Vacuum ultraviolet microscope

Abstract

This invention discloses a mirror for reflecting vacuum ultraviolet (VUV) light. The VUV mirror may include a substrate. The VUV mirror may include a reflective layer deposited on the substrate, wherein the reflective layer reflects light with wavelengths between 100 nm and 200 nm. The VUV mirror may include a noble metal layer deposited on the reflective layer, wherein the noble metal layer provides environmental stability to the reflective layer and transmits light with wavelengths between 100 nm and 200 nm.

Description

[0001] Cross-reference of related applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 556,417, filed February 22, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to mirrors for use in vacuum ultraviolet (VUV) optical systems, and more particularly, to reflective optical coatings for mirrors that maintain high reflectivity in the wavelength range of 100 nm to 200 nm. Background Technology

[0004] Laser-sustaining plasma (LSP) sources are widely used in broadband inspection tools to generate VUV light for semiconductor inspection and imaging. In VUV plasma-based optical systems, there are few options for mirrors that maintain a moderately high reflectivity between 100 nm and 200 nm in the vicinity of the bright plasma used for broadband light generation. Standard mirrors for high-intensity light are typically based on platinum or iridium films, which offer high stability in this range but low reflectivity. Coatings for low-intensity applications (e.g., aluminum protected with magnesium fluoride) have high initial reflectivity but degrade rapidly when used near bright plasma. Therefore, it is desirable to provide a mirror and a method for forming the mirror that overcomes the shortcomings of the prior methods described above. Summary of the Invention

[0005] A mirror for reflecting vacuum ultraviolet light is disclosed. In one embodiment, the mirror includes a substrate. In another embodiment, the mirror includes a reflective layer deposited on the substrate, wherein the reflective layer reflects light with wavelengths between 100 nm and 200 nm. In yet another embodiment, the mirror includes a noble metal layer deposited on the reflective layer, wherein the noble metal layer provides environmental stability to the reflective layer and transmits light with wavelengths between 100 nm and 200 nm. In one embodiment, the mirror is implemented within a laser-sustaining broadband light source. In yet another embodiment, the mirror is implemented within an optical characterization system.

[0006] A method for forming a mirror for reflecting vacuum ultraviolet light is disclosed. In one embodiment, the method includes providing a substrate. In another embodiment, the method includes depositing an aluminum layer on the substrate, wherein the aluminum layer reflects light with wavelengths between 100 nm and 200 nm. In yet another embodiment, the method includes depositing a noble metal layer on the aluminum layer, wherein the noble metal layer provides environmental stability to the aluminum layer and transmits light with wavelengths between 100 nm and 200 nm.

[0007] It should be understood that the foregoing overview and the following detailed description are merely illustrative and explanatory and do not necessarily limit this disclosure. The accompanying drawings, incorporated in and forming part of this specification, illustrate the subject matter of this disclosure. The description and drawings together serve to illustrate the principles of this disclosure. Attached Figure Description

[0008] By referring to the accompanying drawings, those skilled in the art can better understand the many advantages of this disclosure.

[0009] Figure 1 This describes a series of penetration depth curves that vary according to the wavelength of various precious metals, based on one or more embodiments of this disclosure.

[0010] Figure 2 This description illustrates a mirror with high reflectivity to VUV light according to one or more embodiments of the present disclosure.

[0011] Figures 3A to 3C This document describes a series of simulated reflectance data for VUV mirrors made of platinum (Pt), iridium (Ir), and rhodium (Rh) according to one or more embodiments of this disclosure.

[0012] Figure 4 The present disclosure describes a mirror with a cover layer that exhibits high reflectivity to VUV light according to one or more alternative embodiments.

[0013] Figures 5A to 5C This document describes a series of simulated reflectance data for a VUV mirror made of platinum (Pt), iridium (Ir), and rhodium (Rh) and equipped with a magnesium fluoride (MgF2) cover layer, according to one or more embodiments of this disclosure.

[0014] Figure 6 A simplified schematic diagram illustrating a laser-maintained plasma broadband light source implementing a VUV mirror according to one or more embodiments of the present disclosure.

[0015] Figure 7 A simplified schematic diagram illustrating an optical characterization system for a laser-supplied plasma broadband light source equipped with a VUV mirror, according to one or more embodiments of the present disclosure.

[0016] Figure 8 A flowchart illustrating a method for forming a VUV mirror according to one or more embodiments of the present disclosure is provided. Detailed Implementation

[0017] Reference will now be made in detail to the disclosed subject matter illustrated in the accompanying drawings. This disclosure has been specifically shown and described with respect to particular embodiments and their specific features. The embodiments set forth herein are to be considered illustrative rather than restrictive. Those skilled in the art will readily understand that various changes and modifications in form and detail may be made without departing from the spirit and scope of this disclosure.

[0018] General reference Figures 1 to 7 According to one or more embodiments of this disclosure, a VUV mirror suitable for operation near a VUV laser-sustaining plasma broadband source is described.

[0019] Embodiments of this disclosure relate to reflective optical coatings in mirrors for use in broadband plasma optics systems. The reflective coatings of this disclosure may comprise one or more reflective layers (e.g., aluminum films) protected by a thin protective layer of noble metal. The coatings utilize the high reflectivity of aluminum for VUV light (e.g., 100 nm to 200 nm) and the environmental stability of noble metals in harsh environments to produce reflective optics that do not degrade after prolonged use in laser-sustaining plasma light sources. Several practical optical designs utilizing a basic noble metal-aluminum film stack are described.

[0020] Embodiments of this disclosure utilize the chemical inertness of noble metals (e.g., Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au) and their moderate transmission of photons in the 100 nm to 200 nm range. Figure 1 As shown, for photons with wavelengths in the 100 nm to 200 nm range, the 1 / e transmission depth (i.e., the depth at which the noble metal has absorbed approximately 63% of the incident photons) of most noble metals is approximately 10 nm to 20 nm. This depth indicates that extremely thin (a few nm thick) layers of noble metal can be used to provide an environmentally stable protective layer over more reflective materials (e.g., aluminum) that would otherwise be destroyed in harsh environments near plasma. As an example, aluminum provides significantly higher reflectivity in the 100 nm to 200 nm range than any other known material. However, aluminum reacts rapidly with oxygen- or fluorine-containing species to form surface oxides or fluorides. These oxides or fluorides alter the optical properties of the initial aluminum layer and can significantly reduce reflectivity in the 100 nm to 200 nm band. Therefore, using aluminum as a reflective material in the 100 nm to 200 nm range requires a transparent (or translucent) protective layer to prevent chemical changes in the initial aluminum layer.

[0021] Embodiments of this disclosure utilize a thin noble metal film to provide a transmissive yet environmentally stable protective layer over a highly reflective layer (e.g., an aluminum layer). The overall reflectivity of the film stack can be tuned at the expense of the environmental protection provided by the noble metal film (i.e., by reducing the thickness of the noble metal layer). This allows for the optimization of reflective optics for specific applications.

[0022] Figure 2 This invention describes a mirror 200 implemented within an LSP broadband light source according to one or more embodiments of the present disclosure.

[0023] In one embodiment, mirror 200 includes a substrate 202, a reflective layer 204, and a noble metal layer 206. In another embodiment, the reflective layer reflects VUV light (e.g., wavelengths between 100 nm and 200 nm). For example, reflective layer 204 may include, but is not limited to, an aluminum layer. In this example, noble metal layer 206 may be deposited on the aluminum layer. Noble metal layer 206 provides environmental stability to the reflective layer 204 and transmits VUV light (e.g., wavelengths between 100 nm and 200 nm). For example, mirror 200 may be used to collect and reflect broadband light 212 emitted by laser-sustaining plasma 208. In this example, noble metal 206 may transmit broadband light 212 emitted by plasma 208. The broadband light 212 transmitted through noble metal layer 206 is then reflected by reflective layer 204 and transmitted back through noble metal layer 206, where it is utilized downstream of mirror 200.

[0024] Substrate 202 may comprise any suitable material that will allow the deposition of aluminum and noble metal coatings. For example, substrate 202 may comprise (but is not limited to) fused silica, MgF2, CaF2, or silicon. In embodiments, substrate 202 may be planar to form a flat mirror. In alternative embodiments, substrate 202 may comprise more complex optical surfaces (e.g., spherical, parabolic, elliptical) to form a curved mirror. The deposited aluminum layer should be as dense and chemically pure (e.g., oxygen-free) as possible and thick enough to be optically opaque in the 100 nm to 200 nm wavelength range (e.g., greater than 100 nm) to prevent photons from reaching the aluminum-substrate interface. Similarly, the noble metal film should be dense and free of impurities.

[0025] The noble metal used to form the noble metal layer 206 may comprise any noble metal. For example, the noble metal may comprise Ru, Rh, Pd, Ag, Os, Ir, Pt, or Au. In an embodiment, the thickness of the noble metal layer 206 is selected such that the noble metal layer 206 transmits broadband light 212. For example, the noble metal layer 206 may be deposited such that the thickness of the layer is between 2 nm and 8 nm.

[0026] Figures 3A to 3C This describes a series of simulated reflectance data for a mirror formed by Pt, Ir, and Rh. Figure 3A A graph 300 illustrates a series of simulated reflectance curves varying with the wavelengths of aluminum mirrors coated with 2 nm, 4 nm, and 8 nm Pt. Reflectance curves for pure Pt are also provided to provide baseline reflectance information. Figure 3B A graph 310 illustrates a series of simulated reflectance curves varying with the wavelengths of aluminum mirrors coated with 2 nm, 4 nm, and 8 nm Ir. Reflectance curves for pure Ir are also provided to provide baseline reflectance information. Figure 3CA graph 320 illustrates a series of simulated reflectance curves varying with the wavelength of aluminum mirrors coated with 2 nm, 4 nm, and 8 nm Rh. Reflectance curves for pure Rh are also provided to provide baseline reflectance information. Figures 3A to 3C The behavior shown illustrates that when the noble metal layer thickness reaches 8 nm, the absorbance of the noble metal layer becomes too high to utilize the reflectivity of the aluminum sublayer. However, the intermediate noble metal layer thickness can be tuned to trade environmental stability (e.g., a thicker noble metal layer) for reflectivity (e.g., a thinner noble metal layer) to meet the requirements of specific applications.

[0027] Figure 4 This describes a mirror 200 comprising an additional cover layer 402 for implementation within an LSP broadband light source, according to one or more alternative and / or additional embodiments of the present disclosure.

[0028] In this embodiment, the capping layer 402 comprises an oxide or a fluoride. For example, the capping layer 402 may comprise a metal oxide or silicon dioxide. For instance, in the case of a metal oxide, the metal oxide may comprise, but is not limited to, aluminum oxide. By another example, the capping layer 402 may comprise a metal fluoride. For example, the metal fluoride may comprise, but is not limited to, lithium fluoride, magnesium fluoride, or calcium fluoride. It should be noted that the capping layer 402 may be transparent over most of the 100 nm to 200 nm wavelength band.

[0029] In this embodiment, the noble metal layer 206 may act as a diffusion barrier between the capping layer 402 and the reflective layer 204. For low lifetime dose applications, a metal oxide or metal fluoride coating may be placed directly above the reflective aluminum layer, with a thickness that prevents oxygen or fluorine species in the surrounding atmosphere from interacting with the reflective layer 204 (e.g., the aluminum layer). The thickness of this metal oxide or metal fluoride capping layer may also be chosen to take advantage of constructive interference in a small frequency band around a given wavelength. Without a protective layer, the metal oxide or metal fluoride coating will rapidly degrade near bright plasma due to photochemistry, ultimately leading to the diffusion of oxygen or fluorine into the reflective aluminum layer. If a thin noble metal layer is placed between the aluminum layer and the metal oxide or metal fluoride capping layer 402, then the noble metal layer 206 will act as a diffusion barrier, preventing the degradation of optical performance caused by the migration of oxygen or fluorine into the aluminum layer 402.

[0030] Figures 5A to 5C This document describes a series of simulated reflectance data for a mirror formed of Pt, Ir, and Rh having a magnesium fluoride capping layer 402, according to one or more embodiments of the present disclosure. Figure 5AThe illustration depicts a series of simulated reflectance curves varying according to the wavelength of a bare Pt mirror (e.g., 100 nm thick Pt), an aluminum-coated mirror protected by a 2 nm Pt protective layer, and an aluminum-coated mirror protected by a 2 nm Pt protective layer and a 28 nm MgF2 capping layer. Figure 5B The illustration depicts a series of simulated reflectance curves varying according to the wavelengths of a bare Ir mirror (e.g., 100 nm thick Ir), an aluminum-coated mirror protected by a 2 nm Ir protective layer, and an aluminum-coated mirror protected by a 2 nm Ir protective layer and a 28 nm MgF2 capping layer. Figure 5C Figure 520 illustrates a series of simulated reflectance curves varying with wavelength, including a bare Rh mirror (e.g., 100 nm thick Rh), an aluminum-coated mirror protected with a 2 nm Rh protective layer, and an aluminum-coated mirror protected with a 2 nm Rh protective layer and a 28 nm MgF2 capping layer. Note that the MgF2 capping layer is optimized for maximum reflectance near 120 nm. If the metal oxide or metal fluoride coating can be maintained near bright plasma during use, then... Figure 4 The optical design presented can be used to further enhance reflectivity in small subbands within the wavelength range of 100 nm to 200 nm (e.g., around 120 nm in this example).

[0031] Figure 6 This diagram illustrates a simplified schematic of an LSP broadband light source 600 incorporated into a VUV mirror 200 according to one or more embodiments. In one embodiment, the light source 600 includes a gas containment structure 603 for containing a selected gas or gas mixture (e.g., xenon, argon, krypton, and mixtures thereof). In another embodiment, the light source 600 includes a laser pump source 602 configured to generate an optical pump 605. The laser pump source 602 and one or more focusing optics 604 can guide and focus the optical pump 605 through an input window 606 to maintain a plasma 208 within the gas containment structure 603 to generate broadband light 212. The laser pump source 602 may include any laser known in plasma-based broadband light generation techniques, such as, but not limited to, one or more continuous wave (CW) pump lasers and / or one or more pulsed lasers. The laser pump source 602 may be configured to emit light in the visible, IR (e.g., NIR), or ultraviolet regions. In one embodiment, the broadband light 212 exits the gas containment structure 603 through an exit window 608. In this embodiment, the VUV mirror 200 receives broadband light 212 and reflects it to one or more downstream applications. It should be noted that... Figure 6The configurations depicted herein should not be construed as limiting the scope of this disclosure. It should be appreciated that mirror 200 can be implemented in any broadband light generation context that may require different gas containment arrangements (e.g., plasma bulbs, plasma units, plasma chambers), different light collection arrangements (e.g., flat mirrors, curved reflectors), and the position of mirror 200 relative to plasma 208. For example, mirror 200 may be placed near the plasma within gas containment structure 603.

[0032] Figure 7 This illustration shows a simplified schematic of an optical characterization system 700 incorporated into an LSP broadband light source 600 according to one or more embodiments of the present disclosure, wherein the optical characterization system 700 incorporates one or more mirrors 200. In an embodiment, the system 700 includes an LSP light source 600 comprising one or more mirrors 200, an illumination arm 703, a light-collecting arm 705, a detector assembly 714, and a controller 718 comprising one or more processors 720 and a memory 722.

[0033] It should be noted herein that system 700 may include any imaging, inspection, metrology, lithography, or other characterization system known in the art. In this respect, system 700 may be configured to perform inspection, optical metrology, lithography, and / or any form of imaging on sample 707. Sample 707 may comprise any sample known in the art, including but not limited to wafers, photomasks, photomasks, and the like. It should be noted that system 700 may be incorporated into one or more of the various embodiments of the LSP light source 600 and one or more mirrors 200 described herein.

[0034] In one embodiment, sample 707 is placed on stage assembly 712 to facilitate movement of sample 707. Stage assembly 712 may include any stage assembly 712 known in the art, including but not limited to XY stages, R-θ stages, and the like.

[0035] In one embodiment, illumination arm 703 is configured to direct broadband light 212 from broadband LSP source 600 onto sample 707. Illumination arm 703 may include any number and type of optical components known in the art. In one embodiment, illumination arm 703 includes one or more optical elements 702, beam splitter 704, and objective lens 706. In this respect, illumination arm 703 may be configured to focus broadband light 212 from broadband LSP source 600 onto the surface of sample 707. The one or more optical elements 702 may include any optical element or combination of optical elements known in the art, including, but not limited to, one or more mirrors, one or more lenses, one or more polarizers, one or more gratings, one or more filters, one or more beam splitters, and the like. It should be noted herein that the light-gathering position may include, but is not limited to, one or more of optical elements 702, beam splitter 704, or objective lens 706.

[0036] In one embodiment, system 700 includes a light-collecting arm 705 configured to collect light reflected, scattered, diffracted, and / or emitted from sample 707. In another embodiment, the light-collecting arm 705 may guide and / or focus light from sample 707 onto sensor 716 of detector assembly 714. It should be noted that sensor 716 and detector assembly 714 may comprise any sensor and detector assembly known in the art.

[0037] In one embodiment, the detector assembly 714 is communicatively coupled to a controller 718 including one or more processors 720 and a memory 722. For example, one or more processors 720 may be communicatively coupled to the memory 722, wherein the one or more processors 720 are configured to execute a set of program instructions stored on the memory 722. In one embodiment, the one or more processors 720 are configured to analyze the output of the detector assembly 714.

[0038] It should be noted that system 700 can be configured as any optical configuration known in the art, including but not limited to dark-field configuration, bright-field orientation, and the like. System 700 can be configured as any type of inspection or metrology tool known in the art.

[0039] Additional details of various embodiments of the optical characterization system 700 are described in the following: U.S. Patent Publication 7,957,066B2, entitled "Split Field Inspection System Using Small Catadioptric Objectives," published June 7, 2011; U.S. Patent Publication 2007 / 0002465, entitled "Beam Delivery System for Laser Dark-Field Illumination in a Catadioptric Optical System," published January 4, 2007; U.S. Patent 5,999,310, entitled "Ultra-broadband UV Microscope Imaging System with Wide Range Zoom Capability," published December 7, 1999; and U.S. Patent Publication 28, 2009, entitled "Surface Inspection System Using Laser Line Illumination with Two..." U.S. Patent 7,525,649 entitled “Dimensional Imaging”; U.S. Patent Application Publication 2013 / 0114085 entitled “Dynamically Adjustable Semiconductor Metrology System” published by Wang et al. on May 9, 2013; U.S. Patent Publication 5,608,526 entitled “Focused Beam Spectroscopic Ellipsometry Method and System” published by Piwonka-Corle et al. on March 4, 1997; and U.S. Patent 6,297,880 entitled “Apparatus for Analyzing Multi-Layer Thin Film Stacks on Semiconductors” published by Rosencwaig et al. on October 2, 2001, the entire contents of which are incorporated herein by reference.

[0040] One or more processors 720 of this disclosure may comprise any one or more processing elements known in the art. In this sense, one or more processors 720 may comprise any microprocessor-type device configured to execute software algorithms and / or instructions. In one embodiment, one or more processors 720 may comprise a desktop computer, a host computer system, a workstation, a graphics computer, a parallel processor, or other computer systems (e.g., network-linked computers) configured to execute programs configured to operate system 700 and / or broadband LSP light source 600 as described throughout this disclosure. It should be appreciated that the steps described throughout this disclosure may be performed by a single computer system or alternatively by multiple computer systems. Generally, the term "processor" may be broadly defined to encompass any device having one or more processing elements that execute program instructions from memory 722 (e.g., non-transitory memory media). Furthermore, different subsystems of the various systems disclosed may include processor or logic elements suitable for performing at least a portion of the steps described throughout this disclosure. Therefore, the foregoing description should not be construed as limiting the disclosure but is merely illustrative.

[0041] Memory 722 may comprise any storage medium known in the art suitable for storing program instructions executable by one or more associated processors 720. For example, memory 722 may comprise non-transitory memory media. For instance, memory 722 may comprise, but is not limited to, read-only memory, random access memory, magnetic or optical memory devices (e.g., magnetic disks), magnetic tape, solid-state drives, and the like. In another embodiment, memory 722 is configured to store one or more results and / or outputs of the various steps described herein. It should be further noted that memory 722 may be housed in a common controller housing with one or more processors 720. In alternative embodiments, memory 722 may be remotely located relative to the physical location of processor 720. For example, one or more processors 720 may access remote memory (e.g., a server) accessible via a network (e.g., the Internet, an intranet, and the like). In another embodiment, memory 722 holds program instructions for causing one or more processors 720 to perform the various steps described throughout this disclosure.

[0042] Figure 8 This document describes a process flow diagram of a method 800 for forming a VUV mirror for reflecting vacuum ultraviolet light according to one or more alternative and / or additional embodiments. It should be noted herein that the steps of method 800 may be incorporated into all or part of the features of mirror 200. However, it should be further appreciated that method 800 is not limited to mirror 200.

[0043] In step 802, method 800 includes providing a substrate. In step 804, method 800 includes depositing an aluminum layer on the substrate. In an embodiment, the aluminum layer reflects light with wavelengths between 100 nm and 200 nm. The aluminum layer can be deposited by any method known in thin film deposition techniques. For example, the aluminum layer can be deposited via chemical vapor deposition, sputtering, or evaporation.

[0044] In step 806, method 800 includes depositing a noble metal layer onto the aluminum layer. In an embodiment, the noble metal layer provides environmental stability to the aluminum layer and transmits light with wavelengths between 100 nm and 200 nm. The noble metal layer can be deposited by any method known in thin film deposition techniques. For example, the noble metal layer can be deposited via chemical vapor deposition, sputtering, or evaporation.

[0045] In step 808, method 800 includes the additional step of depositing a capping layer of at least one of an oxide or a fluoride onto the noble metal layer. In embodiments, the capping layer may comprise an oxide or fluoride material (e.g., a metal oxide or a metal fluoride). The capping layer may be deposited by any method known in thin film deposition techniques. For example, the capping layer may be deposited via chemical vapor deposition, sputtering, or evaporation.

[0046] Those skilled in the art will recognize that the components, operations, devices, objects, and accompanying discussions described herein are used as examples for clarity of concept and take into account various configuration modifications. Therefore, as used herein, the specific examples and accompanying discussions are intended to represent their more general categories. In general, the use of any specific example is intended to represent its category, and the omission of specific components, devices, and objects should not be considered as a limitation.

[0047] Regarding the use of virtually any plural and / or singular terms in this document, those skilled in the art may convert plural to singular and / or singular to plural as needed by the context and / or application. For clarity, various singular / plural arrangements are not explicitly described herein.

[0048] The objects described herein sometimes refer to different components contained within or connected to other components. It should be understood that such depicted architectures are merely illustrative, and many other architectures can in fact be implemented to achieve the same functionality. Conceptually, any arrangement of components achieving the same functionality is effectively “associated” to achieve the desired functionality. Therefore, without regard to architecture or intermediate components, any two components in this document combined to achieve a particular functionality can be considered “associated” with each other to achieve the desired functionality. Similarly, any two such associated components can also be considered “connected” or “coupled” to each other to achieve the desired functionality, and any two components that can be suchly associated can also be considered “coupleable” to each other to achieve the desired functionality. Specific examples of coupleability include, but are not limited to, components that can be physically mated and / or physically interact, and / or components that can wirelessly interact and / or wirelessly interact, and / or components that can logically interact and / or logically interact.

[0049] Furthermore, it should be understood that the invention is defined by the appended claims. Those skilled in the art will understand that, generally, the terms used herein, and especially in the appended claims (e.g., the body of the appended claims), are intended to be “open-ended” terms (e.g., the term “comprising” should be interpreted as “comprising but not limited to,” the term “having” should be interpreted as “at least having,” the term “comprising” should be interpreted as “comprising but not limited to,” and the like). Those skilled in the art will further understand that if a particular number of the introduced claim statements are intended, then this intention will be explicitly stated in the claims, and the absence of such a statement will not indicate this intention. For example, to aid understanding, the appended claims may contain the introductory phrases “at least one” and “one or more” to introduce the claim statements. However, the use of such phrases should not be construed as implying that the introduction of a claim statement by the indefinite article “a” or “an” limits any particular claim containing such an introduction to an invention containing only one such statement, even if the same claim contains the introductory phrases “a or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and / or “an” should generally be interpreted as meaning “at least one” or “a or more”); the same applies to the use of definite articles used to introduce a claim statement. Furthermore, even if a specific number of introduced claim statements are explicitly stated, those skilled in the art will recognize that such a statement should generally be interpreted as indicating at least the number stated (e.g., a simple statement of “two statements” without other modifiers generally indicates at least two statements or two or more statements). Furthermore, in examples where a convention similar to "at least one of A, B, and C and similar ones" is used, generally, those skilled in the art should understand that the meaning of the convention is intended for this construction (e.g., "a system having at least one of A, B, and C" will include, but is not limited to, systems having only A, only B, only C, both A and B, both A and C, both B and C, and / or both A, B, C, and similar ones). In examples where a convention similar to "at least one of A, B, or C and similar ones" is used, generally, those skilled in the art should understand that the meaning of the convention is intended for this construction (e.g., "a system having at least one of A, B, or C" will include, but is not limited to, systems having only A, only B, only C, both A and B, both A and C, both B and C, and / or both A, B, C, and similar ones). Those skilled in the art should further understand that any transitional word and / or phrase (whether in the description, claims or figures) that presents two or more alternative terms should be understood to include the possibility of including one, any, or both of the terms.For example, the phrase “A or B” should be understood as including the possibility of “A” or “B” or “A and B”.

[0050] It is believed that this disclosure and its many accompanying advantages will be understood from the foregoing description, and it should be understood that various changes can be made to the form, construction, and arrangement of the components without departing from the subject matter of the disclosure or sacrificing all its significant advantages. The forms described are merely illustrative, and the appended claims are intended to cover and encompass such changes. Furthermore, it should be understood that the invention is defined by the appended claims.

Claims

1. A mirror comprising: Substrate; A reflective layer, which is deposited on the substrate, wherein the reflective layer reflects light with wavelengths between 100 nm and 200 nm; and A noble metal layer is deposited on the reflective layer, wherein the noble metal layer provides environmental stability to the reflective layer and transmits light with wavelengths between 100 nm and 200 nm.

2. The mirror according to claim 1, wherein the noble metal comprises at least one of Ru, Rh, Pd, Ag, Os, Ir, Pt, or Au.

3. The mirror according to claim 1, wherein the thickness of the noble metal layer is between 2 nm and 8 nm.

4. The mirror according to claim 1, wherein the reflective layer comprises an aluminum layer.

5. The mirror according to claim 4, wherein the thickness of the aluminum layer is greater than 100 nm.

6. The mirror according to claim 1, further comprising: A capping layer, wherein the capping layer comprises at least one of an oxide or a fluoride deposited on the noble metal layer.

7. The mirror of claim 6, wherein the noble metal layer acts as a diffusion barrier between the reflective layer and the cover layer.

8. The mirror according to claim 6, wherein the oxide comprises at least one of a metal oxide or silicon dioxide.

9. The mirror according to claim 8, wherein the metal oxide comprises aluminum oxide.

10. The mirror according to claim 6, wherein the fluoride comprises a metal fluoride, and the metal fluoride comprises at least one of lithium fluoride, magnesium fluoride, or calcium fluoride.

11. The mirror of claim 1, wherein the substrate comprises at least one of a flat substrate or a curved substrate.

12. A laser-sustaining broadband light source, comprising: A gas containment structure used to contain gas; A laser pump source configured to generate an optical pump to maintain plasma within the gas-containing structure; and A mirror configured to reflect broadband light generated by the plasma, wherein the mirror comprises: Substrate; A reflective layer, deposited on the substrate, wherein the reflective layer reflects light with wavelengths between 100 nm and 200 nm; and A noble metal layer is deposited on the reflective layer, wherein the noble metal layer provides environmental stability to the reflective layer and transmits light with wavelengths between 100 nm and 200 nm.

13. The source according to claim 12, wherein the noble metal comprises at least one of Ru, Rh, Pd, Ag, Os, Ir, Pt, or Au.

14. The source according to claim 12, wherein the thickness of the noble metal layer is between 2 nm and 8 nm.

15. The source of claim 12, wherein the reflective layer comprises an aluminum layer.

16. The source according to claim 12, wherein the thickness of the aluminum layer is greater than 100 nm.

17. The source according to claim 12, further comprising: A capping layer, wherein the capping layer comprises at least one of an oxide or a fluoride deposited on the noble metal layer.

18. The source of claim 17, wherein the noble metal layer acts as a diffusion barrier between the reflective layer and the capping layer.

19. The source of claim 18, wherein the oxide comprises at least one of a metal oxide or silicon dioxide.

20. The source of claim 19, wherein the metal oxide comprises aluminum oxide.

21. The source of claim 17, wherein the fluoride comprises a metal fluoride, and the metal fluoride comprises at least one of lithium fluoride, magnesium fluoride, or calcium fluoride.

22. The source of claim 12, wherein the substrate comprises at least one of a flat substrate or a curved substrate.

23. A characterization system, comprising: Broadband light sources, including: A gas containment structure used to contain gas; A laser pump source configured to generate an optical pump to maintain plasma within the gas-containing structure; A mirror configured to reflect broadband light generated by the plasma toward one or more downstream optical elements, wherein the mirror comprises: Substrate; A reflective layer, deposited on the substrate, wherein the reflective layer reflects light with wavelengths between 100 nm and 200 nm; and A noble metal layer is deposited on the reflective layer, wherein the noble metal layer provides environmental stability to the reflective layer and transmits light with wavelengths between 100 nm and 200 nm. A set of illumination optics configured to direct broadband light from the broadband light source to one or more samples; A set of light-collecting optics configured to collect light from said one or more samples; and Detector assembly.

24. The system of claim 23, wherein the characterization system comprises at least one of an inspection system or a metrology system.

25. The system of claim 23, further comprising: A capping layer, wherein the capping layer comprises at least one of an oxide or a fluoride deposited on the noble metal layer.

26. A method for forming a mirror for reflecting vacuum ultraviolet light, comprising: Provide substrate; An aluminum layer is deposited on the substrate, wherein the aluminum layer reflects light with wavelengths between 100 nm and 200 nm; and A noble metal layer is deposited on the aluminum layer, wherein the noble metal layer provides environmental stability to the aluminum layer and transmits light with wavelengths between 100 nm and 200 nm.

27. The method of claim 26, further comprising: A capping layer of at least one of oxides or fluorides is deposited on the noble metal layer.

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