Pellicle frame and pellicle assembly

Abstract

A pellicle frame (17) for supporting a pellicle, the frame (17) comprising a first surface (17B) and a second surface (17A) opposite the first surface (17A), and a structure (18) disposed between the first surface (17A) and the second surface (17B); wherein the first surface (17A) and the second surface (17B) and the structure (18) at least partially define between them at least one volume (28) free of material forming the frame (17).

Description

[0001] This application is a divisional application of the international application PCT / EP2018 / 073095, which entered the Chinese national phase on April 27, 2020 and has application number 201880070179.4. Technical Field

[0002] The present invention relates to a pellicle frame and a pellicle assembly. The pellicle assembly may include a pellicle and a pellicle frame for supporting the pellicle. The pellicle may be suitable for use with a pattern forming device for a lithography apparatus. The present invention has specific but not exclusive use in relation to EUV lithography apparatus and EUV lithography tools. Background Art

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

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

[0005] The use of pellicles in lithography is well known and recognized. A typical pellicle in a DUV lithography apparatus is a diaphragm that is positioned away from the pattern forming device and outside the focal plane of the lithography apparatus when in use. Since the pellicle is outside the focal plane of the lithography apparatus, the contaminant particles that fall on the pellicle are outside the focus of the lithography apparatus. Therefore, the image of the contaminant particles is not projected onto the substrate. If the pellicle is not present, the contaminant particles that fall on the pattern forming device will be projected onto the substrate and will introduce defects into the projected pattern.

[0006] It may be desirable to use a pellicle in an EUV lithography apparatus. EUV lithography differs from DUV lithography in that it is typically performed in a vacuum and the patterning device is typically reflective rather than transmissive.

[0007] It is desirable to provide a pellicle frame and / or pellicle assembly that overcomes or mitigates one or more problems associated with the prior art. Embodiments of the invention described in this invention may be used for EUV lithography equipment. Embodiments of the invention may also be used for DUV lithography equipment and / or other forms of lithography tools. Summary of the invention

[0008] According to a first aspect of the present invention, a membrane frame is provided for supporting a membrane, the frame comprising a first surface and a second surface opposite to the first surface, and a structure arranged between the first surface and the second surface; wherein at least one volume portion that does not contain material forming the frame is at least partially defined between the first surface, the second surface and the structure.

[0009] This may have the following advantages: the weight of the frame may be reduced relative to a corresponding frame having no volume without the material forming the frame, and the eigenfrequency of the frame may be increased. This may allow the use of different materials to form the frame. Using different materials may allow the coefficient of thermal expansion (CTE) of the diaphragm to be more closely matched, which may reduce thermal stresses during fabrication of the diaphragm.

[0010] At least one portion of the frame may have a different cross-sectional profile than at least one other portion of the frame. The distribution of the volume may be different around the frame, or at least different between the at least one portion of the frame and the at least one other portion. This may have the advantage that the volume may be located in a portion of the frame that does not substantially contribute to the stiffness of the frame (e.g. the bending stiffness of the frame and / or the torsional stiffness of the frame).

[0011] The form of the structure and / or the amount of volume provided between the first surface and the second surface may differ between the at least one portion and the at least one other portion of the frame.

[0012] The volume may define or include at least one void, space, hollow, recess or chamber.

[0013] The volume may extend around at least a portion of a perimeter of the frame.

[0014] The volume may be open.

[0015] The volume may be comprised in a matrix of the volume between the first surface and the second surface.

[0016] The structure may include at least a first wall connecting the first surface and the second surface.

[0017] The frame may include a second wall opposite the first wall and connecting the first surface and the second surface, and wherein the volume extends through or between the first wall and the second wall.

[0018] The first and second surfaces and the first and second walls may form a hollow tube along at least a portion of a length of one side of the frame.

[0019] The first surface, the second surface and the first wall may form an I-shaped cross-section along at least a portion of a length of one side of the frame.

[0020] The side of the frame may be a free side that is not directly attached or attachable to a patterning device.

[0021] The side of the frame may be a support side configured to be attachable to a patterning device.

[0022] At least one of the first surface and the second surface may be continuous.

[0023] At least one of the first surface and the second surface may have at least one recess therein.

[0024] The frame may comprise at least one engagement mechanism for attaching the frame to a patterning device. This is advantageous because it avoids potentially damaging thermal stresses arising in the frame.

[0025] The side of the frame may be a supporting side and a hollow tube may extend from a free side of the frame to the engagement mechanism.

[0026] The frame may include a plurality of engagement mechanisms, each of which may be oriented to face away from a side of the frame perpendicular to the engagement mechanism on which it is positioned. This may have the advantage of allowing thermal expansion of the frame relative to the patterning device and may help prevent stress buildup in the patterning device.

[0027] Each engagement mechanism may face substantially towards a centre point of the frame.

[0028] The engagement mechanism may be configured such that the attachment member is removably secured in a substantially central location in the engagement mechanism. This may have the advantage of reducing twisting.

[0029] The engagement mechanism may include a pair of first leaf springs and a pair of second leaf springs respectively connected to the first leaf springs, and each leaf spring may extend in substantially the same direction.

[0030] An intermediate body may be positioned between the first leaf spring and the second leaf spring.

[0031] A ratio of the length of the first leaf spring to the length of the second leaf spring may be between 1.5:1 and 2.5:1.

[0032] The first leaf spring may comprise a plurality of resiliently bendable engagement arms, and a beam may be positioned between two of the engagement arms, wherein the beam may extend more than halfway across the engagement mechanism. This may have the advantage of providing space for the attachment member.

[0033] The diaphragm frame may be made of at least one of aluminum and / or aluminum nitride.

[0034] According to a second aspect of the present invention, a method for manufacturing a diaphragm frame for supporting a diaphragm is provided, the method comprising: forming the diaphragm frame from a frame material, the frame comprising a first surface, a second surface opposite to the first surface, and a structure located between the first surface and the second surface; and forming at least one volume portion that does not contain frame material between the first surface and the second surface.

[0035] The at least one volume may be formed by removing at least one volume of frame material between the first surface and the second surface.

[0036] The method may further include forming the volume in a portion of the frame that does not substantially contribute to the stiffness of the frame, the bending stiffness of the frame, and / or the torsional stiffness of the frame.

[0037] The frame material may be formed of at least one of aluminum and aluminum nitride.

[0038] According to a third aspect of the present invention, there is provided a pellicle assembly, comprising a pellicle frame and a pellicle as described above.

[0039] The diaphragm assembly may further comprise a diaphragm boundary. This may have the advantage of reducing stresses in the diaphragm.

[0040] The pellicle border and the pellicle frame may be of the same material.

[0041] The pellicle border may be made of at least one of aluminum and / or aluminum nitride.

[0042] The diaphragm frame may be made of at least one of aluminum and / or aluminum nitride.

[0043] The pellicle frame may include an engagement mechanism.

[0044] The block portion for holding the engagement mechanism may be formed of the same material as the diaphragm frame.

[0045] According to a fourth aspect of the invention, there is provided a pellicle frame comprising four engagement mechanisms, wherein each engagement mechanism is substantially oriented towards a centre point of the frame. This may have the advantage of allowing thermal expansion of the frame relative to the patterning device and helping to prevent stress build-up in the patterning device.

[0046] According to a fifth aspect of the present invention, there is provided a pellicle frame comprising an engagement mechanism, wherein the engagement mechanism is configured such that an attachment member is removably secured substantially centrally in the engagement mechanism. This may have the advantage of reducing torsion.

[0047] It should be understood that one or more aspects or features described above or referenced in the following description may be combined with one or more other aspects or features. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0049] - Figure 1 schematically depicts a lithographic system including a lithographic apparatus including a pellicle assembly;

[0050] - Figure 2A Describing the film assembly and the patterning device;

[0051] - Figure 2B Describing the film assembly and the patterning device;

[0052] - Figure 3 schematically depicting a cross section of a pellicle assembly and a patterning device;

[0053] - Figure 4 A top view of the pellicle frame is schematically depicted;

[0054] - FIG. 5A to FIG. 5F Schematically depicting the passage Figure 4 cut sections and detailed sections;

[0055] - Fig. 6A A perspective view of the frame is schematically depicted.

[0056] - Figure 6B A perspective view schematically depicting a cross section of a frame.

[0057] - Figure 7 schematically depicting a top view of the engagement mechanism;

[0058] - Fig. 8A Schematically depicting the passage Figure 7 A cross section of the engagement mechanism taken along line AA;

[0059] - Figure 8B Schematically depicting the passage Figure 7 A cross section of the engagement mechanism taken along line BB.

[0060] - Fig. 9 A perspective view of a coupling mechanism is schematically depicted.

[0061] - Fig.10 Schematically depicting the passage Fig. 9 A stereoscopic view of a cross section of the engagement mechanism taken along line CC.

[0062] - Fig.11A An end view of an attachment member is schematically depicted.

[0063] - Fig. 11B Schematically depict Fig.11A A side view of the attachment member.

[0064] - Fig.12 Schematically depicting the passage Fig. 9 Side view of a cross section of the engagement mechanism taken along line CC. DETAILED DESCRIPTION

[0065] Figure 1 A lithography system including a pellicle assembly 15 according to an embodiment of the present invention is shown. 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 pattern forming device MA (e.g., a mask), a projection system PS, and a substrate table WT configured to support a substrate W. The illumination system IL is configured to condition the radiation beam B before the radiation beam B is incident on the pattern forming device MA. The projection system is configured to project the radiation beam B (now patterned by the mask MA) onto the substrate W. The substrate W may include a previously formed pattern. In this case, the lithography apparatus aligns the patterned radiation beam B with the pattern previously formed on the substrate W.

[0066] 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 (e.g., hydrogen) at a pressure below atmospheric pressure may be provided in the radiation source SO. A vacuum may be provided in the illumination system IL and / or the projection system PS. A small amount of gas (e.g., hydrogen) at a pressure much below atmospheric pressure may be provided in the illumination system IL and / or the projection system PS.

[0067] Figure 1The radiation source SO shown in is of a type that may be referred to as a laser produced plasma (LPP) source. A laser 1, which may be, for example, a CO2 laser, is arranged to deposit energy by means of a laser beam 2 into a fuel, such as tin (Sn), which is provided from a fuel emitter 3. Although tin is mentioned in the following description, any suitable fuel may be used. The fuel may, for example, be in liquid form and may, for example, be a metal or an alloy. The fuel emitter 3 may include 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 at the plasma formation region 4. The deposition of laser energy into the tin generates a plasma 7 at the plasma formation region 4. Radiation, including EUV radiation, is emitted from the plasma 7 during de-excitation and recombination of ions of the plasma.

[0068] EUV radiation is collected and focused by a near normal incidence radiation collector 5 (sometimes more generally referred to as a normal incidence radiation collector). Collector 5 may have a multilayer structure arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm). Collector 5 may have an elliptical configuration having two elliptical foci. The first focus may be at the plasma formation region 4 and the second focus may be at the intermediate focus 6, as discussed below.

[0069] The laser 1 may be remote from the radiation source SO. In this case, the laser beam 2 may be delivered from the laser 1 to the radiation source SO by means of a beam delivery system (not shown) comprising, for example, suitable directional mirrors and / or beam expanders and / or other optical devices. The laser 1 and the radiation source SO may together be considered a radiation system.

[0070] The radiation reflected by the collector 5 forms a radiation beam B. The radiation beam B is focused at a point 6 to form an image of the plasma formation region 4 serving as a virtual radiation source for illuminating the 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 an opening 8 in an enclosure 9 of the radiation source.

[0071] The radiation beam B is transmitted from the radiation source SO to the illumination system IL, which is configured to condition the radiation beam. The illumination system IL may include a faceted field mirror device 10 and a faceted pupil mirror device 11. The faceted field mirror device 10 and the faceted pupil mirror device 11 together provide the radiation beam B with a desired cross-sectional shape and a desired angular intensity distribution. The radiation beam B is transmitted from the illumination system IL and is incident on a pattern forming device MA held by a support structure MT. The pattern forming device MA is protected by a pellicle 19, which is held in place by a pellicle frame 17 (referred to as a frame in the remainder of the description). The pellicle 19 and the frame 17 together constitute a pellicle assembly 15. The pattern forming device MA (which may be, for example, a mask) reflects and patterns the radiation beam B. In addition to or instead of the faceted field mirror device 10 and the faceted pupil mirror device 11, the illumination system IL may also include other mirrors or devices.

[0072] After 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 reduction factor to the radiation beam so as to form an image in which features are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 may be applied. Although the projection system PS is Figure 1 There are two mirrors in the embodiment, but the projection system can include any number of mirrors (e.g., six mirrors).

[0073] Figure 1 The radiation source SO shown in FIG. 1 may include components not shown. For example, a spectral filter may be provided in the radiation source. The spectral filter may substantially transmit EUV radiation but substantially block radiation of other wavelengths, such as infrared radiation.

[0074] As briefly described above, the pellicle assembly 15 includes a pellicle 19 disposed adjacent to the pattern forming device MA. The pellicle 19 is disposed in the path of the radiation beam B so that the radiation beam B passes through the pellicle 19 both when it approaches the pattern forming device MA from the illumination system IL and when it is reflected by the pattern forming device MA toward the projection system PS. The pellicle 19 includes a thin film that is substantially transparent to EUV radiation (although it will absorb a small amount of EUV radiation). In the present invention, an EUV transparent pellicle or a substantially transparent film for EUV radiation means that the pellicle 19 transmits at least 65% of the EUV radiation, preferably at least 80% and more preferably at least 90% of the EUV radiation. The pellicle 19 is used to prevent the pattern forming device MA from being contaminated by particles. The pellicle 19 may be referred to as an EUV transparent pellicle in the present invention. The pellicle 19 may be made of molybdenum silicide (MoSi). MoSi is stronger than silicon at high temperatures because MoSi cools more rapidly than silicon. In other examples, the pellicle may be made of other materials such as silicon.

[0075] Efforts may be made to maintain a clean environment inside the lithographic apparatus LA, but particles may still be present inside the lithographic apparatus LA. In the absence of the pellicle 19, particles may be deposited onto the patterning device MA. Particles on the patterning device MA may adversely affect the pattern imparted to the radiation beam B and therefore the pattern transferred to the substrate W. The pellicle 19 provides a barrier between the patterning device MA and the environment in the lithographic apparatus LA so as to prevent particles from being deposited on the patterning device MA.

[0076] In use, pellicle 19 is disposed at a distance from patterning device MA sufficient so that any particles incident on the surface of pellicle 19 are not in the focal plane of radiation beam B. This separation between pellicle 19 and patterning device MA serves to reduce the extent to which any particles on the surface of pellicle 19 impart a pattern to radiation beam B. It will be appreciated that where particles are present at locations in radiation beam B but not in the focal plane of radiation beam B (i.e. not at the surface of patterning device MA), then any image of the particles will not be focused at the surface of substrate W. In some embodiments, the separation distance between pellicle 19 and patterning device MA may be, for example, between 2 mm and 3 mm (e.g., about 2.5 mm). In some embodiments, the separation distance between pellicle 19 and patterning device MA may be adjustable, as described in more detail below.

[0077] Figure 2A 1 is a perspective view of the membrane assembly 15 and the pattern forming device MA. The membrane assembly 15 may include a frame 17 and a membrane 19 without a membrane boundary 20 (see Figure 2B ). The pellicle 19 can be formed directly on the frame 17. The pattern forming device MA has a patterned surface 21.

[0078] In other examples, the pellicle assembly may also include a border 20 . Figure 2B 1 is a perspective view of the pellicle assembly 15A and the pattern forming device MA. The pellicle assembly 15A may include a pellicle 19, a frame 17, and a pellicle border 20. The border 20 may be optionally integrated with the pellicle 19, included therein, or physically separated therefrom. The border 20 may be significantly thicker than the main portion of the pellicle 19 and may be positioned around the outer periphery of the pellicle 19. Such a border 20 is attached to the frame 17. The frame 17 supports the pellicle 19 around the peripheral portion of the pellicle 19 by the border 20. The border 20 may be glued to the frame 17 or may be attached in another way. In the described example, the frame 17 may be used with a pellicle 19 without a border 20 or with a pellicle 19 having a border 20.

[0079] Figure 3 is a schematic illustration of the pellicle assembly 15 and the pattern forming device MA in cross section and in more detail. A contaminant particle 26 is schematically shown. The contaminant particle 26 is incident on the pellicle 19 and is retained by the pellicle 19. The pellicle 19 retains the contaminant particle 26 sufficiently away from the patterned surface 21 of the mask MA so that the contaminant particle 26 is not imaged onto the substrate by the lithographic equipment LA. The pellicle assembly according to an embodiment of the present invention can allow the pellicle to provide a mask pattern (on the pattern forming device) that is free from contamination, so that the pattern produced using the mask remains substantially defect-free during use. In other examples, the pellicle assembly 15A (i.e., having a boundary 20) can be used in a similar manner.

[0080] The pellicle assembly 15A can be constructed by depositing the pellicle 19 directly on top of the substrate that will provide the border 20. After depositing the thin film of pellicle 19, the substrate can be selectively etched back to remove the central portion of the substrate and leave only the outer perimeter, thereby forming the border 20 to support the pellicle 19.

[0081] In other examples, an etch stop layer (e.g., SiO2) may be deposited first, followed by a pellicle core material, followed by another etch stop layer (e.g., SiO2). The silicon wafer material may be etched away until the etch stop layer. The etch stop layer may then be etched away with a different etchant that attacks neither silicon nor molybdenum silicide MoSi. This leaves an independent diaphragm (pellicle). The pellicle 19 may have a thickness of, for example, on the order of 15 nm to 50 nm. In other examples, the pellicle assembly 15 may be constructed by depositing the pellicle 19 directly on top of a substrate that will provide the frame 17.

[0082] The diaphragm 19 requires a level of "pre-stress" (i.e., a level of stress present within the diaphragm 19 when not in use). The pre-stress within the diaphragm 19 allows the diaphragm 19 to withstand pressure differentials caused by temperature and gas pressure changes during scanning operations. However, if the pre-stress is too great, this will reduce the overall life of the diaphragm assembly 15. Thus, it is desirable to give the diaphragm 19 a minimum pre-stress (in the depicted xz plane) in order to limit the deflection (in the z-direction) for a given pressure on the diaphragm 19. When the deflection of the diaphragm 19 in the z-direction is too great, the diaphragm 19 may rupture and / or touch other components in the surrounding area of ​​the diaphragm 19.

[0083] The prestress of the diaphragm 19 is preferably limited, since the stress of the diaphragm 19 is preferably significantly lower than the ultimate tensile stress or yield strength of the material forming the diaphragm 19. The tolerance between the prestress and the ultimate tensile stress should be as large as possible, thereby increasing the life and reliability of the diaphragm 19.

[0084] Prestress may be incorporated into the pellicle 19 by one or more mechanisms including stoichiometry, hydrogenation, control of crystal size, doping, and selective mismatching of the coefficient of thermal expansion (CTE) during deposition of the pellicle 19 onto the substrate. The pellicle 19 may also include multiple layers (e.g., a capping layer to protect the pellicle 19 from, for example, hydrogen radicals). Due to the CTE mismatch between the layers of the pellicle 19 portion of the pellicle assembly 15 and the heteroepitaxial process by which the different layers of the pellicle 19 may be deposited, the stress in each layer of the multilayer pellicle 19 may be different.

[0085] The tension in the pellicle 19 in use will be determined to some extent by the applied prestress, as detailed above. The attachment of the pellicle 19 to the border 20 may also be controlled so as to achieve a desired tension in the pellicle 19. For example, the tension in the pellicle 19 may be measured during or after the pellicle 19 is attached to the border 20, and the tension may be adjusted in response to the measurement so as to achieve a desired tension in the pellicle 19. For example, the tension in the pellicle 19 may be maintained by applying an outward force to components of the border 20 so as to stretch the pellicle 19. The tension in the pellicle 19 may be maintained, for example, by using a difference in the coefficient of thermal expansion between the frame and the pellicle.

[0086] Although the illustrated embodiments show that the frame is attached to the front of the pattern forming device MA, in other examples, the frame can be attached to other parts of the pattern forming device MA. For example, the frame can be attached to multiple sides of the pattern forming device MA. This can be achieved, for example, using sub-mounts that provide releasably engaged attachments between the frame and multiple sides of the pattern forming device MA. In an alternative arrangement, the frame can be attached to the pattern forming device MA by combining some attachment sites on multiple sides of the pattern forming device MA with some attachment sites on the front of the pattern forming device MA. Attachment can be provided, for example, by a sub-mount that releasably engages the frame with the pattern forming device MA.

[0087] The attachment of the frame 17 to the patterning device MA may be controlled to achieve a desired tension in the pellicle 19. For example, the tension in the pellicle 19 may be measured during attachment of the frame 17 to the patterning device MA, and the tension may be adjusted in response to the measurement to achieve a desired tension in the pellicle 19.

[0088] The frame 17 may include an engagement mechanism 22 configured to allow the frame 17 to be removably attached to the patterning device MA (i.e., to allow the frame 17 to be attached to and removed from the patterning device MA). The engagement mechanism 22 may be positioned at a block 23 of the frame 17 (see Figure 4 ). The engagement mechanism 22 is configured to engage with an attachment member 24 provided on the pattern forming device MA. For example, the attachment member 24 may be a protrusion or a stud extending from the pattern forming device MA. The engagement mechanism 22 may, for example, include a locking member 32 (see Figure 7 ).

[0089] A plurality of engagement mechanisms 22 and associated attachment members 24 may be provided. The engagement mechanisms 22 may be distributed around the frame 17 (e.g., two engagement mechanisms 22A, 22B on one side of the frame and two engagement mechanisms 22C, 22D on the opposite side of the frame). The associated attachment members may be distributed around the perimeter of the patterning device MA. The engagement mechanisms 22 may be positioned at a block 23 of the frame 17 (see FIG. Figure 4 )middle.

[0090] Reference Figure 4, a top view of the frame 17 is shown. The frame 17 is provided with four engagement mechanisms 22A to 22D. Each engagement mechanism 22 can be positioned in a corresponding block 23 of the frame 17, and the block protrudes radially outward from the rest of the corresponding side of the periphery of the frame 17. Each engagement mechanism 22A to 22D is configured to receive a corresponding attachment member 24A to 24D (described below) extending from the pattern forming device MA. The frame 17 has four sides in this example. Two engagement mechanisms 22A, 22B are arranged on one side 30A of the frame 17, and two engagement mechanisms 22C, 22D are arranged on the opposite side of the frame 17. These sides will be referred to as support sides 30A, 30B. The other two sides that connect the support sides 30A, 30B together and do not have the engagement mechanisms 22A to 22D are referred to as free sides 30C, 30D. Other combinations may also be possible, such as the engagement mechanism being located on each of the four frame sides, and so on. A plurality of engagement mechanisms 22 are arranged to be arranged along a scanning direction (in a conventional notation) during use in the lithographic apparatus. Figure 3 and Figure 4 However, multiple engagement mechanisms may be provided on multiple sides of the frame 17 which are oriented perpendicular to the scanning direction (indicated as the y direction in the figure). However, multiple engagement mechanisms may be provided which will be perpendicular to the scanning direction (indicated as the y direction in the figure) during use in the lithographic apparatus. Figure 3 and Figure 4 On multiple sides of the frame 17 oriented in the x-direction (indicated in FIG. 1 ).

[0091] The attachment members 24A to 24D (protrusions) received by the engagement mechanisms 22A to 22D may be positioned on the front surface of the patterning device MA, i.e., the patterned surface 21. Additionally or alternatively, multiple protrusions may be positioned on multiple sides of the patterning device. Multiple protrusions may extend vertically from multiple sides of the patterning device. In such an arrangement, each protrusion may have a flattened side surface to facilitate secure engagement with the side of the patterning device.

[0092] Each engagement mechanism 22A to 22D may be oriented obliquely to the side of the frame, for example so that the side substantially faces the center point CP of the frame 17 in the xy plane. In this case, the center point CP is the geometric center of the frame 17. That is, each engagement mechanism 22A to 22D has been rotated away from being oriented perpendicular to the side of the frame 17 so that it generally faces the center of the frame 17. Thus, the engagement mechanism 22A faces the engagement mechanism 22D, and the engagement mechanism 22B faces the engagement mechanism 22C. Figure 4The lines drawn from each engagement mechanism in the center point CP intersect at the center point CP. This forms two planes of symmetry, resulting in a thermal center in the center point CP of the frame 17. This allows the frame 17 to thermally expand relative to the patterning device MA and prevents stress from accumulating in the patterning device MA. In other examples, the engagement mechanism 22 may not rotate all the way to face the center point CP of the frame 17. In this case, the benefit of reduced stress accumulation will not be as great, but there will still be an increased thermal expansion capability.

[0093] Reference again Figure 3 , the frame 17 may have a first surface 17A and a second surface 17B opposite the first surface 17A. The first surface 17A and the second surface 17B may be continuous. When applicable, the film 19 or the border 20 may be in contact with the first surface 17A of the frame around its entire perimeter. In other examples, the first surface 17A and / or the second surface 17B may have at least one recess (not shown). Figure 3 In the embodiment, the first surface 17A is the top surface and the second surface 17B is the bottom surface. When the membrane 19 is in use, the first surface 17A may face downward and the second surface may face upward, but the terms used here are only used to assist understanding and the directions in which the first surface 17A and the second surface 17B face when in use may be different or reversed.

[0094] The frame 17 may include a structure 18 disposed between and connecting and separating the first and second surfaces 17A, 17B. The structure 18 at least partially defines volumes 28A-28C, such as voids, spaces, hollows, pockets, chambers, and the like.

[0095] In an example, structure 18 includes a first wall 17C. The first wall 17C may be positioned at the inner periphery of frame 17 and may extend around at least a portion of the perimeter of frame 17. In an embodiment, the first wall 17C may be located between the inner periphery and the outer periphery of frame 17 and may extend around at least a portion of the perimeter of frame 17. The first wall 17C may be continuous around at least a portion of the perimeter of frame 17 or around the entire perimeter of frame 17. Frame 17 may have a second wall 17D connecting first surface 17A and second surface 17B. The second wall 17D may be positioned at the outer periphery of frame 17 and may extend around at least a portion of the perimeter of frame 17. In an embodiment, the second wall 17D may be located between the inner periphery and the outer periphery of frame 17 and may extend around at least a portion of the perimeter of frame 17. The second wall 17D may be continuous around at least a portion of the perimeter of frame 17 or around the entire perimeter of frame 17. In an embodiment, the first wall 17C and / or the second wall 17D extend substantially perpendicularly to the first surface 17A and the second surface 17B or substantially obliquely to the first surface 17A and the second surface 17B.

[0096] FIG. 5A to FIG. 5F Shown through Figure 4 The cross section is taken. FIG. 5A to FIG. 5D As shown in , volumes 28A to 28C are provided in the frame 17 in which material has been removed or missing from the frame 17. That is, the first surface 17A and the second surface 17B at least partially define a plurality of volumes 28 between the first surface 17A and the second surface 17B, which do not contain material forming the frame 17. In an embodiment, the frame 17 may be formed without material in the volumes 28. The volumes 28 may be open or closed to the environment (e.g., air, process gas, or vacuum). In other examples, the volumes 28 may be filled with a material different from the material of the frame 17. For example, the volumes 28 may be filled with a material having a lower density than the material forming the majority of the rest of the frame 17.

[0097] There may be a plurality of volumes 28 located at different locations along the perimeter of the frame 17, which may be joined to each other to form a larger volume or may be separated by the first wall 17C and / or the second wall 17D. That is, there may be a lattice of volumes 28 formed between the first surface 17A and the second surface 17B.

[0098] In addition, at least one portion of the frame can have a different cross-sectional profile than at least one other portion of the frame. In particular, the form of the structure 18 disposed between the first surface 17A and the second surface 17B (e.g., the number of walls 17C, 17D, the relative arrangement of the walls 17C, 17D, etc.) and the relative amount of the volume 28 and the structure 18 can optionally be different between at least one portion of the frame and at least one other portion, for example, to provide desired mechanical and thermal properties at those locations. For example, at least one portion of the frame 17 can have an I-shaped cross-section, and at least one other portion of the frame 17 can have a box shape or a hollow tube segment.

[0099] Figure 5B A side view of the free side 30C is shown, which illustrates that the support sides 30A, 30B are at least partially hollowed out to form an open tube structure (i.e., a hollow tube) extending in the y direction. The open space within the hollow tube is the volume 28A. This situation is Figure 5E 17A and 17B and the first wall 17C and the second wall 17D form a hollow tube along at least a portion of the length of the support side 30A of the frame 17. The volume portion 28A can be considered to extend through the first wall 17C and the second wall 17D or extend between them. Preferably, the hollow tube extends from the free side 30C in the support side 30A to the engagement mechanism 22A. In other examples, the hollow tube can extend from the free side 30C in the support side 30A to the block 23 that holds the engagement mechanism 22A. The hollow tube can extend along the full length of one or both of the support sides 30A and 30B. The hollow tube can extend only along a portion of the length of one or both of the support sides 30A and 30B. In other examples, the hollow tube can extend along at least a portion of one or both of the free sides 30C and 30D. In other examples, the cross-section of one or both of the support sides 30A, 30B may be another shape or a hollow structure other than a hollow tube, so long as the desired torsional rigidity is provided.

[0100] Figure 5C Shown through Figure 4 The cross-sectional view taken along the line DD of FIG. 1 shows the free sides 30C, 30D having an I-shaped cross section extending in the x-direction. Fig. 5F. The I-shaped cross section provides bending stiffness. The first surface 17A and the second surface 17B and the first wall 17C form an I-shaped cross section along at least a portion of the length of the free side 30C. Due to the I-shaped cross section, there are two volume portions 28B extending on either side of the first wall 17C along at least a portion of the length of the side 30C in the x direction. Preferably, the I-shaped cross section extends from the support side 30A to the support side 30B in the free side 30C. The I-shaped cross section can extend along the full length of one or both of the free sides 30C and 30D. In other examples, the I-shaped cross section can extend only along a portion of the length of one or both of the free sides 30C and 30D. In other examples, the I-shaped cross section can extend along at least a portion of one or both of the support sides 30A and 30B. In other examples, the cross section of one or both of the free sides 30C and 30D can be another shape other than the I-shaped, as long as the required bending stiffness is provided.

[0101] Figure 5A A cross-sectional view taken through line CC is shown, which illustrates at least one block of the blocks 23 on the support side 30A with the volume 28C removed. Figure 5D 23. The first surface 17A and the second surface 17B defining the volume portion 28C need only be used as reference surfaces. That is, the volume portion 28C does not need to have a material for strength or rigidity. The second wall 17D is considered to extend around the periphery of the block 23, and the volume portion 28C can be considered to extend to the second wall 17D in the x direction. In other examples, the volume portion 28C can extend through the second wall 17D in the x direction at the inner periphery of the frame 17 all the way to the first wall 17C. The volume portion 28C can extend through the second wall 17D and through the inner wall 17C so that the volume portion 28C extends completely or partially through the support side 30A in the x direction. The volume portion 28C in the block 23 can be any suitable size and can be positioned in another part of the frame 17. That is, the volume portion 28C can extend through the first wall 17C and / or the second wall 17D or between them at any position around the periphery of the frame 17.

[0102] Figure 4 The outer corners of the block 23 are shown removed. That is, material that would otherwise be present in a standard frame can be removed from the corners of the block 23. This is because, due to the rotation of the engagement mechanism 22 as described above, support of the block 23 is no longer required in this area.

[0103] Fig. 6A A perspective view of a frame 17 is shown with four engagement mechanisms 22A to 22D positioned in a block 23. Volumes 28A to 28C are shown in the support sides 30A, 30B and the free sides 30C, 30D.

[0104] Figure 6B A perspective view of a planar cross section of the frame 17 is shown. The volumes 28A to 28C are shown in more detail. The volume 28A is shown as a hollow tube extending from the free side 30C to the block 23 of the retaining engagement mechanism 22A in the support side 30A. Another volume 28A is shown as a hollow tube extending from the free side 30C to the block 23 of the retaining engagement mechanism 22C in the support side 30B. Another volume 28A is shown as a hollow tube extending from the free side 30D to the block 23 of the retaining engagement mechanism 22B in the support side 30A. Another volume 28A is shown as a hollow tube extending from the free side 30D to the block 23 of the retaining engagement mechanism 22D in the support side 30B.

[0105] Volume 28B is shown extending along either side of an I-shaped cross section extending from support side 30A to support side 30B in free sides 30C, 30D. Volume 28C is shown extending from outside the periphery of block 23 to second wall 17D, i.e., volume 28C is in the form of a triangular cavity.

[0106] As about Figure 4 and 5A to Fig. 5F As described, material of the frame 17 has been removed from the frame 17 in the volume 28, or the material was not included in the volume 28 when the frame 17 was made. The removal of the material of the frame 17 in the volume 28 can be performed by any method known in the art, such as grinding, etching, etc. In other examples, such as by 3D printing, the frame can be made without placing any of the material in the volume 28A to 28C, that is, the volume has been free of material. The volume 28 without the material of the frame 17 means that the weight of the frame 17 has been reduced when compared to the frame 17 with material in these volume 28. In addition, since the volume 28 does not contain the material of the frame 17, the eigenfrequency of the frame 17 has been increased.

[0107] Phramics have previously been fabricated directly onto wafers of crystalline silicon (c-Si). In a similar manner as mentioned above, this is accomplished by depositing a thin layer directly on top of a SiOx layer (e.g., approximately 300 nm), which is then deposited on a silicon wafer, wherein the diaphragm (phram) becomes freestanding by selectively and anisotropically etching back the c-Si. Thus, a frame of c-Si remains with a freestanding diaphragm (e.g., 11 cm x 14 cm, with a thickness on the order of 15 to 50 nm) spanning above it.

[0108] The substrate on which the diaphragm is grown affects the stress that ends up in the pellicle. Minimizing thermal stress during the fabrication process is important. This is important because minimizing stress leads to increased availability, robustness, and service life of the pellicle. The more stress there is, the more likely the pellicle will fail. In order to minimize stress during fabrication, the coefficient of thermal expansion (CTE) of the substrate is preferably matched to the CTE of the diaphragm being formed. As mentioned, crystalline silicon has been used to fabricate the pellicle. As an example, when the coefficient of thermal expansion (CTE) of a crystalline silicon wafer matches the CTE of a polycrystalline core (2.6um / m / K vs. ~4um / m / K), a significant amount of thermal stress is not added during fabrication.

[0109] The use of the border 20 is advantageous because the stress in the pellicle 19 can be reduced by bonding the border 20 of high CTE material to the pellicle 19. A CTE of about 7 to 8 μm / m / K and higher can be considered a high CTE relative to the pellicle. This switches the CTE-induced stress between the frame 17 and the pellicle 19 with the CTE-induced stress between the border 20 and the pellicle 19. Therefore, it is advantageous to provide the border 20, the frame 17, and the block 23 with the same material. The material of the border 20 can be the same as the material of the frame 17. The material of the block 23 can be the same as the material of the frame 17.

[0110] The increased CTE of the membrane means that the stresses will increase.In many cases, the use of a crystalline silicon substrate will not be suitable because it will not be able to match the CTE of the membrane.

[0111] Silicon has a relatively high specific modulus (ie, Young's modulus / density) and has a relatively high thermal conductivity. Therefore, silicon is a good construction material for light and rigid engineering.

[0112] Using materials other than silicon as the frame material presents difficulties in achieving the specifications required for the diaphragm assembly 15. These specifications may be, for example, the natural frequency of the diaphragm frame, the maximum weight of the diaphragm assembly, temperature fluctuations within the assembly, and the like.

[0113] Constructing the diaphragm frame 17 with a volume 28 positioned in the locations described above allows other materials to be used instead of silicon for the frame 17, and in some examples for the diaphragm border 20. That is, having a volume 28 without the material of the frame 17 means that the diaphragm assembly 15 can be constructed within the desired specifications (eigenfrequency, weight, etc.).

[0114] The frame 17 and / or the border 20 may be made of crystalline silicon. The frame 17 and / or the border 20 may be made of aluminum. The frame 17 and / or the border 20 may be made of aluminum nitride. Although the present specification mentions aluminum and aluminum nitride as materials for forming the diaphragm assembly, other materials may be used, such as beryllium or its compounds.

[0115] Using different materials (such as aluminum or aluminum nitride) for the frame 17 and / or the border 20 of the diaphragm 19 means that the CTE of the diaphragm can be better matched. This in turn reduces thermal stress during the fabrication of the diaphragm 19. For example, the diaphragm 19 can be formed of MoSi (which is a relatively high CTE material) and the frame 17 can be made using aluminum or aluminum nitride. This provides a more closely matched CTE between the frame 17 and the diaphragm 19, which can reduce thermal stress during the fabrication of the diaphragm 19.

[0116] Aluminum and aluminum nitride have lower Young's moduli than silicon, with the Young's modulus of aluminum being less than that of aluminum nitride. This means that for the same density, aluminum and aluminum nitride are less stiff than silicon. Because aluminum has a lower Young's modulus than aluminum nitride, a frame made of aluminum may benefit very much from a volume without material, while a frame made of aluminum nitride may not benefit as much from a volume without material. However, the design of a frame made of aluminum or aluminum nitride may have the same or similar corresponding increase in eigenfrequency (i.e., having the same volume without material).

[0117] The volume 28 without material is in a specific area so that the stiffness of the frame 17 (whether torsional or bending stiffness) is not substantially reduced. This means that, because aluminum and silicon have similar densities, the necessary stiffness for the required weight is achieved for an aluminum or aluminum nitride frame 17. Therefore, the volume 28 of the frame 17 that does not relatively contribute to the stiffness has been removed. The volume 28 without material does not substantially weaken the stiffness of the frame 17. The stiffness of the frame 17 is matched to the load on the frame 17.

[0118] The stiffness of the frame 17 is required in specific locations and in specific directions. For example, in the free sides 30C, 30D of the frame 17, stiffness is required in the plane of the diaphragm frame (xy plane), so an I-shaped cross section is used in this area. The volume 28 does not substantially weaken the bending stiffness of the frame 17. For example, in the support sides 30A, 30B of the frame 17, torsional stiffness is required, so a hollow tube is used in this area. The volume 28 does not substantially weaken the torsional stiffness of the frame 17.

[0119] The stresses derived from the deposition process can decouple from the desired stress (eg, pre-stress). For example, if a microstructure provides a desired service life but generates too little stress, the structure can be tuned to provide the desired balance.

[0120] Although examples have been shown in which material of the frame 17 has been removed from the volume 28 at specific locations, it should be appreciated that the weight of the frame 17 may be reduced by removing material from the volume in any portion of the frame 17. Furthermore, it should be appreciated that although an I-shaped cross-section and a hollow tube have been shown as examples, other cross-sectional shapes may be used to provide the desired stiffness of the frame, whether in torsional stiffness or bending stiffness.

[0121] As an example, aluminum is used as a material and is used in Figure 4 , FIG. 5A to FIG. 5F , the weight of the frame 17, border 20, block 23 and attachment member 24 can be reduced from 14 grams (which would be the weight using a standard frame made of aluminum) to 10 grams.

[0122] As mentioned, removing material of the frame 17 in the volume 28 at specific locations in the frame 17 raises the eigenfrequency of the frame 17. As an example, aluminum is used as the material and in Figure 4 , FIG. 5A to FIG. 5F For the frame shown in , the lowest eigenfrequency may be 405 Hz, compared to 355 Hz for a standard frame made of silicon.

[0123] Figure 7 A top view of the engagement mechanism 22 fastened to the block 23 of the frame 17 is shown. In this example, the engagement mechanism 22 has been rotated away from a state of being oriented perpendicular to the side of the frame 17, but in other examples, the engagement mechanism can be aligned in the x-direction. The engagement mechanisms 22A to 22D allow for the x-direction and the y-direction (see FIG. Figure 4 ). The engagement mechanism 22 is configured to allow engagement to an attachment member 24 (not depicted). The attachment member 24 may be, for example, glued to the patterning device MA or may be attached by other bonding means (optical contact, magnetism or van der Waals forces, etc.).

[0124] Engagement mechanism 22 and attachment member 24 suspend pellicle frame 17 relative to patterning device MA so that the pellicle frame is in contact with the patterning device (see FIG. Figure 3 ) between the pellicle and the pattern forming device. The gap G may be maintained by some movement limiting components. The gap G may be wide enough to allow equalization of pressure between the external environment and the space between the pellicle and the pattern forming device. The gap G may also be narrow enough so that it provides a desired restriction of the route of potential contaminating particles from the external environment to the space between the pellicle and the pattern forming device. The gap G may, for example, be at least 100 microns so as to allow equalization of pressure between the external environment and the space between the pellicle and the pattern forming device. The gap G may, for example, be less than 500 microns, more preferably less than 300 microns. The gap G may, for example, be between 200 microns and 300 microns.

[0125] The engagement mechanism 22 has a locking member 32 configured to lock to the attachment member 24. The locking member 32 has two elastically bendable engagement arms 34 in the form of two first leaf springs extending from an intermediate body 36 approximately in the y-direction. The engagement arms 34 provide a surface to rest the attachment member 24 on. The intermediate body 36 extends approximately in the x-direction. The intermediate body 36 is in turn connected to two additional elastically bendable engagement arms 38, which are also in the form of two second leaf springs extending approximately in the y-direction but at another distance compared to the engagement arms 34. The ratio of the length of the first leaf spring 34 to the length of the second leaf spring 38 is between 1.5:1 and 2.5:1, for example 2:1. This keeps the attachment member (or stud) as flush as possible with the resting surface.

[0126] The beam 40 is positioned between the two engagement arms 34 and extends generally in the y-direction from the opposite side of the engagement member 22 relative to the intermediate body 36. The beam 40 acts as a stop to secure the attachment member 24 against the engagement arms 34. Space is provided for the attachment member 24 by the beam 40 extending generally in the y-direction. Thus, the beam 40 of the engagement mechanism 22 extends a distance that allows the attachment member 24 to be inserted into the engagement mechanism 22. The beam 40 may extend more than halfway across the engagement member 22.

[0127] Fig. 8A Schematically depicting the passage Figure 7 A cross section of the engagement mechanism 22 taken along line AA. Figure 8B Schematically depicting the passage Figure 7 A cross section of the engagement mechanism 22 taken along line BB.

[0128] Fig. 9 A perspective view of an engagement mechanism 22 fixed to a block 23 of a frame 17 is schematically depicted.

[0129] Fig.10 Schematically depicting the passage Fig. 9 A perspective view of a cross section of the engagement mechanism 22 taken along line CC.

[0130] Fig.11A is an end view of the attachment member 24 (stud) used to lock the engagement mechanism 22 to the patterning device MA. Fig. 11B is a side view of an attachment member 24 (stud) used to lock the engagement mechanism 22 to the patterning device MA. In other examples, the attachment member may be another shape and size.

[0131] Fig.12 Schematically depicting the passage Fig. 91 and 1 . A side view of a cross section of the engagement mechanism 22 taken along line CC of FIG. 1 . The attachment member 24 extends from and is fixed to the patterning device MA (not shown). In order to use the locking member 32 to lock the frame 17 to the patterning device MA, the frame 17 is pressed against the attachment member 24 and then the engagement mechanism 22 is pressed downward to create space for the frame 17 to be slotted into place. In particular, the attachment member 24 is moved relative to the engagement mechanism 22 in the direction of arrow D. Then, the attachment member 24 is moved in the direction of arrow E ( Figure 7 The intermediate body 36 of the engagement mechanism 22 is pushed downward in the z-direction (in the z direction), which in turn pushes the two engagement arms 34 of the engagement mechanism 22 downward.

[0132] With the engagement arms 34 pressed downwards, space is created in the engagement mechanism 22 for the attachment member 24 to slot into position below the stop of the beam 40. To perform this operation, the frame 17 and therefore the engagement mechanism 22 is moved in the direction of arrow F, which in turn means that the attachment member 24 is effectively moved relative to the engagement mechanism 22 in the direction of the dashed arrow G. The attachment member 24 is then in its locked position.

[0133] Once the intermediate body 36 and thus the engagement arm 34 are released, i.e. the force pushing the intermediate body and the engagement arm in the direction of arrow E is removed, the attachment member 24 is clamped between the stop of the beam 40 and the engagement arm 34. The engagement mechanism 22 is thus locked to the attachment member 24, and when the engagement mechanism 22 is fixed to the frame 17 and the attachment member 24 is fixed to the patterning device MA, the frame 17 is locked to the patterning device MA. The locking process described above may be performed for each of the engagement mechanisms 22A to 22D.

[0134] The configuration of the engagement mechanism 22 has the advantage of loading the engagement mechanism 22 in the center of the engagement mechanism 22, which avoids introducing unwanted torsion. Thus, the engagement mechanism 22 is configured so that the attachment member 24 is removably secured in a substantially central location in the engagement mechanism 22. This is in contrast to standard engagement mechanisms that have support arms positioned toward the sides of the engagement mechanism that introduce unwanted torsion.

[0135] With attachment members 24 secured to engagement mechanisms 22 and engagement mechanisms 22 allowing frame 17 to flex in both the x-direction and the y-direction, thermal stresses during fabrication of pellicle 19 can be reduced. The movement / flexibility or elasticity provided by engagement mechanisms 22A to 22D and attachment members 24 allows pellicle frame 17 to flex relative to patterning device MA as needed when temperature changes occur. This is advantageous because it avoids potentially damaging thermal stresses generated in pellicle frame 17.

[0136] In an embodiment, the present invention may form part of a mask inspection device. The mask inspection device may use EUV radiation to illuminate the mask and use an imaging sensor to monitor the radiation reflected from the mask. The image received by the imaging sensor is used to determine whether there are defects in the mask. The mask inspection device may include an optical device (e.g., a reflector) configured to receive EUV radiation from an EUV radiation source and form it into a radiation beam to be guided at the mask. The mask inspection device may also include an optical device (e.g., a reflector) configured to collect EUV radiation reflected from the mask and form an image of the mask at the imaging sensor. The mask inspection device may include a processor configured to analyze the image of the mask at the imaging sensor and determine whether there are any defects on the mask based on the analysis. The processor may be further configured to determine whether a mask defect detected when the mask is used by the lithography device will cause unacceptable defects in the image projected onto the substrate.

[0137] In an embodiment, the present invention may form part of a metrology apparatus. The metrology apparatus may be used to measure the alignment of a projected pattern formed in a resist on a substrate relative to a pattern already present on the substrate. Such a measurement of relative alignment may be referred to as an overlay. The metrology apparatus may, for example, be positioned proximate to a lithographic apparatus and may be used to measure overlay before a substrate (and resist) has been processed.

[0138] Although specific reference may be made herein to embodiments of the invention in the context of lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or a mask (or other pattern forming device). These apparatuses may generally be referred to as lithographic tools. Such lithographic tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0139] The term "EUV radiation" may be taken to encompass electromagnetic radiation having a wavelength in the range of 4 nm to 20 nm, for example in the range of 13 nm to 14 nm. EUV radiation may have a wavelength less than 10 nm, for example in the range of 4 nm to 10 nm, such as 6.7 nm or 6.8 nm.

[0140] although Figure 12 depicts the radiation source SO as a laser produced plasma LPP source, but any suitable source may be used to produce EUV radiation. For example, a plasma emitting EUV may be produced by using an electric discharge to convert a fuel (e.g., tin) into a plasma state. This type of radiation source may be referred to as a discharge produced plasma (DPP) source. The discharge may be produced by a power supply, which may form part of the radiation source or may be a separate entity connected to the radiation source SO by an electrical connection.

[0141] Although specific reference may be made in the present invention to the use of lithographic equipment in IC manufacturing, it should be understood that the lithographic equipment described in the present invention may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection for magnetic domain memory, flat panel displays, liquid crystal displays (LCDs), pellicle heads, etc.

[0142] Although the above may specifically refer to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications, for example, in imprint lithography, and is not limited to optical lithography where the context permits. In imprint lithography, the topography in the patterning device defines the pattern produced on the substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate, on which the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. The patterning device is removed from the resist after the resist has been cured, leaving a pattern therein.

[0143] Although specific embodiments of the present invention have been described above, it will be appreciated that the present invention may be practiced in other ways than those described. The above description is intended to be illustrative rather than restrictive. Therefore, it will be appreciated by those skilled in the art that modifications may be made to the described invention without departing from the claims set forth below and the scope of the claims.

Claims

1. A membrane frame for supporting a membrane, the membrane frame comprising: a first surface and a second surface opposite to the first surface, and a structure disposed between the first surface and the second surface; wherein the first surface and the second surface and the structure at least partially define at least one volume portion therebetween that is free of material forming the pellicle frame; wherein the frame comprises a plurality of engagement mechanisms for connecting the frame to a patterning device, the plurality of engagement mechanisms being arranged along one or more sides of the frame, Wherein each engagement mechanism is oriented obliquely relative to the side of the frame in the plane of the frame.

2. A membrane frame for supporting a membrane, the membrane frame comprising: a first surface and a second surface opposite to the first surface, and a structure disposed between the first surface and the second surface; wherein the first surface and the second surface and the structure at least partially define at least one volume portion therebetween that is free of material forming the pellicle frame; The first surface, the second surface and the first wall form an I-shaped cross-section along at least a portion of the length of one side of the pellicle frame.

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