CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application 19156434.3 which was filed on February 11, 2019 and which is incorporated herein in its entirety by reference.

FIELD

[0002] The present invention relates to a shielding apparatus, method, and a lithographic tool comprising said shielding apparatus. In particular, the shielding apparatus and method relate to a plasma and particulate debris shielding apparatus through which a fluid, such as a gas, may flow.

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] So-called “clean” regions of the lithographic apparatus may be kept substantially in vacuum, i.e. at a very low pressure, with a purging fluid (e.g. Hydrogen gas) used to keep critical components (e.g. optical components) clean. The EUV radiation may interact with the purging fluid and form a plasma in the clean regions. So-called “dirty” regions of the lithographic apparatus comprise parts and devices that generate debris, e.g. moveable components that generate particulates. Plasma should be prevented from reaching the dirty regions to avoid unwanted effects (e.g. damage to and/or outgassing from components). Debris should be prevented from reaching the clean regions to avoid unwanted effects (e.g. contamination of optical components).

[0006] It is known to arrange a shielding plate between a clean region and a dirty region. The known shielding plate reduces an amount of plasma travelling from the clean region to the dirty region and reduces an amount of debris travelling from the dirty region to the clean region. It is also known to provide a flow of purging fluid travelling from a clean region to a dirty region. The flow of purging fluid further reduces the amount of debris travelling from the dirty area to the clean area. The known shielding plate is however limited in practical use, because the known shielding plate may block and/or otherwise interfere with the flow of purging fluid. Similarly, the closed plate-like structure of the known shielding plate divides the regions into separate environments, which may be disadvantageous in certain applications. In general, the known shielding plate has a limited scope of applicability, and can introduce problems regarding the flow of purging fluid.

SUMMARY

[0007] It may be desirable to provide a lithographic apparatus which addresses the problem identified above or some other problem associated with the prior art. In particular, a shielding apparatus with a larger scope of applicability may be desirable.

[0008] According to an aspect of the present disclosure, there is provided a lithographic tool comprising a first region comprising a first component, a second region comprising a second component, and a shielding apparatus arranged between the first region and the second region. The shielding apparatus is configured to reduce transfer of a contaminant between the first and second regions. The shielding apparatus comprises a fluid flow path between the first and second regions. [0009] The contaminant may comprise particulate debris. The shielding apparatus may be configured to at least partially block the particulate debris.

[00010] The contaminant may comprise plasma. The shielding apparatus may be configured to at least partially block the plasma.

[00011] The shielding apparatus may be configured to protect the first component from a contaminant originating from the second region. The shielding apparatus may be configured to protect the second component from a contaminant originating from the first region.

[00012] The contaminant originating from the second region may comprise particulate debris. The contaminant originating from the first region may comprise plasma. The shielding apparatus may be configured to at least partially block both the particulate debris and the plasma.

[00013] The shielding apparatus may be arranged such that the fluid flow path meanders through the shielding apparatus.

[00014] The shielding apparatus may be electrically grounded.

[00015] The shielding apparatus may comprise a first row of shielding elements separated by a first series of gaps adj acent the first region. The shielding apparatus may comprise a second row of shielding elements separated by a second series of gaps adjacent the second region. The first and second rows of shielding elements may be arranged such that a contaminant pathway through the second series of gaps is at least partially blocked by the first row of shielding elements.

[00016] The first and second rows of shielding elements may be arranged such that a contaminant pathway through the first series of gaps is at least partially blocked by the second row of shielding elements.

[00017] The shielding apparatus may comprise a plurality of at least partially overlapping shielding elements. [00018] The plurality of at least partially overlapping shielding elements may comprise a row of diagonally oriented plates forming a shutter blind arrangement. The plurality of at least partially overlapping shielding elements may comprise a row of chevron structures.

[00019] The shielding apparatus may comprise a first perforated plate adjacent the first region. The shielding apparatus may comprise a second perforated plate adjacent the second region. Perforations of the first and second plates may be arranged such that a contaminant pathway through the perforations of the second plate is at least partially blocked by the first plate.

[00020] Perforations of the first and second plates may be arranged such that a contaminant pathway through the perforations of the first plate is at least partially blocked by the second plate.

[00021] According to another aspect of the present disclosure, there is provided a lithographic apparatus arranged to project a pattern from a patterning device onto a substrate. The lithographic apparatus comprises the lithographic tool of the present disclosure. The first region comprises a radiation beam. The first component is configured to interact with the radiation beam.

[00022] The second region may comprise an actuation system. The second component may form part of the actuation system.

[00023] The second region may comprise a housing configured to house the actuation system. An exhaust outlet may be provided in the housing.

[00024] According to another aspect of the present disclosure, there is provided a method comprising locating a first component in a first region of a lithographic tool, locating a second component in a second region of the lithographic tool and arranging a shielding apparatus between the first region and the second region. The method comprises using the shielding apparatus to reduce transfer of a contaminant between the first and second regions. The method comprises providing a fluid flow path between the first and second regions through the shielding apparatus.

[00025] The contaminant may comprise particulate debris. The method may comprise using the shielding apparatus to at least partially block the particulate debris.

[00026] The contaminant may comprise plasma. The method may comprise using the shielding apparatus to at least partially block the plasma.

[00027] The method may comprise using the shielding apparatus to protect the first component from a contaminant originating from the second region. The method may comprise using the shielding apparatus to protect the second component from a contaminant originating from the first region. [00028] The first contaminant may comprise particulate debris. The second contaminant may comprise plasma. The method may comprise using the shielding apparatus to at least partially block both the particulate debris and the plasma.

[00029] The method may comprise arranging the shielding apparatus such that the fluid flow path meanders through the shielding apparatus.

[00030] The method may comprise electrically grounding the shielding apparatus. [00031] The method may comprise projecting a pattern from a patterning device onto a substrate. The method may comprise locating a radiation beam in the first region. The method my comprise using the first component to interact with the radiation beam.

[00032] The method may comprise locating an actuation system in the second region. The second component may form part of the actuation system.

[00033] Features described in the context of one aspect or embodiment described above may be used with others of the aspects or embodiments described above.

BRIEF DESCRIPTION OF THE DRAWINGS

[00034] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

Fig. 1 schematically depicts a lithographic system comprising a lithographic apparatus, a radiation source and a shielding apparatus in accordance with the present disclosure.

Fig. 2 A schematically depicts a view from above a lithographic tool comprising a shielding apparatus according to an embodiment of the present disclosure.

Fig. 2B schematically depicts a perspective view from the side of the lithographic tool of Fig. 2 A.

Fig. 3 schematically depicts a view from above a lithographic tool comprising a first example shielding apparatus according to an embodiment of the present disclosure.

Fig. 4 schematically depicts a view from above a lithographic tool comprising a second example shielding apparatus according to an embodiment of the present disclosure.

Fig. 5 schematically depicts a perspective view from the side of a lithographic tool comprising a third example shielding apparatus according to an embodiment of the present disclosure.

Fig. 6 shows a flowchart of a method according to the present disclosure.

DETAIFED DESCRIPTION

[00035] Fig. 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 FA. The lithographic apparatus FA comprises an illumination system IF, a support structure MT configured to support a patterning device MA (e.g., a mask), a projection system PS and a substrate table WT configured to support a substrate W.

[00036] The illumination system IF 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 IF 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 illumination system IF may include other mirrors or devices in addition to, or instead of, the faceted field mirror device 10 and faceted pupil mirror device 11.

[00037] After being thus conditioned, the EUV radiation beam B interacts with the patterning device MA. 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 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 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 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 Fig. 1, the projection system PS may include a different number of mirrors (e.g., six or eight mirrors).

[00038] 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.

[00039] 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.

[00040] The radiation source SO shown in Fig. 1 is, for example, of a type which may be referred to as a laser produced plasma (LPP) source. A laser system 1, which may, for example, include a CO2 laser, is arranged to deposit energy via a laser beam 2 into a fuel, such as tin (Sn) which is provided from, e.g., a fuel emitter 3. Although tin is referred to 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 alloy. The fuel emitter 3 may comprise a nozzle configured to direct tin, e.g. in the form of droplets, along a trajectory towards a plasma formation region 4. The laser beam 2 is incident upon the tin at the plasma formation region 4. The deposition of laser energy into the tin creates a tin plasma 7 at the plasma formation region 4. Radiation, including EUV radiation, is emitted from the plasma 7 during de excitation and recombination of electrons with ions of the plasma.

[00041] The EUV radiation from the plasma is collected and focused by a collector 5. The collector 5 comprises, for example, a near-normal incidence radiation collector 5 (sometimes referred to more generally as a normal-incidence radiation collector). The collector 5 may have a multilayer mirror structure that is arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm). The collector 5 may have an ellipsoidal configuration, having two focal points. A first one of the focal points may be at the plasma formation region 4, and a second one of the focal points may be at an intermediate focus 6, as discussed below.

[00042] The laser system 1 may be spatially separated from the radiation source SO. Where this is the case, the laser beam 2 may be passed from the laser system 1 to the radiation source SO with the aid of a beam delivery system (not shown) comprising, for example, suitable directing mirrors and/or a beam expander, and or other optics. The laser system 1, the radiation source SO and the beam delivery system may together be considered to be a radiation system.

[00043] Radiation that is reflected by the collector 5 forms the EUV radiation beam B. The EUV radiation beam B is focused at intermediate focus 6 to form an image at the intermediate focus 6 of the plasma present at the plasma formation region 4. The image at the intermediate focus 6 acts as a virtual radiation source for the illumination system IL. The radiation source SO is arranged such that the intermediate focus 6 is located at or near to an opening 8 in an enclosing structure 9 of the radiation source SO.

[00044] Although Fig. 1 depicts the radiation source SO as a laser produced plasma (LPP) source, any suitable source such as a discharge produced plasma (DPP) source or a free electron laser (FEL) may be used to generate EUV radiation.

[00045] As previously discussed, 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. The gas may be provided to keep debris-sensitive components clean. Debris-sensitive components may comprise components that interact with the EUV radiation B, B’ propagating through the lithographic apparatus LA. EUV radiation propagating through the lithographic apparatus LA may interact with the gas and produce a plasma.

[00046] The lithographic apparatus LA may be understood as having one or more regions, comprising one or more debris-sensitive components, in which plasma originates. Such regions may be referred to as “clean” regions. Examples of said debris-sensitive components include mirrors 10, 11, 13, 14, the reticle MA and the substrate W. If debris, such as particulate matter, reaches a debris- sensitive component, the lithographic process could be negatively affected. For example, a reflectivity of one or more mirrors 10, 11, 13, 14 may be reduced, particulate debris on the reticle MA may negatively affect a pattern of the patterned radiation beam B’, particulate debris on the substrate W may negatively affect a pattern formed on the photoresist of the substrate W, etc. It is therefore important to protect debris-sensitive components from particulate debris originating from other, less clean regions. [00047] The lithographic apparatus LA comprises one or more regions in which particulate debris originates. These regions are typically found outside of a light path of the EUV radiation B, B’, and tend to house non-optical components such as cables and actuation systems (e.g. motors). An example of such a component is a reticle actuation system 50. The reticle actuation system 50 may comprise one or more motors configured to move the support structure MT, and the reticle, MA with respect to the radiation beam B. The actuation system 50 may be housed in a housing 60. Such components do not need to be kept as clean as critical optical components as they do not interact with the EUV radiation B, B’ . For example, when actuation systems generate movement of one or more parts of the lithographic apparatus LA, said actuation systems may generate particulate debris through frictional forces. These regions may therefore be referred to as “dirty” regions when compared to the “clean” regions. Whilst these components are substantially insensitive to particulate debris, they may be plasma-sensitive. For example, components such as cables and actuation systems may become damaged by plasma and/or begin outgassing because of an interaction with plasma. It is therefore important to protect plasma- sensitive components from plasma originating from, for example, the “clean” regions discussed above. A shielding apparatus 100 according to an embodiment of the invention may be used to reduce transfer of a contaminant between the “clean” and “dirty” regions. Example of such shielding apparatus 100 are shown and described with respect to Figs. 2A-5.

[00048] It is known to arrange a shielding plate between a clean region and a dirty region. The known shielding plate reduces an amount of plasma travelling from the clean region to the dirty region and reduces an amount of debris travelling from the dirty region to the clean region. It is also known to provide a flow of purging fluid travelling from a clean region to a dirty region. The flow of purging fluid further reduces the amount of particulate debris travelling from the dirty region to the clean region. The flow of purging fluid may be provided in normal use and or during special cleaning procedures. The provision of purging fluid from a clean region to a dirty region may be referred to as common flow. If purging fluid ever flows from the dirty region to the clean region, this is known as a common flow violation. Common flow violations transfer particulate debris from the dirty regions to the clean regions and therefore must be minimized or entirely avoided.

[00049] Fig. 2 A schematically depicts a view from above a lithographic tool 200 according to an embodiment of the present disclosure. Fig. 2B schematically depicts a perspective view from the side of the lithographic tool 200 of Fig. 2A. The lithographic tool 200 comprises a first region 210 comprising a debris-sensitive component 215. In the example of Fig. 2A, the first region 210 corresponds to a reticle environment and the debris-sensitive component 215 may be, for example, the patterning device (i.e. reticle MA) of Fig. 1. The lithographic tool 200 comprises a second region 220 comprising a plasma-sensitive component 225. In the example of Fig. 2 A, the second region 220 corresponds to an actuation system environment and the plasma-sensitive component 225 is an actuation system. The actuation system may be, for example, the reticle actuation system 50 of Fig. 1. The lithographic tool 200 comprises a shielding apparatus 230 arranged between the first region 210 and the second region 220. The shielding apparatus 230 is configured to reduce transfer of a contaminant between the first and second regions. In the example of Figs. 2A and 2B, the shielding apparatus 230 is configured to protect the debris-sensitive component 215 from debris (e.g. ballistic particles) originating from the second region 220, and to protect the plasma- sensitive component 225 from plasma originating from the first region 210. The shielding apparatus 230 comprises a fluid flow path 240 from the first region 210 to the second region 220. In the example of Fig. 2A there are a plurality of fluid flow paths from the first region 210 to the second region 220. The fluid flow path 240 meanders through the shielding apparatus 230 such that debris travelling from the second region 220 to the first region 215 is at least partially blocked by the shielding apparatus 230, and plasma travelling from the first region 210 to the second region 220 is at least partially blocked by the shielding apparatus 230. The plasma comprises ions and electrons. The plasma may be formed from Hydrogen gas after an interaction with EUV light. The shielding apparatus 230 is electrically grounded. Electrically grounding the shielding apparatus 230 allows plasma and/or any electric charge that gathers on the shielding apparatus 230 to be removed. Preferably, the shielding apparatus 230 is formed from metal for effective plasma shielding. The shielding apparatus 230 may be formed of, for example, aluminum or stainless steel.

[00050] In the example of Fig. 2A the shielding apparatus 230 comprises a first row 250 of shielding elements 252 separated by a first series of gaps 254 adjacent the first region 210. The shielding apparatus 230 further comprises a second row 260 of shielding elements 262 separated by a second series of gaps 264 adjacent the second region 220. The first and second rows 250, 260 of shielding elements 252, 262 are arranged such that a contaminant pathway through the second series of gaps 264 is at least partially blocked by the first row 250 of shielding elements 252, and a contaminant pathway through the first series of gaps 254 is at least partially blocked by the second row 260 of shielding elements 262. That is, the first and second rows 250, 260 of shielding elements 252, 262 are configured to block at least some contaminants from travelling between the first and second regions 210, 220. In the example of Figs. 2A and 2B, the first and second rows 250, 260 of shielding elements 252, 262 are arranged such that particulate debris travelling through the second series of gaps 264 is at least partially blocked by the first row 250 of shielding elements 252, and plasma travelling through the first series of gaps 254 is at least partially blocked by the second row 260 of shielding elements 262.

[00051] In the example of Fig. 2A and Fig. 2B, the shielding apparatus 230 further comprises a third row 270 of shielding elements 272 separated by a third series of gaps 274 adjacent the second region 220. The third row of shielding elements 272 may act as a first line of defense against a contaminant travelling from the second region 220 to the first region 210 and a final line of defense against a contaminant travelling from the first region 210 to the second region 220. The first row 250 of shielding elements 252 may act as a first line of defense against a contaminant travelling from the first region 210 to the second region 220 and a final line of defense against a contaminant travelling from the second region 220 to the first region 210. The second row 260 of shielding elements 262 may act as a second line of defense against contaminants travelling between the first and second regions 210, 220. The shielding apparatus 230 may comprise a greater or lesser number of rows 250, 260, 270 of shielding elements 252, 262, 272.

[00052] In the example of Fig. 2A and Fig. 2B, the shielding elements 252, 262 are substantially identical. Each shielding element 252, 262 may have a width of less than about 1 meter. Each shielding element 252, 262 may have a width of about 100 mm or less. Each shielding element 252, 262 may have a width of about 10 mm or more. Each shielding element 252, 262 may have a width of about 30 mm. Each shielding element 252, 262 may have a thickness of about 1 mm or more. Each shielding element 252, 262 may have a thickness of about 10 mm or less. Alternatively, the shielding elements 252, 262 may have different shapes and or sizes. In the example of Fig. 2A and Fig. 2B, the gaps 254, 264 are substantially identical. Each gap 254, 264 may have a width that is equal to or greater than about 30% of the width of the shielding elements 252, 262. Each gap 254, 264 may have a width that is equal to or less than about 90% of the width of the shielding elements 252, 262. Each gap 254, 264 may have a width of about 20 mm. Alternatively, the gaps 254, 264 may have different shapes and/or sizes.

[00053] The rows of shielding elements 250, 260, 270 are arranged to allow a flow of fluid along a fluid flow path 240 from the first region 210 to the second region 220. The fluid may comprise purging gas configured to remove particulate debris from the lithographic tool 200. The second region 220 may comprise an exhaust outlet 290 configured to allow the fluid to exit the lithographic tool 200. A size and or number of the gaps 254, 264, 274 between the shielding elements 252, 262, 272 may at least partially determine an ease with which fluid may flow from the first region 210 to the second region 220 along the fluid flow path 240. Increasing the size and or number of the gaps 254, 264, 274 between the shielding elements 252, 262, 272 may enable a greater rate of fluid flow through the shielding apparatus 230. A separation 280 between adjacent rows 250, 260, 270 of shielding elements 252, 262, 272 may at least partially determine an ease with which fluid may flow from the first region 210 to the second region 220. Increasing the separation 280 between adjacent rows 250, 260, 270 of shielding elements 252, 262, 272 may enable a greater rate of fluid flow through the shielding apparatus 230. Increasing the rate of fluid flow through the shielding apparatus 230 may decrease a risk of contaminants (e.g. particulate debris) being incident on critical components (e.g. the reticle MA). The separation 280 between adjacent rows 250, 260, 270 of shielding elements 252, 262, 272 may be substantially equal to the width of the gaps 254, 264, 274 between the shielding elements 252, 262, 272. The separation 280 between adjacent rows 250, 260, 270 of shielding elements 252, 262, 272 may be equal to or greater than about 30% of the width of the shielding elements 252, 262, 272. The separation 280 between adjacent rows 250, 260, 270 of shielding elements 252, 262, 272 may be equal to or less than about 90% of the width of the shielding elements 252, 262, 274.

[00054] It will be appreciated that the shielding apparatus 230 may take other forms. Fig. 3 schematically depicts a view from above a lithographic tool 300 comprising a first example shielding apparatus 330 according to an embodiment of the present disclosure. The shielding apparatus 330 comprises a plurality of at least partially overlapping shielding elements 352. In the example of Fig. 3, the plurality of at least partially overlapping shielding elements comprises a row 350 of diagonally oriented plates 352 forming a shutter blind arrangement. In the example of Fig. 3, the plates 352 are substantially identical. Each plate 352 may have a width of about 10 mm or more. Each plate 352 may have a width of about 100 mm or less. Each plate 352 may have a thickness of about 1 mm or more. Each plate 352 may have a thickness of about 10 mm or less. Alternatively, the plates 352 may have different shapes and/or sizes. The plates 352 may be arranged such that about 10% or more of the width of each plate 352 overlaps the width of an adjacent plate 352. The plates 352 may be arranged such that about 90% or less of the width of each plate 352 overlaps the width of an adjacent plate 352. A separation between each plate 352 may be, for example, about 20 mm.

[00055] Fig. 4 schematically depicts a view from above a lithographic tool 400 comprising a second example shielding apparatus 430 according to an embodiment of the present disclosure. The shielding apparatus 430 comprises a plurality of at least partially overlapping shielding elements 452. In the example of Fig. 4, the plurality of at least partially overlapping shielding elements comprises a row 450 of chevron structures 452. In the example of Fig. 4, the chevron structures 452 are substantially identical. Each chevron structure 452 may have a width of about 10 mm or more. Each chevron structure 452 may have a width of about 100 mm or less. Each chevron structure 452 may have a thickness of about 1 mm or more. Each chevron structure 452 may have a thickness of about 10 mm or less. Alternatively, the chevron structures 452 may have different shapes and/or sizes. The chevron structures 452 may be arranged such that about 10% or more of the width of each chevron structure 452 overlaps the width of an adjacent chevron structure 452. The chevron structures 452 may be arranged such that about 90% or less of the width of each chevron structure 452 overlaps the width of an adjacent chevron structure 452. A separation between each chevron structure 452 may be, for example, about 20 mm. Each chevron structure 452 comprises two arms. An angle between the two arms may be about 30° or more. The angle between the two arms may be about 150° or less. The angle between the two arms may be, for example, about 90°.

[00056] Fig. 5 schematically depicts a perspective view from the side of a lithographic tool 500 comprising a third example shielding apparatus 530 according to an embodiment of the present disclosure. In the example of Fig. 5, the shielding apparatus 530 comprises a first perforated plate 510 adjacent the first region 210. The shielding apparatus 530 further comprises a second perforated plate 520 adjacent the second region 220. Perforations of the first and second plates 520, 520 are arranged such that a contaminant pathway through the perforations of the second plate 520 is at least partially blocked by the first plate 510, and a contaminant pathway through the perforations of the first plate 510 is at least partially blocked by the second plate 520. In the example of Fig. 5, perforations 515, 525 of the first and second plates 510, 520 are arranged such that particulate debris travelling through the perforations 525 of the second plate 520 is at least partially blocked by the first plate 510, and plasma travelling through the perforations 515 of the first plate 510 is at least partially blocked by the second plate 520. In the example of Fig. 5, the perforations 515, 525 are substantially identical. Each perforation 515, 525 may have a diameter of about 10 mm or more. Each perforation 515, 525 may have a diameter of about 100 mm or less. Each plate 510, 520 may have a thickness of about 1 mm or more. Each plate 510, 520 may have a thickness of about 10 mm or less. Alternatively, the perforations 515, 525 and/or plates 510, 520 may have different shapes and or sizes. A separation between adjacent perforations 515, 525 (i.e. a pitch of the perforations 515, 525) may be about two-and-a-half times greater than a diameter of the perforations 515, 525. A separation between adjacent perforations 515, 525 (i.e. a pitch of the perforations 515, 525) may be about ten times greater than a diameter of the perforations 515, 525. A closed area of each plate 510, 520 may be about two-and-a-half times greater than an open area of each plate 510, 520. A closed area of each plate 510, 520 may be about ten times greater than an open area of each plate 510, 520.

[00057] In all of the examples shown in Figs. 2A-5, the shielding apparatus are arranged such that lines of sight from angles of interest are blocked. Referring again to Fig. 3, a complete field of view 360 covering all possible angles of incidence 370-372 from one region 210 to the other region 220 may be considered to be 180° across any given plane when facing the shielding apparatus 330. In the example of Fig. 3, only three example angles of incidence 370-372 are shown, but others exist. It will be appreciated that the complete field of view 360, and the blocking action of the shielding apparatus 330, applies to all of Figs. 2A-5. The shielding apparatus 330 may be configured to block contaminants travelling along about 90% of all possible angles of incidence 370-372. In the example of a field of view that is 180°, the shielding apparatus 330 may be configured to block contaminants having an angle of incidence of about 10° or more. In the example of a field of view that is 180°, the shielding apparatus may be configured to block contaminants having an angle of incidence of about 160° or less.

[00058] Any of the lithographic tools of Figs 2-5 may form part of the lithographic apparatus LA of Fig. 1. The first region 210 may comprise a radiation beam B, B’ . The debris- sensitive component may be configured to interact with the radiation beam B, B’. For example, the debris-sensitive component may comprise a mirror, 10, 11, 13, 14, the patterning device MA, the substrate W, etc. The second region may comprise an actuation system and the plasma-sensitive component may form part of the actuation system.

[00059] An example of an area of the lithographic apparatus LA that may use both a shielding apparatus and a flow of purging fluid is the reticle environment. A first region in the reticle environment comprises the reticle MA itself. As previously discussed, the reticle MA may be considered a debris- sensitive component. EUV radiation and purging gas present in the first region may give rise to plasma. As such, the first region is a region in which plasma may originate. The first region may be considered a clean region.

[00060] A second region in the reticle area comprises an actuation system configured to control reticle masking blades (not shown) which define the extent of the field on the reticle MA which is illuminated. The illumination system IL is operable to illuminate a region of the reticle MA when disposed on the support structure MT. This region may be referred to as the slit of the illumination system IL, and is at least partially defined by a plurality of reticle masking blades (e.g. four reticle masking blades) which define a generally rectangular region of the reticle MA which can receive radiation. Each of the masking blades is disposed close to, but slightly out of the plane of the reticle MA on the support structure MT. Each of the masking blades defines one edge of a rectangular field region in the plane of the patterning device MA that can receive radiation. Each blade may be independently movable between a retracted position wherein it is not disposed in the path of the radiation beam and an inserted position wherein it at least partially blocks the radiation beam projected onto the reticle MA by the illumination system IL. By moving the masking blades into the path of the radiation beam, the radiation beam B can be truncated (in the x and/or y direction) thus limiting the extent of the field region which receives radiation beam B. The actuation system that is configured to move the reticle masking blades may be considered to be a plasma-sensitive component because the actuation system may become damaged by plasma. Movement of the actuation system in the second region may give rise to debris (e.g. particulates). As such, the second region is a region in which debris may originate. The second region may be considered a “dirty” region. The actuation system may be located in the second region (i.e. the “dirty” region). At least a portion of the reticle masking blades may extend into the first region (i.e. the “clean” region) to interact with the radiation beam B.

[00061] A known shielding plate may be provided between the first region (comprising the debris- sensitive reticle MA) and the second region (comprising the plasma-sensitive actuation system) to protect both the reticle MA and the actuation system. Common flow may be provided from the first region to the second region to further protect the reticle MA from debris originating from the actuation system in the second region.

[00062] During normal operation of the lithographic apparatus LA pressures in the first and second regions fluctuate at least in part due to the movement of the reticle masking blades. In some instances, the pressure in the first region may temporarily drop lower than the pressure in the second region, causing purging fluid to flow from the second (“dirty”) region to the first (“clean”) region and thereby resulting in a common flow violation. Debris originating from the movement of the actuation system may be incident on the reticle MA resulting in reticle contamination that negatively affects the lithographic process. During cleaning and or maintenance operations, the pressure in the first region may experience greater fluctuations due to a stronger flow of purging fluid, which in turn may increase a risk of common flow violations. A fluid flow path (such as an exhaust) may be provided between the second region and a third region (e.g. another dirty region) having a lower pressure than the second region to reduce the risk of common flow violations taking place. That is, particulate debris generated by movement of the actuation system may travel from the second region to the third region via the fluid flow path. However, the closed structure of the known shielding plate may block or otherwise interfere with the common flow from the first region to the third region via the second region, leading to common flow violations.

[00063] The shielding apparatus of any of Figs. 2-5 may be incorporated into the reticle environment. The fluid flow enabled by the shielding apparatus of the present disclosure may advantageously enable an exhaust function (e.g. exhaust outlet 290) to be utilized in the reticle environment, while maintaining debris shielding and plasma shielding functions. An improved exhaust function enabled by the shielding apparatus of the present disclosure also allows the exhaust flow to be increased compared to known systems. This advantageously improves purging gas flow (thereby increasing purging efficiency) without having to increase a pressure difference between the regions. [00064] The shielding apparatus of the present disclosure may enable further modifications to further improve common flow. For example, holes may be formed in a housing (e.g. housing 60) that houses the actuation system (e.g. actuation system 50). The shielding apparatus of the present disclosure enables better outflow from the housing when performing cleaning and/or maintenance procedures (e.g. pump-down/flushing) and improved common flow from the first “clean” region to the second “dirty” region. This advantageously enables the volume of gas in a region to be replaced in a shorter amount of time. That is, a volume of fluid in a region of interest is replaced or “refreshed” in a shorter period of time compared to known systems. This may be known as “refreshment”. Increasing the refreshment of a region reduces the amount of time that a contaminant may be present in the region, thereby reducing a risk of a component becoming contaminated. Providing holes in the housing may enable better common flow through the second region during lithographic processes (which significantly improves the cleanliness of the clean area), and better outflow during maintenance purging processes (thereby reducing the risk of common flow violations).

[00065] The above discussion of locating the shielding apparatus between the reticle masking blade actuation system and the reticle MA is merely an example. With reference to Fig. 1, it will be appreciated that the shielding apparatus 100 of the present disclosure may be located in one or more alternative areas of the lithographic apparatus LA. For example, a support structure actuation system 50 may be used to move the support structure MT, and the reticle MA, with respect to the radiation beam B. The support structure actuation system 50 may comprise a short stroke module for fine movements and a long stroke module for coarse movements. The support structure actuation system 50 may be sensitive to plasma. Movement of the support structure actuation system 50 may generate debris. A shielding apparatus 100 according to the present disclosure may be located between the support structure actuation system 50 and the reticle MA and/or optics IL, PS configured to interact with the radiation beam B, B’ . As another example, a shielding apparatus 100 according to the present disclosure may be located between the illumination system IL and the reticle MA and/or optics configured to interact with the radiation B, B’ (e.g. along an upper surface of the illumination system IL). The illumination system IL may include a uniformity correction system (not shown), which is configured to correct or reduce non-uniformities, e.g., intensity non-uniformities, present in the radiation beam B. The uniformity correction system may comprise a uniformity actuation system (not shown) configured to insert one or more fingers into an edge of a radiation beam B to correct intensity variations. The uniformity correction system may be sensitive to plasma. Movement of the uniformity actuation system may generate debris. As another example, a shielding apparatus 100 according to the present disclosure may be located between the uniformity actuation system and the reticle MA and or optics configured to interact with the radiation beam B, B’.

[00066] As another example, a shielding apparatus 100 according to the present disclosure may be located between the projection system PS and the reticle MA and or optics configured to interact with the radiation beam B, B’ (e.g. along an upper surface of the projection system PS). The lithographic apparatus LA may comprise a reticle exchange device (not shown). The reticle exchange device may comprise a reticle actuation system (not shown), such as a robotic arm, that is configured to collect a reticle MA from a reticle store (not shown) and move the reticle MA to the support structure MT. The reticle actuation system may be sensitive to plasma. Movement of the reticle actuation system may generate debris. As another example, a shielding apparatus 100 according to the present disclosure may be located between the reticle actuation system and the reticle MA and/or optics IL, PS configured to interact with the radiation beam B, B’. The lithographic apparatus LA may comprise a substrate actuation system (not shown) configured to move the substrate table WT, and the substrate W, with respect to the radiation beam B’ . The substrate actuation system may be sensitive to plasma. Movement of the substrate actuation system may generate debris. As another example, a shielding apparatus 100 according to the present disclosure may be located between the substrate actuation system and the substrate W and/or optics IL, PS configured to interact with the radiation beam B’.

[00067] Any area of the lithographic apparatus LA that includes the radiation beam B (i.e. a “light” area) and an opening towards another area that does not include the radiation beam B (i.e. a “dark” area) could benefit from the advantages provided by the shielding apparatus 100 of the present disclosure. As light areas tend to contain debris-sensitive components (e.g. optics) and dark areas tend to contain plasma-sensitive components (e.g. actuation systems and/or cables), it is desirable to reduce debris and or plasma transfer between the light and dark areas. Purging fluid flow from light areas to dark areas to maintain clean optics is able to flow through the shielding apparatus 100 of the present disclosure, thereby improving a cleanliness of the lithographic apparatus LA. Any module having moving parts and/or intricate internal structure close to plasma-sensitive and/or debris-sensitive components may benefit from the protection provided by the shielding apparatus 100 of the present disclosure.

[00068] Fig. 6 shows a flowchart of a method according to the present disclosure. The method comprises a first step 400 of locating a first component in a first region of a lithographic tool. The method comprises a second step 410 of locating a second component in a second region of the lithographic tool. The method comprises a third step 420 of arranging a shielding apparatus between the first region and the second region. The method comprises a fourth step 430 of using the shielding apparatus to reduce transfer of a contaminant between the first and second regions. The method comprises a fifth step 440 of providing a fluid flow path between the first and second regions through the shielding apparatus.

[00069] The contaminant may comprise particulate debris or plasma. The method may comprise an optional step of using the shielding apparatus to protect the first component from a contaminant originating from the second region. The method may comprise an optional step of using the shielding apparatus to protect the second component from a contaminant originating from the first region. The method may comprise an optional step of arranging the fluid flow path to meander through the shielding apparatus. The method may comprise an optional step of electrically grounding the shielding apparatus. [00070] The method may comprise an optional step of projecting a pattern from a patterning device onto a substrate. The method may comprise an optional step of locating a radiation beam in the first region. The method may comprise an optional step of using the first component to interact with the radiation beam. The method may comprise an optional step of locating an actuation system in the second region. The second component may form part of the actuation system.

[00071] 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, liquid- crystal displays (LCDs), thin-film magnetic heads, etc.

[00072] 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.

[00073] Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention, where the context allows, is not limited to optical lithography and may be used in other applications, for example imprint lithography.

[00074] 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.

[00075] 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.