Substrate holder, lithographic apparatus, device manufacturing method, and method of manufacturing a

专利摘要:
A substrate holder for a lithographic apparatus has a main body having a thin-film stack provided on a surface thereof. The thin-film stack forms an electronic or electric component such as an electrode, a sensor, a heater, a transistor or a logic device, and has a top isolation layer. A plurality of burls to support a substrate are formed on the thin-film stack or in apertures of the thin-film stack.
公开号:NL2010140A
申请号:NL2010140
申请日:2013-01-17
公开日:2013-08-06
发明作者:Raymond Lafarre；Sjoerd Donders；Nicolaas Kate；Nina Dziomkina；Yogesh Karade；Elisabeth Rodenburg
申请人:Asml Netherlands Bv；
IPC主号:

专利说明:

SUBSTRATE HOLDER. LITHOGRAPHIC APPARATUS. DEVICE MANUFACTURINGMETHOD. AND METHOD OF MANUFACTURING A SUBSTRATE HOLDER
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application clauses the benefit of US provisional application 61/594,857,which was filed on February 3, 2012, US provisional application 61/621,648, which wasfiled on April 9, 2012 and US provisional application 61/621,660, which was filed onApril 9, 2012 and which are incorporated herein in its entirety by reference.
FIELD
[0002] The present invention relates to a substrate holder, a lithographic apparatus, adevice manufacturing method, and a method of manufacturing a substrate holder.
BACKGROUND
[0003] A lithographic apparatus is a machine that applies a desired pattern onto asubstrate, usually onto a target portion of the substrate. A lithographic apparatus can beused, for example, in the manufacture of integrated circuits (ICs). In that instance, apatterning device, which is alternatively referred to as a mask or a reticle, may be usedto generate a circuit pattern to be formed on an individual layer of the IC. This patterncan 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 ontoa layer of radiation-sensitive material (resist) provided on the substrate. In general, asingle substrate will contain a network of adjacent target portions that are successivelypatterned. Known lithographic apparatus include so-called steppers, in which eachtarget portion is irradiated by exposing an entire pattern onto the target portion at onetime, and so-called scanners, in which each target portion is irradiated by scanning thepattern through a radiation beam in a given direction (the “scanning”-direction) whilesynchronously scanning the substrate parallel or anti-parallel to this direction. It is alsopossible to transfer the pattern from the patterning device to the substrate by imprintingthe pattern onto the substrate.
[0004] It has been proposed to immerse the substrate in the lithographic projection apparatus in a liquid having a relatively high refractive index, e.g. water, so as to fill aspace between the final element of the projection system and the substrate. In anembodiment, the liquid is distilled water, although another liquid can be used. Anembodiment of the present invention will be described with reference to liquid.
However, another fluid may be suitable, particularly a wetting fluid, an incompressiblefluid and/or a fluid with higher refractive index than air, desirably a higher refractiveindex than water. Fluids excluding gases are particularly desirable. The point of this isto enable imaging of smaller features since the exposure radiation will have a shorterwavelength in the liquid. (The effect of the liquid may also be regarded as increasingthe effective numerical aperture (NA) of the system and also increasing the depth offocus.) Other immersion liquids have been proposed, including water with solid particles(e.g. quartz) suspended therein, or a liquid with a nano-particle suspension (e.g.particles with a maximum dimension of up to 10 nm). The suspended particles may ormay not have a similar or the same refractive index as the liquid in which they aresuspended. Other liquids which may be suitable include a hydrocarbon, such as anaromatic, a fluorohydrocarbon, and/or an aqueous solution.
SUMMARY
[0005] In a conventional lithography apparatus, the substrate to be exposed may besupported by a substrate holder which in turn is supported by a substrate table. Thesubstrate holder is often a flat rigid disc corresponding in size and shape to thesubstrate (although it may have a different size or shape). It has an array of projections,referred to as burls or pimples, projecting from at least one side. In an embodiment, thesubstrate holder has an array of projections on two opposite sides. In this case, whenthe substrate holder is placed on the substrate table, the main body of the substrateholder is held a small distance above the substrate table while the ends of the burls onone side of the substrate holder lie on the surface of the substrate table. Similarly, whenthe substrate rests on the top of the burls on the opposite side of the substrate holder,the substrate is spaced apart from the main body of the substrate holder. One purposeof this is to help prevent a particle (i.e. a contaminating particle such as a dust particle)which might be present on either the substrate table or substrate holder from distorting the substrate holder or the substrate. Since the total surface area of the burls is only asmall fraction of the total area of the substrate or substrate holder, it is highly probablethat any particle will lie between burls and its presence will have no effect.
[0006] Due to the high accelerations experienced by the substrate in use of a high-throughput lithographic apparatus, it is not sufficient to allow the substrate simply to reston the burls of the substrate holder. It is clamped in place. Two methods of clampingthe substrate in place are known - vacuum clamping and electrostatic clamping. Invacuum clamping, the space between the substrate holder and substrate and optionallybetween the substrate table and substrate holder are partially evacuated so that thesubstrate is held in place by the higher pressure of gas or liquid above it. Vacuumclamping however may not be feasible where the beam path and/or the environmentnear the substrate or substrate holder is kept at a low or very low pressure, e.g. forextreme ultraviolet (EUV) radiation lithography. In this case, it may not be possible todevelop a sufficiently large pressure difference across the substrate (or substrateholder) to clamp it. Electrostatic clamping can therefore be used in such a circumstance(or in other circumstances). In electrostatic clamping, an electrode provided on thesubstrate table and/or substrate holder is raised to a high potential, e.g. 10 to 5000 V,and electrostatic forces attract the substrate. Thus another purpose of the burls is tospace the substrate, substrate holder and substrate table apart in order to enableelectrostatic clamping.
[0007] Burls can be used in various other places within a lithographic apparatus, forexample in a support for a patterning device such as a mask, in a gripper of substrateor patterning device handling apparatus, and/or a reticle clamp. Burls in different placesmay have different requirements as to one or more of their dimensions and otherphysical properties. A different method of manufacture may apply. In many cases,damage to one or more burls may necessitate replacement of an entire component.
[0008] It is desirable, for example, to provide an object holder for use in a lithographicapparatus, the holder having burls, e.g. of different shapes, sizes and/or compositions,and a method of manufacturing an object holder having such burls.
[0009] According to an aspect of the invention, there is provided a method ofmanufacturing an object holder for use in a lithographic apparatus, the method comprising: providing a main body having a surface; and forming a plurality of burls onthe surface, the burls projecting from the surface and having end surfaces to support anobject, wherein forming at least part of at least one of the burls comprises laser¬sintering.
[0010] According to an aspect of the invention, there is provided an object holder foruse in a lithographic apparatus, the object holder comprising: a main body having asurface; and a plurality of burls provided on the surface and having end surfaces tosupport an object, wherein at least part of at least one of the burls has been formed bylaser-sintering.
[0011] According to an aspect of the invention, there is provided a lithographicapparatus, comprising: a support structure configured to support a patterning device; aprojection system arranged to project a beam patterned by the patterning device onto asubstrate; and a substrate holder arranged to hold the substrate, the substrate holderbeing as described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Embodiments of the invention will now be described, by way of example only,with reference to the accompanying schematic drawings in which correspondingreference symbols indicate corresponding parts, and in which:
[0013] - Figure 1 depicts a lithographic apparatus according to an embodiment of theinvention;
[0014] - Figures 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;
[0015] - Figure 4 depicts a further liquid supply system for use in a lithographicprojection apparatus;
[0016] - Figure 5 depicts, in cross-section, a barrier member which may be used in anembodiment of the present invention as an immersion liquid supply system;
[0017] - Figure 6 depicts a lithographic apparatus according to an embodiment of theinvention;
[0018] - Figure 7 is a more detailed view of the apparatus 4100;
[0019] - Figure 8 is a more detailed view of the source collector apparatus SO of the apparatus of Figures 6 and 7;
[0020] - Figure 9 depicts in cross-section a substrate table and a substrate holderaccording to an embodiment of the invention;
[0021] - Figures 10A to 10E depict steps in a method of manufacturing a substrateholder according to an embodiment of the invention;
[0022] - Figure 11 depicts a substrate holder according to an embodiment of theinvention;
[0023] - Figure 12 depicts a support structure for a patterning device according to anembodiment of the invention;
[0024] - Figure 13 depicts in plan a part of a support structure according to anembodiment of the invention;
[0025] - Figure 14 depicts the support structure of Figure 13 in cross-section;
[0026] - Figure 15 depicts a substrate handler and gripper according to anembodiment of an invention;
[0027] - Figure 16 depicts a substrate table according to an embodiment of the invention;
[0028] - Figures 17A to C depict steps in a method of repairing a substrate holderaccording to an embodiment of the invention; and
[0029] - Figure 18A to C depict steps in a method of repairing a substrate holderaccording to an embodiment of the invention.
DETAILED DESCRIPTION
[0030] Figure 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:
[0031] - an illumination system (illuminator) IL configured to condition a radiation beamB (e.g. UV radiation, DUV radiation or EUV radiation);
[0032] - a support structure (e.g. a mask table) MT constructed to support a patterningdevice (e.g. a mask) MA and connected to a first positioner PM configured to accuratelyposition the patterning device in accordance with certain parameters;
[0033] - a substrate table (e.g. a wafer table) WT constructed to hold a substrate (e.g.a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate in accordance with certain parameters; and
[0034] - a projection system (e.g. a refractive projection lens system) PS configured toproject a pattern imparted to the radiation beam B by patterning device MA onto atarget portion C (e.g. comprising one or more dies) of the substrate W.
[0035] The illumination system may include various types of optical components, suchas refractive, reflective, magnetic, electromagnetic, electrostatic or other types of opticalcomponents, or any combination thereof, for directing, shaping, or controlling radiation.
[0036] The support structure MT holds the patterning device. The support structure MTholds the patterning device in a manner that depends on the orientation of thepatterning device, the design of the lithographic apparatus, and other conditions, suchas for example whether or not the patterning device is held in a vacuum environment.The support structure MT can use mechanical, vacuum, electrostatic or other clampingtechniques to hold the patterning device. The support structure MT may be a frame or atable, for example, which may be fixed or movable as required. The support structureMT may ensure that the patterning device is at a desired position, for example withrespect to the projection system. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device”.
[0037] The term “patterning device” used herein should be broadly interpreted asreferring to any device that can be used to impart a radiation beam with a pattern in itscross-section such as to create a pattern in a target portion of the substrate. It shouldbe noted that the pattern imparted to the radiation beam may not exactly correspond tothe desired pattern in the target portion of the substrate, for example if the patternincludes phase-shifting features or so called assist features. Generally, the patternimparted to the radiation beam will correspond to a particular functional layer in adevice being created in the target portion, such as an integrated circuit.
[0038] The patterning device may be transmissive or reflective. Examples of patterningdevices include masks, programmable mirror arrays, and programmable LCD panels.Masks are well known in lithography, and include mask types such as binary,alternating phase-shift, and attenuated phase-shift, as well as various hybrid masktypes. An example of a programmable mirror array employs a matrix arrangement ofsmall mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiationbeam which is reflected by the mirror matrix.
[0039] The terms “projection system” used herein should be broadly interpreted asencompassing any type of system, including refractive, reflective, catadioptric,magnetic, electromagnetic and electrostatic optical systems, or any combinationthereof, as appropriate for the exposure radiation being used, or for other factors suchas the use of an immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the more general term“projection system”.
[0040] As here depicted, the apparatus is of a transmissive type (e.g. employing atransmissive mask). Alternatively, the apparatus may be of a reflective type (e.g.employing a programmable mirror array of a type as referred to above, or employing areflective mask).
[0041] The lithographic apparatus may be of a type having two or more substratesupport structures, such as substrate stages or substrate tables, and/or two or moresupport structures for patterning devices. In an apparatus with multiple substratestages, all the substrate stages can be equivalent and interchangeable. In anembodiment, at least one of the multiple substrate stages is particularly adapted forexposure steps and at least one of the multiple substrate stages is particularly adaptedfor measurement or preparatory steps. In an embodiment of the invention one or moreof the multiple substrate stages is replaced by a measurement stage. A measurementstage includes at least part one or more sensor systems such as a sensor detectorand/or target of the sensor system but does not support a substrate. The measurementstage is positionable in the projection beam in place of a substrate stage or a supportstructure for a patterning device. In such apparatus the additional stages may be usedin parallel, or preparatory steps may be carried out on one or more stages while one ormore other stages are being used for exposure.
[0042] Referring to Figure 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may be separateentities, for example when the source is an excimer laser. In such cases, the source isnot considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery systemBD comprising, for example, suitable directing mirrors and/or a beam expander. In othercases the source may be an integral part of the lithographic apparatus, for examplewhen the source is a mercury lamp. The source SO and the illuminator IL, together withthe beam delivery system BD if required, may be referred to as a radiation system.
[0043] The illuminator IL may comprise an adjuster AM configured to adjust theangular intensity distribution of the radiation beam. Generally, at least the outer and/orinner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of theintensity distribution in a pupil plane of the illuminator can be adjusted. In addition, theilluminator IL may comprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiation beam, to have adesired uniformity and intensity distribution in its cross-section. Similar to the sourceSO, the illuminator IL may or may not be considered to form part of the lithographicapparatus. For example, the illuminator IL may be an integral part of the lithographicapparatus or may be a separate entity from the lithographic apparatus. In the lattercase, the lithographic apparatus may be configured to allow the illuminator IL to bemounted thereon. Optionally, the illuminator IL is detachable and may be separatelyprovided (for example, by the lithographic apparatus manufacturer or another supplier).
[0044] The radiation beam B is incident on the patterning device (e.g., mask) MA,which is held on the support structure (e.g., mask table) MT, and is patterned by thepatterning device. Having traversed the patterning device MA, the radiation beam Bpasses through the projection system PS, which focuses the beam onto a target portionC of the substrate W. Substrate W is held on the substrate table WT by a substrateholder according to an embodiment of the present invention and described furtherbelow. With the aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), the substrate table WT canbe moved accurately, e.g. so as to position different target portions C in the path of theradiation beam B. Similarly, the first positioner PM and another position sensor (whichis not explicitly depicted in Figure 1) can be used to accurately position the patterningdevice MA with respect to the path of the radiation beam B, e.g. after mechanicalretrieval from a mask library, or during a scan. In general, movement of the support structure MT may 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 may be realized using a long-strokemodule and a short-stroke module, which form part of the second positioner PW. In thecase of a stepper (as opposed to a scanner) the support structure MT may beconnected to a short-stroke actuator only, or may be fixed. Patterning device MA andsubstrate W may be aligned using patterning device alignment marks M1, M2 andsubstrate alignment marks P1, P2. Although the substrate alignment marks asillustrated occupy dedicated target portions, they may be located in spaces betweentarget portions (these are known as scribe-lane alignment marks). Similarly, insituations in which more than one die is provided on the patterning device MA, thepatterning device alignment marks may be located between the dies.
[0045] The depicted apparatus could be used in at least one of the following modes:
[0046] 1. In step mode, the support structure MT and the substrate table WT arekept essentially stationary, while an entire pattern imparted to the radiation beam isprojected onto a target portion C at one time (i.e. a single static exposure). Thesubstrate table WT is then shifted in the X and/or Y direction so that a different targetportion C can be exposed. In step mode, the maximum size of the exposure field limitsthe size of the target portion C imaged in a single static exposure.
[0047] 2. In scan mode, the support structure MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam is projected ontoa target portion C (i.e. a single dynamic exposure). The velocity and direction of thesubstrate table WT relative to the support structure MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scanmode, the maximum size of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereas the length of thescanning motion determines the height (in the scanning direction) of the target portion.
[0048] 3. In another mode, the support structure MT is kept essentially stationaryholding a programmable patterning device, and the substrate table WT is moved orscanned while a pattern imparted to the radiation beam is projected onto a targetportion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of thesubstrate table WT or in between successive radiation pulses during a scan. This modeof operation can be readily applied to maskless lithography that utilizes programmablepatterning device, such as a programmable mirror array of a type as referred to above.
[0049] Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.
[0050] In many lithographic apparatuses, a fluid, in particular a liquid, is providedbetween the final element of the projection system using a liquid supply system IH toenable imaging of smaller features and/or increase the effective NA of the apparatus.
An embodiment of the invention is described further below with reference to such animmersion apparatus, but may equally be embodied in a non-immersion apparatus.Arrangements to provide liquid between a final element of the projection system andthe substrate can be classed into at least two general categories. These are the bathtype arrangement and the so called localized immersion system. In the bath typearrangement substantially the whole of the substrate and optionally part of the substratetable is submersed in a bath of liquid. The localized immersion system uses a liquidsupply system in which liquid is only provided to a localized area of the substrate. In thelatter category, the space filled by liquid is smaller in plan than the top surface of thesubstrate and the area filled with liquid remains substantially stationary relative to theprojection system while the substrate moves underneath that area. Anotherarrangement, to which an embodiment of the invention is directed, is the all wet solutionin which the liquid is unconfined. In this arrangement substantially the whole top surfaceof the substrate and all or part of the substrate table is covered in immersion liquid. Thedepth of the liquid covering at least the substrate is small. The liquid may be a film,such as a thin-film, of liquid on the substrate.
[0051] Four different types of localized liquid supply systems are illustrated in Figures2 to 5. Any of the liquid supply devices of Figures 2 to 5 may be used in an unconfinedsystem; however, sealing features are not present, are not activated, are not as efficientas normal or are otherwise ineffective to seal liquid to only the localized area.
[0052] One of the arrangements proposed for a localized immersion system is for aliquid supply system to provide liquid on only a localized area of the substrate and in between the final element of the projection system and the substrate using a liquidconfinement system (the substrate generally has a larger surface area than the finalelement of the projection system). One way which has been proposed to arrange forthis is disclosed in PCT patent application publication no. WO 99/49504. As illustratedin Figures 2 and 3, liquid is supplied by at least one inlet onto the substrate, desirablyalong the direction of movement of the substrate relative to the final element, and isremoved by at least one outlet after having passed under the projection system. That is,as the substrate is scanned beneath the element in a -X direction, liquid is supplied atthe +X side of the element and taken up at the -X side.
[0053] Figure 2 shows the arrangement schematically in which liquid is supplied viainlet and is taken up on the other side of the element by outlet which is connected to alow pressure source. The arrows above the substrate W illustrate the direction of liquidflow, and the arrow below the substrate W illustrates the direction of movement of thesubstrate table. In the illustration of Figure 2 the liquid is supplied along the direction ofmovement of the substrate relative to the final element, though this does not need to bethe case. Various orientations and numbers of in-and out-lets positioned around thefinal element are possible, one example is illustrated in Figure 3 in which four sets of aninlet with an outlet on either side are provided in a regular pattern around the finalelement. Arrows in liquid supply and liquid recovery devices indicate the direction ofliquid flow.
[0054] A further immersion lithography solution with a localized liquid supply system isshown in Figure 4. Liquid is supplied by two groove inlets on either side of theprojection system PS and is removed by a plurality of discrete outlets arranged radiallyoutwardly of the inlets. The inlets and outlets can be arranged in a plate with a hole inits center and through which the projection beam is projected. Liquid is supplied by onegroove inlet on one side of the projection system PS and removed by a plurality ofdiscrete outlets on the other side of the projection system PS, causing a flow of a thin-film of liquid between the projection system PS and the substrate W. The choice ofwhich combination of inlet and outlets to use can depend on the direction of movementof the substrate W (the other combination of inlet and outlets being inactive). In thecross-sectional view of Figure 4, arrows illustrate the direction of liquid flow in to inlets and out of outlets.
[0055] Another arrangement which has been proposed is to provide the liquid supplysystem with a liquid confinement member which extends along at least a part of aboundary of the space between the final element of the projection system and thesubstrate table. Such an arrangement is illustrated in Figure 5. The liquid confinementmember is substantially stationary relative to the projection system in the XY plane,though there may be some relative movement in the Z direction (in the direction of theoptical axis). A seal is formed between the liquid confinement member and the surfaceof the substrate. In an embodiment, a seal is formed between the liquid confinementmember and the surface of the substrate and may be a contactless seal such as a gasseal. Such a system is disclosed in United States patent application publication no. US2004-0207824.
[0056] The fluid handling structure 12 includes a liquid confinement member and atleast partly contains liquid in the space 11 between a final element of the projectionsystem PS and the substrate W. A contactless seal 16 to the substrate W may beformed around the image field of the projection system so that liquid is confined withinthe space between the substrate W surface and the final element of the projectionsystem PS. The space is at least partly formed by the fluid handling structure 12positioned below and surrounding the final element of the projection system PS. Liquidis brought into the space below the projection system and within the fluid handlingstructure 12 by liquid inlet 13. The liquid may be removed by liquid outlet 13. The fluidhandling structure 12 may extend a little above the final element of the projectionsystem. The liquid level rises above the final element so that a buffer of liquid isprovided. In an embodiment, the fluid handling structure 12 has an inner periphery thatat the upper end closely conforms to the shape of the projection system or the finalelement thereof and may, e.g., be round. At the bottom, the inner periphery closelyconforms to the shape of the image field, e.g., rectangular, though this need not be thecase.
[0057] In an embodiment, the liquid is contained in the space 11 by a gas seal 16which, during use, is formed between the bottom of the fluid handling structure 12 andthe surface of the substrate W. The gas seal is formed by gas, e.g. air, synthetic air, N2 or another inert gas. The gas in the gas seal is provided under pressure via inlet 15 tothe gap between fluid handling structure 12 and substrate W. The gas is extracted viaoutlet 14. The overpressure on the gas inlet 15, vacuum level on the outlet 14 andgeometry of the gap are arranged so that there is a high-velocity gas flow 16 inwardlythat confines the liquid. The force of the gas on the liquid between the fluid handlingstructure 12 and the substrate W contains the liquid in a space 11. The inlets/outletsmay be annular grooves which surround the space 11. The annular grooves may becontinuous or discontinuous. The flow of gas 16 is effective to contain the liquid in thespace 11. Such a system is disclosed in United States patent application publication no.US 2004-0207824.
[0058] The example of Figure 5 is a localized area arrangement in which liquid is onlyprovided to a localized area of the top surface of the substrate W at any one time.
Other arrangements are possible, including fluid handling systems which make use of asingle phase extractor or a two phase extractor as disclosed, for example, in UnitedStates patent application publication no US 2006-0038968.
[0059] Another arrangement which is possible is one which works on a gas dragprinciple. The so-called gas drag principle has been described, for example, in UnitedStates patent application publication nos. US 2008-0212046, US 2009-0279060, andUS 2009-0279062. In that system the extraction holes are arranged in a shape whichdesirably has a corner. The corner may be aligned with the stepping or scanningdirections. This reduces the force on the meniscus between two openings in the surfaceof the fluid handing structure for a given speed in the step or scan direction comparedto a fluid handling structure having two outlets aligned perpendicular to the direction ofscan.
[0060] Also disclosed in US 2008-0212046 is a gas knife positioned radially outsidethe main liquid retrieval feature. The gas knife traps any liquid which gets past the mainliquid retrieval feature. Such a gas knife may be present in a so called gas dragprinciple arrangement (as disclosed in US 2008-0212046), in a single or two phaseextractor arrangement (such as disclosed in United States patent application publicationno. US 2009-0262318) or any other arrangement.
[0061] Many other types of liquid supply system are possible. The present invention is neither limited to any particular type of liquid supply system, nor to immersionlithography. The invention may be applied equally in any lithography. In an EUVlithography apparatus, the beam path is substantially evacuated and immersionarrangements described above are not used.
[0062] A control system 500 shown in Figure 1 controls the overall operations of thelithographic apparatus and in particular performs an optimization process describedfurther below. Control system 500 can be embodied as a suitably-programmed generalpurpose computer comprising a central processing unit and volatile and non-volatilestorage. Optionally, the control system may further comprise one or more input andoutput devices such as a keyboard and screen, one or more network connectionsand/or one or more interfaces to the various parts of the lithographic apparatus. It willbe appreciated that a one-to-one relationship between controlling computer andlithographic apparatus is not necessary. In an embodiment of the invention onecomputer can control multiple lithographic apparatuses. In an embodiment of theinvention, multiple networked computers can be used to control one lithographicapparatus. The control system 500 may also be configured to control one or moreassociated process devices and substrate handling devices in a lithocell or cluster ofwhich the lithographic apparatus forms a part. The control system 500 can also beconfigured to be subordinate to a supervisory control system of a lithocell or clusterand/or an overall control system of a fab.
[0063] Figure 6 schematically depicts an EUV lithographic apparatus 4100 including asource collector apparatus SO. The apparatus comprises: - an illumination system (illuminator) EIL configured to condition a radiation beam B(e.g. EUV radiation); - a support structure (e.g. a mask table) MT constructed to support a patterning device(e.g. a mask or a reticle) MA and connected to a first positioner PM configured toaccurately position the patterning device; - a substrate table (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accuratelyposition the substrate; and - a projection system (e.g. a reflective projection system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portionC (e.g. comprising one or more dies) of the substrate W.
[0064] These basic components of the EUV lithographic apparatus are similar infunction to the corresponding components of the lithographic apparatus of Figure 1.
The description below mainly covers areas of difference and duplicative description ofaspects of the components that are the same is omitted.
[0065] In an EUV lithographic apparatus, it is desirable to use a vacuum or lowpressure environment since gases can absorb too much radiation. A vacuumenvironment can therefore be provided to the whole beam path with the aid of avacuum wall and one or more vacuum pumps.
[0066] Referring to Figure 6, the EUV illuminator EIL receives an extreme ultra violetradiation beam from the source collector apparatus SO. Methods to produce EUVradiation include, but are not necessarily limited to, converting a material into a plasmastate that has at least one element, e.g., xenon, lithium or tin, with one or moreemission lines in the EUV range. In one such method, often termed laser producedplasma ("LPP") the plasma can be produced by irradiating a fuel, such as a droplet,stream or cluster of material having the desired line-emitting element, with a laserbeam. The source collector apparatus SO may be part of an EUV radiation systemincluding a laser, not shown in Figure 6, to provide the laser beam exciting the fuel. Theresulting plasma emits output radiation, e.g., EUV radiation, which is collected using aradiation collector, disposed in the source collector apparatus. The laser and the sourcecollector apparatus may be separate entities, for example when a C02 laser is used toprovide the laser beam for fuel excitation.
[0067] In such cases, the laser is not considered to form part of the lithographicapparatus and the radiation beam is passed from the laser to the source collectorapparatus with the aid of a beam delivery system comprising, for example, suitabledirecting mirrors and/or a beam expander. In other cases the source may be an integralpart of the source collector apparatus, for example when the source is a discharge-produced plasma EUV generator, often termed as a DPP source.
[0068] The EUV illuminator EIL may comprise an adjuster to adjust the angularintensity distribution of the radiation beam EB. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensitydistribution in a pupil plane of the illuminator can be adjusted. In addition, the EUVilluminator EIL may comprise various other components, such as facetted field andpupil mirror devices. The EUV illuminator EIL may be used to condition the radiationbeam EB, to have a desired uniformity and intensity distribution in its cross section.
[0069] The radiation beam EB is incident on the patterning device (e.g., mask) MA,which is held on the support structure (e.g., mask table) MT, and is patterned by thepatterning device. After being reflected from the patterning device (e.g. mask) MA, theradiation beam EB passes through the projection system PS, which focuses the beamonto a target portion C of the substrate W. With the aid of the second positioner PWand position sensor PS2 (e.g. an interferometric device, linear encoder or capacitivesensor), the substrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam EB. Similarly, the firstpositioner PM and another position sensor PS1 can be used to accurately position thepatterning device (e.g. mask) MA with respect to the path of the radiation beam EB.Patterning device (e.g. mask) MA and substrate W may be aligned using maskalignment marks M1, M2 and substrate alignment marks P1, P2.
[0070] The depicted apparatus could be used the same modes as the apparatus ofFigure 1.
[0071] Figure 7 shows the EUV apparatus 4100 in more detail, including the sourcecollector apparatus SO, the EUV illumination system EIL, and the projection system PS.The source collector apparatus SO is constructed and arranged such that a vacuumenvironment can be maintained in an enclosing structure 4220 of the source collectorapparatus SO. An EUV radiation emitting plasma 4210 may be formed by a dischargeproduced plasma source. EUV radiation may be produced by a gas or vapor, forexample Xe gas, Li vapor or Sn vapor in which the plasma 4210 is created to emitradiation in the EUV range of the electromagnetic spectrum. The plasma 4210 iscreated by, for example, an electrical discharge causing an at least partially ionizedplasma. Partial pressures of, for example, 10 Pa of Xe, Li, Sn vapor or any othersuitable gas or vapor may be required for efficient generation of the radiation. In anembodiment, a plasma of excited tin (Sn) is provided to produce EUV radiation.
[0072] The radiation emitted by the plasma 4210 is passed from a source chamber4211 into a collector chamber 4212 via an optional gas barrier and/or contaminant trap4230 (in some cases also referred to as contaminant barrier or foil trap) which ispositioned in or behind an opening in source chamber 4211. The contaminant trap4230 may include a channel structure. Contamination trap 4230 may also include a gasbarrier or a combination of a gas barrier and a channel structure. The contaminant trapor contaminant barrier 4230 further indicated herein at least includes a channelstructure, as known in the art.
[0073] The collector chamber 4212 may include a radiation collector CO which may bea so-called grazing incidence collector. Radiation collector CO has an upstreamradiation collector side 4251 and a downstream radiation collector side 4252. Radiationthat traverses collector CO can be reflected by a grating spectral filter 4240 to befocused in a virtual source point IF. The virtual source point IF is commonly referred toas the intermediate focus, and the source collector apparatus is arranged such that theintermediate focus IF is located at or near an opening 4221 in the enclosing structure4220. The virtual source point IF is an image of the radiation emitting plasma 4210.
[0074] Subsequently the radiation traverses the illumination system IL, which mayinclude a facetted field mirror device 422 and a facetted pupil mirror device 424arranged to provide a desired angular distribution of the radiation beam 421, at thepatterning device MA, as well as a desired uniformity of radiation intensity at thepatterning device MA. Upon reflection of the beam of radiation 421 at the patterningdevice MA, held by the support structure MT, a patterned beam 426 is formed and thepatterned beam 426 is imaged by the projection system PS via reflective elements 428,430 onto a substrate W held by the substrate stage or substrate table WT.
[0075] More elements than shown may generally be present in illumination optics unitIL and projection system PS. The grating spectral filter 4240 may optionally be present,depending upon the type of lithographic apparatus. There may be more mirrors presentthan those shown in the Figures, for example there may be from 1 to 6 additionalreflective elements present in the projection system PS than shown in Figure 7.
[0076] Collector optic CO, as illustrated in Figure 7, is depicted as a nested collectorwith grazing incidence reflectors 4253, 4254 and 4255, just as an example of a collector (or collector mirror). The grazing incidence reflectors 4253, 4254 and 4255 aredisposed axially symmetric around an optical axis O and a collector optic CO of thistype is preferably used in combination with a discharge produced plasma source, oftencalled a DPP source.
[0077] Alternatively, the source collector apparatus SO may be part of an LPPradiation system as shown in Figure 8. A laser LA is arranged to deposit laser energyinto a fuel, such as xenon (Xe), tin (Sn) or lithium (Li), creating the highly ionizedplasma 4210 with electron temperatures of several 10's of eV. The energetic radiationgenerated during de-excitation and recombination of these ions is emitted from theplasma, collected by a near normal incidence collector optic CO and focused onto theopening 4221 in the enclosing structure 4220.
[0078] Figure 9 depicts a substrate holder according to an embodiment of theinvention. It may be held within a recess in substrate table WT and supports substrateW. The main body of the substrate holder 100 has the form of a flat plate, for examplea disc substantially corresponding in shape and size to the substrate W. The substrateholder can, for example, be formed from Si, SiC, SiSiC, aluminum nitride (AIN),Zerodur, cordierite, or some other suitable ceramic or glass-ceramic material. At leaston a top side, in an embodiment on both sides, the substrate holder has projections106, commonly referred to as burls. In an embodiment, the substrate holder is anintegral part of the substrate table and does not have burls on the lower surface. Theburls are not shown to scale in Figure 9. Some or all of the burls are formed by lasersintering as described below.
[0079] In a practical embodiment, there can be many hundreds or thousands of burls,e.g. more than 10,000 or more than 40,000, distributed across a substrate holder, e.g.,of width (e.g., diameter) 200 mm, 300 mm or 450 mm. The tips of the burls have asmall area, e.g. less than 1 mm2. Thus the total area of all of the burls on one side ofthe substrate holder 100 is less than about 10%, e.g. from 1 to 3%, of the total surfacearea of the substrate holder. Because of the burl arrangement, there is a highprobability that any particle that might lie on the surface of the substrate, substrateholder or substrate table will fall between burls and will not therefore result in adeformation of the substrate or substrate holder.
[0080] The burl arrangement may form a pattern and/or may have a periodicarrangement. The burl arrangement can be regular or can vary as desired to provideappropriate distribution of force on the substrate W and substrate table WT. The burlscan have any shape in plan but are commonly circular in plan. The burls can have thesame shape and dimensions throughout their height but are commonly tapered. Thedistance that the burls project from the rest of the surface of the main body 100a of thesubstrate holder 100 is in the range of from about 1 pm to about 5 mm, desirably fromabout 5 pm to about 250 pm. The thickness of the main body 100a of the substrateholder 100 can be in the range of about 1 mm to about 50 mm, desirably in the range ofabout 5 mm to 20 mm, typically 10 mm.
[0081] Beneficially, the burls may be formed with very consistent dimensions.
Desirably the variation between heights of different burls is very small. Short burls canbe formed (e.g. shorter than 20 pm, shorter than 15 pm, shorter than 5 pm or shorterthan 3 pm). Shorter burls are beneficial because they increase the heat transferbetween the substrate and the substrate holder. The gap between the top of thesubstrate holder away from the burls and the supported surface of a substrate on thesubstrate holder is smaller than a support with a greater height. Such a small gapfacilitates the transfer of heat from a temperature conditioning element (e.g., heater) tothe supported substrate. The minimum burl height is determined by the variations in thetotal height of the thin-film stack and the amount of unflatness of the substrate andsubstrate holder. In an embodiment the burl height is greater than or equal to 1 pm or 2pm.
[0082] The burls can have a width (e.g., diameter) less than or equal to 0.5 mm. In anembodiment the burls have a width (e.g., diameter) in the range of from about 200 pmto about 500 pm. The spacing between burls is between about 1.5 mm to about 3 mm.
[0083] Further, an embodiment of the invention allows use of a wider range ofmaterials for the substrate holder. Materials that are not suitable for previous methodsof forming burls or substrate holders can be used in an embodiment of the invention. Inan embodiment, it is possible to use material such as cordierite, a low CTE glass-ceramic, which cannot easily be machined to form burls. Cordierite has good propertiesfor use in a substrate holder. For example, cordierite has a high Young’s modulus of about 140 Gpa and a low thermal conductivity of about 4 W/mK.
[0084] A substrate holder manufactured according to an embodiment of the inventioncan have a long usable life time due to robust manufacturing methods. An embodimentof the invention can exhibit desirable wear properties, for example good wearresistance and therefore low generation of particular contaminants. Beneficially, anembodiment of the invention can avoid the need for coating the substrate holder.
[0085] A substrate holder according to an embodiment of the invention can have athin-film component 110 formed on one or both surfaces. A thin-film component mayhave a layer thickness in the range of from about 2 nm to about 100 pm. Such a thinfilm component may have one or a plurality of layers. Each layer may be formed by aprocess including chemical vapor deposition, physical vapor deposition (e.g. sputtering),dip coating, spin coating and/or spray coating. In an embodiment, a component formedon the substrate holder comprises a thin-film stack, i.e. including a plurality of thin-filmlayers. Such components are described further below. Although reference in thisdescription is to a thin film stack formed on the top surface of a substrate holder, thethin film stack may be formed on the undersurface of the substrate holder, or on asubstrate table beneath a substrate holder, or on any other surface of the substratetable or substrate holder, including a surface of an integral substrate holder andsubstrate table.
[0086] An electronic or electric component to be formed on the substrate table caninclude, for example, an electrode, a resistive heater and/or a sensor, such as (in anon-limiting list) a strain sensor, a magnetic sensor, a pressure sensor, a capacitivesensor or a temperature sensor. A heater and sensor can be used to control and/ormonitor locally the temperature of the substrate holder and/or substrate. Such localcontrol and/or monitoring can reduce undesired, or induce desired, temperaturevariation and stress in the substrate holder or substrate. Desirably, the heater andsensor are formed on, around and/over the same region as each other. It is desirable tocontrol temperature and/or stress of the substrate in order to reduce or eliminateimaging errors such as overlay errors due to local expansion or contraction of thesubstrate. For example, in an immersion lithography apparatus, evaporation of residualimmersion liquid (e.g., water) on the substrate can cause localized cooling, may apply a heat load to the surface on which the liquid is located, and hence shrinkage of thesubstrate. Conversely, the energy delivered to the substrate by the projection beamduring exposure can cause significant heating and therefore expansion of the substrate.
[0087] In an embodiment, the component to be formed is an electrode for anelectrostatic clamp. In electrostatic clamping, an electrode provided on the substratetable and/or substrate holder is raised to a high potential, e.g. from 10 to 5,000 V. Thesubstrate can be grounded or floating. Electrostatic forces in the electric field generatedby the electrode attract the substrate to the substrate table and/or holder to provide aclamping force. This is described further below.
[0088] One or more electrical connections can be provided to connect the electric orelectronic component on the substrate holder to a voltage source (not shown forconvenience). If the component is an electrostatic clamp, the electrode on the substratehas an electrical connection to the voltage source. The component may be on a topsurface of the substrate support. At least part of the electrical connection may passthrough the body of the substrate support as described in U.S. patent application no.
US 61/555,359, filed on 3 November 2011, which is hereby incorporated by referencein its entirety.
[0089] In an embodiment, one or more localized heaters 101 are controlled bycontroller 103 to provide a desired amount of heat to the substrate holder 100 andsubstrate W to control the temperature of the substrate W. One or more temperaturesensors 102 are connected to controller 104 which monitors the temperature of thesubstrate holder 100 and/or substrate W. Arrangements using one or more heaters andtemperature sensors to locally control the temperature of a substrate are described incopending U.S. patent application publication no. US 2012-0013865, which documentis incorporated herein by reference in its entirety. The arrangements described thereincan be modified to make use of a resistive heater and temperature sensor as describedherein. Further details of thin-film stacks including components thereof and a method ofmanufacture thereof are given in U.S. patent application no. US 13/403,706 filed on 23February 2012 and co-pending U.S. patent application no. 61/621,648, filed on April 9,2012, which documents are hereby incorporated by reference in their entireties.
[0090] A substrate holder for use in a conventional (e.g., DUV) lithographic apparatus (e.g. an immersion lithographic apparatus) is desirably provided with one or more thin-film temperature sensors and/or one or more thin-film heaters. Other forms of sensorand/or heater can be provided in, on and/or under the substrate holder.
[0091] A substrate holder for use in an EUV lithographic apparatus is desirablyprovided with a thin-film electrostatic clamp and optionally one or more thin-filmtemperature sensors and/or one or more thin-film heaters. Other forms of sensor and/orheater can be provided in, on and/or under the substrate holder.
[0092] As mentioned, laser sintering may be used to form the burls. This method isillustrated in Figures 10A to E and starts with a flat plate of the desired shape whichforms the main body 400 of the substrate holder. The flat plate may be pre-formed byanother technique. In an embodiment the plate is formed of SiSiC but one or moreother materials such as Invar™, Zerodur™, ULE™, fused silica, cordierite, boronnitride, silicon nitride, aluminum nitride (AIN) and/or SiC can be used. Desirably, asurface 400a of the plate is ground and/or polished to a desired degree of flatness. Inan embodiment, the surface is cleaned, e.g. with ozone, but this step can be omitted. Inan embodiment, the surface 400a is treated to promote adherence of one or moresubsequent layers, e.g. by application of a primer layer, but this step can be omitted.
On the plate, an isolation layer 410 is applied to isolate one or more metal layers to beformed above it from the main body of the substrate holder. In an embodiment, theisolation layer 410 improves flatness. The isolation layer 410 may be made of BOBapplied by spin or spray coating as described above or of Si02 applied by a PECVDprocess, or other suitable material. On top of the isolation layer, a metal layer 440 isapplied, e.g. by PVD, to arrive at the situation shown in Figure 10A.
[0093] The metal layer is then patterned, e.g. by lithography and selective etching, e.g.a wet etch, to define the desired pattern to form a desired component, e.g. anelectrode, a sensor or a heater. This step also removes the metal layer in an areawhere burls are to be formed in a subsequent step. At this stage, the substrate holder isas illustrated in Figure 10B.
[0094] Over the patterned metal layer, an isolation or dielectric layer 450 is appliedand an opening through to the main body or a base layer, i.e. through both isolationlayers, are formed in locations where burls are desired. The substrate holder is now as illustrated in Figure 10C. Optionally, the exposed areas 400b of the surface of the mainbody 400 are cleaned, e.g. with ozone, and/or treated, e.g. by application of a primerlayer to promote adhesion of the burls which are to be formed subsequently.
[0095] Burls 406 are now formed in the opening through the thin film stack by a lasersintering process. Other structures on the substrate holder, for example a vacuum ring,can be formed concurrently with the burls. It is also possible to form one or moreprojections between the burls that are shorter than the burls but have a larger area.Such a projection improves thermal transfer between the substrate and the substrateholder. Such a projection can be, for example 10 pm or more shorter than the burls406. There are two types of laser sintering methods, both are usable.
[0096] In the first method, a thin layer of powder is applied to the area where burls areto be formed. Then one or more laser beams are used to selectively sinter the powderin the area where the burls are to be formed. When that is complete, another thin layerof powder is applied and selectively heated and sintered. This is repeated so that theburl is built up layer by layer. In an embodiment, each layer has a thickness in the rangeof from 1 to 1.5 pm. Since the sintering pattern can be varied at each layer, the burl canbe built up with any desired shape and/or profile. In this method, the powder may beapplied over a large area and multiple burls formed simultaneously or concurrently.Alternatively, powder may be applied to a small area and each burl formedindependently. Further details of this process can be found in “Laser micro sintering - aquality leap through improvement of powder packing” by A Streek et al published athttp://laz.htwm.de/43_rapidmicro/55_Ver%C3%B6ffentlichungen/Laser%20micro%20sintering%20- %20a%20quality%20leap%20through%20improvement%20of%20powder%20packing.
pdf.
[0097] In the second method, powder is jetted in an inert gas over the area where aburl is to be formed while one or more laser beams irradiate the precise locations whereburls are to be formed. Powder selectively adheres to the positions irradiated by thelaser beam. By suitably shifting the point of irradiation, a burl of desired profile can bebuilt up. Further details of this process can be found in “MICRO-CLADDING USING APULSED FIBRE LASER AND SCANNER” by S. Kloetar et al published at http://laz.htwm.de/43_rapidmicro/55_Ver%C3%B6ffentlichungen/Microcladding_LPM20 10.pdf.
[0098] As with other sintering techniques, laser sintering works by partially meltingparticles of the powder so that they adhere together when they cool. Laser sintering hasan advantage in that the controlled application of the laser beam allows for spatialcontrol of where sintering takes place. In both methods described above, the powdercan be pre-heated to a temperature close to the relevant melting point so that lessenergy need be applied by the laser beam to complete the sintering. A wide variety ofmaterials can be used in sintering techniques. The powder can be formed of a singlematerial, e.g. a metal such as titanium, a semiconductor such as silicon or a ceramicsuch as fused silica, cordierite and/or aluminum nitride. In an embodiment, the powderis made of two or more components. One component has a relatively low melting pointwhich melts to form a matrix in which the other particulate component(s) is(are)embedded. The matrix-forming component of the powder can be provided as separateparticles or as a coating on particles of another material(s). The matrix formingcompound can be any of the single materials mentioned above. The particulatecomponent can be one or more components selected from the group comprising cubicboron nitride, silicon nitride, silicon carbide, titanium nitride, titanium carbide and/ordiamond, e.g. diamond-like carbon (DLC). The sintering process can be carried out inan inert atmosphere or a vacuum to help prevent chemical change to the material beingsintered or in a controlled atmosphere to promote a chemical change.
[0099] Thus, the material from which the burl is to be formed can be selected from awide range of materials to provide a desired property such as strength of adherence tothe material of the base body of the substrate holder. Desirably, the burl is made of thesame material as, or a material compatible with, the material of the main body of thesubstrate holder. For example, it is generally desirable that the burl bond well to thebase material of the main body of the substrate so as to provide longevity androbustness in use. In some applications, it is desirable that the burls have high thermalconductivity to assist in temperature conditioning of the substrate. In other applications,a low thermal conductivity can be desirable in order to isolate the substrate. Otherrelevant properties of the burls that can be affected through choice of material include electrical conductivity, dielectric strength and wear resistance.
[00100] The laser sintering technique for forming the burls generally results in a roughupper surface to the burls as depicted in Figure 10D. If so, it is desirable to perform afinal polishing step so as to provide a smooth upper surface to the burls as illustratedFigure 10E. In some cases, e.g. if the final polishing is performed with a coarse-grainedslurry, it might be desirable to first protect the thin film stacks with an additional coating.However this is often not necessary, for example where the thin film stack contains onlyelectrodes for clamping purposes.
[00101] A further advantage of the laser sintering process is that it allows thecomposition of a burl to be varied through its height. It is therefore possible tomanufacture burls having one or more sections or layers of different composition and/orproperty as illustrated in Figure 11. For example, a lower part 406a of a burl can beformed of material that bonds well to the material of the base body of the substrateholder, while the upper part 406b of the burl is formed of a material having, e.g., animproved wear property. (Note that the base body may be made using a differenttechnique from the burls.) For example, particles of diamond, such as diamond-likecarbon (DLC), can be included in the upper part 406b of the burl to improve wearresistance. Alternatively, diamond particles (e.g. DLC) can be included in the lower part406a to improve thermal conductivity. In an embodiment, a burl is formed with morethan two distinct layers. In an embodiment, a burl is formed with a gradual change incomposition, content or material property through at least a part of its height.
[00102] It is also possible to vary the composition of the powder to be sintered in adirection substantially parallel to the surface on which the burl is being formed. In thepowder layer method of sintering, this can be achieved through variation of thecomposition of the powder within each layer of powder as it is applied. In the powderjetting method, this can be achieved through variation of the composition of the jettedpowder with time in synchronization with movement of the point of laser irradiation.Varying the material composition of the burl in a direction substantially parallel to thesurface on which it is formed, optionally in addition to variation in the height direction,can allow fine control over one or more mechanical and other properties of the burl, e.g.stiffness.
[00103] An advantage of an embodiment of the invention is that burls can be formedwith almost any shape in three dimensions. In an embodiment, a burl has a constantcross-section throughout its height. In an embodiment, a burl tapers away from themain body of the substrate holder. In an embodiment, the cross-section of a burl varieswith height. In an embodiment, a burl has a cross-section, substantially parallel to thesurface of the main body of the substrate holder, that is selected from the groupconsisting of circle, square, rectangle, oval, rhombus and “racetrack” or “stadium”shape. A “racetrack” or “stadium” shape has two straight parallel sides joined by curves,e.g. semicircles.
[00104] In an embodiment, a thin-film stack is provided on only one side of thesubstrate holder. In an embodiment, no thin film stacks are provided on the substrateholder. In an embodiment, thin-film stacks are provided on both sides of the substrateholder. In an embodiment, burls are provided on both sides of the substrate holder. Ifburls are provided on both sides of the substrate holder it is not necessary that thesame method of forming the burls is used on both sides.
[00105] An embodiment of the present invention can be employed to form burls onother components in a lithographic apparatus where controlled contact between acomponent of the apparatus and an object to be handled is desired.
[00106] Figure 12 shows an embodiment of the invention which is a support structurefor a patterning device, for example a mask table MT to support a mask MA. The mainbody 500 of the mask table is, in contrast with a substrate table, provided with a throughhole 501 for passage for the projection beam B. The mask MA is supported by burlareas 502 formed by laser sintering on the mask table 500. The use of burls to supportthe mask MA has similar functions of the use of burls to support a substrate on thesubstrate table or holder. For example, burls can prevent or reduce the chance of themask being misaligned or distorted by the presence of a particle between the mask anda surface on which it is supported. Burls can allow a mask to be clamped to a masktable or other support structure using a vacuum and/or electrostatic clamping technique.Since in most lithographic apparatuses the projection system PS reduces the projectedimage by a factor of 4 or 5, in a scanning mode of operation, the mask is moved with avelocity and acceleration 4 or 5 times greater than the substrate table. Therefore, a commensurately larger clamping force should be exerted. Desirably, a mask is held onthe support structure in such a manner that no or minimal stress is generated in themask. The use of burls can contribute to this aim.
[00107] In Figure 12, burls are shown as provided in discrete areas either side of theaperture 501. In an embodiment, burls can be provided in a continuous area completelysurrounding the aperture or in multiple locations spaced around the aperture. The exactlocation of the burls can be determined in construction of an embodiment. Burls used tosupport a mask, e.g. on a mask table or mask handling device, can have a diameter offrom 100 pm to 1 pm, desirably 300 to 500 pm. The burls can have an elongate shapein plan such as an ellipse or rectangle.
[00108] In an embodiment, burls are formed by laser sintering on a clamp for a mask orreticle. The clamp can be a layered structure of, for example, a ULE-Zeodur-ULE or athin film stack-Zerodur-thin film stack. Such a clamp can have a thickness of about 10mm. The burls can have a pitch of from 2 to 10 mm.
[00109] Figure 13 depicts in plan a support structure for a patterning device, e.g. amask or a reticle, according to an embodiment of the invention. Figure 14 depicts thesame support structure in cross-section along line XX of Figure 13. The supportstructure comprises a support member 512 that is supported above a main body 510 bya leaf spring 513. The upper surface of the support member 512 has a central recess515 surrounded by an area of burls 106. The central recess 515 is connected viaconduit 516 to a low pressure (e.g., vacuum) source 517.
[00110] When a patterning device such as mask MA is placed on support member 512and pressure in the central recess 515 is reduced, the patterning device is clampedsecurely in place. By virtue of the leaf spring 513, the position of the support member512 in a direction substantially perpendicular to the surface of the patterning device MAis well defined. Flowever, the support member 512 is allowed to move in at least onedirection substantially parallel to the surface of the patterning device MA. This meansthat it help ensure that no or minimal stresses arise in the patterning device MA. Suchstresses are undesirable as they might distort the pattern defined by patterning deviceMA. The provision of burls 106 formed by laser sintering on the support member 512helps ensure that the patterning device MA is accurately positioned.
[00111] Figure 15 illustrates a substrate handling arm or gripper 600 according to anembodiment of the invention. Substrate handling arm 600 is driven by one or moreactuators (not shown). Substrate handling arm 600 is used to transfer a substratebetween, e.g., a loading dock and a pre-alignment stage, between the pre-alignmentstage and the substrate table and/or between the substrate table and an unloadingdock. Similar handling devices may be used in the track part of a lithocell or may beused to move a patterning device (e.g., a mask). The substrate handling arm 600comprises a pair of fingers or prongs 601 spaced apart in a substantially horizontalplane. An upper surface, or part thereof, of each of the prongs 601 is provided with anarea 602 having burls formed by laser sintering. The use of burls on the substratehandling arm can have one or more of the same advantages as described above, thatis, e.g., enabling the use of a vacuum and/or electrostatic clamping technique and/orpreventing particulates distorting the substrate.
[00112] Figure 16 shows an embodiment of the invention in which a substrate holder isintegrated with the substrate table WT. The holder WT has a main body 700 in which isformed a recess 701 within which the substrate W can be accommodated. The lowersurface of the recess 701 is provided with burls 106 formed by laser sintering describedabove. The depth of the recess 701 and height of burls 106 are determined to helpensure that the upper surface of the substrate W is substantially coplanar with theupper surface of the main body 700. In this way, one or more sensors, such as atransmission image sensor TIS, provided in the substrate table WT can makemeasurements at a substantially same vertical position as the exposures onto thesubstrate W will be performed.
[00113] An advantage of embodiment of the present invention is that burls can beformed reliably and accurately on a wider variety of surfaces than previously knownmethods of forming burls. Thus, burls can be provided on a component that would nothave been suitable for provision of burls by prior techniques such as a material removaltechnique, for example electric discharge machining (EDM).
[00114] A further advantage is that methods described herein can be used to repairburls, individually or collectively. Two methods of repairing burls according toembodiments of the invention will be described below. These methods can be used to repair burls formed by any method, not just burls formed by laser sintering.
[00115] In a repair method according to an embodiment of the invention, steps of whichare illustrated in Figures 17A to 17C, individual burls are repaired. As shown in Figure17A, an object holder 800 has a plurality of burls 801 and a damaged burl 802. Thedamaged burl 802 has a rough upper surface 802a caused by, for example, wear orphysical damage. The damaged burl is further ground down to provide a smoothsurface 802b as shown in Figure 17B. A temporary protective coating can be providedto cover intact burls 801 during this process. If desired, the ground surface 802b can becleaned, e.g. with ozone, and/or pre-treated, e.g. by application of a primer. A lasersintering technique, as described above, is next used to rebuild the burl to its originalshape and/or height (or to a different desired shape and/or height). This may involvebuilding the repaired burl 803 to a height higher than the ultimately designed height andpolishing back to a level matching the height of intact burls 801, as shown in Figure17C.
[00116] In a further repair method, steps of which are depicted in Figure 18A to 18C, aplurality of burls 901 on an object holder 900 are repaired simultaneously. Thisapproach is particularly applicable for the periodic rehabilitation of an object holder toaccount for wear rather than to address isolated incidences of damage. This methodcan also be used to adjust the height of burls to suit changed operating parameters,e.g. a change in thickness of a substrate to be exposed.
[00117] In the method of this embodiment, the upper surfaces of burls 901, shown inFigure 18A, can optionally be cleaned, e.g. using ozone, or prepared, e.g. byapplication of a primer. Then an additional layer 902 is built up on the burls 901 by alaser sintering process as described above. In an embodiment, the additional layer 902has a thickness in the range of from 1 to 5 pm, desirably 2 to 3 pm. In most cases thiswill provide a rough upper surface 902a, shown in Figure 18B, which is at a higherheight than the ultimate desired height for the burls. The burls can then be polishedback to provide a desired flatness and desired roughness of top surface 902b at thedesired height, as shown in Figure 18C.
[00118] As well as a direct benefit of providing a method of repairing burls, namely thatdamaged components do not always need to be replaced, the existence of a repair technique enables burls to be formed directly on a component where it would beeconomically undesirable to replace the component in the invent of damage to one ormore burls.
[00119] An embodiment of the present invention advantageously enables the use ofburls on a component of a lithographic apparatus such as a substrate table, a supportstructure for a patterning device, a mask table, a wafer handler, a mask handler, agripper, a pre-alignment stage, a process device in a track, a substrate handling robot,a conditioning plate, a substrate conditioning unit and/or a sensor mount. Burlsmanufactured according to an embodiment of the invention can be used wherever anobject - such as a substrate, patterning device, optical element or sensor - is to beheld or mounted at a precise location. A sensor which can be mounted on burls formedaccording to an embodiment of the invention may include a transmission image sensorand/or an interferometric aberration sensor.
[00120] An advantage of embodiment of the present invention is that it can form burlsmore accurately than a subtractive technique such as electric discharge machining.With an embodiment of the invention, burls may be formed reliably and accurately. Anyburls that are missing or damaged in the manufacturing process can be easily added orrepaired. In an embodiment the body may be made by a different technique from theburls formed thereon.
[00121] As will be appreciated, any of the above described features can be used withany other feature and it is not only those combinations explicitly described which arecovered in this application.
[00122] Although specific reference may be made in this text to the use of lithographicapparatus in the manufacture of ICs, it should be understood that the lithographicapparatus described herein may have other applications in manufacturing componentswith microscale, or even nanoscale features, such as the manufacture of integratedoptical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The skilledartisan will appreciate that, in the context of such alternative applications, any use ofthe terms “wafer” or “die” herein may be considered as synonymous with the moregeneral terms “substrate” or “target portion", respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool thattypically applies a layer of resist to a substrate and develops the exposed resist), ametrology tool and/or an inspection tool. Where applicable, the disclosure herein maybe applied to such and other substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layer 1C, so that theterm substrate used herein may also refer to a substrate that already contains multipleprocessed layers.
[00123] The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelengthof or about 365, 248, 193, 157 or 126 nm).
[00124] The term “lens”, where the context allows, may refer to any one or combinationof various types of optical components, including refractive and reflective opticalcomponents.
[00125] While specific embodiments of the invention have been described above, it willbe appreciated that the invention, at least in the form of a method of operation of anapparatus as herein described, may be practiced otherwise than as described. Forexample, the embodiments of the invention, at least in the form of a method ofoperation of an apparatus, may take the form of one or more computer programscontaining one or more sequences of machine-readable instructions describing amethod of operating an apparatus as discussed above, or a data storage medium (e.g.semiconductor memory, magnetic or optical disk) having such a computer programstored therein. Further, the machine readable instruction may be embodied in two ormore computer programs. The two or more computer programs may be stored on oneor more different memories and/or data storage media.
[00126] Any controllers described herein may each or in combination be operable whenthe one or more computer programs are read by one or more computer processorslocated within at least one component of the lithographic apparatus. The controllersmay each or in combination have any suitable configuration for receiving, processingand sending signals. One or more multiple processors are configured to communicatewith at least one of the controllers. For example, each controller may include one ormore processors for executing the computer programs that include machine-readable instructions for the methods of operating an apparatus as described above. Thecontrollers may include data storage media for storing such computer programs, and/orhardware to receive such media. So the controller(s) may operate according to themachine readable instructions of one or more computer programs.
[00127] An embodiment of the invention may be applied to substrates with a width (e.g.,diameter) of 300 mm or 450 mm or any other size.
[00128] One or more embodiments of the invention may be applied to any immersionlithography apparatus, in particular, but not exclusively, those types mentioned above,whether the immersion liquid is provided in the form of a bath, only on a localizedsurface area of the substrate, or is unconfined on the substrate and/or substrate table.
In an unconfined arrangement, the immersion liquid may flow over the surface of thesubstrate and/or substrate table so that substantially the entire uncovered surface ofthe substrate table and/or substrate is wetted. In such an unconfined immersionsystem, the liquid supply system may not confine the immersion liquid or it may providea proportion of immersion liquid confinement, but not substantially completeconfinement of the immersion liquid.
[00129] A liquid supply system as contemplated herein should be broadly construed. Incertain embodiments, it may be a mechanism or combination of structures that providesa liquid to a space between the projection system and the substrate and/or substratetable. It may comprise a combination of one or more structures, one or more liquidinlets, one or more gas inlets, one or more gas outlets, and/or one or more liquid outletsthat provide liquid to the space. In an embodiment, a surface of the space may be aportion of the substrate and/or substrate table, or a surface of the space maycompletely cover a surface of the substrate and/or substrate table, or the space mayenvelop the substrate and/or substrate table. The liquid supply system may optionallyfurther include one or more elements to control the position, quantity, quality, shape,flow rate or any other features of the liquid.
[00130] In a first aspect of the invention there is provided a method of manufacturing anobject holder for use in a lithographic apparatus, the method comprising: providing amain body having a surface; and forming a plurality of burls on the surface, the burlsprojecting from the surface and having end surfaces to support an object, wherein forming at least part of at least one of the burls comprises laser-sintering.
[00131] The laser-sintering may comprise: applying a layer of powder to the surface;and selectively irradiating the layer of powder with a radiation beam so as to cause atleast partial melting of the powder at irradiated locations. In an embodiment, the laser¬sintering comprises: irradiating a location on the surface; and jetting powder at theirradiated location.
[00132] The main body may be formed of a different material than the at least one burl.The at least one burl may comprise at least one material selected from the groupconsisting of: Ti, Si, fused silica, Cordierite, diamond-like carbon, SiC, S1O2, AIN, TiNand CrN. The at least one burl may be formed of a matrix material and particlesembedded in the matrix material. The matrix material may comprise at least onematerial selected from the group consisting of: Ti, Si, fused silica, Cordierite, diamond¬like carbon, SiC, Si02, AIN, TiN and CrN. The particles may comprise at least onematerial selected from the group consisting of: cubic boron nitride, silicon nitride, siliconcarbide, titanium nitride, titanium carbide and diamond.
[00133] At least one burl may comprise a first layer of a first material and a second layerof a second material that is different from the first material. The first and secondmaterials may be different in a property or a component.
[00134] In an embodiment, the object is a substrate or a patterning device. A thin filmstack may be provided on the surface, the plurality of burls projecting further from thesurface than the thin film stack.
[00135] In a second aspect of the invention there is provided a method of repairing anobject holder having burls for use in a lithographic apparatus, the method comprising:preparing a burl to be repaired; applying a layer of material to the burl to be repaired bylaser-sintering; and polishing the layer of material.
[00136] In a third aspect of the invention there is provided an object holder for use in alithographic apparatus, the object holder comprising: a main body having a surface; anda plurality of burls provided on the surface and having end surfaces to support anobject, wherein at least part of at least one of the burls has been formed by laser¬sintering.
[00137] In an embodiment, the main body is formed of a different material than the part of the burl. The at least one burl may comprise at least one material selected from thegroup consisting of: Ti, Si, fused silica, cordierite, diamond-like carbon, SiC, Si02, AIN,TiN and CrN. The at least one burl may be formed of a matrix material and particlesembedded in the matrix material. The matrix material may comprise at least onematerial selected from the group consisting of: Ti, Si, fused silica, cordierite, diamond¬like carbon, SiC, Si02, ALN, TiN and CrN. The particles may comprise at least onematerial selected from the group consisting of cubic boron nitride, silicon nitride, siliconcarbide, titanium nitride, titanium carbide and diamond.
[00138] At least one burl may comprise a first layer of a first material and a second layerof a second material that is different from the first material. The first and secondmaterials may be different in a property or a component. The at least one burl mayhave a substantially constant cross-section substantially parallel to the surface. The atleast one burl may taper away from the surface. A cross-section, substantially parallelto the surface, of the at least one burl may be selected from the group consisting of:circle, square, rectangle, oval, rhombus and “racetrack” or “stadium” shape. The mainbody may comprise at least one material selected from the group consisting of:
Zerodur, cordierite, SiC, SiSiC, AIN, Invar, ceramic and glass-ceramic.
[00139] The object holder is constructed and arranged to support, as the object, at leastone selected from: a substrate, a patterning device, a sensor, and optical element. Inan embodiment the object is a substrate and the object holder is a substrate holder.
The substrate holder may have a diameter substantially equal to 200 mm, 300 mm or450 mm. The object may be a patterning device and the object holder is a supportstructure for the patterning device. The object holder may be a reticle clamp. Theobject holder may be a substrate gripper. A thin film stack may be provided on thesurface, the plurality of burls projecting further from the surface than the thin film stack.
[00140] In a fourth aspect of the invention there is provided a lithographic apparatus,comprising: a support structure configured to support a patterning device; a projectionsystem arranged to project a beam patterned by the patterning device onto a substrate;and a substrate holder arranged to hold the substrate, the substrate holder beingaccording to features of the third aspect of the invention.
[00141] The lithographic apparatus may comprise a substrate table and wherein the substrate holder is integrated into the substrate table.
[00142] In a fifth aspect of the invention there is provided a table for use in alithographic apparatus, the table comprising: a main body having a surface; and aplurality of burls on the surface and having end surfaces to support an object, forexample a substrate, wherein the burls have been formed by laser-sintering.
[00143] In a sixth aspect of the invention there is provided a lithographic apparatus,comprising: a support structure configured to support a patterning device; a projectionsystem arranged to project a beam patterned by the patterning device onto a substrate;and a table according to the fifth aspect of the invention.
[00144] In a seventh aspect of the invention, there is provided a device manufacturingmethod using a lithographic apparatus, the method comprising: projecting a beampatterned by a patterning device onto a substrate while holding the substrate on asubstrate holder, wherein the substrate holder comprises: a main body having asurface; and a plurality of burls on the surface and having end surfaces to support thesubstrate, wherein the burls have been formed by laser-sintering.
[00145] The descriptions above are intended to be illustrative, not limiting. Thus, it willbe apparent to one skilled in the art that modifications may be made to the invention asdescribed without departing from the scope of the clauses set out below. Other aspectsof the invention are set-out as in the following numbered clauses.
CLAUSES
1. A method of manufacturing an object holder for use in a lithographic apparatus,the method comprising: providing a main body having a surface; and forming a plurality of burls on the surface, the burls projecting from the surfaceand having end surfaces to support an object, wherein forming at least part of at leastone of the burls comprises laser-sintering.
2. The method of clause 1, wherein the laser-sintering comprises:applying a layer of powder to the surface; and selectively irradiating the layer of powder with a radiation beam so as to cause atleast partial melting of the powder at irradiated locations.
3. The method of clause 1, wherein the laser-sintering comprises:irradiating a location on the surface; and jetting powder at the irradiated location.
4. The method of any of clauses 1 to 3, wherein the main body is formed of adifferent material than the at least one burl.
5. The method of any of clauses 1 to 4, wherein the at least one burl comprises atleast one material selected from the group consisting of: Ti, Si, fused silica, Cordierite,diamond-like carbon, SiC, Si02, AIN, TiN and CrN.
6. The method of any of clauses 1 to 4, wherein the at least one burl is formed of amatrix material and particles embedded in the matrix material.
7. The method of any of clauses 1 to 6, wherein at least one burl comprises a firstlayer of a first material and a second layer of a second material that is different from thefirst material.
8. The method of clause 7, wherein the first and second materials are different in aproperty or a component.
9. The method of any of clauses 1 to 8, wherein the object is a substrate or apatterning device.
10. The method of any of clauses 1 to 9, where a thin film stack is provided on thesurface, the plurality of burls projecting further from the surface than the thin film stack.
11. An object holder for use in a lithographic apparatus, the object holdercomprising: a main body having a surface; and a plurality of burls provided on the surface and having end surfaces to supportan object, wherein at least part of at least one of the burls has been formed by laser¬sintering.
12. The object holder of clause 11, wherein the object holder is constructed andarranged to support, as the object, at least one selected from: a substrate, a patterningdevice, a sensor, and optical element.
13. The object holder of clause 11 or 12, where a thin film stack is provided on thesurface, the plurality of burls projecting further from the surface than the thin film stack.
14. The object holder of clause 11, wherein the object holder is at least one of: asubstrate holder for a substrate; a support structure for a patterning device; a reticleclamp for a reticle; or a substrate gripper for a substrate.
15. A lithographic apparatus, comprising: a support structure configured to support a patterning device; a projection system arranged to project a beam patterned by the patterningdevice onto a substrate; and a substrate holder arranged to hold the substrate, the substrate holder beingaccording to clause 14.

权利要求:
Claims (1)
[1]
A lithography device comprising: an illumination device adapted to deliver a radiation beam; a carrier constructed to support a patterning device, the patterning device being capable of applying a pattern in cross-section of the radiation beam to form a patterned radiation beam; a substrate table constructed to support a substrate; and a projection device adapted to project the patterned radiation beam onto a target area of the substrate, characterized in that the substrate table is oriented for positioning the target area of the substrate in a focal plane of the projection device.

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法律状态:
2014-10-29| WDAP| Patent application withdrawn|Effective date: 20141008 |

优先权:

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申请号 | 申请日 | 专利标题

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US201261594857P| true| 2012-02-03|2012-02-03|

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US201261594857|2012-02-03|

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US201261621648P| true| 2012-04-09|2012-04-09|

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US201261621660P| true| 2012-04-09|2012-04-09|

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US201261621648|2012-04-09|

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US201261621660|2012-04-09|

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