Masking module

Abstract

A masking module for use in a lithographic apparatus, comprising a moveable masking blade configured to prevent part of a patterning device from being illuminated during operation of the lithographic apparatus. The masking module is configured to rotate the moveable masking blade about an axis substantially parallel to a plane in which the patterning device is held in the lithographic apparatus. The masking module may further comprise a support and a masking assembly, rotatable relative to the support. The masking assembly may comprise a moveable masking blade and an arm, extending from the moveable masking blade. The arm extends from the moveable masking blade in a first direction, and the masking assembly is rotatable relative to the support such that the moveable masking blade has at least a component of motion in a second direction, generally perpendicular to the first direction.

Description

MASKING MODULECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application 23199526.7 which was filed on September 25, 2023 and EP application 23213184.7 which was filed on November 30, 2023 and which are incorporated herein in its entirety by reference.FIELD

[0002] The present invention relates to a masking module which may be suitable for a lithographic apparatus. The lithographic apparatus may be an extreme ultraviolet (EUV) lithographic apparatus.BACKGROUND

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

[0004] To project a pattern on a substrate a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which can be formed on the substrate. A lithographic apparatus, which uses extreme ultraviolet (EUV) radiation, having a wavelength within the range 4-20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than a lithographic apparatus which uses, for example, radiation with a wavelength of 193 nm.

[0005] The volume around the patterning device of existing lithographic apparatus is very space constrained due to a large number of components and assemblies / modules existing close to the patterning device.

[0006] One such module is the masking module which typically acts to restrict the area of the patterning device illuminated by electromagnetic radiation by means of one or more moveable masking blades, adjacent to the patterning device, configured to block or reflect incident electromagnetic radiation. In this way, the moveable masking blade(s) of the masking module prevent part(s) of the patterning device from being illuminated during operation of the lithographic apparatus.

[0007] Existing moveable masking blades are typically actuated by remote actuators via long unsupported members because space constraints in the volume around the patterning device preclude placement of the actuators nearer the moveable masking blades. This makes the conventional moveable masking blades and their support very heavy. Accelerating heavy, long components is difficult and energy-intensive.

[0008] It may be desirable to provide an apparatus that obviates or mitigates one or more problems associated with the prior art.SUMMARY

[0009] According to a first aspect there is provided a masking module for use in a lithographic apparatus, comprising a moveable masking blade configured to prevent part of a patterning device from being illuminated during operation of the lithographic apparatus, wherein the masking module is configured to rotate the moveable masking blade about an axis substantially parallel to a plane in which the patterning device is held in the lithographic apparatus.

[0010] Due to space constraints, conventional moveable masking blades are typically actuated by remote actuators via long unsupported members. This makes the conventional moveable masking blades and their support very heavy. By rotating the moveable masking blades instead of translating them, the associated actuators can be placed relatively close by and can be coupled to the moveable masking blades by relatively short members. This enables a reduction in mass and extent of the masking module. This reduction in mass and extent reduces the energy consumption of the masking module.

[0011] The masking module may comprise a support and a masking assembly that is rotatable relative to the support. The masking assembly may comprise a moveable masking blade and an arm that extends from the moveable masking blade in a first direction. The masking assembly may be rotatable relative to the support such that the moveable masking blade has at least a component of motion in a second direction, generally perpendicular to the first direction.

[0012] The provision of arms extending perpendicular to a component of moveable masking blade motion enables a reduction in mass and extent of the supporting mechanism. The reduction in mass and extent of the supporting mechanism reduces the energy consumption of the masking module.

[0013] The masking assembly may comprise one or more flexures, configured to flexibly couple the masking assembly and the support.

[0014] The masking assembly may comprise one or more air bearings, configured to enable rotation about an axis of rotation.

[0015] A further arm may extend from the moveable masking blade in the first direction.

[0016] Three, four, five or more arms may extend from the moveable masking blade.

[0017] A radial separation between the moveable masking blade and the associated support may be at least 12cm.

[0018] Advantageously a radial separation between the moveable masking blade and the associated support of at least 12cm minimises movement of the moveable masking blade out of a focal plane of the lithographic apparatus

[0019] The radial separation between the moveable masking blade and the associated support may be up to 13cm.

[0020] The masking assembly may weigh up to 5 kg.

[0021] The masking module may comprise one or more actuators, configured to rotate the arms.

[0022] Multiple actuators may be configured to rotate multiple arms.

[0023] The one or more actuators may be position-controlled motors.

[0024] The one or more actuators may be linear actuators and / or rotational actuators.

[0025] The masking module may comprise one or more linkages, configured to connect the one or more actuators to the one or more arms.

[0026] The masking module may comprise a further masking assembly, rotatable relative to the support, the further masking assembly comprising: a further moveable masking blade; and an arm, extending from the further moveable masking blade; wherein the arm extends from the further moveable masking blade in a third direction, and wherein the masking assembly is rotatable relative to the support such that the further moveable masking blade has at least a component of motion in a fourth direction, generally perpendicular to the third direction.

[0027] The further masking assembly may comprise any of the optional features above.

[0028] The moveable masking blade and the further moveable masking blade may be moveable within mutually non-overlapping envelopes of motion.

[0029] The term envelope of motion should be taken to mean the locus encompassing all possible positions occupied by an object.

[0030] The masking assembly and further masking assembly may be fixed with respect to each other.

[0031] The masking module may comprise a common linkage configured to allow actuation of more than one masking assembly by a single actuator.

[0032] According to a second aspect there is provided a lithographic apparatus comprising: an illumination system configured to condition a radiation beam; a patterning device support structure constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; and a projection system configured to project the patterned radiation beam onto the substrate; and a masking module according to the first aspect, adjacent to the patterning device support structure.

[0033] The lithographic apparatus may comprise any of the optional features above.

[0034] The or each moveable masking blade may not be moveable in a non-scanning direction of the lithographic apparatus.

[0035] The non-scanning direction should be taken as parallel to the patterning deviceBRIEF DESCRIPTION OF THE DRAWINGS

[0036] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:Figure 1 depicts a lithographic system comprising a lithographic apparatus and a radiation source;Figure 2A is a schematic plan view of a support structure and patterning device of the lithographic apparatus shown in Figure 1, disposed in a first end position;Figure 2B is a schematic plan view of the support structure and patterning device shown in Figure 1, disposed in a second end position;Figure 3 illustrates a masking module according to an embodiment of the present disclosure;Figure 4A schematically illustrates a configuration of the masking module shown in Figure 3 at the start of a dynamic exposure.Figure 4B schematically illustrates the configuration of Figure 4A of the masking module shown in Figure 3 from an alternate view.Figure 4C schematically illustrates another configuration of the masking module shown in Figure 3.Figure 4D schematically illustrates the configuration of Figure 4C of the masking module shown in Figure 3 from an alternate view.Figure 4E schematically illustrates a configuration of the masking module shown in Figure 3 at the end of a dynamic exposure.Figure 4F schematically illustrates the configuration of Figure 4C of the masking module shown in Figure 3 from an alternate view.Figure 5 illustrates a masking module according to another embodiment of the present disclosure; andFigure 6 illustrates the masking module shown in Figure 5 from an alternate view.DETAIEED DESCRIPTION

[0037] Figure 1 shows a lithographic system comprising a radiation source SO and a lithographic apparatus FA. The radiation source SO is configured to generate an EUV radiation beam B and to supply the EUV radiation beam B to the lithographic apparatus LA. The lithographic apparatus LA comprises an illumination system IL, a patterning device support structure MT configured to support a patterning device MA (e.g., a mask or reticle), a projection system PS and a substrate table WT configured to support a substrate W.

[0038] The illumination system IL is configured to condition the EUV radiation beam B before the EUV radiation beam B is incident upon the patterning device MA. Thereto, the illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. The faceted field mirror device 10 and faceted pupil mirror device 11 together provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. The illuminationsystem IL may include other mirrors or devices in addition to, or instead of, the faceted field mirror device 10 and faceted pupil mirror device 11.

[0039] After being thus conditioned, the EUV radiation beam B interacts with the patterning device MA. The region of the patterning device MA illuminable by the radiation beam B may be at least partially defined by a masking module 12. As a result of this interaction, a patterned EUV radiation beam B’ is generated. The projection system PS is configured to project the patterned EUV radiation beam B’ onto a target region of the substrate W. For that purpose, the projection system PS may comprise a plurality of mirrors 13,14 which are configured to project the patterned EUV radiation beam B’ onto a target region of the substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B’, thus forming an image at the target region of the substrate W with features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS is illustrated as having only two mirrors 13,14 in Figure 1, the projection system PS may include a different number of mirrors (e.g. six or eight mirrors).

[0040] The substrate W may include previously formed patterns. Where this is the case, the lithographic apparatus LA aligns the image, formed by the patterned EUV radiation beam B’, with a pattern previously formed on the substrate W.

[0041] A relative vacuum, i.e. a small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure, may be provided in the radiation source SO, in the illumination system IL, and / or in the projection system PS.

[0042] The radiation source SO may be a laser produced plasma (LPP) source, a discharge produced plasma (DPP) source, a free electron laser (FEL) or any other radiation source that is capable of generating EUV radiation.

[0043] The region of the patterning device MA which may be illuminated by the radiation beam B as partially or wholly defined by the masking module 12 may be referred to as the illuminable region. The illuminable region may be smaller than the patterning device MA in one or more directions.

[0044] In an example, the patterning device MA may be a reticle.

[0045] A description of some additional features of an example type of lithographic apparatus LA, in particular some features and components around the patterning device support structure MT, is now provided with reference to Figures 2A to 6.

[0046] The patterning device support structure MT may be movable in a scanning direction so as to expose a greater region of the patterning device MA in a single dynamic scanning exposure, as now discussed with reference to Figures 2A and 2B. Figures 2A and 2B show a schematic plan view of the patterning device support structure MT and a patterning device MA in two different positions.

[0047] The patterning device support structure MT is movably mounted within a region 15. The lithographic apparatus LA may be considered to comprise a scanning module operable to move the patterning device support structure MT relative to a support frame within region 15. In particular, the patterning device support structure MT is movable in a scanning direction, as indicated by arrow 16, between a first end position (as shown in Figure 2A) and a second end position (as shown in Figure 2B).

[0048] The EUV radiation beam B may have an extent which can only illuminate a portion of the patterning device MA in the scanning direction at any one time. The movement of the patterning device support structure MT allows all portions of the patterning device MA to move through the path of the EUV radiation beam B, cumulatively exposing a greater region of the patterning device MA in a single dynamic scanning exposure.

[0049] Put alternatively, the line X-X of Figures 2A and 2B illustrates a selected portion of the EUV radiation beam B - the movement in a scanning direction, indicated by arrow 16, of patterning device support structure MT traverses X-X over the whole patterning device MA from a first patterning device edge 17 to a second patterning device edge 19.

[0050] During a dynamic exposure of a target region of the substrate W, the target region is moved through an exposure region, cumulatively exposing a greater region of the target region of the substrate W in a single dynamic scanning exposure. The exposure region is the area in the plane of the substrate W intersecting the patterned radiation beam B’ projected by the projection system PS.

[0051] Unless stated otherwise, throughout this specification, the following set of Cartesian coordinates will be used. The scanning direction is labelled as the y-direction. A direction which is parallel to the plane of the patterning device support structure MT and is perpendicular to the scanning direction is referred to as the non-scanning direction and is labelled as the x-direction. A direction which is normal to the plane of the patterning device support structure MT is labelled as the z-dir ection.

[0052] Figure 3 schematically illustrates an embodiment of the masking module 12 and portions of the surrounding lithographic apparatus. A selected ray R of the EUV radiation beam B and patterned EUV radiation beam B’ is also shown. The masking module comprises two masking assemblies - first masking assembly 20 and second masking assembly 22. The first and second masking assemblies 20, 22 are rotatable relative to a support 24. The support is fixed with respect to the projection system PS and the illumination system IL.

[0053] The first masking assembly 20 comprises a first moveable masking blade 26 and a first arm 30. The first arm 30 extends from the first moveable masking blade 26 toward the support 24 in a first direction. The first direction is a generally radial direction.

[0054] The first masking assembly 20 is rotatable relative to the support 24 as indicated by locus 34, such that the first moveable masking blade 26 has at least a component of motion in a second direction, generally perpendicular to the first direction. The first masking assembly 20 is rotatablyconnected to the support 24 by a first air bearing (obscured by the support 24). The first air bearing is configured to enable rotation of the first masking assembly 20 relative to the support 24 about an axis of rotation 25, parallel to the non-scanning x direction. The axis of rotation 25 is substantially parallel to a plane in which the patterning device MA is supported or held by the patterning device support structure MT. By rotating the first masking assembly 20 relative to the support 24 about the axis of rotation 25 the first moveable masking blade 26 is rotated about an axis substantially parallel to the plane in which the patterning device MA is held in the lithographic apparatus LA.

[0055] The second direction has a component in the y direction, but not the x direction, such that the first moveable masking blade 26 is not moveable in the non-scanning direction (x direction) of the lithographic apparatus.

[0056] The second masking assembly 22 comprises a second moveable masking blade 28 and a second arm 32. The second arm 32 extends from the second moveable masking blade 28 toward the support 24 in a third direction. The third direction is a generally radial direction.

[0057] The second masking assembly 20 is rotatable relative to the support 24 as indicated by locus 36, such that the second moveable masking blade 28 has at least a component of motion in a fourth direction, generally perpendicular to the third direction. The second masking assembly 22 is rotatably connected to the support 24 by a second air bearing (obscured by the support 24). The second air bearing is configured to enable rotation of the second masking assembly 22 relative to the support 24 about the axis of rotation 25. By rotating the second masking assembly 22 relative to the support about the axis of rotation 25 the second moveable masking blade 28 is rotated about an axis substantially parallel to the plane in which the patterning device MA is held in the lithographic apparatus LA.

[0058] The fourth direction has a component in the y direction, but not the x direction, such that the second moveable masking blade 28 is not moveable in the non-scanning direction (x-direction) of the lithographic apparatus

[0059] The masking module comprises a first actuator 42 and a coaxial second actuator (obscured by the support 24), configured to rotate the first arm 30 and second arm 32 respectively. Rotating the first and / or second arms 30, 32 also rotates the first and second masking assemblies 20, 22 respectively.

[0060] Each of the first and second moveable masking blades 26, 28 are disposed adjacent to, but out of the plane of, the patterning device MA on the patterning device support structure MT.

[0061] During operation of lithographic apparatus LA, EUV radiation beam B emerges from the illumination system IL toward the patterning device. The illumination system IL is operable to illuminate a region of the patterning device MA with radiation beam B when held by the patterning device support structure MT. This region may be referred to as the illumination slit of the illumination system IL. The extent and shape of the slit is partially defined by optics within the illumination system IL.

[0062] By moving the first and second moveable masking blades 26, 28 into the path of the EUV radiation beam B, the EUV radiation beam B can be truncated (in the y direction) thus limiting the extent of an illuminable region 40 of the patterning device MA and preventing illumination of (an)other part(s) of the patterning device MA. The illuminable region 40 is the region of the patterning device MA which can (potentially) receive radiation. This limited illuminable region 40 is at least partially defined by the rotational positions of the first and second moveable masking blades 26, 28 which define the extent in the y-direction of the region of the patterning device which can receive radiation.

[0063] The slit of the illumination system IL may coincide with a part of the illuminable region 40. The slit of the illumination system IL may be partially or wholly within the illuminable region 40.

[0064] Truncation of the EUV radiation beam B results in a similarly truncated patterned EUV radiation beam B’ being generated and projected into the projection system PS.

[0065] When exposure of a die (or other target region) on a substrate is completed, the moveable masking blades 26, 28 are moved together to fully block the EUV radiation beam B from reaching the patterning device MA.

[0066] The first moveable masking blade 26 comprises a first masking blade edge 27, parallel to the non-scanning direction. The first moveable masking blade 28 comprises a first masking blade edge 29, parallel to the non-scanning direction.

[0067] The rotational positions of the first and second moveable masking blades 26, 28 can be independently changed by rotating the first and second moveable masking blades. These rotations are achieved using the first actuator 42 and the second actuator, respectively.

[0068] The first and second moveable masking blades 26, 28 are angled with respect to the plane of the patterning device MA. The orientation of the first and second moveable masking blades 26, 28 results in a greater proportion of any reflected EUV radiation being reflected away from the projection system (relative to conventional moveable masking blades which are parallel to the plane of the patterning device MA), improving imaging performance (contrast is improved).

[0069] An example of masking module 12 operation is schematically illustrated in Figures 4A- 4F.

[0070] Figure 4A schematically illustrates the initial configuration of the first and second masking assemblies 20, 22 at the beginning of a dynamic exposure (scanning exposure) of a target region of a substrate W (see Figure 1). Figure 4B illustrates the same initial configuration viewed from a direction normal to the plane of the patterning device MA (parallel to the z direction).

[0071] The first and second masking assemblies 20, 22 are positioned such that the first and second masking blade edges 27, 29 substantially coincide. No part of the substrate W receives substantial radiation.

[0072] As exposure begins, the y position of the first patterning device edge 17 of the patterning device MA substantially coincides with the y position of the first and second masking blade edges 27,29. The first patterning device edge 17 moves in the scanning direction (movement indicated by arrow 107). The second masking assembly 22 rotates such that the second masking blade edge 29 moves in tandem (as indicated by arrow 106) with the first patterning device edge 17. This progressively expands the illuminable region 40 (see Figure 4D) in the scanning or y direction whilst restricting or truncating the illuminable region 40 to the patterning device MA.

[0073] Movement in tandem should be taken to mean movement such that the y positions of the first or second masking blade edge 27, 29 and first or second patterning device edge 17, 19 substantially coincide or correlate such that the illuminable region 40 stays within the first or second patterning device edge 17, 19.

[0074] The second masking assembly 22 rotates until the illuminable region 40 expands to a full extent A (see Figure 4D) in the y direction.

[0075] The resulting middle configuration of the of the first and second masking assemblies 20, 22 is shown in Figure 4C. Figure 4D illustrates the same configuration viewed from a direction normal to the plane of the patterning device MA (parallel to the z direction).

[0076] The full extent A in the y direction may be selected based on a desired dose at the substrate W and / or the shape / extent of the illumination slit, among other factors.

[0077] In some embodiments, the full extent A of the illuminable region 40 may be greater than or equal to the extent in the y-direction of the illumination slit, such that the full y-direction extent of the illumination slit illuminates the patterning device MA.

[0078] The patterning device MA moves through the path of the radiation beam B in the scanning direction such that the illumination slit traverses the patterning device MA. The first and second masking assemblies 20, 22 are held in the middle configuration until the second patterning device edge 19 begins to enter the illuminable region 40 (indicated in Figure 4D). The first masking assembly 20 then rotates such that the first masking blade edge 27 moves in tandem (as indicated by arrow 108) with the second patterning device edge 19 (movement indicated by arrow 109) restricting or truncating the illuminable region 40 to the patterning device MA.

[0079] The first masking assembly 20 rotates until the first and second masking blade edges 27, 29 substantially coincide with each other, so that no part of the substrate W receives radiation, ending the dynamic exposure of the target region.

[0080] Figure 4E schematically illustrates the configuration of the first and second masking assemblies 20, 22 at the end of a dynamic exposure of a target region of the substrate W. Figure 4F illustrates the same configuration viewed from a direction normal to the plane of the patterning device MA (parallel to the z direction).

[0081] The above-described rotations of the first and second masking assemblies 20, 22 result in substantially uniform duration of exposure (and thus EUV dose) received by any point on the patterning device MA and thus a uniform dose at its conjugate image plane, the substrate W.

[0082] The first and second edges of the patterning device MA are conjugate with edges of the target region. By restricting the illuminable region 40 within the first and second edges of the patterning device MA, no part of the substrate W outside the target region receives radiation.

[0083] Although not shown in Figures 4A, 4B, 4E and 4F, in some embodiments, the first and second masking blade edges 27, 29 may be slightly separated so as to avoid collision between them, without admitting substantial radiation to the patterning device MA.

[0084] In some embodiments, the patterning device MA may comprise a patterning area (i.e. areas which generate the patterned EUV radiation beam B’) and a non-patterning area (e.g. markings for alignment). In such embodiments, references to the first and second patterning device edges 17,19 should be taken to mean edges of the patterning area of the patterning device MA.

[0085] Figure 5 and Figure 6 schematically illustrate an alternative embodiment of the masking module, masking module 200, viewed in the x and y directions respectively. Masking module 200 forms an apparatus of the general type described with reference to Figures 3-4F and like parts are labelled accordingly.

[0086] Masking module comprises a support 24, a first masking assembly 20 and a second masking assembly 22. Both the first and second masking assemblies 20, 22 are rotatable about the support 24.

[0087] The first masking assembly 20 comprises a first moveable masking blade 26 (itself comprising a first masking blade edge 27) and two first arms 230. The two first arms 230 extend from the first moveable masking blade 26 toward the support 24.

[0088] The second masking assembly 22 comprises a second moveable masking blade 28 (itself comprising a second masking blade edge 29) and two second arms 232. The two second arms 232 extend from the second moveable masking blade 28 toward the support 24.

[0089] Each of the first and second moveable masking blades 26, 28 are disposed adjacent to, but out of the plane of a patterning device MA on a patterning device support structure MT.

[0090] The first arms 230 and the second arms 232 are offset from each other in the x-direction in a nested manner as shown in Figure 6.

[0091] The first masking assembly 20 further comprises a first pair of air bearings 225, 226 which rotatably connect the first masking assembly 20 to the support 24.

[0092] The second masking assembly 22 further comprises a second pair of air bearings 225, 226 which rotatably connect the second masking assembly 22 to the support 24.

[0093] Masking module 200 of Figures 5 and 6 is distinguished from masking module 12 of Figure 3 in that the first moveable masking blade 26 and the second moveable masking blade 28 are moveable within a mutually non-overlapping first envelope of motion, indicated by locus 202, and a second envelope of motion, indicated by locus 204. The first and second moveable masking blades 26, 28 are disposed at different radial separations relative to the associated support 24. In the depicted embodiment, the first arms 230 are longer than the second arms 232 (the opposite configuration mayalso be used). In use, the first and second moveable masking blades 26,28 cannot collide as the first and second masking assemblies 20, 22 rotate within non-overlapping envelopes of motion.

[0094] The first and second pairs of air bearings 225, 226 are configured to enable rotation of the first and second masking assemblies 20, 22 relative to the support about an axis of rotation 201.

[0095] The masking module 200 further comprises a first linkage 206 and a second linkage 208.

[0096] The first linkage 206 connects the first masking assembly 20 with a first rotational actuator 210. The first rotational actuator 210 is disposed at a separation from the first masking assembly 20.

[0097] The second linkage 208 connects the second masking assembly 22 with a second rotational actuator 211. The second rotational actuator 211 is disposed at a separation from the second masking assembly 22.

[0098] The first linkage 206 is pivotally coupled to a first arm 230 of the first masking assembly 20.

[0099] The second linkage 208 is pivotally coupled to a second arm 232 of the second masking assembly.[000100] The first linkage 206 is pivotally and eccentrically coupled to the first rotational actuator 210. On rotational actuation of the first rotational actuator 210, the first masking assembly 20 rotates about the axis of rotation 201 so as to truncate the EUV radiation beam B.[000101] The second linkage 208 is pivotally and eccentrically coupled to the second rotational actuator 211. On rotational actuation of the second rotational actuator 211, the second masking assembly 22 rotates about the axis of rotation 201 so as to truncate the EUV radiation beam B. [000102] In some embodiments, the actuators may be linear actuators.[000103] In the embodiments described in relation to Figures 2-6, the first and second masking assemblies 20, 22 rotate relative to the support 24. As a result, the first and second masking blade edges 27, 29 also have a component of motion in the z direction. The component of motion in the z direction causes the first and second masking blade edges to move further out of the plane of the patterning device MA (which is a focal plane of lithographic apparatus LA) on the patterning device support structure MT. It may be desirable to minimise movement of the first and second masking blade edges 27, 29 out of the plane of the patterning device MA. The greater a radial separation separation between a moveable masking blade and the associated support, the smaller the movement out of the plane of the patterning device.[000104] In some embodiments the radial separation between the moveable masking blade and the associated support is at least 12cm.[000105] In some embodiments the radial separation between the moveable masking blade and the associated support may be limited by space constraints of the Lithographic apparatus LA.[000106] In some embodiments a radial separation between the moveable masking blade and the associated support is up to 13cm.[000107] In some embodiments, the actuators may be position-controlled motors.[000108] In some embodiments, the actuators may be linear actuators.[000109] In some embodiments, the masking assembly may weigh up to 5 kg.[000110] The embodiments described in relation to Figures 2-6 comprise multiple actuators, configured to rotate the arms of the masking assemblies such that the masking assemblies are independently rotatable. In an alternative, the masking module may comprise a common linkage configured to allow actuation of more than one masking assembly by a single actuator, wherein the positions of the masking assemblies are dependent on each other. In an example, the first and second masking assemblies may be fixed with respect to each other so the separation of the first and second moveable masking blades is fixed. At the beginning of an exposure, the common linkage may be configured to move the first and second moveable masking blade such that an edge of the illuminable region defined by the second moveable masking blade stays within the first patterning device edge. The common linkage may be further configured to then move the first and second moveable masking blades such that an edge of the illuminable region defined by the first moveable masking blade stays within the second patterning device edge. The first and second moveable masking blade may be configured to move continuously during an exposure. Between exposures, the EUV radiation beam may be blocked from the patterning device plane by the first or second moveable masking blade.[000111] The masking module 200 described with reference to Figures 5 and 6 comprises a first and second pair of air bearings 225, 226 which rotatably connect the first and second masking assemblies 20, 22 to the support 24. In an alternative, the masking assembly may comprise one or more flexures, configured to couple the masking assembly and the support. The flexures may comprise a portion of thinner, resilient material disposed between two thicker rigid ends, wherein one of the rigid ends is connected to the support and the other rigid end is connected to the one of the arms of the masking assembly. The thinner, resilient material can bend, enabling rotation of the masking assemblies relative to the support[000112] Although specific reference has been made herein to a masking module having two moveable masking blades, it should be understood that the invention is not limited thereto and may also be used with a single moveable masking blade or with more than two moveable masking blades. [000113] Although specific reference has been made herein to a masking module having moveable masking blades that are moveable in the scanning direction (y direction) and not moveable in the nonscanning direction (x direction), it should be understood that the invention is not limited thereto and may also be used with moveable masking blades that are moveable in the non-scanning direction (x direction) and not moveable in the scanning direction (y direction).[000114] Although specific reference has been made herein to moveable masking blades, it should be understood that the invention is not limited thereto and may also be used with moveable masking elements that are differently shaped.[000115] Although specific reference has been made herein to an EUV lithographic apparatus, it should be understood that embodiments of the invention may be used in deep ultraviolet (DUV) lithographic apparatus. DUV lithographic apparatus may use radiation with wavelengths of approximately 193 nm or 248 nm.[000116] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquidcrystal displays (LCDs), thin-film magnetic heads, etc.[000117] Although specific reference may be made in this text to embodiments of the invention in the context of a 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 mask (or other patterning device). These apparatus may be generally referred to as lithographic tools. Such a lithographic tool may use vacuum conditions or ambient (non- vacuum) conditions.[000118] Where the context allows, embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine -readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g. carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. and in doing that may cause actuators or other devices to interact with the physical world.[000119] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

CLAIMS1. A masking module for use in a lithographic apparatus, comprising a moveable masking blade configured to prevent part of a patterning device from being illuminated during operation of the lithographic apparatus, wherein the masking module is configured to rotate the moveable masking blade about an axis substantially parallel to a plane in which the patterning device is held in the lithographic apparatus.

2. The masking module of claim 1, further comprising a support; and a masking assembly, rotatable relative to the support, the masking assembly comprising: the moveable masking blade; and an arm, extending from the moveable masking blade; wherein the arm extends from the moveable masking blade in a first direction, and wherein the masking assembly is rotatable relative to the support such that the moveable masking blade has at least a component of motion in a second direction, generally perpendicular to the first direction.

3. The masking module of claim 2 wherein the masking assembly comprises one or more flexures, configured to flexibly couple the masking assembly and the support.

4. The masking module of claim 1 or claim 2 wherein the masking assembly comprises one or more air bearings, configured to enable rotation about an axis of rotation.

5. The masking module of any one of claims 2 to 4 wherein a further arm extends from the moveable masking blade in the first direction.

6. The masking module of any one of claims 2 to 5 wherein a radial separation between the moveable masking blade and the associated support is at least 12cm.

7. The masking module of any one of claims 2 to 6 wherein a radial separation between the moveable masking blade and the associated support is up to 13cm.

8. The masking module of any one of claims 2 to 7 wherein the masking assembly weighs up to 5 kg-9. The masking module of any one of claims 2 to 8 wherein the masking module comprises one or more actuators, configured to rotate the arm and / or the further arm.

10. The masking module of claim 9 wherein the one or more actuators are position-controlled motors.

11. The masking module of claim 9 or claim 10 wherein the masking module comprises one or more linkages, configured to connect the one or more actuators to the one or more arms.

12. The masking module of any one of claims 2 to 11 wherein the masking module comprises a further masking assembly, rotatable relative to the support, the further masking assembly comprising: a further moveable masking blade; and an arm, extending from the further moveable masking blade; wherein the arm extends from the further moveable masking blade in a third direction, and wherein the masking assembly is rotatable relative to the support such that the further moveable masking blade has at least a component of motion in a fourth direction, generally perpendicular to the third direction.

13. The masking module of claim 12 wherein the moveable masking blade and the further moveable masking blade are moveable within mutually non-overlapping envelopes of motion.

14. A lithographic apparatus comprising: an illumination system configured to condition a radiation beam; a patterning device support structure constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; and a projection system configured to project the patterned radiation beam onto the substrate; and the masking module of any one of the preceding claims, adjacent to the patterning device support structure.

15. The lithographic apparatus of claim 14 wherein the or each moveable masking blade is not moveable in a non-scanning direction of the lithographic apparatus.

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