Chamber erosion byproduct filter

Abstract

A lithographic apparatus includes a chamber that produces radiation. The chamber includes an internal wall having a surface facing into the chamber and a filter attached to the surface of the internal wall of the chamber. The filter includes a plurality of screens stacked on top of one another along a stacking direction that is perpendicular to the surface of the internal wall of the chamber on which the filter is disposed. The plurality of screens include a central region and an edge region surrounding the central region. A first separation between the central region and the surface of the internal wall of the chamber along the stacking direction is greater than a second separation between the edge region and the surface of the internal wall of the chamber along the stacking direction.

Description

CHAMBER EROSION BYPRODUCT FILTERCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 614,948 which was filed on 27 December 2023 and which is incorporated herein in its entirety by reference.TECHNICAL FIELD

[0002] This disclosure relates to reducing a discharge byproduct in a discharge chamber, in particular to filtering an electrode erosion byproduct from a radiation discharge chamber.BACKGROUND

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which can be a mask or a reticle, can be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiationsensitive material (photoresist or simply “resist”) provided on the substrate. Light commonly used in the transfer process includes Deep Ultraviolet (DUV) or Extreme Ultraviolent (EUV) light.

[0004] To expose the pattern, a lithographic apparatus employs one or more sources of light. In some cases, the light may be created using a discharge chamber, in which light for the lithographic apparatus is generated by discharging an electric voltage from one electrode to another through a process gas. Generating certain types of light, for example, DUV light, requires using highly reactive process gases that include halogen or other corrosive gases. The combination of the high electric voltage and reactive process gases leads, in some cases, to electrodes that experience erosion. As one example, brass electrodes may react with fluorine gas, particularly under high electric voltage, to form C11F2 and ZnF2byproduct dust, respectively. Of course, other metal halide byproduct dusts are formed based on the particular electrode materials and process gases used in the specific discharge process.

[0005] Accumulation of such byproduct dusts in a discharge chamber presents a hazard to the longevity of the chamber, and thus existing discharge chambers may implement methods for removing byproduct dust from the chamber. In some cases, filters may be used to remove the byproduct dust(s) from the environment inside the chamber. However, existing filter configurations suffer from uneven byproduct dust accumulation, leading to a shortened lifetime and reduced trapping efficiency of the filter, resulting in a shortened operational lifespan of the discharge chamber. Accordingly, there exists a need for an improved method of removing byproduct dust(s) from a discharge chamber.SUMMARY

[0006] According to some aspects, a lithographic apparatus may comprise a chamber configured to produce radiation and comprising an internal wall having a surface facing into the chamber. A filter may be attached to the surface of the internal wall of the chamber and comprise a plurality of screens stacked on top of one another along a stacking direction that is perpendicular to the surface of the internal wall of the chamber on which the filter is disposed. The plurality of screens may include a central region and an edge region surrounding the central region. A first separation between the central region and the surface of the internal wall of the chamber along the stacking direction may be greater than a second separation between the edge region and the surface of the internal wall of the chamber along the stacking direction.

[0007] According to some aspects, a filter may comprise a plurality of screens. The plurality of screens may comprise a bottom screen configured to be disposed closest to a surface of an internal wall of a chamber of a lithographic apparatus along a stacking direction that is perpendicular to the surface, a top screen configured to be disposed away from the surface of the internal wall of the chamber along the stacking direction, and at least one intermediate screen disposed between the bottom screen and the top screen along the stacking direction. The plurality of screens may comprise a central region and an edge region surrounding the central region. A first separation between the central region of the plurality of screens from the surface of the internal wall of the chamber along the stacking direction may be configured to be greater than a second separation between the edge region of the plurality of screens from the surface of the internal wall of the chamber along the stacking direction.

[0008] According to some aspects, a method may comprise attaching a filter comprising a plurality of screens to a surface of an internal wall of a chamber, the plurality of screens being stacked on top of one another along a stacking direction that is perpendicular to the surface of the internal wall of the chamber. The plurality of screens may comprise a central region and an edge region surrounding the central region. The edge region may be attached to the surface of the internal wall of the chamber with a first fastener. The central region may be attached to the surface of the internal wall of the chamber with a second fastener having a height greater than the a height of the first fastener. A separation between the central region of the plurality of screens from the surface of the internal wall of the chamber along the stacking direction may be greater than a separation between the edge region of the plurality of filters from the surface of the internal wall of the chamber along the stacking direction.

[0009] Implementations of any of the techniques described above may include an EUV or DUV light source, a system, a method, a process, a device, or an apparatus. The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.DESCRIPTION OF THE DRAWINGS

[0010] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable those skilled in the relevant art(s) to make and use aspects described herein.

[0011] FIG. 1 shows a reflective lithographic apparatus, according to some aspects.

[0012] FIG. 2 shows a transmissive lithographic apparatus, according to some aspects.

[0013] FIG. 3 shows a lithographic cell, according to some aspects.

[0014] FIG. 4 shows a cross-sectional view of a discharge chamber of a lithographic apparatus, according to some aspects.

[0015] FIG. 5 A shows a plan view of a filter, according to some aspects.

[0016] FIG. 5B shows a cross-sectional view of a filter, according to some aspects.

[0017] FIG. 6A shows plan view of a filter, according to some aspects.

[0018] FIG. 6B shows a cross-sectional view of a filter, according to some aspects.

[0019] FIG. 7 shows a cross-sectional view of a filter, according to some aspects.

[0020] The features of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. Additionally, generally, the leftmost digit(s) of a reference number identifies the drawing in which the reference number first appears. Unless otherwise indicated, the drawings provided throughout the disclosure should not be interpreted as to-scale drawings.DETAILED DESCRIPTION

[0021] The aspects described herein, and references in the specification to “one aspect,” “an aspect,” “an exemplary aspect,” “an example aspect,” etc., indicate that the aspects described can include a particular feature, structure, or characteristic, but every aspect may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same aspect. Further, when a particular feature, structure, or characteristic is described in connection with an aspect, it is understood that it is within the knowledge of those skilled in the art to effect such feature, structure, or characteristic in connection with other aspects whether or not explicitly described.

[0022] Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “on,” “upper” and the like, can be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein can likewise be interpreted accordingly.

[0023] The terms “about,” “approximately,” or the like can be used herein to indicate the value of a given quantity that can vary based on a particular technology. Based on the particular technology, the terms “about,” “approximately,” or the like can indicate a value of a given quantity that varies within, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

[0024] Before describing such aspects in more detail, however, it is instructive to present an example environment in which aspects of the present disclosure can be implemented.Example Lithographic Systems

[0025] FIGS. 1 and 2 show a lithographic apparatus 100 and a lithographic apparatus 200, respectively, in which aspects of the present disclosure can be implemented. Lithographic apparatus 100 and lithographic apparatus 200 each include the following: an illumination system (illuminator) IL configured to condition a radiation beam B (for example, deep ultra violet or extreme ultra violet radiation); a support structure (for example, a mask table) MT configured to support a patterning device (for example, a mask, a reticle, or a dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA; and, a substrate table (for example, a wafer table) WT configured to hold a substrate (for example, a resist coated wafer) W and connected to a second positioner PW configured to accurately position the substrate W. Lithographic apparatus 100 and 200 also have a projection system PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion (for example, comprising one or more dies) C of the substrate W. In lithographic apparatus 100, the patterning device MA and the projection system PS are reflective. In lithographic apparatus 200, the patterning device MA and the projection system PS are transmissive.

[0026] The illumination system IL can include various types of optical components, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for directing, shaping, or controlling the radiation beam B.

[0027] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA with respect to a reference frame, the design of at least one of the lithographic apparatus 100 and 200, and other conditions, such as whether or not the patterning device MA is held in a vacuum environment. The support structure MT can use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterning device MA. The support structure MT can be a frame or a table, for example, which can be fixed or movable. By using sensors, the support structure MT can ensure that the patterning device MA is at a desired position, for example, with respect to the projection system PS.

[0028] The term “patterning device” MA should be broadly interpreted as referring to any device that can be used to impart a radiation beam B with a pattern in its cross-section, such as to create a pattern in the target portion C of the substrate W. The pattern imparted to the radiation beam B can correspond to a particular functional layer in a device being created in the target portion C to form an integrated circuit.

[0029] The paterning device MA can be transmissive (as in lithographic apparatus 200 of FIG. 2) or reflective (as in lithographic apparatus 100 of FIG. 1). Examples of paterning devices MA include reticles, masks, programmable mirror arrays, or programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase shift, or atenuated phase shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a patern in the radiation beam B, which is reflected by a matrix of small mirrors.

[0030] The term “projection system” PS can encompass any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors, such as the use of an immersion liquid on the substrate W or the use of a vacuum. A vacuum environment can be used for EUV or electron beam radiation since other gases can absorb too much radiation or electrons. A vacuum environment can therefore be provided to the whole beam path with the aid of a vacuum wall and vacuum pumps.

[0031] Lithographic apparatus 100 and / or lithographic apparatus 200 can be of a type having two (dual stage) or more substrate tables WT (and / or two or more mask tables). In such “multiple stage” machines, the additional substrate tables WT can be used in parallel, or preparatory steps can be carried out on one or more tables while one or more other substrate tables WT are being used for exposure. In some situations, the additional table may not be a substrate table WT.

[0032] The lithographic apparatus can also be of a type wherein at least a portion of the substrate can be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between the projection system and the substrate. An immersion liquid can also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid. For example, a liquid can be located between the projection system and the substrate during exposure.

[0033] Referring to FIGS. 1 and 2, the illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus 100, 200 can be separate physical entities, for example, when the source SO is an excimer laser. In such cases, the source SO is not considered to form part of the lithographic apparatus 100 or 200, and the radiation beam B passes from the source SO to the illuminator IL with the aid of a beam delivery system BD (in FIG. 2) including, for example, suitable directing mirrors and / or a beam expander. In other cases, the source SO can be an integral part of the lithographic apparatus 100, 200, for example, when the source SO is a mercury lamp. A radiation system can comprise the source SO, the illuminator IL, and / or the beam delivery system BD.

[0034] The illuminator IL can include an adjuster AD (in FIG. 2) for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radial extent (commonly referred to as “outer” and “inner,” respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL can comprise various other components (in FIG. 2), such as an integrator IN and a condenser CO. The illuminator IL can be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross section.

[0035] Referring to FIG. 1, the radiation beam B is incident on the patterning device (for example, mask) MA, which is held on the support structure (for example, mask table) MT, and is patterned by the patterning device MA. In lithographic apparatus 100, the radiation beam B is reflected from the patterning device (for example, mask) MA. After being reflected from the patterning device (for example, mask) MA, the radiation beam B passes through the projection system PS, which focuses the radiation beam B onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF2 (for example, an interferometric device, linear encoder, or capacitive sensor), the substrate table WT can be moved accurately (for example, so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor IF1 can be used to accurately position the patterning device (for example, mask) MA with respect to the path of the radiation beam B. Patterning device (for example, mask) MA and substrate W can be aligned using mask alignment marks Ml, M2 and substrate alignment marks PI, P2.

[0036] Referring to FIG. 2, the radiation beam B is incident on the patterning device (for example, mask MA), which is held on the support structure (for example, mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. The projection system has a pupil conjugate PPU to an illumination system pupil IPU. Portions of radiation emanate from the intensity distribution at the illumination system pupil IPU and traverse a mask pattern without being affected by diffraction at the mask pattern and create an image of the intensity distribution at the illumination system pupil IPU.

[0037] The projection system PS projects an image of the mask pattern MP, where the image is formed by diffracted beams produced from the mark pattern MP by radiation from the intensity distribution, onto a photoresist layer coated on the substrate W. For example, the mask pattern MP can include an array of lines and spaces. A diffraction of radiation at the array and different from zeroth order diffraction generates diverted diffracted beams with a change of direction in a direction perpendicular to the lines. Undiffracted beams (i.e., so-called zeroth order diffracted beams) traverse the pattern without any change in propagation direction. The zeroth order diffracted beams traverse an upper lens or upper lens group of the projection system PS, upstream of the pupil conjugate PPU of the projection system PS, to reach the pupil conjugate PPU. The portion of the intensity distribution in the plane of the pupil conjugate PPU and associated with the zeroth order diffracted beams is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. The aperturedevice PD, for example, is disposed at or substantially at a plane that includes the pupil conjugate PPU of the projection system PS.

[0038] The projection system PS is arranged to capture (e.g., using a lens or lens group L) the zeroth order diffracted beams, first order diffracted beams, and / or higher order diffracted beams (not shown). In some aspects, dipole illumination for imaging line patterns extending in a direction perpendicular to a line can be used to utilize the resolution enhancement effect of dipole illumination. For example, first- order diffracted beams interfere with corresponding zeroth-order diffracted beams at the level of the wafer W to create an image of the line pattern MP at highest possible resolution and process window (i.e., usable depth of focus in combination with tolerable exposure dose deviations). In some aspects, astigmatism aberration can be reduced by providing radiation poles (not shown) in opposite quadrants of the illumination system pupil IPU. Further, in some aspects, astigmatism aberration can be reduced by blocking the zeroth order beams in the pupil conjugate PPU of the projection system associated with radiation poles in opposite quadrants. This is described in more detail in US 7,511,799 B2, issued Mar. 31, 2009, which is incorporated by reference herein in its entirety.

[0039] With the aid of the second positioner PW and position sensor IFD (for example, an interferometric device, linear encoder, or capacitive sensor), the substrate table WT can be moved accurately (for example, so as to position different target portions C in the path of the radiation beam B). Similarly, the first positioner PM and another position sensor (not shown in FIG. 2) can be used to accurately position the mask MA with respect to the path of the radiation beam B (for example, after mechanical retrieval from a mask library or during a scan).

[0040] In general, movement of the mask table MT can be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT can be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the mask table MT can be connected to a short-stroke actuator or can be fixed. Mask MA and substrate W can be aligned using mask alignment marks Ml, M2, and substrate alignment marks PI, P2. Although the substrate alignment marks (as illustrated) occupy dedicated target portions, they can be located in spaces between target portions (known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks can be located between the dies.

[0041] Mask table MT and patterning device MA can be in a vacuum chamber V, where an in-vacuum robot IVR can be used to move patterning devices such as a mask in and out of vacuum chamber. Alternatively, when mask table MT and patterning device MA are outside of the vacuum chamber, an out-of-vacuum robot can be used for various transportation operations, similar to the in-vacuum robot IVR. Both the in-vacuum and out-of-vacuum robots can be calibrated for a smooth transfer of any payload (e.g., mask) to a fixed kinematic mount of a transfer station.

[0042] The lithographic apparatus 100 and 200 can be used in at least one of the following modes:1. In step mode, the support structure (for example, mask table) MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam B is projected onto a target portion C at one time (i.e., a single static exposure). The substrate table WT is then shifted in the X and / or Y direction so that a different target portion C can be exposed.2. In scan mode, the support structure (for example, mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam B is projected onto a target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (for example, mask table) MT can be determined by the (de-) magnification and image reversal characteristics of the projection system PS.3. In another mode, the support structure (for example, mask table) MT is kept substantially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. A pulsed radiation source SO can be employed and the programmable patterning device is updated as needed after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes a programmable patterning device, such as a programmable mirror array.

[0043] Combinations and / or variations on the described modes of use or entirely different modes of use can also be employed.

[0044] In some aspects, lithographic apparatus 100 includes an extreme ultraviolet (EUV) source, which is configured to generate a beam of EUV radiation for EUV lithography. In general, the EUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the EUV radiation beam of the EUV source.

[0045] In some aspects, lithographic apparatus 200 includes a deep ultraviolet (DUV) source, which is configured to generate a beam of DUV radiation for DUV lithography. In general, the DUV source is configured in a radiation system, and a corresponding illumination system is configured to condition the DUV radiation beam of the DUV source.Example Lithographic Cell

[0046] FIG. 3 shows a lithographic cell 300, also sometimes referred to as a lithocell or cluster, according to some aspects. Lithographic apparatus 100 or 200 can form part of lithographic cell 300. Lithographic cell 300 can also include one or more apparatuses to perform pre- and post-exposure processes on a substrate. Conventionally these include spin coaters SC to deposit resist layers, developers DE to develop exposed resist, chill plates CH, and bake plates BK. A substrate handler, or robot, RO picks up substrates from input / output ports I / O I, I / O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus 100 or 200. These devices, which are often collectively referred to as the track, are under the control of a track control unit TCU, which is itself controlled by a supervisory control system SCS, which also controlsthe lithographic apparatus via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.Example Discharge Chamber

[0047] FIG. 4 shows a cross-sectional view of a discharge chamber 400 according to some aspects. In some aspects, discharge chamber 400 includes a chamber wall 401, an internal wall 402, and one or more traps (not shown). In some aspects, the traps may be, for example, a electrostatic precipitator configured to charge metal halide particles and precipitate the charged particles onto one or more internal surfaces of the trap, thereby trapping the metal halide particles, such as metal fluoride.

[0048] Internal wall 402 may have a surface 403 that faces into discharge chamber 400. Internal wall 402 and surface 403 may enclose an electrode structure 411 (including, e.g., a cathode, an anode, a discharge region, an anode support, and a ground rod), a circulation fan 418, and one or more filters 450.

[0049] According to some aspects, a discharge of electric voltage in electrode structure 411 creates DUV light for use in a fabrication process.

[0050] In some aspects, circulation fan 418 causes one or more process gases, such as, for example, fluorine, argon, neon, xenon, krypton gases, or the like, to flow around an interior periphery of discharge chamber 400.

[0051] In some aspects, particles generated by electrode structure 411 may be captured by one or more traps. Byproduct dust (not shown) may be generated around electrode structure 411 and may be circulated throughout discharge chamber 400 by circulation fan 418.

[0052] According to some aspects, one or more filters 450 may be attached to surface 403 of internal wall 402 of chamber 400. For simplicity, only one filter 450 is shown in FIG. 4. However, aspects are not limited to only one filter, and it should be understood that multiple filters 450 may be disposed along one or more surfaces of internal wall(s) 402.

[0053] FIG. 5A shows a plan view of a filter 450 according to some aspects. Filter 450 may comprise a plurality of screens 451. The plurality of screens 451 may be stacked on top of one another along a stacking direction. In the example shown in FIG. 5 A, the stacking direction is perpendicular to the plane of the page.

[0054] FIG. 5B shows a cross-sectional view of the plurality of screens 451 of filter 450 along the dotted line X-X’ in FIG. 5A, according to some aspects. For example, plurality of screens 451 may comprise a bottom screen 45 la, a top screen 451c, and one or more intermediate screens 45 lb.

[0055] In some aspects, bottom screen 45 la may be configured to be disposed closest to surface 403 of internal wall 402 of chamber 400, while top screen 451c may be configured to be disposed away from surface 403 of internal wall 402 of chamber 400 along the stacking direction. For example, as shown by the solid black arrow in FIG. 5B, the stacking direction may be from the bottom of the page towards the top of the page.

[0056] Each intermediate screen 45 lb may be configured to be disposed between bottom screen 45 la and top screen 451c along the stacking direction. Although FIG. 5B shows seven total screens 451, including five intermediate screens 45 lb, alternative aspects are not limited to this configuration, and more or fewer intermediate screens 451b may be used.

[0057] In some aspects, the number of intermediate screens may be four, or three, or two, or only one. In some aspects, no intermediate screen 451b may be used. Likewise, more than five intermediate screens 45 lb may also be used, so that the number of intermediate screens 45 lb is limited by practical concerns of space within the chamber. Thus, in some aspects, the number of screens may be a minimum of two screens, or even only one screen. In some aspects, the maximum number of screens may be limited by practical considerations, such as the space within the chamber and the limiting of airflow through the filter by the number of screens. In some aspects, a maximum number of screens may be 10, 12, or 20 total screens.

[0058] In one example, filter 450 may be installed in chamber 400, bottom screen 451a may be disposed closest to surface 403 of internal wall 402 of chamber 400, one or more intermediate screens 45 lb may be disposed on top of bottom screen 45 la along the stacking direction that is from the bottom of the page towards the top of the page, and top screen 451c may be disposed on top of intermediate screens 45 lb to be away from surface 403 of internal wall 402 of chamber 400 along the stacking direction

[0059] In some aspects, each screen of the plurality of screens 451 may be characterized as having at least one of a porosity, a pore size, or other similar characterizing feature. According to some aspects, the porosity, pore size, or other similar feature may be the same for each of the plurality of screens 451. However, in some aspects, the porosity, pore size, or other similar feature may be different for one or more of the plurality of screens 451. For example, in some aspects, bottom screen 451a may have a porosity, pore size, or other similar feature that is greater than or equal to that of the intermediate screen(s) 451b. Likewise, in some aspects, top screen 451c may have a porosity, pore size, or other similar feature that is greater than or equal to that of the intermediate screen(s) 45 lb. In some aspects, top screen 451c may have a porosity, pore size, or other similar feature that is greater than that of bottom screen 451a. In some aspects, bottom screen 451a and top screen 451c may have a substantially equal porosity, pore size, or other similar feature. In one exemplary aspect, bottom screen 451a and top screen 451c may have a substantially equal porosity, pore size, or other similar feature that is greater than that of the intermediate screen(s) 451b.

[0060] According to some aspects, the porosity, pore size, or other similar feature is from approximately 50 pm to approximately 500 pm. In one aspect, bottom screen 45 la and top screen 451c may have a pore size of 250 pm, while each intermediate screen may have a pore size of 100 pm. In some aspects, three or more pore sizes may be used. In one example, bottom screen 451a may have a pore size of, for example, 250 pm, each intermediate screen may have a pore size that is smaller than the pore size of the screen below it, and top screen 451c may have a pore size of, for example, 100 pm.This configuration may achieve more effective trapping of particles coming from a bottom side of the filter. In some aspects, top screen 451c and bottom screen may have substantially equal pore sizes, and the intermediate screens may have pore sizes chosen so that a middle screen of the intermediate screens has a smallest pore size. This configuration may achieve more effective trapping of particles coming from both sides of the filter.

[0061] Returning to FIG. 5A, according to some aspects, each screen 451 may comprise an edge region 452 and a central region 454. In some aspects, edge region 452 and central region 454 may be substantially the same. However, in some aspects, edge region 452 may comprise additional reinforcing, stiffening, or holding material, or may be formed to be stiffer or have a higher hardness than central region 454. Conversely, in some aspects, central region 454 may comprise additional material or may be formed to be stiffer or have a higher hardness than edge region 452.

[0062] According to some aspects, each screen 451 may also comprise a plurality of eyelets 456. Each eyelet 456 may be configured to receive a fastener to attach filter 450 to surface 403 of internal wall 402 of chamber 400. In some aspects, eyelets 456 may constitute holes, through-holes, vias, or the like. In some aspects, eyelets 456 may be divided in subgroups, where one or more edge eyelets 456A may be provided in edge region 452 and one or more central eyelets 456B may be provided in central region 454.

[0063] In some aspects, due to the flow of gas(es) around the periphery of chamber 400 caused by circulation fan 418, filter 450 may comprise an upstream side and a downstream side (shown by the block arrow in FIG. 5A). Thus, edge region 452 may be divided into an upstream edge region 452a and a downstream edge region 452b. Likewise, central region 454 may be divided into an upstream central region 454a and a downstream central region 454b. Edge region eyelets 456A may also be divided into upstream edge eyelets 456a and downstream edge eyelets 456b, while central eyelets 456B may be divided into upstream central eyelets 456c and downstream central eyelets 456d.

[0064] Returning to FIG. 5B, in some aspects edge eyelets 456A each receive a fastener 501 and central eyelets 456B each receive a fastener 502.

[0065] In some aspects, filter 450 is configured to be fastened by fasteners 501 and 502 to surface 403 of internal wall 402 of chamber 400.

[0066] In some aspects, a first separation 5A may be provided between surface 403 of internal wall 402 of chamber 400 and edge region 452 of filter 450 along the stacking direction. A second separation 5B may be provided between surface 403 of internal wall 402 of chamber 400 and central region 454 of filter 450 along the stacking direction. According to some aspects, separation 5A is less than separation 5B.

[0067] In some aspects, separation 5A may be as small as possible, so that separation 5A is substantially zero. In contrast, separation 5B may be larger than zero.

[0068] In some exemplary aspects, separation 5B is from approximately 1.0 mm to approximately 4.5 mm. If separation 5B is smaller than 1.0 mm, space between the filter and the surface is insufficient,resulting in a decreased particle trapping rate, in some instances. If separation 5B is greater than 4.5 mm, the upstream central region clogs easily, resulting in a decreased particle trapping rate, in some instances.

[0069] The configuration shown in FIG. 5B may, in some aspects, be achieved using appropriate fasteners 501 and 502. For example, in some aspects, fastener 501 may comprise a standard bolt, while fastener 502 may comprise a standard bolt with one or more washers. In some aspects, fastener 502 may use a plurality of washers while fastener 501 uses no washers.

[0070] According to some aspects, fastener 501 may use N washers while fastener 502 uses N+l or more washers, where N is any whole positive integer number.

[0071] In some aspects, fastener 501 may comprise a bolt while fastener 502 comprises a standoff bolt of an appropriate height, as shown in FIG. 5B. Likewise, fasteners 501 and 502 may each comprise a standoff bolt, where fastener 502 comprises a standoff bolt of a height that is greater than that of a standoff bolt used as fastener 501.

[0072] By the configuration shown in FIGS. 5A and 5B, it is possible to optimize the filtering of byproduct dust using filter 450. In some aspects, byproduct dust may be more evenly spread across the surface of filter 450 in comparison with other approaches, so that a larger surface area of filter 450 is used in filtering.

[0073] FIG. 6A shows a plan view of a filter 650 according to some aspects. In some aspects, filter 650 may be similar in many aspects to filter 450. In some aspects, filter 650 may include edge region 652 (including upstream edge region 652a and downstream edge region 652b) and central region 654 (including upstream central region 654a and downstream central region 654b). Filter 650 may also include edge eyelets 656A (including upstream edge eyelet 656a and downstream edge eyelet 656b) and central eyelets 656B (including upstream central eyelet 656c and downstream central eyelet 656d). According to some aspects, filter 650 may comprise a plurality of screens 651 stacked on top of one another along a stacking direction. In the example shown in FIG. 6A, the stacking direction is perpendicular to the plane of the page.

[0074] FIG. 6B shows a cross-sectional view of filter 650 along the dotted line Y-Y’ in FIG. 6A, according to some aspects. Separation between filter 650 and the surface of the internal wall of the chamber may be further refined based on the direction of the flow of process gas around the periphery of the chamber (shown as the block arrow in FIG. 6B). According to some aspects, the separation between filter 650 and the surface of the internal wall of the chamber (shown as the dotted line in FIG. 6B) varies across filter 650 from the upstream side to the downstream side.

[0075] According to some aspects, a first separation 6A is provided between upstream edge region 652a and the surface of the internal wall of the chamber, a second separation 6B is provided between upstream central region 654a and the surface of the internal wall of the chamber, a third separation 6C is provided between downstream central region 654b and the surface of the internal wall of the chamber,and a fourth separation 6D is provided between downstream edge region 652b and the surface of the internal wall of the chamber.

[0076] In some aspects, separation 6B may be larger than separation 6D. In some aspects, separation 6A and separation 6C may each be greater than separation 6D and less than separation 6B. In some aspects, separation 6A and separation 6C may be substantially equal. For example, in some aspects, separations 6A and 6C may be each be greater than or equal to 1 mm and less than or equal to 2 mm. In one exemplary aspect, separations 6A and 6C may each be approximately 1.5 mm.

[0077] According to some aspects, separation 6D may be as small as possible so that separation 6D is approximately zero. In one exemplary aspect, separation 6D may be substantially zero. In addition, in some aspects, separation 6A may also be approximately or substantially zero. One reason for making separation 6A approximately or substantially zero is to reduce backflow of trapped dust out of the fdter.

[0078] In some aspects, separation 6B may be substantially larger than separation 6A and / or separation 6C. For example, in one aspect, separation 7B may be greater than or equal to 2 mm and less than or equal to 4.5 mm.

[0079] It should be noted that, although certain exemplary ranges are provided above for separations 6A-6D, aspects are not limited to such configurations, and other separation distances may be used so long as separation 6B is greater than separations 6A, 6C, and 6D.

[0080] In some aspects, the configuration of filter 650 may be achieved using a plurality of fasteners 601, 602, 603, and 604. In some aspects, fastener 604 may comprise a standard bolt, while fasteners 601, 602, and 603 each comprise a standard bolt with one or more washers or a standoff bolt, respectively.

[0081] In some aspects, fastener 602 may have a height greater than that of fasteners 601 and 603, which may be greater than a height of fastener 604. According to one non-limiting example shown in FIG. 6B, fasteners 601 and 603 may each comprise a bolt with one washer 610, fastener 602 may comprise a bolt with two washers 610, and fastener 604 may comprise a bolt with no washers . However, any of the configurations described above may be used for fasteners 601-604.

[0082] In some aspects, it is possible to optimize the flow of gas through filter 650 while creating a “volume” between filter 650 and the surface of the internal wall of the chamber, so that byproduct dust becomes trapped in this volume. For example, process gas and dust may flow more easily through separation 6A than separation 6D, so that the flow of the process gas and dust from the upstream side of filter 650 is substantially unimpeded.

[0083] In some aspects, once the byproduct dust enters the volume, large dust particles may be trapped against the surface of the internal wall of the chamber by the bottom screen of filter 650. In addition, smaller dust particles that are not trapped by the bottom screen of filter 650 may subsequently be trapped by one or more of the intermediate screen(s) and / or top screen of filter 650. In this way, filter 650 may allow increased airflow while optimizing the trapping of byproduct dust both between filter 650 and the surface of the internal wall of the chamber and within filter 650 itself.

[0084] FIG. 7 shows another configuration of a filter 750 according to some aspects. Filter 750, in some aspects, comprises a plurality of screens 751 and a plurality of fasteners 705. In some aspects, plurality of screens 751 may comprise a bottom screen 751a, one or more intermediate screen(s) 751b, and a top screen 751c, although plurality of screens 851 may include more or fewer than these screens.

[0085] In some aspects, filter 750 may differ from filter 450 at least in that one or more spacers 708a- d may be placed between adjacent screens among plurality of screens 751. As a non-limiting example, FIG. 7 shows that four spacers 708a-d are provided for each fastener 705. For example, according to some aspects, a spacer 708a may be placed between bottom screen 751a and an intermediate screen 751b that is adjacent to bottom screen 75 la. In some aspects, a spacer 708d may be placed between top screen 751c and an intermediate screen 751b that is adjacent to top screen 751c. In some aspects, a spacer 708b may be placed between adjacent intermediate screens. In some aspects, a spacer 708c may be placed between adjacent intermediate screens such that spacer 708c is also adjacent to another spacer 708d.

[0086] According to some aspects, one or more spacers 708a-d may be placed between each adjacent screen among the plurality of screens 751. In other aspects, a spacer 708a-d may be placed only between certain screens among the plurality of screens. As shown in the example of FIG. 7, in some aspects, the arrangement of spacers may be the same for each fastener 705. However, in many aspects, the arrangement of spacers may be determined for each individual fastener 705, and thus aspects are not limited to the example shown in FIG. 7. In addition, although not shown in FIG. 7, in some aspects, more than one spacer 708a-d may be disposed between adjacent screens to achieve a desired separation between the adjacent screens.

[0087] According to some aspects, spacers 708a-d may be formed of any appropriate material. In some aspects, spacers 708a-d may be formed of materials such as metal, plastic, rubber, or the like. In some aspects, spacers 708a-d may be formed of the same material as the plurality of screens 751. In some aspects, spacers 708a-d may be formed of a material having a substantially higher or lower hardness than the material used in the plurality of screens 751.

[0088] In some aspects, a spacer 708a-d may be separate from fastener 705 and screens 751. For example, each spacer 708a-d may be a washer, an O-ring, or any toroidal spacing element which may be positioned between adjacent screens 751. In some aspects, each spacer 708a-d may be part of, or may be fixedly attached to, one or more of fastener 705 and screens 751. For example, each spacer 708a-d may comprise a metal washer or ring that is connected to or forms a part of fastener 805. In at least one aspect, a fastener 705 may comprise a standoff bolt, and one or more spacers 708a-d may form part of the standoff bolt. In some aspects, a spacer 708a-d may be connected to one or more screens 751. For example, each spacer 708a-d may be a washer or an O-ring that is embedded in a screen 751, so that portions of the spacer(s) 708a-d protrude from a top and / or a bottom of the screen 751.

[0089] According to aspects, the above various types of spacers may be freely combined. As a nonlimiting example, in at least aspect, fastener 705 may form a standoff bolt configured to secure pluralityof screens 751 to a surface of an internal wall of a chamber. A spacer 708d may form part of the standoff bolt of fastener 705. An intermediate screen 751b may be positioned under top screen 751c and separated from top screen 751c by spacer 708d. A second spacer 708c may be threaded over bolt 705, and positioned to separate bottom screen 751a from intermediate screen 751b. Of course, aspects are not limited to this example and other combinations of spacers and fasteners could readily be used based on the specific implementation.

[0090] In addition, it should be understood that various aspects shown in FIGS. 4-7 can be readily combined. As a non-limiting example, in at least one aspect, a filter having spacers as shown in FIG. 7 may be attached to a surface of an internal wall of chamber using a configuration as shown in one of FIGs. 5 and 6.

[0091] As discussed above, the filters shown in the above figures may be attached to a surface of the internal wall of the chamber for semiconductor manufacturing, such as etch, deposition, and implantation processes. In some aspects, a method comprises attaching a filter to the surface of the internal wall of the chamber using a plurality of fasteners. In some aspects, a fastener may be passed through each eyelet of the filter, so that each eyelet receives one fastener. Each fastener may then be attached to the surface of the internal wall of the chamber by, for example, screwing the fastener into a respective hole in the surface of the internal wall of the chamber. Each fastener for each respective eyelet may be chosen based on one of the above configurations to provide a particular separation between the surface of the filter and the surface of the internal wall of the chamber at that particular point. This method of attaching a filter to the surface of the internal wall of the chamber maintains an ease of installing the filter while creating benefits of optimized separation(s) between the filter and the surface of the internal wall of the chamber to increase byproduct dust filtering and optimize the flow of process gas around the filter, as discussed above.

[0092] Although some aspects of the present disclosure are described in the context of lithographic apparatuses in the manufacture of ICs, it should be understood that lithographic apparatuses described herein can be used in other applications, for example, in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, LCDs, thin-film magnetic heads, etc. Those skilled in the art will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein can be considered as specific examples of the more general terms “substrate” or “target portion”, respectively. A substrate can be processed before or after exposure in, for example, a track unit (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) and / or a metrology unit. Where applicable, aspects disclosed herein can be applied to such and other substrate processing tools. Furthermore, a substrate can be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein can also refer to a substrate that already contains multiple processed layers.

[0093] It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by those skilled in relevant art(s) in light of the teachings herein.

[0094] The present disclosure has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. The foregoing description of specific aspects will so fully reveal the general nature of the present disclosure that others can, by applying knowledge within the skill of the art, readily modify and / or adapt for various applications such specific aspects, without undue experimentation and without departing from the general concept of the present disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed aspects, based on the teaching and guidance presented herein.

[0095] Other aspects of the invention are set out in the following numbered clauses:1. A lithographic apparatus comprising: a chamber configured to produce radiation, the chamber comprising an internal wall having a surface facing into the chamber; and a filter attached to the surface of the internal wall of the chamber and comprising a plurality of screens stacked on top of one another along a stacking direction, the stacking direction being perpendicular to the surface of the internal wall of the chamber on which the filter is disposed, wherein the plurality of screens include a central region and an edge region surrounding the central region, and wherein a first separation between the central region and the surface of the internal wall of the chamber along the stacking direction is greater than a second separation between the edge region and the surface of the internal wall of the chamber along the stacking direction.2. The lithographic apparatus of clause 1, wherein: the edge region is attached to the surface of the internal wall of the chamber with a first fastener, the central region is attached to the surface of the internal wall of the chamber with a second fastener having a height that is greater than that of the first fastener, and the second fastener causes the second separation between the central region and the surface of the internal wall of the chamber to be greater than the first separation between the edge region and the surface.3. The lithographic apparatus of clause 2, wherein the first fastener and second fastener comprise standard bolts.4. The lithographic apparatus of clause 2, wherein: the first fastener comprises a bolt; and the second fastener comprises a bolt and a washer.5. The lithographic apparatus of clause 2, wherein: the first fastener comprises a standard bolt; the second fastener comprises a first standoff bolt.6. The lithographic apparatus of clause 1, wherein the first separation is greater than 1 mm and less than 4.5 mm.7. The lithographic apparatus of clause 1, wherein: the chamber further comprises a fan configured to cause a stream of process gas to flow around a periphery of the chamber, such that each of the plurality of screens comprises an upstream side and a downstream side.8. The lithographic apparatus of clause 7, wherein: the edge region of the filter comprises an upstream edge region and a downstream edge region; the central region further comprises an upstream central region and a downstream central region; a third separation between the downstream edge region and the surface of the internal wall of the chamber along the stacking direction is less than a fourth separation between the upstream edge region and the surface of the internal wall of the chamber along the stacking direction; and the fourth separation is less than a fifth separation between the upstream central region and the surface of the internal wall of the chamber along the stacking direction.9. The lithographic apparatus of clause 8, wherein: the downstream edge region is attached to the surface of the internal wall of the chamber with a first fastener; the upstream edge region is attached to the surface of the internal wall of the chamber with a second fastener having a height that is greater than that of the first fastener; and the upstream central region is attached to the surface of the internal wall of the chamber with a third fastener having a height that is greater than that of the second fastener.10. The lithographic apparatus of clause 9, wherein: the downstream central region is attached to the surface of the internal wall of the chamber with a fourth fastener having a height that is substantially equal to that of the second fastener.11. The lithographic apparatus of clause 9, wherein: the first fastener is a bolt; the second fastener is a first standoff bolt; and the third fastener is a second standoff bolt.12. The lithographic apparatus of clause 9, wherein: the first fastener is a bolt; the second fastener is a bolt and at least one washer; and the third fastener is a bolt and at least one more washer than a number of washers used for the second fastener.13. The lithographic apparatus of clause 8, wherein:the downstream edge region is substantially directly contacting the internal wall; a separation between the upstream edge region and the surface of the internal wall of the chamber is greater than 1 mm and less than 2 mm; and a separation between the upstream central region and the surface of the internal wall of the chamber is greater than 2 mm and less than 4.5 mm.14. The lithographic apparatus of clause 1, wherein the plurality of screens comprises: a bottom screen disposed closest to the surface of the internal wall of the chamber; a top screen disposed away from the surface of the internal wall of the chamber along the stacking direction; and at least one intermediate screen disposed between the bottom screen and the top screen along the stacking direction.15. The lithographic apparatus of clause 14, wherein: a pore size of the top screen is greater than a pore size of the bottom screen and a pore size of the at least one intermediate screen.16. The lithographic apparatus of clause 14, wherein: a pore size of the bottom screen is substantially equal to a pore size of the top screen.17. The lithographic apparatus of clause 16, wherein: the pore size of the bottom screen and the top screen is less than a pore size of the at least one intermediate screen.18. The lithographic apparatus of clause 14, wherein: the at least one intermediate screen comprises n screens, where n is an integer number that is equal to or greater than one and less than or equal to five.19. The lithographic apparatus of clause 14, wherein: a pore size of the bottom screen is substantially equal to a pore size of the at least one intermediate screen and less than a pore size of the top screen.20. A filter comprising: a plurality of screens comprising a bottom screen configured to be disposed closest to a surface of an internal wall of a chamber of a semiconductor manufacturing apparatus along a stacking direction that is perpendicular to the surface; a top screen configured to be disposed away from the surface of the internal wall of the chamber along the stacking direction; and at least one intermediate screen configured to be disposed between the bottom screen and the top screen along the stacking direction, wherein the plurality of screens comprise a central region and an edge region surrounding the central region, and wherein a first separation between the central region of the plurality of screens from the surface of the internal wall of the chamber along the stacking direction is configured to be greater than a secondseparation between the edge region of the plurality of screens from the surface of the internal wall of the chamber along the stacking direction.21. The fdter of clause 20, wherein: the edge region comprises an upstream edge region and a downstream edge region; the central region comprises an upstream central region and a downstream central region; a separation between the downstream edge region from the surface of the internal wall of the chamber along the stacking direction is configured to be less than a separation between the upstream edge region from the surface of the internal wall of the chamber along the stacking direction; and a separation between the upstream edge region from the surface of the internal wall of the chamber along the stacking direction is configured to be less than a separation between the upstream central region from the surface of the internal wall of the chamber along the stacking direction.22. The filter of clause 21, wherein: a pore size of the top screen is equal to a pore size of the bottom screen and greater than a pore size of the at least one intermediate screen.23. The filter of clause 21, wherein: a pore size of the bottom screen is equal to a pore size of the at least one intermediate screen and less than a pore size of the top screen.24. A method comprising: attaching a filter comprising a plurality of screens to a surface of an internal wall of a chamber, the plurality of screens being stacked on top of one another along a stacking direction that is perpendicular to the surface of the internal wall of the chamber, wherein: the plurality of screens comprise a central region and an edge region surrounding the central region; the edge region is attached to the surface of the internal wall of the chamber with a first fastener;

[0096] It is to be understood that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections can set forth one or more, but not necessarily all, aspects of the present disclosure as contemplated by the inventor(s), and thus, are not intended to limit the present disclosure and the appended claims in any way. The breadth and scope of the protected subject matter should not be limited by any of the above-described aspects, but should be defined in accordance with the following claims and their equivalents.

Claims

CLAIMS1. A lithographic apparatus comprising: a chamber configured to produce radiation, the chamber comprising an internal wall having a surface facing into the chamber; and a filter attached to the surface of the internal wall of the chamber and comprising a plurality of screens stacked on top of one another along a stacking direction, the stacking direction being perpendicular to the surface of the internal wall of the chamber on which the filter is disposed, wherein the plurality of screens include a central region and an edge region surrounding the central region, and wherein a first separation between the central region and the surface of the internal wall of the chamber along the stacking direction is greater than a second separation between the edge region and the surface of the internal wall of the chamber along the stacking direction.

2. The lithographic apparatus of claim 1, wherein: the edge region is attached to the surface of the internal wall of the chamber with a first fastener, the central region is attached to the surface of the internal wall of the chamber with a second fastener having a height that is greater than that of the first fastener, and the second fastener causes the second separation between the central region and the surface of the internal wall of the chamber to be greater than the first separation between the edge region and the surface.

3. The lithographic apparatus of claim 1, wherein the first separation is greater than 1 mm and less than 4.5 mm.

4. The lithographic apparatus of claim 1, wherein: the chamber further comprises a fan configured to cause a stream of process gas to flow around a periphery of the chamber, such that each of the plurality of screens comprises an upstream side and a downstream side.

5. The lithographic apparatus of claim 4, wherein: the edge region of the filter comprises an upstream edge region and a downstream edge region; the central region further comprises an upstream central region and a downstream central region;a third separation between the downstream edge region and the surface of the internal wall of the chamber along the stacking direction is less than a fourth separation between the upstream edge region and the surface of the internal wall of the chamber along the stacking direction; and the fourth separation is less than a fifth separation between the upstream central region and the surface of the internal wall of the chamber along the stacking direction.

6. The lithographic apparatus of claim 5, wherein: the downstream edge region is attached to the surface of the internal wall of the chamber with a first fastener; the upstream edge region is attached to the surface of the internal wall of the chamber with a second fastener having a height that is greater than that of the first fastener; and the upstream central region is attached to the surface of the internal wall of the chamber with a third fastener having a height that is greater than that of the second fastener.

7. The lithographic apparatus of claim 6, wherein: the downstream central region is attached to the surface of the internal wall of the chamber with a fourth fastener having a height that is substantially equal to that of the second fastener.

8. The lithographic apparatus of claim 5, wherein: the downstream edge region is substantially directly contacting the internal wall; a separation between the upstream edge region and the surface of the internal wall of the chamber is greater than 1 mm and less than 2 mm; and a separation between the upstream central region and the surface of the internal wall of the chamber is greater than 2 mm and less than 4.5 mm.

9. The lithographic apparatus of claim 1, wherein the plurality of screens comprises: a bottom screen disposed closest to the surface of the internal wall of the chamber; a top screen disposed away from the surface of the internal wall of the chamber along the stacking direction; and at least one intermediate screen disposed between the bottom screen and the top screen along the stacking direction.

10. The lithographic apparatus of claim 9, wherein: a pore size of the top screen is greater than a pore size of the bottom screen and a pore size of the at least one intermediate screen.

11. The lithographic apparatus of claim 9, wherein:a pore size of the bottom screen is substantially equal to a pore size of the top screen.

12. The lithographic apparatus of claim 11, wherein: the pore size of the bottom screen and the top screen is less than a pore size of the at least one intermediate screen.

13. The lithographic apparatus of claim 9, wherein: the at least one intermediate screen comprises n screens, where n is an integer number that is equal to or greater than one and less than or equal to five.

14. The lithographic apparatus of claim 9, wherein: a pore size of the bottom screen is substantially equal to a pore size of the at least one intermediate screen and less than a pore size of the top screen.

15. A filter comprising : a plurality of screens comprising a bottom screen configured to be disposed closest to a surface of an internal wall of a chamber of a semiconductor manufacturing apparatus along a stacking direction that is perpendicular to the surface; a top screen configured to be disposed away from the surface of the internal wall of the chamber along the stacking direction; and at least one intermediate screen configured to be disposed between the bottom screen and the top screen along the stacking direction, wherein the plurality of screens comprise a central region and an edge region surrounding the central region, and wherein a first separation between the central region of the plurality of screens from the surface of the internal wall of the chamber along the stacking direction is configured to be greater than a second separation between the edge region of the plurality of screens from the surface of the internal wall of the chamber along the stacking direction.

16. The filter of claim 15, wherein: the edge region comprises an upstream edge region and a downstream edge region; the central region comprises an upstream central region and a downstream central region; a separation between the downstream edge region from the surface of the internal wall of the chamber along the stacking direction is configured to be less than a separation between the upstream edge region from the surface of the internal wall of the chamber along the stacking direction; anda separation between the upstream edge region from the surface of the internal wall of the chamber along the stacking direction is configured to be less than a separation between the upstream central region from the surface of the internal wall of the chamber along the stacking direction.

17. The filter of claim 16, wherein: a pore size of the top screen is equal to a pore size of the bottom screen and greater than a pore size of the at least one intermediate screen.

18. The filter of claim 16, wherein: a pore size of the bottom screen is equal to a pore size of the at least one intermediate screen and less than a pore size of the top screen.

19. A method comprising: attaching a filter comprising a plurality of screens to a surface of an internal wall of a chamber, the plurality of screens being stacked on top of one another along a stacking direction that is perpendicular to the surface of the internal wall of the chamber, wherein: the plurality of screens comprise a central region and an edge region surrounding the central region; the edge region is attached to the surface of the internal wall of the chamber with a first fastener; the central region is attached to the surface of the internal wall of the chamber with a second fastener having a height greater than a height of the first fastener, wherein a separation between the central region of the plurality of screens from the surface of the internal wall of the chamber along the stacking direction is greater than a separation between the edge region of the plurality of filters from the surface of the internal wall of the chamber along the stacking direction.

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