Pellicle membranes and methods of manufacture

Abstract

A pellicle membrane is provided comprising a thermal emission crystal supported by a matrix wherein the average thickness of the pellicle membrane is greater than the average grain size of the emission crystal. Also provided is a pellicle assembly comprising such a pellicle membrane, and a lithographic apparatus comprising such a pellicle membrane or pellicle assembly. Also described is a method of making a pellicle membrane comprising an emissive crystal in a matrix, the method comprising controlling at least one of a chemical composition of the emissive crystal, a morphology of the emissive crystal, and annealing conditions to provide a pellicle membrane having a thickness greater than an average grain size of the emissive crystal.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to European Application No. 22213011.4, filed on December 13, 2022, the entire content of which is incorporated herein by reference. Technical field

[0003] The present invention relates to a pellicle diaphragm for a lithographic apparatus, a pellicle assembly for a lithographic apparatus, a method of manufacturing a pellicle diaphragm, and the use of such a pellicle diaphragm, pellicle assembly or method in a lithographic apparatus or method. The present invention has a particular but not exclusive application to EUV lithographic apparatus and methods. Background art

[0004] A lithographic apparatus is a machine configured to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can, for example, project a pattern from a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) disposed on a substrate.

[0005] The wavelength of the radiation used by a lithographic apparatus to project a pattern onto a substrate determines the minimum size of the features that can be formed on the substrate. Compared to conventional lithographic apparatus which can use (for example) electromagnetic radiation having a wavelength of 193 nm, a lithographic apparatus using EUV radiation which is electromagnetic radiation having a wavelength in the range of 4 nm to 20 nm can be used to form smaller features on a substrate.

[0006] A lithographic apparatus includes a patterning device (e.g., a mask or reticle). Radiation is provided through or reflected from the patterning device to form an image on the substrate. A diaphragm assembly (also referred to as a pellicle) can be provided to protect the patterning device from airborne particles and other forms of contamination. Contamination on the surface of the patterning device can cause manufacturing defects on the substrate.

[0007] A pellicle can also be provided for protecting optical components other than the patterning device. A pellicle can also be used to provide a path for lithographic radiation between sealed zones of a lithographic apparatus. A pellicle can also be used as a filter (such as a spectral purity filter) or as part of a dynamic air lock of a lithographic apparatus.

[0008] A mask assembly can include a pellicle for protecting a patterning device (e.g., a mask) from particle contamination. The pellicle can be supported by a pellicle frame to form a pellicle assembly. The pellicle can be attached to the frame, for example, by gluing or otherwise attaching the pellicle border region to the frame. The frame can be attached to the patterning device permanently or removably.

[0009] Since the pellicle is present in the optical path of the EUV radiation beam, it is necessary for the pellicle to have a high EUV transmittance. A high EUV transmittance allows a large proportion of the incident radiation to pass through the pellicle. Additionally, reducing the amount of EUV radiation absorbed by the pellicle can lower the operating temperature of the pellicle. Since the transmittance depends at least in part on the thickness of the pellicle, it is desirable to provide a pellicle that is as thin as possible while maintaining a reliable strength sufficient to withstand the sometimes harsh environment within the lithographic apparatus.

[0010] Accordingly, it is desirable to provide a pellicle that can withstand the harsh environment of a lithographic apparatus (in particular, an EUV lithographic apparatus). In particular, it is desirable to provide a pellicle that can withstand higher power than previously. It is also desirable to provide a pellicle diaphragm that is not susceptible to damage caused by shock.

[0011] Although the present application generally refers to pellicles in the context of a lithographic apparatus (in particular, an EUV lithographic apparatus), the invention is not limited to pellicles and lithographic apparatuses only, and it should be understood that the subject matter of the invention can be used in any other suitable device or situation.

[0012] For example, the method of the present invention can equally be applied to a spectral purity filter. Some EUV sources, such as those that use a plasma to generate EUV radiation, emit not only the desired "in-band" EUV radiation but also unwanted (out-of-band) radiation. Such out-of-band radiation is most prominent in the deep UV (DUV) radiation range (100 nm to 400 nm). Additionally, in the case of some EUV sources, such as laser-produced plasma EUV sources, radiation from the laser that is typically below 10.6 micrometers presents significant out-of-band radiation.

[0013] In a lithographic apparatus, spectral purity is desirable for several reasons. One reason is that the resist is sensitive to radiation at out-of-band wavelengths, and thus the image quality of the pattern applied to the resist can deteriorate when the resist is exposed to such out-of-band infrared radiation. Additionally, out-of-band infrared radiation, such as the 10.6 micrometer radiation in some laser-produced plasma sources, causes unwanted and unnecessary heating of the patterning device, substrate, and optics within the lithographic apparatus. Such heating can lead to damage to these components, deterioration of their lifespan, and / or defects or distortions in the pattern projected onto the substrate coated with resist and applied to the substrate coated with resist.

[0014] A typical spectral purity filter can be formed, for example, by a silicon infrastructure (such as a silicon grid, or other member provided with holes) coated with a reflective metal such as molybdenum. In use, a typical spectral purity filter can be subjected to a high thermal load from, for example, incident infrared and EUV radiation. The thermal load may cause the temperature of the spectral purity filter to be higher than 800 °C. Thus, the spectral purity filter can be used as a pellicle, and vice versa. Therefore, references to "pellicle" in this application also refer to references to "spectral purity filter". Although mainly referring to pellicles in this application, all features can equally be applied to spectral purity filters.

[0015] The present invention has been designed to attempt to solve at least some of the problems identified above. Summary of the Invention

[0016] According to a first aspect of the present disclosure, there is provided a pellicle diaphragm comprising a thermally emissive crystal supported by a matrix, wherein an average thickness of the pellicle diaphragm is greater than an average grain size of the emissive crystal.

[0017] The pellicle as a device has a set of performance specifications that are ensured by the functionality of the constituent materials of the pellicle. The relevant performance specifications are the requirements that the pellicle does not distort imaging, transmits EUV light sufficiently (EUVT) and does not contaminate critical components in the scanner. There are various different types of pellicles, including single material cores containing additive layers with multiple individual desired functionalities or single layers exhibiting multiple functionalities.

[0018] For multi-layer diaphragms, multiple individual functionalities can be tuned through multiple single layers, whereby changing a parameter in one layer can change the definition of another layer in the stack to have a conformal performance for the entire multi-stack. For example, increasing the thickness of one layer will result in less restrictive thicknesses for other layers to achieve sufficient EUV transmittance. On the other hand, for single-layer diaphragms, it is not possible to easily tune multiple individual functionalities unless another material component is added to the material, thereby changing at least one functionality to a greater extent than other functionalities. Adding a material component in the form of a dopant or alloying element may cause phase segregation or phase separation, and may result in multiple individual functionalities being distributed on different phases. A diaphragm having such segregated or separated phases is referred to as a composite pellicle.

[0019] An example of a single-layer multiphase pellicle is a pellicle in which molybdenum silicide MoSix crystals mainly provide high thermal emissivity, high ductility and high hardness, i.e., high rigidity (all of which are beneficial properties). However, MoSix crystals also provide high brittleness and very high mechanical pre-tension of the pellicle, which is not preferred. Here, MoSix includes various stoichiometries, such as MoSi2, Mo5Si3 and Mo3Si silicides of molybdenum.

[0020] Such a pellicle diaphragm may be vulnerable to impact, which may cause damage or breakage of the pellicle diaphragm. Without wishing to be bound by scientific theory, it is believed that a composite pellicle including a crystalline phase supported in a matrix is vulnerable to impact due to defects present in the crystals therein, and the matrix itself may be crystalline or non-crystalline. Defects include in particular twin grain boundaries, dislocations and stacking faults. Larger crystals have an increased number of faults that pile up at the edges, resulting in a lower force required to push a dislocation into the next grain, which may then lead to the initiation and propagation of cracks and consequent material failure. It has been found that material failure of existing pellicle diaphragms occurs along grain boundaries rather than through the grains. Thus, it can be expected that reducing the grain size while keeping other elements of the pellicle diaphragm unchanged improves the yield strength. However, this has not been observed in practice.

[0021] Existing pellicle diaphragms include emissive crystals having a grain size large enough to span the thickness of the diaphragm. It has been found that improved impact resistance is provided by a pellicle diaphragm in which the thickness of the diaphragm is greater than the thickness of the emissive crystals therein. This implementation also provides a lower limit for the thickness of the pellicle diaphragm, since in the case where the thickness is substantially one grain thick, the likelihood of weak spots and stress concentration increases and it is thus highly vulnerable to mechanical impact.

[0022] The thickness of the pellicle diaphragm is at least 1.5 times the average grain size of the emissive crystals. By making the pellicle diaphragm thickness greater than the average grain size of the emissive crystals, the risk of weak spots, stress concentration, etc. is reduced.

[0023] The thickness of the pellicle diaphragm may be in the range from about 5 nm to about 30 nm. Thus, the average grain size of the emissive crystals in the pellicle diaphragm is less than this range.

[0024] The pellicle diaphragm may include MoSiSi-X, MoSiC-X or MoSiN-X, where X is selected from N, Y, O, S, C, Hf, Nb, W, Ta, Zr or a combination thereof. It has been found that adding such elements provides smaller emissive crystals to be formed. In this way, it may be possible to tune the size of the emissive crystals such that they are smaller than the thickness of the pellicle diaphragm. It should be understood that based on the fact that such a pellicle diaphragm already includes N or C, doping MoSiN with N and doping MoSiC with C are waived.

[0025] The emission crystal may include a Mo content of from about 20 at.% to about 22 at.%. A reduction in the Mo content in the emission crystal from greater than 22 at.% to 20 at.% or less results in a halving of the grain size while maintaining favorable emissivity and transmittance. Thus, a pellicle diaphragm may be provided that has desired emissivity and transmittance characteristics but has a grain size that allows the emission crystal to be less than the thickness of the pellicle diaphragm.

[0026] For a MoSiSi composite pellicle, the pellicle core may include an N content of from about 3 at.% to about 13 at.%. It has been found that adding N to the core results in a roughly halving of the grain size of the emission crystal.

[0027] The pellicle diaphragm includes at least two layers having a single grain thickness or a polycrystalline grain thickness separated by a separating layer. Grain size reduction can be achieved by depositing layers using segmented stacked layers and then depositing a second layer such that the first and second deposited layers are separated by a segmented layer rather than depositing a single layer. This applies to any composite pellicle, including MoSi-based composite pellicles and non-MoSi-based composite pellicles.

[0028] If the composite pellicle diaphragm includes two crystalline phases and only one of the crystalline phases allows grain size reduction (such that the other type of grain remains unaffected and thus remains relatively large), the thickness of the pellicle can be divided into two segments with reduced grain size separated by a separating layer.

[0029] The pellicle diaphragm may include a cover layer on one or both sides of the pellicle diaphragm. It should be understood that the diaphragm has two sides or surfaces. The cover layer may be provided on one or both sides or surfaces to protect the pellicle diaphragm from the environment within the lithographic apparatus. Any known cover layer may be provided and the present disclosure is not limited to any particular cover layer.

[0030] The emission crystal may be non-circular. The morphology of the emission crystal may be selected to provide robustness or ruggedness to the pellicle diaphragm. As the grain size decreases, the likelihood of grain sliding and creep increases, which occurs when the grains slide past each other. Grains with a circular morphology are more prone to sliding compared to grains with a more irregular shape. Thus, by providing non-circular grains, sliding and creep can be reduced. Adding an element such as C results in irregularly shaped emission grains.

[0031] The average crystal grain size of the emission crystals can be 20 nm or less, 18 nm or less, 15 nm or less, 12 nm or less, 10 nm or less, 8 nm or less, less than 5 nm or less, 3 nm or less, 2 nm or less, or 1 nm or less; or from 1 nm to 20 nm, from 2 nm to 18 nm, from 5 nm to 15 nm, or from 8 nm to 12 nm or from 8 nm to 10 nm. Preferably, the average crystal grain size is 1.5 times smaller than the thickness of the pellicle diaphragm. For example, when the thickness of the pellicle diaphragm is 15 nm, the average crystal grain size of the emission crystals is 15 nm / 1.5 = 10 nm or less. Thus, the average crystal grain size is the average thickness of the pellicle diaphragm / 1.5 or less. The denominator can be 1.5 or greater, such as 1.6, 1.7, 1.8, 1.9, or 2.0. Preferably, the pellicle thickness does not include the thickness of any covering layer.

[0032] According to a second aspect of the present disclosure, there is provided a pellicle assembly including a pellicle diaphragm according to the first aspect. The pellicle assembly may include additional elements as conventionally found in a pellicle assembly. For example, the pellicle assembly may include a frame, and the pellicle diaphragm may be supported via the frame.

[0033] According to a third aspect of the present disclosure, there is provided a lithographic apparatus including a pellicle diaphragm according to the first aspect or a pellicle assembly according to the second aspect of the present disclosure.

[0034] According to a fourth aspect of the present disclosure, there is provided a method of manufacturing a pellicle diaphragm including emission crystals in a substrate, the method including controlling at least one of the chemical composition of the emission crystals, the morphology of the emission crystals, and annealing conditions to provide a pellicle diaphragm having a thickness greater than the average crystal grain size of the emission crystals.

[0035] As described with respect to the first aspect of the present disclosure, it has been found that a pellicle diaphragm having a thickness of the pellicle diaphragm greater than the average crystal grain size of the emission crystals therein is advantageous. This can be achieved by adjusting the chemical composition of the emission crystals, adjusting the morphology of the emission crystals, and / or adjusting the annealing conditions.

[0036] The morphology of the emission crystals can be controlled such that the emission crystals are non-circular. This can be achieved, for example, by including an element such as C.

[0037] The emission crystals include at least one metal, and the concentration of the metal can be adjusted to control the crystal grain size of the emission crystals. For example, as described with respect to the first aspect of the present disclosure, the metal can be Mo, and the concentration of Mo can be from about 20 at.% to about 22 at.% of Mo.

[0038] The method may include including nitrogen in the core to control the grain size of the emission crystals. The pellicle core includes a matrix and emission crystals.

[0039] The method may include incorporating one or more of N, Y, O, S, C, Hf, Nb, W, Ta, Zr, or combinations thereof into the pellicle core to control the grain size of the emission crystals.

[0040] The method may include controlling the annealing temperature during manufacturing to control the grain size of the emission crystals. During the manufacture of the pellicle diaphragm, the diaphragm is annealed to produce crystal growth. The grain size increases at higher temperatures, and crystallization is observed from about 650°C to 700°C. If the annealing time is maintained and only the temperature is changed, larger crystals are observed to form at higher temperatures. Thus, the annealing temperature is preferably from about 650°C to about 750°C.

[0041] The method may include providing at least two layers separated by a separating layer, wherein the thickness of one, two, or all of the layers is greater than the average grain size of the emission crystals. As described with respect to the first aspect of the present disclosure, a multi-layer pellicle diaphragm can be manufactured, including two layers separated by a dividing layer with emission crystals having a reduced grain size.

[0042] The method may include controlling the morphology of the emission crystals by including an element such as carbon to provide irregularly shaped grains.

[0043] According to a fifth aspect of the present disclosure, there is provided a use of a pellicle diaphragm according to the first aspect, a pellicle assembly according to the second aspect, a lithographic apparatus according to the third aspect, or a method according to the fourth aspect of the present disclosure in a lithographic apparatus or method.

[0044] It should be understood that features described with respect to one embodiment can be combined with any features described with respect to another embodiment, and all such combinations are explicitly contemplated and disclosed herein.

[0045] It should also be understood that the present disclosure is applicable to single-layer pellicles, multi-layer pellicles, single-layer single-phase pellicles, single-layer multi-phase pellicles, multi-layer multi-phase pellicles, molybdenum-silicon pellicles, metal-silicon pellicles, and pellicles containing a metal, or a metal and a second element. The pellicle can be an EUV pellicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which corresponding reference numerals indicate corresponding parts, and in which:

[0047] Figure 1Depict a lithographic apparatus according to an embodiment of the present invention; and

[0048] Figure 2 Depict a pellicle assembly having a composite film;

[0049] Figure 3 Is a transmission electron microscope image of a MoSiSi composite pellicle diaphragm in a (top-down) cross-section and a (bottom-up) side view;

[0050] Figure 4 Is Figure 3 A schematic depiction of the pellicle diaphragm shown in;

[0051] Figure 5 Is a top-view STEM image of a molybdenum silicide (MoSiSi) pellicle diaphragm;

[0052] Figure 6 Is a schematic depiction of options for increasing the stability, i.e., robustness, of the pellicle diaphragm;

[0053] Figure 7 Depict a comparison of the grain size of molybdenum silicide crystals in a MoSiSi pellicle film in the presence and absence of nitrogen; and

[0054] Figure 8 Show various scanning electron microscopy images of MoSiSi pellicle diaphragms of different thicknesses annealed at different temperatures.

[0055] According to the detailed description set forth below in connection with the accompanying drawings, the features and advantages of the present invention will become more apparent, in which like reference numerals always identify corresponding elements. In the accompanying drawings, like reference numerals generally indicate identical, functionally similar, and / or structurally similar elements. Detailed Description

[0056] Figure 1Shows a lithographic system according to the present invention comprising a pellicle 15 (also referred to as a diaphragm assembly). The lithographic system includes a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an extreme ultraviolet (EUV) radiation beam B. The lithographic apparatus LA includes an illumination system IL, a support structure MT configured to support a patterning device MA (such as a mask), a projection system PS, and a substrate table WT configured to support a substrate W. The illumination system IL is configured to condition the radiation beam B before it is incident on the patterning device MA. The projection system is configured to project the radiation beam B (now patterned by the mask MA) onto the substrate W. The substrate W may include a previously formed pattern. In this case, the lithographic apparatus aligns the patterned radiation beam B with the previously formed pattern on the substrate W. In this embodiment, the pellicle 15 is depicted as being in the path of the radiation and protecting the patterning device MA. It should be understood that the pellicle 15 may be located in any desired position and may be used to protect any of the mirrors in the lithographic apparatus.

[0057] The radiation source SO, the illumination system IL, and the projection system PS can all be constructed and arranged such that they can be isolated from the external environment. A gas (such as hydrogen) at a pressure below atmospheric pressure can be provided in the radiation source SO. A vacuum can be provided in the illumination system IL and / or the projection system PS. A small amount of gas (such as hydrogen) at a pressure well below atmospheric pressure can be provided in the illumination system IL and / or the projection system PS.

[0058] Figure 1 The illustrated radiation source SO is of a type that can be referred to as a laser-produced plasma (LPP) source. A laser, which can be, for example, a CO2 laser, is arranged to deposit energy via a laser beam into a fuel such as tin (Sn) provided from a fuel emitter. Although tin is mentioned in the following description, any suitable fuel can be used. The fuel can be, for example, in liquid form and can be, for example, a metal or an alloy. The fuel emitter can include a nozzle configured to direct tin, for example in the form of droplets, along a trajectory towards a plasma formation region. The laser beam is incident on the tin at the plasma formation region. The deposition of laser energy into the tin creates a plasma at the plasma formation region. Radiation including EUV radiation is emitted from the plasma during the de-excitation and recombination of the ions of the plasma.

[0059] The EUV radiation is collected and focused by a near-normal incidence collector (sometimes more commonly referred to as a normal incidence collector). The collector can have a multilayer structure arranged to reflect EUV radiation (such as EUV radiation having a desired wavelength such as 13.5 nm). The collector can have an elliptical configuration with two elliptical foci. The first focus can be at the plasma formation region, and the second focus can be at an intermediate focus, as discussed below.

[0060] The laser can be separated from the radiation source SO. In this case, the laser beam can be transmitted from the laser to the radiation source SO by means of a beam delivery system (not shown) including, for example, suitable steering mirrors and / or beam expanders and / or other optical devices. The laser and the radiation source SO can be considered together as a radiation system.

[0061] The radiation reflected by the collector forms a radiation beam B. The radiation beam B is focused at a point to form an image of the plasma formation region, which serves as a virtual radiation source for the illumination system IL. The point at which the radiation beam B is focused can be referred to as an intermediate focus. The radiation source SO is arranged such that the intermediate focus is located at or near an opening in the enclosure structure of the radiation source.

[0062] The radiation beam B is transmitted from the radiation source SO into the illumination system IL, which is configured to condition the radiation beam. The illumination system IL can include a faceted field mirror device 10 and a faceted pupil mirror device 11. The faceted field mirror device 10 and the faceted pupil mirror device 11 together provide the radiation beam B with a desired cross-sectional shape and a desired angular distribution. The radiation beam B is transmitted from the illumination system IL and incident on a patterning device MA held by a support structure MT. The patterning device MA reflects and patterns the radiation beam B. In addition to or instead of the faceted field mirror device 10 and the faceted pupil mirror device 11, the illumination system IL can also include other mirrors or devices.

[0063] After being reflected from the patterning device MA, the patterned radiation beam B enters a projection system PS. The projection system includes a plurality of mirrors 13, 14, which are configured to project the radiation beam B onto a substrate W held by a substrate table WT. The projection system PS can apply a reduction factor to the radiation beam, thereby forming an image with features smaller than the corresponding features on the patterning device MA. For example, a reduction factor of 4 can be applied. Although the projection system PS has two mirrors 13, 14 in Figure 1 it, the projection system can include any number of mirrors (e.g., six mirrors).

[0064] Figure 1 The illustrated radiation source SO can include components not shown. For example, a spectral filter can be provided in the radiation source. The spectral filter can substantially transmit EUV radiation but substantially block radiation of other wavelengths, such as infrared radiation.

[0065] In an embodiment, the diaphragm assembly 15 is the pellicle of the patterning device MA for EUV lithography. The diaphragm assembly 15 of the present invention can be used for a dynamic air lock or for a pellicle or for another purpose. To ensure maximum EUV transmission and minimal impact on imaging performance, it is preferred that the diaphragm is supported only at the boundaries.

[0066] Figure 2 is a schematic depiction of the pellicle assembly 15 according to the present disclosure. The pellicle assembly includes a support 16 configured to support the pellicle diaphragm 17. In the figure, the support 16 is presented as two separate elements, but this need not be the case, and the support 16 can be in the form of surrounding the boundary defining the pellicle diaphragm 17. The pellicle diaphragm 17 includes a cover layer 18 configured to protect the pellicle diaphragm 17 (especially the emission layer 19) from degradation. The cover layer can be any known cover layer, and the present disclosure is not particularly limited to any specific cover layer material. The emission layer 19 includes a matrix 20 that provides the required pre-tension and strength. Since the pellicle diaphragm 17 is subjected to a pressure difference during use and must accommodate such a difference, pre-tension is required. The matrix material 20 can include one or more of elemental silicon, silicon oxide, silicon fluoride, silicon sulfide, or silicon selenide. The emission layer 19 includes thermally emissive crystals 21 disposed within the matrix 20. The thermally emissive crystals 21 are included to increase the thermal emissivity of the pellicle diaphragm 17, thereby allowing the pellicle diaphragm to operate at a lower temperature than would otherwise be possible at a given power, or at the same temperature as a pellicle diaphragm without emissive crystals but at a higher power. The thermally emissive crystals 21 can include one or more of metal carbides, metal borides, metal nitrides, metal fluorides, metal silicides, or metals. The metal can be selected from one or more of molybdenum, zirconium, yttrium, lanthanum, scandium, niobium, iridium, chromium, vanadium, platinum, rhodium, hafnium, and ruthenium.

[0067] If the patterning device MA is not protected, contamination may require cleaning or discarding the patterning device MA. Cleaning the patterning device MA interrupts valuable manufacturing time, and discarding the patterning device MA is costly. Replacing the patterning device MA also interrupts valuable manufacturing time.

[0068] The emissive crystals can be, for example, one or more of the following materials: metal carbides (such as Mo2C), metal borides (such as ZrB2, MoB2), metal silicides (such as ZrSi2, MoSi2, YSi2, LaSi2, ScSi2, NbSi2, RuSi2), or metals (such as Mo, Ru, Sc).

[0069] Figure 3It is a cross-sectional view (upper 100 nm image) and a top view (lower 50 nm image) of a transmission electron microscope image of a composite pellicle diaphragm. As can be seen, the MoSi2 crystals in the silicon matrix extend through the entire thickness of the pellicle diaphragm and are thus vulnerable to impact. A large number of dislocations in the large emission crystals are also visible. Figure 4 It is a schematic depiction showing how large molybdenum disilicide crystals have a grain size (such as (for example) 40 nm) larger than the thickness of the pellicle diaphragm (such as (for example) 15 nm). The average grain size can be measured by measuring the maximum length of the emission crystals in the transmission electron microscope image and averaging the measurements from the crystals.

[0070] Figure 5 It is a top view STEM image of a molybdenum silicide pellicle diaphragm. As can be seen, the rupture of the diaphragm occurs along the boundaries of the grains of the emission crystals therein. Although a number of dislocations are visible in the STEM image, the rupture occurs along the grain boundaries rather than through the individual grains. Although it can be considered that bulk nanocrystalline materials may exhibit an inverse Hall-Petch mechanism, whereby making the grains smaller would result in more creep and thus a weaker pellicle, it has been recognized that the pellicle diaphragm can be considered substantially a 2D material. It is predicted that under the Hall-Petch mechanism, materials with larger grains have a smaller yield stress resistance, while for small grains, diffusion creep and sliding of the grains become dominant, resulting in a weaker material. Thus, according to the Hall-Petch mechanism and the inverse Hall-Petch mechanism, a grain size from about 20 nm to about 40 nm is considered optimal in terms of yield strength, and it is not expected that the yield strength will be improved by changing the grain size, whether increasing or decreasing. Even so, it has been observed that a pellicle with such a grain size is vulnerable to impact, and the invention of the present disclosure solves this contradictory problem. It has been found that a pellicle diaphragm having a thickness of about 10 nm to about 30 nm and including emission crystals of 10 nm or less (such as 8 nm to 10 nm) is less vulnerable to impact.

[0071] Figure 6Depict options for modifying the pellicle diaphragm to increase stability. The existing pellicle diaphragm is shown where the emission crystal (shown in light gray) extends across the entire thickness of the diaphragm. Such a diaphragm has been shown to be vulnerable to shock, while the other two depicted pellicle diaphragms according to the present disclosure are less vulnerable to shock. In the second figure, the grains of the emission crystal are shown to be smaller than the thickness of the pellicle diaphragm such that more than one grain can be accommodated within the thickness of the pellicle diaphragm. The ability to have multiple grains of the emission crystal across the thickness of the pellicle diaphragm equalizes weak and strong bonds and increases pellicle stability. Similarly, the third figure depicts an embodiment where there are two layers separated by a separating layer. The grains of the emission crystal are smaller than the thickness of the multi-layer pellicle diaphragm.

[0072] Figure 7 Depict a comparison of the grain size of emission molybdenum silicide crystals in a silicon matrix with and without additional nitrogen. As shown, when no additional nitrogen is present, the grains are larger and more rounded, and when 13 at.% of N is included, the grains are smaller and less rounded. It should be understood that the crystal can be molybdenum disilicide or can have the general formula MoSi x .

[0073] Figure 8 Show various scanning electron microscopy images of the pellicle diaphragms of different thicknesses that have been annealed at different temperatures. As can be seen, crystal growth was observed in the diaphragm that had been annealed at 700 °C for 8 hours. When the diaphragm had been annealed at a higher temperature for the same time, the grains were larger. It has been found that once the crystals start to form, the stress curve flattens. Since it has been found desirable to have crystals with a grain size smaller than the thickness of the pellicle diaphragm, the crystal size can be selected by controlling the annealing temperature.

[0074] Although specific embodiments of the invention have been described above, it should be understood that the invention can be practiced in other ways different from the described manner.

[0075] The above description is intended to be illustrative, not restrictive. Thus, those skilled in the art will appreciate that the described invention can be modified without departing from the scope of the aspects and aspects set forth below.

[0076] In summary, the present invention provides a pellicle diaphragm that is more stable than existing pellicle diaphragms and components or devices including such a pellicle diaphragm. This is achieved not only by the size of the individual emission grains but also by the combination of the grain size and the lower limit of the thickness of the pellicle diaphragm. If the pellicle diaphragm thickness is so small that the grains span the thickness such that the pellicle diaphragm is essentially one grain thick, the likelihood of weak spots and stress concentration increases and the pellicle is thus vulnerable to mechanical shock.

Claims

1. A pellicle diaphragm, comprising a thermally emissive crystal supported by a matrix, wherein, The average thickness of the surface film diaphragm is greater than the average grain size of the emission crystal.

2. The membrane diaphragm according to claim 1, wherein, The thickness of the surface film diaphragm is at least 1.5 times the average grain size of the emission crystal.

3. The pellicle diaphragm according to claim 1 or 2, wherein, The thickness of the surface film diaphragm is in the range from about 5 nm to about 30 nm.

4. The pellicle diaphragm according to any one of claims 1 to 3, wherein, The surface film includes MoSiSi-X, MoSiC-X or MoSiN-X, where X is selected from N, Y, O, S, C, Hf, Nb, W, Ta, Zr or a combination thereof.

5. The pellicle diaphragm according to any one of claims 1 to 4, wherein, The crystal includes about 20 at.% to 22 at.% of Mo, and / or wherein the matrix and the thermionic emission crystal define a core, and the core includes about 3 at.% to about 13 at.% of nitrogen.

6. The pellicle diaphragm according to any one of claims 1 to 5, wherein, The surface film diaphragm includes at least two layers having a single grain thickness or a polycrystalline grain thickness separated by a separation layer.

7. The pellicle diaphragm according to any one of the preceding claims, wherein The surface film diaphragm includes a covering layer on one or both sides of the surface film diaphragm.

8. The pellicle diaphragm according to any one of the preceding claims, wherein, The emission crystal is non-circular.

9. The pellicle diaphragm according to any one of the preceding claims, wherein, The average grain size of the emission crystal is: i) 20 nm or less, 18 nm or less, 15 nm or less, 12 nm or less, 10 nm or less, 8 nm or less, less than 5 nm or less, 3 nm or less, 2 nm or less, or 1 nm or less; or ii) from 1 nm to 20 nm, from 2 nm to 18 nm, from 5 nm to 15 nm or from 8 nm to 12 nm or from 8 nm to 10 nm; or iii) less than the quotient of the thickness of the surface film diaphragm divided by 1.

5.

10. A surface film assembly comprising the surface film diaphragm according to any one of the preceding claims.

11. A lithographic apparatus comprising the surface film diaphragm according to any one of claims 1 to 9 or the surface film assembly according to claim 10.

12. A method of manufacturing a surface film diaphragm including emissive crystals in a substrate, the method comprising: Control at least one of the chemical composition of the emission crystal, the morphology of the emission crystal, and the annealing conditions to provide a surface film diaphragm having a thickness greater than the average grain size of the emission crystal.

13. The method according to claim 12, wherein, Control the morphology of the emission crystal such that the crystal is non-circular.

14. The method according to claim 12 or 13, wherein the emission crystal comprises at least one metal, The concentration of the metal is adjusted to control the grain size of the emission crystal.

15. The method according to any one of claims 12 to 14, wherein, The method includes including nitrogen in the surface film core to control the grain size of the emission crystal.

16. The method according to any one of claims 12 to 15, wherein, The method includes incorporating one or more of N, Y, O, S, C, Hf, Nb, W, Ta, Zr or a combination thereof into the surface film core to control the grain size of the emission crystal.

17. The method according to any one of claims 12 to 16, wherein, The method includes controlling the annealing temperature during manufacturing to control the grain size of the emission crystal, optionally the annealing temperature is from about 650 °C to about 750 °C.

18. The method according to any one of claims 12 to 17, wherein, The method includes providing at least two layers separated by a separation layer, wherein the thickness of one, two or all of the layers is greater than the average grain size of the emission crystal.

19. The method according to any one of claims 12 to 18, wherein, The method includes controlling the morphology of the emission crystal by including an element such as carbon to provide irregularly shaped grains.

20. Use of a pellicle diaphragm according to any one of claims 1 to 9, a pellicle assembly according to claim 10, a lithographic apparatus according to claim 11 or a method according to any one of claims 12 to 19 in a lithographic apparatus or method.

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