Actuator using phase-change material

Abstract

An actuator for positioning a motion stage, the actuator comprising a coil and a temperature regulating unit for transferring heat to and from the coil, wherein the temperature regulating unit comprising: a thermal conducting cooling plate provided with a cooling fluid channel; a potting layer surrounding the coil for transferring actuation force, transferring dissipated heat from the coil to the cooling plate and electrically insulating the coil; and a phase-change material arranged proximate to the coil for buffering heat.

Description

ACTUATOR USING PHASE-CHANGE MATERIALCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application 23218003.4 which was filed on 19 December 2023; and which is incorporated herein in its entirety by reference.FIELD

[0002] The present invention relates to an actuator for positioning a motion stage, to a motion stage comprising such an actuator, to a wafer exposure apparatus comprising such a motion stage, and to a method for manufacturing such an actuator.BACKGROUND

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern (also often referred to as “design layout” or “design”) of a patterning device (e.g., a mask) onto a layer of radiation- sensitive material (resist) provided on a substrate (e.g., a wafer).

[0004] As semiconductor manufacturing processes continue to advance, the dimensions of circuit elements have continually been reduced while the amount of functional elements, such as transistors, per device has been steadily increasing over decades, following a trend commonly referred to as ‘Moore’s law’. To keep up with Moore’s law the semiconductor industry is chasing technologies that enable to create increasingly smaller features. To project a pattern on a substrate a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which are patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm. A lithographic apparatus, which uses extreme ultraviolet (EUV) radiation, having a wavelength within a range of 4 nm to 20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than a lithographic apparatus which uses, for example, radiation with a wavelength of 193 nm.

[0005] Actuators like voice-coil actuators, reluctance actuators, Lorentz actuators and piezoactuators are used in lithographic apparatus for positioning motion stages, such as wafer stages and mask stages. Such actuators usually comprise at least a coil through which an electric current flows for creating an electric-magnetic field and for generating a driving force to the motion stage.

[0006] Modern advanced lithographic apparatus keeps chasing for higher productivity in order to lower the cost per wafer. Motion stages with higher speed and acceleration are desired, which is translated into more driving force and thus more electric current flowing through the coil wire.

[0007] The increasing current generates undesired heat in the coil wire which degrades the lifetime of the coil and the output power of the actuator. In addition to that, a motion stage and the drivingactuator may undergo various working conditions under which the coil temperature fluctuates, and the lifetime and the output power of the actuator is further degraded.SUMMARY

[0008] It is an object of the invention to provide an actuator with an improved cooling mechanism. It is a further object of the invention to reduce the temperature fluctuation of an actuator coil. Another object of the invention is to improve the lifetime of the actuator. One or more of the objects of the invention is reached by the actuator for positioning a motion stage according to the first aspect of the invention, as defined in claim 1, the actuator comprising:- a coil, and- a temperature regulating unit for transferring heat to and from the coil, the temperature regulating unit comprising:- a thermal conducting cooling plate provided with a cooling fluid channel,- a potting layer surrounding the coil for transferring actuation force and transferring dissipated heat from the coil to the cooling plate, and- a phase-change material proximate to the coil for buffering heat.

[0009] The phase-change material in an actuator proximate to the coil absorbs and stores heat when the coil temperature rises above a certain level, and releases heat when the coil temperature drops below the certain level. In this way, heat is buffered by the phase-change material, the temperature fluctuation of the actuator coil is reduced, and the lifetime of the actuator is improved.

[0010] The phase-change material may have a melting temperature for buffering heat generated by the coil.

[0011] The phase-change material may be arranged in the core of the coil.

[0012] The actuator may comprise two or more coils, and the phase-change material may be arranged in a gap between two coils of the two or more coils.

[0013] The temperature regulating unit may comprise a thermal conducting material which penetrates a volume of the phase-change material. The thermal conducting material may be electrical insulating or electrical conducting.

[0014] The temperature regulating unit may comprise a chamber, wherein the chamber walls are of a thermal conductive material, and the chamber encloses the phase-change material and an air pocket.

[0015] The phase-change material may be applied as a layer of coating to the coil wire.

[0016] The phase-change material coating layer may be electrical insulating.

[0017] An electrical insulating material may be applied as a layer of coating to the coil wire in addition to the coating of the phase-change material.

[0018] The temperature regulating unit may comprise two or more phase-change materials having different melting temperatures.

[0019] The thermal conducting cooling plate and the phase-change material may be in thermal contact with the coil.

[0020] According to a second aspect, there is provided a motion stage comprising an actuator as disclosed in at least one of the embodiments above for positioning the motion stage.

[0021] According to a third aspect, there is provided a wafer exposure apparatus comprising the motion stage described above.

[0022] According to a fourth aspect, there is provided a method for manufacturing an actuator as disclosed in at least one of the embodiments above, comprising:-applying a potting layer surrounding the coil,-placing a phase-change material proximate to the coil, and-placing a thermal conducting cooling plate provided with a cooling fluid channel. The phasechange material may be applied as a coating layer to the coil, or arranged in the core of the coil, or in case of the actuator comprising two or more coils, placed in a gap between two coils of the two or more coils.

[0023] Further features of the present disclosure, as well as the structure and operation of various embodiments, are described in detail below with reference to the accompanying drawings. It is noted that the present disclosure is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:Figure 1 depicts a schematic overview of a lithographic apparatus;Figure 2(a) depicts a sectional view of a schematic of an actuator;Figure 2(b) depicts a side view of figure 2(a) looking from the right-hand side;Figure 3(a) depicts a top view of a racetrack coil;Figure 3(b) depicts a cross-section Illb-IIIb of figure 3(a);Figure 4(a) depicts a top view of an edge-wound racetrack coil;Figure 4(b) depicts a cross-section IVb-IVb of figure 4(a);Figure 5 depicts a sectional view of the coil of figure 3(b) with a temperature conditioning unit;Figure 6 depicts a heat buffering effect achieved by using a temperature conditioning unit having a PCM proximate an actuator coil;Figures 7, 8, and 9 depict sectional views of arrangements of a stack of coils with a temperature conditioning unit having a PCM in the cores and / or in a gap between two coils;Figure 10 depicts a sectional view of a stack of two coils with a temperature conditioning unit having a thermal conducting material penetrating a PCM;Figure 11 depicts a sectional view of a stack of two coils with a temperature conditioning unit having a chamber enclosing a PCM and an air pocket;Figure 12 depicts a sectional view of a coil with a temperature conditioning unit having a PCM coating layer on the coil surface;Figure 13 depicts a sectional view of a coil with a temperature conditioning unit having a PCM coating layer and an electrical insulating coating layer on the coil surface;Figure 14 depicts a sectional view of a stack of two coils with a temperature conditioning unit having with a first PCM in the gap between the two coils, and a second PCM in the cores of the two coils, wherein the first and the second PCM have different melting temperatures;Figure 15 depicts a sectional view of a stack of two coils with a temperature conditioning unit having two PCMs having different melting temperatures in the core and in the gap between the two coils;Figure 16 depicts a heat buffering effect achieved by a temperature conditioning unit having two PCMs having different melting temperatures.DETAILED DESCRIPTION

[0025] In the present document, the terms “radiation” and “beam” are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g., with a wavelength of 365, 248, 193, 157 or 126 nm) and EUV (extreme ultra-violet radiation, e.g., having a wavelength in the range of about 5-100 nm).

[0026] The term “reticle”, “mask” or “patterning device” as employed in this text may be broadly interpreted as referring to a generic patterning device that can be used to endow an incoming radiation beam with a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate. The term “light valve” can also be used in this context. Besides the classic mask (transmissive or reflective, binary, phase-shifting, hybrid, etc.), examples of other such patterning devices include a programmable mirror array and a programmable LCD array.

[0027] Figure 1 schematically depicts a lithographic apparatus LA. The lithographic apparatus LA includes an illumination system (also referred to as illuminator) IL configured to condition a radiation beam B (e.g., UV radiation, DUV radiation or EUV radiation), a mask support (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 MA in accordance with certain parameters, a substrate support (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 support in accordance with certain parameters, and 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.

[0028] In operation, the illumination system IL receives a radiation beam from a radiation source SO, e.g., via a beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, and / or other types of optical components, or any combination thereof, for directing, shaping, and / or controlling radiation. The illuminator IL may be used to condition the radiation beam B to have a desired spatial and angular intensity distribution in its cross section at a plane of the patterning device MA.

[0029] The term “projection system” PS used herein should be broadly interpreted as encompassing various types of projection system, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, and / 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” PS.

[0030] The lithographic apparatus LA may be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g., water, so as to fill a space between the projection system PS and the substrate W - which is also referred to as immersion lithography. More information on immersion techniques is given in US6952253, which is incorporated herein by reference.

[0031] The lithographic apparatus LA may also be of a type having two or more substrate supports WT (also named “dual stage”). In such “multiple stage” machine, the substrate supports WT may be used in parallel, and / or steps in preparation of a subsequent exposure of the substrate W may be carried out on the substrate W located on one of the substrate support WT while another substrate W on the other substrate support WT is being used for exposing a pattern on the other substrate W.

[0032] In addition to the substrate support WT, the lithographic apparatus LA may comprise a measurement stage. The measurement stage is arranged to hold a sensor and / or a cleaning device. The sensor may be arranged to measure a property of the projection system PS or a property of the radiation beam B. The measurement stage may hold multiple sensors. The cleaning device may be arranged to clean part of the lithographic apparatus, for example a part of the projection system PS or a part of a system that provides the immersion liquid. The measurement stage may move beneath the projection system PS when the substrate support WT is away from the projection system PS.

[0033] In operation, the radiation beam B is incident on the patterning device, e.g., mask, MA which is held on the mask support MT, and is patterned by the pattern (design layout) present on patterning device MA. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and a position measurement system IF, the substrate support WT can be moved accurately, e.g., so as to position different target portions C in the path of the radiation beam B at a focused and aligned position. Similarly, the first positioner PM and possibly another position sensor (which is not explicitly depicted in Figure 1) may be used to accurately position the patterning deviceMA with respect to the path of the radiation beam B. Patterning device MA and substrate W may be aligned using mask alignment marks Ml, M2 and substrate alignment marks Pl, P2. Although the substrate alignment marks Pl, P2 as illustrated occupy dedicated target portions, they may be located in spaces between target portions. Substrate alignment marks Pl, P2 are known as scribe-lane alignment marks when these are located between the target portions C.

[0034] To clarify the invention, a Cartesian coordinate system is used. The Cartesian coordinate system has three axes, i.e., an x-axis, a y-axis, and a z-axis. Each of the three axis is orthogonal to the other two axis. A rotation around the x-axis is referred to as an Rx-rotation. A rotation around the y- axis is referred to as an Ry-rotation. A rotation around about the z-axis is referred to as an Rz-rotation. The x-axis and the y-axis define a horizontal plane, whereas the z-axis is in a vertical direction. The Cartesian coordinate system is not limiting the invention and is used for clarification only. Instead, another coordinate system, such as a cylindrical coordinate system, may be used to clarify the invention. The orientation of the Cartesian coordinate system may be different, for example, such that the z-axis has a component along the horizontal plane.

[0035] The first positioner PM and the second positioner PW each are provided with an actuator to move respectively the mask support MT and the substrate support WT. The actuator may be a linear actuator to provide a driving force along a single axis, for example the y-axis. Multiple linear actuators may be applied to provide driving forces along multiple axis. The actuator may be a planar actuator to provide a driving force along multiple axis. For example, the planar actuator may be arranged to move the substrate support WT in 6 degrees of freedom. The actuator may be an electro-magnetic actuator comprising at least one coil and at least one magnet. The actuator is arranged to move the at least one coil relative to the at least one magnet by applying an electrical current to the at least one coil. The actuator may be a moving-magnet type actuator, which has the at least one magnet coupled to the substrate support WT respectively to the mask support MT. The actuator may be a moving-coil type actuator which has the at least one coil coupled to the substrate support WT respectively to the mask support MT. The actuator may be a voice-coil actuator, a reluctance actuator, a Lorentz-actuator or a piezo-actuator, or any other suitable actuator.

[0036] The first positioner PM may comprise a long-stroke module and a short-stroke module. The short-stroke module is arranged to move the mask support MT relative to the long-stroke module with a high accuracy over a small range of movement. The long-stroke module is arranged to move the shortstroke module relative to the projection system PS with a relatively low accuracy over a large range of movement. With the combination of the long-stroke module and the short-stroke module, the first positioner PM is able to move the mask support MT relative to the projection system PS with a high accuracy over a large range of movement. Similarly, the second positioner PW may comprise a long- stroke module and a short-stroke module. The short-stroke module is arranged to move the substrate support WT relative to the long-stroke module with a high accuracy over a small range of movement. The long-stroke module is arranged to move the short-stroke module relative to the projection systemPS with a relatively low accuracy over a large range of movement. With the combination of the long- stroke module and the short- stroke module, the second positioner PW is able to move the substrate support WT relative to the projection system PS with a high accuracy over a large range of movement.

[0037] Figure 2 depicts a schematic of an actuator 1 of prior art. Figure 2(a) is a sectional view of the actuator, and figure 2(b) is a side view of the actuator looking from the right-hand side of figure 2(a). The actuator 1 comprises a mover 2 having a coil 3 and a stator 4 having permanent magnets 5. The coil 3 winds around a coil core 6. An electric current flowing through the coil 3 generates an electromagnetic field surrounding the coil. The interaction of the said electromagnetic field and the magnetic field of the magnets 5 creates an actuation force between the coil and the magnets, resulting in a relative displacement between the mover and the stator. The current flow in the coil may generate undesired heat which may degrade the lifetime and may degrade the actuation force of the actuator. A temperature regulating unit 11 is arranged to dissipate the said undesired heat. The temperature regulating unit comprises thermal conducting cooling plates 7 having cooling fluid channels 8, and a potting layer 9 surrounding the coil for transferring the actuation force and transferring the dissipated heat from the coil to the cooling plates and thereby to the cooling fluid. The thermal conducting potting layer may comprise materials like thermosetting plastics, silicone rubber gels or epoxy resins, for example, which materials are suitable for encapsulating and may protect the coil from corrosion, vibration, and other impacts. The cooling fluid flowing in the cooling fluid channels may be water, deionized water, glycol / water solutions, and dielectric fluids such as fluorocarbons and polyalphaolefin (PAO), for example. An electrical insulating layer 10 is arranged to electrically insulate the cooling plates from the coil. The said electrical insulating layer may comprise materials like glass, rubber, ceramics, polymers, etc. Note that Figure 2 depicts a moving coil actuator. The working principle of a moving magnet actuator is similar, wherein the mover comprises a magnet and the stator comprises a coil.

[0038] Two examples of coil types that can be used as the above-mentioned coil 3 in the prior art actuator 1 are provided in Figure 3 and 4. Note that the disclosure does not limit the application for yet other types of coils.

[0039] Figure 3(a) depicts a top view of a racetrack coil 303 wherein a flat wire 333 winds around the coil core 306 in a way that the windings stack along direction SI. Figure 3(b) depicts cross-section Illb-IIIb of the racetrack coil 303.

[0040] Figure 4(a) depicts a top view of an edge-wound racetrack coil 403 wherein a flat wire 433 winds around the coil core 406 in a way that the windings stack from the coil core outwards. Figure 4(b) depicts cross-section IVb-IVb of the edge-wound racetrack coil 403.

[0041] For both coils 303 and 403 as shown in Figure 3 and 4 according to prior art, the flat wires 333 and 433 are insulated using electrical insulating layers 312 and 412. The said electrical insulating layer may for example be made of materials like glass, rubber, ceramics or polymers.

[0042] Figure 5 depicts a sectional view of a coil 503 with a temperature conditioning unit 511 according to this invention. The temperature conditioning unit comprises a potting layer 509 surrounding the coil, electrical insulating layers 510, thermal conducting cooling plates 507 having cooling fluid channels 508, and a phase-change material (PCM) 513 arranged in the core 506 of the coil 503. Electrical insulating layers 512 are arranged between the coil wires 533. When the ambient temperature of the PCM increases, a solid-state PCM absorbs heat and changes at least partially from solid to liquid state when the ambient temperature achieves the PCM’s melting point. Here the ambient temperature is the temperature of the elements surrounding the PCM. The mixture of solid and liquid state PCM remains at a substantially constant temperature. When the ambient temperature decreases below the PCM’s melting point, the liquid-state PCM releases heat and changes from liquid to solid state. Due to such physical characteristic of a PCM, it can be used for buffering excessive amount of heat such that the ambient temperature is maintained at a more constant level while a nearby heat source experiences large temperature fluctuations. PCMs that can be used for such purpose are for example organics, hydrates, molten salts, metal alloys, paraffin waxes, and fatty acids, and preferably paraffin waxes.

[0043] Figure 6 depicts a heat buffering effect that may be achieved in the actuator coil 503 by using the temperature conditioning unit 511 of the invention. Depicted in Figure 6 is a scenario wherein the actuator coil alternates between a high-current duty cycle and a low-current duty cycle, which leads to a high-temperature duty cycle T1 and a low-temperature duty cycle T2 in the coil and the elements in the temperature conditioning unit. Curve 61 is the temperature of a same coil without a PCM added for comparison purposes to visualize the effect of the use of a PCM more clearly. Curve 62 is the temperature of the coil having a PCM in the coil core. Curve 63 is the temperature of the PCM 513. Note that the melting point of the PCM in this example is tuned to be about 51 degrees Celsius for an effective heat buffering for the temperature profile in this exemplary scenario. As a result, the PCM remains at 51 degrees Celsius during the high-temperature duty cycle by absorbing the heat generated in the latent heat of melting. The coil as a result rises to less extreme temperatures than without the PCM. In the low-temperature duty cycle the PCM releases the buffered heat by solidifying again, such that the coil temperature drops to less extreme temperatures than without the PCM. A different melting point or a different PCM may be chosen in dependence of a desired temperature profile.

[0044] Figure 7 depicts a sectional view of two coils 7031 and 7032 stacked in parallel in direction S wherein the electromagnetic fields of the coils are combined for a stronger actuation force. As a difference with regard to figure 5 wherein the PCM 513 is arranged in the core 506 of the coil 503, a PCM 713 is arranged in the gap between 7031 and 7032 for buffering the heat generated in both coils. The PCM 713 is insulated by electrical insulating layers 710.

[0045] In Figure 8, generally similar to figure 7, a PCM 813 is arranged in the coil cores 8061 and 8062 in addition to the PCM 813 arranged in the gap between the stacked coils 8031 and 8032.

[0046] Figure 9 depicts a sectional view of four coils 9031-9034 stacked in parallel in direction S, wherein the electromagnetic fields of the coils are combined for a stronger actuation force. A PCM 913 is arranged in the cores 9061-9064 of the four coils 9031-9034 and in a gap between the coils 9032 and 9033. Optionally the PCM in the cores 9061 - 9064 and the PCM in the gap between the coils 9032 and 9033 are different.

[0047] Figure 10 depicts a sectional view of a stack of two coils and a temperature regulating unit, wherein a thermal conducting material 1014 and a PCM 1013 are arranged in the coil cores and in the gap between the coils. It is arranged such that the thermal conducting material 1014 penetrates in a volume of the PCM 1013, and in this exemplar configuration, the thermal conducting material 1014 penetrates the PCM 1013 as parallel sheets. Such arrangement improves thermal conductivity from the coils to the PCM and thus improves the thermal buffering effectiveness. The thermal conducting material may be a metal such as gold, silver, platinum, titanium, aluminium or copper, metal oxides such as titanium dioxide, zinc oxide, silica, alumina, manganese oxide or iron oxide, for example, carbon nanotubes including single layer and multilayer, graphene, graphene oxide, graphite, etc. Note that the way the thermal conducting material penetrates the volume of the PCM may be designed in various forms, for example in a parallel configuration as shown in figure 10, or in a series configuration, as particles, fibres or as ligaments.

[0048] Figure 11 depicts a sectional view of a stack of coils with a temperature conditioning unit 1111. The temperature conditioning unit comprises chambers 1115, wherein the chamber walls 1116 are of a thermal conducting material, and each of the chambers enclose a PCM 1113 and an air pocket 1114. When a PCM changes from solid to liquid state or vice versa, the volume of the PCM also changes slightly. When the PCM volume expands, the air pocket compresses such that less pressure is exerted to the chamber walls, thus less stress and deformation are introduced to the surrounding structures.

[0049] In Figure 12, a PCM 1213 is applied as a layer of coating to the flat wires 1233 of the coil 1203. Due to the direct contact of the PCM and the flat wires, the heat generated in the coil is buffered by the PCM in a highly effective way. The PCM is preferably electrical insulating.

[0050] In Figure 13, a PCM 1313 is applied as a layer of coating to the flat wires 1333 of the coil 1303, while another layer of coating 1310 is applied to the flat wires 1333. The coating 1310 comprises an electrical insulating material for insulating the flat wires.

[0051] Figure 14 depicts an application of PCMs having different melting points at separate locations in the temperature regulating unit 1411. PCMs having different melting points can be chosen for further averaging out the coil temperature fluctuation. PCM 1414 located closer to the coil may have a higher average temperature than PCM 1413. In this case, a PCM with higher melting point can be chosen for PCM 1414, and a PCM with a lower melting point can be chosen for PCM 1413. In this case, both PCM can change states and work as heat buffers as desired.

[0052] Figure 15 and Figure 16 depict another application of PCM heat buffering, wherein PCMs 1513 and 1514 have different melting points, and the melting points are chosen based on expectedtemperature profiles of coils 1503 and 1504. The peak coil temperatures may shift higher or lower due to a varying coil current profile designed for various operating conditions of the motion stage. In this example, PCM 1513 is chosen to have a melting point at around 51°C and PCM 1514 is chosen to have a melting point at around 61°C. When the temperature in the gap of coils 1503 and 1504 swings above 51 °C and below 61 °C, PCM 1513 absorbs the heat and at least partially changes from solid to liquid state, while PCM 1514 remains at solid state. When the temperature in the gap of coils 1503 and 1504 swings above 61 °C, both 1513 and 1514 absorb the heat and at least partially change from solid to liquid state. In Figure 16, curve 1620 depicts the temperature of the coils without any PCM. Curves 1603, 1613 and 1614 respectively depict the temperatures of the coils (1503, 1504), PCM 1513 and PCM 1514 when the above-described PCMs are applied. Note that for an actuator having more variations in its operating conditions, more than two PCMs having different melting points can be applied for improving the heat buffering effect during various temperature duty cycles.

[0053] Although specific reference may be made in this text to the use of a lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquidcrystal displays (LCDs), thin-film magnetic heads, etc.

[0054] Although specific reference may be made in this text to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatus. Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or mask (or other patterning device). This apparatus may be generally referred to as lithographic tools. Such a lithographic tool may use vacuum conditions or ambient (non- vacuum) conditions.

[0055] Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention, where the context allows, is not limited to optical lithography, and may be used in other applications, for example imprint lithography.

[0056] Where the context allows, embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine -readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine -readable medium may include read only memory (ROM); random access memory (RAM); magnetic storage media; optical storage media; flash memory devices; electrical, optical, acoustical, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and thatsuch actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. and in doing that may cause actuators or other devices to interact with the physical world.

[0057] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below. Other aspects of the invention are set-out as in the following numbered clauses.1. An actuator for positioning a motion stage, the actuator comprising: a coil; and a temperature regulating unit for transferring heat to and from the coil, wherein the temperature regulating unit comprising: a thermal conducting cooling plate provided with a cooling fluid channel; a potting layer surrounding the coil for transferring actuation force, transferring dissipated heat from the coil to the cooling plate and electrically insulating the coil; and a phase-change material arranged proximate to the coil for buffering heat.2. The actuator according to clause 1, wherein the phase-change material has a melting temperature for buffering heat generated by the coil.3. The actuator according to clause 1 or 2, wherein the phase-change material is arranged in the core of the coil.4. The actuator according to clause 1 or 2, comprising two or more coils, wherein the phasechange material is arranged in a gap between two coils of the two or more coils.5. The actuator according to clause 3 or 4, wherein a thermal conducting material penetrates a volume of the phase-change material.6. The actuator according to clause 5, wherein the thermal conducting material is electrical insulating.7. The actuator according to clause 5, wherein the thermal conducting material is electrical conducting.8. The actuator according to any of the previous clauses, comprising a chamber, wherein the chamber walls are of a thermal conductive material, and the chamber encloses the phase-change material and an air pocket.9. The actuator according to clause 1 or 2, wherein the phase-change material is applied as a layer of coating to the coil wire.10. The actuator according to clause 9, wherein the phase-change material is electrical insulating.11. The actuator according to clause 9, wherein an electrical insulating material is applied as another layer of coating to the coil wire.12. The actuator according to any of the previous clauses, comprising two or more phase-change materials having different melting temperatures.13. The actuator according to any of the previous clauses, wherein the thermal conducting cooling plate and the phase-change material are in thermal contact with the coil. 14. A motion stage comprising the actuator according to any of the previous clauses, for positioning the motion stage.15. A wafer exposure apparatus comprising the motion stage according to clause 14.16. A method for manufacturing an actuator according to any of the clauses 1-13, comprising:- applying a potting layer surrounding the coil; - placing a phase-change material proximate to the coil; and- placing a thermal conducting cooling plate provided with a cooling fluid channel.17. The method according to clause 16, wherein the phase-change material is applied as a coating layer to the coil, or arranged in the core of the coil, or in case of the actuator comprising two or more coils, placed in a gap between two coils of the two or more coils.

Claims

CLAIMS1. An actuator for positioning a motion stage, the actuator comprising: a coil; and a temperature regulating unit for transferring heat to and from the coil, wherein the temperature regulating unit comprising: a thermal conducting cooling plate provided with a cooling fluid channel; a potting layer surrounding the coil for transferring actuation force, transferring dissipated heat from the coil to the cooling plate and electrically insulating the coil; and a phase -change material arranged proximate to the coil for buffering heat.

2. The actuator according to claim 1, wherein the phase-change material has a melting temperature for buffering heat generated by the coil.

3. The actuator according to claim 1 or 2, wherein the phase-change material is arranged in the core of the coil.

4. The actuator according to claim 1 or 2, comprising two or more coils, wherein the phasechange material is arranged in a gap between two coils of the two or more coils.

5. The actuator according to claim 3 or 4, wherein a thermal conducting material penetrates a volume of the phase-change material.

6. The actuator according to any of the previous claims, comprising a chamber, wherein the chamber walls are of a thermal conductive material, and the chamber encloses the phase-change material and an air pocket.

7. The actuator according to claim 1 or 2, wherein the phase-change material is applied as a layer of coating to the coil wire.

8. The actuator according to claim 7, wherein the phase-change material is electrical insulating.

9. The actuator according to claim 7, wherein an electrical insulating material is applied as another layer of coating to the coil wire.

10. The actuator according to any of the previous claims, comprising two or more phase-change materials having different melting temperatures.

11. The actuator according to any of the previous claims, wherein the thermal conducting cooling plate and the phase-change material are in thermal contact with the coil.

12. A motion stage comprising the actuator according to any of the previous claims, for positioning the motion stage.

13. A wafer exposure apparatus comprising the motion stage according to claim 12.

14. A method for manufacturing an actuator according to any of the claims 1-11, comprising:- Applying a potting layer surrounding the coil;- Placing a phase-change material proximate to the coil; and - Placing a thermal conducting cooling plate provided with a cooling fluid channel.

15. The method according to claim 14, wherein the phase-change material is applied as a coating layer to the coil, or arranged in the core of the coil, or in case of the actuator comprising two or more coils, placed in a gap between two coils of the two or more coils.

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