Pellicle Frame for EUV Lithography

Abstract

The pellicle frame (17) comprises a first portion (40) and a plurality of second portions (42). The first portion is for connecting to the edge (19a) of the pellicle (19). The first portion includes a hollow, generally rectangular body. The plurality of second portions are for connecting to a patterning device (MA). The first portion and the plurality of second portions are all formed from a first material. Each of the second portions is connected to the first portion by a spring portion (44) formed from the first material. Such a pellicle frame is advantageous because the first portion, the plurality of second portions, and the spring portion are all formed from the same material. This greatly simplifies the manufacture of the pellicle frame. For example, all components of the pellicle frame may be integrally formed.

Description

Technical Field

[0001] Cross - reference to related applications

[0001] This application claims priority to European application 20170977.1 filed on April 23, 2020, the entire contents of which are incorporated herein by reference.

[0002]

[0002] The present invention relates to a pellicle frame suitable for use within an extreme ultraviolet (EUV) lithography apparatus. The pellicle frame may facilitate the connection of the pellicle to a reticle or mask. The present invention also relates to a pellicle assembly comprising the pellicle frame and a mask assembly comprising the pellicle frame.

Background Art

[0003]

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

[0004]

[0004] The wavelength of the radiation used by a lithography apparatus to project a pattern onto a substrate determines the minimum feature size that can be formed on that substrate. Using a lithography apparatus that uses EUV radiation, which is electromagnetic radiation having a wavelength within the range of 4 - 20 nm, smaller features can be formed on a substrate than with conventional lithography apparatuses (e.g., those that can use electromagnetic radiation with a wavelength of 193 nm).

[0005]

[0005] A patterning device (e.g., a mask) used to impart a pattern to a radiation beam in a lithography apparatus may form part of a mask assembly. The mask assembly may comprise a pellicle that protects the patterning device from particle contamination. The pellicle may be supported by a pellicle frame.

[0006]

[0006] It may be desirable to provide an apparatus that prevents or mitigates one or more problems associated with the prior art.

SUMMARY OF THE INVENTION

[0007]

[0007] According to a first aspect of the present invention, there is provided a pellicle frame comprising a first portion connected to the edge of the pellicle, the first portion including a hollow generally rectangular body, and a plurality of second portions connected to a patterning device, wherein all of the first portion and the plurality of second portions are formed from a first material, and each of the second portions is connected to the first portion by a spring portion formed from the first material.

[0008]

[0008] The pellicle frame according to the first aspect of the present invention is advantageous because the first portion, the plurality of second portions, and the spring portions are all formed from the same material, i.e., the first material. This significantly simplifies the manufacture of the pellicle frame. For example, all parts of the pellicle frame may be integrally formed.

[0009]

[0009] This is in contrast to existing configurations where the first portion connected to the edge of the pellicle is formed from one material (e.g., silicon) and the plurality of second portions connected to the patterning device are formed from another material (e.g., titanium or a titanium alloy). Such existing configurations are quite complex to manufacture because the parts have to be manufactured separately and then assembled. And this significantly increases the cost of manufacturing such existing pellicle frames (compared to the pellicle frame according to the first aspect of the present invention). This is even more so because the assembly of these separate parts is not straightforward as a result of the quite stringent requirements regarding the pellicle frame used in EUV lithography apparatuses.

[0010] [

[0010] ] First, the pellicle frame (and the pellicle assembly including the resulting pellicle frame) is important to be clean in order to reduce the risk of contaminating the patterning device (reticle) that will be attached during use. For example, it may be desirable to ensure that the number of particles on the pellicle frame is less than a desired particle threshold (preferably no particles are disposed on the pellicle frame). To achieve this, the components of the pellicle frame may be kept in a clean environment until assembled. Assembly may be achieved in a clean environment. These clean environments may be maintained under vacuum conditions. Maintaining multiple clean environments (or a large-sized clean environment) will increase the manufacturing cost. Also, assembly in a clean environment is difficult.

[0011] [

[0011] ] Second, during use, the pellicle frame will be attached to the reticle supported by the reticle stage. In a lithography apparatus called a scanner in which the patterning device and the wafer are synchronously scanned with an EUV radiation beam, the reticle stage and the pellicle frame attached thereto will be subjected to significant acceleration. It is important that all components of the movable mask assembly are well connected so as to remain connected despite these large accelerations. For this reason, it may be preferable to reduce the total number of components connected together. The novel pellicle frame according to the first aspect of the present invention achieves this.

[0012] [

[0012] ] It will be understood that each spring portion may include a portion of a first material having a dimension smaller than the dimensions of the first portion and the plurality of second portions.

[0013] [

[0013] ] In some embodiments, the first material is 10*10 -6 K -1 smaller, preferably 10 -6 K -1It may have a smaller coefficient of thermal expansion (CTE). The first material may be elastic. The first material may be ductile. In some embodiments, the first material may have a Young's modulus greater than 100 GPa. In some embodiments, the first material may have a yield stress less than 1000 MPa, preferably less than 900 MPa. In some embodiments, the first material may have a density less than 5000 kg / m 3 Less, more preferably less than 1500 kg / m 3 Less density. The properties of the first material are selected to ensure reticle deformation in an imaging area of 400 pm or less. The first material may be suitable for use in a vacuum environment. The first material may be suitable for use in an environment within an EUV lithography apparatus.

[0014]

[0014] The first material may contain titanium.

[0015]

[0015] For example, the first material may be a titanium alloy. For example, the first material may contain titanium grade 5. Titanium grade 5 may also be referred to as Ti6Al4V, Ti-6Al-4V or Ti6-4. Titanium grade 5 contains 6% aluminum (Al), 4% vanadium (V) and trace amounts of iron and oxygen, and the remaining portion contains titanium.

[0016]

[0016] The first material may contain at least 50% titanium. The first material may contain at least 70% titanium. The first material may contain at least 85% titanium.

[0017]

[0017] Titanium is suitable for use in a vacuum environment, specifically suitable for use in an environment within an EUV lithography apparatus. Also, titanium provides a spring portion and has sufficient elasticity so that the pellicle frame is not brittle enough to break during use.

[0018]

[0018] There may be four second parts, each connected to the first part by a spring part.

[0019]

[0019] Each of the four second parts may be close to a corner of the first part.

[0020]

[0020] Two of the second parts may be provided on one side of the generally rectangular hollow body of the first part, and the other two of the second parts may be provided on the opposite side of the generally rectangular hollow body of the first part.

[0021]

[0021] Each of the plurality of second parts may include a generally cubic body such that each of the second parts is rectangular in the main plane of the pellicle frame.

[0022]

[0022] Thus, each of the second parts provides a generally rectangular surface that can be attached to the surface of the patterning device.

[0023]

[0023] Each of the spring parts may be configured to enable relative movement in the moving direction between the first part and the second part.

[0024]

[0024] Each of the spring parts may include a generally cubic body. One of the dimensions of the spring part may be significantly smaller than the other two dimensions such that each spring part is generally planar. Specifically, the dimension of the spring part in its moving direction may be significantly smaller than the other two dimensions of the spring part.

[0025]

[0025] In the plane of the pellicle frame, each of the spring parts may include a portion of a first material extending in the connecting direction from the first part to one of the second parts. The spring part has a smaller dimension in the moving direction, which is in the plane of the pellicle frame and perpendicular to the connecting direction, to enable relative movement in the moving direction between the second part and the first part.

[0026]

[0026] That is, each spring part is a relatively thin portion of the first material extending in the connecting direction from the first part to one of the second parts.

[0027]

[0027] During use, the movement and flexibility provided by the spring portions enable the flexure of the pellicle frame with respect to the patterning device to which the second portion is connected. This can adjust the differential thermal expansion of the patterning device, the pellicle frame, and the pellicle. This is advantageous for reducing the thermal stress that may occur in the pellicle frame, which may damage the pellicle, and the thermal stress that may occur in the patterning device, which may distort the pattern imaged on the wafer. Also, it reduces the load on the adhesives that connect the pellicle to the patterning device (i.e., the adhesive layers between the first portion of the pellicle frame and the pellicle, and between each of the second portions of the pellicle frame and the patterning device).

[0028]

[0028] Each of the spring portions generally includes a substantially cubic body, but the dimension of the body in the moving direction is significantly smaller than the other two dimensions. Specifically, the spring portion has a dimension such that the spring portion enables relative movement between the second portion and the first portion in the moving direction. It will be understood that the dimensions suitable for achieving this generally depend on the elastic properties of the first material (e.g., titanium or a titanium alloy).

[0029]

[0029] The dimension of the spring portion in the direction perpendicular to the plane of the pellicle frame is preferably large enough to prevent or at least significantly reduce the out-of-plane relative movement of the first portion and the plurality of second portions of the pellicle frame.

[0030]

[0030] Generally, each spring portion may have a different moving direction.

[0031]

[0031] Each pair of diagonally opposed spring portions may have the same moving direction such that two spring portions have a first moving direction and two spring portions have a second moving direction.

[0032]

[0032] Each of the spring portions may be configured such that its moving direction generally points to the center of the first portion.

[0033]

[0033] This is advantageous because it allows each spring portion to move the attached pellicle near each of the pellicle frame and the second portion (i.e., the position where it is connected to the patterning device during use) in a direction passing through the center of the first portion. This enables the pellicle frame (and the pellicle assembly) to expand equally in all directions without rotating relative to the attached patterning device, which is beneficial. Thus, according to such a configuration, when there is uniform heating of the pellicle frame (relative to the temperature of the attached patterning device), the orientation and the center position of the pellicle frame relative to the patterning device will not change.

[0034]

[0034] Each of the spring portions may be configured such that its connection direction extends through the center point of the second portion to which it is connected. In certain embodiments, one or more spring portions may form a spring, for example, the first spring portion and the second spring portion may form a spring. The spring ensures mechanical separation of the frame from the reticle, for example, when the frame gets hot and undergoes thermal deformation. The mechanical separation ensures that a minimum force and moment are applied to the reticle. The frame may be constrained by the spring, for example, at four points on the reticle.

[0035]

[0035] The spring may be a leaf spring, for example, a single leaf spring or a double leaf spring. Preferably, the spring is a single leaf spring with a substantially small spring moment such that reticle deformation occurs in the z - direction rather than in the xy - plane of the reticle.

[0036]

[0036] The spring may be oriented at the thermal center of the frame. The thermal center is the point of the frame that does not move when a temperature change is applied. The advantage of the spring being oriented at the thermal center is that frame deformation, stress, and strain are symmetric around the thermal center. The spring may rotate within the frame such that the thermal center of the frame is at the center and coincides with the symmetry center.

[0037]

[0037] Each of the second parts may be arranged outside the generally rectangular hollow body of the first part.

[0038]

[0038] The pellicle frame may further comprise a plurality of side protrusions from the generally rectangular hollow body. Each side protrusion may be formed from a first material. Each side protrusion and the generally rectangular hollow body may define an opening, and each of the plurality of second parts may be arranged in one of the openings.

[0039]

[0039] That is, each side protrusion, together with the first part, forms a frame around one of the second parts (and its corresponding spring part).

[0040]

[0040] The side protrusions may be integrally formed with the first part. Each side protrusion from the generally rectangular first part may be generally in the shape of a hollow triangle. A gap may be provided between each second part and the side protrusion and / or the first part. This gap allows limited movement of each second part relative to the first part in the direction of movement. However, the side protrusions may have dimensions that are large enough to be substantially rigid. Thus, the side protrusions can serve as a physical stop to limit the range of movement of each second part relative to the first part in the direction of movement. Advantageously, this may prevent failure of the spring part. Such a risk of failure may be present during handling of the pellicle frame, for example during installation of the spring part into the pellicle assembly and / or the mask assembly.

[0041]

[0041] According to a second aspect of the present invention, there is provided a pellicle assembly comprising a pellicle frame according to a first aspect of the present invention, and a pellicle having a generally rectangular hollow edge and a film bounded by the edge, wherein the edge of the pellicle is attached to the first part of the pellicle frame.

[0042]

[0042] The edge of the pellicle may be attached to the generally rectangular hollow body of the first part of the pellicle frame.

[0043]

[0043] The edge of the pellicle may be formed from a second material different from the first material in which the pellicle frame is formed.

[0044]

[0044] The edge of the pellicle may be formed from silicon.

[0045]

[0045] As is known in the art, a pellicle may be formed by the attachment of one or more layers of a thin material to a generally rectangular silicon substrate. The silicon substrate supports one or more thin layers during the fabrication stage of this pellicle. When the desired or target thickness and composition of the layer are applied, the central portion of the silicon substrate is removed by etching (which may be referred to as back etching). The peripheral portion of the rectangular silicon substrate is not etched (or is etched to a lesser extent than the central portion). This peripheral portion forms the edge of the final pellicle, while one or more thin layers form the film of the pellicle (bounded by the edge).

[0046]

[0046] Such a pellicle generally requires support from a more rigid pellicle frame. The pellicle frame provides the following two functions. (a) Support the pellicle and may further tension the pellicle film, and (b) facilitate the connection of the pellicle to the patterning device (reticle) of the pellicle. In order to provide flexibility that allows for the different thermal expansions of the pellicle and the reticle over the range of operating temperatures that these components experience during use, it is desirable to select a material that is sufficiently elastic and suitable for use under the conditions within the EUV lithography apparatus for connection to the patterning device. One suitable material is titanium. Since the main hollow rectangular portion of the pellicle frame is generally attached to the edge in a known assembly, the main hollow rectangular portion of this pellicle frame is formed from a material whose thermal properties generally match the thermal properties of the edge of the pellicle. For example, silicon is generally used. Thus, a known pellicle frame comprises a silicon body pasted to the pellicle and four titanium attachment mechanisms pasted to the sides of this body.

[0047]

[0047] Since the thermal properties of silicon and titanium are very different (titanium has a thermal expansion coefficient about four times that of silicon), there is a significant prejudice in the art against using a material (such as titanium) having thermal properties different from those of silicon for the main body of the pellicle frame. The reason is that when the temperature of the pellicle assembly changes, the differential thermal expansion of the frame and the edge will cause the pellicle assembly to warp or bend. And this can stress the patterning device and cause imaging errors such as an increase in overlay. However, surprisingly, the inventors have found that when using the novel pellicle frame, the overlay does not deteriorate more than when using a known pellicle frame. Therefore, the novel pellicle frame provides a simpler and lower-cost configuration without compromising on imaging performance.

[0048]

[0048] The edge of the pellicle may be attached to the first part of the pellicle frame by an adhesive.

[0049]

[0049] The adhesive may be a poly(methyl methacrylate)-based adhesive.

[0050]

[0050] Alternatively, the adhesive may be an epoxy adhesive. According to a third aspect of the present invention, there is provided a mask assembly comprising the pellicle assembly according to the second aspect of the present invention and a patterning device, wherein a plurality of second parts of the pellicle frame are attached to the patterning device.

[0051]

[0051] The mask assembly according to the third aspect of the present invention is particularly advantageous over known configurations that generally use an intermediate fixing member (known as a stud) that is fixed to the patterning device and engages with the pellicle assembly, as will be considered hereinafter.

[0052]

[0052] The mask assembly according to the third aspect of the present invention comprises fewer components than a mask assembly that uses an intermediate fixing member such as a stud (fixed to the patterning device) and an engagement mechanism (provided in the pellicle assembly) that engages with the intermediate fixing member (stud). Thus, advantageously, the mask assembly according to the third aspect of the present invention may be relatively easy to manufacture. The reduction in the number of components and the simplification of the manufacturing procedure may result in lower manufacturing costs.

[0053]

[0053] This is even more so since the assembly of the mask assembly is not straightforward as a result of the rather strict requirements regarding mask assemblies used in EUV lithography apparatuses.

[0054]

[0054] First, it is important that the mask assembly is clean in order to reduce the risk of contaminating the patterning device (reticle). For example, it may be desirable to ensure that the number of particles on the mask assembly is below a desired particle threshold (preferably no particles are placed on the mask assembly). To achieve this, the components of the mask assembly may be kept in a clean environment until they are assembled. The assembly may be achieved in a clean environment. These clean environments may be maintained under vacuum conditions. Maintaining multiple clean environments (or a large clean environment) will increase the manufacturing costs. Also, assembly in a clean environment is difficult.

[0055] Second, in use, the mask assembly will be supported by a reticle stage. In a lithographic apparatus called a scanner, in which the patterning device and the wafer are synchronously scanned with an EUV radiation beam, the reticle stage and the pellicle frame attached thereto will be subjected to a large acceleration. It is important that all parts of the movable mask assembly are well connected so as to remain connected despite these large accelerations. For this reason, it may be preferred to reduce the total number of parts connected together. The novel mask assembly according to the third aspect of the present invention achieves this.

[0056]

[0056] It is estimated that there is a significant reduction in the cost of manufacturing the mask assembly according to the third aspect of the present invention compared to the cost of manufacturing a known mask assembly. For example, the cost of manufacturing a known mask assembly may be about 10 times greater than the cost of manufacturing the mask assembly according to the third aspect of the present invention.

[0057]

[0057] Also, by significantly reducing the complexity of the mask assembly and its manufacture, the number of components and the number of handling steps in the process of manufacturing the mask assembly are reduced, and furthermore, these handling steps may be less related. As a result, the risk of particles and debris being present on the final mask assembly is reduced. This is beneficial because such particles can cause imaging errors and defects.

[0058]

[0058] In some embodiments, the distance between the pellicle and the patterning device may be, for example, about 1 mm to 10 mm, for example 1 mm to 5 mm, for example 2 mm to 2.5 mm.

[0059]

[0059] The plurality of second portions of the pellicle frame may be attached to the patterning device by an adhesive.

[0060]

[0060] The adhesive may be a poly(methyl methacrylate)-based adhesive.

[0061]

[0061] Due to the material properties of the PMMA paste, specifically the elasticity of the PMMA paste and the dimensions to which the PMMA paste can be applied, the deformation of the patterning device caused by the curing of the PMMA paste is relatively small (compared to other pastes). In contrast, if a pellicle frame is directly fixed to the patterning device using another paste, the deformation of the patterning device caused by the curing of the other paste becomes significantly large, and as a result, errors may occur in the pattern projected onto the substrate by the lithography apparatus.

[0062]

[0062] The PMMA paste is, for example, more easily removable than an epoxy paste and has relatively high elasticity. Advantageously, this may make it possible to more easily replace the pellicle assembly that forms part of the mask assembly according to the third aspect of the present invention.

[0063]

[0063] Alternatively, the adhesive may be an epoxy adhesive.

[0064]

[0064] It will be understood that one or more of the aspects or features described above or referred to in the following description may be combined with one or more other aspects or features.

Brief Description of the Drawings

[0065]

[0065] Embodiments of the present invention will be described below by way of example only with reference to the accompanying drawings.

[0066]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

DETAILED DESCRIPTION OF THE INVENTION

[0067]

[0066] FIG. 1 shows a lithography system. The lithography system includes a radiation source SO and a lithography apparatus LA. The radiation source SO is configured to generate an extreme ultraviolet (EUV) radiation beam B. The lithography apparatus LA includes an illumination system IL, a support structure MT configured to support a mask assembly 15 including a patterning device MA (e.g., a mask), a projection system PS, and a substrate table WT configured to support a substrate W. The illumination system IL is configured to condition the radiation beam B before it is incident on the patterning device MA. The projection system is configured to project the radiation beam B (now patterned by the mask MA) onto the substrate W. The substrate W may include a previously formed pattern. In that case, the lithography apparatus aligns the patterned radiation beam B with the pattern previously formed on the substrate W.

[0068]

[0067] The radiation source SO, the illumination system IL, and the projection system PS may all be constructed and arranged so as to be isolated from the external environment. A gas at a pressure lower than atmospheric pressure (e.g., hydrogen) may be provided within the radiation source SO. A vacuum may be provided within the illumination system IL and / or the projection system PS. A small amount of gas at a pressure sufficiently lower than atmospheric pressure (e.g., hydrogen) may be provided within the illumination system IL and / or the projection system PS.

[0069]

[0068] The radiation source SO shown in FIG. 1 is of a type that can be called a laser-produced plasma (LPP) source. For example, a laser 1, which can be a CO2 laser, is arranged to impart energy to a fuel such as tin (Sn) supplied from a fuel dispenser 3 via a laser beam 2. Although tin is referred to in the following description, any suitable fuel may be used. The fuel may be, for example, in liquid form or, for example, a metal or alloy. The fuel dispenser 3 may comprise a nozzle configured to direct tin, for example in the form of droplets, along a trajectory towards a plasma formation region 4. The laser beam 2 is incident on the tin in the plasma formation region 4. The application of laser energy to the tin generates a plasma 7 in the plasma formation region 4. During the de-excitation and recombination of plasma ions, radiation including EUV radiation is emitted from the plasma 7.

[0070]

[0069] The EUV radiation is collected and focused by a near-normal incidence radiation collector 5 (which may more generally be referred to as a normal incidence radiation collector). The collector 5 may have a multilayer structure arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm). The collector 5 may have an elliptical configuration with two elliptical foci. As will be discussed below, the first focus may be in the plasma formation region 4 and the second focus may be at an intermediate focus 6.

[0071]

[0070] In other embodiments of the laser-produced plasma (LPP) source, the collector 5 may be a so-called grazing incidence collector configured to receive EUV radiation at a grazing incidence angle and focus this EUV radiation onto an intermediate focus. The grazing incidence collector may be, for example, a nested collector including a plurality of grazing incidence reflectors. The grazing incidence reflectors may be arranged axially symmetrically about an optical axis.

[0072]

[0071] The radiation source SO may comprise one or more contamination traps (not shown). For example, the contamination trap may be located between the plasma formation region 4 and the radiation collector 5. The contamination trap may be, for example, a rotating foil trap or any other suitable form of contamination trap.

[0073]

[0072] The laser 1 may be separated from the radiation source SO. In that case, the laser beam 2 may be passed from the laser 1 to the radiation source SO with the aid of, for example, a beam delivery system (not shown) comprising suitable guiding mirrors and / or beam expanders and / or other optical components. The laser 1 and the radiation source SO may be regarded together as a radiation system.

[0074]

[0073] The radiation reflected by the collector 5 forms a radiation beam B. The radiation beam B is focused at point 6 to form an image of the plasma formation region 4, which acts as a virtual radiation source for the illumination system IL. The point 6 at which the radiation beam B is focused may be referred to as an intermediate focus. The radiation source SO is arranged such that the intermediate focus 6 is located at or near the opening 8 of the containment structure 9 of the radiation source SO.

[0075]

[0074] The radiation beam B proceeds from the radiation source SO into an illumination system IL configured to condition the radiation beam. The illumination system IL may comprise a facet field mirror device 10 and a facet pupil mirror device 11. Together, the facet field mirror device 10 and the facet pupil mirror device 11 impart a desired cross-sectional shape and a desired angular distribution to the radiation beam B. The radiation beam B exits the illumination system IL and is incident on a mask assembly 15 held by a support structure MT. The mask assembly 15 comprises a patterning device MA and a pellicle 19 held in a predetermined position by a pellicle frame 17. The patterning device MA reflects the radiation beam B and imparts a pattern thereto. The illumination system IL may comprise other mirrors or devices in addition to or instead of the facet field mirror device 10 and the facet pupil mirror device 11.

[0076]

[0075] Following reflection from the patterning device MA, the patterned radiation beam B enters the projection system PS. The projection system comprises a plurality of mirrors configured to project the radiation beam B onto a substrate W held by a substrate table WT. The projection system PS may apply a certain reduction factor to the radiation beam and form an image having features smaller than the corresponding features on the patterning device MA. For example, a reduction factor of 4 may be applied. In FIG. 1, the projection system PS has two mirrors, but the projection system may include any number of mirrors (for example, six mirrors).

[0077]

[0076] The lithographic apparatus may be used, for example, in a scanning mode. In the scanning mode, while synchronously scanning a support structure (for example, a mask table) MT and a substrate table WT, the pattern imparted to the radiation beam is projected onto the substrate W (that is, dynamic exposure). The speed and direction of the substrate table WT relative to the support structure (for example, the mask table) MT may be determined by the reduction and image inversion characteristics of the projection system PS. The patterned radiation beam incident on the substrate W may include a certain radiation band. This radiation band may be called an exposure slit. During scanning exposure, the substrate table WT and the support structure MT may move such that the exposure slit advances over the exposure field of the substrate W.

[0078]

[0077] The radiation source SO and / or the lithographic apparatus shown in FIG. 1 may comprise components not shown. For example, a spectral filter may be provided within the radiation source SO. The spectral filter may be substantially transmissive to EUV radiation but may substantially block radiation of other wavelengths such as infrared radiation.

[0079]

[0078] In other embodiments of the lithographic system, the radiation source SO may take other forms. For example, in an alternative embodiment, the radiation source SO may include one or more free electron lasers. The one or more free electron lasers may be configured to emit EUV radiation that can be provided to one or more lithographic apparatuses.

[0080]

[0079] As briefly described above, the mask assembly 15 comprises a pellicle 19 provided adjacent to the patterning device MA. Since the pellicle 19 is provided in the path of the radiation beam B, the radiation beam B passes through the pellicle 19 both when approaching the patterning device MA from the illumination system IL and when reflected by the patterning device MA towards the projection system PS. The pellicle 19 comprises a thin film that is substantially transparent to EUV radiation (although it will absorb a small amount of EUV radiation). As used herein, an EUV transmissive pellicle or a film that is substantially transparent to EUV radiation means that the pellicle 19 is transparent to at least 65%, preferably at least 80%, more preferably at least 90% of the EUV radiation. The pellicle 19 serves to protect the patterning device MA from particle contamination.

[0081]

[0080] Despite efforts to maintain a clean environment within the lithographic apparatus LA, particles may still be present within the lithographic apparatus LA. Without the pellicle 19, particles may adhere to the patterning device MA. Particles on the patterning device MA may adversely affect the pattern imparted to the radiation beam B and thus the pattern transferred to the substrate W. The pellicle 19 advantageously provides a barrier between the patterning device MA and the environment within the lithographic apparatus LA to prevent particles from adhering to the patterning device MA.

[0082]

[0081] The pellicle 19 is positioned at a sufficient distance from the patterning device MA so that particles incident on the surface of the pellicle 19 do not exist within the field plane of the lithographic apparatus LA. This spacing between the pellicle 19 and the patterning device MA serves to suppress the degree to which particles on the surface of the pellicle 19 impart a pattern to the radiation beam B that is imaged onto the substrate W. Even if a particle exists within the radiation beam B, if its position is not within the field plane of the radiation beam B (i.e., not on the surface of the patterning device MA), it will be understood that the image of this particle will be out of focus on the surface of the substrate W. If there are no other considerations, it may be desirable to position the pellicle 19 at a relatively large distance from the patterning device MA. However, in practice, since there are other components within the lithographic apparatus LA, the space available for accommodating the pellicle is limited. In some embodiments, the spacing between the pellicle 19 and the patterning device MA may be, for example, about 1 mm to 10 mm, such as 1 mm to 5 mm, more preferably 2 mm to 2.5 mm.

[0083]

[0082] A mask assembly may be prepared for use in a lithographic apparatus by attaching a pellicle to a pellicle frame and attaching this pellicle frame to a patterning device. A mask assembly comprising a patterning device MA and a pellicle supported by a pellicle frame adjacent to the patterning device may be prepared remotely from the lithographic apparatus LA, and this mask assembly may be transported to the lithographic apparatus LA for use in the lithographic apparatus LA. For example, at the location where a pattern is imparted to the patterning device, a pellicle frame supporting the pellicle may be attached to the patterning device to form a mask assembly. Subsequently, the mask assembly may be transported to another location where the lithographic apparatus LA is located, and the mask assembly may be provided to the lithographic apparatus LA for use in the lithographic apparatus LA.

[0084]

[0083] A mask assembly in which a pellicle is held in a predetermined position by a pellicle frame may be fragile, and transporting the mask assembly may risk damaging the pellicle. Also, by assembling the mask assembly in an environment separate from the lithography apparatus LA, the mask assembly may be exposed to various pressure conditions. For example, the mask assembly may be transported to the lithography apparatus under ambient pressure conditions. The mask assembly may then be loaded into the lithography apparatus LA via a load lock that is evacuated to a vacuum pressure condition. Changes in the pressure conditions to which the mask assembly is exposed may create a pressure differential across the pellicle, causing the pellicle to flex and risking damage to the pellicle. In one embodiment, the lithography system may include a lithography apparatus LA connected to a pellicle frame attachment device. In this case, a mask assembly comprising a mask and a pellicle may be transferred directly from the pellicle frame attachment device to the lithography apparatus while remaining in a controlled environment (e.g., a vacuum environment).

[0085]

[0084] Since manufacturing a mask assembly is a complex process, the cost of manufacturing a mask assembly is very high. Embodiments of the present invention relate to a novel pellicle frame that significantly reduces the complexity of mask assemblies and their manufacture. This results in a cost reduction of approximately tenfold. Also, by significantly reducing the complexity of mask assemblies and their manufacture, the number of components and the number of handling steps in the process of manufacturing a mask assembly are reduced, and these handling steps may be less related. As a result, the risk of particles and debris being present on the final mask assembly is reduced. This is beneficial since such particles can cause imaging errors and defects.

[0086]

[0085] Figure 2 is a schematic view of a known apparatus suitable for assembling a known type of mask assembly 15' and transferring this mask assembly to a lithographic apparatus LA. Figure 2 shows a pellicle mounting device 855 that can be used to attach a pellicle 19 to a known pellicle frame 17', and a pellicle assembly transport device 881 that can be used to transport a pellicle assembly 16'. Further shown is a stud mounting device 840 that can be used to attach a stud 51 to a patterning device MA. The stud 51 enables releasable attachment of the pellicle frame 17' (and thus the supported pellicle 19) to the patterning device MA. Also shown is a mask transport device 880 that can be used to transport the mask to which the stud is attached. Also shown is a pellicle frame mounting device 857 that can be used to form a mask assembly 15' by attaching a pellicle frame 17' (and a pellicle 19) to a patterning device MA. Also shown is a mask assembly transport device 853 that can be used to transport the mask assembly 15' from the pellicle frame mounting device 857 to the lithographic apparatus LA.

[0087]

[0086] The pellicle mounting device 855 may be located in a location different from the location where the lithographic apparatus is located. The stud mounting device 840 may be located in a location different from the location where the lithographic apparatus LA is located. Alternatively, one or both of the pellicle mounting device 855 and the stud mounting device 840 may be located in the same location as the location where the lithographic apparatus LA is located (e.g., within a lithographic manufacturing facility).

[0088]

[0087] The pellicle mounting device 855 houses the pellicle 19, a known pellicle frame 17', and an engagement mechanism (not shown). The pellicle 19 and the known pellicle frame 17' may be manually placed into the pellicle mounting device 855. Adhesive is dispensed into the engagement mechanism receiving opening of the known pellicle frame 17' (e.g., the location further described below with reference to FIGS. 3 and 4). The dispensing of the adhesive may be manual or may be automated (or partially automated).

[0089]

[0088] The engagement mechanism and the known pellicle frame 17' are aligned with each other (e.g., using an optical alignment device), and then the engagement mechanism is inserted into the opening of the known pellicle frame 17'.

[0090]

[0089] Adhesive is also dispensed onto the known pellicle frame 17' (e.g., at spaced locations around the perimeter of the known pellicle frame 17'). The dispensing of the adhesive may be manual or may be automated (or partially automated). The pellicle 19 is aligned with the known pellicle frame 17' using an optical alignment system and then pressed against the known pellicle frame 17'.

[0091]

[0090] The pellicle 19 may be operated by a pellicle operating portion that forms part of the pellicle mounting device 855. The pellicle operating portion may include means for applying tension to the pellicle 19. The pellicle operating portion may apply tension to the pellicle 19 at room temperature for a period sufficient for the adhesive to cure, and press the pellicle 19 against the known pellicle frame 17' to fix the pellicle 19 to the known pellicle frame 17'. Thereafter, the pressure on the pellicle 19 is removed. Then, a curing oven (which may form part of the pellicle mounting device 855) is used to effect further curing of the adhesive at an elevated temperature. This will also cure the adhesive attaching the engagement mechanism to the known pellicle frame 17'. In an alternative approach, when pressing the pellicle 19 against the known pellicle frame 17', some heat may be applied to cure the adhesive (without allowing curing to proceed at room temperature).

[0092]

[0091] The adhesive may be provided by an adhesive dispenser. The adhesive dispenser may form part of the pellicle mounting device 855.

[0093]

[0092] The resulting known pellicle assembly 16’ is inspected using a particle inspection tool. The particle inspection tool may form part of the pellicle mounting device 855 (or may be a separate tool). The particle inspection tool may be configured to inspect particles disposed on the pellicle 19 and / or the known pellicle frame 17’. The particle inspection tool may reject, for example, a known pellicle assembly 16’ having a number of particles greater than a given particle threshold. Also, the particle inspection tool may be used to inspect the pellicle 19 and / or the known pellicle frame 17’ before the pellicle and the pellicle frame are joined with the adhesive.

[0094]

[0093] After inspection, the pellicle mounting device 855 may be configured to enclose the known pellicle assembly 16’ within a pellicle assembly transport device 881 (a sealed box). As shown, the pellicle assembly transport device 881 may be configured to hold the pellicle assembly with the pellicle 19 positioned under the known pellicle frame 17’. Since the transport device 881 is sealed, the known pellicle assembly 16’ can be transported without being contaminated. The known pellicle assembly 16’ may be transported by the transport device 881 to the pellicle frame mounting device 857.

[0095]

[0094] The pellicle mounting device 855 has a clean environment to reduce the number of particles inside the sealed environment, which may reduce the number of particles that can adhere to the pellicle 19. The pellicle mounting device 855 may be located, for example, at the place where the pellicle is manufactured. The pellicle 19 may be provided directly from a pellicle manufacturing tool (not shown) where the pellicle 19 is manufactured to the pellicle mounting device 855. The pellicle 19 may be provided from the pellicle manufacturing tool to the pellicle mounting device 855 while, for example, holding the pellicle 19 inside a clean environment. This may reduce the possibility that the pellicle 19 is contaminated or damaged before being provided to the pellicle mounting device 855. The clean environment may be, for example, a sealed environment (i.e., completely isolated from the external environment). The sealed environment may be evacuated to maintain a vacuum inside the sealed environment.

[0096]

[0095] The attachment of the pellicle 19 to a known pellicle frame 17' may be controlled to achieve a desired tension in the pellicle 19. For example, the tension in the pellicle 19 may be measured during or after the attachment of the pellicle 19 to a known pellicle frame 17', and the tension may be adjusted in response to this measurement to achieve a desired tension in the pellicle 19. The tension in the pellicle 19 may be maintained, for example, by applying an outward force to a component of the known pellicle frame 17' to stretch the pellicle 19. The tension in the pellicle 19 may be maintained, for example, by using the difference in the thermal expansion coefficients of the pellicle frame and the pellicle.

[0097]

[0096] The patterning device (which may be called a mask) MA may include protrusions that are received by an engagement mechanism (further described below with reference to FIGS. 3 and 4, for example). The patterning device may receive, for example, four protrusions (referred to herein as studs). As shown in FIG. 2, the stud mounting device 840 may be used to attach the stud 51 to the patterning device MA.

[0098]

[0097] The stud 51 and the patterning device MA may be manually placed in the stud mounting device 840. The patterning device MA may be held in a controlled environment 841 that is separated from the rest of the stud mounting device 840. This separation may be effected by a partition 842 having an opening through which the stud 51 can project to contact the patterning device MA. The controlled environment 841 may be maintained at a higher pressure than other components of the stud mounting device 840 (e.g., by delivering gas through an outlet of the controlled environment). This will suppress or prevent the intrusion of contaminant particles from other components of the stud mounting device into the controlled environment 841.

[0099]

[0098] The stud mounting device 840 may include a stud operating part (not shown), such as a robot or actuator, for accurately positioning the stud. An example of an actuator suitable for placing the stud on the patterning device is a Lorentz actuator (not shown). Further, the stud mounting device 840 may include a device for automatically providing a given amount of paste or adhesive to the stud surface to be attached to the patterning device MA. The application of paste or adhesive may also be done manually. The air flow from the controlled environment 841 above the partition 842 to below the partition prevents or reduces the contamination of the patterning device MA by contaminants from the paste or adhesive (this air flow is caused by the pressure above the partition being higher than the pressure below the partition).

[0100]

[0099] The stud mounting device 840 may further include an optical alignment system for aligning the stud with alignment markers present on the reticle for accurately positioning the stud. For example, alignment markers that have conventionally been provided on the patterning device MA and used for pattern alignment may also be used for stud alignment.

[0101] [000100] The stud mounting device may include a support structure movable in the X - Y - Z and Rz directions to adjust the position of the patterning device MA. The position of the support structure holding the patterning device MA can be adjusted manually by means of coarse and fine mechanical adjustment devices, or by using an automated (or semi - automated) actuator or any other type of device suitable for alignment and positioning coupled to the patterning device table.

[0102] [000101] Once the stud 51 and the patterning device MA are aligned, the stud 51 is pressed against the patterning device MA. The stud 51 may be fixed to the mask MA by pressing the stud 51 against the patterning device MA at room temperature for a period sufficient for the paste to cure. Alternatively, the stud 51 may be heated to accelerate the curing of the paste. Further curing of the paste at a high temperature may then be carried out using a curing oven (which may form part of the stud mounting device 840).

[0103] [000102] The paste may be provided by a paste dispenser. The paste dispenser may form part of the stud mounting device 840.

[0104] [000103] The patterning device MA and the stud 51 may be inspected using a particle inspection tool (which may form part of the stud mounting device 840).

[0105] [000104] The stud mounting device 840 seals the patterning device MA and the stud 51 inside a mask transfer device 880 (a sealed box). Since the mask transfer device 880 is sealed, the patterning device MA and the stud 51 may be transported without the mask MA being contaminated. The patterning device MA and the stud may be transported to the pellicle frame mounting device 857 in the mask transfer device 880.

[0106] [000105] Mask MA may be provided to the stud mounting device 840 in a sealed box (to reduce the risk of contamination). This box remains sealed until immediately before the stud 51 is attached to the patterning device MA, thereby potentially minimizing the time during which contamination can migrate to the mask MA.

[0107] [000106] The controlled environment 841 of the stud mounting device 840 may in part be provided by a housing that later forms part of the patterning device MA transport device 880 (sealed box). This housing may form the walls and roof of the mask transport device 880, and the floor of the mask transport device 880 is formed by a plate that is fitted after (e.g., immediately after) the stud 51 is attached. Using the housing in this way may help prevent contamination from entering the patterning device MA. The housing may comprise a pod cover. The mask table of the stud mounting device 840 may be configured to accommodate the housing.

[0108] [000107] Similarly, the pellicle mounting device 855 may in part be formed by a housing that later forms part of the pellicle assembly transport device 881.

[0109] [000108] The known pellicle assembly 16' within the pellicle assembly transport device 881 and the patterning device MA (and stud 51) within the mask transport device 880 are both transported to the pellicle frame mounting device 857. The pellicle frame mounting device 857 may be provided within a manufacturing facility that also provides one or more lithography devices.

[0110] [000109] The pellicle frame mounting device 857 is configured to attach a known pellicle frame 17' of a known pellicle assembly 16' to a stud 51 on a patterning device MA in order to form a mask assembly 15. The pellicle frame mounting device 857 may comprise a controlled environment 860 that is separated from the remainder of the pellicle frame mounting device 857. This separation may be effected by a partition 862 having an opening, through which an operating part extends (not shown in FIG. 2). The operating part may be operated by a control system 870 (described further below). The controlled environment 860 is maintained as a clean environment in order to reduce the number of particles inside the controlled environment, thereby potentially reducing the number of particles that can adhere to a known mask assembly 15'. The controlled environment 860 may be maintained at a higher pressure than other parts of the pellicle frame mounting device 857 (for example, by delivering gas through an outlet of the controlled environment 860). This will suppress or prevent the ingress of contaminating particles from other parts of the pellicle frame mounting device 857 into the controlled environment 860.

[0111] [000110] A known mask assembly 15' assembled by the pellicle frame mounting device 857 is transported from the pellicle frame mounting device 857 to a lithography apparatus LA by a mask assembly transport device 853. The mask assembly transport device 853 may comprise a sealed clean environment in which the known mask assembly 15' is transported. This reduces the likelihood that the known mask assembly 15' will be contaminated or damaged during transport. The sealed clean environment may be evacuated, for example.

[0112] [000111] The known pellicle assembly 16' is attached to the patterning device MA using the pellicle frame mounting device 857. The pellicle frame mounting device 857 comprises an operating part arranged to operate an engagement mechanism of the pellicle frame 17 (described further below).

[0113] [000112] The patterning device MA may be provided with, for example, alignment marks. The known pellicle frame 17' may be positioned with respect to the alignment marks on the patterning device MA. Aligning the pellicle frame 17 with respect to the alignment marks on the patterning device MA may advantageously improve the accuracy with which the known pellicle frame 17' is positioned on the patterning device MA during the attachment of the known pellicle frame 17' to the patterning device MA.

[0114] [000113] The pellicle frame attachment device 857 may include a particle inspection tool (not shown). The particle inspection tool may be configured to inspect a known mask assembly 15' for particles disposed on the known mask assembly 15'. The particle inspection tool may, for example, reject a known mask assembly 15' on which a number of particles greater than a given particle threshold are disposed.

[0115] [000114] The pellicle frame attachment device 857 may include a pattern inspection system that inspects for defects in the pattern on the patterning device MA. The pattern inspection system may inspect the pattern on the patterning device MA before and / or after the known pellicle frame 17' is attached to the patterning device MA.

[0116] [000115] The lithography apparatus LA may include a component configured to receive a known mask assembly 15' from the mask assembly transfer device 853 and load the known mask assembly 15' onto the support structure MT of the lithography apparatus LA.

[0117] [000116] A known pellicle assembly 16’ may be attached to a patterning device MA to form a known mask assembly 15’ under vacuum conditions within a pellicle frame mounting device 857. The known mask assembly 15’ may then be transported under vacuum conditions by a mask assembly transport device 853 to a lithography apparatus LA and may be held within the lithography apparatus LA under vacuum conditions. Thus, the known mask assembly 15’ may be subjected to substantially the same pressure conditions throughout the period of assembly within the pellicle frame mounting device 857 and use within the lithography apparatus LA. This has the advantage of reducing the pressure changes to which the known mask assembly 15’ is subjected and thus reducing the pressure differences that may occur in the pellicle 19.

[0118] [000117] The patterning device MA and / or the pellicle 19 may be inspected for particles and / or defects within the pellicle frame mounting device 857 while holding the components within a vacuum. Thus, the patterning device MA and / or the pellicle 19 has the advantage of being inspected under the same pressure conditions as those to which it is subjected during use in the lithography apparatus LA. This is advantageous because particles that may adhere to the patterning device MA and / or the pellicle during pumping down to vacuum conditions may be detected in the pellicle frame mounting device 857.

[0119] [000118] During the various operations shown in FIG. 2, it should be noted that the patterned side of the patterning device MA faces downward. Keeping the patterned side of the patterning device MA downward is advantageous as it reduces the possibility of contaminant particles impinging on the pattern. Larger contaminant particles tend to fall downward due to gravity and thus will impinge on the opposite side of the mask. Smaller contaminant particles are less affected by gravity but may be affected by other transport physics instead. The apparatus may include devices aimed at addressing this. For example, the apparatus may include an ionization device for removing static charge, which may reduce the risk of static electricity attaching particles to the pellicle.

[0120] [000119] A known pellicle assembly 16’ is shown in FIG. 3, and a known mask assembly including this known pellicle assembly 16’ is shown in FIG. 4.

[0121] [000120] The known pellicle assembly 16’ shown in FIG. 3 includes a pellicle 19 and a known pellicle frame 17’. The pellicle 19 includes an edge 19a and a membrane 19b. The edge 19a is hollow and generally rectangular and surrounds the membrane 19b, and the membrane 19b is bounded by the edge 19a. The edge 19a may be formed from silicon.

[0122] [000121] The known pellicle frame 17’ includes a hollow generally rectangular body having four projections 20a - 20d extending from the generally rectangular body in the main plane of the known pellicle frame 17’. The four projections 20a - 20d are generally trapezoidal. Two of the projections 20a - 20b project from one side of the generally rectangular body, and the other two projections 20c - 20d project from the opposite side of the generally rectangular body. The generally rectangular body and the four projections 20a - 20d are integrally formed and are formed from silicon.

[0123] [000122] The known pellicle frame 17’ is provided with four engagement mechanisms 22a to 22d. Each of the four protrusions 20a to 20d defines a recess for receiving one of the engagement mechanisms 22a to 22d.

[0124] [000123] Each of the engagement mechanisms 22a to 22d is configured to engage with a protrusion 24 (which may be referred to as a stud 51, for example) extending from a patterning device MA (shown rather schematically in FIG. 4).

[0125] [000124] The pellicle 19 is attached to the known pellicle frame 17’. Specifically, the edge 19a of the pellicle 19 is attached to the generally rectangular body of the known pellicle frame 17’. The edge 19a of the pellicle 19 may be, for example, glued to the known pellicle frame 17’.

[0126] [000125] The protrusion 51 received by the engagement mechanisms 22a to 22d is located on the front surface of the patterning device MA.

[0127] [000126] FIG. 3 shows the four engagement mechanisms 22a to 22d fixed to the pellicle frame 17. The four engagement mechanisms 22a to 22d are all configured to achieve the engagement between the engagement mechanisms 22a to 22d and a protrusion 51 (not shown) through movement in the y direction.

[0128] [000127] Each engagement mechanism 22a - 22d includes an outer portion 24 that is generally square and is fixed (e.g., glued) to a recess defined by one of the protrusions 20a - 20b of the pellicle frame 17. Each engagement mechanism 22a - 22d is provided on the outer portion 24 with a flange 26 (sometimes called a tab 26), which facilitates the engagement and alignment of the engagement mechanisms 22a - 22d with a known pellicle frame 17'. Also, each engagement mechanism 22a - 22d includes an inner portion 28 that is generally square (inside the outer portion 24) and engages with a protrusion 51 on the patterning device MA. The inner portion 28 is connected to the outer portion 24 via two arms 30 and is supported by the outer portion 24. These two arms 30 allow movement / flexibility in the x - direction or y - direction. Two engagement mechanisms 22a, 22d are configured to allow movement in the y - direction (i.e., provide flexibility or compliance in the y - direction). Two engagement mechanisms 22b, 22c are configured to allow movement in the x - direction (i.e., provide flexibility or compliance in the x - direction).

[0129] [000128] Although not described in detail herein, the inner portion 28 of each engagement mechanism 22a - 22d includes an engagement arm 32 that is deflectable out of the main plane of the engagement mechanisms 22a - 22d by an actuating force that allows the insertion of the tip of one protrusion 51. When the protrusion 51 comes to a fixed position, the actuating force is removed and the protrusion 51 remains constrained within the engagement mechanisms 22a - 22d. This requires that an operating part be provided within a pellicle frame mounting device 857 having several independently movable arms. Generally, for each engagement mechanism 22a - 22d, at least two arms are required to hold the engagement mechanisms 22a - 22d, while at least a third arm is required to apply the actuating force to the engagement arm 32. Providing such four actuators (one for each engagement mechanism 22a - 22d) that can operate in a clean environment is very difficult.

[0130] [000129] Figure 4 shows, in cross-section, one engaging mechanism 22a together with a protruding body 51 protruding from the patterning device MA. The protruding body 51, sometimes called a stud, may be, for example, glued to the patterning device MA or attached by other coupling means (such as optical contact, magnetism or van der Waals forces). The protruding body 51 is formed from a material containing titanium.

[0131] [000130] Figure 5 is another cross-sectional view of a portion of the above-described known mask assembly 15'. The cross-section shown in Figure 5 is perpendicular to the y-direction (i.e., perpendicular to the plane of Figure 4) and lies in a plane passing through one of the engaging mechanisms 22a and the associated stud 51. The stud 51 is fixed to the patterning device MA using glue.

[0132] [000131] Figure 6 is a perspective view of a novel pellicle frame 17 according to an embodiment of the present invention.

[0133] [000132] The pellicle frame 17 includes a first portion 40, four second portions 42, and four spring portions 44. The first portion 40, the four second portions 42, and the four spring portions 44 are all integrally formed and are formed from the same material, sometimes called the first material. In this embodiment, the first portion 40, the four second portions 42, and the four spring portions 44 are all formed from a material containing titanium (e.g., a titanium alloy). Specifically, the first portion 40, the four second portions 42, and the four spring portions 44 are all formed from titanium (grade 5). Titanium grade 5 may also be called Ti6Al4V, Ti-6Al-4V, or Ti6-4. Titanium grade 5 contains 6% aluminum (Al), 4% vanadium (V), and trace amounts of iron and oxygen, with the remaining portion being titanium.

[0134] [000133] As will be further described below, the first portion is for connecting to the edge 19a of the pellicle 19. The first portion 40 includes a hollow, generally rectangular body.

[0135] [000134] As further described below, the four second portions 42 are for connecting to the patterning device MA.

[0136] [000135] Each of the second portions 42 is connected to the first portion 40 by a spring portion 44. Each of the four second portions 42 is close to a corner of the first portion 40. Two of the second portions 42 are provided on one side 46 of the hollow generally rectangular member of the first portion 40. The other two of the second portions 42 are provided on the opposite side 48 of the hollow generally rectangular member of the first portion 40.

[0137] [000136] Each of the plurality of second portions 42 includes a generally cubic body. In the main plane (the xy plane of FIG. 6) of the pellicle frame 17, each of the second portions 42 is rectangular. Thus, each of the second portions 42 provides a generally rectangular surface that can be fixed to the surface of the patterning device MA (as further considered below).

[0138] [000137] Each of the spring portions 44 is configured to allow relative movement between the first portion 40 and the second portion 42 so as to connect to the first portion in the moving direction, as described hereinafter.

[0139] [000138] Each of the spring portions 44 includes a generally cubic body. In the main plane of the pellicle frame 17 (the xy plane in FIG. 6), each of the spring portions 44 extends in the connection direction from one of the first portion 40 to the second portion 42. Each spring portion 44 lies within the main plane of the pellicle frame 17 and has a dimension smaller than that in the moving directions 50, 52 perpendicular to the connection direction. The moving directions of each spring portion 44 are indicated by arrows 50, 52 in FIG. 6. Generally, each spring portion 44 may have different moving directions 50, 52. In this embodiment, each pair of the spring portions 44 that are diagonally opposed has the same moving directions 50, 52 such that two spring portions 44 have the first moving direction 50 and two spring portions 44 have the second moving direction 52. Each of the spring portions 44 includes a generally cubic body, but the dimensions of the body in the moving directions 50, 52 are significantly smaller than the other two dimensions. Specifically, the spring portion 44 has dimensions such that the spring portion 44 allows relative movement of the second portion 42 and the first portion 40 in the moving directions 50, 52. It will be understood that the dimensions suitable for achieving this generally depend on the elastic properties of the first material (titanium alloy in this example). In one embodiment, the spring portion 44 may have the following approximate dimensions. Width 0.2 mm, length 5.5 mm, and height 1.4 mm.

[0140] [000139] Each spring portion 44 is a relatively thin portion of a first material (where the first portion 40 and the second portion 42 are formed) that extends in the connection direction from one of the first portion 40 to the second portion 42. In use, the movement and flexibility provided by the spring portion 44 allows for the deflection of the pellicle frame 17 (and the attached pellicle 19) relative to the patterning device MA to which the second portion 42 is connected. This can adjust the differential thermal expansion of the patterning device MA, the pellicle frame 17, and the pellicle 19. This is advantageous for reducing the thermal stress that may occur in the pellicle frame 17, which may damage the pellicle 19, and the thermal stress that may occur in the patterning device MA, which may distort the pattern imaged on the wafer W. Also, it reduces the load on the adhesive that attaches the pellicle 19 to the patterning device MA (i.e., the adhesive layer between the first portion 40 of the pellicle frame 17 and the pellicle 19, and the adhesive layer between each of the second portions 42 of the pellicle frame 17 and the patterning device MA).

[0141] [000140] Further, since the materials of the pellicle 19 and the pellicle frame 17 are different, differential thermal expansion may occur between the pellicle 19 and the pellicle frame 17, which may cause distortion in the pellicle assembly 16 formed by these components. The movement and flexibility provided by the spring portion 44 also adjusts such distortion without (or at least reducing) loading the patterning device MA or the adhesive that attaches the pellicle 19 to the patterning device MA. The differential thermal expansion may occur between the pellicle 19 and the pellicle frame 17, which may cause distortion in the pellicle assembly 16 formed by these components. The movement and flexibility provided by the spring portion 44 also adjusts such distortion without (or at least reducing) loading the patterning device MA or the adhesive that attaches the pellicle 19 to the patterning device MA.

[0142] [000141] The dimension of the spring portion 44 in a direction perpendicular to the main plane of the pellicle frame 17 is preferably large enough to prevent or at least significantly reduce the out-of-plane (i.e., in the z - direction in FIG. 6) relative movement of the first portion 40 and the second portion 42 of the pellicle frame.

[0143] [000142] Each second portion 42 and the spring portion 44 to which the second portions 42 are connected may be regarded as forming a system cantilevered from the first portion 40. Similarly, the spring portion 44 and the first portion 40 may be regarded as forming a system cantilevered from the second portion 42 connected to the spring portion 44.

[0144] [000143] In the main plane of the pellicle frame 17 (the xy plane of FIG. 6), the dimension of the second portion 42 may be on the order of the thickness of the first portion, for example, about 5 mm. In the main plane of the pellicle frame 17 (the xy plane of FIG. 6), the spring portion 44 may have a length on the order of the dimension of the second portion 42 and the thickness of the first portion, for example, about 5 mm. In one embodiment, in the main plane of the pellicle frame 17 (the xy plane of FIG. 6), the dimension of the second portion 42 is 4.5 mm × 4.5 mm, the thickness of the first portion is about 3.85 mm, and the length of the spring portion 44 is about 5.5 mm.

[0145] [000144] In the main plane of the pellicle frame 17 (the xy plane of FIG. 6), the spring portion 44 may have a width that is about 20 times smaller than its length, the dimension of the second portion 42, and the thickness of the first portion.

[0146] [000145] Perpendicular to the main plane of the pellicle frame 17, the dimensions of all components of the pellicle frame 17 may be approximately equal, for example, about 1.4 mm.

[0147] [000146] Each of the spring portions 44 is configured such that its moving directions 50, 52 generally point to the center 54 of the first portion 40. To better illustrate this, a plurality of straight lines are shown in FIG. 6. Two dashed lines are shown, each extending between corners that are opposite on the diagonal of the first portion 40. The intersection of these two dashed lines is the center 54 of the first portion 40. Straight lines from the center point of each second portion 42 to the center 54 of the first portion 40 are also shown. It can be seen that the moving directions 50, 52 of each spring portion 44 generally point to the center 54 of the first portion 40. This is achieved by orienting each spring portion 44 such that its connection direction (from the first portion 40 to the second portion 42 in the plane of the pellicle frame 17) is perpendicular to the straight line from the center point of the second portion 42 to the center 54 of the first portion 40. This is advantageous because it allows each spring portion 44 to move in a direction passing through the geometric center 54 of the first portion 40 (and thus the geometric center of the pellicle assembly) of the pellicle frame 17 and the pellicle near each of the four second portions 42 (i.e., the four positions connected to the patterning device MA). Thereby, the pellicle frame 17 (and the pellicle assembly) can expand equally in all directions without rotating with respect to the patterning device MA, which is beneficial. Therefore, according to such a configuration, when there is uniform heating of the pellicle frame 17 (with respect to the temperature of the patterning device MA), the orientation and the central position of the pellicle frame 17 with respect to the patterning device MA will not change. The intersection of the straight lines from the center point of each second portion 42 to the center 54 of the first portion 40 may be regarded as the "starting point" of expansion, and since these lines intersect at one joint point, the system will expand equally in all directions.

[0148] [000147] Each of the spring portions 44 is configured such that its connection direction (from the first portion 40 to the second portion 42 in the plane of the pellicle frame 17) extends through the center point of the second portion 42.

[0149] [000148] Each of the second portions 42 is disposed outside the hollow generally rectangular body of the first portion 40.

[0150] [000149] The pellicle frame 17 further includes four side protrusions 56 from the first portion 40. The protrusions 56 are also formed from the first material (titanium alloy in this example). The protrusions 56 are integrally formed with the first portion 40. Each side protrusion 56, together with the first portion 40, defines an opening, and each of the second portions 42 (and its corresponding spring portion 44) is disposed in one of the openings. That is, each side protrusion 56, together with the first portion 40, forms a frame around one of the second portions 42 (and its corresponding spring portion 44). Each protrusion 56 from the generally rectangular first portion 40 is generally in the shape of a hollow triangle. A gap is provided between the second portion 42 and the protrusion 56 and / or the first portion 40 (to be further described below with reference to FIG. 7). This gap allows limited movement of each second portion 42 and the first portion 40 in the movement directions 50, 52. However, the protrusions 56 are of a sufficient size to be substantially rigid. In one embodiment, in the main plane of the pellicle frame 17 (i.e., the xy plane of FIG. 6), the protrusions 56 may have a thickness of about 1 mm. The dimension of the side protrusion 56 in a direction perpendicular to the main plane of the pellicle frame may be substantially the same as the dimensions of the other parts of the pellicle frame, for example, about 1.4 mm. Thus, the protrusions 56 serve as physical stops to limit the range of movement of each second portion 42 and the first portion 40 in the movement directions 50, 52. Advantageously, this may prevent failure of the spring portion 44. Specifically, the protrusions 56 are beneficial in protecting the spring portion 44 from such obstacles during handling of the pellicle frame 17 (e.g., during assembly of the pellicle assembly and the mask assembly).

[0151] [000150] The novel pellicle frame 17 is advantageous because the first part 40, the plurality of second parts 42, and the spring part 44 are all formed from the same material, for example a titanium alloy. This greatly simplifies the manufacture of the pellicle frame 17. For example, all parts of the pellicle frame may be integrally formed.

[0152] [000151] This is in contrast to the existing configuration (described above with reference to FIGS. 2 to 4) in which the first part (the known pellicle frame 17') connected to the edge 19a of the pellicle 19 is formed from one material (for example silicon), and the plurality of second parts (the engagement mechanisms 22a to 22d) connected to the patterning device MA are formed from another material (for example a titanium alloy). Such an existing configuration is quite complex to manufacture because the parts have to be manufactured separately and then assembled (for example in the pellicle mounting device 855). And this significantly increases the cost of manufacturing such an existing pellicle frame assembly 17', 22a to 22d (compared to the novel pellicle frame 17). This is all the more so because, as explained above with reference to FIG. 2, the assembly of these separate parts is not straightforward as a result of the quite stringent requirements regarding the pellicle frame used in an EUV lithography apparatus.

[0153] [000152] First, the pellicle frame (and the pellicle assembly including the resulting pellicle frame) is important to be clean in order to reduce the risk of contaminating the patterning device (reticle) that is attached during use. For example, it may be desirable to ensure that the number of particles on the pellicle frame is less than a desired particle threshold (preferably no particles are disposed on the pellicle frame). To achieve this, the components of a known pellicle frame 17' may be kept in a clean environment until assembled. Assembly may be achieved in a clean environment. These clean environments may be maintained under vacuum conditions. Maintaining multiple clean environments (or a large-sized clean environment) will increase the manufacturing cost. Also, assembly in a clean environment is difficult.

[0154] [000153] Second, during use, the pellicle frame will be attached to the reticle that will be supported by the reticle stage. In a lithography apparatus LA called a scanner in which the patterning device MA and the wafer W are synchronously scanned with an EUV radiation beam, the reticle stage MT and the pellicle frame attached thereto will be subjected to significant acceleration. It is important that all parts of the movable mask assembly are well connected so that they remain connected despite these large accelerations. For this reason, it may be preferable to reduce the total number of parts that are connected together. The novel pellicle frame 17 achieves this.

[0155] [000154] The above-mentioned pellicle frame 17 is formed from a titanium alloy, but in alternative embodiments, different materials may be used. In some embodiments, the material may have a coefficient of thermal expansion (CTE) smaller than 10 -6 K -1 and may be elastic. The material may be ductile. In some embodiments, the material may have a Young's modulus greater than 100 GPa. In some embodiments, the material is 1500 kg / m 3may have a smaller density. The material may be suitable for use in a vacuum environment. Specifically, the material may be suitable for use in the environment within an EUV lithography apparatus.

[0156] [000155] Titanium and titanium alloys are suitable for use in a vacuum environment, specifically in the environment within an EUV lithography apparatus. Also, titanium and its alloys provide the spring portion 44 and have sufficient elasticity so that the pellicle frame 17 is not brittle enough to break during use.

[0157] [000156] According to some embodiments of the present invention, a pellicle assembly 16 including the above-described pellicle frame 17 and pellicle 19 may be provided. According to some embodiments of the present invention, a mask assembly 15 including such a pellicle assembly 16 and a patterning device may be provided. An example of such a mask assembly will be described hereinafter with reference to FIG. 7.

[0158] [000157] FIG. 7 is a schematic cross-section of a portion of a novel mask assembly 15. The cross-section shown in FIG. 7 is in a plane perpendicular to the y-direction and passing through one of the second portions 42. In this cross-section, one of the second portions 42 of the pellicle frame 17 shown in FIG. 6 is seen. On one side of the second portion 42 (the left side in FIG. 7), a part of a hollow generally triangular protrusion 56 is seen. On the other side of the second portion 42 (the right side in FIG. 7), another part of the hollow generally triangular protrusion 56 is seen together with a part of the first portion 40 of the pellicle frame. Since the first portion 40 and the protrusion 56 are integrally formed from the same material, it will be understood that no boundary is shown between the first portion 40 and the protrusion 56. However, below FIG. 7, there is an indication showing which part corresponds to the first portion 40 and which part corresponds to the protrusion 56.

[0159] [000158] As will be further described below with reference to FIG. 7, it can be clearly seen from FIG. 7 that a gap is provided between the second portion 42 and the protrusion 56 and / or between the second portion 42 and the first portion 40. This gap allows for limited movement of each second portion 42 and the first portion 40 in the movement directions 50, 52.

[0160] [000159] The mask assembly further comprises a pellicle 19 and a patterning device MA.

[0161] [000160] The pellicle 19 includes an edge portion 19a and a film 19b. The edge portion 19a is hollow and generally rectangular, surrounds the film 19b, and the film 19b is bounded by the edge portion 19a. The edge portion 19a of the pellicle 19 is attached to the first portion 40 of the pellicle frame 17.

[0162] [000161] The pellicle 19 may be in the form of a known pellicle 19 (and may have the features described above for the pellicle). As is known in the art, the pellicle 19 may be formed by the attachment of one or more thin material layers to a generally rectangular silicon substrate. The silicon substrate supports one or more thin layers during the fabrication stage of this pellicle 19. When the desired or target thickness and composition of the layer are applied, the central portion of the silicon substrate is removed by etching (which may be referred to as back-etching). The peripheral portion of the rectangular silicon substrate is not etched (or is etched to a lesser extent than the central portion). This peripheral portion forms the edge portion 19a of the final pellicle, while one or more thin layers form the film 19b of the pellicle (bounded by the edge portion 19a).

[0163] [000162] The edge 19a of the pellicle 19 is attached to the first portion 40 of the pellicle frame 17 by an adhesive G. The adhesive may include, for example, a poly(methyl methacrylate)-based adhesive (sometimes referred to as a PMMA adhesive). Alternatively, the adhesive may be an epoxy adhesive. It will be understood that other types of adhesives are possible. In general, the choice of adhesive is made such that the gas evolution from the adhesive is low enough not to contaminate the area, suitable for use with EUV radiation, and / or does not affect the performance of the lithographic apparatus and its optical system.

[0164] [000163] The pellicle 19 and the pellicle frame 17 may be regarded as forming a pellicle assembly 16 together.

[0165] [000164] The edge 19a may be formed from silicon. As described above, the pellicle frame 17 is generally formed from a more elastic material such as a titanium alloy.

[0166] [000165] The pellicle 19 generally requires support from a generally harder pellicle frame 17. The pellicle frame provides the following two functions: (a) supporting the pellicle 19 and further stretching the pellicle film 19b taut, and (b) facilitating the connection of the pellicle 19 with the patterning device MA. In order to provide flexibility that allows for the different thermal expansions of the pellicle 19 and the reticle MA over the range of operating temperatures that these components experience during use, it is desirable to select a material that is sufficiently elastic and suitable for use under the conditions within an EUV lithography apparatus for the connection with the patterning device. One suitable material contains titanium. Since the main hollow rectangular portion of the pellicle frame is generally attached to the edge in a known assembly, the main hollow rectangular portion of this pellicle frame is formed from a material whose thermal properties generally match those of the edge of the pellicle. For example, silicon is generally used. Thus, a known pellicle frame 17' comprises a silicon body pasted to the pellicle 19 and four titanium attachment mechanisms 22a - 22d pasted to the sides of this body 17'.

[0167] [000166] Since the thermal properties of silicon and titanium are very different (titanium has a thermal expansion coefficient approximately four times that of silicon), there is a significant prejudice in the art against using a material (such as titanium or a titanium alloy, etc.) having thermal properties different from those of silicon for the body of the pellicle frame. The reason for this is that when the temperature of the pellicle assembly changes, the differential thermal expansion of the frame and the edge will cause the pellicle assembly to bend or flex, which may stress the patterning device MA and result in imaging errors such as an increase in overlay. However, surprisingly, the inventors have found that when using the novel pellicle frame 17, the overlay does not deteriorate more than when using the known pellicle frame 17'. Thus, the novel pellicle frame 17 provides a simpler and lower - cost configuration without compromising on imaging performance.

[0168] [000167] The plurality of second portions 42 of the pellicle frame 17 are attached to the patterning device MA. The second portions 42 of the pellicle frame 17 are attached to the patterning device MA by an adhesive G.

[0169] [000168] The adhesive may be a poly(methyl methacrylate)-based adhesive, sometimes called PMMA paste. Due to the material properties of the PMMA paste, specifically the elasticity of the PMMA paste and the dimensions to which the PMMA paste can be applied, the deformation of the patterning device MA due to the curing of the PMMA paste is relatively small (compared to other pastes). The PMMA paste is more easily removable, for example, than an epoxy paste and is relatively elastic. Advantageously, this may make it possible to more easily replace the pellicle assembly 16.

[0170] [000169] Alternatively, the adhesive may be an epoxy adhesive.

[0171] [000170] It will be understood that other types of adhesives are possible, although this is repeated. In general, the choice of adhesive may be made such that the gas evolution from the adhesive is low enough not to contaminate the area, suitable for use with EUV radiation, and / or does not affect the performance of the lithographic apparatus and its optical system.

[0172] [000171] The novel mask assembly 15 is particularly advantageous over known configurations that generally use an intermediate fixing member (known as stud 51) that is fixed to the patterning device MA and engages with the pellicle assembly 17', as will be considered hereinafter.

[0173] [000172] The novel mask assembly 15 comprises fewer components than a mask assembly 15' that uses intermediate fixing members such as studs 51 (fixed to the patterning device) and engagement mechanisms 22a - 22d (provided on the pellicle assembly 16') that engage with the intermediate fixing members (studs 51). Thus, advantageously, the novel mask assembly 15 is relatively simple to manufacture. The reduction in the number of components and the simplification of the manufacturing procedure may result in lower manufacturing costs.

[0174] [000173] This is all the more so since the assembly of the mask assembly 15 is not straightforward as a result of the fairly strict requirements regarding mask assemblies used in EUV lithography apparatuses.

[0175] [000174] First, it is important that the mask assembly is clean in order to reduce the risk of contaminating the patterning device (reticle). For example, it may be desirable to ensure that the number of particles on the mask assembly is below a desired particle threshold (preferably no particles are placed on the mask assembly). To achieve this, the components of the mask assembly may be kept in a clean environment until they are assembled. The assembly may be achieved in a clean environment. These clean environments may be maintained under vacuum conditions. Maintaining multiple clean environments (or a large - sized clean environment) will increase the manufacturing costs. Also, assembly in a clean environment is difficult.

[0176] [000175] Second, in use, the mask assembly will be supported by the reticle stage. In a lithographic apparatus called a scanner in which the patterning device and the wafer are synchronously scanned with an EUV radiation beam, the reticle stage and the pellicle frame attached thereto will be subjected to a large acceleration. It is important that all parts of the movable mask assembly are well connected so as to remain connected despite these large accelerations. For this reason, it may be preferable to reduce the total number of parts that are connected together. The novel mask assembly according to the third aspect of the present invention achieves this.

[0177] [000176] It is estimated that there is a significant reduction in the cost of manufacturing the novel mask assembly 15 compared to the cost of manufacturing a known mask assembly 15' of the type described above with reference to FIGS. 2 to 4. For example, the cost of manufacturing a known mask assembly 15' may be about 10 times greater than the cost of manufacturing a novel mask assembly 15 of the type shown in FIG. 7.

[0178] [000177] There are several reasons for this. The first is that the number of parts in the novel mask assembly 15 is less than that in the known mask assembly 15'. There are a number of related problems associated with the attachment of some parts. That is, the attachment needs to be performed in a clean environment, and some parts need to be accurately aligned under these difficult conditions. Second, some of the parts of the known mask assembly 15' are very costly to manufacture.

[0179] [000178] In some embodiments, the distance between the pellicle 19 and the patterning device MA may be, for example, about 1 mm to 10 mm, for example 1 mm to 5 mm, more preferably 2 mm to 2.5 mm.

[0180] [000179] In the above-described embodiment, each of the pellicle frames 17 includes four second portions 42 each connected to the first portion 40 by a spring portion 44. However, in other embodiments, various numbers of second portions 42 each connected to the first portion 40 by a spring portion 44 may be provided.

[0181] [000180] The assembly of the pellicle assembly 16 may be achieved by gluing the pellicle 19 to the pellicle frame 17. This process may share one or more features common to existing processes for gluing a pellicle 19 to a known pellicle frame 17'.

[0182] [000181] The gluing of the pellicle 19 to the first portion 40 of the pellicle frame 17 and / or the gluing of the second portion 42 to the patterning device may be achieved using any suitable glue dispenser.

[0183] [000182] The glue dispenser may include a syringe. The syringe may dispense one or more components of a regulated amount of glue. The glue dispenser may include a nozzle. For example, the nozzle may be connected to the syringe, and one or more components of the glue may be provided using a syringe connected to the nozzle. The glue may be applied with a cylindrical nozzle. The glue may be applied with a tapered nozzle. The glue dispenser may include a brush and may apply one or more components of the glue using the brush. The glue dispenser may include a sponge and may apply one or more components of the glue using the sponge. The glue dispenser may include a printing device (e.g., a screen printing device) for providing one or more components of the glue. The glue dispenser may include a dispensing device for providing one or more components of the glue as a spray (e.g., an aerosol spray dispensing system may be used). It will be understood that the glue may be provided in any known manner.

[0184] [000183] A paste dispenser may provide a paste of multiple components (e.g., a paste accelerator and an initiator). One component of the paste may have a higher viscosity than another component of the paste. That is, there may be a component of the paste having a relatively high viscosity (the "thick component") and a component of the paste having a relatively low viscosity (the "thin component"). In an exemplary embodiment, the paste dispenser may dispense the thick component of the paste using a syringe and a nozzle. In an exemplary embodiment, the paste dispenser may dispense the thin component of the paste using a brush, a sponge, a screen printing device, or an aerosol spray dispensing system.

[0185] [000184] Although it has been described above that paste is used to attach the pellicle 19 to the pellicle frame 17, the pellicle may be attached to the pellicle frame using any suitable joining method (including not using paste).

[0186] [000185] Although it has been described above that paste is used to attach the pellicle frame 17 to the patterning device MA, the pellicle frame 17 may be attached to the patterning device MA using any suitable joining method (including not using paste).

[0187] [000186] References herein to a mask or a reticle may be interpreted as references to a patterning device (a mask or a reticle is an example of a patterning device), and these terms may be used interchangeably. Specifically, the term mask assembly is synonymous with reticle assembly and patterning device assembly.

[0188] [000187] Although embodiments of the present invention are specifically referred to herein in connection with lithographic apparatus, embodiments of the present invention may also be used in other apparatus. Embodiments of the present invention may form part of any apparatus for measuring or processing an object such as a mask inspection apparatus, a metrology apparatus, or a wafer (or other substrate) or mask (or other patterning device). These apparatuses are sometimes generally referred to as lithographic tools. Such lithographic tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0189] [000188] The term "EUV radiation" may be considered to encompass electromagnetic radiation having a wavelength within the range of 4 to 20 nm, for example within the range of 13 to 14 nm. EUV radiation may have a wavelength within the range of 4 to 10 nm, less than 10 nm, for example 6.7 nm or 6.8 nm.

[0190] [000189] Although the present text specifically refers to the use of a lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein has other uses. Other possible uses are in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0191] [000190] Having thus described specific embodiments of the present invention, it will be understood that the invention may be practiced otherwise than as described. The foregoing description is exemplary and not restrictive. Thus, it will be apparent to those skilled in the art that the invention as described may be modified without departing from the scope of the claims.

Claims

1. A first part connected to the edge of the pellicle, including a generally rectangular hollow body, and a plurality of second parts connected to the patterning device, wherein all of the first part and the plurality of second parts are formed from a first material, each of the second parts is connected to the first part by a spring part formed from the first material, the spring part is a pellicle frame extending in the plane of the pellicle frame.

2. The pellicle frame according to claim 1, wherein the first material contains titanium.

3. The pellicle frame according to claim 1 or claim 2, having four second parts each connected to the first part by a spring part.

4. The pellicle frame according to claim 3, wherein each of the four second parts is close to a corner of the first part.

5. The pellicle frame according to claim 3 or claim 4, wherein two of the second parts are provided on one side of the generally rectangular hollow body of the first part, and the other two of the second parts are provided on the opposite side of the generally rectangular hollow body of the first part.

6. The pellicle frame according to any one of claims 1 to 5, wherein each of the plurality of second parts includes a generally cubic body such that each of the second parts is rectangular in the main plane of the pellicle frame.

7. The pellicle frame according to any one of claims 1 to 6, wherein each of the spring parts is configured to enable relative movement between the first part and the second part in a moving direction within the plane of the pellicle frame.

8. Within the plane of the pellicle frame, each of the spring parts includes a portion of the first material extending in the connecting direction from the first part to one of the second parts, and the spring part has a smaller dimension in a moving direction within the plane of the pellicle frame and perpendicular to the connecting direction to enable relative movement between the second part and the first part in the moving direction. The pellicle frame according to any one of claims 1 to 7.

9. For each pair of diagonally opposed spring parts, the two spring parts have a first moving direction, and the two spring parts have the same moving direction such that the two spring parts have a second moving direction. The pellicle frame according to claim 7 or claim 8.

10. The pellicle frame according to any one of claims 7 to 9, wherein each of the spring portions is configured such that its moving direction generally points to the center of the first portion.

11. The pellicle frame according to claim 8, or claim 9 or 10 when dependent on claim 8, wherein each of the spring portions is configured such that its connection direction extends through the center point of the second portion to which it is connected.

12. The pellicle frame according to any one of claims 1 to 11, further comprising a plurality of side protrusions from the hollow generally rectangular body, each side protrusion being formed of the first material, each side protrusion and the hollow generally rectangular body defining an opening, and each of the plurality of second portions being disposed in one of the openings.

13. A pellicle frame according to any one of claims 1 to 12, comprising a pellicle having a hollow generally rectangular edge and a film bounded by the edge, a pellicle assembly in which the edge of the pellicle is attached to the first portion of the pellicle frame.

14. The pellicle assembly according to claim 13, wherein the edge of the pellicle is formed of a second material different from the first material of which the pellicle frame is formed.

15. A mask assembly comprising the pellicle assembly according to claim 13 or 14, and a patterning device, wherein the plurality of second portions of the pellicle frame are attached to the patterning device.

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