Light source apparatus and cleaning method

Abstract

Provided are: a light source apparatus capable of suppressing a change in pressure on a light source side due to a change in pressure on an introduction side of radiation light; and a cleaning method.　A light source apparatus according to one embodiment of the present invention is provided with a first vacuum chamber, a light source unit, and a debris reduction device. The light source unit generates plasma which serves as a light source in the first vacuum chamber. The debris reduction device reduces debris dissipated from the plasma. The debris reduction device forms a vacuum path that allows radiation light emitted from the plasma to pass therethrough, and that connects the first vacuum chamber and a second vacuum chamber into which the radiation light is introduced, and generates a high-pressure region whose pressure is higher than the pressure of the first vacuum chamber and the pressure of the second vacuum chamber so as to block the vacuum path.

Description

Light source device and cleaning method

[0001] The present invention relates to a light source device that uses plasma as a light source and a cleaning method.

[0002] Conventionally, light source devices that generate synchrotron radiation using plasma as a light source have been developed. For example, synchrotron radiation in the X-ray region can be obtained by appropriately selecting the type of plasma raw material and the excitation energy for generating the plasma. Among such synchrotron radiation, for example, X-rays with short wavelengths are used for various applications such as X-ray photography, non-destructive testing, X-ray analysis, and X-ray spectroscopy. In recent years, extreme ultraviolet light (hereinafter also referred to as "EUV (Extreme Ultra Violet) light") with a wavelength of 13.5 nm in the soft X-ray region has been used as exposure light or inspection light.

[0003] Generally, EUV light source devices include a DPP (Discharge Produced Plasma) light source device, an LDP (Laser Assisted Discharge Produced Plasma) light source device, and an LPP (Laser Produced Plasma) light source device.

[0004] A DPP light source device applies a high voltage between electrodes to which a gaseous plasma raw material (discharge gas) containing EUV radiation species is supplied, generating a high-density, high-temperature plasma through discharge, and utilizes the extreme ultraviolet light emitted from the plasma.

[0005] An LDP light source device is an improved version of a DPP light source device, and for example, it supplies a liquid high-temperature plasma raw material (e.g., Sn (tin) or Li (lithium)) containing EUV radiating species to the surface of an electrode (discharge electrode) that generates a discharge, irradiates the raw material with an energy beam (e.g., an electron beam or a laser beam) to vaporize the raw material, and then generates high-temperature plasma by discharge.

[0006] An LPP light source device generates high-temperature plasma by exciting an EUV radiating species with a laser beam or the like. A known example of this type of light source device is one that generates plasma by focusing laser light on EUV radiating target material, such as tin (Sn) or lithium (Li) ejected in the form of tiny droplets. Another known LPP light source device generates plasma by supplying a liquid high-temperature plasma raw material containing EUV radiating species to the surface of a rotating body and irradiating the surface of the rotating body with an energy beam (laser beam).

[0007] Furthermore, debris is dispersed at high speed from the plasma generated by these light source devices. This debris includes particles of high-temperature plasma raw materials and particles of discharge electrode material sputtered during plasma generation. If such debris reaches a utilization device that utilizes radiation such as EUV light, it may damage or contaminate optical elements such as reflective films provided within the utilization device. For this reason, light source devices are provided with a debris mitigation tool (DMT) that captures debris between the plasma and the utilization device to prevent debris dispersed from the plasma from entering the utilization device.

[0008] Thus, in a light source device that generates radiation using plasma as a light source, it is important to maintain the pressure in the space on the light source side where the plasma is generated. For example, Patent Document 1 describes a DPP-type light source device that maintains the pressure on the light source side using an aperture member. In this light source device, an aperture member is provided between a discharge space where plasma is generated by discharge and a collector space where an EUV light collector is provided. Furthermore, a gas curtain is formed downstream of the aperture member to reduce debris from the plasma. This configuration maintains a pressure difference between the collector space and the discharge space, making it possible to efficiently reduce debris (see, for example, paragraphs

[0027] and

[0033] , Figure 1, etc., of the specification of Patent Document 1).

[0009] Incidentally, there are cases where the pressure in the space on the introduction side into which the synchrotron radiation is introduced needs to be changed. For example, Patent Document 2 describes a method for cleaning optical elements irradiated with light in an irradiation device that irradiates extreme ultraviolet rays or the like. In this method, a reaction partner containing hydrogen or halogen is supplied to the vicinity of the optical element while the irradiation device is in operation, and debris and the like adhering to the optical element are cleaned using the reaction partner that has been converted into a radical by the light (see, for example, FIG. 1 in paragraphs

[0114] -

[0116] of the specification of Patent Document 1). In this method, it is conceivable that the pressure in the space in which the optical element is located will change when the reaction partner is supplied or when the supply is stopped. In addition, there may be cases where the pressure on the introduction side of the synchrotron radiation needs to be changed in response to maintenance of the device, changes in conditions, or the like.

[0010] JP 2007-179881 A JP 2006-529057 A

[0011] Thus, when the pressure on the introduction side where the synchrotron radiation is introduced is changed, there is a possibility that the pressure on the light source side will change accordingly. In this case, the plasma generation conditions on the light source side may be disrupted, and the emission of synchrotron radiation may become unstable. Therefore, there is a need for a technology that suppresses the change in pressure on the light source side due to the change in pressure on the introduction side of the synchrotron radiation.

[0012] In view of the above circumstances, an object of the present invention is to provide a light source device and a cleaning method that can suppress changes in pressure on the light source side due to changes in pressure on the radiation light entrance side.

[0013] To achieve the above object, a light source device according to one aspect of the present invention includes a first vacuum chamber, a light source unit, and a debris mitigation device. The light source unit generates plasma that serves as a light source within the first vacuum chamber. The debris mitigation device reduces debris emitted from the plasma, connects the first vacuum chamber and a second vacuum chamber into which radiation light emitted from the plasma is introduced, forms a vacuum path through which the radiation light passes, and generates a high-pressure region whose pressure is higher than that of the first vacuum chamber and the second vacuum chamber so as to interrupt the vacuum path.

[0014] In this light source device, the debris mitigation device forms a vacuum path connecting a first vacuum chamber that generates plasma and a second vacuum chamber into which radiated light from the plasma is introduced. Furthermore, a high-pressure region with a pressure higher than that of the first vacuum chamber and the second vacuum chamber is formed so as to interrupt the vacuum path. This allows pressure changes in, for example, the second vacuum chamber to be absorbed by the high-pressure region. This makes it possible to suppress changes in pressure on the light source side due to changes in pressure on the radiated light introduction side.

[0015] The debris mitigation device may include a conductance reducer that reduces the conductance of the vacuum path between the high-pressure region and the second vacuum chamber, thereby making it possible to maintain the high-pressure region without being affected by the pressure of the second vacuum chamber, for example, and to sufficiently absorb changes in pressure on the introduction side.

[0016] The conductance reduction unit may be a fixed foil trap having a plurality of foils arranged in the vacuum path and a fixing member that fixes the plurality of foils, thereby making it possible to reduce debris by the fixed foil trap.

[0017] The debris mitigation device may include a cylindrical member disposed between the high-pressure region and the first vacuum chamber and having a cross section intersecting the path direction of the vacuum path larger than that of the high-pressure region, thereby enabling, for example, the pressure in the high-pressure region to be reduced over a short distance and maintained at the pressure of the first vacuum chamber.

[0018] The debris mitigation device may include a rotary foil trap having a plurality of foils and a rotary member that radially supports the plurality of foils. In this case, the cylindrical member may be a rotary foil trap cover that surrounds the rotary foil trap. This makes it possible to reduce debris using the rotary foil trap.

[0019] The debris mitigation apparatus may be configured to keep the pressure of the first vacuum chamber substantially constant when the pressure of the second vacuum chamber changes at least within a range equal to or less than the pressure of the high-pressure region, thereby enabling the pressure of the first vacuum chamber to be sufficiently maintained even when the pressure of the second vacuum chamber changes.

[0020] The pressure in the high-pressure region may be six times or more the pressure in the first vacuum chamber, which makes it possible to reliably absorb pressure changes on the introduction side, for example.

[0021] The light source device may further include an inlet for introducing a buffer gas that changes the pressure in the second vacuum chamber, and a pressure adjustment mechanism that adjusts the pressure in the second vacuum chamber, which makes it possible to easily adjust the pressure in the second vacuum chamber, for example, and realize various operation modes.

[0022] The high-pressure region may be a region into which the buffer gas is introduced. In this case, the inlet may include a first inlet connected to the high-pressure region. This makes it possible to change the pressure of the second vacuum chamber while realizing the high-pressure region, for example.

[0023] The light source device may further include the second vacuum chamber. In this case, the inlet may include a second inlet provided in the second vacuum chamber. This makes it possible to easily change the pressure in the second vacuum chamber, for example.

[0024] The buffer gas may be an ionized gas that is ionized by the synchrotron radiation. In this case, the light source device may be capable of both a normal operation and a cleaning operation using the ionized gas. This makes it possible to clean optical elements and the like provided in the second vacuum chamber while stably generating synchrotron radiation, for example.

[0025] The cleaning operation may include introducing the ionized gas into a second vacuum chamber maintained at a first pressure that is the pressure during normal operation, increasing the pressure of the second vacuum chamber to a second pressure higher than the first pressure, and sputtering a target placed in the second vacuum chamber with the ionized gas ionized by the synchrotron radiation while maintaining the second pressure. This makes it possible to sputter, for example, an optical element or the like provided in the second vacuum chamber at a desired rate.

[0026] The second pressure may be equal to or greater than 6 Pa. This makes it possible to perform sputtering at a desired rate, for example.

[0027] The pressure of the first vacuum chamber during normal operation may be set to a third pressure at which the radiation is stable. In this case, the second pressure may be three times or more the third pressure. This allows sputtering at a relatively high rate, for example.

[0028] The ionized gas may be a rare gas, which can prevent components in each chamber from being corroded by the ionized gas and can easily treat the gas exhausted from each chamber.

[0029] The light source device may further include the second vacuum chamber and a light intensity monitor provided in the second vacuum chamber and configured to detect the intensity of the emitted light. In this case, the normal operation and the cleaning operation may be switched based on the detection result of the light intensity monitor. This allows cleaning to be performed in response to contamination of an optical element, for example.

[0030] The pressure adjustment mechanism may be at least one of a flow rate adjustment valve that adjusts the flow rate of the buffer gas introduced from the inlet and an exhaust rate adjustment valve that adjusts the exhaust rate of the second vacuum chamber, thereby enabling, for example, accurate adjustment of the pressure in the second vacuum chamber.

[0031] The radiation may be EUV light, which makes it possible to realize an EUV light source device that is easy to maintain and has a stable light output.

[0032] The light source unit may include a pair of rotating electrodes arranged within the first vacuum chamber on either side of a discharge region, a raw material supply unit that supplies plasma raw material to the pair of rotating electrodes, an energy beam injection unit that injects an energy beam that vaporizes the plasma raw material onto a portion of one of the pair of rotating electrodes that faces the discharge region, and a voltage source that applies a voltage to the pair of rotating electrodes to plasmaize the plasma raw material vaporized by the energy beam.

[0033] The light source unit may include a rotating body arranged in the first vacuum chamber, a raw material supply unit that supplies plasma raw material to the rotating body, and an energy beam incident unit that incidents an energy beam that converts the plasma raw material supplied to the rotating body into plasma.

[0034] A cleaning method according to one aspect of the present invention is a cleaning method performed using the light source device, and includes the following steps: a pressure increasing step of introducing an ionized gas that is ionized by the synchrotron radiation into a second vacuum chamber maintained at a first pressure that is a pressure during normal operation while the plasma is generated, and increasing the pressure of the second vacuum chamber to a second pressure that is higher than the first pressure; and a sputtering step of sputtering a target placed in the second vacuum chamber with the ionized gas ionized by the synchrotron radiation while maintaining the second pressure.

[0035] This makes it possible to suppress changes in pressure on the light source side due to changes in pressure on the input side of the synchrotron radiation, and enables stable generation of synchrotron radiation even when sputtering is performed by introducing an ionized gas, thereby making it possible to easily clean optical elements and the like provided in the second vacuum chamber.

[0036] The light source device may further include the second vacuum chamber and a light intensity monitor provided in the second vacuum chamber for detecting the intensity of the emitted light. In this case, the pressure increasing step and the sputtering step may be executed when the light intensity detected by the light intensity monitor falls below a first threshold. Furthermore, the light source device may include a pressure decreasing step of decreasing the pressure of the second vacuum chamber to the first pressure when the light intensity detected by the light intensity monitor exceeds a second threshold that is equal to or greater than the first threshold. This makes it possible to perform cleaning in response to contamination of optical elements, for example.

[0037] The sputtering step may include a step of changing the intensity of the synchrotron radiation from the intensity of the synchrotron radiation during the normal operation while maintaining the second pressure, thereby enabling precise control of, for example, the sputtering rate.

[0038] As described above, according to the present invention, a change in pressure on the light source side due to a change in pressure on the radiation light introduction side can be suppressed. Note that the effects described here are not necessarily limited to those described herein, and may be any of the effects described in this disclosure.

[0039] FIG. 1 is a schematic diagram showing an example of the configuration of a light source device according to an embodiment of the present invention. FIG. 1 is a schematic diagram showing an example of the configuration of a debris mitigation device mounted on a light source device. FIG. 2 is a schematic cross-sectional view showing an example of the configuration of a rotary foil trap. FIG. 3 is a schematic front view showing an example of the configuration of a rotary foil trap cover. FIG. 4 is a schematic cross-sectional view showing an example of the configuration of a fixed foil trap. FIG. 5 is a schematic front view showing an example of the configuration of a fixed foil trap cover. FIG. 6 is a schematic cross-sectional view showing an example of the configuration of a fixed foil trap cover. FIG. 7 is a schematic cross-sectional view showing an example of the configuration of a debris mitigation device. FIG. 8 is a graph showing simulation results of the pressure in the light source device. FIG. 9 is a graph showing the relationship between the pressures of the first vacuum chamber and the second vacuum chamber. FIG. 10 is a schematic diagram showing an example of the arrangement of samples used in sputtering experiments. FIG. 11 is a graph showing the relationship between the sputtering rate and pressure. FIG. 12 is a graph showing the relationship between the sputtering rate, pressure, and sample position. FIG. 13 is a graph showing the relationship between the sputtering rate and the plasma emission frequency. Fig. 1 is a flowchart showing an example of the operation of a light source device; Fig. 2 is a schematic diagram illustrating a sputtering region where sputtering occurs; Fig. 3 is a schematic diagram showing an example of the configuration of an optical system using a light-shielding plate; Fig. 4 is a schematic diagram showing another example of the configuration of an optical system using a light-shielding plate; Fig. 5 is a schematic diagram showing an example of the configuration of an LPP-type light source section; Fig. 6 is a schematic diagram showing another example of the configuration of an LPP-type light source section.

[0040] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0041] [Outline of Light Source Device] Fig. 1 is a schematic diagram showing an example of the configuration of a light source device according to an embodiment of the present invention. Fig. 1 is a diagram showing a schematic cross section of the light source device 100 cut horizontally at a predetermined height from the installation surface, as viewed from the positive Z direction. In the following description, the X direction is the left-right direction (the positive side of the X axis is the right side, and the negative side is the left side), the Y direction is the depth direction (the positive side of the Y axis is the front side, and the negative side is the back side), and the Z direction is the up-down direction (the positive side of the Z axis is the top side, and the negative side is the bottom side). Of course, the application of the present technology is not limited to the orientation in which the light source device 100 is used.

[0042] The light source device 100 is an LDP type EUV light source device, and emits extreme ultraviolet light (EUV light 1). The wavelength of the EUV light 1 is, for example, 13.5 nm.

[0043] Light source device 100 can be used, for example, as a light source device for a lithography apparatus in semiconductor device manufacturing, or as a light source device for an inspection apparatus for a mask used in lithography. For example, when light source device 100 is used as a light source device for a mask inspection apparatus, a portion of EUV light 1 emitted from plasma P is extracted and guided to a mask inspection apparatus. Then, the mask inspection apparatus performs mask blank inspection or pattern inspection using the EUV light 1 emitted from light source device 100 as inspection light.

[0044] In this embodiment, EUV light 1 is an example of radiation emitted from plasma. However, the type of radiation is not limited. The present invention is also applicable to cases where light in the soft X-ray region other than EUV light 1 or hard X-rays with higher energy is emitted.

[0045] The light source device 100 has a first vacuum chamber 10, a second vacuum chamber 20, a light source unit 30, and a debris mitigation device 40. The first vacuum chamber 10 is a vacuum chamber in which the light source unit 30 generates plasma P. The second vacuum chamber 20 is a vacuum chamber into which EUV light 1 emitted from the plasma P is introduced. The debris mitigation device 40 is a device that reduces debris dispersed from the plasma P between the first vacuum chamber 10 and the second vacuum chamber 20.

[0046] [First Vacuum Chamber] The first vacuum chamber 10 is a housing that houses various mechanisms of the light source unit 30. The first vacuum chamber 10 has, for example, a rectangular parallelepiped or cylindrical shape and is made of a rigid body such as metal. Of course, the specific shape, material, etc. of the first vacuum chamber 10 are not limited.

[0047] The interior of the first vacuum chamber 10 is maintained at a reduced pressure below a predetermined pressure by a vacuum pump (not shown). Feedthroughs FA and FB are arranged on the left side wall 10a of the first vacuum chamber 10. The feedthroughs FA and FB are sealing members that allow electrical wires and the like to be inserted into the first vacuum chamber 10 while maintaining the reduced pressure atmosphere inside the first vacuum chamber 10.

[0048] A transparent window 11 is disposed in the front side wall 10b of the first vacuum chamber 10. The transparent window 11 is made of a material that is transparent to the laser beam LB, which will be described later. Specific configurations such as the material and shape of the transparent window 11 are not limited. A through-hole 12 for connecting the first vacuum chamber 10 to the second vacuum chamber 20 is provided in the right side wall 10c. In this embodiment, a debris mitigation device 40 is disposed inside the first vacuum chamber 10 so as to cover the through-hole 12.

[0049] [Second Vacuum Chamber] The second vacuum chamber 20 is a housing that houses, for example, an optical element 21 onto which the EUV light 1 is incident. The optical element 21 is, for example, a collector mirror for collecting the EUV light 1, or a reflecting mirror for bending the optical path of the EUV light 1. Furthermore, for example, the second vacuum chamber 20 may be configured as a container that connects a utilization device that utilizes the EUV light 1 (such as a mask inspection device or a lithography device) to a light source device. The second vacuum chamber 20 has, for example, a rectangular parallelepiped or cylindrical shape and is made of a rigid body such as metal. Of course, the specific shape, material, etc. of the second vacuum chamber 20 are not limited.

[0050] The interior of the second vacuum chamber 20 is maintained at a reduced pressure of not more than a predetermined pressure by a vacuum pump (not shown). A through-hole 22 communicating with the through-hole 12 of the first vacuum chamber 10 is arranged in the left side wall 20a of the second vacuum chamber 20. Furthermore, for example, an exit port (not shown) for emitting the EUV light 1 that has passed through the optical element 21 is appropriately provided in the second vacuum chamber 20.

[0051] It should be noted that the light source device 100 does not necessarily need to include the second vacuum chamber 20. For example, the second vacuum chamber 20 may be provided on the utilization device side. In this case, a vacuum chamber or the like provided in the utilization device for introducing the EUV light 1 is used as the second vacuum chamber.

[0052] [Light Source Unit] The light source unit 30 generates plasma P, which serves as a light source, within the first vacuum chamber 10. The light source unit 30 has a discharge module 31, a control unit 32, a pulsed power supply unit 33, a laser source 34, a condenser lens 35, and a movable mirror 36. Of these, the control unit 32, the pulsed power supply unit 33, the laser source 34, the condenser lens 35, and the movable mirror 36 are provided outside the first vacuum chamber 10.

[0053] The discharge module 31 is a module that performs discharge to generate plasma P in the first vacuum chamber 10. The discharge module 31 has containers CA and CB, discharge electrodes EA and EB, and motors MA and MB. Of these, the containers CA and CB and the discharge electrodes EA and EB are disposed inside the first vacuum chamber 10.

[0054] Containers CA and CB are vessels for storing plasma raw materials. In this embodiment, containers CA and CB are made of a conductive material. Plasma raw material SA is stored in container CA. Plasma raw material SB is stored in container CB. Plasma raw materials SA and SB are heated liquid phase raw materials. In this embodiment, tin (Sn) is used as plasma raw materials SA and SB. Alternatively, other raw materials capable of generating plasma, such as lithium (Li), may be used.

[0055] The discharge electrodes EA and EB have a disk shape and are made of a high-melting-point metal such as molybdenum (Mo), tungsten (W), or tantalum (Ta). The specific material of the discharge electrodes EA and EB is not limited.

[0056] For example, the discharge electrode EA is used as a cathode, and the discharge electrode EB is used as an anode. The discharge electrodes EA and EB are arranged to be spaced apart from each other. The discharge electrodes EA and EB are also arranged so that parts of the peripheral edges of the discharge electrodes EA and EB are close to each other. The gap at the position where the peripheral edges of the discharge electrodes EA and EB are closest to each other forms a discharge region D formed by the discharge electrodes EA and EB.

[0057] The discharge electrode EA is positioned so that its lower portion is immersed in the plasma raw material SA stored in the container CA. Similarly, the discharge electrode EB is positioned so that its lower portion is immersed in the plasma raw material SB.

[0058] The motor MA rotates the discharge electrode EA. The motor MA has a rotation axis JA. A base portion of the motor MA is disposed outside the left side of the first vacuum chamber 10, and the rotation axis JA connected to the base portion extends from the outside to the inside of the first vacuum chamber 10. The end of the rotation axis JA on the inside side of the first vacuum chamber 10 is connected to the center (center of the circular surface) of the discharge electrode EA.

[0059] The gap between the rotating shaft JA and the wall of the first vacuum chamber 10 is sealed with a sealing member PA. For example, a mechanical seal is used as the sealing member PA. The sealing member PA rotatably supports the rotating shaft JA while maintaining the reduced pressure atmosphere inside the first vacuum chamber 10.

[0060] Similarly, the motor MB has a rotation shaft JB, which is connected to the center of the discharge electrode EB. The gap between the rotation shaft JB and the wall of the first vacuum chamber 10 is sealed with a seal member PB.

[0061] The discharge electrodes EA and EB are arranged so that their axes (extension directions of the rotation axes) are not parallel. Specifically, as shown in FIG. 1 , the discharge electrode EA is arranged with its front side (lower side in FIG. 1 ) tilted to the right and its rear side (upper side in FIG. 1 ) tilted to the left. On the other hand, the discharge electrode EB is arranged with its front side tilted to the left and its rear side tilted to the right. The distance between the rotation axes JA and JB in the depth direction (the vertical direction, Z direction in FIG. 1 ) is also narrower on the side of the motors MA and MB and wider on the side of the discharge electrodes EA and EB. Furthermore, the discharge electrode EB, motor MB, and rotation axis JB are arranged slightly to the left of the discharge electrode EA, motor MA, and rotation axis JA.

[0062] The control unit 32 controls the operation of each unit of the light source unit 30. For example, the control unit 32 controls the rotational driving of the motors MA and MB, causing the discharge electrodes EA and EB to rotate at a predetermined rotation speed. The control unit 32 also controls the operation of the pulsed power supply unit 33 and the timing of laser beam irradiation by the laser source 34.

[0063] The control unit 32 is realized by a controller having hardware necessary for configuring a computer, such as a processor such as a CPU, GPU, or DSP, memory such as a ROM or RAM, a storage device such as an HDD, etc. Specifically, the control unit 32 is realized as a functional block by the CPU of the controller executing a program related to the present technology (for example, an application program).

[0064] The pulsed power supply unit 33 supplies pulsed power to the discharge electrodes EA and EB, thereby generating a discharge in the discharge region D. Power feeders QA and QB are connected to the pulsed power supply unit 33. The power feeder QA is inserted into the first vacuum chamber 10 via a feedthrough FA and connected to a container CA. The power feeder QB is inserted into the first vacuum chamber 10 via a feedthrough FB and connected to a container CB.

[0065] The laser source 34 emits an energy beam that vaporizes the plasma raw materials SA and SB. The laser source 34 is disposed outside the first vacuum chamber 10. The laser source 34 may be, for example, a Nd:YVO ４A neodymium-doped yttrium orthovanadate (Neodymium-doped Yttrium Orthovanadate) laser device is used. In this case, a laser beam LB in the infrared region with a wavelength of 1064 nm is emitted from the laser source 34. Of course, as long as it is possible to vaporize the plasma raw materials SA and SB, the specific configuration of the laser source 34, such as the type of device and the wavelength of the irradiated laser beam LB, is not limited.

[0066] The condenser lens 35 is disposed on the optical path of the laser beam LB outside the first vacuum chamber 10. The laser beam LB emitted by the laser source 34 is incident on the condenser lens 35, whereby the spot diameter of the laser beam LB is adjusted.

[0067] The movable mirror 36 is disposed on the optical path of the laser beam LB outside the first vacuum chamber 10. Here, the movable mirror 36 is disposed on the optical path of the laser beam LB, behind the condenser lens 35. Therefore, the laser beam LB that has passed through the condenser lens 35 is incident on the movable mirror.

[0068] The laser beam LB incident on the movable mirror 36 is reflected by the movable mirror 36 and passes through the transparent window 11 of the first vacuum chamber 10. The laser beam LB then reaches the peripheral edge of the discharge electrode EA near the discharge region D inside the first vacuum chamber 10. Note that by changing the attitude of the movable mirror 36, it is possible to adjust the irradiation position of the laser beam LB on the discharge electrode EA.

[0069] As described above, in the light source unit 30, discharge electrodes EA and EB are arranged in the first vacuum chamber 10 on either side of the discharge region D. Plasma raw materials SA and SB are supplied to the discharge electrodes EA and EB from containers CA and CB, respectively. In this embodiment, the discharge electrodes EA and EB correspond to a pair of rotating electrodes, and the containers CA and CB correspond to a raw material supply unit.

[0070] Furthermore, a laser beam LB is incident on a portion of one of the discharge electrodes EA and EB, that faces the discharge region D, by means of a laser source 34, a condenser lens 35, and a movable mirror 36. As a result, the liquid-phase plasma raw material SA transported to the vicinity of the discharge region D as the discharge electrode EA rotates becomes a gas-phase plasma raw material SA. Similarly, the plasma raw material SB transported by the discharge electrode EB also becomes a gas-phase plasma raw material SB in the discharge region D. In this embodiment, an energy beam incident portion is realized using the laser source 34, the condenser lens 35, and the movable mirror 36. Furthermore, the laser beam LB corresponds to an energy beam that vaporizes the plasma raw material.

[0071] Furthermore, a voltage (pulsed power) is applied to the discharge electrodes EA and EB by the pulsed power supply 33 to convert the plasma raw material vaporized by the laser beam LB into plasma. This generates a discharge in the discharge region D between the discharge electrodes EA and EB. This discharge heats and excites the gaseous plasma raw materials SA and SB present in the discharge region D with a current, generating a plasma P. In this embodiment, the pulsed power supply 33 corresponds to a voltage source.

[0072] EUV light 1 is emitted from the plasma P generated in the discharge region D. A portion of the emitted EUV light 1 (light directed to the right) passes through a debris mitigation device 40, which will be described later, and is introduced into the second vacuum chamber 20. In Figure 1, an example of the optical path of the EUV light 1 is shown by a dashed arrow. The plasma P corresponds to an embodiment of a light source according to the present technology.

[0073] In this embodiment, the interior of the first vacuum chamber 10 is maintained at a reduced pressure of less than a predetermined pressure. This makes it possible to effectively generate a discharge for heating and exciting the plasma raw materials SA and SB. It also makes it possible to suppress attenuation of the EUV light 1.

[0074] Furthermore, debris is dispersed from the plasma P at high speed in various directions together with the EUV light 1. The debris includes tin particles, which are the plasma raw materials SA and SB. The debris also includes material particles of the discharge electrodes EA and EB that are sputtered as the plasma P is generated. Specifically, the debris includes ions, neutral atoms, and electrons that move at high speed. This debris gains a large amount of kinetic energy as the plasma P undergoes contraction and expansion processes. Some of the debris is dispersed toward the debris mitigation device 40.

[0075] [Debris mitigation device] Figure 2 is a schematic diagram showing an example configuration of the debris mitigation device 40 mounted on the light source device 100. Figure 2 shows a cross section of the light source device 100 cut along the XZ plane, viewed from the front side. Note that Figure 2 omits the configuration of the light source unit 30 other than the discharge module 31. The configuration of the discharge module 31 is also omitted from the illustration.

[0076] The debris mitigation device 40 is a device that reduces debris emitted from the plasma P. The debris mitigation device 40 is arranged so as to overlap with the optical path of the EUV light 1 that travels from the plasma P generated in the first vacuum chamber 10 toward the second vacuum chamber 20. The debris mitigation device 40 also includes a mechanism for capturing debris on the optical path of the EUV light. In other words, the debris mitigation device 40 is configured to allow the EUV light 1 from the plasma P to pass through while capturing debris from the plasma P. The debris mitigation device 40 is also sometimes called a DMT (Debris Mitigation Tool).

[0077] In this embodiment, foil traps (a rotating foil trap 43 and a fixed foil trap 45, which will be described later) are used as mechanisms for capturing debris. A foil trap is a debris trap that uses multiple foils to capture debris from the plasma P. In a foil trap, multiple foils are arranged at a distance from each other. This allows the EUV light 1 to pass through between the foils. By using a foil trap, it is possible to capture debris ranging from large debris of, for example, mm size to small debris of atomic size.

[0078] Furthermore, the debris mitigation system 40 forms a vacuum path 13 that connects the first vacuum chamber 10 and the second vacuum chamber 20 and allows the EUV light 1 to pass through. Here, the vacuum path 13 refers to a structure that connects, for example, two independent vacuum chambers without leaks to form an exhaust path. For example, when only one of two vacuum chambers connected by the vacuum path 13 is evacuated, the other vacuum chamber will always be evacuated via the vacuum path 13 (exhaust path).

[0079] Such a vacuum path 13 is formed inside the debris mitigation device 40. The internal spaces of the first vacuum chamber 10 and the second vacuum chamber 20 are connected by this vacuum path 13 without leaking. The vacuum path 13 also functions as a passage for passing the EUV light 1. For this reason, the vacuum path 13 includes at least a straight path that allows the EUV light 1 to pass through without being blocked. Here, the direction of the straight path through which the EUV light 1 passes is referred to as the path direction of the vacuum path 13. In Figure 2, the path direction of the vacuum path 13 is schematically illustrated using a dotted arrow.

[0080] Furthermore, the debris mitigation device 40 generates a high-pressure region 14 where the pressure is higher than the pressure in the first vacuum chamber 10 and the pressure in the second vacuum chamber 20 so as to block the vacuum path 13. Here, a region that blocks the vacuum path 13 means, for example, a region that completely covers the cross section of the vacuum path 13, intersecting the path direction of the vacuum path 13. Therefore, in order to pass through the vacuum path 13, it is necessary to pass through the high-pressure region 14. The debris mitigation device 40 is configured to be able to generate such a high-pressure region 14 midway through the vacuum path 13. In Figure 2, the part that becomes the high-pressure region 14 is schematically illustrated by a hatched area using dots.

[0081] As described above, the high-pressure region 14 is a region in which the internal pressure can be maintained higher than the pressure in either the first vacuum chamber 10 or the second vacuum chamber 20. That is, in the high-pressure region 14, the pressure (density) of the buffer gas 2 (ambient gas) can be made higher than the pressure in each vacuum chamber. The debris mitigation device 40 is basically used in a state in which the high-pressure region 14 has been generated.

[0082] For example, suppose the pressure in one of the vacuum chambers changes. In this case, the presence of the high-pressure region 14 absorbs the pressure change. This makes it difficult for the pressure change in one vacuum chamber to be transmitted to the other vacuum chamber. In other words, the high-pressure region 14 can be said to be a region that separates the pressure in the first vacuum chamber 10 from the pressure in the second vacuum chamber 20.

[0083] As a configuration for forming the high pressure region 14, the debris mitigation device 40 is provided with a cylindrical member 41 and a conductance reduction section 42.

[0084] The cylindrical member 41 is a cylindrical member that surrounds the space that becomes the vacuum path 13, and is provided between the high pressure region 14 and the first vacuum chamber 10. The cylindrical member 41 has an opening (an exit side opening KO of the rotary foil trap cover 44) that is connected to the high pressure region 14, and an opening (an entrance side opening KI of the rotary foil trap cover 44) that is connected to the first vacuum chamber 10, and forms the vacuum path 13.

[0085] The cylindrical member 41 has a cross section larger than that of the high-pressure region 14, intersecting the path direction of the vacuum path 13. In other words, the cylindrical member 41 serves to expand the diameter of the vacuum path 13 formed by the high-pressure region 14 on the first vacuum chamber 10 side. With this configuration, the buffer gas 2 flowing from the high-pressure region 14 toward the cylindrical member 41 is caught in a rotary foil trap 43 (described later) and diffuses into a wide space, where it is exhausted by a vacuum pump (first vacuum pump 54) that exhausts the first vacuum chamber 10. This allows the pressure of the high-pressure region 14 to be reduced over a short distance. That is, the pressure of the vacuum path 13 drops rapidly while passing through the cylindrical member 41. This allows the pressure of the first vacuum chamber 10 to be maintained with almost no influence from the pressure of the high-pressure region 14.

[0086] The conductance reducing unit 42 is a member that reduces the conductance of the vacuum path 13 between the high pressure region 14 and the second vacuum chamber 20. The conductance reducing unit 42 has a cylindrical structure that forms the vacuum path 13, and has an opening (the entrance end of the fixed foil trap 45) that is connected to the high pressure region 14, and an opening (the exit end of the fixed foil trap 45) that is connected to the second vacuum chamber 20. A member that reduces the conductance of the vacuum compared to the rest of the vacuum path 13 is disposed between these two openings.

[0087] Vacuum conductance is a parameter that indicates the ease of flow of the buffer gas 2, and corresponds to, for example, the reciprocal of the exhaust resistance. The lower the conductance, the higher the exhaust resistance, and the more difficult it is for the buffer gas 2 to flow. Therefore, the conductance reduction section 42 can be said to be a component that makes it difficult for the buffer gas 2 to flow. By providing the conductance reduction section 42, it becomes difficult for the buffer gas 2 to flow between the second vacuum chamber 20 and the high-pressure region 14. As a result, it becomes possible to maintain the high-pressure region 14 without being affected by the pressure of the second vacuum chamber 20, and it becomes possible to sufficiently absorb changes in pressure on the introduction side.

[0088] The debris mitigation device 40 includes a rotary foil trap 43, a rotary foil trap cover 44, a fixed foil trap 45, and a fixed foil trap cover 46, as shown in FIG.

[0089] The rotating foil trap 43 is a foil trap in which multiple foils are rotated to actively collide with debris. The rotating foil trap 43 is also called an RFT (Rotating Foil Trap). The rotating foil trap cover 44 is a cylindrical cover configured to cover the outer periphery of the rotating foil trap 43. The rotating foil trap 43 and the rotating foil trap cover 44 are arranged on the first vacuum chamber 10 side.

[0090] The fixed foil trap 45 is a foil trap in which the positions of multiple foils are fixed. The fixed foil trap 45 is also called an SFT (Static Foil Trap). The fixed foil trap cover 46 is a cover that covers the fixed foil trap 45. The fixed foil trap cover 46 also functions as a member that connects the fixed foil trap 45 to the rotary foil trap cover 44. Note that the rotary foil trap cover 44 and the fixed foil trap cover 46 do not necessarily need to be completely connected; for example, a small gap may exist as long as the pressure in the high pressure region 14 can be maintained. The fixed foil trap 45 and the fixed foil trap cover 46 are disposed on the second vacuum chamber 20 side.

[0091] The above-described vacuum path 13, cylindrical member 41, and conductance reduction unit 42 are realized by utilizing these configurations for capturing debris. In this embodiment, a hollow region formed by connecting the rotary foil trap cover 44, the fixed foil trap cover 46, and the fixed foil trap 45 forms the vacuum path 13. The rotary foil trap cover 44 functions as the cylindrical member 41. The fixed foil trap 45 functions as the conductance reduction unit 42. Therefore, a high-pressure region 14 is formed in the space from the rotary foil trap cover 44 to the fixed foil trap 45. The specific configuration of each foil trap and the like will be described in detail later.

[0092] [Buffer Gas Inlet] The light source device 100 is provided with an inlet 47 for introducing the buffer gas 2. The buffer gas 2 functions as a gas that changes the pressure in the second vacuum chamber 20. Only one inlet 47 for the buffer gas 2 may be provided, or multiple inlets 47 may be provided. A pipe through which the buffer gas 2 passes is connected to the inlet 47, and a flow rate adjustment valve that adjusts the flow rate of the buffer gas 2 is attached to the pipe.

[0093] In this embodiment, the high-pressure region 14 is a region in the debris mitigation device 40 into which the buffer gas 2 is introduced, and the debris mitigation device 40 is provided with an inlet 47 that connects to the high-pressure region 14. This allows the buffer gas 2 to be supplied directly to the high-pressure region 14, making it possible to easily maintain the pressure in the high-pressure region 14 at a high level. This inlet 47 is provided, for example, in the fixed foil trap cover 46. In Figure 2, the inlet 47 that connects to the high-pressure region 14 is schematically illustrated by a dotted circle. In this embodiment, the inlet 47 that connects to the high-pressure region 14 corresponds to a first inlet.

[0094] Furthermore, a buffer gas inlet (not shown) may be provided in the second vacuum chamber 20. In this case, the buffer gas 2 is supplied directly to the second vacuum chamber 20, making it possible to easily change the pressure in the second vacuum chamber 20. In this embodiment, the inlet provided in the second vacuum chamber 20 corresponds to the second inlet.

[0095] As described above, the light source device 100 has a structure in which the first vacuum chamber 10 in which the EUV light 1 (plasma P) is generated and the second vacuum chamber 20 in which optical elements and the like for utilizing the EUV light 1 are housed are connected via a vacuum path 13 formed by the debris mitigation device 40. An inlet 47 for a buffer gas 2 is provided in the debris mitigation device 40 (high-pressure region 14) or downstream of the debris mitigation device 40 (towards the second vacuum chamber 20).

[0096] A rare gas is used as the buffer gas 2. Typically, the buffer gas 2 is argon gas. Argon gas is an inert gas that does not easily form compounds with other atoms. Therefore, unlike activated gases such as hydrogen gas and halogen gas, argon gas does not corrode metals or the like in the chamber. Furthermore, since argon gas can be exhausted without any process such as inactivation, the exhaust system can be made smaller and less expensive than when exhausting activated gases.

[0097] Furthermore, it is known that light in the EUV region excites and ionizes argon atoms (Ar). Therefore, argon plasma can be generated by irradiating the EUV light 1. In this way, argon gas (buffer gas 2) is an ionized gas that is ionized by the EUV light 1. This phenomenon is utilized in the light source device 100 to perform cleaning operations, which will be described later.

[0098] Although argon atoms have some absorption of the 13.5 nm wavelength, the absorption is one order of magnitude lower than that of light of 30 nm to 80 nm. Therefore, attenuation of the actinic wavelength of 13.5 nm is small, and a sufficient amount of light can be ensured even when argon gas is used as the buffer gas 2.

[0099] [Partition Plate] As shown in FIG. 2, the first vacuum chamber 10 is provided with a first partition plate 16 and a second partition plate 17 between the debris mitigation device 40 and the discharge module 31 .

[0100] The first partition plate 16 is a plate-shaped member having a larger planar size than the debris mitigation device 40 (rotary foil trap cover 44), and is arranged to cover the side of the debris mitigation device 40 that faces the plasma P. The first partition plate 16 has an opening 16a to which the second partition plate 17 is attached. The first partition plate 16 restricts, for example, liquid-phase plasma raw material vapor (tin vapor in this case) from leaking into the space on the debris mitigation device 40 side, the second vacuum chamber 20, etc.

[0101] The second partition plate 17 is a plate-shaped member that covers the opening 16a provided in the first partition plate 16, and is fixed to the side of the first partition plate 16 that faces the plasma P. The second partition plate 17 has an opening 17a through which the EUV light 1 to be introduced into the second vacuum chamber 20 passes, and an opening 17b through which the EUV light 1 to be introduced into a predetermined measuring instrument (first light intensity monitor 25a) passes. The second partition plate 17 reduces the thermal load applied to the debris mitigation device 40 from the plasma P generated by the discharge, and limits the amount of debris heading toward the debris mitigation device 40.

[0102] [Exhaust System] As shown in Figure 2, the light source device 100 has a first vacuum valve 50 and a first vacuum gauge 51 connected to the first vacuum chamber 10, and a second vacuum valve 52 and a second vacuum gauge 53 connected to the second vacuum chamber 20.

[0103] The first vacuum chamber 10 is provided with an exhaust hole 18 and a measurement hole 19. The first vacuum valve 50 is connected to the exhaust hole 18 and is a valve that connects the first vacuum chamber 10 to a first vacuum pump 54. The first vacuum gauge 51 is connected to the measurement hole 19 and detects the pressure in the first vacuum chamber 10. The second vacuum chamber 20 is provided with an exhaust hole 28 and a measurement hole 29. The second vacuum valve 52 is connected to the exhaust hole 28 and is a valve that connects the second vacuum chamber 20 to a second vacuum pump 55. The second vacuum gauge 53 is connected to the measurement hole 29 and detects the pressure in the second vacuum chamber 20.

[0104] In this way, the first vacuum chamber 10 and the second vacuum chamber 20 of the light source device 100 are evacuated separately. Furthermore, the high-pressure region 14 described above is formed in the vacuum path 13 connecting the vacuum chambers, restricting the flow of buffer gas. As a result, although the first vacuum chamber 10 and the second vacuum chamber 20 are connected by the vacuum path 13, differential pumping is possible, evacuating the internal spaces of each chamber independently.

[0105] In this embodiment, the pressure of the second vacuum chamber 20 is mainly adjusted. For this reason, the light source device 100 is provided with a pressure adjustment mechanism that adjusts the pressure of the second vacuum chamber 20. The pressure adjustment mechanism is a mechanism that adjusts, for example, the amount of buffer gas 2 flowing out of the second vacuum chamber 20 or the amount of buffer gas 2 flowing into the second vacuum chamber 20.

[0106] For example, a flow rate adjustment valve (not shown) that adjusts the flow rate of the buffer gas 2 introduced from the inlet 47 is used as the pressure adjustment mechanism. In this case, for example, by increasing the flow rate of the buffer gas 2, the flow rate of the buffer gas 2 flowing into the second vacuum chamber 20 increases, and it is possible to increase the pressure of the second vacuum chamber 20.

[0107] Furthermore, for example, the second vacuum valve 52 that adjusts the exhaust rate of the second vacuum chamber 20 is used as the pressure adjustment mechanism. In this case, for example, by reducing the exhaust rate, the flow rate of the buffer gas 2 flowing out from the second vacuum chamber 20 decreases, and as a result, it is possible to increase the pressure of the second vacuum chamber 20. In this embodiment, the second vacuum valve 52 corresponds to the exhaust rate adjustment valve.

[0108] As the pressure adjustment mechanism, both the buffer gas flow rate adjustment valve and the second vacuum valve 52 may be used, or either one may be used. Also, any mechanism other than the above may be used as long as it is capable of adjusting the pressure of the second vacuum chamber 20. By using the pressure adjustment mechanism, for example, it becomes possible to easily adjust the pressure of the second vacuum chamber, and various operation modes can be realized.

[0109] [Light Intensity Monitors] The light source device 100 has light intensity monitors that detect the light intensity of the EUV light 1. Here, a first light intensity monitor 25a and a second light intensity monitor 25b are provided. The first light intensity monitor 25a is connected to the right sidewall 10c of the first vacuum chamber 10, and detects the EUV light 1 that has passed through the rotary foil trap 43. Therefore, the first light intensity monitor 25a functions as a sensor that detects the light intensity of the EUV light 1 from the plasma P, i.e., the emission intensity of the plasma P.

[0110] The second light intensity monitor 25b is provided in the second vacuum chamber 20 and detects the intensity of the EUV light 1. For example, the second light intensity monitor 25b is provided at a position where the EUV light that has passed through the optical element 21 (here, a cylindrical collector mirror) is irradiated. However, the present invention is not limited to this, and the EUV light 1 that has been branched using, for example, a reflecting mirror may also be used to detect the EUV light 1. This enables the second light intensity monitor 25b to detect the intensity of the EUV light 1 that has been guided via the collector mirror or reflecting mirror.

[0111] For example, if the surfaces of the collector mirror or reflector mirror are contaminated with debris, the reflectivity of the EUV light decreases, and the amount of EUV light 1 that is collected or reflected decreases. Therefore, the detection result of the second light amount monitor 25b functions as a parameter that indicates the degree of contamination of the collector mirror or reflector mirror. Utilizing this, the detection result of the second light amount monitor 25b is used to determine whether or not to perform a cleaning operation.

[0112] [Configuration of Each Part of the Debris Reduction Apparatus] The configuration of each part of the debris mitigation apparatus 40 will be specifically described below.

[0113] [Rotary Foil Trap] Fig. 3 is a schematic cross-sectional view showing an example of the configuration of the rotary foil trap 43. Fig. 4 is a schematic front view showing an example of the configuration of the rotary foil trap 43. As shown in Figs. 3 and 4, the rotary foil trap 43 has a plurality of foils (blades) F, a central support post 60, and an outer ring 61. The central support post 60 is connected to a shaft member 63 that rotates around a rotation axis.

[0114] The multiple foils F are thin films or thin flat plates. The central support 60 is a member that radially supports the multiple foils F. The outer ring 61 is arranged concentrically with the central support 60 and is connected to the tip of each foil F extending radially from the central support 60. In this embodiment, the central support 60 corresponds to a rotating member. The foils F are arranged radially around the central support 60 at approximately equal angular intervals. At this time, each foil F lies on a plane including the central axis C0 of the central support 60. The material of the rotary foil trap 43 is, for example, a high-melting-point metal such as tungsten (W) or molybdenum (Mo).

[0115] 4, the multiple foils F of the rotary foil trap 43 are arranged parallel to the beam direction of the EUV light 1 so as not to block the EUV light 1 traveling from the plasma P (light-emitting point) to the second vacuum chamber 20. That is, the rotary foil trap 43, in which each foil F is arranged on a plane including the central axis C0 of the central support 60, is arranged so that the plasma P (light-emitting point) is on an extension of the central axis C0 of the central support 60 (see FIG. 11). As a result, except for the central support 60 and the outer ring 61, the EUV light is blocked only by the thickness of each foil F, making it possible to maximize the proportion of EUV light 1 that passes through the rotary foil trap 43 (also referred to as transmittance).

[0116] [Rotary Foil Trap Cover] Figure 5 is a schematic cross-sectional view showing an example of the configuration of the rotary foil trap cover 44. Figure 6 is a schematic front view showing an example of the configuration of the rotary foil trap cover 44. The rotary foil trap cover 44 surrounds the outer periphery of the rotary foil trap 43 and collects debris scattered from the rotary foil trap 43. By providing the rotary foil trap cover 44, it is possible to prevent debris captured by the rotary foil trap 43 from scattering inside the first vacuum chamber 10.

[0117] Hereinafter, the side onto which the EUV light 1 is incident (the side directed toward the plasma P) will be referred to as the incident side, and the opposite side will be referred to as the exit side. The rotating foil trap cover 44 has an incident side opening KI, an exit side opening KO, and an exit side opening KO'.

[0118] The entrance-side opening KI is provided at a position where the EUV light entering the rotary foil trap 43 is not blocked. The exit-side opening KO is provided at a position where the EUV light 1 passing through the opening 17a of the second partition plate 17 and entering the entrance-side opening KI is not blocked. The EUV light 1 that passes through the exit-side opening KO becomes light that is introduced into the second vacuum chamber 20. The exit-side opening KO' is provided at a position where the EUV light 1 passing through the opening 17b of the second partition plate 17 and entering the entrance-side opening KI is not blocked. The EUV light 1 that passes through the exit-side opening KO' becomes light that is introduced into the first light intensity monitor 25a.

[0119] Furthermore, a through-hole 64 is provided on the emission side surface of the rotary foil trap cover 44, through which a shaft member 63 serving as the rotation shaft of the rotary foil trap 43 passes. Note that one end of the through-hole 64 is connected to, for example, the inner wall of the first vacuum chamber 10, and is not an open end. Furthermore, an exhaust pipe 65 for exhausting debris is provided at the bottom of the rotary foil trap cover 44.

[0120] At least a portion of the debris captured by the rotary foil trap 43 moves radially on the foil F of the rotary foil trap 43 due to centrifugal force, detaches from the end of the foil F, and adheres to the inner surface of the rotary foil trap cover 44. The rotary foil trap cover 44 is heated by a heating means (cover heating unit) (not shown) or by radiation associated with the emission of EUV light, and the debris adhered to the inner surface of the rotary foil trap cover 44 by this heating does not solidify but remains in a liquid state. The debris adhering to the inner surface of the rotary foil trap cover 44 collects at the bottom of the rotary foil trap cover 44 due to gravity and is discharged to the outside of the rotary foil trap cover 44 via the discharge pipe 65 to become waste material. The waste material debris is stored in a debris storage unit (not shown).

[0121] The internal space of the rotary foil trap cover 44 is large enough to accommodate the rotary foil trap 43. This size is sufficiently larger than the diameter of the exit-side opening KO connected to the second vacuum chamber 20. As such, when viewed from the exit-side opening KO, the width of the space that forms the vacuum path 13 (the cross-sectional area intersecting with the path direction) increases rapidly. In addition, the rotational effect of the rotary foil trap also makes it possible to rapidly reduce the pressure of the buffer gas 2.

[0122] [Fixed Foil Trap] Fig. 7 is a schematic cross-sectional view showing an example of the configuration of the fixed foil trap 45. Fig. 8 is a schematic front view showing an example of the configuration of the fixed foil trap 45. The fixed foil trap 45 is a foil trap FT having multiple foils F fixed thereto, and is disposed downstream of the rotary foil trap 43 to capture debris that has passed through the rotary foil trap 43. The fixed foil trap 45 is disposed based on the central path of the ray bundle (EUV extracted light) of the EUV light 1 extracted from the through-hole 12 of the first vacuum chamber 10. The central path is, for example, a path connecting the light emission point of the plasma P and the center point of the through-hole 12.

[0123] Fig. 7 is a cross-sectional view of the fixed foil trap 45 taken along the central path of the EUV light. Fig. 8 is a view of the fixed foil trap 45 viewed from the direction of the central path of the EUV light. As shown in Figs. 7 and 8, the fixed foil trap 45 includes a plurality of foils F arranged in the vacuum path 13 and a fixed frame 66 that fixes the plurality of foils F. In this embodiment, the fixed frame 66 corresponds to a fixing member.

[0124] As shown in Fig. 8, the multiple foils F are arranged at equal intervals when viewed from the direction of the central path of the EUV light 1. Furthermore, the fixed frame 66 has, for example, a rectangular shape when viewed from the front. The outer shape of the fixed frame 66 may be any shape. Furthermore, as shown in Fig. 7, the multiple foils F are arranged radially so as to extend in the beam direction of the EUV light in a cross section cut along the central path.

[0125] The multiple foils F of the fixed foil trap 45 serve to reduce the conductance of the portion by dividing the space in which the fixed foil trap 45 is disposed into smaller portions. For example, the buffer gas 2 is supplied to the fixed foil trap 45 from the high-pressure region 14. The buffer gas 2 does not easily flow through the fixed foil trap 45, and therefore tends to stagnate between the foils F.

[0126] High-speed debris that cannot be captured by the rotating foil trap 43 slows down due to an increased probability of collision with the gas remaining in the fixed foil trap 45. Collisions with the gas also change the direction of the debris's movement. The fixed foil trap 45 captures the debris that has slowed down and changed direction in this way using the foil F or the fixed frame 66. In this way, by providing the rotating foil trap 43 and the fixed foil trap 45, it is possible to sufficiently capture debris.

[0127] Furthermore, since the fixed foil trap 45 has low conductance, it limits the outflow of the buffer gas 2 to the second vacuum chamber 20 and the inflow of the buffer gas 2 from the second vacuum chamber 20. This makes it difficult for the buffer gas 2 to leak from the high-pressure region 14, for example, and also makes it difficult for pressure changes in the second vacuum chamber 20 to affect the pressure in the high-pressure region 14. This makes it possible to maintain the high-pressure region 14 regardless of the pressure in the second vacuum chamber 20.

[0128] [Fixed Foil Trap Cover] Fig. 9 is a schematic cross-sectional view showing an example of the configuration of a fixed foil trap cover. Fig. 10 is a schematic front view showing an example of the configuration of a fixed foil trap cover. The fixed foil trap cover 46 is a cover that surrounds the fixed foil trap 45 and is a member that connects the fixed foil trap 45 to the rotatable foil trap cover 44. The fixed foil trap cover 46 has a support plate 68 in which an opening 67 and an introduction port 47 are provided, and an enclosure part 69 that extends from the outer edge of the support plate 68 toward the EUV light 1 emission side.

[0129] The support plate 68 is a plate to which the fixed foil trap 45 is fixed. The surrounding portion 69 is formed so as to surround the side surface of the fixed foil trap 45. An opening 67 provided in the support plate 68 is an entrance port for the EUV light 1. An inlet 47 for introducing a buffer gas 2 is also provided inside the support plate 68 so as to communicate with the opening 67. Here, two inlets 47 are provided at positions opposite each other with the opening 67 in between. When the buffer gas 2 is supplied from the inlet 47, the space defining the opening 67 becomes a high-pressure region 14.

[0130] Figure 11 is a schematic cross-sectional view showing an example configuration of the debris mitigation device 40. The debris mitigation device 40 shown in Figure 11 is configured by assembling the above-mentioned rotary foil trap 43, rotary foil trap cover 44, fixed foil trap 45, and fixed foil trap cover 46.

[0131] Specifically, the rotary foil trap 43 is disposed inside the rotary foil trap cover 44. A support plate 68 of the fixed foil trap cover 46 is connected to the rear of the rotary foil trap cover 44 so that the exit-side opening KO and an opening 67 overlap. A fixed frame 66 of the fixed foil trap 45 is connected inside the fixed foil trap cover 46 so as to cover the opening 67 of the support plate 68. A rear end of the fixed foil trap cover 46 is connected to the through-hole 22 of the second vacuum chamber 20 via a flange or the like (not shown).

[0132] With this configuration, the first vacuum chamber 10 and the second vacuum chamber 20 are connected by a vacuum path 13 that passes through a high-pressure region 14 inside the debris mitigation device 40. The pressure inside the light source device 100 when the debris mitigation device 40 is used will be specifically described below.

[0133] [Pressure in the Light Source Device] Figure 12 is a graph showing the results of a simulation of the pressure in the light source device. For this simulation, a model of the debris mitigation device 40 shown in Figure 11 was created, and the pressure distribution in the model was calculated. Figure 12 shows the pressure profile along the central path O of the EUV light 1. The horizontal axis of the graph represents the distance along the central path O. Here, the relative distance to the distance D from the plasma P to the measurement end in the second vacuum chamber 20 is used. The vertical axis of the graph represents the pressure [Pa] at each position.

[0134] Point Oa on the graph corresponds to the generation position of plasma P. Point Ob corresponds to the entrance end of vacuum path 13 (entrance side opening KI of rotary foil trap cover 44). Point Oc corresponds to high pressure region 14 (opening 67 of support plate 68). Point Od corresponds to the exit end of vacuum path 13 (rear end of fixed foil trap 45).

[0135] 12 shows a pressure profile (solid line graph) when the pressure P2 of the second vacuum chamber 20 is set to 0.7 Pa, and a pressure profile (dotted line graph) when P2 is set to 5 Pa. In both graphs, the simulation was performed with the exhaust rate of the first vacuum pump 54 that evacuates the first vacuum chamber 10 and the flow rate of the buffer gas 2 set to constant values. As a result, the pressure P1 of the first vacuum chamber 10 became 3 Pa.

[0136] For example, a high pressure is maintained in the shaded area centered on point Oc. This shaded area is the high-pressure area 14. For example, the area formed by the entrance-side opening KI of the rotary foil trap cover 44 and the opening 67 of the fixed foil trap cover 46 is the high-pressure area 14. From this simulation, when P2 = 0.7 Pa, the pressure Ph in the high-pressure area 14 is 18 Pa or higher relative to the pressure near point Oa.

[0137] A fixed foil trap 45 is provided from the high pressure region 14 to point Od on the second vacuum chamber 20 side, and the pressure decreases substantially uniformly. A rotary foil trap cover 44 including a rotary foil trap 43 is provided from the high pressure region 14 to point Ob on the first vacuum chamber 10 side, and the pressure also decreases toward point Ob. The bent portion of the pressure gradient corresponds to the end of the rotary foil trap 43 on the entrance side. The decrease in pressure up to point Ob occurs due to the rapid expansion of the buffer gas 2 within the rotary foil trap cover 44.

[0138] Now, let's assume that the pressure P2 in the second vacuum chamber 20 increases from 0.7 Pa to 5 Pa. The pressure Ph in the high-pressure region 14 increases slightly as P2 increases. In this case, the increase in Ph is about 0.5 Pa, which is about 1 / 8 of the increase in P2 (4.3 Pa). Thus, the change in Ph is sufficiently small compared to the change in P2. In other words, the change in pressure P2 in the second vacuum chamber 20 is almost entirely absorbed by the gas diffusion effect in the high-pressure region 14 and the rotary foil trap 43, and is not easily transmitted to the first vacuum chamber 10.

[0139] Furthermore, even if P2 increases, the pressure distribution from the high-pressure region 14 to the first vacuum chamber 10 side hardly changes. For example, the pressure from point Oa to point Ob (the pressure from the plasma P to the entrance end of the debris mitigation device 40) is approximately constant (about 3 Pa) regardless of whether P2 increases or decreases. This means that the pressure P1 in the first vacuum chamber 10 is approximately constant, regardless of the pressure P2 in the second vacuum chamber 20.

[0140] In this way, the debris mitigation system 40 can separate P1 and P2 by generating the high-pressure region 14 so as to block the vacuum path 13. As a result, it is possible to suppress changes in the pressure P1 on the light source side due to changes in the pressure P2 on the EUV light entrance side.

[0141] Furthermore, taking into consideration the debris capture capability of the debris mitigation device 40, it is preferable to set the pressure Ph of the high-pressure region 14 to a pressure that is six times or more the pressure P1 of the first vacuum chamber 10. This makes it possible to reliably maintain the pressure P1 of the first vacuum chamber 10 while sufficiently capturing debris from the plasma P.

[0142] Fig. 13 is a graph showing the relationship between the pressures of the first vacuum chamber 10 and the second vacuum chamber 20. Fig. 13 shows the relationship between the pressure P1 of the first vacuum chamber 10 and the pressure P2 of the second vacuum chamber 20, which were actually measured in the light source device 100. The vertical axis of the graph represents P1, and the horizontal axis represents P2. Here, the pressure P2 of the second vacuum chamber 20 was changed while the exhaust rate of the first vacuum chamber 10 was kept constant so that P1 was approximately 2 Pa.

[0143] 13, it was found that even when the pressure P2 in the second vacuum chamber 20 was changed within a range of 20 Pa or less, the pressure P1 in the first vacuum chamber 10 showed a value of around 2 Pa. In other words, even though the pressure on the downstream side of the debris mitigation device 40 was high, the pressure in the upstream space where the plasma P was generated hardly changed from the set value. In other words, it was found that the pressure P1 in the first vacuum chamber 10 where the plasma P was generated could be kept constant regardless of whether the pressure P2 in the second vacuum chamber 20 was high or low.

[0144] 13, the flow rate of the buffer gas 2 supplied to the high-pressure region 14 was set to approximately the same as the flow rate used in the simulation shown in FIG. 12. Therefore, the pressure Ph of the high-pressure region 14 is approximately 20 Pa. Therefore, it can be said that the debris mitigation device 40 does not substantially change the pressure of the first vacuum chamber 10 when the pressure P2 of the second vacuum chamber changes at least within a range equal to or less than the pressure of the high-pressure region Ph. This makes it possible to sufficiently maintain the pressure of the first vacuum chamber, for example, even if the pressure of the second vacuum chamber changes.

[0145] [Sputtering by EUV Light and Buffer Gas] Up to this point, we have mainly explained the pressure characteristics in the light source device 100. Hereinafter, we will explain sputtering caused by the EUV light 1 and buffer gas 2 in the light source device 100.

[0146] In general, optical systems that handle EUV light 1 can be contaminated by debris dispersed from the plasma P and carbon-based deposits (carbon contamination), which can result in a decrease in performance. High-speed debris flying within the chamber can collide with the optical system, potentially scraping off reflective films and other surfaces on the optical system. One known method for dealing with this problem is to reduce high-speed debris by colliding it with buffer gas 2. Another known method is to remove debris and carbon contamination that has adhered to the optical system using radicals from activated gases and the like.

[0147] The inventors have studied a method for protecting the optical elements 21 and other elements downstream of the debris mitigation device 40 (DMT) by utilizing the pressure distribution of argon gas, which is the buffer gas 2. In this method, for example, low-speed debris is captured by a rotating foil trap 43, and high-speed debris is decelerated by the buffer gas 2 and captured by a fixed foil trap 45.

[0148] On the other hand, it is possible that debris not captured by the debris mitigation device 40 may enter the second vacuum chamber 20. In this case, high-speed debris may collide with the optical element 21 downstream of the debris mitigation device 40, causing sputtering of the optical element 21. Therefore, when the pressure of the argon gas around the optical element 21 (the pressure in the second vacuum chamber 20) was increased in the hope of suppressing sputtering of the optical element 21 by debris, it was found that this actually promoted sputtering of the optical element 21.

[0149] As described above, the present inventors have discovered that introducing argon gas causes sputtering. It is believed that this occurs when argon gas ionized by the EUV light 1 collides with the optical element 21, sputtering the surface of the optical element 21. For example, irradiation with the EUV light 1 ionizes the argon gas, forming plasma (EUV-induced plasma). When the EUV-induced plasma is formed, argon ions are accelerated toward the optical element 21, and the ions collide with the surface of the optical element 21, causing sputtering. The ion acceleration is believed to be due to a potential difference between the EUV-induced plasma and the optical element 21. Thus, by using an ionized gas (here, argon gas) that is ionized by the EUV light 1 as the buffer gas 2, sputtering by the ionized gas can be achieved. The results of the sputtering experiment are described below.

[0150] 14A and 14B are schematic diagrams showing an example of the arrangement of samples used in sputtering experiments. In the experiment, a sputtering sample 27 was placed on a stage 26 located downstream of the debris mitigation device 40. Here, a thin film of ruthenium (Ru) was formed on the sample 27, and the sputtering rate for the sample 27 was measured. A thin film of ruthenium is a material used for, for example, a reflective surface that reflects EUV light 1.

[0151] 14A, the tilt angle of the stage 26 with respect to the central path O of the EUV light 1 is set to approximately 20°. The pressure P1 in the first vacuum chamber 10 where the plasma P that radiates the EUV light 1 is generated (the pressure in the area on the left side of the debris mitigation device 40 in the drawing) is set to approximately 2 Pa. The pressure P2 in the second vacuum chamber 20 where the sample 27 is placed (the pressure in the area on the left side of the debris mitigation device 40 in the drawing) is set in the range of approximately 0.5 Pa to approximately 11 Pa.

[0152] 14A, five samples 27 were placed on the stage 26 so as to be irradiated with the EUV light 1. Hereinafter, these samples 27 will be referred to as Sample 1, Sample 2, Sample 3, Sample 4, and Sample 5, in order from the side closest to the plasma P. The distance between the plasma P and the end of Sample 1 on the plasma P side was set to about 35 cm. The intervals between Samples 1 to 5 were set to about 5 cm.

[0153] 14B, the tilt angle of the stage 26 with respect to the central path O of the EUV light 1 was set between approximately 25° and approximately 45°. The pressure P1 in the first vacuum chamber 10 was set to approximately 2 Pa, as in FIG. 14A. The pressure P2 in the second vacuum chamber 20 was set in the range of approximately 13 Pa to approximately 19 Pa. One sample 27 (referred to as Sample 6) was placed on the stage 26 so as to be irradiated with the EUV light 1. The distance between the plasma P and the end of Sample 6 on the plasma P side was set to approximately 35 cm, as in the case of Sample 1 in FIG. 14A.

[0154] 15 is a graph showing the relationship between the sputtering rate and pressure. The horizontal axis of the graph is the pressure P2 [Pa] in the second vacuum chamber 20. The vertical axis of the graph is the sputtering rate. The unit of the sputtering rate is nm / Gpulse. This is when the number of times the plasma P emits light (the number of power pulses) is 1×10 9 The graphs show the thickness (nm) of the film sputtered when the number of times is 1.

[0155] 15, all points except the rightmost point are the results of evaluating the sputtering rate for Sample 1 shown in FIG. 14A, where the tilt angle was set to approximately 20°. The rightmost point is the result of evaluating the sputtering rate for Sample 6 shown in FIG. 14B, where the tilt angle was set to approximately 25°. The distance from the plasma P for all points was set to approximately 35 cm.

[0156] 15, when the pressure P2 in the second vacuum chamber 20 is 6 Pa or less, the sputtering rate for the ruthenium thin film does not change significantly even when the pressure is changed, and is approximately 5 nm / Gpulse or less. In contrast, when P2 is 6 Pa or more, it was confirmed that the sputtering rate increases as the pressure increases.

[0157] Fig. 16 is a graph showing the relationship between sputtering rate, pressure, and sample position. Fig. 16 uses a bar graph with rectangular columns to show the sputtering rates for the five samples 27 (Sample 1 to Sample 5) shown in Fig. 14A when the pressure P2 in the second vacuum chamber 20 is set to 0.7 Pa, 2.0 Pa, 5.5 Pa, and 11 Pa. Note that for the condition of P2 = 11 Pa, only the data for Sample 1, Sample 3, and Sample 5 are shown.

[0158] For example, the sputtering rate for Sample 1 is low when P2 is in the range up to 5.5 Pa, but when P2 = 11 Pa, the sputtering rate increases significantly compared to the previous values. Similarly, for Sample 3 and Sample 5, the sputtering rate is low when P2 is in the range of 5.5 Pa or less, but when P2 = 11 Pa, the sputtering rate increases significantly. From this, as with the data shown in Figure 15, it can be seen that below a certain pressure, a sufficient sputtering rate cannot be obtained and significant sputtering does not occur.

[0159] Furthermore, for example, when P2 = 0.7 Pa, the sputtering rate is greatest in Sample 1, which is close to the plasma P, and decreases the further away from the plasma P, with the sputtering rate being approximately 0 in Sample 5, for example. In other words, it can be seen that the sputtering rate decreases the further away from the plasma P. This is also true for other pressures (P2 = 2.0 Pa and P2 = 5.5 Pa) where the sputtering rate is generally low. Furthermore, even at pressures (P2 = 11 Pa) where the sputtering rate increases, the sputtering rate decreases the further away from the plasma P. This shows that the sputtering rate decreases the greater the distance from the plasma P, regardless of the pressure P2.

[0160] Fig. 17 is a graph showing the relationship between the sputtering rate and the emission frequency of the plasma. Fig. 17 shows the frequency dependency of the sputtering rate on the emission frequency of the plasma P (EUV light 1). Here, for Sample 6 shown in Fig. 14B, the sputtering rate was measured at emission frequencies of 3000 Hz and 6000 Hz. The pressure P2 of the second vacuum chamber 20 was set to about 13 Pa, and the inclination angle of the sample 27 was set to about 25°.

[0161] As shown in Fig. 17, the sputtering rate increased when the emission frequency was 6000 Hz compared to when the emission frequency was 3000 Hz. In other words, it was confirmed that the sputtering rate increased according to the emission frequency. Generally, when the emission frequency is increased, the average power (light amount) of the EUV light 1 increases, and the total number of argon atoms ionized by the EUV light 1, i.e., the total number of argon ions generated by the EUV light 1, increases. It is believed that this is the reason why the sputtering rate increased in Fig. 17.

[0162] For example, when the emission frequency is set low, setting the P2 value to the same pressure as when the emission frequency is high will slow down the sputtering speed. In such cases, P2 can be increased to ensure the cleaning speed. Conversely, when it is difficult to adjust P2, the sputtering rate can be changed by adjusting the emission frequency.

[0163] [Cleaning Operation by Sputtering] The sputtering phenomenon caused by the ionized gas (buffer gas 2) ionized by the EUV light 1 has the effect of scraping the surface of the optical element 21 provided in the second vacuum chamber 20 in the light source device 100. In other words, by using sputtering, debris and carbon contamination adhering to the optical element 21 can be removed, and the optical element 21 can be sputter cleaned.

[0164] The inventors have focused on this point and provided the light source device 100 with a function to perform a cleaning operation using the ionized gas that is the buffer gas 2, in addition to a normal operation of supplying the EUV light 1 to a utilization device, etc. In other words, the light source device 100 is capable of both a normal operation and a cleaning operation.

[0165] Normal operation is, for example, operation in which plasma P (EUV light 1) is stably generated and EUV light 1 is supplied to a utilization device or the like. In other words, normal operation is operation in which the light source device 100 operates as a light source of EUV light 1, which is its original purpose. Hereinafter, the pressure P2 in the second vacuum chamber 20 during normal operation may be referred to as a normal pressure P2n. In this embodiment, the normal pressure P2n corresponds to the first pressure.

[0166] The pressure P1 in the first vacuum chamber 10 during normal operation is set to a pressure P0 at which the EUV light 1 is stable. P0 is typically the pressure at which the plasma P is stably generated, and is, for example, about 2 Pa. The specific value of P0 is not limited. For example, P0 may be set to a pressure at which the plasma P can be stably generated depending on the type of plasma raw material, discharge conditions, etc. In this embodiment, the pressure P0 at which the EUV light 1 is stable corresponds to the third pressure.

[0167] The cleaning operation differs from the normal operation in that it cleans optical elements by sputtering. The light source device 100 switches between the normal operation and the cleaning operation as appropriate. Hereinafter, the pressure P2 in the second vacuum chamber 20 during the cleaning operation may be referred to as a cleaning pressure P2c. In this embodiment, the cleaning pressure P2c corresponds to the second pressure.

[0168] As described above, in the light source device 100, it is possible to change only the pressure P2 in the second vacuum chamber 20 (the pressure around the optical element 21) while maintaining the pressure P1 in the first vacuum chamber 10. By utilizing this characteristic, it is possible to control the amount of sputtering on the optical element 21 without changing the pressure P1 on the plasma P side.

[0169] For example, if the optical element 21 provided in the second vacuum chamber 20 is contaminated with debris or the like flying in from the plasma P that is the light source, by changing the pressure P2 in the second vacuum chamber 20 while the light source is turned on in the first vacuum chamber 10, the debris or the like adhering to the optical element 21 can be scraped off by a sputtering phenomenon, thereby cleaning the optical element 21. In this way, in the light source device 100, for example, the optical element 21 or the like provided in the second vacuum chamber 20 can be cleaned while stably generating the EUV light 1.

[0170] 15 and 16, sputtering due to the buffer gas 2 occurs when the pressure P2 in the second vacuum chamber 20 is higher than a certain pressure. Therefore, at pressures lower than that pressure, sputtering hardly occurs. For this reason, the normal pressure P2n is set to a pressure at which no sputtering occurs, and the cleaning pressure P2c is set to a pressure higher than P2n at which significant sputtering occurs.

[0171] In other words, the cleaning operation is an operation in which buffer gas 2 is introduced into the second vacuum chamber 20, which is maintained at the normal pressure P2n, which is the pressure during normal operation, the pressure in the second vacuum chamber 20 is increased to a cleaning pressure P2c, which is higher than the normal pressure P2n, and, while maintaining the cleaning pressure P2c, sputtering is performed on the optical element 21 placed in the second vacuum chamber 20 using the buffer gas 2 ionized by the EUV light 1.

[0172] In this way, in the cleaning operation, sputtering is performed by increasing the pressure P2 in the second vacuum chamber 20 from the normal pressure P2n to the cleaning pressure P2c. In this method, the cleaning operation can be easily performed by simply adjusting, for example, the exhaust rate of the second vacuum chamber 20.

[0173] Even if the pressure in the second vacuum chamber 20 changes, the pressure P1 in the first vacuum chamber 10 changes very little due to the action of the high-pressure region 14 of the debris mitigation system 40, and is maintained at the pressure P0 at which the EUV light 1 is stable. Therefore, when starting a cleaning operation or returning to normal operation, there is no need to adjust the exhaust rate of the first vacuum chamber 10, etc.

[0174] In this embodiment, the cleaning pressure P2c is set to 6 Pa or higher. For example, referring to Fig. 15, it can be seen that the sputtering rate increases in accordance with the pressure above 6 Pa. Therefore, by setting the cleaning pressure P2c in the range of 6 Pa or higher, it becomes possible to perform sputtering at a desired sputtering rate, for example.

[0175] Furthermore, it is preferable that the cleaning pressure P2c is set to a pressure three or more times higher than the pressure P0 at which the EUV light 1 is stabilized and set in the first vacuum chamber 10. For example, if P2c is about the same pressure as P0, it is difficult to achieve a sufficient sputtering rate, but by setting the pressure to three or more times higher, a relatively high sputtering rate can be achieved. This makes it possible to shorten the cleaning time for the optical element 21.

[0176] On the other hand, the normal pressure P2n of the second vacuum chamber 20 is set to, for example, a pressure equivalent to the pressure P0 at which the EUV light 1 is stable. In this case, the sputtering rate can be sufficiently reduced, and a state in which no significant sputtering occurs during normal operation can be maintained. This makes it possible to avoid a situation in which the optical element 21 is unnecessarily sputtered during normal operation.

[0177] During the cleaning operation, the optical element 21 is sputtered while the second vacuum chamber 20 is maintained at the cleaning pressure P2c. For example, the sputtering time is calculated based on the sputtering rate corresponding to the cleaning pressure P2c and the target sputtering amount. The cleaning pressure P2c is then maintained for the sputtering time. Alternatively, the cleaning pressure P2c can be maintained until the characteristics of the optical element 21 (such as the amount of reflected light) return to their pre-contamination states.

[0178] The sputtering step may also include a step of changing the intensity of the EUV light 1 from the intensity of the EUV light 1 during normal operation while maintaining the cleaning pressure P2c. For example, as described with reference to Fig. 17, the sputtering rate can also be adjusted when the intensity (average power) of the EUV light 1 is changed. Therefore, in this step, any parameter that can change the intensity of the EUV light 1 is adjusted.

[0179] For example, the light emission frequency may be adjusted as in the case of Figure 17. In this case, to increase the sputtering rate, the light emission frequency may be increased. Alternatively, the irradiation intensity of the laser beam LB may be adjusted, or the pulse power (charging energy) applied to the discharge electrodes EA and EB may be adjusted. The sputtering rate can be increased by increasing the irradiation intensity or pulse power of the laser beam.

[0180] Furthermore, in the sputtering process, other conditions that change the sputtering rate may be changed as appropriate. For example, the sputtering rate may be increased by moving the optical element 21 closer to the plasma. Furthermore, the experiments in FIGS. 14A and 14B have shown that the sputtering rate can be adjusted by changing the tilt angle of the sample 27. That is, in order to adjust the sputtering rate, the irradiation angle of the EUV light 1 with respect to the optical element 21, etc. may be adjusted. In this case, the sputtering rate can be reduced by making the irradiation angle shallower. In addition, the types of parameters that can be adjusted in the sputtering process are not limited.

[0181] [Operation of Light Source Device] Fig. 18 is a flowchart showing an example of operation of the light source device 100. The process shown in Fig. 18 is a process for executing the cleaning method according to this embodiment. The following describes an example in which the optical element 21 provided in the second vacuum chamber 20 is cleaned.

[0182] The determination as to whether or not to perform the cleaning operation is based on the detection result of the second light intensity monitor 25b (see FIG. 2) which detects the light intensity of the EUV light 1 that has passed through the optical element 21. That is, in the process shown in FIG. 18, the normal operation and the cleaning operation are switched and performed based on the detection result of the second light intensity monitor 25b.

[0183] 18 may be performed automatically using a controller or the like of the light source device 100. In this case, the pressure and the like are automatically controlled based on the detection result of the second light intensity monitor 25b. Alternatively, the user of the light source device 100 may manually control the pressure and the like by checking the detection result of the second light intensity monitor 25b. Alternatively, the controller may read the detection result of the second light intensity monitor 25b and output an instruction to the user to perform a cleaning operation.

[0184] First, normal operation is performed (step 101). In normal operation, the pressure P1 in the first vacuum chamber 10 is set to a pressure P0 that stabilizes the EUV light 1. The pressure P2 in the second vacuum chamber 20 is set to a normal pressure P2n. This allows stable EUV light 1 to be supplied to a utilization device or the like.

[0185] Next, it is determined whether or not to start the cleaning operation (step 102). Specifically, it is determined whether or not the light amount detected by the second light amount monitor 25b (light amount of the EUV light 1 that has passed through the optical element 21) is lower than a predetermined threshold (start determination threshold). The start determination threshold is, for example, the lower limit of the light amount of the EUV light 1 supplied to the utilization device or the like in normal operation. There are no other limitations on the method for setting the start determination threshold. In this embodiment, the start determination threshold corresponds to the first threshold.

[0186] For example, if the light amount is equal to or greater than the start determination threshold, it is determined that the contamination of the optical element 21 is within an acceptable range and that the cleaning operation should not be started (No in step 102). In this case, the process returns to step 101 and normal operation continues.

[0187] On the other hand, if the light intensity is lower than the start determination threshold, it is determined that the contamination of the optical element 21 has reached an unacceptable level, and a cleaning operation is to be started (Yes in step 102). In this case, a pressure increase step is executed to increase the pressure in the second vacuum chamber 20 (step 103).

[0188] The pressure increasing step is a step in which, while the plasma P is being generated, an ionized gas (buffer gas 2) that is ionized by the EUV light 1 is introduced into the second vacuum chamber 20, which is maintained at a normal pressure P2n that is the pressure during normal operation, to increase the pressure P2 of the second vacuum chamber 20 to a cleaning pressure P2c that is higher than the normal pressure P2n. For example, the exhaust rate of the second vacuum chamber 20 is reduced, and the second vacuum valve 52 is adjusted so that P2 = P2c. Alternatively, for example, the flow rate control valve may be adjusted so that the flow rate of the buffer gas 2 flowing into the second vacuum chamber 20 increases.

[0189] When the pressure in the second vacuum chamber 20 reaches the cleaning pressure, a sputtering step is performed to sputter the optical element 21 (step 104). The sputtering step is a step in which, while maintaining the cleaning pressure P2c, the optical element 21, which is a target placed in the second vacuum chamber 20, is sputtered with the buffer gas 2 ionized by the EUV light 1. Here, by maintaining the second vacuum chamber 20 at the cleaning pressure P2c, the surface of the optical element 21 is sputtered at a sputtering rate according to P2c, and debris and the like are removed.

[0190] Furthermore, in the sputtering step, a step (light intensity adjustment step) of changing the light intensity of the EUV light 1 from the light intensity of the EUV light 1 during normal operation may be performed while maintaining the cleaning pressure P2c. The light intensity adjustment step is a step of adjusting parameters (such as the emission frequency of the EUV light 1, the brightness and pulse power of the laser beam LB) that can change the light intensity of the EUV light 1 so as to obtain, for example, a desired sputtering rate.

[0191] By introducing the light intensity adjustment process, it becomes possible to achieve a desired sputtering rate even in cases where it is difficult to adjust the sputtering rate using only the cleaning pressure P2c. Note that the method for adjusting the sputtering rate is not limited. For example, the position (distance from the plasma P) or the attitude (irradiation angle of the EUV light 1) of the optical element 21 may be adjusted.

[0192] 18, when the light quantity detected by the second light quantity monitor 25b falls below the start determination threshold, the pressure increase step and the sputtering step are executed. This makes it possible to perform the cleaning operation (pressure increase step and sputtering step) at the timing when cleaning of the optical element 21 becomes necessary. It also makes it possible to avoid unnecessary cleaning operations.

[0193] When the sputtering process is performed, it is determined whether or not the cleaning operation is to be terminated (step 105). Specifically, it is determined whether or not the light amount detected by the second light amount monitor 25b is higher than a predetermined threshold (termination threshold). The termination threshold is set to a value equal to or greater than the start threshold. In this embodiment, the termination threshold corresponds to the second threshold.

[0194] For example, the termination judgment threshold is set to an appropriate value for the amount of EUV light 1 supplied to the utilization device during normal operation. This makes it possible to return the amount of EUV light 1 to an appropriate value. Alternatively, the termination judgment threshold may be set to an upper limit value for the amount of EUV light 1. Furthermore, the termination judgment threshold may be set to the same value as the start judgment threshold. There are no other limitations on the method for setting the termination judgment threshold.

[0195] If the light amount detected by the second light amount monitor 25b is lower than the termination determination threshold, it is determined that contamination remains on the optical element 21 and the cleaning operation should not be terminated (No in step 105). In this case, the process returns to step 104 and the sputtering process continues.

[0196] On the other hand, if the light amount is higher than the termination determination threshold, it is determined that the optical element 21 has been cleaned to an acceptable level, and the cleaning operation is terminated (Yes in step 105). In this case, a pressure reduction step is executed to reduce the pressure in the second vacuum chamber 20 (step 106).

[0197] The pressure reduction step is a step of reducing the pressure P2 in the second vacuum chamber 20 to a normal pressure P2n when the light amount detected by the second light amount monitor 25b becomes higher than the end determination threshold. For example, the second vacuum valve 52 is adjusted so that the exhaust rate of the second vacuum chamber 20 becomes larger and P2=P2n holds. Alternatively, for example, the flow rate control valve may be adjusted so that the flow rate of the buffer gas 2 flowing into the second vacuum chamber 20 decreases.

[0198] This step can be said to be a step of returning, for example, the second vacuum valve 52 and the flow rate control valve to their normal operating states. Note that if the parameters for changing the light intensity of the EUV light 1 or the position and attitude of the optical element 21 are adjusted during the sputtering step, they are returned to their normal operating states. This ends the cleaning operation, making it possible to return to normal operation.

[0199] When the pressure P2 in the second vacuum chamber 20 returns to the normal pressure P2n, it is determined whether or not to stop the operation of the light source device 100 (step 107). For example, if the operation is to be stopped for maintenance or the like (Yes in step 107), the light source device 100 is stopped. If the operation is not to be stopped (No in step 107), the process returns to step 101 and normal operation is resumed.

[0200] In this way, the cleaning operation is an operation that changes the pressure downstream of the debris mitigation device 40 in which the optical element 21 is placed (pressure P2 in the second vacuum chamber 20). In contrast, in the light source device 100, even if the pressure downstream of the debris mitigation device 40 is changed, the pressure in the space where the emission point of the plasma P, upstream of the debris mitigation device 40, is located (pressure P2 in the first vacuum chamber 10) does not change. In other words, even when performing a cleaning operation, there is no need to change the main operating conditions on the light source side. This makes it possible to quickly return to normal operation when the cleaning operation is completed.

[0201] 19 is a schematic diagram illustrating the sputtering region where sputtering occurs. Here, an experiment conducted to confirm the region (sputtering region 70) where sputtering occurs due to the buffer gas 2 irradiated with EUV light 1 will be described using the schematic diagram. The sputtering region 70 refers to the region where the surface of the sample 27 is actually etched by the sputtering phenomenon.

[0202] The left diagram in Figure 19 is a schematic diagram showing the state of sample 27 before sputtering. In the experiment, plate-shaped sample 27 was fixed with bolts to stage 26 introduced into second vacuum chamber 20. A thin film of tungsten (W) with an oxidized surface was used as sample 27. The tungsten oxide formed on the surface of sample 27 was black and lacked metallic luster. Here, the color of tungsten oxide is schematically illustrated as dark gray.

[0203] Next, as shown in the center diagram of Figure 19, the sample 27 was introduced into the second vacuum chamber 20 so that a portion of it overlapped with the optical path of the EUV light 1, and sputtering was performed at P2 = 13 Pa. The dotted line area in the diagram represents the optical path of the EUV light 1. In the experiment, the sample 27 was placed at the end of the optical path of the EUV light 1 (the irradiation range of the EUV light 1), and the EUV light 1 was irradiated only onto the left half of the sample 27, without using a light-shielding member that would generate impurities.

[0204] The right side of Figure 19 is a schematic diagram showing the state of sample 27 after sputtering. In the right half of sample 27, which was not irradiated with EUV light 1, the black color of tungsten oxide remained. On the other hand, a metallic luster was observed in the left half of sample 27, which was irradiated with EUV light 1. In other words, tungsten oxide was etched in the area irradiated with EUV light 1. Here, the color of the tungsten exposed after the tungsten oxide was removed is schematically illustrated in light gray. The light gray area of ​​sample 27 is the sputtered area 70.

[0205] Thus, it was found that the region irradiated with the EUV light 1 becomes the sputtering region 70 where etching by sputtering occurs. It was also found that even inside the second vacuum chamber 20, in regions not irradiated with the EUV light 1, etching by sputtering hardly occurs. In other words, by limiting the irradiation of the EUV light 1, it is possible to limit the sputtering region 70. Below, a configuration for limiting the irradiation of the EUV light 1 by using a light-shielding plate will be described.

[0206] Figure 20 is a schematic diagram showing an example configuration of an optical system using a light-shielding plate. The optical system 24a shown in Figure 20 is an optical system that collects the EUV light 1 emitted from the plasma P and passed through the debris mitigation device 40. To the left of the debris mitigation device 40 is the space inside the first vacuum chamber 10 where the plasma P is generated, and to the right of the debris mitigation device 40 is the space inside the second vacuum chamber 20 where the optical system 24a is located.

[0207] The optical system 24a has a cylindrical collecting mirror 71a and a light-shielding plate 72a. The collecting mirror 71a is an example of the optical element 21 provided in the second vacuum chamber 20. The optical system 24a has a configuration in which the light-shielding plate 72a is added to the light source device 100 described with reference to FIG. 2, for example.

[0208] The collector mirror 71a has a rotationally symmetric cylindrical reflective surface on its inner side, and is arranged so that the central axis of the reflective surface coincides with the central path O of the EUV light 1. The collector mirror 71a is supported so as to be rotatable around the central path O. The light-shielding plate 72a is a plate-shaped member that blocks part of the EUV light that passes through the debris mitigation device 40 and heads toward the collector mirror 71a. Here, the light-shielding plate 72a is arranged so as to cover the upper half of the area on the collector mirror 71a onto which the EUV light 1 is incident. It is also possible to use a light-shielding plate 72a that covers two-thirds or three-quarters of the area onto which the EUV light 1 is incident.

[0209] In the optical system 24a, of the EUV light 1 that has passed through the debris mitigation device 40, that which is not blocked by the light-shielding plate 72a and is incident on the collector mirror 71a is collected. In this case, the reflective surface of the collector mirror 71a that is irradiated with the EUV light 1 is etched by the buffer gas 2. This may cause deterioration of the reflective surface over time. On the other hand, the reflective surface that is shielded by the light-shielding plate 72a is not etched by the buffer gas 2, so the reflective surface can be maintained without deterioration.

[0210] For example, if the characteristics of the reflective surface that has been reflecting the EUV light 1 deteriorate, the collector mirror 71a can be rotated to use a reflective surface that is not deteriorated. Furthermore, since the collector mirror 71a rotates about the axis of the central path O, the optical path of the EUV light 1 is not changed by the rotation of the collector mirror 71a. This makes it possible to maintain the collecting performance without replacing the collector mirror 71a, and makes it possible, for example, to extend the maintenance interval.

[0211] Fig. 21 is a schematic diagram showing another example of the configuration of an optical system using a light-shielding plate. The optical system 24b shown in Fig. 21 is provided in, for example, the first vacuum chamber 10, and is an optical system that collects the EUV light 1 emitted from the plasma P. The optical system 24b has a concave collector mirror 71b and a light-shielding plate 72b.

[0212] The collector mirror 71b has a concave reflective surface formed, for example, by a curved surface of revolution, and is disposed with the reflective surface facing the plasma P. The collector mirror 71b is supported so as to be rotatable about the central axis C of the reflective surface. The collector mirror 71b may be formed of a plurality of mirrors as long as the configuration does not change the focused position of the EUV light 1 when the collector mirror 71b rotates about the central axis C. The light-shielding plate 72b shields a portion of the EUV light traveling from the plasma P toward the collector mirror 71b. Here, the light-shielding plate 72b is disposed so as to cover the reflective surface of the lower half of the collector mirror 71b, but the range of the reflective surface covered by the light-shielding plate 72b is not limited.

[0213] For example, even in the first vacuum chamber 10 where the plasma P is generated, sputtering that deteriorates optical elements such as the collector mirror 71b may occur depending on the light emission conditions of the plasma P. In the optical system 24b, for example, if the characteristics of the reflecting surface of the collector mirror 71b deteriorate, the collector mirror 71b can be rotated to use a reflecting surface that is not deteriorated, as in the case of Fig. 20. This makes it possible to maintain the light-collecting performance without replacing the collector mirror 71b.

[0214] As described above, in the light source device 100 according to this embodiment, the debris mitigation device 40 forms a vacuum path 13 connecting the first vacuum chamber 10, which generates the plasma P, and the second vacuum chamber 20, into which the EUV light 1 from the plasma P is introduced. Furthermore, a high-pressure region 14, whose pressure is higher than the pressure P1 of the first vacuum chamber 10 and the pressure P2 of the second vacuum chamber 20, is formed so as to block the vacuum path 13. This allows changes in pressure in, for example, the second vacuum chamber 20 to be absorbed by the high-pressure region 14. This makes it possible to suppress changes in the pressure P1 on the light source side due to changes in the pressure P2 on the introduction side of the EUV light 1.

[0215] Generally, radiation such as the EUV light 1 emitted from the plasma P is introduced into the utilization device through a passage maintained in a vacuum state. For this reason, if the pressure on the introduction side is changed due to maintenance of an optical system installed midway through the passage or a change in the conditions on the utilization device side, it is conceivable that this will lead to a change in the pressure around the plasma P. In this case, the light emission conditions of the plasma P will change, and there is a possibility that the radiation such as the EUV light 1 will become unstable.

[0216] In the light source device 100 according to this embodiment, a high-pressure region 14 that enables differential pumping is formed inside the debris mitigation device 40. As a result, changes in the pressure P2 in the second vacuum chamber 20, which is the introduction side of the EUV light 1, are absorbed by the flow rate of the buffer gas 2 in the high-pressure region 14, and do not affect the pressure P1 in the first vacuum chamber 10, which is the light source area where the plasma P is generated. Of course, the debris mitigation device 40 that generates the high-pressure region 14 also maintains the function of reducing debris from the plasma P.

[0217] This makes it possible to suppress the intrusion of debris into the second vacuum chamber 20 and to fully prevent the EUV light 1 from becoming unstable due to changes in the pressure P2 in the second vacuum chamber 20. Therefore, even when the pressure P2 in the second vacuum chamber 20 is changed, for example, to perform maintenance on the optical system or to change the conditions on the utilization device side, it is possible to stably emit the EUV light 1. This makes it possible to improve the operability and maintainability of the light source device 100 and the utilization device that uses it.

[0218] Furthermore, in this embodiment, the characteristic of the light source device 100, which is capable of changing the pressure P2 of the second vacuum chamber 20 while stably supplying EUV light 1, is utilized to perform sputtering cleaning of the optical element 21 provided in the second vacuum chamber 20.

[0219] In sputtering cleaning, the sputtering rate can be changed by increasing or decreasing the pressure in the second vacuum chamber 20. For example, if damage to the optical element 21 or the like is to be avoided, the apparatus is operated under conditions that make sputtering less likely. Furthermore, if the contamination of the optical element 21 or the like exceeds an allowable level, the pressure can be deliberately set to perform sputtering, making it possible to etch and clean the contaminated surface.

[0220] The sputtering rate can also be adjusted by increasing or decreasing the light emission output (light intensity of the EUV light 1) in the first vacuum chamber 10. Also, unevenness in sputtering can be improved by changing the position and attitude of the optical element 21. It is also possible to limit the area to be sputtered by placing a shield in front of the optical element 21.

[0221] As the ionized gas that generates this sputtering phenomenon, a rare gas (typically argon gas) that has relatively little absorption of the EUV light 1 is used. That is, the ionized gas hardly reduces the amount of EUV light 1, and therefore can be used as the buffer gas 2. Conversely, a gas that can be used as the buffer gas 2 can also be used as the ionized gas that generates sputtering. This eliminates the need to prepare a dedicated gas for cleaning optical elements, etc., and makes it possible to simplify the system configuration and reduce equipment costs and running costs.

[0222] For example, one method for cleaning an optical system for EUV light 1 is chemical cleaning using a highly explosive gas or a highly reactive gas. For example, in Patent Document 2, in an extreme ultraviolet light source using metal vapor, a reactive gas such as hydrogen gas or halogen gas is supplied to a foil trap or downstream thereof. The reactive gas is then excited using vacuum ultraviolet light generated from the light source or ultraviolet light generated from a dedicated ultraviolet light source, and the optical elements are cleaned.

[0223] However, hydrogen gas is explosive and therefore dangerous to use. Furthermore, halogen gases are highly reactive and difficult to handle. Therefore, ensuring the safety of the equipment and ensuring corrosion resistance of the equipment containers requires expert operation and equipment costs. For example, to safely exhaust reactive gases without adversely affecting the equipment, a device for treating the reactive gas must be installed before the exhaust system. Furthermore, components installed inside the light source and the equipment being used are corroded by reactive gases. Therefore, it is necessary to maintain the interior of the equipment to prevent corrosion and to use materials and coatings that are corrosion-resistant to reactive gases.

[0224] Japanese Patent Application Laid-Open No. 2007-13054 describes a method for cleaning an optical system in a projection exposure apparatus equipped with an EUV light source using an inert gas, in which an inert gas such as nitrogen gas is cooled and the liquid or solid inert gas is sprayed onto optical elements, cleaning contaminants that have adhered to the optical elements due to the impact.

[0225] However, to turn nitrogen gas or other gases into liquid or solid, they must be cooled to at least -50°C or below, which requires a huge amount of liquid nitrogen or other cooling medium. Furthermore, in extreme ultraviolet light sources that use metal vapor, it is conceivable that metals emitted from the light source will cool and solidify at low-temperature locations. Such solidification of metals can have various adverse effects on the optical path and components installed inside the light source. Furthermore, when vaporized metals cool, they can generate tiny metal particles. If these metal particles enter a vacuum pumping system, they can significantly shorten the life of the pumping system.

[0226] In contrast, the sputtering phenomenon discovered by the present inventors allows sputtering (etching) using an inert ionized gas (buffer gas 2) such as a rare gas. Using an inert gas in this way makes it possible to realize a light source device 100 that can be operated safely. Furthermore, the light source device 100 does not require a mechanism for processing or removing reactive gases. This allows for a significant reduction in device costs compared to devices that use reactive gases. Furthermore, the device configuration is simplified, allowing for a more compact device. Furthermore, ionized gases do not cause corrosion like activated gases. This allows for a relatively wide range of materials to be selected for the container, etc., making it possible to reduce device costs.

[0227] Furthermore, unlike methods that use cooled inert gas, there is no need to install cooling equipment to turn the ionized gas into a liquid or solid, which reduces the cost of the device and simplifies its configuration. Furthermore, because there are no areas within the device that become extremely cold, there are no problems such as concentrated solidification of metals such as tin, or an increase in metal particles that affect the exhaust system.

[0228] Furthermore, as described above, it is possible to use, as the ionized gas, a gas that has little absorption of the EUV light 1. This makes it possible to clean components downstream of the debris mitigation device 40 without attenuating the EUV light 1. As a result, for example, a relatively high sputtering rate can be achieved, and cleaning can be completed in a short time.

[0229] <Other Embodiments> The present invention is not limited to the above-described embodiment, and various other embodiments can be realized.

[0230] In the above embodiment, an LDP type light source unit is used, which converts the plasma raw material into plasma by using a laser beam LB and discharge. The type of light source unit is not limited, and any type may be used as long as it is a type that generates radiant light from plasma.

[0231] Fig. 22 is a schematic diagram showing an example of the configuration of an LPP-type light source unit. Fig. 22 schematically shows an LPP-type light source unit 80 that directly converts a plasma raw material into plasma using a laser beam LB. The light source unit 80 has a rotor 81 arranged in the first vacuum chamber 10, a container C that supplies the plasma raw material S to the rotor 81, and a laser source 82 that applies a laser beam LB to convert the plasma raw material S supplied to the rotor 81 into plasma. In the light source unit 80, the container C corresponds to the raw material supply unit, and the laser source 82 corresponds to the energy beam input unit.

[0232] The rotor 81 transports the plasma raw material S to the region where the plasma P is generated. Here, the main surface of the disk-shaped rotor 81 is irradiated with a laser beam LB. This irradiation position is the position where the plasma P is generated. As shown in FIG. 22 , the rotor 81 is supported so as to be rotatable along the vertical direction. The rotor 81 may also be disposed in a state tilted from the vertical direction. The shape of the rotor 81 is not limited to a disk shape; for example, a polygonal rotor may also be used. The rotor 81 is made of a high-melting-point metal such as tungsten (W), molybdenum (Mo), or tantalum (Ta).

[0233] The container C is provided so that the lower part of the rotor 81 is immersed therein, and supplies liquid plasma raw material S to the rotor 81. For example, the plasma raw material S contained in the container C adheres to the surface of the rotor 81. As the rotor 81 rotates in this state, the plasma raw material S is supplied to the irradiation position of the laser beam LB. When the laser beam LB is incident on the irradiation position, plasma P is generated and radiation such as EUV light is emitted.

[0234] In this way, the light source unit 80 of the type in which a part of the rotor 81 is immersed in the container C can, for example, achieve a thinner light source module. Furthermore, unlike the light source unit of the LDP system described with reference to Fig. 1, the LPP system requires only one rotor and does not require equipment for supplying pulsed power. This makes it possible to reduce the size of the device and the cost of the device.

[0235] Figure 23 is a schematic diagram showing another example of the configuration of an LPP-type light source unit. The light source unit 90 shown in Figure 23 is provided in the first vacuum chamber 10 and is equipped with a rotating drum 91 that rotates while storing liquid plasma raw material S. The light source unit 90 is an LPP-type light source module that converts the plasma raw material S stored in the rotating drum 91 into plasma by a laser beam LB.

[0236] The rotating drum 91 has a storage section 92 that is open at the top and stores liquid plasma raw material S. The plasma raw material S is supplied to the storage section 92 in a liquid or solid state from a raw material supply section (not shown). The rotating drum 91 is also provided with a heating mechanism (not shown) to maintain the plasma raw material S supplied to the storage section 92 in a liquid state. The heating mechanism may be a heater that directly heats the rotating drum 91 using an electric heating wire or the like. Alternatively, a heater that heats the rotating drum 91 from the outside using radiation or the like may be used.

[0237] The rotating drum 91 has a disk-shaped base body 93 and an annular outer wall portion 94 formed on one surface of the base body 93 along the periphery of the base body 93. In the rotating drum 91, the area surrounded by the base body 93 and the outer wall portion 94 forms a storage portion 92 that stores liquid plasma raw material S. A shaft member 95 that rotates about a predetermined rotation axis is connected to the surface of the rotating drum 91 opposite to the surface on which the storage portion 92 is formed, so that the central axis of the rotating drum 91 coincides with the rotation axis. The shaft member 95 is driven to rotate by a motor (not shown).

[0238] When the rotating drum 91 is continuously rotated about its axis of rotation, the liquid plasma raw material S supplied to the reservoir 92 moves by centrifugal force toward the inner circumferential surface 94a of the outer wall 94, and is distributed along the inner circumferential surface 94a. The film thickness of the liquid plasma raw material S distributed on the inner circumferential surface 94a is adjusted according to the rotational speed of the rotor.

[0239] In this way, the rotating drum 91 stores the liquid plasma raw material S on the inner circumferential surface 94a of the storage section 92. The inner circumferential surface 94a of the storage section 92 is irradiated with a laser beam LB, which converts the liquid plasma raw material S into plasma. This generates plasma P at the position irradiated by the laser beam LB, and radiant light such as EUV light is emitted. In a light source section 90 that uses the rotating drum 91 as the rotating body, there is no need to provide, for example, a container for storing a large amount of plasma raw material. This makes it possible to reduce the power required to heat the plasma raw material.

[0240] In the above embodiment, a debris mitigation device including both a rotating foil trap and a fixed foil trap has been described. The configuration of the debris mitigation device is not limited, and any configuration may be used as long as it is capable of generating a high-pressure region to interrupt the vacuum path formed within the device.

[0241] For example, instead of a fixed foil trap, other components that reduce conductance may be used as components disposed on the second vacuum chamber side of the debris mitigation system. For example, components that reduce conductance using a mesh structure or honeycomb structure may be used. Furthermore, when the beam diameter of EUV light is small, components that reduce conductance by narrowing the vacuum path may be used.

[0242] Furthermore, for example, the rotary foil trap and rotary foil trap cover may not be disposed on the first vacuum chamber side of the debris mitigation device. In this case, a high-pressure region can be maintained by providing a cylindrical member, such as a rotary foil trap cover, whose cross section intersecting the path direction suddenly widens.

[0243] In the above embodiment, the buffer gas is used as the ionized gas for generating sputters. However, the present invention is not limited to this, and the buffer gas and the ionized gas may be different types of gases.

[0244] For example, an inert gas such as nitrogen or helium may be used as the buffer gas, and a rare gas such as argon gas may be used as the ionized gas. In this case, for example, during normal operation, a high-pressure region may be generated using the buffer gas (nitrogen, helium, etc.), and an ionized gas (argon, etc.) may be released into the second vacuum chamber only when a cleaning operation is performed. Even with this configuration in which an ionized gas is introduced only when necessary, it is possible to clean optical elements, etc., by utilizing sputtering with the ionized gas.

[0245] In the light source device 100 described with reference to Figures 1 and 2, the debris mitigation device 30 is provided inside the first vacuum chamber 10. The location where the debris mitigation device is provided is not limited. For example, the debris mitigation device may be provided outside the first vacuum chamber and the second vacuum chamber. In this case, the debris mitigation device is provided so as to connect the outer wall of the first vacuum chamber and the outer wall of the second vacuum chamber. Alternatively, the debris mitigation device may be provided inside the second vacuum chamber.

[0246] In the above embodiment, a method for performing sputtering using radiation from plasma and ionized gas has been described, using a light source device equipped with a debris reduction device that generates a high-pressure region on a vacuum path. However, the configuration of the device for performing sputtering using radiation and ionized gas is not limited.

[0247] For example, in a light source device, the debris mitigation device does not necessarily have to form a vacuum path. In this case, the vacuum path connecting the space where plasma is generated (first vacuum chamber) and the space where the synchrotron radiation is introduced (second vacuum chamber) is formed by a separate member from the debris mitigation device. The debris mitigation device is appropriately positioned on the optical path of the synchrotron radiation. Even with such a light source device, it is possible to perform sputtering using the synchrotron radiation and the ionized gas by releasing an ionized gas into the space where the synchrotron radiation is introduced.

[0248] In addition, the configuration of the light source device for performing sputtering and the configuration of the debris mitigation device mounted on the light source device are not limited, and for example, the above-mentioned sputtering phenomenon can be generated using any device that can release ionized gas into the area irradiated with synchrotron radiation.

[0249] In the present disclosure, expressions using "than", such as "greater than A" and "smaller than A", are expressions that comprehensively include both concepts that include the case where something is equivalent to A and concepts that do not include the case where something is equivalent to A. For example, "greater than A" is not limited to cases that do not include the case where something is equivalent to A, but also includes "A or more". Furthermore, "smaller than A" is not limited to "less than A" but also includes "A or less". When implementing the present technology, specific settings and the like can be appropriately adopted from the concepts included in "greater than A" and "smaller than A" so that the effects described above can be achieved.

[0250] It is also possible to combine at least two of the features of the present technology described above. That is, the various features described in each embodiment may be arbitrarily combined without distinguishing between the embodiments. Furthermore, the various effects described above are merely examples and are not intended to be limiting, and other effects may also be achieved.

[0251] P... plasma 1... EUV light 2... buffer gas 10... first vacuum chamber 13... vacuum path 14... high pressure region 20... second vacuum chamber 21... optical element 30, 80, 90... light source section 40... debris reduction device 41... cylindrical member 42... conductance reduction section 44... rotating foil trap cover 45... fixed foil trap 47... introduction port 100... light source device

Claims

1. A light source device comprising: a first vacuum chamber; a light source unit that generates plasma as a light source within the first vacuum chamber; and a debris reduction device that reduces debris dispersed from the plasma, the debris reduction device forming a vacuum path that connects the first vacuum chamber and a second vacuum chamber into which radiation light emitted from the plasma is introduced and allows the radiation light to pass through, and generating a high-pressure region whose pressure is higher than that of the first vacuum chamber and the second vacuum chamber so as to interrupt the vacuum path.

2. A light source device according to claim 1, wherein the debris reduction device has a conductance reduction section that reduces the conductance of the vacuum path between the high pressure region and the second vacuum chamber.

3. A light source device according to claim 2, wherein the conductance reducing portion is a fixed foil trap having a plurality of foils arranged in the vacuum path and a fixing member for fixing the plurality of foils.

4. A light source device according to claim 1, wherein the debris mitigation device is provided between the high pressure region and the first vacuum chamber and has a cylindrical member whose cross section intersecting the path direction of the vacuum path is larger than that of the high pressure region.

5. A light source device according to claim 4, wherein the debris mitigation device comprises a rotary foil trap having a plurality of foils and a rotating member that radially supports the plurality of foils, and the cylindrical member is a rotary foil trap cover that surrounds the rotary foil trap.

6. A light source device according to claim 1, wherein the debris mitigation device does not substantially change the pressure in the first vacuum chamber when the pressure in the second vacuum chamber changes at least within a range equal to or less than the pressure of the high pressure region.

7. A light source device according to claim 1, wherein the pressure in the high pressure region is six times or more the pressure in the first vacuum chamber.

8. A light source device according to claim 1, further comprising: an inlet for introducing a buffer gas for changing the pressure in the second vacuum chamber; and a pressure adjustment mechanism for adjusting the pressure in the second vacuum chamber.

9. A light source device according to claim 8, wherein the high pressure region is a region into which the buffer gas is introduced, and the inlet includes a first inlet connected to the high pressure region.

10. A light source device according to claim 8, further comprising the second vacuum chamber, and the inlet includes a second inlet provided in the second vacuum chamber.

11. A light source device according to any one of claims 1 to 10, wherein the buffer gas is an ionized gas that is ionized by the radiation, and the light source device is capable of normal operation and cleaning operation using the ionized gas.

12. A light source device as described in claim 11, wherein the cleaning operation is an operation in which the ionized gas is introduced into a second vacuum chamber maintained at a first pressure which is the pressure during normal operation, the pressure of the second vacuum chamber is increased to a second pressure higher than the first pressure, and, while maintaining the second pressure, sputtering is performed on a target placed in the second vacuum chamber using the ionized gas ionized by the synchrotron radiation.

13. A light source device according to claim 12, wherein the second pressure is 6 Pa or more.

14. A light source device as described in claim 12, wherein the pressure of the first vacuum chamber during normal operation is set to a third pressure at which the emitted light is stable, and the second pressure is at least three times the third pressure.

15. A light source device according to claim 11, wherein the ionized gas is a rare gas.

16. A light source device as claimed in claim 11, further comprising: the second vacuum chamber; and a light intensity monitor provided in the second vacuum chamber for detecting the intensity of the radiated light, wherein the normal operation and the cleaning operation are switched and executed based on the detection result of the light intensity monitor.

17. A light source device according to claim 8, wherein the pressure adjustment mechanism is at least one of a flow rate adjustment valve that adjusts the flow rate of the buffer gas introduced from the inlet, or an exhaust rate adjustment valve that adjusts the exhaust rate of the second vacuum chamber.

18. A light source device according to claim 1, wherein the synchrotron radiation is EUV light.

19. A light source device as described in claim 1, wherein the light source unit comprises: a pair of rotating electrodes arranged in the first vacuum chamber on either side of a discharge region; a raw material supply unit which supplies plasma raw material to the pair of rotating electrodes; an energy beam injection unit which injects an energy beam that vaporizes the plasma raw material onto a portion of one of the pair of rotating electrodes facing the discharge region; and a voltage source which applies a voltage to the pair of rotating electrodes to plasmaize the plasma raw material vaporized by the energy beam.

20. A light source device as described in claim 1, wherein the light source unit has a rotating body arranged in the first vacuum chamber, a raw material supply unit that supplies plasma raw material to the rotating body, and an energy beam incident unit that incidents an energy beam to convert the plasma raw material supplied to the rotating body into plasma.

21. A cleaning method performed using a light source device, comprising: the light source device having: a first vacuum chamber; a light source unit that generates plasma as a light source in the first vacuum chamber; and a debris reduction device that reduces debris dispersed from the plasma, the debris reduction device forming a vacuum path connecting the first vacuum chamber and a second vacuum chamber into which radiation light emitted from the plasma is introduced and allowing the radiation light to pass, and generating a high-pressure region having a pressure higher than that of the first vacuum chamber and that of the second vacuum chamber so as to block the vacuum path, the cleaning method comprising: a pressure increasing step of introducing an ionized gas that is ionized by the radiation light into the second vacuum chamber maintained at a first pressure that is a pressure during normal operation while the plasma is generated, and increasing the pressure of the second vacuum chamber to a second pressure that is higher than the first pressure; and a sputtering step of performing sputtering using the ionized gas ionized by the radiation light while maintaining the second pressure.

22. A cleaning method as recited in claim 21, wherein the light source device further comprises the second vacuum chamber and a light intensity monitor provided in the second vacuum chamber for detecting the amount of the radiated light, and when the amount of light detected by the light intensity monitor becomes lower than a first threshold, the pressure increasing step and the sputtering step are executed, and further comprising a pressure decreasing step of decreasing the pressure of the second vacuum chamber to the first pressure when the amount of light detected by the light intensity monitor becomes higher than a second threshold that is equal to or higher than the first threshold.

23. A cleaning method for a light source device according to claim 21, wherein the sputtering step includes a step of changing the amount of the radiated light from the amount of the radiated light during the normal operation while maintaining the second pressure.

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