Motion system

Abstract

Disclosed herein is a motion system comprising a base and a mover configured to move relative to the base. One of the base and the mover comprises magnets and the other of the base and the mover comprises coils and magnetic material such that a driving force for moving the mover relative to the base comprises a Lorentz force between the magnets and the coils and a magnetic force between the magnets and the magnetic material. The motion system is arranged such that a ratio of a magnetic flux associated with the magnets that passes through the coils to a magnetic flux associated with the magnets that passes through the magnetic material is greater than 2:3.

Description

MOTION SYSTEMCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 739,916 which was filed on 30 December 2024, and which is incorporated herein in its entirety by reference.FIELD

[0002] The present invention relates to a motion system, an actuatable stage, a lithographic apparatus and a method for making a motion system.BACKGROUND

[0003] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which 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.

[0004] The lithographic apparatus may comprise one or more motion systems or moving respective components of the lithographic apparatus. An example motion system may have a coil unit comprising iron cores that moves relative to a magnet unit. The sample motion system is called a linear motor motion system. Such linear motor motion systems suffer from cogging and / or an undesirably great attractive force between the coil unit and the magnet unit.SUMMARY

[0005] There is a need to provide a motion system with reduced cogging and / or a reduced attractive force.

[0006] According to a first aspect, there is provided motion system comprises a base, and a mover configured to move relative to the base, wherein one of the base and the mover comprises magnets and the other of the base and the mover comprises coils and magnetic material such that a driving force formoving the mover relative to the base comprises a Lorentz force between the magnets and the coils and a magnetic force between the magnets and the magnetic material, and wherein the motion system is arranged such that a ratio of a magnetic flux associated with the magnets that passes through the coils to a magnetic flux associated with the magnets that passes through the magnetic material is greater than 2:3.

[0007] According to a second aspect, there is provided a method for making a motion system, the method comprises providing one of a base and a mover with magnets, providing the other of the base and the mover with coils and magnetic material such that a driving force for moving the mover relative to the base comprises a Lorentz force between the magnets and the coils and a magnetic force between the magnets and the magnetic material, and arranging the motion system such that a ratio of a magnetic flux associated with the magnets that passes through the coils to a magnetic flux associated with the magnets that passes through the magnetic material is greater than 2:3.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Embodiments will now be described, by way of example only, with reference to the accompanying schematic drawings.

[0009] Figure 1 depicts a lithographic apparatus, according to some aspects.

[0010] Figure 2 depicts a lithographic apparatus, according to some aspects.

[0011] Figure 3 is a more detailed view of the apparatus of Figure 2, according to some aspects.

[0012] Figure 4 schematically depicts a motion system, according to some aspects.

[0013] Figure 5 schematically depicts an alternative motion system, according to some aspects.

[0014] Figure 6 is a schematic view of flux penetrating part of the motion system shown in Figure 5, according to some aspects.

[0015] Figure 7 schematically depicts an alternative motion system, according to some aspects.

[0016] Figure 8 schematically depicts flux within part of the motion system of Figure 7, according to some aspects.

[0017] Figure 9 schematically depicts a coil unit, for example of the motion system shown in Figure 4, according to some aspects.

[0018] Figure 10 schematically depicts an alternative coil unit, according to some aspects.

[0019] Figure 11 schematically depicts an alternative coil unit, according to some aspects.

[0020] Figure 12 schematically depicts an alternative motion system, for example comprising the coil unit shown in Figure 10, according to some aspects.

[0021] Figure 13 is a perspective view of a motion system such as the motion system shown in Figure 4 or Figure 12, according to some aspects.

[0022] Figure 14 is a plan view of the motion system shown in Figure 13, according to some aspects.

[0023] Figure 15 is a perspective view of part of the motion system shown in Figure 12, according to some aspects.

[0024] Figure 16 is a cross-sectional view of part of the motion system shown in Figure 15, according to some aspects.

[0025] Figure 17 is a schematic view of a step in making a motion system, according to some aspects.

[0026] Figure 18 is a perspective view of another step in making the motion system, according to some aspects.

[0027] While the aspects are susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and may herein be described in detail. The drawings may not be to scale. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the aspects to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.DETAILED DESCRIPTION

[0028] Figures 1 and 2 schematically depict lithographic apparatuses that may use an electrostatic clamp according to an embodiment. Each apparatus may comprise:

[0029] - an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation, DUV radiation or EUV radiation);

[0030] - a support structure (e.g. a mask table) MT constructed to hold (e.g. 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;

[0031] - a substrate table (e.g. a wafer table) WT constructed to hold a substrate holder, the substrate holder being arranged 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. A substrate holder as described herein can be used to hold the substrate W on the substrate table WT ; and

[0032] - a projection system (e.g. a refractive or reflective 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.

[0033] 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.

[0034] 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 projectionsystem. Any use of the terms "reticle" or "mask" herein may be considered synonymous with the more general term "patterning device."

[0035] 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.

[0036] 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.

[0037] The term "projection system" used herein, like the term "illumination system", should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems or other types of optical components, 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". The projection system, like 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, as appropriate for the exposure radiation being used, or for other factors such as the use of a vacuum. It may be desired to use a vacuum for EUV radiation since other gases may absorb too much radiation. A vacuum environment may therefore be provided to the whole beam path with the aid of a vacuum wall and vacuum pumps.

[0038] As depicted in Figure 1, the apparatus is of a transmissive type (e.g. employing a transmissive mask). Alternatively, as depicted in Figure 2, the lithographic apparatus 100 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).

[0039] The lithographic apparatus 100 may be of a type having two or more tables (or stage(s) or holder(s)) which may be referred to as dual stage, e.g., two or more substrate tables or a combination of one or more substrate tables and one or more sensor or measurement tables. In such "multiple stage" machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure. The lithographic apparatus100 may have two or more patterning device tables (or stage(s) or holder(s)) which may be used in parallel in a similar manner to substrate, sensor and measurement tables.

[0040] Referring to Figures 1 and 2, the illuminator IL receives a radiation beam from a radiation source SO in Figure 1 or a source collector apparatus SO in Figure 2. 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.

[0041] 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. In one such method, often termed laser produced plasma ("LPP") the plasma can be produced by irradiating a fuel, such as a droplet, stream or cluster of material having the desired line-emitting element, with a laser beam. The source collector apparatus SO may be part of an EUV radiation system including a laser, not shown in Figure 2, to provide the laser beam exciting the fuel. The resulting plasma emits output radiation, e.g. , EUV radiation, which is collected using a radiation collector, disposed in the source collector apparatus. The laser and the source collector apparatus may be separate entities, for example when a CO2 laser is used to provide the laser beam for fuel excitation. In such cases, the laser is not considered to form part of the lithographic apparatus and the radiation beam is passed from the laser to the source collector apparatus with the aid of a beam delivery system comprising, for example, suitable directing mirrors and / or a beam expander. In other cases the source may be an integral part of the source collector apparatus, for example when the source is a discharge produced plasma EUV generator, often termed as a DPP source.

[0042] The illuminator IL may comprise an adjuster AD configured to adjust the angular intensity distribution of the radiation beam. Generally, at least the outer and / or inner radial extent (commonly referred to as o-outer and o-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, a condenser CO, a facetted field mirror device and / or a pupil mirror device. 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).

[0043] The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor PSI (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 Ml, M2 and substrate alignment marks PI, 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.

[0044] The depicted apparatus could be used in at least one of the following modes:

[0045] 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.

[0046] 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.

[0047] 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 modeof 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.

[0048] Combinations and / or variations on the above described modes of use or entirely different modes of use may also be employed.

[0049] Figure 3 shows the lithographic apparatus 100 in more detail, including the source collector apparatus SO, the illumination system IL, 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 very hot plasma 4210 is created to emit radiation in the EUV range of the electromagnetic spectrum. The very hot plasma 4210 is created by, for example, an electrical discharge causing an at least partially ionized plasma. Partial pressures of, for example, 10 Pa of Xe, Li, Sn vapor or any other suitable gas or vapor may be required for efficient generation of the radiation. A plasma of excited tin (Sn) may be provided to produce EUV radiation.

[0050] The radiation emitted by the hot plasma 4210 is passed from a source chamber 4211 into a collector chamber 4212 via an optional gas barrier 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. The contaminant trap 4230 may include a channel structure. Contaminant trap 4230 may include a gas barrier or a combination of a gas barrier and a channel structure. The contaminant trap or contaminant barrier 4230 further indicated herein at least includes a channel structure, as known in the art.

[0051] 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 off 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.

[0052] 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 table WT.

[0053] More elements than shown may generally be present in illumination optics unit IL and projection system PS. The grating spectral filter 4240 may optionally be present, depending upon thetype of lithographic apparatus 100. There may be more mirrors present than those shown in the Figures, for example there may be 1- 6 additional reflective elements present in the projection system PS than shown in Figure 3.

[0054] Collector optic CO, as illustrated in Figure 3, 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.

[0055] Alternatively, the source collector apparatus SO may be part of an LPP radiation system. A laser is arranged to deposit laser energy into a fuel, such as xenon (Xe), tin (Sn) or lithium (Li), creating the highly ionized plasma with electron temperatures of several ten'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 and focused onto an opening in an enclosing structure.

[0056] In many lithographic apparatus a fluid, in particular a liquid for example an immersion lithographic apparatus, is provided between the final element of the projection system using a liquid supply system IH to enable imaging of smaller features and / or increase the effective NA of the apparatus. Many types of liquid supply system are possible. The embodiments are neither limited to any particular type of liquid supply system, nor to immersion lithography. The embodiments may be applied equally in any lithography. In an EUV lithography apparatus, the beam path is substantially evacuated and immersion arrangements are not used.

[0057] A controller 500 shown in Figure 1 controls the overall operations of the lithographic apparatus and in particular performs an optimization process described further below. Controller 500 can be embodied as a suitably-programmed general purpose computer comprising a central processing unit, volatile and non-volatile storage means, one or more input and output devices such as a keyboard and screen, one or more network connections and 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 implementation one computer can control multiple lithographic apparatuses. In an implementation, multiple networked computers can be used to control one lithographic apparatus. The controller 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 controller 500 can also be configured to be subordinate to a supervisory controller of a lithocell or cluster and / or an overall controller of a fab.

[0058] Figure 4 is a schematic view of a motion system 10. The motion system 10 may be for a lithographic apparatus. In an embodiment the first positioner PM comprises the motion system 10. For example, the long-stroke module of the first positioner PM may comprise the motion system 10. Additionally or alternatively, the short-stroke module of the first positioner PM may comprise the motion system 10. In an embodiment the second positioner PW comprises the motion system 10. Forexample, the long-stroke module and / or the short-stroke module of the second positioner PW may comprise the motion system 10.

[0059] The motion system 10 may be comprised in one or more other components of the lithographic apparatus. For example, the lithographic apparatus may comprise one or more blades configured to selectively cover one or more respective portions of the patterning device MA. The motion system 10 may be configured to actuate the one or more blades so as to controllably cover selected portions of the patterning device MA.

[0060] In an embodiment the motion system 10 comprises a base and a mover. The mover is configured to move relative to the base. As shown in Figure 4, in an embodiment the motion system 10 comprises a magnet unit 11 and a coil unit 14. In an embodiment, one of the base and the mover of the motion system 10 comprises magnets 12. The other of the base and the mover of the motion system 10 comprises coils 13 and magnetic material 14. For example, in an embodiment the base of the motion system 10 comprises magnets 12 and the mover of the motion system 10 comprises coils 13 and magnetic material 14. In an alternative embodiment, the base of the motion system 10 comprises coils 13 and magnetic material 14, while the mover of the motion system 10 comprises magnets 12. The component (i.e. one of the base and the mover) that comprises the magnets may be referred to as the magnet unit. The component (i.e. the other of the base and the mover) that comprises coils 13 and magnetic material 14 may be referred to as the coil unit.

[0061] In this document, the motion system 10 is described primarily in the context of the base comprising the magnet unit 11 and the mover comprising the coil unit 19. However, this is not an essential feature of the embodiment. Any described embodiment may alternatively have the base comprising the coil unit 19 and the mover comprising the magnet unit 11.

[0062] In an embodiment the motion system 10 is configured such that a driving force for moving the mover relative to the base comprises Lorentz force between the magnets 12 and the coils 13. In an embodiment the motion system 10 is configured such that the driving force for moving the mover relative to the base further comprises a magnetic force between the magnets 12 and the magnetic material 14. The Lorentz force is the force of a linear motor caused when an electric current is carried by the coils 13. The Lorentz force acts between the magnets 12 and the coils 13. In the arrangement shown in Figure 4, the Lorentz force may generally act to move the coil unit 19 in the Y direction relative to the magnet unit 11. The Lorentz force would be present even if the magnetic material 14 were replaced with a non-magnetic material. The Lorentz force does not depend on the magnetic material 14.

[0063] The magnetic force between the magnets 12 and the magnetic material 14 depends on the magnetic material 14 being magnetic. As shown in Figure 4, in an embodiment the magnetic material 14 is provided as a core of a respective coil 13. By providing a magnetic core to the coil 13, the magnetic field is altered. In particular, the magnetic flux density may be increased at the core of the coil 13. In the orientation shown in Figure 4, the magnetic force between the magnets 12 and the magnetic material14 may be bi-directional. For example, the magnetic force between the magnets 12 and the magnetic material 14 may act in the Y direction and the Z direction. The coil unit 19 may have an inherent negative stiffness which is a function of the offsets OS1, OS2 between the magnets 12 and the magnetic material 14.

[0064] In an embodiment the motion system 10 is arranged such that a ratio of a magnetic flux associated with the magnets 12 that passes through the coils 13 to a magnetic flux associated with the magnets 12 that passes through the magnetic material 14 is greater than 2:3. By increasing the magnetic flux through the coils 13 relative to the overall magnetic flux that passes through the coils 13 and the magnetic material 14, the Lorentz force may be increased relative to the total driving force. In general, the Lorentz force may increase when the magnetic flux that passes through the coils 13 increases. The magnetic force of the driving force may increase when the magnetic flux that passes through the magnetic material 14 increases. The force may be roughly correlated with the magnetic flux.

[0065] An embodiment is expected to reduce cogging. By reducing the portion of the driving force made of the magnetic force between the magnetic material 14 and the magnets 12, the overall effect of cogging on the motion system 10 may be reduced. The magnetic force acts to move the mover in the drive direction (e.g. the Y direction in the arrangement shown in Figure 4). The strength of the magnetic force that is in the Y direction varies as the mover moves relative to the magnet track 15 comprising the magnets 12 in the magnet unit 11. As a result of these variations in the force, cogging may be observed. By reducing the relative strength of the magnetic force compared to the overall driving force, the effective cogging may be reduced.

[0066] An embodiment is expected to reduce undesirable attractive force between the coil unit 19 and the magnet unit 11. In use of the motion system 10, the magnetic force between the magnetic material 14 and the magnets 12 as a component in the Z direction, i.e. the normal direction. By reducing the relative strength of the magnetic force, the undesirable attractive force may be reduced.

[0067] By providing the magnetic material 14 in the core of the coils 13, the strength of the overall driving force of the mover relative to the base may be increased. An embodiment is expected to increase the driving force without unduly increasing cogging or the attractive force.

[0068] In an embodiment the relative permeability of the material in the cores of the coils 13 is selected such that the ratio of the magnetic flux associated with the magnets 12 that passes through the coils 13 to a magnetic flux associated with the magnets 12 that passes through the magnetic material 14 is greater than 2:3. In an embodiment the geometry of the coils 13 is selected such that the ratio of the magnetic flux associated with the magnets 12 that passes through the coils 13 to the magnetic flux associated with the magnets 12 that passes through the magnetic material 14 is greater than 2:3. By tuning the relative permeability in the coil cores, and optimising geometry of the coils, cogging may be reduced and attractive forces may be reduced. By reducing cogging and / or attractive forces, the motion system 10 may be expected to be compatible for use in a greater number and variety of different components of the lithographic apparatus.

[0069] In an embodiment the motion system 10 is arranged such that the ratio of the magnetic flux associated with the magnets 12 that passes through the coils 13 to the magnetic flux associated with the magnets 12 that passes through the magnetic material 14 is at least 1:1, optionally at least 3:2, optionally at least 2:1, optionally at least 3:1 and optionally at least 4:1. In an embodiment the motion system 10 is arranged such that the magnetic flux that passes through the coils is at least 40%, optionally at least 50%, optionally at least 60%, optionally at least 70% and optionally at least 80% of the total magnetic flux that passes through the magnetic material 14 and the coils 13. In an embodiment the motion system 10 is arranged such that the Lorentz force between the magnets 12 and the coils 13 contributes at least 40%, optionally at least 50%, optionally at least 60%, optionally at least 70% and optionally at least 80% of the total driving force for moving the mover relative to the base of the motion system 10.

[0070] Figure 5 schematically depicts part of an alternative motion system 10. In the arrangement shown in Figure 5, the magnetic material 14 extends further in the Z-direction compared to the arrangement shown in Figure 4. A greater amount of magnetic material 14 may be provided within the cores of the coils 13.

[0071] Figure 6 schematically depicts a close up view of the part shown in Figure 5 surrounded by the dashed lines. Figure 6 schematically shows the magnetic flux associated with the magnets 12 that passes through the coil 13 and the magnetic material 14 within the core of the coil 13. In the arrangement shown in Figure 6, a majority of the magnetic flux passes through the magnetic material 14 compared to through the coil 13.

[0072] Figure 7 schematically depicts part of an alternative motion system 10. In the motion system 10 shown in Figure 7, the cores of the coils 13 comprise a smaller amount of magnetic material 14. The amount of magnetic material 14 is less than in the arrangement shown in Figure 5. The magnetic in each core may be in the arrangement shown in Figure 4, for example.

[0073] Figure 8 schematically depicts a close-up view of the part of Figure 7 surrounded by a dashed box, which comprises the coil core region 17. Figure 8 schematically depicts the magnetic flux passing through the magnetic material 14 and the coil 13. As can be seen from a comparison between Figure 8 and Figure 6, the arrangement shown in Figure 8 has a greater amount of magnetic flux passing through the coil 13 compared to what is shown in Figure 6. By providing a smaller amount of magnetic material 14 in the cores of the coils 13, a greater amount of magnetic flux passes through the coil 13 and a smaller amount of magnetic flux passes through the magnetic material 14.

[0074] In general, the magnetic flux is associated with the respective forces. In general, the Lorentz force for the arrangement shown in Figure 8 may be expected to be greater than for the arrangement shown in Figure 6. This is because the magnetic flux through the coil 13 is greater in Figure 8 compared to in Figure 6. In general, the magnetic force between the magnetic material 14 and the magnets 12 may be expected to be less in the Figure 8 arrangement compared to in the Figure 6 arrangement. This is because the amount of magnetic flux passing through the magnetic material 14 is generally less in the Figure 8 arrangement compared to in the Figure 6 arrangement.

[0075] The arrangement shown in Figure 8 may be expected to experience lower cogging and a lower attractive force between the coil unit 19 and the magnet unit 11.

[0076] As shown in Figure 4, in an embodiment the magnets 12 are arranged in two magnet tracks 15. The magnet tracks 15 are comprised in the magnet unit 11. As shown in Figure 4, in an embodiment the coils 13 and the magnetic material 14 are provided between the two magnet tracks 15.

[0077] By providing two magnet tracks 15, the driving force between the mover and the base may be increased. However, it is not essential for two magnet tracks 15 to be provided. In an alternative arrangement, the magnet unit 11 may comprise a single magnet track 15.

[0078] As shown in Figure 4, in an embodiment the magnetic material 14 is located within the coils 13. The magnetic material 14 forms a core of the respective coils 13. As shown in Figure 4, in an embodiment substantially each of the coils 13 comprises magnetic material 14 within it. In an alternative arrangement, a subset (i.e. some but not all) of the coils 13 may be provided with magnetic material 14 within the coil 13.

[0079] As shown in Figure 4, in an embodiment substantially all of the magnetic material 14 associated with a respective coil 13 is located within the coil core region 17 of the coil 13. The coil core region 17 (e.g. shown in Figure 7) is defined by the coil 13. However, it is not essential for all of the magnetic material 14 to be provided exclusively within the coil core region 17. For example, in an embodiment part of the magnetic material 14 associated with a coil 13 may be located in the +Z direction and / or the -Z direction relative to the coil core region 17. Coil core region 17 may be referred to as a volume defined within the coil 13.

[0080] As shown in Figure 4, in an embodiment the unit 11 comprises a backiron 16. The backiron 16 may be configured to mechanically support the magnets 12 of the magnet track 13. The backiron 16 may be configured to secure the locations of the magnets 12 of the magnet track 15 relative to each other. In an embodiment the backiron 16 is formed of a magnetic material. This may help to increase the magnetic flux associated with the magnets 12. In an alternative arrangement, the backiron 16 may comprise a non-magnetic material. As shown in Figure 4, in an embodiment the magnets 12 of the magnet tracks 15 are located between the backiron 16 and the coil unit 19. However, it is not essential for a backiron to be provided.

[0081] As shown in Figure 4, in an embodiment the magnet tracks 15 are substantially linearly arranged. In an alternative arrangement, the magnet tracks 15 may be curved in the Y-Z plane.

[0082] As shown in Figure 4, in an embodiment the magnets 12 comprise Halbach magnets. The orientation of the magnets 12 are indicated in Figure 4 by arrows within the magnets 12. As shown in Figure 4, in an embodiment the widths (i.e. dimension in the Y-direction) of the magnets 12 may vary along the magnet track 15. In an alternative arrangement, the magnets 12 may have substantially uniform widths along the magnet track 15. As shown in Figure 4, magnets 12 that have their plurality aligned substantially with the Z-direction may be wider than other magnets 12. However, it is not essential for the widths to be varied in this way. As shown in Figure 4, in an embodiment the twomagnet tracks 15 comprise substantially similar magnets 12 opposing each other in the Z-direction. The pluralities of magnets 12 of the two tracks 15 at the same location along the Y axis may be substantially the same. It may help to increase the overall driving force.

[0083] As shown in Figure 4, the backiron 16 may have a backiron height BH the term “height” is generally used to refer to the dimension in the Z direction shown in Figure 4. The Z direction is the normal direction, namely normal to the plane of the magnet unit 11 and the coil unit 19. The term “width” is used to refer to the dimension in the Y direction. The term “depth” (or alternatively “length”) is used to refer to the dimension in the X direction (i.e. into and out from the plane of the paper in the orientation shown in Figure 4).

[0084] In an embodiment the backiron height BH is at least 1mm, optionally at least 2 mm, optionally at least 5 mm and optionally at least 10 mm. In an alternative embodiment the backiron 16 is omitted. In an embodiment the magnet height MH is at least 5 mm, optionally at least 10 mm and optionally at least 20 mm. In an embodiment the magnet height is at most 100 mm, optionally at most 50 mm and optionally at most 20 mm.

[0085] In an embodiment the coil width CW is selected so as to achieve a desired Lorentz force between the coils 13 and the magnets 12. In an embodiment the coil width CW is at least 5 mm, optionally at least 10 mm and optionally at least 20 mm. in an embodiment the coil width is at most 100 mm, optionally at most 50 mm, optionally at most 20 mm and optionally at most 10 mm.

[0086] The magnetic material 14 may have a width referred to as a tooth width TW. The magnetic material 14 may have a height referred to as a tooth height TH. The tooth width TW and the tooth height TH may be selected so as to achieve a desired proportion of the driving force that is due to the magnetic force between the magnetic material 14 and the magnets 12. In general, a greater tooth width TW may increase the magnetic force. In general, a greater tooth height TH may increase the magnetic force. In an embodiment the tooth width TW is at least 0.5 mm, optionally at least 1 mm, optionally at least 2 mm, optionally at least 5 mm and optionally at least 10 mm. In an embodiment the tooth width TW is at most 100 mm, optionally at most 50 mm, optionally at most 20 mm, optionally at most 10 mm, optionally at most 5 mm and optionally at most 2 mm. In an embodiment the tooth height TH is 0.5 mm, optionally at least 1 mm, optionally at least 2 mm, optionally at least 5 mm, optionally at least 10 mm, optionally at least 20 mm, optionally at least 50 mm and optionally at least 100 mm. In an embodiment the tooth height TH is at most 200 mm, optionally at most 100 mm, optionally at most 50 mm, optionally at most 20 mm, optionally at most 10 mm, optionally at most 5 mm, and optionally at most 2 mm.

[0087] In an embodiment the coils 13 have a coil height CH of at least 5mm, optionally at least 10 mm and optionally at least 20 mm, optionally at least 50 mm and optionally at least 100 mm. In an embodiment the coil height CH is at most 200 mm, optionally at most 100 mm, optionally at most 50 mm, optionally at most 20 mm and optionally at most 10 mm.

[0088] As shown in Figure 4, during use of the motion system 10 the coil unit 19 may be offset from the magnet tracks 15 of the magnet unit 11 by a first offset OS1 and a second offset OS2. Each of the first offset OS1 and the second offset OS2 may be of the order of 0.2 mm, optionally at least 0.5 mm, optionally at least 1 mm, optionally at least 2 mm and optionally at least 5mm. In an embodiment each of the first offset OS1 and / or the second offset OS2 may be at most 20 mm, optionally at most 10 mm, optionally at most 5 mm, optionally at most 2 mm and optionally at most 1 mm.

[0089] Figure 9 schematically depicts an alternative coil unit 19. The coil unit 19 may be part of a motion system 10, for example of the type shown in Figure 4. Figure 9 schematically depicts three coils 13a, 13b, 13c stacked relative to each other. In an embodiment the coil unit 19 comprises a plurality of each of the three coils 13a, 13b, 13c shown in Figure 9. For example, the coil unit 19 may comprise a layer of coils 13a a layer of second coils 13b and a layer of the coils 13c. Although three coils 13a, 13b, 13c are shown stacked in Figure 9, the number of stacked coils may be, for example, two, four or more than four. In an alternative embodiment, only a single coil 13 is provided at each location in the X-Y plane.

[0090] In an embodiment, the volume of the magnetic material 14 is selected so as to control the relative amounts of magnet flux that pass through the magnetic material 14 compared to through the coil. This helps to control the magnitude of the Eorentz force relative to the magnetic force in the overall driving force between the mover and the base of the motion system 10. For example, the volume of the magnetic material 14 may be controlled by selecting the tooth width TW and / or the tooth height TH. Additionally or alternatively, the tooth depth may be selected.

[0091] As shown in Figure 9, for at least one of the coils 13 the associated magnetic material 14 is less wide than the coil 13 on one side of the magnetic material 14. The width of the coil 13 on one side of the magnetic material 14 is referred to as the coil width CW in Figure 4. Here, one side of the magnetic material 14 refers to one side in the Y direction of the magnetic material 14. The coil 13 is provided on both sides (in the Y direction) of the magnetic material 14. The tooth width TW may be less than the coil width CW. By providing a smaller tooth width TW, the strength of the magnetic force may be reduced. However, it is not essential for the tooth width TW to be less than the coil width CW. In an alternative arrangement, the tooth width is substantially equal to or greater than the coil width CW.

[0092] As shown in Figure 9, in an embodiment the magnetic material 14 is distanced from ends of the coils 13 in a height direction of the coils 13. This is shown in Figure 9, where the magnetic material 14 does not extend as far in the Z direction compared to the stack of three coils 13a, 13b, 13c. In an embodiment the magnetic material 14 is distanced from ends of the individual coil 13 in which the magnetic material 14 is provided. The tooth height TH may be less than the coil height CH. Coil height CH may refer to the coil height of a single coil 13a, 13b, 13c or to the height of a stack of coils as shown in Figure 9.

[0093] By providing that the magnetic material 14 is distanced from ends of the coils 13, the magnetic material 14 has a smaller height compared to the coils 13. By reducing the height of the magneticmaterial 14, the overall volume of the magnetic material 14 may be reduced. By reducing the volume of magnetic mater 14, the magnetic force may be reduced.

[0094] However, it is not essential for the magnetic material 14 to be distanced from ends of the coils 13 in the height direction of the coils 13. In an alternative arrangement, the magnetic material 14 may end at substantially the same point in the Z direction as the coils 13 (e.g. as shown in Figure 10). Alternatively, the magnetic material 14 may extend beyond the coils 13 in the Z direction (e.g. as shown in Figure 11, for example).

[0095] As shown in Figure 9, in an embodiment the coil unit 19 comprises a core housing component 21. The core housing component 21 is configured to secure the magnetic material 14 in position relative to the coils 13a, 13b, 13c. The core housing component 21 may be configured to mechanically support the magnetic material 14 relative to the coil 13 in which the magnetic material 14 is provided.

[0096] As shown in Figure 9, in an embodiment the motion system 10 comprises a plurality of layers of coils 13a, 13b, 13c stacked in a height direction of the coils 13. However, it is not essential. In an alternative arrangement, the coil unit 19 comprises a single layer of coils 13.

[0097] As shown in Figure 9, in an embodiment the motion system 10 comprises at least one plate 24. The plate separates adjacently stacked layers of coils 13a, 13b, 13c. For example, Figure 9 shows four plates 24. The middle two plates 24 separate adjacently stacked layers of coils 13a, 13b, 13c.

[0098] As shown in Figure 9, in an embodiment the motion system 10 comprises one or more further plates 24 provided at the top and / or bottom of the coil unit 19. However, it is not essential for the top and / or bottom plates 24 to be provided. In an alternative arrangement, the top and / or bottom plates 24 are omitted. It is not essential for any plate to be provided. For example, when there is only one layer of coils 13, then no plates may be provided.

[0099] As shown in Figure 9, in an embodiment the magnetic material 14 extends through at least one of the plates 24. In the arrangement shown in Figure 9, the magnetic material 14 extends through the two middle plates 24. In an embodiment the plates 24 are provided with apertures for accommodating the magnetic material 14. The apertures may be provided at the cores of the coils 13. However, it is not essential for the magnetic material 14 to extend through the plates 24. For example, Figure 10 shows an alternative embodiment in which the magnetic material 14 does not extend through the plates 24. The plates 24 are not required to have apertures for accommodating the magnetic material 14. The plates 24 may be provided to be substantially continuous across the X-Y plane of the coil unit 19.

[0100] In an embodiment the plate 24 is configured to thermally condition the coils 13. For example, as shown in Figure 9, the plates 24 may comprise one or more thermal conditioning channels 25. The thermal conditioning channels 25 may be referred to as cooling channels. The thermal conditioning channels 25 may extend in the X-Y plane. The thermal conditioning channels 25 within a single plate 24 may be connected to other thermal conditioning channels 25 within that plate 24.

[0101] In an embodiment a thermal conditioning fluid is provided for flowing through the thermal conditioning channels 25. The thermal conditioning fluid may be a liquid such as water (e.g. ultra-purewater). Alternatively, the thermal conditioning fluid may be a gas such as air. In an embodiment the temperature of the thermal conditioning fluid is controlled so as to thermally condition the coils 13. For example, the thermal conditioning channels 25 may be configured to cool the coils 13 so as to prevent the coils 13 from overheating or reducing in performance.

[0102] However, it is not essential for the plates 24 to be provided with thermal conditioning channels 25.

[0103] As shown in Figure 9, in an embodiment the motion system 10 comprises electrical insulation 23. The electrical insulation 23 may be provided between the coils 13 and the magnetic material 14. The electrical insulation 23 may be configured to electrically isolate the coils 13 from the magnetic material 14. Additionally or alternatively, electrical insulation 23 is configured to mechanically protect the coils 13 from the magnetic material 14. Additionally or alternatively, electrical insulation 23 is configured to secure a position of the magnetic material 14 within the coils 13. As shown in Figure 9, in an embodiment electrical insulation 23 is provided at a radially inner surface of the coils 13. The electrical insulation 23 may substantially cover the radially inward surface of the coils 13 in parallel to the Z direction. In an embodiment the electrical insulation 23 is referred to as potting. The electrical insulation may comprise a material that is electrically non-conductive. The electrical insulation 23 may comprise a polymer. The electrical insulation may comprise an epoxy.

[0104] In an embodiment the plate 24 comprises a thermally conductive material. For example, the plate 24 may comprise a metal such as stainless steel.

[0105] As shown in Figure 9, in an embodiment the coil unit 19 comprises further electrical insulation 22. The electrical insulation 22 may be provided at one or more surfaces of the plates 24. For example, the further electrical insulation 22 may be configured to electrically insulate the plates 24 from the coils 13. The further electrical insulation 22 may be configured to electrically insulate the plates 24 from the magnetic material 14. In an embodiment the further electrical insulation 22 comprises a polymer. The further electrical insulation 22 may comprise a a polyimide such as Kapton.

[0106] Figure 10 schematically depicts an alternative coil unit 19. Features that are the same as described with reference to Figure 4 or Figure 9, for example, are not described again for brevity.

[0107] As shown in Figure 10, in an embodiment the core is split. In an embodiment for at least one of the coils the associated magnetic material 14 comprises a plurality of magnetic members 14a, 14b, 14c. The magnetic material 14 comprises the magnetic members 14a, 14b, 14c. As shown in Figure 10, the stack of coils 13a, 13b, 13c has three magnetic members 14a, 14b, 14c provided within it. In an embodiment each coil of the stack of coils is provided with a respective magnetic member. In an alternative embodiment, one or more (but not all) of the coils within a stack of coils is provided with a magnetic member. As shown in Figure 10, in an embodiment the core housing component 21 of the arrangement shown in Figure 9 may be omitted. The magnetic members 14a, 14b, 14c may substantially fill the volume defined by the electrical insulation 23 and the further electrical insulation 22.Alternatively, within each volume, a core housing component 21 may be provided so as to secure the location of the magnetic member relative to the respective coil 13.

[0108] As shown in Figure 10, in an embodiment at least one of the plates 24 separates magnetic members 14a, 14b, 14c of the magnetic material 14. In an embodiment the further electrical insulation 22 is configured to electrically insulate the magnetic members from the plates 24.

[0109] Figure 11 schematically depicts an alternative coil unit 19. For brevity, features that are the same as described with reference to Figure 4, Figure 9 or Figure 10, for example, are not repeated.

[0110] As shown in Figure 11, in an embodiment the magnetic material 14 substantially fills the volume within the core of the coil 13. The magnetic material 14 may extend between different stacked coils 13a, 13b, 13c. The magnetic material 14 may have a height that is greater than each of the individual coils and optionally greater than the combined height of all of the coils within a stack. As shown in Figure 11, in an embodiment the core housing component 21 shown in Figure 9 may be omitted.

[0111] As shown in Figure 11 , in an embodiment the electrical insulation 23 shown in Figure 9 and Figure 10 may be omitted. As shown in Figure 11, in an embodiment the magnetic material 14 may be substantially adjacent and optionally in physical contact with, the coils 13.

[0112] In an embodiment for at least one of the coils 13, the associated magnetic material 14 is substantially electrically insulating. For example, ferromagnetic material may be mixed with an electrically insulating material so as to form the magnetic material 14. For example, epoxy may be mixed with an iron powder formed by matrix. The magnetic material may be diluted by the electrically non-conductive material. The magnetic material 14 may have a greater volume compared to that shown in Figure 9 or Figure 10, for example.

[0113] Although the volume of the magnetic material 14 shown in Figure 11 is greater, the magnetic permeability of the magnetic material 14 is selected such that the magnetic force is sufficiently low relative to the overall driving force of the mover relative to the base of the motion system 10.

[0114] In an embodiment for at least one of the coils 13, the associated magnetic material 14 comprises a substance selected from the group consisting of a cobalt-iron material, a silicon-steel material, silicon and a ferromagnetic material such as iron, and epoxy and a ferromagnetic material such as iron. For example, the magnetic material 14 may comprise a cobalt-iron laminate block. Alternatively, the magnetic material 14 may comprise a silicon-steel laminate block. Alternatively, the magnetic material 14 may comprise a stainless steel alloy 410s with slips or laminated. Alternatively, the magnetic material 14 may comprise a pressed silicon and iron powder block. Alternatively, in an embodiment the magnetic material 14 comprises epoxy and iron powder. For example, high purity spherical iron powder may be combined with epoxy, degassed and poured. An embodiment is expected to reduce the cost of manufacturing the magnetic material 14 provided as the cores of the coils 13.

[0115] Figure 12 schematically depicts a motion system 10 comprising a split core, for example of the type shown in Figure 10. An embodiment is expected to make it easier to make the coil unit 19 of the motion system 10.

[0116] In an embodiment, for at least one of the coils, a centroid of the coil 13 is substantially coincident of a centroid of magnetic material 14 within the coil 13. An embodiment is expected to increase the accuracy of control of movement of the mover relative to the base.

[0117] Figure 13 is a schematic perspective view of a motion system 10. Figure 10 schematically shows the coil unit 19 of the motion system 10 sandwiched between the two parts (comprising the two magnetic tracks 15) of the unit 11. Figure 13 schematically shows six coils, any number of coils 13 may be provided in the coil unit 19.

[0118] Figure 14 schematically depicts a plan view of the motion system 10 shown in Figure 13. Figure 14 mainly shows the coils 13, with the magnet unit 11 shown in outline.

[0119] As shown in Figure 14, in an embodiment the magnets 12 extend beyond an end of at least one of the volumes defined within the coils in a length (or depth) direction of the coils 13. As can be seen in Figure 14, the magnet unit 11 extends further in the X direction than the volumes that the coils 13 are wound around. In other words, the magnets 12 overhang the end turns 31 of the coils 13. By providing that the magnets 12 overhang the end turns 31 of the coils 13, additional driving force may be generated. An embodiment is expected to increase the driving force of the mover relative to the base, without unduly increasing the required power.

[0120] By providing an additional force from the end turns 31, the motion system 10 may be made more compactly compared to standard designs. As shown in Figure 14, in an embodiment the magnet unit 11 extends beyond the volumes around which the coils 13 are wound in both the +X direction and the -X direction.

[0121] In an embodiment the magnets 12 extend further beyond one end of the at least one of the volumes in the length direction than beyond the other end in the length direction. In the arrangement shown in Figure 14, the magnets 14 extend beyond the volumes by substantially the same amount both in the +X direction and in the -X direction. In an alternative embodiment, the magnet unit 11 is positioned asymmetrically with respect to the coils 13 in the X direction. The overhang of the end turns 31 may be greater in one of the +X direction and the -X direction compared to in the other of the +X direction and the -X direction. By providing an asymmetric overhang over one end turn 31 , a desirable driving force in the X direction may be provided. The driving force may be controlled in both the X direction and the Y direction with a single motion system 10.

[0122] In an embodiment an actuatable stage for the lithographic apparatus comprises the motion system 10. The actuatable stage may be configured to support at least one of the substrate W and a patterning device MA. For example, the actuatable stage may form the first positioner PM. Alternatively, the actuatable stage may form the second positioner PW.

[0123] Figure 15 schematically depicts an expanded view of part of the coil unit 19 of the type shown in Figure 10 or Figure 12, for example. The magnetic material 14 comprises a plurality of magnetic members 14a, 14b, 14c. Figure 16 is an extended view of the boxed part of Figure 15.

[0124] There is provided a method for making the motion system 10. In an embodiment the method comprises providing one of a pace and a mover with magnets 12. In an embodiment the method comprises providing the other of the pace and the mover with coils 13 and magnetic material 14 such that a driving force for moving the mover relative to the base comprises a Lorentz force between the magnets 12 and the coils 13 and a magnetic force between the magnets 12 and the magnetic material 14. In an embodiment the method comprises arranging the motion system 10 such that the ratio of the magnetic flux associated with the magnets 12 that passes through the coils 13 to a magnetic flux associated with the magnets 12 that passes through the magnetic material 14 is greater than 2:3.

[0125] In an embodiment the method for making the motion system 10 comprises electrically insulating the magnetic material 14 from the coils 13. By electrically insulating the magnetic material 14 from the coils 13, the possibility of undesirable electrical breakdown may be reduced. An embodiment is expected to reduce the possibility of damage to the motion system 10 during use of the motion system 10.

[0126] In an embodiment the magnetic material 14 is electrically insulated from the coils 13 by flowing an electrical insulation 23 between the magnetic material and the coils 13. In an embodiment the coils 13a, 13b, 13c may be stacked together with the plates 24 to form the structure shown in Figure 15. Subsequently, electrical insulation may be flowed between the magnetic material 14 and the coils 13 so as to electrically insulate the magnetic material 14 from the coils 13.

[0127] In order to allow the electrical insulation to flow into the right places, the magnetic material 14, the plates 24 and the coils 13 may be located relative to each other so as to leave volume for the electrical insulation.

[0128] As shown in Figure 16, in an embodiment the coil unit 19 comprises one or more retention blocks 33. The retention blocks 33 are configured to enforce the core-plate gap to allow for the electrical insulation 23 to flow into the gap. In an embodiment the retention blocks 33 are configured to hold the magnetic material 14 relative to the coils 13. For example, in an embodiment a retention block 33 is U-shaped and extends around an end (in the X direction) of the magnetic material 14. In an embodiment each piece of magnetic material 14 is provided with two retention blocks at the +X direction end and the -X direction end of the piece of magnetic material 14.

[0129] As shown in Figure 16, in an embodiment the coil unit 19 comprises at least one spacer sticker 34. The spacer sticker 34 is configured to enforce the core-coil insulation distance. By providing the spacer sticker 34, the gap between the core magnetic material 14 and the coil 13 is retained during manufacture of the structure (before the electrical insulation is flowed in). As shown in Figure 16, in an embodiment each spacer sticker 34 forms a U-shape extending around the edges of the magneticmaterial 14. For example, one or more pairs of spacers 34 may be provided at the +Y edge and the -Y direction edge of the magnetic material 14.

[0130] As shown in Figure 16, in an embodiment the coil unit 19 comprises at least one coil-plate spacer sticker 35. The coil-plate spacer sticker is configured to retain a gap between the coil 13 and the plate 24 that can be filled with electrical insulation.

[0131] An embodiment is expected to make it easier to manufacture the coil unit 19 of the motion system 10. In an embodiment the electrical insulation 23 is flowed substantially in a vacuum. In an embodiment the method of making the motion system 10 comprises applying spacers (e.g. the retention block 33, the spacer sticker 34 and / or the coil-plate spacer sticker 35) for spacing the magnetic material 14 from the coils 13 before the electrical insulation is flowed.

[0132] As shown in Figure 15 and Figure 16, in an embodiment the method comprises stacking a plurality of layers of coils 13a, 13b, 13c in a height direction of the coils. In an embodiment the layers of coils 13a, 13b, 13c are stacked before the electrical insulation 23 is flowed.

[0133] In an alternative embodiment, the electrical insulation is flowed before the layers of coils are stacked.

[0134] For example, Figure 17 schematically depicts a step in making a motion system 10. As shown in Figure 17, in an embodiment a plurality of coils 13 are provided on a carrier 36. The electrical insulation 23 is provided around the coils 13. This forms a single unit comprising the carrier 36, the coils 13 and the electrical insulation 23. In an embodiment the unit further comprises the magnetic material 14 in the cores of the coils 13.

[0135] Figure 18 schematically depicts a subsequent step in the method of making the motion system 10. As shown in Figure 18, in an embodiment a plurality of the units are stacked relative to each other. In the arrangement shown in Figure 18, four units are stacked in the Z direction. However, it is not essential to stack multiple units. In an alternative arrangement, the motion system 10 comprises a single unit. Alternatively, two, three or more than four units may be stacked relative to each other. In an embodiment electrical insulation is provided between the units when they are stacked together.

[0136] In an embodiment one or both of a top plate 24 and a bottom plate 24 is provided to the stack of units shown in Figure 18. In an embodiment further electrical insulation is provided to electrically insulate the top plate and / or bottom plate from the other units sandwiched between them.

[0137] Embodiments include the module being used in any lithographic apparatus. The lithographic apparatus may include any apparatus used in substrate manufacture, testing and inspection, such as an electron-beam inspection apparatus.

[0138] Example embodiments of the present technology are set out in the following numbered clauses: 1. A motion system comprising:a base; anda mover configured to move relative to the base;wherein one of the base and the mover comprises magnets and the other of the base and the mover comprises coils and magnetic material such that a driving force for moving the mover relative to the base comprises a Lorentz force between the magnets and the coils and a magnetic force between the magnets and the magnetic material; andwherein the motion system is arranged such that a ratio of a magnetic flux associated with the magnets that passes through the coils to a magnetic flux associated with the magnets that passes through the magnetic material is greater than 2:3.2. The motion system of clause 1 , wherein the magnets are arranged in two magnet tracks, between which the coils and magnetic material are provided.3. The motion system of clause 1 or 2, wherein the magnetic material is located within the coils.4. The motion system of any preceding clause, wherein volumes are defined within the coils, and the magnets extend beyond an end of at least one of the volumes in a length direction of the coils. 5. The motion system of clause 4, wherein the magnets extend further beyond one end of at least one of the volumes in the length direction than beyond the other end in the length direction.6. The motion system of any preceding clause, wherein for at least one of the coils the associated magnetic material is less wide than the coil on one side of the magnetic material.7. The motion system of any preceding clause, wherein the magnetic material is distanced from ends of the coils in a height direction of the coils.8. The motion system of any preceding clause, wherein for at least one of the coils the associated magnetic material comprises a plurality of magnetic members.9. The motion system of any preceding clause, wherein for at least one of the coils the associated magnetic material is substantially electrically insulating.10. The motion system of any preceding clause, comprising a plurality of layers of coils stacked in a height direction of the coils.11. The motion system of clause 10, comprising:at least one plate separating adjacently stacked layers of coils.12. The motion system of clause 11, wherein the magnetic material extends through the plate. 13. The motion system of clause 11, wherein the plate separates magnetic members of the magnetic material.14. The motion system of any of clauses 11-13, wherein the plate is configured to thermally condition the coils.15. The motion system of any preceding clause, comprising:electrical insulation between the coils and the magnetic material.16. The motion system of any preceding clause, wherein for at least one of the coils the associated magnetic material comprises a substance selected from the group consisting of (i) a cobalt-iron material, (ii) a silicon-steel material, (iii) a stainless steel alloy, (iv) silicon and iron and (v) epoxy and a ferromagnetic particle.17. The motion system of any preceding clause, wherein for at least one of the coils, a centroid of the coil is substantially coincident with a centroid of magnetic material within the coil.18. The motion system of any preceding clause, wherein the motion system is arranged such that the ratio of the magnetic flux associated with the magnets that passes through the coils to the magnetic flux associated with the magnets that passes through the magnetic material is at least 1:1, optionally at least 3:2, optionally at least 2:1, optionally at least 3:1 and optionally at least 4:1.19. An actuatable stage for a lithographic apparatus, wherein the actuatable stage is configured to support at least one of a substrate and a patterning device and comprises:the motion system of any preceding clause.20. A lithographic apparatus for exposing a substrate with patterned radiation, wherein the lithographic apparatus comprises:the actuatable stage of clause 19.21. A method for making a motion system, the method comprising:providing one of a base and a mover with magnets;providing the other of the base and the mover with coils and magnetic material such that a driving force for moving the mover relative to the base comprises a Lorentz force between the magnets and the coils and a magnetic force between the magnets and the magnetic material; andarranging the motion system such that a ratio of a magnetic flux associated with the magnets that passes through the coils to a magnetic flux associated with the magnets that passes through the magnetic material is greater than 2:3.22. The method of clause 21, comprising:electrically insulating the magnetic material from the coils.23. The method of clause 22, wherein the magnetic material are electrically insulated from the coils by flowing an electrical insulation between the magnetic material and the coils.24. The method of clause 23, wherein the electrical insulation is flowed substantially in a vacuum.25. The method of clause 23 or 24, comprising:applying spacers for spacing the magnetic material from the coils before the electrical insulation is flowed.26. The method of any of clauses 23-25, comprising:stacking a plurality of layers of coils in a height direction of the coils.27. The method of clause 26, wherein the layers of coils are stacked before the electrical insulation is flowed.28. The method of clause 26, wherein the electrical insulation is flowed before the layers of coils are stacked.

[0139] Although specific reference may have been made above to the use of embodiments in the context of object inspection and optical lithography, it will be appreciated that the invention, where thecontext allows, is not limited to these contexts and may be used in other applications, for example imprint lithography.

[0140] Where the context allows, embodiments may be implemented in hardware, firmware, software, or any combination thereof. Embodiments 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 that such 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.

[0141] While specific embodiments have been described above, it will be appreciated that 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 embodiments as described without departing from the scope of the claims set out below.

Claims

CLAIMS1. A motion system comprising:a base; anda mover configured to move relative to the base;wherein one of the base and the mover comprises magnets and the other of the base and the mover comprises coils and magnetic material such that a driving force for moving the mover relative to the base comprises a Lorentz force between the magnets and the coils and a magnetic force between the magnets and the magnetic material; and wherein the motion system is arranged such that a ratio of a magnetic flux associated with the magnets that passes through the coils to a magnetic flux associated with the magnets that passes through the magnetic material is greater than 2:3.

2. The motion system of claim 1, wherein:the magnets are arranged in two magnet tracks, between which the coils and magnetic material are provided; andthe magnetic material is located within the coils.

3. The motion system of claim 1, wherein:volumes are defined within the coils, and the magnets extend beyond an end of at least one of the volumes in a length direction of the coils; andthe magnets extend further beyond one end of at least one of the volumes in the length direction than beyond the other end in the length direction.

4. The motion system of claim 1, wherein:for at least one of the coils the associated magnetic material is less wide than the coil on one side of the magnetic material; andthe magnetic material is distanced from ends of the coils in a height direction of the coils.

5. The motion system of claim 1, wherein for at least one of the coils the associated magnetic material comprises a plurality of magnetic members and is substantially electrically insulating.

6. The motion system of claim 1, comprising:a plurality of layers of coils stacked in a height direction of the coils; andat least one plate separating adjacently stacked layers of coils, wherein:the magnetic material extends through the plate;the plate separates magnetic members of the magnetic material; and the plate is configured to thermally condition the coils.

7. The motion system of claim 1, comprising electrical insulation between the coils and the magnetic material.

8. The motion system of claim 1, wherein for at least one of the coils the associated magnetic material comprises a substance selected from the group consisting of (i) a cobalt-iron material, (ii) a silicon-steel material, (iii) a stainless steel alloy, (iv) silicon and iron and (v) epoxy and a ferromagnetic particle.

9. The motion system of claim 1, wherein for at least one of the coils, a centroid of the coil is substantially coincident with a centroid of magnetic material within the coil.

10. The motion system of claim 1, wherein the motion system is arranged such that the ratio of the magnetic flux associated with the magnets that passes through the coils to the magnetic flux associated with the magnets that passes through the magnetic material is at least 1:1, optionally at least 3:2, optionally at least 2:1, optionally at least 3:1 and optionally at least 4:1.

11. An actuatable stage for a lithographic apparatus, wherein the actuatable stage is configured to support at least one of a substrate and a patterning device and comprises:the motion system of claim 1.

12. A lithographic apparatus for exposing a substrate with patterned radiation, wherein the lithographic apparatus comprises:the actuatable stage of claim 11.

13. A method for making a motion system, the method comprising:providing one of a base and a mover with magnets;providing the other of the base and the mover with coils and magnetic material such that a driving force for moving the mover relative to the base comprises a Lorentz force between the magnets and the coils and a magnetic force between the magnets and the magnetic material; and arranging the motion system such that a ratio of a magnetic flux associated with the magnets that passes through the coils to a magnetic flux associated with the magnets that passes through the magnetic material is greater than 2:3.

14. The method of claim 13, comprising:electrically insulating the magnetic material from the coils, wherein:the magnetic material are electrically insulated from the coils by flowing an electrical insulation between the magnetic material and the coils; andthe electrical insulation is flowed substantially in a vacuum;15. The method of claim 14, comprising:applying spacers for spacing the magnetic material from the coils before the electrical insulation is flowed; andstacking a plurality of layers of coils in a height direction of the coils, wherein:the layers of coils are stacked before the electrical insulation is flowed; and the electrical insulation is flowed before the layers of coils are stacked.

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