S11, the processor 14 sets the first charging voltage Vhv1 to the charger 11, and after the charging capacitor C0 is charged, turns on the switch SW1 to discharge the pre-ionization electrode 19 and the main electrode 20. This generates corona discharge and main discharge.

[0127] After step S11, the processor 14 returns the process to step S10. The processor 14 repeatedly executes steps S10 and S11 until a negative determination is made in step S10.

[0128] When the processor 14 determines that the oscillation trigger signal has not been received (step S10 : NO), the process proceeds to step S12 (step S12 ).

[0129] In step S12, the processor 14 determines whether a predetermined time has passed since the last oscillation trigger signal was received. If the processor 14 determines that a predetermined time has passed since the last oscillation trigger signal was received (step S12: YES), the process proceeds to step S13.

[0130] In step S13 , the processor 14 sets the second charging voltage Vhv2 to the charger 11 , and after the charging capacitor C0 is charged, turns on the switch SW1 to discharge only the pre-ionization electrode 19 (step S13 ).

[0131] When the processor 14 determines that the predetermined time has not elapsed since the last reception of the oscillation trigger signal (step S12 : NO), the processing returns to step S10 .

[0132] In this manner, after the processor 14 executes the first discharge control for discharging the main electrode 20 and the pre-ionization electrode 19 based on an instruction from the exposure device 100, it executes the second discharge control for discharging only the pre-ionization electrode 19 after a predetermined time has elapsed. That is, the processor 14 does not generate the main discharge but only the corona discharge during the period when the pulsed laser light PL is not output.

[0133] When the processor 14 executes the above processing and the exposure apparatus 100 is in a rest state such as for maintenance, the exposure apparatus 100 does not send an oscillation trigger signal to the gas laser apparatus 2 , so that only the pre-ionization electrode 19 discharges.

[0134] Furthermore, when the gas laser device 2 repeatedly performs burst oscillation and stops burst oscillation, the preionization electrode 19 and the main electrode 20 discharge during the burst oscillation period, and only the preionization electrode 19 discharges during the stop period. Burst oscillation refers to the operation of the gas laser device 2 to output pulsed laser light PL at a fixed frequency in response to an oscillation trigger signal transmitted at a fixed frequency from the exposure device 100. The stop period is when the gas laser device 2 stops burst oscillation and is the interval between burst oscillation periods. During the burst oscillation period, the exposure device 100 irradiates the wafer with pulsed laser light PL supplied at a fixed frequency from the gas laser device 2 via the reticle. During the stop period, the wafer and reticle can be replaced in the exposure device 100.

[0135] 2.3 Effect

[0136] In this embodiment, the concentration of carbon fluoride in the laser gas increases by repeatedly generating the main discharge. However, during the period when pulsed laser light PL is not being emitted, only corona discharge is generated, producing UV light. During this period, the UV light and corona discharge decompose the carbon fluoride in the laser gas, thereby reducing the concentration of carbon fluoride in the laser gas. Therefore, according to this embodiment, the concentration of carbon fluoride in the laser gas can be reduced, suppressing the decrease in the pulse energy of the pulsed laser light PL output from the gas laser device 2.

[0137] 3. Second Implementation

[0138] 3.1 Structure

[0139] The gas laser device 2 according to the second embodiment of the present disclosure has the same configuration as the gas laser device 2 according to the first embodiment, except for the processing executed by the processor 14 and the configuration of the power supply device 30 .

[0140] Figure 5 The configuration of the power supply device 30 according to the second embodiment is schematically shown. In this embodiment, the power supply device 30 includes a switch SW2 in addition to the charger 11, the PPM 12, and the voltage dividing circuit 31.

[0141] The switch SW2 is connected between the charging capacitor C0 and the voltage dividing circuit 31. Specifically, the switch SW2 is connected between the connection point P1 and the connection point P2, wherein the connection point P1 is the connection point between the charger 11 and the charging capacitor C0, and the connection point P2 is the connection point between the capacitor C0 and the charging capacitor C1. 11 With capacitor C 12 In addition, the switch SW2 is an example of the "second switch" of the technology disclosed in this disclosure.

[0142] The switch SW2 is a semiconductor switching element such as an IGBT. The switch SW2 is turned on / off based on a control signal from the processor 14. The processor 14 controls the flow of current from the charging capacitor C0 to the capacitor C via the switch SW2. 12 The current I is turned on / off.

[0143] In this embodiment, the processor 14 controls switches SW1 and SW2 to execute a first discharge control for discharging the preionization electrode 19 and the main electrode 20, and a second discharge control for discharging only the preionization electrode 19. In this embodiment, the charging voltage Vhv set for the charger 11 is a value corresponding to the target pulse energy Et.

[0144] In this embodiment, as a first discharge control, processor 14 performs the following processing: After charging capacitor C0 is charged, processor 14 sets charging voltage Vhv to charger 11 and, while switch SW2 remains off, closes switch SW1. Charging voltage Vhv is a voltage equal to or higher than the dielectric breakdown voltage. This causes preionization electrode 19 and main electrode 20 to discharge.

[0145] In this embodiment, as the second discharge control, the processor 14 performs the following processing: after the charging capacitor C0 is charged, the switch SW2 is turned on while the switch SW1 is kept off. In the second discharge control, the switch SW2 is turned on, thereby charging the capacitor C0 and the capacitor C0. 12 As a result, the current I flows through the capacitor C 12 A voltage is applied to the pre-ionization electrode 19, and only the pre-ionization electrode 19 is discharged.

[0146] 3.2 Action

[0147] Next, the operation of the gas laser device 2 according to the second embodiment will be described. In this embodiment, the flow of the processing executed by the processor 14 is the same as that of the second embodiment. Figure 4 The flow of the processing shown is the same.

[0148] In this embodiment, in step S11, the processor 14 sets the charging voltage Vhv to the charger 11. After the charging capacitor C0 is charged, the processor 14 turns on the switch SW1 while keeping the switch SW2 off, thereby discharging the preionization electrode 19 and the main electrode 20. This generates the main discharge in conjunction with the corona discharge.

[0149] In step S13 , the processor 14 sets the charging voltage Vhv to the charger 11 , and after charging the charging capacitor C0 is charged, the processor 14 turns on the switch SW2 while keeping the switch SW1 off, thereby discharging only the preionization electrode 19 .

[0150] Figure 6 The simulation results of various voltages applied to the power supply device 30 of the second embodiment are shown. C0 Represents the voltage of the charging capacitor C0. V C12 Represents capacitor C 12 The voltage. V SW2 Indicates the voltage of the control signal applied from the processor 14 to the switch SW2.

[0151] In this simulation, the capacitance of the charging capacitor C0 is set to be larger than that of the capacitor C 12 The capacitance is large enough. In this case, Figure 6 As shown, V C12 In V C0 The fluctuation range is less than twice.

[0152] 3.3 Effect

[0153] According to this embodiment, similarly to the first embodiment, only corona discharge is generated during the period when the pulse laser light PL is not output to reduce the concentration of carbon fluoride in the laser gas. This can suppress a decrease in the pulse energy of the pulse laser light PL.

[0154] 4. Third Implementation

[0155] 4.1 Structure

[0156] The gas laser device 2 according to the third embodiment of the present disclosure has the same structure as the gas laser device 2 according to the second embodiment, except that the structure of the power supply device 30 is different.

[0157] Figure 7 The configuration of the power supply device 30 according to the third embodiment is schematically shown. In this embodiment, the power supply device 30 includes a transformer TC2 and a switch SW2 in addition to the charger 11, the PPM 12, and the voltage dividing circuit 31.

[0158] Transformer TC2 is connected between charging capacitor C0 and voltage divider circuit 31. Specifically, the primary side of transformer TC2 is connected to the aforementioned connection point P1, and the secondary side is connected to the aforementioned connection point P2. In this embodiment, transformer TC2 has an additive polarity. Transformer TC2 is an example of a "second transformer" in the disclosed technology.

[0159] In this embodiment, switch SW2 is connected to the primary side of transformer TC2. Switch SW2 is, for example, a semiconductor switching element such as an IGBT. Switch SW2 switches on and off based on a control signal from processor 14. Processor 14 controls the flow of current I1 from charging capacitor C0 to the primary side of transformer TC2 via switch SW2. Switch SW2 is an example of a "second switch" in the disclosed technology.

[0160] In this embodiment, since transformer TC2 has an additive polarity, when current I1 flows through the primary side of transformer TC2, current I2 flows in the reverse direction on the secondary side of transformer TC2. Alternatively, transformer TC2 may have a subtractive polarity.

[0161] In this embodiment, similar to the second embodiment, the processor 14 controls switches SW1 and SW2 to execute a first discharge control for discharging the preionization electrode 19 and the main electrode 20, and a second discharge control for discharging only the preionization electrode 19. In this embodiment, the charging voltage Vhv set for the charger 11 is a value corresponding to the target pulse energy Et.

[0162] 4.2 Action

[0163] Next, the operation of the gas laser device 3 according to the second embodiment will be described. In this embodiment, the flow of the processing executed by the processor 14 is the same as that of the second embodiment.

[0164] In this embodiment, in step S13, the processor 14 turns on the switch SW2 while keeping the switch SW1 off, thereby causing the current I1 to flow through the primary side of the transformer TC2 and the current I2 to flow through the secondary side. 12 A voltage is applied to the pre-ionization electrode 19, and only the pre-ionization electrode 19 discharges, thereby generating only corona discharge. The remaining operations of the gas laser device 2 of this embodiment are the same as those of the second embodiment.

[0165] Figure 8 The simulation results of various voltages applied to the power supply device 30 of the third embodiment are shown. C0 Represents the voltage of the charging capacitor C0. V C12 Represents capacitor C 12 The voltage. V SW2 Indicates the voltage of the control signal applied from the processor 14 to the switch SW2.

[0166] In this simulation, the capacitance of the charging capacitor C0 is set to be larger than that of the capacitor C 12 The capacitance is large enough. In this case, V C12 The absolute value of V C0In this simulation, N1 / N2=2 is set. In addition, in this simulation, since the transformer TC2 is set to add polarity, V C12 polarity reversal.

[0167] 4.3 Effect

[0168] According to this embodiment, similarly to the first embodiment, only corona discharge is generated during the period when the pulse laser light PL is not output to reduce the concentration of carbon fluoride in the laser gas. This can suppress a decrease in the pulse energy of the pulse laser light PL.

[0169] 5. Fourth Implementation

[0170] 5.1 Structure

[0171] The gas laser device 2 according to the fourth embodiment of the present disclosure has the same configuration as the gas laser device 2 according to the second embodiment, except for the processing executed by the processor 14 and the configuration of the power supply device 30 .

[0172] Figure 9 The configuration of a power supply device 30 according to a fourth embodiment is schematically shown. In this embodiment, the power supply device 30 includes a transformer TC2 and a full-bridge circuit 32 in addition to the charger 11 , the PPM 12 , and the voltage divider circuit 31 .

[0173] Transformer TC2 is provided between charging capacitor C0 and voltage divider circuit 31. Full-bridge circuit 32 is connected between charging capacitor C0 and the primary side of transformer TC2. Specifically, the primary side of transformer TC2 is connected to connection point P1 via full-bridge circuit 32, and the secondary side is connected to connection point P2. In this embodiment, transformer TC2 has a subtractive polarity. Transformer TC2 is an example of a "second transformer" in the disclosed technology.

[0174] Full-bridge circuit 32 is composed of switches SW2, SW3, SW4, and SW5, and can control the on / off and direction of the current flowing through the primary side of transformer TC2. Switches SW2, SW3, SW4, and SW5 are semiconductor switching elements such as IGBTs.

[0175] Switches SW2 and SW3 are connected in series between connection point P1 and ground. Switches SW4 and SW5 are connected in series between connection point P1 and ground. One end of the primary side of transformer TC2 is connected between switches SW2 and SW3. The other end of the primary side of transformer TC2 is connected between switches SW4 and SW5. Switches SW2 and SW5 are turned on and off based on a first control signal from processor 14. Switches SW3 and SW4 are turned on and off based on a second control signal from processor 14.

[0176] Processor 14 controls the on / off switching and direction of the current flowing from charging capacitor C0 to the primary side of transformer TC2 via full-bridge circuit 32. Specifically, processor 14 alternately turns on switches SW2 and SW5 and switches SW3 and SW4. This causes a forward current I1 and a reverse current I1r to flow alternately through the primary side of transformer TC2. Consequently, a forward current I2 and a reverse current I2r flow alternately through the secondary side of transformer TC2, alternating positive and negative voltages to be applied to preionization electrode 19.

[0177] In this embodiment, because transformer TC2 has a subtractive polarity, current I1 flowing through the primary side of transformer TC2 causes current I2 to flow in the same direction on the secondary side. Furthermore, current I1r flowing through the primary side of transformer TC2 causes current I2r to flow in the same direction on the secondary side. Alternatively, transformer TC2 may have an additive polarity.

[0178] In this embodiment, the processor 14 controls the switch SW1 and the full-bridge circuit 32 to execute, similar to the second embodiment, a first discharge control for discharging the preionization electrode 19 and the main electrode 20, and a second discharge control for discharging only the preionization electrode 19. In this embodiment, the charging voltage Vhv set for the charger 11 is a value corresponding to the target pulse energy Et.

[0179] 5.2 Action

[0180] Next, the operation of the gas laser device 4 according to the second embodiment will be described. In this embodiment, the flow of the processing executed by the processor 14 is the same as that of the second embodiment. Figure 4 The flow of the processing shown is the same.

[0181] In this embodiment, in step S11, processor 14 sets charging voltage Vhv to charger 11. After charging capacitor C0 is charged, processor 14 turns on switch SW1 while keeping all switches SW2, SW3, SW4, and SW5 of full-bridge circuit 32 open. This causes pre-ionization electrode 19 and main electrode 20 to discharge.

[0182] In step S13 , the processor 14 sets the charging voltage Vhv to the charger 11 , and after charging capacitor C0 is charged, the processor 14 turns on one of switches SW2 and SW5 and switches SW3 and SW4 while keeping switch SW1 off, thereby discharging only the preionization electrode 19 .

[0183] Furthermore, each time the processor 14 executes step S13, it turns on a different pair of switches SW2, SW5 and switches SW3, SW4 than the pair that was turned on last time. In other words, the processor 14 turns on switches SW2, SW5 and switches SW3, SW4 alternately. This alternately generates positive corona discharge and negative corona discharge.

[0184] Figure 10 The simulation results of various voltages applied to the power supply device 30 of the fourth embodiment are shown. C0 Represents the voltage of the charging capacitor C0. V C12 Represents capacitor C 12 The voltage. V SW25 V represents the voltage of the first control signal applied from the processor 14 to the switches SW2 and SW5. SW34 The voltage of the second control signal applied from the processor 14 to the switches SW3 and SW4 is shown.

[0185] In this simulation, the capacitance of the charging capacitor C0 is set to be larger than that of the capacitor C 12 The capacitance is large enough. In this case, V C12 The absolute value of V C0 The value of the output voltage should fluctuate within the range of 2×N1 / N2 times or less.

[0186] 5.3 Effect

[0187] According to this embodiment, similarly to the first embodiment, only corona discharge is generated during the period when the pulse laser light PL is not output to reduce the concentration of carbon fluoride in the laser gas. This can suppress a decrease in the pulse energy of the pulse laser light PL.

[0188] 6. Fifth Implementation

[0189] 6.1 Structure

[0190] The gas laser device 2 according to the fifth embodiment of the present disclosure has the same configuration as the gas laser device 2 according to the first embodiment, except for the processing executed by the processor 14 and the configuration of the power supply device 30 .

[0191] Figure 11 The structure of the power supply device 30 of the fifth embodiment is schematically shown. In this embodiment, the power supply device 30 includes the charger 11, the PPM 12, and a pulse power supply 33. In this embodiment, the voltage divider circuit 31 is not provided, and the pre-ionization electrode 19 is separated from the charger 11 and the PPM 12. The pulse power supply 33 is an example of a "second power supply" in the technology disclosed herein. In this embodiment, the PPM 12 supplies power to the main electrode 20, and the pulse power supply 33 supplies power to the pre-ionization electrode 19.

[0192] The pulse power supply 33 is connected to the preionization electrode 19. Specifically, the pulse power supply 33 is connected between the preionization outer electrode 19a and the preionization inner electrode 19c. The pulse power supply 33 is connected to the processor 14 and applies a pulse voltage to the preionization electrode 19 based on a control signal from the processor 14. For example, the pulse voltage is within a range of 3 kV to 8 kV.

[0193] In this embodiment, the processor 14 controls the charger 11 and the pulse power supply 33 to execute a first discharge control for discharging the pre-ionization electrode 19 and the main electrode 20 and a second discharge control for discharging only the pre-ionization electrode 19 .

[0194] 6.2 Action

[0195] Next, the operation of the gas laser device 5 according to the second embodiment will be described. In this embodiment, the flow of the processing executed by the processor 14 is the same as that of the second embodiment. Figure 4 The flow of the processing shown is the same.

[0196] In this embodiment, in step S11, the processor 14 sets the charging voltage Vhv for the charger 11, controls the pulse power supply 33 while keeping the switch SW1 off, and applies the pulse voltage to the pre-ionization electrode 19, thereby discharging the pre-ionization electrode 19. After the charging capacitor C0 is charged, the switch SW1 is turned on to discharge the main electrode 20.

[0197] Furthermore, in step S13 , the processor 14 controls the pulse power supply 33 while keeping the switch SW1 in the off state to apply a pulse voltage to the pre-ionization electrode 19 , thereby causing only the pre-ionization electrode 19 to discharge.

[0198] 6.3 Effect

[0199] According to this embodiment, similarly to the first embodiment, only corona discharge is generated during the period when the pulse laser light PL is not output to reduce the concentration of carbon fluoride in the laser gas. This can suppress a decrease in the pulse energy of the pulse laser light PL.

[0200] Furthermore, according to this embodiment, since the pulse power supply 33 is used independently of the charger 11, a pulse voltage can be directly applied to the preionization electrode 19 without using a capacitor for preionization. This improves the efficiency of corona discharge.

[0201] 7. Modifications

[0202] In the above embodiments, Figure 4As shown, the processor 14 executes the second discharge control when a predetermined time has elapsed after the first discharge control, based on an oscillation trigger signal transmitted from the exposure device 100. Alternatively, the processor 14 may execute the second discharge control when receiving a signal from the exposure device 100 indicating that the exposure device 100 is in a dormant state. Furthermore, the processor 14 may execute the second discharge control when receiving a signal from the exposure device 100 indicating that the burst oscillation is stopped.

[0203] In addition, in the above embodiments, Figure 4 As shown, after a predetermined period of time has elapsed, the processor 14 repeatedly executes the second discharge control unless an oscillation trigger signal is received from the exposure device 100. However, the number of times the second discharge control is executed may be limited. Specifically, when executing the second discharge control, the number of times the second discharge control is executed may be limited based on the number of times the first discharge control was executed immediately before. For example, the number of times the second discharge control is executed may be limited to a range of 0.001% to 1% of the number of times the first discharge control was executed immediately before before. For example, after the main discharge is executed 100,000 times, the corona discharge may be executed only 1 to 1,000 times.

[0204] 8. Method for manufacturing electronic devices

[0205] Figure 12 An example configuration of an exposure apparatus 100 is schematically shown. Exposure apparatus 100 includes an illumination system 104 and a projection system 106. Illumination system 104 illuminates the reticle pattern of a mask (not shown) positioned on reticle stage RT using pulsed laser light PL incident from, for example, a gas laser device 2. Projection system 106 reduces and projects the pulsed laser light PL transmitted through the reticle, forming an image on a workpiece (not shown) positioned on workpiece stage WT. The workpiece is a photosensitive substrate such as a semiconductor wafer coated with photoresist.

[0206] Exposure apparatus 100 synchronously moves reticle stage RT and workpiece stage WT in parallel, exposing a workpiece to pulsed laser light PL reflecting the reticle pattern. After the reticle pattern is transferred to a semiconductor wafer through the aforementioned exposure process, semiconductor devices can be manufactured through multiple steps. Semiconductor devices are an example of "electronic devices" in this disclosure.

[0207] Furthermore, the gas laser device 2 is not limited to the manufacture of electronic devices, but can also be used for laser processing such as hole drilling.

[0208] The above description is intended to be illustrative rather than limiting, and therefore, it will be apparent to those skilled in the art that modifications may be made to the various embodiments of the present disclosure without departing from the scope of the appended claims.

[0209] The terms used in this specification and the appended claims should be interpreted as "non-limiting" terms. For example, the terms "include" or "comprise" should be interpreted as "not limited to the parts recorded as included". The term "have" should be interpreted as "not limited to the parts recorded as having". In addition, the phrase "one" recorded in this specification and the appended claims should be interpreted as "at least one" or "one or more". In addition, the phrases "at least one of A, B and C" should be interpreted as "A", "B", "C", "A+B", "A+C", "B+C" or "A+B+C", and should also be interpreted to include combinations of them with contents other than "A", "B" and "C".

Claims

1. A gas laser device, wherein: The gas laser device comprises: a laser chamber in which laser gas containing fluorine gas is sealed; a main electrode disposed inside the laser chamber; a pre-ionization electrode, which is disposed inside the laser chamber; a power supply device for supplying power to the main electrode and the pre-ionization electrode; as well as A processor controls the power supply device to execute a first discharge control for discharging the pre-ionization electrode and the main electrode, and a second discharge control for discharging only the pre-ionization electrode without discharging the main electrode.

2. The gas laser device according to claim 1, wherein The processor executes the second discharge control when a predetermined time has elapsed after executing the first discharge control based on an instruction from the exposure device.

3. The gas laser device according to claim 1, wherein The processor executes the second discharge control when the exposure device is in a dormant state.

4. The gas laser device according to claim 1, wherein The processor executes the second discharge control during a period during which the burst oscillation is stopped.

5. The gas laser device according to claim 1, wherein The power supply device includes: a first power source; and a power generation circuit including a charging capacitor charged by the first power source. The power generation circuit supplies power to the main electrode and the pre-ionization electrode.

6. The gas laser device according to claim 5, wherein: The processor executes the first discharge control and the second discharge control by changing a charge voltage of the charging capacitor.

7. The gas laser device according to claim 6, wherein: The processor sets a first charging voltage for the first power supply when executing the first discharge control, and sets a second charging voltage lower than the first charging voltage for the first power supply when executing the second discharge control.

8. The gas laser device according to claim 7, wherein: The first charging voltage is above 10 kV, The second charging voltage is within a range of 4 kV to 9 kV.

9. The gas laser device according to claim 5, wherein The power generation circuit includes: a first transformer; a first switch provided between the primary side of the first transformer and the charging capacitor; a magnetic pulse compression circuit provided on the secondary side of the first transformer; and a peak capacitor connected to the magnetic pulse compression circuit. The main electrode is connected in parallel with the peak capacitor, The pre-ionization electrode is connected to the peak capacitor via a voltage divider circuit.

10. The gas laser device according to claim 9, wherein The power supply device further includes a second switch connected between the charging capacitor and the voltage dividing circuit. The processor performs the first discharge control and the second discharge control by controlling the first switch and the second switch.

11. The gas laser device according to claim 9, wherein The power supply device further includes: a second transformer connected between the charging capacitor and the voltage dividing circuit; and a second switch connected to the primary side of the second transformer. The processor performs the first discharge control and the second discharge control by controlling the first switch and the second switch.

12. The gas laser device according to claim 9, wherein The power supply device further includes: a second transformer provided between the charging capacitor and the voltage dividing circuit; and a full-bridge circuit connected between the charging capacitor and the primary side of the second transformer. The processor performs the first discharge control and the second discharge control by controlling the first switch and the full-bridge circuit.

13. The gas laser device according to claim 1, wherein The power supply device includes: a first power supply; a power generation circuit including a charging capacitor charged by the first power supply; and a second power supply. The power generation circuit supplies electric power to the main electrode, The second power supply supplies power to the pre-ionization electrode.

14. The gas laser device according to claim 13, wherein The second power supply applies a pulse voltage to the pre-ionization electrode.

15. The gas laser device according to claim 1, wherein The number of times the processor executes the second discharge control is within a range of 0.001% to 1% of the number of times the processor executes the first discharge control.

16. A method for manufacturing an electronic device, wherein: The manufacturing method of the electronic device comprises the following steps: generating laser light by a gas laser device; outputting the laser light to an exposure device; and exposing the laser light on a photosensitive substrate in the exposure device to manufacture an electronic device, The gas laser device comprises: a laser chamber in which laser gas containing fluorine gas is sealed; a main electrode disposed inside the laser chamber; a pre-ionization electrode, which is disposed inside the laser chamber; a power supply device for supplying power to the main electrode and the pre-ionization electrode; as well as A processor controls the power supply device to execute a first discharge control for discharging the pre-ionization electrode and the main electrode, and a second discharge control for discharging only the pre-ionization electrode without discharging the main electrode.

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