Protective coatings for nonlinear optical crystals

Abstract

To provide a simpler and / or less expensive method for protecting CLBO crystals. [Solution] An amorphous layer is used as a protective coating for a hygroscopic nonlinear optical crystal. The amorphous layer is composed of one or more types of alkali metal borates and / or alkaline earth metal borates. The amorphous layer slows down or prevents the diffusion of water and / or oxygen into the hygroscopic nonlinear optical crystal, thereby simplifying the requirements for handling, storage, and operating environment. One or more additional coating layers, which contain conventional optical materials, may be placed on top of the amorphous layer. The thickness of the amorphous layer and / or additional layer should be selected so as to reduce the reflectivity of the optical component at one or more specific wavelengths. This coated nonlinear optical crystal is used in lighting sources used in semiconductor inspection systems, weighing systems, or lithography systems.

Description

[Technical Field]

[0001] This disclosure relates to nonlinear optical crystals generally used in semiconductor manufacturing (e.g., for inspecting and / or measuring photomasks, reticles, and semiconductor wafers). Specifically, this disclosure relates to nonlinear optical crystals suitable for generating deep UV wavelengths by harmonic conversion, and to optical coating materials and coating processes for protecting such nonlinear optical crystals. [Background technology]

[0002] Cross-references to related applications This application asserts the benefits of U.S. Provisional Patent Application No. 63 / 227,342 dated July 30, 2021, and incorporates its entirety by reference.

[0003] In the integrated circuit industry, there is a growing demand for inspection tools with increasingly higher sensitivity to detect defects and particles that are becoming smaller and can be as small as tens of nanometers (nm) or less. To inspect a large portion, or even 100%, of a photomask, reticle, or wafer surface area in a short time, these inspection tools must operate at high speed. For example, inspection times should be less than one hour for production inspections and at most a few hours for R&D and troubleshooting. To achieve this speed, inspection tools use pixels or spots larger than the dimensions of the defect or particle of interest, while detecting only minute signal changes caused by the defect or particle. Detecting small signal changes requires high light levels and low noise levels. High-speed inspection is most commonly performed during production using inspection tools that operate with ultraviolet (UV) light. R&D inspections may be performed with UV light or electronics.

[0004] In the integrated circuit industry, high-precision weighing tools are required to accurately measure the dimensions of tiny features (external features) on semiconductor wafers that are less than a few nanometers in size. By performing weighing processes on wafers at various points in the semiconductor manufacturing process, it is possible to measure various characteristics of those wafers, such as the width of the patterned structures on the wafer, the thickness of the films formed on the wafer, and the overlay of patterned structures on one layer of the wafer to patterned structures on other layers of the wafer. These measurement results can be used to perform process control and / or improve efficiency during the manufacturing of semiconductor dies. Weighing can be performed using visible light, UV light, or electrons (as in scanning electron microscopes), but light is generally preferred because high-brightness light sources allow for shorter measurement times and more measurements per wafer compared to electron microscopes.

[0005] Optical frequency conversion, such as harmonic generation and frequency summation, is a conventional method for generating short-wavelength DUV and VUV radiation from longer-wavelength (e.g., infrared or green) laser radiation. With a suitable nonlinear optical crystal, known techniques such as critical phase matching, noncritical phase matching, and pseudo-phase matching can be used to ensure phase matching between the incident and exit wavelengths. Only a few nonlinear optical crystals possess the necessary optical properties, including transparency, refractive index, nonlinear coefficients, and damage threshold, to be useful for generating DUV or VUV radiation. The two most commonly used nonlinear optical materials for DUV wavelengths are beta-barium borate (BBO) and lithium cesium borate (CLBO). Of these two, CLBO is particularly useful for high-power DUV light sources due to its higher damage threshold. Since CLBO is transparent down to wavelengths as low as approximately 184 nm, it is also useful for generating light at the long-wavelength end of the VUV spectrum.

[0006] However, CLBO has the disadvantage of being highly hygroscopic. See, for example, Non-Patent Document 1. Immediately after exposure to the atmosphere, CLBO crystals begin to absorb moisture. During several weeks of exposure to air, the crystal may absorb enough moisture to cause uneven expansion and cracking. As is well known, when used as a nonlinear optical element that generates light with DUV wavelengths, CLBO must be kept in a low-humidity environment. Even a few minutes of exposure to air, even when not in operation, can cause sufficient moisture to be absorbed, so even if the crystal still functions well at lower DUV power intensities, its stability and lifespan may be compromised when subsequently exposed to high power densities at DUV wavelengths. Therefore, it is necessary to keep such crystals in an extremely low-humidity environment at all times while handling, shipping, transporting, manufacturing, and operating lasers or equipment that incorporate them. For example, a glove box with a controlled low-humidity environment may be required to protect the crystals during removal from storage containers and during implementation in lasers. Finished lasers will require continuous purging with low-humidity gases, such as dry air or nitrogen, including during non-operational periods and during transportation from one location to another. This will add considerable cost and time to the manufacturing and operation processes, and necessitate investment in specialized equipment and facilities for the transportation and storage of crystals and lasers. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] U.S. Patent No. 10921261 [Patent Document 2] U.S. Patent No. 11360032 [Patent Document 3] U.S. Patent No. 7705331 [Patent Document 4] U.S. Patent No. 9723703 [Patent Document 5] U.S. Patent No. 9865447 [Patent Document 6] U.S. Patent No. 9,255,887 [Patent Document 7] U.S. Patent No. 9,645,287 [Patent Document 8] U.S. Patent No. 9,709,510 [Patent Document 9] U.S. Patent No. 9,726,617 [Patent Document 10] U.S. Patent No. 9,891,177 [Patent Document 11] U.S. Patent No. 9,279,774 [Patent Document 12] U.S. Patent No. 7,957,066 [Patent Document 13] U.S. Patent No. 7,817,260 [Patent Document 14] U.S. Patent No. 5,999,310 [Patent Document 15] U.S. Patent No. 7,525,649 [Patent Document 16] U.S. Patent No. 9,080,971 [Patent Document 17] U.S. Patent No. 7,474,461 [Patent Document 18] U.S. Patent No. 9,470,639 [Patent Document 19] U.S. Patent No. 9,228,943 [Patent Document 20] U.S. Patent No. 5,608,526 [Patent Document 21] U.S. Patent No. 6,297,880 [Patent Document 22] U.S. Patent No. 8,873,596 [Patent Document 23] U.S. Patent No. 9,097,683 [Patent Document 24] U.S. Patent No. 9,413,134 [Patent Document 25] U.S. Patent No. 9,250,178 [Patent Document 26] U.S. Patent No. 9459215 [Patent Document 27] U.S. Patent No. 10283366 [Non-patent literature]

[0008] [Non-Patent Document 1] L.Isaenko et al. “CsLiB6O10crystals with Cs deficit: structure and properties,” J. Crystal Growth, 282, 407-413 (2005) [Overview of the project] [Problems that the invention aims to solve]

[0009] Therefore, what is needed is a simpler and / or less expensive method for protecting CLBO crystals that overcomes some or all of the limitations of conventional methods. [Means for solving the problem]

[0010] A characterization system is disclosed according to one or more embodiments of the present disclosure. In some embodiments, the characterization system includes a light source configured to generate incident light having a wavelength in the range of 100 nm to 300 nm, a sensor, and an optical system configured to direct the incident light onto a sample and the light from the sample onto the sensor. In some embodiments, the light source has a nonlinear optical crystal, the nonlinear optical crystal comprises a substrate made of a hygroscopic nonlinear optical material and configured to convert incident light having a wavelength greater than 300 nm into output light having a wavelength of 100 nm to 300 nm, and a first amorphous material layer disposed on the substrate, the first amorphous material layer forming a continuous encapsulation structure surrounding the outer surface of the substrate, and the first amorphous material layer being mainly composed of one or more types of alkali metal borates.

[0011] Characterization systems are disclosed in accordance with one or more additional and / or alternative embodiments of the present disclosure. In some embodiments, the characterization system comprises a light source configured to generate incident light having a wavelength in the range of 100 nm to 300 nm, and an optical system configured to direct the incident light onto a sample. In some embodiments, the light source comprises at least one nonlinear optical crystal, the nonlinear optical crystal comprising a substrate comprising a hygroscopic nonlinear optical material and configured to convert incident light having a wavelength greater than 300 nm into output light having a wavelength of 100 nm to 300 nm, a first amorphous material layer disposed on the substrate, and a second optical material layer disposed on the top surface of the first amorphous material layer. In some embodiments, the first amorphous material layer forms a continuous encapsulation structure surrounding the outer surface of the substrate, and the first amorphous material layer is mainly composed of one or more types of alkali metal borates. In various embodiments, the second optical material layer comprises a second optical material having a refractive index lower than that of the amorphous material layer, and the first amorphous layer and the second optical material layer are configured such that a portion of the emitted light passes through both the first and second optical material layers and reaches the top surface of the substrate.

[0012] Disclosed are methods for preparing and coating a nonlinear optical crystal according to one or more embodiments of the disclosure. In the methods of the embodiments, a nonlinear optical crystal is prepared, the nonlinear optical crystal is annealed, the nonlinear optical crystal is placed in an inert environment above a liquid, the temperature of the liquid is set to a first desired temperature Tl, and the temperature of the nonlinear optical crystal is set to a desired temperature Tl. C The nonlinear optical crystal is set to descend into the liquid, an amorphous layer is formed on the nonlinear crystal, and the nonlinear optical crystal is removed from the liquid after a predetermined time, provided that the nonlinear optical crystal comprises at least one of CLBO crystals and CBO crystals, and the liquid is mainly composed of at least one of alkali metal borates and alkaline earth metal borates.

[0013] As can be understood, both the above-mentioned summary and the following-mentioned detailed description are purely illustrative and explanatory, and do not necessarily limit the disclosure. The accompanying drawings are incorporated into and constitute part of this specification and illustrate the subject matter of the disclosure. Together, these descriptions and drawings are useful in explaining the principles of the disclosure.

[0014] By referring to the attached drawings, those skilled in the art will better understand the numerous advantages of this disclosure. [Brief explanation of the drawing]

[0015] [Figure 1] This figure depicts a characterization system configured to inspect or measure semiconductor manufacturing-related samples, relating to one or more embodiments of the present disclosure. [Figure 2A] This figure depicts an optical component having a borate nonlinear optical crystal coated with an amorphous material layer, relating to one or more embodiments of the present disclosure. [Figure 2B] This figure depicts an optical component having a borate nonlinear optical crystal coated with an amorphous material layer, relating to one or more embodiments of the present disclosure. [Figure 2C] This figure depicts an optical component having a borate nonlinear optical crystal coated with an amorphous material layer, relating to one or more embodiments of the present disclosure. [Figure 3] This figure depicts an apparatus for depositing a coating amorphous layer onto a substrate, relating to one or more embodiments of the present disclosure. [Figure 4] This flowchart illustrates a method for preparing and coating a nonlinear optical crystal according to one or more embodiments of the present disclosure. [Modes for carrying out the invention]

[0016] The subject matter of the disclosure depicted in the attached drawings will be referenced in detail below. The disclosure is illustrated and described in relation to specific embodiments and their individual features. The embodiments described herein should be understood as illustrative rather than limiting. As will be immediately apparent to those skilled in the art, various modifications and alterations can be made to the form and details without deviating from the essence and technical scope of the disclosure.

[0017] The embodiments of this disclosure aim to slow down the absorption of water by hygroscopic nonlinear optical crystals of CLBO and other borates by using amorphous alkali metal borate or alkaline earth metal borate coatings, thereby allowing the crystals to be exposed for several minutes or hours in environments with relative humidity of several percent or more. The disclosure further aims to coat CLBO and other hygroscopic nonlinear optical crystals with an amorphous layer of alkali metal borate or alkaline earth metal borate. In some embodiments, the alkali metal borate is lithium triborate (LiB3O5, LBO), lithium tetraborate (Li2B4O7, LB4), lithium cesium borate (Cs2LiB6O 10 It can be composed of one or more of the following: ,CLBO, cesium triborate (CsB3O5,CBO), and cesium tetraborate (Cs2B4O7,CB4). In another embodiment, the alkaline earth metal borate can be composed of strontium tetraborate (SrB4O7,SBO).

[0018] The use of strontium tetraborate as an optical coating is discussed in Patent Document 1, issued on February 16, 2021, and Patent Document 2, issued on June 14, 2022. Therefore, the entire details of these documents will be incorporated into this application by reference.

[0019] Figure 1 shows a characterization system 100 configured to inspect or measure semiconductor manufacturing-related samples 108, such as silicon wafers, reticles, or photomasks. This characterization system 100 may also include an inspection system or a weighing system. The system 100 generally comprises an illumination source (light source) 102, a detector assembly 104 containing a sensor 106, and a stage 112.

[0020] The illumination source 102 emits deep UV (DUV) and / or vacuum UV (VUV) incident light (radiation) L having a wavelength in the range of 100 nm to 300 nm. in It can be configured to generate (emit) light, but it may also be configured to generate light having a wavelength greater than 300 nm. In certain embodiments, the illumination source 102 uses one or more lasers and one or more optical elements (e.g., frequency converter 200-0) to generate incident light L inThis is generated. In one embodiment, the illumination source 102 may have a continuous light source, such as an arc lamp, a laser-excited plasma light source, or a continuous-wave (CW) laser. In another embodiment, the illumination source 102 may have a pulsed light source, such as a mode-locked laser, a Q-switched laser, or a plasma light source excited (pumped) by a mode-locked or Q-switched laser. Suitable light sources that can be incorporated into the illumination source 102 are described in Patent Document 3, entitled "Methods and systems for providing illumination of a specimen for a process performed on the specimen," Patent Document 4, entitled "System and method for transverse pumping of laser-sustained plasma," entitled "System and method for transverse pumping of laser-sustained plasma," and Patent Document 5, entitled "High brightness laser-sustained plasma broadband source," which will be incorporated into this application by reference.

[0021] Stage 112 is positioned to receive sample 108 and to facilitate the movement of sample 108 relative to optical system 103 (i.e., by optical system 103, incident light L in The system is configured such that it can be focused on various regions of the sample 108. The stage 112 may comprise an XY stage or an Rθ stage. In one embodiment, the stage 112 can be used to adjust the height of the sample 108 to maintain focus during inspection. In another embodiment, the optical system 103 can be adjusted to maintain focus.

[0022] The optical system (optical system) 103 receives incident light L inconfigured to be directed and focused onto the sample 108, and the reflected or scattered light L from the sample 108 r / s comprises a plurality of optical members configured to be directed towards the sensor 106. For example, among the optical members of the optical system 103 depicted in FIG. 1, but not limited thereto, are a illumination tube lens 132, an objective lens 150, a condenser tube lens 122, a condenser lens 133, and a beam splitter 140.

[0023] During operation of the system 100, the incident light L emitted by the illumination source 102 in is directed towards the beam splitter 140 by the condenser lens 133 and the illumination tube lens 132, whereby the incident light L in is directed downward onto the sample 108 through the objective lens 150. The reflected light L r / s represents the portion of the incident light L in that is reflected and / or scattered upward into the objective lens 150 by the surface features of the sample 108, and is directed towards the sensor 106 by the objective lens 150 and the condenser tube lens 122. The sensor 106 generates an output signal / data based on the reflected light L received from the sample 108 r / s . The output of the sensor 106 is connected to the controller 114, where the output is analyzed. One or more processors 115 provided in the controller 114 are configured by program instructions 118 that can be stored on a carrier medium 116. In certain embodiments, the structure on the sample 108 is inspected or measured by controlling the characterization system 100 and the detector assembly 104 by the controller 114. In certain embodiments, the system 100 is configured to irradiate a line on the sample 108 and to collect the reflected / scattered light in one or more dark field and / or bright field collection channels. In this embodiment, the detector assembly 104 may be a time delay integration (TDI) sensor, a line sensor, or an electron bombardment line sensor.

[0024] In one embodiment, the illumination tube lens 132 is configured to image the illumination pupil aperture 131 onto the pupil diaphragm in the objective lens 150 (i.e., the illumination tube lens 132 is configured such that the illumination pupil aperture 131 and the pupil diaphragm are conjugate to each other). The illumination pupil aperture 131 can be configured, for example, by switching and inserting various apertures at the location of the illumination pupil aperture 131, or by adjusting the diameter or shape of the opening of the illumination pupil aperture 131. In this way, the sample 108 can be illuminated in a range of angles by measurements or inspections performed under the control of the controller 114. In Figure 1, the illumination is depicted as being directed to the sample 108 via the objective lens 150, but in some embodiments, the illumination may be directed to the sample 108 passing outside the objective lens 150.

[0025] In one embodiment, the focusing tube lens 122 is configured to image the pupil diaphragm in the objective lens 150 onto the focusing pupil aperture 121 (i.e., the focusing tube lens 122 is configured such that the focusing pupil aperture 121 and the pupil diaphragm in the objective lens 150 are conjugate to each other). The focusing pupil aperture 121 can be configured, for example, by switching and inserting various apertures at the location of the focusing pupil aperture 121, or by adjusting the diameter or shape of the opening of the focusing pupil aperture 121. In this way, light from various angular ranges reflected or scattered from the sample 108 can be directed to the detector assembly 104 under the control of the controller 114.

[0026] One or both of the illumination pupil aperture 131 and the focusing pupil aperture 121 can be equipped with a programmable aperture, for example, one described in Patent Document 6 under the name of Brunner, titled "2D programmable aperture mechanism," or one described in Patent Document 7 under the name of Brunner, titled "Flexible optical aperture mechanisms." Methods for selecting aperture configurations for wafer inspection are described in Patent Document 8 under the name of Kolchin et al., titled "Determining a configuration for an optical element positioned in a collection aperture during wafer inspection," and Patent Document 9 under the name of Kolchin et al., titled "Apparatus and methods for finding a best aperture and mode to enhance defect detection," so these will be incorporated into this application by reference.

[0027] In various embodiments, at least one borate-based nonlinear optical element used in the illumination source 102 is provided with amorphous layers formed on multiple surfaces of the substrate structure of the element. These amorphous layers are mainly composed of alkali metal borate, a mixture of alkali metal borate, or alkaline earth metal borate. In one embodiment, the frequency converter 200-0 of the illumination source 102 may have an amorphous material layer of lithium triborate or lithium cesium borate. In another embodiment, the frequency converter 200-0 of the illumination source 102 may have an alkali metal borate material layer that forms a continuous encapsulation structure, and this structure may completely enclose the substrate structure of the nonlinear optical element. This structure will be further described with reference to Figures 2A and 2B. The lifespan of borate nonlinear optical components can be improved by the amorphous layer, as the amorphous layer slows down the penetration of water and / or oxygen into the borate nonlinear optical crystal. The processes for manufacturing, operating, transporting, and storing system 100 and / or illumination source 102 can be simplified or reduced in cost by protecting the borate nonlinear optical components in the frequency converter 200-0 with the amorphous layer.

[0028] Additional details of various embodiments of the inspection or weighing system 100 are provided in Patent Document 10, titled "TDI Sensor in a Darkfield System," by Vazhaeparambil et al.; Patent Document 11, titled "Wafer inspection," by Romanovsky et al.; Patent Document 12, titled "Split field inspection system using small catadioptric objectives," by Armstrong et al.; Patent Document 13, titled "Beam delivery system for laser dark-field illumination in a catadioptric optical system," by Chuang et al.; Patent Document 14, titled "Ultra-broadband UV microscope imaging system with wide range zoom capability," by Shafer et al.; and "Surface inspection system using laser Patent document 15, titled "Line illumination with two-dimensional imaging," under the name of Leong et al.; Patent document 16, titled "Metrology systems and methods," under the name of Kandel et al.; and "Broad band objective having improved lateral color performance," under the name of Chuang et al.This is described in Patent Document 17, Patent Document 18 titled "Optical metrology with reduced sensitivity to grating anomalies" by Zhuang et al., Patent Document 19 titled "Dynamically Adjustable Semiconductor Metrology System" by Wang et al., Patent Document 20 titled "Focused Beam Spectroscopic Ellipsometry Method and System" issued on March 4, 1997, by Piwonka-Corle et al., and Patent Document 21 titled "Apparatus for Analysing Multi-Layer Thin Film Stacks on Semiconductors" issued on October 2, 2001, by Rosencwaig et al.; therefore, these will be incorporated into this application by reference.

[0029] Figures 2A to 2C depict an optical member 200 having a borate nonlinear optical crystal (substrate) 201 coated with an amorphous material layer (sometimes referred to in this application as an amorphous layer or amorphous coating) over its entire outer surface. Figure 2A shows a perspective view of the optical member, and Figure 2B shows a longitudinal cross-section 200A that passes through the optical member, corresponding to 2-2 in Figure 2A. Figure 2C shows a longitudinal cross-section 200C in an embodiment in which the top (outside) of the amorphous material layer is coated with one or more additional layers. In one embodiment of the characterization system 100 shown in Figure 1, the illumination source 102 is said to have a laser that generates deep UV wavelengths, for example, wavelengths less than 300 nm. For example, the illumination source 102 can incorporate a laser configured to generate wavelengths around 266 nm by generating the fourth harmonic of light with a wavelength of approximately 1064 nm, which is generated by a solid-state or fiber laser. This laser can be configured to generate the second harmonic of its 1064 nm light using a lithium triborate (LBO) crystal. LBO is not hygroscopic and can be operated in air even when laser power levels of several tens of watts or more are used. The fourth harmonic can be generated using a CLBO crystal configured to double the frequency of its second harmonic light. CLBO is hygroscopic and must always be kept in an extremely low humidity environment, whether the laser is operating or not. For high-power operation, for example, with a fourth harmonic power of approximately 10 W or more, it would be desirable to reduce the oxygen level of the crystal's environment to much lower than that of the atmosphere in order to minimize surface damage to the crystal. In another example, the illumination source 102 may have a laser configured to generate wavelengths around 213 nm or around 193 nm using harmonic generation and frequency summation in multiple nonlinear optical crystals, as represented by the frequency conversion crystal (optical component) 200-0. CLBO and CBO are the most useful materials for frequency conversion at these wavelengths, but both materials are hygroscopic.The frequency conversion crystal 200 shown in Figures 2A to 2C comprises a substrate 201 composed of either CLBO or CBO and configured to generate deep UV wavelengths, for example, one configured to double the wavelength of light having a wavelength around 532 nm, or one configured to generate light having a wavelength around 213 nm by summing the frequencies of light having wavelengths around 266 nm and around 1064 nm.

[0030] As shown in Figures 2A to 2C, the entire circumferential surface of the nonlinear crystal (e.g., CLBO or CBO) substrate 201 is covered (e.g., encapsulated) by an amorphous layer 202 mainly composed of one or more types of alkali metal borates, alkaline earth metal borates, or mixtures thereof. In the illustrated example, the crystal substrate 201 has a rectangular prism (e.g., cuboid) shape and is provided with a top surface 201T and a bottom surface 201B on opposite sides, sides 201S1 and 201S2 on opposite sides, and end surfaces 201E1 and 201E2 on opposite sides that, in order, form the light incident surface and light exit surface of the frequency conversion crystal 200. In this example, the amorphous layer 202 has a continuous rectangular parallelepiped structure, with parts of this structure extending across all six faces 201T, 201B, 201S1, 201S2, 201E1, and 201E2. Figure 2A shows a cross-section 200A passing over an example of a frequency conversion crystal, in which the amorphous layer 202 directly forms a single layer coating on the circumferential surface of the substrate 201 (e.g., the top face 201T, the bottom face 201B, and the end faces 201E1 and 201E2). In other embodiments, the amorphous layer may be part of a multilayer encapsulation structure having one or more conventional optical material layers 203 disposed on top of (i.e., outside of) the amorphous layer, as depicted in Figure 2C. In both embodiments, the thickness of the amorphous layer 202 is selected so as to slow down or prevent at least the penetration of water into the crystal substrate 201. The thickness of the amorphous layer 202 may be approximately 10 nm or more, or approximately 100 nm. The thickness of the amorphous layer 202 does not need to be uniform, as long as it is thick enough to slow down or prevent the diffusion of water, and as long as the layer is free of pinholes. The thickness of the amorphous layer on the incident surface 201E1 and the exit surface 201E2 may be further selected to reduce the reflectance at one or more wavelengths used or generated in the frequency conversion. For example, if the refractive index of the amorphous layer 202 is lower than that of the substrate 201, this can be done by setting its thickness (measured along the direction of light propagation) to be approximately equal to an odd multiple of a quarter wavelength of the wavelengths used or generated in the frequency conversion.For example, if the refractive index of the amorphous layer 202 is higher than that of the substrate 201, its reflectivity can be set to approximately equal to an odd multiple of half a wavelength of the wavelength used or generated in the frequency conversion. In the embodiment shown in Figure 2C, the thickness and refractive index of one or more conventional optical material layers 203 can be selected to further reduce the reflectivity at the wavelength of interest. By controlling the uniformity of the coating on the end faces 201E1 and 201E2, excessive fluctuations in the specified optical properties of those faces, such as reflectivity, can be avoided. Even if the amorphous coating is not completely impermeable to water and oxygen, if the diffusion of those molecules is sufficiently slowed, it may be possible to store and / or operate the hygroscopic nonlinear crystal in environments with higher water and oxygen content than the uncoated crystal, thereby reducing storage and operating costs.

[0031] The amorphous layer 202 is mainly composed of one or more types of alkali metal borates, alkaline earth metal borates, or mixtures thereof. Examples of materials used in the amorphous layer 202 include lithium triborate (LiB3O5, LBO), lithium tetraborate (Li2B4O7, LB4), and lithium cesium borate (CsLiB6O 10These include CLBO, cesium triborate (CsB3O5,CBO), cesium tetraborate (Cs2B4O7,CB4), and strontium tetraborate (SrB4O7,SBO). Because borate materials have similar chemical compositions, they adhere strongly to each other, and therefore, when a borate substrate is coated with a borate, the borate coating may be more impermeable to water and / or oxygen penetration than coating with conventional optical materials, such as SiO2. In the first embodiment, the amorphous layer 202 is mainly composed of LBO. LBO is not hygroscopic and exhibits good light transmission properties over a wavelength range extending from approximately 2.6 μm in the infrared (IR) to approximately 160 nm in the VUV. LBO allows hygroscopic crystals to be effectively sealed against their environment while transmitting the wavelengths most important in semiconductor inspection and weighing applications. In the second embodiment, the amorphous layer 202 is mainly composed of CLBO. Amorphous CLBO can be slightly hygroscopic, but due to its amorphous structure, it is less permeable to water and / or oxygen than crystalline CLBO, thus mitigating the environmental requirements related to the storage and / or operation of nonlinear optical crystals. For example, while storage of uncoated CLBO crystals requires fairly low humidity, CLBO nonlinear optical crystals with an amorphous CLBO coating can be stored in an environment with humidity of approximately 1% or approximately 0.1%. In one embodiment, the amorphous layer 202 will be mainly composed of a mixture of alkali metal borates and / or alkaline earth metal borates, for example, a mixture of two or more of the above-mentioned alkali metal borates and alkaline earth metal borates. To help you understand, the amorphous layer 202 may comprise certain crystalline or polycrystalline alkali metal borate and / or alkaline earth metal borate materials, particularly on non-optical surfaces such as 201T, 201B, 201S1, and 201S2. Since light can be scattered at intercrystalline boundaries within the polycrystalline material, in one embodiment, the polycrystalline regions of the amorphous layer 202 on surfaces 201E1 and 201E2 are kept to less than about 10% of the surface area of ​​those surfaces.

[0032] The amorphous layer 202 can be attached to the substrate 201 by immersing its crystals in a tank containing the amorphous layer material in a molten state or in a solvent, as will be explained later in relation to Figure 3. Alternatively, the amorphous layer 202 may be attached to the substrate 201 by sputtering, vapor deposition, or other known coating techniques. In the embodiment shown in Figure 2C, one or more optical material layers 203 can be attached to layer 202 by sputtering, vapor deposition, or other known coating techniques.

[0033] Figure 3 shows an apparatus for depositing a coating amorphous layer 202 onto a substrate 201 according to one or more embodiments of the present disclosure. In some embodiments, a nonlinear optical crystal substrate 301 (e.g., substrate 201 in Figure 2) is supported by two or more wires 302A and 302B passing under the substrate 301. The wires 302A and 302B may be made of an inert, high-melting-point material, such as platinum. In an alternative embodiment (not shown), the substrate 301 is supported by a wire mesh instead of the wires 302A and 302B. In some embodiments, a liquid 320 containing the material to be coated onto the substrate 301 is placed in a crucible 310. For example, the liquid 320 may contain an alkali metal borate, an alkaline earth metal borate, or a mixture thereof, which is the same composition as the intended amorphous layer. In some embodiments, the liquid 320 is composed of a molten amorphous layer material. In another embodiment, the composition of liquid 320 may differ from that of the amorphous layer. For example, liquid 320 may contain a certain component in greater or less quantities than the assumed composition of the amorphous layer. Alternatively, liquid 320 may contain additional components not present in the amorphous layer. The composition of liquid 320 may be selected to modify physical properties, such as viscosity, or chemical properties, such as OH removal from the liquid. The crucible 310 may be made of an inert, high-melting-point material, such as platinum.

[0034] In one embodiment, the liquid 320 is maintained at a temperature near the melting point of the amorphous layer material, for example, within ±5°C of its melting point. The substrate 301 may be preheated to a temperature just below the melting point of the amorphous layer material, for example, about 5°C or about 10°C below the temperature of the molten material. Then the substrate 301 is lowered into the liquid 320. Due to the temperature of the substrate 301, the material will begin to deposit on the substrate 301. The deposition rate can be controlled by the initial temperature of the substrate 301 and the temperature of the liquid 320. By further adjusting the temperature of the liquid 320 after the substrate 301 has been lowered into the liquid 320, a desired growth rate for the amorphous layer can be achieved or maintained. After a predetermined time for the amorphous layer to grow to the desired thickness, the substrate 301 is lifted out of the liquid 320 by raising, for example, wires 302A and 302B.

[0035] Since the crystalline substrate 301 must be held in place (for example by wires 302A and 302B) during the coating process, in one embodiment, the entire surface is coated using two coating operations, with the wires moved relative to the substrate 301 prior to the second coating operation so that the areas on the substrate 301 that were in contact with wires 302A and 302B during the first coating operation are exposed during the second coating operation. The total time of these two coating operations is selected so that the final thickness of the amorphous layer generated on their optical surfaces (e.g., 201E1 and 201E2 shown in Figures 2A and 2C) is the desired thickness.

[0036] Figure 4 shows a flowchart illustrating a method 400 for preparing and coating a nonlinear optical crystal according to one or more embodiments of the present disclosure. In step 401, a Boolean of the nonlinear optical crystal is grown by known crystal growth techniques, such as the Czochralski method or the Kilopoulos method. One or more nonlinear optical crystals are cut from the Boolean in the desired shape, size, and orientation relative to the crystal axis for the intended frequency conversion application. The optical surfaces of the one or more nonlinear optical crystals (e.g., 201E1 and 201E2 shown in Figures 2A and 2B) are polished to the desired degree of smoothness, thereby minimizing light scattering from those surfaces. This polishing process typically involves several polishing steps, such as a rough polishing step followed by a fine polishing step. Although the Boolean is grown in an inert, extremely low-humidity environment or in a vacuum, the subsequent cutting and polishing steps can also be carried out in an environment with several percent humidity. Because these processes can take a considerable amount of time to complete, some moisture is usually absorbed by one or more of the nonlinear optical crystals. In step 401, one or more of the nonlinear optical crystals in the process may be annealed to remove at least some of the moisture absorbed during the cutting and polishing processes. For example, the annealing process may be performed between the completion of the rough polishing process and the start of the fine polishing process.

[0037] In step 402, at least one of the one or more polished nonlinear optical crystals obtained in step 401 is annealed to reduce the moisture content of the crystal and / or the number of defects in the crystal. Examples of annealing processes are described in Patent Documents 22 and 23, both titled "Laser with high quality, stable output beam, and long life high conversion efficiency non-linear crystal" and attributed to Dribinski et al., Patent Document 24, also attributed to Dribinski et al., titled "Multi-stage ramp-up annealing for frequency-conversion crystals", and Patent Documents 25, 26, and 27, both titled "Passivation of nonlinear optical crystals", and these will be incorporated into this application by reference.

[0038] In step 403, at least one annealed nonlinear optical crystal is suspended above a vat containing liquid, for example, as shown in Figure 3, in a dry environment (e.g., an environment containing only a dry inert gas, such as argon, or a vacuum environment). In some embodiments, the time between steps 402 and 403 is kept to the minimum to minimize any moisture absorbed by the nonlinear crystal after the annealing process. In some embodiments, at least one nonlinear optical crystal remains in a dry, inert environment while being moved from step 402 to step 403 or while being stored between steps. The humidity of such an environment should be less than 0.1%, preferably less than 0.01%.

[0039] In step 404, the temperature of at least one of the nonlinear optical crystals is T C The value is set to T, and the temperature of the liquid is TL It is set to a value such that, in various embodiments, T C However, the melting point of the amorphous layer that covers the nonlinear crystal is set to be several degrees below that point. For example, T C It is preferable to set the temperature to approximately 1°C below its melting point, approximately 1°C to 5°C below its melting point, or approximately 5°C to 10°C below its melting point. In various embodiments, T C However, it is said to be several degrees above the melting point of the amorphous layer. For example, T C It is preferable to set it to approximately 1°C above its melting point, or approximately 1°C to 5°C above its melting point. In one embodiment, T L However, it is said to be several degrees above the melting point of the amorphous layer. For example, T L It is preferable to set it to approximately 1°C above its melting point, or approximately 1°C to 5°C above its melting point. In another embodiment, T L However, the melting point of the amorphous layer is said to be several degrees below. For example, T L It is best to set the temperature approximately 1°C below the melting point of the amorphous layer.

[0040] In step 405, at least one of the nonlinear optical crystals is lowered into the liquid to initiate the growth of its amorphous layer.

[0041] In an optional step 406, the growth rate of the amorphous layer on at least one nonlinear crystal is controlled by adjusting the temperature of the liquid. In various embodiments, the temperature of the liquid is lowered to a temperature just below its melting point, for example, about 1°C below the melting point, about 1°C to 5°C below the melting point, or about 5°C to 10°C below the melting point. The temperature T set in step 405 L If it is sufficient to achieve and maintain the desired growth rate, step 406 may be omitted.

[0042] In step 407, at least one nonlinear optical crystal is removed from the liquid after a predetermined time. The predetermined time is selected so that a desired thickness is achieved for the amorphous layer on the at least one nonlinear optical crystal.

[0043] In step 408, at least one of the coated nonlinear optical crystals is cooled to room temperature.

[0044] Figure 4 aims to illustrate the important basic steps within the coating process. Similar results can be obtained with many variations that incorporate process addition, process combination, process omission, and process reordering, and these are within the technical scope of this disclosure. The duration of each step, or any time interval between one step and the next, may be adjusted to achieve the desired results. Nonlinear optical crystals may be processed one at a time, or they may be processed in batches so that multiple crystals are processed substantially simultaneously in each step.

[0045] While the coating materials and processes disclosed herein are expected to be particularly useful in semiconductor inspection and weighing systems, it is also anticipated that these coatings and materials may be useful in other applications where VUV and DUV radiation is present, such as photolithography systems, and in other applications where high-intensity visible or IR radiation is present, such as IR systems.

[0046] The coating materials and methods described herein are not intended to be limited to the specific embodiments illustrated and described, but rather should be tied to the maximum technical scope that corresponds to the principles and novel features disclosed herein. That is, the disclosure is considered to be limited only by the attached claims and their reasonable interpretation.

[0047] As those skilled in the art will recognize, the components, operations, devices, objects, and accompanying discussions described herein are used as examples to contribute to conceptual clarity, and various structural modifications have been carefully considered. Therefore, as used herein, the specific examples and accompanying discussions described are intended to represent their more general classifications. Generally, the use of any specific example is intended to represent its classification, and the absence of specific components, operations, devices, and objects should not be considered a limitation.

[0048] With regard to the use of substantially all plural and / or singular words in this application, a person skilled in the art can interpret them as appropriate to the context and / or use, changing them from plural to singular and / or singular to plural. For clarity, this application does not explicitly explain various singular / plural substitutions.

[0049] The above description is provided so that a person skilled in the art can prepare and use the disclosure as presented in accordance with the context of a specific use and its requirements. The directional terms used in this application, such as “top,” “bottom,” “up,” “down,” “upward,” “upward,” “downward,” “downward,” and “downward,” are intended to indicate relative positions for descriptive purposes and not to specify an absolute reference coordinate system. Various modifications to the preferred embodiment will be obvious to a person skilled in the art, and the general principles set forth in this application are applicable to other embodiments as well. Accordingly, this disclosure is not intended to be limited to the specific embodiments illustrated and described, but rather should be tied to the maximum technical scope that corresponds to the principles and novel features of the disclosure.

[0050] Furthermore, as can be understood, the present invention is defined by the claims of a separate section. As can be understood by those skilled in the art, the terms used in this application, particularly in the claims of a separate section (e.g., the text of the claims of a separate section), are generally intended to be "open" terms (e.g., the term "contains ~" should be interpreted as "contains ~ but is not limited to ~", the term "has ~" should be interpreted as "has at least ~", the term "contains ~" should be interpreted as "contains ~ but is not limited to ~", etc.). As can also be understood by those skilled in the art, if there is an intention to introduce a specific number of claim requirements, that intention will be clearly stated in the claim; if such requirements are not stated, then there is no such intention. For example, to aid understanding, some of the appended claims listed below incorporate the introduction of claim requirements by using the introductory phrases "at least one" and "one or more". However, the use of the indefinite article "a" or "an" in a claim should not be interpreted as implying that the introduction of a claim-specific requirement limits all individual claims containing that requirement to inventions that include only one of the constituent elements, nor should it be interpreted in this way even when the introductory phrase "one or more" or "at least one" coexists with the indefinite article, such as "a" or "an" (for example, "a" and / or "an" should normally be understood to mean "at least one" or "one or more"), and the same applies to the introduction of a claim-specific requirement using the definite article. In addition, even when a specific number is explicitly stated for a claim-specific requirement, the number should normally be interpreted as meaning at least that explicitly stated number, as can be understood by a person skilled in the art (for example, the bare expression "two constituent elements" without other modifying phrases usually means at least two requirements or two or more requirements).Furthermore, in examples where a clause similar to "at least one of A, B, and C, etc." is used, there is generally an intention to follow the sense that a person skilled in the art would understand the clause (e.g., "a system having at least one of A, B, and C" would 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 systems having all three A, B, and C, etc.). In examples where a clause similar to "at least one of A, B, or C, etc." is used, there is generally an intention to follow the sense that a person skilled in the art would understand the clause (e.g., "a system having at least one of A, B, or C" would 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 systems having all three A, B, and C, etc.). As those skilled in the art will understand, almost all separable conjunctions and / or separable phrases that present two or more alternative words, whether found in the specification, claims, or drawings, should be understood to take into account the possibility of including one word, either word, or both words. For example, the phrase "A or B" would be understood to include the possibilities of "A" or "B" or "A and B".

[0051] Many of the advantages of this disclosure and its associated benefits can be understood from the above description, and it will also be clear that various modifications can be made to the form, configuration, and arrangement of the components without deviating from the disclosed subject matter or compromising all of its main advantages. The forms described are for illustrative purposes only, and the intent of the claims below is to encompass and include such modifications. Furthermore, the claims in another section define the present invention.

Claims

1. It is a system, A light source configured to generate incident light having a wavelength in the range of 100 nm to 300 nm, Sensors and, An optical system configured to direct the incident light onto a sample and the light from the sample onto the sensor, It has, The light source has a nonlinear optical crystal, and the nonlinear optical crystal is A substrate comprising a hygroscopic nonlinear optical material, configured to convert incident light having a wavelength greater than 300 nm into output light having a wavelength of 100 nm to 300 nm, A first amorphous material layer disposed on the substrate, Equipped with, The first amorphous material layer forms a continuous encapsulation structure that surrounds the outer surface of the substrate. The first amorphous material layer is mainly composed of one or more types of alkali metal borates. The first amorphous material layer comprises a crystalline or polycrystalline alkali metal borate and / or alkaline earth metal borate material on the non-optical surface of the substrate, and the crystalline or polycrystalline alkali metal borate and / or alkaline earth metal borate material is maintained in an area of ​​10% or less of the surface area on the optical surface composed of an incident surface and an exit surface.

2. The system according to claim 1, wherein the hygroscopic nonlinear optical material comprises at least one of cesium lithium borate (CLBO) crystals and cesium triborate (CBO) crystals.

3. A system according to claim 1, wherein the one or more types of alkali metal borates include at least one of lithium triborate (LBO), lithium tetraborate (LB4), lithium cesium borate (CLBO), cesium triborate (CBO), and cesium tetraborate (CB4).

4. A system according to claim 1, wherein the first amorphous material layer is configured to minimize the reflectance of at least one surface of the nonlinear optical crystal at one or both of the wavelengths of the incident light and the wavelength of the emitted light.

5. The system according to claim 1, wherein the first amorphous material layer has a thickness in the range of 30 nm to 200 nm.

6. The system according to claim 1, wherein the first amorphous material layer is formed directly on the surface of the substrate.

7. A system according to claim 1, wherein the light source further comprises at least one optical material layer disposed above the first amorphous material layer, and the first amorphous material layer and the at least one optical material layer are configured such that at least one of the incident light and the emitted light passes through the first amorphous material layer, the at least one optical material layer, and the outer surface of the substrate.

8. The system according to claim 7, wherein the at least one optical material layer comprises an optical material having a refractive index lower than that of the first amorphous material layer.

9. The system according to claim 7, wherein the at least one optical material layer comprises at least one of magnesium fluoride, calcium fluoride, aluminum fluoride, and silicon dioxide.

10. A system according to claim 1, comprising at least one of a semiconductor inspection system and a semiconductor weighing system.

11. A system according to claim 1, comprising a lithographic system, configured to expose and form a pattern on the sample.

12. It is a system, A light source configured to generate incident light having a wavelength in the range of 100 nm to 300 nm, An optical system configured to direct the incident light onto the sample, It has, The light source has at least one nonlinear optical crystal, and the nonlinear optical crystal is A substrate comprising a hygroscopic nonlinear optical material, configured to convert incident light having a wavelength greater than 300 nm into output light having a wavelength of 100 nm to 300 nm, A first amorphous material layer disposed on the substrate, A second optical material layer is disposed on the top surface of the first amorphous material layer, Equipped with, The first amorphous material layer forms a continuous encapsulation structure that surrounds the outer surface of the substrate. The first amorphous material layer is mainly composed of one or more types of alkali metal borates. The second optical material layer comprises a second optical material having a refractive index lower than that of the first amorphous material layer. A system wherein the first amorphous material layer and the second optical material layer are configured such that a portion of the emitted light passes through both the first and second optical material layers to the top surface of the substrate, the first amorphous material layer comprises a crystalline or polycrystalline alkali metal borate and / or alkaline earth metal borate material on the non-optical surface of the substrate, and the crystalline or polycrystalline alkali metal borate and / or alkaline earth metal borate material is maintained at 10% or less of the surface area on the optical surface composed of the incident surface and the exit surface.

13. A system according to claim 12, comprising at least one of a semiconductor inspection system and a semiconductor weighing system.

14. A system according to claim 12, comprising a lithographic system, configured to expose and form a pattern on the sample.

15. A crystal assembly, A nonlinear optical crystal is provided, and the nonlinear optical crystal is configured to convert incident light having a wavelength greater than 300 nm into output light having a wavelength of 100 nm to 300 nm, and A first amorphous material layer disposed on the substrate of the nonlinear optical crystal, Equipped with, The first amorphous material layer forms a continuous encapsulation structure that surrounds the outer surface of the substrate. A crystal assembly wherein the first amorphous material layer is mainly composed of one or more types of alkali metal borates, the first amorphous material layer comprises crystalline or polycrystalline alkali metal borate and / or alkaline earth metal borate material on the non-optical surface of the substrate, and the crystalline or polycrystalline alkali metal borate and / or alkaline earth metal borate material is maintained in 10% or less of the surface area on the optical surface composed of an incident surface and an exit surface.

16. A crystal assembly, A nonlinear optical crystal is provided, and the nonlinear optical crystal is configured to convert incident light having a wavelength greater than 300 nm into output light having a wavelength of 100 nm to 300 nm, and A first amorphous material layer disposed on the substrate, A second optical material layer is disposed on the top surface of the first amorphous material layer, Equipped with, The first amorphous material layer forms a continuous encapsulation structure that surrounds the outer surface of the substrate. The first amorphous material layer is mainly composed of one or more types of alkali metal borates. The second optical material layer comprises a second optical material having a refractive index lower than that of the first amorphous material layer. A crystal assembly wherein the first amorphous material layer and the second optical material layer are configured such that a portion of the emitted light passes through both the first and second optical material layers to the top surface of the substrate, the first amorphous material layer comprises a crystalline or polycrystalline alkali metal borate and / or alkaline earth metal borate material on the non-optical surface of the substrate, and the crystalline or polycrystalline alkali metal borate and / or alkaline earth metal borate material is maintained in 10% or less of the surface area on the optical surface composed of the incident surface and the exit surface.

17. It is a method, Prepare a nonlinear optical crystal, The aforementioned nonlinear optical crystal is annealed, The nonlinear optical crystal is placed in an inert environment above the liquid, The temperature of the liquid is set to a first desired temperature Tl. The temperature of the nonlinear optical crystal is set to a desired temperature T. Ｃ Set it to, The nonlinear optical crystal is lowered into the liquid, An amorphous layer is formed on the nonlinear optical crystal, and A method for removing the nonlinear optical crystal from the liquid after a predetermined time, The nonlinear optical crystal comprises at least one of CLBO crystals and CBO crystals, and the liquid is mainly composed of at least one of alkali metal borates and alkaline earth metal borates, and the amorphous layer comprises crystalline or polycrystalline alkali metal borate and / or alkaline earth metal borate material on the non-optical surface of the nonlinear optical crystal, and on the optical surface composed of the incident surface and the exit surface, the crystalline or polycrystalline alkali metal borate and / or alkaline earth metal borate material is maintained in an area of ​​10% or less of the surface area. method.

18. A method according to claim 17, wherein the predetermined time is selected such that an amorphous layer of a thickness is obtained in which the reflectance of the nonlinear optical crystal at a specified wavelength is reduced.

19. A method according to claim 18, wherein the specified wavelength is between 130 nm and 550 nm.

20. A method according to claim 18, wherein the thickness is in the range of 30 nm to 200 nm.

21. A method according to claim 17, further comprising lowering the nonlinear optical crystal into the liquid and then adjusting the temperature of the liquid.

22. A method according to claim 17, further comprising a second coating step, wherein a second layer is formed on the amorphous layer in the second coating step.

23. A method according to claim 22, wherein the second layer comprises at least one of magnesium fluoride, calcium fluoride, aluminum fluoride, and silicon dioxide.

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