Extreme ultraviolet light generating apparatus and method for manufacturing electronic devices

Abstract

To provide an extreme ultraviolet light generation device capable of emitting laser light which can satisfy performance which is required by an exposure device and an inspection device, and capable of suppressing reduction of reliability of an EUV light generation device.SOLUTION: An extreme ultraviolet light generation device comprises: a target supply part; a target passage detector; a delay circuit; a laser device; a target image imaging device; and a processor. The processor controls a vibration application element so that an interval between adjacent droplet targets becomes irregular, and identifies the droplet target in which a standard deviation of a distance from a second detection position to a droplet target is a first threshold or lower, from a plurality of pieces of image data, and sets a delay time, on the basis of the distance from the identified droplet target to the second detection position, the droplet target being identified so that the identified droplet target is arranged at the second detection position.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to an extreme ultraviolet light generating device and a method for manufacturing an electronic device.

Background Art

[0002] In recent years, with the miniaturization of semiconductor processes, the miniaturization of transfer patterns in optical lithography of semiconductor processes has been rapidly progressing. In the next generation, microfabrication of 10 nm or less will be required. For this reason, the development of a semiconductor exposure device that combines a device for generating extreme ultraviolet (EUV: Extreme UltraViolet) light with a wavelength of about 13 nm and a reduction projection reflection optical system has been expected.

[0003] As an EUV light generating device, the development of a Laser Produced Plasma (LPP) type device that uses plasma generated by irradiating a target material with laser light has been progressing.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

[0005] An extreme ultraviolet light generating apparatus according to one aspect of the present disclosure includes a target supply unit including a tank for storing a target substance, a pressure regulator for adjusting the pressure inside the tank, a nozzle for discharging the target substance from the tank, and an excitation element for generating droplet targets of the target substance by vibrating the target substance discharged from the nozzle; a target passage detection device for detecting the passage of the droplet targets supplied from the target supply unit into the chamber to a first detection position and outputting a passage timing signal each time detection occurs; a delay circuit that receives the passage timing signal and outputs a light emission trigger signal and an imaging trigger signal at a timing delayed by a predetermined delay time from the time the passage timing signal is input; and each time the light emission trigger signal is input, the droplet targets move beyond the first detection position. The system comprises a laser device that generates extreme ultraviolet light by irradiating a droplet target with laser light at a second detection position downstream in the direction; a target image acquisition device that, each time an imaging trigger signal is input, images droplet targets located within a region including the second detection position and generates image data of the region and the droplet targets located within the region; and a processor. The processor may control the excitation elements so that the spacing between adjacent droplet targets is irregular, identify droplet targets for which the standard deviation of the distance from the second detection position to the droplet target is less than or equal to a first threshold, and set a delay time based on the distance from the identified droplet target to the second detection position so that the identified droplet target is located at the second detection position.

[0006] Furthermore, a method for manufacturing an electronic device according to one aspect of the present disclosure includes a target supply unit including a tank for storing a target substance, a pressure regulator for adjusting the pressure inside the tank, a nozzle for discharging the target substance from the tank, and an excitation element for generating a droplet target of the target substance by vibrating the target substance discharged from the nozzle; a target passage detection device that detects the passage of the droplet target supplied from the target supply unit into the chamber at a first detection position and outputs a passage timing signal each time detection occurs; a delay circuit that receives the passage timing signal and outputs a light emission trigger signal and an imaging trigger signal at a timing delayed by a predetermined delay time from the time the passage timing signal is input; and each time the light emission trigger signal is input, a laser beam is irradiated onto the droplet target at a second detection position downstream of the first detection position in the direction of travel of the droplet target. The system includes a laser device that generates extreme ultraviolet light, a target image acquisition device that, each time an imaging trigger signal is input, images droplet targets located within a region including a second detection position and generates image data of the region and the droplet targets located within the region, and a processor, wherein the processor controls an excitation element so that the spacing between adjacent droplet targets is irregular, identifies droplet targets whose standard deviation of the distance from the second detection position to the droplet target is less than or equal to a first threshold, sets a delay time based on the distance from the identified droplet target to the second detection position so that the identified droplet target is located at the second detection position, outputs the extreme ultraviolet light generated by the extreme ultraviolet light generator to an exposure apparatus, and may include exposing a photosensitive substrate to extreme ultraviolet light in the exposure apparatus in order to manufacture an electronic device.

[0007] Furthermore, a method for manufacturing an electronic device according to another aspect of the present disclosure includes a target supply unit including a tank for storing a target substance, a pressure regulator for adjusting the pressure inside the tank, a nozzle for discharging the target substance from the tank, and an excitation element for vibrating the target substance discharged from the nozzle to generate a droplet target of the target substance; a target passage detection device for detecting the passage of the droplet target supplied from the target supply unit into the chamber at a first detection position and outputting a passage timing signal each time detection occurs; a delay circuit that receives the passage timing signal and outputs a light emission trigger signal and an imaging trigger signal at a timing delayed by a predetermined delay time from the time the passage timing signal is input; and, each time the light emission trigger signal is input, irradiating the droplet target with laser light at a second detection position downstream of the first detection position in the direction of travel of the droplet target to generate extreme ultraviolet light. The system includes a laser device, a target image acquisition device that, each time an imaging trigger signal is input, images droplet targets located within a region including a second detection position and generates image data of the region and the droplet targets located within the region, and a processor, wherein the processor controls an excitation element so that the spacing between adjacent droplet targets is irregular, identifies droplet targets whose standard deviation of the distance from the second detection position to the droplet target is less than or equal to a first threshold, sets a delay time based on the distance from the identified droplet target to the second detection position so that the identified droplet target is located at the second detection position, irradiates a mask with extreme ultraviolet light generated by an extreme ultraviolet light generator to inspect the mask for defects, selects a mask using the inspection results, and exposes and transfers the pattern formed on the selected mask onto a photosensitive substrate. [Brief explanation of the drawing]

[0008] Some embodiments of this disclosure are described below, merely as examples, with reference to the accompanying drawings. [Figure 1] Figure 1 is a schematic diagram showing an example of the overall configuration of an electronic device manufacturing apparatus. [Figure 2]Figure 2 is a schematic diagram showing an example of the overall configuration of an electronic device manufacturing apparatus, different from the one shown in Figure 1. [Figure 3] Figure 3 is a schematic diagram showing an example of the overall configuration of a comparative example of an extreme ultraviolet light generation device. [Figure 4] Figure 4 illustrates the target passage detection device and target image acquisition device of the comparative example extreme ultraviolet light generation device. [Figure 5] Figure 5 shows an example of a control flowchart for a comparative example processor. [Figure 6] Figure 6 is a timing chart of the control flowchart shown in Figure 5. [Figure 7] Figure 7 shows a portion of the control flowchart of the processor in Embodiment 1. [Figure 8] Figure 8 shows another part of the control flowchart of Embodiment 1. [Figure 9] Figure 9 shows another part of the control flowchart of Embodiment 1. [Figure 10] Figure 10 shows the remaining portion of the control flowchart for Embodiment 1. [Figure 11] Figure 11 shows a portion of the control flowchart for setting the delay time in Embodiment 1. [Figure 12] Figure 12 shows another part of the control flowchart for the delay time setting process in Embodiment 1. [Figure 13] Figure 13 shows the remaining portion of the control flowchart for the delay time setting process in Embodiment 1. [Figure 14] Figure 14 is a control flowchart for the fine-tuning process of the delay time. [Figure 15] Figure 15 shows a portion of the control flowchart of the processor in Embodiment 2. [Figure 16] Figure 16 is a portion of the control flowchart for setting the delay time in Embodiment 2. [Figure 17]FIG. 17 is another part of the control flowchart in the delay time setting process of Embodiment 2. [Figure 18] FIG. 18 is the remaining part of the control flowchart in the delay time setting process of Embodiment 2. [Figure 19] FIG. 19 is a diagram showing a part of the control flowchart of the processor in Embodiment 3. [Figure 20] FIG. 20 is a part of the control flowchart in the delay time setting process of Embodiment 3. [Figure 21] FIG. 21 is another part of the control flowchart in the delay time setting process of Embodiment 3. [Figure 22] FIG. 22 is a diagram for explaining the allocation in step SP143. [Figure 23] FIG. 23 is the remaining part of the control flowchart in the delay time setting process of Embodiment 3. Embodiment

[0009] 1. Overview 2. Description of the manufacturing apparatus for electronic devices 3. Description of the extreme ultraviolet light generation apparatus of the comparative example 3.1 Configuration 3.2 Operation 3.3 Problems 4. Description of the extreme ultraviolet light generation apparatus of Embodiment 1 4.1 Configuration 4.2 Operation 4.3 Function and Effect 5. Description of the extreme ultraviolet light generation apparatus of Embodiment 2 5.1 Configuration 5.2 Operation 5.3 Function and Effect 6. Description of the extreme ultraviolet light generation apparatus of Embodiment 3 6.1 Configuration 6.2 Operation 6.3 Function and Effect

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The embodiments described below are examples of the disclosure and are not intended to limit the scope of this disclosure. Not all configurations and operations described in each embodiment are necessarily essential to the configurations and operations of the disclosure. The same reference numerals are used for identical components, and redundant descriptions are omitted.

[0011] 1. Overview Embodiments of this disclosure relate to an extreme ultraviolet (EUV) light generation apparatus that generates light of a wavelength called EUV, and an electronic device manufacturing apparatus. In the following, extreme ultraviolet light may be referred to as EUV light.

[0012] 2. Description of manufacturing equipment for electronic devices Figure 1 is a schematic diagram showing an example of the overall configuration of an electronic device manufacturing apparatus. The electronic device manufacturing apparatus shown in Figure 1 includes an EUV light generator 100 and an exposure apparatus 200. The exposure apparatus 200 includes a mask irradiation unit 210 which includes a plurality of mirrors 211, 212 which are reflective optical systems, and a workpiece irradiation unit 220 which includes a plurality of mirrors 221, 222 which are reflective optical systems separate from those of the mask irradiation unit 210. The mask irradiation unit 210 illuminates the mask pattern on the mask table MT via the mirrors 211, 212 with EUV light 101 incident from the EUV light generator 100. The workpiece irradiation unit 220 images the EUV light 101 reflected by the mask table MT onto a workpiece (not shown) placed on the workpiece table WT via the mirrors 221, 222. The workpiece is a photosensitive substrate such as a semiconductor wafer coated with photoresist. The exposure apparatus 200 exposes the workpiece to EUV light 101 reflecting the mask pattern by synchronously moving the mask table MT and the workpiece table WT in parallel. By transferring the device pattern to the semiconductor wafer through this exposure process, a semiconductor device can be manufactured.

[0013] Figure 2 is a schematic diagram showing an overall schematic configuration example of an inspection device 300 connected to an EUV light generator 100. The inspection device 300 includes an illumination optical system 310, which is a reflective optical system and includes a plurality of mirrors 311, 313, 315, and a detection optical system 320, which is a separate reflective optical system from the illumination optical system 310 and includes a plurality of mirrors 321, 323 and a detector 325. The illumination optical system 310 reflects the EUV light 101 incident from the EUV light generator 100 using the mirrors 311, 313, 315 to illuminate a mask 333 placed on a mask stage 331. The mask 333 includes mask blanks before a pattern is formed. The detection optical system 320 reflects the EUV light 101 reflecting the pattern from the mask 333 using the mirrors 321, 323 to form an image on the light-receiving surface of the detector 325. The detector 325, which receives the EUV light 101, acquires an image of the mask 333. The detector 325 is, for example, a TDI (Time Delay Integration) camera. The image of the mask 333 acquired through the above process is used to inspect for defects in the mask 333, and the results of the inspection are used to select a mask suitable for manufacturing an electronic device. Then, the pattern formed on the selected mask is exposed and transferred onto a photosensitive substrate using the exposure apparatus 200 to manufacture the electronic device.

[0014] 3. Description of the comparative example extreme ultraviolet light generator 3.1 Configuration A comparative example of the EUV light generation apparatus 100 will now be described. Note that the comparative examples in this disclosure are forms that the applicant recognizes as being known only to the applicant, and are not publicly known examples acknowledged by the applicant. Furthermore, the following description will use an EUV light generation apparatus 100 that emits EUV light 101 toward an exposure apparatus 200 as an external device, as shown in Figure 1. Note that similar effects and benefits can be obtained with an EUV light generation apparatus 100 that emits EUV light 101 toward an inspection apparatus 300 as an external device, as shown in Figure 2.

[0015] Figure 3 is a schematic diagram showing an example of the overall configuration of the EUV light generator 100 in this example. As shown in Figure 3, the EUV light generator 100 mainly includes a chamber 10, a laser device LD, a laser light delivery optical system 30, a processor 121, and a delay circuit 122.

[0016] Chamber 10 is a sealable container. Chamber 10 includes an inner wall 10b enclosing an internal space with a low-pressure atmosphere. Chamber 10 also includes a sub-chamber 15. A target supply unit 40 is mounted in the sub-chamber 15 so as to penetrate the wall of the sub-chamber 15. The target supply unit 40 includes a tank 41, a nozzle 42, and a pressure regulator 43, and supplies droplet targets DL to the internal space of Chamber 10. Droplet targets DL may be abbreviated as droplets or targets.

[0017] Tank 41 stores a target substance, which will become a droplet target DL, inside. The target substance contains tin. The inside of Tank 41 is in communication with a pressure regulator 43 that maintains a constant pressure inside Tank 41. A heater 44 and a temperature sensor 45 are attached to Tank 41. The heater 44 heats Tank 41 with an electric current supplied from a heater power supply 46. This heating melts the target substance inside Tank 41. The temperature sensor 45 measures the temperature of the target substance inside Tank 41 via Tank 41. The pressure regulator 43, temperature sensor 45, and heater power supply 46 are electrically connected to a processor 121.

[0018] The nozzle 42 is attached to the tank 41 and discharges the target substance. The nozzle 42 is fitted with a piezoelectric element 47, which is an excitation element. The piezoelectric element 47 is electrically connected to a piezoelectric power supply 48 and is driven by the voltage applied from the piezoelectric power supply 48. The piezoelectric power supply 48 is electrically connected to the processor 121. The piezoelectric element 47 vibrates the target substance discharged from the nozzle 42, generating a droplet target DL of the target substance.

[0019] The chamber 10 includes a target recovery unit 14. The target recovery unit 14 is a box-shaped body attached to the inner wall 10b of the chamber 10 and communicates with the internal space of the chamber 10 through an opening 10a provided in the inner wall 10b of the chamber 10. The opening 10a is located directly below the nozzle 42, and the target recovery unit 14 is a drain tank that recovers unwanted droplet targets DL that pass through the opening 10a and reach the target recovery unit 14.

[0020] At least one through-hole is provided in the inner wall 10b of the chamber 10. This through-hole is blocked by a window 12, and pulsed laser light 90 emitted from the laser device LD passes through the window 12.

[0021] Furthermore, a laser focusing optical system 13 is arranged in the internal space of the chamber 10. The laser focusing optical system 13 includes a laser beam focusing mirror 13A and a high-reflection mirror 13B. The laser beam focusing mirror 13A reflects and focuses the laser beam 90 that passes through the window 12. The high-reflection mirror 13B reflects the laser beam 90 that is focused by the laser beam focusing mirror 13A. The positions of the laser beam focusing mirror 13A and the high-reflection mirror 13B are adjusted by the laser beam manipulator 13C so that the focusing position of the laser beam 90 in the internal space of the chamber 10 is a position specified by the processor 121. This focusing position is adjusted to be located directly below the nozzle 42, and when the laser beam 90 irradiates the target material at this focusing position, plasma is generated by the irradiation, and EUV light 101 is generated from the plasma. The region where plasma is generated is sometimes called the plasma generation region AR.

[0022] An EUV light focusing mirror 75, including, for example, a spheroidal reflecting surface 75a, is arranged in the internal space of the chamber 10. The reflecting surface 75a reflects EUV light 101 emitted from the plasma in the plasma generation region AR. The reflecting surface 75a has a first focal point and a second focal point. The reflecting surface 75a may be arranged such that, for example, the first focal point is located in the plasma generation region AR and the second focal point is located in the intermediate focal point IF. In Figure 3, a straight line passing through the first and second focal points is shown as the focal line La. The focal line La is along the central axis of the reflecting surface 75a.

[0023] Furthermore, the EUV light generator 100 includes a connecting section 19 that connects the internal space of the chamber 10 and the internal space of the exposure apparatus 200. Inside the connecting section 19, there is a wall with an aperture formed therein. Preferably, this wall is positioned so that the aperture is located at the second focal point. The connecting section 19 is the outlet for the EUV light 101 in the EUV light generator 100, and the EUV light 101 is emitted from the connecting section 19 and incident on the exposure apparatus 200.

[0024] The EUV light generator 100 also includes a pressure sensor 26. The pressure sensor 26 is mounted in the chamber 10 and electrically connected to the processor 121. The pressure sensor 26 measures the pressure in the internal space of the chamber 10 and outputs a signal indicating this pressure to the processor 121.

[0025] The processor 121 of this disclosure is a processing unit that includes a storage device storing a control program and a CPU (Central Processing Unit) that executes the control program. The processor 121 is specially configured or programmed to perform various processes included in this disclosure and controls the entire EUV light generation apparatus 100. The processor 121 receives signals related to the pressure in the internal space of the chamber 10 measured by the pressure sensor 26, and burst signals from the exposure apparatus 200 that instruct burst operation, etc. The processor 121 processes the above various signals and may control, for example, the timing of ejection of the droplet target DL, the ejection direction of the droplet target DL, etc. The processor 121 may also control the emission timing of the laser apparatus LD, the direction of propagation of the laser beam 90, the focusing position, etc. The various controls described above are merely examples, and other controls may be added as needed, as described later.

[0026] In this example, the processor 121 is electrically connected to the laser device LD via a delay circuit 122. The delay circuit 122 receives a pass timing signal from a target pass detection device (described later) via the processor 121. The delay circuit 122 outputs a light emission trigger signal to the laser device LD at a timing delayed by a predetermined delay time from the time the pass timing signal is input.

[0027] The laser device LD emits laser light 90 when a light emission trigger signal is input. Such a laser device LD includes a master oscillator, which is a burst-operating light source. The master oscillator emits pulsed laser light 90 when burst-on. The master oscillator is a laser device that emits laser light 90 by exciting a gas, such as helium or nitrogen mixed in carbon dioxide, by discharge. Alternatively, the master oscillator may be a quantum cascade laser device. The master oscillator may also emit pulsed laser light 90 using a Q-switching method. Furthermore, the master oscillator may include an optical switch or a polarizer. Burst operation refers to the operation in which continuous pulsed laser light 90 is emitted at a predetermined repetition frequency when burst-on, and the emission of laser light 90 is suppressed when burst-off.

[0028] The direction of propagation of the laser beam 90 emitted from the laser device LD is adjusted by the laser beam delivery optical system 30. The laser beam delivery optical system 30 includes a plurality of mirrors 31, 32 that adjust the direction of propagation of the laser beam 90. The position of at least one of the mirrors 31, 32 is adjusted by an actuator (not shown). By adjusting the position of at least one of the mirrors 31, 32, the laser beam 90 can be properly propagated from the window 12 into the internal space of the chamber 10.

[0029] Chamber 10 is equipped with a central gas supply unit 81 that supplies etching gas to the internal space of Chamber 10. As described above, since the target material contains tin, the etching gas is a hydrogen-containing gas that can be considered to have a hydrogen gas concentration of 100%, for example. Alternatively, the etching gas may be a balance gas with a hydrogen gas concentration of about 3%, for example. The balance gas contains nitrogen (N2) gas and argon (Ar) gas. When the target material constituting the droplet target DL is irradiated with the main pulse laser light MPL in the plasma generation region AR and turned into plasma, tin nanoparticles and charged tin particles are generated. The tin constituting these nanoparticles and charged particles reacts with hydrogen contained in the etching gas supplied to the internal space of Chamber 10. When tin reacts with hydrogen, it becomes stannane (SnH4), which is a gas at room temperature.

[0030] The central gas supply unit 81 has a frustoconical shape and is inserted through a through-hole 75c formed in the center of the EUV light focusing mirror 75. The central gas supply unit 81 is sometimes called a cone. The central gas supply unit 81 also includes a central gas supply port 81a, which is a nozzle. The central gas supply port 81a is located on the focal line La of the reflective surface 75a. The central gas supply port 81a supplies etching gas from the center of the reflective surface 75a toward the plasma generation region AR. Preferably, the etching gas is supplied from the central gas supply port 81a along the focal line La, from the center of the reflective surface 75a toward the reflective surface 75a. The central gas supply port 81a is connected to a gas supply device (not shown), which is a tank, via piping (not shown) of the central gas supply unit 81, and etching gas is supplied from the gas supply device. The gas supply device is controlled by the processor 121. A supply gas flow rate control unit, which is a valve, may be located in the piping (not shown).

[0031] The central gas supply port 81a is a gas supply port that supplies etching gas to the internal space of the chamber 10, and also an outlet through which the laser beam 90 is emitted into the internal space of the chamber 10. The laser beam 90 travels through the window 12 and the central gas supply port 81a towards the internal space of the chamber 10.

[0032] An exhaust port 10E is provided in the inner wall 10b of the chamber 10. Since the exposure apparatus 200 is positioned on the focal line La, the exhaust port 10E is provided in the inner wall 10b to the side of the focal line La. The direction along the central axis of the exhaust port 10E is, for example, perpendicular to the focal line La. Also, when viewed from a direction perpendicular to the focal line La, the exhaust port 10E is provided on the opposite side from the reflective surface 75a with respect to the plasma generation region AR. The exhaust port 10E exhausts the gas from the internal space of the chamber 10. The exhaust port 10E is connected to the exhaust pipe 10P, and the exhaust pipe 10P is connected to the exhaust pump 60.

[0033] As described above, when the target material is plasma-generated in the plasma generation region AR, residual gas is generated in the internal space of the chamber 10 as exhaust gas. The residual gas contains tin fine particles and charged particles produced by the plasma generation of the target material, stannans formed when these react with the etching gas, and unreacted etching gas. Some of the charged particles are neutralized in the internal space of the chamber 10, and these neutralized charged particles are also included in the residual gas. The residual gas is drawn into the exhaust pump 60 via the exhaust port 10E and the exhaust pipe 10P.

[0034] Figure 4 illustrates the target passage detection device and target image acquisition device provided in the chamber 10 of the EUV light generation apparatus 100 in this example. In Figure 4, some of the components, such as the EUV light focusing mirror 75 shown in Figure 3, are omitted from the illustration. Hereafter, the target passage detection device may simply be referred to as the detection device 400, and the target image acquisition device as the imaging device 500.

[0035] The detection device 400 is positioned upstream of the imaging device 500 in the direction of travel of the droplet target DL. The detection device 400 detects the passage of the droplet target DL, and the imaging device 500 images the droplet target DL.

[0036] The detection device 400 includes an illumination unit 410 and a detection unit 420. The illumination unit 410 is positioned on the opposite side of the detection unit 420 with respect to the trajectory of the droplet target DL. The direction in which the illumination unit 410 and the detection unit 420 are aligned is perpendicular to the trajectory, but may be non-perpendicular to the trajectory. The illumination unit 410 and the detection unit 420 are attached to the inner wall 10b on the outside of the chamber 10, with the illumination unit 410 positioned coaxially with a window 731a provided on the inner wall 10b, and the detection unit 420 positioned coaxially with the window 731a provided on the inner wall 10b.

[0037] The illumination unit 410 includes a container 411 and a light source 413 and illumination optical system 415 housed in the container 411. The light source 413 is electrically connected to a processor 121, which controls the timing of the emission of light 92 emitted from the light source 413. The light source 413 may be, for example, a light source that emits monochromatic laser light, or a flash lamp that emits light containing multiple wavelengths. The illumination optical system 415 includes a focusing lens and focuses the light 92 onto the trajectory of the droplet target DL via a window 731a.

[0038] The detection unit 420 includes a container 421 and a light-receiving optical system 423 and a light sensor 425 housed in the container 421. The light-receiving optical system 423 includes a lens that transfers the image of the illuminated droplet target DL onto the light sensor 425. The light sensor 425 is, for example, a photodiode. When the droplet target DL blocks the light 92, the amount of light 92 received by the light sensor 425 fluctuates. Based on this fluctuation, the light sensor 425 generates a pass timing signal to indicate the passage of the droplet target DL and outputs it to the processor 121. Hereinafter, the detection position of the detection device 400 relative to the droplet target DL may be referred to as the first detection position P1. The first detection position P1 is located between the illumination unit 410 and the detection unit 420 of the detection device 400 and is the point of focus of the light 92 from the illumination unit 410 on the trajectory of the droplet target DL.

[0039] The imaging device 500 includes an illumination unit 510 and an imaging unit 520. The illumination unit 510 is positioned on the opposite side of the imaging unit 520 with respect to the trajectory of the droplet target DL. The direction in which the illumination unit 510 and the imaging unit 520 are aligned is perpendicular to the trajectory, but may be non-perpendicular to the trajectory. The illumination unit 510 and the imaging unit 520 are attached to the inner wall 10b on the outside of the chamber 10, with the illumination unit 510 positioned coaxially with a window 731c provided on the inner wall 10b, and the imaging unit 520 positioned coaxially with a window 731d provided on the inner wall 10b.

[0040] The illumination unit 510 includes a container 521 and a light source 513 and illumination optical system 515 housed in the container 521. The light source 513 is electrically connected to a processor 121, which controls the timing of the emission of light 94 from the light source 513 to the droplet target DL in the plasma generation region AR. The light source 513 is, for example, a flash lamp that emits light containing multiple wavelengths. The illumination optical system 515 includes a collimating lens.

[0041] The imaging unit 520 includes a container 521, an imaging optical system 523 housed in the container 521, a shutter 525, and an imaging main unit 527. The imaging optical system 523 includes a first lens and a second lens. The shutter 525 is electrically connected to a delay circuit 122. The imaging main unit 527 is, for example, a CCD (Charge-Coupled Device) and is electrically connected to a processor 121 and a delay circuit 122. When the processor 121 receives a pass-through timing signal from the detection device 400, it outputs an imaging trigger signal to the shutter 525 and the imaging main unit 527 via the delay circuit 122, delayed by a predetermined time from the input of the pass-through timing signal. Hereinafter, the imaging trigger signal for the shutter 525 may be referred to as the shutter trigger signal, and the imaging trigger signal for the imaging main unit 527 may be referred to as the imaging trigger signal. When the shutter 525 receives the shutter trigger signal from the delay circuit 122, it opens for a very short time and then closes. The imaging unit 527 receives an imaging trigger signal from the delay circuit 122 and receives light 94 while the shutter 525 is open. The imaging unit 527 then images the droplet target DL to generate image data and outputs the image data as an electrical signal to the processor 121. In the following, the detection position of the imaging device 500 relative to the droplet target DL may be referred to as the second detection position P2. The second detection position P2 is located downstream of the first detection position P1 in the direction of travel of the droplet target DL, within the plasma generation region AR, and within the illumination area of ​​light 92 from the illumination unit 510 on the trajectory of the droplet target DL.

[0042] In the following explanation, the direction along the trajectory of the droplet target DL may be referred to as the Y direction, the direction in which the illumination unit 410 and the detection unit 420 are aligned and perpendicular to the Y direction as the X direction, and the direction perpendicular to both the Y and X directions as the Z direction. Note that the X direction is also the direction in which the illumination unit 510 and the imaging unit 520 are aligned.

[0043] 3.2 Operation Next, the operation of the comparative example processor 121 will be described. Figure 5 shows an example of a control flowchart for the comparative example processor 121. This control flow includes steps SP11 to SP16. In the initial state shown in Figure 3, the processor 121 receives a drive instruction signal for the target supply unit 40 from the exposure processor of the exposure apparatus 200. Also in the initial state, the processor 121 emits light 92 from the illumination unit 410 and light 94 from the illumination unit 510.

[0044] (Step SP11) In this step, the processor 121 supplies current from the heater power supply 46 to the heater 44 to heat and maintain the target substance in the tank 41 at a predetermined temperature above its melting point, thereby raising the temperature of the heater 44. At this time, the processor 121 adjusts the value of the current supplied from the heater power supply 46 to the heater 44 based on the output from the temperature sensor 45, thereby controlling the temperature of the target substance to the predetermined temperature. The predetermined temperature is, in the case of tin, a temperature above the melting point of tin, 231.93°C, for example, between 240°C and 290°C. Thus, preparation for ejecting the droplet target DL is complete.

[0045] Once preparation is complete, the processor 121 adjusts the pressure in the tank 41 by supplying inert gas from a gas supply source (not shown) via a pressure regulator 43 so that the molten target material is discharged from the nozzle hole of the nozzle 42 at a predetermined rate. Under this pressure, the target material is discharged from the nozzle hole of the nozzle 42 into the chamber 10. The target material discharged from the nozzle hole may take the form of a jet. At this time, the processor 121 applies a voltage of a predetermined waveform from the piezoelectric power supply 48 to the piezoelectric element 47 in order to generate a droplet target DL. The piezoelectric power supply 48 applies a voltage such that the waveform of the voltage value is, for example, sinusoidal, square, or sawtooth. As a result, the piezoelectric element 47 vibrates at a predetermined frequency. The vibration of the piezoelectric element 47 can propagate through the nozzle 42 to the target material discharged from the nozzle hole of the nozzle 42. The target material is divided at a predetermined period by this vibration, becoming droplet targets DL, and the spacing between adjacent droplet targets DL becomes approximately constant. Hereafter, droplet targets DL with approximately constant spacing between adjacent droplet targets DL may be referred to as coupled droplet targets DL. Therefore, in this step, the processor 121 drives the piezoelectric element 47 to generate and eject coupled droplet targets DL. The diameter of the droplet targets DL is approximately 20 μm or less. Once the processor 121 ejects the droplet targets DL, it proceeds the control flow to step SP12. Note that all droplet targets DL in each of the following steps in this example are coupled droplet targets DL.

[0046] Prior to step SP12, the droplet target DL discharged from the target supply unit 40 moves to the target retrieval unit 14. During this process, the droplet target DL passes through the first detection position P1 of the detection device 400 relative to the droplet target DL, and the second detection position P2 of the imaging device 500 relative to the droplet target DL, i.e., the plasma generation region AR.

[0047] When the droplet target DL passes the first detection position P1, the droplet target DL blocks the light 92 from the light source 413 of the detection device 400. This causes the amount of light received by the light sensor 425 of the detection device 400 to fluctuate. Based on this fluctuation, the light sensor 425 generates a passage timing signal to indicate the passage of the droplet target DL and outputs it to the processor 121. The light sensor 425 outputs a passage timing signal each time the droplet target DL blocks the light 92. In this way, the detection device 400 detects the passage of the droplet target DL supplied from the target supply unit 40 into the chamber 10 at the first detection position P1, and outputs a passage timing signal to the processor 121 each time it is detected.

[0048] The processor 121 applies a masking process to the multiple input pass timing signals and recognizes only the pass timing signals within a predetermined time interval from among the multiple input pass timing signals. The number of recognized pass timing signals is multiple, but less than the number of pass timing signals input to the processor 121. The droplet targets DL corresponding to these recognized pass timing signals become the target of imaging by the imaging device 500 and the target of irradiation by the laser light 90 of the laser device LD. In other words, not all droplet targets DL become the target of imaging and irradiation; rather, droplet targets DL within approximately a predetermined period become the target of imaging and irradiation. Then, for each of the pass timing signals recognized after masking, the processor 121 inputs a trigger signal, which is the starting signal for the imaging trigger signal and the light emission trigger signal, to the delay circuit 122. This trigger signal can also be understood as a pass timing signal input to the delay circuit 122 via the processor 121. The delay circuit 122 outputs the imaging trigger signal to the shutter 525 and the imaging main unit 527, and the light emission trigger signal to the laser device LD, each time a trigger signal is input, at a predetermined delay time from the time the trigger signal is input. Therefore, it can be understood that the processor 121 outputs the imaging trigger signal and the light emission trigger signal via the delay circuit 122 at a predetermined delay time from the time the pass timing signal recognized after mask processing is input.

[0049] When an imaging trigger signal is input, the shutter 525 opens, and the imaging unit 527 images the droplet target DL located within a predetermined imaging area including the second detection position P2 while the shutter 525 is open. The imaging unit 527 then generates image data of the imaging area and the droplet target DL located within the imaging area.

[0050] The imaging trigger signal is output individually according to each of the multiple passage timing signals recognized after mask processing. Each time an imaging trigger signal is input, the imaging device 500 images the droplet target DL located within the imaging area including the second detection position P2, and generates image data of the imaging area and the droplet target DL located within the imaging area. The imaging main unit 527 outputs each image data as an electrical signal to the processor 121. By driving the imaging main unit 527 with the imaging trigger signal, the imaging device 500 can image the droplet target DL that has been detected by the detection device 400 to have passed the first detection position P1 and has been identified as the target of measurement by the mask processing of the processor 121. In other words, the imaging device 500 can image the droplet target DL in synchronization with the time when the droplet target DL that has passed the first detection position P1 is located at the second detection position P2.

[0051] (Step SP12) In this step, the processor 121 calculates the target velocity of the droplet target DL from the frequency of the piezoelectric element 47 and the distance between adjacent droplet targets DL. The distance between adjacent droplet targets DL is measured by the processor 121 from the image data of the droplet targets DL captured by the imaging unit 527. The processor 121 then adjusts the pressure in the tank 41 using the pressure regulator 43 so that the molten target material is discharged from the nozzle hole of the nozzle 42 at the target velocity and the droplet targets DL reach the plasma generation region AR at that velocity. In other words, in this step, the processor 121 controls the velocity of the coupled droplet target DL. As a result, the droplet targets DL are supplied from the nozzle 42 to the plasma generation region AR at a predetermined velocity and frequency. After adjusting the pressure in the tank 41, the processor 121 proceeds to step SP13.

[0052] (Step SP13) In this step, the processor 121 calculates a delay time based on the speed of the droplet target DL calculated in step SP12 and the distance from the first detection position P1 to the second detection position P2, and sets the calculated delay time in the delay circuit 122. The distance is a pre-designed design distance. Once the processor 121 sets the delay time as a fixed value in the delay circuit 122, it proceeds to step SP14 of the control flow.

[0053] (Step SP14) In this step, the processor 121 outputs light emission trigger signals individually via the delay circuit 122 according to each of the pass timing signals recognized after the masking process. The light emission trigger signals are then input to the laser device LD with a delay of the time set in the delay circuit 122 in step SP13. Each time a light emission trigger signal is input to the laser device LD, it outputs laser light 90 and irradiates the droplet target DL at the second detection position P2 with the laser light 90. The laser light 90 irradiates the droplet target DL at the second detection position P2 through the laser light delivery optical system 30 and the laser focusing optical system 13. This droplet target DL corresponds to the droplet target DL recognized by the masking process. The processor 121 controls the laser light manipulator 13C of the laser focusing optical system 13 so that the laser light 90 is focused into the plasma generation region AR.

[0054] Furthermore, in this step, the processor 121 outputs the imaging trigger signal individually via the delay circuit 122 according to each of the multiple passage timing signals recognized after the masking process, as described above. As a result, the imaging device 500 can image the droplet target DL, which has been detected by the detection device 400 to have passed the first detection position P1 and has been identified as the target of measurement by the masking process of the processor 121, at the second detection position P2.

[0055] When the processor 121 outputs the light emission trigger signal and the imaging trigger signal, it proceeds to step SP15 in the control flow.

[0056] (Step SP15) In this step, when the laser beam 90 is irradiated onto the droplet target DL in the plasma generation region AR, a plasma is generated by the irradiation, and light including EUV light 101 is generated from this plasma. Of the light including EUV light 101 generated in the plasma generation region AR, the EUV light 101 is focused at the intermediate focal point IF by the EUV light focusing mirror 75 and then incident on the exposure apparatus 200 from the connection part 19.

[0057] When the target material is plasma-generated, tin particles are generated as described above. These particles diffuse into the internal space of the chamber 10. The particles diffusing into the internal space of the chamber 10 react with the hydrogen-containing etching gas supplied from the central gas supply unit 81 to form stannans. Much of the stannans obtained by the reaction with the etching gas flow into the exhaust port 10E on the flow of unreacted etching gas. In addition, at least a portion of the unreacted charged particles, fine particles, and etching gas also flows into the exhaust port 10E. The unreacted etching gas, fine particles, charged particles, and stannans that flow into the exhaust port 10E flow into the exhaust pump 60 from the exhaust pipe 10P as residual gas and undergo predetermined exhaust treatment such as detoxification.

[0058] When EUV light 101 is incident on the exposure apparatus 200, the control flow proceeds to step SP16.

[0059] (Step SP16) In this step, the processor 121 returns the control flow to step SP14 and continues generating EUV light 101 unless a stop signal is received from the exposure apparatus 200, and terminates the control flow if a stop signal is received.

[0060] Figure 6 is a timing chart of the control flowchart shown in Figure 5. Figure 6(A) corresponds to step SP11 and is a timing chart of the generation of the pass-through timing signal. As described above, a pass-through timing signal is generated for each droplet target DL that passes through the first detection position P1. The interval between the pass-through timing signals is constant. The blacked-out parts of Figure 6(A) are pass-through timing signals that are recognized after masking, and the other parts are pass-through timing signals that are not recognized by masking.

[0061] Figure 6(B) is a diagram corresponding to step SP11 and shows a timing chart for trigger signal generation. The trigger signal is generated based on the pass-through timing signal and delay time recognized after mask processing, and as described above, it is the starting signal for the emission trigger signal and imaging trigger signal. In Figure 6(B), time interval T1 shows the delay time of the trigger signal synchronized with the pass-through timing signal, and time interval dt shows the time interval of the trigger signal, i.e., the time interval of the coupled droplet target DL corresponding to the pass-through timing signal recognized by mask processing.

[0062] Figure 6(C) is a diagram corresponding to step SP14, and is a timing chart showing when the laser device LD irradiates the droplet target DL, which has reached the second detection position P2, with laser light 90. In Figure 6(C), T2 indicates the time interval from the input of the pass timing signal to the processor 121 to the input of the light emission trigger signal to the laser device LD. Time interval T2 is the same as time interval T1. Then, the laser light 90 travels from the laser device LD to the plasma generation region AR over a fixed time, and irradiates the droplet target DL. In Figure 6(C), T3 indicates the time interval from the input of the light emission trigger signal to the laser device LD to the irradiation of the droplet target DL with laser light 90.

[0063] Figure 6(D) is a diagram corresponding to step SP14, and is a timing chart showing when the imaging device 500 images the droplet target DL when it reaches the second detection position P2. In Figure 6(D), T4 indicates the time interval from the input of the transit timing signal to the processor 121 to the input of the imaging trigger signal to the imaging device 500. Time interval T4 is the same as time interval T1. The light 94 then travels from the light source 513 to the imaging main unit 527 over a fixed time. In Figure 6(D), T5 indicates the time interval from the input of the imaging trigger signal to the imaging device 500 to the imaging main unit 527 capturing the light 94.

[0064] 3.3 Challenges In the comparative example EUV light generator 100, as explained in step SP13, the delay time is calculated based on the velocity of the droplet target DL and the distance from the first detection position P1 to the second detection position P2. This distance is preferably the actual measured distance after the detection device 400 and imaging device 500 are installed in the chamber 10. However, since it is not easy to measure the distance after installation, a pre-designed distance is used. In other words, the delay time is calculated based on the velocity of the droplet target DL and the pre-designed distance from the first detection position P1 to the second detection position P2. However, during the assembly of the EUV light generator 100, the detection device 400 and imaging device 500 may shift from their pre-set installation positions in the chamber 10, resulting in an error in the distance from the first detection position P1 to the second detection position P2 compared to the pre-designed distance. In this case, the delay time may not be calculated accurately. This can cause the laser beam 90 to irradiate a droplet target DL other than the one previously assumed. Another droplet target DL is one that corresponds to a passing timing signal that is not recognized by the masking process. Furthermore, even if the laser beam 90 is irradiated onto the droplet target DL intended for use, the irradiation position on that droplet target DL may shift. Moreover, because the velocity of the droplet target DL fluctuates slightly, even if the laser beam 90 is irradiated onto the droplet target DL intended for use, the irradiation position on that droplet target DL may shift. As a result, there is a concern that the EUV light 101 that meets the performance requirements of the exposure device 200 and inspection device 300 will not be emitted, and the reliability of the EUV light generator 100 will be reduced.

[0065] Therefore, in the following embodiment, an EUV light generation apparatus 100 is provided in which a decrease in reliability can be suppressed.

[0066] 4. Description of the extreme ultraviolet light generating device of Embodiment 1 Next, the EUV light generator 100 of Embodiment 1 will be described. Components similar to those described above will be denoted by the same reference numerals, and redundant descriptions will be omitted unless otherwise specified.

[0067] 4.1 Configuration The configuration of the EUV light generator 100 in this embodiment is the same as that of the EUV light generator 100 in the comparative example, so a description will be omitted.

[0068] 4.2 Operation Next, the operation of the processor 121 of this embodiment will be described. Figure 7 is a diagram showing a part of the control flowchart of the processor 121 of this embodiment. Figures 8 and 9 are diagrams showing other parts of the control flowchart. Figure 10 is a diagram showing the remaining part of the control flowchart. The control flowchart of this embodiment includes steps SP21 to SP37.

[0069] In the initial state shown in Figure 7, the processor 121 receives a drive instruction signal for the target supply unit 40 from the exposure processor of the exposure apparatus 200. Also in the initial state, the processor 121 emits light 92 from the illumination unit 410 and light 94 from the illumination unit 510. In the initial state, the processor 121 has completed preparations for discharging the droplet target DL, such as melting the target material in the tank 41, similar to the comparative example. In this embodiment, in the delay time setting process, an unbound droplet target DL is used, which is different from the bound droplet target DL described in the comparative example, where the spacing between adjacent droplet targets DL is approximately constant. An unbound droplet target DL is a droplet target DL in which the spacing between adjacent droplet targets DL is irregular.

[0070] (Step SP21) Steps SP27 through this step are preparation steps before the EUV light generator 100 is put into full operation. In this step, the processor 121 reads parameters from the storage device. The parameters in this embodiment include the target applied voltage Vpz of the piezoelectric element 47, the reference delay time td0, the upper limit delay time td_upper_limit, the lower limit delay time td_lower_limit, the threshold d_limit, the target number n_target for the number of image data n of the uncoupled droplet target DL, and the threshold σ_limit.

[0071] The target applied voltage Vpz is the voltage at which the coupled droplet target DL is ejected by the vibration of the piezoelectric element 47 to which the voltage is applied. The reference delay time td0 is the time calculated from the design distance between the first detection position P1 and the second detection position P2 and the theoretical velocity of the coupled droplet target DL. The theoretical velocity of the coupled droplet target DL is the value obtained by dividing the distance between adjacent coupled droplet targets DL obtained from previously captured image data by the generation frequency of the coupled droplet target DL. The upper limit delay time td_upper_limit is the upper threshold of the delay time, and the lower limit delay time td_lower_limit is the lower threshold of the delay time. The threshold d_limit is the distance threshold from the second detection position P2 to the coupled droplet target DL. The threshold σ_limit is the standard deviation σ of the variation of the uncoupled droplet target DL with respect to the second detection position P2. The threshold σ_limit may be 3σ. After the processor 121 reads the various parameters, it proceeds the control flow to step SP22.

[0072] (Step SP22) In this step, similar to step SP11, the processor 121 adjusts the pressure in the tank 41 using the pressure regulator 43 and discharges the target substance in the tank 41 into the chamber 10 through the nozzle hole of the nozzle 42. At this time, unlike the comparative example, the processor 121 applies a target applied voltage Vpz to the piezoelectric element 47 from the piezoelectric power supply 48. As a result, the piezoelectric element 47 vibrates at a predetermined frequency. Therefore, in this step, the processor 121 drives the piezoelectric element 47 to generate and discharge coupled droplet targets DL. In other words, the spacing between adjacent droplet targets DL is approximately constant. Once the droplet targets DL as coupled droplet targets DL are discharged, the processor 121 proceeds to step SP23.

[0073] Prior to step SP23, when the droplet target DL passes the first detection position P1, the detection device 400 outputs a passage timing signal as an electrical signal to the processor 121, similar to the comparative example. The detection device 400 outputs a passage timing signal for each droplet target DL passing through the first detection position P1. The processor 121 applies a masking process to the multiple input passage timing signals and recognizes only the predetermined passage timing signals. The processor 121 also outputs an imaging trigger signal to the shutter 525 and the imaging unit 527 via the delay circuit 122, delayed by a reference delay time td0 from the input of the passage timing signal recognized after masking. As a result, the shutter 525 opens, and the imaging unit 527 images the droplet target DL located within the imaging area including the second detection position P2. The imaging unit 527 then generates image data of the imaging area and the droplet target DL located within the imaging area. The imaging unit 527 outputs the generated image data as an electrical signal to the processor 121. Furthermore, the processor 121 outputs an imaging trigger signal individually according to each of the multiple pass-through timing signals recognized after mask processing. As a result, the imaging unit 527 captures an image, generates image data, and outputs it each time an imaging trigger signal is input.

[0074] (Step SP23) In this step, similar to step SP12, the processor 121 calculates the target speed of the coupled droplet target DL from the frequency of the piezoelectric element 47 and the spacing of the coupled droplet target DL, and controls the speed of the coupled droplet target DL. Then, the processor 121 proceeds the control flow to step SP24.

[0075] (Step SP24) In this step, the processor 121 proceeds to the delay time setting process, which will be described later. In the delay time setting process, the standard deviation σ of the variation of the uncoupled droplet target DL with respect to the second detection position P2 is calculated. The standard deviation σ will be explained in detail in the delay time setting process. Then, the delay time is calculated using the standard deviation σ, and the calculated delay time is set in the delay circuit 122. Once the delay time is set and the delay time setting process is completed, the processor 121 proceeds to step SP25, which is shown in Figure 8 of the control flow.

[0076] Next, steps SP25 to SP27 will be explained using Figure 8.

[0077] (Step SP25) In this step, if the standard deviation σ is less than or equal to the threshold σ_limit described in step SP21, the processor 121 proceeds to step SP28 shown in Figure 9 of the control flow; otherwise, if the standard deviation σ is greater than the threshold σ_limit, the control flow proceeds to step SP26.

[0078] (Step SP26) In this step, if the processor 121 does not output an error signal to the exposure apparatus 200, it proceeds to step SP28 shown in Figure 9 of the control flow; if it does output an error signal to the exposure apparatus 200, it proceeds to step SP27 of the control flow. Whether or not to output an error signal is determined by the exposure apparatus 200 based on predetermined criteria. If the standard deviation σ in step SP24 is important to the exposure apparatus 200, the processor 121 outputs an error signal; if the standard deviation σ is not important to the exposure apparatus 200, the processor 121 does not output an error signal.

[0079] (Step SP27) In this step, the processor 121 remains in standby mode unless a maintenance signal is received from the exposure apparatus 200. If a maintenance signal is received, the control flow proceeds to step SP36, as shown in Figure 10.

[0080] Next, steps SP28 to SP32 will be explained using Figure 9. Steps SP28 and beyond are the steps in which the EUV light generator 100 begins full operation.

[0081] (Step SP28) In this step, the processor 121 applies a target applied voltage Vpz to the piezoelectric element 47, similar to step SP22, generates and ejects a droplet target DL as a coupled droplet target DL, and proceeds the control flow to step SP29.

[0082] When a droplet target DL passes the first detection position P1, the detection device 400 outputs a passage timing signal to the processor 121, similar to the comparative example. The detection device 400 outputs a passage timing signal for each droplet target DL passing through the first detection position P1. The processor 121 applies a masking process to the multiple input passage timing signals and recognizes only the predetermined passage timing signals. The processor 121 also outputs an imaging trigger signal to the shutter 525 and the imaging unit 527 via the delay circuit 122, delayed by a delay time td from the input of the passage timing signal recognized after masking. The imaging unit 527 takes an image and generates and outputs image data each time an imaging trigger signal is input.

[0083] (Step SP29) In this step, similar to step SP23, the processor 121 calculates the target speed of the droplet target DL from the frequency of the piezoelectric element 47 and the spacing of the droplet target DL, and controls the speed of the coupled droplet target DL. Then, the processor 121 proceeds the control flow to step SP30.

[0084] (Step SP30) In this step, the processor 121 performs the delay time fine-tuning process described later and proceeds to step SP31 of the control flow.

[0085] (Step SP31) In this step, the processor 121 outputs a light emission trigger signal to the laser device LD via the delay circuit 122. The light emission trigger signal is input to the laser device LD after a delay time, which is finely adjusted in step SP30, following the input of the transit timing signal to the processor 121. When the laser device LD receives the light emission trigger signal, it outputs laser light 90. The laser light 90 irradiates the droplet target DL in the plasma generation region AR through the laser light delivery optical system 30 and the laser focusing optical system 13.

[0086] Furthermore, in this step, when the processor 121 receives a pass timing signal from the detection device 400, it outputs an imaging trigger signal to the shutter 525 and the imaging main unit 527 via the delay circuit 122, with a delay time from the input of the pass timing signal. As a result, the imaging device 500 can detect the passage of the first detection position P1 by the detection device 400 and, through mask processing by the processor 121, become the target of measurement and can image the droplet target DL.

[0087] When the processor 121 outputs the light emission trigger signal and the imaging trigger signal, it proceeds to step SP32 in the control flow.

[0088] (Step SP32) In this step, similar to step SP15, when the laser beam 90 is irradiated onto the droplet target DL in the plasma generation region AR, light including EUV light 101 is emitted. The EUV light 101 is focused at the intermediate focal point IF by the EUV light focusing mirror 75 and then incident into the exposure apparatus 200 from the connection part 19. Once the EUV light 101 is incident into the exposure apparatus 200, the control flow proceeds to step SP33 shown in Figure 10.

[0089] Next, steps SP33 to SP37 will be explained using Figure 10. Steps SP33 to SP37 are steps in which the EUV light generator 100 starts full operation based on the EUV output signal from the exposure apparatus 200.

[0090] (Step SP33) In this step, the processor 121 returns the control flow to step SP30 in order to continue generating EUV light 101 if no stop signal is input from the exposure apparatus 200 or if the delay time does not deviate from a predetermined value. The processor 121 also advances the control flow to step SP34 in order to stop generating EUV light 101 if a stop signal is input from the exposure apparatus 200. Furthermore, the processor 121 also advances the control flow to step SP34 in order to have the exposure apparatus 200 determine whether or not it is necessary to stop generating EUV light 101 if the delay time deviates from a predetermined value.

[0091] (Step SP34) In this step, the processor 121 returns the control flow to step SP30 if it does not output an error signal to the exposure device 200, as in step SP26, and advances the control flow to step SP35 if it outputs an error signal to the exposure device 200. The processor 121 does not output an error signal if the delay time is within the limits of what the exposure device 200 can tolerate, and outputs an error signal if a stop signal is input from the exposure device 200 or if the delay time is outside the limits of what the exposure device 200 can tolerate.

[0092] (Step SP35) In this step, the processor 121, similar to step SP27, waits after outputting an error signal unless a maintenance signal is received from the exposure apparatus 200. If a maintenance signal is received, the control flow proceeds to step SP36.

[0093] (Step SP36) In this step, the processor 121 stops the EUV light generator 100 and performs maintenance on the EUV light generator 100. Once the maintenance on the EUV light generator 100 is complete, the control flow proceeds to step SP37.

[0094] (Step SP37) In this step, the processor 121 restarts the EUV light generator 100 and returns the control flow to step SP22.

[0095] Next, the delay time setting process of this embodiment in step SP22 will be explained using Figures 11, 12, and 13. Figure 11 is a part of the control flowchart of the processor 121 in the delay time setting process of this embodiment in step SP22. Figure 12 is another part of the control flowchart. Figure 13 is the remaining part of the control flowchart. The control flowchart of this embodiment includes steps SP51 to SP67.

[0096] First, steps SP51 to SP54 will be explained using Figure 11. Steps SP51 to SP54 are preparation steps before the EUV light generator 100 is put into full operation.

[0097] (Step SP51) In this step, the processor 121 controls the voltage applied to the piezoelectric element 47 so that uncoupled droplet targets DL with irregular spacing between adjacent droplet targets DL are generated. In this embodiment, the processor 121 changes the voltage applied to the piezoelectric element 47 from the target applied voltage Vpz described in step SP22 to 0V. As a result, the piezoelectric element 47 stops and does not vibrate, and the vibration frequency of the piezoelectric element 47 is controlled to zero. In this state, when droplet targets DL are discharged, the spacing between adjacent droplet targets DL changes from the approximately constant spacing described in step SP22 to an irregular spacing. Therefore, the droplet targets DL are discharged as uncoupled droplet targets DL. Since the pressure in the tank 41 is regulated by the pressure regulator 43, the speed of the discharged uncoupled droplet targets DL is approximately constant. When the processor 121 discharges droplet targets DL which are uncoupled droplet targets DL, it proceeds the control flow to step SP52.

[0098] (Step SP52) In this step, the processor 121 sets the delay time td to the reference delay time td0. The reference delay time td0 in this step is not the reference delay time td0 in step SP21, but is calculated from the design distance from the first detection position P1 to the second detection position P2 and the velocity of the droplet target DL calculated in step SP23. Once the processor 121 sets the delay time td to the reference delay time td0, it proceeds the control flow to step SP53.

[0099] Prior to step SP53, when the uncoupled droplet target DL passes the first detection position P1, the detection device 400 outputs a pass timing signal to the processor 121, similar to the comparative example. The detection device 400 outputs a pass timing signal for each uncoupled droplet target DL passing through the first detection position P1. The processor 121 applies a masking process to the multiple input pass timing signals and recognizes only the predetermined pass timing signals. The processor 121 outputs imaging trigger signals to the shutter 525 and the imaging main unit 527 via the delay circuit 122, delayed by a delay time from the input of the pass timing signals recognized after masking.

[0100] (Step SP53) In this step, the processor 121 outputs an imaging trigger signal individually according to each of the multiple pass-through timing signals recognized after mask processing. Therefore, multiple imaging trigger signals are input to the imaging unit 527, and the imaging unit 527 takes an image each time an imaging trigger signal is input. As a result, multiple image data are generated. The processor 121 counts the number n of image data in which the uncoupled droplet target DL is located within the imaging area including the second detection position P2, as recorded by the imaging device 500. Since the image data of the uncoupled droplet target DL is input to the processor 121 sequentially, multiple image data are input to the processor 121. Once the processor 121 begins counting the number n of such image data, it proceeds the control flow to step SP54.

[0101] (Step SP54) In this step, if the number of image data points n of the uncoupled droplet target DL has not reached the target number n_target described in step SP21, the processor 121 returns the control flow to step SP54 and continues counting the number of image data points n. If the number of image data points n has reached the target number n_target, the processor 121 proceeds to step SP55 shown in Figure 12. The target number n_target is 2 or greater.

[0102] Next, steps SP55 to SP60 will be explained using Figure 12. Steps SP55 to SP60 are preparation steps before the EUV light generator 100 is put into full operation.

[0103] (Step SP55) In this step, the processor 121 calculates the distance Di from the second detection position P2 to the uncoupled droplet target DL for each of the multiple image data. Distance Di is the distance from the second detection position P2 to the uncoupled droplet target DL closest to the second detection position P2. Since distance Di is calculated for each of the multiple image data, multiple distance Di values ​​are calculated. The coordinates of the second detection position P2 are specified within the image data. If multiple uncoupled droplet targets DL exist in the image data, the uncoupled droplet target DL closest to the second detection position P2 is used as described above. After calculating multiple distance Di values, the processor 121 proceeds to step SP56 of the control flow.

[0104] (Step SP56) In this step, the processor 121 calculates the average distance Dave of the multiple calculated distances Di, and then proceeds the control flow to step SP57.

[0105] (Step SP57) In this step, the processor 121 calculates the standard deviation σ of the variability of the uncoupled droplet target DL relative to the second detection position P2 by substituting the number n of image data, the distance Di, and the average distance Dave into the following equation (1). Once the processor 121 has calculated the standard deviation σ, it proceeds to step SP58 of the control flow. TIFF0007900931000001.tif25170

[0106] (Step SP58) In this step, if the standard deviation σ is less than or equal to the threshold σ_limit described in step SP21, the processor 121 proceeds to step SP59 of the control flow; otherwise, if the standard deviation σ is greater than the threshold σ_limit, the control flow proceeds to step SP61 shown in Figure 13.

[0107] Next, steps SP61 to SP67 will be explained using Figure 13. Steps SP61 to SP67 are preparation steps before the EUV light generator 100 is put into full operation.

[0108] (Step SP61) In this step, the processor 121 advances the control flow to step SP62 if the current delay time td is greater than or equal to the reference delay time td0 in step SP52, and advances the control flow to step SP66 if the current delay time td is less than the reference delay time td0.

[0109] (Step SP62) In this step, the processor 121 sets the delay time td to the value obtained by adding the delay time change time Δt1 to the delay time td, and proceeds to step SP63 of the control flow. At this time, the processor 121 sets the change time Δt1 to a time that is less than or equal to the generation period of the coupled droplet target DL when the piezoelectric element 47 is driven. The change time Δt1 may be any time.

[0110] (Step SP63) In this step, if the delay time td set in step SP62 is less than or equal to the upper limit delay time td_upper_limit set in step SP21, the processor 121 proceeds to step SP64. If the delay time td is greater than the upper limit delay time td_upper_limit, the processor 121 proceeds to step SP65. The upper limit delay time td_upper_limit is calculated in advance from the error in the design distance between the first detection position P1 and the second detection position P2, and the design error in the velocity of the coupled droplet target DL.

[0111] (Step SP64) In this step, the processor 121 resets the number of image data points n to 0 and returns the control flow to step SP54. Since the number of image data points n is 0, the control flow proceeds sequentially from step SP54 to steps SP55, SP56, and SP57. Then, with the delay time td set in steps SP62 and SP64, the standard deviation σ is recalculated in step SP57, and in step SP58, it is determined whether the standard deviation σ is greater than the threshold σ_limit. In this way, the control flow of each step shown in Figure 13 is repeated, and the processor 121 identifies an uncoupled droplet target DL whose standard deviation σ is less than or equal to the first threshold, which is the threshold σ_limit.

[0112] (Step SP65) In this step, the processor 121 sets the delay time td to the reference delay time td0 in step SP52 and proceeds the control flow to step SP66.

[0113] (Step SP66) In this step, the processor 121 sets the delay time td to a value obtained by subtracting the delay time change time Δt1 from the delay time td, and proceeds to step SP67 of the control flow.

[0114] (Step SP67) In this step, if the delay time td set in step SP65 is greater than or equal to the lower limit delay time td_lower_limit set in step SP21, the processor 121 proceeds to step SP64. The lower limit delay time td_lower_limit is calculated in advance from the error in the design distance between the first detection position P1 and the second detection position P2, and the design error in the velocity of the combined droplet target DL. In step SP64, the processor 121 resets the number of image data n to 0 and returns the control flow to step SP54. Since the number of image data n is 0, the control flow proceeds sequentially from step SP54 to steps SP55, SP56, and SP57. Then, with the delay time td set in step SP66, the standard deviation σ is recalculated in step SP57, and in step SP58, it is determined whether the standard deviation σ is greater than the threshold σ_limit. As the control flow of steps SP54-SP58, SP61-SP63, SP65-SP67, and step SP64 is repeated in this manner, the processor 121 identifies an uncoupled droplet target DL whose standard deviation σ is less than or equal to a first threshold, which is the threshold σ_limit.

[0115] Furthermore, in this step, if the delay time td is less than the upper delay time td_upper_limit, the processor 121 proceeds to step SP60 shown in Figure 12. If the control flow proceeds from step SP67 to step SP60, the delay time td will not be greater than or equal to the lower delay time td_lower_limit and less than or equal to the upper delay time td_upper_limit, and the uncoupled droplet target DL will not be checked. Therefore, the delay time setting process will be terminated.

[0116] (Step SP59) The control flow returns from step SP64 to step SP54 in steps SP54 to SP58 and steps SP61 to SP67. As a result, the delay time td is greater than or equal to the lower delay time td_lower_limit and less than or equal to the upper delay time td_upper_limit. In this step, the processor 121 sets the delay time td to a value obtained by adding the change time Δt corresponding to the average distance Dave to the delay time td. The change time Δt is the value obtained by dividing the average distance Dave calculated in step SP56 by the velocity of the droplet target DL calculated in step SP23. Once the delay time td is set, the identified uncoupled droplet target DL is located at the second detection position P2. Therefore, the processor 121 sets the delay time td based on the average distance Dave from the specific uncoupled droplet target DL to the second detection position P2 such that the standard deviation σ calculated in step SP57 is less than or equal to the first threshold, so that the identified uncoupled droplet target DL is located at the second detection position P2. Once the delay time td is set, the processor 121 advances the control flow to step SP60.

[0117] (Step SP60) In this step, the processor 121 stops the imaging of the uncoupled droplet target DL by the imaging device 500 and stops counting the number n of image data. Then, the processor 121 finishes the delay time setting process and proceeds to step SP25 of the control flow.

[0118] Figure 14 is a control flowchart of the processor 121 in the fine-tuning of the delay time in step SP30. This control flowchart includes steps SP81 to SP85. Even after the delay time is set in the delay time setting process in step SP24, the position of the droplet target DL may shift in the direction of travel of the droplet target DL due to minute fluctuations in the speed of the droplet target DL. To correct this shift, the delay time is fine-tuned according to the shift using this flowchart.

[0119] (Step SP81) In this step, the processor 121 calculates the distance d from the second detection position P2 to the combined droplet target DL from the image data acquired in step SP28. If there are multiple combined droplet targets DL in the image data, the processor 121 calculates the distance d from the second detection position P2 to the combined droplet target DL closest to the second detection position P2. The coordinates of the second detection position P2 are specified in the image data. Once the processor 121 has calculated the distance d, it proceeds to step SP82 of the control flow.

[0120] (Step SP82) In this step, if the absolute value of distance d is less than or equal to the second threshold d_limit in step SP21, the processor 121 terminates the fine-tuning of the delay time and proceeds to step SP31. If the absolute value of distance d is greater than the threshold d_limit, the processor 121 proceeds to step SP83.

[0121] (Step SP83) In this step, if the coupled droplet target DL is located downstream of the second detection position P2 in the direction of travel of the coupled droplet target DL, the processor 121 advances the control flow to step SP84. If the coupled droplet target DL is located upstream of the second detection position P2 in the direction of travel of the coupled droplet target DL, the processor 121 advances the control flow to step SP85.

[0122] (Step SP84) In this step, the processor 121 sets the delay time td to a value obtained by subtracting the delay time re-modification time Δt2 from the delay time td, finishes the fine-tuning of the delay time, and proceeds to step SP31 of the control flow. The re-modification time Δt2 is shorter than the modification time Δt1.

[0123] (Step SP85) In this step, the processor 121 sets the delay time td to a value obtained by adding the delay time re-modification time Δt2 to the delay time td, finishes the fine-tuning of the delay time, and proceeds to step SP31 of the control flow.

[0124] In steps SP84 and SP85, the processor 121 sets the delay time re-modification time Δt2 to less than the modification time Δt1. Therefore, after setting the delay time td in the delay time setting process in step SP24, if the distance from the second detection position P2 to the combined droplet target DL in the imaging area is greater than the second threshold in step SP82, the processor 121 re-sets the delay time td based on the delay time re-modification time Δt2 which is less than the modification time Δt1.

[0125] 4.3 Action and Effects In this embodiment, when the processor 121 controls the piezoelectric element 47 in step SP51, uncoupled droplet targets DL with irregular spacing between adjacent droplet targets DL are generated. Each time the detection device 400 detects the passage of an uncoupled droplet target DL at the first detection position P1, the detection device 400 inputs a passage timing signal to the processor 121, so that multiple passage timing signals are input to the processor 121. The processor 121 applies a masking process to the multiple passage timing signals and outputs an imaging trigger signal to the imaging device 500 for each of the passage timing signals recognized after the masking process. Each time an imaging trigger signal is input to the imaging device 500, the imaging device 500 images the uncoupled droplet targets DL located within the imaging area including the second detection position P2, and generates image data of the imaging area and the uncoupled droplet targets DL located within the imaging area. Since the imaging device 500 generates image data each time an imaging trigger signal is input, multiple image data are generated. Incidentally, the speed of the uncoupled droplet targets DL ejected from the nozzle 42 is approximately constant. Therefore, each of the uncoupled droplet targets DL with irregular spacing, other than the uncoupled droplet target DL corresponding to the passing timing signal recognized by the masking process, is not synchronized with the imaging timing of the imaging device 500 and tends to deviate from the second detection position P2. As a result, when comparing multiple image data, each of the uncoupled droplet targets DL that is not synchronized with the imaging timing of the imaging device 500 will have positional variations relative to the second detection position P2. Therefore, in step SP57, the processor 121 calculates the standard deviation σ of the distance from the second detection position P2 to the uncoupled droplet target DL from multiple image data, and identifies an uncoupled droplet target DL for which the calculated standard deviation σ is smaller than the first threshold, which is the threshold σ_limit. Furthermore, in step SP59, the processor 121 sets the delay time td in the delay circuit 122 based on the average distance Dave from the position of the uncoupled droplet target DL to the second detection position P2, so that the identified uncoupled droplet target DL is located at the second detection position P2.When the processor 121 sets a delay time td, the delay circuit 122 outputs a light emission trigger signal at a timing delayed by the delay time td for each of the pass timing signals recognized after the masking process. This allows the laser beam 90 to be irradiated onto the pre-specified coupled droplet target DL, i.e., the coupled droplet target DL corresponding to the pass timing signal recognized by the masking process, and suppresses deviations in the irradiation position on the droplet target DL. Therefore, even if the detection device 400 and the imaging device 500 are moved from their pre-set installation positions in the chamber 10, irradiation of a droplet target DL other than the pre-specified one with the laser beam 90 can be suppressed, and deviations in the irradiation position on the pre-specified coupled droplet target DL can be suppressed. Furthermore, even if the velocity of the droplet target DL fluctuates slightly, deviations in the irradiation position on the pre-specified coupled droplet target DL can be suppressed. Therefore, laser beam 90 that meets the performance requirements of the exposure device 200 and the inspection device 300 can be emitted, and a decrease in the reliability of the EUV light generator 100 can be suppressed.

[0126] Furthermore, in step SP51, the processor 121 controls the vibration frequency of the piezoelectric element 47, which is an excitation element, to zero. With this configuration, since the piezoelectric element 47 does not vibrate, it is possible to generate uncoupled droplet targets DL with irregular spacing between adjacent droplet targets DL.

[0127] Furthermore, if the processor 121 cannot identify an uncoupled droplet target DL in step SP58 whose standard deviation σ is less than or equal to the first threshold σ_limit, in steps SP62 and SP65, it changes the delay time change time Δt1 to a time less than or equal to the generation period of droplet target DL when the interval between adjacent droplet target DLs is the same. Then, the processor 121 identifies an uncoupled droplet target DL whose standard deviation σ is smaller than the threshold σ_limit. With this configuration, it is possible to identify an uncoupled droplet target DL corresponding to the passage timing signal recognized by the mask processing located within the imaging area during imaging by the imaging device 500, within the range from the lower delay time td_lower_limit to the upper delay time td_upper_limit.

[0128] Furthermore, after setting the delay time td in the delay time setting process in step SP24, if the distance from the second detection position P2 to the combined droplet target DL in the imaging area is greater than the second threshold, which is the threshold d_limit, in step SP82, the processor 121 readjusts the delay time td based on the readjustment time Δt2 of the delay time less than the change time Δt1. In this configuration, even if the droplet target DL is shifted from the second detection position P2 after the delay time td has been changed, the delay time td is readjusted. This further suppresses the possibility of the laser beam 90 irradiating a droplet target DL other than the one detected by the detection device 400.

[0129] 5. Description of the extreme ultraviolet light generation device of Embodiment 2 Next, the EUV light generator 100 of Embodiment 2 will be described. Components similar to those described above will be denoted by the same reference numerals, and redundant descriptions will be omitted unless otherwise specified.

[0130] 5.1 Configuration The configuration of the EUV light generator 100 in this embodiment is the same as that of the EUV light generator 100 in the comparative example and Embodiment 1, so a description will be omitted.

[0131] 5.2 Operation Next, the operation of the processor 121 of this embodiment will be described. Figure 15 shows a part of the control flowchart of the processor 121 of this embodiment. The control flowchart of this embodiment differs from the control flowchart of Embodiment 1 in that it includes steps SP91, SP92, and SP93 instead of steps SP21, SP22, and SP28. Steps SP91, SP92, and SP93 are preparation steps before the EUV light generator 100 goes into full operation.

[0132] In Embodiment 1, the EUV light generator 100 generates uncoupled droplet targets DL by changing the voltage applied to the piezoelectric element 47 to 0V. In contrast, the EUV light generator 100 of this embodiment generates droplet targets DL by irregularly changing the frequency of the voltage applied to the piezoelectric element 47. Since the spacing between adjacent droplet targets DL depends on the vibration frequency of the piezoelectric element 47, by irregularly controlling the frequency of the voltage applied to the piezoelectric element 47, the vibration frequency is irregularly controlled, thereby generating coupled droplet targets DL with pseudo-irregular spacing.

[0133] (Step SP91) In this step, the processor 121 reads parameters from the storage device that are different from the parameters of Embodiment 1. The parameters of this embodiment include the target vibration frequency f0 of the piezoelectric element 47, the vibration level number m of the piezoelectric element 47, the applied voltage frequency fm of the piezoelectric element 47 at each vibration level number m, the target number nm_target of image data of the uncoupled droplet target DL to be acquired at each vibration level number m, the reference delay time td0, the upper limit delay time td_upper_limit, the lower limit delay time td_lower_limit, the threshold d_limit of the distance from the second detection position P2 to the coupled droplet target DL, and the threshold σ_limit of the uncoupled droplet target DL. The target vibration frequency f0 is the frequency that generates the coupled droplet target DL. The vibration level number m, the applied voltage frequency fm, and the target number nm_target of image data of the uncoupled droplet target DL are linked to each other. m is a natural number greater than or equal to 1. The applied voltage frequency fm is the value at which at least one uncoupled droplet target DL is located within the imaging region. For example, if the imaging area is 200 μm long in the direction of propagation of the droplet target DL, centered on the second detection position P2, the applied voltage frequency fm is a value such that the distance between adjacent droplet targets DL is 200 μm or less. Such an applied voltage frequency fm is the value obtained by dividing the theoretical velocity of the droplet target DL by the target distance between adjacent droplet targets DL. After the processor 121 reads the various parameters, it proceeds the control flow to step SP92.

[0134] (Steps SP92, SP93) In this step, similar to step SP22, the processor 121 adjusts the pressure in the tank 41 using the pressure regulator 43, causing the target substance in the tank 41 to be discharged into the chamber 10 through the nozzle hole of the nozzle 42. Unlike in step SP22, the processor 121 applies a voltage from the piezo power supply 48 to the piezoelectric element 47 so that the piezoelectric element 47 vibrates at a target vibration frequency f0, and this vibration generates and discharges the coupled droplet target DL. Therefore, in this step, similar to step SP22, the processor 121 drives the piezoelectric element 47 to generate and discharge the coupled droplet target DL. The processor 121 then proceeds the control flow to step SP23 after step SP92, and to step SP29 after step SP93.

[0135] Although not shown in the diagram, in this control flow, when the processor 121 finishes step SP37, it returns the control flow to step SP92.

[0136] Furthermore, in this embodiment, the delay time setting process differs from that of Embodiment 1. Figure 16 is a part of the control flowchart of the processor 121 in the delay time setting process of this embodiment. Figure 17 is another part of the control flowchart. Figure 18 is the remaining part of the control flowchart. The control flowchart of this embodiment differs from that of Embodiment 1 in that step SP51 is omitted, and steps SP101 to SP103 are provided between steps SP52 and SP53. Also, steps SP104 to SP108 are provided between steps SP53 and SP56, and step SP112 is provided instead of step SP60, which is different from the control flowchart of Embodiment 1. Furthermore, step SP113 is provided instead of step SP64, which is different from the control flowchart of Embodiment 1. In the control flowchart of this embodiment, the processor 121 advances the control flow to step SP52 after the start, and then to step SP101 after step SP52.

[0137] (Step SP101) In this step, the processor 121 starts counting the vibration level number m of the piezoelectric element 47 and advances the control flow to step SP102. The initial value of vibration level number m is 1.

[0138] (Step SP102) In this step, the processor 121 sets the applied voltage frequency of the piezoelectric element 47 to the applied voltage frequency fm corresponding to the current vibration level number m of the piezoelectric element 47, and proceeds the control flow to step SP103. When the control flow proceeds to step SP102 for the first time, the initial value of vibration level number m is 1, so the applied voltage frequency becomes the applied voltage frequency f1. Once the applied voltage frequency fm is set, coupled droplet targets DL are ejected with a different spacing between adjacent droplet targets DL than when the applied voltage frequency is f1.

[0139] (Step SP103) In this step, the processor 121 sets the target number of image data for the uncoupled droplet target DL to the target number nm_target corresponding to the current vibration level number m of the piezoelectric element 47, and proceeds the control flow to steps SP53 and SP104 in order.

[0140] (Step SP104) In this step, if the number of image data points n has not reached the target number nm_target set in step SP103, the processor 121 returns the control flow to step SP104 and continues counting the number of image data points n. If the number of image data points n has reached the target number nm_target, the processor 121 proceeds the control flow to step SP105.

[0141] (Step SP105) In this step, the processor 121 stops counting the number n of image data and proceeds to step SP106, as shown in Figure 17 of the control flow.

[0142] Next, we will explain steps SP106 and beyond using Figure 17.

[0143] (Step SP106) In this step, the processor 121 adds 1 to the vibration level number m of the piezoelectric element 47, setting the current vibration level number m of the piezoelectric element 47 to vibration level number m+1, and proceeds to step SP107 of the control flow.

[0144] (Step SP107) In this step, if the current vibration level number m of the piezoelectric element 47 has not reached the maximum value m_target, the processor 121 returns the control flow to step SP102. If the current vibration level number m of the piezoelectric element 47 has reached the maximum value m_target, the processor 121 advances the control flow to step SP108.

[0145] (Step SP108) In this step, the processor 121 calculates the distance Di from the second detection position P2 to the uncoupled droplet target DL closest to the second detection position P2 for each of the multiple image data for each vibration level number m. In other words, the processor 121 calculates the distance Di for each of the multiple image data for each of the applied voltage frequencies f1 to fm. Once the processor 121 has calculated the distance Di, it proceeds to step SP56 of the control flow.

[0146] (Step SP56) In this step, the processor 121 calculates the average distance Dave for all the calculated distances Di. Once the processor 121 has calculated the average distance Dave, it proceeds through steps SP57 and SP58. If the standard deviation σ in step SP58 is less than or equal to the threshold σ_limit, the processor 121 proceeds through steps SP59 and SP112.

[0147] (Step SP112) In this step, the processor 121 stops counting the vibration level number m of the piezoelectric element 47. Then, the processor 121 finishes setting the delay time and proceeds to step SP25 of the control flow.

[0148] Furthermore, if the standard deviation σ in step SP58 is greater than the threshold σ_limit, the processor 121 proceeds to step SP61, as shown in Figure 18 of the control flow.

[0149] (Step SP113) As shown in Figure 18, in this step, the processor 121 resets the vibration level number m of the piezoelectric element 47 to 0 and returns the control flow to step SP102.

[0150] 5.3 Action and Effects In the EUV light generator 100 of this embodiment, the processor 121 irregularly controls the vibration frequency of the piezoelectric element 47 in step SP102. Since the spacing between adjacent droplet targets DL depends on the vibration frequency of the piezoelectric element 47, this configuration makes it possible to generate coupled droplet targets DL with different spacings between adjacent droplet targets DL, even when the piezoelectric element 47 is driven.

[0151] 6. Description of the extreme ultraviolet light generating device of Embodiment 3 Next, the EUV light generator 100 of Embodiment 3 will be described. Components similar to those described above will be denoted by the same reference numerals, and redundant descriptions will be omitted unless otherwise specified.

[0152] In Embodiment 1, the EUV light generator 100 calculates the standard deviation σ based on the uncoupled droplet target DL closest to the second detection position P2. In contrast, the EUV light generator 100 in this embodiment calculates the standard deviation σ based on all uncoupled droplet targets DL located in the image data.

[0153] 6.1 Configuration The configuration of the EUV light generator 100 in this embodiment is the same as that of the EUV light generator 100 in the comparative example and embodiments 1 and 2, so a description will be omitted.

[0154] 6.2 Operation Next, the operation of the processor 121 of this embodiment will be described. Figure 19 is a diagram showing a part of the control flowchart of the processor 121 of this embodiment. As shown in Figure 19, the control flowchart of this embodiment differs from the control flowchart of Embodiment 1 in that it includes steps SP131 and SP132 instead of steps SP21 and SP25. Steps SP131 and SP132 are preparation steps before the EUV light generator 100 goes into full operation.

[0155] (Step SP131) In this step, the processor 121 reads parameters from the storage device that are different from the parameters of Embodiment 1. The parameters of this embodiment include the initial width L0 of the observation area in the imaging area of ​​the imaging unit 527, the target width L1 of the observation area, and the parameters of Embodiment 1. After reading the various parameters, the processor 121 proceeds to step SP22 of the control flow.

[0156] The observation region includes the second detection position P2. The initial width L0 and target width L1 of the observation region are the lengths in the Y direction along the trajectory of the droplet target DL. In the delay time setting process of step SP24, in order to calculate the standard deviation σ, the initial width L0 is preferably the size of the observation region where one coupled droplet target DL exists, for example, 80% of the distance between adjacent coupled droplet target DLs. The target width L1 is larger than the initial width L0 and less than the value obtained by multiplying the time interval dt of the masking process by the velocity of the coupled droplet target DL. The target width L1 is also the size of the observation region where multiple uncoupled droplet target DLs exist.

[0157] (Step SP132) In this step, if there is an uncoupled droplet target that satisfies the standard deviation σ ≤ threshold σ_limit, the processor 121 proceeds to step SP26 shown in Figure 8. If there is an uncoupled droplet target DL that satisfies the standard deviation σ ≤ threshold σ_limit, the processor 121 proceeds to step SP28 shown in Figure 9.

[0158] Furthermore, in this embodiment, the delay time setting process differs from that of Embodiment 1. Figure 20 is a part of the control flowchart of the processor 121 in the delay time setting process of this embodiment. Figure 21 is another part of the control flowchart. The control flowchart of this embodiment differs from that of Embodiment 1 in that it includes step SP141 between step SP52 and step SP53, as shown in Figure 20. Also, the control flowchart of this embodiment differs from that of Embodiment 1 in that it includes steps SP142 to SP146 instead of steps SP55 to SP59, and step SP147 after step SP60, as shown in Figure 21. Figure 22 is a diagram illustrating the allocation in step SP143. Figure 23 is the remaining part of the control flowchart in the delay time setting process of this embodiment. Also, the control flowchart of this embodiment differs from that of Embodiment 1 in that it includes steps SP148 and SP149 instead of steps SP62 and SP66, as shown in Figure 23.

[0159] (Step SP141) As shown in Figure 20, in this step, the processor 121 sets the width of the observation area to the target width L1 of the observation area as described in step SP131, and proceeds the control flow to step SP53.

[0160] Next, we will explain steps SP142 and beyond using Figure 21.

[0161] (Step SP142) Prior to this step, in step SP141, the width of the observation region is set to the target width L1, so the image data will contain multiple unconnected droplet targets DL. In this step, the processor 121 calculates the distance Di between each of the unconnected droplet targets DL present in the observation region of the target width L1 in a given image data and the second detection position P2. The processor 121 also calculates the distance Di for all image data. In other words, in the observation region of each image data in this step, there are k unconnected droplet targets DL, where k is a natural number greater than or equal to 2, and each unconnected droplet target DL is located at a sequential distance from the second detection position P2. For each image data, the processor 121 calculates the distance Di-j for each unconnected droplet target DL. i and j are natural numbers greater than or equal to 1. The definition of distance Di-j is the distance of the j-th unconnected droplet target DL from the second detection position P2 in the i-th image data. For example, if there are 3 image data points, and the k values ​​for the 1st and 2nd image data points are 3, and the k value for the 3rd image data point is 6, then 12 distances Di-j are calculated: D1-1 to D1-3, D2-1 to D2-3, and D3-1 to D3-6. In this way, the processor 121 calculates the distance from the second detection position P2 to the droplet target that is k-th furthest from the first droplet target furthest from the second detection position P2 for each image data point. In the following explanation, we will assume that there are three uncoupled droplet targets DL in the first image data point. The three uncoupled droplet targets DL may be referred to as uncoupled droplet target DL1-1, uncoupled droplet target DL1-2, and uncoupled droplet target DL1-3, in order of proximity to the second detection position P2. After the processor 121 calculates the distance Di-j for each of the i image data points, it proceeds the control flow to step SP143.

[0162] (Step SP143) In this step, the processor 121 calculates the average distance Dave of the multiple calculated distances Di-j. Specifically, the processor 121 allocates the unconnected droplet target DL of the first image data and the unconnected droplet targets DL of each image data other than the first one that approximate the respective distances D1-j in the first image data as a group. Figure 22 is a diagram illustrating this allocation. In Figure 22, there are three image data, i=3, and the first, second, and third image data are shown as image data D1, D2, and D3, respectively. The k of the first and second image data D1 and D2 is set to 3, and the k of the third image data D3 is set to 6. In image data D1, D2, and D3, the unconnected droplet targets DL1-1 to DL1-3, DL2-1 to DL2-3, and DL3-1 to DL3-6 are shown in order of closest to the second detection position P2. In step SP142, the distance D between the second detection position P2 and each unconnected droplet target in the image data D1, D2, and D3 is calculated.

[0163] In this step, the processor 121 identifies an unconnected droplet target DL from among the unconnected droplet targets DL of the second and third image data D2 and D3 whose distance D approximates the distance D of the unconnected droplet target DL1-1 that is closest to the second detection position P2 in the first image data D1, based on the calculated distance D. In this step, the unconnected droplet targets DL identified in the second and third image data D2 and D3 are described as unconnected droplet targets DL2-1 and 3-1. Then, the processor 121 assigns the unconnected droplet targets DL1-1, 2-1, and 3-1 as a group G1.

[0164] Furthermore, based on the calculated distance, the processor 121 identifies an unconnected droplet target DL from among the unconnected droplet targets DL of the second and third image data D2 and D3 whose distance D approximates the distance D of the unconnected droplet target DL1-2 that is second closest to the second detection position P2 in the first image data D1. In this step, the unconnected droplet targets DL identified in the second and third image data D2 and D3 are described as unconnected droplet targets DL2-2 and 3-4. Then, the processor 121 assigns the unconnected droplet targets DL1-2, 2-2 and 3-4 as a group G2.

[0165] Furthermore, based on the calculated distance, the processor 121 identifies an unconnected droplet target DL from among the unconnected droplet targets DL of the second and third image data D2 and D3 whose distance D approximates the distance D of the unconnected droplet target DL1-3 that is the third closest to the second detection position P2 in the first image data D1. In this step, the unconnected droplet targets DL identified in the second and third image data D2 and D3 are described as unconnected droplet targets DL2-2 and 3-6. Then, the processor 121 assigns the unconnected droplet targets DL1-3, 2-3, and 3-6 as a group G3.

[0166] As described above, the processor 121 identifies unconnected droplet target DLs from the image data D2 and D3 (other than the first image data D1) whose distance D approximates the distance D between the second detection position P2 and each of the unconnected droplet target DLs that are k-th furthest from the second detection position P2 in the first image data D1. For example, unconnected droplet targets DL2-2 and 3-4 are the unconnected droplet target DLs that are located within a predetermined tolerance range for the distance D of unconnected droplet target DL1-2 in the image data D2 and D3, and whose distance D is closest to the distance D of unconnected droplet target DL1-2. The processor 121 then assigns the unconnected droplet target DLs from the first image data D1 and the unconnected droplet target DLs identified from the second and third image data D2 and D3 as a group. For example, if unconnected droplet target DL2-2 does not exist in group G2, unconnected droplet targets DL1-2 and 3-4 are assigned to group G2. If unbound droplet target DL2-2 does not exist, either unbound droplet target DL2-1 or unbound droplet target DL2-3 becomes the unbound droplet target DL whose distance D approximates that of unbound droplet target DL1-2. However, the distance D of both unbound droplet targets DL2-1 and DL2-3 exceeds the predetermined tolerance range for the distance D of unbound droplet target DL1-2 and therefore does not approximate the distance D of unbound droplet target DL1-2. For this reason, if unbound droplet target DL2-2 does not exist, neither unbound droplet target DL2-1 nor unbound droplet target DL2-3 is assigned to group G2.

[0167] As a result of the aforementioned allocation, multiple groups are created, and the average distance Davej is calculated for each group. Specifically, the processor 121 calculates the average distance Dave1 for each of the unconnected droplet targets DL1-1, 2-1, and 3-1 in group G1 relative to the unconnected droplet target DL1-1, which is closest to the second detection position P2 in the first image data D1. The processor 121 also calculates the average distance Dave2 for each of the unconnected droplet targets DL1-2, 2-2, and 3-4 in group G2 relative to the unconnected droplet target DL1-2, which is second closest to the second detection position P2 in the first image data D1. The processor 121 also calculates the average distance Dave3 for each of the unconnected droplet targets DL1-3, 2-3, and 3-6 in group G3 relative to the unconnected droplet target DL1-3, which is third closest to the second detection position P2 in the first image data D1. Once the processor 121 has calculated each average distance Dave, it proceeds the control flow to step SP144.

[0168] (Step SP144) In this step, the processor 121 calculates the standard deviation σ1 of the variability of unconnected droplet targets DL1-1, 2-1, and 3-1 for the second detection position P2 by substituting the number of image data points n, the distance Di-j, and the average distance Dave1 into equation (1) for the group G1. Similarly, the processor 121 calculates the standard deviation σ2 of the variability of unconnected droplet targets DL1-2, 2-2, and 3-4 for the group G2 and the standard deviation σ3 of the variability of unconnected droplet targets DL1-3, 2-3, and 3-6 for the group G3. Thus, the processor 121 calculates the standard deviation σ for each of the unconnected droplet targets DL whose distances are approximated in each image data point D1, D2, and D3. This calculates k standard deviations σ for image data point D1. Once the processor 121 has calculated the standard deviations σ1, σ2, and σ3, it proceeds to step SP145 of the control flow. Furthermore, among the standard deviations σ1, σ2, and σ3, we assume that σ1 is the smallest standard deviation.

[0169] (Step SP145) In this step, if there is an uncoupled droplet target DL that satisfies the standard deviation σ ≤ threshold σ_limit calculated in step SP144, the processor 121 proceeds to step SP61 shown in Figure 23. If there is no uncoupled droplet target DL that satisfies the standard deviation σ ≤ threshold σ_limit, the processor 121 proceeds to step SP146. In other words, if all of the standard deviations σ1, σ2, and σ3 are greater than the threshold σ_limit, the processor 121 proceeds to step SP61 shown in Figure 23, and if any of the standard deviations σ1, σ2, and σ3 are less than or equal to the threshold σ_limit, the processor 121 proceeds to step SP146. The processor 121 also determines that the droplet target DL with a standard deviation less than or equal to the threshold σ_limit among the standard deviations σ1, σ2, and σ3 is the droplet target DL synchronized with the imaging timing, and determines that an uncoupled droplet target DL with a standard deviation less than or equal to the threshold σ_limit exists.

[0170] Next, steps SP148 and SP149 will be explained using Figure 23.

[0171] (Step SP148) In this step, the processor 121 sets the delay time td to a value obtained by adding the delay time change time Δt3 to the delay time td, and proceeds to step SP63 of the control flow. The change time Δt3 is set within the time that the imaging device 500 can image the droplet target DL within the region, and specifically it is the value obtained by dividing the target width L1 by the velocity of the droplet target DL. The change time Δt3 may be any time. The change time Δt3 is a value greater than the re-change time Δt2 in the delay time fine-tuning process in step SP30.

[0172] (Step SP149) In this step, the processor 121 sets the delay time td to a value obtained by subtracting the delay time change time Δt3 from the delay time td, and proceeds to step SP67 of the control flow.

[0173] In this embodiment as well, in step SP64, the processor 121 resets the number of image data points n to 0 and returns the control flow to step SP54. Since the number of image data points n is 0, the control flow proceeds sequentially from step SP54 to steps SP142, SP143, and SP144. Then, with the delay time td set in steps SP148 and SP149, the standard deviation σ is recalculated in step SP144, and in step SP145, it is determined whether or not there is an uncoupled droplet target DL that satisfies the standard deviation σ ≤ threshold σ_limit. In this way, by repeating the control flow of steps SP54, SP142 to SP145, and each step shown in Figure 21, the processor 121 identifies an uncoupled droplet target DL in which the smallest standard deviation among multiple standard deviations σ is less than or equal to the first threshold, which is the threshold σ_limit.

[0174] Next, we will return to Figure 21 and explain steps SP146 and SP147.

[0175] (Step SP146) The delay time td is changed by the change time Δt3 in steps SP148 and SP149, and the resulting delay time td is greater than or equal to the lower delay time td_lower_limit and less than or equal to the upper delay time td_upper_limit. In this step, the processor 121 sets the delay time td to a value obtained by adding the change time Δt corresponding to the average distance Dave to the delay time td. The average distance Dave in this step is the average distance of the uncoupled droplet target DL that is less than or equal to the threshold σ_limit and corresponds to the smallest standard deviation σ among the standard deviations σ1, σ2, and σ3. The change time Δt is the value obtained by dividing the average distance Dave by the velocity of the droplet target DL calculated in step SP23. Once the delay time td is set, the identified uncoupled droplet target DL is located at the second detection position P2. Therefore, in this step, the processor 121 sets a delay time td based on the average distance Dave from the specific uncoupled droplet target DL to the second detection position P2 such that the standard deviation σ1 calculated in step SP144 is less than or equal to the first threshold, so that the identified uncoupled droplet target DL is located at the second detection position P2. Once the processor 121 has set the delay time td, it proceeds through steps SP60 and SP147 in that order.

[0176] (Step SP147) In this step, the processor 121 sets the width of the observation region to the initial width L0 of the observation region as described in step SP131, finishes the delay time setting process, and proceeds to step SP25 of the control flow.

[0177] In the fine-tuning process for the delay time in this embodiment, in steps SP84 and SP85, the processor 121 sets the delay time re-modification time Δt2 to less than the modification time Δt3. Therefore, after setting the delay time td in the delay time setting process in step SP24, if the distance from the second detection position P2 to the combined droplet target DL in the imaging area is greater than the second threshold in step SP82, the processor 121 re-sets the delay time td based on the delay time re-modification time Δt2 which is less than the modification time Δt3.

[0178] 6.3 Action and Effects In the EUV light generator 100 of this embodiment, even if the detection device 400 and the imaging device 500 are displaced from their pre-set installation positions in the chamber 10, irradiation of a droplet target DL other than the pre-specified droplet target DL with laser light 90 can be suppressed. Furthermore, even if the velocity of the droplet target DL fluctuates slightly, the deviation of the irradiation position at the pre-specified coupled droplet target DL can be suppressed. Therefore, laser light 90 that meets the performance requirements of the exposure device 200 and the inspection device 300 can be emitted, and a decrease in the reliability of the EUV light generator 100 can be suppressed.

[0179] The above description is intended to be illustrative and not restrictive. It will therefore be apparent to those skilled in the art that modifications can be made to the embodiments of this disclosure without departing from the claims. It will also be apparent to those skilled in the art that the embodiments of this disclosure can be used in combination. Terms used throughout this specification and the claims should be interpreted as "non-limiting" unless otherwise specified. For example, terms such as "includes," "have," "equip," and "possess" should be interpreted as "not excluding the existence of components other than those described." Also, the modifier "one" should be interpreted as "at least one" or "one or more." Furthermore, the term "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 as including combinations of these with anything other than "A," "B," and "C."

Claims

1. A target supply unit including a tank for storing a target substance, a pressure regulator for adjusting the pressure inside the tank, a nozzle for discharging the target substance from the tank, and a vibration element for generating droplet targets of the target substance by vibrating the target substance discharged from the nozzle, A target passage detection device that detects the passage of the droplet target supplied from the target supply unit into the chamber to a first detection position and outputs a passage timing signal each time detection occurs, A delay circuit that receives the aforementioned passage timing signal and outputs a light emission trigger signal and an imaging trigger signal at a timing delayed by a predetermined delay time from the time the passage timing signal is input, A laser device that generates extreme ultraviolet light by irradiating the droplet target with laser light at a second detection position downstream of the first detection position in the direction of movement of the droplet target each time the aforementioned light emission trigger signal is input, A target image acquisition device that, each time the aforementioned imaging trigger signal is input, images the droplet target located within the region including the second detection position and generates image data of the region and the droplet target located within the region, Processor and Equipped with, The processor controls the vibration frequency of the excitation element to zero so that the spacing between adjacent droplet targets becomes irregular, identifies a droplet target whose standard deviation of the distance from the second detection position to the droplet target is less than or equal to a first threshold, and sets the delay time based on the distance from the identified droplet target to the second detection position so that the identified droplet target is located at the second detection position. Extreme ultraviolet light generator.

2. An extreme ultraviolet light generating device according to Claim 1, Let n be the number of the multiple image data images that have been captured. In each of the plurality of image data, the distance from the second detection position to the droplet target is defined as distance Di. The average distance of multiple distances Di is defined as the average distance Dave. If we denote the aforementioned standard deviation as σ, The aforementioned standard deviation σ is calculated by the following formula (1).

3. A target supply unit including a tank for storing a target substance, a pressure regulator for adjusting the pressure inside the tank, a nozzle for discharging the target substance from the tank, and a vibration element for generating droplet targets of the target substance by vibrating the target substance discharged from the nozzle, A target passage detection device that detects the passage of the droplet target supplied from the target supply unit into the chamber to a first detection position and outputs a passage timing signal each time detection occurs, A delay circuit that receives the aforementioned passage timing signal and outputs a light emission trigger signal and an imaging trigger signal at a timing delayed by a predetermined delay time from the time the passage timing signal is input, A laser device that generates extreme ultraviolet light by irradiating the droplet target with laser light at a second detection position downstream of the first detection position in the direction of movement of the droplet target each time the aforementioned light emission trigger signal is input, A target image acquisition device that, each time the aforementioned imaging trigger signal is input, images the droplet target located within the region including the second detection position and generates image data of the region and the droplet target located within the region, Processor and Equipped with, The processor irregularly controls the vibration frequency of the excitation element so that the spacing between adjacent droplet targets is irregular, identifies a droplet target whose standard deviation of the distance from the second detection position to the droplet target is less than or equal to a first threshold, and sets the delay time based on the distance from the identified droplet target to the second detection position so that the identified droplet target is located at the second detection position. Extreme ultraviolet light generator.

4. An extreme ultraviolet light generating device according to Claim 3, Let n be the number of the multiple image data images that have been captured. In each of the plurality of image data, the distance from the second detection position to the droplet target is defined as distance Di. The average distance of multiple distances Di is defined as the average distance Dave. If we denote the aforementioned standard deviation as σ, The aforementioned standard deviation σ is calculated by the following formula (1).

5. A target supply unit including a tank for storing a target substance, a pressure regulator for adjusting the pressure inside the tank, a nozzle for discharging the target substance from the tank, and a vibration element for generating droplet targets of the target substance by vibrating the target substance discharged from the nozzle, A target passage detection device that detects the passage of the droplet target supplied from the target supply unit into the chamber to a first detection position and outputs a passage timing signal each time detection occurs, A delay circuit that receives the aforementioned passage timing signal and outputs a light emission trigger signal and an imaging trigger signal at a timing delayed by a predetermined delay time from the time the passage timing signal is input, A laser device that generates extreme ultraviolet light by irradiating the droplet target with laser light at a second detection position downstream of the first detection position in the direction of movement of the droplet target each time the aforementioned light emission trigger signal is input, A target image acquisition device that, each time the aforementioned imaging trigger signal is input, images the droplet target located within the region including the second detection position and generates image data of the region and the droplet target located within the region, Processor and Equipped with, The processor controls the excitation element so that the spacing between adjacent droplet targets is irregular, identifies a droplet target whose standard deviation of the distance from the second detection position to the droplet target is less than or equal to a first threshold, and sets the delay time based on the distance from the identified droplet target to the second detection position so that the identified droplet target is located at the second detection position. The processor identifies a droplet target whose standard deviation of the distance from the second detection position to the droplet target closest to the second detection position is less than or equal to the first threshold. If it cannot identify a droplet target whose standard deviation is less than or equal to the first threshold, it sets the delay time change time Δt1 to a time less than or equal to the generation period of the droplet target when the distance between adjacent droplet targets is the same, and identifies a droplet target whose standard deviation is less than or equal to the first threshold. Extreme ultraviolet light generator.

6. An extreme ultraviolet light generating apparatus according to claim 5, If, after setting the delay time, the processor determines that the distance from the second detection position to the droplet target within the region is greater than the second threshold, it sets the delay time to readjustment time Δt2 to less than the change time Δt1 and readjusts the delay time.

7. An extreme ultraviolet light generating device according to Claim 5, Let n be the number of the multiple image data images that have been captured. In each of the plurality of image data, the distance from the second detection position to the droplet target is defined as distance Di. The average distance of multiple distances Di is defined as the average distance Dave. If we denote the aforementioned standard deviation as σ, The aforementioned standard deviation σ is calculated by the following formula (1).

8. A target supply unit including a tank for storing a target substance, a pressure regulator for adjusting the pressure inside the tank, a nozzle for discharging the target substance from the tank, and a vibration element for generating droplet targets of the target substance by vibrating the target substance discharged from the nozzle, A target passage detection device that detects the passage of the droplet target supplied from the target supply unit into the chamber to a first detection position and outputs a passage timing signal each time detection occurs, A delay circuit that receives the aforementioned passage timing signal and outputs a light emission trigger signal and an imaging trigger signal at a timing delayed by a predetermined delay time from the time the passage timing signal is input, A laser device that generates extreme ultraviolet light by irradiating the droplet target with laser light at a second detection position downstream of the first detection position in the direction of movement of the droplet target each time the aforementioned light emission trigger signal is input, A target image acquisition device that, each time the aforementioned imaging trigger signal is input, images the droplet target located within the region including the second detection position and generates image data of the region and the droplet target located within the region, Processor and Equipped with, The processor controls the excitation element so that the spacing between adjacent droplet targets is irregular, identifies a droplet target whose standard deviation of the distance from the second detection position to the droplet target is less than or equal to a first threshold, and sets the delay time based on the distance from the identified droplet target to the second detection position so that the identified droplet target is located at the second detection position. The processor calculates the distance between the second detection position and the droplet target that is the kth furthest from the first furthest droplet target in each of the image data, where k is a natural number greater than or equal to 2. The processor identifies droplet targets from each of the image data other than the first one whose distance approximates the distance between the second detection position and each of the droplet targets that are the kth furthest from the first furthest droplet target in the first image data. The processor calculates the standard deviation for each of the droplet targets whose distance approximates in each of the image data, and identifies the droplet target for which the smallest standard deviation among the k standard deviations in the first image data is less than or equal to the first threshold. Extreme ultraviolet light generator.

9. An extreme ultraviolet light generating apparatus according to claim 8, If the processor cannot identify a droplet target whose standard deviation is less than or equal to the first threshold, it sets the delay time change time Δt3 to within the time that the target image acquisition device can image the droplet target within the region, and identifies a droplet target whose smallest standard deviation among the k standard deviations is less than or equal to the first threshold.

10. An extreme ultraviolet light generating apparatus according to claim 9, If, after setting the delay time, the processor determines that the distance from the second detection position to the droplet target within the region is greater than the second threshold, it sets the delay time to readjustment time Δt2 to less than the readjustment time Δt3 and readjusts the delay time.

11. An extreme ultraviolet light generating apparatus according to claim 8, Let n be the number of the multiple image data images that have been captured. In each of the plurality of image data, the distance from the second detection position to the droplet target is defined as distance Di. The average distance of multiple distances Di is defined as the average distance Dave. If we denote the aforementioned standard deviation as σ, The aforementioned standard deviation σ is calculated by the following formula (1).

12. A target supply unit including a tank for storing a target substance, a pressure regulator for adjusting the pressure inside the tank, a nozzle for discharging the target substance from the tank, and a vibration element for generating droplet targets of the target substance by vibrating the target substance discharged from the nozzle, A target passage detection device that detects the passage of the droplet target supplied from the target supply unit into the chamber to a first detection position and outputs a passage timing signal each time detection occurs, A delay circuit that receives the aforementioned passage timing signal and outputs a light emission trigger signal and an imaging trigger signal at a timing delayed by a predetermined delay time from the time the passage timing signal is input, A laser device that generates extreme ultraviolet light by irradiating the droplet target with laser light at a second detection position downstream of the first detection position in the direction of movement of the droplet target each time the aforementioned light emission trigger signal is input, A target image acquisition device that, each time the aforementioned imaging trigger signal is input, images the droplet target located within the region including the second detection position and generates image data of the region and the droplet target located within the region, Processor and Equipped with, The processor controls the vibration frequency of the excitation element to zero so that the spacing between adjacent droplet targets is irregular, identifies a droplet target whose standard deviation of the distance from the second detection position to the droplet target is less than or equal to a first threshold, sets the delay time based on the distance from the identified droplet target to the second detection position so that the identified droplet target is located at the second detection position, and outputs the extreme ultraviolet light generated by the extreme ultraviolet light generator to the exposure apparatus. In order to manufacture an electronic device, the photosensitive substrate is exposed to the extreme ultraviolet light in the exposure apparatus. A method for manufacturing electronic devices, including the following.

13. A target supply unit including a tank for storing a target substance, a pressure regulator for adjusting the pressure inside the tank, a nozzle for discharging the target substance from the tank, and a vibration element for generating droplet targets of the target substance by vibrating the target substance discharged from the nozzle, A target passage detection device that detects the passage of the droplet target supplied from the target supply unit into the chamber to a first detection position and outputs a passage timing signal each time detection occurs, A delay circuit that receives the aforementioned passage timing signal and outputs a light emission trigger signal and an imaging trigger signal at a timing delayed by a predetermined delay time from the time the passage timing signal is input, A laser device that generates extreme ultraviolet light by irradiating the droplet target with laser light at a second detection position downstream of the first detection position in the direction of movement of the droplet target each time the aforementioned light emission trigger signal is input, A target image acquisition device that, each time the aforementioned imaging trigger signal is input, images the droplet target located within the region including the second detection position and generates image data of the region and the droplet target located within the region, Processor and Equipped with, The processor irregularly controls the vibration frequency of the excitation element so that the spacing between adjacent droplet targets is irregular, identifies a droplet target whose standard deviation of the distance from the second detection position to the droplet target is less than or equal to a first threshold, sets the delay time based on the distance from the identified droplet target to the second detection position so that the identified droplet target is located at the second detection position, and outputs the extreme ultraviolet light generated by the extreme ultraviolet light generator to the exposure apparatus. In order to manufacture an electronic device, the photosensitive substrate is exposed to the extreme ultraviolet light in the exposure apparatus. A method for manufacturing electronic devices, including the following.

14. A target supply unit including a tank for storing a target substance, a pressure regulator for adjusting the pressure inside the tank, a nozzle for discharging the target substance from the tank, and a vibration element for generating droplet targets of the target substance by vibrating the target substance discharged from the nozzle, A target passage detection device that detects the passage of the droplet target supplied from the target supply unit into the chamber to a first detection position and outputs a passage timing signal each time detection occurs, A delay circuit that receives the aforementioned passage timing signal and outputs a light emission trigger signal and an imaging trigger signal at a timing delayed by a predetermined delay time from the time the passage timing signal is input, A laser device that generates extreme ultraviolet light by irradiating the droplet target with laser light at a second detection position downstream of the first detection position in the direction of movement of the droplet target each time the aforementioned light emission trigger signal is input, A target image acquisition device that, each time the aforementioned imaging trigger signal is input, images the droplet target located within the region including the second detection position and generates image data of the region and the droplet target located within the region, Processor and Equipped with, The processor controls the excitation element so that the spacing between adjacent droplet targets is irregular, identifies a droplet target whose standard deviation of the distance from the second detection position to the droplet target is less than or equal to a first threshold, and sets the delay time based on the distance from the identified droplet target to the second detection position so that the identified droplet target is located at the second detection position. The processor identifies a droplet target whose standard deviation of the distance from the second detection position to the droplet target closest to the second detection position is less than or equal to the first threshold, and if it is not possible to identify a droplet target whose standard deviation is less than or equal to the first threshold, it sets the delay time change time Δt1 to a time less than or equal to the generation period of the droplet target when the distance between adjacent droplet targets is the same, and outputs the extreme ultraviolet light generated by the extreme ultraviolet light generator that identifies the droplet target whose standard deviation is less than or equal to the first threshold to the exposure apparatus. In order to manufacture an electronic device, the photosensitive substrate is exposed to the extreme ultraviolet light in the exposure apparatus. A method for manufacturing electronic devices, including the following.

15. A target supply unit including a tank for storing a target substance, a pressure regulator for adjusting the pressure inside the tank, a nozzle for discharging the target substance from the tank, and a vibration element for generating droplet targets of the target substance by vibrating the target substance discharged from the nozzle, A target passage detection device that detects the passage of the droplet target supplied from the target supply unit into the chamber to a first detection position and outputs a passage timing signal each time detection occurs, A delay circuit that receives the aforementioned passage timing signal and outputs a light emission trigger signal and an imaging trigger signal at a timing delayed by a predetermined delay time from the time the passage timing signal is input, A laser device that generates extreme ultraviolet light by irradiating the droplet target with laser light at a second detection position downstream of the first detection position in the direction of movement of the droplet target each time the aforementioned light emission trigger signal is input, A target image acquisition device that, each time the aforementioned imaging trigger signal is input, images the droplet target located within the region including the second detection position and generates image data of the region and the droplet target located within the region, Processor and Equipped with, The processor controls the excitation element so that the spacing between adjacent droplet targets is irregular, identifies a droplet target whose standard deviation of the distance from the second detection position to the droplet target is less than or equal to a first threshold, and sets the delay time based on the distance from the identified droplet target to the second detection position so that the identified droplet target is located at the second detection position. The processor calculates the distance from the second detection position to the k-th droplet target that is furthest from the first droplet target furthest from the second detection position in each of the image data, where k is a natural number of 2 or more, and identifies from each of the image data other than the first that the distance from the second detection position to each of the k-th droplet targets that is furthest from the first droplet target furthest from the second detection position in the first image data is approximated by the processor, calculates the standard deviation for each of the droplet targets whose distance is approximated in each of the image data, and identifies the droplet target for which the smallest standard deviation among the k standard deviations in the first image data is less than or equal to the first threshold, and outputs the extreme ultraviolet light generated by the extreme ultraviolet light generator to the exposure device. In order to manufacture an electronic device, the photosensitive substrate is exposed to the extreme ultraviolet light in the exposure apparatus. A method for manufacturing electronic devices, including the following.

16. A target supply unit including a tank for storing a target substance, a pressure regulator for adjusting the pressure inside the tank, a nozzle for discharging the target substance from the tank, and a vibration element for generating droplet targets of the target substance by vibrating the target substance discharged from the nozzle, A target passage detection device that detects the passage of the droplet target supplied from the target supply unit into the chamber to a first detection position and outputs a passage timing signal each time detection occurs, A delay circuit that receives the aforementioned passage timing signal and outputs a light emission trigger signal and an imaging trigger signal at a timing delayed by a predetermined delay time from the time the passage timing signal is input, A laser device that generates extreme ultraviolet light by irradiating the droplet target with laser light at a second detection position downstream of the first detection position in the direction of movement of the droplet target each time the aforementioned light emission trigger signal is input, A target image acquisition device that, each time the aforementioned imaging trigger signal is input, images the droplet target located within the region including the second detection position and generates image data of the region and the droplet target located within the region, Processor and Equipped with, The processor controls the vibration frequency of the excitation element to zero so that the spacing between adjacent droplet targets is irregular, identifies a droplet target whose standard deviation of the distance from the second detection position to the droplet target is less than or equal to a first threshold, sets the delay time based on the distance from the identified droplet target to the second detection position so that the identified droplet target is located at the second detection position, and irradiates the mask with the extreme ultraviolet light generated by the extreme ultraviolet light generator to inspect the mask for defects. Using the results of the above inspection, select a mask. The pattern formed on the selected mask is then exposed and transferred onto a photosensitive substrate. A method for manufacturing electronic devices, including the following.

17. A target supply unit including a tank for storing a target substance, a pressure regulator for adjusting the pressure inside the tank, a nozzle for discharging the target substance from the tank, and a vibration element for generating droplet targets of the target substance by vibrating the target substance discharged from the nozzle, A target passage detection device that detects the passage of the droplet target supplied from the target supply unit into the chamber to a first detection position and outputs a passage timing signal each time detection occurs, A delay circuit that receives the aforementioned passage timing signal and outputs a light emission trigger signal and an imaging trigger signal at a timing delayed by a predetermined delay time from the time the passage timing signal is input, A laser device that generates extreme ultraviolet light by irradiating the droplet target with laser light at a second detection position downstream of the first detection position in the direction of movement of the droplet target each time the aforementioned light emission trigger signal is input, A target image acquisition device that, each time the aforementioned imaging trigger signal is input, images the droplet target located within the region including the second detection position and generates image data of the region and the droplet target located within the region, Processor and Equipped with, The processor irregularly controls the vibration frequency of the excitation element so that the spacing between adjacent droplet targets is irregular, identifies a droplet target whose standard deviation of the distance from the second detection position to the droplet target is less than or equal to a first threshold, sets the delay time based on the distance from the identified droplet target to the second detection position so that the identified droplet target is located at the second detection position, and irradiates the mask with the extreme ultraviolet light generated by the extreme ultraviolet light generator to inspect the mask for defects. Using the results of the above inspection, select a mask. The pattern formed on the selected mask is then exposed and transferred onto a photosensitive substrate. A method for manufacturing electronic devices, including the following.

18. A target supply unit including a tank for storing a target substance, a pressure regulator for adjusting the pressure inside the tank, a nozzle for discharging the target substance from the tank, and a vibration element for generating droplet targets of the target substance by vibrating the target substance discharged from the nozzle, A target passage detection device that detects the passage of the droplet target supplied from the target supply unit into the chamber to a first detection position and outputs a passage timing signal each time detection occurs, A delay circuit that receives the aforementioned passage timing signal and outputs a light emission trigger signal and an imaging trigger signal at a timing delayed by a predetermined delay time from the time the passage timing signal is input, A laser device that generates extreme ultraviolet light by irradiating the droplet target with laser light at a second detection position downstream of the first detection position in the direction of movement of the droplet target each time the aforementioned light emission trigger signal is input, A target image acquisition device that, each time the aforementioned imaging trigger signal is input, images the droplet target located within the region including the second detection position and generates image data of the region and the droplet target located within the region, Processor and Equipped with, The processor controls the excitation element so that the spacing between adjacent droplet targets is irregular, identifies a droplet target whose standard deviation of the distance from the second detection position to the droplet target is less than or equal to a first threshold, and sets the delay time based on the distance from the identified droplet target to the second detection position so that the identified droplet target is located at the second detection position. The processor identifies a droplet target whose standard deviation of the distance from the second detection position to the droplet target closest to the second detection position is less than or equal to the first threshold, and if it is not possible to identify a droplet target whose standard deviation is less than or equal to the first threshold, it sets the delay time change time Δt1 to a time less than or equal to the generation cycle of the droplet target when the interval between adjacent droplet targets is the same, and irradiates the mask with the extreme ultraviolet light generated by the extreme ultraviolet light generator that identifies the droplet target whose standard deviation is less than or equal to the first threshold to inspect the mask for defects. Using the results of the above inspection, select a mask. The pattern formed on the selected mask is then exposed and transferred onto a photosensitive substrate. A method for manufacturing electronic devices, including the following.

19. A target supply unit including a tank for storing a target substance, a pressure regulator for adjusting the pressure inside the tank, a nozzle for discharging the target substance from the tank, and a vibration element for generating droplet targets of the target substance by vibrating the target substance discharged from the nozzle, A target passage detection device that detects the passage of the droplet target supplied from the target supply unit into the chamber to a first detection position and outputs a passage timing signal each time detection occurs, A delay circuit that receives the aforementioned passage timing signal and outputs a light emission trigger signal and an imaging trigger signal at a timing delayed by a predetermined delay time from the time the passage timing signal is input, A laser device that generates extreme ultraviolet light by irradiating the droplet target with laser light at a second detection position downstream of the first detection position in the direction of movement of the droplet target each time the aforementioned light emission trigger signal is input, A target image acquisition device that, each time the aforementioned imaging trigger signal is input, images the droplet target located within the region including the second detection position and generates image data of the region and the droplet target located within the region, Processor and Equipped with, The processor controls the excitation element so that the spacing between adjacent droplet targets is irregular, identifies a droplet target whose standard deviation of the distance from the second detection position to the droplet target is less than or equal to a first threshold, and sets the delay time based on the distance from the identified droplet target to the second detection position so that the identified droplet target is located at the second detection position. The processor calculates the distance from the second detection position to the k-th droplet target that is furthest from the first droplet target furthest from the second detection position in each of the image data, where k is a natural number of 2 or more, and identifies from each of the image data other than the first that the distance from the second detection position to each of the k-th droplet targets that is furthest from the first droplet target furthest from the second detection position in the first image data is approximated by the extreme ultraviolet light generated by the extreme ultraviolet light generator, and irradiates the mask with the extreme ultraviolet light generated by the extreme ultraviolet light generator to inspect the mask for defects, and identifies the droplet target for which the smallest standard deviation among the k standard deviations in the first image data is less than or equal to the first threshold. Using the results of the above inspection, select a mask. The pattern formed on the selected mask is then exposed and transferred onto a photosensitive substrate. A method for manufacturing electronic devices, including the following.

Images