Optical component for a deep ultraviolet light source

Abstract

An optical component includes a calcium fluoride substrate including an atomically-smooth substrate surface forming at least a portion of an optical interaction surface, and an encapsulant layer covering the atomically-smooth substrate surface forming a smooth interface between the calcium fluoride substrate and the encapsulant layer. A profile roughness parameter Ra of the atomically-smooth substrate surface is in a range from 0.01 nanometers (nm) to 0.17 nm, inclusive, the profile roughness parameter Ra being defined as an average deviation of a profile of the atomically-smooth substrate surface.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Application No. 63 / 107,827, entitled "Optical Components for Deep Ultraviolet Light Sources," filed October 30, 2020, and U.S. Application No. 63 / 163,348, entitled "Optical Components for Deep Ultraviolet Light Sources," filed March 19, 2021, each of which is incorporated herein by reference. Technical Field

[0003] The disclosed subject matter relates to an optical component for a deep ultraviolet light source that is more optically robust. Background Technology

[0004] A gas discharge source used in photolithography is called an excimer laser or excimer laser. Typically, an excimer laser uses a combination of one or more rare gases and reactive gases, where the rare gases may include argon, krypton, or xenon, and the reactive gas may include fluorine or chlorine. An excimer laser can generate excimers, i.e., pseudomolecules, under appropriate electrical simulation (the supplied energy) and high-pressure conditions (of the gas mixture). The excimers in the excited state produce amplified light in the ultraviolet range. An excimer laser source can use a single gas discharge chamber or multiple gas discharge chambers. When the excimer laser source is operating, it produces a deep ultraviolet (DUV) beam. DUV light can include wavelengths, for example, from approximately 100 nanometers (nm) to approximately 400 nm. Summary of the Invention

[0005] In some general aspects, an optical component includes a calcium fluoride substrate comprising an atomically smooth substrate surface forming at least a portion of an optically interacting surface; and a sealant layer covering the atomically smooth substrate surface to form a smooth interface between the calcium fluoride substrate and the sealant layer. The profile roughness parameter Ra of the atomically smooth substrate surface is in the range of 0.01 nanometers (nm) to 0.17 nm and is defined as the average deviation of the profile of the atomically smooth substrate surface.

[0006] Each implementation may include one or more of the following features. For example, another profile roughness parameter Rz of the atomically smooth substrate surface may be in the range of 1.0 nm to 1.6 nm, and this profile roughness parameter Rz is defined as the average of the peak and valley heights of the profile within a selected sampling length of the atomically smooth substrate surface.

[0007] Optical components can be configured for beams with a wavelength of 193 nm. These optical components can be windows of a gas discharge chamber, beam reversers, beam expanders, output couplers, or beam splitters. Optical components can also be configured for beams with wavelengths in the deep ultraviolet range.

[0008] The sealant layer can be configured to prevent the depletion of fluorine in the calcium fluoride substrate.

[0009] Atomic-smooth substrate surfaces can actually be formed using accelerated neutral atom beams. Forming atomically smooth substrate surfaces excludes (i.e., does not include) mechanical processing, ionized plasma treatment, or chemical etching. Atomic-smooth substrate surfaces are likely free of defects, scratches, contaminant particles, and subsurface damage.

[0010] In other general aspects, an optical system for deep ultraviolet (DUV) optical lithography includes a gas discharge system comprising one or more gas discharge chambers, each containing an energy source and a gas mixture including a gain medium; and one or more optical components associated with the gas discharge system. Each optical component includes a substrate having an atomically smooth substrate surface forming at least a portion of an optically interacting surface; and a protective layer configured to mitigate or prevent at least partial damage to the atomically smooth substrate surface caused by DUV light irradiation, the protective layer being deposited on the atomically smooth substrate surface to form a smooth interface between the substrate and the protective layer.

[0011] Various implementations may include one or more of the following features. For example, a gas discharge system may include two discharge chambers, each including a master oscillator configured to generate a pulsed seed beam; and a power amplifier configured to generate a pulsed output beam from the seed beam. At least one of the optical components may be configured to feed the pulsed seed beam from the master oscillator to the power amplifier.

[0012] Optical components may be a window of a gas discharge chamber within a gas discharge chamber, a beam reverser, a beam expander prism, an output coupler, or a beam splitter.

[0013] The profile roughness Ra of an atomically smooth substrate surface may range from 0.01 nanometers (nm) to 0.17 nanometers and is defined as the average deviation of the profile of an atomically smooth substrate surface.

[0014] Atomic-smooth substrate surfaces can actually be formed using accelerated neutral atom beams. Atomic-smooth substrate surfaces are likely free of defects, scratches, contaminant particles, and subsurface damage.

[0015] In other general aspects, a method is provided for mitigating or preventing damage to the optical surfaces of optical components in a deep ultraviolet (DUV) light source. The method includes: providing a substrate including a substrate surface forming at least a portion of the optical surface of the optical component; smoothing the substrate surface by bombarding it with at least one accelerated neutral atom beam; and after smoothing the substrate surface, depositing a protective layer onto the substrate surface such that an interface is formed between the substrate and the protective layer, the protective layer being configured to mitigate or prevent damage to the optical surface.

[0016] Each implementation may include one or more of the following features. For example, the substrate surface can be smoothed by removing high regions at the substrate surface and leaving low regions at the substrate surface. The substrate surface can be smoothed by reducing the surface profile roughness Ra to a value below and including 0.17 nanometers (nm).

[0017] The material removal rate can be adjusted to impact the substrate surface, depending on the atomic cluster density and processing time. Impacting the substrate surface using at least one accelerated neutral atom beam can include: impacting the substrate surface with a different accelerated neutral atom beam in each of a series of steps. Furthermore, the material removal rate can be adjusted at each impact step. The material removal rate can range from 0.3 nanometers per step to 30 nanometers per step.

[0018] The substrate can be made of calcium fluoride.

[0019] The substrate surface can be smoothed by bombarding it with at least one accelerated neutral atom beam until the profile roughness Ra of the substrate surface is in the range of 0.01 nm to 0.17 nm and inclusive. The profile roughness Ra is defined as the average deviation of the substrate surface profile.

[0020] The optical components can be configured for a beam with a wavelength of 193 nm. The optical components can be windows of a gas discharge chamber, beam reversers, beam expanding prisms, output couplers, or beam splitters.

[0021] A substrate surface can be smoothed by removing a redeposited layer formed during mechanical polishing prior to surface smoothing. Substrate surfaces can also be smoothed by removing subsurface damage, scratches, defects, and contaminant particles. Furthermore, substrate surfaces can be smoothed by removing damage and defects without introducing additional damage or defects.

[0022] In other general aspects, an optical component includes a calcium fluoride substrate having a smooth substrate surface that forms at least a portion of an optically interactive surface; and a sealant layer deposited on the smooth substrate surface. The smooth substrate surface is actually formed using an accelerated neutral atom beam.

[0023] Each implementation may include one or more of the following features. For example, the profile roughness Ra of a smooth substrate surface may be in the range of 0.01 nanometers (nm) to 0.17 nm and inclusive, and the profile roughness Ra is defined as the average deviation of the profile of the smooth substrate surface.

[0024] The sealant layer can be configured to prevent the depletion of fluorine in the calcium fluoride substrate.

[0025] Optical components can be configured for beams with wavelengths in the deep ultraviolet range. Optical components can also be configured for beams with a wavelength of 193 nm. These optical components can be windows of a gas discharge chamber, beam reversers, beam expanding prisms, output couplers, or beam splitters.

[0026] Forming a smooth substrate surface can exclude (that is, not include) mechanical processing, ionized plasma processing, or chemical etching.

[0027] In other general aspects, the optical component is actually formed using a process comprising: providing a substrate including a substrate surface that forms at least a portion of the optical surface of the optical component; smoothing the substrate surface by bombarding it with at least one accelerated neutral atom beam; and after smoothing the substrate surface, depositing a protective layer on the substrate surface such that an interface is formed between the substrate and the protective layer, the protective layer being configured to mitigate or prevent damage to the optical surface. Attached Figure Description

[0028] Figure 1 This is a block diagram of an optical system that generates a light beam. The optical system includes a gas discharge system, which includes one or more gas discharge chambers and one or more optical components.

[0029] Figure 2A yes Figure 1A side cross-sectional view of the substrate of the optical component after it has been treated with an accelerated neutral atom beam.

[0030] Figure 2B yes Figure 2A A perspective view of the substrate.

[0031] Figure 3A yes Figure 1 The optical components are treated with an accelerated neutral atom beam to form an atomically smooth substrate surface, and a protective layer is applied to the atomically smooth substrate surface. This is a side cross-sectional view.

[0032] Figure 3B yes Figure 3A A perspective view of the optical components.

[0033] Figure 4 It is used to form Figure 1 , Figure 3A and Figure 3B A flowchart of the process for manufacturing optical components.

[0034] Figure 5A It shows Figure 4 A schematic diagram of a cross-sectional view of a substrate treated with an accelerated neutral atom beam during the process.

[0035] Figure 5B yes Figure 5A A schematic diagram of a cross-sectional view of the substrate after it has been treated with an accelerated neutral atom beam.

[0036] Figure 6A It shows Figure 4 A schematic diagram of a cross-sectional view of a substrate, including the damaged layer and the redeposited layer, processed by an accelerated neutral atom beam during the process.

[0037] Figure 6B yes Figure 6A A schematic cross-sectional view of a substrate including a damaged layer after a redeposited layer has been removed using an accelerated neutral atom beam.

[0038] Figure 6C yes Figure 6A A schematic diagram of a cross-sectional view of the substrate after treatment with an accelerated neutral atom beam to remove the redeposited layer and the damaged layer.

[0039] Figure 7A It is a gas discharge system comprising two gas discharge chambers. Figure 1 The implementation method of optical systems and Figure 1 The implementation of the optical components is shown in a cross-sectional view on the XZ plane.

[0040] Figure 7Byes Figure 7A In the main view of the optical components in the XY plane, one of the optical components is held... Figure 7A Inside the chamber wall of one of the gas discharge chambers.

[0041] Figure 7C It is kept inside the chamber wall Figure 7B The optical component is shown in a cross-sectional view in the XZ plane taken along line 7C-7C'. Detailed Implementation

[0042] refer to Figure 1 The optical system 100 generates a light beam 105 (which may be an amplified beam) with a deep ultraviolet (DUV) spectral wavelength, which is used for DUV lithography in the photolithography exposure apparatus 110. Therefore, the wavelength of the light beam 105 is in the range of approximately 100 nanometers (nm) to approximately 400 nm. The optical system 100 includes a gas discharge system 115, which includes one or more gas discharge chambers 120 and one or more optical components 125. Any optical component in the optical components 125 may be associated with any gas discharge chamber 120 in the gas discharge chambers 120, or may be associated with other optical elements within the gas discharge system 115. Although Figure 1 A gas discharge chamber 120 and optical components 125 are shown, but there may be more than one gas discharge chamber 120 and more than one optical component 125. Each gas discharge chamber 120 includes an energy source 121 and contains a gas mixture 122, which includes a gain medium. For example, if the gain medium includes argon fluoride (ArF), the wavelength of the beam 105 is approximately 193 nm. The beam 105 may be a pulsed beam.

[0043] Each optical component 125 is configured to interact with a forward beam 104, which ultimately forms a beam 105 output from the gas discharge system 115. Therefore, the optical components 125 can be arranged at any suitable location within the gas discharge system 115. Depending on the location of the optical components 125, the forward beam 104 interacting with the optical components 125 can have the same energy and / or power as the beam 105, or it can have a different energy and / or power. In various cases, the forward beam 104 can be a beam circulating within a laser cavity. In any case, the forward beam 104 can be a pulsed beam, which can damage the optical components 125 over time. Therefore, the optical components 125 are made of a material capable of withstanding the high levels of flux applied to the optical components 125 when irradiated by the forward beam 104. For example, the beam 105 is a pulsed beam, which can have a pulse energy greater than, for example, 20 millijoules (mJ / s) per pulse. The optical components 125 can withstand up to 80 mJ / cm per pulse. 2 Flux. For example, in some implementations, optical component 125 includes a substrate made of calcium fluoride (CaF2).

[0044] Over time, optical components 125 will be damaged by the illumination of the forward beam 104. This damage to optical components 125 will degrade the performance of the gas discharge system 115, thereby reducing the performance of the optical system 100 and shortening the lifespan of the gas discharge chamber 120. For example, if the substrate 126 of optical components 125 is made of CaF2, and at a specific wavelength of the forward beam 104, the optical interaction region 127 in optical components 125 may be damaged due to fluorine evaporation and crystal collapse caused by the forward beam 104 incident on the surface of the substrate of optical components 125. To reduce this damage, the substrate 126 of optical components 125 is coated with a sealant layer or protective layer 128, but even this protective layer 128 can eventually crack and cause localized surface damage on optical components 125.

[0045] To extend the lifetime of the optical component 125 (and the gas discharge chamber 120), the interface 129 between the protective layer 128 and the CaF2 substrate 126 should be as defect-free and clean as possible. For this purpose, the optical component 125 is fabricated using an accelerated neutral atom beam process.

[0046] Specifically, such as Figure 2A and Figure 2BAs shown, prior to coating the protective layer 128, an atomically smooth substrate surface 124 of the substrate 126 is actually formed or has already been formed using an accelerated neutral atom beam. At the atomically smooth substrate surface 124, the original lattice of the substrate material is exposed, that is, its lattice as it was initially grown. In other words, the surface 124 of the CaF2 substrate, where the interface 129 between the protective layer 128 and the CaF2 substrate 126 will ultimately form, is subjected to an impact or collision (e.g., from an accelerated neutral atom beam) of at least one accelerated neutral atom beam. Figure 5A As shown, this allows for the uniform and clean removal of the CaF2 thin layer (i.e., the substrate material) as well as defects and contaminants from surface 124 without adding additional damage to the surface or subsurface of substrate 126. Thus, surface 124 of substrate 126 is formed as an atomically smooth substrate surface 124 free from these defects and contaminants that could damage optical components 125 and optical system 100.

[0047] An atomically smooth substrate surface 124 forms at least a portion of the optical interaction region 127 of the optical component 125. Specifically, the optical interaction region 127 is the region of the substrate 126 that interacts with the light beam 104. Therefore, the optical interaction region 127 includes all surfaces, materials, and interfaces that interact with the light beam 104. Since the optical component 125 is a transmission optics device, the light beam 104 interacts with the protective layer 128, the interface 129, the substrate surface 124, and even the substrate 126.

[0048] The atomically smooth substrate surface 124 has a profile roughness parameter Ra, which is defined as the average deviation of the profile of the atomically smooth substrate surface 124, and the average deviation is in the range of 0.01 nanometers (nm) to 0.17 nanometers (nm) and inclusive. In some implementations, the atomically smooth substrate surface 124 also has another profile roughness parameter Rz, which is defined as the average peak-valley height of the profile within a selected sampling length of the atomically smooth substrate surface 124, and the average value is in the range of 1.0 nm to 1.6 nm. Therefore, the atomically smooth substrate surface 124 is free from defects, damage, scratches, and contaminants that can damage the optical component 125 and cause degradation of the optical system 100 over time. Because the atomically smooth substrate surface 124 is actually formed using accelerated neutral atom beam treatment (rather than alternatively using chemical etching, mechanical treatment, or ionized plasma treatment), processing and forming this atomically smooth substrate surface 124 does not introduce additional damage to the surface of the substrate 126. In other words, the final smoothing step in forming the atomically smooth substrate surface 124 does not include mechanical treatment, ionized plasma treatment, or chemical etching. Therefore, the atomically smooth substrate surface 124 contains little or no defects, scratches, contaminant particles, and subsurface damage.

[0049] In addition, such as Figure 3A and Figure 3B As shown, when the protective layer 128 covers (or is deposited) on the atomically smooth substrate surface 124, the interface 129 is formed as a smooth (or atomically smooth) interface 129 between the surface 124 of the CaF2 substrate 126 and the protective layer 128. This interface 129 is free of defects and contaminants, thereby extending the lifespan of the optical components 125 and the optical system 100.

[0050] refer to Figure 4 The process 430 is performed to mitigate or prevent damage to the surface 124 (within the optical region 127) of the optical component 125 in the optical system 100 (or DUV source). This is for the optical component 125 in the optical system 100 (…). Figures 1 to 3B ) Surface 124, execute step 430.

[0051] The process 430 includes: providing (431) a substrate 126 ( Figure 5A The substrate 126 includes a raw substrate surface 443, which, once processed and smoothed, forms at least a portion of the optical interaction region 127 of the optical component 125. For example, as Figure 5A As shown, substrate 126 can be made of calcium fluoride (CaF2).

[0052] Before the pristine substrate surface 443 is smoothed using an accelerated neutral atom beam treatment, the substrate 126 may have scratches, defects, damage, and / or contaminants on the pristine substrate surface 443, caused by, for example, mechanical polishing or chemical etching, as described below. Figure 6A The polishing of substrate 126, as discussed, leaves a damaged thin layer (e.g., Figure 6A The subsurface damaged layer 626d in the substrate 126 consists of a fractured, mechanically stressed material. Additionally, after polishing, polishing compounds, other process contaminants, and moisture may remain on the original substrate surface 443 (e.g., thus forming a layer such as...). Figure 6A The redeposited layer 626r is shown. Therefore, without additional remedial steps (using the accelerated neutral atom beam treatment discussed below), any protective layer 128 applied to the substrate 126 adheres to the potentially contaminated substrate 126, which is broken in different forms. Without smoothing the original substrate surface 443 to form a smooth substrate surface 124, the imperfect interface formed between the substrate 126 and the protective layer 128 may cause changes in the effectiveness of the protective layer 128 in protecting the substrate 126 (and substrate surface 124).

[0053] like Figure 5A As shown, the original substrate surface 443 is smoothed (433) by bombarding the original substrate surface 443 with at least one accelerated neutral atom beam 440. The accelerated neutral atom beam is scanned in the X and Y directions to interact with and smooth the entire original substrate surface 443, thereby forming a smooth substrate surface 124. Figure 5B Each accelerated neutral atom beam 440 can be appropriately adjusted to uniformly and cleanly remove the thin layer from the original substrate surface 443, thereby forming an atomically smooth substrate surface 124. Figure 5B For example, for each accelerated neutral atom beam 440 interacting with the original substrate surface 443, one or more of the following can be adjusted: cluster density, energy, beam flux, and atom type. Additionally, the processing time for the accelerated neutral atom beam 440 to interact with the original substrate surface 443 (and any intermediate surfaces formed before forming the smooth substrate surface 124) can be adjusted. Furthermore, in these ways, the material removal rate of the CaF2 substrate 126 at the original substrate surface 443 can be adjusted. Smoothing the substrate surface (433) can include removing the high region 441 at the original substrate surface 443 while leaving the low region 442 at the original substrate surface 444.

[0054] Also refer to Figures 6A to 6CThe original substrate surface 443 of the bulk material 626b of substrate 126 is shown. Smoothing the original substrate surface 443 to form a smooth substrate surface 124 (433) may include: removing the redeposited layer 626r at the original substrate surface 443 of substrate 126. Figure 6A Before forming a smooth substrate surface 124 in process 430, a redeposited layer 626r is formed during mechanical polishing of the substrate surface. Thus, the redeposited layer 626r includes or is formed of at least partially polishing impurities 645 (shown as solid stars) generated during the mechanical polishing process. Furthermore, the original substrate surface 443 can be smoothed, for example, by removing subsurface damage, scratches, defects, and contaminant particles from the original substrate surface 443. Alternatively or additionally, smoothing the original substrate surface 443 (433) can include removing a subsurface damaged layer 626d also located on the original substrate surface 443a of the substrate 126. The damaged layer 626d includes subsurface damage and defects such as microcracks 646 (shown as wavy lines) and plastic scratches 647 (shown as triangles). Additionally, the original substrate surface 443 can be smoothed (433) by, for example, removing damage and defects from the original substrate surface 443 without adding additional damage or defects to the original substrate surface 443. Therefore, in some implementations, smoothing the substrate surface 443 (433) may include: removing the redeposited layer 626r ( Figures 6A to 6B ) or subsurface damaged layer 626d ( Figures 6B to 6C (or a combination thereof) such that the substrate surface 124 is formed in the bulk material 626b of the substrate 126, and there are no damage, defects or contaminant particles at the substrate surface 124.

[0055] The impact (433) on the pristine substrate surface 443 may include adjusting the material removal rate, which depends on the atomic cluster density within the accelerated neutral atom beam 440 and the processing time associated with how long the accelerated neutral atom beam 440 impacts the pristine substrate surface 443. In some implementations, impacting the pristine substrate surface 443 with at least one accelerated neutral atom beam 440 includes impacting the pristine substrate surface 440 with a different accelerated neutral atom beam at each step in a series of steps. In other words, the substrate surface 124 can be smoothed by repeatedly (sequentially) removing a thin layer from the pristine substrate surface 443 using a different accelerated neutral atom beam 440. The material removal rate may be adjusted at each impact step. For example, the rate of material removal from the pristine substrate surface 443 may range from 0.3 nanometers per step to 30 nanometers per step.

[0056] By performing accelerated neutral atom beam treatment on the pristine substrate surface 443 to form a smooth substrate surface 124 (before applying the protective layer 128), the pristine substrate surface 443 can be smoothed without increasing other subsurface damage or forming lattice pits (which could be caused by etching). Furthermore, when tested with a CaF2 substrate 126, the smoothness (433) has been shown not to preferentially remove fluorine, thus avoiding the formation of colloidal calcium nanoparticles. The formation of colloidal calcium nanoparticles is undesirable because they may cause absorption of light at a wavelength of 193 nm at the substrate 126.

[0057] If it is determined that the substrate surface 124 is smooth (435), then a protective layer 128 is deposited on the substrate surface 124 to form an interface 129 (437) between the substrate 126 and the protective layer 128, such as Figure 3A and Figure 3B As shown. The protective layer 128 mitigates or prevents damage to the surface 124. If the profile roughness parameter Ra of the substrate surface 124 is in the range of 0.01 nanometers (nm) to 0.17 nm and inclusive, and this profile roughness parameter Ra is defined as the average deviation of the profile of an atomically smooth substrate surface 124, then the substrate surface 124 can be determined to be smooth (or atomically smooth). If it is determined that the substrate surface 124 is not smooth (435), then process 430 continues in step 433. Process 430 can continue until the substrate surface 124 is determined to be smooth (or atomically smooth). Therefore, the interface 129 between the protective layer 128 and the CaF2 substrate 126 is free from damage, defects, scratches, and contaminants that could damage the optical component 125. This extends the lifespan of the optical component 125 and the light source 100.

[0058] refer to Figure 7A Optical system 100 ( Figure 1 The implementation 700 includes a gas discharge system 715, which includes two gas discharge chambers 720A and 720B and an optical component 125 associated with the gas discharge system 714. Figure 1 Implementations of the optical system 700 include 725A_1, 725A_2, 725A_3, 725B_1, 725B_2, and 725B_3. The optical system 700 is configured to generate a pulsed output beam 705o in the ultraviolet range for use, for example, by a photolithography exposure apparatus 710, for patterning a semiconductor substrate or wafer 762. In this implementation, a discharge chamber 720A forms a master oscillator configured to generate a pulsed seed beam 705s, and a discharge chamber 720B forms a power amplifier configured to generate the pulsed output beam 705o from the seed beam 705s. Other implementations of the optical system 700 are possible.

[0059] Each discharge chamber 720A, 720B is configured to hold a corresponding gas mixture 722A, 722B, including a gain medium, within a corresponding internal cavity 751A, 751B. The gas mixture 722A, 722B used in the corresponding discharge chambers 720A, 720B can be a combination of suitable gases for generating corresponding light beams 705s, 705o around the desired wavelength, bandwidth, and energy. For example, the gas mixture 722A, 722B may include argon fluoride (ArF), which emits light at a wavelength of approximately 193 nm. Each discharge chamber 401A, 401B is defined by corresponding chamber walls 753A, 754A, 753B, 754B. In operation, the chamber walls 753A, 754A, 753B, 754B of each discharge chamber 720A, 720B can be sealed to hermetically seal each internal cavity 751A, 751B. Each discharge chamber 720A, 720B contains a corresponding energy source 721A, 721B, which is configured to supply energy to the gas mixture 722A, 722B in each internal cavity 751A, 751B. For example, each energy source 721A, 721B may include a pair of electrodes that form a potential difference and excite the gain medium of the gas mixture 722A, 722B during operation.

[0060] Optical components 725A_1, 725A_2, and 725A_3 are associated with the master oscillator 720A, and optical components 725B_1, 725B_2, and 725B_3 are associated with the power amplifier 720B. Each of the optical components 725A_1, 725A_2, 725A_3, 725B_1, 725B_2, and 725B_3 is manufactured using an accelerated neutral atom beam process. Thus, each of the optical components 725A_1, 725A_2, 725A_3, 725B_1, 725B_2, and 725B_3 includes a substrate with an atomically smooth substrate surface, thereby forming a smooth interface between the protective layer and the substrate surface of each optical component 725A_1, 725A_2, 725A_3, 725B_1, 725B_2, and 725B_3. Each of the optical components 725A_1, 725A_2, 725A_3, 725B_1, 725B_2, and 725B_3 can be, for example, a window of one of the gas discharge chambers 720A and 720B, a beam reverser, a beam expanding prism, an output coupler, or a beam splitter. Figure 7AIn this implementation, each of the optical components 725A_1, 725A_2, 725A_3, 725B_1, 725B_2, and 725B_3 is configured for a light beam having a wavelength in the DUV range, such as a seed beam 705s or an output beam 705o. For example, each of the optical components 725A_1, 725A_2, 725A_3, 725B_1, 725B_2, and 725B_3 is configured for a light beam with a wavelength of 193nm, such as a seed beam 705s or an output beam 105.

[0061] In addition, refer to Figure 7B and Figure 7C Optical component 725A_1 is a window of the gas discharge chamber 720A (which forms the main oscillator). Optical component 725A_1 is arranged within an opening 755 of the chamber wall 753A of the main oscillator 720A. Window 725A_1 allows a light beam to enter and exit the internal cavity 751A of the gas discharge chamber 720A. Figure 7C Therefore, window 725A_1 is configured to feed the pulsed seed beam 705s from gas discharge chamber 720A to gas discharge chamber 720B.

[0062] Window 725A_1 (that is, the optical component) includes substrate 726 ( Figure 7C The substrate 726 includes an atomically smooth substrate surface 724. Figure 7C A protective layer 728 is provided, wherein the atomically smooth substrate surface 724 forms at least a portion of the optical interaction surface 727. The protective layer 728 is configured to mitigate or prevent damage to the atomically smooth substrate surface 724 caused at least partially by irradiation with DUV light (such as seed beams 705s). In one example, the substrate 726 may be made of CaF2, and the sealant or protective layer 728 may be configured to prevent depletion of fluorine in the substrate 726. By depositing the protective layer 728 on the atomically smooth substrate surface 724, a smooth interface 729 is formed between the substrate 726 and the protective layer 728. Because the window 725A_1 includes a substrate 726 with an atomically smooth substrate surface 724, the smooth interface 729 is free of defects and contaminants, thereby extending the lifetime of the window 725A_1 and the optical system 700. In another example, the optical component 725A_1 may be a partially reflective / partially transmittive optical coupler that enables the seed beam 705s to exit the gas discharge chamber 720A.

[0063] Moreover, in Figure 7AIn one implementation, optical component 725B_1 can be a window of gas discharge chamber 720B (which forms a power amplifier), disposed within an opening in the chamber wall 753B of the power amplifier 720B. Optical component 725B_1 allows light beams (such as seed beam 705s and output beam 705o) to enter and exit the internal cavity 751B of the gas discharge chamber 720B. In another example, optical component 725B_1 can be a partially reflective / partially transmissive optical coupler.

[0064] Optical components 725A_2 and 725B_2 may also be windows that allow the light beam to enter and exit the corresponding internal cavities 751A and 751B of the discharge chambers 720A and 720B. In this example, optical component 725A_2 is held within an opening in the chamber wall 754A, and optical component 725B_2 is held within an opening in the chamber wall 754B. Optical component 725A_3 may be a component of a spectral feature module that selects the wavelength and / or bandwidth of the seed beam 705s output from the gas discharge chamber 720A. In this example, optical component 725A_3 is arranged outside the gas discharge chamber 720A. For example, the spectral feature module 725A_3 may include one or more of a beam spreading prism or a beam splitter. Moreover, optical component 725B_3 may be a beam reverser or deflector configured to guide the seed beam 705s back through the gas discharge chamber 720B. In this example, the optical component 725B_3 is arranged outside the gas discharge chamber 720B.

[0065] During the operation of the optical system 700, optical components 725A_1, 725A_2, 725A_3, 725B_1, 725B_2, and 725B_3 may be damaged by irradiation from beams 705s and 705o. Damage to optical components 725A_1, 725A_2, 725A_3, 725B_1, 725B_2, and 725B_3 reduces the performance of the gas discharge system 715 and the optical system 700, thus shortening the lifespan of the gas discharge chambers 720A and 720B. To reduce this damage, each of the optical components 725A_1, 725A_2, 725A_3, 725B_1, 725B_2, and 725B_3 is manufactured using an accelerated neutral atom beam treatment. As described above, each of the optical components 725A_1, 725A_2, 725A_3, 725B_1, 725B_2, and 725B_3 includes a substrate comprising an atomically smooth substrate surface (such as...). Figure 7CThe substrate surface 724 is used to form a smooth interface between the protective layer and the substrate surface of each optical component 725A_1, 725A_2, 725A_3, 725B_1, 725B_2, and 725B_3. Because the atomically smooth substrate surface lacks defects, damage, scratches, and contaminants that could damage the corresponding optical components 725A_1, 725A_2, 725A_3, 725B_1, 725B_2, and 725B_3, the lifespan of the optical system 700 and the optical components 725A-1, 725A-2, 725A-3, 725B_1, 725B_2, and 725B_3 is extended.

[0066] The embodiments can be further described using the following terms:

[0067] 1. An optical component, comprising:

[0068] A calcium fluoride substrate, including an atomically smooth substrate surface that forms at least a portion of an optically interactive surface; and

[0069] A sealant layer covers an atomically smooth substrate surface, thereby forming a smooth interface between the calcium fluoride substrate and the sealant layer;

[0070] The profile roughness parameter Ra of the atomically smooth substrate surface ranges from 0.01 nanometers (nm) to 0.17 nanometers and includes 0.17 nanometers. This profile roughness parameter Ra is defined as the average deviation of the profile of the atomically smooth substrate surface.

[0071] 2. The optical component according to Clause 1, wherein another profile roughness parameter Rz of the atomically smooth substrate surface is in the range of 1.0 nm to 1.6 nm, and the profile roughness parameter Rz is defined as the average value of the peak and valley heights of the profile within a selected sampling length of the atomically smooth substrate surface.

[0072] 3. The optical component as described in Clause 1, wherein the optical component is configured for a light beam with a wavelength of 193 nm.

[0073] 4. The optical component as described in Clause 1, wherein the optical component is a window of a gas discharge chamber, a beam reverser, a beam expander prism, an output coupler, or a beam splitter.

[0074] 5. The optical component according to Clause 1, wherein the sealant layer is configured to prevent depletion of fluorine in the calcium fluoride substrate.

[0075] 6. The optical component as described in Clause 1, wherein the optical component is configured for a light beam with a wavelength in the deep ultraviolet range.

[0076] 7. The optical component according to Clause 1, wherein the atomically smooth substrate surface is actually formed by processing with an accelerated neutral atom beam.

[0077] 8. The optical component as described in Clause 7, wherein the formation of an atomically smooth substrate surface does not involve mechanical processing, ionized plasma treatment, or chemical etching.

[0078] 9. The optical component according to Clause 1, wherein the atomically smooth substrate surface is free from defects, scratches, contaminant particles and subsurface damage.

[0079] 10. An optical system for deep ultraviolet (DUV) optical lithography, the optical system comprising:

[0080] A gas discharge system includes one or more gas discharge chambers, each gas discharge chamber containing an energy source and comprising a gas mixture including a gain medium; and

[0081] One or more optical components are associated with a gas discharge system, wherein each optical component includes:

[0082] A substrate, including an atomically smooth substrate surface that forms at least a portion of an optically interactive surface; and

[0083] A protective layer, configured to mitigate or prevent at least part of the damage to an atomically smooth substrate surface caused by DUV light irradiation, is deposited on the atomically smooth substrate surface to form a smooth interface between the substrate and the protective layer.

[0084] 11. The optical system according to Clause 10, wherein the gas discharge system includes two discharge chambers, each discharge chamber including a master oscillator configured to generate a pulsed seed beam; and a power amplifier configured to generate a pulsed output beam from the seed beam.

[0085] 12. The optical system according to Clause 11, wherein at least one of the optical components is configured to feed a pulse seed beam from the master oscillator to the power amplifier.

[0086] 13. The optical system according to Clause 10, wherein the optical components are a window of a gas discharge chamber, a beam reverser, a beam expanding prism, an output coupler, or a beam splitter.

[0087] 14. The optical system according to Clause 10, wherein the profile roughness Ra of the atomically smooth substrate surface is in the range of 0.01 nanometers (nm) to 0.17 nanometers and inclusive, and the profile roughness Ra is defined as the average deviation of the profile of the atomically smooth substrate surface.

[0088] 15. The optical system according to Clause 10, wherein the atomically smooth substrate surface is actually formed by processing with an accelerated neutral atom beam.

[0089] 16. The optical system according to Clause 10, wherein the atomically smooth substrate surface is free from defects, scratches, contaminant particles and subsurface damage.

[0090] 17. A method for mitigating or preventing optical surface damage to optical components in a deep ultraviolet (DUV) light source, the method comprising:

[0091] A substrate is provided, the substrate including a substrate surface that forms at least a portion of the optical surface of an optical component;

[0092] The substrate surface is smoothed by bombarding it with at least one accelerated neutral atom beam; and

[0093] After smoothing the substrate surface, a protective layer is deposited onto the substrate surface, thereby forming an interface between the substrate and the protective layer, which is configured to mitigate or prevent damage to the optical surface.

[0094] 18. The method according to Clause 17, wherein smoothing the substrate surface comprises: removing high regions at the substrate surface and leaving low regions at the substrate surface.

[0095] 19. The method according to Clause 17, wherein smoothing the substrate surface comprises: reducing the surface profile roughness Ra to a value of less than and including 0.17 nanometers (nm).

[0096] 20. The method according to Clause 17, wherein impacting the substrate surface includes: adjusting the material removal rate depending on the atomic cluster density and the processing time.

[0097] 21. The method according to Clause 20, wherein impacting the substrate surface with at least one accelerated neutral atom beam comprises: at each of a series of steps, impacting the substrate surface with a different accelerated neutral atom beam from the accelerated neutral atom beam, and wherein at each impact step, the material removal rate is adjusted.

[0098] 22. The method according to Clause 21, wherein the material removal rate is in the range of 0.3 nanometers per step to 30 nanometers per step.

[0099] 23. The method according to Clause 17, wherein the substrate is made of calcium fluoride.

[0100] 24. The method according to Clause 17, wherein smoothing the substrate surface comprises: bombarding the substrate surface with at least one accelerated neutral atom beam until the profile roughness Ra of the substrate surface is in the range of 0.01 nm to 0.17 nm and including 0.17 nm, the profile roughness being defined as the average deviation of the profile of the substrate surface.

[0101] 25. The method according to Clause 17, wherein the optical components are configured for a light beam with a wavelength of 193 nm.

[0102] 26. The method according to Clause 17, wherein the optical component is a window of a gas discharge chamber, a beam reverser, a beam expander prism, an output coupler, or a beam splitter.

[0103] 27. The method according to Clause 17, wherein smoothing the substrate surface comprises: removing a redeposited layer at the substrate surface of the substrate, the redeposited layer being formed during mechanical polishing of the substrate surface prior to smoothing the substrate surface.

[0104] 28. The method according to Clause 17, wherein smoothing the substrate surface includes: removing subsurface damage, scratches, defects and contaminant particles from the substrate surface.

[0105] 29. The method according to Clause 17, wherein smoothing the substrate surface comprises: removing damage and defects from the substrate surface without adding additional damage or defects to the substrate surface.

[0106] 30. An optical component, comprising:

[0107] A calcium fluoride substrate having a smooth substrate surface, the smooth substrate surface forming at least a portion of an optically interactive surface; and

[0108] A sealant layer is deposited onto a smooth substrate surface;

[0109] The smooth substrate surface is actually formed using accelerated neutral atom beams.

[0110] 31. The optical component according to Clause 30, wherein the profile roughness Ra of the smooth substrate surface is in the range of 0.01 nanometers (nm) to 0.17 nm and inclusive, and the profile roughness Ra is defined as the average deviation of the profile of the smooth substrate surface.

[0111] 32. The optical component according to Clause 30, wherein the sealant layer is configured to prevent depletion of fluorine in the calcium fluoride substrate.

[0112] 33. The optical component as described in Clause 30, wherein the optical component is configured for a light beam with wavelengths in the deep ultraviolet range.

[0113] 34. The optical component as described in Clause 33, wherein the optical component is configured for a light beam with a wavelength of 193 nm.

[0114] 35. The optical component as described in Clause 30, wherein the optical component is a window of a gas discharge chamber, a beam reverser, a beam expander prism, an output coupler, or a beam splitter.

[0115] 36. The optical component according to Clause 30, wherein the formation of a smooth substrate surface does not involve mechanical processing, ionized plasma treatment, or chemical etching.

[0116] 37. An optical component, actually formed using a process comprising the following steps:

[0117] A substrate is provided, the substrate including a substrate surface that forms at least a portion of the optical surface of an optical component;

[0118] The substrate surface is smoothed by bombarding it with at least one accelerated neutral atom beam; and

[0119] After smoothing the substrate surface, a protective layer is deposited onto the substrate surface, thereby forming an interface between the substrate and the protective layer, which is configured to mitigate or prevent damage to the optical surface.

[0120] Other implementations are within the scope of the claims.

Claims

1. An optical component, comprising: a calcium fluoride substrate comprising an atomically-smooth substrate surface forming at least a portion of an optically-interacting surface; and a sealant layer covering the atomically-smooth substrate surface, thereby forming a smooth interface between the calcium fluoride substrate and the sealant layer; wherein a profile roughness parameter Ra of the atomically-smooth substrate surface is in a range from 0.01 nanometers (nm) to 0.17 nm, inclusive, the profile roughness parameter Ra being defined as an average deviation of a profile of the atomically-smooth substrate surface.

2. The optical component of claim 1, wherein another profile roughness parameter Rz of the atomically-smooth substrate surface is in a range from 1.0 nm to 1.6 nm, the other profile roughness parameter Rz being defined as an average of peak-to-valley heights of a profile within a selected sampling length of the atomically-smooth substrate surface.

3. The optical component of claim 1, wherein the optical component is configured for a light beam having a wavelength of 193 nm.

4. The optical component of claim 1, wherein the optical component is a window of a gas discharge chamber, a beam reverser, a beam expander prism, an output coupler, or a beam splitter.

5. The optical component of claim 1, wherein the sealant layer is configured to prevent depletion of fluorine in the calcium fluoride substrate.

6. The optical component of claim 1, wherein the optical component is configured for a light beam having a wavelength in a deep-ultraviolet range.

7. The optical component of claim 1, wherein the atomically-smooth substrate surface is formed using an accelerated neutral atom beam treatment.

8. The optical component of claim 7, wherein the formation of the atomically-smooth substrate surface does not include mechanical treatment, ionized plasma treatment, or chemical etching.

9. The optical component of claim 1, wherein the atomically-smooth substrate surface is free of defects, scratches, contaminant particles, and subsurface damage.

10. An optical system for deep-ultraviolet (DUV) optical lithography, the optical system comprising: a gas discharge system comprising one or more gas discharge chambers, each gas discharge chamber housing an energy source and containing a gas mixture, the gas mixture including a gain medium; and one or more optical components associated with the gas discharge system, wherein each optical component comprises: a substrate comprising an atomically-smooth substrate surface forming at least a portion of an optically-interacting surface; and a protective layer configured to mitigate or prevent damage to the atomically-smooth substrate surface caused at least in part by illumination of DUV light, the protective layer being deposited onto the atomically-smooth substrate surface, thereby forming a smooth interface between the substrate and the protective layer. wherein a profile roughness parameter Ra of the substrate surface is in a range from 0.01 nanometers (nm) to 0.17 nm inclusive, the profile roughness parameter Ra being defined as an average deviation of a profile of the atomically-smooth substrate surface.

11. The optical system of claim 10, wherein the gas discharge system comprises two discharge chambers, the two discharge chambers comprising a master oscillator configured to generate a pulsed seed beam; and a power amplifier configured to generate a pulsed output beam from the pulsed seed beam.

12. The optical system of claim 11, wherein at least one of the optical components is configured to feed the pulsed seed beam from the master oscillator to the power amplifier.

13. The optical system of claim 10, wherein the optical component is a window, a beam reverser, a beam expansion prism, an output coupler, or a beam splitter of one of the gas discharge chambers.

14. The optical system of claim 10, wherein the atomically-smooth substrate surface is formed using an accelerated neutral atom beam treatment in practice.

15. The optical system of claim 10, wherein the atomically-smooth substrate surface is free of defects, scratches, contaminant particles, and subsurface damage.

16. A method for mitigating or preventing damage to an optical surface of an optical component in a deep ultraviolet (DUV) light source, the method comprising: providing a substrate comprising a substrate surface, the substrate surface forming at least a portion of the optical surface of the optical component; smoothing the substrate surface by impinging the substrate surface with at least one accelerated neutral atom beam, a profile roughness parameter Ra of the substrate surface being in a range from 0.01 nanometers (nm) to 0.17 nm inclusive, the profile roughness parameter Ra being defined as an average deviation of a profile of the substrate surface; and after smoothing the substrate surface, depositing a protective layer onto the substrate surface such that an interface is formed between the substrate and the protective layer, the protective layer being configured to mitigate or prevent damage to the optical surface.

17. The method of claim 16, wherein smoothing the substrate surface comprises: removing high areas at the substrate surface and leaving low areas at the substrate surface.

18. The method of claim 16, wherein affecting the substrate surface comprises: adjusting a material removal rate, the material removal rate depending on an atomic cluster density and a treatment time.

19. The method of claim 18, wherein impinging the substrate surface with the at least one beam of accelerated neutral atoms comprises: at each of a series of steps, impinging the substrate surface with a different one of the accelerated neutral atom beams, and wherein at each impinging step, the material removal rate is adjusted.

20. The method of claim 19, wherein the material removal rate is in a range from 0.3 nm per step to 30 nm per step.

21. The method of claim 16, wherein the substrate is made of calcium fluoride.

22. The method of claim 16, wherein the optical component is configured for a light beam having a wavelength of 193 nm.

23. The method of claim 16, wherein the optical component is a window of a gas discharge chamber, a beam reverser, a beam expansion prism, an output coupler, or a beam splitter.

24. The method of claim 16, wherein smoothing the substrate surface comprises: removing a re-deposition layer at the substrate surface of the substrate, the re- deposition layer formed during mechanical polishing of the substrate surface prior to smoothing the substrate surface.

25. The method of claim 16, wherein smoothing the substrate surface comprises: removing sub-surface damage, scratches, defects, and contaminant particles from the substrate surface.

26. The method of claim 16, wherein smoothing the substrate surface comprises: removing damage and defects from the substrate surface without adding additional damage or defects to the substrate surface.

27. An optical component, comprising: a calcium fluoride substrate having a smooth substrate surface forming at least a portion of an optical interaction surface; and a sealant layer deposited onto the smooth substrate surface; wherein the smooth substrate surface is formed using an accelerated neutral atom beam treatment and a profile roughness parameter Ra of the smooth substrate surface is in a range from 0.01 nanometers (nm) to 0.17 nanometers and including 0.17 nanometers, the profile roughness parameter Ra defined as an average deviation of a profile of the smooth substrate surface.

28. The optical component of claim 27, wherein the sealant layer is configured to prevent depletion of fluorine in the calcium fluoride substrate.

29. The optical component of claim 27, wherein the optical component is configured for a light beam having a wavelength in a deep ultraviolet range.

30. The optical component of claim 29, wherein the optical component is configured for a light beam having a wavelength of 193 nanometers.

31. The optical component of claim 27, wherein the optical component is a window of a gas discharge chamber, a beam reverser, a beam expansion prism, an output coupler, or a beam splitter.

32. The optical component of claim 27, wherein formation of the smooth substrate surface does not include mechanical treatment, ionized plasma treatment, or chemical etching.

33. An optical component, actually formed using a process comprising: providing a substrate, the substrate including a substrate surface, the substrate surface forming at least a portion of the optical surface of the optical component; smoothing the substrate surface by impinging the substrate surface with at least one accelerated neutral atom beam, a profile roughness parameter Ra of the substrate surface being in a range from 0.01 nanometers (nm) to 0.17 nanometers and including 0.17 nanometers, the profile roughness parameter Ra defined as an average deviation of a profile of the substrate surface; and after smoothing the substrate surface, depositing a protective layer onto the substrate surface such that an interface is formed between the substrate and the protective layer, the protective layer configured to mitigate or prevent damage to the optical surface.

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