Pellicle for EUV lithography

Abstract

To solve one of problems accompanying pellicles produced according to known methods and known techniques for producing pellicles.SOLUTION: A mask includes at least one scribe line that overlaps at least part of the opposite side where at least one layer is substantially absent. A method for preparing a pellicle is provided, which includes the steps of providing a wafer that includes a mask and at least one layer on the opposite side of one surface, defining a scribe line on the mask, and selectively removing part of at least one layer that at least partially overlaps the scribe line. Furthermore, a method for preparing a pellicle is provided, which includes the steps of providing a pellicle core and removing at least a portion of the material from at least one surface of the pellicle core in a non-oxidizing environment. In any of the embodiments, the pellicle may include a metal nitride layer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS)

[0001] This application claims priority to EP application no. 18170855.3, filed May 4, 2018, which is hereby incorporated by reference in its entirety.

[0002] The present invention relates to a wafer, a method for preparing a wafer, a pellicle for a lithographic apparatus comprising said wafer, a method for preparing a pellicle, and a lithographic apparatus comprising a pellicle. [Background technology]

[0003] A lithographic apparatus is a machine constructed 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. mask) onto a layer of radiation-sensitive material (resist) provided on the substrate.

[0004]

[0004] The wavelength of 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. Lithographic apparatus using EUV radiation, which is electromagnetic radiation having a wavelength within 4-20 nm, can be used to form smaller features on a substrate than conventional lithographic apparatus, which can use electromagnetic radiation with a wavelength of, for example, 193 nm.

[0005]

[0005] A lithographic apparatus includes a patterning device (e.g. a mask or reticle). Radiation is transmitted through or reflected from the patterning device to form an image on the substrate. A pellicle may be provided to protect the patterning device from airborne particles or other forms of contamination. Contamination on the surface of the patterning device can cause manufacturing defects on the substrate.

[0006]

[0006] Pellicles can also be provided to protect optical components other than the patterning device. Pellicles can also be used to provide a passageway for lithographic radiation between regions of the lithographic apparatus that are sealed from one another. Pellicles can also be used as filters, such as spectral purity filters.

[0007]

[0007] Known pellicles may include freestanding membranes, such as, for example, silicon membranes, silicon nitride, graphene or graphene derivatives, carbon nanotubes, or other membrane materials. A mask assembly may include a pellicle that protects a patterning device (e.g., a mask) from particle contamination. The pellicle may be supported by a pellicle frame to form a pellicle assembly. The pellicle may be attached to a frame, for example, by gluing a pellicle boundary area to the frame. The frame may be permanently or removably attached to the patterning device.

[0008]

[0008] During use, the temperature of a pellicle in a lithographic apparatus can rise to anywhere between about 500° C. and 1000° C. or more. These high temperatures can be damaging to the pellicle. Therefore, improved techniques for dissipating heat are desirable to reduce the operating temperature of the pellicle and improve pellicle life.

[0009]

[0009] One approach to achieving this is to apply a thin metal film (coating layer) to the pellicle, for example a ruthenium film. The metal film increases the emissivity of the pellicle, thereby increasing the rate of heat emission from the pellicle, thereby lowering the equilibrium temperature at which the pellicle's rate of heat emission and rate of heat absorption are the same. The metal layer is applied on the face of the pellicle's core, which may be a silicon wafer, for example.

[0010]

[0010] Because the pellicle is in the optical path of the EUV radiation beam, it is necessary for the pellicle to be as particle-free as possible, since the presence of particles can cause imaging defects on the wafer and also hot spots on the pellicle, which can ultimately cause premature failure of the pellicle. Existing methods for preparing pellicles, including a core and a coating layer, produce a relatively large number of particles that can contaminate the surface of the pellicle.

[0011]

[0011] It is therefore desirable to provide a method for producing a pellicle that results in a pellicle with less particle contamination than pellicles produced using existing techniques, and a pellicle produced according to such a method.

[0012]

[0012] Additionally, since the pellicle must be sufficiently resilient to withstand the harsh environment within the lithography apparatus, and is in the 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 that can be imaged in a given period of time.

[0013]

[0013] It would therefore be desirable to provide a pellicle that exhibits improved EUV transmission while also exhibiting good performance and being reliably manufacturable.

[0014]

[0014] Although this application refers to pellicles generally in the context of lithographic apparatus, and specifically in the context of EUV lithographic apparatus, it will be appreciated that the present invention is not limited to pellicles and lithographic apparatus and that the subject matter of the present invention may be used in any other suitable apparatus or environment.

[0015] For example, the method of the present invention is equally applicable to spectral purity filters. Practical EUV 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 most prominent in the deep UV (DUV) radiation range (100-400 nm). Furthermore, for some EUV sources, such as laser-produced plasma EUV sources, the radiation emitted by the laser, typically at 10.6 microns, produces significant out-of-band radiation.

[0016]

[0016] Spectral purity is desirable in lithographic apparatus for several reasons. One reason is that resist is sensitive to radiation at out-of-band wavelengths, and exposure of the resist to such out-of-band radiation can degrade the image quality of the pattern applied to the resist. Furthermore, out-of-band infrared radiation, such as the 10.6 micron radiation in some laser-produced plasma sources, can cause unwanted and unnecessary heating of the patterning device, substrate, and optics in the lithographic apparatus. Such heating can damage or shorten the life of these elements, and / or cause defects or distortions in the pattern projected and applied to the resist-coated substrate.

[0017]

[0017] A typical spectral purity filter may be formed from a silicon base structure (e.g. a silicon grid or other member with apertures) coated with a reflective metal such as molybdenum. In use, a typical spectral purity filter may be subjected to high thermal loads, for example from incident infrared and EUV radiation. High thermal loads may cause the temperature of the spectral purity filter to exceed 800°C. Under high thermal loads, the coating may spall due to differences in the linear expansion coefficient between the reflective molybdenum coating and the underlying silicon support structure. The spalling and degradation of the silicon base structure is accelerated by the presence of hydrogen. Hydrogen is often used as a gas in the environment in which the spectral purity filter is used to suppress debris (e.g. debris such as particles) from entering or leaving certain parts of the lithographic apparatus. In this way, a spectral purity filter may be used as a pellicle and vice versa. Thus, any reference in this application to a "pellicle" is also a reference to a "spectral purity filter". Although this application primarily refers to a pellicle, all features may be equally applicable to a spectral purity filter.

[0018]

[0018] In a lithographic apparatus (and / or method), it is desirable to minimise intensity losses in the radiation used to apply a pattern to a resist coated substrate. One reason for this is that ideally as much radiation as possible is available for utilising in applying a pattern to a substrate, for example to reduce exposure times and increase throughput. At the same time, it is desirable to minimise the amount of unwanted radiation (e.g. out of band) that passes through the lithographic apparatus and is incident on the substrate. Furthermore, it is desirable to ensure that any spectral purity filters used in a lithographic method or apparatus have a reasonable lifetime and are suitable for use with the high thermal loads to which they may be exposed and / or the hydrogen (H * and H.O. *It is desirable to ensure that the spectral purity filters do not degrade rapidly over time as a result of photoinduced free radical species, including photoabsorption, ...

[0019]

[0019] Additionally, although this application generally refers to silicon pellicles, it will be appreciated that any suitable pellicle material may be used. For example, the pellicle may include any suitable carbon-based material, including graphene. Summary of the Invention

[0020]

[0020] The present invention has been made in consideration of the aforementioned problems associated with known methods of manufacturing pellicles and pellicles manufactured according to known techniques.

[0021] According to a first aspect of the present invention, there is provided a wafer comprising a mask on one side and at least one layer on an opposite side, the mask including at least one scribe line that overlaps at least a portion of the opposite side where the at least one layer is substantially absent.

[0022]

[0022] Some pellicles are manufactured by depositing one or more layers of material on the surface of a silicon wafer. Then, portions of the wafer are selectively removed to obtain the final pellicle. The silicon wafers used are circular, which is the common shape for silicon wafers due to the way they are produced. Due to the constraints of the wafer processing equipment, it is desirable to maintain the circular shape for as long as possible to facilitate the manipulation of the wafer. However, pellicles are generally not circular and therefore need to be shaped to remove excess material. This is conventionally done by etching grooves, also called scribe lines, into the silicon wafer. The scribe lines define the edge or perimeter of the pellicle and act as weak points through which the pellicle can be removed from the rest of the wafer. For practical reasons, the scribe lines are formed in the same step that etches the silicon wafer from below the material on the wafer surface to form a "window" through which EUV radiation passes during use of the pellicle in a lithography apparatus. The scribe lines can be formed in the mask and / or the wafer.

[0023]

[0023] With current techniques, it is inevitable that the material deposited on the wafer surface will bridge over the scribe lines because the etching process does not etch through the material deposited on the wafer surface. This bridged material is cut in a process known as "dicing". When excess material is removed from the material that will ultimately form the pellicle, the bridged material is broken and particle contamination is generated. These particles can remain on the surface of the pellicle and degrade the performance of the pellicle. Attempts have been made to overcome this problem by breaking the bridged material in the presence of a vacuum to suck up the generated particles. Also, attempts have been made to overcome this problem by protecting the film on the wafer surface with a cap. However, both of these attempts have proven unsuccessful.

[0024]

[0024] It will be appreciated that the term "overlie" assumes that the wafer is in a generally horizontal configuration, with the mask on the bottom surface of the wafer and at least one layer on the top surface of the wafer. The important feature is that the scribe line and the portion of the opposite surface where the at least one layer is substantially absent overlap each other, such that a line substantially parallel to the wafer surface passes through the scribe line and the portion where the at least one layer is substantially absent. Thus, preferably, the at least one layer does not extend over the entire wafer surface. It will also be appreciated that the scribe line may be inclined relative to the wafer surface, i.e., the scribe line may not be perpendicular to the wafer surface. In this case, overlapping is understood to mean positioned such that the scribe line connects the portions of the mask and at least one layer that have been removed or are otherwise absent. Thus, if the scribe line is etched through the wafer, the scribe line connects the two portions where the mask and at least one layer are substantially absent.

[0025]

[0025] The wafer preferably comprises silicon.

[0026]

[0026] Silicon is preferably used as it is a well-characterized and well-defined material in the field of lithography. Silicon also exhibits good EUV transmission and can withstand the conditions within a lithography apparatus. However, it will be appreciated that other suitable materials can be used and the invention according to the first aspect of the invention is not limited to silicon alone. Other suitable materials are those known to be used in pellicles.

[0027]

[0027] The mask may comprise a positive or negative resist. Positive and negative resist are well known terms in the art of lithography and any suitable resist may be used.

[0028]

[0028] When the mask comprises a negative resist, the resist is less soluble in a developer when exposed to radiation. Therefore, the pattern of the resist corresponds to the material that will not be removed from the wafer to form the pellicle. Thus, in the present invention, it is preferred that the mask comprises a negative resist.

[0029]

[0029] The mask serves to define which parts of the wafer will remain and which will be removed in subsequent processing steps. The mask includes at least one scribe line that outlines the perimeter of the pellicle that may ultimately be produced from the wafer. Thus, when using a negative resist, the scribe line is substantially free of resist to allow the material below the scribe line to be etched away. In one embodiment, the mask protects the material that forms the pellicle itself, i.e., the frame of wafer material that supports the layer of material that was initially deposited on one side of the wafer.

[0030] The at least one layer may include one or more of a membrane, a sacrificial layer, and a pellicle layer.

[0031]

[0031] While some pellicles are simple silicon pellicles, it has been found that the performance of the pellicle can be improved by providing one or more materials on the surface of the silicon, or by depositing material on the silicon and then removing the underlying silicon leaving only the material deposited on the surface of the silicon wafer to form the portion of the pellicle through which the EUV radiation passes.

[0032]

[0032] The pellicle layer may comprise at least one of a metal layer, an oxide layer, a nitride layer, a silicide layer, a semi-metallic layer, and a non-metallic layer. The pellicle layer may comprise any suitable material that is chemically and / or thermally stable at operating conditions in the lithographic apparatus and allows EUV transmission.

[0033]

[0033] Suitable metal layers may include molybdenum, zirconium, and / or ruthenium. The oxide layer may include silicon dioxide or a metal oxide. The nitride layer may include silicon nitride, silicon oxynitride, carbon nitride, boron nitride, or the like. The silicide layer may include a metal silicide, such as molybdenum silicide, ruthenium silicide, or zirconium silicide. The non-metal layer may include any suitable form of carbon, preferably graphene.

[0034]

[0034] Surprisingly, it has been found that the metal nitride layer can provide several advantages to the final pellicle. The metal nitride layer can include titanium nitride and / or tantalum nitride. The metal nitride layer can be of any suitable thickness. It is desirable for the pellicle to maximize the transmittance to radiation used in lithography, such as EUV radiation, while also preferably meeting other physical requirements suitable for use in a lithography machine, such as an EUV lithography machine. For this reason, it is preferable to make the pellicle as thin as possible while still maintaining the necessary physical characteristics required for the pellicle. The metal nitride layer can be about 0.1 nm to about 6 nm thick. Preferably, the metal nitride layer is less than about 1 nm thick. The metal nitride can function as a seed layer. Thus, the metal nitride can function as a layer on which another layer, sometimes referred to as a capping layer, is deposited. The capping layer can include any suitable material, including ruthenium, molybdenum, boron, zirconium, and combinations thereof. The capping layer can preferably include ruthenium. Surprisingly, it has been found that the metal nitride layer increases the emissivity of the pellicle, so that the same or better emissivity can be achieved with the same or a thinner metal layer thickness than conventional pellicles. It has also been found that the metal nitride layer reduces or prevents dewetting of an overlying metal layer, such as ruthenium. This allows the pellicle to sustain higher powers while maintaining its integrity. Thermal stability is also increased, which increases the pellicle's power capability. Yet another advantage is that the amount of pinholes in the pellicle layer is reduced, and the percentage of the pellicle surface that is covered by the metal layer is increased. This reduces drift in pellicle transmission over time with use by preventing oxidation of the underlying material. It is desirable to avoid changes in pellicle transmission with use to enable consistent wafer imaging. Additionally, the metal nitride layer can act as a barrier to slow or prevent the formation of metal silicides due to reaction of silicon with the metal layer.The metal nitride allows the pellicle to operate reliably at higher powers and / or temperatures by increasing the temperature at which silicon and the metal in the metal layer react to form a metal silicide. The metal nitride layer may be provided by any suitable method known in the art. For example, the metal nitride may be provided by atomic layer deposition or chemical vapor deposition.

[0035]

[0035] By making the pellicle layer sufficiently strong, the pellicle can be formed without a silicone support layer, so that in use, EUV radiation only needs to pass through the pellicle layer and not the silicone layer.

[0036]

[0036] The sacrificial layer may be any layer that can be easily removed from the wafer without damaging the wafer, and is preferably removed from the wafer prior to using the wafer as a pellicle.

[0037] The wafer may further include a protective layer.

[0038]

[0038] The protective layer preferably covers at least one layer (i.e., one or more layers of material deposited on one side of the wafer core). The protective layer acts as a barrier to prevent damage to the at least one layer and also acts as a support for the at least one layer when the wafer is etched away from below. Without the protective layer, the at least one layer may be damaged and / or the wafer may break along the scribe line if the at least one layer is not strong enough to support the weight of the silicon wafer.

[0039]

[0039] The protective layer may include at least one of a polymer, a resist, and a lacquer. It will be appreciated that any suitable protective layer may be used.

[0040]

[0040] Preferably, the protective layer comprises poly(p-xylylene) (parylene). It will be appreciated that any suitable polymer may be used. A polymer is suitable if it is non-reactive with at least one layer on the wafer and can be removed from the wafer without causing damage. For example, the protective layer may be dissolved with a solvent that does not dissolve the other materials that make up the wafer, or it may be reacted with a reactant that does not react, or reacts very slowly, with any of the other materials that make up the wafer.

[0041] According to a second aspect of the present invention, there is provided a method of preparing a pellicle, the method comprising the steps of providing a wafer including a mask on one side and at least one layer on an opposite side, defining scribe lines in the mask, and selectively removing portions of the at least one layer that at least partially overlap the scribe lines.

[0042]

[0042] Due to limitations in known methods of producing pellicles, there has been no suitable method of pellicle preparation that does not generate particle contamination that may be unnecessarily deposited on the pellicle surface. The method according to the second aspect of the present invention allows for the production of pellicles while minimizing particle generation. By selectively removing at least a portion of at least one layer that at least partially overlaps the scribe line, the wafer can be etched away without at least one layer straddling the scribe line. As a result, there is no need to dice or cut material straddling the scribe line, thus reducing particle generation.

[0043]

[0043] The mask can be a positive or negative resist, and the scribe lines can be defined in the resist using any suitable lithographic technique. Thus, the scribe lines can be formed in the mask using lithography.

[0044]

[0044] At least a portion of at least one layer can be removed by any suitable technique. Preferably, the technique used is etching, more preferably dry etching, although wet etching or a combination of dry and wet etching is also envisaged.

[0045] The method may further include providing a protective layer over at least a portion of the at least one layer.

[0046]

[0046] As in the first aspect of the present invention, the protective layer serves to support the wafer and can prevent damage to the wafer during etching, and can protect at least one layer on the wafer that may be damaged by etching.

[0047]

[0047] At least a portion of the protective layer can be removed to allow excess wafer material to be removed from the pellicle. The protective layer can be removed from substantially the entire wafer, or can be removed substantially along the scribe lines to allow the pellicle to be removed from excess material while leaving behind a protective and support layer on the pellicle.

[0048]

[0048] At least one layer may comprise any of the materials described with respect to the first aspect of the invention. Thus, the pellicle may comprise a metal nitride layer. A metal layer may be deposited on the metal nitride layer.

[0049] The protective layer may comprise any of the materials described in relation to the first aspect of the invention.

[0050] According to a third aspect of the present invention, there is provided a method of preparing a pellicle, the method comprising the steps of providing a pellicle core and removing at least a portion of material from at least one surface of the pellicle core in a non-oxidizing environment.

[0051]

[0051] It is desirable to provide a pellicle that provides high EUV transmission while maintaining the ability to withstand the harsh conditions in a lithography tool. Current EUV pellicles are extremely thin (less than about 100 nm) free-standing membranes suspended on a frame. Existing pellicles include a silicon core and an additional layer includes silicon nitride and molybdenum and / or ruthenium. The additional layer acts to extend the life of the pellicle, but at the cost of reduced EUV transmission and increased imaging impact, mainly due to EUV reflection. Efforts have focused on making pellicles as robust as possible to ensure that failures do not occur. However, making highly complex pellicles is expensive, and to enable high throughput of the lithography tool, it is necessary to increase the EUV transmission while reducing the impact on imaging of the pellicle. Reference to a pellicle can be considered to include reference to a wafer. Thus, a pellicle produced by a method according to the third aspect of the invention can be a wafer of the first and second aspects of the invention.

[0052]

[0052] The native oxide layer that develops between the pellicle core and the capping layer has been found to be one cause of EUV transmission loss. Efforts to reduce the thickness of this layer have been undertaken but have not yet been successful and have not been shown to eliminate the native oxide.

[0053]

[0053] In the method according to the third aspect of the invention, the native oxide layer is removed when the pellicle core is in a non-oxidizing environment, such as a vacuum, to avoid regrowth of the native oxide layer. The non-oxidizing environment may be substantially free of oxygen. It may include a non-reactive gas, such as a noble gas or nitrogen, or may include hydrogen. These gases are preferably at low pressure.

[0054]

[0054] The method may include removing at least a portion of the native oxide layer, and may alternatively or additionally include thinning the pellicle core material.

[0055]

[0055] By removing the native oxide layer, the EUV transmittance of the pellicle is increased, and the subsequent deposition of the capping layer(s) is more uniform, as the surface is more uniform on which the capping layer(s) are deposited. Furthermore, thinning the pellicle core has the same advantages, with the added benefit of further reducing the overall thickness of the final pellicle.

[0056]

[0056] The method may also include depositing a capping layer on at least one surface of the pellicle.

[0057]

[0057] The capping layer may be any of the materials described with respect to the first aspect of the invention, or any other suitable capping material. Prior to deposition of the capping layer, a metal nitride layer as described herein may be provided. As mentioned above, the presence of a metal nitride layer may provide a number of advantages to the final pellicle.

[0058]

[0058] The capping layer or layers can provide improved performance for the pellicle, for example, the capping layer can reduce the operating temperature of the pellicle by increasing the rate of heat release from the pellicle.

[0059]

[0059] Material may be removed from the pellicle by any suitable means. Preferably, material is removed by etching. Etching may be dry etching, wet etching, or a combination of the two. Dry etching may include sputtering of a silicon oxide layer. For example, a beam of ions of a noble gas may be directed at the undesired silicon oxide layer to remove it from the surface. Sputtering may continue to thin the pellicle core. Alternatively or additionally, C x F y The etching can also be performed using an etching gas such as a gas or the like.

[0060]

[0060] The capping layer is deposited under vacuum to prevent oxidation or other contamination. This reduces the risk of contaminants being trapped between the pellicle core and the capping layer, weakening the final pellicle. For this reason, the etching and deposition steps are preferably performed without removing the pellicle from a non-oxidizing environment. By keeping the pellicle in a non-oxidizing environment, regrowth of an oxide layer on the surface of the pellicle core is avoided.

[0061] According to a fourth aspect of the present invention there is provided a pellicle for a lithographic apparatus comprising a silicon core and one or more capping layers, the pellicle being substantially free of an oxide layer between the silicon core and the one or more capping layers.

[0062]

[0062] The absence of a native oxide layer in the pellicle results in a pellicle with increased transmission and improved uniformity of the capping layer or layers, which provides a more predictable and reproducible pellicle. The oxide layer that is removed is preferably silicon oxide.

[0063] A pellicle according to the fourth aspect of the invention may comprise any of the materials described in relation to the first aspect of the invention.

[0064]

[0064] Thus, the pellicle according to the fourth aspect of the present invention may include a metal nitride layer. The metal nitride layer may include ruthenium, molybdenum, boron, zirconium, titanium, tantalum, or a combination thereof. Preferably, the metal nitride layer includes at least one of titanium nitride and tantalum nitride.

[0065]

[0065] According to a fifth aspect of the present invention, there is provided a pellicle for a lithographic apparatus manufactured from or including a wafer according to the first or fourth aspect of the present invention, or a pellicle according to the second, third or seventh aspect of the present invention.

[0066] According to a sixth aspect of the present invention there is provided the use of a pellicle according to any of the first to fifth and seventh aspects of the present invention in a lithographic apparatus.

[0067] According to a seventh aspect of the present invention, there is provided a pellicle comprising at least one metal nitride layer.

[0068] As discussed above, the presence of a metal nitride layer provides a number of advantages over pellicles that do not include such a layer.

[0069]

[0069] The at least one metal nitride layer may comprise ruthenium, molybdenum, boron, zirconium, titanium, tantalum, or a combination thereof. Preferably, the at least one metal nitride layer comprises titanium nitride or tantalum nitride.

[0070]

[0070] The at least one metal nitride layer may have any suitable thickness. The at least one metal nitride layer may be about 0.1 nm to about 6 nm thick. Preferably, the at least one metal nitride layer is less than about 1.5 nm thick. In other pellicles, for example, a metal layer of molybdenum may be provided under the capping layer. The metal nitride layer may partially or entirely replace this molybdenum layer. Due to the advantageous properties provided by the metal nitride layer, the metal nitride layer may be thinner than a layer placed at a comparable position in other pellicles. Furthermore, if the metal nitride layer oxidizes during use, the resulting oxide layer is much thinner than the oxide layer produced by oxidation of the original layer, which is thicker than the metal nitride layer. This reduces the change in pellicle transmittance over time, which is desirable. If a metal layer, such as a molybdenum layer, is replaced with a metal nitride layer, such as titanium nitride, which is thinner than the molybdenum layer, the transmission of the resulting pellicle will increase, less change in EUV transmission will be observed during use, and the pellicle will be able to withstand higher powers or temperatures.

[0071]

[0071] The pellicle may include a metal capping layer deposited on at least one metal nitride layer. The metal capping layer may include ruthenium, molybdenum, boron, zirconium, titanium, tantalum, or a combination thereof. Preferably, the metal capping layer includes ruthenium.

[0072]

[0072] The metal capping layer can be of any suitable thickness. The metal capping layer can have a thickness of about 0.1 nm to about 6 nm.

[0073]

[0073] The pellicle may include one or more other layers known in the art. The pellicle may include a frame that supports the pellicle membrane.

[0074]

[0074] It will be appreciated that the first to seventh aspects of the invention may be combined in any combination, and that features described with respect to one aspect may be combined with features described with respect to another aspect of the invention. For example, a wafer produced according to the method of the third aspect of the invention may be used with a method according to the second aspect of the invention. Similarly, a wafer according to the first aspect of the invention may include a wafer formed according to the third aspect of the invention. That is, in a wafer according to the first aspect of the invention, there may be substantially no native oxide layer between the wafer and at least one layer, which may be a capping layer. In one example, any of the methods or apparatuses of any aspect of the invention may include a step of providing a metal nitride layer or have a metal nitride layer. Furthermore, advantages associated with features described with respect to one aspect of the invention are also applicable to other aspects of the invention.

[0075]

[0075] In summary, the method of the present invention allows the manufacture of pellicles with more predictable and reproducible performance than previous pellicles. The resulting pellicles are suitable for use in lithography equipment, such as EUV lithography equipment. It was not possible to manufacture such pellicles before. A pellicle manufactured according to the method of the present invention can withstand the high temperatures achieved during use of the pellicle and can also withstand attack by free radical species or other reactive species due to the coating material layers on each side of the pellicle. Furthermore, in embodiments where the method includes providing a metal nitride layer or the pellicle includes a metal nitride layer, the final pellicle benefits from the advantages of having the layers described herein.

[0076]

[0076] The invention will now be described with reference to silicon-based pellicles, however it will be appreciated that the invention is not limited to silicon-based pellicles and is equally applicable to spectral purity filters and core materials other than silicon. [Brief description of the drawings]

[0077]

[0077] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings.

[0078] [Figure 1] 1 depicts a lithography system including a lithographic apparatus and a radiation source according to an embodiment of the invention. [Diagram 2] 1 shows a schematic diagram of a prior art pellicle. [Figure 3a] 1 shows a pellicle and method according to first and second aspects of the present invention; [Figure 3b] 1 shows a pellicle and method according to first and second aspects of the present invention; [Figure 3c] 1 shows a pellicle and method according to first and second aspects of the present invention; [Figure 3d] 1 shows a pellicle and method according to first and second aspects of the present invention; [Figure 4] 1 shows a prior art method for covering a pellicle core. [Figure 5a] 3 shows a pellicle and method according to third and fourth aspects of the present invention; [Figure 5b] 3 shows a pellicle and method according to third and fourth aspects of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0079]

[0078] Figure 1 shows a lithographic system including a pellicle 15 manufactured according to the second, fourth, fifth and seventh aspects of the invention or according to the method of the first or third aspects of the invention according to an embodiment of the invention. The lithographic system includes a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate a beam of extreme ultraviolet (EUV) radiation 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 on the patterning device MA. The projection system is configured to project the radiation beam (which is now patterned by a mask MA) onto the substrate W. The substrate W may include a previously formed pattern. If this is the case, the lithographic apparatus aligns the patterned radiation beam B with the previously formed pattern on the substrate W. In this embodiment, a pellicle 15 is shown in the radiation path, protecting the patterning device MA, it will be appreciated that the pellicle 15 can be placed in any required location and can be used to protect any of the mirrors in the lithographic apparatus.

[0080]

[0079] The source SO, the illumination system IL and the 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 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.

[0081]

[0080] The radiation source SO shown in Fig. 1 is of a type sometimes referred to as a laser-produced plasma (LPP) source. A laser, which may be, for example, a CO2 laser, is arranged to deposit energy via a laser beam into a fuel, such as tin (Sn), provided by a fuel emitter. Although the following description refers to tin, any suitable fuel may be used. The fuel may be, for example, in the form of a liquid, or may be, for example, a metal or alloy. The fuel emitter may comprise a nozzle configured to direct the tin, for example in the form of droplets, along a trajectory towards the plasma formation region. The laser beam is incident on the tin in the plasma formation region. The deposition of the laser energy on the tin creates a plasma in the plasma formation region. During de-excitation and recombination of the plasma ions, radiation is emitted from the plasma, including EUV radiation.

[0082]

[0081] 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 discussed below.

[0083]

[0082] The laser may be separate from the radiation source SO. If this is the case, the laser beam may be passed from the laser to the radiation source SO by a beam delivery system (not shown) including, for example, suitable directing mirrors and / or beam expanders and / or other optics. The laser and the radiation source SO together may be considered as a radiation system.

[0084]

[0083] 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 of 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 an aperture of a closure structure of the radiation source.

[0085]

[0084] The radiation beam B travels from a radiation source SO into an illumination system IL 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. Together the facetted field mirror device 10 and the facetted pupil mirror device 11 impart a desired cross-sectional shape and a desired angular distribution to the radiation beam B. The radiation beam B exits the illumination system IL and is incident on a patterning device MA held by a support structure MT. The patterning device MA reflects and patterns the radiation beam B. The illumination system IL may also include other mirrors or devices in addition to or instead of the facetted field mirror device 10 and the facetted pupil mirror device 11.

[0086]

[0085] After reflecting from the patterning device MA, the patterned radiation beam B is incident on a projection system PS. The projection system comprises a number of mirrors 13, 14 arranged to project the radiation beam B onto a substrate W held by a substrate table WT. The projection system PS can apply a demagnification factor to the radiation beam to form images of features that are smaller than corresponding features on the patterning device MA. For example a demagnification factor of 4 can 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).

[0087]

[0086] The radiation source SO shown in Figure 1 may include components not shown. For example, a spectral filter may be provided within the radiation source. The spectral filter may be substantially transparent to EUV radiation but may substantially block radiation of other wavelengths, such as infrared radiation.

[0088]

[0087] Figure 2a shows a schematic diagram of a cross section of a pellicle produced according to a prior art method, in which the silicon support has already been etched away, leaving a boundary 18 and a wafer remainder 19 separated by a scribe line 16. A capping layer 17 spans the scribe line 16. Thus, to separate the boundary 18 from the wafer remainder 19, it is necessary to break or cut the capping layer 17 that spans the scribe line 16, which may generate undesirable particles that may contaminate the capping layer 17.

[0089]

[0088] Figure 2b shows a schematic plan view of the pellicle shown in Figure 2a. Boundary 18 is shown as a phantom line inside scribe line 16. It will be appreciated that scribe line 16 is not visible due to the presence of capping layer 17, but is shown for clarity. Boundary 18 of the silicon wafer acts as a frame around capping layer 17 to support it when used as a pellicle.

[0090] 3a shows a wafer according to the invention, comprising a wafer 23, a capping layer (at least one layer) 17, a scribe line 16, and a mask 20. The capping layer 17 is continuous on the surface of the wafer 23, and the mask 20 on the opposite side of the wafer 23 defines the scribe line 16. The capping layer 17 may comprise a metal nitride layer (not shown). The capping layer 17 may comprise a metal layer and a metal nitride layer disposed between the metal layer and the wafer 23. As mentioned above, the presence of the metal nitride layer has surprisingly been found to have a number of advantages.

[0091] 3b shows the wafer after a portion 27 of the capping layer 17 that overlapped the scribe line 16 has been removed. The arrows 21 show how at least a portion of the gap 27 in the capping layer 17 overlaps at least a portion of the scribe line 16.

[0092] In Figure 3c, a protective layer 22 has been applied to the wafer and the wafer 23 has been etched away where not protected by the mask 20. The etching process does not remove the protective layer 22. Importantly, there is no capping layer 17 spanning over the scribe lines 16.

[0093]

[0092] As shown in FIG. 3c, the protective layer 22 may have a protrusion 28 that extends into the gap 27.

[0094] In Figure 3d, the protective layer 22 has been removed and excess material has been removed to reach the pellicle. The remaining material of the wafer 23 acts as a frame to support the capping layer 17 when used as a pellicle. It will be appreciated that these figures are not drawn to scale and are used merely to illustrate the various layers of the pellicle and not to denote dimensions.

[0095]

[0094] Figure 4 shows a schematic diagram of a pellicle according to the prior art. The core material comprises a wafer 23 core covered by a native oxide layer 24. If a capping layer 25 is deposited on the wafer, the native oxide layer 24 is between the core 23 and the capping layer 25.

[0096]

[0095] Figure 5a shows the same wafer as shown in Figure 4, but the native oxide layer is removed from the wafer 23 in a non-oxidizing atmosphere or vacuum 26. A capping layer is subsequently deposited on the core in a non-oxidizing atmosphere or vacuum 26, resulting in a pellicle that is free of the native oxide layer. Once the native oxide layer is removed, a metal nitride layer (not shown) can be provided on the core layer. A metal capping layer can then be provided on the metal nitride layer. The metal nitride layer and metal layer can comprise any of the metals described with respect to any aspect of the invention.

[0097]

[0096] Figure 5b is similar to Figure 5a, but illustrates the case where the native oxide layer 24 is removed and the wafer 23 is thinned, resulting in a pellicle that is thinner and has better transmission than existing pellicles. After the native oxide layer is removed and / or the pellicle core is thinned, a capping layer 25 is deposited. Again, once the native oxide layer is removed and / or the pellicle core is thinned, a metal nitride layer can be provided. In this way, a metal nitride layer can be provided between the wafer 23 and the capping layer 25. Removing the native oxide layer and part of the pellicle core, followed by depositing the capping layer, is performed in a non-oxidizing environment.

[0098]

[0097] An embodiment of the present invention can also be described as expressed in the following clauses. 1. A wafer comprising a mask on one side and at least one layer on an opposite side, the mask including at least one scribe line that overlaps at least a portion of the opposite side where the at least one layer is substantially absent. 2. A wafer as described in clause 1, wherein the wafer comprises silicon. 3. A wafer as described in clause 1 or 2, wherein the mask comprises a positive or negative resist. 4. A wafer according to any of clauses 1 to 3, wherein the at least one layer comprises one or more of a membrane, a sacrificial layer, and a pellicle layer. 5. The wafer of clause 4, wherein the pellicle layer comprises at least one of a metal layer, an oxide layer, a nitride layer, a silicide layer, a semi-metallic layer, a non-metallic layer, and a metal nitride layer, and optionally, the metal layer and / or the metal nitride layer comprises ruthenium, molybdenum, boron, zirconium, titanium, tantalum, or a combination thereof. 6. The wafer of any of clauses 1 to 5, wherein the wafer further comprises a protective layer. 7. The wafer of clause 6, wherein the protective layer is disposed over the at least one layer, and the at least one layer is disposed between the protective layer and the mask. 8. The wafer of clause 7, wherein the protective layer has a protrusion that extends into a gap formed in at least one layer at a location on a portion of the opposite surface where the at least one layer is substantially absent. 9. A wafer according to any of clauses 6 to 8, wherein the protective layer comprises at least one of a polymer, a resist, and a lacquer, preferably the polymer is poly(p-xylylene). 10. An assembly including a wafer, a mask disposed on one side of the wafer, and at least one layer disposed on an opposing side of the wafer, the mask including at least one scribe line that overlaps at least a portion of the opposing side where the at least one layer is substantially absent. 11. The assembly of claim 10, wherein the wafer comprises silicon. 12. The assembly of clause 10 or 11, wherein the mask comprises a positive or negative resist. 13. An assembly according to any of clauses 10 to 12, wherein at least one layer comprises one or more of a membrane, a sacrificial layer, and a pellicle layer. 14. The assembly of clause 13, wherein the pellicle layer comprises at least one of a metal layer, an oxide layer, a nitride layer, a silicide layer, a semi-metallic layer, a non-metallic layer, and a metal nitride layer, and optionally, the metal layer and / or the metal nitride layer comprises ruthenium, molybdenum, boron, zirconium, titanium, tantalum, or a combination thereof. 15. The assembly of any of clauses 10 to 14, wherein the assembly further comprises a protective layer. 16. The assembly of clause 15, wherein at least one layer is disposed between the protective layer and the wafer. 17. The assembly of clause 16, wherein the protective layer has a protrusion that extends into a gap formed in the at least one layer at a portion of an opposing surface where the at least one layer is substantially absent. 18. The assembly of any of clauses 10 to 18, wherein the protective layer comprises at least one of a polymer, a resist, and a lacquer, preferably the polymer is poly(p-xylylene). 19. A method of preparing a pellicle, comprising the steps of providing a wafer including a mask on one side and at least one layer on an opposing side, defining scribe lines in the mask, and selectively removing portions of the at least one layer that at least partially overlap the scribe lines. 20. The method of claim 19, wherein the method further comprises providing a protective layer over at least a portion of the at least one layer. 21. The method of claim 19, wherein the method further comprises providing a protective layer over at least a portion of the at least one layer, such that at least a portion of the at least one layer is disposed between the protective layer and the mask. 22. The method of claim 20 or 21, wherein the protective layer is provided with a protrusion that extends into a gap formed by the selectively removed portion of the at least one layer. 23. The method of any of clauses 19 to 22, wherein the method further comprises etching at least a portion of the wafer. 24. The method of claim 23, wherein the method further comprises removing at least a portion of the protective layer. 25. The method of any of clauses 19 to 24, wherein the scribe lines and / or the mask are defined by lithography. 26. The method of any of clauses 19 to 25, wherein the at least one layer includes one or more of a membrane, a sacrificial layer, and a pellicle layer. 27. The method of any of clauses 23 to 26, wherein the etching is a dry etch, a wet etch, or a combination of the two. 28. The method of any of clauses 19 to 27, wherein the protective layer comprises at least one of a polymer, a resist, and a lacquer. 29. The method of claim 28, wherein the protective layer comprises poly(p-xylylene). 30. A method of preparing a pellicle, comprising: providing a pellicle core; and removing at least a portion of material from at least one surface of the pellicle core in a non-oxidizing environment. 31. The method of claim 30, wherein the method further comprises depositing a capping layer on at least one surface of the pellicle, optionally wherein the capping layer comprises a metal nitride layer and / or a metal layer. 32. The method of clause 30 or 31, wherein the material is removed by etching. 33. The method of claim 32, wherein the etching is a dry etch, a wet etch, or a combination of the two. 34. The method of claim 32 or 33, wherein etching is performed by directing a beam of ions of a noble gas onto the surface of the pellicle core. 35. The method of any of clauses 31 to 34, wherein the capping layer is deposited under vacuum. 36. The method of any of clauses 30 to 35, wherein the non-oxidizing environment is a vacuum. 37. A pellicle for a lithographic apparatus comprising a silicon core and one or more capping layers, wherein the pellicle is substantially free of an oxide layer between the silicon core and the one or more capping layers. 38. A pellicle for a lithographic apparatus manufactured from or comprising a wafer according to any of clauses 1 to 9 or an assembly according to any of clauses 10 to 18 or clause 37, or according to a method according to 19 to 36. 39. Use of a pellicle manufactured according to the method of clauses 19 to 36 or according to any of clauses 1 to 18 or clause 37 in a lithographic apparatus. 40. A pellicle for a lithographic apparatus, the pellicle comprising at least one metal nitride layer. 41. The pellicle of claim 40, wherein the at least one metal nitride layer comprises at least one of titanium nitride and tantalum nitride.

[0099]

[0098] Although specific embodiments of the present invention have been described above, it will be understood that the present invention can be practiced in ways other than as described. The above description is illustrative and not restrictive. Thus, it will be apparent to one skilled in the art that modifications can be made to the present invention as described without departing from the scope of the claims set forth below.

Claims

1. 1. An assembly comprising a wafer, a mask disposed on one side of the wafer, and at least one layer disposed on an opposing side of the wafer, the mask including at least one scribe line that overlaps at least a portion of the opposing side where the at least one layer is substantially absent.

2. The assembly of claim 1 , wherein the wafer comprises silicon.

3. 3. The assembly of claim 1 or 2, wherein the mask comprises a positive or negative resist.

4. The assembly of claim 1 , wherein the at least one layer comprises one or more of a membrane, a sacrificial layer, and a pellicle layer.

5. 5. The assembly of claim 4, wherein the pellicle layer comprises at least one of a metal layer, an oxide layer, a nitride layer, a silicide layer, a semi-metallic layer, a non-metallic layer, and a metal nitride layer, and optionally the metal layer and / or the metal nitride layer comprises ruthenium, molybdenum, boron, zirconium, titanium, tantalum, or a combination thereof.

6. The assembly of claim 1 , further comprising a protective layer.

7. The assembly of claim 6 , wherein the at least one layer is disposed between the protective layer and the wafer.

8. 8. The assembly of claim 7, wherein the protective layer has a protrusion that extends into a gap formed in the at least one layer at the portion of the opposing surface that is substantially free of the at least one layer.

9. 9. An assembly according to any of claims 6 to 8, wherein the protective layer comprises at least one of a polymer, a resist and a lacquer, preferably the polymer is poly(p-xylylene).

10. 1. A method of preparing a pellicle, comprising the steps of: providing an assembly including a wafer, a mask on one side, and at least one layer on an opposing side; defining scribe lines in the mask; and selectively removing a portion of the at least one layer that at least partially overlaps the scribe lines.

11. The method of claim 10 , wherein the method further comprises providing a protective layer over at least a portion of the at least one layer.

12. 11. The method of claim 10, wherein the method further comprises providing a protective layer over at least a portion of the at least one layer, such that the at least a portion of the at least one layer is disposed between the protective layer and the mask.

13. 13. The method of claim 11 or 12, wherein the protective layer is provided with a protrusion that extends into a gap formed by the selectively removed portion of the at least one layer.

14. The method of claim 10 , further comprising etching at least a portion of the wafer.

15. The method of claim 14 , further comprising removing at least a portion of the protective layer.

16. The method according to any of claims 10 to 15, wherein the scribe lines and / or the mask are defined lithographically.

17. The method of any of claims 10 to 16, wherein the at least one layer comprises one or more of a membrane, a sacrificial layer, and a pellicle layer.

18. 18. The method of any of claims 14 to 17, wherein the etching is a dry etch, a wet etch, or a combination of the two.

19. The method of any of claims 10 to 18, wherein the protective layer comprises at least one of a polymer, a resist, and a lacquer.

20. The method of claim 19, wherein the protective layer comprises poly(p-xylylene).

21. 1. A method of preparing a pellicle, comprising the steps of providing a pellicle core and removing at least a portion of material from at least one surface of the pellicle core in a non-oxidizing environment.

22. 22. The method of claim 21, wherein the method further comprises depositing a capping layer on at least one side of the pellicle, optionally wherein the capping layer comprises a metal nitride layer and / or a metal layer.

23. 23. The method of claim 21 or 22, wherein the material is removed by etching.

24. 24. The method of claim 23, wherein the etching is a dry etch, a wet etch, or a combination of the two.

25. 25. The method of claim 23 or 24, wherein the etching is performed by directing a beam of ions of a noble gas onto the surface of the pellicle core.

26. 26. The method of any of claims 22 to 25, wherein the capping layer is deposited under vacuum.

27. 27. The method of any of claims 21 to 26, wherein the non-oxidizing environment is a vacuum.

28. 1. A pellicle for a lithographic apparatus comprising a silicon core and one or more capping layers, said pellicle being substantially free of an oxide layer between said silicon core and said one or more capping layers.

29. A pellicle for a lithographic apparatus manufactured from or comprising a wafer according to any of claims 1 to 9 or claim 28 or according to the method of claims 10 to 27.

30. 28. Use of a pellicle manufactured according to the method of claims 10 to 27 or according to any of claims 1 to 9 or 28 in a lithographic apparatus.

31. A pellicle for a lithographic apparatus, the pellicle comprising at least one metal nitride layer.

32. 30. The pellicle of claim 28, wherein said at least one metal nitride layer comprises at least one of titanium nitride and tantalum nitride.

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