Strontium tetraborate as an optical glass material

Abstract

Strontium tetraborate can be used as an optical material. It exhibits a high refractive index, a high optical damage threshold, and high microhardness. The transmission window of strontium tetraborate covers a very wide wavelength range, from 130 nm to 3200 nm, making this material particularly useful at VUV wavelengths. Optical components made from strontium tetraborate can be incorporated into optical systems such as semiconductor inspection systems, metrology systems, or lithography systems. These optical components can include mirrors, lenses, lens arrays, prisms, beam splitters, windows, lamp cells, or Brewster angle optics.

Description

[Technical field]

[0001] The present disclosure relates generally to optical glass materials. In particular, the present disclosure relates to strontium tetraborate (SrB4O7) optical glass materials for linear optical components such as mirrors, lenses, prisms, beam splitters, windows and lamp cells suitable for use in metrology and inspection systems in semiconductor manufacturing, including those used to inspect and / or measure photomasks, reticles, and semiconductor wafers. [Background technology]

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 871,887, filed July 9, 2019, and entitled “STRONTIUM TETRABORATE AS OPTICAL MATERIAL,” named by Yung-Ho Alex Chuang, Yinying Xiao-Li, Elena Loginova, and John Fielden as inventors, which is incorporated herein by reference in its entirety.

[0003] The integrated circuit industry requires inspection tools with increasingly high sensitivity to detect ever smaller defects and particles that may be tens of nanometers (nm) or less in size. These inspection tools must operate at high speeds to quickly inspect a large portion, or even 100%, of the area of ​​a photomask, reticle, or wafer. For example, inspection times may be one hour or less for inspection during production, and at most a few hours for R&D or troubleshooting. To perform such rapid inspections, inspection tools use pixel or spot sizes larger than the dimensions of the defect or particle of interest to detect small changes in signal caused by the defect or particle. High light levels and low noise levels are necessary to detect small changes in signal. High speed inspection is most commonly performed in production using inspection tools that operate with ultraviolet (UV) light. Inspection in R&D may be performed with UV light or electrons.

[0004] The integrated circuit (IC) industry also requires high precision metrology tools to accurately measure the dimensions of small features on semiconductor wafers, measuring a few nanometers or less. Metrology processes are performed on the wafers at various points in the semiconductor manufacturing process to measure various characteristics of the wafer, such as the width of patterned structures on the wafer, the thickness of films formed on the wafer, and the overlay of patterned structures on one layer of the wafer with patterned structures on another layer of the wafer. These measurements are used to facilitate process control and / or yield efficiency in the manufacture of semiconductor dies. Metrology may be performed using UV light or electrons.

[0005] The semiconductor industry, which aims to produce integrated circuits with higher integration density, lower power consumption and lower cost, is one of the major drivers of UV optics. The development of powerful UV light sources such as excimer lasers and frequency-doubled solid-state lasers has led to a growth in research and development efforts in the field of UV photon applications.

[0006] Optical glasses are used in many applications such as cameras, telescopes, microscopes, binoculars, virtual reality systems, semiconductor systems, among others. Optical glasses are prevalent in semiconductor inspection and metrology. They are found in optical components such as mirrors, lenses, prisms, beam splitters, windows and lamp cells in most inspection and metrology systems.

[0007] Optical glasses in the deep ultraviolet (DUV) spectral range of about 200 nm to 280 nm, and vacuum ultraviolet (VUV) spectral range of about 100 nm to 200 nm, are challenging. DUV and VUV lasers can have high power levels from a few milliwatts (mW) to over 10 watts (W), and high photon energies (e.g., 6.5 eV at 193 nm and 4.66 eV at 266 nm). Pulsed lasers can have short pulse lengths (e.g., ns or less) and high repetition rates (e.g., tens of kHz or more). In addition to being transparent in the DUV / VUV wavelength range, optical glasses must withstand these extreme conditions with high optical damage thresholds, high hardness, and excellent stability.

[0008] There are several glass materials known in the art that are suitable for DUV and VUV wavelengths. Among them, the most widely and commonly used is fused silica, known by trade names such as Suprasil, Spectrosil, and Lithosil. Fused silica is made from quartz and is widely used because it exhibits excellent thermal dimensional stability and durability, and is therefore inexpensive to manufacture. However, fused silica can only operate at wavelengths up to 190 nm, and most grades have a UV cutoff near or above 200 nm. Optical components made from fused silica are often smaller than that, due to the difficulty of finding UV-grade blanks of 100 mm size or larger. Fused silica also has an absorption dip near 240 nm, making it a poor choice for light sources operating in this region. In addition, the internal structure of fused silica glass can be destroyed with prolonged exposure to intense UV light.

[0009] Calcium fluoride (CaF2) is another common UV glass material. CaF2 is transparent from 130 nm to almost 10 μm and has a low refractive index in the UV (n ~ 1.46). Most fluorides are hygroscopic, i.e., they absorb water from the atmosphere. As a result, UV performance degrades over time when exposed to the atmosphere. Water absorbs UV light, and the absorption causes volume changes that lead to stresses and potential shape changes. In addition, strong UV radiation can promote the reaction of water and oxygen with calcium fluoride. CaF2 material is soft and brittle, so it chips easily during polishing. It is difficult to achieve high curvature and good surface roughness together. CaF2 also requires extensive cleaning between lapping, as particles from the lapping process can get trapped and reattach to the surface, increasing scattering sites and reducing overall performance.

[0010] Magnesium fluoride (MgF2) has a similar transmission window as CaF2. MgF2 is also the most common coating material for UV optics. Unlike CaF2, the performance of MgF2 is not affected by water. However, MgF2 has a lower optical damage threshold (~0.1 GW / cm 2 ). Also, because MgF2 is ionic, it cannot withstand high voltages. Additionally, MgF2 is birefringent, which may make it unsuitable for certain applications. When MgF2 is exposed to ultraviolet radiation, its transmission decreases due to absorption, and the transmission deteriorates over time.

[0011] The damage threshold of all the above materials is reduced by impurities or defects in the material. These impurities and defects can create color centers that absorb DUV and / or VUV radiation. Color centers can grow upon exposure to VUV or DUV radiation, reducing the transmittance of UV wavelengths over time.

[0012] Although there has been great interest for decades in producing glass materials that are stable under VUV and DUV illumination, there are only a few optical glass material options in the DUV and VUV wavelength ranges. Current applications in high-speed inspection and metrology require optical glasses to have high optical damage thresholds, significant hardness, and good stability. It is further desirable for such glasses to have low permeability to water and oxygen diffusion to reduce oxidation. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] US Patent Application Publication No. 2006 / 0103315 Summary of the Invention [Problem to be solved by the invention]

[0014] Therefore, optical glass materials that overcome some or all of the limitations discussed above are desirable. [Means for solving the problem]

[0015] A linear optical component including strontium tetraborate (SrB4O7) in accordance with one or more embodiments of the present disclosure is disclosed.

[0016] An optical system is disclosed in accordance with one or more embodiments of the present disclosure. In one exemplary embodiment, the optical system includes one or more linear optical components, at least a portion of which is formed from strontium tetraborate.

[0017] An optical system is disclosed according to one or more additional and / or alternative embodiments of the present disclosure. In one exemplary embodiment, the optical system includes a stage for supporting the sample. In another exemplary embodiment, the optical system includes an illumination source. In another exemplary embodiment, the optical system includes one or more linear optical components configured to direct illumination from the illumination source to the sample, at least a portion of the one or more linear optical components being formed from strontium tetraborate.

[0018] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the general description, serve to explain the principles of the invention. [Brief description of the drawings]

[0019] Many advantages of the present disclosure may be better understood by those skilled in the art by reference to the following drawings. [Figure 1] FIG. 1 is a block diagram of a characterization system in accordance with one or more embodiments of the present disclosure. [Diagram 2] FIG. 1 illustrates an ultraviolet lamp incorporating SrB4O7 as an optical glass material for one or more optical components in accordance with one or more embodiments of the present disclosure. [Diagram 3] FIG. 1 shows a typical transmission curve of SrB4O7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The present disclosure has been particularly shown and described with respect to certain embodiments and certain features thereof. The embodiments described herein are considered to be illustrative and not limiting. It should be readily apparent to those skilled in the art that various changes and modifications in form and details may be made without departing from the spirit and scope of the present disclosure. Reference will now be made in detail to the disclosed subject matter, which is illustrated in the accompanying drawings.

[0021] Embodiments of the present disclosure are directed to incorporating strontium tetraborate (SrB4O7) as an optical glass material in one or more linear optical components of a semiconductor inspection and / or metrology system. For example, embodiments of the present disclosure incorporate SrB4O7 as an optical glass material in linear optical components found in inspection and metrology systems such as, but not limited to, mirrors, lenses, lens arrays, prisms, beam splitters, windows, and lamp cells.

[0022] It should be noted that SrB4O7 exhibits unique optical and mechanical properties. The transparency range of SrB4O7 is from 130 to 3200 nm wavelength. See YS Ozeredchik, AL Prosvirnin, AI Pisarevskiy, VV Starshenko, VV Osadchuk, SP Belokrys, NV Svitanko, AS Korol, SA Krikunov, and AF Selevich, "New nonlinear optical crystals: strontium and lead tetraborates," Opt. Mater. 4, 669 (1995), which is incorporated herein by reference in its entirety. This wide transmission window makes SrB4O7 a good candidate for optical glass material, especially for the DUV and VUV wavelength ranges. If SrB4O7 is grown under optimal conditions, the transmission can reach more than 80% for wavelengths longer than 200 nm and more than 50% for wavelengths between 130 nm and 200 nm. The refractive index of SrB4O7 is high compared to other glass materials such as CaF2. For example, the refractive index at 266 nm is 1.7883 in the x-direction, 1.7909 in the y-direction, and 1.7936 in the z-direction. It should be noted that the difference between these refractive indices is relatively small, so birefringence effects are small in components made from crystalline SrB4O7. SrB4O7 is not hygroscopic, and borates are oxides, so they are resistant to further oxidation in the presence of oxygen or water during exposure to DUV or VUV radiation. The optical damage threshold is very high (14.7 GW / cm) compared to other glass materials. 2 The surface laser-induced damage threshold of SrB4O7 is approximately 16 J / cm 2 , which is much higher than that of fused silica and calcium fluoride. The microhardness of SrB4O7 is also high (1750 kg / mm ​​in the x direction). 2 , 1460kg / mm ​​in the y direction 2 , 1350kg / mm ​​in the z direction 2). High optical damage threshold and microhardness allow SrB4O7 glass to withstand extreme conditions when exposed to DUV and VUV radiation. DUV and VUV lasers can have high power levels, from a few milliwatts (mW) to over a few watts (W), and high photon energies (e.g., 6.5 eV at 193 nm and 4.66 eV at 266 nm). Pulsed lasers can have short pulse lengths (ns or less) and high repetition rates (tens of kHz or more).

[0023] According to embodiments of the present disclosure, one or more linear optical components made of SrB4O7 disclosed herein can be incorporated into inspection and metrology systems. Semiconductor inspection tools must operate at high speeds to inspect a large portion, even 100%, of the area of ​​a photomask, reticle, or wafer in a short period of time. For example, inspection times may be one hour or less for inspection during production, and at most a few hours for R&D or troubleshooting. To perform such rapid inspections, inspection tools use pixel or spot sizes larger than the dimensions of the defect or particle of interest to detect only small changes in signal caused by the defect or particle. High speed inspections are most commonly performed in production using inspection tools that operate with ultraviolet (UV) light. High accuracy metrology tools are required to accurately measure dimensions of small features on semiconductor wafers, down to a few nanometers or less. Metrology processes are performed on wafers at various points in the semiconductor manufacturing process to measure various characteristics of the wafer, such as the width of patterned structures on the wafer, the thickness of films formed on the wafer, and the overlay offset between patterned structures on one layer of the wafer and patterned structures on another layer of the wafer. These measurements are used to facilitate process control and / or yield efficiency in the manufacturing of semiconductor dies. High speed inspection and metrology requires high light levels and stable signals. Optical components are components of inspection and metrology systems. Optical glass materials that do not degrade or that degrade more slowly than existing glass materials can provide a more stable signal, making it easier to detect small changes in the signal. Such glass materials can also lower the operating costs of an inspection or metrology tool by reducing the frequency of replacement of optical components.

[0024] FIG. 1 illustrates a simplified schematic diagram of a characterization system 100 in accordance with one or more embodiments of the present disclosure. In one embodiment, the characterization system 100 (or “tool”) includes a characterization subsystem 101 and a controller 114. The characterization system 100 can be configured as an inspection system or a metrology system. For example, the characterization system 100 can be an optical-based inspection system (or “tool”), a review system (or “tool”), or an image-based metrology system (or “tool”). In this regard, the characterization subsystem 101 can be, without limitation, an inspection subsystem or a metrology subsystem configured to inspect or measure the sample 108. The characterization subsystem 101 of the characterization system 100 can be communicatively coupled to a controller 114. The controller 114 can receive measurement data from the detector assembly 104 of the characterization subsystem to characterize (e.g., inspect or measure) structures on or within the sample 108 and / or to control one or more portions of the characterization system 100.

[0025] The sample 108 may include any sample known in the art, such as, without limitation, a wafer, a reticle, a photomask, etc. In one embodiment, the sample 108 may be placed on a stage assembly 112 to facilitate movement of the sample 108. The stage assembly 112 may include any stage assembly known in the art, including, without limitation, an XY stage, an R-θ stage, etc. In another embodiment, the stage assembly 112 may adjust the height of the sample 108 during inspection to maintain focus on the sample 108. In yet another embodiment, the characterization subsystem 101 may move up and down during inspection to maintain focus on the sample 108.

[0026] In another embodiment, the characterization system 100 includes an illumination source 102 configured to generate an illumination beam 111. The illumination source 102 may include any illumination source known in the art suitable for generating the illumination beam 111. For example, the illumination source 102 may emit near infrared (NIR) radiation, visible radiation, ultraviolet (UV) radiation, near UV (NUV), deep UV (DUV) radiation, vacuum UV (VUV) radiation, etc. For example, the illumination source 102 may include one or more lasers. In another example, the illumination source 102 may include a broadband illumination source.

[0027] In another embodiment, the characterization system 100 includes an illumination arm 107 configured to direct illumination from the illumination source 102 to the sample 108. The illumination arm 107 can include any number and type of optical components known in the art. In one embodiment, the illumination arm 107 includes one or more optical elements 103. In this regard, the illumination arm 107 can be configured to focus illumination from the illumination source 102 onto a surface of the sample 108. It is noted herein that the one or more optical elements 103 can include any optical element known in the art, including, but not limited to, one or more lenses (e.g., objective lens 105), one or more mirrors, one or more polarizers, one or more prisms, one or more beam splitters, etc.

[0028] In another embodiment, the collection arm 109 is configured to collect reflected, scattered, diffracted, and / or emitted illumination from the sample 108. In another embodiment, the collection arm 109 can direct and / or focus illumination from the sample 108 to the sensor 106 of the detector assembly 104. It is noted herein that the sensor 106 and the detector assembly 104 can include any sensor and detector assembly 104 known in the art. It is noted that the detector assembly 104 can include any sensor and detector assembly known in the art. The sensor can include, but is not limited to, a charge-coupled device (CCD detector), a complementary metal-oxide semiconductor (CMOS) detector, a time-delay integration (TDI) detector, a photomultiplier tube (PMT), an avalanche photodiode (APD), a line sensor, an electron-bombarded line sensor, and the like.

[0029] In another embodiment, the detector assembly 104 is communicatively coupled to one or more processors 116 of the controller 114. The one or more processors 116 may be communicatively coupled to a memory 118. The one or more processors 116 are configured to execute a set of program instructions stored in the memory 118 to obtain measurement data from the one or more sensors 106 of the detector assembly 104 and / or to control one or more portions of the characterization system 100.

[0030] In one embodiment, the characterization system 100 illuminates a line on the sample 108 and collects scattered and / or reflected illumination in one or more dark-field and / or bright-field collection channels. In this embodiment, the detector assembly 104 may include a line sensor or an electron bombarded line sensor.

[0031] In one embodiment, the illumination source 102 is a continuous light source. For example, the illumination source 102 can include, but is not limited to, an arc lamp, a laser-produced plasma source, or a continuous wave (CW) laser. In another embodiment, the illumination source 102 is a pulsed light source. For example, the illumination source 102 can include, but is not limited to, a mode-locked laser, a Q-switched laser, or a plasma source pumped by a mode-locked or Q-switched laser. Examples of suitable light sources that may be included in the illumination source 102 are described in U.S. Patent No. 7,705,331 to Kirk et al., entitled "Methods and systems for providing illumination of a specimen for a process performed on the specimen," U.S. Patent No. 9,723,703 to Bezel et al., entitled "System and method for transverse pumping of laser-sustained plasma," and U.S. Patent No. 9,865,447 to Chuang et al., entitled "High brightness laser-sustained plasma broadband source," each of which is incorporated herein by reference.

[0032] In one embodiment, the one or more optical elements 103 include an illumination tube lens 133. The illumination tube lens 133 can be configured to image the illumination pupil aperture 131 to a pupil in the objective lens 105. For example, the illumination tube lens 133 can be configured such that the illumination pupil aperture 131 and the pupil in the objective lens 105 are conjugate to one another. In one embodiment, the illumination pupil aperture 131 may be configurable by switching a different aperture into the position of the illumination pupil aperture 131. In another embodiment, the illumination pupil aperture 131 may be configurable by adjusting a diameter or shape of an opening of the illumination pupil aperture 131. In this regard, the sample 108 may be illuminated at different angular ranges depending on the characterization (e.g., measurement or inspection) being performed under the control of the controller 114.

[0033] In one embodiment, the one or more optical elements 103 include a collection tube lens 123. For example, the collection tube lens 123 can be configured to image a pupil in the objective lens 105 onto the collection pupil aperture 121. For example, the collection tube lens 123 can be configured such that the collection pupil aperture 121 and the pupil in the objective lens 105 are conjugate to one another. In one embodiment, the collection pupil aperture 121 can be configurable by switching a different aperture into the position of the collection pupil aperture 121. In another embodiment, the collection pupil aperture 121 can be configurable by adjusting the diameter or shape of the opening of the collection pupil aperture 121. In this regard, illumination of different angular ranges reflected or scattered from the sample 108 can be directed to the detector assembly 104 under the control of the controller 114.

[0034] In another embodiment, the illumination pupil aperture 131 and / or the collection pupil aperture 121 may include a programmable aperture. Programmable apertures are generally described in U.S. Pat. No. 9,255,887, issued Feb. 9, 2016 to Brunner, entitled "2D programmable aperture mechanism," and U.S. Pat. No. 9,645,287, issued May 9, 2017 to Brunner, entitled "Flexible optical aperture mechanisms," both of which are incorporated herein by reference in their entireties. Methods for selecting an aperture configuration for inspection are generally described in U.S. Pat. No. 9,709,510, issued July 18, 2017 to Kolchin et al., entitled "Determining a configuration for an optical element positioned in a collection aperture during wafer inspection," and U.S. Pat. No. 9,726,617, issued August 8, 2017 to Kolchin et al., entitled "Apparatus and methods for finding a best aperture and mode to enhance defect detection," both of which are incorporated herein by reference in their entireties.

[0035] In one embodiment, one or more linear optical components of the optical system 103 and / or illumination source 102 are formed from SrB4O7. Linear optical components herein may include mirrors, lenses, lens arrays, prisms, beam splitters, windows, and / or lamp cells. The overall light throughput of the system 100 may be improved by the appropriate use of SrB4O7 as an optical glass material for one or more linear optical components. The lifetime of the primary linear optical components may also be improved by using SrB4O7. The linear optical components may be made from a single SrB4O7 crystal or from SrB4O7 glass. It is noted that the glass version of the SrB4O7 linear optical components may be weaker (lower damage threshold and lower microhardness) than the corresponding single crystal form of the SrB4O7 optical components. Nevertheless, SrB4O7 glass is robust enough for many applications. Furthermore, it is noted that SrB4O7 glass has the added advantage of not having birefringence. Thus, SrB4O7 glass can be implemented in settings where birefringence is not required (e.g., high numerical aperture lenses). Where birefringence effects are small (e.g., low numerical aperture lenses) or desirable (e.g., polarizing beam splitters), single crystal SrB4O7 may be implemented, with the advantage of being more resistant to damage than glass.

[0036] In one embodiment, the illumination beam 111 is polarized, such as light generated by a laser. In this embodiment, at least one of the one or more linear optical components of the optical system 103 and the illumination source 102 is configured to operate at substantially Brewster's angle with respect to the polarization direction of the illumination beam 111. For example, the one or more linear optical components can include one of Brewster's angle wavefront processing optics, Brewster's angle lens, Brewster's angle dual wave plate, and harmonic separation optics with Brewster's angle input face. Because the refractive index of SrB4O7 is higher than most other optical materials, there may not be a suitable material to use as an anti-reflective coating for SrB4O7, especially at DUV and VUV wavelengths. The advantage of an optical system configured to operate at Brewster's angle is that it has a low reflectivity without the use of an anti-reflective coating. Furthermore, anti-reflective coatings tend to be more susceptible to damage when operated under high UV intensities. By avoiding anti-reflective coatings, optical components made from SrB4O7 can fully benefit from the high damage threshold of SrB4O7. It should be noted that the reflectivity of the surface is low at angles close to the Brewster angle. When the surface is oriented a few degrees away from the Brewster angle (such as about 2° or less), the reflectivity becomes very low. The Brewster angle of SrB4O7 crystal is about 60.5±1° over a wide range of visible and UV wavelengths. For this reason, Brewster angle optics made from SrB4O7 can be used with polarized broadband light as well as laser light. Further details of optics configured to operate at Brewster angle can be found in U.S. Patent Nos. 8,711,470, 9,152,008, and 9,753,352, all entitled "High Damage Threshold Frequency Conversion System," all to Armstrong, and incorporated herein by reference in their entireties.

[0037] Characterization systems may be used in a variety of applications, including but not limited to, U.S. Pat. No. 9,891,177, issued February 13, 2018 to Vazhaeparambil et al., entitled "TDI Sensor in a Darkfield System," U.S. Pat. No. 9,279,774, issued March 8, 2018 to Romanovsky et al., entitled "Wafer Inspection," U.S. Pat. No. 7,957,066, issued June 7, 2011 to Armstrong et al., entitled "Split Field Inspection System Using Small Catadioptric Objectives," U.S. Pat. No. 7,817,260, issued October 19, 2010 to Chuang et al., entitled "Beam Delivery System for Laser Dark-Field Illumination in a Catadioptric Optical System," U.S. Pat. No. 7,817,260, issued December 7, 1999 to Shafer et al., entitled "Ultra-Broadband UV Microscope," U.S. Pat. No. 5,999,310 entitled "Surface Inspection System Using Laser Line Illumination with Two Dimensional Imaging" issued on April 28, 2009 to Leong et al., U.S. Patent No. 7,525,649 entitled "Surface Inspection System Using Laser Line Illumination with Two Dimensional Imaging" issued on July 14, 2015 to Kandel et al., U.S. Patent No. 9,080,971 entitled "Metrology Systems and Methods" issued on July 14, 2015 to Kandel et al., U.S. Patent No. 7,474,461 entitled "Broad Band Objective Having Improved Lateral Color Performance" issued on January 6, 2009 to Chuang et al., U.S. Patent No. 7,474,461 entitled "Optical Metrology With Reduced Sensitivity To Grating" issued on October 18, 2016 to Zhuang et al.No. 9,470,639 to Wang et al., entitled "Dynamically Adjustable Semiconductor Metrology System," issued on January 5, 2016; U.S. Pat. No. 5,608,526 to Piwonka-Corle et al., entitled "Focused Beam Spectroscopic Ellipsometry Method and System," issued on March 4, 1997; and U.S. Pat. No. 6,297,880 to Rosencwaig et al., entitled "Apparatus for Analyzing Multi-Layer Thin Film Stacks on Semiconductors," issued on October 2, 2001, each of which is incorporated herein by reference in its entirety.

[0038] It should be noted that the scope of the present disclosure is not limited to the characterization system 100. Rather, systems incorporating the SrB4O7 optics of the present disclosure can include any other optical systems known in the art, including lithography systems / tools.

[0039] It is noted herein that one or more components of system 100 may be communicatively coupled to various other components of system 100 in any manner known in the art. For example, one or more processors 116 may be communicatively coupled to each other and to the other components via a wired connection (e.g., copper wire, fiber optic cable, etc.) or a wireless connection (e.g., RF coupling, IR coupling, WiMAX, Bluetooth, 3G, 4G, 4GLTE, 5G, etc.).

[0040] The one or more processors 116 may include any one or more processing elements known in the art. In this sense, the one or more processors 116 may include any microprocessor-type device configured to execute software algorithms and / or instructions. The one or more processors 116 may be comprised of a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, or other computer system (e.g., a network computer) configured to execute programs configured to operate the system 100 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, multiple computer systems. Furthermore, it should be appreciated that the steps described throughout this disclosure may be performed by any one or more of the one or more processors 116. In general, the term "processor" may be broadly defined to encompass any device having one or more processing elements that execute program instructions from the memory 118. Additionally, different subsystems of the system 100 (e.g., the illumination source 102, the detector assembly 104, the controller 114, etc.) may include processors or logic elements suitable for executing at least some of the steps described throughout this disclosure. Therefore, the above description should not be construed as a limitation on the present disclosure, but merely as illustrative.

[0041] The memory 118 may include any storage medium known in the art suitable for storing program instructions executable by the associated one or more processors 116 as well as data received from the metrology subsystem and / or inspection subsystem. For example, the memory 118 may include a non-transitory memory medium. For example, the memory 118 may include, but is not limited to, a read-only memory (ROM), a random access memory (RAM), a magnetic or optical memory device (e.g., disk), a magnetic tape, a solid-state drive, and the like. It is further noted that the memory 118 may be housed in a common controller housing with the one or more processors 116. In alternative embodiments, the memory 118 may be located remotely relative to the physical locations of the processors 116, the controller 114, and the like. In another embodiment, the memory 118 maintains program instructions for causing the one or more processors 116 to perform various steps described throughout this disclosure.

[0042] FIG. 2 shows a simplified schematic diagram of an ultraviolet lamp incorporating SrB4O7 as an optical glass material for one or more optical components, according to one or more embodiments of the present disclosure. The ultraviolet lamp 200 may be a laser-driven light source. In this example, a laser 211 emits a laser beam 212 that is directed by a mirror 213 and focused by a lens 214 and a lens 225 to generate a plasma 202 in a lamp cell 201. The plasma 202 emits broadband ultraviolet light 205 over a wide range of wavelengths, including DUV and / or VUV wavelengths. One or more windows 203 may be disposed in the walls of the lamp cell 201 to allow the broadband ultraviolet light 205 to be transmitted from the lamp cell 201. In one embodiment, the lamp cell 201 may be made of SrB4O7. In this embodiment, SrB4O7 may be used to form a transparent bulb that contains a gas for generating the plasma 202. In another embodiment, the one or more windows 203 may be formed from SrB4O7. In yet another embodiment, both the lamp cell 201 and the one or more windows 203 may be made of SrB4O7. The overall light throughput of the ultraviolet lamp 200 may be improved by the appropriate use of SrB4O7 as an optical glass material for one or more optical components. The life of the ultraviolet lamp 200 and the main optical components may also be improved by using SrB4O7. Any of the aforementioned optical components may be made using SrB4O7 crystals or glasses, and the scope of the present disclosure is in no way limited to SrB4O7-based windows or plasma cells. Rather, as previously discussed herein, any number of linear optical components of the present disclosure may be formed from SrB4O7 and may be implemented in any optical context, including, but not limited to, semiconductor inspection or metrology.

[0043] SrB4O7 crystallizes in the orthorhombic system with P21 nm and unit cell dimensions a=4.237 Å, b=4.431 Å, and c=10.706 Å (A. Perloff and S. Block, "The crystal structure of the strontium and lead tetraborates, SrO.2B2O3and PbO.2B2O3", Acta Cryst. 20, 274-279 (1966)). All boron atoms are coordinated tetrahedra, and oxygen atoms are common to three tetrahedra. Despite the three-dimensional network of tetrahedra, the borate network appears as a layered structure due to the relatively few bonds in the c-direction of the unit cell.

[0044] FIG. 3 shows a typical transmission curve 300 for SrB4O7 (YS Ozeredchik, AL Prosvirnin, AI Pisarevskiy, VV Starshenko, VV Osadchuk, SP Belokrys, NV Svitanko, AS Korol, SA Krikunov, and AF Selevich, "New nonlinear optical crystals: strontium and lead tetraborates", Opt. Mater. 4, 669 (1995)). As shown in the transmission curve 300, the transmission range of SrB4O7 is very wide, i.e., from about 130 nm to about 3200 nm, which covers the VUV, DUV, visible and near infrared (IR) wavelength ranges. The VUV and DUV ranges are particularly important for semiconductor inspection and metrology. It is also notable for its high transmittance. For example, the transmittance is greater than 80% from about 250 nm to about 2500 nm. This high transmittance makes SrB4O7 a good candidate for optical glass materials, especially for the UV wavelength range. If SrB4O7 is grown under optimal conditions, a better transmission curve can be obtained, and the transmittance can reach greater than 80% for wavelengths longer than 200 nm and greater than 50% for wavelengths from 130 nm to 200 nm. The dielectric and optical properties of strontium tetraborate glasses are described in MV Shankar and KBR Varma, "Dielectric and Optical Properties of Strontium Tetraborate Glass," Journal of Materials Science Letters 15 (1996) 858-860, which is incorporated herein by reference in its entirety.

[0045] Various modifications to the described embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments. Although the optical glass materials disclosed herein are expected to be particularly useful in semiconductor inspection and metrology systems, it is envisioned that these glass materials may also be useful in other applications where VUV and DUV radiation is present, as well as other applications where high intensity visible or IR radiation is present, such as IR light sources or camera systems.

[0046] The glass materials and methods described herein are not intended to be limited to the particular embodiments shown and described, but are to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0047] 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 configuration variations are contemplated. As such, as used herein, the specific examples described and accompanying discussions are intended to be representative of their more general classes. In general, the use of any specific example is intended to be representative of its class, and the inclusion of the specific components, operations, devices, and objects should not be construed as limiting.

[0048] The foregoing description is presented to enable one skilled in the art to make and use the invention as provided in the context of a particular application and its requirements. As used herein, directional terms such as "top", "bottom", "above", "below", "upper", "upward", "lower", "under" and "downward" are intended to indicate relative positions for purposes of description and are not intended to specify an absolute frame of reference. Various modifications to the described embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the specific embodiments shown and described, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0049] With respect to the use of virtually any plural and / or singular term herein, those of skill in the art can convert from plural to singular and / or from singular to plural as appropriate to the context and / or application. The various singular / plural permutations are not expressly set forth herein for the sake of clarity.

[0050] The subject matter described herein sometimes shows different components contained within or connected to other components. It should be understood that the architectures so shown are merely exemplary and that in fact many other architectures that achieve the same functionality can be implemented. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Thus, any two components combined herein to achieve a particular functionality can be considered to be "associated" with each other such that the desired functionality is achieved, regardless of the architecture or intermediate components. Similarly, any two components so associated can also be considered to be "connected" or "coupled" with each other to achieve the desired functionality, and any two components that can be so associated can also be considered to be "couplable" with each other to achieve the desired functionality. Specific examples of what can be coupled include, but are not limited to, physically matable and / or physically interacting components, and / or wirelessly interacting and / or wirelessly interacting components, and / or logically interacting and / or logically interacting components. It should further be understood that the present invention is defined by the appended claims. In general, it will be understood by those skilled in the art that the terms used in this specification, and particularly in the appended claims (e.g., the body of the appended claims), are generally intended as "open" terms (e.g., the term "including" 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.). It will be further understood by those skilled in the art that if a specific number of introduced claim recitations is intended, such intention will be explicitly stated in the claim, and in the absence of such recitation, no such intention exists.For example, to aid in understanding, the following appended claims may include the use of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be interpreted as meaning that the introduction of a claim recitation with the indefinite article "a" or "an" limits any particular claim that includes such an introduced claim recitation to an invention that includes only one such recitation, even if the same claim includes the introductory phrase "one or more" or "at least one" and an indefinite article such as "a" or "an" (e.g., "a" and / or "an" should typically be interpreted to mean "at least one" or "one or more"), and the same applies to the use of definite articles used to introduce claim recitations. In addition, even if a specific number of introduced claim recitations is explicitly recited, one of ordinary skill in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the sole recitation of "two recitations" without other modifiers typically means at least two recitations, or more than two recitations). Furthermore, when phrases similar to "at least one of A, B, and C, etc." are used, such configurations are generally intended in the sense that one of ordinary skill in the art would understand the phrase (e.g., "a system having at least one of A, B, and C" includes, 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, and C, etc.). When phrases similar to "at least one of A, B, or C, etc." are used, such configurations are generally intended in the sense that one of ordinary skill in the art would understand the phrase (e.g., "a system having at least one of A, B, or C" includes, 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, and C, etc.).It will be further understood by those skilled in the art that virtually any disjunction word and / or phrase presenting two or more alternative terms, whether in the specification, claims, or drawings, should be understood to contemplate the possibility of including one of the terms, either of the terms, or both terms. For example, "A or B" is understood to include the possibilities of "A" or "B" or "A and B."

Claims

1. A stage for supporting the sample; A light source; one or more linear optics configured to direct light from the light source to the sample, at least a portion of the one or more linear optics being formed from strontium tetraborate; Equipped with the one or more linear optical components include at least one of a mirror, a lens, a lens array, a prism, a beam splitter, a window, or a lamp cell; At least one of the one or more linear optical components is configured to operate at substantially the Brewster angle with respect to a direction of polarization of light incident on the at least one of the one or more linear optical components and does not employ an anti-reflection coating.

1. An optical system comprising:

2. 2. The optical system of claim 1, wherein the strontium tetraborate comprises a glass phase.

3. 2. The optical system of claim 1, wherein the light source is configured to emit light having a wavelength in the range of 130 nm to 400 nm.

4. 2. The optical system of claim 1, wherein the light source is a broadband ultraviolet lamp comprising at least one of a window or a lamp cell, and at least a portion of the at least one of the window or the lamp cell is formed from strontium tetraborate.

5. 5. The optical system of claim 4, wherein the broadband ultraviolet lamp is configured to emit wavelengths in the range of 130 nm to 400 nm.

6. 10. The optical system of claim 1, wherein the optical system is configured as a semiconductor characterization system.

7. 7. The optical system of claim 6, comprising at least one of a semiconductor inspection system or a semiconductor metrology system.

8. 7. An optical system according to claim 6, a sensor, the one or more linear optics formed from strontium tetraborate configured to direct light reflected or scattered from the sample to the sensor. An optical system comprising:

9. 10. The optical system of claim 1, comprising a lithography system.

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