Extreme ultraviolet light generation apparatus and method of manufacturing electronic device

Abstract

To solve the problem that, in an LPP for generating extreme ultraviolet light, the trajectory of a droplet is largely deviated by the influence of a buffer gas flow, and the droplet may reach an inner wall without being recovered to contaminate the inside.SOLUTION: A target supply unit configured to supply a droplet of a target substance toward a plasma generation region; a target collection unit disposed on a trajectory along which the target substance is ejected and configured to collect the target substance not irradiated with the laser beam; a first gas supply unit configured to supply a buffer gas into the chamber; and a processor, during a period in which the target supply unit ejects droplets, the processor makes a first flow rate, which is a flow rate of the buffer gas supplied from the first gas supply unit during at least a part of a first period in which the droplets are not irradiated with the laser beam, smaller than a second flow rate, which is a flow rate of the buffer gas supplied from the first gas supply unit during a second period in which the droplets are irradiated with the laser beam.SELECTED DRAWING: Figure 11

Description

[Technical Field]

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

[0002] In recent years, with the miniaturization of semiconductor processes, the miniaturization of transfer patterns in optical lithography for semiconductor processes has progressed rapidly. In the next generation, fine processing of 10 nm or less will be required. For this reason, there is a demand for the development of semiconductor exposure equipment that combines a device for generating extreme ultraviolet (EUV) light with a wavelength of approximately 13 nm and a reduced projection reflective optical system.

[0003] As an extreme ultraviolet light generating device, development of a laser produced plasma (LPP) type device that uses plasma generated by irradiating a target material with laser light is progressing. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 10,225,917 [Patent Document 2] U.S. Patent No. 1,109,2896 [Patent Document 3] Summary of the specification of U.S. Patent No. 9,661,730

[0005] An extreme ultraviolet light generation apparatus according to one aspect of the present disclosure is an extreme ultraviolet light generation apparatus comprising: a chamber that generates extreme ultraviolet light by irradiating laser light onto a target material supplied to a plasma generation region in an internal space; a laser device that generates the laser light; a target supply unit that supplies droplets of the target material toward the plasma generation region; a target recovery unit that is positioned on the trajectory along which the target material is ejected and recovers the target material not irradiated by the laser light; a first gas supply unit that supplies buffer gas into the chamber; and a processor, wherein the processor controls the first gas supply unit to reduce a first flow rate, which is the flow rate of the buffer gas supplied from the first gas supply unit during at least a part of a first period during which the droplets are not irradiated with laser light, compared to a second flow rate, which is the flow rate of the buffer gas supplied from the first gas supply unit during a second period during which the droplets are irradiated with laser light, during a period during which the target supply unit ejects droplets.

[0006] a target collection unit disposed on a trajectory along which the target material is ejected and collections the target material not irradiated with the laser light; a first gas supply unit that supplies a buffer gas into the chamber; and a processor. The processor controls the first gas supply unit to reduce a first flow rate, which is a flow rate of the buffer gas supplied from the first gas supply unit during at least a part of a first period during which the droplets are not irradiated with the laser light, compared to a second flow rate, which is a flow rate of the buffer gas supplied from the first gas supply unit during a second period during which the droplets are irradiated with the laser light. The processor controls the first gas supply unit to reduce a first flow rate, which is a flow rate of the buffer gas supplied from the first gas supply unit during at least a part of a first period during which the droplets are not irradiated with the laser light, during a period during which the target supply unit ejects the droplets, compared to a second flow rate, which is a flow rate of the buffer gas supplied from the first gas supply unit during a second period during which the droplets are irradiated with the laser light. The method includes outputting the extreme ultraviolet light generated by the extreme ultraviolet light generation unit to an exposure apparatus, and exposing a photosensitive substrate in the exposure apparatus to the extreme ultraviolet light to manufacture an electronic device.

[0007] a target collection unit disposed on a trajectory along which the target material is ejected and collection unit that collects the target material not irradiated with the laser light; a first gas supply unit that supplies a buffer gas into the chamber; and a processor, wherein the processor controls the first gas supply unit to reduce a first flow rate, which is a flow rate of the buffer gas supplied from the first gas supply unit during at least a part of a first period during which the droplets are not irradiated with the laser light, compared to a second flow rate, which is a flow rate of the buffer gas supplied from the first gas supply unit during a second period during which the droplets are irradiated with the laser light, during a period during which the target supply unit ejects the droplets; [Brief explanation of the drawings]

[0008] Some embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 is a schematic diagram showing an example of the overall configuration of an electronic device manufacturing apparatus. [Figure 2] FIG. 2 is a schematic diagram showing an example of the overall schematic configuration of an electronic device manufacturing apparatus different from the electronic device manufacturing apparatus shown in FIG. [Figure 3] FIG. 3 is a schematic diagram illustrating an example of the overall configuration of an extreme ultraviolet light generation system according to a comparative example. [Figure 4] FIG. 4 is a schematic diagram showing a cross section of an extreme ultraviolet light generation device perpendicular to the droplet trajectory in a comparative example. [Figure 5] FIG. 5 is a schematic diagram showing a cross section of an extreme ultraviolet light generation device along the trajectory of a droplet in a comparative example. [Figure 6] FIG. 6 is a flowchart showing the operation flow of the extreme ultraviolet light generation system according to the comparative example. [Figure 7] (A) A diagram showing the transition of gas pressure in the space where the target supply unit is placed at each step in Figure 6. (B) A diagram showing the transition of gas supply amount at each step in Figure 6. (C) A diagram showing the transition of temperature and pressure in the target supply unit at each step in Figure 6. (D) A diagram showing the transition of duty of the piezoelectric element of the target supply unit at each step in Figure 6. (E) A diagram showing the transition of droplet spacing determination results at each step in Figure 6. (F) A diagram showing the transition of extreme ultraviolet light stability determination results at each step in Figure 6. [Figure 8] FIG. 8 is a partially enlarged view of FIG. [Figure 9] FIG. 9 is a schematic diagram of FIG. 5 as viewed from the opening side. [Figure 10] FIG. 10 is a schematic diagram showing the case where droplets with small diameters are ejected in FIG. [Figure 11] FIG. 11 is a flowchart illustrating the operation flow of the extreme ultraviolet light generation system according to the first embodiment. [Figure 12] (A) A diagram showing the transition of gas pressure in the space where the target supply unit is placed at each step in Figure 11. (B) A diagram showing the transition of gas supply amount at each step in Figure 11. (C) A diagram showing the transition of temperature and pressure in the target supply unit at each step in Figure 11. (D) A diagram showing the transition of duty of the piezoelectric element of the target supply unit at each step in Figure 11. (E) A diagram showing the transition of droplet spacing determination results at each step in Figure 11. (F) A diagram showing the transition of extreme ultraviolet light stability determination results at each step in Figure 11. [Figure 13] FIG. 13 is a schematic diagram showing a case where droplets with small diameters are ejected in the first embodiment. [Figure 14] FIG. 14 is a flowchart illustrating an operation flow of the extreme ultraviolet light generation system according to the first modification of the first embodiment. [Figure 15]FIG. 15 is a flowchart illustrating an operation flow of the extreme ultraviolet light generation system according to the second modification of the first embodiment. [Figure 16] FIG. 16 is a flowchart showing the operation flow of the extreme ultraviolet light generation system according to the second embodiment. [Figure 17] (A) A diagram showing the transition of gas pressure in the space where the target supply unit is placed at each step in Figure 16. (B) A diagram showing the transition of gas supply amount at each step in Figure 16. (C) A diagram showing the transition of temperature and pressure in the target supply unit at each step in Figure 16. (D) A diagram showing the transition of duty of the piezoelectric element of the target supply unit at each step in Figure 16. (E) A diagram showing the transition of droplet spacing determination results at each step in Figure 16. (F) A diagram showing the transition of extreme ultraviolet light stability determination results at each step in Figure 16. [Figure 18] FIG. 18 is a flowchart illustrating an operation flow of the extreme ultraviolet light generation system according to the first modification of the second embodiment. [Figure 19] 19A is a diagram showing the transition of gas pressure in a space where a target supply part is arranged in each step of FIG. 18. FIG. 19B is a diagram showing the transition of gas supply amount in each step of FIG. [Figure 20] FIG. 20 is a schematic diagram showing a cross section of the extreme ultraviolet light generation system along the trajectory of a droplet in Modification 2 of Embodiment 2. In FIG. [Figure 21] FIG. 21 is a flowchart illustrating an operation flow of the extreme ultraviolet light generation system according to the second modification of the second embodiment. [Figure 22] 22A is a diagram showing the transition of gas pressure in a space where a target supply part is disposed in each step of FIG. 21. FIG. 22B is a diagram showing the transition of gas supply amount in each step of FIG. [Figure 23] FIG. 23 is a flowchart showing the operation flow of the extreme ultraviolet light generation system according to the third embodiment. [Figure 24](A) A diagram showing the transition of gas pressure in the space where the target supply part is arranged in each step of Fig. 23. (B) A diagram showing the transition of gas supply amount in each step of Fig. 23. (C) A diagram showing the transition of gas exhaust amount in each step of Fig. 23. Embodiment

[0009] 1. Overview 2. Description of electronic device manufacturing equipment 3. Description of the extreme ultraviolet light generation device as a comparative example 3.1 Configuration 3.2 Operation 3.3 Challenges 4. Description of the extreme ultraviolet light generation device according to the first embodiment 4.1 Configuration 4.2 Operation 4.3 Actions and Effects 4.4 Variation 1 4.4.1 Configuration 4.4.2 Operation 4.4.3 Actions and Effects 4.5 Variation 2 4.5.1 Configuration 4.5.2 Operation 4.5.3 Actions and Effects 5. Description of the extreme ultraviolet light generation device according to the second embodiment 5.1 Configuration 5.2 Operation 5.3 Actions and Effects 5.4 Variation 1 5.4.1 Configuration 5.4.2 Operation 5.4.3 Actions and Effects 5.5 Variation 2 5.5.1 Configuration 5.5.2 Operation 5.5.3 Actions and Effects 6. Description of the extreme ultraviolet light generation device according to the third embodiment 6.1 Configuration 6.2 Operation 6.3 Actions and Effects

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The embodiments described below show some examples of the present disclosure and do not limit the content of the present disclosure. Furthermore, not all of the configurations and operations described in each embodiment are necessarily essential as the configurations and operations of the present disclosure. Note that the same components are given the same reference symbols, and redundant explanations will be omitted.

[0011] 1. Overview An embodiment of the present disclosure relates to an extreme ultraviolet light generation apparatus that generates light with a wavelength called extreme ultraviolet (EUV), and an electronic device manufacturing apparatus. Note that hereinafter, extreme ultraviolet light may also be referred to as EUV light.

[0012] 2. Description of electronic device manufacturing equipment FIG. 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 FIG. 1 includes an extreme ultraviolet light generation system 100 and an exposure apparatus 200. The exposure apparatus 200 includes a mask irradiation unit 210 including multiple mirrors 211 and 212, which are a reflective optical system, and a workpiece irradiation unit 220 including multiple mirrors 221 and 222, which are a reflective optical system separate from the reflective optical system of the mask irradiation unit 210. The mask irradiation unit 210 illuminates a mask pattern on a mask table MT via the mirrors 211 and 212 with EUV light 101 incident from the extreme ultraviolet light generation system 100. The workpiece irradiation unit 220 forms an image of the EUV light 101 reflected by the mask table MT onto a workpiece (not shown) placed on a workpiece table WT via the mirrors 221 and 222. The workpiece is a photosensitive substrate such as a semiconductor wafer coated with photoresist. Exposure apparatus 200 synchronously translates mask table MT and workpiece table WT to expose the workpiece to EUV light 101 that reflects the mask pattern. By using the exposure process described above, a device pattern can be transferred onto a semiconductor wafer, thereby manufacturing a semiconductor device.

[0013] FIG. 2 is a schematic diagram illustrating an example of the overall configuration of an electronic device manufacturing apparatus different from the electronic device manufacturing apparatus illustrated in FIG. 1. The electronic device manufacturing apparatus illustrated in FIG. 2 includes an extreme ultraviolet light generation apparatus 100 and an inspection apparatus 300. The inspection apparatus 300 includes an illumination optical system 310 including multiple mirrors 311, 313, and 315, which are reflective optical systems, and a detection optical system 320 including multiple mirrors 321 and 323, which are reflective optical systems separate from the reflective optical system of the illumination optical system 310, and a detector 325. The illumination optical system 310 reflects the EUV light 101 incident from the extreme ultraviolet light generation apparatus 100 by the mirrors 311, 313, and 315, and irradiates the mask 333 placed on a mask stage 331. The mask 333 includes a mask blank before a pattern is formed. The detection optical system 320 reflects the EUV light 101, which reflects a pattern from the mask 333, by the mirrors 321 and 323, and forms an image on the light-receiving surface of the detector 325. The detector 325 receives the EUV light 101 and 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 the mask 333 for defects, and the inspection results 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, thereby manufacturing an electronic device.

[0014] 3. Description of the extreme ultraviolet light generation device as a comparative example 3.1 Configuration A comparative example of an extreme ultraviolet light generation apparatus 100 will be described. Note that the comparative example of the present disclosure refers to a configuration that the applicant recognizes as being known only by the applicant, and is not a publicly known example that the applicant acknowledges. In the following, the extreme ultraviolet light generation apparatus 100 that emits EUV light 101 toward an exposure apparatus 200 as a next process apparatus, as shown in FIG. 1, will be used for the description. Note that the same functions and effects can be obtained with an extreme ultraviolet light generation apparatus 100 that emits EUV light 101 toward an inspection apparatus 300 as a next process apparatus, as shown in FIG. 2.

[0015] 3 shows a schematic configuration of an LPP-type extreme ultraviolet light generation system 11. The extreme ultraviolet light generation apparatus 100 is optically connected to a laser apparatus 3. In the present disclosure, a system including the laser apparatus 3 and the extreme ultraviolet light generation apparatus 100 is referred to as the extreme ultraviolet light generation system 11.

[0016] The laser device 3 includes a master oscillator, which is a light source that performs burst operation. The master oscillator emits pulsed laser light 31 in burst-on mode. The master oscillator is, for example, a solid-state laser device that excites a YAG crystal doped with niobium (Nb) or ytterbium (Yb), or a laser device that emits pulsed laser light 31 by exciting a gas in which helium, nitrogen, or the like is mixed with carbon dioxide gas through discharge. Alternatively, the master oscillator may be a quantum cascade laser device. The master oscillator may also emit the pulsed laser light 31 using a Q-switching method. The master oscillator may also include an optical switch, a polarizer, or the like. The laser device 3 may also include an amplifier that amplifies the pulsed laser light 31 emitted by the master oscillator. Note that burst operation refers to an operation that repeatedly performs burst-on, in which the pulsed laser light 31 is emitted at a predetermined repetition rate, and burst-off, in which the emission of the pulsed laser light 31 is suppressed.

[0017] The extreme ultraviolet light generation device 100 mainly includes a chamber 2 which is a sealable container, a laser light transmission device 34 which transmits pulsed laser light 31 emitted from a laser device 3 to the chamber 2, and a processor 5 which controls the extreme ultraviolet light generation system 11.

[0018] The laser beam transmission device 34 includes an optical element (not shown) for defining the transmission state of the pulsed laser beam 31 and an actuator (not shown) for adjusting the position, attitude, etc. of the optical element. The pulsed laser beam 31 emitted from the laser device 3 is guided to the chamber 2 by the laser beam transmission device 34. The chamber 2 includes a window 21, and the pulsed laser beam 31 enters the internal space of the chamber 2 through the window 21. A laser beam focusing mirror 22 is disposed in the internal space of the chamber 2, and the pulsed laser beam 31 is reflected and focused by the laser beam focusing mirror 22. The position of the laser beam focusing mirror 22 is adjusted so that the focusing position of the pulsed laser beam 31 in the internal space of the chamber 2 is a position specified by the processor 5. The focusing position is adjusted to be located directly below a nozzle 43 (described later). When the pulsed laser beam 31 is irradiated onto a target material at the focusing position, plasma is generated from the target material, and radiation 251 is emitted from the plasma. The radiation 251 includes EUV light 252. The region where plasma is generated is called the plasma generation region 25. The plasma generation region 25 is a region having a radius of, for example, 40 mm centered on the plasma point, and is located in the internal space of the chamber 2.

[0019] An EUV collector mirror 23 including, for example, an ellipsoidal reflective surface is disposed in the internal space of the chamber 2. The EUV collector mirror 23 includes, for example, a multilayer film in which silicon layers and molybdenum layers are alternately stacked, and the multilayer film selectively reflects EUV light 252 from the synchrotron radiation 251. A through-hole 24 is formed in the center of the EUV collector mirror 23, and the pulsed laser beam 31 passes through the through-hole 24. The EUV collector mirror 23 has a first focal point and a second focal point. For example, the first focal point is positioned in the plasma generation region 25, and the second focal point is positioned at an intermediate focal point 292.

[0020] The extreme ultraviolet light generation system 100 includes a connection part 29 that connects the internal space of the chamber 2 and the internal space of the exposure system 200. A wall 291 having an aperture 293 formed therein is disposed in the connection part 29. This wall 291 is preferably disposed so that the aperture 293 is located at the second focal point. The connection part 29 also serves as an exit port for the EUV light 252 in the chamber 2, and the EUV light 252 is emitted from the connection part 29 and enters the exposure system 200.

[0021] A target supply unit 26 is attached so as to penetrate the wall of the chamber 2. The target supply unit 26 includes a tank 42 and a pressure regulator 48, and supplies droplets 27 into the internal space of the chamber 2 from a nozzle 43 attached to the tank 42.

[0022] The tank 42 stores a target material to be used as the droplets 27. In this comparative example, the target material is tin. The target material may include tin, terbium, gadolinium, lithium, xenon, or a combination of two or more of these. The interior of the tank 42 is connected to a pressure regulator 48 that adjusts the pressure within the tank 42. A heater 47 and a temperature sensor 46 are attached to the tank 42. The heater 47 heats the tank 42 with current supplied from a heater power supply (not shown). This heating melts the target material within the tank 42. The temperature sensor 46 measures the temperature of the target material within the tank 42 via the tank 42. The pressure regulator 48, the temperature sensor 46, and the heater power supply are electrically connected to the processor 5.

[0023] The nozzle 43 is attached to the tank 42 and ejects the target material. A piezoelectric element 44 is attached to the nozzle 43. The piezoelectric element 44 is electrically connected to a piezoelectric element power supply 45 and is vibrated by a voltage applied from the piezoelectric element power supply 45. The piezoelectric element power supply 45 is electrically connected to the processor 5.

[0024] The chamber 2 includes a target collection unit 28. The target collection unit 28 is a box attached to the chamber 2, and its opening is positioned on the trajectory along which the target material is ejected. The target collection unit 28 is a drain tank that collects unwanted droplets 27 that pass through the opening and reach the target collection unit 28.

[0025] A gas supply unit 40 is connected to the chamber 2. The buffer gas contains hydrogen gas, and in this example, the buffer gas is hydrogen gas with a hydrogen concentration that can be considered to be 100%. The gas supply unit 40 may be provided with a gas flow rate regulator (not shown), which is a valve. When the gas flow rate regulator is provided, for example, the processor 5 controls the gas flow rate regulator to adjust the flow rate of the buffer gas being supplied. The buffer gas may be a balance gas with a hydrogen gas concentration of about 3%, and in this case, the balance gas contains, for example, nitrogen (N2) gas or argon (Ar) gas.

[0026] The extreme ultraviolet light generation device 100 also includes a pressure sensor 30 and a target sensor 4. The pressure sensor 30 and the target sensor 4 are attached to the chamber 2 and electrically connected to the processor 5. The pressure sensor 30 measures the pressure in the internal space of the chamber 2 and outputs a signal indicating this pressure to the processor 5.

[0027] The target sensor 4 includes, for example, an imaging function and detects the presence, spacing, trajectory, position, flow velocity, etc. of the droplets 27 ejected from the nozzle hole of the nozzle 43 in response to instructions from the processor 5. The target sensor 4 may be disposed inside the chamber 2 or may be disposed outside the chamber 2 and detect the droplets 27 through a window (not shown) provided in the wall of the chamber 2. The target sensor 4 includes a light-receiving optical system (not shown) and an imaging unit (not shown), such as a charge-coupled device (CCD) or photodiode. The light-receiving optical system forms an image of the trajectory of the droplet 27 and its surroundings on the light-receiving surface of the imaging unit to improve the detection accuracy of the droplet 27. A light source (not shown) is disposed to improve the contrast within the field of view of the target sensor 4. As the droplet 27 passes through the light-collecting area of ​​the light from the light source, the imaging unit detects changes in the light passing through the trajectory of the droplet 27 and its surroundings. The imaging unit converts the detected changes in light into an electrical signal. The electrical signal may include image data of the droplet 27. The imaging unit outputs this electrical signal to the processor 5.

[0028] The chamber 2 includes a gas exhaust port 205 for exhausting the buffer gas. The gas supply port 202 is connected to a gas supply unit 40 that supplies the buffer gas. The gas exhaust port 205 is connected to a gas exhaust unit 50 that exhausts the buffer gas.

[0029] The processor 5 of the present disclosure is a processing device including a memory 501 storing a control program and a central processing unit (CPU) 502 that executes the control program. The processor 5 is specially configured or programmed to execute various processes described herein and controls the entire extreme ultraviolet light generation system 11. The processor 5 receives inputs such as a signal related to the pressure in the internal space of the chamber 2 measured by the pressure sensor 30, a signal related to image data of the droplets 27 captured by the detection unit, and a burst signal instructing a burst operation from the exposure apparatus 200. The processor 5 processes the various signals and may control, for example, the timing and direction of ejection of the droplets 27. The processor 5 may also control the emission timing of the laser device 3, the direction and focus position of the pulsed laser beam 31, and the like. The various controls described above are merely examples, and other controls may be added as necessary, as described below.

[0030] 4 and 5 show a detailed configuration of an extreme ultraviolet light generation system 100 including a chamber 2 according to a comparative example. Note that the same components as those described in FIG. 3 are designated by the same reference numerals, and redundant description will be omitted. The extreme ultraviolet light generation system 100 of this comparative example operates on the same principle as the extreme ultraviolet light generation system 11 of FIG. 3, but differs primarily in that it includes a first partition 37 and a second partition 39, which will be described later. The optical path of the pulsed laser beam 31, indicated by the dashed-dotted line, is also different from that shown in FIG. 3. FIG. 4 shows the configuration from the perspective of the trajectory direction of the droplet 27, and FIG. 5 shows the configuration from the perspective of the optical axis direction of the pulsed laser beam 31. Furthermore, FIG. 5 corresponds to the cross-sectional configuration taken along line AA in FIG. 4. Line AA in FIG. 4 passes through approximately the center of the EUV collector mirror 23, and therefore, in FIG. 5, the EUV collector mirror 23 is shown as having an approximately semi-elliptical shape.

[0031] 4, in the extreme ultraviolet light generation system 100, a first partition wall 37 and a second partition wall 39 are disposed in the internal space of the chamber 2. The first partition wall 37 is disposed to separate a first space 20a including the plasma generation region 25 in the chamber 2 from a second space 20b in which the sensors 4b, 4c, and 4d and the pressure sensor 30 are disposed. The first partition wall 37 also functions to suppress the diffusion of tin debris into the chamber 2, and is therefore sometimes referred to as a debris shield. The second partition wall 39 separates the second space 20b inside the chamber 2 from a third space 20c and a fourth space 20d.

[0032] The first partition wall 37 is made of stainless steel or metallic molybdenum. The first partition wall 37 has a cylindrical shape. The first partition wall 37 penetrates the side surface of the chamber 2.

[0033] A part of the first partition 37 is a cylinder located inside the chamber 2 and is arranged to cover the plasma generation region 25. That is, the plasma generation region 25 is located inside a through-hole of the cylinder. Inside the chamber 2, the first partition 37 has openings 371 to 377. These openings 371 to 377 communicate the first space 20a inside the first partition 37, which is inside the chamber 2, with the space around the first partition 37. The opening 371 is an opening that passes the radiation 251 including the EUV light 252. The opening 372 is an opening that passes the pulsed laser beam 31. The openings 373 and 375 are openings that pass the droplets 27. The openings 374, 376, and 377 are openings for sensors. The opening 371 is a first cylinder opening provided at the end opposite to the gas exhaust unit 50 side.

[0034] The configuration of the extreme ultraviolet light generation system 100 can prevent tin from adhering to the EUV collector mirror 23 and the sensors 4b, 4c, and 4d. Furthermore, the EUV collector mirror 23 does not have a through-hole for passing the pulsed laser beam 31. The plasma generation region 25 is located between the target supply unit 26 and the target recovery unit 28 and inside the first partition wall 37.

[0035] Sensors 4b, 4c, and 4d are attached to the chamber 2. The sensors 4b, 4c, and 4d are similar to the target sensor 4. In this specification, the sensors 4b, 4c, and 4d may be individually referred to as target sensors 4. Although not shown, each of the sensors 4b, 4c, and 4d may include an image sensor or an optical sensor and an optical system that forms an image of the plasma generation region 25 inside the first partition wall 37 or its vicinity on the image sensor or the optical sensor. The sensors 4b, 4c, and 4d have detection windows 404b, 404c, and 404d, respectively, that transmit light, on the inner space side of the chamber 2. Buffer gas supply ports 504b, 504c, and 504d, which are outlets for buffer gas, are arranged near the detection windows 404b, 404c, and 404d of the sensors 4b, 4c, and 4d, respectively. The buffer gas supply ports 504b, 504c, and 504d are connected to the gas supply unit 40c. Contamination of the sensors 4b, 4c, and 4d is suppressed by outputting the buffer gas from the vicinity of the detection windows 404b, 404c, and 404d toward the inside of the chamber 2 as indicated by the dashed arrows. Instead of a sensor, a light source that illuminates the plasma generation region 25 with visible light may be disposed at the position of any one of the sensors 4b, 4c, and 4d.

[0036] The openings 374, 376, and 377 are located between the sensors 4d, 4b, and 4c, respectively, and the plasma generation region 25. This allows light emitted from the plasma generation region 25 or its vicinity to reach the sensors 4d, 4b, and 4c. Alternatively, light emitted from a light source disposed at the position of any one of the sensors 4d, 4b, and 4c reaches the plasma generation region 25. In this way, the openings 374, 376, and 377 allow light to pass through for observing a portion of the first space 20a.

[0037] The EUV collector mirror 23 is located in a third space 20c inside the chamber 2 and outside the first partition 37. An opening 371 in the first partition 37 is located in the optical path of the synchrotron radiation 251 that is generated in the plasma generation region 25 and travels toward the EUV collector mirror 23. A connection part 29 is located in the optical path of the EUV light 252 that travels from the EUV collector mirror 23 toward the intermediate focus 292.

[0038] The chamber 2 includes a first gas supply port 202a, a second gas supply port 202b, and a gas exhaust port 205. The second gas supply port 202b is also referred to as a second opening. The first gas supply port 202a is connected to a gas supply unit 40a via a first gas supply pipe 212a. The second gas supply port 202b is connected to a gas supply unit 40b via a second gas supply pipe 212b. Buffer gas is supplied to the third space 20c via the first gas supply port 202a, and to the first space 20a and the fourth space 20d via the second gas supply port 202b and the laser optical path pipe 36. A common gas supply unit 40a and a common gas supply unit 40b may be used, and the flow rate of the buffer gas from each gas supply port may be controlled by the processor 5 using a gas flow rate regulator provided in each gas supply pipe. In this specification, the gas supply units 40a, 40b, and 40c may be collectively referred to as the gas supply unit 40.

[0039] The first partition wall 37 is a cylindrical body and serves as an exhaust pipe for exhausting the buffer gas in the chamber 2 to the outside of the chamber 2. The opening 371 functions as an intake port for the exhausted buffer gas. The first partition wall 37 is provided with a gas exhaust port 205, which is a second cylindrical opening, and the gas exhaust port 205 is connected to the gas exhaust unit 50 via an exhaust pipe 216. The exhaust pipe 216 may be configured integrally with the first partition wall 37.

[0040] The gas exhaust unit 50 exhausts the gas in the first space 20a inside the first partition 37 through the gas exhaust port 205 to the outside of the first partition 37 and outside the chamber 2. This maintains the pressure in the first space 20a lower than the pressure in the second space 20b. As a result, through the openings 371 to 377, the buffer gas flows from the second space 20b toward the first space 20a, as indicated by the dashed arrows in FIGS. 4 and 5.

[0041] The buffer gas supplied from the second gas supply port 202b passes through the openings 372 to 377, passes near the plasma generation region 25, and is exhausted to the outside of the chamber 2. This prevents tin debris from moving from the first space 20a to the second space 20b, and prevents tin debris from accumulating on the EUV collector mirror 23 and the like.

[0042] Processor 5 is electrically connected to the following components and performs specific functions. Specifically, it controls the gas supply amount to gas supply units 40a and 40b, controls the gas exhaust amount to gas exhaust unit 50, and controls the laser light pulse energy and pulse interval to laser device 3. Processor 5 also controls the ejection of droplets 27 and the combination of droplets 27 to target supply unit 26. Processor 5 also receives detection signals from sensors 4b, 4c, and 4d and calculates control amounts for laser device 3 and target supply unit 26 based on the signals.

[0043] The droplets 27 output from the target supply unit 26 pass through the opening 373 and reach the plasma generation region 25. The droplets 27 that are not irradiated with the pulsed laser beam 31 pass through the plasma generation region 25 and further pass through the opening 375 to be collected by the target collection unit 28.

[0044] The pulsed laser beam 31 passes through the laser beam line 36 and is emitted from the first opening 35 of the laser beam line 36, passes through the opening 372, and travels inside the first partition wall 37, where it is irradiated onto the droplets 27 in the plasma generation region 25. The second gas supply pipe 212b is connected to the gas inlet port 38 of the laser beam line 36, and buffer gas supplied from the gas supply unit 40b is discharged from the first opening 35 of the laser beam line 36 toward the opening 372, with most of the gas flowing into the first space 20a but some flowing into the fourth space 20d.

[0045] The gas supply unit 40a supplies buffer gas from the first gas supply port 202a to the third space 20c. The flow rate of the buffer gas at the first gas supply port 202a is, for example, 40 nlm or more and 60 nlm or less. While the laser device 3 is operating, the gas supply units 40a and 40b continue to supply gas to the chamber 2, and the gas exhaust unit 50 continues to exhaust gas from the chamber 2.

[0046] 3.2 Operation Returning to Fig. 3, the operation of the exemplary LPP-type extreme ultraviolet light generation system 11 will be described. Note that the extreme ultraviolet light generation apparatus 100 described in Fig. 3 operates in a similar manner to the extreme ultraviolet light generation apparatus 100 described in detail in Figs. 4 and 5.

[0047] The target supply unit 26 outputs a droplet 27 formed from the target material toward the plasma generation region 25 in the internal space of the chamber 2. The droplet 27 is irradiated with a pulsed laser beam 31. The droplet 27 irradiated with the pulsed laser beam 31 is converted into plasma, and the plasma emits radiation 251. EUV light 252 contained in the radiation 251 is reflected by the EUV collector mirror 23 with a higher reflectance than light in other wavelength ranges. The EUV light 252 reflected by the EUV collector mirror 23 is focused at an intermediate focus 292, which is a second focus, and output to the external device 6. Note that one droplet 27 may be irradiated with multiple pulses contained in the pulsed laser beam 31.

[0048] When the droplets 27 are converted into plasma, tin particles and charged particles are generated, some of which adhere to the surfaces of the EUV collector mirror 23 and other components. Hereinafter, these tin particles and charged particles are referred to as "tin debris." While the extreme ultraviolet light generation system 11 is operating, the gas supply unit 40 continues to supply buffer gas to the chamber 2, and the gas exhaust unit 50 continues to exhaust the buffer gas from the chamber 2. When the buffer gas is hydrogen gas, radicals or ions generated from the hydrogen gas react with the tin constituting the tin debris to generate stannane (SnH4) gas. During this process, the tin adhering to the surfaces of the EUV collector mirror 23 and other components is removed. The stannane gas and unreacted hydrogen gas are exhausted to the outside of the chamber 2 by the gas exhaust unit 50.

[0049] The processor 5 controls the entire extreme ultraviolet light generation system 11. Based on the detection results of the target sensor 4, the processor 5 controls the passage timing, trajectory, position, size, and plasma point of the droplet 27. Furthermore, the processor 5 controls the output timing, focusing position, intensity, gas supply unit 40, and gas exhaust unit 50 of the pulsed laser beam 31. Based on the detection results of the pressure sensor 30, the processor 5 controls the gas supply unit 40 and gas exhaust unit 50 so that the pressure inside the chamber 2 is maintained at a predetermined level.

[0050] FIG. 6 is a flowchart showing the operation of the extreme ultraviolet light generation system 11 of the comparative example.

[0051] (Step S11) This step is a start-up step of the extreme ultraviolet light generation system 11. When the extreme ultraviolet light generation system 11 is started up, the processor 5 activates the gas supply unit 40 and the pressure sensor 30, and starts supplying buffer gas to the vacuum chamber 2. The processor 5 starts controlling the gas supply unit 40 and the gas exhaust unit 50, which will be described later, so that the fourth space 20d is kept constant at a predetermined gas pressure.

[0052] The processor 5 activates the gas exhaust unit 50, and the buffer gas starts to flow into the first space 20a in a vacuum state from each opening. The buffer gas that has flowed in is exhausted to the outside of the chamber 2.

[0053] The processor 5 activates the heater 47 and starts controlling the heating of the target in the tank 42. When the target reaches its melting temperature, the processor 5 controls the heater 47 so that the target is maintained at a predetermined melting temperature. When the target is tin, the predetermined melting temperature is a temperature within a range of 232°C to 300°C.

[0054] The processor 5 activates the pressure regulator 48 and starts controlling the supply of inert gas into the tank 42. When the pressure inside the tank 42 reaches a predetermined pressure, the processor 5 controls the pressure to be maintained at the predetermined pressure. When the target is tin, the predetermined pressure is within the range of 0.2 MPa to 40 MPa. When this pressure is reached, a jet of liquid tin is output from the nozzle 43.

[0055] The processor 5 activates the piezoelectric element power supply 45, which starts supplying drive power to the piezoelectric element 44. A rectangular wave electrical signal is output as the drive power, causing the piezoelectric element 44 to vibrate at a predetermined frequency. The nozzle 43 then vibrates in response to the vibration of the piezoelectric element 44. The electrical signal is controlled to a duty that separates the liquid target output from the nozzle 43 and causes the separated targets to combine to form droplets. The target duty at startup is a provisional one calculated in advance, and is hereafter referred to as the provisional duty. The optimal duty is reselected in a later step.

[0056] The processor 5 activates the target sensor 4, and the target sensor 4 is ready to output a detection signal. Based on these signals, the processor 5 starts monitoring whether the intervals and diameters of the passing targets are normal and whether the position and intensity of the generated EUV light 252 are maintained at a predetermined stability.

[0057] The processor 5 activates the laser device 3 and the laser light transmission device 34, and when a light emission trigger signal is given, control is initiated so that the plasma generation region 25 is irradiated with a predetermined pulsed laser light 31.

[0058] In this specification, the times corresponding to steps S11, S12, and S13 are defined as the start-up of the extreme ultraviolet light generation system 11.

[0059] (Step S12) In this step, the processor 5 starts controlling the generation of provisional droplets. When a predetermined state is reached, the liquid tin separates, and the separated targets begin to combine. Hereinafter, the combined targets will also be referred to simply as droplets 27. Furthermore, droplets 27 generated by the provisional duty will be referred to as provisional droplets 27p. The diameter of the provisional droplets 27p and the spacing between adjacent provisional droplets 27p are also provisional and will be changed to target values ​​in a later process. Therefore, most of the monitoring results in this step indicate an "abnormal" state.

[0060] (Step S13) In this step, the processor 5 controls the piezoelectric element 44 of the target supply unit 26 to search for an optimal duty. For example, the search method involves first varying the duty from 1% to 99% in predetermined increments, e.g., 0.1%, and calculating the abnormal value occurrence rate of the provisional droplet 27p at each duty. Then, among the range of continuous duties where the abnormal value occurrence rate is less than the threshold, the duty with the central value in the widest region is determined to be the optimal duty. This step is executed by the processor 5 based on the detection signal from the target sensor 4.

[0061] The abnormality here refers to an abnormality in the diameter of the provisional droplets 27p or an abnormality in the spacing between adjacent provisional droplets 27p.

[0062] In this specification, a period during which the target supply unit 26 discharges the droplets 27 and the pulsed laser beam 31 is not irradiated onto the droplets 27 is referred to as a first period. The first period is a period that includes at least a part of a search period during which an optimal duty of the electrical signal to be applied to the piezoelectric element 44 is searched for and determined.

[0063] (Step S14) In this step, the processor 5 starts controlling the generation of the EUV light 252. The processor 5 operates the duty based on the optimal duty and starts control to maintain the bonded state of the droplets 27 using the abnormal value occurrence rate as a control variable. Then, irradiation of the pulsed laser beam 31 onto the droplets 27 begins, and the synchrotron radiation 251 is generated. As described above, the droplets 27 generated at the optimal duty are not provisional droplets 27p, but droplets 27 that stably generate the EUV light 252. The processor 5 controls the position where the EUV light 252 is generated and the intensity of the EUV light 252 by adjusting the intensity and optical axis of the pulsed laser beam 31 and the trajectory of the droplets 27 based on the detection signal from the target sensor 4, so that the position where the EUV light 252 is generated and the intensity of the EUV light 252 become predetermined values.

[0064] (Step S15) In this step, the processor 5 determines whether the spacing between the droplets 27 is normal. In addition, in this step, it may also be determined whether the stability of the EUV light 252 is normal. Specifically, it is determined whether the stability of the intensity and generation position of the EUV light 252 is normal. If it is outside the threshold, it is determined to be abnormal, and step S151 is executed. If it is within the threshold, it is determined to be normal, and step S16 is executed.

[0065] (Step 151) In this step, the processor 5 controls the stopping of the generation of the EUV light 252. The processor 5 stops the generation of the oscillation trigger signal for the pulsed laser beam 31, and the generation of the EUV light 252 is stopped. In other words, the period during which the processor 5 determines that the spacing between the droplets 27 is abnormal and stops the generation of the EUV light 252 is the period during which the pulsed laser beam 31 is not irradiated onto the droplets 27 while the target supply unit 26 is discharging the droplets 27. The duty at this point remains the initially set optimal duty 1, but since the provisional droplets 27p have been generated, the process returns to step S13 and a new optimal duty 2 is searched for and determined.

[0066] (Step S16) This step is a step in which the processor 5 receives a request to stop generating the EUV light 252. If the request to stop generating the EUV light 252 is received, the process proceeds to step S17, and if the request to stop generating the EUV light 252 is not received, the process returns to step S15.

[0067] (Step S17) In this step, the processor 5 controls the extreme ultraviolet light generation system 100 to stop.

[0068] Figures 7(A) to 7(F) are timing charts showing the state changes of each component when steps S11 to S16 in Figure 6 are executed. The horizontal axis in Figures 7(A) to 7(F) represents the passage of time, and the time is the same. The dashed lines indicate the points where the state changes. The S numbers in the upper row are the numbers of the steps executed between adjacent dashed lines.

[0069] 7A, the vertical axis represents the pressure in the fourth space 20d. After step S11 in which the extreme ultraviolet light generation system 100 is started, the pressure in the fourth space 20d is maintained approximately constant from step S12 onward.

[0070] 7(B), the vertical axis represents the gas supply amount. Specifically, it represents the gas supply amount supplied from gas supply unit 40b via laser optical path 36, the gas supply amount supplied from gas supply unit 40a via first gas supply port 202a, and the gas supply amount supplied from gas supply unit 40c via buffer gas supply ports 504b, 504c, and 504d disposed near target sensor 4. The above three gas supply amounts are maintained constant from step S12 onwards.

[0071] 7(C), the vertical axis represents the temperature T and pressure P in the vicinity of the target supply part 26. The temperature T and pressure P are maintained approximately constant after step S12.

[0072] FIG. 7D shows the transition of the duty of the piezoelectric element 44. Specifically, the voltage of the piezoelectric element power supply 45 applied to the piezoelectric element 44 is changed from a predetermined voltage duty of 0% to 100%. During step S13, the duty changes between 0 and 100 due to the search operation, so the transition is represented by a slope. During step S14, the duty is shown in a state in which optimal duty 1 is selected based on the search results. The duty during step S151 is the same value as optimal duty 1 during step S14, but since the stability of the EUV light 252 is determined to be abnormal during this period as shown in FIG. 7F, it is no longer the optimal duty. Based on this, the duty during this period is referred to as provisional duty 2 to distinguish it from optimal duty 1. Provisional duty 2 may be changed to the same value as provisional duty 1 during step S12 if the separated targets are recombined.

[0073] FIG. 7(E) shows the transition of the determination result of whether the spacing between adjacent droplets 27 is normal. During step S12, while an electrical signal with a provisional duty of 1 is applied to the piezoelectric element 44, provisional droplets 27p are generated after the pressure in the fourth space 20d, the amount of gas supplied from each component, the temperature T of the target supply unit 26, and the pressure P reach predetermined values. The spacing between these provisional droplets 27p is determined to be "abnormal." During step S13, the optimal duty is searched for, and "normal" or "abnormal" is determined randomly depending on the time. To indicate this state, both "normal" and "abnormal" are indicated by dashed lines during this period. During step S14, laser light is irradiated at the optimal duty.

[0074] FIG. 7(F) shows the transition of the stability determination of the EUV light 252. During steps S14 to S16, the EUV light 252 is emitted stably, and the determination result is "normal." The laser light irradiation continues as long as the spacing between the droplets 27 is determined to be "normal," as shown in FIG. 7(E). When the spacing is eventually determined to be "abnormal," the stability of the EUV light 252 is also determined to be "abnormal," as shown in FIG. 7(F). When the stability of the EUV light 252 is determined to be abnormal, the spacing between the droplets 27 is also in an "abnormal" state. Furthermore, when the stability of the EUV light 252 is determined to be "abnormal," the duty shown in FIG. 7(D) is also treated as provisional duty 2.

[0075] 8 is a partial enlarged view of FIG. 4 at steps S14, S15, and S16 in FIG. 6. The third space 20c in which the EUV collector mirror 23 is disposed is in communication with the gas exhaust port 205 via an opening 371. The position and diameter of this opening 371 are set so that the entire reflective surface of the EUV collector mirror 23 can be seen from the plasma generation region 25. Therefore, the buffer gas exhausted through the first partition wall 37 proceeds from all positions on the reflective surface of the EUV collector mirror 23 toward the plasma generation region 25. In other words, the buffer gas proceeds through the region of the synchrotron radiation 251 surrounded by the plasma generation region 25 and the reflective surface of the EUV collector mirror 23, generally in the opposite direction to the synchrotron radiation 251.

[0076] Some of the tin debris generated by the plasma advances toward the EUV collector mirror 23, but is blocked by the flow of buffer gas and stops just before the EUV collector mirror 23, and is eventually exhausted together with the buffer gas. This action prevents contamination of any position on the reflective surface of the EUV collector mirror 23.

[0077] FIG. 9 is a partial enlarged view of FIG. 5 in steps S14, S15, and S16 of FIG. 6, viewed from the opening 371 side. The buffer gas supplied from the second gas supply port 202b flows into the first space 20a inside the first partition wall 37 through the openings 372-377 and is exhausted to the outside of the chamber 2. This gas flow prevents tin debris from entering the fourth space 20d and prevents contamination of the sensors 4b-4d and the window 21. If the stability of the EUV light 252 generated during the circulation of steps S15-S16 is normal, the spacing between the droplets 27 is also determined to be normal. The diameter of droplets 27 determined to be normal is considered to be constant. In the drawing, droplets 27 with this diameter are designated as droplets 27normal. The trajectory of the droplets 27normal is significantly affected by the buffer gas flowing into the first space 20a. However, since the flow rate of the buffer gas from each opening during steps S14, S15, and S16 is limited to a flow rate at which the droplets 27normal are collected in the target collection section 28, all of the droplets 27normal that are not irradiated with the laser light reach the target collection section 28.

[0078] 3.3 Challenges 10 is a partially enlarged view of FIG. 3 during execution of steps S11 to S13 and steps S151 to S13 in FIG. 6. During the above periods, as shown in FIGS. 7(D), 7(E), and 7(F), the spacing between droplets 27 often indicates "abnormal" because the states of some components are unstable or temporary. When the spacing between droplets 27 is abnormal, droplets 27small, which have a diameter smaller than that of droplets 27normal, often occur.

[0079] As shown in Figures 8 and 10, buffer gas continues to flow in through each opening during the above steps. Therefore, droplets 27small generated during this period are affected by the buffer gas flow and experience significant deviations in their trajectories. If their trajectories deviate, they are not collected by the target collection unit 28 and reach the inner wall of the first partition 37, contaminating the interior. For example, droplets 27small that adhere to the wall surface form flocculent targets C on the inner wall. Over time, the flocculent targets C may grow to the point where they interfere with the optical path of the EUV light 252, the optical path to the target sensor 4, and the trajectory of the droplets 27. Some of the enlarged flocculent targets C are separated by the buffer gas flow and adhere to the openings, eventually preventing the generation of EUV light 252.

[0080] Therefore, in the following embodiment, an extreme ultraviolet light generation apparatus 100 in which contamination inside the chamber 2 during operation is suppressed will be exemplified.

[0081] 4. Description of the extreme ultraviolet light generation device according to the first embodiment 4.1 Configuration The following describes the configuration of the extreme ultraviolet light generation apparatus 100 of the embodiment 1. Note that the same components as those described above are denoted by the same reference numerals, and redundant description will be omitted unless otherwise specified.

[0082] The extreme ultraviolet light generation apparatus 100 of this embodiment is similar in configuration to the extreme ultraviolet light generation apparatus 100 of the comparative example, except for the control of the amount of buffer gas supplied to the laser optical path 36. Therefore, a description of the overall configuration of the extreme ultraviolet light generation apparatus 100 of this embodiment will be omitted. However, in this embodiment, the gas supply unit 40b will be read as a first gas supply unit 40b.

[0083] 4.2 Operation Fig. 11 is a flowchart showing the operation of the extreme ultraviolet light generation system 11 in this embodiment. Operations with the same step numbers as those in the flowchart of Fig. 6 are performed in the same manner as in Fig. 6. Fig. 11 differs from the flowchart described in Fig. 6 in that step S112, step S131, step S132, step S152, and step S153 are included in the control flow.

[0084] In this specification, the flow rate of the buffer gas supplied from the first gas supply unit 40b during the first period described above is referred to as a “first flow rate.” Furthermore, during the period in which the target supply unit 26 discharges the droplets 27, the flow rate of the buffer gas supplied from the first gas supply unit 40b during the second period in which the droplets 27 are irradiated with the pulsed laser beam 31 is referred to as a “second flow rate.”

[0085] The processor 5 sets a target flow rate of the buffer gas supplied from the first gas supply unit 40b to the laser optical path 36 at startup to a first flow rate, and sets a target flow rate of the buffer gas supplied from the first gas supply unit 40b during the period when the pulsed laser beam 31 is irradiated onto the droplets 27 to a second flow rate. The processor 5 sets the flow rates of the buffer gas so that the first flow rate is smaller than the second flow rate.

[0086] (Step S112) In this step, the processor 5 controls the flow rate of the buffer gas supplied from the first gas supply unit 40b via the laser optical path pipe 36 to the first flow rate.

[0087] (Step S131) In this step, the processor 5 controls the flow rate of the buffer gas supplied from the first gas supply unit 40b via the laser optical path pipe 36 to the second flow rate.

[0088] (Step S132) In this step, the processor 5 causes the extreme ultraviolet light generation apparatus 100 to wait until the target supply unit 26 reaches the normal temperature and normal pressure. The normal temperature and normal pressure are the target temperature and target pressure when the extreme ultraviolet light generation system 11 is operating normally, and may be determined in advance and stored in the memory 501. When the target supply unit 26 reaches the normal temperature and normal pressure, the process proceeds to step S14. If the target supply unit 26 does not reach the normal temperature and normal pressure, the processor 5 continues with step S132.

[0089] (Step S152) In this step, the processor 5 sets the target flow rate of the buffer gas supplied from the first gas supply unit 40b to the first flow rate.

[0090] (Step S153) In this step, the processor 5 waits until the target supply unit 26 reaches the normal temperature and normal pressure. If the target supply unit 26 has not yet reached the normal temperature and normal pressure, the processor 5 continues with step S153. If the target supply unit 26 has reached the normal temperature and normal pressure, the processor 5 proceeds to step S13.

[0091] In step S153, the duty remains the initially set optimum duty 1, but since the provisional droplet 27p has been generated, the process returns to step S13, where a new optimum duty 2 is searched for and determined.

[0092] Figures 12(A) to 12(F) are timing charts showing the state changes of each component when steps S11 to S16 in Figure 11 are executed. The horizontal axis of each diagram represents the passage of time, and the time is the same. The dashed lines indicate the points at which the state changes. The S numbers in the upper row are the numbers of the steps executed between adjacent dashed lines.

[0093] 12(A) shows the transition of the pressure in the fourth space 20d. Here, normal pressure is used in steps S131 and S132, as well as steps S14, S15, and S16. In contrast, a preparation pressure lower than normal pressure is used between steps S12 and S13. This is because, during the latter period, the supply amount of buffer gas supplied from the first gas supply unit 40b via the laser optical path pipe 36 is a first flow rate, which is smaller than the second flow rate, which is the supply amount of gas during the former period.

[0094] 12(B) differs from FIG. 7(B) in the transition of the gas supply rate supplied from the laser optical path pipe 36. The gas supply rate supplied from the laser optical path pipe 36 is the second flow rate in steps S131 and S132, as well as steps S14, S15, and S16. In contrast, the gas supply rate is the first flow rate, which is lower than the second flow rate, between steps S12 and S13.

[0095] 12(C) , steps S131 and S132, and steps S151 and S152 differ from those in FIG. 7(C) in that the temperature and pressure of the target supply unit 26 temporarily fluctuate. The former is caused by the gas supply rate supplied from the laser optical path pipe 36 fluctuating from a first flow rate, which is the preparation flow rate, to a second flow rate, which is the normal flow rate, causing a fluctuation in the pressure of the buffer gas, which changes the heat transfer state from the heater 47 of the target supply unit 26 to the buffer gas, and also fluctuating the temperature and pressure of the target supply unit 26. The latter is caused by the gas supply rate supplied from the laser optical path pipe 36 fluctuating from the second flow rate to the first flow rate, conversely.

[0096] 4.3 Actions and Effects 13 is a schematic diagram illustrating a case where a small-diameter droplet 27small is ejected in the first embodiment. The period during which the droplet 27small may be ejected is the start-up of the extreme ultraviolet light generation system 100, i.e., the periods of steps S11, S12, and S13, and the period during which the generation of EUV light 252 is stopped, i.e., the periods of steps S151 and S152. In this embodiment, during the above periods, the first flow rate, which is the amount of buffer gas supplied from the laser optical path tube 36, is less than the second flow rate, so that the small droplet 27small, which has a small mass, is prevented from being swept away by the flow of buffer gas. This can prevent the trajectory of the droplet 27 from being changed by the supplied buffer gas, making it easier for the droplet 27 to be collected by the target collector 28, and reducing contamination of the chamber 2.

[0097] 4.4 Variation 1 4.4.1 Configuration A description will be given of Modification 1 of Embodiment 1. The configuration of the extreme ultraviolet light generation apparatus 100 of Modification 1 is similar to that of Embodiment 1, and therefore a description thereof will be omitted. 4.4.2 Operation Next, the operation of Modification 1 of Embodiment 1 will be described. FIG. 14 is a flowchart showing the operation of the extreme ultraviolet light generation system 11 in this modification. Operations with the same step numbers as those in the flowchart of FIG. 11 are performed in the same manner as in FIG. 11. This operation differs from the operation flow of Embodiment 1 in that, at startup, the supply amount of buffer gas from the laser optical path duct 36 is set to a second flow rate, which is the normal flow rate. Also, this operation differs from the operation flow of FIG. 11 in that, when the generation of EUV light 252 is stopped, the supply amount of buffer gas from the laser optical path duct 36 is set to a first flow rate, which is lower than the second flow rate, before a new search for an optimal duty is performed.

[0098] The flowchart in FIG. 14 will be described below, focusing on the differences from FIG.

[0099] (Step S113) In this step, the processor 5 sets the amount of buffer gas supplied from the laser optical path pipe 36 to the second flow rate, which is the normal flow rate.

[0100] In this modification, the period during which the target supply unit 26 discharges the droplets 27 and the pulsed laser beam 31 is not irradiated onto the droplets 27 is the period during which the generation of the EUV light 252 is stopped. The operation during this period will be described below.

[0101] (Step S154) In this step, the processor 5 sets the target flow rate of the buffer gas supplied from the first gas supply unit 40b to the first flow rate, which is a preparation flow rate. As in the first embodiment, the first flow rate is lower than the second flow rate, which is a normal flow rate.

[0102] (Step S155) In this step, the processor 5 waits until the target supply unit 26 reaches the normal temperature and normal pressure. The processor 5 waits until the target supply unit 26 reaches the normal temperature and normal pressure. If the target supply unit 26 has not reached the normal temperature and normal pressure, the processor 5 continues with step S155. If the target supply unit 26 has reached the normal temperature and normal pressure, the processor 5 proceeds to step S156.

[0103] (Step S156) This step is a step in which the processor 5 controls the piezoelectric element 44 of the target supply unit 26 to search for an optimum duty. The operation is the same as that in step S13, so a description thereof will be omitted.

[0104] (Step S157) In this step, the processor 5 sets the target flow rate of the buffer gas to be supplied to the laser optical path pipe 36 to the second flow rate.

[0105] (Step S158) In this step, the processor 5 waits until the target supply unit 26 reaches the normal temperature and normal pressure. The processor 5 waits until the target supply unit 26 reaches the normal temperature and normal pressure. If the target supply unit 26 has not reached the normal temperature and normal pressure, the processor 5 continues with step S158. If the target supply unit 26 has reached the normal temperature and normal pressure, the processor 5 proceeds to step S14.

[0106] 4.4.3 Actions and Effects According to this modification, during the startup period from step S12 to step S13, the flow rate of the buffer gas supplied from the first gas supply unit 40b to the laser beam path pipe 36 is set to the second flow rate, which is the normal flow rate. Therefore, the extreme ultraviolet light generation system 100 does not need to wait until the target supply unit 26 reaches the normal temperature and pressure. This can shorten the waiting time.

[0107] 4.5 Variation 2 4.5.1 Configuration A description will be given of Modification 2 of Embodiment 1. The configuration of the extreme ultraviolet light generation apparatus 100 of Modification 2 is similar to that of Embodiment 1, and therefore a description thereof will be omitted.

[0108] 4.5.2 Operation Next, the operation of Modification 2 of Embodiment 1 will be described. Fig. 15 is a flowchart showing the operation of the extreme ultraviolet light generation system 11 in this modification. Similar operations are performed in steps having the same step numbers as in the flowchart of Fig. 11. The operation flow differs from that of Embodiment 1 in that the processor 5 sets the supply amount of buffer gas from the laser optical path pipe 36 to the first flow rate only at startup.

[0109] The flowchart in Fig. 15 will be described below in terms of differences from Fig. 11. In this modification, during the periods when the target supply unit 26 discharges the droplets 27 and stops generating the EUV light 252, i.e., during steps S151, S159, and S160, the supply rate of the buffer gas from the laser optical path pipe 36 is not changed from the second flow rate.

[0110] (Step S157) This step is a step in which the processor 5 starts generating and controlling the provisional droplets 27p. The operation is the same as in step 12, so a description thereof will be omitted.

[0111] (Step S158) In this step, the processor 5 controls the piezoelectric element 44 of the target supply unit 26 to search for an optimum duty. The operation is the same as in step S13, so a description thereof will be omitted. After step S158, the process proceeds to step S14.

[0112] 4.5.3 Actions and Effects According to this modification, during a period in which the target supply unit 26 discharges the droplets 27 but the pulsed laser beam 31 is not irradiated onto the droplets 27, the processor 5 does not set the flow rate of the buffer gas supplied from the first gas supply unit 40b to the laser optical path 36 to the first flow rate, which is lower than the normal flow rate. Therefore, the extreme ultraviolet light generation system 100 does not need to wait until the target supply unit 26 reaches the normal temperature and normal pressure. This reduces the waiting time.

[0113] 5. Description of the extreme ultraviolet light generation apparatus according to the second embodiment 5.1 Configuration A description will be given of embodiment 2. The configuration of the extreme ultraviolet light generation apparatus 100 of embodiment 2 is the same as that of embodiment 1, and therefore a description thereof will be omitted.

[0114] 5.2 Operation Next, the operation of the second embodiment will be described. FIG. 16 is a flowchart showing the operation of the extreme ultraviolet light generation system 11 in this modification. Similar operations are performed in steps having the same step numbers as those in the flowchart of FIG. 11. The operation flow of this embodiment differs from that of the first embodiment in that, when the processor 5 changes the gas supply rate of the buffer gas from the laser optical path duct 36 from the second flow rate, which is the normal flow rate, to the first flow rate, which is lower than the normal flow rate, at startup or when the generation of the EUV light 252 is stopped, the processor 5 changes the gas supply rate from the gas supply unit 40a to the third flow rate, which is the preparatory flow rate, which is higher than the fourth flow rate, which is the normal flow rate. In the description of this embodiment, the gas supply unit 40a will be read as the second gas supply unit 40a.

[0115] The flowchart in FIG. 16 will be described below in terms of differences from FIG.

[0116] (Step S114) In this step, the processor 5 controls the flow rate of the buffer gas supplied from the laser optical path pipe 36 and the flow rate of the buffer gas supplied from the gas supply unit 40a. The processor 5 sets the target flow rate of the buffer gas supplied from the first gas supply unit 40b to a first flow rate. The processor 5 also sets the target flow rate of the buffer gas supplied from the second gas supply unit 40a to a third flow rate, which is a preparatory flow rate that is higher than a fourth flow rate, which is a normal flow rate.

[0117] (Step S133) In this step, the processor 5 changes the target flow rate of the buffer gas supplied from the laser optical path pipe 36 and the target flow rate of the buffer gas supplied from the gas supply unit 40a. The processor 5 sets the target flow rate of the buffer gas supplied from the first gas supply unit 40b to the second flow rate, which is a normal flow rate. The processor 5 also sets the target flow rate of the buffer gas supplied from the second gas supply unit 40a to the fourth flow rate, which is a normal flow rate.

[0118] (Step S161) In this step, the processor 5 controls the flow rate of the buffer gas supplied from the laser optical path pipe 36 and the flow rate of the buffer gas supplied from the gas supply unit 40a. The processor 5 sets the target flow rate of the buffer gas supplied from the first gas supply unit 40b to a first flow rate. The processor 5 also sets the target flow rate of the buffer gas supplied from the second gas supply unit 40a to a third flow rate, which is a preparatory flow rate that is higher than a fourth flow rate, which is a normal flow rate. (Step S162) In this step, the processor 5 waits until the target supply unit 26 reaches the normal temperature and normal pressure. The processor 5 waits until the target supply unit 26 reaches the normal temperature and normal pressure. If the target supply unit 26 has not reached the normal temperature and normal pressure, the processor 5 continues with step S162. If the target supply unit 26 has reached the normal temperature and normal pressure, the processor 5 proceeds to step S13.

[0119] 17(A) to 17(F) are timing charts showing the state changes of each component when steps S11 to S16 in FIG. 16 are executed. The horizontal axis of each diagram represents the passage of time, and the time is the same. The dashed lines indicate the points where the state changes. The S numbers in the upper rows are the numbers of the steps executed between adjacent dashed lines.

[0120] Figure 17(A) shows the transition of the pressure in the fourth space 20d. Compared to Figure 12(A) of the first embodiment, it differs in that the pressure in the fourth space 20d is maintained at a substantially constant pressure throughout the entire period from step S11 to step S16. The processor 5 controls the pressure in the fourth space 20d so that it is maintained at a normal pressure throughout the entire period from step S11 to step S16. The pressure fluctuation in the fourth space 20d is maintained within ±1.0 Pa of the target pressure. It is preferable that the pressure fluctuation in the fourth space 20d is within ±0.5 Pa of the target pressure.

[0121] 17(B), in steps S14, S15, and S16, the flow rate of the buffer gas supplied from the second gas supply unit 40a is the fourth flow rate, which is the normal flow rate. In contrast, between steps S12 and S13, the flow rate of the buffer gas supplied from the second gas supply unit 40a is the third flow rate, which is the preparation flow rate and is higher than the fourth flow rate, which is the normal flow rate. Therefore, as shown in FIG. 17(A), the pressure in the fourth space 20d is maintained approximately constant.

[0122] Furthermore, the temperature T and pressure P of the target supply part 26 shown in FIG. 17(C) differ from those in FIG. 12(C) of the first embodiment in that fluctuations due to changes in the flow rate of the buffer gas are negligibly small in any period.

[0123] 5.3 Actions and Effects According to this embodiment, when the buffer gas supply rate from the laser path tube 36 is changed from the second flow rate, which is the normal flow rate, to the first flow rate, which is lower than the normal flow rate, the gas supply rate from the second gas supply unit 40a is changed to the third flow rate, which is the preparatory flow rate, which is higher than the fourth flow rate, which is the normal flow rate. Therefore, even when the gas supply rate from the laser path tube 36 fluctuates, fluctuations in the pressure of the buffer gas can be suppressed, and changes in the heat transfer state from the heater 47 of the target supply unit 26 to the buffer gas can be suppressed. Furthermore, fluctuations in the temperature and pressure of the target supply unit 26 can be minimized to a negligible level. Therefore, the extreme ultraviolet light generation system 100 does not need to wait until the target supply unit 26 reaches the normal temperature and pressure. This reduces the waiting time.

[0124] 5.4 Variation 1 5.4.1 Configuration The configuration of the extreme ultraviolet light generation apparatus 100 of Modification 1 of Embodiment 2 is similar to that of Embodiment 1, and therefore a description thereof will be omitted. This modification differs from Embodiment 2 in that, when the processor 5 sets the supply rate of buffer gas from the laser optical path 36 from the second flow rate, which is the normal flow rate, to the first flow rate, which is lower than the normal flow rate, upon startup or when the generation of EUV light 252 is stopped, the processor 5 sets the supply rate of gas from the gas supply unit 40c to the fifth flow rate, which is higher than the sixth flow rate, which is the normal flow rate. Here, buffer gas is supplied from the gas supply unit 40c through at least one of buffer gas supply ports 504b, 504c, and 504d located near sensors 4b, 4c, and 4d. Note that in the description of this modification, the gas supply unit 40c will be referred to as the second gas supply unit 40c.

[0125] 5.4.2 Operation Next, an operation of Modification 1 of Embodiment 2 will be described. Fig. 18 is a flowchart showing the operation of the extreme ultraviolet light generation system 11 in this modification. Similar operations are performed in steps having the same step numbers as those in the flowchart of Fig. 11.

[0126] The flowchart in FIG. 18 will be described below, focusing on the differences from FIG.

[0127] (Step S115) In this step, the processor 5 controls the flow rate of the buffer gas supplied from the laser optical path pipe 36 and the flow rate of the buffer gas supplied from the gas supply unit 40c. The processor 5 sets the target flow rate of the buffer gas supplied from the first gas supply unit 40b to a first flow rate. The processor 5 also sets the gas supply amount supplied from the second gas supply unit 40c through at least one of the buffer gas supply ports 504b, 504c, and 504d to a fifth flow rate, which is a preparation flow rate that is higher than the sixth flow rate, which is a normal flow rate.

[0128] (Step S135) In this step, the processor 5 changes the target flow rate of the buffer gas supplied from the laser optical path pipe 36 and the target flow rate of the buffer gas supplied from the gas supply unit 40c. The processor 5 sets the target flow rate of the buffer gas supplied from the first gas supply unit 40b to a second flow rate, which is a normal flow rate. The processor 5 also sets the amount of gas supplied from the second gas supply unit 40c through at least one of the buffer gas supply ports 504b, 504c, and 504d to a sixth flow rate, which is a normal flow rate.

[0129] (Step S136) In this step, the processor 5 waits until the target supply unit 26 reaches the normal temperature and normal pressure. The processor 5 waits until the target supply unit 26 reaches the normal temperature and normal pressure. If the target supply unit 26 has not reached the normal temperature and normal pressure, the processor 5 continues with step S136. If the target supply unit 26 has reached the normal temperature and normal pressure, the processor 5 proceeds to step S14.

[0130] (Step S163) In this step, the processor 5 controls the flow rate of the buffer gas supplied from the laser optical path pipe 36 and the flow rate of the buffer gas supplied from the gas supply unit 40c. The processor 5 sets the target flow rate of the buffer gas supplied from the first gas supply unit 40b to a first flow rate. The processor 5 also sets the gas supply amount supplied from the second gas supply unit 40c through at least one of the buffer gas supply ports 504b, 504c, and 504d to a fifth flow rate. Then, the process returns to step S13.

[0131] 19(A) and 19(B) are timing charts showing the state changes of each component in steps S11 to S16 of FIG. 18. The horizontal axis of each diagram represents the passage of time, and the time is the same. The dashed lines indicate the points at which the state changes. The S numbers in the upper rows are the numbers of the steps executed between adjacent dashed lines.

[0132] 19(A) shows the transition of the pressure in the fourth space 20d. The pressure in the fourth space 20d is maintained at a substantially constant pressure throughout the entire period from step S12 to step S16. The processor 5 controls the pressure in the fourth space 20d so that the normal pressure is maintained throughout the entire period from step S11 to step S16. The pressure fluctuation in the fourth space 20d is maintained within ±1.0 Pa of the target pressure. It is preferable that the pressure fluctuation in the fourth space 20d is within ±0.5 Pa of the target pressure.

[0133] 19(B), the flow rate of the buffer gas supplied from the second gas supply unit 40c is the sixth flow rate, which is the normal flow rate, in steps S14, S15, and S16. In contrast, the flow rate of the buffer gas supplied from the second gas supply unit 40c is the fifth flow rate, which is the preparatory flow rate and is higher than the normal flow rate, between steps S12 and S13.

[0134] 5.4.3 Actions and Effects According to this modification, when the processor 5 sets the gas supply rate of the buffer gas from the laser path tube 36 from the second flow rate, which is the normal flow rate, to the first flow rate, which is lower than the normal flow rate, the processor 5 sets the gas supply rate from the second gas supply unit 40c to the fifth flow rate, which is the preparatory flow rate, which is higher than the sixth flow rate, which is the normal flow rate. Therefore, even if the gas supply rate from the laser path tube 36 fluctuates, fluctuations in the pressure of the buffer gas can be suppressed, changes in the heat transfer state from the heater 47 of the target supply unit 26 to the buffer gas can be suppressed, and fluctuations in the temperature and pressure of the target supply unit 26 can be minimized to a negligible level. Therefore, the extreme ultraviolet light generation apparatus 100 does not need to wait until the target supply unit 26 reaches the normal temperature and pressure. This reduces the waiting time.

[0135] 5.5 Variation 2 5.5.1 Configuration A second modification of the second embodiment will now be described. As shown in Fig. 20, the configuration of the extreme ultraviolet light generation apparatus 100 of the second modification differs from that of the first embodiment in that it includes a dedicated gas supply unit 40d dedicated to supplying buffer gas and a dedicated gas supply pipe 41 that supplies the buffer gas from the dedicated gas supply unit 40d into the chamber 2. The other configurations are the same as those of the first embodiment, and therefore will not be described again.

[0136] 5.5.2 Operation Next, the operation of Modification 2 of Embodiment 2 will be described with reference to FIG. 21. At startup or when the generation of EUV light 252 is stopped, the processor 5 sets the gas supply rate of the buffer gas from the laser optical path 36 from the second flow rate, which is the normal flow rate, to the first flow rate, which is a preparatory flow rate that is lower than the normal flow rate. The processor 5 also sets the gas supply rate supplied from the dedicated gas supply unit 40d through the dedicated gas supply duct 41 to the seventh flow rate, which is a preparatory flow rate that is higher than the eighth flow rate, which is the normal flow rate. At this time, the processor 5 controls the pressure in the fourth space 20d so that it is maintained at the normal pressure throughout the entire period from step S11 to step S16. The pressure fluctuation in the fourth space 20d is maintained within ±1.0 Pa of the target pressure. It is preferable that the pressure fluctuation in the fourth space 20d be within ±0.5 Pa of the target pressure.

[0137] The following describes the differences between the flowchart in Fig. 21 and Fig. 18. In steps with the same step numbers as in the flowchart in Fig. 18, the same operations are performed.

[0138] (Step S116) In this step, the processor 5 controls the flow rate of the buffer gas supplied from the laser optical path pipe 36 and the flow rate of the buffer gas supplied from the dedicated gas supply unit 40d. The processor 5 sets the target flow rate of the buffer gas supplied from the first gas supply unit 40b to a first flow rate. The processor 5 also sets the amount of gas supplied from the dedicated gas supply unit 40d through the dedicated gas supply pipe 41 to a seventh flow rate that is higher than the eighth flow rate, which is the normal flow rate.

[0139] (Step S137) In this step, the processor 5 changes the target flow rate of the buffer gas supplied from the laser optical path pipe 36 and the target flow rate of the buffer gas supplied from the dedicated gas supply unit 40d. The processor 5 sets the target flow rate of the buffer gas supplied from the first gas supply unit 40b to the second flow rate, which is a normal flow rate. The processor 5 also sets the gas supply amount supplied from the dedicated gas supply unit 40d through the dedicated gas supply pipe 41 to the eighth flow rate, which is a normal flow rate.

[0140] (Step S138) In this step, the processor 5 waits until the target supply unit 26 reaches the normal temperature and normal pressure. The processor 5 waits until the target supply unit 26 reaches the normal temperature and normal pressure. If the target supply unit 26 has not reached the normal temperature and normal pressure, the processor 5 continues with step S138. If the target supply unit 26 has reached the normal temperature and normal pressure, the processor 5 proceeds to step S14.

[0141] (Step S164) In this step, the processor 5 controls the flow rate of the buffer gas supplied from the laser optical path pipe 36 and the flow rate of the buffer gas supplied from the dedicated gas supply unit 40d. The processor 5 sets the target flow rate of the buffer gas supplied from the first gas supply unit 40b to the first flow rate. The processor 5 also sets the gas supply amount supplied from the dedicated gas supply unit 40d through the dedicated gas supply pipe 41 to the seventh flow rate. Next, the process returns to step S13.

[0142] 22(A) and 22(B) are timing charts showing the state changes of each component when steps S11 to S16 in FIG. 21 are executed. The horizontal axis of each diagram represents the passage of time, and the time is the same. The dashed lines indicate the points where the state changes. The S numbers in the upper row are the numbers of the steps executed between adjacent dashed lines.

[0143] 22(A) shows the transition of the pressure in the fourth space 20d. The pressure in the fourth space 20d is maintained at a substantially constant pressure throughout the entire period from step S11 to step S16.

[0144] 22(B), in steps S14, S15, and S16, the flow rate of the buffer gas supplied from the dedicated gas supply unit 40d is the eighth flow rate, which is the normal flow rate. In contrast, in steps S12 and S13, the flow rate of the buffer gas supplied from the dedicated gas supply unit 40d is the seventh flow rate, which is the preparation flow rate and is higher than the normal flow rate.

[0145] 5.5.3 Actions and Effects According to this modification, when the processor 5 changes the buffer gas supply rate from the laser path conduit 36 ​​from the second flow rate, which is the normal flow rate, to the first flow rate, which is lower than the normal flow rate, the processor 5 also changes the gas supply rate from the dedicated gas supply unit 40d to the seventh flow rate, which is the preparatory flow rate, which is higher than the eighth flow rate, which is the normal flow rate. Therefore, even if the gas supply rate from the laser path conduit 36 ​​fluctuates, fluctuations in the buffer gas pressure can be suppressed, changes in the heat transfer from the heater 47 of the target supply unit 26 to the buffer gas can be suppressed, and fluctuations in the temperature and pressure of the target supply unit 26 can be minimized to a negligible level. Therefore, the extreme ultraviolet light generation system 100 does not need to wait until the target supply unit 26 reaches the normal temperature and pressure. This shortens the waiting time. It is preferable to orient the supply port of the dedicated gas supply conduit 41 away from the trajectory of the droplets 27. With such a configuration, the buffer gas from the dedicated gas supply pipe 41 can be circulated at a position away from the trajectory of the droplets 27, thereby further suppressing deviation of the trajectory of the droplets 27small.

[0146] 6. Description of the extreme ultraviolet light generation device according to the third embodiment 6.1 Configuration The configuration of the extreme ultraviolet light generation apparatus 100 of this embodiment is similar to that of Embodiments 1 and 2, and therefore a description thereof will be omitted. This embodiment differs from Embodiment 2 in that, when the processor 5 sets the gas supply rate of the buffer gas from the laser optical path 36 from the second flow rate, which is the normal flow rate, to the first flow rate, which is the preparatory flow rate lower than the normal flow rate, during startup or when the generation of EUV light 252 is stopped, the processor 5 sets the exhaust rate from the gas exhaust unit 50 to a preparatory exhaust rate lower than the normal exhaust rate so as to reduce pressure fluctuations in the fourth space 20d. At this time, the processor 5 controls the pressure in the fourth space 20d so that the normal pressure is maintained throughout the entire period from Step S11 to Step S16. The pressure fluctuation in the fourth space 20d is maintained within ±1.0 Pa of the target pressure. It is preferable that the pressure fluctuation in the fourth space 20d be within ±0.5 Pa of the target pressure.

[0147] 6.2 Operation Next, the operation of the third embodiment will be described. Fig. 23 is a flowchart showing the operation of the extreme ultraviolet light generation system 11 in this modification. Similar operations are performed in steps having the same step numbers as in the flowchart of Fig. 11. The operation flow differs from that of the second embodiment in that, when the processor 5 changes the gas supply rate of the buffer gas from the laser optical path tube 36 from the second flow rate, which is the normal flow rate, to the first flow rate, which is lower than the normal flow rate, at the time of startup or when the generation of the EUV light 252 is stopped, the processor 5 changes the gas exhaust rate exhausted from the gas exhaust unit 50 to the first exhaust rate, which is a preparatory exhaust rate, which is lower than the second exhaust rate, which is the normal exhaust rate.

[0148] The flowchart in FIG. 23 will be described below in terms of differences from FIG.

[0149] (Step S117) In this step, the processor 5 controls the flow rate of the buffer gas supplied from the laser optical path pipe 36 and the exhaust amount of the buffer gas exhausted from the gas exhaust unit 50. The processor 5 sets the buffer gas supplied from the first gas supply unit 40b to a first flow rate. The processor 5 also sets the gas exhaust amount exhausted from the gas exhaust unit 50 to a first exhaust amount, which is a preliminary exhaust amount that is smaller than the second exhaust amount, which is a normal exhaust amount.

[0150] (Step S139) In this step, the processor 5 changes the target flow rate of the buffer gas supplied from the laser optical path pipe 36 and the target exhaust volume of the buffer gas exhausted from the gas exhaust unit 50. The processor 5 sets the buffer gas supplied from the first gas supply unit 40b to a second flow rate, which is a normal flow rate. The processor 5 also sets the gas exhaust volume exhausted from the gas exhaust unit 50 to a second exhaust volume, which is a normal exhaust volume.

[0151] (Step S140) In this step, the processor 5 waits until the target supply unit 26 reaches a normal temperature and normal pressure. The processor 5 waits until the target supply unit 26 reaches a normal temperature and normal pressure. If the target supply unit 26 has not reached a normal temperature and normal pressure, the processor 5 continues with step S140. If the target supply unit 26 has reached a normal temperature and normal pressure, the processor 5 proceeds to step S14.

[0152] (Step S165) In this step, the processor 5 controls the flow rate of the buffer gas supplied from the laser optical path pipe 36 and the exhaust amount of the buffer gas exhausted from the gas exhaust unit 50. The processor 5 sets the buffer gas supplied from the first gas supply unit 40b to a first flow rate. The processor 5 also sets the gas exhaust amount exhausted from the gas exhaust unit 50 to a first exhaust amount, which is a preliminary exhaust amount that is smaller than the second exhaust amount, which is a normal exhaust amount. Then, the process returns to step S13.

[0153] 24(A) to 24(C) are timing charts showing the state changes of each component when steps S11 to S16 in FIG. 23 are executed. The horizontal axis of each diagram represents the passage of time, and the time is the same. The dashed lines indicate the points where the state changes. The S numbers in the upper rows are the numbers of the steps executed between adjacent dashed lines.

[0154] 24(A) shows the transition of the pressure in the fourth space 20d. The pressure in the fourth space 20d is maintained at a substantially constant pressure throughout the entire period from step S12 to step S16. The pressure fluctuation in the fourth space 20d is maintained within ±1.0 Pa of the target pressure. It is preferable that the pressure fluctuation in the fourth space 20d be within ±0.5 Pa of the target pressure.

[0155] 24(C), in steps S14, S15, and S16, the flow rate of gas exhausted from the gas exhaust section 50 is the second exhaust rate, which is the normal exhaust rate. In contrast, between steps S12 and S13, the flow rate of gas exhausted from the gas exhaust section 50 is the first exhaust rate, which is a preparatory exhaust rate that is smaller than the normal exhaust rate.

[0156] 6.3 Actions and Effects According to this embodiment, when the processor 5 sets the gas supply rate of the buffer gas from the laser path tube 36 from the second flow rate, which is the normal flow rate, to the first flow rate, which is lower than the normal flow rate, the processor 5 sets the exhaust rate of the gas exhausted from the gas exhaust unit 50 to the first exhaust rate, which is the preliminary exhaust rate, which is lower than the second exhaust rate, which is the normal exhaust rate. Therefore, even if the gas supply rate supplied from the laser path tube 36 fluctuates, pressure fluctuations of the buffer gas can be suppressed, changes in the heat transfer state from the heater 47 of the target supply unit 26 to the buffer gas can be suppressed, and fluctuations in the temperature and pressure of the target supply unit 26 can be minimized to a negligible level. Therefore, the extreme ultraviolet light generation apparatus 100 does not need to wait until the target supply unit 26 reaches the normal temperature and pressure. This reduces the wait time.

[0157] Note that the processor 5 and other processors in the present disclosure, such as the laser control processor that controls the laser device 3 and the exposure control processor that controls the exposure device 200, may be physically configured in the form of hardware to execute the various processes included in the present disclosure. For example, the processor may be a computer including a memory that stores a control program that defines the various processes and a processing device that executes the control program. The control program may be stored in a single memory, or may be stored separately in multiple physically separate memories, with the various processes defined by the control program as a collection of these memories. The processing device may be a general-purpose processing device such as a CPU, or a processing device for a specific purpose such as a GPU. The processor may also be programmed in the form of software to execute the various processes included in the present disclosure. For example, the processor may be a dedicated device such as an ASIC or a programmable device such as an FPGA, with the functions to execute the various processes implemented in the processor.

[0158] The various processes included in the present disclosure may be performed by a single computer, a single dedicated device, or a single programmable device, or may be performed by cooperation of multiple physically separate computers, multiple dedicated devices, or multiple programmable devices. The various processes may be performed by a combination of at least two of one or more computers, one or more dedicated devices, and one or more programmable devices.

[0159] The above description is intended to be illustrative, not limiting. Accordingly, it will be apparent to those skilled in the art that modifications can be made to the embodiments of the present disclosure without departing from the scope of the claims. It will also be apparent to those skilled in the art that the embodiments of the present disclosure can be used in combination. Terms used throughout this specification and claims should be construed as "open-ended" terms unless expressly stated. For example, terms such as "comprise," "have," "comprise," and "equip" should be interpreted as meaning "without excluding the presence of elements other than those listed." The modifier "a" or "an" should be interpreted as meaning "at least one" or "one or more." 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," including combinations other than "A," "B," and "C."

Claims

1. An extreme ultraviolet light generating device, a chamber in which extreme ultraviolet light is generated by irradiating a target material supplied to a plasma generation region in an internal space with laser light; a laser device that generates the laser light; a target supply unit that supplies droplets of the target material toward the plasma generation region; a target recovery unit that is disposed on a trajectory along which the target material is discharged and that recovers the target material that is not irradiated with the laser light; a first gas supply unit that supplies a buffer gas into the chamber; a processor; Equipped with The processor controls the first gas supply unit to make a first flow rate, which is the flow rate of the buffer gas supplied from the first gas supply unit during at least a part of a first period during which the laser light is not irradiated onto the droplet, less than a second flow rate, which is the flow rate of the buffer gas supplied from the first gas supply unit during a second period during which the laser light is irradiated onto the droplet, during a period during which the target supply unit ejects the droplet.

2. 2. The extreme ultraviolet light generating apparatus according to claim 1, The first period is the time when the extreme ultraviolet light generation device is started up.

3. 2. The extreme ultraviolet light generating apparatus according to claim 1, The processor further determines the stability of the extreme ultraviolet light; The first period is a period during which the processor stops generating the extreme ultraviolet light when it determines that the stability of the extreme ultraviolet light is abnormal.

4. 2. The extreme ultraviolet light generating apparatus according to claim 1, the target supply unit includes a nozzle that ejects the droplets of the target material; a piezoelectric element that vibrates the nozzle; Equipped with The first period is a period that includes at least a part of a search period in which an optimum duty of the electrical signal to be applied to the piezoelectric element is searched for and determined.

5. The extreme ultraviolet light generating apparatus according to claim 4, The first period further includes a period until the electrical signal of the optimum duty determined in the search period is applied to the nozzle.

6. 2. The extreme ultraviolet light generating apparatus according to claim 1, The buffer gas includes hydrogen gas.

7. 2. The extreme ultraviolet light generating apparatus according to claim 1, an optical path pipe enclosing an optical path of the laser light within the chamber; The optical path tube has a first opening that opens toward the plasma generation region, and the buffer gas is supplied toward the plasma generation region through the first opening, and the laser light is irradiated toward the plasma generation region through the first opening.

8. The extreme ultraviolet light generating apparatus according to claim 7, The light pipe further includes a second opening for directing the buffer gas into the light pipe.

9. 2. The extreme ultraviolet light generating apparatus according to claim 1, The apparatus further includes a gas exhaust section that exhausts gas from the internal space.

10. The extreme ultraviolet light generating apparatus according to claim 9, The processor further controls the gas exhaust section to reduce the amount of gas exhausted from the gas exhaust section compared to when the flow rate of the buffer gas is the second flow rate, so that the pressure in the plasma generation region is within a predetermined range from a predetermined target pressure, during at least a portion of the period during which the flow rate of the buffer gas is the first flow rate.

11. The extreme ultraviolet light generating apparatus according to claim 10, The predetermined range is within ±1.0 Pa of the target pressure.

12. The extreme ultraviolet light generating apparatus according to claim 9, a cylinder that guides the gas in the chamber to the gas exhaust portion, The plasma generation region is located within the through-hole of the cylindrical body.

13. The extreme ultraviolet light generating apparatus according to claim 12, The cylinder has a first cylinder opening at an end opposite to the gas exhaust portion side, and a second cylinder opening at an end on the gas exhaust portion side.

14. The extreme ultraviolet light generating apparatus according to claim 12, The chamber is provided with a partition wall that separates a first space including the cylinder and an optical path tube that surrounds the optical path of the laser light provided on the side of the cylinder, from a second space in which an extreme ultraviolet light focusing mirror that focuses the extreme ultraviolet light is disposed.

15. 2. The extreme ultraviolet light generating apparatus according to claim 1, a second gas supply unit that supplies the buffer gas into the chamber; The processor further controls the second gas supply unit to increase the flow rate of the buffer gas supplied from the second gas supply unit during the first period compared to the flow rate during the second period so that the pressure in the plasma generation region is within a predetermined range of the target pressure.

16. The extreme ultraviolet light generating apparatus according to claim 15, The predetermined range is within ±1.0 Pa of the target pressure.

17. The extreme ultraviolet light generating apparatus according to claim 15, A supply port for supplying the buffer gas from the second gas supply unit is provided near a detection window of a sensor that detects the droplets.

18. The extreme ultraviolet light generating apparatus according to claim 15, A supply port for supplying the buffer gas from the second gas supply unit does not open toward the plasma generation region.

19. A method for manufacturing an electronic device, comprising: a chamber in which extreme ultraviolet light is generated by irradiating a target material supplied to a plasma generation region in an internal space with laser light; a laser device that generates the laser light; a target supply unit that supplies droplets of the target material toward the plasma generation region; a target recovery unit that is disposed on a trajectory along which the target material is discharged and that recovers the target material that is not irradiated with the laser light; a first gas supply unit that supplies a buffer gas into the chamber; a processor; Equipped with the processor controls the first gas supply unit to make a first flow rate, which is a flow rate of the buffer gas supplied from the first gas supply unit during at least a part of a first period during which the laser beam is not irradiated to the droplets, less than a second flow rate, which is a flow rate of the buffer gas supplied from the first gas supply unit during a second period during which the laser beam is irradiated to the droplets, during a period during which the target supply unit discharges the droplets of the target material;

20. A method for manufacturing an electronic device, comprising: a chamber in which extreme ultraviolet light is generated by irradiating a target material supplied to a plasma generation region in an internal space with laser light; a laser device that generates the laser light; a target supply unit that supplies droplets of the target material toward the plasma generation region; a target recovery unit that is disposed on a trajectory along which the target material is discharged and that recovers the target material that is not irradiated with the laser light; a first gas supply unit that supplies a buffer gas into the chamber; a processor; Equipped with the processor controls the first gas supply unit to make a first flow rate, which is a flow rate of the buffer gas supplied from the first gas supply unit during at least a part of a first period during which the laser beam is not irradiated to the droplets, less than a second flow rate, which is a flow rate of the buffer gas supplied from the first gas supply unit during a second period during which the laser beam is irradiated to the droplets.

Images