Viewport Assembly for Extreme Ultraviolet Light Source

Abstract

The assembly includes a window having a specific transmission band useful for optical access to the inside of an extreme ultraviolet (EUV) light source container, and a protector configured to protect the window from the inside of the EUV light source container. The protector includes a sheet having a surface facing the window through a gap, and the sheet has a thermal conductivity in the range of 10 to 2000 W / (m·K). The sheet can be a sapphire sheet, and an optical coating for reflecting at least a part of the radiation outside the transmission band can be provided on the surface facing the window, and the opposite side of the sheet can be bare sapphire.

Description

Technical Field

[0001] Cross - Reference to Related Applications

[0001] This application claims priority to U.S. Application No. 63 / 351,457, filed on June 13, 2022, which is hereby incorporated by reference in its entirety.

[0002]

[0002] The subject matter of the present disclosure relates to a viewport assembly for an extreme ultraviolet (EUV) light source.

Background Art

[0003]

[0003] Extreme ultraviolet (EUV) light, for example, electromagnetic radiation having a wavelength of generally 50 nanometers (nm) or less (also called soft X - rays), including light having a wavelength of about 13 nm, can be used in photolithography processes to create extremely small features on a substrate (e.g., a silicon wafer).

[0004]

[0004] As a method for generating EUV light, converting a material having element emission lines in the EUV range into a plasma state can be mentioned, but it is not necessarily limited to this. Suitable materials include, for example, xenon, lithium, and tin. In one such method, often called laser - produced plasma (“LPP”) or laser - induced breakdown (LIB), a necessary plasma can be generated by irradiating a target material (e.g., a material in the form of droplets, streams, or clusters) with an amplified light beam called a drive laser. For this process, the plasma is generated within a sealed container such as a vacuum chamber, and such plasma is monitored using various metrology devices.

Summary of the Invention

[0005]

[0005] In one general aspect, the assembly is a window configured to enable optical access to the inside of an extreme ultraviolet (EUV) light source container, having an outer facing surface configured to face the outside of the EUV light source container and an inner facing surface on the opposite side of the outer facing surface, and further having a window having a transmission band including wavelengths of radiation that the window can transmit, and a protector configured to protect the window from the inside of the EUV light source container, including a sheet having a window facing surface and an inner facing surface on the opposite side of the window facing surface, the window facing surface facing the inner facing surface of the window through a gap, and the sheet including a material having a thermal conductivity in the range of 10 to 2000 W / (m·K).

[0006]

[0006] Some embodiments can include one or more of the features described below. That is, the thermal conductivity of the material can be in the range of 20 to 50 W / (m·K). The transmission band can include wavelengths at which the window can transmit at least 90% of the radiation of that wavelength, or can be defined as a wavelength band including such wavelengths. The protector can include a coating on the window facing surface of the sheet, and this coating reflects at least a part of the radiation having a wavelength longer than the wavelengths included in the transmission band. For example, the coating can reflect 50% or more, or even 70% or more of the radiation having a wavelength longer than the wavelengths included in the transmission band and up to 8000 nm. The coating can reflect at least a part, or even 50% or more of the radiation having a wavelength shorter than the wavelengths included in the transmission band and up to 150 nm. The coating can reflect 50% or more of the radiation having wavelengths in the range of 150 to 845 nm and wavelengths in the range of 1090 to 8000 nm.

[0007]

[0007] Some embodiments can also include one or more of the features described below. That is, the material (of the above sheet) can transmit one or more of visible light and near-infrared light. The window can be configured to withstand a pressure difference between its inner opposing surface and its outer opposing surface, and further can be configured to withstand a pressure difference of at least 100 kPa between both of its surfaces, which is caused as a result of a low pressure and / or vacuum on its inner opposing surface, between its inner opposing surface and its outer opposing surface. The window-facing surface of the sheet can be angled with respect to the inner opposing surface of the window. The sheet can be made to include sapphire or can be made of sapphire. The window can be made to include glass or can be made of glass. The glass can be made to include borosilicate glass or can be borosilicate glass. The borosilicate glass can be made to include Schott N-BK7 or can be Schott N-BK7. The protector can include a coating on the window-facing surface of the sheet, and this coating reflects at least a portion of radiation having a wavelength longer than the wavelengths included in the transmission band. Such a coating can be made to reflect at least a portion of radiation having a wavelength shorter than the wavelengths included in the transmission band.

[0008]

[0008] Some embodiments can also include one or more of the features described below. That is, the inner opposing surface of the sheet can be bare sapphire. The window can be made to include sapphire or can be made of sapphire. The thickness of the sheet can be in the range of 2.2 to 3.2 mm. The thickness of the sheet can also be in the range of 2.39 to 2.59 mm. The thickness of the window can be in the range of 4.0 to 6.5 mm. The thickness of the window can also be in the range of 5.9 to 6.1 mm. This assembly can be attached to an opening defined by penetrating the wall of the vacuum chamber of an extreme ultraviolet (EUV) light source, and the vacuum chamber can be in a vacuum state.

[0009]

[0009] In another general aspect, a metrology apparatus for an extreme ultraviolet (EUV) light source container includes a detection module configured to detect light propagating from within the EUV light source container and / or an illumination module configured to supply light into the EUV light source container, and an assembly disposed along a beam path of the detected light or a beam path of the supplied light, the assembly including: (1) a window configured to enable optical access to the inside of the EUV light source container, the window having an outer facing surface configured to face the outside of the EUV light source container and an inner facing surface on the opposite side of the outer facing surface, and further having a transmission band including wavelengths of radiation that the window can transmit; and (2) a protector configured to protect the window from the inside of the EUV light source container, the protector including a sheet having a window facing surface and an inner facing surface on the opposite side of the window facing surface, the window facing surface facing the inner facing surface of the window with a gap therebetween, the sheet including or consisting of a material having a thermal conductivity in the range of 10 to 2000 W / (m·K).

[0010]

[0010] Some embodiments can include one or more of the features described below. That is, the detection module can include or be a target detection module. The detection module can include or be a target imaging module. The illumination module can include or be an illumination module configured to search for a target moving toward an illumination region within the EUV light source container. The illumination module can be a target back-illumination module configured to search for a target within the EUV light source container. This metrology device can include an optical coating on the window-facing surface of the sheet, and this optical coating reflects at least a portion of the radiation having a wavelength longer than the wavelengths included in the transmission band. The optical coating can be made to reflect at least a portion of the radiation having a wavelength shorter than the wavelengths included in the transmission band. The sheet can include or be made of sapphire. The window can include or be made of glass.

[0011]

[0011] In another general aspect, an extreme ultraviolet (EUV) light source can include: (1) a vacuum chamber including a vacuum chamber wall, where an opening to the inside of the chamber is defined by the wall; (2) a window coupled to the chamber and positioned to close the opening, the window having an inner facing surface facing the inside of the chamber and an outer facing surface on the opposite side of the inner facing surface, and further having a transmission band including the wavelengths of radiation that the window can transmit through; and (3) a protector positioned to protect the window from the inside of the chamber, the protector including a sheet having a window-facing surface and an inner facing surface on the opposite side of the window-facing surface, the window-facing surface facing the inner facing surface of the window through a gap, and the sheet including a material having a thermal conductivity in the range of 10 to 2000 W / (m·K).

[0012]

[0012] Some embodiments can include one or more of the features described below. That is, an optical coating can be provided on the window-facing surface of the sheet, and this optical coating can reflect at least a portion of the radiation having a wavelength longer than the wavelengths included in the transmission band. The optical coating can also be one that reflects at least a portion of the radiation having a wavelength shorter than the wavelengths included in the transmission band. The sheet can include sapphire or can be made of sapphire. The window can include glass or can be made of glass. The window can include sapphire or can be made of sapphire. The vacuum chamber can be in a vacuum state.

[0013]

[0013] Details of one or more embodiments are described in the accompanying drawings and the following description. Other features will become apparent from such description and drawings, and also from the claims.

Brief Description of the Drawings

[0014]

Figure 1A

[0014] It is a schematic diagram of an extreme ultraviolet (EUV) light source, showing a container (e.g., a vacuum chamber) with a target position defined inside.

Figure 1B

[0015] It is a detailed view of the viewport assembly inside the container of the EUV light source of FIG. 1A.

Figure 2A

[0016] It is a cross-sectional view of the metrology device of the light source of FIGS. 1A and 1B.

Figure 2B

[0016] It is a cross-sectional view of the metrology device of the light source of FIGS. 1A and 1B.

Figure 3

[0017] It is a schematic cross-sectional view of the viewport assembly.

Figure 4A

[0018] It is a graph showing the transmittance of exemplary materials used in the viewport assembly.

Figure 4B

Figure 5A

[0019] A cross-sectional view showing another aspect of a metrology apparatus.

Figure 5B

[0019] A cross-sectional view showing another aspect of a metrology apparatus.

Figure 6

[0020] A diagram showing an EUV light source together with a lithography apparatus.

DETAILED DESCRIPTION OF THE INVENTION

[0015]

[0021] An assembly for reducing or minimizing the thermal lens effect of a viewport assembly of an extreme ultraviolet (EUV) light source is disclosed.

[0016]

[0022] Referring to FIGS. 1A and 1B, an embodiment 100 of an EUV light source is shown. The viewport assembly 155 (FIG. 1B) is an observation mechanism positioned with respect to an opening 164 defined by a wall 161 of a container 160. The viewport assembly 155 includes a window 180 through which the inside 170 of the container 160 can be viewed, or through which light 111 can travel between a component or system on the outside 171 and the inside 170 of the container 160. The container 160 may be a chamber having a sealed (in a vacuum state) and environmentally controlled inside 170. The viewport assembly 155 can be incorporated inside any of the elements or modules 162, 163, 165 shown as passing through one of the walls 161 of the container 160. Details regarding the elements 162, 163, 165 will be described later.

[0017]

[0023] During operation of the EUV light source 100, materials such as glass used as the material of the window 180 may be heated by the incident light 111 absorbed by the window assembly 155, that is, the light moving between the outer side 171 and the inner side 170 of the container 160, or the light moving from the inner side 170 to the outer side 171 of the container 160. For example, the window material may be heated by absorbing the light 111 transmitted from the inside of the container 160. The refractive index of most optical materials changes as a function of temperature. Therefore, heating of the window material may cause the window 180 to suffer a harmful effect called the thermal lens effect, which is a change as a function of temperature in the optical wavefront transmitted by the window. Possible changes in the wavefront include: (1) a uniform phase shift when the temperature rise of the window material is uniform over the entire surface; (2) a non-uniform and smoothly varying phase shift when a uniform temperature gradient occurs over the entire surface of the window material, which causes an increase in the light output; (3) an irregular phase shift when a non-uniform temperature gradient occurs over the entire window surface, which causes a combination of an increase in the light output and an increase in the optical aberration, etc.

[0018]

[0024] The protector 181 can be used to protect the window 180 from the light 111 coming from the inside of the container 160 and other conditions inside the container 160, such as chemical and / or physical damage, and / or the light 111 caused by the deposition of light-absorbing substances. The material of the protector 181 may also be subject to the thermal lens effect, and such a thermal lens effect may increase over time as the light-absorbing substances deposit on the protector 181.

[0019]

[0025] The EUV light source 100 operates to generate EUV light 146 by converting a target material (e.g., tin) having emission lines in the EUV range into a "plasma state" or "plasma" 106. In one exemplary technique, inside the container 160, by irradiating the target 114 (clearly shown in FIG. 1A) made of the target material with the amplified light beam 110, the target material is converted into a plasma state. The conversion to the plasma state 106 emits the radiation of the emission spectrum of the material of the target 114. This emission spectrum may include deep ultraviolet (DUV) light, visible light, near-infrared (NIR) light, and mid-wave infrared (MWIR) light in addition to the desired EUV light 146. The light having wavelengths in these ranges propagates as "incident" light toward the viewport assembly 155 (positioned within the wall 161) and may reach there. Further, due to the interaction between the amplified light beam 110 and the target material 114, the amplified light beam 110 may be scattered and reflected. A part of the scattered and reflected amplified light beam may also reach the viewport assembly 155 as incident light.

[0020]

[0026] One or more viewport assemblies 155 may be used by various metrology modules and / or illumination modules (such as modules 162, 163, and 165 shown in FIG. 1A, etc.) to add light entering the interior 170 of the container 160 and / or to sense or detect light coming from the interior 170 of the container 160 for purposes such as measurement, detection, process monitoring and control. Due to the thermal lens effect, or a change in the optical properties of components within the viewport assembly 155 due to thermal action, the light 111 transmitted into the viewport assembly 155, or the light 111 transmitted through it, and / or the image or light collected through the viewport assembly 155 may be distorted. The light emitted through the viewport assembly and the light received through the viewport assembly are used for system diagnosis and system control, for example, for directing the stream of the target 114. Therefore, distorted light and / or a distorted image formed from such light may degrade the performance of the EUV light source 100 and may reduce the amount or quality of the EUV light 146 generated.

[0021]

[0027] The viewport assembly 155 is configured to prevent or reduce the thermal lens effect. In one aspect of the present disclosure, the viewport assembly 155 includes a window 180 that is configured to enable optical access to the inside 170 of the EUV light source container 160. The window 180 has an outer opposing surface 182 and an inner opposing surface 184, and has a transmission band that includes the wavelengths of radiation that the window 180 can transmit. In one embodiment, the transmission band can be defined as the band of wavelengths at which the window 180 can transmit 90% or more of the radiation of that wavelength. The viewport assembly 155 further includes a protector 181 configured to protect the window 180 from the inside 170 of the EUV light source container 160. The protector 181 includes a sheet 186 having a window-facing surface 183 and an inner opposing surface 185. The window-facing surface 183 faces the inner opposing surface 184 of the window 180 through a gap 187, and the sheet 186 includes a material having a relatively high thermal conductivity, i.e., a thermal conductivity in the range of 10 to 2000 W / (m·K), in the range of 30 to 2000 W / (m·K), or in the range of 30 to 50 W / (m·K). The high thermal conductivity of the protector material rapidly dissipates the thermal gradient across the surface of the protector 181, thereby reducing the thermal lens effect in the protector 181. In one embodiment, the protector 181 includes a coating 189 on the window-facing surface 183 of the sheet 186. This coating 189 reflects at least 50% of the incident intensity of the reflected radiation having a wavelength longer than the wavelengths included in the transmission band of the window 180, for example, thereby reflecting at least a portion of the radiation having a wavelength longer than the wavelengths included in the transmission band of the window 180. This reflected radiation reduces the thermal load on the window 180 that would occur if the radiation reflected by the coating 189 were at least partially absorbed, and thus reduces or eliminates the thermal lens effect in the window 180.During the operation of the EUV source 100, when a thermal lens effect occurs in the viewport assembly 155, optical disturbances may occur in the operations of various metrology modules and / or illumination modules 162, 163, 165 used for operation control, which may reduce the operation efficiency of the EUV source. By reducing the thermal lens effect, the viewport assembly 155 enables, for example, the EUV light source 100 to generate more EUV light 146 by performing the plasma conversion process at a higher speed. At the same time, it is also possible to reduce the possibility of system failures or performance degradation that may occur when the thermal effect increases.

[0022]

[0028] Before providing a more detailed description of the viewport assembly 155, first, the components of the EUV light source 100 will be described.

[0023]

[0029] As shown in FIG. 1A, EUV light source 100 generates EUV light 146 by irradiating target 114 at target position 105 with an amplified light beam 110 that moves along the beam path toward target position 105. Target position 105, also referred to as the irradiation site, is inside 170 of container 160, where container 160 can be a vacuum chamber 160. FIG. 1A shows that the path of target 114 is in the plane of the page. However, the path of target 114 may enter at any angle with respect to the plane of the page or exit the plane of the page at any angle. Thus, for example, the path of target 114 may proceed into the page or proceed out of the page, and may be, for example, a path in a plane perpendicular to the plane of the page that includes the path of amplified light beam 110. When amplified light beam 110 strikes target 114 at target position 105, the target material in target 114 is converted to a plasma state 106 having elements with emission lines in the EUV range. The generated plasma 106 has certain characteristics depending on the composition of the target material in target 114. These characteristics may include, for example, the wavelength of the EUV light generated by plasma 106, the type and amount of debris emitted from plasma 106, and the like.

[0024]

[0030] Further, the EUV light source 100 also includes a target material delivery system 125 that delivers, controls, and guides the target 114, and each target 114 takes the form of liquid droplets, a liquid stream, solid particles or clusters, solid particles contained within the liquid droplets, or solid particles contained within the liquid stream. The EUV light source 100 further includes a target catcher 126 positioned to receive unused targets and / or residues of used targets. Each target 114 includes a target material, for example, water, tin, lithium, xenon, or any material that has emission lines in the EUV range when converted to a plasma state. For example, the tin element can be used as pure tin (Sn), as a tin compound (e.g., SnBr4, SnBr2, SnH4), or as a tin alloy (e.g., tin-gallium alloy, tin-indium alloy, tin-indium-gallium alloy, or any combination of these alloys). One or more targets 114 may contain impurities such as non-target particles. Thus, in the absence of impurities, one or more targets 114 are composed of only the target material. One or more targets 114 are delivered by the target material delivery system 125 to the inside 170 of the container 160 and then to the target position 105.

[0025]

[0031] The EUV light source 100 includes a drive laser system 115, which is a system that generates an optical beam 110 amplified by population inversion in one or more gain media of the laser system 115. The drive laser system 115 includes a beam delivery system that includes a beam transport system and a focus assembly 122. The beam transport system and the focus assembly 122 direct and modify the amplified optical beam 110 as needed and align the focus of the amplified optical beam 110 with the target position 105. The term "amplified optical beam" encompasses one or more of the light from the laser system 115 that is only amplified and not necessarily a coherent laser oscillation, and the light from the laser system 115 that is amplified and also a coherent laser oscillation.

[0026]

[0032] The optical amplifier of the laser system 115 can include a filling gas containing CO2 as a gain medium and can amplify light with a wavelength of about 9100 to about 11000 nanometers (nm), particularly light with a wavelength of about 10600 nm, with a gain of 1000 or more. Amplifiers and lasers suitable for use in the laser system 115 include pulsed laser devices, for example, pulsed gas discharge CO2 laser devices that generate radiation at about 9300 nm or about 10600 nm with DC or RF excitation and operate, for example, with a relatively high output of 10 kW or more and a high pulse repetition rate of 50 kHz or more. The optical amplifier of the laser system 115 may include a cooling system such as water that can be used when operating the laser system 115 at a higher output.

[0027]

[0033] The EUV light source 100 includes a collector mirror 135 having an aperture 140 that allows the amplified light beam 110 to pass through and reach the target position 105. The collector mirror 135 is, for example, an elliptical mirror having a primary focus at the target position 105 and a secondary focus at an intermediate position 145 (also called an intermediate focus). At this intermediate position 145, EUV light 146 is output from the EUV light source 100 and can be input, for example, into an integrated circuit lithography tool (not shown in FIG. 1A). The EUV light source 100 can also include an open-ended hollow cone 149 (for example, a gas cone) that tapers from the collector mirror 135 toward the target position 105 so as to reduce the amount of plasma generation debris entering the focus assembly 122 while allowing the amplified light beam 110 to reach the target position 105. For this purpose, a gas flow directed toward the target position 105 may be supplied into the cone 149.

[0028]

[0034] The EUV light source 100 can include one or more target detection and sensing modules 162 and one or more light sources 163 that provide illumination used by the target detection and sensing module 162. The target detection and sensing module 162 provides an output representing the position and velocity of the target 114, for example, the position and velocity of the target 114 relative to the target position 105, to control the operation of one or more of the target material delivery system 125, the drive laser system 115, and the focus assembly 122, adjusting the timing of the pulses of the amplified light beam 110 and the position and / or the focusing force of the beam focus, enabling the focused pulses of the amplified light beam 110 to strike one or more targets 114 at the target position 105 to generate EUV light 146.

[0029]

[0035] Further, the EUV light source 100 can include one or more source detectors 165 that measure one or more EUV light parameters including, but not limited to, pulse energy, energy distribution as a function of wavelength, energy within a specific wavelength band, energy outside a specific wavelength band, and angular distribution of EUV intensity and / or average output. Information from the source detector 165 can be used to control and optimize parameters such as the timing and focus of the pulses of the amplified light beam 110 to appropriately capture the target 114 (within the target position 105) at the appropriate place and time to perform effective and efficient generation of EUV light 146.

[0030]

[0036] Thus, in summary, the EUV light source 100 generates an amplified light beam 110, which is guided along the beam path as a pulse train to irradiate the target 114 at the target position 105, converting the target material within the target 114 into a plasma 106 that emits light in the EUV range (EUV light 146). The amplified light beam 110 operates at a specific wavelength (also called the source wavelength) determined based on the design and characteristics of the drive laser system 115.

[0031]

[0037] Figure 2A shows a side view of a wall 261 of an exemplary container 260 (which may be a vacuum chamber 260). This container 260 may be similar to the container 160 described above with respect to FIG. 1A. In use, the container 260 is sealed, whereby the inner space 270 of the container 260 is maintained in a controlled environment (e.g., a vacuum).

[0032]

[0038] The interior 270 of the container 260 and / or an object therein is illuminated, monitored, and / or observed by a metrology device 250. The metrology device 250 may take the form of a light source or a detection device, and may be, for example, in the form of (1) one or more light source detectors 165 of FIG. 1A, (2) a target detection and sensing module 162, or (3) one or more light sources 163. The metrology device 250 includes a valve assembly 252, a viewport assembly 255 (which is an embodiment of the viewport assembly 155), and a metrology or illumination module 258. The metrology device 250 is attached to an opening 264 that forms a passage from the outside 271 to the inside 270 of the vacuum chamber 260 through the wall 261 of the vacuum chamber 260. In use, the valve assembly 252 and the viewport assembly 255 are coupled to each other and aligned with the metrology or illumination module 258 so that the metrology or illumination module 258 can observe or illuminate the inside 270, or perform observation or illumination towards the inside 270. The valve assembly 252 includes a gate valve 253, which, when closed (FIG. 2B), allows the viewport assembly 255 to be removed from the valve assembly 252 for replacement, adjustment, or cleaning without disturbing the vacuum in the inside 270.

[0033]

[0039] Figure 3 shows a schematic cross-sectional view of an embodiment of the viewport assembly 255 of FIG. 2 in the form of a viewport assembly 355. The viewport assembly 355 includes a window 380 configured to enable optical access to the inside 170 of an extreme ultraviolet (EUV) light source container 160 (of FIGS. 1A, 1B, 2A, and 2B). The window 380 has an outer opposing surface 382 configured to face the outside 371 of the EUV light source container 160 and an inner opposing surface 384 on the opposite side of the outer opposing surface 382. The window 380 has a transmission band that includes the radiation wavelengths that the window 380 can transmit (described later in relation to FIG. 4A).

[0034]

[0040] Further, the viewport assembly 355 also includes a protector 381 configured to protect the window 380 from the inside 370 of the EUV light source container 160. The protector 381 includes a sheet 386 having a window-facing surface 383 and an inner opposing surface 385 on the opposite side of the window-facing surface 383. The window-facing surface 383 faces the inner opposing surface 384 of the window 380 via a gap 387. The sheet 386 is made of a material having a thermal conductivity in the range of 10 to 2000 watts per (meter·kelvin) (W / (m·K)), or in the range of 20 to 50 W / (m·K). As shown, the window-facing surface 383 of the sheet 386 can be angled with respect to the inner opposing surface 384 of the window 380 or non-perpendicular to the optical axis OA of the viewport assembly 355 to reduce or avoid back reflection.

[0035]

[0041] When a material with high thermal conductivity is used for the sheet 386, the thermal lens effect in the sheet 386 is reduced, and as a result, the thermal lens effect in the protector 381 is reduced. Examples of materials with high thermal conductivity and good light transmittance include sapphire and diamond. Currently commercially available diamond sheets tend to scatter light with a wavelength near 1000 nm, and among the light used for illumination and / or detection in the EUV light source 100, there may be light with a wavelength of 1000 nm or near 1000 nm. Therefore, in the sheet 386 of such an EUV light source, sapphire can be a suitable material.

[0036]

[0042] In some embodiments, the window 380 can be sealed between the two halves 390a, 390b of the sleeve 390 by seals such as O-rings 391a, 391b. With the O-rings 391a, 391b, or other suitable seals, the window 380 is configured to withstand the pressure difference between its inner opposing surface 384 and its outer opposing surface 382. For example, the window 380 can be configured to withstand a pressure difference of at least 100 kilopascals (kPa) between the inner opposing surface 384 and the outer opposing surface 382 resulting from low pressure and / or vacuum at its inner opposing surface.

[0037]

[0043] The window 380 can be made of or include glass such as borosilicate glass. As the borosilicate glass, for example, Schott N BK7 can be used.

[0038]

[0044] Figure 4A is a graph 401 of a transmittance curve 464 showing the transmittance of radiation on the vertical axis as a function of wavelength in nanometers (nm) for a 10 mm thick sheet of Schott N BK7 or equivalent glass without coating. As can be seen from this transmittance curve 464, the glass can transmit more than 90% of the radiation with wavelengths from about 375 nm to about 1800 nm. Therefore, the transmission band 402 (of window 180, 380), which is defined as the band of wavelengths through which the window can transmit more than 90% of the radiation, extends from about 375 nm to about 1800 nm as shown in Figure 4A.

[0039]

[0045] Figure 4B is a graph 403 of a transmittance curve 465 of optical sapphire for a 10 mm sheet without coating, and sapphire is one of the materials useful as the sheet 386 of the protector 381. The transmittance curve 465 shows the ratio of the transmitted radiation as a function of wavelength in nanometers (nm). For comparison, in Figure 4B, the transmittance curve 464 of the glass in Figure 4A and the associated transmission band 402 (of window 180, 380) are also shown. As can be seen from the comparison between the transmittance curves 464 and 465, sapphire transmits a wider range of wavelengths than glass. The sheet 386 of the protector 381 resists the thermal lens effect due to its high thermal conductivity, while for the window 380, when it is made of glass, its thermal conductivity is not high, so it is desirable to limit the energy absorbed by the window 380.

[0040]

[0046] Thus, in some embodiments, the protector 381 further includes a coating 389 on the window-facing surface 383 of the sheet 386. The coating 389 reflects at least a portion of radiation having a wavelength longer than the wavelengths encompassed by the transmission band of the window 380. As shown in FIGS. 4A and 4B, the transmittance of the glass material of this embodiment decreases from about 90% at about 1800 nm to nearly zero at about 2750 nm and above. However, as shown in FIG. 4B, sapphire has a relatively high transmittance even at 2750 nm and longer wavelengths. Thus, in order to prevent or reduce the thermal lens effect in the window 380, it is important to reflect at least a portion of the radiation having a wavelength longer than about 1800 nm if the window is made of glass. For example, the coating 389 can be configured to reflect 50% or more, or even 70% or more, of the radiation having a wavelength longer than the wavelengths encompassed by the transmission band of the window 380 and up to about 8000 nanometers (nm).

[0041]

[0047] In additional embodiments, the coating 389 may also reflect at least a portion of the radiation having a wavelength shorter than the wavelengths encompassed by the transmission band. For example, the coating can be configured to reflect 50% or more of the radiation having a wavelength shorter than the wavelengths encompassed by the transmission band and up to about 150 nm.

[0042]

[0048] Coating 389 may be preferably considered to be positioned on the inner facing surface 385 rather than on the window facing surface 383 of the sheet 386 because a part of the radiation that can be at least partially absorbed by the sheet 386 may be reflected by the coating 389. However, the protector 381 is exposed to the harsh thermal, physical, and chemical environment inside the vacuum chamber 360. For example, inside the vacuum chamber 160 (360), a hydrogen gas flow may be used to cool the inner surface and / or to protect the inner surface of the wall 161 (361) of the chamber 160 (360) from the deposition of the target material. Hydrogen in this gas flow may be activated or ionized by the energy released inside the vacuum chamber 160 (360), and such activated or ionized hydrogen may damage some of the materials and / or surfaces facing the inside 170 (370) of the vacuum chamber 160 (360). To protect the coating 389 from the environment present inside the inner 170 (370) of the chamber 160 (360) during the operation of the EUV light source 100, according to one aspect, the coating 389 is positioned on the window facing surface 383 of the sheet 386. The inner facing surface 385 can be made of bare sapphire, which has good chemical, physical, and thermal resistance to the environment inside the inner 170 (370) of the vacuum chamber 160 (360) during the operation of the EUV light source 100.

[0043]

[0049] According to another aspect, the material of the sheet 386 transmits one or more of visible light and near-infrared light, and / or the coating 389 also transmits one or more of visible light and near-infrared light. For example, the sheet 386 and the coating 389 transmit light having wavelengths used for illumination and / or observation inside the vacuum chamber 160 (360), for example, light having wavelengths within the "metrology band" 466 shown in FIGS. 4A and 4B. The metrology band 466 can extend, for example, from about 800 nm to about 1000 nm.

[0044]

[0050] In another aspect, the sheet 386 is thinner than the window 380 as measured along the normal to the surfaces of the sheet 386 and the window 380. The relatively small thickness of the sheet 386 results in less radiation being absorbed by the sheet 386, reducing the absorption energy available to create a thermal gradient and thus reducing the thermal lens effect of the sheet 386. The thermal lensing effect in a sheet or other element having a given thermal gradient typically scales with the thickness or optical path length of that element. For this reason, the relatively small thickness of the sheet 386, resulting in a relatively short optical path length, also reduces the thermal lensing effect. By making the thickness of the window 380 relatively greater than the thickness of the sheet 386, the window 380 can provide the aforementioned pressure resistance. For example, the thickness of the sheet 386 can range from 2.2 to 3.2 millimeters (mm), from 2.2 to 2.8 mm, or from 2.39 to 2.59 mm. In contrast, the thickness of the window 380 can range from 4.0 to 6.5 mm, from 5.5 to 6.5 mm, or from 5.9 to 6.1 mm.

[0045]

[0051] Referring to FIG. 5A, in another aspect, a metrology apparatus 550 used in an extreme ultraviolet (EUV) light source (e.g., EUV light source 100) includes a detection module 558 configured to detect light propagating from within an EUV light source container 560, and / or an illumination module 558 configured to supply light into the EUV light source container 560. The metrology apparatus 550 also includes a viewport assembly 555 disposed along the beam path of the detected light or the supplied light. Referring to FIG. 3, the viewport assembly 555 is designed similarly to the viewport assembly 355, and thus includes a window 380 configured to enable optical access to the inside 570 of the EUV light source container 560. Similar to the viewport assembly 355, the window 380 has an outer facing surface 382 configured to face the outside 571 of the EUV light source container 560 and an inner facing surface 384 on the opposite side of the outer facing surface 382. Further, the window 380 has a transmission band that includes the wavelengths of radiation that the window can transmit. The viewport assembly 555 further includes a protector 381 configured to protect the window 380 from the inside 570 of the EUV light source container 560. The protector 381 includes a sheet 386 having a window facing surface 383 and an inner facing surface 385 on the opposite side of the window facing surface. The window facing surface 383 faces the inner facing surface 384 of the window 380 through a gap 387. The sheet 386 is made of a material having a thermal conductivity in the range of 10 to 2000 W / (m·K). In this aspect, as shown in FIG. 5A, when the metrology module 558 is disconnected from the valve assembly 552, the viewport assembly 555 remains attached to or incorporated into the metrology module 558. As described above, before removing the viewport assembly 555 and the metrology module 558a, the gate valve 553 of the valve assembly 552 can be closed to maintain the vacuum or low pressure environment inside 570 of the container 560.

[0046]

[0052] In various embodiments, the metrology module 558 of the metrology apparatus 550 can function as a target detection module, or as a target imaging module, or as an illumination module configured to search for a target moving within the EUV light source vessel 560, or as a target backlighting module configured to search for a target within the EUV light source vessel 560.

[0047]

[0053] In another aspect shown in FIG. 5B, the viewport assembly 555 itself can be split into a structure 555a including a window and a structure 555b including a protector, and when the metrology module is disconnected from the valve assembly 552, the structure including the protector remains with the valve assembly 552 and the structure including the window remains with the metrology module 558, so that these two structures 555a and 555b can be separated.

[0048]

[0054] In another aspect with reference to FIGS. 1A, 1B, and 3, the EUV light source 100 includes a vacuum chamber 160, 360 including vacuum chamber walls 161, 361, and an opening 364 to the inside 370 of the chamber is defined by this wall. The window 380 is coupled to the chamber 360 and positioned to close the opening 364. The window 380 has an inner opposing surface 384 facing the inside 370 of the chamber 360 and an outer opposing surface 382 on the opposite side of this inner opposing surface 384. The window 380 further has a transmission band including wavelengths of radiation that the window 380 can transmit, such as, for example, a portion exceeding 90% of the transmittance curve of FIG. 4A. The EUV light source 100 further includes a protector 381 positioned to protect the window 380 from the inside 370 of the vacuum chamber 360. The protector 381 includes a sheet 386 having a window facing surface 383 and an inner opposing surface 385 on the opposite side of this window facing surface 383. The window facing surface 383 faces the inner opposing surface 384 of the window 380 through a gap 387. The sheet 386 is made of a material having a thermal conductivity in the range of 10 to 2000 W / (m·K).

[0049]

[0055] In yet another aspect, an optical coating 389 is provided on the window-facing surface 383 of the sheet 386, and this optical coating 389 reflects at least a portion of radiation having a wavelength longer than the wavelengths included in the transmission band of the window 380. Also, the optical coating 389 may reflect at least a portion of radiation having a wavelength shorter than the wavelengths included in the transmission band. The sheet 386 can comprise or consist of sapphire. The window 380 can comprise or consist of glass.

[0050]

[0056] In another aspect, the window 380 can, optionally, (further) comprise or consist of sapphire.

[0051]

[0057] FIG. 6 is a diagram showing an EUV light source 600 that can be an EUV light source having any one of the EUV light source containers 160, 260, 360, 560 disclosed herein. This EUV light source 600 is positioned together with an EUV lithography exposure apparatus 690. The lithography exposure apparatus 690 receives EUV light 646 generated by the EUV light source 600, reflects this with one or more illumination mirrors 672, and illuminates a reflective pattern or reticle 673. The EUV light reflected from the pattern or reticle 673 is further reflected and reduced by one or more reduction mirrors 674 and irradiated onto a substrate or wafer 675 (or one or more photosensitive layers on the substrate or wafer 675), making it possible to form a patterned structure on the substrate or wafer 675.

[0052]

[0058] Reviewing and pointing out some advantages of the disclosed viewport assemblies 155, 355, 555, due to the high thermal conductivity of the materials forming the sheets 186, 386, the thermal lens effect of the sheets 186, 386 is reduced. When sapphire is used for the windows 180, 380, due to its high thermal conductivity, the thermal lens effect of the windows is reduced. Alternatively or additionally, by the optical coatings 189, 389 on the sheets 186, 386, even when glass is used for the windows 180, 380, at least a part of the radiation that should be at least partially absorbed by the windows is reflected, thereby preventing or reducing the thermal lens effect of the windows.

[0053]

[0059] By positioning the optical coatings 189, 389 on the window-facing surfaces 383 of the sheets 186, 386, the optical coatings are protected from any chemical, physical, and thermal effects occurring inside the vacuum chambers 160, 360, i.e., 170, 370, during the operation of the EUV light source 100.

[0054]

[0060] By keeping the sheets 186, 386 relatively thin, the amount of radiation absorbed by the sheets 186, 386 is reduced, and the thermal lens effect is further reduced. The windows 180, 380 can be made relatively thick, thereby providing sufficient strength to withstand the pressure difference between the inside 170, 370 and the outside of the vacuum chambers 160, 360.

[0055]

[0061] Providing gaps 187, 387 between the protectors 181, 381 and the windows 180, 380 contributes to thermally insulating the windows 180, 380 from the protectors 181, 381. In some embodiments, also referring to FIG. 3, the protector 381 is not sealed within the sleeve 390, whereby the gap 387 can be made the same as, or equal to, the vacuum (or ultra-low pressure) inside the vacuum chamber 360 during use, contributing to the thermal insulation between the window 380 and the protector 381, and also the sheet 386 can be made thin as it does not need to withstand the pressure difference.

[0056]

[0062] These embodiments can be further described using the following clauses. 1. A window configured to enable optical access to the inside of an extreme ultraviolet (EUV) light source container, having an outer facing surface configured to face the outside of the EUV light source container and an inner facing surface on the opposite side of the outer facing surface, and further having a transmission band including wavelengths of radiation that the window can transmit. A protector configured to protect the window from the inside of the EUV light source container, including a sheet having a window facing surface and an inner facing surface on the opposite side of the window facing surface, the window facing surface facing the inner facing surface of the window through a gap, and the sheet including a material having a thermal conductivity in the range of 10 to 2000 W / (m·K). An assembly including the above. 2. The assembly according to clause 1, wherein the thermal conductivity of the above material is in the range of 20 to 50 W / (m·K). 3. The assembly according to clause 1, wherein the transmission band is a wavelength band including wavelengths at which the window can transmit at least 90% of the radiation of that wavelength. 4. The assembly according to clause 1, wherein the protector further includes a coating on the window facing surface of the sheet, and the coating reflects at least a part of the radiation having a wavelength longer than the wavelengths included in the transmission band. 5. The assembly according to clause 1, wherein the protector further includes a coating on the window facing surface of the sheet, and the coating reflects more than 50% of the radiation having a wavelength longer than the wavelengths included in the transmission band and up to 8000 nm. 6. The assembly according to clause 1, wherein the protector further includes a coating on the window facing surface of the sheet, and the coating reflects more than 70% of the radiation having a wavelength longer than the wavelengths included in the transmission band and up to 8000 nm. 7. The protector further includes a coating on the window-facing surface of the sheet, the coating reflecting more than 50% of the radiation having a wavelength longer than the wavelengths included in the transmission band and up to 8000 nm, and reflecting more than 50% of the radiation having a wavelength shorter than the wavelengths included in the transmission band and up to 150 nm, the assembly according to clause 1. 8. The protector further includes a coating on the window-facing surface of the sheet, the coating reflecting at least a portion of the radiation having a wavelength longer than the wavelengths included in the transmission band and further reflecting at least a portion of the radiation having a wavelength shorter than the wavelengths included in the transmission band, the assembly according to clause 1. 9. The protector further includes a coating on the window-facing surface of the sheet, the coating reflecting at least a portion of the radiation having a wavelength longer than the wavelengths included in the transmission band, and the coating reflecting more than 50% of the radiation having wavelengths in the range of 150 - 845 nm and wavelengths in the range of 1090 - 8000 nm, the assembly according to clause 1. 10. The above material transmits one or more of visible light and near-infrared light, the assembly according to clause 1. 11. The window is configured to withstand a pressure difference between its inner-facing surface and its outer-facing surface, the assembly according to clause 1. 12. The window is configured to withstand a pressure difference between its inner-facing surface and its outer-facing surface, which results from a low pressure and / or vacuum on its inner-facing surface, and is at least 100 kPa between its two surfaces, the assembly according to clause 1. 13. The window-facing surface of the sheet is angled with respect to the inner-facing surface of the window, the assembly according to clause 1. 14. The sheet includes sapphire, the assembly according to clause 1. 15. The sheet includes sapphire and the window includes glass, the assembly according to clause 1. 16. The sheet includes sapphire and the glass includes borosilicate glass, the assembly according to clause 1. 17. The assembly according to clause 1, wherein the sheet contains sapphire and the window contains Schott N-BK7 borosilicate glass. 18. The assembly according to clause 1, wherein the sheet contains sapphire, the window contains Schott N-BK7 borosilicate glass, and the protector further contains a coating on the window-facing surface of the sheet, and this coating reflects at least a part of the radiation having a wavelength longer than the wavelength included in the transmission band. 19. The assembly according to clause 1, wherein the sheet contains sapphire, the window contains Schott N-BK7 borosilicate glass, the protector further contains a coating on the window-facing surface of the sheet, and this coating reflects at least a part of the radiation having a wavelength longer than the wavelength included in the transmission band, and further reflects at least a part of the radiation having a wavelength shorter than the wavelength included in the transmission band. 20. The assembly according to clause 1, wherein the sheet contains sapphire, the window contains Schott N-BK7 borosilicate glass, the protector further contains a coating on the window-facing surface of the sheet, and this coating reflects at least a part of the radiation having a wavelength longer than the wavelength included in the transmission band, and the inner-facing surface of the sheet is bare sapphire. 21. The assembly according to clause 1, wherein the sheet contains sapphire and the window contains sapphire. 22. The assembly according to clause 1, wherein the thickness of the sheet ranges from 2.2 to 3.2 mm. 23. The assembly according to clause 1, wherein the thickness of the sheet ranges from 2.39 to 2.59 mm. 24. The assembly according to clause 1, wherein the thickness of the window ranges from 4.0 to 6.5 mm. 25. The assembly according to clause 1, wherein the thickness of the window ranges from 5.9 to 6.1 mm. 26. The assembly according to clause 1, which is attached to an opening defined by penetrating the wall of the vacuum chamber of an extreme ultraviolet (EUV) light source, and the vacuum chamber is in a vacuum state. 27. A metrology apparatus for an extreme ultraviolet (EUV) light source container, comprising: An illumination module configured to supply light into the EUV light source container and / or a detection module configured to detect light propagating from within the EUV light source container; An assembly disposed along a beam path of the detected light or a beam path of the supplied light; The assembly includes: A window configured to enable optical access to the inside of the EUV light source container, having an outer facing surface configured to face the outside of the EUV light source container and an inner facing surface on the opposite side of the outer facing surface, and further having a transmission band including wavelengths of radiation that the window can transmit; A protector configured to protect the window from the inside of the EUV light source container, including a sheet having a window facing surface and an inner facing surface on the opposite side of the window facing surface, the window facing surface facing the inner facing surface of the window with a gap therebetween, and the sheet including a material having a thermal conductivity in the range of 10 to 2000 W / (m·K); The metrology apparatus. 28. The metrology apparatus according to clause 27, wherein the detection module includes a target detection module. 29. The metrology apparatus according to clause 27, wherein the detection module includes a target imaging module. 30. The metrology apparatus according to clause 27, wherein the illumination module includes an illumination module configured to search for a target moving towards an illumination area within the EUV light source container. 31. The metrology apparatus according to clause 27, wherein the illumination module includes a target back-illumination module configured to search for a target within the EUV light source container. 32. The metrology apparatus according to clause 27, further including an optical coating on the window facing surface of the sheet, the optical coating reflecting at least a portion of radiation having a wavelength longer than the wavelengths included in the transmission band. 33. The metrology device according to clause 27, further comprising an optical coating on the window-facing surface of the sheet, the optical coating reflecting at least a portion of radiation having a wavelength longer than the wavelengths included in the transmission band, and further reflecting at least a portion of radiation having a wavelength shorter than the wavelengths included in the transmission band. 34. The metrology device according to clause 27, wherein the sheet comprises sapphire. 35. The metrology device according to clause 27, wherein the sheet comprises sapphire and the window comprises glass. 36. The metrology device according to clause 27, wherein the sheet comprises sapphire and the window comprises sapphire. 37. An extreme ultraviolet (EUV) light source, a vacuum chamber including a vacuum chamber wall, the vacuum chamber having an opening defined therethrough by the wall, a window coupled to the chamber and positioned to close the opening, the window having an inner facing surface facing the inside of the chamber and an outer facing surface on the opposite side of the inner facing surface, and further having a transmission band including the wavelengths of radiation that the window can transmit, a protector positioned to protect the window from the inside of the chamber, the protector including a sheet having a window-facing surface and an inner facing surface on the opposite side of the window-facing surface, the window-facing surface facing the inner facing surface of the window through a gap, and the sheet including a material having a thermal conductivity in the range of 10 to 2000 W / (m·K), comprising an extreme ultraviolet (EUV) light source. 38. The EUV light source according to clause 37, further comprising an optical coating on the window-facing surface of the sheet, the optical coating reflecting at least a portion of radiation having a wavelength longer than the wavelengths included in the transmission band. 39. The EUV light source according to clause 37 further includes an optical coating on the window-facing surface of the sheet, and this optical coating reflects at least a part of the radiation having a wavelength longer than the wavelength included in the transmission band, and further reflects at least a part of the radiation having a wavelength shorter than the wavelength included in the transmission band. 40. The EUV light source according to clause 37, wherein the sheet includes sapphire. 41. The EUV light source according to clause 37, wherein the sheet includes sapphire and the window includes glass. 42. The EUV light source according to clause 37, wherein the sheet includes sapphire and the window includes sapphire. 43. The EUV light source according to clause 37, wherein the vacuum chamber is in a vacuum state.

[0057]

[0063] The above-described embodiments and other embodiments are included in the appended claims.

Claims

1. A window configured to enable optical access to the inside of an extreme ultraviolet (EUV) light source container, having an outer facing surface configured to face the outside of the EUV light source container and an inner facing surface on the opposite side of the outer facing surface, and further having a transmission band including wavelengths of radiation that the window can transmit. A protector configured to protect the window from the inside of the EUV light source container, including a sheet having a window facing surface and an inner facing surface on the opposite side of the window facing surface, the window facing surface facing the inner facing surface of the window with a gap therebetween, and the sheet including a material having a thermal conductivity in the range of 10 to 2000 W / (m·K). An assembly including the above.

2. The assembly according to claim 1, wherein the thermal conductivity of the material is in the range of 20 to 50 W / (m·K).

3. The assembly according to claim 1, wherein the transmission band is a wavelength band including wavelengths at which the window can transmit at least 90% of the radiation of that wavelength.

4. The assembly according to claim 1, wherein the protector further includes a coating on the window facing surface of the sheet, and the coating reflects at least a part of the radiation having a wavelength longer than the wavelength included in the transmission band.

5. The assembly according to claim 1, wherein the protector further includes a coating on the window facing surface of the sheet, and the coating reflects 50% or more of the radiation having a wavelength longer than the wavelength included in the transmission band and up to 8000 nm.

6. The assembly according to claim 1, wherein the protector further includes a coating on the window facing surface of the sheet, and the coating reflects 70% or more of the radiation having a wavelength longer than the wavelength included in the transmission band and up to 8000 nm.

7. The protector further includes a coating on the window-facing surface of the sheet, the coating reflecting at least 50% of radiation having a wavelength longer than the wavelength included in the transmission band and up to 8000 nm, and reflecting at least 50% of radiation having a wavelength shorter than the wavelength included in the transmission band and up to 150 nm. The assembly according to claim 1.

8. The protector further includes a coating on the window-facing surface of the sheet, the coating reflecting at least a portion of radiation having a wavelength longer than the wavelength included in the transmission band, and the coating further reflecting at least a portion of radiation having a wavelength shorter than the wavelength included in the transmission band. The assembly according to claim 1.

9. The protector further includes a coating on the window-facing surface of the sheet, the coating reflecting at least a portion of radiation having a wavelength longer than the wavelength included in the transmission band, and the coating reflecting at least 50% of radiation having wavelengths in the range of 150 to 845 nm and in the range of 1090 to 8000 nm. The assembly according to claim 1.

10. The material transmits one or more of visible light and near-infrared light. The assembly according to claim 1.

11. The window is configured to withstand a pressure difference between its inner-facing surface and its outer-facing surface. The assembly according to claim 1.

12. The window is configured to withstand a pressure difference between its inner-facing surface and its outer-facing surface, the pressure difference being at least 100 kPa between the two surfaces, resulting from a low pressure and / or vacuum at the inner-facing surface. The assembly according to claim 1.

13. The window-facing surface of the sheet is angled with respect to the inner-facing surface of the window. The assembly according to claim 1.

14. The sheet includes sapphire. The assembly according to claim 1.

15. The sheet includes sapphire and the window includes glass. The assembly according to claim 1.

16. The sheet includes sapphire and the glass includes borosilicate glass. The assembly according to claim 1.

17. The assembly according to claim 1, wherein the sheet comprises sapphire and the window comprises Schott N-BK7 borosilicate glass.

18. The assembly according to claim 1, wherein the sheet comprises sapphire, the window comprises Schott N-BK7 borosilicate glass, the protector further comprises a coating on the window-facing surface of the sheet, and the coating reflects at least a portion of radiation having a wavelength longer than the wavelength included in the transmission band.

19. The assembly according to claim 1, wherein the sheet comprises sapphire, the window comprises Schott N-BK7 borosilicate glass, the protector further comprises a coating on the window-facing surface of the sheet, the coating reflects at least a portion of radiation having a wavelength longer than the wavelength included in the transmission band, and the coating further reflects at least a portion of radiation having a wavelength shorter than the wavelength included in the transmission band.

20. The assembly according to claim 1, wherein the sheet comprises sapphire, the window comprises Schott N-BK7 borosilicate glass, the protector further comprises a coating on the window-facing surface of the sheet, the coating reflects at least a portion of radiation having a wavelength longer than the wavelength included in the transmission band, and the inner-facing surface of the sheet is bare sapphire.

21. The assembly according to claim 1, wherein the sheet comprises sapphire and the window comprises sapphire.

22. The assembly according to claim 1, wherein the thickness of the sheet ranges from 2.2 to 3.2 mm.

23. The assembly according to claim 1, wherein the thickness of the sheet ranges from 2.39 to 2.59 mm.

24. The assembly according to claim 1, wherein the thickness of the window ranges from 4.0 to 6.5 mm.

25. The assembly according to claim 1, wherein the thickness of the window ranges from 5.9 to 6.1 mm.

26. The assembly according to claim 1, wherein the assembly is attached to an opening defined by penetrating a wall of a vacuum chamber of an extreme ultraviolet (EUV) light source, and the vacuum chamber is in a vacuum state.

27. A metrology device for an extreme ultraviolet (EUV) light source container, An illumination module configured to supply light into the EUV light source container and / or a detection module configured to detect light propagating from within the EUV light source container, An assembly disposed along the beam path of the detected light or the beam path of the supplied light, The assembly includes A window configured to enable optical access to the inside of the EUV light source container, having an outer facing surface configured to face the outside of the EUV light source container and an inner facing surface on the opposite side of the outer facing surface, and further having a transmission band including the wavelengths of radiation that the window can transmit, A protector configured to protect the window from the inside of the EUV light source container, including a sheet having a window facing surface and an inner facing surface on the opposite side of the window facing surface, the window facing surface facing the inner facing surface of the window through a gap, and the sheet including a material having a thermal conductivity in the range of 10 to 2000 W / (m·K), A metrology device.

28. The metrology device according to claim 27, wherein the detection module includes a target detection module.

29. The metrology device according to claim 27, wherein the detection module includes a target imaging module.

30. The metrology device according to claim 27, wherein the illumination module includes an illumination module configured to search for a target moving toward an illumination area within the EUV light source container.

31. The metrology device according to claim 27, wherein the illumination module includes a target back-illumination module configured to search for a target within the EUV light source container.

32. The metrology device according to claim 27, further including an optical coating on the window facing surface of the sheet, the optical coating reflecting at least a portion of the radiation having a wavelength longer than the wavelength included in the transmission band.

33. The metrology device according to claim 27, further comprising an optical coating on the window-facing surface of the sheet, the optical coating reflecting at least a part of radiation having a wavelength longer than the wavelength included in the transmission band, and the optical coating further reflecting at least a part of radiation having a wavelength shorter than the wavelength included in the transmission band.

34. The metrology device according to claim 27, wherein the sheet comprises sapphire.

35. The metrology device according to claim 27, wherein the sheet comprises sapphire and the window comprises glass.

36. The metrology device according to claim 27, wherein the sheet comprises sapphire and the window comprises sapphire.

37. An extreme ultraviolet (EUV) light source, comprising: A vacuum chamber including a vacuum chamber wall, the wall defining an opening therethrough; A window coupled to the chamber and positioned to close the opening, the window having an inner facing surface facing the inside of the chamber and an outer facing surface on the opposite side of the inner facing surface, and further having a transmission band including wavelengths of radiation that the window can transmit; A protector positioned to protect the window from the inside of the chamber, the protector including a sheet having a window-facing surface and an inner facing surface on the opposite side of the window-facing surface, the window-facing surface facing the inner facing surface of the window with a gap therebetween, and the sheet including a material having a thermal conductivity in the range of 10 to 2000 W / (m·K); An extreme ultraviolet (EUV) light source including the above.

38. The EUV light source according to claim 37, further comprising an optical coating on the window-facing surface of the sheet, the optical coating reflecting at least a part of radiation having a wavelength longer than the wavelength included in the transmission band.

39. The EUV light source according to claim 37, further comprising an optical coating on the window-facing surface of the sheet, the optical coating reflecting at least a part of radiation having a wavelength longer than the wavelength included in the transmission band, and the optical coating further reflecting at least a part of radiation having a wavelength shorter than the wavelength included in the transmission band. Claim 40 The EUV light source according to claim 37, wherein the sheet contains sapphire. Claim 41 The EUV light source according to claim 37, wherein the sheet contains sapphire and the window contains glass. Claim 42 The EUV light source according to claim 37, wherein the sheet contains sapphire and the window contains sapphire. Claim 43 The EUV light source according to claim 37, wherein the vacuum chamber is in a vacuum state.

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