Membrane for EUV lithography

Abstract

To provide a membrane for EUV lithography having high emissivity and a low possibility of failing.SOLUTION: In one arrangement, a membrane comprises a stack having layers in the following order: a first capping layer comprising an oxide of a first metal; a base layer comprising a compound comprising a second metal and an additional element selected from the group consisting of Si, B, C and N; and a second capping layer comprising an oxide of a third metal, where the first metal is different from the second metal and the third metal is the same as or different from the first metal.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Patent Application No. 16166775.3, filed April 25, 2016, European Patent Application No. 16195123.1, filed October 21, 2016, and European Patent Application No. 16205298.9, filed December 20, 2016, all of which are incorporated by reference in their entireties herein.

[0002] The present invention relates to a membrane, a patterning device assembly, and a dynamic gas lock assembly for EUV lithography. [Background technology]

[0003]

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, alternatively called a mask or reticle, can be used to generate the circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on the substrate (e.g. a silicon wafer). Transfer of the pattern is typically by imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. Generally, a single substrate will contain a network of adjacent target portions that are successively patterned.

[0004]

[0004] Lithography is widely recognized as one of the primary steps in manufacturing ICs and other devices and / or structures. However, as the dimensions of features produced using lithography become finer, lithography is becoming a more critical factor in enabling the manufacture of miniature ICs or other devices and / or structures.

[0005]

[0005] A theoretical estimate of the limit of pattern printing is given by the Rayleigh resolution criterion as shown in equation (1).

number

[0006]

[0006] To shorten the exposure wavelength and therefore the minimum printable size, it has been proposed to use extreme ultraviolet (EUV) radiation sources. EUV radiation is electromagnetic radiation having a wavelength in the range of 10-20 nm, for example in the range of 13-14 nm. It has also been proposed that EUV radiation having a wavelength less than 10 nm, for example in the range of 5-10 nm, such as 6.7 nm or 6.8 nm, may be used. Such radiation is called extreme ultraviolet radiation or soft x-ray radiation. Possible radiation sources include, for example, laser-produced plasma sources, discharge plasma sources, or radiation sources based on synchrotron radiation provided by electron storage rings.

[0007]

[0007] A lithographic apparatus includes a patterning device (e.g. a mask or a reticle). Radiation is provided through or reflected from the patterning device to form an image on a substrate. A membrane assembly may be provided to protect the patterning device from airborne particles and other forms of contamination. A membrane assembly for protecting the patterning device may be called a pellicle. Contamination on a surface of the patterning device may cause manufacturing defects on the substrate. The membrane assembly may include a border and a membrane stretched across the border.

[0008] It is desirable for the membrane to have a combination of high emissivity and low probability of failure. It is also desirable for the membrane to have high EUV transmittance. Summary of the Invention

[0009]

[0009] According to one aspect of the present invention, there is provided a membrane for EUV lithography, the membrane comprising a stack having multiple layers in the following order: a first capping layer comprising an oxide of a first metal; a base layer comprising a compound comprising a second metal and an additional element selected from the group consisting of Si, B, C, and N; and a second capping layer comprising an oxide of a third metal, wherein the first metal is different from the second metal and the third metal is the same as or different from the first metal in the second capping layer.

[0010] According to one aspect of the invention, there is provided a membrane for EUV lithography, the membrane comprising a membrane layer comprising a compound comprising a metal and an additional element, at least a portion of both outer surfaces of the membrane being formed by an oxide of the compound or the additional element, the membrane layer comprising: the metal is Mo and the additional element is Si; the metal is Ru and the additional element is Si; the metal is Zr and the additional element is Si; the metal is La and the additional element is Si; the metal is Sc and the additional element is Si; the metal is Y and the additional element is Si; the metal is Nb and the additional element is Si; The metal is Mo and the additional element is B, or the metal is Ru and the additional element is B; The metal is Zr and the additional element is B, or The metal is Nb and the additional element is B, or The metal is Ti and the additional element is B, or the metal is La and the additional element is B, or The metal is Zr and the additional element is C; A membrane is provided.

[0011]

[0011] According to one aspect of the present invention, there is provided a method for manufacturing a membrane for EUV lithography, the method comprising providing a base layer and providing an emissivity layer, the emissivity layer having a higher emissivity in the infrared than the base layer, the emissivity layer being provided on an irregular support surface, the emissivity layer having a thickness such that irregularities in the irregular support surface produce corresponding irregularities in a surface of the emissivity layer opposite the irregular support surface.

[0012]

[0012] One aspect of the present invention provides a method for manufacturing a membrane for EUV lithography, the method comprising using a mask to define an area in a support structure to be etched and etching the defined area, wherein the mask has a shape defined by a mask perimeter that includes a plurality of straight line sections, and the interior angle between each pair of directly adjacent straight line sections is greater than 90 degrees.

[0013]

[0013] One aspect of the present invention provides a membrane for EUV lithography including a freestanding portion, the shape of the freestanding portion being defined by a freestanding portion boundary including a plurality of substantially straight sections, and the interior angle between each pair of immediately adjacent straight sections is greater than 90 degrees.

[0014]

[0014] One aspect of the present invention provides a membrane for EUV lithography, the membrane comprising a base layer and a capping layer comprising an alloy of Mo and at least one other metal.

[0015]

[0015] According to one aspect of the present invention, there is provided a membrane for EUV lithography, the membrane including a base layer and a capping layer, the capping layer including borosilicate glass.

[0016] According to one aspect of the present invention, there is provided a membrane for EUV lithography, the membrane comprising: YSi 2 , ZrSi 2 , LaSi 2 , and NbSi 2 A membrane is provided that includes a base layer that includes one or more of:

[0017]

[0017] According to one aspect of the present invention, there is provided a membrane for EUV lithography using EUV radiation having a wavelength λ, the membrane comprising a stack of multiple layers in the following order: a first protective capping layer, a first emissivity layer having a thickness of λ / 2, a first barrier layer having a thickness of λ / 4, and a base layer, the first protective capping layer having a refractive index matched to the refractive index of the first emissivity layer and the refractive index of the first barrier layer, and the thicknesses of the multiple layers selected to achieve destructive interference between EUV reflections from interfaces on either side of the membrane.

[0018] According to one aspect of the present invention, there is provided a cleaning tool for cleaning a membrane for EUV lithography, the cleaning tool including a chamber including an inlet opening and an exhaust opening for providing a laminar gas flow through the chamber such that the direction of the laminar flow is parallel to an outer surface of the membrane, an interface plate arranged to hold the membrane in the chamber, and a vibration stage coupled to the interface plate and arranged to vibrate the membrane such that contaminant particles are released from the outer surface of the membrane. Alternatively, instead of the vibration stage, an acoustic speaker in front of the membrane is arranged to vibrate the membrane with sound waves.

[0019]

[0019] One aspect of the present invention provides a method for manufacturing a membrane for EUV lithography, the method including providing a base layer or a stack including a base layer, and forming an amorphous capping layer on the base layer or stack.

[0020] According to one aspect of the invention, there is provided a membrane for EUV lithography, the membrane including a base layer and an amorphous capping layer providing an outer surface of the membrane.

[0021]

[0021] According to one aspect of the invention, a membrane for EUV lithography is provided, the membrane comprising a base layer and a capping layer providing an outer surface of the membrane, the capping layer having a proportion of at least 20% sp 3 and a carbon-containing capping layer having carbon.

[0022]

[0022] One aspect of the present invention provides a membrane for EUV lithography, the membrane including a base layer and a capping layer providing an outer surface of the membrane, the capping layer including a transition metal doped with an alkali metal or alkaline earth metal.

[0023] According to one aspect of the invention, a membrane for EUV lithography is provided, the membrane comprising a base layer and a capping layer providing an outer surface of the membrane, the capping layer being M1. x M2 y O z wherein M1 is an alkali metal or an alkaline earth metal and M2 is a transition metal, optionally a rare earth metal.

[0024]

[0024] One aspect of the present invention provides a method for manufacturing a membrane for EUV lithography, the method comprising forming at least one base layer on a support structure and etching into the support structure in selected areas below the base layer to form a free-standing membrane including the base layer, wherein the difference in thermal expansion coefficients between the support structure and the base layer is less than the difference in thermal expansion coefficients between silicon and the base layer.

[0025]

[0025] One aspect of the present invention provides a membrane for EUV lithography including a free-standing portion, the free-standing portion including a base layer and connected to a non-free-standing portion supported by a support structure, wherein the difference in thermal expansion coefficients between the support structure and the base layer is less than the difference in thermal expansion coefficients between silicon and the base layer.

[0026]

[0026] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, in which: [Brief description of the drawings]

[0027] [Figure 1] 1 depicts a lithographic apparatus according to one embodiment of the invention; [Diagram 2]

[0028] 1 depicts a more detailed view of the lithographic apparatus; [Diagram 3]

[0029] 1A-1D illustrate, in schematic cross-sectional view, membranes according to different embodiments of the invention; [Figure 4]

[0029] Membranes according to different embodiments of the invention are illustrated diagrammatically in cross-section. [Diagram 5]

[0029] Membranes according to different embodiments of the invention are illustrated diagrammatically in cross-section. [Figure 6]

[0029] Membranes according to different embodiments of the invention are illustrated diagrammatically in cross-section. [Figure 7]

[0029] Membranes according to different embodiments of the invention are illustrated diagrammatically in cross-section. [Figure 8]

[0029] Membranes according to different embodiments of the invention are illustrated diagrammatically in cross-section. [Figure 9]

[0030] 1 is a graph comparing the fracture toughness and yield strength of various materials. [Figure 10]

[0031] 1 is a graph showing the temperature dependence of yield strength for various materials. [Figure 11]

[0032] 13A-13C are graphs showing the transmittance, reflectance, and absorbance as a function of wavelength for MoSi2 of different thicknesses, respectively, according to theory and experiment. [Figure 12] 1 is a graph showing the transmittance, reflectance, and absorbance as a function of wavelength for MoSi2 of different thicknesses according to theory and experiment, respectively. [Figure 13] 1 is a graph showing the transmittance, reflectance, and absorbance as a function of wavelength for MoSi2 of different thicknesses according to theory and experiment, respectively. [Figure 14]

[0033] The distribution of EUV transmittance through a 1.5 cm diameter MoSi2 membrane is shown. [Figure 15]

[0034] Figure 1 shows the variation of EUV transmittance with wavelength for a MoSi2 membrane exposed at 0.65 W / cm2 for 20 hours (no significant difference is observed between the central and other areas of the membrane). [Figure 16]

[0035] 1 shows the variation of EUV transmittance with wavelength for a MoSi2 membrane exposed at 1.8 W / cm2 for 20 hours (the dashed line indicates the transmittance in the central region). [Figure 17]

[0036] 1 illustrates an example process flow for producing a membrane according to one embodiment. [Figure 18] 1 illustrates an example process flow for producing a membrane according to one embodiment. [Figure 19] 1 illustrates an example process flow for producing a membrane according to one embodiment. [Figure 20] 1 illustrates an example process flow for producing a membrane according to one embodiment. [Figure 21] 1 illustrates an example process flow for producing a membrane according to one embodiment. [Figure 22] 1 illustrates an example process flow for producing a membrane according to one embodiment. [Figure 23] 1 illustrates an example process flow for producing a membrane according to one embodiment. [Figure 24] 1 illustrates an example process flow for producing a membrane according to one embodiment. [Diagram 25] 1 illustrates an example process flow for producing a membrane according to one embodiment. [Figure 26]

[0037] 1 illustrates, in cross-sectional view, a schematic diagram of a membrane having an emissivity layer formed on an irregular support surface formed by anisotropic etching of a polysilicon base layer. [Figure 27]

[0038] 1A-1C are schematic cross-sectional views illustrating steps in a method of manufacturing a membrane having an emissivity layer formed on an irregular support surface formed by anisotropic etching of a layer of polysilicon in addition to a base layer. [Figure 28]

[0038] The steps in a method for manufacturing a membrane having an emissivity layer formed on an irregular support surface formed by anisotropic etching of a layer of polysilicon in addition to a base layer are illustrated generally in cross-sectional views. [Figure 29]

[0039] FIG. 1 illustrates a schematic top view of the mask used to define the areas to be etched to release the membrane (left) and the resulting free-standing portion of the membrane (right), where the mask and free-standing portion have 90 degree corners. [Diagram 30]

[0040] FIG. 1 illustrates a schematic top view of the mask (left) used to define the areas to be etched to release the membrane, and the resulting free-standing portion of the membrane (right), where the mask and free-standing portion have corners with internal angles greater than 90 degrees to reduce stress concentrations at the corners. [Diagram 31]

[0041] 1 illustrates generally in cross-section a membrane having a base layer and a capping layer, the capping layer comprising an alloy of Mo and at least one other metal or comprising borosilicate glass. [Diagram 32]

[0042] 1 shows a schematic diagram of a membrane in cross-section having a base layer, a capping layer first sub-layer comprising MoSi2 or Si, and a capping layer second sub-layer comprising B. [Diagram 33]

[0043] 1 illustrates a schematic diagram of a cleaning tool for monitoring and cleaning a membrane according to the present invention. [Diagram 34]

[0044] 1 shows schematic diagrams of stages in a method for producing a membrane; [Diagram 35]

[0045] 35 illustrates diagrammatically a further stage in the manufacturing method of FIG. 34; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028]

[0046] 1 illustrates a lithographic apparatus 100 including a source collector module SO according to an embodiment of the present invention. an illumination system (or illuminator) IL configured to condition a radiation beam B (eg EUV radiation); - a support structure (e.g. mask table) MT configured to support a patterning device (e.g. mask or reticle) MA and connected to a first positioner PM configured to accurately position the patterning device; and a substrate table (e.g., a wafer table) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate; and - a projection system (e.g. a reflection projection system) PS configured to project a pattern imparted to a radiation beam B by a patterning device MA onto a target portion C (e.g. comprising one or more dies) of a substrate W.

[0029]

[0047] The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping or controlling radiation.

[0030]

[0048] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as whether or not the patterning device is held in a vacuum environment. The support structure MT may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device MA. The support structure MT may be for example a frame or a table, which may be fixed or movable as required. The support structure MT may ensure that the patterning device MA is at a desired position, for example with respect to the projection system PS.

[0031]

[0049] The term "patterning device" should be interpreted broadly as referring to any device that can be used to impart a radiation beam B with a pattern in its cross-section to create a pattern in a target portion C of a substrate W. The pattern imparted to the radiation beam B corresponds to a particular functional layer in a device being created in the target portion C, such as an integrated circuit.

[0032]

[0050] The patterning device MA may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable liquid crystal display (LCD) panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern to the radiation beam which is reflected by the mirror matrix.

[0033]

[0051] Like the illumination system IL, the projection system PS may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, etc. optical components, or any combination thereof, as appropriate to the exposure radiation used, or other factors such as the use of a vacuum. It may be desirable to use a vacuum for EUV radiation, as other gases may be too absorbing of the radiation. Therefore, a vacuum environment may be provided throughout the beam path using a vacuum wall and vacuum pumps.

[0034]

[0052] As here depicted, lithographic apparatus 100 is of a reflective type (e.g., uses a reflective mask).

[0035]

[0053] Lithographic apparatus 100 may be of a type having two (dual stage) or more substrate tables WT (and / or two or more support structures MT). In such a "multi-stage" lithographic apparatus, the additional substrate tables WT (and / or the additional support structures MT) may be used in parallel, or preparatory steps may be performed on one or more substrate tables WT (and / or one or more support structures MT) while another one or more substrate tables WT (and / or one or more other support structures MT) are being used for exposure.

[0036]

[0054] Referring to FIG. 1, the illumination system IL receives a beam of extreme ultraviolet radiation from a source collector module SO. Methods for generating EUV light include, but are not necessarily limited to, converting a material having one or more emission lines in the EUV range and having at least one element, such as, for example, xenon, lithium, or tin, into a plasma state. In one such method, often referred to as laser-produced plasma ("LPP"), the required plasma can be generated by irradiating a fuel, such as a droplet, stream, or cluster of a material having the required line-emitting element, with a laser beam. The source collector module SO can be part of an EUV radiation system that includes a laser, not shown in FIG. 1, to provide the laser beam for exciting the fuel. The resulting plasma emits output radiation, e.g., EUV radiation, which is collected using a radiation collector disposed in the source collector module. The laser and source collector module SO can be coupled to a CO 2 laser to provide the laser beam for fuel excitation. 2 If a laser is used, it may be a separate component.

[0037]

[0055] In such a case, the laser is not considered to form part of the lithographic apparatus 100 and the radiation beam B is passed from the laser to the source collector module SO with the aid of a beam delivery system, e.g. comprising suitable directing mirrors and / or beam expanders. In other cases the source may be an integral part of the source collector module SO, for example when the source is a discharge produced plasma EUV generator, often referred to as a DPP source.

[0038]

[0056] The illumination system IL may comprise an adjuster for adjusting the angular intensity distribution of the radiation beam. Typically, at least the outer and / or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illumination system may be adjusted. The illumination system IL may also include various other components, such as faceted field and pupil mirror devices. The illumination system IL may condition the radiation beam B to have a desired uniformity and intensity distribution across its cross-section.

[0039]

[0057] The radiation beam B is incident on a patterning device (e.g. mask) MA, held on a support structure (e.g. mask table) MT, and is patterned by the patterning device MA. After reflection from the patterning device (e.g. mask) MA, the radiation beam B passes through a projection system PS, which focuses the radiation beam B onto a target portion C of a substrate W. With the aid of a second positioner PW and a position sensor PS2 (e.g. an interferometer arrangement, a linear encoder or a capacitive sensor), the substrate table WT can be accurately moved, for example to position a different target portion C in the path of the radiation beam B. Similarly, the patterning device (e.g. mask) MA can be accurately positioned with respect to the path of the radiation beam B using a first positioner PM and another position sensor PS1. The patterning device (e.g. mask) MA and substrate W can be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0040]

[0058] 2 shows lithographic apparatus 100 in more detail, including a source collector module SO, an illumination system IL, and a projection system PS. An EUV radiation-emitting plasma 210 may be formed by a plasma source. EUV radiation may be produced by a gas or vapor, such as Xe gas, Li vapor, or Sn vapor, from which the radiation-emitting plasma 210 is created to emit radiation in the EUV range of the electromagnetic spectrum. In one embodiment, a plasma of excited tin (Sn) is provided to produce EUV radiation.

[0041]

[0059] Radiation emitted by the radiation emitting plasma 210 passes from the source chamber 211 into the collector chamber 212 .

[0042]

[0060] The collector chamber 212 may include a radiation collector CO. Radiation traversing the radiation collector CO may be focused at a virtual source point IF. The virtual source point IF is commonly referred to as an intermediate focus, and the source collector module SO is positioned such that the virtual source point IF is located at or near an opening 221 of the enclosure structure 220. The virtual source point IF is an image of the radiation emitting plasma 210.

[0043]

[0061] The radiation then traverses an illumination system IL, which may include a faceted field mirror device 22 and a faceted pupil mirror device 24 arranged to provide a desired angular distribution of the unpatterned beam 21 at the patterning device MA as well as a desired uniformity of the radiation intensity at the patterning device MA. Upon reflection of the unpatterned beam 21 off the patterning device MA, held by a support structure MT, a patterned beam 26 is formed, which is imaged by the projection system PS via reflective elements 28, 30 onto a substrate W held by a substrate table WT.

[0044]

[0062] In general, there may be more elements in the illumination system IL and projection system PS than are shown, and furthermore there may be more mirrors than are shown, for example there may be one to six additional reflective elements in the projection system PS than are shown in Figure 2.

[0045]

[0063] Alternatively, the source collector module SO may be part of an LPP radiation system.

[0046]

[0064] As shown in Figure 1, in an embodiment, lithographic apparatus 100 includes an illumination system IL and a projection system PS. The illumination system IL is configured to emit a radiation beam B. The projection system PS is separated from a substrate table WT by an intervening space. The projection system PS is configured to project a pattern imparted to the radiation beam B onto a substrate W. This pattern is for EUV radiation in the radiation beam B.

[0047]

[0065] The intervening space between the projection system PS and the substrate table WT may be at least partially evacuated, The intervening space may be bounded at the location of the projection system PS by a solid surface from which the used radiation is directed towards the substrate table WT.

[0048]

[0066] In one embodiment, the lithographic apparatus 100 includes a dynamic gas lock. The dynamic gas lock includes a membrane assembly 80. In one embodiment, the dynamic gas lock includes a hollow portion covered by the membrane assembly 80 located in an intervening space. The hollow portion is located around the path of the radiation. In one embodiment, the lithographic apparatus 100 includes a gas blower configured to flush the inside of the hollow portion with a flow of gas. The radiation travels through the membrane assembly before impinging on the substrate W.

[0049]

[0067] In one embodiment, the lithographic apparatus 100 includes a membrane assembly 80. As explained above, in one embodiment, the membrane assembly 80 is for a dynamic gas lock. In this case, the membrane assembly 80 acts as a filter to filter out DUV radiation. Additionally or alternatively, in one embodiment, the membrane assembly 80 is a pellicle for a patterning device MA for EUV lithography. The membrane assembly 80 of the present invention can be used for other purposes, such as a dynamic gas lock or pellicle, or a spectral purity filter. In one embodiment, the membrane assembly 80 includes a membrane 40, which is also referred to as a membrane stack. In one embodiment, the membrane is configured to transmit at least 80% of the incident EUV radiation.

[0050]

[0068] In one embodiment, membrane assembly 80 is configured to enclose the patterning device MA to protect it from airborne particles and other forms of contamination that can cause manufacturing defects on the substrate W. For example, in one embodiment, the pellicle is configured to reduce the likelihood of particles migrating into the stepping field of the patterning device MA in lithographic apparatus 100.

[0051]

[0069] If the patterning device MA is left unprotected, contamination may result which requires cleaning or discarding the patterning device MA. Cleaning the patterning device MA interrupts valuable production time, discarding the patterning device MA is expensive, and replacing the patterning device MA also interrupts valuable production time.

[0052]

[0070] The EUV radiation incident on the membrane 40 will add heat to the membrane 40. This heat will increase the temperature of the membrane 40. With current EUV sources, the temperature of the membrane typically reaches about 800-900° C. Future EUV sources will have higher power and may apply a larger heat load. If the temperature of the membrane 40 increases too much, the performance or lifespan of the membrane 40 may be reduced. It may even cause the membrane 40 to fail completely.

[0053]

[0071] The materials used for the various layers of membrane 40 need to fulfill various functional requirements, such as a) having an emissivity layer to increase heat load resistance, b) having an outer capping layer (OLT) to protect the membrane from the harsh EUV scanner environment and extend its lifetime, and c) having a barrier layer to prevent diffusion / mixing of any of these layers.

[0054]

[0072] It is therefore desirable to design a robust membrane 40 that has extremely low EUV reflectivity (eg, EUVR<0.05%) while meeting all other functional requirements and allowing a large process window for sufficient manufacturability yield.

[0055]

[0073] Materials used in some existing membranes have good mechanical properties and EUV transmittance, but relatively low emissivity in the infrared. This low emissivity limits the rate at which membranes made from such materials can radiate heat. If no additional layers are added, the membranes will become too hot during use and fail. To increase the emissivity and improve performance, capping layers with high emissivity have been added to such membranes. However, such capping layers can undesirably increase EUV reflectance. For example, metals such as Ru, Mo, Zr, and Nb have good emissivity but relatively high reflectance. Furthermore, it has been found that capping layers can degrade during use. For example, metals such as Ru, Mo, Zr, and Nb will oxidize during use if not protected. Photoionic etching is used to remove SiN and SiO, which are inherently relatively stable at high temperatures. 2 This can cause deterioration of materials such as:

[0056]

[0074] FIG. 3 illustrates a membrane 40 that has been found to provide an improved balance of properties. In this embodiment, the membrane 40 includes a stack having multiple layers, in the following order: a first capping layer 70, a base layer 60, and a second capping layer 80. The first capping layer 70 includes an oxide of a first metal. The base layer 60 includes a compound including a second metal and an additional element. The additional element is selected from the group consisting of Si, B, C, and N. The second capping layer 80 includes an oxide of a third metal. The first metal is different from the second metal. The third metal is the same as the first metal or the third metal is different from the first metal. In one embodiment, either the first capping layer 70 or the second capping layer 80, or both, form the outer surface of the membrane 40. In this orientation of the figure, the membrane 40 has an upper outer surface (facing up) and a lower outer surface (facing down). The first capping layer 70 forms the upper outer surface. A second capping layer 80 forms the lower outer surface.

[0057]

[0075] In one embodiment, the base layer 60 has a high emissivity in the infrared. For example, when the emissivity varies between 0 (minimum) and 1 (maximum), the emissivity can be greater than 0.2, optionally greater than 0.3, and optionally greater than 0.4. Thus, the base layer 60 effectively radiates heat and prevents the membrane 40 from overheating. The first capping layer 70 and the second capping layer 80 protect the base layer 60 from degradation due to, for example, incident EUV radiation and / or oxidative environmental conditions. In one embodiment, the base layer 60 is thicker than each of the first capping layer 70 and the second capping layer 80, optionally at least 5 times thicker, and optionally at least 10 times thicker. In one embodiment, the base layer 60 has a thickness of at least 8 nm, optionally at least 10 nm, optionally at least 15 nm, optionally at least 20 nm, and optionally at least 25 nm. In one embodiment, each of the first capping layer 70 and the second capping layer 80 has a thickness less than 5 nm, optionally less than 4 nm, optionally less than 3 nm, optionally less than 2 nm, and optionally less than 1 nm. In one embodiment, the membrane includes a membrane base layer, e.g., a polysilicon layer, and a barrier layer (e.g., a SiN layer) onto which the emissivity layer and protective capping layer OLT are added. The EUV reflectivity (EUVR) of such a membrane can be minimized by using best-matched emissivity and OLT capping layers and exploiting destructive interference. For example, if EUV radiation has a wavelength of 13.5 nm, one can use a "quarter lambda" thickness for the barrier layer, i.e., 13.5 nm / 4 ≈ 3.3 nm, and a "half lambda" thickness for the emissivity layer, i.e., 13.5 nm / 2 ≈ 6.7 nm, and match the refractive index of the emissivity layer and OLT capping layer to that of the barrier layer, e.g., n_1 for the barrier layer. SiN =0.97, for the OLT cap layer n_ OLT ≒0.97, for the emissivity layer n_en=n_ SiN 2 ≒0.94.

[0058]

[0076] Table 1 below shows the optimum parameters and material selection along with their respective functions in a membrane 40 having a symmetric sandwich configuration around a membrane core layer (which is the base layer). 2 is the thin native oxide layer that naturally forms on the polysilicon core layer in contact with the SiN barrier layer. Thickness values ​​are given in nm. [Table 1]

[0059]

[0077] Such a membrane design can maximize the process window for the capping layer and membrane base layer materials. This particular design allows for a very large process window for the Si base layer and the SiN barrier layer.

[0060]

[0078] Although a specific EUV wavelength (13.5 nm) and membrane materials are described above to illustrate the best match between the polysilicon membrane base layer and any additional functional layers, this specification includes any combination of materials and layers that meet the above criteria for a given EUV wavelength.

[0061]

[0079] In one embodiment, the thickness of the base layer 60 is selected to achieve destructive interference between the EUV reflections from the first capping layer 70 and the second capping layer 80. The destructive interference desirably reduces the overall reflectance of the membrane 40. In one embodiment, the thickness of the base layer 60 is 9 nm + / - 2 nm, preferably + / - 1 nm, which has been found to cause destructive interference due to the separation between the first capping layer 70 and the second capping layer 80. In one embodiment, the thickness of the base layer 60 is 16 nm + / - 2 nm, preferably + / - 1 nm, which has been found to cause destructive interference due to the separation between the first capping layer 70 and the second capping layer 80. These embodiments of enhancing the destructive interference between the EUV reflections from the first capping layer 70 and the second capping layer 80 have been found to be particularly effective when either or both of the first metal and the third metal include Zr.

[0062]

[0080] In one embodiment, either or both of the first metal oxide and the third metal oxide are oxygen conductive oxides. Oxygen conductive oxides are oxides that allow oxygen transport through the oxide lattice. Oxygen conductive oxides are particularly stable in oxidizing environments and are therefore suitable for the first and second capping layers. Oxygen conductive oxides are known to have excellent robustness and are used in high temperature catalysis. Oxygen conductive oxides can act as a buffer against oxygen and therefore maintain their properties well in environments with fluctuating oxygen content. Oxygen conductive oxides can absorb and release oxygen in response to changes in the oxygen content of the environment. EUV radiation often increases the number of vacancies and other defects in the protective layer. Oxygen conductive oxides that are stable even at high levels of lattice oxygen deficiency, such as ZrO 2 exists.

[0063]

[0081] In one embodiment, either or both of the first metal and the third metal are selected from the group consisting of Nb, Zr, Ce, Ti, La, Y, and Al, e.g., NbO 2 , ZrO 2 , CEO 2 , TiO 2 , La 2 O 3 , Y 2 O 3 Optionally, either or both of the first metal and the third metal are selected from the group consisting of Zr and Y. An oxide of Zr has been found to be particularly effective. An oxide of Y has also been found to be particularly effective. Either oxide can be doped. For example, if an oxide of Zr is used, it can be doped with yttria (Y 2 O 3 ) to form yttria stabilized zirconia. Any mixture of different oxides can also be used.

[0064]

[0082] In one embodiment, the compound comprising the second metal and the additional element in the base layer consists of the second metal and the additional element (i.e., no other elements are present in the compound, except optionally for a dopant).

[0065]

[0083] In one embodiment, in the compound of the base layer 60, the second metal is Mo and the additional element is, for example, MoSi 2 and / or Si as any other stable stoichiometry. In one embodiment, the compound consists of Mo and Si.

[0066]

[0084] In one embodiment, in the compound of the base layer 60, the second metal is Ru and the additional element is, for example, RuSi 2 and / or RuSi and / or Si in any other stable stoichiometry. In one embodiment, the compound consists of Ru and Si.

[0067]

[0085] In one embodiment, in the compound of the base layer 60, the second metal is Zr and the additional element is, for example, ZrSi 2 and / or Si as any other stable stoichiometry. In one embodiment, the compound consists of Zr and Si.

[0068]

[0086] In one embodiment, in the compound of the base layer 60, the second metal is La and the additional element is, for example, LaSi 2 and / or Si as any other stable stoichiometry. In one embodiment, the compound consists of La and Si.

[0069]

[0087] In one embodiment, in the compound of the base layer 60, the second metal is Sc and the additional element is, for example, ScSi 2 and / or Si as any other stable stoichiometry. In one embodiment, the compound consists of Sc and Si.

[0070]

[0088] In one embodiment, in the compound of the base layer 60, the second metal is Y and the additional element is, for example, YSi 2 and / or Si as any other stable stoichiometry. In one embodiment, the compound consists of Y and Si.

[0071]

[0089] In one embodiment, in the compound of the base layer 60, the second metal is Nb and the additional element is, for example, NbSi 2 and / or Si as any other stable stoichiometry. In one embodiment, the compound consists of Nb and Si.

[0072]

[0090] In one embodiment, in the compound of the base layer 60, the second metal is Mo and the additional element is, for example, MoB 2 and / or B as any other stable stoichiometry. In one embodiment, the compound consists of Mo and B.

[0073]

[0091] In one embodiment, in the compound of the base layer 60, the second metal is Ru and the additional element is, for example, RuB 2 and / or B as any other stable stoichiometry. In one embodiment, the compound consists of Ru and B.

[0074]

[0092] In one embodiment, the second metal in the compound of the base layer 60 is Zr, and the additional element is, for example, ZrB 2 and / or B as any other stable stoichiometry. In one embodiment, the compound consists of Zr and B.

[0075]

[0093] In one embodiment, in the compound of the base layer 60, the second metal is Nb and the additional element is, for example, NbB 2 and / or B as any other stable stoichiometry. In one embodiment, the compound consists of Nb and B.

[0076]

[0094] In one embodiment, the second metal in the compound of the base layer 60 is Ti, and the additional element is, for example, TiB 2 and / or B as any other stable stoichiometry. In one embodiment, the compound consists of Ti and B.

[0077]

[0095] In one embodiment, in the compound of the base layer 60, the second metal is La and the additional element is, for example, LaB 6 and / or B as any other stable stoichiometry. In one embodiment, the compound consists of La and B.

[0078]

[0096] In one embodiment, the second metal in the compound of the base layer 60 is Zr and the additional element is, for example, ZrC and / or C as any other stable stoichiometry. In one embodiment, the compound consists of Zr and C.

[0079]

[0097] The inventors have determined that a combination in which the first metal is Zr, the second metal is Mo, the additional element is Si, and the third metal is Zr is particularly effective.

[0080]

[0098] The first metal oxide and the third metal oxide are not limited to single metal oxides. In one embodiment, the first metal oxide is a mixed metal oxide comprising the first metal and one or more additional metals. In one embodiment, the third metal oxide is a mixed metal oxide comprising the third metal and one or more additional metals. In one embodiment, the first metal oxide is a mixed metal oxide comprising the first metal and one or more additional metals, and the third metal oxide is a mixed metal oxide comprising the third metal and one or more additional metals.

[0081]

[0099] In an embodiment of the type shown in Figure 3, at least a portion of the compound comprising the second metal and the additional element in the base layer 60 is in contact with either or both of the oxide of the first metal in the first capping layer 70 and the oxide of the third metal in the second capping layer 80. This arrangement is relatively easy to manufacture. This arrangement can be used when the oxide of the first metal in the first capping layer 70 and the oxide of the third metal in the second capping layer 80 provide adequate protection for the base layer 60 in the situation in which the membrane 40 is to be used. Figures 4-6 show embodiments in which more complex structures are provided.

[0082]

[0100] FIG. 4 illustrates an embodiment in which the base layer 60 includes multiple base layer sublayers 61-63. At least one of the base layer sublayers 61-63 includes a compound including the second metal and the additional element. In the illustrated example, the base layer 60 includes a base layer first sublayer 61, a base layer second sublayer 62, and a base layer third sublayer 63. The base layer second sublayer 62 is disposed between the base layer first sublayer 61 and the base layer third sublayer 63. The base layer second sublayer 62 includes a compound including the second metal and the additional element. The base layer first sublayer 61 includes an oxide of the additional element. The base layer third sublayer 63 includes an oxide of the additional element.

[0083]

[0101] In one embodiment, at least a portion of the base layer first sublayer 61 is in contact with an oxide of the first metal in the first capping layer 70, as shown in Figure 4. In one embodiment, at least a portion of the base layer third sublayer 63 is in contact with an oxide of the third metal in the second capping layer 80, as shown in Figure 4.

[0084]

[0102] In one embodiment, the base layer first sublayer 61 and the base layer third sublayer 63 protect the base layer second sublayer 62 from damage during use. The base layer first sublayer 61 and the base layer third sublayer 63 can act as, for example, an anti-oxidation diffusion barrier layer. When the additional element is Si, either or both of the base layer first sublayer 61 and the base layer third sublayer 63 can be made of silica (SiO 2 ). The base layer first sublayer 61 and the base layer third sublayer 63 may be referred to as scale. This scale may form naturally on the base layer second sublayer 62 (i.e., by being thermodynamically favorable in an oxidizing environment). In this case, the scale may be referred to as native scale or native oxide.

[0085]

[0103] The first capping layer 70 and the second capping layer 80 protect the base layer first sublayer 61 and the base layer third sublayer 63, for example, by preventing or reducing the rate of etching of these sublayers by EUV photons.

[0086]

[0104] When the second metal is Mo or Ru and the additional element is Si, the formation of a silica scale is particularly thermodynamically favorable: the scale thus formed is dense and stable at high temperatures.

[0087]

[0105] The ability of a silicide to form a protective silica scale upon oxidation can be judged based on the heat of two reactions:

[0088]

[0106] Reaction 1: MSi 2 +O 2 →M x S y +SiO 2

[0089]

[0107] Reaction 2: nMSi 2 +(4n+k)O 2 →M n O k +2nSiO 2

[0090]

[0108] Reaction 1 produces a silica scale and a silicide. Reaction 2 produces a mixture of the two oxides: metal oxide and silica. The latter situation is undesirable since in this case no protective scale is formed at all. The thermodynamic probability of the two reactions can be evaluated by using the heats of the two reactions calculated by a formula similar to that shown below:

number

[0091]

[0109] The enthalpy of reaction 1 at 298 K is calculated per number of oxygen atoms and normalized. By comparing the enthalpies of reaction 1 and reaction 2, it is possible to determine which reaction is more thermodynamically favored. The temperature dependence of the enthalpy is not taken into account. This simplification has been shown to be valid by Nicolet et al. in Solid State Electronics (1978, 21, 667-675).

[0092]

[0110] A comparison of the enthalpies of reaction 1 and reaction 2 for different silicides is shown in Table 2 below. [Table 2]

[0093]

[0111] ΔH of reaction 2 298 r is the ΔH of reaction 1 298 r If the silicide is more passive, protective silica scale formation is thermodynamically favored. The table shows that the silicide most favorably forming silica scale is RuSi 2 and MoSi 2 Moreover, by analyzing the oxidation kinetics, the inventors have shown that MoSi 2 has the highest activation energy and is therefore the least susceptible to oxidation (MoSi 2 This is favorable for the formation of a stable protective layer rather than the oxidation of the material itself.

[0094]

[0112] FIG. 5 illustrates an embodiment in which the first capping layer 70 includes a first capping layer first sublayer 71 and a first capping layer second sublayer 72. The first capping layer first sublayer 71 includes an oxide of a first metal. The first capping layer second sublayer 72 includes a first capping layer deposited oxide. The first capping layer second sublayer 72 is positioned between the first capping layer first sublayer 71 and the base layer 60. The first capping layer deposited oxide may be deposited on the base layer 60 to provide protection similar to that which would be provided by a native oxide, such as silica, formed on a compound including the second metal and the additional element in the base layer 60 (such as the base layer first sublayer 61 and base layer third sublayer 63 in the embodiment described above in connection with FIG. 4). The first capping layer deposited oxide may be provided in cases where a native oxide does not readily or stably form (e.g., at high temperatures) on a compound including the second metal and the additional element. In one embodiment, the native oxide may have a low melting point, for example, which may cause instability or failure during use. In such cases, the native oxide may be removed prior to applying the first capping layer deposited oxide. In one embodiment, the first capping layer deposited oxide comprises an oxide of silicon (e.g., silica).

[0095]

[0113] In one embodiment, the second capping layer 80 is configured in a corresponding manner. In such an embodiment, the second capping layer 80 includes a second capping layer first sublayer 81 and a second capping layer second sublayer 82. The second capping layer first sublayer 81 includes an oxide of a third metal. The second capping layer second sublayer 82 includes a second capping layer deposited oxide. The second capping layer second sublayer 82 is positioned between the second capping layer first sublayer 81 and the base layer 60. In one embodiment, the second capping layer deposited oxide includes an oxide of silicon (e.g., silica).

[0096]

[0114] FIG. 6 illustrates a membrane 40 corresponding to a combination of the embodiments of FIG. 4 and FIG. 5. In this membrane 40, the base layer 60 includes a base layer first sublayer 61, a base layer second sublayer 62, and a base layer third sublayer 63, as described above in connection with FIG. 4. Additionally, the membrane 40 includes a first capping layer 70 including a first capping layer first sublayer 71 and a first capping layer second sublayer 72, as described above in connection with FIG. 5. Additionally, the membrane 40 includes a second capping layer 80 including a second capping layer first sublayer 81 and a second capping layer second sublayer 82, as described above in connection with FIG. 5. The additional layers to the embodiments of FIG. 4 and FIG. 5 can increase the robustness of the membrane 40 by providing improved protection of a portion of the base layer 60 that includes a compound including the second metal and the additional element (the radiating portion of the base layer 60 within the base layer second sublayer 62).

[0097]

[0115] 3-6 show an embodiment having a first capping layer 70 and a second capping layer 80. However, these layers are not essential. In other embodiments, such as those shown in FIGS. 7 and 8, the first capping layer 70 and the second capping layer 80 can be omitted. This type of membrane 40 is easier to manufacture. It has been found that such a membrane 40 can function effectively for at least limited EUV powers.

[0098]

[0116] FIG. 7 illustrates membrane 40 including membrane layer 50. Membrane layer 50 includes a compound including a metal and an additional element. In the embodiment of FIG. 7, at least a portion of both outer surfaces of membrane 40 is formed by the compound in membrane layer 50. The compound in membrane layer 50 can have any of the compositions described above for the compound including the second metal and the additional element in the embodiments of FIGS. 3-6. The thickness of membrane layer 50 can be any of the thicknesses described above for base layer 60 in the embodiments of FIGS. 3-6.

[0099]

[0117] FIG. 8 illustrates a membrane 40 including a membrane layer 50. The membrane layer 50 includes a compound including a metal and an additional element. In the embodiment of FIG. 8, at least a portion of both outer surfaces of the membrane 40 is formed by an oxide of the additional element in the compound in the membrane layer 50. The compound in the membrane layer 50 can have any of the compositions described above for the compound including the second metal and the additional element in the embodiments of FIGS. 3-6. The membrane 50 includes a membrane layer first sublayer 51, a membrane layer second sublayer 52, and a membrane layer third sublayer 53. The membrane layer first sublayer 51 can have any of the compositions described above for the base layer first sublayer 61 in the embodiments of FIGS. 4 and 6. The membrane layer second sublayer 52 can have any of the compositions described above for the base layer second sublayer 62 in the embodiments of FIGS. 4 and 6. The membrane layer third sublayer 53 can have any of the compositions described above for the base layer third sublayer 63 in the embodiments of FIGS. 4 and 6. Membrane layer first sublayer 51 and membrane layer third sublayer 53 thereby protect membrane layer second sublayer 52 from damage during use. The thickness of membrane layer 50 (including all of membrane layer sublayers 51-53) can be any of the thicknesses described above for base layer 60 in the embodiment of Figures 3-6.

[0100]

[0118] Optionally, one or more additional layers may be provided to further protect the membrane 40. For example, Al 2 O 4 may be provided above and below the base layer 60 (with or without any intervening layers). 2 O 3 A thin layer (eg, 1 nm or less) of

[0101]

[0119] Membranes 40 of the type shown in Figures 7 and 8 have been found to be particularly effective when the metal is Mo or Ru and the additional element is Si, due to the thermodynamically favorable formation of a protective silica scale (forming membrane layer first sublayer 51 and membrane layer third sublayer 53 in the arrangement of Figure 8).

[0102]

[0120] In any of the above embodiments, it has been found that the membrane 40 works particularly well when the layer providing the high emissivity (base layer 60 or membrane layer 50) comprises a compound containing Mo and Si or Ru and Si, in particular a compound consisting of Mo and Si or Ru and Si. The formation of a protective silica scale ensures a high degree of robustness against damage by oxidation or photonic etching. It has further been found that the thermomechanical properties of these compounds are particularly well suited for use in EUV. MoSi 2 The thermomechanical properties of RuSi are discussed in detail below. Similar considerations apply to RuSi 2 is expected to be applied to

[0103]

[0121] Mechanically, MoSi 2 is similar to SiN (RuSi 2 (The same is expected for MoSi 2 can be made thicker than SiN. 2 The MoSi based membrane 40 can be stronger than a corresponding SiN based membrane while still having high EUV transparency at 13.5 nm. 2 and RuSi 2 MoSi has an inherently high emissivity and would not require an additional metallic capping layer (which, as mentioned above, tends to increase EUV reflection). 2 The EUV reflection from the surface has been found to be less than 0.1%.

[0104]

[0122] Figure 9 shows the approximate yield strength and fracture toughness (as ellipses) of various materials. MoSi 2The ellipse representing bulk MoSi 2 The figure is drawn using values ​​for MoSi. For thinner films, the values ​​become more favorable. For example, a membrane 40 for EUV use as a pellicle must have a yield strength of at least 0.1 GPa (i.e., to the right of the dashed line labeled MIN). The yield strengths of pSi and SiN pellicles are shown in dashed lines in the lower portion of the figure. 2 has a yield strength well above the minimum required. 2 has a relatively high fracture toughness (compared to the fracture toughness of, for example, pSi). 2 This means that the panel can be made thinner and have improved EUV transmittance.

[0105]

[0123] Furthermore, the ductile-brittle transition temperature (DBTT) of MoSi 2 1000°C. This is the maximum temperature T that the membrane 40 can reach during normal use. MAX (shown in Figure 10 below). Therefore, MoSi 2 Membrane 40 based on T MAX This material can be thermally cycled through the DBTT during use without being more likely to suffer significant creep and corresponding tensile loss than a material having a lower DBTT (e.g., pSi shown by the dashed line labeled pSi DBTT in FIG. 10).

[0106]

[0124] The temperature dependence of yield strength is shown in Figure 10. For example, MoSi 2 The yield strength of remains stable and exceeds the minimum value of 0.1 GPa up to 1500°K.

[0107]

[0125] 11-13 show the results of experimental and theoretical studies investigating the absorbance (corresponding to emissivity) of MoSi of different thicknesses in a relevant wavelength range to radiate heat during use. The absorbance (emissivity) can be derived from the transmittance and reflectance, which can be measured experimentally or estimated theoretically. FIG. 11 shows the variation of transmittance in this wavelength range. FIG. 12 shows the variation of reflectance in this wavelength range. FIG. 13 shows the variation of absorbance (emissivity) in this wavelength range. In each graph, four theoretically determined curves are provided, labeled 301, 302, 303, and 304, and shown as dashed lines. In addition, three experimentally determined curves are provided, labeled 311, 312, and 313, and shown as solid lines. Curve 301 in each figure shows the MoSi on one side of a 25 nm thick layer of SiN (which does not contribute significantly to the emissivity). 2 Curve 302 in each figure shows theoretical results for a 3.5 nm layer of MoSi on either side of a 25 nm thick layer of SiN. 2 Curve 303 in each figure shows theoretical results for a 3.5 nm layer of pSi on either side of a 50 nm thick layer of MoSi (which does not contribute significantly to the emissivity). 2 The curves 304 in each figure show theoretical results for a 3.5 nm layer of MoSi 2 The theoretical results for a 31 nm thick layer of MoSi on SiN alone are shown in Fig. 1. Curve 311 in each figure shows the MoSi 2 Curve 312 in each figure shows experimental results for 3.5 nm thick layers of MoSi on either side of the SiN layer. Curve 313 in each figure shows experimental results for 3.5 nm thick layers of MoSi on either side of the pSi layer. 2 Experimental results for a 3.5 nm thick layer of

[0108]

[0126] 11 to 13 show the MoSi 2 This shows that even with a thin layer of MoSi, an absorbance (emissivity) of about 0.2 or more can be achieved. 2 For thicker layers of MoSi in the range of 10-50 nm, an absorbance higher than 0.4 can be achieved. 2It is expected that a membrane 40 including a layer of MoSi should achieve an absorbance (emissivity) of greater than 0.4. 2 The high observed emissivity achieved even for very thin layers of MoSi 2 This suggests that the emissivity of membrane 40 may remain relatively high even if it degrades and thins during use, and thus the heat load may remain under control for a significant period of time, thus delaying failure of membrane 40.

[0109]

[0127] MoSi with a diameter of 1.5 cm and a thickness of 20 nm 2 Exemplary membranes 40 have been fabricated. FIG. 14 shows that the transmittance of the exemplary membranes 40 was found to vary across the surface of the membrane 40. The transmittance varied between 84% and 88%, with the most common transmittance (peak of the graph) being approximately 86.5%. It is expected that process improvements, for example to increase densification, reduce oxidation, or both, could further improve the transmittance. Membrane 40 had an absorbed transmittance of 2 Watts / cm 2 The EUV reflectance of the alloy was lower than that of Ru, Mo, and Zr, and was also lower than the target standard of 0.05%.

[0110]

[0128] As described above in relation to Figs. 3 to 8, MoSi 2 forms a protective silica scale. Experiments have shown that this silica scale is 2 The silica scale was stable at an EUV output equivalent to 1.8 W / cm 2 These results suggest that etching by EUV photons begins at EUV powers equivalent to 100 nm. The results of these experiments are described below in conjunction with FIGS.

[0111]

[0129] 15 and 16 show the absorbed 0.65 W / cm 2 (Figure 15) and absorbed 1.8 W / cm 2FIG. 16 shows the measured variation in % transmission as a function of EUV wavelength for the MoSi 40. In the experiment of FIG. 15, the transmission was found to be roughly uniform throughout the membrane. However, in the experiment of FIG. 16, a significantly higher transmission was found in the central region of the membrane 40 (shown by the dashed line). The central region was also found to be red hot. This is likely due to removal or damage to the protective scale in the central region. 2 This suggests that it was removed by etching.

[0112]

[0130] The experiments of Figures 15 and 16 suggest that the embodiment of Figure 8 can be used for lower EUV powers, but for higher EUV powers, embodiments including additional protective layers such as those described above in connection with Figures 3-6 may be desirable.

[0113]

[0131] 17-25 illustrate an example process flow for manufacturing membrane 40 according to one embodiment. This process flow is not particularly limited; various other process flows can be used as desired.

[0114]

[0132] FIG. 17 illustrates a starting state including a silicon wafer 320.

[0115]

[0133] As shown in FIG. 18, an oxide layer 322 is formed by thermal oxidation of a silicon wafer 320 .

[0116]

[0134] The next step is to apply MoSi 2 A layer 324 is deposited on the oxide layer 322. This deposition may be performed using any suitable technique, such as, for example, chemical vapor deposition (CVD), atomic layer deposition (ALD), or physical vapor deposition (PVD).

[0117]

[0135] In the next step, as shown in FIG. 20, a tetraethylorthosilicate (TEOS) oxide layer 326 is formed on the MoSi 2 It is formed on layer 324 .

[0118]

[0136] In the next step, the oxide layer 322 is removed on the back side of the stack, as shown in FIG.

[0119]

[0137] In the next step, an encapsulation layer 328 is provided around the stack, as shown in Figure 22. The encapsulation layer 328 is a Si 3N 4O 5 deposited by plasma enhanced chemical vapor deposition (PECVD) or low pressure chemical vapor deposition (LPCVD). x N y Mask (e.g., Si 3 N 4 ).

[0120]

[0138] The next step involves patterning and dry etching windows in the encapsulation layer 328, as shown in FIG.

[0121]

[0139] In the next step, a KOH etch is applied to selectively remove a portion of the silicon wafer 320 on the backside.

[0122]

[0140] Finally, a wet or dry etch is applied to remove at least a portion of the TEOS layer 326 and the oxide layer 324 to form the membrane 40.

[0123]

[0141] In the above embodiments, a metal oxide material having a high emissivity in the infrared (a compound containing a second metal and an additional element, e.g., MoSi 2) is used for the base layer 60 of the membrane 40. A variety of different capping layers can be provided to improve robustness and reliability during use. Figures 26-28 show examples of steps in a manufacturing process to produce an alternative membrane 40 with high emissivity in the infrared. Alternative membranes do not necessarily use a second metal and additional elements in the base layer 60. Standard materials such as polysilicon can be used for the base layer 60. High emissivity in the infrared is provided by an emissivity layer (a layer with high emissivity in the infrared) provided in addition to the base layer 60. The range of materials that can be used to provide high emissivity is increased by adapting the topology of the surface of the emissivity layer to reduce harmful EUV reflections from the emissivity layer.

[0124]

[0142] The method includes providing a base layer 60. The method further includes providing an emissivity layer 400. The emissivity layer 400 has a high emissivity in the infrared. For example, where the emissivity ranges between 0 (lowest) and 1 (highest), the emissivity can be greater than 0.2, optionally greater than 0.3, and optionally greater than 0.4. Thus, the emissivity layer 400 effectively radiates heat and prevents the membrane 40 from overheating during use. In one embodiment, the emissivity of the emissivity layer 400 is higher than the emissivity of the base layer 60.

[0125]

[0143] In one embodiment, the base layer 60 comprises polysilicon.

[0126]

[0144] In one embodiment, the emissivity layer 400 includes one or more of Ru, Mo, Zr, and Nb. Ru has been found to provide particularly good emissivity (when provided in a thickness range of about 1 nm to 10 nm). When provided as a layer with a smooth surface, Ru and other materials have a relatively high reflectivity for near-normal incidence EUV (about 1% for Ru). This high reflectivity undesirably reduces contrast.

[0127]

[0145] There are several main strategies for making a low EUV reflective pellicle, including using materials that are inherently low EUV reflective. Another strategy is to use roughened interfaces and / or intermediate layers, as described below.

[0128]

[0146] The reflectance for near-normal incidence is reduced by providing the emissivity layer 400 on an irregular support surface. The irregular support surface can be formed by a planar support layer 402 or the surface of the base layer 60 (or both, if the irregularities in the surface of the base layer 60 are transferred to the planar support layer). The emissivity layer 402 has a thickness such that irregularities in the irregular support surface generate corresponding irregularities in the surface of the emissivity layer 400 opposite the support surface. Irregularities in the surface of the emissivity layer 400 can be described as surface roughness if the scale of the irregularities is relatively small. For a smooth film of 4 nm Ru on 30 nm polysilicon, the inventors have determined that the normal incidence EUV reflectance R=about 1.2%. In contrast, an emissivity layer 400 of Ru formed on an irregular support surface defined by a characteristic length scale roughness of 1 nm has R=about 0.5%. In one embodiment, the characteristic length scale is defined as the average peak-to-trough height difference of the surface topology. However, the in-plane separation between the peaks should not be too large. Typically, the average in-plane separation between the peaks is less than about 100 nm. An emissivity layer 400 of Ru formed on an irregular support surface defined by a roughness with a characteristic length scale of 3 nm has an R of less than 0.001%. In embodiments, the irregularities in the surface of the emissivity layer 400 have a characteristic length scale of at least 2 nm, optionally at least 3 nm. The irregularities in the surface of the emissivity layer 400 can have length scales significantly longer than 3 nm, up to and beyond EUV wavelengths. Such irregular surfaces can be described as surfaces having facets with random orientations and sizes. The facets redirect zero-order (normal incidence) reflections in random directions out of the image, thereby reducing or eliminating the negative effect on contrast. This effect is similar to roughness, even if the facets are significantly larger than the irregularities normally associated with surface roughness.

[0129]

[0147] The irregular support surface can be formed in a variety of ways. In one embodiment, the base layer 60 and / or the planar support layer 402 formed on the base layer 60 are processed to generate the irregular support surface. Figure 26 illustrates the result of this type of method. In this embodiment, a bottom-etched silicon wafer 320 is formed on a lower capping layer 401 (e.g., Si 3 N 4 ), which supports the polysilicon base layer 60, the planar support layer 402, and the emissivity layer 400 in a bottom-up fashion. An anisotropic etch is applied to the top surface of the polysilicon base layer 60 prior to deposition of the planar support layer 402. The polysilicon crystallite size is selected such that the anisotropic etch produces a top surface in the base layer 60 with the desired irregularities. The planar support layer 402 is then provided as a sufficiently thin layer such that irregularities in the top surface of the base layer 60 produce corresponding irregularities in the top surface of the planar support layer, thereby forming the desired irregular support surface for the emissivity layer 400. The emissivity layer 400 is likewise provided as a sufficiently thin layer such that irregularities in the top surface of the planar support layer 402 produce corresponding irregularities in the surface of the emissivity layer 400. The planar support layer 402 and the emissivity layer 400 may have thicknesses, for example, within the range of about 1 nm to about 10 nm.

[0130]

[0148] 27 and 28 illustrate steps in an alternative method for forming the emissivity layer 400 in which an additional layer 406 is provided between the silicon wafer 320 and the base layer 60. In one embodiment, the additional layer 406 comprises a polycrystalline material such as polysilicon. The additional layer 406 is formed on a planar support layer 402 (e.g., Si 3 N 4 ) is processed to produce an irregular top surface before being attached to the top surface of the base layer 60. This processing may include, for example, anisotropic etching. The base layer 60 may also include a polycrystalline layer, for example polysilicon, and is formed on the planar support layer 402. In the embodiment shown, an upper capping layer 407 (e.g., Si 3 N 427. A backside etch is then applied to remove a portion of the silicon wafer 320 and a portion of the additional layer 406 down to the bottom surface of the planar support layer 402 (which may act as an etch stop). The bottom surface of the planar support layer 402 is an irregular support surface because the planar support layer 402 was originally formed on the irregular top surface of the additional layer 406. The emissivity layer 400 is then deposited on the irregular support surface to produce the arrangement of FIG. 28. The emissivity layer 400 is provided as a sufficiently thin layer such that irregularities in the irregular support surface produce corresponding irregularities on both surfaces of the emissivity layer 400.

[0131]

[0149] In an arrangement of the type shown in FIG. 28, irregularities (e.g. roughness) provided in the additional layer 406 between the base layer 60 and the silicon wafer 320 can also improve adhesion between the base layer 60 and the silicon wafer 320.

[0132]

[0150] In embodiments where the irregular support surface is formed by anisotropic etching of a polycrystalline material, the average angle of the crystallite faces in the irregular support surface with respect to the normal of the membrane is preferably less than 85%, optionally less than 80%, optionally less than 70%, optionally less than 60%, optionally less than 50%. This property can be achieved by appropriate selection of the crystallite size in the polycrystalline material and the etching conditions in the anisotropic etching. Deviations from 90 degrees induce the specular reflection of normally incident radiation from the crystallite faces away from the normal direction. It has been found that for angles less than the above 90 degrees, most of the specular reflection is induced so far away from the normal that it is not captured by the imaging device, thus negatively affecting the contrast.

[0133]

[0151] As shown diagrammatically in FIG. 29, the membrane is typically formed using a rectangular mask 410 (left) to define an area of ​​a support structure (e.g., a silicon wafer) and then etching away the area, thereby releasing the membrane 40. The resulting free-standing portion of the membrane 40 (right) will have the same overall shape as the mask 410. The shape of the free-standing portion of the membrane 40 is defined by the free-standing portion perimeter 412. For the rectangular mask 410, the free-standing portion perimeter 412 will include four straight sides and 90 degree corners 414 (within a small angle range). The inventors have determined that the 90 degree corners 414 cause significant stress concentrations in the free-standing portion of the membrane 40. This stress concentration increases the likelihood of failure of the membrane 40 and / or reduces the life of the membrane 40. The stress concentration is created by slight changes in the size of the membrane 40 during manufacturing, meaning that the membrane 40 no longer fits snugly into the support frame (e.g., causing bulging).

[0134]

[0152] The inventors have determined that creating corners with interior angles greater than 90 degrees reduces or avoids stress concentrations, which may improve the reliability and / or lifespan of membrane 40. Optical disturbances near the corners are also reduced.

[0135]

[0153] Thus, in one embodiment, a membrane 40 for EUV lithography is provided, as illustrated, for example, in FIG. 30. The membrane 40 can be produced by using a mask 410 (left) to define areas of a support structure to be etched, and then etching the defined areas. The support structure can include a silicon wafer supporting a layer of the membrane 40. Etching the defined areas includes removing a portion of the silicon wafer to release the membrane 40. A portion of the membrane 40 becomes freestanding. The shape of the freestanding portion of the membrane 40 is defined by a freestanding portion perimeter 412 (right). The freestanding portion perimeter 412 includes a plurality of substantially straight sections. In the example illustrated in FIG. 30, the freestanding portion perimeter 412 includes eight substantially straight sections. The interior angle 416 between each pair of directly adjacent straight sections is arranged to be greater than 90 degrees, optionally at least 95 degrees, optionally at least 100 degrees, optionally at least 110 degrees, and optionally at least 120 degrees. 30 for only one of the interior angles, it can be clearly seen that all of the interior angles 416 are greater than 90 degrees. The exterior angle 418 is 180 degrees minus the interior angle 416, which is less than 90 degrees. This reduces stress concentrations and improves the reliability and / or lifespan of the membrane. Optical disturbances near the corners of the membrane 40 (caused by stress concentrations) are also reduced.

[0136]

[0154] If an anisotropic etch is used to release the membrane 40, the etch will follow the crystal planes. This may mean that the interior angle 416 does not perfectly represent the corner morphology on a microscopic scale. However, the transition from one straight section to another, provided by this embodiment, is further improved in terms of reducing stress concentrations than if a 90 degree corner were provided. The pellicle area lost at the corner (relative to the rectangular case) does not need to be very large (e.g., it can be on the order of about 10-100 square microns). Thus, the change in corner geometry can be easily designed so as not to interfere with the area of ​​the membrane 40 through which EUV radiation passes in use.

[0137]

[0155] Polysilicon or a compound containing a second metal and an additional element (e.g., MoSi 2 The membrane 40 includes a base layer 60 formed from SiO 2 , which protects the base layer from excessive oxidation. 2 However, this native oxide can be etched away by EUV radiation and ultimately cease to fully protect the base layer 60 during use. The inventors have determined that a capping layer comprising borosilicate glass can improve protection of the base layer 60. FIG. 31 shows an example of an arrangement in which the membrane 40 includes a base layer 60 protected on each side by a capping layer 420 comprising borosilicate glass. The capping layer 420 comprising borosilicate glass can generally be used in combination with a variety of base layer 60 compositions, including polysilicon, compounds comprising a second metal and an additional element, and a variety of other compositions such as MoC and other carbides.

[0138]

[0156] The borosilicate glass can be formed in place of the native oxide of the base layer 60. Alternatively, the borosilicate glass can be formed by converting the native oxide of the base layer to borosilicate glass. Alternatively, the borosilicate glass can be formed over the native oxide of the base layer 60.

[0139]

[0157] The variety of borosilicate glass compositions available allows for the desired tuning of the properties of capping layer 420. The inventors have determined that, for example, by appropriate selection of the composition of the borosilicate glass, superior stability can be achieved compared to native oxide.

[0140]

[0158] CMOS compatible methods of depositing thin layers of borosilicate glass are known in the art (see, for example, J. Leib, O. Gyenge, U. Hansen, S. Maus, K. Hauck, I. Ndip, M. Toepper, Low Temperature Glass-Thin-Films for use in Power Applications, 2011 Electronic Components and Technology Conference, 978-1-61284-498-5 / 1l). Methods have been reported that result in coatings with a coefficient of thermal expansion (CTE) that matches very closely with that of Si. In the case where the base layer 60 comprises polysilicon, this matching should result in superior mechanical properties in high-power EUV applications compared to native oxide layers (where the CTE is generally not well matched). Moreover, formulations of borosilicate glass are available that can be softened at relatively low temperatures, reducing the risk of crack formation and the associated loss of protective properties.

[0141]

[0159] A variety of techniques are available for depositing the borosilicate glass capping layer 420. The base layer 60 is first deposited with a native oxide (e.g., a 1.5-2 nm layer of SiO ) on the outer surface of the base layer 60. 2 ) are provided below in three examples.

[0142]

[0160] In a first example method, the native oxide is stripped. This can be accomplished, for example, by immersing the membrane 40 in HF. A layer of borosilicate glass (e.g., a few nm thick, e.g., 2 nm thick) is then deposited on the base layer 60 to form the capping layer 420. For example, plasma-enhanced electron beam deposition can be used to deposit the borosilicate glass.

[0143]

[0161] A second example method involves depositing a layer of borosilicate glass over the native oxide, which can provide additional protection against oxidation, but the presence of the native oxide reduces EUV transmission.

[0144]

[0162] In the third example method, SiO as a native oxide is used. 2 is converted to borosilicate glass, e.g., SiO 2 B 2 O 3 and other additives known in the art for such transformations. For example, B 2 O 3 The layer is Na 2 O, Li 2 O, P 2 O 5 or SiO together with what is needed for the desired properties of the glass. 2 A high temperature anneal step can be applied to complete this conversion.

[0145]

[0163] In an alternative embodiment, the capping layer 420 includes an alloy of Mo with at least one other metal, such as one or more of Ta, Ti, Cr, Ni, and Nb. Such a capping layer 420 may be used in combination with a base layer 60 including, for example, polysilicon. Mo has a desirably high emissivity in the infrared, but is subject to oxidation in air even at room temperature and will oxidize rapidly at elevated temperatures. Additional capping layers may be provided to protect Mo from oxidation, but this would increase the complexity of the membrane 40. Alloying Mo with other metals significantly reduces oxidation of Mo without the need for additional capping layers. Alloying Mo with less than about 5 wt. % of other metals is expected to substantially increase the stability of Mo against oxidation (see, for example, A. List, C. Mitterer, G. Mori, J. Winkler, N. Reinfried, W. Knabl, Oxidation of Sputtered Thin Films of Molybdenum Alloys as Ambient Conditions, 17th Plansee Seminar 2009, Vol. 1). Alloying Mo with Ti and with Ta provides particularly good protection against oxidation. Thus, a capping layer 420 formed from such alloys is in effect a bifunctional layer providing both the functions of high emissivity in the infrared and protection against oxidation.

[0146]

[0164] In an alternative embodiment, the membrane 40 may include YSi 2 , ZrSi 2 , LaSi 2 , and NbSi 2 A base layer 60 is provided that includes one or more of these four materials. Each of these four materials is MoSi 2 It is more transparent to EUV light. 2 and ZrSi 2 is particularly effective, and MoSi 2 The emissivity and thermo-mechanical properties of the four materials are comparable to those of MoSi 2The high emissivity means that no additional emissive metal layers are required. The thermo-mechanical properties mean that the base layer 60 can be made substantially thinner than polysilicon alternatives, which also helps to promote high EUV transmission. YSi 2 , ZrSi 2 , LaSi 2 , or NbSi 2 A base layer 60 formed from will not be stable to oxidation, so a capping layer 430 may be provided to provide protection against oxidation.

[0147]

[0165] An example of this type of membrane 40 is shown in Figure 32. The membrane 40 is made of YSi 2 , ZrSi 2 , LaSi 2 , and NbSi 2 A capping layer 430 is provided. In the particular example shown, the capping layer 430 is provided on both the upper and lower surfaces of the base layer 60.

[0148]

[0166] In the illustrated example, the capping layer 430 includes a capping layer first sublayer 431 and a capping layer second sublayer 432. The capping layer first sublayer 431 contacts the base layer 60, and the capping layer second sublayer 432 is positioned on one side of the capping layer first sublayer 431 opposite the base layer 60. In one embodiment, the capping layer first sublayer 431 is MoSi 2 or Si. A variety of materials can be used to form the capping layer second sublayer 432. In one embodiment, the capping layer second sublayer 432 includes B.

[0149]

[0167] In one detailed example, the membrane 60 is a 20-30 nm thick YSi 2 or ZrSi 2 The first step is to provide a base layer 60 containing Si or MoSi 2A capping layer first sublayer 431 (2-4 nm) is applied to the base layer 60 (to provide an anti-oxidation barrier and make the stack robust to typical manufacturing process flow conditions). In a next step, SiO 2 The native oxide is removed (e.g., using a He / H plasma etch). SiO 2 The removal of the native oxide also provides dangling bonds that improve the bond between the subsequently applied capping layer first sublayer 431 and capping layer second sublayer 432. In a next step, the capping layer second sublayer 432 is applied over the capping layer first sublayer 431 (e.g., B). The capping layer second sublayer 432 is applied in-situ and is made of SiO 2 It is ensured that the native oxide does not reform on the capping layer first sublayer 431 .

[0150]

[0168] In the absence of countermeasures, the capping layer may degrade during EUV exposure conditions. For example, it has been observed that metals such as Ru, Mo, B, and Zr (as well as their respective alloys, combinations including their borides, carbides, or silicides) are oxidized. Oxidation reduces EUV transmission. Oxidation also reduces the emissivity of the membrane due to the reduction in metal content and corresponding electrical conductivity. Chemical stability may be compromised due to the oxide surface containing reactive O vacancies. Changes in the thickness, composition, and roughness of the capping layer will also affect the EUV reflectance. The inventors have recognized that a key factor in the oxidation resistance and chemical stability of the capping layer is the crystal microstructure. Many typical capping layers, especially metallic capping layers, are polycrystalline. Grain boundaries cause poor performance as an oxidation barrier because they provide a path for atomic diffusion. Also, grain boundaries are more susceptible to chemical attack than grain interiors due to their imperfect structure. The embodiments of the present invention provide improved performance by providing an amorphous capping layer.

[0151]

[0169] In one embodiment, the method of manufacturing the membrane 40 includes providing a base layer 60 (or a stack including the base layer 60 and one or more other layers) and a capping layer 70. The capping layer 70 is an amorphous capping layer. The capping layer 70 provides the outer surface of the membrane 40. The base layer 60 and the capping layer 70 may, for example, adopt the general configuration of FIG. 3. In this configuration, two capping layers are provided (a first capping layer 70 and a second capping layer 80). In other embodiments, the capping layer 70 may be provided on only one side of the membrane 40 (e.g., in the case of a membrane for protecting a patterning device, the capping layer 70 may be provided on the side of the membrane 40 facing the patterning device). The composition and thickness of the base layer 60 and any other layers may be as described in any of the above embodiments, or other compositions and thicknesses may be used. The advantage of providing an amorphous capping layer 70 does not depend specifically on the nature of the other layers of the membrane 40. Therefore, this method is suitable for, for example, polysilicon, SiN, MoSi 2 The present invention can be applied to current and future membrane designs, including those that include graphene-containing base layers.

[0152]

[0170] In one embodiment, the capping layer 70 is metallic. In one embodiment, the capping layer 70 comprises an alloy. As described in more detail below, the use of an alloy can inhibit crystallization in the capping layer 70, thereby promoting an amorphous state. In one embodiment, the alloy comprises one or more of Ru, Mo, B, C, Cr, Ir, Nb, Pd, Pt, Re, Rh, Ti, V, Y, preferably one or more of B, C, Y. For example, 1) Ru and one or more of Rh, Pd, Pt, Y, B, Ti, C, and P; 2) Mo and one or more of B, Ta, Nb, Cr, and Ru.

[0153]

[0171] In one embodiment, the alloy is Ru doped with B (e.g., 10-20% B), Ru doped with P, or Mo. (1-x-y) Rux B y These materials include H, O, and H 2 Provides higher resistance to penetration by O than pure Ru. EUV, H 2 Increased stability when exposed to plasma and thermal loads is also achieved, and the beneficial amorphous structure is preserved under these conditions. Surface reaction characteristics are improved compared to pure Ru, resulting in less reactance with respect to metal contaminants emanating from, for example, metal-containing resists on the substrate W. Thus, the cleanliness of the capping layer 70 is improved. In one embodiment, a graded concentration profile within the capping layer is provided, where the concentration of dopant (e.g., B or P) is higher near at least one surface of the capping layer 70 than deeper within the capping layer 70, thereby providing high cleanliness without excessive overall levels of dopant.

[0154]

[0172] The increased oxidation resistance provided by the lack of grain boundaries will reduce variations in EUV transmission and EUV reflection over time. Retaining the metallic nature of the capping layer 70 minimizes changes in emissivity, allowing the membrane to survive at high temperatures for longer.

[0155]

[0173] Additionally, the amorphous nature of the capping layer 70 results in reduced reflectivity for many material choices, and the optical contrast between the capping layer 70 and the base layer 60 of the membrane 40 is typically lower when the capping layer 70 is amorphous compared to when the capping layer 70 is polycrystalline.

[0156]

[0174] An example of a technique for producing a membrane 40 having an amorphous capping layer 70 is described below.

[0157]

[0175] In one embodiment, forming the amorphous capping layer 70 involves simultaneously depositing (e.g., by co-sputtering) at least two different metals to form an alloy. The different sizes and types of metal atoms disrupt the crystallization process, thereby promoting the creation of an amorphous layer. During this co-deposition process, a bias can be applied to increase the energy of the particles impinging on the surface of the layer being formed, which alters the phase formation. Thus, the applied bias contributes to the amorphization of the capping layer 70. The applied bias can also be advantageously used to adjust other properties of the capping layer 70 (e.g., stress, resistivity, adhesion) that depend on the film's microstructure.

[0158]

[0176] In an alternative embodiment, forming the amorphous capping layer 70 includes depositing the amorphous capping layer 70 in the presence of a first gas and a second gas, the presence of the second gas inhibiting crystallization of the amorphous capping layer 70 compared to the same deposition process carried out in the presence of only the first gas. Including such a second gas during formation (e.g., deposition), such as a small amount of nitrogen (N) added to argon (Ar), can disrupt the structure of the deposited amorphous capping layer 70, thereby promoting the formation of an amorphous rather than crystalline structure. The second gas (e.g., nitrogen) can reduce the atomic mobility and activation energy of the deposited atoms. The second gas (e.g., nitrogen) can slow down the crystallization kinetics, thereby stabilizing the amorphous phase.

[0159]

[0177] In an alternative embodiment, forming the amorphous capping layer 70 is performed while the base layer 60 (or a stack including the base layer 60 and other layers) is held at a temperature below room temperature to inhibit crystallization. Thus, the membrane 40 can be pre-cooled before deposition and actively held at a low temperature during the deposition process (e.g., using water or gas as a coolant). This low temperature inhibits grain growth and inhibits interdiffusion / interlayer formation. Once the deposition process is complete, the energy required for atoms to move and interdiffuse has increased. Thus, warming to room temperature is no longer sufficient to initiate the interdiffusion process, and the capping layer 70 will remain in a stable amorphous phase.

[0160]

[0178] The degree of amorphization of the amorphous capping layer 70 can be measured and monitored using various techniques, including, for example, atomic force microscopy (AFM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) measurements, thus contributing to improving product quality through process control.

[0161]

[0179] The advantages associated with providing the amorphous capping layer 70 discussed above are not only applicable to membranes such as pellicles. 2 O, EUV, H 2 The advantages in terms of increased resistance to plasma, heat loads, etc., are also applicable to EUV mirrors or reflective reticles. Furthermore, for example, B or P doped Ru and / or Mo (1-x-y) Ru x B y It is expected that Ru and / or Mo will have better optical properties (e.g., lower EUV absorption and higher reflectance) than pure Ru or Mo. For EUV mirrors, B or P doped Ru and / or Mo are preferred. (1-x-y) Ru x B y Reduces blistering and optional ZrO 2 It is expected that the ZrO 2 coating will provide an improved underside for overcoating. 2It may be possible to eliminate the need for overcoatings such as those described above. The Mo layer in the multilayer reflective structure is B or P doped Ru and / or Mo. (1-x-y) Ru x B y , thereby providing lower roughness and lower EUV scattering layer by layer.

[0162]

[0180] In an alternative embodiment, a membrane 40 for EUV lithography is provided having a base layer 60 and a capping layer 70. The capping layer has at least 20% (less than 80% sp 2 carbon), optionally at least 50%, optionally at least 75%, optionally substantially 100% of sp 3 The capping layer 70 provides an outer surface of the membrane 40. 3 and sp 2 Carbon containing both carbons is called diamond-like carbon. 3 Carbon has a high EUVT, is resistant to etching by H plasma, and can withstand high temperatures. Moreover, sp 2 Carbon can be purified with H plasma, so sp 3 Carbon does not pose any risk of problems related to the lifetime of the optical components. The base layer 60 and the capping layer 70 may, for example, adopt the general configuration of FIG. 3. In this configuration, two capping layers are provided (first capping layer 70 and second capping layer 80). In other embodiments, the capping layer 70 may be provided on only one side of the membrane 40 (e.g., in the case of a membrane for protecting a patterning device, the capping layer 70 may be provided on the side of the membrane 40 facing the patterning device). The composition and thickness of the base layer 60 and any other layers may be as described in any of the above embodiments, or other compositions and thicknesses may be used. The capping layer 70 may, for example, be MoSi 2 , B / B 4 C, pSi, ZrSi 2, graphene, and the like.

[0163]

[0181] In one embodiment, the capping layer 70 is made of, for example, boron and ZrO for the Si-containing base layer 60. 2 In another embodiment, the capping layer 70 is used in combination with a base layer 60 that includes carbon, such as multi-layer graphene or carbon nanotubes, thereby providing valuable resistance to H plasma. In one embodiment, by providing an all-carbon base layer 60 and an all-carbon capping layer 70, the membrane 60 can be formed entirely from a single chemical element, thereby reducing the risk of the membrane 60 contaminating the environment in which it is used with problematic elements. The membrane 60 is superior to graphene-only pellicles because of its ability to withstand higher temperatures and H plasma due to the capping layer 70. In one embodiment, both the base layer 60 and the capping layer 70 are formed from carbon, but the base layer 60 has less diamond-like properties (i.e., a lower percentage of sp 3 Therefore, the base layer 60 is made of sp 3 The carbon fraction is sp in the carbon of the capping layer 70 3 Diamond can contain a lower percentage of carbon than pure sp 2 It has a very low IR emissivity compared to carbon, so in the case of a pure carbon membrane, pure sp 2 Carbon content (or high proportion of sp 2 A carbon-containing component is required.

[0164]

[0182] sp 3 The carbon percentage has a strong influence on the properties of the layer. Pure diamond is pure sp 3 and has excellent etching resistance (diamond is etched 75-7000 times slower than graphite by low-energy H atoms). 3and sp 2 The diamond-like carbon layer containing both carbon and pure sp 2 It exhibits significantly improved etch resistance compared to carbon.

[0165]

[0183] A variety of processes are known for depositing diamond-like carbon, including, for example, plasma enhanced CVD, deposition, ion assisted deposition, sputtering, cathodic vacuum arc (CVA), plasma vapor deposition, and pulsed laser deposition (PLD). Variations in the deposition method affect the sp 3 / sp 2 The deposition method therefore determines the desired sp 3 / sp 2 The ratio of the sp 3 / sp 2 Ratio (50% of sp 3 ) can be reached.

[0166]

[0184] In an alternative embodiment, a membrane 40 for EUV lithography is provided having a base layer 60 and a capping layer 70 comprising a first metal doped with a second metal. The capping layer 70 provides an outer surface of the membrane 40. In one embodiment, the first metal comprises a transition metal. In one embodiment, the second metal comprises an alkali metal or an alkaline earth metal. The base layer 60 and the capping layer 70 may, for example, adopt the general configuration of FIG. 3. In this configuration, two capping layers are provided (first capping layer 70 and second capping layer 80). In other embodiments, the capping layer 70 may be provided on only one side of the membrane 40 (e.g., in the case of a membrane for protecting a patterning device, the capping layer 70 may be provided on the side of the membrane 40 facing the patterning device). The composition and thickness of the base layer 60 and any other layers may be as described in any of the above embodiments, or other compositions and thicknesses may be used.

[0167]

[0185] Doping of metals, particularly transition metals, especially Ru, with other metals, particularly alkali or alkaline earth metals, especially Sr or Ca, provides improved performance in a variety of respects.

[0168]

[0186] Doping can increase the thermal stability of the capping layer 70. Alkaline earth metals have a relatively high vapor pressure and can therefore reduce the volatility of the material being doped. For example, in the case of Ru doped with Sr, the higher vapor pressure associated with Sr means that the volatility of Ru is reduced.

[0169]

[0187] Doping can increase the uniformity of capping layer 70 by relieving epitaxial strain in capping layer 70 .

[0170]

[0188] Doping can increase EUV transmission, for example in the case of Ru doped with Sr, higher transmission is achieved since Sr is significantly more transparent to EUV than Ru.

[0171]

[0189] Doping can increase EUV reflection, for example Ru doped with Sr, where the Sr reduces the difference in refractive index between the capping layer 70 and the base layer 60.

[0172]

[0190] Alkaline earth metals are stable elements and can be doped to higher concentrations before phase separation occurs (typical doping ranges are around 1-10%). Furthermore, metallic Sr can contribute to the Fermi level of Ru to promote enhanced electrical conductivity / emissivity.

[0173]

[0191] Doping can be performed in a variety of ways, including, for example, various PVD techniques, and can therefore be efficiently integrated into existing manufacturing flows. Co-sputtering of Sr and Ru (from separate targets) would be appropriate for doping Ru with Sr. Alternatively, a Ru target could be doped with Sr. Also, doping with Sr, for example as a chemical precursor to Sr, could be used. 3 (CO) 12 CVD can also be used in conjunction with

[0174]

[0192] The degree of doping can be measured, for example, by X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), and Rutherford backscattering spectroscopy (RBS). Lower concentrations of dopants are more difficult to measure, and good control of metal flux during deposition is known to result in the desired stoichiometry in the film.

[0175]

[0193] In an alternative embodiment, a base layer 60 and M1 x M2 y O z and a capping layer 70, wherein M1 comprises one or more alkali metals and / or one or more alkaline earth metals, and M2 is a transition metal, optionally a rare earth metal. The capping layer 70 provides an outer surface of the membrane 40. In one embodiment, the capping layer 70 is SrRuO 3 , SrVO 3 , CaVO 3 , La 0.67 Sr 0.33 MnO 33. The base layer 60 and capping layer 70 may, for example, adopt the general configuration of FIG. 3. In this configuration, two capping layers are provided: a first capping layer 70 and a second capping layer 80. In other embodiments, the capping layer 70 may be provided on only one side of the membrane 40 (e.g., in the case of a membrane for protecting a patterning device, the capping layer 70 may be provided on the side of the membrane 40 facing the patterning device). The composition and thickness of the base layer 60 and any other layers may be as described in any of the embodiments above, or other compositions and thicknesses may be used.

[0176]

[0194] M1 x M2 y O z The material offers a variety of advantages as a capping layer: it is exceptionally stable and non-volatile; a wide range of lattice constants are available, facilitating the formation of capping layers with little or no strain; the flexible band structure allows the material to be easily tuned; by doping and applying different strains, it is possible to shift the respective Fermi level electron densities, thus allowing control of the respective electrical conductivity and emissivity.

[0177]

[0195] M1 x M2 y O z The material has relatively high EUV transmission compared to other metals and alloys, and the flexibility of its composition and crystal structure allows for its optical properties to be tailored to match other layers in the membrane, thereby reducing reflectivity.

[0178]

[0196] High quality M1 x M2 y O zThe material layers can be deposited using a number of physical vapor deposition (PDV) techniques, such as RF sputtering, molecular beam epitaxy (MBE), electron beam evaporation, and pulsed laser ablation (PLD), some of which are so advanced that they allow control of the film thickness down to the atomic layer, which is particularly advantageous for membrane 40 for use in EUV lithography.

[0179]

[0197] M1 x M2 y O z The physical properties of material layers (e.g. conductivity) can be measured using the four-probe PPMS technique. These layers are generally very stable with respect to the measurement conditions, so any in-plane and out-of-plane measurement technique can be used to measure their properties.

[0180]

[0198] For example, MoSi 2 , ZrSi 2 Various promising base layer materials, including silicides, silicides, and other silicides, as well as multi-layer graphene, have excessively high thermal conductivity (MoSi 2 , ZrSi 2, and other silicides) or too low (multilayer graphene) stress. Too high stress causes premature failure of the membrane. Too low stress causes undesirable wrinkling of the membrane. The inventors believe that the undesirable level of stress is caused by a mismatch in the thermal expansion coefficients of the support structure that supports the base layer when it is deposited and the base layer itself. A typical membrane is subjected to one or more high temperature steps during fabrication. For example, annealing can be performed at temperatures above 700° C. to optimize density and prevent annealing and shrinkage of the membrane during use. Deposition techniques can use high temperatures. CVD of multilayer graphene may need to be performed at temperatures above 700° C., for example. At these high temperatures, the base layer relaxes to its lowest stress state and is restrained by the much thicker support structure. When the assembly is subsequently cooled, the base layer and the support structure shrink by different amounts depending on the mismatch in thermal expansion coefficients. If the support structure has a higher coefficient of thermal expansion, it will shrink more than the base layer, resulting in a wrinkled base layer, and if the support structure has a lower coefficient of thermal expansion, it will shrink less than the base layer, resulting in high stresses in the base layer.

[0181]

[0199] 34 and 35 illustrate steps of a method according to one embodiment in which the membrane 40 is manufactured in such a way as to reduce the problems associated with the mismatch of thermal expansion coefficients mentioned above. The method includes forming a base layer 60 on a support structure 802 to provide the arrangement shown in FIG. 34. The support structure 802 is then etched in selected regions 804 below the base layer 60 to form a free-standing membrane 40 including the base layer 60 as shown in FIG. 35 (the boundaries of the selected regions 804 are illustrated by dashed lines). The membrane 40 includes a free-standing portion connected to a non-free-standing portion supported by the remaining portions of the support structure 802 (which may be referred to as a boundary). Since many variations are possible, the details of the process flow are not described here or shown in FIGS. 34 and 35. For example, appropriately adapted versions of the process flows described above in relation to FIGS. 17-25 may be used.

[0182]

[0200] By providing a support structure 802 in which the difference in thermal expansion coefficient between the support structure 802 and the base layer 60 is less than the difference in thermal expansion coefficient between silicon and the base layer 60, a more favorable stress is achieved in the membrane 40. Thus, the mismatch in thermal expansion coefficients is less than if a standard silicon wafer were used as the support structure 802. In one embodiment, the support structure 802 comprises sapphire. In one embodiment, the support structure 802 comprises a silicate glass, such as soda-lime glass. In one embodiment, the support structure 802 comprises quartz. These materials provide a thermal expansion coefficient that provides a good match with the otherwise problematic base layer material. In one embodiment, the base layer 60 is MoSi 2 , ZrSi 2 , B, and B 4 C, and the support structure 802 comprises sapphire. 2 8. The support structure 802 comprises quartz and the support structure 802 comprises carbon (eg, multi-layer graphene).

[0183]

[0201] In any of the above embodiments, particularly when a layer having a relatively high reflectivity in EUV (e.g., B) is used, the thickness of the base layer 60 can be selected to achieve destructive interference between EUV reflected from the interfaces on either side of the base layer 60, thereby reducing the overall reflectivity. In one embodiment, the thickness of the base layer 60 is selected to be one of 9 nm + / - 2 nm, preferably + / - 1 nm, 16 nm + / - 2 nm, preferably + / - 1 nm, 22 + / - 2 nm, preferably + / - 1 nm, and 29 + / - 2 nm, preferably + / - 1 nm. Each of these thicknesses has been found to achieve destructive interference. These thicknesses are preferred when the base layer 60 is a silicide, particularly YSi 2 or ZrSi 2 It has been found to be particularly effective when a further layer (e.g., capping layer second sublayer 432) is used that includes B. Larger thicknesses can also cause destructive interference, but the increased thickness undesirably reduces EUV transmission.

[0184]

[0202] In an embodiment, the membrane 40 is applied as a pellicle or as part of a dynamic gas lock. Alternatively, the membrane 40 can be applied in other filtering areas such as identification or for beam splitters. In an embodiment, the dynamic gas lock is configured to block debris in the lithographic apparatus 100. In an embodiment, the dynamic gas lock is positioned between the projection system PS and the substrate W. The dynamic gas lock reduces the likelihood that particles from or near the substrate W reach optical components in or around the projection system PS. Similarly, the dynamic gas lock can protect the illumination system IL. In an alternative embodiment, the dynamic gas lock is positioned at a virtual source point IF. For example, the dynamic gas lock can be positioned between the source collector module SO and the illumination system IL.

[0185]

[0203] It has been found that at least when a dynamic gas lock is positioned between the projection system PS and the substrate W, the lifetime of the membrane 40 can be shortened due to contamination from outgassed species / molecules from the exposed substrate W. This problem is particularly severe when the resist contains a metallic component, such as metal-based inorganic resists, as currently proposed for EUV applications. Species outgassed from such resists can be relatively small and heavy (e.g., stannanes) and therefore can be difficult to suppress using gas flows alone. In one embodiment, the lifetime of the membrane 40 is extended by providing a capping layer on at least the side of the membrane 40 facing the substrate W, which has a relatively low affinity and / or high self-cleaning efficiency for metallic contaminants. The capping layer can be, for example, ZrO 2 , or an oxide of one or more of Ti, Hf, Y, Nb, Sc, Ta, V, and La. In one embodiment, for example, H 2 It is also provided that the purge gas flow includes: It is expected that the combination of the capping layer and the purge gas flow will enable the dynamic gas lock between the projection system PS and the substrate W to have a lifetime of more than 6 months even for metal containing resists in EUV applications.

[0186]

[0204] In one embodiment, the purge gas flow can be controlled to enhance self-cleaning of the capping layer. This can be done, for example, by increasing the overall flow rate and / or pressure at the substrate side of the membrane 40. Upward angled slits can be provided to improve the flow pattern towards the surface of the membrane 40. The flow can be controlled to minimize or avoid dead zones in the flow pattern at the surface of the membrane 40. Multiple gas inlets can provide flexibility to avoid undesirable pressure gradients in the dynamic gas lock volume and / or provide a flow pattern that accounts for asymmetries in the membrane 40.

[0187]

[0205] In one embodiment, the purge gas flow can be improved by generating additional hydrogen radicals and / or ions in the flow. This can be accomplished, for example, using a hot metal filament (e.g., tungsten) or a microwave plasma. The hydrogen radicals and / or ions will increase the cleaning rate of both organic and metallic contamination.

[0188]

[0206] In one embodiment, surfaces positioned near the membrane 40 of the dynamic gas lock that will be encountered by contamination particles from the substrate W (e.g., the inner surface of the funnel structure) can be treated to increase gettering. Such surfaces can be coated, for example, with a Ru nanolayer, which will getter outgassed metallic species (e.g., Sn). Treating the surfaces in this manner reduces the amount of material that reaches the membrane 40 itself, thereby improving the lifetime of the membrane.

[0189]

[0207] In one embodiment, the membrane 40 may become contaminated with particles during manufacture, shipping, or use. In particular, it is conceivable that the membrane may become contaminated during production of a pellicle assembly that includes the membrane 40 and a frame. However, for EUV lithography, it is particularly desirable for such membranes to be particle-free, otherwise the coating will be considered damaged, resulting in reduced yields and higher costs.

[0190]

[0208] Therefore, a cleaning tool may be required to remove particle contamination from the surface of the membrane 40. It is proposed herein to use a cleaning tool that utilizes vibration of the membrane 40 and / or an additional gas pressure difference to remove such particle contamination without the risk of breaking the membrane. Removal of the particles applied on the membrane 40 will improve the imaging performance of an EUV lithography apparatus that uses a patterning device having the membrane 40 attached thereto via a removable or permanently attached frame. It has been found that the membrane 40 can handle large impact forces without breaking when protected in a specially designed transport device. By selecting a combination of under pressure and purge flow, it has been possible to move the particles from the critical surfaces of the membrane 40.

[0191]

[0209] FIG. 33 shows an example of a cleaning device for the membrane 40. A vacuum chamber 500 is provided with a linear vibration stage 501 for vibrating the membrane 40 to loosen particles from its surface, with diameters ranging from tenths of a nanometer to hundreds of microns or millimeters in size. The linear vibration stage 501 can include one or more attachment means for mounting an interface plate 502 for supporting and bonding to the membrane 40. The interface plate can be provided with attachment means such as studs so that the membrane frame can be easily attached to and detached from the interface plate. On one side of the vacuum chamber 500, an inlet opening 503 is provided through which a laminar gas flow is provided. An exhaust opening 504 can be provided on the other side of the vacuum chamber 500, preferably opposite the inlet opening 503 for the laminar gas flow. The exhaust opening 503 allows the laminar gas flow to preferably flow parallel to the membrane surface, allowing the loosened particles to be guided by the laminar flow and exhausted from the vacuum chamber 500. A vacuum source or vacuum cleaner coupled to the exhaust opening can be provided (not shown) to further assist in exhausting particles and creating a laminar flow through the vacuum chamber. The vacuum chamber 500 can be part of the transport device 800. Preferably, the linear vibration stage 501, the interface plate 502, and the membrane 40 are oriented vertically along the force of gravity.

[0192]

[0210] The cleaning device may also include an in-line measurement method for detecting particles by using an inspection camera 600 and a line light source 700, such as a diffuse LED strip or a line laser. The inspection camera 600 may be located in a position that allows it to capture light from the line light source 700 scattered by particles from the surface of the membrane 40. For example, the inspection camera 600 may be located opposite the membrane surface in an optimal position and orientation to capture scattered light to detect particles from the membrane surface 40. The line light source 700 may be located, for example, beside the inlet opening 503, to illuminate particles that are on the membrane surface or that have been induced into the laminar flow by vibrating the interface plate 502 by the linear vibration stage 501.

[0193]

[0211] Alternatively, an acoustic speaker can be placed in front of the vertically mounted membrane 40 while held in a downflow cabinet so that particles can be removed by acceleration (not shown). By exciting the membrane with acoustic waves, high accelerations can be reached to dislodge the contaminant particles. In this way, the membrane 40 does not experience high airflow velocities that may occur in linear accelerations and potentially damage the membrane. Tests have shown that vacuum conditions are desirable to achieve the most effective particle release. This is believed to be due at least in part to the lack of water. In one embodiment, the acoustic cleaning process described above is performed under vacuum conditions using the following sequence: 1) providing an enclosed volume and pumping the enclosed volume to a vacuum level, 2) evacuating the enclosed volume with a gas (e.g., dry air), and 3) (immediately after evacuating with the gas) performing the acoustic cleaning process.

[0194]

[0212] Although particular reference is made herein to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein has other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, LCDs, thin film magnetic heads, etc. The substrates described herein may be processed, before or after exposure, for example in a track (a tool that typically applies a layer of resist to the substrate and develops the exposed resist), a metrology tool, and / or an inspection tool. Where appropriate, the disclosure herein may be applied to these and other substrate processing tools. Furthermore, the substrate may be processed multiple times, for example to produce a multi-layer IC, and thus the term substrate as used herein may also refer to a substrate that already includes multiple processed layers.

[0195]

[0213] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, various photoresist layers may be replaced with non-photoresist layers which perform the same functions.

[0196]

[0214] The above description is illustrative and not limiting. Thus, it will be apparent to one skilled in the art that modifications can be made to the invention as described without departing from the scope of the claims set out below.

Claims

1. 1. A membrane for EUV lithography, comprising: a first capping layer comprising an oxide of a first metal; a base layer comprising a compound comprising a second metal and an additional element selected from the group consisting of Si, B, C, and N; a second capping layer comprising an oxide of a third metal, said first metal being different from said second metal, and said third metal being the same as or different from said first metal; The membrane includes a stack having a plurality of layers in the order:

2. 2. The membrane of claim 1, wherein the base layer is at least five times thicker than either or both of the first capping layer and the second capping layer.

3. 3. The membrane of claim 1, wherein either or both of the first metal and the third metal are selected from the group consisting of Nb, Zr, Ce, Ti, La, Y, and Al.

4. The membrane of claim 3 , wherein either or both of the first metal and the third metal are selected from the group consisting of Zr and Y.

5. In the compound of the base layer, the second metal is Mo and the additional element is Si; the second metal is Ru and the additional element is Si; the second metal is Zr and the additional element is Si; the second metal is La and the additional element is Si; the second metal is Sc and the additional element is Si; the second metal is Y and the additional element is Si; the second metal is Nb and the additional element is Si; the second metal is Mo and the additional element is B; the second metal is Ru and the additional element is B; the second metal is Zr and the additional element is B; the second metal is Nb and the additional element is B; the second metal is Ti and the additional element is B; the second metal is La and the additional element is B; or 5. The membrane of claim 1 , wherein the second metal is Zr and the additional element is C.

6. In the compound of the base layer, the second metal is Mo and the additional element is Si; or The membrane of claim 5 , wherein the second metal is Ru and the additional element is Si.

7. In the compound of the base layer, the second metal is Mo and the additional element is B; or The membrane of claim 5 , wherein the second metal is Ru and the additional element is B.

8. 8. The membrane of claim 1, wherein in the base layer, the compound comprising the second metal and the additional element consists of the second metal and the additional element.

9. the first metal is Zr; the second metal is Mo and the additional element is Si; The membrane of claim 1 , wherein the third metal is Zr.

10. the oxide of the first metal is a mixed metal oxide comprising the first metal and one or more further metals; the oxide of the third metal is a mixed metal oxide comprising the second metal and one or more further metals; or 10. The membrane of claim 1, wherein the oxide of the first metal is a mixed metal oxide comprising the first metal and one or more further metals, and the oxide of the third metal is a mixed metal oxide comprising the third metal and one or more further metals.

11. 11. The membrane of claim 1, wherein the base layer comprises a plurality of base layer sublayers, at least one of the base layer sublayers comprising the compound comprising the second metal and the additional element.

12. the base layer includes a base layer first sublayer, a base layer second sublayer, and a base layer third sublayer; the base layer second sublayer is disposed between the base layer first sublayer and the base layer third sublayer and includes the compound including the second metal and the additional element; the base layer first sublayer comprises an oxide of the additional element; The membrane of claim 11 , wherein the base layer third sublayer comprises an oxide of the additional element.

13. The membrane of claim 12 , wherein at least a portion of the base layer first sublayer is in contact with the oxide of the first metal in the first capping layer.

14. 14. The membrane of claim 12 or 13, wherein at least a portion of the base layer third sublayer is in contact with the oxide of the third metal in the second capping layer.

15. 11. The membrane of claim 1, wherein at least a portion of the compound comprising the second metal and the additional element in the base layer is in contact with either or both of the oxide of the first metal in the first capping layer and the oxide of the third metal in the second capping layer.

16. 13. The membrane of claim 1, wherein the first capping layer comprises a first capping layer first sublayer and a first capping layer second sublayer, the first capping layer first sublayer comprising the oxide of the first metal, the first capping layer second sublayer comprising a first capping layer deposited oxide, and the first capping layer second sublayer positioned between the first capping layer first sublayer and the base layer.

17. The membrane of claim 16 , wherein the first capping layer deposited oxide comprises an oxide of silicon.

18. 18. The membrane of claim 1, wherein the second capping layer comprises a second capping layer first sublayer and a second capping layer second sublayer, the second capping layer first sublayer comprising the oxide of the third metal, the second capping layer second sublayer comprising a second capping layer deposited oxide, and the second capping layer second sublayer is positioned between the second capping layer first sublayer and the base layer.

19. The membrane of claim 18 , wherein the second capping layer deposited oxide comprises an oxide of silicon.

20. 20. The membrane of claim 1, wherein the first capping layer and the second capping layer each have a thickness less than 5 nm.

21. 21. The membrane of claim 1 , wherein the base layer has a thickness equal to or greater than 8 nm.

22. 22. The membrane of claim 21, wherein the thickness of the base layer is selected to achieve destructive interference between EUV reflections from the first capping layer and the second capping layer.

23. 23. The membrane of claim 21 or 22, wherein the base layer has a thickness of 9+ / -2 nm or 16 nm+ / -2 nm.

24. 24. The membrane of claim 1, wherein either or both of the first capping layer and the second capping layer form at least a portion of an outer surface of the membrane.

25. 25. The membrane of claim 1, wherein the oxide of the first metal and the oxide of the third metal are oxygen conducting oxides.

26. 1. A membrane for EUV lithography, comprising: the membrane comprises a membrane layer comprising a compound comprising a metal and an additional element; At least a portion of both outer surfaces of the membrane is formed by the compound or an oxide of the additional element, and in the membrane layer: the metal is Mo and the additional element is Si; the metal is Ru and the additional element is Si; the metal is Zr and the additional element is Si; the metal is La and the additional element is Si; the metal is Sc and the additional element is Si; the metal is Y and the additional element is Si; the metal is Nb and the additional element is Si; the metal is Mo and the additional element is B; the metal is Ru and the additional element is B; the metal is Zr and the additional element is B; the metal is Nb and the additional element is B; the metal is Ti and the additional element is B; the metal is La and the additional element is B, or The metal is Zr and the additional element is C.

27. 27. The membrane of claim 26, wherein the membrane layer has a thickness equal to or greater than 8 nm.

28. 28. The membrane of claim 27, wherein the thickness of the membrane layer is selected to achieve destructive interference between EUV reflections from interfaces on either side of the membrane layer.

29. 29. The membrane of claim 27 or 28, wherein the membrane layer has a thickness of 9 nm + / - 2 nm or 16 nm + / - 2 nm.

30. the metal is Mo and the additional element is Si; or 30. The membrane of any one of claims 26 to 29, wherein the metal is Ru and the additional element is Si.

31. the metal is Mo and the additional element is B, or 30. The membrane of any one of claims 26 to 29, wherein the metal is Ru and the additional element is B.

32. 1. A membrane for EUV lithography using EUV radiation having a wavelength λ, said membrane comprising: a first protective capping layer; a first emissivity layer having a thickness of λ / 2; a first barrier layer having a thickness of λ / 4; A base layer; wherein the first protective capping layer has a refractive index matched to the refractive index of the first emissivity layer and the refractive index of the first barrier layer, and the thicknesses of the layers are selected to achieve destructive interference between EUV reflections from interfaces on either side of the membrane.

33. a second protective capping layer; and a second emissivity layer having a thickness of λ / 2; a second barrier layer having a thickness of λ / 4; 33. The membrane of claim 32, further comprising: the second protective capping layer having a refractive index matched to the refractive index of the second emissivity layer and the refractive index of the second barrier layer.

34. 1. A method of manufacturing a membrane for EUV lithography, comprising the steps of: Providing a base layer; providing an emissivity layer, the emissivity layer having a higher emissivity in the infrared than the base layer; Including, the emissivity layer is disposed on an irregular support surface; A method wherein the emissivity layer has a thickness such that irregularities in the irregular support surface produce corresponding irregularities in a surface of the emissivity layer opposite the irregular support surface.

35. 35. The method of claim 34, wherein the irregular support surface is formed by anisotropic etching of a polycrystalline material.

36. 36. The method of claim 34 or 35, wherein the average angle of the crystallite faces in the irregular support surface with respect to the normal to the membrane is less than 85%.

37. 37. The method of any of claims 34 to 36, wherein the base layer comprises polysilicon.

38. 38. The method of any of claims 34 to 37, wherein the emissivity layer comprises one or more of Ru, Mo, Zr, and Nb.

39. 39. The method of any of claims 34 to 38, wherein the irregularities of the surface of the emissivity layer are such that the average peak to trough height difference is at least 2 nm.

40. 1. A method of manufacturing a membrane for EUV lithography, comprising the steps of: Using a mask to define areas in the support structure to be etched; Etching the defined area; Including, the mask having a shape defined by a mask boundary including a plurality of straight line sections; The method wherein the included angle between each pair of immediately adjacent straight line sections is greater than 90 degrees.

41. 41. A membrane produced using the method of any one of claims 34 to 40.

42. 1. A membrane for EUV lithography comprising a free-standing portion, comprising: the shape of the free-standing portion is defined by a free-standing portion perimeter that includes a plurality of substantially straight line sections; A membrane wherein the included angle between each pair of immediately adjacent straight sections is greater than 90 degrees.

43. 1. A membrane for EUV lithography, comprising: A base layer; a capping layer comprising an alloy of Mo and at least one other metal; A membrane comprising:

44. 44. The membrane of claim 43, wherein the at least one other metal comprises one or more of Ta, Ti, Cr, Ni, and Nb.

45. 1. A membrane for EUV lithography, comprising: A base layer; a capping layer comprising a borosilicate glass; and A membrane comprising:

46. 46. ​​The membrane of claim 45, wherein the borosilicate glass is formed in place of a native oxide of the base layer, by converting a native oxide of the base layer to the borosilicate glass, or over a native oxide of the base layer.

47. 1. A membrane for EUV lithography, comprising: YSi ２ , ZrSi ２ , LaSi ２ , and NbSi ２ A base layer including one or more of A membrane comprising:

48. further comprising a capping layer including a capping layer first sublayer and a capping layer second sublayer; the capping layer first sublayer contacts the base layer and the capping layer second sublayer is positioned on one side of the capping layer first sublayer opposite the base layer; The first sublayer of the capping layer is MoSi ２ or Si.

49. 49. The membrane of claim 48, wherein the capping layer second sublayer comprises B.

50. 50. A membrane according to any of claims 42 to 49, wherein the thickness of the base layer is selected to achieve destructive interference between EUV reflections from interfaces on either side of the base layer.

51. 51. The membrane of any of claims 42 to 50, wherein the thickness of the base layer is one of 9 nm + / - 2 nm, 16 nm + / - 2 nm, 22 + / - 2 nm, and 29 + / - 2 nm.

52. 1. A method of manufacturing a membrane for EUV lithography, comprising the steps of: Providing a base layer or a stack including a base layer; forming an amorphous capping layer on the base layer or the stack; A method comprising:

53. 53. The method of claim 52, wherein forming the amorphous capping layer comprises simultaneously depositing at least two different metals to form an alloy.

54. 54. The method of claim 52 or 53, wherein forming the amorphous capping layer comprises depositing the amorphous capping layer in the presence of a first gas and a second gas, the presence of the second gas inhibiting crystallization of the amorphous capping layer compared to the same deposition process performed in the presence of only the first gas.

55. 55. The method of any of claims 52 to 54, wherein forming the amorphous capping layer is carried out while the base layer or stack is held at a temperature below room temperature.

56. 1. A membrane for EUV lithography, comprising: A base layer; an amorphous capping layer providing an outer surface of the membrane; A membrane comprising:

57. 57. The membrane of claim 56, wherein the amorphous capping layer is metallic.

58. 58. The membrane of claim 56 or 57, wherein the amorphous capping layer comprises an alloy.

59. 59. The membrane of claim 58, wherein the alloy comprises one or more of Ru, Mo, B, C, Cr, Ir, Nb, Pd, Pt, Re, Rh, Ti, V, Y, preferably one or both of: 1) Ru and one or more of Rh, Pd, Pt, Y, B, Ti, C, and P; 2) Mo and one or more of B, Ta, Nb, Cr, and Ru.

60. The alloy is selected from the group consisting of B-doped Ru, P-doped Ru, and Mo-doped Ru. （１－ｘ－ｙ） Ru ｘ B ｙ 60. The membrane of claim 59, comprising:

61. 1. A membrane for EUV lithography, comprising: A base layer; A capping layer providing an outer surface of the membrane, the capping layer having a proportion of at least 20% sp ３ a carbon-containing capping layer having carbon; A membrane comprising:

62. The base layer is a carbon nanotube having a sp ３ The proportion of carbon is lower than sp ３ 62. The membrane of claim 61 comprising carbon having a percentage of carbon.

63. 1. A membrane for EUV lithography, comprising: A base layer; a capping layer providing an outer surface of the membrane, the capping layer comprising an alkali metal or alkaline earth metal doped transition metal; A membrane comprising:

64. 1. A membrane for EUV lithography, comprising: A base layer; A capping layer providing an outer surface of the membrane, M1 ｘ M2 ｙ O ｚ wherein M1 comprises one or more alkali metals and / or one or more alkaline earth metals, and M2 comprises a transition metal, optionally a rare earth metal; A membrane comprising:

65. The capping layer is made of SrRuO ３ , SrVO ３ , CaVO ３ , La ０．６７ Sr ０．３３ MnO ３ 65. The membrane of claim 64, comprising one or more of:

66. 1. A method of manufacturing a membrane for EUV lithography, comprising the steps of: forming at least one base layer on a support structure; etching into the support structure in selected areas beneath the base layer to form a free-standing membrane including the base layer; Including, The method, wherein the difference in thermal expansion coefficient between the support structure and the base layer is less than the difference in thermal expansion coefficient between silicon and the base layer.

67. The base layer is MoSi ２ , ZrSi ２ , B, and B ４ C, and the support structure comprises sapphire; or The base layer is sp ２ 67. The method of claim 66, comprising carbon and the support structure comprises quartz.

68. 1. A membrane for EUV lithography comprising a free-standing portion, comprising: A membrane, wherein the free-standing portion includes a base layer and is connected to a non-free-standing portion supported by a support structure, and wherein the difference in thermal expansion coefficients between the support structure and the base layer is less than the difference in thermal expansion coefficients between silicon and the base layer.

69. 68. A membrane produced using the method of any of claims 52-55 and 66-67.

70. 70. A patterning device assembly for EUV lithography comprising a membrane according to any of claims 1 to 33, 41 to 51, 56 to 65 and 68 to 69.

71. 70. A dynamic gas lock assembly for EUV lithography comprising a membrane according to claims 1 to 33, 41 to 51, 56 to 65 and 68 to 69.

72. 1. A cleaning tool for cleaning a membrane for EUV lithography, comprising: a chamber including an inlet opening and an outlet opening for providing a laminar gas flow through the chamber, the laminar flow direction being parallel to an outer surface of the membrane; an interface plate positioned to hold the membrane within the chamber; a vibration stage coupled to the interface plate and positioned to vibrate the membrane such that contaminant particles are released from the outer surface of the membrane; Including cleaning tools.

73. 1. A cleaning tool for cleaning a membrane for EUV lithography, comprising: a chamber including an inlet opening and an outlet opening for providing a laminar gas flow through the chamber, the laminar flow direction being parallel to an outer surface of the membrane; an interface plate positioned to hold the membrane within the chamber; an acoustic speaker disposed in front of the membrane and arranged to vibrate the membrane with sound waves such that contaminant particles are released from the outer surface of the membrane; Including cleaning tools.

74. 74. A cleaning tool according to claim 72 or 73, further comprising an inspection camera and a light source.

75. 75. The cleaning tool of claims 72 to 74, wherein the membrane is in a vertical position and the inlet opening and the exhaust opening of the chamber are positioned such that the laminar flow removes the contaminant particles from the cleaning tool.

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