Light source device

Abstract

To provide a light source device for improving the measurement accuracy of the thickness of a target material.SOLUTION: A light source device 100 according to the present embodiment includes a target holding part that rotates around a rotation axis, holds a target material of a plasma source on a holding surface, and moves the target material to a plasma formation region, a cover part that covers an opening of the target holding part, and a sensor assembly 7 that acquires a surface position of the target material using light. The sensor assembly 7 includes a support member for supporting the sensor body 71 at a position where the sensor body 71 is located outside the target holding part when viewed from a direction perpendicular to the opening.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a light source device. [Background technology]

[0002] Patent Document 1 describes a light source in which a molten metal target material is held by centrifugal force on the inner wall of a crucible that rotates around a rotation axis, and light is emitted by irradiating the target material with excitation light. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-168463 Summary of the Invention [Problem to be solved by the invention]

[0004] When measuring the thickness of a target material using light, there is a problem that the optical system is affected by heat, resulting in a decrease in measurement accuracy.

[0005] The present disclosure has been made in consideration of such problems, and provides a light source device that improves the accuracy of measuring the thickness of a target material. [Means for solving the problem]

[0006] A light source device according to one aspect of this embodiment includes: a target holding unit that rotates around a rotation axis, holds a target material of the plasma source on a holding surface, and moves the target material to a plasma generation region; a cover portion that covers the opening of the target holding portion; a sensor assembly for detecting the surface position of the target material using light; Equipped with The sensor assembly includes: a sensor body that emits the light; a first mirror provided at the same height as the holding surface of the target holding unit and reflecting the light toward the holding surface; a second mirror that reflects light from the sensor body toward the first mirror; a mirror support portion connected to the cover portion and supporting the second mirror; a support member that supports the sensor body at a position where the sensor body is outside the target holding part when viewed in a direction perpendicular to the opening; Equipped with. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to provide a light source device that improves the accuracy of measuring the thickness of a target material. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view illustrating a light source device according to a first embodiment. [Figure 2] 10 is a cross-sectional view illustrating a light source device according to a modified example of the first embodiment. [Figure 3] 3 is a cross-sectional view illustrating a light source device according to a modified example of the first embodiment, showing a cross section taken along line II in FIG. 2. FIG. [Figure 4] 10 is a cross-sectional view illustrating a light source device according to a modified example of the first embodiment. [Figure 5] FIG. 10 is a cross-sectional view illustrating a light source device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The following description shows preferred embodiments of the present disclosure, and the scope of the present disclosure is not limited to the following embodiments. In the following description, components with the same reference numerals indicate substantially similar content.

[0010] Embodiment 1 A light source device according to a first embodiment will be described. The light source device of this embodiment generates light such as illumination light and exposure light used in optical devices such as inspection devices and exposure devices. The light source device may be provided integrally with the optical device, or may be disposed near the optical device as a separate entity. When the optical device is an inspection device, the light source device generates illumination light that illuminates an inspection object in the inspection device. When the optical device is an exposure device, the light source device generates exposure light that exposes an exposure object in the exposure device.

[0011] The light source device generates light such as illumination light and exposure light by irradiating excitation light onto a target material held in a target holder. Therefore, the optical device performs lithography or inspection based on the light generated from the target material. Below, an example of a light source device will be described in which molten metal held in a crucible is used as the target material. Note that the light source device is not limited to one that uses molten metal held in a crucible as the target material, and may also use liquid metal in droplet form, a solid fixed to a cylindrical drum, or the like as the target material.

[0012] 1 is a cross-sectional view illustrating a light source device 100 according to embodiment 1. As shown in FIG. 1, the light source device 100 includes a crucible 2, a laser light source 3, a mirror 4, a debris shield 5, a crucible cover 6, and a sensor assembly 7.

[0013] The crucible 2 holds a target material 8. The crucible 2 is capable of melting metal inside. The crucible 2 holds the target material 8, such as molten metal, which generates plasma 11 when irradiated with excitation light LR. The excitation light LR is, for example, laser light including IR (Infrared) light.

[0014] The target material 8 may be held in a cylindrical drum. In this case, the target material 8 is held by fixing a substance to be the target material 8, such as xenon (Xe), frozen on the surface of the drum in a solid state, for example.

[0015] The target material 8 is not limited to the molten metal held in the crucible 2, but may be a solid substance, solid metal, liquid droplets, or the like, as long as it is a substance that generates plasma 11 when irradiated with excitation light LR. The molten metal is, for example, melted tin (Sn) or lithium (Li), but is not limited to tin, lithium, or the like, as long as it generates plasma 11 when irradiated with excitation light LR.

[0016] The crucible 2 is placed in a chamber 9. The inside of the chamber 9 may be depressurized to, for example, a vacuum, or may be filled with a predetermined gas.

[0017] The crucible 2 has a rotation axis R and rotates around the rotation axis R. For example, a rod-shaped shaft 21 that extends coaxially with the rotation axis R is connected to the crucible 2. When the shaft 21 rotates around the rotation axis R, a rotational force is transmitted to the crucible 2. Therefore, the crucible 2 rotates around the rotation axis R.

[0018] The shaft 21 is connected to a rotary motor 22. The rotary motor 22 transmits power to the shaft 21 to rotate it about the rotation axis R. As a result, the rotary motor 22 rotates the crucible 2 about the rotation axis R via the shaft 21.

[0019] The crucible 2 is, for example, cylindrical with one opening closed. The closed portion of the crucible 2 is called the bottom. The cylindrical portion of the crucible 2 is called the cylindrical portion. The rotation axis R of the crucible 2 extends, for example, vertically. The bottom is located at the bottom and the open opening is located at the top. The inner surface of the bottom is called the bottom surface. The outer surface of the bottom is called the bottom surface. The bottom surface is the surface opposite the bottom surface. When the rotation axis R extends vertically and the opening is located at the top, the bottom surface faces upward and the bottom surface faces downward. The shaft 21 is connected to the bottom surface of the bottom.

[0020] The inner wall surface of the cylindrical portion is called the inner wall surface. The inner wall surface surrounds the rotation axis R. When the crucible 2 holding the target material 8 is rotated around the rotation axis R, the target material 8 is held on the inner wall surface by centrifugal force.

[0021] The inner wall surface of the crucible 2 may have a groove formed along the inner periphery. The groove is formed, for example, along the intersection line between the inner wall surface and a plane perpendicular to the rotation axis R. The groove is recessed in the inner wall surface in a direction away from the rotation axis R.

[0022] A heater may be provided near the crucible 2. A target material 8 such as molten metal can be formed in the crucible 2 by heating with the heater.

[0023] The bottom of the crucible 2 may be thinned from the bottom surface side at the peripheral edge portion. By thinning the bottom, a recess 20 is formed at the peripheral edge portion of the bottom surface of the crucible 2.

[0024] Here, for the sake of convenience in explaining light source device 100, an XYZ Cartesian coordinate system is introduced. The direction along rotation axis R is defined as the Z-axis direction, and the two directions perpendicular to rotation axis R are defined as the X-axis direction and the Y-axis direction, respectively. For example, the +Z-axis direction is referred to as the upward direction, and the −Z-axis direction is referred to as the downward direction. Note that the terms upward and downward are used for the sake of convenience in explaining light source device 100, and do not indicate the directions in which light source device 100 is actually disposed.

[0025] The laser light source 3 generates excitation light LR. The laser light source 3 irradiates the generated excitation light LR onto a target material 8. The laser light source 3 may irradiate the target material 8 with the excitation light LR via an optical member such as a condenser lens. The target material 8 generates plasma 11 by being irradiated with the excitation light LR. When ions and electrons in the plasma 11 are de-excited, EUV (Extreme Ultraviolet) light LE is generated. In this way, by irradiating the target material 8 with the excitation light LR, EUV light LE is generated from the plasma 11.

[0026] As the EUV light LE is emitted, the target material 8 scatters as debris. The film thickness of the target material 8, which changes over time, is measured by the sensor assembly 7.

[0027] The mirror 4 reflects the EUV light LE generated from the plasma 11. The mirror 4 may be a plane mirror or a concave mirror. The mirror 4 is disposed above the crucible 2 in which the target material 8 is held. The EUV light LE reflected by the mirror 4 is extracted to the outside of the light source device 100.

[0028] The debris shield 5 covers the opening of the crucible 2. The debris shield 5 has openings formed therein for extracting the excitation light LR and the EUV light LE. The debris shield 5 prevents debris that scatters with the generation of plasma 11 from adhering to the mirror 4 and the like. The temperature of the debris shield 5 may be adjusted to be equal to or higher than the melting point of the target material 8. This allows the target material 8 that has become debris to be reused to generate plasma.

[0029] The debris shield 5 is separated from the crucible 2 so as not to affect the rotation of the crucible 2. The debris shield 5 may be supported by, for example, the chamber 9 or a housing (not shown) that houses the rotation motor 22. Note that a plurality of debris shields may be further arranged between the plasma formation region and the sensor surface of the sensor main body 71. For example, a plurality of debris shields may be arranged in the crucible 2 between the plasma formation region and the region where the sensor cover 74 is arranged.

[0030] The crucible cover 6 covers the opening of the crucible 2 from above the debris shield 5. The crucible cover 6 may be supported by, for example, the chamber 9 or a housing that houses the rotation motor 22. The crucible cover 6 is farther from the crucible 2 than the debris shield 5 and is cooler than the debris shield 5. The crucible cover 6 may be connected to a heat sink.

[0031] The cover portion corresponds to at least one of the debris shield 5 and the crucible cover 6. The light source device 100 only needs to be provided with at least one of the debris shield 5 and the crucible cover 6.

[0032] The sensor assembly 7 includes a sensor body 71 , a mirror 72 , a mirror holder 73 , and a sensor cover 74 .

[0033] The sensor body 71 acquires the surface position of the target material 8 in the radial direction of the crucible 2 using the light L0. The sensor body 71 may be, for example, a confocal displacement sensor. In this case, the sensor body 71 emits white light and receives reflected light of a wavelength that is focused on the surface of the target material 8. The sensor body 71 then acquires the surface position of the target material 8 based on the wavelength of the reflected light. The sensor body 71 may be, for example, a chromatic aberration lens and a lens barrel that supports the chromatic aberration lens. The lens barrel may be connected to an optical fiber that guides the white light and the reflected light. The sensor body 71 may further include a light source and a photodetector. Note that the sensor body 71 is not limited to a confocal displacement sensor and may be a triangulation displacement sensor.

[0034] The mirror 72 is provided at the same height as the holding surface of the target material 8. The mirror 72 reflects the light L0 from the sensor main body 71 toward the surface of the target material 8. The mirror 72 reflects the light reflected from the surface of the target material 8 toward the mirror 75.

[0035] The mirror holder 73 holds the mirror 72. The mirror holder 73 includes a side cover 731, a side cover 732, and a bottom cover 733. The side cover 731 is provided at least on the plasma formation region side, i.e., the plasma 11 side, as viewed from the mirror 72. The side cover 732 is provided on the opposite side of the mirror 72 from the plasma formation region side. The side cover 732 has an opening that allows light L0 from the sensor main body 71 to irradiate the surface of the target material 8. In this case, the side cover 732 also serves as a front cover portion, which will be described later. A transparent member that transmits the light L0 may be fitted into the opening. The bottom cover 733 is provided between the optical axis of the light L0 directed from the mirror 72 toward the surface of the target material 8 and the bottom surface of the crucible 2. The side cover 731, the side cover 732, and the bottom cover 733 may be configured as a single unit. The plasma formation region side as viewed from the mirror 72 may refer to the side closer to the plasma formation region in the circumferential direction of rotation of the holder as viewed from the mirror 72. In this case, as will be described later, the sensor assembly 7 (mirror holder 73) may include a front cover part separate from the side covers 731 and 732, and the front cover part may have an opening that allows light L0 from the sensor main body 71 to irradiate the surface of the target material 8.

[0036] The mirror holder 73 is thermally connected to the crucible cover 6. The mirror holder 73 may be supported by the crucible cover 6.

[0037] The mirror holder 73 includes, for example, a cylindrical body with a bottom and a flange protruding outward from the upper end of the cylindrical body. In this case, the flange of the mirror holder 73 may contact the crucible cover 6. The mirror 72 may be disposed inside the cylindrical body.

[0038] The sensor cover 74 covers the mirror 72 from the outside of the mirror holder 73. The sensor cover 74 may cover the mirror holder 73. The sensor cover 74 includes a side cover 741, a side cover 742, and a bottom cover 743. The side cover 741 is provided on the plasma formation region side as viewed from the mirror 72. The side cover 742 is provided on the opposite side of the mirror 72 from the plasma formation region side. The bottom cover 743 is provided between the bottom cover 733 of the mirror holder 73 and the bottom surface of the crucible 2. The bottom cover 743 may be placed in a recess 20 formed in the bottom surface of the crucible 2.

[0039] The sensor cover 74 is thermally connected to the debris shield 5. The sensor cover 74 may be supported by the debris shield 5.

[0040] The sensor cover 74 includes, for example, a cylindrical body with a bottom and a flange that protrudes outward from the upper end of the cylindrical body. In this case, the flange of the sensor cover 74 may come into contact with the debris shield 5.

[0041] The mirror 75 reflects the light L0 from the sensor main body 71 toward the mirror 72. The mirror 75 also reflects the light reflected from the mirror 72 toward the sensor main body 71.

[0042] The support member 76 supports the mirror 75. The support member 76 is thermally connected to the crucible cover 6. The support member 76 may be supported by the crucible cover 6.

[0043] The sensor main body 71 is supported by a support member 77 at a position outside the crucible 2 when viewed from the positive side of the Z axis. The support member 77 is attached to the chamber 9. The sensor main body 71 may also be supported by a support member 76. The dotted line extending in the Z axis direction represents the outer wall of the crucible 2 extending in the Z axis direction. The sensor main body 71 is located on the negative side of the Y axis relative to the dotted line.

[0044] The light source device 100 may include a gas inlet that introduces a buffer gas that flows along the surface of the mirror 72 toward the target material 8. For example, a transparent member that transmits the light L0 may be disposed above the mirror holder 73, and an inlet for introducing the buffer gas may be provided in the transparent member. The buffer gas may include an inert gas, such as at least one of argon (Ar), helium (He), nitrogen (N), and hydrogen (H), or may include other gases. Flowing the buffer gas can prevent the mirror 72 of the sensor assembly 7 from being contaminated by debris.

[0045] The light source device 100 may further include a supply mechanism that feeds out a linear target material 8 wound and held on a bobbin or the like onto the inner wall surface of the crucible 2.

[0046] The light source device 100 may further include an adjustment mechanism that adjusts the focusing position of the laser light from the laser light source 3 based on the measurement results of the sensor assembly 7. Furthermore, the light source device 100 may change the supply state (e.g., supply amount, temperature) of the target material 8 based on the measurement results of the sensor assembly 7.

[0047] The effects of the light source device 100 according to the first embodiment will be described. When the sensor main body 71 is located above the crucible 2, there is a risk that the measurement accuracy of the surface position of the target material 8 will decrease due to the influence of heat. For example, if the position of the lens supported by the lens barrel changes, the measurement accuracy of the surface position will decrease. In the light source device 100 according to the first embodiment, the sensor main body 71 is supported at a position that is outside the crucible 2 when viewed from the positive Z-axis direction. This makes the sensor main body 71 less susceptible to the influence of heat from the crucible 2, thereby improving the measurement accuracy of the surface position of the target material 8.

[0048] When the mirror holder 73 supporting the mirror 72 is thermally connected to the relatively cool crucible cover 6, it is possible to prevent the position of the mirror 72 from shifting due to heat, which would otherwise reduce the accuracy of measuring the surface position of the target material 8. In addition, by covering the mirror holder 73 with the relatively hot sensor cover 74, adhesion of debris is suppressed.

[0049] When the sensor assembly 7 includes at least one of the side cover 731 of the mirror holder 73 and the side cover 741 of the sensor cover 74, it is possible to prevent the mirror 72 of the sensor assembly 7 from being contaminated with debris. This allows the light source device 100 according to the first embodiment to further improve the accuracy of measuring the surface position of the target material 8.

[0050] Variation 1 The irradiation position of the excitation light LR from the laser light source 3 is not limited to a position symmetrical with respect to the rotation axis R as the measurement position of the thickness of the target material 8. FIG. 2 illustrates a cross-sectional view of a light source device 100 according to a modified example of the first embodiment. Note that some components are omitted in FIG. 2 to avoid cluttering the drawing. In FIG. 2, the irradiation position 101 of the excitation light LR is located on the positive side of the X-axis with respect to the measurement position 102 of the thickness of the target material 8. FIG. 3 shows a cross section taken along line II in FIG. 2. Note that some components are omitted in FIG. 3 to avoid cluttering the drawing. Side covers 731 and 741 provided on the plasma formation region side are provided on the positive side of the X-axis. Side covers 732 and 742 provided on the opposite side from the plasma formation region side are provided on the negative side of the X-axis.

[0051] The irradiation position 101 of the excitation light LR may be located on the negative X-axis side with respect to the measurement position 102 for the thickness of the target material 8. In this case, the side covers 731 and 741 provided on the plasma formation region side are provided on the negative X-axis side. The side covers 732 and 742 provided on the opposite side from the plasma formation region side are provided on the positive X-axis side.

[0052] The sensor assembly 7 may further include a front cover portion provided between the holding surface of the target material 8 and the mirror 72. The front cover portion has an opening that serves as an optical path for light reflected by the mirror 72. When a buffer gas is caused to flow along the surface of the mirror 72, the buffer gas is discharged to the holding surface from at least a part of the opening. In FIG. 1, the side cover 742 provided on the opposite side to the plasma formation region constitutes the front cover portion, but the front cover portion may also be provided separately from the side covers 741 and 742.

[0053] Variation 2 Fig. 4 illustrates a cross-sectional view of a light source device 100 according to Modification 2. Comparing Fig. 1 with Fig. 4, the light source device 100 shown in Fig. 4 further includes a mirror 78, a reference surface 79, and a support member 710.

[0054] The mirror 78 reflects the light L0 that has passed through the mirror 75, such as a half mirror, toward the reference surface 79. The mirror 78 also reflects the light reflected from the reference surface 79 toward the sensor main body 71.

[0055] The reference surface 79 is a mirror or a mirror-finished member with a low linear expansion coefficient. It is also called a reference mirror. The reference surface 79 reflects the light L0 from the mirror 78 toward the sensor body 71. Specifically, the reference surface 79 reflects the light L0 toward the mirror 78.

[0056] The sensor body 71 measures the distance from the sensor body 71 to the surface of the target material 8 and the distance from the sensor body 71 to a reference surface 79, and acquires the surface position of the target material 8 based on the difference between the two distances. The sensor body 71 measures the surface position of the target material 8 using the distance from the sensor body 71 to the reference surface 79 as a reference. This allows the sensor body 71 to eliminate the influence of temperature drift from the measurement results of the surface position of the target material 8.

[0057] The support member 710 supports the mirror 78 and the reference surface 79. The support member 710 is thermally connected to the crucible cover 6. The support member 710 may be supported by the crucible cover 6. The support member 710 may be supported by the support member 76.

[0058] In the light source device 100 according to the second modification, the influence of temperature drift due to heat from the crucible 2 can be eliminated, and the measurement accuracy of the surface position of the target material 8 can be further improved.

[0059] Embodiment 2 5 is a cross-sectional view illustrating a light source device 200 according to embodiment 2. The light source device 200 includes a sensor assembly 7 having the reference surface 79 shown in the second modification of embodiment 1 described above.

[0060] The separating section 72a is, for example, a half mirror, which separates the light L0 from the sensor main body 71, directing a part of the light L0 toward the target material 8 and the remaining part toward a reference surface 79 (for example, a mirror).

[0061] The reference surface 79 reflects the light from the separation portion 72a toward the sensor main body 71. Specifically, the reference surface 79 reflects at least a portion of the light from the separation portion 72a toward the separation portion 72a, and a portion of the light reflected from the reference surface 79 may be guided to the sensor main body 71 via the separation portion 72a.

[0062] The target material 8 is held by a holder 2a, which may be the inner wall of a crucible, the surface of a cylindrical body such as a drum, or a tape.

[0063] The sensor body 71 measures the distance from the sensor body 71 to the surface of the target material 8 and the distance from the sensor body 71 to a reference surface 79, and acquires the surface position of the target material 8 based on the difference between the two distances. The sensor body 71 may measure the surface position of the target material 8 using the distance from the sensor body 71 to the reference surface 79 as a reference. This allows the sensor body 71 to eliminate the effects of temperature drift from the measurement results of the surface position of the target material 8. Furthermore, the reference surface 79 may be thermally connected to the holder 2a so that the same degree of temperature drift occurs in the measurement of the reference surface 79 and the measurement of the surface of the target material 8. This allows the sensor body 71 to measure the surface position of the target material 8 more accurately, without being affected by temperature drift.

[0064] Although the embodiments of the present disclosure have been described above, the present disclosure includes appropriate modifications that do not impair the objects and advantages thereof, and is not limited to the above-described embodiments. In addition, combinations of the configurations of Embodiments 1 and 2 are also within the scope of the technical concept of the present disclosure.

[0065] For example, the target material may be solidified on the surface of a drum that rotates around a rotation axis, or may be solidified in the form of a tape. In such cases, the sensor assembly may also include a side cover portion, thereby improving the accuracy of measuring the surface position of the target material.

[0066] Furthermore, the following light source devices are also within the scope of the technical concept of the embodiments. (Appendix 1) a target holder that holds a target material of the plasma source on a holding surface; a sensor assembly for detecting the surface position of the target material using light; Equipped with The sensor assembly includes: a sensor body that emits the light; a separation unit that separates the light from the sensor body; a reference surface that reflects a portion of the light separated by the separation portion toward the sensor body, the separation unit separates the light from the sensor body so that a portion of the light is directed toward the reference surface and a remaining portion of the light is directed toward the target material on the holding surface; the sensor main body acquires a surface position of the target material based on a measurement result of the light reflected from the reference surface and a measurement result of the light reflected from the target material on the holding surface. Light source device. [Explanation of symbols]

[0067] 100, 200 light source device 11. Plasma 2 Crucible 2a Holding part 20 recess 21 Shaft 22 Rotary motor 3 Laser light source 4, 72, 75, 78 Mirror 5 Debris Shield 6 Crucible cover 7 Sensor Assembly 71 Sensor body 72a Separation section 73 Mirror Holder 731, 732, 741, 742 side covers 733, 743 bottom cover 74 Sensor cover 76, 77, 710 Support members 79 Reference plane 8 Target material 9 Chamber R rotation axis LR excitation light LE EUV light

Claims

1. a target holding unit that rotates around a rotation axis, holds a target material of the plasma source on a holding surface, and moves the target material to a plasma generation region; a cover portion that covers the opening of the target holding portion; a sensor assembly for detecting the surface position of the target material using light; Equipped with The sensor assembly includes: a sensor body that emits the light; a first mirror provided at the same height as the holding surface of the target holding unit and configured to reflect the light toward the holding surface; a second mirror that reflects light from the sensor body toward the first mirror; a mirror support portion connected to the cover portion and supporting the second mirror; a support member that supports the sensor body at a position where the sensor body is outside the target holding part when viewed in a direction perpendicular to the opening; Equipped with Light source device.

2. The sensor assembly has a first side cover portion provided at least on the plasma generation region side as viewed from the first mirror. The light source device according to claim 1 .

3. The sensor assembly has a second side cover portion provided on the opposite side of the first mirror from the plasma generation region side. The light source device according to claim 2 .

4. The cover portion has a bottom cover portion provided between the optical axis of light directed from the first mirror toward the holding surface, which is the inner wall surface of the crucible, and the bottom surface of the crucible.

4. The light source device according to claim 2 or 3.

5. The peripheral portion of the bottom of the crucible is thinned from the bottom surface side, At least a portion of the bottom cover portion is thinned to be disposed in a recess provided in the bottom surface of the crucible. The light source device according to claim 4 .

6. The sensor assembly includes a gas inlet for introducing a buffer gas that flows along the surface of the first mirror toward the support surface.

3. The light source device according to claim 1.

7. the sensor assembly includes a front cover portion provided between the holding surface and the mirror and having an opening that serves as an optical path for the light; The buffer gas is discharged to the holding surface through at least a portion of the opening. The light source device according to claim 6 .

8. a plurality of debris shields provided between the plasma generation region and a sensor surface of the sensor assembly; 3. The light source device according to claim 1.

9. The holding surface, which is the inner wall surface of the crucible, holds the target material by centrifugal force generated when the crucible rotates around the rotation axis.

3. The light source device according to claim 1.

10. the second mirror is a half mirror that transmits a portion of the light from the sensor body and reflects a portion of the light from the sensor body toward the first mirror, The sensor assembly includes a reference surface that reflects the light transmitted through the half mirror toward the sensor body.

3. The light source device according to claim 1.

11. the holding surface is an inner wall surface of a crucible, the sensor assembly includes a mirror holder that holds the first mirror; the cover portion includes a debris shield that covers the opening of the crucible, and a crucible cover that covers the opening of the crucible on the side of the opening of the crucible closer to the opening of the crucible than the debris shield; the first side cover portion is thermally connected to the debris shield; The mirror holder is thermally connected to the crucible cover, which is adjusted to a lower temperature than the debris shield. The light source device according to claim 2 .

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