Pellicles and membranes for lithographic apparatus

Abstract

First and second novel membranes for a lithography apparatus are disclosed. The first membrane includes a core substrate and a metal silicate layer. The metal silicate layer is the outermost layer of the first membrane. The second membrane includes a core substrate and a yttrium silicate layer. The yttrium silicate layer can be the outermost layer of the membrane, or the yttrium silicate layer can be disposed between the core substrate and a layer of yttrium or yttrium oxide. The first and second membranes can be provided in an EUV lithography apparatus. For example, the membranes can form part of a pellicle. The pellicle can be suitable for use adjacent a reticle in an EUV lithography apparatus. The membranes can also form part of a dynamic gas lock. The membranes can also form part of a spectral filter.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Application No. 22158569.8, filed February 24, 2022, the entire contents of which are incorporated by reference into this specification. [Background technology]

[0002] The present invention relates to a pellicle for a lithographic apparatus and an associated method for forming such a pellicle. The present invention further relates to a lithographic apparatus including a membrane disposed in the path of a radiation beam of the lithographic apparatus (used to form an image on a substrate).

[0003]

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can, for example, project a pattern from a patterning device (e.g. mask) onto a layer of radiation-sensitive material (resist) provided on the substrate.

[0004]

[0004] The wavelength of radiation used by a lithographic apparatus to project a pattern onto a substrate determines the minimum size of features that can be formed on the substrate. Lithographic apparatus using EUV radiation, which is electromagnetic radiation having a wavelength in the range of 4-20 nm, can be used to form smaller features on a substrate compared to conventional lithographic apparatus (which may use electromagnetic radiation having a wavelength of 193 nm, for example).

[0005]

[0005] A patterning device (e.g. a mask) used in a lithographic apparatus to impart a pattern to a radiation beam may form part of a mask assembly. The mask assembly may include a pellicle that protects the patterning device from particle contaminants. The pellicle may be supported by a pellicle frame.

[0006] It may be desirable to provide an apparatus and / or method that avoids or mitigates one or more problems associated with the prior art. Summary of the Invention

[0007] According to one aspect of the present disclosure, there is provided a membrane for a lithographic apparatus, the membrane comprising a core substrate and a metal silicate layer, the metal silicate layer being an outermost layer of the membrane.

[0008] The membrane may be provided in an EUV lithography apparatus.

[0009]

[0009] For example, the membrane may form part of a pellicle. The pellicle may be suitable for use adjacent to a reticle in an EUV lithography apparatus. In use, such a (reflective) pellicle is illuminated with EUV radiation, such as from an illumination system. It will be appreciated that the reticle is configured to impart a radiation beam received from the illumination system with a pattern in its cross-section to form a patterned radiation beam. A projection system collects the (reflected) patterned radiation beam and forms a (diffraction-limited) image of the reticle on a substrate (e.g. a resist-coated silicon wafer). Any contaminants on the reticle will typically alter the image formed on the substrate, which will lead to printing errors.

[0010]

[0010] To avoid particle contamination of the reticle, it is known to use a thin film known as a pellicle to protect the reticle. The pellicle is placed in front of the reticle and prevents particles from adhering to the reticle. The pellicle is positioned such that it is not sharply imaged by the projection system, so that particles on the pellicle do not interfere with the imaging process. The pellicle should be thick enough to prevent particles from impinging on the reticle, which could cause unacceptable printing errors, while being as thin as possible to reduce the absorption of EUV radiation by the pellicle. To protect the other layers of the pellicle, it is known to provide an outer layer on the pellicle that has better stability in the environment of the EUV lithography apparatus. Such an outer layer is sometimes called a capping layer.

[0011]

[0011] Alternatively, the membrane may form part of a dynamic gas lock. Alternatively, the membrane may form part of a spectral filter.

[0012]

[0012] Designing a film that is stable in the environment of a lithography tool is difficult for several reasons. First, the environment of a lithography tool causes alternating reduction and oxidation in the presence of EUV photons, high temperature, free radicals, ions and electrons. Second, it is desirable to provide a capping layer with a thickness as small as 5 nm to minimize attenuation of EUV radiation. For many materials, such a layer thickness is prone to significant degradation when provided in the environment of an EUV lithography tool. For example, most nitrides tend to oxidize, most oxides tend to reduce, and most metals tend to cause dewetting when typically provided in such a thin layer thickness. In addition, most materials tend to be subject to thermally induced outgassing and desorption phenomena.

[0013]

[0013] The membrane according to the first aspect is particularly advantageous, as discussed below.

[0014]

[0014] The metal silicate layer is usually Me x Sy O z where Me is a metal. Advantageously, it has been found that the metal silicate layer is suitable for use as a protective layer for the rest of the pellicle. In particular, under the conditions of use in an EUV lithography tool, such metal silicate layers have been found to be stable even at thicknesses of the order of 5 nm or less (which advantageously reduces the absorption of EUV radiation by the pellicle to an acceptable level). In particular, at high temperatures, it has been found that metal silicate layers on membranes with thicknesses of less than 5 nm are not susceptible to oxidation, to thermal dewetting, and to etching in the presence of hydrogen radicals, hydrogen ions (having energies of up to the order of 50 eV), and hydrogen plasmas with energies in the range of 1-30 eV.

[0015]

[0015] During use, the pellicle will be subjected to a large thermal load from EUV radiation. It is known to reduce the operating temperature of the pellicle by providing a metal layer on the pellicle that acts as an emissive layer. Metals typically absorb EUV radiation well and have a relatively high extinction coefficient for EUV radiation (compared to most pellicles that may be made from, for example, silicon). It is therefore desirable to minimize the thickness of such an emissive layer while still reducing the operating temperature of the pellicle to an acceptable level. A desirable thickness of the metal emissive layer may be on the order of 5 nm. However, metal layers having such thickness are susceptible to thermal dewetting and degrade unacceptably quickly in the environment of an EUV lithography apparatus. It has previously been proposed to use a metal silicate layer (wherein the metal is ruthenium, zirconium, or hafnium) between the silicon substrate and the metal (emissive) layer, since it has been found that such an intermediate metal silicate layer can prevent or reduce dewetting of the metal layer. In contrast to such an intermediate metal silicate layer, the film according to the first embodiment is the outermost layer of the film and acts as a protective layer for the rest of the film.

[0016]

[0016] The membrane may include two metal silicate layers. The two metal silicate layers may be disposed on either side of the core substrate. Each metal silicate layer may be an outermost layer of the membrane.

[0017] At least one metal of the metal silicate layer may be yttrium.

[0018]

[0018] In other words, the metal silicate layer is made of yttrium silicate (Y x S y O z For example, the metal silicate layer may include yttrium orthosilicate (Y2Si1O5) or ceramic Y2Si2O7.

[0019] At least one metal of the metal silicate layer may be ruthenium.

[0020] At least one of the metal silicate layers may be stable in the environment of an EUV lithography apparatus.

[0021]

[0021] It will be understood that the stability of the metal silicate layer is intended to mean that the metal silicate layer is less susceptible to oxidation, less susceptible to thermal dewetting, and less susceptible to plasma etching.

[0022] It will be appreciated that within the environment of an EUV lithography apparatus, the temperature of the film may typically cycle in the range of 20-600° C. Within the lithography apparatus, the hydrogen plasma may have an energy in the range of 1-30 eV. Typical hydrogen ion energies generated within the lithography apparatus may be, for example, ion energies of up to 50 eV (e.g., 1-30 eV).

[0023] At least one of the metal silicate layers may have a thickness of 10 nm or less.

[0024] At least one of the metal silicate layers may have a thickness of 5 nm or less.

[0025] In some embodiments, the thickness of the metal silicate layer may be about 4.5 nm or less. In some embodiments, the thickness of the metal silicate layer may be about 3.5 nm or less.

[0026]

[0026] The EUV transmittance of at least one of the metal silicate layers may be 96% or greater.

[0027] In some embodiments, the EUV transmittance of at least one of the metal silicate layers is 97% or greater. In some embodiments, the EUV transmittance of at least one of the metal silicate layers is 98% or greater. In some embodiments, the EUV transmittance of at least one of the metal silicate layers is 99% or greater.

[0028] According to a second aspect of the present disclosure, there is provided a membrane for a lithographic apparatus, the membrane comprising an yttrium silicate layer.

[0029]

[0029] In use, the membrane may be provided within an EUV lithography apparatus. For example, the membrane may form part of a pellicle. Alternatively, the membrane may form part of a dynamic gas lock. Alternatively, the membrane may form part of a spectral filter. As mentioned above, designing a membrane that is stable in the environment within a lithography apparatus is challenging for several reasons.

[0030]

[0030] The membrane according to the second aspect is particularly advantageous, as discussed below.

[0031]

[0031] The yttrium silicate layer is usually Y x S y O zAdvantageously, it has been found that the yttrium silicate layer is suitable for use as a protective layer for the rest of the pellicle. In particular, under the conditions of use in an EUV lithography tool, such a yttrium silicate layer has been found to be stable even at thicknesses of the order of 5 nm or less (which advantageously reduces the absorption of EUV radiation by the pellicle to an acceptable level). In particular, at high temperatures, it has been found that yttrium silicate layers on the membrane are particularly stable (e.g., resistant to oxidation, resistant to thermal dewetting, and resistant to plasma etching) even at thicknesses of less than 5 nm.

[0032]

[0032] The yttrium silicate layer may comprise yttrium orthosilicate (Y2Si1O5) or ceramic Y2Si2O7.

[0033] The membrane may further include a core substrate.

[0034]

[0034] The membrane may include two yttrium silicate layers. The two yttrium silicate layers may be disposed on either side of a core substrate.

[0035] At least one of the yttrium silicate layers may be the outermost layer of the membrane.

[0036] At least one of the yttrium silicate layers may be disposed between the core substrate and the layer of yttrium or yttrium oxide.

[0037] At least one of the yttrium silicate layers may have a thickness of 10 nm or less.

[0038] At least one of the yttrium silicate layers may have a thickness of 5 nm or less.

[0039] In some embodiments, the thickness of the yttrium silicate layer may be about 4.5 nm or less. In some embodiments, the thickness of the yttrium silicate layer may be about 3.5 nm or less.

[0040]

[0040] The EUV transmittance of at least one of the yttrium silicate layers may be 96% or greater.

[0041] In some embodiments, the EUV transmittance of at least one of the yttrium silicate layers is 97% or greater. In some embodiments, the EUV transmittance of at least one of the yttrium silicate layers is 98% or greater. In some embodiments, the EUV transmittance of at least one of the yttrium silicate layers is 99% or greater.

[0042]

[0042] The core substrate of the membrane of the first or second aspect of the present disclosure may include a silicon-based substrate.

[0043]

[0043] The silicon-based substrate is silicon and / or silicon nitride (SiN x ).

[0044] The core substrate of the membrane of the first or second aspect of the present disclosure may include a metal layer.

[0045]

[0045] Such a metal layer can act as an emissive layer, improving the removal of the EUV heat load from the film.

[0046]

[0046] The film of the first or second aspect of the present disclosure may further include a seed layer disposed between the silicon-based substrate and the metal layer.

[0047] According to a third aspect of the present disclosure there is provided a pellicle for a lithographic apparatus, the pellicle comprising a membrane according to any of the preceding claims.

[0048]

[0048] The pellicle may further include a boundary portion at the peripheral portion of the membrane.

[0049]

[0049] The pellicle may further include a frame positioned to support the pellicle.

[0050] According to a fourth aspect of the present disclosure, there is provided a patterning device and pellicle assembly comprising a patterning device and a pellicle of the third aspect of the present disclosure releasably engaged with the patterning device.

[0051]

[0051] According to a fifth aspect of the present disclosure, there is provided a lithographic apparatus operable to form an image of a patterning device on a substrate using a radiation beam, the lithographic apparatus including a patterning device and pellicle assembly of the fourth aspect of the present disclosure.

[0052]

[0052] According to a sixth aspect of the present disclosure, there is provided a lithographic apparatus operable to form an image of a patterning device on a substrate using a radiation beam, the lithographic apparatus including a film of the first or second aspect of the present disclosure positioned in the path of the radiation beam.

[0053]

[0053] The membrane may form part of a dynamic gas lock.

[0054]

[0054] The membrane may form part of a spectral filter.

[0055]

[0055] The membrane may form part of a pellicle.

[0056]

[0056] According to a seventh aspect of the present disclosure, there is provided a method of forming a film according to the first or second aspect of the present disclosure, the method comprising providing a silicon based substrate, applying a metal or metal oxide layer onto the silicon based substrate to form an intermediate film, and annealing the intermediate film to form a metal silicate layer from the silicon based substrate and the metal or metal oxide layer.

[0057]

[0057] The silicon-based substrate may include an outer layer of silicon oxide or silicon oxynitride.

[0058]

[0058] The silicon-based substrate may further include a silicon substrate. The silicon substrate may include, for example, a polycrystalline silicon substrate.

[0059]

[0059] Annealing the interlayer may include increasing the temperature of the interlayer to at least 700°C for an annealing period.

[0060] In some embodiments, annealing the interlayer may include increasing the temperature of the interlayer to at least 800° C. for an annealing period. In some embodiments, annealing the interlayer may include increasing the temperature of the interlayer to at least 900° C. for an annealing period.

[0061]

[0061] It will be understood that the annealing period can be long enough to form a metal silicate layer from a silicon-based substrate and a metal or metal oxide layer. Thus, the annealing period can be selected based on the material (e.g., the type of metal and silicon-based substrate used), the thickness of the metal or metal oxide layer, and / or the desired target thickness of the metal silicate layer. For metal silicate layers with a thickness of less than 10 nm (e.g., less than 5 nm), a relatively short annealing time may be sufficient.

[0062]

[0062] The annealing period may be long enough to ensure that substantially all of the metal or metal oxide layer is converted to a metal silicate layer.

[0063] In some embodiments, the annealing period may be longer than necessary, for example, to ensure that substantially all of the metal or metal oxide layer is converted to a metal silicate layer.

[0064] The annealing period may be at least 1 hour.

[0065] In some embodiments, the annealing period may be at least 2 hours.

[0066]

[0066] Annealing of the interlayer may be carried out in the presence of nitrogen gas at a pressure of 1 bar.

[0067]

[0067] In other embodiments, annealing of the intermediate film may be performed in vacuum. In some other embodiments, annealing of the intermediate film may be performed in situ (e.g., in a lithography apparatus). Such in situ annealing may be achieved by exposing the film to EUV radiation.

[0068]

[0068] It will be appreciated that one or more aspects or features set out above or referred to in the following description may be combined with one or more other aspects or features. [Brief description of the drawings]

[0069]

[0069] Some embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings. [Figure 1] 1 depicts a schematic diagram of a lithography system including a lithographic apparatus and a radiation source; [Diagram 2] 2 is a schematic diagram of a first embodiment of a novel membrane for a lithographic apparatus of the type shown in FIG. 1; [Diagram 3] 2 is a schematic diagram of a second embodiment of a novel membrane for a lithographic apparatus of the type shown in FIG. 1; [Figure 4] FIG. 2 is a schematic diagram of a third embodiment of a novel membrane for a lithographic apparatus of the type shown in FIG. [Diagram 5] FIG. 2 is a schematic diagram of a fourth embodiment of a novel membrane for a lithographic apparatus of the type shown in FIG. 1 . [Figure 6] FIG. 6 is a schematic diagram of a method for forming a novel membrane of the type shown in FIGS. 2-5. [Figure 7]7 shows an interlayer formed by the first and second steps of the method shown in FIG. 6. [Figure 8A] For one embodiment of a method by which a membrane of the type shown in FIG. 2 is obtained, the result of the third step of the method is shown in FIG. [Figure 8B] For one embodiment of a method by which a membrane of the type shown in FIG. 4 is obtained, the result of the third step of the method is shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0070]

[0070] Figure 1 shows a lithography system. The lithography system includes a radiation source SO and a lithography apparatus LA. The radiation source SO is configured to generate an extreme ultraviolet (EUV) radiation beam B. The lithography apparatus LA includes an illumination system IL, a support structure MT configured to support a reticle assembly 15 including a patterning device MA (e.g. a reticle or mask), a projection system PS, and a substrate table WT configured to support a substrate W. The illumination system IL is configured to condition the radiation beam B before it is incident on the patterning device MA. The projection system is configured to project the radiation beam B (here patterned by the patterning device MA) onto the substrate W. The substrate W may comprise a pattern already formed. In this case, the lithography apparatus aligns the patterned radiation beam B with a pattern already formed on the substrate W.

[0071]

[0071] The radiation source SO, the illumination system IL, the areas adjacent the support structure MT and the patterning device MA, and the projection system PS may all be constructed and arranged such that they can be isolated from the external environment. A gas (e.g. hydrogen) at a pressure below atmospheric pressure may be provided in the radiation source SO. A vacuum may be provided in the illumination system IL, the areas adjacent the support structure MT and the patterning device MA, and / or the projection system PS. A small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure may be provided in the illumination system IL, the areas adjacent the support structure MT and the patterning device MA, and / or the projection system PS.

[0072]

[0072] The radiation source SO shown in Fig. 1 is of a type that may be called a laser-produced plasma (LPP) source. A laser 1 (which may be, for example, a CO2 laser) is arranged to deposit energy via a laser beam 2 into a fuel, such as tin (Sn), provided from a fuel emitter 3. Tin is mentioned in the following description, but any suitable fuel may be used. The fuel may be, for example, in the form of a liquid and may be, for example, a metal or an alloy. The fuel emitter 3 may include a nozzle configured to direct the tin, for example in the form of droplets, along a trajectory towards a plasma formation region 4. The laser beam 2 is incident on the tin in the plasma formation region 4. A plasma 7 is created in the plasma formation region 4 by the deposition of laser energy in the tin. Radiation, including EUV radiation, is emitted from the plasma 7 during de-excitation and recombination of the ions of this plasma.

[0073]

[0073] The EUV radiation is collected and focused by a near-normal incidence radiation collector 5 (sometimes more commonly referred to as a normal incidence radiation collector). Collector 5 may have a multi-layer structure arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm). Collector 5 may have an elliptical configuration with two elliptical foci. The first focus may be located at the plasma formation region 4 and the second focus may be at an intermediate focus 6, as discussed below.

[0074]

[0074] In another embodiment of the laser produced plasma (LPP) source, the collector 5 may be a so-called grazing incidence collector configured to receive the EUV radiation at a grazing incidence angle and to focus the EUV radiation to an intermediate focus. The grazing incidence collector may for example be a nested collector including multiple grazing incidence reflectors. The grazing incidence reflectors may be arranged axially symmetrically with respect to the optical axis.

[0075]

[0075] The radiation source SO may include one or more contaminant traps (not shown). For example, the contaminant trap may be located between the plasma formation region 4 and the radiation collector 5. The contaminant trap may, for example, be a rotating foil trap, or any other suitable form of contaminant trap.

[0076]

[0076] The laser 1 may be separate from the radiation source SO. In this case, the laser beam 2 may be delivered from the laser 1 to the radiation source SO using, for example, a beam delivery system (not shown) including suitable directing mirrors and / or beam expanders, and / or other optics. The laser 1 and the radiation source SO may be collectively referred to as a radiation system.

[0077]

[0077] The radiation reflected by the collector 5 forms a radiation beam B. The radiation beam B is focused at a point 6 and forms an image of the plasma formation region 4, which acts as a virtual radiation source for the illumination system IL. The point 6 at which the radiation beam B is focused may be referred to as an intermediate focus. The radiation source SO is positioned such that the intermediate focus 6 is at or near an opening 8 in a closing structure 9 of the radiation source SO.

[0078]

[0078] The radiation beam B travels from a radiation source SO into an illumination system IL, which is configured to condition the radiation beam. The illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. Together, the facetted field mirror device 10 and the facetted pupil mirror device 11 provide the radiation beam B with a desired cross-sectional shape and a desired angular distribution. The radiation beam B travels from the illumination system IL and is incident on a reticle assembly 15, which is held by a support structure MT. The reticle assembly 15 includes a patterning device MA and a pellicle 19. The pellicle is attached to the patterning device MA via a pellicle frame 17. The reticle assembly 15 may be referred to as a reticle and pellicle assembly 15. The patterning device MA reflects the radiation beam B and patterns it. The illumination system IL may include other mirrors or devices in addition to or instead of the facetted field mirror device 10 and the facetted pupil mirror device 11.

[0079]

[0079] Following reflection from the patterning device MA, the patterned radiation beam B enters a projection system PS. The projection system includes a number of mirrors 13, 14 configured to project the radiation beam B onto a substrate W held by a substrate table WT. The projection system PS may form an image having smaller features than corresponding features on the patterning device MA by applying a demagnification factor to the radiation beam. For example, a demagnification factor of 4 may be applied. Although the projection system PS has two mirrors 13, 14 in Figure 1, the projection system PS may include any number of mirrors (for example six mirrors).

[0080]

[0080] The lithographic apparatus may, for example, be used in a scan mode, in which the support structure (e.g. mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto the substrate W (i.e. dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (e.g. mask table) MT may be determined by the de-magnification and image reversal characteristics of the projection system PS. The patterned radiation beam incident on the substrate W may include a band of radiation. The band of radiation may be referred to as an exposure slit. During a scan exposure, the movement of the substrate table WT and the support structure MT may be such that the exposure slit steps across an exposure field of the substrate W.

[0081]

[0081] The source SO and / or the lithographic apparatus shown in Figure 1 may include components that are not shown. For example, a spectral filter may be provided in the source SO. The spectral filter may be substantially transmissive to EUV radiation, while being substantially blocking to radiation of other wavelengths, such as infrared radiation.

[0082]

[0082] In other embodiments of the lithography system, the source SO may take other forms. For example, in another embodiment, the source SO may include one or more free electron lasers. The one or more free electron lasers may be configured to emit EUV radiation that may be provided to one or more lithography apparatus.

[0083]

[0083] As briefly mentioned above, the reticle assembly 15 includes a pellicle 19 disposed adjacent to the patterning device MA. The pellicle 19 is disposed in the path of the radiation beam B such that the radiation beam B passes through the pellicle 19 as it approaches the patterning device MA from the illumination system IL and as it is reflected by the patterning device MA towards the projection system PS. The pellicle 19 comprises a thin film or membrane that is substantially transparent to EUV radiation (although it will absorb small amounts of EUV radiation). An EUV transmissive pellicle or membrane that is substantially transparent to EUV radiation as described herein means that the pellicle 19 is transparent to at least 65% of EUV radiation, preferably at least 80% of EUV radiation, and more preferably at least 90% of EUV radiation. The pellicle 19 functions to protect the patterning device MA from particle contaminants.

[0084]

[0084] Despite efforts to maintain a clean environment inside the lithographic apparatus LA, particles may still be present inside the lithographic apparatus LA. In the absence of the pellicle 19, particles may accumulate on the patterning device MA. Particles on the patterning device MA may adversely affect the pattern imparted to the radiation beam B and therefore the pattern transferred to the substrate W. The pellicle 19 has the advantage of providing a barrier between the patterning device MA and the environment within the lithographic apparatus LA to prevent particles from accumulating on the patterning device MA.

[0085]

[0085] The pellicle 19 is positioned at a sufficient distance from the patterning device MA such that particles incident on the surface of the pellicle 19 are not within the field plane of the lithographic apparatus LA. This separation between the pellicle 19 and the patterning device MA serves to reduce the extent to which particles on the surface of the pellicle 19 impart a pattern to the radiation beam B imaged onto the substrate W. It will be appreciated that if a particle is present in the radiation beam B but at a position that is not in the field plane of the radiation beam B (e.g. at a position that is not at the surface of the patterning device MA), the image of the particle will not be in focus at the surface of the substrate W. In the absence of other considerations, it may be desirable to position the pellicle 19 at a significant distance from the patterning device MA. In practice, however, the space available within the lithographic apparatus LA to accommodate the pellicle is limited by the presence of other components. In some embodiments, the separation between pellicle 19 and patterning device MA may for example be between about 1 mm and 10 mm, such as between 1 mm and 5 mm, such as between 2 mm and 2.5 mm.

[0086]

[0086] The pellicle may include a boundary portion and a membrane. The boundary portion of the pellicle may be hollow and generally rectangular, and the membrane may be surrounded by the boundary portion. As known in the art, one type of pellicle may be formed by depositing one or more thin layers of material on a generally rectangular silicon substrate. The silicon substrate supports one or more of the multiple thin layers at this stage of building the pellicle. Once the desired or targeted layer thickness and composition is applied, a central portion of the silicon substrate is removed by etching (this is sometimes called back etching). A peripheral portion of the rectangular silicon substrate is not etched (or is etched to a lesser extent than the central portion). This peripheral portion forms the boundary portion of the final pellicle, while the one or more thin layers form the membrane of the pellicle (surrounded by the boundary portion). The boundary portion of the pellicle may be formed from silicon.

[0087]

[0087] A pellicle (e.g., including a membrane and a boundary) may require support from a more rigid pellicle frame. The pellicle frame may provide two functions. First, the pellicle frame may support the pellicle and tension the pellicle membrane. Second, the pellicle frame may facilitate connection of the pellicle to a patterning device (reticle). In one known arrangement, the pellicle frame may include a generally rectangular body portion that is bonded to the boundary portion of the pellicle and a titanium attachment mechanism that is bonded to the side of the body. An intermediate fixation member (called a stud) is fixed to the patterning device (reticle). The intermediate fixation member (stud) on the patterning device (reticle) may engage (e.g., releasably engage) with an attachment member of the pellicle frame.

[0088]

[0088] Ideally, the EUV transmittance of the pellicle 19 is as high as possible. However, in practice, a portion of the EUV radiation beam B is absorbed by the pellicle 19. Because the pellicle 19 is located in the direct path of the EUV radiation beam B and the power of the radiation beam B is large, the pellicle 19 absorbs a significant amount of power in use. Furthermore, as mentioned above, the area adjacent to or near the reticle assembly 15 (including the pellicle 19) may be in a vacuum state or may be supplied with a gas (such as hydrogen) at a pressure much lower than atmospheric pressure, which limits the removal of the EUV heat load by conduction and convection. Thus, the combination of the high heat load experienced by the pellicle 19 and this low operating ambient gas pressure may cause the temperature of the pellicle 19 film to increase significantly. Under the conditions in the lithographic apparatus LA, the pellicle 19 may degrade over time. The low pressure hydrogen gas supplied in the lithographic apparatus LA forms a hydrogen plasma in the presence of EUV radiation (during exposure). It has been found that hydrogen ions and hydrogen free radicals from the hydrogen plasma can chemically affect (e.g. reduce or etch) the pellicle 19, limiting its potential lifetime. The environment within the lithography apparatus LA, in the presence of the EUV radiation beam B, free radicals, ions and electrons, alternately causes reduction and oxidation. Furthermore, the associated degradation processes often proceed more rapidly at elevated temperatures.

[0089]

[0089] Related degradation effects often also occur on the outer surface of the membrane of the pellicle 19. Therefore, one way to extend the life of the pellicle is to apply a layer with higher stability in the environment of the EUV lithography tool (e.g., a layer with increased resistance to plasma etching) to the outer surface of the pellicle. Such an outer layer is sometimes called a capping layer. As mentioned above, the EUV transmittance of the pellicle 19 should be as high as possible (while still functioning to prevent particles from impacting the patterning device) to avoid high temperatures of the membrane. The choice of material for the capping layer should be based on a compromise between performance characteristics (EUV transmittance) and protection properties (protection of the layer itself and all its underlying layers).

[0090]

[0090] Some embodiments of the present disclosure relate to novel types of membranes (which may form part of pellicle 19) and methods of forming such membranes.

[0091] 2 is a schematic diagram of a first embodiment of a novel membrane 100 for a lithographic apparatus LA (e.g. as a membrane of a pellicle 19). The membrane comprises a core substrate 102 and a metal silicate layer 104. The metal silicate layer 104 is the outermost layer of the membrane 100. The metal silicate layer 104 can be considered to be a capping layer.

[0092] 3 is a schematic diagram of a second embodiment of a novel membrane 100a for a lithographic apparatus LA (for example as a membrane of a pellicle 19). The membrane 100a includes a core substrate 102 and two metal silicate layers 104a, 104b. The two metal silicate layers 104a, 104b are disposed on either side of the core substrate 102. Each metal silicate layer 104a, 104b is the outermost layer of the membrane 100a. The metal silicate layers 104a, 104b can be considered as capping layers.

[0093]

[0093] The membranes 100, 100a may form part of a pellicle 19 of the type shown in Figure 1 and described above. As mentioned above, it is desirable for the pellicle 19 to be as thin as possible to reduce absorption of EUV radiation by the pellicle 19, whilst desirably having a sufficient thickness to prevent particles from impinging on the reticle MA which could cause unacceptable printing errors.

[0094] Alternatively, the membrane 100, 100a may form part of a dynamic gas lock. Alternatively, the membrane 100, 100a may form part of a spectral filter.

[0095]

[0095] Designing a film that is stable in the environment of the lithography tool LA is difficult for several reasons. First, the environment of the lithography tool LA causes alternating reduction and oxidation in the presence of EUV photons, high temperature, free radicals, ions and electrons. Second, it is desirable to provide a capping layer with a small thickness, for example, on the order of 5 nm or less, to minimize attenuation of the EUV radiation beam B. For many materials, layers of such thickness are prone to significant degradation when provided in the environment of the EUV lithography tool LA. For example, in general, when provided in layers of such small thickness, most nitrides tend to oxidize, most oxides tend to reduce, and most metals tend to cause dewetting. Furthermore, most materials tend to be subject to thermally induced outgassing and desorption phenomena.

[0096]

[0096] The membranes 100, 100a shown diagrammatically in Figures 2 and 3 are particularly advantageous, as will be discussed below.

[0097] The metal silicate layers 104, 104a, and 104b are typically made of Me x S y O z where Me is a metal. Advantageously, it has been found that the metal silicate layer is suitable for use as a protective layer for the rest of the pellicle 19. In particular, under the conditions of use in an EUV lithography apparatus LA, such metal silicate layers 104, 104a, 104b have been found to be stable even at thicknesses of the order of 5 nm or less (which advantageously reduces the absorption of EUV radiation by the pellicle 19 to an acceptable level). In particular, at high temperatures, it has been found that the respective metal silicate layers 104, 104a, 104b on the membranes 100, 100a, even at thicknesses of less than 5 nm, are not susceptible to oxidation, to thermal dewetting, and to etching in the presence of hydrogen radicals, hydrogen ions (having energies of up to the order of 50 eV), and hydrogen plasmas having energies in the range of 1-30 eV.

[0098]

[0098] During use, the pellicle 19 will be subject to a large thermal load from the EUV radiation. It is known to reduce the operating temperature of the pellicle 19 by providing a metal layer on the pellicle 19, which acts as an emissive layer. Metals typically absorb EUV radiation well and have a relatively high extinction coefficient for EUV radiation (compared to the bulk of the pellicle 19, which may be made from silicon, for example). It is therefore desirable to minimize the thickness of such an emissive layer while still reducing the operating temperature of the pellicle 19 to an acceptable level. A desirable thickness of the metal emissive layer may be on the order of 5 nm. However, metal layers having such a thickness are susceptible to thermal dewetting and degrade unacceptably quickly in the environment of the EUV lithography apparatus LA. It has previously been proposed to use a metal silicate layer between the silicon substrate and the metal (emissive) layer, since it has been found that such an intermediate metal silicate layer can prevent or reduce dewetting of the metal layer. In contrast to such intermediate metal silicate layers, the metal silicate layers 104, 104a, 104b of the films 100, 100a shown in Figures 2 and 3 are the outermost layers of the films 100, 100a and act as protective layers for the remainder of the films 100, 100a.

[0099] In one embodiment known to work well, the metal of the metal silicate layers 104, 104a, 104b is yttrium. That is, the metal silicate layers 104, 104a, 104b are made of yttrium silicate (Y x S y O z For example, the metal silicate layers 104, 104a, 104b may include yttrium orthosilicate (Y2Si1O5) or ceramic Y2Si2O7.

[0100] [000100] In another embodiment, the metal of the metal silicate layers 104, 104a, 104b is ruthenium. That is, the metal silicate layers 104, 104a, 104b are ruthenium silicate (Ru x Sy O z ).

[0101] [000101] It is expected that there may be other metal silicates that may be stable in the environment of the EUV lithography tool LA. Thus, in other embodiments, the metal of the metal silicate layer 104, 104a, 104b may be a metal whose metal silicate is stable in the environment of the EUV lithography tool LA. It is understood that the stability of the metal silicate layer is intended to mean that the metal silicate layer is not susceptible to oxidation, is not susceptible to thermal dewetting, and is not susceptible to plasma etching. It is further understood that in the environment of the EUV lithography tool LA, the temperature of the film 100, 100a may typically cycle between about 20-600°C. In the lithography tool LA, the hydrogen plasma may have an energy in the range of 1-30 eV. The energy of typical hydrogen ions generated in the lithography tool LA may be, for example, an ion energy of up to about 50 eV (e.g., 1-30 eV).

[0102] [000102] In some embodiments, each metal silicate layer 104, 104a, 104b is 10 nm or less in thickness. In some embodiments, each metal silicate layer 104, 104a, 104b is 5 nm or less in thickness. In some embodiments, each metal silicate layer 104, 104a, 104b may be about 4.5 nm or less in thickness. In some embodiments, each metal silicate layer 104, 104a, 104b may be about 3.5 nm or less in thickness.

[0103] [000103] In some embodiments, the EUV transmittance of each metal silicate layer 104, 104a, 104b is 96% or greater. In some embodiments, the EUV transmittance of each metal silicate layer 104, 104a, 104b is 97% or greater. In some embodiments, the EUV transmittance of each metal silicate layer 104, 104a, 104b is 98% or greater. In some embodiments, the EUV transmittance of each metal silicate layer 104, 104a, 104b is 99% or greater.

[0104] 4 is a schematic diagram of a third embodiment of a novel membrane 200 for use in a lithographic apparatus LA (e.g., as a membrane of a pellicle 19). The membrane includes a core substrate 202, a yttrium silicate layer 204, and an outer layer 206. The yttrium silicate layer 204 is disposed between the core substrate 202 and the outer layer 206 of the membrane 200. The outer layer 206 may include yttrium or yttrium oxide.

[0105] [000105] Figure 5 is a schematic diagram of a fourth embodiment of a novel membrane 200a for a lithographic apparatus LA (e.g. as a membrane of a pellicle 19). The membrane 200a includes a core substrate 202, two yttrium silicate layers 204a, 204b, and two outer layers 206a, 206b. The two yttrium silicate layers 204a, 204b are disposed on either side of the core substrate 102. Each yttrium silicate layer 204a, 204b is disposed between the core substrate 202 and one of the outer layers 206a, 206b of the membrane 200a. The outer layers 206a, 206b may include yttrium or yttrium oxide.

[0106] [000106] The membranes 200, 200a may form part of a pellicle 19 of the type shown in Figure 1 and described above. As mentioned above, it is desirable for the pellicle 19 to be as thin as possible to reduce absorption of EUV radiation by the pellicle 19, while desirably having a sufficient thickness to prevent particles from impinging on the reticle MA that could cause unacceptable printing errors. Alternatively, the membranes 200, 200a may form part of a dynamic gas lock. Alternatively, the membranes 200, 200a may form part of a spectral filter.

[0107] [000107] As mentioned above, designing a membrane that is stable in the environment within the lithographic apparatus LA is challenging for a number of reasons. The membranes 200, 200a, shown generally in Figures 4 and 5, are particularly advantageous, as will be discussed below.

[0108] [000108] The yttrium silicate layers 204, 204a, 204b are typically x S y O z Advantageously, it has been found that the yttrium silicate layer is suitable for use as a protective layer for the rest of the pellicle 19. In particular, under the conditions of use in the EUV lithography apparatus LA, such yttrium silicate layers 204, 204a, 204b have been found to be stable even at thicknesses of the order of 5 nm or less (which advantageously reduces the absorption of EUV radiation by the pellicle 19 to an acceptable level). In particular, at high temperatures, it has been found that the respective yttrium silicate layers 204, 204a, 204b on the membranes 200, 200a, even at thicknesses of less than 5 nm, are not susceptible to oxidation, to thermal dewetting, and to etching in the presence of hydrogen radicals, hydrogen ions (having energies of up to the order of 50 eV), and hydrogen plasmas having energies in the range of 1-30 eV.

[0109] [000109] In some embodiments, each yttrium silicate layer 204, 204a, 204b may be 10 nm or less in thickness. In some embodiments, each yttrium silicate layer 204, 204a, 204b may be 5 nm or less in thickness. In some embodiments, each yttrium silicate layer 204, 204a, 204b may be about 4.5 nm or less in thickness. In some embodiments, each yttrium silicate layer 204, 204a, 204b may be about 3.5 nm or less in thickness.

[0110] [000110] In some embodiments, the EUV transmittance of each yttrium silicate layer 204, 204a, 204b is 96% or greater. In some embodiments, the EUV transmittance of each yttrium silicate layer 204, 204a, 204b is 97% or greater. In some embodiments, the EUV transmittance of each yttrium silicate layer 204, 204a, 204b is 98% or greater. In some embodiments, the EUV transmittance of each yttrium silicate layer 204, 204a, 204b is 99% or greater.

[0111] [000111] The core substrate 102, 202 of the membrane 100, 100a, 200, 200a may include a silicon-based substrate. The silicon-based substrate may be, for example, silicon and / or silicon nitride (SiN x ).

[0112] [000112] In some embodiments, the core substrate 102, 202 of the membrane 100, 100a, 200, 200a may include a metal layer. Such a metal layer may act as an emissive layer, thereby improving removal of EUV heat load from the membrane 100, 100a, 200, 200a.

[0113] [000113] The membrane 100,100a,200,200a may further include a seed layer disposed between the silicon based substrate and the metal layer of the core substrate 102,202.

[0114] [000114] A pellicle 19 of the type shown in Figure 1 and described above may include novel membranes 100, 100a, 200, 200a of the type shown above. Such a pellicle 19 may further include a boundary portion at the periphery of the membrane 100, 100a, 200, 200a. Additionally or alternatively, such a pellicle 19 may further include a frame disposed to support the pellicle 19, as is known in the art.

[0115] [000115] A pellicle 19 including novel membranes 100, 100a, 200, 200a of the type shown above may form part of a patterning device and pellicle assembly 15 that also includes a patterning device MA, with the pellicle 19 being releasably engaged with the patterning device MA.

[0116] [000116] Figure 6 is a schematic diagram of a method 300 for forming the novel membranes 100, 100a, 200, 200a.

[0117] [000117] First, the method 300 includes providing 302 a silicon-based substrate. The silicon-based substrate may include an outer layer of silicon oxide or silicon oxynitride. The silicon-based substrate may further include a silicon substrate. The silicon substrate may include, for example, a polycrystalline silicon substrate.

[0118] [000118] Next, the method 300 comprises depositing a metal or metal oxide layer (MeO x ) onto the silicon-based substrate to form an intermediate film. The thickness of the metal or metal oxide layer applied in step 304 may be less than 5 nm. For example, the thickness of the metal or metal oxide layer applied in step 304 may be less than 4 nm. For example, the thickness of the metal or metal oxide layer applied in step 304 may be less than 3 nm. For example, the thickness of the metal or metal oxide layer applied in step 304 may be less than 2 nm. For example, the thickness of the metal or metal oxide layer applied in step 304 may be less than 1 nm. For example, the thickness of the metal or metal oxide layer applied in step 304 may be less than 0.5 nm. The silicon-based substrate may include a barrier layer (such as SiO2) that may have substantially the same thickness as the thickness of the metal or metal oxide layer applied in step 304.

[0119] [000119] Finally, the method 300 includes annealing the intermediate film to form a metal silicate layer from the silicon-based substrate and the metal or metal oxide layer 306. As a result of annealing the intermediate film, the metal or metal oxide layer may partially or completely react with the silicon-based substrate to form a metal silicate layer.

[0120] [000120] Annealing the interlayer may include increasing the temperature of the interlayer to at least 700°C for the annealing period. In some embodiments, annealing the interlayer may include increasing the temperature of the interlayer to at least 800°C for the annealing period. In some embodiments, annealing the interlayer may include increasing the temperature of the interlayer to at least 900°C for the annealing period.

[0121] [000121] It will be appreciated that the annealing period may be long enough to form a metal silicate layer from the silicon-based substrate and the metal or metal oxide layer. Thus, the annealing period may be selected based on the material (e.g., the type of metal and silicon-based substrate used), the thickness of the metal or metal oxide layer, and / or the desired target thickness of the metal silicate layer. For metal silicate layers with thicknesses of less than 10 nm (e.g., less than 5 nm), a relatively short annealing time may be sufficient. In some embodiments, the annealing period is long enough to ensure that substantially all of the metal or metal oxide layer is converted to the metal silicate layer. In some embodiments, the annealing period may be longer than necessary, for example, to ensure that substantially all of the metal or metal oxide layer is converted to the metal silicate layer. For example, in some embodiments, the annealing period may be at least 1 hour. In some embodiments, the annealing period may be at least 2 hours.

[0122] [000122] Annealing of the intermediate film may be performed in the presence of nitrogen gas at a pressure of 1 bar. In other embodiments, annealing of the intermediate film may be performed in vacuum. In other embodiments, annealing of the intermediate film may be performed in situ (e.g., in the lithography apparatus LA). Such in situ annealing may be achieved by exposing the film to EUV radiation using the lithography apparatus LA.

[0123] [000123] The first step 302 and the second step 304 of the method shown in Figure 6 are illustrated diagrammatically in Figure 7. In particular, a silicon based substrate 400 is provided. In this example, the silicon based substrate 400 comprises a silicon substrate 402 and an outer layer 404 of silicon oxide or silicon oxynitride. In step 304, a metal or metal oxide layer 406 is applied onto the silicon based substrate 400, in particular onto the layer 404 of silicon oxide or silicon oxynitride, to form an intermediate film 408.

[0124] [000124] The result of the third step 306 of the method shown in Figure 6 is illustrated diagrammatically in Figures 8A and 8B. Figure 8A illustrates an embodiment of a method for obtaining a membrane 100 of the type shown in Figure 2. Figure 8B illustrates an embodiment of a method for obtaining a membrane 200 of the type shown in Figure 4.

[0125] [000125] As shown in Figure 8A, the intermediate film 408 is annealed to form the metal silicate layer 104 from the silicon-based substrate 400 and the metal or metal oxide layer 406. In particular, the silicon oxide or silicon oxynitride layer 404 and the metal or metal oxide layer 406 are combined by the annealing process to form the metal silicate layer 104. After the annealing process, the silicon oxide or silicon oxynitride layer 404 may be partially or completely absent (as shown in Figure 8A). In this embodiment, after the annealing process, the metal oxide layer 406 is completely absent such that the metal silicate layer 104 is the outermost layer of the resulting film 100.

[0126] [000126] As shown in Figure 8B, the intermediate film 408 is annealed to form the metal silicate layer 204 from the silicon-based substrate 400 and the metal or metal oxide layer 406. In particular, the silicon oxide or silicon oxynitride layer 404 and the metal or metal oxide layer 406 are combined by the annealing process to form the metal silicate layer 204. After the annealing process, the silicon oxide or silicon oxynitride layer 404 may be partially or completely absent (as shown in Figure 8B). In this embodiment, after the annealing process, the metal oxide layer 406 is partially absent such that the metal silicate layer 104 is disposed between the core substrate 202 and the metal oxide layer 406 of the resulting film 200.

[0127] [000127] The method 300 shown in Figure 6 and described above with reference to Figures 7 to 8B was used to form membranes 100, 100a, 200, 200a of the type shown in Figures 2 to 5. First, a SiN x Next, a silicon wafer was prepared by coating the silicon wafer with a metal oxide of various thicknesses using physical vapor deposition (PVD). x In particular, yttrium oxide (Y2O3), aluminum oxide (Al2O3), zirconium oxide (ZrO2), and hafnium oxide (HfO2) were all deposited by PVD. The deposited metal oxides were then subjected to the following conditions (see step 306): thermal annealing at 900°C in the presence of nitrogen gas at a pressure of 1 bar for 2 hours. This thermal annealing was performed in a tube oven at a pressure of 1 bar, with a nitrogen gas flow supplied from one end of the tube oven and the other end of the tube oven open to ambient conditions.

[0128] [000128] A silicon-containing underlayer (SiN x As a result of the combination of deposition of the material on a silicon substrate and a subsequent thermal annealing treatment, the metal oxide film formed a metal silicate layer, which was confirmed using X-ray photoelectron spectroscopy (XPS) when the metal oxide thickness was on the order of 5 nm or less.

[0129] [000129] After formation of the yttrium silicate layer, the resulting films 100, 100a, 200, 200a were subjected to the following conditions: (i) a temperature of 700°C and a flow rate of 10 21 cm 2 (ii) exposure to thermal hydrogen radicals at a flow rate of 10 at a temperature of 650 °C; 19 / cm 2 or (iii) exposure to 50 eV hydrogen ions at a temperature of 550 °C with an ion flux of 10 19 / cm 2 Exposure of the yttrium silicate to a -8 eV hydrogen plasma. Yttrium silicate was found to be stable under these conditions (e.g., based on XPS analysis). Furthermore, the underlying SiN x It was found that the hydrogen plasma etch rate of the substrate decreased from 0.15 nm / min to 0.0 nm / min.

[0130] [000130] The EUV absorption (extinction) coefficient of Y2Si1O5 is 0.0114 nm -1 Therefore, this material has 90% EUV transmission at a thickness of about 9 nm. If this thickness of material meets the pellicle specifications, this material can serve as a pellicle core material.

[0131] [000131] However, in some embodiments, yttrium silicate is provided as a capping layer, in which case less material is required. A 2.5 nm thick capping layer of Y2Si1O5 applied as a protective layer to both sides of a pellicle core has an EUV transmission of 94.5%. Thus, when applied to a 95.3% pellicle core, it results in a total EUV transmission of 90%.

[0132] [000132] As an alternative to the method 300 shown in Figure 6, in some embodiments, a metal silicate layer (e.g., a yttrium silicate layer) may be deposited directly on the base substrate 102, 202. For example, this may be accomplished using physical vapor deposition (PVD). For such embodiments, the base substrate 102, 202 may be a silicon substrate, and this process provides improved control of the thickness of the metal silicate layer.

[0133] [000133] References herein to a mask or reticle may be construed as a reference to a patterning device (a mask or reticle is an example of a patterning device), and these terms may be used interchangeably. In particular, the term mask assembly is synonymous with reticle assembly and patterning device assembly.

[0134] [000134] Although specific reference is made herein to embodiments of the invention in the context of lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatus may be commonly referred to as lithography tools. Such lithography tools may use vacuum or ambient (non-vacuum) conditions.

[0135] [000135] The term "EUV radiation" may be taken to encompass electromagnetic radiation having a wavelength in the range of 4 to 20 nm, for example in the range of 13 to 14 nm. EUV radiation may have a wavelength less than 10 nm, for example in the range of 4 to 10 nm, such as 6.7 nm or 6.8 nm.

[0136] [000136] Although specific reference is made in this specification to the use of lithographic apparatus in IC manufacture, it should be understood that the lithographic apparatus described herein may have other applications. Other possible applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0137] [000137] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The above description is intended to be illustrative and not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the appended claims.

Claims

1. 1. A membrane for a lithographic apparatus, comprising: A core substrate; a metal silicate layer which is the outermost layer of the film; Including, a membrane.

2. The membrane of claim 1 , wherein the membrane comprises two metal silicate layers disposed on opposite sides of the core substrate, each metal silicate layer being an outermost layer of the membrane.

3. 3. The membrane of claim 1 or claim 2, wherein at least one metal of the metal silicate layer is yttrium.

4. 3. The membrane of claim 1 or claim 2, wherein at least one metal of the metal silicate layer is ruthenium.

5. The membrane of any one of claims 1 to 4, wherein at least one of the metal silicate layers is stable in the environment of an EUV lithography apparatus.

6. The membrane of any one of claims 1 to 5, wherein at least one of the metal silicate layers has a thickness of 10 nm or less.

7. The membrane of claim 6 , wherein at least one of the metal silicate layers has a thickness of 5 nm or less.

8. The film of any one of claims 1 to 7, wherein the EUV transmittance of at least one of the metal silicate layers is 96% or greater.

9. A membrane for a lithographic apparatus, the membrane comprising a yttrium silicate layer.

10. The membrane of claim 9 further comprising a core substrate.

11. The membrane of claim 10 , wherein the membrane comprises two yttrium silicate layers, the two yttrium silicate layers disposed on opposite sides of the core substrate.

12. The membrane of any one of claims 9 to 11, wherein at least one of the yttrium silicate layers is an outermost layer of the membrane.

13. The membrane of any one of claims 9 to 11, wherein at least one of the yttrium silicate layers is disposed between the core substrate and a layer of yttrium or yttrium oxide.

14. The membrane of any one of claims 9 to 13, wherein at least one of the yttrium silicate layers has a thickness of 10 nm or less.

15. 15. The membrane of claim 14, wherein at least one of the yttrium silicate layers has a thickness of 5 nm or less.

16. The membrane of any one of claims 9 to 15, wherein the EUV transmission of at least one of the yttrium silicate layers is 96% or greater.

17. The membrane of any one of claims 1 to 16 when depending directly or indirectly from claim 1 or claim 10, wherein the core substrate of the membrane comprises a silicon-based substrate.

18. The membrane of any one of claims 1 to 17 when depending directly or indirectly from claim 1 or claim 10, wherein the core substrate of the membrane comprises a metal layer.

19. 20. The film of claim 18 when dependent on claim 17, wherein the film further comprises a seed layer disposed between the silicon-based substrate and the metal layer.

20. A pellicle for a lithographic apparatus, comprising a membrane according to any one of claims 1 to 19.

21. 21. The pellicle of claim 20, further comprising a boundary portion at a peripheral portion of the membrane.

22. 22. The pellicle of claim 20 or claim 21, further comprising a frame arranged to support the pellicle.

23. 1. A patterning device and pellicle assembly, comprising: A patterning device; A pellicle according to any one of claims 20 to 22 releasably engaged with the patterning device; a patterning device and pellicle assembly comprising:

24. A lithographic apparatus operable to form an image of a patterning device on a substrate using a radiation beam, the lithographic apparatus comprising the patterning device and pellicle assembly according to claim 23.

25. A lithographic apparatus operable to form an image of a patterning device on a substrate using a radiation beam, the lithographic apparatus comprising a membrane according to any one of claims 1 to 19 positioned in a path of the radiation beam.

26. The lithographic apparatus of claim 25, wherein the membrane forms part of a dynamic gas lock.

27. The lithographic apparatus of claim 25, wherein the membrane forms part of a spectral filter.

28. The lithographic apparatus of claim 25, wherein the membrane forms part of a pellicle.

29. A method for forming the film according to any one of claims 1 to 19, comprising the steps of: Providing a silicon based substrate; applying a metal or metal oxide layer onto the silicon-based substrate to form an intermediate film; annealing the intermediate film to form the metal silicate layer from the silicon-based substrate and the metal or metal oxide layer; A method comprising:

30. 30. The method of claim 29, wherein the silicon-based substrate comprises an outer layer of silicon oxide or silicon oxynitride.

31. 31. The method of claim 29 or claim 30, wherein annealing the interlayer comprises increasing the temperature of the interlayer to at least 700°C for an annealing period.

32. 32. The method of claim 31, wherein the annealing period is long enough to ensure that substantially all of the metal or metal oxide layer is converted to the metal silicate layer.

33. 33. The method of claim 31 or claim 32, wherein the annealing period is at least 1 hour.

34. The method of any one of claims 29 to 33, wherein annealing the intermediate film is carried out in the presence of nitrogen gas at a pressure of 1 bar.

Images