Metal silicide nitriding for stress reduction

Abstract

To solve problems with known pellicles and known methods of producing and designing pellicles.SOLUTION: The invention provides: a pellicle for a lithographic apparatus including nitridated metal silicide or nitridated silicon, and a method of manufacturing the same. Also disclosed is the use of a nitridated metal silicide pellicle or nitridated silicon pellicle in a lithographic apparatus. Also disclosed is a pellicle for a lithographic apparatus including at least one compensating layer selected and configured to counteract changes in transmissivity of the pellicle upon exposure to EUV radiation, as well as a method of controlling the transmissivity of a pellicle and a method of designing a pellicle.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] [Cross-reference of related applications]

[0001] This application claims priority to European Application No. 17200069.7 filed on 6 November 2017 and European Application No. 18179205.2 filed on 22 June 2018, both of which are incorporated herein by reference in their entirety.

[0002]

[0002] The present invention relates to a pellicle for a lithography apparatus, a method for manufacturing a pellicle for a lithography apparatus, a lithography apparatus equipped with a pellicle, and the use thereof. [Background technology]

[0003]

[0003] A lithography apparatus is a machine constructed to impart a desired pattern onto a substrate. A lithography apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithography apparatus can project a pattern from a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate.

[0004]

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

[0005]

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

[0006]

[0006] Pellicles can also be provided to protect optical components other than patterning devices. Pellicles can also be used to provide passages for lithography radiation between sealed areas of a lithography apparatus. Pellicles can also be used as filters, such as spectral purity filters. Because the inside of a lithography apparatus, especially an EUV lithography apparatus, can be a harsh environment, pellicles are required to exhibit excellent chemical and thermal stability.

[0007]

[0007] Known pellicles may include, for example, self-supporting graphene membranes, graphene derivatives such as graphene halides, graphane, fullerenes, carbon nanotubes, or other carbon-based materials. A mask assembly may include a pellicle that protects a patterning device (e.g., a mask) from particle contamination. The pellicle may also be supported by a pellicle frame to form a pellicle assembly. The pellicle can be attached to a frame, for example, by bonding the boundary region of the pellicle to the frame. The frame can be attached to the patterning device permanently or removablely. Self-supporting graphene membranes can be formed by floating a thin film of graphene on a liquid surface and scooping the thin film onto a silicon frame. The quality of membranes formed by this method has been known to be variable and difficult to control. Furthermore, it is difficult to reliably produce large graphene membranes.

[0008]

[0008] It is known that the lifespan of known pellicles, such as self-supporting graphene membranes and other carbon-based membranes, is limited.

[0009]

[0009] Known pellicles can be etched in an atmosphere containing free radical species such as H* and HO*, and are therefore known to degrade over time with use. Because pellicles are very thin, they can become brittle due to reactions with free radical species and eventually become non-functional. Therefore, alternative materials are needed for use as pellicles.

[0010]

[0010] In addition, it is known that the transmittance of the pellicle can change over time. This affects the amount of radiation that can pass through the pellicle, which can lead to underexposure or overexposure of the resist used in the lithography apparatus. Furthermore, a decrease in transmittance may cause the pellicle to operate at a higher temperature than it would otherwise, which can lead to pellicle damage and a reduction in pellicle life. Therefore, an alternative pellicle that does not change transmittance easily during use is desirable.

[0011]

[0011] High-melting-point metal silicides such as molybdenum disilicide, niobium disilicide, tantalum disilicide, and tungsten disilicide have been studied for use as gate materials, ohmic contacts, and heating elements due to their chemical and thermal stability and electrical conductivity. Until the present invention, it was not possible to use such materials as pellicles.

[0012]

[0012] Metal silicide compounds can be used in transistor gates. Transistor gates can be formed by depositing a layer of metal silicide compound on a silicon wafer. The metal silicide layer or metal silicide film can be deposited on silicon by vapor deposition techniques such as physical vapor deposition (PVD) or chemical vapor deposition (CVD). In the deposition step, a high-melting-point metal with a high melting point, such as molybdenum, is deposited on the silicon wafer and reacts there to form a metal silicide layer. To protect the metal silicide layer, a sacrificial layer of silicon or silicon oxide may be provided on the metal silicide layer. Such layered materials have been used in semiconductor devices to reduce the electrical resistance of silicon gate electrodes or silicon wiring layers formed on a semiconductor substrate or on source and drain regions, or diffuse wiring layers formed in the main plane of a single-crystal silicon semiconductor substrate, as much as possible.

[0013]

[0013] However, in the semiconductor industry, it has been found that such materials known for use in microelectronics are not suitable for use as pellicles. It will be understood that pellicles are much larger than microelectronics chips and are subjected to much harsher operating environments. In addition, while the electronic properties of such materials are most important when used in microelectronics, physical properties become more important when used as pellicles. Furthermore, since it has been impossible to manufacture metal silicide films larger than approximately 1 cm × 1 cm, known metal silicide films cannot be used as pellicles.

[0014]

[0014] In conventional manufacturing of self-supporting metal silicide films, the film is heated to approximately 900°C or higher to anneal it. Annealing brings the metal silicide to its minimum stress state at a specific temperature and increases the density of the metal silicide film. Upon cooling, the metal silicide shrinks more than the silicon substrate (e.g., silicon wafer) on which the metal silicide film grows, resulting in large tensile stresses within the metal silicide layer after cooling. The rest of the wafer is etched away to recover the metal silicide layer. The metal silicide layer floats in the etchant and becomes recoverable. However, the large tensile stresses within the metal silicide film are retained.

[0015]

[0015] Although we do not wish to be bound by scientific theory, it is thought that the metal silicide film formed by this method cannot grow beyond an area of ​​1 cm × 1 cm due to stress caused by the mismatch between the thermal expansion coefficient of the silicon substrate and the thermal expansion coefficient of the metal silicide film. In particular, the metal silicide film expands more than the silicon substrate when heated and contracts more when cooled, resulting in large tensile stress within the metal silicide layer.

[0016]

[0016] In order to increase the density of the metal silicide layer, it is necessary to anneal the metal silicide layer. If annealing is not performed before the material is used as a pellicle in the lithography apparatus, the material will become denser and shrink when heated during exposure in the lithography apparatus. As a result, large tensile stresses will be generated within the material, which may cause the pellicle to break.

[0017]

[0017] Another reason for exposing the pellicle film to high temperatures is to enable the deposition of high-quality sacrificial oxides. The deposition of the sacrificial oxide layer is intended to allow for the peeling of the extremely thin pellicle film. By depositing the sacrificial oxides at high temperatures, it is ensured that no microscopic pores are formed within the sacrificial oxide layer. Therefore, the deposition of sacrificial oxides necessary for pellicle recovery incorporates high temperatures into the manufacturing process. Sacrificial oxides can be produced by the decomposition of tetraethyl orthosilicate (TEOS). At temperatures above approximately 600°C, TEOS decomposes into silicon dioxide and diethyl ether.

[0018]

[0018] In practice, the metal silicide layer is deposited on the surface of a single-crystal silicon wafer. The wafer is then annealed, which can be achieved by heating it to a temperature of about 400°C to 600°C, for example, up to 500°C. The pellicle is then heated to a temperature of at least about 725°C, preferably at least about 750°C, to allow for the decomposition of sacrificial oxides such as TEOS and thermal oxides, as well as the stabilization of the metal silicide layer. These temperatures generate large tensile stresses of about 0.5 to 1.5 GPa, for example, 1 GPa, within the metal silicide film. The silicon wafer is preferably a single-crystal silicon wafer, but germanium wafers or wafers made from other materials suitable for EUV transmission can also be used.

[0019]

[0019] Such films, while having good density, have excessively high tensile stress, preventing them from growing large enough to be used as pellicles in lithography equipment, and are otherwise unstable due to their high internal stress.

[0020]

[0020] Therefore, it is desirable to provide a method for manufacturing a pellicle that enables the production of a metal silicide film that is large and stable enough to be used as a pellicle, preferably in a lithography apparatus, and especially in an EUV lithography apparatus. It is also desirable to provide a pellicle that is thermally and chemically stable and has higher strength than known metal silicide materials.

[0021]

[0021] This application generally refers to pellicles in the context of lithographic apparatuses, particularly EUV lithographic apparatuses, but the invention is not limited to only pellicles and lithographic apparatuses, and it is understood that the subject matter of the invention may be used in any other suitable apparatus or situation.

[0022]

[0022] For example, the method of the present invention can equally well be applied to spectral purity filters. EUV sources such as EUV sources that generate EUV radiation using a plasma actually emit not only the desirable "in-band" EUV radiation but also undesirable (out-of-band) radiation. This out-of-band radiation is most prominent in the deep UV (DUV) radiation range (100 to 400 nm). Further, in the case of some EUV sources, such as laser-produced plasma EUV sources, radiation from a laser of typically 10.6 microns can also form a significant undesirable (out-of-band) infrared (IR) radiation source.

[0023]

[0023] In a lithographic apparatus, spectral purity is desired for several reasons. One reason is that the resist is sensitive to wavelengths outside the band of the radiation, and thus, if the resist is exposed to such out-of-band radiation, the image quality of the exposure pattern imparted to the resist can be degraded. Further, out-of-band infrared radiation, such as the 10.6-micron radiation in some laser-produced plasma sources, causes unwanted and unnecessary heating of the patterning device, substrate, and optical components inside the lithographic apparatus. Such heating can lead to damage to these elements, a reduction in their lifespan, and / or defects or distortions in the pattern projected and imparted onto the resist-coated substrate.

[0024]

[0024] Typical spectral purity filters can be formed from a silicon membrane coated with a reflective metal such as molybdenum or ruthenium. During use, typical spectral purity filters may be exposed to high thermal loads from incident infrared and EUV radiation, for example. This thermal load can cause the temperature of the spectral purity filter to exceed 800°C, resulting in delamination of the coating. Delamination and degradation of the silicon membrane are accelerated by the presence of hydrogen, which is often used as a gas in the environment in which spectral purity filters are used to prevent debris (e.g., molecular outgassing from resists and particulate debris) from entering or leaving specific parts of the lithography equipment.

[0025]

[0025] Thus, the metal silicide film according to the present invention can be used as a spectral purity filter to block unwanted radiation, and can also be used as a pellicle to protect a lithography mask from particle contamination. Therefore, references to “pellicle” in this application also refer to “spectral purity filter” (these terms are interchangeable). Although this application primarily refers to pellicles, all features can be similarly applied to spectral purity filters. A spectral purity filter is understood to be a type of pellicle.

[0026]

[0026] In a lithographic apparatus (and / or method), it is desirable to minimize the loss of intensity of radiation used to pattern a resist-coated substrate. One reason for this is that, for example, in order to reduce the exposure time and increase the throughput, ideally as much radiation as possible should be available for patterning the substrate. At the same time, it is desirable to minimize the amount of unwanted (e.g., out-of-band) radiation incident on the substrate passing through the lithographic apparatus. Further, it is desirable that the pellicle used in a lithographic method or apparatus has a sufficient lifetime and does not rapidly deteriorate over time as a result of high thermal loads to which the pellicle can be exposed, and / or hydrogen (or similar species such as free radical species including H* and HO*) to which the pellicle can be exposed. Accordingly, it is desirable to provide an improved (or alternative) pellicle and a pellicle suitable for use, for example, in a lithographic apparatus and / or method.

[0027]

[0027] Further, although this application generally refers to molybdenum disilicide pellicles, it will be understood that any suitable metal silicide material can be used. For example, the pellicle may include zirconium disilicide, niobium disilicide, lanthanum disilicide, yttrium disilicide, and / or beryllium disilicide. Additionally, embodiments of the present invention relating to a pellicle having at least one sacrificial layer selected and configured to cancel out changes in the transmittance of the pellicle when exposed to EUV radiation, and related methods, may be applicable to pellicles including nitridated metal silicide or nitridated silicon, and may be applicable to any other type of pellicle.

Summary of the Invention

[0028]

[0028] The present invention has been made in view of the above problems related to known pellicles and known methods of producing and designing pellicles.

[0029]

[0029] According to a first aspect of the present invention, a pellicle for a lithography apparatus is provided, comprising a nitrided metal silicide or nitrided silicon.

[0030]

[0030] Surprisingly, it has been found that adding nitrogen to metal silicides results in numerous advantages over nitrogen-free metal silicides, or silicon layers, silicon wafers, silicon films, or the like. These advantages make it possible to provide pellicles containing metal silicide films, which was previously impossible. The metal silicide substrate may be a molybdenum silicide or zirconium silicide substrate.

[0031]

[0031] By nitriding a metal silicide substrate, nitrogen reacts with the metal silicide to form a metal silicide nitride on the pellicle substrate. The metal silicide nitride layer can be formed on a silicon substrate. The silicon substrate may be a silicon wafer. Similarly, to improve the strength of a polycrystalline silicon pellicle, it is possible to dope pure silicon with nitrogen. In this case, the substrate is substantially pure silicon.

[0032]

[0032] Firstly, surprisingly, it has been found that the addition of nitrogen keeps the film more amorphous than when nitrogen is not added. As a result, strength, heat resistance, and resistance to mechanical loads are increased. This is demonstrated by the improved tensile strength.

[0033]

[0033] In addition, the addition of nitrogen keeps the metal silicide film more compressed during the annealing process. As a result, although the metal silicide nitride film shrinks as it cools to room temperature, the degree of shrinkage is smaller than in the case without nitrogen addition, and consequently, the residual tensile stress inside the film at room temperature is smaller. Furthermore, during high-power exposure at high temperatures of approximately 450°C to 600°C, the film remains in a zero density of states state and without stress accumulation. In particular, because the pellicle is already dense at the time of deposition due to the addition of nitrogen, the pellicle does not shrink when heated, thereby making it more resistant to changes in density during use.

[0034]

[0034] A further surprising advantage of including nitrogen is the reduction of oxidation of the metal silide and the reduction of the native oxide thickness. Reduced susceptibility to oxidation improves the chemical and thermal stability of the metal silide, and the reduced thickness of the native oxide reduces the stress on the metal silide. Although we do not wish to be bound by scientific theory, it is thought that the native oxide layer generates compressive stress, which acts tensile stress on the pellicle film and thus weakens the film. Reducing the thickness of the native oxide layer is thought to reduce tensile stress. Furthermore, the reduction in the thickness of the native oxide also promotes improved EUV transmission. It is important that as much EUV radiation as possible can pass through the pellicle without being absorbed, in order to avoid a reduction in the power of the EUV radiation, which in turn reduces the overall efficiency of the device and thus the throughput of the device.

[0035]

[0035] It is also known that the addition of nitrogen to the metal silicide layer reduces the linear thermal expansion coefficient of the material. This reduces the tensile stress within the material caused by temperature changes, and by reducing the tensile stress, it becomes possible to create a larger film.

[0036]

[0036] Similar advantages can also be observed in silicon nitride pellicles.

[0037]

[0037] Preferably, the metal silicide nitride has the formula M x (Si) y N z where x ≦ y ≦ 2x and 0 < z ≦ x. The exact amount of nitrogen added can be adjusted according to the nature of the metal in the compound and the operating conditions for the pellicle. For example, compared to a molybdenum silicide compound, it is possible to include a greater amount of nitrogen in a zirconium silicide compound, because although an increase in the amount of nitrogen reduces EUV transmission, this is balanced by the improved transmission rate of zirconium, since zirconium has a higher transmission to EUV radiation than molybdenum.

[0038]

[0038] Thus, in the metal silicide nitride film, the atomic concentration of silicon is higher than that of the metal. Preferably, the atomic concentration of silicon is about twice that of the metal, i.e., y = 2x. It will be understood that non-stoichiometric values are possible. For example, the value of y can be any number between x and 2x, including x and 2x.

[0039]

[0039] Since the presence of nitrogen is necessary to provide desirable physical properties to the metal silicide film, the value of z is greater than zero. Adding nitrogen at high concentrations reduces the electrical conductivity of the metal silicide material, and at high nitrogen concentrations the EUV transmission rate decreases. Therefore, the nitrogen content of the metal silicide layer is preferably as low as possible while still being high enough to exhibit the above advantages. Having x less than 1 does not adversely affect the EUV transmission rate, but has been found to provide the mechanical advantages described herein. Therefore, the value of z is less than or equal to the value of x. Preferably, the value of z is 1 or less.

[0040]

[0040] Preferably, the nitrided silicon has the formula SiN aThe equation has the following properties: 0.01 ≤ a ≤ 1. Preferably, a ≤ 0.5, and more preferably a ≤ 0.1. Nitrogen-doped silicon is known to be used in microelectronics, but the maximum amount of nitrogen in doped silicon is about 1 nitrogen atom per 10,000 silicon atoms, i.e., 0.01 atomic percent. In the current context, this may mean that the maximum value of "a" is 0.0001. In lightly doped silicon, the value of "a" would be orders of magnitude smaller. Furthermore, in silicon nitride (Si3N4), the proportion of nitrogen atoms is greater than the proportion of silicon atoms, i.e., "a" > 1. Therefore, the pellicle equation of the present invention deviates from the equation used in microelectronics, and also from the equation when silicon nitride is used as a bulk material in bearings or turbochargers, for example.

[0041]

[0041] The formulas of the materials constituting the pellicle do not need to be stoichiometric. The formulas should be interpreted as being reduced to the least common denominator and / or shown in a shortened form. For example, if the formula of the film is Mo2Si4Ni1, then this should be interpreted as MoSi2Ni 0.5 It can also be expressed as follows. In another example, if the formula of the film is Zr3Si6Ni1, this can be expressed as ZrSi2N 0.33 It can also be expressed as follows. In reality, since silicon is only partially nitrided, the formula is not stoichiometric.

[0042]

[0042] Preferably, the metal (M) is selected from the group including Ce, Pr, Sc, Eu, Nd, Ti, V, Cr, Zr, Nb, Mo, Ru, Rh, La, Y, and Be. Preferably, the metal (M) is Mo, Zr, or Be.

[0043]

[0043] Typical compositions of the pellicle are ZrSi2N, MoSi2N, LaSi2N, and YSi2N. In each of these examples, x=1, y=2, and z=1.

[0044]

[0044] Other typical compositions are Mo2Si4N, Zr2Si4N, Mo3Si6N, and Zr3Si6N. As can be seen from these examples, the atomic concentration of nitrogen is less than the atomic concentration of the metal. Preferably, the atomic concentration of nitrogen is less than about 25% of the total atomic concentration of metal, silicon, and nitrogen. Therefore, it is preferable that the metal and silicon constitute more than about 75% of the total number of metal, silicon, and nitrogen atoms in the metal silicide film. In other words, more than about 75% of the total atoms in the metal silicide nitride pellicle are metal or silicon atoms, and the remaining about 25% are nitrogen atoms.

[0045]

[0045] The nitrogen atomic concentration may be less than about 20%, less than about 15%, less than about 10%, less than about 5%, or less than about 1%.

[0046]

[0046] The pellicle may further include at least one capping layer. The pellicle may include a capping layer on each side of the metal silide nitride or nitrided silicon film. The metal silide nitride or nitrided silicon film may have a thickness of 10 nm to about 40 nm, preferably about 15 nm to about 30 nm. At least one capping layer may have a thickness of about 0.1 nm to about 10 nm, preferably about 1 nm to about 5 nm. The capping layer may include any suitable capping material. Suitable capping materials are thermally and chemically stable in the environment of the EUV lithography apparatus and do not significantly impede the transmission of EUV through the pellicle. The capping layer must also conform to the pellicle so that it can adhere to the nitrided metal silide or silicon. Suitable coating materials include ruthenium Ru, boron B, metal boride, carbon boride B4C, boron nitride BN, or similar.

[0047]

[0047] The capping material can be applied using any preferred method, such as chemical vapor deposition or sputtering.

[0048]

[0048] In reality, M xSi y N z can be manufactured at ambient temperature on a wafer. The wafer may then be etched in a suitable liquid, and the pellicle film may be lifted from the liquid onto the frame. In this case, the addition of nitrogen mainly increases the density of the film, and thus the heat resistance. This can be used to produce EUV filters for various applications. M x Si y N z can also be manufactured using a CMOS (Complementary Metal Oxide Semiconductor) process incorporating high-temperature annealing and high-temperature deposition of a sacrificial oxide. The low thermal expansion coefficient resulting from the addition of nitrogen and the improved resistance to structural changes resulting from the addition of nitrogen mainly help to reduce stress and enable the production of full-size pellicles.

[0049]

[0049] According to a second aspect described herein, there is provided a method of manufacturing a pellicle for a lithographic apparatus, the method comprising nitriding a metal silicide substrate or a silicon substrate.

[0050]

[0050] Nitriding of the metal silicide or silicon is caused by sputtering the metal silicide substrate or the silicon substrate with a plasma. The sputtering may be reactive sputtering. The plasma may be any suitable plasma. The plasma preferably contains nitrogen. Preferably, the plasma contains a mixture of argon and nitrogen gas. Argon gas is included to provide an inert atmosphere. Argon is preferably used because it is less expensive than other noble gases, but other noble gases may be used.

[0051]

[0051] The ratio of argon to nitrogen can vary. A higher proportion of nitrogen in the gas mixture results in a greater amount of nitrogen being incorporated into the metal silicide film. For example, when the nitrogen flow rate ratio, calculated by dividing the amount of nitrogen by the amount of argon added to nitrogen, was approximately 10%, the atomic concentration of nitrogen in the metal silicide nitride film was approximately 18%. When the nitrogen flow rate ratio was approximately 40%, the atomic concentration of nitrogen in the metal silicide nitride film was approximately 42%. Similarly, as the nitrogen flow rate ratio increased from 10% to 40%, the atomic concentration of oxygen decreased correspondingly from approximately 34% to approximately 15%, indicating a reduction in the thickness of the native oxide layer. Therefore, the ratio of argon to nitrogen can vary depending on the required degree of nitriding.

[0052]

[0052] The metal that forms the metal silicide may be selected from the group including Ce, Pr, Sc, Eu, Nd, Ti, V, Cr, Zr, Nb, Mo, Ru, Rh, La, Y, and Be. Of this group, molybdenum, zirconium, and beryllium are preferred elements. Molybdenum is the most preferred.

[0053]

[0053] Due to the limitations of known methods for producing pellicles, to date there has been no suitable method for producing pellicles containing metal silide.

[0054]

[0054] Nitrided metal silicide materials have so far been used only to form gates in semiconductor transistors, but these gates are orders of magnitude smaller than pellicles and do not need to withstand the harsh thermal and chemical environments of lithography equipment, especially EUV equipment.

[0055]

[0055] Accordingly, according to a third aspect of the present invention, a pellicle for a lithography apparatus is provided which is obtainable or obtainable by the method according to the second aspect of the present invention.

[0056]

[0056] According to a fourth aspect of the present invention, the use of a pellicle manufactured by the method according to the second aspect of the present invention, or a pellicle according to the first aspect of the present invention, in a lithography apparatus is provided.

[0057]

[0057] It has been impossible to manufacture metal silide pellicles that possess the required physical properties for use as pellicles, and therefore it has been impossible to use such pellicles in lithography equipment. Furthermore, surprisingly, it has been found that nitriding silicon can increase the strength of the silicon pellicle as a result.

[0058]

[0058] According to a fifth aspect of the present invention, the use of reactive sputtering is provided for manufacturing a pellicle according to the first aspect of the present invention.

[0059]

[0059] According to a sixth aspect of the present invention, an assembly for a lithography apparatus is provided, comprising a pellicle according to any of the above aspects of the present invention, a frame supporting the pellicle, and a patterning device attached to the frame.

[0060]

[0060] According to a seventh aspect of the present invention, a pellicle for a lithography apparatus is provided, comprising at least one compensating layer selected and configured to counteract changes in the transmittance of the pellicle when exposed to EUV radiation.

[0061]

[0061] It is known that the transmittance of a pellicle changes when exposed to EUV radiation. The change may be irreversible. The change may occur rapidly when exposed to EUV, or the degree of the change may depend on the length of time the pellicle is exposed to EUV radiation and the power level used. Changes in transmittance can be caused by many factors. For example, certain materials used in pellicles oxidize when exposed to the occasional extreme temperatures in the EUV lithography apparatus. The oxides produced during the use of the pellicle are volatile, such as silicon oxide or carbon monoxide. Therefore, these gaseous oxides may leave the pellicle, reducing the thickness of the pellicle over time, which increases the transmittance of the pellicle. In contrast, certain oxides remain on the pellicle, and these may have lower transmittance than the material in its unoxidized form. Changes in transmittance may also occur due to erosion or etching of the material from the pellicle during use, with or without oxidation.

[0062]

[0062] To date, changes in the permeability of the pellicle during use and the limits of the pellicle's lifespan have been accepted as inevitable, or attempts have been made to prevent oxidation of the materials constituting the pellicle by including oxidation-resistant materials within the pellicle. The compensating layer can be sacrificed by being removed from the pellicle or by physically changing while remaining as part of the pellicle. Therefore, the compensating layer can be a sacrificial layer.

[0063]

[0063] The seventh aspect of the present invention takes a different approach from the prior art by attempting to balance the change in transmittance of one material in the pellicle by including another material that exhibits the opposite change in transmittance when exposed to EUV radiation.

[0064]

[0064] Preferably, at least one compensation layer includes a material that, when exposed to EUV radiation, alters to increase or decrease the transmittance of at least one compensation layer.

[0065]

[0065] At least one compensating layer is configured such that a change in the transmittance of at least one compensating layer reflects a change in the transmittance of the pellicle, such that the overall transmittance of the pellicle remains substantially constant. It will be understood that the transmittance of the pellicle will not always remain perfectly constant, as the compensating layer will eventually be completely sacrificed. Even so, the presence of a compensating layer selected and configured to counteract the change in the transmittance of the pellicle will extend the operational life of the pellicle.

[0066]

[0066] The compensation layer may contain one or more of silicon dioxide, silicon, silicon nitride, silicon carbide, carbon, boron carbide, ruthenium dioxide, boron, zirconium boride, and molybdenum. The compensation layer may contain any material that can withstand the conditions inside the EUV lithography apparatus and whose transmittance changes when exposed to EUV radiation.

[0067]

[0067] Boron, zirconium boride, and molybdenum are known to exhibit a decrease in EUV transmittance when exposed to EUV radiation. Not wishing to be bound by scientific theory, but for illustrative purposes, when exposed to the operating conditions of an EUV lithography apparatus, boron may oxidize to produce boron oxide. Since boron oxide has a much greater EUV absorption effect than boron, the formation of boron oxide on the pellicle results in a decrease in transmittance. Therefore, these materials can be used to counteract the increase in EUV transmittance.

[0068]

[0068] On the other hand, silicon dioxide, silicon, silicon nitride, silicon carbide, carbon, boron carbide, and ruthenium dioxide are known to exhibit increased EUV transmittance when exposed to EUV radiation. Again, not wishing to be bound by scientific theory, but for illustrative purposes, carbon can be oxidized to form carbon monoxide or carbon dioxide. Both of these compounds are gaseous under the operating conditions of the EUV lithography apparatus and therefore leave the pellicle. Over time, the decrease in material leads to an increase in the transmittance of the pellicle.

[0069]

[0069] Therefore, a compensating layer can be provided on the pellicle to take into account the tendency of the pellicle material to increase or decrease the EUV transmittance during use. The thickness of the compensating layer may be adjusted to provide an oxide layer of sufficient thickness to counteract or compensate for the loss of pellicle material over the life of the pellicle, or to provide sufficient material to counteract the decrease in pellicle transmittance as it leaves the pellicle.

[0070]

[0070] According to an eighth aspect of the present invention, a method is provided for controlling a change in the transmittance of an EUV pellicle, the method comprising the step of providing at least one layer whose transmittance increases when exposed to EUV radiation, and / or at least one layer whose transmittance decreases when exposed to EUV radiation.

[0071]

[0071] Surprisingly, it has been found that it is possible to control the transmittance of the pellicle during use in an EUV lithography apparatus by providing at least one layer, sometimes called a compensating layer, whose transmittance increases or decreases (as appropriate) when exposed to EUV radiation and / or when exposed to the operating environment of an EUV lithography apparatus. To date, attempts have been made to prevent the degradation of the pellicle by preventing physical changes such as oxidation and etching of the pellicle. In contrast, the method according to the eighth aspect of the present invention solves the problem of fluctuating transmittance of the pellicle by providing a compensating layer.

[0072]

[0072] According to a ninth aspect of the present invention, a method is provided for designing a pellicle for a lithography apparatus, the method comprising the steps of measuring a change in the transmittance of a pellicle when exposed to EUV radiation, and selecting one or more materials using the measured change in transmittance to be included in a new pellicle, the one or more materials having a change in transmittance that most closely reflects the change in the transmittance of the pellicle when exposed to EUV radiation. Once selected, the materials constituting the compensation layer are added to the pellicle to thus form a pellicle containing the identified materials.

[0073]

[0073] This method makes it possible to produce a pellicle that has a more stable transmittance than conventional pellicles when in use. Changes in the transmittance of the pellicle, or material that can function as a compensating layer, can be measured periodically using known techniques and equipment. Thus, it is possible to measure how the transmittance of the pellicle changes over time and then compare it with a material that shows the opposite change, and as a result when the pellicle and the material are combined to form an updated pellicle, they cancel each other out so that the transmittance of the pellicle is more constant than that of the original pellicle.

[0074]

[0074] The change in the transmittance of the pellicle when exposed to EUV radiation may be measured over a predetermined length of time. The predetermined length of time is approximately the same as the time the pellicle is used in the EUV lithography apparatus.

[0075]

[0075] Since the pellicle is preferably meant to withstand use in the EUV lithography machine for at least one day, and preferably for a longer period, the measured change in transmittance is taken over a period roughly the same as the expected lifespan of the pellicle. This allows for the determination of the change in the pellicle's transmittance over time and for more accurate selection of the sacrificial compensation layer. For example, the pre-selected period may be between 1 and 24 hours, but may be up to 7 days if necessary.

[0076]

[0076] The change in the transmittance of the pellicle when exposed to EUV radiation may be measured at a pre-selected temperature and / or power level. The temperature and / or power level may be approximately the same as the temperature and / or power level to which the pellicle is exposed during use in the EUV lithography apparatus.

[0077]

[0077] In order to provide a suitable model of the change in pellicle transmittance, it is necessary to expose the pellicle to the conditions under which it will be used. This allows for the selection of the most appropriate compensating layer to be included in the updated pellicle. For example, the pellicle may be tested at temperatures ranging from about 400°C to a maximum of about 900°C. For example, the pellicle may be tested at power levels ranging from about 50W to about 500W.

[0078]

[0078] Once the updated pellicle, including the sacrificial compensation layer, is provided, the updated pellicle can be subjected to further testing to determine how the transmittance of the updated pellicle changes over time under the conditions inside the EUV lithography apparatus. Based on this further information, the updated pellicle can then be improved and refined by adjusting the compensation layer, for example, by changing the thickness, position, and / or composition of the compensation layer. This refinement can be repeated until an optimized pellicle is achieved.

[0079]

[0079] According to a tenth aspect of the present invention, a pellicle designed in accordance with the method of the eighth or ninth aspect of the present invention is provided.

[0080]

[0080] The pellicle according to the tenth aspect of the present invention exhibits improved stability with respect to EUV transmittance compared to other pellicles.

[0081]

[0081] According to an eleventh aspect of the present invention, a method is provided for manufacturing a membrane assembly for EUV lithography, the method comprising: providing a stack comprising a planar substrate including an internal region and a boundary region around the internal region; at least one membrane layer; an oxide layer between the planar substrate and at least one membrane layer; and at least one further layer between the planar substrate and at least one membrane layer; and selectively removing the internal region of the planar substrate, thereby the membrane assembly comprising at least a membrane formed from at least one membrane layer and a boundary holding at least one membrane layer, wherein the boundary comprises at least a portion of the planar substrate, at least one further layer, and an oxide layer located between the boundary and at least one membrane layer.

[0082]

[0082] It has been noted that some membrane layers are prone to weakening during manufacturing due to over-etching. Different etching processes etch different materials at different rates. Therefore, in a particular etching process, one material may be etched at a different rate than another. Furthermore, it has been found that during etching, certain parts of a given layer may be etched at a different rate than other parts of the same layer. In particular, the edges of a given layer are generally etched at a faster rate than the central parts of that given layer. Although we do not wish to be bound by scientific theory, it is thought that the etchant solution may be diluted by the etching product in the central region of a given layer more than in the edges of the same layer. Therefore, the etching rate near the central part of a given layer is reduced compared to the edges of the same layer, resulting in non-uniform etching. The degree of non-uniformity determines the minimum thickness of the etched layer and ultimately leads to a lack of uniformity in the final membrane assembly. This non-uniformity may weaken the membrane layer, leading to premature failure of the membrane layer in use or requiring more frequent replacement of the pellicle, including the stack, compared to when there is no non-uniformity.

[0083]

[0083] According to the method of the eleventh aspect of the present invention, the presence of at least one additional layer between the planar substrate and at least one membrane layer may help reduce or overcome the problem of over-etching. Preferably, the at least one additional layer is etched at a rate significantly slower than the oxide layer. Preferably, the at least one additional layer is substantially resistant to the etchant used to etch the oxide layer. Therefore, during the bulk etching step of the planar substrate, the etching process continues to etch away the internal regions of the planar substrate until it reaches an oxide layer, which may also be called an embedded oxide layer. The etchant used to etch away the internal regions of the planar substrate may be a tetramethylammonium hydroxide (TMAH) based etchant or other suitable etchant known in the art that selectively etches silicon relative to silicon oxide. The oxide layer is substantially resistant to the etchant used to etch away the internal regions of the planar substrate, and therefore, upon reaching the embedded oxide layer, the etching process stops or slows down significantly. The above etchants do not etch away the embedded oxide layer, or etch it away only at a very slow rate, meaning there is a low risk of over-etching the embedded oxide layer. Subsequently, at least a portion of the embedded oxide layer is removed using an etchant capable of etching away the embedded oxide layer. Suitable etchants include buffer oxide etchants (BOE), as known in the art. The etchant used etches at least one further layer at a slower rate than the oxide layer, so any over-etching of the embedded oxide layer does not lead to at least one further layer. Because the embedded oxide layer is thin, only a short etching time is required to remove it, reducing the likelihood of uneven etching of at least one further layer overlapping it. At least one further layer can then be removed using a second etching step with a TMAH etchant or other suitable etchant that selectively etches silicon relative to silicon oxide.Indeed, an oxide layer superimposed on at least one additional layer is resistant to the etchant used to etch away at least one additional layer, thus reducing the risk of over-etching, and the resulting stack contains a more uniform oxide layer beneath at least one membrane layer.

[0084]

[0084] A further advantage of the eleventh aspect of the present invention is that the embedded oxide layer between the planar substrate and at least one membrane layer can be made thinner. Wrinkling can weaken the membrane assembly, but this advantage reduces the tendency for wrinkles to form in the membrane assembly. This is because the oxide layer contains compressive stress, and having a thinner oxide layer reduces the compressive stress inside the stack.

[0085]

[0085] Preferably, at least one membrane layer comprises molybdenum silicon nitride, but it will be understood that the present invention can be applied to any membrane layer, such as pSi. At least one membrane layer may be any of the membrane layers described in relation to any aspect of the present invention. For example, the membrane layer may comprise nitrided metal silicide or silicon. Molybdenum silicon nitride is highly sensitive to over-etching using buffer oxide etching (BOE), including HF. Again, although we do not wish to be limited to scientific theory, it is thought that when the sacrificial layer of silicon dioxide on top is removed, the silicon nitride in the molybdenum silicon nitride is also etched, thereby creating notches that weaken the layer. If the etching step is continued for an excessively long time, the entire layer may be damaged or destroyed. The present invention helps to overcome this problem.

[0086]

[0086] Preferably, at least one further layer comprises silicon. Preferably, at least one further layer comprises cSi, pSi, or aSi. In the TMAH etchant, silicon is etched faster than silicon oxide, while in the BOE, silicon oxide is etched faster than silicon. Therefore, it is possible to selectively remove the silicon layer or the silicon oxide layer without etching the overlying silicon oxide layer or silicon layer, respectively.

[0087]

[0087] There may be further oxide layers, which may be thermal oxide layers between at least one further layer and at least one membrane layer. Thus, the order of the layers in the stack from top to bottom may be membrane layer, thermal oxide layer, silicon layer, embedded oxide layer, planar substrate. The membrane layer may be capped with a layer of tetraethyl orthosilicate (TEOS), which can be converted into a silicon oxide layer.

[0088]

[0088] The planar substrate may contain silicon. Silicon is a well-characterized material that can withstand the harsh environment inside a lithography apparatus during use.

[0089]

[0089] The step of removing the internal region of the planar substrate may include etching using a TMAH etchant. The stack may be exposed to the etchant until the etchant reaches the embedded oxide layer.

[0090]

[0090] The embedded oxide layer can then be removed using a different etchant, for example, BOE. Different etchants can be used until the etchant reaches at least one further layer which may contain silicon.

[0091]

[0091] Next, at least one further layer can be etched away using a further etching step with TMAH etchant. The etchant can be used until it reaches the thermal oxide layer.

[0092]

[0092] According to a twelfth aspect of the present invention, a membrane assembly for EUV lithography is provided, which comprises a membrane formed from at least one layer comprising molybdenum silicon nitride and a boundary holding the membrane, the boundary region being formed from a planar substrate comprising an internal region and a boundary region around the internal region, the boundary being formed by selectively removing the internal region of the planar substrate, and the assembly comprising an embedded oxide layer, a silicon layer and a thermal oxide layer between the boundary and the membrane.

[0093]

[0093] A membrane assembly according to a twelfth aspect of the present invention includes a thermal oxide layer that is thinner than the thermal oxide layer of other assemblies. Because thermal oxide is compressible, this can cause wrinkles in the membrane layer. Having a thinner oxide layer reduces compressive force and thus reduces wrinkles in the membrane. In addition, etching of the thermal oxide is more uniform, and as a result, radiation transmission through the assembly is more uniform.

[0094]

[0094] Preferably, the planar substrate contains silicon.

[0095]

[0095] An assembly manufactured according to the 11th aspect of the present invention or according to the 12th aspect of the present invention can be used as a pellicle, preferably in an EUV lithography apparatus.

[0096]

[0096] According to a thirteenth aspect of the present invention, a method for preparing a stack is provided, comprising the steps of providing a planar substrate, a membrane layer, and a tetraethyl orthosilicate layer, and annealing the stack, wherein the tetraethyl orthosilicate layer contains boron, and at least a portion of the boron from the tetraethyl orthosilicate layer diffuses into the membrane layer during annealing.

[0097]

[0097] Membrane layers, such as those containing pSi and molybdenum silicon nitride, are susceptible to over-etching, which can reduce the strength of the layer and lead to premature failure. It is desirable to prevent over-etching, which can be achieved by adding an additional sacrificial layer that functions as an etching homogenization layer, as described above. Alternatively, or in addition to that, it has been found that it is possible to make such membrane layers more resistant to etching by adding boron to the layer. It has been found that adding boron to silicon reduces the etching rate in the TMAH to about 1 / 100th. Although we do not wish to be bound by scientific theory, it is thought that boron preferentially occupies the grain boundaries within the membrane layer. Furthermore, since the pellicle is thought to be highly sensitive to etchants, especially at the grain boundaries, the presence of boron at the grain boundaries is thought to be the reason for the higher etching resistance of the resulting film.

[0098]

[0098] It has been found that the addition of boron to the TEOS layer and subsequent annealing causes the diffusion of boron into the membrane layer. For molybdenum silicide and molybdenum silicon nitride membranes, this has been found to increase the consistency of the physical properties of membrane assemblies fabricated from the stack according to this embodiment of the present invention, i.e., there are fewer fragile assemblies. Furthermore, it is possible to produce larger membrane assemblies, and the resulting membrane assemblies perform in thermal load testing similarly to boron-free membrane assemblies.

[0099]

[0099] In addition, the pSi layer manufactured according to this method is at least about 50% stronger than a similar layer that does not contain boron. In fact, the exact limit of the increase in strength has not yet been determined, as the tested samples did not malfunction at the limits of the test apparatus (3 GPa). In addition, the EUV transmittance of such a membrane containing boron is not reduced. Furthermore, the emissivity of the pSi membrane manufactured according to this method is much higher than that of the pSi membrane without boron. This increased emissivity is beneficial because it reduces the importance of the performance of any metal cap and may even make it possible to eliminate the radioactive metal cap altogether.

[0100] [000100] The planar substrate may contain any suitable material. Preferably, the planar substrate contains silicon.

[0101] [000101] The membrane layer may contain any suitable material. Preferably, the membrane layer contains at least one of silicon, molybdenum silicide, and molybdenum silicon nitride.

[0102] [000102] Annealing may be carried out at any suitable temperature. The temperatures at which TEOS is annealed are known in the art. Preferably, annealing is carried out at temperatures between about 400°C and about 1000°C. For example, annealing may be carried out at 600°C, 700°C, 800°C, or 900°C, and intermediate temperatures. Annealing may be carried out at a constant temperature or at an unspecified temperature.

[0103] [000103] The tetraethyl orthosilicate layer may contain about 0.1% to about 15% by weight of boron, preferably about 2% to about 10% by weight of boron, and more preferably about 4% to about 8% by weight of boron.

[0104] [000104] The TEOS layer can be provided by chemical vapor deposition or any other suitable technique.

[0105] [000105] According to a fourteenth aspect of the present invention, a stack is provided which includes a planar substrate and a membrane layer, wherein the membrane layer is doped with boron.

[0106] [000106] The planar substrate may contain silicon.

[0107] [000107] The membrane layer may surround the planar substrate, at least partially. The membrane layer may comprise at least one of silicon, molybdenum silicide, molybdenum silicon nitride, or any other membrane layer material described herein.

[0108] [000108] The stack may further include a thermal oxide layer between the planar substrate and the membrane layer.

[0109] [000109] The stack may further include a boron-containing TEOS layer that at least partially surrounds the membrane layer. Preferably, the boron-containing TEOS layer is in contact with the membrane layer to allow the diffusion of boron atoms into the membrane layer.

[0110] [000110] A stack manufactured according to the method of the thirteenth aspect of the present invention, or a stack according to the fourteenth aspect of the present invention, can be used in any of the other methods described herein, or in the manufacture of an assembly according to any aspect of the present invention. For example, a stack according to the fourteenth aspect of the present invention may be used in the method of the twelfth aspect of the present invention. Boron doping of the membrane layer is applicable to all aspects of the present invention.

[0111] [000111] As described in detail above, features described in any aspect of the present invention can be combined with features described in any other aspect of the present invention. For example, features of a pellicle according to a second aspect of the present invention can be combined with features of the first, third, fourth, and / or fifth aspects of the present invention. In addition, a pellicle according to a second aspect of the present invention can also be designed by the method according to a ninth aspect of the present invention. All combinations of aspects of the present invention can be combined with each other, except when the features of the aspects of the present invention are mutually exclusive.

[0112] [000112] In summary, the method of the present invention enables the production of pellicles, particularly molybdenum silicide pellicles or silicon pellicles, which are nitrided to improve their physical properties. The resulting pellicles are suitable for use in lithography equipment, such as EUV lithography equipment. Conventionally, it was not possible to produce such pellicles. Pellicles produced according to the method of the present invention can withstand the high temperatures reached during pellicle use and can also withstand corrosion by free radical species or other reactive species. The method of the present invention makes it possible to produce pellicles with a surface area of ​​up to 10 cm × 14 cm. The method of the present invention also enables the design and production of pellicles that exhibit improved stability in the context of EUV transmittance when used in EUV lithography machines. Pellicles including a compensating layer will extend the lifespan of the pellicle and reduce changes in pellicle transmittance over its lifespan, thus enabling imaging of a stable number of wafers within a given period.

[0113] [000113] The present invention will be described below with reference to an EUV lithography apparatus. However, it will be understood that the present invention is not limited to pellicles and is similarly applicable to spectral purity filters. [Brief explanation of the drawing]

[0114] [000114] Some embodiments of the present invention will be described below, merely as examples, with reference to the attached schematic diagrams. [Figure 1] This document shows a lithography system comprising a lithography apparatus and a radiation source according to one embodiment of the present invention. [Figure 2] This is a schematic diagram of a pellicle according to the present invention and manufactured by the method of the present invention. [Figure 3] This is a diagram of the steps used when selecting an appropriate compensation layer for a given pellicle. [Figure 4] This is a schematic cross-sectional view of a membrane assembly manufactured according to an existing method. [Figure 5a] This is a schematic cross-sectional view of a membrane assembly manufactured according to the method of the 11th aspect of the present invention. [Figure 5b] This is a schematic cross-sectional view of a membrane assembly manufactured according to the method of the 11th aspect of the present invention. [Figure 5c] This is a schematic cross-sectional view of a membrane assembly manufactured according to the method of the 11th aspect of the present invention. [Figure 6] This is a diagram of a method according to a thirteenth aspect of the present invention. [Modes for carrying out the invention]

[0115] [000115] Figure 1 shows a lithography system comprising a pellicle 15 according to a first aspect of the present invention, or a pellicle 15 manufactured according to a method of a second aspect of the present invention, according to one embodiment of the present invention. The lithography system comprises a radiation source SO and a lithography apparatus LA. The radiation source SO is configured to generate an extreme ultraviolet (EUV) radiation beam 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 adjust the radiation beam B before it is incident on the patterning device MA. The projection system is configured to project the radiation beam B (which is patterned by the mask MA) onto the substrate W. The substrate W may contain a previously formed pattern. In that case, the lithography apparatus aligns the patterned radiation beam B with the previously formed pattern on the substrate W. In this embodiment, the pellicle 15 is drawn in the path of radiation and protects the patterning device MA. It will be understood that the pellicle 15 may be placed in any required position and may be used to protect any of the mirrors in the lithography apparatus.

[0116] [000116] The radiation source SO, the illumination system IL, and the projection system PS are all constructed and positioned to be isolated from the external environment. A gas (e.g., hydrogen) at a pressure below atmospheric pressure can be supplied to the radiation source SO. A vacuum can be supplied to the illumination system IL and / or the projection system PS. A small amount of gas (e.g., hydrogen) at a pressure much lower than atmospheric pressure can also be supplied to the illumination system IL and / or the projection system PS.

[0117] [000117] The radiation source SO shown in Figure 1 is of a type that may be called a laser-generated plasma (LPP) source. Laser 1 may be, for example, a CO2 laser and is positioned to deposit energy into a fuel such as tin (Sn) supplied from a fuel ejector 3 via a laser beam 2. In the following description, tin will be referred to, but any suitable fuel may be used. The fuel may be, for example, liquid and may be, for example, a metal or alloy. The fuel ejector 3 may be equipped with a nozzle configured to guide the tin, for example, in the form of droplets, along a trajectory toward the plasma-forming region 4. Laser beam 2 is incident on the tin in the plasma-forming region 4. Plasma 7 is generated in the plasma-forming region 4 by the deposition of laser energy into the tin. Radiation, including EUV radiation, is emitted from the plasma 7 during the de-excitation and recombination of ions in the plasma.

[0118] [000118] EUV radiation is collected and focused by a per-normal incident radiation collector 5 (sometimes more commonly called a normal incident radiation collector). Collector 5 may have a multilayer structure arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm). Collector 5 may have an elliptical configuration having two elliptical foci. As will be discussed below, the first focal point may be in the plasma-forming region 4, and the second focal point may be in the intermediate focal point 6.

[0119] [000119] The laser 1 can be separated from the radiation source SO. In this case, the laser beam 2 can be passed from the laser 1 to the radiation source SO using a beam delivery system (not shown), which includes, for example, a suitable guide mirror and / or beam expander and / or other optical components. The laser 1 and the radiation source SO together can be considered as a radiation system.

[0120] [000120] The radiation reflected by the collector 5 forms a radiation beam B. The radiation beam B is focused at point 6 to form an image of the plasma-forming region 4, which acts as a virtual radiation source for the illumination system IL. Point 6, where the radiation beam B is focused, can be called the intermediate focus. The radiation source SO is positioned such that the intermediate focus 6 is located at or near the aperture 8 in the closed structure 9 of the radiation source.

[0121] [000121] The radiation beam B passes from the radiation source SO and enters an illumination system IL configured to adjust the radiation beam. The illumination system IL may include a faceted field mirror device 10 and a faceted pupil mirror device 11. Together, the faceted field mirror device 10 and the faceted 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 from the illumination system IL and is incident on a patterning device MA held by a support structure MT. The patterning device MA reflects the radiation beam B and imparts a pattern to the radiation beam B. In addition to the faceted field mirror device 10 and the faceted pupil mirror device 11, or instead thereof, the illumination system IL may include other mirrors or devices.

[0122] [000122] Following reflection from the patterning device MA, the patterned radiant beam B enters the projection system PS. The projection system comprises several mirrors 13, 14 configured to project the radiant beam B onto a substrate W held by a substrate table WT. The projection system PS can apply a reduction factor to the radiant beam to form an image with features smaller than the corresponding features on the patterning device MA. For example, a reduction factor of 4 may be applied. In Figure 1, the projection system PS has two mirrors 13, 14, but the projection system may include any number of mirrors (e.g., six mirrors).

[0123] [000123] The radiation source SO shown in Figure 1 may include components not shown. For example, a spectral filter may be provided in the radiation source. The spectral filter may be substantially transparent to EUV radiation but substantially block radiation of other wavelengths such as infrared radiation. In fact, the spectral filter may be a pellicle according to any embodiment of the present invention.

[0124] [000124] Figure 2 is a schematic representation of the pellicle according to the present invention. The pellicle 15 includes a metal silicide nitride or nitrided silicon layer 16 sandwiched between capping layers 17.

[0125] [000125] The term "EUV radiation" can be considered to encompass electromagnetic radiation having wavelengths in the range of 4 to 20 nm, for example, in the range of 13 to 14 nm. EUV radiation may have wavelengths in the range of 4 to 10 nm, such as less than 10 nm, for example, 6.7 nm or 6.8 nm.

[0126] [000126] Figures 3a to 3c illustrate the steps used in selecting a suitable compensation layer for a given pellicle. The pellicle P is subjected to conditions within a lithography apparatus and the change in the transmittance of the pellicle P is measured. In the schematic diagram, the pellicle P is shown as consisting of a single layer, but this is for simplicity and it will be understood that the pellicle P may include a pellicle stack. Thus, the pellicle P may have one or more layers. Once the change in transmittance of a given pellicle P is measured, the measured change in transmittance is used to select a compensation layer CL material that most closely shows the reverse change in transmittance. This information is then used to produce an updated pellicle P containing the compensation layer CL. The updated pellicle can then be subjected to the same tests to improve the properties of the compensation layer CL. As shown in Figure 3c, the thickness of the compensation layer CL is increasing, but this is not the only possible change. It will be understood that other possible changes include providing a thinner compensation layer CL, moving the compensation layer to a different part of the pellicle P, or changing the material that makes up the compensation layer CL.

[0127] [000127] For example, MoSiN x When the pellicle was exposed to EUV radiation at 580°C for 20 hours under a hydrogen pressure of 3 Pa, the transmittance of the pellicle increased by approximately 1%. This is thought to be because the surface eventually became silicon oxynitride, which is easily photonic etched, and thus became thinner. Another MoSiN x The pellicle was coated with a boron layer and tested at approximately 540°C for 20 hours under a hydrogen pressure of 3 Pa. As a result, the pellicle's transmittance decreased by approximately 1%. Thus, the boron layer counteracted the change in transmittance caused by the etching of silicon oxynitride. Therefore, the thickness of the boron layer can be changed to form a thinner boron oxide layer, bringing the change in pellicle's transmittance closer to 0%.

[0128] [000128] Figure 4 shows a cross-section of a membrane assembly manufactured according to an existing method. The membrane assembly 18 includes a boundary 19 manufactured from a planar substrate. Any suitable planar substrate may be used, but in this specification we consider a silicon boundary. A thermooxide layer 20 is provided on the boundary 19. In this example, the thermooxide layer 20 is a silicon oxide layer. A membrane layer 21 is provided on the oxide layer 20. The membrane layer 21 contains molybdenum silicon nitride, but other materials may be used. A TEOS layer 22 is provided on the membrane layer 21. The TEOS layer can later be treated to form a silicon oxide layer. Alternatively, layers 20 and / or 22 may be SiN layers with a thickness of up to 10 nm, for example, in the range of 1 nm to 5 nm, instead of thermooxide or TEOS.

[0129] [000129] During manufacturing, a TMAH-based etchant is used to etch away the interior regions of the planar substrate. The etching step is continued for a sufficient length of time for the etchant to begin etching away the thermal oxide layer to ensure that the required amount of the planar substrate is removed. The TMAH-based etchant etches silicon oxide at a lower rate than silicon, but etching continues as it is necessary to ensure the interior regions of the planar substrate are etched, and notches are formed around the edges of the thermal oxide layer. The etching step can take more than an hour, and over-etching can occur for about one minute. Therefore, the thermal oxide layer needs to be relatively thick, which may be 50 nm or more, to prevent the etchant from etching the membrane layer. Because the thermal oxide layer is compressible, this can induce wrinkles in the membrane and weaken the assembly. In addition, the increased thickness of the thermal oxide layer can reduce the EUV transmittance of the membrane assembly.

[0130] [000130] Figure 5a shows a schematic cross-sectional view of a membrane assembly manufactured according to the present invention. Figure 5a shows the membrane assembly at an early stage of manufacturing. The same numbers are used for features corresponding to the features in Figure 4. In contrast to the membrane assembly in Figure 4, the membrane assembly 18 shown in Figure 5a further includes an embedded oxide layer 24 and a further layer 25 located between the boundary 19 and the membrane layer 21. The further layer 25 may be a silicon layer.

[0131] [000131] During manufacturing, the internal region of the planar substrate is bulk etched using TMAH etchant, similar to the method shown in Figure 4, to create the boundary 19. The embedded oxide layer 24 serves the same purpose as the thermal oxide layer 20 in Figure 4, in that it withstands the etchant used to etch silicon from the internal region of the planar substrate. As shown in Figure 5a, this results in the formation of notches 23 around the edges of the embedded oxide layer 24.

[0132] [000132] In the next step shown in Figure 5b, the interior of the embedded oxide layer 24 is removed using a different etchant such as BOE. Since the additional layer 25 containing silicon that is superimposed on top is resistant to etching by BOE, over-etching of the embedded oxide layer 24 does not progress to the additional layer 25. In this way, these layers function as etching homogenization layers.

[0133] [000133] Next, as shown in Figure 5c, a further etching step can be performed to remove the internal region of the further layer 25 using an etchant such as TMAH etchant. Since the further layer 25 is much thinner than the planar substrate, the time the thermal oxide layer 20 is exposed to the etchant is reduced from more than an hour to a few minutes. Since any over-etching that may occur lasts only a few seconds, this dramatically reduces the possibility of over-etching the thermal oxide layer 20, and therefore makes it possible to make the thermal oxide layer 20 thinner than in the case of existing manufacturing methods. For example, the thickness of the thermal oxide can be reduced from more than 50 nm to less than 50 nm.

[0134] [000134] The embedded oxide layer and the thermal oxide layer may be produced by the same method or by different methods, and the exact method for producing these layers does not particularly limit the present invention. The membrane layer may include multiple layers. For example, the membrane layer may include a molybdenum silicon nitride layer sandwiched between two molybdenum silicide layers.

[0135] [000135] The method according to the eleventh aspect of the present invention realizes a membrane assembly with reduced over-etching, resulting in a stronger and more stable membrane assembly. This method allows for a thinner sacrificial oxide layer without the risk of over-etching, thus reducing stress mismatch between layers of the membrane assembly. This reduces compressive forces on the assembly and the risk of wrinkle formation. In addition, the planar substrate, embedded oxide layer, and the silicon layer on top can be provided as a silicon-on-insulator wafer (SOI), thereby reducing the number of manufacturing steps before etching, which can reduce costs and the risk of particle contamination.

[0136] [000136] The membrane assembly can be used as a pellicle, preferably in an EUV lithography machine, but can also be applied as a spectral purity filter.

[0137] [000137] Figure 6 schematically illustrates a method according to a thirteenth aspect of the present invention. A stack 26 is provided, comprising a planar substrate 27, an optional thermooxide layer 28 at least partially surrounding the planar substrate 27, a membrane layer 29 at least partially surrounding the thermooxide layer 28, and a boron-doped TEOS layer 30. Before annealing, the membrane layer 29 is substantially boron-free. The pattern of the boron-doped layer 30 is intended to show the presence of boron atoms in the layer and how the boron atoms migrate into the membrane layer 29 after annealing.

[0138] [000138] In the annealing step, the stack is heated to a temperature sufficient to diffuse the boron in the boron-doped TEOS layer 30 into the membrane layer 29. As a result, the membrane layer 29 becomes boron-rich and the amount of boron in the boron-doped TEOS layer 30 is reduced. It will be understood that not all boron can diffuse into the membrane layer 29, and the exact amount of boron that diffuses into the membrane layer 29 can be controlled by adjusting the temperature and duration of the annealing step, as well as the concentration of boron in the boron-doped TEOS layer 30. The membrane layer may contain at least one of silicon, molybdenum silicide, and molybdenum silicon nitride.

[0139] [000139] Assemblies containing boron-doped membranes are highly suitable for use as pellicles in EUV lithography machines and as spectral purity filters.

[0140] [000140] While embodiments of the present invention are specifically referenced in the context of lithography apparatus, embodiments of the present invention can also be used in other apparatuses. Embodiments of the present invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus for measuring or processing objects such as wafers (or other substrates) or masks (or other patterning devices). These apparatuses may generally be called lithography tools. Such lithography tools may operate under vacuum conditions or ambient (non-vacuum) conditions.

[0141] [000141] Although specific embodiments of the present invention have been described above, it is clear that the present invention can be implemented in forms other than those described above. The above description is intended to be illustrative and not restrictive. Accordingly, as will be obvious to those skilled in the art, modifications to the invention described herein may be made without departing from the scope of the appended claims.

Claims

1. A self-supporting membrane formed from at least one layer comprising nitrided metal silicide or doped and nitrided metal silicide, wherein the nitrided metal silicide is of formula M x (Si) y N z A self-supporting membrane having, where M is a metal selected from Mo and Zr, x, y, and z are each greater than 0, 0 < z ≤ x, the atomic concentration of nitrogen is less than approximately 25% of the total atomic concentration of the metal, silicon, and nitrogen, and the nitrided metal silicide is amorphous, The boundary that holds the membrane and A membrane assembly for lithography tools, including [the specified component].

2. The membrane assembly according to claim 1, wherein the membrane comprises a layer of nitrided molybdenum silicide having a thickness of 10 nm to about 40 nm.

3. The membrane assembly according to claim 1, wherein the formula of the nitrided metal silide has a stoichiometric value or a non-stoichiometric value.

4. The aforementioned nitrided metal silicide is of formula M x (Si) y N z The membrane assembly according to claim 1, wherein x ≤ y ≤ 2x.

5. The membrane assembly according to claim 1 or 2, wherein the nitrogen atom concentration in the nitrided metal silide is less than 5%.

6. The membrane assembly according to claim 1 or 2, wherein the membrane further comprises at least one capping layer.

7. The membrane assembly according to claim 6, wherein the at least one capping layer has a thickness of about 0.1 nm to about 10 nm.

8. The membrane assembly according to any one of claims 1 to 7, further comprising at least one compensating layer selected and configured to counteract changes in the transmittance of one or more layers of the membrane when exposed to EUV radiation.

9. The membrane assembly according to claim 8, wherein the at least one compensation layer comprises a material that, when exposed to EUV radiation, alters to increase or decrease the transmittance of the at least one compensation layer.

10. The membrane assembly according to any one of claims 1 to 7, wherein the membrane assembly includes an embedded oxide layer between the boundary and the membrane.

11. The membrane assembly according to any one of claims 1 to 7, wherein the membrane assembly includes a silicon layer between the boundary and the membrane.

12. The membrane assembly according to any one of claims 1 to 7, wherein the membrane assembly includes a thermal oxide layer between the boundary and the membrane.

13. The membrane assembly according to claim 1, wherein the membrane is doped with boron.

14. A membrane assembly according to any one of claims 1 to 13, A frame for supporting the membrane assembly at the boundary, A spectral purity filter or pellicle for EUV lithography tools, including [specific components / features].

15. The spectral purity filter according to claim 14, wherein the spectral purity filter is provided in an EUV radiation source, an EUV lithography apparatus, a mask inspection apparatus, a metrology apparatus, or an apparatus for measuring or processing a substrate.

16. A membrane assembly according to any one of claims 1 to 13, A frame for supporting the membrane assembly at the boundary, A pellicle, including

17. The pellicle according to claim 16, wherein the pellicle is provided on an EUV radiation source, an EUV lithography apparatus, a mask inspection apparatus, a metrology apparatus, or an apparatus for measuring or processing a substrate.

18. A membrane assembly according to any one of claims 1 to 13, A frame configured to support the membrane assembly at the boundary, A patterning device attached to the frame, A mask assembly for lithography tools, including [specific components / features].

19. A method for manufacturing a membrane assembly for EUV lithography, A planar substrate including an internal region and a boundary region surrounding the internal region, A membrane formed at least from at least one membrane layer containing a nitrided metal silicide or a doped nitrided metal silicide, wherein the nitrided metal silicide has the formula M x (Si) y N z where M is a metal selected from Mo and Zr, x, y, z are each greater than 0, 0 < z ≤ x, the atomic concentration of nitrogen is less than about 25% of the total atomic concentration of metal, silicon and nitrogen, and the nitrided metal silicide is amorphous, and a membrane To provide a stack that includes, The method involves selectively removing the internal region of the planar substrate, and as a result, the membrane assembly is A self-supporting membrane formed from at least one of the aforementioned membrane layers, A boundary holding the at least one membrane layer, the boundary including at least a portion of the planar substrate defined as a boundary region Methods that include...

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