Optical elements and pellicle membranes for lithographic apparatus

Abstract

An optical element for a lithographic apparatus is described, the optical element comprising an anchor layer selected to support a top layer having self-terminating growth in an operating lithographic apparatus or plasma-containing environment. A method for manufacturing the optical element is also described, the method comprising depositing a top layer on the anchor layer via exposure to a plasma, preferably an electromagnetically induced plasma. A lithographic apparatus comprising such an optical element is also described.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Application No. 20176421.4, filed May 26, 2020, which is incorporated herein by reference in its entirety.

[0002] The present invention relates to an optical element for a lithographic apparatus, an assembly for a lithographic apparatus, and the use of a pellicle film in a lithographic apparatus or method. The present invention also relates to a method for manufacturing an optical element and a pellicle film, and a pellicle film for a lithographic apparatus and method. [Background technology]

[0003] A lithographic apparatus is a machine configured to apply a desired pattern onto a substrate. 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) provided on the substrate.

[0004]

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

[0005]

[0005] 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 a substrate. To protect the patterning device from airborne particles and other forms of contamination, a membrane assembly, also called a pellicle, may be provided. Contamination on the surface of the patterning device can cause manufacturing defects in the substrate.

[0006]

[0006] Pellicles may also be provided to protect optical components other than the patterning device. Pellicles may also be used to provide a passageway for lithography radiation between mutually sealed regions of the lithography apparatus. Pellicles may also be used as filters, such as spectral purity filters, or as part of a dynamic gas lock in the lithography apparatus.

[0007]

[0007] The mask assembly may include a pellicle that protects the patterning device (e.g., mask) from particle contamination. The pellicle may be supported by a pellicle frame to form a pellicle assembly. The pellicle may be attached to the frame, for example, by gluing or otherwise attaching an edge region of the pellicle to the frame. The frame may be permanently or removably attached to the patterning device.

[0008]

[0008] Because pellicles reside in the optical path of the EUV radiation beam, they need to have high EUV transmittance. High EUV transmittance allows a large proportion of the incident radiation to pass through the pellicle. Reducing the amount of EUV radiation absorbed by the pellicle can also reduce the operating temperature of the pellicle. Because 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 still ensuring that it remains strong enough to withstand the sometimes harsh environment within a lithography apparatus.

[0009]

[0009] It is therefore desirable to provide a pellicle that can withstand the harsh environment of a lithography tool, particularly an EUV lithography tool, and it is particularly desirable to provide a pellicle that can withstand higher powers than previously possible.

[0010]

[0010] Although this application generally refers to pellicles in the context of lithographic apparatus, and particularly EUV lithographic apparatus, it is understood that the present invention is not limited to pellicles and lithographic apparatus alone, and that the subject matter of the present invention may be used in any other suitable apparatus or context.

[0011] For example, the method of the present invention may be equally applied to spectral purity filters. Some EUV radiation sources, such as those that use plasma to generate EUV radiation, emit not only the desired "in-band" EUV radiation, but also undesired (out-of-band) radiation. This out-of-band radiation is particularly in the deep UV (DUV) radiation range (100 nm to 400 nm). Furthermore, for some EUV radiation sources, for example laser-produced plasma EUV radiation sources, the radiation from the laser, typically at 10.6 microns, exhibits significant out-of-band radiation.

[0012]

[0012] Spectral purity is desirable in lithographic apparatus for several reasons. One reason is that resists are sensitive to out-of-band wavelengths of radiation, and therefore, exposure of the resist to such out-of-band radiation can degrade the image quality of patterns applied to the resist. Also, out-of-band infrared radiation, for example, the 10.6 micron radiation in some laser-produced plasma radiation sources, can cause unwanted and unnecessary heating of patterning devices, substrates, and optical components within the lithographic apparatus. Such heating can lead to damage or reduced lifetime of these components, and / or defects or distortions in the patterns projected and applied to resist-coated substrates.

[0013] A typical spectral purity filter may be formed from a silicon underlying structure (e.g. a silicon grating or other member with an aperture) coated with a reflective metal such as molybdenum. In use, a typical spectral purity filter may be exposed to high heat loads, for example from incident infrared and EUV radiation. This heat load may cause the temperature of the spectral purity filter to exceed 800°C. Under high head loads, delamination of the coating may occur due to differences in the linear expansion coefficients between the reflective molybdenum coating and the underlying silicon support structure. Delamination and degradation of the silicon underlying structure may be accelerated by the presence of hydrogen, which is often used as a gas in environments in which spectral purity filters are used to suppress debris (e.g. debris such as particles) from entering or leaving certain parts of a lithographic apparatus. In this way, a spectral purity filter may be used as a pellicle, and vice versa. Therefore, when referring to a "pellicle" in this application, reference is also made to a "spectral purity filter". Although reference is made primarily to pellicles in this application, all of its features may equally apply to spectral purity filters.

[0014]

[0014] The present invention is additionally or alternatively directed to optical elements, such as mirrors, in lithographic apparatus or other apparatus in which the optical elements, such as mirrors or windows, are exposed to a plasma environment.

[0015]

[0015] The present invention has been devised in an attempt to address at least some of the problems identified above. Summary of the Invention

[0016]

[0016] According to a first aspect of the present invention, an optical element for a lithographic apparatus is provided, the optical element comprising an anchor layer selected to support a top layer having self-terminating growth in the lithographic apparatus during operation.

[0017]

[0017] Existing optical elements use a thin layer of ruthenium metal to prevent chemical degradation under the influence of EUV radiation and plasma. Ruthenium is somewhat chemically inert and forms a thin native oxide layer that is easily reduced when exposed to EUV-excited hydrogen plasma. A zirconium oxide layer may also be included to prevent blistering of the ruthenium layer used.

[0018] One drawback of using ruthenium is its tendency to catalytically decompose volatile hydrogen compounds of materials such as silicon and phosphorus. The decomposition of such compounds results in the deposition of such materials on the ruthenium surface. This reduces the reflectivity of the mirror or the transparency of the pellicle, which in turn requires an increased power supply to maintain the same scanner throughput or reduces scanner throughput over time. It is desirable to address this drawback. While it is possible to add a zirconium dioxide layer that does not form volatile hydrogen compounds, zirconium dioxide is not produced under conditions found in an operating lithography apparatus and can change form over time. Thus, the protective effect of zirconium dioxide diminishes over time. Furthermore, ruthenium cannot protect underlying layers from oxidation under all conditions.

[0019]

[0019] Surprisingly, it has been found possible to provide an anchor layer for an optical element that supports a top layer having self-terminating growth used in an operating lithography apparatus. These self-terminating top layers are surprisingly resistant to etching by hydrogen ions and radicals, and also to the deposition of unwanted additional materials, such as silicon, during exposure in the lithography apparatus. The self-terminating top layer does not grow in thickness beyond a given point by the deposition of additional material thereon, and does not decrease in thickness as a result of plasma etching. This form of coating is therefore very important for lithography apparatus and methods, as the performance of the optical element does not change over time and is stable under operating conditions. Experiments have shown that such self-limiting growth layers are very difficult, if not impossible, because they would be removed by plasma etching.

[0020]

[0020] The optical element may further comprise a substrate layer. The substrate layer may comprise one or more of silicon, carbon, quartz, and sapphire. Silicon is often used as a substrate for optical elements, particularly those used in lithography, because it has high EUV transmittance and can withstand the conditions within a lithography apparatus during operation. Carbon, preferably in the form of nanotubes, which may be single-walled, double-walled, or multi-walled, can also be used as a substrate given its resistance to very high temperatures. Quartz and sapphire are materials often used for mirrors and viewing windows in lithography apparatus and other devices in which plasma is generated. Sapphire windows are generally very etch-resistant, but quartz is preferred in some cases where etching of quartz can be problematic. In either case, the volume of contaminants, such as silicon, can be a problem. The substrate may also be a multi-layer stack of mirrors.

[0021]

[0021] The optical element may also include a wetting layer. The wetting layer may include one or more elements selected from the group consisting of chromium, titanium, and molybdenum. The wetting layer may include nitrides of one or more of these metals. The wetting layer is preferably disposed between the substrate layer and the anchor layer. The wetting layer prevents or reduces thermal dewetting of a metal anchor layer disposed on the wetting layer. A suitable wetting layer has a high oxygen affinity, which provides passivation for silicon oxide layers often used as substrates. The wetting layer also adheres well to the overlying layer on which it is deposited, which provides attenuation of surface migration. Wetting materials have atoms with large atomic radii, which provides attenuation of atomic migration into the substrate material.

[0022]

[0022] The thickness of the wetting layer can be selected depending on the application to which the optical element is applied. In the case of a pellicle, it is desirable that the thickness of the wetting layer be as thin as possible while still functioning as intended. Preferably, the thickness of the wetting layer is 5 nm or less. The thickness of the wetting layer may be 2 nm or less. The thickness of the wetting layer may be 1 nm or less. The thickness of the wetting layer may be 0.5 nm or less.

[0023] The optical element may comprise a top layer. The top layer may comprise one or more elements selected from the group consisting of Si, Ge, Sn, B, P, Mg, and Al. The top layer may comprise an oxide of one or more of such elements.

[0024] The anchor layer and the top layer may form a plasma etch barrier. Plasma etch barriers with self-terminating growth have been found to be particularly resistant to erosion or attack by plasma.

[0025] The anchor layer comprises one or more elements selected from the list consisting of platinum, ruthenium, osmium, rhodium, iridium, and palladium. The anchor layer acts as an adhesive to the self-limiting top layer. It has been found that not all elements serve as suitable anchor layers because not all elements result in a top layer with self-limiting growth and high stability in a plasma environment.

[0026]

[0026] The optical element may be a pellicle assembly or a mirror. The pellicle assembly may be a pellicle assembly for a lithography apparatus, such as an EUV lithography apparatus or a lithography apparatus using light of a wavelength longer or shorter than EUV. Similarly, the mirror may be a mirror used in a lithography apparatus, such as a field facet mirror.

[0027] According to a second aspect of the present invention there is provided a method for manufacturing an optical element, the method comprising the step of depositing a top layer on an anchor layer via exposure to a plasma, preferably an electromagnetically induced plasma, i.e. a plasma formed by exposure to electromagnetic radiation.

[0028] It will be appreciated that features of the first aspect of the invention may be combined with features of the second aspect, and vice versa.

[0029] The method according to the second aspect of the invention allows the production of optical elements that exhibit self-limiting growth when used in an operating lithographic apparatus.

[0030] The top layer may comprise one or more elements selected from the group consisting of silicon, germanium, tin, lead, boron, phosphorus, magnesium, and aluminum.

[0031] The wetting layer may comprise one or more elements selected from the group consisting of chromium, titanium, and molybdenum. The wetting layer may comprise a nitride of such an element.

[0032] The anchor layer may comprise one or more elements selected from the group consisting of Pt, Ru, Os, Rh, Ir, and Pd.

[0033] The optical element may comprise any of the substrates mentioned in relation to the first aspect of the invention.

[0034]

[0034] The optical element is made of [Ru-SiO x ],[Pt-SiO x ],[Rh-SiO x ],[Ru-GeO x ],[Rh-GeO x ],[Ru-SnO x ], and [Rh-SnO x

[0023] These anchor layer and top layer combinations exhibit resistance to etching by hydrogen plasma as well as self-limiting growth in a lithography apparatus.

[0035]

[0035] An optical element according to any preceding claim, comprising a carbon nanotube substrate, a molybdenum wetting layer, a ruthenium anchor layer, and a silicon oxide top layer. The carbon nanotubes may be single-walled carbon nanotubes. This layer combination also exhibits advantageous resistance to etching by hydrogen plasma and self-limiting growth of the top layer when used in a lithography apparatus.

[0036] According to a third aspect of the present invention, there is provided an optical element manufactured by the method of the second aspect of the present invention. The optical element may be suitable for use in a lithography apparatus, such as an EUV lithography apparatus. The optical element may be a pellicle or a mirror.

[0037] According to a fourth aspect of the present invention, there is provided a pellicle membrane for a lithographic apparatus, the pellicle membrane comprising a non-volatile sacrificial material.

[0038]

[0038] It will be understood that the pellicle membrane described with respect to the fourth aspect of the present invention may be included in an optical element of the first or third aspect of the present invention, or may be manufactured at least in part by a method according to the second aspect of the present invention.

[0039] It will be appreciated that certain layers or portions of a pellicle film may be damaged during use in a lithographic apparatus. For example, pellicle films comprising silicon and silicon compounds exhibit hydrogen-induced outgassing. Hydrogen can remove the native oxide layer and then react with the silicon core to release silane gas. Similarly, carbon-based pellicles may be eroded by exposure to a hydrogen plasma. It is desirable to prevent etching of the pellicle film, as this can lead to weakening and possibly failure of the film. It is desirable to extend the life of the pellicle film to ensure the maximum amount of operational uptime of the lithographic apparatus. According to a fourth aspect of the present invention, non-volatile sacrificial materials are provided as part of the pellicle film, which protects other portions of the pellicle film from erosion. Thus, these materials are sacrificed to prevent or reduce degradation of other materials. By non-volatile, it is meant that these materials are not gases in their oxidized, native, or reduced forms. For example, silane is a gas at ambient temperature and pressure and is therefore considered volatile. In contrast, both metallic silver and silver oxide are solids at ambient temperature. Sacrificial is understood to mean that this material is preferentially attacked by the plasma and therefore sacrificed to protect the remaining pellicle membrane.

[0040]

[0040] The optical element according to the fourth aspect of the invention may include any of the features described in relation to the first aspect of the invention.

[0041] The non-volatile sacrificial material may comprise a material that has a higher redox potential than at least one other material in the film, and thus the non-volatile sacrificial material may have a higher redox potential than the material to be protected.

[0042]

[0042] The redox potential can be positive or negative. In this application, a higher redox potential means a more positive redox potential. For example, a redox potential of -0.1 V is higher than a redox potential of -0.8 V, and a positive redox potential is higher than a negative redox potential, regardless of the absolute magnitude of the potential.

[0043] A highly reducing atmosphere is present within the environment of a lithographic apparatus, and therefore materials such as carbon and silicon can be easily reduced to silanes and hydrocarbons, respectively. By providing a sacrificial material with a more positive reaction potential, the sacrificial material is preferentially reduced, thereby preserving other materials such as silicon or carbon. Thus, the sacrificial material preferably has a higher (positive) redox potential than silicon or carbon, which have redox potentials of −0.14 V and +0.13 V, respectively, in terms of the reduction of elemental silicon or elemental carbon to silane or methane. It is desirable for the oxidized or reduced sacrificial material to be non-volatile so that it is not released into the atmosphere of the lithographic apparatus, where it could reach other parts of the apparatus and cause damage or loss of performance.

[0044]

[0044] Examples of redox reactions that occur in an operating lithographic apparatus include the following:

[0045] [ka]

[0046]

[0045] The reaction potential for the reduction of silicon oxide is -0.91 V. The reaction potential for the reduction of silicon is -0.14 V. The reaction potential for the reduction of carbon is +0.13 V. The reaction potential for the reduction of ruthenium oxide is +0.68 V. Therefore, in a system with these elements / compounds, ruthenium oxide will be the first to be reduced because it has the most positive reduction potential and therefore a higher affinity for electrons and a higher tendency to be reduced.

[0047] The non-volatile sacrificial material may have a redox potential at least 0.35 V higher than another material of the pellicle membrane. Specifically, its redox potential will be at least 0.35 V higher than the material in the pellicle membrane that is desired to be protected, such as silicon or carbon.

[0048] The non-volatile sacrificial material and / or its reaction products with hydrogen are preferably stable in air. That is, the sacrificial material does not react rapidly (within minutes or seconds) in air under ambient conditions, except for the creation of a thin native oxide layer. The non-volatile sacrificial material and / or its reaction products with hydrogen are preferably stable in the atmosphere of the lithographic apparatus during operation. For example, if the sacrificial material is a metal oxide, the metal oxide and the metal product of its reduction with hydrogen are non-volatile.

[0049] The non-volatile sacrificial material may comprise one or more elements selected from the list consisting of silver, gold, platinum, iron, manganese, and tellurium. The material may comprise an oxidized form of such an element, such as an oxide. The oxides of these materials have a more positive redox potential than silicon and carbon and are therefore reduced first, thereby protecting the silicon and carbon.

[0050]

[0049] The non-volatile sacrificial material may comprise an oxide that can be reduced to a metallic element by a hydrogen plasma. By reacting more readily with hydrogen than other materials of the pellicle membrane, these materials are preferentially reduced so that the other materials are not eroded, or at least eroded at a much slower rate than they would otherwise be. This in turn extends the operational life of the pellicle membrane.

[0051]

[0050] The film may be configured to place the non-volatile sacrificial material in direct contact with the plasma environment of the lithographic apparatus. Thus, the non-volatile sacrificial material may be on the surface of the pellicle film. Thus, the sacrificial material can react with the hydrogen plasma to protect the remaining pellicle film.

[0052] The nonvolatile sacrificial material can be in the form of a continuous or discontinuous layer. The nonvolatile sacrificial layer can be in the form of discrete islands and / or grains. The sacrificial material need not be provided over the entire extent of the pellicle membrane, as it can protect an area of ​​the pellicle membrane that is larger than the area covered by the sacrificial material. Also, since it is desirable to have a highly permeable pellicle membrane, it would be undesirable to include additional layers of material when not necessary. The use of discontinuous layers or islands / grains allows the membrane to retain high permeability while also benefiting from the protective effect of the nonvolatile sacrificial material.

[0053]

[0052] The non-volatile sacrificial material is provided in an area of ​​the film that is outside the main optical path of the operating lithographic apparatus. It will be understood that the pellicle film is within the path of the light used in the lithographic apparatus. Light is not distributed uniformly across the entire surface of the pellicle film. Instead, there are areas that are exposed to the highest intensity of light. Because it is desirable to allow the greatest amount of light to pass through the pellicle film, it is desirable that the areas of greatest light intensity also have the greatest transmittance. Therefore, the non-volatile sacrificial material is preferably positioned away from the areas of greatest light intensity. In this way, the beneficial effects of the sacrificial material are realized while the reduction in transmittance is managed.

[0054]

[0053] The non-volatile sacrificial material can be provided in the edge region of the pellicle membrane. Since the greatest intensity of light passes through the central region of the pellicle membrane, positioning the sacrificial material in the area surrounding the central region limits the decrease in transparency caused by the addition of the sacrificial material.

[0055] A pellicle membrane according to the fourth aspect of the invention may form part of the optical element of the first aspect of the invention.

[0056] According to a fifth aspect of the present invention, there is provided a pellicle assembly comprising a pellicle membrane according to the fourth aspect of the present invention.

[0057] According to a sixth aspect of the present invention there is provided the use of an optical element or pellicle membrane according to any aspect of the present invention in a lithographic apparatus or method.

[0058] According to a seventh aspect of the present invention, there is provided a lithographic apparatus comprising an optical element or pellicle membrane according to any aspect of the present invention.

[0059]

[0058] It will be understood that any feature described with respect to one embodiment may be combined with any feature described with respect to another embodiment, and all such combinations are expressly contemplated and disclosed in this specification. [Brief explanation of the drawings]

[0060]

[0059] 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 symbols indicate corresponding parts, and in which:

[0061] [Figure 1]

[0060] There is depicted a lithographic apparatus according to one embodiment of the present invention. [Figure 2]

[0061] FIG. 1 is a schematic diagram of an optical element according to one embodiment of the present invention. [Figure 3]

[0062] 1 is a schematic diagram of a portion of an optical element according to an embodiment of the present invention;

[0062]

[0063] The features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the drawings, in which like reference numerals identify corresponding elements throughout and generally indicate identical, functionally similar, and / or structurally similar elements. DETAILED DESCRIPTION OF THE INVENTION

[0063]

[0064] Figure 1 shows a lithography system including a pellicle 15 (also referred to as a thin film assembly) according to the present invention. The lithography system comprises a radiation source SO and a lithography apparatus LA. The radiation source SO is configured to generate a beam of extreme ultraviolet (EUV) radiation B. The lithography 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 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 that case, the lithography apparatus aligns the patterned radiation beam B with the pattern previously formed on the substrate W. In this embodiment, a pellicle 15 is shown in the path of the radiation to protect the patterning device MA. It will be appreciated that the pellicle 15 may be in any desired location and may be used to protect any of the mirrors within the lithographic apparatus.

[0064]

[0065] The 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 (e.g., hydrogen) at a pressure below atmospheric pressure may be provided in the source SO. A vacuum may be provided in the illumination system IL and / or projection system PS. A small amount of gas (e.g., hydrogen) at a pressure significantly below atmospheric pressure may be provided in the illumination system IL and / or projection system PS.

[0065]

[0066] The radiation source SO shown in FIG. 1 is of a type that may be referred to as a laser-produced plasma (LPP) source. A laser, which may be, for example, a CO laser, is arranged to deposit energy via a laser beam onto a fuel, such as tin (Sn), provided from a fuel emitter. While the following description refers to tin, any suitable fuel may be used. The fuel may be, for example, in liquid form and may be, for example, a metal or alloy. The fuel emitter may include a nozzle configured to direct the tin, for example, in the form of droplets, along a trajectory toward the plasma formation region. The laser beam is incident on the tin in the plasma formation region. Deposition of laser energy on the tin creates a plasma in the plasma formation region. Radiation, including EUV radiation, is emitted from the plasma upon de-excitation and recombination of the ions of the plasma.

[0066]

[0067] The EUV radiation is collected and focused by a near-normal incidence radiation collector (sometimes more commonly referred to as a normal incidence radiation collector). The collector may have a multi-layer structure 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, with two elliptical foci. The first focus may be at the plasma formation region, and the second focus may be at an intermediate focus, as described below.

[0067]

[0068] The laser may be separate from the radiation source SO, in which 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), for example comprising appropriate directing mirrors and / or beam expanders and / or other optical components. The laser and radiation source SO may together be considered a radiation system.

[0068]

[0069] 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 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 positioned such that the intermediate focus is located at or near an aperture in an enclosure structure of the radiation source.

[0069]

[0070] The radiation beam B enters from the radiation source SO into an illumination system IL configured to condition the radiation beam. The illumination system IL may include a faceted field mirror device 10 and a faceted pupil mirror device 11. Together the facetted field mirror device 10 and facetted pupil mirror device 11 provide the radiation beam B with a desired cross-sectional shape and a desired angular distribution. The radiation beam B passes through the illumination system IL and is incident on a patterning device MA held by a support structure MT. The patterning device MA reflects and pattern the radiation beam B. The illumination system IL may include other mirrors or devices in addition to or instead of the facetted field mirror device 10 and facetted pupil mirror device 11.

[0070]

[0071] Following reflection from the patterning device MA, the patterned radiation beam B enters a projection system PS. The projection system comprises a number of mirrors 13, 14 configured to project the radiation beam B onto a substrate W held by a substrate table WT. The projection system PS may apply a demagnification factor to the radiation beam to form an image having smaller features than corresponding features on the patterning device MA. For example, a demagnification factor of four may be applied. Although in Figure 1 the projection system PS has two mirrors 13, 14, the projection system may include any number of mirrors (for example six mirrors).

[0071]

[0072] The radiation source SO shown in Figure 1 may include components not shown. For example, the radiation source may be provided with a spectral filter that may be substantially transparent to EUV radiation but substantially blocking radiation of other wavelengths, such as infrared radiation.

[0072]

[0073] In one embodiment, the membrane assembly 15 is a pellicle for a patterning device MA for EUV lithography. The membrane assembly 15 of the present invention can be used for a dynamic gas lock, a pellicle, or for another purpose. In one embodiment, the membrane assembly 15 comprises a membrane formed from at least one membrane layer configured to transmit at least 90% of the EUV radiation incident thereon. Preferably, the membrane is supported only at the edges to ensure maximum EUV transmission and minimal impact on imaging performance.

[0073]

[0074] If the patterning device MA is left unprotected, contamination may require the patterning device MA to be cleaned or discarded. Cleaning the patterning device MA interrupts valuable production time, discarding the patterning device MA is expensive, and replacing the patterning device MA also interrupts valuable production time.

[0074]

[0075] FIG. 2 illustrates one embodiment of a pellicle membrane according to the present invention. Pellicle assembly 15 includes a pellicle membrane, generally designated 16. Pellicle membrane 16 includes substrate 17, which is generally thicker than the other layers comprising pellicle membrane 16. The illustration in FIG. 2 is illustrative and does not depict the actual relative thicknesses of the various layers. Substrate 17 is typically silicon or carbon, which may be in the form of carbon nanotubes. Disposed on substrate 17 is wetting layer 18, which serves to reduce or eliminate dewetting of the overlying anchor layer 19. Disposed on anchor layer 19 is self-limiting top layer 20. The dashed line between anchor layer 19 and self-limiting top layer 20 represents a strong bond between the two layers, which serves to prevent etching of self-limiting top layer 20.

[0075]

[0076] FIG. 3 illustrates one embodiment of a pellicle membrane according to the present invention. Specifically, FIG. 3 illustrates a portion of a pellicle membrane comprising a carbon nanotube (CNT) substrate 22. The carbon nanotubes 22 have a hollow core 26. The illustrated embodiment is single-walled carbon nanotubes, although it will be understood that double-walled and multi-walled carbon nanotubes are also possible substrates. In the illustrated embodiment, the CNTs have a diameter of approximately 10 nm, although the present invention is not particularly limited to this diameter and other diameters may be used. Disposed on the CNT substrate 22 is a wetting layer 23 of molybdenum. The thickness of the molybdenum layer is from about 0.1 nm to about 1 nm. The molybdenum layer functions as a wetting layer to prevent or substantially reduce the tendency of the overlying anchor layer 24 to dewet. In the illustrated embodiment, the anchor layer 24 comprises ruthenium. The thickness of the ruthenium layer is from about 2 nm to about 4 nm. A self-terminating non-etchable top layer 25 is provided on the anchor layer 24. In the illustrated embodiment, the self-terminating non-etchable top layer 25 comprises silicon oxide. The silicon oxide layer has a thickness of about 1 nm to about 2.5 nm. A pellicle film having such a configuration exhibits nearly complete resistance to etching in a lithography tool, while also having an EUV transmittance of greater than 90% and a thermal emissivity of greater than 50%. Thus, a pellicle device including such a film has an advantageous mechanical life in a lithography tool, particularly an EUV lithography tool, and improved etching resistance to plasma.

[0076] example

[0077] The following examples provide specific embodiments of the present invention, but are not intended to limit the scope of the invention.

[0077]

[0078] The table below includes combinations of anchor layers and self-limiting top layers that are particularly suitable for withstanding etching in lithographic equipment.

[0078] [Table 1]

[0079]

[0079] The combination of a ruthenium anchor layer with a silicon oxide top layer and the combination of a platinum anchor layer with a silicon oxide top layer have been found to be particularly stable to etching in a lithographic apparatus.

[0080]

[0080] On the other hand, it has been found that an aluminum copper anchor layer does not provide the same self-limiting growth top layer that is resistant to etching.

[0081]

[0081] Whilst specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

[0082]

[0082] The above description is intended to be illustrative and not limiting. Thus, those skilled in the art will appreciate that modifications to the invention as described may be made within the scope of the following claims. and clauses It will be apparent that this can be done without departing from the principles set forth herein. 1. An optical element for a lithographic apparatus, comprising an anchor layer selected to support a top layer having self-terminating growth in an operating lithographic apparatus or plasma-containing environment. 2. The optical element of clause 1, wherein the optical device further comprises a substrate layer. 3. The optical element according to clause 1 or 2, wherein the optical device further comprises a wetting layer. 4. The optical element of clause 1 or 2, wherein the optical element comprises the top layer. 5. The optical element of clause 1 or 2, wherein the anchor layer and the top layer form a plasma etch barrier. 6. The optical element of clause 1 or 2, wherein the substrate layer comprises one or more of silicon, carbon, quartz, and sapphire. 7. The optical element of clause 1 or 2, wherein the top layer comprises one or more elements selected from the group consisting of Si, Ge, Sn, B, P, Mg, and Al, and optionally the top layer comprises an oxide of one or more of such elements. 8. The optical element of clause 1 or 2, wherein the wetting layer comprises one or more elements selected from the group consisting of Cr, Ti, and Mo, and optionally the wetting layer comprises TiN. 9. The optical element of clause 1 or 2, wherein the anchor layer comprises one or more elements selected from the group consisting of Pt, Ru, Os, Rh, Ir, and Pd. 10. The optical element of clause 1 or 2, wherein the optical element is a pellicle assembly or a mirror. 11. The optical element is made of [Ru-SiO x ],[Pt-SiO x ],[Rh-SiO x ],[Ru-GeO x ],[Rh-GeO x ],[Ru-SnO x ], and [Rh-SnO x 3. An optical element according to clause 1 or 2, comprising an anchor layer-top layer combination selected from the list consisting of: 12. The optical element of clause 2, wherein the substrate comprises a top layer having carbon nanotubes, a wetting layer, an anchor layer, and self-terminating growth, such as carbon nanotubes coated with a wetting layer of molybdenum, an anchor layer of ruthenium, and a top layer of silicon oxide. 13. A method for manufacturing an optical element, comprising depositing a top layer onto an anchor layer via exposure to a plasma, preferably an electromagnetically induced plasma. 14. The method of clause 13, wherein the top layer comprises one or more elements selected from the group consisting of Si, Ge, Sn, B, P, Mg, and Al, and / or the wetting layer comprises one or more elements selected from the group consisting of Cr, Ti, and Mo, optionally the wetting layer comprises TiN, and / or the anchor layer comprises one or more elements selected from the group consisting of Pt, Ru, Os, Rh, Ir, and Pd. 15. Optical elements manufactured by the method of clause 13 or 14. 16. A pellicle membrane for a lithographic apparatus, the pellicle membrane comprising a non-volatile sacrificial material. 17. The pellicle membrane of clause 16, wherein the non-volatile sacrificial material comprises a material having a higher redox potential than at least one other material of the membrane. 18. The pellicle membrane of clause 17, wherein the non-volatile sacrificial material has a redox potential that is at least 0.35 V greater than another material of the pellicle membrane. 19. The pellicle film of any of clauses 16 to 18, wherein the non-volatile sacrificial material comprises one or more elements selected from the list consisting of silver, gold, platinum, iron, manganese, and tellurium. 20. The pellicle membrane of clause 19, wherein the non-volatile sacrificial material is in an oxidized form, such as an oxide. 21. A pellicle film according to any of clauses 16 to 18, wherein the film is configured to place the non-volatile sacrificial material in direct contact with a plasma environment of a lithographic apparatus. 22. A pellicle membrane according to any of clauses 16 to 18, wherein the non-volatile sacrificial material is in the form of a continuous or discontinuous layer. 23. A pellicle membrane according to any of clauses 16 to 18, wherein the non-volatile sacrificial material is in the form of discrete islands and / or grains. 24. A pellicle film according to any of clauses 16 to 18, wherein the non-volatile sacrificial material is provided in an area of ​​the film outside a main optical path of an operating lithographic apparatus. 25. A pellicle membrane according to any of clauses 16 to 18, wherein the non-volatile sacrificial material is provided at an edge portion of the pellicle membrane. 26. A pellicle film according to any one of clauses 16 to 18, wherein the pellicle film forms part of the optical element of any one of clauses 1 to 12. 27. A pellicle assembly for use in a lithographic apparatus, the pellicle assembly comprising a pellicle membrane according to any one of clauses 16 to 25. 28. Use of an optical element according to any one of clauses 1 to 12 or a pellicle film according to any one of clauses 16 to 26 in a lithographic apparatus or method. 29. A lithographic apparatus comprising an optical element according to any one of clauses 1 to 12 or a pellicle membrane according to any one of clauses 16 to 26.

Claims

1. 1. An optical element for a lithographic apparatus, the optical element being a pellicle assembly or a mirror, the optical element comprising: a top layer that self-limits thickness growth in an operating lithography apparatus or plasma-containing environment; an anchor layer selected to support the top layer; the top layer comprises one or more elements selected from the group consisting of Si, Ge, Sn, B, P, Mg, and Al, and optionally the top layer comprises an oxide of one or more of such elements; The optical element, wherein the anchor layer comprises one or more elements selected from the group consisting of Pt, Ru, Os, Rh, Ir, and Pd.

2. The optical element of claim 1 further comprising a substrate layer.

3. The optical element of claim 2 , further comprising a wetting layer disposed on the substrate layer, the wetting layer having a thickness of 5 nm or less.

4. 4. The optical element of claim 3, wherein the wetting layer comprises one or more elements selected from the group consisting of Cr, Ti, and Mo or nitrides of these elements, and optionally the wetting layer comprises TiN.

5. 4. The optical element of claim 3, wherein the wetting layer is a molybdenum layer, and the thickness of the molybdenum layer is between 0.1 nm and 1 nm thick.

6. The optical element of claim 1 or 2, wherein the anchor layer and the top layer form a plasma etch barrier.

7. 3. The optical element of claim 1, wherein the anchor layer comprises a ruthenium layer, the ruthenium layer having a thickness of 2 nm to 4 nm.

8. 3. The optical element of claim 1, wherein the optical element comprises an anchor layer-top layer combination selected from the list consisting of [Ru-SiOx], [Pt-SiOx], [Rh-SiOx], [Ru-GeOx], [Rh-GeOx], [Ru-SnOx], and [Rh-SnOx].

9. The optical element of claim 2 , wherein the substrate layer comprises carbon nanotubes.

10. The optical element of claim 1 , wherein the optical element comprises a carbon nanotube substrate and a molybdenum wetting layer.

11. The optical element of claim 10 , wherein the carbon nanotube substrate is a single-walled, double-walled, or multi-walled carbon nanotube.

12. The optical element of claim 1 , wherein the top layer comprises a silicon oxide layer, the silicon oxide layer having a thickness of 1 nm to 2.5 nm.

13. The optical element of claim 1 , wherein the optical element has an EUV transmission of greater than 90% and a thermal emissivity of greater than 50%.

14. The optical element of claim 3, wherein the optical element is a pellicle membrane, a portion of the pellicle membrane comprising a carbon nanotube substrate having a hollow core, and all surfaces of the carbon nanotube substrate are covered with one or more of the top layer, the anchor layer, and the wetting layer.

15. 6. A method for manufacturing an optical element according to any one of claims 1 to 5, comprising the step of depositing a top layer on the anchor layer via exposure to a plasma, preferably an electromagnetically induced plasma.

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