WO2025004512A1 - Light source apparatus and cleaning method - Google Patents

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

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

Conventionally, light source devices have been developed that generate synchrotron radiation using plasma as a light source. 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 purposes such as X-ray photography, non-destructive testing, X-ray analysis, and X-ray spectroscopy. In recent years, extreme ultraviolet light with a wavelength of 13.5 nm (hereinafter referred to as "EUV (Extreme Ultra Violet) light") in the soft X-ray region has also been used as exposure light and inspection light.

Typical EUV light source devices include DPP (Discharge Produced Plasma) light source devices, LDP (Laser Assisted Discharge Produced Plasma) light source devices, and LPP (Laser Produced Plasma) light source devices.

The DPP light source device applies a high voltage between electrodes to which 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 it.

The LDP light source device is an improved version of the DPP light source device, and for example, it supplies liquid high-temperature plasma raw material (such as 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 (such as an electron beam or laser beam) to vaporize the raw material, and then generates high-temperature plasma by discharging the material.

　LPP light source devices excite EUV radiating species with a laser beam or the like to generate high-temperature plasma. A known light source device of this type generates plasma by focusing laser light on droplets of EUV radiating target material, such as tin (Sn) or lithium (Li), ejected in the form of tiny liquid droplets. Another known LPP light source device generates plasma by supplying 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).

In addition, 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 the material of the discharge electrodes that are sputtered as the plasma is generated. If such debris reaches the utilization device that utilizes radiation such as EUV light, it is possible that it will damage or contaminate optical elements such as reflective films installed in the utilization device. For this reason, the light source devices are equipped with a debris reduction device (also called a DMT (Debris Mitigation Tool)) that captures debris between the plasma and the utilization device to prevent debris dispersed from the plasma from entering the utilization device.

In this way, in a light source device that uses plasma as a light source to generate radiation, 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 the discharge space where plasma is generated by discharge and the collection space where the EUV light collector is provided. In addition, a gas curtain is formed downstream of the aperture member to reduce debris from the plasma. This configuration makes it possible to maintain a pressure difference between the collection space and the discharge space and efficiently reduce debris (see Patent Document 1, paragraphs [0027] and [0033], Figure 1, etc.).

Incidentally, there are cases where the pressure in the space on the introduction side where 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 and the like. In this method, a reaction partner containing hydrogen or halogen is supplied near the optical element while the irradiation device is in operation, and the reaction partner that has become a radical due to the light is used to clean debris and the like that has adhered to the optical element (see, for example, paragraphs [0114]-[0116], Figure 1 in the specification of Patent Document 1). In this method, it is considered that the pressure in the space in which the optical element is located changes 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, etc.

JP 2007-179881 A Special Publication No. 2006-529057

In this way, 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 conditions for generating plasma on the light source side may be disrupted, and the emission of synchrotron radiation may become unstable. For this reason, there is a demand for technology that can suppress changes in pressure on the light source side caused by changes in pressure on the introduction side of the synchrotron radiation.

In view of the above, the object of the present invention is to provide a light source device and cleaning method that can suppress changes in pressure on the light source side caused by changes in pressure on the input side of the radiation light.

In order 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 reduction device.
The light source unit generates plasma that serves as a light source in the first vacuum chamber.
The debris mitigation device is a debris mitigation device that reduces debris dispersed from the plasma, and forms a vacuum path that connects the first vacuum chamber and a second vacuum chamber into which radiation emitted from the plasma is introduced and allows the radiation to pass through, 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.

In this light source device, the debris reduction device forms a vacuum path connecting a first vacuum chamber that generates plasma and a second vacuum chamber into which radiation from the plasma is introduced. Furthermore, a high-pressure region with a pressure higher than the pressure in the first vacuum chamber and the pressure in the second vacuum chamber is formed so as to block 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 radiation introduction side.

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

The conductance reducing portion may be a fixed foil trap having a plurality of foils disposed in the vacuum path and a fixing member that fixes the plurality of foils.
This allows for debris reduction with fixed foil traps.

The debris mitigation apparatus may include a tubular member disposed between the high pressure region and the first vacuum chamber, the tubular member having a cross section intersecting with a path direction of the vacuum path larger than that of the high pressure region.
This makes it possible, for example, to reduce the pressure in the high pressure region over a short distance and maintain it at the pressure of the first vacuum chamber.

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 which case the cylindrical member may be a rotary foil trap cover that surrounds the rotary foil trap.
This allows for debris reduction with a rotating foil trap.

The debris mitigation apparatus may allow the pressure in the first vacuum chamber to remain substantially unchanged when the pressure in the second vacuum chamber varies at least within a range equal to or less than the pressure of the high pressure region.
This makes it possible to sufficiently maintain the pressure in the first vacuum chamber even if the pressure in the second vacuum chamber changes, for example.

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

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 for adjusting the pressure in the second vacuum chamber.
This makes it possible to easily adjust the pressure in, for example, the second vacuum chamber, and thus realize various operation modes.

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 leading to the high pressure region.
This makes it possible, for example, to change the pressure in the second vacuum chamber while realizing a high pressure region.

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

The buffer gas may be an ionized gas that is ionized by the radiation. In this case, the light source device may be capable of 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 radiation, for example.

The cleaning operation may be an operation of introducing the ionized gas into a second vacuum chamber maintained at a first pressure which is the pressure during normal operation, increasing the pressure of the second vacuum chamber to a second pressure higher than the first pressure, and performing sputtering on a target placed in the second vacuum chamber using 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 disposed in the second vacuum chamber at a desired rate.

The second pressure may be 6 Pa or more.
This makes it possible to perform sputtering at a desired rate, for example.

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, for example, sputtering to be carried out at a relatively high rate.

The ionizable gas may be a noble gas.
This makes it possible to prevent, for example, the members inside each chamber from being corroded by the ionized gas, and also makes it possible to easily treat the gas exhausted from each chamber.

The light source device may further include the second vacuum chamber and a light amount monitor provided in the second vacuum chamber and configured to detect an amount of the radiated light. In this case, the normal operation and the cleaning operation may be switched and executed based on a detection result of the light amount monitor.
This makes it possible to perform cleaning in response to contamination of, for example, optical elements.

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, or an exhaust rate adjustment valve that adjusts the exhaust rate of the second vacuum chamber.
This makes it possible to precisely adjust the pressure in, for example, the second vacuum chamber.

The radiation may be EUV light.
This makes it possible to realize, for example, an EUV light source device that is easy to maintain and has a stable light output.

The light source unit may include a pair of rotating electrodes arranged in 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 facing the discharge region, and a voltage source that applies a voltage to the pair of rotating electrodes to convert the plasma raw material vaporized by the energy beam into plasma.

The light source unit may have a rotating body disposed 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.

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 being generated, and increasing the pressure of the second vacuum chamber to a second pressure that is higher than the first pressure.
a sputtering step of performing sputtering on a target disposed in the second vacuum chamber with the ionized gas ionized by the synchrotron radiation while maintaining the second pressure;

This makes it possible to suppress changes in pressure on the light source side caused by changes in pressure on the side where the synchrotron radiation is introduced, and makes it possible to generate stable synchrotron radiation even when sputtering is performed by introducing ionized gas. This makes it possible to easily clean optical elements and the like installed in the second vacuum chamber.

The light source device may further include the second vacuum chamber and a light quantity monitor provided in the second vacuum chamber and detecting the quantity of the emitted light. In this case, the pressure increasing step and the sputtering step may be executed when the quantity of light detected by the light quantity monitor becomes lower than a first threshold. The light source device may further include a pressure decreasing step of decreasing the pressure of the second vacuum chamber to the first pressure when the quantity of light detected by the light quantity monitor becomes higher than a second threshold equal to or higher than the first threshold.
This makes it possible to perform cleaning in response to contamination of, for example, optical elements.

The sputtering step may include a step of changing an amount of the synchrotron radiation from an amount of the synchrotron radiation during the normal operation while maintaining the second pressure.
This allows fine control of, for example, the sputtering rate.

As described above, according to the present invention, changes in pressure on the light source side caused by changes in pressure on the introduction side of the radiation light are 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.

1 is a schematic diagram showing a configuration example of a light source device according to an embodiment of the present invention; FIG. 2 is a schematic diagram showing a configuration example of a debris reduction device mounted on a light source device. FIG. 2 is a schematic cross-sectional view showing a configuration example of a rotary foil trap. FIG. 2 is a schematic front view showing a configuration example of a rotary foil trap. FIG. 2 is a schematic cross-sectional view showing a configuration example of a rotary foil trap cover. FIG. 2 is a schematic front view showing a configuration example of a rotary foil trap cover. FIG. 2 is a schematic cross-sectional view showing a configuration example of a fixed foil trap. FIG. 2 is a schematic front view showing a configuration example of a fixed foil trap. FIG. 2 is a schematic cross-sectional view showing a configuration example of a fixed foil trap cover. FIG. 2 is a schematic front view showing a configuration example of a fixed foil trap cover. 1 is a schematic cross-sectional view showing an example of the configuration of a debris reduction device. 11 is a graph showing a simulation result of the pressure inside the light source device. 4 is a graph showing a relationship between the pressure in a first vacuum chamber and a second vacuum chamber. FIG. 1 is a schematic diagram showing an example of the arrangement of samples used in a sputtering experiment. 1 is a graph showing the relationship between sputtering rate and pressure. 1 is a graph showing the relationship between sputter rate, pressure, and sample position. 1 is a graph showing the relationship between the sputtering rate and the emission frequency of plasma. 4 is a flowchart showing an example of the operation of the light source device. FIG. 2 is a schematic diagram illustrating a sputtering region where sputtering occurs. FIG. 1 is a schematic diagram showing an example of the configuration of an optical system using a light shielding plate. FIG. 13 is a schematic diagram showing another example of the configuration of an optical system using a light-shielding plate. FIG. 2 is a schematic diagram showing a configuration example of an LPP type light source unit. FIG. 13 is a schematic diagram showing another example of the configuration of the light source unit of the LPP method;

Below, an embodiment of the present invention will be described with reference to the drawings.

[Light source device overview]
FIG. 1 is a schematic diagram showing a configuration example of a light source device according to an embodiment of the present invention. FIG. 1 is a schematic cross-section of the light source device 100 cut horizontally at a position of a predetermined height from the installation surface, as viewed from the positive side of the 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 upper side, and the negative side is the lower side). Of course, the application of this technology is not limited to the orientation in which the light source device 100 is used.

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.

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

In this embodiment, EUV light 1 is an example of radiation emitted from plasma. 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, etc. are emitted.

The light source device 100 has a first vacuum chamber 10, a second vacuum chamber 20, a light source unit 30, and a debris reduction 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 the EUV light 1 emitted from the plasma P is introduced. The debris reduction device 40 is a device that reduces debris dissipated from the plasma P between the first vacuum chamber 10 and the second vacuum chamber 20.

[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.

The inside of the first vacuum chamber 10 is maintained at a reduced pressure atmosphere 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, etc. to be inserted into the first vacuum chamber 10 while maintaining the reduced pressure atmosphere inside the first vacuum chamber 10.

A transparent window 11 is disposed on the side wall 10b on the front side of the first vacuum chamber 10. The transparent window 11 is made of a material that is transparent to the laser beam LB described below. The specific configuration of the transparent window 11, such as its material and shape, is not limited. A through hole 12 for connecting to the second vacuum chamber 20 is provided on the right side wall 10c of the first vacuum chamber 10. In this embodiment, a debris reduction device 40 is disposed inside the first vacuum chamber 10 so as to cover the through hole 12.

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

The interior of the second vacuum chamber 20 is maintained at a reduced pressure atmosphere below a predetermined pressure by a vacuum pump (not shown). A through hole 22 that communicates 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. In addition, for example, an exit port (not shown) for emitting the EUV light 1 that has passed through the optical element 21, etc. are appropriately provided in the second vacuum chamber 20.

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 on the utilization device for introducing the EUV light 1 is used as the second vacuum chamber.

[Light source]
The light source unit 30 generates plasma P, which serves as a light source, in 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.

The discharge module 31 is a module that performs discharge to generate plasma P within 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.

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.

The discharge electrodes EA and EB have a disk shape. The discharge electrodes EA and EB 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.

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 at a distance from each other. The discharge electrodes EA and EB are also arranged so that a portion of the periphery of each of the discharge electrodes EA and EB is close to each other. The gap at the position where the peripheries of the discharge electrodes EA and EB are closest to each other becomes the discharge region D formed by the discharge electrodes EA and EB.

Furthermore, the discharge electrode EA is positioned so that the lower part of the discharge electrode EA is immersed in the plasma raw material SA stored in the container CA. Similarly, the discharge electrode EB is positioned so that the lower part of the discharge electrode EA is immersed in the plasma raw material SB.

The motor MA rotates the discharge electrode EA. The motor MA has a rotation axis JA. The base part of the motor MA is placed outside the first vacuum chamber 10 on the left side, and the rotation axis JA connected to the base part 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 of the discharge electrode EA (the center of the circular surface).

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 supports the rotating shaft JA so that it can rotate freely while maintaining the reduced pressure atmosphere inside the first vacuum chamber 10.

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

The discharge electrodes EA and EB are arranged so that their axes (extension directions of the rotation shafts) 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 shafts JA and JB in the depth direction (up and down direction in FIG. 1, Z direction) 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 shaft JB are arranged slightly to the left of the discharge electrode EA, motor MA and rotation shaft JA.

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, and the discharge electrodes EA and EB rotate at a predetermined number of rotations.
Furthermore, the control unit 32 controls the operation of the pulsed power supply unit 33 and the timing of laser beam irradiation by the laser source 34 .

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, and a storage device such as a HDD. 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 (e.g., an application program).

The pulsed power supply unit 33 generates a discharge in the discharge region D by supplying pulsed power to the discharge electrodes EA and EB. Power feed lines QA and QB are connected to the pulsed power supply unit 33. The power feed line QA is inserted into the first vacuum chamber 10 via a feedthrough FA and is connected to a container CA. The power feed line QB is inserted into the first vacuum chamber 10 via a feedthrough FB and is connected to a container CB.

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. For example, a Nd:YVO ₄ (Neodymium-doped Yttrium Orthovanadate) laser device is used as the laser source 34. In this case, the laser source 34 emits a laser beam LB in the infrared region with a wavelength of 1064 nm. 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 of the laser source 34 and the wavelength of the irradiated laser beam LB, is not limited.

The focusing lens 35 is disposed on the optical path of the laser beam LB outside the first vacuum chamber 10. The spot diameter of the laser beam LB is adjusted by the laser beam LB emitted by the laser source 34 being incident on the focusing lens 35.

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 focusing lens 35. Therefore, the laser beam LB that passes through the focusing lens 35 is incident on the movable mirror.

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 periphery of the discharge electrode EA near the discharge region D inside the first vacuum chamber 10. Note that by changing the position of the movable mirror 36, it is possible to adjust the irradiation position of the laser beam LB with respect to the discharge electrode EA.

In this way, in the light source unit 30, the discharge electrodes EA and EB are arranged in the first vacuum chamber 10 on either side of the discharge region D. Furthermore, 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 the raw material supply unit.

In addition, the laser source 34, the condenser lens 35, and the movable mirror 36 cause the laser beam LB to be incident on the portion of one of the discharge electrodes EA and EB, the discharge electrode EA, that faces the discharge region D. 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 gas-phase plasma raw material SA. Similarly, the plasma raw material SB transported by the discharge electrode EB also becomes gas-phase plasma raw material SB in the discharge region D. In this embodiment, the energy beam incident portion is realized using the laser source 34, the condenser lens 35, and the movable mirror 36. In addition, the laser beam LB corresponds to the energy beam that vaporizes the plasma raw material.

The pulsed power supply unit 33 also applies a voltage (pulsed power) to the discharge electrodes EA and EB 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 the current, generating plasma P. In this embodiment, the pulsed power supply unit 33 corresponds to a voltage source.

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 FIG. 1, an example of the optical path of the EUV light 1 is shown by a dashed arrow. The plasma P corresponds to one embodiment of the light source related to this technology.

In this embodiment, the inside of the first vacuum chamber 10 is maintained at a reduced pressure atmosphere below 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.

In addition, 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. More specifically, the debris includes ions, neutral atoms, and electrons that move at high speed. This debris gains large kinetic energy through the contraction and expansion processes of the plasma P. Part of the debris is dispersed towards the debris mitigation device 40.

[Debris Reduction Device]
Fig. 2 is a schematic diagram showing an example of the configuration of the debris mitigation device 40 mounted on the light source device 100. Fig. 2 shows a cross section of the light source device 100 cut in the XZ plane as viewed from the front side. Note that Fig. 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 in the illustration.

The debris mitigation device 40 is a device that reduces debris dispersed from the plasma P. The debris mitigation device 40 is positioned so as to overlap with the optical path of the EUV light 1 traveling 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 sometimes called a DMT (Debris Mitigation Tool).

In this embodiment, a foil trap (a rotating foil trap 43 and a fixed foil trap 45, described below) is used as a mechanism 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 mm-sized debris to small atomic-sized debris.

Furthermore, the debris reduction device 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).

Such a vacuum path 13 is formed inside the debris mitigation device 40. The internal space of the first vacuum chamber 10 and the internal space of the second vacuum chamber 20 are connected by this vacuum path 13 without leaks. 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 without being blocked. Here, the direction of the straight path through which the EUV light 1 passes is described as the path direction of the vacuum path 13. In Figure 2, the path direction of the vacuum path 13 is diagrammatically illustrated using a dotted arrow.

Furthermore, the debris mitigation device 40 generates a high pressure region 14 , the pressure of which 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, the region that blocks the vacuum path 13 means, for example, a region that completely covers the cross section of the vacuum path 13 and intersects with 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 so as 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 diagrammatically illustrated by a hatched region using dots.

As described above, the high pressure region 14 is a region in which it is possible to maintain an internal pressure higher than the pressure in either the first vacuum chamber 10 or the second vacuum chamber 20. In other words, 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 reduction device 40 is basically used in a state in which the high pressure region 14 has been generated.

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 change in pressure. This makes it difficult for the change in pressure 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 of the first vacuum chamber 10 from the pressure of the second vacuum chamber 20.

The debris reduction device 40 is provided with a cylindrical member 41 and a conductance reduction section 42 as a configuration for forming the high pressure region 14.

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 (the exit side opening KO of the rotating foil trap cover 44) that is connected to the high pressure region 14, and an opening (the entrance side opening KI of the rotating foil trap cover 44) that is connected to the first vacuum chamber 10, and forms the vacuum path 13.

The cylindrical member 41 is a member whose cross section intersecting the path direction of the vacuum path 13 is larger than that of the high pressure region 14. In other words, the cylindrical member 41 is a member that expands the width 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 out from the high pressure region 14 to the cylindrical member 41 side is diffused into a wide space while being caught in the rotary foil trap 43 described later, and is exhausted by the vacuum pump (first vacuum pump 54) that exhausts the first vacuum chamber 10. For this reason, it is possible to reduce the pressure of the high pressure region 14, for example, over a short distance. In other words, the pressure of the vacuum path 13 drops suddenly while passing through the cylindrical member 41. As a result, the pressure of the first vacuum chamber 10 is maintained almost without being affected by the pressure of the high pressure region 14.

The conductance reduction section 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 reduction section 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. Between these two openings, a member that reduces the conductance of the vacuum compared to the other vacuum paths 13 is placed.

The vacuum conductance is a parameter that indicates how easily the buffer gas 2 flows, and corresponds to, for example, the inverse 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 member 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 fully absorb changes in pressure on the introduction side.

Here, the configuration for capturing debris will be described. As shown in FIG. 2, the debris reduction device 40 has a rotating foil trap 43, a rotating foil trap cover 44, a fixed foil trap 45, and a fixed foil trap cover 46.

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.

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 rotating foil trap cover 44. Note that the rotating foil trap cover 44 and the fixed foil trap cover 46 do not necessarily need to be completely connected, and for example, there may be some gaps 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 arranged on the second vacuum chamber 20 side.

The above-mentioned vacuum path 13, cylindrical member 41, and conductance reduction section 42 are realized by utilizing these configurations for capturing debris. In this embodiment, the hollow area formed by connecting the rotating foil trap cover 44, the fixed foil trap cover 46, and the fixed foil trap 45 becomes the vacuum path 13. The rotating foil trap cover 44 also functions as the cylindrical member 41. The fixed foil trap 45 also functions as the conductance reduction section 42. Therefore, a high pressure area 14 is formed in the space from the rotating foil trap cover 44 to the fixed foil trap 45. The specific configuration of each foil trap etc. will be explained in detail later.

[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 of 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 for adjusting the flow rate of the buffer gas 2 is attached to the pipe.

In this embodiment, the high pressure region 14 is the region in the debris mitigation device 40 where the buffer gas 2 is introduced, and the debris mitigation device 40 is provided with an inlet 47 that leads 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 of the high pressure region 14 at a high level. This inlet 47 is provided, for example, in the fixed foil trap cover 46. In FIG. 2, the inlet 47 that leads to the high pressure region 14 is diagrammatically illustrated by a dotted circle. In this embodiment, the inlet 47 that leads to the high pressure region 14 corresponds to the first inlet.

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.

In this way, 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 is connected to the second vacuum chamber 20 in which optical elements and the like for utilizing the EUV light 1 are housed, via a vacuum path 13 formed by the debris reduction device 40. In addition, an inlet 47 for a buffer gas 2 is provided in the debris reduction device 40 (high pressure region 14) or downstream of the debris reduction device 40 (on the second vacuum chamber 20 side).

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 active gases such as hydrogen gas and halogen gas, there is no need to worry about argon gas corroding metals in the chamber. In addition, since argon gas can be exhausted without any inactivation treatment, the exhaust system can be made smaller and less expensive than when exhausting active gases.

Furthermore, it is known that light in the EUV region excites and ionizes argon atoms (Ar). Therefore, it is possible to generate argon plasma 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. Using this phenomenon, the light source device 100 performs cleaning operations, which will be described later.

Although argon atoms have some absorption at wavelengths of 13.5 nm, the amount of absorption is an order of magnitude lower than that of light at 30 nm to 80 nm. Therefore, there is little attenuation of the actinic wavelength of 13.5 nm, and it is possible to ensure a sufficient amount of light even when argon gas is used as buffer gas 2.

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

The first partition plate 16 is a plate-shaped member with a larger planar size than the debris reduction device 40 (rotary foil trap cover 44), and is arranged to cover the side of the debris reduction device 40 facing 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 reduction device 40 side or into the second vacuum chamber 20, etc.

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 specified 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.

[Exhaust system]
As shown in FIG. 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.

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 the first vacuum pump 54. The first vacuum gauge 51 is connected to the measurement hole 19 and detects the pressure of 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 the second vacuum pump 55. The second vacuum gauge 53 is connected to the measurement hole 29 and detects the pressure of the second vacuum chamber 20.

In this way, in the light source device 100, the first vacuum chamber 10 and the second vacuum chamber 20 are each evacuated separately. Furthermore, the high pressure region 14 described above is formed in the vacuum path 13 connecting each vacuum chamber, 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 evacuation is possible, which evacuates each internal space independently.

In this embodiment, the pressure in 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 in the second vacuum chamber 20. The pressure adjustment mechanism is, for example, a mechanism that adjusts 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.

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.

Also, for example, the second vacuum valve 52 that adjusts the exhaust volume of the second vacuum chamber 20 is used as a pressure adjustment mechanism. In this case, for example, by reducing the exhaust volume, the flow rate of the buffer gas 2 flowing out from the second vacuum chamber 20 is reduced, 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 an exhaust volume adjustment valve.

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, making it possible to realize various operating modes.

[Light level monitor]
The light source device 100 has a light intensity monitor that detects the amount of 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 side wall 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 amount of EUV light 1 from the plasma P, i.e., the emission intensity of the plasma P.

The second light intensity monitor 25b is provided in the second vacuum chamber 20 and detects the amount of 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. Without being limited to this, for example, the EUV light 1 that has been branched using a reflecting mirror or the like may be detected. This allows the second light intensity monitor 25b to detect the amount of EUV light 1 that has been guided through the collector mirror or reflecting mirror.

For example, if the surface of the collector mirror or reflector mirror becomes contaminated by 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. Taking advantage of this, the detection result of the second light amount monitor 25b is used to determine whether or not to perform a cleaning operation.

[Configuration of each part of the debris mitigation device]
The configuration of each part of the debris mitigation device 40 will be specifically described below.

[Rotary foil trap]
Fig. 3 is a schematic cross-sectional view showing a configuration example of the rotary foil trap 43. Fig. 4 is a schematic front view showing a configuration example 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 60, and an outer ring 61. The central support 60 is connected to a shaft member 63 that rotates around a rotation axis.

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 around the central support 60 and is connected to the tip of each foil F that extends radially from the central support 60. In this embodiment, the central support 60 corresponds to a rotating member. Each foil F is radially arranged around the central support 60 at approximately equal angular intervals. At this time, each foil F is on a plane that includes the central axis C0 of the central support 60. The material of the rotating foil trap 43 is, for example, a high-melting point metal such as tungsten (W) or molybdenum (Mo).

As shown in FIG. 4, the multiple foils F of the rotating foil trap 43 are arranged parallel to the light 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 rotating 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 rotating foil trap 43 (also called the transmittance).

[Rotating foil trap cover]
Fig. 5 is a schematic cross-sectional view showing a configuration example of the rotary foil trap cover 44. Fig. 6 is a schematic front view showing a configuration example 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 the debris captured by the rotary foil trap 43 from scattering inside the first vacuum chamber 10.

In the following, the side where the EUV light 1 is incident (the side that is directed toward the plasma P) is referred to as the incident side, and the opposite side is 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'.

The entrance side opening KI is provided at a position where the EUV light entering the rotating 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 the 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 that passes 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 the light that is introduced into the first light quantity monitor 25a.

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

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

The internal space of the rotary foil trap cover 44 is large enough to accommodate the rotary foil trap 43. This is a size sufficiently larger than the diameter of the exit opening KO that connects to the second vacuum chamber 20. In this way, when viewed from the exit opening KO, the width of the space that becomes the vacuum path 13 (the cross-sectional area that intersects with the path direction) suddenly expands. In addition, the effect of the rotation of the rotary foil trap is also combined, making it possible to suddenly reduce the pressure of the buffer gas 2.

[Fixed foil trap]
7 is a schematic cross-sectional view showing a configuration example of the fixed foil trap 45. FIG. 8 is a schematic front view showing a configuration example of the fixed foil trap 45. The fixed foil trap 45 is a foil trap FT having a plurality of 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 a central path through which a ray bundle (EUV extracted light) of the EUV light 1 extracted from the through hole 12 of the first vacuum chamber 10 passes. The central path is, for example, a path connecting the emission point of the plasma P and the center point of the through hole 12.

FIG. 7 is a cut through the fixed foil trap 45 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.
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 the present embodiment, the fixed frame 66 corresponds to a fixing member.

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 is, for example, rectangular 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 direction of the beam of the EUV light in a cross section cut along the central path.

The multiple foils F of the fixed foil trap 45 serve to reduce the conductance of the portion by finely dividing the space in which the fixed foil trap 45 is disposed. For example, the buffer gas 2 is supplied to the fixed foil trap 45 from the high pressure region 14.
The buffer gas 2 is less likely to flow through the fixed foil trap 45 and is therefore more likely to remain between the foils F.

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 trapped in the fixed foil trap 45. Collisions with gas also cause the debris to change direction. The fixed foil trap 45 captures the debris that has slowed down and changed direction in this way using the foil F or fixed frame 66. In this way, by providing the rotating foil trap 43 and the fixed foil trap 45, it is possible to adequately capture the debris.

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 in the high pressure region 14 to leak, 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.

[Fixed foil trap cover]
Fig. 9 is a schematic cross-sectional view showing a configuration example of the fixed foil trap cover. Fig. 10 is a schematic front view showing a configuration example of the 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 rotary 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 to the EUV light 1 emission side.

The support plate 68 is a plate to which the fixed foil trap 45 is fixed. The surrounding portion 69 is formed to surround the side of the fixed foil trap 45. The opening 67 provided in the support plate 68 is the entrance port for the EUV light 1. An inlet 47 for introducing buffer gas 2 is 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 buffer gas 2 is supplied from the inlet 47, the space constituting the opening 67 becomes the high pressure region 14.

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

Specifically, the rotary foil trap 43 is disposed inside the rotary foil trap cover 44. Further, the 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 the opening 67 overlap with each other.
Moreover, inside the fixed foil trap cover 46, the fixed frame 66 of the fixed foil trap 45 is connected so as to cover the opening 67 of the support plate 68. Moreover, the 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).

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 reduction device 40. Below, we will specifically explain the pressure inside the light source device 100 when the debris reduction device 40 is used.

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

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).

FIG. 12 shows the pressure profile (solid line graph) when the pressure P2 of the second vacuum chamber 20 is set to 0.7 Pa, and the pressure profile (dotted line graph) when P2 is set to 5 Pa. In both graphs, the simulation was performed with the exhaust volume 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.

For example, high pressure is maintained in the shaded area centered on point Oc. This shaded area is high pressure area 14. For example, the area formed by the entrance side opening KI of the rotating foil trap cover 44 and the opening 67 of the fixed foil trap cover 46 becomes high pressure area 14. From this simulation, when P2 = 0.7 Pa, the pressure Ph of high pressure area 14 is 18 Pa or more compared to the pressure near point Oa.

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 drops almost 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 drops toward point Ob. The part where the pressure gradient is bent corresponds to the end of the entrance side of the rotary foil trap 43. The drop in pressure up to point Ob occurs due to the sudden expansion of the buffer gas 2 inside the rotary foil trap cover 44.

Now, suppose 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. Here, the increase in Ph is about 0.5 Pa, which is about 1/8 of the increase in P2 (4.3 Pa). In this way, 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.

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.

In this way, the debris reduction device 40 can separate P1 and P2 by generating a high pressure region 14 that blocks the vacuum path 13. As a result, it is possible to suppress changes in pressure P1 on the light source side caused by changes in pressure P2 on the EUV light introduction side.

In addition, taking into account the debris capture capability of the debris reduction 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 adequately capturing debris from the plasma P.

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 is P1, and the horizontal axis is P2. Here, the pressure P2 of the second vacuum chamber 20 was changed while keeping the exhaust volume of the first vacuum chamber 10 constant so that P1 was approximately 2 Pa.

As shown in the graph in Figure 13, it was found that even when the pressure P2 of the second vacuum chamber 20 was changed within a range of 20 Pa or less, the pressure P1 of the first vacuum chamber 10 showed a value of around 2 Pa. In other words, even though the pressure was high on the downstream side across the debris reduction device 40, 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 of the first vacuum chamber 10 where the plasma P was generated could be kept constant regardless of whether the pressure P2 of the second vacuum chamber 20 was high or low.

When measuring the pressure shown in FIG. 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. As a result, 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 below 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.

[Sputtering by EUV light and buffer gas]
Up to this point, the description has been mainly given of the pressure characteristics in the light source device 100. In the following, sputtering caused by the EUV light 1 and the buffer gas 2 in the light source device 100 will be described.

In general, the optical system that handles the EUV light 1 can become contaminated by debris dispersed from the plasma P and carbon-based deposits (carbon contamination), which can degrade its performance. In addition, high-speed debris flying inside the chamber can collide with the optical system, potentially scraping off the reflective film on the surface of the optical system. As a countermeasure to this, a method is known in which high-speed debris is reduced by colliding it with buffer gas 2, for example. In addition, a method is known in which debris and carbon contamination that has adhered to the optical system can be removed by using radicals from active gases, etc.

The inventors have studied a method of protecting the optical elements 21 and other elements downstream of the debris mitigation device 40 (DMT) by utilizing the pressure distribution of the 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.

On the other hand, debris that is 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 the optical element 21 to be sputtered. In response, the argon gas pressure around the optical element 21 (pressure in the second vacuum chamber 20) was increased in the hope of suppressing sputtering of the optical element 21 due to debris, but it was found that this actually promoted sputtering of the optical element 21.

In this way, the inventors have found that sputtering occurs by introducing argon gas. It is believed that this is because argon gas ionized by the EUV light 1 collides with the optical element 21, causing the surface of the optical element 21 to be sputtered. For example, argon gas is ionized by irradiation with the EUV light 1 to form 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 to cause sputtering. It is believed that the ions are accelerated because of a potential difference between the EUV-induced plasma and the optical element 21. In this way, sputtering by ionized gas can be achieved by using an ionized gas (argon gas in this case) that is ionized by the EUV light 1 as the buffer gas 2. The results of the sputtering experiment are described below.

[Sputtering experiment]
14 is a schematic diagram showing an example of the arrangement of samples used in a sputtering experiment. As shown in Fig. 14A and Fig. 14B, in the experiment, a sample 27 for sputtering was arranged on a stage 26 arranged downstream of a debris mitigation device 40. Here, the sample 27 was a sample on which a thin film of ruthenium (Ru) was formed, and the sputtering rate for the sample 27 was measured. The thin film of ruthenium is a material used for a reflective surface that reflects, for example, EUV light 1.

In FIG. 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 of the first vacuum chamber 10 (pressure in the area on the left side of the debris mitigation device 40 in the figure) where the plasma P that radiates the EUV light 1 is generated is set to approximately 2 Pa. The pressure P2 of the second vacuum chamber 20 (pressure in the area on the left side of the debris mitigation device 40 in the figure) where the sample 27 is placed is set in the range of approximately 0.5 Pa to approximately 11 Pa.

As shown in FIG. 14A, five samples 27 were placed on the stage 26 so that they would be irradiated with the EUV light 1. Below, 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 approximately 35 cm. The intervals between Samples 1 to 5 were approximately 5 cm.

In FIG. 14B, the tilt angle of the stage 26 with respect to the central path O of the EUV light 1 was set between about 25° and about 45°. The pressure P1 in the first vacuum chamber 10 was set to about 2 Pa, as in FIG. 14A. The pressure P2 in the second vacuum chamber 20 was set in the range of about 13 Pa to about 19 Pa. One sample 27 (referred to as Sample 6) was placed on the stage 26 so that it was 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 about 35 cm, as in the case of Sample 1 in FIG. 14A.

15 is a graph showing the relationship between the sputtering rate and pressure. The horizontal axis of the graph is the pressure P2 [Pa] of 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 represents the film thickness (nm) sputtered when the number of times the plasma P emits light (the number of power pulses) is 1×10 ⁹ times.

Among the points shown in FIG. 15, the points other than the rightmost point are results obtained by evaluating the sputtering rate for Sample 1 shown in FIG. 14A, and are results at an inclination angle of about 20°.
14B, the sputtering rate was evaluated when the tilt angle was set to about 25°. The distance from the plasma P to each point was set to about 35 cm.

As shown in FIG. 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.

Figure 16 is a graph showing the relationship between sputter rate, pressure, and sample position. In Figure 16, the sputter rate for the five samples 27 (Sample 1 to Sample 5) shown in Figure 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 is shown in the form of a bar graph using rectangular columns. Note that for the condition of P2 = 11 Pa, only the data for Sample 1, Sample 3, and Sample 5 are shown.

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 below 5.5 Pa, but when P2 = 11 Pa, a significant increase in the sputtering rate is observed. From this, as with the data shown in Figure 15, it can be seen that below a certain pressure, a sufficient sputtering rate is not obtained and significant sputtering does not occur.

For example, when P2 = 0.7 Pa, the sputter rate is highest in Sample 1, which is close to the plasma P, and the sputter rate decreases the further away from the plasma P; for example, in Sample 5, the sputter rate is approximately 0. In other words, it can be seen that the sputter 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 sputter rate is generally low. Also, even at pressures (P2 = 11 Pa) where the sputter rate increases, the sputter rate decreases the further away from the plasma P. From this, it can be seen that, regardless of pressure P2, the sputter rate decreases the greater the distance from the plasma P.

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

As shown in Figure 17, when the emission frequency was 6000 Hz, the sputtering rate increased compared to when it was 3000 Hz. In other words, it was confirmed that the sputtering rate increases according to the emission frequency. Generally, when the emission frequency is increased, the average power (amount of light) 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 Figure 17.

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 a case, P2 can be increased to ensure sufficient cleaning speed. Conversely, when it is difficult to adjust P2, the sputtering rate can be changed by adjusting the emission frequency.

[Spatter cleaning operation]
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 utilizing sputtering, debris and carbon contamination adhering to the optical element 21 can be removed, and the optical element 21 can be sputter cleaned.

The inventors focused on this point and equipped the light source device 100 with the function of performing a cleaning operation using an ionized gas, which is the buffer gas 2, in addition to the normal operation of supplying the EUV light 1 to the utilization device, etc. In other words, the light source device 100 is capable of both normal operation and cleaning operation.

Normal operation is, for example, an 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 an 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 normal pressure P2n. In this embodiment, normal pressure P2n corresponds to the first pressure.

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 a pressure at which the plasma P is stably generated, and is, for example, about 2 Pa. Note that the specific value of P0 is not limited. For example, a pressure at which the plasma P can be stably generated may be set to P0 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.

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

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.

For example, if the optical element 21 provided in the second vacuum chamber 20 becomes contaminated with debris flying in from the plasma P, which is the light source, it is possible to clean the optical element 21 by changing the pressure P2 in the second vacuum chamber 20 while the light source is turned on in the first vacuum chamber 10, thereby scraping off the debris adhering to the optical element 21 through the sputtering phenomenon. In this way, the light source device 100 can clean the optical element 21 provided in the second vacuum chamber 20 while stably generating, for example, EUV light 1.

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

In other words, the cleaning operation involves introducing buffer gas 2 into the second vacuum chamber 20, which is maintained at normal pressure P2n, which is the pressure during normal operation, increasing the pressure in the second vacuum chamber 20 to a cleaning pressure P2c that is higher than the normal pressure P2n, and, while maintaining the cleaning pressure P2c, sputtering the optical element 21 placed in the second vacuum chamber 20 with the buffer gas 2 ionized by the EUV light 1.

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. With this method, it is possible to easily perform the cleaning operation by simply adjusting, for example, the exhaust volume of the second vacuum chamber 20.

Even if the pressure in the second vacuum chamber 20 changes, the pressure P1 in the first vacuum chamber 10 hardly changes due to the action of the high pressure region 14 of the debris reduction device 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 volume of the first vacuum chamber 10.

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

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

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, it is possible to sufficiently lower the sputtering rate, and a state in which no significant sputtering occurs during normal operation can be maintained. This makes it possible to avoid situations in which the optical element 21 is unnecessarily sputtered during normal operation.

In 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 according to the cleaning pressure P2c and the desired amount of sputtering. The cleaning pressure P2c is then maintained for the sputtering time. Alternatively, it is also possible to maintain the cleaning pressure P2c until the characteristics of the optical element 21 (such as the amount of reflected light) return to the state before contamination.

The sputtering process may also include a process of changing the amount of EUV light 1 from the amount of 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 amount of EUV light 1 (average power) is changed. Therefore, in this process, any parameter that can change the amount of EUV light 1 is adjusted.

For example, the emission frequency may be adjusted as in the case of FIG. 17. In this case, to increase the sputtering rate, the emission frequency may be increased. Also, 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. By increasing the irradiation intensity or pulse power of the laser beam, it is possible to increase the sputtering rate.

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 position of the optical element 21 closer to the plasma. Furthermore, from the experiments in Figures 14A and 14B, it was found 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. Besides this, the types of parameters that are adjusted in the sputtering process are not limited.

[Operation of light source device]
Fig. 18 is a flowchart showing an example of the operation of the light source device 100. The process shown in Fig. 18 is a process for executing the cleaning method according to the present embodiment. In the following, an example of cleaning the optical element 21 provided in the second vacuum chamber 20 will be described.

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

The process shown in FIG. 18 may be performed automatically using a controller 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. 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. The controller may also read the detection result of the second light intensity monitor 25b and output an instruction to the user to perform a cleaning operation.

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, etc.

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, etc. in normal operation. There are no other limitations on the method of setting the start determination threshold. In this embodiment, the start determination threshold corresponds to the first threshold.

For example, if the light amount is equal to or greater than the start determination threshold, it is determined that the dirt on 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.

On the other hand, if the light amount 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).

The pressure increase process is a process in which, while plasma P is being generated, an ionized gas (buffer gas 2) that is ionized by EUV light 1 is introduced into the second vacuum chamber 20, which is maintained at normal pressure P2n, which is the pressure during normal operation, and the pressure P2 in the second vacuum chamber 20 is increased to a cleaning pressure P2c that is higher than the normal pressure P2n. For example, the exhaust volume of the second vacuum chamber 20 is reduced, and the second vacuum valve 52 is adjusted so that P2 = P2c. Also, 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 is increased.

When the pressure in the second vacuum chamber 20 reaches the cleaning pressure, a sputtering process is performed to sputter the optical element 21 (step 104). The sputtering process is a process in which the optical element 21, which is the target placed in the second vacuum chamber 20, is sputtered with the buffer gas 2 ionized by the EUV light 1 while maintaining the cleaning pressure P2c. 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.

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

By introducing the light amount adjustment process, it becomes possible to realize a desired sputtering rate even in cases where it is difficult to adjust the sputtering rate using only the cleaning pressure P2c.
The method for adjusting the sputtering rate is not limited to a specific one. 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.

In this way, in the process shown in FIG. 18, the pressure increase process and the sputtering process are executed when the light amount detected by the second light amount monitor 25b becomes lower than the start determination threshold. This makes it possible to perform the cleaning operation (pressure increase process and sputtering process) at the timing when cleaning of the optical element 21 becomes necessary. It also makes it possible to avoid unnecessary cleaning operations.

When the sputtering process is performed, it is determined whether or not to end the cleaning operation (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 (end determination threshold). The end determination threshold is set to a value equal to or greater than the start determination threshold described above. In this embodiment, the end determination threshold corresponds to the second threshold.

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

If the light amount detected by the second light amount monitor 25b is lower than the end judgment threshold, it is determined that dirt remains on the optical element 21 and the cleaning operation is not to be ended (No in step 105). In this case, the process returns to step 104 and the sputtering process continues.

On the other hand, if the light amount is higher than the end determination threshold, it is determined that the optical element 21 has been cleaned to an acceptable level, and the cleaning operation is to be ended (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).

The pressure reduction process is a process in which the pressure P2 in the second vacuum chamber 20 is reduced to the 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 volume of the second vacuum chamber 20 is increased and P2=P2n is satisfied. Also, for example, the flow control valve may be adjusted so that the flow rate of the buffer gas 2 flowing into the second vacuum chamber 20 is reduced.

This process can be said to be a process 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 amount of EUV light 1 or the position and attitude of the optical element 21 are adjusted during the sputtering process, they are returned to their normal operating states. This makes it possible to end the cleaning operation and return to normal operation.

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.

In this way, the cleaning operation is an operation that changes the pressure downstream of the debris reduction device 40 in which the optical element 21 is placed (pressure P2 in the second vacuum chamber 20). In contrast, even if the pressure downstream of the debris reduction device 40 is changed in the light source device 100, the pressure in the space where the emission point of the plasma P is located upstream of the debris reduction device 40 (pressure P2 in the first vacuum chamber 10) does not change. In other words, even when a cleaning operation is performed, 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.

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

The diagram on the left side of Figure 19 is a schematic diagram showing the state of sample 27 before it is sputtered. In the experiment, plate-shaped sample 27 was fixed with bolts to stage 26 which was 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 with no metallic luster. Here, the color of tungsten oxide is diagrammatically shown as dark gray.

Next, as shown in the center diagram of Figure 19, the sample 27 was introduced into the second vacuum chamber 20 so that part of it overlapped with the optical path of the EUV light 1, and sputtering was performed with P2 = 13 Pa. The dotted 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 (irradiation range of the EUV light 1), and the EUV light 1 was irradiated only to the left half of the sample 27, without using a light-shielding member that would generate impurities.

The diagram on 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. Meanwhile, a metallic luster was confirmed 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 shown as light gray. The light gray area of sample 27 becomes the sputtered area 70.

In this way, it was found that the area irradiated with the EUV light 1 becomes the sputtering area 70 where etching by sputtering occurs. It was also found that even inside the second vacuum chamber 20, in areas not irradiated with the EUV light 1, etching by sputtering hardly occurs at all. In other words, it is possible to limit the sputtering area 70 by limiting the irradiation of the EUV light 1. Below, a configuration for limiting the irradiation of the EUV light 1 by using a light shielding plate will be described.

Figure 20 is a schematic diagram showing an example of the configuration of an optical system that uses 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 reduction device 40. The left side of the debris reduction device 40 is the space in the first vacuum chamber 10 where the plasma P is generated, and the right side of the debris reduction device 40 is the space in the second vacuum chamber 20 where the optical system 24a is located.

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

The collector mirror 71a has a rotationally symmetric cylindrical reflective surface on the inside, and is positioned 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 that it can rotate around the central path O. The light shielding plate 72a is a plate-shaped member that shields a portion 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 positioned so as to cover the upper half of the area on the collector mirror 71a where the EUV light 1 is incident. Note that a light shielding plate 72a that covers 2/3 of the area on which the EUV light 1 is incident, or a light shielding plate 72a that covers 3/4 of the area may also be used.

In the optical system 24a, the EUV light 1 that has passed through the debris mitigation device 40 and 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.

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 an undegraded reflective surface. Furthermore, since the collector mirror 71a rotates around the central path O as an axis, 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 collection performance without replacing the collector mirror 71a, making it possible, for example, to extend the maintenance period.

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 an optical system that is provided, for example, in the first vacuum chamber 10, and 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.

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 a central axis C of the reflective surface. Note that the collector mirror 71b may be composed of multiple mirrors as long as the focusing position of the EUV light 1 does not change when the collector mirror 71b rotates about the central axis C.
The light shielding plate 72b blocks 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 lower half of the reflecting surface of the collecting mirror 71b, but the range of the reflecting surface covered by the light shielding plate 72b is not limited.

For example, even in the first vacuum chamber 10 where the plasma P is generated, depending on the light emission conditions of the plasma P, sputtering that deteriorates optical elements such as the collecting mirror 71b may occur. In the optical system 24b, for example, if the characteristics of the reflecting surface of the collecting mirror 71b deteriorate, the collecting mirror 71b can be rotated to use an undegraded reflecting surface, as in the case of FIG. 20. This makes it possible to maintain the collecting performance without replacing the collecting mirror 71b.

As described above, in the light source device 100 according to this embodiment, the debris reduction 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, for example, pressure changes in the second vacuum chamber 20 to be absorbed by the high-pressure region 14. This makes it possible to suppress changes in pressure P1 on the light source side due to changes in pressure P2 on the introduction side of the EUV light 1.

Generally, radiation such as EUV light 1 emitted from 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 the optical system installed in the middle of the passage or a change in the conditions on the utilization device side, it is thought that this will lead to a change in the pressure around plasma P. In this case, the light emission conditions of plasma P will change, and radiation such as EUV light 1 may become unstable.

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 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.

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.

Furthermore, in this embodiment, the characteristic of the light source device 100 that allows the pressure P2 of the second vacuum chamber 20 to be changed while stably supplying the EUV light 1 is utilized to perform sputter cleaning of the optical element 21 provided in the second vacuum chamber 20.

In cleaning by sputtering, it is possible to change the sputtering rate, for example, by increasing or decreasing the pressure in the second vacuum chamber 20. For example, if it is desired to avoid damaging the optical element 21, the device is operated under conditions that make sputtering less likely. Also, if contamination of the optical element 21, etc., exceeds an acceptable level, the pressure can be deliberately set to perform sputtering, making it possible to etch and clean the contaminated surface.

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

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

For example, one method for cleaning the optical system of the 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, reactive gases such as hydrogen gas or halogen gas are supplied to the foil trap or downstream thereafter. 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.

However, hydrogen gas is explosive and dangerous to use. Furthermore, halogen gas is highly reactive and difficult to handle. For this reason, to ensure the safety of the equipment and the corrosion resistance of the equipment containers, operation by experts and the cost of equipment are required. For example, to exhaust reactive gases safely and without adversely affecting the equipment, a device to treat the reactive gas must be installed before the exhaust device. Furthermore, the components installed inside the light source and the equipment used will be corroded by the reactive gas. For this reason, it is necessary to maintain the inside of the equipment against corrosion and to use materials and coatings that are resistant to corrosion by reactive gases.

In addition, Japanese Patent Application Laid-Open No. 2007-13054 describes a method of cleaning an optical system using an inert gas in a projection exposure apparatus equipped with an EUV light source. This method involves cooling an inert gas such as nitrogen gas, spraying the liquid or solid inert gas onto optical elements, and cleaning contaminants that have adhered to the optical elements due to the impact.

However, in order to turn nitrogen gas or the like into a liquid or solid, it is necessary to cool it to at least −50° C. or lower, and this cooling requires a huge amount of a cooling medium such as liquid nitrogen.
In addition, in extreme ultraviolet light sources that use metal vapor, it is possible that metal coming from the light source will cool and solidify at low temperature locations. If the metal solidifies in this way, it can have various adverse effects on the optical path and components installed inside the light source. In addition, when vaporized metal cools, it can generate tiny metal particles. If such metal particles enter the vacuum exhaust system, they can be a factor in significantly shortening the life of the exhaust system.

In contrast, the sputtering phenomenon discovered by the present inventors makes it possible to perform sputtering (etching) using an inert ionized gas (buffer gas 2) such as a rare gas. In this way, because an inert gas is used, a light source device 100 that can be operated safely can be realized. Furthermore, the light source device 100 does not require a mechanism for processing reactive gases or a mechanism for removing reactive gases. This makes it possible to significantly reduce device costs compared to devices that use reactive gases. In addition, the device configuration is simplified, making it possible to configure the device compactly. Furthermore, ionized gases do not cause corrosion like active gases. This allows a relatively wide range of materials to be selected for the container, etc., making it possible to reduce device costs.

Also, 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 equipment costs and simplifies the device configuration. Also, because there are no areas within the device that become extremely cold, there are no problems with concentrated solidification of metals such as tin, or an increase in metal particles that affect the exhaust system.

As described above, the ionized gas can be a gas that has low absorption of the EUV light 1. This makes it possible to clean components downstream of the debris mitigation device 40 without dimming 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.

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

In the above embodiment, an LDP type light source unit was used, which uses a laser beam LB and discharge to turn the plasma raw material into plasma. There are no limitations on the type of light source unit, and any type may be used as long as it generates radiant light from plasma.

FIG. 22 is a schematic diagram showing an example of the configuration of an LPP type light source unit. FIG. 22 shows a schematic diagram of an LPP type light source unit 80 that directly converts 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 plasma raw material S to the rotor 81, and a laser source 82 that irradiates a laser beam LB that converts 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 incidence unit.

The rotor 81 transports the plasma raw material S to a 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 be disposed in a state inclined from the vertical direction.
Furthermore, the shape of the rotor 81 is not limited to a disk shape, and for example, a polygonal rotor may be used. The rotor 81 is made of a high melting point metal such as tungsten (W), molybdenum (Mo), or tantalum (Ta).

The container C is arranged 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. When 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.

In this way, the light source unit 80, in which part of the rotating body 81 is immersed in the container C, can, for example, make the light source module thinner. Also, unlike the light source unit of the LDP type described with reference to Figure 1, the LPP type requires only one rotating body and does not require equipment for supplying pulsed power. This makes it possible to miniaturize the device and reduce the device costs.

FIG. 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 FIG. 23 is provided in the first vacuum chamber 10 and includes 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 using a laser beam LB.

The rotating drum 91 has a storage section 92 that opens upward and stores liquid plasma raw material S. The plasma raw material S is supplied to the storage section 92 in 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 used is 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.

The rotating drum 91 has a disk-shaped base 93 and an annular outer wall portion 94 formed on one side of the base 93 along the periphery of the base 93. In the rotating drum 91, the area surrounded by the base 93 and the outer wall portion 94 becomes a storage portion 92 that stores liquid plasma raw material S. A shaft member 95 that rotates around a predetermined rotation axis is connected to the side of the rotating drum 91 opposite the side 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 rotated by a motor (not shown).

When the rotating drum 91 is rotated continuously around the rotation axis, the liquid plasma raw material S supplied to the storage section 92 moves toward the inner surface 94a of the outer wall section 94 due to centrifugal force and is distributed along the inner surface 94a. The film thickness of the liquid plasma raw material S distributed on the inner surface 94a is adjusted according to the rotation speed of the rotor.

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 that converts the liquid plasma raw material S into plasma. This generates plasma P at the irradiation position of the laser beam LB, and radiant light such as EUV light is emitted. In a light source section 90 of the type that uses a rotating drum 91 as a 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.

In the above embodiment, a debris reduction device equipped with both a rotating foil trap and a fixed foil trap has been described. The configuration of the debris reduction 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.

For example, instead of the fixed foil trap, other members that reduce conductance may be used as the member disposed on the second vacuum chamber side of the debris mitigation apparatus, such as a member having a mesh structure or a honeycomb structure that reduces conductance.
Furthermore, when the beam diameter of the EUV light is small, a member for narrowing the vacuum path and lowering the conductance may be used.

Also, for example, the rotating foil trap and rotating foil trap cover do not need to be placed on the first vacuum chamber side of the debris reduction device. In this case, it is possible to maintain a high pressure region by providing a cylindrical member that abruptly widens the cross section that intersects with the path direction, like the rotating foil trap cover.

In the above embodiment, a configuration has been described in which a buffer gas is used as the ionized gas that generates sputtering. However, this is not limited to this, and for example, the buffer gas and the ionized gas may be different types of gas.

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 with 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 a configuration in which an ionized gas is introduced when necessary in this way, it is possible to clean optical elements, etc. by utilizing sputtering with the ionized gas.

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

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

For example, in a light source device, the debris reduction device does not necessarily need 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 composed of a separate member from the debris reduction device. The debris reduction 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 synchrotron radiation and ionized gas by releasing ionized gas into the space where the synchrotron radiation is introduced.

In addition, the configuration of the light source device for performing sputtering and the configuration of the debris reduction device mounted on the light source device are not limited, and for example, any device capable of releasing ionized gas into the area irradiated with synchrotron radiation can be used to generate the above-mentioned sputtering phenomenon.

In this disclosure, expressions using "more than", such as "greater than A" and "smaller than A", are expressions that comprehensively include both concepts that include equivalent to A and concepts that do not include equivalent to A. For example, "greater than A" is not limited to cases that do not include equivalent to A, but also includes "A or greater". 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 may be appropriately adopted from the concepts included in "greater than A" and "smaller than A" so that the effects described above can be achieved.

It is also possible to combine at least two of the characteristic features of the present technology described above. In other words, the various characteristic features described in each embodiment may be combined in any way, without distinction between the embodiments. Furthermore, the various effects described above are merely examples and are not limiting, and other effects may be achieved.

Reference Signs List 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 (23)

a first vacuum chamber;
a light source unit that generates plasma serving 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 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, and generating a high-pressure region whose pressure is higher than that of the first vacuum chamber and that of the second vacuum chamber so as to interrupt the vacuum path. The light source device according to claim 1 ,
The debris mitigation device includes a conductance reducer that reduces the conductance of the vacuum path between the high pressure region and the second vacuum chamber. The light source device according to claim 2 ,
The conductance reducing portion is a fixed foil trap having a plurality of foils arranged in the vacuum path and a fixing member that fixes the plurality of foils. The light source device according to claim 1 ,
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 with a path direction of the vacuum path is larger than that of the high pressure region. The light source device according to claim 4,
The debris mitigation device includes a rotary foil trap having a plurality of foils and a rotating member that radially supports the plurality of foils;
The cylindrical member is a rotary foil trap cover that surrounds the rotary foil trap. The light source device according to claim 1 ,
The debris mitigation apparatus prevents the pressure in the first vacuum chamber from substantially changing 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. The light source device according to claim 1 ,
A light source device, wherein the pressure in the high pressure region is six times or more the pressure in the first vacuum chamber. The light source device according to claim 1 , further comprising:
a buffer gas supply port for supplying a buffer gas that changes the pressure in the second vacuum chamber; and a pressure adjustment mechanism for adjusting the pressure in the second vacuum chamber. The light source device according to claim 8,
the high pressure region is a region into which the buffer gas is introduced,
The light source device, wherein the inlet includes a first inlet communicating with the high pressure region. The light source device according to claim 8, further comprising:
The second vacuum chamber includes:
the introduction port includes a second introduction port provided in the second vacuum chamber. 11. The light source device according to claim 1, wherein the buffer gas is an ionized gas that is ionized by the radiation,
The light source device is capable of a normal operation and a cleaning operation using the ionized gas. The light source device according to claim 11,
The cleaning operation is an operation of introducing the ionized gas into a second vacuum chamber maintained at a first pressure which is the pressure during normal operation, increasing the pressure of the second vacuum chamber to a second pressure higher than the first pressure, and, while maintaining the second pressure, performing sputtering on a target placed in the second vacuum chamber using the ionized gas ionized by the synchrotron radiation. The light source device according to claim 12,
The second pressure is 6 Pa or more. The light source device according to claim 12,
a pressure of the first vacuum chamber during normal operation is set to a third pressure at which the radiation is stable; and
The second pressure is three times or more as high as the third pressure. The light source device according to claim 11,
The ionized gas is a rare gas. The light source device according to claim 11, further comprising:
the second vacuum chamber; and a light amount monitor provided in the second vacuum chamber and configured to detect an amount of the radiation light,
The normal operation and the cleaning operation are switched and executed based on a detection result of the light quantity monitor. The light source device according to claim 8,
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 amount adjustment valve that adjusts the exhaust amount of the second vacuum chamber. The light source device according to claim 1 ,
The light source device, wherein the synchrotron radiation is EUV light. The light source device according to claim 1 ,
The light source unit includes:
A pair of rotating electrodes disposed in the first vacuum chamber with a discharge region therebetween;
a raw material supply unit for supplying a 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;
a voltage source that applies a voltage to the pair of rotating electrodes to convert the plasma raw material vaporized by the energy beam into plasma. The light source device according to claim 1 ,
The light source unit includes:
a rotor disposed in the first vacuum chamber;
A raw material supply unit that supplies a plasma raw material to the rotor;
an energy beam incident section that incidents an energy beam onto the rotating body to convert the plasma raw material supplied to the rotating body into plasma. A cleaning method performed using a light source device, comprising:
The light source device includes:
a first vacuum chamber;
a light source unit that generates plasma serving as a light source in the first vacuum chamber;
a debris mitigation apparatus for reducing debris dispersed from the plasma, the debris mitigation apparatus comprising: a first vacuum chamber and a second vacuum chamber into which radiation light emitted from the plasma is introduced, forming a vacuum path through which the radiation light passes, 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 interrupt the vacuum path;
a pressure increasing step of introducing an ionized gas that is ionized by the radiation into a second vacuum chamber that is maintained at a first pressure that is a pressure during normal operation while the plasma is being generated, and increasing the pressure of the second vacuum chamber to a second pressure that is higher than the first pressure;
a sputtering step of performing sputtering on a target placed in the second vacuum chamber with the ionized gas ionized by the synchrotron radiation while maintaining the second pressure. 22. The cleaning method according to claim 21,
the light source device further includes the second vacuum chamber and a light amount monitor provided in the second vacuum chamber and configured to detect an amount of the emitted light,
When the amount of light detected by the light amount monitor becomes lower than a first threshold, the pressure increasing step and the sputtering step are performed;
The cleaning method further comprises a pressure reducing step of reducing the pressure in the second vacuum chamber to the first pressure when the amount of light detected by the light amount monitor becomes higher than a second threshold value that is equal to or greater than the first threshold value. 22. The light source device according to claim 21,
The sputtering step includes a step of changing an amount of the synchrotron radiation from an amount of the synchrotron radiation during the normal operation while maintaining the second pressure.

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