Method and system for bonding high-flux optics to light-machine assembly

Abstract

The invention relates to a method for bonding a first optical element to a substrate. The method may include receiving a first optical element and a substrate. The method may include positioning an indium foil between the first optical element and the substrate. The method may include securing the first optical element to the substrate to create a pre-bonded assembly, wherein the indium foil is disposed between the first optical element and the substrate. The method may include heating the pre-bonded assembly above a melting temperature of the indium foil. The method may include cooling the pre-bonded assembly. The method may include releasing the pre-engagement assembly, wherein releasing the pre-engagement assembly releases the engagement structure.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 462,531, filed Apr. 28, 2023, under 35 U.S.C. § 119(e), the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to the production of optical systems, and in particular, to joining optical elements within an optical system without affecting the optical properties of the optical elements. BACKGROUND ART

[0004] Illumination systems based on high-power deep UV lasers include optical elements such as mirrors, lenses, birefringent crystals, nonlinear optical crystals, and wave plates, polarizer beam splitters. It is generally difficult to fix these optical elements within the system (e.g., by joining the optical elements to a substrate). Current methods for bonding optical elements to a substrate typically result in a change in one or more optical properties of the optical element, including but not limited to changes in reflection, transmission, wavefront, polarization purity, and stress-induced birefringence.

[0005] Accordingly, there is a desire to provide methods that overcome the deficiencies of the prior methods discussed above. SUMMARY OF THE INVENTION

[0006] According to one or more embodiments of the present disclosure, a method for joining a first optical element to a substrate is disclosed. In one embodiment, the method includes receiving a first optical element and a substrate. In another embodiment, the method includes positioning an indium foil between the first optical element and the substrate. In another embodiment, the method includes bringing the first optical element into contact with the substrate to produce a pre-joined assembly, wherein the indium foil is disposed between the first optical element and the substrate. In another embodiment, the method includes heating the pre-joined assembly to a temperature above the melting temperature of the indium foil. In another embodiment, the method includes cooling the pre-joined assembly. In another embodiment, the method includes releasing the pre-joined assembly, wherein releasing the pre-joined assembly releases a joining structure.

[0007] According to one or more embodiments of the present disclosure, a system for bonding a first optical element to a substrate is disclosed. In one embodiment, the system includes a base plate configured to receive a plurality of components and configured to receive the first optical element and the substrate. In another embodiment, the system includes a heating element thermally coupled to the base plate. In another embodiment, the system includes a top plate coupled to the tops of the plurality of holding elements, wherein tightening the plurality of holding elements into the base plate increases the clamping force on the first optical element and the substrate.

[0008] According to one or more embodiments of the present disclosure, an apparatus is disclosed. In one embodiment, the apparatus includes a first optical element. In another embodiment, the apparatus includes a substrate. In another embodiment, the apparatus includes indium foil, wherein the first optical element is bonded to the substrate via the indium foil.

[0009] It should be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily limiting of the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the general description serve to explain the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Those skilled in the art will better understand many advantages of the present disclosure by referring to the accompanying drawings, wherein:

[0011] Figure 1 A block diagram illustrating a system for bonding a first optical element to a substrate according to one or more embodiments of the present disclosure.

[0012] Figure 2 A simplified schematic diagram illustrating a clamping assembly for bonding a first optical element to a substrate via indium foil according to one or more embodiments of the present disclosure.

[0013] Figure 3 A simplified schematic diagram illustrating a clamping assembly for bonding a first optical element to a second optical element via indium foil according to one or more embodiments of the present disclosure.

[0014] Figure 4 A simplified schematic diagram illustrating a system for bonding a first optical element to a second optical element according to one or more embodiments of the present disclosure, the system including a clamping assembly and a gas purge subsystem.

[0015] Figure 5 A process flow diagram depicting a method for bonding a first optical element to a substrate according to one or more embodiments of the present disclosure. DETAILED DESCRIPTION

[0016] Reference will now be made in detail to the disclosed subject matter illustrated in the accompanying drawings. The present disclosure has been particularly shown and described with respect to particular embodiments and specific features thereof. The embodiments set forth herein are to be considered illustrative and not restrictive. Those of ordinary skill in the art will readily appreciate that various changes and modifications in form and detail can be made without departing from the spirit and scope of the present disclosure.

[0017] Figures 1 - 5 Systems and methods for bonding an optical element to a substrate are described. Embodiments of the present disclosure relate to using indium foil as an adhesive for bonding an optical element to a substrate. Embodiments of the present disclosure also relate to a clamping assembly for securing an optical element to a substrate, where the indium foil is placed at the interface of the optical element and the substrate (e.g., as a sandwich). Once the optical element and the substrate are secured, the clamping assembly is subjected to a predetermined pressure and temperature, effectively creating a strongly bonded optical element / substrate device due to the bonding action of the indium foil. Since indium has a relatively low melting point (156 °C), the device can be reworked by applying heat above the melting point.

[0018] Embodiments of the present disclosure are particularly advantageous for several reasons. For example, the bonding method reduces or eliminates stress-induced degradation common in mechanical clamping. In another example, the bonding method reduces or eliminates subsequent outgassing and is not particularly sensitive to bonding materials with different coefficients of thermal expansion (CTE) common in epoxy bonding. In another example, the bonding method does not utilize the potentially damaging high temperatures common in welding methods. Finally, the bonding method requires significantly less labor and time costs common in optical bonding.

[0019] Figure 1 Conceptual diagram of a system 100 for bonding a first optical element 101 to a substrate 102 according to one or more embodiments of the present disclosure is illustrated. In an embodiment, the system 100 includes a clamping assembly 103, a heater 104, a gas purge subsystem 105, and a controller 106. In an embodiment, the clamping assembly 103 is configured to clamp the first optical element 101 to the substrate 102 during the bonding process. In an embodiment, the heater 104 is configured to heat the first optical element 101 and the substrate 102 to a working temperature during the bonding process (e.g., when the first optical element 101 and the substrate 102 are placed in the clamping assembly 103). In an embodiment, the gas purge subsystem 105 is configured to purge the clamping assembly 103 containing the first optical element 101 and the substrate 102 with an inert gas.

[0020] In an embodiment, the controller 106 includes one or more processors 108 and a memory 110. For example, the memory 110 may maintain program instructions configured to cause the one or more processors 108 to perform any of the one or more process steps described throughout the present disclosure.

[0021] In an embodiment, one or more processors 108 of the controller 106 are communicatively coupled to the heater 104 and the gas purge subsystem 104. In this regard, the one or more processors 108 are configured to control the temperature of the clamping assembly 103, the first optical element 101, and the substrate 102 via the heater 104. Additionally, the one or more processors 108 are configured to control the flow of an inert gas through the clamping assembly 103 via the gas purge subsystem 105.

[0022] In an embodiment, the heater 104 includes any heating element that can raise the temperature of the first optical element 101 and the substrate 102 to a temperature higher than the melting point of indium (156 °C). The heater 104 can utilize any type of thermal energy for heating, including but not limited to conductive heat, convective heat, and radiant heat. The heater 104 can include any type of heater form. For example, the heater 104 can include a heater that raises the temperature of the first optical element 101 and the substrate 102 primarily through conduction. For example, the heater 104 can include a cylindrical heater, such as a 1 / 4" cylindrical heater.

[0023] In an embodiment, the heater 104 is controlled (e.g., via one or more processors 108 acting as a temperature controller) to heat the first optical element 101 and the substrate 102 to a temperature (e.g., a working or melting temperature). For example, the heater 104 can be configured to heat the first optical element 101 and the substrate 102 to a temperature of at least 156 °C, at least 160 °C, at least 165 °C, or at least 175 °C or a temperature higher than 175 °C. For example, the heater 104 can be configured to heat the first optical element 101 and the substrate 102 to a temperature in the range of 156 °C to 175 °C. In another example, the heater 104 can be configured to heat the first optical element 101 and the substrate 102 to a temperature in the range of 156 °C to 165 °C. In another example, the heater 104 can be configured to heat the first optical element 101 and the substrate 102 to a temperature in the range of 165 °C to 175 °C.

[0024] In an embodiment, the heater 104 is controlled via one or more processors 108 to heat or cool the first optical element 101 and the substrate 102 via a slope (e.g., °C / min). For example, the heater 104 can be configured to change the temperature at about 1 °C / min. In another example, the heater 104 can be configured to change the temperature at about 2 °C / min. In another example, the heater 104 can be configured to change the temperature at about 0.5 °C / min. In another example, the heater 104 can be configured to change the temperature at about 0.25 °C / min. Controlling the slope of the heater 104 ensures the thermalization of the first optical element 101 and the other substrate 102, which significantly reduces the thermal stress of crystalline optical elements (e.g., single-crystalline optical elements) (e.g., CaF2 crystal, MgF2 crystal, β-barium borate (BBO) crystal, and cesium lithium borate (CLBO) crystal).

[0025] In an embodiment, the gas purge subsystem 105 includes any gas dispersion system for dispersing and purging an inert gas (e.g., nitrogen, argon, carbon dioxide, helium). The gas purge subsystem 105 can include a gas storage tank and one or more valves, where at least one valve is controlled by the controller 106.

[0026] In an embodiment, the first optical element 101 can include any type of optical element, including but not limited to a lens, mirror, window, platform, filter, prism, or beam splitter. The first optical element 101 can include any optical element material or component, including but not limited to CaF2, MgF2, BBO, CLBO, KTP, PPKTP, LBO, DKDP, ADP, KDP, LiIO3, KNbO3, LiNbO3, AgGaS2, AgGaSe2, BaF2, LiF, YAG, TGG, TiO2, ZnS, ZnSe, GaAs, or SiGe. The first optical element can include a coating, including but not limited to oxide coatings Ta2O5, ZrO2, HfO2, A12O3, SiO2, Nb2O5, TiO2, FS, SBO, fluoride coatings LiF, CaF2, MgF2, LaF3, AlF3, LiF, LaF3, GdF3, or NdF3. In an embodiment, the substrate 102 can include any material for bonding to the first optical element 101, including but not limited to a mount, bottom surface, substrate, metal surface, or a second optical element. The second optical element can include any optical element described for the first optical element 101.

[0027] Figure 2Simplified schematic illustration of a clamping assembly 103 for joining a first optical element 101 (e.g., a CaF2 polarizing beam splitter cube (PBSC)) to a substrate 102 (e.g., a metal mount for the first optical element 101, such as a nickel-plated aluminum mount) via an indium foil 200 in accordance with one or more embodiments of the present disclosure. In an embodiment, the clamping assembly 103 includes one or more of the following: a bottom plate 204, a heater 104, a thermometer 208, a top plate 212, and a plurality of holding elements 216a - 216b (e.g., holding screws) configured to couple to the top ends of the bottom plate 204 and the top plate 212. In an embodiment, the clamping assembly includes a plurality of spring clips for fixing the plurality of holding elements 216a - 216b in place. The thermometer 208 is communicatively coupled to one or more processors 108. When clamped together, the first optical element 101, the substrate 102, and the indium foil 200 form a pre - joining assembly 220. Tightening the holding elements 216a - 216b increases the clamping force on the pre - joining assembly 220.

[0028] In use, the clamping assembly 103 receives the first optical element 101 and the substrate 102 on the bottom plate 204, with the indium foil 200 positioned between the first optical element 101 and the substrate 102. The first optical element 101 or the substrate 102 may be first positioned on the bottom plate 204. Then the top plate 212 is placed on the first optical element 101 / substrate 102 assembly. The holding elements 216a - 216b are then fixed to the bottom plate 205 while being mechanically coupled to the top plate 212, effectively clamping the first optical element 101 and the substrate 102 to the clamping assembly, and clamping the indium foil 200 (e.g., disposed) between the first optical element 101 and the substrate 102 to the clamping assembly.

[0029] The indium foil 200 may comprise any indium - containing foil. For example, the indium foil 200 may comprise a foil having greater than 50% indium, greater than 66% indium, greater than 80% indium, greater than 90% indium, greater than 95% indium, greater than 99.9% indium, or a foil having 99.99% indium or greater. For example, the indium foil 200 may comprise a foil having 99.99% indium or approximately 99.99% indium. The indium foil 200 may have a thickness, including but not limited to a 2mm thickness, a 0.127mm thickness, a 0.1mm thickness, an 80μm thickness, a 60μm thickness, a 50um thickness, a 40μm thickness, or an approximate thickness thereof. For example, the indium foil 200 may comprise a 99.99% indium - containing foil having a thickness of 50μm.

[0030] Figure 3Simplified schematic illustration of a clamping assembly 103 for bonding a first optical element 101 to a second optical element (e.g., a substrate 102) via an indium foil 200 according to one or more embodiments of the present disclosure. A thermometer 208 may be positioned on the base plate 204, the substrate 102, or other components of the clamping assembly 103.

[0031] Figure 4 Simplified schematic illustration of a system 100 for bonding a first optical element to a second optical element according to one or more embodiments of the present disclosure, the system including a clamping assembly, a heater 104, and a gas purge subsystem 105. Figure 4 The system 100 may include Figures 2 - 3 one or more components of the bonding assembly 103, and may further include one or more thermal insulation plates 404, a container 408, an input purge line 412, an output purge line 416, and an electrical feedthrough 420 (e.g., for feeding the thermometer 208, the heater 104, and associated electrical wires into the container 408), an air filter 424, and a temperature controller 428 (e.g., including at least one of one or more processors).

[0032] In an embodiment, the container 408 is configured to house the clamping assembly 103 while the first optical element 101 and the substrate 102 are purged with an inert gas during a heating (e.g., baking) process. The container 408 may include stainless steel, which provides an isothermal environment to the clamping assembly 103. The container 408 may further include a top flange to allow connection via the input purge line 412, the output purge line 416, and the electrical feedthrough 420.

[0033] In an embodiment, the gas purge subsystem 105 purges the first optical element 101, the substrate 102, and the indium foil 200 with a filtered inert gas. For example, the gas purge subsystem 105 may purge the first optical element 101, the substrate 102, and the indium foil 200 with a gaseous molecular contaminant (AMC) filtered inert gas (e.g., such as ultra-pure N2 gas). In an embodiment, the inert gas used to purge the first optical element 101, the substrate 102, and the indium foil 200 flows at a rate of 0.1 L / min, 0.25 L / min, 0.5 L / min, 1.0 L / min, or 2.0 L / min or an approximate rate thereof. For example, the first optical element 101, the substrate 102, and the indium foil 200 may be purged with AMC filtered ultra-pure N2 gas at a rate of 0.5 L / min.

[0034] In an embodiment, one or more processors 108 of the controller 106 of the system 100 control the heater 104. For example, one or more processors 108 of the controller 106 of the system 100 may perform at least one of the following: controlling the on / off of the heater 104, controlling the ramp of the heater 104, controlling the soak time or hold time of the heater 104 at a specific temperature, monitoring the thermometer 208, and changing the heating parameters based on the reading of the thermometer 208. In an embodiment, one or more processors 108 of the controller 106 of the system control the gas purge subsystem 105. For example, one or more processors 108 of the controller 106 of the system 100 may perform at least one of controlling the inflow and / or outflow of an inert gas into the container 408.

[0035] In an embodiment, the system 100 includes a user interface device communicatively coupled to one or more processors 108 of the controller 106. The user interface device may be used by the controller 106 to receive information, selections, and / or instructions from a user. For example, a display may be used to display data or prompts (not shown) to the user. The user may also input information, selections, and / or instructions into the memory 110 of the controller 106 via the user interface device.

[0036] Although the above description has focused on the heater 104 and the gas purge subsystem 105 placed in communication with one or more processors 108, this configuration does not limit the scope of the embodiments of the present disclosure. In an embodiment, the heating protocol or the gas purge protocol described herein may be input by the user into the memory 110 of the controller 106 via the user interface. In this regard, the heating and gas purging described previously herein may be implemented according to the protocol input into the memory 110 via the user interface.

[0037] One or more processors 108 of the controller 106 may include any one or more processing elements known in the art. In this sense, one or more processors 108 may include any microprocessor-type device configured to execute software algorithms and / or instructions. In an embodiment, one or more processors 108 may consist of a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, or other computer systems (such as networked computers) configured to execute programs configured to operate the system 100, as described throughout this disclosure. It should be appreciated that the steps described throughout this disclosure may be performed by a single computer system or alternatively by multiple computer systems. Generally, the term "processor" may be broadly defined to cover any device having one or more processing elements that execute program instructions from a non-transitory memory medium 110. Additionally, different subsystems of the system 100 (such as the heater 104, the gas purge subsystem 105, or the user interface) may include processors or logic elements suitable for performing at least part of the steps described throughout this disclosure.

[0038] The memory medium 110 may include any memory medium known in the art suitable for storing program instructions executable by one or more associated processors 108. For example, the memory medium 110 may include, but is not limited to, read-only memory, random access memory, magnetic or optical memory devices (such as magnetic disks), magnetic tapes, solid-state drives, and the like. In an embodiment, the memory medium 110 is configured to store one or more results from the heater 104, the gas purge subsystem 105, and / or the outputs of the various data processing steps described herein. It should be further noted that the memory medium 110 may be housed together with one or more processors 108 in a common controller housing. In an embodiment, the memory medium 110 may be remotely located relative to the physical location of the processor and the controller 106. For example, one or more processors 108 of the controller 106 may access a remote memory (such as a server) that can be accessed via a network (such as the Internet, an intranet, and the like).

[0039] It should be further noted that although Figure 1 the controller 106 is depicted as being embodied separately from the heater 104 and the gas purge subsystem 105, this configuration of the system 100 does not limit the scope of the present disclosure but is for illustrative purposes only. For example, the controller 106 may be embodied as the controller of the heater 104 and the gas purge subsystem 105.

[0040] The user interface device may include any user interface known in the art. For example, the user interface may include, but is not limited to, a keyboard, a keypad, a touch screen, a joystick, a knob, a roller, a trackball, a switch, a dial, a slider, a scroll bar, a slide, a handle, a touchpad, a fin, a steering wheel, a gamepad, a bezel input device, or the like.

[0041] Figure 5 The process flow diagram illustrates a method 500 for bonding a first optical element 101 to a substrate 102. In an embodiment, the method 500 includes a step 502 of receiving the first optical element 101 and the substrate 102. In an embodiment, the method 500 includes a step 504 of positioning an indium foil 200 between the optical element 101 and the substrate 102.

[0042] In an embodiment, the method includes a step 506 of clamping (e.g., fixing, fastening, attaching) a first optical element 101 to a substrate 102, wherein clamping the first optical element 101 to the substrate 102 produces a pre-bonded assembly 220, wherein an indium foil 200 is sandwiched (e.g., placed) between the first optical element 101 and the substrate 102. Clamping the first optical element 101 to the substrate 102 includes a clamping force. The clamping force can include, but is not limited to, clamping with a vertical clamping force of about 5 N or less, about 10 N, about 15 N, or about 20 N or 30 N or more. The clamping force can further include, but is not limited to, clamping with a horizontal holding force of about 3.0 N or less, about 4.5 N, or about 6.0 N or more. For example, clamping the first optical element 101 and the substrate 102 (e.g., clamping a CaF2 PBSC and a metal mount) can include a vertical clamping force of 15 N and a horizontal holding force of 4.5 N.

[0043] In an embodiment, the method 400 includes a step 508 of heating the pre-bonded assembly 220 (e.g., the pre-bonded assembly 220 including the first optical element 101, the substrate 102, and the indium foil 200) to a temperature above the melting temperature of the indium foil (e.g., 156 °C). The heating can include any heating point or range of heating points disclosed herein. For example, step 508 of method 500 can include heating the pre-bonded assembly 220 to 165 °C by a heating ramp protocol that raises the temperature of the pre-bonded assembly 220 at about 1 °C / min. After reaching the target temperature, the pre-bonded assembly 220 can be maintained (e.g., held) at the target temperature for a predetermined soak or hold time. The soak time can be about 1 hour or less, about 2 hours, about 3 hours, about 4 hours, about 5 hours, or about 6 hours or more. For example, the pre-bonded assembly 220 can be held at 165 °C for 4 hours.

[0044] In an embodiment, the method 400 includes a step 510 of cooling the pre-bonded assembly 220 (e.g., to room temperature). Cooling the pre-bonded assembly 220 can include the ramp protocol described herein. For example, the pre-bonded assembly 220 can be cooled at a rate of 1 °C / min. In an embodiment, the method includes a step 512 of releasing the pre-bonded assembly 220, wherein releasing the pre-bonded assembly 220 releases a bonded structure (e.g., including the first optical element 101, the substrate 102, and the indium foil 200 bonded together). The bonded structure can then be incorporated into an appropriate optical system.

[0045] In an embodiment, a device is disclosed. The device includes a bonding structure made of a first optical element 101, a substrate 102, and indium foil 200, wherein the first optical element 101 is bonded to the substrate 102 via the indium foil. The first optical element 101 may include any optical type or material disclosed herein. For example, the first optical element 101 of the bonding structure may include CaF2, such as a CaF2 beam splitter. The substrate 102 of the bonding structure may include a metal, such as aluminum, nickel, or nickel-plated aluminum.

[0046] In an embodiment, the bonding structure has a natural frequency greater than that of a device having the same components (such as the first optical element 101 and the substrate 102) but bonded by other methods (such as clamping without using a bonding element (such as indium foil 200)). The bonding structure may have a natural frequency higher than 300 Hz, higher than 500 Hz, higher than 750 Hz, or higher than 1 kHz. For example, although a pre-bonded assembly without indium foil 200 may have a natural frequency below 300 Hz, the bonding structure of the present disclosure will have a natural frequency higher than 1 kHz. Devices with higher natural frequencies are generally more stable than devices with lower natural frequencies.

[0047] The bonding structure of the present disclosure has several advantages over bonding assemblies of the following techniques.

[0048] In terms of mechanical clamping, optical components are held using spring flexures, spring caps, or otherwise by mechanical members such as flexures and fixing screws. Even though mechanical clamping is a common method of mounting the first optical element 101 to the substrate 102, these mounts require careful design to reduce the clamping force, especially for single crystals (such as CaF2 or MgF2), to avoid stress-induced birefringence or damage to the optical device, while maintaining optical alignment during tool or spare part transportation where these parts will experience vibrations on the order of 10G to 25G. These are conflicting requirements because a weaker clamping force can lead to misalignment during transportation and handling, while a strong clamping force can lead to degradation of optical performance or peeling and cracking of the optical components. Degradation of optical performance can lead to stress-induced birefringence and induced wavefront errors. In addition, the resulting natural frequency of the bonding structure produced by mechanical clamping is typically limited to <300 Hz.

[0049] For epoxy bonding, the ends of the optical components and optomechanical parts are coated with a thin layer of epoxy, brought into contact, and then cured at room temperature over time or by heat or UV light. In deep ultraviolet (DUV) optical systems, epoxy bonding needs to be carefully designed to avoid exposing the epoxy to any scattered or direct DUV. Any exposure to UV light will cause outgassing, resulting in optical contamination damage, and the epoxy bond strength will also be severely impaired by UV exposure. This typically involves designing metal shields against scattered light and / or additional reflective coatings to protect the epoxy-bonded components from scattered light. In addition, epoxy-bonded components are not easily reworked. Epoxies generally have a coefficient of thermal expansion (CTE) of thermal mismatch, which can cause bond failure and temperature fluctuations.

[0050] For optical bonding, two optical components are polished smooth on at least one surface, and the two optically polished surfaces are brought into close contact at room temperature. Under these extremely smooth conditions, van der Waals and other interatomic and intermolecular forces are maximized, and thus a bond is formed by the attraction of atoms and molecules between the surfaces. Optical bonding can be further improved by chemical activation and diffusion bonding. Optical bonding has limited success and is very expensive in bonding optical devices to metal components because optically polished surfaces are required and the surfaces usually need to be further chemically activated to produce a strong bond. Chemical activation can also cause optical contamination damage.

[0051] For indium bonding / welding, indium or other low-temperature eutectic alloys are typically used to weld a chipset or wafer to a heat sink or other substrate. This technique also uses a flux to assist in the welding. However, indium welding cannot be used to bond high-throughput optical devices because the welding produces local heating, which can cause thermally induced stresses in the bulk of the glass / single crystal. For coated (anti-reflection, reflective, or polarizer coating) optical devices, local heating and thermal stress are likely to damage the optical coatings. There is also a risk of gas fumes from the thermally welded components and the flux contaminating the optical devices and coatings optically.

[0052] In an embodiment, method 400 includes the step of purging the pre-bond assembly 220 with an inert gas (e.g., via the gas purge subsystem 105). For example, AMC-filtered ultra-pure N2 gas can be used to purge the pre-bond assembly 220 at a rate of 0.5 L / min.

[0053] In an embodiment, method 400 includes the step of reworking the bonded structure. For example, the bonded structure can be heated to a temperature above the melting point of the indium foil. After the indium foil melts, the bonded structure will be easily separated into the first optical element 101 and the substrate 102. Then, the first optical element 101 and the substrate that are separated at this moment can be reassembled into a new pre-bond assembly 220 as described herein.

[0054] While embodiments of method 400 are discussed herein, it should be further considered that the various steps of method 400 can be included, excluded, rearranged, and / or implemented in many ways without departing from the essence of the present disclosure. Accordingly, the above examples and embodiments of method 400 are included only as examples and are in no way intended to limit the present disclosure.

[0055] All methods described herein can include storing the result of one or more steps of a method embodiment in a memory medium. The result can include any result described herein and can be stored in any manner known in the art. The memory medium can include any memory medium described herein or any other suitable memory medium known in the art. After storing the result, the result can be accessed in the memory medium and used by any of the methods or system embodiments described herein, formatted for display to a user, used by another software module, method, or system, and so on. Additionally, the result can be stored "permanently", "semi-permanently", "temporarily", or for a certain period of time. For example, the memory medium can be random access memory (RAM) and the result may not remain in the memory medium indefinitely.

[0056] Upon further consideration, each of the embodiments of the above methods can include any other steps of any other method described herein. Additionally, each of the embodiments of the above methods can be performed by any of the systems described herein.

[0057] As described in the present disclosure, bonding the first optical component 101 to the substrate 102 is performed in an AMC controlled environment with (<0.1 ng / L total outgassing) with an inert N2 purge gas. This ensures an ultra-clean environment during the high-temperature bonding process. The N2 gas is used to ensure that the oxygen stoichiometry remains constant in the optical coatings (e.g., oxides such as SiO2, HfO2, Al2O3).

[0058] As disclosed herein, the bonding temperature is maintained equal to or close to 165 °C, which is lower than 350 °C for the dense IBS optical coatings (antireflective or highly reflective) on the optical surface. The slow slope (0.5 °C / min to 1 °C / min) ensures that a single crystal such as CaF2 remains optically homogeneous or has a negative impact on the optical quality of the optical coating. For example, the slope can protect sensitive optical and metal surfaces used in DUV and extreme ultraviolet (EUV) applications during the bonding process to reduce the risk of light contamination. The slow heating and cooling slopes (e.g., 0.5 °C to 1 °C) ensure that the first optical element 101 is thermally bonded to the substrate 102. This significantly reduces the thermal stress in the single crystal optical element (e.g., but not limited to CaF2, MgF2, BBO, and CLBO crystals). This ensures that the optical element has little to no degradation in optical performance.

[0059] The ductility of indium foil 200 allows materials with different coefficients of thermal expansion (CTE) to be joined together. Indium is prone to deformation under pressure, fills the voids between two surfaces, and can be used at low temperatures. No surface preparation or polishing is required to join two surfaces. Unlike epoxy resins, indium metal is not affected by scattered DUV light and does not outgas. The resulting indium foil bond is not affected by scattered DUV light. Indium foil also provides excellent thermal contact between optical devices and other optical devices or mechanical components, and joined indium components can be reprocessed or manipulated by reheating to above 156 °C. Using indium foil 200, various optical materials such as fused silica, CaF2, MgF2, and nonlinear optical crystals (such as BBO, CLBO) can be joined to metals such as Ni-plated aluminum, copper, stainless steel, or other optical materials. The slope and heat soak time may need to be optimized for joining different materials.

[0060] Those skilled in the art should recognize that devices and / or processes in the art are typically described in the manner set forth herein and then engineering practices are used to integrate such described devices and / or processes into a data processing system. That is, at least portions of the devices and / or processes described herein can be integrated into a data processing system with a reasonable amount of experimentation. Those skilled in the art should recognize that a typical data processing system generally includes one or more of the following: a system unit housing, a video display device, memory (such as volatile and non-volatile memory), a processor (such as a microprocessor and a digital signal processor), a computing entity (such as an operating system), a driver, a graphical user interface and application programs, one or more interaction devices (such as a touchpad or a screen), and / or a control system that includes feedback loops and control motors (such as for sensing position and / or speed feedback; control motors for moving and / or adjusting components and / or amounts). A typical data processing system can be implemented using any suitable commercially available components (such as those commonly available in data computing / communication and / or network computing / communication systems).

[0061] The subject matter described herein sometimes illustrates different components that are included within or connected to different other components. It should be understood that such a depicted architecture is merely exemplary, and in fact, many other architectures that achieve the same functionality can be implemented. In a conceptual sense, any arrangement of components that achieve the same functionality is effectively "associated" such that the desired functionality is achieved. Thus, regardless of the architecture or intermediate components, any two components that are combined herein to achieve a particular functionality can be considered to be "associated" with each other such that the desired functionality is achieved. Similarly, any two components so associated can also be considered to be "operably connected" or "operably coupled" to each other to achieve the desired functionality, and any two components that can be so associated can also be considered to be "operably coupled" to each other to achieve the desired functionality. Specific instances of "operably coupled" include, but are not limited to, components that can physically mate and / or physically interact and / or can wirelessly interact and / or wirelessly interact and / or logically interact and / or can logically interact.

[0062] Those skilled in the art should understand that, generally speaking, the terms used in this text and especially in the appended claims (e.g., the body of the appended claims) are generally intended to be "open" terms (e.g., the term "including" should be interpreted as "including but not limited to", the term "having" should be interpreted as "having at least", the term "include" should be interpreted as "including but not limited to", etc.). Those skilled in the art should further understand that if a specific number of the recited claims is intended, then this intention will be explicitly recited in the claims, and in the absence of such a recitation, there is no such intention. For example, for the sake of assisting understanding, the following appended claims may contain the use of introductory phrases such as "at least one" and "one or more" to introduce the claim recitations. However, the use of such phrases should not be construed as implying that any particular claim that introduces a claim recitation by the indefinite article "a" or "an" limits the invention of this introduced claim recitation to an invention containing only one such recitation, even when the same claim contains an introductory phrase "one or more" or "at least one" and an indefinite article (e.g., "a" and / or "an") (e.g., "a" and / or "an" should generally be interpreted as meaning "at least one" or "one or more"); the same is true for the use of the definite article to introduce a claim recitation. Additionally, even if a specific number of the introduced claim recitation is explicitly recited, those skilled in the art will still recognize that this recitation is generally to be interpreted as meaning at least the recited number (e.g., the mere recitation of "two recitations" without other modifiers generally means at least two recitations, or two or more recitations). Furthermore, in those examples where conventional expressions similar to "at least one of A, B, and C, etc." are used, generally this construction is intended in the sense that those skilled in the art will understand the meaning of the conventional expression (e.g., "a system having at least one of A, B, and C" will include but not be limited to a system having only A, only B, only C, A and B simultaneously, A and C simultaneously, B and C simultaneously, and / or A, B, and C simultaneously, etc.). In those examples where conventional expressions similar to "at least one of A, B, or C, etc." are used, generally this construction is intended in the sense that those skilled in the art will understand the meaning of the conventional expression (e.g., "a system having at least one of A, B, or C" will include but not be limited to a system having only A, only B, only C, A and B simultaneously, A and C simultaneously, B and C simultaneously, and / or A, B, and C simultaneously, etc.). Those skilled in the art will further understand that, regardless of whether in the description, claims, or drawings, almost any disjunctive conjunction and / or phrase presenting two or more alternatives should be understood as contemplating the possibility of including one of the items, any one of the items, or both. For example, the phrase "A or B" will be understood as including the possibilities of "A" or "B" or "A and B".

[0063] Although specific aspects of the subject matter of the invention described herein have been shown and described, those skilled in the art will understand that, based on the teachings herein, changes and modifications can be made without departing from the subject matter described herein and its broader aspects, and accordingly the appended claims are intended to cover all such changes and modifications within their scope, as within the true spirit and scope of the subject matter described herein. In addition, it should be understood that the invention is defined by the appended claims.

Claims

1. A method for bonding a first optical element to a substrate, comprising: Receiving the first optical element and the substrate; Positioning an indium foil between the first optical element and the substrate; Fixing the first optical element to the substrate to produce a pre-bonded assembly, wherein the indium foil is disposed between the first optical element and the substrate; Heating the pre-bonded assembly to a temperature higher than the melting temperature of the indium foil; Cooling the pre-bonded assembly; And Releasing the pre-bonded assembly, wherein releasing the pre-bonded assembly releases a bonding structure.

2. The method according to claim 1, further comprising purging the pre-bonded assembly with an inert gas.

3. The method according to claim 1, further comprising reprocessing the bonding structure.

4. The method according to claim 3, wherein reprocessing the bonding structure includes heating the bonding structure to a temperature higher than the melting temperature of the indium foil.

5. The method according to claim 1, wherein the substrate includes a metal layer.

6. The method according to claim 1, wherein the first optical element includes CaF2.

7. The method according to claim 1, wherein the substrate includes a second optical element.

8. The method according to claim 1, wherein heating the pre-bonded assembly to a temperature higher than the melting temperature of the indium foil includes heating the pre-bonded assembly to a range of 102 to 156 °C to 175 °C.

9. The method according to claim 1, wherein heating the pre-bonded assembly to a temperature higher than the melting temperature of the indium foil includes heating the pre-bonded assembly to 165 °C.

10. The method according to claim 9, wherein heating the pre-bonded assembly to 165 °C for 4 hours.

11. The method according to claim 1, wherein the indium foil includes more than 99.99% indium.

12. The method according to claim 1, wherein the indium foil has a thickness of 50 μm.

13. A system for bonding a first optical element to a substrate, comprising: A bottom plate configured to receive a plurality of holding elements and configured to receive the first optical element and the substrate; A heating element thermally coupled to the bottom plate; And A top plate coupled to the tops of the plurality of holding elements, wherein tightening the plurality of holding elements into the bottom plate increases the clamping force on the first optical element and the substrate.

14. The system according to claim 13, further comprising: A container configured to accommodate the bottom plate and the top plate, the container including: An input purge line; and An output purge line.

15. The system according to claim 14, further comprising an air filter configured to be in line with the input purge line.

16. The system according to claim 13, further comprising a thermometer and a temperature controller.

17. An apparatus, comprising: A first optical element; A substrate; And An indium foil, wherein the first optical element is bonded to the substrate via the indium foil.

18. The apparatus according to claim 17, wherein the first optical element includes CaF2.

19. The device according to claim 17, wherein the substrate comprises a metal.

20. The device according to claim 19, wherein the substrate comprises nickel.

21. The device according to claim 17, wherein the device comprises a natural frequency greater than 1 kHz.

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