Protective assembly and method of forming a reduced scale mask assembly and increasing the life of a protective film

Abstract

A pellicle assembly and methods of forming pellicle assemblies and increasing pellicle lifetime include a pellicle membrane and a conformal coating on an outer surface of the pellicle membrane. The pellicle membrane can be formed of multiple layers and have a combination of high transmissivity, low deflection, and small pore size. The conformal coating is intended to protect the pellicle membrane from damage that can occur due to heat and hydrogen plasma generated during EUV exposure.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to pellicle assemblies, and methods of forming a reticle assembly and increasing pellicle lifetime. BACKGROUND

[0002] Photolithographic patterning processes use a reticle (i.e., a mask) that includes a desired mask pattern. The reticle can be a reflective mask or a transmissive mask. In the process, ultraviolet light is reflected off the surface of the reticle (for a reflective mask) or transmitted through the reticle (for a transmissive mask) to transfer the pattern to a photoresist on a semiconductor wafer. The exposed portions of the photoresist are modified photochemically. After exposure, the resist is developed to define openings in the resist, and one or more semiconductor processing steps (e.g., etching, epitaxial layer deposition, metallization, etc.) are performed for the areas of the wafer surface exposed by the openings in the resist. After this semiconductor processing, the resist is removed by a suitable resist stripper or the like.

[0003] The minimum feature size of a pattern is limited by the wavelength of light. Deep ultraviolet (UV) lithography (e.g., using a wavelength of 193 nm or 248 nm in some standard deep UV platforms) typically employs transmissive masks and can provide smaller minimum feature sizes than lithography at longer wavelengths. Extreme ultraviolet (EUV) light, using wavelengths as small as 10 nm down from 124 nanometers (nm), is currently used to provide even smaller minimum feature sizes. At shorter wavelengths, particulate contaminants on the reticle can cause defects in the transferred pattern. Therefore, a pellicle assembly (or simply a pellicle) is used to protect the reticle from such particulates. The pellicle assembly includes a pellicle film attached to a frame. The frame supports the pellicle film over the reticle. In this way, any contaminant particles that land on the pellicle film are kept out of the focal plane of the reticle, thereby reducing or preventing defects in the transferred pattern caused by the contaminant particles. SUMMARY

[0004] According to embodiments of the present disclosure, a pellicle assembly is provided, including a pellicle film having an outer surface and an inner surface, and a conformal coating on at least the outer surface of the pellicle film.

[0005] According to embodiments of the present disclosure, a method of forming a reticle assembly is provided, including disposing a pellicle assembly over a mask pattern of a reticle, wherein the pellicle assembly includes a multi-layer pellicle film having a conformal coating on an outer surface thereof.

[0006] According to embodiments of the disclosure, there is provided a method of increasing the lifetime of a pellicle, comprising applying a conformal coating to at least one outer surface of the pellicle, wherein the conformal coating has a transmittance greater than 90% when measured at an EUV wavelength of 13.5 nm and at a thickness between 1 nm and 10 nm. BRIEF DESCRIPTION OF DRAWINGS

[0007] Aspects of the disclosure can best be understood with reference to the following detailed description when read in conjunction with the accompanying drawings. It should be noted that the various features are not necessarily drawn to scale. In fact, the dimensions of the various features can be arbitrarily increased or decreased for the sake of clarity. This description is not to be taken as limiting the scope of the disclosure, as defined by the appended claims and their equivalents.

[0008] Figure 1 Cross-sectional view of an exemplary pellicle and pellicle assembly according to some embodiments;

[0009] Figure 2 Exploded view of a pellicle, pellicle assembly, and first embodiment of a pellicle assembly according to some embodiments;

[0010] Figure 3 Exploded view of a pellicle, pellicle assembly, and second embodiment of a pellicle assembly according to some embodiments;

[0011] Figure 4 Exploded view of a pellicle, pellicle assembly, and third embodiment of a pellicle assembly according to some embodiments;

[0012] Figure 5 Exploded view of a pellicle, pellicle assembly, and fourth embodiment of a pellicle assembly according to some embodiments;

[0013] Figure 6 Exploded view of a pellicle, pellicle assembly, and fifth embodiment of a pellicle assembly according to some embodiments;

[0014] Figure 7 Exploded view of a pellicle, pellicle assembly, and sixth embodiment of a pellicle assembly according to some embodiments;

[0015] Figure 8 Exploded view of a pellicle, pellicle assembly, and seventh embodiment of a pellicle assembly according to some embodiments;

[0016] Figure 9 Exploded view of a pellicle, pellicle assembly, and eighth embodiment of a pellicle assembly according to some embodiments;

[0017] Figure 10 Side view of a pellicle assembly attached to an EUV pellicle according to some embodiments;

[0018] Figures 11A-11C For different views of the mounting frame according to some embodiments, Figure 11A This is a planar cross-sectional view. Figure 11B This is the first side view, and Figure 11C This is a front view;

[0019] Figure 12 A flowchart illustrating a first method for preparing a nanotube thin film layer is provided according to some embodiments;

[0020] Figures 13A-13D To illustrate according to some embodiments Figure 12 A set of figures for the method, Figure 13A The first attached figure is shown. Figure 13B The second attached figure is shown below. Figure 13C This is the third attached figure, and Figure 13D This is the fourth attached figure;

[0021] Figure 14 A flowchart illustrating a second method for preparing nanotube thin film layers is provided according to some embodiments;

[0022] Figures 15A-15C To illustrate according to some embodiments Figure 14 A set of figures for the method, Figure 15A The first attached figure is shown. Figure 15B This is the second attached figure, and Figure 15C This is the third attached figure;

[0023] Figure 16 A flowchart illustrating a method for preparing a graphene thin film layer is provided, based on some embodiments.

[0024] Figures 17A-17B To illustrate according to some embodiments Figure 16 A set of figures for the method, Figure 17A The first attached figure is shown below. Figure 17B This is the second attached figure;

[0025] Figure 18 A flowchart illustrating a method for preparing a multilayer structure of a protective film, according to some embodiments;

[0026] Figures 19A-19C To illustrate according to some embodiments Figure 18 A set of figures for the method, Figure 19A The first attached figure is shown. Figure 19B This is the second attached figure, and Figure 19C This is the third attached figure;

[0027] Figure 20 A flowchart illustrating another method for preparing a multilayer structure of a protective film, based on some embodiments; Figures 21A-21C To illustrate according to some embodiments Figure 20 A set of figures for the method,Figure 21A FIG. 1 is a first diagram, Figure 21B FIG. 2 is a second diagram, and Figure 21C FIG. 3 is a third diagram;

[0028] Figures 22A-22D FIG. 4 is a set of diagrams illustrating a method for coating an outer surface of a protective film, according to some embodiments, Figure 22A FIG. 1 is a first diagram, Figure 22B FIG. 2 is a second diagram, Figure 22C FIG. 3 is a third diagram, and Figure 22D FIG. 4 is a fourth diagram.

[0029] LEGEND

[0030] 100: demagnifying optical mask

[0031] 102: substrate

[0032] 104: reflective layer

[0033] 105: demagnifying optical mask assembly

[0034] 106: spacer layer

[0035] 107: image

[0036] 108: capping layer

[0037] 110: EUV absorbing layer

[0038] 112: anti-reflective coating

[0039] 114: conductive backside layer

[0040] 120: protective assembly

[0041] 122: mounting frame

[0042] 123: vent hole

[0043] 124: adhesive layer

[0044] 128: bezel

[0045] 129: adhesive layer

[0046] 130: protective film

[0047] 132: outer surface

[0048] 134: inner surface

[0049] 150, 152, 154, 156: nanotube film layer

[0050] 160: graphene film layer

[0051] 170: protective film assembly

[0052] 172: outermost layer

[0053] 200, 210, 220: steps

[0054] 230: nanotubes

[0055] 232: liquid

[0056] 236: surface

[0057] 238: solution

[0058] 240: initial nanotube film

[0059] 250: press

[0060] 252: platen

[0061] 254: ram

[0062] 260: nanotube film layer

[0063] 300, 310, 320: steps

[0064] 330: reaction vessel

[0065] 332: heat source

[0066] 334: reactants

[0067] 336: catalyst

[0068] 338: carrier gas

[0069] 339: fibers

[0070] 342: surface

[0071] 400, 410: steps

[0072] 430: initial graphene layer

[0073] 432: graphene sheet or platelet

[0074] 434: surface

[0075] 500, 510, 520, 530, 535, 540, 550, 560, 570, 575: steps DETAILED DESCRIPTION

[0076] To implement the different features of the subject matter recited, the following disclosure provides a number of different embodiments or examples. Specific examples of components, configurations, etc. are described below to simplify the present disclosure. Of course, these are merely examples and are not intended to be limiting in nature. Other components, values, operations, materials, configurations, etc. are contemplated. For example, in the description below, forming a first feature on or over a second feature can include embodiments in which the first feature and the second feature are formed in direct contact, and can also include embodiments in which additional features are formed between the first feature and the second feature such that the first feature and the second feature can not be in direct contact. Additionally, the present disclosure can repeat reference numerals and / or letters in various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and / or configurations discussed.

[0077] In addition, spatially relative terms, such as "beneath", "below", "lower", "above", "upper" and the like, can be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientations depicted in the figures. The devices can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0078] Numerical values in the specification and claims of this application should be understood to include same values when reduced to the same number of significant figures and values that differ by less than the experimental error of conventional measurement techniques used in the type of analysis at issue in this application. All ranges disclosed herein are inclusive of the endpoints.

[0079] The present disclosure can cite temperatures for particular method steps. It should be noted that such citations generally refer to the temperature at which a heat source is set, and are not specifically representative of the temperature to which a particular material must be exposed to heat.

[0080] Figure 1A cross-sectional view of an exemplary demagnification reticle assembly 105 useful in microlithography is illustrated in accordance with some embodiments. The demagnification reticle assembly 105 includes a demagnification reticle 100 and a protective assembly 120. The illustrative demagnification reticle 100, also known in the art as a mask, photomask, or the like, is a reflective type of mask commonly used in EUV microlithography and includes a substrate 102, alternating reflective layers 104 and spacer layers 106, a capping layer 108, an EUV absorbing layer 110 patterned to define a mask pattern, an anti-reflective coating (ARC) 112, and a conductive backside layer 114. The illustrative demagnification reticle 100 is merely a non-limiting example. More generally, the protective assembly as disclosed herein can be used with substantially any type of reflective or transmissive demagnification reticle. As another example (not shown), the demagnification reticle can be a transmissive demagnification reticle, in which case the substrate is transmissive to the wavelength at which microlithography is performed. Generally, the reflective or transmissive demagnification reticle includes a substrate (e.g., substrate 102) and a mask pattern (e.g., EUV absorbing layer 110) disposed on the substrate. The protective assembly 120 includes a mounting frame 122, an adhesive layer 124, and a protective film 130. In some non-limiting illustrative embodiments, the demagnification reticle and protective assembly are intended for use with EUV light wavelengths, such as light wavelengths from 124 nm to 10 nm, including about 13.5 nm.

[0081] In embodiments, the substrate 102 is made of a low thermal expansion material (LTEM), such as quartz or titania silicate glass, which can be purchased from Corning (trademark ULE). This reduces or prevents warping of the demagnification reticle due to absorbed energy and subsequent heating. The reflective layers 104 and spacer layers 106 cooperate to form a Bragg reflector for reflecting EUV light. In some embodiments, the reflective layers 104 can include molybdenum (Mo). In some embodiments, the spacer layers 106 can include silicon (Si). The capping layer 108 serves to protect the reflector formed by the reflective layers 104 and spacer layers 106, for example, from oxidation. In some embodiments, the capping layer 108 includes ruthenium (Ru). The EUV absorbing layer 110 absorbs EUV wavelengths and is patterned with a desired pattern. In some embodiments, the EUV absorbing layer 110 includes tantalum boron nitride. The anti-reflective coating 112 further reduces reflection from the EUV absorbing layer 110. In some embodiments, the anti-reflective coating 112 includes oxidized tantalum boron nitride. The conductive backside layer 114 permits mounting of the illustrative demagnification reticle on an electrostatic chuck and allows for temperature regulation of the mounted substrate 102. In some embodiments, the conductive backside layer 114 includes chromium nitride.

[0082] The mounting frame 122 supports the protective film 130 at a height sufficient to place the protective film 130 out of the focal plane of the lithography, e.g., at several millimeters (mm) above the reticle in some non-limiting illustrative embodiments. The mounting frame 122 itself can be made of a suitable material, such as anodized aluminum, stainless steel, plastic, silicon (Si), titanium, silicon dioxide, aluminum oxide (AI2O3), or titanium dioxide (TiO2). There can be vent holes in the mounting frame 122 for equalizing pressure on both sides of the protective film 130.

[0083] The adhesive layer 124 is used to secure the protective film 130 to the mounting frame 122. A suitable adhesive layer 124 can include silicon, acrylic, epoxy, thermoplastic elastomer rubber, acrylic polymer or copolymer, or a combination thereof. In some embodiments, the adhesive layer 124 can have a crystalline and / or amorphous structure. In some embodiments, the adhesive layer 124 can have a glass transition temperature (Tg) higher than the maximum operating temperature of the photolithography system to prevent the adhesive layer 124 from exceeding the Tg during system operation.

[0084] The protective film 130 is typically stretched over the mounting frame 122 to obtain a uniform and flat surface. However, sagging of the protective film 130 can occur, causing the film to significantly deflect from the desired flat and uniform orientation. Such deflection can affect the light reflected from the reticle and the resulting transferred pattern.

[0085] Protective films are made using complex fabrication processes from known protective materials such as porous silicon (pSi), SiN, SiC, MoSi, or MoSi x N y Films made from these materials are also prone to breakage when exposed to large pressure differentials. These materials also require a metal layer to be coated on them to increase thermal conductivity. Films made entirely of carbon nanotubes can be damaged by hydrogen during EUV exposure. Carbon nanotube films are also typically non-uniform and thus also have non-uniform transmittance and reflectance. Low-density carbon nanotube films typically have large openings / pores with a size large enough that can permit particle contaminants to penetrate the mask and fall on the reticle and cause critical dimension (CD) errors. Low-density carbon nanotube films can also be a source of particle contaminants due to single bundle vibrations of the nanotubes in the vacuum system during EUV exposure.

[0086] Additionally, for safety and protection during lithography patterning and other processes, the reticle (and its protective shield assembly) is maintained in a reticle pod. Current EUV lithography systems typically use a dual-pod configuration, which consists of an inner metal pod under vacuum and an outer pod proximate to the atmospheric environment. The inner pod is opened only when inside the tool. Pressure differential, gravity, and other external forces can cause the shield membrane to deflect or sag. If the shield membrane sags far enough to contact the inner surface of the inner metal pod, which holds the reticle therein, contamination of the shield membrane can occur, or the shield membrane itself can break.

[0087] The present disclosure is thus directed to a protective membrane and a method for producing a protective membrane that aims to reduce the deflection of the protective membrane while maintaining high transmissivity of EUV light and the particle protection capability of the protective membrane. In some embodiments, the protective membrane is a single layer structure, and in other embodiments, the protective membrane is a multi-layer structure. In some embodiments, the layers of the multi-layer structure can be made of the same material, and in other embodiments, the layers of the multi-layer structure can be made of different materials selected for specific purposes and arranged in order as needed. For example, in some embodiments, the protective membrane can include one or more nanotube membrane layers and one or more graphene membrane layers. The protective membrane can be attached to a border or to a suitably shaped mounting frame. A conformal coating is then applied to the outer surface of the protective membrane (which can be a single layer or a multi-layer structure). The coated protective membrane / border can then be fixed to the mounting frame (as needed) to form a protective assembly that can be mounted to a reticle. A combination of several low-density membrane layers can be used to obtain a protective membrane with a combination of high transmissivity, small pore size, and minimized any potential deflection. The protective membrane can be suitable for use with EUV light sources as well as deep ultraviolet (DUV) light sources or other types of photolithography light sources.

[0088] Figure 2 An exploded view of a first embodiment of a protective membrane 130, a protective membrane assembly 170, and a protective assembly 120 according to the present disclosure. In this first embodiment, the protective membrane 130 is a multi-layer structure formed of a first nanotube membrane layer 150 and a second nanotube membrane layer 152. As illustrated here, the first nanotube membrane layer 150 and the second nanotube membrane layer 152 are formed of randomly oriented nanotubes, and the two layers are in contact with each other. In some embodiments, each nanotube membrane layer has a thickness of about 10 nm to about 100 nm.

[0089] Herein, the second nanotube film layer 152 is also considered to be an outer surface 132 of the protective film 130, on which a conformal coating is applied. The conformal coating can be considered to form an outermost layer 172 of the protective film 130. In some embodiments, the outermost layer 172 has a thickness of about 1 nanometer (nm) to about 10 nm. The first nanotube film layer 150 is also considered to be an inner surface 134 of the protective film 130, and is attached to the bezel 128. The bezel 128 extends along a perimeter of the protective film 130. The bezel 128 is also attached to the mounting frame 122.

[0090] Herein, the combination of the outermost layer (conformal coating) 172 and the protective film 130 is referred to as a protective film assembly 170. Herein, the combination of the protective film assembly 170, the bezel 128, and the mounting frame 122 is referred to as a protective assembly 120.

[0091] Figure 3 is an exploded view of a second embodiment of a protective film 130, protective film assembly 170, and protective assembly 120 according to the present disclosure. As with the first embodiment of the protective film 130, protective film assembly 170, and protective assembly 120, the protective film 130 is a multilayer structure formed of a graphene film layer 160, a first nanotube film layer 150, and a second nanotube film layer 152. The graphene film layer 160 is also considered to be an outer surface 132 of the protective film 130, on which a conformal coating is applied. The conformal coating can be considered to form an outermost layer 172 of the protective film 130. In some embodiments, the outermost layer 172 has a thickness of about 1 nanometer (nm) to about 10 nm. The first nanotube film layer 150 is also considered to be an inner surface 134 of the protective film 130, and is attached to the bezel 128. The bezel 128 extends along a perimeter of the protective film 130. The bezel 128 is also attached to the mounting frame 122. Figure 2 In contrast, the first nanotube film layer 154 and the second nanotube film layer 156 are formed of directionally oriented nanotubes. In some embodiments, the directionally oriented nanotube film layers are aligned at an angle relative to each other. Here, the two nanotube film layers (first nanotube film layer 154, second nanotube film layer 156) are aligned at 90° relative to each other.

[0092] Figure 4 is an exploded view of a third embodiment of a protective film 130, protective film assembly 170, and protective assembly 120 according to the present disclosure. Here, the protective film 130 is a multilayer structure formed of a graphene film layer 160, a first nanotube film layer 150, and a second nanotube film layer 152. The graphene film layer 160 is also considered to be an outer surface 132 of the protective film 130. In some embodiments, the graphene film layer 160 can be a porous membrane or a continuous membrane without micropores. The first nanotube film layer 150 is also considered to be an inner surface 134 of the protective film 130, and is attached to the bezel 128. The first nanotube film layer 150 and the second nanotube film layer 152 are formed of randomly oriented nanotubes. In some embodiments, the graphene film layer 160, the first nanotube film layer 150, and the second nanotube film layer 152 are in direct contact with each other.

[0093] Figure 5 is an exploded view of a fourth embodiment of a protective film 130, protective film assembly 170, and protective assembly 120 according to the present disclosure. This protective film 130 is similar to the protective film 130 of the third embodiment, except that the first nanotube film layer 154 and the second nanotube film layer 156 are formed of directionally oriented nanotubes, as shown in the second embodiment. Figure 4 Figure 3 is an exploded view of a fourth embodiment of a protective film 130, protective film assembly 170, and protective assembly 120 according to the present disclosure. This protective film 130 is similar to the protective film 130 of the third embodiment, except that the first nanotube film layer 154 and the second nanotube film layer 156 are formed of directionally oriented nanotubes, as shown in the second embodiment.​

[0094] Figure 6 is an exploded view of a fifth embodiment of a protective film 130, protective film assembly 170, and protective assembly 120 according to the present disclosure. Here, in contrast to the first embodiment, the graphene film layer 160 forms the inner surface 134 of the protective film 130 and is attached to the bezel 128. The second nanotube film layer 152 is to be considered the outer surface 132 of the protective film 130. Both the first nanotube film layer 150 and the second nanotube film layer 152 are formed of randomly oriented nanotubes and are in contact with each other. Figure 4

[0095] Figure 7 is an exploded view of a sixth embodiment of a protective film 130, protective film assembly 170, and protective assembly 120 according to the present disclosure. Here, in contrast to the first embodiment, both the first nanotube film layer 154 and the second nanotube film layer 156 are formed of directionally oriented nanotubes and are in contact with each other. Figure 6

[0096] Figure 8 is an exploded view of a seventh embodiment of a protective film 130, protective film assembly 170, and protective assembly 120 according to the present disclosure. Here, the protective film 130 is a multi-layer structure formed of a graphene film layer 160, a first nanotube film layer 150, and a second nanotube film layer 152. The graphene film layer 160 is positioned between the first nanotube film layer 150 and the second nanotube film layer 152. The first nanotube film layer 150 is also considered the inner surface 134 of the protective film 130 and is attached to the bezel 128. The second nanotube film layer 152 is considered the outer surface 132 of the protective film 130. Both the first nanotube film layer 150 and the second nanotube film layer 152 are formed of randomly oriented nanotubes.

[0097] Figure 9 is an exploded view of an eighth embodiment of a protective film 130, protective film assembly 170, and protective assembly 120 according to the present disclosure. Here, in contrast to the first embodiment, both the first nanotube film layer 154 and the second nanotube film layer 156 are formed of directionally oriented nanotubes. Figure 8

[0098] Figure 10 is a side view of a protective assembly attached to an EUV reticle. As illustrated here, the EUV reticle 100 includes a patterned image 107. The protective assembly 120 includes a protective film 130 attached to a bezel 128. The bezel 128 is joined to a mounting frame 122 via an adhesive layer 129 and protects the patterned image 107 from particulate contamination. As seen here, the mounting frame 122 can include a vent 123.

[0099] Figures 11A-11C ​​​Different views of the mounting frame 122 according to some embodiments of the present disclosure. Figure 11A A plan view cross-section through the exhaust hole 123, Figure 11B A first side view, and Figure 11C A front view. The exhaust hole 123 is visible on all sides of the mounting frame 122. However, it is contemplated that the exhaust hole 123 can only be present on one, two, or three sides of the mounting frame 122.

[0100] The bezel and mounting frame can each be made of a suitable material, such as anodized aluminum, stainless steel, plastic, silicon (Si), titanium, silicon dioxide, aluminum oxide (AI2O3), or titanium dioxide (TiO2). As seen here, the mounting frame 122 can have an exhaust hole 123 for equalizing pressure on both sides of the protective film. In some embodiments, the total area of the exhaust hole 123 can range from zero to about 100 square millimeters (mm2). Note that the protective film itself is relatively porous and thus can provide an exhaust function itself. The exhaust hole 123 can be spaced apart from each other as desired. 2 ). Note that the protective film itself is relatively porous and thus can provide an exhaust function itself. The exhaust hole 123 can be spaced apart from each other as desired.

[0101] As noted above, in some embodiments, one or more layers of the protective film are formed of nanotubes. In some embodiments, the nanotubes can be carbon nanotubes (CNTs) or boron nitride nanotubes (BNNTs) or silicon carbide nanotubes (SiCNTs). In some embodiments, the nanotubes can be single-walled nanotubes or multi-walled nanotubes. Multi-walled nanotubes can be made of different materials, such as CNTs inside BNNTs, or vice versa. In some embodiments, the nanotubes can be metallic, semiconducting, or electrically insulating. The length and diameter of individual nanotubes are not important. Nanotubes can be made by known synthesis methods, such as arc discharge, laser vaporization of graphite, catalyzed chemical vapor deposition (CVD) of hydrocarbons on metal catalysts, ball milling and annealing of graphite powders, diffusion flame synthesis, electrolysis, low-temperature solid pyrolysis, floating catalyst chemical vapor deposition, or the High Pressure Carbon Monoxide (HiPco) process. Carbon nanotubes can have a Young's modulus of about 1.33 TPa, a maximum tensile strength of about 100 GPa, a thermal conductivity of about 3000 to about 40000 W / mK, and be stable in air up to temperatures of about 400 °C. Boron nitride nanotubes can have a Young's modulus of about 1.18 TPa, a maximum tensile strength of about 30 GPa, a thermal conductivity of about 3000 W / mK, and be stable in air up to temperatures of about 800 °C.

[0102] Generally, the nanotubes of each nanotube film layer can be randomly oriented, or can be directionally oriented in a desired direction. Nanotube film layers, whether randomly oriented or directionally oriented, can be combined as desired. In some embodiments, all of the nanotube film layers in the protective film are randomly oriented. In some embodiments, all of the nanotube film layers in the protective film are directionally oriented. In such embodiments, the directionally oriented nanotube film layers are aligned at an angle relative to one another. The angle can be any angle between 0° and 180°, and can be, for example, 0°, 30°, 45°, 60°, 75°, 90°, 120°, 135°, 145°, 160°, or 180°.

[0103] Additionally, in some embodiments, one or more layers of the protective film are formed from graphene or graphite. Layers formed from graphene or graphite can provide greater stiffness compared to layers formed from nanotubes. Graphite is composed of stacked graphene layers, and thus should be considered equivalent to graphene in this disclosure. Graphene and graphite are in the shape of flat sheets or porous sheets, as opposed to nanotubes. Graphene has a Young's modulus of approximately 1000 GPa.

[0104] In some embodiments, the nanotube film layers, graphene film layers, and resulting protective film should generally not include any other materials. For example, the film should not contain any moisture or any other adhesives, metals, plastics, surfactants, acids, or other compounds that can be present in the precursor materials or used in previous processing steps. In some embodiments, each nanotube film layer can have a thickness ranging from about 10 nanometers (nm) to about 100 nm, although thicknesses outside this range are also contemplated. In some embodiments, each graphene film layer can have a thickness ranging from about 1 nm to about 10 nm, although thicknesses outside this range are also contemplated.

[0105] Several different fabrication processes can be used to form the nanotube film layers and graphene film layers. For example, these fabrication processes can include chemical vapor deposition such as flow catalyst CVD or plasma enhanced CVD, electrophoretic deposition, dispersion in a solution and concentration by solvent removal, vacuum filtration, and the like.

[0106] Figure 12 A flowchart is presented to illustrate some embodiments of a method for preparing a nanotube film layer. In step 200, a suspension of nanotubes (such as carbon nanotubes or boron nitride nanotubes) is formed. The nanotubes can be suspended in water or some other suitable liquid. Other ingredients such as a surfactant can also be present to uniformly disperse the nanotubes. Ultrasonic waves can also be used for uniform dispersion of the nanotubes. The nanotubes can then be filtered, treated, and / or cleaned as appropriate. For example, the surfactant can be removed via filtration after achieving dispersion. A weak acid such as hydrochloric acid or nitric acid can be used to remove particles such as amorphous carbon.

[0107] Next, in step 210, an initial nanotube film is formed by depositing the suspension on a surface and separating the liquid from the nanotubes. For example, as illustrated here, the suspension can be poured over a filter paper such as a polytetrafluoroethylene (PTFE) film having a pore size of about 0.02 micrometers (pm) to about 1.2 pm. Suction can be applied to the opposite side of the filter paper to obtain a uniform dispersion of nanotubes on the filter paper.

[0108] Finally, in step 220, the initial nanotube film is processed to reduce its thickness and obtain a nanotube film layer. This can be done in a variety of ways. In some embodiments, the thickness is reduced by applying a compressive pressure (e.g., uniaxial compression) to the initial nanotube film, thereby reducing the thickness of the initial nanotube film. In some embodiments, the compressive pressure applied is from about 0.1 bar to about 20 bar (about 0.01 MPa to about 2 MPa). In some embodiments, the compressive pressure is applied for a time period of from about 1 minute to about 60 minutes. The degree of pressure can be varied during this time period. For example, the force can be gradually increased to a given level of force and then maintained at this level of force.

[0109] In some other embodiments, the thickness is reduced by immersing the initial nanotube film in a solution and then passing the solution through the initial nanotube film (e.g., by applying a suction force). Note that the resulting nanotube film layer is made of randomly oriented nanotubes.

[0110] In one embodiment, Figures 13A-13D A set of drawings illustrating Figure 12 the method of FIG. 1. Figure 13A A suspension of nanotubes is illustrated. Nanotubes 230 are suspended in a liquid 232 within a container 234. In Figure 13B , an initial nanotube film 240 is formed by depositing the suspension on a surface 236, such as a filter paper.

[0111] In Figure 13C , a first method for processing the initial nanotube film to reduce its thickness and obtain a nanotube film layer is illustrated. As shown, the initial nanotube film 240 and the surface 236 are placed within a pressing machine 250, which includes a bolster plate 252 and a ram 254. The initial nanotube film 240 is compressed between the bolster plate 252 and the ram 254 to obtain a nanotube film layer 260. The nanotube film layer 260 also has a higher density than the initial nanotube film 240, and the nanotube film layer 260 is thinner (i.e., has a reduced thickness) than the initial nanotube film 240. Without being bound by theory, it is believed that the deformation of the nanotube film layer introduced by the uniaxial compression is maintained after the compressive force is removed by van der Waals forces. In other words, after the compressive force is removed, the nanotube film layer does not recover to its original thickness.

[0112] In Figure 13DIn some embodiments, the initial nanotube film is treated to reduce its thickness and obtain a nanotube film layer. In one embodiment, the initial nanotube film is compressed to reduce its thickness. In another embodiment, the initial nanotube film is immersed in a solution to reduce its thickness. In some embodiments, the solution is deionized water or an alcohol such as isopropyl alcohol (IPA). In some embodiments, the resulting nanotube film layer has a higher density than the initial nanotube film.

[0113] Figure 14 A flowchart illustrating some additional embodiments of a method for making a nanotube film layer is shown. In step 300, a nanotube fiber is produced, such as a fiber made of carbon nanotubes or boron nitride nanotubes. Next, in step 310, an initial nanotube film is formed from the nanotube fiber. In some embodiments, the initial nanotube film is formed by placing the nanotube fiber adjacent to one another. Without being limited by theory, it is believed that the nanotube fibers are held together by van der Waals forces of sufficient strength to form the initial nanotube film. The initial nanotube film can be annealed. The annealing can occur at a temperature of about 1000 °C to about 2000 °C. Finally, in step 320, the initial nanotube film is treated to reduce its thickness and obtain a nanotube film layer. This can be done as previously described, such as by compression or immersion in a solution. Note that the resulting nanotube film layer is made of directionally oriented nanotubes.

[0114] In one embodiment, Figures 15A-15C To illustrate Figure 14 a set of drawings of the method. Figure 15A One embodiment of an apparatus that can be used to produce nanotube fibers using flow-through catalyst CVD is shown. A reaction vessel 330 is shown with a heat source 332 for heating material that passes through the reaction vessel. Reactants 334, catalyst 336, and carrier gas 338 enter the reaction vessel. Nanotubes, in the form of aerogels, are nucleated, grown, and aggregated, and then the aerogels are spun into fibers 339. In some embodiments, this process occurs at a temperature of about 1100 °C to about 1300 °C. This results in the nanotubes being directionally oriented (i.e., oriented in the same direction). An organic solvent is used to densify the fibers. In some embodiments, the organic solvent can be acetone or an alcohol such as isopropyl alcohol. In Figure 15B In some embodiments, the initial nanotube film is treated to reduce its thickness and obtain a nanotube film layer. In one embodiment, the initial nanotube film is compressed to reduce its thickness. In another embodiment, the initial nanotube film is immersed in a solution to reduce its thickness. In some embodiments, the solution is deionized water or an alcohol such as isopropyl alcohol (IPA). In some embodiments, the resulting nanotube film layer has a higher density than the initial nanotube film. Figure 15CIn this process, an initial nanotube film 240 is processed to reduce its thickness and obtain a nanotube film layer 260. As described herein, the initial nanotube film 240 is supported by a surface 342, which is placed within a press 250, which includes a pad 252 and a pressure head 254. The initial nanotube film 240 is compressed between the pad 252 and the pressure head 254 to obtain the nanotube film layer 260.

[0115] Figure 16 This is a flowchart illustrating one embodiment of a method for preparing a graphene film layer. In step 400, an initial graphene layer is formed by dispersing relatively small graphene flakes or plates on a surface to obtain a relatively large initial film. Smaller flakes or plates can be arranged such that micropores of desired size exist between the smaller flakes / plates. Note that such an initial film may easily disperse because the individual flakes / plates are not firmly bonded to each other. Finally, in step 410, the initial graphene layer is processed to reduce its thickness and obtain a graphene film layer. In some embodiments, the thickness is reduced by applying compressive pressure (e.g., uniaxial compression) to the initial graphene layer, thereby reducing the volume of the initial graphene layer. The resulting graphene film layer can then be attached to a frame or another film layer.

[0116] In one embodiment, Figure 17A and Figure 17B For illustration Figure 16 A set of accompanying figures for the method. Figure 17A In this process, an initial graphene layer 430 is formed by dispersing graphene sheets or plates 432 on a surface 434. For example... Figure 17B As illustrated, a graphene film layer 160 is prepared by compressing an initial graphene layer 430 between a pad 252 and a press head 254 in a press 250.

[0117] In some embodiments, each initial nanotube or graphene film has a thickness of at least 0.7 micrometers (700 nm) prior to processing, and processing steps are performed to reduce the thickness, thereby producing individual nanotube or graphene film layers with a thickness of 200 nm or less. In some embodiments, the initial films may each have a thickness ranging from about 1 micrometer (μm) to about 10 μm. In some embodiments, the resulting nanotube or graphene film layers have a thickness ranging from about 10 nanometers (nm) to about 100 nm. At higher thicknesses, the mechanical properties may be altered in undesirable ways.

[0118] After the thin film layers for use as a protective film are formed, the thin film layers are then bonded together to form a protective film. In some embodiments, the final protective film made of one or more thin film layers should have a thickness from about 10 nanometers (nm) to about 100 nm.

[0119] Figure 18This is a flowchart illustrating one embodiment of a method for preparing a multilayer structure of a protective film. Generally, in step 500, a frame is placed adjacent to the surface of a first film layer. Next, in step 510, pressure is applied to secure the first film layer to the frame. The first film layer and the frame are held attached by van der Waals force. If the protective film needs to be made of more than one layer, in step 520, the frame and any attached film layer are laid on the surface of an additional film layer. The outermost attached film layer contacts the surface of the additional film layer. Next, in step 530, pressure is applied again to secure the additional film layer to the attached film layer. Steps 520 and 530 can be repeated with additional film layers until the desired multilayer structure of the protective film is assembled. In step 535, a conformal coating is applied to the protective film.

[0120] In one embodiment, Figures 19A-19C For illustration Figure 18 A set of accompanying figures for the method. Figure 19A In this process, the first nanotube thin film layer 150 is fixed to the frame 128 by pressure applied by a press 250 including a pad 252 and a pressure head 254. Figure 19B Next, the frame 128 and the first nanotube thin film layer 150 (already attached to the frame 128) are deposited on the graphene thin film layer 160. Figure 19C In the next step, pressure is applied again via press 250 to attach the graphene film layer 160 to the first nanotube film layer 150. Thus, a multilayer protective film can be successfully constructed. It is worth noting that the thickness of the multilayer protective film may vary slightly between the center and the edges of the protective film (where pressure has been used to attach the layers to the frame).

[0121] Figure 20 This is a flowchart illustrating another embodiment of a method for preparing a multilayer structure of a protective film. Generally, in step 540, individual film layers are stacked on top of each other in a desired order. Next, in step 550, pressure is applied to reduce the thickness and bond the individual layers together to obtain a multilayer protective film. Two or more individual layers may be bonded together in this single compression step. Next, in step 560, a mounting frame or border is positioned adjacent to the surface of the protective film. Next, in step 570, pressure is applied to secure the protective film to the mounting frame or border. In step 575, a conformal coating is applied to the protective film.

[0122] In one embodiment, Figures 21A-21C For illustration Figure 20 A set of accompanying figures for the method. Figure 21AIn some embodiments, two initially oriented nanotube films 240 are illustrated. They can be placed at any angle relative to each other, ranging from 0° to 100° and any range in between, although the relative angle is not important. In Figure 21B In some embodiments, both initially oriented nanotube films 240 are compressed between a backing plate 252 and a press head 254, forming a multi-layer protective film 130. In Figure 21C In some embodiments, a bezel 128 is laid over the protective film 130 and a compressive pressure is applied to bond them together.

[0123] Once the protective film has been attached to the bezel, a conformal coating is applied to the outer surface of the protective film. In one embodiment, the conformal coating is applied to the outer surface of the protective film in Figures 22A-22D This situation is illustrated in Figure 22A An assembly of a bezel 128 and a protective film 130 is shown, the protective film 130 including a nanotube film layer 150 and a graphene film layer 160. The bezel 128 is directly attached to the nanotube film layer 150, which serves as the inner surface 134 of the protective film 130. The graphene film layer 160 serves as the outer surface 132 of the protective film 130. As seen in Figure 22B A coating is applied to the outer surface 132 of the protective film 130 to form an outermost layer 172, as seen in Figure 22C In some embodiments, the coated protective film 130 and bezel 128 are then attached to a mounting frame 122, such as via an adhesive layer 129, to form a protective assembly 120. In Figure 22D In some embodiments, the protective assembly 120 is mounted to a reticle 100 (with a desired mask pattern) by fastening the mounting frame to the reticle, with the protective film disposed over the mask pattern, to produce a final reticle assembly, such as shown by the non-limiting illustrative example in Figure 1

[0124] The conformal coating can be applied by known methods known in the art, such as spray coating, dip coating, etc. The conformal coating should conform to the exposed surfaces of the protective film, so that the micropores present in the protective film remain present and are not filled by the conformal coating. Such exposed surfaces can be present in any or all of the different layers of the multi-layer protective surface. In addition, the conformal coating will penetrate into the protective film, rather than being a single, separate layer on the protective film. For example, when the conformal coating is applied to the protective film illustrated in Figure 4 It is contemplated that the sides of some of the nanotubes of both nanotube film layers can also be covered by the conformal coating when the conformal coating is applied to the protective film illustrated in

[0125] ​The conformal coating is intended to protect the pellicle from damage that can occur due to heat and hydrogen plasma generated during EUV exposure. In general, the material used for the coating should have a low refractive index, i.e., as close to 1 as possible when measured at a wavelength of 13.5 nm. The material used for the coating should also have a low extinction coefficient at a wavelength of 13.5 nm. The extinction coefficient measures how easily a material can be penetrated by a wavelength. Ideally, the material used for the conformal coating has a transmittance (T%) of greater than 90%, greater than 92%, greater than 94%, or greater than 95% when measured at a thickness between 1 and 10 nm and at an EUV wavelength of 13.5 nm. This reduces EUV absorption of the conformal coating (permitting further downstream processing) while at the same time protecting the pellicle.

[0126] In some embodiments, the coating includes B, BN, B4C, B2O3, SiN, Si3N4, SiN2, SiC, SiC x N y , Nb, NbN, NbSi, NbSiN, Nb2O5, NbTi x N y , ZrN x , ZrY x O y , ZrF4, YN, Y2O3, YF, Mo, Mo2N, MoSi, MoSiN, Ru, RuNb, RuSiN, TiN, TiC x N y , HfO2, HfN x , HfF4, or VN. In some embodiments, the outermost layer has a thickness of about 1 nanometer (nm) to about 10 nm. This thickness should be measured as the coating thickness on the individual components of each layer in the pellicle, e.g., the coating thickness on the carbon nanotubes. The coating can penetrate deeper into the pellicle than this thickness.

[0127] Referring to Figures 11A-11C and Figure 22B , it is noted that one significant difference between the bezel 128 and the mounting frame 122 is that the mounting frame 122 includes exhaust holes 123. These exhaust holes 123 typically have a very small diameter, which can be on the order of 0.1 mm or less. These exhaust holes 123 are typically located on the mounting frame 122 in the vicinity of the mounting frame 122 where the mounting frame 122 is in contact with the bezel 128. These exhaust holes 123 are typically located on the mounting frame 122 in the vicinity of the mounting frame 122 where the mounting frame 122 is in contact with the bezel 128. Figure 22BThe coating processes illustrated in the middle easily fill or clog such exhaust holes. The use of the border 128 facilitates the application of a conformal coating to the pellicle while also protecting the exhaust holes 123 of the mounting frame 122. If desired, the use of the border 128 can be omitted, with the pellicle being attached directly to the appropriately structured mounting frame 122. For example, in some embodiments of such mounting frames, exhaust holes are present at the end of the mounting frame opposite the end to which the pellicle is attached. Referring to Figure 10 Such a mounting frame can be envisioned as a combination of separate components (mounting frame 122, adhesive layer 129, and border 128).

[0128] Because the pellicle is in the optical path between the reticle and the wafer on which the transferred pattern will be imaged, the pellicle needs certain optical properties. For example, the pellicle should have high transmission of EUV wavelengths (i.e., be optically transparent), low reflectivity of EUV wavelengths, low inhomogeneity, and low scattering. During exposure and routine handling, the pellicle will be exposed to high temperatures, and thus also needs certain thermal properties. For example, the pellicle should have low thermal expansion, high thermal conductivity, and high thermal emissivity. The pellicle should also have good mechanical properties, such as high stiffness (i.e., low sag or deflection) and stability. The pellicle of the present disclosure has a combination of these desired properties.

[0129] The methods described herein provide a pellicle with an improved combination of EUV transmissivity, pore size, stiffness, and service life. The pellicle of the present disclosure maintains high transmission in the EUV wavelength range. This permits more light to reach the reticle for a given exposure energy, and also reduces heat buildup in the pellicle. In some embodiments, the pellicle has a transmissivity of greater than 90%, greater than 95%, greater than 96%, or greater than 97% when measured at an EUV wavelength of 13.5 nm.

[0130] One means of obtaining high transmissivity is the presence of micropores in the protective film, as micropores do not reflect or absorb EUV wavelengths. The protective films of the present disclosure have an average micropore size that is small enough to prevent particles from passing through the protective film and falling on the reticle / photomask. In some embodiments, the largest micropore size of the micropores in the protective film is less than 30 nm (after the conformal coating has been applied) in terms of diameter. In this regard, a micropore is considered to be any straight path that goes completely through the protective film. Micropores can exist due to spaces between nanotubes or between sheets / plates of graphene or graphite. The micropore size is the smallest diameter of this straight path (as only the particle has to be captured before it passes through the protective film, not necessarily stopped at the outer surface of the protective film). In a multi-layer protective film, the micropore size of the protective film is typically much smaller as the micropores of a given film layer are not aligned with the micropores of another film layer. Micropore size can be measured using known methods, for example, by imaging the film and measuring the size of each micropore.

[0131] The increased stiffness of the protective film minimizes any potential sagging or deflection that can occur over time. For example, the size (length and width) of the protective film is approximately 100 millimeters. The protective films of the present disclosure can sag or deflect in the range of 700 micrometers or less under an applied pressure difference of two pascals (Pa). In embodiments, the protective film can have a thickness ranging from about 10 nanometers (nm) to about 100 nm.

[0132] The protective films of the present disclosure also have a low reflectivity for EUV wavelengths. Again, this permits more light to reach the photomask for a given exposure energy and also reduces critical dimension errors. In some embodiments, the protective film has a reflectivity (R%) of 5% or less, 3% or less, 2% or less, 1% or less, 0.5% or less when measured at an EUV wavelength of 13.5 nm.

[0133] The protective films of the present disclosure also have a low non-uniformity at EUV wavelengths, or in other words, a high uniformity. This reduces local critical dimension errors that can occur. In some embodiments, the protective film has a non-uniformity (U%) of 1% or less, 0.5% or less, 0.3% or less, 0.1% or less when measured at an EUV wavelength of 13.5 nm.

[0134] Some embodiments of the present disclosure thus describe a protective film comprising a protective film having an outer surface and an inner surface, and a conformal coating on at least the outer surface of the protective film.

[0135] In some embodiments, the protective film includes at least one nanotube film layer. In some embodiments, the nanotube film layer has a thickness of 10 nm to 100 nm. In some embodiments, the nanotube film layer includes carbon nanotubes or boron nitride nanotubes. In some embodiments, the nanotube film layer includes randomly oriented nanotubes or directionally oriented nanotubes. In some embodiments, the protective film includes at least one graphene film layer. In some embodiments, the protective film includes at least a first nanotube film layer and a second nanotube film layer. In some embodiments, the protective film further includes a graphene film layer. In some embodiments, the graphene film layer forms an outer surface or an inner surface of the film. In some embodiments, the graphene film layer is between the first nanotube film layer and the second nanotube film layer. In some embodiments, the conformal coating includes B, BN, B4C, B2O3, SiN, Si3N4, SiN2, SiC, SiC x N y , Nb, NbN, NbSi, NbSiN, Nb2O5, NbTi x N y , ZrN x , ZrY x Oy, ZrF4, YN, Y2O3, YF, Mo, Mo2N, MoSi, MoSiN, Ru, RuNb, RuSiN, TiN, TiC x N y , HfO2, HfN x , HfF4, VN, or combinations thereof. In some embodiments, the conformal coating has a thickness of 1 nm to 10 nm. In some embodiments, the protective assembly further includes a bezel or a mounting frame contacting an inner surface of the protective film. In some embodiments, the protective assembly further includes a mounting frame attached to a bezel, the bezel contacting an inner surface of the protective film. In some embodiments, the mounting frame includes vent holes and the bezel does not include vent holes. In some embodiments, the protective film has an EUV transmittance of at least 90% at 13.5 nm wavelength, a maximum deflection of 700 pm, and a maximum pore size of 30 nm.

[0136] Other embodiments of the present disclosure describe a demagnification mask assembly including a demagnification mask and a protective assembly, and a method for forming such a demagnification mask assembly. The demagnification mask has a mask pattern thereon. The protective assembly is disposed over the mask pattern and mounted / fixed to the demagnification mask. The protective assembly includes a multilayer protective film having a conformal coating on an outer surface thereof.

[0137] In some embodiments, the protective film has an EUV transmittance of at least 90% at 13.5 nm wavelength, a maximum deflection of 700 pm, and a maximum pore size of 30 nm.

[0138] Other embodiments of the present disclosure are directed to a method for increasing the lifetime of a pellicle. A conformal coating is applied to at least an outer surface of the pellicle. The conformal coating has a transmittance greater than 90% when measured at an EUV wavelength of 13.5 nm and at a thickness between 1 nm and 10 nm.

[0139] In some embodiments, the conformal coating comprises B, BN, B4C, B2O3, SiN, Si3N4, SiN2, SiC, SiC x N y , Nb, NbN, NbSi, NbSiN, Nb2O5, NbTi x N y , ZrN x , ZrY x O y , ZrF4, YN, Y2O3, YF, Mo, Mo2N, Ru, RuNb, RuSiN, TiN, TiC x N y , HfO2, HfN x , HfF4, or VN.

[0140] The foregoing summary of some embodiments has been presented for the purposes of illustration and description. It is, of course, not intended to be an exhaustive overview of the disclosure and its various aspects. It is also not intended to limit the scope of the disclosure to the examples described, as various modifications are possible and can be made to the disclosure without deviating from the spirit and scope of the disclosure.

Claims

1. A protective assembly, characterized in that, comprising: a protective film having an outer surface and an inner surface, the protective film comprising at least one first nanotube film layer, a second nanotube film layer, and a graphene film layer, the graphene film layer forming the outer surface of the protective film; a conformal coating on at least the outer surface of the protective film; and a mounting frame attached to a bezel, the bezel contacting the inner surface of the protective film.

2. The guard assembly of claim 1, wherein, The at least one first nanotube film layer has a thickness of 10 nm to 100 nm.

3. The guard assembly of claim 1, wherein, The second nanotube film layer has a thickness of 10 nm to 100 nm.

4. The guard assembly of claim 1, wherein, The at least one first nanotube film layer comprises carbon nanotubes or boron nitride nanotubes.

5. The guard assembly of claim 1, wherein, The at least one first nanotube film layer comprises randomly oriented nanotubes.

6. The guard assembly of claim 1, wherein, The second nanotube film layer comprises carbon nanotubes or boron nitride nanotubes.

7. The guard assembly of claim 1, wherein, The second nanotube film layer comprises randomly oriented nanotubes.

8. The guard assembly of claim 1, wherein, The protective film has a maximum deflection of 700 pm.

9. The guard assembly of claim 1, wherein, The protective film has a maximum pore size of 30 nm.

10. The guard assembly of claim 1, wherein, The at least one first nanotube film layer comprises directionally oriented nanotubes.

11. The guard assembly of claim 1, wherein, The conformal coating includes B, BN, B4C, B2O3, SiN, Si3N4, SiN2, SiC, SiC x N y , Nb, NbN, NbSi, NbSiN, Nb2O5, NbTi x N y , ZrN x , ZrY x Oy, ZrF4, YN, Y2O3, YF, Mo, Mo2N, MoSi, MoSiN, Ru, RuNb, RuSiN, TiN, TiC x N y , HfO2, HfN x , HfF4, VN, or combinations of the foregoing.

12. The guard assembly of claim 1, wherein, The conformal coating has a thickness of 1 nm to 10 nm.

13. The guard assembly of claim 1, wherein, The second nanotube film layer comprises directionally oriented nanotubes.

14. The guard assembly of claim 1, wherein, The conformal coating coats sides of the protective film and terminates at the bezel.

15. The guard assembly of claim 1, wherein, The mounting frame comprises vent holes and the bezel does not comprise vent holes.

16. The guard assembly of claim 1, wherein, The protective film has an EUV transmittance of at least 90% at a wavelength of 13.5 nm.

17. A method of forming a one-time photomask assembly, comprising: comprising: positioning a protective assembly over a mask pattern of a demagnification mask, wherein the protective assembly comprises a multilayer protective film comprising at least one first nanotube film layer, a second nanotube film layer, and a graphene film layer, the graphene film layer forming an outer surface of the multilayer protective film, the protective assembly comprising a conformal coating penetrating into the multilayer protective film.

18. The method of claim 17, wherein, The multilayer protective film has an EUV transmittance of at least 90% at a wavelength of 13.5 nm, a maximum deflection of 700 pm, and a maximum pore size of 30 nm.

19. A method of increasing the service life of a protective film, characterized by, comprising: A conformal coating is applied to at least one outer surface of a protective film comprising at least one first nanotube film layer, a second nanotube film layer, and a graphene film layer, the graphene film layer forming the outer surface of the protective film, the graphene film layer being a non-porous, continuous film, the conformal coating comprising Nb, Nb2O5, ZrY x Oy, ZrF4, YN, Y2O3, YF, or HfF4, wherein the conformal coating has a transmittance greater than 90% when measured at an EUV wavelength of 13.5 nm and at a thickness between 1 nm and 10 nm.

20. The method of claim 19, wherein, The conformal coating has a thickness of 1 nm to 10 nm.

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