Patent ID: 12204255

DETAILED DESCRIPTION

FIG.1schematically depicts a lithographic apparatus according to one embodiment of the invention. The apparatus comprises:an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or DUV radiation);a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters;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; anda projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.

The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.

The support structure MT holds the patterning device. The support structure MT holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as 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 clamping techniques to hold the patterning device. The support structure MT may be a frame or a table, for example, which may be fixed or movable as required. The support structure MT may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples of patterning devices 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 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 pattern in a radiation beam which is reflected by the mirror matrix.

The term “projection system” used herein should be broadly interpreted as encompassing 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 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”.

As here depicted, the apparatus is of a transmissive type (e.g. employing a transmissive 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 a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more patterning device tables). In such “multiple stage” machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure.

Referring toFIG.1, the illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not 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 system BD comprising, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD configured to adjust the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may comprise various other components, such as an integrator IN and a condenser CO. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section. Similar to the source SO, the illuminator IL may or may not be considered to form part of the lithographic apparatus. For example, the illuminator IL may be an integral part of the lithographic apparatus or may be a separate entity from the lithographic apparatus. In the latter case, the lithographic apparatus may be configured to allow the illuminator IL to be mounted thereon. Optionally, the illuminator IL is detachable and may be separately provided (for example, by the lithographic apparatus manufacturer or another supplier).

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 the patterning device. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF (e.g. an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. 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 (which is not explicitly depicted inFIG.1) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval 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-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 support structure MT may be connected to a short-stroke actuator only, or may be fixed. Patterning device MA and substrate W may be aligned using patterning device alignment marks M1, M2and substrate alignment marks P1, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the following modes:

1. In step mode, the support structure MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam 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. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure.

2. In scan mode, the support structure MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam 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 MT may be determined by the (de-) magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion.

3. In another mode, the support structure MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required 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 programmable patterning device, such as a programmable mirror array of a type as referred to above.

Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed.

Arrangements for providing liquid between a final element of the projection system PS and the substrate can be classed into two general categories. These are the bath type arrangement in which the whole of the substrate W and optionally part of the substrate table WT is submersed in a bath of liquid and the so called localized immersion system which uses a liquid supply system in which liquid is only provided to a localized area of the substrate. In the latter category, the space filled by liquid is smaller in plan than the top surface of the substrate and the area filled with liquid remains substantially stationary relative to the projection system PS while the substrate W moves underneath that area. A further arrangement, to which an embodiment of the present invention is directed, is the all wet solution in which the liquid is unconfined. In this arrangement substantially the whole top surface of the substrate and all or part of the substrate table is covered in immersion liquid. The depth 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. Any of the liquid supply devices ofFIGS.2-5may be used in such a system; however, sealing features are not present, are not activated, are not as efficient as normal or are otherwise ineffective to seal liquid to only the localized area. Four different types of localized liquid supply systems are illustrated inFIGS.2-5. The liquid supply systems disclosed inFIGS.2-4were described above.

Another arrangement which has been proposed is to provide the liquid supply system with a liquid confinement member which extends along at least a part of a boundary of the space between the final element of the projection system and the substrate table. Such an arrangement is illustrated inFIG.5. The liquid confinement member 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 the optical axis). A seal is formed between the liquid confinement and the surface of the substrate. In an embodiment, a seal is formed between the liquid confinement structure and the surface of the substrate and may be a contactless seal such as a gas seal. Such a system is disclosed in United States patent application publication no. US 2004-0207824.

FIG.5schematically depicts a localized liquid supply system with a barrier member12, IH. The barrier member extends along at least a part of a boundary of the space between the final element of the projection system and the substrate table WT or substrate W. (Please note that reference in the following text to surface of the substrate W also refers in addition or in the alternative to a surface of the substrate table, unless expressly stated otherwise.) The barrier member12is 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 the optical axis). In an embodiment, a seal is formed between the barrier member and the surface of the substrate W and may be a contactless seal such as a fluid seal, desirably a gas seal.

The barrier member12at least partly contains liquid in the space11between a final element of the projection system PS and the substrate W. A contactless seal16to the substrate W may be formed around the image field of the projection system so that liquid is confined within the space between the substrate W surface and the final element of the projection system PS. The space is at least partly formed by the barrier member12positioned below and surrounding the final element of the projection system PS. Liquid is brought into the space below the projection system and within the barrier member12by liquid inlet13. The liquid may be removed by liquid outlet13. The barrier member12may extend a little above the final element of the projection system. The liquid level rises above the final element so that a buffer of liquid is provided. In an embodiment, the barrier member12has an inner periphery that at the upper end closely conforms to the shape of the projection system or the final element thereof and may, e.g., be round. At the bottom, the inner periphery closely conforms to the shape of the image field, e.g., rectangular, though this need not be the case.

In an embodiment, the liquid is contained in the space11by a gas seal16which, during use, is formed between the bottom of the barrier member12and the surface of the substrate W. The gas seal is formed by gas, e.g. air or synthetic air but, in an embodiment, N2or another inert gas. The gas in the gas seal is provided under pressure via inlet15to the gap between barrier member12and substrate W. The gas is extracted via outlet14. The overpressure on the gas inlet15, vacuum level on the outlet14and geometry of the gap are arranged so that there is a high-velocity gas flow16inwardly that confines the liquid. The force of the gas on the liquid between the barrier member12and the substrate W contains the liquid in a space11. The inlets/outlets may be annular grooves which surround the space11. The annular grooves may be continuous or discontinuous. The flow of gas16is effective to contain the liquid in the space11. Such a system is disclosed in United States patent application publication no. US 2004-0207824.

Other arrangements are possible and, as will be clear from the description below, an embodiment of the present invention may use any type of localized liquid supply system. An embodiment of the invention is particularly relevant to use with any localized liquid supply systems as the liquid supply system.

FIG.6illustrates a barrier member12which is part of a liquid supply system. The barrier member12extends around the periphery (e.g., circumference) of the final element of the projection system PS such that the barrier member (which is sometimes called a seal member) is, for example, substantially annular in overall shape. The projection system PS may not be circular and the outer edge of the barrier member12may also not be circular so that it is not necessary for the barrier member to be ring shaped. The barrier has an opening through which the projection beam may pass out from the final element of the projection system PS. Thus, during exposure, the projection beam may pass through liquid contained in the opening of the barrier member and onto the substrate W.

The function of the barrier member12is at least partly to maintain or confine liquid in the space between the projection system PS and the substrate W so that the projection beam may pass through the liquid. The top level of liquid is simply contained by the presence of the barrier member12.

The immersion liquid is provided to the space11by the barrier member12(thus the barrier member may be considered to be a fluid handling structure). A passageway or flow path for immersion liquid passes through the barrier member12. Part of the flow path is comprised by a chamber26. The chamber26has two side walls28,22. Liquid passes through the first side wall28into chamber26from chamber or outlet24and then through the second side wall22into the space11. A plurality of outlets20provide the liquid to the space11. The liquid passes through through holes29,20in side walls28,22respectively prior to entering the space11. The location of the through holes20,29may be random.

A seal is provided between the bottom of the barrier member12and the substrate W. InFIG.6a seal device is configured to provide a contactless seal and is made up of several components. Radially outwardly from the optical axis of the projection system PS, there is provided a (optional) flow control plate50which extends into the space (though not into the path of the projection beam) which helps maintain substantially parallel flow of the immersion liquid out of outlet20across the space. The flow control plate50has through holes55in it to reduce the resistance to movement in the direction of the optical axis of the barrier member12relative to the projection system PS and/or substrate W.

Radially outwardly of the flow control plate50on the bottom surface of the barrier member12may be an extractor assembly70to extract liquid from between the barrier member12and the substrate W and/or the substrate table WT. The extractor may operate as a single phase or as a dual phase extractor.

Radially outwardly of the extractor assembly70may be a recess80. The recess is connected through an inlet82to the atmosphere. The recess is connected via an outlet84to a low pressure source. Radially outwardly of the recess80may be a gas knife90. An arrangement of the extractor, recess and gas knife is disclosed in detail in United States patent application publication no. US 2006/0158627.

The extractor assembly70comprises a liquid removal device or extractor or inlet such as the one disclosed in United States patent application publication no. US 2006-0038968. Any type of liquid extractor may be used. In an embodiment, the extractor assembly or liquid removal device70comprises an inlet which is covered in a porous material75which is used to separate liquid from gas to enable single-liquid phase liquid extraction. A chamber78downstream of the porous material75is maintained at a slight under pressure and is filled with liquid. The under pressure in the chamber78is such that the meniscuses formed in the holes of the porous material prevent ambient gas from being drawn into the chamber78of the extractor assembly70. However, when the porous surface75comes into contact with liquid there is no meniscus to restrict flow and the liquid can flow freely into the chamber78of the extractor assembly70.

During use (e.g., during the time that the substrate moves under the barrier member12and projection system PS), a meniscus320extending between the substrate W and the barrier member12is provided.

Although not specifically illustrated inFIG.6, the liquid supply system has an arrangement to deal with variations in the level of the liquid. This is so that liquid which builds up between the projection system PS and the barrier member12can be dealt with and does not spill.

A substrate W is normally positioned in a recess (e.g. a substrate supporting area) within the substrate table WT. In order to account for variations in the width (e.g., diameter) of the substrate W, the recess is usually made a little larger than the maximum likely size of the substrate W. Therefore, there exists a gap between the edge of the substrate and the substrate table W. With all arrangements for providing liquid, there may be a difficulty in the treatment of the gap5between the substrate and the substrate table. This is because liquid can enter this gap5. It is desirable to remove liquid from the gap5to prevent it from working its way under the substrate. It is also desirable to prevent bubbles of gas entering the immersion liquid from the gap5. For this purpose an inlet may be provided below the gap between the edge of the substrate and substrate table. The inlet is connected to an underpressure source so that liquid and/or gas can be removed from the gap5.

FIG.7is a schematic cross-section through a substrate table WT and a substrate W. The gap5exists between an edge of the substrate W and an edge of the substrate table WT. The gap5is at an outer area or edge of a recess in which the substrate is placed during imaging. The substrate W can be supported on a substrate supporting area of the substrate table WT.

In order to deal with the liquid entering that gap, at least one drain10,17may be provided at the edge of the substrate W to remove any liquid which enters the gap5. In the embodiment ofFIG.7, two drains10,17are illustrated though there may be only one drain or there could be more than two drains.

The primary function of the first drain10is to prevent bubbles of gas from entering the liquid11of the liquid supply system12. Any such bubbles can deleteriously affect the imaging of the substrate W. The second drain17may be provided to prevent any liquid which finds its way from the gap5to underneath the substrate W from preventing efficient release of the substrate W from the substrate table WT after imaging. As is conventional, the substrate W is held by a pimple table or burl plate30comprising a plurality of projections32called burls. An underpressure applied between the substrate W and the substrate table WT by the pimple table30ensures that the substrate W is held firmly in place. The provision of the second drain17under the pimple table30reduces or eliminates problems which may occur due to liquid finding its way underneath the substrate W.

The first drain10removes liquid by way of an underpressure. That is, the first drain10is connected via outlet142to an underpressure source. This underpressure source effectively removes any liquid which enters the drain.

The exact geometry of the first drain10is not important. Typically, the first drain10comprises an inlet110which puts a chamber140into fluid communication with the gap5. The chamber140may be annular, for example. The outlet(s)142is in fluid communication with the chamber140.

The second drain17will now be described. An outlet95of the second drain17is held at an under pressure (e.g. 0.6 bar) which is a little larger than the under pressure (e.g. 0.5 bar) of the pimple table30. This ensures that there is a flow of gas from the pimple table30as well as from the gap5to the outlet95. In an alternative embodiment, the second drain17can be held at an over pressure. In this case there is a flow of gas out of the outlet95towards the gap5. Combined with capillary pressure this can be used to reduce or prevent immersion liquid getting into the pimple table30.

As can be seen, two projections91and92are provided underneath the substrate W. The radially outer projection91is a so-called “wet seal” and is likely to have immersion liquid passing between it and the bottom surface of the substrate W. The radially inner projection92is a dry seal and only gas is likely to pass between it and the substrate W.

Between the two projections91,92is a channel93which leads to a chamber94. The chamber94is in fluid communication with the outlet95which is connected to the under pressure source. More detail of this second drain17and of the first drain10can be found in United States patent application publication no. US 2008-0297744.

If gas is removed through the gap, then this may lead to undesirable evaporation of any liquid in the gap5. This can in turn lead to localized cooling. Localized cooling is undesirable because it may lead to thermal contraction of the substrate table and thereby to possible overlay errors.

One way in which this phenomenon may be dealt with is to provide a channel for a heat transfer fluid in the substrate table WT. The temperature of the substrate table can be maintained constant in this way. Additionally, as disclosed in United States patent publication no. US 2008-0137055, a further heater may be used to heat in the vicinity of the inlet. Therefore, the extra thermal load which is generated at that point may be compensated for by the use of that further heater.

FIG.8illustrates one such arrangement.FIG.8is a plan view of the substrate support area of a substrate table WT. The inlet110is indicated. A central channel200for heat transfer fluid is provided. The central channel200follows a path under the position of the substrate W. The path of the central channel200is such that an even heating can be applied by passing a heating fluid through the channel200. The temperature of the heat transfer fluid entering the channel200is detected by a first temperature sensor210. The temperature of heat transfer fluid exiting the channel200is to be detected by a second temperature sensor220. A third temperature sensor230may be provided in the channel200to detect the temperature at a local point. A controller can be provided with data from the temperature sensors210,220,230and can control the temperature of the heat transfer fluid using a heater240which is used to heat heat transfer fluid prior to the heat transfer fluid entering the channel200.

In order to deal with the excessive cooling which can be generated by the drain10, a heating element250may be provided. The heating element250is a single heating element which is adjacent the inlet110and extends around the periphery (e.g., circumference) of the inlet110.

The heating element250may be positioned underneath the chamber140or on either side of the chamber140, as illustrated inFIG.7. There may be other appropriate positions for the heater250.

A fourth temperature sensor260is provided. The fourth temperature sensor260is provided in the vicinity of the inlet110. A controller can use the information obtained from the fourth temperature sensor260to control the power applied to the heating element250.

Although the system illustrated inFIG.8does alleviate some difficulties, particularly when a localized area liquid supply system is used, the cooling around the periphery of the inlet110is not necessarily uniform. Therefore, the position of the fourth temperature sensor260is significant. If the fourth temperature sensor260is in a position which has experienced a large amount of local cooling, then although that cooling may be compensated, other areas of the inlet110may be heated too much. The difficulty with sensor260means that it may be better to control the heating element250based on the temperature difference between the second and third temperature sensors220and230. The controller uses this difference as a measure of the thermal load on the substrate table edge. If on a part of the total periphery of the substrate table a thermal load is applied, the balancing heat load is applied over the total periphery. As a result, the heating element undercompensates the loaded area and disturbs the unloaded area. If for instance 1 W is over ⅓rdof the substrate table edge, this is compensated with 1 W over the total edge. So, only 0.33 W of that localized load is compensated, the other 0.66 W is disturbing the rest of the edge. Even by the provision of further temperature sensors around the inlet110, this problem may not be alleviated.

The solution ofFIG.8has the following short-comings: 1) the heater-sensor combination reaction time is too slow (long time constant). The heaters and sensors are glued to the substrate table WT resulting in relatively high contact resistances. 2) The heaters and sensors are only applied at the substrate table edge and not to its core (central portion), which provides a partial solution. 3) Water conditioning is limited to a maximum flow which leads to a non-uniform temperature distribution. Because the water channel is small in cross-section and rather long the flow resistance is high. For high flows the pressure drop becomes too large, leading to non-uniform mechanical deformations of the wafer table itself. High flows also lead to high velocities and high dynamic forces, which lead to uncorrectable disturbance forces. Any flow (not only the maximum flow) leads to a non-uniform temperature distribution. The water cools down from inlet to outlet. This temperature difference results in non-uniformity. The higher the flow the lower the dT, of course. 4) Water conditioning can lead to uncorrectable dynamic disturbances because of pressure pulses. 5) Water conditioning involves a ‘thick’ (10 mm), and therefore heavy substrate table WT causing scan-up-scan-down problems.

In an embodiment heaters400and/or temperature sensors500are on a surface of the substrate table WT. The heaters400and/or temperature sensors500may be on a surface adjacent (e.g. under) the substrate supporting area. One such surface is a surface of a burl plate600.

A burl plate600of an embodiment is illustrated inFIG.9. The burl plate600is comprised of a plate with projections on an upper surface and on a lower surface. The projections on the upper surface are burls32on which the substrate W, in use, is supported. The burls34on the underside are for supporting the burl plate600on a surface of the substrate table WT.

InFIG.7the burl plate30is shown as an integral part of the substrate table WT and no burls equivalent to burls34orFIG.9are present.

InFIG.9the heater400and/or temperature sensor500are on a surface of the burl plate600, formed between the burls32,34. The heater400and/or temperature sensor500may be on a upwardly facing surface and/or on a downwardly facing surface of the burl plate600.

In one embodiment the heater400and/or temperature sensor500are formed as a thin film. Therefore, the heater400and/or temperature sensor500are attached directly to the surface without the use of an adhesive such as glue or solder etc. Thus, the heater400and/or temperature sensor500are directly bonded to the surface, for example deposited on the surface. In one embodiment the heater400and/or temperature sensor500are formed of platinum. If the burl plate600is made of a conductive material (such as SiSiC), an insulating layer and/or a bonding layer may be deposited before the platinum heater400and/or temperature sensor500is deposited. It may be necessary additionally to coat the heater400and/or temperature sensor500(with another dielectric layer) once it has been deposited in order to ensure electrical isolation of the heater400and/or temperature sensor500and protection from moist gas which might otherwise create a short circuit. In an embodiment an additional insulating layer is provided over the heater400and/or temperature sensor500so heat goes into the surface. This results in more directing of heat into the body (e.g. burl plate600).

Normally the thin films have 4 layers in total. On top of the substrate table (e.g. burl plate600) there is a bonding layer, then an isolating dielectric layer, then the platinum layer and then again a dielectric layer on top to avoid short-circuiting. To avoid electro-magnetic interference of the platinum lines there may be 2 extra shielding layers. The heaters and/or temperature sensors are thin, say below 100 μm, preferably below 10 μm or even 1 μm thick.

The heater400and/or temperature sensor500are positioned adjacent the substrate supporting area. Because they are bonded directly to the surface, heat is conducted to/from the heater400and/or temperature sensor500to the material behind the surface quickly. If the surface to which the heater400and/or temperature sensor500are applied is the burl plate, the transfer of heat to/from the substrate W is extremely quick because of their proximity to the substrate W.

FIG.10shows, in plan, one embodiment of an arrangement of a plurality of heaters400and/or temperature sensors500. A plurality of heaters400A-F and/or temperature sensors500A-F are elongate. They are substantially parallel in elongate direction and extend across the substrate supporting area from one edge to an opposite edge. The benefit of this arrangement will be explained with reference toFIG.11below.

Surrounding the central portion of the substrate supporting area where the heaters400A-F and/or temperature sensors500A-F are located, are a plurality of edge heaters410A-L and/or temperature sensors510A-L. The edge heaters410A-L and/or temperature sensors510A-L are of different sizes around the edge of the substrate supporting area. The sizes are to match the dimension in the direction of the heaters400A-F and/or temperature sensors500A-F in the central portion.

The plurality of edge heaters is designed to do the job of the heating element250inFIG.8. That is, they are designed to compensate for the high evaporational loads around the edge of the substrate W as described in connection withFIG.7. The edge heaters410A-L and/or temperature sensors510A-L may be positioned on a surface of the burl plate600or on a different surface.

An embodiment of the present invention may be used on its own or in combination with an edge heater250as illustrated inFIG.8and/or a passage230adjacent the substrate supporting area for the passage of a thermal conditioning fluid therethrough such as illustrated inFIG.8. Additionally, the heaters and/or temperature sensors of an embodiment of the invention may be employed in combination with a substrate table WT conditioned by a two-phase fluid. In such an embodiment a chamber is provided in the body of the substrate table WT which is filled with a fluid in both gaseous and liquid phases. Such a substrate table conditioning system is described in U.S. patent application No. 61/246,276, filed on 28 Sep. 2009 and U.S. 61/246,268, filed on 28 Sep. 2009, both hereby incorporated in their entirety by reference.

An advantage of an embodiment of the present invention is present both for heaters and for temperature sensors. The substrate table WT may comprise one or the other or both. Both heaters and temperature sensors take advantage of the fast thermal response of the thin film heaters and/or temperature sensors.

The arrangement of heaters and/or sensors illustrated inFIGS.10and11, in particular, are also relevant to other types of heaters and/or temperature sensors which are not necessarily thin films.

In one embodiment the heaters and/or temperature sensors are not on a surface but are enclosed within a component of the substrate table WT. The heaters and/or temperature sensors may be embedded in a top plate (e.g. a quartz plate) of the substrate table WT. The top plate may comprise two sections, with the heaters and/or sensors embedded therebetween.

FIG.11shows an embodiment, in plan. InFIG.11the edge heaters410A-L and/or temperature sensors510A-L are not present. It may not be necessary to include edge heaters, depending on the design of the substrate table WT at the edge of the substrate W. Such an embodiment is illustrated inFIG.11.

Also illustrated inFIG.11is a meander path700which the substrate table WT takes under the projection system PS. The general overall motion of the meander path is illustrated by line800.

As can be seen by comparing line700and line800, whilst following the general path800moving backwards and forwards in the X direction takes place. Scanning in the Y direction is very fast. As a result, it can be seen that the substrate table WT moves fairly slowly from the top of the substrate (as illustrated) down to the bottom of the substrate along the Y direction. For this reason the heaters and/or temperature sensors400A-F,500A-F (and edge heaters and/or temperature sensors) are elongate in the X direction. The heaters and/or temperature sensors are elongate in a first direction. The first direction is orientated such that the length of time a given heater and/or temperature sensor400,500stays under the projection system during imaging of the substrate W is greater than if the heater and/or sensor were orientated with its elongate direction perpendicular to the first direction (in which case it would be passed over several separate times during imaging of the whole substrate). In particular, the time that a given heater and/or temperature sensor is under the projection system during imaging of the substrate is substantially maximized. In one embodiment this is done by ensuring that the elongate direction of the heaters and/or temperature sensors is parallel with the scanning direction. However, other geometries may be more suitable for different scanning patterns. Thus during imaging the substrate steps in the X direction along the top heater/temperature sensor400A/500A while scanning in the Y direction. This results in the area at the top of the substrate receiving a heat load and this is sensed and compensated for by the top heater and temperature sensor combination400A/500A. The substrate then moves in the Y direction to move the second heater/temperature sensor combination400B/500B under the projection system and scans in the Y direction. The heat load is concentrated at that Y position and the sensor/heater combination400B/500B compensates accordingly. While stepping in the X direction any heat load is concentrated in that X direction. In positions along the Y axis away from the projection system, little heat load will be present.

An advantage of having elongate heaters and/or temperature sensors is that then the number of heaters and/or temperature sensors can be reduced than would be the case if the heaters and/or temperature sensors were made with an aspect ratio of substantially one (i.e. the same dimension in both the X and Y directions). The reduced number eases control and reduces the complexity of the system and in particular reduces the difficulty of connecting the heaters and/or temperature sensors. As will be illustrated with reference toFIG.12, with the embodiment ofFIGS.10and11, the heaters and/or temperature sensors may be connected to a controller at the edge of the burl plate600relatively easily.

The plurality of heaters and/or temperature sensors are elongate in substantially parallel directions.

FIG.12illustrates, in plan, a single integrated heater and corresponding temperature sensor. Similar principles may be used for only a heater or for only a temperature sensor. The heater and temperature sensor are integrated in terms of heating and sensing the temperature of the same area.

As illustrated inFIG.12, the heater and temperature sensor are formed as lines or wires. The lines or wires cover the area of the overall heater and/or temperature sensor. This is done by making the lines follow a tortuous path. In the embodiment illustrated, the lines follow a tortuous path between burls32but that is not necessarily the case. As illustrated inFIG.12, the line of the heater follows a substantially parallel path to the line of the temperature sensor. The two lines do not cross and weave their way in and out of the burls to cover as much area of the overall heater as is possible. The lines terminate at electrodes to allow connection to a control system.

A controller is provided. The controller attempts to maintain the measured temperature at a given set point. The faster the response the better the performance which can be expected. The lower the thermal time constants, the smaller the net maximum temperature change which will occur on the application of a heat load. The controller may control the heaters based on feedback from sensors. Feed forward control is possible based on the position of the liquid handling system12relative to the substrate table WT.

As depicted inFIG.26, an embodiment of the invention is to apply one or more thin film platinum sensors and/or heaters on the top or bottom of the substrate table WT. In an embodiment the burl plate600is positioned between the substrate table WT and the substrate W. In an embodiment, the thin film heaters400and/or temperature sensors500are applied to the top of the burl plate600. In an embodiment, the thin film heaters400and/or temperature sensors500are applied to the bottom surface of the burl plate600. In an embodiment, the thin film heaters400and/or temperature sensors500are applied to the bottom surface of the substrate table WT.

The thin film heaters400and/or temperature sensors500may be applied to the upper surface or lower surface of a sensor that is positioned on the substrate table WT.FIG.26depicts a sensor261on the surface of the substrate table WT. The sensor261may be a dose sensor, an aberration sensor, an illumination sensor, a uniformity sensor or an aerial image sensor, for example. The sensor261may comprise an encoder grid plate to control the position of the substrate table WT. The sensor261may comprise a protective plate262at its upper surface. The protective plate262may be formed of a glass. The one or more thin film heaters400and/or temperature sensors500may be applied to the upper surface and/or lower surface of the protective plate262.

FIG.29depicts a lithographic apparatus comprising a substrate table WT, a reference frame RF, a grating50and a sensor20. The grating50is attached to the substrate table WT or the reference frame RF. The sensor20is attached to the other of the substrate table WT and the reference frame RF.FIG.29depicts the case in which the grating50is attached to the substrate table WT and the sensor20is attached to the reference frame RF.

The sensor20is to detect radiation diffracted and/or reflected by the grating50, thereby to measure the relative position between the substrate table WT and the reference frame RF. This is a type of positional measurement device used in a lithographic apparatus in which the grating50and sensor20are mounted on different objects which are moveable relative to one another and whose relative position is desired to be measured.

The thin film heaters400and/or temperature sensors500may be applied to the upper surface or lower surface of the grating50and/or the sensor20. The grating50may be formed on a plate of optically transparent material such as quartz or a glass-ceramic, for example. This plate may be termed an encoder grid plate. In this description, the term grating50is understood to mean the encoder grid plate with a grating pattern formed thereon.

The thin film heaters400and/or temperature sensors500may be applied directly to the surface of the encoder grid plate. In an embodiment, the thin film heaters400and/or temperature sensors500are applied directly to the surface of the encoder grid plate that is exposed to the immersion liquid. This is because the material of the plate, such as quartz or glass-ceramic, may have a relatively low thermal conductivity. Hence, local temperature changes due to thermal loads can be corrected more quickly by positioning the thin film heaters400and/or temperature sensors500on the exposed surface of the grating50than by positioning the thin film heaters400and/or temperature sensors500on the rear side of the grating50.

This controls the temperature of the grating50and/or sensor20. Control of the temperature of the grating50and/or sensor20helps to reduce positional errors that would otherwise lead to overlay errors. The positional errors are caused by thermal deformation of a surface of the grating50and/or sensor20. Such thermal deformation is caused by a thermal load on the surface. A thermal load may be applied to the surface if a liquid not the same temperature as the surface comes into contact with the surface. For example, the liquid may evaporate, or in any case thermally equilibrate with the surface. This may be a problem for the grating50as depicted inFIG.29because the grating50is located on the upper surface of the substrate table WT and over which the fluid confinement structure12is located. The fluid confinement structure12may become located over part or all of the grating50during normal operation of the lithographic apparatus. Immersion liquid may escape from the fluid confinement structure12and splash onto or remain on the grating50as a droplet. Of course, the same problem can occur if the sensor20is positioned on the top surface of the substrate table WT and the grating50is positioned on the reference frame RF.

The grating50may comprise a grid plate and a grating surface formed on an under side of the grid plate. The purpose of this is to prevent the grating surface itself from coming into contact with the immersion liquid.

Although in the above, an embodiment of the invention has been described with respect to the grating50, the same advantages and mechanisms are applicable to the temperature control of the sensor20. For example,FIG.30depicts an embodiment in which the grating50is attached to the reference frame RF and the sensor20is attached to the substrate table WT. The thin film heaters400and/or temperature sensors500may be applied to the upper surface or lower surface of the sensor20.

FIG.31depicts an embodiment in which additionally or alternatively to the thin film temperature sensors500, the lithographic apparatus may comprise a non-contact temperature sensor311. The non-contact temperature sensor311may comprise an infrared temperature sensor. In an embodiment, the non-contact temperature sensor311comprises an array of infrared sensors. The sensors may face towards the grating50. For example, in an embodiment in which the grating50is positioned on an upper surface of the substrate table WT, the non-contact temperature sensor311may face downward to the grating50.

The non-contact temperature sensor311may be attached to the reference frame RF as depicted inFIGS.29and30, or the contact temperature sensor311may be attached to a measurement frame that is different from the reference frame RF.

The non-contact temperature sensor311may comprise a line of infrared sensors located above the substrate table WT. The non-contact temperature sensor311measures the temperature of the grating50as the substrate table passes under the non-contact temperature sensor311. This measurement may be performed during the alignment/focus measurement phase, the exposure phase or the substrate/substrate table swap phase, for example.

In an embodiment, the thin film heaters400and/or temperature sensors500are applied to a surface of a measurement table.

Whether the thin film heaters400and/or temperature sensors500are applied to a surface of the burl plate600, the substrate table WT or a sensor261, the heaters400and/or temperature sensors500may be applied by a number of different methods.

The heaters400and/or temperature sensors500may be glued on to the appropriate surface. The layer of glue between the heaters400and/or temperature sensors500should be as thin as possible in order to reduce the contact resistance. The glue may comprise a polymer. The glue may further comprise at least one metal and/or carbon fiber. The purpose of this is to make the glue electrically conductive and/or more thermally conductive. The glue may be a pressure sensitive adhesive. This means that when pressure is applied to the glue, the layer of glue becomes thinner. The glue may also be termed an adhesive.

An alternative way to apply the thin film heaters400and/or temperature sensors500to a surface is to form the network of heaters400and/or sensors50as a coating on the surface. The coating may be formed by using either a positive photoresist or a negative photoresist.

In the case of using a positive photoresist, a coating of positive photoresist is applied (e.g. sprayed) onto the surface. An isolation layer, which may be made of SiO2, may be applied prior to the positive photoresist coating such that the isolation layer is between the positive photoresist coating and a surface.

Once the positive photoresist coating has been applied to the surface, the coating is exposed at positions where the network of heaters400and/or temperature sensors500is not to be applied, thereby to harden the positive photoresist at those positions. The remaining sections of photoresist are removed, thereby opening a gap where the thin film is to be applied. The thin film, which may be made of platinum or an alloy of titanium and platinum, for example, is applied to the surface and the photoresist. The photoresist that remains on the surface is stripped via, for example, an ultrasonic stripping technique to remove the unwanted sections of thin film. The result is a network of thin film in the desired places.

A two-step photoresist method may be used in which two layers of photoresist are applied. The top layer of photoresist is exposed so as to be hardened in positions where the thin film is not to be applied. When the photoresist is developed by removing the section of photoresist that is not hardened, the upper layer of photoresist overhangs the lower layer of photoresist such that the top layer of photoresist does not touch the surface of the substrate W. This reduces defects in the photoresist.

If a negative photoresist is used, a layer of negative photoresist is coated onto the surface. This may be done by spraying. An isolation layer may be applied before the negative photoresist layer. The photoresist is exposed in regions where the thin film is to be applied. These sections of photoresist are then removed. The thin film material is disposed on the surface. The remaining sections of photoresist are stripped, thereby leaving the desired pattern of thin film material.

A further way to apply the thin film to the surface is to pre-apply adhesive to one side of the thin film material. The thin film with adhesive pre-applied to one surface may be termed a sticker. The sticker may then be applied to the surface. In the case of a sticker, the thin film material may be housed within an insulating material, such as a polyimide. In particular Kapton@ may be used as the insulating material for the sticker.

It is desirable for the thin film to be directly bonded to the surface in order to reduce the thermal resistance between the thin film and the surface. However, an adhesive, which is desirably thermally conductive, may be used to apply the thin film to the surface.

The material of the thin film heaters400and/or temperature sensors500may be platinum, or a platinum alloy. The thin film material may comprise at least one of copper, aluminum, silver, gold and a semiconductor material, which may comprise a metal oxide and/or silicon. In the case of a sticker (i.e. thin film pre-applied with an adhesive, the thin film within an insulating housing), copper may in particular be used. The material for the thin film should be stable over time.

If the thin film is applied to the surface as a coating, a mask may be used to provide that the thin film material is applied to the desired sections of the surface. In particular, a mask may be used when the one or more thin film heaters400and/or temperature sensors500are applied to a surface of the burl plate600.FIG.28depicts a mask that may be used.FIG.28depicts thick lines indicating positions for the thin film heaters400and thin lines indicating positions for the temperature sensors500. The mask is used to avoid the thin film material from being deposited undesirably on the burls32.

FIG.27is a graph that illustrates the effectiveness of using one or more thin film heaters400and/or sensors500. The graph includes four lines showing how the fingerprint size varies as a function of time depending on the type of conditioning used to control the temperature of the system. The line formed of long, broken sections represents the situation where no temperature conditioning is applied. The solid line represents the situation where a heat transfer fluid channel200(as depicted inFIG.8) is used to perform temperature conditioning. The dot-chain line represents thin film conditioning, using a configuration as depicted inFIG.9. The line formed from short, broken sections represents ideal conditioning.

It is clear that the thin film conditioning has a result that is far closer to the theoretical ideal conditioning than conditioning by a heat transfer fluid flowing in a heat transfer fluid channel200in the substrate table WT under the substrate supporting area.

An advantage of using thin film technology is that the sensing and heating lines are well connected to the surface, resulting in a very low thermal contact resistance. Another advantage is that both sensors and heaters are made from the same material and that the complete layout of multiple sensors and heaters can be attached in one process step.

Because the thermal resistance is very low, thermal simulations of a substrate table with thin film sensors and heaters show that substrate table temperatures can stay within mK's making it an almost ideal table conditioning concept. To cope for heating loads in one embodiment a substrate table has heaters and sensors on the top as described above in relation toFIGS.10and11and water conditioning in the middle. In one embodiment the substrate table WT does not have water conditioning. This is possible for immersion machines were cooling loads are dominant. In order to minimize the number of sensors and heaters to be controlled, the following layout ofFIG.10is suitable, with a 18 or 22 areas which each consist of 1 sensor-heater combination.

Of course, other layouts with more or less areas may be used. Because scanning in X-direction takes typically less than 2 seconds for one row, one heater-sensor-combination over the full width of the substrate W is sufficient. In the Y-direction more combinations may be required to cope with longer time scales, typically 10-20 seconds. The meander takes a longer time to move in Y-direction. The sensor-heater combination is able to react within 0.5 second, so field size in Y shall be limited. The multiple edge heater-sensor-combinations (12 or 16 areas, respectively) are provided to cope with the extra gap5evaporation loads. If these gap5evaporational loads are much reduced, then the edge combinations can be left out. Then the layout becomes as inFIG.11.

The heater and sensor within one area shall be evenly distributed over the total surface of its area for instance as illustrated inFIG.12

Overlay performance increases because thermal cooling loads are measured and corrected locally and within short time scales.

Doing away with water conditioning is advantageous because no water hoses and no hydrodynamic pressure pulses are then present and this allows for thinner substrate tables resulting in less scan-up scan-down problems.

A further advantage of using one or more thin film heaters400and/or temperature sensors400is that they have a lower mass than other types of heaters or temperature sensors. This results in a substrate table WT that has a lower mass than otherwise.

An embodiment of the invention is applicable to both 300 and 450 mm diameter substrates W. For a 450 mm diameter substrate, the number of sensors/heaters400/500will increase. The center sensors/heaters400/500will be 450 mm in X and still 50 mm in Y, resulting in 9 sensors/heaters400/500in Y, while for a 300 mm diameter substrate, there are 6 sensors/heaters400/400in Y. The edge sensors/heaters410/510will get a similar pattern to the 300 mm diameter substrate resulting in 21 or 25 sensors/heaters410/510(i.e., the 300 mm diameter substrate may have 18 or 22 sensors/heaters).

The number of heaters and/or temperature sensors in the center portion of the substrate supporting area may in one embodiment be only one (for example covering a large proportion of the area) for global temperature correction. In another embodiment a ‘check-board’ with many sensors/heaters400/500(for instance 1 sensor/heater400/500per die size 26 mm×32 mm) of heaters and/or temperature sensors may be present, for local correction.

The temperature sensor and heater lines within one die are not necessarily aligned with the die orientation. The line length, line width, burl pattern and wire connection points will determine the layout.

The edge heaters and/or sensors may be within or outside of the burls of the burl plate600or on the side edge or on the substrate table ring.

The following are aspects of the invention:a) optimized bands of integrated heater and/or temperature sensor: variations are possible to the optimal arrangement of heater and/or temperature sensor if the standard immersion hood path were to vary;b) having a heater across the table surface;c) having a sensor across the table surface;d) having a sensor and heater integrated with each other, over the surface of the table;e) having the sensor and/or heater integrated with the burls;f) having the sensor and/or heater as a thin film;g) using an integrated sensor/heater with an existing wafer edge heater, two phase table control, and/or internal fluid conditioning system;i) that there are systems on one side or both of the substrate support; and)j) an optimal arrangement for integrating the sensors and the heaters.

The heater400and/or temperature sensor500may be of any shape, in plan.FIG.13shows one example in which a heater and/or sensor400,500comprises a line forming a meandering path. A heater400and a sensor500may be associated with one another (as for example, inFIG.12). The shape, in plan, of the heater400and sensor500may or may not be substantially the same.

FIG.14shows a further shape, in plan, of a sensor500and/or heater400. In the case ofFIG.14the overall shape of the sensor500and/or heater400, in plan, is that of concentric circles which are joined together to form a circuit.

The heater/sensor400/500embodiments ofFIGS.13and14can be formed of one line to form a heater400and an associated sensor500in the form of a self-regulating thermal system, as described below, particularly with reference toFIG.19or as a micro-electro-mechanical system (MEMS) described below with reference toFIGS.16and17.

The embodiment ofFIG.15is an embodiment in which the heater400and sensor500are separate lines and are both formed as concentric interwoven circles.

The self-regulating system is a device that activates or deactivates a heater due to local change in temperature. This heater provides the desired thermal compensation at the right place and at the right time without any external input apart from the local change in temperature. In general, there are two ways to make a self-regulating device: (i) a heater with a MEMS switch, (ii) a heater made of a self-regulating material that has a high non-linear relationship between its electromagnetic (EM) properties and temperature.

These devices are only a few micrometers thick, and their manufacturing can be done by advanced direct writing or thin film technologies such as metal and dielectric deposition, photolithography, wet and dry etching, galvanic and electro-less plating, diffusion and ion implantation among others. Due to the reduction in size of self-regulating devices, they can be placed easily on any configuration, number (in the order of thousands), geometry or on any surface.

The system can be trimmed using laser adjustment by removing material, reshaping the actuators, or changing its material crystallinity (if that is possible), among other methods. In the case of complex surfaces, the self-regulating system can be assembled first on a thin flat film and then transferred onto the final surface.

The heater400and/or temperature sensor500may form a self-regulating thermal system. That is, no control signals need to be provided to the heater400and no signals need to be received from the temperature sensor500by a remote controller. Instead, a voltage is applied to the heater400and/or temperature sensor500which then compensates for local temperature variation without the need for a separate controller.

One form of self-regulating thermal system is a MEMS based self-regulating heater described below with reference toFIGS.16and17. A further form is an EM-temperature based self-regulating heater described with reference toFIGS.18,19and20.

A MEMS heater400is a heater activated and/or deactivated by a MEMS sensor500. In one embodiment the sensor500is a switch. The switch can be made of a positive coefficient of thermal expansion material, or a negative coefficient of thermal expansion material, or a bi-metallic material.FIG.16shows a MEMS based self-regulating heater400and sensor500, in cross-section.FIG.17shows a detail of the temperature sensor500ofFIG.16.

InFIG.16a heater400is connected in series with a temperature sensor500. The temperature sensor500is in the form of a self-regulating switch. A material600with a positive or negative coefficient of thermal expansion or a bi-metallic material operates the switch. Useful materials for construction of the sensor include silicon, polysilicon or a silicon compound such as silicon nitride or a metal such as gold. Thermal expansion and/or contraction of the material600results in the switch being open above or below a certain temperature (top figure ofFIG.17) and the switch is conversely closed below or above the certain temperature. Current runs through the heater400when the switch is closed. In one embodiment when the heater400is connected to a power supply, and a change in temperature occurs, for example during cooling, the MEMS switch closes the circuit. Then an electrical current flows through the heater400and warms the surface on which the heater400is formed. As the temperature increases, the material600of the switch starts to deform (expansion, contraction or bending depending on the selective material) until the switch is opened stopping current from passing through the heater400and thereby stopping heating.

The geometry of the MEMS structure can vary depending on the functionality (for example to include an overheat protection and improve the manufacturability of the switch). Desirably the MEMS switch is adjacent or inside the heater400layout in order to react quickly to the temperature change produced by the heater400. The embodiment ofFIG.14shows a position700which would be suitable for positioning of the MEMS sensor/switch when the embodiment ofFIG.14is a MEMS based self-regulating heater.

In one embodiment the self-regulating heater may be an EM-temperature based self-regulating heater. This embodiment has an advantage (also present in the MEMS embodiment) that only a single line needs to be placed on the surface.

A heater400made of a self-regulating material (for example a semi-conductive polymer) may also act as a sensor500and switch as it is deactivated or activated as its EM property changes in response to the surrounding temperature.FIG.18shows an example in which the resistance (Y axis) of a self-regulating heater varies as a function of temperature (along the X axis). Therefore, if an electrical EM-temperature based self-regulating heater is connected to a power supply (for example of a fixed voltage), then under a change in temperature, for example during cooling, the electrical resistance of the self-regulating material decreases considerably. This process allows a flow of electrical current through the heater thereby warming the surface. The heat increases the temperature of the heater and its surroundings thereby increasing the electrical resistance until the current ceases completely at a given temperature. This situation stops the heating process.

The construction of an EM-temperature based self-regulating heater can be made by placing on a surface a thermal and electrically conductive layer800, then a self-regulating material film810and an electrically conductive but similarly isolating layer820on top, as illustrated inFIG.19.

An EM-temperature based self-regulating heater can have any shape, in plan. Indeed, the heater need not be in the form of a line and could be in the form of blocks as illustrated, in perspective view, inFIG.20. InFIG.20heater/temperature sensors which are comprised of an EM-temperature based self-regulating heater420are illustrated. The central electrical connection450is common to all EM-temperature self-regulating heaters420and two electrodes460on either side of the EM-temperature based self-regulating heaters420can be used to complete the electrical circuit.

A non uniform temperature on a substrate W, due to liquid evaporation, can be corrected by a self-regulating substrate table WT. The self-heating devices can be placed on the upper or lower burl plate600surface. Under the presence of cold spots, for example droplets, electrical heaters400closer to those zones will be self-activated to compensate thermally the substrate by heat conduction through the burls. Only two wires are required to power the substrate table WT. This system can reduce considerably the weight of the substrate table WT while increasing its reliability due to multiple self-regulating heaters400placed on it.

The heaters400and/or temperature sensors500are described above as being applied to a surface of the substrate table WT adjacent a substrate W supporting area. However, an embodiment of the invention can be applied to any surface of a lithographic apparatus, particularly a projection apparatus, more particularly an immersion lithographic projection apparatus.FIGS.21and22illustrate various different locations at which heaters and/or temperature sensors400,500might be placed in a lithographic apparatus.

FIG.21is a plan view of a substrate table WT. The position of heaters400and temperature sensors500adjacent the substrate supporting area have already been discussed. Other sites may be around any sensor1000, particularly around the edge of any sensor1000. This is because there may be a gap between the edge of a sensor1000and the edge of the substrate table WT which is held at an underpressure to remove liquid from the gap and thereby can see a high evaporation loss. The sensor100may be a transmission image sensor (TIS) or an ILIAS sensor, for example. Another area may be a drain around a dummy substrate1100. The dummy substrate1100is used to close the bottom of a fluid handling system12, during, for example, substrate swap, by positioning the dummy substrate1100under the projection system PS. Thereby the fluid handling system12may be maintained on during, for example, substrate swap which is advantageous in terms of avoiding drying stains on the final element of the projection system PS. Another way in which it is possible to maintain the fluid handling system12operational during, for example, substrate swap is to provide a swap bridge1200on the substrate table WT. The swap bridge1200is a surface which extends from the substrate table WT (optionally retractably) and provides a surface which can move under the fluid handling system12while, for example, a new second substrate table WT replaces the first substrate table WT. A gap between the top surface of the substrate table WT and a top surface of the swap bridge1200may be provided with an under pressure source to remove any liquid which finds its way into the gap. This area may be provided with heaters and/or sensors described herein, as well as the top surface of the substrate table WT itself adjacent the swap bridge1200. During, for example, substrate swap, the swap bridge1200engages with the second substrate table WT. A further area1300where a swap bridge1200will engage with a substrate table WT is also provided with an under pressure source to remove liquid between the gap between the swap bridge1200and substrate table WT. This area1300may be provided with a heater and/or temperature sensor described herein.

FIG.22shows those areas mentioned above as well as a fluid handling system12and a projection system PS. Surfaces of the fluid handling system12which may make use of the heaters and/or temperature sensors described herein include any surface which comes into contact with immersion liquid during use. These include an under surface40of the fluid handling system12, an inside surface42which defines a space in which liquid is held between the final end of projection system PS and the substrate W, in use as well as a top surface44. The top surface44may be in contact with immersion liquid and in particular with a meniscus of liquid extending between the fluid handling system12and the final element of the projection system PS. As the position of that meniscus on the top surface44moves, evaporational loads can be applied to the top surface44so that heaters and/or temperature sensors may usefully be placed there. For similar reasons, heaters and/or temperature sensors may be placed around the edge of the projection system PS where the meniscus between the projection system PS and the fluid handling system12may be positioned or where splashes may occur. For example, the heaters and/or temperature sensors may be placed around the outer edge of a final element of the projection system PS.

The thin film heaters400described above may be combined with temperature sensors that measure the temperature of a single point on a surface, rather than take an average of a temperature over a portion of the surface. For example,FIGS.23,24and25depict a temperature sensor that is configured to measure the temperature of a single point on a surface that may be used according to an embodiment of the present invention.

FIG.23depicts an embodiment of the invention.FIG.23depicts how a temperature sensor500may be attached to the channel200or to the substrate table WT. The part to which the temperature sensor500is attached is given the reference numeral131. The temperature sensor500is configured to measure the temperature of the part131. The part131may be, for example, the channel200or the substrate table WT. However, part131may be any surface of the lithographic apparatus. The temperature sensor500is on the surface of the part131. The temperature sensor500is attached to the surface by a thermally conductive paste132.

The temperature sensor500may comprise a thermistor, or other thermometer equipment. According to the construction depicted inFIG.23, the temperature sensor500is pressed directly against the part131. The thermally conductive paste132may be provided intermediate the temperature sensor500and the part131. The paste may be heat conductive glue. The temperature sensor500is connected to an electrical assembly134via at least one lead133. The electrical assembly134takes temperature readings from the temperature sensor500. The electrical assembly134may be a PCB. In an embodiment, the temperature sensor500is mounted directly onto the electrical assembly134without the need of the lead133.

A drawback of the construction depicted inFIG.23is that it can be difficult to position the temperature sensor500at the precise location where it is desired to measure the temperature. This is partly due to the presence of the electrical assembly134on which the temperature sensor500is mounted, or the presence of the lead133connecting the temperature sensor500to the electrical assembly134. A further drawback is that the lead133puts pressure on the temperature sensor500. This can undesirably affect temperature measurement taken by the temperature sensor.

The temperature sensor500may be made of a semiconductor material. The temperature sensor500is configured to measure the temperature at a single location.

FIGS.24and25depict an alternative to the construction ofFIG.23for attaching the temperature sensor500to a part131.FIG.24depicts a side view of the construction.FIG.25depicts a plan view of the construction.

The temperature sensor500, which may be a thermistor, is attached to the part131at the location at which the temperature is to be measured. At this location, the part131is coated with an electrically conductive coating141. The temperature sensor500is connected to the electrical assembly134via the coating141. The temperature sensor500is on the surface of the part131. The temperature sensor500is connected to the surface via the coating141. In an embodiment, the temperature sensor500is connected to the surface via the coating141and a layer of glue132.

Desirably, the electrically conductive coating is thermally conductive. As is most clearly seen inFIG.25, the electrically conductive coating141takes the form of a pattern. The purpose of the pattern of the coating141is to allow the electrically conductive coating141to be connected to the electrical assembly134at an appropriate position. For example, an appropriate position may be where there is more space for the electrical assembly134or for the lead133to connect to the electrical assembly134. For this purpose, the coating141may comprise at least one elongate portion.

The electrically conductive coating141also provides electrical shielding to the part131and/or to the temperature sensor500. In this way, electrical shielding can be provided without any additional production steps. Measurement signals from the temperature sensor500can be read out via the electrical assembly134, which may be connected directly to the coating141, or indirectly via a lead133.

The temperature sensor500may be attached directly to the coating141. The temperature sensor500may be embedded within the coating141. In an embodiment, the temperature sensor500is connected to a coating141via a bonding layer132. The bonding layer132may be formed of a thermally conductive adhesive (i.e. glue). The bonding layer132may be formed of a material for soldering. Desirably, the bonding layer132is less than 10 μm thick.

A gap142may be provided between the temperature sensor500and the coating141. The purpose of the gap142is to prevent short-circuiting. The coating141is formed of two coating sections. Each section acts as an electrode to provide power to the temperature sensor500and/or receive signals from the temperature sensor500. The gap142separates the two coating sections from each other. The gap142may be filled with an electrically insulating material.

The thickness of the coating is less than 10 μm, less than 5 μm, less than 3 μm, or between 0.2 and 2.0 μm.

The electrically conductive coating141may be made of platinum, or a predominately platinum alloy, for example. The coating141may comprise at least one of copper, aluminum, silver and gold.

The same principle of use a coating141as an intermediary between the electrical assembly134and the temperature sensor500may be used in the context of a heater400instead of the temperature sensor500.

In an embodiment, the bonding layer132is not present. The temperature sensor500may be deposited as a coating. In an embodiment, the coating141and the temperature sensor500may have positions that are interchanged from the positions described above. The temperature sensor500may attach to the part131directly.

Although an embodiment of the present invention has been described above with reference to an immersion lithographic apparatus, this need not necessarily be the case. Other types of lithographic apparatus may suffer from uneven cooling (or heating) around the edge of a substrate. For example, in an EUV apparatus (extreme ultra-violet apparatus) heating due to the impingement of the projection beam can occur. This can give a localized heating to the substrate rather in the same way as the passage of the edge of substrate under the localized liquid supply system can give a cooling effect. If the heat transfer fluid in the channel200is given a small negative temperature offset with respect to the desired temperature in a normal operating condition, all the heaters can be on to obtain the desired temperature. A local cooling load can then be applied by switching a heater off. In this circumstance it may be that the localization of the heaters only at the edge of the substrate is too limited and that heaters may be additionally or alternatively be placed at different radial distances from the center of the substrate supporting area. However, the same principles as described above apply in this case also.

Therefore, as can be seen, an embodiment of the present invention can be implemented in many types of immersion lithographic apparatus. For example, an embodiment of the invention may be implemented in an I-line lithographic apparatus.

In an aspect, there is provided a lithographic apparatus comprising a heater and/or temperature sensor on a surface.

In an embodiment, the surface is a surface of at least one selected from: a substrate table configured to support a substrate on a substrate supporting area, a fluid handling system, a projection system, a surface of a grating or a sensor of a positional measurement device, and/or a swap bridge.

In an embodiment, the surface is a surface on a substrate table configured to support a substrate on a substrate supporting area which is: adjacent the substrate supporting area, or adjacent a sensor or adjacent a swap bridge.

In an embodiment, the lithographic apparatus further comprises a burl plate to support the substrate, wherein the surface on which the heater and/or temperature sensor is formed is a surface of the burl plate.

In an embodiment, the heater and/or temperature sensor is formed on the burl plate between the burls.

In an embodiment, the surface is a surface of a final element of a projection system.

In an embodiment, the heater and/or temperature sensor is a thin film heater and/or temperature sensor.

In an embodiment, the heater and/or temperature sensor is directly bonded to the surface without use of an adhesive.

In an embodiment, the heater and/or temperature sensor is formed, in plan, as a line following a tortuous path.

In an embodiment, the heater and/or temperature sensor is formed of platinum

In an embodiment, the temperature sensor is connected to an electrical assembly to read measurements from the channel temperature sensor indirectly via an electrically conductive coating on the component to which the temperature sensor is applied.

In an aspect, there is provided a lithographic projection apparatus comprising a substrate table configured to support a substrate on a substrate supporting area, the substrate table comprising a plurality of heaters and/or temperature sensors adjacent a central portion of the substrate supporting area, the plurality of heaters and/or sensors being elongate.

In an embodiment, the plurality of heaters and/or sensors are elongate in substantially parallel directions.

In an embodiment, the plurality of heaters and/or sensors extend across the substrate supporting area from one edge to an opposite edge.

In an embodiment, the plurality of heaters are elongate in a first direction such that the length of time a given heater and/or temperature sensor is under a projection system during imaging of a substrate is greater than if the heater and/or sensor were oriented with its elongate direction perpendicular to the first direction.

In an embodiment, the first direction is such that the length of time is maximized.

In an embodiment, the plurality of heaters and/or temperature sensors are comprised of a thin film.

In an embodiment, the lithographic apparatus further comprises a burl plate to support the substrate and wherein the plurality of heaters and/or temperature sensors are formed on a surface of the burl plate.

In an embodiment, the plurality of heaters and/or temperature sensors are formed on the burl plate between the burls.

In an embodiment, the plurality of heaters and/or temperature sensors are positioned on the top and/or bottom of the burl plate.

In an embodiment, the plurality of heaters and/or temperature sensors are comprised of a line of material, in plan, which meanders in a tortuous path, in plan.

In an embodiment, the substrate table further comprises plurality of edge heaters adjacent different portions of an edge of the substrate supporting area and/or a chamber in the substrate table containing a fluid in both gaseous and liquid phases and/or a passage adjacent the substrate supporting area for the passage of a thermal conditioning fluid therethrough.

In an embodiment, the substrate table comprises one heater and/or temperature sensor per die on the substrate.

In an embodiment, the lithographic apparatus comprises a plurality of the heaters and a plurality of the temperature sensors.

In an embodiment, the plurality of heaters and plurality of temperature sensors are, in plan, laid out in a two-dimensional grid.

In an embodiment, each heater is integrated with a corresponding temperature sensor.

In an embodiment, each of the plurality of heaters is associated with a corresponding one temperature sensor of the plurality of temperature sensors.

In an embodiment, a heater and an associated sensor form a self-regulating thermal system.

In an embodiment, the self-regulating thermal system is configured to activate or deactivate the heater due to local change in temperature.

In an embodiment, the heater and associated sensor form a micro-electro-mechanical system.

In an embodiment, the associated sensor comprises a thermally activated switch.

In an embodiment, the heater and associated sensor are a self-regulated heater having an electromagnetic property that varies as a function of temperature such that a change in temperature results in a change in heat output at constant applied voltage.

In an aspect, there is provided a lithographic apparatus comprising a substrate table configured to support a substrate on a substrate supporting area and comprising a heater and/or a temperature sensor which extends across the substrate supporting area from one edge to an opposite edge.

In an aspect, there is provided a lithographic apparatus comprising a heater and a temperature sensor integrated with each other.

In an embodiment, the heater and temperature sensor are formed on a surface.

In an embodiment, the lithographic apparatus further comprises a burl plate to support a substrate, and the surface on which the heater and temperature sensor are formed is a surface of the burl plate.

In an aspect, there is provided a substrate table configured to support a substrate on a substrate supporting area and a heater and/or temperature sensor on a surface adjacent the substrate supporting area.

In an aspect, there is provided a method of compensating for a local heat load in an immersion lithographic projection apparatus the method comprising controlling a heater or using a signal from a temperature sensor to compensate for a local heat load wherein the heater and/or temperature sensor is on a surface.

In an embodiment, the heater and associated sensor form a self-regulating thermal system.

In an aspect, there is provided a lithographic apparatus comprising an electrically conductive coating on a surface, and a heater and/or temperature sensor connected to the coating.

In an embodiment, an electrical assembly is electrically connected to the heater and/or temperature sensor via the coating.

In an embodiment, the heater and/or temperature sensor is connected to the coating by a bonding layer.

In an embodiment, the bonding layer comprises an adhesive.

In an embodiment, the bonding layer comprises a material for soldering.

In an embodiment, an electrically insulating gap is provided between the surface and the heater and/or temperature sensor.

In an embodiment, the heater and/or temperature sensor is embedded in the coating.

In an embodiment, the coating comprises at least one of platinum, copper, aluminum, silver, gold and a semiconductor material.

In an embodiment, the heater and/or temperature sensor is substantially wholly within the coating in plan view.

In an embodiment, the coating is patterned.

In an embodiment, the coating comprises at least one elongate portion.

In an embodiment, the coating is formed of at least two distinct coating sections. In an embodiment, the coating is an electrode.

In an embodiment, the coating is configured to provide electrical power to, or receive electrical signals from, the heater and/or temperature sensor.

In an embodiment, a thickness of the coating is less than 10 μm, less than 5 μm, less than 3 μm, or less than 1 μm.

Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications in manufacturing components with microscale, or even nanoscale features, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general 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 that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelength of or about 365, 248, 193, 157 or 126 nm).

The term “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive and reflective optical components.

While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, the embodiments of the invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (e.g. semiconductor memory, magnetic or optical disk) having such a computer program stored therein. Further, the machine-readable instruction may be embodied in two or more computer programs. The two or more computer programs may be stored on one or more different memories and/or data storage media.

The controllers described above may have any suitable configuration for receiving, processing, and sending signals. For example, each controller may include one or more processors for executing the computer programs that include machine-readable instructions for the methods described above. The controllers may also include data storage medium for storing such computer programs, and/or hardware to receive such medium.

One or more embodiments of the invention may be applied to any immersion lithography 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 localized surface 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 the substrate and/or substrate table so that substantially the entire uncovered surface of the substrate table and/or substrate is wetted. In such an unconfined immersion system, the liquid supply system may not confine the immersion liquid or it may provide a proportion of immersion liquid confinement, but not substantially complete confinement of the immersion liquid.

A liquid supply system as contemplated herein should be broadly construed. In certain embodiments, it may be a mechanism or combination of structures that provides a liquid to a space between the projection system and the substrate and/or substrate table. It may comprise a combination of one or more structures, one or more liquid inlets, one or more gas inlets, one or more gas outlets, and/or one or more liquid outlets that provide liquid to the space. In an embodiment, a surface of the space may be a portion of the substrate and/or substrate table, or a surface of the space may completely cover a surface of the substrate and/or substrate table, or the space may envelop the substrate and/or substrate table. The liquid supply system may optionally further include one or more elements to control the position, quantity, quality, shape, flow rate or any other features of the liquid.

The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.