Growth of strontium tetraborate crystals

Abstract

A method for growing strontium tetraborate (SrB4O7) crystals is provided. In this method, a seed crystal is lowered into a melt which is a mixture containing Sr, B, O, and a Cl source. In this method, the mixture is heated and melted to a temperature sufficient for the formation of strontium tetraborate crystals.

Description

[Technical Field]

[0001] [Cross-references to related applications] This application relates to U.S. Provisional Patent Application No. 63 / 656193 dated 5 June 2024 and U.S. Provisional Patent Application No. 63 / 537558 dated 11 September 2023, and therefore incorporates all disclosures of those respective applications by reference.

[0002] [Areas of Disclosure] This disclosure relates to crystal growth, more specifically to the growth of strontium tetraborate (SrB4O7) as a single crystal material for linear or nonlinear optical components used in weighing and inspection systems during semiconductor manufacturing, including photomasks, reticles, and semiconductor wafers used for inspection and / or measurement, such as mirrors, lenses, prisms, beam splitters, windows, lamp cells, pseudo-phase-matched frequency converters, and other types of frequency converters. [Background technology]

[0003] As semiconductor devices become smaller, the minimum size of particles or pattern defects that can cause device malfunctions also decreases. This creates a need to detect smaller particles and defects on patterned and unpatterned semiconductor wafers and reticles. The intensity of light scattered by particles smaller than its wavelength generally increases or decreases according to a higher-order power of the particle's size (for example, the total scattering intensity from a small, isolated spherical particle increases or decreases proportionally to the sixth power of the sphere's diameter and inversely proportional to the fourth power of its wavelength). Because of the increased intensity of scattered light, shorter wavelengths generally provide better sensitivity for detecting small particles and defects than longer wavelengths. Therefore, high-speed inspection in the semiconductor industry has typically been performed in machines utilizing ultraviolet (UV) light. One method of generating UV light involves frequency conversion from longer wavelengths to UV wavelengths using a UV-transparent, nonlinear crystal.

[0004] Since the intensity of light scattered from small particles and defects is generally very low, high illumination intensity is required to generate a signal that can be detected in a very short time. Therefore, it is necessary to use windows, lenses, and other optical systems with a high damage threshold, and in addition, they must have high UV transmittance.

[0005] Linear and nonlinear optical crystals are used, for example, in microscopes, virtual reality systems, lasers, and semiconductor systems. Optical crystals are widely used in semiconductor inspection and weighing systems, particularly in prisms, lenses, laser crystals, windows, and other components.

[0006] Only a few optical crystals exist that are transparent in the deep ultraviolet (DUV) and vacuum ultraviolet (VUV) wavelength ranges of approximately 200-280 nm and 100-200 nm, respectively. The most widely used optical crystals for linear optical system applications are calcium fluoride and magnesium fluoride, which transmit light with wavelengths of approximately 130 nm or less. However, most fluorides are hygroscopic, meaning they absorb water from the atmosphere. This water absorbs UV light, and the absorbed water can create stress within the crystal, which can lead to changes in the shape of the optical system and a decrease in performance.

[0007] Nonlinear optical crystals capable of frequency conversion for wavelengths below approximately 190 nm are not commercially available. Several materials, such as potassium beryllium borate fluoride KBe2BO3F2 (KBBF) and other materials in the form of ABe2BO3F2 (A=Na,K,Rb,Cs,Tl,NH4), can transmit wavelengths below 190 nm and can be phase-matched. However, the transmittance of KBBF drops significantly at wavelengths below 190 nm. In addition, mass growth of these materials has not yet been achieved, and further research is needed on their damage thresholds and lifetimes.

[0008] Strontium tetraborate (SrB4O7, SBO) is a material that overcomes many of the above-mentioned obstacles. SBO is transparent to wavelengths less than approximately 125 nm (see Non-Patent Document 1, the full details of which are incorporated into this application by reference), is not hygroscopic, and has a damage threshold of 16.4 J / cm² at 266 nm. 2 This is higher than that of CaF2 (Non-Patent Literature 2) and other nonlinear crystals such as CLBO. SBO cannot be phase-matched in DUV or VUV due to its low birefringence, but it has a large nonlinear coefficient d 33 Because it has this feature, pseudo-phase matching can be achieved. The following are incorporated into this application by reference: U.S. Provisional Patent Application No. 63 / 038134 dated June 12, 2020, titled "177nm and 133nm CW Lasers Using Stacked Strontium Tetraborate Plates"; U.S. Provisional Patent Application No. 63 / 076391 dated September 10, 2020, titled "152nm and 177nm CW Lasers Using Stacked Strontium Tetraborate Plates"; Patent Document 1 titled "Frequency Conversion Using Stacked Strontium Tetraborate Plates"; and "Frequency Conversion Using a Finger-Crossing Nonlinear Crystal Lattice". See U.S. Provisional Patent Application No. 63 / 282706 dated November 24, 2021, entitled Interdigitated Nonlinear Crystal Gratings, and U.S. Patent Application (KLA P6074) entitled 193nm Laser Using Strontium Tetraborate For Frequency Conversion.

[0009] For SBO growth, the Czochralski method, micro-dropping method, hydrothermal method, and top-seed solution growth method have been investigated. Crystals produced by the Czochralski method have a group of non-parallel domains of random thickness along the z-crystal axis. This is probably because the incomplete formation of the boron ion network during growth is caused by microscopic fluctuations in growth parameters, which serve as seeds for inverted domains (Non-Patent Literature 3). The micro-dropping method does not produce sufficiently large crystals and is not suitable for most optical applications. The hydrothermal method has shown promise for SBO growth, but large crystals have not yet been achieved, so more work is needed to develop this technique. The top-seed solution method has so far demonstrated the largest and purest SBO single crystals, with a mass of 300g as shown in Non-Patent Literature 4, the full details of which are incorporated into this application by reference. The melt used in Non-Patent Document 4 was a B-rich self-flux, composed of 67.3% B2O3 and 32.7% SrCO3. Such a high B2O3 concentration in the melt increases viscosity, reaching around 1 Pa·s. High viscosity due to high B2O3 concentration has also been observed during the growth of other borate crystals; for example, a viscosity of 6.3 Pa·s was observed for LBO with 87.5 wt% B2O3 (Non-Patent Document 5). High viscosity melts reduce the fluid velocity during crystal growth, decreasing mixing, resulting in a higher defect density and consequently greater light absorption and scattering. Furthermore, achieving sufficient mixing in a high-viscosity melt inevitably leads to a lower crystal growth rate. For cutting, polishing, and etching SBO for use in linear and nonlinear optical components, a sufficient quantity of SBO boules several centimeters in size must be grown, requiring a high growth rate and low defect density.

[0010] Solution growth is the process of growing crystals from a non-stoichiometric melt containing a solvent, i.e., a flux. This is one method for growing larger crystals with a lower defect density or at a lower temperature. Finding a suitable flux from the almost countless available options can be challenging; the flux must have the appropriate melting point, boiling point, and viscosity, and must not penetrate into the target crystal during growth. For example, before the discovery that high-quality crystals could be produced with a flux such as Na2O, arrays of various fluxes were used to grow β-BBO of varying qualities. Non-patent document 2 describes growing SBO from a high-viscosity melt using a self-flux containing trace amounts of borate, but to our knowledge, flux growth of SBO using other compounds has not been attempted or explored. One flux compound, SrCl2, has been used as a flux in crystal growth, including in the seedless solution growth of lead tungstate (PbWO4) as shown in non-patent document 6. According to Non-Patent Document 7, SrCl2 is SrAl2O4:Eu 2+ ,Dy 3+ It has also been used as a flux in high-temperature solid-state reaction growth. The growth methods, crystal structures, crystal quality, crystal size, and uses of these two types of materials are distinct from those of high-quality SBOs required for VUV optics and frequency conversion. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] U.S. Patent No. 11237455 [Patent Document 2] U.S. Patent No. 11567391 [Patent Document 3] U.S. Patent No. 6201601 [Patent Document 4] U.S. Patent No. 6,271,916 [Patent Document 5] U.S. Patent No. 7525649 [Patent Document 6] U.S. Patent No. 7817260, Specification [Patent Document 7] U.S. Patent No. 8298335, Specification [Patent Document 8] U.S. Patent No. 8824514, Specification [Patent Document 9] U.S. Patent No. 8976343, Specification [Patent Document 10] U.S. Patent No. 9023152, Specification [Patent Document 11] U.S. Patent No. 9461435, Specification [Patent Document 12] U.S. Patent No. 9059560, Specification [Patent Document 13] U.S. Patent No. 9293882, Specification [Patent Document 14] U.S. Patent No. 9660409, Specification [Patent Document 15] U.S. Patent No. 9250178, Specification [Patent Document 16] U.S. Patent No. 9459215, Specification [Patent Document 17] U.S. Patent No. 9509112, Specification [Patent Document 18] U.S. Patent No. 10044166, Specification [Patent Document 19] U.S. Patent No. 10283366, Specification [Patent Document 20] U.S. Patent Application Publication No. 2014 / 0305367, Specification [Patent Document 21] U.S. Patent No. 11255797 (B2), Specification [Patent Document 22] U.S. Patent No. 9255887, Specification [Patent Document 23] U.S. Patent No. 9645287, Specification [Patent Document 24] U.S. Patent No. 9709510, Specification [Patent Document 25] U.S. Patent No. 9726617, Specification

Non-licensed literature

[0012]

Non-licensed literature 1

Non-licensed Document 2

Non-licensed Document 4

Non-licensed Document 5

[0013] If there is an SBO growth method that can overcome the aforementioned limitations, it will be readily accepted by the relevant industries. [Means for solving the problem]

[0014] The present disclosure relates to methods for growing SBO by melt or solution methods, and to methods using strontium chloride (SrCl2) as the flux and component of the melt or solution according to one or more embodiments of the present disclosure. These SBO crystals are grown by the kiloporous method, the high-temperature solution top seeding method, the seeded hydrothermal method or other seeded or seedless flux method, the solution method or the melt method.

[0015] An optical system is disclosed in accordance with one or more embodiments of the present disclosure. In one illustrative embodiment, the optical system has one or more linear and nonlinear optical members, at least a portion of which is formed of strontium tetraborate.

[0016] An optical system is disclosed in accordance with one or more additional and / or alternative embodiments of the present disclosure. In one illustrative embodiment, the optical system has a stage for supporting a specimen. In another illustrative embodiment, the optical system has an illumination source. In yet another illustrative embodiment, the optical system has one or more linear or nonlinear optical members configured to direct illumination from the illumination source to a specimen, with at least a portion of the linear and nonlinear optical members being formed of strontium tetraborate.

[0017] A crystal growth method is disclosed in accordance with one or more embodiments of the present disclosure. In one illustrative embodiment, the crystal growth method involves growing a crystal in a furnace. In another illustrative embodiment, strontium tetraborate is grown in a solution containing strontium, oxygen, boron, and a strontium chloride source.

[0018] For your understanding, the above summary description and the following detailed description are both purely illustrative and explanatory, and do not necessarily limit the invention described in the claims. The attached drawings are incorporated into the specification and constitute a part thereof, illustrating various embodiments of the present invention and, together with the above summary description, serve to explain the principles of the present invention.

[0019] Those skilled in the art will be able to better understand the numerous advantages of this disclosure by referring to the attached drawings below. [Brief explanation of the drawing]

[0020] [Figure 1] This is a schematic block diagram showing an example of an inspection or measurement system related to one aspect of the disclosure. [Figure 2] This figure depicts an ultraviolet lamp that incorporates SrBO as an optical glass material for one or more optical components, relating to one or more embodiments of the present disclosure. [Figure 3]This is a schematic diagram showing an example of an SBO growth reactor related to one aspect of the disclosure. [Modes for carrying out the invention]

[0021] This disclosure relates to improvements in the growth quality and growth rate of SBO crystals for semiconductor inspection systems. The following descriptions are presented to enable a person skilled in the art to implement and use the invention under conditions consistent with specific usage and requirements. As used in this application, directional terms such as "up," "left," "right," "side," and "down" are intended to indicate relative positions for descriptive purposes and not to specify an absolute reference coordinate system. It will be obvious to a person skilled in the art that various modifications can be made to the embodiments described, and the general principles set forth in this application can be applied to other embodiments as well. Therefore, this disclosure is not intended to be limited to the specific embodiments illustrated and described, but rather should be tied to the greatest technical scope that corresponds to the principles and novel features disclosed in this application.

[0022] The following references are relevant to various aspects of this disclosure, and their entire contents are incorporated into this application by reference: U.S. Provisional Patent Application No. 63 / 521880 dated June 20, 2023, entitled "Growth of Quasi-Phase Matched Strontium Tetraborate and Lithium Triborate Crystals for Frequency Conversion"; U.S. Provisional Patent Application No. 63 / 038134 dated June 12, 2020, entitled "177nm and 133nm CW Lasers Using Stacked Strontium Tetraborate Plates"; and 152nm and 177nm CW Lasers Using Stacked U.S. Provisional Patent Application No. 63 / 076391 dated September 10, 2020, entitled "Strontium Tetraborate Plates"; U.S. Patent Application No. 17 / 991198 dated November 21, 2022, entitled "193nm Laser Using Strontium Tetraborate For Frequency Conversion"; Patent Documents 1, 2, 3, 4, 5, 6, 7 and 8, 7 and 8, 9, 9, 10, 11 and 12, 13 and 14, 13 and 14, 14, 12, 13, 14 Patent documents 15-19 under the name of al., and patent document 20 under the name of Dribinski et al.

[0023] It is noted that SBO exhibits unique optical and mechanical properties. The wavelength of the transparent region of SBO is 130-3200 nm. Reference is made to Non-Patent Document 1, the entire content of which is incorporated herein by reference. This wide transparent region covers VUV, DUV, visible and near-infrared (IR) wavelength ranges. The VUV region and DUV region are particularly interesting regions for semiconductor inspection and metrology. It is also noted that the transmittance thereof is high. For example, the transmittance exceeds 80% at about 250 nm to about 2500 nm. This high transmittance makes SBO a good candidate especially for frequency generation in the UV wavelength range. If SBO is grown under optimal conditions, a better transmittance curve can be obtained: the transmittance thereof can reach more than 80% at wavelengths of 200 nm or more, and more than 50% at wavelengths of 130 to 200 nm. Since the dielectric and optical properties of strontium tetraborate glass are described in Non-Patent Document 8, the entire content thereof is incorporated herein by reference.

[0024] SBO is one of the materials that have recently attracted attention for DUV frequency generation. SBO has the Pmn2₁ space group and the mm2 point group, which means that the nonlinear coefficient d 33 is capable of quasi-phase matching. Measurement results have been obtained for this nonlinear coefficient d 33 as 1.5 pm / V in frequency doubling from 800 nm to 400 nm (Non-Patent Document 9). Furthermore, it is known that SBO exhibits DUV transparency at wavelengths of 125 nm or less, enabling frequency conversion to such wavelengths. The UV light-induced damage threshold of SBO is 16.4 J / cm 2 at 266 nm, which is considerably higher than that of CaF₂ (11.4 J / cm 2 ) and that of silica (4.8 J / cm 2 ) (Non-Patent Document 2). Although biaxial, SBO is nearly isotropic (Non-Patent Document 1), and therefore frequency conversion cannot be performed in the DUV range via birefringent phase matching. The nonlinear coefficient d 33Because of its high SBO, SBO is a candidate for quasi-phase matching, in which the fundamental and second harmonics are polarized parallel to each other and parallel to the c-axis. Phase mismatch caused by the exponential difference between the fundamental and higher harmonics is compensated for by alternating 180° inversions of the c-crystal axis direction of the material, thereby reducing the phase difference between these harmonics due to the difference in the sign of the nonlinear coefficients. See U.S. Provisional Patent Application No. 63 / 521880, entitled "Growth of Quasi-Phase Matched Strontium Tetraborate and Lithium Triborate Crystals for Frequency Conversion," which is incorporated into this application in full by reference.

[0025] Due to its low birefringence, SBO is a good candidate material for various linear optical components, such as windows, lenses, coatings, bulbs, and other components. See Patent Document 21, titled "Strontium tetraborate as optical glass material," which is incorporated into this application by reference in its entirety.

[0026] Figure 1 shows an example of the inspection system 100, which is configured according to one or more embodiments of the present disclosure to inspect a sample 108 or to measure it. The inspection system 100 can be configured as an inspection system or weighing system for inspecting and / or measuring a sample 108. The inspection system 100 can also be configured to cut, perforate or excise material from the sample 108, or to expose and form a pattern on a photoresist on the sample 108.

[0027] The specimen 108 may be any specimen known in the present art, for example, a wafer, reticle, photomask, etc., although this is not limited to these. In one embodiment, the specimen 108 can be placed on a stage assembly 112 to handle its movement. The stage assembly 112 may be any stage assembly known in the present art, including an XY stage, an Rθ stage, etc., although this is not limited to these. In another embodiment, the stage assembly 112 can be made capable of adjusting the height of the specimen 108 during inspection, thereby keeping the specimen 108 in focus. Furthermore, in another embodiment, a lens, such as an objective lens 150, can be moved up and down during inspection to keep the specimen 108 in focus.

[0028] The inspection system 100 has an illumination source 102, and the emitted light L generated by the laser 200-0 incorporated therein is OUT However, the emission frequency ω corresponds to a wavelength in the range of approximately 120 nm to approximately 200 nm. OUT The illumination source 102 may have an additional light source, such as a laser or broadband light source operating at longer or shorter wavelengths. The laser 200-0 may have a grown SBO incorporated into it. One or more optical components in the inspection system 100, such as a beam splitter, mirror, lens, aperture and waveplate, of which optical L OUT The system configured to dim and direct the light onto specimen 108 can be based on the grown SBO. The optical element may be configured to illuminate a certain area, line, or spot on specimen 108. In one embodiment, a beam splitter or mirror 134, mirrors 137 and 138 and lens 152 are configured to illuminate specimen 108 from below, and the light L INT It is possible to inspect or measure the specimen 108 by passing light through the specimen. In one embodiment, the beam splitter or mirrors 134 and 135, mirror 136 and lens 151 allow light L at an oblique angle of incidence to pass through. OblThus, the specimen 108 is illuminated, for example, at an incident angle greater than 60° with respect to the normal to the specimen surface. In this embodiment, specular reflected light L Spec The light may be blocked or discarded without being focused. Furthermore, in one embodiment, the optical system 103 receives the illumination light L IN It is jointly configured to point towards the top surface of specimen 108.

[0029] When the specimen 108 is illuminated using one or more of the modes described above, the optical system 103 also receives the light L reflected, scattered, diffracted, transmitted and / or emitted from the specimen 108. R / S / T Gathering light, R / S / T The detector assembly 104 is configured to be directed towards and focused on the sensor 106. It should be noted that the sensor 106 and the detector assembly 104 may be any sensor known in the art. Possible sensors include, but are not limited to, charge-coupled device (CCD) detectors, complementary metal-oxide-semiconductor (CMOS) detectors, time-delay integral (TDI) detectors, photomultiplier tubes (PMTs), avalanche photodiodes (APDs), line sensors, and electron shock line sensors. The detector assembly 104 is communicably coupled to the information processing system 114.

[0030] The information processing system 114 is configured to store and / or analyze data from the detector assembly 104 under the control of program instructions 118 stored on the carrier medium 116. The information processing system 114 may also be configured to control other components of the inspection system 100, such as the stage 112, the illumination source 102, and the optical system 103.

[0031] In one embodiment, an illumination tube lens 132 is provided within the optical system 103. The illumination tube lens 132 can be configured such that an image of the illumination pupil aperture 131 is formed in the pupil of the objective lens 150. For example, the illumination tube lens 132 may be configured such that the illumination pupil aperture 131 and the pupil of the objective lens 150 are conjugate to each other. In one embodiment, the illumination pupil aperture 131 may be configured to be changeable by switching and inserting various apertures at the location of the illumination pupil aperture 131. In another embodiment, the illumination pupil aperture 131 may be configured to be changeable by adjusting the aperture diameter or aperture shape of the illumination pupil aperture 131. In this case, the specimen 108 can be illuminated in different angular ranges depending on the characteristic analysis (e.g., measurement or inspection) being performed under the control of the controller 114. Furthermore, the illumination pupil aperture 131 can be illuminated by illumination light L IN It may also include a polarizing element for controlling the polarization state.

[0032] In one embodiment, a condensing tube lens 122 is included in one or more of the aforementioned optical elements 103. For example, the condensing tube lens 122 can be configured such that an image of the pupil in the objective lens 150 is formed on the condensing pupil aperture 121. For example, the condensing tube lens 122 may be configured such that the condensing pupil aperture 121 and the pupil in the objective lens 150 are conjugate to each other. In one embodiment, the condensing pupil aperture 121 may be configured to be changeable by switching and inserting various apertures at the location of the condensing pupil aperture 121. In another embodiment, the condensing pupil aperture 121 may be configured to be changeable by adjusting the aperture diameter or aperture shape of the condensing pupil aperture 121. In this case, illumination from different angular ranges reflected or scattered from the specimen 108 can be directed to the detector assembly 104 under the control of the controller 114. Also, the light-gathering pupil aperture 121 is light L R / S / T It is also possible to have a polarizing element that selects a specific polarization from among them and transmits it to the sensor 106.

[0033] Furthermore, in one embodiment, the illumination pupil aperture 131 and / or the focusing pupil aperture 121 may have programmable apertures. Programmable apertures are outlined in Patent Document 22, published on February 9, 2016, under the name of Brunner, entitled "2D programmable aperture mechanism," and Patent Document 23, published on May 9, 2017, under the name of Brunner, entitled "Flexible optical aperture mechanisms." Therefore, the entire contents of both documents will be incorporated into this application by reference. Methods for selecting aperture configurations for inspection are outlined in Patent Document 24, published on July 18, 2017, under the name of Kolchin et al., entitled "Determining a configuration for an optical element positioned in a collection aperture during wafer inspection," and Patent Document 25, published on August 8, 2017, under the name of Kolchin et al., entitled "Apparatus and methods for finding a best aperture and mode to enhance defect detection." Therefore, the entire contents of both documents will be incorporated into this application by reference.

[0034] The various optical elements and operating modes depicted in Figure 1 are merely intended to illustrate how the laser 200-0 can be used within the inspection system 100, and are not intended to limit the technical scope of this disclosure. In actual inspection systems 100, subsets or supersets of the modes and optical systems depicted in Figure 1 may be implemented. Additional optical elements and subsystems may be incorporated depending on the specific application requirements. Many other important details regarding systems into which the laser 200-0 of the present invention can be incorporated are disclosed in the related references cited above and in other references cited in this application.

[0035] Figure 2 shows a schematic appearance of an ultraviolet lamp, in which SBO is incorporated as an optical glass material for one or more optical components according to one or more embodiments of the disclosure. This ultraviolet lamp can be a laser-driven light source. In this example, a laser beam 212 emitted from a laser 211 is redirected by a mirror 213 and focused by lenses 214 and 225, thereby generating plasma 202 within a lamp cell 201. Broadband ultraviolet light 205 is emitted from the plasma 202 over a wide wavelength range including DUV and / or VUV wavelengths. One or more windows 203 are located in the wall of the lamp cell 201 so that the broadband ultraviolet light 205 can pass out of the lamp cell 201. According to one embodiment, the lamp cell 201 can be made of SBO. According to this embodiment, a gas for generating plasma 202 can be contained within a transparent bulb formed using SBO. Furthermore, according to one embodiment, one or more windows 203 may be formed from SBO. Moreover, according to one embodiment, both the lamp cell 201 and one or more windows 203 may be made from SBO. By appropriately using SBO as an optical glass material for one or more optical components, the overall optical throughput of the ultraviolet lamp can be improved. By using SBO, the lifespan of the ultraviolet lamp and the core optical components can also be improved. Since any of the optical components described above can be made from SBO crystal or glass, the technical scope of the present disclosure is not at all limited to SBO-based windows or plasma cells. Rather, as discussed earlier in this application, any number of the linear optical components of the present disclosure may be formed from SBO, and may not be limited to this, but may be implemented in any optical context, including semiconductor inspection or weighing.

[0036] Figure 3 shows an outline of a furnace 301 for growing SBO from seed 305 using the top-seed kiloporous method. The furnace 301 is equipped with a resistance heating furnace having 5, 6 or more zones and can be fitted with a platinum crucible 303 with a diameter of approximately 150 mm and a height of approximately 150 mm. The platinum crucible 303 can be made larger or smaller depending on the final size of the grown crystal, and should be approximately twice the diameter of the desired final crystal size. The seed crystal 305 is fixed to the alumina tube 302 to prevent it from falling into the melt 304 and to supply coolant or air to the seed crystal 305 to prevent melting during growth.

[0037] Melt 304 contains strontium carbonate (SrCO3), boron trioxide (B2O3), and strontium chloride (SrCl2). Melt mixing can be promoted using L-shaped or twin-shaped stirring blades. The temperature of Melt 304 should be maintained at around 1000°C. Since B2O3 exhibits a high viscosity of approximately 9.8 Pa·s at around 1000°C (see Non-Patent Literature 10), under the self-flux of B2O3 in Non-Patent Literature 4, an overall solution viscosity of approximately 1 Pa·s is generated, which is detrimental to mixing and consequently to crystal growth. Strontium chloride is a salt with a melting point of 874°C and a boiling point of 1250°C. Since the melting point of SBO is around 1015°C and the recrystallization temperature is around 950°C, and therefore SrCl2 recrystallizes at a lower temperature than SBO, SrCl2 is an ideal flux for top seed solution growth of SBO. In addition, since the water solubility of SrCl2 is 53.8 g / 100 mL at 20 °C, any excess SrCl2 can be easily removed from the SBO crystal by rinsing with water after growth is complete. The viscosity of SrCl2 has been measured to be 2.25 to 3.75 mPa·s at 880 to 1050 °C (Non-Patent Literature 11), which is three orders of magnitude lower than the viscosity of B2O3. Due to this low viscosity, the melt that is used up near the surface of the growing crystal is replenished, improving temperature uniformity and thus improving single crystal growth, which in turn suppresses the growth of other crystalline phases. Cl -The ions have a different number of valence shell electrons than the other atoms that make up SBO, and have a larger ionic radius than those other atoms, thus reducing Cl substitution defects and intralattice defects. Sr originates from the ionic liquid of molten SrCl2. 2+ The number of valence electrons originates from the dissolved SrCO3. 2+ Since the number of valence electrons is the same as in SrCl2, Sr 2+ This will likely play a significant role in crystal growth.

[0038] This is an example of a chemical reaction in which SBO is formed, involving the raw materials B2O3 and SrCO3. 2B2O3 + SrCO3 → SrB4O7 + CO2 There is. Other chemical reactions may occur involving the same or different stoichiometric reactants. Other reactants, such as SrCl2, may also be involved. Sr from molten SrCl2 in solution 2+ The ions originate from dissolved SrCO3. 2+ It would be indistinguishable from an ion. Among the other phases of the SrO-B2O3 system, the phase that crystallizes at a composition and temperature similar to that of SrB4O7 formation has an Sr:B ratio greater than 1:4 (Non-Patent Literature 12), thus promoting their preferential formation over SrB4O7 using stoichiometric Sr:B raw materials. As observed in both the top-seed solution growth method and the hydrothermal method, B-rich initiation stoichiometry is more desirable to avoid the formation of other Sr-BO phases. However, a higher B2O3 ratio will increase the viscosity of the melt.

[0039] Another example of a chemical reaction that forms SBO involves the raw materials H3BO3 and SrCO3. 4H3BO3+SrCO3→ SrB4O7+CO2+6H2O There is. Other chemical reactions involving the same or different stoichiometric reactants may occur. Other reactants may also be involved. In this reaction, a SrCl2 flux is added so that the Sr:B ratio in the solution is 1:4 or higher.

[0040] The seed crystal 305 can be composed of a single crystal with a fixed orientation or a patterned crystal, and an example of such a patterned crystal can be found in U.S. Provisional Patent Application 63 / 521880 entitled "Growth of Quasi-Phase Matched Strontium Tetraborate and Lithium Triborate Crystals for Frequency Conversion," the full details of which will be incorporated into this application by reference.

[0041] Optical glass containing SBO can be formed by melting single crystal SBO grown with SrCl2 contained in a melt. For details on the manufacturing of SBO glass, please refer to Patent Document 21, titled "Strontium tetraborate as optical glass material," published under the name of Chuang et al. This patent document is incorporated into this application by reference. SBO optical coatings, such as those used in anti-reflective coatings, can be deposited from these pre-grown SBO single crystals by sputtering, electron beam deposition, thermal deposition, pulsed laser deposition, molecular beam epitaxy, and other thin-film deposition methods known to those skilled in the art. These optical glasses and coatings, with their high damage threshold and DUV and VUV transparency, can be used in a variety of components, including mirrors, lenses, laser crystals, windows, and lamps, as well as in semiconductor inspection and weighing systems.

[0042] Although the crystal growth method described in this application uses various temperatures, pressures, melt stoichiometry, furnace types, crucible sizes, crucibles, and crystal rotation speeds, we believe that other temperatures, pressures, melt stoichiometry, furnace types, crucible sizes, and crucibles and crystal rotation speeds are also within the technical scope of the present invention, unless otherwise specified in the attached claims.

[0043] Nonlinear crystals exhibiting transparency below approximately 120 nm are not commercially available. In particular, there are no prior technologies capable of mass-producing SBO crystals larger than 350 g that exhibit high purity, high damage threshold, large nonlinear coefficients, and high transparency in the sub-200 nm region. In the embodiments of the present method, a lower viscosity melt is provided for SBO growth, enabling the formation of larger and higher-purity Boule crystals. In addition, since the growth method uses a non-toxic melt composition, it is easy and inexpensive to implement and maintain the equipment for.

[0044] As will be immediately apparent to those skilled in the art, the ingenious laser crystal growth method described herein has many potential applications beyond semiconductor inspection and weighing. For example, a laser incorporating an SBO crystal grown by this method and operating at a wavelength of around 193.4 nm can be used in a lithography system configured to pattern-expose a photoresist covering a substrate such as a semiconductor wafer. Alternatively, a laser incorporating an SBO crystal grown by this method and operating at a wavelength of approximately 120 nm to 200 nm can be used in a system configured to cut or excise biological tissue. While this disclosure has been described in relation to specific embodiments, as will be obvious to those skilled in the art, the ingenious features of this disclosure are equally applicable to other embodiments, all of which fall within the technical scope of this disclosure.

Claims

1. Strontium tetraborate (SrB) ４ O ７ ) A method for growing crystals, This is a method of lowering the seed crystal into the melt, and that melt is A mixture containing Sr, B, O and a Cl source is formed, and The mixture was heated and melted to a temperature sufficient to form strontium tetraborate crystals. A method that is a certain way.

2. SrB according to claim 1 ４ O ７ A crystal growth method comprising heating the mixture of Sr, B, O, and Cl to a temperature of approximately 960 to 1030°C to melt it, and then cooling it to a temperature of approximately 950°C to form the strontium tetraborate crystal.

3. SrB according to claim 1 ４ O ７ A crystal growth method wherein the Cl source is SrCl ２ The way of doing so.

4. The SrB according to claim 1 ４ O ７ A crystal growth method, wherein the Sr, B, O and Cl sources are B ２ O ３ , SrCO ３ and SrCl ２ A method, which contains at least one selected from the group consisting of the above.

5. SrB according to claim 3 ４ O ７ A crystal growth method wherein the melt is approximately 0.5 to 34 mol% SrCl ２ A method that contains [a specific substance].

6. SrB according to claim 4 ４ O ７ A crystal growth method wherein the melt is approximately 0.5 to 34 mol% SrCO ３ A method that contains [a specific substance].

7. SrB according to claim 4 ４ O ７ A crystal growth method wherein the melt is approximately 66 to 90 mol% B ２ O ３ A method that contains [a specific substance].

8. SrB according to claim 3 ４ O ７ A crystal growth method wherein the melt is approximately 2 to 15 mol% SrCl ２ A method that contains [a specific substance].

9. SrB according to claim 1 ４ O ７ A crystal growth method wherein the mixture is H ２ A method that additionally contains an oxygen source.

10. SrB according to claim 1 ４ O ７ A crystal growth method, further comprising growing the strontium tetraborate crystal by a top seed solution method.

11. SrB according to claim 1 ４ O ７ A crystal growth method, further comprising growing the strontium tetraborate crystal by a flux method.

12. SrB according to claim 1 ４ O ７ A crystal growth method, further comprising growing the strontium tetraborate crystal by a melting method.

13. SrB according to claim 1 ４ O ７ A crystal growth method that enables pseudo-phase matching by using a seed crystal consisting of alternatingly arranged crystal plates.

14. SrB according to claim 1 ４ O ７ A crystal growth method comprising heating the mixture of Sr, B, O, and Cl to a temperature of approximately 960 to 1030°C to melt it, and then cooling it to a temperature of approximately 900°C to form the strontium tetraborate crystal.

15. SrB according to claim 1 ４ O ７ A crystal growth method comprising heating the mixture of Sr, B, O, and Cl to a temperature of approximately 960 to 1030°C to melt it, and then cooling it to a temperature of approximately 875°C to form the strontium tetraborate crystal.

16. SrB according to claim 1 ４ O ７ A crystal growth method comprising heating the mixture of Sr, B, O, and Cl to a temperature of approximately 1001 to 1030°C to melt it, and then cooling it to a temperature of approximately 1000°C to form the strontium tetraborate crystal.

17. SrB according to claim 1 ４ O ７ A method for growing crystals, comprising heating the mixture of Sr, B, O, and Cl to a temperature of approximately 1016 to 1030°C to melt it, and then cooling it to a temperature of approximately 1015°C to form the strontium tetraborate crystal.

18. SrB according to claim 1 ４ O ７ A crystal growth method comprising heating the mixture of Sr, B, O, and Cl to a temperature of approximately 960 to 1030°C to melt it, and then cooling it to a temperature of approximately 875 to 1015°C to form the strontium tetraborate crystal.

19. A frequency converter containing a crystal grown by the method of claim 1.

20. A linear optical apparatus containing a crystal grown by the method of claim 1.

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