Actuator and lithographic, substrate inspection or wafer metrology apparatus

Abstract

An actuator comprises a coil and a magnet arrangement. The coil is arranged in a plane defined by first and second directions, wherein main coil portions of the coil extends in the first direction, The magnet arrangement comprises first and second magnet portions arranged at opposite sides of the coil, each magnet portion comprises a central magnet unit and an edge magnet unit having different polarization directions. The central magnet units of the two magnet portions are substantially aligned in a third direction perpendicular to the plane of the coil, and each with a polarization direction in the third direction wherein the polarization directions of the central magnet units of the two magnet portions are opposite to each other. The magnet arrangement is configured to generate a primary magnetic flux substantially transverse the main coil portions in the second direction.

Description

ACTUATOR AND LITHOGRAPHIC. SUBSTRATE INSPECTION OR WAFER METROLOGYAPPARATUSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP applications 24167418.3 which was filed on 28 March 2024, 24195231.6 which was filed on 19 August 2024, and 24217806.9 which was filed on 5 December 2024 and which are incorporated herein in their entirety by reference .FIELD

[0002] The present invention relates to an actuator and a lithographic apparatus, a substrate inspection apparatus or a wafer metrology apparatus comprising 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] The substrate may be held by a substrate table which is positioned by a positioner. The positioner may comprise a long stroke - short stroke positioner, comprising a long stroke positioner configured to position the substrate table with a long range of movement, and a short stroke positioner configured to position the substrate table with a short range of movement. The long stroke positioner may provide a coarse positioning while the short stroke positioner may provide an accurate, fine positioning of the substrate table. A similar long stroke short stroke positioning may be provided to position a mask support, such as a reticle stage. Both the long and short-stroke in the wafer / reticle stage may have equal setpoints in terms of position, velocity, and / or acceleration. In order to increase thethroughput of the lithographic apparatus, the setpoints on both parts of the stages must be scaled, which may lead to a significant increase in power consumption.

[0006] The power consumption may be reduced by introducing a small horizontal displacement (approximately 1 mm) between the long and short-stroke. For example, the setpoint for the long-stroke, which may have the highest moving mass, may be adjusted to reduce the power consumption. This concept may be referred to as lagging long-stroke, which also enables an increase in throughput for an equal power consumption per wafer with respect to the current generation. Similarly a lagging short stroke may be applied to reduce a power consumption.

[0007] In the case of a lagging long stroke or a lagging short stroke, an increased horizontal displacement to which e.g. the short-stroke positioners are exposed, should not compromise their behavior, e.g., position accuracy and force production. Moreover, the short-stroke positioners are still exerted to the entire setpoint, thus for an increasing throughput, the load on the short-stroke positioner may increase.SUMMARY

[0008] Considering the above, it is an object of the invention to provide an actuator that may be able to cope with the horizontal displacements, which are required to realize the lagging long-stroke or lagging short stroke concept.

[0009] According to an aspect of the invention, there is provided an actuator comprising a coil and a magnet arrangement, wherein- the coil is arranged in a plane defined by a first direction and a second direction, and the coil being configured to carry an electric current during use, wherein main coil portions of the coil extends in the first direction,- the magnet arrangement comprises a first and a second magnet portion, which are arranged at opposite sides of the coil, wherein each of the two magnet portions comprises a central magnet unit and an edge magnet unit, characterized in that the central magnet unit and the edge magnet unit of each magnet portion have different polarization directions, the central magnet units of the two magnet portions are substantially aligned in a third direction perpendicular to the plane of the coil, and each with a polarization direction in the third direction wherein the polarization directions of the central magnet units of the two magnet portions are opposite to each other, and the magnet arrangement is configured to generate a primary magnetic flux substantially transverse the main coil portions in the second direction.According to an aspect of the invention, there is provided a lithographic apparatus, a substrate inspection apparatus or a wafer metrology apparatus comprising the actuator according to the invention.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] 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 in which the present invention may be embodied;Figure 2 depicts a detailed view of a part of the lithographic apparatus of Figure 1 ;Figure 3 schematically depicts an embodiment of a position control system as may be comprised in the lithographic apparatus;Figure 4 schematically depicts a cross sectional view of an actuator;Figure 5 schematically depicts another cross sectional view of the actuator in accordance with Figure 4;Figure 6A schematically depicts another embodiment of an actuator;Figure 6B schematically depicts a further embodiment of an actuator;Figure 7 schematically depicts a perspective view of the actuator in accordance with Figure 4; Figure 8 schematically depicts a perspective view of a further embodiment of an actuator;Figure 9 schematically depicts a partly cut-out view of the actuator in accordance with Figure 8;Figure 10 schematically depicts a perspective view of yet another embodiment of an actuator;Figure 11 schematically depicts a partly cut-out view of the actuator in accordance with Figure 10;Figure 12 schematically depicts a cross sectional view of another embodiment of an actuator;Figure 13 schematically depicts a perspective view of the actuator in accordance with Figure 12;Figure 14 schematically depicts a perspective view of another embodiment of an actuator;Figure 15 schematically depicts a cross sectional view of the actuator in accordance with Figure 14;Figure 16 schematically depicts a cross sectional view of another embodiment of an actuator; andFigure 17 schematically depicts a cross sectional view of a further embodiment of an actuator.DETAILED DESCRIPTION

[0011] 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).

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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 carriedout 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.

[0018] 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.

[0019] 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 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 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 device MA 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 P 1 , P2 are known as scribe-lane alignment marks when these are located between the target portions C.

[0020] 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 axes is orthogonal to the other two axes. 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.

[0021] Figure 2 shows a more detailed view of a part of the lithographic apparatus LA of Figure 1. The lithographic apparatus LA may be provided with a base frame BF, a balance mass BM, a metrology frame MF and a vibration isolation system IS. The metrology frame MF supports the projection system PS. Additionally, the metrology frame MF may support a part of the position measurement system PMS. The metrology frame MF is supported by the base frame BF via the vibrationisolation system IS. The vibration isolation system IS is arranged to prevent or reduce vibrations from propagating from the base frame BF to the metrology frame MF.

[0022] The second positioner PW is arranged to accelerate the substrate support WT by providing a driving force between the substrate support WT and the balance mass BM. The driving force accelerates the substrate support WT in a desired direction. Due to the conservation of momentum, the driving force is also applied to the balance mass BM with equal magnitude, but at a direction opposite to the desired direction. Typically, the mass of the balance mass BM is significantly larger than the masses of the moving part of the second positioner PW and the substrate support WT.

[0023] In an embodiment, the second positioner PW is supported by the balance mass BM. For example, wherein the second positioner PW comprises a planar motor to levitate the substrate support WT above the balance mass BM. In another embodiment, the second positioner PW is supported by the base frame BF. For example, wherein the second positioner PW comprises a linear motor and wherein the second positioner PW comprises a bearing, like a gas bearing, to levitate the substrate support WT above the base frame BF.

[0024] The position measurement system PMS may comprise any type of sensor that is suitable to determine a position of the substrate support WT. The position measurement system PMS may comprise any type of sensor that is suitable to determine a position of the mask support MT. The sensor may be an optical sensor such as an interferometer or an encoder. The position measurement system PMS may comprise a combined system of an interferometer and an encoder. The sensor may be another type of sensor, such as a magnetic sensor, a capacitive sensor or an inductive sensor. The position measurement system PMS may determine the position relative to a reference, for example the metrology frame MF or the projection system PS. The position measurement system PMS may determine the position of the substrate table WT and / or the mask support MT by measuring the position or by measuring a time derivative of the position, such as velocity or acceleration.

[0025] The position measurement system PMS may comprise an encoder system. An encoder system is known from for example, United States patent application US2007 / 0058I73AI, filed on September 7, 2006, hereby incorporated by reference. The encoder system comprises an encoder head, a grating and a sensor. The encoder system may receive a primary radiation beam and a secondary radiation beam. Both the primary radiation beam as well as the secondary radiation beam originate from the same radiation beam, i.e., the original radiation beam. At least one of the primary radiation beam and the secondary radiation beam is created by diffracting the original radiation beam with the grating. If both the primary radiation beam and the secondary radiation beam are created by diffracting the original radiation beam with the grating, the primary radiation beam needs to have a different diffraction order than the secondary radiation beam. Different diffraction orders are, for example, +lstorder, -1storder, +2ndorder and -2ndorder. The encoder system optically combines the primary radiation beam and the secondary radiation beam into a combined radiation beam. A sensor in the encoder head determines a phase or phase difference of the combined radiation beam. The sensor generates a signal based on thephase or phase difference. The signal is representative of a position of the encoder head relative to the grating. One of the encoder head and the grating may be arranged on the substrate structure WT. The other of the encoder head and the grating may be arranged on the metrology frame MF or the base frame BF. For example, a plurality of encoder heads is arranged on the metrology frame MF, whereas a grating is arranged on a top surface of the substrate support WT. In another example, a grating is arranged on a bottom surface of the substrate support WT, and an encoder head is arranged below the substrate support WT.

[0026] The position measurement system PMS may comprise an interferometer system. An interferometer system is known from, for example, United States patent US6,020,964, fded on July 13, 1998, hereby incorporated by reference. The interferometer system may comprise a beam splitter, a mirror, a reference mirror and a sensor. A beam of radiation is split by the beam splitter into a reference beam and a measurement beam. The measurement beam propagates to the mirror and is reflected by the mirror back to the beam splitter. The reference beam propagates to the reference mirror and is reflected by the reference mirror back to the beam splitter. At the beam splitter, the measurement beam and the reference beam are combined into a combined radiation beam. The combined radiation beam is incident on the sensor. The sensor determines a phase or a frequency of the combined radiation beam. The sensor generates a signal based on the phase or the frequency. The signal is representative of a displacement of the mirror. In an embodiment, the mirror is connected to the substrate support WT. The reference mirror may be connected to the metrology frame MF. In an embodiment, the measurement beam and the reference beam are combined into a combined radiation beam by an additional optical component instead of the beam splitter.

[0027] 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 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 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.

[0028] 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 actuatorsmay 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.

[0029] The lithographic apparatus LA comprises a position control system PCS as schematically depicted in Figure 3. The position control system PCS comprises a setpoint generator SP, a feedforward controller FF and a feedback controller FB. The position control system PCS provides a drive signal to the actuator ACT. The actuator ACT may be the actuator of the first positioner PM or the second positioner PW. The actuator ACT drives the plant P, which may comprise the substrate support WT or the mask support MT. An output of the plant P is a position quantity such as position or velocity or acceleration. The position quantity is measured with the position measurement system PMS. The position measurement system PMS generates a signal, which is a position signal representative of the position quantity of the plant P. The setpoint generator SP generates a signal, which is a reference signal representative of a desired position quantity of the plant P. For example, the reference signal represents a desired trajectory of the substrate support WT. A difference between the reference signal and the position signal forms an input for the feedback controller FB. Based on the input, the feedback controller FB provides at least part of the drive signal for the actuator ACT. The reference signal may form an input for the feedforward controller FF. Based on the input, the feedforward controller FF provides at least part of the drive signal for the actuator ACT. The feedforward FF may make use of information about dynamical characteristics of the plant P, such as mass, stiffness, resonance modes and eigenfrequencies.

[0030] Figure 4 depicts a cross sectional view of an actuator according to the present invention. The actuator comprises a coil, of which the main coil portions CL are depicted. The main coil portions extend in a direction perpendicular to the plane of drawing of Figure 4. The coil may comprise plural coil windings. The actuator further comprises a magnet arrangement, which comprises a first magnet portion FMP and a second magnet portion SMP, the first and second magnet portions being arranged on opposite sides of the coil. The first and second magnet portion each comprises a central magnet unit CMU and edge magnet units EMU. The central magnet units are substantially aligned in the vertical direction z, denoted in Figure 4 as 3DIR. Likewise, the edge magnet units are substantially aligned in the vertical direction z. The magnets of the central magnet unit and the edge magnet units may be permanent magnets. The magnets of the central magnet unit and the edge magnet units each have arespective polarization direction as indicated by the respective arrows in the central magnet unit and the edge magnet units depicted in Figure 4. The polarization directions of the central magnet units differ from the polarization directions of the edge magnet units. As indicated by the arrows, the magnetization directions of the central magnet units are in the z-direction, i.e. in the vertical direction. According to the present invention, the magnetization directions of the central magnet units are opposite to each other. Thus, in case the magnetization direction of the central magnet unit of the first magnet portion FMP is upward, i.e. upward in the z-direction, the magnetization direction of the central magnet unit of the second magnet portion SMP is downward, i.e. downward in the z-direction. Alternatively, in case the magnetization direction of the central magnet unit of the first magnet portion is downward in the z- direction, the magnetization direction of the central magnet unit of the second magnet portion is upward in the z-direction. Magnetic field lines of the magnetic field by the central magnet unit and edge magnet units of the first magnet portion will propagate from the central magnet unit of the first magnet portion to the edge magnet units of the first magnet portion and from the edge magnet units to the central magnet unit. Similarly, for the second magnet portion, magnetic field lines of the magnetic field by the central magnet unit and edge magnet units of the second magnet portion will propagate from the central magnet unit of the second magnet portion to the edge magnet units of the second magnet portion and from the edge magnet units to the central magnet unit. As a result of the substantially aligned central magnet units with opposite polarization direction in the z-direction, the magnetic field lines of the magnetic field will divert from the z-direction towards the horizontal direction, i.e. horizontally from the central magnet units to the edge magnet units. A substantially horizontal magnetic field, i.e. a substantially horizontal primary magnetic flux (PMF) may be created at the main coil portions of the coil. As a result of the substantially horizontal primary magnetic flux (PMF) at the main coil portions, the force generated as a result of an electric current flowing in operation through the main coil portions may be relatively independent of the position of the coil in respect of the first and second magnet portions. In other words, a displacement of the main coil portions in respect of the first and second magnet portions, may have a low effect on the force generated by the electrical current through the main coil portions. The first and second magnet portions of the actuator may each further comprise a back iron BI at a side of the central magnet unit and the edge magnet units facing away from the main coil portions, to provide a defined path for the magnetic field at the sides facing away from the main coil portions.

[0031] In general terms, the direction perpendicular to the plane of the drawing of Figure 4 may be understood as a first direction 1DIR. The direction from left to right and right to left in the plane of the drawing of Figure 4 may be understood as a second direction 2DIR. Similarly, the vertical direction or z-direction may be understood as a third direction 3DIR. Accordingly, the coil is arranged in a plane defined by the first direction and the second direction, whereby the main coil portions of the coil extend in the first direction. The edge magnet units are offset in the second direction in respect of the central magnet units. A force in the third direction may be generated by operation of the actuator, i.e. by an electrical current carried by the coil in use.

[0032] Figure 5 depicts another cross sectional view of the actuator in accordance with Figure 4, whereby the magnetic field lines have been omitted. As indicated by the dot and cross in the main coil portions, the electric current in one of the main coil portions flows in opposite direction in respect of the electrical current in the other one of the main coil portions.

[0033] In Figure 5, the polarization directions of the edge magnet units are directed in the third direction, opposite the polarization direction of the corresponding central magnet units of the respective magnet portion. As a result, a relatively large volume may be defined at the main coil portions where the magnetic field strength is substantially uniform in the second direction.

[0034] Another embodiment of the actuator is explained with reference to Figure 6A. Figure 6A depicts a cross sectional view of the actuator according to the embodiment, similar to the views in Figures 4 and 5. In the embodiment depicted in Figure 6A, the coil comprising the first and second main coil portions, the first and second magnet portions each comprising a central magnet unit and edge magnet units are likewise depicted. The central magnet units are aligned in the third direction.

[0035] In the embodiment as depicted in Figure 6A, the edge magnet units are arranged in a Halbach configuration, i.e. the polarization direction of the edge magnet units extends in the second direction instead of in the third direction. The polarization directions of the two edge magnet units of the first magnet portion are opposite to each other. Likewise, the polarization directions of the two edge magnet units of the second magnet portion are opposite to each other. As a result of the Halbach configuration of the edge magnet units, the horizontal magnetic field, i.e. the primary magnetic flux at the main coil portions may further be enhanced, resulting in a more homogeneous magnetic field at the main coil portions.

[0036] Figure 7 depicts a perspective view of the actuator as described with reference to Figures 4 and 5. In the embodiment depicted in Figure 7, the coil extends in the plane defined by the first direction 1DIR and second directions 2DIR. The coil comprises the first and second main coil portions CL extending in the first direction. The first and second magnet portions each comprising a central magnet unit and edge magnet units extending in the first direction. The first and second magnet portions are spaced apart in the third direction whereby the coil is arranged between the first and second magnet portions. The central magnet units are aligned in the third direction.

[0037] In an embodiment, as seen in the embodiments depicted in Figures 4 - 7, the central magnet unit and the edge magnet units extend in the first direction, whereby, seen along the second direction, the main coil portions of the coil extend along edges between the respective central magnet units and the edge magnet units. Seen along the second direction, the magnetic field may be the substantially homogeneous and horizontal at the edges between the central magnet units and the edge magnet units. The edges between the central magnet units and the edge magnet units extend in the first direction, i.e. substantially parallel to the main coil portions of the coil.

[0038] In an embodiment, the first and second magnet portions are spaced apart in the third direction, wherein the coil is arranged between the first and second magnet portions. As the first andsecond magnet portions each both provide a substantially horizontal magnetic field from opposite sides of the coil (seen in the third direction), distortion of the substantially horizontal magnetic fields from the two magnet portions may at least partly compensate each other due to the opposite sides from which the magnetic field emerges.

[0039] In an embodiment, as depicted in figure 6B, the actuator further comprises a third magnet portion TMP arranged between the main coil portions, the third magnet portion comprising first and second auxiliary magnets FAM, SAM having polarization directions in the second direction and opposite to each other. As a result of the third magnet portions TMP comprising the first and second auxiliary magnets, the horizontal magnetic field, i.e. the primary magnetic flux at the main coil portions may further be enhanced, resulting in a further enhancement of the homogeneity of the magnetic field at the main coil portions.

[0040] In an embodiment, as seen in for example Figures 4, 5 and 7, the polarization directions of the edge magnet units of the two magnet portions are opposite to the polarization directions of the central magnet units of the respective magnet portions.

[0041] In an alternative embodiment, as seen in for example Figure 6, the polarization directions of the edge magnet units of the two magnet portions extend in the second direction to form a Halbach configuration.

[0042] In an embodiment, along the first direction, a length of the main coil portion exceeds a length of the central magnet unit and the edge magnet unit. As a result, a displacement of the coil in the first direction may have a low effect on the vertical force generated by the actuator.

[0043] In an embodiment, along the second direction, a width of the first and second magnet portions exceeds a width of the coil. The width of the coil may be understood as a dimension of the coil in the second direction. The width of the coil may be understood as an outer dimension of the windings of the coil in the second direction. As a result, edge effects by a displacement of the coil in the second direction may be reduced.

[0044] In the embodiments described with reference to Figures 4 - 7, the second direction is perpendicular to the first direction. Thus, the first and second directions form perpendicular directions spanning a plane, the third direction being perpendicular to the first and second directions.

[0045] Radial or circular embodiments will be described below with reference to Figures 8 - 11:

[0046] In a first alternative embodiment, the first direction is radial in respect of an axis extending in the third direction and the second direction is circular around the axis. As depicted in Figure 8, the actuator may comprise a plurality of the coils, whereby the main coil portions of the coils extend in the radial direction 1DIR. The central magnet units and the edge magnet units may likewise extend in the radial direction. Each coil, associated central magnet and edge magnets may form a sector shaped assembly. As shown in Figure 8 and 9, plural of the assemblies being arranged around the third direction. A partially cut out view of the actuator in accordance with Figure 8 is depicted in Figure 9. A substantially vertical force may be generated by operation of the actuator.

[0047] In a further alternative embodiment, the second direction is radial in respect of the axis extending in the third direction and wherein the first direction is circular around the axis. The main coil portion of the coil circularly extends around the axis extending in the third direction. The central magnet units CMU likewise circularly extend around the axis extending in the third direction. The edge magnet units EMU circularly extend around the central magnet units. A substantially vertical force may be generated by operation of the actuator. Figure 10 depicts a perspective view of such an embodiment of the actuator. A partially cut out view of the actuator in accordance with Figure 10 is depicted in Figure 11.

[0048] Another embodiment of the actuator according to the invention is shown in and explained with Figure 12 and 13. An actuator comprises a coil (CL) arranged in a space between a first magnet arrangement (FMA) and a second magnet arrangement (SMA) and extending in a plane (PL), wherein the first magnet arrangement (FMA) is configured to generate a first magnetic flux (MFI) and a second magnetic flux (MF2), and the second magnet arrangement (SMA) is configured to generate a third magnetic flux (MF3) and a fourth magnetic flux (MF4). The first and the third magnetic flux interact with a first coil portion (CL1) of the coil in a first direction (1DIR), and the second and the fourth magnetic flux interact with a second coil portion (CL2) of the coil in a second direction (2DIR) which is opposite to the first direction, wherein the first and second direction are parallel to the plane, thereby enabling a force between the coil and the first and second magnet arrangement in a direction (3DIR) perpendicular to the plane. The first and the second magnet arrangements and the first and the second coil portions may extend in a fourth direction (4DIR), which is parallel to the plane, and perpendicular to the first and the second direction.

[0049] Another embodiment of the actuator according to the invention is shown in and explained with Figure 14 and 15. The actuator comprises a first coil (FCL) and a second coil (SCL) which are arranged in a space between a first and a second magnet arrangement (FMA, SMA), wherein the first coil (FCL) extends in a first plane (PL1), the second coil (SCL) extends in a second plane (PL2) perpendicular to the first plane (PL1). The first magnet arrangement (FMA) is configured to generate a first magnetic flux (MF 1) and a second magnetic flux (MF2), and the second magnet arrangement (SMA) is configured to generate a third magnetic flux (MF3) and a fourth magnetic flux (MF4). The first and the third magnetic flux interact with a first coil portion (FCL 1 ) of the first coil in a first direction ( 1 DIR), and the second and the fourth magnetic flux interact with a second coil portion (FCL2) of the first coil in a second direction (2DIR) which is opposite to the first direction, wherein the first and second direction are parallel to the first plane (PL1). The interaction between the magnetic fluxes and the first coil enables a force between the first coil and the first and second magnet arrangements in a direction perpendicular to the first plane, i.e. in the third or fourth direction in Figure 14 and 15. The direction of the enabled force depends on the direction of the electric current in the first coil and the directions of the magnetic fluxes . The first and the second magnetic flux (MF 1 , MF2) interact with a first coil portion of the second coil (SCL1) in a third direction (3DIR), and the third and the fourth magnetic flux (MF3,MF4) interact with a second coil portion of the second coil (SCL2) in a fourth direction (4DIR) which is opposite to the third direction (3DIR), wherein the third and fourth directions are parallel to the second plane (PL2). The interactions between the magnetic fluxes and the second coil enables a force between the second coil and the first and second magnet arrangements in a direction perpendicular to the second plane (PL2), i.e. in the first or second direction in Figure 14 and 15. The direction of the enabled force depends on the direction of the electric current in the second coil and the directions of the magnetic fluxes. By adding a second coil compared to the embodiment in Figure 12 and 13, a force / movement in an additional degree of freedom is enabled compared to the embodiments as shown in Figure 4, 5, or 6A. Note that in Figure 15, directions (1DIR-4DIR) indicated using reference signs and arrows are correspondent with directions (1DIR-4DIR) in the coordinate system.

[0050] Figure 16 schematically depicts a cross sectional view of another embodiment of an actuator. A third magnet portion (TMA) is arranged between the coil portions of the first coil of Figure 14 and 15. The third magnet portion comprises an auxiliary magnet having a polarization direction in the second direction (2DIR) and interacting with the second and the fourth magnetic flux. The third magnet portion is added to create an offset force against the first and second magnet arrangements in the first direction (1DIR), so that the net force in the first direction is increased. For example, when the actuator of Figure 16 is used to generate a vertical force to move a mass attached to the coils or the first and second magnet arrangements, the third magnet portion may be designed to compensate the gravity of said mass. Note that depending on the polarizations of the magnet arrangements, and depending on the physical connection of the actuator with the mass, the polarization of the auxiliary magnet may be in the first direction.

[0051] The third magnet portion may comprise more than one auxiliary magnet, and one example is shown in Figure 17. In this example, a second auxiliary magnet is arranged to interact mainly with the first and the third magnetic flux, thereby further enhancing the force against the first and second magnet arrangements in the first direction (1DIR).

[0052] The actuator, such as described above with reference to Figures 4 - 17, may be comprised in a lithographic apparatus, a substrate inspection apparatus or a wafer metrology apparatus.

[0053] For example, the lithographic apparatus, the substrate inspection apparatus or the wafer metrology apparatus may comprise a stage and a long stroke positioner and a short stroke positioner configured to actuate the stage . The long stroke positioner may provide a coarse positioning of the stage, and may provide a relatively large range of movement. The short stroke positioner may provide a fine positioning of the stage and may provide a relatively small range of movement. The short stroke positioner may comprise the actuator. As explained above, the actuator may be configured to generate a force that is substantially independent on a position of the coil relative to the magnets (over a range of movement of the coil relative to the magnets), as the magnetic field that interacts with the coil is substantially homogeneous. The movements of the short stroke positioner may be within the range of movement of the coil relative to the magnets, over which range the magnetic field may be substantiallyhomogeneous. The short stroke positioner may be configured to generate a force in one or more directions, e.g. in one or more of the first, second and third directions. Accordingly, the short stroke positioner may be configured to position the stage in one or more of the first, second and third directions.

[0054] For example, the actuator may be configured to exert a force on the stage in the vertical direction (i.e. the third direction). The actuator may be configured to position the stage in the vertical direction and / or the actuator may be configured to compensate a gravity on the stage, i.e. the actuator may be configured to generate a force that substantially compensates gravity on the stage. For example, a gravity on a substrate table of the apparatus may be compensated by the actuator acting on the substrate table. As another example, the gravity on a mask table, such as a support that supports a patterning device, may be compensated by the actuator. The actuator may accordingly be operated by a gravity compensation setpoint generator to generate a gravity compensation setpoint resulting in the generation of a force in the vertical direction to substantially compensate gravity. As a result of the substantially homogeneous magnetic field at the main coil portions of the coil, as described above, the actuator may be driven to provide a gravity compensation substantially independent of a position change of the coil in the first, second or third directions.

[0055] For example, the coil of the actuator may be connected to the substrate table while the magnets of the actuator are connected to a reference structure. Accordingly, a force may be exerted between the substrate table and the reference structure, so as to substantially compensate a gravity acting on the substrate table. As another example, the coil of the actuator may be connected to the support that supports the patterning device while the magnets of the actuator are connected to a reference structure. Accordingly, a force may be exerted between the support and the reference structure, so as to substantially compensate a gravity acting on the support. The short stroke positioner may comprise a plurality of the actuators as described above, the actuators being driven by the gravity compensation setpoint generator so as to generate an upward force to substantially compensate gravity. The short stroke positioner may further be provided with short stroke positioner setpoints to actuate the stage in one or more of the first, second and third directions, i.e. one or more of the y, x and z directions.

[0056] Referring to the lithographic apparatus as described with reference to Figures 1 and 2, the long stroke positioner and a short stroke positioner may be comprised in the first positioner PM that is configured to position the support MT or the second positioner PW that is configured to position the substrate table WT.

[0057] The lithographic apparatus, substrate inspection apparatus or wafer metrology apparatus may further comprise a setpoint generator configured to provide a long stroke setpoint to the long stroke positioner and a short stroke setpoint to the short stroke positioner, wherein one of the long stroke setpoint provided to the long stroke positioner and the short stroke setpoint provided to the short stroke positioner is a lagging setpoint in respect of the other one of the long stroke setpoint provided to the long stroke positioner and the short stroke setpoint provided to the short stroke positioner. The lagging setpoint may be applied to for example reduce a power consumption of the stage. For example, shortrange, high acceleration movements may be predominantly performed by the short stroke positioner, while long range, constant velocity movements may be predominantly performed by the long stroke positioner. The lagging setpoint may provide for a relative movement of the short stroke in respect of the long stroke. As explained above, the gravity compensator may for example act between the stage and the long stroke positioner. As a result, due to the lagging setpoint, in use, the short stroke may move in respect of the long stroke. The relatively uniform magnetic field of the actuator may provide for a defined force in the vertical direction over a range of movement of the short stroke positioner relative to the long stroke positioner, thereby facilitating an implementation of the lagging setpoint. Moreover, due to the relatively uniform magnetic field and the resulting defined vertical force, which exhibits a low sensitivity to displacements of the coil relative to the permanent magnets, the gravity compensation force may be accurately defined, which may provide that disturbance forces on the stage may be reduced, the disturbance forces due to a mismatch between an intended vertical force by the gravity compensator and the actual vertical force exerted on the stage. For example, in case the gravity compensator comprises a plurality of the actuators according to the invention, a deformation of the stage may be reduced.

[0058] Summarizing the above, in order to realize the lagging long-stroke concept or lagging short stroke concept, the increased horizontal displacement should be accommodated for in each short-stroke positioner. In a prior art short stroke actuator configured to generate a vertical force, the magnetic gap between the stator and mover would need to increase in order to accommodate the additional displacement. Consequently, an efficiency of the actuator would decrease and to compensate for such effect, a volume and mass of the actuator may require to be increased. Such an effect may even be more pronounced when the accelerations of the stage would be increased. Additionally, the horizontal displacement of a mover in the short stroke actuator may introduce unbalanced forces, which may cause torques and deformations.

[0059] A schematic 3D representation of an embodiment of the actuator according to the present invention is shown in Figure 7. The actuator comprises a double-sided permanent-magnet array, each attached to its own back-iron. In between the permanent-magnet arrays, a coil is placed, which may have a “racetrack” shape. The actuator may be used either in a moving -coil or moving magnet configuration, where the former may be more beneficial in terms of moving-mass and the latter may omits connections to a moving side.

[0060] As may be understood from Figure 4, the permanent-magnets may be arranged such that the magnetic flux near the coil may primarily have a component in the second direction. Furthermore, the current in the coils may flow in the first direction (except for the end-winding, i.e., the round part), thus a force in the third direction, i.e., the vertical direction, may be created as a result of the magnetic field.

[0061] Compared to the prior art, the actuator according to the present invention may be designed to accommodate horizontal displacement. Along the first direction, the rectangular part, i.e. the main coilportion of the coil, which generates the force, may be several millimeters longer compared to the permanent-magnet, such that a horizontal displacement in this direction may have an insignificant effect on the vertical force. A horizontal displacement along the second direction may introduce edge-effects; however, these may be suppressed by increasing the width of the permanent magnets along this direction or adding additional permanent-magnets to the arrays. Furthermore, the distance between the permanent-magnets remains constant, despite horizontal displacements, thus a force unbalance and risk of stage deformation may be significantly reduced.

[0062] Several design variations on the actuator according to the present invention may be provided. Firstly, the actuator may also be functional with a single permanent-magnet array, albeit less efficient. The second permanent-magnet array may improve the vertical force-producing capability since the magnetic field may be forced into a parallel pattern near the coil. Secondly, as depicted in Figure 6, the permanent-magnets may be arranged in a Halbach configuration, such that the magnetic field may be focused towards the airgap and diverted from the back -iron. Consequently, the vertical force -producing capability may be enhanced, while also a thickness of the back -iron may be reduced, or may be omitted entirely. Thirdly, to possibly further improve the vertical force -producing capability, permanentmagnets may be added in a center of the coil. The additional permanent-magnets are magnetized along the second-direction, such that the magnetic field component that generates the force may be enhanced near the coil. A disadvantage if adding the additional permanent magnets may be that the stiffness may also be affected. Finally, the concept may be adjusted to cylindrical geometries, as shown in Figures 8 and 10 as well as Figures 10 and 11.

[0063] 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.

[0064] 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). These apparatus may be generally referred to as lithographic tools. Such a lithographic tool may use vacuum conditions or ambient (non-vacuum) conditions.

[0065] 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.

[0066] 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 beimplemented 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.

[0067] 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. Other aspects of the invention are set-out as in the following numbered clauses.1. An actuator comprising a coil and a magnet arrangement, wherein- the coil is arranged in a plane defined by a first direction and a second direction, and the coil being configured to carry an electric current during use, wherein main coil portions of the coil extends in the first direction,- the magnet arrangement comprises a first and a second magnet portion, which are arranged at opposite sides of the coil, wherein each of the two magnet portions comprises a central magnet unit and an edge magnet unit, characterized in that the central magnet unit and the edge magnet unit of each magnet portion have different polarization directions, the central magnet units of the two magnet portions are substantially aligned in a third direction perpendicular to the plane of the coil, and each with a polarization direction in the third direction wherein the polarization directions of the central magnet units of the two magnet portions are opposite to each other, and the magnet arrangement is configured to generate a primary magnetic flux substantially transverse the main coil portions in the second direction.2. The actuator according to clause 1, wherein the central magnet unit and the edge magnet units extend in the first direction and wherein, seen along the second direction, the main coil portions of the coil extend along an edge between the respective central magnet units and the edge magnet units.3. The actuator according to any one of the preceding clauses, wherein the first and second magnet portions are spaced apart in the third direction and wherein the coil is arranged between the first and second magnet portions.4. The actuator according to any one of the preceding clauses, further comprising a third magnet portion arranged between the main coil portions, the third magnet portion comprising first and second auxiliary magnets having polarization directions in the second direction and opposite to each other.5. The actuator according to any one of the preceding clauses, wherein the polarization directions of the edge magnet units of the two magnet portions are opposite to the polarization directions of the central magnet units of the respective magnet portions.6. The actuator according to any one of clauses 1 - 4, wherein the polarization directions of the edge magnet units of the two magnet portions extend in the second direction to form a Halbach configuration.7. The actuator according to any one of the preceding clauses, wherein along the first direction, a length of the main coil portion exceeds a length of the central magnet unit and the edge magnet unit.8. The actuator according to any one of the preceding clauses, wherein along the second direction, a width of the first and second magnet portions exceeds a width of the coil.9. The actuator according to any one of the preceding clauses, wherein the second direction is perpendicular to the first direction.10. The actuator according to any one of clauses 1 - 8, wherein the first direction is radial in respect of an axis extending in the third direction and wherein the second direction is circular around the axis.11. The actuator according to any one of clauses 1 - 8, wherein the second direction is radial in respect of the axis extending in the third direction and wherein the first direction is circular around the axis.12. An actuator comprising a coil arranged in a space between a first and a second magnet arrangement and extending in a plane, wherein- the first magnet arrangement is configured to generate a first magnetic flux and a second magnetic flux,- the second magnet arrangement is configured to generate a third magnetic flux and a fourth magnetic flux, and wherein the first and the third magnetic flux interact with a first coil portion of the coil in a first direction, and the second and the fourth magnetic flux interact with a second coil portion of the coil in a second direction which is opposite to the first direction, wherein the first and second direction are parallel to the plane, thereby enabling a force between the coil and the first and second magnet arrangements in a third direction perpendicular to the plane.13. The actuator according to clause 12, wherein the first and the second magnet arrangements and the first and the second coil portions extend in a fourth direction.14. The actuator according to clauses 12 or 13, further comprising a third magnet arrangement arranged between the first and the second coil portions, the third magnet arrangement comprising a first auxiliary magnet having polarization direction in the first direction and a second auxiliary magnet having polarization direction in the second direction.15. The actuator according to any one of clauses 12-14, wherein along the fourth direction, a length of the first and the second coil portion exceeds a length of the first and the second magnet arrangements.16. The actuator according to any one of the clauses 12-15, wherein along the first and the second directions a width of the first and second magnet arrangements exceeds a width of the coil.17. The actuator according to any one of the clauses 12-16, wherein the fourth direction is perpendicular to the first and the second direction.18. The actuator according to any one of clauses 12 - 17, wherein the fourth direction is radial in respect of an axis extending in the third direction and wherein the first and the second direction are circular around the axis.19. The actuator according to any one of clauses 12 - 17, wherein the first and the second direction are radial in respect of the axis extending in the third direction and wherein the fourth direction is circular around the axis.20. An actuator comprising a first coil and a second coil arranged in a space between a first and a second magnet arrangement, wherein- the first coil extends in a first plane,- the second coil extends in a second plane perpendicular to the first plane,- the first magnet arrangement is configured to generate a first magnetic flux and a second magnetic flux,- the second magnet arrangement is configured to generate a third magnetic flux and a fourth magnetic flux, and wherein- the first and the third magnetic flux interact with a first coil portion of the first coil in a first direction, and the second and the fourth magnetic flux interact with a second coil portion of the first coil in a second direction which is opposite to the first direction, wherein the first and second direction are parallel to the first plane, thereby enabling a force between the first coil and the first and second magnet arrangements in a direction perpendicular to the first plane, and- the first and the second magnetic flux interact with a first coil portion of the second coil in a third direction, and the third and the fourth magnetic flux interact with a second coil portion of the second coil in a fourth direction which is opposite to the third direction, wherein the third and fourth directions are parallel to the second plane, thereby enabling a force between the second coil and the first and second magnet arrangements in a direction perpendicular to the second plane.21. The actuator of clause 20, wherein the second coil is arranged between the first and second coil portion of the first coil.22. The actuator of clause 20 or 21, further comprising a third magnet portion arranged between the coil portions of the first coil, the third magnet portion comprising one or more auxiliary magnets having polarization directions in the first or second direction.23. A lithographic apparatus, a substrate inspection apparatus or a wafer metrology apparatus comprising the actuator according to any one of the preceding clauses.24. The lithographic apparatus, substrate inspection apparatus or wafer metrology apparatus according to clause 23, comprising a stage, a long stroke positioner and a short stroke positioner configured to actuate the stage, wherein the short stroke positioner comprises the actuator.25. The lithographic apparatus, substrate inspection apparatus or wafer metrology apparatus according to clause 24, the actuator is configured to compensate a gravity on the stage.26. The lithographic apparatus, substrate inspection apparatus or wafer metrology apparatus according to clause 24 or 25, further comprising a setpoint generator configured to provide a long stroke setpoint to the long stroke positioner and a short stroke setpoint to the short stroke positioner, wherein one of the long stroke setpoint provided to the long stroke positioner and the short stroke setpoint provided to the short stroke positioner is a lagging setpoint in respect of the other one of the long stroke setpoint provided to the long stroke positioner and the short stroke setpoint provided to the short stroke positioner.

Claims

CLAIMS1. An actuator comprising a coil and a magnet arrangement, wherein- the coil is arranged in a plane defined by a first direction and a second direction, and the coil being configured to carry an electric current during use, wherein main coil portions of the coil extends in the first direction,- the magnet arrangement comprises a first and a second magnet portion, which are arranged at opposite sides of the coil, wherein each of the two magnet portions comprises a central magnet unit and an edge magnet unit, characterized in that the central magnet unit and the edge magnet unit of each magnet portion have different polarization directions, the central magnet units of the two magnet portions are substantially aligned in a third direction perpendicular to the plane of the coil, and each with a polarization direction in the third direction wherein the polarization directions of the central magnet units of the two magnet portions are opposite to each other, and the magnet arrangement is configured to generate a primary magnetic flux substantially transverse the main coil portions in the second direction.

2. The actuator according to claim 1, wherein the central magnet unit and the edge magnet units extend in the first direction and wherein, seen along the second direction, the main coil portions of the coil extend along an edge between the respective central magnet units and the edge magnet units.

3. The actuator according to any one of the preceding claims, wherein the first and second magnet portions are spaced apart in the third direction and wherein the coil is arranged between the first and second magnet portions.

4. The actuator according to any one of the preceding claims, further comprising a third magnet portion arranged between the main coil portions, the third magnet portion comprising first and second auxiliary magnets having polarization directions in the second direction and opposite to each other.

5. The actuator according to any one of the preceding claims, wherein along the first direction, a length of the main coil portion exceeds a length of the central magnet unit and the edge magnet unit.

6. The actuator according to any one of the preceding claims, wherein along the second direction, a width of the first and second magnet portions exceeds a width of the coil.

7. An actuator comprising a coil arranged in a space between a first and a second magnet arrangement and extending in a plane, wherein- the first magnet arrangement is configured to generate a first magnetic flux and a second magnetic flux,- the second magnet arrangement is configured to generate a third magnetic flux and a fourth magnetic flux, and wherein the first and the third magnetic flux interact with a first coil portion of the coil in a first direction, and the second and the fourth magnetic flux interact with a second coil portion of the coil in a second direction which is opposite to the first direction, wherein the first and second direction are parallel to the plane, thereby enabling a force between the coil and the first and second magnet arrangements in a third direction perpendicular to the plane.

8. The actuator according to claim 7, wherein the first and the second magnet arrangements and the first and the second coil portions extend in a fourth direction.

9. The actuator according to claims 7 or 8, further comprising a third magnet arrangement arranged between the first and the second coil portions, the third magnet arrangement comprising a first auxiliary magnet having polarization direction in the first direction and a second auxiliary magnet having polarization direction in the second direction.

10. The actuator according to any one of claims 7-9, wherein along the fourth direction, a length of the first and the second coil portion exceeds a length of the first and the second magnet arrangements.

11. The actuator according to any one of the claims 7-10, wherein along the first and the second directions a width of the first and second magnet arrangements exceeds a width of the coil.

12. An actuator comprising a first coil and a second coil arranged in a space between a first and a second magnet arrangement, wherein- the first coil extends in a first plane,- the second coil extends in a second plane perpendicular to the first plane,- the first magnet arrangement is configured to generate a first magnetic flux and a second magnetic flux,- the second magnet arrangement is configured to generate a third magnetic flux and a fourth magnetic flux, and wherein- the first and the third magnetic flux interact with a first coil portion of the first coil in a first direction, and the second and the fourth magnetic flux interact with a second coil portion of the first coil in a second direction which is opposite to the first direction, wherein the first and second directionare parallel to the first plane, thereby enabling a force between the first coil and the first and second magnet arrangements in a direction perpendicular to the first plane, and- the first and the second magnetic flux interact with a first coil portion of the second coil in a third direction, and the third and the fourth magnetic flux interact with a second coil portion of the second coil in a fourth direction which is opposite to the third direction, wherein the third and fourth directions are parallel to the second plane, thereby enabling a force between the second coil and the first and second magnet arrangements in a direction perpendicular to the second plane.

13. The actuator of claim 12, wherein the second coil is arranged between the first and second coil portion of the first coil.

14. The actuator of claim 12 or 13, further comprising a third magnet portion arranged between the coil portions of the first coil, the third magnet portion comprising one or more auxiliary magnets having polarization directions in the first or second direction.

15. A lithographic apparatus, a substrate inspection apparatus or a wafer metrology apparatus comprising the actuator according to any one of the preceding claims.

Images