OPTICAL ARRANGEMENT WITH COATING AND USAGE METHOD

Abstract

Optical arrangement with: a matrix consisting of a plurality of nanotube bundles (602), wherein the majority of nanotube bundles (602) contain carbon nanotubes (600); and a coating (604) on the plurality of nanotube bundles (602), wherein the coating (604) encloses individual nanotubes (600) of the individual nanotube bundles (602) and wherein the coating (604) on the majority of nanotube bundles (602) comprises a coating (604) on one nanotube bundle (602) and a coating (604) on individual carbon nanotubes (600) of the nanotube bundle (602).

Description

BACKGROUND

[0001] The present invention relates to the field of ultraviolet and extreme ultraviolet lithography and optical arrangements used in ultraviolet and extreme ultraviolet lithography.

[0002] In the IC industry (IC: semiconductor integrated circuit), technological advances in IC materials and designs have produced generations of ICs, each generation featuring smaller and more complex circuits than the previous one. Over the course of IC evolution, feature density (i.e., the number of interconnected devices per unit area of ​​the chip) has generally increased, while feature size (i.e., the smallest component (or trace) that can be produced using a manufacturing process) has decreased. This miniaturization process generally offers advantages by increasing production yield and reducing associated costs. However, this miniaturization has also increased the complexity of machining and manufacturing ICs.

[0003] In a photolithographic process, a structured resist layer is produced for various structuring processes, such as etching or ion implantation. The minimum size of a structural element that can be structured using such a lithographic process is limited by the wavelength of the projected radiation source. Developments in lithography devices have progressed from the use of ultraviolet light with a wavelength of 365 nanometers to the use of deep ultraviolet (DUV) light, such as a krypton fluoride laser (KrF) at 248 nanometers and an argon fluoride laser (ArF) at 193 nanometers, and to the use of extreme ultraviolet (EUV) light with a wavelength of 13.5 nanometers, improving resolution at each step.

[0004] In the photolithographic process, a photomask (or mask) is used. The mask comprises a substrate and a structured layer that defines an integrated circuit to be transferred onto a semiconductor substrate during the photolithographic process. Typically, a mask is integrated with a pellicle assembly, and collectively, these are referred to as a mask system. The pellicle assembly has a transparent, thin membrane and a pellicle frame, with the membrane mounted over the pellicle frame. The pellicle protects the mask from falling particles and ensures that the particles remain out of focus, preventing them from creating a structured image that could cause defects in the structured semiconductor substrate when the mask is used. The membrane is typically stretched and mounted over the pellicle frame and is attached to the frame with adhesive or other bonding agents.An inner space can be formed by the mask, the membrane and the pellicle frame.

[0005] US 2018 / 0329291 A1 discloses an optical arrangement with a matrix of a plurality of nanotube bundles and a coating thereof, wherein the coating encloses individual nanotubes of the individual nanotube bundles. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic representation of a lithography system according to some embodiments of the present invention. Fig. Figure 2 is a schematic sectional view of a mask for use in embodiments of the present invention. The Fig. Figures 3A-3C are a top view, a perspective view and a sectional view along a line AA' of a mask pellicle system according to some embodiments of the present invention. The Fig. Figures 4A-4D are schematic sectional views of several pellicle membranes according to the embodiments described herein. Fig. Figure 5A is a schematic perspective view of a nanotube with a partially removed cover layer according to some embodiments of the present invention. Fig. Figure 5B is a view of a cover layer on an outside and on an inside of a nanotube according to some embodiments of the present invention. Fig. Figure 5C is a schematic perspective representation of a nanotube with a partially removed cover layer and an adhesive layer according to some embodiments of the present invention. Fig. Figure 6A is a schematic representation of a nanotube bundle according to some embodiments of the present invention. Fig. Figure 6B is a sectional view of a nanotube bundle with a cover layer according to some embodiments of the present invention. The Fig. Figures 7A-7D are representations of uncoated nanotubes, nanotubes after deposition of a cover layer, an exploded view of coated nanotubes, and another exploded view of the carbon nanotubes according to some embodiments of the present invention. Fig. Figure 8 is a flowchart illustrating a method according to an embodiment of the present invention. Fig. Figure 9 is a flowchart illustrating a method according to an embodiment of the present invention. Fig. Figure 10 is a schematic representation of a system for applying a protective layer or a cover layer to a nanotube according to an embodiment of the present invention. Fig. Figure 11 is a flowchart illustrating a method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0006] The following description outlines thicknesses and materials for various layers and structures in an integrated circuit chip. Specific dimensions and materials are given as examples for different embodiments. Those skilled in the art will recognize that, in many cases, other dimensions and materials can be used without deviating from the scope of protection of the present invention.

[0007] The invention is defined in the appended claims. The invention below provides many different embodiments or examples for implementing elements of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present description. These are, of course, merely examples and are not intended to be limiting. For example, the fabrication of a first element above or on top of a second element in the description below may include embodiments in which the first and second elements are fabricated in direct contact, and it may also include embodiments in which additional elements can be fabricated between the first and second elements, such that the first and second elements are not in direct contact.Furthermore, reference numerals and / or letters may be repeated in the various examples in the present invention. This repetition serves the purpose of simplicity and clarity and does not in itself imply any relationship between the various embodiments and / or configurations discussed.

[0008] Furthermore, to simplify the description of the relationship of an element or structure to one or more other elements or structures depicted in the figures, spatially relative terms such as "below," "under," "lower," "above," "upper," and the like may be used. These spatially relative terms are intended to cover orientations of the device during use or operation in addition to the orientation shown in the figures. The device may be oriented differently (rotated by 90 degrees or in other orientations), and the spatially relative descriptors used here can be interpreted similarly.

[0009] “Vertical direction” and “horizontal direction” are to be understood as indicating relative directions. Consequently, the horizontal direction is to be understood as being essentially perpendicular to the vertical direction, and vice versa. Nevertheless, it is within the scope of protection of the present invention that the described embodiments and aspects can be rotated in their entirety so that the dimension designated as the vertical direction is horizontally oriented, and at the same time, the dimension designated as the horizontal direction is vertically oriented.

[0010] The following description sets out specific details to facilitate a better understanding of various embodiments of the invention. However, a person skilled in the art should recognize that the invention can also be used without these specific details. In other cases, known structures associated with electronic components and manufacturing processes are not described in detail to avoid unnecessarily obscuring the description of the embodiments of the present invention.

[0011] Throughout the entire description and in all claims, the term "exhibit" and variations thereof, such as "..., which exhibits ...", "comprise", "..., which includes ...", "have", "..., which has ...", "with", etc., are to be interpreted in an open, inclusive sense, that is, as "exhibit, but not be limited to", unless the context requires otherwise.

[0012] The use of ordinal numbers, such as "first", "second" and "third", does not necessarily imply an order of ranks, but merely serves to distinguish between multiple instances of a process or structure.

[0013] Throughout the patent description, references to "one embodiment" or "some embodiments" mean that a specific element, structure, implementation, or feature described in connection with one or more embodiments is a component of at least one embodiment of the present invention. Therefore, the use of the phrases "in one embodiment" or "in some embodiments" at various points in the description does not necessarily always refer to one and the same embodiment. Furthermore, the specific elements, structures, or features may be appropriately combined in one or more embodiments.

[0014] The singular forms “ein(e)” and “der / die / das” used in the description and the attached claims also include plural forms unless the context clearly indicates otherwise. It should also be noted that the term “oder” is generally used to mean “and / or” unless the context clearly indicates otherwise.

[0015] Embodiments according to the present invention provide optical arrangements suitable for transmitting UV or EUV radiation and for protecting UV- or EUV-reflecting components of a lithography system. The optical arrangements exhibit desirable UV / EUV transparency levels and promote heat transfer from the optical arrangement. The optical arrangements are also resistant to damage when exposed to gases such as hydrogen, oxygen, and H+ gas.

[0016] The invention is defined in the appended claims. The various advantages and purposes of embodiments according to the present invention, as described above and below, are achieved by providing an optical arrangement according to aspects of the present invention, which comprises a matrix of a plurality of nanotube bundles or a matrix of individual nanotubes. According to the invention, the individual nanotubes are coated with a coating for protection. According to the invention, the individual nanotubes of the nanotube bundles are coated with a coating, and the nanotube bundle is formed from such coated individual nanotubes. These optical arrangements prove useful in methods for structuring materials on a semiconductor substrate. These methods include the generation of UV radiation in a UV lithography system.UV radiation is transmitted through a coating of an optical arrangement, e.g., a pellicle arrangement. The UV radiation that has passed through the coating is then transmitted through a matrix of individual nanotubes or a matrix of nanotube bundles. UV radiation passing through the matrix of individual nanotubes or the matrix of nanotube bundles is reflected by a mask and received by a semiconductor substrate. In other embodiments, the coating is applied to a transparent layer of a pellicle arrangement.

[0017] In Fig. Figure 1 shows a schematic representation of a lithography system 100 according to some embodiments. The lithography system 100 can also be generally referred to as a scanner that can be operated to perform lithographic processes, such as exposure with a particular radiation source and in a particular exposure mode. In at least some of the present embodiments, the lithography system 100 comprises an ultraviolet lithography system (UV lithography system) designed to expose a resist layer with UV radiation, i.e., UV light. In this respect, the resist layer in various embodiments comprises a material that is sensitive to UV light (e.g., a UV resist). The lithography system 100 of Fig. 1 comprises a plurality of subsystems, such as a radiation source 102, an exposure device 104, a mask stage 106 configured to hold a mask 108, a projection optic 110, and a substrate stage 118 configured to hold a semiconductor substrate 116. The following description of a UV photolithography system according to embodiments of the present invention relates to extreme ultraviolet radiation as an exemplary ultraviolet radiation. Embodiments according to the present invention are not limited to lithography systems using extreme ultraviolet radiation. In other words, embodiments described with reference to extreme ultraviolet lithography systems include embodiments that use ultraviolet radiation.The following is a general description of the operation of the lithography system 100: EUV light from the radiation source 102 is directed to the exposure device 104 (which has a group of reflective mirrors) and projected onto the reflective mask 108. A reflected mask image is directed to the projection optics 110, which focuses the EUV light and projects it onto the semiconductor substrate 116 to expose an EUV resist layer deposited thereon. Additionally, in various examples, each subsystem of the lithography system 100 can be integrated and thus operate in a high-vacuum environment, for example, to reduce atmospheric absorption of the EUV light.

[0018] In the embodiments described here, the radiation source 102 can be used to generate the EUV light. In some embodiments, the radiation source 102 comprises a plasma source, such as discharge-produced plasma (DPP) or laser-produced plasma (LPP). In some embodiments, the EUV light can have a wavelength in the range of about 1 nm to about 100 nm. In one particular example, the radiation source 102 generates EUV light with a wavelength centered at about 13.5 nm. Accordingly, the radiation source 102 can also be referred to as an EUV radiation source 102.In some embodiments, the radiation source 102 also has a collector which can be used to collect EUV light generated by the plasma source and to direct the collected EUV light to the imaging optics, such as the exposure device 104.

[0019] As described above, EUV light from the radiation source 102 is directed to the exposure device 104. In some embodiments, the exposure device 104 may include a mirror optic (e.g., for the EUV lithography system 100), such as a single mirror or a system of multiple mirrors, to direct light from the radiation source 102 onto the mask stage 106, and in particular onto the mask 108, which is held on the mask stage 106. In some embodiments, the exposure device 104 may, for example, include a zone plate (not shown) to improve the focus of the EUV light. In some embodiments, the exposure device 104 may be configured to shape the EUV light passing through it according to a specific pupil shape, such as a dipole shape, a quadruple shape, annular shape, a single-beam shape, a multi-beam shape, and / or a combination thereof.In some embodiments, the exposure device 104 can be operated such that it configures the mirrors (i.e., of the exposure device 104) to provide a desired exposure of the mask 108. In one example, the mirrors of the exposure device 104 can be configured to reflect EUV light to different exposure positions. In some embodiments, a table (not shown) in front of the exposure device 104 can additionally have further configurable mirrors that can be used, together with the mirrors of the exposure device 104, to direct the EUV light to different exposure positions. In some embodiments, the exposure device 104 is configured to provide on-axis illumination (ONI) for the mask 108.In some embodiments, the exposure device 104 is configured to provide off-axis illumination (OAI) for the mask 108. It should be noted that the optics used in the EUV lithography system 100, and in particular the optics used for the exposure device 104 and the projection optics 110, may have mirrors with multilayer thin-film coatings, also known as Bragg reflectors. Such a multilayer thin-film coating may, for example, have alternating layers of Mo and Si, thereby providing high reflectivity at EUV wavelengths (e.g., about 13 nm).

[0020] As discussed above, the lithography system 100 also includes the mask stage 106, which is configured to hold the mask 108 in the lithography system. Since the lithography system 100 can be installed and therefore operated in a high-vacuum environment, the mask stage 106 can have an electrostatic clamping device (e-clamping device) for holding the mask 108. Like the optics of the EUV lithography system 100, the mask 108 is also reflective. Details of the mask 108 are given below with reference to the example of Fig. 2 discussed in more detail. As in Fig. As shown in Figure 1, light is reflected from the mask 108 and directed to the projection optics 110, which collects the EUV light reflected from the mask 108. For example, the EUV light collected by the projection optics 110 (reflected from the mask 108) carries an image of the structure defined by the mask 108. In various embodiments, the projection optics 110 ensures that the structure of the mask 108 is imaged onto the semiconductor substrate 116, which is held on the substrate stage 118 of the lithography system 100. In particular, in various embodiments, the projection optics 110 focuses the collected EUV light and projects it onto the semiconductor substrate 116 to expose an EUV resist layer deposited on the semiconductor substrate 116. As described above, the projection optics 110 can have a mirror optic such as that used in EUV lithography systems, such as the lithography system 100.In some embodiments, the exposure device 104 and the projection optics 110 are collectively referred to as an optical module of the lithography system 100.

[0021] As discussed above, the lithography system 100 also includes the substrate stage 118 for holding the semiconductor substrate 116 to be patterned. In various embodiments, the semiconductor substrate 116 comprises a semiconductor wafer, such as a silicon wafer, germanium wafer, silicon-germanium wafer, III-V wafer, or another type of wafer. The semiconductor substrate 116 may be coated with a resist layer (e.g., an EUV resist layer) that is sensitive to EUV light. EUV resists can have stringent performance standards. For illustrative purposes, an EUV resist may be designed to provide a resolution of at least about 22 nm, a linewidth roughness (LWR) of at least about 2 nm, and a sensitivity of at least about 15 mJ / cm².In the embodiments described here, the various subsystems of the lithography system 100, such as those described above, are integrated and can be operated in such a way that they can perform lithographic exposure processes, such as EUV lithography processes. Of course, the lithography system 100 can also include other modules or subsystems that can be integrated (or coupled) with one or more of the subsystems or components described here.

[0022] The lithography system may include other components and may have other alternatives. In some embodiments, the lithography system 100 may include a pupil phase modulator 112 for modulating an optical phase of the EUV light directed by the mask 108, such that the light has a phase distribution along a projection pupil plane 114. In some embodiments, the pupil phase modulator 112 includes a mechanism for tuning the reflecting mirrors of the projection optics 110 for phase modulation. In some embodiments, for example, the mirrors of the projection optics 110 may be configured to reflect the EUV light through the pupil phase modulator 112, thereby modulating the phase of the light through the projection optics 110. In some embodiments, the pupil phase modulator 112 uses a pupil filter placed on the projection pupil plane 114.The pupil filter can be used, for example, to filter out specific spatial frequency components of the EUV light reflected by the mask 108. In some embodiments, the pupil filter can serve as a phase-pupil filter that modulates the phase distribution of the light directed by the projection optics 110.

[0023] In Fig. Figure 2 shows that the mask 108 has a structured pattern comprising one or more absorbers 208 with an anti-reflective coating (ARC layer) 210. The one or more absorbers 208 and the anti-reflective coating are on a multilayer structure 204, e.g., Mo-Si multilayers, which is on a substrate 202. Examples of materials for the absorbers 208 include a tantalum nitride layer or a Ta x B y O z N u Examples of materials used for anti-reflective coatings include Ta x By O z N u , an Hf x O y -layer or a Si x O y N z -layer. One example of a substrate 202 is a substrate material with low thermal expansion, such as SiO2 doped with TiO2. In the Fig. In the embodiment shown in Figure 2, the multilayer structure 204 is covered by a top layer 206, and the back side of the substrate 202 is covered with a back coating 203. An exemplary material for the top layer 206 is, among others, ruthenium. An exemplary material for the back coating 203 is, among others, chromium nitride.

[0024] As discussed above, the mask 108 is used to transfer circuit and / or device structures onto a semiconductor wafer (e.g., the semiconductor substrate 116) using the lithography system 100. The lithography process should be defect-free to achieve high dimensional accuracy during the structure transfer from the structured mask 108 to the semiconductor substrate 116. Undesired particles, such as particles of tin (Sn), which is used to generate the EUV light in the radiation source 102, can be inadvertently deposited on the surface of the cover layer 206 and can lead to degradation of lithographically transferred structures if they are not removed. Particles can be introduced not only through EUV light generation but also through a variety of processes, such as during an etching process, a cleaning process, and / or during handling of the EUV mask 108.Accordingly, the mask 108 is integrated with a pellicle and protected by the pellicle assembly. The mask and the pellicle assembly are collectively referred to as a mask-pellicle system. During the lithographic structuring process with the lithography system 100, the mask-pellicle system is held in place, for example, on the mask table 106.

[0025] It will be directed to the Fig. 3A, Fig. 3B and Fig. Reference is made to Figure 3C, which shows a top view, a perspective view, and a section view along a line AA' of a mask-pellicle system 300. In the Fig. 3A, Fig. 3B and Fig. Section 3C describes the mask-pellicle system 300 and a method for its use. While embodiments of the present invention are described with reference to a mask of a photolithographic system, it is understood that the embodiments of the present invention are also useful for other UV- or EUV-reflecting components of a lithography system that reflect UV or EUV radiation.

[0026] The mask-pellicle system 300 comprises a mask 302, a pellicle frame 304, and an optical arrangement, e.g., a membrane (or pellicle membrane) 306, which are integrated together by adhesive layers 308 and 310. As discussed above, the mask 302 also has a structured surface 314, which is used to structure a semiconductor substrate by a lithographic process. In some embodiments, the mask 302 may be essentially the same as the mask 108 discussed above. In the present embodiment, the mask 302 is integrated into the mask-pellicle system 300 and is held on the mask stage 106 together with the membrane 306 and the pellicle frame 304 during a lithographic structuring process.

[0027] The membrane 306 is configured to be close to the mask 302 and is attached to the pellicle frame 304 by the adhesive layer 308. Specifically, the membrane 306 is attached to the pellicle frame 304 by the adhesive layer 308. The mask 302 is further attached to the pellicle frame 304 by the adhesive layer 310. Consequently, the mask 302, the pellicle frame 304, and the membrane 306 are configured and integrated to enclose an inner space 312. The structured surface 314 of the mask 302 is enclosed within the inner space 312 and is therefore protected against contamination during a lithographic structuring process, mask transport, and mask handling. In the illustrated embodiment of Fig. In Figure 3C, the pellicle frame 304 is provided with two ventilation holes 320. Embodiments according to the present invention can have only one ventilation hole 320 or more than two ventilation holes 320. Ventilation holes serve to equalize the air pressure between the open space bounded by the pellicle frame 304 and the pellicle membrane 306 and the environment outside the pellicle frame 304 and the pellicle membrane 306. Ventilation holes 320 can be provided with filters (not shown) configured to prevent particles from entering the ventilation holes 320.

[0028] Membrane 306 is made of a thin film that is transparent to the light beam used in a lithographic structuring process and also has a thermally conductive surface. Membrane 306 is also configured to closely resemble the structured surface 314 on mask 302, as shown in Fig. Figure 3C is shown. In various embodiments, the membrane 306 has a transparent material layer with a heat dissipation layer on one surface (or both surfaces).

[0029] Fig. Figure 4 is a sectional view of the membrane 306, which is designed according to some embodiments. The membrane 306 comprises a transparent layer 402 or core material layer made of one or more materials, including silicon, such as polycrystalline silicon (Poly-Si), amorphous silicon (a-Si), doped silicon (such as phosphorus-doped silicon SiP or SiC), or a silicon-based compound, such as SiN or MoSi. x N y,or a combination (SiN / MoSiN). Alternatively, the transparent layer 402 comprises polymer, graphene, carbon network membranes, carbon nanotubes, silicon-carbon nanotubes, boron nitride nanotubes, carbon nanotube bundles, or other suitable material, such as bundles of nanotubes. In some embodiments, the membrane 306 is characterized by the absence of oxygen-containing materials, e.g., SiO2. Membranes 306 without oxygen-containing materials are less susceptible to H₂ corrosion. +H+ radicals cause deterioration to which membranes 306 are exposed during the photolithographic process or during maintenance of the photolithography system. When a membrane 306 containing oxygen-containing materials, such as SiO2, is exposed to H+ radicals, coatings provided on the SiO2 have been observed to detach. The transparent layer 402 has a thickness that provides sufficient mechanical strength, but in some embodiments, the thickness is such that the transparency of the membrane to extreme ultraviolet radiation from the radiation source is degraded by no more than 15% in some embodiments, by no more than 10% in some embodiments, or by no more than 5% in some embodiments. In some examples, the transparent layer 402 has a thickness in the range between 30 nm and 50 nm.

[0030] In some embodiments, the membrane 306 comprises a first coating 404, which is produced on the outer surface 322 of the transparent layer 402, and a second coating 406, which is produced on the inner surface 324 of the transparent layer 402. Fig. 4A is the outer surface 322 of the transparent layer 402, its top side, and the inner surface 324 of the transparent layer 402 is its bottom side. According to the in Fig. In the embodiment shown in Figure 4A, the material of coating 404 and the material of coating 406 are the same. In other embodiments according to Fig. 4A, the material of coating 404 and the material of coating 406 are different. In other embodiments according to Fig. In 4A, the coating 404 has multiple material layers. Similarly, in other embodiments, the coating 406 has multiple material layers. Such multiple layers can be of the same material or different materials. Furthermore, the multiple material layers forming the coating 404 and / or the coating 406 can have the same thickness or different thicknesses. Fig. In 4B, the coating 406 is provided only on the inside 324 and not on the outside 322. In other embodiments according to Fig. 4B has coating 406 with multiple material layers. Furthermore, the multiple material layers that make up coating 406 in Fig. 4B form, have the same thickness or different thicknesses. In Fig. In 4C, the coating 404 is provided only on the outer surface 322 and not on the inner surface 324. In other embodiments according to Fig. 4C has coating 404 with multiple material layers. Furthermore, the multiple material layers that make up coating 404 in Fig. 4B form, have the same thickness or different thicknesses. The coating (404 or 406) protects the transparent layer 402 against attack, such as by chemicals and / or particles. In some embodiments, the coating 404 and 406 promotes heat transfer from the transparent layer 402. According to another embodiment of the present invention, Fig. Figure 4D is an example where a first coating 408a is on the transparent layer 402 and a second coating 408b is on the first coating 408a. According to the embodiment of Fig. 4D, the material of the first coating 408a and the material of the second coating 408b can be the same or they can be different (for example: 408a: MoSiN and 408b:SiN2).

[0031] According to some embodiments of the present invention, when selecting a particular material for use as the first coating 404 and / or the second coating 406, a number of different factors should be taken into account, such as, among others, how thick a layer of material must be to provide a conformal coating, the scattering effect of the material for UV or EUV, the transparency for UV or EUV and the reflection of UV or EUV, the absorption of UV or EUV, the resistance to the desorption of oxygen and to attack by ionized gases that come into contact with the coatings, e.g. H+ gas.

[0032] For example, materials that are applied as a thinner layer and simultaneously provide a conformal coating are preferred over materials that must be applied as a thicker layer to provide a conformal coating. In some embodiments, the coatings 404 or 406 have a thickness on the order of 1 to 10 nanometers.

[0033] Materials that scatter less of the EUV radiation directed at the mask are preferred over materials that scatter more of the same EUV radiation. Examples of such materials include boron nitride (BN) and silicon nitride (Si3N4). Ruthenium is not a suitable material for coatings according to the embodiments of the present invention because ruthenium has a differential scattering cross-section of EUV radiation at 0° and 360° that is about 6 times larger than the differential scattering cross-section of EUV radiation at 0° and 360° for a transparent material coated with boron nitride or silicon nitride. In general, a material with a lower refractive index produces more scattering than a material with a higher refractive index.When selecting a material for coatings 404 and 406 solely on the basis of its refractive index, a material with a higher refractive index would therefore be preferred over a material with a lower refractive index.

[0034] In general, a material with a higher extinction coefficient k, indicating higher radiation absorption, is less desirable than a material with a lower extinction coefficient k because the material with a higher extinction coefficient transmits less UV or EUV radiation. Therefore, when selecting a material for coatings 404 and 406 solely based on its extinction coefficient k, a material with a lower extinction coefficient would be preferred over one with a higher extinction coefficient.

[0035] Materials that transmit more of the UV or EUV radiation directed at the mask are preferred over materials that transmit less of the same UV or EUV radiation. For example, in some embodiments, materials that transmit 80% or more of the radiation directed at the mask are suitable. In other embodiments, materials that transmit 85% or more of the radiation directed at the mask are suitable. In still other embodiments, materials that transmit 90% or more of the radiation directed at the mask are suitable. In other embodiments, materials that transmit 95% or more of the radiation directed at the mask are suitable.

[0036] Materials that reflect less of the radiation directed at the mask are preferred over materials that reflect more of the same EUV radiation.

[0037] Materials that absorb less of the EUV radiation directed at the mask are preferred over materials that absorb more of the same EUV radiation.

[0038] Materials that exhibit higher resistance to oxygen desorption are preferred over materials that exhibit lower resistance to oxygen desorption.

[0039] Materials containing higher-grade oxides are less suitable for coating 404 or 406 because they are susceptible to radiation-induced oxygen desorption, which is initiated by the creation of holes in near-surface hull levels. These resulting holes cause the coating to be more reactive to gas molecules to which it is exposed during the photolithographic or maintenance processes, compared to the reactivity of a coating that does not contain higher-grade oxides. According to embodiments of the present invention, materials that do not contain higher-grade oxides are preferred over materials that do.

[0040] Particles, e.g., tin particles from the EUV radiation source, can fall onto the pellicle surface. Such particles can be removed by etching the pellicle surface with an ionized gas, such as H+. The ability of the ionized gas to etch the particles, e.g., tin particles, from the pellicle surface depends in part on the electronegativity difference between tin and the pellicle surface material. Accordingly, when selecting a suitable material for coatings 404 and / or 406, the electronegativity difference between the particle to be etched, e.g., tin particles with an electronegativity of 1.96, and the coating material is taken into account. Materials with a lower electronegativity than the particle to be etched are preferred over materials with a higher electronegativity as coating materials.According to some embodiments, suitable materials for coatings 404 and / or 406 include materials with an electronegativity of less than 1.96 to about -0.2.

[0041] Examples of materials that can be used for coatings 404 and / or 406 are presented below, taking into account the criteria described above.

[0042] In some embodiments, the coating 404 comprises boron (B), boron nitride (BN), borosilicon nitride (BNSi), boron carbide (B4C), borosilicon carbide (BCSi), silicon mononitride (SiN), silicon nitride (Si3N4), silicon disitride (SiN2), silicon carbide (SiC), silicon carbonitride (SiCxNy), niobium (Nb), niobium nitride (NbN), niobium monosilicide (NbSi), niobium silicide (NbSi2), niobium silicon nitride (NbSiN), niobium titanium nitride (NbTixNy), zirconium nitride (ZrN), zirconium fluoride (ZrF4), yttrium nitride (YN), yttrium fluoride (YF), molybdenum (Mo), molybdenum nitride (MoN2), molybdenum carbide (Mo4C and Mo2C), molybdenum silicide (MoSi₂), molybdenum silicon nitride (MoS₆Ny), ruthenium-niobium alloys (RuNb), ruthenium silicon nitride (RuSiN), titanium nitride (TiN), titanium carbon nitride (TiC₆Ny), hafnium nitride (HfN₆), hafnium fluoride (HfF₄), or vanadium nitride (VN). Materials containing higher-grade oxides, such as TiO₂, V₂O₅, ZrO₂, Ta₂O₅, MoO₃, WO₃, CeO₂, Er₂O₃, SiO₂, Y₂O 3,Nb2O5, V2O3 and HfO2 are excluded as materials for coating 404.

[0043] In some embodiments, materials for coating 404 are selected from materials that do not contain higher-value oxides, such as boron (B), borosilicate nitride (BNSi), silicon nitride (Si3N4), silicon disitride (SiN2), niobium (Nb), niobium nitride (NbN), niobium monosilicide (NbSi), niobium silicide (NbSi2), niobium silicon nitride (NbSiN), niobium titanium nitride (NbTixNy), zirconium nitride (ZrN), zirconium fluoride (ZrF4), yttrium nitride (YN), yttrium fluoride (YF), molybdenum (Mo), molybdenum nitride (MoN2), molybdenum silicide (MoSi2), molybdenum silicon nitride (MoSixNy), ruthenium-niobium alloys (RuNb), ruthenium silicon nitride (RuSiN). Titanium nitride (TiN), titanium carbon nitride (TiCxNy), hafnium nitride (HfNx), hafnium fluoride (HfF4) or vanadium nitride (VN).

[0044] In some embodiments, materials for the coating 404 are selected from materials that do not contain ruthenium or molybdenum, such as boron (B), borosilicon nitride (BNSi), silicon nitride (Si3N4), silicon disinitride (SiN2), niobium (Nb), niobium nitride (NbN), niobium monosilicide (NbSi), niobium silicide (NbSi2), niobium silicon nitride (NbSiN), niobium titanium nitride (NbTixNy), zirconium nitride (ZrN), zirconium fluoride (ZrF4), yttrium nitride (YN), yttrium fluoride (YF), titanium nitride (TiN), titanium carbon nitride (TiCxNy), hafnium nitride (HfNx), hafnium fluoride (HfF4), or vanadium nitride (VN).

[0045] In some embodiments, the coating 404 comprises borosilicon nitride (BNSi), borosilicon carbide (BCSi), molybdenum carbide (Mo4C) or molybdenum carbide (Mo2C).

[0046] The 404 coating is thin and does not impair the transparency of the 306 membrane to UV or EUV light. In some examples, the thickness of the coating (404 and also 406, if present) ranges from 1 nm to 10 nm. One example coating has a thickness of 5 nm with a variation of 10% or less. The coating can be produced by a suitable deposition method, such as chemical vapor deposition (CVD), atomic layer deposition (ALD), plasma-enhanced ALD (PEALD), physical vapor deposition (PVD), electron beam evaporation, electroplating, electroless deposition, or any other suitable method.

[0047] According to some embodiments of the present invention, the coating 404 also serves as a heat dissipation layer, which promotes the transfer of heat energy from the transparent layer 402 to the environment around the coating 404.

[0048] According to some embodiments of the present invention, the transparent layer 402 (core membrane) is treated prior to the application of the coating 404 or the coating 406 to create minor defects in the surface of the transparent layer 402 and / or to remove unwanted silicon dioxide. Creating minor defects in the surface of the transparent layer 402 and / or removing unwanted silicon dioxide improves the adhesion of the coating 404 or the coating 406 to the surface of the transparent layer 402. Exemplary suitable processes for treating the surface of the transparent layer 402 prior to the application of the coatings 404 or 406 include treatment with a nitrogen, oxygen, carbon fluoride, or argon gas plasma.The transparent layer 402 is treated with the gas plasma, applying a combination of frequency, power, pressure and time duration sufficient to create minor defects in the surface of the transparent layer 402, which improve the adhesion of the coating, and / or to remove unwanted silicon dioxide.

[0049] The mask-pellicle system 300 also includes a pellicle frame 304 configured to allow the membrane 306 to be attached to and held in place by the pellicle frame 304. The pellicle frame 304 can be designed in various dimensions, shapes, and configurations. In these and other alternatives, the pellicle frame 304 can have one or more components. The pellicle frame 304 is made of a material with mechanical strength, and its shape, dimensions, and configuration are designed to properly hold the membrane 306 across the pellicle frame 304. In some embodiments, the pellicle frame 304 can be made entirely of a porous material.

[0050] The pellicle frame 304 has a porous material designed for ventilation and pressure equalization, since the pellicle mask system 300 is in a vacuum environment when held on the mask table 106 during the lithographic structuring process. As shown in Fig. As shown in Figure 3C, the porous material of the pellicle frame 304 has interconnected pore channels extending from an inner surface 316 to an outer surface 318 of the pellicle frame 304 for ventilation. Alternatively, the pellicle frame 304 includes one or more ventilation openings 320 for ventilation or pressure equalization.

[0051] According to another embodiment of the present invention, the transparent layer comprises a plurality of nanotubes forming a nanotube matrix, e.g., carbon nanotubes, boron nitride nanotubes, silicon carbide nanotubes, or combinations thereof. In some embodiments, the transparent layer containing the nanotubes is porous. Methods for producing layers of a plurality of nanotubes are known. When treated according to embodiments of the present invention, such layers of nanotubes form a combination of a transparent layer and a coating, which are useful in optical arrangements, e.g., a pellicle membrane, according to embodiments of the present invention.

[0052] According to embodiments of the present invention, the carbon nanotubes are single-walled or multi-walled. In some embodiments, the nanotubes are carbon nanotubes. The nanotubes can be directional or non-directional. The nanotubes can be individual, unbundled nanotubes or bundled individual nanotubes. Carbon nanotubes are susceptible to degradation when exposed to hydrogen or oxygen gas, such as that used during the operation or maintenance of a photolithography system.

[0053] In Fig. 5A comprises an embodiment of the present invention comprising a non-bundled, single-walled carbon nanotube 500 with a coating 502, which is produced on an outer surface 504 from one or more of the materials described above for the coatings 404 and / or 406. As in previously described embodiments, the coating 502 may have a single layer of the same material, or it may have multiple layers of the same material, or multiple layers of different materials. The coating 502 has a thickness t. In some embodiments, t is 1 to 10 nanometers. Fig. Figure 5B is a representation of a cross-section of a coated carbon nanotube according to embodiments of the present invention. Fig. Figure 5B shows how both the outer surface 504 of the carbon nanotube 500 and the inner surface 506 of the carbon nanotube 500 are coated with coating material 502 according to some embodiments of the present invention.

[0054] According to some embodiments of the present invention, the surfaces of the carbon nanotube 500 are treated before the coating material 502 is applied to the outer surface 504 and the inner surface 506 in order to modify the surface of the carbon nanotube 500, i.e., to create minor defects in it, and / or to introduce functional groups, e.g., hydrophilic groups, into the surfaces of the carbon nanotube. Modifying the surfaces of the carbon nanotube 500 improves the adhesion of the coating 502 to the outer surface 504 or the inner surface 506 of the carbon nanotube 500. Exemplary suitable processes for treating the surfaces of the carbon nanotube 500 before applying the coating 502 include, among others, treatment with nitrogen, oxygen, carbon fluoride, or argon gas plasma.According to some embodiments, the surfaces of the carbon nanotube 500 are treated with gas plasma using a combination of frequency, power, pressure, and duration sufficient to achieve the desired surface modifications, thereby improving the adhesion of the coating 502 to the nanotube surfaces. In one embodiment, the carbon nanotube is treated with oxygen plasma at a frequency of approximately 13.6 MHz, a power of approximately 100–200 W, and a pressure of approximately 1–200 mTorr. The duration of this treatment is sufficient to provide the desired surface modifications without damaging the carbon nanotube.

[0055] In Fig. In other embodiments of the invention, the surfaces of the nanotubes 500, e.g., the carbon nanotubes, are coated with a layer 508 that promotes adhesion between the surface of the carbon nanotube 500 and the coating 502. Such adhesion-promoting materials are deposited on the surfaces of the carbon nanotubes 500 by deposition processes such as ALD and PEALD. Examples of materials for the layer 508 include amorphous carbon or other materials that can be deposited by ALD or PEALD processes and that promote adhesion between the surfaces of the carbon nanotubes 500 and the coating 502. According to another embodiment of the present invention, the layer 508 is a protective layer that serves to protect the nanotubes against degradation by a plasma of a PEALD process used to deposit the coating 502.When a protective layer is fabricated on the nanotubes, it is produced by a first deposition process, for example, a thermal atomic layer deposition process in the absence of a plasma. Several cycles of the first deposition process can be used to fabricate multiple protective layers on the nanotubes. After one or more protective layers have been fabricated on the nanotubes, the coating 502 can be deposited using a second deposition process, for example, plasma-enhanced atomic layer deposition (PEALD). Due to the presence of the protective layer, the membrane nanotubes are not damaged by the plasma of the PEALD process. Examples of materials that can be used as a protective layer include, but are not limited to, the same materials described above for fabricating the coating 502.

[0056] In Fig. 6A comprises another embodiment of the use of nanotubes in an optical arrangement, e.g. a pellicle membrane 306, the bundling of several nanotubes. Fig. In 6A, seven nanotubes 600a-600g are bundled to form a nanotube bundle 602. Methods for bundling nanotubes to form a nanotube bundle 602, which can be used for embodiments according to this disclosure, are known. In other embodiments, the number of nanotubes forming a nanotube bundle is less than seven or greater than seven. Reducing the number of individual carbon nanotubes forming the nanotube bundle 602 decreases the refractive index of the nanotube bundle 602. As discussed above, a decrease in the refractive index reduces the scattering of incident EUV radiation, thereby increasing the transparency to incident EUV radiation. Consequently, in some embodiments, a nanotube bundle with fewer individual nanotubes is preferred over a nanotube bundle with a larger number of individual nanotubes.

[0057] In Fig. 6B, the nanotube bundle 602 is coated with or enclosed by a coating 604 according to embodiments of the present invention. The description of materials that can be used for the aforementioned coatings 404 and 406 can be applied to the materials used for the coating 604. In the Fig. In the embodiment shown in Figure 6B, the coating 604 is arranged such that it surrounds the nanotube bundle 602, but does not cover all surfaces of the individual nanotubes 600a–600g. According to other embodiments, the coating 604 covers more surfaces of the individual nanotubes 600a–600b than shown in Figure 6B. Fig. Figure 6B shows this. For example, the coating 604 can cover the surfaces of the nanotubes 600a-600e and 600g, which are exposed on the outside of the nanotube bundle 602. In this embodiment, the outside of the nanotube 600f is not covered with the coating 604. In other embodiments, the outside of each of the seven nanotubes 600a-600g is covered with the material that forms the coating 604. In embodiments according to the invention, the transparent layer comprises individual nanotubes that have been partially or completely coated with the coating 604 and bundled together to form the nanotube bundle 602, and then the nanotube bundle is coated / enclosed with an additional layer of coating material 604.In some embodiments, the coating 604 covers the entire surface of the nanotube on which it is located; however, in other embodiments, the coating covers less than the entire surface of the nanotube on which it is located.

[0058] In the embodiment of Fig. 6A and Fig. Figure 6B shows the individual nanotubes packed closely together. In other embodiments, the individual nanotubes may be packed less closely together, as shown in the Fig. 6A and Fig. Figure 6B is shown. For example, in other embodiments, parts of the outer surfaces of the nanotubes may not be in contact with each other.

[0059] In another embodiment, the pellicle membrane 306 comprises a plurality of nanotube bundles 602 and a plurality of individual unbundled nanotubes 500. In this embodiment, the plurality of nanotube bundles 602 and the plurality of individual unbundled nanotubes 500 are coated according to the preceding description.

[0060] The foregoing description regarding the selection of a specific material for coating 404 applies equally to the selection of a specific material for coating 604. The foregoing description regarding layer 508 as an adhesive layer or a protective layer applies equally to the use of layer 508 in combination with the nanotube bundles of the Fig. 6A and Fig. 6B and the coating 604.

[0061] Nanotube designs according to the Fig. 5A, Fig. 5B, Fig. 6A and Fig. 6B provides a pellicle membrane 306 that transmits 85% or more of the UV or EUV radiation incident on the transparent layer. In other embodiments, the pellicle membrane 306, which has coated nanotubes or coated nanotube bundles, transmits 90% or more of the UV or EUV radiation incident on the transparent layer. In some embodiments, the pellicle membrane 306, which has coated nanotubes or coated nanotube bundles, transmits 95% or more of the UV or EUV radiation incident on the transparent layer.

[0062] Fig. 7A is an image of the surface of a matrix of nanotubes before the deposition of a coating. Fig. 7B is an image of the matrix of nanotubes from Fig. 7A after applying a coating. Fig. 7C is an enlarged view of part of Fig. 7B. Fig. 7D is an enlarged view of a part of Fig. 7B.

[0063] In Fig. 8 is a method 800 for structuring a material on a semiconductor substrate in an EUV photolithography system with reference to the Fig. Figures 1 and 4A-4D show and describe the process. The method is not part of the present invention. The method comprises generating EUV radiation in step 820. EUV radiation can be generated, for example, using the radiation source 102 of Fig. 1, as described above. The generated EUV radiation is passed through a coating of a pellicle membrane in step 830. Examples of such coatings include coatings 404, 406, 502, or 604. The passing of the generated EUV radiation through the coating is carried out according to the description provided above. An example of a pellicle membrane is pellicle membrane 306. In step 840, the EUV radiation is passed through a transparent layer of the pellicle membrane. An example of a transparent layer of the pellicle membrane is transparent layer 402, which is described with reference to the above. Fig. The transmission of EUV radiation through a transparent layer of a pellicle membrane can be carried out as described above. EUV radiation that has passed through the transparent layer is reflected by a mask in step 850. A mask suitable for reflecting the EUV radiation is, for example, the mask 108 described above. The mask 108 reflects EUV radiation as described above. In step 860, the EUV radiation is received on a semiconductor substrate. An example semiconductor substrate is the semiconductor substrate 116 described above.

[0064] In Fig. 9 is referred to in the Fig. Figures 1 and 4A-4D show and describe below a method 900 for structuring a material on a semiconductor substrate in an EUV photolithography system. The method is not part of the present invention. The method comprises generating EUV radiation in step 920. EUV radiation can be generated, for example, using the radiation source 102 of Fig. 1, as described above. The generated EUV radiation is passed through a coating of a pellicle membrane in step 930. Examples of such coatings include coatings 404, 406, 502, or 604. The passing of the generated EUV radiation through the coating is carried out according to the description provided above. An example of a pellicle membrane is pellicle membrane 306. In step 940, the EUV radiation is passed through a matrix of nanotubes of the pellicle membrane. Examples of nanotubes of the pellicle membrane include the nanotubes and nanotube bundles described above with reference to the Fig. 5A, Fig. 5B, Fig. 6A and Fig. 6B. The EUV radiation can be guided through a matrix of nanotubes of a pellicle membrane as described above. The EUV radiation that has passed through the matrix of nanotubes of the pellicle membrane is reflected by a mask in step 950. A mask suitable for reflecting the EUV radiation is, for example, the mask 108 described above. The mask 108 reflects the EUV radiation as described above. In step 960, the EUV radiation is received on a semiconductor substrate. An example of a semiconductor substrate is the semiconductor substrate 116 described above.

[0065] Fig. Figure 11 is a flowchart illustrating a method according to the present invention for producing protective, adhesive, or coatings on a transparent layer 402 or a matrix of nanotubes forming a membrane 950. In a method 1000 of Fig. 11. The transparent layer 402 or a matrix of nanotubes, provided as a membrane 950, is held, for example, on a frame or encasement 952, e.g., vertically, in a chamber 942 in which a thermal ALD or CVD process and a plasma-assisted ALD or CVD process can be carried out. The transparent layer 402 or the frame 952 is held in the chamber 942 such that it has several freedoms of movement. In the Fig. In the embodiment shown in Figure 10, for example, the frame 950 can be rotated about a vertical axis or tilted about a horizontal axis. Embodiments according to the present invention are not limited to rotating the frame about the vertical axis or tilting it about the horizontal axis. In other embodiments, the frame has further freedom of movement in addition to rotation about the vertical axis or tilting it about the horizontal axis. This rotation and tilting can be carried out during a thermal process and / or a plasma-assisted process to promote the uniform coating of nanotubes of the membrane 950 with a coating, adhesive layer, or protective layer. The conditions in the chamber are maintained to promote uniform deposition of the coating, adhesive layer, or protective layer, e.g., temperatures in the range of 500 degrees Celsius to 1200 degrees Celsius.Such temperatures are provided by supplying thermal energy from the chamber walls or heating elements associated with the chamber walls. Embodiments according to the present invention for producing protective, adhesive, or coating layers on a matrix of nanotubes or the transparent layer 402 are not limited to the use of thermal PVD or CVD and plasma-enhanced PVD or CVD. These layers can be produced using ion beam deposition processes. The preceding description regarding the use of thermal PVD or CVD and plasma-enhanced PVD or CVD also applies to the use of ion beam deposition. In step 1030, a protective layer is produced on the transparent layer or on the nanotubes of the membrane by a thermal atomic layer deposition process. The chamber 942, which is described in . Fig.Figure 10 shows an exemplary chamber in which both thermal atomic layer deposition and plasma-enhanced atomic layer deposition can be performed. Method 1000 is not limited to the use of a single chamber in which both thermal and plasma-enhanced atomic layer deposition can be performed. For example, in other embodiments, the thermal deposition process can be carried out in one chamber and the plasma-enhanced deposition can be carried out in another chamber.

[0066] In one embodiment, the present invention describes an optical arrangement, e.g., a pellicle arrangement, comprising a matrix of a plurality of nanotube bundles according to the appended claims. According to the invention, a coating is provided on the matrix of the plurality of nanotube bundles. The coating encloses individual nanotubes within individual nanotube bundles.

[0067] Likewise, a method not belonging to the present invention is provided, which comprises generating EUV radiation in an EUV lithography system. The EUV radiation is passed through a coating of a pellicle membrane. The EUV radiation that has passed through the coating of the pellicle membrane is passed through a transparent layer of the pellicle membrane. The EUV radiation that has passed through the transparent layer of the pellicle membrane is reflected by a mask and received on a semiconductor substrate.

[0068] Likewise, a method not belonging to the present invention is provided, which comprises generating EUV radiation in an EUV lithography system. The EUV radiation is passed through a coating of a pellicle membrane. The EUV radiation that has passed through the coating of the pellicle membrane is passed through a matrix of nanotubes of the pellicle membrane. The EUV radiation that has passed through the matrix of nanotubes of the pellicle membrane is reflected by a mask and received on a semiconductor substrate.

[0069] The various embodiments described above can be combined to provide further embodiments. Aspects of the embodiments can, if necessary, be modified to utilize principles from the various patents, applications, and publications to provide yet more embodiments.

Claims

[1] Optical arrangement with: a matrix consisting of a plurality of nanotube bundles (602), wherein the majority of nanotube bundles (602) contain carbon nanotubes (600); and a coating (604) on the plurality of nanotube bundles (602), wherein the coating (604) encloses individual nanotubes (600) of the individual nanotube bundles (602) and wherein the coating (604) on the majority of nanotube bundles (602) comprises a coating (604) on one nanotube bundle (602) and a coating (604) on individual carbon nanotubes (600) of the nanotube bundle (602). [2] Optical arrangement according to claim 1, wherein the coating (604) is boron (B), borosilicon nitride (BNSi), silicon nitride (Si3N4), silicon disitride (SiN2), niobium (Nb), niobium nitride (NbN), niobium monosilicide (NbSi), niobium silicide (NbSi2), niobium silicon nitride (NbSiN), niobium titanium nitride (NbTixNy), molybdenum (Mo), molybdenum nitride (MoN2), molybdenum carbide (Mo2C and Mo4C), molybdenum silicide (MoSi2), molybdenum silicon nitride (MoSixNy), zirconium nitride (ZrN), zirconium fluoride (ZrF4), yttrium nitride (YN), yttrium fluoride (YF), titanium nitride (TiN), titanium carbon nitride (TiCxNy), contains hafnium nitride (HfNx), hafnium fluoride (HfF4) and / or vanadium nitride (VN). [3] Optical arrangement according to claim 1, wherein the coating (604) comprises boron (B), borosilicon nitride (BNSi), silicon nitride (Si3N4), silicon disinitride (SiN2), niobium (Nb), niobium nitride (NbN), niobium monosilicide (NbSi), niobium silicide (NbSi2), niobium silicon nitride (NbSiN), niobium titanium nitride (NbTixNy), zirconium nitride (ZrN), zirconium fluoride (ZrF4), yttrium nitride (YN), yttrium fluoride (YF), titanium nitride (TiN), titanium carbon nitride (TiCxNy), hafnium nitride (HfNx), hafnium fluoride (HfF4) and / or vanadium nitride (VN). [4] Optical arrangement according to one of the preceding claims, further comprising a plurality of individual non-bundled nanotubes (500). [5] Optical arrangement according to claim 4, wherein a coating (502) is arranged on the plurality of individual non-bundled nanotubes (500). [6] Procedure with the following steps: Fabrication of a matrix of nanotubes (500); Producing a protective layer (508) on the nanotubes (500) of the nanotube matrix (500) by a first process, wherein the production by the first process comprises producing two or more protective layers (508) using two or more cycles of thermal atomic layer deposition; and Producing a coating (502) over the protective layer (508) by a second process. [7] Method according to claim 6, wherein the nanotubes (500) of the matrix of nanotubes (500) comprise a plurality of individual non-bundled nanotubes (500). [8] Method according to claim 6, wherein the nanotubes (500, 600) of the matrix of nanotubes (500, 600) comprise a plurality of bundled nanotubes (602). [9] Method according to claim 8, wherein the bundled nanotubes (602) comprise seven or more individual nanotubes (600). [10] Method according to any one of claims 7 to 9, wherein the nanotubes (500, 600) are carbon nanotubes (500, 600).

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