NL2011652A - Gripper, lithographic apparatus, method of thermally conditioning a substrate, and device manufacturing method. - Google Patents

Description

GRIPPER. LITHOGRAPHIC APPARATUS-METHOD OF THERMALLY CONDITIONING A SUBSTRATE. AND DEVICE

MANUFACTURING METHOD

FIELD

[0001] The present invention relates to a gripper, a lithographic apparatus, a method of thermally conditioning a substrate, and a device manufacturing method.

BACKGROUND

[0002] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0003] 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 a space between the final element of the projection system and the substrate. In an embodiment, the liquid is distilled water, although another liquid can be used. An embodiment of the present invention will be described with reference to liquid. However, another fluid may be suitable, particularly a wetting fluid, an incompressible fluid and/or a fluid with higher refractive index than air, desirably a higher refractive index than water. Fluids excluding gases are particularly desirable.

The point of this is to enable imaging of smaller features since the exposure radiation will have a shorter wavelength in the liquid. (The effect of the liquid may also be regarded as increasing the effective numerical aperture (NA) of the system and also increasing the depth of focus.) 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 or may not have a similar or the same refractive index as the liquid in which they are suspended. Other liquids which may be suitable include a hydrocarbon, such as an aromatic, a fluorohydrocarbon, and/or an aqueous solution.

SUMMARY

[0004] Prior to positioning a substrate on a substrate table for exposure it is desirable to thermally condition the substrate. A thermal conditioning table may be provided for this purpose. A gripper may be provided, driven for example by a robotic arm, to transfer the substrate from the thermal conditioning table to the substrate table for exposure.

[0005] It is challenging to avoid a change in the temperature of the substrate during transfer of the substrate to the substrate table for exposure. For example, the gas surrounding the substrate during transfer may not be at the same temperature as the substrate. Where the gripper is moved using a robotic arm, heat from a driving motor may be conducted through the robotic arm to the gripper causing the temperature of the gripper to rise. One or more other devices such as an actuator or a sensor, on the robotic arm for the gripper and/or on another, nearby robotic arm, and/or other heat producing apparatus near the gripper may in addition, or alternatively, contribute to heating of the gripper. A variation in the temperature of the environmental gas and/or in the gripper can lead to a “thermal fingerprint” being imposed on the substrate when it is positioned on the substrate table. The thermal fingerprint can lead to overlay error.

[0006] Thermal conditioning prior to transfer onto the substrate table for exposure by the gripper can be time consuming and reduce throughput.

[0007] It is desirable, for example, to provide a gripper that reduces or avoids a thermal fingerprint and/or which facilitates improved overlay and/or which facilitates improved throughput.

[0008] According to an aspect of the invention, there is provided a gripper configured for transporting an object in a lithographic apparatus, the gripper comprising: a gripper body with an engaging surface for engaging with the object; and three or more channels formed in the gripper body for channeling a thermal conditioning fluid and configured to be driven in parallel with each other, wherein: each of the channels comprises a loop having a plurality of pairs of adjacent sections, the sections of each pair being adjacent to each other in a direction perpendicular to the flow in the sections of the pair, with the flow in one section of the pair being in the opposite direction to the flow in the other section of the pair, and the plurality of pairs of adjacent sections constitute at least half of the total length of each channel; and the gripper body comprises one or more slits, each slit traversing the gripper body in a direction perpendicular to the engaging surface and having an opening at one end for allowing a support pin for supporting the object, and which is oriented perpendicular to the engaging surface, to move along the slit relative to the gripper body.

[0009] According to an aspect of the invention, there is provided a gripper configured for transporting a object in a lithographic apparatus, the gripper comprising: a gripper body with an engaging surface for engaging with the object; a thermal conditioning system for controlling a temperature of the engaging surface; and one or more temperature sensors for measuring the temperature at one or more respective positions on the engaging surface and/or on the engaged object, wherein the gripper body comprises one or more slits, each slit traversing the gripper body in a direction perpendicular to the engaging surface and having an opening at one end for allowing a support pin for supporting the object, and which is oriented perpendicular to the engaging surface, to move along the slit relative to the gripper body.

[0010] According to an aspect of the invention, there is provided a lithographic apparatus comprising: a projection system configured to project a patterned radiation beam onto an object; a gripper that is configured to engage with the object when held on a first support and, while engaged with the object, remove the object from the first support, transport the object to a second support, and release the object onto the second support, the gripper comprising: a gripper body with an engaging surface for engaging with the object; a thermal conditioning system for controlling a temperature of the engaging surface; one or more temperature sensors for measuring the temperature at one or more respective positions on the engaging surface and/or on the engaged object; and a controller configured to use the output from the one or more temperature sensors to actively control the temperature of the engaging surface and/or of the engaged object using the thermal conditioning system.

[0011] According to an aspect of the invention, there is provided a method of thermally conditioning a object in a lithographic apparatus, comprising: using a gripper to engage with a object when held on a first support and, while engaged with the object, remove the object from the first support, transport the object to a second support, and release the object onto the second support; and during transporting the object from the first support to the second support, driving a thermal conditioning fluid through a plurality of channels formed in a gripper body of the gripper.

[0012] According to an aspect of the invention, there is provided a method of thermally conditioning an object, comprising: using a gripper to engage with a object when held on a first support and, while engaged with the object, remove the object from the first support, transport the object to a second support, and release the object onto the second support; and during transporting the object from the first support to the second support, measuring the temperature at one or more respective positions on the engaging surface and/or on the engaged object, and using the measured temperature or temperatures to actively control the temperature of the engaged surface and/or the engaged object.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0014] Figure 1 depicts a lithographic apparatus according to an embodiment of the invention;

[0015] Figures 2 and 3 depict a liquid supply system for use in a lithographic projection apparatus;

[0016] Figure 4 depicts a further liquid supply system for use in a lithographic projection apparatus;

[0017] Figure 5 depicts, in cross-section, a barrier member which may be used in an embodiment of an immersion liquid supply system;

[0018] Figure 6 depicts a lithographic apparatus according to an embodiment of the invention;

[0019] Figure 7 is a more detailed view of a lithographic apparatus according to an embodiment of the invention;

[0020] Figure 8 is a more detailed view of the source collector apparatus SO of the apparatus of Figures 6 and/or 7;

[0021] Figure 9 depicts a gripper being moved towards a position of engagement with a substrate on a thermal conditioning table;

[0022] Figure 10 depicts a substrate being transported from a thermal conditioning table to a substrate table for exposure using the gripper of Figure 9;

[0023] Figure 11 depicts the gripper of Figure 10 being moved away after release of the substrate onto the substrate table for exposure;

[0024] Figure 12 depicts a gripper according to an embodiment being moved towards a position of engagement with a substrate on a first substrate support;

[0025] Figure 13 depicts a substrate being transported from the first substrate support to a second substrate support using the gripper of Figure 12;

[0026] Figure 14 depicts the gripper of Figure 13 being moved away after release of the substrate onto the second substrate support;

[0027] Figure 15 is a top view of a gripper having thermal conditioning fluid channels;

[0028] Figure 16 is a bottom view of the gripper of Figure 15;

[0029] Figure 17 is a side sectional view along line B-B in Figure 15;

[0030] Figure 18 is a side sectional view along line C-C in Figure 15;

[0031] Figure 19 is an end view, looking from a handle part end, of the gripper of Figures 15 and 16;

[0032] Figure 20 is a side sectional view along stepped line A-A in Figure 19;

[0033] Figure 21 depicts burls on a portion of a gripper to support a substrate;

[0034] Figure 22 depicts a gripper comprising a support structure for a heat transfer element;

[0035] Figure 23 depicts a gripper comprising a plurality of temperature sensors and a plurality of heat transfer elements, and a controller;

[0036] Figure 24 depicts a channel loop, two adjacent sections in the loop, and a distance from a point of fluid entry to one of the sections;

[0037] Figure 25 depicts the channel loop and adjacent sections of Figure 24 and a distance from the point of fluid entry to the other one of the sections;

[0038] Figure 26 depicts the channel loop of Figure 24, two different adjacent sections, and a distance from a point of fluid entry to one of the sections; and

[0039] Figure 27 depicts the channel loop and adjacent sections of Figure 26, and a distance from the point of fluid entry to the other one of the sections.

DETAILED DESCRIPTION

[0040] Figure 1 schematically depicts a lithographic apparatus according to one embodiment of the invention. The apparatus comprises:

[0041] - an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation, DUV radiation or EUV radiation);

[0042] - 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;

[0043] - 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

[0044] - a 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.

[0045] 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.

[0046] 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”.

[0047] 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.

[0048] 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.

[0049] The terms “projection system” used herein should be broadly interpreted as encompassing any type of 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”.

[0050] 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).

[0051] The lithographic apparatus may be of a type having two or more substrate support structures, such as substrate stages or substrate tables, and/or two or more support structures for patterning devices. In an apparatus with multiple substrate stages, all the substrate stages can be equivalent and interchangeable. In an embodiment, at least one of the multiple substrate stages is particularly adapted for exposure steps and at least one of the multiple substrate stages is particularly adapted for measurement or preparatory steps. In an embodiment of the invention one or more of the multiple substrate stages is replaced by a measurement stage. A measurement stage includes at least part one or more sensor systems such as a sensor detector and/or target of the sensor system but does not support a substrate. The measurement stage is positionable in the projection beam in place of a substrate stage or a support structure for a patterning device. In such apparatus the additional stages may be used in parallel, or preparatory steps may be carried out on one or more stages while one or more other stages are being used for exposure.

[0052] Referring to Figure 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.

[0053] The illuminator IL may comprise an adjuster AM 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).

[0054] 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. Substrate W is held on the substrate table WT by a substrate holder according to an embodiment of the present invention and described further below. With the aid of the second positioner PW and position sensor PS1 (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 in Figure 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, M2 and 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.

[0055] The depicted apparatus could be used in at least one of the following modes:

[0056] 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.

[0057] 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.

[0058] 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.

[0059] Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed.

[0060] Arrangements for providing liquid between a final element of the projection system PS and the substrate can be classed into three general categories. These are the bath type arrangement, the so-called localized immersion system and the allwet immersion system. In a bath type arrangement substantially the whole of the substrate W and optionally part of the substrate table WT is submersed in a bath of liquid.

[0061] A localized immersion system uses a liquid supply system in which liquid is only provided to a localized area of the substrate. The space filled by liquid is smaller in plan than the top surface of the substrate and the volume filled with liquid remains substantially stationary relative to the projection system PS while the substrate W moves underneath that volume. Figures 2-5 show different supply devices which can be used in such a system. A sealing feature is present to seal liquid to the localized area. One way which has been proposed to arrange for this is disclosed in PCT patent application publication no. WO 99/49504.

[0062] In an all wet arrangement the liquid is unconfined. 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. Immersion liquid may be supplied to or in the region of a projection system and a facing surface facing the projection system (such a facing surface may be the surface of a substrate and/or a substrate table). Any of the liquid supply devices of Figures 2-5 can also be used in such a system. However, a sealing feature is not present, not activated, not as efficient as normal or otherwise ineffective to seal liquid to only the localized area.

[0063] As illustrated in Figures 2 and 3, liquid is supplied by at least one inlet onto the substrate, preferably along the direction of movement of the substrate relative to the final element. Liquid is removed by at least one outlet after having passed under the projection system. As the substrate is scanned beneath the element in a -X direction, liquid is supplied at the +X side of the element and taken up at the -X side. Various orientations and numbers of in- and outlets positioned around the final element are possible; one example is illustrated in Figure 3 in which four sets of an inlet with an outlet on either side are provided in a regular pattern around the final element. Note that the direction of flow of the liquid is shown by arrows in Figures 2 and 3.

[0064] A further immersion lithography solution with a localized liquid supply system is shown in Figure 4. Liquid is supplied by two groove inlets on either side of the projection system PS and is removed by a plurality of discrete outlets arranged radially outwardly of the inlets. Note that the direction of flow of fluid and of the substrate is shown by arrows in Figure 4.

[0065] Another arrangement which has been proposed is to provide the liquid supply system with a liquid confinement structure which extends along at least a part of a boundary of the space between the final element of the projection system and the substrate, substrate table or both. Such an arrangement is illustrated in Figure 5.

[0066] Figure 5 schematically depicts a localized liquid supply system or fluid handling system with a liquid confinement structure 12, 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 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.) In an embodiment, a seal is formed between the liquid confinement structure 12 and the surface of the substrate W and which may be a contactless seal such as a gas seal (such a system with a gas seal is disclosed in European patent application publication no. EP-A-1,420,298) or a liquid seal.

[0067] The liquid confinement structure 12 at least partly contains liquid in the space 11 between a final element of the projection system PS and the substrate W. The space 11 is at least partly formed by the liquid confinement structure 12 positioned below and surrounding the final element of the projection system PS. Liquid is brought into the space below the projection system PS and within the liquid confinement structure 12 by liquid inlet 13. The liquid may be removed by liquid outlet 13.

[0068] The liquid may be contained in the space 11 by a gas seal 16 which, during use, is formed between the bottom of the barrier member 12 and the surface of the substrate W. The gas in the gas seal is provided under pressure via inlet 15 to the gap between barrier member 12 and substrate W. The gas is extracted via outlet 14. The overpressure on the gas inlet 15, vacuum level on the outlet 14 and geometry of the gap are arranged so that there is a high-velocity gas flow 16 inwardly that confines the liquid. The force of the gas on the liquid between the barrier member 12 and the substrate W contains the liquid in a space 11. Such a system is disclosed in United States patent application publication no. US 2004-0207824, which is hereby incorporated by reference in its entirety. In an embodiment, the liquid confinement structure 12 does not have a gas seal.

[0069] An embodiment of the present invention may be applied to any fluid handling structure including those disclosed, for example, in United States patent application publication nos. US 2006-0158627, US 2006-0038968, US 2008-0212046, US 2009-0279060, US 2009-0279062, US 2004-0207824, US 2010-0313974 and US 2012-0120376, the contents of all of which are hereby incorporated in their entirety by reference.

[0070] Many other types of liquid supply system are possible. An embodiment of the present invention is neither limited to any particular type of liquid supply system, nor to immersion lithography. An embodiment of the invention may be applied equally in any lithography. In an EUV lithography apparatus, the beam path is substantially evacuated and immersion arrangements described above are not used.

[0071] A control system 500 shown in Figure 1 controls the overall operations of the lithographic apparatus and in particular performs an optimization process described further below. Control system 500 can be embodied as a suitably-programmed general purpose computer comprising a central processing unit and volatile and nonvolatile storage. Optionally, the control system may further comprise one or more input and output devices such as a keyboard and screen, one or more network connections and/or one or more interfaces to the various parts of the lithographic apparatus. It will be appreciated that a one-to-one relationship between controlling computer and lithographic apparatus is not necessary. In an embodiment of the invention one computer can control multiple lithographic apparatuses. In an embodiment of the invention, multiple networked computers can be used to control one lithographic apparatus. The control system 500 may also be configured to control one or more associated process devices and substrate handling devices in a lithocell or cluster of which the lithographic apparatus forms a part. The control system 500 can also be configured to be subordinate to a supervisory control system of a lithocell or cluster and/or an overall control system of a fab.

[0072] Figure 6 schematically depicts an EUV lithographic apparatus 4100 including a source collector apparatus SO. The apparatus comprises:

[0073] - an illumination system (illuminator) EIL configured to condition a radiation beam B (e.g. EUV radiation);

[0074] - 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 to accurately position the patterning device;

[0075] - 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; and

[0076] - 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 portion C (e.g. comprising one or more dies) of the substrate W.

[0077] These basic components of the EUV lithographic apparatus are similar in function to the corresponding components of the lithographic apparatus of Figure 1. The description below mainly covers areas of difference and duplicative description of aspects of the components that are the same is omitted.

[0078] In an EUV lithographic apparatus, it is desirable to use a vacuum or low pressure environment since gas can absorb too much radiation. A vacuum environment can therefore be provided to the whole beam path with the aid of a vacuum wall and one or more vacuum pumps.

[0079] Referring to Figure 6, the EUV illuminator EIL receives an extreme ultra violet radiation beam from the source collector apparatus SO. Methods to produce EUV radiation include, but are not necessarily limited to, converting a material into a plasma state that has at least one element, e.g., xenon, lithium or tin, with one or more emission lines in the EUV range.

[0080] 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 the patterning device. After being reflected from the patterning device (e.g. mask) MA, the radiation beam EB 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 PS2 (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 EB. Similarly, the first positioner PM and another position sensor PS1 can be used to accurately position the patterning 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 mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0081] The depicted apparatus could be used the same modes as the apparatus of Figure 1.

[0082] Figure 7 shows the EUV apparatus 4100 of Figure 6 in more detail, including the source collector apparatus SO, the EUV illumination system EIL, and the projection system PS. The source collector apparatus SO is constructed and arranged such that a vacuum environment can be maintained in an enclosing structure 4220 of the source collector apparatus SO. An EUV radiation emitting plasma 4210 may be formed by a discharge produced plasma source. EUV radiation may be produced by a gas or vapor, for example Xe gas, Li vapor or Sn vapor in which the plasma 4210 is created to emit radiation in the EUV range of the electromagnetic spectrum.

[0083] The radiation emitted by the plasma 4210 is passed from a source chamber 4211 into a collector chamber 4212 via an optional gas barrier and/or contaminant trap 4230 (in some cases also referred to as contaminant barrier or foil trap) which is positioned in or behind an opening in source chamber 4211.

[0084] The collector chamber 4212 may include a radiation collector CO which may be a so-called grazing incidence collector. Radiation collector CO has an upstream radiation collector side 4251 and a downstream radiation collector side 4252. Radiation that traverses collector CO can be reflected by a grating spectral filter 4240 to be focused in a virtual source point IF. The virtual source point IF is commonly referred to as the intermediate focus, and the source collector apparatus is arranged such that the intermediate focus IF is located at or near an opening 4221 in the enclosing structure 4220. The virtual source point IF is an image of the radiation emitting plasma 4210.

[0085] Subsequently the radiation traverses the illumination system IL, which may include a facetted field mirror device 422 and a facetted pupil mirror device 424 arranged to provide a desired angular distribution of the radiation beam 421, at the patterning device MA, as well as a desired uniformity of radiation intensity at the patterning device MA. Upon reflection of the beam of radiation 421 at the patterning device MA, held by the support structure MT, a patterned beam 426 is formed and the patterned 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.

[0086] Collector optic CO, as illustrated in Figure 7, is depicted as a nested collector with 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 are disposed axially symmetric around an optical axis O and a collector optic CO of this type is preferably used in combination with a discharge produced plasma source, often called a DPP source.

[0087] Alternatively, the source collector apparatus SO may be part of an LPP radiation system as shown in Figure 8. A laser LA is arranged to deposit laser energy into a fuel, such as xenon (Xe), tin (Sn) or lithium (Li), creating the highly ionized plasma 4210 with electron temperatures of several 10's of eV. The energetic radiation generated during de-excitation and recombination of these ions is emitted from the plasma, collected by a near normal incidence collector optic CO and focused onto the opening 4221 in the enclosing structure 4220.

[0088] An embodiment of the present invention can be applied to any type of lithographic apparatus.

[0089] Figures 9-11 depict use of a substrate transfer device 30 to transfer a substrate from a thermal conditioning table 20 to a substrate table for exposure 22. The substrate transfer device 30 comprises a gripper 24, a robot arm 26, and a robot arm motor 28. Figure 9 depicts the gripper 24 being moved by the robot arm 26 towards the substrate W on the thermal conditioning table 20. Figure 10 depicts the gripper 24 transporting the gripped substrate W towards the substrate table for exposure 22. Figure 11 depicts the gripper 24 being moved away from the substrate W after release of the substrate W onto the substrate table for exposure 22.

[0090] In the arrangement depicted the gripper 24 has a cut-out portion 25 to allow the gripper 24 to be slid underneath the substrate W past one or more support pins used to support the substrate vertically above the thermal conditioning table 20 and/or the substrate table for exposure 22. When the gripper 24 is in position beneath the substrate W, the gripper 24 is, for example, raised to disengage the substrate W from the thermal conditioning table 20. The substrate W can then be transported towards the substrate table for exposure 22, and then, for example, lowered down until the substrate W rests on a support element (e.g. a support pin, not shown in Figures 9-11) associated with the substrate table for exposure 22, thus releasing the substrate W from the gripper 24. The gripper 24 can then be removed as shown in Figure 11.

[0091] As described in the introductory part of the description, the gripper 24 may cause a “thermal fingerprint” to be transferred to the substrate W during the transfer process. In the example shown, the thermal fingerprint may arise due to a difference between the temperature of the gripper 24 during the transfer process and the temperature of the substrate W. For example, heat generated by the robot arm motor 28 may be conducted along the robot arm 26 and cause an increase in temperature of the gripper 24. The difference in temperature between the gripper 24 and the substrate W may cause a fingerprint that has a shape corresponding to the shape of the gripper 24. For example, a region of the substrate W directly adjacent to the gripper 24 (e.g. region 27 shown in Figure 10) may exchange more heat with the substrate W than a region which is not directly adjacent to the gripper 24 (e.g. region 29 shown in Figure 10). Such a directly adjacent region 27 may approach the temperature of the gripper 24 more than the region 29 which is not directly adjacent to the gripper 24. The region 27 may also be shielded from environmental gas more than region 29. Where the environmental gas is not at the same temperature as the gripper 24, this difference in shielding may also cause or contribute to a thermal fingerprint.

[0092] A thermal fingerprint introduced during the transfer of a substrate from one substrate support to another may be reduced or avoided by providing a gripper that interacts with the substrate during transfer in a more thermally uniform manner. If there is a difference in temperature between the gripper and the substrate during transfer the resulting change in temperature of the substrate may be more uniform than would be the case with prior grippers. The gripper may provide a shielding effect, for example by reducing the flow of environmental gas (which may have a different temperature to the substrate) over a side of the substrate and/or by preventing radiation from hitting the substrate on the portion of the side covered by the gripper. If the shielding is provided in a more uniform manner (e.g. by covering a greater proportion of the substrate), a change in temperature of the substrate during substrate transfer will tend to be more uniform. A spatially uniform temperature change tends to have a less negative effect on overlay than a temperature change that is less spatially uniform. Shielding a greater proportion of the substrate will also tend to increase the total amount of shielding, thereby reducing the extent of unwanted heat transfer to/from the substrate. Alternatively or additionally, the gripper is thermally conditioned. In an embodiment, the thermal conditioning of the gripper is active. Thermally conditioning the gripper can reduce a temperature difference between the gripper and the substrate. Alternatively or additionally, thermal conditioning of the gripper can be used to thermally condition the substrate during the transfer process. For example, the temperature of the substrate can be thermally conditioned during the transfer process so as to be at a more similar temperature to the temperature of the substrate table for exposure or more similar to another target temperature. In an embodiment, the arranging of the gripper to interact with the substrate during transfer in a more thermally uniform manner results in a better thermal coupling between the gripper and the substrate. Improving the thermal coupling (i.e. decreasing the thermal resistance associated with the coupling) between the gripper and the substrate during transfer may facilitate thermal conditioning of the substrate via the gripper.

[0093] In an embodiment, the gripper has a gripper body comprising an engaging surface to engage with the substrate. The engaging surface is arranged to overlap substantially evenly over a portion of a face of the substrate when the substrate is engaged with the gripper. The overlapping portion represents more than half of the surface area of the face, optionally more than 90%, optionally more than 95%, optionally more than 99%, optionally 100% (e.g. where the gripper is provided without slits). The gripper provides a thermal coupling that is substantially uniform over the overlapping portion.

[0094] In an embodiment, the engaging surface is a continuous surface adjacent to the overlapping portion (e.g. where the gripper is provided without slits). In an embodiment, the distance between the engaging surface and the overlapping portion of the substrate is substantially constant during engagement of the substrate. In an embodiment, the overlap is substantially even when assessed at a spatial resolution of 1 cm or less, 5 mm or less, 1 mm or less, or 0.1 mm or less. In an embodiment, the thermal coupling is substantially uniform when assessed at a spatial resolution of 1 cm or less, 5 mm or less, 1 mm or less, or 0.1 mm or less.

[0095] Figures 12 to 14 depict use of a substrate transfer device 31, according to an example embodiment, to transfer a substrate W from a first substrate support 33 to a second substrate support 35. In an embodiment, the first substrate support 33 is a thermal conditioning table to thermally condition (i.e. control the temperature of) the substrate W. In an embodiment, the second substrate support 35 is a substrate table for exposure. The substrate table for exposure is a table on which the substrate W is supported and/or scanned (moved) underneath a patterned radiation beam during a lithography process. In the embodiment shown, the substrate transfer device 31 comprises a gripper 34, a robot arm 36, and a robot arm motor 38.

[0096] Figure 12 depicts the gripper 34 being moved by the robot arm 36 towards the substrate W on the first substrate support 33. In an embodiment, the gripper 34 engages with the substrate W to remove the substrate W from the first substrate support 33. In an embodiment, the gripper 34 is inserted between a lower face of the substrate W and an upper surface of the first substrate support 33. In an embodiment, one or more support pins (not shown in Figures 12-14) are used to support the substrate W above the upper surface of the first substrate support 33. The gripper 34 then engages with the substrate W by, for example, being moved upwards to lift the substrate W off the first substrate support 33.

[0097] Figure 13 depicts the substrate W being transported from the first substrate support 33 to the second substrate support 35.

[0098] Figure 14 depicts the gripper 34 being moved away from the substrate W after release of the substrate W onto the second substrate support 35. In an embodiment, the substrate W is released onto the second substrate support 35 by lowering the substrate W onto one or more support pins. The gripper 34 is then moved out from between the substrate W and an upper surface of the second substrate support 35, leaving the substrate W on the second substrate support 35.

[0099] In an embodiment, the substrate transfer device 31 further comprises a thermal conditioning system to control the temperature of the engaging surface. In an embodiment, the thermal conditioning system comprises one or more channels formed in the gripper body to channel a thermal conditioning fluid. In an embodiment, the temperature of the thermal conditioning fluid is controlled, for example to be at or near a certain (e.g., predefined) target temperature. In an embodiment, the thermal conditioning fluid is a liquid, for example high purity water.

Embodiments having a channel for a thermal conditioning fluid are described in further detail below with reference to Figures 15 to 20 and 24 to 27. In an embodiment, the substrate transfer device 31 is provided without channels for a thermal conditioning fluid.

[00100] In an embodiment, the thermal conditioning fluid is a phase change material. The phase change material is chosen such that it changes phase at a desired set point temperature and is therefore capable of transferring heat much more efficiently than a thermal conditioning fluid that does not change phase.

[00101] In an embodiment comprising one or more channels for a thermal conditioning fluid, the one or more channels are configured to be part of one or more heat pipes. In the channel of a heat pipe of an embodiment, a thermal conditioning fluid is provided that is a liquid at one end of the channel and a mixture of gas and liquid at the other end of the channel. Changing from a gas to a liquid and vice versa absorbs and lets out heat and so this is an efficient way of transferring heat between one end of the channel and the other.

[00102] In an embodiment, the thermal conditioning element is configured to cool the gripper 34, heat the gripper 34, or both. In an embodiment, the thermal conditioning element comprises a heater and/or a Peltier element.

[00103] In an embodiment, the substrate transfer device 31 further comprises a controller 42 configured to actively control the temperature of the engaging surface 70 (see, e.g., Figure 15) during at least a portion of the period of engagement between the substrate W and the gripper 34. In an embodiment, the active control comprises controlling the heating and/or cooling according to the output from one or more sensors. In an embodiment, the gripper 34 comprises one or more temperature sensors 37 configured to measure the temperature of all or a portion of the gripper 34. In an embodiment, the one or more temperature sensors 37 are configured to measure the temperature at one or more respective positions on the engaging surface 70. The controller 42 is configured to use the output from the one or more temperature sensors 37 to actively control the temperature of the engaging surface 70. In the embodiment shown, two temperature sensors 37 are provided. In other embodiments, more than two temperature sensors 37 may be provided. In embodiments where a plurality of temperature sensors 70 is provided, an average temperature value may be obtained. In such an embodiment, the controller 42 may be configured to drive the average temperature value obtained from the plurality of sensors 37 towards a target temperature. For example, the controller 42 may be configured to control a set target temperature of thermal conditioning fluid to be driven through channels in the gripper body based on the average temperature value obtained from the plurality of sensors 37. Alternatively or additionally, the controller 42 may be configured to drive different temperature sensors towards different target temperatures. In an embodiment, the controller 42 controls operation of the thermal conditioning system as a function of an output from the one or more temperature sensors 37. In an embodiment, one or more provided target temperatures is/are equal to a measured temperature of a portion of the second substrate support 35. Figure 23 is a schematic side view of an example embodiment in which the gripper 34 comprises a plurality of heat transfer elements (e.g., heaters) 116 and a plurality of temperature sensors 37. In this embodiment, the controller 42 controls the amount of thermal transfer (e.g., heating) provided by the heat transfer elements 116 as a function of the temperatures measured by the temperature sensors 37.

[00104] In an embodiment the controller 42 actively controls the temperature of all or part of the gripper 34 and/or engaging surface 70, and thereby of all or part of the substrate W, during at least part of the transport of the substrate W between the first substrate support 33 and the second substrate support 35. A change in the temperature of the substrate W due to unwanted heat exchange during the transport process can thereby be reduced. In an embodiment, the thermal conditioning of the substrate W during the transport process reduces the amount of thermal conditioning that has to be carried out prior to the transport process (for example at the first substrate support 33 when the first substrate support 33 is a thermal conditioning table). Time spent thermally conditioning the substrate prior to the transport process can thereby be reduced, improving throughput.

[00105] Figures 15 to 20 depict an example gripper 34 having channels 50 for thermal conditioning fluid. Figure 15 is a top view of the gripper 34. Figure 16 is a bottom view of the gripper 34. Figure 17 is a side sectional view along the line B-B in Figure 15. Figure 18 is a side sectional view along line C-C in Figure 15. Figure 19 is an end view of the gripper 34, viewed from a handle part end of the gripper 34, with the top of the gripper 34 being on the right hand side. Figure 20 is a side sectional view along stepped line A-A in Figure 19.

[00106] In the embodiment shown, the gripper 34 comprises a handle part 45 to connect the gripper to an adjacent apparatus. In an embodiment, the handle part 45 is configured to connect the gripper 34 to a robot arm. The gripper 34 comprises a gripper body. In the embodiment shown, the gripper body comprises a raised surface portion 44 and an indented surface portion. When the gripper 34 is orientated so as to engage with a substrate that is horizontal, the indented surface portion will be lower than the raised surface portion 44. In an embodiment, the engaging surface 70 forms all or part of the indented surface portion.

[00107] In an embodiment, the gripper 34 further comprises a connecting surface 47 that connects the raised surface portion 44 to the indented surface portion. In an embodiment, the connecting surface 47 is arranged such that a line of contact between at least part of the connecting surface 47 and the indented surface portion forms part of the circumference of a circle. In an embodiment, the part of the circumference that is not present is sufficiently large to allow a substrate to be inserted through the part. In an embodiment the part of the circumference of a circle comprises half the circumference or less. In an embodiment, the diameter of the circle may be 300 mm or 450 mm or 12 inches or 18 inches. Thus, the line of contact may conform with part of the outer peripheral shape of a common format of lithography substrate (e.g., a circular disc having a diameter of 300 mm or 450 mm or 12 inches or 18 inches). Where the substrate has a different form, for example a different shape (e.g. non-circular) or size, the shape of the line of contact, and therefore the connecting surface, can be adapted accordingly. The connecting surface 47 can be used to locate a substrate on the engaging surface 70. For example, an engagement process may comprise sliding the gripper 34 underneath a substrate until the substrate W comes into contact with the connecting surface 47, or is detected as being adequately close to the connecting surface 47. In an embodiment, the connecting surface 47 is configured to be substantially vertical when the engaging surface 70 is horizontal. In such an embodiment, the surface profile of the connecting surface 47 corresponds to the surface formed by moving the line of contact vertically upwards.

[00108] In other embodiments, the engaging surface 70 is at the same level as the top surface of the gripper 34 (i.e. is not indented).

[00109] In an embodiment, one or more slits 46 are provided to allow the gripper 34 to be inserted past one or more vertical support pins (not shown in Figure 15) supporting the substrate. In the orientation of Figure 15 for example, insertion of the gripper beneath a substrate W mounted on a support pin may be achieved by moving the gripper 34 vertically upwards. The support pin would move vertically downwards, relative to the gripper 34, into the slit 46. Each slit 46 traverses the gripper body in a direction perpendicular to the engaging surface 70. Each slit 46 has an opening 49 to allow the respective support pin to enter the slit 46.

[00110] In an embodiment, a plurality of channels is provided that are configured to be driven in parallel (as opposed to being driven in series). In an embodiment, at least three channels are provided and configured to be driven in parallel. The provision of at least three channels improves the uniformity of the thermal conditioning. In an embodiment, the channels are configured to be driven in series.

A plurality of channels can be driven in parallel, for example, by connecting the inputs to the channels to a first common volume at a first pressure and the outputs from the channels to a second common volume at a second pressure. The difference between the first and second pressures is the pressure difference that determines the flow rate through the plurality of channels. A plurality of channels can be driven in series by connecting the output from each channel to the input of the next channel. A pressure difference is then applied across the series of channels (i.e. between the input to the first channel and the output from the last channel) to drive flow through the channels. In the example shown in Figures 15 to 20, a plurality of channels 50 are provided. The plurality of channels 50 are configured to be driven in parallel. In the example shown, the channels 50 are fed by an (arcuate) upper channel 62 and a (arcuate) lower channel 64. In the embodiment shown, the upper and lower channels 62, 64 are sealed by seal members 63 and 65 respectively (see Figures 17 and 18). The arcuate form is not essential. The upper and lower channels 62, 64 are examples of the first and second common volumes mentioned above. Applying different pressures to the upper and lower channels 62, 64 results in fluid being driven in parallel through the plurality of channels 50. Fluid is fed to the upper channel 62 via inlet 52 and in-flow channel 54. The fluid then passes in parallel through the plurality of channels 50. The fluid is removed via lower channel 64, the out-flow channel 58 and the outlet 56. In an embodiment, the flow is reversed.

[00111] As can be seen most clearly in Figure 20, each of the plurality of channels 50 is arranged in a loop. In the embodiment shown, each loop comprises two straight sections 50A and 50B connected together by a “U”-shaped bend. In other embodiments sections having the same function are not straight. Straight section 50A extends from a connection 53 (see Figure 17) with the upper channel 62 towards a leading edge 51 of the gripper 34. Straight section 50B extends from a connection 55 (see Figure 18) with the lower channel 64 towards the leading edge 51. The straight sections 50A and 50B are connected to each other by connecting element 50C. Fluid thus flows in opposite directions in the sections 50A and 50B.

[00112] Providing the flow in parallel reduces the overall flow resistance through the channels 50. Within each channel loop, friction with the channel walls and/or within the fluid itself will tend to increase the temperature of the fluid in the channel. The temperature of the fluid will therefore tend to increase as the distance along the flow in the channel increases. In the absence of a countermeasure, this change in the fluid temperature along the channel could lead to a corresponding change in the temperature of the engaging surface 70 adjacent to the channel. In an embodiment, this issue is addressed as follows, referring to Figures 24 to 27.

[00113] In an embodiment, at least three channels are provided, each formed into a loop and configured to be driven in parallel to each other. Figures 24 to 27 each illustrate one such channel 144. The channel has inlet and outlet channels 124 and 126 to respectively supply and withdraw fluid from the channel 144. In an embodiment each channel 144 comprises a plurality of pairs of adjacent sections configured to support anti-parallel flow. In the example shown, only two such pairs are shown for clarity: a first pair comprising a first section 131 and a second section 133, and a second pair comprising a third section 135 and a fourth section 137. The sections of each pair are adjacent to each other in a direction perpendicular to the flow. In an embodiment, the plurality of pairs of adjacent sections constitute at least half of the total length of each channel 144, optionally at least 95% of the total length of each channel 144. In other words, at least half (optionally at least 95%) of the total length of the channel 144 is made up from sections that can be identified as part of a pair of adjacent sections.

[00114] This geometry of loops having adjacent sections, exemplified by Figures 24 to 27, results in the average amount of heating or cooling supplied by the fluid to regions of the gripper body between different pairs of adjacent sections being more uniform. In an embodiment, this improved uniformity may be increased by suitable selection (e.g. by tuning) of the distance 150 between the sections of each of the pairs. In the embodiment shown the distance 150 between the sections of the two pairs shown is the same. However, this is not essential. In other embodiments, the distance 150 may be different for different pairs of sections. In an embodiment, the distance 150 is chosen to be small enough that the contribution to heating or cooling in the region between the adjacent sections arises predominantly from the fluid in those adjacent sections.

[00115] In an embodiment, heating or cooling provided by the adjacent sections is substantially the same for different pairs of adjacent sections because the sum of the amount of frictional heating of fluid that has arrived at one of the two sections and the amount of frictional heating of fluid that has arrived at the other of the two sections is substantially constant. In an embodiment, the amount of frictional heating undergone by a given portion of fluid is at least approximately proportional to the distance that that portion of fluid has traveled from a point of entry of the fluid into the channel. Thus, according to an embodiment, the following expression is arranged to be satisfied for at least two pairs of adjacent sections: S1 = S2, where S1 = d1 + d2, S2 = d3 + d4, d1 is a distance along the flow between a first section 131 of a first pair and a point of entry 141 of the thermal conditioning fluid into the channel, d2 is a distance along the flow between a second section of the first pair and the point of entry 141 of the thermal conditioning fluid into the channel, d3 is a distance along the flow between a third section 135 of a second pair and a point of entry 141 of the thermal conditioning fluid into the channel, and d4 is a distance along the flow between a fourth section 137 of the second pair and a point of entry 141 of the thermal conditioning fluid into the channel. In the embodiment shown, the distances d1, d2, d3 and d4 are calculated from a midpoint of the corresponding sections. However, this is not essential. The distances could instead be calculated from the start or end of the corresponding sections. In the geometries shown it can be seen that the sums d1 + d2 and d3 + d4 equal the total length of a single channel. In the geometry shown it can be seen that corresponding sums for other pairs of adjacent sections in the channel would also equal the total length of the channel and therefore tend to lead to the same uniform heating or cooling to the gripper body. The embodiment of Figures 15 to 20 also shows channels satisfying these requirements.

[00116] As shown in Figure 20, for example, one or more of the plurality of channels 50 is arranged so as to comprise a plurality of pairs 82, 84 of adjacent sections. The adjacent sections are shown as 82A, 82B and 84A, 84B respectively in Figure 20. Section 82A may be considered as an example of a second section, 82B as an example of a first section, 84A as an example of a fourth section, and 84B as an example of a third section. In Figure 20, only two pairs 82, 84 are shown for clarity. However, as in the examples of Figures 24-27, it is clear that where the channel comprises two straight portions 50A and 50B, a continuum of pairs of adjacent channel sections is present. The channel 50 is arranged so the combined frictional heating per unit length from at least two of the plurality of pairs 82, 84 is substantially the same. In an embodiment, the combined frictional heating per unit length from the plurality of pairs of channel portions is arranged to be substantially the same over at least half of the channel, optionally for at least 95% of the channel.

[00117] In an embodiment, the channels 50 are configured to have a cross-section perpendicular to the flow that is larger in the direction parallel to the engaging surface of the gripper and/or the substrate W than in the perpendicular direction.

This configuration facilitates the provision of a larger cross-sectional area in the case where the thickness of the gripper body 71 adjacent to the engaging surface 70 is small. Providing channels having a larger cross-sectional area reduces the frictional heating and pressure drop across the channels.

[00118] In an embodiment, the plurality of channels comprises a plurality of parallel portions (i.e. portions that are geometrically parallel). The parallel portions may be driven in parallel or in series. In an embodiment, such as the embodiment shown in Figures 15-20, the parallel portions are straight. Using straight portions, particularly parallel straight portions, facilitates manufacture.

[00119] In an embodiment, the gripper 34 comprises a vacuum clamp configured to hold the substrate W during engagement of the substrate W with the gripper 34. In an embodiment, the gripper 34 comprises an electrostatic clamp to hold the substrate W during engagement of the substrate W with the gripper 34. An electrostatic clamp may be used for example in a lithographic apparatus configured to expose the substrate with EUV radiation. In an embodiment of this type, H2gas may be introduced between the substrate W and the first and/or second substrate table 33, 35 to increase thermal contact between the substrate W and the first and/or second substrate table 33, 35. In an embodiment, another gas can be used instead of, or in addition to, H2, for example N2, He or air.

[00120] Figure 21 depicts a portion of a substrate W held on a gripper 34. In an embodiment, the substrate W may be directly adjacent to an engaging surface 70 of the gripper 34 during engagement of the substrate W with the gripper 34 (directly in contact with the engaging surface 70 or held apart from the engaging surface 70). In an embodiment, the substrate W is held apart from the engaging surface 70 by one or more burls 72. In an embodiment, the height 74 of one or more burls 72 is less than 150 microns, optionally less than 100 microns, optionally less than 50 microns, or optionally less than 20 microns, in order to improve thermal contact between the substrate W and the engaging surface 70.

[00121] Figure 22 is a schematic end view depicting an example gripper 34 that further comprises a support structure 86 to support a gripper body portion 71. In an embodiment, the engaging surface 70 is a surface of the gripper body portion 71. In embodiment, the gripper body portion 71 defines or supports an element of the thermal conditioning system, such as one or more channels, heat transfer elements (e.g., heaters and/or coolers) and/or sensors. In an embodiment, the support is such as to reduce mechanical deformation of the gripper body portion 71. In an embodiment, the support structure is thermally insulated from the gripper body portion 71, for example by a thermally insulating layer 88. In the embodiment shown, the support structure 86 is thermally insulated from the gripper body portion 71 by the layer 88. In an embodiment, the layer 88 is formed from a material having a very low thermal conductivity.

[00122] The support structure 86 makes it possible to reduce the size of the gripper body portion 71, without the portion being deformed, for example due to its own weight. In an embodiment, the gripper body portion 71 has a thickness so as not to be self-supporting. Reducing the size of the gripper body portion 71 makes it possible to reduce the heat capacity of the gripper body portion 71. Reducing the heat capacity of the gripper body portion 71 makes it easier to control the temperature of the gripper body portion 71. For example, a lower heat capacity will facilitate rapid change in temperature of the gripper body portion 71 and therefore of the engaging surface 70. Thermally insulating the gripper body portion 71 from the support structure 86 prevents heat exchange with the support structure 86 interfering with temperature control of the gripper body portion 71 and, therefore, of the engaging surface 70.

[00123] In an embodiment, the first and/or second substrate supports have a structure configured to support the substrate in an elevated position to facilitate loading or unloading of a substrate onto the substrate support. In the embodiments discussed in detail above, one or more support pins (not shown in the Figures) are provided and the gripper comprises one or more slits to allow the gripper to be inserted past the support pin. However, other techniques to lift the substrate into a position that facilitates insertion of a gripper underneath may be used. For example, apparatus may be provided to levitate the substrate above the support table in a contactless manner. Such levitation may be implemented using, e.g., a gas bearing or an electromagnet. Where the substrate is levitated in a contactless manner, the gripper 34 may be provided without slits or the equivalent. In such an embodiment, the overlap between the engaging surface 70 and the one face of the substrate may represent 100% of the surface area of the face.

[00124] While the discussion herein has focused on using the discussed gripper with a substrate, the gripper may be used to transport additional or alternative objects.

For example, the gripper may be used to transport a patterning device. The gripper may be used to transport an optical element.

[00125] Further, the gripper has been described as supporting the substrate (or more generically the object) from the bottom against gravity. However, it may be that the gripper holds to the object from the top. For example, the object and the gripper may interact magnetically (e.g., the gripper may have an electromagnet and the object has a metal or magnet), electrostatically (e.g., the gripper may have an electrostatic clamp that interacts with an appropriate arrangement of the object), fluidly (e.g., the gripper may have a low pressure source to attract the object), etc. to hold the object against gravity from the top.

[00126] As will be appreciated, any of the above described features can be used with any other feature and it is not only those combinations explicitly described which are covered in this application.

[00127] 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.

[00128] 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).

[00129] 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.

[00130] While specific embodiments of the invention have been described above, it will be appreciated that the invention, at least in the form of a method of operation of an apparatus as herein described, may be practiced otherwise than as described.

For example, the embodiments of the invention, at least in the form of a method of operation of an apparatus, may take the form of one or more computer programs containing one or more sequences of machine-readable instructions describing a method of operating an apparatus as discussed 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.

[00131] Any controllers described herein may each or in combination be operable when the one or more computer programs are read by one or more computer processors located within at least one component of the lithographic apparatus. The controllers may each or in combination have any suitable configuration for receiving, processing and sending signals. One or more multiple processors are configured to communicate with at least one of the controllers. For example, each controller may include one or more processors for executing the computer programs that include machine-readable instructions for the methods of operating an apparatus as described above. The controllers may include data storage media for storing such computer programs, and/or hardware to receive such media. So the controller(s) may operate according to the machine readable instructions of one or more computer programs.

[00132] 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.

[00133] One or more embodiments of the invention may be applied to any immersion lithographic 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.

[00134] 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.

[00135]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 clauses set out below. Other aspects of the invention are set out as in the following numbered clauses: 1. A gripper configured to transport an object in a lithographic apparatus, the gripper comprising: a gripper body with an engaging surface to engage with the object; and three or more channels, formed in the gripper body, to channel a thermal conditioning fluid and configured to be driven in parallel with each other, wherein: each of the channels comprises a loop having a plurality of pairs of adjacent sections, the sections of each pair being adjacent to each other in a direction perpendicular to the flow in the sections of the pair, with the flow in one section of the pair being in the opposite direction to the flow in the other section of the pair, and the plurality of pairs of adjacent sections constitute at least half of the total length of each channel.

2. The gripper according to clause 1, wherein: for each of the pairs of adjacent sections present in one or more of the channels, the distance between the sections of the pair is arranged so that the average amount of heating or cooling supplied by the fluid to the region of the gripper body in between the sections of the pair will be substantially the same as the average amount of heating or cooling supplied by the fluid to the region of the gripper body in between the sections of each of the other pairs of adjacent sections.

3. The gripper according to clause 1 or clause 2, wherein: for each of the plurality of channels, the plurality of pairs of adjacent sections comprises at least a first pair having a first section and a second section, and a second pair having a third section and a fourth section; and S1 is substantially equal to S2, S1 and S2 is defined as follows: 51 = d1 +d2; 52 = d3 + d4, wherein d1 is a distance along the flow between the first section and a point of entry of the thermal conditioning fluid into the channel, d2 is a distance along the flow between the second section and the point of entry of the thermal conditioning fluid into the channel, d3 is a distance along the flow between the third section and the point of entry of the thermal conditioning fluid into the channel, and d4 is a distance along the flow between the fourth section and the point of entry of the thermal conditioning fluid into the channel.

4. The gripper according to any of the preceding clauses, wherein one or more of the channels is/are configured to have a cross-section perpendicular to the flow that has a first dimension in a direction substantially parallel to the engaging surface of the gripper and a second dimension in another direction substantially perpendicular to the engaging surface, wherein the first dimension is larger than the second dimension.

5. The gripper according to any of the preceding clauses, further comprising a temperature sensor configured to measure the temperature at a position on the engaging surface and/or on the engaged object.

6. A gripper configured to transport an object in a lithographic apparatus, the gripper comprising: a gripper body with an engaging surface to engage with the object; a thermal conditioning system configured to control a temperature of the engaging surface; and a temperature sensor configured to measure the temperature a position on the engaging surface and/or on the engaged object.

7. The gripper according to clause 6, wherein the thermal conditioning system comprises a channel formed in the gripper body to channel a thermal conditioning fluid.

8. The gripper according to clause 7, wherein a plurality of channels are provided and configured to be driven in parallel.

9. The gripper according to any of clauses 6-8, wherein the thermal conditioning system comprises a heater, or a Peltier element, or both.

10. The gripper according to any of the preceding clauses, wherein the engaging surface overlaps substantially evenly over a portion of a face of the object when the object is engaged with the gripper, the portion representing more than half of a surface area of the face.

11. The gripper according to clause 10, wherein the overlapping portion represents more than 90% of the surface area of the face.

12. The gripper according to any of the preceding clauses, wherein: the gripper further comprises a support structure configured to support a portion of the gripper body comprising the engaging surface and/or defining or supporting an element of the thermal conditioning system, to reduce mechanical deformation of the portion of the gripper body; and the support structure is thermally insulated from the portion of the gripper body.

13. The gripper according to any of the preceding clauses, wherein the gripper body further comprises a slit, the slit traversing the gripper body in a direction perpendicular to the engaging surface and having an opening at one end to allow a support pin to support the object, and which is oriented perpendicular to the engaging surface, to move along the slit relative to the gripper body.

14. A lithographic apparatus comprising: a projection system configured to project a patterned radiation beam onto a substrate; a gripper according to any of clauses 6-13 that is configured to engage with the object when held on a first support and, while engaged with the object, remove the object from the first support, transport the object to a second support, and release the object onto the second support; and a controller configured to use the output from the temperature sensor to actively control the temperature of the engaging surface and/or of the engaged object using the thermal conditioning system.

15. The lithographic apparatus according to clause 14, wherein the thermal conditioning system is configured to both heat and cool the engaging surface and/or the engaged object, as required, in response to an output from the controller.

16. A lithographic apparatus comprising: a projection system configured to project a patterned radiation beam onto a substrate; and a gripper according to any of clauses 1 -5 or 10-13 that is configured to engage with the object when held on a first support and, while engaged with the object, remove the object from the first support, transport the object to a second support, and release the object onto the second support.

17. The lithographic apparatus according to any of clauses 14-16, wherein the second support is configured to move the object underneath a path of a projection beam of radiation to expose the object to the radiation beam.

18. The lithographic apparatus according to any of clauses 14-17, configured to control the temperature of the engaging surface such that the temperature of the engaging surface is substantially the same as the second support when the object is released onto the second support.

19. A method of thermally conditioning an object in a lithographic apparatus, the method comprising: using a gripper to engage with an object when held on a first support and, while engaged with the object, remove the object from the first support, transport the object to a second support, and release the object onto the second support; and during transporting the object from the first support to the second support, driving a thermal conditioning fluid through a plurality of channels formed in a gripper body of the gripper.

20. The method according to clause 19, wherein the thermal conditioning fluid is driven in parallel through three or more channels formed in the gripper body, and wherein: each of the channels comprises a loop having a plurality of pairs of adjacent sections, the sections of each pair being adjacent to each other in a direction perpendicular to the flow in the sections of the pair, with the flow in one section of the pair being in the opposite direction to the flow in the other section of the pair; and the plurality of pairs of adjacent sections constitute at least half of the total length of each channel.

21. A method of thermally conditioning an object, the method comprising: using a gripper to engage with an object when held on a first support and, while engaged with the object, remove the object from the first support, transport the object to a second support, and release the object onto the second support; and during transporting the object from the first support to the second support, measuring the temperature at a position on an engaging surface and/or on the engaged object, and using the measured temperature to actively control the temperature of the engaged surface and/or the engaged object.

22. The method according to any of clauses 19-21, wherein the second support is configured to move the object underneath a projection beam to expose the object to the projection beam.

23. The method according to any of clauses 19-22, wherein the temperature of an engaging surface of the gripper to engage with the object is controlled such that the temperature of the engaging surface is substantially the same as the second support when the object is released onto the second support.

24. The method according to any of clauses 19-23, wherein the gripper comprises a slit traversing a gripper body in a direction perpendicular to an engaging surface and having an opening at one end to allow a support pin to support the object, and which is oriented perpendicular to the engaging surface, to move along the slit relative to the gripper body.

25. A device manufacturing method comprising: using the method of any of clauses 19-24 to thermally condition a substrate; and using the lithographic apparatus to perform a lithographic process on the substrate after the thermally conditioning.

26. A device manufacturing method, comprising: using a gripper according to any of clauses 1 -13 to transport a substrate in a lithographic apparatus; and using the lithographic apparatus to perform a lithographic process on the substrate.

Claims (1)

A lithography device comprising: an illumination device adapted to provide a radiation beam; a carrier constructed to support a patterning device, the patterning device being capable of applying a pattern in a 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 adapted to position the target area of the substrate in a focal plane of the projection device.