Laser-sustained plasma light source with tapered window.

Abstract

An LSP broadband light source is disclosed. The light source can include a gas-filled structure. The light source can include a laser pump source configured to generate an optical pump to sustain a plasma within the gas-filled structure and generate broadband light. The light source can include a tapered window configured to transmit broadband light through an opening in a wall of the gas-filled structure, the tapered window having a tapered portion with a tapered surface configured to deflect light impinging on a peripheral portion of the tapered window away from a portion of the gas-filled structure, thereby protecting that portion of the gas-filled structure.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 63 / 451,049, filed March 9, 2023, the entire contents of which are incorporated herein by reference.

[0002] This disclosure relates generally to plasma-based radiation sources, and more particularly to a high-power vacuum ultraviolet (VUV) laser-sustained plasma (LSP) light source having a tapered window that deflects broadband light away from an enclosed area. Regarding. [Background technology]

[0003] Laser-sustained plasma (LSP) sources are widely used in broadband inspection tools for semiconductor inspection and imaging. Typically, near-infrared (NIR) continuous-wave (CW) pump laser light is focused into a gas-filled vessel, where a plasma is ignited and sustained by absorption of the pump laser radiation. This vessel can be a lamp (e.g., a glass bulb with or without electrodes used to ignite the plasma), a cell (e.g., an optomechanical assembly with transparent walls that allow laser and plasma radiation to enter and exit the cell), a chamber (e.g., a metal vessel with transparent windows for the laser light input and plasma light output), or similar assembly. These various plasma vessels exhibit high internal pressures, reaching tens or even hundreds of atmospheres during operation. The high-pressure gas contained within these vessels is critical for LSP operation. The plasma light is focused through the vessel's transparent walls or windows and used as the illumination source for the inspection tool.

[0004] Various versions of various light sources have already been developed. Most of these sources are designed for operation in the visible (VIS) or ultraviolet (UV) spectral range. When using such sources to generate light in the vacuum ultraviolet (VUV) spectral range, particularly in the range of approximately 125–150 nm, the practical configuration options are relatively limited and the pump power is relatively low. A typical light source for VUV light generation has a metal chamber with multiple windows that couple laser light into and out of the chamber. While various materials are available for the laser windows, there are fewer options for VUV generation. The most widely used materials are MgF2, which has a transmission cutoff wavelength of approximately 115 nm, and CaF2, which has a transmission cutoff wavelength of approximately 125 nm.

[0005] One of the most significant limitations of the operation of such VUV light sources is that the construction of high-pressure windows for use with LSP light sources requires a trade-off between practical window size and the amount of radiant heat load that the window and window seal elements must withstand. Currently, windows can be sealed on three different sides, which determines how close the window seal components must be to the plasma. As shown in Figures 1A-1C, window seals can be located on the front, side, and back of the window, as shown in figures 10, 20, and 30, respectively. In each case, broadband light 14 impinges on a given window assembly 10, 20, or 30. A portion 18 of the broadband light 14 is transmitted through the center of the window 11, while a portion 16 of the broadband light impinges on one or more portions of the window assembly, such as the seal 113. This radiant heat load on the seal 113 causes the seal 113 to deteriorate over time. A cross-sectional view 40 is depicted in FIG. 2, showing in more detail the paths of the portions of broadband light. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] US Patent No. 7957066 (B2) [Patent Document 2] US Patent Application Publication No. 2007 / 0002465 [Patent Document 3] U.S. Patent No. 5,999,310 [Patent Document 4] U.S. Patent No. 7,525,649 [Patent Document 5] US Patent Application Publication No. 2013 / 0114085 [Patent Document 6] U.S. Patent No. 5,608,526 [Patent Document 7] U.S. Patent No. 6,297,880 Summary of the Invention [Problem to be solved by the invention]

[0007] As shown in the figure, in the conventional configuration, the window is located very close to the high-power plasma light source, and the plasma light directly irradiates the sealing portion or various components, which places a heavy thermal load on the sealing portion and / or sealing components, making the removal and cooling of this heat a limiting factor in the window performance. Therefore, it would be desirable to provide an LSP broadband light source that overcomes the limitations outlined above. [Means for solving the problem]

[0008] A laser-sustained plasma (LSP) broadband light source is disclosed that, in certain embodiments, includes a gas containment structure containing a gas, a laser pump source configured to generate an optical pump and direct the optical pump into the gas containment structure to sustain a plasma within the gas containment structure, where broadband light is generated by the plasma, and a window configured to pass the broadband light into an opening in a wall of the gas containment structure, the window having a tapered portion with a tapered surface configured to deflect a portion of light impinging on a peripheral portion of the window away from the gas containment structure, thereby protecting one or more portions of the gas containment structure.

[0009] A semiconductor characterization system is disclosed. In certain embodiments, the characterization system includes a broadband light source. The broadband light source includes a gas-containing structure containing a gas; a laser pump source configured to generate an optical pump and direct the optical pump into the gas-containing structure to sustain a plasma within the gas-containing structure, where broadband light is generated by the plasma; and a window configured to pass the broadband light into an opening in the gas-containing structure, the window being an exit optical window having a tapered portion with a tapered surface configured to deflect a portion of light impinging on a peripheral portion of the window and away from the opening in the gas-containing structure, thereby protecting a portion or portions of the gas-containing structure. In certain embodiments, the characterization system further includes a set of illumination optics configured to direct the broadband light from the broadband light source toward one or more samples, a set of collection optics configured to collect light emitted from the one or more samples, and a detector assembly.

[0010] Disclosed are methods for generating VUV broadband light. Certain embodiments of the method include placing a gas within a gas containment structure, generating and directing an optical pump into the gas containment structure to sustain a plasma within the gas containment structure to generate broadband light, deflecting a portion of the broadband light impinging on a peripheral portion of a window away from an opening in a wall of the gas containment structure to protect one or more portions of the gas containment structure, and transmitting the broadband light impinging on a central portion of the window through the central portion of the window and into the opening in the wall of the gas containment structure. In certain aspects, a laser-sustained broadband light source includes a gas-containing structure containing a gas; a laser pump source configured to generate an optical pump, the laser pump source configured to direct the optical pump into the gas-containing structure to sustain a plasma within the gas-containing structure, the broadband light being generated by the plasma; and a window configured to pass the broadband light into an opening in a wall of the gas-containing structure, the window having a tapered portion with a tapered surface configured to deflect a portion of light impinging on a peripheral portion of the window away from the gas-containing structure, thereby protecting one or more portions of the gas-containing structure.

[0011] Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily limiting of the present disclosure. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate the subject matter of the present invention. Together, the description and the drawings serve to explain the principles of the invention.

[0012] Those skilled in the art will be able to better appreciate the numerous advantages of the present disclosure by reviewing the accompanying drawings. [Brief explanation of the drawings]

[0013] [Figure 1A] FIG. 1 illustrates a method for sealing the window of a high-voltage LSP broadband light source. [Figure 1B] FIG. 1 illustrates a method for sealing the window of a high-voltage LSP broadband light source. [Figure 1C]FIG. 1 illustrates a method for sealing the window of a high-voltage LSP broadband light source. [Figure 2] FIG. 1 is a cross-sectional view illustrating a method for sealing the window of a high-voltage LSP broadband light source. [Figure 3] FIG. 1 is a simplified schematic diagram illustrating an external view of an LSP broadband light source having a tapered window according to one or more embodiments of the present disclosure. [Figure 4A] FIG. 1 depicts a cross-sectional view of a tapered window in a high-pressure LSP broadband light source according to one or more embodiments of the present disclosure. [Figure 4B] FIG. 1 depicts a simplified schematic overview of a tapered window in a high-pressure LSP broadband light source according to one or more embodiments of the present disclosure. [Figure 5A] 1 is a diagram illustrating a cross-sectional view of a tapered window with a convex surface that collimates light transmitted through the tapered window, according to one or more embodiments of the present disclosure. FIG. [Figure 5B] FIG. 2 illustrates a cross-sectional view of a tapered window with a convex surface that focuses light transmitted through the tapered window, according to one or more embodiments of the present disclosure. [Figure 6] FIG. 10 depicts a simplified schematic overview of a characterization system incorporating an LSP broadband light source according to one or more alternative and / or additional embodiments of the present disclosure. [Figure 7] FIG. 1 is a process flow diagram depicting a method of generating VUV light with an LSP broadband light source that deflects the broadband light away from portions of a window, according to one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0014] Reference will now be made in detail to the disclosed subject matter, which is illustrated in the accompanying drawings. The present disclosure has been particularly shown and described with reference to certain embodiments and particular features thereof. The embodiments described herein are to be understood as illustrative and not limiting. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail can be made therein without departing from the spirit and scope of the present disclosure.

[0015] 1A-7, in accordance with one or more embodiments of the present disclosure, a laser-sustained plasma broadband light source with tapered windows that divert light from designated portions of the plasma chamber will be described.

[0016] Embodiments of the present disclosure are directed to an LSP broadband light source equipped with one or more tapered windows configured to deflect broadband light away from one or more portions of a chamber used to generate the plasma light source. For example, embodiments of the present disclosure may include a tapered window (e.g., a polished tapered conical surface) designed to deflect broadband light emitted by a plasma and away from one or more seals forming a window-to-wall seal of the chamber.

[0017] FIG. 3 depicts a simplified schematic view of an LSP broadband light source 100 having one or more tapered windows according to one or more embodiments. In various embodiments, the light source 100 includes a gas containment structure 102 containing one or more gases 103. For example, the gas containment structure 102 may contain one or more high-pressure gases (e.g., 50-300 atmospheres). In various embodiments, the light source 100 includes a tapered window 104 configured to transmit broadband light into an opening 107 in a wall 105 of the gas containment structure 102. In various embodiments, the tapered window 104 includes a tapered portion having a tapered surface 122. The tapered surface 122 may be configured to deflect a portion 118 of light impinging on a peripheral portion of the tapered window 104 away from the gas containment structure 102, thereby protecting a portion 123 of the gas containment structure 102. For example, the tapered window 104 can be configured to deflect illumination 118 away from one or more seals 123. In embodiments, the tapered window 104 can allow some illumination 120 to pass into a central surface 124 of the window 104 and into the opening 107 while avoiding one or more seals 123. In embodiments, the tapered surface 122 of the tapered window 104 can internally reflect some illumination 121 so that the illumination 121 passes into the opening 107 while avoiding one or more seals 123. In embodiments, the illumination 120, 121 that passes into the opening 107 is transmitted to one or more downstream optics 111.

[0018] This tapered window can be used as an entrance or exit window. Although window 104 is depicted as an exit window in this disclosure, this configuration should not be construed as a limitation on the scope of the disclosure, and in other embodiments, a window can be used as an entrance window. For example, window 110 can be replaced by window 104.

[0019] In various embodiments, the light source 100 includes a laser pump source 106 configured to generate an optical pump 108. The laser pump source 106 is configured to direct the optical pump 108 into the gas containment structure 102 to sustain a plasma 112 within the gas containment structure 102 and generate broadband light 116. For example, the laser pump source 106 and a focusing lens 109 can direct and focus the optical pump 108 through a window 110 into the gas containment structure 102 to sustain the plasma 112.

[0020] The laser pump source 106 may include any laser known in the art for plasma-based broadband light generation. In various embodiments, the laser pump source 106 may include one or more continuous wave (CW) pump lasers and / or one or more pulsed lasers. The laser pump source 106 may be configured to emit infrared (IR), near-infrared (NIR), ultraviolet (UV), visible, or other suitable radiation that, upon incidence on a suitable target material, forms a plasma.

[0021] In various embodiments, light source 100 includes one or more collection optics 114. For example, the collection optics 114 may include one or more mirrors and / or one or more lenses. For example, as shown in FIG. 3, the collection optics 114 may include a retroreflector configured to collect broadband light 116 from plasma 112 and redirect the illumination through tapered window 104 toward aperture 107.

[0022] The gas fill within gas containment structure 102 used to generate plasma 112 can include any gas or mixture of gases suitable for use in broadband light generation by a laser-sustained plasma light source, such as, but not limited to, one or more gases including Ar, Xe, Kr, Ne, or He, or a mixture of two or more of Ar, Xe, Kr, Ne, and He.

[0023] The broadband light source 100 may be configured to emit broadband light in one or more of the spectral ranges including UV light, VUV light, and / or DUV light.

[0024] FIG. 4A depicts a cross-sectional view of a tapered window 104 according to one or more embodiments of the present disclosure. Broadband light 116 may impinge upon the tapered window 104. A central portion 120 of the light 116 passes through a front surface 124 of the tapered window 104 and may enter an opening 107 in a wall 105 without impinging upon one or more seals 123. A peripheral portion of the light 116 may impinge upon a tapered surface 122 of the tapered window 104. A first portion 118 of the light impinging upon the tapered surface 122 is deflected away from the tapered window 104 and may be directed away from one or more seals 123. A second portion 121 of the light impinging upon the tapered surface 121 is internally reflected through a bulk portion of the tapered window 104 and may enter an opening 107 in a wall 105 while avoiding one or more seals 123.

[0025] In some embodiments, the tapered surface 122 of the tapered window 104 will be polished (brightened) to reflect a portion 119 of the broadband light impinging on the peripheral portion of the window 104 away from the opening 107 in the wall 105 of the gas containment structure 102, thereby protecting a portion or portions of the gas containment structure 102. In some embodiments, the tapered surface 122 has a ground (roughened) tapered surface configured to scatter a portion 119 of the light impinging on the peripheral portion of the window 124 away from the opening 107 in the wall 105 of the gas containment structure 102, thereby protecting a portion or portions of the gas containment structure 102.

[0026] Tapered window 104 may be made of any optical material known in the art that is suitable for operating a high pressure VUV light source, including, but not limited to, MgF2, CaF2, LiF, sapphire, quartz, etc.

[0027] FIG. 4B depicts a simplified schematic view of a tapered window 104 according to one or more embodiments of the present disclosure. The tapered window 104 can be formed as a monolithic structure having a tapered cylindrical shape. For example, the tapered window 104 can include a cylindrical body 126, a tapered surface 122, and a surface 124. In various embodiments, the tapered surface 122 includes a conical surface. The conical surface can include one or more conical sections. It should be noted that the scope of the present disclosure is not limited to the conical structure depicted in FIG. 4B, which is provided for illustrative purposes only.

[0028] 5A and 5B depict simplified schematic views of a tapered window 104 having a convex lens surface according to one or more embodiments of the present disclosure. In various embodiments, the convex lens surface 130 can be formed in a central portion of the tapered window 104. For example, as shown in FIG. 5A, the convex lens surface 130 can be configured to collimate light impinging on the convex lens surface 130 of the tapered window 104. Alternatively, as shown in FIG. 5B, the convex lens surface 130 can be configured to focus light impinging on the convex lens surface 130 of the tapered window 104. The convex lens surface 130 can include, but is not limited to, a spherical lens surface. The surface of the tapered window 104 can be modified to condition broadband light in a desired manner. For example, the tapered window 104 can include a lens surface or a filtering surface.

[0029] 6 depicts a simplified schematic overview of an optical characterization system 600 incorporating a compact LSP broadband light source according to one or more alternative and / or additional embodiments. In embodiments, system 600 includes LSP light source 100, illumination arm 603, collection arm 605, detector assembly 614, and controller 618, which includes one or more processors 620 and memory 622.

[0030] It is noted that system 600 can include any imaging, inspection, metrology, lithography, or other characterization system known in the art. In that regard, system 600 can be configured to perform inspection, optical metrology, lithography, and / or some form of imaging on specimen 607. Specimen 607 can include any specimen known in the art, including, but not limited to, wafers, reticles, photomasks, etc. It is noted that system 600 can incorporate one or more of the various embodiments of LSP light source 100 described throughout this disclosure.

[0031] In one embodiment, the specimen 607 is positioned on a stage assembly 612 to facilitate movement of the specimen 607. The stage assembly 612 may include any stage assembly 612 known in the art, including, but not limited to, an XY stage, an Rθ stage, etc. In another embodiment, the stage assembly 612 is adjustable to adjust the height of the specimen 607 during inspection or imaging to maintain focus on the specimen 607.

[0032] In one embodiment, illumination arm 603 is configured to direct broadband light 117 from broadband LSP light source 100 toward specimen 607. Illumination arm 603 can include any number of optical components known in the art. In one embodiment, illumination arm 603 includes one or more optical elements 602, a beam splitter 604, and an objective lens 606. In that regard, illumination arm 603 can be configured to focus broadband light 117 from broadband LSP light source 100 onto the surface of specimen 607. The one or more optical elements 602 can 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, etc. It is noted that this collection location may include, but is not limited to, one or more of optical elements 602, beam splitter 604, or objective lens 606.

[0033] In one embodiment, system 600 includes a collection arm 605 configured to collect light reflected, scattered, diffracted, and / or emitted from specimen 607. In another embodiment, collection arm 605 can direct and / or focus light from specimen 607 onto a sensor 616 of a detector assembly 614. It is noted that sensor 616 and detector assembly 614 can include any sensor and detector assembly known in the art. Sensor 616 can include, but is not limited to, a CCD sensor or a CCD-TDI sensor. Additionally, sensor 616 can include, but is not limited to, a line sensor or an electron bombardment line sensor.

[0034] In one embodiment, the detector assembly 614 is communicatively coupled to a controller 618 having one or more processors 620 and a memory 622. For example, the one or more processors 620 can be communicatively coupled to the memory 622 and configured to execute a set of program instructions stored on the memory 622. In one embodiment, the one or more processors 620 are configured to analyze the output of the detector assembly 614. In one embodiment, the set of program instructions are configured to cause the one or more processors 620 to analyze one or more characteristics of the specimen 607. In another embodiment, the set of program instructions are configured to cause the one or more processors 620 to modify one or more characteristics of the system 600 to remain in focus on the specimen 607 and / or the sensor 616. For example, one or more processors 620 can be configured to adjust the objective lens 606 or one or more optical elements 602 to focus broadband light 117 from broadband LSP light source 100 onto the surface of specimen 607. According to another example, one or more processors 620 can be configured to adjust the objective lens 606 and / or one or more optical elements 610 to collect illumination from the surface of specimen 607 and focus the collected illumination onto sensor 616.

[0035] It is noted that the system 600 can be configured according to any optical configuration known in the art, including, but not limited to, a dark-field configuration, a bright-field adaptation, etc. The system 600 can be configured as any type of metrology tool known in the art, including, but not limited to, a spectroscopic ellipsometer with single or multiple illumination angles, a spectroscopic ellipsometer for Mueller matrix element measurements (e.g., using a rotational compensator), a single-wavelength ellipsometer, an angle-resolved ellipsometer (e.g., a beam profile ellipsometer), a spectroscopic reflectometer, a single-wavelength reflectometer, an angle-resolved reflectometer (e.g., a beam profile reflectometer), an imaging system, a pupil imaging system, a spectral imaging system, or a scatterometer.

[0036] Additional details regarding various embodiments of the optical characterization system 600 are found in U.S. Patent No. 6,201,211 entitled "Split Field Inspection System Using Small Catadioptric Objectives," issued on June 7, 2011; U.S. Patent No. 6,202,213 entitled "Beam Delivery System for Laser Dark-Field Illumination in a Catadioptric Optical System," issued on January 4, 2007; U.S. Patent No. 6,202,213 entitled "Ultra-broadband UV Microscope Imaging System with Wide Range Zoom Capability," issued on December 7, 1999; U.S. Patent No. 6,202,213 entitled "Surface Inspection System Using Laser Line Illumination with Two Dimensional Imaging," issued on April 28, 2009; al., entitled "Dynamically Adjustable Semiconductor Metrology System," issued on May 9, 2013; U.S. Patent No. 6,613,626, issued on March 4, 1997, to Piwonka-Corle et al., entitled "Focused Beam Spectroscopic Ellipsometry Method and System"; and U.S. Patent No. 6,613,626, issued on March 4, 1997, to Rosencwaig et al., entitled "Focused Beam Spectroscopic Ellipsometry Method and System."and Patent Document 7, entitled "Apparatus for Analyzing Multi-Layer Thin Film Stacks on Semiconductors," issued on October 2, 2001 in the name of , the entire contents of which are incorporated herein by reference.

[0037] The one or more processors 620 of the present disclosure may include one or more of any processing elements known in the art. In this sense, the one or more processors 620 may include any microprocessor-based device configured to execute software algorithms and / or instructions. In some embodiments, the one or more processors 620 may be a desktop computer, mainframe computer system, workstation, image computer, parallel processor, or other computer system (e.g., networked computer) configured to execute programs configured to operate the system 600 and / or broadband LSP light source 100 as described elsewhere in this disclosure. It should be recognized that the steps described elsewhere in this disclosure may be performed by a single computer system, or alternatively, by multiple computer systems. In general, the term "processor" may be broadly defined to encompass any device having one or more processing elements that executes program instructions obtained from a non-transitory storage medium 622. Additionally, processors or logic elements suitable for performing at least a portion of the steps described anywhere in this disclosure may be provided within the various subsystems of the various disclosed systems. Accordingly, the above description should be taken as merely illustrative and not as a limitation on the disclosure.

[0038] The storage medium 622 may include any storage medium known in the art suitable for storing program instructions executable by one or more cooperating processors 620. For example, the storage medium 622 may include a non-transitory storage medium. For example, the storage medium 622 may include, but is not limited to, read-only memory, random access memory, magnetic or optical storage devices (e.g., disks), magnetic tape, solid-state drives, etc. In another embodiment, the memory 622 may be configured to store one or more results and / or output of the various steps described herein. It is further noted that the memory 622 may be contained within a common controller housing along with one or more processors 620. In an alternative embodiment, the memory 622 may be located remotely relative to the physical location of the processors 620. For example, one or more processors 620 may access a remote memory (e.g., a server) accessible via a network (e.g., the Internet, an intranet, etc.). In another embodiment, storage medium 622 holds program instructions that cause one or more processors 620 to perform the various steps described throughout this disclosure.

[0039] 7 illustrates a process flow diagram of a method 700 for generating VUV light with an LSP broadband light source with a tapered window according to one or more alternative and / or additional embodiments. It is noted that the steps of method 700 may be performed in whole or in part by broadband LSP light source 100. However, it is further recognized that method 700 is not limited to broadband LSP light source 100, in that all or a portion of the steps of method 700 may be performed by additional or alternative system-level embodiments.

[0040] In step 702 of method 700, a gas is enclosed within a gas containment structure. In step 704 of method 700, an optical pump is generated and directed into the gas containment structure to sustain a plasma within the gas containment structure and generate broadband light. In step 706 of method 700, a portion of the gas containment structure is protected by diverting a portion of the broadband light impinging on a peripheral portion of a window away from an opening in a wall of the gas containment structure. In step 708 of the method, the broadband light impinging on a central portion of the window is transmitted and passed through the central portion of the window into an opening in a wall of the gas containment structure.

[0041] Those skilled in the art will recognize that the components, operations, devices, objects, and accompanying discussions described herein are used as examples for conceptual clarity, and that various structural modifications are contemplated. Therefore, as used herein, the specific exemplars described above and their accompanying discussions are intended to be representative of their more general class. In general, the use of any specific exemplar is intended to be representative of that class, and the absence of specific components (e.g., operations), devices, and objects should not be construed as a limitation.

[0042] With respect to the use of substantially all plural and / or singular terms herein, those skilled in the art will be able to translate from the plural to the singular and / or from the singular to the plural as appropriate to the context and / or use. In the interest of clarity, the various singular / plural permutations have not been explicitly set forth herein.

[0043] The subject matter described herein is sometimes depicted as various components embedded within, or connected or coupled to, other components. Such illustrated architectures are merely exemplary; in fact, many other architectures that achieve the same functionality can be implemented. Conceptually, any arrangement of components that achieves the same functionality is effectively "integrated" to achieve the desired functionality. Thus, any two components herein that combine to achieve a particular function can be considered to be "integrated" with each other to achieve the desired functionality, regardless of the architecture or intervening components. Similarly, any two components so integrated can be considered to be "connected" or "coupled" to each other to achieve the desired functionality, and any two components that can be integrated in this way can be considered to be "combinable" with each other to achieve the desired functionality. Examples of what is connectable include, but are not limited to, physically interlocking and / or physically interacting elements, and / or wirelessly interlocking and / or wirelessly interacting elements, and / or logically interlocking and / or logically interacting elements.

[0044] The present invention is further defined by the appended claims. As would be understood by one of ordinary skill in the art, the terms used herein, particularly in the appended claims (e.g., the body of the appended claims), are generally intended to be "open" (e.g., the term "comprising" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "including" should be interpreted as "including but not limited to," etc.). As would also be understood by one of ordinary skill in the art, if a specific number of claim-introducing features is intended, that intention will be clearly stated in the claim, and the absence of such features indicates no intention. For example, as an aid to understanding, some of the appended claims below incorporate claim-introducing features through the use of the introductory phrases "at least one" and "one or more." However, the use of the indefinite article "a" or "an" should not be construed as implying that the introduction of a claim feature with the indefinite article "a" or "an" implies that all individual claims containing that claim feature are limited to inventions containing only one of that feature, nor should such construing be done when the introductory phrase "one or more" or "at least one" coexists with an indefinite article, such as "a" or "an," in the very same claim (e.g., "a" and / or "an" should generally be interpreted as meaning "at least one" or "one or more"). The same is true with regard to the introduction of claim features with the definite article. Additionally, even when a specific number of a claim feature is specified, the number should generally be interpreted to mean at least that specified number (e.g., the bare phrase "two features" without any other modifier generally means at least two features or more than two features).Furthermore, where a convention similar to "at least one of A, B, and C, etc." is used, the syntax is generally intended to conform to the way a person skilled in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include, but is not limited to, a system having only A, only B, only C, both A and B, both A and C, both B and C, and / or a system having all three of A, B, and C, etc.). Where a convention similar to "at least one of A, B, or C, etc." is used, the syntax is generally intended to conform to the way a person skilled in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include, but is not limited to, a system having only A, only B, only C, both A and B, both A and C, both B and C, and / or a system having all three of A, B, and C, etc.). As will also be understood by those skilled in the art, nearly all presentations of two or more alternative terms by disjunctive conjunctions and / or disjunctive phrases, whether appearing in the specification, claims, or drawings, should be understood to contemplate the inclusion of either, either, or both terms. For example, the phrase "A or B" would be understood to encompass the possibilities of "A" or "B" or "A and B."

[0045] The present disclosure and many of its attendant advantages will be understood from the foregoing description, and it will also be apparent that various changes can be made in the form, construction and arrangement of the parts without departing from the disclosed subject matter or diminishing all of its essential advantages. The described form is illustrative only, and it is the intent of the following claims to encompass and embrace all such modifications. It is the appended claims which further define the invention.

Claims

1. 1. A laser-sustained plasma broadband light source comprising: a gas sealing structure in which a gas is sealed; a laser pump source configured to generate an optical pump, the laser pump source configured to direct the optical pump into the gas containment structure to sustain a plasma within the gas containment structure, the broadband light being generated by the plasma; and a window configured to transmit a portion of the broadband light into an opening in a wall of the gas-filled structure, the window having a tapered portion with a tapered surface configured to deflect a portion of the broadband light impinging on a peripheral portion of the window away from a portion or portions of the gas-filled structure to protect the portion or portions of the gas-filled structure; 1. A laser-sustained plasma broadband light source comprising:

2. 2. The broadband light source of claim 1, wherein the window comprises a cylindrical window having the tapered portion.

3. 10. The broadband light source of claim 1, wherein the tapered portion comprises a conical portion.

4. 10. The broadband light source of claim 1, wherein the tapered surface is configured to deflect a portion of broadband light impinging on the peripheral portion of the window away from one or more seals of the gas containment structure.

5. 2. The broadband light source of claim 1, wherein the tapered surface is configured to transmit a portion of broadband light impinging on the peripheral portion of the window into the opening in the gas containment structure.

6. 2. The broadband light source of claim 1, wherein a central portion of the window is configured to pass broadband light impinging on the central portion of the window into the aperture.

7. 10. The broadband light source of claim 1, wherein the tapered surface is configured to reflect a portion of broadband light impinging on the peripheral portion of the window away from the opening in the wall of the gas containment structure, thereby protecting one or more portions of the gas containment structure.

8. 10. The broadband light source of claim 1, wherein the tapered surface is configured to scatter a portion of broadband light impinging on the peripheral portion of the window away from the opening in the wall of the gas containment structure, thereby protecting one or more portions of the gas containment structure.

9. 2. A broadband light source as described in claim 1, wherein the window has a convex lens surface in a central portion of the window, the convex lens surface being configured to collimate or focus broadband light impinging on the central portion of the window.

10. 10. The broadband light source of claim 9, wherein the convex lens surface comprises a spherical lens surface.

11. 10. The broadband light source of claim 1, wherein the window is MgF ２ , CaF ２ and a broadband light source formed of at least one of LiF.

12. 10. The broadband light source of claim 1, wherein the window comprises at least one of an exit window and an entrance window.

13. 2. The broadband light source of claim 1, wherein the pressure of the gas in the gas containment structure is between 50 and 300 atmospheres.

14. 2. The broadband light source of claim 1, wherein the broadband light transmitted through the window includes at least vacuum ultraviolet light.

15. 1. A characterization system comprising: a broadband light source, a gas-filled structure in which gas is filled; a laser pump source configured to generate an optical pump, the laser pump source configured to direct the optical pump into the gas containment structure to sustain a plasma within the gas containment structure, the broadband light being generated by the plasma; and a window configured to transmit a portion of the broadband light into an opening in the gas-filled structure, the window having a tapered portion with a tapered surface configured to deflect a portion of light impinging on a periphery of the window and away from the opening in the gas-filled structure, thereby protecting one or more portions of the gas-filled structure; a broadband light source comprising: a set of illumination optics configured to direct broadband light from the broadband light source onto one or more specimens; a set of collection optics configured to collect light emanating from the one or more specimens; a detector assembly; A characterization system comprising:

16. 16. The characterization system of claim 15, wherein the window comprises a cylindrical window having the tapered portion.

17. 16. The characterization system of claim 15, wherein the tapered portion comprises a conical portion.

18. 16. The characterization system of claim 15, wherein the tapered surface is configured to deflect a portion of broadband light impinging on the peripheral portion of the window away from one or more seals of the gas containment structure.

19. 16. The characterization system of claim 15, wherein the tapered surface is configured to transmit a portion of broadband light impinging on the peripheral portion of the window into the opening in the gas containment structure.

20. 16. The characterization system of claim 15, wherein a central portion of the window is configured to pass broadband light impinging on the central portion of the window into the aperture.

21. 16. The characterization system of claim 15, wherein the tapered surface comprises a polished tapered surface configured to reflect a portion of broadband light impinging on the peripheral portion of the window away from the opening in a wall of the gas containment structure, thereby protecting one or more portions of the gas containment structure.

22. 16. The characterization system of claim 15, wherein the tapered surface comprises a ground tapered surface configured to scatter a portion of broadband light impinging on the peripheral portion of the window away from the opening in the wall of the gas containment structure, thereby protecting one or more portions of the gas containment structure.

23. 16. The characterization system of claim 15, wherein the optical window has a convex lens surface at a central portion of the optical window, the convex lens surface configured to collimate or focus broadband light impinging on the central portion of the optical window.

24. 24. The characterization system of claim 23, wherein the convex lens surface comprises a spherical lens surface.

25. 16. The characterization system of claim 15, wherein the window is MgF ２ , CaF ２ and LiF.

26. 16. The characterization system of claim 15, wherein the window comprises at least one of an exit window and an entrance window.

27. 16. The characterization system of claim 15, wherein the pressure of the gas in the gas containment structure is between 50 and 300 atmospheres.

28. 16. The characterization system of claim 15, wherein the broadband light transmitted through the window includes at least vacuum ultraviolet light.

29. 1. A method for producing VUV broadband light, comprising: Gas is poured into the gas-filled structure, generating an optical pump and directing the optical pump into the gas containment structure to sustain a plasma within the gas containment structure and generate broadband light; protecting a portion or portions of the gas containment structure by diverting a portion of the broadband light impinging on the peripheral portion of the window away from the opening in the wall of the gas containment structure; and transmitting broadband light impinging on a central portion of the window through the central portion of the window and into the opening in the wall of the gas containment structure; method.

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