Method of manufacturing a membrane assembly

Abstract

A method for manufacturing a diaphragm assembly for EUV lithography, the method comprising: providing a stack comprising: at least one diaphragm layer supported by a planar substrate wherein the planar substrate comprises an inner region and a boundary region surrounding the inner region; the first sacrificial layer is positioned between the planar substrate and the diaphragm layer; selectively removing the interior region of the planar substrate, wherein the step of selectively removing the interior region of the planar substrate includes using an etchant having a similar etch rate for the diaphragm layer and its oxide and a substantially different etch rate for the first sacrificial layer; the diaphragm assembly includes: a diaphragm formed from the at least one diaphragm layer; and a boundary portion that holds the diaphragm, the boundary portion including the boundary region of the planar substrate and the first sacrificial layer between the boundary portion and the diaphragm layer.

Description

[0001] This application is a divisional application of the patent application with application number 201980068236.X and invention name “Method for Manufacturing Diaphragm Assembly”, which entered the Chinese national phase on April 15, 2021 (international application date is 2019-10-02, international application number is PCT / EP2019 / 076667). Technical Field

[0002] The present invention relates to a method for manufacturing a diaphragm assembly and to a diaphragm assembly, as well as to an optical element for a lithographic apparatus and a method for manufacturing the optical element. Background Art

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

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

[0005] The lithographic apparatus includes a patterning device (e.g., a mask or reticle). Radiation is provided to pass through or reflect from the patterning device to form an image on a substrate. A diaphragm assembly (also referred to as a pellicle) may be provided to protect the patterning device from airborne particles and other forms of contaminants. Contaminants on the surface of the patterning device may cause manufacturing defects on the substrate.

[0006] A pellicle may also be provided for protecting optical components other than the patterning device. A pellicle may also be used to provide a path for lithographic radiation between sealed regions of a lithographic apparatus. A pellicle may also be used as a filter, such as a spectral purity filter, or as part of a dynamic gas lock of a lithographic apparatus.

[0007] The 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 the frame, for example, by gluing or otherwise attaching the pellicle boundary region to the frame. The frame may be permanently or releasably attached to the patterning device.

[0008] The diaphragm assembly may include a boundary portion and a diaphragm extending across the boundary portion. For example, due to the thinness of the diaphragm, it is difficult to manufacture a diaphragm assembly and the diaphragm assembly does not deform during the process. In particular, when the diaphragm in the diaphragm assembly is supported only at the boundary portion, there are no other supports or reinforcements such as grids or substrates below the diaphragm to provide additional mechanical strength, so that the diaphragm assembly may become more susceptible to deformation. In addition, diaphragm assemblies with large diaphragm areas required for photolithographic patterning devices are likely to deform under stress. Deformation of the diaphragm assembly may result in reduced performance, damage to the diaphragm, or even rupture, which is not desired.

[0009] Due to the presence of the pellicle in the optical path of the EUV radiation beam, it is desirable for the pellicle to have a high EUV transmittance. High EUV transmittance allows a larger proportion of the incident radiation to pass through the pellicle and reducing the amount of EUV radiation absorbed by the pellicle can reduce the operating temperature of the pellicle. Because the transmittance depends at least in part on the thickness of the pellicle, it is desirable to provide a pellicle that is as thin as possible while maintaining a reliable strength sufficient to withstand the sometimes harsh environment within the lithographic equipment. It is also desirable to provide a method of providing a diaphragm assembly with predictable and constant physical properties. If the method provides pellicles with different physical properties, it may be the case that one pellicle is able to withstand use in a lithographic equipment while another pellicle fails or malfunctions within a shorter period of time. This unpredictability in how a pellicle can withstand use necessitates a very conservative approach to the expected life of a pellicle, which may result in the pellicle being replaced more frequently than it may need to be replaced.

[0010] It is therefore desirable to provide a method for producing a pellicle and a pellicle produced according to this method, the method resulting in a pellicle having high EUV transmittance and the method can reliably produce a pellicle having constant physical properties. It is also desirable to increase the life of the pellicle in order to reduce equipment downtime.

[0011] Although the present application generally relates to pellicles in the context of lithographic apparatus, particularly EUV lithographic apparatus, the present invention is not limited to pellicles and lithographic apparatus, and it will be appreciated that the subject matter of the present invention may be used in any other suitable apparatus or situation.

[0012] For example, the method of the present invention may be equally applicable to spectral purity filters. Some EUV sources, such as those that use plasma to generate EUV radiation, emit not only desired "in-band" EUV radiation, but also undesirable (out-of-band) radiation. This out-of-band radiation is most notably in the deep ultraviolet (DUV) radiation range (100nm to 400nm). Furthermore, in some EUV sources, such as in the case of laser-generated plasma EUV sources, the radiation from the laser, typically at 10.6 microns, exhibits significant out-of-band radiation.

[0013] In lithographic equipment, spectral purity is required for several reasons. One reason is that resists are sensitive to radiation of out-of-band wavelengths, and thus the image quality of a pattern applied to the resist may deteriorate if the resist is exposed to such out-of-band radiation. In addition, out-of-band radiative infrared radiation (e.g., 10.6 micron radiation in some laser-generated plasma sources) causes undesirable and unnecessary heating of pattern forming devices, substrates, and optics within the lithographic equipment. Such heating may cause damage to these components, degradation of their lifetime, and / or defects or distortions / deformations in the pattern projected onto and applied to the resist-coated substrate.

[0014] A typical spectral purity filter may, for example, be formed from a silicon infrastructure (e.g. a silicon grid, or other element having apertures) coated with a reflective metal such as molybdenum. In use, a typical spectral purity filter may be subjected to high thermal loads from, for example, incident infrared and EUV radiation. The thermal loads may result in temperatures of the spectral purity filter exceeding 800°C. Under high head-end loads, the coating may delaminate due to differences in the linear expansion coefficients between the reflective molybdenum coating and the underlying silicon support structure. Delamination and degradation of the silicon infrastructure is accelerated by the presence of hydrogen, which is often used as a gas in the environment in which spectral purity filters are used in order to inhibit debris (e.g. debris such as particles) from entering or leaving certain parts of the lithographic apparatus. Thus, a spectral purity filter may be used as a pellicle, and vice versa. Therefore, references to "pellicle" in this application also refer to references to "spectral purity filter". Although reference is primarily made to a pellicle in this application, all features may equally apply to a spectral purity filter.

[0015] In addition, it is desirable to improve the life of optical elements within a lithographic apparatus, such as collector mirrors, diaphragms, or components of a dynamic gas lock. These optical elements are exposed to the harsh environment of the lithographic apparatus when in use and can therefore become damaged over time. It is desirable to prevent, reduce, or eliminate damage to optical elements.

[0016] In a lithographic apparatus (and / or method), it is desirable to minimize the intensity loss of radiation being used to apply a pattern to a resist coated substrate. One reason for this is that ideally, as much radiation as possible should be available for applying the pattern to the substrate, for example to reduce exposure time and increase throughput. At the same time, it is desirable to minimize the amount of undesired radiation (e.g. out-of-band) that is transmitted through the lithographic apparatus and incident on the substrate. Furthermore, it is desirable to ensure that the spectral purity filter used in the lithographic method or apparatus has a sufficient service life and does not degrade rapidly over time due to the high thermal loads to which the spectral purity filter may be exposed and / or hydrogen (etc., such as free radical species, including H* and HO*) to which the spectral purity filter may be exposed. It is therefore desirable to provide an improved (or alternative) spectral purity filter, and for example to provide a spectral purity filter suitable for use in a lithographic apparatus and / or method.

[0017] Because any defects in the diaphragm may reduce the performance and / or life of the diaphragm, it is desirable to reduce the likelihood that a diaphragm assembly, such as a diaphragm, will become deformed or damaged during its manufacture.

[0018] The present invention has been designed in an attempt to address at least some of the problems identified above. Summary of the invention

[0019] According to a first aspect of the present invention, there is provided a method for manufacturing a diaphragm assembly for EUV lithography, the method comprising:

[0020] i) providing a stack, the stack comprising:

[0021] at least one diaphragm layer supported by a planar substrate, wherein the planar substrate includes an interior region and a border region surrounding the interior region; and a first sacrificial layer located between the planar substrate and the diaphragm layer;

[0022] ii) selectively removing the inner region of the planar substrate, wherein the step of selectively removing the inner region of the planar substrate comprises using an etchant having a similar etch rate for the diaphragm layer and its oxide and having a substantially different etch rate for the first sacrificial layer;

[0023] The diaphragm assembly includes: a diaphragm formed by at least the one diaphragm layer; and a boundary portion that holds the diaphragm, the boundary portion including the boundary area of ​​the planar substrate and the first sacrificial layer located between the boundary portion and the diaphragm layer.

[0024] The method according to the invention reduces the risk caused by over-etching of the stack, which can weaken the final pellicle and increase the risk of failure of the pellicle. It is believed that in methods where the etching rates of the sacrificial layer and the diaphragm layer and its oxide are approximately the same, there is a risk of over-etching the sacrificial layer. In addition, in the case where the etching rates of the diaphragm layer (or indeed any other layer in the stack) and its oxide are approximately different, the preferential etching of the material of the diaphragm (or other layer) or its oxide may lead to the formation of weak points (possibly in the form of notches) in the diaphragm assembly. Because any remaining sacrificial layer can reduce the EUV transmittance of the diaphragm assembly, it is desirable to ensure that the sacrificial layer is completely removed from the diaphragm assembly. However, the thickness of the sacrificial layer and the rate at which the sacrificial layer is etched away can vary. In this way, there is a risk that the diaphragm assembly can be etched for a longer time than necessary. Without wishing to be bound by scientific theory, it is believed that over-etching of the native oxide along the grain boundaries during etching may lead to the formation of notches in the surface. These notches act as weak points in the final diaphragm assembly and may thereby weaken the assembly.

[0025] Preferably, at least the first sacrificial layer is a tensile layer. By tensile, it will be understood that it means that the layer applies a tensile force opposite to the compressive force. In other methods of producing a diaphragm assembly, the first sacrificial layer is a compressive layer, in other words, the layer applies a compressive force. During processing, the compressive force can cause the diaphragm assembly to wrinkle, which can cause damage to the diaphragm assembly, such as the formation of microcracks, ultimately weakening the diaphragm assembly. In addition, at least the diaphragm layer according to the present invention can also be stretched. Providing a stretched first sacrificial layer reduces the stress difference between the sacrificial layer and the at least one diaphragm layer. Since the diaphragm is thin, the diaphragm may deform out of plane when there is a pressure difference between the two faces of the diaphragm. There is an acceptable maximum out-of-plane deflection. The diaphragm assembly according to the present invention may include a pre-tensioning degree to resist the out-of-plane deflection. It will be understood that in other embodiments, one or more layers may have substantially no compressive or tensile forces.

[0026] The stack may further comprise a second sacrificial layer located on the at least one diaphragm layer. In this way, the stack comprises at least one diaphragm layer between the first sacrificial layer and the second sacrificial layer. The first sacrificial layer and the second sacrificial layer may comprise the same material or may comprise different materials. Preferably, the first sacrificial layer and the second sacrificial layer comprise the same material.

[0027] The method may also include removing at least a portion of the second sacrificial layer from at least one face of the stack prior to selectively removing the interior region of the planar substrate. Because the second sacrificial layer may be disposed on both faces of the stack and may be substantially resistant to the etchant, it may be necessary to remove at least a portion of the second sacrificial layer from the stack in order to expose the at least one diaphragm layer to the etchant. It will be appreciated that this step may not be necessary in the case where the second sacrificial layer is disposed only on the upper surface of the stack, thereby exposing the lower surface of the stack (i.e., the diaphragm layer).

[0028] This step in the method exposes the at least one diaphragm layer to the etchant to allow the etchant to etch away the diaphragm layer and the interior region of the planar substrate.

[0029] The method may also include providing a resist on the stack and patterning the resist. This step preferably occurs before selectively removing the inner region of the planar substrate. The patterning of the resist is used to define the area of ​​the stack to be removed by a subsequent etching step. Any suitable type of resist can be used.

[0030] The resist is resistant to etching by the etchant and protects portions of the stack that are not desired to be etched away and leaves exposed portions of the resist that are desired to be etched away. The etching may be allowed to continue until the etching has reached the planar substrate.

[0031] As such, the method may further include etching the second sacrificial layer, the diaphragm, and at least a portion of the first sacrificial layer before selectively removing the inner region of the planar substrate.

[0032] The method may further include applying a protective layer to the front side of the layer stack to protect layers at the front side of the layer stack from subsequent etching steps before selectively removing the interior region of the planar substrate.

[0033] This step is optional and can be used to hold the stack together while the interior region of the planar substrate is etched.

[0034] After removing the inner region of the planar substrate, the protective layer can be removed from the stack. This leaves a stack including a non-etched border region of the planar substrate having an optional first sacrificial layer on the bottom side, a first sacrificial layer on the top side, the at least one diaphragm layer on the first sacrificial layer on the top side, and a second sacrificial layer on the at least one diaphragm layer, such that the at least one diaphragm layer is located between the first sacrificial layer and the second sacrificial layer, and the first sacrificial layer is located between the at least one diaphragm layer and the border region of the planar substrate.

[0035] The method may further include removing any remaining second sacrificial layer from the upper surface of the at least one diaphragm layer.

[0036] The step of removing any remaining second sacrificial layer from the upper surface of the at least one diaphragm layer may include etching using an etchant having an etching rate for the second sacrificial layer that is substantially higher than an etching rate for the at least one diaphragm layer and its oxide. Preferably, the etchant etches the sacrificial layer at a rate that is at least ten times the rate at which the etchant etches the at least one diaphragm layer and its oxide.

[0037] By using an etchant that etches the second sacrificial material at a higher rate than the rate at which the at least one diaphragm layer and its oxide are etched, the problem of over-etching is mitigated. Even if the diaphragm assembly is retained in the etchant for a longer time than necessary to remove the second sacrificial layer, very little etching of the at least one diaphragm layer and its oxide occurs because the etchant etches the at least one diaphragm layer and its oxide at a low rate. In addition, the formation of notches in the surface is avoided or reduced and does not weaken the resulting diaphragm assembly.

[0038] In either aspect, the etchant may be a chemical etchant. Preferably, the etchant used to remove the second sacrificial material comprises phosphoric acid. Phosphoric acid has been found to etch the second sacrificial material at a rate of about 25 times the rate at which it etches the material of the at least one diaphragm and its oxide. As such, even if the diaphragm assembly is exposed to the etchant for a time longer than necessary to remove the second sacrificial layer, the etchant will not etch the remainder of the diaphragm assembly to any significant extent. It will be appreciated that any etchant having a similar etch rate for the material of the diaphragm and its oxide may be used, and wherein such etch rate is significantly less than the etch rate that may be used for the sacrificial layer.

[0039] The planar substrate may be a wafer. Preferably, the wafer comprises silicon. Silicon is a well-characterized material commonly used in the technical field.

[0040] At least one of the first sacrificial layer and the second sacrificial layer may include silicon nitride. Silicon nitride is a tensile material, which means that the assembly does not wrinkle during the manufacture of the diaphragm assembly, as is the case when a compressive material is used. In addition, silicon nitride is substantially inert to the etchant used to etch away the inner region of the planar substrate and its oxide, so silicon nitride is not etched together with the inner region of the planar substrate and its oxide. In addition, silicon nitride is etched by a different etchant in the final processing step at a much higher rate than the boundary region of the at least one diaphragm layer and the planar substrate. Because silicon nitride can be easily removed without over-etching the boundary region of the planar substrate and the at least one diaphragm layer, this reduces the risk of notches being formed in the surface of the at least one diaphragm layer, thereby weakening the at least one diaphragm layer.

[0041] The at least one diaphragm layer may include at least one polycrystalline silicon layer preferably formed by crystallizing at least one amorphous silicon layer. Silicon has good EUV transmittance and is therefore a suitable material for the at least one diaphragm layer. The at least one diaphragm layer may be coated with one or more materials, the one or more materials being used to provide additional chemical resistance or thermal resistance, and / or which increases the emissivity of the diaphragm assembly.

[0042] The protective layer may include a cross-linked polymer. The polymer may be a poly(p-xylene) polymer. The polymer may be a poly(p-xylene) or a ProTek® type material.

[0043] According to a second aspect of the present invention, there is provided a diaphragm assembly for EUV lithography, the diaphragm assembly comprising:

[0044] a diaphragm formed of at least one diaphragm layer including polycrystalline silicon or single crystal silicon; and

[0045] a boundary portion that holds the diaphragm;

[0046] wherein the border region is formed by a planar substrate including an inner region and a border region surrounding the inner region, wherein the border portion is formed by selectively removing the inner region of the planar substrate,

[0047] wherein the planar substrate comprises a core layer and a sacrificial layer, such that the boundary portion comprises the core layer and the sacrificial layer, wherein the sacrificial layer is located between the core layer and the at least one diaphragm layer,

[0048] The etching rates of the core layer and the at least one diaphragm layer in the etchant are substantially different from the etching rate of the sacrificial layer in the etchant.

[0049] As described above, a sacrificial layer having an etching rate in an etchant that is substantially different from the etching rate of the core layer and the at least one diaphragm layer in the etchant reduces or prevents over-etching of the core layer and the at least one diaphragm layer, thereby reducing the risk of notch formation that produces a weakened diaphragm assembly.

[0050] The sacrificial layer may comprise a stretched material. As described above, the presence of a stretched sacrificial layer means that the diaphragm does not wrinkle during manufacture and therefore this further reduces possible weaknesses introduced into the diaphragm assembly. In addition, the internal stresses within the multiple layers comprising the diaphragm assembly are more closely matched, resulting in smaller differential stresses existing in the diaphragm assembly, particularly during use when the diaphragm assembly may be heated to high temperatures (such as 500° C. or even higher), causing stresses to be created within the diaphragm assembly. It is believed that the diaphragm assembly according to the present invention is more stable, i.e. more robust, and can be manufactured to more consistent specifications than other diaphragms.

[0051] The sacrificial layer may include silicon nitride. Silicon nitride is a tensile material and therefore is not used to wrinkle the diaphragm assembly during manufacturing. Additionally, silicon nitride is resistant to certain etchants used to etch the planar substrate and its oxide, but is etched more quickly with other etchants that the planar substrate and its oxide are resistant to. Thus, silicon nitride can be used to carefully manage the various etching steps used in the manufacture of the diaphragm assembly.

[0052] The core layer may comprise silicon.The at least one diaphragm layer may comprise silicon.Silicon has high EUV transmittance and is a very well characterized and understood material.

[0053] The etching rate of the core layer and the at least one diaphragm layer is substantially lower than the etching rate of the sacrificial layer. As explained above, this prevents or at least reduces the possibility of damage to the diaphragm assembly due to over-etching.

[0054] The etchant may include phosphoric acid.It will be appreciated that other etchants that etch the sacrificial layer at a much higher rate than the core layer and the at least one diaphragm layer may be used in any aspect of the invention.

[0055] The diaphragm assembly can be used in a patterning device or a dynamic air lock.

[0056] According to a third aspect of the present invention, there is provided a method of using a diaphragm assembly manufactured according to the method of the second or fifth aspect of the present invention or the first or sixth aspect of the present invention. The method may be in a lithographic apparatus. The method may be as a pellicle, as part of a dynamic air lock, and / or as a spectral purity filter.

[0057] According to a fourth aspect of the present invention, there is provided a lithographic apparatus comprising a diaphragm assembly manufactured according to the method of the second aspect or the fifth aspect of the present invention or the first aspect or the sixth aspect of the present invention.

[0058] According to a fifth aspect of the present invention, there is provided an optical element for a lithographic apparatus, the optical element comprising a stack, wherein the stack comprises a core, a cover layer and an oxygen barrier layer between the cover layer and the core.

[0059] It has been found that during operation, the optical elements of the lithographic apparatus become oxidized. This limits the life of the optical elements and reduces the availability of the lithographic apparatus. It has been found that the layers of the optical elements below the protective cover layer can become oxidized during operation. Without wishing to be bound by scientific theory, it is believed that water and oxygen present in the lithographic apparatus can pass through the protective cover layer and react with one or more base layers. The one or more base layers may include an IR suppression layer that loses its IR suppression ability when oxidized. The core layer (which may include silicon) may also become oxidized. The presence of the oxygen barrier layer (which may also be a water barrier layer) is used to protect the optical element from unwanted oxidation and the resulting performance loss.

[0060] The oxygen barrier layer may include at least one silicon oxide layer and at least one zirconium oxide or yttrium oxide layer.

[0061] The at least one silicon oxide layer acts as part of a barrier layer for oxygen and / or water, as it inhibits the passage of oxygen and / or water.Zirconium oxide or yttrium oxide may act as both the capping layer and part of the oxygen barrier layer.

[0062] The oxygen barrier layer may include a zirconium oxide silicon layer and a yttrium oxide silicon layer. The zirconium oxide silicon layer or the yttrium oxide silicon layer may be disposed between the silicon oxide layer and the zirconium oxide layer or the yttrium oxide layer as appropriate.

[0063] The silicon oxide layer and the zirconium oxide layer can form a zirconium oxide silicon layer located between them. Similarly, the silicon oxide layer and the yttrium oxide layer can form a yttrium oxide silicon layer located between them. It has been unexpectedly found that the zirconium oxide silicon layer or the yttrium oxide silicon layer provides favorable oxygen barrier properties. It has also been unexpectedly found that the thickness of the zirconium oxide layer covering the silicon layer has only a very small effect on the ability of the zirconium oxide layer to prevent oxidation of the underlying silicon layer. Thus, without wishing to be bound by scientific theory, it is believed that there is an intermediate layer that acts as an oxygen barrier including zirconium oxide silicon or yttrium oxide silicon. Thus, it has been found that an oxygen barrier can be provided without increasing the thickness of the optical element. Thus, an optical element for a lithographic device is provided, wherein the optical element includes a zirconium oxide silicon layer or a yttrium oxide silicon layer as an oxygen barrier.

[0064] Since the thickness of the multiple layers has been found to have a low impact on the oxidation resistance provided, it has been appreciated that the number of interfaces or energy barriers determines the growth rate of the base oxide layer.As such, the oxygen barrier may comprise multiple alternating layers of material.

[0065] The alternating layers provide a number of interfaces between each layer to inhibit the transfer of oxygen and / or water. The interfaces may be structural barriers and / or energy barriers for oxygen and / or water to cross. In order for an interface to exist, the materials of the immediately adjacent layers need to be different. As such, the multiple layers preferably alternate between different materials. It will be understood that two materials may alternate, but it will also be understood that there may be three or more different materials arranged to provide multiple interfaces.

[0066] The alternating material layers include silicon oxide, zirconium oxide, zirconium oxide silicon, zirconium nitride, yttrium oxide, silicon nitride, zirconium boride, aluminum oxide, aluminum nitride, titanium oxide, titanium nitride, tantalum oxide and tantalum nitride, preferably wherein the oxygen barrier layer includes alternating layers of silicon oxide and zirconium oxide or alternating layers of silicon oxide and yttrium oxide.

[0067] The present application illustrates an oxygen barrier layer comprising alternating layers of silicon oxide and zirconium oxide. However, other materials may be used for the oxygen barrier layer of the present invention. It has been found that the materials described above provide oxygen barrier capabilities and do not or only weakly absorb EUV radiation. As such, it has been found that these materials are suitable for use in optical elements of lithographic equipment, particularly EUV lithographic equipment. Because there are interfaces between the material layers, these materials can be used in any combination. In addition, two or more materials may be selected to form alternating material layers. Because the core layer can be conveniently composed of silicon, it is convenient to have silicon oxide as one of the materials forming the oxygen barrier, because silicon oxide can be easily formed during manufacturing. It will be understood that the first to third aspects of the present invention also apply to the fourth aspect. In addition, because the cover layer can be zirconium oxide or yttrium oxide, it may be desirable to form an oxygen barrier from the same material. In fact, the cover layer itself can be regarded as the first layer in a multilayer oxygen barrier.

[0068] The optical element may include an IR suppression layer. The IR suppression layer may include molybdenum, niobium, ruthenium or a combination thereof. The IR suppression layer may preferably include metallic molybdenum. Such a layer serves to increase the emissivity of the optical element and suppress unwanted IR radiation.

[0069] The core of the optical element preferably comprises two sides. Preferably, an oxygen barrier layer is disposed on both sides of the optical element. Preferably, the oxygen barrier layer is disposed between each side of the core and a corresponding cover layer on each side of the core. Thus, in one embodiment, an optical element for a lithographic apparatus is provided, the optical element comprising a stack, wherein the stack comprises: a core, preferably comprising silicon; a cover layer, comprising zirconium oxide or yttrium oxide on each side of the core; a silicon oxide layer, the silicon oxide layer being disposed between the core and the corresponding cover layer on each side of the core; and a zirconium oxide silicon layer or yttrium oxide silicon layer, the zirconium oxide silicon layer or yttrium oxide silicon layer being disposed between the silicon oxide layer and the zirconium oxide layer or yttrium oxide layer on each side of the core. Preferably, an IR suppression layer is disposed on one side of the core, but the IR suppression layer may be disposed on both sides of the core.

[0070] The optical element may include a pellicle, a mirror, a dynamic air lock, or any other element within the lithographic apparatus that interacts with the lithographic radiation.

[0071] The oxygen barrier layer may include alternating layers of materials each having a thickness of from about 0.1 nm to about 2 nm. Because it has been unexpectedly realized that the thickness of the layers is less important than the presence of interfaces between the layers, this allows the layers to be thinner than would have been expected previously and provides a new way to maintain good optical properties while mitigating oxidation, particularly useful in lithography equipment, preferably EUV lithography equipment.

[0072] According to a sixth aspect of the present invention, there is provided a method for manufacturing an optical element for a lithographic apparatus, the method comprising:

[0073] providing a core;

[0074] providing a first material on one or both sides of the core;

[0075] providing the first material to a second material, or providing the second material on the first material, the first material and the second material forming an oxygen barrier layer,

[0076] The first material and the second material are different and are selected from the following: silicon oxide, zirconium oxide, zirconium oxide silicon, silicon nitride, zirconium nitride, yttrium oxide, zirconium boride, aluminum oxide, aluminum nitride, titanium oxide, titanium nitride, tantalum oxide and tantalum nitride, preferably, one of the first material and the second material is silicon oxide and the other is zirconium oxide or yttrium oxide.

[0077] As explained above, it has been unexpectedly realized that it is possible to provide an oxygen barrier layer comprising a plurality of alternating thin layers, and that the oxygen barrier layer is an interface between the plurality of layers that provides the necessary physical barrier and / or energy barrier for oxygen diffusion through the material. Compared to simply increasing the thickness of the cover layer (which has been found to have very little correlation with a reduction in oxidation of the base layer), the provision of a multi-layer oxygen barrier layer allows the plurality of individual layers to be relatively thin, from about 0.1 nm to about 2 nm in thickness, which avoids or reduces any reduction in the transmittance of the optical element.

[0078] The method may include providing one or more IR suppressing layers prior to depositing the first material. The IR suppressing layer is preferably disposed on the core such that the IR suppressing layer is disposed between the core and the oxygen barrier layer. In this way, the oxygen barrier layer prevents or reduces oxidation of the IR suppressing layer. It will also be understood that the core is also protected from oxidation by the oxygen barrier layer.

[0079] The steps of depositing the first material and the second material may be repeated at least once to form an oxygen barrier comprising a plurality of layers. As mentioned, because it is believed that the interfaces between the plurality of layers provide the desired oxygen barrier properties, the provision of multiple layers results in an increase in the number of interfaces and physical / energy barriers through which oxygen is transmitted.

[0080] The steps of providing the first material and providing the second material may be repeated 2 to 10 times. The exact number of times this step is repeated will depend on the number of layers desired to be provided. It will be appreciated that this step may be repeated more than ten times if necessary and that the present invention is not particularly limited by the exact number of layers. As such, a third material may also be included in the formation of the oxygen barrier. Other materials may also be present.

[0081] The first material and / or the second material may be provided by physical vapor deposition (PVD), reactive sputtering, co-sputtering, atomic layer deposition (ALD), plasma enhanced ALD, thermal oxidation, or wet chemical passivation, or any other suitable deposition technique. The present invention is not particularly limited to the techniques used to provide the various layers of the optical element and any suitable technique may be used.

[0082] It will be understood that features described with respect to one embodiment may be combined with any features described with respect to another embodiment, and that all such combinations are expressly contemplated and disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which corresponding reference numerals indicate corresponding parts, and in which:

[0084] Figure 1depicts a lithographic apparatus according to an embodiment of the invention;

[0085] Figures 2 to 9 schematically depicts the various stages of a method for manufacturing a pellicle according to the invention;

[0086] FIG. 10 depicts a comparison between an assembly according to the present invention and another assembly;

[0087] Fig.11 schematically depicts a cross section through a stack that does not include an oxygen barrier layer as described herein;

[0088] Fig.12 schematically depicts a cross section through a stack according to an embodiment of the invention; and

[0089] Fig.13 A cross section through a stack according to an embodiment of the invention is schematically depicted.

[0090] The features and advantages of the present invention will become more apparent from the detailed description set forth below in conjunction with the accompanying drawings, in which like reference numerals identify corresponding elements throughout. In the accompanying drawings, like reference numerals generally indicate identical, functionally similar, and / or structurally similar elements. DETAILED DESCRIPTION

[0091] Figure 1 A lithographic system is shown comprising a pellicle 15 (also referred to as a diaphragm assembly) according to the second aspect of the invention or manufactured according to the method of the first aspect of the invention. The lithographic system comprises a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an extreme ultraviolet (EUV) radiation beam B. The lithographic apparatus LA comprises an illumination system IL, a support structure MT configured to support a pattern forming 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 the radiation beam B is incident on the pattern forming device MA. The projection system is configured to project the radiation beam B (currently patterned by the mask MA) onto the substrate W. The substrate W may comprise a previously formed pattern. In this case, the lithographic apparatus aligns the patterned radiation beam B with the pattern previously formed on the substrate W. In this embodiment, the pellicle 15 is depicted in the path of the radiation and is protecting the pattern forming device MA. It should be appreciated that the pellicle 15 may be located in any desired position and may be used to protect any of the mirrors in the lithographic apparatus.

[0092] The radiation source SO, the illumination system IL and the projection system PS may all be constructed and arranged so that they may be isolated from the external environment. A gas (e.g. hydrogen) at a pressure below atmospheric pressure may be provided in the radiation 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 substantially below atmospheric pressure may be provided in the illumination system IL and / or the projection system PS.

[0093] Figure 1 The radiation source SO shown in is of a type that may be 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 from a fuel emitter. Although tin is mentioned in the following description, any suitable fuel may be used. The fuel may be, for example, in liquid form and may be, for example, a metal or an alloy. The fuel emitter may include a nozzle configured to direct tin, for example, in the form of droplets, along a trajectory toward a plasma formation region. The laser beam is incident on the tin at the plasma formation region. The deposition of laser energy into the tin generates a plasma at the plasma formation region. Radiation, including EUV radiation, is emitted from the plasma during de-excitation and recombination of ions of the plasma.

[0094] EUV radiation is collected and focused by a near normal incidence radiation collector or near normal incidence radiation collector (sometimes more commonly referred to as a normal incidence radiation collector or a normal incidence radiation collector). The collector may have a multilayer 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 having 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.

[0095] The laser may be separate from the radiation source SO. In this case, the laser beam may be transferred from the laser to the radiation source SO by means of a beam delivery system (not shown) comprising, for example, suitable guide mirrors and / or beam expanders, and / or other optical devices. The laser and the radiation source SO may be considered together as a radiation system.

[0096] The radiation reflected by the collector forms a radiation beam B. The radiation beam B is focused at a point to form an image of the plasma formation region, which acts as a virtual radiation source for illuminating the system IL. The point at which the radiation beam B is focused may be referred to as an intermediate focus. The radiation source SO is configured so that the intermediate focus is located at or near an opening in an enclosure of the radiation source.

[0097] A radiation beam B is transmitted from a radiation source SO to an illumination system IL which is configured to condition the radiation beam. The illumination system IL may include a faceted field mirror device 10 and a faceted pupil mirror device 11. The faceted field mirror device 10 and the faceted pupil mirror device 11 together provide a radiation beam B having a desired cross-sectional shape and a desired angular distribution. The radiation beam B is transmitted from the illumination system IL and is incident on a pattern forming device MA held by a support structure MT. The pattern forming device MA reflects and patterns the radiation beam B. In addition to the faceted field mirror device 10 and the faceted pupil mirror device 11, or instead of the faceted field mirror device 10 and the faceted pupil mirror device 11, the illumination system IL may also include other mirrors or devices.

[0098] After reflection from the patterning device MA, the patterned radiation beam B enters a projection system PS. The projection system comprises a plurality of mirrors 13, 14 configured to project the radiation beam B onto a substrate W held by a substrate table WT. The projection system PS may apply a reduction factor to the radiation beam so as to form an image in which features are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 may be applied. Although in Figure 1 The projection system PS is shown having two mirrors 13, 14, but the projection system may comprise any number of mirrors (eg six mirrors).

[0099] Figure 1 The radiation source SO shown in FIG. 1 may include components not shown. For example, a spectral filter may be provided in the radiation source. The spectral filter may substantially transmit EUV radiation but substantially block radiation of other wavelengths, such as infrared radiation.

[0100] In an embodiment, the diaphragm assembly 15 is used for a dynamic gas lock. In such a case, the diaphragm assembly 15 acts as a filter for filtering DUV radiation. Additionally or alternatively, in an embodiment, the diaphragm assembly 15 is a diaphragm of a pattern forming device MA for EUV lithography. The diaphragm assembly 15 of the present invention can be used for a dynamic gas lock or for a diaphragm or for another purpose. In an embodiment, the diaphragm assembly 15 includes a diaphragm formed by at least one diaphragm layer 50, the at least one diaphragm layer being configured to transmit at least 90% of the incident EUV radiation. In order to ensure maximum EUV transmission and minimize the impact on imaging performance, it is preferred that the diaphragm is supported only at the borders.

[0101] If the patterning device MA is not protected, contamination may require cleaning or discarding the patterning device MA. Cleaning the patterning device MA interrupts valuable manufacturing time and discarding the patterning device MA is costly. Replacing the patterning device MA also interrupts valuable manufacturing time.

[0102] Figures 2 to 9 The various stages of the method for producing a diaphragm assembly 15 according to the invention are schematically depicted.

[0103] Figure 2 A stack 16 is depicted that includes a diaphragm layer 19 supported on a planar substrate 17. In the depicted embodiment, a single diaphragm layer 19 is shown, but it will be appreciated that more than one diaphragm layer may be present. The planar substrate 17 includes an interior region 17b and a border region 17a. Dashed lines schematically delimit the interior region 17b and the border region 17a, but it will be appreciated that the precise relative sizes of the interior region 17b and the border region 17a may vary as desired. Additionally, due to Figure 2 Depicting a cross section through the stack 16, it should also be understood that the boundary region 17a preferably forms a continuous ring around the inner region 17b. The stack also includes a first sacrificial layer 18 disposed on the planar substrate 17. The first sacrificial layer 18 is depicted as completely surrounding the planar substrate 17, but in some embodiments, the first sacrificial layer 18 may only partially surround the planar substrate 17. The planar substrate 17 may include a thin oxide layer on its surface, but preferably the planar substrate 17 is substantially free of an oxide layer. In an embodiment, the planar substrate 17 is a silicon-on-insulator (SOI) substrate. In such an SOI substrate, a pair of Si layers may be separated by an insulating layer (e.g., a SiO2 layer). In such an embodiment, the typical dimensions of the Si layer and the insulating layer may be, for example, 500 μm or more for the bottom Si layer, 1 μm or less for the insulating layer and 30 μm or less for the top Si layer. By using an SOI substrate instead of a Si substrate, the adverse effects of overetching may be further reduced, as will be illustrated below.

[0104] The stack also includes a diaphragm layer 19 disposed on the first sacrificial layer 18. Furthermore, the diaphragm layer 19 is depicted as surrounding the first sacrificial layer 18, but in alternative embodiments, the diaphragm layer 19 may only partially surround the first sacrificial layer 18 or be deposited on one face of the stack 16.

[0105] The stack also includes a second sacrificial layer 20. The second sacrificial layer 20 surrounds the diaphragm layer 19, but in alternative embodiments, the second sacrificial layer may only partially surround the diaphragm layer 19. In one embodiment, the second sacrificial layer 20 does not extend below or over the back side of the diaphragm layer 19. The below or back side of the stack is the side shown at the bottom of the figures and the above or front side of the stack is the side shown at the top of the figures.

[0106] In an embodiment of the present invention, the second sacrificial layer comprises tetraethyl orthosilicate (TEOS). In an embodiment, the second sacrificial layer may be applied to the stack by means of chemical vapor deposition (CVD) or the like. In such an embodiment, the step of applying the sacrificial layer is, for example, followed by an annealing step. Alternatively, in such an embodiment, the annealing step may be applied before the second sacrificial layer is deposited. In an embodiment of the present invention, boron silicate TEOS (B-TEOS) is applied instead of TEOS. In such an embodiment, the annealing step is applied after the second sacrificial layer is deposited. When a boron-containing TEOS (e.g. containing 4% to 8% boron) is used instead of TEOS, the diaphragm layer 19 will become doped with boron during the annealing step, thereby obtaining a doped diaphragm layer 19. By such doping of the diaphragm layer with boron, the diaphragm layer 19 can be made more resistant to etching, resulting in an increased yield of the manufacturing process of the diaphragm (e.g., a manufacturing process as illustrated below). The doping of the diaphragm layer 19 may also result in an increased strength of the diaphragm as manufactured.

[0107] The stack may also include several other material layers deposited on the planar substrate 17, which layers have various protective functions during the manufacturing process of the diaphragm assembly 15, or are used to enhance the properties of the diaphragm assembly 15, such as resistance to chemicals / environment and / or improved (thermo)mechanical strength and / or reduced imaging effects (for example by reducing surface film reflection).

[0108] In an embodiment, the planar substrate 17 is formed of silicon. For example, the planar substrate 17 has a shape such as a square, a circle, or a rectangle. The shape of the planar substrate 17 is not particularly limited. The size of the planar substrate 17 is not particularly limited.

[0109] Silicon may crystallize in a diamond cubic crystal structure. In an embodiment, the planar substrate 17 comprises cubic crystals of silicon. In an embodiment, the planar substrate 17 has a <100> crystallographic orientation.

[0110] The portion of the planar substrate 17, further referred to herein as the border region 17a, forms (after removal of the inner region of the planar substrate) part of the border of the diaphragm assembly 15. The border region 17a holds the diaphragm 19 of the diaphragm assembly 15.

[0111] The diaphragm layer 19 may include polycrystalline silicon (pSi). In an embodiment, polycrystalline silicon is formed by crystallizing amorphous silicon in at least one diaphragm layer 19. For example, in an embodiment, the diaphragm layer 19 is added to the stack 16 as an amorphous silicon layer. When the temperature increases, the amorphous silicon layer crystallizes into a polycrystalline silicon layer.

[0112] Alternatively, the diaphragm layer 19 as applied in the present invention may include MoSi2 or MoSiNx.

[0113] Figure 3 Depicts the stack 16 after a step in which the second sacrificial layer 20 has been removed from the underside of the stack 16. This step is optional and may not be necessary, where the initial stack 16 is provided without the second sacrificial layer on the underside. The second sacrificial layer 20 may be removed by any suitable means and the method of the present invention is not particularly limited by the particular method used.

[0114] Figure 4 A further step in the method is depicted in which a resist 21 is applied to the stack 16. The resist 21 may be a positive resist or a negative resist, and the method is not particularly limited by which resist is used. The resist is patterned so as to define portions of the stack 16 that will be etched in a subsequent etching step.

[0115] The stack 16 may then be etched by any suitable etching means to remove the second sacrificial layer 20, the diaphragm layer 19 and a portion of the first sacrificial layer 18 not protected by the resist 21. Again, the present invention is not particularly limited to the etching means used in this step and any suitable means may be used. Figure 5 The layer stack 16 is shown after the first etching step and after removal of the resist.

[0116] like Figure 6 As shown, a protective layer 22 is then added to the front side of the stack 16 to protect the multiple layers located at the front side of the stack 16 from subsequent etching steps. The protective layer 22 may include a cross-linked poly(p-xylene) polymer. For example, poly(p-xylene C) may be pinhole-free, which is used for layer thicknesses as small as about 600 nm. The protective layer 22 is applied as a continuous layer that is substantially free of pores so that the continuous layer provides a layer that is impermeable to the etchant. The protective layer 22 is not added to the back side of the stack 16, allowing the etchant to enter the planar substrate 17 and any diaphragm layer 19 located on the back side of the stack 16.

[0117] Figure 7The stack 16 is depicted after a bulk etching step of the interior region 17b of the planar substrate 17. In the depicted example, a wet anisotropic etch using tetramethylammonium hydroxide (TMAH) may be used to etch away the remaining diaphragm layer 19 as well as the interior region 17b of the planar substrate 17, but it will be appreciated that any suitable etchant that etches silicon at a substantially greater rate than silicon nitride may be used. TMAH has a substantially negligible etch rate for silicon nitride, and thus the silicon planar substrate 17 and diaphragm layer 19 are etched with a strong preference. Furthermore, it will be appreciated that other etchants may be used and that a key consideration is that the etchant selected largely prefers to etch the material of the planar substrate 17 and the diaphragm layer 19 over the material of the first sacrificial layer 18. Figure 7 It is seen that the diaphragm assembly 15 has now been roughly defined.

[0118] In an embodiment of the present invention, the planar substrate 17 is a SOI substrate including a bottom Si layer, a top Si layer, and an insulating layer (eg, a SiO2 layer) arranged between the bottom Si layer and the top Si layer. In such an arrangement, Figure 7 The bulk etching step illustrated in FIG. 1 can be replaced by the following three consecutive etching steps:

[0119] In a first etching step, the bottom Si layer may be removed using, for example, TMAH as etchant.

[0120] In a second etching step, the insulating layer buried between the two Si layers can be etched away, for example, by means of a buffered oxide etch (BOE). It can be noted that any overetching in the buried oxide layer will not affect the top Si layer, since Si etches much slower in BOE than oxide etching in TMAH.

[0121] In the third etch step, a shorter TMAH etch can be performed to remove the thinner top layer of Si. Because the third etch step can be much shorter than the first etch step, any over-etching effect on the sacrificial layer 18 will be less severe. Figure 7The effect of the body etching step illustrated in is much smaller. Therefore, the sacrificial layer 18 can be made very thin. Typically, a TOX layer having a thickness in the range of, for example, 150 nm thickness or less (such as a TOX layer of 5 nm to 100 nm) can be applied as the first sacrificial layer 18. When applied to an SOI substrate and the above-mentioned three-step etching process is applied, a TOX layer having a thickness in the range of, for example, 20 nm or less (such as 1 nm to 15 nm) can be applied instead of a 100 nm layer. As an alternative to the TOX layer acting as the sacrificial layer 18, a SiN layer can also be applied. Such a SiN layer can, for example, have a thickness of about 10 nm or less, such as from 1 nm to 5 nm. It should be noted that SiN can also be used as an alternative to TEOS or B-TEOS acting as the sacrificial layer. In an embodiment, the top Si layer and the bottom Si layer of the SOI substrate can be made of cSi.

[0122] Figure 8 The stack 16 is depicted once the protective layer 22 has been removed. Since the second sacrificial layer 20 is protected by the protective layer 22, the next step is a method of removing the second sacrificial layer 20 from the stack 16. In such an etching step, the etchant is selected so that the etchant preferentially etches the material of the second sacrificial layer 20 above the material of the diaphragm layer 19 and the planar substrate 17. In an example, the etchant includes phosphoric acid because this etchant etches silicon nitride at a rate of about 5 nm / min, while the etchant etches silicon oxide, silicon, and TEOS at a rate of about 0.2 nm / min. As such, the etchant etches the second sacrificial layer at a rate of about 25 times that of the other layers. In addition, the etchant etches silicon and its oxide at approximately the same rate. Since polysilicon oxidizes after deposition, silicon dioxide is formed that can migrate into the grain boundaries. In the case where the etchant etches both silicon and its oxide at approximately the same rate, the etchant may preferentially etch silicon oxide if the stack is exposed to the etchant for too long, thereby forming a recess in the surface, causing a weak spot. Furthermore, it will be appreciated that any etchant that etches the material of the planar substrate 17 and the material of the diaphragm layer 19 and its oxide at substantially the same rate, and substantially less than the rate at which the etchant etches the material of the first sacrificial layer, may be used.

[0123] Fig. 9 The diaphragm assembly 15 is depicted, comprising a frame including a boundary region 17 a of the planar substrate 17 , a layer of the first sacrificial layer 18 , and a diaphragm layer 19 , wherein the first sacrificial layer 18 is disposed between the boundary region 17 a and the diaphragm layer 19 .

[0124] Fig.10a and Fig.10b Depicted is a comparison of a diaphragm assembly 15 according to the present invention and a diaphragm assembly of another method before a final etching step. Both assemblies still include an upper sacrificial layer, but the upper sacrificial layer can be removed to provide the final diaphragm assembly. For clarity, the same reference numerals are used for equivalent features. Fig.10a The assembly of depicts a cross section of an assembly according to an embodiment of the present invention. On the boundary region 17a there is a stretched first sacrificial layer 18. On top of the stretched first sacrificial layer 18 is a diaphragm layer 19, which itself is stretched, and on top of the diaphragm layer 19 is a stretched second sacrificial layer 20. Because the first sacrificial layer 18 and the second sacrificial layer 20 are stretched, the resulting stack is wrinkle-free and substantially planar. In contrast, Fig.10b An assembly is depicted in which the first sacrificial layer 18 and the second sacrificial layer 20 are compressed and in which the diaphragm layer 19 is stretched. Due to the differences in the compression / tensile properties of the layers used, the resulting stack is wrinkled. The wrinkling may cause the diaphragm assembly to be weakened compared to the diaphragm assembly of the present invention.

[0125] In order to investigate the advantages of the present invention, tests were conducted in which the membrane assemblies of the present invention were overetched for 10 minutes and their physical properties were investigated. Each of the assemblies had an EUV transmittance of more than 92%, which is within the expected range of transmittance for EUV applications. In addition, the strength of the membrane assemblies produced according to the present invention is higher than that of the assemblies produced according to the previous method. In addition, the strength of the membrane assemblies produced is very consistent and no sample is produced that is significantly weaker than other samples. The method according to the present invention is also faster than the previous method, resulting in a reduction in cycle time of about 40%, and the stack is kept in a stretched state at all stages of the process, thereby preventing film damage caused by folding during production. The problem of notch formation caused by overetching is also solved, and a stronger membrane is formed. Due to the ability to produce stronger membranes more reliably and continuously, it may be possible to manufacture even thinner membrane layers, thereby obtaining improved EUV transmittance. Finally, because the membrane produced according to the present invention includes a stretching layer, there is a pre-tensioning degree in the final membrane assembly, which can allow the membrane layer to be further thinned without wrinkling or excessive weakening of the assembly.

[0126] Fig.11 A schematic cross section through a stack is depicted. The stack comprises a core 21, an IR suppressing layer 23, and capping layers 22a, 22b on each side of the core 21. The core 21 may be silicon, preferably p-silicon. It has been found that Fig.11The stack of structures in the embodiment of the present invention is sensitive to the IR suppressing layer 23 and / or the core 21 becomes oxidized during use in a lithography apparatus, in particular an EUV lithography apparatus. The thickness of the capping layers 22a, 22b is generally greater than about 2 nm. The capping layers may include a metal oxide.

[0127] Fig.12 Depicted is a schematic cross section through a stack according to an embodiment of the present invention. Fig.11 A stack of layers comprising a core 21, preferably comprising p-silicon, and an IR suppressing layer 23 on one side of the core 21, but it will be appreciated that the IR suppressing layer may be provided on the other side of the core 21 or indeed on both sides of the core 21. In this embodiment, the IR suppressing layer comprises metallic molybdenum, but the IR suppressing layer may comprise ruthenium or niobium. In some cases, the IR suppressing layer 23 may not be present. The stack also comprises a silicon oxide layer 25a, 25b on each side of the core 21. The stack also comprises a capping layer 22a, 22b, which in the depicted embodiment comprises zirconium oxide, but the capping layer may comprise yttrium oxide or another suitable capping layer material. There is an intermediate layer or interlayer 24 between the silicon oxide layer 25a, 25b and the capping layer 22a, 22b. The intermediate layer 24 in the depicted embodiment comprises zirconium oxide silicon, but it will be appreciated that the properties of the intermediate layer will depend on the material forming the intermediate layer. The addition of silicon oxide layers and silicon zirconium oxide layers results in the presence of a barrier that impedes the diffusion of oxygen and water through the stack and thereby protects the base IR suppressing layer 23 and the core 21 layer from oxidation. The silicon oxide layer may be from about 0.1 nm to about 3 nm thick. The cap layer may be from about 0.1 nm to about 2 nm thick. The intermediate layer may be from about 0.1 nm to about 2 nm thick.

[0128] Fig.13 Depicts a schematic cross section through a stack according to an embodiment of the present invention. Fig.12 The layers in Fig.13The stack is provided with silicon oxide layers 25a, 25b adjacent to the capping layers 22a, 22b. Because it has been unexpectedly realized that the thickness of the capping layer has no strong correlation with the effectiveness of the capping layer as an oxygen barrier, it has been found that the presence of multiple alternating material layers provides the desired oxygen barrier properties. For example, it has been found that simply doubling the thickness of the capping layer has no significant effect on the oxidation of the underlying silicon layer. Of course, significantly thicker capping layers can reduce or interrupt the oxidation of the underlying layer, but this will produce optical elements that are no longer suitable for use in lithographic equipment, for example the transmittance of the surface film will be reduced to below acceptable levels. Intermediate layers between the zirconium oxide capping layer and the silicon oxide layer are not shown, but it will be understood that an interface layer will be formed between adjacent layers. A certain number (n) of material layers can be provided to form the oxygen barrier layer, and n can be any number between 1 and 10, but it will be understood that the present invention is not particularly limited to ten alternating layers, and any suitable number that provides sufficient protection against oxidation and optical properties for lithographic equipment can be selected. Although the depicted embodiment indicates that two materials are used for the multilayer oxygen barrier, more than two materials can be used.

[0129] will understand, Fig.12 The embodiment shown in FIG. 1 has a single interface between multiple layers and Fig.13 An embodiment is depicted where multiple interfaces are present. Alternating thin layers (from about 0.1 nm to about 2 nm) of different materials creates a number of interfaces that act as oxygen barriers, and because the layers comprising the oxygen barrier layers are thinner, the reduction in transmittance of the stack is mitigated.

[0130] In an embodiment of the present invention, the stack includes a core layer of p-silicon, for example, a core layer having a thickness of 30 nm to 60 nm (preferably about 40 nm). The stack may also include a ruthenium-based capping layer. Such a Ru-based capping layer can be achieved, for example, by applying a molybdenum layer to the core layer and applying a Ru-based layer to the Mo layer by means of sputtering (e.g., DC sputtering). In such an embodiment, a Mo layer having a thickness in the range of 3 nm to 5 nm can be applied to the core layer, for example, and a Ru layer of approximately the same thickness (e.g., in the range of 3 nm to 5 nm) can be applied to the Mo layer. In such an arrangement, a Ru / Mo intermixed layer will be achieved at the interface between the Mo layer and the Ru layer. Such an intermixed layer will be amorphous or amorphous and will be a good barrier layer in the case of a high crystallization transition temperature. In order to withstand the higher EUV power during use, the applied Ru can be alloyed with Mo, Nb, Ta, Ti or Zr, i.e., to form an alloy. In an embodiment, the applied capping layer may be a multilayer structure having multiple Ru / Mo interface layers or multiple Ru / Mo intermixed layers. Such an embodiment may be achieved, for example, by applying Mo layers and Ru layers alternately to the core layer. Such a stack may, for example, include the following layer sequence: pSi-Mo-Ru-Mo-Ru. At each interface between the Mo layer and the Ru layer, a Ru / Mo intermixed layer will be produced, resulting in the following layer sequence: pSi-Mo-Ru / Mo intermixed-Ru-Ru / Mo intermixed-Mo-Ru / Mo intermixed-Ru. In such an embodiment, due to the use of multiple Mo and Ru layers, the thickness of the applied layer may be reduced. Such a multilayer capping layer with a thinner capping layer (for example, compared with a Mo and / or Ru layer having a thickness of 3 nm to 5 nm) will have a more amorphous structure, which will achieve improved barrier properties. Specifically, the diffusion of Mo through the Ru layer, which leads to oxidation of Mo at the surface, can be avoided or mitigated. In this regard, it can be pointed out that a Ru layer having a thickness of 3 nm to 5 nm will generally be crystalline or semi-crystalline. It has been observed that the crystallinity of Ru can be a limiting factor for a good barrier member. The application of multiple Ru layers with a more amorphous structure can thus provide an improved barrier layer. The multilayer structure with multiple Ru / Mo interfaces can be applied directly to the pSi core layer. Alternatively, the pSi core layer can be enclosed by a SiO2 layer or a SiON layer, onto which the multilayer structure with multiple Ru / Mo interfaces is applied.

[0131] The provided layer is not particularly limited by the method of providing the layer and any suitable method may be used. For example, the silicon oxide layer may be deposited by PVD from a silicon oxide target, or by reactive sputtering from a silicon target, or by an atomic layer deposition method. Wet chemical passivation of a p-Si core or thermal oxidation of a p-Si core may be used to provide the silicon oxide layer. Similarly, zirconium oxide or yttrium oxide or indeed any of the other suitable materials disclosed herein may be provided by similar techniques including but not limited to PVD, sputtering or ALD.

[0132] Although the lithographic apparatus is described in detail herein for use in the manufacture of ICs (integrated circuits), it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), diaphragm heads, etc. The substrate referred to herein may be processed before or after exposure, such as in a track or coating and developing system (a tool that typically applies a resist layer to a substrate and develops the exposed resist), a metrology tool, and / or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. In addition, the substrate may be processed more than once, such as to produce a multi-layer IC, so that the term "substrate" used herein may also refer to a substrate that already contains multiple processed layers.

[0133] Although specific embodiments of the present invention have been described above, it should be appreciated that the present invention may be practiced in other ways than those described. For example, individual layers may be replaced by multiple other layers that perform the same functions.

[0134] The above description is intended to be illustrative, and not limiting. It will therefore be apparent to those skilled in the art that modifications may be made to the invention described without departing from the scope of the claims set forth hereinafter.

[0135] 1. A method for manufacturing a diaphragm assembly for EUV lithography, the method comprising:

[0136] i) providing a stack, the stack comprising:

[0137] at least one diaphragm layer supported by a planar substrate, wherein the planar substrate includes an interior region and a border region surrounding the interior region; and a first sacrificial layer located between the planar substrate and the diaphragm layer;

[0138] ii) selectively removing the inner region of the planar substrate, wherein the step of selectively removing the inner region of the planar substrate comprises using an etchant having a similar etch rate for the diaphragm layer and its oxide and having a substantially different etch rate for the first sacrificial layer;

[0139] The diaphragm assembly includes: a diaphragm formed by the at least one diaphragm layer; and a boundary portion holding the diaphragm, the boundary portion including the boundary area of ​​the planar substrate and the first sacrificial layer located between the boundary portion and the diaphragm layer.

[0140] 2. The method of aspect 1, wherein the first sacrificial layer is a tensile layer.

[0141] 3. The method according to aspect 1 or 2, wherein the stack further comprises a second sacrificial layer on the at least one diaphragm layer.

[0142] 4. The method according to any one of aspects 1 to 3, wherein the method comprises removing at least a portion of the second sacrificial layer from at least one face of the layer stack before step ii).

[0143] 5. The method according to any one of aspects 1 to 4, wherein the method further comprises providing a resist on the layer stack and patterning the resist before step ii).

[0144] 6. The method of clause 5, wherein the method further comprises etching the second sacrificial layer, the diaphragm, and at least a portion of the first sacrificial layer before step ii).

[0145] 7. The method of clause 6, wherein before step ii), the method further comprises applying a protective layer to the front side of the layer stack to protect layers at the front side of the layer stack from subsequent etching steps.

[0146] 8. The method of aspect 7, wherein the method further comprises removing the protective layer from the stack.

[0147] 9. The method of clause 8, wherein the method further comprises removing any remaining second sacrificial layer from the upper surface of the at least one diaphragm layer.

[0148] 10. A method according to any preceding aspect, wherein the planar substrate is a wafer, optionally a silicon wafer, and / or wherein at least one of the first sacrificial layer and the second sacrificial layer comprises silicon nitride, and / or wherein the at least one diaphragm layer comprises at least one polycrystalline silicon layer, preferably formed by crystallizing at least one amorphous silicon layer, and / or wherein the protective layer comprises a cross-linked polymer, preferably a poly(p-xylene) polymer, preferably a poly(p-xylene) or a ProTEK® type material.

[0149] 11. A method according to any preceding aspect, wherein the step of removing any remaining second sacrificial layer from the upper surface of the at least one diaphragm layer comprises etching using an etchant having an etch rate for the second sacrificial layer that is substantially higher than the etch rate for the at least one diaphragm layer and its oxide.

[0150] 12. The method of clause 11, wherein the etchant comprises phosphoric acid.

[0151] 13. A diaphragm assembly for EUV lithography, the diaphragm assembly comprising:

[0152] a diaphragm formed of at least one diaphragm layer including polycrystalline silicon or single crystal silicon; and

[0153] a boundary portion that holds the diaphragm;

[0154] wherein the border region is formed by a planar substrate including an inner region and a border region surrounding the inner region, wherein the border portion is formed by selectively removing the inner region of the planar substrate,

[0155] wherein the planar substrate comprises a core layer and a sacrificial layer, such that the boundary portion comprises the core layer and the sacrificial layer, wherein the sacrificial layer is located between the core layer and the at least one diaphragm layer,

[0156] The etching rate of the etchant on the core layer and the at least one diaphragm layer is substantially different from the etching rate of the etchant on the sacrificial layer.

[0157] 14. The diaphragm assembly of aspect 13, wherein the sacrificial layer comprises a tensile material.

[0158] 15. The diaphragm assembly of aspects 13 or 14, wherein the sacrificial layer comprises silicon nitride.

[0159] 16. The diaphragm assembly of aspects 13 to 15, wherein the core layer comprises silicon.

[0160] 17. The diaphragm assembly of any one of aspects 13 to 16, wherein the core layer and the at least one diaphragm layer comprise silicon.

[0161] 18. The diaphragm assembly of any one of aspects 13 to 17, wherein an etch rate of the core layer and the at least one diaphragm layer is substantially less than an etch rate of the sacrificial layer.

[0162] 19. The diaphragm assembly of aspect 18, wherein the etchant comprises phosphoric acid.

[0163] 20. The diaphragm assembly of any one of aspects 13 to 19, wherein the diaphragm assembly is used in a patterning device or a dynamic air lock.

[0164] 21. The diaphragm assembly of any one of aspects 13 to 20, wherein the diaphragm assembly comprises a ruthenium-based capping layer.

[0165] 22. The diaphragm assembly of aspect 21, wherein the ruthenium-based capping layer is disposed on a molybdenum layer.

[0166] 23. The diaphragm assembly of aspect 22, wherein the molybdenum layer is disposed on the core layer.

[0167] 24. The diaphragm assembly according to aspect 22 or 23 further includes a Ru / Mo intermixed layer at the interface of the molybdenum layer and the ruthenium-based capping layer.

[0168] 25. The diaphragm assembly according to aspect 24 further comprises a plurality of Ru / Mo intermixed layers.

[0169] 26. Use of a diaphragm assembly manufactured according to any of aspects 1 to 12 or according to any of aspects 13 to 25 or an optical element according to any of aspects 28 to 37 in a lithographic apparatus, preferably an EUV lithographic apparatus.

[0170] 27. A lithographic apparatus comprising a diaphragm assembly manufactured according to the method of any one of aspects 1 to 12, or a diaphragm assembly according to any one of aspects 13 to 25, or an optical element manufactured according to the method of any one of aspects 28 to 37 or according to aspects 38 to 42.

[0171] 28. An optical element for a lithographic apparatus, the optical element comprising a stack, wherein the stack comprises a core, a cover layer, and an oxygen barrier layer between the cover layer and the core.

[0172] 29. An optical element according to aspect 28, wherein the oxygen barrier layer comprises at least one silicon oxide layer and at least one zirconium oxide or yttrium oxide layer.

[0173] 30. An optical element according to aspect 28 or 29, wherein the oxygen barrier layer comprises a zirconium oxide silicon layer or a yttrium oxide silicon layer.

[0174] 31. An optical element according to aspect 30, wherein the zirconium oxide silicon layer or the yttrium oxide silicon layer is disposed between the silicon oxide layer and the zirconium oxide layer or the yttrium oxide silicon layer.

[0175] 32. An optical element according to any of aspects 28 to 31, wherein the oxygen barrier layer comprises a plurality of alternating layers of material.

[0176] 33. An optical element according to aspect 32, wherein the alternating material layers include silicon oxide, zirconium oxide, zirconium oxide silicon, zirconium nitride, silicon nitride, yttrium oxide, zirconium boride, aluminum oxide, aluminum nitride, titanium oxide, titanium nitride, tantalum oxide and tantalum nitride, preferably, wherein the oxygen barrier layer includes alternating layers of silicon oxide and zirconium oxide or yttrium oxide.

[0177] 34. An optical element according to any one of aspects 28 to 33, wherein the optical element also comprises an IR suppressive layer, preferably wherein the IR suppressive layer comprises molybdenum, niobium, ruthenium or a combination thereof.

[0178] 35. An optical element according to any one of aspects 28 to 34, wherein the core comprises two sides, and wherein an oxygen barrier is disposed between each side of the core and a respective cover layer on each side of the core.

[0179] 36. An optical element according to any one of clauses 28 to 35, wherein the optical element comprises a pellicle, a mirror, a dynamic air lock, or any other element within a lithographic apparatus that interacts with lithographic radiation.

[0180] 37. An optical element according to any of aspects 32 to 36, wherein the oxygen barrier layer comprises alternating layers of materials having a thickness from about 0.1 nm to about 2 nm.

[0181] 38. A method of manufacturing an optical element for a lithographic apparatus, the method comprising:

[0182] providing a core;

[0183] providing a first material on one or both sides of the core;

[0184] providing the first material to a second material, or providing the second material on the first material, the first material and the second material forming an oxygen barrier layer,

[0185] The first material and the second material are different and are selected from the following: silicon oxide, zirconium oxide, zirconium oxide silicon, silicon nitride, zirconium nitride, yttrium oxide, zirconium boride, aluminum oxide, aluminum nitride, titanium oxide, titanium nitride, tantalum oxide and tantalum nitride, preferably, one of the first material and the second material is silicon oxide and the other is zirconium oxide or yttrium oxide.

[0186] 39. A method of manufacturing an optical element for a lithographic apparatus, wherein the method comprises providing one or more IR suppressing layers prior to depositing the first material.

[0187] 40. The method of aspect 38 or 39, wherein the steps of providing a first material and providing a second material are repeated at least once to form an oxygen barrier layer comprising a plurality of layers.

[0188] 41. The method according to aspect 40, wherein the steps of providing the first material and providing the second material are repeated 2 to 10 times.

[0189] 42. A method according to any one of aspects 38 to 41, wherein the first and / or second material is provided by physical vapor deposition (PVD), reactive sputtering, co-sputtering, atomic layer deposition (ALD), plasma enhanced ALD, thermal oxidation, or wet chemical passivation, or any other suitable deposition technique.

Claims

1. A diaphragm assembly for EUV lithography, the diaphragm assembly comprising: a diaphragm formed from at least one core layer comprising MoSiNx; and a boundary portion that holds the diaphragm; The membrane also includes a cover layer, which forms an amorphous barrier layer. 2 . The diaphragm assembly of claim 1 , wherein the amorphous barrier layer comprises Ru alloyed with Mo, Nb, Ta, Ti, or Zr. The diaphragm assembly of claim 1 , wherein the amorphous barrier layer comprises a Ru / Mo intermixed layer. 4 . The diaphragm assembly according to claim 3 , wherein the Ru / Mo intermixed layer is disposed at an interface of the molybdenum layer and the ruthenium-based capping layer. 5 . The diaphragm assembly according to claim 3 , further comprising a plurality of Ru / Mo intermixed layers.

6. The diaphragm assembly of claim 4, wherein the molybdenum layer is disposed on the core layer.

7. The diaphragm assembly of claim 1 further comprising an oxygen barrier layer between the core layer and the cover layer.

8. The diaphragm assembly of claim 7, wherein the oxygen barrier layer is a multilayer oxygen barrier comprising at least two materials.

9. The diaphragm assembly of claim 8, wherein the multi-layer oxygen barrier layer comprises alternating layers of material having a thickness of from 0.1 nm to about 2 nm.

10. The diaphragm assembly of claim 7, wherein the oxygen barrier layer comprises a zirconium oxide silicon layer or a yttrium oxide silicon layer.

11. The diaphragm assembly of any one of claims 1 to 10, wherein the diaphragm assembly is used in a patterning device or a dynamic gas lock. 12 . A diaphragm assembly comprising the diaphragm assembly according to claim 1 and a frame attached to the boundary portion holding the diaphragm.

13. A mask assembly comprising a patterning device and the pellicle assembly according to claim 12 attached to the patterning device.

14. A component of a lithographic apparatus comprising a diaphragm assembly according to any one of claims 1 to 11.

15. An optical component of a lithographic apparatus, comprising: a core layer comprising MoSiNx; and A capping layer forms an amorphous barrier layer comprising Ru alloyed with Mo, Nb, Ta, Ti or Zr.

16. The optical element of claim 15, further comprising an oxygen barrier layer between the core layer and the cover layer.

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