Window assembly for extreme ultraviolet light source

Abstract

An assembly comprising: a window for optical access to an interior of an extreme ultraviolet (EUV) light source container, the window having a transmission band; the present invention relates to an EUV light source container comprising a window, a shield disposed on the window, and a protector configured to isolate the window from an interior shield of the EUV light source container, the protector comprising a sheet having a surface facing the window across a gap, the sheet having a thermal conductivity in a range of 10 W / (# imgabs 0 #) to 2000 W / (# imgabs 1 #). The sheet may be a sapphire sheet and may have an optical coating on a surface facing the window, the coating reflecting at least some of the radiation outside the transmission band, and an opposite side of the sheet may be bare sapphire.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. application No. 63 / 351,457, filed on June 13, 2022, and the entire contents of that U.S. application are incorporated herein by reference. Technical Field

[0003] The disclosed subject matter relates to a window assembly for an extreme ultraviolet (EUV) light source. Background Art

[0004] Extreme ultraviolet (“EUV”) light, e.g., electromagnetic radiation having a wavelength of about 50 nanometers (nm) or less (sometimes referred to as soft x-rays) and including wavelengths of about 13 nm, can be used in photolithography processes to create very small features on substrates (e.g., silicon wafers).

[0005] Methods for generating EUV light include, but are not necessarily limited to, converting a material having elemental emission lines in the EUV range into a plasma state. Suitable materials include, for example, xenon, lithium, and tin. In one such method, often referred to as laser produced plasma ("LPP") or laser induced decomposition (LIB), the desired plasma may be generated by irradiating a target material, for example in the form of droplets, streams, or clusters of material, with an amplified beam of light, which may be referred to as a drive laser. For this process, the plasma is generated in a sealed container, such as a vacuum chamber, and various types of metrology equipment are used to monitor the plasma. Summary of the invention

[0006] In one general aspect, an assembly includes: a window configured to allow optical access to the interior of an extreme ultraviolet (EUV) light source container, the window having an exterior-facing surface configured to face the exterior of the EUV light source container and an interior-facing surface opposite the exterior-facing surface, the window also having a transmission band covering wavelengths of radiation that the window can transmit; and a protector configured to shield the window from the interior of the EUV light source container, the protector comprising a sheet having a surface facing the window and an interior-facing surface opposite the window-facing surface, the window-facing surface spanning a gap and facing the interior-facing surface of the window, the sheet comprising a thermal conductivity having a thermal conductivity of 10 W / ( ) to 2000 W / ( ) range of thermal conductivity materials.

[0007] Implementations may include one or more of the following features: The thermal conductivity of the material may be within 20 W / ( ) to 50 W / ( ). The transmission band may encompass or be defined as a wavelength band of wavelengths in which the window can transmit at least 90% of the radiation. The protector may include a coating on the surface of the sheet facing the window, wherein the coating reflects at least some radiation having a wavelength longer than the wavelength encompassed by the transmission band. For example, the coating may reflect 50% or more, or even 70% or more, of radiation having a wavelength longer than the wavelength encompassed by the transmission band and up to 8000 nm. The coating may reflect at least some or even 50% or more of radiation having a wavelength shorter than the wavelength encompassed by the transmission band, as low as 150 nm. The coating may reflect 50% or more of radiation having a wavelength in the range of 150 nm to 845 nm and in the range of 1090 nm to 8000 nm.

[0008] Implementations may also include one or more of the following features: the material (of the sheet) is capable of transmitting one or more of visible light and near infrared light. The window may be configured to withstand a pressure difference between the inner-facing surface of the window and the outer-facing surface of the window, and even withstand a pressure difference of at least 100 kPa between the two surfaces of the window between the inner-facing surface of the window and the outer-facing surface of the window due to low pressure and / or vacuum at the inner-facing surface of the window. The surface of the sheet facing the window may be inclined relative to the inner-facing surface of the window. The sheet may include or be formed of sapphire. The window may include or be formed of glass. The glass may include or may be borosilicate glass. The borosilicate glass may include or may be Schott N-BK7. The protector may include a coating on the surface of the sheet facing the window, wherein the coating reflects at least some radiation having a wavelength longer than the wavelength covered by the transmission band. The coating may reflect at least some radiation having a wavelength shorter than the wavelength covered by the transmission band.

[0009] Implementations may also include one or more of the following features: The interior-facing surface of the sheet may be bare sapphire. The window may include or may be formed of sapphire. The sheet may have a thickness in the range of 2.2 mm to 3.2 mm. The sheet may also have a thickness in the range of 2.39 mm to 2.59 mm. The window may have a thickness in the range of 4.0 mm to 6.5 mm. The window may also have a thickness in the range of 5.9 mm to 6.1 mm. The assembly may be mounted in an opening defined by a wall of a vacuum chamber through an extreme ultraviolet (EUV) light source, and the vacuum chamber may be under vacuum.

[0010] 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 provide light into the EUV light source container; and an assembly arranged along a beam path of the detected light or the provided light, the assembly comprising: (1) a window configured to allow optical access to the interior of the EUV light source container, the window having an exterior-facing surface configured to face the exterior of the EUV light source container and an interior-facing surface opposite the exterior-facing surface, the window also having a transmission band covering wavelengths of radiation that the window can transmit; and (2) a protector configured to shield the window from the interior of the EUV light source container, the protector comprising a sheet having a surface facing the window and an interior-facing surface opposite the window-facing surface, the window-facing surface spanning a gap and facing the interior-facing surface of the window, the sheet comprising a light having a power rating of 10 W / ( ) to 2000 W / ( ) or is formed from a material having a thermal conductivity within a range of ).

[0011] Implementations may include one or more of the following features: The detection module may include or may be a target detection module. The detection module may include or may be a target imaging module. The illumination module may include or may be an illumination module configured to detect a target traveling toward an illumination zone within the EUV light source container. The illumination module may be a target backlight module configured to detect a target within the EUV light source container. The measurement device may include an optical coating located on a surface of the sheet facing the window, wherein the optical coating reflects at least some radiation having a wavelength longer than the wavelength covered by the transmission band. The optical coating may reflect at least some radiation having a wavelength shorter than the wavelength covered by the transmission band. The sheet may include or may be formed of sapphire. The window may include or be formed of glass.

[0012] In another general aspect, an extreme ultraviolet (EUV) light source may include: (1) a vacuum chamber, the vacuum chamber including a vacuum chamber wall, the vacuum chamber wall defining an opening into an interior of the chamber; (2) a window coupled to the chamber, the window positioned to close the opening, the window having an interior-facing surface facing the interior of the chamber and an exterior-facing surface opposite the interior-facing surface, the window also having a transmission band covering wavelengths of radiation that the window is capable of transmitting; and (3) a protector positioned to shield the window from the interior of the chamber, the protector including a sheet having a surface facing the window and an interior-facing surface opposite the window-facing surface, the window-facing surface spanning a gap and facing the interior-facing surface of the window, the sheet including a sheet having a power rating of 10 W / ( ) to 2000 W / ( ) range of thermal conductivity materials.

[0013] Implementations may include one or more of the following features: An optical coating may be on a surface of the sheet facing the window, and the optical coating may reflect at least some radiation having a wavelength longer than the wavelength encompassed by the transmission band. The optical coating may also reflect at least some radiation having a wavelength shorter than the wavelength encompassed by the transmission band. The sheet may include or be formed of sapphire. The window may include or be formed of glass. The window may include or be formed of sapphire. The vacuum chamber may be under vacuum.

[0014] The details of one or more implementations are set forth in the accompanying drawings and detailed description below. Other features will be apparent from the detailed description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1A is a simplified diagram showing an extreme ultraviolet (EUV) light source defining a container, such as a vacuum chamber, with a target location.

[0016] Figure 1B yes Figure 1A A close-up view of the window assembly within the container of the EUV light source.

[0017] Figure 2A and Figure 2B yes Figure 1A and Figure 1B Cross-sectional view of the measurement equipment for the light source.

[0018] Figure 3 is a simplified cross-sectional view of a viewport assembly.

[0019] Figure 4A and Figure 4B is a graph of the transmission of exemplary materials used in window assemblies.

[0020] Figure 5A and Figure 5B is a cross-sectional view of another aspect of the measurement device.

[0021] Figure 6 It is a schematic diagram of EUV light source together with lithography equipment. DETAILED DESCRIPTION

[0022] An assembly for reducing or minimizing thermal lensing of a window assembly of an extreme ultraviolet (EUV) light source is disclosed.

[0023] refer to Figure 1A and Figure 1B , showing an embodiment of an EUV light source 100. Window assembly 155 ( Figure 1B ) is an observation mechanism positioned relative to an opening 164 defined by a wall 161 of the container 160. The window assembly 155 includes a window 180 through which the interior 170 of the container 160 can be observed or through which light 111 can travel between the exterior 171 of the container 160 and a component or system at the interior 170 of the container 160. The container 160 can be a chamber that is sealed (and under vacuum) and has an environmentally controlled interior 170. The window assembly 155 can be integrated into any of the elements or modules 162, 163, 165 shown as passing through one of the walls 161 of the container 160. Details about the elements 162, 163, 165 are provided below.

[0024] During operation of the EUV light source 100, a material (such as glass) used as the material of the window 180 may be heated by incident light 111 absorbed by the window assembly 155, i.e., light traveling between the exterior 171 and interior 170 of the container 160, or light traveling from the interior 170 to the exterior 171 of the container 160. For example, the window material may be heated by absorbing light 111 transmitted from the interior of the container 160. The refractive index of most optical materials varies as a function of temperature. Thus, heating of the window material may cause the window 180 to experience an adverse effect known as thermal lensing, which is a temperature-dependent change in the optical wavefront transmitted by the window. Possible changes in the wavefront include: (1) a uniform phase shift in the case where the increase in the temperature of the window material is uniform across the surface; (2) a non-uniform, smoothly varying phase shift resulting in an increase in optical power in the case where a uniform thermal gradient is produced across the surface of the window material; and (3) an irregular phase shift resulting in a combination of additional optical power and added optical aberrations in the case where a non-uniform thermal gradient is produced across the window surface.

[0025] The protector 181 can be used to shield the window 180 from light 111 from inside the container 160 and other conditions in the container 160, such as from chemical and / or physical damage and / or deposition of light attenuating materials. The material of the protector 181 can also be subject to thermal lensing, and as light attenuating materials can be deposited on the protector 181, such thermal lensing can increase over time.

[0026] EUV light source 100 operates to generate EUV light 146 by converting a target material having emission lines in the EUV range, such as tin, into a "plasma state" or into a "plasma" 106. In one exemplary technique, a target 114 made of the target material (in an interior 170 of a container 160) is irradiated with an amplified light beam 110. Figure 1A 14), and converts the target material into a plasma state. Converting to a plasma state 106 releases radiation in the emission spectrum of the material of the target 114. In addition to the desired EUV light 146, the emission spectrum may also include deep ultraviolet (DUV) light, visible light, near infrared (NIR) light, and mid-wavelength infrared (MWIR) light. Light having a wavelength within these ranges may propagate toward and arrive at the window assembly 155 (positioned in the wall 161) as "incident" light. In addition, the interaction between the amplified light beam 110 and the target material 114 may scatter and reflect the amplified light beam 110. Some of the scattered and reflected amplified light beams may also arrive at the window assembly 155 as incident light.

[0027] One or more window assemblies 155 may be comprised of various measurement and / or lighting modules such as, Figure 1A Modules 162, 163, and 165 shown in FIG. 1 are used to add light into the interior 170 of the container 160 and / or sense or detect light from the interior 170 of the container 160 for purposes of measurement, detection, process monitoring, and control, etc. Thermal lensing, or the modification of the optical properties of components within the window assembly 155 by thermal effects, can distort the light 111 transmitted into or through the window assembly 155 and / or the image or light collected by the window assembly 155. Because the light emitted through the window assembly and the light received through the window assembly are used for system diagnostics and system control, such as for manipulating the stream of the target 114, the distorted light and / or distorted image formed by the light can degrade the performance of the EUV light source 100 and reduce the amount or quality of the EUV light 146 produced.

[0028] The window assembly 155 is configured to prevent or reduce the effects of thermal lensing. In one aspect of the present invention, the window assembly 155 includes a window 180 configured to allow optical access to the interior 170 of the EUV light source container 160. The window 180 has an exterior-facing surface 182 and an interior-facing surface 184, and a transmission band covering the wavelengths of radiation that the window 180 can transmit. In an implementation, the transmission band can be defined as a wavelength band in which the window 180 can transmit 90% or more of the radiation. The window assembly 155 also includes a protector 181, which is configured to shield and isolate the window 180 from the interior 170 of the EUV light source container 160. The protector 181 includes a sheet 186 having a window-facing surface 183 and an interior-facing surface 185. The window-facing surface 183 spans a gap 187 and faces the interior-facing surface 184 of the window 180, and the sheet 186 includes a material having a relatively high thermal conductivity, i.e., a relative high thermal conductivity of 10 W / ( ) to 2000 W / ( ) range, within 30 W / ( ) to 2000 W / ( ) or within 30 W / ( ) to 50 W / ( ). The high thermal conductivity of the protector material reduces the effects of thermal lensing in the protector 181 by rapidly dissipating heat gradients across the surface of the protector 181. In one embodiment, the protector 181 includes a coating 189 located on the surface 183 of the sheet 186 facing the window. The coating 189 reflects at least some radiation having wavelengths longer than those covered by the transmission band of the window 180, such as by reflecting at least 50% of the incident intensity of the reflected radiation having wavelengths longer than those covered by the transmission band of the window 180. The reflected radiation reduces the thermal load on the window 180 that would otherwise be caused by at least partial absorption of the radiation reflected by the coating 189, thereby reducing or eliminating the effects of thermal lensing at the window 180. During operation of the EUV source 100, thermal lensing in the window assembly 155 can reduce the efficiency of source operation by causing optical interference in the operation of various measurement and / or illumination modules 162, 163, 165 used for operational control. By reducing the effects of thermal lensing, the window assembly 155 may also allow the EUV light source 100 to produce more EUV light 146 , such as by running the plasma conversion process at a higher rate, while also reducing the chance of system failure or performance degradation due to increased thermal effects that would otherwise occur.

[0029] A description of the components of EUV light source 100 is initially described before a more detailed description of window assembly 155 is provided.

[0030] like Figure 1A , EUV light source 100 generates EUV light 146 by irradiating a target 114 located at a target location 105 with an amplified light beam 110 that travels along a beam path toward the target location 105. The target location 105, also referred to as an irradiation site, is within an interior 170 of a container 160, which may be a vacuum chamber 160. Figure 1A The path of target 114 is shown in the plane of the page. However, the path of target 114 may enter or leave the plane of the page at any angle relative to the plane of the page. Thus, for example, the path of target 114 may enter or leave the page, such as traveling in a plane that includes the path of amplified light beam 110 and is perpendicular to the plane of the page. When amplified light beam 110 impinges on target 114 at target position 105, the target material within target 114 is converted into a plasma state 106 of an element having emission lines in the EUV range. The generated plasma 106 has certain properties that depend on the composition of the target material within target 114. These properties may include the wavelength of EUV light generated by plasma 106, and the type and amount of debris released from plasma 106.

[0031] The EUV light source 100 also includes a target material delivery system 125 that delivers, controls, and guides the targets 114, wherein each target 114 is in the form of a droplet, a liquid stream, a solid particle or cluster, a solid particle included in a droplet, or a solid particle included in a liquid stream. The EUV light source 100 also includes a target catcher 126 positioned to receive unused targets and / or some remaining targets among the used targets. Each of the targets 114 includes a target material such as, for example, water, tin, lithium, xenon, or any material having an emission line in the EUV range when converted into a plasma state. For example, elemental tin can be used as pure tin (Sn); as a tin compound such as SnBr4, SnBr2, SnH4; as a tin alloy such as a tin-gallium alloy, a tin-indium alloy, a tin-indium-gallium alloy, or any combination of these alloys. One or more targets 114 may also include impurities such as non-target particles. Therefore, in the absence of impurities, one or more targets 114 are composed only of target materials. One or more targets 114 are delivered by target material delivery system 125 into interior 170 of container 160 and to target location 105 .

[0032] The EUV light source 100 includes a driving laser system 115 that produces an amplified light beam 110 due to a population inversion within one or more gain media of the laser system 115. The driving laser system 115 includes a beam delivery system that includes a beam transport system and a focusing assembly 122. The beam transport system and the focusing assembly 122 steer and modify the amplified light beam 110 as needed and focus the amplified light beam 110 to a target location 105. The term "amplified light beam" encompasses one or more of the following: light from the laser system 115 that is merely amplified but not necessarily coherently oscillating laser light, and light from the laser system 115 that is amplified and is also coherently oscillating laser light.

[0033] The optical amplifier in the laser system 115 may include a fill gas containing CO2 as a gain medium and may amplify light at a wavelength between about 9100 nanometers and about 11000 nanometers (nm), and particularly at about 10600 nm, with a gain greater than or equal to 1000. Suitable amplifiers and lasers for use in the laser system 115 may include pulsed laser devices, such as pulsed gas discharge CO2 laser devices that produce radiation at about 9300 nm or about 10600 nm using DC or RF excitation operating at relatively high power (e.g., 10 kW or more) and high pulse repetition rate (e.g., 50 kHz or more). The optical amplifier in the laser system 115 may also include a cooling system, such as water, that may be used when operating the laser system 115 at higher powers.

[0034] The EUV light source 100 includes a collector mirror 135 having an aperture 140 to allow the amplified light beam 110 to pass through and reach a target location 105. The collector mirror 135 can be, for example, an ellipsoidal mirror having a primary focus at the target location 105 and a secondary focus (also referred to as an intermediate focus) at an intermediate location 145, wherein EUV light 146 can be output from the EUV light source 100 and can be input to, for example, an integrated circuit lithography tool ( Figure 1A The EUV light source 100 may also include an open-ended hollow cone 149 (e.g., a gas cone) that tapers from the collector mirror 135 toward the target location 105 to reduce the amount of plasma-generated debris that enters the focusing assembly 122 while allowing the amplified light beam 110 to reach the target location 105. To this end, a gas flow may be provided in the cone 149 that is directed toward the target location 105.

[0035] The EUV light source 100 may include one or more target detection and sensing modules 162 and one or more light sources 163 for providing illumination for use by the target detection and sensing modules 162. The target detection and sensing modules 162 may provide outputs indicative of the position and velocity of the target 114, for example relative to the target location 105, to allow control of the operation of one or more of the target material delivery system 125, the drive laser system 115, and the focusing assembly 122 to adjust the timing of the pulses of the amplified light beam 110 and the position and / or focality of the beam focal spot, thereby causing the focused pulses of the amplified light beam 110 to meet the one or more targets 114 at the target location 105 for producing EUV light 146.

[0036] In addition, the EUV light source 100 may include one or more light 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 power. Information from the light source detector 165 may be used, for example, to control and optimize parameters such as the timing and focus of pulses of the amplified light beam 110 to properly intercept the target 114 at the appropriate place and time (within the target location 105) for effective and efficient generation of EUV light 146.

[0037] Thus, in general, EUV light source 100 generates an amplified light beam 110 that is directed as a pulse train along a beam path to irradiate a target 114 located at a target location 105, thereby converting a target material located within target 114 into a plasma 106 that emits light in the EUV range (EUV light 146). Amplified light beam 110 operates at a specific wavelength (also referred to as a source wavelength) determined based on the design and properties of a drive laser system 115.

[0038] Figure 2A A side view of a wall 261 of an exemplary container 260 (the container 260 may be a vacuum chamber 260) is shown. The container 260 may be similar to the one described above with respect to Figure 1A The container 160 discussed. During use, the container 260 is sealed so that the interior space 270 of the container 260 is maintained as a controlled environment, such as a vacuum.

[0039] The interior 270 of the container 260 and / or the objects therein are illuminated, monitored, and / or observed using a metrology device 250. The metrology device 250 may take the form of a light source or detection device, such as, for example, any of the following: (1) one or more light source detectors 165, (2) object detection and sensing module 162, or (3) Figure 1A The measuring device 250 includes a valve assembly 252, a window assembly 255 (the window assembly 255 is an embodiment of the window assembly 155), and a measuring or illuminating module 258. The measuring device 250 is installed in an opening 264 that passes through a wall 261 of the vacuum chamber 260 to form a passage from the exterior 271 of the vacuum chamber 260 to the interior 270. During use, the valve assembly 252 and the window assembly 255 are coupled together and aligned with the measuring or illuminating module 258 to allow the measuring or illuminating module 258 to observe or illuminate in the interior 270. The valve assembly 252 includes a gate valve 253, which, when closed ( Figure 2B ) allows the window assembly 255 to be removed from the valve assembly 252 for replacement, adjustment, or cleaning without disturbing the vacuum in the interior 270.

[0040] Figure 3 A diagrammatic cross section of an embodiment of the window assembly 255 of FIG. 2 is shown in the form of a window assembly 355. The window assembly 355 includes a Figure 1A , Figure 1B , Figure 2A , Figure 2B The window 380 is a window 380 for optical access to the interior 170 of the EUV light source container 160. The window 380 has an exterior-facing surface 382 configured to face the exterior 371 of the EUV light source container 160 and an interior-facing surface 384 opposite to the exterior-facing surface 382. The window 380 has a transmission band covering the wavelengths of radiation that the window 380 can transmit (hereinafter referred to as Figure 4A discussed).

[0041] The window assembly 355 also includes a protector 381 configured to shield the window 380 from the interior 370 of the EUV light source container 160. The protector 381 includes a sheet 386 having a surface 383 facing the window and an interior-facing surface 385 opposite to the surface 383 facing the window. The surface 383 facing the window spans a gap 387 and faces the interior-facing surface 384 of the window 380. The sheet 386 is made of a material having a 10W / ( ) to 2000 watts / ( )(W / ( ) or at 20 W / ( ) to 50 W / ( ) in the range of thermal conductivity. As shown, the window-facing surface 383 of the sheet 386 may be tilted relative to the interior-facing surface 384 of the window 380, or may not be perpendicular to the optical axis OA of the window assembly 355 to reduce or avoid back reflections.

[0042] Using a high thermal conductivity material for sheet 386 reduces thermal lensing in sheet 386 and, therefore, protector 381. Materials with high thermal conductivity and good optical transmittance include sapphire and diamond, among others. Current commercially available diamond sheets tend to scatter light having wavelengths approaching 1000 nm, and some of the light used for illumination and / or sensing within EUV light source 100 may have wavelengths at or near 1000 nm. For this reason, sapphire may be a preferred material in sheet 386 in these EUV light sources.

[0043] In an embodiment, the window 380 can be sealed between the halves 390a, 390b of the sleeve 390 by a seal such as an O-ring 391a, 391b. The window 380 is configured to withstand a pressure differential between the interior-facing surface 384 of the window and the exterior-facing surface 382 of the window by the O-ring 391a, 391b or other suitable seal. For example, the window 380 can be configured to withstand a pressure differential of at least 100 kilopascals (kPa) between the interior-facing surface 384 of the window and the exterior-facing surface 382 of the window due to low pressure and / or vacuum at the interior-facing surface of the window.

[0044] The window 380 may be made of or include glass such as borosilicate glass. For example, the borosilicate glass may be Schott N BK7.

[0045] Figure 4A Graph 401 is a transmission curve 464 showing the percentage of transmitted radiation on the vertical axis as a function of wavelength in nanometers (nm) on the horizontal axis for a Schott N BK7 or equivalent glass for an uncoated sheet having a thickness of 10 mm. As can be seen in the transmission curve 464, the glass is capable of transmitting 90% or more of radiation having a wavelength from about 375 nm to about 1800 nm. Figure 4A The transmission band 402 (of the window 180 , 380 ) shown in , which is defined as the wavelength band over which the window is capable of transmitting 90% or more of the radiation, thus extends from about 375 nm to about 1800 nm.

[0046] Figure 4B is a graph 403 of a transmission curve 465 for a 10 mm uncoated sheet of optical sapphire, one of the materials used as sheet 386 of protector 381. The transmission curve 465 is shown as the percentage of transmitted radiation as a function of wavelength in nanometers (nm). Figure 4A The glass transmission curve 464 and the associated transmission band 402 (of windows 180, 380) are also shown in FIG. Figure 4B464 and 465 for comparison. As can be seen from a comparison of transmission curves 464 and 465, sapphire transmits a wider range of wavelengths than glass. While sheet 386 of protector 381 resists thermal lensing due to its high thermal conductivity, if window 380 is made of glass, window 380 does not have high thermal conductivity and therefore it is desirable to limit the energy absorbed by window 380.

[0047] Thus, in an embodiment, the protector 381 further comprises a coating 389 on the surface 383 of the sheet 386 facing the window. The coating 389 reflects at least some radiation having a wavelength longer than the wavelength covered by the transmission band of the window 380. Figure 4A and Figure 4B As can be seen in FIG. 1 , the transmittance of the glass material of this embodiment decreases substantially from about 90% at about 1800 nm to zero at about 2750 nm and above. Figure 4B As shown in , sapphire still has a relatively high transmittance at 2750 nm and even longer wavelengths. Therefore, when the window is made of glass, it is important to reflect at least some radiation having wavelengths longer than about 1800 nm in order to prevent or reduce thermal lensing in window 380. For example, coating 389 can reflect 50% or more, or even 70% or more, of radiation having wavelengths longer than the wavelengths covered by the transmission band of window 380 and up to 8000 nanometers (nm).

[0048] In additional aspects, the coating 389 can also reflect at least some radiation having a wavelength shorter than the wavelengths covered by the transmission band. For example, the coating can reflect 50% or more of radiation having a wavelength shorter than the wavelength covered by the transmission band, down to 150 nm.

[0049] It may be considered preferable to have the coating 389 positioned on the interior facing surface 385 of the sheet 386 rather than on the window facing surface 383, since the coating 389 can then potentially reflect some of the radiation that may be at least partially absorbed by the sheet 386. However, the protector 381 faces a thermally, physically, and chemically challenging environment in the interior 370 of the vacuum chamber 360. For example, a hydrogen gas flow may be used in the vacuum chamber 160 (360) to cool the interior surfaces and / or protect the interior surfaces of the walls 161 (361) of the chamber 160 (360) from the deposition of target materials. The hydrogen in the 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 materials and / or surfaces facing the interior 170 (370) of the vacuum chamber 160 (360). In order to protect the coating 389 from the environmental influences present on the interior 170 (370) of the chamber 160 (360) during 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 interior-facing surface 385 can be bare sapphire, which has good chemical, physical, and thermal resistance to the environment in the interior 170 (370) of the vacuum chamber 160 (360) during operation of the EUV light source 100.

[0050] According to another aspect, the material of sheet 386 transmits one or more of visible light and near infrared light, and / or coating 389 also transmits one or more of visible light and near infrared light. For example, sheet 386 and coating 389 transmit light having a wavelength for illumination and / or observation within vacuum chamber 160 (360), such as having a wavelength in the range of 100 to 1000 nm. Figure 4A and Figure 4B 466. The measurement band 466 may extend, for example, from about 800 nm to about 1000 nm.

[0051] In another aspect, sheet 386 is thinner than window 380, the thickness being measured along the normal of the surface of sheet 386 and window 380. Making the thickness of sheet 386 relatively small reduces the amount of radiation absorbed by sheet 386, thereby reducing the thermal lensing of sheet 386 by reducing the absorbed energy that can be used to generate a thermal gradient. The effect of thermal lensing in a sheet or other element with a given thermal gradient is generally proportional to the thickness or optical path length in the element, so making the thickness of sheet 386 relatively small and the resulting optical path length relatively short also reduces the effect of thermal lensing for this reason. Making the thickness of window 380 relatively greater than the thickness of sheet 386 allows window 380 to provide the compression resistance mentioned above. For example, sheet 386 can have a thickness that can be in the range of 2.2 millimeters to 3.2 millimeters (mm), 2.2 mm to 2.8 mm, or 2.39 mm to 2.59 mm. In contrast, window 380 may have a thickness in a range of 4.0 mm to 6.5 mm, 5.5 mm to 6.5 mm, or 5.9 mm to 6.1 mm.

[0052] refer to Figure 5A In another aspect, a metrology device 550 for use in an extreme ultraviolet (EUV) light source, such as the 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 provide light into the EUV light source container 560. The metrology device 550 also includes a window assembly 555 arranged along a beam path of the detected light or the provided light. Figure 3 , the window assembly 555 is designed similarly to the window assembly 355 and thus includes a window 380 configured to allow optical access to the interior 570 of the EUV light source container 560. Similar to the window assembly 355, the window 380 has an exterior-facing surface 382 configured to face the exterior 571 of the EUV light source container 560 and an interior-facing surface 384 opposite to the exterior-facing surface 382. The window 380 also has a transmission band covering the wavelengths of radiation that the window can transmit. The window assembly 555 also includes a protector 381, which is configured to shield and isolate the window 380 from the interior 570 of the EUV light source container 560. The protector 381 includes a sheet 386, which has a surface 383 facing the window and an interior-facing surface 385 opposite to the surface facing the window. The surface 383 facing the window spans a gap 387 and faces the interior-facing surface 384 of the window 380. The sheet 386 is made of a material having a power supply at 10 W / ( ) to 2000 W / ( ) is made of a material with a thermal conductivity within the range of . Figure 5A, when the measurement module 558 is removed from the valve assembly 552, the window assembly 555 remains attached or integrated with the measurement module 558. As mentioned above, before removing the window assembly 555 and the measurement module 558a, the gate valve 553 in the valve assembly 552 can be closed to maintain a vacuum or low pressure environment in the interior 570 of the container 560.

[0053] In various embodiments, the measurement module 558 of the measurement device 550 can be used as a target detection module, or a target imaging module, or an illumination module configured to detect a target traveling within the EUV light source container 560, or a target backlight module configured to detect a target within the EUV light source container 560.

[0054] exist Figure 5B In another aspect represented in , the window assembly 555 itself can be divided into a window structure 555a and a protector structure 555b, and the two structures 555a and 555b can be separated, wherein, when the measuring module is removed from the valve assembly 552, the protector structure is retained together with the valve assembly 552 and the window structure is retained together with the measuring module 558.

[0055] In reference Figure 1A , Figure 1B ,and Figure 3 In another aspect of the invention, EUV light source 100 includes a vacuum chamber 160, 360 including a vacuum chamber wall 161, 361 defining an opening 364 into an interior 370 of the chamber. A window 380 is coupled to chamber 360 and positioned to close opening 364. Window 380 has an interior-facing surface 384 facing the interior 370 of chamber 360 and an exterior-facing surface 382 opposite interior-facing surface 384. Window 380 also has a transmission band covering wavelengths of radiation that window 380 is capable of transmitting, such as, for example, Figure 4A The portion of the transmission curve above 90%. EUV light source 100 also includes a protector 381, which is positioned to shield window 380 from interior 370 of vacuum chamber 360. Protector 381 includes a sheet 386 having a surface 383 facing the window and an interior-facing surface 385 opposite to the surface 383 facing the window. The surface 383 facing the window spans a gap 387 and faces the interior-facing surface 384 of window 380. Sheet 386 is made of a material having a power supply at 10 W / ( ) to 2000 W / ( ) range of thermal conductivity.

[0056] In other aspects, the surface 383 of the sheet 386 facing the window has an optical coating 389 thereon, and the optical coating 389 reflects at least some radiation having wavelengths longer than those covered by the transmission band of the window 380. The optical coating 389 may also reflect at least some radiation having wavelengths shorter than those covered by the transmission band. The sheet 386 may include or be made of sapphire. The window 380 may include or be made of glass.

[0057] In another aspect, window 380 may (also) include or be made of sapphire, if desired.

[0058] Figure 6 6 is a schematic diagram showing an EUV light source 600, which may be an EUV light source having any of the EUV light source containers 160, 260, 360, 560 disclosed herein. The 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, and reflects the EUV light 646 in one or more illumination mirrors 672 so as to illuminate a reflective pattern or mask 673. The EUV light reflected from the pattern or mask 673 is further reflected and attenuated by one or more reduction mirrors 674, and irradiated onto a substrate or wafer 675 (or onto one or more photosensitive layers on the substrate or wafer 675) to allow a patterned structure to be formed on the substrate or wafer 675.

[0059] To review and point out some of the advantages of the disclosed window assembly 155, 355, 555, the high thermal conductivity of the material of the sheet 186, 386 reduces the thermal lensing of the sheet 186, 386. If sapphire is used in the window, the high thermal conductivity of the window 180, 380 reduces the thermal lensing of the window. Alternatively or additionally, even if glass is used in the window, the optical coating 189, 389 on the sheet 186, 386 prevents or reduces the thermal lensing of the window 180, 380 by reflecting at least some of the radiation that would otherwise be at least partially absorbed by the window.

[0060] Positioning the optical coating 189 , 389 on the window-facing surface 383 of the sheet 186 , 386 protects the optical coating from some of the chemical, physical, and thermal effects present in the interior 170 , 370 of the vacuum chamber 160 , 360 during operation of the EUV light source 100 .

[0061] The sheet 186, 386 is kept relatively thin to reduce the amount of radiation absorbed by the sheet 186, 386, further reducing the effects of any thermal lensing. The window 180, 380 may be relatively thick to allow sufficient strength to resist the pressure differential between the interior 170, 370 and the exterior of the vacuum chamber 160, 360.

[0062] Having a gap 187, 387 between the protector 181, 381 and the window 180, 380 helps to thermally insulate the window 180, 380 from the protector 181, 381. In some aspects, and with reference to Figure 3 , the protector 381 is not sealed in the sleeve 390, which allows the gap 387 to have a vacuum level (or very low pressure) similar to or equal to the interior 370 of the vacuum chamber 360 during use, thereby facilitating thermal isolation of the window 380 from the protector 381 and allowing the sheet 386 to be thinner because the sheet 386 does not need to withstand pressure differences.

[0063] The embodiments may be further described using the following aspects:

[0064] 1. A component comprising:

[0065] a window configured to allow optical access to an interior of an extreme ultraviolet (EUV) light source container, the window having an exterior-facing surface configured to face the exterior of the EUV light source container and an interior-facing surface opposite the exterior-facing surface, the window also having a transmission band covering wavelengths of radiation that the window is capable of transmitting; and

[0066] A protector configured to isolate the window from the internal shielding of the EUV light source container, the protector comprising a sheet having a surface facing the window and an inner-facing surface opposite to the surface facing the window, the surface facing the window spanning a gap and facing the inner-facing surface of the window, the sheet comprising a material having a thermal conductivity of 10 W / ( ) to 2000 W / ( ) range of thermal conductivity materials.

[0067] 2. The assembly according to aspect 1, wherein the thermal conductivity of the material is 20 W / ( ) to 50 W / ( ) within the range of .

[0068] 3. The assembly of aspect 1, wherein the transmission band is a band of wavelengths that includes at least 90% of the wavelengths of radiation that the window is capable of transmitting.

[0069] 4. An assembly according to aspect 1, wherein the protector further comprises a coating located on the surface of the sheet facing the window, wherein the coating reflects at least some radiation having wavelengths longer than the wavelengths covered by the transmission band.

[0070] 5. A component according to aspect 1, wherein the protector further comprises a coating located on the surface of the sheet facing the window, and the coating reflects 50% or more of radiation having wavelengths longer than the wavelength covered by the transmission band and up to 8000 nm.

[0071] 6. A component according to aspect 1, wherein the protector further comprises a coating located on the surface of the sheet facing the window, and the coating reflects 70% or more of radiation having wavelengths longer than the wavelength covered by the transmission band and up to 8000 nm.

[0072] 7. A component according to aspect 1, wherein the protector further comprises a coating located on the surface of the sheet facing the window, and the coating reflects 50% or more of radiation having a wavelength longer than the wavelength covered by the transmission band and up to 8000 nm, and reflects 50% or more of radiation having a wavelength shorter than the wavelength covered by the transmission band and down to 150 nm.

[0073] 8. A component according to aspect 1, wherein the protector further comprises a coating located on the surface of the sheet facing the window, wherein the coating reflects at least some radiation having a wavelength longer than the wavelength covered by the transmission band and the coating also reflects at least some radiation having a wavelength shorter than the wavelength covered by the transmission band.

[0074] 9. A component according to aspect 1, wherein the protector further comprises a coating located on the surface of the sheet facing the window, wherein the coating reflects at least some radiation having wavelengths longer than the wavelength covered by the transmission band and the coating reflects 50% or more of radiation having wavelengths in the range of 150 nm to 845 nm and in the range of 1090 nm to 8000 nm.

[0075] 10. The assembly of aspect 1, wherein the material transmits one or more of visible light and near infrared light.

[0076] 11. The assembly of aspect 1, wherein the window is configured to withstand a pressure differential between an interior-facing surface of the window and an exterior-facing surface of the window.

[0077] 12. A component according to aspect 1, wherein the window is configured to withstand a pressure difference of at least 100 kPa between the two surfaces of the window between the inward-facing surface of the window and the outward-facing surface of the window caused by low pressure and / or vacuum at the inward-facing surface of the window.

[0078] 13. The assembly of aspect 1, wherein a surface of the sheet facing the window is inclined relative to an inwardly facing surface of the window.

[0079] 14. The assembly of clause 1, wherein the sheet material comprises sapphire.

[0080] 15. The assembly of clause 1, wherein the sheet comprises sapphire and the window comprises glass.

[0081] 16. The assembly of aspect 1, wherein the sheet material comprises sapphire and the glass comprises borosilicate glass.

[0082] 17. The assembly of aspect 1, wherein the sheet material comprises sapphire, and wherein the window comprises Schott N-BK7 borosilicate glass.

[0083] 18. A component according to aspect 1, wherein the sheet comprises sapphire and the window comprises Schott N-BK7 borosilicate glass, and the protector further comprises a coating on the surface of the sheet facing the window, wherein the coating reflects at least some radiation having a wavelength longer than the wavelength covered by the transmission band.

[0084] 19. A component according to aspect 1, wherein the sheet includes sapphire and the window includes Schott N-BK7 borosilicate glass, and the protector also includes a coating located on the surface of the sheet facing the window, the coating reflecting at least some radiation having a wavelength longer than the wavelength covered by the transmission band, and the coating also reflects at least some radiation having a wavelength shorter than the wavelength covered by the transmission band.

[0085] 20. A component according to aspect 1, wherein the sheet comprises sapphire and the window comprises Schott N-BK7 borosilicate glass, the protector further comprises a coating located on the surface of the sheet facing the window, the coating reflects at least some radiation having wavelengths longer than the wavelengths covered by the transmission band, and wherein the inner-facing surface of the sheet is bare sapphire.

[0086] 21. The assembly of aspect 1, wherein the sheet comprises sapphire and the window comprises sapphire.

[0087] 22. The assembly of aspect 1, wherein the sheet has a thickness in the range of 2.2 mm to 3.2 mm.

[0088] 23. The assembly of aspect 1, wherein the sheet has a thickness in the range of 2.39 mm to 2.59 mm.

[0089] 24. The assembly of aspect 1, wherein the window has a thickness in the range of 4.0 mm to 6.5 mm.

[0090] 25. The assembly of aspect 1, wherein the window has a thickness in the range of 5.9 mm to 6.1 mm.

[0091] 26. The assembly of clause 1, wherein the assembly is mounted in an opening defined through a wall of a vacuum chamber of an extreme ultraviolet (EUV) light source, the vacuum chamber being under vacuum.

[0092] 27. A measurement device for an extreme ultraviolet (EUV) light source container, the measurement device comprising:

[0093] an illumination module configured to provide light into the EUV light source container and / or a detection module configured to detect light propagating from within the EUV light source container; and

[0094] A component arranged along a beam path of the detected light or the provided light, the component comprising:

[0095] a window configured to allow optical access to an interior of the EUV light source container, the window having an exterior-facing surface configured to face an exterior of the EUV light source container and an interior-facing surface opposite the exterior-facing surface, the window also having a transmission band covering wavelengths of radiation that the window is capable of transmitting; and

[0096] A protector configured to isolate the window from the internal shielding of the EUV light source container, the protector comprising a sheet having a surface facing the window and an inner-facing surface opposite to the surface facing the window, the surface facing the window spanning a gap and facing the inner-facing surface of the window, the sheet comprising a material having a thermal conductivity of 10 W / ( ) to 2000 W / ( ) range of thermal conductivity materials.

[0097] 28. The metrology device of clause 27, wherein the detection module comprises an object detection module.

[0098] 29. The metrology device of clause 27, wherein the detection module comprises an object imaging module.

[0099] 30. The metrology apparatus of clause 27, wherein the illumination module comprises an illumination module configured to detect an object traveling within the EUV light source vessel toward an illumination zone.

[0100] 31. The metrology apparatus of clause 27, wherein the illumination module comprises a target backlight module configured to detect a target within the EUV light source container.

[0101] 32. The metrology apparatus of aspect 27, further comprising an optical coating on a surface of the sheet facing the window, wherein the optical coating reflects at least some radiation having wavelengths longer than the wavelengths encompassed by the transmission band.

[0102] 33. The measurement device according to aspect 27 further includes an optical coating located on the surface of the sheet facing the window, wherein the optical coating reflects at least some radiation having a wavelength longer than the wavelength covered by the transmission band, and wherein the optical coating also reflects at least some radiation having a wavelength shorter than the wavelength covered by the transmission band.

[0103] 34. The metrology apparatus of clause 27, wherein the sheet material comprises sapphire.

[0104] 35. The metrology apparatus of clause 27, wherein the sheet material comprises sapphire and the window comprises glass.

[0105] 36. The metrology apparatus of clause 27, wherein the sheet comprises sapphire and the window comprises sapphire.

[0106] 37. An extreme ultraviolet (EUV) light source, the EUV source comprising:

[0107] a vacuum chamber, the vacuum chamber comprising a vacuum chamber wall, the vacuum chamber wall defining an opening therethrough;

[0108] a window coupled to the chamber, the window being positioned to close the opening, the window having an interior-facing surface facing the interior of the chamber and an exterior-facing surface opposite the interior-facing surface, the window further having a transmission band encompassing wavelengths of radiation that the window is capable of transmitting; and

[0109] a protector positioned to shield the window from the interior of the chamber, the protector comprising a sheet having a surface facing the window and an interior-facing surface opposite the window-facing surface, the window-facing surface spanning a gap and facing the interior-facing surface of the window, the sheet comprising a ) to 2000 W / ( ) range of thermal conductivity materials.

[0110] 38. The EUV light source of clause 37, further comprising an optical coating on a surface of the sheet facing the window, wherein the optical coating reflects at least some radiation having wavelengths longer than the wavelengths encompassed by the transmission band.

[0111] 39. The EUV light source of aspect 37, further comprising an optical coating on a surface of the sheet facing the window, wherein the optical coating reflects at least some radiation having a wavelength longer than the wavelength covered by the transmission band, and wherein the optical coating also reflects at least some radiation having a wavelength shorter than the wavelength covered by the transmission band.

[0112] 40. The EUV light source of clause 37, wherein the sheet material comprises sapphire.

[0113] 41. The EUV light source of clause 37, wherein the sheet comprises sapphire and the window comprises glass.

[0114] 42. The EUV light source of clause 37, wherein the sheet comprises sapphire and the window comprises sapphire.

[0115] 43. The EUV light source of clause 37, wherein the vacuum chamber is under vacuum.

[0116] The implementations described above and other implementations are within the scope of the following claims.

Claims

1. A component comprising: a window configured to allow optical access to an interior of an extreme ultraviolet (EUV) light source container, the window having an exterior-facing surface configured to face the exterior of the EUV light source container and an interior-facing surface opposite the exterior-facing surface, the window also having a transmission band covering wavelengths of radiation that the window is capable of transmitting; and A protector configured to isolate the window from the internal shielding of the EUV light source container, the protector comprising a sheet having a surface facing the window and an inner-facing surface opposite to the surface facing the window, the surface facing the window spanning a gap and facing the inner-facing surface of the window, the sheet comprising a material having a thermal conductivity of 10 W / ( ) to 2000 W / ( ) range of thermal conductivity materials.

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

3. The assembly according to claim 1, wherein: The transmission band is a band of wavelengths including wavelengths at which the window is capable of transmitting at least 90% of radiation.

4. The assembly according to claim 1, wherein: The protector also includes a coating on the surface of the sheet facing the window, wherein the coating reflects at least some radiation having wavelengths longer than the wavelengths encompassed by the transmission band.

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

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

7. The assembly according to claim 1, wherein: The protector also includes a coating located on the window-facing surface of the sheet, and the coating reflects 50% or more of radiation having wavelengths longer than the wavelength covered by the transmission band and up to 8000 nm, and reflects 50% or more of radiation having wavelengths shorter than the wavelength covered by the transmission band down to 150 nm.

8. The assembly of claim 1, wherein: The protector also includes a coating located on the window-facing surface of the sheet, wherein the coating reflects at least some radiation having wavelengths longer than the wavelengths covered by the transmission band and the coating also reflects at least some radiation having wavelengths shorter than the wavelengths covered by the transmission band.

9. The assembly of claim 1, wherein: The protector also includes a coating located on the window-facing surface of the sheet, wherein the coating reflects at least some radiation having wavelengths longer than the wavelengths covered by the transmission band and the coating reflects 50% or more of radiation having wavelengths in the range of 150 nm to 845 nm and in the range of 1090 nm to 8000 nm.

10. The assembly of claim 1, wherein: The material transmits one or more of visible light and near infrared light.

11. The assembly according to claim 1, wherein: The window is configured to withstand a pressure differential between an interior-facing surface of the window and an exterior-facing surface of the window.

12. The assembly of claim 1, wherein: The window is configured to withstand a pressure differential of at least 100 kPa between the two surfaces of the window between the interior facing surface of the window and the exterior facing surface of the window due to low pressure and / or vacuum at the interior facing surface of the window.

13. The assembly of claim 1, wherein: The surface of the sheet facing the window is inclined relative to the inwardly facing surface of the window.

14. The assembly of claim 1, wherein: The sheet material includes sapphire.

15. The assembly of claim 1, wherein: The sheet material comprises sapphire and the window comprises glass.

16. The assembly of claim 1, wherein: The sheet material comprises sapphire and the glass comprises borosilicate glass.

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

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

19. The assembly of claim 1, wherein: The sheet includes sapphire and the window includes Schott N-BK7 borosilicate glass, and the protector also includes a coating located on the surface of the sheet facing the window, which reflects at least some radiation with a wavelength longer than the wavelength covered by the transmission band, and the coating also reflects at least some radiation with a wavelength shorter than the wavelength covered by the transmission band.

20. The assembly of claim 1, wherein: The sheet comprises sapphire and the window comprises Schott N-BK7 borosilicate glass, the protector further comprising a coating on the surface of the sheet facing the window, the coating reflecting at least some radiation having a wavelength longer than the wavelength covered by the transmission band, and wherein the inner-facing surface of the sheet is bare sapphire.

21. The assembly of claim 1, wherein: The sheet comprises sapphire and the window comprises sapphire.

22. The assembly of claim 1, wherein: The sheet has a thickness in the range of 2.2 mm to 3.2 mm.

23. The assembly of claim 1, wherein: The sheet has a thickness in the range of 2.39 mm to 2.59 mm.

24. The assembly of claim 1, wherein: The window has a thickness in the range of 4.0 mm to 6.5 mm.

25. The assembly of claim 1, wherein: The window has a thickness in the range of 5.9 mm to 6.1 mm.

26. The assembly of claim 1, wherein: The assembly is mounted in an opening defined through a wall of a vacuum chamber of an extreme ultraviolet (EUV) light source, the vacuum chamber being under vacuum.

27. A measurement device for an extreme ultraviolet (EUV) light source container, the measurement device comprising: an illumination module configured to provide light into the EUV light source container and / or to provide light to a detection module configured to detect light propagating from within the EUV light source container; and A component arranged along a beam path of the detected light or the provided light, the component comprising: a window configured to allow optical access to an interior of the EUV light source container, the window having an exterior-facing surface configured to face an exterior of the EUV light source container and an interior-facing surface opposite the exterior-facing surface, the window also having a transmission band covering wavelengths of radiation that the window is capable of transmitting; and A protector configured to isolate the window from the internal shielding of the EUV light source container, the protector comprising a sheet having a surface facing the window and an inner-facing surface opposite to the surface facing the window, the surface facing the window spanning a gap and facing the inner-facing surface of the window, the sheet comprising a material having a thermal conductivity of 10 W / ( ) to 2000 W / ( ) range of thermal conductivity materials.

28. The measurement device according to claim 27, wherein: The detection module includes a target detection module.

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

30. The measurement device according to claim 27, wherein: The illumination module includes an illumination module configured to detect a target traveling toward an illumination zone within the EUV light source container.

31. The measurement device according to claim 27, wherein: The illumination module includes a target backlight module configured to detect a target within the EUV light source container.

32. The metrology apparatus of claim 27, further comprising an optical coating on a surface of the sheet facing the window, wherein: The optical coating reflects at least some radiation having wavelengths longer than the wavelengths encompassed by the transmission band.

33. The metrology apparatus of claim 27, further comprising an optical coating on a surface of the sheet facing the window, wherein: The optical coating reflects at least some radiation having wavelengths longer than the wavelengths encompassed by the transmission band, and wherein the optical coating also reflects at least some radiation having wavelengths shorter than the wavelengths encompassed by the transmission band.

34. The measurement device according to claim 27, wherein: The sheet material includes sapphire.

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

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

37. An extreme ultraviolet (EUV) light source, the EUV light source comprising: a vacuum chamber, the vacuum chamber comprising a vacuum chamber wall, the vacuum chamber wall defining an opening therethrough; a window coupled to the chamber, the window being positioned to close the opening, the window having an interior-facing surface facing the interior of the chamber and an exterior-facing surface opposite the interior-facing surface, the window further having a transmission band encompassing wavelengths of radiation that the window is capable of transmitting; and a protector positioned to shield the window from the interior of the chamber, the protector comprising a sheet having a surface facing the window and an interior-facing surface opposite the window-facing surface, the window-facing surface spanning a gap and facing the interior-facing surface of the window, the sheet comprising a ) to 2000 W / ( ) range of thermal conductivity materials.

38. The EUV light source of claim 37, further comprising an optical coating on a surface of the sheet facing the window, wherein The optical coating reflects at least some radiation having wavelengths longer than the wavelengths encompassed by the transmission band.

39. The EUV light source of claim 37, further comprising an optical coating on a surface of the sheet facing the window, wherein The optical coating reflects at least some radiation having wavelengths longer than the wavelengths encompassed by the transmission band, and wherein the optical coating also reflects at least some radiation having wavelengths shorter than the wavelengths encompassed by the transmission band.

40. The EUV light source according to claim 37, wherein: The sheet material includes sapphire.

41. The EUV light source of claim 37, wherein: The sheet material comprises sapphire and the window comprises glass.

42. The EUV light source of claim 37, wherein: The sheet comprises sapphire and the window comprises sapphire.

43. The EUV light source of claim 37, wherein: The vacuum chamber is under vacuum.

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