A transmissive window member that emits amplified light of extreme ultraviolet or soft X-rays, and a method for manufacturing the transmissive window member.

Abstract

The present invention provides a mountable transmission window member that can emit amplified extreme ultraviolet (EUV) or soft X-ray light, coherently amplified by a superfluorescent medium, with low loss and long lifespan, while hermetically separating the high-density superfluorescent medium from the external vacuum environment. [Solution] The transparent window member 1 includes a transparent film 2 made of a low atomic number material that transmits light in the wavelength range of EUV or soft X-rays, with a thickness of 1 nm to 500 nm. The transparent film 2 hermetically separates the inside of the housing 31, which encloses a superfluorescent medium 34 excited to a population inversion state, from the vacuum environment outside, while transmitting and emitting coherently amplified light L3 into the vacuum environment while retaining the spatial information of the circuit pattern. The transparent film 2 is made of a CNT nonwoven fabric film or the like, is divided into a plurality of partial openings 2a by a support grid 3 that supports the pressure difference, and has a capping layer 4 on at least one of the vacuum side and the medium side.

Description

[Technical Field]

[0001] The present disclosure relates to a transmission window member that transmits amplified light, which is coherently amplified by a superfluorescent medium excited to an population inversion state in an extreme ultraviolet (EUV) or soft X-ray wavelength region, to a vacuum environment outside a casing enclosing the superfluorescent medium and emits the amplified light, and to a method of manufacturing the transmission window member. [Background Art]

[0002] Various ultra-thin film members are used as members that transmit light in the wavelength range of EUV or soft X-rays. For example, in the field of EUV lithography, an ultra-thin pellicle made of carbon nanotubes (CNT) or the like is known as a dust-proof cover that prevents foreign matter from adhering to a photomask. It has been reported that the pellicle has high transmittance for EUV and resistance to the hydrogen plasma environment and high heat load in an exposure apparatus (Non-Patent Documents 1 and 2).

[0003] Further, in the field of soft X-ray analyzers, an X-ray window in which a thin film of silicon nitride (SiN) or the like is supported by a support mesh is known as a window member that separates the vacuum of a detector from a gas atmosphere (Non-Patent Document 3). Furthermore, it is known that an ultra-thin film of ruthenium (Ru) or the like is provided as a capping layer that protects the surface of a multilayer optical element for EUV from hydrogen plasma and oxidation (Non-Patent Document 4). [Prior Art Documents] [Non-Patent Documents]

[0004] [Non-Patent Document 1] I.Pollentier et al.,“CNT EUV pellicle:moving towards a full-size solution”,Proceedings of SPIE,Vol.10450,2017. [Non-Patent Document 2] D. Brouws et al., “NXE pellicle: offering a EUV pellicle solution to the industry”, Proceedings of SPIE, Vol. 9776, 2016. [Non-Patent Document 3] Literature on ultrathin silicon nitride X-ray windows (reporting that a window with a diameter of approximately 31 mm, supported by a polysilicon mesh with an aperture ratio of approximately 75% and consisting of a SiN film with a thickness of approximately 40 nm, can withstand a differential pressure of approximately 3 atmospheres). [Non-Patent Document 4] Literature on the EUV irradiation durability of multilayer mirrors with a ruthenium cap layer (reporting that a ruthenium layer approximately 2 nm thick extends the lifespan of the multilayer film). [Overview of the project] [Problems that the invention aims to solve]

[0005] However, when attempting to extract powerful light of the EUV or soft X-ray wavelength range from a housing containing a medium consisting of high-density gas or plasma to an external vacuum environment, the window material on the emission side must simultaneously satisfy unique and complex requirements that differ from those of conventional EUV pellicles or soft X-ray windows. Specifically, the window material must simultaneously satisfy the following requirements: (i) transmit powerful light in the strongly absorbed EUV or soft X-ray wavelength range with virtually no loss; (ii) airtightly separate the high-density medium held inside the housing from the external vacuum environment while withstanding the pressure difference between the two; (iii) withstand the opposing extreme environments on both sides, being exposed to plasma and high-temperature gas on the medium side and hydrogen plasma and residual gas on the vacuum side; and (iv) eliminate heat generation associated with the passage of light and withstand repeated exposures.

[0006] This disclosure aims to provide a physically and chemically implementable transparent window member that simultaneously satisfies the above-mentioned unique and complex requirements, hermetically separating a high-density medium from the external vacuum environment while emitting powerful light in the EUV or soft X-ray wavelength range with low loss and long lifetime. It also aims to provide a method for manufacturing the transparent window member. [Means for solving the problem]

[0007] To solve the above problems, the transparent window member according to the present disclosure is a transparent window member used for exposure in the wavelength region of extreme ultraviolet (EUV) or soft X-rays, provided in a housing that encloses a superfluorescent medium excited to a population inversion state, and transmits and emits amplified light in the wavelength region, which has been coherently amplified in the superfluorescent medium while retaining spatial information of a circuit pattern, to a vacuum environment outside the housing, and is characterized in that it comprises a transparent film that transmits light in the wavelength region, and the transparent film is configured to transmit and emit the amplified light to the vacuum environment while hermetically separating the superfluorescent medium enclosed inside the housing from the vacuum environment outside.

[0008] Furthermore, this disclosure also provides a method for manufacturing the above-mentioned transparent window member. [Effects of the Invention]

[0009] This disclosure provides a transmissive window member that can emit amplified light, coherently amplified by a superfluorescent medium, with low loss and long lifespan, while hermetically separating the high-density superfluorescent medium from the external vacuum environment. This makes it possible to realize an exposure apparatus that directly exposes a substrate without passing through a large group of projection mirrors, which causes light loss, in a mountable form that can withstand repeated exposures. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional view showing the configuration of a transparent window member according to one embodiment. [Figure 2]This is a schematic plan view of the permeable film and support grid of a permeable window member according to one embodiment, as seen from the injection side. [Figure 3] This is a partially enlarged cross-sectional view showing the configuration of the capping layer of a transparent window member according to one embodiment. [Figure 4] This is a schematic diagram showing the configuration of a medium cell and exposure apparatus equipped with a transmissive window member according to one embodiment as the window material on the injection side. [Figure 5] This is a flowchart showing a method for manufacturing a transparent window member according to one embodiment. [Modes for carrying out the invention]

[0011] Preferred embodiments of this disclosure will be described in detail below with reference to the drawings. Common components in each drawing are denoted by the same reference numerals, and redundant explanations are omitted. Each drawing is a schematic diagram for ease of understanding, and the dimensions and proportions of each part do not necessarily correspond to actual dimensions.

[0012] (Overall configuration of the transparent window component) As shown in Figure 1, a transmissive window member 1 according to one embodiment is provided in a housing 31 that encloses a superfluorescent medium 34 excited to a population inversion state. The transmissive window member 1 is an ejection-side window material that transmits and ejects amplified light L3, which has been coherently amplified in the superfluorescent medium 34 while retaining the spatial information of the circuit pattern, to the vacuum environment outside the housing 31. The transmissive window member 1 comprises a transmissive film 2 that transmits light in the wavelength range of EUV to soft X-rays, a support grid 3 that divides and supports the transmissive film 2 into a plurality of partial openings 2a, a capping layer 4 provided on the surface of the transmissive film 2, and a frame 5 that holds the transmissive film 2 and the support grid 3. The transmissive film 2 hermetically separates the superfluorescent medium 34 enclosed inside the housing 31 from the vacuum environment outside the housing 31 (for example, the space inside a vacuum chamber where a substrate W coated with a photosensitive resin R is placed), and transmits and ejects the amplified light L3 to the vacuum environment.

[0013] Here, the superfluorescent medium 34 is a medium that, when excited to a population inversion state, has gain at the target wavelength and generates cooperative emission (photon avalanche) triggered by a patterned seed light L2 injected from the outside. It broadly includes high-density gases containing noble gases such as xenon (Xe), krypton (Kr), or argon (Ar), plasmas containing polyvalent ions with neon-like (Ne-like) or nickel-like (Ni-like) electron configurations, or plasmas containing polyvalent ions of tin (Sn). The atomic number density (ion density) of the superfluorescent medium 34 is optimized to be in the range of approximately 10^12 cm^-3 to 10^19 cm^-3 so that cooperative emission is possible at the target wavelength. When patterned seed light L2 is incident on the superfluorescent medium 34 excited to a population inversion state, the group of light emitters within the medium 34 produces cooperative emission synchronized with the spatial mode of the patterned seed light L2. The instantaneous peak intensity is coherently amplified while retaining the spatial phase information and intensity information of the circuit pattern carried by the patterned seed light L2, and is emitted from the transmission window member 1 as amplified light (photon avalanche) L3.

[0014] (Material of the permeable membrane) The transparent film 2 is composed of an ultrathin film mainly made of a low atomic number material that has low absorption at the target wavelength, in order to transmit the amplified light L3 with virtually no loss. Specifically, suitable materials for the transparent film 2 include carbon nanotube (CNT) films, graphene or multilayer graphene films, silicon nitride (SiN) films, polycrystalline silicon films, single-crystal silicon films, beryllium (Be) films, zirconium (Zr) films, niobium (Nb) films, molybdenum (Mo) films, carbon (C) films, or boron carbide (B4C) films. Its thickness is, for example, 1 nm to 500 nm, more preferably several nm to tens of nm, depending on the balance between transmittance at the target wavelength and mechanical strength.

[0015] In particular, carbon nanotube films are especially suitable as permeable films 2 through which powerful amplified light L3 passes and which are exposed to high-temperature and hydrogen environments, because they have extremely high transmittance to EUV or soft X-rays and excellent resistance to high temperatures of around 1000°C and hydrogen plasma. It is especially preferable that the permeable film 2 is composed of a porous, self-supporting film (CNT nonwoven film) in which a large number of carbon nanotubes (CNTs) are interwoven three-dimensionally in a nonwoven manner. This CNT nonwoven film ensures self-support and mechanical strength by having individual nanotubes or bundles thereof distributed in random directions and intertwined with each other, while exhibiting extremely high transmittance to EUV or soft X-rays due to the fine voids formed between the nanotubes. As an example, it is known that the CNT nonwoven film can be used as a pellicle for EUV lithography, with a single-pass transmittance of approximately 97% or more at a wavelength of 13.5 nm (for example, approximately 97-99%), and good in-plane uniformity of transmittance (for example, approximately 0.4% at half width), and that a full-field size film (for example, approximately 110 mm x 144 mm) can be fabricated. Furthermore, it is known that the film has thermal resistance that does not cause substantial changes in properties when exposed to EUV light source power equivalent to that of a mass-production EUV exposure apparatus (for example, 500 W class) (Non-patent documents 1 and 2). The transparent film 2 of this embodiment only needs to have an area of ​​approximately 26 mm x 33 mm, corresponding to the exposure field, which is sufficiently smaller than the area of ​​the proven self-supporting CNT film for pellicles. Therefore, it can be fabricated by directly applying the existing manufacturing technology for CNT films for pellicles.

[0016] (Selection of permeable films for each wavelength band) It is preferable that the material and thickness of the transmission film 2 are selected according to the wavelength band of the amplified light L3. For EUV in a wavelength band of 13.5 nm, a polycrystalline silicon film, a single-crystal silicon film, an SiN film, a Zr film, an Nb film, a Mo film or a CNT film is suitable. On the other hand, for soft X-rays in a wavelength band of 3.1 nm, a film formed as thin as possible in consideration of absorption at said wavelength is suitable. Here, the K absorption edge of carbon is about 284 eV (wavelength of about 4.4 nm), and the wavelength of 3.1 nm (about 400 eV) is located on the higher energy side than this, so absorption of a carbon-based film relatively increases at said wavelength. Therefore, in the wavelength band of 3.1 nm, a carbon-based film such as a single-layer or several-layer graphene film or a CNT film is formed extremely thin (for example, to a thickness of 1 nm or more and 30 nm or less), or a material with a lower atomic number and lower absorption such as beryllium or boron (including boron carbide) is used, and the pitch of the support grid 3 described later is relatively reduced, whereby it is preferable to achieve both a reduction in film thickness and mechanical strength.

[0017] (Structure and Pressure Resistance of Support Grid) When a high-density gas or plasma having an atomic number density of 10^12 to 10^19 cm^-3 is used as the superfluorescent medium 34, the pressure thereof can be about several tens of Pa to several tens of kPa corresponding to the atomic number density. For example, an atomic number density of 10^19 cm^-3 corresponds to a pressure of approximately 4×10^4 Pa (about 40 kPa) in terms of room temperature (when n=10^25 m^-3 and T=300 K in the pressure equation p=nkT). When this pressure difference is applied to the transmission film 2 having a large area corresponding to an exposure field (for example, 26 mm × 33 mm), non-negligible mechanical stress occurs in the ultrathin film. Therefore, as shown in FIG. 1 and FIG. 2, it is preferable that the transmission film 2 is divided into a plurality of partial openings 2a (for example, having an opening dimension of 0.1 mm to several mm) and supported by the support grid 3 that mechanically supports the pressure difference between the inside and outside of the housing 31. The support grid 3 is, for example, a mesh-shaped or honeycomb-shaped structure made of silicon, silicon carbide or metal, and can be formed integrally with the transmission film 2 by deep reactive ion etching (DRIE) or the like. This reduces the force acting on each partial opening 2a, and allows the pressure difference to be maintained without breaking the ultrathin transmission film 2.

[0018] The pressure resistance of an ultra-thin film window material is determined by the breaking strength, thickness, and opening dimension of the film, and the pressure resistance increases as the opening dimension is reduced. As an example, it has been reported that a large-area window with a diameter of approximately 31 mm, in which a silicon nitride film with a thickness of about 40 nm is supported by a polysilicon mesh with an aperture ratio of approximately 75%, withstands a differential pressure of about 3 atmospheres (approximately 3×10^5 Pa). It is also reported that even a silicon nitride film with a thickness of about 30 nm can withstand a differential pressure of about 1 atmosphere (approximately 1×10^5 Pa) if the opening area is divided into sections of less than about 5 mm^2 (Non-Patent Document 3). As described above, the pressure of the super-fluorescent medium 34 in the present embodiment is at most about 40 kPa, which is sufficiently lower than these proven pressure resistances (about 1×10^5 to 3×10^5 Pa). Therefore, the configuration of the present embodiment, in which the permeable membrane 2 with a thickness of several nm to several tens of nm is partitioned and supported by the support grid 3 having an opening dimension of 0.1 mm to several mm, has a sufficient pressure resistance margin even when a safety factor is taken into account. From the viewpoint of securing the geometric transmittance of the amplified light L3, the aperture ratio of the support grid 3 is preferably, for example, 75% or more.

[0019] (Suppression of Grid Shadows) Since the shielding portions (beam portions) of the support grid 3 block part of the amplified light L3, it is preferable to suppress the shadow thereof from being transferred onto the substrate W. For this purpose, it is preferable to adopt at least one of the following: (i) setting the pitch and orientation of the support grid 3 to be non-matching with the period and orientation of the image of the circuit pattern to be transferred, so as to avoid moiré-like interference; (ii) increasing the aperture ratio of the support grid 3 (for example, 75% or more) and forming narrow beam widths (for example, several μm to several tens of μm); (iii) if necessary, slightly displacing the transparent window member 1 in a direction orthogonal to the optical axis during exposure, and time-averaging the shadow by overlapping a plurality of shots. In addition, the shadow of the support grid 3 can also be smoothed in the process of reaching the substrate W by the propagation and diffusive spreading of the amplified light L3 within the gain layer of the super-fluorescent medium 34. As an example of a specific mechanism to achieve the minute displacement described in (iii) above, a configuration is used in which the housing 31 and the frame 5 are connected by a flexible and airtight joint member such as a bellows (metal bellows), and the frame 5 (i.e., the entire transmissive window member 1) is driven minutely in a plane perpendicular to the optical axis using a driving means such as a piezo actuator or a voice coil motor. This ensures that the transfer of shadows from the support grid 3 is reliably and effectively suppressed while strictly maintaining airtightness between the superfluorescent medium 34 and the vacuum environment.

[0020] (Capping layer) It is preferable to provide a capping layer 4 on the surface of the permeable film 2 through which the amplified light L3 passes to protect the permeable film 2. As shown in Figure 3, the capping layer 4 includes at least one of a first capping layer 4a provided on the vacuum environment side (bottom surface) of the permeable film 2 and a second capping layer 4b provided on the superfluorescent medium 34 side (top surface) of the permeable film 2. The first capping layer 4a protects the permeable film 2 from the strong etching effect of hydrogen plasma that may be generated in the external vacuum environment and oxidation by residual gases. The second capping layer 4b protects the permeable film 2 from thermal and chemical damage caused by direct contact between the superfluorescent medium 34 and multivalent ion plasma or high-temperature gases generated by femtosecond excitation or the like. The capping layer 4 (4a, 4b) can preferably be made of ruthenium (Ru), zirconium oxide (ZrO2), niobium oxide (NbOx), molybdenum oxide (MoOx), or boron carbide (B4C), provided that the transmittance at the target wavelength is not substantially sacrificed. Its thickness is, for example, 5 nm or less, more preferably several nm or less.

[0021] Here, it is known that a ruthenium capping layer, with a thickness of approximately 2 nm, can significantly extend the lifespan of a multilayer film or window material under water vapor and EUV irradiation environments (Non-Patent Literature 4). On the other hand, when polyvalent ions of tin (Sn) are used as the superfluorescent medium 34, it is known that when tin adheres to the surface, hydrogen permeation through the ruthenium layer is promoted, and blistering (swelling) due to hydrogen trapped within the layer can occur. Therefore, when the superfluorescent medium 34 contains polyvalent ions of tin, it is preferable to select zirconium oxide, niobium oxide, or boron carbide as the capping layer 4, or, when using ruthenium, it is preferable to combine it with the removal of tin deposits by the cleaning mechanism 6 described later. This eliminates the trade-off between transmittance and durability under extreme environments, and extends the lifespan of the permeable film 2.

[0022] (Frame and airtight sealing) The permeable membrane 2 and support grid 3, together with a frame 5 such as a silicon frame that supports them, are sealed to the housing 31 (for example, the cell body containing the superfluorescent medium 34) by hermetically sealing methods such as indium sealing, metal brazing, diffusion bonding, or anodic bonding. These sealing methods are suitable for ultra-high vacuum (UHV) and suppress leakage of the medium gas. The frame 5 and housing 31 are preferably made of a material that provides both mechanical rigidity and low outgassing (for example, molybdenum, titanium, stainless steel, silicon carbide, aluminum nitride, or low thermal expansion ceramics). In particular, since silicon-containing gases such as siloxanes cause irreversible silicon oxide (SiOx) deposition under EUV irradiation, it is preferable to use low-outgassing materials that substantially do not contain siloxanes for the frame 5, sealing material, and surrounding components.

[0023] (Cleaning mechanism) Carbon contamination may grow on the surface of the permeable film 2 due to outgassing from the photosensitive resin R on the substrate W. To suppress this, it is preferable to provide a cleaning mechanism 6 that removes contamination adhering to the permeable film 2. The cleaning mechanism 6 can be a mechanism that performs dry cleaning by supplying a small amount of oxygen or hydrogen radicals near the permeable film 2, or a mechanism that removes attached carbon by irradiating the permeable film 2 with ultraviolet (UV) light during standby. In addition, to prevent irreversible contamination caused by siloxanes, etc. (such as SiOx deposition), it is even more preferable to provide an exhaust mechanism that quickly and locally exhausts outgassing generated from the substrate W from the vicinity of the permeable film 2.

[0024] (cooling) Since the amplified light L3 is partially absorbed by the transparent film 2 at the target wavelength, heat may be generated in the transparent film 2. To eliminate this heat generation, it is preferable to provide a cooling mechanism including a cooling channel in the support grid 3 or frame 5, and conduction cooling of the heat generated in the transparent film 2 through the support grid 3 and frame 5. As mentioned above, the CNT nonwoven film has excellent resistance to high temperatures, and therefore operates stably even with the heat generated by the passage of strong amplified light L3.

[0025] Specific cooling mechanisms include, for example, a structure in which microchannels are formed inside the frame 5 to circulate cooling water or cooling gas. Furthermore, by using silicon carbide (SiC) or metals (such as molybdenum or tungsten) with high thermal conductivity as the material for the support grid 3, heat dissipation from the transparent film 2 to the frame 5 can be further promoted. This makes it possible to effectively dissipate the heat load associated with continuous or high-repetition-rate exposure.

[0026] (Application to medium cells and exposure equipment) As shown in Figure 4, the transmission window member 1 is provided as the output-side window material of a medium cell 30, which comprises a superfluorescent medium 34 having gain in the EUV or soft X-ray wavelength region when excited to a population inversion state, a housing 31 enclosing the superfluorescent medium 34, and an input-side window material 32 for injecting patterned seed light L2 in the said wavelength region into the superfluorescent medium 34. When a weak seed light L1 in the wavelength region in which the superfluorescent medium 34 has gain is irradiated onto a photomask 21 having a circuit pattern, patterned seed light L2 is generated, which is imbued with spatial phase information and intensity information of the circuit pattern. The patterned seed light L2 is injected into the superfluorescent medium 34 through the input-side window material 32, inducing cooperative emission from the group of light emitters within the superfluorescent medium 34. As a result, amplified light L3, which is coherently amplified while retaining the spatial information of the circuit pattern, is emitted through the transmission window member 1 into the vacuum environment outside the housing 31.

[0027] The exposure apparatus 100 comprises a light source unit 10 that generates seed light L1, a photomask 21 and a medium cell 30, an excitation means (excitation unit 37) that excites the superfluorescent medium 34 into a population inversion state, a wafer stage 40 that holds a substrate W coated with a photosensitive resin R, and a control unit 50 that manages these components, all located within a vacuum chamber 60 maintained at a high vacuum. The amplified light L3 emitted from the transmissive window member 1 directly exposes the photosensitive resin R on the substrate W without passing through a group of projection mirrors. The transmissive window member 1 and the substrate W are separated by a small gap G that allows for close-range exposure. This, in principle, avoids the reflectivity barrier of multilayer mirrors, enabling the transfer of circuit patterns with high energy efficiency.

[0028] (calculation example) The following is a more specific calculation example. A laser-generated plasma containing nickel-like polyvalent ions with gain in the 3.1 nm wavelength band is used as the superfluorescent medium 34 and is held in a flat housing 31 with an ion number density of approximately 10^18 to 10^19 cm^-3. At this time, the pressure inside the housing 31 is generally several hundred Pa to several kPa (for example, an atomic number density of 10^18 cm^-3 corresponds to approximately 4 × 10^3 Pa), and the pressure difference with the external vacuum environment (for example, less than 10^-2 Pa) is at most approximately 4 × 10^3 to 4 × 10^4 Pa. The 26mm x 33mm transparent film 2 is partitioned by support grids 3 with aperture dimensions of approximately 0.2 to 0.5mm (aperture ratio approximately 80%, beam width approximately several tens of μm). It is made of a graphene or carbon nanotube film (thickness approximately 1 to 5 nm as an example) or an extremely thin beryllium film, thinned to a single layer or several layers to suppress absorption at a wavelength of 3.1 nm. As mentioned above, this pressure difference is significantly lower than the approximately 3 x 10^5 Pa that a SiN film with a thickness of approximately 40 nm and an aperture ratio of approximately 75% can withstand at a diameter of approximately 31 mm. Therefore, even with the thinned transparent film 2 described above, the inside and outside of the housing can be airtightly separated with sufficient pressure resistance margin. A capping layer 4 (B4C or ZrO2 as an example) with a thickness of several nanometers or less is provided on the vacuum-side surface of the transparent film 2 as needed. This allows the amplified light L3, which is amplified while retaining the spatial information of the circuit pattern, to be emitted toward the substrate W with low loss and long life.

[0029] (Manufacturing method for transparent window members) Referring to Figure 5, an example of a manufacturing method for the transparent window member 1 will be explained. First, a transparent film 2 with a thickness of 1 nm to 500 nm is formed on a substrate such as a silicon wafer, made of a low atomic number material that transmits light of the target wavelength (S1: transparent film formation step). In the transparent film formation step, as an example, a silicon nitride film or a polycrystalline silicon film is formed by low-pressure chemical vapor deposition (LPCVD), or a graphene film grown separately by chemical vapor deposition is transferred onto the substrate, or carbon nanotubes are deposited by extraction and floating deposition to form a self-supporting film (CNT nonwoven film) to form an extremely thin transparent film 2.

[0030] Next, a portion of the substrate is removed by deep etching (DRIE) or anisotropic etching using potassium hydroxide (KOH), etc., to form a support grid 3 that supports the pressure difference between the inside and outside of the housing, integrally with the permeable film 2 (S2: support grid formation step). This results in a large-area, ultra-thin permeable film 2 partitioned and supported by a mesh-like or honeycomb-like support grid 3 in multiple partial openings 2a. Subsequently, a capping layer 4 containing ruthenium, zirconium oxide, niobium oxide, molybdenum oxide, or boron carbide is deposited on at least one surface of the permeable film 2 by sputtering or atomic layer deposition (ALD) (S3: capping step). Atomic layer deposition allows for the deposition of an ultra-thin and uniform capping layer 4 without substantially sacrificing the permeability of the permeable film 2. Finally, the permeable film 2 and the support grid 3 are held in a frame 5, and the frame 5 is finished to a state where it can be hermetically sealed to the housing 31 by indium encapsulation, metal brazing, diffusion bonding, or anodic bonding. This results in the aforementioned transparent window member 1.

[0031] Furthermore, a specific calculation example is shown for the case where a superfluorescent medium 34 having gain in the industrially important 13.5 nm wavelength band EUV is used. As an example, if a polycrystalline silicon film or CNT nonwoven fabric film with a thickness of several tens of nanometers (e.g., 20-50 nm) is used as the transparent film 2, and the aperture size of the support grid 3 is set to approximately 0.5 mm to 1 mm (aperture ratio of approximately 80% or more), it has sufficient pressure resistance against the assumed pressure (tens of kPa) of a medium using xenon, etc. With this configuration, while maintaining an extremely high transmittance of a single pass at a wavelength of 13.5 nm (e.g., 90% or more, preferably 97% or more), a large-area window member covering the entire exposure field can stably extract powerful amplified light L3 to the external vacuum environment.

[0032] Although embodiments of the present disclosure have been described above, the disclosure is not limited thereto, and various design modifications are possible without departing from its essence. The embodiments and modifications described above can be combined as appropriate without technical inconsistency. For example, the wavelength of the amplified light L3 is not limited to 13.5 nm or 3.1 nm, but may be other EUV / soft X-ray wavelengths for which the superfluorescent medium 34 has gain (for example, the wavelength of nickel-like silver ions at 13.9 nm, the wavelength of nickel-like cadmium ions at 13.2 nm, or the wavelength of neon-like argon ions at 46.9 nm), and the material and thickness of the transparent film 2 should be selected considering the absorption at the relevant wavelength.

[0033] This specification includes at least the following: (1) A transmissive window member used for exposure in the wavelength region of extreme ultraviolet (EUV) or soft X-rays, provided in a housing that encloses a superfluorescent medium excited to a population inversion state, and transmits and emits amplified light in the wavelength region, which has been coherently amplified in the superfluorescent medium while retaining spatial information of a circuit pattern, to a vacuum environment outside the housing, comprising a transmissive film that transmits light in the wavelength region, wherein the transmissive film is configured to transmit and emit the amplified light to the vacuum environment while hermetically separating the superfluorescent medium enclosed inside the housing from the vacuum environment outside. This configuration makes it possible to realize an ejection-side window material that simultaneously satisfies unique and complex requirements, such as extracting powerful EUV or soft X-ray amplified light, which can be amplified by approximately 100 million times, with low loss, while reliably hermetically separating the high-density superfluorescent medium from the external vacuum environment. (2) A permeable window member comprising a support grid that divides and supports the permeable membrane into a plurality of partial openings and mechanically supports the pressure difference between the superfluorescent medium inside the housing and the vacuum environment outside. With this configuration, even a large-area, extremely thin permeable film can withstand the pressure difference between the high-density medium and the vacuum, preventing rupture. (3) A permeable window member wherein the permeable film includes at least one selected from the group consisting of a carbon nanotube film, a graphene film, a silicon nitride film, a polycrystalline silicon film, a single-crystal silicon film, a beryllium film, a zirconium film, a niobium film, a molybdenum film, a carbon film, and a boron carbide film. This configuration allows amplified light to be transmitted with low loss using a low atomic number material that exhibits low absorption at the target wavelength. (4) A permeable window member wherein the permeable membrane is a porous, self-supporting membrane in which a large number of carbon nanotubes are intertwined three-dimensionally in a nonwoven fabric-like manner. This configuration allows for extremely high transmittance due to the fine voids formed between the nanotubes, while simultaneously achieving self-supporting properties, mechanical strength, and resistance to high temperatures and hydrogen plasma. (5) A transparent window member wherein the wavelength of the amplified light is in the 13.5 nm band, and the transparent film comprises at least one selected from the group consisting of a polycrystalline silicon film, a single-crystal silicon film, a silicon nitride film, a zirconium film, a niobium film, a molybdenum film, and a carbon nanotube film. This configuration allows for low-loss extraction of amplified light in the 13.5nm wavelength band of current EUV lithography. (6) A transmission window member wherein the wavelength of the amplified light is in the 3.1 nm band, and the transmission film comprises at least one selected from the group consisting of a single-layer or multi-layer graphene film, a carbon nanotube film, a beryllium film, and a boron-based film containing boron carbide, and its thickness is set to 1 nm to 30 nm so as to suppress absorption at the wavelength located on the higher energy side of the carbon K absorption edge. With this configuration, even in the 3.1 nm wavelength band, where absorption increases at higher energies than the K absorption edge of carbon, amplified light can be extracted with low loss while simultaneously achieving reduced film thickness and high mechanical strength. (7) A permeable window member wherein the support grid is a mesh-like or honeycomb structure comprising at least one selected from the group consisting of silicon, silicon carbide, and metal, and is formed integrally with the permeable membrane, and the opening dimensions of the partial opening are 0.1 mm or more and several mm or less. This configuration allows for increased pressure resistance by reducing the size of the partial opening, enabling the support of pressure differences without rupturing the ultrathin film. (8) A transparent window member wherein the aperture ratio of the support grid is 75% or more, and the support grid has planar dimensions corresponding to the area of ​​the image formed on the substrate by the circuit pattern related to exposure. This configuration makes it possible to ensure a high geometric transmittance of amplified light while realizing a large-area transmissive window member that covers the entire exposure field. (9) A transparent window member having a capping layer with a thickness of 5 nm or less provided on the vacuum environment side of the transparent film, the capping layer containing at least one selected from the group consisting of ruthenium, zirconium oxide, niobium oxide, molybdenum oxide, and boron carbide. This configuration allows for increased durability of the permeable film against hydrogen plasma and oxidation on the vacuum side, and thus extends its lifespan, without substantially sacrificing transmittance. (10) A transparent window member having a capping layer with a thickness of 5 nm or less provided on the superfluorescent medium side of the transparent film, the capping layer containing at least one selected from the group consisting of ruthenium, zirconium oxide, niobium oxide, molybdenum oxide, and boron carbide. This configuration protects the permeable film from thermal and chemical damage caused by plasma or high-temperature gases on the medium side, thereby extending its lifespan. (11) A transparent window member wherein, when the superfluorescent medium contains polyvalent ions of tin, the capping layer comprises at least one selected from the group consisting of zirconium oxide, niobium oxide, and boron carbide. This configuration avoids hydrogen permeation and blistering through the ruthenium layer caused by tin deposition, and ensures reliable protection of the permeable film even when using a tin-multivalent ion medium. (12) A transmissive window member in which the pitch and orientation of the support grid are set to be inconsistent with the period and orientation of the image of the circuit pattern formed on the substrate by the amplified light. This configuration avoids moiré-like interference between the shadow of the support grid and the circuit pattern, suppresses the transfer of the grid's shadow onto the substrate, and enables highly accurate pattern transfer. (13) A transparent window member provided attached to the transparent membrane, comprising a cleaning mechanism for removing contaminants adhering to the transparent membrane, the cleaning mechanism including at least one of a mechanism for supplying oxygen or hydrogen radicals to the vicinity of the transparent membrane and a mechanism for irradiating the transparent membrane with ultraviolet light. This configuration removes carbon contamination and other impurities that could grow on the permeable film, and maintains a high transmittance of the film over a long period of time. (14) A permeable window member wherein the permeable membrane and the support grid are configured to withstand a pressure difference of 10^5 Pa or less that occurs between the inside of the housing and the vacuum environment outside when the atomic number density of the superfluorescent medium is 10^12 cm^-3 or more and 10^19 cm^-3 or less. This configuration allows for the extraction of amplified light while reliably supporting a pressure difference corresponding to the medium density at which cooperative emission is possible. (15) A permeable window member further comprising a frame that supports the permeable membrane, wherein the frame is configured to be sealed to the housing by at least one hermetically sealing selected from the group consisting of indium sealing, metal brazing, diffusion bonding and anodic bonding. This configuration is suitable for ultra-high vacuum and allows for reliable sealing of the permeable window member to the housing while suppressing leakage of the medium gas. (16) A method for manufacturing the above-described transparent window member, comprising: a transparent film forming step of forming the transparent film on a substrate; and a support grid forming step of removing a part of the substrate and integrally forming a support grid with the transparent film to divide the transparent film into a plurality of partial openings and support it. According to this method, a large-area, ultra-thin permeable film that can withstand the pressure difference between the inside and outside can be formed reproducibly and integrally with the support grid. (17) A method for manufacturing a permeable window member, wherein the permeable film formation step includes at least one of film formation by chemical vapor deposition, transfer of graphene, or deposition of carbon nanotubes, and the support grid formation step is performed by anisotropic etching or deep etching. According to this method, transmission window components can be mass-produced using thin-film formation and etching processes established as semiconductor manufacturing technology and X-ray window / pellicle manufacturing technology. (18) A method for manufacturing a transparent window member, further comprising a capping step of forming a capping layer with a thickness of 5 nm or less on at least one surface of the transparent film by sputtering or atomic layer deposition, the capping layer containing at least one selected from the group consisting of ruthenium, zirconium oxide, niobium oxide, molybdenum oxide, and boron carbide. According to this method, a transparent window component with enhanced durability under extreme conditions can be manufactured without substantially sacrificing transmittance. [Explanation of Symbols]

[0034] 1. Transparent window member 2 Permeable membrane 2a Partial opening 3 Support grid 4. Capping layer 4a First capping layer (vacuum environment side) 4b Second capping layer (superfluorescent medium side) 5 Frame 6. Cleaning mechanism 10 light source units 21 Photomasks 30 medium cells 31. Enclosure (cell body) 32. Entrance side window material 34. Superfluorescent medium 37 Excitation section (excitation means) 40 wafer stages 50 Control Unit 60 Vacuum Chamber 100 Exposure equipment W substrate (wafer) R Photosensitive resin (resist) G Gap L1 Seed Light L2 Patterned Seed Light L3 Amplified light (photon avalanche)

Claims

1. A transmission window member used for exposure in the wavelength range of extreme ultraviolet (EUV) or soft X-rays, A transmission window member provided in a housing that encloses a superfluorescent medium excited to a population inversion state, transmits and emits amplified light in the wavelength range, which has been coherently amplified in the superfluorescent medium while retaining the spatial information of the circuit pattern, to the vacuum environment outside the housing, The system includes a transparent film that transmits light in the aforementioned wavelength range, The permeable membrane is configured to hermetically separate the superfluorescent medium sealed inside the housing from the external vacuum environment, while transmitting and emitting the amplified light into the vacuum environment. A transparent window member characterized by the following.

2. In the transparent window member according to claim 1, The permeable membrane is divided into a plurality of partial openings and supported, and the housing further comprises a support grid that mechanically supports the pressure difference between the superfluorescent medium inside the housing and the vacuum environment outside. A transparent window member characterized by the following.

3. In the transparent window member according to claim 1 or 2, The aforementioned permeable film has a thickness of 1 nm or more and 500 nm or less, and includes at least one selected from the group consisting of carbon nanotube film, graphene film, silicon nitride film, polycrystalline silicon film, single crystal silicon film, beryllium film, zirconium film, niobium film, molybdenum film, carbon film, and boron carbide film. A transparent window member characterized by the following.

4. In the transparent window member according to claim 1 or 2, The aforementioned permeable membrane is a porous, self-supporting membrane in which numerous carbon nanotubes are intertwined three-dimensionally in a nonwoven fabric-like manner. A transparent window member characterized by the following.

5. In the transparent window member according to claim 1 or 2, The wavelength of the amplified light is in the 13.5 nm band, and the transparent film includes at least one selected from the group consisting of polycrystalline silicon film, single-crystal silicon film, silicon nitride film, zirconium film, niobium film, molybdenum film, and carbon nanotube film. A transparent window member characterized by the following.

6. In the transparent window member according to claim 1 or 2, The wavelength of the amplified light is in the 3.1 nm band, and the transparent film includes at least one selected from the group consisting of a single-layer or multi-layer graphene film, a carbon nanotube film, a beryllium film, and a boron-based film containing boron carbide, and its thickness is set to 1 nm to 30 nm so as to suppress absorption at the wavelength located on the higher energy side of the carbon K absorption edge. A transparent window member characterized by the following.

7. In the transparent window member according to claim 2, The support grid is a mesh-like or honeycomb-like structure comprising at least one selected from the group consisting of silicon, silicon carbide, and metal, and is formed integrally with the permeable membrane, with the opening dimensions of its partial opening being 0.1 mm or more and several mm or less. A transparent window member characterized by the following.

8. In the transparent window member according to claim 2, The support grid has an aperture ratio of 75% or more, and the circuit pattern related to exposure has planar dimensions corresponding to the area of ​​the image formed on the substrate placed in the vacuum environment. A transparent window member characterized by the following.

9. In the transparent window member according to claim 1 or 2, A capping layer with a thickness of 5 nm or less is provided on the vacuum environment side of the permeable film, which protects the permeable film from hydrogen plasma or oxidation, and which contains at least one selected from the group consisting of ruthenium, zirconium oxide, niobium oxide, molybdenum oxide, and boron carbide. A transparent window member characterized by the following.

10. In the transparent window member according to claim 1 or 2, A capping layer with a thickness of 5 nm or less is provided on the surface of the permeable film facing the superfluorescent medium, protecting the permeable film from thermal and chemical damage caused by the plasma or high-temperature gas generated by the superfluorescent medium, and comprising at least one selected from the group consisting of ruthenium, zirconium oxide, niobium oxide, molybdenum oxide, and boron carbide. A transparent window member characterized by the following.

11. In the transparent window member according to claim 9 or 10, When the superfluorescent medium contains polyvalent ions of tin, the capping layer contains at least one selected from the group consisting of zirconium oxide, niobium oxide, and boron carbide. A transparent window member characterized by the following.

12. In the transparent window member according to claim 2, The pitch and orientation of the support grid are set to be inconsistent with the period and orientation of the image of the circuit pattern formed by the amplified light on the substrate placed in the vacuum environment. A transparent window member characterized by the following.

13. In the transparent window member according to claim 1 or 2, A cleaning mechanism for removing contaminants adhering to the permeable membrane, comprising at least one of a mechanism for supplying oxygen or hydrogen radicals to the vicinity of the permeable membrane and a mechanism for irradiating the permeable membrane with ultraviolet light, is provided attached to the permeable membrane. A transparent window member characterized by the following.

14. In the transparent window member according to claim 1 or 2, The permeable membrane and the support grid are configured to withstand the pressure difference that occurs between the inside of the housing and the vacuum environment outside when the atomic number density of the superfluorescent medium is 10^12 cm^-3 or more and 10^19 cm^-3 or less, and the pressure difference is 10^5 Pa or less. A transparent window member characterized by the following.

15. In the transparent window member according to claim 1 or 2, The system further comprises a frame supporting the permeable membrane, and the frame is configured to be sealed to the housing by at least one hermetically sealed method selected from the group consisting of indium sealing, metal brazing, diffusion bonding, and anodic bonding. A transparent window member characterized by the following.

16. A method for manufacturing a transmission window member used for exposure in the wavelength region of extreme ultraviolet (EUV) or soft X-rays, provided in a housing that encloses a superfluorescent medium excited to a population inversion state, and for transmitting and emitting amplified light in the wavelength region, coherently amplified in the superfluorescent medium, to the vacuum environment outside the housing, A process of forming a transparent film on a substrate, in which a transparent film made of a low atomic number material that transmits light in the wavelength range is formed with a thickness of 1 nm to 500 nm, A support grid forming step involves removing a portion of the substrate and integrally forming a support grid with the permeable film to divide the permeable film into a plurality of partial openings and support it. A method for manufacturing a transparent window member, characterized by including the following:

17. In the method for manufacturing a transparent window member according to claim 16, The aforementioned permeable film formation step includes at least one of the following steps: forming a silicon nitride film or a polycrystalline silicon film by chemical vapor deposition; transferring a graphene film grown by chemical vapor deposition; and depositing carbon nanotubes to form a self-supporting film. The support grid formation step is performed by anisotropic etching or deep etching. A method for manufacturing a transparent window member characterized by the following.

18. In the method for manufacturing a transparent window member according to claim 16 or 17, The process further includes a capping step of forming a capping layer with a thickness of 5 nm or less on at least one surface of the aforementioned permeable film by sputtering or atomic layer deposition, the capping layer containing at least one selected from the group consisting of ruthenium, zirconium oxide, niobium oxide, molybdenum oxide, and boron carbide. A method for manufacturing a transparent window member characterized by the following.

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