EP3811151A1

EP3811151A1 - Euv pellicles

Info

Publication number: EP3811151A1
Application number: EP19728916.8A
Authority: EP
Inventors: Maxim Aleksandrovich NASALEVICH; Alexander Ludwig KLEIN; Evgenia KURGANOVA; Arnoud Willem NOTENBOOM; Pieter-Jan VAN ZWOL; David Ferdinand VLES
Original assignee: ASML Netherlands BV
Current assignee: ASML Netherlands BV
Priority date: 2018-06-22
Filing date: 2019-05-29
Publication date: 2021-04-28
Also published as: NL2023229A; WO2019243009A1; TW202010861A; TWI822799B; CA3104593A1; CN112334832A; NL2023229B1; KR20210022001A

Abstract

A pellicle comprising a core comprising a material other than silicon carbide, a silicon carbide adhesion layer, and a ruthenium capping layer, the ruthenium capping layer being in contact with the silicon carbide adhesion layer. Also described is a method of preparing a pellicle comprising the steps of: (i) providing a pellicle core; (ii) providing a silicon carbide adhesion layer on the pellicle core; and (iii) providing a ruthenium capping layer in contact with the silicon carbide adhesion layer. Also provided is the use of silicon carbide as an adhesion layer in an EUV pellicle as well as an assembly.

Description

EUV Pellicles

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of EP application 18179320.9 which was filed on June 22, 2018 and EP application 18203954.5 which was filed on November 1, 2018 which are incorporated herein in its entirety by reference.

FIELD

[0002] The present invention relates to a pellicle, a method of preparing a pellicle, the use of a pellicle in a lithography apparatus, the use of silicon carbide as an adhesion layer, an assembly for a lithographic apparatus comprising a pellicle, and a lithographic apparatus comprising a pellicle.

BACKGROUND

[0003] A lithographic apparatus is a machine constructed 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 may for example project a pattern from a patterning device (e.g. a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate.

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

[0005] A lithographic apparatus includes a patterning device (e.g. a mask or reticle). Radiation is provided through or reflected off the patterning device to form an image on a substrate. A pellicle may 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.

[0006] Pellicles may also be provided for protecting optical components other than patterning devices. Pellicles may also be used to provide a passage for lithographic radiation between regions of the lithography apparatus which are sealed from one another. Pellicles may also be used as filters, such as spectral purity filters. Due to the sometimes harsh environment inside a lithography apparatus, particularly an EUV lithography apparatus, pellicles are required to demonstrate excellent chemical and thermal stability.

[0007] A mask assembly may include the pellicle which protects a patterning device (e.g. a mask) from particle contamination. The pellicle may be supported by a pellicle frame, forming a pellicle assembly. The pellicle may be attached to the frame, for example, by gluing a pellicle border region to the frame. The frame may be permanently or releasably attached to a patterning device. [0008] During use, the temperature of a pellicle in a lithographic apparatus increases to anywhere from around 500 up to 1000°C or higher. These high temperatures can damage the pellicle and it is therefore desirable to improve ways by which to dissipate the heat in order to lower the operating temperature of the pellicle and improve pellicle lifespan.

[0009] One way in which this has been attempted is by applying a thin metallic film (a coating layer) on the pellicle. The metallic film increases the emissivity of the pellicle and thereby raises the rate at which heat is emitted from the pellicle, thereby causing the equilibrium temperature at which the pellicle emits heat at the same rate as it absorbs heat to be decreased. The metallic layer is provided on a face of the core of the pellicle, which may be, for example, a silicon wafer.

[00010] However, metallic films deposited at a relatively low temperature on an inert substrate are in an energetically unfavourable state and the heating or annealing of a thin metallic film on a substrate leads to thermal instability at temperatures well below the melting point of the metallic film. As such, when the metallic films are heated, sufficient energy is provided to cause the formation of holes in the metallic film, which form via a surface diffusion process. The holes grow and eventually coalesce to form irregularly shaped islands. This process of a film rupturing to form holes and ultimately islands or droplets is known as dewetting. Although this process may be beneficial in certain circumstances, such as for the formation of catalyst particles for the growth of carbon nanotubes, in other fields this is highly undesirable. For example, in the field of microelectronics, dewetting causes electrical interconnections to fail, and for pellicles, such as EUV pellicles, the dewetting alters the functionality of the emissive metallic layer. It is therefore an object of the present invention to retard or prevent dewetting of metallic films.

[00011] Since the metallic layer increases the thermal emissivity of the pellicle, as the pellicle heats up, the metallic film radiates and controls the temperature of the pellicle. When the metallic film dewets to form islands, the emissivity drops very rapidly to negligible values bringing about a significant temperature rise and consequent pellicle failure.

[00012] Even though the ruthenium film of a thickness exceeding a specific threshold thickness is stable in the operating conditions of an EUV lithography apparatus, the thickness of the metallic layer causes the pellicle to absorb more of the incident EUV radiation and therefore the EUV transmissivity of the pellicle is reduced. The reduced amount of EUV radiation which is able to pass through the pellicle means that the throughput of the lithography apparatus is reduced as longer exposure times are required. Of course, it is possible to increase the EUV transmissivity of the pellicle by reducing the thickness of the metallic layer, but this causes the undesirable dewetting of the metallic layer as described above, which results in overheating and ultimate failure of the pellicle.

[00013] It is therefore desirable to provide a method of manufacturing a pellicle which is able to withstand the operating conditions of a lithography apparatus, particularly EUV lithographic apparatus, and which has sufficient EUV transmissivity to allow high scanner yield, namely the number of exposed wafers per hour. It is also desirable to provide a pellicle which is thermally and chemically stable, and which demonstrates acceptable EUV transmissivity.

[00014] In addition, although a pellicle must be resilient enough to withstand the harsh environment inside a lithography apparatus, since it is in the optical path of the EUV radiation, it is desirable to reduce the amount of EUV radiation absorbed by the pellicle as this affects the number of wafers which can be imaged in a given time period.

[00015] It is therefore desirable to provide a pellicle having improved EUV transmissivity, but which also demonstrates good performance and reliability, and which can be manufacture reliably.

[00016] During use, radiation within the lithographic apparatus passes through low pressure hydrogen. This generates hydrogen radicals or hydrogen plasma which can etch or otherwise react with materials within the apparatus. The material of the pellicle may be etched by the hydrogen radicals and thereby weaken the pellicle potentially leading to premature failure. Carbon-based materials are readily etched by hydrogen radicals. For example, the lifespan of a graphene sheet without a protective layer may be less than one hour when exposed to the plasma densities encountered in the main body of a lithographic apparatus during operation.

[00017] Since changing the pellicle of a lithographic apparatus requires the apparatus to be turned off and may be time consuming, it is desirable to provide a pellicle which is resistant to etching in order to minimise the frequency at which the pellicle needs to be replaced, but which still demonstrates good EUV transmissivity and is cheap to manufacture. Although the removal of material by etching could be balanced by simply increasing the thickness of the material being etched, this is undesirable as making the pellicle thicker would result in lower transmission of radiation through the pellicle, thereby reducing the throughput of the apparatus.

[00018] Whilst the present application generally refers to pellicles in the context of lithography apparatus, in particular EUV lithography apparatus, the invention is not limited to only pellicles and lithography apparatus and it is appreciated that the subject matter of the present invention may be used in any other suitable apparatus or circumstances.

[00019] For example, the methods of the present invention may equally be applied to spectral purity filters. Practical EUV sources, such as those which generate EUV radiation using a plasma, do not only emit desired‘in-band’ EUV radiation, but also undesirable (out-of-band) radiation. This out-of-band radiation is most notably in the deep UV (DUV) radiation range (100 to 400 nm). Moreover, in the case of some EUV sources, for example laser produced plasma EUV sources, the radiation from the laser, usually at 10.6 microns, presents a significant out-of-band radiation.

[00020] In a lithographic apparatus, spectral purity is desired for several reasons. One reason is that the resist is sensitive to out of-band wavelengths of radiation, and thus the image quality of patterns applied to the resist may be deteriorated if the resist is exposed to such out-of-band radiation. Furthermore, out-of-band radiation infrared radiation, for example the 10.6 micron radiation in some laser produced plasma sources, leads to unwanted and unnecessary heating of the patterning device, substrate, and optics within the lithographic apparatus. Such heating may lead to damage of these elements, degradation in their lifetime, and/or defects or distortions in patterns projected onto and applied to a resist-coated substrate.

[00021] A spectral purity filter may be formed, for example, from a silicon foundation structure (e.g. a silicon grid, or other member, provided with apertures) that is coated with a reflective metal, such as molybdenum. In use, a spectral purity filter might be subjected to a high heat load from, for example, incident infrared and EUV radiation. The heat load might result in the temperature of the spectral purity filter being above 800°C. Under the high head load, the coating can delaminate due to a difference in the coefficients of linear expansion between the reflective molybdenum coating and the underlying silicon support structure. Delamination and degradation of the silicon foundation structure is accelerated by the presence of hydrogen, which is often used as a gas in the environment in which the spectral purity filter is used in order to suppress debris (e.g. debris, such as particles or the like), from entering or leaving certain parts of the lithographic apparatus. Thus, the spectral purity filter may be used as a pellicle, and vice versa. Therefore, reference in the present application to a‘pellicle’ is also reference to a‘spectral purity filter’. Although reference is primarily made to pellicles in the present application, all of the features could equally be applied to spectral purity filters.

[00022] In a lithographic apparatus (and/or method) it is desirable to minimise the losses in intensity of radiation which is being used to apply a pattern to a resist coated substrate. One reason for this is that, ideally, as much radiation as possible should be available for applying a pattern to a substrate, for instance to reduce the exposure time and increase throughput. At the same time, it is desirable to minimise the amount of undesirable radiation (e.g. out-of-band) radiation that is passing through the lithographic apparatus and which is incident upon the substrate. Furthermore, it is desirable to ensure that a spectral purity filter used in a lithographic method or apparatus has an adequate lifetime, and does not degrade rapidly over time as a consequence of the high heat load to which the spectral purity filter may be exposed, and/or the hydrogen (or the like, such as free radical species including H* and HO*) to which the spectral purity filter may be exposed. It is therefore desirable to provide an improved (or alternative) spectral purity filter, and for example a spectral purity filter suitable for use in a lithographic apparatus and/or method.

[00023] Furthermore, whilst the present application generally refers to silicon pellicles, it will be appreciated that any suitable pellicle material may be used. For example, the pellicle may comprise any suitable carbon-based material, including, for example, graphene or may comprise silicon (oxy) nitride or zirconium or any other suitable core material.

SUMMARY

[00024] The present invention has been made in consideration of the aforementioned problems with known methods of manufacturing pellicles and pellicles manufactured according to known techniques. According to a first aspect of the present invention, there is provided a pellicle comprising: a pellicle core;

a silicon carbide adhesion layer; and

a ruthenium capping layer, the ruthenium capping layer being in contact with the silicon carbide adhesion layer.

[00025] In an embodiment, there is provided a pellicle comprising a core comprising a material other than silicon carbide, a silicon carbide adhesion layer, and a ruthenium capping layer, the ruthenium capping layer being in contact with the silicon carbide adhesion layer.

[00026] In an embodiment of the first aspect of the present invention, there is provided a pellicle comprising a graphene core, a silicon carbide adhesion layer, and a ruthenium capping layer, the ruthenium capping layer being in contact with the silicon carbide adhesion layer.

[00027] The presence of a silicon carbide adhesion layer has been surprisingly found to reduce or eliminate dewetting of the ruthenium capping layer, with little or no dewetting being observed at up to around 700°C. In a pellicle comprising a silicon core material that is capped with a thin ruthenium layer, the ruthenium serves as an emissive layer enhancing the radiative cooling of the pellicle and brings down the operating temperature of the pellicle when in use. Even so, the ruthenium layer suffers from dewetting and island formation once the temperature is more than around 500°C. It is possible to use metals with much higher melting points, such as molybdenum, in order to try to avoid or limit dewetting. However, molybdenum undergoes oxidation in air at room temperature and becomes fully oxidized at high temperatures, which causes its emissivity to drop and the operating temperature of the pellicle to rise. In another approach, silicon has been coated with zirconium and boron, but the operating temperature of such a pellicle is limited to less than 600°C since the boron can oxidise and react with hydrogen present in the lithographic apparatus to form boron hydroxide, which is gaseous at this temperature and can cause outgassing from the pellicle.

[00028] It has been surprisingly found that a pellicle comprising a silicon carbide adhesion layer does not degrade as quickly as other pellicles and that the stress within a pellicle comprising a silicon carbide adhesion layer does not significantly alter on use. Furthermore, the transmissivity of a pellicle according to the present invention is more stable than that of some prior art pellicles whose transmissivity may drop from over 80% to around 75% after use. Without wishing to be limited by scientific theory, it is believed that the silicon carbide adhesion layer provides a surface which better adheres the overlying ruthenium layer to the core of the pellicle and thereby reduces the tendency of the ruthenium to dewet. This advantageously leads to a longer life for the pellicle. Preferably, the silicon carbide is not perfectly smooth and has at least a degree of surface roughness. This lowers the effect of reflection of the EUV radiation passing through the pellicle when the radiation encounters the interface between the silicon carbide and the ruthenium.

[00029] The core may comprise any suitable material. For example, the core may comprise silicon, graphene, silicon nitride, zirconium, or any other suitable core material. Preferably, the core comprises silicon, and may be silicon oxynitride. [00030] Silicon is preferably used as it is a well-characterized and well-defined material in the field of lithography. Silicon also demonstrates good EUV transmissivity and is able to withstand the conditions within a lithographic apparatus. However, it will be appreciated that other suitable materials may be used and the invention according to the first aspect of the present invention is not limited to only silicon. Other suitable materials are ones which are known to be used in pellicles.

[00031] In addition, silicon may be used as the core as it is possible to manufacture silicon wafers that are able to self-support using known techniques. It is also possible to manufacture silicon wafers which are large enough to be used as pellicles. Another advantage of using silicon in an EUV lithography apparatus is that silicon absorbs little of the EUV radiation passing through the pellicle. Even so, the emissivity of silicon is lower than other materials, so although it does not absorb EUV radiation to a high degree, the silicon radiates heat relatively slowly and therefore heats up when EUV radiation is passed through.

[00032] The ruthenium capping layer preferably covers substantially the entirety of the silicon carbide adhesion layer.

[00033] Since the ruthenium capping layer serves to increase the emissivity of the pellicle, it preferably covers as much of the surface of the pellicle as possible. In addition, since the silicon carbide adhesion layer serves to prevent dewetting of the ruthenium layer, it is preferable to cover any of the silicon carbide with the ruthenium to maximize the benefit of having the extra layer of silicon carbide. It is preferable for all of the ruthenium to be in contact with the silicon carbide adhesion layer as any ruthenium which is not on contact with the silicon carbide adhesion layer may dewet during use.

[00034] The silicon carbide adhesion layer is preferably provided directly on the core. In this way, there is no additional layer between the core and the silicon carbide adhesion layer. The addition of additional layers may increase the complexity of manufacture of the pellicle and has the potential to introduce unwanted flaws in the pellicle which may result in premature failure of the pellicle. In addition, additional layers could decrease the transmissivity of the pellicle.

[00035] The silicon carbide adhesion layer is preferably thinner than the core. Since the role of the adhesion layer is to improve the adhesion of the ruthenium layer to the pellicle, the silicon carbide adhesion layer is preferably from around 1 to around 5 nm thick. This is sufficient for it to reduce or eliminate dewetting of the ruthenium layer whilst also providing good transmissivity.

[00036] The ruthenium capping layer may be provided on one or both sides of the pellicle. The advantage of having the ruthenium capping layer on one side of the pellicle is that it has better transmissivity than a similar pellicle having a ruthenium capping layer on both sides of the pellicle, but has lower emissivity. On the other hand, the advantage of having a ruthenium capping layer on both sides of the pellicle is that there is better emissivity, but at a cost of decreased transmissivity.

[00037] The ruthenium layer may be from around 1 to around 5 nm thick. If the ruthenium layer is too thin, it will be more vulnerable to dewetting and may not have the required emissivity. On the other hand, if the ruthenium layer is too thick, increasing its thickness any further will not increase the emissivity, but will reduce the transmissivity. It is therefore desirable to have a ruthenium layer which is thick enough to provide maximum emissivity, but which is thin enough not to reduce transmissivity to too great a degree or to cause de wetting.

[00038] The core may be from around 20 to around 60 nm thick. Since the core provides the majority of the physical strength of the pellicle, it is generally thicker than the coating layers. In order to have high transmissivity, the core is preferably as thin as possible, but it still needs to be thick enough to support the weight of the pellicle and to be resilient enough to withstand handling and use.

[00039] According to a second aspect of the present invention, there is provided a method of preparing a pellicle comprising the steps of: providing a pellicle core, providing a silicon carbide adhesion layer on the pellicle core; and providing a ruthenium capping layer in contact with the silicon carbide adhesion layer.

[00040] The silicon carbide adhesion layer may be provided on the pellicle core by any suitable means. The silicon carbide adhesion layer may be directly deposited on the pellicle core. The deposition may be effected by, for example, chemical vapour deposition or sputtering. The silicon carbide adhesion layer may be provided by thermal decomposition of a polymer, such as poly(methylsilyne) under an inert atmosphere. A silicon core material may be bombarded with carbon atoms in order to form the silicon carbide adhesion layer.

[00041] The ruthenium capping layer may be provided on the silicon carbide adhesion layer by any suitable means. For example, the ruthenium may be directly deposited on the adhesion layer by chemical vapour deposition or sputtering.

[00042] The method according to the second aspect of the present invention provides a reliable method of preparing a pellicle according to the first aspect of the present invention.

[00043] According to a third aspect of the present invention, there is provided the use of silicon carbide as an adhesion layer for a ruthenium capping layer for an EUV pellicle.

[00044] It will be appreciated that the present invention may be used for other purposes than an EUV pellicle and is suitable for non-EUV pellicles as well as spectral purity filters. It has been surprisingly found that the combination of a silicon carbide adhesion layer and a ruthenium capping layer reduces or eliminates dewetting of the ruthenium when used in an EUV lithography machine. The silicon carbide can be in contact with a pellicle core that provides structural strength to the pellicle. Without wishing to be limited by scientific theory, it is believed that the silicon carbide provides a surface to which the ruthenium can advantageously bond and which can at least partially mitigate any differences in crystal structure between the ruthenium and the pellicle core, thereby leading to lower stresses in the pellicle and also reducing or eliminating dewetting.

[00045] According to a fourth aspect of the present invention, there is provided an assembly for a lithographic apparatus comprising a pellicle according to the first aspect of the present invention or manufactured according to the method of the second aspect of the present invention. The assembly may further comprise a frame for supporting the pellicle. The assembly may further comprise a reticle [00046] According to a fifth aspect of the present invention, there is provided a lithographic apparatus comprising an assembly according to the fourth aspect of the present invention.

[00047] According to a sixth aspect of the present invention, there is provided a pellicle according to any of the first to third aspects of the present invention, wherein the pellicle has an EUV transmissivity of greater than 87%.

[00048] It will be appreciated that a higher transmissivity is desirable as it allows a greater number of wafers to be imaged within a given time period. In addition, by absorbing less radiation, the pellicle will operate at a lower temperature, which can help to extend the operating lifetime of the pellicle.

[00049] Preferably, the transmissivity of the pellicle according to any aspect of the present invention is substantially unchanged after the pellicle has been heated up to operating temperature and allowed to cool at least once. Preferably, the change in transmissivity is around ± 2%, more preferably around ± 1%, and even more preferably around ± 0.5%.

[00050] The presence of the silicon carbide adhesion layer provides for a pellicle which is more resilient than other pellicles and therefore, the physical parameters of the pellicle according to the present invention are more consistent and change less than the physical parameters of other pellicles. This results in the transmissivity of the pellicle before and after exposure to EUV radiation being largely unchanged.

[00051] It is desirable to provide a pellicle which offers high EUV transmissivity whilst retaining its ability to withstand the harsh conditions within a lithographic apparatus. Current EUV pellicles are extremely thin (less than around lOOnm) free standing membranes suspended in a frame.

[00052] According to a seventh aspect of the present invention, there is provided a pellicle comprising a carbonaceous cover layer on one face and a non-carbonaceous cover layer on the opposing face.

[00053] It has been surprisingly realised that the hydrogen plasma density within a lithographic apparatus is not uniform and that the hydrogen plasma density between the pellicle and the reticle is considerably lower than at other parts of the apparatus. As such, despite carbonaceous materials being readily etched by hydrogen radicals, it has been surprisingly realised that the face of a pellicle which, in use, faces the area between the pellicle and the reticle may be carbonaceous and still have a sufficient lifespan for use as a pellicle. In this context, a lifespan is considered to be sufficient if it allows operation of the pellicle for at least 20 hours, preferably at least 40 hours, preferably at least 60 hours, preferably at least 80 hours, and even more preferably at least 100 hours.

[00054] Since the opposing face is exposed to the higher hydrogen plasma density, if this face were carbonaceous, it would likely be etched at an undesirably high rate and shorten the operating lifespan of the pellicle. As such, the opposing face preferably comprises a material which is substantially resistant to hydrogen plasma etching. For example, the non-carbonaceous cover layer on the opposing face may comprise MoSE, SEN4, C3N4, ZrN, or SiC, or any other suitable material. The non- carbonaceous cover layer may comprise a metallic layer. The non-carbonaceous cover layer may comprise a metal oxide or nitride. By carbonaceous, it should be understood that this term means that the material comprises a majority of carbon by weight. Preferably, carbonaceous cover layer comprises at least 90wt%, preferably at least 95wt%, and more preferably about 99wt% carbon. The non- carbonaceous cover layer may be the same material as the core of the pellicle. The non-carbonaceous cover layer may be continuous with the core layer. In other embodiments, the non-carbonaceous cover layer comprises a different material to the core layer.

[00055] The carbonaceous cover layer may be ordered and/or may be amorphous. Ordered carbon compounds include graphene and graphite. As such, the carbonaceous cover layer may be graphitic. It has been found that amorphous carbon is etched around thirty times as fast as graphitic carbon. As such, a graphitic carbon layer is expected to last considerably longer than an amorphous carbon layer. In addition, a graphitic cover layer is not expected to dewet from a SiC or pSi core material. Dewetting can lead to island formation and drastically reduce the emissivity of a pellicle resulting in a higher operating temperature and possible premature failure of the pellicle. In addition, with a pellicle according to the seventh aspect of the present invention, the amount of EUV reflection is within specification. It will be appreciated that one or both of the cover layers may comprise surface oxides. The carbonaceous cover layer serves as an emissive layer in order to increase the emissivity of the pellicle relative to an uncoated pellicle.

[00056] The pellicle preferably comprises a core. Preferably, the core comprises silicon carbide or pSi, but it will be appreciated that any other core material on which a carbonaceous cover layer may be provided could be used.

[00057] According to an eighth aspect of the present invention, there is provide a lithographic apparatus comprising the pellicle according to the seventh aspect of the present invention, wherein the carbonaceous cover layer is on the reticle side of the pellicle.

[00058] It will be appreciated that the pellicle according to the seventh aspect of the present invention is asymmetrical in that the cover layer material of each face is different. It will also be appreciate that in a lithographic apparatus, one face of the pellicle will be closer to the reticle than the other. Since it has been surprisingly realised that it is possible to make one cover layer from carbon and that the resulting pellicle will still have a reasonable lifespan whilst in use, the pellicle needs to be oriented within the lithographic apparatus such that the carbonaceous cover layer is exposed to the lower density of hydrogen radicals found between the pellicle and the reticle. The skilled person would be familiar with the configuration of a lithographic apparatus and would recognize that in situ, the pellicle has a reticle side, namely the side facing the reticle, and a non-reticle side, namely the side facing away from the reticle.

[00059] A graphitic layer may be provided on a core layer by any suitable method and the pellicle according to the present invention is not particularly limited by the method by which the graphitic layer is provided. For example, a graphitic cover layer may be grown by sublimation of silicon from the surface of a silicon carbide sheet above around 1300°C. Another option is to coat a silicon carbide, or other suitable core material, using a graphitic precursor material applied to the core material and then converted into graphene-like carbon by EUV exposure or annealing at around 1000°C. Other methods include forming the film from reduced graphene oxide flakes or by chemical vapour deposition.

[00060] It will be appreciated that the first to eight aspects of the present invention may be combined in any combination and that the features described in respect of one aspect may be combined with the features described in respect of another aspect of the invention.

[00061] In summary, the pellicle according to the present invention which demonstrates decreased dewetting compared to other pellicles and which has a stable EUV transmissivity, even after use. Pellicles according to the present invention are able to resist the sometimes high temperatures achieved when the pellicle is in use. Pellicles according to one aspect of the present invention comprise a carbon- based cover layer, which is cheap to manufacture and provides good EUV transmissivity as well as increased emissivity.

[00062] The present invention will now be described with reference to a silicon based pellicle. However, it will be appreciated that the present invention is not limited to silicon based pellicles and is equally applicable to spectral purity filters, as well as core materials other than silicon.

BRIEF DESCRIPTION OF THE DRAWINGS

[00063] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

Figure 1 depicts a lithographic system comprising a lithographic apparatus and a radiation source according to an embodiment of the invention;

Figure 2 depicts a schematic view of a pellicle according to an aspect of the present invention: and

Figure 3 depicts a schematic view of a pellicle according to an aspect of the present invention.

DETAILED DESCRIPTION

[00064] Figure 1 shows a lithographic system including a pellicle 15 according to the first or seventh aspects of the present invention or manufactured according to the methods of the second aspect of the present invention. The lithographic system comprises 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 comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g. 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 upon 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 previously formed patterns. Where this is the case, the lithographic apparatus aligns the patterned radiation beam B with a pattern previously formed on the substrate W. In this embodiment, the pellicle 15 is depicted in the path of the radiation and protecting the patterning device MA. It will be appreciated that the pellicle 15 may be located in any required position and may be used to protect any of the mirrors in the lithographic apparatus.

[00065] The radiation source SO, illumination system IL, and projection system PS may all be constructed and arranged such that they can be isolated from the external environment. A gas at a pressure below atmospheric pressure (e.g. hydrogen) may be provided in the radiation source SO. A vacuum may be provided in illumination system IL and/or the projection system PS. A small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure may be provided in the illumination system IL and/or the projection system PS.

[00066] The radiation source SO shown in Figure 1 is of a type which may

be referred to as a laser produced plasma (LPP) source. A laser, which may for example be a CO2 laser, is arranged to deposit energy via a laser beam into a fuel, such as tin (Sn) which is provided from a fuel emitter. Although tin is referred to in the following description, any suitable fuel may be used. The fuel may for example be in liquid form, and may for example be a metal or alloy. The fuel emitter may comprise a nozzle configured to direct tin, e.g. in the form of droplets, along a trajectory towards a plasma formation region. The laser beam is incident upon 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 de-excitation and recombination of ions of the plasma.

[00067] The EUV radiation is collected and focused by a near normal incidence radiation collector (sometimes referred to more generally as a normal incidence radiation collector). The collector may have a multilayer structure which is arranged to reflect EUV radiation (e.g. EUV radiation having a desired wavelength such as 13.5 nm). The collector may have an elliptical configuration, having two ellipse focal points. A first focal point may be at the plasma formation region, and a second focal point may be at an intermediate focus, as discussed below.

[00068] The laser may be separated from the radiation source SO. Where this is the case, the laser beam may be passed from the laser to the radiation source SO with the aid of a beam delivery system (not shown) comprising, for example, suitable directing mirrors and/or a beam expander, and/or other optics. The laser and the radiation source SO may together be considered to be a radiation system.

[00069] Radiation that is 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 acts as a virtual radiation source for the illumination system IL. The point at which the radiation beam B is focused may be referred to as the intermediate focus. The radiation source SO is arranged such that the intermediate focus is located at or near to an opening in an enclosing structure of the radiation source.

[00070] The radiation beam B passes from the radiation source SO into the illumination system IL, which is configured to condition the radiation beam. The illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. The faceted field mirror device 10 and 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 passes from the illumination system IL and is incident upon the patterning device MA held by the support structure MT. The patterning device MA reflects and patterns the radiation beam B. The illumination system IL may include other mirrors or devices in addition to or instead of the faceted field mirror device 10 and faceted pupil mirror device 11

[00071] Following reflection from the patterning device MA the patterned radiation beam B enters the projection system PS. The projection system comprises a plurality of mirrors 13, 14 which are configured to project the radiation beam B onto a substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the radiation beam, forming an image with features that are smaller than corresponding features on the patterning device MA. A reduction factor of 4 may for example be applied. Although the projection system PS has two mirrors 13, 14 in Figure 1, the projection system may include any number of mirrors (e.g. six mirrors).

[00072] The radiation sources SO shown in Figure 1 may include components which are not illustrated. For example, a spectral filter may be provided in the radiation source. The spectral filter may be substantially transmissive for EUV radiation but substantially blocking for other wavelengths of radiation such as infrared radiation.

[00073] Figure 2 is a schematic depiction of a cross-section of a pellicle according to the present invention. The pellicle comprises a pellicle core 16, a silicon carbide adhesion layer 17 and a ruthenium capping layer 18. The pellicle core 16 is in contact with the silicon carbide adhesion layer 17 and the adhesion layer 17 is in contact with the ruthenium capping layer 18. It will be appreciated that there may be one or more layers between the pellicle core 16 and the silicon carbide adhesion layer 17. It will also be appreciated that the silicon carbide adhesion layer 17 may be provided on both faces of the pellicle. Similarly, it will be appreciated that the ruthenium capping layer 18 may be provided on both faces of the pellicle. The cross-section shown is schematic and is not to scale.

[00074] In a method of producing the pellicle of Figure 2, the silicon carbide adhesion layer 17 may be provided on a pellicle core by any suitable means, for example chemical vapour deposition. Once the silicon carbide adhesion layer 17 has been deposited, the ruthenium capping layer 18 may subsequently be deposited. The method may comprise additional steps, such as, for example, annealing, between the deposition steps.

[00075] Figure 3 is a schematic depiction of a cross-section of a pellicle according to an aspect of the present invention. The pellicle comprises a pellicle core 19, a carbonaceous cover layer 20, which is preferably a graphitic layer, and a non-carbonaceous cover layer 21. It will be appreciated that there may be additional layers present within the pellicle in any aspect of the present invention. In use, the carbonaceous cover layer 20 is oriented to face the reticle (patterning device MA).

[00076] The invention may also be described by the following clauses:

Clause 1. A pellicle comprising: a pellicle core;

a silicon carbide adhesion layer; and

Clause 2. A pellicle according to clause 1, wherein the core comprises a material other than silicon carbide.

Clause 3. A pellicle according to clause 1 or 2, wherein the core comprises silicon, graphene, silicon nitride, zirconium, or other suitable core material, preferably the core comprises silicon oxynitride or graphene.

Clause 4. A pellicle according to any preceding clause, wherein the ruthenium capping layer covers substantially the entirety of the silicon carbide adhesion layer.

Clause 5. A pellicle according to any preceding clause, wherein the silicon carbide adhesion layer is provided directly on the core.

Clause 6. A pellicle according to any preceding clause, wherein the silicon carbide adhesion layer is thinner than the core.

Clause 7. A pellicle according to any preceding clause, wherein the silicon carbide adhesion layer is provided on one or both sides of the core.

Clause 8. A pellicle according to any preceding clause, wherein a ruthenium capping layer is provided on one or both sides of the pellicle.

Clause 9. A pellicle according to any preceding clause, wherein the silicon carbide adhesion layer is from around 1 to around 5 nm thick.

Clause 10. A pellicle according to any preceding clause, wherein the ruthenium capping layer is from around 1 to around 5 nm thick.

Clause 11. A pellicle according to any preceding clause, wherein the core is from around 20 to around 60 nm thick.

Clause 12. A method of preparing a pellicle comprising the steps of:

(i) providing a pellicle core;

(ii) providing a silicon carbide adhesion layer on the pellicle core; and

(iii) providing a ruthenium capping layer in contact with the silicon carbide adhesion layer. Clause 13. A method according to Clause 12, wherein the silicon carbide adhesion layer is deposited directly on the pellicle core, and wherein the ruthenium capping layer is deposited directly on the silicon carbide adhesion layer.

Clause 14. The use of a pellicle according to any of Clauses 1 to 11, or manufactured according to the method of any of Clauses 12 to 13 in a lithography apparatus, preferably an EUV lithography apparatus. Clause 15. Use of silicon carbide as an adhesion layer for a ruthenium capping layer for an EUV pellicle. Clause 16. An assembly for a lithographic apparatus comprising a pellicle according to any of Clauses 1 to 11 or manufactured according to a method of Clause 12 or 13, and a frame for supporting the pellicle.

Clause 17. An assembly according to Clause 16 further comprising a reticle.

Clause 18. A lithographic apparatus comprising the assembly of any of Clauses 16 or 17.

Clause 19. A pellicle according to any preceding Clause, wherein the pellicle has an EUV transmissivity of greater than 87%.

Clause 20. A pellicle comprising a carbonaceous cover layer on one face and a non-carbonaceous cover layer on the opposing face.

Clause 21. A pellicle according to Clause 20, further comprising a pellicle core, the carbonaceous cover layer being arrange on one face of the pellicle core and the non-carbonaceous cover layer being arranged on an opposing face of the pellicle core.

Clause 22. A pellicle according to Clause 21, wherein the one face of the pellicle core is a reticle-facing side of the pellicle.

Clause 23. A pellicle according to Clause 20, 21 or 22, wherein the non-carbonaceous cover layer is substantially resistant to EUV-induced plasma etching.

Clause 24. A pellicle according to Clause 23, wherein the non-carbonaceous cover layer comprises MoSE, S1₃N₄, C₃N₄, ZrN, SiC, a metal, a metal nitride, or a metal oxide.

Clause 25. A pellicle according to any of Clauses 20 to 24, wherein the carbonaceous cover layer is ordered.

Clause 26. A pellicle according to Clause 25, wherein the carbonaceous cover layer is graphitic.

Clause 27. A pellicle according to any of Clauses 20 to 26, wherein the pellicle core comprises silicon carbide or pSi.

Clause 28. A lithographic apparatus comprising the pellicle according to any of Clauses 20 to 27, wherein the carbonaceous cover layer is on the reticle-facing side of the pellicle.

[00077] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

CLAIMS:

l.A pellicle comprising:

a pellicle core;

a silicon carbide adhesion layer; and

2. A pellicle according to Claim 1, wherein the core comprises a material other than silicon carbide.

3. A pellicle according to Claim 1 or 2, wherein the core comprises silicon, graphene, silicon nitride, zirconium, or other suitable core material, preferably the core comprises silicon oxynitride or graphene.

4. A pellicle according to any preceding claim, wherein the ruthenium capping layer covers substantially the entirety of the silicon carbide adhesion layer.

5. A pellicle according to any preceding claim, wherein the silicon carbide adhesion layer is provided directly on the core.

6. A pellicle according to any preceding claim, wherein the silicon carbide adhesion layer is thinner than the core.

7. A pellicle according to any preceding claim, wherein the silicon carbide adhesion layer is provided on one or both sides of the core.

8. A pellicle according to any preceding claim, wherein a ruthenium capping layer is provided on one or both sides of the pellicle.

9. A pellicle according to any preceding claim, wherein the silicon carbide adhesion layer is from around 1 to around 5 nm thick.

10. A pellicle according to any preceding claim, wherein the ruthenium capping layer is from around 1 to around 5 nm thick.

11. A pellicle according to any preceding claim, wherein the core is from around 20 to around 60 nm thick.

12. A method of preparing a pellicle comprising the steps of: (i) providing a pellicle core;

(ii) providing a silicon carbide adhesion layer on the pellicle core; and

(iii) providing a ruthenium capping layer in contact with the silicon carbide adhesion layer.

13. A method according to Claim 12, wherein the silicon carbide adhesion layer is deposited directly on the pellicle core, and wherein the ruthenium capping layer is deposited directly on the silicon carbide adhesion layer.

14. The use of a pellicle according to any of Claims 1 to 11, or manufactured according to the method of any of Claims 12 to 13 in a lithography apparatus, preferably an EUV lithography apparatus.

15. Use of silicon carbide as an adhesion layer for a ruthenium capping layer for an EUV pellicle.

16. An assembly for a lithographic apparatus comprising a pellicle according to any of Claims 1 to 11 or manufactured according to a method of Claim 12 or 13, and a frame for supporting the pellicle.

17. An assembly according to Claim 16 further comprising a reticle.

18. A lithographic apparatus comprising the assembly of any of Claims 16 or 17.

19. A pellicle according to any preceding claim, wherein the pellicle has an EUV transmissivity of greater than 87%.

20. A pellicle comprising a carbonaceous cover layer on one face and a non-carbonaceous cover layer on the opposing face.

21. A pellicle according to Claim 20, further comprising a pellicle core, the carbonaceous cover layer being arrange on one face of the pellicle core and the non-carbonaceous cover layer being arranged on an opposing face of the pellicle core.

22. A pellicle according to Claim 21, wherein the one face of the pellicle core is a reticle-facing side of the pellicle.

23. A pellicle according to any of the Claims 20 to 22, wherein the non-carbonaceous cover layer is substantially resistant to EUV-induced plasma etching.

24. A pellicle according to any of the Claims 20 to 23, wherein the non-carbonaceous cover layer comprises MoSC, S13N4, C3N4, ZrN, SiC, a metal, a metal nitride, or a metal oxide.

25. A pellicle according to any of Claims 20 to 24, wherein the carbonaceous cover layer is ordered.

26. A pellicle according to Claim 25, wherein the carbonaceous cover layer is graphitic.

27. A pellicle according to any of Claims 21 to 26 referring to Claim 21, wherein the pellicle core comprises silicon carbide or pSi.

28. A lithographic apparatus comprising the pellicle according to any of claims 20 to 27, wherein the carbonaceous cover layer is on the reticle-facing side of the pellicle.