How to clean extreme ultraviolet reflective mirrors

Abstract

To provide a method for cleaning extreme-ultraviolet light reflection mirror that can shorten the cleaning period and reduce the cleaning cost.SOLUTION: A cleaning method includes a contact step SP21 of contacting α-tin with solid tin debris adhering to an extreme-ultraviolet light reflection mirror, and an aging step SP22 that promotes tin-pestation of tin debris by leaving tin debris in contact with α-tin in a sub-zero ambient temperature environment. Also, the cleaning method further includes a removal step SP23 of removing the tin-pested tin debris from the extreme-ultraviolet light reflection mirror.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present disclosure relates to a method for cleaning an extreme ultraviolet light reflective mirror. [Background technology]

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

[0003] As an EUV light generation device, development is underway on Laser Produced Plasma (LPP) type devices that use plasma generated by irradiating a target material with laser light. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 7,211,810 [Patent Document 2] Summary of JP2005-268358A

[0005] A method for cleaning an extreme ultraviolet light reflective mirror according to one aspect of the present disclosure may include a contacting step of bringing alpha-tin into contact with solid tin debris adhering to the extreme ultraviolet light reflective mirror, an aging step of leaving the tin debris in contact with the alpha-tin in a sub-freezing temperature environment to promote conversion of the tin debris to tin pest, and a removal step of removing the tin-pested tin debris from the extreme ultraviolet light reflective mirror. [Brief description of the drawings]

[0006] Some embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings. [Figure 1] FIG. 1 is a schematic diagram showing an example of the overall configuration of an electronic device manufacturing apparatus. [Diagram 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. [Diagram 3] FIG. 3 is a schematic diagram showing an example of the overall configuration of an extreme ultraviolet light generation apparatus. [Figure 4] FIG. 4 is a cross-sectional view of an EUV light reflective mirror with tin debris attached thereto. [Diagram 5] FIG. 5 is an enlarged cross-sectional view of the EUV light reflective mirror in the vicinity of the tin debris shown in FIG. [Figure 6] FIG. 6 is a diagram showing an example of a flowchart of a cleaning method for an EUV light reflective mirror in a comparative example. [Figure 7] FIG. 7 is an enlarged cross-sectional view of the EUV light reflective mirror from which the tin debris and the reflective film have been removed. [Figure 8] FIG. 8 is an enlarged cross-sectional view of the EUV light reflective mirror on which the reflective film has been re-formed. [Figure 9] FIG. 9 is a diagram showing an example of a flowchart of the method for cleaning the EUV light reflective mirror in the first embodiment. [Figure 10] FIG. 10 is a cross-sectional view of the EUV light reflective mirror at the contacting step. [Figure 11] FIG. 11 is an enlarged cross-sectional view of the EUV light reflective mirror around the tin debris shown in FIG. [Figure 12] FIG. 12 is an enlarged cross-sectional view of the EUV light reflective mirror around the tin debris in the aging step. [Figure 13] FIG. 13 is a diagram showing the removal step. [Figure 14] FIG. 14 is a cross-sectional view of the EUV light reflective mirror after the removal step. [Figure 15]FIG. 15 is a diagram illustrating an example of a flowchart of the cleaning method according to the second embodiment. [Figure 16] FIG. 16 is a diagram showing the film formation step. [Figure 17] FIG. 17 is an enlarged cross-sectional view of the EUV light reflective mirror around the tin debris shown in FIG. [Figure 18] FIG. 18 is an enlarged cross-sectional view of the EUV light reflective mirror around the tin debris in the contact step of the second embodiment. [Figure 19] FIG. 19 is an enlarged cross-sectional view of the EUV light reflective mirror around the tin debris in the contact step of the third embodiment. Embodiment

[0007] 1. Overview 2. Description of electronic device manufacturing equipment 3. Description of the extreme ultraviolet light generating device of the comparative example 3.1 Configuration 3.2 Operation 3.3 How to clean the extreme ultraviolet reflective mirror 3.4 Challenges 4. Description of the cleaning method for the extreme ultraviolet light reflective mirror of embodiment 1 4.1 How to clean the extreme ultraviolet reflective mirror 4.2 Actions and Effects 5. Description of the cleaning method for the extreme ultraviolet light reflective mirror of the second embodiment 5.1 How to clean the extreme ultraviolet reflective mirror 5.2 Actions and Effects 6. Description of the cleaning method for the extreme ultraviolet light reflective mirror of the third embodiment 6.1 How to clean the extreme ultraviolet reflective mirror 6.2 Actions and Effects

[0008] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The embodiments described below are merely examples of the present disclosure and do not limit the contents of the present disclosure. Furthermore, not all of the configurations and operations described in each embodiment are necessarily essential to the configurations and operations of the present disclosure. Note that the same components are given the same reference symbols and redundant descriptions are omitted.

[0009] 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 be referred to as EUV light.

[0010] 2. Description of electronic device manufacturing equipment FIG. 1 is a schematic diagram showing an example of the overall schematic configuration of an electronic device manufacturing apparatus. The electronic device manufacturing apparatus shown in FIG. 1 includes an EUV light generation apparatus 100 and an exposure apparatus 200. The exposure apparatus 200 includes a mask irradiation unit 210 including a plurality of mirrors 211 and 212 that are reflective optical systems, and a workpiece irradiation unit 220 including a plurality of mirrors 221 and 222 that are reflective optical systems different 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 the EUV light 101 incident from the EUV light generation apparatus 100. The workpiece irradiation unit 220 forms an image of the EUV light 101 reflected by the mask table MT on a workpiece (not shown) arranged on a workpiece table WT via the mirrors 221 and 222. The workpiece is a photosensitive substrate such as a semiconductor wafer on which a photoresist is applied. Exposure apparatus 200 synchronously translates mask table MT and workpiece table WT to expose a workpiece to EUV light 101 reflecting a mask pattern. By performing the exposure steps described above, a device pattern can be transferred onto a semiconductor wafer, thereby manufacturing a semiconductor device.

[0011] FIG. 2 is a schematic diagram showing an example of a schematic configuration of an entire electronic device manufacturing apparatus different from the electronic device manufacturing apparatus shown in FIG. 1. The electronic device manufacturing apparatus shown in FIG. 2 includes an EUV light generation apparatus 100 and an inspection apparatus 300. The inspection apparatus 300 includes an illumination optical system 310 including a plurality of mirrors 311, 313, and 315 that are reflection optical systems, and a detection optical system 320 including a plurality of mirrors 321 and 323 that are reflection optical systems different from the reflection 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 EUV light generation apparatus 100 by the mirrors 311, 313, and 315, and irradiates a mask 333 arranged 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 reflecting 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 that receives the EUV light 101 acquires an image of the mask 333. The detector 325 is, for example, a TDI (Time Delay Integration) camera. The image of the mask 333 acquired by the above steps 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.

[0012] 3. Description of the extreme ultraviolet light generating device of the comparative example 3.1 Configuration Below, an EUV light generation apparatus 100 as a comparative example will be described. Note that the comparative example of the present disclosure is a form that the applicant recognizes as being known only by the applicant, and is not a publicly known example that the applicant acknowledges. Also, below, an EUV light generation apparatus 100 that emits EUV light 101 toward an exposure apparatus 200 as an external apparatus as shown in FIG. 1 will be used for the description. Note that the same action and effect can be obtained with an EUV light generation apparatus 100 that emits EUV light 101 toward an inspection apparatus 300 as an external apparatus as shown in FIG. 2.

[0013] 3 is a schematic diagram showing an example of the overall schematic configuration of the EUV light generation system 100 of this embodiment. As shown in FIG. 3, the EUV light generation system 100 mainly includes a laser device LD, a chamber device 10, a processor 120, and a laser light delivery optical system 30.

[0014] The chamber apparatus 10 is a sealable container. The chamber apparatus 10 includes a sub-chamber 15, and a target supply apparatus 40 is disposed in the sub-chamber 15. The target supply apparatus 40 is attached so as to penetrate a wall of the sub-chamber 15. The target supply apparatus 40 includes a tank 41, a nozzle 42, and a pressure regulator 43, and supplies droplets DL to the internal space of the chamber apparatus 10. The droplets DL are also called targets.

[0015] The tank 41 stores therein a target material that becomes a droplet DL. The target material contains tin. The inside of the tank 41 is in communication with a pressure regulator 43 that regulates the pressure inside the tank 41. A heater 44 and a temperature sensor 45 are attached to the tank 41. The heater 44 heats the tank 41 with a current supplied from a heater power supply 46. This heating melts the target material in the tank 41. The temperature sensor 45 measures the temperature of the target material in the tank 41 via the tank 41. The pressure regulator 43, the temperature sensor 45, and the heater power supply 46 are electrically connected to the processor 120.

[0016] The nozzle 42 is attached to the tank 41 and discharges a target material. A piezoelectric element 47 is attached to the nozzle 42. The piezoelectric element 47 is electrically connected to a piezoelectric power supply 48 and is driven by a voltage applied from the piezoelectric power supply 48. The piezoelectric power supply 48 is electrically connected to the processor 120. By the operation of the piezoelectric element 47, the target material discharged from the nozzle 42 is turned into droplets DL.

[0017] The chamber apparatus 10 includes a target collection unit 14. The target collection unit 14 is a box attached to an inner wall 10b of the chamber apparatus 10, and communicates with the internal space of the chamber apparatus 10 via an opening 10a that is continuous with the inner wall 10b of the chamber apparatus 10. The opening 10a is disposed directly below the nozzle 42, and the target collection unit 14 is a drain tank that collects unwanted droplets DL that pass through the opening 10a and reach the target collection unit 14.

[0018] At least one through hole is provided in the inner wall 10b of the chamber apparatus 10. This through hole is covered by a window 12, through which pulsed laser light 90 emitted from the laser device LD passes.

[0019] Further, a laser focusing optical system 13 is disposed in the internal space of the chamber apparatus 10. The laser focusing optical system 13 includes a laser beam focusing mirror 13A and a high reflection mirror 13B. The laser beam focusing mirror 13A reflects and focuses the laser beam 90 passing through the window 12. The high reflection mirror 13B reflects the light focused by the laser beam focusing mirror 13A. The positions of the laser beam focusing mirror 13A and the high reflection mirror 13B are adjusted by a laser beam manipulator 13C so that the focusing position of the laser beam 90 in the internal space of the chamber apparatus 10 is a position designated by the processor 120. The focusing position is adjusted to be located directly below the nozzle 42, and when the laser beam 90 irradiates the target material constituting the droplet DL at the focusing position, plasma is generated by the irradiation, and EUV light 101 is emitted from the plasma. Hereinafter, the region where the plasma is generated may be referred to as a plasma generation region AR.

[0020] An EUV light reflecting mirror 75 is disposed in the internal space of the chamber apparatus 10. The EUV light reflecting mirror 75 has a first focal point and a second focal point. The EUV light reflecting mirror 75 may be disposed, for example, such that the first focal point is located in the plasma generation region AR and the second focal point is located in the intermediate focus point IF. In FIG. 3, a straight line passing through the first focal point and the second focal point is shown as a focal line L0. The focal line L0 is located along the central axis direction of the EUV light reflecting mirror 75. The EUV light reflecting mirror 75 includes a substrate 75a having an ellipsoidal shape and a reflecting film 75b disposed on the surface of the substrate 75a facing the plasma generation region AR. The reflecting film 75b reflects the EUV light 101 emitted from the plasma in the plasma generation region AR, and the EUV light reflecting mirror 75 focuses the EUV light 101 at the second focal point due to its shape. In FIG. 3, the reflecting film 75b is simply illustrated to avoid complicating the drawing.

[0021] The reflective film 75b includes a reflective body film laminated on the substrate 75a, and a protective film laminated on the reflective body film. The reflective body film is a laminated film in which silicon layers and molybdenum layers are alternately laminated. The number of layers in the reflective body film is preferably, for example, 50 to 100. For EUV light 101 with a wavelength of 13.5 nm, the real refractive index of the silicon layer is approximately 0.99, and the real refractive index of the molybdenum layer is approximately 0.92. The outermost layer of the reflective body film is a silicon layer, and the protective film is laminated on the silicon layer. The protective film is made of zirconium oxynitride (ZrON), zirconium nitride (ZrN), zirconia (ZrO 2 ), titanium nitride (TiN), titanium oxynitride (TiON), titanium dioxide (TiO 2 ), ruthenium dioxide (RuO 2 ), silicon nitride (Si 3 N 4 ), silicon dioxide (SiO 2 ), molybdenum dioxide (MoO 2 ). One surface of the protective film is the outermost layer of the reflective film 75b, and is exposed to the internal space of the chamber apparatus 10. Note that the reflective main body film may be a film other than a silicon layer or a molybdenum layer, and for example, a single layer film of ruthenium may be provided.

[0022] The EUV light generation system 100 includes a connection part 19 that communicates the internal space of the chamber apparatus 10 with the internal space of the exposure system 200. A wall in which an aperture is formed is disposed inside the connection part 19. This wall is preferably disposed so that the aperture is located at the second focal point. The connection part 19 is an exit port for the EUV light 101 in the EUV light generation system 100, and the EUV light 101 is emitted from the connection part 19 and enters the exposure system 200.

[0023] The EUV light generation apparatus 100 also includes a pressure sensor 26 and a target sensor 27. The pressure sensor 26 and the target sensor 27 are attached to the chamber apparatus 10 and electrically connected to the processor 120. The pressure sensor 26 measures the pressure in the internal space of the chamber apparatus 10 and outputs a signal indicating the measured pressure to the processor 120. The target sensor 27 includes, for example, an imaging function, and detects the presence, trajectory, position, flow velocity, and the like of the droplet DL discharged from the nozzle hole of the nozzle 42 in response to an instruction from the processor 120. The target sensor 27 may be disposed inside the chamber apparatus 10, or may be disposed outside the chamber apparatus 10 and detect the droplet DL through a window (not shown) provided on the wall of the chamber apparatus 10. The target sensor 27 includes a light receiving optical system (not shown) and an imaging unit (not shown), such as a charge-coupled device (CCD) or a photodiode. The light receiving optical system forms an image of the trajectory of the droplet DL and its surroundings on the light receiving surface of the imaging unit in order to detect the droplet DL. When the droplet DL passes through a light collection area of ​​the light source unit (not shown) of the target sensor 27 arranged to ensure the field of view of the target sensor 27, the imaging unit detects the trajectory of the droplet DL and changes in the light passing around it. The imaging unit converts the detected changes in light into an electrical signal that is a signal related to the image data of the droplet DL. The imaging unit outputs this electrical signal to the processor 120.

[0024] The laser device LD includes a master oscillator, which is a light source that performs burst operation. The master oscillator emits a pulsed laser light 90 in burst-on. The master oscillator is a laser device that emits the laser light 90 by exciting a gas in which helium, nitrogen, or the like is mixed in carbon dioxide gas by discharging. Alternatively, the master oscillator may be a quantum cascade laser device. The master oscillator may also emit the pulsed laser light 90 by a Q-switch method. The master oscillator may also include an optical switch, a polarizer, or the like. The burst operation is an operation in which continuous pulsed laser light 90 is emitted at a predetermined repetition frequency during burst-on, and the emission of the laser light 90 is suppressed during burst-off.

[0025] The traveling direction of the laser light 90 emitted from the laser device LD is adjusted by the laser light delivery optical system 30. The laser light delivery optical system 30 includes a plurality of mirrors 30A, 30B that adjust the traveling direction of the laser light 90. The position of at least one of the mirrors 30A, 30B is adjusted by an actuator (not shown). By adjusting the position of at least one of the mirrors 30A, 30B, the laser light 90 can be appropriately propagated from the window 12 to the internal space of the chamber apparatus 10.

[0026] The processor 120 of the present disclosure is a processing device including a storage device in which a control program is stored and a CPU that executes the control program. The processor 120 is specially configured or programmed to execute various processes included in the present disclosure. The processor 120 controls the entire EUV light generation apparatus 100. The processor 120 is also electrically connected to the exposure apparatus 200 and transmits and receives various signals to and from the exposure apparatus 200.

[0027] The chamber apparatus 10 is provided with a central gas supply unit 81 that supplies an etching gas to the internal space of the chamber apparatus 10. As described above, since the target material contains tin, the etching gas is, for example, a hydrogen-containing gas in which the hydrogen gas concentration is considered to be 100%. Alternatively, the etching gas may be a balance gas in which the hydrogen gas concentration is, for example, about 3%. The balance gas may include nitrogen (N 2 The gases include tin (Sn) gas and argon (Ar) gas. When the target material constituting the droplet DL is irradiated with the laser beam 90 in the plasma generation region AR and turned into plasma, tin fine particles and tin charged particles are generated. The tin constituting these fine particles and charged particles reacts with hydrogen contained in the etching gas supplied to the internal space of the chamber apparatus 10. When tin reacts with hydrogen, stannane (SnH 4 ) becomes.

[0028] The center side gas supply unit 81 has a side shape of a truncated cone, and may be called a cone. The center side gas supply unit 81 passes through a through hole 75c formed in the center of the EUV light reflective mirror 75.

[0029] The center-side gas supply unit 81 includes a center-side gas supply port 81a which is a nozzle. The center-side gas supply port 81a is provided on the focal line L0. The center-side gas supply port 81a supplies an etching gas from the center side of the EUV light reflecting mirror 75 toward the plasma generation region AR. The center-side gas supply port 81a preferably supplies an etching gas from the center side of the EUV light reflecting mirror 75 in a direction away from the EUV light reflecting mirror 75 along the focal line L0. The center-side gas supply port 81a is connected to a gas supply device (not shown) which is a tank via a piping (not shown) of the center-side gas supply unit 81, and is supplied with an etching gas from the gas supply device. The gas supply device is controlled by the processor 120. A supply gas flow rate regulator (not shown) which is a valve may be disposed in the piping (not shown).

[0030] The center-side gas supply port 81a is a gas supply port that supplies an etching gas to the internal space of the chamber apparatus 10, and also an emission port through which the laser light 90 is emitted to the internal space of the chamber apparatus 10. The laser light 90 passes through the window 12 and the center-side gas supply port 81a and advances toward the internal space of the chamber apparatus 10.

[0031] An exhaust port 10E is continuous with the inner wall 10b of the chamber device 10. Since the exposure device 200 is disposed on the focal line L0, the exhaust port 10E is provided on the inner wall 10b on the side of the focal line L0, not on the focal line L0. The direction along the central axis of the exhaust port 10E is perpendicular to the focal line L0. Moreover, when viewed from a direction perpendicular to the focal line L0, the exhaust port 10E is provided on the opposite side of the reflective film 75b with respect to the plasma generation region AR. The exhaust port 10E exhausts residual gas, which will be described later, from the internal space of the chamber device 10. The exhaust port 10E is connected to an exhaust pipe 10P, which is connected to an exhaust pump 60.

[0032] When the target material is turned into plasma in the plasma generation region AR as described above, residual gas is generated as exhaust gas in the internal space of the chamber apparatus 10. The residual gas contains tin particles and charged particles generated by turning the target material into plasma, stannane which reacts with the etching gas, and unreacted etching gas. Note that some of the charged particles are neutralized in the internal space of the chamber apparatus 10, and the neutralized charged particles are also included in the residual gas. The residual gas is sucked into the exhaust pump 60 via the exhaust port 10E and the exhaust pipe 10P.

[0033] 3.2 Operation Next, the operation of the EUV light generation apparatus 100 of the comparative example will be described. In the EUV light generation apparatus 100, for example, when the apparatus is newly installed or during maintenance, the atmosphere in the internal space of the chamber apparatus 10 is exhausted. At that time, purging and exhausting of the internal space of the chamber apparatus 10 may be repeated to exhaust the atmospheric components. For the purge gas, an inert gas such as nitrogen or argon is preferably used. After that, when the pressure in the internal space of the chamber apparatus 10 becomes equal to or lower than a predetermined pressure, the processor 120 starts introducing an etching gas from the gas supply apparatus into the internal space of the chamber apparatus 10 via the central gas supply unit 81. At this time, the processor 120 may control the supply gas flow rate regulator and the exhaust pump 60 (not shown) so that the pressure in the internal space of the chamber apparatus 10 is maintained at a predetermined pressure. After that, the processor 120 waits until a predetermined time has elapsed since the start of the introduction of the etching gas.

[0034] In addition, the processor 120 controls the exhaust pump 60 to exhaust gas from the internal space of the chamber apparatus 10 through the exhaust port 10E, and maintains the pressure in the internal space of the chamber apparatus 10 at an approximately constant pressure based on a signal indicating the pressure in the internal space of the chamber apparatus 10 measured by the pressure sensor 26.

[0035] Furthermore, in order to heat and maintain the target material in the tank 41 at a predetermined temperature equal to or higher than the melting point, the processor 120 applies a current from the heater power supply 46 to the heater 44, thereby raising the temperature of the heater 44. At this time, the processor 120 adjusts the value of the current applied from the heater power supply 46 to the heater 44 based on the output from the temperature sensor 45, thereby controlling the temperature of the target material to a predetermined temperature. Note that, when the target material is tin, the predetermined temperature is a temperature equal to or higher than the melting point of tin, 231.93°C, for example, 240°C to 290°C.

[0036] The processor 120 also supplies an inert gas from a gas supply source (not shown) into the tank 41 by the pressure regulator 43 so that the molten target material is discharged from the nozzle hole of the nozzle 42 at a predetermined flow rate, and adjusts the pressure in the tank 41 by the pressure regulator 43. Under this pressure, the target material is discharged from the nozzle hole of the nozzle 42. The target material discharged from the nozzle hole may take the form of a jet. At this time, the processor 120 applies a voltage of a predetermined waveform from the piezoelectric power supply 48 to the piezoelectric element 47 in order to generate the droplets DL. The piezoelectric power supply 48 applies a voltage so that the waveform of the voltage value is, for example, sinusoidal, rectangular, or sawtooth. The vibration of the piezoelectric element 47 can be propagated to the target material discharged from the nozzle hole of the nozzle 42 via the nozzle 42. The target material is divided at a predetermined period by this vibration, and becomes droplets DL of liquid droplets.

[0037] The target sensor 27 detects the passing timing of the droplet DL passing through a predetermined position in the internal space of the chamber apparatus 10. The processor 120 outputs an emission trigger signal synchronized with the signal from the target sensor 27 to the laser device LD. When the emission trigger signal is input, the laser device LD emits a pulsed laser beam 90. The emitted laser beam 90 passes through the laser beam delivery optical system 30 and the window 12 and enters the laser focusing optical system 13. The laser beam 90 also travels from the laser focusing optical system 13 to the center side gas supply unit 81, which is an emission unit. The laser beam 90 is emitted from the center side gas supply port 81a, which is an emission port of the center side gas supply unit 81, toward the plasma generation region AR along the focal line L0, and irradiates the droplet DL in the plasma generation region AR. At this time, the processor 120 controls the laser beam manipulator 13C of the laser focusing optical system 13 so that the laser beam 90 is focused on the plasma generation region AR. The processor 120 also controls the timing of emitting the laser beam 90 from the laser device LD based on a signal from the target sensor 27 so that the droplet DL is irradiated with the laser beam 90. As a result, the laser beam 90 collected by the laser beam collecting mirror 13A irradiates the droplet DL in the plasma generation region AR. This irradiation generates plasma, and light including EUV light is emitted from the plasma.

[0038] Of the light including EUV light generated in the plasma generation region AR, EUV light 101 is focused at an intermediate focus point IF by an EUV light reflecting mirror 75 and then enters the exposure device 200 from a connection part 19 .

[0039] When the target material is turned into plasma, tin particles are generated as described above. These particles diffuse into the internal space of the chamber apparatus 10. The particles diffusing into the internal space of the chamber apparatus 10 react with the etching gas containing hydrogen supplied from the center side gas supply unit 81 to become stannane. Most of the stannane obtained by the reaction with the etching gas is carried by the flow of the unreacted etching gas and flows into the exhaust port 10E. In addition, at least a portion of the unreacted charged particles, particles, and etching gas also flows into the exhaust port 10E.

[0040] Unreacted etching gas, fine particles, charged particles, stannane, and the like that flow into the exhaust port 10E flow as residual gas from the exhaust pipe 10P into the exhaust pump 60, where they are subjected to a predetermined exhaust process such as being rendered harmless.

[0041] 3.3 How to clean the extreme ultraviolet reflective mirror Tin that is generated when the target material is turned into plasma and diffuses in the internal space of the chamber apparatus 10 may adhere to the reflective film 75b as tin debris 151. FIG. 4 is a cross-sectional view of the EUV light reflecting mirror 75 to which the tin debris 151 is attached. FIG. 5 is an enlarged cross-sectional view of the EUV light reflecting mirror 75 around the tin debris 151 shown in FIG. 4. In FIG. 4, for ease of viewing, only one tin debris 151 is labeled, and the other tin debris 151 is omitted. In FIG. 4, the reflective film 75b is simply illustrated, and hatching of the tin debris 151 is omitted, in order to avoid complicating the drawing. In FIG. 5, two of the tin debris 151 shown in FIG. 4 are enlarged. As shown in FIG. 4 and FIG. 5, the tin debris 151 tends to adhere to the reflective film 75b in a scattered manner. Therefore, each tin debris 151 adheres to the reflective film 75b while being separated from each other. Although an example in which the tin debris 151 is scattered on a part of the reflective film 75b is shown in Fig. 4, the tin debris 151 may be scattered over the entire reflective film 75b. The tin debris 151 may also adhere to the reflective film 75b.

[0042] The tin debris 151 is solid tin containing at least β-tin. β-tin is metallic tin that tends to exist at temperatures higher than about 13.2° C. and is harder than α-tin. α-tin is an allotrope of tin that tends to exist at temperatures below about 13.2° C. and is more brittle than β-tin. α-tin is a gray cubic crystal, and β-tin is a white tetragonal crystal. When the tin debris 151 adheres to the reflective film 75b, the reflectance of the reflective film 75b decreases, and the energy of the EUV light 101 emitted from the EUV light generation apparatus 100 toward the exposure apparatus 200 decreases. Therefore, in the EUV light generation apparatus 100 of the comparative example, cleaning of the EUV light reflection mirror 75 is performed to maintain a high reflectance.

[0043] Fig. 6 is a diagram showing an example of a flowchart of a cleaning method for the EUV light reflecting mirror 75 in a comparative example. Hereinafter, the cleaning method for the EUV light reflecting mirror 75 may be simply referred to as the cleaning method. As shown in Fig. 6, the cleaning method includes a polishing step SP11 and a re-deposition step SP12. In the starting state shown in Fig. 6, tin debris 151 is attached to the reflective film 75b as shown in Figs. 4 and 5.

[0044] (Polishing step SP11) In this step, the entire reflective film 75b is polished, and the reflective film 75b is removed together with the tin debris 151 as shown in Fig. 7. Therefore, in this step, the entire surface of the substrate 75a is exposed. After the reflective film 75b is removed, the flow proceeds to a re-deposition step SP12.

[0045] (Re-deposition step SP12) In this step, as shown in Fig. 8, a new reflective film 75b without tin debris 151 attached thereto is re-formed on the entire surface of the substrate 75a. This causes the reflectance of the reflective film 75b to return to and recover the reflectance before the tin debris 151 attached to the reflective film 75b. When the reflective film 75b is re-formed, the flow ends.

[0046] 3.4 Challenges In the comparative example, cleaning of the EUV light reflective mirror 75, which involves removing the entire reflective film 75b and re-forming the reflective film 75b on the entire surface of the substrate 75a, takes time and costs money. For this reason, there is a demand for shortening the cleaning period and reducing the cleaning costs.

[0047] Therefore, in the following embodiment, a cleaning method for the EUV light reflective mirror 75 that can shorten the cleaning period and reduce the cleaning cost will be exemplified.

[0048] 4. Description of the cleaning method for the extreme ultraviolet light reflective mirror of embodiment 1 Next, a description will be given of the cleaning method of embodiment 1. Note that the same components as those described above are given the same reference numerals, and duplicated descriptions will be omitted unless otherwise specified.

[0049] 4.1 How to clean the extreme ultraviolet reflective mirror Fig. 9 is a diagram showing an example of a flowchart of the cleaning method in this embodiment. The cleaning method in this embodiment includes a contact step SP21, an aging step SP22, and a removal step SP23. The starting state shown in Fig. 9 is the same as the starting state in the cleaning method of the comparative example. Therefore, in this starting state, tin debris 151 is attached to the reflective film 75b in a scattered manner, as shown in Figs. 4 and 5.

[0050] (Contact step SP21) FIG. 10 is a cross-sectional view of the EUV light reflection mirror 75 in this step. FIG. 11 is an enlarged cross-sectional view of the EUV light reflection mirror 75 around the tin debris 151 shown in FIG. 10. In FIG. 10, for ease of viewing, only one tin debris 151 is labeled, and the other tin debris 151 are omitted. Also, in FIG. 10, in order to avoid complicating the drawing, the reflection film 75b and an α-tin film 153 described later are simply illustrated, and hatching of the tin debris 151 is omitted. In FIG. 11, two of the tin debris 151 shown in FIG. 10 are enlarged. In FIG. 10, the plasma emitted from the plasma generation region AR is indicated by an arrow 171. The tin plasma indicated by the arrow 171 is generated in an environment containing hydrogen by a process device not shown and described later.

[0051] This step is a step of bringing α-tin into contact with solid tin debris 151 adhering to the EUV light reflection mirror 75. FIG. 10 and FIG. 11 show an example in which an α-tin film 153 containing α-tin is formed on the tin debris 151 by exposure to tin ions and tin neutral atoms emitted from the plasma. In this step, the reflective film 75b is also exposed to the tin ions and tin neutral atoms, so that the α-tin film 153 is also formed on the reflective film 75b. The film thickness of the α-tin film 153 is approximately 20 μm or more and 1 mm or less. The film thickness of the α-tin film 153 is approximately the same at any position, but the α-tin film 153 formed on the tin debris 151 may be thicker or thinner than the α-tin film 153 formed on the reflective film 75b.

[0052] The process equipment forms an α-tin film 153 on the tin debris 151 by tin ions and tin neutral atoms emitted from plasma generated by irradiating droplets or solid tin with laser light. The process equipment may also form the α-tin film 153 on the tin debris 151 by tin ions and tin neutral atoms emitted from plasma generated from stannane. In the above process equipment, the energy of each of the tin ions and tin neutral atoms emitted from the plasma is set to less than 0.5 eV. Alternatively, the process equipment may form the α-tin film 153 by sputtering.

[0053] In this step, tin plasma is generated in an environment containing hydrogen. The temperature of the EUV light reflective mirror 75 is adjusted to be equal to or lower than approximately 13.2°C, which is the phase transition temperature of α-tin. As a result, the temperatures of the tin debris 151 and the reflective film 75b are also adjusted to be equal to or lower than approximately 13.2°C. In this case, the tin debris 151 is exposed to tin ions and neutral tin atoms, so that seed crystals of α-tin are generated on the surface of the tin debris 151. The pressure in the hydrogen-containing environment is approximately 0.1 Pa or more and 1000 Pa or less.

[0054] The purity of the tin used in the process equipment is preferably about 99.999% or more. The higher the purity of the tin, the more the tin pest described below is promoted.

[0055] When the α-tin film 153 is formed directly on the tin debris 151 and the reflective film 75b, the flow proceeds to an aging step SP22. At this time, a part of the tin debris 151 may be turned into tin paste.

[0056] (Aging step SP22) This step is a step in which the tin debris 151 on which the α-tin film 153 containing α-tin has been formed is left in a subzero temperature environment to promote the formation of tin pest in the tin debris 151. The formation of tin pest is a phenomenon in which a seed crystal of α-tin comes into contact with β-tin, and the phase transition from β-tin to α-tin occurs starting at the contact point between the seed crystal and β-tin. Since α-tin tends to exist at approximately 13.2°C or lower, the phase transition from β-tin to α-tin in the formation of tin pest begins at approximately 13.2°C or lower. Therefore, when the α-tin film 153 is formed on the tin debris 151 containing β-tin in the contact step SP21, the phase transition begins and the tin debris 151 becomes tin pest. In addition, in a sub-zero temperature environment such as in this step, the tin pest formation is accelerated by the temperature environment, so the storage period in a sub-zero temperature environment, which will be described later, is shorter than the storage period in an environment in which the tin pest formation is less accelerated. The temperature of the environment is generally higher than 0°C and generally equal to or lower than 13.2°C.

[0057] In this step, in order to promote the formation of tin pest, the α-tin film 153, the tin debris 151, and the EUV light reflecting mirror 75 are stored in a subzero temperature environment in the internal space of a storage device (not shown). In the tin debris 151 in which the formation of tin pest is promoted, the proportion of α-tin in the tin debris 151 increases with the passage of time. FIG. 12 is an enlarged cross-sectional view of the EUV light reflecting mirror 75 around the tin debris 155 in the aging step SP22. In FIG. 12, the tin debris 151 and the α-tin film 153 shown in FIG. 11 are shown by dashed lines for comparison with the enlarged cross-sectional view shown in FIG. 11. The tin debris 155 is composed of the α-tin film 153 and the tin debris 151 that has been tin-pested by the α-tin film 153. The period required for the formation of tin pest, that is, the storage period for the tin debris 151 in the internal space of the storage device, varies depending on the temperature in the internal space. In a sub-freezing temperature environment, the storage period is shorter than in an environment where tin pest is less likely to develop. In a sub-freezing temperature environment, when the temperature is approximately -50°C or higher and -20°C or lower, the storage period is even shorter. In addition, when the temperature is approximately -40°C, the phase transition speed is the fastest and the storage period is the shortest.

[0058] In the tin pest process of this step, as the proportion of α-tin in the tin debris 151 increases, the volume of the tin debris 151 gradually increases, the strength of the tin debris 151 gradually decreases, and the color of the tin debris 151 gradually changes. When the tin debris 155 is pested, the volume of the tin debris 155 increases by about 30% compared to before the tin pest process, and the tin debris 155 turns gray. The volume before the tin pest process is the sum of the volumes of the tin debris 151 and the α-tin film 153 before the tin pest process. Since most of the tin debris 155 is sand-like, the tin debris 155 becomes brittle compared to the tin debris 151, and is removed by the removal step SP23. If the tin debris 155 is removed in the removal step SP23, the proportion of α-tin in the tin debris 151, 155 does not need to be 100%. In this step, the tin debris 151 is left in a subzero temperature environment so that the tin debris 155 is removed by the removal step SP23, and if the ratio of α-tin in the tin debris 151 becomes equal to or greater than a predetermined value, the tin debris 151 can be considered to have become tin pest. In Fig. 12, the increase in volume and the illustration of sand grains are omitted to avoid complicating the drawing.

[0059] The moisture content in the environment in which this step is performed is 0.1 wt % or less, which is a dry environment in which moisture does not condense on the tin debris 151, 155, the α-tin film 153, and the reflective film 75b.

[0060] When the tin debris 155 is generated, the flow proceeds to a removal step SP23.

[0061] (Removal step SP23) 13 is a diagram showing the state of this step. This step is a step of removing the tin debris 155 that has become tin plaster from the EUV light reflecting mirror 75. In this step, the EUV light reflecting mirror 75 is taken out from the storage device, and the tin debris 155 is removed from the EUV light reflecting mirror 75 by a jet. Examples of the removal method using a jet include a dry ice jet method in which dry ice 187 is sprayed toward the tin debris 155, and a gas jet method in which gas is sprayed toward the tin debris 155.

[0062] The dry ice jet method includes, for example, a first dry ice jet method in which pellet-like dry ice 187 is sprayed toward the tin debris 155, and a second dry ice jet method in which snow-like dry ice 187 is sprayed toward the tin debris 155. FIG. 13 shows an example in which the cleaning device 185 sprays the dry ice 187 in the first dry ice jet method toward a part of the tin debris 155. The dry ice 187 is sprayed toward the entire tin debris 155. In addition, in FIG. 13, the shape of the dry ice 187 is illustrated as a circle, but the shape is not particularly limited.

[0063] In the first dry ice jet method, the cleaning device 185 sprays pellet-shaped dry ice 187 generated from liquefied carbon dioxide gas from a nozzle hole 185a of the cleaning device 185 toward the tin debris 155. The dry ice 187 is sprayed in a state where it is mixed with compressed air. The pressure of the compressed air is approximately 0.5 MPa. In the first dry ice jet method, when the cleaning device 185 sprays the dry ice 187, most of the tin debris 155 is peeled off and scattered from the reflective film 75b by the spraying of the dry ice 187, and is removed from the reflective film 75b. The dry ice 187 collides at high speed with the remaining part of the tin debris 155 that is not removed by the spraying. The tin debris 155 that the dry ice 187 collides with undergoes thermal contraction due to cooling by the dry ice 187 at approximately -79°C. The collision and thermal contraction cause cracks (not shown) in the tin debris 155. Furthermore, the dry ice 187 ejected from the nozzle hole 185a is sent into the cracks one after another. When the dry ice 187 vaporizes and expands in the cracks, the tin debris 155 is peeled off and scattered from the reflective film 75b by the vaporization and expansion of the dry ice 187, and is removed from the reflective film 75b.

[0064] In the second dry ice jet method, the cleaning device 185 sprays snow-like dry ice 187 generated from liquefied carbon dioxide gas from a nozzle hole 185a of the cleaning device 185 toward the tin debris 155. The dry ice 187 is sprayed in a state mixed with compressed air, similar to the first dry ice jet method. In this case, the tin debris 155 is removed similar to the first ice jet method. In the second ice jet method, the snow-like dry ice 187 penetrates into a minute gap between the tin debris 155 and the surface of the reflective film 75b. When the dry ice 187 vaporizes and expands in the gap, the tin debris 155 is peeled off and scattered from the reflective film 75b by the vaporization and expansion of the dry ice 187, and is removed from the reflective film 75b.

[0065] In the dry ice jet method, the volume of the dry ice 187 expands to about 400 to 800 times its original volume before expansion. Also, the dry ice 187 sublimes into gas and does not remain on the reflective film 75b.

[0066] In the gas jet method, the cleaning device 185 injects a gas such as air or nitrogen from a nozzle hole 185a of the cleaning device 185 toward the tin debris 155. The tin debris 155 is peeled off and scattered from the reflective film 75b by the injection, and is removed from the reflective film 75b. Cleaning by the gas jet method may be performed after cleaning by the dry ice jet method. As a result, the tin debris 155 that remains on the reflective film 75b without being removed from the reflective film 75b even by the vaporization and expansion of the dry ice 187 is removed from the reflective film 75b by the injection of gas. Also, cleaning by the gas jet method may be performed before cleaning by the dry ice jet method.

[0067] The proportion of moisture in the environment in which this step is carried out is 0.1 wt % or less, similar to the aging step SP22.

[0068] In this step, the tin debris 155 may be removed by a wet cleaning method, in which case, for example, a fluorine-based inert liquid is used.

[0069] When the tin debris 155 is removed in removal step SP23, the flow ends. Figure 14 is a cross-sectional view of the EUV light reflecting mirror 75 after removal step SP23. The enlarged cross-sectional view of the EUV light reflecting mirror 75 after removal step SP23 is the same as the enlarged cross-sectional view shown in Figure 8. After removal step SP23, the tin debris 155 is removed and the reflective film 75b is exposed. When the reflective film 75b is exposed, the reflectance of the reflective film 75b returns to the reflectance before the tin debris 151 was attached and recovers.

[0070] 4.2 Actions and Effects The cleaning method of this embodiment includes a contact step SP21 in which α-tin is brought into contact with solid tin debris 151 adhering to the EUV light reflecting mirror 75, an aging step SP22 in which the tin debris 151 in contact with the α-tin is left in a sub-freezing temperature environment to promote the conversion of the tin debris 151 to tin pest, and a removal step SP23 in which the tin debris 155 that has been converted into tin pest is removed from the EUV light reflecting mirror 75.

[0071] In the contact step SP21, α-tin comes into contact with the solid tin debris 151, and in the aging step SP22, the tin debris 151 is left in a subzero temperature environment, which accelerates the tin pest of the tin debris 151. As the tin pest accelerates, the tin debris 155 that has been turned into tin pest becomes more fragile than the tin debris 151 before the tin pest. The fragile tin debris 155 is removed from the EUV light reflective mirror 75 in the removal step SP23. In this cleaning method, the cleaning period can be shortened and the cleaning cost can be reduced compared to removing the entire reflective film 75b by polishing and re-forming the reflective film 75b on the entire surface of the substrate 75a. In addition, in the cleaning method of this embodiment, the removal of the entire reflective film 75b by polishing and the re-forming of the reflective film 75b on the entire surface of the substrate 75a may not be necessary. In addition, in the cleaning method of this embodiment, the tin debris 151 is left in a subzero temperature environment to promote the transformation of the tin debris 151 into tin pest. This can shorten the cleaning period compared to a case where the transformation into tin pest is not promoted. In the cleaning method of this embodiment, the tin debris 155 is made brittle by the transformation into tin pest. This can make it easier to remove the tin debris 155 compared to a case where the tin debris 155 is not brittle.

[0072] Furthermore, in the contact step SP21 of the cleaning method of this embodiment, an α-tin film 153 containing α-tin is formed on the tin debris 151. In this case, compared to when the α-tin makes point contact with the tin debris 151, the contact area between the α-tin and the β-tin is wider, which may promote the conversion of the tin debris 151 into tin pest in the aging step SP22, and may shorten the period of the aging step SP22.

[0073] In the cleaning method of this embodiment, the thickness of the α-tin film 153 is 20 μm or more and 1 mm or less. The thicker the film is, the easier it is for the α-tin film 153 to be formed on the tin debris 151 without any gaps, and the easier it is for the tin debris 155 to be removed from the reflective film 75b in the removal step SP23. The film thickness may be less than 20 μm or greater than 1 mm.

[0074] Furthermore, in the cleaning method of this embodiment, the α-tin film 153 is formed on the tin debris 151 by tin ions and neutral tin atoms emitted from tin plasma generated in an environment containing hydrogen. This may make it easier for α-tin seed crystals to be generated on the surface of the tin debris 151 compared to a case in which the tin film 153 is not formed. When α-tin seed crystals are more easily generated, the α-tin film 153 containing α-tin may be more easily formed.

[0075] In the cleaning method of this embodiment, the energy of each of the tin ions and neutral tin atoms emitted from the plasma is less than 0.5 eV. The tin ions and neutral tin atoms collide with and damage the protective film of the reflective film 75b, and may also penetrate into the interior of the reflective film 75b, deteriorating the reflective body film and causing a decrease in reflectance. When the energy is less than 0.5 eV as described above, damage to the protective film and deterioration of the reflective body film can be suppressed compared to when the energy is 0.5 eV or more. Note that each energy may be 0.5 eV or more.

[0076] In the aging step SP22 of the cleaning method of this embodiment, the temperature of the sub-freezing temperature environment is generally −50° C. or higher and −20° C. or lower. In a sub-freezing temperature environment, the cleaning period can be shorter than in an environment where tin pest is less likely to be promoted. Note that the temperature may be lower than −50° C. or higher than −20° C. as long as it is below freezing.

[0077] Moreover, the proportion of moisture in the environment in which the aging step SP22 and the removal step SP23 of the cleaning method of this embodiment are performed is 0.1 wt% or less. This can suppress adhesion of moisture to the reflective film 75b and oxidation of the reflective film 75b due to the adhesion. Also, an increase in the thickness of the reflective film 75b due to oxidation and a decrease in reflectance due to the increase can be suppressed. The proportion in each step may be greater than 0.1 wt%.

[0078] In addition, in the removal step SP23 of the cleaning method of this embodiment, the tin debris 155 that has become tin plaster is removed by a jet. When the tin debris 155 is removed by polishing, the reflective film 75b is also polished, and the reflective film 75b may be damaged by polishing. When the tin debris 155 is removed by a jet, damage to the reflective film 75b may be suppressed and the time required to remove the tin debris 155 may be shortened, compared to when the tin debris 155 is removed by polishing. In addition, in the first dry ice jet method that sprays pellet-like dry ice 187, the dry ice 187 is larger than in the second dry ice jet method that sprays snow-like dry ice 187. Therefore, in the first dry ice jet method, cracks may occur more easily in the tin debris 155 due to the collision of the dry ice 187 and thermal contraction caused by the dry ice 187, compared to the second dry ice jet method. When cracks are more likely to occur in the tin debris 155, the dry ice 187 may be more likely to enter the cracks, and the tin debris 155 may be more likely to be removed. Furthermore, in the second dry ice jet method, the dry ice 187 is smaller than in the first dry ice jet method. Therefore, in the second dry ice jet method, the dry ice 187 may be more likely to enter the minute gap between the tin debris 155 and the surface of the reflective film 75b than in the first dry ice jet method. When the dry ice 187 enters the gap and vaporizes and expands in the gap, the tin debris 155 attached to the reflective film 75b may be more likely to be removed.

[0079] In the contact step SP21, it is sufficient that the tin ions and tin neutral atoms emitted from the plasma expose at least the tin debris 151, and the α-tin film 153 is formed at least on the tin debris 151. Therefore, it is not necessary that the tin ions and tin neutral atoms emitted from the plasma expose the reflective film 75b, and the α-tin film 153 is not formed on the reflective film 75b. Also, the α-tin film 153 may be formed individually on each tin debris 151. The pressure in the hydrogen-containing environment may be less than 0.1 Pa or greater than 1000 Pa.

[0080] 5. Description of the cleaning method for the extreme ultraviolet light reflective mirror of the second embodiment Next, a description will be given of a cleaning method according to embodiment 2. Note that the same components as those described above are given the same reference numerals, and duplicated descriptions will be omitted unless otherwise specified.

[0081] 5.1 How to clean the extreme ultraviolet reflective mirror 15 is a diagram showing an example of a flowchart of the cleaning method in this embodiment. The flowchart of this embodiment differs from the flowchart of embodiment 1 in that it includes a film-forming step SP31 between the start state and the contact step SP21.

[0082] (Deposition step SP31) Fig. 16 is a diagram showing the state of this step. Fig. 17 is an enlarged cross-sectional view of the EUV light reflective mirror 75 around the tin debris 151 shown in Fig. 16. In Fig. 16, for ease of viewing, only one tin debris 151 is labeled, and the labels of the other tin debris 151 are omitted. Fig. 17 shows an enlarged view of two of the tin debris 151 shown in Fig. 16.

[0083] This step is a step of forming a β-tin film 157 containing β-tin 157a on the reflective film 75b to which the tin debris 151 is attached. FIG. 16 shows an example in which the film forming device 189 sprays droplets of β-tin 157a from a nozzle hole 189a toward the tin debris 151 scattered on the reflective film 75b and the reflective film 75b, and the β-tin film 157 is formed on the tin debris 151 and the reflective film 75b. In FIG. 16, the shape of the mist-like β-tin 157a is illustrated as a circle, but the shape is not particularly limited. The thickness of the β-tin film 157 is approximately the same at any position, but the β-tin film 157 formed on the tin debris 151 may be thicker or thinner than the β-tin film 157 formed on the reflective film 75b. The particle size of the β-tin 157a is approximately 15 μm or more and 25 μm or less. Therefore, even if β-tin 157a is sprayed at a temperature above its melting point, the particle size is so small that the heat capacity of the β-tin film 157 is small, and thermal damage to the reflective film 75b caused by the β-tin film 157 at that temperature can be ignored, while the temperature rise of the tin debris 151 is suppressed. In the contact step SP21, the β-tin film 157 formed on the reflective film 75b serves as a protective film that protects the reflective film 75b from tin ions and neutral tin atoms emitted from the tin plasma. In this step, the β-tin film 157 is formed in an environment containing hydrogen or in a vacuum environment. The pressure in the hydrogen-containing environment is approximately 0.1 Pa or more and 1000 Pa or less, and the pressure in the vacuum environment is approximately 1×10 -3 Pa or less. The β-tin film 157 does not necessarily have to be formed on the tin debris 151, and may be formed on at least a part of the region of the reflective film 75b excluding the tin debris 151. The film forming apparatus 189 may form the β-tin film 157 by deposition as described above. The pressure in the hydrogen-containing environment may be less than 0.1 Pa or more than 1000 Pa. The pressure in the vacuum environment may be less than 1×10 -3 It may be larger than Pa.

[0084] Once the β-tin film 157 is formed on the tin debris 151 and the reflective film 75b, the flow proceeds to a contacting step SP21.

[0085] (Contact step SP21) FIG. 18 is an enlarged cross-sectional view of the EUV light reflection mirror 75 around the tin debris 151 in this step. In this step, the β-tin in the β-tin film 157 is made into tin pest by contacting the β-tin film 157 with α-tin, and the α-tin in the tin pest is brought into contact with the tin debris 151. In this step, similar to the contact step SP21 in the first embodiment, the α-tin film 153 is formed on the β-tin film 157 by exposure to tin ions and tin neutral atoms emitted from plasma generated in an environment containing hydrogen. In the contact step SP21 in the first embodiment, the respective energies of the tin ions and tin neutral atoms are set to approximately less than 0.5 eV so as to suppress damage and deterioration of the reflective film 75b. However, in this embodiment, a protective film for the β-tin film 157 is formed as described above. For this reason, in the contact step SP21 in this embodiment, the respective energies are set to approximately 0.5 eV or more. The collision flux of tin ions is approximately 1×10 7 (Sn ion / m 2 / 5ms) or more 1×10 10 (Sn ion / m 2 / 5 ms) or less. The plasma exposure time is approximately 5 minutes, which is shorter than the exposure time in embodiment 1. As a result, seed crystals of α-tin are generated on the surface of the β-tin film 157, and the α-tin film 153 is formed on the β-tin film 157. When the α-tin film 153 is formed on the β-tin film 157, the β-tin film 157 becomes tin pest, and the α-tin that has undergone a phase transition from the β-tin of the β-tin film 157 comes into contact with the tin debris 151. As a result, the tin debris 151 becomes tin pest. The collision flux of tin ions is 1×10 7 (Sn ion / m 2 / 5ms) or 1×10 10 (Sn ion / m 2 / 5 ms). The exposure time may be longer than 5 minutes.

[0086] (Aging step SP22 and removal step SP23) In the aging step SP22, the EUV light reflection mirror 75 including the tin debris 151, the α-tin film 153, and the β-tin film 157 is stored in a storage device as in the first embodiment. When the EUV light reflection mirror 75 is stored in the storage device, tin pesting of the tin debris 151 and the β-tin film 157 is promoted, and tin-pested tin debris 155 is generated. Although not shown, the tin debris 155 is composed of the α-tin film 153, the β-tin film 157 tin-pested by the α-tin film 153, and the tin debris 151 tin-pested by the α-tin phase-transferred from the β-tin of the β-tin film 157. The tin debris 155 is removed in the removal step SP23 as in the first embodiment. Therefore, in the removal step SP23, the tin-pested β-tin film 157 is also removed from the EUV light reflection mirror 75.

[0087] Note that part of the aging step SP22 overlaps with the contacting step SP21, and the contacting step SP21 may be performed in a sub-freezing temperature environment in the aging step SP22. When the α-tin film 153 is formed on the β-tin film 157 in the contacting step SP21, the α-tin comes into contact with the β-tin film 157 in the aging step SP22 where the contacting step SP21 overlaps, accelerating the formation of tin pest in the β-tin film 157. When the formation of tin pest in the β-tin film 157 is accelerated, in the aging step SP22, the α-tin that has undergone a phase transition from the β-tin in the β-tin film 157 comes into contact with the tin debris 151, accelerating the formation of tin pest in the tin debris 151.

[0088] 5.2 Actions and Effects The cleaning method of this embodiment further includes a film formation step SP31 for forming a β-tin film 157 containing β-tin 157a on the reflective film 75b to which the tin debris 151 is attached, prior to the contact step SP21. In this case, the β-tin film 157 can be formed more easily than when the β-tin film 157 is formed only on the tin debris 151. In addition, in the contact step SP21 of the cleaning method of this embodiment, the β-tin film 157 is brought into contact with α-tin to convert the β-tin 157a in the β-tin film 157 into tin pest, and the α-tin in the tin pest is brought into contact with the tin debris 151. In addition, in the aging step SP22, the β-tin film 157 is left in a subzero temperature environment to promote the conversion of the β-tin film 157 into tin pest, and in the removal step SP23, the tin-pested β-tin film 157 is removed from the EUV light reflection mirror 75. Therefore, the β-tin film 157 can be prevented from remaining on the EUV light reflective mirror 75, and the decrease in reflectance of the reflective film 75b due to the β-tin film 157 can be prevented. Note that the larger the surface area of ​​the β-tin film 157, the greater the area of ​​the β-tin film 157 exposed to tin ions and neutral tin atoms. If the area increases, α-tin seed crystals can be more easily generated in the β-tin film 157 in the contact step SP21.

[0089] In contact step SP21 of the cleaning method of this embodiment, the α-tin film 153 is formed on the β-tin film 157. In this case, the contact area between the α-tin and the β-tin is wider than when the α-tin is in point contact with the β-tin film 157, which may promote the formation of tin pest in the β-tin film 157.

[0090] In the cleaning method of this embodiment, the energy of each of the tin ions and tin neutral atoms emitted from the plasma is 0.5 eV or more. This can shorten the plasma exposure time in the contact step SP21 compared to when the energy is less than 0.5 eV. In addition, the reflective film 75b is protected from the tin ions and tin neutral atoms by the β-tin film 157. Therefore, compared to when the β-tin film 157 is not formed on the reflective film 75b, even if the energy is 0.5 eV or more in the contact step SP21, the β-tin film 157 can suppress the progress of the tin ions and tin neutral atoms to the reflective film 75b. This can suppress damage to the protective film caused by the tin ions and tin neutral atoms and deterioration of the reflective main body film caused by the tin ions and tin neutral atoms. The energy may be less than 0.5 eV.

[0091] 6. Description of the cleaning method for the extreme ultraviolet light reflective mirror of the third embodiment Next, a description will be given of a cleaning method according to embodiment 3. Note that the same components as those described above are given the same reference numerals, and duplicated descriptions will be omitted unless otherwise specified.

[0092] 6.1 How to clean the extreme ultraviolet reflective mirror The flowchart of the cleaning method of this embodiment is the same as that of the first embodiment, but the contacting step SP21 of this embodiment is different from the contacting step SP21 of the first embodiment.

[0093] (Contact step SP21) This step differs from the contact step SP21 of the first embodiment in which the α-tin film 153 containing α-tin is formed on the tin debris 151 in that the tin 159 containing α-tin is brought into contact with the tin debris 151. FIG. 19 is an enlarged cross-sectional view of the EUV light reflective mirror 75 around the tin debris 151 in this step. Since most of the tin 159 is α-tin, the tin 159 is in the form of sand grains. FIG. 19 shows an example in which the sand grain-shaped tin 159 comes into contact with each of the scattered tin debris 151. The particle size of the tin 159 is generally not less than 10 nm and not more than 20 nm, but is not particularly limited thereto.

[0094] The tin 159 may be pressed against the tin debris 151. The pressure for pressing is about 10 g / cm. 2 More than 10kg / cm 2 The pressure application time is about 10 seconds or less. The tin 159 may be applied with the finger of the cleaning worker or may be applied with a member including a curved surface having the same curvature as the curved surface of the EUV light reflective mirror 75. The pressure, time, and method for application of pressure are not limited to those described above.

[0095] (Aging step SP22 and removal step SP23) In the aging step SP22, the EUV light reflecting mirror 75 including the tin debris 151 and the tin 159 is stored in a storage device similar to the first embodiment. When the EUV light reflecting mirror 75 is stored in the storage device, the tin debris 151 is accelerated to become tin pested, and tin-pested tin debris 155 is generated. Although not shown in the figure, the tin debris 155 is composed of tin 159 and tin debris 151 that has been tin-pested by the tin 159. The tin debris 155 is removed in a removal step SP23 similar to the first embodiment.

[0096] 6.2 Actions and Effects In the cleaning method of this embodiment, in the contact step SP21, tin 159 containing α-tin is attached to the tin debris 151. As a result, the tin debris 151 can become tin pest without using plasma. The surface of the tin debris 151 may be covered with an oxide film. In this case, the oxide film may make it difficult for the tin 159 to come into contact with the tin debris 151 simply by contacting the oxide film. In such a case, when the tin 159 is pressed against the tin debris 151, the tin 159 penetrates the oxide film and comes into contact with the tin debris 151. Therefore, when the tin 159 is pressed against the tin debris 151, the tin 159 can come into contact with the tin debris 151 more easily than when the tin 159 is not pressed against the tin debris 151, and the tin pest can be promoted. The pressure may be applied to the β-tin film 157 in the contact step SP21 of the second embodiment. In addition, part of the aging step SP22 in this embodiment may overlap with the contact step SP21, and the contact step SP21 may be performed in an environment of below freezing temperature in the aging step SP22.

[0097] The above description is intended to be illustrative rather than restrictive. Thus, it will be apparent to one skilled in the art that modifications may be made to the disclosed embodiments without departing from the scope of the claims. It will also be apparent to one skilled in the art that the disclosed embodiments may be used in combination. Terms used throughout this specification and claims should be interpreted as "open ended" terms unless otherwise specified. For example, the terms "include" or "included" should be interpreted as "not limited to what is described as including." The term "having" should be interpreted as "not limited to what is described as having." The indefinite article "a" should be interpreted as "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." It should also be interpreted as including combinations of these with other than "A," "B," and "C."

Claims

1. A contacting step of contacting α-tin with solid tin debris adhering to the extreme ultraviolet light reflective mirror; an aging step in which the tin debris in contact with the α-tin is left in a subzero temperature environment to promote the conversion of the tin debris into tin pest; a removing step of removing the tin-plastered tin debris from the extreme ultraviolet light reflective mirror; Equipped with In the contact step, an α-tin film containing the α-tin is formed on the tin debris by tin ions and tin neutral atoms emitted from tin plasma generated in an environment containing hydrogen. How to clean extreme ultraviolet reflective mirrors.

2. 2. A method for cleaning the extreme ultraviolet light reflecting mirror according to claim 1, comprising the steps of: The thickness of the α-tin film is 20 μm or more and 1 mm or less.

3. 2. A method for cleaning the extreme ultraviolet light reflecting mirror according to claim 1, comprising the steps of: The pressure in the hydrogen-containing environment is 0.1 Pa or more and 1000 Pa or less.

4. 2. A method for cleaning the extreme ultraviolet light reflecting mirror according to claim 1, comprising the steps of: The α-tin film is formed on the tin debris by the tin ions and neutral tin atoms emitted from the plasma generated by irradiating droplets or solid tin with laser light.

5. 2. A method for cleaning the extreme ultraviolet light reflecting mirror according to claim 1, comprising the steps of: The energy of each of the tin ions and the tin neutral atoms is less than 0.5 eV.

6. 2. A method for cleaning the extreme ultraviolet light reflecting mirror according to claim 1, comprising the steps of: In the aging step, the temperature of the air environment is −50° C. or higher and −20° C. or lower.

7. 2. A method for cleaning the extreme ultraviolet light reflecting mirror according to claim 1, comprising the steps of: The proportion of moisture in the environment in which each of the aging step and the removing step is performed is 0.1 wt % or less.

8. 2. A method for cleaning the extreme ultraviolet light reflecting mirror according to claim 1, comprising the steps of: In the removing step, the tin-pestoized tin debris is removed by a jet.

9. 9. A method for cleaning an extreme ultraviolet light reflecting mirror according to claim 8, comprising the steps of: In the removing step, dry ice pellets are sprayed onto the tin-pesticated tin debris.

10. 9. A method for cleaning an extreme ultraviolet light reflecting mirror according to claim 8, comprising the steps of: In the removing step, snow-like dry ice is sprayed onto the tin-pesticated tin debris.

11. A film forming step of forming a β-tin film containing β-tin on an extreme ultraviolet light reflective mirror having solid tin debris attached thereto; a contacting step of bringing α-tin into contact with the β-tin film to convert the β-tin in the β-tin film into tin pest and bringing the α-tin in the tin pest into contact with the tin debris; an aging step in which the tin debris in contact with the α-tin is left in a subzero temperature environment to promote the conversion of the tin debris into tin pest; a removing step of removing the tin-plastered tin debris from the extreme ultraviolet light reflective mirror; Equipped with In the aging step, the β-tin film is left in the temperature environment to promote the conversion of the β-tin film into tin pest, In the removing step, the tin-pested β-tin film is removed from the extreme ultraviolet light reflective mirror. How to clean extreme ultraviolet reflective mirrors.

12. 12. A method for cleaning an extreme ultraviolet light reflecting mirror according to claim 11, comprising the steps of: In the contacting step, an α-tin film containing the α-tin is formed on the β-tin film.

13. 13. A method for cleaning an extreme ultraviolet light reflecting mirror according to claim 12, comprising the steps of: In the contacting step, the α-tin film is formed on the β-tin film by tin ions and neutral tin atoms emitted from tin plasma generated in an environment containing hydrogen.

14. 14. A method for cleaning an extreme ultraviolet light reflecting mirror according to claim 13, comprising the steps of: The energy of each of the tin ions and the tin neutral atoms is 0.5 eV or more.

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