Networked thin film membranes and methods of forming the same

Abstract

The present disclosure relates to a networked thin film membrane and methods of forming the same. A thin film for protecting a photomask from contaminant particles is provided. The thin film includes a thin film membrane including at least one porous membrane. The at least one porous membrane includes a network of a plurality of nanotubes. At least one nanotube of the plurality of nanotubes includes a core nanotube and a shell nanotube surrounding the core nanotube. The core nanotube includes a material different from the shell nanotube. The thin film further includes a thin film border attached to the thin film membrane along a peripheral region of the thin film membrane and a thin film frame attached to the thin film border.

Description

Technical Field

[0001] This disclosure generally relates to network-type thin film membranes and methods for forming them. Background Technology

[0002] In the semiconductor integrated circuit (IC) industry, technological advancements in IC materials and design have resulted in multiple generations of ICs, each featuring smaller and more complex circuitry than the previous generation. Throughout IC development, functional density (i.e., the number of interconnect devices per chip area) has generally increased, while geometry (i.e., the smallest component (or line) that can be created using manufacturing processes) has decreased. This miniaturization typically provides benefits through increased production efficiency and reduced associated costs. However, this miniaturization also increases the complexity of IC processing and manufacturing.

[0003] In the manufacturing process of IC devices, photolithography is used to form circuit patterns on a wafer. In photolithography, a photomask is used to transfer the desired pattern onto the wafer. When the photomask is contaminated by foreign matter (such as particles) from the surrounding environment, defects may appear on the wafer where the pattern has been transferred. Summary of the Invention

[0004] A first aspect of this disclosure relates to a thin film comprising: a thin film membrane including at least one porous membrane, the at least one porous membrane comprising a network of a plurality of nanotubes, at least one of the plurality of nanotubes comprising a core nanotube and a shell nanotube surrounding the core nanotube, the core nanotube comprising a material different from the shell nanotube; a thin film boundary attached to the thin film membrane along a peripheral region of the thin film membrane; and a thin film frame attached to the thin film boundary.

[0005] A second aspect of this disclosure relates to a method for forming a mask film system, comprising: forming a thin film membrane comprising a porous membrane over a filter membrane, the porous membrane comprising a network of a plurality of nanotubes, at least one of the plurality of nanotubes comprising a core nanotube and a shell nanotube surrounding the core nanotube; transferring the thin film membrane from the filter membrane to a film boundary; attaching the film boundary to a film frame; and mounting the film frame onto a photomask comprising a patterned region.

[0006] A third aspect of this disclosure relates to a method for photolithography, comprising: providing a thin film comprising a thin film, wherein the thin film comprises at least one porous film formed of a network of a plurality of nanotubes, at least one of the plurality of nanotubes comprising a core nanotube and a shell nanotube surrounding the core nanotube, the shell nanotube being composed of a boron-containing compound; mounting the thin film onto a photomask, wherein the photomask comprises a patterned surface; loading the photomask on which the thin film is mounted onto a photolithography system; loading a semiconductor wafer onto a substrate stage of the photolithography system; and performing a photolithography exposure process to transfer a pattern of the patterned surface from the photomask to the semiconductor wafer. Attached Figure Description

[0007] The various aspects of this disclosure can be best understood from the following detailed description when read in conjunction with the accompanying drawings. It should be noted that, according to industry standard practice, the various features are not drawn to scale. In fact, for clarity of discussion, the dimensions of the various features may be arbitrarily enlarged or reduced.

[0008] Figure 1 This is a flowchart of a method for manufacturing a mask film system according to some embodiments.

[0009] Figures 2A-2E This is a cross-sectional view of various stages of a mask film forming system according to some embodiments.

[0010] Figure 3 This is a schematic perspective view of nanotubes according to some embodiments.

[0011] Figure 4 This is an illustration of a thin film frame shown in cross-sectional and side views according to some embodiments.

[0012] Figure 5 This is a cross-sectional view of a photomask according to some embodiments.

[0013] Figure 6 This is a schematic diagram of a photolithography system according to some embodiments. Detailed Implementation

[0014] The following disclosure provides numerous different embodiments or examples for implementing various features of the provided subject matter. Specific examples of components and arrangements are described below to simplify this disclosure. Of course, these are merely examples and are not intended to be limiting. For example, in the following description, forming a first feature above or on a second feature may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which an additional feature may be formed between the first and second features such that the first and second features do not need to be in direct contact. Furthermore, reference numerals and / or letters may be repeated in various examples in this disclosure. Such repetition is for the purpose of simplicity and clarity and does not in itself indicate a relationship between the various embodiments and / or configurations discussed.

[0015] In addition, for ease of description, spatially related terms (e.g., "below," "below," "lower than," "above," "upper") may be used herein to describe the relationship of one element or feature shown in the figure relative to another element(s) or feature(s). These spatially related terms are intended to cover different orientations of the device in use or operation other than those shown in the figure. The device may be oriented in other ways (rotated 90 degrees or in other orientations), and the spatially related descriptors used herein shall be interpreted accordingly.

[0016] In semiconductor manufacturing, various photolithography processes are widely used in defining device and circuit patterns. Different photolithography processes are used depending on the size of the feature to be defined. In photolithography, a pattern existing on a photomask or mask is transferred to a photosensitive photoresist coating by irradiating the photomask. Light is modulated by the mask pattern and imaged onto the wafer coated with photoresist. Typically, as the pattern becomes smaller, shorter wavelengths are used. In extreme ultraviolet (EUV) lithography, wavelengths of approximately 13.5 nm are typically used to produce feature sizes smaller than 32 nanometers.

[0017] Thin films, including pellicle membranes, are typically placed over the patterned side of a photomask (with gaps) to protect the photomask from contamination during processing and exposure. Therefore, the film protects the photomask from unwanted particles that would otherwise adversely affect the fidelity of pattern transfer on the wafer. Because the film continuously covers the photomask during exposure, stringent requirements are placed on its absorbency, durability, and particle shielding capabilities.

[0018] Finding suitable thin-film materials with high transmittance and stability at EUV wavelengths has always been challenging in EUV lithography. During EUV lithography, film damage occurs due to the heat generated by EUV exposure and hydrogen plasma. This film damage can shorten the film's lifespan.

[0019] Embodiments of this disclosure provide thin-film membranes with improved chemical and thermal stability against EUV light. The thin-film membrane is formed from a network of multiple heterostructured nanotubes. The nanotubes have a core-shell structure comprising a carbon nanotube as a core and a boron nitride nanotube as a shell. Boron nitride has higher chemical and thermal stability than carbon, thus helping to prevent damage to the carbon nanotube core from EUV exposure and hydrogen flow. As a result, the reliability and lifetime of the thin-film membrane are improved.

[0020] Figure 1 This is a flowchart of a method 100 for manufacturing a mask film structure according to some embodiments of the present disclosure. Figures 2A-2E It is based on Figure 1 A cross-sectional view of a mask film system 200 manufactured by one or more steps of method 100. It should be understood that, for additional embodiments of the method, additional steps may be provided before, during, and after method 100, and some steps described below may be replaced or eliminated. It should also be understood that, for additional embodiments of semiconductor structures, additional features may be added to the thin-film-mask structure, and some features described below may be replaced or eliminated.

[0021] refer to Figure 1 and Figure 2A According to some embodiments, method 100 includes operation 102, in which a thin film membrane 210 is formed over filter membrane 202. Figure 2A This is a cross-sectional view of a mask film system 200 after a thin film 210 has been formed on a filter membrane 202, according to some embodiments.

[0022] refer to Figure 2AA filter membrane 202 is provided. The filter membrane 202 is a porous membrane. In some embodiments, the filter membrane 202 has pores with a diameter between about 0.1 μm and about 5 μm. In one example, the pore size is about 0.1 μm to about 2 μm. In another example, the pore size is about 0.45 μm. In some embodiments, the filter membrane 202 is formed or coated with polyethylene terephthalate (PET). In some embodiments, the filter membrane 202 is formed or coated with other suitable materials such as nylon, cellulose, polymethyl methacrylate (PMMA), polystyrene (PS), polytetrafluoroethylene (PTFE), or polybenzoxazole (PBO). In some embodiments, the filter membrane 202 is formed from cellulose-based filter paper. In some embodiments, the filter membrane 202 is a hydrophilic membrane. In some other embodiments, the filter membrane 202 is a hydrophobic membrane.

[0023] Thin film 210 is suitable for preventing contaminant particles from falling onto the photomask (e.g., photomask 250). Figure 2E On the photomask, and to prevent the deterioration of the photolithography process (e.g., by keeping contaminant particles away from the focal plane of the photomask).

[0024] The thin film 210 is transparent to the radiation beam used in the photolithography patterning process. In some embodiments, the thin film 210 is transparent to UV light. In some embodiments, the thin film 210 is transparent to EUV light. The thickness of the thin film 210 is configured to provide sufficient strength to withstand the pressure generated by the collision of contaminant particles with the film without causing film degradation. In some embodiments, the thin film 210 may have a thickness between about 5 nm and 50 nm. The thickness of the thin film 210 may be greater, depending on the porosity of the thin film 210.

[0025] Thin film 210 is a porous membrane comprising one or more porous films 212. Each porous film 212 comprises a network of nanotubes 214 arranged intersecting each other. Individual nanotubes 214 are randomly arranged within the porous film 212 such that the nanotubes 214 are not arranged along a main or dominant direction within the porous film 212. However, the nanotubes 214 of the porous film 212 can be provided in an ordered manner. The nanotubes 214 can be provided, for example, along a main direction or multiple main directions.

[0026] Nanotubes 214 can also be bundled within the porous film 212, such that multiple individual nanotubes 214 form a bundle (i.e., a wire or rope-like structure). As a result, the porous film 212 comprises a network of multiple bundles of nanotubes 214. A nanotube bundle can include, for example, 2-20 individual nanotubes 214. Within a nanotube bundle, the individual nanotubes 214 can be aligned and connected along their longitudinal direction. Nanotubes 214 in a bundle can also be connected end-to-end, such that the length of the nanotube bundle is greater than the length of an individual nanotube. The nanotubes 214 are typically connected by van der Waals forces.

[0027] Due to the presence of open regions within the network of nanotubes 214, the porous film 212 exhibits a relatively low density. In some embodiments, the porous film 212 may have a density of approximately 0.01 g / cm³. 3 Approximately 2g / cm 3 The density of the porous film 212 is important. In some cases, if the density of the porous film 212 is too low, large openings in the porous film 212 may cause particles to penetrate into the photomask, resulting in critical size (CD) errors in the resist pattern. In some cases, if the density of the porous film 212 is too high, it may hinder the transmission of EUV light. To prevent particle penetration, in some embodiments, the film 210 may include multiple porous films 212 arranged in a stacked manner on top of each other to reduce the opening area. Since the nanotubes in the low-density porous film are subjected to beam vibrations under vacuum, this is considered a particle source in EUV lithography. Stacking low-density porous films also helps to reduce beam vibrations, thereby preventing the formation of contaminant particles.

[0028] Nanotube 214 can have various cross-sectional shapes, such as, but not limited to, circular, elliptical, or polygonal cross-sectional shapes. In some embodiments, nanotube 214 can have a heterogeneous structure comprising at least two different materials.

[0029] Figure 3 This is a schematic perspective view of a heterostructured nanotube 214 according to some embodiments. In some embodiments and as... Figure 3 As shown, nanotube 214 has a core-shell structure comprising a nanotube core 214A of a first material and a nanotube shell 214B of a second material surrounding the nanotube core 214A. The core material (i.e., the first material) is transparent to EUV light. In some embodiments, the nanotube core 214A is formed of carbon nanotubes, including single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). In some embodiments, the SWCNT core may have a diameter of about 0.5 nm to about 2 nm. In some embodiments, the MWCNT core may have a diameter of about 5 nm to about 30 nm. In some embodiments, the nanotube core 214A has a length of about 1 μm to about 10 mm.

[0030] The nanotube shell 214B comprises a material with high oxidation and chemical resistance. The nanotube shell 214B thus helps protect the nanotube core 214A from UV or EUV light and from ionized gases (e.g., H+ gas) in contact with the nanotube shell 214B. The nanotube shell 214B also functions as a thermally conductive layer, facilitating the transfer of heat energy from the nanotube core 214A to the environment surrounding the thin film 210. In some embodiments, the nanotube shell 214B comprises a low extinction coefficient material to ensure sufficient transmission of UV or EUV light. In some embodiments, the shell material (i.e., the second material) may have an extinction coefficient less than or equal to 0.02. In some embodiments, the shell material allows 80% or more, 85% or more, 90% or more, or 95% or more of radiation to be transmitted to the photomask. In some embodiments, the nanotube shell 214B may comprise boron nitride (BN), boron (B), boron carbide (B4C), boron carbonitride (BCN), silicon nitride (SiN), silicon carbide (SiC), silicon boron nitride (SiBN), or silicon boron carbide (SiBC). In some embodiments, the nanotube shell 214B is formed of single-walled boron nitride nanotubes (BNNTs). In some other embodiments, the nanotube shell 214B is formed of multi-walled BNNTs. The thickness of the nanotube shell 214B is controlled such that the nanotube shell 214B does not reduce the transparency of the thin film 210 to UV or EUV light, while providing reliable protection for the nanotube core 214A. In some embodiments, the nanotube shell 214B may have a thickness between about 1 nm and about 10 nm. In some cases, if the thickness of the nanotube shell 214B is too small, the protection of the nanotube core 214A from UV or EUV radiation or chemical attack may be insufficient. In some cases, if the thickness of the nanotube shell 214B is too large, the transparency of the thin film 210 decreases. In some embodiments, the thickness of the nanotube shell 214 is 5 nm (varying within 10%).

[0031] In some embodiments, nanotubes 214 can be formed by growing one or more nanotubes of a first material within a nanotube template of a second material. The nanotube template of the second material acts as an encapsulation shell, wherein the confined second material can be reconfigured into at least one nanotube of the first material. The size of the nanotube core 214A is thus limited by the size of the nanotube shell 214B. In some embodiments, the nanotube shell 214B is formed by plasma arc discharge, laser vaporization, ball milling, laser ablation, or thermal plasma jetting. The aggregation of molecules of the first material into the nanotube core inside the nanotube shell 214B can be achieved by electron beam irradiation or heat treatment.

[0032] In some embodiments, the nanotube 214 may alternatively be formed by coating the nanotube core 214A with a shell material. In some embodiments, the nanotube core 214A may be formed by plasma arc discharge, laser vaporization, ball milling, laser ablation, or thermal plasma jetting. The deposition of the shell material providing the nanotube shell 214B may be performed using deposition processes such as ion beam deposition, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), physical vapor deposition (PVD), or atomic layer deposition (ALD). During deposition, the stage may be rotated or tilted to ensure that the shell material is conformally and uniformly deposited onto the nanotube core 214A. In some embodiments, and when the nanotube shell 214B comprises BN, the BN shell may be formed by flowing boron (e.g., boron oxide B2O3 or borate H3BO3) and nitrogen (e.g., nitrogen N2, ammonia NH3, or urea CO(NH2)2) precursors into the reaction chamber. In some other embodiments, the BN shell can be formed by CVD by flowing boron trihalide (boron trichloride BCl3 or boron trifluoride BF3) with N2 or NH3, diborane B2H6 with NH3, and a single-source precursor (e.g., borazine B3H6N3 or ammoniaborane H3NBH3). In some embodiments, CVD can be performed at a temperature between about 500°C and about 1200°C.

[0033] In some embodiments, the porous film 212 can be formed by first forming a suspension of nanotubes 214 in a liquid medium. In some embodiments, the suspension is formed by adding nanotubes 214 to the liquid medium under mixing conditions. The mixture is then sonicated to ensure that the nanotubes 214 are well dispersed in the liquid medium. The liquid medium is a non-solvent liquid medium in which the nanotubes 214 do not react with the nanotubes 214 and in which the nanotubes 214 are substantially insoluble. The liquid medium also has a low boiling point, allowing for easy and rapid removal of the liquid medium, which is beneficial for the drying of the subsequently formed continuous nanotube network. Examples of suitable non-solvent liquid media that can be used to prepare the nanotube suspension include, but are not limited to, water, volatile organic liquids such as acetone, ethanol, methanol, n-hexane, diethyl ether, acetonitrile, chloroform, DMF, and mixtures thereof. In some embodiments, the suspension is formed by dispersing the nanotubes 214 in water.

[0034] In some embodiments, the suspension may also include a surfactant to maintain the suspension and / or other chemical agents to promote nanotube network formation or dehydration. For example, Triton X-100 and sodium dodecylbenzenesulfonate may be used. However, sometimes, a surfactant may not be necessary if the nanotubes 214 can form a stable suspension in a liquid medium without a surfactant.

[0035] The concentration of nanotubes 214 in the suspension is controlled to promote dispersion and minimize aggregation of nanotubes 214. In some embodiments, the concentration of nanotubes 214 in the suspension is less than 500 mg / L. In some embodiments, the concentration of nanotubes 214 in the suspension is from about 25 mg / L to about 150 mg / L. In some embodiments, the concentration of nanotubes 214 in the suspension is from about 40 mg / L to about 100 mg / L.

[0036] Next, a suspension of nanotubes 214 is applied to the surface of the filter membrane 202, for example, by spin coating or dip coating. The suspension is filtered by the filter membrane 202 to remove the liquid medium, leaving a layer of continuous nanotubes 214 on the filter membrane 202. The layer of continuous nanotubes 214 constitutes a monolayer of the porous membrane 212. In some embodiments, the filtration step is performed with the aid of a vacuum to pull the liquid medium through the filter membrane 202. The amount of vacuum used depends on factors such as the porosity of the filter membrane 202, the viscosity of the liquid medium, the movement speed of the filter membrane 202, and the concentration of nanotubes 214 in the suspension. All these parameters can be manipulated to achieve the desired properties of the nanotube network, including the thickness and porosity of the continuous network. The deposited porous membrane 212 can then be cleaned with a cleaning solvent to remove any contaminants thereon. Suitable cleaning solvents include, but are not limited to, water and alcohol, such as ethanol. In some embodiments, the suspension application, filtration, and cleaning process can be repeated several times to form a stack of porous membranes 212 to reduce the open area in the resulting membrane 210.

[0037] refer to Figure 1 and Figure 2B According to some embodiments, the method proceeds to operation 104, in which the film boundary 220 is attached to the film membrane 210. Figure 2B According to some embodiments, after attaching the thin film boundary 220 to the thin film 210 Figure 2A A cross-sectional view of the mask film system 200.

[0038] refer to Figure 2BA thin film boundary 220 is attached along the peripheral portion of the thin film membrane 210. In some embodiments, the thin film boundary 220 is made of silicon, silicon carbide, silicon nitride, silicon dioxide, silicon oxynitride, Al2O3, Ti, or a combination thereof. To attach the thin film boundary 220 to the thin film membrane 210, in some embodiments, the thin film boundary 220 is first brought into solid contact with the thin film membrane 210. The thin film boundary 220 is then pressed onto the thin film membrane 210 to secure the thin film boundary 220 to the thin film membrane 210 (assuming sufficient force is applied). In some embodiments, the thin film boundary 220 and the thin film membrane 210 are held together by van der Waals forces. In some embodiments, an adhesive is used to attach the thin film boundary 220 to the thin film membrane 210 to ensure better adhesion. The adhesive needs to have low gas release to avoid material deposition on the mask surface. In some embodiments, the low-gas-release adhesive exhibits a gas release amount of TML of 1.0 or less when tested according to the method specified in ASTM E595-93. Here, TML is the total mass loss as defined in ASTM E595-93.

[0039] refer to Figure 1 and Figure 2C According to some embodiments, the method proceeds to operation 106, in which filter membrane 202 is removed from membrane membrane 210. Figure 2C According to some embodiments, after removing filter membrane 202 from membrane membrane 210 Figure 2B A cross-sectional view of the mask film system 200.

[0040] refer to Figure 2C ,Will Figure 2B The components of the membrane 210 and filter membrane 202 shown are inverted, such that the filter membrane 202 is on top of the membrane 210. The filter membrane 202 is then removed from the membrane 210. In some embodiments, the filter membrane 202 can be removed by peeling or pulling it away from the membrane 210. Figure 2C As shown, after the filter membrane 202 is removed, the membrane membrane 210 is supported by the membrane boundary 220 along the peripheral portion of the membrane membrane 210.

[0041] refer to Figure 1 and Figure 2D According to some embodiments, the method proceeds to operation 108, in which the components of the thin film 210 and the thin film boundary 220 are attached to the thin film frame 230. Figure 2D According to some embodiments, after attaching the components of the thin film 210 and the thin film boundary 220 to the thin film frame 230... Figure 2C A cross-sectional view of the mask film system 200.

[0042] refer to Figure 2DThe thin film frame 230 is configured to properly fix the thin film 210 to the photomask 250. Figure 2E The film frame 230 can be designed in various sizes, shapes, and configurations. In some embodiments, the film frame 230 can have a circular, rectangular, or any other suitable shape.

[0043] The film frame 230 may include a rigid material with sufficient mechanical strength and is designed in a shape, size, and configuration to properly secure the film 210 to the film frame 230. In some embodiments, the film frame 230 may include a porous material. Exemplary materials that may be used for the film frame 230 include, but are not limited to, anodized aluminum formed using aluminum (Al), aluminum alloys, titanium (Ti), nickel (Ni), gold (Au), silver (Ag), copper (Cu), molybdenum (Mo), platinum (Pt), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), palladium (Pd), tantalum (Ta), tungsten (W), silicon, polymers, other suitable materials, and / or combinations thereof. In some embodiments, the film frame 230 may include a frame material having a coefficient of thermal expansion (CTE) determined according to design specifications. In some embodiments, the film frame 230 is formed of an aluminum-titanium alloy.

[0044] In some embodiments, the membrane frame 230 may include a plurality of vent holes 232. The vent holes 232 are configured to accommodate equivalent air pressure. Figure 4 This is an illustration of a membrane frame 230 shown in cross-sectional and side views according to some embodiments. Vent holes 232 are provided on the longer side member 230A and the shorter side member 230B of the membrane frame 230. Because the membrane 210 is formed of a porous membrane 212, which helps to achieve equivalent air pressure, in some embodiments, vent holes 232 in the membrane frame 230 are not required.

[0045] The height of the thin film frame 230 is chosen to position the thin film 210 outside the focal point of incident radiation reaching the photomask 250 through the thin film 210. In some embodiments, the height of the thin film frame 230 is in the range of about 1 mm to about 10 mm. In some cases, if the height is too small, the risk of imaging particles and other contaminants residing on the thin film 210 increases. In some cases, if the height is too large, it unnecessarily increases the weight of the film.

[0046] An assembly of the film 210 and the film boundary 220 is attached to the film frame 230 via the film boundary 220, such that the film 210 is stretched over the film frame 230. In some embodiments, the film boundary 220 is attached to the film frame 230 via a frame adhesive 234. In some embodiments, the frame adhesive 234 comprises a thermosetting adhesive material, such as epoxy resin, acrylic resin, fluoropolymer, benzocyclobutene (BCB), methylsilsesquioxane (MSQ), polyimide, other thermosetting materials, and / or combinations thereof. In some embodiments, the frame adhesive 234 comprises an adhesive or another material configured to secure the film boundary 220 to the film frame 230.

[0047] This forms a thin film 240. The thin film 240 includes a thin film frame 230 and a thin film 210 attached to the thin film frame 230 via a thin film boundary 220. The thin film 240 helps prevent particles from reaching the photomask 250 and interfering with pattern transfer.

[0048] refer to Figure 1 and Figure 2E According to some embodiments, the method proceeds to operation 110, in which the thin film 240 is attached to the photomask 250. Figure 2E According to some embodiments, after attaching the thin film 240 to the photomask 250 Figure 2D A cross-sectional view of the mask film system 200.

[0049] refer to Figure 2E The film 240 is mounted onto the boundary region of the photomask 250. In some embodiments, a film frame 230 is attached to the boundary region 250B at the front surface 252 of the photomask 250 using a film adhesive 254. The film adhesive 254 may comprise the same or different material as the frame adhesive 234. For example, in some embodiments, the film adhesive 254 may comprise a thermosetting adhesive material, such as epoxy resin, acrylic resin, fluoropolymer, BCB, MSQ, or polyimide. In some other embodiments, the film frame 230 may be attached to the photomask 250 in a manner different from the film adhesive 254 (e.g., at least one suction cup, vacuum, or electrostatic sticker). In such embodiments, the film adhesive 254 is omitted.

[0050] Photomask 250 includes a patterned region 250A that can be used to transfer a pattern onto a semiconductor wafer via photolithography. A thin film 210 extends over the patterned region 250A of photomask 250 to protect the patterned region 250A from contaminant particles. Particles unintentionally deposited on the patterned region 250A can introduce defects and cause deterioration of the transferred pattern. Particles can be introduced in any of a variety of ways, such as during cleaning processes and / or during processing of photomask 250. By keeping contaminant particles outside the focal plane of photomask 250, high-fidelity pattern transfer from the patterned region 250A to the semiconductor wafer can be achieved.

[0051] Figure 5 An exemplary photomask 250, which can be used for EUV lithography according to some embodiments, is shown. Figure 5 As shown, in some embodiments, photomask 250 may include a substrate 502 having a backside coating 503, a multilayer structure 504, a capping layer 506, and one or more absorbers 508 having an anti-reflective coating (ARC) layer 510.

[0052] In some embodiments, substrate 502 comprises low thermal expansion (LTE) glass, fused silica, silicon carbide, black diamond, or other suitable materials. In some embodiments, substrate 502 has a thickness between about 6.3 mm and about 6.5 mm. In some cases, if the thickness is too small, the risk of breakage or warping increases. In some cases, if the thickness is too large, the weight of photomask 250 increases unnecessarily.

[0053] In some embodiments, the rear coating 503 includes chromium nitride (Cr). x N y The back coating 503 can be tantalum nitride (TaN) or tantalum boride (TaB). The thickness of the back coating 503 helps ensure the reflection of incident radiation. In some cases, if the thickness of the back coating 503 is too small, the risk of radiation passing through the back coating 503 increases. In some cases, if the thickness of the back coating 530 is too large, it wastes material and increases production costs without significantly improving performance. In some examples, the back coating 503 has a thickness between about 70 nm and about 100 nm.

[0054] The multilayer structure 504 may include, for example, a molybdenum-silicon (Mo-Si) multilayer deposited on top of the substrate 502 using an ion deposition technique. In some embodiments, the multilayer structure 504 has a thickness between about 250 nm and about 350 nm, and in some examples, each Mo-Si layer pair has a thickness between about 3 nm (for the Mo layer) and about 4 nm (for the Si layer).

[0055] In some embodiments, the capping layer 506 comprises a ruthenium (Ru) capping layer. In some embodiments, the Ru capping layer 506 has a thickness between about 2.5 nm and about 3 nm. In some embodiments, the capping layer 506 comprises a Si capping layer. In some embodiments, the Si capping layer has a thickness between about 4 nm and about 4.5 nm. The thickness of the capping layer 506 helps protect the multilayer structure 504 (e.g., during the fabrication of the photomask 250), thereby extending the lifetime of the multilayer structure 504. The capping layer 506 can also be used as an etch stop layer for subsequent absorber layer etching processes. In some cases, if the thickness of the capping layer 506 is too small, the lifetime of the photomask 250 will be reduced. In some cases, if the thickness of the capping layer 506 is too large, material will be wasted without a significant improvement in performance.

[0056] In some embodiments, absorber 508 is configured to absorb EUV light (e.g., having a wavelength of about 13.5 nm). In some embodiments, absorber 508 may include, for example, Ta. x N y Layer or Ta x B y O z N u Layer. In some examples, other materials may be used for absorber 508, such as Al, Cr, Ta, and W. In some embodiments, absorber 508 may have a thickness between about 50 nm and about 75 nm. In some cases, if the thickness of absorber 508 is too small, absorber 508 may not absorb a sufficient amount of EUV light. In some cases, if the thickness of absorber 508 is too large, mask 3D effects become severe, leading to undesirable feature-size-dependent focus and pattern placement offsets.

[0057] In some examples, ARC layer 510 includes Ta x ByO z Nu layer, Hf x O y Layer or Si x O y N z At least one of the layers or other suitable antireflective materials for the wavelength of the incident radiation.

[0058] While some examples of materials that may be used for each of the substrate 502, back coating 503, multilayer structure 504, capping layer 506, absorber 508 and ARC layer 510 have been given, it should be understood that other suitable materials known in the art may be used equivalently without departing from the scope of this disclosure.

[0059] For illustrative purposes, this article describes the use of Figure 5An exemplary method for manufacturing a photomask 250 is described. In some embodiments, the manufacturing process includes two process stages: (1) a mask preform manufacturing process and (2) a mask patterning process. During the mask preform manufacturing process, the mask preform is formed by depositing a suitable layer (e.g., a reflective multilayer, such as a Mo-Si multilayer) on a suitable substrate (e.g., an LTM substrate with a flat, defect-free surface). In various embodiments, the surface roughness of the mask preform is less than about 50 nm. For example, a capping layer (e.g., ruthenium) is formed on the multilayer coated substrate, and then an absorber layer is deposited. The mask preform can then be patterned (e.g., the absorber layer can be patterned) to form a desired pattern on the photomask 250. In some embodiments, an ARC layer can be deposited on the absorber layer before patterning the mask preform. The photomask 250 can then be used to transfer circuit and / or device patterns onto a semiconductor wafer. In various embodiments, the pattern defined by the photomask 250 can be transferred onto multiple wafers over and over using various photolithography processes. In addition, a set of photomasks (e.g., photomask 250) can be used to construct complete integrated circuit (IC) devices and / or circuits.

[0060] In various embodiments, the photomask 250 (as described above) can be fabricated to include different structural types, such as a binary intensity mask (BIM) or a phase-shifting mask (PSM). An exemplary BIM includes opaque absorption regions and reflective regions, wherein the BIM includes a pattern (e.g., an IC pattern) to be transferred to a semiconductor substrate. The opaque absorption regions include absorbers as described above, configured to absorb incident light (e.g., incident EUV light). In the reflective regions, the absorbers have been removed (e.g., during the mask patterning process described above), and the incident light is reflected by multiple layers. Furthermore, in some embodiments, the photomask 250 can be a PSM that utilizes interference generated by the phase difference of the light reflected from it. Examples of PSMs include alternating PSM (AltPSM), attenuated PSM (AttPSM), and chromium-free PSM (cPSM). For example, an AltPSM can include phase shifters (with opposite phases) disposed on either side of each patterned mask feature. In some examples, AttPSM may include an absorber layer with a transmittance greater than zero (e.g., Mo-Si with an intensity transmittance of about 6%). In some cases, cPSM may be described as a 100% transmittance AtPSM, for example, because cPSM does not include phase shifter material or chromium on the mask. In some illustrative embodiments of PSM, absorber 508 is a reflective layer having a material stack similar to the material stack of multilayer structure 204.

[0061] Figure 6The diagram shown is a schematic of a lithography system 600 according to some embodiments. The lithography system 600, also collectively referred to as a scanner, is operable to perform lithography processes, including exposure with a suitable radiation source and in a specific exposure mode. In at least some embodiments of the invention, the lithography system 600 includes an ultraviolet (UV) lithography system designed to expose a resist layer with UV radiation (i.e., UV light). Therefore, in various embodiments, the resist layer comprises a material sensitive to UV light (e.g., a UV resist). Figure 6 The lithography system 600 includes multiple subsystems, such as a radiation source 602, an illuminator 604, a mask stage 606 configured to receive the mask film system 200 of this disclosure, a projection optics 610, and a substrate stage 618 configured to receive a semiconductor substrate 616. The following description of the UV lithography system according to embodiments of this disclosure refers to EUV radiation as an example of ultraviolet radiation. Embodiments according to this disclosure are not limited to EUV lithography systems. In other words, embodiments described with reference to EUV systems include embodiments utilizing ultraviolet radiation. The general operation of the lithography system 600 is described as follows: EUV light from the radiation source 602 is directed to the illuminator 604 (which includes a set of mirrors) and projected onto a reflective mask 608. The reflective mask image is directed to the projection optics 610, which focuses the EUV light and projects it onto the semiconductor substrate 616 to expose an EUV resist layer deposited thereon. Furthermore, in various examples, each subsystem of the lithography system 600 can be housed in a high vacuum environment and thus operate in a high vacuum environment, for example, to reduce atmospheric absorption of EUV light.

[0062] In the embodiments described herein, radiation source 602 can be used to generate EUV light. In some embodiments, radiation source 602 includes a plasma source, such as discharge-generated plasma (DPP) or laser-generated plasma (LPP). In some examples, EUV light can include light with wavelengths between about 1 nm and about 100 nm. In a particular instance, radiation source 602 generates EUV light with a wavelength centered at about 13.5 nm. Therefore, radiation source 602 may also be referred to as EUV radiation source 602. In some embodiments, radiation source 602 further includes a collector that can be used to collect the EUV light generated from the plasma source and guide the collected EUV light to imaging optics, such as illuminator 604.

[0063] As described above, EUV light from radiation source 602 is directed to illuminator 604. In some embodiments, illuminator 604 may include reflective optics (e.g., for EUV lithography system 600), such as a single mirror or a mirror system having multiple mirrors, to guide light from radiation source 602 onto mask stage 606, particularly to mask film system 200 fixed to mask stage 606. In some examples, illuminator 604 may include zone plates (not shown), for example, to improve the focusing of EUV light. In some embodiments, illuminator 604 may be configured to shape EUV light passing through it according to a specific pupil shape, including, for example, dipole shapes, quadrupole shapes, annular shapes, single-beam shapes, multi-beam shapes, and / or combinations thereof. In some embodiments, illuminator 604 is operable to configure mirrors (i.e., those of illuminator 604) to provide desired illumination to photomask 250 in mask film system 200. In one example, the mirrors of illuminator 604 may be configured to reflect EUV light to different illumination locations. In some embodiments, the stage (not shown) preceding illuminator 604 may additionally include other configurable mirrors that can be used to direct EUV light to different illumination positions within the mirrors of illuminator 604. In some embodiments, illuminator 604 is configured to provide coaxial illumination (ONI) to the mask film system 200. In some embodiments, illuminator 604 is configured to provide off-axis illumination (OAI) to the mask film system 200. It should be noted that the optics employed in the EUV lithography system 600, particularly the optics for illuminator 604 and projection optics 610, may include mirrors with a multilayer thin-film coating called a Bragg reflector. For example, such a multilayer thin-film coating may include alternating Mo and Si layers, which provides high reflectivity at EUV wavelengths (e.g., about 13 nm).

[0064] As described above, the lithography system 600 also includes a mask stage 606 configured to hold the mask film system 200 within the lithography system 600. Since the lithography system 600 can be housed in and therefore operate in a high vacuum environment, the mask stage 606 may include an electrostatic chuck to hold the mask film system 200. For the optics of the EUV lithography system 600, the photomask 250 is also reflective. Figure 6As shown, light is reflected from photomask 250 and directed to projection optics 610, which collects the EUV light reflected from photomask 250. For example, the EUV light collected by projection optics 610 (reflected from photomask 250) carries an image of the pattern defined by photomask 250. In various embodiments, projection optics 610 provides the imaging of the pattern of photomask 250 onto a semiconductor substrate 616 fixed on a substrate stage 618 of lithography system 600. Specifically, in various embodiments, projection optics 610 focuses the collected EUV light and projects the EUV light onto semiconductor substrate 616 to expose an EUV resist layer deposited on semiconductor substrate 616. As described above, projection optics 610 may include reflective optics, such as those used in EUV lithography systems (e.g., lithography system 600). In some embodiments, illuminator 604 and projection optics 610 are collectively referred to as the optical module of lithography system 600.

[0065] As described above, the lithography system 600 also includes a substrate stage 618 to hold a semiconductor substrate 616 to be patterned. In various embodiments, the semiconductor substrate 616 includes a semiconductor wafer, such as a silicon wafer, germanium wafer, silicon-germanium wafer, III-V wafer, or other types of wafer. The semiconductor substrate 616 may be coated with a photoresist layer sensitive to EUV light (e.g., an EUV photoresist layer). EUV photoresists may have stringent performance standards. For illustrative purposes, EUV photoresists may be designed to provide a resolution of at least about 22 nm, a linewidth roughness (LWR) of at least about 2 nm, and at least about 15 mJ / cm². 2 Sensitivity. In the embodiments described herein, various subsystems of the lithography system 600, including the subsystems described above, are integrated and operable to perform lithography exposure processes, including EUV lithography. Of course, the lithography system 600 may also include other modules or subsystems that may be integrated with (or coupled to) one or more of the subsystems or components described herein.

[0066] The lithography system may include other components and may have other alternatives. In some embodiments, the lithography system 600 may include a pupil phase modulator 612 to modulate the optical phase of EUV light guided from the photomask 250 such that the light has a phase distribution along the projection pupil plane 614. In some embodiments, the pupil phase modulator 612 includes a mechanism for tuning a mirror of the projection optics 610 to perform phase modulation. For example, in some embodiments, the mirror of the projection optics 610 may be configured to reflect EUV light passing through the pupil phase modulator 612, thereby modulating the phase of the light passing through the projection optics 610. In some embodiments, the pupil phase modulator 612 utilizes a pupil filter placed on the projection pupil plane 614. For example, the pupil filter may be used to filter out specific spatial frequency components of the EUV light reflected from the photomask 250. In some embodiments, the pupil filter may be used as a phase pupil filter that modulates the phase distribution of the light guided through the projection optics 610.

[0067] During the photolithography process, the particles 620 are held outside the focal plane of the photomask 250 by the thin film 210, which enables high-fidelity pattern transfer from the photomask 250 to the semiconductor substrate 616.

[0068] One aspect of this specification relates to thin films. The thin film includes a thin film membrane comprising at least one porous membrane. The at least one porous membrane comprises a network of multiple nanotubes. At least one of the multiple nanotubes comprises a core nanotube and a shell nanotube surrounding the core nanotube, the core nanotube comprising a material different from the shell nanotube. The thin film also includes a thin film boundary attached to a peripheral region of the thin film membrane and a thin film framework attached to the thin film boundary.

[0069] Another aspect of this specification relates to a method for forming a mask film system. The method includes forming a thin film membrane comprising a porous membrane over a filter membrane. The porous membrane comprises a network of multiple nanotubes. At least one of the multiple nanotubes comprises a core nanotube and a shell nanotube surrounding the core nanotube. The method further includes transferring the thin film membrane from the filter membrane to a film boundary, attaching the film boundary to a film frame, and mounting the film frame onto a photomask comprising a patterned region.

[0070] Another aspect of this specification relates to a method for a photolithography process. The method includes providing a thin film comprising a thin film membrane. The thin film membrane comprises at least one porous membrane formed of a network of multiple nanotubes. At least one of the multiple nanotubes comprises a core nanotube and a shell nanotube surrounding the core nanotube. The shell nanotube is composed of a boron-containing compound. The method further includes mounting the thin film onto a photomask. The photomask comprises a patterned surface. The method further includes loading the photomask with the thin film mounted thereon into a photolithography system. The method further includes loading a semiconductor wafer onto a substrate stage of the photolithography system. The method further includes performing a photolithographic exposure process to transfer a pattern of the patterned surface from the photomask to the semiconductor wafer.

[0071] The foregoing has outlined features of several embodiments to enable those skilled in the art to better understand various aspects of this disclosure. Those skilled in the art should understand that they can readily use this disclosure as a basis for designing or modifying other processes and structures to achieve the same purposes and / or the same advantages of the embodiments described herein. Those skilled in the art should also recognize that such equivalent constructions do not depart from the spirit and scope of this disclosure, and that various changes, substitutions, and modifications can be made herein without departing from the spirit and scope of this disclosure.

[0072] Example 1. A thin film comprising:

[0073] A thin film membrane, comprising at least one porous membrane, the at least one porous membrane comprising a network of multiple nanotubes, at least one of the multiple nanotubes comprising a core nanotube and a shell nanotube surrounding the core nanotube, the core nanotube comprising a material different from the shell nanotube;

[0074] The film boundary is attached to the film along the peripheral region of the film; and

[0075] A thin film frame is attached to the boundary of the thin film.

[0076] Example 2. A thin film as described in Example 1, wherein the core nanotube comprises carbon nanotubes or a bundle of multiple carbon nanotubes.

[0077] Example 3. A thin film as described in Example 2, wherein the carbon nanotubes comprise single-walled carbon nanotubes or multi-walled carbon nanotubes.

[0078] Example 4. A thin film as described in Example 1, wherein the shell nanotube comprises silicon nitride or silicon carbide.

[0079] Example 5. The thin film as described in Example 1, wherein the shell nanotube comprises boron nitride, boron, boron carbide, boron carbonitride, or silicon boron carbide.

[0080] Example 6. The film as described in Example 1 further includes a frame adhesive between the film boundary and the film frame.

[0081] Example 7. A thin film as described in Example 1, wherein the thin film comprises a plurality of porous films stacked on top of each other.

[0082] Example 8. A method for forming a mask film system, comprising:

[0083] A thin film membrane comprising a porous membrane is formed on a filter membrane, the porous membrane comprising a network of multiple nanotubes, at least one of the multiple nanotubes comprising a core nanotube and a shell nanotube surrounding the core nanotube;

[0084] The thin film is transferred from the filter membrane to the membrane boundary;

[0085] Attaching the film boundary to the film frame; and

[0086] The thin film frame is mounted onto a photomask that includes a patterned area.

[0087] Example 9. The method as described in Example 8, wherein the core nanotube comprises carbon nanotubes or a bundle of multiple carbon nanotubes, and the shell nanotube comprises boron nitride nanotubes.

[0088] Example 10. The method as described in Example 8, wherein forming the thin film comprises:

[0089] A suspension consisting of multiple nanotubes formed in a liquid medium;

[0090] Apply the suspension to the filter membrane; and

[0091] A vacuum is applied to draw the liquid medium through the filter membrane, leaving the porous membrane on the filter membrane.

[0092] Example 11. The method of Example 10 further includes using a cleaning solvent to clean the porous membrane.

[0093] Example 12. The method as described in Example 10, wherein forming the thin film further includes forming another porous film on the porous film to form a stack of porous films.

[0094] Example 13. The method as described in Example 8, wherein transferring the thin film membrane from the filter membrane to the membrane boundary comprises:

[0095] Attach the film boundary along the peripheral region of the thin film; and

[0096] Remove the filter membrane.

[0097] Example 14. The method as described in Example 13, wherein attaching the film boundary along the peripheral region of the film membrane includes applying a force to the film boundary and the film membrane.

[0098] Example 15. A method for photolithography, comprising:

[0099] Provided a thin film comprising a thin film membrane, wherein the thin film membrane comprises at least one porous membrane formed of a network of a plurality of nanotubes, at least one of the plurality of nanotubes comprising a core nanotube and a shell nanotube surrounding the core nanotube, the shell nanotube being composed of a boron-containing compound;

[0100] The thin film is mounted onto a photomask, wherein the photomask includes a patterned surface;

[0101] The photomask on which the thin film is mounted is loaded into the photolithography system;

[0102] Loading a semiconductor wafer onto the substrate stage of the lithography system; and

[0103] A photolithography process is performed to transfer the pattern of the patterned surface from the photomask to the semiconductor wafer.

[0104] Example 16. The method as described in Example 15, wherein the core nanotube comprises carbon nanotubes or a bundle of multiple carbon nanotubes.

[0105] Example 17. The method of Example 15, wherein the boron-containing compound is selected from the group consisting of boron nitride, boron, boron carbide, boron carbonitride, and silicon boron carbide.

[0106] Example 18. The method as described in Example 15, wherein the thin film comprises:

[0107] The thin film; and

[0108] A film frame, wherein the film frame fixes the film to the film frame.

[0109] Example 19. The method as described in Example 15, wherein the photomask comprises:

[0110] Substrate;

[0111] A coating on the first side of the substrate;

[0112] A multilayer structure on a second side of the substrate opposite to the first side, the multilayer structure comprising alternating molybdenum layers and silicon layers;

[0113] A covering layer on top of the multilayer structure; and

[0114] One or more absorbers above the covering layer.

[0115] Example 20. The method of Example 15 further includes using a suspension comprising nanotubes in a liquid medium to form the thin film.

Claims

1. A thin film, comprising: A thin film membrane, comprising at least one porous membrane, the at least one porous membrane comprising a network of multiple nanotubes, at least one of the multiple nanotubes comprising a core nanotube and a shell nanotube surrounding the core nanotube, wherein the core nanotube comprises a carbon nanotube or a bundle of multiple carbon nanotubes, and wherein the shell nanotube comprises a compound selected from the group consisting of boron carbonitride, silicon boronitride, and silicon boron carbide. The film boundary is attached to the film along the peripheral region of the film; and A thin film frame is attached to the boundary of the thin film.

2. The thin film as claimed in claim 1, wherein, The carbon nanotubes include single-walled carbon nanotubes or multi-walled carbon nanotubes.

3. The film of claim 1, further comprising a frame adhesive between the film boundary and the film frame.

4. The thin film as claimed in claim 1, wherein, The thin film membrane comprises multiple porous membranes stacked on top of each other.

5. A method for forming a mask film system, comprising: A thin film membrane comprising a porous membrane is formed on a filter membrane. The porous membrane comprises a network of multiple nanotubes, at least one of which comprises a core nanotube and a shell nanotube surrounding the core nanotube. The core nanotube comprises a carbon nanotube or a bundle of multiple carbon nanotubes, and the shell nanotube comprises a compound selected from the group consisting of boron carbonitride, silicon boronitride, and silicon boron carbide. The thin film is transferred from the filter membrane to the membrane boundary; Attaching the film boundary to the film frame; and The thin film frame is mounted onto a photomask that includes a patterned area.

6. The method of claim 5, wherein, Forming the thin film includes: A suspension comprising the plurality of nanotubes is formed in a liquid medium; Apply the suspension to the filter membrane; and A vacuum is applied to draw the liquid medium through the filter membrane, leaving the porous membrane on the filter membrane.

7. The method of claim 6, further comprising using a cleaning solvent to clean the porous membrane.

8. The method of claim 6, wherein, Forming the thin film also includes forming another porous film on the porous film to form a stack of porous films.

9. The method of claim 5, wherein, Transferring the thin film from the filter membrane to the membrane boundary includes: Attach the film boundary along the peripheral region of the thin film; and Remove the filter membrane.

10. The method of claim 9, wherein, Attaching the film boundary along the peripheral region of the film membrane includes applying force to the film boundary and the film membrane.

11. A method for photolithography, comprising: Provided a thin film comprising a thin film membrane, wherein the thin film membrane comprises at least one porous membrane formed of a network of a plurality of nanotubes, at least one of the plurality of nanotubes comprising a core nanotube and a shell nanotube surrounding the core nanotube, wherein the core nanotube comprises a carbon nanotube or a bundle of a plurality of carbon nanotubes, and wherein the shell nanotube comprises a compound selected from the group consisting of boron carbonitride, silicon boronitride, and silicon boron carbide; The thin film is mounted onto a photomask, wherein the photomask includes a patterned surface; The photomask on which the thin film is mounted is loaded into the photolithography system; Loading a semiconductor wafer onto the substrate stage of the lithography system; and A photolithography process is performed to transfer the pattern of the patterned surface from the photomask to the semiconductor wafer.

12. The method of claim 11, wherein, The thin film includes: The thin film; and A film frame, wherein the film frame fixes the film to the film frame.

13. The method of claim 11, wherein, The photomask includes: Substrate; A coating on the first side of the substrate; A multilayer structure on a second side of the substrate opposite to the first side, the multilayer structure comprising alternating molybdenum layers and silicon layers; A covering layer on top of the multilayer structure; and One or more absorbers above the covering layer.

14. The method of claim 11, further comprising using a suspension comprising nanotubes in a liquid medium to form the thin film.

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